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The effect of electrode material on the generation of oxidants and microbial inactivation in the electrochemical disinfection processes
Abstract
Electrochemical disinfection has gained increasing attention as an alternative for conventional drinking water treatment due to its high effectiveness and environmental compatibility. The most common method of electrochemical disinfection is the use of electro-generated oxidants, such as active chlorine and reactive oxygen species, as disinfectants. This study examined the role of electrode material on the generation of oxidants, and elucidated the different reaction pathways for generating individual oxidants by employing boron-doped diamond (BDD), Ti/RuO(2), Ti/IrO(2), Ti/Pt-IrO(2), and Pt as anode materials. The efficiency of ()OH production, as determined by para-chlorobenzoic acid (pCBA) degradation, was in the order of BDD>Ti/RuO(2) approximately Pt. No significant production of ()OH was observed at Ti/IrO(2) and Ti/Pt-IrO(2). The ()OH was found to play a key role in O(3) generation at BDD, but not at the other electrodes. The production of active chlorine was in the order of Ti/IrO(2)>Ti/RuO(2)>Ti/Pt-IrO(2)>BDD>Pt. The large difference in this order from that of ROS was attributed to the difference in the electrocatalytic activity of each electrode material toward the production of active chlorine, as evidenced by linear sweep voltammetry (LSV) measurements. In addition, the characteristics of microbial inactivation as a function of electrode material were examined under the presence of an inert electrolyte, using Escherichia coli as an indicator microorganism.
... Consuming suitable electrodes, EO could also generate reactive oxygen species (ROSs) like hydroxyl radicals ( • OH) [27] [28] [29]. Demobilizing bacteria, like E. coli, could take place during EO usage via reactions with the generated oxidants in water [28] [30] [31] [32]. Like conventional disinfection processes [33], EO will produce DBPs when the oxidants and NOM enter in interactions [25]. ...
... The nature of metals or coated metals utilized as electrodes is crucial to the EO efficacy [28] [55] [77]. For EO, MMOs and BDD are the most frequent electrode kinds employed [1] [25] [83]. ...
... The anode material dictates the critical route of the EO process [55] [77] [78]. MMO electrodes are dictated mainly by producing free chlorine, besides the coating affecting the chlorine formation rate [28]. On the other hand, BDD electrodes possibly generate ROSs [25] [85]. ...
Although the literature mainly reports on the inactivation of bacteria by various electrochemical disinfectants, the impact of process variables and reactor design on bactericidal performance is not fully understood. This review concentrates on recent achievements of electrocoagulation (EC) and electrooxidation (EO) in killing pathogens such as Escherichia coli. Lynn et al. [1] [2] showed that in addition to EC alone, EC-EO enhanced E. coli reduction only after pH adjustment. They proposed that additional process optimization may lead to further improvements, such as adjusting the iron dosage for natural organic matter (NOM) removal, which would limit the effectiveness of oxidant scavengers. Additionally, more efficient filtration techniques (e.g., granular filtration) will reduce NOM and total iron content in the EO feed-water, decreasing the need for oxidants. Furthermore, continuous EC-EO treatment requires more elevated EO current densities to improve E. coli removal. Investigating the pathways of demobilizing E. coli in drinking water at high iron concentrations in the EO range will also provide deep insights into ongoing setup design. This review provides crucial, reliable, safe, and versatile alternatives to the widespread trouble of human drinking water pollution. Using and propagating the EC-EO technique will diminish health risks related to water quality, economic burden, lost labor time, import washout to the national economy, and natural resource management. Commercial-scale deployment of EC-EO technology will undoubtedly increase the socioeconomic burden on local communities via secured water supply and result in a reduction in government health expenditures.
... A key factor in the electrocatalytic process is the selection of suitable anode materials, which affects the reaction selectivity and the efficiency of the process (Feng et al. 2016). The research papers in Tables 4 and 5 all used different anodes to evaluate and optimize their activity for the generation of reactive oxygen species (ROS) and reactive chlorine species, such as boron-doped diamond electrodes (BDD), size-stabilized anodes (DSA), and mixed metal oxide anodes (MMO), in order to explore their role in disinfection (Bruguera-Casamada et al. 2017, Ghasemian et al. 2017, Huang et al. 2016, Jeong et al. 2009, Rajab et al. 2015. Dbira et al. (2019) employed different anode materials including boron-doped diamond (BDD), dimensionally stable anode (DSA: IrO 2 and RuO 2 ), and platinum (Pt), in order to compare their disinfection efficacy and the production of disinfection by-products. ...
... The majority of literature focuses on testing electrochemical disinfection performance by optimizing the disinfection system (e.g., electrolyte concentration, type, voltage, current, electrolysis time, temperature) or disinfection equipment (electrode material, area, spacing, electrolyzer structure, material, etc.). These optimizations investigate the optimal parameters to enhance disinfection, provide practical applications guidance, and expand prospects of practicality (Hand and Cusick 2021, Isidro et al. 2020, Jeong et al. 2009, Ming et al. 2018, Qi et al. 2015, Sandoval et al. 2022, Song et al. 2019. ...
... Depending on the reaction conditions, inorganic or organic DBPs may be produced, limiting the safe application of electrochemical water treatment systems (Nieuwenhuijsen et al. 2000). For instance, highly oxidizing anodes like BDD anodes, Ti/SnO 2 -based anodes, and magnesium phase titanium suboxide (Ti 4 O 7 ) anodes can oxidize chlorides to chlorates and perchlorates, which are toxic to plants and animals, thereby compromising the quality of treated water (Comninellis 1994, Ghernaout et al. 2011, Jeong et al. 2009, Lim and Shin 2022. Moreover, chlorine reacts rapidly with organic matter to form trihalomethanes (THMs), haloacetic acids (HAAs), and other chlorinated organic DBPs (Palmas et al. 2018). ...
The removal of waterborne pathogens from water is critical in preventing the spread of waterborne diseases. Electrochemical methods have been extensively researched and implemented for disinfection, primarily owing to their simplicity, efficiency, and eco-friendliness. Thus, it is essential to conduct a review about the research progress and hotspots on this promising technique. In this paper, we provided a comprehensive bibliometric analysis to systematically study and analyze the current status, hotspots, and trends in electrochemical disinfection research from 2002 to 2022. This study analyzed literature related to electrochemical disinfection or electrochemical sterilization published in the Web of Science database from 2002 to 2022 using CiteSpace and Biblioshiny R language software packages. The analysis focused on the visualization and assessment of annual publication volume, discipline and journal distribution, collaborative networks, highly cited papers, and keywords to systematically understand the current status and trends of electrochemical disinfection. The results showed that between 2002 and 2022, 1171 publications related to electrochemical disinfection were published, with an exponential increase in the cumulative number of publications (y=17.518e0.2147x, R2= 0.9788). The publications covered 76 disciplines with many articles published in high-impact journals. However, the research power was characterized by a large number of scattered research efforts and insufficient cooperation, indicating the need for further innovative collaboration. The citation analysis and keyword analysis suggest that future development in this field may focus on optimizing electrode materials, investigating the disinfection performance of ·OH based systems, optimizing conditions for actual wastewater treatment, and reducing energy consumption to promote practical applications.
... But, along with high performance, such Ti/TiO 2 (SnO 2 )-IrO 2 DSAs have a significant drawback, which is expressed in their high cost, low availability and laboriousness of production. 31 One of the most accessible materials for DSAs is platinized titanium (Ti/Pt). 32 The platinum coating is of relatively low cost, can be easily formed by electrochemical methods, can operate in the region of high anodic and cathodic polarizations, has high corrosion resistance in the presence of strong oxidizing agents and chlorides, etc. 31 However, during the electrolysis of low-concentration (less than 0.3 mol L −1 ) NaCl solutions on platinized titanium, the CE of hypochlorite does not exceed 50%. ...
... 31 One of the most accessible materials for DSAs is platinized titanium (Ti/Pt). 32 The platinum coating is of relatively low cost, can be easily formed by electrochemical methods, can operate in the region of high anodic and cathodic polarizations, has high corrosion resistance in the presence of strong oxidizing agents and chlorides, etc. 31 However, during the electrolysis of low-concentration (less than 0.3 mol L −1 ) NaCl solutions on platinized titanium, the CE of hypochlorite does not exceed 50%. 33 In addition, platinum promotes the oxidation of hypochlorite to chlorite and chlorate. ...
