Advanced treatment of heavy oil wastewater for reuse by the combination of microwave enhanced coagulation and iron/carbon micro-electrolysis

A combination process was developed in laboratory scale including microwave (MW) coagulation and iron/carbon micro-electrolysis (Fe/C ME) in series for treatment of heavy oil produced water (HOPW) with high concentrations of oil and chemical oxygen demand and high corrosion rates. The effects of coagulant dosage, MW irradiation time, settling time, and Fe:C mass ratio on the actual treatment results were investigated. The use of MW irradiation brought some benefits including enhancing oil removal, reducing coagulation consumption, shortening settling time and lowering corrosion rate. During the 30-day continuous treatment period, the Fe-based metallic glasses/activated carbon (MGs/AC) ME system exhibited high performance stability, whereas the iron shavings/AC ME system had good performance for only 8 days. The total reduction percentages of oil, suspended solids and corrosion rate were 95.5%, 98.3% and 96.5%, respectively, in the combined MW coagulation-MGs/AC ME system, and the corrosion rate of the treated HOPW was only 0.025 mm/year. The quality parameters of the treated heavy oil produced water (HOPW) could completely meet the requirements of the C1 grade in the SY/T 5329-1994 standard for wastewater reinjection in oilfields. Moreover, the biodegradability of the HOPW was greatly improved after treatment, creating favorable conditions for subsequent biological treatment if not reinjection.