1. Please check and comment entries here.
Table of Contents

    Topic review

    Microbial Fuel Cell and Wastewater

    Submitted by: N. Evelin Paucar


    In recent years, wastewater has been considered as a renewable resource of water, nutrients, and energy. Domestic wastewater is estimated to contain 13 kJ/g of COD of chemical energy, which is nine fold more than the energy required to treat it (Heidrich et al., 2010; Yang et al., 2018). Therefore, if its energy were effectively recovered, no external energy input would be required to operate WWTPs.

    1. Introduction

    Water, energy, and food are essential for all living forms to survive and thrive, and they are inseparably linked. Although humans have made great strides in securing those resources, the world is facing an uphill battle due largely to the increasing human population and climate change. By the next decade, the world is expected to face 40% freshwater and 36% energy shortages [1][2], together with increasing demand for food [3][4] and treatment of wastewater.

    In recent years, wastewater has been considered as a renewable resource of water [5], nutrients, and energy [5][6][7][8][9][10]. Domestic wastewater is estimated to contain 13 kJ/g of COD of chemical energy, which is nine fold more than the energy required to treat it (Heidrich et al. , 2010; Yang et al., 2018). Therefore, if its energy were effectively recovered, no external energy input would be required to operate WWTPs [11][12].

    The increase of atmospheric pollution partly due to the emission of sulfur and nitrogen oxides during fuel combustions may induce irreparable damages to the earth [13][14]. To overcome the energy and environmental crisis caused by the utilization of fossil fuels, a new energy revolution based on renewable resources is beginning to take shape, with electricity as the backbone of energy.

    The discharge of wastewater containing high levels of nutrients and organics to a receiving water body is a potential cause of eutrophication and hypoxia in the water environment [15][16]. Therefore, nutrients such as phosphate (PO 43− ) and ammonium (NH 4+ ) are being removed or recovered in WWTPs using methods that require large energy input in order to meet the discharge requirements [17].

    2. Microbial Fuel Cell

    The EAB act as a biocatalyst for the oxidation of substrate and transferring electrons to the anode [18][19][20]. Microscopic observations have revealed that EAB proliferates over the anode surface to form a multi-layered biofilm [21][22]. The EAB in the monolayer biofilm that is in direct contact with the anode typically utilizes outer-membrane redox proteins and cytochrome cascades to transfer electrons directly to the anode [23]. On the other hand, the microbes in the outer layers develop nanowire structures to connect with the anode surface or use other microbes via an extracellular conductive matrix to transfer electrons, known as interspecies electron transfer [24][25]. In addition to the direct electron transfer, the indirect transfer can also occur via soluble electron shuttles or mediators that transfer extracellular electrons to the anode [26][27]. Based on electron transfer mediators, MFCs can be divided into mediator and non-mediator (or mediator-less) microbial fuel cells. There are two main types of mediators added to microbial fuel cells. The first category is synthetic mediators, mainly dye-based substances, such as phenazine, phenothiazine, indophenol, and thionine [28]. The second type is those synthesized by microorganisms and used by the same organisms or by other organisms for transferring electrons. For instance, Pseudomonas aeruginosa strain KRP1 synthesizes mediator substances such as pyocyanin and phenazine-1-carboxamide [29].

    The cathode chamber contains electron acceptors (e.g., O 2) to facilitate reduction reactions, typically given as [30]: 2H 2O + O 2 + 4e − → 4OH − (3)

    While electrons flow through the external circuit, protons pass through the PEM to react with oxygen to form water molecules in the cathode chamber [31][32]: 2H + + 2e − + O 2 → 2H 2O (4)

    Given the facts that domestic, agricultural, and industrial wastewaters contain various substrates that can serve as a renewable fuel source for MFCs [33][34] and that MFCs have the potential ability to capture a large faction of chemical energy from wastewater [35][12], MFCs can be self-sustaining wastewater treatment technologies that require no external power sources [36]. Specifically, as compared to the conventional wastewater treatment, the MFC technology offers the following potential advantages: (a) Energy-saving—MFCs require no or reduced aeration [37][38][39][40][41][42][43]; (b) Production of less sludge [38][43][44][45][46][47]—MFCs produce less sludge compared to the conventional activated sludge processes [39][40] or even anaerobic digestion processes [37][41][42]. In an MFC, a large fraction of the organic mass in wastewater is converted to electrical energy at a high conversion efficiency [39][40][41][42][43][46][48] with faster reaction kinetics [38]; (c) No generation of harmful toxic byproducts [49][50] such as trihalomethanes (THMs) produced in the chlorination of wastewater [51]; (d) Ability to recover valuable products from wastewater; i.e., electricity [43][46][48] and nutrients [11][15][52][53]; (e) Easy operation under the different conditions [49] such as various temperatures [39] even at low temperatures [37][41][42], various pH values, and with diverse biomass [39]; (f) Clean and efficient technology [49][50]. MFCs can produce electricity with less environmental burdens and a low carbon footprint [54][37][45].

    Despite the inherent limitations of MFC technology, overall, it possesses several advantages over conventional wastewater treatment methods, and thus, it is gaining recognition as a potential sustainable wastewater treatment technology. The new advanced electrode materials such as 2D nanomaterials are expected to promote the development of electromicrobiology [50].

