**12. Two-compartment MFC systems**

Two-compartment MFCs are frequently run in a batch before equilibrium is established to produce energy in the MFC device with a well-defined chemical media such as glucose or acetate. Once the stability is maintained the dairy wastewater is pumped into the anodic chamber continuously through a peristaltic pump, which is currently only being used in the laboratories. A standard twocompartment MFC has two chambers one for the anode and the other for the cathode linked by a PEM or a salt bridge, to enable protons to travel to the cathode whilst preventing oxygen diffusion towards the anode. The compartments would be taking numerous functional forms. Mansoorian et al. [96] constructed noncatalyst and non-mediator membrane microbial fuel cell (CAML-MMFC), as seen in **Figure 3**, for simultaneous treatment of wastewater and bioelectricity production. The CAML-MMFC was equipped with two chambers with an anaerobic anode and aerobic cathode container and divided from one another by a proton exchange membrane. The chambers were constructed of plexiglass sheets 2 cm in diameter, each with an effective volume of 2 L with the gaskets tightly sealed. The anode and cathode electrodes were formed from a graphite plate 14 × 6 × 0.5 cm3 . The electrode in the anode was 5 cm from the membrane, and the electrode in the cathode was 2 cm from the membrane. Via a resistance, the electrodes were attached to copper wire 2 mm in diameter and 35 cm in total.

Jadhav et al. [97] used a cow urine administered another type of dual-chambered MFC with an outer cathodic chamber volume of 2.5 L, made of a plastic bucket and

**115**

respectively.

**Figure 5.**

**Figure 4.**

region (80 mm = 6400 mm2

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

*Dual chambered MFC treating cow urine as a substrate in the anodic chamber (adapted from [97]).*

inner clay container as an anodic chamber with a working volume of 0.4 L as seen in **Figure 4**. The substance of the clayware pot wall itself worked as a separator between the anodized chamber and the cathodic chamber. The anode and cathode

*Schematic drawing of the MFC reactor. (1) Graphite fiber brush; (2) graphite granules; (3) proton exchange membrane (PEM); (4) Ag/AgCl reference; (5) blade stirrer; (6) air; (7) air bubbles; (8) external resistance;* 

Zhang et al. [98] constructed a novel design for the treatment of dairy manure as shown in **Figure 5**. The MFC consisted of one cylinder (Ø100 mm × 90 mm, anode compartment with two identical square vision windows (80 mm × 80 mm)) and two rectangular cubes (80 mm × 80 mm × 50 mm, two cathode compartments attached to a Plexiglas conduit (Ø20 mm) and a catholic compartment passing freely between them). The anode and the cathode compartments were divided by two proton exchange membranes (PEM) with the same cross-sectional

300 ml min−1, to maintain dissolved oxygen at the cathode, and the anolyte was agitated with a blade stirrer (300 rpm) every other hour. The anodic and cathodic

Owing to their complicated architectures, two-compartment MFCs are challenging to scale up, but they can be run either in batch or continuous mode. One

chamber had appropriate volumes of 617 ml and 321 ml.

**13. Single-compartment MFC systems**

and 755 cm2

). The cathode chambers were constantly aerated at

of estimated surface area,

are constructed of carbon felt with 394 cm<sup>2</sup>

*(9) inlet; (10) outlet (adapted from [98]).*

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

**Figure 3.** *The schematic view of the CAML-MMFC reactor (adapted from [96]).*

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

**Figure 4.**

*Environmental Issues and Sustainable Development*

A MFC consists of an anode chamber divided by a PEM, and a cathode chamber. By exposing the cathode into the air directly, a mono-compartment MFC eradicates

