The first one is also known as biotransformation and is the use of microorganisms to carry out a chemical reaction that is more costly or not feasible nonbiologically. The microorganisms converts a substance to a chemically modified form. An example is the industrial production of cortisone. One step is the bioconversion of Progesterone to 11-alfa-Hydroxyprogesterone by Rhizopus nigricans.
New cellulosic ethanol conversion processes have enabled the variety and volume of feedstock that can be bioconverted to expand rapidly. Feedstock now includes materials derived from plant or animal waste such as paper, auto-fluff, tires, fabric, construction materials, municipal solid waste (MSW), sludge, sewage, etc.
There are two principal processes for bioconversion:
1 - Enzymatic hydrolysis - a single source of feedstock, switchgrass for example, is mixed with strong enzymes which convert a portion of cellulosic material into sugars which can then be fermented into ethanol. Genencor and Novozymes are two companies that have received United States government Department of Energy funding for research into reducing the cost of cellulase, a key enzyme in the production cellulosic ethanol by this process.
2 - Synthesis gas fermentation - a blend of feedstock, not exceeding 30% water, is gasified in a closed environment into a syngas containing mostly carbon monoxide and hydrogen. The cooled syngas is then converted into usable products through exposure to bacteria or other catalysts. BRI Energy, LLC is a company whose pilot plant in Fayetteville, Arkansas is currently using synthesis gas fermentation to convert a variety of waste into ethanol. After gasification, anaerobic bacteria (Clostridium ljungdahlii) are used to convert the syngas (CO, CO2, and H2) into ethanol. The heat generated by gasification is also used to co-generate excess electricity.