Simultaneous Cr Research Articles

Raspberry stalks-derived biochar, magnetic biochar and urea modified magnetic biochar - Synthesis, characterization and application for As(V) and Cr(VI) removal from river water

Raspberry stalks-derived biochar (BC), magnetic biochar-iron oxide composite (BC–Fe) and its derivative modified with urea (BC–Fe–U) were synthesized, characterized and tested as(V) and Cr(VI) ion sorbents. The surface area of BC, BC-Fe and BC-Fe-U was 259, 163 and 117 m2 g−1, respectively. The structure of BC was dominated by micropores, while in BC-Fe and BC-Fe-U mesopores predominated. Based on the XRD results, it was found that the magnetic properties of the biochar-iron oxide composites are due to the presence of ferrimagnetic magnetite (Fe3O4) and maghemite (Fe2O3). The optimal pH of As(V) and Cr(VI) adsorption onto the studied sorbents is in the range of 2.3–5.7. Pristine biochar (BC) does not adsorb As(V) ions; however, it enables rapid adsorption of Cr(VI) with the static adsorption capacity of 19.2 mg g−1. The maximum static adsorption capacities of As(V) and Cr(VI) ions onto BC-Fe and BC-Fe-U are within the range of 13.5–16.3 mg g−1. For most adsorption systems tested, adsorption equilibrium is reached within 4 h, though even a few minutes is enough to reach half of the adsorption static value. Phosphates over 0.005 mol L−1 hinder adsorption of As(V) and Cr(VI) ions. Application of at least 5 mol L−1 nitric acid allows about 95% of Cr(VI) and As(V) to be desorbed from adsorbate-loaded BC-Fe material. For other materials, the desorption efficiencies are significantly lower. BC-Fe and BC-Fe-U materials were successfully used for simultaneous Cr(VI) and As(V) removal from river water.

Kraft lignin-based carbon xerogel/zinc oxide composite for 4-chlorophenol solar-light photocatalytic degradation: effect of pH, salinity, and simultaneous Cr(VI) reduction

Kraft lignin-based carbon xerogel/zinc oxide composite for 4-chlorophenol solar-light photocatalytic degradation: effect of pH, salinity, and simultaneous Cr(VI) reduction

Simultaneous photocatalytic tetracycline oxidation and chromate reduction via a jointed synchronous pathway upon Z-scheme Bi12O17Cl2/AgBr: insight into intermediates and mechanism

A 2D/0D Bi12O17Cl2/AgBr Z-scheme photocatalyst provides a jointed synchronous pathway for simultaneous Cr(vi) and TC removal.

Facile fabrication of magnetically recyclable Fe3O4/BiVO4/CuS heterojunction photocatalyst for boosting simultaneous Cr(VI) reduction and methylene blue degradation under visible light

It is a challenging problem that develops a low-cost, efficient and sustainable technology in order to remove heavy metals and organic contaminants in the practical wastewater. Herein, a novel recyclable Fe3O4/BiVO4/CuS (FBCu) heterojunction photocatalyst was facilely fabricated by a method, coating CuS nanoparticles on the surface of Fe3O4 and BiVO4 simultaneously. FBCu composite not only has the ability to degrade Cr(VI) or methylene blue (MB) alone under visible light irradiation, but also exhibits higher photocatalytic ability in simultaneously removing Cr(VI) and MB mixed pollutants. The superior photocatalytic performance of FBCu is related to the formation of p-n heterojunction, which extends the spectral response and facilitates the efficiency of charge carriers separation and utilization. Moreover, FBCu exhibits satisfactory properties of reusability and stability after five cycling experiments in the Cr(VI)-MB coexistence system. Furthermore, the detailed mechanism for simultaneous removal of mixed pollutants was proposed and verified by DRS results, photoelectrochemical analysis, scavenger experiments and electron spin resonance determination. This work provides a recyclable photocatalyst with eco-friendliness and multifunctional applications in water pollution.

