Enhancing humification enzymatic activity and antibiotic resistance gene attenuation in aerobic composting of sewage sludge and food waste: The role of calcium oxide amendment.

Organic municipal solid waste (OMSW) management remains a global challenge, intensifying with rapid urbanization and the widespread use of antibiotics for various purposes. These practices contribute to the dissemination of emerging contaminants, particularly antibiotic resistance genes (ARGs). Composting is widely applied for OMSW treatment, however the effectiveness of calcium oxide (CaO) amendment in mitigating ARGs and enhancing humification remains limited. This research investigated the effects of CaO amendment at varying levels (T1-0.25 %, T2-0.5 %, and T3-1 % w/w) on humification, enzymatic activities, microbial community succession, changes in dissolved organic matter (DOM), and ARG attenuation during aerobic composting. The results show that T3 (1 % CaO) achieved the highest humic acid formation (51.07 g/kg) and ARG reduction (2.3 log). However, T2 (0.5 % CaO) provided the most favorable overall balance across the evaluated parameters, including compost maturity, microbial community diversity, enzymatic activity, and ARG attenuation, without the inhibitory effects associated with excessive alkalinity. The initial ARG abundance was 2.82 × 1010 copies/g dry weight (dw) compost, ARG-subtypes aadD, aac(6')-lb-01, mefA, and sul1 were the pre-dominated subtypes ranging 1.42 × 108 - 2.74 × 1010 copies/g dry dw compost significantly reduced by 2.3 log in T3 and 2.1 log in T1 compared to CK trial (0.88 log). Microbial study indicated a rapid succession towards communities dominated by Actinobacteria and Chloroflexi at moderate CaO concentrations. These results demonstrate that CaO regulates composting through several physicochemical and microbial mechanisms, offering a promising strategy to enhance compost maturity and environmental safety.