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Electron Microscopic Investigation of the Bactericidal Action of Electrochemical Disinfection in Comparison with Chlorination, Ozonation and Fenton Reaction
Abstract
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.
... b) Resistencia de los microorganismos a los tratamientos de desinfección. Los patógenos se pueden clasificar en orden decreciente de acuerdo con su resistencia a los tratamientos de desinfección en cuatro grupos principales: esporas de bacterias, quistes de protozoarios, virus y bacterias libres (Diao et al., 2004(Diao et al., :1421(Diao et al., -1426. La resistencia relativa a la desinfección de estos microorganismos se atribuye a diferencias que tienen en su cito-estructura. ...
... La deshidratación parcial de las esporas puede ser una causa de fuerte resistencia, esto ocurre también en el caso de los quistes. La gran resistencia de los virus se atribuye a la ausencia de enzimas y otros sistemas sensibles por lo que su inactivación se logra mediante la desnaturalización de proteínas de la cápsula (Diao et al., 2004(Diao et al., : 1421(Diao et al., -1426Gehra et al., 2003: 4573-4586). ...
... La destrucción de agentes patógenos se produce directamente por la desintegración de la pared celular, debido a la generación de radicales libres. Esta condición convierte al ozono en un eficiente agente destructor de bacterias, quistes resistentes de bacterias, esporas, hongos y posiblemente sea igual de efectivo para la eliminación de virus (Algolini et al., 2001: 213-281;Gehra et al., 2003: 4573-4586;Diao et al., 2004Diao et al., : 1421Diao et al., -1426. A diferencia del cloro, la capacidad desinfectante del ozono no depende del periodo de contacto en el agua, sino de la dosis suministrada. ...
La capacidad de estos organismos al provocar enfermedades en el
hombre depende de su actividad y concentración, así como de la forma
contacto (uso y/o consumo del recurso hídrico contaminado) y de la resistencia
del organismo ante el agente patógeno. Por este motivo, surge
la necesidad de desarrollar alternativas que promuevan la distribución y
uso confiable del recurso hídrico.
... The effect of the Fenton system on cell metabolism depends on the concentration of Fe 2+ and H 2 O 2 used in the inactivation processes [125]. Diao et al. [126] uncovered the mechanism of Fenton reagents on E. coli inactivation. SEM images of the bacteria treated by Fenton showed that the reaction resulted in the deformation of the cell surface with leakage of cell components. ...
... However, the conventional Fenton processes are still of low efficiency toward H 2 O 2 decomposition because of the sluggish kinetics of the Fe 3+ / Fe 2+ redox cycles. It is crucial to enhance Fenton system with the additional energy input or inducing reductive agents [126]. ZVI showed promising results on the removal of pathogens and contaminants in drinking water, including viruses and bacteria, DBPs and heavy metal ions [127]. ...
... They uncovered that the disinfection performance was improved with a higher operational current, and chlorination remained the key disinfection mechanism for synthetic stormwater while using 9 mg L -1 of chloride. The presence of Cl − in the electrolyte improved the cell inactivation efficiency, while H 2 PO 4 − , HCO 3 − , and CO 3 2− have inhibitory effects on the inactivation [126,157]. Lacasa et al. [158] showed 6-log reduction of E. coli was achieved in 3 min by BDD electrode under a current density 25.5 mA cm − 2 with Cl − concentration of 18.3 g L -1 . Moreno-Andrés et al. [62] reported that BDD could disinfect 4-log of marine heterotrophic bacteria at 0.019 Ah L -1 . ...
The disinfection of microbial pathogens plays an important role in control of waterborne diseases and health issues. Recently, advanced oxidation processes (AOPs) are applied as powerful and effective technologies for wastewater purification and pathogen elimination. This review will showcase the recent endeavors in the fields and provide a comprehensive understanding of pathogens inactivation by diverse AOPs (i.e., Fenton processes, photocatalysis, electrochemical advanced oxidation processes (EAOPs), sonolysis, ozonation, and persulfate-based AOPs). The mechanisms of AOPs-based disinfection include the destruction of cell envelope, enzymes, and intracellular substances via diverse reactive oxygen species (ROS). The primary ROS are HO•, SO4•−, O2•−, ¹O2, and O3, which exhibit different oxidative capacities, and can react with cell envelope to destroy the permeability of cell membrane. Specifically, this review emphasizes on the performances and mechanisms of different AOPs systems in microbial inactivation as well as perspectives in practical applications of disinfection in terms of feasibility, operating cost, and sustainability.
... The EC technique was greatly efficient for wastewater remediation [21]. An E. coli eliminating performance of 100% may be obtained for the model water with a residence time of only 0.5 min and a current density (CD) of 25 mA/cm 2 ( Table 2). ...
... Diao et al. [21] concluded that all of the disinfection techniques studied in their research (i.e., EC disinfection, chlorination, ozonation and the Fenton reaction), were powerful in eliminating E. coli with an initial density of 10 8 /mL in the examined wastewater. With an eliminating performance of 99.4% or greater, almost all of the cells in the disinfected samples lost their viability from the viewpoint of being biologically available to incubation ( Figure 2). ...
... As mentioned previously, the elevated performance of EC disinfection may be given by short-lived and energy rich intermediate products with a more efficient killing capacity [21]. These chemical products obviously comprise free radicals an oxidizing strength comparable to that of free radicals and much powerful than that of Cl 2 [21]. ...
Killing pathogens by different electrochemical (EC) disinfection means has been largely reported in the literature, even if the influence of process variables and reactor conception on kill performance has not been well comprehended. This review concentrates on EC microbial killing mechanisms especially the free radicals' contribution and the effect of the electric field (EF), which are by their nature poisonous to microbes. Some mechanisms have been suggested to interpret the deadliness of EC application. Such pathways comprise: 1) oxidative stress and cell loss of life because of electro-chemically produced oxidants, 2) irreversible permeabilization of cell membranes by the placed EF, 3) electrooxidation of vital cellular constituents during exposure to electric current or induced EFs, and 4) electrosorption of negatively charged E. coli cells to the anode surface followed by direct electron transfer reaction. Future investigations have to be more dedicated to the EF influence in the EC disinfection, as it is the main part of the involved mechanisms. Employing granular activated carbon post-treatment could greatly reduce the concentrations and poisonous effects of disinfection by-products. Moreover, secure multi-barrier techniques, like distillation, plasma discharge, nanotechnologies, and membrane processes remain to be suggested, tested, and industrially encouraged. Despite their limitations, both adsorptive techniques and membrane processes persist to be an encouraging domain of research thanks to their relatively low costs and ease of applications.
... Increasing the current density to 2.27 mA cm −2 resulted in a log reduction of 1.21 at the same 6 min contact time. The major contributing factor of the inactivation of R. solani under these conditions was most likely indirect oxidation by ROS ( (Michaud et al. 2003;Diao et al. 2004;Jeong et al. 2006;Kraft 2008;Bruguera-Casamada et al. 2017;Liang et al. 2018). OH • are thought to be the major ROS player in these systems (Diao et al. 2004), although inactivation attributable to OH • in these systems is limited to the immediate vicinity of the electrode due to OH • instability (Jeong et al. 2006; Martínez-Huitle and Brillas 2008). ...
... The major contributing factor of the inactivation of R. solani under these conditions was most likely indirect oxidation by ROS ( (Michaud et al. 2003;Diao et al. 2004;Jeong et al. 2006;Kraft 2008;Bruguera-Casamada et al. 2017;Liang et al. 2018). OH • are thought to be the major ROS player in these systems (Diao et al. 2004), although inactivation attributable to OH • in these systems is limited to the immediate vicinity of the electrode due to OH • instability (Jeong et al. 2006; Martínez-Huitle and Brillas 2008). The combination of all ROS causes damage to the cell membrane, which ruptures and releases cell constituents, leading to inactivation (Diao et al. 2004). ...
... OH • are thought to be the major ROS player in these systems (Diao et al. 2004), although inactivation attributable to OH • in these systems is limited to the immediate vicinity of the electrode due to OH • instability (Jeong et al. 2006; Martínez-Huitle and Brillas 2008). The combination of all ROS causes damage to the cell membrane, which ruptures and releases cell constituents, leading to inactivation (Diao et al. 2004). This combination of diverse ROS activity may explain the observed pathogen inactivation efficacy; however, there are likely other contributing factors that should be considered when evaluating the overall system. ...
Boron-Doped Diamond (BDD) anodes and stainless-steel cathodes were employed in an electrochemical flow cell and evaluated for inactivation efficacy on the plant pathogen Rhizoctonia solani in hydroponic fertigation water. The electrochemical system showed promise as an electrochemical advanced oxidation process (EAOP) in that significant reductions in R. solani were achieved; however, in order to achieve complete inactivation, the system required supplemental chloride (20 mg/L), while using 9.09 mA/cm2. The chloride allowed for low levels of free chlorine ( 0.17 mg/L) that were more active in the bulk solution, complementing the electrode surface EAOP reactions. Perchlorate production was an initial concern but was found to be negligible under the conditions tested. Small but significant increases in nitrate, ammonium, and sulphate were observed following treatment. These increases are hypothesized to originate from the degradation of proteins and amino acids released during pathogen cell disruption.
... During electrochemical disinfection of wastewater, influent flows through a disinfection chamber equipped with electric current-charged electrodes (Diao et al. 2004). The most influencing parameters of the electro-disinfection process are reactor configuration, electrodes, electrolyte composition, microorganisms, current density, and pH (Chen 2004;Kerwick et al. 2005;Jeong et al. 2007Jeong et al. , 2009Schmalz et al. 2009). ...
... According to Mook et al. (2014), the setups of the electrochemical disinfection treatment process can be divided into two groups: (a) direct electrolyzer and (b) mixed oxidants generator. In a direct electrolyzer, oxidants are produced directly from the wastewater using the electrolyzer, while strong oxidizing species such as active chlorine (Cl 2 , HOCl, and OCl − ), chlorine dioxide (ClO 2 ), O 3 , H 2 O 2 , and other short-live radicals are fabricated from the supplied concentrated brine solution in the mixed oxidants generator (Diao et al. 2004;Kerwick et al. 2005;Jeong et al. 2007). The reactions that take place in Table 4 General mechanism of ammonia removal in electrooxidation process M: metal *a = 1 or 2; **b = 1 or 2 ...
Wastewater from the livestock industries contains high concentration of nutrients, organic pollutants, suspended solids, and pathogenic microorganisms. Discharge of livestock wastewater without proper treatment can therefore cause serious pollution, calling for advanced treatment methods. For instance, electrochemical treatments are gaining attention because they are clean and flexible. Compared to conventional biological treatment methods, electrochemical processes exhibit higher pollutant removal efficiencies within shorter time periods. Here, we review the electrochemical treatment of livestock wastewater with focus on electrocoagulation, electrooxidation, and electro-disinfection. We present factors controlling effective process design and operation. Pollutants removal from livestock wastewater, economic analysis, and scaling-up considerations are also discussed. The oxidation of electrodes during electrocoagulation induces periodical replacement and thus influences the operational cost. Dimensionally stable metal oxide-layered titanium electrodes such as Ti/PbO2, Ti/RuO2, Ti/IrO2, and Ti/IrO2–Ta2O5–Pt are becoming popular due to their stability. Reactor design and operational parameters govern the effectiveness of the treatment process. Further pilot-scale studies are required to scale up and demonstrate the potential of electrochemical livestock wastewater treatment techniques.
... Active chlorine production was targeted in the working solution prepared by adding sodium chloride (NaCl) as a salt to the bi-distilled water [9,12]. Other studies include combined use of chlorine, ozone and electrolytic reactions [41,52]. Clearly, wastewaters contain complex mixtures of chemical and biological content. ...
