Simultaneous phenol removal and biological reduction of hexavalent chromium in a packed‐bed reactor

BACKGROUND: Phenol and hexavalent chromium are considered industrial pollutants that pose severe threats to human health and the environment. The two pollutants can be found together in aquatic environments originating from mixed discharges of many industrial processes, or from a single industry discharge. The main objective of this work was to study the feasibility of using phenol as an electron donor for Cr(VI) reduction, thus achieving the simultaneous biological removal/reduction of the two pollutants in a packed‐bed reactor. RESULTS: A pilot‐scale packed‐bed reactor was used to estimate phenol removal with simultaneous Cr(VI) reduction through biological mechanisms, using a new mixed bacterial culture originated from Cr(VI)‐reducing and phenol‐degrading bacteria, operated in draw–fill mode with recirculation. Experiments were performed for feed Cr(VI) concentration of about 5.5 mg L^?1, while phenol concentration ranged from 350 to 1500 mg L^?1. The maximum reduction/removal rates achieved were 0.062 g Cr(VI) L^?1 d^?1 and 3.574 g phenol L^?1 d^?1, for a phenol concentration of 500 mg L^?1. CONCLUSION: Phenol removal with simultaneous biological Cr(VI) reduction is feasible in a packed‐bed attached growth bioreactor. Phenol was found to inhibit Cr(VI) reduction, while phenol removal was rather unaffected by Cr(VI) concentration increase. However, the recorded removal rates of phenol and Cr(VI) were found to be much lower than those obtained from previous research, where the two pollutants were examined separately. Copyright © 2008 Society of Chemical Industry     

Electrically conductive polyaniline/polyimide microfiber membrane prepared via a combination of solution blowing and subsequent in situ polymerization growth

Dodecylbenzene sulfonic acid (DBSA) doped-polyaniline (PANI) coated conductive polyimide (PI) microfiber membrane was prepared by chemical oxidation polymerization. PI nanofiber membrane was prepared by solution blowing. Fourier transform infrared spectra (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) proved that the successful preparation of composite microfiber membrane with core-shell structures. At the same time, the PANI had an effect of protection on PI nanofiber, which was detected by thermal gravimetric analysis (TGA). The orthogonal experiments were designed to determine the optimal reaction conditions for the conductivity of PANI/PI microfiber membranes as following: ANI concentration (0.15 mol L^?1), APS concentration (0.1 mol L^?1) and DBSA concentration (0.3 mol L^?1). The conductivity of PANI/PI microfiber membranes could arrive to 3.83 × 10^?2 S cm^?1. Moreover, the PANI/PI microfiber membranes had a superior hexavalent chromium (Cr (VI)) adsorption performance. The factors affecting the performance of hexavalent chromium (Cr (VI)) removal from the aqueous solutions were investigated.     

Biological Cr(VI) reduction in a trickling filter under continuous operation with recirculation

BACKGROUND: Hexavalent chromium (Cr(VI)) is toxic to humans, animals and plants. Conventional treatment technologies reduce Cr(VI) to the less toxic and mobile Cr(III), but these methods are usually expensive and generate secondary waste. Microbial Cr(VI) reduction has recently gained attention as a detoxification process, since it enables Cr(VI) reduction through relatively cheap and simple methods. The aim of this work was to investigate the mechanism and the performance of biological Cr(VI) reduction using mixed cultures originated from industrial sludge under continuous operation with recirculation in a pilot‐scale trickling filter. RESULTS: Biological Cr(VI) reduction was studied using a pilot‐scale trickling filter filled with plastic media under continuous operation with recirculation and the use of indigenous bacterial population. The effect of the organic carbon (electron donor) concentration was examined for constant Cr(VI) influent concentration at about 5.5 mg L^?1 and volumetric flow rates ranging from 60 to 900 mL min^?1. The highest reduction rate achieved was 1117 g Cr(VI) m^?2 d^?1 for a volumetric flow rate of 900 mL min^?1. The system's reduction capacity was significantly affected by chromate loadings, resulting in frequent backwashing of the filter. The determination of the reduction mechanism was also studied using batch cultures of free suspended cells and culture supernatant. CONCLUSION: The high reduction rates combined with the low operating cost indicate that the above technology can be a viable solution for the treatment of industrial chromate effluents. Copyright © 2008 Society of Chemical Industry     

