Which microorganisms are primarily used in secondary treatment?

Secondary treatment in wastewater treatment primarily relies on microorganisms, specifically bacteria and protozoa, to break down organic matter present in the wastewater. This phase of treatment focuses on the biological processes that take place in aeration tanks, where bacteria metabolize the organic pollutants, essentially converting them into biomass, carbon dioxide, and water.

Bacteria play a crucial role in this process as they can utilize a wide range of organic materials as their food source, thereby helping to reduce biochemical oxygen demand (BOD) and organic solids in the effluent. Protozoa, on the other hand, assist in controlling the bacterial population and contribute to the clarification of the wastewater by consuming bacteria and flocculating particles, which helps improve the clarity of the effluent.

While other microorganisms like fungi and algae can contribute to wastewater treatment processes, they are not the primary agents during secondary treatment. Fungi are more relevant in specific biological processes or in bio-remediation scenarios, and algae are typically associated with natural treatment systems or secondary treatment in certain setups but to a lesser extent than bacteria and protozoa.

In summary, bacteria and protozoa are the main players in the secondary treatment stage due to their effectiveness in degrading organic pollutants and improving effluent quality.