What additional percentage of BOD removal is achieved through secondary municipal wastewater treatment?

Secondary municipal wastewater treatment typically involves biological processes that further reduce the biochemical oxygen demand (BOD) of wastewater after primary treatment has been completed. Primary treatment usually removes a significant portion of solids and some organic matter, but the secondary treatment is where the majority of biological decomposition occurs, significantly enhancing the removal of BOD.

Achieving an additional 45-55% removal rate through secondary treatment is consistent with common standards in wastewater management. This level of reduction is essential not only for protecting aquatic ecosystems but also for meeting regulatory requirements for effluent quality before discharge into surface waters. This process often includes methods such as activated sludge, trickling filters, or sequencing batch reactors, which effectively utilize microbes to digest remaining organic material.

In contrast, higher percentages like 60-70 or 70-80 may be possible in highly optimized systems or advanced treatments but are not typically considered representative for standard municipal systems, making the 45-55% figure reliable and realistic for general understanding.