Date Published: February 16, 2016
Publisher: Springer Berlin Heidelberg
Author(s): Ramansu Goswami, Pritam Chattopadhyay, Arunima Shome, Sambhu Nath Banerjee, Amit Kumar Chakraborty, Anil K. Mathew, Shibani Chaudhury.
Biogas is a combination of methane, CO2, nitrogen, H2S and traces of few other gases. Almost any organic waste can be biologically transformed into biogas and other energy-rich organic compounds through the process of anaerobic digestion (AD) and thus helping in sustainable waste management. Although microbes are involved in each step of AD, knowledge about those microbial consortia is limited due to the lack of phylogenetic and metabolic data of predominantly unculturable microorganisms. However, culture-independent methods like PCR-based ribotyping has been successfully employed to get information about the microbial consortia involved in AD. Microbes identified have been found to belong mainly to the bacterial phyla of Proteobacteria, Chloroflexi, Firmicutes and Bacteroidetes. Among the archaeal population, the majority have been found to be methanogens (mainly unculturable), the remaining being thermophilic microbes. Thus, the AD process as a whole could be controlled by regulating the microbial consortia involved in it. Optimization in the feedstock, pH, temperature and other physical parameters would be beneficial for the microbial growth and viability and thus helpful for biogas production in AD. Besides, the biogas production is also dependent upon the activity of several key genes, ion-specific transporters and enzymes, like genes coding for methyl-CoM reductase, formylmethanofuran transferase, formate dehydrogenase present in the microbes. Fishing for these high-efficiency genes will ultimately increase the biogas production and sustain the production plant.
Worldwide energy consumption and demand are continuously growing up. But, most of the resources used like petroleum, natural gas, coal are not sustainable sources of energy. Numbers of countries in the world including India are currently passing through the critical phase of population explosion and the growing population demands more energy inputs. Therefore, the whole world is now concerned about sustainable renewable energy. As a burning example, the European Union policies have set a fixed target of supplying 20 % of the total European energy demands by the year 2020 from renewable energy systems (Holm-Nielsen et al. 2009).
Worldwide energy consumption and demand are growing up since past 50 years. With the growth of population, demand for energy is also increasing leading to an uneven supply and distribution of resources. Therefore, the requirement of sustainable and eco-friendly energy in India to satisfy the energy demand is inevitable. Along with the source of sustainable green energy, biogas production is an alternative way to produce clean energy through solid waste management. As it is produced by the action of several microbes upon the waste products, knowledge about the eco-physiology of the microbes will help in understanding their particular roles. Bearing in mind that the higher biogas production rate of the thermophilic system must have been accompanied by intensified intermediate production, it is noteworthy that the concentration of VFA within the UAFP effluent was equally low at both temperatures. Consequently, the acetogenesis and methanogenesis steps must also have been more active and the intermediates from hydrolysis and acidogenesis were instantly converted to methane within the thermophilic UAFP reactor. For biogas production methanogenesis is often the rate-limiting step. However, when plant biomasses are used as substrate, hydrolysis is the rate-limiting step because of higher content of lignocellulosic materials. Thus, to enhance the overall production rate in such processes, it is necessary to understand the primary degradation steps, i.e., hydrolysis and acidogenesis, for the control and optimization of the whole process. As all the microbes involved in AD are not culturable, attempts could be made to design ideal media and optimize the growth conditions for the non-culturable microbes with the aid of metagenomic improvements, so that extensive research could be done in cost-effective and easier ways. The eco-physiological effect of a microbe in the consortium can also be understood properly only if it can be cultured in vitro. Several microbes detected in the AD system have been found to be methane oxidizers and sulphate reducers, which are hindrances to the yield of biogas. Thus, studies on inhibiting the growth of such microbes would be beneficial for the biogas yield. Besides, the performance of AD in terms of biogas production is dependent upon the activity of several ion-specific transporters and enzyme systems. Detailed information on structure and biosynthesis of all the enzymes, biogenesis of the prosthetic groups involved in such enzyme systems is also not readily available. Hence, further studies could be designed to explore these steps. Fishing for these high-efficiency genes that control these enzyme systems will ultimately increase the production of biogas and sustain the production plant.