Performance and mechanism of removal and detoxification of typical polycyclic aromatic hydrocarbons in shale gas flowback water by aerobic granular sludge
Shale gas development is a crucial element of China's significant energy strategy,and managing flowback water presents a substantial challenge for the industry.The presence of PAHs in flowback water has received particularly concerns due to their high environmental risks.This study utilizes aerobic granular sludge,which is capable of treating shale gas flowback water,to explore its effectiveness in processing typical PAHs such as naphthalene and phenanthrene,and examine the behavior of these compounds and their degradation pathways by analyzing the intermediates via HPLC and GC-MS.Additionally,the capacity of aerobic granular sludge to reduce the toxicity associated with PAHs was evaluated,highlighting its potential benefits in environmental remediation.The results showed that the aerobic granular sludge could remove 93.8％of naphthalene and 91.3％of phenanthrene with a sustained efficacy over time.Biodegradation served as the primary pathway for a long-term stable removal of typical PAHs by this AGS system,contributing 64.1％to naphthalene removal and 72.2％to phenanthrene removal.Constrained by adsorption capacity,adsorption only played a fleeting yet crucial role at the initial stage with the distinct pathways:chemisorption for naphthalene in a multimolecular layer and a combination of physisorption and chemisorption influenced by electrostatic forces for phenanthrene.Notably,the treatment significantly reduced the biotoxicity of PAH-laden wastewater to 1％and 16％for naphthalene and phenanthrene,respectively.Degradation intermediates such as 2,4-dimethylbenzaldehyde,2,4-di-tert-butylphenol,and 2,2'-methylenebis(4-methyl-6-tert-butylphenol)for naphthalene,while those for phenanthrene degradation included naphthalene,tris(2,4-di-tert-butylphenyl)phosphite,2,4-dimethylbenzaldehyde,2,4-di-tert-butylphenol,and 2,2'-methylenebis(4-methyl-6-tert-butylphenol),ultimately transformed into salicylic acid and phthalic acid,facilitating detoxification and mineralization through the tricarboxylic acid cycle.These insights affirmed the potential of aerobic granular sludge systems in efficiently mitigating PAHs toxicity in shale gas flowback water,provides the technical support for the application of this technology to treat the shale gas flowback water.
shale gas flowback wateraerobic granular sludgePAHsadsorptionbiodegradationbiotoxicity
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