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Contributions of electrochemical oxidation to waste-water treatment: Fundamentals and review of applications
Journal of Chemical Technology and Biotechnology
Abstract
OVERVIEW: This paper provides an overview of some fundamental aspects of electrochemical oxidation and gives updated information on the application of this technology to waste-water treatment. In recent years, electrochemical oxidation has gained increasing interest due to its outstanding technical characteristics for eliminating a wide variety of pollutants normally present in waste-waters such as refractory organic matter, nitrogen species and microorganisms.
IMPACT: The strict disposal limits and health quality standards set by legislation may be met by applying electrochemical oxidation. However, treatment costs have to be cut down before full-scale application of this technology. Deployment of electrochemical oxidation in combination with other technologies and the use of renewable sources to power this process are two steps in this direction.
APPLICATIONS: Effluents from landfill and a wide diversity of industrial effluents including the agro-industry, chemical, textile, tannery and food industry, have been effectively treated by this technology. Its high efficiency together with its disinfection capabilities makes electro-oxidation a suitable technology for water reuse programs. Copyright
... Examples of active anodes include platinum (Pt), iridium (iv) oxide (IrO2), and ruthenium (iv) oxide (RuO2) substrates [46]. As reported by Anglada et al. [64], active anodes exhibit O2 evolution potentials that are generally below 1.9 V compared to SHE. Therefore, the O2 evolution reaction is catalyzed in the anodic zone, resulting in the formation of O2 bubbles on the anode surface. ...
... Examples of active anodes include platinum (Pt), iridium (iv) oxide (IrO 2 ), and ruthenium (iv) oxide (RuO 2 ) substrates [46]. As reported by Anglada et al. [64], active anodes exhibit O 2 evolution potentials that are generally below 1.9 V compared to SHE. Therefore, the O 2 evolution reaction is catalyzed in the anodic zone, resulting in the formation of O 2 bubbles on the anode surface. ...
... Thus, for non-active electrodes, potential values vs. SHE in the range of 1.9-2.6 V are normal [64]. The boron-doped diamond (BDD) and titanium dioxide (TiO 2 ) electrodes are commonly used electrodes of this type, along with lead (iv) oxide (PbO 2 ), tin (iv) oxide (SnO 2 ), and titanium heptoxide (Ti 4 O 7 ). ...
Dairy wastewater (DW) contains a high concentration of organic and inorganic pollutants. In recent years, extensive research has been conducted to develop more efficient techniques for the treatment of DW. Electrochemical advanced oxidation processes (EAOPs) have gained significant attention among the various treatment approaches. EAOPs rely on electrochemical generation of hydroxyl radicals (•OH) which are considered highly potent oxidizing compounds for the degradation of pollutants in DW. In this paper, we provide an overview of the treatment of DW using
various EAOPs, including anodic oxidation (AO), electro-Fenton (EF), photo electro-Fenton (PEF), and solar photo electro-Fenton (SPEF) processes, both individually and in combination with other techniques. Additionally, we discuss the reactor design and operating parameters employed in EAOPs. The variation in degradation efficiency is due to different oxidizing agents produced in specific approaches and their pollutant degradation abilities. In AO process, •OH radicals generated on electrode surfaces are influenced by electrode material and current density, while EF procedures use Fe2+ to create oxidizing agents both on electrodes and in the DW solution, with degradation mechanisms being affected by Fe2+, pH, and current density; additionally, PEF and SPEF approaches enhance oxidizing component production and pollutant degradation using ultraviolet (UV) light. Integration of EAOPs with other biological processes can enhance the pollutant removal efficiency of the treatment system. There is a scope of further research to exhibit the effectiveness of EAOPs for DW treatment in large scale implementation.
... In EAOPs, a wide range of organic pollutants are eradicated through electron exchange or the generation of oxidizing radicals, primarily hydroxyl radicals ( • OH) [16]. EAOPs present several advantages over conventional methods: (I) operations can be conducted at ambient temperature and pressure, with electrochemical systems offering automation feasibility and requiring minimal floor space [17,18]; (II) EAOPs are environmentally friendly, utilizing clean reagents like electrons, and some processes, such as electro-oxidation, necessitate only electricity without further treatment for contaminant degradation [18,19]; (III) the versatility of EAOPs enables their integration with various techniques for organic pollutant removal, thereby facilitating a broad range of relevant applications [17,20]. ...
... The removal efficiency decreased from 86.6% in the absence of HCO3 − to 81.0% with a concentration of 10 mmol·L −1 at 30 min, indicating that the degradation of MNZ was hindered in the presence of HCO3 − . This outcome can be attributed to the scavenging action of HCO3 − on free radicals, resulting in the production of less reactive CO3 •− , as depicted in Equations (19) and (20) [49]. ...
The investigation into the degradation of metronidazole (MNZ), a frequently employed antibiotic, through the electrochemical activation of peroxymonosulfate (PMS) utilizing either bo-ron-doped diamond (BDD) or dimensional stable anode (DSA) as the anode, was conducted in a systematic manner. The enhancement of MNZ removal was observed with increasing current density , PMS dosage, and initial pH. Response surface methodology (RSM), based on a Box-Benken design, was utilized to evaluate the efficiency of MNZ elimination concerning current density (rang-ing from 11.1 to 33.3 mA/cm 2), initial pH (ranging from 3 to 9), PMS dosage (ranging from 1 to 5 mmol·L −1), and reaction time (ranging from 25 to 45 min). The optimal operational conditions for MNZ removal were determined as follows: a current density of 13.3 mA/cm 2 , a pH of 3.7, a PMS dosage of 2.4 mmol·L −1 , and a reaction time of 40 min. Electron paramagnetic resonance (EPR), quenching experiments, and chemical probe experiments confirmed the involvement of • OH, SO4 •− and 1 O2 radicals as the primary reactive species in MNZ degradation. The presence of HCO3 − and H2PO4 − hindered MNZ removal, whereas the presence of Cl − accelerated it. The degradation pathways of MNZ were elucidated by identifying intermediates and assessing their toxicity. Additionally , the removal efficiencies of other organic pollutants, such as sulfamethoxazole (SMX), carbam-azepine (CBZ), and nitrobenzene (NB), were compared. This study contributes to a comprehensive understanding of MNZ degradation efficiency, mechanisms, and pathways through electrochemi-cal activation of PMS employing BDD or DSA anodes, thereby offering valuable insights for the selection of wastewater treatment systems.
... Nevertheless, the typical system configuration employed in the electrochemical oxidation of wastewater promotes the desorption of chlorine, impeding its effectiveness as an oxidizing agent. Consequently, higher pH values theoretically enhance the electrooxidation of pollutants, as HClO and ClO − are relatively unaffected by gas desorption and can function as oxidizing reagents throughout the entirety of the wastewater volume (Anglada 2009). ...
... It is widely recognized that temperature has negligible impact on direct oxidation processes. However, it has been observed that mediated oxidation processes, involving inorganic electrogenerated reagents such as active chlorine and peroxodisulfate, exhibit enhanced performance as temperature rises (Anglada et al. 2009). ...
Embroidery industry wastewater contains high levels of polyvinyl alcohol (PVA), making it resistant to biodegradation and conventional treatment methods such as coagulation and adsorption. Chemical oxidation processes have been successfully used to treat PVA-containing effluents, but the high chemical demand raises significant environmental and sustainability concerns. Recent studies are focused on finding innovative and efficient chemical approaches to effectively treat PVA-containing effluents. This work used an electrooxidation process (EO) with boron-doped diamond electrodes to treat wastewater containing PVA for the first time in the literature. The effects of pH (2.0–8.0), temperature (25–45 °C), current (3.0–6.0 A), electrolyte concentration (NaCl of 3.0–8.0 g/L), and oxidation time (0–6000 min) on the removal of total organic Carbon (TOC) were investigated. The pollutant removal mechanism of the process was elucidated using high-performance size exclusion chromatography, Fourier-transform infrared, Ultraviolet–visible, and Fluorescence Spectroscopy methods. The results showed that TOC concentrations significantly dropped from 6584 to 159.10 mg/L after 10 h of treatment at 6.0 A, pH 5.01, and 25, with an estimated 97.6% removal efficiency. Characterization studies showed that much of the wastewater’s PVA is broken down, and the halogens are bound to the degraded part of the polymer. The raw wastewater used contained a wide range of pollutants (103–1010 Da). The results showed that the pollutants in the wastewater were successfully removed by EO irrespective of the molecular size. These results demonstrate the superiority of EO over treatment techniques that exhibit selectivity for pollutants with different molecular weights.
... Electro-oxidation has been used in different studies due to its numerous advantages: (i) easy operation with simple equipment; (ii) environmentally friendly process with clean reagents (electrons) and without additional chemicals; (iii) versatile technology that can be used for the removal of a wide range of contaminants, including organic pollutants, heavy metals, and microorganisms; and (iv) need of lower pressure and lower temperatures compared with non-electrochemical alternatives [61][62][63]. The main disadvantages are: (i) the need of high energy; (ii) the use of expensive materials as electrodes that can increase the initial capital cost; and (iii) electrode fouling when materials accumulate on the electrode surface [64]. The degradation efficiency is also influenced by the initial pollutant concentration. ...
... Electro-oxidation has been used in different studies due to its numerous advantages: (i) easy operation with simple equipment; (ii) environmentally friendly process with clean reagents (electrons) and without additional chemicals; (iii) versatile technology that can be used for the removal of a wide range of contaminants, including organic pollutants, heavy metals, and microorganisms; and (iv) need of lower pressure and lower temperatures compared with non-electrochemical alternatives [61][62][63]. The main disadvantages are: (i) the need of high energy; (ii) the use of expensive materials as electrodes that can increase the initial capital cost; and (iii) electrode fouling when materials accumulate on the electrode surface [64]. ...
The many pollutants detected in water represent a global environmental issue. Emerging and persistent organic pollutants are particularly difficult to remove using traditional treatment methods. Electro-oxidation and sulfate-radical-based advanced oxidation processes are innovative removal methods for these contaminants. These approaches rely on the generation of hydroxyl and sulfate radicals during electro-oxidation and sulfate activation, respectively. In addition, hybrid activation, in which these methods are combined, is interesting because of the synergistic effect of hydroxyl and sulfate radicals. Hybrid activation effectiveness in pollutant removal can be influenced by various factors, particularly the materials used for the anode. This review focuses on various organic pollutants. However, it focuses more on pharmaceutical pollutants, particularly paracetamol, as this is the most frequently detected emerging pollutant. It then discusses electro-oxidation, photocatalysis and sulfate radicals, highlighting their unique advantages and their performance for water treatment. It focuses on perovskite oxides as an anode material, with a particular interest in calcium copper titanate (CCTO), due to its unique properties. The review describes different CCTO synthesis techniques, modifications, and applications for water remediation.
... On the other hand, the Fenton process produces sludge as a byproduct, which contains iron hydroxide, which is the significant drawback of this process. Anglada, et al (2009). The biodegradation process oxidizes the dye molecules in the presence of oxygen which liberates toxic volatile compounds Morshed, et al (2012). ...
