Fly ash and zero-valent iron-based in situ advanced anaerobic digestion with emphasis on the removal of antibiotics and antibiotic resistance genes from sewage sludge

This study investigated the removal of antibiotics and antibiotic resistance genes from sewage sludge by using fly ash (FA)-based in situ advanced anaerobic digestion (AAD) under mesophilic conditions. Five antibiotics (sulfadiazine, sulfamethoxazole, ofloxacin, tetracycline, and roxithromycin) and 11 corresponding antibiotic resistance genes (Ib-cr, qnr S, erm F, erm T, erm X, sul 1, sul 2, sul 3, tet A, tet B, and tet G) were selected as the targets. Adding FA to anaerobic digestion to remove antibiotics and resistance genes allows waste to be treated with waste. FA-based in situ AAD of sewage sludge effectively enhanced the process stability and methane yield, and the optimal FA-added dosage was 50 mg/L. The cumulative methane yield could be well described with the improved Gompertz model. FA addition effectively increased the overall removal of ofloxacin, by up to 85.3% at 50 mg/L FA and 10 μg/L antibiotics, and the combination of zero-valent iron and FA enhanced only the overall removal of ofloxacin to 92.4% and tetracycline to 85.6%. However, FA-based in situ AAD could not enhance the overall removal of other antibiotics from sewage sludge. Not all the same types of antibiotic resistance genes were strongly positively correlated with the concentrations of antibiotics. The removal of antibiotic resistance genes influenced by FA addition varied largely with the types of antibiotic resistance genes, FA dosage, antibiotic content, and the combination with zero-valent iron. FA addition could not be verified to enhance the removal of antibiotic resistance genes. The addition of FA or zero-valent iron and the antibiotic concentrations significantly changed the microbial community structure during in situ AAD, and the combination of zero-valent iron and FA significantly reduces the species diversity and microbial abundance. The most abundant bacteria were Methanogarcina , Methanoberium , unidentified_Archaea , Terrimonas , Methomethoxychlorovorans , and Candidatus_Cloacimonas in the ZVI-FA test.