Electrochemical Wastewater Treatment Research Articles

Combined Electro-Chemical Coagulation Treatment of Urban, Peri-Urban and Textile Wastewaters: Process Evaluation and Sludge Setting Characteristics

Combined Electro-Chemical Coagulation Treatment of Urban, Peri-Urban and Textile Wastewaters: Process Evaluation and Sludge Setting Characteristics

Demulsification performance and mechanism of oil droplets by electrocoagulation: Role of surfactant

Surfactants are widely used to improve the solubility of oil in water in petrochemical, making it more difficult to remove oil–water emulsions during the water treatment process. Electrocoagulation (EC) is an appropriate method for treating oily wastewater and destabilizing emulsions. However, the demulsification mechanism of oil–water droplets emulsified by surfactants with different charges have not been investigated systematically. The demulsification performance of electrocoagulation on emulsions wastewater containing cationic, non-ionic, and anionic surfactants was studied. The results showed that the removal rate of total organic carbon (TOC) in oily wastewater with anionic surfactant by EC reached 92.98% ± 0.40% at a current density of 1 mA/cm2, while that of the non-ionic surfactant was 84.88% ± 0.63%. The characterization of flocs showed that EC has the highest coagulation and demulsification of oil droplets with a negative charge on the surface (−70.50 ± 10.25 mV), which indicated that the charge neutralization of oil droplets was beneficial for the destabilization of the formed oily flocs. However, when the zeta potential of the oil droplets reached 75.50 ± 1.25 mV, the TOC removal efficiency was only 11.80% ± 1.43%. The TOC removal could achieve 33.23% ± 3.21% when the current density improved from 1 mA/cm2 to 10 mA/cm2. The enhanced removal was due to the sweep coagulation rather than charge neutralization. This study provides a fundamental basis for the electrochemical treatment of oily wastewater.

Utilizing Spent Batteries to Fabricate Ni/ZnO-MnO2 Electrodes for Electrochemical Ammonia Oxidation

In this work, a novel Ni/ZnO-MnO2 electrode was fabricated by utilizing spent zinc-manganese batteries and then was applied to the electrochemical treatment of ammonia-containing wastewater. The obtained Ni/ZnO-MnO2 electrode was characterized by scanning electron microscopy, X-ray diffraction, and linear scanning voltammetry, suggesting that the fabricated electrode had a flower-like structure and showed high oxygen evolution potential and electrochemical activity. The electrochemical performance of the ZnO-MnO2 electrode in regard to ammonia removal and product selectivity was then investigated with different operating factors (i.e., electrolyte concentration, initial pH value, current density, and Cl− concentration), and the results indicated that the ammonia removal efficiency could reach 100% with a N2 selectivity of 91.8% under optimal conditions. Additionally, the mechanism of ammonia oxidation was proposed by cyclic voltammetry tests and active radical measurements, showing that ammonia was mainly oxidized via direct electron transfer, hydroxyl radicals, and active chlorine. Finally, the ZnO-MnO2 electrode was equipped for the treatment of actual pharmaceutical wastewater, results for which showed that ammonia could be completely removed with a current efficiency of 26.2% and an energy consumption of 52.7 kWh/kg N. Thus, the ZnO-MnO2 electrode prepared by recycling spent batteries is a promising anode for wastewater treatment.

Electrochemical treatment of wastewater contaminated by organics and containing chlorides: Effect of operative parameters on the abatement of organics and the generation of chlorinated by-products

In the last years, large attention has been devoted to the electrochemical treatment of wastewater polluted by recalcitrant organics and containing chlorides. However, the utilization on an applicative scale of this route is limited by the fact that usually it is not possible to achieve high removals of organics without the generation of significant amounts of chlorinated by-products. Here, the role of several operative parameters on the performances of the process was systematically evaluated using phenol as a model organic pollutant. It was shown that the removal of phenol and TOC and the generation of many by-products including chlorophenols, chloroacetic acids, chlorate and perchlorate dramatically depend on the adopted operative conditions (i.e., nature of anode and cathode, current density and concentration of chlorides). The use of boron doped diamond (BDD) anode gave the highest removal of TOC but also the highest final concentrations of chlorate and perchlorate and the lowest concentrations of chloroacetic acids. Conversely, the use of Ti/IrO2-Ta2O5 gave the lowest generation of chlorate and no perchlorate. The use of lower current densities allowed as well to reduce the concentrations of these compounds. It is worth to mention that lower amounts of chlorinated by-products were achieved using suitable cathodes. Carbon felt cathodes, as previously reported for the water disinfection, allowed to reduce the generation of chlorate. Moreover, it was shown, for the first time, that the use of silver cathodes minimized the concentrations of chloroacetic acids. In addition, it was found that the use of a system equipped with both silver and carbon felt cathodes and proper current densities allowed to increase remarkably the removals of TOC and the current efficiency and to achieve very low concentrations of chlorinated by-products.

