A comparative study of electrocoagulation and electro-Fenton for treatment of wastewater from liquid organic fertilizer plant

Analysis of factors influencing on Electro-Fenton and research on combination technology (II): a review

The principle of Fenton reagent is to produce ·OH by mixing H2O2 and Fe2+ to realize the oxidation of organic pollutants, although Fenton reagent has the advantages of non-toxicity and short reaction time, but there are its related defects. The Fenton-like technology has been widely studied because of its various forms and better results than the traditional Fenton technology in terms of pollutant degradation efficiency. This paper reviews the electro-Fenton technology among the Fenton-like technologies and provides an overview of the homogeneous electro-Fenton. It also focuses on summarizing the effects of factors such as H2O2, reactant concentration, reactor volume and electrode quality, reaction time and voltage (potential) on the efficiency of electro-Fenton process. It is shown that appropriate enhancement of H2O2 concentration, voltage (potential) and reaction volume can help to improve the process efficiency; the process efficiency also can be improved by increasing the reaction time and electrode quality. Feeding modes of H2O2 have different effects on process efficiency. Finally, a considerable number of experimental studies have shown that the combination of electro-Fenton with ultrasound, anodic oxidation and electrocoagulation technologies is superior to the single electro-Fenton process in terms of pollutant degradation.

A Fenton-based approach at neutral and un-conditioned pH for recalcitrant COD removal in tannery wastewater: Experimental test and sludge characterization

The combination of raw animal skin manufacturing processes involves the use of large amounts of chemicals, resulting in the generation of complex and highly polluted tannery wastewater. In this context, the high concentration of chloride in tannery wastewater represents a crucial bottleneck. Indeed, sodium chloride, commonly used in tannery industry to prevent skin rot, increases the concentration of chlorides up to 50 %. At the same time, most of the advanced oxidation processes usually employed in tannery wastewater treatment to remove recalcitrant COD involve the use of conditioning agents, thus increasing the overall concentration of chlorides in the treated effluent. The aim of this study was to evaluate the electrochemical peroxidation process (ECP) efficiency in the treatment of tannery wastewater without changing pH, to improve Fenton technology by avoiding the use of chemicals. The influence of different electric currents on COD and color removal was investigated. The characterization of the produced sludge was conducted through FTIR, SEM and XRD analysis, exploring the morphology and composition of precipitate, depending on the applied current. Although an electrical current of 750 mA yields the highest COD and color removal efficiency (69.7 % and 97.8 %, respectively), 500 mA can be considered the best compromise because of energy consumptions. Iron oxides and hydroxides were generated during the ECP process, playing the role of coagulants through the absorption of organic and inorganic contaminants. The consumption of energy increased as a function of time and applied current; however, cost analysis showed that the electrodes contributed the most to the total cost of the process. In authors' knowledge, the application of ECP process as a tertiary treatment for the removal of recalcitrant COD in tannery wastewater represents a novelty in the literature and the results obtained can be considered as the basis for scaling up the process in future research.

Electrochemical-based approaches for the treatment of pharmaceuticals and personal care products in wastewater

In recent times, emerging contaminants (ECs) like pharmaceuticals and personal care products (PPCPs) in water and wastewater have become a major concern in the environment. Electrochemical treatment technologies proved to be more efficient to degrade or remove PPCPs present in the wastewater. Electrochemical treatment technologies have been the subject of intense research for the past few years. Attention has been given to electro-oxidation and electro-coagulation by industries and researchers, indicating their potential to remediate PPCPs and mineralization of organic and inorganic contaminants present in wastewater. However, difficulties arise in the successful operation of scaled-up systems. Hence, researchers have identified the need to integrate electrochemical technology with other treatment technologies, particularly advanced oxidation processes (AOPs). Integration of technologies addresses the limitation of indiviual technologies. The major drawbacks like formation of undesired or toxic intermediates, s, energy expenses, and process efficacy influenced by the type of wastewater etc., can be reduced in the combined processes. The review discusses the integration of electrochemical technology with various AOPs, like photo-Fenton, ozonation, UV/H2O2, O3/UV/H2O2, etc., as an efficient way to generate powerful radicals and augment the degradation of organic and inorganic pollutants. The processes are targeted for PPCPs such as ibuprofen, paracetamol, polyparaben and carbamezapine. The discussion concerns itself with the various advantages/disadvantages, reaction mechanisms, factors involved, and cost estimation of the individual and integrated technologies. The synergistic effect of the integrated technology is discussed in detail and remarks concerning the prospects subject to the investigation are also stated.

