Enhanced household food waste composting through biochar-immobilised composite bioaugmentation inoculum

Household food waste (HFW) composting is an effective approach to minimise the burden on urban waste management and mitigate environmental impacts. However, its efficiency is limited due to insufficient lipid degradation, which leads to material agglomeration and poor compost maturity. In this study, three sequential experimental stages were conducted: (i) identification of key bacterial and fungal strains involved in lipid degradation and compost stabilisation, (ii) optimisation of immobilisation time and biochar loading ratio to enhance microbial viability and functional activity, and (iii) preparation of three types of biochar-immobilised bioaugmentation inocula (bacterial, fungal, and composite) followed by evaluation in simulated household composting experiments. The immobilisation was conducted at 45°C and 30°C for bacteria and fungi, respectively. Results showed that Bacillus coagulans and Aspergillus niger were the key lipid-degrading strains during biochar-mediated composting. A biochar-immobilised composite bioaugmentation inoculum was developed by optimising immobilisation conditions (24 h and 2% biochar for B. coagulans, 48 h and 3% biochar for A. niger ). The bioaugmented composite inoculum significantly reduced residual oil content by 24.7% relative to the control, increased weight loss by 5.4%, and raised the seed germination index by 14.8%, compared to the control treatment, resulting in a loose and stable compost structure. The combined action of extracellular lipases secreted by B. coagulans and hydrolytic enzymes produced by A. niger , broadened substrate degradation pathways and maintained a well-aerated compost structure. The biochar carrier further stabilised microbial activity by providing protective pore habitats and buffering against physicochemical fluctuations offering a practical solution for HFW management.