... Therefore, a direct comparison of the obtained results the ones available in the literature is technically not possible. For instance, the works by Diao et al, Bergman et al and Scialdone et al show the existence of oxidizer production and indicates/explains the disinfection process, but do not provide any quantitative results for the oxidizers or the disinfection rates [52,53,56]. The work by Martinez-Huitle and Brillas provide a detailed analysis of electrochemical methods for disinfection, however the scope was limited to drinking water case, unlike the groundwater application herein [46]. ...
... The bactericidal effect of this species can be limited depending on the initial concentration (Ölmez and Kretzschmar, 2009). For this reason, the activation of H 2 O 2 with other oxidants or catalysts to improve the processes efficiencies has been reported in literature (Diao et al., 2004;Liu et al., 2018;Yang et al., 2012). The combined effect of H 2 O 2 and ozone (O 3 ) promotes the generation of large amounts of hydroxyl radicals (Eq. ...
... Other AOPs applied to water disinfection are technologies based on electrochemistry which are commonly known as electrochemical advanced oxidation processes (EAOPs) (Diao et al., 2004;Griessler et al., 2011). EAOPs are processes in which a direct current electric field is applied across the contaminated effluent, promoting the generation of large amounts of highly reactive species that destroy chemical and biological pollutants. ...
The occurrence of antibiotic-resistant bacteria (ARB) in water bodies poses a sanitary and environmental risk. These ARB and other mobile genetic elements can be easily spread from hospital facilities, the point in which, for sure, they are more concentrated. For this reason, novel clean and efficient technologies are being developed for allowing to remove these ARB and other mobile genetic elements before their uncontrolled spread. In this paper, a review on the recent knowledge about the state of the art of the main disinfection technologies to control the antibiotic resistance spread from natural water, wastewater, and hospital wastewater (including urine matrices) is reported. These technologies involve not only conventional processes, but also the recent advances on advanced oxidation processes (AOPs), including electrochemical advanced oxidation processes (EAOPs). This review summarizes the state of the art on the applicability of these technologies and also focuses on the description of the disinfection mechanisms by each technology, highlighting the promising impact of EAOPs on the remediation of this important environmental and health problem.
... pneumoniae during the electrolysis of urines with the MIKROZON® cell but their disinfection mechanism can differ: disinfectant species can cause damage on the cell wall [39,40] or directly penetrate inside the cell [39,41] and destroy the genetic material. For this reason, to understand the role of disinfectants on the cell damage, the crystal violet assay was carried out. ...
... These results suggest that the main mechanism of the electrogenerated oxidants for killing bacteria could be the damage on the cell wall and, the subsequent attack to the genetic material. This agrees previous works reported in literature where the cell permeability during the electrochemical disinfection is evaluated and changes on cell wall were observed [29,39,40,43]. Proteins and genetic material (DNA) are needed for bacteria survival [44]. ...
In this work, the disinfection of urines polluted with Klebsiella pneumoniae (K. pneumoniae) using a commercial electro-ozonizer is described. The device consists of a membrane-electrode assembly flow cell that specially promotes the electrochemical generation of ozone. Results show that a complete disinfection is attained in less than 180 min when working at current intensities higher than 0.5 A. The higher the current intensity, the higher the disinfection rate. Furthermore, the use of an electro-ozonizer for treating diluted urines leads to higher disinfection efficiencies. Ozone and chlorine-based disinfectants (hypochlorite and chloramines) were identified as the main oxidant species involved in killing bacteria. The combined effect of all disinfectants promotes higher removal efficiencies in comparison with the single effect of ozone evaluated in a urine matrix without chlorides, being more remarkable at lower current intensities. The crystal violet assay showed that cell wall is damaged by the electrogenerated oxidants and it is more remarkable by the combined effect of ozone and chlorine disinfectants when increasing the current intensity. Finally, the degradation of total proteins and genetic material (DNA) were also monitored and related to the oxidants produced during the electrochemical process.
... High trans-membrane potential (>1 V) and long exposure to an electric field cause an irreversible damage to the lipid bi-layer membrane, leading eventually to the death of the cell. 72 Diao et al. 73 concluded that electrochemical disinfection was closer in its mechanism to the action of hydroxyl radicals than to chlorination. ...
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.
... In recent years, several concentration ranges of oxidants have been tested for FP; however, a high concentration (>20 mM) of H 2 O 2 is necessary in order to react with the cell membrane directly to increase its permeability and damage all the macromolecules [4,12]. In addition, most of the studies were performed using simple matrices (distilled water), without the presence of compounds present in the real wastewater [13,14] which can reduce the efficiency of the disinfection interfering as a scavenger to the radicals formed. Thus, there is a need to increase the knowledge related to the disinfection under conditions similar to real applications. ...
Disinfection is an essential and significant process for water treatment to protect the environment and human beings from pathogenic infections. In this study, disinfection through the generation of hydroxyl (Fenton process (FP)) and sulfate (Fenton-like process (FLP)) radicals was validated and optimized. The optimization was carried out in synthetic water through an experimental design methodology using the bacteria Escherichia coli as a model microorganism. Different variables were evaluated in both processes: precursor concentration (peroxymonosulfate (PMS) and H2O2), catalyst concentration (Fe+2), and pH in the Fenton process. After that, the optimized conditions (FP: 132.36 mM H2O2, 0.56 mM Fe+2 and 3.26 pH; FLP: 3.82 mM PMS and 0.40 mM Fe+2) were applied to real matrices from wastewater treatment plants. The obtained results suggest that both processes are promising for disinfection due to the high oxidant power of hydroxyl and sulfate radicals.
... There are also emerging technologies such as electrochemical disinfection (Hong, 2014;Stewart-Wade, 2011) using Dimensionally Stable Anodes (DSA) (Hong, 2014) and Boron-Doped Diamond (BDD) electrodes (Lévesque et al., 2020). Conventional and emerging water treatment technologies have been compared for their efficacy for pathogen removal (Diao et al., 2004;Kerwick et al., 2005;Li et al., 2011), albeit primarily in drinking water applications. There is notable research that explores using electrochemical disinfection methods in hydroponics (Bakheet et al., 2020;Bandte et al., 2016;Dannehl et al., 2016;Rodriguez et al., 2018); however, much of this research focusses on electrochemical methods to produce concentrated chlorine on site, which is then inject into the solution. ...
Capturing and reusing fertigation drainage is a key strategy for maximizing greenhouse production efficiency while minimizing the impact of wastewater discharge on receiving ecosystems. Fertigation drainage, in this regard, refers to irrigation water mixed with fertilizer that has once passed through soilless culture. Although an economically and environmentally prudent practice, recirculating fertigation solutions does pose an increased risk of pathogen proliferation. There are many water disinfection technologies currently available to growers, including ozone (O3(aq)) and Advanced Oxidation Processes (AOP). Beyond currently available treatment options there are emerging technologies that have yet to be optimized for recirculating hydroponics. Electrochemical systems based on Dimensionally Stable Anodes (DSA) offer a novel method for disinfecting fertigation. Using Cyclamen persicum as a representative greenhouse floriculture crop, fertigation solutions were inoculated with Fusarium oxysporum isolated from a diseased C. persicum sample. Following inoculation, solutions were treated with one of either a DSA electrochemical system, a UV/Ozone AOP system, or ozonation. Solutions were then applied to the crop and disease progression was monitored. The positive control group (F. oxysporum added) exhibited pathogenicity following the recirculation of the fertigation solution, while the negative control (F. oxysporum absent) did not show pathogenicity in C. persicum. All water treatment systems achieved a log-4 reduction in F. oxysporum, which prevented pathogenicity in plants. Furthermore, there were no significant differences in plant physiology between the water treatment methods in comparison to the negative control group. However, all treatments performed significantly better than the positive control group which experienced pathogenicity. Solution nutrient analysis indicated stability across all treatments. Energy consumption was also monitored and demonstrated a two-fold reduction in electricity use with the electrochemical flow cell (EFC) compared to the AOP system.
... The indirect sterilization process occurs through the generation of strong oxidizing and bactericidal agents such as active chlorine and free radicals under the action of the voltage, which can attack the cell membrane, nucleic acids, proteins and other macromolecules of microorganisms, causing the cells to die. Due to these two effects, the growth of microbes in irrigation water decreased, and the hardness of the water source also decreased, but the water quality was improved (Chung et al., 2019;Diao et al., 2004;Gerrity et al., 2018). The average Cl − concentration in the R-RWs used in this study was 93.7 mg/l (Table S1), and the cumulative Cl − removal by EO in a single operating cycle (12 h) was about 61% and achieved a sterilization rate of more than 90% (Fig. S6). ...
Biofilm formation in reclaimed water (RW) distribution systems presents significant technical challenges to RW utilization. Two main technologies to control biofilm formation, microbial antagonism (MA) and electrochemical oxidation (EO), are not yet widely used in drip irrigation systems (DIS) and their mechanisms of action need further clarification. In this study, we first showed that the MA and EO treatments reduced biofilm formation by about 62% and 68%, respectively, and extracellular polymeric substance (EPS) content by 14% and 49%, respectively, in biofilms compared with raw RW type 1 (R-RW1) in unused pipes, thus effectively improving the performance of DIS. When MA-RW and EO-RW were applied to already clogged systems, the degree of clogging alleviation varied depending on the severity of the original clogging. We recommend adding the antagonist, Bacillus subtilis, to RW at 25% clogging for the maximum effect and to slow the microbial adaptation process. Compared to MA, the recovery effect of EO was slower initially but lasted longer and had a significantly better alleviating effect on severely clogged pipelines. Illumina Mi-SEQ high-throughput sequencing data showed that both MA and EO resulted in a significant decrease in microbial diversity, dynamic changes in bacterial community structure, and disruption of network interaction and network modularity. Meanwhile, both treatments promoted the growth of specific microorganisms, enhanced the interaction between certain microbial components, and improved the efficiency of information, matter, and energy exchange within the modules. In summary, we verified the dredging effect of two strategies on DIS under different water conditions, revealed the differences in their mechanisms of action, and proposed their application scenarios. Our results will help improve the efficiency of RW in agricultural drip irrigation systems and effectively reduce maintenance costs.
... collapse were more obvious, and there was no obvious cellular material around the cell ( Fig. 7c and d). Electrochemical oxidation could destroy the integrity of the cell structure of cyanobacteria and degrade the leaking intracellular contents, leading to the death of cyanobacteria cells and resulting in their removal (Diao et al., 2004;Ma et al., 2012). ...
In this study, the simultaneous removal effects of electrochemical oxidation with boron-doped diamond anodes at different current densities were tested on Microcystis aeruginosa and sulfamethoxazole. Flow cytometry and non-invasive micro-test technology were applied to study the physiological states of M. aeruginosa and Vallisneria spiralis leaf cells. As the current density increased, the degradation effect of electrochemical oxidation on sulfamethoxazole and microcystin-LR increased and exceeded 60% within 6 h. In addition, population density of M. aeruginosa, fluorescence response of chlorophyll a, and cytoplasmic membrane integrity decreased, whereas the proportion of cells with excessive accumulation of intracellular reactive oxygen species (ROS) increased. The effect of electrochemical oxidation on the cell population of M. aeruginosa continued after the power was turned off. The physiological state of V. spiralis leaf cells was not severely affected at 10 mA/cm² for 24 h. Higher current intensity and longer electrolysis time would induce apoptosis or necrosis. In order to achieve a higher target pollutant removal effect and simultaneously avoid damage to the lake ecosystem, the current intensity of the electrochemical oxidation device should not exceed 10 mA/cm², and a single electrolysis treatment should range from 6 h to 24 h.
