LAUSR

Abstract Biochar (B) addition is considered to be an effective optimization method for accelerating the composting process and improving the quality of the final compost. Many studies have focused on the use of B in sludge compost as additives. However, the optimal level of B in the composting process and the effect of greenbelts utilization after composting have not been explained yet. In this study, autocontrol composting reactors were constructed and the effects of different B concentrations on nutrient transformation and morphological changes of heavy metals in sewage sludge-corn cob (C) aerobic composting were carried out. The feasibility of lawn grass (Festuca arundinacea) planting in soil composed of garden soil and different concentrations of composting sludge (40%, 60%, and 80%) was analyzed. The results revealed that a longer high temperature period can be maintained when the ratio of sludge:C:B is 10:6:1 (v/v). The detection result of TN, TP and TK indicated that B plays a positive role in nutrient retention in sludge. The addition of B has a positive effect on the passivation of Cu, Zn, Pb, Ni, and Cr in sludge. After composting, the residual fraction of heavy metals increased and exchangeable fraction decreased. The bacterial community diversity and richness showed dynamic changes during composting process. The enriched microbial groups of different treatments were analyzed. The linear discriminant analysis effect size (LEFSe) results showed that enriched microbial groups were totally different between different treatments and more bacterial clades were enriched at treatment S2. The heavy metal concentrations in the leached water were safe for plant and groundwater. The best growth conditions for F. arundinacea was the addition of composting sludge with a ratio of sludge:C:B of 10:6:1 (v/v) under an addition rate of 40%.