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Electrochemical Alternatives for Drinking Water Disinfection
Angewandte Chemie International Edition
Abstract
Chlorination is the most common method worldwide for the disinfection of drinking water. However, the identification of potentially toxic products from this method has encouraged the development of alternative disinfection technologies. Among them, electrochemical disinfection has emerged as one of the more feasible alternatives to chlorination. This article reviews electrochemical systems that can contribute to drinking water disinfection and underscores the efficiency of recently developed diamond films in chlorine-free electrochemical systems.
... EC uses iron or aluminum electrodes to create the same products as CC [73] [75] [76]. Also, EO electrode materials are selected based on the oxidant required for disinfection (e.g., MMO) promotes higher free chlorine production, while BDD is employed for higher ROS production [25] [28] [55]. ...
... EO is a disinfection technique employed in treating water electrochemically [31] [55]. For small potable water setups, EO has many benefits over conventional chlorine disinfection, including ease of use, environmental protection, and cost-effectiveness [27] [31] [55]. ...
... EO is a disinfection technique employed in treating water electrochemically [31] [55]. For small potable water setups, EO has many benefits over conventional chlorine disinfection, including ease of use, environmental protection, and cost-effectiveness [27] [31] [55]. Throughout EO, the electrolysis phenomenon could reduce numerous biological and chemical pollutants through direct oxidation (DO) and indirect oxidation (IO) methods [27] [38] [55]. ...
Although the literature mainly reports on the inactivation of bacteria by various electrochemical disinfectants, the impact of process variables and reactor design on bactericidal performance is not fully understood. This review concentrates on recent achievements of electrocoagulation (EC) and electrooxidation (EO) in killing pathogens such as Escherichia coli. Lynn et al. [1] [2] showed that in addition to EC alone, EC-EO enhanced E. coli reduction only after pH adjustment. They proposed that additional process optimization may lead to further improvements, such as adjusting the iron dosage for natural organic matter (NOM) removal, which would limit the effectiveness of oxidant scavengers. Additionally, more efficient filtration techniques (e.g., granular filtration) will reduce NOM and total iron content in the EO feed-water, decreasing the need for oxidants. Furthermore, continuous EC-EO treatment requires more elevated EO current densities to improve E. coli removal. Investigating the pathways of demobilizing E. coli in drinking water at high iron concentrations in the EO range will also provide deep insights into ongoing setup design. This review provides crucial, reliable, safe, and versatile alternatives to the widespread trouble of human drinking water pollution. Using and propagating the EC-EO technique will diminish health risks related to water quality, economic burden, lost labor time, import washout to the national economy, and natural resource management. Commercial-scale deployment of EC-EO technology will undoubtedly increase the socioeconomic burden on local communities via secured water supply and result in a reduction in government health expenditures.
... This section is focused on recent advances achieved since 2015, considering the fundamentals of the EO treatment of organic pollutants in water. constantly and repeatedly used in several reviews and books [1,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27], generating positive and negative point of views as well as representations or adaptations that have created myths and misunderstandings. For example, on the one hand, the wrong model representation to illustrate the production of hydroxyl radicals and/or other oxidants at the anodic surface, omitting the Nernst layer dimensions. ...
... When the water matrices or solutions contain chloride, a different type and number of oxidizing species are produced [7,25,29,33,44]. This EO approach is commonly named electrochemical Clmediated oxidation, oxidation with active chlorine or indirect EO by chloride oxidation, which is considered a volume-based chemical oxidation approach and turns out to be more significant than mediated oxidation by free heterogeneous OH (see section 3). ...
... Many authors have shown that electrogenerated active chlorine can be used effectively, using suitable anodes and operation conditions, to inactivate a large variety of microorganisms ranging from bacteria to viruses and algae [25,32,216,225,226]. Hence, the treatment with electrogenerated active chlorine can be potentially used for the simultaneous mineralization of organic pollutants (i.e., water decontamination) and water disinfection. ...
... In addition, in the presence of M(•OH), the electrochemical process can promote the formation of a series of relatively weaker oxidants (Eqs. 4-9) (Garcia-Segura et al., 2018;Liang et al., 2005;Martinez-Huitle and Brillas, 2008), which are also involved in the inactivation of PMs. However, the competitive side reactions of oxygen evolution reduce the efficiency of ECO process during the inactivation of PMs (Eqs. 10 and 11) (Martinez-Huitle and Brillas, 2021;Martinez-Huitle and Ferro, 2006). ...
... In addition to Cl -, the SO 4 2-(or HSO 4 -), CO 3 2-(or HCO 3 -) and PO 4 3existing in the water will also be oxidized at some anodes such as PbO 2 and boron-doped-diamond (BDD) to form some weak oxidants, such as S 2 O 8 2-, C 2 O 6 2and P 2 O 8 4-(Eqs. 25-29) (Martinez-Huitle and Brillas, 2008;Phillips et al., 2018;Kraft, 2007), however whether they can participate in the PMs inactivation requires further study. ...
... Electrode material is considered to be one of the most important parameters to control the type and yield of electrogenerated oxidants (Sopaj et al., 2015;Martinez-Huitle and Brillas, 2008). According to the electrolyte and the quality parameters of water/wastewater, different types of electrodes should be used. ...
Compared with other conventional water disinfection processes, (photo) electrochemical oxidation (P/ECO) processes have the characteristics of environmental friendliness, convenient installation and operation, easy control and high efficiency of inactivating waterborne pathogenic microorganisms (PMs), so that more and more research work has been focused on this topic, but there is still a huge gap between the research and practical application. Here, the research network of inactivating PMs by P/ECO processes has been comprehensively summarized, and the electrode/reactor/process design strategies based on strengthening direct and indirect oxidation, enhancing mass transfer efficiency and electron transfer efficiency, and improving the effective dose of electrogenerated oxidants are discussed. Furthermore, the factors affecting the inactivation of PMs and the issues regarding to stability and lifetime of the electrode are discussed respectively. Finally, the important research priorities and possible research challenges of P/ECO processes are put forward to make significant progress of this technology.
... Various electrochemical membrane disinfection processes have already achieved high treatment performance with conventional or novel mechanisms [14,15]. Multiple studies and proposed processes pose an enormous challenge for the critical assessment of electrochemical membrane disinfection technology. ...
... After a brief overview of established electrochemical membrane disinfection technologies, a deeper look is warranted by making assessments and comparisons between different disinfection mechanisms based on (1) disinfection performance, and (2) energy consumption to create general guidelines for future research. The shortest contact time or hydraulic retention time (HRT) needed to achieve complete disinfection (i.e., no live microbes in the effluent) can be used to evaluate disinfection capability and upper limitation [15,32,62,63]. To analyze the treatment efficiency of disinfection processes in laboratories, researchers often apply cultivable model microbes (e.g., Escherichia coli and Bacillus subtilis) to represent bacteria, and Ms2 to represent viruses. ...
Water disinfection is the most important process to control the risks caused by the microbes within water. Conventional water disinfection processes, including chlorination, ozonation, and ultraviolet, show intrinsic disadvantages such as low disinfection efficiency, harmful byproduct formation, and microbial reactivation/regrowth during extensive applications. In order to overcome these limitations, electrochemical membrane technology is explored as an emerging efficient water disinfection approach, with novel disinfection mechanisms achieved by the specific physical, electrochemical, and biological characteristics of electrochemical membranes. This chapter gives an overview into the main mechanisms involved in the disinfection process by electrochemical membranes, as well as the development progress of the reactor configuration designs. Different water disinfection mechanisms and reactor configurations are comprehensively compared with the aspect of disinfection efficiency and energy consumption. Furthermore, the limitations and future perspectives of electrochemical membrane technology for water disinfection are also proposed.
... Therefore, it is necessary to eliminate the contaminants before human consumption [10]. Over the period, numerous disinfection techniques have been developed, including (1) chemical systems based on chlorine and ozone, (2) photocatalysis and photodynamic disinfection, (3) physical methods such as ultraviolet irradiation, and (4) electrochemical disinfection [11]. Compared to alternatives, ozonation and ultraviolet (UV) radiation have gained acceptance in commercial water treatment systems. ...
... Various treatment agents are typically employed to achieve primary water disinfection including active chlorine, combined chlorines, chlorine dioxide, ozone, and ultraviolet (UV) radiation (Crittenden et al., 2012). Among these methods, only chlorine-based treatment methods offer long-lasting water disinfection within water distribution networks and equipment (Martínez-Huitle and Brillas, 2008). However, centralized chlorination methods have limitations associated with handling of hazardous chemicals and possible formation of halogenated disinfection by-products (DBPs). ...
... However, traditional disinfection technologies such as chlorination and ozonation processes are limited by the formation of DBPs and the addition of extra chemicals. Physical disinfection processes such as UV irradiation, membrane separation, and thermal disinfection are expensive to operate and maintain and do not meet the requirements for primary and residual water disinfection (Li and Ni 2012, Martinez-Huitle and Brillas 2008, Rajab et al. 2015. Consequently, there is an urgent need to develop new, efficient, and cost-effective methods for water disinfection. ...
The removal of waterborne pathogens from water is critical in preventing the spread of waterborne diseases. Electrochemical methods have been extensively researched and implemented for disinfection, primarily owing to their simplicity, efficiency, and eco-friendliness. Thus, it is essential to conduct a review about the research progress and hotspots on this promising technique. In this paper, we provided a comprehensive bibliometric analysis to systematically study and analyze the current status, hotspots, and trends in electrochemical disinfection research from 2002 to 2022. This study analyzed literature related to electrochemical disinfection or electrochemical sterilization published in the Web of Science database from 2002 to 2022 using CiteSpace and Biblioshiny R language software packages. The analysis focused on the visualization and assessment of annual publication volume, discipline and journal distribution, collaborative networks, highly cited papers, and keywords to systematically understand the current status and trends of electrochemical disinfection. The results showed that between 2002 and 2022, 1171 publications related to electrochemical disinfection were published, with an exponential increase in the cumulative number of publications (y=17.518e0.2147x, R2= 0.9788). The publications covered 76 disciplines with many articles published in high-impact journals. However, the research power was characterized by a large number of scattered research efforts and insufficient cooperation, indicating the need for further innovative collaboration. The citation analysis and keyword analysis suggest that future development in this field may focus on optimizing electrode materials, investigating the disinfection performance of ·OH based systems, optimizing conditions for actual wastewater treatment, and reducing energy consumption to promote practical applications.
