*10.3.1 Conductive polymer coatings*

Provided their high conductivity and biocompatibility, conductive polymer coatings have drawn considerable interest [85]. Composite polyaniline (PANI) mesoporous tungsten trioxide (m-WO3) had been formed and utilized as a catalyst, free of precious metals [63, 64]. PANI was mounted onto m-WO3 by

**113**

**10.4 Metal-based anode**

*Treatment of Dairy Wastewaters: Evaluating Microbial Fuel Cell Tools and Mechanism*

cal conductivity. The achieved maximum power density of 257 mW/m<sup>2</sup>

highest existing density obtained in that analysis was 8 A/m2

liable for the improved overall efficiency of the system [94].

bial fuel cells has attracted increasing interest [95].

sponds to an increase of 343% and 186%, respectively, when compared with those achieved with the pristine GF MFC and the PANI/GF MFC, respectively [89].

Vertically targeted TiO2 modified carbon paper shapes vertically breaching pores which offer the bacteria a large area of contact for direct electron transmission. This was particularly useful in a recent study for improving the delivery of nutrients, attaining high biocompatibility, and supporting the electron transport routes [90]. Through using a TiO2-NSs or CP as a bio-anode, a mixed consortium inoculated MFC's average power production density was improved by 64% relative to using a pure CP as a bio-anode. In a different study, dual nanofiber mats TiO2 (rutilo)–C (semi-grafito)/C (semi-grafito) were used for MFC anode, one fiber consisting mainly of O, Ti, and C, while the content of the other fiber was predominantly Carbon. The dual nanofiber had stronger efficiency than a single nanofiber. The

carbon (AC) with SSM (AcM) and Fe3O4 anode was also investigated for MFCs, and capability enhancement was related to device efficiency [92]. Nano-goethite was added with 0, 2.5, 5.0, and 7.5% (mass percentage) to the activated carbon (AC) powder and pressed onto the stainless steel wire. The composite material anodes produced 35 percent more power than a non-modified AC anode. The improved performance was achieved due to reduced transfer charge resistance (Rct) and strengthened the current exchange rate (Io) [92]. Several experiments have shown that start-up time for MFCs in nitric acid or ammonium nitrate can be reduced by electrochemically oxygenated carbon wire. It has been replicated in one report [93] that the coulombic performance of the anodes adjusted by this process was 71 percent. Responsive groups containing oxygen on the carbon surface could be

Many metals such as gold, titanium, and copper have been used as anodes in MFCs for use in the last ten years. Because of their corrosive nature, most of those metals were unsuitable. Conversely, the use of stainless steel as an anode for micro-

corre-

[91]. The activated

the chemical oxidative process. The composite's catalytic nature was elaborated through the application of electrochemical techniques. Significant efficiency changes were observed with the composite based on the-WO3 and PANI combinations. The m-WO3 has excellent biocompatibility while PANI has strong electrical conductivity [63, 64]. PANI networks' electrode location on graphene nanoribbons (GNRs)-coated carbon paper (CP/GNRs/PANI) has been found to increase power generation as opposed to GNR and CP usage. The improvement was due to the positively charged PANI backbone which increased the affinity of interaction with negatively charged microbial cells and thus favored direct transfer of electrons through cytochromes. Conductive GNRs significantly enhanced CP/GNRs/ PANI electrode conductivity in neutral environments. This discovery explicitly shows that the synergistic impact of both components was responsible for major energy production changes. In another report, carbon nanotubes/polyaniline carbon paper (CNT/PANI carbon paper) is used and correlated with other conventional carbon paper [63, 64]. The findings revealed that the CNT/PANI carbon paper has obtained a lower ohmic loss and improved power generation. The use of CNTs enhanced the surface area for the biofilm span, as well as achieved a higher electri-

*DOI: http://dx.doi.org/10.5772/intechopen.93911*

*10.3.2 Graphite/carbon surface modifications*

#### *Treatment of Dairy Wastewaters: Evaluating Microbial Fuel Cell Tools and Mechanism DOI: http://dx.doi.org/10.5772/intechopen.93911*

the chemical oxidative process. The composite's catalytic nature was elaborated through the application of electrochemical techniques. Significant efficiency changes were observed with the composite based on the-WO3 and PANI combinations. The m-WO3 has excellent biocompatibility while PANI has strong electrical conductivity [63, 64]. PANI networks' electrode location on graphene nanoribbons (GNRs)-coated carbon paper (CP/GNRs/PANI) has been found to increase power generation as opposed to GNR and CP usage. The improvement was due to the positively charged PANI backbone which increased the affinity of interaction with negatively charged microbial cells and thus favored direct transfer of electrons through cytochromes. Conductive GNRs significantly enhanced CP/GNRs/ PANI electrode conductivity in neutral environments. This discovery explicitly shows that the synergistic impact of both components was responsible for major energy production changes. In another report, carbon nanotubes/polyaniline carbon paper (CNT/PANI carbon paper) is used and correlated with other conventional carbon paper [63, 64]. The findings revealed that the CNT/PANI carbon paper has obtained a lower ohmic loss and improved power generation. The use of CNTs enhanced the surface area for the biofilm span, as well as achieved a higher electrical conductivity. The achieved maximum power density of 257 mW/m<sup>2</sup> corresponds to an increase of 343% and 186%, respectively, when compared with those achieved with the pristine GF MFC and the PANI/GF MFC, respectively [89].