... Regarding the direct effects of MFs on microorganisms, the literature indicates possible modifications in the physiology and shape of the cells, changes in the chemical-physical characteristics of the cellular membrane [15], and in membrane permeability [16,17]. The most commonly observed exposure effects concern changes in growth dynamics [18][19][20][21], the ability of bacteria to adhere and form biofilms [22,23], gene transcription [24,25] and sensitivity to antimicrobial substances [26], as well as irreversible damage to the microorganisms, mostly due to the loss of integrity of the cellular wall/membrane [27][28][29][30][31]. ...
Methicillin-resistant strains of Staphylococcus aureus (MRSA) have developed resistance to most β-lactam antibiotics and have become a global health issue. In this work, we analyzed the impact of a rotating magnetic field (RMF) of well-defined and strictly controlled characteristics coupled with β-lactam antibiotics against a total of 28 methicillin-resistant and sensitive S. aureus strains. The results indicate that the application of RMF combined with β-lactam antibiotics correlated with favorable changes in growth inhibition zones or in minimal inhibitory concentrations of the antibiotics compared to controls unexposed to RMF. Fluorescence microscopy indicated a drop in the relative number of cells with intact cell walls after exposure to RMF. These findings were additionally supported by the use of SEM and TEM microscopy, which revealed morphological alterations of RMF-exposed cells manifested by change of shape, drop in cell wall density and cytoplasm condensation. The obtained results indicate that the originally limited impact of β-lactam antibiotics in MRSA is boosted by the disturbances caused by RMF in the bacterial cell walls. Taking into account the high clinical need for new therapeutic options, effective against MRSA, the data presented in this study have high developmental potential and could serve as a basis for new treatment options for MRSA infections.
... Previously studies have compared the antimicrobial activity of common drinking water disinfectants, including OCl -, chlorine dioxide, ozone and chloramines in the context of centralised and distribution networks 44,45 . This study directly compared the antimicrobial activity of OCl − , HOCl and ECAS solutions against planktonic and bacterial biofilms for potential POU drinking water applications. ...
Chlorine solutions are used extensively for the production of biologically safe drinking water. The capability of point-of-use [POU] drinking water treatment systems has gained interest in locations where centralised treatment systems and distribution networks are not practical. This study investigated the antimicrobial and anti-biofilm activity of three chlorine-based disinfectants (hypochlorite ions [OCl-], hypochlorous acid [HOCl] and electrochemically activated solutions [ECAS]) for use in POU drinking water applications. The relative antimicrobial activity was compared within bactericidal suspension assays (BS EN 1040 and BS EN 1276) using Escherichia coli. The anti-biofilm activity was compared utilising established sessile Pseudomonas aeruginosa within a Centre for Disease Control [CDC] biofilm reactor. HOCl exhibited the greatest antimicrobial activity against planktonic E. coli at >50 mg L−1 free chlorine, in the presence of organic loading (bovine serum albumen). However, ECAS exhibited significantly greater anti-biofilm activity compared to OCl- and HOCl against P. aeruginosa biofilms at ≥50 mg L−1 free chlorine. Based on this evidence disinfectants where HOCl is the dominant chlorine species (HOCl and ECAS) would be appropriate alternative chlorine-based disinfectants for POU drinking water applications.
... A membrana e o citoplasma, constituintes da estrutura celular das bactérias, possuem cargas opostas em seus lados. O processo de EC gera uma sobrecarga aumentando a troca de cargas e causando rupturas e modificações nas membranas além de vazamento substancial de material intracelular, sendo estes os principais mecanismos de remoção e inativação das bactérias (Elazzouzi et al., 2017;Diao et al., 2004). ...
Para alcançar uma qualidade mais nobre e prevenir a degradação dos corpos hídricos, o tratamento de esgoto é imprescindível. Neste estudo, o processo unitário de eletrocoagulação (EC) foi aplicado para o tratamento de efluente doméstico proveniente de tanque séptico. Os testes foram conduzidos em um reator cilíndrico (1 L), com eletrodos de alumínio (108 cm²) e conectados a uma fonte de corrente contínua. Na primeira etapa, realizou-se o dimensionamento dos parâmetros operacionais do reator por meio de um experimento bifatorial 3² (3x3). A condição otimizada resultou em corrente de 2.0 A, tempo de eletrólise de 12 min, massa de cátion de 0.13 g, tensão de 20.60 V e custo médio total de operação de R$.m-³ 4.43. Na segunda etapa, a realizou-se o monitoramento para avaliar o desempenho do reator em relação ao atendimento das legislações e eficiências. As eficiências médias de redução de cargas alcançadas no período foram: > 99.6% para o P-PO43-, 84.6% para DQO, 2.32 log de decaimento de coliformes totais e 2.30 log de E. coli, 97.4% de remoção de turbidez, 96.1% de cor aparente, 11.5% de condutividade elétrica, aumento de 14.5% no pH e 20.9% na temperatura. Durante todo o período monitorado, o efluente do reator de EC atendeu os valores limites fixados pelas normativas brasileiras de lançamento de efluentes sanitários, Resolução CONAMA 430/2011 e Resolução CONSEMA 355/2017. Assim, a EC mostrou-se como um processo efetivo e promissor no tratamento de esgoto doméstico.
... In summary, there are three points of view: First, in the electrolysis process, the chlorine produced by the electrolysis of chloride ions in the water has a bactericidal effect [29][30] ; Second, the power plant's effects include electrical breakdown of the cell membrane, which can cause the bacteria to eventually hydrolyze and die by significantly changing the growth environment of the bacteria, or through the electron transfer between the bacterial cell and the click, causing the bacterial cell's respiratory system to become imbalanced and lead to the death of the bacteria; Third, some high-activity, low-life free radicals generated during the electrolysis process, such as oxygen anion radicals, hydroxyl radicals, hypochlorous acid anion radicals and chlorine dioxide anion radicals, are very strong. Bactericidal effect [31][32] . ...
In recent years, with the reclaimed water being more and more widely used, people begin to pay more and more attention to the security of it. Because the reclaimed water comes from the sewage, which has been deeply treated, its quality is quite complex and it may contain many bacteria, viruses and poisonous that are harm to people. When it’s reused, it is inevitable that the reclaimed water may come into contact with people’s body, which has exposure risk. In order to reduce the risk of exposure, ensure the security of the quality of the reclaimed water, the disinfection becomes the most critical factors in dealing with the reclaimed water in the process. In the paper, the current disinfection techniques were discussed and compared in the aspects of technical features, the effects of disinfection and economy. And a brief summary of the new disinfection technology that was widely studied was made.
... The mechanism(s) by which chlorine inactivates bacteria have been widely studied, but not fully elucidated (Diao et al 2004;Cho et al 2010;Xu et al 2018). This is because the events that trigger cell death involve many complex pathways, and chlorine -a potent and non-specific oxidant -is known to damage an array of cellular components, including membranes, lipids, DNA and proteins, making it difficult to resolve the specific site(s) of primary action. ...
The most widespread health risk associated with drinking-water is contamination with human or animal faeces, in which pathogenic microorganisms may be present. Under the Drinking-water Standards for New Zealand 2005 (Revised 2018), water suppliers must monitor and enumerate both total coliforms and Escherichia coli (E. coli) as indicators of the possible contamination of a supply. Total coliforms are a functional group of bacteria that can be found in both environmental and faecal sources, while E. coli are a species within this group that are more specific to faecal sources. The two indicators have slightly different roles as water quality indicators, and only the detection of E. coli in any 100 ml sample is considered a transgression of the Standards. The detection of total coliforms can therefore be difficult for water suppliers to interpret and respond to. This paper provides four vignettes of small, independent projects, each designed to provide information to help water suppliers interpret their monitoring results and safely manage their drinking-water supplies. The first describes trends in the detection of microbial indicators in New Zealand drinking-water supplies. The second is an assessment of the performance of the reference method test for E. coli. The third reviews literature describing the detection of microbial indicators in chlorinated drinking water supplies. Finally, the fourth item describes a small study investigating the diversity of coliforms in drinking-waters as a potential means to identify their source.
... In particular, chlorine (Cl 2 ) has been widely used to remove microorganisms, organic matters, and ammonia effectively along with other oxidants such as ozone, hydroxyl, and sulphate radicals. 1,4,5,10,[12][13][14][15][16] The generated Cl 2 diffuses to the bulk solution (below eqn (1)-(3)), and they exist three major species including Cl 2 (pH < 3), HOCl (pH [3][4][5][6][7][8], and OCl À (pH > 8). 1 2Cl À / Cl 2(aq) + 2e À (E 0 ¼ 1. 36 ...
Recently, reduced TiO2nanotube arraysviaelectrochemical self-doping (r-TiO2) are emerging as a good alternative to conventional dimensionally stable anodes (DSAs) due to their comparable performance and low-cost. However, compared with conventional DSAs, they suffer from poor stability, low current efficiency, and high energy consumption. Therefore, this study aims to advance the electrochemical performances in the chlorine evolution of r-TiO2with a thin RuO2layer coating on the nanotube structure (RuO2@r-TiO2). The RuO2thin layer was successfully coated on the surface of r-TiO2. This was accomplished with a self-synthesized layer of ruthenium precursor originating from a spontaneous redox reaction between Ti³⁺and metal ions on the r-TiO2surface and thermal treatment. The thickness of the thin RuO2layer was approximately 30 nm on the nanotube surface of RuO2@r-TiO2without severe pore blocking. In chlorine production, RuO2@r-TiO2exhibited higher current efficiency (∼81.0%) and lower energy consumption (∼3.0 W h g⁻¹) than the r-TiO2(current efficiency of ∼64.7% of and energy consumption of ∼5.2 W h g⁻¹). In addition, the stability (ca.22 h) was around 20-fold enhancement in RuO2@r-TiO2compared with r-TiO2(ca.1.2 h). The results suggest a new route to provide a thin layer coating on r-TiO2and to synthesize a high performance oxidant-generating anode.
... 19,20 In addition to destruction of organic contaminants, inactivation of bacteria, viruses (bacteriophages) and algae using eAOPs has been demonstrated. [21][22][23][24][25] eAOPs also have demonstrated effectiveness for mineralization of numerous organic compounds, and the mechanism of their action is relatively well-understood with respect to the advanced oxi-3 dation component of eAOPs. Radicals produced through advanced oxidation rapidly react with organic compounds via electron transfer, dehydrogenation, or hydroxylation producing organic radicals which, through the resulting radical oxidation chain, produce CO 2 and H 2 O. 26,27 In contrast to advanced oxidation, the exact mechanisms of disinfection and decontamination by the electrochemical component of eAOPs are less well-understood, a problem attributed to the broad range of cellular components that can be damaged by oxidizing and reducing agents alike. ...
We present an electrochemical advanced oxidation process (eAOP) reactor employing expanded graphite, potassium iodide (KI), and electrical current, which demonstrates an exceptionally high rate of inactivation of E. coli (6log reduction in viable cells) at low current density 0.6 mA/cm^2), with low contact time (5 minutes) and low concentration of KI (10 ppm). Operando X-ray fluorescence mapping is used to show the distribution of iodine species in the reactor, and operando X-ray absorption spectroscopy in the anodic chamber reveals iodine species with higher effective oxidation state than periodate. Operando electrochemical measurements confirm the conditions in the anodic chambers are favourable for the creation of highly oxidized iodine products. The killing efficiency of this new eAOP reactor far exceeds that expected from either traditional iodine-based electrochemical water treatment or advanced oxidation systems alone, a phenomenon that may be associated with the production of highly oxidized iodine species reported here.
