Plant based surfactant combined sonication pretreatment on food waste for biomethane generation: Cost and energy procurement

Food waste (FW) can be used as an appropriate feedstock for bioenergy generation. However, the rate limiting hydrolysis step during Anaerobic Digestion (AD) limits the biodegradation of substrate. Hence, pretreatment of food waste is essential prior to AD to circumvent the rate limiting step. Ultrasonic pretreatment of FW has been restricted owing to its greater energy requirement, aggregation of FW particles and lignin binding to methanogenic enzymes during biomethanation process. These limitations could reduce the efficiency of the whole treatment. In this study an effort has been made to enhance the hydrolysis and to improve the methanogenesis by pretreating the FW with plant-based surfactant (saponin) coupled ultrasonic pretreatment. The ultrasonic alone (US alone) pretreatment experimental run was done by varying the ultrasonic power from 80 to 180 Watt and pretreatment time from 0 to 20 min. The ultrasonic combined saponin (US-saponin) pretreatment experimental run was done by varying the time from 0 to 10 min and saponin dosage from 0.0005 to 0.008 g/g TS. The outcome reveals that the specific energy input of 5052 kJ/kg TS, saponin concentration of 0.002 g/g SS, and 2 min pretreatment time was optimum to achieve the maximum solubilization of 37 % in US- saponin sample. The US alone demands a specific energy input of 25263 kJ/kg TS and a pretreatment time 10 min to achieve the maximum solubilization of 30.5 %. The US-saponin pretreatment shows 269 mL/gCOD of methane production, higher than the US alone (148 mL/gCOD) and control (53 mL/gCOD). Regarding energy and cost assessment, the US- saponin pretreatment shows 12.07 USD/ton of net profit, greater than the US alone pretreatment (-260.8 USD/ton).