Efficiency and mechanism of three different additives in enhancing vermicomposting of dewatered sludge

This study aimed to investigate the effects of garden waste (GW), spent mushroom substrate (SMS), and bamboo residue (BR) as additives on dewatered sludge vermicomposting. The changes in physicochemical parameters, earthworm activities, and microbial communities were detected during the vermicomposting process. Results revealed that GW, SMS, and BR significantly enhanced the vermicomposting process by accelerating organic matter (OM) degradation, humus (HS) formation, and maturity degree. In different additive treatments, the OM degradation rate was enhanced by 60.70-226.05%, and the increase rates of TN, TP and HS were enhanced by 65.94-155.61%, 77.16-121.13%, and 91.37-205.33% as compared to CK. The GI value in all additive treatments increased by 23.07-41.34% compared with that in CK. GW, SMS, or BR addition also significantly reduced the content of Cu (16.87-33.99%), Zn (19.29-32.51%), Cr (18.34-39.98%), and Pb (22.62-37.83%) in vermicomposts compared with CK. Data showed that GW, SMS, and BR addition significantly enhanced the survival rate (54.55-72.73%) and growth and reproduction of earthworms compared with CK. The process of vermicomposting primarily relies on microbial activities and interactions between microorganisms and earthworms. The composition and succession of microbial communities are closely related to the quality of the vermicompost. Adding GW, SMS, or BR enhanced the richness and diversity of bacterial communities during the vermicomposting process. The additives remarkably stimulated beneficial bacteria, such as Dokdonella and Luteimonas, which were closely related to OM decomposition. The dewatered sludge in combination with GW, SMS, or BR can be successfully vermiconversion into useful vermicompost employing earthworms.