Iron Electrocoagulation Research Articles

General Potential-Current Model and Validation for Electrocoagulation

A model relating potential and current in continuous parallel plate iron electrocoagulation (EC) was developed for application in drinking water treatment. The general model can be applied to any EC parallel plate system relying only on geometric and tabulated input variables without the need of system-specific experimentally derived constants. For the theoretical model, the anode and cathode were vertically divided into n equipotential segments in a single pass, upflow, and adiabatic EC reactor. Potential and energy balances were simultaneously solved at each vertical segment, which included the contribution of ionic concentrations, solution temperature and conductivity, cathodic hydrogen flux, and gas/liquid ratio. We experimentally validated the numerical model with a vertical upflow EC reactor using a 24cm height 99.99% pure iron anode divided into twelve 2cm segments. Individual experimental currents from each segment were summed to determine total current, and compared with the theoretically derived value. Several key variables were studied to determine their impact on model accuracy: solute type, solute concentration, current density, flow rate, inter-electrode gap, and electrode surface condition. Model results were in good agreement with experimental values at cell potentials of 2-20V (corresponding to a current density range of approximately 50-800 A/m2), with mean relative deviation of 9% for low flow rate, narrow electrode gap, polished electrodes, and 150mg/L NaCl. Highest deviation occurred with a large electrode gap, unpolished electrodes, and Na2SO4 electrolyte, due to parasitic H2O oxidation and less than unity current efficiency. This is the first general model which can be applied to any parallel plate EC system for accurate electrochemical voltage or current prediction.

Arsenic removal from groundwater using iron electrocoagulation: Effect of charge dosage rate

We demonstrate that electrocoagulation (EC) using iron electrodes can reduce arsenic below 10 μg/L in synthetic Bangladesh groundwater and in real groundwater from Bangladesh and Cambodia, while investigating the effect of operating parameters that are often overlooked, such as charge dosage rate. We measure arsenic removal performance over a larger range of current density than in any other single previous EC study (5000-fold: 0.02 – 100 mA/cm2) and over a wide range of charge dosage rates (0.060 – 18 Coulombs/L/min). We find that charge dosage rate has significant effects on both removal capacity (μg-As removed/Coulomb) and treatment time and is the appropriate parameter to maintain performance when scaling to different active areas and volumes. We estimate the operating costs of EC treatment in Bangladesh groundwater to be $0.22/m3. Waste sludge (∼ 80 – 120 mg/L), when tested with the Toxic Characteristic Leachate Protocol (TCLP), is characterized as non-hazardous. Although our focus is on developing a practical device, our results suggest that As[III] is mostly oxidized via a chemical pathway and does not rely on processes occurring at the anode. Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Environmental Science and Health, Part A, to view the free supplemental file.

In-situ identification of iron electrocoagulation speciation and application for natural organic matter (NOM) removal

In this work, iron speciation in electrocoagulation (EC) was studied to determine the impact of operating parameters on natural organic matter (NOM) removal from natural water. Two electrochemical EC parameters, current density (i) and charge loading rate (CLR), were investigated. Variation of these parameters led to a near unity current efficiency (φ = 0.957 ± 0.03), at any combination of i in a range of 1–25 mA/cm2 and CLR in a range of 12–300 C/L/min. Higher i and CLR led to a higher bulk pH and limited the amount of dissolved oxygen (DO) reduced at the cathode surface due to mass transfer limitations. A low i (1 mA/cm2) and intermediate CLR (60 C/L/min) resulted in low bulk DO (<2.5 mg/L), where green rust (GR) was identified by in-situ Raman spectroscopy as the primary crystalline electrochemical product. Longer electrolysis times at higher i led to magnetite (Fe3O4) formation. Both higher (300 C/L/min) and lower (12 C/L/min) CLR values led to increased DO and/or increased pH, with lepidocrocite (γ-FeOOH) as the only crystalline species observed. The NOM removal of the three identified species was compared, with conditions leading to GR formation showing the greatest dissolved organic carbon removal, and highest removal of the low apparent molecular weight (<550 Da) chromophoric NOM fraction, determined by high performance size exclusion chromatography.

