Influence of nickel (II) and chromium (VI) on the laboratory scale rotating biological contactor

High concentration of heavy metals is toxic for most microorganisms and cause strict damage in wastewater treatment operations and often a physico-chemical pretreatment prior to biological treatment is considered necessary. However, in this study it has been shown that biological systems can adapt to Ni (II) and Cr (VI) when their concentration is below 10 and 20 mg/L, respectively. The aim of this study was to evaluate the effect of Ni (II) and Cr (VI) on the lab-scale rotating biological contactor process. It was found that, addition of Ni (II) up to 10 mg/L did not reduce the chemical oxygen demand removal efficiency and on the contrary concentrations below 10 mg/L improved the performance. The influent Ni (II) concentration of 1 mg/L was the concentration where the treatment efficiency produced a maximum COD removal of 86.5%. Moreover, Ni (II) concentration above 10 mg/L was relatively toxic to the system and produced lower treatment efficiencies than the baseline study without Ni (II). Turbidity and suspended solids removals were not stimulated to a great extent with nickel. Addition of Ni (II) did not seem to affect the pH of the system during treatment. The dissolved oxygen concentration did not drop below 4 mg/L at all concentrations of Ni (II) indicating aerobic conditions prevailed in the system. Experiments conducted with Cr (VI) revealed that addition of Cr (VI) up to 20 mg/L did not reduce the COD removal efficiency and on the contrary concentrations below 20 mg/L improved the performance. The influent Cr (VI) concentration of 1 mg/L was the concentration where the treatment efficiency produced a maximum COD removal of 88%. Turbidity and SS removals were more efficient at 5 mg/L Cr (VI) concentration, rather than 1 mg/L, which lead to the conclusion that 5 mg/L Cr (VI) concentration is the optimum concentration, in terms of COD, turbidity and SS removals. Similar with Ni (II) experiments, addition of Cr (VI) did not significantly affect the pH value of the effluent. The DO concentration remained above 5 mg/L.     

Biosorption of Chromium(VI) and Lead(II): Role of Spirulina platensis in the Treatment of Industrial Effluent

Biosorption is the process of removal of any chemical molecules by the treatment of biological material. Industrialization resulted in the discharge of various toxic heavy metals into water bodies, which poses serious health hazards to humans and animals. In the present study, live Spirulina platensis was used as a biosorbent for the removal of the heavy metals chromium (Cr(VI)) and lead (Pb(II)) from the aqueous samples. S. platensis were cultured in the presence of different concentrations of heavy metals. The growth of the algal cells was found to be decreased by 59% and 36% in media containing 50 ppm Cr(VI) and Pb(II), respectively. To assess the biosorption of heavy metals, at different time intervals, the spent culture media were used to detect Cr(VI) by atomic absorption spectroscopy method and Pb(II) by 4-(2-pyridylazo)resorcinol indicator method. Results suggested that there was a significant uptake of Cr(VI) and Pb(II) from the medium by S. platensis, with corresponding decrease of metals in the medium. When metal salt solutions or industrial effluent samples were passed through the column containing immobilized live S. platensis in calcium alginate beads, the concentration of Cr(VI) was found to be reduced drastically. The present study indicates the application of S. platensis for the bioremediation of heavy metals from the samples obtained from industrial effluents.     

Effective bioremoval of reactive dye and heavy metals by Aspergillus versicolor

In this study, bioaccumulation of heavy metal and dye by Aspergillus versicolor was investigated. Optimum pH values of the maximum heavy metal bioaccumulation was found as 6 for 50 mg/L Cr(VI), Ni(II) and 5 for Cu(II) ions with the 99.89%, 30.05% and 29.06% removal yield, respectively. The bioremoval of the dye up to 800 mg/L at pH 5 and 6 was investigated and 27.15% and 28.95% removal rates were measured respectively. The presence of Cr(VI) with dye, decreased the uptake yield for both pollutants. In the medium with Cu(II) and dye, dye removal was not affected by Cu(II), but Cu(II) removal rate increased from 29.06% to 37.91% by the existence of the dye. When Ni(II) and dye were combined, neither pollutant affected the other’s removal yield. These results indicate that the isolated A. versicolor strain deserves attention as a promising bioaccumulator of heavy metal ions and reactive dyes in wastewater effluents.     

