*3.3.3 Advantages and disadvantages (Limitations) of MFCs in WWT*

MFCs present several advantages and disadvantages (**Table 2**), both operational and functional in comparison to currently implemented wastewater treatment technologies for both high organic pollutant removals in the form of CODs and for the valorization of bioenergy in the form of electricity [98]. The generation of bioenergy from wastewater treatment is mostly considered to be the green or blue energy aspect of MFCs [92]. Electricity is generated in a direct way from biomass and organic matter, hence chemical energy is directly converted to electrical energy. The direct conversion of wastewater substrates to bioenergy has also been reported to be a third of the input during the thermal combustion of biogas [85]. Due to the harvesting of electrical energy, the bacterial growth yield in a MFC is considerably lower than the sludge output of an aerobic process [85, 99]. Generally the off-gas of an anaerobic process has a high content of nitrous gases together with the targeted hydrogen and methane [78]. The off-gases of MFCs has less economic viability, since the energy contained in the substrate was previously directed towards the anodic chamber of the MFC during processing [78]. The gas produced in the anodic chamber of the MFC can be literally discharged, considering no large amounts or other odorous compounds are present, and in addition no aerosols with noxious or undesired bacterial contents are liberated into the environment. Power generation from MFCs have improved considerably and reached the level of primary power target, at least in small scale systems, but the scale up is still a big challenge and a major limitation of the application of MFC technologies. The high cost of cation exchange membranes, the potential for biofouling and associated high internal resistance restrain the power generation and limit the practicality and commercial application of this technique [100].

Domestic wastewater is organic matter with embedded energy content of almost 10 times the energy needed for treatment [101]. While emerging techniques are promising, none of the processes available today can yet fully extract all the energy available in wastewater without further investment in their research and development [100]. A major setback of MFC applications is associated with the process start up time, and sequence which may be between 4 to 103 days depending on the inoculum, electrode materials, reactor design and operating conditions (temperature, external loading rates etc.), but it is largely affected by the type of substrate being fed into the MFC system [96]. Another vital impediment in scaling up of MFCs for wastewater treatment is the shortage of buffer capacity of electrolytes. This might require some external mediators, or chemical substance to maintain and stabilize the hydrogen potential of the anodic and cathodic chambers. This has to enhance the wastewater treatment process but still favor the valorization of bioenergy within the MFC system.


**Table 2.**

*List of advantages and disadvantages of MFCs, sourced from Quach-Cu et al., 2018 [61].*

*Emerging Trends in Wastewater Treatment Technologies: The Current Perspective DOI: http://dx.doi.org/10.5772/intechopen.93898*
