Valorization of Agro-industrial Solid Waste by Two-stage Anaerobic Digestion for Biohythane Production

This study investigated the valorization of agro-industrial solid waste for biohythane production through a two-stage anaerobic digestion process. Seventeen waste samples were characterized, revealing diverse physico-chemical properties suitable for anaerobic digestion. The highest biohythane yields were obtained from waste-activated sludge (WAS) from a frozen convenience food wastewater treatment plant (895.63 mL/g VS), WAS from a processed chicken wastewater treatment plant (835.73 mL/g VS), and WAS from a municipal wastewater treatment plant (830.79 mL/g VS). Kinetic analysis using the modified Gompertz model provided insights into the biohythane production potential, with predicted yields ranging from 0 to 111.85 mL/g VS and production rates from 0 to 21.37 mL/d. The comparative analysis highlighted the superior biohythane production potential of the studied waste materials compared to other substrates, such as food waste (180.5 mL/g VS) and sugarcane bagasse (165.2 mL/g VS). The highest hydrogen and methane contents in the produced biohythane were 26.57% and 67.85%, respectively. The techno-economic assessment of scaled-up biohythane production demonstrated the economic feasibility, with a payback period of 2.05 years for a plant capacity of 100 ton waste/day, a biohythane yield of 500 m3/ton waste, and a biohythane production of 50,000 m3/day. The capital cost was estimated at 15 million USD, with an operating cost of 0.2 USD/m3 biohythane and a revenue of 0.6 USD/m3 from biohythane sales. The results of this study demonstrate the high potential of agro-industrial solid waste valorization for biohythane production and its contribution to sustainable waste management and renewable energy production.