EPA Climate Change Research Programme 2007–2013 The Potential for Grass Biomethane as a Biofuel Compressed Biomethane Generated from Grass, Utilised as a Transport Biofuel CCRP Report End of Project Report available for download on http://erc.epa.ie/safer/reports Prepared for the Environmental Protection Agency by Environmental Research Institute, University College Cork Authors: Jerry D. Murphy, Nicholas E. Korres, Anoop Singh, Beatrice Smyth, Abdul-Sattar Nizami and Thanasit Thamsiriroj ENVIRONMENTAL PROTECTION AGENCY An Ghníomhaireacht um Chaomhnú Comhshaoil PO Box 3000, Johnstown Castle, Co. Wexford, Ireland Telephone: +353 53 916 0600 Fax: +353 53 916 0699 Email: info@epa.ie Website: www.epa.ie © Environmental Protection Agency 2011 ACKNOWLEDGEMENTS This report is published as part of the Climate Change Research Programme 2007–2013. The programme is financed by the Irish Government under the National Development Plan 2007–2013. It is administered on behalf of the Department of the Environment, Community and Local Government by the Environmental Protection Agency which has the statutory function of co-ordinating and promoting environmental research. The authors acknowledge the support of the EPA and, in particular, Dr Philip O’Brien, Dr Frank McGovern and Ms Laura Burke. They also wish to acknowledge the support of Dr Padraig O’Kiely (Teagasc, Grange) which has enhanced our understanding of the production of grass silage, and Dr Rogier Shulte, Grange, Johnstown Castle, Wexford. Dr I.N. Vogiatzakis, Centre for AgriEnvironmental Research, University of Reading, UK, was responsible for constructing the maps included in this report. DISCLAIMER Although every effort has been made to ensure the accuracy of the material contained in this publication, complete accuracy cannot be guaranteed. Neither the Environmental Protection Agency nor the author(s) accept any responsibility whatsoever for loss or damage occasioned or claimed to have been occasioned, in part or in full, as a consequence of any person acting, or refraining from acting, as a result of a matter contained in this publication. All or part of this publication may be reproduced without further permission, provided the source is acknowledged. The EPA Climate Change Research Programme addresses the need for research in Ireland to inform policymakers and other stakeholders on a range of questions in relation to environmental protection. These reports are intended as contributions to the necessary debate on the protection of the environment. EPA CLIMATE CHANGE RESEARCH PROGRAMME 2007–2013 Published by the Environmental Protection Agency, Ireland PRINTED ON RECYCLED PAPER ISBN: 978-1-84095-427-2 Price: Free 12/11/150 ii Details of Project Partners Jerry D. Murphy Environmental Research Institute University College Cork Cork Ireland Tel.: +353 21 4902286 Email: jerry.murphy@ucc.ie Nicholas E. Korres Environmental Research Institute University College Cork Cork Ireland Anoop Singh Environmental Research Institute University College Cork Cork Ireland Beatrice Smyth Environmental Research Institute University College Cork Cork Ireland Abdul-Sattar Nizami Environmental Research Institute University College Cork Cork Ireland Thanasit Thamsiriroj Environmental Research Institute University College Cork Cork Ireland iii Table of Contents Acknowledgements ii Disclaimer ii Details of Project Partners iii Executive Summary vii 1 2 3 4 Why Grass and Why Biomethane? 1 1.1 Overarching Policy and Strategy 1 1.2 Ireland: The Food Island 1 1.3 Agricultural Legislation 1 1.4 Agri-Environmental Schemes 1 1.5 Renewable Energy in Transport 2 1.6 Biofuels in Ireland – Targets and Options 2 1.7 The Renewable Energy Directive 2 1.8 Advantages of Grass Methane 3 1.9 Waste Management and Residues 5 1.10 Conclusions 5 What is Grass? 6 2.1 Grassland 6 2.2 Grassland Classification 6 2.3 Grassland and Farming Practices 6 2.4 Grass in Animal and Biomethane Production Systems 7 2.5 Suitability of Grass Species for Biomethane and Animal Production in Ireland 9 2.6 Fertilisation 10 2.7 Harvesting Date 11 2.8 Ensiling of Grass 12 2.9 Mixed Pastures 13 2.10 Conclusions 13 How Do We Convert Grass to Biomethane? 15 3.1 Anaerobic Digestion 15 3.2 Anaerobic Digesters 15 3.3 Upgrading and Injection 18 3.4 Conclusions 20 Life-Cycle Analysis of Grass Biomethane 21 4.1 21 Aims and Methodology v 5 6 4.2 Grass Silage Production 22 4.3 Biogas Production 23 4.4 Compressed Biomethane Production 24 4.5 Energy and GHG Emissions Associated with Grass Silage Production 24 4.6 Direct Energy Consumption and Related Emissions Associated with Biomethane Production 29 4.7 Sensitivity Analysis 30 4.8 Conclusions 32 What is the Market for Grass Biomethane? 33 5.1 The Relationship between Grass, Farming and Energy 33 5.2 Biomethane Potential in Ireland from Numerous Sources 33 5.3 Economic Analysis of Grass Biomethane System 35 5.4 Economic Analysis of Grass Biogas and Biomethane under Current Conditions 37 5.5 Improving the Viability of Grass Biomethane for the Farmer and the Consumer 41 5.6 Conclusions 46 Conclusions and Recommendations 47 6.1 Conclusions 47 6.2 Recommendations 47 References 49 Peer-Reviewed Journal Publications from Report 58 Acronyms and Annotations 59 vi Executive Summary Grass is an excellent energy crop due to long of biomethane are shown to be difficult. There is a persistence of high yields accompanied by low energy requirement for innovative policy and marketing of the inputs. Approximately 91% of Irish agricultural land is industry. A compressed natural gas transport fuel under grass. The national herd has decreased and will market continue to do so. Cross compliance does not biomethane as a transport fuel. Mandating a certain encourage the conversion of permanent pastureland to percentage of biomethane in natural gas sales is of arable land; thus we have and will continue to have benefit to biomethane as both a transport and a increased quantities of excess grassland. Therefore, thermal biofuel. Government policy is required to grass must be considered a significant source of support a biomethane industry. is an essential prerequisite to using biomass. Current grass species and cultivation Further research is required in the following areas: practices are favourable for anaerobic digestion (AD), which is a mature technology. Upgrading biogas to • biomethane, injecting into the gas grid, leads to an derived from includes the municipal solid waste (OFMSW), slurry, slaughter waste The Renewable Energy Directive allows a double biofuels This highlight sources of the organic fraction of to all major cities and 620,000 houses. for mapping: creation of a Geographical Information System to effective bioenergy system complete with distribution credit Bioresource residues and areas of high-yielding silage production. The system would include distribution and systems (natural gas grid, electricity grid) and lignocellulosic material (such as grass). It is shown that demand nodes (e.g. transport fleets, district 100,000 ha of grass (2.3% of agricultural land) will heating, new towns) to propose areas with allow compliance with the 10% renewable energy in significant potential for biomethane production. transport target for 2010. Alternatively, this would substitute for 35% of residential gas consumption. • Reactor design must take account of the specific Assessment of biomethane facilities: This includes full life-cycle analysis of different feedstock or combinations of feedstock; the reactor biomethane facilities, including co-digestion of must be suited to the feedstock. This is not technically slurries and grass silage, mono-digestion of difficult. Of significant concern in the sustainability of OFMSW, the biofuel produced is the parasitic energy demand of and mono-digestion of slaughter wastes. The research should allow assessment the process and the vehicle efficiency. Emission of the cost of the produced biomethane. reductions are optimised by the use of green electricity and the use of biomass for thermal energy input. On a • Digester design: This basic research should field-to-wheel basis, it is essential that the vehicle assess optimal digester systems for different operating on biomethane has an equivalent efficiency feedstocks. (expressed as MJ/km) as the displaced fossil fuel. The • Renewable Energy Directive requires an emission Agricultural impact of AD: This research savings of 60% compared with the displaced fuel for includes monitoring carbon sequestration in new facilities constructed after 2017. This is readily grasslands where silage is cut and digestate is achieved for grass biomethane through optimisation of applied. This should be compared with carbon the system. Allowing for carbon (C) sequestration in sequestration on grazed pastures. The fertiliser grassland of 0.6 t C ha/year will lead to emissions value of different digestates needs to be savings of 89%. This would suggest that grass assessed along with the emissions associated biomethane is one of the most sustainable indigenous, with application of digestate. The research should non-residue-based transport biofuels. The economics also assess the effect on biodiversity. vii 1 Why Grass and Why Biomethane? 1.1 Overarching Policy and Strategy 1.3 Mid-Term Review of the Common Agricultural Policy (CAP) made agricultural support payments conditional upon compliance with environmental standards and ‘good farming practice’. Community initiatives, amongst others, aim to limit agricultural pollution, to promote the production and use of biofuels, and to protect biodiversity (Osterburg et al., 2005). Attaching conditions to the receipt of agricultural subsidies is a policy mandatory tool known as cross compliance (EC, 2003). It consists of two strands (i.e. Good Agricultural and Environmental Condition and the Statutory Management Requirements) (Mussner et al., 2006) and aims to improve standards in modern farming practices (Farmer and Swales, 2004). Cross-compliance regulations (Article 5) require that the land declared as under permanent pasture in 2003 is maintained under permanent pasture. It also requires that the ratio of land under permanent pasture to the total agricultural area of each Member State must not decrease by 10% or more from the 2003 reference ratio. Ireland is therefore under obligation not to allow any significant reduction in the total area of permanent pasture; this restricts the type of energy crops that can be grown. In the same CAP reforms, a special aid for energy crops grown on non-set-aside land was introduced. Energy crops (crops grown for the production of biofuels including biogas or for use as biomass in the production of electric and thermal energy) are eligible for a premium of €45/ha. An additional top-up of €80/ha, funded by the National Exchequer, is also paid. Major reform of the CAP is expected in 2013 and this may have implications for energy crops and biofuels. The The deployment of biofuels is affected by policy in energy and agriculture. In the agricultural sector, policy enforces environmentally friendly production systems that will affect agricultural status quo and production chains. In the energy sector, concerns regarding the sustainability of biofuel systems and their impact on food prices led to a set of sustainability criteria in the Renewable Energy Directive (EC, 2009a). In addition, the site specificity of biofuel feedstock production, agricultural practices, and indirect land-use change will significantly affect growth trends in biofuel usage and the ability of an EU Member State to reach a 10% renewable energy in transport target by 2020. 1.2 Ireland: The Food Island The agri-food sector is one of the most important and dynamic indigenous manufacturing elements in the Irish economy and accounts for an estimated 8.1%, 8.1% and 9.8% of gross domestic product (GDP), employment and exports, respectively Agricultural Legislation (DAFF, undated). Irish agriculture, influenced by the wet and mild climate, has traditionally been characterised by extensive grass-based farming systems and relies heavily on grassland-based livestock farming. Grass and grass crops cover around 91% (i.e. 3.9 million ha) of all agricultural land (O’Mara, 2008). Livestock and livestock products account for most of total agricultural output (Jensen et al., 2003). About 53% of farms are classified as beef and they account for 40% of the agricultural area used (AAU), while they contribute to over a third (€1.3 billion) of agricultural export earnings 2003 (Anonymous, 2008a). Farm profitability associated with beef production is not competitive (Anonymous, 1.4 2008a). Projections estimate a decline in cattle The Rural Environment Protection Scheme (REPS) numbers (Donnellan and Hanrahan, 2008; CSO, was undated), particularly those of suckler cows (Binfield et EEC/2078/1992 in order to encourage farmers to carry al., 2008) by possible trade and policy reform out scenarios. environmentally friendly manner (Hynes et al., 2008). 1 Agri-Environmental Schemes introduced their activities under in a Council more Regulation extensive and The potential for grass biomethane as a biofuel This was introduced due to the realisation of the severe lignocellulosic material, the use of electricity in ecological and environmental impacts of agricultural transport is encouraged in the EU by Directives intensification under previous EU agricultural support 2009/28/EC and 2009/33/EC (EC, 2009a,b). mechanisms (Clergue et al., 2005). The Sixth 1.6 Environment Action Programme (EC, 2001), the Water Framework Directive (EC, 2000) and the Nitrate Directive (EEC, 1991) introduce a series of measures The share of biofuels in Ireland in 2008 (as a that should lead to an overall reduction in greenhouse percentage of energy content in petrol and diesel) was gas (GHG) emissions at farm level through lower 1.2%, although significant increases from 1 ktoe1 in stocking rates. This, in turn, could free up grassland for 2005 to 56 ktoe in 2008 were recorded (Howley et al., other purposes, such as grass biomethane. The 2009a). Biodiesel was the dominant biofuel in 2007 adoption of batch storage for slurry has also been followed by bioethanol and pure plant oil at 76%, 16% suggested (Chardon and Schoumans, 2008), which and 8%, respectively, (Foley et al., 2009) whereas the could make it amenable to anaerobic digestion (AD) contribution of biomethane is still negligible. The target and biofuel production. Biofuels are also influenced by for biofuels was 4% by volume of biofuel (DCENR, the Biodiversity Action Plan (Caslin, 2009), which aims 2009) by 2010. For 2020, two approaches to national to improve or maintain biodiversity and prevent further energy forecasts for Ireland were employed for the biodiversity loss due to agricultural activities. Priorities quantification of the 10% target for transport energy; include restricting intensive farming and establishing these were termed Baseline and White Paper Plus sustainable resource management. Most grassland in (Walker et al., 2009). The White Paper Plus approach the EU is devoted to meat production, where allowed consideration of the energy savings in profitability is low and farmers often rely on EU single- transport associated with Ireland’s National Energy farm payments to survive; thus, grassland farming can Efficiency Action Plan. Estimated values of 24.7 PJ and 23.8 PJ for Baseline and White Paper Plus were calculated, respectively. In this report, a value of 24 PJ will be used as the renewable energy in transport target for 2020. The Electric Vehicles Plan sets an ambition of 10% of private vehicles powered by electricity in combination with the 40% target of electricity from renewable energy (Howley et al., 2008) by 2020. It has been shown that the utilisation of electricity in transport (vehicles, trams and rail) will account for 3.6 PJ by 2020 (Foley et al., 2009; Walker et al., 2009) or 1.5% of energy in transport, leaving a shortfall of 8.5%, which must be filled by biofuels. These biofuels may be sourced from various feedstock sources, which may be imported or indigenous energy crops, wastes and residues, or lignocellulosic biomass. In order to achieve Ireland’s renewable energy target, the biofuel system must meet certain sustainability criteria. face considerable challenges in implementing new environmental measures without financial supports (Boyle, 2008). 1.5 Biofuels in Ireland – Targets and Options Renewable Energy in Transport Renewable energy originates from energy resources that are continuously replenished through the cycles of nature, and their supply is unlikely, compared with fossil fuels, to be exhausted. The use of biofuels as a means of greening the transport sector is strongly supported by European policy (EEA, 2004). EU Directive 2009/28/EC on renewable energy sets a mandatory target for each EU Member State for 10% of transport energy (road and rail) to be met by renewable sources by 2020 (EC, 2009a). Liquid biofuels (i.e. biodiesel from rapeseed, soybean and palm oil and bioethanol from maize, wheat, sugar beet and sugar cane) are the main renewable fuels produced and consumed in the EU (USDA, 2006). The 1.7 use of biogas as a transport fuel after its upgrading to biomethane has started gaining attention in many The Renewable Energy Directive Biofuels eligible to contribute to the mandatory target European countries, such as Sweden, Austria, France of 10% as set in the EU Renewable Energy Directive and Switzerland (Mathiasson, 2008). Additional to the 1. ktoe, kilotonnes of oil equivalent. production of biofuels from wastes, residues and 2 J.D. Murphy et al. (2007-CCRP-1.7) the renewables and creating jobs in the energy sector requirements summarised in Box 1.1. The Directive (DCMNR, 2007). However, the use of grass for biofuel allows for double credit/counting of biofuels produced (biomethane) production has been highlighted by from wastes, residues and lignocellulosic materials. Murphy and Power (2009a). The energy balance of the Singh et al. (2010b) consider grass as a lignocellulosic grass biomethane system is significantly better than source and as such it is liable for a double credit. alternative Irish biofuel crops and compares favourably 2009/28/EC 1.8 (EC, 2009a) should meet with tropical biofuels (Fig. 1.1) such as sugar-cane Advantages of Grass Methane ethanol and palm-oil biodiesel (Smyth et al., 2009; Smyth et al. (2010a) reported on sustainability issues Korres et al., 2010). In terms of GHG emissions, an concerning imported biofuels (such as corn ethanol analysis by Korres et al (2010) found grass and soybean diesel), which may not allow these biomethane to be one of the most sustainable imported biofuels count in achieving the 10% target. indigenous, non-residue-based European transport The issues relate to: biofuels. The advantages of perennial grasses over • Poor or negative energy balances; • Adverse environmental impacts; • Habitat destruction; • Low GHG savings; • High land requirements; and first-generation agro-fuels include long persistency of high dry matter (DM) yield, intercropping potential with legumes and subsequent reduction in fertiliser application rates, lower rates of pesticide application, and the protection of grassland area in the present CAP cross-compliance system (Peeters, 2009). The reduction in the cattle herd will lead to reduced requirements for grazing and for silage production. • Carbon leakage. Cross compliance will limit the ability to convert excess grassland to arable land. Even allowing for the Imported biofuels from tropical regions such as Brazil, conversion of grassland to forest, significant quantities Malaysia and Indonesia have significant issues with of high-value grassland will be available for grass land-use change and deforestation. Higher demand for palm oil leads to significant land-use change, which biomethane by 2020 (Smyth et al., 2010a). Smyth et al. results in lower GHG emission savings, accompanied (2009, 2010a) suggested an excess of 0.39 Mha by by adverse social and environmental impacts. In 2020 and allowing for grass biomethane from 25% of addition, importing biofuels at the expense of local this area (ca. 100 kha) could produce 11.9 PJ of industry could make it difficult for indigenous producers biomethane. This is equivalent to 5% of energy in to find a place in the energy market. This is contrary to transport in 2020 and 10% when the double credit for the government’s goals of accelerating the growth of lignocellulosic material is allowed (Table 1.1). Box 1.1 Significant Articles in The Renewable Energy Directive (2009/28/EC) relating to sustainable biofuels • Article 17 (2): From 1 January 2017, the greenhouse gas emissions of biofuels from new facilities must be reduced by 60% compared with the alternative fossil fuel use. • Article 17 (3): No damage may be done to sensitive or important ecosystems in producing biofuels. • Article 17 (4): In the production of sustainable biofuels, wetland, forestry or grassland may not be converted to energy crop production. • Article 21 (2): The contribution from biofuels made from wastes, residues, non-food cellulosic material and lignocellulosic material shall be considered to be twice that made by other biofuels. 