What is primarily responsible for biological treatment in a conventional onsite treatment system?

The primary responsibility for biological treatment in a conventional onsite treatment system lies with the soil. In these systems, the treatment process occurs as wastewater from the septic tank is distributed into the soil, where a natural biological process takes place. Microorganisms present in the soil, such as bacteria, play a crucial role in breaking down organic matter and nutrients found in the effluent. This process not only helps to reduce the levels of harmful pathogens but also facilitates the removal of contaminants, leading to cleaner effluent that can be safely assimilated into the surrounding environment.

In contrast, the septic tank serves as a preliminary treatment chamber where solids settle out and some initial anaerobic digestion occurs. An effluent filter aids in providing further clarification by filtering out residual solids before the effluent moves to the soil but is not directly responsible for the biological treatment. The geo-textile biomat can assist in filtration and provide a medium for microbial growth, but the primary biological breakdown in these systems predominantly happens within the soil matrix. Therefore, the correct answer highlights the essential role that soil plays in the overall treatment process.