    3. Energy Generation by MFCs

    The typical biological factors are the types, numbers, and catalytic activity of the microorganisms in the MFC. The energy losses at the anode can be attributed to the loss of electrochemical activity of the microorganisms [55] and the anode overpotential transport loss [56]. The physicochemical and electrochemical factors include, but are not limited to, the types and effective surface area of the electrode, electrolytic resistance [50], rate of the proton transport through the PEM, rate of the reduction reaction at the cathode [38][57], and external resistance applied across the electrodes [58][59][60]. The organic loading rates [12][61][62][63], and type and concentration of the substrate are the operational parameters. The intricate interdependence of these factors and parameters makes the optimization of the MFC difficult. For instance, the rate of substrate conversion can be affected by the total amount of electroactive bacterial cells, a phenomenon of mixing mass transfer, bacterial growth kinetics [64][65][66], organic loading rate per biomass (grams of substrate per gram of biomass per day), transmembrane efficiency for the proton transport [67], and total potential of the MFC [64][68].

    Internal resistance is one of the major electrochemical factors that affect MFC performance. The internal resistance can be divided into ohmic resistance, charge transfer resistance, and diffusion resistance [69][70]. The ohmic losses occur due to the resistances of the electrodes, PEM, and electrolytes [71]. On the other hand, the charge transfer and diffusion resistance take place in the interface between the electrodes and the surrounding electrolyte [72][73]. The power generation in an MFC is affected by the surface area of the PEM [74]. If the surface area of the PEM is smaller than that of the electrodes (anode and cathode), the internal resistance of the MFC will increase to limit power output [71]. Internal resistance is also a function of the distance between the cathode and anode. For the optimal design, the anode and cathode should be situated as close as possible.

    In a dual-chamber MFC, the higher COD loading to the anode chamber can lead to membrane fouling adversely affecting its performance [75]. In contrast, lower COD loadings could facilitate higher electricity generation [63][76]. It has also been found that at low OLRs, MFCs require more time to reach their maximum performance (i.e., maximum current density and maximum power density) [77]. The Coulombic efficiency can be optimized by improving the electrode surface area per reactor volume [46][78].

    In an MFC, the external resistance regulates the flow of electrons and consequently regulates the power generation efficiency. In other words, the lower resistance facilitates the electron flow from the anode to the cathode, supporting the microbial electron respiration on the anode, thus enhances the substrate removal efficiency [61][59]. On the other hand, the higher resistance reduces electron flow towards the cathode maintaining a high potential difference, thus enhances the power harvest [58][60][79]. The low voltage at a high external resistance may be due to the slower speed of electrons used on the cathode, compared to its transfer rate [61]. The maximum power density is achieved when the internal and external resistances are equal [80][81]. Various factors such as the distance between the electrodes, electrode material, ionic strength of the anolyte and catholyte, substrate properties, operation modes, and MFC design affect the internal resistance of MFCs. The optimization of these factors can improve the MFC performance. In general, a single-chamber MFC exhibits lower internal resistance than the dual-chamber MFC: such information should be taken into consideration when designing MFC systems [69].

    4. Nutrient Removal and Recovery

    The removal of nutrients from the WWTP effluent can reduce the eutrophication potential in the receiving water environment. In comparison with energy-intensive nutrient removal technologies currently employed in the conventional WWTPs, MFCs have the advantage that they generate electricity. The effectiveness of different types of MFCs for the removal and/or recovery of nutrients from various wastewaters and operational conditions are summarized in Table 1 .