... Validation of the process of electrochlorination as one of the emerging and efficient methods of disinfecting drinking water was previously shown by many researchers [21,[23][24][25]. In fact, a few researchers also demonstrated that electrochemical remediation of bacterial population is highly effective even for the treatment of wastewater [26][27][28]. Research related to the current COVID-19 pandemic confirmed the presence of genetic materials of SARS-CoV-2 in wastewater in the Indian subcontinent [29,30], Australia [31], The Netherlands [32], Germany [33], USA [34], and in many other places. Poor treatment of drinking water, and wastewater, and inadequate sanitation facilities may lead to faecal-oral transmission of SARS-CoV-2 [35]. ...
Bacteriological contamination in drinking water is known to be responsible for the spread of various waterborne diseases. Although chlorine is frequently used as disinfectant in water treatment, low-cost disinfecting technologies in the villages of developing and under-developed countries are not yet successfully implemented. This study contributed in designing a simple and inexpensive water disinfection unit to produce chlorine from the naturally available dissolved chloride of groundwater by electrochlorination, using inert and cheap graphite electrodes. Laboratory-based experiments were performed in both batch and continuous flow reactors to study the effect of time, current, electro charge loading (ECL), and surface area of electrodes in chlorine generation and bacterial inactivation. Controlled experiments in continuous mode in the absence of chlorine further indicated the possibility of partial inactivation of bacteria under the influence of the electric field. Finally, a treatment unit with drilled anodes, and undrilled cathode electrodes, in continuous flow set-up was installed in four schools of four different villages in West Bengal, India. An average residual chlorine concentration and removal efficiency of total coliform in the designed systems were determined as 0.3 ± 0.07 mg/L, and 98.4% ± 1.6%, respectively.
... The use of anolyte produced by membrane electrolysis of water and NaCl solution for the disinfection of water and wastewater has a higher disinfection effect than chlorine, which is the most known disinfectant. Anolyte solution will also eliminate some chlorine-resistant pathogens due to the presence of a combination of different oxidants and active radicals (Diao et al., 2004;Huang et al., 2016). With the injection of anolyte into the water distribution network line, there will be more residual chlorine with longer durability in the water, which will reduce both the required injected chlorine concentration and the production of harmful disinfection byproducts. ...
Anolyte solution produced by membrane electrolysis of NaCl solution contains a high level of available chlorine content (ACC) and other oxidizing compounds, rendering this solution a strong disinfectant property. In this paper, some process parameters affecting the anolyte production efficiency, such as total inlet flow (240–320 L/h), saline solution concentration (1.65–3.50 g/L), and the type of membrane (cation exchange, anion exchange, and bipolar membranes) were investigated in an electrolysis cell. Changes in the quality of anolytes produced at three initial concentrations of very high (ACC1 = 816.5 mg/L), relatively high (ACC2 = 461.5 mg/L), and medium (ACC3 = 355.0 mg/L) during storage (from the production up to 20 weeks) were examined by adjusting the total inlet flow, saline concentrations, and membrane types. Changes in the ACC of the produced anolyte solution were generally affected by the type of membrane used in the electrolysis cell. The use of anion exchange membrane resulted in the lowest durability of anolyte quality (60–80% ACC reduction after 4 weeks of storage) and the cation exchange membrane had the highest durability (less than 40% decrease after 4 weeks of storage). In addition, changes in the pH and the oxidation–reduction potential of the anolyte were investigated during the storage period, which had a different trend depending on the type of applied membrane.
... It has been reported that cultivating Enterobacter dissolvens in a 10 mA DC electric field for 24 h disrupted its surface morphology (She et al., 2006). Furthermore, in the ES process, the DC intensity applied is generally below 20 mA (Diao et al., 2004) to avoid the bactericidal effects that occur at high intensities; in this study, 10 mA DC was applied. We speculated that the ES increased the membrane permeability and inhibited cell growth, causing overproduction and secretion of exMPs, especially Y-MPs, during the SBF. ...
This study investigated the effects of cofactor metabolism on secondary metabolite production in M. purpureus through the application of different cofactor engineering strategies. Total pigment production dramatically increased by 39.08% and 40.89%, and yellow pigment production increased by 74.62% and 114.06% after the addition of 1.0 mg/L of the exogenous cofactor reagents methyl viologen and rotenone, respectively, in submerged batch-fermentation. The extracellular red pigment tone changed to yellow with the application of electrolytic stimulation at 800 mV/cm², but almost no citrinin production was detected. In addition, the total pigment, yellow pigment and citrinin production increased by 35.46%, 54.89% and 6.27% after disruption of the nuoⅠ gene that encodes NADH-quinone oxidoreductase, respectively. Thus, cofactor metabolic engineering strategies could be extended to the industrial production of Monascus pigment or high yellow pigment with free citrinin production.
... Therefore, it can be inferred that the killing of bacteria was carried out but no perceptible modification in the structure of bacterial cells was observed at the employed scan level. In agreement with other studies, neither chlorine disinfection nor electrical shock results in damage to the bacterial membrane cells [63][64][65]. Hence, the electrical treatment solely causes dysfunction of bacterial cells without inducing any bacterial morphology alteration. ...
Biofouling of membranes in water treatment is considered as one of the major practical problems. A novel and an efficient approach for cleaning biofilm grown on the membrane surface is proposed by applying a direct electric current (124 mA, 90 s) through platinum electrodes inside a cross-flow ultrafiltration channel. Depending on the electrochemical reactions occurring at the electrodes, either chlorine or hydrogen-producing configuration is realized by interchanging the current polarity. Baseline determination of the amount of chlorine generated and change in pH is assessed as a function of current intensity, linear cross-flow velocity, and duration of applied current. The efficiency of the proposed method is determined by investigating electrically treated biofilm through bacterial inactivation using Confocal Laser Scanning Microscopy (CLSM), bacterial cell structure changes through Scanning Electron Microscopy (SEM), and by estimating the amount of biomass removal through Optical Coherence Tomography (OCT). When a chlorine-producing electrode is placed at the inlet of the flow cell, 68% of bacterial inactivation is achieved without any modification of bacterial cell shape. Furthermore, a high and near-complete biomass removal is achieved (99%) after a subsequent forward flush of the electrically treated biofilm. However, placing a hydrogen-producing electrode at the inlet reveals a slightly lower bacterial inactivation (65%) and lower biomass removal (77%). Additional systematic experiments using individually sodium hydroxide (NaOH), sodium hypochlorite (NaOCl), or gas microbubbles enabled to elucidate the cause of biofilm removal, synergic effect of caustic agent NaOH and microbubbles.
... Virus removal has been attributed to both iron hydroxide floc entrapment ( Heffron et al., 2019a, Tanneru & Chellam, 2012, and inactivation by either ROS or chlorine-based oxidants formed by reduction in the anode . Formation of Cl 2 was ruled out as a mechanism of disinfection in our experiments, since Cl − concentration was measured by ICP-MS before and after the application of current, and no variations were detected in any of the samples, also in line with the findings of Delaire et al., (2015) and Diao et al., (2004) . Inactivation due to the effect of electric current has been the least reported biocidal pathway, with the research from Jeong et al. (2006) giving it a larger relevance at high current densities, from 33 to 100mA/cm 2 . ...
In this paper we analyse the feasibility of low voltage iron electrocoagulation as a means of municipal secondary effluent treatment with a focus on removal of microbial indicators, Antibiotic Resistant Bacteria (ARB) and nutrients. A laboratory scale batch unit equipped with iron electrodes was used on synthetic and real secondary effluent from a municipal wastewater treatment plant. Synthetic secondary effluent was separately assayed with spiked Escherichia coli WR1 and with bacteriophage ΦX174, while real effluent samples were screened before and after treatment for E. coli, Extended Spectrum Betalactamase-producing E. coli, Enterococci, Vancomycin Resistant Enterococci, Clostridium perfringens spores and somatic coliphages. Charge dosage (CD) and charge dosage rate (CDR) were used as the main process control parameters. Experiments with synthetic secondary effluent showed >4log10 and >5log10 removal for phage ΦX174 and for E. coli WR1, respectively. In real effluents, bacterial indicator removal exceeded 3.5log10, ARB were removed below detection limit (≥2.5log10), virus removal reached 2.3log10 and C. perfringens spore removal exceeded 2.5log10. Experiments in both real and synthetic wastewater showed that bacterial removal increased with increasing CD and decreasing CDR. Virus removal increased with increasing CD but was irresponsive to CDR. C. perfringens spore removal increased with increasing CD yet reached a removal plateau, being also irresponsive to CDR. Phosphate removal exceeded 99%, while total nitrogen and chemical oxygen demand removal were below 15% and 58%, respectively. Operational cost estimates were made for power and iron plate consumption, and were found to be in the range of 0.01 to 0.24€/m³ for the different assayed configurations. In conclusion, low voltage Fe-EC is a promising technology for pathogen reduction of secondary municipal effluents, with log10 removals comparable to those achieved by conventional disinfection methods such as chlorination, UV or ozonation.
... Microorganisms are footstone for the formation and growth of biofilm matrix. The generation of strong oxidants (reactive chlorine species or reactive oxygen species) (Jeong et al., 2009;Martínez-Huitle and Brillas, 2009) were believed to attack and destroy the cell membrane structure, nucleic acid, protein, and other macromolecular substances of microorganisms (Diao et al., 2004), which led to the inactivation of microorganisms. In other words, ECT could prevent the attachment of inactivated microorganisms or remove existing microorganisms on surfaces (Busalmen and de Sanchez, 2005;Chung et al., 2016). ...
... Jeong et al. (2006) demonstrated that ROS as the additional disinfectants, such as O 3 and %OH generated by EW, can contribute a lot in microorganism inactivation, as much as chlorine component in the electrochemical disinfection. The changes of bacteria induced by EW were viewed as similar to that caused by the %OH formed from Fenton reaction (Diao et al., 2004). ...
Bactericidal effects of low concentration electrolysed water (LcEW) on microorganisms are previously well reported ; however, the inactivation mechanism of EW is not understood. The lethal and sublethal injuries of L. monocytogenes and L. innocua by EW treatments were determined and the metabolic profile changes for L. in-nocua were characterised using nuclear magnetic resonance (NMR). Microbial metabolomics approach combined with multivariate data analyses was used to interpret the cellular chemical fingerprints of L. innocua. The relative amount of intracellular reactive oxygen species (ROS) was assayed using 2′,7-dichlorodihydrofluorescein dia-cetate (H 2 DCFDA). The results showed that the proportion of the sublethally injured microbial cells L. mono-cytogenes and L. innocua increased from 40% to 70% and from 35% to 65%, respectively, when the free available chlorine (FAC) of LcEW increased from 2 to 8 mg/L. Overall, 36 low-molecular-weight metabolic compounds in L. innocua extracts were characterised by NMR spectroscopy. EW perturbation resulted in a drastic and multitude disruption across a wide range of biochemical process including peptidoglycan synthesis, nucleotides bio-synthesis and amino acid metabolism. Elevated levels of α-ketoglutarate and succinate implicated the enhanced glutamate decarboxylase (GAD) system and γ-aminobutyric acid (GABA) shunt for the protection against oxi-dative stress. These findings provided the comprehensive insights into the metabolic response of Listeria to EW oxidative stress and can serve as a basis for better utilisation for sanitisation.
... As an illustration, a CuO-nanowire-modified copper foam with an elevated conductivity was tried as the electrode to remedy an influent (~10 7 colony-forming units (CFU)/mL bacteria in normal saline) at the operating voltage of 1 V applied by direct current (DC) power supply. It attained nearly 7 log elimination of bacteria (i.e., no live microbes observed) at the hydraulic retention time (HRT) of 7 s [22], which was low juxtaposed with chlorination [23], and flow-by electrodisinfection [24]. Nevertheless, the chemical in- [25]. ...
