Microbial Fuel Cells for Mitigating Greenhouse Gas Emissions from Paddy Fields
2025 Volume 13 Issue 3 Pages 45-56
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2025 Volume 13 Issue 3 Pages 45-56
Paddies contribute significantly to global emissions of greenhouse gases (GHGs), particularly methane (CH4) and nitrous oxide (N2O), and conventional mitigation strategies, such as fertilizer management and water regulation, often fail to address the complex microbial interactions that are the major drivers of these emissions. Thus, microbial fuel cells (MFCs) have been explored as innovative bioelectrochemical technologies for mitigating CH4 and N2O emissions. MFCs mitigate GHG emissions by modifying soil redox potential, fostering microbial competition, and enhancing electron transfer (the oxidation–reduction state of the soil). This systematic literature review, which assesses the findings of 24 relevant studies, is aimed at evaluating the mitigation effects of MFCs on CH4 and N2O emissions from paddy fields. The findings indicate that electron competition consistently suppresses CH4 emission by diverting microbial electron donors from methanogenesis. Conversely, N2O reduction proceeds through a more complex mechanism, relying on the inhibition of the NO3⁻ to NO2⁻ or NO pathway and the activation of the nosZ pathway, which ensures the complete reduction of N2O to N2 without accumulating GHGs as intermediate products, thereby suppressing N2O emission. A follow-up comparative analysis reveals that the mitigation of CH4 emission is more straightforward, whereas that of N2O requires the precise adjustments of the redox–microbial balance. Among the various MFC configurations assessed, that integrating constructed wetlands with MFCs (CW-MFCs) is the most promising owing to its scalability, efficiency, and mitigation effects on CH4 and N2O emissions. Despite these advantages, CW–MFCs still suffer from electrode longevity, energy efficiency, and large-scale implementability issues. Thus, future related studies must explore hybrid bioelectrochemical strategies incorporating CW-MFCs to enhance GHG mitigation and promote sustainable rice farming.
Agriculture is a major contributor to the emission of anthropogenic greenhouse gases (GHGs), particularly methane (CH4) and nitrous oxide (N2O), which are released from agricultural soils. Rice agriculture, as well as wetlands, play crucial roles in driving global CH4 emissions, accounting for 27 ± 6 Tg/y of CH4 in the last decade [1]. Additionally, CH4 emissions from rice fields (hereafter referred to as paddies or paddy fields (PFs)) have been projected to remain stable or increase, thereby exacerbating climate change risks. Collectively, rice cultivation accounts for 9–19% of global agricultural emissions [2]. Although CH4 emissions have been widely studied, N2O emissions also pose a significant concern, particularly under varying water-management practices [3]. Zou et al. [3] estimated direct N2O emissions from paddies during the growing season to be 29.0 Gg N2O-N, constituting 7–11% of total cropland emissions in mainland China. These statistics highlight the necessity of integrated and comprehensive mitigation strategies for both CH4 and N2O emissions, thereby ensuring sustainable agricultural practices with minimized environmental impacts.
Consequently, strategies, including fertilizer management, water regulation, and biochar incorporation, alongside the selection of rice varieties with reduced aerenchyma, have been explored as potential mitigation strategies for GHG emissions from paddies [4]. However, these approaches cannot directly address the fundamental microbial interactions that drive CH4 and N2O emissions. Notably, plant rhizodeposits can act as electron donors, inadvertently stimulating microbial activities that enhance methanogenesis and incomplete denitrification [5]. Recent advances in bioelectrochemical technologies indicate that integrating microbial fuel cells (MFCs) into PFs (PF-MFCs) can be a promising alternative approach to mitigating GHG emissions, as this strategy can simultaneously suppress CH4 and N2O emissions [6].
MFCs were first developed to address global energy challenges and reduce fossil fuel dependence [7]. Thereafter, MFCs have evolved into multifunctional environmental tools for pursuing the United Nations Sustainable Development Goal 7 to provide clean, reliable, and renewable energy sources. Microorganisms utilize soil oxidants as electron acceptors in anaerobic environments during anaerobic digestion, a process that drives organic-matter decomposition and biogas production (primarily CH4 and CO2), thereby promoting GHG emissions [8].
