Delineating cathodic extracellular electron transfer pathways in microbial electrosynthesis: Modulation of polarized potential and Pt@C addition.

Microbial electrosynthesis (MES) is an innovative technology that employs microbes to synthesize chemicals by reducing CO2. A comprehensive understanding of cathodic extracellular electron transfer (CEET) is essential for the advancement of this technology. This study explores the impact of different cathodic potentials on CEET and its response to introduction of hydrogen evolution materials (Pt@C). Without the addition of Pt@C, H2-mediated CEET contributed up to 94.4 % at -1.05 V. With the addition of Pt@C, H2-mediated CEET contributions were 76.6 % (-1.05 V) and 19.9 % (-0.85 V), respectively. BRH-c20a was enriched as the dominated microbe (>80 %), and its relative abundance was largely affected by the addition of Pt@C NPs. This study highlights the tunability of MES performance through cathodic potential control and the addition of metal nanoparticles.

Tandem Acidic CO2 Electrolysis Coupled with Syngas Fermentation: A Two-Stage Process for Producing Medium-Chain Fatty Acids.

The tandem application of CO2 electrolysis with syngas fermentation holds promise for achieving heightened production rates and improved product quality. However, the significant impact of syngas composition on mixed culture-based microbial chain elongation remains unclear. Additionally, effective methods for generating syngas with an adjustable composition from acidic CO2 electrolysis are currently lacking. This study successfully demonstrated the production of medium-chain fatty acids from CO2 through tandem acidic electrolysis with syngas fermentation. CO could serve as the sole energy source or as the electron donor (when cofed with acetate) for caproate generation. Furthermore, the results of gas diffusion electrode structure engineering highlighted that the use of carbon black, either alone or in combination with graphite, enabled consistent syngas generation with an adjustable composition from acidic CO2 electrolysis (pH 1). The carbon black layer significantly improved the CO selectivity, increasing from 0% to 43.5% (0.05 M K+) and further to 92.4% (0.5 M K+). This enhancement in performance was attributed to the promotion of K+ accumulation, stabilizing catalytically active sites, rather than creating a localized alkaline environment for CO2-to-CO conversion. This research contributes to the advancement of hybrid technology for sustainable CO2 reduction and chemical production.

Enhanced Microbial Protein Production from CO2 and Air by a MoS2 Catalyzed Bioelectrochemical System.

Carbon dioxide can be relatively easily reduced to organic matter in a bioelectrochemical system (BES). However, due to insufficient reduction force from in-situ hydrogen evolution, it is difficult for nitrogen reduction. In this study, MoS2 was firstly used as an electrocatalyst for the simultaneous reduction of CO2 and N2 to produce microbial protein (MP) in a BES. Cell dry weight (CDW) could reach 0.81±0.04 g/L after 14 d operation at -0.7 V (vs. RHE), which was 108±3 % higher than that from non-catalyst control group (0.39±0.01 g/L). The produced protein had a better amino acid profile in the BES than that in a direct hydrogen system (DHS), particularly for proline (Pro). Besides, MoS2 promoted the growth of bacterial cell on an electrode and improved the biofilm extracellular electron transfer (EET) by microscopic observation and electrochemical characterization of MoS2 biocathode. The composition of the microbial community and the relative abundance of functional enzymes revealed that MoS2 as an electrocatalyst was beneficial for enriching Xanthobacter and enhancing CO2 and N2 reduction by electrical energy. These results demonstrated that an efficient strategy to improve MP production of BES is to use MoS2 as an electrocatalyst to shift amino acid profile and microbial community.

Improving the electrochemical characteristics and performance of a neutral all-iron flow battery by using the iron reduction bacteria.

