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Article

The Application of Sediment Microbial Fuel Cells in Aquacultural Sediment Remediation

by
Jiarui Qi
1,2,
Zhuteng Sun
2,
Jinfeng Zhang
2,* and
Chen Ye
1
1
College of Harbour and Coastal Engineering, Jimei University, Xiamen 361021, China
2
State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin 300072, China
*
Author to whom correspondence should be addressed.
Water 2022, 14(17), 2668; https://doi.org/10.3390/w14172668
Submission received: 23 July 2022 / Revised: 23 August 2022 / Accepted: 25 August 2022 / Published: 29 August 2022
(This article belongs to the Section Wastewater Treatment and Reuse)
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Abstract

:
To successfully apply sediment microbial fuel cells (SMFCs) in remediating aquacultural sediments and water bodies on a large scale, SMFC systems with different electrode materials (carbon fiber brush, graphite felt, and carbon fiber cloth) and structural forms were constructed, and the advantages and disadvantages of various electrodes were compared in terms of electricity generation, pollutant removal, and application cost. The results revealed that (1) introducing SMFCs accelerated the removal of pollutants from the overlying water, promoted the degradation of organic matter and the fixation of phosphorus in the sediments, and inhibited water eutrophication and algal blooms; (2) SMFC systems with carbon fiber brushes and graphite felt electrodes exhibited better electricity generation, but the smooth surface of the carbon fiber cloth was not conducive to microbial attachment, leading to a relatively low electrode power density; and (3) the low external resistance accelerated electron transfer and increased the pollutant removal rate.

1. Introduction

In recent years, the scale of aquaculture has been increasing with the rising demand for aquatic products in China, and the excessive use of bait in pursuit of fishery products has led to severely polluted aquacultural waters and sediments. Aquacultural water pollution not only reduces the quality of aquaculture products and increases the incidence of aquaculture microorganisms but also poses a great threat to the surrounding aquatic environment. As an important component of aquatic ecosystems, sediments are involved in continuous material exchange with the overlying water, and the long-term accumulation of pollutants in a water body makes sediments an enrichment site of various pollutants. Even if the pollution source is controlled, pollutants such as organic matter and nitrogen (N) and phosphorus (P) nutrients will be rereleased into the overlying water after the surrounding environment is disturbed, causing secondary pollution. Therefore, starting with sediment treatment is necessary for eliminating aquacultural water pollution.
Sediment microbial fuel cells (SMFCs) are an environmentally friendly bioelectrochemical approach that can effectively control pollutants such as organic matter, N, and P in sediments and overlying water [1,2,3], showing potential for sediment remediation and water purification. In terms of organic matter removal, the removal rate of easily degradable organic matter in sediments reached 32.7% after six months of SMFC operation [4], and the degradation rate of total organic carbon (TOC) was 22.1% after two years of electricity generation by the system; this rate was 5.8-fold higher than that of the open-circuit control group [1]. Moreover, compared with the original sediments, the sediments near the anode of the system underwent a significant increase in the degree of humification and a certain increase in the average molecular weight of the organic matter, which made them more easily degraded [3], effectively improving the biodegradability of the refractory organic matter in the sediments [5]. In addition, SMFCs are very effective in degrading pollutants such as petroleum hydrocarbons [6], polycyclic aromatic hydrocarbons [7], polychlorinated biphenyls [8], and phenols [9].
