Influence of microbial agents-loaded biochar on bacterial community assembly and heavy metals morphology in sewage sludge compost: Insights from community stability and complexity

Abstract

Enhancing the passivation of heavy metals and increasing organic matter content during the composting of sewage sludge poses significant challenges for maximizing its utilization value. Results indicated that in the control, biochar, microbial agents and microbial agents-loaded biochar (BCLMA) groups, BCLMA addition led to a higher composting temperature, with increases of 17–62% in humic acid, 25–73% in germination index, and 30–35% in organic matter consumption. And the residual fraction of Cu, Zn, Cr and Cd were increased by 30%, 12%, 22% and 17%, respectively. Furthermore, BCLMA promotes community cohesion, robustness, and microbial nutrient cycling, and increases the relative abundance of heavy metals-degrading bacteria (Acinetobacter and Corynebacterium) and resistance genes. Structural equation model analysis revealed that heavy metal passivation is attributed to improved community cohesion and robustness, which facilitates the proliferation of heavy metal-resistant microorganisms. These results indicate that community robustness and cohesion are critical for mitigating the heavy metals bioavailability.