Electricigens in the anode of microbial fuel cells: pure cultures versus mixed communities

Electroactive biofilm communities in microbial fuel cells for the synergistic treatment of wastewater and bioelectricity generation

Increasing industrialization and urbanization have contributed to a significant rise in wastewater discharge and exerted extensive pressure on the existing natural energy resources. Microbial fuel cell (MFC) is a sustainable technology that utilizes wastewater for electricity generation. MFC comprises a bioelectrochemical system employing electroactive biofilms of several aerobic and anaerobic bacteria, such as Geobacter sulfurreducens, Shewanella oneidensis, Pseudomonas aeruginosa, and Ochrobacterum pseudiintermedium. Since the electroactive biofilms constitute a vital part of the MFC, it is crucial to understand the biofilm-mediated pollutant metabolism and electron transfer mechanisms. Engineering electroactive biofilm communities for improved biofilm formation and extracellular polymeric substances (EPS) secretion can positively impact the bioelectrochemical system and improve fuel cell performance. This review article summarizes the role of electroactive bacterial communities in MFC for wastewater treatment and bioelectricity generation. A significant focus has been laid on understanding the composition, structure, and function of electroactive biofilms in MFC. Various electron transport mechanisms, including direct electron transfer (DET), indirect electron transfer (IET), and long-distance electron transfer (LDET), have been discussed. A detailed summary of the optimization of process parameters and genetic engineering strategies for improving the performance of MFC has been provided. Lastly, the applications of MFC for wastewater treatment, bioelectricity generation, and biosensor development have been reviewed.

Hydrogen Production in Microbial Electrolysis Cells Using an Alginate Hydrogel Bioanode Encapsulated with a Filter Bag

The bacterial anode of microbial electrolysis cells (MECs) is the limiting factor in a high hydrogen evolution reaction (HER). This study focused on improving biofilm attachment to a carbon-cloth anode using an alginate hydrogel. In addition, the modified bioanode was encapsulated by a filter bag that served as a physical barrier, to overcome its low mechanical strength and alginate degradation by certain bacterial species in wastewater. The MEC based on an encapsulated alginate bioanode (alginate bioanode encapsulated by a filter bag) was compared with three controls: an MEC based on a bare bioanode (non-immobilized bioanode), an alginate bioanode, and an encapsulated bioanode (bioanode encapsulated by a filter bag). At the beginning of the operation, the Rct value for the encapsulated alginate bioanode was 240.2 Ω, which decreased over time and dropped to 9.8 Ω after three weeks of operation when the Geobacter medium was used as the carbon source. When the MECs were fed with wastewater, the encapsulated alginate bioanode led to the highest current density of 9.21 ± 0.16 A·m-2 (at 0.4 V), which was 20%, 95%, and 180% higher, compared to the alginate bioanode, bare bioanode, and encapsulated bioanode, respectively. In addition, the encapsulated alginate bioanode led to the highest reduction currents of (4.14 A·m-2) and HER of 0.39 m3·m-3·d-1. The relative bacterial distribution of Geobacter was 79%. The COD removal by all the bioanodes was between 62% and 88%. The findings of this study demonstrate that the MEC based on the encapsulated alginate bioanode exhibited notably higher bio-electroactivity compared to both bare, alginate bioanode, and an encapsulated bioanode. We hypothesize that this improvement in electron transfer rate is attributed to the preservation and the biofilm on the anode material using alginate hydrogel which was inserted into a filter bag.

Experimental Proof of Principle of 3D-Printed Microfluidic Benthic Microbial Fuel Cells (MBMFCs) with Inbuilt Biocompatible Carbon-Fiber Electrodes

Microbial fuel cells (MFCs) represent a promising avenue for sustainable energy production by harnessing the metabolic activity of microorganisms. In this study, a novel design of MFC-a Microfluidic Benthic Microbial Fuel Cell (MBMFC)-was developed, fabricated, and tested to evaluate its electrical energy generation. The design focused on balancing microfluidic architecture and wiring procedures with microbial community dynamics to maximize power output and allow for upscaling and thus practical implementation. The testing phase involved experimentation to evaluate the performance of the MBMFC. Microbial feedstock was varied to assess its impact on power generation. The designed MBMFC represents a promising advancement in the field of bioenergy generation. By integrating innovative design principles with advanced fabrication techniques, this study demonstrates a systematic approach to optimizing MFC performance for sustainable and clean energy production.

Microbial Biofilms: Features of Formation and Potential for Use in Bioelectrochemical Devices

Microbial biofilms present one of the most widespread forms of life on Earth. The formation of microbial communities on various surfaces presents a major challenge in a variety of fields, including medicine, the food industry, shipping, etc. At the same time, this process can also be used for the benefit of humans-in bioremediation, wastewater treatment, and various biotechnological processes. The main direction of using electroactive microbial biofilms is their incorporation into the composition of biosensor and biofuel cells This review examines the fundamental knowledge acquired about the structure and formation of biofilms, the properties they have when used in bioelectrochemical devices, and the characteristics of the formation of these structures on different surfaces. Special attention is given to the potential of applying the latest advances in genetic engineering in order to improve the performance of microbial biofilm-based devices and to regulate the processes that take place within them. Finally, we highlight possible ways of dealing with the drawbacks of using biofilms in the creation of highly efficient biosensors and biofuel cells.

Electricity generation and real oily wastewater treatment by Pseudomonas citronellolis 620C in a microbial fuel cell: pyocyanin production as electron shuttle

In the present study, the potential of Pseudomonas citronellolis 620C strain was evaluated, for the first time, to generate electricity in a standard, double chamber microbial fuel cell (MFC), with oily wastewater (OW) being the fuel at 43.625 mg/L initial chemical oxygen demand (COD). Both electrochemical and physicochemical results suggested that this P. citronellolis strain utilized efficiently the OW substrate and generated electricity in the MFC setup reaching 0.05 mW/m2 maximum power. COD removal was remarkable reaching 83.6 ± 0.1%, while qualitative and quantitative gas chromatography/mass spectrometry (GC/MS) analysis of the OW total petroleum and polycyclic aromatic hydrocarbons, and fatty acids revealed high degradation capacity. It was also determined that P. citronellolis 620C produced pyocyanin as electron shuttle in the anodic MFC chamber. To the authors' best knowledge, this is the first study showing (phenazine-based) pyocyanin production from a species other than P. aeruginosa and, also, the first time that P. citronellolis 620C has been shown to produce electricity in a MFC. The production of pyocyanin, in combination with the formation of biofilm in the MFC anode, as observed with scanning electron microscopy (SEM) analysis, makes this P. citronellolis strain an attractive and promising candidate for wider MFC applications.

Living Synthelectronics: A New Era for Bioelectronics Powered by Synthetic Biology

Bioelectronics, which converges biology and electronics, has attracted great attention due to their vital applications in human-machine interfaces. While traditional bioelectronic devices utilize nonliving organic and/or inorganic materials to achieve flexibility and stretchability, a biological mismatch is often encountered because human tissues are characterized not only by softness and stretchability but also by biodynamic and adaptive properties. Recently, a notable paradigm shift has emerged in bioelectronics, where living cells, and even viruses, modified via gene editing within synthetic biology, are used as core components in a new hybrid electronics paradigm. These devices are defined as "living synthelectronics," and they offer enhanced potential for interfacing with human tissues at informational and substance exchange levels. In this Perspective, the recent advances in living synthelectronics are summarized. First, opportunities brought to electronics by synthetic biology are briefly introduced. Then, strategic approaches to designing and making electronic devices using living cells/viruses as the building blocks, sensing components, or power sources are reviewed. Finally, the challenges faced by living synthelectronics are raised. It is believed that this paradigm shift will significantly contribute to the real integration of bioelectronics with human tissues.

