Landfill leachates pretreatment by coagulation-flocculation

After biological and/or physico-chemical treatment of stabilised landfill leachates, COD and salinity content are often larger than reject requirements. In this case, reverse osmosis can be used to treat effectively these residual COD and salinity. However, reverse osmosis feasibility is limited by the membrane fouling. In order to reduce the landfill leachates high fouling power, coagulation-flocculation is examined in this work as reverse osmosis pretreatment. Using the jar-test procedure, physico-chemical conditions were optimised. It concerns the most effective coagulant between ferric chloride and aluminium sulphate, the optimal pH and the most effective flocculant between anionic, cationic and nonionic polymers. Although 97% reduction turbidity was achieved, the supernatant still presented a pronounced fouling power (Fouling Index above 15 min(-1)), according to the large supernatant iron content. By adding upstream coagulation phase both H2O2 as oxidant and lime for pH control, iron content and Fouling Index supernatant were reduced underneath 2 mg/l(-1) and 5 min(-1), respectively. Also, supernatant could be treated by reverse osmosis without entailing an important membrane fouling. (C) 1997 Elsevier Science Ltd.