Electrochemical Oxidation Technology Research Articles

Electrochemical oxidative degradation of indigo wastewater based on chlorine-containing system

PurposeIn this study, the oxidative degradation performance of indigo wastewater based on electrochemical systems was explored. The decolourization degrees, removal rate of chemical oxygen demand and biochemical oxygen demand of the indigo wastewater after degradation were evaluated and optimized treatment conditions being obtained.Design/methodology/approachThe single factor method was first used to select the electrolyte system and electrode materials. Then the response surface analysis based on Box–Behnken Design was chosen to determine the influence of four independent variables such as FeCl3 concentration, NaCl concentration, decolourization time and voltage on the degradation efficiency.FindingsOn the basis of single factor experiment, the electrode material of stainless steel was selected in the double cell, and the indigo wastewater was electrolyzed with FeCl3 and NaCl electrolytes. The process conditions of electrochemical degradation of indigo wastewater were optimized by response surface analysis: the concentration of FeCl3 and NaCl was of 16 and 9 g/L, respectively, with a decolourization time of 50 min, voltage of 10 V and decolourization percentage of 98.94. The maximum removal rate of chemical oxygen demand reached 75.46 per cent. The highest ratio of B/C was 3.77, which was considered to be more biodegradable.Research limitations/implicationsDyeing wastewater is bringing out more and more pollution problems to the environment. However, there are some shortcomings in traditional technologies such as adsorption and filtration. As a kind of efficient and clean water treatment technology, electrochemical oxidation has been applied to the treatments of various types of wastewater. The decolourization and degradation of indigo wastewater is taken as an example to provide reference for the treatment of wastewater in actual plants.Practical implicationsThe developed method provided a simple and practical solution for efficiently degrading indigo wastewater.Originality/valueThe method for the electrochemical oxidation technology was novel and could find numerous applications in the degradation of printing and dyeing wastewater.

Electrochemical oxidation treatment of coal tar wastewater with lead dioxide anodes.

In this study, coal tar wastewater was treated by electrochemical oxidation technology using lead dioxide anodes. The influence of operating parameters, including applied current density, electrode gap and initial pH value, on the removal ratio of chemical oxygen demand (COD) was investigated. The results demonstrated that the COD removal ratio reached 90.5% after 3.5 h electrolysis with the current density at 3 A dm-2 and electrode gap at 1.0 cm. Correspondingly, the COD decreased from 5,125 mg L-1 to 487 mg L-1, which fitted the wastewater discharge standards of China, and the specific energy consumption (SECCOD) was 35.3 kWh kgCOD -1. Not only was the COD removal ratio only 77.1% after 2 h electrolysis but the BOD5/COD ratio of the wastewater reached 0.44, which could be biochemically treated, and the SECCOD decreased by 34.3%. Moreover, the main composition of pristine wastewater before and after 2 h electrolysis was analyzed by GC-MS, and the disappearance of macromolecules (such as ethyl-2-pyrenemethanol) and the production of small molecules (such as propane-1,3-diol) could improve the biodegradability of the wastewater. Therefore, electrochemical oxidation for 2 h is a promising alternative for pretreatment of coal tar wastewater prior to biological treatment.

Employing Electrochemical-Fenton process for conditioning and dewatering of anaerobically digested sludge: A novel approach

