Tertiary treatment of a secondary effluent by the coupling of coagulation–adsorption–ultrafiltration for reuse

We considered the treatment of secondary effluent by coagulation–adsorption coupled with ultrafiltration. Tests were performed on the secondary effluent of the wastewater treatment plant at Staoueli (Algeria) where the average chemical oxygen demand (COD) was 46 (mg O2/L) and turbidity, 16 NTU. The ultrafiltration tests were made with mineral tubular CARBOSEP membranes — M5 (10 kg/ mol), M2 (15 kg/mol) — in the dynamic mode with a transmembrane pressure )P = 1 bar and cross flow velocity = 3 m/s. The reagents were calcium chloride (as coagulant agent) and powder activated carbon. Coagulation improved the ultrafiltration performances significantly. In the first step, the optimal conditions for coagulation were determined considering the best elimination of turbidity as well as organic matter. In the second step, the efficiency of different processes (coagulation, adsorption, ultrafiltration) was compared when used alone or in combination. The coagulation test showed a COD elimination equal to 12 mg/L at pH = 6.5 for a concentration of CaCl2 = 50 mg/L and a turbidity equal to 3 NTU.

This study made it possible to determine the optimum conditions for coagulation of a secondary effluent to a pH of 6.5 with a concentration of CaCl2 at C = 50 mg/l. Coagulation improves permeate flux in a very significant way for the two membranes tested. The coupling of coagulation with UF makes it possible to modify the configuration of the deposit on the membrane surface to greater sized flocs (formation). We observed a significant reduction of turbidity. The coupling of