    Table 1. MFCs for nutrient removal/recovery from different types of wastewaters and operational conditions.
    Type of Wastewater System Type/Operation Mode Initial Wastewater Characteristics COD Removal/HRT NH4+-N Removal/Recovery PO43-P Removal/Recovery Reference
    Synthetic wastewater Mediator-less dual chamber MFC
    2-stage feed-batch mode
    (Two sets of dual-chamber H-type bottles, operated for 120 days)
    COD: 1.5 g/L
    pH: >8
    HRT = 48 h
    --------------- 38% recovery [53]
    Primary effluent of municipal wastewater 200 L Modularized MFC system (96 tubular MFC modules of 2 L/each)
    Continuous mode, operated for one-year
    TCOD: 155 ± 37 mg/L
    SCOD: 73 ± 23 mg/L
    NH4+: 25.7 ± 5.5 mg/L
    TSS: 72.9 ± 16.6 mg/L
    pH: >8
    HRT = 18 h
    68% removal ~20% biomass uptake [7]
    Dairy industrial wastewater Catalyst-less and mediator-less membrane dual chamber MFC.
    Continuous mode.
    COD: 3620 mg/L
    NH4+: 174 mg/L
    Total P: 187 mg/L
    NH3: 167 mg/L
    TSS: 1430 mg/L
    VSS: 647 mg/L
    BOD5: 2115 mg/L
    pH: 8.5–10.3
    90.46% 69.43% removal Removal efficiencies: 31.18% dissolved phosphorus, 72.45% phosphorus in suspended solids [61]
    Untreated human urine 3-stage MFC system in a continuous mode
    (System of MFCs that fits urinals).
    NH4+: 363 mg/L
    PO43−: 202 mg/L
    HRT = 18 min for individual MFCs for 5 days
    20% removal
    7% recovery
    82% removal
    78% recovery
    Domestic wastewater Algal biofilm MFC.
    Continuous mode.
    COD: 186.8 327.9 mg/L
    Total N: 25.3–52.5 mg/L
    Total P: 2.9–8.3 mg/L
    HRT = 12 days
    TN removal: 95.5%
    50% recovered by harvested algae
    TP removal: 96.4%
    62% recovered by harvested algae
    Effluent drain of vegetable oil industry Dual chambered MFC.
    Batch mode at 35 °C.
    pH: 5.7
    TDS: 517 mg/L
    TSS: 252 mg/L
    40–80% at 25 °C
    HRT = 72 h
    --------------- 73.6% removal
    56.9% at 25 °C
    Digestate coming from an anaerobic digester MET (MFC or MEC) coupled with struvite crystallization using seawater bitterns (SWB).
    Single chamber, air-cathode MFC batch mode.
    NH4+: 1943 ± 53 mg/L
    PO4+−: 60 ± 3 mg/L
    COD: 7.2 ± 1.6 g/L
    44.7 ± 1.6% MFC: 10.1 ± 0.5% removal
    Further removal by precipitation: 14.7 ± 0.6%
    MFC: 35.8 ± 1.2% removal
    Further removal by precipitation: 83.1 ± 3.7%
    Pre-hydrolyzed human urine Electrodialysis system embedded in an MFC.
    Continuous mode.
    NH4+: 7.8 g/L
    PO4+−: 0.33 g/L
    TCOD: 9.5 g/L
    pH = 8.8
    40–65 days 1.2% recovery 0.002% recovery [6]
    Synthetic domestic wastewater Photoautotrophic H-type MFC.
    Continuous mode.
    Inoculated microalgal biomass: 0.75 g/L 93.2%
    HRT = 11.8 h
    95.9% removed in anodic chamber.
    27.7–50.0% removed/recovery in cathodic chamber by microalgae.
    82.7% removed in anodic chamber.
    37.1–67.9% removed/recovery in cathodic chamber by microalgae.
    Synthetic domestic wastewater Double-chamber MFC.
    Continuous mode.
    COD: 300–600 mg/L
    OLR: 435–870 mg COD/L.d
    90% (from a wide range of organic loading rate (435 to 870 mg COD/L.d).
    HRT = 0.69 d
    Removed in anode chamber: 14% at OLR of 435 mg COD/L.d and
    75.13% at OLR of 870 mg COD/L.d.
    Recovered in cathode chamber: 85.11% at OLR of 435 mg COD/L.d and
    24.34% at OLR of 870 mg COD/L.d.
    Removed in anode chamber: 12.43% at OLR of 435 mg COD/L.d and
    71.5% at OLR of 870 mg COD/L.d.
    Recovered in cathode chamber: 24.4% average recovery.
    Synthetic municipal wastewater Double–compartment MFC.
    Continuous mode.
    COD: 300 ± 15 mg/L
    NH4+-N: 5–40 mg/L
    OLR: 435 mg COD/L.d
    >85% for wide range of NH4+-N concentrations (5 to 40 mg/L).
    HRT = 0.69 d
    Removal: ~14% at 5 mg. NH4+-N/L and ~14.10% at 40 mg.NH4+-N/L.
    Recovery: 85.11% at 5 mg. NH4+-N/L and 15.33% at 40 mg. NH4+-N/L.
    Removal: ~12.45% at 5 mg. NH4+-N/L and 13.33% at 40 mg.NH4+-N/L.
    Recovery: 83.23% at 5 mg. NH4+-N/L and 80.5% at 40 mg.NH4+-N/L.
    Synthetic urine-containing wastewater Three-chamber resource recovery MFC.
    Batch mode.
    COD: 24.60 mg
    NH4+: 0.10 mg
    TN: 20.20 mg
    PO4+−: 0.90 mg
    pH: 6.9
    HRT = ~3 days
    40% of NH4+ removed.
    98% of TN removed.
    42% of TN recovered in middle chamber
    99% removed.
    37% recovered in middle chamber.
    Synthetic municipal wastewater Two-chambered MFC.
    Continuous mode.
    COD: 300 ± 15 mg/L
    pH: 7.00 ± 0.02
    OLR: 435–870 mg COD/L.d
    >90% (from a wide range of organic loading rate (435 to 870 mg COD/L.d) and
    HRT = 0.69-0.35 days.
    Removed in anode chamber: 13%-15% at different OLR (435–870) mg COD/L.d) and different HRT (0.69 d-0.35 d).
    Recovered in cathode chamber: ~85% at different OLR (435–870 mg COD/L.d) and different HRT (0.69 d-0.35 d).
    Removed in anode chamber: 12–14% at different OLR (435–870 mg COD/L.d) and different HRT (0.69 d–0.35 d).
    Recovered in cathode chamber: ~83% at different OLR (435–870 mg COD/L.d) and different HRT (0.69 d-0.35 d).

    To date, only a few studies have been undertaken to recover nutrients using MFCs [6][8][10][12][52][85][86]. The recovery of P and N by MFCs has been accomplished mainly by the formation of struvite, NH 4MgPO 4.6H 2O [83][86][87][88][89][90]. Struvite has been demonstrated to be slow-release fertilizer [91] and has a commercial value [92][93][94][95].

    In a dual-chamber MFC, nutrient removal usually occurs in the anode chamber and recovery in the cathode chamber [12][52][84]. Almatouq & Babatunde [53] investigated the P recovery and electricity generation using a two-stage, mediator-less dual-chamber MFC system, which was operated in a fed-batch mode. In the first cycle, synthetic wastewater was fed to the anode chamber to remove organics (measured as COD). At the end of the first cycle, the effluent from the anode chamber was filtered and fed to the cathode chamber to recover P as struvite. In their study, 8 mM of NH 4Cl and 8 mM of MgCl 2 solutions were added to the cathode chamber at a rate of 6 mL/day. When the COD concentration was increased from 0.7 to 1.5 g/L, the P recovery efficiency increased from 7% to as high as 38%. The reported power density is 72 mW/m 2 [53]. The COD concentration and aeration rate were shown to be the key factors that affect the P recovery and electricity generation. Since the dual-chamber MFC creates an alkaline environment around the cathode, it provides better nutrient recovery efficiencies [96].

