Advanced phosphorus removal via coagulation, flocculation and microsieve filtration in tertiary treatment

The applicability of microsieve technology together with coagulation and flocculation for advanced phosphorus removal was investigated. A pilot unit including a microsieve with 10 μm mesh size was operated continuously with secondary effluent from Ruhleben wastewater treatment plant in Berlin. By applying a pretreatment of 0.07–0.09 mmol/L (as metal) coagulant and 1.5–2 mg/L cationic polymer, total phosphorus values below 80 μg/L were achieved. Coagulation with polyaluminum chloride (PACl) produced a better effluent quality compared to FeCl₃, as less suspended solids and less residual coagulant were found in the microsieve effluent. In addition, the transmittance of UV radiation through the water was improved by using PACl. The produced amount of backwash water was always below 3% (on average 1.6%). Under optimized mixing conditions, polymer doses of 0.6 mg/L were possible without losses in water quality and filtration performance. Microsieving with chemical pretreatment is a viable option for high quality effluent polishing.