Cavitation-based technologies for pretreatment and processing of food wastes: Major applications and mechanisms – A review

Conversion of food wastes to valuable products is an important topic for sustainable development. Feedstock hydrolysis is a stage strongly affecting the anaerobic digestion process, and resistance of food waste towards hydrolysis causes a decrease in product yield. Such as biomethane, biohydrogen, biohythane, VFAs, and lactic acids. Moreover, mass transfer is a serious limitation of transesterification for the production of biodiesel. Cavitation is a promising pretreatment method for the mitigation of these issues. This work presents a critical review on cavitation-assisted processing of food waste. In several studies, cavitation proved its remarkable potential. Cavitation can also be employed in anaerobic digestion reactors and directly irradiate microorganisms, stimulating enzyme activities. Cavitation led to an increase in SCOD by up to 172 %. Consequently, it caused an increase in biogas, biohydrogen, VFAs, and lactic acid converted from food waste by up to 100 %, 145 %, 100 %, and 62 %, respectively. Cavitation resulted in a reduction in reaction time required for the conversion of food waste into biodiesel by up to 98 % due to its potential in increasing mass transfer. In acoustic cavitation, the optimum power density for the conversion of food waste through anaerobic digestion is in ranges of 230–480 W/L and 40–50 W/L at pretreatment stage and main stage, respectively. Low frequencies in a range of 20–50 kHz are suitable for both anaerobic digestion and transesterification. However, studies on the application of high frequency are scarce and obvious “research-gap” in this field exists. In hydrodynamic cavitation, for disintegration, efficient cavitation number and pressure are in ranges of 0.07–0.15 and 2–4 bar, respectively. The maximum particle size reduction usually occurs within the initial 15 min for both types of cavitation.