Isolation and Electrochemical Analysis of a Facultative Anaerobic Electrogenic Strain Klebsiella sp. SQ-1

Electricigens decompose organic matter and convert stored chemical energy into electrical energy through extracellular electron transfer. They are significant biocatalysts for microbial fuel cells with practical applications in green energy generation, effluent treatment, and bioremediation. A facultative anaerobic electrogenic strain SQ-1 is isolated from sludge in a biotechnology factory. The strain SQ-1 is a close relative of Klebsiella variicola. Multilayered biofilms form on the surface of a carbon electrode after the isolated bacteria are inoculated into a microbial fuel cell device. This strain produces high current densities of 625 μA cm-2 by using acetate as the carbon source in a three-electrode configuration. The electricity generation performance is also analyzed in a dual-chamber microbial fuel cell. It reaches a maximum power density of 560 mW m-2 when the corresponding output voltage is 0.59 V. The facultative strain SQ-1 utilizes hydrous ferric oxide as an electron acceptor to perform extracellular electricigenic respiration in anaerobic conditions. Since facultative strains possess better properties than anaerobic strains, Klebsiella sp. SQ-1 may be a promising exoelectrogenic strain for applications in microbial electrochemistry.

Optimizing electrochemically active microorganisms as a key player in the bioelectrochemical system: Identification methods and pathways to large-scale implementation

The rapid global economic growth driven by industrialization and population expansion has resulted in significant issues, including reliance on fossil fuels, energy scarcity, water crises, and environmental emissions. To address these issues, bioelectrochemical systems (BES) have emerged as a dual-purpose solution, harnessing electrochemical processes and the capabilities of electrochemically active microorganisms (EAM) to simultaneously recover energy and treat wastewater. This review examines critical performance factors in BES, including inoculum selection, pretreatment methods, electrodes, and operational conditions. Further, authors explore innovative approaches to suppress methanogens and simultaneously enhance the EAM in mixed cultures. Additionally, advanced techniques for detecting EAM are discussed. The rapid detection of EAM facilitates the selection of suitable inoculum sources and optimization of enrichment strategies in BESs. This optimization is essential for facilitating the successful scaling up of BES applications, contributing substantially to the realization of clean energy and sustainable wastewater treatment. This analysis introduces a novel viewpoint by amalgamating contemporary research on the selective enrichment of EAM in mixed cultures. It encompasses identification and detection techniques, along with methodologies tailored for the selective enrichment of EAM, geared explicitly toward upscaling applications in BES.

A review of microbial fuel cell and its diversification in the development of green energy technology

The advancement of microbial fuel cell technology is rapidly growing, with extensive research and well-established methodologies for enhancing structural performance. This terminology attracts researchers to compare the MFC devices on a technological basis. The architectural and scientific successes of MFCs are only possible with the knowledge of engineering and technical fields. This involves the structure of MFCs, using substrates and architectural backbones regarding electrode advancement, separators and system parameter measures. Knowing about the MFCs facilitates the systematic knowledge of engineering and scientific principles. The current situation of rapid urbanization and industrial growth is demanding the augmented engineering goods and production which results in unsolicited burden on traditional wastewater treatment plants. Consequently, posing health hazards and disturbing aquatic veracity due to partial and untreated wastewater. Therefore, it's sensible to evaluate the performance of MFCs as an unconventional treatment method over conventional one to treat the wastewater. However, MFCs some benefits like power generation, stumpy carbon emission and wastewater treatment are the main reasons behind the implementation. Nonetheless, few challenges like low power generation, scaling up are still the major areas needs to be focused so as to make MFCs sustainable one. We have focused on few archetypes which majorities have been laboratory scale in operations. To ensure the efficiency MFCs are needed to integrate and compatible with conventional wastewater treatment schemes. This review intended to explore the diversification in architecture of MFCs, exploration of MFCs ingredients and to provide the foreseen platform for the researchers in one source, so as to establish the channel for scaling up the technology. Further, the present review show that the MFC with different polymer membranes and cathode and anode modification presents significant role for potential commercial applications after change the system form prototype to pilot scale.

Sustainable power production from petrochemical industrial effluent using dual chambered microbial fuel cell

Dual chambered microbial fuel cell (DMFC) is an advanced and effective treatment technology in wastewater treatment. The current work has made an effort to treat petrochemical industrial wastewater (PWW) as a DMFC substrate for power generation and organic substance removal. Investigating the impact of organic load (OL) on organic reduction and electricity generation is the main objective of this study. At the OL of 1.5 g COD/L, the highest total chemical oxygen demand (TCOD) removal efficiency of 88%, soluble oxygen demand (SCOD) removal efficiency of 80% and total suspended solids (TSS) removal efficiency of 71% were seen, respectively. In the same optimum condition of 1.5 g COD/L, the highest current and power density of about 270 mW/m2 and 376 mA/m2 were also observed. According to the results of this study, using high-strength organic wastewater in DMFC can assist in addressing the issue of the petrochemical industries and minimize the energy demand.

Detection and Characterization of Electrogenic Bacteria from Soils

Soil microbial fuel cells (SMFCs) are bioelectrical devices powered by the oxidation of organic and inorganic compounds due to microbial activity. Seven soils were randomly selected from Bergen Community College or areas nearby, located in the state of New Jersey, USA, were used to screen for the presence of electrogenic bacteria. SMFCs were incubated at 35-37 °C. Electricity generation and electrogenic bacteria were determined using an application developed for cellular phones. Of the seven samples, five generated electricity and enriched electrogenic bacteria. Average electrical output for the seven SMFCs was 155 microwatts with the start-up time ranging from 1 to 11 days. The highest output and electrogenic bacterial numbers were found with SMFC-B1 with 143 microwatts and 2.99 × 109 electrogenic bacteria after 15 days. Optimal electrical output and electrogenic bacterial numbers ranged from 1 to 21 days. Microbial DNA was extracted from the top and bottom of the anode of SMFC-B1 using the ZR Soil Microbe DNA MiniPrep Protocol followed by PCR amplification of 16S rRNA V3-V4 region. Next-generation sequencing of 16S rRNA genes generated an average of 58 k sequences. BLAST analysis of the anode bacterial community in SMFC-B1 demonstrated that the predominant bacterial phylum was Bacillota of the class Clostridia (50%). However, bacteria belonging to the phylum Pseudomonadota (15%) such as Magnetospirillum sp. and Methylocaldum gracile were also part of the predominant electrogenic bacterial community in the anode. Unidentified uncultured bacteria accounted for 35% of the predominant bacterial community. Bioelectrical devices such as MFCs provide sustainable and clean alternatives to future applications for electricity generation, waste treatment, and biosensors.

