Coagulation and flocculation of metalworking fluid wastewater by polyacrylamide and polyaluminum chloride

Abstract

A coagulation/flocculation process was studied for treatment of metalworking fluid (MWF) wastewater, using cationic polyacrylamide (CPAM) or polyaluminum chloride (PAC) as coagulant with the flocculant, anionic polyacrylamide (APAM). The removal efficiency of turbidity, chemical oxygen demand (COD) and total suspended solid (TSS) as well as the effluent pH were the main evaluating parameters for the treatment of synthetic and real MWF wastewater. The results revealed that all removal increased as coagulant dose increased. For synthetic wastewater at 10% oil-in-water (O/W) emulsion, the optimum doses of both coagulants used were higher than at 3% O/W emulsion. Flocculant dose showed slight effect but beneficial of floc size, especially coagulated by PAC. At the optimum CPAM dosage for synthetic wastewater at 3% and 10% O/W emulsion, removal of turbidity, COD and TSS were higher than 96%. While at optimum PAC dosage, removal of turbidity, COD and TSS were higher than 97%. The pH of wastewater showed a marked effect on PAC performance but practically not affected on CPAM performance. The optimum efficiency was achieved at pH range 6-9. Moreover, pH of the effluent treated by PAC led to a pH decrease but was not changed when treated by CPAM. For real wastewaters, the use of PAC appeared more efficient than CPAM. However, the flocs formed using PAC were unstable and smaller than that using CPAM.