Treatment of wastewater effluents from paper-recycling plants by coagulation process and optimization of treatment conditions with response surface methodology

In the present study, a coagulation process was used to treat paper-recycling wastewater with alum coupled with poly aluminum chloride (PACl) as coagulants. The effect of each four factors, viz. the dosages of alum and PACl, pH and chemical oxygen demand (COD), on the treatment efficiency was investigated. The influence of these four parameters was described using response surface methodology under central composite design. The efficiency of reducing turbidity, COD and the sludge volume index (SVI) were considered the responses. The optimum conditions for high treatment efficiency of paper-recycling wastewater under experimental conditions were reached with numerical optimization of coagulant doses and pH, with 1,550 mg/l alum and 1,314 mg/l PACl and 9.5, respectively, where the values for reduction of 80.02 % in COD, 83.23 % in turbidity, and 140 ml/g in SVI were obtained.