What percentage of Biochemical Oxygen Demand (BOD) is typically removed during primary treatment?

In the context of municipal wastewater treatment, primary treatment primarily focuses on the removal of solids and a portion of the organic matter present in the wastewater. During this phase, physical processes such as sedimentation and flotation are employed to separate solids from the liquid effluent.

The typical removal rate of Biochemical Oxygen Demand (BOD) during primary treatment is around 40%. This percentage reflects the ability of primary treatment processes to address organic material that can contribute to water pollution. The process involves the settling of heavier solids in sedimentation tanks, reducing the amount of organic matter available in the water.

In general, primary treatment is effective at eliminating most settleable solids and a moderate amount of organic loads, leading to this specific percentage of BOD removal. Other treatment stages, such as secondary treatment, would further decrease BOD levels, but in the scope of primary treatment, a 40% reduction is standard and illustrates the efficiency of this initial treatment phase in improving water quality.