Sustainable circular biorefinery approach for novel building blocks and bioenergy production from algae using microbial fuel cell

The imminent need for transition to a circular biorefinery using microbial fuel cells (MFC), based on the valorization of renewable resources, will ameliorate the carbon footprint induced by industrialization. MFC catalyzed by bioelectrochemical process drew significant attention initially for its exceptional potential for integrated production of biochemicals and bioenergy. Nonetheless, the associated costly bioproduct production and slow microbial kinetics have constrained its commercialization. This review encompasses the potential and development of macroalgal biomass as a substrate in the MFC system for L-lactic acid (L-LA) and bioelectricity generation. Besides, an insight into the state-of-the-art technological advancement in the MFC system is also deliberated in detail. Investigations in recent years have shown that MFC developed with different anolyte enhances power density from several µW/m² up to 8160 mW/m². Further, this review provides a plausible picture of macroalgal-based L-LA and bioelectricity circular biorefinery in the MFC system for future research directions.

An Overview of Microbial Fuel Cell Technology for Sustainable Electricity Production

The over-exploitation of fossil fuels and their negative environmental impacts have attracted the attention of researchers worldwide, and efforts have been made to propose alternatives for the production of sustainable and clean energy. One proposed alternative is the implementation of bioelectrochemical systems (BESs), such as microbial fuel cells (MFCs), which are sustainable and environmentally friendly. MFCs are devices that use bacterial activity to break down organic matter while generating sustainable electricity. Furthermore, MFCs can produce bioelectricity from various substrates, including domestic wastewater (DWW), municipal wastewater (MWW), and potato and fruit wastes, reducing environmental contamination and decreasing energy consumption and treatment costs. This review focuses on recent advancements regarding the design, configuration, and operation mode of MFCs, as well as their capacity to produce bioelectricity (e.g., 2203 mW/m2) and fuels (i.e., H2: 438.7 mg/L and CH4: 358.7 mg/L). Furthermore, this review highlights practical applications, challenges, and the life-cycle assessment (LCA) of MFCs. Despite the promising biotechnological development of MFCs, great efforts should be made to implement them in a real-time and commercially viable manner.

Application of halophiles in UMFC (upflow microbial fuel cell) for the treatment of saline olive oil industrial wastewater coupled with eco-energy yield

The olive oil industry faces a major problem of treating the wastewater with high organic content and safe disposal. Olive oil industrial wastewater (OOIWW) consists of highly toxic environmental pollutants with high salinity. Saline olive oil industrial wastewater was treated using halophilic consortium in UMFC (upflow microbial fuel cell) mobilized with carbon felt as electrode. Total and soluble COD (chemical oxygen demand), total suspended solids and phenol content removal were studied at different organic loads (0.56, 0.77, 1.05, 1.26, 1.52 and 1.8 gCOD/L). UMFC with OOIWW was optimized at 1.52 gCOD/L for high organic removal and corresponding electricity production. Total COD, soluble COD, TSS and phenol removal were 91%, 89%, 78%, and complete removal of phenol was accomplished at the optimized organic load (1.52 gCOD/L). Correspondingly, the maximum bioenergy yield was 784 mV with 439 mW/m2 (power density) and 560 mA/m2 (current density), respectively. The presence of prominent halophilic exo-electrogens such as Ochrobactrum, Marinobacter, Rhodococcus and Bacillus potently treated the OOIWW and exhibited high energy yield.

Microfluidic membraneless microbial fuel cells: new protocols for record power densities

The main hurdle in leveraging microfluidic advantages in membraneless MFCs is their low electrode area-normalized power. For nearly a decade, maximum power densities have remained stagnant, while at the same time macrosystems continue to gather pace. To bridge this growing gap, we showcase a strategy that focuses on (i) technology improvements, (ii) establishment of record areal power densities, and (iii) presentation of different normalization methods that complement areal power densities and enable direct comparisons across all MFC scales. Using a pure-culture Geobacter sulfurreducens electroactive biofilm (EAB) in a new membraneless MFC that adheres to the strategy above, we observed optimal anode colonization, resulting in the highest recorded electrode areal power density for a microfluidic MFC of 3.88 W m-2 (24.37 kW m-3). We also consider new power normalization methods that may be more appropriate for comparison to other works. Normalized by the wetted cross-section area between electrodes accounts for constraints in electrode/electrolyte contact, resulting in power densities as high as 8.08 W m-2. Alternatively, we present a method to normalize by the flow rate to account for acetate supply, obtaining normalized energy recovery values of 0.025 kW h m-3. With these results, the performance gap between micro- and macroscale MFCs is closed, and a road map to move forward is presented.

Conductive Polymers and Their Nanocomposites: Application Features in Biosensors and Biofuel Cells

Conductive polymers and their composites are excellent materials for coupling biological materials and electrodes in bioelectrochemical systems. It is assumed that their relevance and introduction to the field of bioelectrochemical devices will only grow due to their tunable conductivity, easy modification, and biocompatibility. This review analyzes the main trends and trends in the development of the methodology for the application of conductive polymers and their use in biosensors and biofuel elements, as well as describes their future prospects. Approaches to the synthesis of such materials and the peculiarities of obtaining their nanocomposites are presented. Special emphasis is placed on the features of the interfaces of such materials with biological objects.

Effectively facilitating the degradation of chloramphenicol by the synergism of Shewanella oneidensis MR-1 and the metal-organic framework

Electroactive bacteria (EAB) and metal oxides are capable of synergistically removing chloramphenicol (CAP). However, the effects of redox-active metal-organic frameworks (MOFs) on CAP degradation with EAB are not yet known. This study investigated the synergism of iron-based MOFs (Fe-MIL-101) and Shewanella oneidensis MR-1 on CAP degradation. 0.5 g/L Fe-MIL-101 with more possible active sites led to a three-fold higher CAP removal rate in the synergistic system with MR-1 (initial bacterial concentration of 0.2 at OD₆₀₀), and showed a superior catalytic effect than exogenously added Fe(III)/Fe(II) or magnetite. Mass spectrometry revealed that CAP was transformed into smaller molecular weight and less toxic metabolites in cultures. Transcriptomic analysis showed that Fe-MIL-101 enhanced the expression of genes related to nitro and chlorinated contaminants degradation. Additionally, genes encoding hydrogenases and c-type cytochromes associated with extracellular electron transfer were significantly upregulated, which may contribute to the simultaneous bioreduction of CAP both intracellularly and extracellularly. These results indicated that Fe-MIL-101 can be used as a catalyst to synergize with EAB to effectively facilitate CAP degradation, which might shed new light on the application in the in situ bioremediation of antibiotic-contaminated environments.

Investigating Variability in Microbial Fuel Cells

In scientific studies, replicas should replicate, and identical conditions should produce very similar results which enable parameters to be tested. However, in microbial experiments which use real world mixed inocula to generate a new "adapted" community, this replication is very hard to achieve. The diversity within real-world microbial systems is huge, and when a subsample of this diversity is placed into a reactor vessel or onto a surface to create a biofilm, stochastic processes occur, meaning there is heterogeneity within these new communities. The smaller the subsample, the greater this heterogeneity is likely to be. Microbial fuel cells are typically operated at a very small laboratory scale and rely on specific communities which must include electrogenic bacteria, known to be of low abundance in most natural inocula. Microbial fuel cells (MFCs) offer a unique opportunity to investigate and quantify variability as they produce current when they metabolize, which can be measured in real time as the community develops. In this research, we built and tested 28 replica MFCs and ran them under identical conditions. The results showed high variability in terms of the rate and amount of current production. This variability perpetuated into subsequent feeding rounds, both with and without the presence of new inoculate. In an attempt to control this variability, reactors were reseeded using established "good" and "bad" reactors. However, this did not result in replica biofilms, suggesting there is a spatial as well as a compositional control over biofilm formation. IMPORTANCE The research presented, although carried out in the area of microbial fuel cells, reaches an important and broadly impacting conclusion that when using mixed inoculate in replica reactors under replicated conditions, different communities emerge capable of different levels of metabolism. To date there has been very little research focusing on this, or even reporting it, with most studies using duplicate or triplicate reactors, in which this phenomenon is not fully observed. Publishing data in which replicas do not replicate will be an important and brave first step in the research into understanding this fundamental microbial process.