Challenges and Future Roadmaps in Heterogeneous Electro-Fenton Process for Wastewater Treatment

The efficiency of heterogeneous electro-Fenton technology on the degradation of recalcitrant organic pollutants in wastewater is glaringly obvious. This green technology can be effectively harnessed for addressing ever-increasing water-related challenges. Due to its outstanding performance, eco-friendliness, easy automation, and operability over a wide range of pH, it has garnered significant attention from different wastewater treatment research communities. This review paper briefly discusses the principal mechanism of the electro-Fenton process, the crucial properties of a highly efficient heterogeneous catalyst, the heterogeneous electro-Fenton system enabled with Fe-functionalized cathodic materials, and its essential operating parameters. Moreover, the authors comprehensively explored the major challenges that prevent the commercialization of the electro-Fenton process and propose future research pathways to countervail those disconcerting challenges. Synthesizing heterogeneous catalysts by application of advanced materials for maximizing their reusability and stability, the full realization of H2O2 activation mechanism, conduction of life-cycle assessment to explore environmental footprints and potential adverse effects of side-products, scale-up from lab-scale to industrial scale, and better reactor design, fabrication of electrodes with state-of-the-art technologies, using the electro-Fenton process for treatment of biological contaminants, application of different effective cells in the electro-Fenton process, hybridization of the electro-Fenton with other wastewater treatments technologies and full-scale analysis of economic costs are key recommendations which deserve considerable scholarly attention. Finally, it concludes that by implementing all the abovementioned gaps, the commercialization of electro-Fenton technology would be a realistic goal.

Graphical Abstract

A comprehensive review on green perspectives of electrocoagulation integrated with advanced processes for effective pollutants removal from water environment

The rapidly expanding global energy demand is forcing a release of regulated pollutants into water that is threatening human health. Among various wastewater remediating processes, electrocoagulation (EC) has scored a monumental success over conventional processes because it combines coagulation, sedimentation, floatation and electrochemical oxidation processes that can effectively decimate numerous stubborn pollutants. The EC processes have gained some attention through various academic and industrial publications, however critical evaluation of EC processes, choices of EC processes for various pollutants, process parameters, mechanisms, commercial EC technologies and performance enhancement via other degradation processes (DPs) integration have not been comprehensively covered to date. Therefore, the major objective of this paper is to provide a comprehensive review of 20 years of literature covering EC fundamentals, key process factors for a reactor design, process implementation, current challenges and performance enhancement by coupling EC with pivotal pollutant DPs including, electro/photo-Fenton (E/P-F), photocatalysis, sono-chemical treatment, ozonation, indirect electrochemical/advanced oxidation (AO), and biosorption that have substantially reduced metals, pathogens, toxic compound BOD, COD, colors in wastewater. The results suggest that the optimum treatment time, current density, pulse frequency, shaking speed and spaced electrode improve the pollutants removal efficiency. An elegant process design can prevent electrode passivation which is a critical limitation of EC technology. EC coupling (up or downstream) with other DPs has resulted in the removal of organic pollutants and heavy metals with a 20% improved efficiency by EC-EF, removal of 85.5% suspended solid, 76.2% turbidity, 88.9% BOD, 79.7% COD and 93% color by EC-electroflotation, 100% decolorization by EC-electrochemical-AO, reduction of 78% COD, 81% BOD, 97% color by EC-ozonation and removal of 94% ammonia, 94% BOD, 95% turbidity, >98% phosphorus by aerated EC and peroxicoagulation. The major wastewater purification achievements, future potential and challenges are described to model the future EC integrated systems.

Electrocoagulation and electrooxidation technologies for pesticide removal from water or wastewater: A review

Pesticides are known to be threats to the environment and human health. Excessive use of pesticides in agricultural practice can contaminate water bodies, leading to cancer, asthma, neurological disorders, reproductive defects, and hormonal disruption. Electrochemical methods such as electrocoagulation and electrooxidation can be used for pesticide removal due to their numerous advantages such as high efficiency, less sludge production, and low operational cost. During electrocoagulation, dissolution of anode metals results in metal hydroxide complexes, which precipitate with the contaminant present in the reactor. Simultaneously, electro-flotation occurs at the cathode and results in the evolution of hydrogen gas bubbles, leading to flotation of floc to the top surface of the reactor. This review focuses on the removal mechanisms, kinetics, modeling, effects of influencing factors, and sludge characterization of pesticide removal using electrocoagulation and electrooxidation. Major influencing factors include cell configuration, electrode material, current density, pH, supporting electrolyte concentration. In general, aluminum and iron are the most common electrodes used for pesticide removal using electrocoagulation, while boron-doped diamond was used to a far greater extent as the electrode in electrooxidation studies. Greater than 99% removal efficiency was observed in both processes. Overall, this review summarizes the use of electrochemical methods for pesticide removal and offers valuable information to researchers in this area of study.

