Bentonite promoted humification in aerobic composting of pig manure through improving physicochemical properties and bacterial community structure

As intensive livestock farming rapidly expands, manure resource utilization faces significant challenges, for which aerobic composting is an effective treatment technology whose product value depends on the quality of humus. To identify mineral additives that effectively promote humification, this study compared the effects of vermiculite (VE), zeolite (ZE), maifanite (MA), and bentonite (BE) on humification during aerobic pig manure composting. The stud y indicated that each mineral treatment enhanced compost maturity and humification, with the BE treatment being more effective than the other mineral treatments. Compared with the control (CT) treatment, BE treatment significantly reduced the C/N ratio by 35.44%, a 25.03% increase in the germination index (GI), and an 87.40% increase in the HA/FA ratio. The humification index (HIX) growth rate was highest in the BE treatment (4.53×10 -3 day⁻¹), reaching 3.17 times that of the CT treatment and 1.15–1.51 times that of other mineral treatments. Compared to other mineral treatments, the BE treatment enriched more OTUs (45), predominantly belonging to Proteobacteria. Correlation analysis revealed that both HA/FA and HIX exhibited significant positive correlations with the relative abundances of Proteobacteria, Actinobacteria, and Gemmatimonadota, while showing significant negative correlations with the C/N ratio and the relative abundances of Bacteroidota, Acidobacteria, and Verrucomicrobia. The partial least square structural equation model (PLS-SEM) suggested that mineral specific surface area may promote humification in compost by directly optimizing its physicochemical properties and influencing bacterial community structure. In summary, adding BE could more effectively enhance the humification level of aerobic pig manure compost.