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

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 played a major role in curing many diseases in East Asia, leading to a large amount of Chinese herbal residues (CHRs) are difficult to dispose of. The present study investigated the feasibility of CHRs on the ARGs reduction in dewatered sludge during vermicomposting. The 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 CHR treatments significantly (P < 0.05) decreased antibiotic concentration and bacterial population by 23.64%-49.68% and 42.58%-93.07%, respectively, compared to counterpart. 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 ARGs content in sludge by decreasing the bacterial population and horizontal gene transfer capacity during vermicomposting.