The Effect of Arsenic on the Photocatalytic Removal of Methyl Tet Butyl Ether (MTBE) Using Fe2O3/MgO Catalyst, Modeling, and Process Optimization

MTBE is an aliphatic matter successfully removed from contaminated water by an advanced oxidation process. Additionally, arsenic is a toxic metalloid that is detected in some water supplies, such as in Iran. Concerning the oxidation potential of arsenic in an aqueous solution, it is expected that its interference in the photocatalytic removal of organic matter includes MTBE. Nevertheless, there is a lack of observation of this effect. In this study, the effect of arsenic on the photocatalytic removal of MTBE using an Fe2O3/MgO catalyst under UV radiation was investigated. Using an experimental design, modeling, and optimizing operational parameters, such as the arsenic and MTBE concentrations, catalyst dosage, pH, and reaction time, were studied. The synthesized nanocatalyst had a uniform and spherical morphological structure and contained 33.06% Fe2O3 and 45.06% MgO. The results indicate that the best model is related to the quadratic (p-value < 0.0001, R2 = 0.97) and that the effect of the MTBE concentration is greater than the others. The highest removal efficiency was taken in an initial concentration of 37.5 mg/L MTBE, 1.58 mg/L Fe2O3/MgO, pH 5, and a reaction time of 21.41 min without any As. The removal efficiency was negatively correlated with the initial MTBE concentration and pH, but it was positively associated with the Fe2O3/MgO dosage and reaction time. Finally, the presence of arsenic decreased the removal efficiency remarkably (90.90% As = 0.25 μg/L and 61% As = 500 μg/L). Consequently, MTBE was removed by the photocatalytic process caused by Fe2O3/MgO, but the presence of arsenic was introduced as a limiting factor. Therefore, pretreatment for the removal of arsenic and more details of this interference effect are suggested.

Recent progress on ultrasound-assisted electrochemical processes: A review on mechanism, reactor strategies, and applications for wastewater treatment

The electrochemical advanced oxidation processes (EAOPs) have received significant attention among the many other water and wastewater treatment technologies. However, achieving a desirable removal effect with a single technique is frequently difficult. Therefore, the integration of ultrasound technique with other processes such as electrocoagulation, electro-Fenton, and electrooxidation is a critical way to achieve effective organic pollutants decomposition from wastewater. This review paper is focused on ultrasound-assisted electrochemical (US/electrochemical) processes, so-called sonoelectrochemical processes of various organic pollutants. Emphasis was given to recently published articles for discussing the results and trends in this research area. The use of ultrasound and integration with electrochemical processes has a synergistic impact owing to the physical and chemical consequences of cavitation, resulting in enhancing the mineralization of organic pollutants. Various types of sonoelectrochemical reactors (batch and continuous) employed in the US/electrochemical processes were reviewed. In addition, the strategies to avoid passivation, enhanced generation of reactive oxygen species, and mixing effect are reviewed. Finally, concluding remarks and future perspectives on this research topic are also explored and recommended.

Advanced treatment of dye manufacturing wastewater by electrocoagulation and electro-Fenton processes: Effect on COD fractions, energy consumption, and sludge analysis

This study investigated chemical oxygen demand (COD), color number (CN), and UV₂₅₄ removal from dye manufacturing wastewater via electrocoagulation (EC) and electro-Fenton (EF) processes. The effects of current density, initial pH, reaction time, and H₂O₂/COD ratio on the EC and EF processes were evaluated and optimum operating conditions were determined. The effects of EC and EF processes on COD fractions and the specific energy consumption of both processes were evaluated. Sludge analyses were conducted by organic removal to sludge ratio (ORSR) and Fourier Transform Infrared Spectroscopy spectra were assessed for characterization of generated sludge. Optimum operation conditions for the EC process were 21 mA/cm² current density, 7.3 initial pH, and 25 min reaction time while they were 21 mA/cm² current density, 3.5 initial pH, 1.25 H₂O₂/COD ratio, and 35 min reaction time for EF process. Under optimum conditions COD, CN, and UV₂₅₄ removal efficiencies were 38.5%, 90.1%, and 52.5%, respectively in EC process and 54.8%, 94.2%, and 88.1%, respectively in EF process. Both processes have a positive effect on the increase of biodegradable and soluble COD fractions. Higher ORSR and lower specific energy consumption were provided by the EF process under optimum conditions. The EF process is more effective when pollutant removal efficiencies, ORSR, and specific energy consumption are considered.

