Optimization of coagulation–flocculation process for a paper-recycling wastewater treatment using response surface methodology

A coagulation–flocculation process was used to treat a paper-recycling wastewater with aluminum chloride as coagulant and a modified natural polymer, chitosan-g-PDMC (poly(2-methacryloyloxyethyl) trimethyl ammonium chloride), as flocculant. To minimize turbidity and sludge volume index (SVI), the experiments were carried out using jar tests and response surface methodology (RSM) was applied to optimize this process. A central composite design, which is the standard design of RSM, was used to evaluate the effects and interactions of three factors, i.e. coagulant dosage, flocculant dosage and pH on the treatment efficiency. The optimal conditions obtained from the compromise of the two desirable responses, turbidity and SVI, were coagulant dosage of 759 mg l−1, flocculant dosage of 22.3 mg l−1 and pH 5.4, respectively. The RSM was demonstrated as an appropriate approach for the optimization of the coagulation–flocculation process by confirmation experiments.