3 The potential for grass biomethane as a biofuel Gross energy Net energy 160 135 140 120 120 122 122 122 GJ/ha/year 120 100 84 80 60 40 74 66 46 78 69 67 43 25 20 4 Grass biomethane, wood chips Grass biomethane, digestate fertilizer Grass biomethane, base case Sugarcane ethanol Palm oil biodiesel Wheat ethanol, WDGS biomethane Wheat ethanol Rapeseed biodiesel 0 Figure 1.1. Comparison of gross and net energy output of selected energy crop biofuel systems (Smyth et al., 2009; Korres et al., 2010). Gross energy is the energy produced in the form of transport fuel. Net energy is the gross energy less all the energy inputs to the system including for all the steps in the production of the crop and all parasitic energy demands in the production system. WDGS, wet distiller’s grains with solubles. ‘Grass biomethane, base case’ excludes the use of digestate as a fertiliser and uses gas to satisfy thermal parasitic demand. ‘Grass biomethane, digestate fertilizer’ allows for the use of digestate as a substitute for mineral fertiliser. ‘Grass biomethane, wood chips’ allows for woodchips to satisfy thermal parasitic demand. Table 1.1. Strategy for meeting the target of 10% renewable energy in transport by 2020 (adapted from Singh and Murphy, 2009). Fuel Feedstock Practical energy in 2020 (PJ) Factor Contribution to target (PJ) Percentage of energy in transport (2020) Biodiesel Tallow 0.715 ×2 1.43 0.58% Used cooking oil 0.455 ×2 0.91 0.38% 0.60 0.25% Rapeseed 0.6 Bioethanol Cheese whey 0.27 ×2 0.54 0.23% Biomethane Slurry 1.88 ×2 3.76 1.57% OFMSW 0.57 ×2 1.14 0.48% Slaughter waste 0.68 ×2 1.36 0.57% Grass 11.93 ×2 23.86 9.94% National grid 1.44 ×2.5 3.60 1.5% 37.20 15.5% Electricity Total 18.54 OFMSW, organic fraction of municipal solid waste. 4 J.D. Murphy et al. (2007-CCRP-1.7) 1.9 (2009) calculated 82% GHG savings for cattle slurry Waste Management and Residues biomethane and 100% for slaughter waste biomethane Treatment of organic wastes is currently of particular when compared with diesel. importance in the European Union (Ward et al., 2008) under the EU Landfill Directive (EC, 1999). Recent 1.10 research for Ireland (Singh and Murphy, 2009) Conclusions estimated the practical transport energy available from The high potential of grassland utilisation as feedstock biodiesel (produced from tallow and used cooking oil for biomethane production, given the environmental (UCO)) and biomethane (from cattle slurry, the organic constraints in agricultural production in conjunction fraction of municipal solid waste (OFMSW) and with slaughter waste) to be 4.3 PJ/year in 2020 (Table 1.1). generation biofuels, suggests grass biomethane to be Allowing for double credits, this equates to 3.6% of an optimum solution for achieving the 2020 renewable energy in transport by 2020. This is based on readily energy in transport target. Diversification of agricultural achievable collection regimes; for example, 2% of enterprise to biomethane production will assist rural cattle slurry, 5% of pig slurry, and 25% of OFMSW. development Significant GHG emissions savings are associated security of energy supply, and environmental benefits with biomethane from residues. Singh and Murphy associated with reduced stocking rates. 5 sustainability issues through associated sustainable with first- employment, The potential for grass biomethane as a biofuel 2 What is Grass? 2.1 Grassland the former type by the Centaureo-Cynosuretum association. The dominant species in this type are Grassland is defined as the habitat where the Lolium perenne, Trifolium repens, Holcus lanatus (Yorkshire fog) and Agrostis spp (bentgrass). Three sub-associations are observed within this type of grassland: vegetation is either dominated by grasses or is ‘grassy’ in appearance, with abundant small sedges or rushes and is mainly used for feeding herbivores and ruminants. It also provides an important regulating ecosystem service and supports biodiversity and (i) Type A is confined to shallow, well-drained, cultural services, for example by contributing to a limestone soils; region’s cultural heritage and to recreational values (ii) Type B is found in the better-drained (Smit et al., 2008). Among its major benefits (i.e. long lowlands or deep, well-drained brown earths persistency of high dry matter yield, intercropping and grey–brown podzolics; and potential with legumes and subsequent reduction in (iii) Type C is common on drumlins in the North fertiliser application rates (Peeters, 2009), protection of formation Midlands, the Castlecomer Plateau and (Prochnow et al., 2009)), grassland is also an some soils in the mid-west and is often important carbon store and potential carbon sink subjected to poaching under wet conditions. soil from erosion, and groundwater (Tilman et al., 2006) and a source of feedstock for the 3. Low-quality swards: Low-quality swards include production of renewable energy in the form of grass poor-quality wet pastures on soils of low natural biomethane (Smyth et al., 2009; Korres et al., 2010). fertility and represent around 11% of Irish grassland. Species of the order Molinietalia 2.2 Grassland Classification Caeruleae such as Juncus spp. (rushes), Lythrum salicaria (purple loosestrife), Lychnis flos-cuculi (ragged robin), Angelica sylvestris (wild angelica), Achillea millefolium (yarrow), Senecio aquaticus (marsh ragwort) and Lotus uliginosus (marsh trefoil) are dominant in this type of grassland. There are various grassland types (based on husbandry practices) and grassland classifications based on botanical composition or phytosociology (Braun-Blanquet, 1932; Feehan, 2003). O’Sullivan (1982) and O’Sullivan and Murphy (1982) distinguished three types of Irish grassland: 2.3 1. High-quality swards: High-quality swards with Grassland and Farming Practices Brockman and Wilkins (2003) classified grassland Molinio-Arrhenatheretea and Lolio-Cynosuretum as the prevailing class and association, respectively, are found in high fertile soils, such as those in the east, south and south-east (i.e. Meath, Kildare, Wicklow, Waterford, Wexford and Cork). The dominant species within this class are Lolium perenne (perennial ryegrass), Poa trivialis (rough meadow grass) and Trifolium repens (white clover). High-quality swards include the majority of reseeded pastures found in Ireland. according to farming practices as rough mountain hill grazing, permanent and rotational or temporary grassland. • Rough mountain grassland is found in unenclosed or relatively large enclosures on hills, uplands, moorland, heaths and downlands. It is uncultivated grassland and is characterised by high levels of species richness, low stocking rates and low production. The soil is usually acidic or peaty and therefore difficult to cultivate. 2. Moderate-quality swards: Moderate-quality MolinioArrhenatheretea class and are distinguished from swards are characterised by • the Permanent grassland is grassland in fields or relatively small enclosures not in arable rotation. 6 J.D. Murphy et al. (2007-CCRP-1.7) It is dominated by perennial grasses and it is grazing, silage production) (Walker, 1995). This is true more productive and usually more highly stocked for the use of grass and grass silage along with animal than mountain hill grazing grassland. feed as a feedstock for the production of biomethane (Nizami et al., 2009). • Rotational or temporary grassland is grassland within an arable rotation. It is characterised by The attention on different perennial grasses, i.e. low abundance and low species richness, high Panicum vigratum (switchgrass) (McLaughlin and Kszos, 2005), Miscanthus × Giganteus (miscanthus) (Clifton-Brown et al., 2004), Phalaris arundinacea (reed canary grass) and Phleum pratense (timothy) (Lewandowski et al., 2003), Andropogon gerardii (big bluestem) (Weimer and Springer, 2007), forage grasses (i.e. ryegrass) (Smyth et al., 2009; Korres et al., 2010), as energy crops, mainly in the USA and Europe, was accelerated when it was realised that they offer good energy balances along with several environmental advantages. Species, varieties and seed mixtures should clearly be chosen to suit the purposes for which the sward is to be used and the environment (Feehan, 2003). The physiology of grasses considering, for example, their photosynthetic (PS) pathway, i.e. C-3 (cool or temperate) versus C-4 (warm or tropical) grasses, imposes environmental specificity and, hence, differences in their productivity (Niu et al., 2006) and biomethane yield (Table 2.1). The main characteristics of cool compared with warm grasses that affect their productivity are that the former fix carbon dioxide (CO2) in a cooler environment, i.e. they respond to nitrogen fertiliser early in the spring, whereas in warm seasons their growth rates are reduced. In contrast, warm species require less nitrogen to achieve the same light-saturated assimilation rate, leading to higher photosynthetic nitrogen use efficiency, are more efficient at gathering carbon dioxide in warm environments and more tolerant at water stress conditions (Winslow et al., 2003; Lunt et al., 2007; Nippert et al., 2007). stocking rates and production. In addition, Lockhart and Wiseman (1988) distinguished two types of grassland, uncultivated and cultivated. The former consists of rough mountain and lowland heaths grassland, whereas the latter includes permanent grassland (over 5 years old) and leys or temporary grassland (less than 5 years old). This, based on perennial ryegrass percentage, can be further distinguished as first- (>30%), second- (20– 29%), third-grade (<20%) and poor (usually dominated by bentgrass) grassland. Cultivated grassland according to Fossitt (2000) can be classified as improved grassland that is highly modified, intensively managed and species poor used for heavy grazing and/or silage production. It includes regularly reseeded monoculture grasslands dominated by perennial ryegrass that is planted as part of an arable rotation. The Irish Central Statistics Office (CSO) displays its data on grassland use based on four categories – pasture, rough grazing, silage and hay. Increased production from grassland has arisen from improved understanding of soil and plant nutrition, plant physiology and cultivar improvement, while improved understanding of feed evaluation, ruminant nutrition, grazing management and silage technology have contributed to increased utilisation of grassland under grazing and cutting. In this report, high-quality, improved first-grade grassland (i.e. pasture and silage) is considered for the analysis of energy balance and related GHG emissions for biomethane production. 2.4 However, productivity of animals (i.e. meat, milk, wool) Grass in Animal and Biomethane Production Systems consuming mostly forage is directly related to the quality of the forage and the amount consumed Grass, more than anything else, is what Irish farming is (Buxton, 1996). The quality of forages consumed by all about (Feehan, 2003) and it evolves as modern animals is accounted for, in large part, by their scientific approaches to farming are developed. digestibility (dry matter digestible (DMD)) and the Agronomists and progressive farmers require the fraction of the DM or energy that remains in the body cultivation of high productive grass species for high on passage through the gut tract (dry matter productive pastures (Connolly, 2001) which allows indigestible them to receive full benefit from its various uses (e.g. digestibility of warm grasses due to their higher fibre 7 (DMI)) (Brown, 1999). The lower The potential for grass biomethane as a biofuel Table 2.1. Potential perennial grasses as energy crops in Europe (data adapted from Lewandowski et al. (2003); Prochnow et al. (2009); Braun et al., undated). Common name Latin name PS pathway Methane (m3/ha) Yield (t DM/ha) Ryegrass Lolium perenne C-3 2,500–6,150 9–16.7a Miscanthus Miscanthus × Giganteus C-4 1,432–5,450 5–44 Switchgrass Panicum vigratum C-4 900–7,820b 5–23 Reed canary grass Phalaris arundinacea C-3 1,700–4,730 7–13 Timothy Phleum pratense C-3 1,362–5,800 9–18 Meadow foxtail Alopecurus pratensis C-3 1463 6–13 Big bluestem Andropogon gerardii C-4 – 8–15 Cocksfoot Dactylis glomerata C-3 1,480–3,800 8–10 Tall fescue Festuca arundinacea C-3 1,462 8–14 Napier grass Pennisetum purpureum C-4 0.19–0.34c 27 Sudan grass Sorghum × drummondii C-4 2,130–6,060 10–20 Cypergrass Cyperus longus C-4 – 4–19 a Yields of early, intermediate and late perennial ryegrass were reported equal to 16.7, 15.3 and 15 t DM/ha/year, respectively (Lockhart and Wiseman, 1988). b Based on 0.18–0.34 m3 CH4/kg dry matter (Pettigrew, 2000; Chynoweth et al., 2001; Samson, 2006). c Litres of methane (CH4) per gram of volatile solids (Wilkie, 2008). PS, photosynthetic; DM, dry matter. Table 2.2. Dry matter indigestible (DMI), dry matter digestible (DMD) and acid detergent fibre (ADF) concentration of C-4 and C-3 grasses, adapted from Brown (1999) Grass type DMIa (g/day/kg0.75) DMDb (%) ADFc (% of DM) C-4 (sheep) 56 62 – C-3 (sheep) 71 71 – C-4 (sheep) 65.7 54.5 42.5 C-3 (sheep) 66.2 65.5 35.8 C-4 (cattle) 89.8 60 42.7 C-3 (cattle) 89.5 67 38.3 a DMI (dry matter indigestible): dietary fibre (sometimes called roughage) is the indigestible portion of plant food. DMD (dry matter digestible): the percentage of the feed dry matter actually digested by animals; high-quality feeds have a DMD of over 65%, whilst feeds below 55% DMD are of poor quality. c ADF (acid detergent fibre): estimation of cellulose and lignin content in a feed; the lower the ADF the higher the DMD (and metabolisable energy). b content (Minson, 1981; Reid et al., 1988) (Table 2.2) is (Robson et al., 1989). It is therefore imperative that the indicative for possible lower biomethane yields since selection of the appropriate type of grass should digestibility of dry matter may be equated to the consider several characteristics in terms of farming potential digestibility of the silage in cattle paunch system, environmental conditions, legislative issues 8 J.D. Murphy et al. (2007-CCRP-1.7) (i.e. cross compliance) and biomethane production cocksfoot gave a biogas yield of 0.65–0.72 m3/kg VDS potential. added. Considering that grass biogas is typically 55% 2.5 methane (CH4), these results indicate that ryegrass Suitability of Grass Species for Biomethane and Animal Production in Ireland yielded 0.45–0.47 m3 CH4/kg VDS added, while cocksfoot yielded 0.36–0.40 m3 CH4/kg VDS added. Perennial ryegrass is one of the most dominant grass The use of grass either as feed for livestock or as a species in Irish grassland (Fig. 2.1). Along with Italian feedstock for biomethane production determines the ryegrass and white clover, it accounts for nearly all of husbandry management and agricultural operations the grass/clover seed sold for forage production in due to differences in environmental factors and the Ireland (Anonymous, 2008b). Additionally, O’Kiely et microbiology of AD as opposed to rumen (Nizami et al., al. (2005) stated that the main attractions in favour of 2009). For example, the level of cellulose degradation perennial ryegrass swards are that they produce high is up to 80% in biogas plants with retention times of yields in response to fertiliser application, have high 30–80 days, while it is 40–60% in rumen with retention digestibility when harvested at the appropriate growth of about 2 days (Ress et al., 1998). In the temperate stage, are relatively easy to preserve as silage due to grassland region, particularly in Ireland, grass silage of their superior content of sugar and they persist as perennial ryegrass is preferred for biomethane permanent swards where favourable management production because of its high digestibility values practices prevail. Tetraploid ryegrass varieties are (Robson et al., 1989), water-soluble carbohydrate recommended due to high sugar levels (Dieterich, (WSC) levels (Smith et al., 2002) and reduced 2008). In recent times diploid varieties have tended to quantities of crude fibre (Table 2.3) (Nizami et al., dominate mixtures in Ireland, but tetraploid varieties 2009). remain an important component of grass seed mixtures because of their higher WSC content, their Mahnert et al. (2005) reported that perennial ryegrass 3 gave the highest biogas yield (0.83–0.86 m /kg volatile increased palatability, which determines higher intake dry solids (VDS) added), compared with other grass by livestock, and their tolerance to drought. However, species, both fresh and ensiled. For example, they tend to have lower tiller densities resulting in more Table 2.3. Comparison of fresh and ensiled grass characteristics in batch and continuously stirred tank reactor (CSTR) digesters (Nizami et al., 2009). Batch digester Fresh grasses CSTR Grass silage Fresh grasses PRG CF MF PRG CF PRG CF MF MIX Total solids (TS) (%FM) 17.6 18.6 15.8 18.7 27.3 25.6 22.9 24.2 24.2 Volatile dry solids (%TS) 90.1 89.1 91.1 88.5 88.8 90.6 88.8 90.6 90 Volatile fatty acids (g/kg FM) 0.5 0.5 0.3 6.9 14.3 0.7 0.5 0.6 0.6 pH 6.5 6.7 6.6 4.6 6.1 6.5 7.1 7.1 6.9 Carbon to nitrogen ratio 16.4 13.7 15.5 14.3 19.8 12 13.5 15.1 Crude protein (%TS) 14.7 18.5 17 18.4 11.8 21.4 18.8 17.4 Crude fibre (%TS) 24.8 24.8 25.3 31.3 30.1 29.1 28 31.5 29.5 Saccharides (%TS) 10.8 9.8 3.3 3.4 3.1 19.3 9.8 9.1 12.7 Crude fat (%TS) 2.1 2.3 2.2 4.9 4.6 2.4 2.6 2.1 2.4 PRG, perennial ryegrass; CF, cocksfoot; MF, meadow foxtail; MIX, mixture; FM, fresh matter. 9 The potential for grass biomethane as a biofuel (a) (c) (b) Figure 2.1. Distribution of (a) perennial ryegrass, (b) Italian ryegrass, and (c) white clover in Irish grassland. Maps constructed based on data provided from the National Biodiversity Network Gateway (http://data.nbn.org.uk). open swards and lower dry matter compared with effects of husbandry factors such as nitrogen diploids. Seeding rates for tetraploid grasses will need fertilisation of timothy, found that increases in to be higher because of their larger seed size fertilisation rate resulted in increases in neutral (Anonymous, 2008b). detergent fibre (NDF). Such fibre is a measure of cellulose and hemicellulose and is a reflection of the Considering the potential of grass and grass silage as total cell wall content. This is supported by findings of a feedstock for biomethane production as a biofuel Keady et al. (2000), where increases of nitrogen (Murphy and Power, 2009b) and the need to increase application rate were accompanied by increases in the biofuel penetration in line with the European Directive cellulose and hemicellulose content of ryegrass for the use of biofuels (EC/28/2009), this then (Fig. 2.2). This leads to a decrease in digestibility. necessitates the rapprochement of grass and grass silage production and their characteristics that make them suitable for both feed and biofuel. Grass for AD is In general, the results of nitrogen fertilisation on fibre grown in the same way as high-quality grass for animal digestibility are moderate. As such, Peyraud et al. feed as, in both cases, the aim is to maximise (1997) found that unfertilised perennial ryegrass was metabolisable energy (ME) by harvesting the grass as accompanied by decreased fibre digestibility of 0.06 long as it is in a leafy, non-lignified stage (Dieterich, units when provided as a feed to dairy cattle but all 2008). agronomical NDF, acid detergent fibre (ADF) and acid detergent fertilisation, lignin ((ADL) estimation of lignin content) moderately harvesting date and frequency, and ensiling, can affect increased with nitrogen application. Additionally, Nevertheless, management decisions, certain such as biomethane yield through mainly changes in chemical several authors have reported lower water-soluble and structural composition of cell walls in grasses. 