Preparation of a coated ZH-scheme (SnS2@CdS)/TiO2(0 0 1) photocatalyst for phenol degradation with simultaneous Cr(VI) conversion

The construction of highly efficient and multifunctional composite photocatalysts has attracted extensive attention in the field of environmental governance. In this study, an efficient coated ZH-scheme (SnS2@CdS)/TiO2(001) photocatalyst is resoundingly prepared by hydrothermal, isoelectric point and continuous ion layer adsorption reaction methods and a sequence of characterizations are carried out. The photocatalytic activity of (SnS2@CdS)/TiO2(001) photocatalyst is evaluated via degradation of phenol with simultaneous conversion of Cr(VI) under sunlight irradiation. Furthermore, the effects of initial concentrations of phenol and Cr(VI), variety of photocatalyst, solution pH, (SnS2@CdS)/TiO2(001) photocatalyst dosage and recyclingtimes on phenol degradation and Cr(VI) conversion are investigated. The crucial active species of phenol degradation are explored by capture experiments. When the coated ZH-scheme (SnS2@CdS)/TiO2(001) photocatalyst dosage is 1.0 g/L, phenol and Cr(VI) concentrations are 20 mg/L and 40 mg/L, respectively and solution pH is 4.0, the phenol degradation rate and the Cr(VI) conversion rate could reach 85.52 % and 95.69 %, respectively. Additionally, the possiblephotocatalyticmechanism of phenol degradation with synchronous Cr(VI) conversion caused by (SnS2@CdS)/TiO2(001) photocatalyst is proposed. It can be hoped that this work will provide a feasible way to treat high concentrations of organic pollutants and simultaneously convert heavy metal ions.

Pengaruh CR dan DER terhadap ROE pada Perusahaan Jasa Sub Sektor Konstruksi dan Bangunan

This research aims to determine how much the impact of CR and DER on ROE at Heavy Constructions and Civil Engineering companies for the period 2014-2019. Sample used were 8 companies using purposive sampling technique. The data used in this study is panel data so that the data will be tested using the help of Eviews 9 application and analysed using panel data regression. The selected panel data regression model is the Random Effect Model. The results of the analysis show that the CR variable partially negatively has no significant effect towards the ROE with a significance level of 0.9427 meanwhile the DER variable partially has a positive significant effect towards the ROE with a significance level of 0.0191. While simultaneous CR and DER variables affect ROE with a coefficient of determination of 15.42%

One-step elimination of Cr(VI) by catalytic hydrogenation of Cr(VI) and simultaneous Cr(OH)3 recovery on Pt catalysts encapsulated in N-doped mesoporous carbon

Hexavalent chromium Cr(VI) is a highly toxic heavy metal, which is commonly eliminated by stepwise reduction at acidic pH and precipitation of Cr(OH)3 at alkaline pH. A unique Pt catalyst with Pt particles embedded in the framework of N-doped mesoporous carbon CMK-3 (denoted as Pt@NCMK-3) was designed and fabricated to one-step eliminate Cr(VI) pollution at near neutral pH via simultaneous Cr(VI) reduction by catalytic hydrogenation and Cr(OH)3 recovery. Structural characterization showed that Pt particles of Pt@NCMK-3 were effectively embedded in the carbon rods of NCMK-3. Batch experiments revealed that Pt@NCMK-3 exhibited a higher catalytic activity and stability than other test catalysts. Fixed-bed column reaction results indicated that under the experimental conditions Pt@NCMK-3 had better breakthrough performances than other catalysts. Additionally, after 4 treatment-recovery cycles Pt@NCMK-3 maintained nearly identical breakthrough performance, whereas other catalysts displayed markedly decreased breakthrough bed volumes, reflecting a substantially higher stability of Pt@NCMK-3.

