Electrochemical Coagulation Processes Research Articles

Evaluation of a Combined Approach for Sulfate and Ammonia Recovery from Treated Brine Using a Simultaneous Chemical Precipitation and Electrocoagulation Processes

Soda ash (Na2CO3) is produced using the traditional Solvay process. It entails the reaction of CO2 with high-salinity water in the presence of ammonia (NH3), which produces insoluble sodium bicarbonate (NaHCO3) and soluble ammonium chloride (NH4Cl). In the current work, a newly combined approach has been developed to effectively manage the removal of ammonia and sulfate from the effluent of the Solvay process. The devised technique centers on an electrochemical coagulation process, complemented with the utilization of calcium oxide (CaO) as a buffering reagent. This innovative approach excels at achieving high recovery rates for both ammonia and sulfate. The recovered ammonia holds the potential for recycling, thereby contributing to the sustainability of the Solvay process by reusing ammonia in its initial stages. Furthermore, sulfate ions are recuperated in the form of calcium sulfate, a value-added product boasting various industrial applications. The results gleaned from this study underscore the efficacy of the ammonia recovery process, particularly when operating at elevated current densities and with higher calcium oxide concentrations. On the other hand, sulfate recovery demonstrates superior performance when exposed to moderate current densities and limited calcium oxide concentrations. Consequently, the integration of both stages within a single, cohesive process necessitates the development of an optimization methodology to cater to varying operational conditions. To address this need, second-order polynomial equations were formulated and employed to anticipate ammonia and sulfate removal rates in the integrated approach. Four independent variables come into play: calcium oxide concentration, current density, temperature, and mixing rate. The findings reveal that most of these variables exert substantial influences on both ammonia and sulfate removal rates, underscoring the need for careful consideration and fine-tuning to optimize the overall process. The maximum ammonia and sulfate removal were found to reach 99.50% and 96.03%, respectively, at a calcium oxide concentration of 3.5 g/100 mL, a current density of 19.95 mA/cm2, a temperature of 35 °C, and a mixing rate of 0.76 R/s. The results are promising, and the developed process is also suitable for recovering high concentrations of sulfate and ammonia from various wastewater sources.

Hospital wastewater treatment coupling electrochemical coagulation and activated sludge process

Abstract Dual treatment of raw hospital wastewater (RHWW) is investigated by coupling electrochemical coagulation (ECC) with the activated sludge process (ASP) to achieve the goal of partial mineralization and reclaim quality water. The quality parameters of focus were chemical oxygen demand (COD), color, mixed liquor suspended solids (MLSS), total dissolved solids (TDS), chloride, total alkalinity, and fecal coliform. The initial ECC process with short hydraulic retention time (HRT) could remove 75–82% of the insoluble constituents in <60 min, while the HRT for ASP was >7–8 h. The combined ECC + ASP hybrid treatment process showed effective removal of COD, color, TDS, and fecal coliform by 98.5, 99.6, 83.1, and 97.9%, respectively, from its initial values of 4,000, 2,200, 77, and 2,400 MPN/100 mL, respectively. By coupling ECC and ASP, both the insoluble and soluble pollutants/contaminants in the RHWW were removed effectively. The ECC–ASP dual treatment offers a small energy and spatial footprint for mineralizing RHWW.

Ayurvedic hospital wastewater degradation using electrochemical treatment.

The goal of this research was to remove COD, oil and grease (O&G) and color from raw ayurvedic hospital wastewater (AHWW) using a novel electrochemical coagulation (ECC) process. Cell voltage was initially optimized using iron electrodes in bipolar mode for both raw AHWW and ayurvedic hospital therapy room wastewater (AH-TRWW) for a pre-optimized electrolysis time (ET) of 60 min. O&G, COD and color removals for AHWW at 8 V optimized cell voltage were 96, 61 and 96% respectively. Different electrode materials, copper, aluminum, graphite, were used to evaluate relative performances at 8 V. Iron electrodes showed maximum pollutant removal from raw AHWW. The sludge obtained after the ECC process showed good settling and filterability properties compared to graphite and aluminum electrodes. The low SVI value of 146 mL/g was obtained exercising absolute control on sludge volume. Solids flux values showed assurances of compact settling tank design with least spatial footprint. EDX analysis for ECC sludge of AHWW using iron showed gross elements 40.19% C, 48.63% O and 7.92% Fe redefining the fate of sludge. The XRD pattern of the ECC sludge showed an amorphous nature. Post-ECC filtration effluent showed clear water reclamation of 80-82%, proving the effectiveness of the novel ECC treatment process.