Hydroxyapatite (HAp) stands as an inorganic compound, recognized as a non-toxic, bioactive ceramic, and its composition closely resembles that of bone material. In this study, nHAp was prepared from waste oyster shells, which are biowaste rich in calcium carbonate. nHAp with its unique catalytic property can be used as an adsorbent in various fields, including wastewater treatment. nHAp with an exceptional surface adsorbent with excellent chemical stability, enabling its catalytic function. Nano hydroxyapatite doped with Zinc oxide (ZnO) by wet chemical precipitation and made into a composite with Graphene oxide (GO) by modified hummers method followed by grinding, which was taken as 9:1 ratio (nHAp/ZnO and GO) of weight, enhances its tensile and mechanical strength. The energy band gap of nHAp photocatalyst was evaluated as 3.39 eV and that of the in nHAp/ZnO/GO photocatalyst was narrowed to 1.77 eV. The ternary nanocomposites are very efficient in generating the photogenerated electrons and holes, thereby improving the degradation potential of dye effluents to by-products such as CO2 and H2O. The nanocomposites photocatalyst were characterized by FTIR, XRD, SEM, TEM, EDS, XPS, DRS, and BET techniques. The UV–visible study shows the complete dye degradation efficiency of the prepared nanocomposites photocatalyst. In this study, the prepared nanocomposites nHAp/ZnO/GO have studied their efficiency for the removal of MB dye in a batch process by varying the dosage from 0.1 to 0.5 g, and the effects of dosage variations, pH, kinetic, scavenger study were evaluated at a time interval of 30 min. The removal of dye was found to be 99% at 150 min of 0.3 g dosage and pH = 12 is most favorable as it reached the same percentage at 90 min. The as-prepared nanocomposite nHAp/ZnO/GO fits the kinetic rate constant equation and shows a pseudo-first-order reaction model. This study indicates the suitability for dye removal due to the synergistic effect and electrostatic interaction of the synthesized ternary nanocomposite, which shows the potential, socially active, low-cost-effective, eco-friendly, and safe for photocatalytic degradation of MB from wastewater.
... For instance, it is a more energy-efficient method compared to UV and ozone [16][17][18]. Moreover, it can remove a wide range of pollutants, including non-biodegradable and toxic pollutants, can operate at a wide range of pH values, and does not require the addition of chemicals [19][20][21][22][23]. ...
... La versatilidad de la electrooxidación se extiende desde la implementación básica a escala laboratorio funcionando por lotes hasta especies electrogeneradas en la solución acuosa. La utilización de un par de electrodos sumergidos produce una serie de reacciones al interior del líquido que contiene la materia orgánica, las cuales ocasionan su degradación por dos mecanismos: directo e indirecto [58], [59] . ...
El intensivo uso de colorantes que realiza la industria textil en la operación de teñido aporta un poco más de la mitad del agua residual coloreada (54 %) al medio ambiente en el mundo. El impacto negativo se produce en cuerpos acuáticos perjudicando la cadena alimenticia, la actividad fotosintética, la cantidad de oxígeno disuelto y otros aspectos. Los seres humanos expuestos también pueden contraer enfermedades desde dermatitis hasta problemas del sistema nervioso central. El tratamiento de aguas residuales coloreadas es entonces un requisito que puede realizarse por las vías física, química o biológica convencionalmente. El método electroquímico alternativo que ha propiciado interés es la oxidación electroquímica inducida con electrolitos añadidos y materiales electródicos diversos. Las publicaciones recientes indican que los electrodos de diamante dopado con boro, platino, grafito, PbO2 dopado, PbO2 sin dopar y dimensionalmente estables, alcanzan remociones de color sobresalientes superiores al 90 % y en algunos casos alrededor de 60 % de materia orgánica, cuantificada como DQO o COT, que se limitó por la presencia de subproductos orgánicos. El aumento del empleo de nanotecnología factible para configurar características electrocatalíticas mejores con base en nanopartículas o nanoestructuras incorporadas al electrodo se vislumbra como posible tendencia futura.
... Electrical safety in water treatment facilities is paramount due to the inherent risks associated with combining electricity and water. The operation of these facilities involves a wide array of electrical equipment, including pumps, motors, control systems, and monitoring devices, all of which are essential for the treatment and distribution of safe, potable water (Anglada, Urtiaga, & Ortiz, 2009;Capodaglio, 2017). The critical nature of these operations necessitates stringent electrical safety practices to prevent accidents, ensure the safety of personnel, and maintain continuous service to communities. ...
This review paper examines the theoretical frameworks guiding electrical safety practices in water treatment facilities, with a focus on comparative analysis between Africa and the United States. It highlights the importance of electrical safety in mitigating risks associated with the operation of these facilities. It underscores the role of regulatory, cultural, economic, and technological factors in shaping safety practices. By analyzing the regulatory context, theoretical approaches, and challenges and opportunities within these regions, the paper identifies best practices and innovative solutions that can inform global standards for electrical safety. The comparative analysis reveals significant differences in regulatory frameworks, the application of theoretical models, and the adoption of safety practices, offering insights into the adaptability and flexibility required to improve electrical safety outcomes globally. The review emphasizes integrating diverse theoretical perspectives and practical experiences to enhance worldwide electrical safety standards and practices in water treatment facilities. Through this analysis, the paper contributes to the development of comprehensive, adaptable, and globally applicable safety frameworks, highlighting the need for international collaboration and knowledge exchange to achieve optimal safety levels across different regions.
... The necessary equipment and procedures are generally straightforward and cost-effective [38]. However, there are various factors such as reactor design and experimental conditions including the choice of electrode material, current density, flow dynamics, pH level, and the presence of mediators need to be considered during the EO process to maximize efficiency [39][40][41]. The electrochemical oxidation process is adaptable and robust, allowing for the treatment of various pollutants and different wastewater volumes [42][43][44]. ...
The release of anaerobically digested dairy wastewater (ANDDW) without a treatment can lead to severe environmental pollution, prompting the exploration of effective and sustainable treatment methods. Amidst various wastewater treatment approaches, the electro-oxidation (EO) process is considered as a promising, clean, and adaptable solution. In this study, the major operational parameters viz. current density, electrolyte concentration, treatment time, and mixing speed of an EO comprising Ti/PbO2 anode and stainless-steel cathode, were optimized using response surface methodology (RSM) for efficient removal of chemical oxygen demand (COD), ammonia nitrogen (NH3-N), total phosphorus (TP), orthophosphate (OP), total nitrogen (TN), and total Kjeldahl nitrogen (TKN) from ANDDW. Optimal conditions were identified as a current density of 90 mA cm⁻², 0.08% electrolyte concentration, 180 min treatment time, and 400 rpm mixing speed. Under the optimum conditions, the COD, NH3-N, TP, OP, TN, and TKN removal efficiencies were 78.36, 63.93, 87.41, 92.39, 67.01, and 81.42%, respectively. Furthermore, the reaction rate followed the first-order kinetic model for the pollutants removal with correlation coefficients (R²) close to 1. The findings highlight the potential of using the EO process to treat high pollutant-laden ANDDW and encourage further studies to confirm the corresponding outcomes on a pilot scale.
Graphical abstract
... Electrical safety in water treatment facilities is paramount due to the inherent risks associated with combining electricity and water. The operation of these facilities involves a wide array of electrical equipment, including pumps, motors, control systems, and monitoring devices, all of which are essential for the treatment and distribution of safe, potable water (Anglada, Urtiaga, & Ortiz, 2009;Capodaglio, 2017). The critical nature of these operations necessitates stringent electrical safety practices to prevent accidents, ensure the safety of personnel, and maintain continuous service to communities. ...
This review paper examines the theoretical frameworks guiding electrical safety practices in water treatment facilities, with a focus on comparative analysis between Africa and the United States. It highlights the importance of electrical safety in mitigating risks associated with the operation of these facilities. It underscores the role of regulatory, cultural, economic, and technological factors in shaping safety practices. By analyzing the regulatory context, theoretical approaches, and challenges and opportunities within these regions, the paper identifies best practices and innovative solutions that can inform global standards for electrical safety. The comparative analysis reveals significant differences in regulatory frameworks, the application of theoretical models, and the adoption of safety practices, offering insights into the adaptability and flexibility required to improve electrical safety outcomes globally. The review emphasizes integrating diverse theoretical perspectives and practical experiences to enhance worldwide electrical safety standards and practices in water treatment facilities. Through this analysis, the paper contributes to the development of comprehensive, adaptable, and globally applicable safety frameworks, highlighting the need for international collaboration and knowledge exchange to achieve optimal safety levels across different regions. Keywords: Electrical Safety, Water Treatment Facilities, Comparative Analysis, Global Standards.
... The energy consumption (ECon) was calculated using Eq. (10)51 and expressed in kWh m −3 . where Q corresponds to specific electrical charge [kAh m −3 ], U reflects the average cell voltage [V], j applied current density [A cm −2 ], A is geometric electrode area [cm 2 ], t refers to the electrolysis time, and V is the volume of the electrolyte [m 3 ]. ...
With growing public concern about water quality particular focus should be placed on organic micropollutants, which are harmful to the environment and people. Hence, the objective of this research is to enhance the security and resilience of water resources by developing an efficient system for reclaiming industrial/military wastewater and protecting recipients from the toxic and cancerogenic explosive compound—2,4,6-trinitrotoluene (TNT), which has been widely distributed in the environment. This research used an anodic oxidation (AO) process on a boron-doped diamond (BDD) electrode for the TNT removal from artificial and real-life matrices: marine water and treated wastewater. During experiments, TNT concentrations were significantly decreased, reaching the anodic degradation efficiency of above 92% within two hours and > 99.9% after six hours of environmental sample treatment. The presented results show the great potential of AO performed on BDD anodes for full-scale application in the industry and military sectors for TNT removal.
... The primary process driving indirect oxidation has been demonstrated by research to be the mineralization of organic matter using HO˙ [26,27]. Equation (1) reveals that H 2 O is initially discharged on the anode's surface (M) to produce HO˙. ...
The degradation of industrial dyes poses a significant environmental challenge due to their persistence and toxicity. Developing efficient and stable electrode materials for the electrochemical degradation of methylene blue (MB) is crucial for addressing environmental concerns associated with dye pollution.
This paper describes the synthesis and electrochemical performance of Cu(Cr0.1,Al0.9)2O4 as a potential electrode material for the degradation of MB. The material was elaborated via nitrate synthesis and heat-treated at 900 °C. Then, characterized using various physico-chemical techniques. For all the electrochemicals tests, an anode based on Cu(Cr0.1,Al0.9)2O4 was prepared by adding activated carbon (AC), NMP and PVDF as binder agents.
Preliminary electrochemical tests indicated that the degradation of MB occurred via an indirect oxidation mechanism, which needs the integration of a supporting electrolyte. In this case, the electrolyte consists of mixture of Na2SO4 and NaCl at equal proportions (in volume). The pH study showed that the degradation efficiency was found vary between 92.4% and 97.2% at pH range 2–11. The electrode also exhibited excellent performance irrespective the dye concentrations, with efficiencies ranging from 91 to 99% for solutions at 6.4 to 40 ppm of MB.
The prepared electrode revealed a maximum degradation efficiency of 99% (within 50 min) at 50 mA applied current, for a 20 ppm MB solution. A higher current is required to decontaminate a concentrated solution. On the other hand, increasing the current reduces the electrolysis time. For a 40 ppm solution, the degradation efficiency reached 97.4% at an applied current of 70 mA within only 40 min.
Graphical abstract
... The inevitable intensification of industrial activities has led to severe environmental pollution consequences in water, soil, and air. Over the years, the accumulation of different recalcitrant pollutants in conventional biological and chemical treatments has directed the research community to further the research on electrochemical advanced oxidation processes (EAOPs) [1]. Significant efforts focused on the mechanisms of electrochemical reactive species production, its application for the removal of aqueous organic pollutants, and its optimization [2][3][4]. ...
