IJERD – International Journal of Environmental and Rural Development (2022) 13-2

Research article
erd

Benefits of Applying Microbial Fuel Cell Technology inOrganic Farming for Sustainable Agriculture
NARONG TOUCH*
Faculty of Regional Environment Science, Tokyo University of Agriculture, Tokyo, Japan
Email: nt207118@nodai.ac.jp

TAKAHIKO NAKAMURA
Faculty of Regional Environment Science, Tokyo University of Agriculture, Tokyo, Japan
Received 14 January 2022

Accepted 27 June 2022(*Corresponding Author)

Abstract Increasing the productivity of organic farming is a strategy to achieve sustainableagriculture. However, it is necessary to maintain soil redox potential (ORP) in continuously
oxidized conditions and to promote bacterial metabolisms in soils to increase productivity.
Previously, applying microbial fuel cell technology (MFCT) into sediment improved ORP
and benthos survival in the sediment. It is thought that these positive effects of MFCT canalso provide many benefits for soil cultivation in organic farming. This study aims to
examine the changes in the biochemical properties of soil following MFCT application. In
laboratory experiments, MFCT was applied to cow manure compost-mixed andosol. An
anode (oxidation reaction) and a cathode (reduction reaction) were installed in the soil, anda 1.5-V solar cell was used to produce an electric current between the two electrodes. Threemonths after MFCT application, the chemical properties and adenosine triphosphate (ATP)of the soil were measured. Our results showed an electric potential distribution in the soil,
and the soil located within 20 cm of the electrode was strongly affected by the electrodereaction. This suggests that applying MFCT to soil can change the soil’s redox conditions.
The ATP and ammonium concentrations increased, suggesting bacterial activation andenhanced organic matter decomposition in the soil. It is recommended that farmers should
apply MFCT into soils for enhancing bacterial metabolism and increasing organic matterdecomposition in soils.
Keywords microbial fuel cell, organic farming, soil reduction, soil oxidation,
nitrogen release, bacterial activation

INTRODUCTION
According to the Ministry of Agriculture, Forestry and Fisheries of Japan (MAFF), organic farming
is a strategy to achieve sustainable agriculture. However, the ratio of total organic farmland to all
cultivated land remains low. In 2018, the ratio was 0.2% in Japan and 1.5% worldwide. On thebasis of the questionnaire survey conducted by MAFF (2018), technologies to enhance productivity
and implementation systems are required to facilitate organic farming. This study focuses ontechnology to enhance the productivity of organic farming.
Understanding of the soil chemical environment (SCE) is useful to ensure healthy soil that cansustain crop production (Yan and Hou, 2018). Because a decline in soil fertility results in adecrease in productivity (Buresh et al., 1997), soil fertility and health management play animportant role in realizing sustainable agriculture (Prasad and Power, 1997). In organic farming, asnutrients are supplied by the decomposition of organic matter, facilitating this decomposition plays
an important role in providing higher productivity. However, the SCE varies with thedecomposition of organic matter (soil reduction). This variation affects biological soil properties,
resulting in a decrease in the decomposition rate of organic matter. Therefore, technology that canreduce changes in the SCE and continuously activating bacterial metabolism is required to provide
higher productivity in organic farming.
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IJERD – International Journal of Environmental and Rural Development (2022) 13-2