The operation mechanism of MFCs is based on the modification of soil redox potential to induce competitive electron-transfer interactions that inhibit methanogenesis and enhance complete denitrification, thereby substantially mitigating CH4 and N2O emissions [9]. Overall, the application of MFCs to rice cultivation aligns with the goals of sustainable farming, offering a potential breakthrough in the mitigation of the effects of climate change while promoting environmental resilience.
The core concept of the MFC technology involves the introduction of an artificial electron acceptor to divert microbial electron transfer (MET) from natural oxidants to a controlled circuit. This is realized by connecting an anaerobic anode to an aerobic cathode, allowing electrogenic microorganisms to oxidize organic matter and rhizodeposits near plant roots [10, 11]. The released electrons during microbial oxidation migrate from the anode to the cathode, thereby simultaneously generating electricity and modifying the soil redox potential. This process inhibits CH4 production and promotes complete denitrification. At the cathode, the electrons react with oxygen to form water, whereas residual oxidants remain in the soil, serving as essential nutrients for plant growth [12]. This bioelectrochemical mechanism harnesses plant-driven solar energy, further contributing to the mitigation of GHG emissions and ensuring sustainable agricultural practices.
Agricultural intensification to satisfy the continuously increasing global food and energy demands presents challenges and opportunities for sustainable development. Thus, this systematic literature review (SLR) is aimed at evaluating the potential of PF-MFCs, specifically analyzing their effectiveness in mitigating CH4 and N2O emissions. By synthesizing the findings of recent relevant studies, this review identifies knowledge gaps, explores microbial competition in paddy soils, and assesses the scalability of MFC systems for large-scale applications in agriculture [13]. Through bibliometric and comparative analyses, this review unearths low-emission rice-cultivation strategies, ensuring sustainable food production while minimizing adverse environmental impacts.
This SLR was based on the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines to ensure transparency and replicability [14]. As illustrated in Figure 1, the research workflow followed a structured sequence, beginning from the initial search to the final study selection.
Using specific search keywords and syntaxes (Table 1), articles were retrieved from highly reputable scientific literature databases, including Scopus, ScienceDirect, PubMed, and Wiley-Blackwell. The search was restricted to English-language, peer-reviewed articles published within the past 15 years (2008–2023), encompassing original research and review articles. As each database employs a unique search syntax, search queries were formulated to align with the characteristics of each source.
| Database | Keywords and syntax |
|---|---|
| ScienceDirect | [(microbial fuel cell OR mfc) AND (rice field OR rice paddy field) AND (methane OR ch4 OR n2o OR Nitrous oxide)] year 2008–2023 |
| Scopus | (TITLE-ABS-KEY (microbial AND fuel AND cell OR mfc) AND TITLE-ABSKEY (rice AND field OR paddy AND field) AND TITLE-ABS-KEY (methane OR ch4) AND TITLE-ABS-KEY (nitrous AND oxide OR n2o)) |
| PubMed | (((microbial fuel cell) OR (mfc)) AND ((rice field) OR (rice paddy field))) AND ((methane OR ch4) AND (nitrous oxide OR n2o)) |
| Wiley-Blackwell | “microbial fuel cell OR mfc” anywhere and “rice field OR rice paddy field” anywhere and “ch4 OR methane OR n2o OR nitrous oxide” anywhere |
Thereafter, the search results were exported to Mendeley Reference Manager (version 2.79.0), where duplicate articles and irrelevant publications were systematically eliminated to ensure the accuracy and consistency of the dataset.
This SLR defines the inclusion criteria based on the population, intervention, comparison, outcome (PICO) framework (Table 2). The PICO approach structures research questions into clear, measurable components, as follows: (P) population: paddy soils, (I) intervention: MFCs, (C) comparison: with vs. without MFCs, and (O) outcome: changes in GHG emissions (CH4 and/or N2O). The studies assessed in this SLR encompassed laboratory or field experiments that met these inclusion criteria, providing quantitative data on GHG emissions or soil redox potential.
| Framework | Criteria |
|---|---|
| Population (P) | Flooded rice paddy soils |
| Intervention (I) | Microbial Fuel Cells |
| Comparison (C) | With vs. without MFC |
| Outcome (O) | Changes in greenhouse gas emissions (CH4 and/or N2O) |
The synthesized studies were selected through multiple stages, following four systematic steps: (1) identification (the extant studies were retrieved from databases, after which duplicate entries were filtered out), (2) screening (their titles and abstracts were reviewed to assess their preliminary relevance), (3) eligibility (full-text articles were examined to ensure that they met the inclusion criteria), and (4) inclusion (the studies that aligned with all the criteria were incorporated into the final synthesis).