Modelling and cost evaluation of electro-coagulation processes for the removal of anions from water

A mathematical model previously proposed by our group has been modified for its application in the modelling of arsenates, nitrates and phosphates electro-coagulation with iron and aluminium. It classifies the coagulant and pollutant species attending to their reactivity in the electro-coagulation process on the basis of the experimental behaviour of the system. The enmeshment of anionic pollutants in a growing coagulant precipitate and their direct precipitation are the mechanisms considered. A good reproducibility of the experimental data is obtained (with r2 above 0.9) with a small number of parameters. The model has been used to predict the amount of coagulant dose required under given conditions for the removal of the anionic pollutants, which allowed obtaining the costs of the electro-coagulation corresponding to the raw material, iron or aluminium sheets, and the energy costs for their electro-dissolution. Results showed that iron electro-coagulation is cheaper than aluminium electro-coagulation, and that the current density does not have an important influence on the costs within the range studied (0.2–4.0mAcm−2). Attending to the results, arsenate and phosphate removal by electro-coagulation seem to be attractive from the economic point of view.

Standardizing electrocoagulation reactor design: Iron electrodes for NOM removal

A novel systematic approach for reactor design was described for iron electrocoagulation (EC) and applied to drinking water treatment. Suwannee NOM was used as a model compound; performance was quantified by UV-abs-254 and DOC removal. Significant EC design variables were identified and examined: current density (i) (2.43–26.8mAcm−2), coagulant or charge loading rate (CLR) (100–1000CL−1min−1), and flocculation methodology (“fast” and “slow”). A correlation was found between increased i and decreased current efficiency (φ), optimum NOM removal was found at i ∼10mAcm−2. A lower CLR showed greater total DOC removal, while a higher CLR led to less reactor residence time and required either longer flocculation times or greater coagulant dose for similar NOM removal. This paper defines and describes the four general EC “classes” of operation that have implications on several important measures of success: coagulant dose, electrical consumption, process speed, volumetric footprint, and post-EC flocculation requirements. Two classes were further examined with or without pH adjustment for DOC removal, showing that a “fast” EC mode without flocculation is more appropriate for smaller applications, while a “slow” EC mode is more effective for large permanent applications, where flocculation and settling can reduce coagulant and electrical consumption. The effect of pH adjustment showed greater impact with the “fast” dosing mode than with the “slow” mode, adjustment to pH 6 with the “fast” mode gave 13.8% and 29.1% greater DOC and UV-abs-254 removal, respectively, compared to the baseline without pH adjustment.

Modeling As(III) Oxidation and Removal with Iron Electrocoagulation in Groundwater

Understanding the chemical kinetics of arsenic during electrocoagulation (EC) treatment is essential for a deeper understanding of arsenic removal using EC under a variety of operating conditions and solution compositions. We describe a highly constrained, simple chemical dynamic model of As(III) oxidation and As(III,V), Si, and P sorption for the EC system using model parameters extracted from some of our experimental results and previous studies. Our model predictions agree well with both data extracted from previous studies and our observed experimental data over a broad range of operating conditions (charge dosage rate) and solution chemistry (pH, co-occurring ions) without free model parameters. Our model provides insights into why higher pH and lower charge dosage rate (Coulombs/L/min) facilitate As(III) removal by EC and sheds light on the debate in the recent published literature regarding the mechanism of As(III) oxidation during EC. Our model also provides practically useful estimates of the minimum amount of iron required to remove 500 μg/L As(III) to <50 μg/L. Parameters measured in this work include the ratio of rate constants for Fe(II) and As(III) reactions with Fe(IV) in synthetic groundwater (k(1)/k(2) = 1.07) and the apparent rate constant of Fe(II) oxidation with dissolved oxygen at pH 7 (k(app) = 10(0.22) M(-1)s(-1)).