Recently, granular activated carbon (GAC) has shown its effectiveness as a cathode material for in situ ROS generation. Here, we present an electrochemically modified GAC cathode using electrode polarity reversal (PR) approach for enhanced H2O2 decomposition via 2-electron oxygen reduction reaction (2e-ORR). The successful GAC modification using PR necessitates tuning of the operational parameters such as frequency, current, and time intervals between the PR cycles. This modification enhances the GAC hydrophilicity by increasing the density of surface oxygen functionalities. After optimization of the electrode polarity, using the 20 (No PR)-2 (PR) interval and 140 mA current intensity, the •OH concentration reaches 38.9 μM compared to the control (No PR) (28.14 μM). Subsequently, we evaluated the enhanced •OH generation for the removal of glyphosate, a persistent pesticide used as a model contaminant. The modified GAC using PR removed 67.6% of glyphosate compared to 40.6% by the unmodified GAC without PR, respectively. The findings from this study will advance the utilization of GAC for in situ ROS synthesis, which will have direct implications on increasing the effectiveness of electrochemical water treatment systems.
... During the indirect oxidation reaction, anodic oxidising agents such as sulfate radical, hydroxyl radical, and hypochlorite are formed near the catalyst surface or in the bulk solution (Fig. 7), with occurring number of reactions in parallel at the same time [103]. It should be noted that both oxidation reactions can coexist during electrochemical oxidation of aqueous effluent [104]. ...
... V. This cell voltage was governed by the EC reactions occurring at the electrodes (anode and cathode, and electrical double layer), and the overall current flow (50 mA/cm 2 ) through the supporting electrolyte (Anglada et al., 2009). While the former is needed to realise the oxidation toward PFAS degradation, the latter generates Joule heat and should be minimised to save energy. ...
... Considering the generally high cost of wastewater treatment [83][84][85][86][87][88][89][90][91], in this work, we investigated the possible on-site depuration of exhaust dye solutions used in the leather industry before discharging them to the traditional sewage system. This work aimed to study the adsorption treatment of the effluent of a specific coloring drum used in the leather industry in place of testing the mixture of diluted dyes transferred to a wastewater treatment plant. ...
Wastewater production is a major environmental issue for the leather and textile industries: in a modern plant, several synthetic dyes are used in separated coloring batches whose wastewaters are usually mixed, diluted with other process water streams, and sent to a unique wastewater treatment plant. This includes specific physical and biochemical tertiary treatments to remove dyes efficiently. One of the main difficulties of these processes is the presence of multiple dyes, which cannot be treated with the same efficiency as a “wide-spectrum” process. This work explores the possibility of using conventional granular activated carbon (GAC) and a new polyurethane foam (PUF) for the adsorption of an acid red dye in the wastewater of a specific coloring batch of the tanning industry. The aim of this work is twofold: on the one hand, we aim to explore the performance of the new PUF sorbent; on the other hand, we aim to explore the possibility of using adsorption as an optimized pre-treatment for single-dye batches, which may take advantage of the presence of a single type of target dye and its higher concentration. The effluent is then sent to the wastewater treatment plant for further depuration.
... The mechanism of electro-oxidation involves a metallic active center that is converted into an unstable and very reactive metal hydroxyl radical, promoting the radical degradation of organic species. This approach did not require any oxidant reagents considering that reactive species are produced directly from aqueous medium, but it requires a great deal of energy [197], limiting its applicability to a few scenarios, including the removal of recalcitrant species from wastewater in the civilian [198][199][200][201][202][203] and pharmaceutical and food [204,205] industries. As an alternative to the mechanism reported in Figure 4, electrooxidation can proceed through the in situ formation of hydrogen peroxide at the cathode of the system, which acts like an oxidant agent [206]. ...
The development of heterogeneous catalysts is one of the pillars of modern material science. Among all supports, carbonaceous ones are the most popular due to their high surface area, limited cost, and tunable properties. Nevertheless, materials such as carbon black are produced from oil-derived sources lacking in sustainability. Pyrolytic carbon produced from biomass, known as biochar, could represent a valid solution to combine the sustainability and performance of supported catalysts. In this review, we report a comprehensive overview of the most cutting-edge applications of biochar-based catalysts, providing a reference point for both experts and newcomers. This review will provide a description of all possible applications of biochar-based catalysts, proving their sustainability for the widest range of processes.
... The dimensionally stable anodes (DSA) consist of a titanium substrate and a conductive layer of metal oxide or mixed metal oxide (Ti, Sn, Ru, Ir, and Sb) on its surface (Anglada et al., 2009;Martinez-Huitle et al., 2015). Unlike sacrificial anodes (such as Fe as the anode), DSA electrodes play an electrochemical catalytic role on organic substances via surface metal oxides and can be reused multiple times. ...
The presence of residual levofloxacin (LEV) in the environment poses an unpredictable threat to the ecosystem. The electrochemical anodic oxidation method was chosen for the study of LEV degradation. Three different anodes (Ti/RuO2-TiO2-SnO2, Ti/Pt, Ti/RuO2-IrO2) were chosen and subjected to X-ray diffraction (XRD) analysis to determine the crystal structure of the anode surface. When the degradation rates of three anode materials for LEV were compared under the same conditions, it was discovered that the Ti/RuO2-TiO2-SnO2 electrode had the highest degradation efficiency for LEV. Scanning electron microscopy (SEM) was then used to investigate the surface morphology of the three different anodes both before and after use. The effects of electrode spacing, current strength, electrolyte concentration, and pH on the degradation of LEV were investigated in independent factor experiments. The optimal conditions for LEV degradation by Ti/RuO2-TiO2-SnO2 electrode were determined using orthogonal experiments, and a degradation efficiency of 94.65% was achieved at 0.9 A, 4 g/L Na2SO4, and pH = 6 for 120 min. In order to investigate the mechanism of electrochemical degradation of LEV, different experiments were done to corroborate each other. Indirect oxidation and·OH were demonstrated to play a major role in LEV degradation by CV curves and radical trapping experiments. Finally, HPLC-Ms experiments identified intermediate products of LEV degradation and proposed three possible degradation pathways to provide theoretical support for real LEV wastewater degradation.
... to H2O (Eq. 11) [61,62]. This phenomenon is illustrated in Figure 3, where the factor BB (current density in quadratic effect) in the Pareto diagram is not statistically significant, implying that higher values of B do not necessarily lead to an increase in oxidant generation. ...
In this study, a continuous flow photo-electro-Fenton (PEF) system was evaluated for its ability to remove pharmaceutically active compounds (PhACs) from irrigation water used in Bogot´a-savanna crops. The PEF system consisted of dimensionally stable anode and graphite diffusion gas cathode, which were irradiated with LEDs. Firstly, the system was optimized using response surface methodology (RSM) in ultrapure water. The most favorable conditions for efficient generation of oxidants (the response variable) were found to be a flow rate of 210 mL/min, a current density of 15 mA/cm2, and an electrolyte concentration of 0.1 mol NaCl/L. Subsequently, model compounds of PhACs, including losartan (LOS), sulfamethoxazole (SMX), and diclofenac (DCF), were
eliminated after only 10 min of treatment under the previously established conditions. After demonstrating the potential of the PEF system to eliminate PhACs, the system was applied to real irrigation water to evaluate the degradation of seven PhACs, namely carbamazepine (CBZ), sulfamethoxazole (SMX), ciprofloxacin (CIP), clarithromycin (CLR), diclofenac (DCF), valsartan (VAL), and trimethoprim (TMP). The results showed that after 30 min of treatment with the PEF system, the concentration of these compounds was drastically reduced remaining undetected. This demonstrates the high potential of the PEF system to reduce the presence of PhACs in irrigation water and associated environmental and food health risks.
... However, the use of higher current densities usually results in higher operating costs due to an increase in energy consumption. It should also be highlighted that an increase in current density does not necessarily increase the process Anglada et al., 2009.) performance. ...
Landfill leachate is a complex mix of organics, inorganics and heavy metals produced from conventional and engineering landfilling practices. The adverse effects of landfill leachate on human and environmental health have forced the relevant authorities to stipulate stringent disposal requirements, producing the need for ground-breaking technological solutions for effective management of landfill leachate. The researchers and field engineers are still looking for robust options for leachate management. This timely book on landfill leachate management is a valued addition to this area of research.
... tegangan lebih O2 akan menjadi lebih besar. Anoda konvensional lainnya yang dapat dipergunakan adalah seperti Platina, dan DSA (anoda stabil dimensi) (Anglada et al., 2009;Martínez-Huitle et al., 2015). Dalam penelitian ini, Platina digunakan sebagai anoda dan juga Platina yang dimodifikasi: Platina-kobal hidroksida dan Platina-kobal untuk mengevaluasi degradasi/eliminiasi AMX dalam air yang dimediasi oleh Co(III). ...
... Other benefits include robustness, adaptability, and automation capabilities. The main disadvantage of this procedure is its high operating cost due to increased energy consumption (Anglada et al. 2009). In the membrane separation process, various commercial membranes from multiple manufacturers are available, many applications and module configurations are available, and a small amount of space is required. ...
Bisphenol A (BPA) is a well-known endocrine-disrupting chemical (EDC) used as a plastic enhancer in producing polycarbonate resins to manufacture hard plastics. Due to strict limitations on the manufacturing and utilization of the BPA, several bisphenol substitutes, bisphenol F (BPF), bisphenol S (BPS), and bisphenol AF (BPAF), have been developed to replace it in various applications. Because of their widespread use in food containers, infant bottles, and reusable water bottles, bisphenols (BPs) have been identified in different environmental circumstances, including drinking water, seawater, industrial effluent, and endocrine systems such as human blood, urine, and breast milk. However, locating and analyzing them in different conditions has proven to be challenging. Therefore, there is a need to reduce the prevalence of BPs in the environment. The significance of advanced treatment options for treating and eliminating BPA and its alternatives from water bodies are reviewed. Also, the research gaps and future scopes are discussed in this review article. According to a literature survey, adsorption and photocatalytic degradation provide synergistic benefits for environmental challenges because of their substantial adsorption capacity, high oxidation capability, and low cost compared to alternative individual treatment options.
... La oxidación electroquímica es uno de los procesos de oxidación avanzada capaz de mineralizar completamente la materia orgánica no biodegradable. Se considera una tecnología amigable con el medio ambiente, ya que no requiere productos químicos, solo corriente eléctrica (Anglada et al., 2009(Anglada et al., , p. 1747 ...
... . (Anglada et al., 2009, Babuponnusami and Muthukumar, 2014, Rhimi et al., 2022 . ...
In the current work, the capability of uncoated titanium anode in the electrochemical treatment
of textile wastewater has been investigated with the aim of simultaneously benefiting from
electrooxidation and electrocoagulation treatment processes. In the present work, the feasibility
of using uncoated titanium anodes for wastewater treatment is studied in an electrochemical prepilot set-up with polymeric casing and an electrical supply power of 150 W, operated under
galvanostatic regime in batch mode, focusing on the current density as the main subject of
assessment, and its performance is evaluated using metrics such as chemical oxygen demand
removal and specific energy consumption. A noticeable finding of this work, is the flexibility of
the set-up to combine the electrocoagulation and electro-oxidation mechanisms with the current
density as the controlling parameter, leading to a remarkable decontamination capability, so that
reductions in the total chemical oxygen demand as large as 75–80% in the neutral and 90–95%
in the acidic environments were achieved. At low current densities (< 100 μA/cm2
), the anodic
corrosion was limited and the electro-oxidation was the dominant wastewater treatment mechanism. At high current densities (> 100 μA/cm2
), the anodic corrosion was accelerated and
the dominant wastewater treatment mechanism was switched to electrocoagulation. Along with
the chemical oxygen demand removal capability, the energetic cost-effectiveness of the set-up
was a major concern, particularly from the industrial point of view, which was assessed in both
neutral and acidic environments, and was realized to get optimized at 600 μA/cm2
, so that the
specific energy consumption and the rate specific energy consumption, were both minimized at
this current density, namely in respective order, 8.9 kWh/kgCOD and 3.52 kWh/kgCOD/h in
neutral, and 10 kWh/kgCOD and 2.34 kWh/kgCOD/h in acidic environments.