2.6 carbohydrates in grasses with increased nitrogen fertilisation (Buxton and Fales, 1994; O’Kiely et al., Fertilisation 2002). These evidences suggest that an excess in Fertilisation of grassland to achieve higher yields is the fertilisation rate could negatively affect biomethane most production important husbandry factor. Nevertheless, since increases of fermentable content of grasses occur. Nordheim-Viken and Volden (2009), investigating the 10 the non-easily J.D. Murphy et al. (2007-CCRP-1.7) Cellulose Hemicellulose 287 Celullose (g/kg) 265 262 286 260 284 280 278 258 281 282 255 251 278 278 252 278 250 249 276 245 274 272 Hemicellulose (g/kg) 288 240 N1 (72) N2 (96) N3 (120) N4 (144) N5 (168) N fertilizer (kg N/ha) Figure 2.2. Effects of nitrogen fertilisation on the concentration of structural carbohydrates (cellulose and hemicellulose). Based on data from Keady et al. (2000). 2.7 Pouech et al. (1998), performing the same experiment, Harvesting Date obtained different results, where 32% lower methane Grass for silage is usually harvested at a less mature yield per kilogram VDS was recorded at the vegetative stage of growth (leafy and non-lignified) (Fig. 2.3), stage than at the flowering stage. Prochnow et al. since the aim is to obtain a crop with a relatively high (2005) described more biogas yield in second-cut than content of fermentable substrate and a low content of first-cut silage, but, in spite of high dry solids (DS) and fibre as the crop at this stage usually has a high leaf– VDS contents present in late-cut grass, a lower stem ratio (Woolford, 1984). methane yield was established. The total solids (TS) and VDS contents in grass, hence yield of biomethane Amon et al. (2007), reporting on a multifaceted crop production (Nizami and Murphy, 2010), depend on rotation to increase the yield of methane per hectare, several factors, such as location, origin, climate, found that the first cut at vegetation stage was selected cultivation practices, soil type, nutrient content of grass as the optimum option for harvesting. Furthermore, De and pretreatment of biomass for AD (Bauer et al., Boever et al. (1993) found significant increases in 2007). Additionally, methane production potential can structural carbohydrates (i.e. NDF and ADF) and lignin also be increased if grass is cut in the afternoon as it between early and late first cut in a permanent pasture increases the concentration of WSC (White, 1973). consisting of a 50:50 ratio between diploid and tetraploid varieties of perennial ryegrass. The same Another important factor affecting the qualitative was reported by Keady et al. (2000) for perennial characteristics of grass silage relates to harvesting ryegrass comprised of intermediate varieties (Fig. 2.4). management (Buxton, 1996) – the methane yield may possibly be affected by harvest frequency. It has been biomethane mentioned by various authors that a cutting cycle of production per kilogram VDS and harvesting date have grass between 2 and 4 weeks in terms of the been reported for clover, ryegrass and timothy in carbon/nitrogen ratio (Holliday, 2005) or at cutting mixed swards. Kaparaju et al. (2002) found that clover intervals of 6 weeks following an early first cut produced 50% more methane per kilogram VDS at the (Murdoch, 1980) can optimise the methane yield in AD vegetative stage than at the flowering stage, whereas through increases in digestibility of grass. Nevertheless, inconsistencies in 11 The potential for grass biomethane as a biofuel Late harvested forage Early harvested forage A Hemicellulose Cellulose Lignins Bound N Cell wall Cell wall Neutral Detergent Fibres Acid Detergent Fibres A Cytoplasm Nucleic acid Amino acid Proteins Other N compounds Monosaccharides Oligosaccharides Refractory compounds Cytoplasm Thin cell wall Low Neutral Detergent Fibres = High intake Low Acid Detergent Fibres = High energy Thick cell wall High Neutral Detergent Fibres = Low intake High Acid Detergent Fibres = Low energy Figure 2.3. Effects of harvesting date on morphological and chemical composition of grass. Cellulose Hemicellulose 283 283 Cellulose (g/kg) 282 258 281 286 281 281 280 300 261 252 350 216 250 200 279 279 150 278 278 100 277 50 276 Hemicellulose (g/kg) 284 0 275 HD1 (May10) HD2 (May 17) HD3 (May 24) HD 4 (May 31) HD 5 (June 7) Harvesting date Figure 2.4. Effects of harvesting date on grass fibre components (based on data from Keady et al., 2000). 2.8 and stored grass ensures lower organic matter losses Ensiling of Grass and independency of weather conditions that might Grass and, in particular, grass silage form the basal cause damage to the dried feedstock. There may be diet for the vast majority of ruminants in many parts of potential to batch digest fresh grass in the summer the world during the winter feeding period (Charmley, months and to utilise other energy crops or biomass in 2001). Additionally, ensiling of grass for AD is the winter months. Grass silage produced higher preferable compared with fresh grass (Nizami et al., methane per tonne of organic dry matter (ODM) than 2009), whilst ensiled grass in comparison with dried fresh grass (Holliday, 2005). During ensiling, the 12 J.D. Murphy et al. (2007-CCRP-1.7) resistive polysaccharides are degraded and Mixtures of grasses and grass silage increase intermediates, such as volatile fatty acids (VFAs), for methane yield when compared with a single grass methanogens are produced, which increase methane type, such as Cynodon spp. (Bermuda grass) yield in the digester (Madhukara et al., 1993). Use of (Gunaseelan and Nallathambi, 1997). Additionally, additives during ensiling is a common practice. Plochl and Heiermann (2006) reported methane production from forage and paddock mixtures of 297– Nevertheless, the use of additives in silage preparation 370 m3/t and 246 m3/t ODM, respectively. The did not increase methane as recorded by Neureiter et efficiency of AD can be considerably improved in al. (2005) and Rani and Nand (2004). Conversely, mixed feedstock such as that of grass with legumes according to Lehtomaki (2006), formic acid addition because the NDF concentration of grasses is usually resulted in higher methane production, possibly due to improvements in silage fermentation greater than that of legumes, which is caused mostly through by differences in the NDF concentration of grass and decreases in pH and ammonia-nitrogen (Keady et al., legume leaves (Buxton, 1996). Hence, increasing the 2000). Acidic conditions are suggested during the proportion of legumes, particularly clover, and, whole ensiling process to produce efficient silage for consequently, the leaf to stem ratio of forage results in the digester (Mosier et al., 2005). Another agronomical lower cell wall concentration, in other words reduced factor that influences biomethane production from indigestible material and increases in digestibility of grass silage is the biological pretreatment of feedstock, feedstock. such as the use of cellulase enzymes during ensiling lignocellulosic decomposers and possibly increases (Clavero and Razz, 2002). This can result in an biomethane production (Table 2.4). This improves the efficiency of increased degradation of cell walls and the breakdown of structural carbohydrates, hence improving the 2.10 potential of biomethane production (Clavero and Razz, • Conclusions The most important husbandry factors that could 2002). Considering the use of inoculants, it has been affect the potential biomethane production from proposed grass and grass silage are species selection, that heterofermentative bacteria (as fertilisation and harvesting date. compared with homofermentative bacteria) could be more beneficial for efficient AD since they facilitate the • production of intermediates for methanogens (Idler et al., 2007). 2.9 The selection of suitable grass species (e.g. perennial meadow ryegrass, foxtail), timothy, based on cocksfoot their and chemical composition and dominance in Irish grasslands, Mixed Pastures can significantly affect biomethane production. Mixtures of species are more common than pure • stands in grazed pastures, with grasses (i.e. ryegrass) Excess fertilisation could negatively affect biomethane production due to increases in the and clover in rotational pastures (Brown, 1999) being structural carbohydrate content of grasses. most common. Such mixtures have advantages over • monospecific pasture because legumes have a higher Late harvesting contributes to decreases in the nutritive value for ruminants and fix atmospheric non-structural carbohydrate content of grasses, nitrogen, whereas the different resource requirements hence the potential for biomethane production. or environmental responses between various species • in mixed pastures allow for broader resource Mixed pastures (e.g. ryegrass and clover) have shown exploitation (Brown, 1999). Additionally, grass species that they might positively affect biomethane production. may vary in terms of their chemical composition – hence methane yields from grassland could possibly • Conservation of grass has been shown to depend on the mixture of species within the vegetation produce higher methane per tonne of organic (Prochnow et al., 2009). matter than fresh grass. 13 The potential for grass biomethane as a biofuel Table 2.4. Effects of pasture type on methane production (Prochnow et al., 2005). Substrate Biogas yield (l/kg VDS) Methane yield (l/kg VDS) Intensive grassland (monoculture fresh, silage) 700–720 – Extensive grassland (fresh and silage) 540–580 – Extensive grassland (fresh and hay) 500–600 – Semi-continuous, 35°C, 18–36 days, co-digestion Extensive grassland (silage) 500–550 – Continuous, 35°C, 20 days, co-digestion Mixed pasture grassland (fresh and silage) 650–860 310–360 Batch, 35°C, 28 days, mono-digestion Mixed pasture grassland (silage) 560–610 300–320 Semi-continuous, 35°C, 28 days, mono-digestion 532, 474, 427a 370, 326, 297a Intensive grassland (monoculture, silage) – 390 Semi-continuous, 37°C, 25–60 days, co-digestion Extensive grassland (silage) – 220 Semi-continuous, 37°C, 25–60 days, co-digestion Grasses and clover (silage) a Conditions Batch, 35°C, 25 days Batch, 37–39°C, 58 days, mono-digestion Harvesting mid-May (before anthesis), end of May (anthesis), mid-June (after anthesis), respectively. VDS, volatile dry solids. 14 J.D. Murphy et al. (2007-CCRP-1.7) 3 How Do We Convert Grass to Biomethane? 3.1 Anaerobic Digestion retention time in the digester, and the organic loading rate (Karagiannidis and Perkoulidis, 2009; Nizami and Anaerobic digestion is an old technology used for Murphy, 2010). stabilising waste and wastewaters and, more recently, for energy production. The process of AD also occurs The history of AD starts with sanitation – septic tanks in nature when organic matter degrades and decays, treating low-strength wastewaters under psychrophilic for example the cow’s digestive system, marshes and temperatures (ambient, less than 20°C) (Rebac et al., swamps, landfills, etc. Biogas, the major end product 1995). of the AD process, is either produced naturally or thermophilic treatment of solid waste (Vandevivere, artificially in airtight vessels known as anaerobic 1999) and the production of gaseous transport fuel digesters The from high solid content feedstocks such as grass biochemical processes in AD, through which the silage (Murphy and Power, 2009b). A significant trend microbial decomposition of organic matter under in AD technology is higher treatment efficiency. This is anaerobic conditions occurs, are distinguished by the made possible by adequate pre- or post-treatments following phases: and by various types of additives or co-substrates that • (Salminen Hydrolysis and Rintala, (complex 2002). organic matter Acidogenesis converted (products into VFAs of and technology has advanced to the improve nutrient composition, metabolic diversity and is resistance towards toxicants (Nizami et al., 2009). The decomposed into smaller units); • The application of AD technology covers a wide range of are uses and substrates, for example farm waste, methanogenic wastewater, industrial organic waste, municipal solid hydrolysis waste, agricultural residues, crops, crop residues, substrates); grass and grass silage (Vandevivere, 1999). • Acetogenesis (products from acidogenesis, which cannot be directly converted to methane by methanogenic bacteria, are converted 3.2 A steady and predictable supply of usable biogas can methanogenic substrates such as acetic acid); be achieved if anaerobic digesters are designed, and • Anaerobic Digesters into operated and maintained properly. Concrete, steel and Methanogenesis (the production of methane and brick or plastic are the materials with which anaerobic carbon dioxide from intermediate products) (Al digesters are made. A variety of shapes, such as silos, Seadi et al., 2008). troughs, basins or ponds, exist. They may be placed underground or on the surface. The same basic The process of biogas production is not efficient unless components in all designs are a premixing area or carried out in a controlled environment within an tank, a digester vessel, a system for using the biogas, anaerobic digester. The digester technology should be and a system for distributing or spreading the effluent designed so as to optimise the conversion of the (Demirbas and Ozturk, 2005). specific organic material to gaseous products (Demirbas and Ozturk, 2005). A range of digester In a one-stage digester, all the AD processes (i.e. types and configurations may be utilised. The hydrolysis, acidification and methanisation) occur in configuration chosen (Fig. 3.1) must be based on one tank. In a two-stage system, all the reactions occur various process parameters, such as the solids in each vessel. In a two-phase reactor, microbiological content of the feedstock, the number of phases or processes are separated: hydrolysis and acidification stages operating occur in the first reactor and acetogenesis and temperature, the method of feeding the substrate, the methanogenesis in the second reactor. In batch of digestion activities, the 15 The potential for grass biomethane as a biofuel Figure 3.1. (a) Design variation in one- and two-stage digesters, (b) one-stage dry continuous digesters, (c) one-stage dry batch digester, (d) two-stage dry batch digesters, and (e) sequencing fed leach bed digesters coupled with an upflow anaerobic sludge blanket (UASB) (Vandevivere et al., 2003; Nizami and Murphy, 2010). CSTR, continuously stirred tank reactor; DRANCO, DRy ANaerobic COnversion. digesters, the feedstock is inserted once into the The majority of digesters treating OFMSW and digester for a certain period of time to complete the biowaste (i.e. 90% of the full-scale plants currently in digestion activity, while in continuous digesters the use in Europe) rely on continuous one-phase systems feedstock is constantly or regularly fed either (Lissens et al., 2001) (Table 3.1). Nevertheless, a mechanically or by force of the new feed. In dry considerable amount of information in the literature exists (e.g. Sachs et al., 2003) on anaerobic treatment digesters, high solid feedstock with dry matter ranging of wastes in two-phase digestion (i.e. the acid-forming from 20% to 50% is used as substrate. The feedstock phase followed by the methanogenic phase). Two- is either sprinkled with recirculating water (dry batch phase systems offer more possibilities to control the digestion) or mixed with digestate (dry continuous). intermediate steps of the digestion process, although Wet digesters, such as the continuously stirred tank the single-phase system is preferred in industry reactor (CSTR), typically operate at less than 12% DS because of simplicity in design and lower investment content. High solid content feedstock may be treated in cost (Arvanitoyannis and Varzakas, 2008) (Table 3.2). a wet continuous system through homogenisation to Currently, only 5% of European biogas plants are liquid state (Nizami and Murphy, 2010), (Fig. 3.1). psychrophilic, 8% are thermophilic, and 87% are 16 J.D. Murphy et al. (2007-CCRP-1.7) Table 3.1. Five-year development in different digesters types (adapted from De Baere and Mattheeuws, 2008). Period One-phase versus two-phase digesters Wet versus dry digesters One-phase Two-phase Wet Dry 1991–1995 85% 15% 37% 63% 1996–2000 91% 9% 38% 62% 2001–2005 92% 8% 59% 41% 2006–2010 (estimated) 98% 2% 29% 71% Table 3.2. Comparison of process weaknesses and benefits of various digester types (Nizami and Murphy, 2010). System One-stage versus two-stage digesters One-stage Two-stage Dry versus wet digesters Dry Wet Batch versus continuous digesters Batch Continuous High rate bioreactors Strengths Weaknesses • Simpler design • Higher retention time • Less technical failure • Foam and scum formation • Low cost • Efficient substrate degradation owing to recirculation of digestate • Complex and expensive to build and maintain • Constant feeding rate to second stage • • More robust process Solid particles need to be removed from second stage • Less susceptible to failure • Higher biomass retention • Complex handling of feedstock • Controlled feeding • Mostly structured substrates are used • Simpler pretreatment • Material handling and mixing is difficult • Lower parasitic energy demands • Good operating history • Scum formation • Degree of process control is higher • High consumption of water and energy • Short-circuiting • Sensitive to shock loads • No mixing, stirring or pumping • • Low energy input process and mechanical • needs • Cost-effective • Channelling and clogging • Simplicity in design and operation • Rapid acidification • Low capital costs • Larger volatile fatty acid production • Higher biomass retention • Larger start-up times • Controlled feeding • Channelling at low feeding rates • Lower investment cost • No support material is needed Larger volume Lower biogas yield mesophilic. In Europe, only Italy and Switzerland use increased process efficiency (Murphy and Power, psychrophilic biogas plants, whereas in Denmark there 2009a) – has become an attractive option as a source are more thermophilic than mesophilic biogas plants for renewable energy production as opposed simply to (Poulsen, 2003). waste treatment (Durand, 2003). Anaerobic digestion recent of grass and grass silage has received increased improvements – reduced technology costs and attention in recent years in Europe (Murphy and Anaerobic digestion technology due to 17 The potential for grass biomethane as a biofuel Power, 2009a), but its use is modest in comparison the vehicle through cascading pressure reduction to with others substrates (Abraham et al., 2007). Most of 250 bar. Alternatively, the existing natural gas the work on digestion of grass and grass silage is infrastructure may be used as a distribution system to carried out at laboratory and pilot scales (Murphy and a service station at a remove from the facility. A Power, 2009b), using manure and maize silage as co- European Commission report (EC, 2006) states that substrates. Nevertheless, in European biogas plants the energy required for local distribution of natural gas during 2002–2004, grass and maize silage were the is zero. This is because the high-pressure trunk lines most used co-substrates (Weiland, 2006). The (typically operating at between 35 and 70 bar) that feed literature regarding the mono-digestion of grass and the low-pressure networks (typically operating at 4 bar) grass silage is limited. However, some studies have provide sufficient energy to supply local distribution. In shown either case, for use as a transport fuel it is necessary a high potential of biogas production (Table 3.3). to scrub and to compress to 300 bar. 3.3 Intermediate pipelines (8 bar) present an interesting Upgrading and Injection option since pressure is similar to some biogas Utilisation of biogas as a vehicular fuel should have as upgrading high as possible a volumetric energy density content processes while injection into the distribution network (4 bar) is the final and most as can be achieved. This is affected by removal of practical solution. However, the gas utility must ensure carbon dioxide and other gases that exist in the biogas that the minimal summer load is greater than the mixture. Apart from methane and carbon dioxide, projected biomethane flow. Furthermore, for security biogas also contains water, hydrogen sulphide, reasons, the utility may require more stringent nitrogen, oxygen, ammonia, siloxanes and particles. monitoring of the gas quality since dilution of These impurities can be removed by cooling, biomethane will be low. Technologies such as compression, precipitation, absorption or adsorption pressure swing adsorption (PSA) and amine scrubbing (Petersson and Wellinger, 2009); collectively this is are promising candidates for simple injection and termed upgrading (Murphy et al., 2004; Persson et al., monitoring systems, since they often provide an 2006). de Hullu et al. (2008) compared five techniques additional assurance that gas quality will meet for upgrading of biogas (Table 3.4): specification (Electrigaz, 2008). 