... The generation of oxidants is influenced by various parameters, such as water quality and chemical composition, type of electrolytic process, applied voltage or electric current, pH, temperature, added electrolytes and electrode material [24][25][26][27]. The anode material is a very important parameter in electrochemical disinfection and various materials such as different metals, carbon electrodes, mixed metal oxides and boron-doped films have been tested [28]. Gholami [27] used a simple two steel electrodes set-up and achieved complete inactivation of E. coli in 5 minutes of treatment time at an applied voltage of 4.5 V and 500 mA current. ...
Potable water is water of acceptable quality in terms of physical, chemical, and microbiological parameters for safe drinking. Although it is a basic human need and right, ensuring access to drinking water has been and continues to be a challenge. Waterborne diseases are still an issue in many developing countries and deaths from diseases such as cholera, typhoid and diarrhoea remain high. Their prevention and control through protection of water sources and proper treatment techniques are of great importance. Disinfection of water is an important step in water treatment and can be achieved by chemical, physical or hybrid methods. Chemical processes include treatment with chlorine, chlorine dioxide, chloramines, ozone, and hydrogen peroxide. Physical methods include disinfection with heat, UV irradiation, and ultrasound. New methods are being developed and studied to advance the disinfection process. This paper provides a brief overview of the most commonly used disinfection methods and a case study on ultrasonic disinfection of raw (surface) water. The disinfection efficiency of a horn probe (20 kHz) and an ultrasonic bath (25/45 kHz) under different operating conditions is investigated. TECTA™ pathogen detection system was used for enumeration of Escherichia coli and total coliform colonies. For a volume of 200 mL, complete inactivation of E. coli is observed after less than 10 minutes of exposure time in a horn probe setup. For larger volumes (1000 mL), the bath operating at 25 kHz provided better disinfection for the same period of time. In general, the smaller the volume and/or the longer the treatment, the higher the disinfection rate for microorganisms. In addition, a "de-clumping" effect was observed in all experiments.
... Therefore, it is necessary to eliminate the contaminants before human consumption [10]. Over the period, numerous disinfection techniques have been developed, including (1) chemical systems based on chlorine and ozone, (2) photocatalysis and photodynamic disinfection, (3) physical methods such as ultraviolet irradiation, and (4) electrochemical disinfection [11]. Compared to alternatives, ozonation and ultraviolet (UV) radiation have gained acceptance in commercial water treatment systems. ...
The electrochemical treatment of canal water was investigated in a batch-wise system in the presence of stainless steel 316-grade electrodes. Three effective process parameters, including current density, reaction time, and electrode spacing, were evaluated in the range of 0.25–2.5 mA/cm2,1–10 min, and 0.5–2.5 cm, respectively. Operational variables of electrochemical disinfection are optimized in response surface methodology (RSM) using Box–Behnken design. Before electrochemical disinfection, a pretreatment process of coagulants mixing for turbidity removal was conducted.
Results revealed that a 10 ppm dosage of Ferric chloride (FeCl3.6H2O) and alum (Al2(SO4)3·16H2O) at neutral pH is appropriate. Furthermore, the RSM analysis shows that interelectrode spacing is the most prominent factor affecting the disinfection performance, and increasing electrode spacing inversely affects the disinfection efficiency. Results revealed that 1.52 mA/cm2
current density, 6.35 min reaction time, and 1.13 cm of electrode spacing are the optimum conditions, resulting in a statistically 98.08% disinfection of the total coliform. The energy required for electrochemically disinfection of water at optimum conditions was 0.256 kWh/m3.
... A few methods have been reported for the degradation of refractory organic pollutants in wastewater, by physical, chemical or biological processes [1,10,11]. Among them, the electrochemical advanced oxidation process (EAOP) has attracted great attention due to its relative simplicity in operation and good environmental compatibility [6,[12][13][14][15][16][17]. It has been adapted for the degradation and mineralization of a wide range of recalcitrant contaminants, such as carboxylic acids and perfluorocarboxylic acids [18]. ...
Tremendous research efforts have been devoted to new methods of water decontamination and water splitting at low cost and less energy consumption. Herein, we developed a robust electrochemical strategy with an efficient membrane electrode to remove refractory organic pollutants and simultaneously produce pure hydrogen in wastewater. Firstly, the membrane anode was constructed with a three-dimensional (3D) nanoneedle array of Co3O4 and Ti membrane, exhibiting superior degradation of phenol and dye with Na2SO4 as the electrolyte in a conventional electrocatalytic membrane reactor (ECMR). For the phenol degradation, ≥99% removal efficiency of phenol, 99.5% chemical oxygen demand (COD) removal rate, 92.5% total organic carbon (TOC) removal rate, 88.7% current efficiency and 0.061 kW h (g COD)−1 energy consumption can be obtained. For the dye degradation, ≥99% decolor efficiency and 95.2% COD removal rate, 87.6% TOC removal rate, 82.1% current efficiency and 0.12 kW h (g COD)−1 energy consumption can be achieved. The obtained membrane electrode can provide more active CoOOH sites, dramatically increase the electric fields and overcome mass transfer limitation in a flow-through configuration, thereby significantly enhance the catalytic performance. Finally, we designed a H-type ECMR with the proton exchange membrane (PEM) as the separator for pure H2 production, i.e., PEM-ECMR, demonstrating superior degradation performance of phenol and dye, stable production of high-purity hydrogen (11–15 mL h−1), and excellent long-term stability (100 days) and low voltage input (below 3.0 V). This work demonstrates a promising pathway towards reducing cost and energy consumption for water decontamination and simultaneous hydrogen production.
... The Electrochemical process is considered a high-efficient, environmental-friendly and versatile technology, which could generate various oxidants in situ [5][6][7][8][9][10][11][12][13][14][15]. In general, the active species generated in the electrochemical process is of high oxidation potentials which could inactivate microorganisms with high efficiency. ...
High efficiency, eco-friendly, and without disinfection byproducts rendered the hydroxyl radical-dominated electrochemical process a promising disinfection technology. Inconsistent disinfection performances have been reported for Gram-positive (G+) and Gram-negative (G-) bacteria in *OH-dominated disinfection system. To thoroughly present and elucidate the different responses of G+ and G-, Fe-Co/CA cathode and Ru-Ir/Ti anode was fabricated. Under 22.73 mA/cm², E.coli were completely inactivated within 45 min, while there were about 2 logs of S.aureus were inactivated. Moreover, the sublethal injury of E.coli outperformed that of S.aureus as well. However, when E.coli and S.aureus coexisted, the disinfection efficiencies were inhibited for both E.coli and S.aureus. The subcellular damage of E.coli and S.aureus were different as well. With the reaction, cell surface hydrophobicity for both E.coli and S.aureus increased. However, E.coli obtained increased negative zeta potential after treatment, which promoted the development of electrochemical disinfection, while S.aureus obtained decreased negative zeta potential which resulted in significant agglomeration. The determination of malondialdehyde (MDA), phosphate concentration, and the leakage of Lactate dehydrogenase (LDH), as well as the degradation of protein, TOC, and nucleic acid, and SEM observation, illustrated the cell well and cell outer membrane were the first barrier to OH-dominated disinfection. The thick and rigid cell wall and the stable structure of peptidoglycan (PGN) in S.aureus cells contributed to the high resistance of S.aureus.
... Taking the above considerations into account, the aim of this work was to develop a highly efficient effluent treatment system which is capable of removing ATZ from methanol (MeOH) or methanol/water (MeOH:H 2 O) solutions. The methanol solutions can be obtained in the first stage of the combined process using adsorption as a preconcentration step, as reported elsewhere (De Mello et al., 2021Muñoz et al., 2020;Muñoz-Morales et al., 2019;Brillas and Martinez-Huitle, 2008). To the best of our knowledge, this is the first work reported in the literature which proposes the use of DSA® for the electrochemical oxidation of ATZ in methanol solutions. ...
This work reports the radicals detected and identified during the degradation of atrazine in methanol medium in the presence and absence of different proportions of water (0%, 5%, and 10%). The determination of these radicals is an important step to understand the electrolysis processes in methanol medium and contribute to clarify the degradation mechanism. Furthermore, the parameters for the successful removal of the contaminant were optimized and the results showed that the application of the technique led to the removal of nearly 99.8% of atrazine after 1 h of electrolysis. The oxidation kinetics was found to be very fast and most of the atrazine molecule in the medium was degraded in the first hour of electrolysis. The results obtained from a thorough analysis conducted with a view to evaluating the effects of different current densities and initial pH values on atrazine degradation showed that the application of higher current densities resulted in lower energy consumption, as this led to faster removal of atrazine. Additionally, the initial pH of the solution was found to favor the formation of different species of active chlorine. The radicals formed during the electro-oxidation process were detected by electron paramagnetic resonance spectroscopy and include hydroxyl, methoxy and hydroxymethyl. The use of methanol for the degradation of pollutants is a highly promising technique and this work shows that the identification of the different radicals formed in the process can be the key to understanding the degradation mechanism.
... Recently, electrochemical advanced oxidation processes gained much attention for elimination of organics due to their great potential in this field (Brillas and Sirés, 2015). These electrochemical treatment techniques have several benefits example (i) there are no harsh chemicals to initiate the reaction, (ii) the use of an electron as a reactive species, (iii) under any pressure and temperature may use to carry out the process (Martínez-Huitle and Brillas, 2008). ...
Pharmaceutical organics are a vital milestone in contemporary human research since they treat various diseases and improve the quality of human life. However, these organic compounds are considered one of the major environmental hazards after the conception, along with the massive rise in antimicrobial resistance (AMR) in an ecosystem. There are various biological and catalytic technologies existed to eliminate these organics in aqueous system with their limitation. Advanced Oxidation processes (AOPs) are used to decompose these pharmaceutical organic compounds in the wastewater by generating reactive species with high oxidation potential. This review focused various photocatalysts, and photocatalytic oxidation processes, especially core-shell materials for photo (electro)catalytic application in pharmaceutical wastewater decomposition. Moreover, we discussed in details about the design and recent developments of core shell catalysts and comparison for photocatalytic, electrocatalytic and photo electrocatalytic applications in pharmaceutical wastewater treatment. In addition, the mixture of inorganic and organic core-shell materials, and metal-organic framework-based core-shell catalysts discussed in detail for antibiotic degradation.
