Effect of operating parameters on the performance of sediment microbial fuel cell treating aquaculture water

Aquatic plants combined with microbial fuel cells promote sulfamethoxazole and sul genes removal from aquaculture pond sediments via bioelectrochemistry

Antibiotics and antibiotic resistance genes (ARGs) in the aquaculture environment are receiving increasing public attention as emerging contaminants. In this study, aquatic plant (P) and sediment microbial fuel cells (SMFC) were used individually and in combination (P-SMFC) to simulate in situ remediation of sulfamethoxazole (SMX) and sul genes in aquaculture environments. The results showed that the average power densities of SMFC and P-SMFC were 622.18 mW m-2 and 565.99 mW m-2, respectively. The addition of 5 mg kg-1 of SMX to the sediment boosted the voltages of SMFC and P-SMFC by 36.3% and 51.5%, respectively. After 20 days of treatment, the removal efficiency of SMX from the sediment was 86.17% and 89.60% for SMFC and P-SMFC group, respectively, which were significantly higher than the control group (P < 0.05). However, removal of SMX by plants was not observed. P-SMFC group significantly reduced the biotoxicity of SMX to Staphylococcus aureus and Escherichia coli in the overlying water (P < 0.05). P and P-SMFC groups significantly reduced the abundance of ARGs intl1 and sul1 (P < 0.05). The removal rate of ARGs intl1, sul1 and sul2 from sediments by P-SMFC ranged from 94.22% to 97.08%. However, SMFC increased the abundance of sul3. SMFC and P-SMFC increased the relative abundance of some of sulfate-reducing bacteria such as Desulfatiglans, Thermodesulfovibrionia and Sva0485 in sediments. These results showed that aquatic plants promoted the removal of ARGs and SMFC promoted the removal of antibiotics, and the combination with aquatic plants and SMFC achieved a synergistic removal of both SMX and ARGs. Therefore, current study provides a promising approach for the in situ removal of antibiotics and ARGs in the aquaculture environment.

Using stacked pot connection of wetland microbial fuel cells to charge the battery: Potential and effecting factor

In the practical application of wetland microbial fuel cells (WMFCs), suitable designs and stacked connection systems have consistently been employed to increase and harvest power generation. Our study compares different WMFCs designs and demonstrates that the cylinder pot design outperforms the small hanging pot design in terms of electrical energy production. Moreover, power generation from the cylinder pot can be further optimized through separator modification and stacked connections. The stacked WMFCs design exhibited no voltage reversal, with an average power output ranging from 0.03 ± 0.01 mW (single pot) to 0.11 ± 0.05 mW (stacked connection of 5 pots) over a 60-day operational period. Additionally, our study identifies distinct patterns in both anodic and cathodic physiochemical factors including electrical conductivity (EC), pH, and nitrate (NO3-), highlighting the significant influence of plant involvement on altering concentrations and levels in different electrode zones. The WMFCs bioelectricity production system, employing 15 pots stacked connections achieves an impressive maximum power density of 9.02 mW/m2. The system's practical application is evidenced by its ability to successfully power a DC-DC circuit and charge a 1.2 V AAA battery over a period of 30 h, achieving an average charging rate of 0.0.2 V per hour.

Elimination of pharmaceuticals from wastewater using microbial fuel cell-based bio-electro-Fenton process

This study highlights the potential of the microbial fuel cell (MFC)-based bio-electro-Fenton (BEF) process as an efficient and highly adaptable strategy for wastewater treatment. The research aims to optimize the pH of the cathodic chamber (3-7) and catalyst doses (Fe) (0-18.56%) on the graphite felt (GF) cathode, and examine the effect of operating parameters on chemical oxygen demand (COD) removal, mineralization efficiency, pharmaceuticals (ampicillin, diclofenac, and paracetamol) removal, and power generation. The study found that lower pH and higher catalyst dosage on the GF led to better performance of the MFC-BEF system. Under neutral pH, mineralization efficiency, paracetamol removal, and ampicillin removal were enhanced by 1.1 times, and power density improved by 1.25 times as catalyst dosage increased from 0 to 18.56%. Additionally, employing full factorial design (FFD) statistical optimization, the study identifies the optimized conditions for maximum COD removal, mineralization efficiency, and power generation, which are determined to be a pH of 3.82 and a catalyst dose of 18.56%.

