What percentage of BOD is typically removed during primary treatment?

During primary treatment of wastewater, the primary objective is to remove a significant amount of suspended solids and associated organic matter, primarily measured as Biochemical Oxygen Demand (BOD). Typically, the percentage of BOD removed during this stage ranges from 30-50%.

This range reflects the effectiveness of physical processes used in primary treatment, such as sedimentation and flotation, where heavier solids settle out and lighter materials may be removed. The removal efficiency is not exceptionally high since primary treatment mainly targets solids rather than treating dissolved organics, which are better addressed in secondary treatment processes. Therefore, in the context of wastewater treatment, stating that 30-50% of BOD is removed during primary treatment is an accurate reflection of observed results and practices in the field.