Reclamation of secondary treatment effluent by nanofiltration and bentonite adsorption

Secondary treatment effluent resulting from combined domestic and industrial sewage is characterized by the presence of undesired pollutants such as heavy metals and hazardous organic materials. The disposal and/or reuse of such effluent necessitate further treatment to remove such pollutants. In this paper, an experimental investigation on the treatment of secondary treated wastewater from 6th October city treatment station is presented. The investigated parameters are COD, BOD, TSS, and heavy metals. The experimental treatment includes nanofiltration (NF) using aluminum–titanium ceramic membranes followed by adsorption using sodium and calcium bentonites. The results indicated removal efficiency of NF for COD, BOD, and TSS of 85, 84, and 100%, respectively. Further, the removal efficiencies of heavy metals are 100, 53, 100, and 100% for nickel, zinc, chromium, and lead, respectively. The overall removal efficiencies of heavy metals are 100, 100, 95, and 81% for chromium, lead, nickel, and zinc, respectively. The level of effluent Ni and Zn is less than 0.2 mg/l while Cr and Pb are not detected. A preliminary study for treating 50,000 m3/d of the secondary treatment effluent using NF/adsorption system concluded plant construction cost of about $ 16 million and a unit production cost of $ 0.16/m3.