A Sewage Treatment Plant (STP) is a facility that treats wastewater from households, industries, and institutions before discharging it into the environment. The design of an STP involves several calculations to ensure that the plant can handle the expected wastewater flow and remove pollutants effectively.

$$ADF = P \times q \times (1 + I)$$

where: $A$ = surface area of the treatment tank (m²)

After aeration, the water enters a clarifier (sedimentation tank) for solid-liquid separation.

BOD load (kg/day) = (Avg. Daily Flow × Influent BOD) / 1000 COD load (kg/day) = (Avg. Daily Flow × Influent COD) / 1000 TSS load (kg/day) = (Avg. Daily Flow × Influent TSS) / 1000

This tank buffers flow and pollutant concentration variations.