The role of zero valent iron on the fate of tetracycline resistance genes and class 1 integrons during thermophilic anaerobic co-digestion of waste sludge and kitchen waste

Activated sludge has been identified as a potential significant source of antibiotic resistance genes (ARGs) to the environment. Anaerobic digestion is extensively used for sludge stabilization and resource recovery, and represents a crucial process for controlling the dissemination of ARG5 prior to land application of digested sludge. The objective of this study is to investigate the effect of zero valent iron (Fe-0) on the attenuation of seven representative tetracycline resistance genes (tet, tet(A), tet(C), tet(G), tet(M), tet(O), tet(W), and tet(X)), and the integrase gene intl1 during thermophilic anaerobic co-digestion of waste sludge and kitchen waste. Significant decrease (P < 0.05) in the quantities of tet (except tet(W)) and intl1 genes was observed at Fe-0 dosage of 5 g/L, whereas no significant differences (P > 0.05) were found for all gene targets between digesters with Fe-0 dosages of 5 and 60 g/L. A first-order kinetic model favorably described the trends in concentrations of tet and intl1 gene targets during thermophilic anaerobic digestion with or without Fe-0. Notably, tet genes encoding different resistance mechanisms behaved distinctly in anaerobic digesters, although addition of Fe-0 could enhance their reduction. The overall results of this research suggest that thermophilic anaerobic digestion with Fe-0 can be a potential alternative technology for the attenuation of tet and intl1 genes in waste sludge. (C) 2016 Elsevier Ltd. All rights reserved.