1. Chemical absorption There are several incentives for using the gas grid for 2. High-pressure water scrubbing (HPWS) distribution of biogas: 3. Pressure swing adsorption • One important advantage is that the grid connects the production site with more densely 4. Cryogenic separation, and populated areas which enables the gas to reach new customers. 5. Membrane separation. • They found that membrane separation and HPWS are An off-site customer may have a year-round demand for electricity and thermal energy (a the simplest processes to operate because they do not brewery for example). need special chemicals or equipment to run. In addition, HPWS provides maximum purity, with up to • 98% methane with minimal cost. An off-site customer may achieve far higher energy conversion efficiency due to economy of scale (a combined cycle gas turbine). Upgraded biogas, biomethane, can either be used directly on the site where it is generated or distributed • to customers via pipelines. After upgrading, it may be An off-site customer may have a large captive fleet (bus service). fed into the distribution grid (Persson et al., 2006). The • on-site option for the use of biomethane as a transport It is also possible to increase the production at a remote site and still use 100% of the gas. fuel is to compress it up to 300 bar and discharge it to 18 Table 3.3. Comparison of the optimal anaerobic digesters for grass silage (adapted from Nizami and Murphy, 2010). Pretreatment Process Quality of digestate HRT Solid contents (days) (%) Operating temperature (°C) Cost Destruction of volatile solids (%) OLR (kg VDS/m3/day) Wet continuous one/ two-stage digester CSTR • • • • Pulping Two-stage Chopping (can be oneSlurry stage) Hydrolysed Juice rich in protein and nutrients, soil conditioner >60 2–14 35–40 Medium 40–70 < 3.5 Two-stage sequential batch digester connected with high-rate bioreactor Leach bed with UASB • • Chopping Pulping Two or multistage Soil conditioner, fertiliser, fibrous materials <40 20–40 35 High 40–70 overall 75–98 from UASB 10–15 One-stage dry continuous digester DRANCO • Shredding Chopping One-stage Dewatered, good quality, fibrous materials < 40 20–50 50–58 Medium 40–70 12 One or multistage dry batch digester BEKON • Chopping One-stage Dewatered, good quality, fibrous materials <40 30–40 35 Low 40–70 12–15 19 HRT, hydraulic retention time; OLR, organic loading rate; VDS, volatile dry solids; CSTR, continuously stirred tank reactor; DRANCO, DRy ANaerobic COnversion; UASB, upflow anaerobic sludge blanket. J.D. Murphy et al. (2007-CCRP-1.7) Example The potential for grass biomethane as a biofuel Table 3.4. Comparison of different biogas upgrading techniques (adapted from de Hullu et al., 2008). Technique Maximum achievable Yield (%) Purity (%) 90 98 Chemical absorption High-pressure water scrubbing 94 Pressure swing adsorption 91 Cryogenic separation 98 98 Membrane separation • 98 91 78 89.5 Advantages Disadvantages • • Only removal of one component in one column • Expensive catalyst Almost complete hydrogen sulphide removal • Removes gases and particulate matter • Limitation of hydrogen sulphide absorption due to changing pH • High purity, good yield • • Simple technique, no special chemicals or equipment required Hydrogen sulphide damages equipment • • Neutralisation of corrosive gases Requires a lot of water, even with the regenerative process • More than 97% methane enrichment • Additional complex hydrogen sulphide removal step needed • Low power demand • Low level of emissions • Adsorption of nitrogen and oxygen • Can produce large quantities with high purity • A lot of equipment is required • Easy scaling up • No chemicals used in the process • Compact and light in weight • Relatively low methane yield • Low maintenance • • Low energy requirements Hydrogen sulphide removal step needed • Easy process • Membranes can be expensive Furthermore, injecting biogas into the gas grid production, based on changing their filling regimes and improves the local security of supply (Persson et co-digestion patterns. There is a need to compare the al., 2006). potential of various pretreatment options (including pressure, 3.4 Conclusions thermal, enzymatic and chemical pretreatments) for increased efficiency. Upgrading of Selection of the proper digester design for grass biogas comprises the removal of carbon dioxide, biomethane important hydrogen sulphide and other possible pollutants from management/design decision that merits further biogas. Membrane separation and HPWS may be the investigation. The wet continuous two-stage system, simplest processes to operate because the use of the leach bed system with an upflow anaerobic sludge special chemicals or equipment is not necessary. Also, blanket (UASB), the dry continuous system and batch HPWS provides maximum purity (up to 98% CH4) with digesters all have potential for biomethanation of grass minimal cost. The technology is evolving and better silage. Nevertheless, comparisons for treating similar results than those indicated in Table 3.4 have and will quantities of grass silage under similar loading rates be achieved. The produced biomethane can either be and characteristics to evaluate optimal digestion used directly on-site as a transport fuel or, after grid configuration are required. These systems can be injection, may be used off-site where better energy further optimised for better and continuous biogas efficiencies and financial returns may be achieved. production is an 20 J.D. Murphy et al. (2007-CCRP-1.7) 4 Life-Cycle Analysis of Grass Biomethane 4.1 Aims and Methodology includes a two-stage CSTR, and biogas upgrading for biomethane production. Biomass, which includes both energy crops and residues, is a renewable energy resource with Life-cycle assessment is one of the most appropriate significant potential in Ireland. This study proposes to methodologies for the evaluation of the environmental assess the use of grass silage as a feedstock for burdens associated with biofuel production, since it biomethane production. The advantages according to allows Murphy and Power (2009b) include: environmental improvement and is widely used for the identification of opportunities for evaluation of sustainability of biofuel production (Singh • • Arable land is not needed for growing grass and et al., 2010a). The scope of the study may be direct food substitution is not an issue; represented by the cradle (grass silage production) to the grave (the utilisation of produced biomethane in the Over 91% of Ireland’s agricultural land is under vehicles) analogy (Fig. 4.1). The analysis takes into grass; • consideration the energy and emissions (both direct Biomethane as a transport fuel is a mature and indirect) associated with all stages of production of technology; silage and biomethane. This facilitates comparison of systems if the boundary conditions are the same. The • Biogas can also be made from wastes and functional unit is defined as cubic metres of residues, thus increasing the availability of biomethane per year and the environmental impacts feedstock; and are expressed as grams carbon dioxide equivalent (CO2e) per megajoule energy replaced. This is • Projections for reductions in animal stock will important; the analysis is a field-to-wheel system release grassland for biomethane production. rather than a field-to-tank system. The vehicle operating on gaseous transport fuel is assumed to Grassland sequesters carbon into the soil, which is not have an efficiency (MJ/km) 18% less than a diesel released on harvesting leading to a potential for vehicle (Korres at al., 2010). This thus reduces the sustainable biofuel production from grass (Tillman et al., 2006). The Renewable Energy efficiency of the whole process. Emissions associated Directive with the manufacture of machinery are not included as recognises the potential for biogas as a transport fuel per the EU Renewable Energy Directive (EC, 2009a). in attributing a GHG saving of 83% to compressed The global warming potential (GWP) for carbon biomethane generated from residues. The aim of this dioxide, nitrogen dioxide and methane is 1 kg CO2, 296 study was to investigate in detail the production of kg CO2 and 23 kg CO2, respectively. grass biomethane as a transport biofuel in accordance with the Renewable Energy Directive sustainability The basis of the analysis is a grass-based farm-to- criteria, in particular GHG emissions savings in biomethane facility visited by the authors in Austria in comparison with the fossil fuel it replaces (diesel in this early 2008. The Austrian facility digests grass from 150 instance). To be deemed sustainable according to the ha, which equates to 1,650 t DM/year based on a Renewable Energy Directive, a reduction in emissions typical yield of 11 t DM/ha/year. Yields in Ireland tend of 35% is required if operated before 2017, 50% after to be higher; the assumption in this analysis is that the 2017, and 60% for new installations installed after farms entering the biomethane industry will be from 2017 (EC, 2009a). The methodology employed areas with good yields. A production of 12 t DM/ha is involves a life-cycle assessment (LCA) of current assumed. Accordingly, the facility modelled under Irish agricultural practices for reseeded perennial ryegrass conditions, pastures for silage production; the process technology exclusively for silage production, requires a farm of 21 assuming that grassland is used The potential for grass biomethane as a biofuel Stage Energy Process Crop production Fertilizer / herbicide / seed / lime Plantation, cultivation + harvesting Diesel Grass Transport Storage Biogas production Product Electricity Macerating Heat + electricity Anaerobic digestion Biomethane production Electricity Silage Biogas Digestate Cleaning + upgrading Biomethane Compression Compressed biomethane Distribution + pumping Diesel Digestate use Transport Fertilizer Figure 4.1. Grass-to-biomethane system (Smyth et al., 2009). 137.5 ha. The energy used in the process is split into method of direct sowing is carried out in the direct and indirect energy. Direct energy is the energy autumn. A seeding rate of 25 kg/ha is used in this used in the production process, e.g. fossil fuel used in study as recommended in the Irish Farmers machinery. Indirect energy is the energy used in Journal (Kilroy, 2007). It is preferable when producing materials that are subsequently used in the reseeding that low or no-till methods are production, e.g. fertiliser, diesel, etc. employed to minimise production of GHG emissions. 4.2 • Grass Silage Production • Reseeding: Harvesting: Reseeding of grassland is recommended in order Harvesting is assumed to take place twice per to improve grass vigour and growth (Kilroy, year, i.e. two-cut silage – the first cut is usually at 2007). Life-cycle assessments of grass systems the end of May, the second at the beginning of in reseeding July. Two cuts are the norm in the Irish livestock frequencies, from 2 to 8 years (Kelm et al., 2004; sector, as a three-cut system is generally Gerin et al., 2008). The Irish Farmers Journal deemed uneconomic due to the high costs of recommends reseeding every 4–8 years (Kilroy, harvesting and lower yields from third (or 2007). A 2004 survey of 180 silage-making farms subsequent) cuts. the literature use various (O’Brien et al., 2008) found that 54% of pasture • farms were more than 10 years old. The Fertiliser application rates: reseeding frequency used in this analysis is once Fertiliser application rates for nitrogen (N), every 8 years and assumes that the traditional phosphorus (P) and potassium (K) used in this 22 J.D. Murphy et al. (2007-CCRP-1.7) study are as recommended by The application of 10 t/ha over the 8-year crop Teagasc cycle is assumed. (Table 4.1). Biomethane production results in the generation of digestate that can replace • conventional fertilisers. In this study, each Silage yields: hectare produced 12 t of DM, equivalent to 54.5 t Silage yields in Ireland are typically between 11 of grass silage at 22% DS content. The resultant and 15 t DM/ha/year; yields are generally higher digestate production is 48.6 t/ha/year (Table 4.2). in the south-west of the country and decrease As digestate contains 2.1 kg/t, 0.087 kg/t and towards the north-east (Ryan, 1974; Brereton, 3.08 kg/t N, P and K, respectively, it can replace 1995; Holden and Brereton, 2002). For this study, 102 kg/ha/year N, 4.2 kg/ha/year P and 149.7 each hectare is assumed to produce 12 t kg/ha/year K. DM/year, which is somewhat conservative. It is assumed that pit silage has a DS content of 22%, • Herbicides: which yields an overall production of 54.5 t/year. Weeds are not a problem for the majority of Irish Grass when cut may be at 18% DS, thus 67 t of pastures, but better weed control has the grass may be cut in every hectare. Losses will potential to increase output in some cases occur in silage production; 12 t DM/ha/year are (O’Mara, 2008). In the case of continuous silage, taken as the solids remaining in the silage pit. weeds (e.g. docks) may become problematic and herbicide spraying is therefore recommended 4.3 Biogas Production every 3–4 years (Fitzgerald, 2007). The herbicide Anaerobic digestion is a ubiquitous technique for glyphosate is assumed to be applied once before converting organic wet biomass into renewable energy ploughing and asulam twice during the life cycle in the form of biogas by bacteria in an oxygen-free of the crop. environment, which may then be upgraded to biomethane (Singh et al., 2010b). It is a well- • Lime: established process and is widely used in many Irish soil tends to be slightly acidic. A common European countries, although research aiming to practice to restore pH to acceptable levels is optimise the process for biogas yields is still ongoing through the application of lime. Lime application (Nizami and Murphy, 2010). enhances nutrient availability, increases the activity of micro-organisms and earthworms, and A CSTR operating at 10% DS is assumed. Typically improves the response to fertiliser (Coulter, slurries with a DS content below 12% are used as a 2004). The optimum pH for grassland in mineral feedstock in a CSTR. The digestion of grass with a soils is 6.3 (Culleton et al., 1999; Coulter, 2004) higher DS content is achieved through the addition of and Teagasc recommends that grassland should water and/or recirculated leachate to reduce the DS be limed at least every 5 years (Coulter, 2004). content below 12%. It is assumed that the digester Table 4.1. Fertiliser application rates (adapted from Coulter, 2004). Nitrogen (kg/ha)a,b Phosphorus (kg/ha)b,c Potassium (kg/ha)b,d 75 70 110 Establishment year First cut Second cut First cut Second cut First cut Second cut First 4 years after establishment 150 125 20 10 200 95 Subsequent years 125 100 20 10 200 95 a In the establishment year, half of the nitrogen is applied at sowing and half 3–4 weeks later. given assume no slurry application. c Phosphorus advice assumes a soil phosphorus index of 2. d Potassium advice assumes a grass only (no clover in the sward), a soil potassium index of 1, and a target yield of 12 t DM/ha. bValues 23 The potential for grass biomethane as a biofuel operates at a mesophilic temperature of 38°C and that biogas per tonne VDS (302 mn3 CH4/t VDS) added to the temperature of the incoming feedstock is 10°C, the AD plant is assumed on the basis of 55% which is typical for the south of Ireland. destruction of VDS. Total biogas production is 816,750 mn3/year (Table 4.2). The daily mass balance for the The loading rate for wet digestion of grass silage is digester is presented in Fig. 4.2. taken as 1.44 kg VDS/m3/day. The working volume of 4.4 each digester for 7,500 t grass silage per year is calculated as 1,413 m3 Compressed Biomethane Production , assuming that digesters are Biogas from the AD of grass consists of approximately cylindrical in shape, with a diameter to height ratio of 55% methane, 45% carbon dioxide and a small 1:1.5 (CropGen, 2007). The volume of the first digester amount of other contaminants. It must be upgraded or is 1,766 m3, assuming an 80% working volume, scrubbed to natural gas standard (about 97% whereas the volume of the second digester is 3,532 methane) before being used in vehicles or in the m3, assuming half of the digester volume is used for natural gas grid. There are two types of filling storage. Approximately 45.2 m3 feedstock (at 10% DS) operations, slow fill and fast fill. Slow-fill stations have are fed into the first digester every day. The total the retention time is 62.5 days, with the substrate connected directly to the compressor, but have longer remaining about half of the time in each digester. The filling times, typically from 20 min to a number of hours. substrate flows by gravity from the first to the second A fast-fill operation is more complex, but gives filling digester and the liquid is circulated back to the first times of only 3–5 min, and is typically used on a digester. The recirculation of the liquid digestate traditional service station forecourt. Fast fill is assumed reduces the water demand and increases the microbial in this analysis. simpler design, with the dispensing lines population, improving the efficiency of the AD facility (Nizami et al., 2009). Maceration of the silage is carried 4.5 Energy and GHG Emissions Associated with Grass Silage Production 4.5.1 process (Nizami et al., 2009). Mixing may allow better Direct energy consumption and related emissions associated with grass silage production digestion of grass silage by keeping the material The primary fuel input into a ryegrass production homogenous and hindering the settling of silage system is diesel for tractors and trucks. The GHG particles. The optimal DS content for grass silage emissions from diesel consumption are 2.688 kg digestion in a CSTR is reported as 10% (Börjesson and CO2e/l (Murphy et al., 2004) and in production are 0.51 out before insertion of feedstock into the first digester. It reduces the particle size of the feedstock, hence preventing physical obstruction of pipes and pumps by the fibres, and increases the surface area available for microbial attack, thus speeding up the digestion Berglund, 2006). The produced grass silage (7,500 kg CO2e/l (Thamsiriroj and Murphy, 2009). The gross t/year) is mixed with up to 9,000 t of water/liquid energy of the diesel equals 36 MJ/l (EC, 2009a), thus digestate to obtain the desired DS level. The water the GHG emissions equal 88.8 g CO2e/MJ. The direct demand is fulfilled by the recirculation of the liquid energy digestate. Varying the recirculation rate of this liquid estimated based on Eqn 4.1 (Romanelli and Milan, digestate can allow control of the relative rate of biogas 2004). The individual values for each component for production in the two vessels and the level of VFA in each field operation were selected among an both vessels. extensive range of publications suitable for grass consumed during field operations was production and the highest value to obtain a more A methane yield of 186–380 m3 CH4/kg VDS is conservative interpretation was chosen. Greenhouse reported in the literature (Steffen et al., 1998; Gerin et gas emissions were then estimated based on Eqn 4.2. al., 2008; Lehtomaki et al., 2008). The destruction of The results from the energy consumed during the 1 kg VDS produces about 1 mn3 of biogas at 55% whole crop cycle and the subsequent GHG emissions methane content. Maximum destruction therefore is are reported in Table 4.3. The average direct energy 3 consumption was estimated as 2.98 GJ/ha/year. 550 l CH4/kg VDS added. A methane yield of 550 mn 24 J.D. Murphy et al. (2007-CCRP-1.7) Table 4.2. Size of the digester tanks and biomethane yield (Korres et al., 2010). Component Quantity Farm size (ha) 137.5 Silage production (t DM/ha/year) 12 Silage biomass (t/ha/year) 54.2 Silage yield (t/year) 7,500 Dry solids (DS) (t/year) at 22% DS 1,650 Volatile dry solids (VDS) (t/year) at 90% of DS 1,485 m3/day) Loading rate (kg VDS 1.44 3 Working volume of each digester (m ) 1,413 3 Volume of Digester 1 (m ) at 80% working volume Volume of Digester 2 1,766 (m3) 3,532 3 Amount of feedstock added (m /day) at 10% DS 45.2 Retention time (days) 62.5 VDS degraded (t/year) at 55% degradation 816.8 3 Biogas production (mn /year) at 55% VDS destruction Biomethane production (mn 3/year) 816,750 at 97% methane 463,105 Losses in upgradation and compression process (mn 3/year) at 2% loss 3 9262 Net biomethane production (mn /year) 453,843 Energy in net biomethane produced (GJ/year) 16,631 Energy in net biomethane produced (GJ/ha/year) 121 Energy displaced vehicle operating 18% less efficiently on gas than diesel (GJ/ha/year) 99 Digestate yield: (t/year) 6,683 (t/ha/year) 48.6 Figure 4.2. Daily mass balance of anaerobic digester (Smyth et al., 2009). DS, dry solids; VDS, volatile dry solids; CSTR, continuous stirred tank reactor. 