Responses mechanisms of resistance genes in partial nitrification and anammox system under single and combined exposure to polystyrene nanoplastics and dodecyl dimethyl benzyl ammonium chloride

Nanoplastics (NPs) and quaternary ammonium compounds (QACs) are commonly found in wastewater treatment plants. However, the effect of the combination of NPs and QACs on anaerobic ammonium oxidation (anammox) process was lack. This study explored the impact of single and combined exposure of typical QACs dodecyl dimethyl benzyl ammonium chloride (DDBAC) and polyethylene NPs (PE NPs) on performance and resistance genes (RGs) spread pattern among water and sludge in partial nitrification and anammox (PN/A) system. 50 mg/L PE NPs inhibited the process of aerobic ammonia oxidation, and 8 mg/L DDBAC inhibited the process of anammox. The coexistence of PE NPs and DDBAC could relieve the inhibition of DDBAC on anammox. DDBAC decreased the relative abundances of Candidatus Jettenia and SM1A02 of 0.42% and 0.97%, respectively. Moreover, due to the leakage of intracellular RGs in sludge (named as si-RGs) caused by the friction of PE NPs, the absolute abundances of extracellular RGs in sludge (named as se-RGs) increased from 1.46 × 10 9 copies/g sludge to 5.15 × 10 9 copies/g sludge, and RGs in water increased from 3.04 × 10 7 copies/mL water to 1.19× 10 13 copies/mL water. DDBAC led to the large proliferation of si-RGs by triggering oxidative stress. The co-selection among QACs RGs, antibiotic RGs and mobile genetic elements existed in the system. Pseudomonas had the obviously positive correlations with si- sul1 and se- blaTEM , revealing that it played the vital role in the spread and transmission of si-RGs and se-RGs. The findings provided crucial understanding for the RGs spread pattern among sludge and water in PN/A system exposed to PE NPs and DDBAC, and provided strategies for the adaptation and removal of NPs and DDBAC.