Kinetic characterization and microbial mechanism of denitrification degradation of low molecular weight polycyclic aromatic hydrocarbons

Shale gas drainage/produced water contains a large number of toxic and hazardous substances, among which naphthalene(NAP),2-methylnaphthalene(2-MN), and phenanthrene(PHE) are the PAHs with the highest environmental risk.The aerobic biodegradation of PAHs in single and mixed matrices has been reported, but there is a lack of relevant studies under denitrification conditions. In this study, the degradation kinetics and microbiological mechanisms of single and mixed substrates were explored by denitrifying microorganisms degrading PHE and NAP respectively. The results showed that the single degradation of NAP, 2-MN, and PHE complied with the first-order kinetics, with NAP being the fastest degraded, followed by PHE and 2-MN. The multi-substrate degradation study revealed that the mixed degradation of NAP and 2-MN in the NAP denitrification microcosm (NAPBR) was competitively inhibited, and the mixed degradation of NAP and PHE was promoted and PHE was inhibited and PHE was degraded only when NAP was depleted, while the degradation of the two sets of binary substrates in the PHE denitrification microcosm (PHEBR) were both inhibited by each other, which was consistent with the competitive inhibition model and the non-competitive inhibition model, respectively. High-throughput sequencing results showed that the diversity of communities in NAPBR and PHEBR was small and similar during the single-substrate degradation stage, while the diversity of communities in both microcosms decreased during the mixed-substrate degradation stage.