    Human urine typically contains 9 g of NH 4+ -N/L, 0.7 g of PO 43− -P/L, and other constituents, and has been used as an electrolyte in an MFC for nutrient recovery system [97][98]. In a study by You et al. [15] nutrients were recovered from human urine in a form of struvite, while generating electricity, using a 3-stage single-chamber MFC/struvite extraction system. The first and third stage MFCs generated 14.32 W/m 3 and 11.76 W/m 3 of power, respectively. The second stage MFC was used for nutrient recovery. The hydrolysis reaction of urea was accelerated in the first stage. In the second stage, magnesium was added to form struvite. In the third stage, after the completion of struvite precipitation, the supernatant was treated for additional power generation and COD removal. In their work, 78% of PO 43− -P and 7% of NH 4+ -N were recovered as struvite. Overall, 82% of PO 43− -P and 20% of COD were removed from human urine. Lu et al. (2019) developed a three-chamber MFC (called a recovery resource MFC or RRMFC) and used it to remove organics and salts, simultaneously recovering nutrients from synthetic wastewater containing urine. The RRMFC consisted of three chambers (anode, middle-recovery, and cathode chambers), and was operated in a batch mode for 33 cycles (~3 days per cycle). Synthetic urine wastewater was fed to the anode chamber where organics were oxidized, and urine was hydrolyzed. Deionized water was fed to the middle chamber where PO 43− and NH 4+ were precipitated as struvite. The effluent of the anode chamber was fed to the cathode chamber for power generation. In their system, the removal efficiencies of COD, NH 4+ , total N, and PO 43− reached 97%, 40%, 98%, and 99%, respectively. At the same time, the RRMFC recovered 42% of total N and 37% of PO 43− in the middle chamber. The NH 4+ mass increased from 0 to 9.01 ± 2.12 mg in the middle chamber, indicating that a large amount of NH 4+ migrated from the anode chamber to the middle chamber through the PEM. Similarly, PO 43− migrated from the cathode chamber to the middle chamber with the effect of the electric field. The decrease of the PO 43− concentration in the cathode chamber may be due to struvite precipitation under the alkali conditions [8]. A fraction of PO 43− may also be removed by microbial assimilation in the anode chamber [99]. The RRMFC produced the maximum currents of 1.30 ± 0.30 mA and maximum power density of 1300 mW/m 2 of the anode surface at an external resistance of 10 Ω. The RRMFC did not require any external energy input for its operation (Lu et al., 2019). Freguia et al. [6] used an MFC/electrodialysis-hybrid system for nutrient recovery from human urine. The fresh urine was left to hydrolyze before the supernatant was collected and used as a feed to the microbial electro-concentration cells. In their study, only about 5% of the influent flow passed through the PEM resulting in a poor nutrient recovery (i.e., the recovery of 1.2% of N and 0.002% of P). It is noteworthy that, if they were designed as an on-site system, their processes not only generate power and recover nutrients, but also save a large amount of water that is necessary to flush and transport urine to a central treatment facility.