Regarding nutrient removal, SMFCs can facilitate the removal of P and N from the overlying water. The extent of P release into the overlying water is closely related to the dissolution of iron-bound P in the sediments [10,11], where P is usually adsorbed onto low-solubility Fe(III)(oxy) hydroxide; in contrast, in an anaerobic environment, Fe(III) is highly reductive and becomes the final electron acceptor, which reacts to form Fe(II) P compounds with high solubility and enters the water body [12]. Therefore, using an SMFC anode to replace Fe(III) as the electron acceptor can inhibit the release of P, and at the same time, Fe(II) in the SMFC cathode loses electrons to form Fe(III) to adsorb and precipitate P, thereby reducing the P concentration in the overlying water, with a maximum phosphate reduction of 94% [13]. The aerobic denitrifying bacteria at the SMFC cathode use the electrons generated by the decomposition of organic matter to denitrify the N bound in sediments to N2 using nitrate and nitrite as the final electron acceptors [14], with a removal rate of 72–91%, which is positively correlated with the external current intensity [15].
Purifying aquacultural water is conducive to the growth of fish and can improve the economic benefits of aquaculture and alleviate the pollution of surrounding water environments caused by the indiscriminate discharge of aquacultural water. Sajana et al. [16,17] studied the remediation of aquacultural water by SMFC and found that SMFC could significantly reduce the chemical oxygen demand (COD) and the concentrations of ammonia-N and total N (TN) in the overlying water. However, SMFCs’ performance is affected by many factors, which can be broadly divided into the categories of controllable and uncontrollable factors that jointly determine the SMFC output power [18]. Controllable factors include the electrode material [19,20], electrode configuration [21], external resistance [22], electrode spacing [23,24], anode burial depth [25,26], and catalyst [8]. Uncontrollable factors are usually determined by the environment and include salinity, temperature [16], Ph [17,27], dissolved oxygen (DO) [28,29], sediment properties [30], and sediment microbial community composition [31,32]. Therefore, research is needed on the application of SMFCs in aquacultural sediment remediation and water quality treatment, and relevant experiments must be performed on the potential for SMFCs in aquaculture pollution remediation.
At present, most of the research focuses on improving the electrical performance by improving the electrode materials, optimizing the electrode configuration, etc. [33,34]. However, the effects of the electrode material and configuration research on the treatment of in situ sediment remediation and water pollution based on SMFC need to be investigated further.
This study analyzed SMFC operation and startup conditions and considered factors such as the performance and cost of electrode materials and the suitability of electrode configurations for field construction. On this basis, several SMFC systems with different structures were designed for aquaculture pollution remediation, and their electricity generation performance and pollutant removal rates were compared to provide the basis and experience for the subsequent field application of SMFCs. In addition, the influence of external resistance on SMFC performance was experimentally investigated to obtain the optimal pollutant removal performance to provide experimental support for applying SMFCs in aquacultural water pollution remediation.

