Effect of mineral additives and ammonia-oxidizing bacteria additions on physicochemical properties, nitrogen retention and microbial dynamics during vermicomposting of chicken manure and green waste

Vermicomposting is an effective technology to transform organic wastes into organic fertilizers. However, a large amount of nitrogen will be lost through ammonia (NH 3 ) volatilization during verimicomposting. Herein, in this study, we investigated the effects of mineral additives (diatomite, zeolite) and exogenous ammonia-oxidizing bacteria (AOB) ( Nitrosomonas europaea , Nitrosospira multiformis ) added individually or combinedly on the physicochemical changes, the conversion of nitrogen, and the resident microbial community succession during chicken manure and green waste co-vermicomposting. The results showed that the combined addition of AOB and mineral additives significantly improved vermicompost quality and maturity in terms of humus, carbon/nitrogen ratio (C/N), humic acid/fulvic acid ratio (HA/FA) and germination index. Compared with the control, jointly adding AOB and mineral additives reduced NH 3 emissions by 65.72%~71.05%, accelerated the conversion of NH 4 + -N to NO 3 − -N, increased total nitrogen (TN) contents by 23.22%~25.21%. The combination of AOB and mineral additives significantly increased the activities of ammonia monooxygenase, hydroxylamine oxidase, and nitrate oxidoreductase, and enhanced the amount of AOB community. Additionally, the combined addition of AOB and mineral additives increased bacterial richness and diversity, accompanied by increased relative abundances of Luteimonas , Cellvibrio, Saccharimonadales , and Pseudomonas . These microbial shifts were correlated with enhanced lignocellulose degradation, organic phosphate mineralization, and promotion of plant growth. Moreover, vermiompost-based growing media with mineral additives and AOB can significantly promote the growth of purple cabbage as compared to the vermicompost without additives. Overall, the synergistic use of AOB and mineral additives (diatomite, zeolite) was recommended as a favorable approach for reducing nitrogen losses and improving the efficiency of chicken manure and green waste vermicomposting. This study offers a novel approach to mediated nitrogen transformation processes and reduce nitrogen loss. • Diatomite and zeolite enriched the ammonia oxidizing bacteria (AOB) in vermicompost • Additions of AOB markedly decreased NH 3 emissions during vermicomposting • Exogenous diatomite, zeolite and/or AOB induced high humus formation • Diatomite, zeolite and/or AOB significantly improved the vermicompost maturity index