Application of response surface method as an experimental design to optimize coagulation–flocculation process for pre-treating paper wastewater

The response surface methodology (RSM) was employed to study the pre-treatment of paper wastewater with polyaluminum chloride (PAC) as the coagulant and cationic polyacrylamide (c-PAM), as the flocculant in the coagulation–flocculation (CF) process. In addition, the three quadratic models of the three factors of PAC dosage, PAM dosage, and pH were established with the chemical oxygen demand (COD), total suspended solids (TSS), and sludge volume index (SVI) as three responses. The optimal conditions obtained from the compromise of the three desirable responses are PAC 3689 mg/L, PAM 39.9 mg/L, and pH 5.4, respectively. From zeta potential measurement, it was concluded that charge neutralization is the main mechanism of coagulation at slightly acid pH, and c-PAM is very effective in the bridge effect. Additionally, the results offered a certain reference value for the practical application of the CF process using hybrid PAC and c-PAM in stabilized paper pretreatment for COD and TSS removal.