Where does most of the wastewater treatment occur in an on-site sewage facility?

Most of the wastewater treatment in an on-site sewage facility occurs in the soil due to the natural processes of filtration and microbial action that take place there. After wastewater is initially settled and partially treated in the tank, it is discharged into the soil, where the remaining contaminants are further broken down by soil microorganisms. This biological treatment process is critical for reducing pathogens and nutrients before the water percolates into the ground, thereby protecting groundwater quality.

While the treatment tank does play a role in initial settling and primary treatment of the wastewater, it is fundamentally the soil that completes the treatment process through complex interactions involving biological, physical, and chemical processes. The distribution field and drainage system are essential for dispersing the treated effluent; however, they closely interface with the soil, which is the primary site of effective treatment. Thus, recognizing the soil’s vital role in the overall efficacy of wastewater treatment is key to understanding the functioning of on-site sewage facilities.