... In this process acidic or basic pH favours pollutants removal, indicating its potential in treatment of water and wastewater from multiple source (Lin et al., 2020). Despite the advantages, ozonation requires high costs for instrumentation, no formation of disinfection residuals, mixing is necessary since ozone is less soluble in the water than chlorine (Garcia et al., 2003;Świetlik et al., 2004; Anglada et al., 2009), and it forms many DBPs than any other disinfectants. ...
Water disinfection by-products (DBPs) are among insitu-generated emerging contaminants (ECs) during water disinfection. Although water disinfectants control acute risks through destruction of water-borne pathogens, the produced DBPs are associated to genotoxicity, carcinogenicity, bladder cancer, early-term miscarriage, and birth defects. Only 30% of trihalomethanes (THMs), 10% of halogenic acetic acids (HAAs) and N-nitrosodimethylamine (NDMA) are the major classes of DBPs gained significant public attention. There is still missing information particularly in their formation, distribution, and public awareness. In the current study it was revealed that persistence, types, and metabolic fragments of DBPs are not informed leaving unsolved puzzle. These findings still indicate a significant knowledge gap on the insight and alternative solutions on where to hide against natural-bases ECs.
In this research, successive electro-oxidation (EO) process was utilized to eliminate
some of the primary organic contaminants in effluent wastewater, specifically phenol and chemical oxygen demand (COD). The performance of the electro-oxidation process was studied by using two graphite electrodes as anodes and three stainless steel electrodes as cathodes, which is a new strategy in this field. Taguchi method has been used to design experiments to approach the best experimental conditions for phenol and COD removal as significant responses. The best operating conditions that resulted in the maximum reduction of phenol and COD were current density (CD=25 mA/cm2), pH=4, support electrolyte (NaCl=2g/l), the distance between electrodes (Dist.=5mm), and time of 60 minutes. At these operating conditions, phenol and COD removal were 99.27% and 99.96%, respectively. This work provides important insights into a novel water and wastewater treatment method with a detailed analysis of the results.
In the study, the removal of dye (methyl blue) from aqueous solutions by batch/agitation adsorption method was investigated using Pinus brutia (PB). For this purpose, first, PB wood was collected and made into wood chips (PB), and then Pinus brutia biochar (PBB) was made. The PBB was modified to gain nano-magnetic properties. The biochar structure was characterized by FT-IR. PBB and nM-PBB were used for the removal of MB dye. The adsorbent amount, temperature, pH, time and dye concentration were investigated in the adsorption process with adsorption isotherms, kinetics and thermodynamics to estimate their MB removal efficiency. Sorption equilibrium for MB dye was reached by nM-PBB within 60 min and adsorption efficiency up to 99.007% was reached. While the adsorption kinetics followed a pseudo-second-order kinetic model, the Langmuir isotherm model, with a maximum adsorption capacity of 107.527 mg/g (nM-PBB), showed homogeneous physiochemical adsorption. The efficiency was found to be a spontaneous endothermic reaction. It can be suggested that nM-PBB can be used to remove MB.
In the world’s rapidly expanding economy, textile industries are recognized as a substantial contributor to economic growth, but they are one of the most significant polluting industrial sectors. Dye-contaminated water sources can pose serious public health concerns, including toxicity, mutagenicity, and carcinogenicity among other adverse health effects. Despite a limited understanding of efficacious decolorization methodologies, the pursuit of a sustainable strategy for the treatment of a wide spectrum of dyes remains a formidable challenge. This article conducted an exhaustive review of extant literature pertaining to diverse physical, chemical, biological, and hybrid processes with the aim of ascertaining their efficacy. It also elucidates the advantages and disadvantages, cost considerations, as well as scalability impediments of the treatment methodologies, thereby facilitating the identification of optimal strategies for establishing techno-economically efficient processes in the sustainable handling of these effluents. The hybrid configuration exhibited superior efficiency and was documented to surmount the limitations and constraints inherent to individual techniques. The study also revealed that most of the proven and established dye removal techniques share a common limitation viz., the generation of secondary pollution (i.e., sludge generation, toxic intermediates, etc.) to the ecosystem.
This series provides information on the nature of dyes, their harmful effects, and dye degrading techniques. The first volume of this series presents a fundamental concept of dye degradation. The information on target-oriented dye mitigation is intended to give readers a better understanding of the dye degradation process to sustain a healthy environment. Chapters present referenced information and highlight novel breakthroughs in the industry.
Key topics:
Foundations of Dye Knowledge: Evaluating Toxicity Nanotechnology Electrochemistry Catalytic Materials and Photocatalysis Microbial Biodegradation
This book serves as a foundational resource for researchers and students in chemistry and chemical engineering courses. It also serves as a reference for industry professionals who work with chemical dyes (for example in textile and plastic industries) and are engaged in the critical field of environmental remediation.
Electrochemical degradation of organic molecules is important in wastewater treatment. In addition, the direct oxidation of small organics can be utilized for electrochemical hydrogen production or fuel cell. This study aimed to provide database for various anode catalysts that can degrade organic molecules such as urea, methanol, ethanol, glucose, ammonia, formic acid, acetic acid, oxalic acid in various pH conditions. Pt, Ni, Cu anodes were employed, and the target molecule concentration was 0.3 M. The activity was analyzed by the peak current densities of cyclic voltammetry. The Cu showed activity in the reaction of decomposing glucose and ammonia at pH 14. The Ni was active in ammonia degradation at pH 7, and the Pt was active in oxalic acid oxidation at pH 0. Relevant mechanisms were proposed for these reactions. We suggest Cu-Ni composites for toilet wastewater treatment and Pt for handling anaerobic digestor effluent.
Water pollution is the major problem seen in today's scenario and even pollutants at low concentration harms our environment. In industrial sector usage of phenol is seen even at low concentrations. The interaction of phenol in the environment provides adverse effects to living beings. This review focuses on the toxicity of phenol and its impact towards environment and human health. The treatment techniques such as distillation, extraction, wet air oxidation, membrane process, electrochemical oxidation, biological treatment and finally adsorption techniques were discussed. Among many treatment techniques so far utilized in the treatment of phenol, adsorption was considered as one of the best technique due to its advantages such as reusability, ease in operation, large availability etc., This review also highlights the adsorption technique for the cleaner removal of phenol from aqueous solution with novel as well as low-cost adsorbents in the removal of phenolic compounds. This review also discusses about the drawbacks and issues related with adsorption of phenolic compounds.
The chlorine evolution reaction (CER) is a key reaction in electrochemical oxidation (EO) of water treatment. Conventional anodes based on platinum group metals can be prohibitively expensive, which hinders further application of EO systems. Crystalline cobalt antimonate (CoSbxOy) was recently identified as a promising alternative to conventional anodes due to its high catalytic activity and stability in acidic media. However, its catalytic sites and reaction mechanism have not yet been elucidated. This study sheds light on the catalytically active sites in crystalline CoSbxOy anodes by using scanning electrochemical microscopy to compare the CER catalytic activities of a series of anode samples with different bulk Sb/Co ratios (from 1.43 to 2.80). The results showed that Sb sites served as more active catalytic sites than the Co sites. The varied Sb/Co ratios were also linked with slightly different electronic states of each element, leading to different CER selectivities in 30 mM chloride solutions under 10 mA cm-2 current density. The high activity of Sb sites toward the CER highlighted the significance of the electronic polarization that changed the oxidation states of Co and Sb.
Every year, a substantial amount of wastewater from industrial sources is discharged into the environment. To combat this pollution, a variety of techniques are employed for wastewater treatment. Among these methods is electrocoagulation (EC), which utilizes electrochemical reactions to generate coagulant substances on-site by dissolving sacrificial anodes typically made of iron or aluminum. By applying an electric current, EC effectively disrupts and removes suspended, dissolved, or emulsified pollutants. It holds great potential for eliminating a broad spectrum of contaminants, encompassing both organic and inorganic substances, from diverse wastewater types. The efficiency of the EC process depends on multiple parameters, including pH, electrode choice, operation duration, and current density. Nonetheless, EC encounters two primary challenges: electrode passivation and energy consumption. Despite these challenges, EC demonstrates advantages over conventional methods, such as decreased energy requirements and lower operational costs.
Zearalenone (ZEN), one of the most common mycotoxins in cereals, poses a severe health risk to humans. In this study, electrochemical oxidation and reduction degraded ZEN in solution completely within 8 min and 20 min. The structure of ZEN products was elucidated by mass spectrometry (MS), and their toxicity was evaluated by ECOSAR software and cytotoxicity assay. From simulation, electrochemical oxidation products had lower acute and chronic toxicity, and the product at 9.0 V is not harmful (LC50/EC50 greater than 100 mg/L, ChV greater than 10 mg/L). CCK-8 assay further confirmed their less cytotoxicity. To our surprise, LC50, EC50, and ChVs of all electrochemical reduction products were lower than 1 mg/L, and cell viabilities were less than ZEN, meaning the higher toxicity of electrochemical reduction products. On this Basis, electrochemical oxidation was applied in ZEN contaminated wheat with a degradation rate of 92.32 ± 2.37%, indicating its potential to degrade ZEN practically.
An expert meeting was organized by the World Health Organization (WHO) and held in Stockholm on 15-18 June 1997. The objective of this meeting was to derive consensus toxic equivalency factors (TEFs) for polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) and dioxinlike polychlorinated biphenyls (PCBs) for both human, fish, and wildlife risk assessment. Based on existing literature data, TEFs were (re)evaluated and either revised (mammals) or established (fish and birds). A few mammalian WHO-TEFs were revised, including 1,2,3,7,8-pentachlorinated DD, octachlorinated DD, octachlorinated DF, and PCB 77. These mammalian TEFs are also considered applicable for humans and wild mammalian species. Furthermore, it was concluded that there was insufficient in viva evidence to continue the use of TEFs for some di-ortho PCBs, as suggested earlier by Ahlborg et al. [Chemosphere 28:1049-1067 (1994)]. In addition, TEFs for fish and birds were determined. The WHO working group attempted to harmonize TEFs across different taxa to the extent possible. However, total synchronization of TEFs was not feasible, as there were orders of a magnitude difference in TEFs between taxa for some compounds. In this respect, the absent or very low response of fish to mono-ortho PCBs is most noticeable compared to mammals and birds. Uncertainties that could compromise the TEF concept were also reviewed, including nonadditive interactions, differences in shape of the dose-response curve, and species responsiveness. In spite of these uncertainties, it was concluded that the TEF concept is still the most plausible and feasible approach for risk assessment of halogenated aromatic hydrocarbons with dioxinlike properties. VA:IBN
The aim of this work is the definition of a clean process for the treatment of landfill leachates by integration of efficient technologies, namely electrooxidation and selective ion exchange, that reduce the initial concentration of the pollutants and allow re‐use of the treated water. Treatment of the leachates by electrochemical oxidation using a boron doped diamond electrode led to complete removal of chemical oxygen demand and ammonium nitrogen. However, as a result of ammonium oxidation the partial formation of nitrate was observed. Ion exchange removal of nitrate was experimentally analyzed using the selective resin Purolite A520 E obtaining satisfactory results.
