Utilizing Agricultural Residue for the Cleaner Biofuel Production and Simultaneous Air Pollution Mitigation Due to Stubble Burning: A Net Energy Balance and Total Emission Assessment

The burning of agricultural residue in open fields poses a serious environmental threat that adversely affects human health and the ecosystem. Overall, this study aims to quantify emissions because of stubble burning followed by pyrolysis conversion of this feedstock and finally evaluate its energy performance. An assessment about pollutant emissions because of open-field burning was made, considering the two scenarios of flaming and smoldering. The inventory includes gaseous pollutants, particulate matter, and greenhouse gases with a total average of 7 TPA emissions per hectare of cultivated land. Subsequently, pyrolysis was carried out in a fixed bed semi-continuous lab-scale setup. The heating value of 18.85, 28.13, and 3.15 MJ kg^–1 was obtained for 36.02, 25.20, and 38.78 wt % yield of bio-oil, biochar, and fuel gas, respectively. Further analysis also indicates phenols, aldehyde, alcohols, and other organic fractions in bio-oil of density 1.06 g cm^–3 and 34.63 cm² s^–1 kinematic viscosity. This study’s significant highlight is a detailed analysis of energy gain from the process in terms of various performance indices. The net energy balance was applied to each co-product. The biochar was evaluated as the most energy valuable pyrolysis product with 0.985 MJ input/MJ output index and 72.35% energy efficiency. The fossil-to-energy ratio was determined as 1.28, indicating a net positive energy gain for the system’s input resources. Altogether, these results establish the viability of this sustainable waste-to-energy process as an alternative to conventional fossil fuels and encourage its commercial upscaling.