Metal biosorption capacity of the organic solvent tolerant Pseudomonas fluorescens TEM08

Many kinds of biomass are being tested as a biosorption material for metal removal from the contaminated waters. In the present study the biosorption capacity of an organic solvent tolerant (OST) bacterium was investigated against Cr(VI) and Ni(II). The OST strain of Pseudomonas fluorescens TEM08 was isolated from an oil contaminated soil sample and grown in normal culture conditions (type I) and in the presence of the cyclohexane (type II). Two types of cells were used in the biosorption experiments to compare the organic solvent effect on the biosorption capacity. The biosorption equilibrium was described by Langmuir and Freundlich adsorption isotherms. The value of Q(0) was higher for type I cells (40.8 for Cr(VI); 12.4 for Ni(II)) then the type II (40.7 for Cr(VI); 11.2 for Ni(II)). The adsorption capacity constants (K(F)) of Freundlich model for type I cells and for type II cells were 10.87 and 8.78 for Ni(II) and 13.60 and 10.99 for Cr(VI), respectively.     

Spontaneous Cr(VI) and Cd(II) biosorption potential of native pinnae tissue of Pteris vittata L., a tropical invasive pteridophyte

Heavy metal pollution is a prevalent and critical environmental concern. Its rampancy is attributed to indiscriminate anthropogenic activities. Several technologies including biosorption have been continuously researched upon to overcome the limitations of the conventional method of treatments in removal of heavy metals. Biosorption technology involves the application of a biomass in its nonliving form. Pteris vittata L., a pteridophyte, considered as an invasive weed was investigated in the present study as a potential decontaminant of toxic metals, Cr(VI) and Cd(II). The adsorption capacity of the biosorbent for Cr(VI) and Cd(II) under equilibrium conditions was investigated. The morphology, elemental composition, functional groups, and thermal stability of the biosorbent before and after metal loading were evaluated. At 303?K and an equilibrium time of 120?min, the maximum loading of Cr(VI) on the biosorbent was estimated to be 166.7?mg/g at pH 2 and Cd(II) to be 31.3?mg/g at pH 6. Isotherm models, kinetic studies, and thermodynamic studies indicated the mechanisms, chemisorption, ion exchange and intraparticle diffusion, controlling the Cr(VI) and Cd(II) uptake, respectively. The interactive effect of multi-metal ions in binary component systems was synergistic for Cd(II) uptake. The results validate the toxic metal removal potency of the biosorbent.     

Ochrobactrum tritici strain 5bvl1 - characterization of a Cr(VI)-resistant and Cr(VI)-reducing strain

Bacterial strain 5bvl1, isolated from a chromium-contaminated wastewater treatment plant and identified as Ochrobactrum tritici, was resistant to a broad range of antibiotics, to Cr(VI), Ni(II), Co(II), Cd(II), and Zn(II), and was able to grow in the presence of 5% NaCl and within the pH range 4-10. Characterization showed that strain 5bvl1 could be considered a halotolerant and alkalitolerant microorganism resistant to high concentrations of Cr(VI). This strain was able to grow aerobically in up to 10 mmolxL(-1) Cr(VI). Cr(VI) resistance was independent of sulphate concentration. Under aerobic conditions strain 5bvl1 was also able to reduce high Cr(VI) concentrations (up to 1.7 mmolxL(-1)). Increasing concentrations of Cr(VI) in the medium lowered the growth rate of strain 5bv11 but the reduction in growth rate could not be directly correlated with the amount of Cr(VI) reduced. Unlike the type strain, which was only able to reduce Cr(VI), strain 5bvl1 was resistant to Cr(VI) and able to reduce it. Moreover, in strain 5bvl1, the rate and extent of Cr(VI)-reduction were higher than in the other strains of the genus Ochrobactrum. Ochrobactrum strain 5bvl1 resists high Cr(VI) concentrations and has a high Cr(VI)-reducing ability, making it a valuable tool in bioremediation.     

Chromium sorption and Cr(VI) reduction to Cr(III) by grape stalks and yohimbe bark

In this work, two low cost sorbents, grape stalks and yohimbe bark wastes were used to remove Cr(VI) and Cr(III) from aqueous solutions. Batch experiments were designed to obtain Cr(VI) and Cr(III) sorption data. The mechanism of Cr(III) and Cr(VI) removal and Cr(VI) reduction to Cr(III) by the two vegetable wastes, has been investigated. Fourier transform infrared rays (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis on solid phase were performed to determine the main functional groups that might be involved in metal uptake and to confirm the presence of Cr(III) on the sorbent, respectively. Results put into evidence that both sorbents are able to reduce Cr(VI) to its trivalent form.     

