Types of Biological Treatment

Types of Biological Treatment based on Process

There are two types of biological treatment process; aerobic and anaerobic.

Biological Aerobic Treatment

Biological wastewater treatment is an extremely cost effective and energy efficient system for the removal of BOD (Biological Oxygen Demand), since only micro-organisms are used. These feed on the complex materials present in the wastewater and convert them into simpler substances, preparing the water for further treatment. Aerobic wastewater treatment is a biological process that takes place in the presence of oxygen. Aerobic wastewater treatment encourages the growth of naturally-occurring aerobic microorganisms as a means of renovating wastewater. Such microbes are the engines of wastewater treatment plants. Organic compounds are high-energy forms of carbon. The oxidation of organic compounds to the low-energy form (carbon dioxide) is the fuel that powers these engines. Understanding how to mix aerobic microorganisms, soluble organic compounds and dissolved oxygen for high-rate oxidation of organic carbon is one of the fundamental tasks of wastewater engineers.

Since anaerobic treatment is preferred when the dissolved organic concentrations of untreated wastewater are high, aerobic treatment is often used as a secondary treatment process and follows an anaerobic stage. Aerobic treatment consists of activated sludge processes or oxidation lagoons. The size of these can be reduced and tolerance against fluctuations and toxics increased by adding a step with moving bed bioreactors (MBBR) prior to the active sludge treatment.



  • Energy efficient
  • Cost effective
  • Can be used in combination with anaerobic processes

Biological Anaerobic Treatment

Anaerobic wastewater treatment is the biological treatment of wastewater without the use of air or elemental oxygen. Many applications are directed towards the removal of organic pollution in wastewater, slurries and sludges. The organic pollutants are converted by anaerobic microorganisms to a gas containing methane and carbon dioxide, known as "biogas". Anaerobic treatment is a slow process and can take up to 3 months, also due to septic decomposition, unpleasant odours may occur.