Effect of Water Vapor on Lifetime of 625 and 120 Foils During Oxidation Between 650 and 800 °C

The oxidation behavior of alloy 625 and 120 foils was studied at 650, 700 and 800 \(^\circ\)C in dry air and flowing air + 10% H\(_2\)O up to 10,000 h (alloy 625) or 30,000 h (alloy 120). The effect of water vapor on Cr loss was investigated. Manganese and iron in the 120 foil induced faster Cr depletion in the foil and breakdown of the Cr\(_2\)O\(_3\) scale into Fe and Cr-rich oxide compared to the alloy 625 foil. In the latter case, the presence of Nb led to the formation of Nb and Cr-rich oxide after breakdown of the Cr\(_2\)O\(_3\) scale. Simultaneous Cr loss due to oxidation and volatilization of the Cr\(_2\)O\(_3\) oxide scale was predicted and compared to experimental Cr loss measurements for exposures up to 30,000 h.

Visible-light-driven Z-scheme Zn3In2S6/AgBr photocatalyst for boosting simultaneous Cr (VI) reduction and metronidazole oxidation: Kinetics, degradation pathways and mechanism

It is urgently needed to develop high-performance materials that can synchronously remove heavy metals and organic pollutants. Herein, the visible-light responsive Zn3In2S6/AgBr composites were prepared for concurrent removals of metronidazole (MNZ) and Cr (VI). In the Cr (VI)-MNZ coexisting system, the removals of MNZ and Cr (VI) using the optimized Zn3In2S6/AgBr-15 photocatalyst reached 98.2% and 94.8% within 2 h, respectively; higher than those using counterparts. The radical species trapping and electron spin resonance (ESR) results demonstrated that ·OH was the most dominated species for MNZ oxidation, and photo-generated electrons were responsible for Cr (VI) reduction. Besides, slight competition for ·O2ˉ during the simultaneous MNZ degradation and Cr (VI) reduction occurred. Energy band structure analysis, ESR and the outstanding photocatalytic performance for MNZ and Cr (VI) removals demonstrated that the Zn3In2S6/AgBr-15 was a Z-scheme photocatalyst, which promoted photo-induced carrier′s separation. Possible MNZ degradation pathways and mechanism over the Z-scheme Zn3In2S6/AgBr were also proposed based on the identified intermediates. This study could inspire new ideas for design of efficient Z-scheme photocatalysts for wastewater treatment.

Speciation analysis of Cr(III) and Cr(VI) in bread and breakfast cereals using species-specific isotope dilution and HPLC-ICP-MS

This study reports the development and validation of a analytical approach for simultaneous Cr(III) and Cr(VI) speciation analysis in bread and breakfast cereals using species specific isotope dilution (SS-ID) and high-performance liquid chromatography (HPLC) coupled to inductively coupled plasma-mass spectrometry (ICP-MS). The species were extracted by sequential complexation of genuine Cr(III) with ethylenediaminetetraacetic acid (EDTA) and subsequently of Cr(III) originating from reduction of Cr(VI) with 1,5-diphenylcarbazone (DPCO) in the same analytical run. Efficient HPLC separation of Cr(III)-EDTA and Cr(III)-DPCO complexes was carried out by anion exchange HPLC in less than 3 min. The method was validated by means of the accuracy profile approach by carrying out 3 measurement series in duplicate on 5 different days over a timespan of one month. The quantification limits were 0.014 μg kg−1 for Cr(III) and 0.047 μg kg−1 for Cr(VI), respectively. The measurement bias ranged from 0.31 to 0.49 %, whereas the coefficient of variation in terms of repeatability (CVr) varied from 1.3–4.4 % for Cr(III) and from 0.6–7.9% for Cr(VI). Similarly, the coefficient of variation in terms of intermediate reproducibility (CVR) ranged from 1.3–4.4% for Cr(III) and from 2.0–8.9% for Cr(VI), respectively. The method was successfully applied to the analysis of a selection of bread and breakfast cereals samples. Cr(VI) was not detected in any of these samples while Cr(III) levels ranged between 5.2 and 176 μg kg−1 for bread samples and between 23.8 and 350 μg kg-1 for breakfast cereals. These results were comparable with the levels of total Cr analysed in the same samples by ICP-MS. The method developed in this study on the basis of SS-ID and sequential species complexation is a powerful analytical tool for accurate and precise quantification of Cr(III) and Cr(VI) at trace levels and allows for correction of any species interconversion during sample preparation.

