Biomethanation of Crop Residues to Combat Stubble Burning in India: Design and Simulation Using ADM1 Mathematical Model

Stubble burning in India continues despite the severe consequences on the environment and the massive health crisis in the country. Farmers resort to such practices as a cheap and hasty solution post-harvest, which helps them prepare for their next crops. This study employs a mathematical model, the ADM1 (Anaerobic Digestion Model No. 1), to design a virtual biogas plant in the SIMBA simulation platform. The plant was designed keeping the small-scale farmers in mind, hence, cost-effectiveness, simplicity in design and operation remained a priority. Simulations were performed with different crop leftovers that are widely subjected to on-farm burning in the country such as from rice, wheat, sugarcane, cotton and maize. Simulation trials were performed for each crop residue for nearly two years, to observe the digester performance and possible disruptions over prolonged periods. The optimal feeding ratio and operating conditions for process stability were determined. Simulations revealed generation of nearly 9–10 m3 methane per day, equivalent to 90–100 kWh electricity. Co-fermentation with animal manures was strongly recommended by the model for process stability and to avoid pH disruptions due to organic acid accumulations. Policy makers and farmers are, thus, encouraged to explore a sustainable alternative to generate energy from stubble.