K.M. Rahman

Understanding bioenergy production and optimisation at the nanoscale - a review

ABSTRACT Nanotechnology has an increasingly large impact on a wide range of biotechnological, pharmacological and pure technological applications. Its current use in bioenergy production from biomass is very limited. This paper examines the potential interrelationships between nanotechnology and bioenergy production through a comprehensive literature review and analysis of data from biomass characterisation studies. The aim of this review is to indicate how nanotechnology can be applied in biomass-to-bioenergy conversion. This study shows currently nanotechnology has been applied in the production of only two types of biomass, i.e. sludge and algae. Hence, interaction of nanomaterials with active sludge and algal cells were examined. Our extensive literature review indicates that anaerobic digestion process in sludge can potentially be enhanced by using magnetite nanoparticles, which gives higher methane yields. On the other hand, nanosilver reduces growth and causes adverse effects on the morphology of green algae. This process for bioenergy generation has already been successfully applied to sludge and algae biomass. Our study confirms that the process can also be used in the production of bioenergy from the other biomasses, such as agricultural wastes and industrial residues. Outcomes of this work will be an important tool for implementing nanotechnology in bioenergy research.

Green-house gas mitigation capacity of a small scale rural biogas plant calculations for Bangladesh through a general life cycle assessment

Calculations towards determining the greenhouse gas mitigation capacity of a small-scale biogas plant (3.2 m3 plant) using cow dung in Bangladesh are presented. A general life cycle assessment was used, evaluating key parameters (biogas, methane, construction materials and feedstock demands) to determine the net environmental impact. The global warming potential saving through the use of biogas as a cooking fuel is reduced from 0.40 kg CO2 equivalent to 0.064 kg CO2 equivalent per kilogram of dung. Biomethane used for cooking can contribute towards mitigation of global warming. Prior to utilisation of the global warming potential of methane (from 3.2 m3 biogas plant), the global warming potential is 13 t of carbon dioxide equivalent. This reduced to 2 t as a result of complete combustion of methane. The global warming potential saving of a bioenergy plant across a 20-year life cycle is 217 t of carbon dioxide equivalent, which is 11 t per year. The global warming potential of the resultant digestate is zero and from construction materials is less than 1% of total global warming potential. When the biogas is used as a fuel for cooking, the global warming potential will reduce by 83% compare with the traditional wood biomass cooking system. The total 80 MJ of energy that can be produced from a 3.2 m3 anaerobic digestion plant would replace 1.9 t of fuel wood or 632 kg of kerosene currently used annually in Bangladesh. The digestate can also be used as a nutrient rich fertiliser substituting more costly inorganic fertilisers, with no global warming potential impact.

Evaluating the Potential of Rice Straw as a Co-digestion Feedstock for Biogas Production in Bangladesh

This research was done to evaluate the potential energy yield capacity of rice straw for anaerobic digestion (AD) as an alternative use of this material. Cattle markets were found to be a potential source that generates a significant amount of a mixture of 80% straw + 20% cattle dung. This waste rice straw/dung mix from cattle markets provides a good mixture with a much better C/N ratio than pure straw. This mix of straw and dung are often left in piles in the market for between 10 and 20 days, where they degrade naturally. Tests involving feeding this mixture into a domestic biogas plant showed that the biogas yield is 0.099 m3/kg feed stock with a methane content of 74.43%. . In the whole of Bangladesh there are 500 cattle markets, so their waste can produce about 35,000,000 MJ of energy through AD. A biogas plant will continue to generate biogas, even after daily feeding has been stopped, although the gas production and the methane content do reduce with time.