Evaluation of reusing alum sludge for the coagulation of industrial wastewatercontaining mixed anionic surfactants

A coagulation-flocculation process is typically employed to treat the industrial wastewater generated by the consumer productsindustry manufacturing detergents, soaps, and others. The expenditure of chemicals including coagulants and chemicals for pHadjustment is costly for treating this wastewater. The objective of this study was to evaluate the feasibility of reusing the aluminumsulfate (alum) sludge as a coagulant or as a coagulation aid so that the fresh alum dosage can be minimized or the removal e ciency canbe enhanced. The experiments were conducted in a jar-test apparatus simulating the coagulation-flocculation process for simultaneousremovals of organic matters, anionic surfactants, suspended solids, and turbidity. At the optimum initial pH value of 10 and the freshalum concentration of 400 mg/L, the total suspended solids (TSS), total chemical oxygen demand (TCOD), total anionic surfactants,and turbidity removal e ciencies were 71.5%, 76.4%, 95.4%, and 98.2%, respectively. The addition of alum sludge as a coagulantalone without any fresh alum addition could significantly remove the turbidity, TCOD, and anionic surfactants. The TSS was left in thesupernatants after the settling period, but would subsequently be removed by adding the fresh alum. The TSS, TCOD, and turbidityremoval e ciencies were also enhanced when both the alum sludge and the fresh alum were employed. The TCOD removal e ciencyover 80% has been accomplished, which has never fulfilled by using the fresh alum alone. It is concluded that the alum sludge couldbe reused for the treatment of industrial wastewater generated by the consumer products industry.