lignocellulosic Biofuel

The biofuel industry is rapidly growing with a promising role in producing renewable energy and tackling climate change. Nanotechnology has tremendous potential to achieve cost-effective and process-efficient biofuel industry. Various nanomaterials have been developed with unique properties for enhanced biofuel production/utilization. The way forward is to develop nanotechnology-based biofuel systems at industrial scale.

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.

Sorghum Bagasse in recent years has emerged as a promising feedstock for production of biofuels and value-added products following various biological conversion pathways. However, adequate conservation is critical for utilising Sorghum Bagasse as a feedstock for fuel production around the year in bioenergy plants. Therefore, this study aims to examine the pressure drop as a function of airflow velocity and construct Shedd's curves for energy Sorghum Bagasse. The ambition was to facilitate large-scale drying systems for biomass conservation. The Bagasse was prepared by extracting the juice from the harvested sorghum and passing through a juicing machine. Afterwards, it was manually chopped and stored on a wooden platform having 2.44 m2 area in a 55-gallon drum at a depth of 0.57 m. The airflow velocities (0.24–1.32 ms−1) caused a pressure drop (9.96–346.23 Pa) across the empty drum. The different pressure drop in the drum containing Sorghum Bagasse (19.92–263.25 Pa) was due to various airflow velocities (0.043–0.799 ms−1). Pressure drop was further increased with increasing airflow velocity, and it was found in line with the values of pressure drop for ear and shelled corn, as reported in ASABE standards. Shedd's curves for Sorghum Bagasse samples were developed, as these curves can be used for designing large-scale aeration systems for chopped energy sorghum. The whole production chain of biofuel by conserving biomass can be improved by the findings of this work, thus allowing the biomass to be used more economically around the year in bioenergy plants.

A sustainable transition is premised upon moving from a carbon energy regime to a renewable energy regime; a highly contested political-economic transformation, to say the least. In places like the United States and European Union the main form of renewable energy is bioenergy, especially biofuels. Recent policy and industry efforts are focusing on the development and implementation of what are known as ‘drop-in’ biofuels, so named because they can be incorporated into existing distribution infrastructure (e.g. pipelines) and conversion devices with relatively few, if any, technical modifications. As with carbon energy, bioenergy has particular materialities that are implicated in the political-economic possibilities and constraints facing societies around the world. These political materialities of bioenergy shape and are shaped by new energy regimes and therefore problematize the notion of a drop-in biofuel. Thus further examination of the political materialities of bioenergy, and of renewable energy more generally, is of critical importance for successful sustainable transitions.

The cost of cellulases remains a key issue in the production of cellulosic ethanol, and the impact of enzymes on greenhouse gas (GHG) emissions of cellulosic ethanol has received little attention. This study evaluates life cycle emissions and cellulase production costs for bioethanol production , considering on-site and off-site production options. A complete enzyme production process was simulated using AspenPlus, generating mass and energy balance information required to calculate GHG emissions and fi nancial metrics. GHG emissions for cellulase production range from 10.2 to 16.0 g CO 2 eq g –1 enzyme protein, depending on on-site or off-site production and the method of transportation. Enzyme GHG emissions are predicted to be 258 g CO 2 eq. L –1 of ethanol for on-site production, versus 403 g CO 2 eq. L –1 for off-site production, based on a 150 MMLY ethanol plant using 11.5 mg enzyme g –1 substrate and a cellulase fermentation yield of 90%. Cellulase production costs were estimated for a range of conditions, including ethanol plant size, enzyme dose and protein yield for on-site production, and enzyme plant size, protein yield and return on investment for off-site production. On-site production costs range between $3.80 and $6.75 kg –1 protein, versus $4.00 to $8.80 kg –1 for off-site production. In both scenarios, the lowest cost corresponds to a 90% protein yield, and a high enzyme demand and production capacity. An enzyme production cost of $4.70 USD kg –1 corresponds to an enzyme cost of 0.46 USD gal –1 ($0.12 L –1) of ethanol in a 150 MMLY plant using 11.5 mg enzyme g –1 substrate.

Lignocellulosic substrates are widely available but not easily applied in biogas production due to their poor anaerobic degradation. The effect of bioaugmentation by anaerobic hydrolytic bacteria on biogas production was determined by the biochemical methane potential assay. Microbial biomass from full scale upflow anaerobic sludge blanket reactor treating brewery wastewater was a source of active microorganisms and brewery spent grain a model lignocellulosic substrate. Ruminococcus flavefaciens 007C, Pseudobutyrivibrio xylanivorans Mz5T, Fibrobacter succinogenes S85 and Clostridium cellulovorans as pure and mixed cultures were used to enhance the lignocellulose degradation and elevate the biogas production. P. xylanivorans Mz5T was the most successful in elevating methane production (+ 17.8 %), followed by the coculture of P. xylanivorans Mz5T and F. succinogenes S85 (+ 6.9 %) and the coculture of C. cellulovorans and F. succinogenes S85 (+ 4.9 %). Changes in microbial community structure were detected by fingerprinting techniques.

Since the 1990s governments in both the Global North and the Global South have been heavily promoting liquid biofuels and enacting policies as a result of concerns related to climate change mitigation, energy security, and rural development. Policy discourses about future technological pathways and landscapes have also been based on framing the lack of energy as an impediment to development and growth (Smith, 2010; Wilkinson and Herrera, 2010). Liquid biofuels have been portrayed as an attractive technological pathway because they can address disparate problems at once without fundamentally altering prevailing energy consumption practices (Smith, 2010; White and Dasgupta, 2010). They are already a major ‘renewable’ energy source in the United States, Brazil, and the European Union where they are presented as a way to sustainably transition away from fossil fuels in the future (Birch and Calvert, forthcoming).