Removal of chromium (VI) from aqueous solutions using poly(4‐vinyl pyridine) beads

Sorption of hexavalent chromium ions from aqueous solution by poly 4‐vinyl pyridine [Poly(4‐VP)] was studied. The batch method was applied for adsorption processes. The effects of initial ion concentration, time, pH and temperature on adsorption were investigated. A treatment time of 60 min was found to be sufficient to reach equilibrium. pH 3.0 was found as the optimum pH value for the process. The maximum adsorption performance was achieved at 86.7 mg g^?1 using 500 mg L^?1 Cr (VI) solutions. The process of adsorption of Cr (VI) was explained by Langmuir isotherm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2865–2870, 2006     

Correlation between cell surface physicochemical properties of bacterial strains and their chromium removal potential

Physicochemical characterization of microbes has gained recently a great interest by scientific community. It is proved of extreme importance in several fields of science and technology applications such as bioremediation. In this work, we investigated the establishment of a possible correlation between chromium removal capacity of seven bacterial strains isolated from contaminated sites with industrial wastes including tanning processing and their cell surface physicochemical properties. Thus, hydrophobicity and donor/acceptor electrons character were obtained using contact angle measurements. Statistical analysis showed a high significant positive correlation between hexavalent chromium (Cr(VI)) removal by the strains and their acceptor electron character γ⁺(r = 0.90). While significant negative correlation between the Cr(VI) removal potential and the ΔGiwi value (r = ?0.844) and also with their donor electron character γ^? (r = ?0.746) were observed. These results may contribute to determine a selectrion criteria of bacteria that can be operated in bioremediation applications.     

A new bioinorganic process for the remediation of Cr(VI)

Palladised biomass of Desulfovibrio desulfuricans ATCC 29577 (bio‐Pd(0)) effected reduction of Cr(VI) to Cr(III) under conditions where biomass alone or chemically‐prepared Pd(0) were ineffective. Reduction of 500 µmol dm^?3 Cr(VI) by 0.4 mg cm^?3 bio‐Pd(0) (Pd : biomass ratio of 1:1) was achieved from 1 mol dm^?3 formate/acetate buffer at pH 1–7 at room temperature; the optimum pH was 3.0. The ratio of mass of Pd : dry mass of biomass, and the need for finely ground bio‐Pd(0) were important parameters for optimal Cr(VI) reduction, with a ratio of 1:1 giving 100% reduction of 500 µmol dm^?3 Cr(VI) within 6 h at room temperature, decreasing to 30 min following heat treatment of the Pd(0)‐loaded biomass. The reduced Cr was recovered quantitatively as soluble Cr(III) at pH 3.0 with no poisoning of the bioinorganic catalyst with respect to continued reduction of Cr(VI). © 2002 Society of Chemical Industry     

Reduction of Cr(VI) by palladized biomass of Desulfovibrio vulgaris NCIMB 8303

Palladized biomass of Desulfovibrio vulgaris (Bio‐Pd(0)) reduced Cr(VI) to Cr(III) at an initial rate four‐fold higher than chemically‐prepared Pd(0) metal. Optimal Cr(VI) reduction by suspended Bio‐Pd(0) occurred at pH 3, whereas pH did not affect the rate of Cr(VI) reduction by Bio‐Pd(0) immobilized in agar beads. The rate of Cr(VI) reduction was concentration‐dependent below 300 µmol dm^?3, and application of enzyme kinetics, considering Bio‐Pd(0) as an ‘artificial enzyme’, gave an apparent K_m (K_mapp) of approx. 650 µmol dm^?3 and V_max of 1667 nmol h^?1 mg Pd(0) for suspended Bio‐Pd(0). The potential of Bio‐Pd(0) as a method for the treatment of Cr(VI)‐wastes is discussed. Copyright © 2005 Society of Chemical Industry     

Reductive removal of hexavalent chromium from aqueous solution using sepiolite-stabilized zero-valent iron nanoparticles: Process optimization and kinetic studies

We studied the optimization of hexavalent chromium (Cr(VI)) removal from aqueous solution using the synthesized zero-valent iron nanoparticles stabilized with sepiolite clay (S-ZVIN), under various parameters such as reaction time (min), initial solution pH and concentration of S-ZVIN (g·L^?1) using response surface methodology (RSM). The kinetic study of Cr(VI) was conducted using three types of the most commonly used kinetic models including pseudo zero-order, pseudo first-order, and pseudo second-order models. The rate of reduction reaction showed the best fit with the pseudo first-order kinetic model. The process optimization results revealed a high agreement between the experimental and the predicted data (R²=0.945, Adj-R²=0.890). The results of statistical analyses showed that reaction time was the most impressive factor influencing the efficiency of removal process. The optimum conditions for maximum response (98.15%) were achieved at the initial pH of 4.7, S-ZVIN concentration of 1.3 g·L^?1 and the reaction time of 75 min.     

