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Review

Application of Microbial Fuel Cell Technology in Potato Processing Industry

by
Renata Toczyłowska-Mamińska
1,* and
Mariusz Ł. Mamiński
2
1
Institute of Biology, Department of Physics and Biophysics, Warsaw University of Life Sciences, 159 Nowoursynowska St., 02-776 Warsaw, Poland
2
Institute of Wood Sciences and Furniture, Warsaw University of Life Sciences, 159 Nowoursynowska St., 02-776 Warsaw, Poland
*
Author to whom correspondence should be addressed.
Energies 2023, 16(18), 6581; https://doi.org/10.3390/en16186581
Submission received: 5 July 2023 / Revised: 27 August 2023 / Accepted: 7 September 2023 / Published: 13 September 2023

Abstract

:
The potato processing industry is among the biggest water-consuming industries, using an average of 17 L of water per 1 kg of processed product. Taking into account that the potato is the fourth-most-important non-cereal food crop with a global production of 376 million tons a year, this branch is a large wastewater producer. Potato-processing wastewater is highly loaded and thus difficult to treat through conventional methods, especially when a low energetic input for environmental benignancy is required. In this review, it was shown that microbial fuel cells (MFCs) are an excellent technology for sustainable potato wastewater treatment. MFCs allow for potato wastewater COD removal with efficiencies as high as 99%, which is accompanied by electricity production that may reach 3.7 W/m2. Thus, the recently published research reviewed in this paper indicates that simultaneous power production and removal of chemical oxygen demand make MFCs superior to conventional treatment methods. Encouraging results and the unique advantages of MFC technology, like significant water and energy use reduction, give a promising perspective on potato-processing wastewater treatments.