NemA Catalyzes Trivalent Organoarsenical Oxidation and Is Regulated by the Trivalent Organoarsenical-Selective Transcriptional Repressor NemR.

Synthetic aromatic arsenicals such as roxarsone (Rox(V)) and nitarsone (Nit(V)) have been used as animal growth enhancers and herbicides. Microbes contribute to redox cycling between the relatively less toxic pentavalent and highly toxic trivalent arsenicals. In this study, we report the identification of nemRA operon from Enterobacter sp. Z1 and show that it is involved in trivalent organoarsenical oxidation. Expression of nemA is induced by chromate (Cr(VI)), Rox(III), and Nit(III). Heterologous expression of NemA in Escherichia coli confers resistance to Cr(VI), methylarsenite (MAs(III)), Rox(III), and Nit(III). Purified NemA catalyzes simultaneous Cr(VI) reduction and MAs(III)/Rox(III)/Nit(III) oxidation, and oxidation was enhanced in the presence of Cr(VI). The results of electrophoretic mobility shift assays and fluorescence assays demonstrate that the transcriptional repressor, NemR, binds to either Rox(III) or Nit(III). NemR has three conserved cysteine residues, Cys21, Cys106, and Cys116. Mutation of any of the three resulted in loss of response to Rox(III)/Nit(III), indicating that they form an Rox(III)/Nit(III) binding site. These results show that NemA is a novel trivalent organoarsenical oxidase that is regulated by the trivalent organoarsenical-selective repressor NemR. This discovery expands our knowledge of the molecular mechanisms of organoarsenical oxidation and provides a basis for studying the redox coupling of environmental toxic compounds.

Pengaruh CR dan DER terhadap ROE pada Perusahaan Makanan dan Minuman Tahun 2015-2018

In this Final Project, the title "Influance of CR and DER on ROE in Food & Beverage in 2015 - 2018". The problems in this Final Project is how the effect of CR and DER variables on ROE in the period 2015 to 2018 seen relation and how big the influence of CR and DER on ROE. This research purpose is to find out the correlation between variable of CR and DER with ROE and the influence between the correlation. The research used descriptive analysis method and verificative analysis method. The results of the analysis show that the CR variable has a significant positive effect on the ROE variable with a significance level of 0.007, while the DER variable has no significant effect on ROE with a significance level of 0,196. While simultaneous CR and DER variables affect ROE with a coefficient of determination of 23% .

Electricity generation from salinity gradient to remove chromium using reverse electrodialysis coupled with electrocoagulation

Electricity generation and simultaneous Cr(VI) removal was achieved for the first time in a system coupling reverse electrodialysis with electrocoagulation (RED-EC). Power from the salinity gradient drove Fe anode dissolution without external electricity input to generate Fe2+ for reducing Cr(VI) and subsequent Fe3+ coagulation for removing total Cr. The results showed that RED-EC can remove 99% of Cr(VI) in 2 h and generate a maximum output power density of 0.482 W/m2, when salinity gradient ratio of high concentration and low concentration solutions was 3/1 and 300/1, respectively. High salinity gradient ratios generated an over-large potential, which caused Fe anode passivation by forming an iron oxide film and led to a decrease in Cr(VI) reduction, while Cl− addition in the electrode rinse solution can reduce passivation through pitting corrosion. Increasing the flow rate of saline solution and the initial Cr(VI) concentration of the electrode rinse solution resulted in electrode polarization and passivation, which was unfavorable to Cr(VI) reduction. The Fe-OOH content in flocs from the electrode rinse solution was highest when the RED-EC achieved optimal Cr(VI) and total Cr removal. The results obtained from Response Surface Methodology diagrams indicated that the best operating parameters were in the range of 20–50 ppm initial Cr(VI) concentration, 170–200 mL/min high concentration (HC) and low concentration (LC) influent flow rate, and 3/1 salinity gradient ratio of HC/LC. Our findings prove the feasibility of energy recovery driving Cr removal with a RED-EC setup, and present a novel method for purifying water with synchronous energy recovery from wastewater.

