What are the mesh-like structures formed by masses of bacteria held together by fungal filaments called in the biological treatment of sewage?

Flocs

The correct answer is Option (3)- Flocs

In the biological treatment of sewage, flocs are mesh-like structures formed by masses of bacteria held together by fungal filaments.

During the biological treatment process, microorganisms, including bacteria and fungi, are used to break down organic matter in sewage. The bacteria consume the organic substances present in the wastewater as a food source, and as they grow and reproduce, they form clumps or aggregates. These clumps of bacteria are then held together by fungal filaments, creating a mesh-like structure known as flocs.

As the aerobic microorganisms grow, they form aggregates or flocs through the association of bacterial cells with fungal filaments. These flocs create a mesh-like structure that helps to improve the settling characteristics of the microorganisms and facilitate their removal from the treated wastewater later in the process.

During their growth, the aerobic microorganisms consume a significant portion of the organic matter present in the effluent. This organic matter includes various organic compounds that contribute to the biochemical oxygen demand (BOD) of the wastewater.

BOD is a measure of the amount of oxygen required by microorganisms to decompose organic matter. By reducing the organic matter content through microbial consumption, the BOD of the effluent is significantly reduced.