A critical review of state-of-the-art electrocoagulation technique applied to COD-rich industrial wastewaters

Electrocoagulation (EC) is one of the emerging technologies in groundwater and wastewater treatment as it combines the benefits of coagulation, sedimentation, flotation, and electrochemical oxidation processes. Extensive research efforts implementing EC technology have been executed over the last decade to treat chemical oxygen demand (COD)-rich industrial wastewaters with the aim to protect freshwater streams (e.g., rivers, lakes) from pollution. A comprehensive review of the available recent literature utilizing EC to treat wastewater with high COD levels is presented. In addition, recommendations are provided for future studies to improve the EC technology and broaden its range of application. This review paper introduces some technologies which are often adopted for industrial wastewater treatment. Then, the EC process is compared with those techniques as a treatment for COD-rich wastewater. The EC process is considered as the most privileged technology by different research groups owing to its ability to deal with abundant volumes of wastewater. After, the application of EC as a single and combined treatment for COD-rich wastewaters is thoroughly reviewed. Finally, this review attempts to highlight the potentials and limitations of EC. Related to the EC process in batch operation mode, the best operational conditions are found at 10 V and 60 min of voltage and reaction time, respectively. These last values guarantee high COD removal efficiencies of > 90%. This review also concludes that considerably large operation costs of the EC process appears to be the serious drawback and renders it as an unfeasible approach for handling of COD rich wastewaters. In the end, this review has attempted to highlights the potential and limitation of EC and suggests that vast notably research in the field of continuous flow EC system is essential to introduce this technology as a convincing wastewater technology.

Electrochemical process employing scrap metal waste as electrodes for dye removal

In the present study, efficiency of electro-coagulation-flotation (EC-F) process using waste metal scrap of Al and Fe collected from construction and demolition waste of Indian Institute of Technology Madras (IIT M) campus for the removal of double azo bond dye Acid Red 66 (AR66) was studied. The key operating parameters such as current density and electrical conductivity were optimized individually with an initial dye concentration of 50 mg/L, at pH 7. Different electrode combinations and connection modes (parallel MP-P, series (MP-S, BP-S)) were tested, at pre-optimized conditions, in order to achieve better removal of AR66 dye with minimum energy consumption. Series connection in bipolar electrode mode (BP-S) showed better COD reduction from 164 mg/L to 26.2 mg/L with complete decolourization (BDL). Hybrid electrode system of Fe-Al-Fe-Al-Fe-Al showed maximum reduction of COD from 164 mg/L to 11.3 mg/L along with 86.3% TSS reduction and complete decolourization. LC-MS analysis showed the formation of intermediates with m/z 195, m/z 210.6 and m/z 159.3 due to the destruction of AR66 dye during electrolysis. Highest current efficiency (CE φ = 107%) was observed in case of hybrid electrode system compared to Al (φ = 30.1%) and Fe (φ = 98.3%) electrode system at similar operating conditions. Compared to the same electrode material as anode and cathode, use of appropriate hybrid electrode combination can improve the removal efficiency and reduce the energy consumption (ENC). The influence of aeration on the performance of the system was also studied. Aeration significantly improved the COD removal efficiency (98.3%) along with complete decolourization (100%). The use of waste metal scrap as electrodes reduced the overall cost of the treatment process from 1.6 $/m³ to 0.06 $/m³. Using waste metal scrap as electrodes not only reduces the metal accumulation in the environment but also reduces the cost of EC-F process.

Evaluation of Electrocoagulation and Activated Carbon Adsorption Techniques Used Separately or Coupled to Treat Wastewater from Industrial Dairy

This present study focuses on the evaluation of the effectiveness and the feasibility of a combined treatment between the electrocoagulation (EC) and the adsorption on an activated carbon in grains (GAC) in a continuous mode. The peculiarity of this work is that the experiments are conducted with real wastewater from an industrial dairy. This combined treatment first required an optimization of the EC followed by an adsorption. For each of these techniques, different influential operating parameters such as the current density, the reaction time, the GAC dose, the initial turbidity of water … etc., have been studied. The Turbidity and the COD have been continuously analyzed, while the phosphorus, the BOD5, TSS, nitrogen and the grease have been punctually analyzed, and this happened before and after the water treatment. The EC adsorption coupling results have shown that the addition of an appropriate dose of GAC (2 gL−1) in a separate column, increases the effectiveness of treatment; more than 98 % of reduction for the COD, the BOD5, the turbidity and the greases. A mechanism explaining the phenomena which are involved in this combined treatment is proposed. On the basis of these results of efficiency, speed, low operational cost (~ 3 $m−3 of the treated water), and in comparison with the EC used alone, the EC coupling/the adsorption GAC, could be recommended as a treatment of separation for waters at a high load in organic pollutants.