Treatment of a wastewater from a galvanizing industry containing chromium(VI) and zinc(II) by liquid surfactant membranes technique

Galvanizing industries generate large amounts of effluents rich in toxic and carcinogenic chromium(VI) species. Effective and sustainable treatments are required to comply with environmental regulations. This work focused on the development of innovative treatments for Cr(VI) by its removal from a galvanizing industry wastewater (pHinitial = 5.9) containing Cr (78 mg.L−1) and Zn (2178 mg.L−1) using the liquid surfactant membranes technique. The membrane phase carrier was Alamine® 336 in Escaid™ 110. For a synthetic solution (Cr(VI) = 353mg.L−1, pHinternal phase = 1.5), 99.9% of Cr(VI) was extracted in three stages ([KOH]internal phase = 0.27 mol.L−1). For the galvanizing wastewater, two selective extractions treatments were proposed: (1) 87% of Cr(VI) and 2% of Zn(II) were extracted in a single stage ([HCl]feed phase = 0.03 mol.L−1, [KOH]internal phase = 0.6 mol.L−1); (2) 95.6% of Cr(VI) and practically no zinc were extracted in a single stage ([HCl] feed phase = 10−6mol.L−1, [HCl] internal phase = 5mol.L−1). In another treatment condition ([HCl] feed phase = 2mol.L−1 and [KOH] internal phase = 1.2 mol.L−1), the simultaneous Cr(VI) and Zn(II) extractions (95% and 70%, respectively) were obtained in a single stage and more than 99% of both metals in three stages. This resulted in a depleted feed phase with 0.01 mg.L−1 of Cr(VI), that allows its discharge, according to the Brazilian legislation (≤0.1 mg/L).

Freezing-Induced Simultaneous Reduction of Chromate and Production of Molecular Iodine: Mechanism, Kinetics, and Practical Implications.

A new method for the concurrent treatment of Cr(VI)-contaminated wastewater and production of the useful I2 chemical was developed. The method is based on the redox reaction between Cr(VI) and I- that occurs when an aqueous wastewater solution containing Cr(VI) and I- is frozen, producing I2 and allowing for the effective removal of Cr. The redox reaction occurs primarily because of the accumulation of Cr(VI), I-, and protons in the ice grain boundaries formed during freezing (i.e., the freeze concentration effect). This effect was verified by confocal Raman spectroscopy and the experiments varying I- concentration and pH. The reduction of Cr(VI) (20 μM) was near complete after freezing at I- concentrations ≥ 100 μM, pH ≤ 3.0, and temperatures ≤ -10 °C. The freezing method (liquid cooling vs air cooling) had little effect on the final Cr(VI) reduction efficiency but had a significant effect on the Cr(VI) reduction rate. The freezing method was also tested with Cr(VI)-contaminated electroplating wastewater samples, and simultaneous Cr(VI) reduction and I2 production proceeded rapidly in a frozen solution but was not observed in an aqueous solution. Additionally, other substances in electroplating wastewater did not reduce the rate and final efficiency of Cr(VI) reduction and I2 production. Therefore, the freezing/Cr(VI)/I- system can be considered a feasible approach to water-energy nexus technology for simultaneous I2 production and Cr(VI)-contaminated wastewater treatment.

