Electrochemical Water Disinfection Research Articles

Simultaneous generation of residue-free reactive oxygen species and bacteria capture for efficient electrochemical water disinfection

Residue-free and highly efficient techniques for drinking water disinfection are urgently needed. Herein, we report an electrochemical water disinfection system equipped with atomically precise Ag28 nanoclusters (NCs) as electrode materials. The deployment of these Ag28 NCs not only provides sufficient electrosorption sites for intelligent microbe enrichment but also ensures high-efficiency dual-mode microbial killing through the in situ electrocatalytic production of residue-free reactive oxygen species (ROS) and the inherent antimicrobial activity of Ag28 NCs. Moreover, the design of the system enables a cyclical “alive microbe capture–killing–dead microbe desorption” process for continuous water disinfection. On this basis, this water disinfection system is efficient against broad-spectrum microbes (with >99.99% antimicrobial activity), durable (with a performance reduction of only 0.75% over 40 cycles and 99.90% antimicrobial efficiency for over 5 h of continuous operation), versatile (i.e., other NCs can be used), scalable (with water productivity of 213.33 L h−1 m−2), energy efficient (with a low energy consumption of 4.91 Wh m−3; 1.04 Wh m−3 without the pumping cost) and applicable for various real water samples. This study may open new avenues for global water disinfection techniques.

Advancing water disinfection strategies: assessing disinfection efficiency with a Bayesian Regularized artificial neural network model

ABSTRACT It is important to find the estimation methodology with the highest accuracy in order to determine the parameters of water disinfection and to provide the most ideal disinfection. In this study, the usability of artificial neural networks in predicting response disinfection efficiency in electrochemical water disinfection processes was investigated. An artificial neural network model was developed using a total of 17 data sets and Response Disinfection Efficiency values were estimated from the model. Current density, treatment time and interelectrode spacing values are defined as input parameters in the network model, which has a multilayer perceptron architecture with 10 neurons in its hidden layer. The coefficient of determination value for the developed model was 0.98682 and the average deviation rate was −0.1%. The study findings showed that neural networks are an ideal tool that can be used to predict response disinfection efficiency in electrochemical water disinfection processes.

In situ generation of highly localized chlorine by laser-induced graphene electrodes during electrochemical disinfection

Laser-induced graphene (LIG) has gained popularity for electrochemical water disinfection due to its efficient antimicrobial activity when activated with low voltages. However, the antimicrobial mechanism of LIG electrodes is not yet fully understood. This study demonstrated an array of mechanisms working synergistically to inactivate bacteria during electrochemical treatment using LIG electrodes, including the generation of oxidants, changes in pH—specifically high alkalinity associated with the cathode, and electro-adsorption on the electrodes. All these mechanisms may contribute to the disinfection process when bacteria are close to the surface of the electrodes where inactivation was independent of the reactive chlorine species (RCS); however, RCS was likely responsible for the predominant cause of antibacterial effects in the bulk solution (i.e., ≥100 mL in our study). Furthermore, the concentration and diffusion kinetics of RCS in solution was voltage-dependent. At 6 V, RCS achieved a high concentration in water, while at 3 V, RCS was highly localized on the LIG surface but not measurable in water. Despite this, the LIG electrodes activated by 3 V achieved a 5.5-log reduction in Escherichia coli (E.coli) after 120-min electrolysis without detectable chlorine, chlorate, or perchlorate in the water, suggesting a promising system for efficient, energy-saving, and safe electro-disinfection.

The Optimization of Operational Variables of Electrochemical Water Disinfection Using Response Surface Methodology

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.

