Investigation of colloidal biogenic sulfur flocculation: Optimization using response surface analysis

Abstract

The colloidal properties of biogenic elemental sulfur (S0) cause solid-liquid separation problems, such as poor settling and membrane fouling. In this study, the separation of S0 from bulk liquids was performed using flocculation. Polyaluminum chloride (PAC), polyacrylamide (PAM) and microbial flocculant (MBF) were compared to investigate their abilities to flocculate S0 produced during the treatment of sulfate-containing wastewater. A novel approach with response surface methodology (RSM) was employed to evaluate the effects and interactions of flocculant dose, pH and stirring intensity, on the treatment efficiency in terms of the S0 flocculation and the supernatant turbidity removal. The dose optimization results indicated that the S0 flocculation efficiency decreased in the following order PAC > MBF > PAM. Optimum S0 flocculation conditions were observed at pH 4.73, a stirring speed of 129 r/min and a flocculant dose of 2.42 mg PAC/mg S. During optimum flocculation conditions, the S0 flocculation rate reached 97.53%. Confirmation experiments demonstrated that employing PAC for S0 flocculation is feasible and RSM is an efficient approach for optimizing the process of S0 flocculation. The results provide basic parameters and conditions for recovering sulfur during the treatment of sulfate-laden wastewaters.