Cr(VI) removal from aqueous solution by thermophilic denitrifying bacterium <Emphasis Type="Italic">Chelatococcus daeguensis</Emphasis> TAD1 in the presence of single and multiple heavy metals

Cr(VI) pollution is increasing continuously as a result of ongoing industrialization. In this study, we investigated the thermophilic denitrifying bacterium Chelatococcus daeguensis TAD1, isolated from the biofilm of a biotrickling filter used in nitrogen oxides (NO_X) removal, with respect to its ability to remove Cr(VI) from an aqueous solution. TAD1 was capable of reducing Cr(VI) from an initial concentration of 10 mg/L to non-detectable levels over a pH range of 7–9 and at a temperature range of 30–50°C. TAD1 simultaneously removed both Cr(VI) and NO₃^?-N at 50°C, when the pH was 7 and the initial Cr(VI) concentration was 15 mg/L. The reduction of Cr(VI) to Cr(III) correlated with the growth metabolic activity of TAD1. The presence of other heavy metals (Cu, Zn, and Ni) inhibited the ability of TAD1 to remove Cr(VI). The metals each individually inhibited Cr(VI) removal, and the extent of inhibition increased in a cooperative manner in the presence of a combination of the metals. The addition of biodegradable cellulose acetate microspheres (an adsorption material) weakened the toxicity of the heavy metals; in their presence, the Cr(VI) removal efficiency returned to a high level. The feasibility and applicability of simultaneous nitrate removal and Cr(VI) reduction by strain TAD1 is promising, and may be an effective biological method for the clean-up of wastewater.     

Comparative Study of Cr(VI) Removal by Exiguobacterium sp. in Free and Immobilized Forms

Cr(VI) is a toxic environmental pollutant. To determine the potential role of microbes towards chromate bioremediation, two bacterial strains, E1 and E4, that could tolerate Cr(VI) at levels up to 2250 μg ml^?1 were isolated from the soil of a tannery. They were identified as Exiguobacterium sp. To estimate the removal of Cr(VI) using immobilized bacterial cells, 2% sodium alginate and 2.5% agar were used as immobilizing matrices. In the case of sodium alginate, 89% and 93% of Cr(VI) removal by E1 and E4, respectively, were observed. When agar beads were used as an immobilizing matrix, removal was recorded as 39% and 48% for E1 and E4, respectively. Removal of Cr(VI) was also estimated in sterile and nonsterile tannery effluent. More Cr(VI) removal was noted in the nonsterile effluent than in the sterile effluent. The maximum uptake of Cr(VI) of bound cells of E1 and E4 was found to be 17.54 and 20.04 μg ml^?1, respectively. Fourier transform infrared (FTIR) spectra of cells of E4 with Cr(VI), without Cr(VI), and immobilized cells depicted several absorption peaks, mainly for P?OH group, C?H bending, C?O bond, and amide II groups, reflecting the complex nature of the bacterial cells and the contribution of these functional groups to the Cr(VI) binding process.     

Concurrent Removal of Mn(II) and Cr(VI) by Achromobacter sp. TY3-4

In this study, we report a bacterium, Achromobacter sp. TY3-4, capable of concurrently removing Mn (II) and Cr (VI) under oxic condition. TY3-4 reduced as much as 2.31?mM of Cr (VI) to Cr (III) in 70?h, and oxidized as much as 20?mM of Mn(II) to Mn oxides in 80?h. When 0.58?mM Cr (VI) and 10?mM Mn(II) were present together, both Cr(VI) and Mn(II) were completely removed by TY3-4 and the generated precipitates are Mn^IIIOOH, Mn^III,IV₃O₄, Mn^IVO₂ and Cr^III(OH)₃. Experiments also show that both biosroption and bioreduction of Mn(II) are the driving forces for Mn(II) removal, whereas bioreduction of Cr(VI) is the driving force for Cr(VI) removal. On the basis of these results, a possible reaction was proposed that TY3-4 concurrently reduces Cr(VI) and oxidizes Mn(II). This study is fundamental for Mn and Cr cycles. The strain shows potential for practical application.     

