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The problem of bacterial resistance has become an important issue in the area of global ecological safety and human health. Waste sludge is an important reservoir and discharge source for antibiotic resistance genes (ARGs). In this study, the quantities of seven tetracycline resistance genes (TC-ARGs), including tetA, tetC, tetG, tetM, tetO, tetW , and tetX , as well as those of class 1 integron ( intI1 ) genes, during anaerobic sludge digestion process were comprehensively quantified by quantitative PCR (qPCR). The effects of different doses of zero valent iron (Fe 0 ) on the decrease and increase in the quantities of TC-ARGs and intI1 genes were investigated. The influence of plasmid conjugation on the horizontal gene transfer (HGT) of the target TC-ARGs was preliminarily analyzed. The correlations between the quantities of TC-ARGs and intI1 gene have been discussed. The results showed that the quantities of TC-ARGs and intI1 genes decreased in different degrees during anaerobic sludge digestion, and the abundance of tetX gene was reduced by 2.4 orders of magnitude. When Fe 0 was added, no significant reduction in the quantities of TC-ARGs and intI1 genes was observed. However, as the addition of Fe 0 increased, the quantities of TC-ARGs and intI1 genes increased correspondingly, as compared to those in the control group. The results obtained from the quantities of TC-ARGs carried by plasmid DNA showed that plasmid conjugation probably promoted the HGT of TC-ARGs. A positive significant correlation was found between the quantities of tetG and intI1 genes, indicating that intI1 might play an important role in the evolution of tetG during sludge anaerobic digestion process.

To investigate the effects of zero valent iron (Fe 0 ) on the decline of antibiotic resistance genes during thermophilic anaerobic digestion of sludge, the abundances of seven tetracycline resistance genes (TC-ARGs, including tetA, tetC, tetG, tetM, tetO, tetW , and tetX ) and class 1 integron gene ( intI1 ) were quantified by quantitative PCR (qPCR). Also, the concentrations of volatile fatty acids (VFAs) were determined. The correlations between the abundances of TC-ARGs and intI1 gene and the concentrations of VFAs were discussed. The results showed that appropriate dose of Fe 0 such as 0.10 g·g -1 VSS could enhance the anaerobic digestion process of sludge, and the production of total VFAs and acetic acid increased significantly. The decrease in the abundances of TC-ARGs and intI1 gene was also enhanced. However, excessive Fe 0 such as 1.17 g·g -1 VSS could not further improve the reduction in the abundances of TC-ARGs and intI1 gene, probably resulted from the occurrence of horizontal gene transfer. The abundances of TC-ARGs except tetO gene, as well as intI1 gene exhibited significant negative correlation with the concentration of acetic acid, indicating that acetic acid probably had an enhanced effect on the decline of TC-ARGs and intI1 gene during thermophilic anaerobic digestion of sludge.

Occurrence and distribution of twelve pharmaceutical and personal care products (PPCPs) were investigated in a sewage treatment plant in Shanghai using solid-phase extraction combined with high-performance liquid chromatography-tandem mass spectrometry (SPE-HPLC-MS/MS). Quantitative PCR (qPCR) was used to determine the distribution and removal of seven erythromycin resistance genes (ERY-ARGs). The results showed that five PPCPs including sulfamethoxazole, erythromycin, tetracycline, carbamazepine and triclosan were detected in the collected wastewater samples with concentrations in the ranges of 24.5- 38.7, 47.5-49.2, 43.1-85.4, 2.5-3.9 and 423.2-8 973.3 ng x L(-1), respectively. During the wastewater treatment process, a significant reduction of triclosan was observed, but the removal efficiencies for the other detected PPCPs were relatively low. Additionally, all target ERY-ARGs were detected in the wastewater samples ranging from 9.28 x 10(3) (ermA) to 1.83 x 10(8) (ereA) copies x L(-1) in raw influent. Though significant reductions (1.19 log-3.97 log) of ERY-ARGs were obtained, their concentrations found in the final effluent were still high. Moreover, the concentration of ERY-ARGs exhibited significant positive correlation with the concentration of erythromycin and triclosan (P < 0.05), respectively, elucidating that erythromycin played an important role in the occurrence and spread of ERY-ARGs, while triclosan may confer cross-selection for ERY-ARGs.