油田压裂返排液的厌氧处理特性

Anaerobic treatment characteristics of oilfield fracturing flowback fluid

油田压裂返排液中含有高浓度有机物、盐类物质和悬浮物等污染物,如不妥善处置直接外排会对环境产生严重危害。以配制的胍胶压裂返排液为研究对象,采用厌氧颗粒污泥对其进行处理,以COD、TOC去除率及甲烷产量为考察指标,研究了压裂返排液的厌氧生物降解特性。结果表明,压裂返排液经168 h厌氧处理后,COD和TOC由处理前的1 735.2 mg·L^(-1)和698.5 mg·L^(-1)降低至277.2 mg·L^(-1)和94.9 mg·L^(-1),去除率分别为84.0%和86.4%,每克COD能产生688.2 mL的甲烷。采用红外光谱、紫外可见光谱以及三维荧光光谱对压裂返排液厌氧处理过程中有机物的组分及光谱特性进行了分析,发现厌氧生物处理可显著去除压裂返排液中芳香族化合物和类腐殖酸等物质。凝胶渗透色谱分析结果表明,压裂返排液中分子质量小于200 Da的有机物在厌氧处理过程中被优先去除。此外,将厌氧工艺出水进行好氧生物处理,COD去除率仅为22.2%,说明厌氧处理后的压裂返排液可生物降解性较差,需要采用高级氧化等方法进行深度处理。

Oilfield fracturing flowback fluid contains pollutants such as high concentrations of organic matter,salinity, and suspended solids. If oilfield fracturing flowback fluid is not disposed properly, direct discharge would cause severe harm to the environment. In this study, anaerobic granular sludge was employed to treat the prepared guar gum fracturing flowback fluid, and its anaerobic biodegradation characteristics was explored with COD and TOC removal rates and methane production as the indicators. The results demonstrated that after 168 h treatment, COD and TOC decreased from 1 735.2 mg·L^(-1)and 698.5 mg·L^(-1)before anaerobic treatment to277.2 mg·L^(-1)and 94.9 mg·L^(-1)after anaerobic treatment with the corresponding removal rates of 84.0% and 86.4%, respectively. Meanwhile, the evolution of dissolved organic matter(DOM) in oilfield fracturing flowback fluid during the anaerobic biological treatment was investigated. The DOM was sampled at different treatment stages and characterized through Fourier transform infrared(FTIR) spectroscopy, fluorescence excitation-emission matrix(EEM), and UV-Vis. The results revealed that organic pollutants such as aromatic compounds and humic substances could be significantly removed by anaerobic biological treatment. Gel permeation chromatography(GPC) indicated that the organic matter with molecular weight(MW) less than 0.2 kDa was first removed during the anaerobic treatment. In addition, aerobic biological treatment was used to treat the effluent from anaerobic treatment unit and the COD removal efficiency was only 22.2%, indicating that the fracturing flowback after anaerobic treatment had low biodegradability and the advanced oxidation method would be needed for deep treatment.