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The risks that have not been noted so far have come from the use of non-antibiotics. In this study, non-antibiotic drug (cyromazine) was used in composting to investigate its possible effects on the distribution of ARGs and changes of bacterial community. Results showed that cyromazine increased the abundances of highly-risky ARGs (blaCTX-M and blaVIM), and heavy metal resistance genes (MRGs). Low and high concentrations of cyromazine increased the abundance of Tn916/1545 by 18.27% and 64.26%, respectively, compared with the control treatment. Mobile genetic elements (MGEs) and MRGs were not the major cause of the dynamic changes in ARGs, but instead the bacterial community succession changed according to the moisture content, pH, and bio-Cu. Network analysis showed that Proteobacteria and Actinobacteria were the major hosts for ARGs, and there was a significant correlation between tcrB, sul1 and Tn916/1545.

Coal gasification slag (GS) is an industrial solid waste with a highly developed pore structure, which can be used in anaerobic digestion (AD) to remove antibiotic resistance genes (ARGs) due to its structure, thereby utilizing this waste resource. This study evaluated the effects of three GS levels (0, 5, and 10 g/L) on the abundances of ARGs, mobile genetic elements, and the bacterial community. With GS added at 10 g/L, the removal rates for ARGs (dfrA7, sul2, tetW, ermF, and ermQ) were 24.81–90.48% after AD, and the removal rate for ISCR1 was 95.4%. In addition, 10 g/L GS was more effective at reducing the abundances of potential human pathogens. The variations in ARGs may have been affected by the succession of the microbial community. The results of this study demonstrate that supplementation with 10 g/L GS is more useful for reducing ARGs during AD.

Antibiotic resistance genes (ARGs) in manure endangered human health, while heavy metals in manure will pose selective pressure on ARGs. This study explored the effects on ARGs of adding woody peat during composting at different ratios (0 (CK), 5% (T1), and 15% (T2)). After composting, the relative abundances of 8/11 ARGs were 6.97-38.09% and 10.73-54.31% lower in T1 and T2, respectively, than CK. The bioavailable Cu content was 1.40% and 18.40% lower in T1 and T2, respectively, than CK. Network analysis showed that ARGs, mobile genetic elements (MGEs), and metal resistance genes possessed common potential host bacteria, such as Streptococcus, Dietzia, and Corynebacterium_1. Environmental factors, especially bioavailable Cu, and MGEs accounted for 80.75% of the changes in the abundances of ARGs. In conclusion, 15% Woody peat is beneficial to decrease the bioavailable Cu content and weaken horizontal gene transfer for controlling the spread of ARGs during composting.

This study investigated the effects of adding nano-zerovalent iron (nZVI) at three concentrations (0, 80, and 160 mg/L) on the methane yield and the fate of antibiotic resistance genes (ARGs) during the anaerobic digestion (AD) of cattle manure. The addition of nZVI effectively enhanced the methane yield, where it significantly increased by 6.56% with 80 mg/L nZVI and by 6.43% with 160 mg/L nZVI. The reductions in the abundances of ARGs and Tn916/1545 were accelerated by adding 160 mg/L nZVI after AD. Microbial community analysis showed that nZVI mainly increased the abundances of bacteria with roles in hydrolysis and acidogenesis, whereas it reduced the abundance of Acinetobacter . Redundancy analysis indicated that the changes in mobile genetic elements made the greatest contribution to the fate of ARGs. The results suggest that 160 mg/L nZVI is a suitable additive for reducing the risks due to ARGs in AD.

Aerobic composting is usually employed to treat livestock manure. In this study, a bio-surfactant (rhamnolipid, RL) and chemical surfactant (Tween 80, Tw) were added to chicken manure during composting and their effects were determined on the variations in ARGs and intI1. After composting, the reductions in the RAs of ARGs and intI1 with the addition of Tw (1-4.7logs) were generally greater than that with the addition of RL (0.8-3.7logs) and the control (CK) (0.3-2.6logs), and the enrichment of ARGs was higher with CK (0.9-1.8logs). The ARG profiles were affected significantly by temperature and the water-soluble carbon contents. RL and Tw effectively reduced the concentrations of bio-available Cu and Zn, thereby hindering the co-selection of ARGs by heavy metals. The effects of RL and Tw on ARGs and intI1 indicate that the addition of Tw was slightly more effective than RL after composting.