Methane emission reduction oriented extracellular electron transfer and bioremediation of sediment microbial fuel cell: A review

Sediment is the internal and external source of water environment pollution, so sediment remediation is the premise of water body purification. Sediment microbial fuel cell (SMFC) can remove the organic pollutants in sediment by electroactive microorganisms, compete with methanogens for electrons, and realize resource recycling, methane emission inhibiting and energy recovering. Due to these characteristics, SMFC have attracted wide attention for sediment remediation. In this paper, we comprehensively summarized the recent advances of SMFC in the following areas: (1) The advantages and disadvantages of current applied sediment remediation technologies; (2) The basic principles and influencing factors of SMFC; (3) The application of SMFC for pollutant removal, phosphorus transformation and remote monitoring and power supply; (4) Enhancement strategies for SMFC in sediments remediation such as SMFC coupled with constructed wetland, aquatic plant and iron-based reaction. Finally, we have summarized the drawback of SMFC and discuss the future development directions of applying SMFC for sediment bioremediation.

Effect of Electrode Spacing on the Performance of a Membrane-Less Microbial Fuel Cell with Magnetite as an Additive

A microbial fuel cell (MFC) is a bioelectrochemical system that can be employed for the generation of electrical energy under microbial activity during wastewater treatment practices. The optimization of electrode spacing is perhaps key to enhancing the performance of an MFC. In this study, electrode spacing was evaluated to determine its effect on the performance of MFCs. The experimental work was conducted utilizing batch digesters with electrode spacings of 2.0 cm, 4.0 cm, 6.0 cm, and 8.0 cm. The results demonstrate that the performance of the MFC improved when the electrode spacing increased from 2.0 to 6.0 cm. However, the efficiency decreased after 6.0 cm. The digester with an electrode spacing of 6.0 cm enhanced the efficiency of the MFC, which led to smaller internal resistance and greater biogas production of 662.4 mL/g VS_fed. The electrochemical efficiency analysis demonstrated higher coulombic efficiency (68.7%) and electrical conductivity (177.9 µS/cm) for the 6.0 cm, which was evident from the enrichment of electrochemically active microorganisms. With regards to toxic contaminant removal, the same digester also performed well, revealing removals of over 83% for chemical oxygen demand (COD), total solids (TS), total suspended solids (TSS), and volatile solids (VS). Therefore, these results indicate that electrode spacing is a factor affecting the performance of an MFC, with an electrode spacing of 6.0 cm revealing the greatest potential to maximize biogas generation and the degradability of wastewater biochemical matter.

Anode modification of sediment microbial fuel cells (SMFC) towards bioremediating mariculture wastewater

Remediation of mariculture wastewater is of great practical importance. In this study, sediment microbial fuel cells (SMFCs) were adopted and carbon felt anodes were modified to enhance COD and ammonia removal in mariculture system. The results showed that the SMFC anode with 5 % (w/w) graphene oxide (GO) coating performed best in pollutants removal and electricity generation. The maximum power density approached 132 mW/m², nearly 4.5 times higher than the unmodified anode. The removal efficiency of COD and ammonia reached 82.1 % and 95.8 % respectively, both improved compared with the control and chemical modification. The modified anode effectively enriched the electrogenic Sulfurovum and Lactobacillus and thus led to a significant improvement in the electrochemical performance of SMFC. This study demonstrates the successful application of SMFCs with GO modified anodes in the in-situ removing pollutants and SMFCs present obvious remediation potential on the contaminated mariculture inhabitant.