25 The potential for grass biomethane as a biofuel Harvesting, spreading of digestate, ensiling and for i operation (ha/h) and GHG is the GHG emissions ploughing are the operations (in that order) that require (kg CO2e/ha/year). the highest energy inputs and thus emit the highest amounts of CO2e. Direct emissions during the crop Volatilisation of herbicides occurs up to 48 h after their cycle equal 2.67 g CO2e/MJ of energy replaced application. Derivation of herbicide emission due to (Table 4.3). volatilisation was estimated from Eqn 4.3 (Baas and Lekkerkerk, 2003). The energy consumed for the i FE = ∑ ( Fci × f c ) / O ci (Eqn 4.1) production of 1 kg of active ingredient (a.i.) as 1 proposed by Saunders et al. (2006) and the GHG = FE × 0.0888 (Eqn 4.2) corresponding emission factors (i.e. kg CO2e/MJ) was where FE is the fuel energy consumed (MJ/ha), Fci is adopted. The final result equated to 5.44 kg the fuel consumption (l/h) for i field operations, ƒc is the CO2e/ha/year or 0.054 g CO2e/MJ energy replaced heating value of the fuel, and Oci is the work capacity and was insignificant in terms of GHG emissions. Table 4.3. Direct energy consumption and related carbon dioxide emissions during the 8-year crop cycle (emissions from diesel production are included) (Korres et al., 2010). Operations Energy consumed (MJ/ha/year) Year 1 Years 2–8 1,141.7 0 Sowing 148.8 Harrowing Average energy consumed (MJ/ha/year) CO2 emissions (kg CO2/ha/year) Average emissions (kg CO2/ha/year) g CO2e/MJ energy replaced Year 1 Years 2–8 142.7 101.4 0.0 12.7 0.13 0 18.6 13.2 0.0 1.7 0.02 238.1 0 29.7 21.2 0.0 2.6 0.03 Rollinga 249.9 0 31.2 22.2 0.0 2.8 0.03 Fertiliserb 154.8 77.4 87.1 13.8 6.9 7.7 0.08 Limec 22.5 0 (22.5) 5.6 2.0 0 (2.0) 0.5 0.01 Herbicided 54 0 (27) 13.5 4.8 0 (2.4) 1.2 0.01 Spreadinge 473.9 947.8 888.6 42.1 84.2 78.9 0.80 Transporte 1.9 37.7 33.2 1.7 3.3 3.1 0.03 Harvestingf 1,309.0 1,309.0 1,309.0 116.3 116.3 116.3 1.17 Ensilinga,g 416.0 416.0 416.0 37.0 37.0 37.0 0.37 4,210.5 2,787.9 (2,814.9, 2810.4)h 2,975.3 375.5 247.7 (250.1, 249.7)h 264.5 2.67 Ploughing Total aData on energy consumption for rolling and ensiling from Smyth et al. (2009). Fertiliser is applied four times during the first year of the crop cycle and twice every subsequent year after each harvesting. c Lime is applied at two intervals during the crop cycle, the first and fifth year after establishment dHerbicides are applied before ploughing and after sowing to favour crop-against-weed competition. Application is in the first year and twice during the rest of the crop cycle in the third and sixth year (corresponding values for energy consumption and related emissions are shown in parentheses). eTransport and spreading were estimated based on the assumption that each load carries 16 t digestate; hence, 418 loads needed per year of which 250 were assumed, excluding empty return. The energy consumption for transport is assumed as 1 and 1.6 MJ/t/km, excluding and including empty return, respectively (Salter and Banks, 2009). Energy required for loading and spreading of digestate is assumed as 2.5 and 17 MJ/t, respectively (Power and Murphy, 2009). f Harvesting includes operations such as cutting, mowing and turning the grass. g Ensiling comprises operations such as silage collection, unloading and inlaying. hThe first number in the parentheses represents values for the 3rd and 6th year, and the second number for the 5th year. b 26 J.D. Murphy et al. (2007-CCRP-1.7) i E Herbicide = ∑ m Herbicide, i × EFHerbicide, i NH3 (t ) = ∑ cfi × (Eqn 4.3) N fertiliseri applied (t) i (Eqn 4.6) 1 NO (t) = 0.0007 × Total N applied (t) where EHerbicide is the total emission of pesticide (kg/year) due to volatilisation, mHerbicide, i is the mass (Eqn 4.7) of the individual herbicide applied (kg/year), and where cƒi values for the most common fertilisers used EFHerbicide, i is the emission factor for the individual herbicide (kg/kg). in Ireland (ammonium nitrate, calcium ammonium nitrate (CAN) and urea) are 0.02, 0.02 and 0.15 t NH3/t N The lime application in the pasture is in the form of crushed limestone (CaCO3). Carbon applied/year, respectively (EMEP/CORINAIR, 2004). dioxide emissions from liming are calculated from the amount The most common source of nitrogen fertiliser used in of crushed limestone applied per year (10 t/ha/year Ireland is CAN; thus, a value of 0.02 is chosen. Indirect over 8 years = 1,250 kg/year) (Eqn 4.4). The emission emissions of nitric oxide (NO) are estimated based on factor equals 0.12 t CO2-C/t of CaCO3 (Baas and Eqn 4.7. Both ammonia (NH3) and nitric oxide Lekkerkerk, 2003). A value of 550 kg CO2e/ha/year emissions was calculated, which equals 5.55 g CO2e/MJ energy (Table 4.4). The total nitrous oxide emission from replaced (see Table 4.8). fertiliser are summed applications is as indirect estimated emissions as 525 kg CO2e/ha/year (Table 4.4). This result is in the lower level of the range observed by Kiely et al. (2009), who (Eqn 4.4) reported nitrous oxide emissions in Irish grassland ecosystems of between 2 and 8.4 kg N2O/ha/year where Elime is the total emission of carbon or carbon (equivalent to 592–2,486 kg CO2e/ha/year). dioxide from liming (t C/year), mlime,i is the mass of the individual liming agent applied (t CaCO3/year), and 4.5.2 EFlime,i is the emission factor (carbon conversion factor) for the individual liming agent (t C/t CaCO3). Indirect emissions result from the energy (and the The fraction of applied nitrogen actually emitted as associated CO2) invested for the production of the Indirect inputs and related emissions associated with grass silage production primary inputs into the crop (i.e. fertilisers and lime, nitrous oxide (N2O) varies on a site-specific basis herbicides and seeds), along with the energy required (Thornton, 1996). Coefficients of variation for nitrous for their transport and application (Table 4.5). oxide emissions typically range from 0.003 to 0.03 (IPCC, 2006). Emissions of nitrous oxide from the use Limestone is transformed into quicklime or calcium of 4.5 oxide (CaO) after heating, and then into hydrated lime (EMEP/CORINAIR, 2004) which includes both direct (Ca(OH)2). The amount of carbon dioxide released into fertiliser were estimated from Eqn and indirect nitrous oxide emissions (Eqns 4.6 and the atmosphere was estimated as a direct emission. 4.7): Nitrogen and potassium have the highest percentages N2O (t) = 0.0125 × N applied (t) + 0.01 (NH3 + NO) emitted (t) of indirect energy consumed in the silage crop (i.e. (Eqn 4.5) 71.4% and 13.3%, respectively) and carbon dioxide Table 4.4. Direct and indirect nitrous oxide emissions (Korres et al., 2010). Direct Indirect Total Year 1 (kg CO2e/ha/year) 923 19.6 942.6 Years 2–8 (kg CO2e/ha/year) 456 9.7 465.7 Average (kg CO2e/ha/year) 514 10.9 525 Emissions (g CO2e/MJ energy replaced) 5.18 0.11 5.29 27 Table 4.5. Indirect energy consumption and related carbon dioxide emissions during the 8-year crop cycle (Korres et al., 2010). Crop production Dose applied (kg/ha/year) Year 1 Years 2–8 Nitrogen 249 123 Phosphorus 97.9 Potassium Energy required (MJ/kg) Energy consumed (MJ/ha/year) Average energy consumed (MJ/ha/year) Year 1 Years 2–8 65 16,185 7,995 9,018.7 26 15 1,468.5 390 330.2 145 10 3,302 2.016 0 550 4.4 0 (4.4) 5,000 0 (5,000) Emission factora (kg CO2e/MJ) CO2 emissions (kg CO2e/ha/year) Average emissions (kg CO2e/ha/year) g CO2 e/MJ energy replaced Year 1 Years 2–8 0.05 809.2 399.7 450.94 4.55 524.8 0.06 88.1 23.4 31.49 0.32 1,450 1,681.5 0.06 198.1 87 100.89 1.02 1,108.8 0 138.6 0.06 66.5 0 8.32 0.08 310 1,364 0 (1,364)e 511.5 0.06 81.8 0 (81.8)f 30.69 0.31 0.6 3,000 0 (3,000) 750.0 – 0 0 0 0 40d 0 5 1.98f,g 49.5 0 6.19 0.06 26,468.3 9,835 (11,199, 12,835) 12,630.2 1,293.3 510.1 (2,670, 592) 628.5 6.34 Fertilisera,b,c Glyphosated Asulamd Limea,b,f 28 Seed Total a 25d Saunders et al. (2006). Kelm et al. (2004). c Styles and Jones (2004). d Smyth et al. (2009). e Energy and emissions in parentheses for the application of herbicide (asulam) in the third and sixth year of the crop cycle. f West and Marland (2002). g kg CO2e/kg seed. b The potential for grass biomethane as a biofuel Herbicidea,b J.D. Murphy et al. (2007-CCRP-1.7) emissions during the crop production period (i.e. through which heat loss is occurring (m2), and ∆T is the 71.7% and 16%, respectively). Indirect energy temperature drop across the surface (°C); consumption and emissions during the crop production q = CQ∆T cycle equate to 12,630 MJ/ha/year and 6.34 CO2e/MJ energy replaced, respectively (Table 4.5). 4.5.3 where q is the heat required to raise feedstock to digester temperature (kJ/s), C is the specific heat of the Emissions from transportation Berglund and Börjesson (2006) Eqn 4.9 feedstock (kJ/kg/°C), and Q is the volume to be added reported that (kg). transportation of grass by truck requires 0.7 MJ energy per tkm excluding empty return. The transportation of The coefficient of heat transfer for the wall, floor and 7,500 t grass/year from field to AD plant (10 km distant) roof of the digester is taken as 0.8, 1.7 and 1 W/m2/°C, requires respectively 52.5 GJ/year. Total emissions in (CropGen, 2007). m3 The volume of transportation of grass are calculated as 0.34 g feedstock added daily is 45.21 CO2e/MJ energy replaced. feedstock has a low solids content, its specific heat is at 10% DS. As the assumed to be similar to that of water (4.2 MJ/t/°C). The summed emissions for lime transport from the UK The production of thermal energy is assumed to be by are 0.5 GJ/t lime (Kongshaug and Jenssen, 2003; natural gas; an emission factor of 240 g CO2e/kWh Harrison et al., 2006), with subsequent carbon dioxide thermal energy (Murphy et al., 2004) is used. This emissions equal to 0.044 kg CO2e/kg of limestone analysis (88.8 g CO2e/MJ diesel). At 10 t of limestone per temperature drop from the floor of the digester must be hectare in an 8-year cycle on 137.5 ha displacing 99.2 less than 28°C and recycled leachate will be warmer GJ/ha/year, this equates to 55 kg CO2e/ha/year, which than 10°C, also the amount of heat provided by equals 0.55 g CO2e/MJ energy replaced. metabolic generation is uncertain and therefore 4.6 4.6.1 be considered conservative as neglected. The annual thermal energy demand is Direct Energy Consumption and Related Emissions Associated with Biomethane Production calculated as 3,703 GJ, which emits 248.8 t CO2e/year, equivalent to 18.25 g CO2e/MJ energy replaced (Table 4.6). The conservativeness of the approach employed here relates to modest loading Heating digesters rates, effective volumes of only 80% of the tank and the The heat requirement of digestion is calculated by oversizing of the second digester to provide storage. summing the energy lost from the digester tank and Thus the stored material is also heated. energy required to heat the feedstock. Equations 4.8 and 4.9 are used (Salter and Banks, 2009): hl = UA∆T may 4.6.2 Biogas losses Even moderate losses of methane can affect Eqn 4.8 significantly the emissions from the biomethane where hl is heat loss (J/s), U is the overall coefficient of production process, since methane is 23 times a more heat transfer (W/m2/°C), A is the cross-sectional area potent GHG than carbon dioxide. Methane losses Table 4.6. Greenhouse gas emissions from digesters (Korres et al., 2010). Energy (GJ/year) Energy (GJ/ha/year) GHG emission (kg CO2e/year) GHG emission (g CO2e/MJ energy replaced) Heat loss from Digester 1 681 4.95 45,785 3.36 Heat loss from Digester 2 1,082 7.87 72,679 5.33 Heating of the feedstock Digester 1 1,940 14.11 130,395 9.56 Heating of the feedstock Digester 2 0.00 0.00 0.00 Total 3,703 248,859 18.25 26.93 29 The potential for grass biomethane as a biofuel during the upgrading and compression of biogas are required electricity. The upgradation and compression taken as 2% of biomethane (Börjesson and Burglund, of biomethane emits 12.6 g CO2e/MJ energy replaced. 2006), whereas losses during the rest of the system are considered negligible. According to Murphy and McKeogh (2004), each cubic metre of biogas that escapes and is not combusted produces 9.16 kg of 4.7.1 Base case and GHG emissions of biomethane production. The or 10.82 g CO2e/MJ energy replaced. Indirect emissions production Sensitivity Analysis Table 4.8 outlines the summary of the energy demand CO2e. Thus, this escape equates to 147.5 t CO2e/year 4.6.3 4.7 total parasitic energy demand is 56.7 GJ/ha/year and from emissions are 6.9 t CO2e/ha/year, equivalent to 69.7 g biomethane CO2e/MJ energy replaced. The net energy production from each hectare is equal to 64.4 GJ (Fig. 4.3) and The energy required for maceration, mixing and water emissions savings equal 21.5% in comparison with pumping activities is supplied by the electric grid. At the fossil diesel (88.8 g CO2e/MJ). Grass silage time of writing, 542.8 kg CO2e/MWh are produced in production, upgrading and compression of biomethane the Irish Grid (SEI, 2009a). The electrical energy and parasitic energy demand of anaerobic digesters requirement for maceration is taken as 2 kWh/t of are the main contributors to GHG emissions. silage added (Smyth et al., 2009), for mixing slurry digesters (operating at about 10% DS) 10 kWh/t of 4.7.2 slurry digested (Murphy et al., 2004), and for pumping Significant of water from the second digester to the first is taken achieved by technology substitution or improvement. as 0.2 kWh/m3 (assuming a 4 kW pump with a capacity Using electricity from wind greatly reduces the 3 of 20 m /h). The total energy consumption and Wind energy for electrical demand GHG emissions reductions can be emissions associated with the grass biomethane emissions from the maceration, mixing and water system. Assessment of GHG per kWeh varies greatly pumping are calculated as 4,760 MJ/year and 98.68 t (8–46.4 g CO2e/kWeh) in the literature (Weisser, 2007; CO2e/year, are Tremeac and Meunier, 2009). Considering the highest equivalent to 7.24 g CO2e/MJ energy replaced respectively. These emissions value, biomethane from grass silage effects a 42% (Table 4.7). reduction in emissions (Fig. 4.3), which would lead to a classification of sustainable biofuel for the years 2010– The electrical demand for biogas scrubbing and 2017. 3 compression ranges between 0.3 and 0.6 kWh/m and 0.35 and 0.63 kWh/m3 upgraded 4.7.3 biomethane, respectively (Persson, 2003; EC, 2006; Murphy and Woodchips for thermal demand The supply of thermal heat demand by utilisation of 3 Power, 2009a). A value of 0.35 kWh/m is assumed for woodchips in biomethane production can provide each operation, which equates to 317.7 MWh/year significant GHG savings. Eriksson and Gustavsson (8,318 MJ/ha/year) electricity demand. Approximately (2010) 172.4 t CO2e are emitted during the production of the production from woodchips under various scenarios. reported 3.5–5.5 kg CO2/MWh energy Table 4.7. Emissions in maceration, mixing and pumping activity during biogas production (Korres et al., 2010). Quantity (t/year) Energy required (kWh/t) Energy required (MJ/ha/year) GHG emissions (kg CO2e/year) GHG emissions (g CO2e/MJ energy replaced) Maceration 7,500 2 392 8,142 0.60 Mixing 16,500 10 4,320 89,562 6.57 Water pumping 9,000 0.2 47 977 0.07 12.20 4,759 98,681 7.24 Total GHG, greenhouse gas. 30 J.D. Murphy et al. (2007-CCRP-1.7) Table 4.8. Energy demand and greenhouse gas (GHG) emissions for biomethane production from grass silage under base-case scenario (adapted from Korres et al., 2010). Activity Energy required (MJ/ha/year) GHG emissions (kg CO2e/ha/year) GHG emissions (g CO2e/MJ energy replaced) 2,975 265 2.67 Herbicide volatilisation – 5.4 0.054 Lime dissolution – 550 5.55 Nitrous oxide emissions – 514 5.18 12,630 629 6.34 – 10.9 0.11 Grass silage 382 33.9 0.34 Lime 750 55 0.55 26,930 1,809.9 18.25 – 1,072.7 10.82 Maceration, mixing and pumping 4,760 717.7 7.24 Upgrading and compression 8,318 1,253.8 12.6 56,745 6,917 69.70 Grass silage production Direct Agronomic operation Indirect Production of inputs Nitrous oxide emissions Transportation Biomethane production Direct Heating of digesters Biogas loss Indirect Total 21.5 Base case 42 Wind energy for electricity Net energy (GJ/ha/annum) 64.4 Wood chips for heat demand 62 63.84 Digester configuration 62.1 66.75 Vehicle efficiency 68.9 66.75 0.6 t/ha/annum C sequestration 89.37 66.75 2.2 t/ha/annum C sequestration 66.75 2.8 t/ha/annum C sequestration 66.75 0 50 % CO2 saving 64.4 100 164.47 260.05 150 200 250 300 Figure 4.3. Percentage carbon dioxide savings over fossil diesel and net energy production under various scenarios in biomethane production (the scenarios are cumulative top to bottom) (adapted from Korres et al., 2010). 31 The potential for grass biomethane as a biofuel Adopting the highest emission value, biomethane from 2. The amount of carbon contained in digestate (2.2 grass silage results in 62% reduction in emissions t C/ha/year). This yields a savings in relation to (Fig. 4.3), which would lead to a classification of fossil fuel for substitution of 164.5%. sustainable biofuel for the years after 2017. The net energy of the system is slightly lower (63.84 3. The sum of carbon contained in the above two GJ/ha/year) than other scenarios, as the energy used cases (2.8 t C/ha/year). This yields a savings in in the production and transport of woodchips has to be relation to fossil fuel for substitution of 260%. taken into account (0.02 MJ of primary energy per 1 MJ of biomass stored (Gasol et al., 2009)). All scenarios secure sustainability of biomethane production from grass silage after 2017. 4.7.4 Digester configuration Half of the volume in the second digester is used as a 4.8 Conclusions storage tank. The heat requirement to maintain a constant temperature within it for maximum microbial The life-cycle analysis is necessarily detailed. It draws activity can be reduced significantly if the second upon data from numerous sources, both agricultural digester is used only for digestion and the digestate is and process engineering. There is potential for stored in a separate tank. This leads to a drop of 2.91 variance in many of the figures. The agricultural data in GJ/ha/year energy demand and cumulative GHG particular are open to discussion – indirect emissions savings of 62.1% compared with diesel. associated with fertiliser, nitrous oxide emissions, and emissions associated with land spreading of digestate. 4.7.5 Vehicle efficiency Carbon sequestration is site specific, depends on the Spark ignition engines converted to use natural gas as land type, and whether the grass is grazed or used for a fuel show a power decrease of 18% (used in this silage production. These topics abound in the scientific study) due to decreases in volumetric efficiency. This literature and are subject to numerous ongoing power loss can be decreased by utilising a higher research studies. Likewise, the process is open to compression ratio and advancement in spark timing debate. How much gas is lost in the biogas plant? (Henham and Makkar, 1998). Improvements in engine What is the efficiency of the upgrading process? What efficiency to a similar km/MJ as diesel will improve the is the vehicle efficiency? emissions. This leads to an overall production of 27.63 g CO2e/MJ instead of 88.8 g CO2e/MJ for diesel, However, allowing for the above, the analysis generating a cumulative saving of 68.9% compared presented in this section suggests that parasitic energy with diesel. 