2. Materials and Methods

2.1. Sediment and Water Sources

The sediments used in the experiment were taken from an old aquaculture fishpond (39°10′22.95′′ N, 117°49′52.70′′ E) at the fishing wharf in the Binhai New Area, Tianjin, China. The sediments were collected 20 cm from the surface layer, and impurities such as dead leaves and stones were removed from the sediments, which were then passed through a 10-mesh stainless steel sieve and further mixed thoroughly using a mechanical stirrer for later use. The overlying water used in the experiment was also taken from the same fishpond without adding any other substances, and the seawater had a salinity of 38.2‰ and a pH of 7.80.

2.2. Construction and Operation of the SMFC

The SMFC reactor was placed in a cylindrical acrylic bucket with a height of 60 cm and a diameter of 15 cm, with holes in the bucket wall at 25 and 40 cm from the bottom to facilitate regular water sampling. The sediments were 15 cm thick, the overlying water was 30 cm deep, the anode was located 2 cm below the sediments, and the cathode and anode were 20 cm apart. A titanium wire was drawn from the cathode and the anode and connected to an external circuit, and a resistor was connected to the external resistor. A voltmeter was connected to both ends of the resistor to record changes in the external voltage. To identify electrode materials and structures with good performance and cost-effectiveness, five electrode configurations and a parallel open-circuit control group was set up in the experiment, denoted as SMFC-A, SMFC-B, SMFC-C100, SMFC-C1000, SMFC-D, and Blank, with the detailed working conditions shown in Table 1. There were two duplicate groups for each electrode configuration, and the data in this paper are the average values of the two groups. The electrodes were pretreated before use by successively soaking them in acetone solution, 1 mol/L NaOH, and 1 mol/L HCl for 2 h each and finally rinsing repeatedly with deionized water until a neutral pH was reached.
The cathode and anode materials of SMFC-A were carbon fiber brushes (Haote New Material Co. Ltd., Wuxi, China) made of carbon fibers tied to high-purity titanium wires. Each carbon fiber brush had a total length of 15 cm, a brush coverage area of 10 cm in length, and a brush diameter of 3 cm. Each electrode was composed of five carbon fiber brushes connected by a titanium wire with a diameter of 2 mm. The cathode and anode were connected through a PVC support column to ensure a fixed distance between the electrodes. The configuration of SMFC-A is shown in Figure 1a.
The anode of SMFC-B was the same as that of SMFC-A and had a carbon fiber brush structure, while the cathode of SMFC-B had a graphite felt structure. The graphite felt cathode consisted of three elements, each of which was made of two layers of graphite felt sandwiching a layer of titanium wire mesh. Each layer of graphite felt was 10 cm long, 10 cm wide, and 2 mm thick and connected by a titanium wire with a diameter of 2 mm.
The electrodes of SMFC-C were graphite felt structures, and their cathode structure was the same as that of SMFC-B. Unlike the graphite felt cathode structure, the graphite felt anode structure was 10 cm long, 10 cm wide, and 5 mm thick. In addition, because the graphite felt material is soft and not easy to insert into the sediments, a PVC securing plate (Figure 1b) was made to frame the graphite felts in place so that the anode could be easily pressed into the sediments. The cathode wrapping around the securing plate had a stable structure, and the graphite felts were fully opened to ensure full contact with the sediments and thus increase the microorganism attachment area.
The cathode of SMFC-D had the same graphite felt structure as SMFC-B and SMFC-C. The anode structure of SMFC-D was prepared by wrapping carbon fiber cloth outside the honeycomb lattice sheet [35], as shown in Figure 1c. Each carbon fiber cloth of the anode had a projected area of 0.08 m2, resulting in a total area of 0.16 m2. Carbon fiber cloth has a large surface area and is more conductive than graphite felt and thus has certain research value.
Prior to the experiment, changes in TOC, TN, and total phosphorus (TP) contents in the sediments, as well as in COD, ammonia-N, TN, and TP concentrations in the overlying water, were measured. To study the SMFC remediation effect on pollutants in the sediments and water, the changes in pollutant contents in the overlying water and sediments were measured regularly.

2.3. Analysis and Calculation

Voltage data were collected every 5 min using a voltmeter [36]. The cathode potential was measured using an Ag/AgCl reference electrode, and the anode potential was obtained from the difference between the cathode potential and the voltage.
The DO concentration of the water was measured using a DO meter, and the pH and salinity of the water were measured using a pH meter and a salinometer, respectively [37]. The concentrations of pollutants such as COD, ammonia-N, TN, and TP in the overlying water were measured regularly, with the water quality indicators determined with reference to the Analytical Methods for Water and Wastewater Monitoring (fourth edition). The TOC, TN, and TP contents of the sediments near the anode were measured before and after the experiment. The TOC content of the sediments was measured using a 3100 + HT1300 solid module (Jena, Germany) [38], TP was analyzed with alkali fusion-molybdenum antimony anti-spectrophotometry [39,40], and TN was analyzed by the Kjeldahl method [16].

