Cold-cathode X-ray irradiation pre-treatment for fouling control of reverse osmosis (RO) in shale gas produced water (SGPW) treatment

For a more sustainable and environmental-friendly management of shale gas produced water (SGPW), it is essential to customize and optimize the treatment options since the characteristics of SGPW vary both spatially and temporally. However, fundamental studies on the foulants of SGPW and their control methods are lacking, particularly in connection with the RO-based process, which has been adopted increasingly in SGPW treatment. This study fundamentally evaluated the feasibility of novel cold-cathode X-ray irradiation as an additional fouling control process prior to the RO process using actual SGPW extracted from the Sichuan shale region (China) for the first time in literature. The foulants incapable of being removed by conventional pre-treatments (e.g., dissolved air flotation (DAF) and ultrafiltration (UF) membrane) induced organic fouling in the RO stage, and they were identified eventually as aliphatic hydrocarbon (oil) components. The fouling mechanism was deduced to be the formation of coalesced hydrocarbon layer on the RO membrane surface. In order to target these identified oily substances surgically, the novel cold-cathode X-ray irradiation process was employed since this technology offers much better energy efficiency compared to the existing thermionic X-ray irradiation. Our work demonstrated that the cold-cathode X-ray irradiation could efficiently remove the aliphatic hydrocarbon in the pre-treatment stage. This new X-ray irradiation process was optimized further with respect to energy consumption by investigating the effect of tube current and voltage. Our experimental observations suggest that the cold-cathode X-ray irradiation process could be an energy-efficient alternative for the treatment of organic-rich (oily) industrial wastewaters such as SGPW.