Novel hexamethylene diamine‐functionalized macroporous copolymer for chromium removal from aqueous solutions

Macroporous copolymers of poly[(glycidyl methacrylate)‐co ‐(ethylene glycol dimethacrylate)] (PGME ) with various crosslinker (ethylene glycol dimethacrylate) concentrations and porosity parameters and additionally functionalized with hexamethylene diamine (PGME‐HD ) were tested as potential Cr(VI ) oxyanion sorbents from aqueous solutions. Kinetics of Cr(VI ) sorption was investigated in the temperature range 298–343 K and the results were fitted to chemical reaction and particle diffusion models. The Cr(VI ) sorption obeys the pseudo‐second‐order model with definite influence of pore diffusion. A temperature rise promotes chromium removal, with a maximum experimental uptake capacity of 4.21 mmol g^?1 at 343 K for the sample with the highest amino group concentration. Equilibrium data were analysed with Langmuir, Freundlich and Temkin adsorption isotherm models. Thermodynamic parameters, i.e. Gibbs free energy (ΔG ⁰), enthalpy (ΔH ⁰) and entropy change (ΔS ⁰) and activation energy of sorption (E _a), were calculated. The Cr(VI) adsorption onto PGME‐HD was found to be spontaneous and endothermic, with increased randomness in the system. Desorption experiments show that chromium anion sorption was reversible and the PGME‐HD sample GMA 60 HD was easily regenerated with 0.1 mol L^?1 NaOH up to 90% recovery in the fourth sorption/desorption cycle. In the fifth cycle, a substantial sorption loss of 37% was observed. © 2016 Society of Chemical Industry     

Removal of Chromium(VI) and Chromium(III) from Aqueous Solution by Grainless Stalk of Corn

Abstract

Grainless stalk of corn (GLSC) was tested for removal of Cr(VI) and Cr(III) from aqueous solution at different pH, contact time, temperature, and chromium/adsorbent ratio. The results show that the optimum pH for removal of Cr(VI) is 0.84, while the optimum pH for removal of Cr(III) is 4.6. The adsorption processes of both Cr(VI) and Cr(III) onto GLSC were found to follow first-order kinetics. Values of k _ads of 0.037 and 0.018 min^?1 were obtained for Cr(VI) and Cr(III), respectively. The adsorption capacity of GLSC was calculated from the Langmuir isotherm as 7.1 mg g^?1 at pH 0.84 for Cr(VI), and as 7.3 mg g^?1 at pH 4.6 for Cr(III), at 20°C. At the optimum pH for Cr(VI) removal, Cr(VI) reduces to Cr(III). EPR spectroscopy shows the presence of Cr(V) + Cr(III)-bound-GLSC at short contact times and adsorbed Cr(III) as the final oxidation state of Cr(VI)-treated GLSC. The results indicate that, at pH ≈ 1, GLSC can completely remove Cr(VI) from aqueous solution through an adsorption-coupled reduction mechanism to yield adsorbed Cr(III) and the less toxic aqueous Cr(III), which can be further removed at pH 4.6.     

Chromium(VI) Biosorption and Bioaccumulation by Live and Acid-Modified Biomass of a Novel Morganella morganii Isolate

Conventional methods of chromium removal are often insufficient for the remediation of chromium-contaminated natural environments, necessitating the development of alternative strategies. In this paper, we report the isolation of a novel Morganella morganii strain capable of reducing hexavalent chromium to its less-toxic and less-soluble trivalent form. Cr(VI) reduction by this strain was evaluated in both acidic environments and conditions reflecting natural freshwater sources. The isolate achieved equilibrium within 3 h and displayed a specific uptake rate of 24.30 ± 1.67 mg Cr(VI)/g biomass following HCl treatment. Without acid treatment, a reduction of over 90% was recorded within 72 h for an initial Cr(VI) concentration 20 mg/L, corresponding to a Cr(VI) removal capacity of 19.36 ± 1.89 mg/g. Absorption data of acid-treated STB5 biomass most closely followed the Toth and Langmuir models. FTIR results indicate that hydroxyl groups and extracellular or cell membrane polysaccharides may be potential adsorption sites for hexavalent chromium. Our results suggest that the isolate may be used in situ for treatment of polluted freshwater environments.     

