Treatment of primary effluent by coagulation–adsorption– ultrafiltration for reuse

This study aims to find news a die of purification for a wastewater reuse. Primary effluent contains organic mineral, dissolved and suspended matter (colloids). Microfiltration or ultrafiltration is adequate for producing disinfected clear water suited for different applications. However, direct filtration on membrane is limited by the fouling phenomena which leads during filtration to constant pressure, to a strong and continuous decrease of the permeate flux. On the other hand, coagulation and adsorption make it possible to removal the colloidal fraction, which plays a significant role in membrane fouling. We considered the treatment of primary effluent by coagulation– adsorption–ultrafiltration for reuse with ultrafiltration membranes. Tests have been performed on the primary effluent of the wastewater treatment plant of Staoueli, Algeria with the average characteristics in the chemical oxygen demand (COD) of 165 mg of O2/l, and turbidity 90 NTU. The ultrafiltration tests have been made on mineral membranes tubular CARBOSEP M5 (10 kDa), M2 (15 kDa), in dynamic mode with a transmembrane pressure ∆P = 1 bar, cross flow velocity U = 3 m/s. The reagents used FeCl3 (as a coagulant agent) and powder activated carbon (PAC) as an adsorbent agent. In the first step, the optimal conditions were determined for coagulation and adsorption corresponding to 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 combined. The coagulation test showed a COD value equal to 23 mg/l at pH = 5.5 for FeCl3, concentration 120 mg/l and a final turbidity equal to 12 NTU. For the process coagulation–adsorption–ultrafiltration, we obtained the best COD final value of 7 mg/l. The best value of the permeate was obtained for the coupling coagulation–ultrafiltration at coagulant concentration equal to 80 mg/l and residual COD equal to 13 mg/l for M2 membrane. Coagulation significantly improves the ultrafiltration performances. The coupling makes it possible to reduce the regeneration membranes.

1 20 Time (min) (b) C(FeCl 3) = 0 mg/l C(FeCl3) = 120 mg/l C(PAC) =40mg/l Turbidity (NTU) (a) Raw water COD (mg/l) Fig. 6 compares the water quality obtained for the different processes tested. The best result was obtained by the process of coagulation–adsorption– ultrafiltration, with COD final value of 7 mg/l for M2 membrane and 20 mg/l for M5 membrane.