Enhanced performance of sulfate reducing bacteria based biocathode using stainless steel mesh on activated carbon fabric electrode

Seasonal and distance-decay patterns of surface sediments microbial nitrogen and sulfur cycling linkage in the eastern coast of China

The surface sediments as a repository of pelagic environment changes and microbial community structural succession tend to have a profound effect on global and local nitrogen and sulfur cycling. In this study, analysis of sediment samples collected from the Bohai Sea, Yellow Sea, and north of the East China Seas (BYnECS) revealed longitude, latitude, depth, and chlorophyll had the strongest influence on microbial community structure (p-values < 0.005). A clear distance-decay pattern was exhibited in BYnECS. The result of co-occurrence network modularization implied that the more active pathway in winter was thiosulfate reduction and nitrate reduction, while in summer it was nitrification. The potential functional genes were predicted in microbial communities, and the most dominant genes were assigned to assimilatory sulfur reduction, denitrification, and dissimilatory nitrate reduction. This study innovatively explored the potential relationships between nitrogen and sulfur cycling genes of these three sea regions in the China Sea.

SRB-based bioelectrochemical system: A potential multipollutant combatant for enhanced landfill waste stabilization

Due to the lower proportion of organic matter and higher toxicity of the aged landfill, most of the advanced treatment technologies are not effective from economic, environmental, and social perspectives. This study evaluates the potential of sulfate-reducing bacteria (SRB) based bioelectrochemical-system (BES) in the decontamination of landfill wastes by reducing GHGs emissions and levels of soluble pollutants. The landfill waste (solid/leachate) collected from the Pirana Landfill site was assessed for economical long-term treatment and scaling up the feasibility of the designed system. The present system demonstrated significant improvement in volumetric hydrogen production of 3.1:1 (H2:CH4) by suppressing methanogenesis with a significant reduction in heavy metals concentration and other organic components. Despite being amended with 0.1 N ammonia, the treated leachate level of NO3 (2.350 ± 1.077 mg/L) was reduced by 5.3 times, hence reducing further groundwater pollution from landfill leaching. The BES-treated solid waste was more stabilized as shown by a fivefold increase in surface area and can be potentially applied for leachate immobilization and bio-fortification of agricultural fields. The vector arrangement and magnitude with differences in magnitudes for both leachate and solid waste supported the on-site applicability of BES treatment. Concerning the affinity in various treatment systems, the dendrogram clearly showed Ca and Fe placed far from each other (3506.08), in comparison to Fe and Mg (1186.6), followed by Fe and Cu (1544.6). Voltammograms proved the efficacy of the enriched electrochemically active bacteria (EAB), to support the treatment of landfill solid waste and leachate sustainably.

Electrosorption of phenolic compounds from olive mill wastewater: Mass transport consideration under a transient regime through an alginate-activated carbon fixed-bed electrode

Olive mill wastewater (OMWW) is an environmentally critical effluent, specifically due to its high content of phenolic compounds (PCs), which are hazardous due to their antimicrobial activities in water. However, their properties have good health effects at suitable doses. For the first time, the electrosorption of PCs from actual OMWW has been proposed for their possible recovery as value-added compounds, while decontaminating OMWW. A bio-sourced alginate-activated carbon (AC) fixed-bed electrode was prepared based on the reuse of olive pomace solid waste as powdered AC. At the optimal AC content (1% w/v), the internal ohmic drop voltage was lower (2.26 V) and the mass transport coefficient was higher (9.7 10^-5 m s^-1) along with the diffusivity (7.3 10^-9 m² s^-1), which led to enhanced electrosorption rates. Afterward, an optimal electrode potential was obtained (-1.1 V vs. Ag/AgCl), while higher voltages led to faradaic reactions. Moreover, the adsorption capacity was lower (123 mg g^-1) than that of electrosorption (170 mg g^-1) and was even higher (307 mg g^-1) with actual effluents. This was probably due to the influence of electromigration, which was confirmed by new models that could predict the electrosorption kinetics well considering mass transport and acid dissociation constants.

Antimony reduction by a non-conventional sulfate reducer with simultaneous bioenergy production in microbial fuel cells