In 2009, hexachlorocyclohexane (HCH) isomers (α-HCH, β-HCH, and γ-HCH [lindane]) were listed as persistent organic pollutants (POP) in the Stockholm Convention. Accordingly, the legacy of HCH/lindane production with the associated large HCH waste deposits has become recognized as an issue of global concern and is addressed in the implementation of the Convention. The current paper gives an overview of the major contaminated sites from lindane production of the INQUINOSA Company. This company operated from 1975 to 1988 in the city of Sabiñánigo, Spain. HCH production resulted in the production of approximately 115,000 tonnes of waste isomers which were mainly dumped in two unlined landfills. These two landfill sites, together with the former production site, are recognized sources of environmental pollution. Assessment and remediation activities at these sites are described. A dense nonaqueous phase liquid (DNAPL) contaminated inter alia with HCH isomers, benzene, chlorobenzenes, and chlorophenols as the main contaminants and an associated contaminated groundwater plume have been discovered at both landfill/dumpsites and at the former production site. The approximately 4,000 t of DNAPLs constitute a serious risk for the environment due to the proximity of the Gállego River. Since 2004, more than 20 tonnes of this DNAPL has been extracted using "pump and treat" techniques. The Aragon Regional Government and the Spanish Environmental Ministry are taking action, focusing on the treatment of DNAPL and on the transfer of the large quantities of solid POP wastes to a new landfill. A range of laboratory tests has been performed in order to plan the aquifer remediation.
The differential environmental fates and toxicities of the various hexachlorocyclohexane (HCH) isomers including lindane and isomers in the technical mixture will be the focus of this review. HCHs are one of the most widely used and most readily detected organochlorine pesticides in environmental samples. The relatively high volatility of HCH has led to global transport, even into formerly pristine locations such as the Arctic. Certain HCHs cause central nervous system, reproductive, and endocrine damage. Because γ-HCH is rapidly metabolized, the β-HCH isomer is consistently found in higher concentrations in human fat, blood, and breast milk. In contrast, α- and γ-HCH are the most prevalent isomers in soil, water, and air samples. The ratio of the α- to γ-isomers can be used to track global transport of HCHs. A new area of HCH research focuses on the selective degradation of the two α-HCH enantiomers in various environmental matrices. These HCH issues and recommendations for future HCH research are presented in this review.
Advances in electrochemical methods for pollutant remediation, recycling and sensing are reviewed. Additionally, applications of these methods in the drinking water industry, and for disinfection scenarios are discussed. Lastly, new electrode materials for environmental applications are described. In a companion review, photoelectrochemical methods will be discussed.
The anodic oxidation of 2-naphthol in acid media was investigated at a synthetic boron-doped diamond thin film electrode (BDD) using cyclic voltammetry and bulk electrolysis. The results have shown that in the potential region, where the supporting electrolyte is stable, reactions involving simple electron transfer, such as oxidation of 2-naphthol to naphthoxy radical and 1,4-naphthoquinone occur. Polymeric materials, which lead to electrode fouling, are also formed in this potential region. Electrolysis at high positive potentials in the region of electrolyte decomposition causes complex oxidation reactions by electrogenerated hydroxyl radicals leading to the complete incineration of 2-naphthol. Electrode fouling is inhibited under these conditions.The experimental results have been also compared with a theoretical model. This model is based on the assumption that the rate of the anodic oxidation of 2-naphthol is a fast reaction and it is under diffusion control.
Hexachlorocyclohexane (HCH) isomers (α-, β- and γ- (Lindane)) were recently included as new persistent organic pollutants (POPs) in the Stockholm Convention, and therefore, the legacy of HCH and Lindane production became a contemporary topic of global relevance. This article wants to briefly summarise the outcomes of the Stockholm Convention process and make an estimation of the amount of HCH waste generated and dumped in the former Lindane/HCH-producing countries.
In a preliminary assessment, the countries and the respective amount of HCH residues stored and deposited from Lindane production are estimated. Between 4 and 7 million tones of wastes of toxic, persistent and bioaccumulative residues (largely consisting of alpha- (approx. 80%) and beta-HCH) are estimated to have been produced and discarded around the globe during 60 years of Lindane production. For approximately 1.9 million tones, information is available regarding deposition. Countries are: Austria, Brazil, China, Czech Republic, France, Germany, Hungary, India, Italy, Japan, Macedonia, Nigeria, Poland, Romania, Slovakia, South Africa, Spain, Switzerland, Turkey, The Netherlands, UK, USA, and former USSR. The paper highlights the environmental relevance of deposited HCH wastes and the related POPs' contaminated sites and provides suggestions for further steps to address the challenge of the legacy of HCH/Lindane production.
It can be expected that most locations where HCH waste was discarded/stockpiled are not secured and that critical environmental impacts are resulting from leaching and volatilization. As parties to the Stockholm Convention are legally required to take action to stop further POPs pollution, identification and evaluation of such sites are necessary.
Background, aim and scope:
Once they have been generated, polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) and other persistent organic pollutants (POPs) can persist in soils and sediments and in waste repositories for periods extending from decades to centuries. In 1994, the US EPA concluded that contaminated sites and other reservoirs are likely to become the major source of contemporary pollution problems with these substances. With this in mind, this article is the first in a new series in ESPR under the title 'Case Studies on Dioxin and POP Contaminated Sites--Contemporary and Future Relevance and Challenges', which will address this important issue. The series will document various experiences from sites contaminated with PCDD/F and other POPs. This article provides an overview of the content of the articles comprising the series. In addition, it provides a review of the subject in its own right and identifies the key issues arising from dioxin/POP-contaminated sites. Additionally, it highlights the important conclusions that can be drawn from these examples. The key aim of this article and of the series as a whole is to provide a comprehensive overview of the types of PCDD/F contaminated sites that exist as a result of historical activities. It details the various processes whereby these sites became contaminated and attempts to evaluate their contemporary relevance as sources of PCDD/Fs and other POPs. It also details the various strategies used to assess these historical legacies of contamination and the concepts developed, or which are under development, to effect their remediation.
Main features:
Special sessions on 'Contaminated sites--Cases, remediation, risk and policy' were held at the DIOXIN conferences in 2006 and 2007, and this theme will be continued at DIOXIN 2008 to be held in Birmingham. Selected cases from the approximately 70 contributions made to these sessions, together with some additional invited case studies are outlined together with the key issues they raise. By evaluating these cases and adding details of experiences published in the current literature, an overview will be given of the different features and challenges of dioxin and POP-contaminated sites.
Results:
This article provides a systematic categorisation of types of PCDD/F and POP-contaminated sites. These are categorised according to the chemical or manufacturing process, which generated the PCDD/Fs or POPs and also includes the use and disposal aspects of the product life cycle in question. The highest historical PCDD/F and dioxin-like polychlorinated biphenyl (PCB) contamination burdens have arisen as a result of the production of chlorine and of chlorinated organic chemicals. In particular, the production of chlorinated pesticides, PCBs and the related contaminated waste streams are identified being responsible for historical releases of toxic equivalents (TEQs) at a scale of many tonnes. Along with such releases, major PCDD/F contaminated sites have been created through the application or improper disposal of contaminated pesticides, PCBs and other organochlorine chemicals, as well through the recycling of wastes and their attempted destruction. In some extreme examples, PCDD/F contaminated sites have also resulted from thermal processes such as waste incinerators, secondary metal industries or from the recycling or deposition of specific waste (e.g. electronic waste or car shredder wastes), which often contain chlorinated or brominated organic chemicals. The examples of PCDD/F and dioxin-like PCB contamination of fish in European rivers or the impact of contaminated sites upon fishing grounds and upon other food resources demonstrate the relevance of these historical problems to current and future human generations. Many of the recent food contamination problems that have emerged in Europe and elsewhere demonstrate how PCDD/F and dioxin like PCBs from historical sources can directly contaminate human and animal feedstuffs and indeed highlight their considerable contemporary relevance in this respect. Accordingly, some key experiences and lessons learnt regarding the production, use, disposal and remediation of POPs from the contaminated sites are summarised.
Discussion:
An important criterion for evaluating the significance and risks of PCDD/Fs and other POPs at contaminated sites is their present or future potential for mobility. This, in turn, determines to a large degree their propensity for off-site transport and environmental accessibility. The detailed evaluation of contaminated site cases reveals different site-specific factors, which influence the varied pathways through which poor water-soluble POPs can be mobilised. Co-contaminants with greater water solubility are also typically present at such sites. Hence, pumping of groundwater (pump and treat) is often required in addition to attempting to physically secure a site. At an increasing number of contaminated sites, securing measures are failing after relatively short time spans compared to the time horizon, which applies to persistent organic pollutant contamination. Due to the immense costs and challenges associated with remediation of contaminated sites 'monitored natural attenuation' is increasingly gaining purchase as a conceptual remediation approach. However, these concepts may well prove limited in their practical application to contaminated sites containing persistent organic pollutants and other key pollutants like heavy metals.
Conclusions:
It is inevitable, therefore, that dioxin/POP-contaminated sites will remain of contemporary and future relevance. They will continue to represent an environmental issue for future generations to address. The securing and/or remediation of dioxin/POP-contaminated sites is very costly, generally in the order of tens or hundreds of millions of dollars. Secured landfills and secured production sites need to be considered as constructions not made for 'eternity' but built for a finite time scale. Accordingly, they will need to be controlled, supervised and potentially repaired/renewed. Furthermore, the leachates and groundwater impacted by these sites will require ongoing monitoring and potential further remediation. These activities result in high maintenance costs, which are accrued for decades or centuries and should, therefore, be compared to the fully sustainable option of complete remediation. The contaminated site case studies highlight that, while extensive policies and established funds for remediation exist in most of the industrialised western countries, even these relatively well-regulated and wealthy countries face significant challenges in the implementation of a remediation strategy. This highlights the fact that ultimately only the prevention of contaminated sites represents a sustainable solution for the future and that the Polluter Pays Principle needs to be applied in a comprehensive way to current problems and those which may emerge in the future.
Recommendations and perspectives:
With the continuing shift of industrial activities in developing and transition economies, which often have poor regulation (and weak self-regulation of industries), additional global challenges regarding POPs and other contaminated sites may be expected. In this respect, a comprehensive application of the "polluter pays principle" in these countries will also be a key to facilitate the clean-up of contaminated areas and the prevention of future contaminated sites. The threats and challenges of contaminated sites and the high costs of securing/remediating the problems highlight the need for a comprehensive approach based upon integrated pollution prevention and control. If applied to all polluting (and potentially polluting) industrial sectors around the globe, such an approach will prove to be both the cheapest and most sustainable way to underpin the development of industries in developing and transition economies.
The work investigated the treatment of the concentrate produced from the reverse osmosis treatment of an MBR effluent. Two conventional chemical processes, coagulation and activated carbon adsorption, and three advanced oxidation processes (electrochemical treatment, photocatalysis and sonolysis) were applied. Coagulation with alum gave dissolved organic carbon (DOC) removals up to 42%, while FeCl(3) achieved higher removals (52%) at lower molar doses. Adsorption with granular activated carbon showed the highest DOC removals up to 91.3% for 5 g/L. The adsorption isotherm was linear with a non-adsorbable organic fraction of around 1.2 mg/L DOC. The three oxidation methods employed, electrolytic oxidation over a boron-doped diamond electrode, UVA/TiO2 photocatalysis and sonolysis at 80 kHz, showed similar behavior: during the first few minutes of treatment there was a moderate removal of DOC followed by further oxidation at a very slow rate. Electrolytic oxidation was capable of removing up to 36% at 17.8A after 30 min of treatment, sonolysis removed up to 34% at 135W after 60 min, while photocatalysis was capable of removing up to 50% at 60 min.