This process is visualized in the flow diagram of the PRISMA framework (Figure 1), which details the number of articles at each selection stage, ensuring transparency and the replicability of the study-selection process.
The data extracted from the selected studies included author names, publication year, experiment type (laboratory or field), MFC type and configuration, sediment, identified microorganisms, and emission-related main findings. Thereafter, the data were classified based on gas type (CH4 or N2O) and presented in two separate tables (Supplementary Table 1 and Supplementary Table 2) for thematic and comparative analyses.
This systematic approach ensured methodological rigor and scientific accountability while enhancing reproducibility and result validity. The implementation of PRISMA guidelines enabled transparent documentation at every stage, from study selection to detailed data extraction.
In this study, 376 records were identified through the systematic search strategy. After screening and thorough eligibility assessment, 24 studies were adjudged to have met the inclusion criteria; these were incorporated into this review. Among these selected studies (24), 18 corresponded to original research articles with the following distributions: six of the studies explored CH4 emissions, six explored N2O emissions, and six simultaneously explored both GHG emissions (CH4 and N2O).
Additionally, six of the studies were review articles (Supplementary Table 3), providing theoretical context, as well as deeper insights, into technological advancements and microbiological profiles related to MFC integration with paddies.
This distribution ensured that the review relied on a thorough, well-rounded analysis, incorporating experimental studies and broader conceptual frameworks than the existing ones to elucidate MFC applications in GHG-emission mitigation.
3.1 Mitigation effects of microbial fuel cells on methane emissionsCH4 emissions from PFs are major contributors to the total agricultural GHG output, and these emissions are primarily driven by microbial activities in anaerobic soil environments. The conventional mitigation strategies mainly comprise water management and alternative-fertilization methods. However, recent studies explored MFCs as promising technologies for mitigating CH4 emission through the modification of MET and the competitive utilization of substrates.
Regarding the operation mechanism of MFCs, they establish an electrochemical gradient that alters the microbial community dynamics, particularly affecting the competition between electrogenic bacteria and methanogens. Several studies revealed that electrogenic microbes, such as Geobacter and Clostridium, outcompete methanogens for electron donors when anodes are introduced into paddy soils, thereby inhibiting methanogenesis. Ishii et al. [15] observed that CH4 production was significantly suppressed in closed-circuit (CC) MFCs compared with open-circuit (OC) MFC systems, indicating that electrical flow disrupts the natural electron-donation pathways driving methanogenesis.
Additionally, PF-MFCs can modify the soil redox potential, thereby shifting the soil redox conditions from the strongly reduced state favored by methanogens (methane producing micro-organisms. Virdis et al. [16] revealed that the redox potential recorded from MFC-based sensors correlated negatively with the CH4-emission flux, revealing the existence of complex interactions between the redox state and microbial activity. Wang et al. [17] demonstrated that MFC integration in hydroponic systems (H-MFCs) halved the CH4 flux without affecting the rice plant biomass, thus reinforcing the theory that controlled electron transfer (ET) can effectively suppress CH4 production without disrupting plant growth.
The CH4-suppression efficacy of MFCs depends on their configuration, with anode placement and resistance tuning playing critical roles in regulating microbial interactions. Lin and Lu [18] revealed that sediment-based MFCs (S-MFCs) significantly suppressed methanogenesis when embedded within rice rhizospheres, whereas Wang et al. [19] observed that a constructed wetland (CW) integrated with MFCs (CW-MFCs) realized up to 36.9% CH4 mitigation under optimized conditions. Notably, single-chamber MFC systems exhibited higher CH4-suppression effectiveness than their dual-chamber counterparts owing to their enhanced ET dynamics.
Relevant studies, such as those by Arends et al. [20] and Kouzuma et al. [21], further emphasize that the enrichment of MFC microbial communities with electrogenic bacteria over time persistently suppresses CH4 emissions. The long-term stabilities of these systems indicate potential scalability if environmental variables, such as substrate availability, electrode materials, and irrigation cycles, are adequately controlled.