Numerous studies have reported that applying microbial fuel cell technology (MFCT) tosediment facilitates the decomposition of organic matter and increases the redox potential of thesediment (Sacco et al., 2012; Sajana et al., 2013; Touch et al., 2014). Furthermore, MFCT has been
proven to effectively improve the benthic habitat environment in highly reduced sediment (Touchet al., 2018a). It is thought that these benefits of MFCT would be also useful for organic farming.
OBJECTIVE
This study aims to examine the benefits of applying MFCT for organic farming. Specifically, we
examined changes in the soil redox potential, biological properties, and nutrient release following
MFCT application. This was conducted by applying MFCT into cow manure compost-mixed
andosol with a generated electric current for 3 months.
METHODOLOGY
Experimental Procedures and Operations
Commercial products, i.e., cow manure compost and andosol, were used in laboratory experiments.
First, cow manure compost was mixed with andosol at a volume ratio of 47% (generally, 40% to60% is used). The mixture was then used in the experiments which were conducted under three
conditions, i.e., without treatment (Case 1), treated with a solar cell (Case 2), and treated with asediment microbial fuel cell (Case 3). Case 2 was conducted in duplicate. In Case 1, no electrodewas installed in the mixture (Fig. 1a).
In Case 2, two electrodes were installed in the soil layer (Fig. 1b). For generating an electricalcurrent, one of the both electrodes were connected to the positive, and another was connected to thenegative terminals of a 1.5-V solar cell (Tamiya, 1.5 V) using the circuit shown in Fig. 1b. A 2.2-Ω
external resistance was loaded between the anode and solar cell. In Case 3, an electrode was placedin the soil layer (anode), and another was placed near the water surface (cathode), as shown in Fig.
1c. For generating an electrical current, a 2.2-Ω external resistance was loaded between the anodeand cathode. This system is generally called a sediment microbial fuel cell (SMFC). Note that both
systems used in Cases 2&3 are different types of MFCT in which the system of Case 2 used a solar
cell as an external power supply. Here the solar cell was used following the study by Touch et al.
(2020), who suggested that using a solar cell increased the electric current of the SMFC andimproved the decomposition of organic matter present in paddy soils. The electrode material wascarbon cloth (News Company, PL200-E), which was heated at 500°C for 1 h prior to use toimprove its performance, as was suggested by Nagatsu et al. (2014). The heated carbon cloth with awidth of 20 cm and height of 10 cm was separated into fibers to form a brush-type electrode (Fig.
1d). The electrode was placed in a plastic net (1-mm mesh) and installed in the soil layer.
After the installation of both electrodes, the container was filled with tap water. As a result, a2-cm water layer was formed on the soil surface, which can prevent the soil from drying due toevaporation. The experiments were conducted from June to November in 2020.The voltage at bothterminals of the external resistance was measured every 15 min using a voltage logger (T&D Corp.,MCR-4V) to calculate the circuit current according to the Ohm’s law. The current density wasobtained by dividing the current by the surface area of the electrode, i.e., 0.02 m 2. To measure theanode potential of each case, the anode and a reference electrode (Toyo Corp., W-RE-7A) placed in
the overlying water were connected to the voltage logger.
AnalysesThree months after the experiments started, soil sampling was conducted. First, 1 cm of surface soil
was removed, and then, pH and redox potential (ORP) were measured using a pH/ORP meter(Horiba, D-50) at intervals of 5 cm from the anode. Soil samples were collected (Fig. 1e) after thepH and ORP measurements. Only half-length of the soil layer should be collected for examiningⒸ ISERD50

IJERD – International Journal of Environmental and Rural Development (2022) 13-2

the effects of solar cell or SMFC on the soil properties. However, in Case 2 (SC), the soils between
the electrodes were collected to determine the effective range of electrode reaction. Next, each soil
sample was centrifuged at 6000 rpm for 5 min (As one, CN-2060) to extract the porewater. Finally,
the nutrient concentration (phosphate, PO43-; ammonium, NH4+), and adenosine triphosphate (ATP)were measured. PO43- and NH4+ concentrations were measured using PACKTEST (Kyoritsu Corp.,WAK). ATP concentration was measured using a lumitester (Kikkoman, Lumitester-Smart), andthe result represents the sum concentration of adenosine triphosphate, adenosine diphosphate, andadenosine monophosphate.
(d) Electrode: carbon fibers(a) Case 1: no treatment14 cm

2 cm Tap water (prevention of soil drying by evaporation)

Cow manure compost-mixed andosol
Voltage logger(b) Case 2: treated with SC⊝
Solar cell (1.5 V)
2.2 Ω
Removal of 1 cm-surface soil before soil sampling

⊕5 cm

2 cm

Cathode14 cm⊝

Soil sampling at intervals of 5 cm
Voltage logger
2.2 Ω⊕ (c) Case 3: treated with SMFC(e) Soil sampling

CathodeTap waterAnode

14 cm

⊝

26 cm
1 cm

56 cm
Plastic container: 14 cm × 56 cm × 26 cm

Fig. 1 Experimental devices and operations
RESULTS AND DISCUSSION
Comparison of Current Density Generated Using SMFC and a Solar Cell
Figure 2 depicts the temporal changes in the current densities generated using the SMFC and solar
cell during the first 30 days of the experiments.
As can be seen from the figure, the maximum current density generated by the SMFC wasapproximately 60 mA/m2, which increased to 200 mA/m2 when using the solar cell. During the firstmonth of the experiments, the total electric charge was 50,415 C/m2/month when the SMFC wasused whereas the total was 59,220 C/m2/month when the solar cell was used. Although, more than
three times the current density was observed, only a 1.17-fold change in the total electric charge
was found between both cases. This is because no electrical current was generated at night when
the solar cell was used.
Changes in Redox Conditions at the End of the Experiment
Figure 3 shows the changes in pH and ORP due to current generation at the end of the experiment.
In the figure, 0 and 45 cm refer to the soil samples at the anode and cathode, respectively (Case 2).
In Fig. 3a, the pH at the anode was 6.97 for Case 1 (without current generation), which decreasedⒸ ISERD51