1. Introduction

The phenomenon of electroactivity in bacteria was observed for the first time by Potter in 1911 [1]. Much work has been carried out in recent decades; however, interest in the electroactivity of microorganisms has increased since the beginning of the 21st century. The literature survey on electrogenic microorganisms performed by Koch and Harnish indicates that over 90 electroactive species are known today [2]. All electrogenic bacteria have cytochrome-c proteins responsible for extracellular electron transfer [3]. Numerous studies have demonstrated that electroactive bacteria are present in most of the natural and anthropogenic habitats on Earth [2,4], including animal guts [5,6], soil [7], sea and lake sediments [8,9], volcanic lakes [10], rivers [11], beach sand [12], and hydrocarbon-contaminated soil [13]. Unexpectedly, electroactive species have also been found in the roots of plants, e.g., sweet potato (Dioscorea esculenta) [14]. Despite much effort having been made in exploring new environments in search of new electrogenic bacteria and isolating and investigating their electrophysiology, there are still many to be discovered. Harvesting energy from waste substrates has been one of the hottest topics in investigations on microbial fuel cells (MFCs) in recent years.
Keeping in mind the ways electrogens function and the complexity of engineered systems necessary to transfer extracellularly released electrons from the microbiome to the outer environment (i.e., electrodes, wiring, commutators, etc.), it is apparent that the development of such systems—called microbial fuel cells (MFCs)—requires an interdisciplinary approach. MFCs are known as a technology enabling for direct electricity production with the use of microorganisms, mainly bacteria. As shown in Figure 1, the MFC’s function is based on oxidation–reduction processes with the use of bacteria as a catalyst. A typical MFC reactor is composed of an anaerobic anodic chamber and aerobic cathodic chamber separated by a proton-exchanging membrane. Under anaerobic conditions, organic substrate is degraded, resulting in protons and electrons being released. The electrons are then transferred to the cathode, where, in the aerobic environment, oxygen reduction occurs. The movement of electrons from the anode to the cathode is responsible for electric current generation in the system.
Thus, in order to properly design and develop MFCs, microbiology, biotechnology, bioinformatics, and electrochemistry and electronics must be engaged because species sampling, culturing, isolation, identification, and even genomic manipulation are necessary steps to build a highly effective MFC.
Because organic compounds are degraded in an MFC to CO2 via oxidation, there are two main results of MFC operation: chemical oxygen demand (COD) removal and/or electric power. Therefore, MFCs can be used, among other technologies, in the bioremediation of wastewater highly loaded with organic contaminants.
The complex compounds used as a substrate for MFCs require microbial consortia, in which, besides electrogens, various microorganisms exhibit a range of different activities, such as fermentation and hydrolysis. This way, it is possible to produce an electric current in MFCs from various waste resources, e.g., cellulose [6], animal manure [15] and urine [16], food industry wastewater [17], and dyes from the textile industry [18]. An especially attractive option is using wastewater as a substrate for MFCs, which now—in traditional technology—is treated with high-energy input. As global wastewater production exceeds 900 km3, its effective management is a serious environmental challenge [19]. Contrary to municipal wastewater, which has been widely studied and reported quite intensively in MFCs, industrial-wastewater-fed MFCs are often overlooked, though industrial wastewater constitutes the majority of global wastewater production and the degree of its contamination is much higher than that of municipal wastewater, which results in a high-COD load. Municipal wastewater pollution, characterized by COD, is in the range 300 to 900 mg/L [19], while industrial wastewater COD is from ca. 400 mg/L for wastewater generated by some processes in energy sectors, through 40,000 mg/L for metallurgy wastewater, up to as much as 200,000 mg/L for wastewater generated by some processes of the food and beverage industry [19].
Among most water-consuming industries, which means the largest wastewater producers, there are many food sectors that may use even 40 m3 of water per 1 ton of final product [19]. Among food-processing sectors, one of the most water-consuming is potato processing. The potato is the most important non-cereal food crop, just after rice, wheat, and maize [20]. The potato owes its popularity to its high nutritional value, as it is a good source of proteins, vitamins, minerals, and antioxidants [21]. Additionally, it can be grown in various environments, and when it is cultivated under harsh conditions, it gives more yield than any other food crop [22]. Usually, potatoes are single-cropped during the year and are cultivated on a large scale. In 2021, global potato production was 376 million tons [23], of which, 2/3 was consumed by people as food [24]. Of that amount, more than 50% is consumed after processing [25]. The potato processing industry delivers products such as French fries, chips, hashbrowns, salads, and other potato snacks. Water is used here for multiple steps, such as washing, steam peeling, cutting, cooking, and blanching, which requires 8 to 28 L of water per 1 kg of processed potatoes, with an average of 17 L of water per 1 kg of processed potatoes [26,27]. Additionally, during processing, potato waste is generated, which may comprise 15–40% of the initial potato weight [28]. Walker et al. report water use on 11 to 22.5 L/kg of product so that the data remain comparable [29]. One of the products also derived from potatoes in abundance is starch, which comprises 12% of the potatoes produced in the EU [30].
Usually, potato processing wastewater is highly loaded with organic compounds. Its COD depends on the type of applied process and may vary from 6000 to 30,000 mg/L [31]. Such wastewater can cause serious environmental problems, as it contains high concentrations of biodegradable compounds such as starch 19–25 g/L, protein 2.8–4 g/L, and glucose 0.3 g/L, as well as inorganic salts containing significant concentrations of minerals (e.g., N 0.1–751 mg/L, P 128–361 mg/L, K 1613–2222 mg/L) and a pH in a wide range of 3.9–7.5 [28,32,33].
On the one hand, the discharge of nutrient-rich (COD or minerals: phosphorus, nitrogen) water streams in the environment, especially aquatic, is strictly prohibited due to the risk of fertilization of water bodies and their eutrophication via the overgrowth of phytoplankton and aquatic plants [34]. Therefore, discharging such a stream of waste, which has proven to be dangerous to ecosystems, must be purified to meet nationally accepted standards. On the other hand, along with increasingly strict water management policies and technologies of reduced energy consumption that come into play and impose closed loops for processing water in industry, the treatments characterized by zero-energy input are gaining momentum and are expected to support or—in the most optimistic scenario—to substitute conventional techniques implemented in industry.
Considering widespread problems with water scarcity, it is especially important now to develop solutions that meet the abovementioned expectations to the greatest extent. One of the approaches is the reduction of water use during potato processing through closed-loop implementation accompanied by effective, environmentally benign wastewater treatment. A vast quantity of potato processing wastewater makes it difficult to treat with conventional methods and increases the cost of the treatment process [35]. The chemical composition of potato processing wastewater, especially the presence of simple sugars and proteins, makes it a potentially good substrate for microorganisms in MFCs. Although anaerobic digestion applied to the treatment of wastes and by-products from the food industry is effective as it produces biogas and conserves nutrients [36], its main disadvantage is that the water content is not recycled or conserved in the process [37]. MFC technology is free from those flaws—it not only recovers water but also reduces COD, while no external energy supply is required [19].
The European Starch Industry Association (Starch Europe) states that the annual production of starches and semiproducts for hydrolysis in the EU exceeds 11 million tons [38]. From that and the abovementioned figures (17 L water/1 kg starch), the volume of the potato wastewater stream can be roughly estimated as 187 × 106 L. Such a stream loaded with 18,000 mg/L, which is the mean for the range reported previously, gives an amount of ca. 3366 tons of nutrients introduced to the ecosystem [31]. However, such an organic load, when converted to MFC, would yield 5.7 × 105 kWh of energy [39]. The above analysis, though rough, demonstrates how valuable feedstock potato wastewater can be when properly managed and how risky it is for ecosystems when managed irresponsibly.
In this article, the research on the application of potato processing wastewater as a substrate for MFCs has been reviewed. The results clearly indicate that MFC technology allows for very efficient treatment of potato processing wastewater with simultaneous electricity production.

