Environmental Microbiology, Soil Microbiology & Microbial Biogeochemistry

Bioenergy is derived from biofuels such as Ethanol, Methanol, Biobutanol and etc., are produced through alternative/contemporary biological processes, derived from such as anaerobic digestion and agriculture, rather than a fuel produced by geological processes such as those involved in the formation of fossil fuels, such as coal and petroleum, from prehistoric biological matter. Biomass can be converted to appropriate or useful energy-containing substances in three different ways: thermal conversion, chemical conversion & biochemical conversion.

Scope and Importance: Furthermore, many experts predict that the rate of world oil production has already peaked and that it will only decrease from now onwards as fewer and fewer oil reserves are discovered. Microbial biofuel production is already in use, principally in the form of sugar fermentation by yeast to produce ethanol. Although many microbes have been used in ethanol production, the yeast species Saccharomyces cerevisiae is primarily used in industry, using starch and sugars from plants as the starting material for the process.The most common feedstocks (carbon source utilized by the microbes) are agricultural products which can easily be processed to create the simple sugars needed for fermentation. This is primarily corn in the United States, wheat in the European Union, and sugar cane in Brazil. Ethanol fermentation by S. cerevisiae is primarily done via the standard glycolysis pathway. In the case of corn and other starch-containing plants, the simple sugars necessary are formed via the hydrolysis of starch to yield monosaccharide subunits, whereas the sugars in sugarcane are hydrolyzed only once and then go straight into the pathway. In the process, a single molecule of glucose is oxidized to two molecules of pyruvate. Anaerobic conditions are required so that molecular oxygen is not available for use as an electron acceptor, and instead, pyruvate must be used as the terminal electron acceptor. This fermentative process involves the decarboxylation of pyruvate to form carbon dioxide and acetaldehyde, and the subsequent reduction of acetaldehyde to produce ethanol. Ethanol fermentation by yeast also helps to address the problem of greenhouse gas emissions, although it does not represent a perfect solution from an environmental perspective either. All biofuels with a positive NEB should theoretically emit less carbon dioxide because the process of carbon fixation occurring within the growing plants should counterbalance the carbon dioxide emissions of both the invested fossil fuel energy and the combustion of ethanol. However, in reality, the nitrogen-rich fertilizer used to sustain the plants and the addition of extra plant matter into the soil supports communities of bacteria that produce nitrous oxide, a much more potent greenhouse gas than carbon dioxide. Considering this entire system, producing ethanol via corn fermentation emits approximately 88% of the greenhouse gas content of gasoline yielding the same amount of energy. This mediocre improvement, coupled with the other environmental implications such as pesticides, make most current ethanol fermentation techniques of limited use, although they are nevertheless a positive alternative to fossil fuels.