In this study, for the first time, the occurrence mechanism of anaerobically digested sludge conditioning for dewatering process based on Electrochemical-Fenton technology was investigated and the optimum condition has been determined to employ a lab-scale reactor. Due to the results of current studies using electrochemical and Fenton methods, a comparative economic-technical investigation has been provided accordingly. The results showed that under optimum operational condition by utilizing Electrochemical-Fenton process e.g. H2O2 = 25 mg/g DS (dry solid), Fe2+ = 15 mg/g DS, retention time = 20 min, electrolysis voltage = 11 V, the specific resistance to filterability (SRF) and time to filter (TTF) parameters reduction equal to 93.8% and 75.9% respectively. The occurrence mechanism of the sludge conditioning was determined by evaluation of extracellular polymeric substances (EPS), particle size distribution, zeta potential and bound water tests. The dry solids concentration of the conditioned sludge by Electrochemical-Fenton process was increased from 2.3% to 41% by dewatering employing filter press system. Furthermore, the estimated cost of conditioning using this method is 41.82 USD$/t DS, which is less than other investigated methods e.g. traditional Fenton process. It can be concluded that the results reached in this comprehensive and comparative study could be a suitable basis for further investigations regarding utilization of novel electrochemical advanced oxidation technologies for efficient sludge conditioning and dewatering purposes.

Stormwater disinfection using electrochemical oxidation: A feasibility investigation

Electrochemical oxidation (ECO) has shown good potential for disinfection of wastewater discharges but has not been tested for stormwater. Due to far lower salinity and chloride levels present in stormwater than in wastewaters, the knowledge so far on the ECO disinfection performance cannot simply be used for stormwater applications. This paper presents the first study on the feasibility of ECO technology for disinfection of pre-treated stormwater. Disinfection performance of E. coli was tested using a dimensional stable anode (DSA) in a series of batch experiments with synthetic stormwater of ‘typical’ chemical and microbial composition. The results showed that effective disinfection could be achieved with very low energy consumption; e.g. the current density of 1.74 mA/cm2 achieved total disinfection in 1.3 min, using only 0.018 kWh per ton of stormwater treatment. Chlorination was found to be the key disinfection mechanism, despite the synthetic stormwater containing only 9 mg/L of chloride. Real stormwater collected from three stormwater treatment systems in Melbourne was then used to validate the findings for indigenous microbe species. Disinfection below the detection limit was achieved for stormwater from the two sites where chloride levels were 9 and 200 mg/l, respectively, but not for the third site where stormwater contained only 2 mg/L chloride. Unfortunately, deterioration of the DSA anode was observed after only 8–10 h of its cumulative operation time, very likely due to high voltage that had to be applied to low saline stormwater to achieve the required current density. In conclusion, ECO was found to be a very promising low energy disinfection technology for stormwater, but far more work is needed to optimise the technology for unique stormwater conditions.

Insight into a highly efficient electrolysis-ozone process for N,N-dimethylacetamide degradation: Quantitative analysis of the role of catalytic ozonation, fenton-like and peroxone reactions

A highly efficient electrolysis catalyzed ozone (ECO) process was developed for N,N-dimethylacetamide (DMAC) degradation. The pseudo-first-order rate constants (kobs) of DMAC degradation by ECO process were 1.73–19.09 times greater than those by ozonation and electrolysis processes in a wide pH range of 3.0–10.0. Interestingly, we found O2•− could be generated from ozone decomposition by a radical chain mechanism instead of monovalent reduction of O2 in ECO system at the initial pH of 3.0. Subsequently, the H2O2 derived from O2•− could participate in Fenton-like and peroxone reactions with the released Fe2+ from iron anode and the aerated O3, respectively. Therefore, the extraordinary DMAC removal efficiency was mainly caused by the more generation of •OH through the multiple reactions of homogeneous catalytic ozonation, Fenton-like and peroxone in ECO system. Importantly, the roles of involved reactions in ECO system at various initial pH were quantitatively evaluated according to a series of trapping experiments. The results reveal that the solution pH could significantly affect the contributions of various reactions and convert the reaction mechanisms of multiple reactions in ECO system. Finally, the degradation intermediates were detected to propose a possible DMAC oxidation pathway in the ECO system. This work provides a deep insight into the quantitative analysis of the role of multiple oxidation reactions mechanism and the design of efficient electrochemical advanced oxidation technology for recalcitrant organic pollutant removal.