    The entry is from 10.3390/pr9081318


    1. Reddy, C.D.; Nguyen, H.T.; Noori, M.T.; Min, B. Potential applications of algae in the cathode of microbial fuel cells for enhanced electricity generation with simultaneous nutrient removal and algae biorefinery: Current statues and future perspectives. Bioresour. Technol. 2019, 292, 122010.
    2. Jingyu, H.; Miwornunyuie, N.; Ewusi-Mensah, D.; Koomson, D.A. Assessing the factors influencing the performance of constructed wetland-microbial fuel cell integration. Water Sci. Technol. 2020, 81, 631–643.
    3. UN Environment Annual Report 2017. Available online: https://www.unenvironment.org/annualreport/2017/index.php (accessed on 20 March 2020).
    4. Tilman, D.; Balzer, C.; Hill, J.; Befort, B.L. Global food demand and the sustainable intensification of agriculture. Proc. Natl. Acad. Sci. USA 2011, 108, 20260–20264.
    5. Shannon, M.A.; Bohn, P.W.; Elimelech, M.; Georgiadis, J.G.; Mariñas, B.J.; Mayes, A.M. Science and technology for water purification in the coming decades. Nat. Cell Biol. 2008, 452, 301–310.
    6. Freguia, S.; Logrieco, M.E.; Monetti, J.; Ledezma, P.; Virdis, B.; Tsujimura, S. Self-powered bioelectrochemical nutrient recovery for fertilizer generation from human urine. Sustainability 2019, 11, 5490.
    7. Ge, Z.; He, Z. Long-term performance of a 200 liter modularized microbial fuel cell system treating municipal wastewater: Treatment, energy, and cost. Environ. Sci. Water Res. Technol. 2016, 2, 274–281.
    8. Lu, S.; Li, H.; Tan, G.; Wen, F.; Flynn, M.T.; Zhu, X. Resource recovery microbial fuel cells for urine-containing wastewater treatment without external energy consumption. Chem. Eng. J. 2019, 373, 1072–1080.
    9. Yan, T.; Ye, Y.; Ma, H.; Zhang, Y.; Guo, W.; Du, B.; Wei, Q.; Wei, D.; Ngo, H.H. A critical review on membrane hybrid system for nutrient recovery from wastewater. Chem. Eng. J. 2018, 348, 143–156.
    10. Ye, Y.; Ngo, H.H.; Guo, W.; Chang, S.W.; Nguyen, D.D.; Zhang, X.; Zhang, S.; Luo, G.; Liu, Y. Impacts of hydraulic retention time on a continuous flow mode dual-chamber microbial fuel cell for recovering nutrients from municipal wastewater. Sci. Total Environ. 2020, 734, 139220.
    11. Yang, Z.; Pei, H.; Hou, Q.; Jiang, L.; Zhang, L.; Nie, C. Algal biofilm-assisted microbial fuel cell to enhance domestic wastewater treatment: Nutrient, organics removal and bioenergy production. Chem. Eng. J. 2018, 332, 277–285.
    12. Ye, Y.; Ngo, H.H.; Guo, W.; Chang, S.W.; Nguyen, D.D.; Liu, Y.; Nghiem, L.; Zhang, X.; Wang, J. Effect of organic loading rate on the recovery of nutrients and energy in a dual-chamber microbial fuel cell. Bioresour. Technol. 2019, 281, 367–373.
    13. Brito, P.S.D.; Sequeira, C.A.C. Electrochemical generators and the environment. Fuel cells and metal/air batteries. Stud. Environ. Sci. 1994, 59, 203–221.
    14. Paucar, N.E.; Kiggins, P.; Blad, B.; De Jesus, K.; Afrin, F.; Pashikanti, S.; Sharma, K. Ionic liquids for the removal of sulfur and nitrogen compounds in fuels: A review. Environ. Chem. Lett. 2020, 19, 1205–1228.
    15. You, J.; Greenman, J.; Melhuish, C.; Ieropoulos, I. Electricity generation and struvite recovery from human urine using microbial fuel cells. J. Chem. Technol. Biotechnol. 2016, 91, 647–654.
    16. Zhou, Y.; Wang, L.; Zhou, Y.; Mao, X.Z. Eutrophication control strategies for highly anthropogenic influenced coastal waters. Sci. Total Environ. 2020, 705, 135760.
    17. Chen, X.; Zhou, H.; Zuo, K.; Zhou, Y.; Wang, Q.; Sun, D.; Gao, Y.; Liang, P.; Zhang, X.; Ren, Z.J.; et al. Self-sustaining advanced wastewater purification and simultaneous in situ nutrient recovery in a novel bioelectrochemical system. Chem. Eng. J. 2017, 330, 692–697.
    18. Nimje, V.R.; Chen, C.Y.; Chen, H.R.; Chen, C.C.; Huang, Y.M.; Tseng, M.J.; Cheng, K.C.; Chang, Y.F. Comparative bioelectricity production from various wastewaters in microbial fuel cells using mixed cultures and a pure strain of Shewanella oneidensis. Bioresour. Technol. 2012, 104, 315–323.
    19. Zhi, W.; Ge, Z.; He, Z.; Zhang, H. Methods for understanding microbial community structures and functions in microbial fuel cells: A review. Bioresour. Technol. 2014, 171, 461–468.
    20. Walter, X.A.; Greenman, J.; Ieropoulos, I.A. Microbial fuel cells directly powering a microcomputer. J. Power Sources 2020, 446, 227328.
    21. Corbella, C.; Garfi, M.; Puigagut, J. Vertical redox profiles in treatment wetlands as function of hydraulic regime and macrophytes presence: Surveying the optimal scenario for microbial fuel cell implementation. Sci. Total Environ. 2014, 470, 754–758.
    22. Li, Z.; Haynes, R.; Sato, E.; Shields, M.S.; Fujita, Y.; Sato, C. Microbial community analysis of a single chamber microbial fuel cell using potato wastewater. Water Environ. Res. 2014, 86, 324–330.
    23. Logan, B.E. Exoelectrogenic bacteria that power microbial fuel cells. Nat. Rev. Microbiol. 2009, 7, 375–381.
    24. Bonanni, P.S.; Schrott, G.D.; Robuschi, L.; Busalmen, J.P. Charge accumulation and electron transfer kinetics in Geobacter sulfurreducens biofilms. Energy Environ. Sci. 2012, 5, 6188–6195.