2. Drawbacks of Conventional Treatment Methods for Potato Processing Wastewater

Currently, to reduce the organic load of potato processing wastewater, various physical, chemical, and biological aerobic and anaerobic methods are used. The most popular are coagulation/flocculation, adsorption, air flotation, and membrane techniques [35]. The most often used is the coagulation–flocculation sequence, as it is the simplest in operation and is economically feasible. Coagulation and flocculation are separate processes that are applied in sequence and allow for the consolidation of particles present in wastewater into aggregates, which, afterward, can be separated from the liquid. First, the addition of coagulants causes the neutralization of the charges on the particles, and then flocculation results in binding them together in the form of bigger aggregates. However, frequently used flocculants such as inorganic metal salts (e.g., polyaluminium chloride) and synthetic polymers such as polyacrylamide are the cause of so-called secondary wastewater pollution. This phenomenon is connected with polluting wastewater with residual metal anions and synthetic polymer monomers, which brings environmental and human health risks [35]. Additionally, treatment efficiency is often not satisfactory in cases of highly contaminated wastewater [29]. An approach to overcome that disadvantage is the application of biopolymers such as chitosan and polyglutamic acid in ionic forms. Such a dual flocculant system was demonstrated to yield better results than those for polyaluminium chloride and polyferric sulfate. Thus, it would seem practicable to discharge sediment directly into the environment without negative environmental effects. However, COD removal efficiencies with the use of the biopolymeric natural flocculants were lower, typically not exceeding 40–50% [39]. Zhang et al. reported that improved water purification efficiency can be obtained when the chitosan–polyglutamic acid system is doped with bentonite to reach 86.2% COD removal [40]. Application of more efficient techniques such as membrane filtration deals with high treatment costs connected with high energy use, but the technique is applicable only to non-turbid water [39]. When full-scale biological aerobic treatment is applied, the problems of high power consumption and the large amount of sludge that needs to be managed appear [41]. It is noteworthy that processes combining chemical coagulation and membrane filtration have been shown to be applicable in potato wastewater treatments. Flocculation yielded 67% COD removal but was an indispensable step to avoid membrane fouling [35]. Although membrane filtration is recommended as the BAT (Best Available Technology), it is not always applicable or practicable because of problems related to membrane fouling. One of the applications that membrane filtration is not recommended for is the purification of potato processing wastewater [42]. The authors also stated that ultrafiltration, as a single operation in potato wastewater purification, is not efficient enough to reduce the concentration of pollutants to a level required by a closed-loop system for water and reuse. Moreover, the coupling of ultrafiltration with nanofiltration does not purify wastewater to the point of enabling it to be discharged into the environment [42]. The main advantages and disadvantages of the abovementioned techniques are summarized and compared in Table 1.
On the other hand, anaerobic treatment is very sensitive to temperature, has a long start-up time, and is restricted to highly loaded wastewaters, mainly sludge treatment [33].
Although MFCs—like those in anaerobic digestion technology—operate in anaerobic conditions too, the approach does not involve aeration, which makes the process less energy-consuming in comparison to conventional biological wastewater treatments performed in sewage treatment plants. In this context, MFC technology is superior to conventionally used treatment techniques in the following ways: (1) no secondary pollution is generated; (2) zero or minimal energy input is needed; (3) treatment is possible in a wide range of CODs and temperatures; and (4) short start-up times are possible.