Nowadays, toxic/persistent organic micropollutants generated from different human activities contaminate natural water streams since conventional water and wastewater treatment plants remain inefficient to eliminate these pollutants. Alternatively, advanced oxidation processes (AOPs) constitute an efficient and environment friendly techniques to remove these pollutants from water and wastewater effluents. These processes are based on in situ generation of strong oxidants, like hydroxyl radicals, that are able to oxidize organic pollutants up to their mineralization. The Fenton process, which is based on the Fenton’s reagent (a mixture of hydrogen peroxide and ferrous iron), is one of the first AOPs. To enhance the efficiency of the Fenton process, several improvements have been achieved in recent years. This chapter focuses on the fundamental characteristics of this process and overviews Fenton-based processes such as photo-Fenton, electro-Fenton, and related processes as well as anodic Fenton and Fered-Fenton processes, including their application to the treatment of contaminated waters.
Electrooxidation as an alternative decentralized wastewater treatment technique has been considerably investigated to develop different remediation and disinfection solutions of diverse classes of wastewater and soil washing effluents. It is a clean technology with distinguished advantages such as high versatility, amenability, limited chemical addition and ease of operation at ambient temperature and pressure. This technology is highly efficient, and it has been established as a powerful decontamination technique for depolluting different classes of contaminated wastewater and soil washing effluents. In this chapter, the prospects, and challenges of electrooxidation and related processes applied to wastewater and contaminated soil treatment were summarized. The recent advances in anode materials applied in electrooxidation, the different anode designs and configurations were examined. Principles and mechanisms of electrooxidation coupled with other processes such as UV, ultrasonic irradiation and sulfate radical-based AOPs to accelerate and enhance pollutants mineralization, their advantages and limitations over electrooxidation alone were enumerated. Applications of electrooxidation and related processes as decentralize and point-of-use clean water technology, electrochemical disinfection and soil washing/flushing effluents treatment were discussed. The challenges and limitations of electrooxidation and related processes critically reviewed.
The food industry has extensively explored postharvest microbial control, seeking viable technologies to ensure food safety. Although numerous chlorine-based commercial sanitizers serve this purpose, many are plagued by constraints such as instability and diminished disinfectant efficacy. These issues arise from exposure to organic matter in wash water, light, or air. As an innovative and promising alternative, slightly acidic electrolyzed water (SAEW) has emerged, captivating attention for its robust sterilization potential and eco-friendliness in agricultural and food sectors. SAEW generated via electrolysis of a diluted hydrochloric acid (HCl) solution with concentrations ranging from 2 to 6% or aqueous solution of sodium chloride (NaCl) in a nonmembrane electrolytic chamber is reported to possess equivalent antimicrobial properties as strong acidic electrolyzed water (StAEW). In contrast to traditional chlorine sanitizers, SAEW leaves less chlorine residue on sanitized foods such fresh-cut fruit and vegetables, meat, poultry, and aquatic products due to its low available chlorine concentration (ACC). Its near neutral pH of 5 to 6.5 not only renders it environmentally benign but also mitigates the production of chlorine gas, a contrast to low pH conditions seen in StAEW generation. The bactericidal effect of SAEW against various strains of foodborne pathogens is widely believed and accepted to be due to the combined action of high oxidation-reduction-potential (ORP) reactions and undissociated hypochlorite/hypochlorous acid (HOCl). Consequently, a burgeoning interest surrounds the potential of SAEW for sanitation in the food industry, offering an alternative to address shortcomings in sodium hypochlorite solutions and even StAEW. It has been hypothesized from a number of studies that SAEW treatment can increase the quality and nutritional value of harvested fruits, which in turn may enhance their ability to be stored. Therefore, SAEW is not only a promising sanitizer in the food industry but also has the potential to be an efficient strategy for encouraging the accumulation of bioactive chemicals in plants, especially if it is used extensively. This review encapsulates the latest insights concerning SAEW, encompassing its antimicrobial effectiveness, sanitization mechanism, advantages vis-à-vis other sanitizers, and plausible applications across the food industry.
Removal of algae by electrochemical treatments through electrochemical
generation of persulfate and hydrogen peroxide was investigated in a fixed bed
reactor. The cell was equipped with two electrodes (two identical graphite
anode and cathode). The effect of different operative parameters, such as
applied potential and amount of initial sodium sulfate added in the case of
persulfate production was evaluated. In addition, the influences of potential
differences in the case of hydrogen peroxide production were addressed. The
two treatments were optimized, and their high efficacy in removing algae-laden
water was proved upon application to collected samples obtained from the
reservoir of Rod El-Farag drinking water station. The pro-type system used
with the proposed methods is simple, fast, and effective to remove algae from
water sources.
Electrolytic water disinfection via metallic ions is a promising technology for water and wastewater treatment. This approach has relatively limited detrimental environmental effects and does not change the taste or odor of the treated water. The mechanisms of electrolytic silver and copper release were investigated, including the current efficiency, the relation between ion generation and current in the systems, and previously examined water chemistries. A comparison of pathogen inactivation rates and pathogen reduction for various combinations of free chlorine and electrolytically generated silver and copper ions has been previously reported. Silver and chlorine do not disinfect as well as free chlorine, but it can be used in combination with low levels of free chlorine to produce disinfection rates comparable to higher levels of free chlorine. These results lay a strong foundation to investigate the use of electrolytic systems in a developing‐world context, particularly where water from the municipal tap contains chlorine but is at risk for recontamination during storage. Upon review of the literature, it was found that more research should be conducted to understand how organic loads and water chemistry affect ion generation and disinfection kinetics in these systems.
Global water shortages force the world to explore every possible way to reduce water consumption and reduction of exploitation of freshwater resources. In 2025, some estimates predict that 60% of the world's population will live in water-deficient regions. Nanofiltration (NF) membranes have been used in many fields, including water treatment, agriculture, pharmaceuticals, and biotechnology. NF stands out for its ability to effectively eliminate impurities, sediments, chemical effluents, and even hazardous substances like arsenic. This makes it a versatile approach for enhancing water quality. Nanofiltration membranes are a cutting-edge type of membrane technology that can be classified into two categories: organic (polymeric) and inorganic. The selection of membranes with appropriate selectivity based on applications of interest are vital to achieving the highest separation efficiency. During the first section of this review, the discussion will follow the background of membrane-based filters with solutes separation from the solution in the range of molecular weight from 500 to 10,000 g/mol, their characteristics, the benefits, and drawbacks of nanofiltration, and their cost-effectiveness of them. In the next part, various types of NF membranes, and their excellent properties, including high permeation to monovalent ions and low permeation to divalent ions, as well as higher flux, reliability, and integrity with longer cycle times and thereby lower costs, are examined. This article aims to discuss some of the most significant and pioneering applications of nanotechnologies in different water sources, including surface water, groundwater, and industrial wastewater streams. Although nanofilters have shown great promise, there are still some outstanding challenges that hinder their widespread adoption. We also provide a comprehensive overview of challenges and opportunities related to using nanotechnology in the future. The next decade is predicted to bring a lot of progress in NF.
Graphical abstract
Discovery of the amazing and vital therapeutic roles of electrical stimulation (ES) on skin has sparked tremendous efforts to investigate ES suppliers. Among them, triboelectric nanogenerators (TENGs), as a self-sustainable bioelectronic system, can generate self-powered and biocompatible ES for achieving superior therapeutic effects on skin applications. Here, a brief review of the application of TENGs-based ES on skin is presented, with specific discussions of the fundamentals of TENGs-based ES and its feasibility to be applied for adjusting physiological and pathological processes of skin. Then, a comprehensive and in-depth depiction of emerging representative skin applications of TENGs-based ES is categorized and reviewed, with particular descriptions about its therapeutic effects on achieving antibacterial therapy, promoting wound healing, and facilitating transdermal drug delivery. Finally, the challenges and perspectives for further advancing TENGs-based ES toward a more powerful and versatile therapeutic strategy are discussed, particularly regarding opportunities in fundamental multidisciplinary research and biomedical applications.
Sustainably addressing the water needs of populations in countries lacking adequate infrastructure is challenging. We discuss the potential of decentralized water and wastewater treatment using electrified processes across Latin American countries and reflect on what would help their implementation in the region.
Light-driven reaction of oxygen and water to hydrogen peroxide (H2O2) is an environmental protection method, which can convert solar energy into green products. In this work, perylene-3, 4, 9, 10-tetracarboxylic diimide (PDINH) could be recrystallized in situ on the surface of porous carbon nitride (PCN), to obtain an all-organic S-scheme heterojunction (PDINH/PCN). The design of the hierarchical porous photocatalyst improved the mass transfer, enhanced the light absorption and increased specific surface area. Moreover, the construction of the S-scheme heterojunction at the interface of PDINH and PCN exhibited suitable band, which facilitated the separation and transfer of carriers. The H2O2 production rate was up to 922.4 μmol g⁻¹ h⁻¹, which was 2.6 and 53.3 times higher than that of PCN and PDINH. Therefore, the all-organic S-scheme heterojunction provides an insight for improving the photocatalytic H2O2 production.
Waterborne pathogens have the risk of spreading waterborne diseases and even pandemics. Some Gram-positive bacteria can form endospores, the hardiest known life form that can withstand heat, radiation, and chemicals. Electrochemical inactivation may offer a promising solution, but is hindered by low inactivation efficiencies resulting from limitation of electrode/endospores interaction in terms of electrochemical reaction selectivity and mass transfer. Herein, these issues were addressed through modifying selectivity of active species formation using electroactive ceramic membrane with high oxygen evolution potential, improving mass transfer property by flow-through operation. In this way, inactivation (6.0-log) of Bacillus atrophaeus endospores was achieved. Theoretical and experimental results demonstrated synergistic inactivation to occur through fragmentation of coat via interfacial electron transfer and electro-produced transient radicals (•OH primarily, •Cl and Cl2•– secondarily), thereby increasing cell permeability to facilitate penetration of electro-produced persistent active chlorine for subsequent rupture of intracellular structures. Numbering-up electrode module strategy was proposed to scale up the system, achieving average 5.3-log inactivation of pathogenic Bacillus anthracis endospores for 30 days. This study demonstrates a proof-of-concept manner for effective inactivation of waterborne bacterial endospores, which may provide an appealing strategy for wide-range applications like water disinfection, bio-safety control and defense against biological warfare.