    25. Busalmen, J.P.; Esteve-Nuñez, A.; Feliu, J.M. Whole cell electrochemistry of electricity-producing microorganisms evidence an adaptation for optimal exocellular electron transport. Environ. Sci. Technol. 2008, 42, 2445–2450.
    26. Arends, J.B.; Verstraete, W. 100 years of microbial electricity production: Three concepts for the future. Microb. Biotechnol. 2012, 5, 333–346.
    27. Ramírez-Vargas, C.A.; Arias, C.A.; Zhang, L.; Brix, H. Microbial community function in electroactive biofilm-based constructed wetlands. Biogeosci. Discuss. 2018, 1–28.
    28. Delaney, G.M.; Bennetto, H.P.; Mason, J.R.; Roller, S.D.; Stirling, J.L.; Thurston, C.F. Electron-transfer coupling in microbial fuel cells. 2. Performance of fuel cells containing selected microorganism-mediator-substrate combinations. J. Chem. Technol. Biotechnol. 1984, 34, 13–27.
    29. Bosire, E.M.; Blank, L.M.; Rosenbaum, M.A. Strain-and substrate-dependent redox mediator and electricity production by Pseudomonas aeruginosa. Appl. Environ. Microbiol. 2016, 82, 5026–5038.
    30. Heijne, A.T.; Liu, F.; Weijden, R.V.D.; Weijma, J.; Buisman, C.J.; Hamelers, H.V. Copper recovery combined with electricity production in a microbial fuel cell. Environ. Sci. Technol. 2010, 44, 4376–4381.
    31. Das, S.; Mangwani, N. Recent developments in microbial fuel cells: A review. J. Sci. Ind. Res. 2010, 69, 727–731.
    32. Sharma, Y.; Li, B. Optimizing energy harvest in wastewater treatment by combining anaerobic hydrogen producing biofermentor (HPB) and microbial fuel cell (MFC). Int. J. Hydrogen Energy 2010, 35, 3789–3797.
    33. Pant, D.; van Bogaert, G.; Diels, L. A review of the substrates used in microbial fuel cells (MFCs) for sustainable energy production. Bioresour. Technol. 2010, 101, 1533–1543.
    34. Pandey, P.; Shinde, V.N.; Deopurkar, R.L.; Kale, S.P.; Patil, S.A.; Pant, D. Recent advances in the use of different substrates in microbial fuel cells toward wastewater treatment and simultaneous energy recovery. Appl. Energy 2016, 168, 706–723.
    35. Callegari, A.; Cecconet, D.; Molognoni, D.; Capodaglio, A.G. Sustainable processing of dairy wastewater: Long-term pilot application of a bio-electrochemical system. J. Clean. Prod. 2018, 189, 563–569.
    36. Akiba, T.; Bennetto, H.P.; Stirling, J.L.; Tanaka, K. Electricity production from alkalophilic organisms. Biotechnol. Lett. 1987, 9, 611–616.
    37. Dong, Y.; Qu, Y.; He, W.; Du, Y.; Liu, J.; Han, X.; Feng, Y. A 90-liter stackable baffled microbial fuel cell for brewery wastewater treatment based on energy self-sufficient mode. Bioresour. Technol. 2015, 195, 66–72.
    38. Gil, G.C.; Chang, I.S.; Kim, B.H.; Kim, M.; Jang, J.K.; Park, H.S.; Kim, H.J. Operational parameters affecting the performance of a mediator-less microbial fuel cell. Biosens. Bioelectron. 2003, 18, 327–334.
    39. He, L.; Du, P.; Chen, Y.; Lu, H.; Cheng, X.; Chang, B.; Wang, Z. Advances in microbial fuel cells for wastewater treatment. Renew. Sustain. Energy Rev. 2017, 71, 388–403.
    40. Li, W.W.; Yu, H.Q.; He, Z. Towards sustainable wastewater treatment by using microbial fuel cells-centered technologies. Energy Environ. Sci. 2014, 7, 911–924.
    41. Lu, M.; Chen, S.; Babanova, S.; Phadke, S.; Salvacion, M.; Mirhosseini, A.; Chan, S.; Carpenter, K.; Cortese, R.; Bretschger, O. Long-term performance of a 20-L continuous flow microbial fuel cell for treatment of brewery wastewater. J. Power Sources 2017, 356, 274–287.
    42. Seo, Y.; Kang, H.; Chang, S.; Lee, Y.-Y.; Cho, K.-S. Effects of nitrate and sulfate on the performance and bacterial community structure of membrane-less single-chamber air-cathode microbial fuel cells. J. Environ. Sci. Health Part A 2017, 53, 13–24.
    43. Zhang, Y.; Liu, M.; Zhou, M.; Yang, H.; Liang, L.; Gu, T. Microbial fuel cell hybrid systems for wastewater treatment and bioenergy production: Synergistic effects, mechanisms and challenges. Renew. Sustain. Energy Rev. 2019, 103, 13–29.
    44. Kim, B.H.; Chang, I.S.; Gadd, G.M. Challenges in microbial fuel cell development and operation. Appl. Microbiol. Biotechnol. 2007, 76, 485–494.
    45. Lefebvre, O.; Shen, Y.; Tan, Z.; Uzabiaga, A.; Chang, I.S.; Ng, H.Y. A comparison of membranes and enrichment strategies for microbial fuel cells. Bioresour Technol. 2011, 102, 6291–6294.
    46. Rabaey, K.; Verstraete, W. Microbial fuel cells: Novel biotechnology for energy generation. Trends Biotechnol. 2005, 23, 291–298.
    47. Zhang, F.; Ge, Z.; Grimaud, J.; Hurst, J.; He, Z. Long-Term Performance of Liter-Scale Microbial Fuel Cells Treating Primary Effluent Installed in a Municipal Wastewater Treatment Facility. Environ. Sci. Technol. 2013, 47, 4941–4948.
    48. Do, M.H.; Ngo, H.H.; Guo, W.S.; Liu, Y.; Chang, S.W.; Nguyen, D.D.; Nghiem, L.D.; Ni, B.J. Challenges in the application of microbial fuel cells to wastewater treatment and energy production: A mini review. Sci. Total Environ. 2018, 639, 910–920.
    49. Jadhav, G.S.; Ghangrekar, M.M. performance of microbial fuel cell subjected to variation in pH, temperature, external load and substrate concentration. Bioresour. Technol. 2009, 100, 717–723.
