Microorganisms in sediment microbial fuel cells: Ecological niche, microbial response, and environmental function

Exploring the impact of fulvic acid on electrochemical hydrogen-driven autotrophic denitrification system: Performance, microbial characteristics and mechanism

In this study, the effect of modulating fulvic acid (FA) concentrations (0, 25 and 50 mg/L) on nitrogen removal in a bioelectrochemical hydrogen autotrophic denitrification system (BHDS) was investigated. Results showed that FA increased the nitrate (NO3--N) removal rate of the BHDSs from 37.8 to 46.2 and 45.2 mg N/(L·d) with a current intensity of 40 mA. The metagenomic analysis revealed that R2 (25 mg/L) was predominantly populated by autotrophic denitrifying microorganisms, which enhanced denitrification performance by facilitating electron transfer. Conversely, R3 (50 mg/L) exhibited an increase in genes related to the heterotrophic process, which improved the denitrification performance through the collaborative action of both autotrophic and heterotrophic denitrification pathways. Besides, the study also identified a potential for nitrogen removal in Serpentinimonas, which have been rarely studied. The interesting set of findings provide valuable reference for optimizing BHDS for nitrogen removal and promoting specific denitrifying genera within the system.

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.

Organic carbon compounds removal and phosphate immobilization for internal pollution control: Sediment microbial fuel cells, a prospect technology

As a current technology that can effectively remove organic carbon compounds and immobilize phosphorus in sediment, sediment microbial fuel cells (SMFCs) can combine sediment remediation with power generation. This review discusses the removal efficiency of SMFCs on organic carbon compounds, including sediment organic matter, antibiotics, oil-contaminated sediments, methane, persistent organic pollutants, and other organic pollutants in sediment, with more comprehensive and targeted summaries, and it also emphasizes the mitigation of phosphorus pollution in water from the perspective of controlling endogenous phosphorus. In this review, the microbial community is used as a starting point to explore more about its roles on phosphorus and organic carbon compounds under SMFCs. Electrode modification, addition of exogenous substances and combinations with other technologies to improve the performance of SMFCs are also reviewed. It is further demonstrated that SMFCs have the prospect of long-term sustainability, but more attention needs to be paid to the study of the mechanism of SMFCs and the continuous improvement of devices for further application in practice.

The promotion of the polycyclic aromatic hydrocarbons degradation mechanism by humic acid as electron mediator in a sediment microbial electrochemical system

To enhance the removal efficiencies of polycyclic aromatic hydrocarbons (PAHs) in sediments and to elucidate the mechanisms by which microbial electrochemical action aids in the degradation of PAHs, humic acid was used as an electron mediator in the microbial electrochemical system in this study. The results revealed that the addition of humic acids led to increases in the removal efficiencies of naphthalene, phenanthrene, and pyrene by 45.91%, 97.83%, and 85.56%, respectively, in areas remote from the anode, when compared to the control group. The investigation into the microbial community structure and functional attributes showed that the presence of humic acid did not significantly modify the microbial community composition or its functional expression at the anode. However, an examination of humic acid transformations demonstrated that humic acid extended the electron transfer range in sediment via the redox reactions of quinone and semiquinone groups, thereby facilitating the PAHs degradation within the sediment.

Microalgae-bacteria nexus for environmental remediation and renewable energy resources: Advances, mechanisms and biotechnological applications

Microalgae and bacteria, known for their resilience, rapid growth, and proximate ecological partnerships, play fundamental roles in environmental and biotechnological advancements. This comprehensive review explores the synergistic interactions between microalgae and bacteria as an innovative approach to address some of the most pressing environmental issues and the demands of clean and renewable freshwater and energy sources. Studies indicated that microalgae-bacteria consortia can considerably enhance the output of biotechnological applications; for instance, various reports showed during wastewater treatment the COD removal efficiency increased by 40%-90.5 % due to microalgae-bacteria consortia, suggesting its great potential amenability in biotechnology. This review critically synthesizes research works on the microalgae and bacteria nexus applied in the advancements of renewable energy generation, with a special focus on biohydrogen, reclamation of wastewater and desalination processes. The mechanisms of underlying interactions, the environmental factors influencing consortia performance, and the challenges and benefits of employing these bio-complexes over traditional methods are also discussed in detail. This paper also evaluates the biotechnological applications of these microorganism consortia for the augmentation of biomass production and the synthesis of valuable biochemicals. Furthermore, the review sheds light on the integration of microalgae-bacteria systems in microbial fuel cells for concurrent energy production, waste treatment, and resource recovery. This review postulates microalgae-bacteria consortia as a sustainable and efficient solution for clean water and energy, providing insights into future research directions and the potential for industrial-scale applications.