Adsorption of 2,4-dichlorophenoxyacetic acid (2,4-D) from water by in situ generated metal hydroxides using sacrificial anodes

This research paper deals with an evaluation of electrochemical coagulation process, where the metal hydroxides are generated in-situ, for the removal of 2,4-dichlorophenoxyacetic acid (2,4-D) from water using different anode materials like iron, magnesium, zinc and aluminum with galvanized iron as the cathode. The optimization of different experimental parameters like current density, pH, temperature, and inter-electrode distance on the removal efficiency of 2,4-D was carried out. The results showed that the maximum removal efficiency of 91.0% was achieved with iron as anode at a current density of 0.10A/dm2 and pH of 7.0. The adsorption of 2,4-D preferably fitting the Langmuir adsorption isotherm. Thermodynamic parameters, including the Gibbs free energy, enthalpy, and entropy, indicated that the adsorption of 2,4-D on iron hydroxides was feasible, spontaneous and endothermic. In addition, the adsorption kinetic studies showed that the electrochemical coagulation process for adsorption of 2,4-D was best described using the second-order kinetic model at the various current densities.

Treatment of copper wastewater using optimal current electrochemical–coagulation

In this study, an automatic current controlling electrochemical-coagulation (EC) process was developed by testing laboratory-scale and pilot-scale reactors for removing copper (Cu) from printed circuit board (PCB) industrial wastewater with an economic use of energy. During tests of the laboratory-scale reactor, the influences of electrode material, electrode gap, current density, hydraulic retention time (HRT), wastewater pH and conductivity on removal performance were explored. The relational expression between conductivity and current density that optimizes Cu removal based on conductivity changes was established and applied to the optimal current EC process. During tests of the pilot-scale reactor, Cu removal from PCB industrial wastewater was investigated by applying an automatic current controlling system for the EC process. More than 90% of the Cu was removed when applying optimal current control for the EC process in both laboratory-scale and pilot-scale experiments, which demonstrated significant energy savings.

Electrochemical dosing of iron and aluminum in continuous processes: A key step to explain electro-coagulation processes

The aim of this work is to study the main differences between aluminum and iron production during electrochemical coagulation processes, attending not only to the coagulant dosage, but also to the characteristics of the coagulants produced. To do this, the influence of both pH and current density have been studied. It has been observed that there is a super-faradaic production of aluminum because of a promoted corrosion at the alkaline pHs produced on the cathode surface. This efficiency decreases for high values of current density because of cathodic protection processes. On the contrary, for iron electrodes, it does not exist a super-faradaic dissolution within the range of current densities studied but simply a decrease in the efficiency for alkaline pH values and high current densities, because of the formation of Fe3+ instead of Fe2+ during the electro-dissolution process. With respect to speciation, it has been observed the formation of monomeric species at acidic pHs and precipitate species for pHs above 5. In addition, for aluminum, monomeric species are also the primary species for pHs above 9 and some polymeric species are formed at pHs between 4 and 6. The superficial charge of both metal precipitates is very similar. For pHs below 9, both aluminum and iron precipitates have a positive charge due to the adsorption of monomeric soluble hydroxometals positively charged or protons on the precipitate surface. For pHs above 9 the aluminum precipitate is negatively charged due to the adsorption of soluble hydroxometal species negatively charged or hydroxyl ions on the precipitate surface. On the contrary, iron precipitate does not have a superficial charge for alkaline pH, because there is almost no formation of soluble negatively-charged species.

Influence of anions on Reactive Red 43 removal in electrochemical coagulation process

The electrochemical coagulation technique (EC) and potentiodynamic polarization tests were used to evaluate the influence of some anions as chloride, sulfate and nitrate on the removal of Reactive Red 43 (RR43) as a model pollutant using aluminum and iron anodes. Higher removal efficiency was obtained using aluminum anodes in the presence of chloride ions. Potentiodynamic polarization tests and determination of total Al 3+ concentration showed that sulfate ions inhibit the release of Al 3+ from the anode while in the existences of chloride and nitrate current efficiency was higher than 100%. Dye removal efficiency was considerably decreased by increasing the anion concentration and adding sulfate and nitrate to the solution containing chloride. In EC using iron anodes, the higher removal efficiency was achieved in the presence of chloride and sulfate ions. Potentiodynamic polarization tests revealed that the passive layer formation on the iron surface in the solution containing nitrate caused a considerable decrease in the current and removal efficiency. This passive layer was destroyed by adding chloride ions and in this condition, the removal efficiency and quantity of Fe 2+ ions increased remarkably. According to the results, iron anode was more efficient than aluminum in the removal of RR43.

