Use of coagulation-flocculation process for the treatment of the landfill leachates of Casablanca city (Morocco)

Abstract

This study aims to investigate the feasibility to apply a coagulation-flocculation process to treat the landfill leachate of the municipal solid waste of Casablanca city (Morocco). Three types of coagulants are assessed: lime (Ca(OH)2), ferric chloride (FeCl3), and alum (Al2(SO4)3). Optimum conditions in terms of the removal of chemical oxygen demand (COD), heavy metals, colour and turbidity contents are determined, using a standard jar test apparatus. Optimum coagulant dosages of 52.5 g Ca(OH)2.l-1, 12 g FeCl3.l-1 and 22.5 g Al2(SO4)3.l-1 are obtained. Lime allows to remove 66.25% of COD, 98% of turbidity, 80% of colour with a low sludge volume generation (30%). When the optimum coagulant dose of FeCl3 is applied a 62.5% of COD, 92.5% of turbidity, 82% of colour are removed with less sludge volume generation (21%).Whereas when Al2(SO4)3 is used 11% COD and 6% of turbidity removal are obtained with a slightly lower sludge volume generation (11%). Regarding the analysis of metallic elements, the results show that a substantial elimination of heavy metals is reached, particularly of Cd, Cr, Cu, Fe, Ni and Pb. Treatment with lime shows a greater affinity to Cr (86%) and lower to Fe (60%). Ferric chloride allows to eliminate most of the detected metal elements with a high affinity toward Cd, Cu, Ni, Cr and Zn. Alum shows to be very suitable for Ni, Pb, Cr elimination with 95 %, 94 % and 93% removal efficiency, respectively. These results show that coagulation-flocculation could be used as a promising process for the pretreatment of landfill leachates of Casablanca city.