**7. Factors Affecting the Performance of MFC Utilizing Food Waste** *7.1. pH*

For ideal microbial growth, MFCs are usually controlled at pH nearby neutral environments. However, due to reduced ionic concentration at neutral pH, the internal resistance of MFCs is strong in comparison to chemical fuel cells that are using alkaline or acid as electrolytes. Unintended pH shift reduces the power generating potential of MFCs. Ghangrekar et al. [141] analyzed the pH-change effect on the overall efficiency of a two-chambered MFC. When the pH gap between the two chambers was high, they measured optimum current and voltage. Cathode alkalization and anode acidification have been documented to affect the efficiency of MFCs [142]. During the short- or long-term activity, the pH gradient is created at the membrane. Because the electrons aggregate at the anode, an equal amount of H<sup>+</sup> is released into the electrolyte and eventually travels into the cathode, where they are absorbed in cathodic reactions. However, the pH of the anodic compartment reduces because of inadequate or slow migration and diffusion of H<sup>+</sup> via the membrane. On the other side, as a consequence of proton intake, the pH of the cathodic compartment decreases for the oxygen reduction reaction (ORR). The presence of H+ is the main element in evaluating the ORR efficiency of electrochemical water splitting devices [143] in the cathode chamber. In the anodic container, the performance of electron transfer and the function of neutrophilic biofilm microbes are decreased if pH is dropped too suddenly. Although alkaline pH decreases power production in the cathode chamber markedly. Zhang et al. [144] analyzed the role of initial pH on the anodic bacteria, biofilm, and MFC's efficiency in power generation. At acidic conditions, they achieved voltage output of 232–284 mV vs. 311–339 mV along with a power density of 95–116 mW/m<sup>2</sup> vs. 182–237 mW/m<sup>2</sup> . Reduced and cracked biofilm at pH 5. Around pH 4, the MFCs were unable to obtain the optimum power around neutral pH. The findings indicated that the power supply corresponds to the output voltage and time-speed pH variance of the cathodic and anodic chambers of the MFCs. MFC's poor performance at pH 4 remained for a long time and could be irreversible; therefore, low pH conditions in MFCs should be avoided.