Studies on the Removal of Arsenate by Electrochemical Coagulation Using Aluminum Alloy Anode

AbstractThe removal of arsenate from aqueous solution was carried out by electrochemical coagulation using aluminum alloy as anode and stainless steel as cathode. Various operating parameters on the removal efficiency of arsenate were investigated, such as initial arsenate ion concentration, initial pH, current density, and temperature. Effect of coexisting anions such as silicate, fluoride, phosphate, and carbonate were studied on the removal efficiency of arsenate. The optimum removal efficiency of 98.4% was achieved at a current density of 0.2 A/dm2 at a pH of 7.0. The experimental data were tested against different adsorption isotherm models for describing the electrochemical coagulation process. The adsorption of arsenate preferably fitting the Langmuir adsorption isotherm suggests monolayer coverage of adsorbed molecules. First and second order rate equations were applied to study adsorption kinetics. The adsorption process follows second order kinetics model with good correlation. Temperature studies showed that adsorption was endothermic and spontaneous in nature.

Electrochemical Coagulation for Chromium Removal: Process Optimization, Kinetics, Isotherms and Sludge Characterization

AbstractThis study presents an electrochemical coagulation process for the removal of chromium from water using magnesium as the anode and galvanized iron as the cathode. The effects of pH, current density, concentration, temperature, adsorption kinetics and adsorption isotherms on chromium removal were investigated. The results showed that an optimum removal efficiency of 98.6% was achieved at a current density of 0.2 A/dm2 and a pH of 7.0. The adsorption kinetics showed that the first order rate expression fitted the adsorption kinetics. The equilibrium isotherm was measured experimentally. Results were analyzed by Langmuir, Freundlich, Dubinin‐Redushkevich and Frumkin isotherms using linearized correlation coefficients. The characteristic parameters for each isotherm were determined. The Langmuir adsorption isotherm was found to fit the equilibrium data best for chromium adsorption. Temperature studies showed that adsorption was endothermic and spontaneous in nature.

Studies on a Mg‐Al‐Zn Alloy as an Anode for the Removal of Fluoride from Drinking Water in an Electrocoagulation Process

AbstractThe present study provides an electrochemical coagulation process for the removal of fluoride from drinking water using a Mg‐Al‐Zn alloy, magnesium, aluminum and mild steel as anodes and stainless steel as cathode. Various parameters which may affect the removal efficiency of fluoride from water, such as pH, concentration of fluoride, current density, temperature and co‐existing ions were studied. Electrochemical coagulation was carried out for 30 min at an initial fluoride concentration of 5.0 mg/L and this was reduced to 0.2 mg/L. A maximum removal efficiency of 96% was achieved with a magnesium alloy as anode and stainless steel as cathode at a current density of 0.2 A/dm2 and a pH of 7.0.

Technical and economic comparison of conventional and electrochemical coagulation processes

AbstractBACKGROUND: Electrocoagulation is an alternative to the conventional coagulation method, to treat different types of waters and wastewaters. Although there have been many reports on the technical suitability of electrocoagulation, no study has made a direct comparison of the economics of the two processes.RESULTS: Concerning the technical feasibility, no significant differences were found in the results achieved by the two technologies in the treatment of synthetic suspensions, emulsions and solutions of dyes, when the same values of pH and aluminium concentration were adopted in the reaction systems. Regarding the economic comparison, the electrocoagulation process presents lower operating costs for low and intermediate aluminium doses, but results depend on the particular coagulant reagent selected at high doses. The highest operational costs were obtained with conventional coagulation with aluminium sulphate (in the range 3–60 mg dm−3 aluminium). Comparing electrocoagulation and conventional coagulation with aluminium polychloride, the electrocoagulation process presents lower operational costs for low and intermediate doses. However, this situation changes for high aluminium doses.CONCLUSION: Coagulation and electrocoagulation techniques give very similar yields in the removal of different types of pollutants; therefore an economic comparison is of major importance in order to recommend the use of one of the technologies. Nevertheless, it has to be noted that operational costs are of the same order of magnitude for the two processes. Thus, the cost of the electrocoagulation process compares favourably with that of conventional coagulation for small coagulant demands, but the results at high doses depend on the particular coagulant reagent selected. Copyright © 2008 Society of Chemical Industry