    50. Jatoi, A.S.; Akhter, F.; Mazari, A.A.; Sabzoi, N.; Aziz, S.; Soomro, A.A.; Mubarak, N.M.; Baloch, H.; Memon, A.Q.; Ahmed, S. Advanced microbial fuel cell for waste water treatment—A review. Environ. Sci. Pollut. Res. 2020, 28, 5005–5019.
    51. Patroescu, V.; Jinescu, C.; Cosma, C.; Cristea, I.; Badescu, V.; Stefan, C.S. Influence of ammonium ion son the treatment process selection of groundwater supplies intended to human consumption. Rev. Chim. 2015, 66, 537–541.
    52. Ye, Y.; Ngo, H.H.; Guo, W.; Chang, S.W.; Nguyen, D.D.; Liu, Y.; Ni, B.-J.; Zhang, X. Microbial fuel cell for nutrient recovery and electricity generation from municipal wastewater under different ammonium concentrations. Bioresour. Technol. 2019, 292, 121992.
    53. Almatouq, A.; Babatunde, A.O. Concurrent phosphorus recovery and energy generation in mediator-less dual chamber microbial fuel cells: Mechanisms and influencing factors. Int. J. Environ. Res. Public Health 2016, 13, 375.
    54. Rossi, R.; Jones, D.; Myung, J.; Zikmund, E.; Yang, W.; Gallego, Y.A.; Pant, D.; Evans, P.J.; Page, M.A.; Cropek, D.M.; et al. Evaluating a multi-panel air cathode through electrochemical and biotic tests. Water Res. 2019, 148, 51–59.
    55. Lu, N.; Zhou, S.; Zhuang, L.; Zhang, J.; Ni, J. Electricity generation from starch processing wastewater using microbial fuel cell technology. Biochem. Eng. J. 2009, 43, 246–251.
    56. Puig, S.; Coma, M.; Desloover, J.; Boon, N.; Colprim, J.S.; Balaguer, M.D. Autotrophic denitrification in microbial fuel cells treating low ionic strength waters. Environ. Sci. Technol. 2012, 46, 2309–2315.
    57. Mardanpour, M.M.; Yaghmaei, S.; Kalantar, M. Modeling of microfluidic microbial fuel cells using quantitative bacterial transport parameters. J. Power Sources 2017, 342, 1017–1031.
    58. Corbella, C.; Puigagut, J. Improving domestic wastewater treatment efficiency with constructed wetland microbial fuel cells: Influence of anode material and external resistance. Sci. Total Environ. 2018, 631, 1406–1414.
    59. Ramírez-Vargas, C.A.; Prado, A.; Arias, C.A.; Carvalho, P.N.; Esteve-Núñez, A.; Brix, H. Microbial Electrochemical Technologies for Wastewater Treatment: Principles and Evolution from Microbial Fuel Cells to Bioelectrochemical-Based Constructed Wetlands. Water 2018, 10, 1128.
    60. Tamta, P.; Rani, N.; Yadav, A.K. Enhanced wastewater treatment and electricity generation using stacked constructed wetland-microbial fuel cells. Environ. Chem. Lett. 2020, 18, 871–879.
    61. Mansoorian, H.J.; Mahvi, A.H.; Jafari, A.J.; Khanjani, N. Evaluation of dairy industry wastewater treatment and simultaneous bioelectricity generation in a catalyst-less and mediator-less membrane microbial fuel cell. J. Saudi Chem. Soc. 2016, 20, 88–100.
    62. Di Lorenzo, M.; Scott, K.; Curtis, T.P.; Head, I.M. Effect of increasing anode surface area on the performance of a single chamber microbial fuel cell. Chem. Eng. J. 2010, 156, 40–48.
    63. Hiegemann, H.; Herzer, D.; Nettmann, E.; Lübken, M.; Schulte, P.; Schmelz, K.G.; Gredigk-Hoffmann, S.; Wichern, M. An integrated 45 L pilot microbial fuel cell system at a full-scale wastewater treatment plant. Bioresour. Technol. 2016, 218, 115–122.
    64. Chiranjeevi, P.; Patil, S.A. Strategies for improving the electroactivity and specific metabolic functionality of microorganisms for various microbial electrochemical technologies. Biotechnol. Adv. 2020, 39, 107468.
    65. Gadkari, S.; Gu, S.; Sadhukhan, J. Towards automated design of bioelectrochemical systems: A comprehensive review of mathematical models. Chem. Eng. J. 2018, 343, 303–316.
    66. Gadkari, S.; Fontmorin, J.M.; Yu, E.; Sadhukhan, J. Influence of temperature and other system parameters on microbial fuel cell performance: Numerical and experimental investigation. Chem. Eng. J. 2020, 388, 12176.
    67. Fan, L.; Shi, J.; Xi, Y. PDVF-modified Nafion membrane for improved performance of MFC. Membranes 2020, 10, 185.
    68. Modestra, J.A.; Reddy, C.N.; Krishna, K.V.; Min, B.; Mohan, S.V. Regulated surface potential impacts bioelectrogenic activity, interfacial electron transfer and microbial dynamics in microbial fuel cell. Renew. Energy 2020, 149, 424–434.
    69. Fan, Y.; Sharbrough, E.; Liu, H. Quantification of the internal resistance distribution of microbial fuel cells. Environ. Sci. Technol. 2008, 42, 8101–8107.
    70. Liang, P.; Huang, X.; Fan, M.Z.; Cao, X.X.; Wang, C. Composition and distribution of internal resistance in three types of microbial fuel cells. Appl. Microbiol. Biotechnol. 2007, 77, 551–558.
    71. ElMekawy, A.; Hegab, H.M.; Dominguez-Benetton, X.; Pant, D. Internal resistance of microfluidic microbial fuel cell: Challenges and potential opportunities. Bioresour. Technol. 2013, 142, 672–682.
    72. He, Z.; Wagner, N.; Minteer, S.D.; Angenet, L.T. An upflow microbial fuel cell with and interior cathode: Assessment of the internal resistance by impedance spectroscopy. Environ. Sci. Technol. 2006, 40, 5212–5217.
    73. Khan, M.J.; Iqbal, M.T. Modelling and analysis of electrochemical, thermal, and reactant flow dynamics for a PEM fuel cell system. Fuel Cells 2005, 4, 463–475.