Simultaneous removal of acidity and lead from acid lead battery wastewater by aluminum and iron electrocoagulation

Simultaneous removal of acidity and lead from acid lead battery wastewater by aluminum and iron electrocoagulation

Optimization of the Iron Electro-Coagulation Process of Cr, Ni, Cu, and Zn Galvanization By-Products by Using Response Surface Methodology

An electrocoagulation laboratory scale system was studied for the removal of inorganic pollutants from a mixture of galvanic process-based by-products. Response surface methodology based on a five-level, four-variable central composite rotatable design was employed for optimization with respect to four important variables—reaction time, agitation velocity, current density, and pH. The electrocoagulation process response was evaluated on the basis of chemical oxygen demand (COD), turbidity, total suspended solid, and element concentration values. Interaction effects between reactor operating variables and response variables were evaluated by using 3-D response surface analysis Second-order models were validated by ANOVA. Predicted yields were in a good agreement with the experimental ones. The reactor optimal performance was achieved at 35 min reaction time, 170 rpm agitation velocity, 97.7 Am−2 current density, and 6.5 initial pH. Under these conditions 100% color and turbidity, 90% COD and total suspended solids, 100% chromium and nickel, and almost 99% zinc and copper were removed. A pseudo-first-order rate model was applied to describe the metal removal kinetics. The EC treatment of heavy metal solutions proved to be more cost-effective than the conventional one, indicating clearly that the method of electro-coagulation is a very promising alternative for industrial applications.

Mechanisms of virus control during iron electrocoagulation – Microfiltration of surface water

Results from a laboratory-scale study evaluating virus control by a hybrid iron electrocoagulation – microfiltration process revealed only 1.0–1.5 log MS2 bacteriophage reduction even at relatively high iron dosages (∼13 mg/L as Fe) for natural surface water containing moderate natural organic matter (NOM) concentrations (4.5 mg/L dissolved organic carbon, DOC). In contrast, much greater reductions were measured (6.5-log at pH 6.4 and 4-log at pH 7.5) at similar iron dosages for synthetic water that was devoid of NOM. Quantitative agreement with Faraday’s law with 2-electron transfer and speciation with phenanthroline demonstrated electrochemical generation of soluble ferrous iron. Near quantitative extraction of viruses by dissolving flocs formed in synthetic water provided direct evidence of their removal by sorption and enmeshment onto iron hydroxide flocs. In contrast, only approximately 1% of the viruses were associated with the flocs formed in natural water consistent with the measured poor removals. 1–2 logs of virus inactivation were also observed in the electrochemical cell for synthetic water (no NOM) but not for surface water (4.5 mg/L DOC). Sweep flocculation was the dominant destabilization mechanism since the ζ potential did not reach zero even when 6-log virus reductions were achieved. Charge neutralization only played a secondary role since ζ potential → 0 with increasing iron electrocoagulant dosage. Importantly, virus removal from synthetic water decreased when Suwanee River Humic Acid was added. Therefore, NOM present in natural waters appears to reduce the effectiveness of iron electrocoagulation pretreatment to microfiltration for virus control by complexing ferrous ions. This inhibits (i) Fe2+ oxidation, precipitation, and virus destabilization and (ii) virus inactivation through reactive oxygen species intermediates or by direct interactions with Fe2+ ions.

Optimization of electrochemical dechlorination of trichloroethylene in reducing electrolytes

Electrochemical dechlorination of trichloroethylene (TCE) in aqueous solution is investigated in a closed, liquid-recirculation system. The anodic reaction of cast iron generates ferrous species, creating a chemically reducing electrolyte (negative ORP value). The reduction of TCE on the cathode surface is enhanced under this reducing electrolyte because of the absence of electron competition. In the presence of the iron anode, the performances of different cathodes are compared in a recirculated electrolysis system. The copper foam shows superior capability for dechlorination of aqueous TCE. Electrolysis by cast iron anode and copper foam cathode is further optimized though a multivariable experimental design and analysis. The conductivity of the electrolyte is identified as an important factor for both final elimination efficiency (FEE) of TCE and specific energy consumption. The copper foam electrode exhibits high TCE elimination efficiency in a wide range of initial TCE concentration. Under coulostatic conditions, the optimal conditions to achieve the highest FEE are 9.525mm thick copper foam electrode, 40mA current and 0.042molL−1 Na2SO4. This novel electrolysis system is proposed to remediate groundwater contaminated by chlorinated organic solvents, or as an improved iron electrocoagulation process capable of treating the wastewater co-contaminated with chlorinated compounds.