Analysis and enhancement of the energy utilization efficiency of corn stover using strain Lsc-8 in a bioelectrochemical system

The strain Lsc-8 can produce a current density of 33.08 µA cm^-2 using carboxymethylcellulose (CMC) as a carbon source in a three-electrode configuration. A co-culture system of strain Lsc-8 and Geobacter sulfurreducens PCA was used to efficiently convert cellulose into electricity to improve the electricity generation capability of microbial fuel cells (MFCs). The maximum current density achieved by the co-culture with CMC was 559 μA cm^-2, which was much higher than that of strain Lsc-8 using CMC as the carbon source. The maximum power density reached 492.05 ± 52.63 mW cm^-2, which is much higher than that previously reported. Interaction mechanism studies showed that strain Lsc-8 had the ability to secrete riboflavin and convert cellulose into acetic acid, which might be the reason for the high electrical production performance of the co-culture system. In addition, to the best of our knowledge, a co-culture or single bacteria system using agricultural straw as the carbon source to generate electricity has not been reported. In this study, the maximum current density of the three-electrode system inoculated with strain Lsc-8 was 14.56 μA cm^-2 with raw corn stover as the sole carbon source. Raw corn stover as a carbon source was also investigated for use in a co-culture system. The maximum current density achieved by the co-culture was 592 μA cm^-2. The co-culture system showed a similar electricity generation capability when using raw corn stover and when using CMC. This research shows for the first time that a co-culture or single bacteria system can realize both waste biomass treatment and waste power generation.

Isolation and Characterisation of Electrogenic Bacteria from Mud Samples

To develop efficient microbial fuel cell systems for green energy production using different waste products, establishing characterised bacterial consortia is necessary. In this study, bacteria with electrogenic potentials were isolated from mud samples and examined to determine biofilm-formation capacities and macromolecule degradation. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry identifications have revealed that isolates represented 18 known and 4 unknown genuses. They all had the capacities to reduce the Reactive Black 5 stain in the agar medium, and 48 of them were positive in the wolfram nanorod reduction assay. The isolates formed biofilm to different extents on the surfaces of both adhesive and non-adhesive 96-well polystyrene plates and glass. Scanning electron microscopy images revealed the different adhesion potentials of isolates to the surface of carbon tissue fibres. Eight of them (15%) were able to form massive amounts of biofilm in three days at 23 °C. A total of 70% of the isolates produced proteases, while lipase and amylase production was lower, at 38% and 27% respectively. All of the macromolecule-degrading enzymes were produced by 11 isolates, and two isolates of them had the capacity to form a strong biofilm on the carbon tissue one of the most used anodic materials in MFC systems. This study discusses the potential of the isolates for future MFC development applications.

Exploitation of renewable energy sources for water desalination using biological tools

The emerging impacts of climate change and the growing world population are driving the demand for more food resources and creating an urgent need for new water resources. About 93% of Earth's surface is made up of water bodies, mainly oceans. Seawater attracted a lot of attention in order to be used as a sustainable source of usable water. However, an essential step in harnessing this source of water is desalination. Utilizing renewable sources of energy, biology offers several tools for removal of salts. This article for the first time reviews all currently available biological water desalination tools and compares their efficiency with industrial systems. Bacteria are employed as electrical power generators to provide the energy needed for desalination in microbial desalination cells. Its salt removal efficiency varied from 0.8 to 30 g/L/d. Many strains of algal cells can grow in high concentrations of salts, adsorb and accumulate it inside the cell, and therefore could be used without prior treatment for seawater desalination. This biological tool can yield salt removal efficiency of 0.4-5 g/L/d. Biopolymers are also used for treatment of seawater through enhancing water evaporation as a component of solar steam generators. Despite significant advances in biological water desalination, further modifications and improvements are still needed to make its use sustainable and cost-effective.

Three-Dimensional Carbon Monolith Coated by Nano-TiO2 for Anode Enhancement in Microbial Fuel Cells

A three-dimensional (3D) anode is essential for high-performance microbial fuel cells (MFCs). In this study, 3D porous carbon monoliths from a wax gourd (WGCM) were obtained by freeze-drying and carbonization. Nano-TiO2 was further coated onto the surface of WGCM to obtain a nano-TiO2/WGCM anode. The WGCM anode enhanced the maximum power density of MFCs by 167.9% compared with the carbon felt anode, while nano-TiO2/WGCM anode additionally increased the value by 45.8% to achieve 1396.2 mW/m2. WGCM enhancement was due to the 3D porous structure, the good conductivity and the surface hydrophilicity, which enhanced electroactive biofilm formation and anodic electron transfer. In addition, nano-TiO2 modification enhanced the enrichment of Acinetobacter, an electricigen, by 31.0% on the anode to further improve the power production. The results demonstrated that the nano-TiO2/WGCM was an effective anode for power enhancement in MFCs.

Bacterial community structure of electrogenic biofilm developed on modified graphite anode in microbial fuel cell

Formation of electrogenic microbial biofilm on the electrode is critical for harvesting electrical power from wastewater in microbial biofuel cells (MFCs). Although the knowledge of bacterial community structures in the biofilm is vital for the rational design of MFC electrodes, an in-depth study on the subject is still awaiting. Herein, we attempt to address this issue by creating electrogenic biofilm on modified graphite anodes assembled in an air-cathode MFC. The modification was performed with reduced graphene oxide (rGO), polyaniline (PANI), and carbon nanotube (CNTs) separately. To accelerate the growth of the biofilm, soybean-potato composite (plant) powder was blended with these conductive materials during the fabrication of the anodes. The MFC fabricated with PANI-based anode delivered the current density of 324.2 mA cm-2, followed by CNTs (248.75 mA cm-2), rGO (193 mA cm-2), and blank (without coating) (151 mA cm-2) graphite electrodes. Likewise, the PANI-based anode supported a robust biofilm growth containing maximum bacterial cell densities with diverse shapes and sizes of the cells and broad metabolic functionality. The alpha diversity of the biofilm developed over the anode coated with PANI was the loftiest operational taxonomic unit (2058 OUT) and Shannon index (7.56), as disclosed from the high-throughput 16S rRNA sequence analysis. Further, within these taxonomic units, exoelectrogenic phyla comprising Proteobacteria, Firmicutes, and Bacteroidetes were maximum with their corresponding level (%) 45.5, 36.2, and 9.8. The relative abundance of Gammaproteobacteria, Clostridia, and Bacilli at the class level, while Pseudomonas, Clostridium, Enterococcus, and Bifidobacterium at the genus level were comparatively higher in the PANI-based anode.