Electrochemical technology for the killing of pathogens has been largely investigated. Lately, Ni et al. [1] published excellent research on the disinfection efficiency of a carbon fiber-based flow-through electrode system (FES) versus Gram-negative bacteria (Escherichia coli and fecal coliform) and Gram-positive bacteria (Enterococcus faecalis and Bacillus subtilis) in normal saline over a large span of applied voltages (1-5 V) and hydraulic retention times (HRTs) (1-10 s). They established that the Gram-negative microbes were more susceptible to FES for their thinner cell walls and over 6.5 log reduction (no live bacteria found) was obtained at the applied voltage of 2 V and HRT of 2 s; however, Gram-positive microbes were demobilized at slightly bigger voltages (3 V, 2 s) or longer HRTs (2 V, 5 s). Demobilizing microorganisms was related to the alteration and laceration of cell membranes mostly via anode direct oxidation in the absence of bacterial regrowth. Further, the disregarding formation of the free chlorine at low voltages (≤2 V) could avert the production of possible chlorinated disinfection by-products. Therefore, FES could furnish an undeveloped substitute to traditional disinfection processes for eliminating pathogens in water. This work concludes that focusing on axial dispersion and velocity profile inside anode will be very useful in comprehending the transport phenomena and proposing a fresh model that merges the axial dispersion and velocity profile for the FES. Such a research trend will more encourage the FES implementation at the large industrial level for disinfecting water.
... The electrochemical disinfection has been studied for its environmental compatibility, easy operation and onsite generation of disinfectants (Diao et al., 2004;Huang et al., 2016;Wouters et al., 2001). The mostly accepted mechanisms of electrochemical disinfection are electric field destruction (such as electroporation (Huo et al., 2016;Liu et al., 2013)), direct oxidation by anode and indirect oxidation by the production of disinfectants, such as hydroxyl radicals ($OH) and chlorine on anode, and hydrogen peroxide (H 2 O 2 ) on cathode (Cotillas et al., 2015;Jelena and Sedlak, 2015;Laxman et al., 2015). ...
The disinfection performance of a carbon fiber-based flow-through electrode system (FES) towards Gram-negative bacteria (Escherichia coli and fecal coliform) and Gram-positive bacteria (Enterococcus faecalis and Bacillus subtilis) in normal saline was systematically investigated over a wide range of applied voltages (1-5 V) and hydraulic retention times (HRTs) (1-10 s). It was revealed that the Gram-negative bacteria were more vulnerable to FES for their thinner cell walls, and over 6.5 log removal (no live bacteria detected) was achieved at the applied voltage of 2 V and HRT of 2 s; while Gram-positive bacteria were inactivated at slightly higher voltages (3 V, 2 s) or longer HRTs (2 V, 5 s). Bacterial inactivation was attributed to the change and rupture of cell membrane mainly by anode direct oxidation without bacterial regrowth/reactivation. In addition, negligible generation of the free chlorine at low voltages (≤ 2 V) can avoid the formation of potential chlorinated disinfection byproducts (DBPs). Hence, FES can offer a potential alternative to conventional disinfection methods for bacteria inactivation in natural and contaminated water.
... Some of those anions, such as SO 4 2− and HCO 3 − , which are probably present in the WWE sample, can have a detrimental effect on the TiO 2 photocatalysis, while others might produce the inverse reaction. For instance, the Cl − anion, which is in high concentration in the saline solution, might react with * OH-initiating chain reactions involving the formation of other free radicals such as HOCl *- (Saran et al. 1999, Diao et al. 2004). Finally, the presence of other microorganisms reduced the probability of light or * OH to reach the targeted bacteria. ...
This research aims to compare the disinfection and degradation effectiveness in water of a commercial suspension of nano-TiO2 (TiO2Levenger) with the standard TiO2Degussa P25. Photo-inactivation and photo-degradation experiments were conducted with UVA-vis light. Concerning the disinfection, the effects of TiO2 dose (0-2 g/l), water matrix, bacterium type (Gram-positive or Gram-negative), and bacterial regrowth after the photo-treatments were studied for each catalyst. The experimental results show that Enterococcus sp. (Gram-positive) was more resistant to the photo-treatments than Escherichia coli (Gram-negative) for both catalyst; however, postirradiation trends showed similar behavior for both bacteria, favoring regrowth for short-treated cells and decay for longer-treated ones. Caffeine was selected as a model substance of pharmaceuticals and personal care products. In terms of caffeine removal, the effects of TiO2 dose (0-2 g/l) and water matrix were analyzed. Besides, the comparison between mechanical coagulation-flocculation-decantation and simple decantation of TiO2 was carried out. The results show that simple decantation allowed the recovery of 97.5% of TiO2 Degussa P25 and TiO2 Levenger within 1 day of simple decantation, while applying the proposed mechanical coagulation-flocculation decantation 99.7% of recovery of both catalysts was achieved in 2 hours. Finally, the subsequent reuse of both catalysts was proved with little loss of efficiency in terms of photo-disinfection during the four cycles. Nevertheless, the standard TiO2 Degussa P25 photo-degradation efficiency of caffeine decreases considerably as compared to commercial suspension of TiO2 Levenger concerning the reutilization.
Corynebacterium pseudotuberculosis is a gram-positive bacterium and is the etiologic agent of caseous lymphadenitis (CL) in small ruminants. This disease is characterized by the development of encapsulated granulomas in visceral and superficial lymph nodes, and its clinical treatment is refractory to antibiotic therapy. An important virulence factor of the Corynebacterium genus is the ability to produce biofilm; however, little is known about the characteristics of the biofilm produced by C. pseudotuberculosis and its resistance to antimicrobials. Silver nanoparticles (AgNPs) are considered as promising antimicrobial agents, and are known to have several advantages, such as a broad-spectrum activity, low resistance induction potential, and antibiofilm activity. Therefore, we evaluate herein the activity of AgNPs in C. pseudotuberculosis , through the determination of minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), antibiofilm activity, and visualization of AgNP-treated and AgNP-untreated biofilm through scanning electron microscopy. The AgNPs were able to completely inhibit bacterial growth and inactivate C. pseudotuberculosis at concentrations ranging from 0.08 to 0.312 mg/mL. The AgNPs reduced the formation of biofilm in reference strains and clinical isolates of C. pseudotuberculosis, with interference values greater than 80% at a concentration of 4 mg/mL, controlling the change between the planktonic and biofilm-associated forms, and preventing fixation and colonization. Scanning electron microscopy images showed a significant disruptive activity of AgNP on the consolidated biofilms. The results of this study demonstrate the potential of AgNPs as an effective therapeutic agent against CL.
E. coli (Escherichia coli) is a bacterium found in human and animal intestines. These bacteria, which can enter the bloodstream through as anyway as the environment or food, can cause many diseases such as diarrhea, respiratory problems, and blood/urinary tract infections especially in human. Therefore, these bacteria have to be removed from drinking water sources by some inactivation methods. Conventional methods as chlorination, ozonation and UV inactivation methods are effective but the development of techniques that do not require the transportation and storage of chemicals and do not produce negative by-products and cost-effective is the basis of environmental engineering studies. In this study, the inactivation effectiveness of hybrid electrode connected electrochemical process as a new approach on E. coli was investigated. The connection system was experienced with Al/SS/SS as Anode/Cathode/Anode electrode. Simultaneously electrocoagulation (EC) and electrooxidation (EO) mechanism works together in this electrode connection system. The inactivation coefficients were determined by the GInaFiT (Geeraerd and Van Impe Inactivation Model Fitting Tool) modeling tool, which is a Microsoft Excel add-on and the model was statistically well fitted with Double-Weibull. 4D degradation of E. coli was achieved as 21 minutes at a current density of 0.3 A and an optical density (O.D.) of 0.21. It has been determined that hybrid electrode connected electro-disinfection process is an effective approach for the E.coli inactivation.
Amoebae are widespread in water and serve as environment vectors for pathogens, which may threaten public health. This study evaluated the inactivation of amoeba spores and their intraspore bacteria by solar/chlorine. Dictyostelium discoideum and Burkholderia agricolaris B1qs70 were selected as model amoebae and intraspore bacteria, respectively. Compared to solar irradiation and chlorine, solar/chlorine enhanced the inactivation of amoeba spores and intraspore bacteria, with 5.1 and 5.2-log reduction at 20 min, respectively. The enhancement was similar in real drinking water by solar/chlorine under natural sunlight. However, the spore inactivation decreased to 2.97-log by 20 min solar/chlorine under oxygen-free condition, indicating that ozone played a crucial role in the spore inactivation, as also confirmed by the scavenging test using tert‑butanol to scavenge the ground-state atomic oxygen (O(3P)) as a ozone precursor. Moreover, solar/chlorine induced the shape destruction and structural collapse of amoeba spores by scanning electron microscopy. As for intraspore bacteria, their inactivation was likely ascribed to endogenous reactive oxygen species. As pH increased from 5.0 to 9.0, the inactivation of amoeba spores decreased, whereas that of intraspore bacteria was similar at pH 5.0 and 6.5 during solar/chlorine treatment. This study first reports the efficient inactivation of amoeba spores and their intraspore pathogenic bacteria by solar/chlorine in drinking water.
It is a long-pursued goal to develop electrified water treatment technology that can remove contaminants without byproduct formation. This study unveiled the overlooked multifunctionality of electro-Fenton (EF) and induced EF (I-EF) processes to remove organics, pathogens, and phosphate in one step without halogenated byproduct formation. The EF and I-EF processes used a sacrificial anode or an induced electrode to generate Fe²⁺ to activate H2O2 produced from a gas diffusion cathode fed by naturally diffused air. We used experimental and kinetic modeling approaches to illustrate that the •OH generation and radical speciation during EF were not impacted by chloride. More importantly, reactive chlorine species were quenched by H2O2, which eliminated the formation of halogenated byproducts. When applied in treating septic wastewater, the EF process removed >80% COD, >50% carbamazepine (as representative trace organics), and >99% phosphate at a low energy consumption of 0.37 Wh/L. The EF process also demonstrated broad-spectrum disinfection activities in removing and inactivating Escherichia coli, Enterococcus durans, and model viruses MS2 and Phi6. In contrast to electrochemical oxidation (EO) that yielded mg/L level byproducts to achieve the same degree of treatment, EF did not generate byproducts (chlorate, perchlorate, trihalomethanes, and haloacetic acids). The I-EF carried over all the advantages of EF and exhibited even faster kinetics in disinfection and carbamazepine removal with 50–80% less sludge production. Last, using septic wastewater treatment as a technical niche, we demonstrated that iron sludge formation is predictable and manageable, clearing roadblocks toward on-site water treatment applications.
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.
The United Nations (UN) has considered water a human right since 1977. However, freshwater available for consumption represents less than 1% of all water on Earth. Groundwater represents one of the largest reserves of drinking water and is susceptible to chemical contamination, especially from pollutants that seep into the soil, such as atrazine, bisphenol A, and tetracycline. These substances, along with Escherichia coli , were selected to simulate contamination in groundwater samples and evaluate the efficiency of electrochemical oxidation using boron‐doped diamond anodes and four different anion salts to analyze their impact on the treatment process. After electrolysis, the degradation of tetracycline, bisphenol A and atrazine was found to increase with decreasing current density, with average values of 77%, 96% and 100% at 15 mA cm ⁻² and 68%, 83% and 99% at 35 mA cm ⁻² , respectively. Moreover, the mineralization of these substances showed the same behavior, decreasing from 67%, 64%, and 54% at 15 mA cm ⁻² to 52%, 35%, and 49% at 35 mA cm ⁻² . The analysis of the results showed that the ions present in the solution significantly affect the degradation process and that they interact with the impurities used. For atrazine and tetracycline, the degradation efficiency followed the same pattern, < < < . However, in the case of bisphenol A and E. coli , phosphate showed better results, similar to nitrate. The high efficiency in eliminating bacteria, even at high concentrations, shows that the electrochemical treatment system has a strong bactericidal effect, eliminating bacterial colonies with up to 5 min of treatment.