Despite their demonstrated potential, the extensive application of MFCs to the mitigation of CH4 emission from PF-MFCs remains constrained by MFC limitations, such as electrode longevity, energy output efficiency, and feasibility for large-scale implementation. Additionally, achieving optimal microbial interactions for CH4 reduction requires the precise management of redox gradients and substrate competition, and these aspects still require further refinement in field applications.
Thus, future related studies must explore hybrid bioelectrochemical systems (BES) integrating denitrification and CH4-oxidation pathways to enhance the mitigation of GHG emissions. Furthermore, advanced electrode materials that enhance electrochemical stability and biocompatibility can be investigated to improve system resilience and cost-effectiveness for agricultural integration.
Overall, the integration of the MFC technology into PF management presents a viable strategy for mitigating CH4 emissions, leveraging microbial competition and MET mechanisms to suppress methanogenesis. Although promising, the scalability and efficiency of MFC systems must be optimized to achieve real-world agricultural applications. Aligning with the urgent demand for climate-smart farming solutions, MFCs may serve as key innovations for pursuing low-carbon rice cultivation.
3.2 Mitigation effects of microbial fuel cells on nitrous oxide emissionsN2O emissions from PFs pose a critical environmental concern, as they contribute to global warming, with a global warming potential (GWP) that is 298 times greater than that of CO2. Notably, the integration of MFCs in paddies represents a promising approach for mitigating N2O emissions through the modification of the MET mechanism and the control of the denitrification pathways.
MFCs influence the microbial nitrogen cycle by introducing a bioelectrochemical gradient, which regulates ET between electrogenic bacteria and denitrifiers. Several studies identified the electrode potential and redox conditions as the key factors for mitigating N2O accumulation in wetland systems. Wang et al. [22] reported that single-chamber electroactive CWs integrating MFCs (ECW-MFCs achieved a 52% reduction of N2O emissions, primarily leveraging on the enhanced microbial competition for electrons, as well as the suppression of incomplete denitrification. Similarly, Ranatunga et al. [23] observed that the denitrification-related total nitrogen loss decreased from 6.6% to 2.3% in PF-MFCs, indicating that BESs improved nitrogen retention while mitigating GHG emissions.
Electron competition in MFC systems inhibits the reductive half-reaction of NO3, thereby suppressing N2O production [23]. This mechanism directly supports the following hypothesis: N2O emissions are primarily mitigated by inhibiting the pathway of the reduction of NO3 to NO2 or NO, representing a key N2O mitigation strategy. In this context, Yu et al. [24] observed that MFC cathodic potential can be regulated to suppress nitrite accumulation and prevent the various reductive reactions to yield N2O.
However, some microbes still gained sufficient access to electrons to reduce NO3 to NO2 and ultimately N2O despite MFCs functioning as electron acceptors, particularly in microaerobic zones or under unstable redox conditions [24, 25]. Therefore, in addition to inhibiting the pathway of NO3 reduction to NO2 or NO, activating the nosZ pathway remains a relevant strategy for ensuring the immediate conversion of N2O into N2, following its formation, thereby avoiding its accumulation.
Niu et al. [26] reported that constructed wetlands integrated with MFCs (CW-MFC) operating at an optimal C/N ratio (5) enhanced nosZ gene expression, thereby effectively decreasing N2O emission. This shift in the microbial gene abundance altered the nosZ/(nirS + nirK) ratio, initiating highly efficient denitrification pathways that prevented N2O accumulation. Additionally, Mamun and Baawain [25] demonstrated that redox imbalance can cause free nitrous acid (FNA) accumulation through elevated NO2 concentrations, thereby enhancing N2O production. However, optimizing the cathodic conditions and pH can allow the nitrogen-reduction pathway to proceed directly to N2 without generating intermediate gases, such as N2O, thereby ensuring a more complete denitrification process.
The mitigation effect of MFCs on N2O emissions depends on the electrode placement, external-resistance tuning, and microbial community dynamics within the system. Yu et al. [24] and Al Mamun and Baawain [25] evaluated cathodic denitrification in BESs, indicating that N2O emissions can be regulated by the adequate control of the electrode potentials of such systems, with lower cathode potentials minimizing the accumulation of intermediates. Wang et al. [27] compared periodic and continuous polarizations in Microbial Electrolysis Cell (MEC) systems, revealing that continuous polarization suppressed N2O accumulation, whereas periodic polarization caused variations in N2O release owing to incomplete ET.