Evidence of competition between electrogens shaping electroactive microbial communities in microbial electrolysis cells

In single-chamber microbial electrolysis cells (MECs), organic compounds are oxidized at the anode, liberating electrons that are used for hydrogen evolution at the cathode. Microbial communities on the anode and cathode surfaces and in the bulk liquid determine the function of the MEC. The communities are complex, and their assembly processes are poorly understood. We investigated MEC performance and community composition in nine MECs with a carbon cloth anode and a cathode of carbon nanoparticles, titanium, or stainless steel. Differences in lag time during the startup of replicate MECs suggested that the initial colonization by electrogenic bacteria was stochastic. A network analysis revealed negative correlations between different putatively electrogenic Deltaproteobacteria on the anode. Proximity to the conductive anode surface is important for electrogens, so the competition for space could explain the observed negative correlations. The cathode communities were dominated by hydrogen-utilizing taxa such as Methanobacterium and had a much lower proportion of negative correlations than the anodes. This could be explained by the diffusion of hydrogen throughout the cathode biofilms, reducing the need to compete for space.

Optimization of soil microbial fuel cell for sustainable bio-electricity production: combined effects of electrode material, electrode spacing, and substrate feeding frequency on power generation and microbial community diversity

BACKGROUND

Microbial fuel cells (MFCs) are among the leading research topics in the field of alternative energy sources due to their multifunctional potential. However, their low bio-energy production rate and unstable performance limit their application in the real world. Therefore, optimization is needed to deploy MFCs beyond laboratory-scale experiments. In this study, we investigated the combined influence of electrode material (EM), electrode spacing (ES), and substrate feeding interval (SFI) on microbial community diversity and the electrochemical behavior of a soil MFC (S-MFC) for sustainable bio-electricity generation.

RESULTS

Two EMs (carbon felt (CF) and stainless steel/epoxy/carbon black composite (SEC)) were tested in an S-MFC under three levels of ES (2, 4, and 8 cm) and SFI (4, 6, and 8 days). After 30 days of operation, all MFCs achieved open-circuit voltage in the range of 782 + 12.2 mV regardless of the treatment. However, the maximum power of the SEC-MFC was 3.6 times higher than that of the CF-MFC under the same experimental conditions. The best solution, based on the interactive influence of the two discrete variables, was obtained with SEC at an ES of 4.31 cm and an SFI of 7.4 days during an operating period of 66 days. Analysis of the experimental treatment effects of the variables revealed the order SFI < ES < EM, indicating that EM is the most influential factor affecting the performance of S-MFC. The performance of S-MFC at a given ES value was found to be dependent on the levels of SFI with the SEC electrode, but this interactive influence was found to be insignificant with the CF electrode. The microbial bioinformatic analysis of the samples from the S-MFCs revealed that both electrodes (SEC and CF) supported the robust metabolism of electroactive microbes with similar morphological and compositional characteristics, independent of ES and SFI. The complex microbial community showed significant compositional changes at the anode and cathode over time.

CONCLUSION

This study has demonstrated that the performance of S-MFC depends mainly on the electrode materials and not on the diversity of the constituent microbial communities. The performance of S-MFCs can be improved using electrode materials with pseudocapacitive properties and a larger surface area, instead of using unmodified CF electrodes commonly used in S-MFC systems.

Versatile mechanisms and enhanced strategies of pollutants removal mediated by Shewanella oneidensis: A review

The removal of environmental pollutants is important for a sustainable ecosystem and human health. Shewanella oneidensis (S. oneidensis) has diverse electron transfer pathways and can use a variety of contaminants as electron acceptors or electron donors. This paper reviews S. oneidensis's function in removing environmental pollutants, including heavy metals, inorganic non-metallic ions (INMIs), and toxic organic pollutants. S. oneidensis can mineralize o-xylene (OX), phenanthrene (PHE), and pyridine (Py) as electron donors, and also reduce azo dyes, nitro aromatic compounds (NACs), heavy metals, and iodate by extracellular electron transfer (EET). For azo dyes, NACs, Cr(VI), nitrite, nitrate, thiosulfate, and sulfite that can cross the membrane, S. oneidensis transfers electrons to intracellular reductases to catalyze their reduction. However, most organic pollutants cannot be directly degraded by S. oneidensis, but S. oneidensis can remove these pollutants by self-synthesizing catalysts or photocatalysts, constructing bio-photocatalytic systems, driving Fenton reactions, forming microbial consortia, and genetic engineering. However, the industrial-scale application of S. oneidensis is insufficient. Future research on the metabolism of S. oneidensis and interfacial reactions with other materials needs to be deepened, and large-scale reactors should be developed that can be used for practical engineering applications.

Fundamentals and recent progress in bioelectrochemical system-assisted biohythane production

Biohythane, a balanced mixture of 10%-30% v/v of hydrogen and 70%-90% v/v of methane, could be the backbone of an all-purpose future energy supply. Recently, bioelectrochemical systems (BES) became a new sensation among environmental biotechnology processes with the potential to sustainably generate biohythane. Therefore, to unleash its full potential for scaling up, researchers are consistently improving microbial metabolic pathways, novel reactors, and electrode designs. This review presents a detailed analysis of recently discovered fundamental mechanisms and science and engineering intervention of different strategies to improve the biohythane composition and production rate from BES. However, several milestones are to be achieved, for instance, improving electrode kinetics using efficient catalysts, engineered microbial communities, and improved reactor configurations, for commercializing this sustainable technology. Thus, a future perspective section is included to recommend novel research lines, mainly focusing on the microbial communities and the efficient electrocatalysts, to enhance reactor performance.

Prospective review on bioelectrochemical systems for wastewater treatment: Achievements, hindrances and role in sustainable environment

Bioelectrochemical systems (BESs) are a relatively new arena for producing bioelectricity, desalinating sea water, and treating industrial effluents by removing organic matter. Microbial electrochemical technologies (METs) are promising for obtaining value-added products during simultaneous remediation of pollutants from wastewater. The search for more affordable desalination technology has led to the development of microbial desalination cells (MDCs). MDC combines the operation of microbial fuel cells (MFC) with electrodialysis for water desalination and energy generation. It has received notable interest of researchers in desalination and wastewater treatment because of low energy requirement and eco-friendly nature. Firstly, this article provides a brief overview of MDC technology. Secondly, factors affecting functioning of MDC and its applications have been accentuated. Additionally, challenges and future outlook on the development of this technology have been delineated. State-of-the-art information provided in this review would expand the scope of interdisciplinary and translational research.

A Review of Recent Advances in Microbial Fuel Cells: Preparation, Operation, and Application

The microbial fuel cell has been considered a promising alternative to traditional fossil energy. It has great potential in energy production, waste management, and biomass valorization. However, it has several technical issues, such as low power generation efficiency and operational stability. These issues limit the scale-up and commercialization of MFC systems. This review presents the latest progress in microbial community selection and genetic engineering techniques for enhancing microbial electricity production. The summary of substrate selection covers defined substrates and some inexpensive complex substrates, such as wastewater and lignocellulosic biomass materials. In addition, it also includes electrode modification, electron transfer mediator selection, and optimization of operating conditions. The applications of MFC systems introduced in this review involve wastewater treatment, production of value-added products, and biosensors. This review focuses on the crucial process of microbial fuel cells from preparation to application and provides an outlook for their future development.

