Application of Dissolved Ozone Flotation in the Advanced Treatment of Drilling Wastewater in Gas Field: Significance of Ozone Microbubble Flocs

Large amount of drilling wastewater was generated during the exploitation of oil and gas field, which contains high concentration of suspended solids and organic matter. The reuse of drilling wastewater was an important way to solve the problem of water shortage during the development of oil and gas field. Therefore, hybrid ozonation-coagulation (HOC) as an integrated water treatment process was applied for the treatment of secondary effluent of drilling wastewater, which combines ozonation and coagulation in one reactor. During the HOC reaction, lots of ozone microbubble flocs were generated. Under the optimal conditions of pH 7, polyaluminum chloride (PAC) dosage 40 mg Al/L, ozone dosage 0.8 mg/L and reaction duration for 15 min, the removal efficiency of UV₂₅₄, UV₂₈₀ and DOC reached 20.07%, 37.97% and 14.51%, respectively. Benzene ring, proteins and humic acids were greatly reduced according to fluorescence analysis. The Fourier transform infrared spectrometer (FT-IR) analysis results showed that adsorption and interphase transfer to ozone microbubble flocs were the major mechanism for C-O functional groups removal. Enhanced decreased proportion of oxygen-containing groups can be observed in the effluent of drilling wastewater treated by ozone microbubble flocs compared with conventional microbubble flocs based on X-ray photoelectron spectroscopy (XPS) analysis. However, the ratio of oxygen-containing groups increased after the treatment of microbubble ozone, which implied that the synergistic effect during the treatment using ozone microbubble flocs, which involved oxidation, adsorption and flotation.