Removal and recovery of Cu(II) from industrial effluent by immobilized cells of Pseudomonas putida II-11

A copper [Cu(II)]-accumulating strain, Pseudomonas putida II-11, isolated from electroplating effluent removed a significantly high amount of Cu(II) from growth medium and buffer. A laboratory-scale fixed bed reactor with cells of P. putida II-11 immobilized in polyacrylamide gel was constructed. The adsorption of Cu(II) by the immobilized cells was pH-dependent. Maximum removal of Cu(II) by the immobilized cells was at pH 8.0. The presence of Cr(IV), Ni(II) and Zn(II) did not significantly inhibit Cu(II) uptake whereas the presence of Pb(II) reduced Cu(II) uptake by fivefold. The presence of borate, carbonate, chloride and sulphate did not significantly inhibit Cu(II) uptake. The Cu(II) removal capacity of the bioreactor with immobilized cells did not change significantly when operated at retention times greater than 3 min. More than 90% of Cu(II) adsorbed on immobilized cells could be recovered by eluting with 0.1 m HCl. The bioreactor could be used for at least five loading-elution cycles without loss of Cu(II) removal capacity. The feasibility of using this bioreactor to remove and recover Cu(II) from electroplating effluent is discussed. Correspondence to: P. K. Wong     

Hexavalent chromium removal by viable, granular anaerobic biomass

Hexavalent chromium in industrial wastewater is a major concern due to its extreme toxicity. This study investigates the removal of Cr(VI) using viable anaerobic granular biomass as a biosorbent. The effect of Cr(VI) concentration on biogas content and COD removal using batch studies indicated that the phase II (methanogenic-rich) culture was more sensitive than the phase I (acidogenic-rich) culture. Toxicity indices for both cultures using COD removal were developed based on linear-log interpolation. The median inhibition Cr(VI) concentration (IC(50)), for phase II cultures was found to be 263mg/L, while that for phase I cultures was 309mg/L. A sorption study was conducted on viable and non-viable (dried) phase I-rich biomass: both followed the Langmuir model. In addition, the biosorption capacity for metabolically inhibited biomass was 25% less indicating some level of cellular uptake associated with Cr(VI) removal. This study demonstrated the potential for a two-phase anaerobic treatment system for a Cr(VI)-contaminated effluent.     

Permeable reactive biobarriers for in situ Cr(VI) reduction: bench scale tests using Cellulomonas sp. strain ES6

Chromate (Cr(VI)) reduction studies were performed in bench scale flow columns using the fermentative subsurface isolate Cellulomonas sp. strain ES6. In these tests, columns packed with either quartz sand or hydrous ferric oxide (HFO)-coated quartz sand, were inoculated with strain ES6 and fed nutrients to stimulate growth before nutrient-free Cr(VI) solutions were injected. Results show that in columns containing quartz sand, a continuous inflow of 2 mg/L Cr(VI) was reduced to below detection limits in the effluent for durations of up to 5.7 residence times after nutrient injection was discontinued proving the ability of strain ES6 to reduce chromate in the absence of an external electron donor. In the HFO-containing columns, Cr(VI) reduction was significantly prolonged and effluent Cr(VI) concentrations remained below detectable levels for periods of up to 66 residence times after nutrient injection was discontinued. Fe was detected in the effluent of the HFO-containing columns throughout the period of Cr(VI) removal indicating that the insoluble Fe(III) bearing solids were being continuously reduced to form soluble Fe(II) resulting in prolonged abiotic Cr(VI) reduction. Thus, growth of Cellulomonas within the soil columns resulted in formation of permeable reactive barriers that could reduce Cr(VI) and Fe(III) for extended periods even in the absence of external electron donors. Other bioremediation systems employing Fe(II)-mediated reactions require a continuous presence of external nutrients to regenerate Fe(II). After depletion of nutrients, contaminant removal within these systems occurs by reaction with surface-associated Fe(II) that can rapidly become inaccessible due to formation of crystalline Fe-minerals or other precipitates. The ability of fermentative organisms like Cellulomonas to reduce metals without continuous nutrient supply in the subsurface offers a viable and economical alternative technology for in situ remediation of Cr(VI)-contaminated groundwater through formation of permeable reactive biobarriers (PRBB).     

