*5.5. Dairy Industry Wastewater*

The most prominent characterization of dairy industrial wastewater is associated with its unique constituents attributed to differentially complex organics, including proteins, lipids, and polysaccharides. The hydrolysis of such wastewater can transform the wastewater components into organic acids, fatty acids, and sugars, respectively. The properties attributed to dairy industrial wastewater were seen as effective and efficient in an anolyte in MFC [117]. However, another important product rich in nutritional constituents from the dairy industry is cheese whey (CW) classified as milk casein obtained after the separation of milk constituents; hence, the diary industrial wastewater containing CW treatment using MFC was evaluated by many researchers and reported in several investigations regarding the bioelectrochemical recovery of electricity from such MFC operations. CW contains high organic carbon-based compounds that can be broken down into simpler constituents that are readily available to microorganisms [118]. Results indicated electron transfer variability using different materials in MFC with different designs, i.e., single, dual, and tubular chambered MFCs, and different anodic materials, e.g., carbon graphite, stainless steel, composites, etc. The highest CE of 37.2% was recorded using a catalyst-free and mediator-less MFC treating wastewater from the dairy industry [119]. The electrical performances of the MFC increased with an increase in organic matter loading rates (OLRs) [120]; albeit, it was noticed that a high acolyte's COD concentration of up to 2800 mg/L could lead to a reduction in electrical energy, and the flow rate of substances in the MFC IEM may be lowered. Overall, CW containing wastewater has shown a promising result with an MFC made up of an H-type-two-chambered system connected to a carbon paper anode and a platinum-coated (0.5 mg/cm<sup>2</sup> ) cathode, achieving the highest energy generation of up to18.4 mW/m<sup>2</sup> with 94% of COD removal being recorded with the said MFC; albeit, operated in a fed-batch mode [121]. A CE of 11.3% was also reported, further showing CW containing wastewater as a promising substrate in MFCs [122]. Another system of an MFC operated in a four-fed batch mode using a cylindrical cathode made from carbon brushes, and carbon powder was determined to serve as an example of a suitable electrode and catalyst configuration for dairy wastewater treatment in MFCs. A comparative account of the substrate used in MFCs and their performance is given in Table 3.


## **Table 3.** MFC efficiency is based on various substrates.