3. Application of MFC Technology to the Potato Processing Industry

In the utilization of MFC technology for the management of potato processing wastewater, two different approaches can be distinguished: (1) the utilization of indigenous microorganisms present in wastewater and (2) the addition of exogenous bacteria, indicating desirable activity (Table 2). One of the first attempts at using potato processing wastewater as a substrate in an MFC was reported by Kiely et al., who worked on single-chamber reactors (28 mL) with brush anodes and air cathodes [43]. MFCs were fed wastewater with a COD of 7700 mg/L. They obtained maximum power production (220 mW/m2) and high TCOD removal efficiency (89%). In this study, indigenous bacteria present in wastewater were utilized for electricity production and wastewater treatment. The investigation of the anode microbial community revealed that >60% of all clones were Geobacteraceae. The dominant species were Geobacter sulfurreducens (37%) and G. lovleyi (14%). Wastewater from potato ethanol production (COD 5000 mg/L) was reported as being used in MFC with an air cathode by Cai et al. The medium needed the addition of phosphate-buffered solution (PBS) 50–200 mmol/L to improve MFC performance. Maximum power density was 334 mW/m2, and COD removal was 92.2%. The authors stated the negative effect of the acidification of the solution on power generation in the system [44]. Sato et al. applied single-chamber air-cathode MFC for electricity production from simulated potato processing wastewater of COD 1000 mg/L. A bamboo charcoal plate was applied here as an anode and a Pt-coated carbon cloth as a cathode. In this case, anaerobic sludge was used as a bacteria source. Maximum power production was 0.65 W/m2, which corresponded to 4 A/m2 [45]. A single-chamber MFC with a working volume of 450 mL, a carbon fiber anode, and a zinc-oxide-nanoparticle-fabricated copper cathode was also studied for the treatment of potato wastewater. Though indigenous wastewater bacteria were utilized, acetate supplementation was applied to promote biofilm formation on the anode. The maximum power production obtained was 3.7 W/m2 (2.5 A/m2) with simultaneous COD removal at 80% efficiency [46]. Durruty et al. investigated tubular MFC (a central graphite felt cathodic chamber and two anodic chambers filled with graphite particles, separated with Nafion from the cathode) fed with synthetic potato wastewater. Wastewater was inoculated with anaerobic sludge microorganisms. In this case, COD reduction efficiency was 87% with a maximum power production of 450 µW [47].
In 250-mL two-chamber MFCs with an air cathode operating on potato and waste activated sludge, the highest observed COD removal was 85%. While the maximum current density varied between 160 and 243 mA/m2, the peak time was 5 days, and coulombic efficiencies ranged from 53.5 to 92.7% [48]. Du and Li investigated potato waste augmented with anaerobic activated sludge as a bacteria source. They found COD removal at 89.6% and current density between 10 and 155 mA/m2 for the best-performing MFCs. The comparison of MFC operation efficacy showed that the addition of activated sludge (1:4 ratio) increased both COD removal and current density [49]. Yaqoob et al. used potato waste as an electron donor source for such species as Enterobacter, Proteus, and Xenorhabdus. Heavy metal remediation varied from 84% to 94%, while peak current reached 36.84 mA/m2 [50]. The MFCs investigated by Xing and co-workers exhibited a maximum power density of 32.1 W/m3 at a cell load of 10 g/L of potato waste pulp and a COD removal of 68.7%. Analysis of microbial community structure indicated Alphaproteobacteria, Bacteroidia, Bacilli, Betaproteobacteria, Flavobacteria, and Clostridia as the dominating classes of bacteria, as well as the two main electrogens, Geobacter (8.2%) and Dysgonomonas (28.5%) [51]. Similar studies focused on electricity generation, COD, and microbial community structure were reported by Du and co-workers. It was demonstrated that an MFC working on a starch-rich liquid substrate could yield a current of 208 mA/m2 and a maximum COD removal of 84%. Microbial consortium analyses revealed the presence of Clostridium sp., Dysgonomonas sp., Bacteroides sp. as well as three electrogen species: Geobacter sp., Aeromonas hydrophila, and Clostridium butyricum [52].