Plant-integrated MFC systems (P-MFCs) have been explored for paddy applications. Arends et al. [20] introduced plant-integrating MFCs (P-MFCs) within rice rhizospheres, noting the shifts in the microbial dynamics among electrogenic bacteria, methanogens, and denitrifiers. Although P-MFCs could not directly control N2O emissions, they influenced microbial competition, thereby indirectly controlling the emission of nitrogen gas (N2).
Although MFC-based systems demonstrate significant potential for N2O mitigation, they are still limited by several challenges. Notably, their electrode longevity, energy efficiency, and large-scale deployment under real-world conditions must be addressed through further investigations. Additionally, optimizing electrode redox potential to balance microbial competition is crucial to ensuring stable performance across varying paddy environments.
Thus, future studies should explore hybrid bioelectrochemical approaches integrating electrogenesis with the nosZ-pathway enhancement to optimize nitrogen cycling while minimizing GHG emissions. Moreover, the scaling up of these innovations could realize low-carbon rice cultivation, offering a sustainable strategy for climate-smart agriculture.
The MFC technology represents a viable approach for mitigating N2O emissions in PFs, leveraging bioelectrochemical mechanisms to redirect nitrogen cycling and suppress the accumulation of intermediates. The interplay between the redox dynamics, microbial interactions, and electrode design in MFCs determines their effectiveness, paving the way for innovative GHG-mitigation strategies.
3.3 Comparison of methane and nitrous oxide emissions in microbial-fuel-cell integrated paddiesCH4 and N2O are significant GHGs emitted from PFs, originating through distinct microbial processes and exerting distinct environmental implications. Notably, the MFC technology represents a promising strategy for mitigating both gases through bioelectrochemical adjustments. However, its mitigation effects on CH4 and N2O differ significantly owing to variations in microbial competition, electron flow, and redox dynamics.
CH4 emissions are mainly driven by anaerobic methanogenesis, where Methanobacterium, Methanomassiliicoccus, and Methanoregula convert organic substrates into CH4 under strictly anaerobic conditions. Conversely, N2O emissions are driven by incomplete denitrification, where Paracoccus denitrificans, Thauera, and Nitrosomonas reduce nitrate (NO3) and NO2 but fail to complete the final step to yield N2, thereby resulting in N2O accumulation.
MFCs disrupt CH4 production by introducing anodic electron competition, thereby effectively diverting electron donors from methanogens toward electrogenic bacteria, such as Geobacter and Shewanella. Wu et al. [28] observed a strong correlation between the voltage signals of MFC sensors and CH4-emission flux, revealing that an enhanced electron flow suppressed methanogenesis in PFs. Similarly, Wang et al. [17] revealed that H-MFCs halved CH4 emissions without reducing the rice biomass, thereby confirming the feasibility of this approach in agricultural systems.
MFCs mitigate N2O emissions by inhibiting NO3 reduction into NO2 or NO, thereby preventing the accumulation of intermediate gases during denitrification. Further, electron competition within MFCs limits the access of microbes to electrons, thereby suppressing N2O production [23]. However, several microbes can still gain sufficient access to electrons and drive NO3 reduction to N2O under microaerobic conditions or unstable redox states. Therefore, activating the nosZ pathway remains a crucial approach to preventing N2O accumulation and ensuring complete denitrification [26].
Further, the redox potential plays a crucial role in differentiating the mitigation effects of MFCs on CH4 and N2O. Lower redox conditions (less than −200 mV) favor methanogenesis, whereas higher redox conditions (+100 to −100 mV) facilitate complete denitrification. Wang et al. [19] observed that CC CW-MFCs elevated the soil redox potential and suppressed CH4 emissions by 36.9%. However, N2O emissions varied with the applied electrode tuning. Ranatunga et al. [23] further confirmed that redox adjustments reduced the total nitrogen loss from 6.6% to 2.3%, thereby preventing the excessive release of N2O.
Comparative studies revealed that CH4 emission in MFC systems is more consistent than N2O reduction owing to the direct competition between electrogenic bacteria and methanogens. However, the mitigation of N2O emissions requires the precise tuning of the soil redox potential and microbial community dynamics. Al Mamun and Baawain [25] highlighted that NO2 accumulation in bio-cathodes resulted in increased N2O production, whereas Wang et al. [27] demonstrated that continuous polarization reduced N2O accumulation more effectively than periodic polarization.