Efficacy of electrode position in microbial fuel cell for simultaneous Cr(VI) reduction and bioelectricity production

Microbial fuel cells (MFCs) that are bio-energy transducers capture bioelectricity produced from the oxidation of organic matter by using the electro-active bacteria grown on the biofilm attached on anode. Previous studies explored the effect of several limiting factors, such as electrode material, catalyst type, membrane structure, and electrolyte, on the electrochemical performance of MFCs. However, the effects of electrode position on Cr(VI) reduction and bioelectricity production remain unknown. In this study, MFCs with different electrode positions (i.e., 4 cm (MFC-4), 3 cm (MFC-3), 2 cm (MFC-2), and 1 cm (MFC-1)) were designed and fabricated to evaluate the overall performance of MFCs. The results of electrochemical analysis confirmed that MFC-2 exhibited low exchange transfer resistance (4.9 Ω) and strong conductivity, resulting in optimal electrochemical performance. In addition, Cr(VI) was completely removed within 11 h in MFC-2 with a large reduction rate of 0.91 g/m3·h. and COD removal efficiency of 78.25%. The overall performance of MFC-2 was comparatively higher than those of MFC-1 (0.80 g/m3·h and 68.82%), MFC-3 (0.64 g/m3·h and 61.67%), and MFC-4 (0.52 g/m3·h and 39.85%). Meanwhile, MFC-2 generated high open voltage (1.02 V) and power density (535.4 mW/m2), which are 1.4- and 3.1-fold larger than those of MFC-4 (0.72 V and 171.3 mW/m2). High COD removal and power density indicated the strong electrochemical activity of electroactive bacteria in the anode chamber of the MFCs, which was due to the low resistance in the MFCs could accelerate electron transfer and boost electrochemical reaction. Consequently, the optimal electrode spacing in MFCs was 2 cm. Further studies confirmed that Cr(VI) was removed and deposited in the form of Cr(III) on the electrode surface. High-throughput analysis suggested Pseudomonas species are the key electroactive bacteria for electricity generation.

3D hierarchically porous NiO/NF electrode for the removal of chromium(VI) from wastewater by electrocoagulation

3D hierarchically porous NiO/NF (Ni foam) was synthesized by a facile hydrothermal method and a subsequent annealing process in different atmospheres for the simultaneous Cr(VI) removal and hydrogen generation from wastewater by the electrocoagulation method. O2 atmosphere for annealing increased the Ni3+ content in NiO, thus led to an enhanced electrostatic interaction with Cr(VI)/OH− anions and subsequently increased the Cr(VI) adsorption and Ni hydroxide flocculant production. Thus, the NiO-O2/NF electrode exhibited the best Cr(VI) removal performance of 99.5% within 20 min at the applied potential of 0.97 V vs. RHE, along with a hydrogen generation rate of 1.1 mmol g−1 h−1. The removal mechanism was suggested, including the reduction of Cr(VI) to Cr(III), direct complexation reactions with the freshly produced amorphous Ni hydroxides, and adsorption on NiO-X/NF electrodes.

Simultaneous removal of chromate and arsenite by the immobilized Enterobacter bacterium in combination with chemical reagents

Simultaneous chromate [Cr(VI)] reduction and arsenite [As(III)] oxidation is a promising pretreatment process for Cr and As removal. Here, a facultative anaerobic bacterium, Enterobacter sp. Z1, presented capacities of simultaneous Cr(VI) reduction and As(III) oxidation during anoxic cultivation in a wild range of temperature (20–45 °C) and pH (Cerkez et al., 2015; Chen et al., 2015; China Environmental Prote, 1996; Fan et al., 2008, 2019) conditions. Strikingly, strain Z1 could simultaneously contribute up to 92.8% of the reduction of Cr(VI) and 45.8% of the oxidation of As(III) in wastewater. The cells of strain Z1 were embedded with sodium alginate to produce biobeads, and the biobeads exhibited stable ratio of Cr(VI) reduction (91.8%) and As(III) oxidation (29.6%) even in the 5 continuous cycles of wastewater treatment. Moreover, in a process pretreated with the Z1 biobeads followed a precipitation with Ca(OH)2 and FeCl3, the removal efficiencies in wastewater were 98.9% and 98.3% for total Cr and As, respectively, which were 44.1% and 9.8% higher than those of using Ca(OH)2 and FeCl3, only. The residual amounts of Cr and As met the national standard levels of wastewater discharge. Proteomics analysis showed that cysteine, sulfur and methionine metabolisms, As resistance and oxidoreductase (CysH, CysI, CysJ, NemA and HemF) were induced by Cr(VI) and As(III). Moreover, the addition of cysteine to the medium also significantly improved bacterial Cr(VI) reduction rate. Our results provide a novel microbial pretreatment approach for enhancing remediation of Cr(VI) and As(III) pollution in wastewater, and reveal the evident that cysteine, sulfur and methionine metabolisms, As resistance and oxidoreductases are associated with the redox conversion of Cr(VI) and As(III).