Effects of electron acceptors and donors on anaerobic biodegradation of PAHs in marine sediments

Polycyclic aromatic hydrocarbons (PAHs) are typical organic pollutants accumulated in the environment. PAHs' bioremediation in sediments can be promoted by adding electron acceptor (EA) and electron donor (ED). Bicarbonate and sulfate were chosen as two EAs, and acetate and lactate were selected as two EDs. Six groups of amendments were added into the sediments to access their role in the anaerobic biodegradation of five PAHs, containing phenanthrene, anthracene, fluoranthene, pyrene, and benzo[a]pyrene. The concentrations of PAHs, EAs and EDs, electron transport system activity, and microbial diversity were analyzed during 126-day biodegradation in serum bottles. The HA group (bicarbonate and acetate) achieved the maximum PAH degradation efficiency of 89.67 %, followed by the SL group (sulfate and lactate) with 87.10 %. As the main PAHs degrading bacteria, the abundance of Marinobacter in H group was 8.62 %, and the addition of acetate significantly increased the abundance of Marinobacter in the HA group by 75.65 %.

Microbiome based approaches for the degradation of polycyclic aromatic hydrocarbons (PAHs): A current perception

Globally, polycyclic aromatic hydrocarbons (PAHs) pollution is primarily driven by their release into the air through various combustion processes, including burning fossil fuels such as coal, oil, and gas in motor vehicles, power plants, and industries, as well as burning organic matter like wood, tobacco, and food in fireplaces, cigarettes, and grills. Apart from anthropogenic pollution sources, PAHs also occur naturally in crude oil, and their potential release during oil extraction, refining processes, and combustion further contributes to contamination and pollution concerns. PAHs are resistant and persistent in the environment because of their inherent features, viz., heterocyclic aromatic ring configurations, hydrophobicity, and thermostability. A wide range of microorganisms have been found to be effective degraders of these recalcitrant contaminants. The presence of hydrocarbons as a result of numerous anthropogenic activities is one of the primary environmental concerns. PAHs are found in soil, water, and the air, making them ubiquitous in nature. The presence of PAHs in the environment creates a problem, as their presence has a detrimental effect on humans and animals. For a variety of life forms, PAH pollutants are reported to be toxic, carcinogenic, mutation-inducing, teratogenic, and immune toxicogenics. Degradation of PAHs via biological activity is an extensively used approach in which diverse microorganisms (fungal, algal, clitellate, and protozoan) and plant species and their derived composites are utilized as biocatalysts and biosurfactants. Some microbes have the ability to transform and degrade these PAHs, allowing them to be removed from the environment. The goal of this review is to provide a critical overview of the existing understanding of PAH biodegradation. It also examines current advances in diverse methodologies for PAH degradation in order to shed light on fundamental challenges and future potential.

Improved electrochemical properties of graphite electrodes incubated with iron powders in rice-paddy fields boost power outputs from microbial fuel cells

Studies have shown that the supplementation of anode-surrounding soil with zero-valent iron (ZVI) boosts power outputs from rice paddy-field microbial fuel cells (RP-MFCs). In order to understand mechanisms by which ZVI boosts outputs from RP-MFCs, the present study operated RP-MFCs with and without ZVI, and compositions of anode-associated bacteria and electrochemical properties of graphite anodes were analyzed after 3-month operation. Metabarcoding using 16S rRNA gene fragments showed that bacterial compositions did not largely differ among these RP-MFCs. Cyclic voltammetry showed improved electrochemical properties of anodes recovered from ZVI-supplemented RP-MFCs, and this was attributed to the adhesion of iron-oxide films onto graphite surfaces. Bioelectrochemical devices equipped with graphite anodes recovered from ZVI-supplemented RP-MFCs generated higher currents than those with fresh graphite anodes. These results suggest that ZVI is oxidized to iron oxides in paddy-field soil and adheres onto graphite anodes, resulting in the boost of power outputs from RP-MFCs.

