Microwave facilitated bacterial liquefaction of sago biomass for efficient biomethane production: Energy and cost assessment

Sago has been considered to be a major staple food throughout the world for centuries. Thus, the sago processing industry also contributes to economic growth. However, waste disposal from this industry is an environmental concern and is addressed in this study. The generated solid waste sago is a starchy-rich substrate that is underutilized and can be exploited for bioenergy production. The present study focused on improving the hydrolytic potential of sago biomass during anaerobic digestion by implementing the combined microwave and bacterial pretreatment techniques. The microwave liquefaction yields the maximum solubilization of 11 % at the microwave power of 720 watts and the time of 11 min. Incorporation of bacterial pretreatment significantly enhances COD solubilization from 11 % to 31.6 %. This combined pretreatment of sago biomass shows the biomethane generation of 0.223 L/gCOD compared to the microwave (0.106 L/gCOD) and control sample (0.044 L/gCOD). Energy and cost analysis of combinative pretreatment shows a positive net energy of 0.97 kWh/kg and a net cost of -1.63 USD/ton. Thus, this combined pretreatment can be effectively adapted on an industrial scale with further improvements.