Two-compartment MFCs are frequently run in a batch before equilibrium is established to produce energy in the MFC device with a well-defined chemical media such as glucose or acetate. Once the stability is maintained the dairy wastewater is pumped into the anodic chamber continuously through a peristaltic pump, which is currently only being used in the laboratories. A standard twocompartment MFC has two chambers one for the anode and the other for the cathode linked by a PEM or a salt bridge, to enable protons to travel to the cathode whilst preventing oxygen diffusion towards the anode. The compartments would be taking numerous functional forms. Mansoorian et al. [96] constructed noncatalyst and non-mediator membrane microbial fuel cell (CAML-MMFC), as seen in **Figure 3**, for simultaneous treatment of wastewater and bioelectricity production. The CAML-MMFC was equipped with two chambers with an anaerobic anode and aerobic cathode container and divided from one another by a proton exchange membrane. The chambers were constructed of plexiglass sheets 2 cm in diameter, each with an effective volume of 2 L with the gaskets tightly sealed. The anode and

cathode electrodes were formed from a graphite plate 14 × 6 × 0.5 cm3

copper wire 2 mm in diameter and 35 cm in total.

*The schematic view of the CAML-MMFC reactor (adapted from [96]).*

trode in the anode was 5 cm from the membrane, and the electrode in the cathode was 2 cm from the membrane. Via a resistance, the electrodes were attached to

Jadhav et al. [97] used a cow urine administered another type of dual-chambered MFC with an outer cathodic chamber volume of 2.5 L, made of a plastic bucket and

. The elec-

**11. MFC components**

the need for the cathode chamber.

**12. Two-compartment MFC systems**

**114**

**Figure 3.**

*Dual chambered MFC treating cow urine as a substrate in the anodic chamber (adapted from [97]).*

#### **Figure 5.**

*Schematic drawing of the MFC reactor. (1) Graphite fiber brush; (2) graphite granules; (3) proton exchange membrane (PEM); (4) Ag/AgCl reference; (5) blade stirrer; (6) air; (7) air bubbles; (8) external resistance; (9) inlet; (10) outlet (adapted from [98]).*

inner clay container as an anodic chamber with a working volume of 0.4 L as seen in **Figure 4**. The substance of the clayware pot wall itself worked as a separator between the anodized chamber and the cathodic chamber. The anode and cathode are constructed of carbon felt with 394 cm<sup>2</sup> and 755 cm2 of estimated surface area, respectively.

Zhang et al. [98] constructed a novel design for the treatment of dairy manure as shown in **Figure 5**. The MFC consisted of one cylinder (Ø100 mm × 90 mm, anode compartment with two identical square vision windows (80 mm × 80 mm)) and two rectangular cubes (80 mm × 80 mm × 50 mm, two cathode compartments attached to a Plexiglas conduit (Ø20 mm) and a catholic compartment passing freely between them). The anode and the cathode compartments were divided by two proton exchange membranes (PEM) with the same cross-sectional region (80 mm = 6400 mm<sup>2</sup> ). The cathode chambers were constantly aerated at 300 ml min−1, to maintain dissolved oxygen at the cathode, and the anolyte was agitated with a blade stirrer (300 rpm) every other hour. The anodic and cathodic chamber had appropriate volumes of 617 ml and 321 ml.

#### **13. Single-compartment MFC systems**

Owing to their complicated architectures, two-compartment MFCs are challenging to scale up, but they can be run either in batch or continuous mode. One compartment of the MFCs provides simplified layout and cost savings. Typically they provide just an anodic chamber in a cathodic chamber without aeration need. Mohanakrishna et al. [35] fabricated single-chamber MFC with "perspex" material with a total working volume of 0.54/0.48 L operated under fed-batch mode in an anaerobic microenvironment (**Figure 6**). Plain graphite plates (5 cm × 5 cm; 1 cm thick; surface area 70cm2 ) were used as electrodes without coating along with NAFION 117 (Sigma–Aldrich) as proton exchange membrane sandwiched between anode and cathode duly after pre-treatment. Whereas the bottom portion was connected to PEM and exposed to liquid, the top section of the cathode was exposed to sunlight. The anode was mounted below the PEM and submerged in the wastewater absolutely. After sealing with epoxy sealant copper wires were used for contact with electrodes. In order to maintain the anaerobic microenvironment in the anode compartment, leak-proof sealing was provided at the joints. Provisions for the sampling ports, wire input points (top), inlet and outlet ports have been developed.