Halobacterium salinarum NRC-1 Sustains Voltage Production in a Dual-Chambered Closed Microbial Fuel Cell

Sustained bioenergy production from organisms that thrive in high salinity, low oxygen, and low nutrition levels is useful in monitoring hypersaline polluted environments. Microbial fuel cell (MFC) studies utilizing single species halophiles under salt concentrations higher than 1 M and as a closed microbial system are limited. The current study aimed to establish baseline voltage, current, and power density from a dual-chambered MFC utilizing the halophile Halobacterium salinarum NRC-1. MFC performance was determined with two different electrode sizes (5 cm² and 10 cm²), under oscillating and nonoscillating conditions, as well as in a stacked series. A closed dual-chamber MFC system of 100 mL capacity was devised with Halobacterium media (4.3 M salt concentration) as both anolyte and catholyte, with H. salinarum NRC-1 being the anodic organism. The MFC measured electrical output over 7, 14, 28, and 42 days. MFC output increased with 5 cm² sized electrodes under nonoscillating (p < 0.0001) relative to oscillating conditions. However, under oscillating conditions, doubling the electrode size increased MFC output significantly (p = 0.01). The stacked series MFC, with an electrode size of 10 cm², produced the highest power density (1.2672 mW/m²) over 14 days under oscillation. Our results highlight the potentiality of H. salinarum as a viable anodic organism to produce sustained voltage in a closed-MFC system.

Gluconobacter Oxydans-Based MFC with PEDOT:PSS/Graphene/Nafion Bioanode for Wastewater Treatment

Microbial fuel cells (MFCs) are a variety of bioelectrocatalytic devices that utilize the metabolism of microorganisms to generate electric energy from organic matter. This study investigates the possibility of using a novel PEDOT:PSS/graphene/Nafion composite in combination with acetic acid bacteria Gluconobacter oxydans to create a pure culture MFC capable of effective municipal wastewater treatment. The developed MFC was shown to maintain its activity for at least three weeks. The level of COD in municipal wastewater treatment was reduced by 32%; the generated power was up to 81 mW/m² with a Coulomb efficiency of 40%. Combining the MFC with a DC/DC boost converter increased the voltage generated by two series-connected MFCs from 0.55 mV to 3.2 V. A maximum efficiency was achieved on day 8 of MFC operation and was maintained for a week; capacitors of 6800 µF capacity were fully charged in ~7 min. Thus, G. oxydans cells can become an important part of microbial consortia in MFCs used for treatment of wastewaters with reduced pH.

Debottlenecking the biological hydrogen production pathway of dark fermentation: insight into the impact of strain improvement

Confronted with the exhaustion of the earth’s fossil fuel reservoirs, bio-based process to produce renewable energy is receiving significant interest. Hydrogen is considered as an attractive energy carrier that can replace fossil fuels in the future mainly due to its high energy content, recyclability and environment-friendly nature. Biological hydrogen production from renewable biomass or waste materials by dark fermentation is a promising alternative to conventional routes since it is energy-saving and reduces environmental pollution. However, the current yield and evolution rate of fermentative hydrogen production are still low. Strain improvement of the microorganisms employed for hydrogen production is required to make the process competitive with traditional production methods. The present review summarizes recent progresses on the screening for highly efficient hydrogen-producing strains using various strategies. As the metabolic pathways for fermentative hydrogen production have been largely resolved, it is now possible to engineer the hydrogen-producing strains by rational design. The hydrogen yields and production rates by different genetically modified microorganisms are discussed. The key limitations and challenges faced in present studies are also proposed. We hope that this review can provide useful information for scientists in the field of fermentative hydrogen production.

Hydrogen can be generated by microorganisms.

Dark fermentation is efficient for biological hydrogen production.

Strain improvement is critical to enhancing hydrogen-producing ability.

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.

The use of marine microalgae in microbial fuel cells, photosynthetic microbial fuel cells and biophotovoltaic platforms for bioelectricity generation

Algal green energy has emerged as an alternative to conventional energy production using fossil fuels. Microbial fuel cells (MFCs), photosynthetic microbial fuel cells (PMFCs) and biophotovoltaic (BPV) platforms have been developed to utilize microalgae for bioelectricity generation, wastewater treatment and biomass production. There remains a lack of research on marine microalgae in these systems, so to the best of our knowledge, all information on their integration in these systems have been gathered in this review, and are used to compare with the interesting studies on freshwater microalgae. The performance of the systems is extremely reliant on the microalgae species and/or microbial community used, the size of the bio-electrochemical cell, and electrode material and distance used. The mean was calculated for each system, PMFC has the highest average maximum power density of 344 mW/m², followed by MFC (179 mW/m²) and BPV (58.9 mW/m²). In addition, the advantages and disadvantages of each system are highlighted. Although all three systems face the issue of low power outputs, the integration of a suitable energy harvester could potentially increase power efficiency and make them applicable for lower power applications.

Microbial fuel cells for mineralization and decolorization of azo dyes: Recent advances in design and materials

Microbial fuel cells (MFCs) exhibit tremendous potential in the sustainable management of dye wastewater via degrading azo dyes while generating electricity. The past decade has witnessed advances in MFC configurations and materials; however, comprehensive analyses of design and material and its association with dye degradation and electricity generation are required for their industrial application. MFC models with high efficiency of dye decolorization (96-100%) and a wide variation in power generation (29.4-940 mW/m²) have been reported. However, only 28 out of 104 studies analyzed dye mineralization - a prerequisite to obviate dye toxicity. Consequently, the current review aims to provide an in-depth analysis of MFCs potential in dye degradation and mineralization and evaluates materials and designs as crucial factors. Also, structural and operation parameters critical to large-scale applicability and complete mineralization of azo dye were evaluated. Choice of materials, i.e., bacteria, anode, cathode, cathode catalyst, membrane, and substrate and their effects on power density and dye decolorization efficiency presented in review will help in economic feasibility and MFCs scalability to develop a self-sustainable solution for treating azo dye wastewater.

Microbial fuel cell compared to a chemostat

Microbial Fuel Cells (MFCs) represent a green and sustainable energy conversion system that integrate bacterial biofilms within an electrochemical two-electrode set-up to produce electricity from organic waste. In this review, we focus on a novel exploratory model, regarding "thin" biofilms forming on highly perfusable (non-diffusible) anodes in small-scale, continuous flow MFCs due to the unique properties of the electroactive biofilm. We discuss how this type of MFC can behave as a chemostat in fulfilling common properties including steady state growth and multiple steady states within the limit of biological physicochemical conditions imposed by the external environment. With continuous steady state growth, there is also continuous metabolic rate and continuous electrical power production, which like the chemostat can be controlled. The model suggests that in addition to controlling growth rate and power output by changing the external resistive load, it will be possible instead to change the flow rate/dilution rate.

Towards sustainable wastewater treatment: Influence of iron, zinc and aluminum as anode in combination with salt bridge on microbial fuel cell performance

Microbial fuel cell (MFC) is a green technology and does not harm the environment. It can be used for wastewater treatment, hydrogen production and power generation. There are lot of avenues need to be investigated to increase the efficiency of MFC and in order to make it acceptable publicly. Efficiency of MFC depends on many factors. In this study, the influence of anode materials (Fe, Al and Zn), their sizes (12, 16 and 20 cm²) and shapes (square, rectangular and circular) were investigated on MFC efficiency. Dual chamber MFC setup was prepared in which Rhodobacter capsulatus was used as biocatalytic agent. Results revealed that Zn anode gave the highest voltage of 1.57 V with corresponding 0.23 A of current. Size of 20 cm² of anode gave maximum voltage of 1.66 V with corresponding value of 0.08 A current, while anode size of 16 cm² gave maximum current of 0.75 A with corresponding voltage of 1.65 V. Regarding their studied shapes, circular shape of anode gave the highest voltages of 1.70 V. Salt bridge played an important role in internal resistance of the fuel cell. The results were checked by changing the diameter and length of the salt bridge. The best results were noticed with 16 cm² circular Zn anode and Fe as cathode. Salt bridge with 7.5 cm length gave the highest voltage of 1.65 V, while 4 gauge diameter salt bridge gave the highest current of 0.85 A.