Removal of hexavalent chromium in wastewater by polyacrylamide modified iron oxide nanoparticle

Iron oxide nanoparticle has been successfully modified by polyacrylamide and the polyacrylamide modified magnetic nanoparticles (PMMNs) were applied to remove Cr(VI) in wastewater. The vibrating sample magnetometer (VSM) spectra indicated the large saturation magnetization and superparamagnetic property of the PMMNs. This made the polyacrylamide modified iron oxide easily separate with liquid phase. Scanning electron microscope (SEM) results showed that both the synthesized iron oxide and the PMMNs were nanoscale. Batch adsorption studies had been carried out to determine the effect of pH, contact time, Cr(VI) initial concentration, and coexisting salts on the adsorption of Cr(VI). Maximum removal (98.30%) was observed from an initial concentration of 100 mg L^?1 Cr(VI) at pH 3.0, 30°C. This process followed pseudo‐second‐order kinetics model and the equilibrium time was 40 min. The experimental data fitted the Langmuir isotherm better than Freundlich. Maximum adsorption amount of Cr(VI) by PMMN was 35.186 mg g^?1. The effect of coexisting salts on Cr(VI) removal was not apparent even the concentration of salt was 10 times as big as the low concentration, 0.01M. It had been proposed that the mechanism of Cr(VI) uptake onto PMMN was adsorption‐coupled reduction. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40945.     

Polypropylene membranes modified with interpenetrating polymer networks for the removal of chromium ions

Polypropylene (PP) membranes incorporating poly[(ar‐vinylbenzyl) trimethylammonium chloride] P(ClVBTA), and poly[sodium (styrene sulfonate)] P(SSNa) were modified via an “in situ” radical polymerization synthesis. Two methods were used for impregnation of the reactive solution: pressure injection and plasma superficial activation with argon gas. The following conditions were varied: the monomer concentrations, number of injections, and cross‐linked concentration. The modified polypropylene membranes were then characterized using scanning electron microscopy/energy dispersive X‐ray spectroscopy, Fourier transform‐infrared spectroscopy, electrokinetic potential, and Donnan dialysis for the chromium ions transport. The modified membranes exhibited a hydrophilic character with a water uptake capacity between 15% and 20% and a percent modification between 2.5% and 4.0%. This was compared with the results of an unmodified polypropylene membrane as the blank and the mentioned polypropylene membrane has not the capacity to uptake water because this kind of material is highly hydrophobic. Hexavalent chromium ions were efficiently transported by the modified membranes containing P(ClVBTA) via a plasma method and it achieved 59.2% extraction at pH 9.0 using a 1‐mol L^?1 NaCl extraction agent. Therefore, unmodified polypropylene membrane shows an extraction percentage close to 10% from the hexavalent chromium ions at pH 9.0. In the same way, the trivalent chromium transport using membranes modified with P(SSNa) achieved 49.0% extraction at pH 2.0 using 1 × 10^?1 mol L^?1 HNO₃ and 1 mol L^?1 NaCl as the extraction agents. Moreover, the unmodified polypropylene membrane reached a value close to 10% from the trivalent chromium ions using 1 × 10^?1 mol L^?1 HNO₃ and 1 mol L^?1 NaCl. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41953.     

Separation of Cr(VI) from Water by Green Reduction Reaction and Adsorptive Removal on Gelatin-Grafted-Yeast Biosorbent

A green chemical method was explored and described for separation and extraction of the toxic hexavalent chromium from aqueous solutions and real water samples. A green reduction reaction for the transformation of toxic hexavalent chromium into the nontoxic trivalent chromium ion was performed by using hydrogen peroxide. The produced Cr(III) was then extracted by biosorption on the surface of a novel and eco-friendly gelatin-grafted-baker’s yeast (Gelatin-Yeast) biosorbent. The investigated biosorbent was characterized by high capacity value of the reduced trivalent chromium species in pH 6.0 as 1.120 mmol g^?1. The biosorption processes were examined, monitored, and optimized in different experimental and controlling parameters. The potential applications of Gelatin-Yeast for separation and removal of Cr(VI) from real industrial and sea water samples were also studied.     