Coagulation and Electrocoagulation of Wastes Polluted with Colloids

The goal of this work has been to compare for both, continuous and batch processes, the efficiencies of the chemical and the electrochemical coagulation processes with hydrolyzing aluminum salts, and to determine the similarities or differences that exist between both coagulation processes. To meet the objective, experiments of both coagulation technologies have been carried out in the same operation conditions and the results have been interpreted in terms of the mechanisms previously proposed in literature for kaolin coagulation. The charge neutralization by the adsorption of monomeric hydroxocations onto the kaolin surface can be the primary coagulation‐mechanism for low concentration of aluminum and acidic pHs (below 4). In the range of pH 4–7, two primary mechanisms can explain the experimental behavior of the system: sweep flocculation for high concentration of aluminum, and a combination of precipitation‐charge‐neutralization and charge neutralization by adsorption of monomeric or polymeric aluminum, for low concentration of aluminum. In the continuously‐operated processes, the efficiency in the turbidity‐removal seems to be much related to the aluminum species present in the treated waste, and not to the way of adding aluminum to the reaction system. For the same steady‐state pH and aluminum concentration, the same turbidity removal is obtained in both, the chemical and the electrochemical coagulation processes. For high aluminum/kaolin ratios, kaolin suspensions which contain sulfate as electrolyte, achieve better removals of turbidity than those containing chloride ions. The operation mode (continuous or discontinuous) influences greatly on the efficiency of the electrocoagulation processes. Similar efficiencies are obtained for low (below 5 mg dm−3) and high doses of aluminum (above 20 mg dm−3). However, at intermediate doses a strong difference is observed, with a more marked decrease in the efficiency in the discontinuous process. This observation has been explained considering that the addition of aluminum in the continuous process is instantaneous (and not progressive as in the discontinuous one), and thus, the sweep coagulation mechanism is more favored in this operation mode.

Preliminary evaluation of the electrochemical and chemical coagulation processes in the post-treatment of effluent from an upflow anaerobic sludge blanket (UASB) reactor

The main objective of this paper was to perform a preliminary comparative study between chemical and electrochemical coagulation processes, both followed by flocculation and sedimentation of an effluent from an upflow anaerobic sludge blanket (UASB) reactor treating simulated wastewater from an unbleached Kraft pulp mill. The electrochemical treatment removed up to 67% (with aluminum electrodes) and 82% (with stainless-steel electrodes) of the remaining chemical oxygen demand (COD) and 84% (stainless steel) and 98% (aluminum) of the color in the wastewater. These efficiencies were achieved with an energy consumption ranging from 14 to 20 Wh l −1. The coagulation–flocculation treatment with ferric chloride and aluminum sulfate removed up to 87% and 90% of COD and 94% and 98% of color, respectively. The addition of a high molecular weight cationic polymer enhanced both COD and color removal efficiencies. The two post-treatment processes proved to be technically feasible; however the economical feasibility could not be assessed since the experiments were performed with small reactors that could distort scale factors.

Coagulation and Electrocoagulation of Wastes Polluted with Dyes

Dyes are common pollutants in a large variety of industrial wastewaters, and the treatment of these wastes by coagulation has been extensively studied in the literature. This work is focused on the comparison of the efficiencies of the chemical and the electrochemical coagulation processes with hydrolyzing aluminum salts, and it tries to determine the similarities or differences that exist between the two coagulation processes. To do this, Eriochrome Black T solutions were used as a model of dye-polluted wastewater, and experiments of both coagulation technologies were planned to meet the same operation conditions. The pH, the aluminum concentration, the type of electrolyte, and the mode of dosing of aluminum were found to influence the process. Moreover, the speciation of aluminum was found to be the key parameter to explain the results, in terms of the mechanisms previously proposed in the literature for dissolved organic matter coagulation.

Electrochemical coagulation of whey protein

This paper explores the possibility of using electrochemical coagulation (EC) directly to extract protein from cheese whey. Different flow configurations for EC were used. The configuration, where the solution first flows through the anode compartment and, after separation of the coagulum, flows through the cathode compartment, was most effective, giving a reduction in protein content of 73.8%. The efficiency of EC was compared to chemical coagulation. Some explanations for the high extraction rates found for the EC process are presented.