Complete genome sequence of Pseudomonas stutzeri S116 owning bifunctional catalysis provides insights into affecting performance of microbial fuel cells

Background

Pseudomonas stutzeri S116 is a sulfur-oxidizing bacteria isolated from marine sludge. It exhibited excellent electricity generation as bioanode and biocathode applied in microbial fuel cells (MFCs). Complete genome sequencing of P. stutzeri and cyclic voltammetry method were performed to reveal its mechanism in microbial fuel cells system.

Results

This study indicated that the MFCs generated a maximum output voltage of 254.2 mV and 226.0 mV, and maximum power density of 765 mW/m² and 656.6 mW/m² respectively. Complete genome sequencing of P. stutzeri S116 was performed to indicate that most function genes showed high similarities with P. stutzeri, and its primary annotations were associated with energy production and conversion (6.84%), amino acid transport and metabolism (6.82%) and inorganic ion transport and metabolism (6.77%). Homology of 36 genes involved in oxidative phosphorylation was detected, which suggests the strain S116 possesses an integrated electron transport chain. Additionally, many genes encoding pilus-assembly proteins and redox mediators (riboflavin and phenazine) were detected in the databases. Thiosulfate oxidization and dissimilatory nitrate reduction were annotated in the sulfur metabolism pathway and nitrogen metabolism pathway, respectively. Gene function analysis and cyclic voltammetry indicated that P. stutzeri probably possesses cellular machinery such as cytochrome c and redox mediators and can perform extracellular electron transfer and produce electricity in MFCs.

Conclusion

The redox mediators secreted by P. stutzeri S116 were probably responsible for performance of MFCs. The critical genes and metabolic pathways involved in thiosulfate oxide and nitrate reduction were detected, which indicated that the strain can treat wastewater containing sulfide and nitrite efficiently.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02552-8.

Boosting microfluidic microbial fuel cells performance via investigating electron transfer mechanisms, metal-based electrodes, and magnetic field effect

The presented paper fundamentally investigates the influence of different electron transfer mechanisms, various metal-based electrodes, and a static magnetic field on the overall performance of microfluidic microbial fuel cells (MFCs) for the first time to improve the generated bioelectricity. To do so, as the anode of microfluidic MFCs, zinc, aluminum, tin, copper, and nickel were thoroughly investigated. Two types of bacteria, Escherichia coli and Shewanella oneidensis MR-1, were used as biocatalysts to compare the different electron transfer mechanisms. Interaction between the anode and microorganisms was assessed. Finally, the potential of applying a static magnetic field to maximize the generated power was evaluated. For zinc anode, the maximum open circuit potential, current density, and power density of 1.39 V, 138,181 mA m^-2 and 35,294 mW m^-2 were obtained, respectively. The produced current density is at least 445% better than the values obtained in previously published studies so far. The microfluidic MFCs were successfully used to power ultraviolet light-emitting diodes (UV-LEDs) for medical and clinical applications to elucidate their application as micro-sized power generators for implantable medical devices.

Mitigation of tannery effluent with simultaneous generation of bioenergy using dual chambered microbial fuel cell

In this study, a dual chambered microbial fuel cell (MFC) was fabricated for the treatment of tannery wastewater with concurrent production of bio-energy. The tannery effluent acts as an anolyte and a synthetic electrolytic solution as the catholyte. Five electrochemically active bacteria from the biofilm were isolated that showed homology with Klebsiella quasipneumoniae, Klebsiella pneumoniae, Cloacibacterium normanese, Bacillus firmus and Pseudomonas reactans, using 16S rDNA analysis. The physiochemical studies of treated wastewater showcased the 88%, 74% and 94% reduction in COD, BOD and TDS level, respectively. The maximum voltage output and power density obtained using electroactive consortium in MFC was 940 mV and 7371 mW/cm³, respectively. The techno-economic feasibility of the bio-electrochemical system was studied for future bioprospecting. The present study reports a significant power generation with simultaneous effluent treatment up to a maximum of ∼85%, in a sustainable and eco-friendly manner.

Recent biotechnological developments in reshaping the microalgal genome: A signal for green recovery in biorefinery practices

The use of renewable energy sources as a substitute for nonrenewable fossil fuels is urgently required. Algae biorefinery platform provides an excellent alternate to overcome future energy problems. However, to let this viable biomass be competent with existing feedstocks, it is necessary to exploit genetic manipulation and improvement in upstream and downstream platforms for optimal bio-product recovery. Furthermore, the techno-economic strategies further maximize metabolites production for biofuel, biohydrogen, and other industrial applications. The experimental methodologies in algal photobioreactor promote high biomass production, enriched in lipid and starch content in limited environmental conditions. This review presents an optimization framework combining genetic manipulation methods to simulate microalgal growth dynamics, understand the complexity of algal biorefinery to scale up, and identify green strategies for techno-economic feasibility of algae for biomass conversion. Overall, the algal biorefinery opens up new possibilities for the valorization of algae biomass and the synthesis of various novel products.

Microbial fuel cells with Photosynthetic-Cathodic chamber in vertical cascade for integrated Bioelectricity, biodiesel feedstock production and wastewater treatment

This study aimed to develop efficient microbial fuel cells (MFCs) for integrated bioelectricity, biodiesel feedstock production and wastewater treatment. Among wastewaters tested, MFC fed with anaerobic digester effluent from rubber industry gave the maximum power density (55.43 ± 1.08 W/m³) and simultaneously removed COD, nitrogen and phosphorus (by 72.4 ± 0.9%, 40.5 ± 0.8% and 24.4 ± 1.5%, respectively). 16S rRNA gene analysis revealed that dominant microbial communities were: Firmicutes (43.68%), Bacteroidetes (25.41%) and Chloroflexi (15.02%), which mostly contributed to bioelectricity generation. After optimizing organic loading rate, photosynthetic oleaginous microalgae were applied in cathodic chamber in order to increase oxygen availability, secondarily treat anodic chamber effluent and produce lipids as biodiesel feedstocks. Four MFCs with photosynthetic-cathodic chamber connected in vertical cascade could improve power density up to 116.9 ± 15.5 W/m³, sequentially treat wastewater, and also produce microalgal biomass (465 ± 10 g/m³) with high lipid content (38.17 ± 0.01%). These strategies may greatly contribute to sustainable development of integrated bioenergy generation and environment.

Enrichment of Clostridia enhances Geobacter population and electron harvesting in a complex electroactive biofilm

Current research on microbial fuel cell or microbial electrolysis cell dealt with finding new electroactive bacteria and understanding the mechanisms of electronic exchange. Complex consortia allowed to obtain better performances than pure cultures in part thanks to inter-species cooperation. However, the role of each bacterium in a complex biofilm in the electron harvest on an electrode remains unclear. Thus, we combined electrochemical monitoring of electron exchange and high throughput sequencing analysis in order to describe the bacterial composition and the electroactive performance of mangrove mud biofilms. In this study, secondary electroactive biofilms were formed on carbon electrodes from Desulfuromonas-dominated inoculum of pre-formed bioanodes. The performances and the Desulfuromonas-dominated profile were the same as those of primary bioanodes when the planktonic community was conserved. However, a Clostridium enrichment allowed to restore the performance in maximal current densities promoting an increase of Geobacter population, becoming the most dominant group among the Deltaproteobacteria, replacing Desulfuromonas. These results highlight a positive collaboration between Clostridium and Geobacter spp. helping a bacterial population to achieve with the depletion of their environment. Our study provides new insight into relationships between dominant electroactive bacteria and other bacteria species living in an organic matter-rich environment as mangrove sediments.