Oxidation of gaseous elemental mercury under ultralow voltage in a foam titanium diffusion electrochemical reactor

Flue gas from coal-fired power stations is an important source of mercury pollution. A diffusion electrochemical reactor is proposed to remove elemental mercury (Hg0) from such gas. Experiments were carried out in a noncompartmentalized column reactor with a stainless-steel mesh cathode and foam titanium anode. When the simulated gas passes through the foam titanium, Hg0 is oxidized. In the electrochemical process, Hg0 first diffuses to the gas–liquid–solid three-phase interface, and the oxidized state (Hg2+) of Hg0 enters the liquid phase after loss of electrons in the anode (solid phase). Operation at voltage of 3 V could achieve removal efficiency of 90 %. The effects of voltage, temperature, flow rate, electrolyte concentration, pH, initial concentration, and other conditions were investigated. The results show that electrochemical oxidation technology is a promising method for Hg0 emission control in flue gas from coal-fired power stations.

Treatment of highly saline RO concentrate using Scenedesmus quadricauda for enhanced removal of refractory organic matter

This study achieves a better understanding how Scenedesmus quadricauda microalgae participate in the phycoremediation of a reverse osmosis (RO) concentrate at a high salinity (8000mgCl−L−1). Algal treatment of the RO concentrate under continuous illumination resulted in a notable increase in the biodegradability of dissolved organic matter, subsequent removal of biodegradable fractions, and simultaneous removal of nutrients (N and P). This is the first time that S. quadricauda is shown to induce the degradation of polymeric organic matter in the RO concentrate, which is typically refractory to microbial decomposition. In this study, the mechanisms for algae-induced degradation were investigated by measuring the hydrogen peroxide (H2O2) released out of algal cells and dispersed in the aqueous phase. The algae-induced biodegradation process has an advantage over typical electrochemical oxidation technologies in that photo-sensitive living organisms are capable of self-repair, reproduction, and nutrient uptake. Our results indicate that the use of algae-induced oxidation is highly feasible as a safe, inexpensive technology to pre-treat non- or slowly-biodegradable organic matter in wastewater prior to downstream biological processing.

Electrochemical advanced oxidation processes as decentralized water treatment technologies to remediate domestic washing machine effluents.

Water scarcity is one of the major concerns worldwide. In order to secure this appreciated natural resource, management and development of water treatment technologies are mandatory. One feasible alternative is the consideration of water recycling/reuse at the household scale. Here, the treatment of actual washing machine effluent by electrochemical advanced oxidation processes was considered. Electrochemical oxidation and electro-Fenton technologies can be applied as decentralized small-scale water treatment devices. Therefore, efficient decolorization and total organic abatement have been followed. The results demonstrate the promising performance of solar photoelectro-Fenton process, where complete color and organic removal was attained after 240min of treatment under optimum conditions by applying a current density of 66.6mAcm-2. Thus, electrochemical technologies emerge as promising water-sustainable approaches.

Advances of the research evolution on aluminum electrochemical anodic oxidation technology

This article gives an overview on the development of aluminum anodization technique in terms of fundamental aspects and practical applications in the past decades. Besides, the formation mechanism and structural characteristics of anodic alumina films as well as the factors affected the formation of porous anodic alumina films are also discussed. Anodic aluminum oxide (AAO) prepared by the anodization method can be divided into two categories: dense anodic alumina (DAA) and porous anodic alumina (PAA). This article also summarizes the optical properties, magnetic properties, solar absorption properties, and catalytic properties of porous anodic alumina film and its applications in nanomaterials, optical materials, magnetic materials, biosensors, solar cells, and so on. In addition, future developmental trend of porous anodic alumina film is covered.

