*5.2. Livestock Compost Wastewater*

Livestock compost wastewater is also one of the effluents most produced in the livestock industry. Livestock compost is described as an important source of some organic and inorganic components [105]. Some of these components can be easily broken down into simpler molecules, which in turn can provide a source of easily fermentable constituents for consortium support in MFCs [106]. Overall, a complex organic substrate may assist in the propagation of different species of microorganisms. Generally, exoelectrogenic bacteria possess a limited ability to utilize complex substrates. Many different microbial populations are needed for the wastewater to undergo the required oxidation processes and with microbial species undergoing directed evolution to decompose semi-biodegradable carbon-based compounds [107]. For example, when wastewater treatment was carried out in an air-cathode MFC using cattle manure sludge as a substrate with and without any mediators, increases in power density up to 200% were observed when methylene blue was used as a mediator [108]. In another study, a maximum power density of 16.3 W/m<sup>3</sup> was recorded using suspended cattle manure as a substrate. This was achieved when a cassette-electrode MFC configuration operating in a batch mode was used, with 41.9% COD removal being reported in the first ten days of the MFC operation [106]. Some studies have demonstrated that using a small number of substances derived from livestock waste via fractionation in combination with compost wastewater as a substrate showed promising results when fed into an MFC. Generally, 67–215 mW/m<sup>2</sup> power density was generated by livestock waste and compost wastewater which was greater than when supplied as a liquefied feedstock in MFCs. When livestock compost was employed and the substrate is halted in MFC, only 15.1 W/m<sup>3</sup> of power density was produced [109].
