Dissolved organic matter in complex shale gas wastewater analyzed with ESI FT-ICR MS: Typical characteristics and potential of biological treatment

Knowledge on the composition and characteristics of dissolved organic matter (DOM) in complex shale gas wastewater (SGW) is critical to evaluate environmental risks and to determine effective management strategies. Herein, five SGW samples from four key shale gas blocks in the Sichuan Basin, China, were comprehensively characterized. Specifically, FT-ICR MS was employed to provide insights into the sources, composition, and characteristics of SGW DOM. Organic matter was characterized by low average molecular weight, high saturation degree, and low aromaticity. Notably, the absence of correlations between molecular-level parameters and spectral indexes might be attributed to the high complexity and variability of SGW. The unique distribution depicted in van Krevelen diagrams suggested various sources of DOM in SGW, such as microbially derived organics in shales and biochemical transformations. Moreover, linear alkyl benzene sulfonates, as well as associated biodegraded metabolites and coproducts, were identified in SGW, implying the distinct anthropogenic imprints and abundant microbial activities. Furthermore, high DOC removal rates (31.42-79.23 %) were ach-ieved by biological treatment, fully supporting the inherently labile nature of SGW and the feasibility of biodegradation for SGW management. Therefore, we conclude that DOM in SGW is a complex but mostly labile mixture reflecting both autochthonous and anthropogenic sources.

Automated summary

Knowledge of the composition and characteristics of dissolved organic matter (DOM) in complex shale gas wastewater (SGW) is crucial for evaluating environmental risks and determining effective management strategies. In this study, comprehensive characterization of five SGW samples from four shale gas blocks in the Sichuan Basin, China, was conducted using FT-ICR MS. The results revealed that DOM in SGW has a low average molecular weight, high saturation degree, and low aromaticity. The unique distribution patterns in van Krevelen diagrams indicated various sources of DOM in SGW, including microbial organic matter in shales and biochemical transformations. Additionally, linear alkyl benzene sulfonates and associated biodegraded metabolites and coproducts were identified in SGW, suggesting anthropogenic influence and abundant microbial activities. Furthermore, high rates of DOC removal (31.42-79.23%) were achieved through biological treatment, highlighting the labile nature of SGW and the feasibility of biodegradation for its management. Therefore, it can be concluded that DOM in SGW is a complex but mostly labile mixture derived from both autochthonous and anthropogenic sources.