Thus, the optimization strategies for MFCs differ depending on the target GHG: (1) CH4: enhancing ET to electrogenic bacteria and increasing the soil redox potential would effectively suppress methanogenesis; (2) N2O: the first mechanism involves the inhibition of the NO3 → NO2/NO reductive pathway, preventing NO2 and intermediate gas accumulations during denitrification. Maintaining stable redox conditions and optimizing the nosZ/(nirS + nirK) ratio are crucial to realizing complete denitrification without the accumulation of intermediate GHGs.
The MFC technology presents distinct pathways for mitigating CH4 and N2O emissions, and each pathway requires targeted controls of the microbial community dynamics, electrode tuning, and redox regulation. Although the mitigation of CH4 emission is mainly driven by electron competition, that of N2O emission requires precise denitrification management to avoid the accumulation of intermediates. Future advancement attempts should focus on exploring hybrid bioelectrochemical approaches integrating these pathways or mechanisms to develop low-emission, climate-resilient paddy systems.
3.4 Insights from previous reviewsMFC configurations have evolved considerably, encompassing classical MFCs, S-MFCs, P-MFCs, and CW-MFCs. Each configuration offers a different approach to leveraging bioelectrochemical mechanisms for GHG-emission mitigation. Gupta et al. [29] evaluated the technology readiness levels (TRLs) of these systems, ranking CW-MFCs as the most field-ready systems (TRL 6–7), followed by MFCs (TRL 5–6), S-MFCs (TRL 3–4), and P-MFCs (TRL 3). Thus, CW-MFCs represent the most feasible options for large-scale applications, particularly in rice-cultivation systems.
CH4 and N2O emissions from paddies pose significant environmental threats, with the GWP of N2O significantly exceeding that of CO2. Studies revealed that electron competition between electrogenic microbes and methanogens in anaerobic environments effectively inhibits CH4 production. For example, Gupta et al. [29] confirmed that CW-MFCs outperformed the other MFC configurations in CH4 mitigation owing to their ability to facilitate enhanced microbial interactions, as well as their more advanced bioelectrochemical control mechanisms. Schamphelaire et al. [30] developed a conceptual framework illustrating the modification effects of electrode placement in sediments on microbial redox conditions, i.e., the mechanism by which it indirectly suppressed methanogenesis. Moreover, Kouzuma et al. [21] emphasized the mitigation effects of S-MFCs on CH4 emissions, although their effectiveness highly relied on the anaerobic conditions and substrate availability.
As already stated, N2O mitigation is more complex than CH4 mitigation, as it relies on microbial denitrification activity and nosZ gene expression to ensure complete reduction to N2. Ranatunga et al. [31] highlighted that imbalances in the denitrification process can result in N2O accumulation, significantly contributing to GHG emissions. In light of MFC and CW-MFC technologies, these findings indicated that redox regulation and ET management are crucial to optimizing denitrification processes, thereby ensuring complete N2O conversion into N2. Nguyen and Babel [32] emphasized the criticality of stable ET to the suppression of N2O accumulation, as shortcut nitrification–denitrification can disrupt the redox balance and promote the excessive release of N2O. Apollon et al. [33] demonstrated that well-optimized CW–MFCs can significantly decrease N2O emissions by promoting nosZ gene activity. This finding was supported by Gupta et al. [29], who observed that CW-MFCs drive complete denitrification, facilitating the complete conversion of N2O to inert N2, making them highly effective in mitigating nitrogen-related emissions from paddies.
Scalability and economic feasibility are critical determinants of MFC implementation in sustainable agriculture. Schamphelaire et al. [30] provided an initial outlook on S-MFC scalability, highlighting electrode limitations in these systems. Kouzuma et al. [21] and Ranatunga et al. [31] emphasized that P-MFCs required further optimization regarding plant selection and electrode materials before they can realize field-scale deployment. Gupta et al. [29] and Apollon et al. [33] identified CW-MFCs as the most economically viable MFC configuration, citing their lower cost-to-benefit ratio compared with those of standalone classical MFCs. Nguyen and Babel [32] revealed that the applications of MFC to wastewater treatment required precise ET management, which directly impacts operational costs and long-term feasibility in agricultural integration.
