Aerobic-anaerobic combined treatment of vegetable residues: bioenergy potential and fugitive loss of methane and carbon dioxide.

Popular conventional biogas plants in India are reactors operated on cattle dung slurry and cannot accommodate solid biomass. The study elucidates the performance of a digestion system for solid discarded vegetable (DV), subjecting it to aerobic composting and utilising the derived leachate as feedstock for biomethanation, and also accounts for the fugitive greenhouse gases (GHGs) loss from the system. Leachates from the composting substrates had a BOD₅ of 15,305.6 ± 845.1 mg L⁻¹, which was reduced to 912.3 ± 94.0 mg L⁻¹ post-biomethanation. The loss of GHGs was highest in the slurry pit (199.33 ± 14.88 g day⁻¹ CH₄ and 315.25 ± 24.59 g day⁻¹) and least from the outlet pipe (0.47 ± 0.03 g day⁻¹ CH₄ and 0.74 ± 0.05 g day⁻¹ CO₂). Organic leachates from composting DV can be suitably used as substrates for biomethanation. However, attention is needed to minimise the fugitive GHGs loss from the system equivalent to ~2.4 kg CO₂e for producing 1.0 m³ of biogas.