What is the main function of the biological treatment phase in wastewater treatment?

The main function of the biological treatment phase in wastewater treatment is to utilize microorganisms to decompose organic matter. During this phase, beneficial bacteria and other microorganisms are introduced into the wastewater to break down organic pollutants and waste materials. This process is crucial as it significantly reduces the levels of biodegradable materials, effectively improving the overall quality of the wastewater before it moves on to further treatment stages or is discharged into the environment.

Microorganisms such as bacteria can metabolize the organic matter, converting it into carbon dioxide, water, and additional microbial biomass. This biological activity is essential for removing nutrients such as nitrogen and phosphorus, which, if left untreated, could contribute to environmental pollution and eutrophication in water bodies.

In contrast, the other choices focus on different aspects of wastewater treatment. Solids filtration is typically addressed in the preliminary or primary treatment stages, while using chemicals to kill pathogens is more relevant in disinfection processes. Aeration, although it plays a role in enhancing biological treatment by providing oxygen to aerobic bacteria, is not the phase's primary function. Thus, the correct answer encapsulates the essential role of microorganisms in managing and reducing organic content in wastewater.