Effect of Electrode Distances on Remediation of Eutrophic Water and Sediment by Sediment Microbial Fuel Cell Coupled Floating Beds

Efficient and sustainable technologies for cleaning of contaminated water and sediments are in urgent demand. In this study, a new type of sediment microbial fuel cell coupled floating bed (FB-SMFC) was developed to repair eutrophic water and sediment in a cleaner way. The effect of electrode spacing on the power generation capacity and the synchronous remediation of pollutants from eutrophic water and sediment were studied. When the electrode distance was 60 cm, the maximum power generation and pollutant removal effects were obtained. At the end of the experiment, the maximum output voltage was 0.4 V, and the chemical oxygen demand (COD_Cr, potassium dichromate method), total nitrogen (TN), and total phosphorus (TP) contents in the overlying water were 8 mg/L, 0.7 mg/L, and 0.39 mg/L. The corresponding removal rates were 88.2%, 78.8%, and 59.0%, respectively. The removal rates of organic matter and TN in the sediment were 12.8% and 86.4%, respectively, and the fixation rate of TP was 29.2%. Proteobacteria was the dominant phylum of bacteria in the sediment and anode. Many anaerobic bacteria were found in the overlying water, which facilitated denitrification. Overall, the results of this research revealed a highly efficient and reliable strategy for eutrophic water and sediment remediation, aquatic ecosystems restoration, and human health protection.

Comparative evaluation of simultaneous nitritation/denitritation and energy recovery in air-cathode microbial fuel cells (ACMFCs) treating low C/N ratio wastewater

Air-cathode microbial fuel cells (ACMFCs) can extract available electrons from the low C/N ratio wastewater (LCNW) for pollutant degradation and power generation. However, the multiple effects of operating parameters and their relationship between the performances and parameters are still lacking. In this study, several ACMFCs for simultaneous nitritation/denitritation (SND) and energy recovery were constructed and evaluated in terms of chemical oxygen demand (COD), NH₄⁺-N, C/N ratio, phosphate buffer solution (PBS), and external resistance (R_ext), and several derived parameters (e.g., organic loading rate (OLR), nitrogen loading rate (NLR)). Results indicated that ACMFCs could be used to treat LCNW successfully with high pollutant removal rates and sustainable current generation. Maximum removal efficiencies of 94% COD, 92% NH₄⁺-N, and 92% total nitrogen (TN) were achieved. A maximum power density of 1400 mW m^-2 and columbic efficiency of 69.2% were also obtained at a low C/N ratio of 1.7-2.6. Low C/N ratios promoted SND by balancing nitritation and denitritation. The microbial community and their predicated function results showed considerable nitrifiers and denitrificans were enriched in the ACMFCs, contributing to SND and power recovery. Further analyses showed that the NH₄⁺-N could inhibit SND, but PBS and R_ext had no obvious effects on this outcome. Co-occurrence network analysis demonstrated that power is positively correlated with COD and R_ext; strong correlations between organic removal and COD, and between nitrogen removal and ammonia, conductivity, and C/N ratio were also noted. Overall, the appropriate control of such parameters is necessary to achieve efficient SND in ACMFCs for LCNW treatment.

A review of the operating parameters on the microbial fuel cell for wastewater treatment and electricity generation

Environmental and economic considerations suggest a more efficient and comprehensive use of biomass for bioenergy production. One of the most attractive technologies is the microbial fuel cell using the catabolic activity of microorganisms to generate electricity from organic matter. The microbial fuel cell (MFC) has operational benefits and higher performance than current technologies for producing energy from organic materials because it converts electricity from the substrate directly (at ambient temperature). However, MFCs are still not suitable for high energy demand due to practical limitations. The overall performance of an MFC depends on the electrode material, the reactor design, the operating parameters, substrates, and microorganisms. Furthermore, the optimization of the parameters will lead to the commercial development of this technology in the near future. The simultaneous effect of the parameters on each other (intensifier or attenuator) has also been investigated. The investigated parameters in this study include temperature, pH, flow rate and hydraulic retention time, mode, external resistance, and initial concentration.

Agricultural Waste and Wastewater as Feedstock for Bioelectricity Generation Using Microbial Fuel Cells: Recent Advances

In recent years, there has been a significant accumulation of waste in the environment, and it is expected that this accumulation may increase in the years to come. Waste disposal has massive effects on the environment and can cause serious environmental problems. Thus, the development of a waste treatment system is of major importance. Agro-industrial wastewater and waste residues are mainly rich in organic substances, lignocellulose, hemicellulose, lignin, and they have a relatively high amount of energy. As a result, an effective agro-waste treatment system has several benefits, including energy recovery and waste stabilization. To reduce the impact of the consumption of fossil energy sources on our planet, the exploitation of renewable sources has been relaunched. All over the world, efforts have been made to recover energy from agricultural waste, considering global energy security as the final goal. To attain this objective, several technologies and recovery methods have been developed in recent years. The microbial fuel cell (MFC) is one of them. This review describes the power generation using various types of agro-industrial wastewaters and agricultural residues utilizing MFC. It also highlights the techno-economics and lifecycle assessment of MFC, its commercialization, along with challenges.