BACKGROUND
The synthesis of sodium hypochlorite solutions by electrolysis of low‐concentration and isotonic NaCl solutions using the most available dimensionally stable anodes from platinized titanium is promising from the point of view of the economics of the process. However, such synthesis is seriously complicated by the formation of toxic sodium chlorate impurity.
RESULTS
It is shown that in low‐concentration NaCl solutions under anodic polarization, the platinum surface rapidly passes into an oxidized passive state with a NaClO current efficiency (CE) of less than 30% and CE of NaClO3 of more than 20%. Carrying out short‐term electrolysis on the reduced surface of platinum makes it possible to increase the CE of NaClO to almost 90% in the absence of chlorate accumulation. Carrying out electrolysis in the mode of periodic change of electrode polarity (current reverse) allows solving the problem of anode passivation and significantly increasing the purity of the resulting sodium hypochlorite solutions.
CONCLUSION
Electrolysis of an isotonic 0.15 mol L⁻¹ NaCl solution in the current reverse mode allows increasing CE(NaClO) from 21% to 40% and significantly decreasing CE(NaClO3) from 21% to 4%. Based on the results obtained, a membraneless electrolyzer can be constructed to produce disinfectant solutions ‘on the spot’ using a commercially available pharmaceutical isotonic solution of NaCl. © 2023 Society of Chemical Industry (SCI).
... From the last paragraphs, it follows that the applied electrode material has a significant effect on the disinfection efficiency. Jeong et al. 70 concluded that the production of OH• with a BDD electrode was much higher than that obtained with Ti/RuO 2 and Pt electrodes and that no significant production of OH• was measured when Ti/IrO 2 and Ti/Pt-IrO 2 electrodes were applied. Saran et al. 71 reported that chloride ions and chloride-derived species played a significant role in the efficiency of electrooxidation-based disinfection via alteration of the cellular oxygen radical processes or intercellular signalling pathways, inducing apoptosis. ...
... 118 That said, application of a cathode coated by a catalyst that has a low overpotential for hydrogen evolution reaction Unfortunately, the 'non-active' electrodes that are highly effective for degradation of organic compounds via anodic generation of reactive oxygen species (i.e., BDD, PbO 2 , SnO 2 ) are less effective for the chlorine evolution reaction that is required for effective ammonia removal. Jeong et al. 70 reported that the production of active chlorine is a function of the anode's material, at the activity order Ti/IrO 2 ≥ Ti/ RuO 2 > Ti/Pt-IrO 2 > BDD > Pt, which is markedly different from that of the OER. ...
Electrochemical water treatment for recirculating aquaculture systems (RAS) is a promising approach for replacing the biological water treatment methods and establishing a new RAS generation with improved cost-effectiveness, lower environmental footprint, and no start-up periods. On top of ammonia oxidation directly into N2(g), electrochemical oxidation results in effective disinfection, and in the removal of organic matter, including specific organic constituents such as off-flavour agents. The paper provides an overview of incentives for the implementation of electrochemical methods in RAS. It covers the electrochemical principles relevant to aquaculture applications, the effects of physical and chemical parameters, as well as design considerations. In addition, the research performed to date for integrating electrochemical methods in RAS operation is reviewed and the variety of designs and operational configurations described. The electrochemical water treatment is perceived beneficial over biological water treatment especially in cold saline-seawater aquaculture (e.g., Atlantic salmon), where large nitrification reactors are required and the large water consumption for purging processes can be curtailed. It is also beneficial for the culturing of nitrate-sensitive species (e.g., L. vannamei). The paper points out the gaps to be overcome for allowing commercial breakthroughs based on electrochemical water treatment, including the need for expanding the practice and improving engineering practices by operating pilot systems for growing fish at both small and large scales; adjusting of electrochemical cell designs for reducing both capital and operational costs; developing full-proof malfunction-free dechlorination strategies, and evaluating and optimizing the disinfection abilities for inactivating typical pathogens in aquaculture. © 2023 The Authors. Reviews in Aquaculture published by John Wiley & Sons Australia, Ltd.
... Gong et al. 27 investigated the synergistic removal of NOx and SO 2 in a diaphragm seawater electrolysis system with two tandem packed towers and showed that higher ACC facilitated NOx removal, but higher pH in the oxidation tower reduced the NO removal efficiency. Jeong et al. 28 investigated the effect of electrode materials on the generation of oxidants and found that the production of AC from electrode materials followed the order of Ti/ IrO 2 > Ti/RuO 2 > Ti/Pt-IrO 2 > BDD > Pt. Jin et al. 29 compared the oxidant yield and NOx removal efficiency of four electrolytic systems and concluded that paired electrolysis can be used as a simple and effective wet scrubbing technique to purify flue gas. ...
... The concentration of AC generated by the electrolysis of CSW and FSW with electrolysis time under different currents (2-10 A) was studied, as shown inFigures 1A and 1D. Since the essence of electrolysis of seawater is that the AC generated on the anode by electrochemical reaction accumulates over time28,37 (Equation 1), in the two groups of experiments, the generated concentration of AC increases linearly with time. And the electrolytic conductivity of high-concentration electrolytes is almost constant under different current conditions; 38 the experimental results are consistent with the equation Equation 2 of AC generation rate evolved from Faraday's law.22 ...
The impact of ship emissions on the environment cannot be ignored and should be controlled. The possibility of applying seawater electrolysis technology and a novel amide absorbent (BAD, C12H25NO) to the simultaneous desulfurization and denitrification of ship exhaust gas is entirely confirmed by using various seawater resources. Concentrated seawater (CSW) with high salinity can effectively reduce the heat generated during electrolysis and the escape of chlorine. The initial pH of the absorbent can greatly affect the NO removal capacity of the system, and the BAD could keep the pH range suitable for NO oxidation in the system for a long time. The use of fresh seawater (FSW) to dilute the ECSW to make an aqueous oxidant is a more reasonable scheme; the average removal efficiencies of SO2, NO, and NOX were 97.10%, 75.41%, and 74.28%, respectively. The synergistic effect of HCO3-/CO32- and BAD was shown to further restrict NO2 escape.
... In typical domestic wastewater containing urine and feces [129,130], the chloride ions are sufficiently concentrated (30e650 mg L À1 ) to generate in situ the reactive chlorine species for disinfection purposes [32,126]. However, some researchers have amended the (waste)water by adding exogenous salts containing Cl À to enhance the electrochemical treatment, as the efficiency of chlorine electrogeneration is dependent on chloride concentration [131,132]. ...
... The second most common chemical produced for disinfection and the advanced oxidation process is the hydroxyl radical (HO ) [132,133]. It requires no specific chemical precursor (e.g., Cl À ions) but water. The HO can be generated as an intermediate during oxygen evolution with MMO electrodes and remains chemisorbed in the oxide lattice of the metal for direct oxidation of pollutants adsorbed at the catalytic site of the anode (equation (8)). ...
Seasonal or permanent water scarcity in off-grid communities can be alleviated by recycling water in decentralized wastewater treatment systems. Nature-based solutions, such as constructed wetlands (CWs), have become popular solutions for sanitation in remote locations. Although typical CWs can efficiently remove solids and organics to meet water reuse standards, polishing remains necessary for other parameters, such as pathogens, nutrients, and recalcitrant pollutants. Different CW designs and CWs coupled with electrochemical technologies have been proposed to improve treatment efficiency. Electrochemical systems (ECs) have been either implemented within the CW bed (ECin-CW) or as a stage in a sequential treatment (CW + EC). A large body of literature has focused on ECin-CW, and multiple scaled-up systems have recently been successfully implemented, primarily to remove recalcitrant organics. Conversely, only a few reports have explored the opportunity to polish CW effluents in a downstream electrochemical module for the electro-oxidation of micropollutants or electro-disinfection of pathogens to meet more stringent water reuse standards. This paper aims to critically review the opportunities, challenges, and future research directions of the different couplings of CW with EC as a decentralized technology for water treatment and recovery.