Comparative experimental study is performed on purification of yellow wastewaters separated and collected in solarCity, Linz, Austria. Three membrane methods (micro-, ultra-, and nano-filtration), and two advanced oxidations (gamma radiation and electrochemical oxidation) were applied. Best results concerning the removal of pharmaceuticals and hormones from urine by membrane separation were achieved using the membrane NF-200 (FilmTec). Pharmaceuticals (ibuprofen and diclofenac), and hormones (oestrone, beta-oestradiol, ethenyloestradiol, oestriol) were removed completely from urine. NF-separation also has some disadvantages: losses of urea, and lowering the conductivity in the product (permeate). The retentates (concentrates) received have to be treated further by oxidation to destroy the "problem" compounds. The results showed that electrochemical oxidation is more suitable than gamma radiation. Gamma-radiation with intensities higher than 10 kGy has to be applied for efficiently destroying of ibuprofen, and especially diclofenac. A high quantity of intermediate "problem" substances with oestrone structure was formed during the gamma oxidation of hormone containing urine samples. The electrochemical oxidation can be successfully applied for elimination of pharmaceuticals such as diclofenac, and hormones (oestrone, beta-oestradiol) from yellow wastewater without loss of urea (nitrogen fertiliser).
An ecotoxicological survey of soils that were polluted with wastes from lindane (γ-HCH) production assessed the effects of organochlorine compounds on the metabolism of microbial communities and the toxicity of these compounds to a native earthworm (Allolobophora chlorotica). Furthermore, the bioremediation role of earthworms as facilitators of soil washing and the microbial degradation of these organic pollutants were also studied. Soil samples that presented the highest concentrations of ε-HCH, 2,4,6-trichlorophenol, pentachlorobenzene and γ-HCH were extremely toxic to earthworms in the short term, causing the death of almost half of the population. In addition, these soils inhibited the heterotrophic metabolic activity of the microbial community. These highly polluted samples also presented substances that were able to activate cellular detoxification mechanisms (measured as EROD and BFCOD activities), as well as compounds that were able to cause endocrine disruption. A few days of earthworm activity increased the extractability of HCH isomers (e.g., γ-HCH), facilitating the biodegradation of organochlorine compounds and reducing the intensity of endocrine disruption in soils that had low or medium contamination levels.
The authors electrochemically decomposed ammonium nitrogen (NH 4-N) using a boron-doped diamond anode and investigated its NH 4-N-decomposing properties. Boron-doped diamond anode, because of its high overpotential for oxygen evolution and high chemical stability, is an effective means to electrochemically reduce chemical oxygen demand (COD) in wastewater. Intensive studies have been done on the electrochemical decomposition of organic compounds using a diamond anode. In actual treatment of wastewater, however, removal of NH 4-N from wastewater is also essential because environmental regulations are becoming tighter. In this paper, the NH 4-N-decomposing properties of a boron-doped diamond anode were compared with those of conventional anodes, a PbO 2/Ti anode and a dimensionally stable anode (DSA).
The Khimprom plant in Ufa was one of the largest organochlorine production facilities in Russia. This paper summarises the residual pollution of the site with polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and highlights the current and future challenges in relation to remediation of the site. Preliminary assessment of the pollution shows large-scale PCDD/F contamination at the site from half a century production of organochlorine pesticides and solvents. This contamination is affecting the city, and 2500 residents live within 3 km with a further 350,000 living within 7 km of the factory. The current PCDD/F pollution of the site and the continuing releases highlight the urgent need for further investigations, for the site to be secured and for the contamination to be remediated. The production history of the plant means that also other unintentionally POPs, mercury and chlorinated solvents need to be considered. The current regulatory framework for PCDD/F-contaminated soil and for defining hazardous waste in the Russian Federation is not appropriate for the management of PCDD/F-contaminated sites. It is therefore suggested that a science-based regulatory framework should be developed. The Russian Federation recently ratified the Stockholm Convention providing a foundation for the development of appropriate regulations and for further assessment, securing and remediation of the site. The impacts of pollution from the Khimprom plant demonstrate that the assessment and management of the organochlorine production sites should be a priority in the implementation of the Stockholm Convention by the Russian Federation and other countries.
ntegration of membrane bioreactor (MBR) with electrochemical process was investigated as treatment of stabilized landfill leachates, collected from Djebel Chekir (Tunisia). Results showed that at optimum conditions for the membrane and with organic loading rates of 1.9 and 2.7 g COD L−1 d−1, MBR treated effluent is still colouring and contains high COD and ammonia concentrations. In order to reduce these high pollutant concentrations, electrochemical oxidation process using Ti/Pt, graphite and PbO2 electrodes, was tested as effluent post-treatment. Ti/Pt electrodes showed the best performance. COD, ammonia and colours removals were affected by the current density (J) and treatment time (t). At optimal operational conditions (t = 1 h, J = 4 A dm−2), the final COD and total kjeldahl nitrogen concentrations (TKN) were 1000 and 86 mg L−1, respectively. The final treated wastewater COD, TKN, colours, pH meet the discharge standards in the sewer. The combination of MBR treatment process with electrochemical oxidation can be a technical suitable solution for stabilized landfill leachates treatment with an efficient reduction of different parameters, essentially COD (85%), TKN (94%), and colour436 (99%).
Treatment of text wastewaters from a large dyeing and finishing mill by a continuous process of combined chemical coagulation, electrochemical oxidation and activated sludge treatment is investigated. The experimental results are assessed in terms of COD and color (turbidity) reductions to determine the overall treatment efficiency of the combined process. Operating variables, such as the wastewater flow rate, conductivity, pH, applied current and amount of polyaluminum chloride (PAC), are explored to determine their respective effects on the efficiency of the electrochemical oxidation of the textile wastewater. Optimum operating range for each of those operating variables are experimentally obtained. Economic evaluation of the combined treatment method indicates that it is highly competitive in comparison to the conventional treatment method practiced in the textile industry.
Samples of four contaminated sites in Hamburg were analysed for hexachlorocy-clohexanes, chlorinated benzenes and phenols, 2,4,5-trichlorophenoxy acetic acid, and PCDD/PCDF. Contaminant patterns (type and quantity of substances, distributions of isomers and homologues) were compared with those of production residues of a company formerly producing pesticides locally. Results show that by this method sources of contaminations can be identified in certain cases. It is concluded that investigation schemes with respect to contaminated sites should be designed in such a way that their results are adequate for risk assessment and tracing the origin of the contaminants.
A new mathematical approach to the electrochemical treatment of wastewater polluted with organic materials is presented in this work. This model is based on several assumptions related to the reactor-level description, as well as to the mass-transfer and kinetics characteristics. The assumptions allow an easy-to-use model without adjustable parameters to be obtained. The model is applied to the electrochemical treatment of aqueous wastes containing carboxylic acids (formic, oxalic, and maleic) or phenol, using cells with non-active anodes (boron-doped diamond). Good agreement between the experimental and modeling results is obtained in all cases, which validates the assumptions on which the model is based.
A novel method of latex wastewater treatment was developed based on in-situ hypochlorous acid generation. The hypochlorous acid was generated in an undivided electrolytic cell consisting of two sets of graphite as anode and stainless sheets as cathode. The generated hypochlorous acid served as an oxidizing agent to destroy the organic present in the latex wastewater. For an influent COD concentration of 3,820 mg/L at an initial pH 4.5; current density of 74.5 mA/cm2; sodium chloride content 3% and electrolysis period of 90 min, resulted in the following residual concentration pH 7.3; COD 78 mg/L; BOD5 55 mg/L; TOC 45 mg/L; residual total chlorine 136 mg/L; turbidity 17 NTU and temperature 54°C, respectively. In the case of 2% sodium chloride content for the above, said operating condition resulted in a residual concentration of pH 7; COD 162 mg/L; BOD5 105 mg/L; TOC 90 mg/L; residual total chlorine 122 mg/L; turbidity 26 NTU and temperature 60°C respectively. The energy requirements were found to be 35 and 50 Wh/L while treating 24 L of latex wastewater at 3 and 2% sodium chloride concentration at a current density 74.5 mA/cm2. The observed energy difference was due to the improved conductivity at high sodium chloride content.
This work has studied the adsorption and electrolytic reaction of ammonia at an IrO2 anode with a change of the pH, and it has evaluated the decomposition rate to nitrogen, the change of the byproducts, and the effect of the chloride ion on the decomposition reaction. Also, the electrolytic decomposition mechanism of ammonia was suggested. The ammonia in the basic solution was oxidized mainly to nitrogen gas through a direct electrolytic reaction accompanying an adsorption at the electrode where the oxygen evolution rarely occurred. The ammonium ion in the neutral and acid solution could be partly decomposed to nitrogen by the OH radicals generated in the condition of oxygen evolution, not by a direct electrode reaction. However, the decomposition rate was much lower than that in the basic condition. The hypochlorite ion generated from the chloride ion by the electrode was very effective for the decomposition of the ammonia and ammonium ion to nitrogen. The ammonium ion by hypochlorite in the neutral condition was changed to NOx as well as to nitrogen.
This review deals with electrochemical methods for water, wastewater, wastes and soils treatment. The electrochemical technique combines both physical chemistry and electronic science and has widely proved to be a clean, flexible and powerful tool for the development of new methods for waste and water treatment. Likewise, electrochemical treatment is generally characterized by simple equipment, ease of operation, short retention time and negligible equipments for adding chemicals. Besides, electrolytic cells can be easily automated and coupled with other processes including, biological, chemical and physical processes to enhance the efficiency of the treatment. A particular focus is given to electrocoagulation (EC), electrodeposition (ED), electroflotation (EF), electrokinetic (EK) and electrooxidation (EO) processes. These technologies are effective in improving the treatment quality of industrial wastes, wastewaters and drinking water on integration into a treatment plant or replacement of conventional processes that are found to be less effective to eliminate specific organic and inorganic pollutants. EC can be used for clarifying water or to eliminate organic, inorganic and microbial pollutants from wastewater. The technology delivers in situ coagulant by anodic dissolution of sacrificial electrodes (aluminium or iron) and is finding wider applications with the possible improvements in the reduction of energy consumption and metallic sludge production. ED is a well-established process for toxic metal removal whose effectiveness can be greatly improved by selecting suitable electrode material (type and geometry of the electrode). EF technology is effective in removing suspended solids, colloidal particles and oil & grease suspension. EK technology is a promising method to remove toxic metals from the matter with low hydraulic permeability or to enhance dewaterability of wastes including soils and sludge. The development of new, more stable and active catalytic electrodes has led to a renewed interest in EO for degrading refractory organic pollutants. This paper covers both established and recent developments in the field of electrochemical technologies for waste, water and wastewater treatment based on more than 158 patents and publications cited or analyzed.