Strong bacterial attachment or biofilm formation on produce surfaces may result in limited penetration ability of sanitizers. This study evaluated the effect of the attachment level of Listeria monocytogenes during storage on the efficacy of chlorine treatment on bell pepper surfaces. Bell peppers inoculated with L. monocytogenes were stored at 4 °C and 25 °C, and attachment strength (SR) and the efficacy of chlorine were examined during storage. The L. monocytogenes population at 4 °C decreased significantly from 6.41 log CFU/g at 1 h to 4.25 log CFU/g at 72 h while remaining constant at all times at 25 °C (6.41 log CFU/g at 1 h to 5.72 log CFU/g at 72 h). The SR value of bacteria at 4 °C remained constant throughout the storage while at 25 °C it remained similar until 48 h and increased significantly at 72 h (0.72). Chlorine washing significantly reduced the bacterial level in the samples stored for 1 h and all the samples stored at 25 °C as compared to washing with water. The survival and attachment of bacterial cells were found to be significantly (P < 0.05) better at 25 °C than at 4 °C. Efficacy of chlorine was affected by the attachment of bacteria.
The present study provides details about the usefulness of chlorination in the recovery effluents of sewage wastewater, and to make it useable for irrigation purposes. Chlorination is one of the effective simplified, and cost-effective traditional methods for disinfection. The study was done for the period of March, 2019 to February, 2020. The disinfection process was optimized by adding sodium hypochlorite to the secondary treated effluents with the help of jar apparatus at a mixing speed of 100 rpm. To optimize the various process variables such as dose, and contact time, several concentrations of NaOCl (0.5, 1, 1.5, 2, 2.5, 3.0) ppm were carefully chosen at different time intervals of 15, 30, and 60 min respectively, which were centered on the foregoing studies. The factors like seasonal variation on MPN index of total coliforms (TCs), CR * T concept, and effect of pH on log elimination of TCs, outcome of pH with rate constant (k), and results of pH against dilution coefficient (n) was also studied. The Chick–Watson, Rennecker–Marinas, Collin–Selleck, and modified Selleck models have shown good reliability to the experimental data of chlorine disinfection to be fit into these kinetic models for the treatment of sewage wastewater. The upgraded CR * T values were attained by using disinfection models. Among these four models, the kinetic modeling by Collin–Selleck, and Selleck–White was investigated as the best modeling to be fitted more finely to the chlorination experimental data to count for the effectiveness of NaOCl. The selected indicator organism in the optimization process of chlorine was Total coliforms (TCs). The residual chlorine and most probable number per log unit (Log) for TCs were measured before the start and after the termination of the disinfection process. The World Health Organization (WHO) standard for pathogenic removal from wastewater, and to irrigate the crops is 3- to 4-log and the chlorine residual under 1 mg/l limit was accomplished.
Zero-valent iron (ZVI) activated Fenton-like processes have been proposed to inactivate ARB that carry diverse antibiotic resistance genes (ARGs) in wastewater, whereas they exhibit very low capacity of degrading ARB-carrying ARGs. Our previous study has revealed that pre-acidification can make cell inactivation and lysis. Thus, the present study investigated the effect of pre-acidification on the inactivation of a multi-drug resistant bacterium Pseudomonas putida MX-2 and the simultaneous degradation of carried seven ARGs by ZVI/H2O2 and ZVI/PDS processes. Results showed that the pre-acidification of bacterial solution to acidic pH greatly promoted the degradation of carried ARGs from 0.14-0.17 logs to 2.48-2.97 logs at the meanwhile of almost completely inactivating P. putida MX-2 in both ZVI/H2O2 and ZVI/peroxydisulfate (PDS) processes. Moreover, the pre-acidification seriously lysed the bacterial cells, released the carried ARGs into the extracellular environment, and facilitated the degradation of extracellular ARGs (e-ARGs) by the generated radicals. During the degradation of the resultant e-ARGs, they were fragmented to short fragments by ZVI/H2O2 and ZVI/PDS processes. The treatment of real wastewater containing P. putida MX-2 further validated the promoting effect of pre-acidification on the degradation of carried ARGs. Therefore, it is extremely crucial to lyse the cells of ARB efficiently via acidification or other methods to promote the degradation of carried ARGs greatly, which may also be applicable for other advanced oxidation processes to reduce antibiotic resistance in wastewater effectively.
Electrified membranes (EMs) possess the capacity to handle the intrinsic restrictions of traditional membrane techniques. EMs show improved functions beyond separation. Electrification can increase the efficacy and sustainability of membrane techniques and encourage novel utilizations in water and wastewater treatment. As a process in which chemical oxidants are produced in situ via redox reactions on the surface of an electrode, electrochemical dis-infection (ED) has recently magnetized increased interest as an option to conventional chemical dosing disinfection techniques. In this review, we focus on fresh improvements in EMs, especially on water and wastewater disin-fection. A brief description is accorded to materials categories, synthesis procedures , and electrified filtration operating modes. A discussion is dedicated to applications of EMs, especially water disinfection via bacterial and viral inactivation. Future challenges and promising applications for EMs are underlined. On the other hand, a brief description of ED concepts and perspectives is given. ED does not demand the transport and storage of hazardous materials and could be scaled across centralized and distributed treatment contexts; it shows promise for use both in resource-limited settings and as a supplement for aging centralized systems. This discussion suggests that EMs would be merged with ED as an intensified process.
A bimetallic Fe/Al disinfection system was developed to examine the feasibility of inactivation of water borne microorganisms. In this study, the effectiveness and mechanisms of the bimetallic Fe/Al system on the inactivation of model bacteria, Escherichia coli (E. coli), were investigated. Results revealed that the Fe/Al system effectively inactivated E. coli to reach nearly 2 logs (99%) removal within 20 min and 4 logs (99.99%) at 24 h, indicating that the Fe/Al composite was able to sustain a long-term disinfection capacity. The inactivation ability resulted from hydroxyl radicals produced by a Fenton reaction through in-situ self-generated Fe²⁺ and H2O2 species in the Fe/Al system. In addition to the attack by the radicals, some of E. coli were adsorbed onto the Fe/Al composite (zeta potential of 30–50 mV) as a result of Coulomb interaction. Scanning electron microscope (SEM) images showed that the adsorbed bacteria had damaged pores at the two ends of their rod-like cells. This phenomenon suggested that a micro-electric field between the Fe/Al galvanic couple induced electroporation of the adsorbed E. coli and thus further advanced additional inactivation ability for the bacteria disinfection.
Use of robust and safe water disinfection technologies which are inexpensive and energy efficient, are need of the hour to combat the problem of inadequate access of safe and clean drinking water. Energy and chemically intensive water treatment technologies warrant the need of a safe and environmentally sound treatment technology. Electrochemical disinfection or electro-disinfection (ED) is experiencing a great resurgence among the scientific communities due to its novel use of electrode materials and electric current in an inexpensive and energy efficient way for achieving the inactivation of microorganisms. Among the various electrodes used in the ED, boron-doped diamond (BDD) emerge as a sustainable alternate for their ability to electro generate strong potent oxidants which result in effective pathogen control in drinking water. ED for disinfecting waters occurs via generation of the reactive species which act in the bacterial inactivation mechanisms. In this mini-review, a critical discussion on the fundamentals as well as applications of promising electrochemical methods using BDD anodes (namely electrochemical oxidation (EO)), evidencing their advantages for the remediation of drinking water infected with waterborne agents is given.
Antibiotic resistant bacteria (ARB) and the antibiotic resistance genes (ARGs) dissemination via plasmid-mediated conjugation have attracted considerable attentions. In this research, sulfidated nanoscale zerovalent iron (S-nZVI)/peroxymonosulfate (PMS) and S-nZVI/peroxydisulfate (PDS) process were investigated to inactivate ARB (Escherichia coli DH5α with RP4 plasmid, Pseudomonas. HLS-6 contains sul1 and intI1 on genome DNA sequence). S-nZVI/PMS system showed higher efficiency than S-nZVI/PDS on ARB inactivation. Thus, the optimal condition 28 mg/L S-nZVI coupled with 153.7 mg/L (0.5 mM) PMS was applied to remove both intracellular ARGs (iARGs) and ARB. The oxidative damage of ARB cell was systemically studied by cell viability, intracellular Mg²⁺ levels, the changes of extracellular and internal structure, integrity of cell walls and membranes and enzymatic activities. S-nZVI/PMS effectively inactivated ARB (~7.32 log) within 15 min. These effects were greatly higher than those achieved individually. Moreover, removal efficiencies of iARGs sul1, intI1 and tetA were 1.52, 1.79 and 1.56 log, respectively. These results revealed that S-nZVI and PMS have a synergistic effect against ARB and iARGs. The regrowth assays illustrated that the ARB were effectively inactivated. By verifying the inhibitory impacts of S-nZVI/PMS treatment on conjugation transfer, this work highlights a promising alternative technique for inhibiting the horizontal gene transfer.
RESUMO A eletrocoagulação (EC) foi aplicada como tratamento terciário para o efluente de wetland construído de escoamento vertical (WCV). O sistema de EC compreendeu um reator cilíndrico de vidro (1 L) e eletrodos de alumínio conectados a uma fonte de alimentação de corrente contínua. O estudo foi desenvolvido em duas etapas. Na primeira, as condições operacionais do reator foram delimitadas por meio de um experimento bifatorial 32 (3×3) de natureza quantitativa × quantitativa, analisando intensidade de corrente e tempo. Com base nos resultados obtidos, a regressão linear resultou na combinação de 1,3 A e 18 min, com custo operacional elétrico de 2,71 R$.m−3. Em seguida, realizou-se a etapa de monitoramento durante quatro meses, aplicando a EC sob essas condições fixas estabelecidas. As eficiências médias de remoção alcançadas foram de 99,7% para P-PO43-, 20,6% para N-NO3−, 2,37 log de coliformes totais, 2,35 log de Escherichia coli, 84,9% para demanda química de oxigênio, 95% para turbidez, 95,1% para cor aparente, aumento de 19% no pH, de 18,6% na temperatura e diminuição de 15,8% na condutividade elétrica. O tratamento demonstrou elevadas e homogêneas eficiências de remoção dos poluentes, principalmente para P-PO43-, indicando que a EC produz efluente com menor potencial poluidor e é indicada para tratamento de efluente doméstico em nível terciário.
Electrochemical disinfection—a method in which chemical oxidants are generated in situ via redox reactions on the surface of an electrode—has attracted increased attention in recent years as an alternative to traditional chemical dosing disinfection methods. Because electrochemical disinfection does not entail the transport and storage of hazardous materials and can be scaled across centralized and distributed treatment contexts, it shows promise for use both in resource limited settings and as a supplement for aging centralized systems. In this Critical Review, we explore the significance of treatment context, oxidant selection, and operating practice on electrochemical disinfection system performance. We analyze the impacts of water composition on oxidant demand and required disinfectant dose across drinking water, centralized wastewater, and distributed wastewater treatment contexts for both free chlorine- and hydroxyl-radical-based systems. Drivers of energy consumption during oxidant generation are identified, and the energetic performance of experimentally reported electrochemical disinfection systems are evaluated against optimal modeled performance. We also highlight promising applications and operational strategies for electrochemical disinfection and propose reporting standards for future work.