... Many authors have shown that electrogenerated active chlorine can be used effectively, using suitable anodes and operation conditions, to inactivate a large variety of microorganisms ranging from bacteria to viruses and algae [25,32,216,225,226]. Hence, the treatment with electrogenerated active chlorine can be potentially used for the simultaneous mineralization of organic pollutants (i.e., water decontamination) and water disinfection. ...
... Effect of the catalytic anode material on the evolution of active chlorine (i = 17 mA cm -2 , 0.017 M NaCl, 25 °C). Adapted with permission from[216].Copyright Elsevier B.V. 2009. IrO 2 based electrocatalysts seem a very interesting option because they also yield a low concentration of chlorinated byproducts (see subsections 3.2.2 and 3.2.3) ...
... TOC was determined using a Shimadzu TOC-L (Japan). In situ Cl 2 free c d e f chlorine present in the effluent water after electrolysis was determined using DPD method using a DR900 multi-index portable colorimeter (USA) as suggested by Dr. Joonseon Jeong and Prof. Yoon Jeyong's group at the Seoul National University, South Korea [21]. HO • and SO 4 ...
... H 2 O 2 concentration was determined using DMP reagent and Cu(II) sulfate 0.1M solution. Ozone concentration was determined using the Indigo Colorimetric Method [21]. The data were then statistically analyzed using an ANOVA two-factor replication, with a significance level of 0.05 (p = 0.05). ...
Textile wastewater effluent includes high concentrations of pollutant such as dyes, detergents, and chemical auxiliaries that bring many negative impacts to humans and the environment. In this study, biologically textile wastewater effluent was first time treated using electrochemical oxidation catalyzed by persulfate on Ti/BDD and Ti/SnO<sub>2</sub>-Nb<sub>2</sub>O<sub>5</sub> anodes. The results show that persulfate catalyst only significantly increases the electrochemical process efficiency at the Ti/BDD anode, but not at the Ti/SnO<sub>2</sub>-Nb<sub>2</sub>O<sub>5</sub> anode. The optimized operation conditions at the Ti/BDD anode are: [NaCl] 3 g/L, [PS] 2 g/L, applied current density 4.16 mA/cm<sup>2</sup>, pH 7.5, stirring speed 200 rpm, electrolysis time 120 minutes that removed 94.78% color, 64.57% COD, and 41.57% TOC in textile wastewater. The optimized operation conditions at the Ti/SnO<sub>2</sub>-Nb<sub>2</sub>O<sub>5</sub> anode are: [NaCl] 3 g/L, [PS] 1 g/L, applied current density 4.16 mA/cm<sup>2</sup>, pH 7.5, stirring speed 200 rpm, electrolysis time 150 minutes that removed 73.04% color, 41.32% COD, and 39.22% TOC. Detected oxidant radicals during the electrochemical oxidation processes could contribute to the oxidation of organic matters in biologically textile wastewater.
... A periodic backwash treatment can overcome the fouling of electrodes, and the deposits could be flushed to areas with higher potential-containing hydroxyl ions to remove the foulants [17]. The microbial inactivation through electrochemical disinfection methods largely depends on the electrolytic cell configuration, electrode material, and other operational parameters such as electrode spacing, treatment time, current density, and flow rate [18]. ...
... Thus, electrochemical treatments (electrocoagulation (EC) and electroxidation) outperform conventional treatments ( Jeong et al. 2009;Feng et al. 2004;Rajkumar & Palanivelu 2004;Gómez-López et al. 2013;Henquín et al. 2013;Can 2014;Mook et al. 2014;García-Montoya et al. 2015;Liu et al. 2015;Sillanpää & Shestakova 2017;Biswas & Goel 2022;Hemalatha & Sanjay 2022;Szarka et al. 2022). ...
The apple industry uses high flows of potable quality water to transport and clean the apple, which is regularly contaminated. Thus, it is necessary to implement an efficient water treatment system during the industrial process, providing reductions in the intake and release flows. A hybrid system was developed by applying the electrolytic treatment by electrocoagulation using a batch process (Step 1) and a continuous process (Step 2), followed by a microfiltration membrane separation (MSP) process (Step 3). The optimal conditions for removal of organic matter, chemical oxygen demand, total suspended solids (TSS), turbidity, color, and fungi obtained in Step 1 were a hydraulic detention time of 40 min, stirring at 40 rpm, current density of 20 A/m2, pH of 8.00, and temperature of 10 °C. These findings led to a successful implementation in Step 2, which evolved into Step 3, where tests in the combined continuous electrolytic reactor together with MSP showed significant removal rates, notably reaching up to 54% organic matter (OM) removal, 72% chemical oxygen demand (COD) removal, 83% TSS removal, 92% haze and color removal, and 100% mildew removal. The hybrid system proved to be a promising alternative for implementation in the processing industry, minimizing environmental impacts and costs.
HIGHLIGHTS
Electrocoagulation associated with the separation process by the microfiltration membrane demonstrated efficiency in the removal of pollutants.;
The hybrid system proved to be a promising alternative to prolong the life cycle of water in the apple processing industry.;
This study contributes to the reduction of input and output flows, minimizing environmental impacts and costs during the industrial processing of apples.;
... The high cost of BDD electrodes restricts large-scale wastewater treatment application, despite the advantages [15]. On the other hand, non-active lead oxide (PbO 2 ) electrodes are quite inexpensive, highly effective, inert, has a wide potential window, and exhibit high oxygen evolution overpotential [16][17][18]. The PbO 2 anode synthesized on titanium substrate is corrosive resistant and cost-effective, which makes it a good alternative for BDD and large-scale application [18]. ...
... Electrochemical chlorine generation brings the Science of the Total Environment 894 (2023) 165017 possibility to eliminate the old production chlorine methods and eliminate the storage and handling of hazardous chlorine gas or corrosive acid solutions (Kraft et al., 1999;Chung et al., 2018). Recent research has shown that catalysts based on dimensionally stable anodes (DSA®), such as RuO 2 /Ti, IrO 2 /Ti, SnO 2 /Ti and Ta 2 O 5 /Ti and TiO 2 /Ti-based electrodes can be used in the electrochemical production of chlorine with very favourable yields to avoid the oxygen evolution reaction (OER) that competes with the formation of chlorine and reduce cost-effective anodic materials (Oliveira et al., 2007;Jeong et al., 2009;Le Luu et al., 2015;Kim et al., 2018;Scialdone et al., 2021). Since TiO 2 is also a photocatalytic material, it has been used in the photoelectrochemical production of chlorine in recent years (Zanoni et al., 2004;Selcuk and Anderson, 2005;Cheng et al., 2007;Fraga et al., 2009;Li et al., 2013;Xiao et al., 2016;Zhao et al., 2019;Mesones et al., 2020;García-Espinoza et al., 2021). ...
Immobilised TiO2 nanotube (TiO2-NT) electrodes were grown via electrochemical anodisation in an aqueous solution containing fluoride ions at 10, 20 and 30 V. The photocatalytic (PC) and photoelectrocatalytic (PEC) activity of TiO2-NTs electrodes in the oxidation of methanol and the inactivation of bacteria and fungi was studied in different chloride salts electrolytes. Low concentrations of electrochemically generated oxidising species, such as free chlorine, were measured in experiments at pH 8.5 and +1 V of applied potential. Increasing the anodising potential results in longer nanotubes with higher photoactivity. The TiO2-NT electrode anodised at 30 V (TiO2-NT30V) generates free chlorine with an average concentration of 0.03 mg·L-1 upon illumination with UV-A at +1 V of potential bias. This concentration was enough to achieve 99.99 % of inactivation of a 106 CFU·mL-1 Gram-negative bacteria (Escherichia coli) in <3 min and Gram-positive bacteria (Enterococcus faecalis) after 7 min, whereas fungi (Candida albicans) required 15 min. The low production of chlorine was found to have a big impact on the bacteria and fungi inactivation even in not favourable chlorine generation conditions. An in situ investigation of the most influential parameters in the inactivation of some microorganisms with PEC and NT30V electrode has been done. It was found that free chlorine production increases with the length of TiO2-NT, with Cl- concentration up to 15 mmol·L-1 and with the application of potential bias. TiO2-NT30V photoanode has been demonstrated to produce active chlorine at levels compatible with the water disinfection process, suggesting that the present method could be considered a promising alternative for in situ chlorine-based disinfection.
