Biomethane

Grass is an excellent energy crop due to long persistence of high yields accompanied by low energy inputs. Approximately 91% of Irish agricultural land is under grass. The national herd has decreased and will continue to do so. Cross compliance does not encourage the conversion of permanent pastureland to arable land; thus we have and will continue to have increased quantities of excess grassland. Therefore, grass must be considered a significant source of biomass. Current grass species and cultivation practices are favourable for anaerobic digestion (AD), which is a mature technology. Upgrading biogas to biomethane, injecting into the gas grid, leads to an effective bioenergy system complete with distribution to all major cities and 620,000 houses. The Renewable Energy Directive allows a double credit for biofuels derived from residues and lignocellulosic material (such as grass). It is shown that 100,000 ha of grass (2.3% of agricultural land) will allow compliance with the 10% renewable energy in transport target for 2010. Alternatively, this would substitute for 35% of residential gas consumption. Reactor design must take account of the specific feedstock or combinations of feedstock; the reactor must be suited to the feedstock. This is not technically difficult. Of significant concern in the sustainability of the biofuel produced is the parasitic energy demand of the process and the vehicle efficiency. Emission reductions are optimised by the use of green electricity and the use of biomass for thermal energy input. On a field-to-wheel basis, it is essential that the vehicle operating on biomethane has an equivalent efficiency (expressed as MJ/km) as the displaced fossil fuel. The Renewable Energy Directive requires an emission savings of 60% compared with the displaced fuel for new facilities constructed after 2017. This is readily achieved for grass biomethane through optimisation of the system. Allowing for carbon (C) sequestration in grassland of 0.6 t C ha/year will lead to emissions savings of 89%. This would suggest that grass biomethane is one of the most sustainable indigenous, non-residue-based transport biofuels. The economics of biomethane are shown to be difficult. There is a requirement for innovative policy and marketing of the industry. A compressed natural gas transport fuel market is an essential prerequisite to using biomethane as a transport fuel. Mandating a certain percentage of biomethane in natural gas sales is of benefit to biomethane as both a transport and a thermal biofuel. Government policy is required to support a biomethane industry. Further research is required in the following areas:
Bioresource mapping: This includes the creation of a Geographical Information System to highlight sources of the organic fraction of municipal solid waste (OFMSW), slurry, slaughter waste and areas of high-yielding silage production. The system would include distribution systems (natural gas grid, electricity grid) and demand nodes (e.g. transport fleets, district heating, new towns) to propose areas with significant potential for biomethane production.
Assessment of biomethane facilities: This includes full life-cycle analysis of different biomethane facilities, including co-digestion of slurries and grass silage, mono-digestion of OFMSW, and mono-digestion of slaughter wastes. The research should allow assessment of the cost of the produced biomethane.
Digester design: This basic research should assess optimal digester systems for different feedstocks.
Agricultural impact of AD: This research includes monitoring carbon sequestration in grasslands where silage is cut and digestate is applied. This should be compared with carbon sequestration on grazed pastures. The fertiliser value of different digestates needs to be assessed along with the emissions associated with application of digestate. The research should also assess the effect on biodiversity.

Many factors enforce the intensification of grassland utilization which is
associated with significant environmental impacts subjected to various legislative
constraints. Nevertheless, the need for diversification in agricultural production and
the sustainability in energy within the European Union have advanced the role of
grassland as a renewable source of energy in grass biomethane production with
various environmental and socio-economic benefits. Here it is underlined that the
essential question whether the gaseous biofuel meets the EU sustainability criteria
of 60% greenhouse gas emission savings by 2020 can be met since savings up to
89.4% under various scenarios can be achieved. Grass biomethane production is
very promising compared to other liquid biofuels either when these are produced
by indigenous or imported feedstocks. Grass biomethane, given the mature and well
known technology in agronomy and anaerobic digestion sectors and the need for
rural development and sustainable energy production, is an attractive solution that
fulfils many legislative, agronomic and environmental requirements.

Biogas upgrading by water scrubbing followed by biomethane compression is an environmentally benign process. It may be achieved using various plant configurations characterised by various power requirements with associated effects on biomethane sustainability. Therefore, the current study has been undertaken to systematically investigate the power requirements of a range of water scrubbing options. Two groups of water scrubbing are analysed: (1) high pressure water scrubbing (HPWS) and (2) near-atmospheric pressure water scrubbing (NAPWS). A water scrubbing plant model is constructed, experimentally validated and simulated for seven upgrading plant configurations. Simulation results show that the power requirement of biogas upgrading in HPWS plants is mainly associated with biogas compression. In contrast, in NAPWS plants the main power is required for water pumping. In both plants the compression of the biomethane from atmosphereic pressure to 20 MPa also contributes remarkably. It is observed that the lowest specific power requirement can be obtained for a NAPWS plant without water regeneration (0.24 kW h/Nm3 raw biogas) but this plant requires cheap water supply, e.g. outlet water from a sewage treatment plant or river. The second is HPWS without flash (0.29 kW h/Nm3 raw biogas). All other HPWS with flash and NAPWS with water regeneration plants have specific power requirements between 0.30 and 0.33 kW h/Nm3 raw biogas. Biogas compression without upgrading requires about 0.29 kW h/Nm3 raw biogas. The thermodynamic efficiency of biogas upgrading is between 2.2% and 9.8% depending on the plant configuration while biomethane compression efficiency is higher, about 55%. This result implies that the upgrading process has a remarkable potential for improvement whereas compression is very close to its thermodynamic limit. The potential for minimising energy dissipation in the state-of-the-art HPWS upgrading plant with flash by applying a rotary hydraulic pumping device is evaluated at about 0.036 kW h/Nm3 raw biogas meaning the specific power requirement reduction of 10%.

