Exploring the effects of zeolite, biochar, and diatomite as additives for enhancing heavy metals passivation and eliminating antibiotic resistance genes in composts during vermicomposting of dewatered sludge and green waste

Abstract

Vermicomposting is an effective technology for disposing of municipal sewage sludge and green wastes; however, it can contain heavy metals (HMs) and antibiotic resistance genes (ARGs); thus, the application of the final product to land is risky. In this study, zeolite (ZL), bamboo biochar (BB), and diatomite (DM) were individually mixed with dewatered sludge and green waste at a rate of 5% (w/w) to investigate their effects on earthworm activities, physicochemical characteristics of vermicompost, HMs and ARGs patterns, and microbial community structure during vermicomposting. The results showed that ZL, BB, and DM stimulated the growth and fecundity of earthworms, accompanied by higher degradation of organic matter, nutritional value, humification level, and maturity of final products. The distribution rate of OXI-Zn and RES-Pb in vermicomposts could be increased by 3.48%−11.53% and 8.64%−17.53%, respectively, under all additives addition treatments in comparison to the control treatment. Moreover, the addition of ZL, BB, and DM significantly enhanced the reduction rate of intI-1 (2.45%−20.86%), sul1 (8.16%−26.46%), sul2 (18.88%−29.55%), ermB (30.25%−40.08%), ermC (19.25%−28.53%), gryA (22.99%−30.04%), parC (18.75%−20.46%), qnrS (11.58%−28.96%) and tetC (18.99%−21.57%) genes in vermicomposts, as compared to control without additives. ZL, BB, and DM addition optimized the bacterial community by decreasing the abundances of the potential ARGs hosts, such as Steroidobacter and Acidibacter, enhancing important organic-decomposing bacteria, such as cellulomonas and Chryseolinea. This study newly suggests that ZL, BB, and DM addition is beneficial for the passivation of Zn and Pb and decreases the dissemination risk of ARGs in vermicomposting dewatered sludge and green waste.