Mechanisms and challenges of microbial fuel cells for soil heavy metal(loid)s remediation

Bioelectrochemical approaches offer a simple, effective, and environmentally friendly solution to pollutant remediation. As a versatile technology, although many studies have shown its potential in soil heavy metal(loid) remediation, the mechanism behind this process is not simple or well-reviewed. Thus, in this review we summarized the impacts of the microbial fuel cells (MFCs) on metal (loids) movement and transformation in the soil environment in terms of changes in soil pH, electromigration, and substrate competition between anode-respiring bacteria and the soil microbial community. Furthermore, the progress of MFCs in the fixation/removal of different elements from the soil environment is described. Hence, this review provides critical insight into the use of the MFC for soil metal(loid) bioremediation.

Modeling and optimization strategies towards performance enhancement of microbial fuel cells

Considering the complexity associated with bioelectrochemical processes, the performance of a microbial fuel cell (MFC) is governed by input operating parameters. For scaled-up applications, a MFC system needs to be modeled from engineering perspectives in terms of optimum operating conditions to get higher performance and energy recovery. Several conceptual numerical models to advanced computational simulation approaches have been developed to represent simple-form of a complex MFC system. Application of mathematical and computation models are explored to establish the relationship between operating input-variables and power output. The present review discusses about the complexity of system, modeling strategies used and reality of such modeling for scaling-up applications of MFCs. Additionally, the selection of an appropriate mathematical model reduces the computational duration and provides better understanding of the system process. It also explores the possibility and progress towards commercialization of MFCs and thus the need of development of model-based optimization and process-control approaches.

Sediment microbial fuel cells as a barrier to sulfide accumulation and their potential for sediment remediation beneath aquaculture pens

Sediment microbial fuel cells (SMFCs) generate electricity through the oxidation of reduced compounds, such as sulfide or organic carbon compounds, buried in anoxic sediments. The ability to remove sulfide suggests their use in the remediation of sediments impacted by point source organic matter loading, such as occurs beneath open pen aquaculture farms. However, for SMFCs to be a viable technology they must remove sulfide at a scale relevant to the environmental contamination and their impact on the sediment geochemistry as a whole must be evaluated. Here we address these issues through a laboratory microcosm experiment. Two SMFCs placed in high organic matter sediments were operated for 96 days and compared to open circuit and sediment only controls. The impact on sediment geochemistry was evaluated with microsensor profiling for oxygen, sulfide, and pH. The SMFCs had no discernable effect on oxygen profiles, however porewater sulfide was significantly lower in the sediment microcosms with functioning SMFCs than those without. Depth integrated sulfide inventories in the SMFCs were only 20% that of the controls. However, the SMFCs also lowered pH in the sediments and the consequences of this acidification on sediment geochemistry should be considered if developing SMFCs for remediation. The data presented here indicate that SMFCs have potential for the remediation of sulfidic sediments around aquaculture operations.

Isolation of two iron-reducing facultative anaerobic electricigens and probing the application performance in eutrophication water

Purpose

Sediment microbial fuel cell (SMFC) is a promising bioremediation technology in which microbes play an important role. Electricigens as the bio-catalysts have effect on pollution control and electricity generation. It is of great significance to screen the microorganisms with the ability of generating electricity.

Methods

The SMFC anode biofilm was used as microbiological source to study the feasibility of electricigens with iron-reducing property for eutrophication water treatment. Preliminarily, we isolated 20 facultative anaerobic pure bacteria and evaluated their cyclic voltammogram (CV) through the three-electrode system and electrochemical workstation. The power generation performance of strains was verified by air-cathode microbial fuel cells (AC-MFCs) under different single carbon sources.

