Enhanced Coagulation/Flocculation by Combining Diatomite with Synthetic Polymers for Oily Wastewater Treatment

The objectives are to evaluate the feasibility of treating oily wastewater using synthetic polymers (polyaluminum chloride (PAC), polyferric sulfate (PFS), and polyacrylamide (PAM)) combined with natural diatomite and to refine the operating parameters using diatomite as an adsorbent and a coagulant aid. The enhanced coagulation/flocculation by combining PAC with diatomite was investigated through mechanism analysis compared to the combination of PFS/PAM with diatomite, respectively. The effects of coagulant dose, initial pH, and settling time on chemical oxygen demand (COD) and turbidity were studied using PAC-diatomite in comparison with using PAC only. The enhanced coagulation/flocculation of diatomite with PAC was better than that with PFS/PAM in terms of COD/turbidity removal and floc settling characteristics, considering costs. The PAC-diatomite system reduced more than 70% of COD and 90% of turbidity over a wide pH range (7–10) within 20 min, with the optimum dose of PAC 50 mg/l and diatomite 1250 mg/l. The added diatomite effectively saved over 85% of PAC dose and simultaneously increased over 50% of COD removal efficiency. This study provided a novel and economical approach for diatomite utilization in the treatment of oily wastewater, satisfying the demands of reuse or reinjection into the ground.