What is septic tank effluent?

Septic tank effluent refers to the liquid that is discharged from a septic tank after the primary treatment process. In a septic system, wastewater from household activities flows into the septic tank, where it undergoes anaerobic digestion. During this process, solids settle to the bottom, forming sludge, while lighter materials float to the top as scum. The liquid that remains in the middle, known as effluent, is partially treated but still contains varying levels of contaminants and bacteria. It is then sent to the drain field or absorption area for further treatment as it percolates through the soil, which provides additional natural filtration before it ultimately reaches groundwater.

The other choices describe different forms of wastewater or treated water. Untreated sewage represents a hazardous condition that has not gone through any treatment, while completely treated water typically refers to effluent that has undergone advanced treatment through municipal processes. Irrigation water comprises a separate context where treated or reused water might be applied to land, which does not accurately describe septic tank effluent specifically pertaining to individual septic systems.