Organic compounds in Weiyuan shale gas produced water: Identification, detection and rejection by ultrafiltration-reverse osmosis processes

Quantification of organic pollutants in flowback and produced water is essential to design appropriate treatment strategy and predict the potential environmental toxicity associated with unconventional energy production. Herein, we firstly characterized the important range chemicals of produced water (PW) collected from Weiyuan shale gas play, China. Ultra-high resolution ( 10 M) electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry was used to gain insights into molecular compositions of mass range 170?1,000 Da. Oxygen-containing organic compounds (CHO) was the dominant type of compounds in the PW, and classes of O8 and O9 had the highest relative abundance. Highly unsaturated phenolic and aliphatic compounds were identified as the main compounds. Three low molecular weight (LMW, <170 Da) compounds, dimethylbenzylamine (DMBA), indoline, and 6-methyl-quinoline, were firstly revealed in the PW, with their concentrations of 137.11 ?g/L, 5.48 ?g/L, and 0.9 ?g/L, respectively, as determined by liquid chromatography coupled to tandem mass spectrometry. An integrated process of ultrafiltration coupled with reverse osmosis was employed to treat the PW and achieved 78.3%, 96.3%, and 100% removal for these three chemicals. The concentration of DMBA in the effluent is 29.75 ?g/L, which potentially cause environmental risks even after advanced membrane treatment, suggesting that LMW chemicals such as DMBA in PW deserves special attention.

Automated summary

The study focused on the quantification of organic pollutants in flowback and produced water to design effective treatment strategies and predict environmental toxicity in unconventional energy production. The analysis of produced water from the Weiyuan shale gas play in China revealed oxygen-containing organic compounds as the dominant type, with highly unsaturated phenolic and aliphatic compounds identified as main components. Advanced membrane treatment achieved significant removal rates for compounds such as dimethylbenzylamine, but low molecular weight chemicals like DMBA still posed potential environmental risks even after treatment.