The race between classical microbial fuel cells, sediment-microbial fuel cells, plant-microbial fuel cells, and constructed wetlands-microbial fuel cells: Applications and technology readiness level

Microbial fuel cell (MFC) is an interesting technology capable of converting the chemical energy stored in organics to electricity. It has raised high hopes among researchers and end users as the world continues to face climate change, water, energy, and land crisis. This review aims to discuss the journey of continuously progressing MFC technology from the lab to the field so far. It evaluates the historical development of MFC, and the emergence of different variants of MFC or MFC-associated other technologies such as sediment-microbial fuel cell (S-MFC), plant-microbial fuel cell (P-MFC), and integrated constructed wetlands-microbial fuel cell (CW-MFC). This review has assessed primary applications and challenges to overcome existing limitations for commercialization of these technologies. In addition, it further illustrates the design and potential applications of S-MFC, P-MFC, and CW-MFC. Lastly, the maturity and readiness of MFC, S-MFC, P-MFC, and CW-MFC for real-world implementation were assessed by multicriteria-based assessment. Wastewater treatment efficiency, bioelectricity generation efficiency, energy demand, cost investment, and scale-up potential were mainly considered as key criteria. Other sustainability criteria, such as life cycle and environmental impact assessments were also evaluated.

Electrokinetic remediation leads to translocation of dissolved organic matter/nutrients and oxidation of aromatics and polysaccharides

Dissolved organic matter (DOM) in the sediment matrix affects contaminant remediation through consumption of oxidants and binding with contaminants. Yet the change in DOM during remediation processes, particularly during electrokinetic remediation (EKR), remains under-investigated. In this work, we elucidated the fate of sediment DOM in EKR using multiple spectroscopic tools under abiotic and biotic conditions. We found that EKR led to significant electromigration of the alkaline-extractable DOM (AEOM) toward the anode, followed by transformation of the aromatics and mineralization of the polysaccharides. The AEOM remaining in the cathode (largely polysaccharides) was resistant to reductive transformation. Limited difference was noted between abiotic and biotic conditions, indicating the dominance of electrochemical processes when relatively high voltages were applied (1-2 V/cm). The water-extractable organic matter (WEOM), in contrast, showed an increase at both electrodes, which was likely attributable to pH-driven dissociations of humic substances and amino acid-type constituents at the cathode and the anode, respectively. Nitrogen migrated with the AEOM toward the anode, but phosphorus remained immobilized. Understanding the redistribution and transformation of DOM could inform studies on contaminant degradation, carbon and nutrient availability, and sediment structural changes in EKR.

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.

Electroactive Bacteria in Natural Ecosystems and Their Applications in Microbial Fuel Cells for Bioremediation: A Review

Electroactive bacteria (EAB) are natural microorganisms (mainly Bacteria and Archaea) living in various habitats (e.g., water, soil, sediment), including extreme ones, which can interact electrically each other and/or with their extracellular environments. There has been an increased interest in recent years in EAB because they can generate an electrical current in microbial fuel cells (MFCs). MFCs rely on microorganisms able to oxidize organic matter and transfer electrons to an anode. The latter electrons flow, through an external circuit, to a cathode where they react with protons and oxygen. Any source of biodegradable organic matter can be used by EAB for power generation. The plasticity of electroactive bacteria in exploiting different carbon sources makes MFCs a green technology for renewable bioelectricity generation from wastewater rich in organic carbon. This paper reports the most recent applications of this promising technology for water, wastewater, soil, and sediment recovery. The performance of MFCs in terms of electrical measurements (e.g., electric power), the extracellular electron transfer mechanisms by EAB, and MFC studies aimed at heavy metal and organic contaminant bioremediationF are all described and discussed.