Based on the findings of this SLR, the following directions must be explored for the effective implementation of the MFC technology to mitigate paddy-emitted GHGs: (1) adapt CW-MFC principles for optimizing redox control and minimizing CH4 emissions in submerged soils; (2) enhance nosZ gene expressions to ensure complete N2O reduction, thereby preventing the accumulation of intermediate gases; (3) develop cost effective electrode materials tailored for agricultural applications, thereby minimizing installation costs while maintaining efficiency; (4) explore hybrid BESs integrating CW-MFC and P-MFC configurations, thereby leveraging plant–root interactions for improved nitrogen cycling; and (5) explore the integration of CW-MFC into sustainable agriculture, thereby ensuring maximized rice yields with minimized environmental impacts.
The analysis of these six review articles [21, 29, 20, 31, 32, 33] offers critical insights into the development, scalability, and effectiveness of the MFC technology for mitigating CH4 and N2O emissions from paddies. Overall, CW-MFCs consistently emerged as the most promising technology among the various MFC configurations for PFs, and this is thanks to their economic feasibility, scalability, and superior performance in minimizing environmental impacts. Future studies should prioritize the optimization of MFC configurations for large-scale agricultural integration, ensuring enhanced rice cultivation while mitigating GHG emissions.
The findings from this SLR highlight the significant potential of MFCs in mitigating GHG (CH4 and N2O) emissions from paddies, mainly by leveraging electron competition and redox-regulation mechanisms.
The mitigation of CH4 emission is powered by the establishment of electron competition between electrogenic microorganisms and methanogens, where the electrogenic microorganisms prevail under higher redox conditions. Studies indicated that CW-MFCs delivered the most remarkable CH4-emission mitigation compared with the other reviewed MFC configurations.
Conversely, N2O-emission mitigation is more complex than CH4-emission mitigation, as it relies on the inhibition of the reductive pathway of NO3 to NO2/NO and the activation of the nosZ pathway to ensure complete NO3 reduction to N2. CW-MFCs exerted the most mitigation effect on N2O emissions by enhancing ET and optimizing bioelectrochemical conditions.
A comparative analysis of CH4 and N2O revealed that CH4 emission can be controlled through consistent, straightforward mechanisms, whereas N2O-emission mitigation requires redox optimization and microbial community adjustments to prevent the accumulation of intermediate gases.
Furthermore, the six reviewed articles consistently identified CW-MFCs as the most promising technology in terms of GHG-emission mitigation and readiness for field-scale application. However, several technical challenges, including electrode optimization, energy efficiency, and large-scale agricultural-deployment feasibility, must first be addressed.
To advance low-carbon agriculture, hybrid bioelectrochemical strategies integrating methanogenesis and denitrification control must be explored, leveraging the CW-MFC technology, which has demonstrated high effectiveness in mitigating paddy-emitted GHGs. For a detailed examination of potential study areas, please refer to Table 3, which outlines key study directions toward implementing MFCs for the mitigation of paddy-emitted GHGs.
| No. | Research Aspect | Focus and Future Directions | Potential Impact |
|---|---|---|---|
| 1 | Optimized Integration of MFCs in Agricultural Systems |
Application of MFCs to the mitigation of paddy-emitted GHGs MFC–biochar/aeration integration to enhance redox efficiency |
Mitigation of CH4 and N2O Emissions Improved sustainability in agriculture |
| 2 | Development of More Efficient Electrode Materials |
Exploration of enhanced-conductivity electrodes Utilization of nanoparticles or porous carbon materials to enhance substrate adsorption |
Improved ET efficiencyLong-term operational stability |
| 3 | Adaptation of MFCs for Wastewater and Agricultural Water Treatment |
Optimization of MFC systems for agricultural wastewater treatment Study of electrogenic microbial communities in MFC systems |
Reduction of nitrogen and azo-compound contaminants Sustainable nutrient cycling |
| 4 | Influence of Polarity Patterns on MFC Performance |
Evaluation of the efficiency of periodic polarization in mitigating CH4 and N2O emissions Development of electron-storage-optimizing electrochemical configurations |
Enhanced GHG-mitigation effects Development of more adaptive electrochemical systems |
| 5 | Optimization and Predictive Modeling for Field-Scale Applications |
Development of mathematical models for predicting MFC efficiency Integration of sensors for real-time redox monitoring |
Increased accuracy of monitoring systems Large-scale implementation in agricultural systems |
