Removal of Phosphorus, BOD, and Pharmaceuticals by Rapid Rate Sand Filtration and Ultrafiltration Systems

This study determined the effectiveness of pilot-scale tertiary sedimentation and filtration systems on lowering phosphorus, biochemical oxygen demand (BOD), and pharmaceutical levels in municipal secondary wastewater effluent. Secondary effluent was diverted into five pilot-scale tertiary treatment systems. The systems used alum and a polymer during coagulation and flocculation, after which sedimentation was used to remove settleable solids, and filtration was used to remove nonsettleable solids. The filtration units following sedimentation were (1)continuous backwash upflow sand filtration following conventional sedimentation, (2)dual-media granular filtration following microsand ballasted sedimentation, (3)dual-media granular filtration following magnetite ballasted sedimentation, (4)ultrafiltration following microsand ballasted sedimentation, and (5)ultrafiltration following magentite ballasted sedimentation. Total phosphorus was 1.11mg/L in the secondary effluent and decreased to 0.015mg/L after sedimentation and ultrafiltration. BOD was 9.9mg/L in the secondary effluent and decreased to <1mg/L after the five systems. The pharmaceutical concentrations found in the secondary effluent were 211ng/L trimethoprim, 323ng/L carbamazepine, and 901ng/L sulfamethoxazole. The range of concentrations following tertiary treatment were 160-255ng/L trimethoprim, 302-335ng/L carbamazepine, and 482-792ng/L sulfamethoxazole. Overall, the tertiary sedimentation and filtration systems did not provide enhanced pharmaceutical removal. The results from this study corroborate other research findings, suggesting that rapid rate sand filtration and ultrafiltration may be inadequate for removing trace concentrations of water soluble pharmaceuticals, although phosphorus and BOD removal was >96% and >91%, respectively, comparing secondary and tertiary effluent.