BiVO4/MnO2 Composite Photocatalytic Material for the Shale Gas Flowback Wastewater Treatment

The management and disposal of the shale gas flowback wastewater is one of the greatest challenges associated with the exploration and extraction of unconventional natural gas resources. High salinity and complex chemical composition of fracturing fluids are the main limiting factors for beneficial reuse of the shale gas flowback wastewater, which has become a tough problem in the global environmental field. In this study, a composite photocatalytic oxidant of MnO2 modified BiVO4 was successfully synthesized with one-step hydrothermal method, and used to treat the shale gas flowback wastewater. The synergistic effect of photocatalysis and oxidation has made a great contribution to the removal of COD value in wastewater. When catalyst dosage was 0.6 g, the pH value was controlled to 3, and visible light exposure was 4 h, the prepared BiVO4/MnO2 exhibited the optimum photocatalytic oxidation activity, and the removal efficiency of COD could reach 65.5%, which is better than that of pure BiVO4 or MnO2. Furthermore, in this case, the COD value could be decreased from 188 mg/L to 64.9 mg/L, complying with the first-level standard limit requirements in the integrated wastewater discharge standard (GB8978-1996). Moreover, in the viewpoint of dynamics, Langmuir isothermal-like equation can better describe the relationship between COD removal efficiency and illumination time.