At present, the all-iron redox flow batteries (RFBs) have greater application potential due to high accessibility of electrolytes compared to traditional RFBs. Meanwhile, although electroactive bacteria can accelerate the electrons transfer, their potential to improve the performance of RFBs has been overlooked. Previously, we had confirmed that ferrous-oxidizing bacteria (FeOB) could enhance the performance of an all-iron RFB, therefore we conducted several batch experiments and chronopotentiometry experiments by using the ferric-reducing bacteria (FeRB) or mixed culture (FeOB and FeRB) to demonstrate whether they have the same or stronger effects on Fe3+-DTPA/Na4[Fe(CN)6] RFB. The results showed that the experimental reactors could achieve higher charging current density and initial cathodic potential during constant voltage charging process. The electrochemical impedance spectroscopy data and cyclic voltammetry curves demonstrated that the polarization impedance increased slower and reduction peak potential of experimental groups also emerged a positive shift compared to CK. According to chronopotentiometry experiments results, the microbes could function at maximum 0.3 M, 12 mA/cm2, and also improved the charging specific capacity. Combined the SEM pictures and microbial composition analysis, the main functional electroactive FeRB were Alcaligenes, Corynebacterium and Bacillus, which indicated to have important potential in improving the performance of RFBs.

Using ferrous-oxidizing bacteria to enhance the performance of a pH neutral all-iron flow battery.

Among various redox flow batteries (RFBs), the all-iron RFBs have greater application potential due to high accessibility of electrolytes. However, the potential of microaerobic ferrous-oxidizing bacteria (FeOB) to improve the performance of RFB has been neglected. Here, several experiments were conducted using Fe2+-diethylenetriaminepentaacetic acid (DTPA)/Na3[Fe(CN)6] as a redox couple for investigating the enhanced performance by FeOB in this RFB. Results showed that the maximum current density of experimental reactors could achieve 22.56 A/m2 at 0.1 M, whereas power density could still maintain 3.42 W/m2(16.96 A/m2 and 1.58 W/m2 for control group); meantime, the polarization impedance of anode increased slower and Fe2+-DTPA oxidation peak emerged maximum 494 mV negative shift. With increased electrolyte concentration in chronopotentiometry experiments, the experimental reactor achieved higher discharging specific capacity at 0.3 M, 10 mA/cm2. Microbial composition analysis showed maximum 75% is Brucella, indicating Brucella has ferrous-oxidizing electroactivity.

Effects of nitrogen supply on hydrogen-oxidizing bacterial enrichment to produce microbial protein: Comparing nitrogen fixation and ammonium assimilation.

To investigate the effects of nitrogen source supply on microbial protein (MP) production by hydrogen-oxidizing bacteria (HOB) under continuous feed gas provision, a sequencing batch culture comparison (N2 fixation versus ammonium assimilation) was performed. The results confirmed that even under basic cultivation conditions, N2-fixing HOB (NF-HOB) communities showed higher levels of CO2 and N2 fixation (190.45 mg/L Δ CODt and 11.75 mg/L Δ TNbiomass) than previously known, with the highest biomass yield being 0.153 g CDW/g COD-H2. Rich ammonium stimulated MP synthesis and the biomass accumulation of communities (increased by 7.4 ～ 14.3 times), presumably through the enhancement of H2 and CO2 absorption. The micro mechanism may involve encouraging the enrichment of species like Xanthobacter and Acinetobacter then raising the abundance of nitrogenase and glutamate synthase to facilitate the nitrogen assimilation. This would provide NF-HOB with ideas for optimizing their MP synthesis activity.

Multi-level advances in databases related to systems pharmacology in traditional Chinese medicine: a 60-year review.

The therapeutic effects of traditional Chinese medicine (TCM) involve intricate interactions among multiple components and targets. Currently, computational approaches play a pivotal role in simulating various pharmacological processes of TCM. The application of network analysis in TCM research has provided an effective means to explain the pharmacological mechanisms underlying the actions of herbs or formulas through the lens of biological network analysis. Along with the advances of network analysis, computational science has coalesced around the core chain of TCM research: formula-herb-component-target-phenotype-ZHENG, facilitating the accumulation and organization of the extensive TCM-related data and the establishment of relevant databases. Nonetheless, recent years have witnessed a tendency toward homogeneity in the development and application of these databases. Advancements in computational technologies, including deep learning and foundation model, have propelled the exploration and modeling of intricate systems into a new phase, potentially heralding a new era. This review aims to delves into the progress made in databases related to six key entities: formula, herb, component, target, phenotype, and ZHENG. Systematically discussions on the commonalities and disparities among various database types were presented. In addition, the review raised the issue of research bottleneck in TCM computational pharmacology and envisions the forthcoming directions of computational research within the realm of TCM.

Super-fast Charging Biohybrid Batteries through a Power-to-formate-to-bioelectricity Process by Combining Microbial Electrochemistry and CO2 Electrolysis.