Electrolytic and electro-irradiated technologies for the removal of chloramphenicol in synthetic urine with diamond anodes

Hospital effluents are a major source for the occurrence of pharmaceuticals in the environment. In this work, the treatment of synthetic urine polluted with chloramphenicol is studied by using three different conductive-diamond electrochemical oxidation technologies: electrolysis (single electrolysis), photoelectrolysis and high-frequency ultrasound sonoelectrolysis. These technologies were evaluated at 10 and 100 mA cm−2. Results shows that not only chloramphenicol but also other organics contained in urine are completely mineralized by electrolysis. Ammonium is the main inorganic nitrogen species formed and it can react with the electrogenerated hypochlorite, favouring the formation of chloramines. These species prevent the potential formation of perchlorate from chlorides contained in urine at low current densities (10 mA cm−2) and delay its occurrence at high current densities (100 mA cm−2). On the other hand, irradiation of ultraviolet (UV) light or high-frequency ultrasound (US) produce changes in the performance of the electrolytic treatment, but these changes are not as important as in other cases of study shown in the literature. Nonetheless, the effect of electroirradiated technologies seems to be higher and depends on the type of pollutant when working at low current densities (10 mA cm−2). It is positive in the case of the degradation of the antibiotic and the uric acid and negative in the case of urea where there is a clear antagonistic effect. Production of oxidants increases with the current density although in lower ratio than expected. These results are of great importance because clearly point out that electrolytic technologies can be applied to minimize the diffuse pollution associated to pharmaceuticals before discharge into municipal sewers.

Functional group influences on the reactive azo dye decolorization performance by electrochemical oxidation and electro-Fenton technologies.

Electrochemical water treatment technologies are highly promising to achieve complete decolorization of dyebath effluents, as demonstrated by several studies reported in the literature. However, these works are focused on the treatment of one model pollutant and generalize the performances of the processes which are not transposable since they depend on the pollutant treated. Thus, in the present study, we evaluate, for the first time, the influence of different functional groups that modify the dye structure on the electrochemical process decolorization performance. The textile azo dyes Reactive Orange 16, Reactive Violet 4, Reactive Red 228, and Reactive Black 5 have been selected because they present the same molecular basis structure with different functional groups. The results demonstrate that the functional groups that reduce the nucleophilicity of the pollutant hinder the electrophilic attack of electrogenerated hydroxyl radical. Thereby, the overall decolorization efficiency is consequently reduced as well as the decolorization rate. Moreover, the presence of an additional chromophore azo bond in the molecule enhances the recalcitrant character of the azo dyes as pollutants. The formation of a larger and more stable conjugated π system increases the activation energy required for the electrophyilic attack of •OH, affecting the performance of electrochemical technologies on effluent decolorization.

Fe@Fe2O3 promoted electrochemical mineralization of atrazine via a triazinon ring opening mechanism

In this study, an electrochemical/electro-Fenton oxidation (EC/EF) system was designed to degrade atrazine, by utilizing boron-doped diamond (BDD) and Fe@Fe2O3 core-shell nanowires loaded active carbon fiber (Fe@Fe2O3/ACF) as the anode and the cathode, respectively. This EC/EF system exhibited much higher degradation rate, decholorination and mineralization efficiency of atrazine than the electrochemical (EC) and electrochemical/traditional electro-Fenton (EC/TEF) oxidation counterpart systems without Fe@Fe2O3 core-shell nanowires. Active species trapping experiment revealed that Fe@Fe2O3 could activate molecular oxygen to produce more OH through Fenton reaction, which favored the atrazine degradation. High performance liquid chromatography, high performance liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry were applied to probe the decomposition and mineralization of atrazine during this novel EC/EF process, which revealed that two intermediates of triazinons (the isomerization of hydroxylated atrazine) were generated during the electrochemical/electro-Fenton oxidation of atrazine in the presence of Fe@Fe2O3 core-shell nanowires. The experimental and theoretical calculation results suggested that atrazine might be degraded via a triazinon ring opening mechanism, while the presence of Fe@Fe2O3 notably accelerated the decholorination process, and produced more hydroxylated products to promote the generation of trazinons and the subsequent ring cleavage as well as the final complete mineralization. This work provides a deep insight into the triazine ring opening mechanism and the design of efficient electrochemical advanced oxidation technologies (EAOTs) for persistent organic pollutant removal.