Mixed Metal Oxide Electrodes and the Chlorine Evolution Reaction

The chlorine evolution reaction (CER) has practical applications in the chlor-alkali industry and electrochemical wastewater treatment. Efficient, stable, and cost-effective electrodes are critical for energy efficient chlorine production, water disinfection, and wastewater treatment. These practical applications require an in-depth understanding of the catalytic mechanism of chlorine evolution, the need for lower-cost electrode materials, and improvements in electrode design at the atomic scale. Herein, we examine factors controlling activity, selectivity, and stability of alternative CER electrodes and provide mechanistic insights for achieving improvements in performance and durability. Steric effects of crystal structure and intermetallic electron polarization provide insights for understanding and tuning the electrode activity and selectivity. Additional insight into electrode deactivation mechanisms was gained by employing model material systems under controlled conditions. Herein, we explore viable strategies for the development of more efficient noble-metal-free CER electrodes for use in a variety of practical applications.

Electrochemical Treatment of Wastewater by ElectroFenton, Photo‐ElectroFenton, Pressurized‐ElectroFenton and Pressurized Photo ElectroFenton: A First Comparison of these Innovative Routes

AbstractIn the last few years increasing attention has been devoted to the utilization of electroFenton (EF) and EF based technologies for the treatment of wastewater polluted by recalcitrant organics. It has been shown that the performances of EF can be strongly improved using ultraviolet (UV) irradiation, e. g., by the photo‐electroFenton (PEF) method, or pressurized air or oxygen, e. g., by the pressurized‐electroFenton (PrEF) one. Although several studies were carried out on the degradation of many organic pollutants using EF, PEF or PrEF, a systematic comparison between PEF and PrEF was never reported as well as the possibility to couple the irradiation with pressurized air. In this study the performances of EF, PEF and PrEF were systematically compared using synthetic solutions of three model organic substrates (e. g., formic acid, oxalic acid and Acid Orange 7). In addition, the pressurized‐photo‐electroFenton (PrPEF) process was proposed for the first time.

Ultrasound-assisted electrochemical treatment of cosmetic industry wastewater: Mechanistic and detoxification analysis

This study aims to investigate the mineralization of cosmetics producing industrial wastewater (CW) using sono-electrochemical (US-EC) treatments. The influence of operating parameters such as current density (j), electrolyte (Na2SO4) concentration (m), initial pH (pHo), and ultrasonic power was investigated using Ti/RuO2 dimensionally stable electrodes. The results demonstrated 80.9% chemical oxygen demand (COD) removal efficiency, 433.5 kWh (kg COD removed)−1 of specific energy consumption at the optimum conditions of P = 100 W, j = 213 A m−2, pHo= 7.6 (natural pH), and m = 1.5 g L−1. With the application of ultrasound, COD removal efficiency increases from 60.2% to 80.9%, with a synergistic effect of 1.1. Kinetics study analysis confirms that mineralization follows the nth order kinetics model. In the presence of ultrasound, the performance of electrochemical treatment gets enhanced due to higher electron transfer, the enhanced production of •OH radicals, and sulfate radicals (SO4•−). The pathway for the degradation of the compound was suggested by quadrupole time of flight mass spectroscopy (QToF-MS). The operating cost of the process was also evaluated to establish the applicability of the US-EC process at the industrial scale.