FTIR, CHNS and XRD analyses define mechanism of glyphosate herbicide removal by electrocoagulation

In this study, the performance of glyphosate removal in an electrocoagulation batch with two electrodes formed by the same metal type, consisting of aluminum, iron, steel and copper have been compared. The aim of this study intends to remove glyphosate from an aqueous solution by an electrocoagulation process using metal electrode plates, which involves electrogeneration of metal cations as coagulant agents. The production of metal cations showed an ability to bind together to form aggregates of flocs composed of a combination of glyphosate and metal oxide. Electrocoagulation using aluminum electrodes indicated a high percentage removal of glyphosate, 94.25%; followed by iron electrodes, 88.37%; steel electrodes, 62.82%; and copper electrodes, 46.69%. The treated aqueous solution was then analyzed by Fourier Transform Infrared Spectroscopy. Percentages of Carbon, Hydrogen, Nitrogen, Sulfur remaining in the treated aqueous solution after the electrocoagulation process have been determined. The treated water and sludge were characterized and the mechanism of the overall process was concluded as an outcome. An X-Ray Diffraction analysis of dried sludge confirmed that new polymeric compounds were formed during the treatment. The sludge composed of new compounds were also verified the removals. This study revealed that an electrocoagulation process using metal electrodes is reliable and efficient.

Sequential "electrochemical peroxidation - Electro-Fenton" process for anaerobic sludge treatment

In this study, we present a sequential electrochemical process for integral treatment of anaerobic sludge, combining for the first time electrochemical peroxidation (ECP) and electro-Fenton (EF). In the first step, ECP (consisting of H₂O₂-assisted electrocoagulation with Fe electrodes) was applied as a conditioning and stabilizing method, whose synergistic electrocoagulation/Fenton oxidation effects considerably reduced the COD, TOC and total suspended solids (TSS) by 89.3%, 75.4% and 85.6%, respectively, under optimized conditions (initial pH of 5, [H₂O₂]/[Fe²⁺] dose ratio of 5, 15.38 mA cm^-2 and 2 h treatment). Furthermore, total coliforms were completely killed within the first hour of treatment. In the second step, EF was successfully applied to mineralize the remaining organic fraction in the liquid effluent after dewatering, achieving 91.6% and 87.2% of COD and TOC removal, respectively, after 4 h of treatment under optimal conditions (pH 3 and 25 mA cm^-2), while almost total COD and TOC removal was attained in 8 h. The Fe sludge generated at the end of the ECP treatment was easily dewatered by filtration and 20.9 g of nutrient-rich dry sludge were produced. The overall cost of the ECP-EF treatment was S$ 0.05 L^-1 sludge. The combined effects of coagulation and Fenton oxidation during ECP revealed that the treatment efficiency is strongly dependent on the rheological properties of the sludge sample.

Treatment of canola-oil refinery effluent using electrochemical methods: A comparison between combined electrocoagulation + electrooxidation and electrochemical peroxidation methods

A comparative study of combined electrocoagulation (EC) + electrooxidation (EO) and electrochemical peroxidation (ECP) treatment processes were carried out to treat canola oil refinery (COR) wastewaters. The effect of applied current density and operation time in the removal of organic pollutants were investigated and discussed. Total chemical oxygen demand (TCOD), soluble chemical oxygen demand (sCOD), total organic carbon (TOC), dissolved organic carbon (DOC) and total suspended solids (TSS) were measured. Using only EC process was found to be significantly successful in removing suspended and colloidal pollutants and could remove more than 90% TCOD and 80% of TOC at current densities between 0.91 and 13.66 mA cm^-2. From the statistical model, the optimized conditions for TCOD at a current density of 7.61 mA cm^-2 and TOC at 7.99 mA cm^-2 under 40 min operation, validated to remove 93.45% and 94.5% respectively. However, the maximum removal of dissolved organic pollutants was relatively low in EC process and reported to be 75% for sCOD and 74% for DOC. Therefore, EC + EO process were run to increase the removal of sCOD and DOC to 99 and 95%, respectively. On the other hand, treatment using ECP process achieved a removal of sCOD and DOC between 77 and 86%. TSS were removed completely in both EC + EO and ECP processes. A statistical model was applied to compare the performance of two methods and found that the combined EC + EO process provided lightly better treatment compared to ECP method.

