The majority of wastewater containing biodegradable compounds can be treated by biological way, provided that the most suitable environmental conditions are created, verified and guaranteed. This type of system, if properly designed and operated, can remove BOD5, COD, surfactants, colloids, TKN, oil and grease and suspended solids for over 90%, without the use of chemical reagents: it is by far the more efficient and economical available process for these types of wastewater. Furthermore, the amount of sludge generated is as low as possible and, being an organic product, it can be mixed with other organic elements to produce compost.  The basic process consists in the transformation (Oxidation) of the biodegradable and particular soluble constituents in final products that include carbon dioxide, nitrates and water. The responsible for this conversion are a mixed colony of living microorganisms, which proliferate in certain environmental conditions; so it is very important that the following parameters are checked and promptly corrected:

The biological wastewater treatment plant (WWTP) includes two interconnected lines: the water line and the sludge line.