Biological Treatment of Effluent and Waste Water

Biological wastewater treatment uses microorganisms to degrade pollutants in the sewage.

Primary treatment uses screening to remove solids and sedimentation to settle suspended particles.

Secondary treatment uses microbial oxidation under aerobic conditions to break down organic waste in sewage. This can be done using trickling filters or the activated sludge process.

In trickling filters, wastewater can be sprayed onto crushed stone or synthetic media coated with biofilms of aerobic bacteria.

Dissolved organic matter diffuses into the biofilms, where aerobic microbes oxidize it into simpler metabolites.

In the activated sludge process, bacteria such as Zoogloea ramigera form flocs with other microbes and oxidize organic carbon, which greatly reduces biochemical oxygen demand.

The sludge then flows to a settling tank, where part of it is recycled, and the excess is removed for further treatment.

Tertiary treatment uses UV disinfection to refine clarified effluent for discharge or reuse.

Finally, anaerobic digestion breaks down the sludge under anaerobic conditions, producing methane-rich biogas and reducing sludge volume.