Removing Arsenic from Synthetic Groundwater with Iron Electrocoagulation: An Fe and As K-Edge EXAFS Study

Electrocoagulation (EC) using iron electrodes is a promising arsenic removal strategy for Bangladesh groundwater drinking supplies. EC is based on the rapid in situ dissolution of a sacrificial Fe(0) anode to generate iron precipitates with a high arsenic sorption affinity. We used X-ray absorption spectroscopy (XAS) to investigate the local coordination environment (<4.0 Å) of Fe and As in EC precipitates generated in synthetic Bangladesh groundwater (SBGW). Fe and As K-edge EXAFS spectra were found to be similar between samples regardless of the large range of current density (0.02, 1.1, 5.0, 100 mA/cm(2)) used to generate samples. Shell-by-shell fits of the Fe K-edge EXAFS spectra indicated that EC precipitates consist of primarily edge-sharing FeO(6) octahedra. The absence of corner-sharing FeO(6) octahedra implies that EC precipitates resemble nanoscale clusters (polymers) of edge-sharing octahedra that efficiently bind arsenic. Shell-by-shell fits of As K-edge EXAFS spectra show that arsenic, initially present as a mixture of As(III) and As(V), forms primarily binuclear, corner-sharing As(V) surface complexes on EC precipitates. This specific coordination geometry prevents the formation of FeO(6) corner-sharing linkages. Phosphate and silicate, abundant in SBGW, likely influence the structure of EC precipitates in a similar way by preventing FeO(6) corner-sharing linkages. This study provides a better understanding of the structure, reactivity, and colloidal stability of EC precipitates and the behavior of arsenic during EC. The results also offer useful constraints for predicting arsenic remobilization during the long-term disposal of EC sludge.

A new approach to increasing the efficiency of low-pH Fe-electrocoagulation applications

Incomplete oxidation of Fe(II) species released from the anode to Fe(III) may impede iron electrocoagulation processes conducted under low dissolved oxygen and/or pH < 7 conditions, accompanied by the typically high buffering capacity of wastewater. This paper introduces a new approach to overcome this drawback by applying a second electrochemical cell (Ti/RuO 2 anode and Ti cathode) to be operated in parallel to the electrocoagulation cell. The second unit oxidizes Cl − ions invariably present in the water to HOCl, which is capable of oxidizing Fe(II) species at a high rate, irrespective of pH or O 2(aq) concentration. An electrolytic cell with a Ti/RuO 2 anode and Ti cathode was shown to successively operate in parallel to a sacrificial electrocoagulation cell (Fe anode and Ti cathode) to attain complete Fe(II) conversion to Fe(III) under low-pH conditions, in which, in the absence of the 2nd cell, unwanted Fe(II) species would have dominated the dissolved iron species. Current efficiency for Cl 2 production was 12.4% and 45.7% at 200 and 1000 mg Cl/l, respectively. Under three practical conditions (pH 6, [Cl −] = 200 mg/l; pH 6, [Cl −] = 400 mg/l; pH 5, [Cl −] = 600 mg/l) the power demand of the combined system was 25.29, 12.7 and 8.1 kWh/kg Fe(III) produced, respectively, suggesting that the presented approach is competitive at [Cl −] > ∼600 mg/l.

Treatment of Acid Blue 113 Dye Solution Using Iron Electrocoagulation

AbstractThe electrocoagulation (EC) treatment of Acid Blue 113 (AB 113) was performed on the basis of chemical oxygen demand (COD) removal efficiency using an iron anode. The process variables, including current density (1–5 A/dm2), pH (5.5–7.5), and supporting electrolyte concentration (1–3 g/L) were investigated. Under the optimum operating conditions, more than 91% COD removal efficiency was found. The optimum conditions were obtained with 3 A/dm2 of current density, pH 6.5, and 2 g/L of supporting electrolyte concentration. COD removal rates obtained during the EC process can be described using a pseudo‐kinetic model. The experimental kinetic data fit well with pseudo first‐order kinetic model, with no significant change on the rate constant after 3 A/dm2 of current density. The absorption spectra and Fourier transform infra red analysis were also performed to characterize the mechanism and nature of dye cleavage.