Result

According to its morphological, physiological, and biochemical characteristics, along with phylogenetic analysis, the two strains (SMFC-7 and SMFC-17) with electrical characteristics were identified as Bacillus cereus. Compared with SMFC-7, SMFC-17 exhibited efficient NH4+-N and NO3−-N removal and PO43−-P accumulation from eutrophic solution with a removal rate of 79.91 ± 6.34% and 81.26 ± 1.11% and accumulation rate of 57.68 ± 4.36%, respectively.

Conclusion

The isolated bacteria SMFC-17 showed a good performance in eutrophic solution, and it might be a useful biocatalyst to enable the industrialized application of SMFC in eutrophic water treatment.

Response-Surface-Optimized and Scaled-Up Microbial Electrosynthesis of Chiral Alcohols

A variety of enzymes can be easily incorporated and overexpressed within Escherichia coli cells by plasmids, making it an ideal chassis for bioelectrosynthesis. It has recently been demonstrated that microbial electrosynthesis (MES) of chiral alcohols is possible by using genetically modified E. coli with plasmid-incorporated and overexpressed enzymes and methyl viologen as mediator for electron transfer. This model system, using NADPH-dependent alcohol dehydrogenase from Lactobacillus brevis to convert acetophenone into (R)-1-phenylethanol, is assessed by using a design of experiment (DoE) approach. Process optimization is achieved with a 2.4-fold increased yield of 94±7 %, a 3.9-fold increased reaction rate of 324±67 μm h-1 , and a coulombic efficiency of up to 68±7 %, while maintaining an excellent enantioselectivity of >99 %. Subsequent scale-up to 1 L by using electrobioreactors under batch and fed-batch conditions increases the titer of (R)-1-phenylethanol to 12.8±2.0 mm and paves the way to further develop E. coli into a universal chassis for MES in a standard biotechnological process environment.

Microbial fuel cell system: a promising technology for pollutant removal and environmental remediation

The microbial fuel cell (MFC) system is a promising environmental remediation technology due to its simple compact design, low cost, and renewable energy producing. MFCs can convert chemical energy from waste matters to electrical energy, which provides a sustainable and environmentally friendly solution for pollutant degradations. In this review, we attempt to gather research progress of MFC technology in pollutant removal and environmental remediation. The main configurations and pollutant removal mechanism by MFCs are introduced. The research progress of MFC systems in pollutant removal and environmental remediation, including wastewater treatment, soil remediation, natural water and groundwater remediation, sludge and solid waste treatment, and greenhouse gas emission control, as well as the application of MFCs in environmental monitoring have been reviewed. Subsequently, the application of MFCs in environmental monitoring and the combination of MFCs with other technologies are described. Finally, the current limitations and potential future research has been demonstrated in this review.

Resource recovery from low strength wastewater in a bioelectrochemical desalination process

In this research, low strength synthetic wastewaters with chemical oxygen demand less than 300 mg L-1 were treated at different concentrations in a bioelectrochemical desalination process. A process optimization model was utilized to study the performance of the photosynthetic bioelectrochemical desalination process. The variables include substrate (chemical oxygen demand) concentration, total dissolved solids, and microalgae biomass concentration in the cathode chamber. Relationships between the chemical oxygen demand concentration, microalgae, and salt concentrations were evaluated. Power densities and potential energy benefits from microalgal biomass growth were discussed. The results from this study demonstrated the reliability and reproducibility of the photosynthetic microbial desalination process performance followed by a response surface methodology optimization. This study also confirms the suitability of bioelectrochemical desalination process for treating low substrate wastewaters such as agricultural wastewaters, anaerobic digester effluents, and septic tank effluents for net energy production and water desalination.

