Synergistic strengthening mechanism of microbial-mediated Fenton system on lignin depolymerization during rice straw composting

Abstract

This study investigated the synergistic strengthening mechanism of a microbial-mediated Fenton system in lignin depolymerization during composting. The Fenton system was constructed using hydrogen peroxide (H₂O₂) produced by lignin-degrading microorganisms along with Fe(Ⅱ). The simultaneous inoculation of bacteria and fungi resulted in optimal enzyme activities related to lignocellulose degradation and lignin degradation rates. Moreover, the addition of 0.5% FeSO₄ further optimized hydroxyl radical (·OH) production. Therefore, four treatments were set: CK (control), BHF (bacterial fungi synchronized inoculation), Fe (FeSO₄), and BHF-Fe (bacterial fungi synchronized inoculation + FeSO₄). BHF-Fe synergistically drove the Fe(Ⅱ)/Fe(Ⅲ) redox cycle and maintained reactive oxygen species ROS, (superoxide anion, H₂O₂ and ·OH) generation. BHF-Fe showed a 22.58% greater lignin loss rate compared to the CK. The correlations between ROS and lignin loss rate were enhanced. Additionally, lignin peroxidase, as an extracellular enzyme, relies on H₂O₂ for its action on lignin. The activities of laccase and lignin peroxidase were significantly correlated. Lignin decomposition was accelerated through the upregulation of key degrading enzyme genes (Lac, LiP, and MnP). The Fenton system showed attenuated pH dependence relative to conventional systems despite pH and Fe (II) effects on ROS. The BHF-Fe achieves efficient lignin degradation through a synergistic mechanism that integrates Fenton reactions, ROS, biocatalytic enzymatic oxidation and microenvironment compensation. This research offers theoretical and technical backing for developing agricultural waste resource recycling and composting technology.