**9. Integrated MEC Systems**

MECs have been shown to be viable options for dealing with the issue of wastewater treatment while also producing hydrogen. However, there have been certain challenges in commercializing these MEC technologies. Thus, combining new technologies with traditional ones may be used to overcome the thermodynamic limits, as well as material prices, methanogens, substrate concentration, and other issues that MES faces on its own. The performance of several integrated systems is highlighted in Table 5. Various patents based on integrated MEC technology are described in Table 6.

**Table 5.** Current integrated MEC configurations.

#### **Table 6.** Various patents associated with integrated MEC technology.

#### **10. Comparison between MEC Technology and Water Electrolysis**

When compared to water electrolysis, the primary advantage of MECs is that they do not produce oxygen [181–184], which is regarded to be a part of the process safety; this process safety asset is essential when producing pressurized hydrogen, such as during water electrolysis, because, when producing pressurized hydrogen at high pressure, there is an increased risk of hydrogen crossover at the anode compartment [163]. A further advantage of MECs is that the anode produces chlorine at a very low potential, eliminating the need for the electrolyte to be dissociated from chlorine, which is required for water electrolysis. This is another advantage of MECs [185,186]. MECs have another operational parameter, which is pH. The pH of the electrolyte is neutral, although many microbial biofilms do not tolerate extremes in pH [183]. Furthermore, the neutral pH offers the additional process safety benefit of allowing electrolytes to be handled without the need for severe safeguards. When disposing of and replacing a phosphate buffer with neutral pH, it is much simpler than when disposing of and replacing pH 14 potassium hydroxide, which is used in water electrolysis [184–186].

#### *Comparison in Terms of Theoretical Energy Yields*

MECs are also more efficient than water electrolysis in terms of energy generation, and two different sources of energy must be considered, with electricity being the most prominent of the two. The reaction in MECs that produces hydrogen consumes a significantly lower amount of energy than water electrolysis, resulting in lower power consumption. It is an endothermic reaction that requires heat in order for the reaction to occur at equilibrium cell voltage. The energy yields from multichannel electrolysis cells (MECs) are up to 10–11.3 γG greater based on MEC configurations.

Chemical energy is the other source of energy, and it is obtained when the oxidation of various compounds present at the anode is completed. During the side production of methane, the energy yield for G, including hydrogen generation, decreased below 10; nevertheless, the thermal energy yield for both increased to 12 Y H. This yield demonstrates that hydrogen produced by MECs can store up to 10 times the electrical energy in the form of Gibbs free energy [187]. Table 7 lists the characteristics of some of these pilot studies including electrical and thermal energy yields.

**Table 7.** Characteristics of MEC pilot studies (volume, ionic conductivity, methane, and hydrogen production rates) with final electrical (γG) and thermal (γH) energy yields.