Electrochemical Advanced Oxidation Process (EAOP) has been applied to the degradation of refractory pollutants in wastewater due to its strong oxidation capacity, high degradation efficiency, simple operation, and mild reaction. Among electrochemical processes, anodic oxidation (AO) is the most widely used and its mechanism is mainly divided into direct oxidation and indirect oxidation. Direct oxidation means that pollutants are oxidized at the anode by direct electron transfer. Indirect oxidation refers to the generation of active species during the electrolytic reaction, which acts on pollutants. The mechanism of AO process is controlled by many factors, including electrode type, electrocatalyst material, wastewater composition, pH, applied current and voltage levels. It is very important to explore the reaction mechanism of electrochemical treatment, which determines the efficiency of the reaction, the products of the reaction, and the extent of reaction. This paper firstly reviews the current research progress on the mechanism of AO process, and summarizes in detail the different mechanisms caused by influencing factors under common AO process. Then, strategies and methods to distinguish direct oxidation and indirect oxidation mechanisms are reviewed, such as intermediate product analysis, electrochemical test analysis, active species detection, theoretical calculation, and the limitations of these methods are analyzed. Finally some suggestions are put forward for the study of the mechanism of electrochemical advanced oxidation.
Comprehensive study on the roles of reactive oxygen species (ROS) and active chlorine species (ACS) on the failure of bacteria cell were crucial for the development of electrochemical oxidation disinfection. Pure Na2SO4 and chloride-containing solution were used to generate ROS and ACS, separately. When 14.4 mA/cm² current density was applied, 5 logs reduction of E.coli was achieved with 60 min treatment in pure Na2SO4 solution, while in the chloride-containing solution, E.coli was completely inactivated in 15 min as the initial concentration was about 7.5 logs. Cell membrane damage is a crucial step in electrochemical oxidation disinfection process. With 3.6 mA/cm², there were ∼1.1 logs cells injured and it was about 37 times to that of inactivated cells with 5 min treatment in pure Na2SO4 solution. Hydroxyl radical and superoxide radical were confirmed responsible for the inactivation of E.coli in pure Na2SO4 electrolyte, while hypochlorite was dominated in chloride-containing solution. Noticeable shrinkages, wrinkles, and indentations were observed on the cell surfaces after treatment without any differences for ROS and ACS. However, total protein would be the attacking point for ROS rather than ACS. The changes of Optical density, total organic carbon, and potassium ions leakage presented slight differences. Nucleic acid matters may be destroyed in the electrochemical disinfection process, while the damage on nucleic acid fragment need more research to reveal.
An electrochemical filtration system via a continuous flow electrochemical reactor was designed, and its application was tested for para-nitroaniline (PNA) and industrial wastewater degradation. Optimization of operational parameters such as nature of electrode, electrolyte, and catalyst concentration was performed for electrochemical treatment of synthetic and discharged pulp mill wastewater effluent (obtained from the Boat Harbour (BH) remediation site, Nova Scotia, Canada). At the optimized conditions, 72% degradation of BH TOC (initially 105.4 mg L−1) with significant reductions of heavy metals Cd (99.9%), Cr (98.8%), and metalloid (As (99.8%) concentrations, was achieved at circumneutral pH values and overall operational cost of 0.05 USD L−1. Results demonstrate an effective and efficient simultaneous removal of organic and inorganic contaminants from industrial pulp mill wastewater effluent.
To improve the performance and solve the restrictions of UV/chlorine process (e.g., the narrow pH application range and high disinfection by-products (DBPs) formation), a Fe²⁺ assisted advanced oxidation process with electrochemically generated chlorine (UV/E-Cl/Fe²⁺) was proposed for carbamazepine (CBZ) degradation, which eliminated CBZ (5 mg/L) within 4 min under the optimal conditions. Compared with UV/electro-generated chlorine (UV/E-Cl) and anodic oxidation-chlorination/Fe²⁺ (AO-Cl/Fe²⁺) processes, the apparent first-order kinetics constant in UV/E-Cl/Fe²⁺ increased by 2.56 and 3.18 times respectively, and the energy consumption was lower (1.15 kWh/m³-log). Simultaneously, the pH application range could be expanded to 9, and DBPs formed in this process were 17.1% less than those in UV/E-Cl. Through quenching tests, electron paramagnetic resonance (EPR) experiments, measurement of •OH concentration, quantification of methyl phenyl sulfoxide (PMSO) and benzosulfone (PMSO2) and processes comparison, possible CBZ degradation pathways and mechanism of UV/E-Cl/Fe²⁺ were proposed, in which Fe(IV) played the dominant role in the early stage, while the production of radicals (i.e., •OH and Cl•) was enhanced with the increase of chlorine generation, accelerating the CBZ removal. Furthermore, this process demonstrated wide application prospect in treating various contaminants and real wastewaters. In conclusion, this study offers an effective and energy-efficient method for organic pollutants degradation.
The control of plant diseases is still widely carried out through the use of synthetic chemicals. However, many fungal and bacterial pathogens have developed resistance to the active ingredients of a wide range of pesticides. In addition, the problems associated with their use (i.e., waste disposal) as well as the increasing public awareness regarding residues and environmental risks have promoted the search for new and safer alternatives. Thus, the replacement of chemical pesticides with non-toxic compounds for consumers and for the environment is gaining considerable attention worldwide. Lowering the loss of products can be achieved through the use of an integrated disease management program, which employs a variety of control means and methods with a focus on preventing, reducing, and eradicating predisposing/instigating factors.
In this Special Issue, we invite scientists and researchers to contribute research articles on the utilization of a range of alternative control strategies, such as biological control using antagonistic/beneficial agents; physical strategies using low temperatures, modified and controlled atmospheres, heat, and irradiation; and substances generally regarded as safe, such as sanitizers, plant extracts, and essential oils. Papers that concentrate on the integrated disease management of agricultural products are also accepted.
In this Special Issue, original research articles and reviews are welcome. Research areas may include (but are not limited to) the following:
Integrated strategies to control plant diseases;
Alternatives to reducing/substituting chemical pesticides;
Natural compounds to control plant diseases;
Physical means of managing plant pathogens/diseases;
The role of biocontrol agents in managing plant diseases;
Nanotechnology as a way to control plant diseases.
We look forward to receiving your contributions.
Prof. Dr. Youssef Khamis
Prof. Dr. Antonio Ippolito
Prof. Dr. Khaled A. El-Tarabily
Guest Editors
Agricultural development, extensive industrialization, and rapid growth of the global population have inadvertently been accompanied by environmental pollution. Water pollution is exacerbated by the decreasing ability of traditional treatment methods to comply with tightening environmental standards. This review provides a comprehensive description of the principles and applications of electrochemical methods for water purification, ion separations, and energy conversion. Electrochemical methods have attractive features such as compact size, chemical selectivity, broad applicability, and reduced generation of secondary waste. Perhaps the greatest advantage of electrochemical methods, however, is that they remove contaminants directly from the water, while other technologies extract the water from the contaminants, which enables efficient removal of trace pollutants. The review begins with an overview of conventional electrochemical methods, which drive chemical or physical transformations via Faradaic reactions at electrodes, and proceeds to a detailed examination of the two primary mechanisms by which contaminants are separated in nondestructive electrochemical processes, namely electrokinetics and electrosorption. In these sections, special attention is given to emerging methods, such as shock electrodialysis and Faradaic electrosorption. Given the importance of generating clean, renewable energy, which may sometimes be combined with water purification, the review also discusses inverse methods of electrochemical energy conversion based on reverse electrosorption, electrowetting, and electrokinetic phenomena. The review concludes with a discussion of technology comparisons, remaining challenges, and potential innovations for the field such as process intensification and technoeconomic optimization.
Reverse osmosis (RO) typically removes >98% arsenate (As[V]) but removes arsenite (As[III]) comparatively poorly (approximately 50%–80%). Therefore, oxidizing As(III) to As(V) can improve arsenic removal using RO. In this study, electrolytic oxidation was used to oxidize As(III) in the feed water, and an extreme low‐pressure RO membrane was subsequently used to remove the arsenic. Using Ti/IrO2 electrodes under 30 mA DC current in 500 mg/L NaCl solution primarily generated free chlorine, which completely oxidized 300 μg/L As(III) to As(V). Subsequent arsenic removal by RO increased from 54.2% without oxidation to 98.2% with oxidation. Using electrolysis‐RO, arsenic removal significantly increased beyond RO alone, even in the presence of ferrous iron and natural organic matter. When sulfide and As(III) are present in water, they react to produce thioarsenate ions, the formation of which increased As(III) removal to 90% without electrolytic oxidation and electrolytic oxidation did not improve arsenic removal beyond these levels.
Due to its potential applications in decentralized water treatment systems, electrochemical synthesis of H2O2 for water decontamination has been widely investigated in recent years. In this study, it is found that the anodic oxidation of the residual H2O2 in the presence of Cl⁻ can be an efficient electrochemical disinfection technology to guarantee the microbiological safety of the treated water. H2O2 can be oxidized by HOCl generated at the anode to form singlet oxygen (¹O2). ¹O2 has been recognized as an important disinfectant in solar disinfection (SODIS) but it has not yet been reported in electrochemical disinfection. The generation of ¹O2 was directly confirmed by the detection of ¹O2 monomol emission using a near infrared imaging system. The concentration of ¹O2 can reach up to 1.64 pM in the anodic oxidation of H2O2 with Cl⁻. ¹O2 plays an important role in Escherichia coli (E. coli) inactivation, and HOCl only plays a subordinate role in the presence of 1 mM H2O2 due to its low concentration. For example, by adding up the inactivation of E. coli by sole H2O2 and micro-concentration HOCl together only attribute to about 2 log in 60 min but ¹O2 itself can account for about 3 log. Besides, the formation of the chlorinated disinfection by-products (Cl-DBPs) was mitigated considerably benefited from the fast reduction of HOCl by H2O2. These findings have potential implications for H2O2-based decentralized water treatment systems and provide a novel strategy for electrochemical disinfection because electrochlorination is having the same problems that chlorination has.