Advanced oxidation comprises a range of similar but different chemical processes aimed at tackling pollution in water, air and soil. Over the past few decades, multidisciplinary research has been carried out to study a broad spectrum of topics such as understanding of process fundamentals, elucidation of kinetics and mechanisms, development of new materials, modelling, process integration and scale-up. This article identifies and discusses certain directions that seem to advance R&D on advanced oxidation for water/wastewater treatment. Copyright © 2008 Society of Chemical Industry
High-strength organic waste like distillery spentwash can be effectively treated by electrolysis in the presence of sodium chloride. Because the graphite anode and stainless steel cathode zones were kept unseparated, chlorine produced during electrolysis forms hypochlorous acid. The hypochlorous acid thus formed oxidizes the organic matter present in the wastewater. The COD removal from the spentwash was found to be 99% for an initial COD concentration of 15 000 mg/L at the end of 240 min of electrolysis. The energy requirements were found to be 36 and 27 W·h/L for treating 20 L of spentwash at 2.5 and 3% sodium chloride concentration, respectively. The observed energy difference is due to improved conductivity of the electrolyte.
A novel method of beer brewery wastewater treatment was developed based on in situ hypochlorous acid generation. The hypochlorous acid was generated in an undivided electrolytic cell that consisted of two sets of graphite as the anode and stainless sheets as the cathode. The generated hypochlorous acid served as an oxidizing agent to destroy the organic present in the brewery wastewater. An influent chemical oxygen demand (COD) concentration of 2470 mg/L at an initial pH 4.5, a current density of 74.5 mA/cm2, a sodium chloride content of 3%, and an electrolysis period of 50 min resulted in the following values: pH, 6.7; COD, 64 mg/L; biochemical oxygen demand (BOD5), 30 mg/L; total organic carbon (TOC), 40 mg/L; residual total chlorine, 162 mg/L; turbidity, 20 NTU (nephelometric turbidity units); ammonia nitrogen (NH3−N), below the detectable limit; and temperature, 40 °C. The energy requirements were determined to be 56 and 39 W/L, while treating 24 L of beer brewery wastewater with sodium chloride concentrations of 2% and 3% and at a current density of 74.5 mA/cm2. The observed energy difference was due to the improved conductivity at high sodium chloride contents. The cost incurred in treating 1 m3 of beer brewery wastewater was determined to be RM 8, when the electrolytic reactor was operated at a current density of 74.5 mA/cm2 and the sodium chloride content was 3%.
This article describes a simple laboratory experiment to teach students how to measure mass-transfer coefficients by an electrochemical technique. The experiment allows the students to increase their knowledge about mass transfer and its importance in chemical processes. A simple Microsoft Excel spreadsheet allows students to correlate experimental data in laminar and turbulent regimes. Results obtained can be compared with those obtained from a well-known equation given in electrochemistry and chemical engineering books. Keywords (Audience): Graduate Education / Research
Background Olive mill wastewater (OMW) constitutes a very strong agro-industrial wastewater posing severe environmental threats in olive oil producing countries. The main objective of this study was to treat olive mill wastewater by electrochemical oxidation. The variables studied included the type and concentration of electrolyte solutions, voltage and time applied.
Results: The electrolyte type and concentration significantly affected the degradation efficiency of the electrochemical oxidation. Optimal conditions for NaCl concentration were 3% (w/v) and 16 V. At these conditions chemical oxygen demand (COD) removal reached 70.8% after 8 h of electrochemical treatment, while color and turbidity were completely removed after short periods of treatment. However, bio-assays indicated that the ecotoxicity of the treated wastewater remained unchanged, possibly due to the formation of chlorinated by-products. Na2SO4 did not demonstrate sufficient efficiency. The simultaneous use of FeCl3 and NaCl contributed to electro-coagulation of OMW. After settlement, two separate phases were formed: the supernatant phase and the settled solids. Under optimal conditions (2% Na2SO4 + 1% FeCl3; 24 V), the removal efficiency of COD reached 85.5% at the supernatant phase.
Conclusion: NaCl was an effective electrolyte for OMW treatment. The electro-coagulation process was also a successful process, but as in the case of NaCl the remaining acute toxicity of treated OMW was high. Copyright
The oxidation ability of the two most used high oxidation power anodes (i.e., anodes with high overpotential for O2 evolution), lead dioxide (PbO2) and boron-doped diamond (BDD), has been compared for the electrochemical incineration of solutions containing the herbicide mecoprop (MCPP) by using an electrolytic flow cell. The influence of several operating parameters such as current, liquid flow rate and MCPP concentration on the performance of both systems with a stainless steel cathode has been studied. Galvanostatic electrolyses always lead to complete mineralization due to the high amounts of effective hydroxyl radicals generated from water oxidation at each anode. The current efficiency using PbO2 is low, thus yielding extremely high energy consumption, while BDD anode exhibits faster oxidation rate and greater current efficiencies, along with a significantly lower energy cost. In this system MCPP disappears at a time similar to that required for overall mineralization, following a pseudo first-order kinetics that is typical of a constant excess of oxidizing hydroxyl radical. GC–MS analyses reveal that the electrochemical degradation pathway involves the same aromatic and carboxylic acid intermediates when using PbO2 or BDD anodes and that oxalic acid is the ultimate by-product prior to conversion to CO2.
α-HCH, β-HCH, and γ-HCH (lindane) were listed as persistent organic pollutants in the Stockholm Convention. Therefore, they need to be globally addressed including the wastes remaining from historic use and production. While at most lindane production sites the unintentionally produced 85 % HCH waste isomers have been deposited, at a former pesticide factory in Hamburg-Moorfleet HCH waste isomers have been recycled from 1953 to 1984 by thermal decomposition to chlorobenzenes and resulted in high polychlorinated dibenzo-p-dioxin/polychlorinated dibenzofuran (PCDD/PCDF)-contaminated residues. The management of the PCDD/PCDF-contaminated waste from the former pesticide factory in Hamburg has been assessed and quantified. Based on past accredited PCDD/PCDF measurements, the registered 3,700 tonnes of disposed thermal HCH decomposition residue contained 333 to 854 kg of PCDD/PCDF toxicity equivalent (I-TEQ) in 53-102 tonnes total sum of PCDD/PCDF. The wastes have been deposited together with other wastes in landfills in Hamburg and other parts of Germany. For the Georgswerder landfill (Hamburg), where approximately 50 % of the PCDD/PCDF is disposed, current and previous situation and remediation activities are described. While PCDD/PCDF leaching from the landfill is controlled and incinerated, more water soluble organochlorines (vinyl chloride, cis-1,2-dichlorethene, chlorobenzenes) and benzene remain as a challenge for groundwater management. A comprehensive aftercare program has been established and will need to be operated by future generations including renewal of containment systems. Former lindane/HCH productions need-in addition to HCH deposits-to be assessed for possible recycling practice of HCH and related PCDD/PCDF-containing deposits. This could systematically be addressed within the Stockholm Convention implementation.
The objective of this work is, first, to analyze the viability of the electrochemical oxidation process by means of a boron-doped diamond electrode to treat leachates from a municipal landfill site, because a high loading of ammonium and chemical oxygen demand (COD) and poor biodegradability are the main characteristics of the leachates. The second objective of this work is to study the influence of operating conditions (i.e., applied current density, initial COD and ammonium loading, and chloride concentration) on the oxidation. Almost-complete removal of both pollutants was experimentally achieved. The kinetics of the COD disappearance was successfully predicted using a model that was based on mass-transfer control of the electrochemical process. Finally, a mathematical model that is able to describe the kinetics of ammonium removal has been reported, depending on the applied current density, the chloride concentration, and the mass-transfer coefficient of the electrochemical cell.
A biofilm airlift suspension (BAS) reactor and an undivided flow cell equipped with a boron-doped diamond (BDD) anode and a stainless-steel cathode were used to investigate the effects of varying operating conditions on process performance in the biological and electrochemical oxidation of a mixture of naphthalenesulfonates contained in the infiltration water of a contaminated industrial site. The experiments were aimed at evaluating the feasibility of process integration and the criteria for optimization (i.e. how to maximize degradation efficiency with minimum energy consumption) in combined biological and electrochemical oxidation of scarcely biodegradable compounds. Because of high reactor biomass concentration and long biomass retention time, the BAS reactor achieved a high degradation capacity (up to 6.8 kg COD m−3 d−1). On the other hand, owing to the recalcitrant character of some of the aromatic sulfonates in the leachate, the overall degradation efficiency did not exceed 70% based on COD measurements. All naphthalene-mono- and -disulfonates (except naphthalene-1,5-disulfonate) were completely degraded in the BAS reactor, whereas more complex molecules (e.g. naphthalenetrisulfonates) were more recalcitrant to biological oxidation. These compounds were completely mineralized by electrochemical oxidation using a boron-doped diamond anode. The energy consumption and the time required for the complete mineralization of the infiltration water decreased from 80 kWh m−3 and 4 h to 61 kWh m−3 and 3 h for the oxidation of raw and biologically pretreated leachate, respectively. Copyright © 2005 Society of Chemical Industry
In this work, the electrochemical oxidation of an actual industrial waste with conductive diamond anodes has been studied. The wastewater is the effluent of a wastewater treatment plant consisting of a Fenton reactor followed by a settler and a sand filter, in which the wastes generated in an olive oil mill are treated. These wastes contain a residual chemical oxygen demand of nearly 700 mg dm−3 which cannot be further oxidized with the Fenton process. The electrolyses were carried out under galvanostatic conditions, using a bench-scale plant equipped with a single-compartment electrochemical flow cell. Boron-doped diamond (BDD) and stainless steel (AISI 304) were use as anode and cathode of the cell, respectively. The complete mineralization of the waste was obtained with high current efficiencies limited only by mass transport processes. This confirms that besides the hydroxyl radical-mediated oxidation that occurs in the Fenton process, the electrochemical oxidation with conductive diamond electrodes combines other important oxidation processes such as direct electro-oxidation on the BDD surface and oxidation mediated by other electrochemically formed compounds generated in this electrode. Copyright © 2006 Society of Chemical Industry
The electrochemical oxidation of an olive mill effluent over Ti–Pt anodes was studied. The effluent had an average total chemical oxygen demand (COD) value of 234 g L−1, soluble COD of 61 g L−1, soluble phenolic content 3.4 g L−1, total solids of 80 g L−1 and pH = 5.1. Experiments were conducted in a 10 L vessel with the effluent recirculating at 1 L s−1. The applied current was varied between 5 and 20 A, the salinity between 1 and 4% NaCl, and experiments were performed with the effluent diluted with water to achieve the desired initial concentration. Emphasis was given to the effect of the presence of solids as well as of varying operating conditions on process performance as assessed in terms of COD, color and phenols removal. In general, degradation of phenols occurred relatively fast with conversion increasing with increasing applied current and decreasing initial organic loading and this was accompanied by low COD removal levels and moderate decolorization. The presence of solids had practically no effect on phenols removal, which, in most cases, was complete in less than about 180 min of reaction. However, oxidation in the presence of solids resulted in a substantial solid fraction being dissolved and this consequently increased sample color and the soluble COD content. The solid content typically found in olive mill effluents may partially impede its treatment by electrochemical oxidation, thus requiring more severe operating conditions and greater energy consumption. Copyright © 2007 Society of Chemical Industry
The electrochemical oxidation of phenol for waste water treatment was studied on doped SnO2 anodes. Analysis of reaction intermediates and a carbon balance has shown that the main reaction is oxidation of phenol to CO2. This unexpected behaviour of the SnO2 anode is explained by a change of the chemical structure of the electrode surface during anodic polarization.