IJERD – International Journal of Environmental and Rural Development (2022) 13-2

Current density (mA/m2)

to 6.44 when using the SMFC (Case 3) and to 6.39 when using the solar cell (Case 2). In Case 3,
the large increases in pH at distances greater than 10 cm were due to the effects of cathode water(Fig. 1c).
200
Case 2

Case 3

150

100
5000

51015
20
Operation time (day)

2530

35

Fig. 2 Comparison of current densities generated using the SMFC and solar cell
In contrast to the literature, our results showed no increase in ORP following SMFC
application. However, increases in ORP were observed when the solar cell was used. The increases
in ORP were caused by large variations in the electrode potential due to the use of the solar cell(Fig. 4). In Fig. 4, the anode potential was in the ranges from 0.2 to 0.4 V and −0.2 to 0.8 V vs.
Ag/AgCl when using the SMFC (Case 3) and the solar cell (Case 2), respectively. The oxidation
reactions at the anode following current generation caused the decrease in pH and increase in ORP.
These results suggest that the solar cell can be used to effectively control the soil redox conditions,i.e., pH and ORP. From the ORP distribution, it is thought that the soil located within 20 cm of theelectrode was affected by current generation using the solar cell. It is expected that nutrient releaseand microbial activation differ in response to these changes in pH and ORP.
7.1

Distance from the anode (cm)

70

6.8

Case 1

6.7

Case 2

6.6

Case 3

6.5
6.4
6.3
6.2
05

10 15 20 25 30 35
Distance from the anode (cm)4045

ORP (mV vs. Ag/AgCl)

pH

6.9

51015

20250-20-40-60-80-100-120-140-160-180-200(a) pH distribution

30354045

Case 1Case 2
Case 3(b) ORP distribution

Anode potential (V )Fig. 3 Changes in pH and ORP due to current generation at the end of the experiment
1
Case 20.8

Case 3

0.6
0.4
0.2

0-0.2

-0.4
05

101520Operation time (day)253035

Fig. 4 Temporal changes of the anode potential during the first month of the experimentⒸ ISERD52IJERD – International Journal of Environmental and Rural Development (2022) 13-2

Nutrient Release due to Current Generation
Figure 5 shows the distributions of ammonium (NH4+) and phosphate (PO43-). No differences wereobserved between Case 1 and Case 3 (differences were within the error range), suggesting that theSMFC had little effect on the decomposition of organic matter. Interestingly, a large increase inNH4+ concentration was observed between Cases 1 and 2, at distances from 15 to 30 cm from theanode. A 2-fold increase in NH4+ concentration was observed 20 cm from the anode. However, thePO43- concentrations in all cases were on the same order of magnitude (Fig. 5b).
The released NH4+ is believed to arise from the decomposition of organic matter. Even though
the generated electric charges were on the same order of magnitude (Case 2: 59,220 C/m2/month;
Case 3: 50,415 C/m2/month), the decomposition behavior of organic matter differed. This may be
due to the differences in electrode potential between Cases 2 and 3 (Fig. 4). The decomposition oforganic matter was facilitated when the solar cell was used, which is in good agreement with theresults obtained by Touch et al. (2020). According to Touch et al. (2018b), the lower NH4+
concentration near both electrodes (Fig. 5a) may be due to the oxidation of NH4+ at the electrodes
due to the high electrode potential when the solar cell is used (Fig. 4).
0.16

PO43- concentration (mg/L)

NH4+ concentration (mg/L)

4035
30

25
2015
105

Case 1Case 2

Case 3

Case 1Case 2

Case 3

0.15
0.14
0.13

0.12
0.11
0.1

005

10 15 20 25 30 35
Distance from the anode (cm)40045(a) Ammonium concentration

510 15 20 25 30 35
Distance from the anode (cm)4045(b) Phosphate concentration

Fig. 5 Comparison of nutrient concentration distributions of each case
Changes in ATP due to Current Generation
Figure 6 illustrates the ATP distribution of each case. Similar to the distribution of NH4+, almost no
difference in ATP was found between Cases 1 and 3. However, two to threefold increases in ATP
were observed when the solar cell was used (Case 2). These results suggest that using the solar cellcan provide a better biological environment, resulting in a higher decomposition rate of organicmatter. This may be the cause of the higher NH4+ concentration observed when the solar cell wasused (Fig. 5a, Case 2).
1800

Case 1Case 2
Case 31600

ATP (RLU)

1400
1200
1000

800
600
400
200
005101520253035
Distance from the anode (cm)4045Fig. 6 Changes in ATP due to current generationⒸ ISERD53