Extensive study on renewable energy storage has been sparked by the growing worries regarding global warming. In this study, incorporating the latest advancements in microbial electrochemistry and electrochemical CO2 reduction, a super-fast charging biohybrid battery was introduced by using pure formic acid as an energy carrier. CO2 electrolyser with a slim-catholyte layer and a solid electrolyte layer was built, which made it possible to use affordable anion exchange membranes and electrocatalysts that are readily accessible. The biohybrid battery only required a 3-minute charging to accomplish an astounding 25-hour discharging phase. In the power-to-formate-to-bioelectricity process, bioconversion played a vital role in restricting both the overall Faradaic efficiency and Energy efficiency. The CO2 electrolyser was able to operate continuously for an impressive total duration of 164 hours under Gas Stand-By model, by storing N2 gas in the extraction chamber during stand-by periods. Additionally, the electric signal generated during the discharging phase was utilized for monitoring water biotoxicity. Functional genes related to formate metabolism were identified in the bioanode and electrochemically active bacteria were discovered. On the other hand, Paracoccus was predominantly found in the used air cathode. These results advance our current knowledge of exploiting biohybrid technology.

Electricity-Driven Microbial Metabolism of Carbon and Nitrogen: A Waste-to-Resource Solution.

Electricity-driven microbial metabolism relies on the extracellular electron transfer (EET) process between microbes and electrodes and provides promise for resource recovery from wastewater and industrial discharges. Over the past decades, tremendous efforts have been dedicated to designing electrocatalysts and microbes, as well as hybrid systems to push this approach toward industrial adoption. This paper summarizes these advances in order to facilitate a better understanding of electricity-driven microbial metabolism as a sustainable waste-to-resource solution. Quantitative comparisons of microbial electrosynthesis and abiotic electrosynthesis are made, and the strategy of electrocatalyst-assisted microbial electrosynthesis is critically discussed. Nitrogen recovery processes including microbial electrochemical N2 fixation, electrocatalytic N2 reduction, dissimilatory nitrate reduction to ammonium (DNRA), and abiotic electrochemical nitrate reduction to ammonia (Abio-NRA) are systematically reviewed. Furthermore, the synchronous metabolism of carbon and nitrogen using hybrid inorganic-biological systems is discussed, including advanced physicochemical, microbial, and electrochemical characterizations involved in this field. Finally, perspectives for future trends are presented. The paper provides valuable insights on the potential contribution of electricity-driven microbial valorization of waste carbon and nitrogen toward a green and sustainable society.

Innovative electrochemical biosensor with nitrifying biofilm and nitrite oxidation signal for comprehensive toxicity detection in Tuojiang River.

Water toxicity detection, as a valuable supplement to conventional water quality measurement, is an important method for evaluating water environmental quality standards. However, the toxicity of composite pollutants is more complicated due to their mixture effects. This study developed a novel, rapid and interference-resistant detection method for water toxicity based on an electrochemical biosensor using peak current from nitrite oxidation as a signal. Toxicants could weaken the characteristic peak current of nitrite to indicate the magnitude of toxicity. The proof-of-concept study was first conducted using a synthetic water sample containing trichloroacetic acid (TCAA), and then the results were compared with those of the traditional toxicity colorimetric method (CCK-8 kit) and laser confocal microscopy (CLSM). The accuracy of the biosensor was further verified with water samples containing individual pollutants such as Cd2+ (50-150 µg/L), Cr6+ (20-80 µg/L) mixture, triclosan (TCS; 0.1-1.0 µg/L) and TCAA (10-80 µg/L), or a mixture of the above. The viability of the sensor was further validated with the actual water sample from the Tuojiang River. The results demonstrated that although the concentration of a single conventional pollutant in water did not exceed the discharge standard for surface water, the comprehensive toxicity of natural water should not be ignored. This method could be a beneficial supplement to conventional water quality detection to understand the characteristics of the water, and thus contribute to the next stage of water treatment.

Biocathode prepared at low anodic potentials achieved a higher response for water biotoxicity monitoring after polarity reversal.