元素掺杂改性电极材料在环境废水处理中的应用

电芬顿技术隶属于电化学高级氧化技术，在环境废水处理方面，其核心和关键是电极材料的元素掺杂改性。本文就电芬顿技术中阴极材料和阳极材料的研究进展以及电化学氧化效率的影响因素几个方面做了介绍，并对其发展趋势进行了展望。 Electro-Fenton technology is subordinate to advanced electrochemical oxidation technology. In the treatment of environmental wastewater, it is important to modify electrode material by element doping. In this paper, we investigated the research and development of cathode and anode materials and influence factors for the treatment of wastewater in electro-Fenton process, and its development tendency is forecast.

Electrochemical degradation of bisphenol A in chloride electrolyte—Factor analysis and mechanisms study

Electrochemical oxidation technology is a powerful method in the degradation of recalcitrant organics, due to the high oxidizing ability of active chlorine and reactive oxygen species generated in the cell. However, influencing factor analysis and intermediates detection during the electrochemical removal of organics has not been extensively studied in the chloride electrolyte. In this study, an orthogonal test array design of L16(4)3 was carried on with Pt anode in NaCl electrolyte, using the typical endocrine disruptor bisphenol A (BPA) as the model pollutant. The influencing order of the three main factors for BPA degradation rate was current density>initial organic concentration>chloride concentration, based on the analysis of variance in this experiment. This emphasized the very significance of the active chlorine and hydroxyl radicals which were closely related with the potential of the system and the applied current density. Then both organic and inorganic Cl-byproducts were determined. The concentration of chloride decreased to 9.88mM with an initial of 10mM in the 480-min electrolysis and extremely low concentration of active chlorine was produced in this system (maximized at 0.037mM) for the first set. Neither chlorate nor perchlorate was detected with the Pt anode. The factor of current density influenced greatest on the formation of chloroform due to the amount of active chlorine affected by the current density. Finally, intermediates generated in the electrolysis cell were concretely investigated. Compared with traditional chlorination, the amount of chlorinated-BPA (2, 2′-D2CBPA and T4CBPA) generated was relatively less (2.46 and 10.00μM equiv BPA), which might be due to their fast simultaneously transformation in the electrochemical system. With the isopropylidene bridge cleavage of chlorinated-BPA, one-ring aromatic compounds (2,6-dichlorophenol, 2,6-dichloro-2,5-cyclohexadiene, 2,4,6-trichlorophenol) occurred at the same time. Finally, chlorinated-BPA was totally transformed and low molecular chlorinated compounds were detected to the end of the experiment. This is one of the very few studies dealing with chlorinated organic intermediates formed in chloride electrolyte, and thus these findings may have significant technical implications for electrochemical treatment of wastewater containing BPA.

Electrochemical treatment of mature landfill leachate using Ti/RuO2–IrO2 and Al electrode: optimization and mechanism

Today, improving the elimination of refractory pollutants in landfill leachate through electrochemical oxidation technology has attracted considerable attention.

Electrochemical oxidation of perfluorinated compounds in water.

Perfluorinated compounds (PFCs) are persistent and refractory organic pollutants that have been detected in various environmental matrices and municipal wastewater. Electrochemical oxidation (EO) is a promising remediation technique for wastewater contaminated with PFCs. A number of recent studies have demonstrated that the "non-active" anodes, including boron-doped diamond, tin oxide, and lead dioxide, are effective in PFCs elimination in wastewater due to their high oxygen evolution potential. Many researchers have conducted experiments to investigate the optimal conditions (i.e., potential, current density, pH value, plate distance, initial PFCs concentration, electrolyte, and other factors) for PFCs elimination to obtain the maximal elimination efficiency and current efficiency. The EO mechanism and pathways of PFCs have been clearly elucidated, which undergo electron transfer, Kolbe decarboxylation or desulfonation, hydrolysis, and radical reaction. In addition, the safety evaluation and energy consumption evaluation of the EO technology have also been summarized to decrease toxic ion release from electrode and reduce the cost of this technique. Although the ultrasonication and hydrothermal techniques combined with the EO process can improve the removal efficiency and current efficiency significantly, these coupled techniques have not been commercialized and applied in industrial wastewater treatment. Finally, key challenges facing EO technology are listed and the directions for further research are pointed out (such as combination with other techniques, treatment for natural waters contaminated by low levels of PFCs, and reactor design).