IJERD – International Journal of Environmental and Rural Development (2022) 13-2

CONCLUSIONS
Laboratory experiments were conducted to examine the benefits of applying MFCT in organic
farming. Specifically, changes in the soil redox potential, biological properties, and nutrient release
following the application of MFCT to cow manure compost-mixed andosol were investigated.
Similar to previous results when applying MFCT into littoral sediments, an increase in ORP nearan electrode was observed. Following current generation using a solar cell, an ORP distribution
was formed in the soil, and the soil located within 20 cm from the electrode was affected by theelectrode reaction. This suggests that applying MFCT to soil can change the soil’s redox conditions.
The ATP and ammonium concentrations increased because of the current generated by the solarcell, suggesting bacterial activation and enhanced organic matter decomposition in the soil. It canbe concluded that applying MFCT can control soil biochemical conditions and can enhancebacterial metabolism and organic matter decomposition in soils, which are the most importantfactors in organic farming.
ACKNOWLEDGMENTS
The authors gratefully acknowledge the partial funding from Tokyo University of Agriculture:
FY2021 Grant-in-Aid for Sustainable Agriculture Research Projects. The authors also would like tothank the students of the Rural Environmental Engineering Laboratory, Tokyo University ofAgriculture, for their efforts in collecting data.
REFERENCES
Buresh, R.J., Sanchez, P.A. and Calhoun, F. 1997. Replenishing soil fertility in Africa. Volume 51, Soil
Science Society of America, ISBN 9780891189466, USA.
Ministry of Agriculture, Forestry and Fisheries of Japan (MAFF). 2018. The promotion statue of organic
farming. Ministry of Agriculture, Forestry and Fisheries of Japan, Retrieved from https://www.maff.
go.jp/j /seisan/kankyo/yuuki/attach/pdf/chosa_jichitai-48.pdf
Nagatsu, Y., Tachiuchi, K., Touch, N. and Hibino, T. 2014. Factors for improving the performance ofsediment microbial fuel cell. Journal of Japan Society of Civil Engineers Ser B2 (Coastal Engineering),
70 (2), 1066-1070, Retrieved from DOI https://doi.org/10.2208/kaigan.70.I_1066 in JapanesePrasad, R. and Power, J.F. 1997. Soil fertility management for sustainable agriculture. Lewis Publishers,
CRC Press, ISBN 9781566702546, New York, USA.
Sacco, N.J., Figuerola, E.L.M., Pataccini, G., Bonetto, M.C., Erijman, L. and Cortón, E. 2012. Performanceof planar and cylindrical carbon electrodes at sedimentary microbial fuel cells. Bioresource Technology,126, 328-335, Retrieved from DOI https://doi.org/10.1016/j.biortech.2012.09.060
Sajana, T.K., Ghangrekar, M.M. and Mitra, A. 2013. Application of sediment microbial fuel cell for in situ
reclamation of aquaculture pond water quality. Aquacultural Engineering, 57, 101-107, Retrieved fromDOI https://doi.org/10.1016/j.aquaeng.2013.09.002
Touch, N., Hibino, T., Kinjo, N. and Morimoto, Y. 2018. Exploratory study on improving the benthic
environment in sediment by sediment microbial fuel cells. International Journal of Environmental
Science and Technology, 15, 507-512, Retrieved from DOI https://doi.org/10.1007/s13762-017-1418-8
Touch, N., Hibino, T., Nagatsu, Y. and Tachiuchi, K. 2014. Characteristics of electricity generation andbiodegradation in tidal river sludge-used microbial fuel cells. Bioresource Technology, 158, 225-230,Retrieved from DOI https://doi.org/10.1016/j.biortech.2014.02.035
Touch, N. and Nakamura, T. 2020. Decomposition of organic matter in steelmaking slag-used sedimentmicrobial fuel cells. International Journal of Environmental Protection, 10 (1), 1-6, Retrieved from http://paper.academicpub.org/PaperInIssue?IssueId=1793
Touch, N., Yamaji, S., Nishimura, K., Sunada, Y. and Hibino, T. 2018. Remediation of sediment depositednear sewage outlet with solar cell-combined sediment microbial fuel cells. International Journal ofEnvironmental Protection, 8 (1), 18-24, Retrieved from http://paper.academicpub.org/Paper?id=17688
Yan, B. and Hou, Y. 2018. Soil chemical properties at different toposequence and fertilizer under continuousrice production, A review. IOP Conference Series, Earth and Environmental Science, 170, 032107 (5pages), Retrieved from https://iopscience.iop.org/article/10.1088/1755-1315/170/3/032107/pdfⒸ ISERD54