Solar-driven interfacial evaporation on balsa for shale gas wastewater treatment: Analysis of system efficiency and water safety

The volume of shale gas wastewater (SGW) surges notably with shale gas extraction booms in China. Solar driven interfacial evaporation technology (SIE), which presents significant advantages in environmentally-friendly and low-cost treatment of high-salinity wastewater, shows potential in SGW treatment. Herein, SIE technology based on balsa wood was introduced to treat SGW from the Sichuan Basin, and the system efficiency and condensate water safety were comprehensively explored. Under two sun intensity irritation, the evaporation rate of SGW reached 1.50 kg/(m2 center dot h) with the evaporation efficiency of over 50 %. To maintain a relatively consistent evaporation rate, the anti-scalant nitrilotriacetic acid was used and the evaporation rate reduced by only 0.15 kg/(m2 center dot h) within 8 h. Meanwhile, the SIE system showed remarkable total dissolved solids (TDS) removal rate exceeding 99 % of SGW. In addition, to ensure the safety of condensate water reuse, the transfer of hazardous organic compounds from raw to condensate water was comprehensively detected. It was found that volatile and semi-volatile organic compounds (VOCs and SVOCs) which were of strong responses in raw SGW exhibited much lower responses or cannot be detected in condensate water, including diisobutyl phthalate, dimethylbenzylamine e and pyridine. The results indicate that SIE is capable of removing the hazardous organic compounds. Compounds of strong response in condensate, such as furfural and 2,6-dimethoxy-phenol, are considered as natural compounds in wood, which are degradable and show low impacts on environment. This study suggested a novel and low-cost approach to SGW treatment.