Septic tank

The level of pollutants reduction provided by septic tanks usually do not allow to use them as the only step of wastewater treatment. In practice WWT solution with septic tank often is combined with secondary treatment alternatives – filtration fields, constructed wetlands and biological ponds – and is used also as pre-treatment for packaged activated sludge processes

Main characteristics

Septic tank provides primary wastewater treatment. It can be both factory manufactured or assembled with concrete details on site. Traditional septic tank contains only one section. The newest models of septic tanks consist of two sections to avoid sludge flushing to output pipe. During operation, the sludge layer consisting of various insoluble matters accumulates on the bottom of a septic tank. This layer should be periodically removed to make in use total volume of septic tank.

Basic principles of operation
Septic tank is container with their own ecosystem of microorganisms, which take in place complex biochemical processes to reduce content of polluting substances of sewage put in. The microorganisms found in domestic sewage are bacteria, which use wastewater containing solubilized nutrients for cell growth and energy. The growth of bacteria population is dependent on the characteristics of the wastewater – temperature, concentration of organic matter, toxic chemicals or cleaners. The main part of septic tank is oxygen-free or anaerobic. Only in the clear zone of septic tank oxygen is available. The treatment processes what are going on in those parts are different. 

The treatment efficiency of septic tank strongly depends not only on characteristics of influent wastewater, but also on the size of septic tank, because optimal retention time gives more viability to the process of treatment.