Sustainable gasification–biochar systems? A case‐study of rice‐husk gasification in Cambodia, Part II: Field trial results, carbon abatement, economic assessment and conclusions

In part I we described the gasification technology and characterised the physio-chemical properties and environmental impacts of the rice husk char (RHC) by-product. In part II we present summary results from field trials using the RHC, and provide an estimate of the carbon abatement and economic evaluation of the system. Statistically significant yield increases are demonstrated for RHC addition in irrigated rice cultivation (33% increase in paddy rice yield for a 41.5 t (dry weight) RHC application per hectare). The carbon abatement from the RHC addition is approximately 0.42 t CO2 t^-1 rice husk; including energy generation from gasification this increases to ca. 0.86 tCO2 t^-1. Assuming a carbon value of $5 t CO2 t^-1, and agronomic value of $3 t^-1 RHC based on the field trials, the economic value of the RHC varies from $9 t^-1 (including only recalcitrant carbon) to $15 t^-1 (including avoided emissions from energy production). We summarise results from parts I and II, concluding that the gasification–biochar system meets many of the criteria of sustainability, but requires better waste water management and more field trials to demonstrate repeatable agronomic efficacy of RHC application.