*7.5. Temperature*

Temperature is a key element in MECs that affects their function because it improves exoelectrogen selectivity and production. Most microbes prefer an optimum temperature range of 35–40 ◦C for growth, enzyme activity, and the development of a durable biofilm, which increases substrate degradation, mass transfer, and power generation. According to the COD removal efficiency and microbe loading at the anode, Omidi et al. reported that 31 ◦C is the most efficient operating temperature for MECs [136]. As a result, the test temperature of an MEC is typically kept at about 30 ◦C. Lu et al., on the other hand, demonstrated that utilizing a single-chambered MEC produces hydrogen at low temperatures such as 4 ◦C, while simultaneously reducing the generation of methane [137]. Additionally,

the anode biofilm and hydrodynamic force both impact hydrogen generation in MECs [138], with the hydrodynamic force having a larger effect on hydrogen production than the anode biofilm [139]. Furthermore, by placing two anodes on each side of the cathode, additional hydrogen may be generated.