... The commercially generated SAEW, possessing the added advantage of being low-cost, easy-to-use, and eco-friendly, is becoming increasingly popular in the food industry. The researcher found that various critical reaction parameters, such as electrode material, water hardness, and electrolyte composition, significantly impacted the production of such oxidants (Cl2, ClO − , and HOCl) [9] . One of the essential critical parameters influencing the yield and species of produced oxidants is the electrode material [10][11] . ...
... The efficiency of electrooxidation technology that removes inorganic nitrogen and sterilizes pathogenic bacteria in rearing seawater has been well validated (Cano et al. 2011;Lopez-Galvez et al. 2012;Jeong et al. 2008;Särkkä et al. 2015). However, the cost of energy and the release of residual chlorine as a by-product of the electrolytic process are still two major unresolved problems that have prevented the extensive application of the electrochemical approach in seawater aquaculture. ...
The energy cost and harmful effect of residual chlorine produced as a by-product in the electrochemical processes are the main obstacles in the extensive use of electrochemical recirculating aquaculture systems (ERAS). In this study, a pilot electrochemical system was used in a shrimp cultivation experiment to investigate the effects of current density, geometric feature, timing, and other parameters on the effective control of inorganic nitrogen, pathogens, and residual chlorine in aquaculture water. A 50-L electrochemical batch reactor (BR) equipped with Ti-RuO2/Ti electrodes could effectively remove inorganic nitrogen (the initial concentration was 4.0 mg/L) and inactivate Vibrio in the aquaculture seawater in 5 min, when a current density of 66 mA/cm2 and electrodes with a surface area of 154 cm2 were used. Air stripping was found to be effective in resolving residual chlorine produced from electrochemical process. In the experiment of shrimp cultivation, the ERAS equipped with a 50-L batch reactor and 500-L shrimp tank effectively kept the inorganic nitrogen concentration in the rearing water to a desirable concentration (0.2 mg/L) when a nitrogen load of 4.3 g (transformed from a daily quota of commercial prawn feeds) was used. By precisely controlling the time at which electrooxidation and air stripping alternated, an electrochemical recirculating aquaculture system could effectively remove inorganic nitrogen and residual chlorine, carry out disinfection, and reduce energy cost.
... At similar concentrations, Whangchai et al. (2013) produced 221.35 mg/L of hypochlorite for an operating time of 60 min and demonstrated that extending the operating time favored the generation of the disinfectant of interest. Jeong et al. (2009) performed an electrolysis process for 10 min with a current density of 17 mA/cm 2 , and achieved a chlorine concentration of 30 mg/L, demonstrating the influence of current density and time. In the conditions of a current intensity of 60 mA/cm 2 and an operating time of 60 min, Song et al. (2019) used titanium electrodes in a 500-mL cell and achieved higher chlorine production (reaching 140 mg/L of disinfectant) than the aforementioned investigations. ...
... The efficiency of electrolyzed water treatments depends highly on the amount of available chlorine, and it varies according to the fruit or vegetable ( Aday, 2016 ). In addition to active chlorine, other compounds are produced during electrolysis, such as reactive oxygen species that contribute to antimicrobial activity ( Jeong, Kim & Yoon, 2009 ). ...
In recent years, minimally processed fruits and vegetables have gained widespread consumer attention due to the need for a convenient yet healthy diet. As several factors can affect the shelf life of minimally processed products, it is essential to use preservation technologies that maintain the freshness of fruits and vegetables ensuring consumer health. In the second part of this review, the main physical preservation methods including heat treatments, refrigeration, irradiation, high pressure, ultraviolet radiation, and electrolyzed water are discussed in terms of their advantages, disadvantages, and applications. Advances in packaging for minimally processed products are also explored, such as active and intelligent packaging, edible films and coatings, and vacuum packaging. Defining the operational parameters related to treatment time and dose/intensity appropriate is one of the greatest difficulties in the application of physical methods. Therefore, these factors must be carefully evaluated, as must the sustainability and economic viability of each method.
... A periodic backwash treatment can overcome the fouling of electrodes, and the deposits could be flushed to areas with higher potential-containing hydroxyl ions to remove the foulants [17]. The microbial inactivation through electrochemical disinfection methods largely depends on the electrolytic cell configuration, electrode material, and other operational parameters such as electrode spacing, treatment time, current density, and flow rate [18]. ...
The electrochemical treatment of canal water was investigated in a batch-wise system in the presence of stainless steel 316-grade electrodes. Three effective process parameters, including current density, reaction time, and electrode spacing, were evaluated in the range of 0.25–2.5 mA/cm2,1–10 min, and 0.5–2.5 cm, respectively. Operational variables of electrochemical disinfection are optimized in response surface methodology (RSM) using Box–Behnken design. Before electrochemical disinfection, a pretreatment process of coagulants mixing for turbidity removal was conducted.
Results revealed that a 10 ppm dosage of Ferric chloride (FeCl3.6H2O) and alum (Al2(SO4)3·16H2O) at neutral pH is appropriate. Furthermore, the RSM analysis shows that interelectrode spacing is the most prominent factor affecting the disinfection performance, and increasing electrode spacing inversely affects the disinfection efficiency. Results revealed that 1.52 mA/cm2
current density, 6.35 min reaction time, and 1.13 cm of electrode spacing are the optimum conditions, resulting in a statistically 98.08% disinfection of the total coliform. The energy required for electrochemically disinfection of water at optimum conditions was 0.256 kWh/m3.
... In recent years, effective electrochemical disinfection has emerged as one of the most promising alternatives to conventional water treatment, which is a convenient and highly efficient way to produce germ-free water [104,105,109]. The advantages of these procedures make them more attractive than other methods. ...
... The increase in BOD 5 /COD ratio is contributed by the COD removal during EOD process as BOD 5 concentration increases. It can be explained by the occurrence of partial COD degradation into more biodegradable compounds on Pt-EOD due to the Pt anode experiencing direct oxidation with low electro-conversion and low active chlorine generation [25,26]. Therefore, in the case of BDD-EOD, the increase of BOD 5 /COD ratio is not clearly observed. ...
Electrochemical process has been widely applied to eliminate recalcitrant contaminants (i.e., organic and nitrogenous compounds) in landfill leachate. This study aimed to evaluate the performance of a hybrid electro-oxidation-dialysis (EOD) system to minimize organic and nitrogenous compounds through a synergistic process of electrochemical oxidation (EO) and electrodialysis (ED) as well as the dissolved organic matter was characterized in terms of fluorescent component and molecular weight distribution. The EOD was carried out using boron-doped diamond (BDD) and Pt alternately. The results have shown that pH adjustment to acidic conditions is beneficial to EO. At optimal pH (pH 4), BDD-based EO is superior to remove COD and NH4+ up to around 56% and 64%, respectively. During EOD process, the lower current density at 20.83 mA cm-2 is preferred for the recovery of nitrogenous ions (i.e., NH4+ and NO3-), especially for BDD-EOD. In addition, the dominant humic acid-like (HAL) and soluble microbial products-like (SMPL) substances in the mature leachate are mostly degraded to smaller molecules from 105 Da to 103 Da in both EOD processes. Overall, BDD-EOD favors indirect oxidation and has a higher energy consumption efficiency than Pt-EOD induced by direct oxidation for simultaneous removal of organic and nitrogenous compounds. BDD-EOD requires a lower total operation cost around $2.33/m3 compared to Pt-EOD. It is concluded that hybrid BDD-EOD process is technically feasible as a powerful pre-treatment approach to mature landfill leachate for refractory organics degradation and nitrogenous nutrients recovery.