Environmental toxicity of antimony (Sb) is significantly increased through the widespread industrial application. The extended release of Sb above the regulatory level became a risk to humans habituated in the ecosystem. Conventional methods to remediate Sb demand high energy or resource input, which further leads to secondary pollution. The bio-electrochemical system offers a promising bioremediation strategy to remove or reduce toxic heavy metals. Thus, this research explores the possibilities of simultaneous metal sulfide (MeS) precipitation and electricity production using a full biological Microbial fuel cell (MFC). A non-conventional sulfate-reducing bacteria (SRB) Citrobacter freundii SR10 was used for this investigation, where the MFC was operated for lactate utilization in the bio-anode and Sb reduction at the bio-cathode. This study observed 81% of coulombic efficiency (bio-anode) and 97% of sulfate reduction with 99.3% Sb (V) reduction (bio-cathode), and it was concluded that the MeS precipitation entirely depends on sulfide concentration via SR10 sulfate reduction. The MFC-SR10 offers a maximum power density of 1652.9 ± 32.1 mW/m^3, and their performance was depicted using cyclic voltammetry and electrochemical impedance spectroscopy. The Sb reduction was evaluated through fluorescence spectroscopy, and the Sb (V) MeS precipitation was confirmed as stibnite (Sb₂S₃) by Raman spectroscopy and X-ray photoelectron spectroscopy. Furthermore, the matured anodic and cathodic biofilm formation was confirmed by Scanning electron microscopy with Energy-dispersive X-ray spectroscopy. Thus the MFC with SRB bio-cathode can be used as an alternative to simultaneously remove sulfate and Sb from the wastewater with electricity production.

Bioelectricity generation using long-term operated biocathode: RFLP based microbial diversity analysis

In the present work, power generation and substrate removal efficiencies of long-term operated microbial fuel cells, containing abiotic cathodes and biocathodes, were evaluated for 220 days. Among the two microbial fuel cell (MFC) types, the one containing biocathode showed higher power density (54 mW/m2), current density (122 mA/m2) coulombic efficiency (33%), and substrate removal efficiency (94%) than the abiotic cathode containing MFC. Voltammetric analysis also witnessed higher and sustainable electron discharge for the MFC with biocathode, when compared with the abiotic cathode MFC. Over the tested period, both MFC have shown a cell voltage drop, after 150 and 165, days, for the MFC with biocathode and abiotic cathodes, respectively. Polymerase chain reaction (PCR) based restriction fragment length polymorphism (RFLP) analysis identified 281 clones. Bacteria belonging to Acinetobacter, Acidovorax, Pseudomonas and Burkholderia were observed in the abiotic cathode MFC. Bacteria belonging to Geobacter, Cupriavidus and Acidobacteria were observed in the biocathode MFC. Almost similar types of archaea (Methanosarcinales, Methanolinea, Nitrososphaera and Methanomicrobiales) were observed in both MFCs.

Bioelectrochemical remediation of phenanthrene in a microbial fuel cell using an anaerobic consortium enriched from a hydrocarbon-contaminated site

Polycyclic aromatic hydrocarbons (PAH) are organic pollutants that require remediation due to their detrimental impact on human and environmental health. In this study, we used a novel approach of sequestering a model PAH, phenanthrene, onto a solid carbon matrix bioanode in a microbial fuel cell (MFC) to assess its biodegradation coupled with power generation. Here, the bioanode serves as a site for enrichment of electroactive and hydrocarbon-degrading microorganisms, which can simultaneously act to biodegrade a pollutant and generate power. Carbon cloth electrodes loaded with two rates of phenanthrene (2 and 20 mg cm^-2) were compared using dual chamber MFCs that were operated for 50 days. The lower loading rate of 2 mg cm^-2 was most efficient in the degradation of phenanthrene and had higher power production capacities (37 mW m^-2) as compared to the higher loading rate of 20 mg cm^-2 (power production of 19.2 mW m^-2). FTIR (Fourier-Transform Infrared Spectroscopy) analyses showed a depletion in absorbance peak signals associated with phenanthrene. Microbes known to have electroactive properties or phenanthrene biodegradation abilities like Pseudomonas, Rhodococcus, Thauera and Ralstonia were enriched over time in the MFCs, substantiating the electrochemical and FTIR analyses. The MFC approach taken here thus offers great promise towards PAH bioelectroremediation.

Comparative Evaluation of Coated and Non-Coated Carbon Electrodes in a Microbial Fuel Cell for Treatment of Municipal Sludge

This study aims to provide insight into the cost-effective catalyst on power generation in a microbial fuel cell (MFC) for treatment of municipal sludge. Power production from MFCs with carbon, Fe2O3, and Pt electrodes were compared. The MFC with no coating on carbon generated the least power density (6.72 mW·m−2) while the MFC with Fe2O3-coating on carbon anodes and carbon cathodes generated a 78% higher power output (30.18 mW·m−2). The third MFC with Fe2O3-coated carbon anodes and Pt on carbon as the cathode catalyst generated the highest power density (73.16 mW·m−2) at room temperature. Although the power generated with a conventional Pt catalyst was more than two-fold higher than Fe2O3, this study suggests that Fe2O3 can be investigated further as an efficient, low-cost, and alternative catalyst of Pt, which can be optimized for improving performance of MFCs. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) results demonstrated reduced resistance of MFCs and better charge transfer between biofilm and electrodes containing coated anodes compared to non-coated anodes. Scanning electron microscopy (SEM) was used to analyze biofilm morphology and microbial community analysis was performed using 16S rRNA gene sequencing, which revealed the presence of known anaerobic fermenters and methanogens that may play a key role in energy generation in the MFCs.