The problem of bacterial antibiotic resistance has attracted considerable research attention, and the effects of water treatment on antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) are being increasingly investigated. As an indispensable part of the water treatment process, disinfection plays an important role in controlling antibiotic resistance. At present, there were many studies on the effects of conventional and new sterilization methods on ARB and ARGs. However, there is a lack of literature relating to the limitations of conventional methods and analysis of new techniques. Therefore, this review focuses on analyzing the deficiencies of conventional disinfection and the development of new methods for antibiotic resistance control to guide future research. Firstly, we analyzed the effects and drawbacks of conventional disinfection methods, such as chlorine (Cl), ultraviolet (UV) and ozone on antibiotic resistance control. Secondly, we discuss the research progress and shortcomings of new sterilization methods in antibiotic resistance. Finally, we propose suggestions for future research directions. There is an urgent need for new effective and low-cost sterilization methods. Disinfection via UV and chlorine in combination, UV/chlorine showed greater potential for controlling ARGs.
Recent studies have demonstrated that human spermatozoa are capable of generating reactive oxygen species and that this activity is significantly accelerated in cases of defective sperm function. In view of the pivotal role played by lipid peroxidation in mediating free radical damage to cells, we have examined the relationships between reactive oxygen species production, lipid peroxidation, and the functional competence of human spermatozoa. Using malondialdehyde production in the presence of ferrous ion promoter as an index of lipid peroxidation, we have shown that lipid peroxidation is significantly accelerated in populations of defective spermatozoa exhibiting high levels of reactive oxygen species production or in normal cells stimulated to produce oxygen radicals by the ionophore, A23187. The functional consequences of lipid peroxidation included a dose-dependent reduction in the ability of human spermatozoa to exhibit sperm oocyte-fusion, which could be reversed by the inclusion of a chain-breaking antioxidant, alpha-tocopherol. Low levels of lipid peroxidation also had a slight enhancing effect on the generation of reactive oxygen species in response to ionophore, without influencing the steady-state activity. At higher levels of lipid peroxidation, both the basal level of reactive oxygen species production and the response to A23187 were significantly diminished. In contrast, lipid peroxidation had a highly significant, enhancing effect on the ability of human spermatozoa to bind to both homologous and heterologous zonae pellucidae via mechanisms that could again be reversed by alpha-tocopherol. These results are consistent with a causative role for lipid peroxidation in the etiology of defective sperm function and also suggest a possible physiological role for the reactive oxygen species generated by human spermatozoa in mediating sperm-zona interaction.
The electrochemical production of Fenton's reagent by simultaneous reduction of dioxygen and ferric ions on a carbon felt electrode, permits a controlled, in situ generation of hydroxyl (OH) radicals. The possibility of using electrochemically produced OH radicals for solving environmental problems is investigated. Continuous and controlled production of hydroxyl radicals was achieved by electrochemical reduction of O2 in the presence of a catalytic amount of ferric or ferrous ion. These radicals are used for remediation of water containing toxic-persistent-bioaccumulative organic pollutants through their transformation into biodegradable compounds or through their mineralization into H2O and CO2. A widely used herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D), was selected as a model for a toxic organic pollutant. High pressure liquid chromatography (HPLC) was used to quantify the distribution of the hydroxylated products obtained. Rate constants for the hydroxylation reactions of 2,4-D, 2,4-dichlorophenol (2,4-DCP), 2,4-dichlororesorcinol (2,4-DCR) and 4,6-dichlororesorcinol (4,6-DCR) were determined. The mineralization of 2,4-D and its derivatives was followed by total organic carbon (TOC) measurements. More than 95% of 2,4-D and the intermediates generated during the electrolysis can be mineralized.
Recent studies have demonstrated that human spermatozoa are capable of generating reactive oxygen species and that this activity is significantly accelerated in cases of defective sperm function. In view of the pivotal role played by lipid peroxidation in mediating free radical damage to cells, we have examined the relationships between reactive oxygen species production, lipid peroxidation, and the functional competence of human spermatozoa. Using malondialdehyde production in the presence of ferrous ion promoter as an index of lipid peroxidation, we have shown that lipid peroxidation is significantly accelerated in populations of defective spermatozoa exhibiting high levels of reactive oxygen species production or in normal cells stimulated to produce oxygen radicals by the ionophore, A23187. The functional consequences of lipid peroxidation included a dose-dependent reduction in the ability of human spermatozoa to exhibit sperm oocyte-fusion, which could be reversed by the inclusion of a chain-breaking antioxidant, alpha-tocopherol. Low levels of lipid peroxidation also had a slight enhancing effect on the generation of reactive oxygen species in response to ionophore, without influencing the steady-state activity. At higher levels of lipid peroxidation, both the basal level of reactive oxygen species production and the response to A23187 were significantly diminished. In contrast, lipid peroxidation had a highly significant, enhancing effect on the ability of human spermatozoa to bind to both homologous and heterologous zonae pellucidae via mechanisms that could again be reversed by alpha-tocopherol. These results are consistent with a causative role for lipid peroxidation in the etiology of defective sperm function and also suggest a possible physiological role for the reactive oxygen species generated by human spermatozoa in mediating sperm-zona interaction.
Seawater used in mariculture has been suspected of being a potential source of infection. In this study, the lethal effects
of low-amperage electric treatment on microorganisms were examined in natural seawater and in seawater inoculated with Vibrio parahaemolyticus. In both cases, bacteria including V. parahaemolyticus in seawater were completely eliminated in 100 ms by a 0.5-A, 12-V direct current. Electron microscopic investigation of the
electrically treated bacteria revealed substantial structural damage at the cellular level. In conclusion, our results indicate
that low-amperage electric treatment is effective for rapid inactivation of microorganisms in seawater.
To evaluate the effect of prechlorination on coagulation of algae by alum, this investigation was conducted. Prechlorination yielding combined and free residuals improved the alum coagulation of high pH (9.6) algal samples significantly. The mechanism is rather complex and may be attributed to the interaction between chlorine and algal cells. Prechlorination either to combined or free residual did not increase the efficiency of alum coagulation of algal samples of low pH (5.8). Alum alone appears to be so effective at this pH that any additional improvement using a combination of chlorine and alum is insignificant. The studies indicate that chlorination can be adopted before alum coagulation and flocculation particularly for high pH waters to improve algal removal efficiency where alum alone is ineffective.
The effects of chlorine, ozone and chlorine dioxide on Scenedesmus sp. cultures were studied. Algal cell viability and chlorophyll concentration decreased, and the concentration of dissolved organic substances increased with increasing applied oxidant concentration. Pretreatment with chlorine dioxide (1, 3 or 5 mg l−1) or ozone (2.6, 4.6 or 8.1 mg l−1) on algal cultures enhanced algal flocculation with alum, while prechlorination with 10 or 20 mg l−1 increased the required dosage of alum by 15%. Scanning electron micrographs of oxidized cells revealed drastically adverse effects upon the cell surface architecture: in addition to the oxidation of noncellular organic materials, the oxidants damaged both cell surface structures and intracellular components. A model explaining the effects of the different oxidants on microalgal flocculation is suggested.
The mechanism of low frequency a.c. electrochemical disinfection was studied. A random oriented graphite fiber-epoxy matrix composite material was employed to fabricate the electrodes. This material was found to have very good electrochemical stability when cycled anodically and cathodically in solutions containing NaCl or NaBr.The lethal species was identified as HClO and HBrO in solutions containing Cl− and Br−, respectively, although the free halogen molecule may contribute to the observed disinfection activity under certain experimental conditions.The efficiency of disinfection increases with increasing concentration of Cl− (or Br−) and with decreasing pH. Deaerating the solution decreases the efficiency of disinfection significantly. NaBr was found to be effective at much lower concentrations than NaCl at all pH values but the effect is enhanced at pH > 7 due to ionization of HClO.The unique advantage of the method described in this paper is that a high transient concentration (in time and space) of the lethal species is generated, enough to destroy the most resistant microorganisms, while the average concentration of active halogen in the effluent liquid remains well below the objectionable level.
This report summarizes results obtained as part of a larger effort to demonstrate the applicability of electrolytic procedures for the direct anodic (oxidative) degradation of toxic organic wastes. The authors refer to this process as electrochemical incineration (ECI) because the ultimate degradation products are equivalent to those achieved by thermal incineration processes. In this work, the ECI of 4-chlorophenol is achieved in an aqueous medium using a platinum anode coated with a quaternary metal oxide film containing Ti, Ru, Sn, and Sb oxides. The electrode is stable and active when used with a solid Nafion membrane without the addition of soluble supporting electrolyte. Liquid chromatography (LC), including reverse phase and ion exchange chromatography, is coupled with electrospray mass spectrometry (ES-MS) and used, along with gas chromatography-mass spectrometry (GC-MS) and measurements of pH, chemical oxygen demand (COD), and total organic carbon (TOC), to study the reaction and identify the intermediate products from the ECI of 4-chlorophenol. Twenty-six intermediate products are identified and reported. The most abundant of these products are benzoquinone, 4-chlorocatechol, maleic acid, succinic acid, malonic acid, and the inorganic anions chloride, chlorate, and perchlorate. After 24 h of ECI, a solution that initially contained 108 ppm 4-chlorophenol yields only 1 ppm TOC with 98% of the original chlorine remaining in the specified inorganic forms. LC-ES-MS and direct infusion ES-MS detection limits are between 80 ppb and 4 ppm for these intermediate products. Elemental analysis of the electrolyzed solutions by inductively coupled plasma mass spectrometry ICP-MS showed that only trace amounts of the metallic elements comprising the metal oxide film were present in the solution.
A long terre BOD test was used for quantitative determination of biodegradability induced by ozone on refractory organic matter remaining in solution after conventional biological and lime treatment. The improvement in biodegradability cansed by ozonation can be assumed as removing inhibitory effects due to changes in molecular structure. In all biodegradability tests of ozonated efltuents acclimation was required. When a seed material consisting of micro-organisms already acclimated is used, the iag period disappears.
A laboratory-scale electrochemical (EC) disinfector was used for the disinfection of various wastewater effluents, including saline primary effluent, saline secondary effluent, and freshwater secondary effluent. Such EC disinfection was highly effective for saline effluent with a salinity content of around 8parts per thousand. A killing efficiency of 99.9% on total coliform bacteria was achieved for saline secondary effluent with a contact time of less than 10 s and a power consumption rate no more than 0.006 kWh/m(3). For primarily treated saline effluent, the same degree of disinfection was obtained with a contact time of less than 20 s and a power consumption of lower than 0.08 kWh/m(3). The efficiency of EC disinfection was regulated by both the contact time (t) and current density (I-d) applied, and a kinetic function in terms of survival ratio (N/N-0) was developed for the saline secondary effluent, i.e., log(N/N-0)= -0.01(I(d)t)(1.87). While EC disinfection is highly applicable for saline effluent, it did not exhibit a similar degree of effectiveness for freshwater sewage effluent, even with a longer contact time and higher power input. Based on the results of the EC disinfection and comparative direct chlorination experiments, it is argued that the main disinfecting action of the EC process may not be electrochlorination. The EC process could produce other short-lived, more powerful germicidal substances that exert the strong killing function within a short contact time.