Effect of Zn(II) on the reduction and accumulation of Cr(VI) by <Emphasis Type="Italic">Arthrobacter</Emphasis> species

Natural habitats are often characterized by the coexistence of Zn and Cr. This study assessed the potential of two Gram-positive, Cr(VI)-reducing, aerobic bacterial strains belonging to Arthrobacter genera, which were isolated from basalt samples taken from the most polluted region of the Republic of Georgia, to remediate Cr(VI) in environments in the presence of Zn(II). Our batch experiments revealed that the addition of Zn(II) to the tested bacterial cells significantly enhanced the accumulation of Cr. According to electron spin resonance (ESR) measurements, the presence of Zn(II) ions did not change the nature of Cr(V) and Cr(III) complexes generated during the microbial reduction of Cr(VI). The efficiency of Cr(VI) reduction also remained unchanged after the addition of 50 mg/l of Zn(II) to the bacterial cells. However, at high concentrations of Zn(II) (higher than 200 mg/l), the transformation of Cr(VI) to Cr(V) and Cr(III) complexes decreases significantly. In addition, it was shown that the accumulation pattern of Zn in the tested bacterial species in the presence of 100 mg/l of Cr(VI) fits the Langmuir–Freundlich model well. The two tested bacterial strains exhibited different characteristics of Zn accumulation.     

Maximizing EPS production from Pseudomonas aeruginosa and its application in Cr and Ni sequestration

Heavy metal contamination of water bodies has been a cause of grave concern around the globe. Analysis of various industrial effluents has revealed a perilous level of Cr (VI) and Ni (II). Pseudomonas aeruginosa is an extracellular polymeric substances (EPSs) producing bacterium. EPS has a great potential in the sequestration of heavy metal ions. In the present study efforts have been made to understand the effect of time, pH, and temperature on production of EPS by P. aeruginosa (MTCC 1688). The extracted EPS has been applied for removal of Ni (II) and Cr (VI) ions from aqueous system. The results revealed that highest EPS yield (26 mg/50 mL) can be obtained after 96 h of incubation at pH 6 and 32 °C temperature in 50 mL of culture. Treatment of 10 mg/L Cr (VI) and Ni (II) with 30 mg/L EPS resulted in the removal of 26% and 9% of Cr (VI) and Ni (II), respectively. Fourier-transform infrared spectral analysis revealed the involvement of –OH, –NH, C–O, diketone, and ester functional groups of EPS in the attachment of Cr (VI) ion while involvement of amide and –CO groups in Ni (II) binding with EPS. Scaling-up the production of EPS using bioreactor may further help in developing an efficient process for treatment of water polluted with Cr and Ni.     

Immobilized chitosan as biosorbent for the removal of Cd(II), Cr(III) and Cr(VI) from aqueous solutions

The generation of layer-by-layer silicate-chitosan composite biosorbent was studied. The films were evaluated on its stability regarding the polymer leakage and its capability in the removal of Cd(II), Cr(III) and Cr(VI) from an aqueous solution. SEM, EDAX and ATR-IR techniques were applied for material characterization. Silicate-chitosan films with a final layer of silicate demonstrated chitosan retention and had better sorption capacities than those without it. For metal species, such as Cd(II) and Cr(III), the greatest adsorption was obtained when the pH of the solution was 7. When Cr(VI) was evaluated, pH 4 was the optimal for its adsorption. Langmuir and Freundlich isotherms were modeled for the equilibrium data. An 80% of the adsorbed metal was recovered by HNO(3) incubation. This non-covalent immobilization method allowed chitosan surface retention and did not affect its adsorption properties. The use of a coated surface would facilitate sorbent removal from medium after adsorption.     

Kinetics of Cr(III) and Cr(VI) removal from water by two floating macrophytes

The aim of this work was to compare Cr(III) and Cr(VI) removal kinetics from water by Pistia stratiotes and Salvinia herzogii. The accumulation in plant tissues and the effects of both Cr forms on plant growth were also evaluated. Plants were exposed to 2 and 6 mg L^?1 of Cr(III) or Cr(VI) during 30 days. At the end of the experiment, Cr(VI) removal percentages were significantly lower than those obtained for Cr(III) for both macrophytes. Cr(III) removal kinetics involved a fast and a slow component. The fast component was primarily responsible for Cr(III) removal while Cr(VI) removal kinetics involved only a slow process. Cr accumulated principally in the roots. In the Cr(VI) treatments a higher translocation from roots to aerial parts than in Cr(III) treatments was observed. Both macrophytes demonstrated a high ability to remove Cr(III) but not Cr(VI). Cr(III) inhibited the growth at the highest studied concentration of both macrophytes while Cr(VI) caused senescence. These results have important implications in the use of constructed wetlands for secondary industrial wastewater treatment. Common primary treatments of effluents containing Cr(VI) consists in its reduction to Cr(III). Cr(III) concentrations in these effluents are normally below the highest studied concentrations in this work.     