Herrero-Hernandez proposed using Escherichia coli as a biocatalyst in a two-chamber MFC fed with potato extract. The reactors operated in batch mode were constructed from a 1 L anode chamber and a 125 mL cathode chamber, separated with Nafion, with titanium platinized mesh electrodes. In the cathode chamber, potassium hexacyanoferrate (III) was applied. The maximum power production was 502 mW/m2, the COD removal efficiency was 60.8%, and the CE (coulombic efficiency) was 18.5% [53]. Diluted potato processing wastewater with a BOD of 300 mg/L (biological oxygen demand) was also used as a substrate in 32 mL single-chamber MFCs, with anaerobic sludge as a bacteria source. The anode was made of plain Toray paper paired with an air cathode. The maximum power density was 216 mW/m, which2 corresponded to 9 W/m3. Additionally, high CE values were observed, with the average CE reaching 36% and the maximum CE reaching 75%. An investigation of the anode consortium revealed it was dominated by Proteobacteria and Firmicutes, known for their electrogenic activity [54].
Original research was undertaken by Radeef and Ismail on a model dual-chamber MFC fed real potato-processing wastewater. They investigated MFC with a working volume of 1.9 L and graphite electrodes. A high maximum COD removal efficiency was obtained, reaching 99%, and power production was 95.7 mW/m2 at room temperature [26]. They also proposed using a potato-chip-processing-wastewater-fed MFC as an online biosensor. Because potato processing wastewater contains a high concentration of suspended solids and also acidic or alkaline materials, they must be removed before biological wastewater treatment. The proposed MFC-based biosensor was designed for the detection of suspended solids and acidic content in potato wastewater so that their quick removal was possible. For the studies, dual-chamber MFCs with a capacity of 1.9 L, a cation exchange membrane and graphite plain electrodes were used. In this study, potato processing wastewater was both the substrate and the inoculum in the MFCs. When the pH of potato wastewater changed or suspended solids appeared, it caused biofilm disruption. As a result, it caused a biosensor current decrease, which was a signal of an undesirable change in wastewater parameters [55]. A dual-chamber MFC with a cation exchange membrane and plane graphite electrodes was also applied for the treatment of real potato chips processing wastewater by Radeef et al. The authors applied anode inoculation with anaerobic sludge. They observed very high COD and total suspended solids removal efficiency, exceeding 99%. Maximum power production in steady state was 0.6 W/m3 what corresponded to 1.7 A/m3 and increased to 1.1 W/m3 (2.1 A/m3) when potato peels were added to the potato processing wastewater [56]. An MFC of a new design (2100 mL) comprising a single cathode chamber and multiple anode chamber (MAC-MFC), working on potato wastewater from a chip factory, was reported by Mathuriya. The results demonstrated that power outputs recorded for the MAC-MFC were higher than those for a single cathode-MFC: 356 mW/m2 vs. 289 mW/m2, while COD removal was ca. 90% vs. 80%, respectively [57]. Lu et al. reported treatment of starch processing wastewater (COD 4852 mg/L) in an air cathode MFC that yielded a 98% COD reduction and a maximum power density of 239.4 mW/m2 [58]. An interesting approach to wastewater treatment was demonstrated by Igatani et al. who investigated power generation from potato waste from alcoholic beverage production in a cassette-electrode MFC (350 mL) that comprised a graphite felt anode and an air cathode. Maximum COD removal was 67.4%, while the power produced achieved 1200 mW/m3 [59].