Performance of anode materials in electrochemical treatment system for indigo dyeing wastewater

PurposeThis study aims to explore suitable anode materials used in the electrochemical system for indigo dyeing wastewater, to achieve optimal treatment performances.Design/methodology/approachThe single factor experiment was used to explore the optimum process parameters for electrochemical decolorization of indigo dyeing wastewater by changing the applied voltage, electrolysis time and electrolyte concentration. At the voltage of 9 V, the morphology of flocs with different electrolytic times was observed and the effect of electrolyte concentration on decolorization rate in two electrolyte systems was also investigated. Further analysis of chemical oxygen demand (COD) removal rate, anode weight loss and sediment quantity after electrochemical treatment of indigo dyeing wastewater were carried out.FindingsComprehensive considering the decolorization degree and COD removal rate of the wastewater, the aluminum electrode showed the best treatment effect among several common anode materials. With aluminum electrode as an anode, under conditions of applied voltage of 9 V, electrolysis time of 40 min and sodium sulfate concentration of 6 g/L, the decolorization percentage obtained was of 94.59% and the COD removal rate reached at 84.53%.Research limitations/implicationsIn the electrochemical treatment of indigo dyeing wastewater, the aluminum electrode was found as an ideal anode material, which provided a reference for the choice of anodes. The electrodes used in this study were homogenous material and the composite material anode needed to be further researched.Practical implicationsIt provided an effective and practical anode material choice for electrochemical degradation of indigo dyeing wastewater.Originality/valueCombined with the influence of applied voltage, electrolysis time and electrolyte concentration and anode materials on decolorization degree and COD removal rate of indigo dyeing wastewater, providing a better electrochemical treatment system for dyehouse effluent.

Embedding wasted hairs in Ti/PbO2 anode for efficient and sustainable electrochemical oxidation of organic wastewater

Despite of the hazardous risk of Pb2+ leakage, lead dioxide has been attributed as a quasi-ideal anode material with high oxygen evolution potential, excellent conductivity, good stability and low cost in electrochemical oxidation wastewater treatment technique. In this study, a novel Ti/PbO2 anode was fabricated by embedding raw materials that are readily and cheaply available, i.e., hairs. The structure-activity relationship of the new electrode was firstly revealed by material and electrochemical characterizations. Then different levels of pollutants (azo dye, phenol and maleic acid) were used to investigate the electrochemical oxidation performance of the new electrode. Finally, the accelerated electrode lifetime and Pb2+ leakage tests were carried out. Results showed that the embedded hairs changed the preferential crystallographic orientation of PbO2 and decreased the grain size. Hairs introduced additional roughness and active sites, and decreased the electrode impedance, especially under 5 mg/cm2 of embedding amount. The removal efficiencies of different target pollutants were enhanced more or less by embedding appropriate amount of hairs, depending on the current density, but loading excessive hairs had a negative effect. The accumulation of intermediate products during phenol degradation was also changed by the hairs. The new electrode could undergo ∼550 h of harsh electrolysis. It is also relieved that the Pb2+ leakage was found to be suppressed during this long-term electrolysis process.

Ultrasound-Induced Intensification of Electrochemical Treatment of Bulk Drug Pharmaceutical Wastewater

Ultrasound-Induced Intensification of Electrochemical Treatment of Bulk Drug Pharmaceutical Wastewater

Progress in research and development of particle electrodes for three-dimensional electrochemical treatment of wastewater: a review.

A three-dimensional (3D) electrochemical technology is regarded as a very effective industrial wastewater treatment method as it has high treatment efficiency, high current efficiency, and low energy consumption, and especially can completely mineralize nonbiodegradable organic pollutants. The core of the 3D electrochemical technology is a particle electrode, and the particle electrode plays several important roles for removing pollutants during the electrochemical reaction process. Many types of particle electrodes have been developed and used for different types of wastewater treatment. In this paper, a comprehensive review on the research and development of particle electrodes of the 3D electrochemical reactors for wastewater treatment is conducted. Specifically, the role that the particle electrode plays during the 3D electrochemical treatment of wastewater is thoroughly investigated and systematized. In addition, the different types of particle electrodes used in the 3D electrochemical wastewater treatment are classified into several types according to the presence or absence of a catalyst and the main components of the particle electrode or carrier. Also, focusing on the recent research results, the structural characteristics, performance, advantages and defects, and the role of catalyst components of each particle electrodes are evaluated. Finally, the direction and prospect of future research on the particle electrode is presented.