A novel electro-coagulation-Fenton for energy efficient cyanobacteria and cyanotoxins removal without chemical addition

Harmful cyanobacterial bloom is a serious threat to global aquatic ecology and drinking water safety. Electro-Fenton (EF) has emerged as an efficient process for cyanobacteria and cyanotoxins removal, but high consumption of energy and chemicals remain a major bottleneck. This study presents a novel convertible three-electrodes Electro-Coagulation-Fenton process for cyanobacteria and cyanotoxins removal with low energy consumption and no chemicals addition. We for the first time demonstrated the freely alternating between Electrocoagulation (EC) and EF by switching electrodes. The optimal aerated EC was operated at pH 8 and 100 mA to remove 91 ± 2% of cyanobaterial cells and 15% of Microcystins (MCs). Coagulants generated in EC were adsorbed on cyanobacterial cells to form a protect layer against algae disruption and cyanotoxins releasing. Residual MCs and cyanobaterial cells were completely mineralized by EF at 28 mA with iron ions and H₂O₂ generated in-situ. Compare to traditional EF, the optimal Electro-Coagulation-Fenton process increased total organic carbon (TOC) removal efficiency by 30%, yet energy consumption reduced up to 92%. The novel Electro-Coagulation-Fenton process is a promising technology for the efficient treatment of the mixture of suspended solid pollutants and persistent organic pollutants in one system with low energy consumption.

Sequential application of Fenton and ozone-based oxidation process for the abatement of Ni-EDTA containing nickel plating effluents

Treatment of Ni-EDTA in industrial nickel plating effluents was investigated by integrated application of Fenton and ozone-based oxidation processes. Determination of integrated sequence found that Fenton oxidation presented higher apparent kinetic rate constant of Ni-EDTA oxidation and capacity for contamination load than ozone-based oxidation process, the latter, however, was favorable to guarantee the further mineralization of organic substances, especially at a low concentration. Serial-connection mode of two oxidation processes was appraised, Fenton effluent after treated by hydroxide precipitation and filtration negatively affected the overall performance of the sequential system, as evidenced by the removal efficiencies of Ni²⁺ and TOC dropping from 99.8% to 98.7%, and from 74.8% to 66.6%, respectively. As a comparison, O₃/Fe²⁺ oxidation process was proved to be more effective than other processes (e.g. O₃-Fe²⁺, O₃/H₂O₂/Fe²⁺, O₃/H₂O₂-Fe²⁺), and the final effluent Ni²⁺ concentration could satisfied the discharge standard (<0.1 mg L^-1, China) under the optimal conditions (H₂O₂ dosage of 1.0 mL L^-1, Fe²⁺: H₂O₂ mole ratio of 1.46, and reaction time of 10 min for Fenton reaction, initial influent pH of 3.0, O₃ dosage of 252 mg L^-1, Fe²⁺ of 150 mg L^-1, and reaction time of 30 min for O₃/Fe²⁺ oxidation). Furthermore, pilot-scale test was carried out to study the practical treatability towards the real nickel plating effluent, revealing the effective removal of some other co-existence contaminations. And Fenton reaction has contributed most, with the percentage ranging from 72.41% to 93.76%. The economic cost advantage made it a promising alternative to the continuous Fenton oxidation.

Simultaneous decomplexation in blended Cu(II)/Ni(II)-EDTA systems by electro-Fenton process using iron sacrificing electrodes

This research explored the application of electro-Fenton (E-Fenton) technique for the simultaneous decomplexation in blended Cu(II)/Ni(II)-EDTA systems by using iron sacrificing electrodes. Standard discharge (0.3 mg L^-1 for Cu and 0.1 mg L^-1 for Ni in China) could be achieved after 30 min reaction under the optimum conditions (i.e. initial solution pH of 2.0, H₂O₂ dosage of 6 mL L^-1 h^-1, current density of 20 mA/cm², inter-electrode distance of 2 cm, and sulfate electrolyte concentration of 2000 mg L^-1). The distinct differences in apparent kinetic rate constants (k_app) and intermediate removal efficiencies corresponding to mere and blended systems indicated the mutual promotion effect toward the decomplexation between Cu(II) and Ni(II). Massive accumulation of Fe(Ⅲ) favored the further removal of Cu(II) and Ni(II) by metal ion substitution. Species distribution results demonstrated that the decomplexation of metal-EDTA in E-Fenton process was mainly contributed to the combination of various reactions, including Fenton reaction together with the anodic oxidation, electro-coagulation (E-coagulation) and electrodeposition. Unlike hypophosphite and citrate, the presence of chlorine ion displayed favorable effects on the removal efficiencies of Cu(II) and Ni(II) at low dosage, but facilitated the ammonia nitrogen (NH₄⁺-N) removal only at high dosage.