... The electrochemical disinfection process can be attained with either direct current (DC) or alternating current (AC), with the frequency in a range of 0.5~800 Hz and an operating time of 5~60 minutes. A number of electrode materials have been in use including stainless steel, graphite fibers, carbon cloth, titanium, platinum, and silver (Jeong et al. 2009). Sometimes salt additives such as sodium chloride (NaCl) and sodium bromide (NaBr) are added to improve the performance of the process. ...
Microorganisms are typically present in all media and they pose a greater threat to environmental sources and general health. The most significant part that has been affected by microorganisms is water since it plays a major role in all vital bodily functions. A sufficient water supply is a basic need for humanity. Yet, many nations around the world do not have access to safe and potable water, and many people die because of waterborne pathogens. For this reason, the immediate actions that many countries have adopted are the construction of water and wastewater treatment plants (WWTPs) to reduce dangers related to these pathogens. Nevertheless, pathogens can escape when the processing of wastewater is not applied correctly. Therefore, pathogens can find their way into sludge, effluent, agricultural land, and ultimately water bodies. Considering all points mentioned above, this review briefly discusses the effects of microorganisms in water resources and displays dangers related to human health, and subsequently focuses on the survival and transport of microorganisms. Conventional and advanced processes for pathogen removal from wastewater are also discussed.
With increasing demand for meat and dairy products, the volume of wastewater generated from the livestock industry has become a significant environmental concern. The treatment of livestock wastewater (LWW) is a challenging process that involves removing nutrients, organic matter, pathogens, and other pollutants from livestock manure and urine. In response to this challenge, researchers have developed and investigated different biological, physical, and chemical treatment technologies that perform better upon optimization. Optimization of LWW handling processes can help improve the efficacy and sustainability of treatment systems as well as minimize environmental impacts and associated costs. Response surface methodology (RSM) as an optimization approach can effectively optimize operational parameters that affect process performance. This review article summarizes the main steps of RSM, recent applications of RSM in LWW treatment, highlights the advantages and limitations of this technique, and provides recommendations for future research and practice, including its cost-effectiveness, accuracy, and ability to improve treatment efficiency.
In this paper, ZnWO4 photocatalysts were prepared by hydrothermal method, after which IrO2 was loaded on ZnWO4 by photodeposition to synthesize IrO2/ZnWO4 composite photocatalysts. The prepared photocatalysts were characterized by XRD, SEM, TEM, XPS, and UV–Vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity was investigated by inactivating bacteria in natural seawater. The effect of varying the deposition amount of IrO2 on the photocatalytic activity was investigated. The mechanism of IrO2 modification to enhance the sterilization of ZnWO4 was as follows: first, IrO2 modification significantly enhanced the effective chlorine yield of the samples. Second, IrO2 modification also promoted the charge separation efficiency of the samples. The present work confirms that photocatalytic production of effective chlorine is an important active species for sterilization in seawater systems, which provides a new idea for photocatalytic purification technology in seawater medium.
Wastewater treatment and reuse have risen as a solution to the water crisis plaguing the world. Global warming-induced climate change, population explosion and fast depletion of groundwater resources are going to exacerbate the present global water problems for the forthcoming future. In this scenario, advanced electrochemical oxidation process (EAOP) utilising electrocatalytic (EC) and photoelectrocatalytic (PEC) technologies have caught hold of the interest of the scientific community. The interest stems from the global water management plans to scale down centralised water and wastewater treatment systems to decentralised and semicentralised treatment systems for better usage efficiency and less resource wastage. In an age of rising water pollution caused by contaminants of emerging concern (CECs), EC and PEC systems were found to be capable of optimal mineralisation of these pollutants rendering them environmentally benign. The present review treads into the conventional electrochemical treatment systems to identify their drawbacks and analyses the scope of the EC and PEC to mitigate them. Probable electrode materials, potential catalysts and optimal operational conditions for such applications were also examined. The review also discusses the possible retrospective application of EC and PEC as point-of-use and point-of-entry treatment systems during the transition from conventional centralised systems to decentralised and semi-centralised water and wastewater treatment systems.
Nitrate and microbial contamination of groundwater can occur in countries that face intense urbanization and inadequate sanitation. When groundwater is the main drinking water source, as is often the case in such countries, the need to remove these contaminants becomes acute. The combination of two technologies is proposed here, a biological step to denitrify and an electrochemical step to disinfect the groundwater, thereby aiming to reduce the chemical input and the footprint of groundwater treatment. As such, a pyrite-based fluidized bed reactor (P-FBR) was constructed to autotrophically denitrify polluted groundwater. The P-FBR effluent was disinfected in an electrochemical cell with electrogenerated Cl 2 . Nitrate was removed with 79% efficiency from an initial 178 mg NO 3 ⁻ L ⁻¹ at an average denitrification rate of 171 mg NO 3 ⁻ L ⁻¹ d ⁻¹ , with 18 h hydraulic retention time (HRT). The electrochemical unit achieved a 3.8-log reduction in total coliforms with a 41.7 A h m ⁻³ charge density.
Pathogenic virus inactivation is crucial to eliminate the substantial risk they cause to human health and to ensure safe drinking water. Conventional water disinfection methods generate harmful disinfection by-products, and...
Laser-induced graphene (LIG) has gained popularity for electrochemical water disinfection due to its efficient antimicrobial activity when activated with low voltages. However, the antimicrobial mechanism of LIG electrodes is not yet fully understood. This study demonstrated an array of mechanisms working synergistically to inactivate bacteria during electrochemical treatment using LIG electrodes, including the generation of oxidants, changes in pH-specifically high alkalinity associated with the cathode, and electro-adsorption on the electrodes. All these mechanisms may contribute to the disinfection process when bacteria are close to the surface of the electrodes where inactivation was independent of the reactive chlorine species (RCS); however, RCS was likely responsible for the predominant cause of antibacterial effects in the bulk solution (i.e., ≥100 mL in our study). Furthermore, the concentration and diffusion kinetics of RCS in solution was voltage-dependent. At 6 V, RCS achieved a high concentration in water, while at 3 V, RCS was highly localized on the LIG surface but not measurable in water. Despite this, the LIG electrodes activated by 3 V achieved a 5.5-log reduction in Escherichia coli (E.coli) after 120-min electrolysis without detectable chlorine, chlorate, or perchlorate in the water, suggesting a promising system for efficient, energy-saving, and safe electro-disinfection.
Understanding the bioelectrical properties of bone tissue is key to developing new treatment strategies for bone diseases and injuries, as well as improving the design and fabrication of scaffold implants for bone tissue engineering. The bioelectrical properties of bone tissue can be attributed to the interaction of its various cell lineages (osteocyte, osteoblast and osteoclast) with the surrounding extracellular matrix, in the presence of various biomechanical stimuli arising from routine physical activities; and is best described as a combination and overlap of dielectric, piezoelectric, pyroelectric and ferroelectric properties, together with streaming potential and electro-osmosis. There is close interdependence and interaction of the various electroactive and electrosensitive components of bone tissue, including cell membrane potential, voltage-gated ion channels, intracellular signaling pathways, and cell surface receptors, together with various matrix components such as collagen, hydroxyapatite, proteoglycans and glycosaminoglycans. It is the remarkably complex web of interactive cross-talk between the organic and non-organic components of bone that define its electrophysiological properties, which in turn exerts a profound influence on its metabolism, homeostasis and regeneration in health and disease. This has spurred increasing interest in application of electroactive scaffolds in bone tissue engineering, to recapitulate the natural electrophysiological microenvironment of healthy bone tissue to facilitate bone defect repair.
Bone degeneration associated with various diseases is increasing due to rapid aging, sedentary lifestyles, and unhealthy diets. Living bone tissue has bioelectric properties critical to bone remodeling, and bone degeneration under various pathological conditions results in significant changes to these bioelectric properties. There is growing interest in utilizing biomimetic electroactive biomaterials that recapitulate the natural electrophysiological microenvironment of healthy bone tissue to promote bone repair. This review first summarizes the etiology of degenerative bone conditions associated with various diseases such as type II diabetes, osteoporosis, periodontitis, osteoarthritis, rheumatoid arthritis, osteomyelitis, and metastatic osteolysis. Next, the diverse array of natural and synthetic electroactive biomaterials with therapeutic potential are discussed. Putative mechanistic pathways by which electroactive biomaterials can mitigate bone degeneration are critically examined, including the enhancement of osteogenesis and angiogenesis, suppression of inflammation and osteoclastogenesis, as well as their anti‐bacterial effects. Finally, the limited research on utilization of electroactive biomaterials in the treatment of bone degeneration associated with the aforementioned diseases are examined. Previous studies have mostly focused on using electroactive biomaterials to treat bone traumatic injuries. It is hoped that this review will encourage more research efforts on the use of electroactive biomaterials for treating degenerative bone conditions.
