Synergistic enhancement of biogas production using solar-thermal energy and supplemental additives

Climate change and the depletion of fossil fuels are driving a rapid global shift toward sustainable energy, making renewable options such as biofuels, solar energy, and anaerobic digestion increasingly relevant. This study investigates a four-pronged optimisation strategy for synergistic enhancement of biogas production, which combines solar thermal heating, optimum dilution, and two selected additives: fish waste and sodium bicarbonate. Experiments were conducted in lab-scale biodigesters under various conditions, including ambient temperature conditions, thermal bath, solar greenhouse, and with the addition of fish waste and sodium bicarbonate. Results show that a combination of enhancement factors, such as using a 1:3 dilution ratio, utilising NaHCO 3 buffer with fish waste, and higher temperatures, significantly improve biogas production. Solar-assisted reactors operating under greenhouse conditions achieved a substantially higher cumulative biogas production of 65,000 mL per kg of cow dung (401 mL/g VS), which was approximately 2.4 times greater than the room-temperature control, underscoring the effectiveness of solar energy in maintaining optimal digestion temperatures for increased biogas production. Futhermore, the reactor in a constant temperature thermal bath at a temperature of 40 °C produced a biogas volume of nearly 66,500 mL per kg cow dung (405 mL/ g.VS), and moreover the reactor in a constant temperature thermal bath and with additives gave the maximum biogas volume of 77,020 mL/ kg cow dung (476 mL/ g.VS). These values were up to three times higher than those of the control reactor at room temperature. The optimised biodigestors also exhibited more stable gas production trends. This confirms the substantial potential of the four-pronged approach, which combines dilution, the two additives (fish waste and NaHCO 3 ), and a constant higher temperature, in enhancing gas generation. These results highlight the potential of synergistically optimised solar-assisted biogas systems for enhanced biogas production. • A four-pronged multi-strategy approach increased biogas production. • The combined use of improved dilution with the addition of fish waste and NaHCO 3 can increase biogas production by nearly twice compared to the control. • The combined approach of solar/thermal heating, along with fish waste, NaHCO 3 , and dilution increased biogas production by up to three times compared to the control.