Mardanpour et al. [36] fabricated a unique annular single chamber microbial fuel cell (ASCMFC) with the spiral anode (**Figure 7**). They used stainless steel mesh coated with graphite as an anode material. The dimensions of the chamber were 3 cm in height, 7.1 cm internal diameter, and 8 cm external diameter. The volume of the anaerobic chamber was 90 cm3 . The anode electrode (63 cm × 2 cm) was composed of stainless steel mesh coated with graphite (mesh 300).

#### **Figure 6.**

*Schematic details of non-catalyzed single-chambered microbial fuel cell (MFC) used in this study with measurement circuits [FT, wastewater feeding tank; DT, decant tank; VR, variable resister; A, ammeter; V, voltmeter; T, pre-programmed timer; P, peristaltic pump; PEM, proton exchange membrane (NAFION 117)] (adapted from [35]).*

#### **Figure 7.**

*Schematic diagram of annular single chamber microbial fuel cell (ASCMFC) with the spiral anode (adapted from [36]).*

**117**

m2

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

In MFC performance, microbial metabolism at anode plays a significant role. Each metabolism follows its metabolic pathway for generating energy, varying the capacity to generate power. The MFC was maintained at an initial concentration of 1601 mg/L COD and a pH 7 anolyte. Phosphate buffer at 10 mM working concentration was used to control anolyte pH. The voltage could be quickly produced in the MFC during the treatment of aerobic as well as anaerobic anodic metabolism in dairy wastewater. Nearly 760 and 780 mV of OCV was recorded for anaerobic and aerobic metabolism, respectively. Considering both aerobic and anaerobic anodic processes, the maximal OCV was observed from the first cycle of operation. Various studies [36, 99] showed the need of lag phase by microbes after which maximal OCV was obtained. The eradication of requirements for the lag phase may be a determinative result of using inherent microorganism of dairy wastewater which limits the microbial growth adaptation phase. MFC's behavior marks a chance to generate current from the first cycle of operation. However, in power generation there was a clear difference when specific anodic metabolism was used. The polarization data suggests that both the MFCs produced maximal power density of external resistance at 470 ohm; for aerobic and anaerobic metabolism it was recorded as

respectively. The COD removal efficiency obtained was 91%

and 92% for anaerobic and aerobic metabolism in a week's time respectively. The efficiency of conversion of chemical to electrical energy was 3.7 folds lower than anaerobic metabolism with 17.15% efficiency making it the major flaw in the aerobic system. In aerobic mode, oxygen was used by the microbes as terminal electron acceptor, which resulted in the loss of electrons reducing CE. While the CE for aerobic metabolism was much lower than anaerobic metabolism it could generate higher power density, this may be the product of aerobic bacteria's fast growth and rapid metabolic activity, resulting in a higher concentration of protons and production of electrons. The speedier removal of COD by aerobic metabolism results from

Anolyte system using a 10 mM concentration phosphate buffer (pH 6.9) reduces the initial anolyte concentration to 7.2 showing a gradual reduction of pH to 6.9 in 8 days. Utilizing orthophosphoric acid, the pH was set to 7 when the device was run in the absence of buffer. The pH variations were found to be crucial in the absence of buffer. In the absence of a buffer system, the MFC pH gradually increased to 7.51 on the 3rd day, and then fell to 7.03 on the 6th day. Though the efficiency of treatment and OCV was the same, a clear difference was observed in system polarization. The MFC's average power density without buffer was 85.97 mW/m<sup>2</sup> which was almost half the system output using a buffer configuration for 161 mW/

 of pH maintenance. The requirement of 8-day batch time for both reactors for 90% COD reduction demonstrated that the pH buffer removal did not affect the bacterial activity. In MFC, the citrate and phosphates remain as proton carriers. While for these carriers the diffusion coefficient is smaller, the concentration gradient is higher across the membrane. In cathode chamber, the concentration gradient is higher due to the deficiency of citrate and phosphates. Due to improved

**14.1 Performance of MFC under different anodic metabolism**

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

**14. Operation parameter**

196 and 162 mW/m<sup>2</sup>

rapid use of substrates [99].

**14.2 Effect of anolyte pH**

*14.2.1 MFC operation without pH buffer*

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