35 / 2023-04-29 21:06:14

A novel strategy for eliminating antibiotic resistance genes during fertilization of dewatered sludge by earthworms: Vermicomposting practice using Chinese herbal residues as a bulking material

Antibiotic resistance genes; Excess sludge; Vermicompost; Chinese herb; Mobile gene elements.

Vermicomposting is a sustainable sludge recycling technology that utilizes an eco-friendly composting using earthworms and microorganisms. However, a high abundance of antibiotic resistance genes (ARGs) remains in dewatered sludge that is not satisfactorily eliminated by vermicomposting. Chinese herbs have been popularly used for treating COVID-19 in East Asia, leading to Chinese herbs residues (CHRs) that are difficult to dispose of. The present study investigated the effects of CHRs on ARG reduction in dewatered sludge during vermicomposting. CHRs derived from Lianhua Qingwen were added separately to sludge with weight ratios of 0%, 10%, 30%, and 50%; sludge was then vermicomposted for 30 days. The results showed that co-vermicomposting of sludge and CHRs is a feasible strategy. The earthworm biomass and nitrate in vermicomposts with CHR addition increased by 0.66−2.33 (P < 0.01) times and 28.9% (P < 0.05)−38.6% (P < 0.05), respectively, relative to the control. The CHR treatments significantly (P < 0.05) decreased bacterial population by 42.58%−93.07% compared to sludge without CHR addition. Compared to the control, the CHR addition lowered the absolute abundances of macrolide, tetracycline, and sulfonamide ARGs by 42.69%−85.15%, 22.03%−75.24%, and 23.59%−90.66%, respectively. In addition, sludge containing 30% CHRs showed significant (P < 0.05) elimination of intⅠ-1 and tnpA-4 genes with abundance reductions of 71.40% and 52.33%, respectively, relative to the control. This study suggests that the CHRs can effectively reduce ARG content in sludge by decreasing the bacterial population and horizontal gene transfer capacity during vermicomposting.