## *10.3.2 Graphite/carbon surface modifications*

Vertically targeted TiO2 modified carbon paper shapes vertically breaching pores which offer the bacteria a large area of contact for direct electron transmission. This was particularly useful in a recent study for improving the delivery of nutrients, attaining high biocompatibility, and supporting the electron transport routes [90]. Through using a TiO2-NSs or CP as a bio-anode, a mixed consortium inoculated MFC's average power production density was improved by 64% relative to using a pure CP as a bio-anode. In a different study, dual nanofiber mats TiO2 (rutilo)–C (semi-grafito)/C (semi-grafito) were used for MFC anode, one fiber consisting mainly of O, Ti, and C, while the content of the other fiber was predominantly Carbon. The dual nanofiber had stronger efficiency than a single nanofiber. The highest existing density obtained in that analysis was 8 A/m2 [91]. The activated carbon (AC) with SSM (AcM) and Fe3O4 anode was also investigated for MFCs, and capability enhancement was related to device efficiency [92]. Nano-goethite was added with 0, 2.5, 5.0, and 7.5% (mass percentage) to the activated carbon (AC) powder and pressed onto the stainless steel wire. The composite material anodes produced 35 percent more power than a non-modified AC anode. The improved performance was achieved due to reduced transfer charge resistance (Rct) and strengthened the current exchange rate (Io) [92]. Several experiments have shown that start-up time for MFCs in nitric acid or ammonium nitrate can be reduced by electrochemically oxygenated carbon wire. It has been replicated in one report [93] that the coulombic performance of the anodes adjusted by this process was 71 percent. Responsive groups containing oxygen on the carbon surface could be liable for the improved overall efficiency of the system [94].

## **10.4 Metal-based anode**

Many metals such as gold, titanium, and copper have been used as anodes in MFCs for use in the last ten years. Because of their corrosive nature, most of those metals were unsuitable. Conversely, the use of stainless steel as an anode for microbial fuel cells has attracted increasing interest [95].

*Environmental Issues and Sustainable Development*

rent density of 336 A/m3

**10.3 Surface modified anodes**

maximal power density of 1573 mW/m2

*10.3.1 Conductive polymer coatings*

stainless steel mesh (GMS) power density was recorded to be 18 times higher than that of a stainless steel mesh anode (SSM) and 17 times higher than that of polytetrafluoroethylene modified SSM (PMS) [68]. The significant improvement was recognized due to increased surface area of the electrodes, improved adhesion of bacterial biofilms, and efficient extracellular electron transfer. The current stainless steel collector (SS) boosts electrical conductivity for electrode, and the overall efficiency of the system is enhanced by the current SS assimilator which reduces internal resistance. Chen et al. [69] used an ice template as an anode to create a versatile macroporous 3D graphene sponge. The microporous 3D graphene allowed the random propagation of bacteria and resulted in a high biofilm span and increased performance [69]. From another study, tin oxide (SnO2) nanomaterials were utilized on the reduced graphene oxide surface (R-GO-SnO2) able to generate electricity that was approximately 5 times higher than the use of an unaltered graphene oxide (reduced). Collegial effects among SnO2 and graphene and strong biocompatibility were liable for the much stable formation of bacterial biofilms and the efficiency of charges transfer [86]. Reduced graphene oxide/carbon nanofibers (R-GO-CNTs sponges) melamine sponges based on dip-coating technique tend to cater to a huge electrically conductive surface area for *Escherichia coli* growth as well as electron transport in MFC [65]. Four R-GO-CNT sponges were tested with varied thicknesses and configurations, but the thinnest one (with a thickness of 1.5 mm) displayed prime efficiency, generating a maximal cur-

[65]. The usage of a redesigned anode built from graphene-

, whereas a

. The two broad surface treatments that are

polyaniline nanocomposite was also found to produce power three times greater than carbon cloth [70]. Often used as an anode for MFC was a 3-dimensional reduced graphene oxide-nickel foam (R-GO-Ni) by accurate deposition of R-GO sheets to the nickel foam substratum. The R-GO thickness may be modified in comparison to the surface region of the electrode by initiation cycles. This macro-porous scaffolding design not only offers a 3-dimensional surface for microbial growth but also promotes the mobility of substrates inside the culture medium. The efficiency was extensively better than with the usage of nickel foam and various graphite materials dependent on anodes [63, 64]. The formation in MFC of highly crystalline graphene or nickel electrode with Shewanella putrefaciens provided the power density of typical MFC carbon cloth anode 13 times greater. Because of the minimal cost of hollow Ni and the low weight percent of graphene (5% w), this composite electrode provides good potential in the development of efficient MFCs for greater power generation [71].

The electrode surface has a tremendous role in the total anode's efficiency. Currently, several reports have stated that surface alteration is advantageous in actuating increased bacterial adhesion and better biocompatibility that favors electron transfer kinetics. The surface alterations using TiO2-carbon fabric-based

changed surface with carbon nanotubes and coated with conductive polymer had a

most generally used are silicone coating and graphite or carbon surface application. Each of these surface alteration forms is discussed in subsequent subsections.

Provided their high conductivity and biocompatibility, conductive polymer coatings have drawn considerable interest [85]. Composite polyaniline (PANI) mesoporous tungsten trioxide (m-WO3) had been formed and utilized as a catalyst, free of precious metals [63, 64]. PANI was mounted onto m-WO3 by

nanofiber usually attain the highest current density of 7.99 A/m2

**112**