An MFC of a novel design anode made of a nanocomposite material graphene oxide-polyaniline (GO-PANI) fed with potato wastes as a substrate and as a bacterial source was described by Yaqoob et al. The authors observed the ability of such a system to remediate heavy metals with high efficiency 65.5% for Cd(II) and 60.3% for Pb(II); however, power production was much lower (1.1 mW/m2) than that of typical carbon electrodes [60]. Recently, Du and Shao performed investigations regarding mixed potato waste/anaerobic activated sludge. The MFCs were dual-chamber (240 mL) with an air cathode. Carbon felt was used as the material both for the anode and cathode electrodes. COD loading varied between 1569 mg/L and 4145 mg/L. The mixture ratio (0:1, 1:0, 2:1, 4:1, 6:1, 8:1, and 10:1) affected the power production, coulombic efficiency, start-up time, operation stability, and degradation of macromolecular organic compounds. The maximum obtained power density was 14.1 mW/m2. The studies revealed that hydrolysis of solid potato waste is a key step limiting energy recovery. The addition of waste-activated sludge to the waste potato greatly improved hydrolysis, which resulted in enhanced waste-to-power conversion [61]. An interesting finding was made by Nara and co-workers, who isolated a new electrogenic bacterium from rotten potato slurry (Providencia rettgeri). Its electroactivity was confirmed via cyclic voltammetry and chronoamperometry. In another novel MFC, electrodes were made of an aluminum sheet covered with graphite paste and paper. Providencia rettgeri in the MFC generated a peak power density of 5020 mW/m3 [62].
Table 2. Performance of MFCs in potato wastewater treatments.
Table 2. Performance of MFCs in potato wastewater treatments.
Bacteria SourceCOD Removal (%)Current Yield 1 MFC DesignRef.
Indigenous89220 mW/m2Brush anode/Pt carbon cloth cathode[43]
Anaerobic sludge92.2334 mW/m2Graphite felt anode/graphite cloth cathode[44]
Anaerobic sludgeNA650 mW/m2Bamboo charcoal anode/Pt carbon cloth cathode[45]
Indigenous/acetate suppl.803700 mW/m2Carbon fiber anode/ZnO-Cu cathode[46]
Anaerobic sludge87450 µWGraphite anode/graphite felt cathode[47]
Anaerobic sludge85243 mA/m2Carbon felt anode/carbon felt cathode[48]
Indigenous/anaerobic sludge89.6155 mA/m2Carbon felt anode/carbon felt cathode[49]
Indigenous68.736.8 mA/m2Graphite brush anode/Pt carbon cloth cathode[51]
Indigenous84208 mA/m2Carbon felt anode/carbon felt cathode[52]
E. coli60.8502 mW/m2Ti anode/Ti cathode[53]
anaerobic sludgeNA216 mW/m2Carbon paper anode/Pt-coated cathode[54]
Indigenous9995.7 mW/m2Graphite anode/graphite cathode[26]
Anaerobic sludge991100 mW/m3Graphite anode/graphite cathode[56]
Indigenous90356 mW/m2Carbon paper anode/graphite plate cathode[57]
Indigenous98239 mW/m2Carbon paper anode/carbon Pt paper cathode[58]
Indigenous67.41200 mW/m3graphite felt anode/carbon cloth cathode[59]
Indigenous/local pondNA1.1 mW/m2GO-PANI anode/graphite cathode[60]
Indigenous/anaerobic sludgeNA14.1 mW/m2Carbon felt anode/carbon felt cathode[61]
IndigenousNA5020 mW/m3Al graphite paper anode/Al graphite paper cathode[62]
Anaerobic consortia from MFC8816.5 mW/m2Carbon felt anode/carbon felt cathode[63]
Cellulose degrading bacteria72152 mW/m2Carbon paper anode/ carbon paper cathode[64]
1 Units given as in the source references.
Usually, research on waste treatment in MFCs is restricted to liquid wastewater. Meanwhile, Du and Li [63] showed the possibility of direct conversion of solid potato waste (potato cubes with sizes 3, 5, and 7 mm) into electricity in a two-chamber MFC with a working volume of 0.24 L. Carbon felts were used as the electrodes, and a cation exchange membrane was applied. An inoculum of anaerobic consortia from MFC-treated artificial wastewater fed with sodium acetate was utilized. The used potato weight corresponded to an initial COD loading of 1828 mg/L. The highest power density was obtained for the smallest potato cubes, which was 16.5 mW/m2. Simultaneously, it was observed that COD removal efficiency reached a final value of 150–220 mg/L (88%). Microbial community analysis proved the presence of bacteria involved in hydrolysis, acidogenesis, and electrogenesis (in the latter, Geobacter sp. were dominant) [63]. Waste potato peels were also used as a substrate in 200 mL dual-chamber MFCs with carbon paper electrodes and potassium ferricyanide catholytes. MFCs were inoculated with a mixed culture of cellulose-degrading bacteria, and the maximum power density obtained here was 150 mW/m2 [64].
Figure 2 shows the progress made in the last decade in power production and COD removal efficiency in MFCs. As far as COD removal rates are concerned, they are rather high and steady—usually above 90%—and the change in power production is impressive, since a few-fold increase in power densities is reported in the literature.