Catalyst Formation and In Operando Monitoring of the Electrocatalytic Activity in Flow Reactors.

Flow reactors are of increasing importance and have become crucial devices due to their wide application in chemical synthesis, electrochemical hydrogen evolution reaction (HER), or electrochemical waste water treatment. In many of these applications, catalyst materials such as transition-metal chalcogenides (TMCs) for the HER, provide the desired electrochemical reactivity for the HER. Generally, the flow electrolyzers' performance is evaluated as the overall output, but the decrease in activity of the electrolyzer is due to localized failure of the catalyst. Herein, we present a method for the spatially resolved (tens of micrometers) In Operando analysis of the catalytic activity under real operation conditions as well as the localized deposition of the catalyst in an operating model flow reactor. For these purposes, scanning electrochemical microscopy was applied for MoSx catalyst deposition and for localized tracking of the TMC activity with a resolution of 25 μm. This approach offers detailed information about the catalytic performance and should find broad application for the characterization and optimization of flow reactor catalysis under real operational conditions.

Mixed metal oxide anodes used for the electrochemical degradation of a real mixed industrial wastewater

Mixed industrial wastewaters are often highly contaminated with heavy metals and organic pollutants. Treating these mixed wastewaters requires many stagewise unit operations. Our work investigates using an electrochemical oxidation-in-situ coagulation (ECO-IC) process as a pre-treatment step toward the efficient treatment of real mixed industrial wastewater rich with heavy metals and organic contaminants. The process degraded organic contaminants in the wastewater via anodic electrochemical oxidation. Simultaneously, heavy metals were precipitated in the solution by coagulants (iron hydroxides) formed in-situ by cathode-generated hydroxyl ions reacting with the significant amounts of dissolved iron in the wastewater. IrO2–RuO2 mixed metal oxide anodes were identified as the best electrodes for organic compound degradation demonstrating 97% degradation of methyl orange (MO) as a model compound within 15 min. These anodes were used to treat real industrial wastewater produced from the industrial cleaning of train tanker cars transporting industrial solvents. The electrochemical treatment experiments resulted in a treated solution with a lower heavy metal content, achieving 96% reduction in Fe and 30% reduction in As content. Only moderate decreases in organic content were observed up to a maximum of 13% reduction in total organic carbon after 1 h of treatment. Electrochemical treatment of the mixed industrial wastewater produced greater effective diameter of the suspended particles and distinct sediment, liquid, and suspended foam phases that could be easily separated for further treatment. ECO-IC shows promise as an efficient and chemical-free method to coagulate heavy metals in real industrial wastewaters and could be an effective pre-treatment in their separation.

Electrochemical treatment of dye wastewater using nickel foam electrode

Removal of dye from wastewater has been investigated using the electrocoagulation method. Batch experiment has been conducted to remove the color from synthetically prepared acid red 87dye wastewater. Stainless steel and nickel foam sheets are used as cathode and anode, respectively. The effect of some operating parameters, such as current density, initial dye concentration and supporting electrolyte concentration, on color removal has been studied. It can be observed from the present investigations that the nickel foam electrode effectively removes color from the wastewater. Nickel hydroxyl species formed during the operation and also, nickel (II) hydroxide flocs formed in a subsequent stage, trap colloidal precipitates and make solid-liquid separation easier during the flotation stage. These stages of electrocoagulation must be optimized to design an economically feasible process.

A prediction method of electrocoagulation reactor removal rate based on Long Term and Short Term Memory–Autoregressive Integrated Moving Average Model

In the process of electrochemical wastewater treatment, the removal rate of electrocoagulation reactor will be affected by various factors such as the pH value of wastewater solution, the current density, the wastewater flow rate and the initial concentration of heavy metal ions. Therefore, this study proposes a prediction method of the removal rate of the electrocoagulation reactor based on deep learning Long and Short-Term Memory (LSTM) network combined with the Autoregressive Integrated Moving Average Model (ARIMA) commonly used in engineering. Firstly, according to the concentration of heavy metal ions in the outlet and inlet solution of the reactor, the calculation formula for the removal rate of the reactor is defined. Secondly, in order to deepen the LSTM network model to analyze and learn the change trend of the historical removal rate data, the gradient value of the historical removal rate of the reactor before and after the change is extracted as its change feature value, and this feature value is taken as one of the input variables of the LSTM network model. Comprehensive analysis considered important factors such as the historical removal rate value of the reactor, the initial pH value of the wastewater solution, the voltage and current value, and the wastewater flow rate as the input variables of the LSTM deep learning network. The predicted value of the removal rate of electrocoagulation reactor is concluded by testing the combination of activation function and the number of fully connected layers, and the error compensation of the predicted value is carried out by using the ARIMA model. The effectiveness of the proposed method is verified by the industrial data collected from a wastewater treatment plant.