Experimental data of electric coagulation and photo-electro-phenton process efficiency in the removal of metronidazole antibiotic from aqueous solution

Pharmaceutical products, particularly antibiotics, due to their cumulative characteristics, undesirable effects and creating drug resistances, as inevitably pollutants, poses a major concern in environmental issues. In recent years, advanced oxidation processes (AOP) have been considerably used for degradation of new and emerging pollutants such as residual medications and resistant compounds in water and wastewater. Present investigation evaluates the removal of metronidazole from aqueous solution by electro coagulation and photoelectrophenton processes. The data will be informative for environmental agencies, pharmaceutical companies and wastewater treatment companies for choosing it as a practical oxidation advance process for treatment of water polluted by resistant material (drugs and pesticides).

Application of electrochemical peroxidation (ECP) process for waste-activated sludge stabilization and system optimization using response surface methodology (RSM)

In this study, the performance of the electrochemical peroxidation (ECP) process for removing the volatile suspended solids (VSS) content of waste-activated sludge was evaluated. The Fe²⁺ ions required by the process were obtained directly from iron electrodes in the system. The performance of the ECP process was investigated in various operational conditions employing a laboratory-scale pilot setup and optimized by response surface methodology (RSM). According to the results, the ECP process showed its best performance when the pH value, current density, H₂O₂ concentration and the retention time were 3, 3.2 mA/cm², 1,535 mg/L and 240 min, respectively. In these conditions, the introduced Fe²⁺ concentration was approximately 500 (mg/L) and the VSS removal efficiency about 74%. Moreover, the results of the microbial characteristics of the raw and the stabilized sludge demonstrated that the ECP process is able to remove close to 99.9% of the coliforms in the raw sludge during the stabilization process. The energy consumption evaluation showed that the required energy of the ECP reactor (about 1.8-2.5 kWh (kg VSS removed)^-1) is considerably lower than for aerobic digestion, the conventional waste-activated sludge stabilization method (about 2-3 kWh (kg VSS removed)^-1). The RSM optimization process showed that the best operational conditions of the ECP process comply with the experimental results, and the actual and the predicted results are in good conformity with each other. This feature makes it possible to predict the introduced Fe²⁺ concentrations into the system and the VSS removal efficiency of the process precisely.

Physico-chemical treatment of liquid waste on an industrial plant for electrocoagulation

Wastewater from washing, oil separators, the metal processing and detergent industries, was tested and treated for treatment of different types of liquid waste at industrial level at Domžale-Kamnik Wastewater Treatment Plant (WWTP). The effect of implementing the electrocoagulation (EC) and flotation processes, respectively, is analysed and includes the duration of the EC implementation, voltage, number of electrodes, and chemical addition, as well as the pH effect and conductivity. The tests were performed not only on various types of liquid waste, but also on different mixtures of liquid waste. Laboratory analysis of the samples before and after EC have shown an effective reduction not only in organic loads in accordance with the COD (chemical oxygen demand) parameter, but also in mineral oil content, toxic metal concentration, and surfactants. The COD in liquid waste from the detergent industry was reduced by 73% and the content of surfactants by 64%. In liquid waste from the metal processing industry, the COD decreased by up to 95%, while the content of toxic metals decreased from 59 to 99%. Similar phenomena were shown in liquid waste from oil separators, where the COD was reduced to 33% and the concentration of mineral oils by 99%. Some of the liquid wastes were mixed together in the ratio 1:1, thus allowing testing of the operation of EC technology in heterogeneous liquid waste, where the final result proved to be effective cleaning as well. After treatment in the process of EC, the limit values of the treated water proved appropriate for discharge into the sewerage system.

Azo dyes wastewater treatment and simultaneous electricity generation in a novel process of electrolysis cell combined with microbial fuel cell

A new process of electrolysis cell (EC) coupled with microbial fuel cell (MFC) was developed here and its feasibility in methyl red (MR) wastewater treatment and simultaneous electricity generation was assessed. Results indicate that an excellent MR removal and electricity production performance was achieved, where the decolorization and COD removal efficiencies were 100% and 89.3%, respectively and a 0.56V of cell voltage output was generated. Electrolysis voltage showed a positive influence on decolorization rate (DR) but also cause a rapid decrease in current efficiency (CE). Although a low COD removal rate of 38.5% was found in EC system, biodegradability of MR solution was significantly enhanced, where the averaged DR was 85.6%. Importantly, COD removal rate in EC-MFC integrated process had a 50.8% improvement compared with the single EC system. The results obtained here would be beneficial to provide a prospective alternative for azo dyes wastewater treatment and power production.

