The combined enhancement of RL, nZVI and AQDS on the microbial anaerobic-aerobic degradation of PAHs in soil

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous persistent organic pollutants in soil, which have carcinogenic, teratogenic and mutagenic hazards. The effects of rhamnolipid (RL), nano zero-valent iron (nZVI), and anthraquinone-2,6-disulfonic acid (AQDS) on the degradation of PAHs in soil were studied. It was found that the treatment of 5 mg·kg−1RL + 1% nZVI +0.2 mmol·kg−1AQDS had the highest degradation rate. The degradation rate of total PAHs and HMW-PAHs was 72.81% and 79.47% respectively after 90 days. High-throughput sequencing showed that in RL + nZVI + AQDS enhanced soil, Clostridium, Geobacter, Anaeromyxobacter and Sphingomonas were the dominant species for anaerobic degradation of PAHs. Rhodococcus, Nocardioides, and Microvirga are the dominant species for aerobic degradation of PAHs. The activities of methyltransferase, dehydrogenase and catechol 1,2-dioxygenase in the anaerobic-aerobic degradation process of PAHs were consistent with the degradation process of PAHs, indicating the role of these enzymes in the degradation of PAHs. RL, nZVI, and AQDS combined enhanced microbial anaerobic-aerobic degradation has great application potential in remediation of PAHs-contaminated soil. [Display omitted] •Total PAHs and HMW-PAHs degradation rate reached 72.81% and 79.47% , respectively by RL-nZVI-AQDS enhanced anaerobic-aerobic treatment.•RL, nZVI and AQDS synergistically enhanced anaerobic bacterial degradation of soil HMW-PAHs.•Clostridium, Geobacter and Rhodococcus are the dominant PAHs-degrading bacteria.•The anaerobic-aerobic degradation pathway of PAHs was inferred based on metabolic enzyme activity.