Removal of total organic carbon from aqueous solution containing polyvinyl alcohol by electrocoagulation technology

The removal of total organic carbon (TOC) from aqueous solution containing polyvinyl alcohol (PVA) using iron electrocoagulation (EC) was investigated. Iron hydroxides generated during EC were used to remove PVA and TOC from the aqueous solution, and the effects of varying current density and solution temperature on PVA and TOC adsorption characteristics were evaluated. The findings indicated that complete PVA removal accompanied by TOC removal of an aqueous PVA solution could be achieved within a reasonable electrolysis time and with relatively low electrical energy consumption. A pseudo-first-order kinetic model provided a good fit to the experimental results at various current densities and solution temperatures. In addition, the experimental data were fitted with several adsorption isotherm models to describe the EC process. The predictions of the Freundlich adsorption isotherm model satisfactorily matched the experimental observations. Thermodynamic parameters, including the Gibbs free energy, enthalpy, and entropy, indicated that the TOC adsorption of the aqueous solution containing PVA on metal hydroxides was feasible, spontaneous and endothermic in the temperature range of 288 K to 318 K.

Industrial Wastewater Treatment by Electrocoagulation-Direct Anodic Oxidation System

This paper shows the results of experimental investigations in industrial wastewater treatment by electrochemical processes, the first one uses iron electrocoagulation and the second employs boron-doped diamond electrooxidation. The coupled treatment reduced chemical oxygen demand (COD) by 99 %, color by 100 % and turbidity by 100 %. The initial and final quality levels in the wastewater were monitored using UV-Vis spectrometry and cyclic voltammetry.

Investigation of process parameters for the removal of polyvinyl alcohol from aqueous solution by iron electrocoagulation

The feasibility of polyvinyl alcohol (PVA) removal from aqueous solution was investigated using iron electrocoagulation. Several parameters, including type of electrode pair, applied voltage, supporting electrolytes, and solution temperature were investigated. The effects of applied voltage, supporting electrolyte, and solution temperature on PVA removal efficiency and specific energy consumption were also investigated. Experimental results indicated that a Fe/Al electrode pair was the most efficient choice of the four electrode pairs tested in terms of PVA removal efficiency. The optimum applied voltage, supporting electrolyte concentration, and solution temperature were found to be 10V, 100mg L−1 NaCl, and 298K, respectively. A pseudo-second-order kinetic model provided a good fit to experimental results at various applied voltages and solution temperatures. In addition, the activation energy was calculated to be 49.45J mol−1 based on pseudo-second-order rate constants from the Arrhenius equation, indicating that PVA precipitation in aqueous solution was attributable to the electrocoagulation process.

Performance of COD removal from oxide chemical mechanical polishing wastewater using iron electrocoagulation

This study investigated the feasibility of chemical oxygen demand (COD) abatement from oxide chemical mechanical polishing (oxide-CMP) wastewater. The process variables, including applied voltage, electrolyte concentration and temperature, were evaluated in terms of COD removal efficiency. In addition, the effects of applied voltage, supporting electrolyte, and temperature on electric energy consumption were evaluated. Under the optimum balance of variables, satisfactory COD removal efficiency and relatively low energy consumption were achieved. The optimum electrolyte concentration, applied voltage, and temperature were found to be 200 mg/L NaCl, 20 V, and 25°C, respectively. Under these conditions, the COD concentration in oxide-CMP wastewater decreased by more than 90%, resulting a final wastewater COD concentration that was below the Taiwan discharge standard (100 mg/L). Since the processed wastewater quality exceeded the direct discharge standard, the effluent could be considered for reuse. COD removal rates obtained during the electrocoagulation process can be described using a pseudo-kinetic model. The present study results show that the kinetic data fit the pseudo first-order kinetic model well. Finally, the morphology and composition of the sludge produced were characterized using scanning electron microscopy (SEM) and energy dispersion spectra (EDS).

