Dynamics of humification and bacterial community during electric field-assisted co-composting of municipal sludge, wheat straw and cattle manure with the amendment of magnetite

Electric field assistance (EA) or magnetite (MGT) addition has been a promising strategy to promote composting efficiency and humification. However, the combined effects between electric field and MGT on humification and bacterial community as well as the underlying mechanisms are largely unknown during co-composting of municipal sludge, wheat straw and cattle manure. To enhance the pile conductivity of composting and to strengthen organic matter (OM) degradation and transformation for humification, the strategy of the combined magnetite addition with EA was proposed. Four treatments (CK; T1: EA; T2: MGT; T3: EA + MGT) were investigated to characterize responses of reactive oxygen species (ROS), functional enzymes, humification and bacterial community. The results showed that the combined addition enhanced the degradation of OM at the initial stages in T3, providing skeleton materials for humification, and achieved a mature compost with the highest humification. T3 possessed an increase of approximate 10.8 % in the humus content. This combined addition significantly prolonged the duration of H 2 O 2 and ·OH production and effectively improved the activity of functional enzymes. The high-throughput results showed that Thermopolyspora of producing heat-resistant hemicellulase became the dominant genus at both thermophilic and maturation stages. Additionally, the highest stability in bacterial community occurred in T3 where the three keystones ( Thermopolyspora , Thermobacillus and JG30-KF-CM45 ) performing potential humification were identified through redundancy analysis (RDA). Structural equation model (SEM) revealed that OM, ROS and enzymes were the most important factors associated with the humification in T3. These results provide a promising strategy for optimizing co-composting of municipal sludge, wheat straw and cattle manure by magnetite and electric field. • A novel method on adding MGT of EA for promoting humification was proposed. • The combined MGT addition with EA prolonged the production of H 2 O 2 and ·OH in T3. • The combined addition reshaped bacterial community and enriched Thermopolyspora . • Three keystones with potential humification were obtained in T3. • OM, ROS and enzymes were the most important factors driving the humification in T3.