Bio-electrochemical system (BES) as an innovative approach for sustainable waste management in petroleum industry

Petroleum industry is one of the largest and fast growing industries due to the ever increasing global energy demands. Petroleum refinery produces huge quantities of wastes like oily sludge, wastewater, volatile organic compounds, waste catalyst, heavy metals, etc., because of its high capacity and continuous operation of many units. Major challenge to this industry is to manage the huge quantities of waste generated from different processes due to the complexity of waste as well as changing stringent environmental regulations. To decrease the energy loss for treatment and also to conserve the energy stored in the chemical bonds of these waste organics, bio-electrochemical system (BES) may be an efficient tool that reduce the economics of waste disposal by transforming the waste into energy pool. The present review discusses about the feasibility of using BES as a potential option for harnessing energy from different waste generated from petroleum refineries.

Effects of salinity, C/S ratio, S/N ratio on the BESI process, and treatment of nanofiltration concentrate

A laboratory-scale biodegradation and electron transfer based on the sulfur metabolism in the integrated (BESI^®) process was used to treat a saline petrochemical nanofiltration concentrate (NFC). The integrated process consisted of activated sludge sulfate reduction (SR), and sulfide oxidation (SO) reactors, and a biofilm nitrification reactor. During the process, the total removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen, and total nitrogen (TN) were 76.2, 83.8, and 73.1%, respectively. In the SR reactor, most of the organic degradation occurred and approximately 70% COD were removed by the sulfate-reducing bacteria (SRB). In the SO reactor, both the autotrophic and heterotrophic denitrifications were observed to take place. In parallel, batch experiments were conducted to detect the effects of different C/S and S/N ratios on COD removal and denitrification efficiency. The batch experiments were also conducted to detect the effects of salinity on COD and sulfate reduction. The composition of pollutants in the wastewater was complex, and some existing organics were not degraded by the SRB. The non-SRB groups also played important roles in the reactor. Under salinity-induced stress, the metabolisms of the SRBs and non-SRB groups were both inhibited. However, 6 g/L NaCl did not have much effect on the final COD removal efficiency. In the batch experiments, the added sulfide served as the electron donor for autotrophic denitrification. The added organics provided substance for heterotrophic denitrification.

A genetic approach for microbial electrosynthesis system as biocommodities production platform

Microbial electrosynthesis is a process that can produce biocommodities from the reduction of substrates with microbial catalysts and an external electron supply. This process is expected to become a new application of a cell factory for novel chemical production, wastewater treatment, and carbon capture and utilization. However, microbial electrosynthesis is still subject to several problems that need to be overcome for commercialization, so continuous development such as metabolic engineering is essential. The development of microbial electrosynthesis can open up new opportunities for sustainable biocommodities production platforms. This review provides significant information on the current state of MES development, focusing on extracellularly electron transfer and metabolic engineering.

Remediation of acid mine drainage using microbial fuel cell based on sludge anaerobic fermentation

The aim of this work is to utilize the microbial fuel cell for removing metals and sulfate from acid mine drainage using sewage sludge organics and simultaneous electricity generation. The enriched sulfate-reducing mixed culture was used as the cathodic biofilm and the sludge as the substrate. Under anaerobic conditions, 71.2% sulfate, 99.7% heavy metals, and 51.6% total chemical oxygen demand are removed at an electrode spacing of 4 cm and a sludge concentration of 30% (v/v) after 10-day treatment. A maximum power density of 51.3 mW/m² is obtained. Approximately 79.5% of the dissipated sulfate is converted to element sulfur or polysulfides. The sulfide concentration is kept at below 20 mg-S/L. The concentrations of heavy metals are in the range of 0.02-0.06 mg/L in the effluent, which are far below the levels required by Chinese legislation. Microbial community analysis reveals that sulfate-reducing bacteria in Desulfuromonadales are dominant on the cathodic biofilm at the end of experiments. This study shows the potential of synchronous degradation of residual sludge and treatment of AMD with electricity harvesting.