The increasing occurrence of micropollutants in water and wastewater threatens human health and ecological security. Electrocatalytic membrane (EM), a new hybrid water treatment platform that integrates membrane separation with electrochemical technologies, has attracted extensive attention in the removal of micropollutants from water and wastewater in the past decade. Here, we systematically review the recent advances of EM for micropollutant removal from water and wastewater. The mechanisms of the EM for micropollutant removal are first introduced. Afterwards, the related membrane materials and operating conditions of the EM are summarized and analyzed. Lastly, the challenges and future prospects of the EM in research and applications are also discussed, aiming at a more efficient removal of micropollutants from water and wastewater.
Electrochemical membrane technology for environmental remediation repository of basic knowledge and recent progress is reviewed in this chapter. The chapter summarizes the key processes in the use of electrochemical membranes, focusing on their need in electrodialytic and the electrocatalytic remediation of contaminated media. The fundamentals (including materials and reactor design) of the electrodialytic remediation technology are presented with consideration given to the critical operating parameters and performance indicators, mathematical simulation/modeling methods, and recent advances in electrodialytic remediation research. Meanwhile, two membrane technologies (i.e., the 3D electrochemical system and the proton-conducting membrane cell) for electrocatalytic remediation of contaminated media under different scenarios are briefly described. Finally, the chapter ends with a critical discussion on the challenges of and the perspectives for future study in electrochemical membrane technology for the purpose of environmental remediation.
Electrocatalysis using low-cost materials is a promising, economical strategy for remediation of water contaminated with organic chemicals and microorganisms. Here, we report the use of iron phosphide (Fe2P) precatalyst for electrocatalytic water oxidation; degradation of a representative aromatic hydrocarbon, the dye rhodamine B (RhB); and inactivation of Escherichia coli (E. coli) bacteria. It was found that during anodic oxidation, the Fe2P phase was converted to iron phosphate phase (Fe2P-iron phosphate). This is the first report that Fe2P precatalyst can efficiently catalyze electrooxidation of an organic molecule and inactivate microorganisms in aqueous media. Using a thin film of Fe2P precatalyst, we achieved 98% RhB degradation efficiency and 100% E. coli inactivation under an applied bias of 2.0 V vs. reversible hydrogen electrode in the presence of in situ generated reactive chlorine species. Recycling test revealed that Fe2P precatalyst exhibits excellent activity and reproducibility during degradation of RhB. High-performance liquid chromatography with UV-Vis detection further confirmed the electrocatalytic (EC) degradation of the dye. Finally, in tests using Lepidium sativum L., EC-treated RhB solutions showed significantly diminished phytotoxicity when compared to untreated RhB. These findings suggest that Fe2P-iron phosphate electrocatalyst could be an effective water remediation agent.
In the present work, electrodeposition of polymelamine (pMel) was realized at relative low onset potentials in melamine aqueous solution containing additives of trace bromide ion (Br⁻), which can greatly drive the polymerization reaction by anodically generated active bromine species. The experimental results showed that in neutral monomer solutions containing even as low as 1 mmol/L Br⁻, the pMel film on glassy carbon electrode was effectively deposited at the anodic potential negatively shifted ca. 0.4 V than in 100 mmol/L chloride containing solutions. The effects of Br⁻ on the electropolymerization of melamine were studied by cyclic voltammetry, potentiostatic control, in situ electrochemical Raman spectra and atomic force microscopy (AFM) techniques, respectively. Based on above results, this method was utilized for electrochemical polymerization of pMel on gold substrates under mild conditions, making it casting a pMel film on noncarbonaceous materials for the first time.
Significant findings for microbial removal have led to expertise on several kinds of nanomaterials that made new paths for removing various biological contaminants in a variety of water resources in recent years. Furthermore, advancements in multifunctional nanocomposites synthesis pave the enhanced possibility for their use in water treatment system design. The adsorption towards microbial elimination has been reviewed and compared in this review article using four common kinds of nanomaterials: carbon materials, metal oxides, metal/metal oxides, polymeric metal oxide nanocomposites and their most important mechanistic behavior also discussed. We also describe and analyze recent findings on the effects of engineered nanomaterials on microbial communities in natural and artificial environments. Understanding the removal mechanistic strategy is crucial to improving the nanoparticles (NPs) efficiency and increasing their applicability against a variety of bacteria in various environmental conditions. Also, our study focused on their behavioral effects on microbial structure and functionality towards the removal. Future research opportunities connected to the use of nanomaterials in microbial control and inactivation with societal and health implications are also discussed. We also highlight a number of interesting research subjects that might be of futuristic interest to the scientific community.
Diverse water microbes in water sources pose serious challenges to conventional disinfection techniques, leading to high oxidant and energy cost and large formation of disinfection by-products. Herein, a piezoelectret aluminium oxide (PEAO) was engineered for water disinfection. The piezo-catalytic disinfection system with ultrasonication induced strong electric field intensity of 8.1×107 V/m on PEAO surface, resulting in microbial cell membrane in-situ electroporation followed by penetration of generated reactive oxygen species (ROS, hydroxyl radical, singlet oxygen and hydrogen peroxide). The proposed piezo-catalytic disinfection strategy exhibited universal water disinfection performances among different microbes, ~1000-fold more efficient than an equivalent amount of preformed hydrogen peroxide, thus significantly improved the oxidant utilization and disinfection efficiency and potentially decreasing the formation of disinfection by-products. This work clearly demonstrates the application and mechanism of in-situ versatile water disinfection process via piezo-catalytic of PEAO and further applications in other water treatment fields are expected.
Written for environmental specialists and electrochemists, this advanced-level book describes the theory and practical application of electrochemical and photoelectrochemical methods for pollution detection, quantification and abatement. (REVIEW EN ENVIRONMENTAL SCIENCE AND TECHNOLOGY)
ENVIRONMENTAL ELECTROCHEMISTRY
Contents
Preface
Chapter 1. The Green Revolution
Chapter 2. Electrochemistry and Photoelectrochemistry: Fundamentals
Chapter 3. Electrochemistry of Pollutant Species
Chapter 4. Electrochemistry as Applied to Pollutant Sensing
Chapter 5. Electrochemical Remediation and Recycling
Chapter 6. Photoelectrochemical and Photocatalytic Approaches to Pollutant
Removal
Chapter 7. Electrochemical and Photoelectrochemical Disinfection of Water
Chapter 8. Commercial Perspective
Appendix A-D.
An electrochemical (EC) disinfection system employing an iridium-antimony-tin-coated titanium anode and direct current was used to inactivate bacteriophage MS2 in synthetic solutions with sodium chloride addition. The inactivation data fit-the modified Chick-Watson (n not equal 1) model well. The model indicates that, although better disinfection could be achieved with increases in salt content, contact time, and applied current, these three parameters influence the EC disinfection of MS2 in distinct manners and to different degrees. Compared with chlorination, our EC disinfection system exhibited superior inactivation capability especially with a longer contact time or in the presence of ammonium. The formation of trihalomethanes and haloacetic acids in the EC system was smaller than that from chlorination but a large formation of chlorate ions was observed. These differences indicate that the EC system is likely to produce other potent oxidants that-enhance inactivation and alter disinfection by-product formation.
This book organized under the following chapters: Fundamental aspects; Practical application of ozone: Principles and case studies; Engineering aspects; Operating an ozonation facility; Economics of ozone systems: New installations and retrofits; and Ozone system terminology, measurements and conversions.
This article will review the work that has been published on disinfection and the killing of cancer cells using photocatalytic chemistry with titanium dioxide (TiO2). This is an application of photocatalytic chemistry that has been under active investigation since 1985. Because the nature of the research is such that it brings together disparate disciplines, this review provides background on photocatalytic chemistry, fundamental characteristics of target organisms, potential applications, and the toxicology of titanium dioxide. Literature identified in searches done through September 1998 is included.
The present paper gives an overview on the current development status of doped-diamond electrodes for electrochemical applications. It starts with a short discussion on the different types of diamond electrodes and their preparation methods. This is followed by a summary of the electrochemical properties of diamond electrodes in different electrolytes. Modification strategies for doped-diamond electrodes are discussed as an important technology to change their electrochemical properties. The second part of the paper deals with practical applications of diamond electrodes from water treatment to inorganic and organic electrosynthesis, electroanalysis and electrochemical energy technology to biotechnology.
Electrochemical studies of diamond were started more than fifteen years ago with the first paper on diamond electrochemistry published by Pleskov. After that, work started in Japan, United States of America, France, Switzerland and other countries. Over the last few years, the number of publications has increased considerably. Diamond films have been the subject of applications and fundamental research in electrochemistry, opening up a new branch known as the electrochemistry of diamond electrodes. Here, we first present a brief history and the process of diamond film synthesis. The principal objective of this work is to summarize the most important results in the electrochemical oxidation using diamond electrodes.
A novel electrochemical reactor employing carbon-cloth electrodes was constructed for disinfection of drinking water. Escherichia coli K-12 (10(2) cells per cm3) was sterilized when a cell suspension was passed through the reactor at a dilution rate of 6.0 h-1, and a potential of 0.7 V versus a saturated calomel electrode was applied to an electrode. The survival ratio increased with increasing dilution rate but was less than 0.1% at dilution rates of less than 6.0 h-1. Although the survival ratio increased with increasing cell concentration above 10(3) cells per cm3, the disinfection rate also increased. The disinfection rate was 6.0 x 10(2) cells per cm3 per h at a cell concentration of 10(2) cells per cm3. Continuous sterilization of E. coli cells was carried out for 24 h. Sterilization is based on an electrochemical reaction between the electrode and the cell which is mediated by intracellular coenzyme A. Sterilization of drinking water by using this reactor was successfully performed, demonstrating the potential of such a reactor for clean and efficient water purification.
Several epidemiologic studies have suggested that the consumption of chlorinated drinking water may be associated with the development of certain cancers in humans. 3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), a byproduct of the chemical reactions that occur in chlorinated drinking water, has been found to be mutagenic in bacteria and mammalian cells; however, its potential to cause tumors in animals has not been tested previously.
The objective of this study was to evaluate the carcinogenicity of MX in rats given MX in their drinking water.
MX was administered to male and female Wistar rats (50 rats per dose group) in drinking water for 104 weeks at concentrations yielding the average daily doses of MX of 0.4 mg/kg of animal weight (low dose), 1.3 mg/kg (mid dose), and 5.0 mg/kg (high dose) for males and 0.6 mg/kg, 1.9 mg/kg, and 6.6 mg/kg for females, respectively. Control rats received water from the same source used for preparation of the MX dose formulations (after its adjustment to the same pH range). Body weight, clinical signs, and food and water consumption were recorded regularly. At the end of the treatment period, the animals were killed and full histopathologic analysis was performed on 47 tissues and all lesions.