Application of Chattim tree (devil tree,Alstonia scholaris) saw dust as a biosorbent for removal of hexavalent chromium from contaminated water

“Devil tree saw dust”; a novel biosorbent has been utilised successfully for the removal of hexavalent chromium from contaminated water. Batch adsorption procedure is utilised to test the ability of saw dust as an adsorbent for hexavalent chromium (reduction coupled adsorption). The contribution of various parameters on sorption, such as contact time, sorbate concentration, pH of the medium and temperature were estimated and maximum uptake of hexavalent chromium from contaminated water was 333.33 mg g^?1 at pH 2.0 and temperature of 35°C. Hexavalent chromium uptake from contaminated water followed the pseudo‐first‐order rate expression. The standard free energy change (ΔG⁰), standard enthalpy change (ΔH⁰) and standard entropy change (ΔS⁰) have also been evaluated and it has been concluded that the sorption was feasible, spontaneous and endothermic in nature. The process follows well Langmuir isotherm. Fourier Transform Infra‐Red (FTIR) spectroscopy and scanning electron microscopy (SEM) of hexavalent chromium loaded and unloaded saw dust were performed, SEM clearly indicates chromium adsorption. FTIR spectroscopy revealed the involvement of carbonyl, hydroxyl and amide groups on the cell surfaces in chromium binding. Very good adsorption capacity and low cost or cost free of devil tree saw dust makes this biosorbent as one of the best adsorbents for removal of hexavalent chromium from contaminated water. © 2012 Canadian Society for Chemical Engineering     

Electroreduction of hexavalent chromium by polyaniline

BACKGROUND: A plate‐gap model interpretation of enzymatic reaction kinetics and rotating disc voltammetry were applied for evaluation of the nature of the reaction of the electroreduction of Cr(VI) (as dichromate ions) on a polyaniline (PANI)‐modified glassy carbon (GC) electrode. RESULTS: The kinetic parameters (the maximal current (V_max) and Michaelis constant (K_M)) for electroreduction of Cr(VI) on the PANI‐modified GC electrode were determined as V_max = 0.34 × 10^?7 mol cm^?3 s^?1 and K_M = 0.47 × 10^?6 mol cm^?3. The reduction of dichromate is intensified by PANI film growth. CONCLUSION: To characterise the electroreduction of Cr(VI) on a PANI‐modified GC electrode, the kinetic parameters of the reaction were determined using a plate–gap model interpretation of enzymatic reaction kinetics and rotating disc voltammetry. The catalytic nature of Cr(VI) electroreduction on the PANI‐modified electrode has been shown. Copyright © 2009 Society of Chemical Industry     

Effect of pre‐treatments on the biosorption of Chromium (VI) ions by the dead biomass of Rhizopus arrhizus

BACKGROUND: This work fulfils the need to develop an eco‐friendly biosorbent, elucidating the mechanism of biosorption. Removal of Cr(VI) by Rhizopus arrhizus was investigated in batch mode. Enhancement in the performance of the biosorbent was attempted by pre‐treating the biomass with inorganic and organic acids, chelating agent, cross‐linker and an organic solvent followed by autoclaving. The surface characterization of the biomass was carried out by potentiometric titration, surface area analysis, infrared spectroscopy, chemical modification of the biomass and scanning electron microscopy. RESULTS: All the physico‐chemical treatments of the biosorbent improved Cr(VI) uptake compared with the native biomass (21.72 mg g^?1). The highest biosorption capacity (31.52 mg g^?1) was achieved after pre‐treating the biomass with 0.5 mol L^?1 HNO₃ followed by autoclaving. Surface characterization of the biomass using pH_zpc, potentiometry and Fourier transform infrared (FTIR) analysis revealed the role of amino and carboxyl groups in Cr(VI) removal by electrostatic attraction. Chemical modification of amino and carboxyl groups significantly decreased Cr(VI) uptake capacity confirming their role in biosorption. SEM analysis showed adsorption of Cr(VI) on the biosorbent surface. CONCLUSION: Rhizopus arrhizus biomass proved to be an effective and low cost alternative biosorbent for removal of Cr(VI) from aqueous solutions. Copyright © 2011 Society of Chemical Industry     