Syntrophic association and performance of Clostridium, Desulfovibrio, Aeromonas and Tetrathiobacter as anodic biocatalysts for bioelectricity generation in dual chamber microbial fuel cell

Anode chamber of a dual chamber microbial fuel cell (MFC) having raw landfill leachate was inoculated with consortium of sulphate-reducing bacteria (SRB) and sulphide-oxidizing bacteria (SOB) to study the phylogenetic architecture, function and mutualism of anolyte community developed in the reactor. Enriched microbial community was analysed with the help of Illumina MiSeq and indicated the dominance of Firmicutes (41.4%), Clostridia (36.4%) and Clostridium (12.9%) at phylum, class and genus level, respectively. Clostridium was associated with fermentation as well as transfer of electrons to the electrode mediated by ferredoxin. Desulfovibrio (6.7%), Aeromonas (6.6%) and Tetrathiobacter (9.8%) were SRB-SOB associated with direct electron transfer to the electrode. Community analysis disclosed a syntrophic association among novel Firmicutes and Proteobacteria species for bioelectricity generation and degradation of organic matter. Complete removal of chemical oxygen demand was observed from landfill leachate within 3 days of inoculation. Lower oxidative slope and polarization resistance revealed from Tafel analysis backed the feasibility of electron transfer from microbes to anodic electrode and thus development of efficient anode-respiring community. Following enrichment and stabilization of the anodic community, maximum power density achieved was 9.15 W/m³ and volumetric current density was 16.17 A/m³. Simultaneous feeding with SRB-SOB and landfill leachate led to the enrichment of a novel, mutually interdependent microbial community capable of synchronized bioremediation of effluents rich in carbon, sulphate, nitrate and aromatic compounds.

RuO2/MWCNT/ stainless steel mesh as a novel positive electrode in vanadium redox flow batteries

The present work describes the preparation and electrochemical characterization of RuO₂/MWCNT/Stainless Steel Mesh (SSM) electrode as compared with a MWCNT/SSM electrode in the positive half-cell of a Vanadium Redox Flow Battery (VRFB).

Electrochemical removal of sulfate from petroleum produced water

Petroleum produced water (PPW) is a waste-stream that entails huge cost on the petroleum industry. Along with other suspended and dissolved solids, it contains sulfate, which is a major hurdle for its alternative use intended toward enhanced oil recovery. This study proposes a two-step process for sulfate removal from PPW. A synthetic PPW was designed for the study using response surface methodology. During the first step, sulfate present in PPW was reduced to sulfide by anaerobic fermentation with 80% efficiency. In the second step, more than 70% of the accumulated sulfide was electrochemically oxidized. This integrated approach successfully removed sulfate from the synthetic wastewater indicating its applicability in the treatment of PPW and its subsequent applications in other oil field operations.

Stimulation of an indigenous thermophillic anaerobic bacterial consortium for enhanced oil recovery

Production of gases, VFAs, solvents and surfactants was achieved by thermophilic methanogenic consortium TERIL63, showing reduction in surface tension from 69 to 35 dynes cm⁻¹. TERIL63 with an optimized nutrient recipe showed 15.49% EOR at 70 °C in a core flood study.

Optimization of electrochemical parameters for sulfate-reducing bacteria (SRB) based biocathode

This study focuses on the effect of operational and physiochemical factors on a stable sulfate reducing bacteria biocathode and their effect on the electrochemical response thereof.

Influence of headspace composition on product diversity by sulphate reducing bacteria biocathode

Mixed culture of sulphate reducing bacteria named TERI-MS-003 was used for development of biocathode on activated carbon fabric fastened to stainless steel mesh for conversion of volatile fatty acids to reduced organic compounds under chronoamperometric conditions of -0.85V vs. Ag/AgCl (3.5M KCl). A range of chemicals were bioelectrosynthesized, however the gases present in headspace environment of the bioelectrochemical reactor governed the product profile. Succinate, ethanol, hydrogen, glycerol and propionate were observed to be the predominant products when the reactor was hermetically sealed. On the other hand, acetone, propionate, isopropanol, propanol, isobutyrate, isovalerate and heptanoate were the predominant products when the reactor was continuously sparged with nitrogen. This study highlights the importance of head space composition in order to manoeuvre the final product profile desired during a microbial electro-synthesis operation and the need for simultaneously developing effective separation and recovery strategies from an economical and practical standpoint.

Microbial catalyzed electrochemical systems: a bio-factory with multi-facet applications

Microbial catalyzed electrochemical systems (MCES) have been intensively pursued in both basic and applied research as a futuristic and sustainable platform specifically in harnessing energy and generating value added bio-products. MCES have documented multiple/diverse applications which include microbial fuel cell (for harnessing bioelectricity), bioelectrochemical treatment system (waste remediation), bioelectrochemical system (bio-electrosynthesis of various value added products) and microbial electrolytic cell (H2 production at lower applied potential). Microorganisms function as biocatalyst in these fuel cell systems and the resulting electron flux from metabolism plays pivotal role in bio-electrogenesis. Exo-electron transfer machineries and strategies that regulate metabolic flux towards exo-electron transport were delineated. This review addresses the contemporary progress and advances made in MCES, focusing on its application towards value addition and waste remediation.