THERMAL PROPERTY OF CARBON RESIN ELECTRODES DEVELOPED FOR ELECTROCHEMICAL TREATMENT OF WATER AND WASTEWATERS

In this paper, thermal conductivity of carbon resin electrodes developed for electrochemical treatment of water and wastewater was investigated. Carbon resin electrodes were developed from used dry cells and resin using non-heat treatment processes. Thermal conductivity of the electrodes was measured and effects of particle size, compacting pressure, carbonisation temperature and percentage of the resin used on thermal conductivity of the electrodes were monitored using standard method through RE 890G and ALDA AVD 890G thermocouples at two different points (5cm apart). Effective thermal conductivity of the electrodes was modelled using Okazaki et al model. The study revealed that thermal conductivity of carbon resin electrodes ranged from 1.39 W/K. cm to 2.24 W/K. cm. Thermal conductivity of the material increased with decreased particle size (1.48 to 2.24 W/K. cm with 245 to 45mm) and decreased percentage resin (1.49 to 2.20 W/K. cm with 12 % to 1%), decreased with decreased compacting pressure (2.12 to 1.44 W/K. cm with 110 MN/ m2 to 60 MN/ m2) and carbonization temperature (2.12 to 1.39 W/K. cm with 260 oC to 30o C). Okazaki et al model agreed reasonably with the experimental data with correlation coefficient of 0.3206 and coefficient of determination 0.9917. It was concluded that particle size, compacting pressure, carbonization temperature and percentage resin play important role in thermal conductivity of carbon resin electrodes.

Iron (III) doped titanium dioxide coated dimensionally stable graphite anode electrode for electro-chemical treatment of domestic wastewater

Availability of clean water is of concern due to pollution and diminishing supply pollution. However, purification is possible depending on the incorporated contaminants. Domestic wastewater contains dissolved organic matter and its remediation can be done by oxidation. The best oxidation can be achieved by electron transfer the same way metabolic processes occur. This study exploited the use of a film of iron (III) doped titanium dioxide applied on an electrode which was found to be effective. Natural light conditions generated electrons that migrated through the electrode leaving behind holes which oxidized the contaminants as the excess electrons were discharged at the cathode after passing through the casted proton exchange membrane (PEM) separating the two half cells of the prepared reactor. This electrochemical method has the advantage in that the organic pollutants are oxidized to carbon dioxide with no secondary pollutants and the inorganic pollutants into insoluble matter. The assembled cell was applied to purify both synthetic and real water samples of green leafy vegetable solution from the kitchen by clarification. The clarification process was monitored by UV-Vis using distilled water as a reference to compare the light that transmitted through a sample. It was observed that the electro-oxidation process took place showing a high potential 105 mV within the first 150 min followed by degradation at a high rate. The oxidation of the organic matter was confirmed by UV-Vis analysis as well as by cyclic voltametric analysis of iron released into the solution of the synthetic samples. The electro chemical treatment of the water was then applied to purify real water samples made from a sample of 4.5 g minced of green vegetables dispersed in one liter of water (4.5 g/l). The green leafy coloured solution was clarified after 154 h of continuous oxidation. The degradation process was confirmed to be independent of intermediates or other species present in solution as it was of first order reaction kinetics. The electrochemical oxidation of organic matter in water using iron (III) doped titanium dioxide coated graphite electrode has potential application on the purification of water.

Comparative Study on Electrochemical Treatment of Cyanide Wastewater.