3. Analysis of Electricity Generation Performance

3.1. Voltage Analysis

The reactors were fully constructed on 1 May 2021. Figure 2 shows the average daily voltage variation curves of the experimental group. The voltage variations in the SMFC can be divided into ascending, stable, and descending stages. Table 2 shows the average voltage of each experimental group in different time periods.
The starting voltages of the five groups of experiments (from SMFC-A to SMFC-D) were 0.078, 0.020, 0.065, 0.300, and 0.020, showing that the voltage of the SMFC with an external resistor of 1000 Ω was significantly higher than that of the other groups. No artificial inoculation was needed since a high abundance of natural microbial flora was present in the sediments. When microorganisms near the anode are engaged in life activities, they decompose organic matter to generate electrons, forming a potential difference; thus, voltage is created once the circuit is connected [3]. As more microorganisms attached to the anode, the voltage increased rapidly, and the average voltages increased to 0.195 V, 0.208 V, 0.200 V, 0.580 V, and 0.145 V for SMFC-A, SMFC-B, SMFC-C100, SMFC-C1000, and SMFC-D, respectively, at 0–15 days. With the same external resistance, the SMFC with a carbon fiber cloth anode had a relatively low voltage, and the SMFCs with a carbon fiber brush anode and a graphite felt anode had a similar voltage. Compared with carbon fiber brushes and graphite felt, carbon fiber cloth has a smooth surface, which may not be conducive to microorganism attachment, resulting in a relatively slow startup speed and low system voltage.
At 16–30 days into the experiment, the voltage continued to rise but at a slower overall rate, with the average voltages of the five groups of SMFC being 0.226 V, 0.206 V, 0.204 V, 0.618 V, and 0.236 V during this period. The voltage of SMFC-D still maintained a relatively rapid increase, presumably related to the relatively large anode area, where microorganisms continued to attach to the anode surface causing the voltage to increase and exceed those of SMFC-A, SMFC-B, and SMFC-C100. In contrast, microorganisms attached to the carbon fiber brush anode and the graphite felt cloth anode faster in the early period and gradually became saturated during this period, causing the voltage to increase at a slower rate.
At 31–45 days into the experiment, with the saturation of the number of microorganisms on the anode, the voltage tended to be stable, and the average voltages of the five groups of SMFC were 0.275 V, 0.265 V, 0.266 V, 0.665 V, and 0.250 V. In this period, the organic matter content near the anode was sufficient, and the microbial metabolic activity was the most intense; hence, the voltages of all experimental groups were maintained at a high level.
At 46–60 days into the experiment, the organic matter in the sediments near the anode was exhausted, the number of electron donors was reduced substantially, and the voltage decreased gradually to final averages of 0.203 V, 0.172 V, 0.150 V, and 0.193 V for SMFC-A, SMFC-B, SMFC-C100, and SMFC-D, respectively. The average voltage of SMFC-C1000 in this period was 0.675 V, showing a slight increase compared with that of the SMFC with an external resistance of 100 Ω. This difference is due to the low current of the circuit with an external resistance of 1000 Ω and the slow consumption of organic matter in the sediments near the anode, which still did not lead to mass transfer limitation. The mass transfer limitation near the anode is an important factor limiting the application of SMFCs, although using carbon fiber brushes as the electrode reduces the mass transfer limitation at the anode to some extent [41].
Throughout the operation, the average voltages of the five groups of SMFC were 0.212 V, 0.194 V, 0.192 V, 0.604 V, and 0.199 V. The SMFC with carbon fiber brushes at the cathode and anode had the highest voltage, while the voltages of the other three groups of SMFCs differed slightly from each other. In addition, the voltage of the SMFC with an external resistance of 1000 Ω was significantly higher than that of the SMFC with an external resistance of 100 Ω.

3.2. Cell Internal Resistance and Power Density

The anode is a substrate on which microorganisms carry out their biological activities, and the surface structure of the anode material affects organic matter decomposition near the anode, which plays a key role in the internal resistance of an SMFC [19]. After the voltage was stabilized, the external circuit resistance changed according to the steady-state discharge method, the corresponding voltage and current values were measured, and the polarization curve was plotted (Figure 3) to determine the maximum power density and the internal resistance of the cell.
The surface area of the carbon fiber brushes was calculated using the volumetric density method [42] with a volume of 3.53 × 10−5 m3. SMFC-A had a maximum anode power density of 2500 mW/m3, its power density per unit area was 44.41 mW/m2 as measured by normalization with the projected surface area on the cathode side, and its internal resistance was 220 Ω. For SMFC-B, the maximum anode power density was 967 mW/m3, the power density per unit area was 32.18 mW/m2 as measured by normalization with the projected surface area on the cathode side, and the internal resistance was 112 Ω. Similarly, SMFC-C100 had a maximum power density of 27.72 mW/m2 and an internal resistance of 210 Ω. For SMFC-C1000, the maximum power density was 58.38 mW/m2, and the internal resistance was 204 Ω. SMFC-D had a maximum power density of 6.94 mW/m2 and an internal resistance of 221 Ω.
Using carbon fiber brushes led to a higher power density. Among the three groups of reactors with different anode materials and the same cathode material, the power density of the carbon fiber brush anode was slightly higher than that of the graphite felt anode, and the power density of the carbon fiber cloth material was the lowest, as shown in Figure 3f. The brush form better distributes the graphite fibers, increasing the surface area of the material; thus, the carbon fiber brush material had a high power density. In contrast, the carbon fiber cloth material has a smooth surface, which is not conducive to microorganism attachment, so its maximum power density was lower than that of the graphite felt material. From the perspective of cost-effectiveness, graphite felt material is less costly and has a higher application value.
In the SMFC-C reactor, the voltage and maximum power density were significantly higher for the SMFC with an external resistance of 1000 Ω vs. 100 Ω, but the two SMFCs differed slightly in internal resistance, and the electricity generation performance of the SMFC increased with the external resistance [22,23].