Bioengineering of biowaste to recover bioproducts and bioenergy: A circular economy approach towards sustainable zero-waste environment

The inevitable need for waste valorisation and management has revolutionized the way in which the waste is visualised as a potential biorefinery for various product development rather than offensive trash. Biowaste has emerged as a potential feedstock to produce several value-added products. Bioenergy generation is one of the potential applications originating from the valorisation of biowaste. Bioenergy production requires analysis and optimization of various parameters such as biowaste composition and conversion potential to develop innovative and sustainable technologies for most effective utilization of biowaste with enhanced bioenergy production. In this context, feedstocks, such as food, agriculture, beverage, and municipal solid waste act as promising resources to produce renewable energy. Similarly, the concept of microbial fuel cells employing biowaste has clearly gained research focus in the past few decades. Despite of these potential benefits, the area of bioenergy generation still is in infancy and requires more interdisciplinary research to be sustainable alternatives. This review is aimed at analysing the bioconversion potential of biowaste to renewable energy. The possibility of valorising underutilized biowaste substrates is elaborately presented. In addition, the application and efficiency of microbial fuel cells in utilizing biowaste are described in detail taking into consideration of its great scope. Furthermore, the review addresses the significance bioreactor development for energy production along with major challenges and future prospects in bioenergy production. Based on this review it can be concluded that bioenergy production utilizing biowaste can clearly open new avenues in the field of waste valorisation and energy research. Systematic and strategic developments considering the techno economic feasibilities of this excellent energy generation process will make them a true sustainable alternative for conventional energy sources.

Effect of erythromycin on epiphytic bacterial communities and water quality in wetlands

The occurrence of antibiotics such as erythromycin (ERY) under macrolide group, has long been acknowledged for negatively affecting ecosystems in freshwater environments. However, the effects of ERY on water quality and microbial communities in epiphytic biofilms are poorly understood. Here, Scanning Electron Microscopy (SEM), High-throughput sequencing, and physicochemical analytical methods were employed to unravel the impact of ERY on the water quality and bacterial morphology, biodiversity, composition, interaction, and ecological function in epiphytic biofilms attached to Vallisneria natans and artificial plants in mesocosmic wetlands. The study showed that ERY exposure significantly impaired the nutrient removal capacity (TN, TP, and COD) and altered the epiphytic bacterial morphology of V. natans and artificial plants. ERY did not affect the bacterial α-diversity. Notwithstanding ERY decreased the bacterial composition, but the relative abundance of Proteobacteria and Patescibacteria spiked by 62.2 % and 54 %, respectively, in V. natans, while Desulfobacteria and Chloroflexi increased by 8.9 % and 11.2 %, respectively, in artificial plants. Notably, ERY disturbed the food web structure and metabolic pathways such as carbohydrate metabolism, amino acid metabolism, energy metabolism, cofactor and vitamin metabolism, membrane transport, and signal transduction. This study revealed that ERY exposure disrupted the bacterial morphology, composition, interaction or food web structure, and metabolic functions in epiphytic biofilm. These data underlined that ERY negatively impacts epiphytic bacterial communities and nutrient removal in wetlands.

Structure and core taxa of bacterial communities involved in extracellular electron transfer in paddy soils across China

Microbial communities with extracellular electron transfer (EET) activity are capable of driving geochemical changes and cycles, but a comprehensive understanding of the key microbiota responsible for EET in complex soil matrices is still lacking. Herein, the EET activities, in terms of maximum current density (j_max) and accumulated charge output (C_out), of 41 paddy soils across China were evaluated from the exoelectrogenic properties with a conventional bioelectrochemical system (BES). The j_max with a range of 8.85 × 10^-4 to 0.41 A/m² and C_out with a range of 0.27 to 172.21C were obtained from these soil-based BESs. The bacterial community analyses revealed that the most abundant phylum, order, and genus were Firmicutes, Clostridiales, and Clostridum-sensus-stricto 10, respectively. Bacterial network analysis displayed the positive correlations between the majority of electroactive bacteria-containing genera and multiple other genera, indicating their underlying cooperation for the EET. Partial least squares regression (PLSR) model showed remarkable performance in describing the EET activity with 75 most abundant genera as input variables, identified that 32 genera were very important for governing the EET activities. Multiple linear regression (MLR) analyses further prioritized that the genera norank-c-Berkelbacteria and Fonticella were the key contributors, while the genus Paenibacillus was the key competitor against bacterial exoelectrogenesis in paddy soils. Moreover, the spearman analysis showed that the abundance of these keystone taxa was mainly influenced by the carbon content and pH. This approach provides a promising avenue to monitor the microbial activities in paddy soils as well as the links between microbial community composition and ecological function.