The electrochemical treatment of wastewater is widely used for cleaning due to its efficiency. In this paper, two-dimensional (2D) and three-dimensional (3D) electrochemical systems were used to treat cyanide wastewater. The effect of the applied voltage and the material of the main electrode on the removal of various ions and the characteristics of chemical reactions were mainly studied. The results show that the applied voltage was the key effect of the electrochemical treatment process. The removal of ions from the wastewater at 2 V is mainly due to the effect of electro adsorption and enrichment precipitation, while at 4 V, it is mainly due to anodization and cathodic deposition. The treatment effect of the 3D electrode system was significantly better than the 2D system. The 3D electrode system by used granular activated carbon as the particle electrode, with the carbon filled stainless mesh (CM) and coal based electrode (CB) as the main electrode, the treatment effect were better than main electrode of stainless steel mesh (M). The 3D system with CB as the main electrode had an applied voltage of 4 V, a treatment time of 5 h, plate spacing of 10 mm, and the dosage of activated carbon particles was 2 g. The removal rates of CNT, Cu, Zn, CN−, and SCN− were 94.14, 94.53, 98.14, 98.55, and 93.13%, respectively. The main reaction in anode was the electroly oxidation of CN− and SCN−, while the electrolytic deposition of Cu, Zn, and other metal ions in the cathode surface. There were not only adsorption and electric adsorption of various ions, but also an electrolytic deposition reaction of Cu, Zn, and other metal ions on the surface of the activated carbon particle electrode. During the electrochemical reaction, the concentration of hydrogen ions near the anode increases locally, which produces the precipitation of CuSCN, Cu2Fe(CN)6, and Zn2Fe(CN)6, etc. in the solution, which are helpful for the removal of cyanide and heavy metal ions in cyanide wastewater.

A study on electrochemical oxidationof phenol for wastewater remediation

This era having been driven by the industrial revolution caused a major outbreak of pollutant quantity in water. Phenol is one of the most toxic chemicals and electrochemical oxidation is undoubtedly one of the attractive alternatives for the degradation of phenol available in wastewater. The present study aims at finding the best combination of operating parameters maximizing the phenol removal by electrochemical treatment of phenolic wastewater. Synthetically prepared phenol solution of various concentrations was electrochemically oxidized using a cylindrical flow cell. It was found that initial phenol concentration, time, current density, and salt concentration have a strong influence on the removal of phenol. Furthermore, based on the results obtained, a second-order regression model was proposed to predict the responses. Analysis of variance (ANOVA) result and the R2 value of the model shows that the model could very well predict the realistic situation. According to the prediction by the model, the best set of operating conditions giving the complete removal of phenol is Time: 9.27 min, Current density: 3.58 A/dm2, supporting Electrolyte concentration: 3.29 g/L, and Initial Concentration: 13.64 ppm.

Electro-enhanced chlorine-mediated ammonium nitrogen removal triggered by an optimized catalytic anode for sustainable saline wastewater treatment.

Electrochemical technology has unique superiorities in chlorine-mediated pollutant oxidation, but has limited application in saline wastewater treatment due to inadequate efficiency and high energy consumption. To promote electrochemical oxidation capacity, a novel but low-cost electrode containing TiO2/Co-WO3/SiC was prepared and optimized, achieving highly efficient chlorine-mediated ammonium nitrogen oxidation (98.3±2.2% in 120min, with initial NH4+-N of 10.2±0.5mgL-1) in a simple electrochemical system with supplied current density only at 1.00mAcm-2. Comparing with unmodified carbon fiber cloth, the catalytic anode achieved 96.0% nitrogen selectivity, enhanced the system current efficiency by 20.6% and reduced the energy consumption by 54.4%, making the treatment of simulated mariculture wastewater both energy-saving (36.5±2.8kWhkg-1 NH4+-N) and cost-effective (1.45US$m-3), comparing with previously reported electrochemical processes (54-622kWhkg-1 NH4+-N). The nitrogen content (<1mgL-1) in the treated wastewater, containing only 0.18mgL-1 NH4+-N, meets the discharge standard of mariculture wastewater. The promoted electrochemical oxidation should be attributed to the chloride derived species (HOCl and ClO-) and related active species (Cl, ClO, OH, etc.). This easily prepared and reusable catalytic electrode is a promising alternative to conventional anode materials in sustainable electrochemical treatment of saline wastewater.