Effect of Electrode Type on Bacteria Removal and Chlorine and Radical Production in Electrochemical Water Disinfection

Formation and contamination of malicious microorganisms and viruses remain to be major problem of water resources. This is mostly due to the fact that, groundwater, which constitutes a large share of available fresh water content, is prone to contamination from urban and industrial wastes. In this work, electrochemical treatment is considered as a disinfection mechanism. The literature presents several cases of individual of electrochemical disinfection experiments. In this particular work, we aim to focus on the comparative disinfection efficiency of Boron-doped diamond electrodes, Iridium metal-oxide electrodes and Graphite plate electrodes at various electrochemical settings, whilst monitoring formation of toxic bi-products, such as chlorine and other radicals. Experiments of electrochemical water disinfection were carried out on real groundwater samples deliberately contaminated with E. coli culture. During the reaction, microorganisms die due to both direct physical damage and due to the electrochemically generated radicals. Therefore, there is a gentle balance of bacteria elimination versus avoiding excessive radical production in the treated water. Since the biological behaviour of the microorganisms and the chemical properties of the available groundwater cannot be changed, the research parameters boil down to experimenting through various popular electrode types and electrical current settings. In both continuous-flow and recursive systems, the Boron-doped diamond electrodes are observed to provide desirable level of disinfection (as good as Iridium metal-oxide), while yielding lower radicals (as low as those of Graphite-plate), making an ideal compromise for the process.

Nanofiltration process combined with electrochemical disinfection for drinking water production: Feasibility study and optimization

In 2014, the first nitrate removal plant, using nanofiltration (NF) coupled to an electrochemical disinfection system, supplied with renewable energies (Photovoltaic and wind energies) was realized at Al Annouar high school of Sidi Taibi (Kenitra, Morocco). This project was designed to supply the 1200 students of the school with potable water, based on the production capacity of 500 L/h (3 L/Day/student). The local underground water, which is slightly brackish and nitrated, was treated by nanofiltration, using a hybrid renewable energy system, photovoltaic and wind; just before the distribution, an electrochemical disinfection setup was used to disinfect the nanofiltered water.In the first part of this work, the feasibility of the processes combination (nanofiltration- electrochemical water disinfection step) is verified by assessing the main factors which have determined the electrolysis performance (Volumetric flow rate, temperature, chloride concentration, energy…). This part of the study is carried out during two years of operation (from April 2014 to February 2016). The second part focused mainly on the optimization of a new membrane treatment plant. The purpose of this installation is twofold; firstly, the objective was to correct the concentration of chloride ions at the inlet of electrolysis. Secondly, it was meant to avoid the quality deterioration of the produced water (nitrates in particular).The results of this study confirmed the feasibility of the process combination: nanofiltration and electrochemical water disinfection, especially with the use of renewable energies (Photovoltaic and wind). On other hand, this installation will be more attractive by blending raw water with the nanofiltered water in order to increase the performances of the plant hydraulically, energetically, and to correct the chloride concentration for safe disinfection of water. Hence, the produced water by the new installation (process bypass blending) is totally mineral for human consumption and slightly corrosive for pipes and equipments.

Design of pico-hydro turbine generator systems for self-powered electrochemical water disinfection devices

Abstract Previous research has demonstrated the potential of pico-hydro turbines to provide reliable electricity in applications such as rural electrification. However, the literature has primarily focused on the development of turbine systems for design environments where spatial and flow rate constraints tend to be non-restrictive. The work detailed in this paper presents the development of a novel, compact, high efficiency turbine capable of powering a compact electrochemical cell for off-grid water disinfection. The turbine with the generator is capable of generating nearly 100 W of power with a footprint of only 8″ in length and 4″ in diameter. A basic mathematical model of a DC generator is coupled to a computational fluid dynamics (CFD) turbine model to evaluate different system configurations. Following a Taguchi Method study to computationally explore the turbine design space, experimental testing of improved turbine configurations is shown to provide electrical power output improvements of 20%. Selection of a more compatible DC generator also provides electrical power output and efficiency improvements of a factor of 2 and 2.5 respectively.