Recent advances in soil microbial fuel cells based self-powered biosensor

The soil microbial fuel cell (SMFC) is a new device that was originally designed to generate electricity from organic matter in soil using microorganisms. Currently, SMFC based biosensors are emerging as a new and promising research direction for real-time and rapid monitoring of soil quality or soil pollution. Compared to conventional biosensors, SMFC based biosensors exhibit advantages such as low-cost, simple design, in-situ, and long-term self-powering monitoring, which makes it become attractive devices for in-situ long-term soil quality or soil pollution monitoring. Thus, this review aims to provide a comprehensive overview of SMFC based biosensors. In this review, different prototypes of SMFC based biosensors developed in recent years are introduced, the biosensing mechanisms and the roles of SMFC are highlighted, and the emerging applications of these SMFC based biosensors are discussed. Since the SMFC based biosensors are applied in open-air conditions, the effects of different environmental factors on the biosensing response are also summarized. Finally, to further expand the understanding and boost the practical application of the SMFC based biosensors, future perspectives including fundamental mechanism exploration and investigation of the full-scale application are proposed.

Transcriptome Analysis Reveals the Algicidal Mechanism of Brevibacillus laterosporus against Microcystis aeruginosa through Multiple Metabolic Pathways

It is widely accepted that eutrophication has played an important role in the formation of harmful cyanobacterial blooms in recent decades, which impacts water quality and ecological environment and causes huge economic losses. Algicidal bacteria have a promising application prospect in controlling cyanobacterial blooms in aquaculture water. Here, the process of the algicidal bacterium Brevibacillus laterosporus strain Bl-zj acting on Microcystis aeruginosa was explored using transcriptome analysis to elucidate the algicidal mechanism. The results of the co-culture of bacterium and alga showed a strong alga-lysing effect of B. laterosporus against M. aeruginosa with an extreme morphology deformation of the algal cells. A total of 2744 differentially expressed genes of B. laterosporus were identified, which were mainly involved in the metabolism of amino acid, carbohydrate, and lipid. In the co-cultured group, the expression of genes mainly enriched in valine, leucine and isoleucine degradation, and fatty acid degradation were significantly increased. However, the expression of the genes related to ribosome were mainly inhibited. Transcriptome analysis showed that B. laterosporus obtained ATP and energy by the degradation of valine, leucine, isoleucine, and fatty acids, and destroyed algal cells by efflux pump transporters, secretion of hydrolytic enzymes, antibiotics, proteases, and other secondary metabolites, resulting in algal death and achieving the algicidal effect.

Electrical generation and methane emission from an anoxic riverine sediment slurry treated by a two-chamber microbial fuel cell

A two-chamber slurry microbial fuel cell (SMFC) was constructed using black-odorous river sediments as substrate for the anode. We tested addition of potassium ferricyanide (K₃[Fe(CN)₆]) or sodium chloride (NaCl) to the cathode chamber (0, 50, 100, 150, and 200 mM) and aeration of the cathode chamber (0, 2, 4, 6, and 8 h per day) to assess their response on electrical generation, internal resistance, and methane emission over a 600-h period. When the aeration time in the cathode chamber was 6 h and K₃[Fe(CN)₆] or NaCl concentrations were 200 mM, the highest power densities were 6.00, 6.45, and 6.64 mW·m^-2, respectively. With increasing K₃[Fe(CN)₆] or NaCl concentration in the cathode chamber, methane emission progressively decreased (mean ± SD: 181.6 ± 10.9 → 75.5 ± 9.8 mg/m³·h and 428.0 ± 28.5 → 157.0 ± 35.7 mg/m³·h), respectively, but was higher than the reference having no cathode/anode electrodes (~ 30 mg/m³·h). Cathode aeration (0 → 8 h/day) demonstrated a reduction in methane emission from the anode chamber for only the 6-h treatment (mean: 349.6 ± 37.4 versus 299.4 ± 34.7 mg/m³·h for 6 h/day treatment); methane emission from the reference was much lower (85.3 ± 26.1 mg/m³·h). Our results demonstrate that adding an electron acceptor (K₃[Fe(CN)₆]), electrolyte solution (NaCl), and aeration to the cathode chamber can appreciably improve electrical generation efficiency from the MFC. Notably, electrical generation stimulates methane emission, but methane emission decreases at higher power densities.