Cr(VI) removal from soils and groundwater using an integrated adsorption and microbial fuel cell (A-MFC) technology

Remediation of hexavalent chromium [Cr(VI)] has been widely studied for its high mobility and toxicity. As Cr(VI) migrates in natural environment, both soils and groundwater are contaminated simultaneously. In the present study, a novel reactor combining adsorption and microbial fuel cell (A-MFC) using Platanus acerifolia leaves was developed for removing Cr(VI) from groundwater and soils. When initial Cr(VI) concentration was 50 mg/L, the adsorption efficiency of A-MFC achieved 98% after 16 h. Afterwards, the leaves were used for fabricating an MFC-integrated leaching reactor. The A-MFC significantly improved the overall Cr(VI) removal efficiency through leaching and 40% of Cr(VI) in the soil column was removed. The electrical voltage and current of A-MFC reactor achieved averagely 343 mV and 141 μA to maintain the system operation without extra energy supply. This novel A-MFC reactor is an environmentally friendly technology which achieved efficient Cr(VI) removal from groundwater and soils using natural materials, proving the concept that integrated self-remediation of Cr(VI) in contaminated soil and groundwater with natural material and energy.

Effect of Operating Parameters on the Performance Evaluation of Benthic Microbial Fuel Cells Using Sediments from the Bay of Campeche, Mexico

Benthic microbial fuel cells (BMFC) are devices that remove organic matter (OM) and generate energy from sediments rich in organic nutrients. They are composed of electrodes with adequate different distances and floating air cathodes in an aqueous medium with saturated oxygen. In this study we proposed to design, build, analyze and evaluate a set of BMFCs with floating air cathodes to test the optimal distance between the electrodes, using sediment from the Bay of Campeche as a substrate. For the analysis of OM removal, COD tests, volatile solids (VS), E4/E6 study and FTIR analysis were performed. Power generation was evaluated through polarization curves, cyclic voltammetry and electrochemical impedance spectroscopy (EIS). We achieved a current density and power density at 10 cm depth of 929.7 ± 9.5 mA/m2 and 109.6 ± 7.5 mW/m2 respectively, with 54% removal of OM from the sediment, obtaining formation of aliphatic structures. BMFCs are proposed as adequate systems for bioremediation and power generation. The system at 10 cm depth and 100 cm distance between sediment and the floating air cathode had a good performance and therefore the potential for possible scaling.

Augmenting atrazine and hexachlorobenzene degradation under different soil redox conditions in a bioelectrochemistry system and an analysis of the relevant microorganisms

Soil microbial fuel cells (MFCs) are a sustainable technology that degrades organic pollutants while generating electricity. However, there have been no detailed studies of the mechanisms of pollutant degradation in soil MFCs. In this study, the effects of external resistance and electrode effectiveness on atrazine and hexachlorobenzene (HCB) degradation were evaluated, the performance of soil MFCs in the degradation of these pollutants under different soil redox conditions was assessed, and the associated microorganisms in the anode were investigated. With an external resistance of 20Ω, the degradation efficiencies of atrazine and HCB were 95% and 78%, respectively. The degradation efficiency, degradation rate increased with decreasing external resistance, while the half-life decreased. There were different degradation trends for different pollutants under different soil redox conditions. The fastest degradation rate of atrazine was in the upper MFC section (aerobic), whereas that of HCB was in the lower MFC section (anaerobic). The results showed that electrode effectiveness played a significant role in pollution degradation. In addition, the microbial community analysis demonstrated that Proteobacteria, especially Deltaproteobacteria involved in current generation was extremely abundant (27.49%) on soil MFC anodes, although the percentage abundances of atrazine degrading Rhodocyclaceae (8.77%), Desulfitobacterium (0.64%), and HCB degrading Desulfuromonas (0.73%), were considerably lower. The results of the study suggested that soil MFCs can enhance the degradation of atrazine and HCB, and bioelectrochemical reduction was the main mechanism for the pollutants degradation.

Internal nitrogen removal from sediments by the hybrid system of microbial fuel cells and submerged aquatic plants

