Aerobic process are based on the use of microbes which require constant supply of oxygen and the temperature of 20-40°С. Disruption of oxygen supply and temperature changes the composition and number of microbes. Purification of wastewater in aerobic conditions is performed by biofilters or by cultivation of microbes in biological sludge, in which biocenosis consists of various groups of organisms(bacteria, worms, fungi, algae etc). Biological sludge is an amphoteric colloid, in which рН = 4-9, and the dry material contains 70-90% organic and 10-30% inorganic substances.
The main goal of the aerobic process is the oxidative mineralization of organics and transformation of reduced nitrogen to oxidized nitrogen (nitrification resulting in formation of nitrite and nitrate ions).
Aerobic biochemical treatment of wastewater removes organic materials using heterotrophic organisms, which feed on organic carbon (proteins, fats, hydrocarbons etc). The nutritional value of carbon varies depending on the properties of the organic substances, as well as physiology of the microbes. In microbial metabolism some carbon is oxidized to form carbon acid and then carbon dioxide. Some carbon atoms are reduced to radicals becoming part of the cell.
The biochemical destruction of organic substances occurs due to several consecutive reactions, which simplify the initial structure of the substance. For instance, the process of oxidation of hydrocarbons, fats and some amino acids results in the same “universal metabolite”, which completely oxidizes into carbon dioxide and water. Therefore, the mechanism of wastewater treatment is related to transformation of components into environmentally safe compounds. The energy exchange in bacteria is characterized by the intensity of oxygen consumption and exceeds that in the cells of higher plants and animals. Bacteria adapt to consumption of new organic substances better than other organisms.
MIcroorganism which oxidize carbon, live in the upper part of the reactor, while nitrification bacteria reside in the lower part, where the competition for oxygen and nutrients is higher.
The process of aerobic treatment is efficient because its products are low-molecular compounds (СО2, H2О). They cannot be further decomposed in a microbial cell and have no reserve energy to release.