Microbial electrochemical sensors equipped with biocathode sensing elements have attracted a growing interest, but their startup and recovery properties remain unclear. In this study, the approach of polarity reversal was applied for the biocathode sensing element fabrication and biosensor recovery. The stimulating/suppressing effect of formaldehyde was determined by the anode potential before polarity reversal as well as the increased trials of toxic exposure. Increasing anode potential from -0.3 V to +0.3 V before polarity reversal, the baseline electric signal was changed from -0.028 ± 0.001 mA to -0.005 ± 0.003 mA, while the maximum normalized electrical signal (NES) was increased from 1.1 ± 0.1 to 4.1 ± 1.9, and thus a general downtrend was observed for Response as a newly induced indicator. Polarity reversal failed to recover the electroactivity of these poisoned bioelectrodes. This study demonstrated that electrode potential was critical when using the approach of polarity reversal to construct the biocathode sensing element, and revealed an urgent need for strategies toward high recoverability of such biosensors.

Microbial electrochemical driven anaerobic ammonium oxidation coupling to denitrification in a single-chamber stainless steel reactor for simultaneous nitrogen and carbon removal.

Anodic ammonium oxidation mainly focuses on autotrophic process, and the removal combined with organic matter oxidation is still unclear in microbial electrolysis cell (MEC). Here, a stainless-steel tank is constructed as an MEC for anaerobic ammonium oxidation and organic matter removal. Results show that MEC increases ammonium oxidation from 3.83 ± 2.51% to 32.90 ± 3.39%, and the organic matter removal rises from 75.69 ± 0.59% to 92.12 ± 0.57%, and the energy consumption is only 0.80 ± 0.09 kWh kg-1N, indicating an energy-efficient approach for simultaneous ammonium and carbon removal. Cyclic voltammetry reveals two pairs of oxidative peaks (-0.4 V and + 0.6 V) which demonstrate the electrochemical activity of biofilms for organic matter and ammonium oxidation, respectively. 16S rRNA gene analysis clarifies the anodic biofilm mainly enriched by the genus of Azoarcus, Hydrogenophaga and Paracoccus. Further analysis indicates that anodic potential controls the community succession of heterotrophic and hydrogenotrophic denitrifying bacteria, and then regulates the nitrogen and carbon removal processes, which extend the insights of anodic anaerobic ammonium oxidation coupling to denitrification under organic conditions.

Improving electroautotrophic ammonium production from nitrogen gas by simultaneous carbon dioxide fixation in a dual-chamber microbial electrolysis cell.

Microbial electrosynthesis is a promising technology for high-value added products generation from organic and inorganic waste. In this work, autotrophic dual-chamber microbial electrolysis cells (MECs) were set up for N2 fixation at -0.9 V vs Ag/AgCl (sat. KCl) cathodic potential under ambient conditions. Higher NH4+ production yield (average value of 0.35 µmol h-1 cm-2, normalized to cathode surface area) and higher faradaic efficiency (FE, 20.25%) were obtained with intermittent addition of N2 and CO2, while the yield and FE were only 0.018 µmol h-1 cm-2 and 4.21% in the absence of CO2. Furthermore, cyclic voltammograms (CV) explained the bioelectrochemical behavior of N2 reduction was coupled with CO2 reduction in the autotrophic MECs. Microbial community analysis and functional prediction in the cathodic chamber revealed that Xanthobacter and Hydrogenophaga played as producers for N2 and CO2 fixation and Pannonibacter acting as a decomposer for converting organic nitrogen to ammonium. This work not only provided an optional bioelectrocatalytic method for N2 fixation with negative CO2-emissions but also revealed the mechanism of simultaneous fixation of N2 and CO2 via Calvin cycle in autotrophic MECs.

Osteosarcoma Cell Growth Inhibition by Isoxanthanol-Nanoparticles through Histone H3 Lysine 27 Trimethylation Downregulation and AMPK Activation.

The present study was aimed to investigate the effect of isoxanthanol-nanoparticles (IXNP) on proliferation of osteosarcoma cells and evaluate the underlying mechanism. In MG-63 and U2-OS cells proliferative potential was reduced significantly (p < 0.05) in dose-dependent manner by IXNP treatment. The IXNP treatment at 15 mg/mL suppressed MG-63 cell viability to 39% and that U2-OS cells to 43% at 48 h. Treatment with IXNP led to a prominent up-regulation of caspases-3 and -9 cleavage compared to untreated cells. Moreover, PARP and Bax levels in the cells showed a remarkable increase on IXNP-treatment in comparison to the control cells. Phosphorylation of AMPKα, expression of p21 and replication of mtDNA was also promoted in MG-63 and U2-OS cells on treatment with IXNP. In MG-63 and U2-OS cells, IXNP-treatment elevated expression of PGC-1α and TFAM while as EED, EZH2, and SUZ12 expression was down-regulated. Thus, IXNP suppress proliferation of osteosarcoma cells through activates AMPK activation and elevation of Histone H3 lysine 27 trimethylation. Therefore, IXNP has therapeutic potential to be developed for treatment of osteosarcoma.