We used electrochemical impedance spectroscopy (EIS) to investigate microbial degradation of polyimides used as insulators in electronic packaging. The microbial inoculum was a fungal consortium isolated from degraded polyimides. Microorganisms grew on these polymers yielding distinctive EIS spectra indicative of failure. Degradation appeared to occur in a number of steps. Two distinctive stages in the decline of film resistance were observed in the inoculated EIS cells within 17 and 72 days after inoculation. The early stage of resistance decrease may be related to the ingress of water molecules and ionic species into the polymeric materials, whereas the second stage probably resulted from partial degradation of the polymers by fungal growth on the polymer film. The active fungal consortium was comprised of Aspergillus versicolor, Cladosporium cladosporioides, and a Chaetomium species. All of these fungi are common environmental contaminats. The relationship between changes of impedance spectra and microbial degradation of the coatings was supported by scanning electron microscopic observations of fungi on the surface of the inoculated polyimides. Our data indicate that the insulating polyimides used in electronic applications are susceptible to fungal degradation under appropriate environmental conditions, particularly in the presence of moisture. © 1996 John Wiley & Sons, Inc.
Electrochemical rupture of cell membranes was performed with a conducting polypyrrole-coated electrode. Erythrocytes, which were employed as a cell model, were ruptured on a polypyrrole-coated electrode in a saline solution by a small potential shift from −0.6 V vs. Ag/AgCl to higher than 0.4 V vs. Ag/AgCl. Erythrocyte lysis on a bare substrate electrode needed a larger potential shift from −0.6 V to higher than 1.4 V. The rupture of erythrocytes on the polypyrrole-coated electrode by a small potential shift was attributed to a dynamic pH change near the polypyrrole-coated electrode surface. Electrically stimulated rupture of a single target erythrocyte was demonstrated with a polypyrrole-coated microfiber electrode, which might be applicable to single cell manipulations.
A novel electrochemical reactor employing activated carbon fiber (ACF) electrodes was constructed for disinfecting bacteria in drinking water. Escherichia coli adsorbed preferentially onto ACF rather than to carbon-cloth or granular-activated carbon. E. coli cells, which adsorbed onto the ACF, were killed electrochemically when a potential of 0.8 V vs. a saturated calomel electrode (SCE) was applied. Drinking water was passed through the reactor in stop-flow mode: 2mL/min for 12 h, o L/min for 24 h, and 1 mL/min for 6 h. At an applied potential of 0.8 V vs, SCE, viable cell concentration reamined below 30 cells/mL. In the absence of an applied potential, bacteria grew to a maximum concentration of 9.5 × 103 cells/mL. After continuous operation at 0.8 V vs. SCE, cells adsorbed onto the ACF could not be observed by scanning electron microscopy. In addition, chlorine in drinking water was completely removed by the reactor. Therefore, clean and efficient inactivation of bacteria in drinking water was successfully performed. © 1994 John Wiley & Sons, Inc.
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.
A catheter surface was modified by coating a cellulose acetate polymer. Adhesion of Pseudomonas aeruginosa ATCC 27853 to the surface was investigated by exposing bacterial cultures to three treatments: polymer impregnated with silver ions (Ag+), polymer surfaces coated with lectins and a combination of Ag+ and a lectin coating. The effective concentration of Ag+ providing protection against bacterial biofilm development was 100g/ml and higher. Lectins alone at 10% also showed inhibition of bacterial attachment. However, the best result was achieved against bacterial adhesion and growth on surfaces using a combination of 100 g Ag+/ml and a lectin coating as a surface treatment. This surface treatment was also effective against both fresh culture and a two-week-old culture containing P. aeruginosa producing exopolymers. Our results suggest that Ag+impregnation combined with a lectin coating warrants further investigation as a potential means of protecting catheters.
We have produced an adherent defect TiO2 film reactor in which the performance is greatly improved by the application of a small positive bias (electric field enhancement) to boost hydroxyl radical production. In the reactor the light, electric field and photocatalyst combined to disinfect water containing Clostridium perfringens spores and Escherichia coli. Singly, neither light, the electric field or the combination of light and fixed film could significantly reduce the numbers of indicator bacteria. We believe that water disinfection using an immobilised titanium dioxide film photochemical reactor with electric field enhancement could provide an effective and energy efficient source of hydroxyl radicals for water disinfection.
Natural water, highly contaminated with coliforms, was electrochemically treated in a stirred batch system with the use of two Ti electrodes and direct current, the polarity of which alternated automatically in half cycles of 1 min. The process was found to be effective and the percentage of the initial concentration of bacteria which were destroyed was found to be proportional to both treatment time and the square of current density obeying the kinetic model α = ki2 t; consequently the time needed for complete disinfection was inversely proportional to the square of current density. The percentage above was found to be independent of the initial concentration of germs at least for the range of concentrations employed. The residual disinfection capacity, after completion of the electrochemical treatment, was also verified by mixing electrochemically treated, disinfected natural water with contaminated water.
Oxygen-derived free radicals and other oxidizing species are thought to be involved in inflammation and ischemic tissue injuries. Recently, oxygen-derived free radicals also have been implicated in tissue injury of the myocardium subjected to ischemia/reperfusion. The purpose of this investigation was to determine if electrolysis of a physiological buffer would serve as a source of free radicals, and if these radicals would lead to alterations in myocardial function. Isolated Langendorff-perfused rabbit hearts perfused with buffer subjected to a 20 mA D.C. current for 2 min demonstrated significant increases in coronary perfusion pressure (37 ± 6 mmHg), left ventricular end diastolic pressure (41 ± 7 mmHg), and loss in left ventricular developed pressure (35 ± 5%). The free radical scavengers, Superoxide dismutase and a combination of tryptophan plus glycine, were effective in protecting the hearts from the effects of electrolysis. The presence of free radicals was semiquantitated with a radical-luminol chemiluminescent assay. In this assay a variety of radical scavengers and antioxidants were effective (i.e., dimethyl sulfoxide, nitro blue tetrazolium, ascorbate, superoxide dismutase, 1, 3-diphenyisobenzofuran, and glycine, catalase), whereas mannitol and tryptophan were not effective. The data indicate that electrolysis of a physiological buffer produces a milieu containing several reactive oxygen species or free radicals that have the potential to produce alterations in a biological system. This method has the advantage over existing protocols for the generation of radicals in that it is a blood-free and an enzyme-free system.
Lethal effects of pulsed electric fields (PEF) on suspensions of various bacteria, yeast, and spores in buffer solutions and liquid foodstuffs were examined. Living-cell counts of vegetative cell types were reduced by PEF treatment by up to more than four orders of magnitude (> 99.99%). On the other hand, endoand ascospores were not inactivated or killed to any great extent. The killing of vegetative cell types depends on the electrical field strength of the pulses and on the treatment time (the product of the pulse number and the decay time constant of the pulses). For each cell type, a specific critical electric field strength (E
c) and a specific critical treatment time (t
c) were determined. Above these critical values, the fractions of surviving cells were reduced drastically. The “limits” E
c and t
c depend on the cell characteristics as well as on the type of medium in which the cells are suspended. Especially in acid media living-cell counts were sufficiently decreased at very low energy inputs. In addition to the inactivation of microorganisms, the effect of PEF on food components such as whey proteins, enzymes and vitamins, and on the taste of foodstuffs was studied. The degree of destruction of these food components by PEF was very low or negligible. Moreover, no significant deterioration of the taste of foodstuffs was detected after PEF treatment. Disintegration of cells by PEF treatment in order to harvest intracellular products was also studied. Yeast cells, suspended in buffer solution, were not disintegrated by electric pulses. Hence, PEF treatment is an excellent process for inactivation of microorganisms in acid and in thermosensive media, but not for complete disintegration of microbial cells.
The present study was designed to identify the free radicals generated during the electrolysis of the solution used to perfuse isolated rat heart Langendorff preparations. The high reactivity and very short half-life of oxygen free radicals make their detection and identification difficult. A diamagnetic organic molecule (spin trap) can be used to react with a specific radical to produce a more stable secondary radical or "spin adduct" detected by electron spin resonance (ESR). Isovolumic left ventricular systolic pressure (LVSP) and left ventricular end diastolic pressure (LVEDP) were measured by a fluid-filled latex balloon inserted into the left ventricle. The coronary flow was measured by effluent collection. Electrolysis was performed with constant currents of 0.5, 1, 1.5, 3, 5, 7.5, and 10 mA generated by a Grass stimulator and applied to the perfusion solution for 1 min. A group of experiments was done using a 1.5 mA current and a Krebs-Henseleit (K-H) solution containing free radical scavengers (superoxide dismutase (SOD): 100 IU/ml or mannitol: 50 mM). Heart function rapidly declined in hearts perfused with K-H buffer that had been electrolyzed for 1 min. The addition of mannitol (50 mM) to the perfusion solution had no effect on baseline cardiac function before electrolysis while SOD (100 IU/ml) increased the coronary flow. However, SOD was more effective than the mannitol in protecting the heart against decreased of cardiac function, 5 min after the end of electrolysis. Samples of the K-H medium subjected to electrolysis were collected in cuvettes containing a final concentration of 125 mM 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and analyzed by spectroscopy. The ESR spectrum consisted of a quartet signal (hyperfine couplings aN = aH = 14.9 G) originating from the hydroxyl adduct signal, DMPO-OH. The intensity of the DMPO-OH signal remained stable during the 60 s of electrolysis and the quantity of free radicals induced by electrolysis was directly proportional to the intensity of the current. The addition of mannitol and SOD to the perfusate scavenged the hydroxyl radicals present in the solution, suggesting that both hydroxyl and superoxide radicals were formed during electrolysis.
Chloride anions and hydrogen peroxide serve as substrates for myeloperoxidase (MPO) in order to produce hypochlorous acid (HOCl) as one of the major killing agents of phagocytic leukocytes. Apart from this role of being a substrate for the MPO-reaction the chloride anion has been considered as unreactive and has not been implicated in radical reactions which contribute to the killing process. From the inherent reactivities of the pertinent radicals (as determined by pulse radiolysis experiments), the great abundance of chloride, and the most probable distribution of reactants within the phagosome, we deduce estimates for the average life-time and free diffusion path-length in this milieu and arrive at a model according to which chloride ions enter into radical chains and influence the killing of ingested bacteria to an extraordinarily high extent. We propose that hydroxyl radicals--despite some controversial arguments in the literature--may still be considered as important contributors to cell killing especially since we show that their reactions are made more effective by producing chlorine radicals in a cyclic process. We furthermore present arguments how the phagocyte may protect itself from harmful actions of HOCl and H2O2 after the superoxide-generating activity of NADPH oxidase is turned off.
Wastewater disinfection, manuals of practice for water pollution control
- K E Longley
Longley KE. Wastewater disinfection, manuals of practice for water
pollution control. Alexandria, VA, USA: Water Pollution Control
Federation; 1986.
Electrolysis-induced myocardial dysfunction
- V J Charles
- K M Judith
- S Kathleen
- S R Parinam
- R L Benedict
Charles VJ, Judith KM, Kathleen S, Parinam SR, Benedict RL.
Electrolysis-induced myocardial dysfunction. J Pharmacol Methods
1986;15:305-20.
Fundamentals of electrochemistry
- V S Bagotzky
Bagotzky VS. Fundamentals of electrochemistry. New York: Plenum;
1993. p. 397-408.
The use of composite electrodes for the electrochemical disinfection of recirculating fluids
- P Natishan
Natishan P. The use of composite electrodes for the electrochemical
disinfection of recirculating fluids. Ph.D. dissertation. Charlottesville,
VA, USA: University of Virginia; 1984.
Susceptibility of electronic insulation polyimides to microbial degradation
- Gu
The mechanism of low frequency AC electrochemical disinfection
- Stoner
Electrolysis-induced myocardial dysfunction
- Charles