4.7.6 demands at the grass biomethane facility are the major source of emissions. Thus, purchase of green Carbon sequestration electricity and minimisation of thermal energy input are Three scenarios are examined: essential. As supported by other researchers, the vehicle must be optimised for biomethane; bi-fuel 1. The amount of carbon sequestered by grassland vehicles may not meet this criterion. as recorded by Byrne et al. (2007) is 2 t C/ha/year (0.6 t soil C/ha/year). This is in agreement with Through process optimisation, an emission reduction Freibauer et al. (2004) and Jones and Donnelly (2004), where a minimum amount of 0.6 t of more than 60% may be effected by grass C/ha/year was reported as the potential soil biomethane. Allowing for grassland sequestering carbon sequestration rate for perennial ryegrass carbon (a value of 0.6 t C/ha/year is deemed and permanent crops under European agricultural conservative), a reduction in emissions of 89% is conditions. This yields a cumulative emissions achievable, which savings in relation to fossil fuel for substitution of biomethane is 89.4%. indigenous, non-residue, European transport biofuels. 32 one would of suggest the most that grass sustainable, J.D. Murphy et al. (2007-CCRP-1.7) 5 What is the Market for Grass Biomethane? 5.1 The Relationship between Grass, Farming and Energy said that it exports grass as this is the feedstock for Farm incomes in Ireland are in decline and many Grass is used in many operational AD plants farmers would operate at a loss in the absence of throughout Europe, and is the second most important subsidies. When inflation is considered, the average energy crop for AD in Germany (Rösch et al., 2009). family farm income (FFI) for all farming systems Grass covers around 91% of Ireland’s agricultural land; decreased by 22% in real terms from 1995 to 2008 thus, as a bioenergy crop, no land-use change is (Connolly et al., 2009). There is a growing dependence required. The energy balance of grass biomethane is on grants and subsidies in all farming sectors. Low better than that of temperate energy crops (Smyth el FFIs lead farmers to seek opportunities for farm al., 2009) and the GHG savings meet the requirements diversification and alternative sources of income. The of the EU Renewable Energy Directive (Korres et al., National Development Plan (NDP, 2007) recognises 2010). An indigenous grass biomethane industry could as a key task the promotion of the diversification of the also provide employment and aid in developing the rural economy. A move away from conventional ‘greentech’ sector. cattle. farming can be further supported by the fact that all grass-based farming systems (beef, dairy, and sheep) Biogas can be burned directly for heat or electricity produce large quantities for the export market. This is generation or can be upgraded to natural gas especially true in the beef sector, which had self- standard, i.e. biomethane. Biomethane and natural sufficiency values of over 600% for each year in the gas are mixable and interchangeable; mixtures of period 2000–2008 (DAFF, 2009; CSO, 2010). This biomethane and natural gas are termed bioNG and means that the cattle industry is effectively subsidised can be sold from the gas grid in a similar manner to for export. renewable electricity. A 10:90 blend could be sold as a transport fuel to aid in meeting the target for 10% Ireland is over 89% dependent on imported energy, renewable energy in transport. While there is currently with imported oil and gas accounting for 81% of energy no market for gas as a transport fuel in Ireland, there supply (Howley et al., 2009a). This has significant are over 10 million compressed natural gas (CNG) implications emissions vehicles worldwide (NGV, 2009) and the use of agreements and national and EU targets for renewable for security of supply, compressed biomethane, either on its own or mixed energy. Targets have been set in Ireland for renewable with natural gas (bioCNG), is growing. energy penetration by 2020 in each of the three energy 5.2 sectors: 1. 40% renewable electricity (Howley et al., 2008); Biomethane Potential in Ireland from Numerous Sources If a biomethane industry develops in Ireland, grass will not be the only source. It is prudent to examine the 2. 12% renewable heat (DCMNR, 2007); and potential of the industry and to assess the bioresource and the relative role of grass in this. Meaney et al. 3. 10% renewable transport fuels (DCMNR, 2007). (2003) categorise agriculture as the single largest Ireland is currently over 99% dependent on oil and oil source of waste in Ireland. Organic agricultural wastes products for transport energy (Howley et al., 2009b), refer to all types of animal excreta (i.e. faeces and while 96% of thermal energy is from non-renewable urine from cattle, sheep, pigs, and poultry) in the form sources (Howley et al., 2009a). Thus, Ireland imports of slurries and farmyard manures. Cattle slurry is energy and exports agricultural produce; it could be generated for 20 weeks of the year (the period that the 33 The potential for grass biomethane as a biofuel animals are housed in the winter). All slurries or litter of OFMSW will be digested in 2020 (in line with Brown from pigs and poultry are collected as the animals are (2004)); this has the potential to produce 0.57 PJ in housed throughout the year (Crowe et al., 2000). Total 2020. Currently, OFMSW is landfilled and a relatively slurry production in Ireland is estimated as 34.89 small proportion is composted. Compliance with the Mt/year in 2020 (Singh et al., 2010b). Slurries are Landfill Directive will dictate that by 2016 practically all applied to land as organic fertiliser; however, the OFMSW will be either composted or digested. release of nutrients is not uniform and, as such, the fertiliser value is not definite, there is significant The National Climate Change Strategy (DEHLG, 2000) potential for run-off and eutrophication. Digested slurry proposed reducing methane from cattle by the is less offensive, has minimal odours and, more equivalent of a 10% reduction in the projected herd importantly, the nutrients are available in the year of size for 2010. As cattle are responsible for 86.6% of application. Assuming 5% of collectable slurry from methane emissions from ruminant animals (1990) and cattle, pigs and sheep and 75% of poultry slurry is 80% of the emissions from cattle come from non-dairy available for digestion, the practical energy production herds (DEHLG, 2000), the main target for herd will be 1.88 PJ in 2020 (Table 5.1). In Ireland reduction is likely to be in the beef sector. Currently, approximately 8 million livestock (mainly cattle, pigs grass is grown on 3.94 Mha (more than 91% of and sheep) and 12 million poultry are slaughtered agricultural land) (CSO, 2009b). If the size of the annually for meat production. This is all collected at the national herd is reduced as set out in the National abattoir and is a ready source of biomethane. The Climate Change Strategy, 0.39 Mha of agricultural practical energy potential in 2020 from digestion of grassland may be surplus to animal feed requirements 50% of amenable slaughter waste (0.42 Mt) is by 2020. Smyth et al. (2009) found that if grass is used estimated to be 0.68 PJ energy (Singh et al., 2010b). in for methane production it will provide 3,240 mn3 categorisation. The organic waste includes paunch CH4/ha; this is equivalent to 122 GJ/ha/year of gross content (belly grass), which is ideally suited for energy. On this basis, 0.39 Mha of surplus grass has digestion. It is offensive and biodegradable and current the potential to generate 47.58 PJ/year energy. If 25% practice is to plough it into arable land. of this area (0.1 Mha) were used in this industry in Abattoir waste varies in composition and 2020, there is potential to generate 11.9 PJ energy The OFMSW comprises food and garden waste only. (Table 5.1). For the practical scenario, there is The quantity of OFMSW is assumed to increase potential to satisfy the Renewable Energy Supply in linearly Population Transport (RES-T) target of 10% through biomethane estimates were taken from CSO data (CSO, 2009a) alone; alternatively, there is potential to substitute and used to calculate projected OFMSW in 2020, i.e. 6.3% of natural gas demand in 2020 or 44% of approximately 0.87 Mt for 2020. It is assumed that 25% residential gas demand. with increasing population. Table 5.1. Biomethane potential in Ireland in 2020 (adapted from Singh et al., 2010b). Feedstock Total energy in 2020 (PJ) Practical energy in 2020 (PJ) Factor for Contribution to Percentage of Percentage of RES-T RES-T target transport energy gas demand in (PJ) in 2020 2020 (240 PJ) (240 PJ) Slurry 15.53 1.88 ×2 3.76 1.57% 0.78% 5.5% OFMSW 2.26 0.57 ×2 1.14 0.48% 0.24% 1.7% Slaughter waste 1.37 0.68 ×2 1.36 0.57% 0.28% 2.0% Grass 47.58 11.90 ×2 23.79 9.90% 4.95% 35.0% Total 66.74 15.03 30.05 12.52% 6.25% 44.2% RES-T, Renewable Energy Supply in Transport; OFMSW, organic fraction of municipal solid waste. 34 Percentage of residential gas consumption (34 PJ) J.D. Murphy et al. (2007-CCRP-1.7) 5.3 Economic Analysis Biomethane System of fuel on site is excluded, as there is unlikely to be a Grass market in the vicinity of a rural farm plant, while container transport of compressed biomethane is not 5.3.1 Methodology considered due to logistical difficulties. It is assumed A simple economic analysis is carried out on a grass that biomethane injected into the gas grid is purchased biomethane system as outlined in Table 4.2 (137.5 ha by a shipper for sale elsewhere on the grid. The of grass silage with an annual production of 7,500 calculation of shipping charges is beyond the scope of 3 3 t/year of pit silage, 820,000 m biogas or 460,000 m this study. biomethane). The values used for costs and incomes are relevant to the Irish context and are taken from the 5.3.2 Capital costs of silage storage and AD plant literature and from discussions with industry in Ireland Silage is to be stored in a horizontal silo or silage pit. In and abroad. Annualised capital costs (R) (€/year) are practice, the farms would already have pits; thus, the calculated from Eqn 5.1: estimated construction cost of €456,250 for 21 pits (Table 5.2) must be viewed as conservative. R = [P(1 + r)Nr] / [(1+r)N – 1] (Eqn 5.1) The cost of an AD plant depends on a number of where P is the principal (€), r is the rate of return (5%), factors, including the plant size and type, with larger and N is the lifetime of the project (15 years). plants generally having lower capital costs per cubic metre of biogas produced. The capital cost of a CSTR Land is assumed to already be in the ownership of the visited by the authors in Austria, of the same size, was farmers’ co-op and the cost of land acquisition and rent €745,000. As AD is a relatively new technology to are excluded from the analysis. The calculated break- Ireland, 10% is added to this value to give €819,500 even tariffs are compared with existing tariffs where (approximately €110/t feedstock). This is assumed to appropriate, and the effectiveness of the tariff system include the cost of in-situ hydrogen sulphide removal. is assessed. The results also compare profitability under the current tariff structure with existing farm incomes. The use of biogas for energy can follow a Capital costs of a CHP and connection to the electricity grid number of different pathways. Two main scenarios are From discussions with industry and values found in the considered in this study: literature (Murphy and McKeogh, 2004; Murphy and • 5.3.3 McCarthy, 2005), the cost of the CHP plant is Scenario 1: biogas for on-site combined heat conservatively taken as €1,500/kWe, which is the fully and power (CHP); • installed cost, including civil works, electrical and piping Scenario 2: upgrading to biomethane standard installations. Assuming 85% operational efficiency, the cost of a 220 kWe CHP plant is and injection into the gas grid. €330,000. The cost of connection to the electricity grid On-site heat production is not considered, as there are is very site specific and depends on the location of the limited markets for heat in Ireland. Sale as a vehicle new generator in relation to the existing loads and Table 5.2. Cost of a silage pit (Smyth et al., 2010b). Component Silo wall Silage base Effluent channel Quantitya Unit costb (Teagasc, 2008) Total cost 22 walls × 25 m long €400/m €220,000 21 pits × 25 m long × 10 m wide €42/m2 €220,500 Assume 250 m €63/m €15,750 Total €456,250 a Typical dimensions for a full silage pit are 25 m long, 10 m wide and 2.1 m high, with a capacity of 360 t silage (ACA, 2008). Therefore 21 such pits would be required. b Costs for silo wall and effluent channel are per linear metre. 35 The potential for grass biomethane as a biofuel generation on the network, as well as the distance from is around 40% higher, it is important that grass silage the grid. A survey of a number of developers puts the is produced on-farm. typical cost for a 200- to 250-kWe facility as €80,000 for connection equipment, €10,000 for a connection 5.3.6 Operating costs of AD plant study, and €10,000 for the substation (if required). The operational cost of an AD plant is made up of the Underground lines cost around €50,000/km; 400-m cost of labour, electricity (for mixing and pumping), lines costing €20,000 are assumed in this analysis, heating giving a total cost of €120,000. suggests annual operational costs of an AD plant fuel, and maintenance. Previous work (excluding feedstock) to be of the order of 10–12% of 5.3.4 Capital costs of upgrading plant and connection to the gas grid the unsubsidised capital costs (Murphy, 2004). Work in the UK (Holliday et al., 2005) and Sweden (Hagen et al., 2001) used values of 4% and 15%, respectively. A The capital cost of an upgrading facility is highly value of 10% is used in this analysis. An additional dependent on plant size, with smaller plants having allowance of 6.67% of the unsubsidised capital costs is higher costs per cubic metre of upgraded gas. A made for depreciation of the AD, CHP and upgrading membrane plant with a capital cost of €500,000 plants. This allows for a fund equal to the initial (€0.10/kWh/year) is assumed, which includes gas investment to be available after the 15-year lifetime of metering and quality monitoring (Murphy and Power, the facility. The inclusion of a depreciation fund results 2009a). The cost of connection to the gas grid can vary in a relatively conservative analysis as not all widely and depends on distance to the network, developers allow for such a fund. ground conditions, and the type of pipes, grid connection and compressor. Contractual costs can 5.3.7 form a significant part of the overall cost. There are currently no biomethane plants with grid injection in Operating costs of CHP and upgrading plants Ireland and a full pricing scheme has yet to be Typical running costs for a CHP plant are given as developed. It is assumed that the upgrading plant is €0.01/kWhe (Murphy and McKeogh, 2004; Murphy located within 0.5 km of the distribution network, which and McCarthy, 2005). The operating cost of the has a pressure of about 4.2 bar. The cost of installing upgrading plant is taken as €0.02/kWh (€0.20/m3) of distribution pipes has been estimated to be between upgraded gas, which equates to around €92,000/year, €150,000 and €400,000 in the literature (Biogasmax, and gives a total (capital + operating) cost of 2008) and in discussions with Bord Gáis (the Irish Gas €0.03/kWh (€0.30/m3) for upgraded gas. This is at the Board). Bearing in mind the variability associated with lower end of the range quoted by the Swedish Gas this, the total capital cost of connection to the gas grid Centre (Persson, 2003) for plants of this size. The plant is estimated as €200,000. Upgrading plants typically in this analysis upgrades around 110 m3/h of raw gas pressurise gas up to 7 bar, hence no additional (85% operational efficiency) and is relatively small compared with operational plants in Germany and compressor is required. Sweden. Membrane plants have lower maintenance 5.3.5 and energy requirements leading to lower operating Operating costs of silage harvesting costs than for other technologies (de Hullu et al., Yield per hectare has the biggest influence on the 2008). It is assumed that the renewable energy tariff silage cost, whereas the machinery and labour costs received for electricity is the net revenue to the affect the cost of harvesting. Oil price fluctuations and renewable energy provider; additional costs have not their direct effects on fuel and fertiliser costs result in been included in the analysis for this. The operating considerable fluctuations on the cost of silage costs of the compression plant for injection into the gas production. The cost of getting grass into the pit is grid are assumed to be included in the upgrading €950/ha (€17/t), which includes fertiliser, reseeding, costs. The operating costs for metering and quality lime, plastic and contractor charges (calculated from monitoring are also included in the cost of the data in Teagasc, 2008). As the market price of silage upgrading plant. 36 J.D. Murphy et al. (2007-CCRP-1.7) 5.3.8 Potential markets and prices are discussed in Finance and subsidies Section 5.5. There is a national scheme in place offering capital grants for biogas CHP plants of up to 30% of the For farm-based AD plants, it is common practice for the eligible capital costs (SEI, 2009b). The maximum grant digestate to be returned to the land as replacement for is assumed in this analysis. There are no specific chemical fertiliser, contributing to financial savings. grants for biomethane plants injecting into the gas grid, The amount of fertiliser replaced depends on the although there are a number of schemes that could nutrient content of the digestate which is highly potentially provide funding. Three sub-scenarios (30%, dependent, amongst other factors, on the type of 50% and no grant towards capital costs) are feedstock. Further difficulties arise as the price of investigated. The CAP is a system of subsidies and chemical fertilisers, and hence the savings achieved support programmes for agriculture in the EU. On top through their replacement, varies considerably from of standard farm payments, there are a number of year to year. Discussions with the AD industry in schemes under the CAP that could provide additional Ireland resulted in a conservative estimate for the net support for a grass biogas/biomethane system, such value of digestate of €4/t. The digestate quantity is as the Energy Crops Scheme and the REPS. The assumed to be 90% of the silage input (Korres et al., average direct payment received by cattle-rearing 2010) and the value of digestate is therefore 4 x 0.9 x farms is €461/ha (from 2006, 2007 and 2008 farm 7,500 = €27,000, or €196/ha. survey data (Connolly et al., 2008, 2009)). 