Decolorization of distillery spent wash effluent by electro oxidation (EC and EF) and Fenton processes: A comparative study

In this study, laboratory scale experiments were performed to degrade highly concentrated organic matter in the form of color in the distillery spent wash through batch oxidative methods such as electrocoagulation (EC), electrofenton (EF) and Fenton process. The effect of corresponding operating parameters, namely initial pH: 2-10; current intensity: 1-5A; electrolysis time: 0.5-4h; agitation speed: 100-500rpm; inter-electrode distance: 0.5-4cm and Fenton's reagent dosage: 5-40mg/L was employed for optimizing the process of spent wash color removal. The performance of all the three processes was compared and assessed in terms of percentage color removal. For EC, 79% color removal was achieved using iron electrodes arranged with 0.5cm of inter-electrode space and at optimum conditions of pH 7, 5A current intensity, 300rpm agitation speed and in 2h of electrolysis time. In EF, 44% spent wash decolorization was observed using carbon (graphite) electrodes with an optimum conditions of 0.5cm inter-electrode distance, pH 3, 4A current intensity, 20mg/L FeSO4 and agitation speed of 400rpm for 3h of electrolysis time. By Fenton process, 66% decolorization was attained by Fenton process at optimized conditions of pH 3, 40mg/L of Fenton's reagent and at 500rpm of agitation speed for 4h of treatment time.

Application of the electro-Fenton process for cutting fluid mineralization

Organic compound is the main pollutant in industrial effluent. Conventional wastewater treatment processes are inefficient for the removal of toxic or non-biodegradable organic pollutants. Advanced electrochemical depollution is a very efficient and economic method, suitable when the wastewater contains toxic and recalcitrant organic pollutants. The aim of the present study was to investigate the application of the electro-Fenton (EF) process for the degradation and mineralization of a stable oil-in-water emulsion (0.01% in v/v). The effects of operating parameters such as cathode material (graphite, Ti/Pt and steel), nature (Na2SO4, NaNO3 and NaCl) and dose of electrolyte (25-75 mM), initial ferrous ions concentration (1-75 mM), current intensity (0.1-0.2 A) and operating time, on chemical oxygen demand (COD) removal efficiency, were studied. Results showed that the EF method can be used efficiently for the degradation of stable cutting oil emulsion. For considered initial conditions (bubbling compressed air at 1 L/min, 0.15 A, pH 3, [Na2SO4]=0.05 M, [FeSO4]=0.015 M, COD0=400 mg O2/L), the best removal efficiencies were obtained under the following conditions: graphite as cathode material, 180 min for treatment duration and 0.05 M [Na2SO4]. For these conditions, treatment of 250 mL of emulsion led to 93.6% of cutting fluid mineralization, which correspond to 25 mg O2/L of final COD, 19 kWh/m3 of treated wastewater and 24.039 kWh/kg of COD removal.

Polyethersulfone (PES)/cellulose acetate butyrate (CAB) composite hollow fiber membranes for BTEX separation from produced water

Polyethersulfone (PES)/cellulose acetate butyrate (CAB) composite hollow fiber membranes were prepared by dry-jet wet-spinning for BTEX (benzene, toluene, ethylbenzene and xylene) separation from oilfield produced water.

Degradation of pentachlorophenol by hydroxyl radicals and sulfate radicals using electrochemical activation of peroxomonosulfate, peroxodisulfate and hydrogen peroxide

The present study is to investigate the reactivity of free radicals (SO4(-) and HO) generated from common oxidants (peroxomonosulfate (PMS), peroxodisulfate (PDS) and hydrogen peroxide (HP)) activated by electrochemically generated Fe(2+)/Fe(3+) ions which furthermore are evaluated to destroy pentachlorophenol (PCP) in aqueous solution. The effect of solution pH and amount of oxidants (PMS, PDS and HP) in electrocoagulation (EC) on PCP degradation is analyzed in detail. The experimental results reveal that, optimum initial solution pH is 4.5 and PMS is more efficient oxidant addition in EC. 75% PCP degradation is achieved at 60min electrolysis time from PMS assisted EC. According to the first order rate constant, faster PCP degradation rate is obtained by PMS assisted EC. The PCP degradation rate by oxidant assisted EC is observed in the following order: EC/PMS>EC/PDS>EC/HP>EC. Further to identify the influences of experimental factors involved in PCP degradation by oxidant assisted EC, an experimental design based on an orthogonal array (OA) L9 (3(3)) is proposed using Taguchi method. The factors that most significantly affect the process robustness are identified as A (oxidant) and B (pH) which together account for nearly 86% of the variance.