The energy cost and the harm of the residual chlorine by-produced in the electrochemical processes are main hinders for the extensive use of the electrochemical recirculating aquaculture systems (ERAS). The present study conducted shrimp-culture experiments using pilot electrochemical systems to investigate the effects of current density, geometric feature, timing, and other parameters on the effective control of inorganic nitrogen, pathogens, and residual chlorine in aquaculture water. The 50-L electrochemical batch reactor, which featured 154 cm ² (area) of Ti-RuO 2 / Ti electrodes and 66 mA/cm ² of current density, eliminated inorganic nitrogen and Vibrio in rearing seawater collected from a shrimp farm with an initial ammonia concentration of 1.2–4.0 mg/L in 5 min. Air strippings were used to resolve residual chlorine derived from electrooxidation, finding hypochlorous acid decreased from 5.0 mg/L initially to 2.5 mg/L in 2 h of continuous of air aeration to the batch reactor. In the experiments of shrimp culture, The ERAS equipped with a 50-L batch reactor and 500-L shrimp tank effectively keep the inorganic nitrogen concentration in rearing water as required when applying 4.3 g of nitrogen loads transformed from a daily quota of commercial prawn feeds. By precisely controlling the times of intermittent processes of electrooxidation and air stripping, an electrochemical recirculating aquaculture system can achieve both the removal of inorganic nitrogen and residual chlorine, disinfection and reduction of energy cost.
Textile wastewater contains many organic compounds and colors that affect aquatic life and human health when discharged into the environment. High coloration due to excess dyes entering the wastewater causes coloration to the receiving water stream, affects the photosynthesis process of aquatic species, and adversely affects the landscape. SnO2-based electrodes have been extensively used in electrochemical water treatment, but their low durability decreases the pollutant treatment ability. Therefore, it is necessary to add another stable oxide to improve the performance and stability of SnO2 electrodes. This study aims to fabricate Ti/SnO2-Nb2O5 electrodes for the textile wastewater treatment using the electrochemical oxidation method. Different molar ratios of SnO2:Nb2O5 coating were prepared using the sol-gel method and then coated on the Ti substrates for calcination in 60 min at 500 °C. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer Emmett Teller (BET), and cyclic voltammetry (CV) were used to determine the surface and electrochemical properties of Ti/SnO2-Nb2O5 electrodes. The SEM images show that SnO2-Nb2O5 electrode surfaces have the appearance of typical cracking structures of mixed metal oxides electrodes. The XRD spectrum show the SnO2 peaks of facet (110), (101), (200), (301), (321) and Nb2O5 peaks of facet (001), (002), (100), (101), (102) on Ti substrates. Furthermore, the specific surface area of the Ti/SnO2-Nb2O5 electrode ranges from 37.354 m²/g (SnO2:Nb2O5 = 9:1) to 71.885 m²/g (SnO2:Nb2O5 = 1:9). The electrochemical properties of SnO2:Nb2O5 electrodes showed high oxygen, chlorine evolution potential and high organic pollutant degradation in textile wastewater with COD removal at 83 %, decolorization at 74 % and the generation of many free radicals such as HO•, H2O2, O3, Cl2. The results demonstrate that the Ti/SnO2-Nb2O5 electrode with the mole ratio of 3:7 is the best in textile wastewater treatment with the longest service life (39 h).
Photoelectrocatalysis (PEC) can effectively degrade organic pollutants by using photoelectrodes without secondary pollution. However, significant mass transport resistance and decreased catalytic activity caused by the shedding of active components remain a barrier to achieving the photocatalytic system with a high degradation rate and long-term durability. Here, an in situ recombination concept is presented to overcome this challenge. The bionic coral-like electrode, obtained by in situ assembly of UIO-66 around TiO2 nanoflowers (TNF) on Ti-foam substrate, is employed as the photoanode in PEC. Ex situ evaluation of photoelectrochemical activity demonstrates that the [email protected]/Ti-foam ([email protected]/T) design significantly improves the light-propagation, light-absorption and charge transfer. In Situ degradation evaluations also shows that the interesting design promotes rapid and stable degradation of organic dye (e.g. Rhodamine B (RhB)). At 2.0 V of bias potential and pH 7.0 in 5 mg L⁻¹ RhB, under the action of active species such as ·O- 2 and ·OH (proved by the degradation mechanism experiments), the removal rate of RhB can reach 96.1% at 120 min and almost complete removal at 200 min (99.1%).
The combination of electrochemical (EC) pretreatment with hydrogen peroxide (HP) and calcium hypochlorite (CHC) was investigated in this study for their effect on soluble chemical oxygen demand (CODs) and disintegration degree (DD) of waste activated sludge (WAS). For this aim, response surface methodology (RSM) and Box-Behnken design (BBD) were applied the determination of the optimum operational conditions. Operational conditions were varied between 0.2 and 2.0 mmol/g SS for HP and CHC dosages, 1-5 A for the applied current, 2-10 for the initial pH, and 15-45 min for the treatment time. Obtained results for each treatment were accurate and significant with correlation coefficients (R2) of 0.8639% and 0.9189% for EC combined with HP pretreatment and EC combined with CHC pretreatment, respectively. According to the obtained results, CODs increased in comparison to the raw sludge (168 mg/L) noting that CODs for EC - CHC (1155 ± 21 mg/L) was higher than EC - HP (811.5 ± 15 mg/L) at optimized conditions (for EC-HP pretreatment: HP dosage: 0.34 mmol/g TSS, Applied current:5 A, Initial pH:10, Time: 45 min, For EC-CHC pretreatment: CHC dosage: 0.23 mmol/g TSS, Applied current:4.83 A, Initial pH:10, Time: 40 min). Besides, the DD in terms of COD, total nitrogen (TN) and total organic carbon (TOC) (DDCOD, DDTN and DDTOC) registered increased values after the application of the EC treatment with both oxidants. The highest DDCOD, DDTN and DDTOC values were obtained with EC-CHC pretreatment for 11.34%, 20.34% and 9.18% respectively compared to EC-HP pretreatment (DDCOD: 7.37%, DDTN: 15.18% and DDTOC: 6.94%).
Fenton chemistry, which is known to play an effective role in degrading toxic chemicals, is difficult to apply to disinfection
in water treatment, since its reaction is effective only at the acidic pH of 3. The presence of oxalate ions and UV-visible
light, which is known as a photoferrioxalate system, allows the Fe(III) to be dissolved at slightly acidic and near-neutral
pHs and maintains the catalytic reaction of iron. This study indicates that the main oxidizing species in the photoferrioxalate
system responsible for microorganism inactivation is OH radical. Escherichia coli was used as an indicator microorganism. The CT value (OH radical concentration × contact time; used to indicate the effect of the combination of the concentration of the
disinfectant and the contact time on inactivation) for a 2-log inactivation of E. coli was approximately 1.5 × 10−5 mg/liter/min, which is approximately 2,700 times lower than that of ozone as estimated by the delayed Chick-Watson model.
Since the light emitted by the black light blue lamp is similar to sunlight in the specific wavelength range of 300 to 420
nm, the photoferrioxalate system, which can have a dual function, treating water for both organic pollutants and microorganisms
simultaneously, shows promise for the treatment of water or wastewater in remote or rural sites. However, the photoferrioxalate
disinfection system is slower in inactivating microorganisms than conventional disinfectants are.
