The energy crisis experienced in the 1970s was followed by increased concern for the environment with major emphasis on protection of the global ecosystem. The luxurious use of fossil fuels yields significant developmental benefits for industrialized societies, but takes its toll on the environment in the form of large amounts of agricultural, domestic and industrial waste. It is therefore important to pursue material and energy recycling, while minimizing waste, at a global level.
A biomass energy system is a typical example of a recycling system, in which CO2 is fixed via photosynthesis, and energies accumulated in biological materials are used to release CO2. CO2 fixation by microalgal mass culture is an attractive proposal since through its metabolic machinery, algal biomass is capable of producing H2. Algal biomass is also applicable as a substrate for lipid conversion to oil and for cyanobacterial H2 production. Both bacterial and cyanobacterial H2 production are currently being investigated with a view to improving productivity through the advanced technology of genetic manipulation. In addition, limited global fossil fuel reserves, make the production of oil from lipids and fatty acids contained in algal biomass an attractive proposition. To this end, thermochemical liquefaction of microalgal biomass is being studied as a means of producing petroleum fuel analogs.
Alcoholic fermentation of cellulosic biomass is of importance because cellulose biomass occurs abundantly in the form of agricultural and forestry wastes. Anaerobic digestion of organic wastes involves a complex series of microbial reactions resulting in the production of methane gas. This process is widely applied in small-scale energy production in rural areas. Modem technologies capable of producing ethanol and methane in larger-scale operations have also been developed.
The potentials and limitations of plant and bacterial photosynthesis and methodologies for improving the quality of biomass energy through microbial conversion processes are discussed in this bulletin. Basic studies on future energy production via microalgal CO2 fixation, and the future of renewable energy biological systems are also reviewed and discussed.