Investigating the effect of Fenton-like pretreatment-clay mineral addition on humic substance during straw composting

Lignocellulose is difficult to directly degrade and mineralize during composting, which further leads to low humic substance content. Therefore, we investigated the effect of the combined Fenton-like pretreatment of the straw materials with clay minerals addition on humic substance during composting. We created six different treatments as CK, Z, FeZ, CK+, Z+, and FeZ+. The results showed that FeZ treatment increased the humic substance precursors content (31.3 %). The addition of clay minerals promoted the humic substance precursors formation, and the order of their content was as follows: FeZ+ > FeZ>Z+ > Z>CK+ > CK. The Fenton-like pretreatment with clay minerals addition increased humic substance (120.0 mg/g in CK, 141.6 mg/g in CK+, 135.8 mg/g in Z, 160.4 mg/g in Z+, 165.2 mg/g in FeZ and 180.9 mg/g in FeZ+ treatment). Upon coupling treatment increased the diversity of microbial communities, changed the composition of dominant genera, thus resulting in complex microbial structure. The structural equation model confirmed that the combined Fenton-like pretreatment with clay minerals addition could affect the content of humic substance by promoting their precursor formation. In addition, it could change the structure of microbial community structure to promote humic substance production and fixation. Our study provides new insights and theoretical support for the stable increase of humic substance content and humic substance fixation.