Surviving fractions of Escherichia coli B exposed to an alternating current (AC) of 50 Hz in a phosphate buffer solution of pH 7.0 at 29°C were closely related to the amount of H202 formed in cell suspensions. At a definite current density, the amount of H202 in the suspensions or in buffer solution without cells increased with increasing AC-exposure time under aerobic conditions. On the other hand, the formation of H202 on AC-exposure was not detected under anaerobic conditions. It was considered that H202 was formed on the surface of carbon electrodes by AC-electrolytic reduction of dissolved oxygen. The amount of H202 formed decreased with increasing concentration of cells suspended or of catalase added to the suspension. When the formation of H202 was significantly suppressed, surviving fractions of cells exposed to AC remained almost unchanged. Growth conditions, modifying the intracellular level of catalase of E. coli, affected the sensitivity of cells to AC-exposure. © 1982, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.
The indigo method for the determination of ozone as formulated for the new Swiss Standard Methods for Drinking Water Analysis is presented with an international list of suppliers of indigo trisulfonate. Such a new selective and simple method will be needed in many countries because current methods for ozone analysis are generally non-selective when applied on real drinking waters or wastewaters. -from Authors Swiss Federal Inst. for Water Resources & Water Pollution Control, EAWAG, CH-8600 Dubendorf, Switzerland.
Peroxodiphosphate salts are strong oxidizing agents that presently can be used as reagents in organics synthesis, cosmetic, agriculture, polluted water treatment, and also as bleaching agents in the detergent industry. They also have potential uses as persulfates substitutes. In this work, a new method for the synthesis of peroxodiphosphate, based on the use of boron-doped diamond electrodes, is described. The procedure developed is able to produce high-purity peroxodiphosphate (no reagents different from phosphate salts are used as raw materials) with a high current efficiency. The efficiencies of the process strongly depend on the pH and on the operating conditions (temperature and current density). The optimum range of pH is 12-13. Current densities over 1000 A m-2, and low temperatures, guarantee high current efficiencies and product conversions. The pH control is considered to be one of the more important operation constraints in the process. Great concentrations of phosphate in the raw materials increase the process efficiencies but they also seem to favor the corrosion of the electrode. Concentrations below 1 M of PO43- are recommended to avoid this problem.
The electrochemical oxidation of acidic aqueous phenol wastes has been studied using boron-doped diamond thin-film (BDD) and
AISI 304 stainless steel (SS) electrodes. A voltammetric study shows marked differences in the electrochemical behavior of
these two electrodes. The surface of the SS electrodes undergoes significant changes when this material is used as the anode
in the treatment of aqueous wastes, even in the potential region of electrolyte stability. These changes have important effects
on the waste treatment process. Conversely, the BDD electrode does not undergo any appreciable change during the electrochemical
oxidation of the wastes. An electrolysis study highlighted significant differences between the behavior of the two electrodes.
First, the oxidation performed using a BDD electrode leads to the rapid sequential formation of aromatic compounds (hydroquinone,
benzoquinone), carboxylic acids (maleic, fumaric, and oxalic), and carbon dioxide. The oxidation performed using SS electrodes,
on the other hand, involves a slower sequential formation of the same compounds, indicating a lower energetic efficiency of
these electrodes in the destruction of the organic matter, and to the formation of some insoluble compounds resulting from
the electrocoagulation of organic matter with iron dissolved from the electrode. © 2002 The Electrochemical Society. All rights
reserved.
Rate constants have been compiled for reactions of various inorganic radicals produced by radiolysis or photolysis, as well as by other chemical means in aqueous solutions. Data are included for the reactions of ⋅CO2−, ⋅CO3⋅-, O3, ⋅N3, ⋅NH2, ⋅NO2, NO3⋅, ⋅PO32-, PO4⋅2-, SO2⋅ -, ⋅SO3 -, SO4⋅-, ⋅SO5⋅-, ⋅SeO3⋅ -, ⋅(SCN)2⋅ -, ⋅CL2⋅-, ⋅Br2⋅ -, ⋅I2⋅ -, ⋅ClO2⋅, ⋅BrO2⋅, and miscellaneous related radicals, with inorganic and organic compounds. © 1988, American Institute of Physics for the National Institute of Standards and Technology. All rights reserved.
Two different Ti/Pt–Ir materials (commercial and home made) and Ti/PdO + Co3O4 were investigated for their electrocatalytic properties versus Cl2 evolution reaction. The materials were used in a batch electrochemical reactor to treat biologically recalcitrant di-azo compound. An electrochemically driven oxidation, mediated by a Cl2/Cl− couple, proved efficient for destruction of this complex organic molecule, causing cleavage of the conjugated double bonds and destruction of unsatured bonds. Both Ti/Pt–Ir materials performed well; lower kinetics obtained with the Ti/PdO + Co3O4 anode was caused by adsorption of the model compound, evidenced in preliminary voltammetric measurements. The dye oxidation reaction followed the second order kinetics with partial orders in the model compound and (time varying) chlorine concentrations equal to one. Specific energy consumption of 3.12 kWh m−3 proved the process more economic than the homogeneous phase oxidation.
Electrolytic production of hypochlorite in very dilute chloride solutions is investigated using platinum and iridium oxide coated titanium expanded metal electrodes as anodes. The dependence of the hypochlorite production rate on temperature, chloride concentration and current density was determined. It was found that the hypochlorite production rate is consistently higher on iridium oxide coated titanium compared to platinum coated titanium electrodes.
Boron-doped diamond (BDD) electrodes were studied with respect to the formation of inorganic by-products in water electrolysis. Experiments in non-divided cells were performed with systems containing sulphate, chloride, chlorite, chlorate and nitrate ions. Discontinuous experiments in thermostated cells with rotating disk diamond anodes and expanded mesh IrO2 cathodes were carried out at 20 °C. Current density was varied between 50 and 300 A m−2. Ion chromatography was mainly used for species detection.It was not possible to demonstrate the decomposition of sulphate although a slight tendency seems to exist in some experiments. Hydrogen peroxide is one of the anodic and cathodic by-products. Active chlorine is detectable at higher chloride concentrations compared with the use of mixed oxide anodes (MIO). One reason for this is the reaction of formed chlorine with ozone or hydrogen peroxide. Chlorate can be formed electrolysing chloride, hypochlorite and chlorite solutions. Perchlorate formation was detected. Cathodic processes are responsible for the formation of nitrite ions and ammonia. If chlorine is present, the formation of monochloramine is one possible side reaction. Results show that the processes are very complex. Reaction spectra may vary from case to case. Perchlorate formation is a high risk in drinking water treatment.
Laboratory experiments were carried out to investigate the mechanisms of electrochemical (EC) disinfection of artificial wastewater contaminated by Escherichia coli culture. Comparative disinfection tests with chlorine, ozone and hydroxyl (OH−) radicals produced by the Fenton reaction were also conducted. It was demonstrated that the EC process was highly effective for wastewater disinfection. Investigation with scanning electron microscopy (SEM) showed different appearances of damage to in the surface morphology and structure of the cells after different forms of disinfection. Substantial leakage of intracellular materials was found for the E. coli cells after EC disinfection, which was also observed for the cells treated by the Fenton reaction. However, such cell lysis was noticeable to a less extent for the ozonated cells and hardly noticeable for the chlorinated cells. Electron microscopic examination suggested that the cells were likely inactivated during the EC process by the chemical products with an oxidising power similar to that of hydroxyl radicals and much stronger than that of chlorine. The SEM results support the hypothesis that the predominant killing action of EC disinfection is provided by high-energy intermediate EC products. Therefore, in addition to electro-chlorination, the great capacity of EC disinfection may be attributable to the generation of short-lived germicidal agents, such as free radicals.
The DiaCell® technology has been successfully tested against Legionella infection in several water types and under various working conditions. Depending on the water composition, Legionella can be completely inactivated with current densities as small as 50 mA/cm2 with low contact times (<5 min). The higher the oxidant concentration in the electrolyzed water, the more rapid is the Legionella inactivation after injection. Bicarbonates in contaminated water were identified as very good supports for electrochemical disinfectants production for Legionella inactivation without high chlorine concentration. At the same time, sulfates in water do not provide any disinfection capacity by DiaCell® electrolysis.
