a b s t r a c tComposting is commonly used for the treatment and resource utilization of sewage sludge, and natural zeolite and nitrification inhibitors can be used for nitrogen conservation during sludge composting, while their impacts on ARGs control are still unclear. Therefore, three lab-scale composting reactors, A (the control), B (natural zeolite addition) and C (nitrification inhibitor addition of 3,4-dimethylpyrazole phosphate, DMPP), were established. The impacts of natural zeolite and DMPP on the levels of ARGs were investigated, as were the roles that heavy metals, mobile genetic elements (MGEs) and the bacterial community play in ARGs evolution. The results showed that total ARGs copies were enriched 2.04 and 1.95 times in reactors A and C, respectively, but were reduced by 1.5% in reactor B due to the reduction of conjugation and co-selection of heavy metals caused by natural zeolite. Although some ARGs (bla CTX-M , bla TEM , ermB, ereA and tetW) were reduced by 0.3e2 logs, others (ermF, sulI, sulII, tetG, tetX, mefA and aac(6 0 )-Ib-cr) increased by 0.3e1.3 logs after sludge composting. Although the contributors for the ARGs profiles in different stages were quite different, the results of a partial redundancy analysis, Mantel test and Procrustes analysis showed that the bacterial community was the main contributor to the changes in ARGs compared to MGEs and heavy metals. Network analysis determined the potential host bacteria for various ARGs and further confirmed our results.

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The polycyclic aromatic hydrocarbons (PAHs) that accumulate during the coking wastewater treatment process are hazardous for the surrounding environment. High molecular weight (HMW) PAHs, account for more than 85% of the total PAHs in coking wastewater and sludge, respectively. The degradation of total PAHs increased by 18.97% due to the increased bioavailability of PAHs, after the biosurfactant-producing bacteria Pseudomonas aeruginosa S5 added. The toxicity of total PAHs to human was reduced by 26.66% after inoculation with S5. The results suggest biosurfactant-producing bacteria Pseudomonas aeruginosa S5 not only increase the biodegradation of PAHs significantly, but also have a better effect on reducing the human toxicity of PAHs. Kinetic analyses show that PAHs biodegradation fits to first-order kinetics. The degradation rate constant (k) value decreases as the number of PAH rings increases indicating that HMW PAHs are more difficult to be biodegraded than low molecular weight (LMW) PAHs. The results indicate the bioaugmentation with biosurfactant-producing strain has significant potential and utility in remediation of PAHs-polluted sites.