How much BOD does primary municipal wastewater treatment typically remove?

Primary municipal wastewater treatment is designed to remove a significant portion of the biochemical oxygen demand (BOD) from wastewater, primarily through physical processes such as sedimentation. During this stage, solid materials and some of the dissolved organic matter are removed, which directly contributes to a reduction in BOD levels.

Typically, primary treatment can achieve BOD removal rates around 30% to 60%, with many sources indicating an average close to 40%. This is due to the mechanical and gravitational processes involved, which effectively separate heavier solids but do not significantly break down the organic matter present in the water. The figure of 40% reflects a commonly accepted estimate based on operational efficiencies and typical outcomes observed in various municipal systems.

Higher percentages, such as 60% or above, are generally associated with more advanced treatment processes, including secondary treatment stages that involve biological processes to significantly reduce BOD further.