4. Conclusions

Though potato processing wastewater has not been a very popular substrate for MFCs, the results of past investigations indicate that it is a very promising substrate for this technology. Research on the use of this wastewater in MFCs over the years showed significant progress in power production and COD removal efficiency (Figure 2). What is noteworthy is that very high COD removal of potato processing wastewater is obtained with the use of MFC technology—often reaching 99%.
Such treatment efficiencies for this type of wastewater are seldom obtained with the use of conventional methods that require high energy input, usually ranging from 0.3–0.6 kWh/kg COD through 0.8–1 kWh/kg COD to 1–6 kWh/kg COD, respectively, for activated sludge processes, aerobic sludge processes, and membrane processes [39]. For comparison, MFC requires 0.02–0.07 kWh/kg COD [39]. These results indicate that MFCs can be utilized as a sustainable wastewater treatment technology for the potato processing industry and bring it closer to closed-loop processing, which will significantly reduce total water use in the production process. Simultaneous electricity production and high COD removal rates make MFC technology a sustainable solution that meets the strict environmental expectations of current governmental policies, as it generates no secondary pollution and requires no external energy supply.
The abovementioned prerequisites make MFCs possibly the most promising anaerobic wastewater treatment technique. However, as the technology is in its infancy, numerous obstacles remain to be overcome, and further enhancements are still necessary before it is scaled up to the industrial scale.
Future research should focus on: (1) screening the environment for new electrogenic species; (2) the development of new electrode materials and designs able to provide increased power densities aimed at kilowatts per m3 of cell volume, so that the self-sufficiency of an MFC; (3) the biostimulation and/or bioaugmentation microbial consortia for maximized efficiency in potato wastewater treatments; (4) genomic analyses of the consortia evolving in working MFCs; and (5) the elucidation of the mechanisms bacteria employ to adapt.
Those findings will provide pathways to scaling up MFC technology and its industrial implementation. If MFC efficiency meets technical requirements, it will likely become a sustainable source of renewable energy and an environmentally benign wastewater treatment method.

Author Contributions

Conceptualization, R.T.-M.; writing—original draft preparation, R.T.-M., M.Ł.M.; writing—review and editing, R.T.-M., M.Ł.M.; visualization, R.T.-M. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Not applicable.

Acknowledgments

The work was financially supported by Warsaw University of Life Sciences.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. The principle of electric current generation in a MFC.
Figure 1. The principle of electric current generation in a MFC.
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Figure 2. The results of research on MFCs fed potato processing wastewater by year, on the basis of literature review: maximum power production (left axis, blue bars) and COD removal efficiency (right axis, red dots).
Figure 2. The results of research on MFCs fed potato processing wastewater by year, on the basis of literature review: maximum power production (left axis, blue bars) and COD removal efficiency (right axis, red dots).
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Table 1. Treatment techniques applicable to food industry wastewater.
Table 1. Treatment techniques applicable to food industry wastewater.
TreatmentMain AdvantagesMain Disadvantages
Anaerobic digestionProduces biogasHigh power consumption
Coagulation/flocculation 1Easy aggregate separationSecondary wastewater pollution with flocculants
Adsorption Easy operationLow selectivity
Membrane filtrationRemoves physical and chemical pollutants Membrane fouling
MFCNo secondary pollutionZero or minimal energy input
1 Preferably used in sequence.
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Toczyłowska-Mamińska, R.; Mamiński, M.Ł. Application of Microbial Fuel Cell Technology in Potato Processing Industry. Energies 2023, 16, 6581. https://doi.org/10.3390/en16186581

AMA Style

Toczyłowska-Mamińska R, Mamiński MŁ. Application of Microbial Fuel Cell Technology in Potato Processing Industry. Energies. 2023; 16(18):6581. https://doi.org/10.3390/en16186581

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Toczyłowska-Mamińska, Renata, and Mariusz Ł. Mamiński. 2023. "Application of Microbial Fuel Cell Technology in Potato Processing Industry" Energies 16, no. 18: 6581. https://doi.org/10.3390/en16186581

APA Style

Toczyłowska-Mamińska, R., & Mamiński, M. Ł. (2023). Application of Microbial Fuel Cell Technology in Potato Processing Industry. Energies, 16(18), 6581. https://doi.org/10.3390/en16186581

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