The oxidation of organic compounds is a very useful reaction in the effluent (sewage) treatment process. Thanks to the oxidizing action of aerobic bacteria, it is possible to convert water full of impurities into water suitable for consumption. Aerobic bacteria are those that develop only in the presence of oxygen.
The oxidation process of organic matter begins when bacteria react with DO (dissolved oxygen in water). The product of the reaction is simpler molecules (CO2, H2O).
The so-called biological oxygen demand (BOD) is the amount of O2 necessary to oxidize the organic material. The BOD serves as an indicator to assess the quality of the water, if it is high, it indicates the presence of a lot of DO (dissolved oxygen), leaving no free oxygen for fish respiration. The death of fish in an aquatic environment leads to an even greater increase in BOD.
Anaerobic bacteria are those that can develop in the absence of O2 in the water, do you know how? They use the oxygen present in the organic waste from the effluents.
In this case a reduction of the residues takes place instead of an oxidation.
The big impasse for the use of anaerobic bacteria in the treatment of effluents is that such bacteria decompose organic material into foul-smelling compounds, such as derivatives of ammonia (NH3) and hydrogen sulfide (H2S). That's why most sewers have an unpleasant smell.
By Líria Alves
Graduated in Chemistry
Source: Brazil School - https://brasilescola.uol.com.br/quimica/oxidacao-compostos-organicos.htm