A vast range of important products and waste treatments, which in the past was manufactured or used chemical processes, now is produced economically and treated by processes of microbial fermentation and biotransformation. Microorganisms also provide valuable services and have proved to be particularly useful because of the ease of their mass cultivation, their speed of growth, use of cheap substrates (waste, in many cases) and the diversity of potential products.
There are two methods of microbial function, aerobic and anaerobic. Oxygen (in O2 form) is required in aerobic digestion, as shown by bubbles in a solution. Anaerobic digestion also requires oxygen but not in O2 form.
Aerobic reactions include odor reduction; biochemical oxygen demand, or BOD; nitrification (ammonia removal); FOG (fat, oil and grease) removal; sludge digestion (up to 50 percent); and acid production. Anaerobic reactions include denitrification (NO2 or NO3 removal); nitrite formation; sludge removal; methane production; alcohol production; and acid production.
The four issues that operators are most likely to encounter in an environmental system are odor (H2S), which is a source of sulfur; FOG (fat, oil and grease), which is a source of carbon; ammonia, a source of nitrogen; and sludge, which contains all of the above plus phosphorus. A microbe needs all of these, as well as certain metals, to function; if any of these materials is deficient, microbial activity ceases. This is why anyone using microbes needs to know the proper balance of materials to maximize their efficiency.
Microbial fermentation can be used in the production of certain chemicals. Acids, as well as certain functional groups, can be produced in a fermentation setting. Examples include processing acids (propionic, acetic and lactic acids, etc.) and additives that can be produced naturally for food, agricultural and pharmaceutical applications.
How Waste Decomposes
Waste is a mixture of proteins (as found in meats, beans and hair), FOG (cooking oil and grease) and carbohydrates (paper, cardboard, sugars, fillers and flour, among others). All of these are chemicals that contain varying combinations of ammonia, phosphate, sulfur, carbon and amino acids.
Proteins, which contain sulfur, ammonia and carbon, sometimes need to be treated aerobically first, then subjected to anaerobic treatment. One example of this is the decomposition of ammonia into nitrogen gas. FOG and carbohydrates, by contrast, can be handled either aerobically or anaerobically and are treated most effectively at their source.