5.4 Economic Analysis of Grass Biogas and Biomethane under Current Conditions which can then be sold, i.e. heat, electricity and 5.4.1 Scenario 1: Biogas to on-site CHP biomethane. The price paid for heat depends on what The base-case analysis considers three different it is replacing. Examples of average commercial fuel cases (Table 5.3): 5.3.9 Income for biogas and digestate Biogas can be used on-site to generate end products, costs (SEI, 2010) are: oil at €0.058–0.069/kWhth 1. The sale of heat (€0.053/kWhth) and electricity (depending on grade); wood pellets at €0.036/kWhth (€0.12/kWhe) with no capital grant (E+H); (bulk) or €0.061/kWhth (bagged); woodchips at €0.034/kWhth; and natural gas at €0.04/kWhth (based 2. The sale of electricity only with capital grant on a medium-sized business and including standing (G+E); and charges). It is assumed that €0.06/kWhth is paid for 3. The sale of electricity and heat with capital grant heat in this analysis. Subtracting VAT of 13.5%, the (G+E+H). income to the biogas plant is €0.053/kWhth. The tariff for electricity from biogas CHP in Ireland is The proposed facility is not profitable and would €0.12/kWhe. Currently, there is no tariff structure for require an electricity tariff of between €0.196 and biomethane injected into the gas grid. There is €0.256/kWhe to break-even, which is significantly considerable volatility in the wholesale price of natural higher than the current tariff of €0.12/kWhe. Even gas, which varies depending on the season and on when the average farming subsidy of €461/ha is international markets. A figure of €0.02–0.03/kWh is included, the plant still operates at a loss (Table 5.4). assumed and this is considered the minimum tariff for biomethane injected into the grid and is used for A relatively high value for operating costs is used in the comparison in the initial analysis. However, a base-case analysis (10% of unsubsidised capital biomethane tariff system should incentivise renewable costs) and an additional allowance is made for gas and offer a higher return than for fossil gas. depreciation (6.67%) of the AD and CHP plants. Using Biomethane injected into the grid can be used in the a less onerous value of 10%, to cover both operating heat, electricity or transport sector, and the existing costs and depreciation, lowers the break-even prices market conditions will influence the price paid. (Table 5.4), but they are still higher than the current 37 The potential for grass biomethane as a biofuel Table 5.3. Scenario 1: Grass to biogas to combined heat and power base-case economic analysis (Smyth et al., 2010b). System boundaries 3 Assumptions Scenarios Biogas yield (m /year) 810,000 Grant included G Energy yield (GJ/year) 16,831 Electricity incl. E Electricity output (GJ/year) 5,891 Heat included H Electricity output (MWhe) 1,636 Electricity output (kWe) 35% electrical efficiency 220 Heat output (GJ/year) 6,732 Heat output (MWht) 1,870 85% operational efficiency 40% thermal efficiency (€) (€/year) Silage pit 456,250 43,956 AD plant 819,500 78,953 Combined heat and power plant 330,000 31,793 Connection to electricity grid 120,000 11,561 1,725,750 166,263 E+H (€/year) G+E (€/year) G+E+H (€/year) Assumptions Capital costs Total capital costs Capital finance Total capital cost incl. grant 1,500 Max. grant (€/kWe) 1,200 166,263 263,714 1,462,036 CHP plant (€/kWe) 140,856 140,856 140,856 Operating costs Depreciation 76,672 % capital costs 6.67 Silage production 130,625 €/ha 950 Anaerobic digestion plant 81,950 % capital costs 10 CHP plant 16,363 €/kWhe Total operating cost 305,610 Capital + operating costs Income 305,610 305,610 305,610 471,873 446,466 446,466 €/kWh Heat 0.053 99,116 Electricity 0.12 196,362 196,362 27,000 27,000 Fertiliser savings Total income 322,477 Estimate (€/t) 322,477 223,362 322,477 –149,395 –223,104 –113,989 Profit (€/ha) –1,087 –1,623 –902 Profit (€/m3 biogas) –0.184 –0.275 –0.153 Profit (€/kWhe) –0.091 –0.136 –0.076 Elec. price for break-even (€/kWhe) 0.211 0.256 0.196 Subsidy for break-even (€/ha) 1,087 1,623 902 Income – costs 0.01 4 AD, anaerobic digestion; CHP, combined heat and power. E+H, the sale of heat and electricity with no capital grant; G+E, the sale of electricity only with capital grant; G+E+H, the sale of electricity and heat with capital grant. 38 J.D. Murphy et al. (2007-CCRP-1.7) Table 5.4. Scenario 2: Biogas to biomethane to grid; tariff required for break-even (Smyth et al., 2010b). Scenario 1a (€/kWhe) Scenario 2a (€/kWh) E+H G+E G+E+H 50%G 30%G NG No subsidy 0.211 0.256 0.196 0.100 0.108 0.121 With subsidy (€461/ha) 0.173 0.218 0.157 0.086 0.095 0.107 No subsidy 0.164 0.209 0.149 0.081 0.089 0.102 With subsidy (€461/ha) 0.126 0.171 0.110 0.067 0.075 0.088 No subsidy 0.100 0.145 0.084 0.059 0.064 0.071 With subsidy (€461/ha) 0.084 0.129 0.068 0.053 0.058 0.066 No subsidy 0.059 0.104 0.043 0.045 0.050 0.058 With subsidy (€461/ha) 0.043 0.088 0.027 0.040 0.045 0.052 Base case Reduced operating costs and depreciation Co-digestionb Co-digestion (reduced operating costs and depreciation) a Figures in bold indicate profitability under current conditions: • €0.12/kWhe is paid for electricity from biogas combined heat and power; and • €0.02–0.03/kWh is the wholesale price of natural gas. b Co-digestion of 7,500 t/year grass and 7,500 t/year belly grass. E+H, the sale of heat and electricity with no capital grant; G+E, the sale of electricity only with capital grant; G+E+H, the sale of electricity and heat with capital grant. 50%G, receipt of grant for 50% of capital cost; 30%G, receipt of grant for 30% of capital cost; and NG, no grant. tariff of €0.12/kWhe. Inclusion of the farming subsidy 2005; Gerin et al., 2008). For a large plant of 1 MWe (€461/ha) brings the best-case scenario (G+E+H) into size, around 625 ha of grass silage are required, giving profit and results in an annual return of €117/ha. an average haul distance of 2.66 km. However, this is lower than the average FFI for cattleAverage haul distance (km) = x = 2/3xτ rearing farms (€279/ha for 2006–2008, inclusive (Connolly et al., 2008; 2009)), and (Eqn 5.2) therefore uncompetitive with current farming practice. where x is the radius of area of supply (km) = Q ⁄ ( ya π ) , τ is the tortuosity factor ( 2 for rural As plant size increases, investment costs per kilowatt roads), y is the silage yield (t/km), Q is the required decrease (Murphy and McCarthy, 2005; Walla and amount of silage (t), a is the factor of silage Schneeberger, availability2. 2008); therefore, increasing the quantity of grass silage could increase profits. However, this would also result in increased transport Under current conditions, profitability of grass biogas distances for silage delivery and digestate disposal. CHP is possible, but difficult, and relies on: Ideally, transport distances should be kept to a minimum because of associated costs, emissions and • Keeping operational costs to a minimum; nuisance on rural roads. The average haul distance for 2. On average in Ireland, silage, hay and pasture make up 50% of the total land area (CSO, 2009b; OSI, 2010). Assuming that half of the grass in a given area is used for AD, the factor of silage availability is 0.5 × 0.5 = 0.25. 137.5 ha of silage is 1.25 km (Eqn 5.2; Walla and Schneeberger (2008)), which is within the range used in the literature (EPA, 2005; Murphy and McCarthy, 39 The potential for grass biomethane as a biofuel • • Finding a year-round market for heat, although Nevertheless, current legislation restricts the use of this may prove challenging due to limited heat substrates from certain sources and may lead to higher markets; and AD processing and digestate disposal costs. Maintaining current farming subsidies. Animal by-products (ABP) may be a suitable feedstock for AD plant but they can pose a threat to animal and 5.4.2 Scenario 2: Biogas to biomethane to grid human health via the environment if not properly The plant produces biomethane on-site and the disposed of. The collection, transport, storage, biomethane is injected into the gas grid. The boundary handling, processing and use or disposal of all ABP are of the analysis is at injection into the grid and the therefore tightly controlled by the Animal By-Products break-even price of biomethane sold to the grid is Regulations (ABPR). Compliance with the ABPR can calculated. Three different scenarios are considered: add significant cost and must be weighed against the gate fees received. While the ABPR are obviously 1. Receipt of grant for 50% of capital cost (50%G); needed to protect human and animal health and the 2. Receipt of grant for 30% of capital cost (30%G); environment, the strict requirements pose challenges and for the development of AD in Ireland and have been a stumbling block for the industry. The Department of 3. No grant (NG). Agriculture, Fisheries and Food has recognised this The break-even price of gas is found to be €0.100, and is currently in consultation with industry with the €0.108 and €0.121/kWh, assuming 50%, 30% and 0% aim of facilitating the growth of AD (Farrar, 2009). capital grant, respectively (Table 5.4). If the farming subsidy of €461/ha is included, the break-even price This study considers a co-operative AD plant among a falls to between €0.086 and €0.107/kWh. There is group of livestock farmers; the co-substrate is considerable volatility in the wholesale price of natural therefore gas, which varies depending on the season and on perspective, cattle slurry is a recommended co- international markets. A figure of €0.02–0.03/kWh is substrate for grass silage (Nizami et al., 2009). assumed and this is considered the minimum tariff for Previous studies (e.g. Yiridoe et al., 2009) have found biomethane injected into the grid and is used for that, if the non-market co-benefits are excluded, the comparison in the initial analysis. Reducing the AD of farm wastes is generally not financially viable. operating costs and depreciation (as for the CHP plant) This is exacerbated by the dilute nature of cattle slurry brings the break-even gas price down to €0.081– and its low methane yield (10% DS, 140 m3 CH4/t 0.102/kWh, excluding the farming subsidy, and VDSadded (Steffen et al., 1998)), meaning that larger €0.067–0.088 if the subsidy is included (Table 5.4). digestion tanks and operational energy demands Even in the best-case scenario, the break-even price is (heating and mixing) are required than for grass silage still more than double the wholesale price of natural (22% DS, 300 m3 CH4/t VDSadded), but with much gas. lower energy return. In the absence of financial cattle slurry. From a microbiological incentives, co-digestion of cattle slurry with grass does 5.4.3 Co-digestion not improve the economic viability of the plant. Grass Co-digestion is a common practice, as this frequently biomethane is cheaper than slurry biomethane. improves the performance of the digester and increases the biogas production. Examples of co- Greater economic benefit could be achieved by substrates include manure, food remains, animal digesting co-substrates that attract a gate fee. For the blood, rumen contents, fermentation slops and CSTR, a low solids content substrate such as OFMSW. A gate fee can often be charged for the co- slaughter waste (belly grass) would be appropriate. substrates, generating additional revenue for the plant, Discussions with the slaughterhouse industry in and larger plants can also take advantage of Ireland suggest that gate fees of around €20/t could be economies of scale, thus lowering the capital and attracted. Equal quantities (7,500 t/year of each) of operational grass silage and belly grass are used and it is costs per tonne of feedstock. 40 J.D. Murphy et al. (2007-CCRP-1.7) conservatively assumed that there are no financial the digestion of wastes is a proven waste treatment savings from the digestate. Substantial profits are option that reduces GHG emissions from uncontrolled achievable with the CHP plant (Table 5.4), showing fermentation and reduces pollution from poor waste that the current tariff system works well for feedstock management practices (Yiridoe et al., 2009). that attracts a gate fee. However, for grid injection even A considerable uncertainty governs the non-market co- the base-case scenario has a higher break-even price benefits of an AD plant and values are likely to change than the wholesale price of natural gas. in the future as concerns over environmental issues 5.4.4 heighten (Yiridoe et al., 2009). At the end of pipe, Viability of grass biogas and biomethane under current conditions savings from methane through avoiding emissions, such Under current conditions, the only financially viable nitrogen oxides and (Biogasmax, 2008), which equates to €1,387/ha of on heat markets and farming subsidies. Profits are low grass digested. In city centres, this rises to €0.89/l and there is little incentive to switch from current diesel replaced (Biogasmax, 2008) or €2,870/ha of farming practice. There is currently no tariff structure in grass. If a waste feedstock is used, the benefit from place for grid injection, although the development of avoided methane leakage is €0.26/l of diesel replaced such a structure is under way. This analysis shows that and the total benefit including improved end-of-pipe grass biomethane injected into the grid is not emissions is €1.15/l of diesel replaced (Biogasmax, competitive with natural gas. Co-digestion can improve 2008). This equates to €13.8/t of cattle slurry digested the economics, but the ABPR pose challenges for the (based on a biogas yield of 22 m3/t of slurry at 55% industry. methane). Improving the Viability of Grass Biomethane for the Farmer and the Consumer 5.5.2 agriculture in Ireland is Competitive advantage of biomethane When non-market benefits are excluded, grass biomethane is not competitive with natural gas. However, renewable energy targets in each of the Why should we subsidise grass biomethane? Grassland dioxide, diesel replaced for a passenger car in an urban area an on-site CHP plant, and viability is heavily dependent 5.5.1 carbon particulate matter, have been estimated as €0.43/l of option for grass biogas/biomethane in Ireland is use in 5.5 as three energy sectors (heat, transport and electricity) effectively subsidised for export (Howley et al., 2009a). It is mean suggested to competition with other renewables. The existing biomethane production will allow the benefit of double natural gas network, which can serve as a vehicle for credits (EC, 2009a) for meeting the 2020 targets for biomethane RES-T. Injecting biomethane into the gas grid is an advantage of biomethane. that diverting some grassland effective means of distributing renewable energy to a gas grid. In addition, transport, (renewable yields the gas) is in competitive reaches all major cities and 23 out of the 32 counties. for new infrastructure beyond the existing modern, natural biomethane The natural gas grid in Ireland is quite extensive and large number of consumers without any requirement extensive that A programme has been completed replacing all of the farm old cast-iron pipes with polyethylene pipes, resulting in diversification is served well leading to a strong case a more efficient network. There are currently about for subsidising grass biomethane and AD plants in 619,100 domestic connections and 24,000 industrial general. The use of biogas/biomethane reduces GHG and commercial connections to the gas grid in the emissions: 82% for cattle slurry biomethane compared Republic of Ireland and another 118,800 domestic with diesel have been reported (Singh and Murphy, customers and 8,400 industrial and commercial 2009), while savings of 75–150% can be achieved for customers (NIAUR, 2009) in Northern Ireland. grass biomethane compared with diesel (Korres et al., 2010). Methane is a clean burning fuel in terms of local For new installations, bioNG has the edge over other pollutants; it improves air quality and benefits health renewable technologies in areas on the gas grid, (Rabl, 2002; Goyal and Sidhartha, 2003). In addition, especially in urban areas where space may be at a 41 The potential for grass biomethane as a biofuel premium. Significant space is required for many As 93% of the installed CHP capacity in Ireland runs on renewable energy solutions, such as woodchips (fuel gas fuels (O’Leary et al., 2007), there is significant storage areas) or horizontal geothermal installations; market potential; however, the renewable bonus of such space may be costly or unavailable in cities and €0.12/kWhe for biomethane does not make financial towns (e.g. in apartment blocks). sense as CHP plants typically displace electricity purchased from the grid and have returns of about There are clearly competitive advantages of grass €0.10–0.11/kWhe. biomethane; the issue is now to find the right market in order to exploit these advantages. It is suggested that a revised system of tariffs be introduced. Currently, a flat rate of €0.12/kWhe is paid 5.5.3 Grass biomethane electricity market in the renewable for biogas CHP. The same electricity tariff is paid regardless of whether a gate fee is received or the Ireland’s 40% renewable electricity target for 2020 feedstock is purchased, and there is no allowance for (Howley et al., 2008) is expected to be provided largely the non-monetary benefits of AD, for example to by wind. There are also targets for electricity from encourage use of cattle slurry. The German tariff ocean energy (500 MWe of installed capacity by 2020) structure (BMELV, 2009) uses graded tariffs that and for 30% biomass co-firing in existing peat-fired depend on feedstock type, plant size and AD power plants (DCMNR, 2007). The presence of viable technology alternatives for renewable electricity means that there International Energy Agency (IEA) has stated (IEA, is not expected to be a large market for electricity from 2007) that the high investor security provided by the grass biomethane; however, there may be some scope German feed-in tariff has been a success, resulting in in the CHP market and in existing power plants running a rapid deployment of renewables, the entrance of on natural gas. The market size is considerable as many new actors to the market, and a subsequent 62% of primary natural gas energy is used for reduction in costs. Using the German tariffs for the electricity generation (SEI, 2009c). grass plant in this analysis, the electricity tariff rises to type, among other factors. The a minimum of €0.1718/kWh for an on-site CHP plant There is a government target to achieve at least 800 and €0.1818/kWh for an off-site CHP plant using MWe from CHP by 2020, with emphasis on biomass- biomethane tapped from the grid (Table 5.5). Sale of fuelled CHP (DCMNR, 2007). The use of grass biogas heat off-site leads to an extra bonus of €0.03/kWhe in an on-site CHP plant struggles economically, due based on the proportion of heat sold. Thus there is largely to the current tariff structure and the lack of heat potential for these rates to rise to €0.21/kWhe. markets in Ireland. However, there is potential for existing natural-gas-fuelled CHP plants to purchase Such a tariff structure would bring the on-site CHP renewable gas from the grid, with the advantages that plant into profit as long as there is a market for the heat the capital investment has already been made and (Table 5.6). The annual income for E+H and G+E+H is there is generally a market for heat at existing plants. over twice the average FFI for cattle-rearing farms Table 5.5. Potential revenues from combined heat and power (CHP) using the German tariff structure (simplified) (Smyth et al., 2010b). Tariff On-site CHP (€/kWhe) Off-site CHP (€/kWhe) 0.0918 0.0918 Emission minimisation bonus 0.01 – Grass as a feedstock 0.07 0.07 – 0.02 0.1718 0.1818 Basic compensation Upgrading Total 42 J.D. Murphy et al. (2007-CCRP-1.7) Table 5.6. Profitability of on-site combined heat and power (CHP) with German tariff structure and farming subsidies (Smyth et al., 2010b). Base case Reduced operating costs and depreciation E+H G+E G+E+H E+H G+E G+E+H Total incomea (€/year) 407,240 308,124 407,240 407,240 308,124 407,240 Total costs (€/year) 471,873 446,466 446,466 395,201 369,794 369,794 Income – costs (€/year) –64,633 –138,342 –39,266 12,039 –61,670 37,446 Income – costs (€/ha) –470 –1,006 –285 88 –459 272 Average annual subsidy (€/ha) 461 461 461 461 461 461 Return including subsidy (€/ha) –9 –545 176 549 12 733 a €0.1718/kWhe received for electricity, €0.053/kWhth received for heat. E+H, the sale of heat and electricity with no capital grant; G+E, the sale of electricity only with capital grant; G+E+H, the sale of electricity and heat with capital grant. and disparity between AD plant output and the demand of depreciation are considered. In the case of the off-site off-site electricity generators. Three-quarters of CHP (€279/ha) when reduced operating costs CHP plant, a return of €0.085/kWh biomethane can be plants in Ireland are in the size range 0.5–1 MWe achieved, assuming 40% thermal and 35% electrical (O’Leary et al., 2007). Assuming 30% co-firing (which efficiency (€0.1818/kWhe + €0.053/kWhth). This is is the target for biomass co-firing in peat plants) in over 25% higher with 0.75-MWe CHP plants, the grass biomethane facility in break-even this analysis would serve only 2.7 such plants. Being biomethane price (from Table 5.4). The viability of off- reliant on such a small customer base puts the site CHP plants can only be assessed on a case-by- biomethane supplier at risk of failure from small case basis. Determining factors