1.4.1. Physical Pretreatment

Physical pretreatment techniques requiring mechanical processes such as chipping, milling, and grinding may decrease particle size, break down crystallinity, and increase the degree of polymerization, both of which significantly enhance the biodegradability of biomass in MFCs. Using a fermentation medium containing solid substrate resulted in a low PD attributable to the sluggish hydrolysis of the biodegradable materials, suggesting that particle size is a significant factor for optimum bioenergy production. Additional particle size reduction under 40 mesh has been reported to impact hydrolysis rates and yields, resulting in a significant amount of usable material in the biodegradation phase in MFCs [22]. Furthermore, various irradiation methods (such as ultrasonication, electron beams, X-rays, or gamma rays) may be used to pretreat biomass physically. Shen et al. (2018) studied the effects of ultrasonic pretreatment on electricity production in a dairy

manure microbial fuel cell (DMMFC). At 600 W ultrasonic power, the pretreated DMMFC had a maximum PD of 102 mW/m<sup>2</sup> , which was 241 percent higher than the untreated substrate [23]. According to Tao et al. (2013), ultrasonication may be an effective pretreatment technique for vegetable or grass wastes [24].