The EU directive on the promotion of the use of energy from renewable sources (Directive 2009/28/EC) sets a mandatory minimum target for the use of fuels produced using renewable energy sources of 10% of total petrol and diesel consumption in the transport sector by the year 2020. In addition, it states that production of renewable fuels should be consistent with sustainable development and must not endanger biodiversity. In the INTERREG IVA Southern Finland–Estonia Sub-programme, efforts towards finding ...

Co-digestion of cassava and winery waste was investigated for the production of biogas. Cassava biomass is a good substrate due to its high carbohydrate yield per hectare (4.742kg/carb) than most plants. Winery waste is a growing problem in South Africa due to high amounts currently being dumped at landfills. Due to the chemical properties of the two substrates it is envisaged that their co-digestion will produce more biogas than use of a single substrate. Biomethane potential (BMP) tests were carried out in a batch, mesophilic (37˚C±0.5) reactor using cassava and winery waste singly and in combination at a ratio of 1:1 and run for 30 days. The results showed that cumulative methane yield for cassava, winery waste and in combination were 42, 21 and 38 mLCH4 respectively. It was concluded that biogas production from anaerobic digestion was dependent on many factors such as pH, substrate properties and the ratio of different feedstocks used during co-digestion.

A pilot high rate algal pond (HRAP) interconnected to an external CO 2 –H 2 S absorption column via settled broth recirculation was used to simultaneously treat a synthetic digestate and to upgrade biogas to a bio-methane with sufficient quality to be injected into natural gas grids. An innovative HRAP operational strategy with biomass recirculation based on the control of algal-bacterial biomass productivity (2.2, 4.4 and 7.5 g m −2 d −1) via settled biomass wastage was evaluated in order to enhance nutrient recovery from digestate at a constant hydraulic retention time. The influence of the recycling liquid to biogas (L/G) ratio on the quality of the upgraded biogas was assessed. The bio-methane composition under a L/G ratio of 1 (0.4 ± 0.1% CO 2 , 0.03 ± 0.04% O 2 , 2.4 ± 0.2% N 2 and 97.2 ± 0.2% CH 4) complied with the technical specifications of most European bio-methane legislations regardless of the biomass productivity established. The HRAP operational strategy applied allowed increasing the N and P recovery from 19 and 22% to 83 and 100%, respectively, when the biomass productivity was increased from 2.2 to 7.5 g m −2 d −1. Finally, the dynamics of microalgae and bacteria population structure were characterized by morphological identification and Denaturing Gradient Gel Electrophoresis analysis.

The performance of two 464-L high rate algal ponds (HRAPs) treating 20- and 10-folds diluted swine manure at 10 days of hydraulic residence time was evaluated under continental climatic conditions in Castilla y Leon (Spain) from January to October. Under optimum environmental conditions (from July to September), both HRAPs supported a stable and efficient carbon and nitrogen oxidation performance, with average COD and TKN removal efficiencies of 76 ± 11% and 88 ± 6%, respectively, and biomass productivities ranging from 21 to 28 g/m2 d. Nitrification was identified as the main TKN removal mechanism at dissolved oxygen concentrations higher than 2 mg/L (accounting for 80–86% of the TKN removed from January to May and for 54% from July to September). On the other hand, empirical evidences of a simultaneous nitrification–denitrification process were found at dissolved oxygen concentrations lower than 0.5 mg/L (high organic loading rates). However, despite the achievement of excellent COD and nitrogen oxidation performance, phosphorous removal efficiencies lower than 10% were recorded in both HRAPs probably due to the high buffer capacity of the piggery wastewater treated (absence of abiotic pH-mediated View the MathML source precipitation). Finally, a detailed monitorization of the dynamics of microalgae population revealed that the combination of moderate temperatures/solar irradiances and high organic loading rates, prevailing during late spring and summer, supported higher microalgae diversities than those found during winter conditions.

The EU directive on the promotion of the use of energy from renewable sources (Directive 2009/28/EC) sets a mandatory minimum target for the use of fuels produced using renewable energy sources of 10% of total petrol and diesel consumption in the transport sector by the year 2020. In addition, it states that production of renewable fuels should be consistent with sustainable development and must not endanger biodiversity. In the INTERREG IVA Southern Finland – Estonia Sub-programme, efforts towards finding solutions to the tasks set by the EU were undertaken in co-operation with Finnish and Estonian researchers.
The purpose of the ”From Waste to Traffic Fuel” (W-Fuel) project was to promote the sustainable production and use of biogas using locally-sourced biodegradable waste materials from the food and beverage industry and the agricultural and municipal sectors. The ultimate aim of the project was to upgrade the biogas (produced based on anaerobic digestion of biodegradable wastes, sludge, manure, slurry and energy crops) to biomethane with a methane content similar to natural gas, to be further used as transport fuel with the aim of reducing traffic-borne emissions, in particular CO2. The project combined waste, energy and traffic solutions in order to decrease emissions, costs and the use of materials.
Six case areas in southern Finland and northern Estonia were selected. The two case areas in Estonia were the counties of Harju and Lääne-Viru in northern Estonia. The project aimed to promote waste and sludge prevention and to commence biogas production and its subsequent upgrading to biomethane for use as a renewable fuel. The project promoted regional businesses and employment in waste treatment and ‘green energy’ production. On basis of the gathered data, the biogas potentials and prerequisites of each case county were analysed. Furthermore, the environmental, economic and other regional effects of the different options were compared. By developing research-based feasibility plans, the project partners provided solutions for public and private companies, local governments and research institutes.
The project was implemented in close co-operation with municipal waste and sewage companies as well as stakeholders in industry and the agricultural and transport sectors. This report presents the project results for Estonia.