Optimization of coagulation–flocculation process for wastewater derived from sauce manufacturing using factorial design of experiments

Abstract

A coagulation–flocculation process was used to pre-treat wastewater derived from sauce manufacturing prior to a subsequent biological treatment. A 5 2 full factorial experimental design and response surface methodology were employed to evaluate and optimize the coagulant and flocculant dosages and to achieve a compromise between efficiency, operational costs and the effects of a possible subsequent biological treatment. The influence of pH was also evaluated to determine the most suitable pH condition (alkaline, neutral or acidic). Although the results were quite similar under all pH conditions, alkaline pH was selected as it permitted ease of operation and lower operational costs due to the elimination of pH adjustment stages. The best regression coefficients ( R 2) were obtained for chemical oxygen demand (COD), turbidity and total soluble organic carbon (TOC soluble) at alkaline pH, reaching values of 0.9136, 0.8397 and 0.8512, respectively. At alkaline pH, the most significant factor in the analysis of variance (ANOVA) study was coagulant dosage for COD and turbidity removals. However, coagulant and flocculant dosages were both significant factors. Multiple response optimization fits the optimum values of the factors and the responses as 0.4 mL/L of coagulant, 7.0 mL/L of flocculant and 82, 72 and 13% of COD, turbidity and TOC soluble removal at alkaline pH, respectively.