Rapid inactivation of waterborne bacteria using boron-doped diamond electrodes

The application of a boron-doped diamond electrode in electrochemical water disinfection was investigated with respect to its inactivation potential of three indicator microorganisms. Drinking water and the effluent of a wastewater treatment plant spiked with Escherichia coli, Enterococcus faecium and Pseudomonas aeruginosa were electrolysed under different conditions in a batch reactor. All three bacteria species could be successfully inactivated in drinking water. The disinfection rate depended on the applied charge, with far more efficiency at high current densities (208 and 333 mA/cm2) under high ozone concentrations measured in contrast to low current densities (42 mA/cm2) where bacterial inactivation was rather driven by hydroxyl radicals. When oxidising a target pharmaceutical compound in the wastewater treatment plant effluent, the water matrix exhibited an ozone scavenging effect. The resulting decrease in the efficiency could not be detected for the disinfection experiments in the complex water matrix compared to drinking water, which indicates a different disinfection mechanism, probably due to reactive chlorine species.

Electrochemical disinfection using boron-doped diamond electrode – The synergetic effects of in situ ozone and free chlorine generation

This work investigated the capability of using a boron-doped diamond (BDD) electrode for bacterial disinfection in different water matrices containing varying amounts of chloride. The feed water containing Pseudomonas aeruginosa was electrochemically treated while applying different electrode conditions. Depending on the applied current density and the exposure time, inactivation between 4- and 8-log of the targeted microorganisms could be achieved. The disinfection efficiency was driven by the generation of free chlorine as a function of chloride concentration in the water. A synergetic effect of generating both free chlorine and ozone in situ during the disinfection process resulted in an effective bactericidal impact. The formation of the undesired by-products chlorate and perchlorate depended on the water matrix, the applied current density and the desired target disinfection level. In case of synthetic water with a low chloride concentration (20mgL−1) and an applied current density of 167mAcm−2, a 6-log inactivation of Pseudomonas aeruginosa could be achieved after 5min of exposure. The overall energy consumption ranged between 0.3 and 0.6kWhm−3 depending on the applied current density and water chemistry. Electrochemical water disinfection represents a suitable and efficient process for producing pathogen-free water without the use of any chemicals.

Physicochemical properties of RuO2 and IrO2 electrodes affecting chlorine evolutions

Electrochemical water disinfection, which is based on anodic oxidants evolution such as chlorine, has received a great deal of attention due to its many advantages such as versatility, ease of operation, bactericidal effectiveness, and low cost, etc. The two most popular DSA electrodes are RuO2 and IrO2, as anodic materials. However, a conflicting observation has been reported in terms of chlorine evolution. The purpose of this study is to examine which DSA electrode, RuO2 or IrO2, is more effective for chlorine evolution with the same moles of Ru or Ir deposited on the surface of each electrode using the thermal decomposition method. The electrochemical properties, atomic composition, point of zero charges, binding energies, resistances, contact angles, and the active surface areas of RuO2 and IrO2 electrodes were examined as potential factors affecting chlorine evolution. The major results showed that the RuO2 electrode has higher electro-catalytic property for chlorine evolution than IrO2 electrode. This result was explained by the lower oxygen/metal atomic fraction, a more positive surface charge, lower binding energy, lower resistance, and more hydrophilic properties of RuO2 electrode than the IrO2 electrode.

Alternative Electrode Materials and Ceramic Filter Minimize Disinfection Byproducts in Point-of-Use Electrochemical Water Treatment

Effects of various electrodes and prefiltration to minimize disinfection byproducts (DBPs) in electrochemical water disinfection was evaluated. The target microorganism, Escherichia coli O157:H7, was effectively inactivated even applying a solar-charged storage battery for the electrolysis process. Extent of microbial inactivation decreased with lower water temperature and higher pH in the free chlorine disinfection system. The RuO2/Ti electrode was most efficient because it produced the lowest concentration of chlorate and the highest generation of free chlorine. Prefiltration using a ceramic filter inhibited formation of halogenated DBPs because it removed precursors of DBPs. For safe point-of-use water treatment, the use of a hybrid prefiltration stage with the electrolysis system is strongly recommended to reduce risks from DBPs. The system is particularly suited to use in developing regions.