Contribution of configurations, electrode and membrane materials, electron transfer mechanisms, and cost of components on the current and future development of microbial fuel cells

Microbial fuel cells (MFCs) are a technology that can be applied to both the wastewater treatment and bioenergy generation. This work discusses the contribution of improvements regarding the configurations, electrode materials, membrane materials, electron transfer mechanisms, and materials cost on the current and future development of MFCs. Analysis of the most recent scientific publications on the field denotes that dual-chamber MFCs configuration offers the greatest potential due to the excellent ability to be adapted to different operating environments. Carbon-based materials show the best performance, biocompatibility of carbon-brush anode favors the formation of the biofilm in a mixed consortium and in wastewater as a substrate resembles the conditions of real scenarios. Carbon-cloth cathode modified with nanotechnology favors the conductive properties of the electrode. Ceramic clay membranes emerge as an interesting low-cost membrane with a proton conductivity of 0.0817 S cm^-1, close to that obtained with the Nafion membrane. The use of nanotechnology in the electrodes also enhances electron transfer in MFCs. It increases the active sites at the anode and improves the interface with microorganisms. At the cathode, it favors its catalytic properties and the oxygen reduction reaction. These features together favor MFCs performance through energy production and substrate degradation with values above 2.0 W m^-2 and 90% respectively. All the recent advances in MFCs are gradually contributing to enable technological alternatives that, in addition to wastewater treatment, generate energy in a sustainable manner. It is important to continue the research efforts worldwide to make MFCs an available and affordable technology for industry and society.

Influence of Fe2+ and Fe3+ on the Performance and Microbial Community Composition of a MFC Inoculated with Sulfate-Reducing Sludge and Acetate as Electron Donor

A sulfidogenic sludge supplemented with acetate was evaluated in the anodic chamber of microbial fuel cells (MFCs) in the presence of sulfate (SO4-2)/Fe3+ and sulfate (SO4-2)/Fe2+ to investigate the MFC performance and the effect of the iron ions on the composition of the microbial community since sulfate and iron ions are frequently present in wastewater derived from several anthropogenic activities. The current densities were up to 0.025 mA/cm2 and 0.017 mA/cm2 for MFCs with Fe2+ and Fe3+, respectively. Accordingly, the redox activity was slightly higher in the presence of Fe2+ than Fe3+. In general, the metabolic activity of the MFC supplemented with Fe2+ was higher than the system with Fe3+ reaching a percentage of sulfate reduction (% SR), sulfide concentration (mg/L HS-), and removal of chemical oxygen demand (% COD removal) of $35.2\pm 0.75$ , $450.3\pm 3.6$ , and $50.05\pm 0.24$ for % SR, HS-, and % COD, respectively, whereas in the MFC with Fe3+, the percentages were of $30.1\pm 1.076$ , $220.6\pm 2.0$ , and $11.78\pm 10.81$ for % SR, HS-, and % COD, respectively. The microbial population determined in each system was also correlated to the metabolic activity. Rhodospirillales, Caulobacterales, and Burkholderiales were the most abundant orders of bacteria in the MFC with Fe3+, whereas with Fe2+, Rhodobacterales, Sphingomonadales, and Rhizobiales. Desulfohalobiaceae and Desulfovibrionaceae were identified in the presence of Fe2+. Unexpected interactions and combinations of microorganisms were observed in a relatively short culturing time, demonstrating the importance of characterizing the anode biofilm prior to shifts in iron ion concentrations on a long-term basis.

Effect of starch-derived organic acids on the removal of polycyclic aromatic hydrocarbons in an aquaculture-sediment microbial fuel cell

This study constructed sediment microbial fuel cells (SMFCs) for polycyclic aromatic hydrocarbons (PAHs) removal in contaminated aquaculture sediment. Starch, a waste deposited in aquaculture sediment, was employed as the co-substrate for electricity generation and PAHs removal, and the effect of starch-derived organic acids on SMFC performance was assessed. The results indicated that sufficient starch promoted PAHs removal (69.9% for naphthalene, 55.6% for acenaphthene, and 46.8% for pyrene) in dual-chamber SMFC, whereas excessive starch attenuated SMFC performance because the organic acids accumulation reduced anode pH, decreased species diversity, and changed the microbial communities. The electricity generation and PAHs removal were positively correlated (R > 0.96), and both of them were related to Macellibacteroides belonging to Bacteroidetes. However, a larger single-chamber SMFC device did not obtain enhanced PAHs removal owing to the restricted "effective range" of the anode. Hence, more challenges need to be addressed to realize the practical application of SMFC.