Optimization of Chromium(VI) Detoxification by Pseudomonas aeruginosa and Its Application for Treatment of Industrial Waste and Contaminated Soil

The reduction of Cr(VI) to Cr(III) is a potential detoxification process. In this study, seven Pseudomonas spp. were isolated and screened for chromium reduction. Isolate P4 was able to grow in the presence of 8000 μM chromium, in spite of the fact that the isolate was not previously exposed to any metal stress. Isolate P4 was identified as Pseudomonas aeruginosa strain SRD chr3 by 16S rDNA sequence analysis. Shake flask study showed 78% reduction of 1000 μM Cr(VI) after 6 h of incubation. The optimum pH for chromium reduction by the isolate was between 6 and 8. Isolate Pseudomonas aeruginosa gave 50–80% Cr(VI) reduction even in the presence of 100 mM of Cu, Mn, Ni, and Zn and 300–800 mM NaCl in 24 h, compared with the absence of any of these metals. In a 5-L reactor, the isolate showed 84.85% reduction of Cr(VI) even at the 70th cycle, with a hydraulic retention time of 24 h from the effluent of a hard chrome plating (electroplating) industry, which contained 2100 mg L^?1 hexavalent chromium. The chromate-amended soil inoculated with the isolate showed 2800 μM chromium removal from 4000 μM Cr(VI) kg^?1 of soil, which corresponds to 70% removal. The isolate had the ability to degrade stimulated waste containing 10,000 μM chromium.     

Oxidation and Mobility of Trivalent Chromium in Manganese-Enriched Clays during Electrokinetic Remediation

This article presents the results of an investigation that assessed the extent and effect of oxidation of Cr(III) in manganese-enriched clays on the electrokinetic remedial efficiency. Because chromium commonly exists along with nickel and cadmium at contaminated sites, the effects of changes in chromium redox chemistry on the migration of the coexisting nickel and cadmium was also studied. Bench-scale electrokinetic experiments were conducted using two different clays: kaolin, a typical low buffering soil, and glacial till, a high buffering soil. Tests were performed with 1000?mg/kg of Cr(III), 500?mg/kg of Ni(II), and 250?mg/kg of Cd(II), both with and without the presence of 1000?mg/kg of manganese. All of these experiments were conducted under a constant voltage gradient of 1.0?VDC/ cm. The experimental results showed that in the presence of manganese, percentages of oxidation of Cr(III) into Cr(VI) ranged from 67% in kaolin to 28% in glacial till even before the application of induced electric potential. The low extent of oxidation of Cr(III) in glacial till may be attributed to the initial precipitation of Cr(III) as Cr(OH)₃ resulting from high soil pH, reducing aqueous Cr(III) concentrations present within the soil. In kaolin, Cr(III), Ni(II), and Cd(II) under electric potential migrated toward cathode and precipitated near the cathode due to high soil pH. When manganese was present in kaolin, Cr(VI) that was formed due to the oxidation of Cr(III) migrated toward anode and adsorbed to the soil surfaces near the anode region due to low soil pH. However, remaining Cr(III) as well as Ni(II), and Cd(II) migrated towards and precipitated near the cathode due to high soil pH. In kaolin, the migration of Ni(II) and Cd(II) was retarded in the presence of manganese due to a larger soil zone of elevated pH near the cathode. In glacial till, the migration of Cr(III), Ni(II) and Cd(II) was insignificant due to precipitation resulting from high soil pH caused by the high buffering capacity of the soil. Cr(VI) that resulted from the partial oxidation of Cr(III) in the presence of manganese, however, migrated toward the anode. Overall, this study demonstrated that the effects of manganese on Cr(III) oxidation in low buffering soils can be significant, which can in turn affect the extent and direction of chromium migration under induced electric potential.