Dose-dependent increases in tumor incidence were observed in rats given MX-containing drinking water; the same MX doses had no obvious toxic effects on animals. MX consumption increased most drastically the prevalence of follicular adenoma (up to 43% and 72% in high-dose males and females, a test [one-sided] for positive trend in all dose groups P = .0045 and P = .0000, respectively) and carcinoma (55% [P = .0000] and 44% [P = .0000], respectively) in thyroid glands and cholangioma in the liver (8% [P = .0009] and 66% [P = .0000] in the high-dose males and females, respectively). Among rats given the higher doses of MX in their drinking water, cortical adenomas of the adrenal glands were increased in both sexes, alveolar and bronchiolar adenomas of the lungs and Langerhans' cell adenomas of the pancreas were increased in males, and lymphomas, leukemias, and adenocarcinomas and fibroadenomas of the mammary glands were increased in females. Even the lowest MX dose studied was carcinogenic.
MX is a potent carcinogen in both male and female rats, and it causes tumors at doses that are not overtly toxic to rats.
Although these findings cannot be extrapolated to humans, MX should be studied as a candidate risk factor in the possible association between consumption of chlorinated drinking water and cancer in humans.
The influence of treatment temperature and pulsed electric fields (PEF) on the viability of Mycobacterium paratuberculosiscells suspended in 0.1% (wt/vol) peptone water and in sterilized cow's milk was assessed by direct viable counts and by transmission
electron microscopy (TEM). PEF treatment at 50°C (2,500 pulses at 30 kV/cm) reduced the level of viable M. paratuberculosis cells by approximately 5.3 and 5.9 log10 CFU/ml in 0.1% peptone water and in cow's milk, respectively, while PEF treatment of M. paratuberculosisat lower temperatures resulted in less lethality. Heating alone at 50°C for 25 min or at 72°C for 25 s (extended high-temperature,
short-time pasteurization) resulted in reductions ofM. paratuberculosis of approximately 0.01 and 2.4 log10 CFU/ml, respectively. TEM studies revealed that exposure to PEF treatment resulted in substantial damage at the cellular
level to M. paratuberculosis.
Membrane permeabilization due to pulsed electric field (PEF) treatment of gram-positive Lactobacillus cells was investigated by using propidium iodide uptake and single-cell analysis with flow cytometry. Electric field strength, energy input, treatment time, and growth phase affected membrane permeabilization of Lactobacillus plantarum during PEF treatment. A correlation between PEF inactivation and membrane permeabilization of L. plantarum cells was demonstrated, whereas no relationship was observed between membrane permeabilization and heat inactivation. The same results were obtained with a Lactobacillus fermentum strain, but the latter organism was more PEF resistant and exhibited less membrane permeabilization, indicating that various bacteria have different responses to PEF treatment. While membrane permeabilization was the main factor involved in the mechanism of inactivation, the growth phase and the acidity of the environment also influenced inactivation. By using flow cytometry it was possible to sort cells in the L. plantarum population based on different cell sizes and shapes, and the results were confirmed by image analysis. An apparent effect of morphology on membrane permeabilization was observed, and larger cells were more easily permeabilized than smaller cells. In conclusion, our results indicate that the ability of PEF treatment to cause membrane permeabilization is an important factor in determining inactivation. This finding should have an effect on the final choice of the processing parameters used so that all microorganisms can be inactivated and, consequently, on the use of PEF treatment as an alternative method for preserving food products.
Wastewater disinfection by ozone was investigated at pilot scale on different wastewater effluents. Variations in operating conditions showed that a very low hydraulic retention time (2 min) was sufficient for efficient fecal coliform inactivation, provided a sufficient ozone dose was transferred to the effluent. Therefore, the transferred ozone dose appeared to be the critical parameter for the design of wastewater disinfection. As a consequence, the "Ct" approach commonly applied in drinking water treatment should not be used for wastewater ozonation. Design parameters of ozonation were proposed for two types of regulations, and for effluents of different qualities. It was demonstrated that only with an efficient filtration step one can meet stringent standards such as the California Title 22 criteria. In all cases, viruses were totally inactivated; consequently, viruses do not constitute a limiting factor in wastewater disinfection by ozone. The standard drinking water model failed to match the experimental data obtained on real wastewater effluents. A modified approach was successfully developed, based on the simultaneous consumption of ozone by the microorganisms and the organic matrix.
The objectives of this study were to investigate the potential application of a low-amperage direct electric current as a non-thermal process for inactivation of Saccharomyces cerevisiae.
Electric current was generated using a direct current power supply connected to a traditional electrochemical cell with two platinum electrodes immersed in conducting solution containing a population of S. cerevisiae. This treatment provoked inactivation of the yeast cells. The microbial destruction illustrated by D-values calculated from survival curves was shown to be proportional to the current amperage (i) (D varies from 1547 min to 140 min when i varies from 0.1 to 1 A, respectively). The efficacy of the treatment was shown to be better at pH < 7. Statistical analysis showed no significant effect (P > 0.05) of ionic strength on yeast lethality induced by electrolysis.
The lethal effect of the electric treatment on S. cerevisiae in phosphate buffer was shown to be due to neither ohmic heating nor toxic hydrogen peroxide. A synergistic effect of temperature and electrolysis was observed when the temperature became lethal for the yeast.
The method described for yeast lethality induced by electrolysis has potential for soft sterilization, particularly when combined with the synergistic effect of moderate heat.
Using high-performance stacked cells, the formation of sodium hypochlorite on Pt and niobium- or silicon-based diamond film electrodes was investigated. The determination of hypochlorite concentration was performed by UV spectroscopy using a new multisensor system. The hypochlorite formation was investigated in the cycled batch mode and in the flow-through mode at different concentrations of sodium chloride. The yield on diamond film electrodes was found to be four to six times higher than that on Pt electrodes. Even at very low chloride contents of 10 mg/l, hypochlorite was still formed in amounts sufficient for certain disinfection purposes.
In a small water treatment system, electrolytically produced mixed oxidants (MIOX; LATA Inc., USA) have shown promise as an alternative disinfectant to chlorine. However, the efficacy of mixed oxidants as a disinfectant for microorganisms such as E. coli and Bacillus subtilis has not been reported widely and those that have been reported are controversial in some aspects, particularly in comparison with free chlorine. In this study, we evaluated the efficacy of a mixed oxidant solution as a disinfectant and compared it with that of a free chlorine solution on the basis of an equal weight of the total oxidants per unit volume. From our results, we found that mixed oxidants are approximately 20 ~ 50% more efficient than free chlorine at inactivating E. coli and Bacillus subtilis spores at certain pH conditions (pH 8.2). This report is consistent with the results of previous studies, in that the disinfection efficacy of a mixed oxidant solution is different than that of a free chlorine solution. However, the extent of the difference contrasts greatly with the results of the previous studies, which reported a significant difference in the disinfection efficacy between mixed oxidants and free chlorine for inactivating Cryptosporidium parvum oocysts.
The anodic oxidn. of H2SO4 to H2S2O8 was investigated on B-doped synthetic diamond electrodes obtained by hot filament chem. vapor deposition. High current efficiency for H2S2O8 formation can be achieved in concd. H2SO4 (7.5 mol dm-3) and using high current densities (200 mA cm-2). The main side reaction is oxygen evolution. [on SciFinder (R)]
Peroxodiphosphate salts are strong oxidizing agents that presently can be used as reagents in organics synthesis, cosmetic, agriculture, polluted water treatment, and also as bleaching agents in the detergent industry. They also have potential uses as persulfates substitutes. In this work, a new method for the synthesis of peroxodiphosphate, based on the use of boron-doped diamond electrodes, is described. The procedure developed is able to produce high-purity peroxodiphosphate (no reagents different from phosphate salts are used as raw materials) with a high current efficiency. The efficiencies of the process strongly depend on the pH and on the operating conditions (temperature and current density). The optimum range of pH is 12-13. Current densities over 1000 A m-2, and low temperatures, guarantee high current efficiencies and product conversions. The pH control is considered to be one of the more important operation constraints in the process. Great concentrations of phosphate in the raw materials increase the process efficiencies but they also seem to favor the corrosion of the electrode. Concentrations below 1 M of PO43- are recommended to avoid this problem.
An electrochemical method for the preparation of sodium peroxycarbonate at boron-doped diamond anodes has been described. Effects of experimental conditions such as current density, electrolyte concentration and anode materials on the formation of sodium peroxycarbonate have been investigated. The maximum current efficiency for producing sodium peroxycarbonate was found to be 82% at a current density of 0.05 A cm(-2) after 30 min of electrolysis in a solution of 1 M Na2CO3. The minimum energy consumption was found to be 2.2 Wh g(-1) at a current density of 0.05 A cm(-2). The X-ray powder diffraction pattern was obtained in order to identify the products. The products were also analyzed using TG/DTA in order to determine the melting point. (C) 2003 The Electrochemical Society.
The interest in heterogeneous photocatalysis is intense and increasing, as shown by the number of publications on this theme which regularly appear in this journal, and the fact that over 2000 papers have been published on this topic since 1981. This article is an overview of the field of semiconductor photocatalysis : a brief examination of its roots, achievements and possible future. The semiconductor titanium dioxide (TiO 2 ) features predominantly in past and present work on semiconductor photocatalysis; as a result, in the most of the examples selected in this overview to illustrate various points the semiconductor is TiO 2 .
Experiments were conducted to investigate the effect of concentration (0, 0.26 or 1.05%) and duration (0, 20 or 60 s) of sodium hypochlorite treatment on subsequent firmness, electrolyte leakage, respiration, and C2H4 production of light-red tomato (Lycopersicon esculentum Mill.) fruit slices during storage at 5°C under modified atmosphere (MA). Pericarp firmness of slices was lower for all treatments than for untreated controls. After 12 days of storage, pericarp firmness of slices from fruit that had been treated with 1.05% sodium hypochlorite for 60 s was less than one-half the firmness of water-treated controls and lower than the other sodium hypochlorite treatments. The effect of sodium hypochlorite on electrolyte leakage of slices stored at 5°C was more closely related to treatment duration than to sodium hypochlorite concentration. The difference in electrolyte leakage between control fruit and fruit treated with 1.05% sodium hypochlorite for 60 s was 14.2, 25.6, and 25% at 4, 8, and 12 days, respectively. Development of water-soaked areas was observed on slices from fruit treated with sodium hypochlorite, but little development of water-soaked areas was detectable on slices from control fruit. An increase in C2H4 and CO2 production due to infection by Alternaria alternata was observed on slices from control fruit. These results suggest that routine surface sterilization of tomato fruit prior to postharvest experimentation may lead to physiological and biochemical alterations in the behavior of fruit.
