Improvement of Biodegradability of Oil Field Drilling Wastewater Using Ozone

The possibility of improving the biodegradability of drilling wastewater using ozone was investigated following coagulation pretreatment. The biodegradability of wastewater was improved significantly following the start of ozonation, and the molecular weight of organic compounds decreased continuously with the progress of oxidation. It is interesting that minimum biochemical oxygen demand, total organic carbon (BOD/TOC) ratio (0.4 g/g) was observed when wastewater was treated with ozone continuously for 15 min. The combination of ozonation for 5 min (ozone consumption ratio of 2.6 g ozone/g TOC) followed by biological degradation produced a total TOC removal rate of 54.3%, which was comparable to direct ozonation for 30 min under the same conditions (TOC removal rate of 54.9%; ozone consumption ratio of 8.7 g ozone/g TOC). It is clear that biological treatment following short-term ozonation was very efficient in TOC removal. A process of successive coagulation-precipitation, ozone oxidation, and biodegradation seemed to be a good option for drilling wastewater treatment.