Modified Illite/smectite clay promoted composting humification and maturation mediated by reducing greenhouse gas emissions

The main purpose of this study was to determine the effectiveness of thermally modified Illite/smectite clay (I/S) in promoting maturation and reducing carbon loss in compost. The aerobic composting experiment lasted 51 days, defining the addition of modified I/S (MI/S) as the mineral test group (MT) and the other group without additives as the control group (CK). The results showed that MI/S was effective in increasing the compost maturity and humus (HS) content and reducing greenhouse gas (GHG) emissions. The maturation indices showed that the MT group had a C/N of 8.01 and the germination index (GI) reached 80% on the day 31, which was earlier than the CK. Furthermore, based on the cumulative accumulation of gas emissions, CO₂ and CH₄ emissions in the MT were reduced by 8.67% and 14.79%, respectively, compared to the CK. According to the correlation analysis, the reduction of CO₂ emission could be attributed to the strong adsorption capacity of MI/S and the higher abundance of Actinobacteria in MT. Lower CH₄ emission in MT was explained that MI/S modulated Actinobacteria and thus reduced methyl coenzyme-M reductase (Mcr) activity. The HS content of MT was 10.69% higher than that of CK, and the increase was closely related to laccase activity and the conversion of Fulvic acid (FA) to Humic acid (HA). Overall, MI/S was a promising compost conditioner in reducing environmental risks.