    74. Oh, S.E.; Logan, B.E. proton exchange and electrode surface areas as factors that affect power generation in microbial fuel cells. Appl. Microbiol. Biotechnol. 2006, 70, 162–169.
    75. Elakkiya, E.; Matheswaran, M. Comparison of anodic metabolisms in bioelectricity production during treatment of dairy wastewater in Microbial Fuel Cell. Bioresour. Technol. 2013, 136, 407–412.
    76. Juang, D.F.; Yang, P.C.; Chou, H.Y.; Chiu, L.J. Effects of microbial species, organic loading and substrate degradation rate on the power generation capability of microbial fuel cells. Biotechnol. Lett. 2011, 33, 2147–2160.
    77. Yang, S.; Jia, B.; Liu, H. Effects of the Pt loading side and cathode-biofilm on the performance of a membrane-less and single-chamber microbial fuel cell. Bioresour. Technol. 2009, 100, 1197–1202.
    78. Logan, B.E.; Regan, J.M. Microbial fuel cell: Challenges and technology. Environ Sci. Technol. 2006, 40, 5172–5180.
    79. Fang, Z.; Cao, X.; Li, X.; Wang, H.; Li, X. Biorefractory wastewater degradation in the cathode of constructed wetland-microbial fuel cell and the study of the electrode performance. Int. Biodeterior. Biodegradation. 2018, 129, 1–9.
    80. Sleutels, T.; Darus, L.; Hamelers, H.V.; Buisman, C.J. Effect of operational parameters on Coulombic efficiency in bioelectrochemical systems. Bioresour. Technol. 2011, 102, 11172–11176.
    81. Shimoyama, T.; Komukai, S.; Yamazawa, A.; Ueno, Y.; Logan, B.E.; Watanabe, K. Electricity generation from model organic wastewater in a cassette-electrode microbial fuel cell. Appl. Microbiol. Biotechnol. 2008, 80, 325–330.
    82. Firdous, S.; Jin, W.; Shahid, N.; Bhatti, Z.A.; Iqbal, A.; Abbasi, U.; Ali, A. The performance of microbial fuel cells treating vegetable oil industrial wastewater. Environ. Technol. Innov. 2018, 10, 143–151.
    83. Sciarria, T.P.; Vacca, G.; Tambone, F.; Trombino, L.; Adani, F. Nutrient recovery and energy production from digestate using microbial electrochemical technologies (METs). J. Clean. Prod. 2019, 208, 1022–1029.
    84. Wang, Y.; Lin, Z.; Su, X.; Zhao, P.; Zhou, J.; He, Q.; Ai, H. Cost-effective domestic wastewater treatment and bioenergy recovery in an immobilized microalgal-based photoautrotophic microbial fuel cell (PMFC). Chem. Eng. J. 2019, 372, 956–965.
    85. Marzorati, S.; Schievano, A.; Colombo, A.; Lucchini, G.; Cristiani, P. Ligno-cellulosic lingomaterials as air-water separators in low-tech microbial fuel cells for nutrients recovery. J. Clean. Prod. 2018, 170, 1167–1176.
    86. Ichihashi, O.; Hirooka, K. Removal and recovery of phosphorus as struvite from swine wastewater using microbial fuel cell. Bioresour. Technol. 2012, 114, 303–307.
    87. Cusick, R.D.; Logan, B.E. Phosphate recovery as struvite within a single chamber microbial electrolysis cell. Bioresour. Technol. 2012, 107, 110–115.
    88. Hirooka, K.; Ichihashi, O. Phosphorus recovery from artificial wastewater by microbial fuel cell and its effect on power generation. Bioresour. Technol. 2013, 137, 368–375.
    89. Nelson, N.O.; Mikkelsen, R.L.; Hesterberg, D.L. Struvite precipitation in anaerobic swine lagoon liquids: Effect of pH and Mg: P ratio and determination of rate constant. Bioresour. Technol. 2003, 89, 229–236.
    90. Parsons, S.A.; Wall, F.; Doyle, J.; Oldring, K.; Churchley, J. Assessing the potential for struvite recovery at sewage treatment works. Environ. Technol. 2001, 22, 1279–1286.
    91. Güney, K.; Weidelener, A.; Krampe, J. Phosphorus recovery from digested sewage sludge as map by the help of metal ion separation. Water Res. 2008, 42, 4692–4698.
    92. Battistoni, P.; Pavan, P.; Prisciandaro, M.; Cecchi, F. Struvite crystallization: A feasible and reliable way to fix phosphorus in anaerobic supernatants. Water Res. 2000, 34, 3033–3041.
    93. Le Corre, K.S.; Valsami-Jones, E.; Hobbs, P.; Parsons, S.A. Phosphorus recovery from wastewater by struvite crystallization: A review. Crit. Rev. Environ. Sci. Technol. 2009, 39, 433–477.
    94. de-Bashan, L.E.; Bashan, Y. Recent advances in removing phosphorus from wastewater and its future use as fertilizer (1997–2003). Water Res. 2004, 38, 4222–4246.
    95. Yetilmezsoy, K.; Ilhan, F.; Kocak, E.; Akbin, H.M. Feasibility of struvite recovery process for fertilizer industry: A study of financial and economic analysis. J. Clean. Prod. 2017, 152, 88–102.
    96. Kelly, P.T.; He, Z. Nutrients removal and recovery in bioelectrochemical systems: A review. Bioresour. Technol. 2014, 153, 351–360.
    97. Kuntke, P.; Śmiech, K.M.; Bruning, H.; Zeeman, G.; Saakes, M.; Sleutels, T.H.J.A.; Hamelers, H.V.M.; Buisman, C.J.N. Ammonium recovery and energy production from urine by a microbial fuel cell. Water Res. 2012, 46, 2627–2636.
    98. Maurer, M.; Pronk, W.; Larsen, T.A. Treatment processes for source-separated urine. Water Res. 2006, 40, 3151–3166.
    99. Mei, X.; Xing, D.; Yang, Y.; Liu, Q.; Zhou, H.; Guo, C.; Ren, N. Adaptation of microbial community of the anode biofilm in microbial fuel cells to temperature. Bioelectrochemistry 2017, 117, 29–33.