Biological treatment of wastewater

The elimination of organic carbonaceous and nitrogenous pollution (in colloidal form or in solution), when it presents a satisfactory biodegradability, is essentially achieved by biological purification processes. They are the most widely used treatment method for urban wastewater and many industrial wastewaters, due to their efficiency and rusticity.

Commonly referred to as secondary treatment, biological processes are generally implemented in a resi-dual water treatment chain. They are located downstream of pre-treatments that separate dense bulky matter (waste, gravel, sand) from troublesome matter (oil, grease, etc.), and of primary or physico-chemical settling treatments, the purpose of which is to ensure partial or total elimination of particulate pollution and, if necessary, toxic pollution.

It should also be noted that, in some cases, biological purification can be used to refine water quality, as part of a finishing or tertiary treatment that reduces residual carbon and nitrogen pollution.

This article :

• a brief review of the fundamental principles of biological purification and, more specifically, of the reaction mechanisms involved in the metabolization of organic matter in aerobic and anaerobic environments;

• a description of the various treatment technologies for bacterial degradation of carbon and nitrogen pollution, including sizing criteria, purification performance and industrial applications.