Integrated simultaneous nitrification/denitrification and comammox consortia as efficient biocatalysts enhance treatment of domestic wastewater in different up-flow bioelectrochemical reactors.

Simultaneous nitrification/denitrification (SND) can efficiently deplete NH4+ by using air-exposed biocathode (AEB) in bioelectrochemical reactors. However, the fluctuation of wastewater adversely affects the functional biofilms and therefore the performance. In this work, four up-flow bioelectrochemical reactors (UBERs) with some novel inocula were investigated to improve domestic wastewater treatment. The UBERs exhibited favorable removal of chemical oxygen demand (COD, 95%), NH4+-N (99%), and total nitrogen (TN, 99%). The maximum of current (2.7 A/m3), power density (136 mW/m3) and coulombic efficiency (20.5%) were obtained. Cyclic voltammetry analysis showed all the electrodes were of diversified catalytic reactions. Illumina pyrosequencing showed the predominant Ignavibacterium, Thauera, Nitrosomonas, Geminicoccus and Nitrospira were in all electrodes, contributing functional biofilms performing SND, comammox, and bioelectrochemical reactions. FAPROTAX analysis confirmed twenty-one functional groups with obvious changes related to chemoheterotrophy, respiration/oxidation/denitrification of nitrite and nitrate. Comfortingly, such novel diversified consortia in UBERs enhance the microbial metabolisms to treat domestic wastewater.

Electrode-dependent ammonium oxidation with different low C/N ratios in single-chambered microbial electrolysis cells.

Alternative method should be found to solve the ammonia accumulation in anaerobic digestion. Herein, electrode-dependent ammonium oxidation was successfully achieved in anaerobic single-chambered microbial electrolysis cells (MECs)under different low C/N ratios (0, 1, and 1.5), with an applied voltage of 0.6 V as well as an initial NH4+-N and NO3--N concentration of 500 and 300 mg/L. The nitrogen removal performance of MECs and the controls indicated that applying a voltage stimulated nitrogen removal under low C/N ratios of 0, 1, and 1.5. However, the remaining organic carbon in MEC with a relatively higher C/N ratio of 3 inhibited the ammonium oxidation. Current changes and cyclic voltammetry demonstrated that the bioanode with several bioelectrochemical activities could promote ammonium oxidation. The dominant genera Truepera, Aquamicrobium, Nitrosomonas, Arenimonas, Comamonas, and Cryobacterium enriched on both electrodes could be the key functional taxa in MECs with C/N ratios of 0, 1, and 1.5. The remaining sodium acetate in MEC with C/N ratio of 3 inhibits microbial community structure and relative abundance, which may adversely affected nitrogen removal. Further caculation showed that nitrogen balance was essentially achieved, while electron balance was disrupted since electrons may be consumed through NO3--N recycle and cell synthesis, and finally caused low coulombic efficiency.

Impact of low temperature on ex situ nitritation/in situ denitritation in field pilot-scale landfill for postclosure care of leachate treatment and gas content.

Leachates and landfill gas (LFG) are the major problems for closed landfills (CL) and cause significant threats to receiving waterbody and ambient air quality. In this study, a field pilot-scale CL with ex situ nitritation/in situ denitritation process was constructed and operated continuously under wide temperature variations. The effect of low temperature on leachate treatment, and LFG content was studied. Results showed that the combined process can efficiently remove nitrogen and organic matters from leachate, and change LFG content under low-temperature condition. In the ex situ nitritaion, maximum removal efficiencies of ammonia and chemical oxygen demand (COD) were over 99% and 85%, respectively. The loading rate of nitrogen and COD reached 0.5 kg N m-3 d-1 and 0.7 kg COD m-3 d-1, respectively. The inhibitions of free ammonia (FA) and free nitrous acid (FNA), and low temperature were the key factors affecting nitritation. With recirculating nitrified leachate, total oxidized nitrogen (TON) was completely reduced, and the refuse decomposition was accelerated. Denitritation was the main reaction responsible in the CL. Additionally, methane content was observed lowly at non-inhibitory TON loading rate of 5.8 ± 3.7 g N ton-1 TS d-1. This decrease was not caused by the increased of TON loading, but a carbon source competition by denitrificans. The estimated COD consumption and methane reduction were 55.0 kg d-1 by TON reduction, and 20 m3 d-1, respectively. Hence, this study served a potential strategy for postclosure care of landfills under low temperature variation.