Surface coastal sediments (0–10cm) collected from three natural environments on the Spanish Northern Atlantic Coast were
analyzed so as to determine concentrations of 6 marker polychlorinated biphenyls (PCBs), 12 dioxin-like PCBs (dl-PCBs) and
17 polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). An analytical procedure based on Soxhlet extraction followed by an automated
cleanup and final high-resolution gas chromatography coupled to high-resolution mass spectrometry was applied for the determination
of the persistent organic pollutants. Marker PCB levels ranged from 385.5 to 4,060.9pg/g dry weight (d.w.) showing a similar
congener pattern in all sediments dominated by the less volatile congeners PCB 153 and PCB 138. Linear correlations were found
between marker and dl-PCBs. Toxicity equivalent values were calculated for PCDD/Fs and dl-PCBs reaching its maximum at 0.52pg
WHO1998-TEQ/g d.w., with an average dl-PCBs contribution on the toxicity of the samples of 75%, and showing to be in good agreement
with background levels in the North-East Atlantic Ocean Coasts of nearly 1pg/g WHO1998-TEQ d.w. Dimensionless environmental quality criteria were much lower than 1 indicating the low probability to induce ecotoxicological
impacts.
KeywordsPCDD/Fs–Dioxin-like PCBs–Marker PCBs–Marine sediments–Cantabrian Coast–Background
This paper presents the results of a study on the scale-up, from a batch to a continuous flow unit, of an electrochemical reactor applied for the treatment of textile wastewater. Decolourisation of the wastewater bearing a reactive dye Red Procion H-EXGL proceeded via indirect electro-oxidation, mediated by “active chlorine”. The kinetics of decolourisation in a single-cell reactor under different operating conditions were second order, with the highest apparent rate constant (k=0.523lmol−1s−1) achieved at 40°C. A low Hatta number (Ha=0.03) indicated that the reaction occurred totally in the bulk solution, hence homogeneous reaction kinetics were used successively to scale-up a continuous flow electrochemical unit: a once-through filter-press reactor. Its hydrodynamic characteristics were defined by the residence time distribution (E(t)) function using a pulse injection method. The decolourisation efficiency experimentally determined in a continuous flow reactor was further compared with that predicted on the basis of the knowledge of the E(t) of the reactor and the homogeneous phase kinetic expression, obtained from the batch study and corrected for the geometric parameters of the reactors. A complete segregation of the fluid inside the flow reactor was assumed. For different applied flow rates, the experimentally defined conversion of the dye was close to the calculated value.
Electrochemical treatment of organic pollutants is a promising treatment technique for substances which are resistant to biodegradation. In this study an electrochemical treatment based on the principle of anodic oxidation was used to treat paper mill effluent from Rakta's Pulp and Paper Company where rice straw is used to produce paper pulp. Experiments were carried out in a cylindrical agitated vessel lined with lead sheet as anode while a concentric cylindrical stainless steel sheet screen was placed as a cathode. The effect of current density, pH, NaCl concentration, impeller rotational speed and temperature on the rate of color and COD removal was studied. The results showed that the use of electrochemical technique reduces the COD from an average value of 5500 to 160. The percentage color removal ranged from 53% to 100% depending on the operating conditions. Energy consumption calculation shows that energy consumption ranges from 4 to 29 kWh/m3 of effluent depending on the operating conditions. The experimental results proved that the electrochemical oxidation is a powerful tool for treating paper mill effluents where rice straw is used as a raw material.
The treatment of tannery wastewater by the electrochemical method using and Ti/Pt/Ir electrodes is investigated. The aim of a satisfactory elimination of NH+4 from wastewaters of different strength was achieved using both types of electrodes. A Ti/Pt/Ir anode proved to have the electrocatalytical properties for NH+4 removal, but it resulted to be more sensitive to poisoning by H2S contained in the wastewater. For both types of the electrodes NH+4 removal followed pseudo-first order kinetics, with the rate decreasing in function of the presence of organic substances. A concurrent removal of COD was observed particularly with a anode, but its magnitude was not sufficient to ensure the discharge limits to be met while treating the raw wastewater only by the electrochemical process. In conclusion the electrochemical process can be applied successfully as a final polishing or an alternative to biological nitrification, but cannot substitute completely the traditional treatment of tannery wastewater.
Wastewater from total dyeing and finishing stages (TDFW) and wastewater only from dyeing stage (DW) from a Textile cellulosic reactive azo dyeing process were treated separately by an electrochemical method using Ti/Pt as anode and Stainless Steel 304 as cathode. In this technique, sodium chloride was used as an electrolyte and the mixture was passed through an electrolytic cell. Due to the strong oxidizing potential of the chemicals produced (chlorine, oxygen, hydroxyl radicals and other oxidants) the COD, BOD of the wastewaters were substantially decreased using this electrochemical technique. A number of experiments were run in a batch 5 litre apparatus and the results of the electrochemical treatment on the two kinds of wastewaters are reported here. The results indicate that the electrochemical method used is feasible for treatment of textile dyeing wastewaters.
A pilot scale membraneless system using immobilized peroxidase on porous Celite beads was constructed for the catalytic oxidation of wastewater released from a petrochemical plant. This system was integrated with the electroenzymatic process for enzymatic catalysis using immobilized peroxidase and the electrochemical process for indirect bulk oxidation using generated hypochlorite (ClO−). As a result, the chemical oxygen demand (COD) removal efficiency of integrated system was two times higher than those of the discrete processes with lower power consumption. Thus, by using the integrated system, aromatic compounds in wastewater were effectively degraded and converted into aliphatic organic compounds. During a 30-day operation, 85–93% of the removal efficiency was maintained with 1.99 W g−1 COD of power consumption without severe deactivation of immobilized peroxidase.
Laboratory experiments were performed to characterize the behaviour of an electrochemical cell equipped with boron-doped diamond anodes and to verify its effectiveness in water disinfection. The hydrodynamic regime was determined when the cell worked either in batch or in continuous mode. Galvanostatic electrolyses of aqueous 1 mM Na2SO4 solutions were performed to investigate on the oxidant production in different experimental conditions. The same solutions contaminated by E. coli, enterococci and coliforms were used as test media to verify the effectiveness of the system in the disinfection process. Experimental results indicated that the major inactivation mechanism of bacteria in the electrochemical cell is a disinfection by electrochemically generated oxidants, however a cooperative effect of superficial reaction has to be taken into account. The great capability of BDD anode to produce reactive oxygen species (ROS) and other oxidizing species during the electrolysis allows to establish a chlorine-free disinfection process.
This paper reviews the development, design and applications of electrochemical technologies in water and wastewater treatment. Particular focus was given to electrodeposition, electrocoagulation (EC), electroflotation (EF) and electrooxidation. Over 300 related publications were reviewed with 221 cited or analyzed. Electrodeposition is effective in recover heavy metals from wastewater streams. It is considered as an established technology with possible further development in the improvement of space-time yield. EC has been in use for water production or wastewater treatment. It is finding more applications using either aluminum, iron or the hybrid Al/Fe electrodes. The separation of the flocculated sludge from the treated water can be accomplished by using EF. The EF technology is effective in removing colloidal particles, oil & grease, as well as organic pollutants. It is proven to perform better than either dissolved air flotation, sedimentation, impeller flotation (IF). The newly developed stable and active electrodes for oxygen evolution would definitely boost the adoption of this technology. Electrooxidation is finding its application in wastewater treatment in combination with other technologies. It is effective in degrading the refractory pollutants on the surface of a few electrodes. Titanium-based boron-doped diamond film electrodes (Ti/BDD) show high activity and give reasonable stability. Its industrial application calls for the production of Ti/BDD anode in large size at reasonable cost and durability.
Treatment of a low ratio landfill leachate was conducted by means of electrochemical oxidation process in this investigation. Under the operating conditions of 15 A/dm2 current density and 7500 mg/l additional chloride concentration, 92% of the COD in the landfall leachate was removed after electrolysis for 240 min with a ternary SnPdRu oxide-coated titanium (SPR) anode. At the same time, about 2600 mg/l of ammonium in the landfill leachate was also removed completely. These results indicate that the electrochemical oxidation process is effective in removing pollutants from landfill leachate. In this investigation, the effects of operating parameters including anode material, current density, and chloride concentration on both chlorine/hypochlorite production and landfill leachate treatment efficiency were studied. It was found that the operating factors have the same effects on both chlorine/hypochlorite production efficiency and landfill leachate treatment efficiency. The results suggest that the removal of pollutants from landfill leachate by electrochemical oxidation process could be mainly attributed to the indirect oxidation effect of chlorine/hypochlorite produced during the electrolysis. Among the four anode materials investigated in this study, including graphite, , DSAR, and SPR anodes, the SPR anode having a high electrocatalytic activity gave the best chlorine/hypochlorite production efficiency and landfill leachate treatment efficiency. In addition, the increases in both operating current density and chloride concentration also enhanced the indirect oxidation effect in the electrochemical oxidation treatment of landfill leachate.
During the electrochemical oxidation of real wastewaters, the different species present in the effluent may interact creating complex scenarios making the prediction of the behavior of the whole system difficult. In this paper the different phenomena that occur during the electro-oxidation process of landfill leachate at a pilot plant scale with boron-doped diamond (BDD) anodes are elucidated. The total BDD anode area of the pilot plant was 1.05 m2. The evolution of the concentration of chloride ions, chlorate, and inorganic carbon and the value of pH and redox potential were found to be inter-related. In turn, the concentration of chloride affected the oxidation of ammonia, which took place through indirect oxidation by active chlorine. Moreover, chloride ions competed with organic matter to be oxidized at the anode. The effect of current density was also investigated. Organic matter and ammonia oxidation were highly influenced by the applied current density value. A change in the mechanism of organic matter oxidation was observed when high current densities were applied. Two mathematical models, previously applied to the oxidation of synthetic wastewaters in the literature, were able to predict the evolution of chemical oxygen demand and ammonia for low current density values.
This paper reports the integration of advanced and conventional technologies to deal with the treatment of landfill leachates. The raw leachate, with average values of COD=4430 mg/L and N-NH(4)(+)=1225 mg/L, was first treated on site by an activated sludge large-scale process reducing the former parameters to 1750 mg/L (av.) of COD and 750 mg/L (av.) of N-NH(4)(+). Next, 50 L/h of the effluent were pumped to a pilot plant that included Fenton oxidation followed by an electrooxidation unit, provided with boron doped diamond anodes (anode area=1.05 m(2)); almost complete removal of the organic matter and ammonium nitrogen was achieved. Comparison of the results with those obtained in the laboratory (70 cm(2) of anode area) was performed observing a similar performance in the kinetics of COD removal, while differences were found in the ammonium removal rates. The specific energy consumption necessary to electro-oxidize the organic load below the disposal limit (COD<160 mg/L) at pilot plant scale was 35 kWh/m(3).
Deposition of stable boron-doped diamond (BDD) films on Ti substrates is believed to be very difficult. In the present study, the stability of Ti/BDD electrodes has been significantly improved by using an organic additive, CH2(OCH3)2. The improved electrodes had service lives of 175-264 h under accelerated life test conditions, which are 2.3-3.0 times longer than the service lives of electrodes prepared with the conventional H2 + CH4 mixture. Raman spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM) examinations demonstrated thatthe films had well-defined diamond features. The current efficiency (CE) obtained on Ti/BDD was 46.9-78.5% in oxidizing acetic acid, maleic acid, phenol, and dyes, which is 1.6-4.3-fold higher than that obtained on the typical Ti/ Sb2O5-SnO2 electrode. We used a Ti/BDD electrode prepared with H2 + CH4 + CH2(OCH3)2 for over 300 h; its activity remained superior. The successful development of stable and active Ti/BDD electrodes significantly increases the feasibility of industrial applications of anodic oxidation in wastewater treatment.