include the plant size, changes in demand. An obligation for CHP plants to the proportion of biomethane/natural gas in the mix, meet renewable energy targets would improve the and the individual circumstances of the plant, for viability through providing greater market stability for example if capital costs have already been paid. There the developing industry, and by putting biomethane in is potential for the use of biomethane in combined competition with other renewables, as opposed to cycle cheap natural gas. than €0.11/kWh) gas turbine (€0.085/kWh the compared best-case (CCGT) plants. The initial advantages of biomethane used in a CCGT facility include: • 5.5.4 Grass biomethane in the renewable transport market An electrical efficiency of around 55% compared There is a target for 10% renewable energy in with 35% in a small-scale CHP; Transport 2020 (DCMNR, 2007). Unlike the electricity • Increasing the priority listing of the CCGT plant as sector where significant progress is being made it is now seen as a renewable source of electricity towards meeting the target, there are significant as opposed to a fossil fuel electricity-generating challenges in the transport sector. Penetration of plant; and renewables in transport currently stands at less than 1.2% (Howley et al., 2009a). The problem is further • Use of electricity from CCGT to power electric compounded by policy constraints in biofuels cars and provide renewable fuel in transport. (sustainability criteria) and agriculture (land use) which restrict the type of biofuels that can be used and the The lack of a comprehensive tariff structure is a type of energy crops that can be grown. Smyth et al. stumbling block for the industry. There is also a (2010a) showed that the largest potential for the 43 The potential for grass biomethane as a biofuel achievement of Irish 2020 targets in renewable energy considerable savings can be achieved if bioCNG is in transport is grass biomethane. sold. If a 10% biomethane/90% CNG blend is used, the break-even price is between €0.0199 and €0.0217/MJ The break-even price of compressed biomethane from (based on UK CNG prices). At 53% of the price of grass varies between €0.078 and €0.132/kWh petrol and 71% of the price of diesel (for the higher (Table 5.7). Excise duty is not charged on gas used as price of €0.0217/MJ), this is competitive. a propellant, but VAT at 21% has to be added (EC, 2010), giving a minimum selling price (i.e. break-even The obvious stumbling block for the sale of price) of between €0.096 and €0.163/kWh. The sale biomethane as a transport fuel in Ireland is the price of petrol and diesel lies within this range absence of a market; there are currently only two (Table 5.8). The price of CNG is significantly lower natural gas vehicles in the country (NGV, 2009). The than that of petrol and diesel, meaning that development of biomethane for transport in other Table 5.7. Break-even of compressed biomethane from grass silage as a vehicle fuel (Smyth et al., 2010b). Base casea Reduced operating costs and depreciationb 50%G 30%G NG 50%G 30%G NG Break-even price of biomethane injected to grid (€/kWh) 0.100 0.108 0.121 0.067 0.075 0.107 Cost of compression to 250 bar + filling station (€/kWh)c 0.011 0.011 0.011 0.011 0.011 0.011 Break-even price of compressed biomethane (€/kWh) 0.111 0.119 0.132 0.078 0.086 0.118 0.134 0.144 0.160 0.094 0.104 0.143 1.37 1.47 1.63 0.96 1.06 1.45 – including 21% VAT (€/kWh) 3 – including 21% VAT (€/m ) a Excludes farming subsidy. Includes farming subsidy (€461/ha). c Estimated from values in the literature (Murphy and Power, 2009b) and discussions with industry. 50%G, receipt of grant for 50% of capital cost; 30%G, receipt of grant for 30% of capital cost; and NG, no grant. b Table 5.8. Comparison of vehicle fuel costs (Smyth et al., 2010b). Fuel Unit cost Energy value Cost per unit energy (€/MJ) Petrola €1.224/l 30 MJ/l 0.0408 €1.150/l 37.4 MJ/l 0.0307 3 37 MJ/m 0.0441 Diesela b 3 Compressed biomethane (high) €1.63/m Compressed biomethane (low)b €0.96/m3 37 MJ/m3 0.0260 3 3 37 MJ/m 0.0241 €0.71/m3 37 MJ/m3 0.0192 3 3 37 MJ/m 0.0189 €0.80/m3 37 MJ/m3 0.0217 3 3 0.0199 CNG – Austria c €0.89/m CNG – UKc CNG – Germany c Bio-CNG (high)d Bio-CNG (low) d €0.70/m €0.74/m a 37 MJ/m Price of petrol and diesel is the price at the pumps (AA Ireland, 2010). Price of compressed biomethane is the minimum selling price of grass biomethane. The highest and lowest prices from Table 5.8 are used. c In the absence of Irish compressed natural gas (CNG) prices, the prices in Austria, Germany and the UK (NGV, 2009) are shown for comparison. d Bio-CNG price calculated using UK CNG prices and a blend of 10% biomethane/90% CNG. b 44 J.D. Murphy et al. (2007-CCRP-1.7) countries has generally been based on an existing gas. The potential for a large number of customers CNG market, and the development of CNG is often offers more flexibility than the electricity market. based on the introduction of CNG to captive fleets (e.g. buses, waste collection lorries, taxis) followed by Obviously, alternatives such as woodchips or wood private cars. The sale of biomethane for transport in pellets could also be employed; however, the installation of these systems requires significant capital other countries has been found to be profitable, investment in both the boiler and biomass storage offering higher returns than heat or electricity. The areas, as well as changes in practice. Figure 5.1 CNG market may develop in Ireland as it has done compares heating costs based on an existing building elsewhere, but would require regulation and incentives remaining on the gas grid (fuel and running costs only from government to do so. for natural gas, grass biomethane and bioNG) and new woodchip and pellet heating systems (fuel, running 5.5.5 Grass biomethane in the renewable heat and annualised capital costs). While grass biomethane market is uncompetitive, a 12:88 (biomethane/CNG) bioNG The government has set a target for 12% renewable fuel is competitive with the renewable energy heat by 2020 and has also stated that the public sector alternatives. The analysis assumes that biomethane is produced from grass only; biomethane produced from will lead the way with the deployment of bioenergy feedstock with a gate fee, such as slaughter waste, heating (DCMNR, 2007). The residential sector is would be considerably more competitive. responsible for the largest share of natural gas final energy consumption, at 40.7% (SEI, 2009c). Twenty- In Fig. 5.1, the cost of grass biomethane is the break- eight per cent of houses have gas central heating even price (highest and lowest values are taken from Table 5.4 and 13.5% VAT is added). The cost of bioNG Dublin, where there are almost 375,000 natural gas is based on a blend of 12% biomethane and 88% customers or about 60% of national customers. natural gas. For the gas systems, estimated running Average residential natural gas demand (weather costs are added to the fuel costs to give the heating corrected) in 2008 was 14.4 MWh (51.8 GJ) per cost. The heating cost of woodchips and wood pellets household. The grass biomethane plant in this analysis includes capital and operational costs. Total woodchip, could fuel about 320 houses solely on biomethane or wood pellet and natural gas heating costs were 2,665 houses on bioNG containing 12% renewable calculated using a heat cost comparison spreadsheet €c/kWh (O’Leary et al., 2008), with the highest proportion in Figure 5.1. Comparison of heating costs for various systems (Smyth et al., 2010b). 45 The potential for grass biomethane as a biofuel (EVA, 2007), current commercial fuel costs (SEI, 2010) uncertainty in the waste sector. The transport market and work undertaken as part of a Master’s thesis offers the potential for profitability and provides a (Smyth, 2007). A 570-kW boiler with 900 h/year cheaper alternative to fossil fuels for the consumer. operation is assumed. However, there is currently no market for CNG in Ireland and the transport market is therefore not a Although Directive 2009/73/EC on the natural gas practical option at present. Unlike other renewable market (EC, 2009c) states that biogas should be technologies in the heat sector, grass biomethane has granted non-discriminatory access to the gas system, a large, easily accessible customer base. Existing and biomethane is injected into the grid in other natural gas customers would not require new countries, as yet there is no system for this in Ireland. installation and their gas supplier would need only a Gaslink (the Irish gas network operator) and Bord Gáis are currently investigating a quality standard for change in their billing system; thus the higher cost of biomethane injection into the grid. renewable gas can be offset against avoided capital investment. Injecting grass biomethane into the grid for 5.6 Conclusions sale as a heating fuel is the path of least resistance. However, there is currently no legislation in place in The key to the competitiveness of biogas/biomethane is the renewable energy targets. The principal Ireland to allow grid injection. Under certain conditions advantage of biomethane over other renewables is grass biogas/biomethane has the potential to be an that it can be distributed through the gas grid to a large economically viable alternative for farmers and for the existing customer base. The renewable electricity consumer. Its cost competitiveness can be further market is largely dominated by wind and it is the view improved by co-digestion with gate fee feedstock and of the authors that electricity is not the most by taking account of the associated non-monetary co- advantageous avenue for biogas. If a biogas electricity benefits. However, a recurring theme is the lack of industry were to develop from grass, a revised tariff consistent legislation regarding AD and the use of structure would be necessary. The existing tariff biogas/biomethane, and this is acting as a barrier to structure works well for feedstock that attracts a gate the development and economic success of the fee but, in spite of this, the industry is faltering, largely industry. For the industry to succeed economically, the due to the strict interpretation of the ABPR and implementation of cohesive legislation is required. 46 J.D. Murphy et al. (2007-CCRP-1.7) 6 Conclusions and Recommendations 6.1 Conclusions of green electricity and minimisation of thermal energy input are essential. In use as a transport • • Grassland is the dominant agricultural landscape fuel in Ireland, covering 91% of agricultural land. The biomethane; bi-fuel vehicles may not meet this size of the national herd has decreased and will criterion. Through process optimisation, a GHG continue to do so. Conversion of grassland to emission reduction of more than 60% as arable land is not encouraged due to cross compared with diesel may be effected. Grassland compliance. agricultural sequesters carbon; a value of 0.6 t C/ha/year is enterprise to grass biomethane production will deemed conservative. This would lead to a assist rural development through sustainable reduction in emissions of 89% which would employment, security of energy supply, and suggest that grass biomethane is one of the most environmental benefits associated with reduced sustainable indigenous non-residue European stocking rates. transport biofuels. Diversification of Perennial ryegrass is an excellent grass species • the vehicle must be optimised for The key to the competitiveness of grass for biogas production. Mixed pastures (ryegrass biomethane is the renewable energy targets. The and biogas principal advantage of biomethane over other fertilisation renewables is that it can be distributed through clover) may result production and requirements. Excess in higher reduced late the gas grid to a large existing customer base. It biogas is suggested that biomethane has advantages in production due to the increased structural the transport and thermal sectors rather than the carbohydrate content of grasses. electricity sector. The transport market offers the harvesting can fertilisation negatively and affect best potential for profitability; however, there is • The selection of the correct digester system for currently no market for CNG in Ireland. Grass grass biomethane is an important decision. The biomethane as a source of renewable thermal wet continuous two-stage system offers readily energy has a large, easily accessible customer available technology. However, grass has a base; existing natural gas customers would not tendency to float to the top of the liquid level in a require new installations. Cost competitiveness wet system, which may inhibit the process; thus, can be further improved by co-digestion with gate great care must be taken in the choice of the fee feedstock and by taking account of the mixing system. Dry-batch leach-bed systems associated non-monetary co-benefits. However, coupled with a UASB have potential for increased a recurring theme is the lack of consistent biogas production in smaller chambers. These legislation systems can be further optimised, particularly in leaching mode Membrane using separation pretreatment and the use of biogas/biomethane, and this is acting as a barrier options. HPWS regarding to the development and economic success of the are industry. recommended for upgrading of biogas (typically For the industry to succeed economically, the implementation of cohesive at 55% CH4) to biomethane (at 97%+ CH4). In legislation is required. addition, HPWS also provides maximum purity • (up to 98% CH4) with minimal cost. 6.2 An essential element of a grass biomethane • Recommendations Employ a tariff scheme that differentiates the facility is the reduction in emissions associated source of biomass: with parasitic energy demands. Thus, purchase Applying one tariff rate to biomass is a relatively 47 The potential for grass biomethane as a biofuel blunt instrument. The present tariff for AD CHP is existing CNG market, and the development of €150/MWeh for facilities smaller than 500 kWe. CNG is often based on the introduction of CNG to This does not differentiate the source of biomass. captive fleets (e.g. buses, waste collection lorries, Biogas may be made from OFMSW, which taxis) followed by private cars. The CNG market carries a gate fee, slurry, which typically has no requires gate fee, or silage, which must be purchased. incentives from government. For example, a Germany employs a tiered system for tariffs for target of CNG vehicles could be introduced to biogas. There is a basic compensation for biogas mirror the target of 10% of all vehicles to be with additional bonuses. One of these bonuses is through regulation and electric powered by 2020. Other examples priced to allow competitiveness for feedstocks, include grant-aiding CNG service stations and such as grass, which offer rural sustainable mandating of public transport fleets to incorporate employment. • support a certain percentage of CNG vehicles by specified dates. Employ a tariff scheme for biomethane: At present, there is a tariff structure for electricity • from biomass. It is suggested that the utilisation • Develop, promote and regulate biomethane of biogas is better employed when upgraded to as a source of thermal energy: biomethane and used as either a source of heat The sale of biomethane for renewable thermal (distributed through the natural gas grid to energy has a significant advantage due to the 620,000 houses) or as a transport fuel. There is existence of a modern, extensive natural gas no tariff scheme for these end uses. The German grid. system allows a bonus for grid injection of connections to the gas grid, with an average biomethane and use at a different site. Support demand of 51.9 GJ/house. This equates to 32 PJ for transport fuel is of particular importance as of thermal energy. If we consider a 12% biomethane is allowed a double credit for Renewable Energy Supply in Heat (RES-H) renewable energy in transport targets. target, then 3.84 PJ/year can be met by 32,000 Develop, promote and regulate the CNG ha of grass or about 0.8% of existing grassland. market: Again, the renewable gas and heat market The sale of biomethane for transport in other requires Government support. This may be done countries has been found to be profitable, offering (similar to the biofuel obligation scheme) by higher returns than heat or electricity. The mandating suppliers of gas to incorporate a development of biomethane for transport in other specific percentage of renewable gas in their countries has generally been based on an sales by specific dates. 48 There are about 619,000 domestic J.D. Murphy et al. (2007-CCRP-1.7) References AA Ireland, 2010. Irish Petrol Prices: February 2010. AA Ireland. 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Is grass biomethane a sustainable transport biofuel? Biofuels, Bioproducts, Biorefinery 4: 310– 325. Smyth, B.M., Murphy, J.D. and O'Brien, C., 2009. What is the energy balance of grass biomethane in Ireland and other temperate northern European climates? Renewable and Sustainable Energy Reviews 13(9): 2349–2360. Nizami, A.S. and Murphy, J.D., 2010. What type of digester configurations should be employed to produce biomethane from grass silage? Renewable and Sustainable Energy Reviews 14: 1558–1568. Smyth, B., Smyth, H. and Murphy, J.D., 2010. Can grass biomethane be an economically viable biofuel for the farmer and the consumer? Biofuels, Bioproducts, Biorefinery 4(5): 519–537. doi:10.1002/bbb.238. Nizami, A.S., Korres, N.E. and Murphy, J.D., 2009. A review of the integrated process for the production of grass biomethane. Environmental Science and Technology 43(22): 8496–8508. Smyth, B., Ó Gallachóir, B., Korres, N. and Murphy, J.D., 2010. Can we meet targets for biofuels and renewable energy in transport given the constraints imposed by policy in agriculture and energy? The Journal of Cleaner Production 18: 1671–1685. Singh, A., Smyth, B.M. and Murphy, J.D., 2010. A biofuel strategy for Ireland with an emphasis on production of biomethane and minimization of land take. Renewable and Sustainable Energy Reviews 14(1): 58 J.D. Murphy et al. (2007-CCRP-1.7) Acronyms and Annotations a.i. Active ingredient: chemical substance of a pesticide that kills the target pest AAU Agricultural area used ABP Animal by-products ABPR Animal By-Product Regulations AD Anaerobic digestion ADF Acid detergent fibre; an estimation of the cellulose and lignin content in a feed ADL Acid detergent lignin: estimates lignin content in feedstock BioCNG Compressed biomethane and natural gas C-3 plant First product of photosynthesis consists of three carbon atoms (cool or temperate grasses) C-4 plant First product of photosynthesis consists of four carbon atoms (warm or tropical grasses) CAD Centralised anaerobic digestion CAN Calcium ammonium nitrate CAP Common Agricultural Policy CCGT Combined cycle gas turbine CF Cocksfoot CH4 Methane CHP Combined heat and power CNG Compressed natural gas CO2e Carbon dioxide equivalent CP Crude protein CSO Central Statistics Office CSTR Continuous stirred tank reactor DAFF Department of Agriculture, Fisheries and Food DM Dry matter DMD Dry matter digestible: percentage of the feed dry matter actually digested by animals DMI Dry matter indigestible: dietary fibre (roughage), the indigestible portion of plant food DS Dry solids FE Fuel efficiency FFI Farm family income FM Fresh matter GDP Gross Domestic Product GHG Greenhouse gas 59 The potential for grass biomethane as a biofuel GWP Global warming potential HPWS High pressure water scrubbing HRT Hydraulic retention time IEA International Energy Agency ktoe Kilotonnes of oil equivalent LCA Life-cycle assessment ME Metabolisable energy: the feed energy actually used by the animal MF Meadow foxtail N, P, K Nitrogen, phosphorus, potassium NDF Neutral detergent fibre; estimation of hemicellulose and cellulose content, cell wall content NDP National Development Plan ODM Organic dry matter OFMSW Organic fraction of municipal solid waste OLR Organic loading rate PRG Perennial ryegrass PS Photosynthetic REPS Rural Environment Protection Scheme RES-H Renewable Energy Supply in Heat RES-T Renewable Energy Supply in Transport TS Total solids UASB Upflow anaerobic sludge blanket UCO Used cooking oil VDS Volatile dry solids VFA Volatile fatty acids WDGS Wet distiller’s grains with solubles WSC Water-soluble carbohydrate 60