In which treatment process are microorganisms encouraged to grow and digest organic waste?

The correct choice is secondary biological treatment because this stage of wastewater treatment is specifically designed to utilize microorganisms to break down organic matter in the wastewater. During this process, bacteria and other microorganisms are introduced into the treatment system, where they thrive on the organic waste present in the wastewater.

In secondary biological treatment, the primary objective is to reduce the biochemical oxygen demand (BOD) and the overall organic pollutant levels, which is achieved through biological processes. As the bacteria consume the organic material, they grow and multiply, forming a mass known as biomass or activated sludge. This biomass can then be separated from the treated water, often in a secondary clarifier.

Primary treatment generally involves physical processes, such as sedimentation and screening, to remove larger solids and particulate matter from the wastewater, but it does not focus on microbial action. Tertiary treatment refers to advanced treatment processes that may include filtration or chemical treatments to further clean the effluent, but it does not rely primarily on microorganisms. Disinfection is the final step in the treatment process, aimed at eliminating pathogens from the treated water using chemical agents or physical methods like UV light, rather than engaging in the degradation of organic material by microorganisms.

Thus, secondary biological treatment is essential for promoting microbial activity