4. Analysis of Overlying Water Remediation

In Section 3, SFMC-C100 and SMFC-C1000 showed higher voltages and currents and therefore stronger redox reactions and higher pollutant removal capacities. Because of their material performance and cost, SFMC-C100 and SMFC-1000 were selected for further study of their contaminant removal efficiency and power generation performance.
This section compares the influence of external resistance on the removal of pollutants such as organic matter, N, and P in the overlying water. Before the experiment, the COD concentration of the overlying water was measured to be 115.30 mg/L. After 2 months of the experiment, the COD concentrations of the open-circuit control group, SMFC-C100, and SMFC-C1000 were 54.64, 45.74, and 44.76 mg/L, respectively, representing decreases of 53%, 60%, and 61%, respectively. Figure 4 shows the COD concentration variation curves during the experiment. The results indicated that the SMFC promoted organic matter degradation in the overlying water and that the change in the external resistance had no significant influence on this degradation.
Before the experiment, the concentrations of ammonia-N and TN in the overlying water were 5.75 mg/L and 17.56 mg/L, respectively. After two months, the concentrations of ammonia-N in the open control group, SMFC-C100, and SMFC-C1000 were 3.22, 2.51, and 2.56 mg/L, respectively, representing decreases of 44%, 55%, and 56% (Figure 5), respectively, and the TN concentrations were 6.03, 4.64, and 4.32 mg/L, respectively, representing decreases of 66%, 74%, and 75% (Figure 6), respectively. The SMFC could accelerate the degradation of ammonia-N and TN in the overlying water to some extent, and the SMFC with an external resistance of 100 Ω did not achieve a higher N removal efficiency than that with an external resistance of 1000 Ω.
Before the experiment, the TP concentration in the overlying water was measured to be 0.210 mg/L. After 2 months, the TP concentrations in the open-circuit control group, SMFC-C100, and SMFC-C1000 were 0.130, 0.057, and 0.073 mg/L, respectively, representing decreases of 38%, 73%, and 65% (Figure 7), respectively. The experimental results indicated that the SMFC could significantly promote the adsorption of P on the sediments, and the effect was more pronounced in the SMFC with an external resistance of 100 Ω vs. 1000 Ω, which was likely related to the higher current density. The current densities in the circuit with external resistances of 100 Ω and 1000 Ω were 37.00 mA/m2 and 11.45 mA/m2, respectively, and a higher current promotes the transfer of P to the sediments [13].
During the experiment, both parallel experiments of the open-circuit control group showed obvious water eutrophication and algal blooms, as shown in Figure 8, with the dominant algal species being green algae and brown algae, respectively. To quantitatively demonstrate the role of the SMFC in inhibiting water eutrophication, the chlorophyll a content in the overlying water of SMFC-C100, SMFC-C1000, and two open-circuit control groups was measured. Chlorophyll a is the main pigment for algal photosynthesis and a common response indicator of eutrophication, and it can be used to assess algal growth [43]. The test results indicated that the average chlorophyll a content of the SMFC system was 97.0 μg/L, while the average chlorophyll a content in the open-circuit control group was 304.5 μg/L, indicating that introducing the SMFC system significantly inhibited rapid algal blooms in water.