Sediment internal nitrogen release is a significant pollution source in the overlying water of aquatic ecosystems. This study aims to remove internal nitrogen in sediment-water microcosms by coupling sediment microbial fuel cells (SMFCs) with submerged aquatic plants. Twelve tanks including four treatments in triplicates were designed: open-circuit (SMFC-o), closed-circuit (SMFC-c), aquatic plants with open-circuit (P-SMFC-o) and aquatic plants with closed-circuit (P-SMFC-c). The changes in the bio-electrochemical characteristics of the nitrogen levels in overlying water, pore water, sediments, and aquatic plants were documented to explain the migration and transformation pathways of internal nitrogen. The results showed that both electrogenesis and aquatic plants could facilitate the mineralization of organic nitrogen in sediments. In SMFC, electrogenesis promoted the release of ammonium from the pore water, followed by the accumulation of ammonium and nitrate in the overlying water. The increased redox potential of sediments due to electrogenesis also contributed to higher levels of nitrate in overlying water when nitrification in pore water was facilitated and denitrification at the sediment-water interface was inhibited. When the aquatic plants were introduced into the closed-circuit SMFC, the internal ammonium assimilation by aquatic plants was advanced by electrogenesis; nitrification in pore water and denitrification in sediments were also promoted. These processes might result in the maximum decrease of internal nitrogen with low nitrogen levels in the overlying water despite the lower power production. The P-SMFC-c reduced 8.1%, 16.2%, 24.7%, and 25.3% of internal total nitrogen compared to SMFC-o on the 55th, 82th, 136th, and 190th days, respectively. The smaller number of Nitrospira and the larger number of Bacillus and Pseudomonas on the anodes via high throughput sequencing may account for strong mineralization and denitrification in the sediments under closed-circuit. The coupled P-SMFC system has shown good potential for the efficient removal of internal nitrogen.

Enhanced phosphorus flux from overlying water to sediment in a bioelectrochemical system

This report proposed a novel technique for the regulation of phosphorus flux based on a bioelectrochemical system. In the simulated water system, a simple in situ sediment microbial fuel cell (SMFC) was constructed. SMFC voltage was increased with time until it was 0.23V. The redox potential of the sediment was increased from -220mV to -178mV during the process. Phosphorus concentration in the water system was decreased from 0.1mg/L to 0.01mg/L, compared with 0.09mg/L in the control. The installation of a SMFC produced an external current and internal circuit, which promoted the transfer of phosphate in overlying water to the sediment, enhanced the microbial oxidation of Fe(2+), and increased the formation of stable phosphorus in sediment. In conclusion, phosphorus flux from the overlying water to sediment was enhanced by SMFC, which has the potential to be used for eutrophication control of water bodies.

Assessing the suitability of sediment-type bioelectrochemical systems for organic matter removal from municipal wastewater: a column study

This study examines the use of bioelectrochemical systems (BES) as an alternative to rock filters for polishing wastewater stabilisation ponds (WSPs) effluent, which often contains soluble chemical oxygen demand (SCOD) and suspended solids mainly as algal biomass. A filter type sediment BES configuration with graphite granules (as the surrogate for rocks in a rock filter) was examined. Three reactor columns were set up to examine three different treatments: (i) open-circuit without current generation; (ii) close-circuit - with current generation; and (iii) control reactor without electrode material. All columns were continuously operated for 170 days with real municipal wastewater at a hydraulic retention time of 5 days. Compared to the control reactor, the two experimental reactors showed significant improvement of SCOD removal (from approximately 25% to 66%) possibly due to retention of biomass on the graphite media. However, substantial amount of SCOD (60%) was removed via non-current generation pathways, and a very low Coulombic efficiency (6%) was recorded due to a poor cathodic oxygen reduction kinetics and a large electrode spacing. Addressing these challenges are imperative to further develop BES technology for WSP effluent treatment.

All ecosystems potentially host electrogenic bacteria

Instead of requiring metal catalysts, MFCs utilize bacteria that oxidize organic matter and either transfer electrons to the anode or take electrons from the cathode. These devices are thus based on a wide microbial diversity that can convert a large array of organic matter components into sustainable and renewable energy. A wide variety of explored environments were found to host electrogenic bacteria, including extreme environments. In the present review, we describe how different ecosystems host electrogenic bacteria, as well as the physicochemical, electrochemical and biological parameters that control the currents from MFCs. We also report how using new molecular techniques allowed characterization of electrochemical biofilms and identification of potentially new electrogenic species. Finally we discuss these findings in the context of future research directions.

Sediment microbial fuel cells as a new source of renewable and sustainable energy: present status and future prospects

SMFCs are a bioelectricity production technology for low power applications. Recent advances in SMFCs are investigated to enhance their performance. Power improvement and organic matter reduction in SMFCs enlarge their range of applications.