Purpose: Co-composting of mango by-products and biogas solid residue eliminates some shortcomings of composting
these wastes separately. Specifically, co-composing solves the problem of the low pH values in mango by-products while enhances biodegradable organic matter of biogas solid residues. However, no research report is available on co-composting of mango by-products (MB) and biogas solid residue (BR).

Method: This study established three in-vessel lab-scale composting bins with 3 different C/N ratios, including Bin 1:
27.4/1 (156 kg MB + 144 kg BR); Bin 2: 30.23/1 (193 kg MB + 107 kg BR); and Bin 3: 37.7/1 (224 kg MB + 76 kg
BR). The raw compost materials underwent 57 days of incubation, including 36 days of raw incubation and 21 days of
mineralization. 

Results: Bin 3 containing larger amounts of mango by-products and less amounts of biogas residue showed a higher percentage of remaining carbon in the final products (17.97%), lower nitrogen loss (17%), and showed 0.5% increase in available P2O5 content, compared to the other bins. From 300 kg of initial raw material, the final compost mass in Bin 1, Bin 2, and Bin 3 were 26.2 kg, 32.7 kg, and 88.1 kg, respectively.

Conclusion: Resultantly, an initial C/N ratio of 37.7/1 could be suggested in the aerobic co-composting of biogas residue with mango by-products.