Biochar amendment combined with green waste for enhancing household food waste co-composting: Optimization of biochar particle size and dosage

This study explores the effects of biochar (BC) and green waste (GW) addition on aerobic co-composting of food waste (FW). Food waste was collected from the households in Kunshan, China. Results revealed that the addition of GW (800 g) can accelerate the thermophilic phase, and enhance the temperature stability and compost maturity. Addition of biochar, specifically initial addition of 200 g with a 1–3 mm particle size, further boosted composting performance by increasing peak temperatures (59 ± 1.1 °C) and reduces the nitrogen loss from 40.0% to 14.7%. Results revealed that addition of biochar can notably improve the moisture removal and increase the germination indices (GI) of the compost. However, larger biochar particles (>7 mm) or excessive dosages (800 g) caused the compost material to stick together in clumps and impaired maturation under 35-49°C temperature and >25% w/w moisture content conditions. Microbial analysis findings showed that Lactobacillus , Bacillus and Aeriscardovia were the dominant bacteria species in the optimal group, while Corynebacterium and Oceanobacillus prevailed in immature groups. Fungal communities were consistently dominated by Candida and Aspergillus in all groups. These results suggest that biochar-amended co-composting can enhance the food waste management and offer potential for sustainable composting systems. • Addition of biochar (1-3 mm size) boosted co-composting of food waste and green waste • Biochar addition improved the compost temperature and reduced nitrogen loss • Larger biochar particles (>7 mm) or excessive dosages (800 g) impaired maturation • Biochar addition reshaped the microbes in household food waste composting • Candida and Aspergillus were the dominant fungal species in all groups