Ferrous and Ferric Ion Generation During Iron Electrocoagulation

Our research on arsenate removal by iron electrocoagulation (EC) produced highly variable results, which appeared to be due to Fe2+ generation without subsequent oxidation to Fe3+. Because the environmental technology literature is contradictory with regard to the generation of ferric or ferrous ions during EC, the objective of this research was to establish the iron species generated during EC with iron anodes. Experimental results demonstrated that Fe2+, not Fe3+, was produced at the iron anode. Theoretical current efficiency was attained based on Fe2+ production with a clean iron rod, regardless of current, dissolved-oxygen (DO) level, or pH (6.5-8.5). The Fe2+ remaining after generation and mixing decreased with increasing pH and DO concentration due to rapid oxidation to Fe3+. At pH 8.5, Fe2+ was completely oxidized, which resulted in the desired Fe(OH)3(s)/ FeOOH(s), whereas, at pH 6.5 and 7.5, incomplete oxidation was observed, resulting in a mixture of soluble Fe2+ and insoluble Fe(OH)3(s)/FeOOH(s). When compared with Fe2+ chemical coagulation, a transient pH increase during EC led to faster Fe2+ oxidation. In summary, for EC in the pH 6.5-7.5 range and at low DO conditions, there is a likelihood of soluble Fe2+ species passing through a subsequentfiltration process resulting in secondary contamination and inefficient contaminant removals.

Study of COD and turbidity removal from real oxide-CMP wastewater by iron electrocoagulation and the evaluation of specific energy consumption

This study explores the feasibility of reducing COD and turbidity from real oxide chemical mechanical polishing (oxide-CMP) wastewater. Based on the dynamic characteristics of batch electrocoagulation, three operating stages (lag, reactive, and stabilizing) are proposed to identify the relationships among the zeta potential of the silica particles, solution turbidity, and the corresponding mean particle size. Experiment results show that the silica particles were destabilized and settled at the critical electrolysis time, which was estimated to be about 12 min under an applied voltage of 20 V and a supporting electrolyte of 200 mg/L. The corresponding turbidity removal occurred mostly during the reactive stage. The process variables, including applied voltage and electrolyte concentration, were investigated in terms of COD removal efficiency and turbidity removal. In addition, the effects of applied voltage and supporting electrolyte on COD removal efficiency and specific energy consumption were evaluated. Under the optimum balance, satisfactory removal efficiency and relatively low energy consumption were obtained. The optimum electrolyte concentration and applied voltage were found to be 200 mg/L NaCl and 20 V, respectively. Under the optimum conditions, COD and turbidity decreased by more than 90% and 98% in real oxide-CMP wastewater, respectively.

Effect of operating parameters on indium (III) ion removal by iron electrocoagulation and evaluation of specific energy consumption

The aim of this study is to investigate the effects of operating parameters on the specific energy consumption and removal efficiency of synthetic wastewater containing indium (III) ions by electrocoagulation in batch mode using an iron electrode. Several parameters, including different electrode pairs, supporting electrolytes, initial concentration, pH variation, and applied voltage, were investigated. In addition, the effects of applied voltage, supporting electrolyte, and initial concentration on indium (III) ion removal efficiency and specific energy consumption were investigated under the optimum balance of reasonable removal efficiency and relative low energy consumption. Experiment results indicate that a Fe/Al electrode pair is the most efficient choice of the four electrode pairs in terms of energy consumption. The optimum supporting electrolyte concentration, initial concentration, and applied voltage were found to be 100 mg/l NaCl, 20 mg/l, and 20 V, respectively. A higher pH at higher applied voltage (20 or 30 V) enhanced the precipitation of indium (III) ion as insoluble indium hydroxide, which improved the removal efficiency. Results from the indium (III) ion removal kinetics show that the kinetics data fit the pseudo second-order kinetic model well. Finally, the composition of the sludge produced was characterized with energy dispersion spectra (EDS).