5. Analysis of Sediment Pollutant Removal

The sediments collected for this experiment had a TOC content of 6.59 mg/g. After two months, the TOC content of the open-circuit control group was 6.21 mg/g, a decrease of 5.77%, while the TOC content of SMFC-C100 and SMFC-C1000 changed to 5.29 mg/g and 5.59 mg/g, respectively, decreases of 19.73% and 15.17%, respectively (Figure 9). The degradation of organic matter in the experimental groups was significantly stronger than that in the open-circuit control group, and the degradation effect was greater for an external resistance of 100 Ω vs. 1000 Ω. At low resistance, more electrons are transferred to the cathode, creating a higher current, resulting in a faster cathodic reaction and higher external electrical activity, and the decrease in electron transport resistance improves the growth of electrogenic bacteria [38,44].
At the beginning of the experiment, the TP content of the sediments was 706 mg/kg. After two months of operation, the TP content of the open-circuit control group was 694 mg/g, a decrease of 1.70%, while the TP contents of SMFC-C100 and SMFC-C1000 changed to 773 mg/g and 726 mg/g, respectively, increases of 9.49% and 2.83%, respectively (Figure 9). The sediment TP content was significantly higher for the experimental groups than for the open-circuit control group, which corresponded to the change in the TP concentration in the overlying water. Introducing the SMFC increased the redox potential of the sediments, thereby significantly increasing their P adsorption capacity and reducing the TP concentration in the overlying water [45].

6. Conclusions

(1)
The average voltage of SMFC-A, which had a carbon fiber brush electrode, was the highest, and the average voltages of SMFCs with the other three electrode structures were relatively close. The power density was slightly higher for the SMFC using carbon fiber brushes vs. a graphite felt electrode, but the graphite felt material has a higher application value because of its lower cost. The SMFC using a carbon fiber cloth electrode had a relatively low power density, probably because of the smooth surface, which is unfavorable for microbial attachment.
(2)
The voltage and maximum output power of the SMFCs were significantly increased when the external resistance was 100 vs. 1000 Ω, and the electricity generation performance of the SMFC increased with increasing external resistance. However, an external resistance of 100 Ω led to a better effect on sediment remediation and water purification. At low resistance, more electrons are transferred to the cathode, forming a higher current, which produces a faster cathodic reaction and higher external electrical activity and thus accelerates the pollutant removal rate.
(3)
Compared with the open-circuit condition, introducing SMFCs accelerated the removal of pollutants from the overlying water. After 60 days of operation, the concentrations of COD, ammonia-N, TN, and TP in the overlying water of SMFC-C100 and SMFC-C1000 were lower than those of the open-circuit control group, and the removal effect on TP was the highest.
(4)
Compared with the open-circuit condition, introducing the SMFC promoted the degradation of organic matter and the fixation of P in sediments. After 2 months of operation, the TOC content in the sediments of SMFC-C100 and SMFC-C1000 decreased by 19.73% and 15.17%, respectively, which were significantly higher rates than that for the open-circuit control group. Compared with the initial state, the TP content in the sediments of SMFC-C100 and SMFC-C1000 increased by 9.49% and 2.83%, respectively, while that in the open-circuit control group decreased slightly. SMFCs increased the redox potential and thus the P adsorption capacity of sediments.
(5)
The SMFCs significantly inhibited water eutrophication and rapid algal blooms. After two months, green algal and brown algal blooms appeared in the two open-circuit control groups but not in the experimental groups with SMFCs. The average chlorophyll a content in the open-circuit control group was found to be significantly higher than that of the experimental groups with SMFCs, demonstrating that the SMFCs had a significant effect on the water quality of the overlying water.

Author Contributions

J.Q., conceptualization, investigation, and formal analysis. Z.S., investigation, formal analysis, validation, and writing—original draft preparation. J.Z., writing—review, funding acquisition. C.Y., investigation. All authors have read and agreed to the published version of the manuscript.

Funding

This study was supported by the National Key Research and Development Program of China (Grant No. 2021YFB2601100), the National Natural Science Foundation of China (Grant Nos. U1906231), and the Open Funds of the State Key Laboratory of Hydraulic Engineering Simulation and Safety of China (Grant No. HESS-2221).

Data Availability Statement

Not applicable.

Acknowledgments

The authors also gratefully acknowledge the comments and suggestions of the anonymous reviewers.

Conflicts of Interest

The authors declare no conflict of interest.