This study investigated the effects of the addition of coal gasification slag (CGS) at three levels (0%, 5%, and 10% w/w) on antibiotic resistance genes (ARGs) and the bacterial community during composting. The addition of CGS effectively facilitated the removal of ARGs and mobile genetic elements (MGEs), where it significantly reduced the relative abundances of 5/11 ARGs and three MGEs in the swine manure composting product. In addition, the enrichment of ARGs and intI1 was lower under the addition of 10% CGS compared with 0% CGS. The bacterial community was distributed according to the composting time under different treatments. Redundancy analysis showed that bacterial community succession and MGE-mediated horizontal gene transfer played important roles in the variations in ARGs. Network analysis indicated the co-occurrence of ARGs and MGEs with specific microorganisms. Thus, 10% CGS may be a suitable additive for reducing the risks of ARGs in compost products.

Superabsorbent polymers (SAPs) are considered suitable amendments for reducing the selection pressure due to heavy metals and the abundances of antibiotic resistance genes (ARGs) during composting. In this study, three SAP (sodium polyacrylate) levels (0, 5, and 15mgkg-1 of compost) were applied and their effects on the abundances of ARGs, mobile genetic elements (MGEs), and the bacterial community were investigated. After composting, the abundances of ARGs and MGEs decreased to different extent, where the removal efficiencies for tetW, dfrA7, ermX, aac(6')-ib-cr and MGEs exceeded 90%. The high SAP concentration significantly reduced the abundances of ARGs and MGEs, and changed the microbial community. Redundancy analysis indicated that the moisture content mainly explained the changes in ARGs and MGEs. Network analysis determined the potential hosts of ARGs and MGEs, and their co-occurrence. The results suggested that applying 15mgkg-1 SAP is appropriate for reducing ARGs in compost.

In this study, swine manure containing sulfachloropyridazine sodium (SCPS) and zinc was subjected to mesophilic (37°C) anaerobic digestion (AD). The absolute abundances (AAs) of antibiotic resistance genes (ARGs) were evaluated, as well as intI1 and intI2, and the degradation of SCPS according to variation in the amount of bio-available zinc (bio-Zn). In digester that only contained SCPS, the concentrations of SCPS were lower than that digesters both contain SCPS and Zn. Compared with the control digester, the addition of SCPS increased the AAs of sul1, sul3, drfA1, and drfA7 by 1.3-13.1 times. However, compared with the digester with SCPS but no added Zn, the AAs of sul3, drfA1, and drfA7 were decreased by 21.4-70.3% in the presence of SCPS and Zn, whereas sul1 and sul2 increased 1.3-10.7 times. There were significant positive correlations (P

This study explored the effects of composting using three temperature regimes, namely, insufficient thermophilic composting (ITC), normal thermophilic composting (NTC), and continuous thermophilic composting (CTC), on antibiotic resistance genes (ARGs), integrons, and human pathogenic bacteria (HPB), as well as the mechanisms involved. The NTC and CTC treatments led to greater decreases in 5/10 ARGs and two integrons than ITC, and the abundances of ARGs (tetC, tetG, and tetQ) and int1 only declined in the NTC and CTC treatments. The abundances of HPB decreased by 82.8%, 76.9%, and 96.9% under ITC, NTC, CTC, respectively. Redundancy analysis showed that both bacterial succession and horizontal gene transfer play important roles in the variation of ARGs, and the changes in different ARGs were due to diverse mechanisms. CTC performed significantly better at reducing ARGs, integrons, and HPB, thus it may be used to manage the public health risks of ARGs in animal manure.