Laboratory experiments were carried out to investigate the mechanisms of electrochemical (EC) wastewater disinfection. Artificial wastewater contaminated by Escherichia coli (E. coli) culture, and which contained different salts of NaCl, Na2SO4, and NaNO3, was used as the test medium. The experimental results do not favor the hypotheses that the EC bactericidal action was due to cell destruction by the electric field and the production of persulfate. In comparison to direct chlorination, the EC process displayed a much stronger disinfecting capability than that of electrochlorination assumed for EC disinfection. Observations with scanning electron microscopy on the E. coli bacteria of wastewater treated by different means of disinfection suggested that the cells were likely killed during the EC treatment by chemical products with oxidizing and germicidal powers similar to that of ozone and much stronger than that of chlorine. All of the findings support the theory that the major killing function of EC disinfection is provided by short-lived and high-energy intermediate EC products, such as free radicals.
Individual papers are processed separately for the appropriate data bases. (PSB)
The inactivation kinetics of two strains of bacterial aerobic spores were investigated in a batch reactor for two pH levels (6.3 and 8.2) and various ozone dosages (0.5–2.5 mg/l). The kinetics of ozone decomposition was found to satisfactorily fit a first-order decay model. The CT (concentration×contact time) values were calculated using the modified Hom equation with exponential disinfectant decay. Lower pH resulted in lower CT values. The environmental spores tested were not as resistant to ozone as the reference strain of B. subtilis. Comparison of CT values for aerobic spores with published data suggests that bacterial spores could be a surrogate for evaluating the ozone inactivation of G. lamblia cysts and C. parvum (oo)cysts during drinking water disinfection. However, more information on the resistance of naturally occurring populations of bacterial spores would be needed before they are used as an indicator of ozone disinfection efficiency.
The electroadsorption of E. coli and S. typhimurium cells on fibrous carbon electrodes was investigated. Anode-cathode pairs were arranged in series to form a multistage electrofilter through which the bacterial suspension flows in a flow-through mode. Both bacteria species were strongly attached to an electrically charged electrode bed and total removal of bacterial cells was achieved.
Pathogens in drinking water supplies can be removed by sand filtration followed by chlorine or ozone disinfection. These processes reduce the possibility of any pathogens entering the drinking water distribution network. However, there is doubt about the ability of these methods to remove chlorine resistant microorganisms including protozoan oocysts. Concern has also been raised about the production of disinfection by-products following the chlorination process. Titanium dioxide (TiO 2) photocatalysis is a possible alternative/complementary drinking water treatment method. TiO 2 electrodes were prepared by the electrophoretic immobilisation of TiO 2 powder (Aldrich and Degussa P25). These electrodes were tested for their photocatalytic bactericidal efficiency. E. coli K12 was used as a model test organism. The rate of disinfection was greater for the P25 electrode compared to the Aldrich electrode under open circuit conditions. The application of an electrical bias to the working electrode increased the rate of disinfection by ∼40% for the P25 electrode and ∼80% for the Aldrich electrode. The effect of applied potential was more pronounced under conditions of high initial bacterial cell loading and high light intensities. Bacterial recovery did not occur up to 48 h after disinfection. © 2002 Elsevier Science B.V. All rights reserved.
In general, chlorination is the method of drinking water disinfection most favoured by the water industry. Occasional outbreaks of water transmitted disease, the identification of chlorine as a source of potentially harmful disinfection by-products, and the emergence of recalcitrant pathogens has led to heightened regulation for the removal of microbial pathogens and disinfection by-products from drinking water. As a result, research and development of alternative disinfection technologies has intensified. Electrochemical disinfection has emerged as one of the more feasible alternatives to chlorination. Research using a range of cell configurations has shown electrochemical disinfection to be effective against a range of pathogens. However, in many of the systems, disinfection efficacy appears to be related to the generation of chlorine species. The apparent prevalence of chlorine as the mechanism of disinfection begs the question as to whether electrochemical disinfection has an advantage over chlorination in terms of its inactivation efficacy and potential to form disinfection by-products. This paper reports on a series of experiments evaluating the disinfection efficacy of an electrochemical disinfection technology against Escherichia coli and bacteriophage MS2. The results of these experiments conclude that electrochemical disinfection can be effective without the generation of chlorine species.
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.
The rate of Cryptosporidium parvum inactivation with free chlorine decreased with increasing pH in the range of 6.0–8.5, consistent with hypochlorous acid being primarily responsible for C. parvum inactivation within this pH range. The rate of sequential inactivation of C. parvum oocysts with free chlorine after pre-ozonation was characterized by an initial rapid decline in viability followed by slower kinetics with respective rates at pH 6.0 of approximately six times and twice that for free chlorine treatment without pre-ozonation under the same conditions. The greatest level of synergy was observed at pH 6; synergy decreased as pH increased until no synergy was observed at pH 8.5. Consistent with hypochlorous acid being the free chlorine species primarily responsible for C. parvum inactivation, within the pH range of 6.0–8.5 the rate of secondary inactivation with free chlorine decreased with increasing pH. Experiments designed to assess the effect of free chlorine concentration on inactivation kinetics provided conclusive evidence for the validity of the CT concept in the case of secondary inactivation of C. parvum oocysts with hypochlorous acid after ozone pre-treatment.
Boron-doped diamond (BDD) electrodes were studied with respect to the formation of inorganic by-products in water electrolysis. Experiments in non-divided cells were performed with systems containing sulphate, chloride, chlorite, chlorate and nitrate ions. Discontinuous experiments in thermostated cells with rotating disk diamond anodes and expanded mesh IrO2 cathodes were carried out at 20 °C. Current density was varied between 50 and 300 A m−2. Ion chromatography was mainly used for species detection.It was not possible to demonstrate the decomposition of sulphate although a slight tendency seems to exist in some experiments. Hydrogen peroxide is one of the anodic and cathodic by-products. Active chlorine is detectable at higher chloride concentrations compared with the use of mixed oxide anodes (MIO). One reason for this is the reaction of formed chlorine with ozone or hydrogen peroxide. Chlorate can be formed electrolysing chloride, hypochlorite and chlorite solutions. Perchlorate formation was detected. Cathodic processes are responsible for the formation of nitrite ions and ammonia. If chlorine is present, the formation of monochloramine is one possible side reaction. Results show that the processes are very complex. Reaction spectra may vary from case to case. Perchlorate formation is a high risk in drinking water treatment.
There are increased activities in development and application of electrochemical disinfection cells using the natural chloride content for disinfectants production by directly electrolysed water. Unfortunately, the process is insufficiently studied until now and the conditions under which the cells are sold and used are not well controlled. Health risks are probable because limiting concentrations may be exceeded as could be shown in special experiments. One main by-product of drinking water electrolysis is chlorine dioxide that can be formed under several conditions. The present work discusses problems of chlorine dioxide formation and reactions during and after electrolysis. First results are presented, which were obtained in synthetic and real drinking waters using titanium anodes with IrO2/RuO2 coatings. Analysis problems and possible mechanisms are discussed. The influence of chloride concentration up to 250 mg L−1, current density (up to 500 A m−2) and other parameters on ClO2 formation is shown. Chlorine dioxide concentrations in the lower milligram per litre range could be measured.
Titanium nitride (TiN) is a biocompatible material and has very low electrical resistance. Electrochemical control of pathogenic microbes derived from a drinking water distribution system was investigated using a TiN electrode. When a potential of 1.2 V vs saturated calomel electrode (SCE) was applied, the survival ratio of microorganisms decreased to below 40%. Changes in pH were not observed at 1.2 V vs SCE. Also, by applying −0.6 V vs SCE for 30 min, 69% of cells on the electrode surface were detached by the electrostatic repulsion. Therefore, an electrochemical disinfection reactor using a TiN mesh as the working electrode and the counter electrode was constructed. The drinking water containing mean viable cell concentration of 73 cells/ml was continuously passed through the reactor at a flow rate of 15 ml/min. The viable cell concentration in treated water decreased to below 5 cells/ml. When no potential was applied, cell concentration in treated water gradually increased after 200 h of reactor operation. In contrast, when alternating potentials of 1.2 and −0.6 V vs silver/silver chloride (Ag/AgCl) were applied to the TiN mesh working electrode, the viable cell concentration remained below 100 cells/ml during a 440 h operation. The reactor for drinking water disinfection incorporated with the TiN mesh electrode worked effectively by applying alternating potentials of 1.2 and −0.6 V vs Ag/AgCl.
Laboratory experiments were performed to characterize the behaviour of an electrochemical cell equipped with boron-doped diamond anodes and to verify its effectiveness in water disinfection. The hydrodynamic regime was determined when the cell worked either in batch or in continuous mode. Galvanostatic electrolyses of aqueous 1 mM Na2SO4 solutions were performed to investigate on the oxidant production in different experimental conditions. The same solutions contaminated by E. coli, enterococci and coliforms were used as test media to verify the effectiveness of the system in the disinfection process. Experimental results indicated that the major inactivation mechanism of bacteria in the electrochemical cell is a disinfection by electrochemically generated oxidants, however a cooperative effect of superficial reaction has to be taken into account. The great capability of BDD anode to produce reactive oxygen species (ROS) and other oxidizing species during the electrolysis allows to establish a chlorine-free disinfection process.
The DiaCell® technology has been successfully tested against Legionella infection in several water types and under various working conditions. Depending on the water composition, Legionella can be completely inactivated with current densities as small as 50 mA/cm2 with low contact times (<5 min). The higher the oxidant concentration in the electrolyzed water, the more rapid is the Legionella inactivation after injection. Bicarbonates in contaminated water were identified as very good supports for electrochemical disinfectants production for Legionella inactivation without high chlorine concentration. At the same time, sulfates in water do not provide any disinfection capacity by DiaCell® electrolysis.