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Water 14 02668 g001 550
Figure 1. Schematic diagrams of the graphite felt anode. (a) Schematic diagram of the carbon fiber brush electrode and SMFC device; (b) schematic diagram of the graphite felt anode; (c) schematic diagram of the graphite felt anode.
Figure 1. Schematic diagrams of the graphite felt anode. (a) Schematic diagram of the carbon fiber brush electrode and SMFC device; (b) schematic diagram of the graphite felt anode; (c) schematic diagram of the graphite felt anode.
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Figure 2. Daily mean voltage curves (1 May to 29 June 2021).
Figure 2. Daily mean voltage curves (1 May to 29 June 2021).
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Figure 3. Polarization and power density of SMFCs. (a) Polarization curve of SMFC-A; (b) Polarization curve of SMFC-B; (c) Polarization curve of SMFC-C100; (d) Polarization curve of SMFC-C1000; (e) Polarization curve of SMFC-D; (f) Power density curves of SMFC.
Figure 3. Polarization and power density of SMFCs. (a) Polarization curve of SMFC-A; (b) Polarization curve of SMFC-B; (c) Polarization curve of SMFC-C100; (d) Polarization curve of SMFC-C1000; (e) Polarization curve of SMFC-D; (f) Power density curves of SMFC.
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Figure 4. COD concentration curves.
Figure 4. COD concentration curves.
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Figure 5. Ammonia-N concentration curves.
Figure 5. Ammonia-N concentration curves.
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Figure 6. TN concentration curves.
Figure 6. TN concentration curves.
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Figure 7. TP concentration curves.
Figure 7. TP concentration curves.
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Figure 8. Eutrophication degree of water in different experimental groups.
Figure 8. Eutrophication degree of water in different experimental groups.
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Figure 9. Comparison of TOC and TP data before and after the experiment.
Figure 9. Comparison of TOC and TP data before and after the experiment.
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Table
Table 1. SMFCs with various components.
Table 1. SMFCs with various components.
Reactor
Type		Anode
Material		Cathode
Material		Anode
Specification		Cathode
Specification		External
Resistance
SMFC-ACarbon fiber brushCarbon fiber brush3 × 10 × 15 cm
(5)		3 × 10 × 15 cm
(5)		100 Ω
SMFC-BCarbon fiber brushGraphite felt3 × 10 × 15 cm
(5)		10 × 10 × 0.2 cm
(3)		100 Ω
SMFC-C100Graphite feltGraphite felt10 × 10 × 0.5 cm
(3)		10 × 10 × 0.2 cm
(3)		100 Ω
SMFC-C1000Graphite feltGraphite felt10 × 10 × 0.5 mm
(3)		10 × 10 × 0.2 cm
(3)		1000 Ω
SMFC-DCarbon fiber clothGraphite felt10 × 10 mm
(6)		10 × 10 × 0.2 cm
(3)		100 Ω
BlankControl group with an open circuit
Table
Table 2. Average voltages in the experimental groups in different time periods.
Table 2. Average voltages in the experimental groups in different time periods.
Reactor Type
Voltage (V)		Startup0–15 Day16–30 Day31–45 Day46–60 DayAverage
SMFC-A0.0780.1950.2260.2750.2030.212
SMFC-B0.0200.2080.2060.2650.1720.194
SMFC-C1000.0650.2000.2040.2660.1500.192
SMFC-C10000.3000.5800.6180.6650.6750.604
SMFC-D0.0200.1450.2360.2500.1930.199
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Qi, J.; Sun, Z.; Zhang, J.; Ye, C. The Application of Sediment Microbial Fuel Cells in Aquacultural Sediment Remediation. Water 2022, 14, 2668. https://doi.org/10.3390/w14172668

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Qi J, Sun Z, Zhang J, Ye C. The Application of Sediment Microbial Fuel Cells in Aquacultural Sediment Remediation. Water. 2022; 14(17):2668. https://doi.org/10.3390/w14172668

Chicago/Turabian Style

Qi, Jiarui, Zhuteng Sun, Jinfeng Zhang, and Chen Ye. 2022. "The Application of Sediment Microbial Fuel Cells in Aquacultural Sediment Remediation" Water 14, no. 17: 2668. https://doi.org/10.3390/w14172668

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