Sustainable production of biobutanol and biodiesel from municipal solid waste: Optimization and process integration

This study focuses on the simultaneous production of biobutanol and biodiesel, viable alternatives to gasoline and diesel used in urban settings, aiming to enhance valorization of municipal solid waste (MSW) as the feedstock. The process involves a multi-stage pretreatment including simultaneous extraction of inhibitors and lipids, dilute acid and crude glycerol pretreatment, and enzymatic hydrolysis followed by anaerobic fermentation using Clostridium acetobutylicum for biobutanol production. The use of crude glycerol, a biodiesel byproduct, as a green solvent in the pretreatment, reduces the need for traditional costly solvents. Optimal conditions were determined for the highest production of acetone, butanol, and ethanol (ABE) were lipid extraction and inhibitor removal by ethanol followed by 1 % w/w dilute acid pretreatment at 120 °C for 10 min. Under these conditions, fermentation of the pretreatment liquid yielded concentrations of 5.42 g/L acetone, 11.32 g/L butanol, and 1.35 g/L ethanol. Moreover, fermentation of the hydrolysate resulted in concentrations of 2.13 g/L acetone, 4.28 g/L butanol, and 0.78 g/L ethanol. Moreover, the optimal conditions for biodiesel production were determined as methanol-to-oil ratio of 9.14:1, temperature of 59.5 °C, catalyst percentage of 0.886 %, and reaction time of 67 min. Under these conditions, a high yield of biodiesel (96.91 %) was achieved from the extracted oil using ethanol:acetone ratio of 1:3. Overall, this integrated approach produced 137.2 g of ABE and 75.1 g of biodiesel per kg of MSW, demonstrating the potential of MSW as a sustainable feedstock for dual-grade biofuel production.