The enhancement of microbial fuel cell performance by anodic bacterial community adaptation and cathodic mixed nickel–copper oxides on a graphene electrocatalyst

Background

Although microbial fuel cells (MFCs) represent a promising technology for capturing renewable energy from wastewater, their scaling-up is significantly limited by a slow-rate cathodic oxygen reduction reaction (ORR) and the development of a resilient anodic microbial community. In this study, mixed transition metal oxides of nickel and copper (Ni and Cu), supported on a graphene (G) (NiO–CuO/G) electrocatalyst, were synthesized and tested as a cost-effective cathode for ORR in MFCs. Electrochemical measurements of electrocatalyst were conducted using a rotating disk electrode (RDE) and linear sweep voltammetry (LSV) in a neutral electrolyte, and compared with a benchmark Pt/C catalyst. Furthermore, the long-term performance of the as-synthesized electrocatalyst was evaluated in a single-chamber MFC by measuring organic matter removal and polarization behavior. The successful enrichment of electroactive biofilm was also monitored using transmission electron microscopy and the Vitek2 compact system technique.

Results

When compared with the benchmark platinum cathode, the NiO–CuO/G electrocatalyst exhibited high selectivity toward ORR. The rotating disk electrode (RDE) experiments reveal that ORR proceeds via a 4-electron ORR mechanism. Furthermore, the NiO–CuO/G electrocatalyst also exhibited a high power density of 21.25 mW m−2 in an air-cathode MFC, which was slightly lower than that of Pt/C-based MFC (i.e., 50.4 mW m−2). Biochemical characterization of the most abundant bacteria on anodic biofilms identified four genera (i.e., Escherichia coli, Shewanella putrefaciens, Bacillus cereus, and Bacillus Thuringiensis/mycoides) that belonged to Gammaproteobacteria, and Firmicutesphyla.

Conclusions

This study demonstrates that the NiO–CuO/G cathode had an enhanced electrocatalytic activity toward ORR in a pH-neutral solution. This novel mixed transition metal oxide electrocatalyst could replace expensive Pt-based catalysts for MFC applications.

Constructed sediment microbial fuel cell for treatment of fat, oil, grease (FOG) trap effluent: Role of anode and cathode chamber amendment, electrode selection, and scalability

For wastewater treatment, sediment microbial fuel cells (SMFCs) have advantages over traditional microbial fuel cells in cost (due to their membrane-less structure) and operation (less intensive maintenance). Nevertheless, the technical obstacles of SMFCs include their high internal electrical resistance due to sediment in the anode chamber and slow oxygen reduction reaction (ORR) in the cathode chamber, which is responsible for their low power density (PD) (0.2-50 mW/m²). This study evaluated several SMFC improvements, including anode and cathode chamber amendment, electrode selection, and scaling the chamber size up to obtain optimally constructed single-chamber SMFCs to treat fat, oil, and grease (FOG) trap effluent. The chemical oxygen demand (COD) removal efficiency, PD, and electrical energy conversion efficiency concerning theoretically available chemical energy from FOG trap effluent treatment (%EC^WW) were examined. Packing biochar in the anode chamber reduced its electrical resistance by 5.76 times, but the improvement in PD was trivial. Substantial improvement occurred when packing the cathode chamber with activated carbon (AC), which presumably catalyzed the ORR, yielding a maximum PD of 109.39 mW/m², 959 times greater than without AC in the cathode chamber. This SMFC configuration resulted in a COD removal efficiency of 85.80 % and a %EC^WW of 99.74 % in 30 days. Furthermore, using the most appropriate electrode pair and chamber volume increased the maximum PD to 1787.26 mW/m², around 1.7 times greater than the maximum PD by SMFCs reported thus far. This optimally constructed SMFC is low cost and applicable for household wastewater treatment.

Di(Thioether Sulfonate)-Substituted Quinolinedione as a Rapidly Dissoluble and Stable Electron Mediator and Its Application in Sensitive Biosensors

The commonly required properties of diffusive electron mediators for point-of-care testing are rapid dissolubility, high stability, and moderate formal potential in aqueous solutions. Inspired by nature, various quinone-containing electron mediators have been developed; however, satisfying all these requirements remains a challenge. Herein, a strategic design toward quinones incorporating sulfonated thioether and nitrogen-containing heteroarene moieties as solubilizing, stabilizing, and formal potential-modulating groups is reported. A systematic investigation reveals that di(thioether sulfonate)-substituted quinoline-1,4-dione (QLS) and quinoxaline-1,4-dione (QXS) display water solubilities of ≈1 m and are rapidly dissoluble. By finely balancing the electron-donating effect of the thioethers and the electron-withdrawing effect of the nitrogen atom, formal potentials suitable for electrochemical biosensors are achieved with QLS and QXS (-0.15 and -0.09 V vs Ag/AgCl, respectively, at pH 7.4). QLS is stable for >1 d in PBS (pH 7.4) and for 1 h in tris buffer (pH 9.0), which is sufficient for point-of-care testing. Furthermore, QLS, with its high electron mediation ability, is successfully used in biosensors for sensitive detection of glucose and parathyroid hormone, demonstrating detection limits of ≈0.3 × 10^-3 m and ≈2 pg mL^-1 , respectively. This strategy produces organic electron mediators exhibiting rapid dissolution and high stability, and will find broad application beyond quinone-based biosensors.

Recent advancements in microbial fuel cells: A review on its electron transfer mechanisms, microbial community, types of substrates and design for bio-electrochemical treatment

The development in urbanization, growth in industrialization and deficiency in crude oil wealth has made to focus more for the renewable and also sustainable spotless energy resources. In the past two decades, the concepts of microbial fuel cell have caught more considerations among the scientific societies for the probability of converting, organic waste materials into bio-energy using microorganisms catalyzed anode, and enzymatic/microbial/abiotic/biotic cathode electro-chemical reactions. The added benefit with MFCs technology for waste water treatment is numerous bio-centered processes are available such as sulfate removal, denitrification, nitrification, removal of chemical oxygen demand and biological oxygen demand and heavy metals removal can be performed in the same MFC designed systems. The various factors intricate in MFC concepts in the direction of bioenergy production consists of maximum coulombic efficiency, power density and also the rate of removal of chemical oxygen demand which calculates the efficacy of the MFC unit. Even though the efficacy of MFCs in bioenergy production was initially quietly low, therefore to overcome these issues few modifications are incorporated in design and components of the MFC units, thereby functioning of the MFC unit have improvised the rate of bioenergy production to a substantial level by this means empowering application of MFC technology in numerous sectors including carbon capture, bio-hydrogen production, bioremediation, biosensors, desalination, and wastewater treatment. The present article reviews about the microbial community, types of substrates and information about the several designs of MFCs in an endeavor to get the better of practical difficulties of the MFC technology.