Microorganisms, such as bacteria, play an important role in the natural cycle of materials and particularly in the decomposition of organic wastes. The role of microorganisms is developed here because they are also important in wastewater treatment. What is waste for humans and higher vertebrates becomes a useful food substrate for microorganisms. In both natural and engineering systems, microorganisms such as bacteria, fungi, protozoa and crustaceans play an essential role in converting organic waste into more stable, less polluting substances. They form what is called the "food chain". For example, inorganic and organic substances in the waste are consumed by bacteria, fungi and algae. These are in turn consumed by protozoa and nematodes (some fungi, however, nematode trap) and the latter by rotifers.
In a natural body of water, p. River or lake, the number and type of microorganisms depends on the degree of contamination. The overall effect of pollution appears to be a reduction in the number of species. For example, in a heavily polluted lake, there are fewer species but more in number, while in a healthy lake there may be many species present, but in fewer numbers.
Wastewater treatment is a process in which contaminants are eliminated. The ultimate goal of wastewater treatment is to produce an effluent that will not affect the environment. In the absence of wastewater treatment, the results can be devastating as wastewater can disrupt the environment.
The general wastewater treatment processes are primary, secondary and tertiary treatment. Primary treatment involves the physical separation of wastewater into solids and liquids by the use of a sedimentation basin. The liquid wastewater is then transferred to a secondary treatment which focuses on the removal of the biological compound dissolved by the use of microorganisms. Microorganisms often use aerobic metabolism to degrade biological matter in liquid sludge. Tertiary treatment is then required to disinfect wastewater so it can be released into the environment. Solid wastewater separated from the primary treatment is transferred to a sludge digestion tank which involves anaerobic degradation using microorganisms.
Wastewater is composed of organic matter such as carbohydrates, fats, oils, fats and proteins mainly from household waste. It also contains dissolved inorganic matter such as nitrogen species and phosphorus species mainly for agricultural use. It is essential to remove nutrients before they are released into the environment, as it interferes with natural habitats by altering the chemical composition, such as pH or oxygen level, both directly and indirectly.