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

The colloidal properties of biogenic elemental sulfur (S-0) 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 S-0 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 S-0 flocculation and the supernatant turbidity removal. The dose optimization results indicated that the S-0 flocculation efficiency decreased in the following order PAC > MBF > PAM. Optimum S-0 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 S-0 flocculation rate reached 97.53%. Confirmation experiments demonstrated that employing PAC for S-0 flocculation is feasible and RSM is an efficient approach for optimizing the process of S-0 flocculation. The results provide basic parameters and conditions for recovering sulfur during the treatment of sulfate-laden wastewaters. (C) 2015 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.