*3.5. Other Agricultural Activity Effluents and Waste*

Most agro-industrial activities in the food, plant, and animal processing industries generate a high quantity of wastewater. Most agricultural wastewater has been demonstrated as suitable for use in MFCs, i.e., either used in a minute and/or large quantities [87]. One of the recent studies has shown that sugar beet processing wastewater at a concentration of 2.56 g COD/L was able to generate a power of 1.41 W/m<sup>2</sup> which in turn contributed to the complete removal of suspended solids up to 97% of organic matter [87]. However, the hydraulic retention time was up to 40 days. Similarly, up to 93% can be removed from coconut husk retting wastewater containing phenols (potent toxicants) with a concentration of up to 320 mg/m3, with 91% COD removal being achieved in a dual-chamber MFC [88]. Similarly, the use of crude starch extracts from potato processing has shown promising results when used in a dual-chamber mediator less MFC, culminating in 18.5% CE and a COD removal of 61% [81]. Furthermore, olive mill wastewater (OMW) is usually produced during the processing of olives and is considered the most pollutant containing wastewater constituted by up to 100,000 mg/L COD. This type of wastewater is characterized by a strong, intensive black color, acidic pH, a strong odor, and toxicant concentration in the range of 200–800 mg/L in the form of polyphenols [89] while possessing differentiated values of electro-conductivity [90].

It has been reported that an MFC made up of a 12 mL inner volume and a singlechambered air-cathode can be used with diluted OMW in a ratio of 1:10 with OMW acting as a sole source of carbon for bioenergy generation. A COD of 65% was removed for this type of set-up, and a total phenolic content of up to 49% was removed while reaching a maximum voltage generation of 381 mV. In a similar study, an MFC made up of a singlechambered air cathode was used; albeit, with a cathode equipped with platinum-coating (0.5 mg Pt/cm<sup>2</sup> ) enveloped with a carbon cloth; a configuration which was demonstrated as being efficient for OMW treatment [91]. However, OMW is not a promising substrate for energy production and as such, is not usually considered as an alternative source of

substrates in MFC technology development. However, a mixture of any other wastewater combined with OMW generated high-power density results whereby COD was removed with a low yield in CE [56]. This combination was determined to produce a virtuous power output and has shown promising results, particularly for OMW treatment [91].
