The anaerobic aspect of this process, the process carried out without oxygen, is performed by anaerobic microorganisms degrading organic substances in the wastewater. An integral process within this part of the separation is hydrolysis, which decomposes the organic compounds into much simpler compounds which can then be passed through microbial cells. This is the first of a four-step process to complete the transformation of organic matter to biogases:
# Hydrolysis: Specifically, enzymatic hydrolysis is used to release proteins from the microorganisms. These processes subsequently break down complex compounds, such as lipids, proteins, and polysaccharides, which have a large molecular mass, to simple compounds such as:
#* Lipids → fatty acids and glycerol
#* Proteins → amino acids
#* Polysaccharides → glucose, fructose, and galactose
# Acidogenesis: Takes the products of hydrolysis, mentioned above, and utilizes acidogenic bacteria to transform them into:
#* Short-chain fatty acids: lactic acid, propionic acid, and butyric acids
#* Ethanol
#* Hydrogen gas
#* Carbon dioxide
# Acetogenesis: Anaerobic bacteria are used to convert the products of acidogenesis to:
#* Acetic acid
#* Hydrogen gas
#* Carbon dioxide
#* Small organic molecules
# Methanogenesis: In the final step, methanogenic bacteria transform the aforementioned intermediate products into biogas(methane and carbon dioxide).
This process has to be carried out under a specific range of temperatures and pH. Most of the time, an anaerobic process will be slowed down if the temperature of the process goes below 35 °C (mesophilic and thermophilic conditions). Since a distinguishing characteristic of anaerobic processes is their slow development, many other factors can further slow down this process such as the organic matter composition, nutrient concentration, and the presence of toxic substances. All of these factors can fully veer the treatment off its course if not analyzed properly.