Biodiesel :: Energy, Biomass

Biomass can be classified as dry biomass (such as wood) or the wet biomass sources such as organic fraction of domestic waste, agro-industrial wastes, slurries and waste water. Thermal conversion or gasification of the dry biomass generates energy. Figure 3 summarizes an approximate worldwide energy consumption level. Nearly 2 kg billion biomass is burned everyday in developing countries. Especially in India, 90% of primary energy use is accounted for biomass in rural areas (wood-56%; crop residues-16%; dung-21%). Combustion of these sources leads to high concentrations of respirable particulates, gases including CO, SO2, nitrogen oxides and toxic compounds such as benzene and formaldehyde [23]. The wet biomass is less suitable for thermal conversion. Biotechnological processes are involved where the reactions are catalysed by microorganisms in an aqueous environment at low temperature and pressure. Aquatic biomass presents an easy adaptability to grow in different conditions and has enhanced CO2 fixation accompanied with a low nitrous oxide release. Some microalgal biomass is considered as a better alternative renewable energy source, either terrestrial or aquatic (Botryococcus braunii) (Fig. 1m). In view of the oil content of many microalgae (Table 2) energy recovery from biomass can be implemented on a large scale readily. The photosynthetic efficiency of aquatic biomass is much higher (6-8%) than that of its terrestrial counterpart (1.8-2.2%) [13]. Further, aquatic biomass presents an easy adaptability to grow in different conditions either in fresh or marine water or in a wide range of pH. This makes the aquatic biomass more adaptive or an enhanced CO2 fixation to afford a high biomass production. The only practicable methods of large scale production of microalgae are tubular photobioreactors [19] and open raceway ponds [20]. Extensive studies have been carried out for the cultivation of different marine microalga using a variety of cultivation systems including open ponds and various types of closed photobioreactors [21, 2 2]. Since already several articles were dealt with large scale production, this paper did not concentrate on these issues. Biomass for power generation has been recognized as an important component of the renewable energy programme in India and this is reflected in the priority attached to it by the MNES. There are niches with substantial potential for the use of biomass for power generation e.g. bagasse cogeneration in sugar mills, decentralized gasifier based diesel cogeneration systems in south India and biomass waste from agricultural operations or agro-industries in concentrated geographical pockets [23]. A biomass power / cogeneration capacity addition of 115 MW in six states was created in the country during the year reaching a cumulative power generation capacity of 727 MW.