The role of active oxygen species in the photocatalytic bactericidal effect was investigated using a thin transparent titanium dioxide (TiO2) film. The viable number of Escherichia coli (E. coli) significantly decreased on the illuminated TiO2 film, and the bactericidal effect was observed even when E. coli was separated from the TiO2 surface with a 50 μm porous membrane. Mannitol, a hydroxyl radical scavenger, inhibited the effect only in the absence of the membrane. In contrast, catalase inhibited the effect in all cases. On the basis of these results, the long-range bactericidal effect of hydrogen peroxide was proposed, together with a cooperative effect due to other oxygen species. © 1997 Elsevier Science S.A.
UV irradiation as a method of disinfecting drinking, waste and feed waters is becoming more and more widespread. Besides the normally used low and medium pressure lamps, a new type has been recently developed, the microwave stimulated electrodeless lamp. This paper presents first results on drinking water disinfection using this new type of lamp. Its suitability for application could be shown in experiments with microorganisms of risk group one. Additionally, research results on the direct electrolysis of water for disinfection purposes are given. The combination of the two methods provides a promising approach to disinfection treatment of drinking water.
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.
Conducting diamond thin film is a new electrode material that has received great attention recently because it possesses several technologically important characteristics such as an inert surface with low adsorption properties, remarkable corrosion stability, even in strong acidic media, and an extremely wide potential window in aqueous and non-aqueous electrolytes. Thanks to these properties diamond electrodes meet the requirements for a wide range of electrochemical applications. The object of this article is to summarise and discuss the recent results available in the literature concerning the application of diamond electrodes to electrochemical processes such as water treatment and electro-synthesis of organic and inorganic compounds.
Aqueous solutions containing the metabolite clofibric acid (2-(4-chlorophenoxy)-2-methylpropionic acid) up to close to saturation in the pH range 2.0–12.0 have been degraded by anodic oxidation with Pt and boron-doped diamond (BDD) as anodes. The use of BDD leads to total mineralization in all media due to the efficient production of oxidant hydroxyl radical (OH). This procedure is then viable for the treatment of wastewaters containing this compound. The effect of pH, apparent current density, temperature and metabolite concentration on the degradation rate, consumed specific charge and mineralization current efficiency has been investigated. Comparative treatment with Pt yields poor decontamination with complete release of stable chloride ion. When BDD is used, this ion is oxidized to Cl2. Clofibric acid is more rapidly destroyed on Pt than on BDD, indicating that it is more strongly adsorbed on the Pt surface enhancing its reaction with OH. Its decay kinetics always follows a pseudo-first-order reaction and the rate constant for each anode increases with increasing apparent current density, being practically independent of pH and metabolite concentration. Aromatic products such as 4-chlorophenol, 4-chlorocatechol, 4-chlororesorcinol, hydroquinone, p-benzoquinone and 1,2,4-benzenetriol are detected by gas chromatography–mass spectrometry (GC–MS) and reversed-phase chromatography. Tartronic, maleic, fumaric, formic, 2-hydroxyisobutyric, pyruvic and oxalic acids are identified as generated carboxylic acids by ion-exclusion chromatography. These acids remain stable in solution using Pt, but they are completely converted into CO2 with BDD. A reaction pathway for clofibric acid degradation involving all these intermediates is proposed.
Characterisation of a commercial heavily doped BDD electrode demonstrated it contains a small sp2 content, which on anodic potential scanning, is oxidised to CO/CO2. This surface modification alters the electrode activity, increasing the overpotential for the hydrogen and oxygen evolution reactions (HER and OER). Ex situ and in situ investigations indicate film morphology is mainly composed of “chain of hills”, presenting relatively high differential capacitance values and morphology factor, which is attributed to the effect of surface states and high surface roughness of the BDD film. The voltammetric behaviour depends on the applied potential; the heavily doped BDD electrode behaving as a metallic electrode at more anodic potentials. Polarisation curves (potentiostatic (1 mV s−1) or galvanostatic (point-by-point)), recorded at different temperatures and H2SO4 concentrations, lead to the same conclusions. The high Tafel coefficients and low apparent electronic transfer coefficient (αA) are independent of overpotential and temperature but show a dependence on H2SO4 concentration. The linear relationship observed between the apparent electrochemical enthalpy of activation (ΔH#η) and overpotential supports αA is constant. An OER mechanism was proposed taking into account the absence of adsorption sites at the BDD surface. The OER is inhibited, explaining the high overpotentials and elevated ΔH#η values.
The inactivation of coliform bacteria and poliovirus 1 was studied in secondary wastewater effluent containing suspensions of titanium dioxide (250 mg 1−1) irradiated with either F40BL fluorescent lights or sunlight. Approximately 150 min were required to achieve two-log inactivation of coliform bacteria under laboratory lights, while the two-log inactivation of poliovirus 1 occurred in approximately 30 min. No differences in photocatalytic disinfection rates were found when the assays were conducted in the pH range of 5–8. The results show that poliovirus 1 was effectively inactivated by titanium dioxide photocatalysis, and the rates were more rapid than for the inactivation of coliform bacteria. However, the photocatalytic disinfection of effluents using titanium dioxide under sunlight may be limited due to the relatively low inactivation rates and resulting long contact times compared to conventional disinfection methods.
The electrogeneration of hydroxyl radicals was studied at a synthetic B-doped diamond (BDD) thin film electrode. Spin trapping was used for detection of hydroxyl radicals with 5,5-dimethyl-1-pyrroline-N-oxide and with salicylic acid using ESR and liq. chromatog. measurements, resp. The prodn. of H2O2 and competitive oxidn. of formic and oxalic acids were also studied using bulk electrolysis. Oxidn. of salicylic acid gives hydroxylated products (2,3- and 2,5-dihydroxybenzoic acids). The oxidn. process on BDD electrodes involves hydroxyl radicals as electrogenerated intermediates. [on SciFinder (R)]
Diamond coatings of 0.1 to 1 mm thickness on silicon disks, used as electrodes in electrochem. reactors or systems like a DiaCell have shown outstanding properties in oxidn. of org. and inorg. compds. This reactivity can be assocd. with the prodn. of hydroxyl radicals, which may also be responsible for the prodn. of chlorine or ozone in naturally mineralized water. By addn. of a small amt. of supplementary NaCl to poolwater (250 to 900 ppm), it is possible to produce up to 10 g/h of chlorine. With the help of a newly developed online and direct measuring-free chlorine amperometric sensor, the loop-controlled prodn. of chlorine can easily be maintained in the range of 0.2 to 0.4 ppm free chlorine and guarantee the perfect disinfection of the poolwater. The simultaneous prodn. of even more powerful oxidants also helps to destroy incorporated org. materials in swimming pools. [on SciFinder (R)]
An effective technique for assessing fungal infections of particulate foods such as cereals, nuts, fruits and vegetables is surface disinfection with a sodium hypochlorite solution before plating directly onto agar media. The surface disinfection procedure is used to inactivate the surface mycoflora then permitting assessment of the percentage of particles invaded by specific fungi. A previously recommended procedure treating samples with 0.4% chlorine for 2 min has been shown to be ineffective for barley highly contaminated with conidia of either A. flavus or A. parasiticus. An international collaborative study has demonstrated that modifying the procedure by increasing the chlorine concentration to 0.8%, or increasing the contact time to 8 min, or increasing the volume of chlorine solution is not the answer, especially with surface contamination loads of approximately 10(6) conidia/g. The inclusion of a 70% ethanol pre-rinse prior to a 0.8% chlorine treatment for 2 min made a significant improvement to the inactivation of surface conidia of A. flavus on barley. However, pretreatment with ethanol inactivated some of the internal Alternaria infections especially when the ethanol was not rinsed off. Further studies including an ethanol pre-rinse are recommended to optimise the surface disinfection procedure for seeds and nuts which have a high concentration of fungal surface contaminants.
An electrochemical reactor employing activated carbon fibers (ACF) was constructed for the disinfection of bacteria in drinking water. The application of an alternating potential of 1.0 V and -0.8 V versus a saturated calomel electrode, for disinfecting and desorbing bacteria, enabled reactor operation for 840 h. Drinking water was passed through the reactor in stop/flow mode: 300 ml/min flow for 12 h and no flow for 12 h, alternately. The bacterial cell density in treated water was always been less than 20 cells/ml. It was also found that the formation of biofilm on the ACF reactor caused an increase in current, enabling the self-detection of microbial fouling.
Nature is the international weekly journal of science: a magazine style journal that publishes full-length research papers in all disciplines of science, as well as News and Views, reviews, news, features, commentaries, web focuses and more, covering all branches of science and how science impacts upon all aspects of society and life.
Cyanide is a chemical widely used in industry, and is a major environmental pollutant. Its toxicity is caused by inhibition of cytochrome oxidase resulting in histotoxic hypoxia. The effect of sublethal doses of cyanide on memory and hippocampal neurotransmitters was studied in male Wistar strain albino rats. Cyanide reduced the memory along with reduction in the levels of dopamine and 5-hydroxytryptamine in the hippocampus. Pre-existing malnutrition in the animals exaggerated these effects.
The production of adequate and safe drinking water is a high priority issue for safeguarding the health and well-being of humans all over the world. Traditionally, microbiological quality of drinking water has been the main concern, but over the last decades the attention of the general public and health officials on the importance of chemical quality and the threat of chemical pollutants have increased with the increase of our knowledge on the hazards of chemical substances. There are many sources of contamination of drinking water. Broadly they can be divided into two categories: contaminants originating from surface and groundwater, and contaminants used or formed during the treatment and distribution of drinking water. Contaminants in surface and groundwater can range from natural substances such as arsenic and manganese leaching from soil, to contaminants introduced by human activities, such as run-off from agricultural activities, controlled discharge from sewage treatment works and industrial plants, and uncontrolled discharges or leakage from landfill sites and from chemical accidents. Disinfectants and disinfectant by-products are well known contaminants resulting from the processes used by the drinking water industry for the treatment and distribution of water. The basic question in the production of drinking water is how to rid drinking water of potentially dangerous microorganisms and chemicals without introducing new hazards that might pose new and different threats to human health. It is the responsibility of toxicologists to provide risk assessments for chemical pollutants and to derive guidelines or standards for drinking water quality below which no significant health risk is encountered, to assure consumers that drinking water is safe and can be consumed without any risk. This paper will focus on the toxicological procedures used by the World Health Organization to derive guideline values for chemical compounds in drinking water, and will touch upon some critical differences in the nature of guidelines and legally binding standards.