Can electrochemical oxidation techniques really decontaminate saline dyes wastewater?

Formation of toxic chlorinated organic byproducts is of great concern when selecting electrochemical oxidation (EO) as decontamination technology for saline dye wastewater, but still not verified. To test the applicability of EO, methyl orange (MO) was used as a model dye for anodic contact glow discharge electrolysis (CGDE) and conventional electrolysis (CE) in the presence of chloride. The degradation kinetics and organic intermediates were analyzed. In the presence of chloride, the rates of dye degradation were significantly increased as CGDE and CE were applied. CE resulted in higher mineralization efficiency than CGDE which needs much energy input. Several refractory chlorinated aromatic and even aliphatic compounds were identified during MO degradation, as well as the other anthraquinone dye, alizarin red S (AR). Therefore, the issues of toxic chlorinated byproducts and energy cost should be preferentially evaluated prior to the selection of EO technologies.

Research Progress of Water Treatment by Advanced Oxidation Technology

Advanced Oxidation Technology (AOPs) is a new water treatment process, especially, for refractory organic wastewater treatment. This paper emphatically introduced the mechanism and research progress of Fenton oxidation method and Fenton method, ozone oxidation, photocatalytic oxidation, wet air oxidation, supercritical water oxidation, electrochemical oxidation, and ultrasonic oxidation technology. The cheaper and more effective catalyst and oxidant is the main development trend in the future AOPs.

Removal of Ammonia Nitrogen by Combining the Ammonia Stripping with Electrochemical Oxidation

The removal of ammonia nitrogen in simulated wastewater with 90mg/L NH4Cl was researched by ammonia stripping, electrochemical oxidation and the combination of the ammonia stripping and electrochemical oxidation. It is shown that the reduction of ammonia is enlarged with increasing of wastewater’s alkalinity during stripping. And the removal rates of ammonia nitrogen are 2.1% at pH2 and 43.1% at pH7 which is not related to the stripping time. The ammonia removal is higher efficiency in pH12 which is in the range of 45.1% and 61.4% when the stripping time is changed from 40 to 100 min. The removal rate of ammonia nitrogen is increased with the extension of electrolysis time by the way of the electrochemical oxidation. For 100min electrolysis, the ammonia removal in the cathodic and anodic compartments are 55.8% and 86.9%, respectively. Moreover, by using the ammonia stripping and electrochemical oxidation simultaneously, the ammonia removal in the cathodic and anodic compartments are up to 91.8% and 99.8% for 100min, respectively. The combining of the ammonia stripping with electrochemical oxidation technology has obviously synergistic effect in purifying ammonia nitrogen wastewater.

Reduction Efficacy of Activated Sludge by Electrochemical Oxidation

As the electrochemical oxidation technology is an effective and reliable clean technology, in this study the electrochemical oxidation activated sludge process was developed, in which the electrolysis reactor with homocentric circle arrangement electrode was installed, with Ti/RuO2 being used as reticular plates. The results showed that the electrochemical oxidation can reduce activated sludge production substantially. The lysis efficiency of activated sludge achieved was 29.98% in the experiment under the optimal oxidation conditions as follows: pH=12, 60 min of intermittent electrolysis time, working voltage of 6 V and initial VSS concentration of 4670 mg·L-1,while the SCOD and TP being released from cell lysis at the maximum of 712.2 and 33 mg·L-1 respectively; and the NH3-N also reached the maximum and presented a declining trend with operation time?, which showed that this conditions were the best for electrolysis oxidation of activated sludge.