Life cycle environmental and economic analysis of regional-scale food-waste biogas production with digestate nutrient management for fig fertilisation

Small-scale biomethane production is a promising option to meet a domestic energy supply in Thailand. As part of domestic energy policies in Thailand (new Alternative Energy Development Plan), a biogas plant with 400 kg-wet/d capacity manufactured by Japanese companies was installed at a university in Thailand in 2013. For sustainable operation of the plant, the primary energy demand (PED) and life-cycle greenhouse gas (GHG) emission associated with well-to-tank, WTT (the food waste transport, conversion to biomethane and biomethane storage) are assessed. GHGs emission associated with well-to-wheel, WTW (the food waste transport, conversion to biomethane, biomethane storage and driving fuelled by the biomethane) are revealed. Economic analysis is also implemented based on the actual operating data including digestate price derived from N-P-K nutrient management (0.2689 THB/kg), and payback time sensitivity analysis. Primary energy demand associated with WTT processes was 0.68 MJ/MJ-CH4. GHG emission from WTW processes is 132.0 kg-CO2eq/km, which is less than one third that of the other biofuels (biohydrogen, biomethanol, bio-dimethylether and Fischer-Tropsch diesel). The economic analysis showed that food waste disposal income and electricity sales are hot spot in the revenue and interest payment and maintenance cost has high impact in expenditure. The most sensitive parameter is biomethane yield, which should be kept higher for profitable operation of the biogas plant in Thailand.