Treatment of drilling wastewater from a sulfonated mud system

Treatment of drilling wastewater from a sulfonated drilling mud system in the Shengli Oilfield, East China, was studied. The wastewater was deeply treated by a chemical coagulation-centrifugal separation-ozone catalytic oxidation combined process. The factors (i.e. pH value, chemical dosage, reaction time, etc.) influencing the treatment effect were investigated, and pH = 7 was determined as optimal for the coagulation; polymeric aluminum chloride (PAC) was selected as the optimal coagulant with a dosage of 18 g/L; cationic Polyacrylamide (CPAM) with molecular weight of 8 million was selected as the optimal coagulant aid with an optimum dosage of 8 mg/L; and the optimal condition of catalytic ozonation was found to be a pH of 12 and an oxidation time of 40 min. The results showed that the combined treatment process was effective. The oil content and suspended solids content of the effluent reached the first class discharge standard according to China’s standard GB 8978-1996 (Integrated Wastewater Discharge Standard) and the chemical oxygen demand (COD) decreased to 195 mg/L from 2.34×10⁴ mg/L after coagulation process and ozone oxidation at pH = 12 for 40 min.