Economic comparison of conventional maintenance and electrochemical oxidation to warrant water safety in dental unit water lines.

Background: In preparation for implementation of a central water processing system at a dental department, we analyzed the costs of conventional decentralized disinfection of dental units against a central water treatment concept based on electrochemical disinfection.Methods: The cost evaluation included only the costs of annually required antimicrobial consumables and additional water usage of a decentralize conventional maintenance system for dental water lines build in the respective dental units and the central electrochemical water disinfection system, BLUE SAFETY™ Technologies.Results: In total, analysis of costs of 6 dental departments reviled additional annual costs for hygienic preventive measures of € 4,448.37. For the BLUE SAFETY™ Technology, the additional annual total agent consumption costs were € 2.18, accounting for approximately 0.05% of the annual total agent consumption costs of the conventional maintenance system. For both water processing concepts, the additional costs for energy could not be calculated, since the required data was not obtainable from the manufacturers.Discussion: For both concepts, the investment and maintenance costs were not calculated due to lack of manufacturer's data. Therefore, the results indicate the difference of costs for the required consumables only. Aside of the significantly lower annual costs for required consumables and disinfectants; a second advantage for the BLUE SAFETY™ Technology is its constant and automatic operation, which does not require additional staff resources. This not only safety human resources, but add additionally to cost saving.Conclusion: Since the antimicrobial disinfection capacity of the BLUE SAFETY™ was demonstrated previously and is well known, this technology, which is comparable or even superior in its non-corrosive effect, may be regarded as method of choice for continuous disinfection and prevention of biofilm formation in dental units’ water lines.

Electrochemical Water Disinfection: A Short Review

Electrochemical water disinfection is a rarely used but convenient and highly efficient way to produce germ-free water. The technique works without the addition of chemical compounds to the water to be treated, but is nevertheless based on the biocidal action of various chemical substances. Electrodes with platinum group metals (pgms) or their oxides as active coatings are generally the best suited to electrochemical water disinfection. In special cases, novel doped diamond electrodes can be applied. A short historical and technical overview of the process is given, augmented by some application examples.

Electrochemical water disinfection Part III: Hypochlorite production from potable water with ultrasound assisted cathode cleaning

A new type of electrochemical reactor for use in electrochemical water disinfection was tested. To solve the problem of the formation of calcium carbonate scales on the cathode surface a cathode which simultaneously acts as a sonotrode was used. This sonotrode is an efficient means for in situ cleaning the cathode surface from calcareous deposits formed during hydrogen evolution from potable water. The production rate of active chlorine from potable water in the new reactor in dependence on current, ultrasound intensity, and flow-through velocity was measured. The production of active chlorine is not significantly changed by the effect of ultrasound.

Electrochemical water disinfection. Part II: Hypochlorite production from potable water, chlorine consumption and the problem of calcareous deposits

The electrolytic production of hypochlorite from tap water in a flow-through reactor system is investigated using stacked platinum or iridium oxide coated titanium sheet or expanded metal electrodes. The influence of fast chlorine consumption and polarity reversal on the hypochlorite production rate was determined along with the dependence of the hypochlorite production rate on temperature, flow through velocity and current density. It was found that in most cases, the hypochlorite production rate was higher on iridium oxide compared to platinum electrodes. An increase in the flow-through velocity leads to an increased hypochlorite production rate while the hypochlorite production rate falls with increasing temperature.

Electrochemical water disinfection Part I: Hypochlorite production from very dilute chloride solutions

Electrolytic production of hypochlorite in very dilute chloride solutions is investigated using platinum and iridium oxide coated titanium expanded metal electrodes as anodes. The dependence of the hypochlorite production rate on temperature, chloride concentration and current density was determined. It was found that the hypochlorite production rate is consistently higher on iridium oxide coated titanium compared to platinum coated titanium electrodes.