Carboxylic acid reduction and sulfate-reducing bacteria stabilization combined remediation of Cr (VI)-contaminated soil.

For controlling heavy metal pollution, the utilization of carboxylic acids (CAs) combined with sulfate-reducing bacteria (SRB) for continuous and stable remediation of Cr (VI)-contaminated soil was comprehensively investigated. At pH 3, citrate and lactate had photocatalysis characteristics that enabled them to reduce high Cr (VI) concentrations. The reduction efficiencies of citrate and lactate were 99.16-100% and 80.78-87.00%, respectively. In the 40 mg L-1 Cr (VI) treatment, the total Cr adsorption rate of soil was 61.39-68.31%; as the pH increased, the Cr species adsorption capacity of the soil decreased. Following the addition of exogenous 100 mg L-1 Cr (VI), the Cr (VI) content of re-contaminated soil was reduced to 16.2734 ± 0.9505 mg L-1 or 15.8618 mg kg-1 by adding citrate or lactate. Then, using SRB via culture by mulching, addition of citrate or lactate markedly reduced the toxicity of Cr (VI). The respective citrate or lactate treatments had sulfur concentrations of sulfide from deep soil (high-sulfide layer) of 70.54 ± 17.59 and 98.85 ± 13.84 mg kg-1, respectively, and released Cr (VI) concentrations of 0.22 ± 0.25 and 3.64 ± 3.32 mg kg-1, respectively, due to oxidation upon air exposure. We used a two-stage remediation strategy for these treatments: First, CAs were used for photocatalytic reduction to reduce Cr (VI); next, CAs were utilized as carbon sources by SRB, which further reduced Cr (VI) and stabilized Cr species. In addition, citrate was more conducive than lactate to maintaining the stability of the soil microbial community. The results show that this method has potential in the remediation of Cr (VI)-contaminated soil.

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

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

Integrative effect of citrate on Cr(â ¥) and total Cr removal using a sulfate-reducing bacteria consortium.

In controlling toxic Cr(Ⅵ) pollution, the sulfate-reducing bacteria (SRB) method-a bioresource technology-is considered more sustainable and stable than synthetic technologies; however, its mechanisms of metal removal are unclear. This study investigated the mechanism of the use of citrate as a carbon source in an SRB bioreactor for Cr(Ⅵ) removal by disassemble or simulation approach. We show that citrate can mask toxicity, whereby the IC50 value (inhibitory concentration affecting 50% of the test population) of citrate was higher than that of lactate, and that citrate can also protect water systems from oxidation. The anti-oxidation rate of citrate ranged from 76.00% to 90.92%; whereas for citrate‒Cr(Ⅲ), the oxidation rate was only 0.185%-0.587%. Citrate can up-regulate microbial genes and functions, causing acetate and sulfide (NaFeS2) accumulation. Acetate addition promoted Cr adsorption by sulfide (mainly NaFeS2) and promoted sulfide sedimentation. Moreover, in addition to Cr(Ⅵ) reduction and Cr(Ⅲ)‒sulfide generation, the addition of sulfide promoted sedimentation; the correlation coefficient between the sedimentation coefficient and the sulfur content was r = -0.88877 at p < 0.01. Therefore, citrate had a systemic radiative effect on every aspect of the SRB‒citrate system model for Cr(Ⅵ) removal. In addition to the reduction in the former simple model, an integrative effect (including adsorption, sedimentation, and metabolism) was combined with NaFeS2 for Cr removal, which was regulated by the SRB‒citrate system. Exploration and understanding of these mechanisms promote SRB‒citrate methods to be wider implications in practice.