1.4.3. Alkali Pretreatment

Basic chemicals such as sodium hydroxide (NaOH), hydrazine, anhydrous ammonia, potassium hydroxide (KOH), or lime (Ca(OH)2) (Figure 4) are used in alkali pretreatment. Even though this process can be used at room temperature, the reaction period is typically long, ranging from hours to days [29]. Song et al. (2018) showed that rice straw could be pretreated with sodium hydroxide (NaOH) for usage in a solid phase microbial fuel cell (SMFC). The SMFC with NaOH (5%) pretreated rice straw could maintain a maximal PD of 140 mW/m<sup>2</sup> , which was 3.6 times that of the untreated SMFC [30]. The viability of alkaline pretreatment for sludge-fueled MFC was also verified by Xiao et al., which achieved a PD of 46.82–55.88 mW/m<sup>2</sup> with a quick alkaline procedure using concentrated sodium hydroxide [31].

**Figure 4.** Schematic representation of agricultural biomass pretreatment using lime (Ca(OH)<sup>2</sup> ).