A continuous electroreduction cell composed of palladium nanocatalyst immobilized on discarded cigarette filters as an active bed for Cr(VI) removal from groundwater

In this research, a unique continuous electrochemical cell was designed and applied for the disinfection of groundwater and simultaneous Cr(VI) reduction and Cr(III) precipitation. Discarded cigarette filters (DCFs) were utilized as an efficient bed for palladium nanoparticles (PdNPs) immobilization located between porous anode and cathode made of graphite felt. The characterization of the bed was performed using FE-SEM, EDS, BET, and FT-IR analysis. The results confirmed the distribution of palladium nanoparticles on the surface of DCFs. The proposed design for electrochemical cell obviated the need to divide the anolyte and catholyte because the anode was located at the outlet of the cell, thereby avoiding the reaction between hydrogen radicals produced on the surface of PdNPs and oxygen and chlorine produced in the anode. The hydrogen gas produced in the cathode was converted to hydrogen radicals, acting as the most prominent species for the reduction. Hydroxide ions produced in the cathode increased the pH of the solution between electrodes, resulting in the precipitation of Cr (III) with an efficiency of 96%. Furthermore, free chlorine at the concentration of 1 mg L−1 was generated through chloride ion oxidation in the anode, which can be effective for disinfection. The effect of initial Cr (VI) concentration (C0), flow rate (Q), and current (I) was investigated, and the maximum removal efficiency (99.7%) was observed at the flow rate of 5 mL min−1 and current of 0.05 A, respectively. No interference ensued from the various coexisting ions in groundwater. The findings of this study suggested that the proposed electrochemical cell is capable of in-situ total chromium removal and free chlorine production in groundwater simultaneously.

FeS@rGO nanocomposites as electrocatalysts for enhanced chromium removal and clean energy generation by microbial fuel cell

Bioelectrochemical removal of Cr(VI) and consequent renewable energy generation from wastewater is a promising technology. However, slow reaction kinetics, expensive catalysts, and hydrophobic binders remain a significant challenge for the commercialization of this emerging technology. In the present study, for the first time, graphite felt modified with iron sulfide wrapped with reduced graphene oxide (FeS@rGO) nanocomposites were used as a cathode in a dual-chamber microbial fuel cell (MFC) for concurrent Cr(VI) reduction and power generation. The MFC with FeS@rGO nanocomposites (MFC-FeS@rGO) exhibited 100% Cr(VI) removal efficiency for the concentration of 15 mg/L and also acquired a high reduction rate of 1.43 mg/L/h, which was approximately 4.6 times higher than MFC-blank. MFC-FeS@rGO delivered the maximum power density of 154 mW/m2, and it was 328% high as that of MFC-blank (36 mW/m2). High cathodic coulombic efficiency for MFC-FeS@rGO (61 ± 0.8%) indicated that the substantial amount of charge produced by exoelectrogens was mainly consumed for Cr(VI) reduction. Overall improved electrochemical performance of MFC-FeS@rGO was attributed to the high conductivity, low internal resistance, and better reaction kinetics of FeS@rGO nanocomposites. This study has demonstrated the highest reduction rate and high power production compared with previous studies, which have used very high concentrations of Cr(VI). Hence, it is expected that current findings will help to scale up the simultaneous Cr(VI) reduction and power generation from real wastewater.