Removal of Cr(VI) from wastewater by adsorption on iron nanoparticles

Due to rapid industrialisation, the presence of heavy metals in water and wastewater is a matter of environmental concern. Though some of the metals are essential for our system but if present beyond their threshold limit value (TLV), they are harmful and their treatment prior to disposal becomes inevitable. The present communication has been addressed to the removal of Cr(VI) from aqueous solutions by nanoparticles of iron. Nanoparticles of iron were prepared by sol–gel method. The characterisation of the nanoparticles was carried out by XRD and TEM analysis. Batch experiments were adopted for the adsorption of Cr(VI) from its solutions. The effect of different important parameters such as contact time and initial concentration, pH, adsorbent dose, and temperature on removal of chromium was studied. The removal of chromium increased from 88. 5% to 99.05% by decreasing its initial concentration from 15 to 5 mg L^?1 at optimum conditions. Removal of Cr(VI) was found to be highly pH dependent and a maximum removal (100%) was obtained at pH 2.0. The process of removal was governed by first and pseudo‐second‐order kinetic equations and their rate constants were determined. The process of removal was also governed by intraparticle diffusion. Values of the thermodynamic parameters viz. ΔG°, ΔH°, and ΔS° at different temperatures were determined. The data generated in this study can be used to design treatment plants for chromium rich industrial effluents. Adsorption results indicate that nanoiron particles can be effective for the removal of chromium from aqueous solutions.     

Multiwalled CNTs for Cr(VI) removal from industrial wastewater: An advanced study on adsorption,kinetics, thermodynamics for the comparison between the embedded and non‐embedded carboxyl group

The adsorption capabilities of multiwalled carbon nanotubes (MWCNTs) with and without the embedded carboxyl group for the removal of parts per million levels of hexavalent chromium were examined as a function of several parameters, namely contact time, pH of initial solution, initial concentration of Cr(VI), adsorbent dosage as well as temperature of solution. Adsorption isotherms have been utilized to explain the adsorption mechanism. Ion exchange, intra‐particle diffusion, and electrostatic interactions are found to be the fundamental mechanisms describing the adsorption of Cr(VI). The maximum adsorption capacities of Cr(VI) ion by raw MWCNTs and functionalized MWCNTs were found to be 84.75 and 78.13 mg · g^?1, respectively, as calculated by the Langmuir adsorption isotherm model. This is with regard to the electron‐rich atoms inside the functional group which repels the negatively charged dichromate ions. Kinetic studies were performed, and the data was found in good agreement with the pseudo‐second‐order.     

Removal of Cr(VI) from Aqueous Solution: Electrocoagulation vs Chemical Coagulation

Abstract

Hydrolyzed products of Al(III) have affinity below pH_zpc for oppositely charged mono and bi‐nuclear species of hexavalent chromium. This study investigates the comparative performance of electrocoagulation (EC) and chemical coagulation (CC) for the removal of Cr(VI) from aqueous solution. The highest removal of Cr(VI) achieved with EC was about 42% with 4.36 mA/cm² current density. Cathodic adsorption of chromium boosted up Cr(VI) removal during EC. Simultaneous electro‐ and chemical‐dissolution lead to high current efficiency of about 178%. Both the pH and the coagulant dosage have a significant impact on Cr(VI) removal in the pH ranges from 4.9 to 7.0. CC with alum and aluminum sulfate (AS) removed about 11% and 12% of Cr(VI). Co‐adsorption of divalent SO₄ ^2? ions with Cr(VI) is responsible for the lower removal observed with chemical coagulants. About 0.061 and 0.099 mole of SO₄ ^2? was adsorbed per mole Al in the precipitate in the pH range 4.9 to 7.0 with AS and alum. A higher coagulant dosage increases the removal of Cr(VI) but adversely affects the removal efficiency (Cr(VI) removed per unit of Al dosing). Cell current density (CD) has shown little effect on Cr(VI) removal and the pH elevation at the same charge density. Higher initial Cr(VI) concentration improves the removal efficiency as the species of Cr(VI) is acidic in solution and decreases the pH elevation rate.