Microbial Electrochemical Technologies for Sustainable Nitrogen Removal in Marine and Coastal Environments

For many years, the world's coastal marine ecosystems have received industrial waste with high nitrogen concentrations, generating the eutrophication of these ecosystems. Different physicochemical-biological technologies have been developed to remove the nitrogen present in wastewater. However, conventional technologies have high operating costs and excessive production of brines or sludge which compromise the sustainability of the treatment. Microbial electrochemical technologies (METs) have begun to gain attention due to their cost-efficiency in removing nitrogen and organic matter using the metabolic capacity of microorganisms. This article combines a critical review of the environmental problems associated with the discharge of the excess nitrogen and the biological processes involved in its biogeochemical cycle; with a comparative analysis of conventional treatment technologies and METs especially designed for nitrogen removal. Finally, current METs limitations and perspectives as a sustainable nitrogen treatment alternative and efficient microbial enrichment techniques are included.

Sediment Microbiota in Response to Circuitry of Sediment Microbial Fuel Cells, Revealed by 16S rRNA Gene Amplicon Sequencing

Information about sediment microbiota affected by sediment microbial fuel cells (SMFC) is limited. A laboratory-scale SMFC was applied to a eutrophic lake sediment under closed-circuit/open-circuit conditions. We analyzed the prokaryotes in the sediment adhering to the anode material. The archaeal family Methanoperedenaceae was a predominant group under closed-circuit conditions.

Ecological impact of antibiotics on bioremediation performance of constructed wetlands: Microbial and plant dynamics, and potential antibiotic resistance genes hotspots

Constructed wetlands (CWs) are nature-based solutions for treating domestic and livestock wastewater which may contain residual antibiotics concentration. Antibiotics may exert selection pressure on wetland's microbes, thereby increasing the global antibiotics resistance problems. This review critically examined the chemodynamics of antibiotics and antibiotics resistance genes (ARGs) in CWs. Antibiotics affected the biogeochemical cycling function of microbial communities in CWs and directly disrupted the removal efficiency of total nitrogen, total phosphorus, and chemical oxygen demand by 22%, 9.3%, and 24%, respectively. Since changes in microbial function and structure are linked to the emergence and propagation of antibiotic resistance, antibiotics could adversely affect microbial diversity in CWs. The cyanobacteria community seemed to be particularly vulnerable, while Proteobacteria could resist and persist in antibiotics contaminated wetlands. Antibiotics triggered excitation responses in plants and increased the root activities and exudates. Microbes, plants, and substrates play crucial roles in antibiotic removal. High removal efficiency was exhibited for triclosan (100%) > enrofloxacin (99.8%) > metronidazole (99%) > tetracycline (98.8%) > chlortetracycline (98.4%) > levofloxacin (96.69%) > sulfamethoxazole (91.9%) by the CWs. This review showed that CWs exhibited high antibiotics removal capacity, but the absolute abundance of ARGs increased, suggesting CWs are potential hotspots for ARGs. Future research should focus on specific bacterial response and impact on microbial interactions.

Progress in microbial biomass conversion into green energy

The increase in global population size over the past 100 decades has doubled the requirements for energy resources. To mitigate the limited fossil fuel available, new clean energy sources being environmental sustainable for replacement of traditional energy sources are explored to supplement the current scarcity. Biomass containing lignin and cellulose is the main raw material to replace fossil energy given its abundance and lower emission of greenhouse gases and NOx when transformed into energy. Bacteria, fungi and algae decompose lignocellulose leading to generation of hydrogen, methane, bioethanol and biodiesel being the clean energy used for heating, power generation and the automobile industry. Microbial Fuel Cell (MFC) uses microorganisms to decompose biomass in wastewater to generate electricity and remove heavy metals in wastewater. Biomass contains cellulose, hemicellulose, lignin and other biomacromolecules which need hydrolyzation for conversion into small molecules by corresponding enzymes in order to be utilized by microorganisms. This paper discusses microbial decomposition of biomass into clean energy and the five major ways of clean energy production, and its economic benefits for future renewable energy security.