The procedure described for the determination of hydrogen peroxide in aqueous solution, at concentrations in the rnage 1−120×10−6 mol l−1, is based on reduction of copper (II) ions by hydrogen peroxide in the presence of excess of 2,9-dimethyl-1,10-phenanthroline (DMP) to form the copper (I)-DMP complex. The copper (I)-DMP complex is determined directly by spectrophotometric measurement at 454 nm.
The concentration of aqueous ozone can best be determined by the decolorization of indigo trisulfonate (600 nm, pH below 4) whenever the ozone cannot be measured directly by its u.v. absorption. The method is stoichiometric and extremely fast. The change of absorbance vs ozone added is −2.0 ± 0.1 × 104 M−1 cm−1 and is independent of the concentration of aqueous ozone in the range 0.005–30 mg 1−1. The precision of the analysis is 2% or 3 μg 1−1 for low concentrations if a spectrophotometer or a good filter instrument is used. Visual methods can be used to measure 0.01 mgl−1 ozone. Secondary oxidants produced by ozone in natural water, including hydrogen peroxide or chlorite, do not interfere; chlorine can be masked. The reagent solution is stable for 3 months. The method is recommended for kinetic measurements, for studies of ozonation processes and for visual field methods.
The electrochemical oxidation (or combustion) of organics with simultaneous oxygen evolution has been investigated using different electrode material (Pt, Ti/IrO2, Ti/SnO2). A simplified mechanism for the electrochemical oxidation or combustion of organics is presented according to which selective oxidation occurs with oxide anodes (MOx) forming the so-called higher oxide MOx+1 and combustion occurs with electrodes at the surface of which OH radicals are accumulated. Detection of OH radicals formed by water discharge at different anodes using N,N-dimethyl-p-nitrosoaniline (RNO) as a spin trap and preparative electrolysis confirm the proposed mechanism.
Conducting diamond thin film is a new electrode material that has received great attention recently because it possesses several technologically important characteristics such as an inert surface with low adsorption properties, remarkable corrosion stability, even in strong acidic media, and an extremely wide potential window in aqueous and non-aqueous electrolytes. Thanks to these properties diamond electrodes meet the requirements for a wide range of electrochemical applications. The object of this article is to summarise and discuss the recent results available in the literature concerning the application of diamond electrodes to electrochemical processes such as water treatment and electro-synthesis of organic and inorganic compounds.
After introductory general thermodynamic and kinetic considerations, the possible factors which can distort the kinetic measurements of Cl2 evolution at oxide electrodes giving rise to mistaken mechanisms are analyzed as resulting from a retrospective analysis of the literature. Such factors include: mixed potentials, porosity, removal of produced Cl2, bubble formation, support passivation, morphology and composition of the active layer, ion specific adsorption, pH effects. In the light of the insight step-by-step gained on the possible interference by the above experimental factors, the various proposals of mechanism are reviewed, mainly chronologically, to highlight the conceptual and experimental progress made in this field in the past 15 years. Conclusions are finally drawn which enable some possible topics for further research in this area to be discussed.
The electrogeneration of hydroxyl radicals was studied at a synthetic B-doped diamond (BDD) thin film electrode. Spin trapping was used for detection of hydroxyl radicals with 5,5-dimethyl-1-pyrroline-N-oxide and with salicylic acid using ESR and liq. chromatog. measurements, resp. The prodn. of H2O2 and competitive oxidn. of formic and oxalic acids were also studied using bulk electrolysis. Oxidn. of salicylic acid gives hydroxylated products (2,3- and 2,5-dihydroxybenzoic acids). The oxidn. process on BDD electrodes involves hydroxyl radicals as electrogenerated intermediates. [on SciFinder (R)]
Electrolysis in aq. 1M HClO4 and 1M H2SO4 solns. was carried out under galvanostatic conditions using B-doped diamond electrodes (BDD). Analyses of the oxidn. products showed that in 1M HClO4 the main reaction is oxygen evolution, while in H2SO4 the main reaction is the formation of H2S2O8. In both electrolytes small amts. of O3 and H2O2 are formed. Finally, a simplified mechanism involving hydroxyl radicals formed by H2O discharge is proposed for H2O oxidn. on B-doped diamond anodes. [on SciFinder (R)]
This paper presents the study of the electrochemical oxidation of the pesticide atrazine at a Ti/Ru(0.3)Ti(0.7)O(2) dimensionally stable anodes (DSA). The effect of using different supporting electrolytes (NaCl, NaOH, NaNO(3), NaClO(4), H(2)SO(4) and Na(2)SO(4)) during the galvanostatic electrolysis of atrazine was investigated. It was observed that the removal of atrazine and total organic carbon (TOC) was only achieved at appreciable rates when NaCl was used as the supporting electrolyte, due to the oxidising species formed in this electrolyte (e.g. ClO(-)). Variation of the NaCl concentration demonstrated that, although only low concentrations of NaCl are necessary to result in the complete removal of atrazine in solution, TOC removal is almost linearly dependent on the quantity of NaCl in solution. Examination of the applied current density indicates that the efficiency of TOC removal reaches a maximum at 60 mA cm(-2). Testing of alternative electrode materials containing SnO(2) did not improve the efficiency of atrazine removal in Na(2)SO(4), but in NaCl a small increase was observed. Overall there appears to be no great advantage in using SnO(2)-containing electrodes over the Ti/Ru(0.3)Ti(0.7)O(2) electrode.
Electrochemical disinfection has emerged as one of the most promising alternatives to the conventional disinfection of water in many applications. Although the mechanism of electrochemical disinfection has been largely attributed to the action of electro-generated active chlorine, the role of other oxidants, such as the reactive oxygen species (ROS) *OH, O3, H2O2, and *O2- remains unclear. In this study, we examined the role of ROS in the electrochemical disinfection using a boron-doped diamond (BDD) electrode in a chloride-free phosphate buffer medium, in order to avoid any confusion caused by the generation of chlorine. To determine which species of ROS plays the major role in the inactivation, the effects of several operating factors, such as the presence of *OH scavenger, pH, temperature, and the initial population of microorganisms, were systematically investigated. This study clearly showed that the *OH is the major lethal species responsible for the E. coli inactivation in the chloride-free electrochemical disinfection process, and that the E. coli inactivation was highly promoted at a lower temperature, which was ascribed to the enhanced generation of O3.
Recently, the electrochemical disinfection has gained a great interest as one of the alternatives to conventional chlorination due to its high effectiveness and environmental compatibility. Despite the extensive reports on electro-chlorination disinfection, few researches were reported on the systems without generating chlorine. This study mainly focused on the potential disinfecting ability of electro-generated oxidants other than chlorine with using an inert medium (chloride-free phosphate buffer solution), which was intended to exclude the formation of chlorine during the electrolysis, as the Escherichia coli as an indicator bacterium was disinfected by applying the current to a platinum anode. The electrochemical inactivation of E. coli without chlorine production was demonstrated to occur in two distinct stages. The first stage inactivation takes place rapidly at the beginning of electrolysis, which appears to be achieved by the electrosorption of negatively charged E. coli cells to the anode surface, followed by a direct electron transfer reaction. As the electrolysis continues further, the inactivation becomes slower but steady, in contrast to the first stage of inactivation. This was attributed to the action of reactive oxidants generated from water discharge, such as hydroxyl radical. Overall, this study suggests that the electrochemical disinfection could be successfully performed even without producing chlorine, recommending the potential application for disinfecting water that does not allow including any chloride ions (such as the production of ultra-pure sterilized water for semiconductor washing).
Chlorination is the most common method worldwide for the disinfection of drinking water. However, the identification of potentially toxic products from this method has encouraged the development of alternative disinfection technologies. Among them, electrochemical disinfection has emerged as one of the more feasible alternatives to chlorination. This article reviews electrochemical systems that can contribute to drinking water disinfection and underscores the efficiency of recently developed diamond films in chlorine-free electrochemical systems.
Ultraviolet Disinfection Guidance Manual. EPA 815-D-03-007
USEPA, 2003. Ultraviolet Disinfection Guidance Manual. EPA
815-D-03-007. Office of Water, Washington, DC.
Electrochemical oxidation of aqueous phenol wastes using active and nonactive electrodes
- P Canizares
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