Electrochemical Inactivation Research Articles

Electrochemical flow-through disinfection of Escherichia coli versus Staphylococcus aureus: Identifying impacts of flow patterns on efficiency

While Ti4O7 reactive electrochemical membrane (REM) treatment exhibits high efficiency in inactivating bacteria, it remains obscure about the disinfection and antifouling mechanism. Herein, we highlighted the decisive impact of flow patterns on the electrochemical inactivation of both Escherichia coli and Staphylococcus aureus during dead-end filtration mode. Specifically, 5.22 and 5.47 log removal for E. coli and S. aureus were achieved by a single pass under anode-to-cathode (AC) flow pattern at 7 mA cm−2 respectively, while the inactivation rates immediately decreased to less than one log for cathode-to-anode (CA) flow pattern. Further analysis demonstrated that the remarkable inactivation efficiency in neutral condition, the complete inactivation of E. coli and S. aureus in the parallel plate batch mode were achieved in 15 min and 30 min at 7 mA cm−2 respectively, was significantly inhibited during alkaline and acidic exposure, thereby which explained the slow disinfection rates in CA flow pattern due to the formed alkaline experiment near anodic reaction section. The disinfection efficiency and comparative differences of E. coli and S. aureus were also affected by their hydraulic condition and cell wall structure. Functional groups model substances experiments and molecular dynamics simulation elucidated that the response changes of cell structure especially denser membrane protein complex under alkaline and acidic exposure resisted electrooxidation attack to the membrane structure. These findings here provide insights into the application of Ti4O7 REM technologies in controlling waterborne disease transmission.

Dry-processed technology for flexible and high-performance FeS2-based all-solid-state lithium batteries at low stack pressure

All-solid-state lithium batteries (ASSLBs) are considered promising energy storage systems due to their high energy density and inherent safety. However, scalable fabrication of ASSLBs based on transition metal sulfide cathodes through the conventional powder cold-pressing method with ultrahigh stacking pressure remains challenging. This article elucidates a dry process methodology for preparing flexible and high-performance FeS2-based ASSLBs under low stack pressure by utilizing polytetrafluoroethylene (PTFE) binder. In this design, fibrous PTFE interweaves Li6PS5Cl particles and FeS2 cathode components, forming flexible electrolyte and composite cathode membranes. Beneficial to the robust adhesion, the composite cathode and Li6PS5Cl membranes are tightly compacted under a low stacking pressure of 100 MPa which is a fifth of the conventional pressure. Moreover, the electrode/electrolyte interface can sustain adequate contact throughout electrochemical cycling. As expected, the FeS2-based ASSLBs exhibit outstanding rate performance and cyclic stability, contributing a reversible discharged capacity of 370.7 mAh g−1 at 0.3C after 200 cycles. More importantly, the meticulous dQ/dV analysis reveals that the three-dimensional PTFE binder effectively binds the discharge products with sluggish kinetics (Li2S and Fe) to the ion–electron conductive network in the composite cathode, thereby preventing the electrochemical inactivation of products and enhancing electrochemical performance. Furthermore, FeS2-based pouch-type cells are fabricated, demonstrating the potential of PTFE-based dry-process technology to scale up ASSLBs from laboratory-scale mold cells to factory-scale pouch cells. This feasible dry-processed technology provides valuable insights to advance the practical applications of ASSLBs.

Electrochemical inactivation of enteric viruses MS2, T4, and Phi6 using doped laser-induced graphene electrodes and filters

Titanium suboxide-doped laser-induced graphene holds great potential to inactivate model enteric viruses MS2, T4, and Phi6. The mechanism of inactivation was recognized as the combination of electric field-induced effects and electrooxidation.

Flow electrochemical inactivation of waterborne bacterial endospores

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 disinfection may increase the spread of antibiotic resistance genes by promoting conjugal plasmid transfer

Current in the milliampere range can be used for electrochemical inactivation of bacteria. Yet, bacteria-including antibiotic resistant bacteria (ARB) may be subjected to sublethal conditions due to imperfect mixing or energy savings measures during electrochemical disinfection. It is not known whether such sublethal current intensities have the potential to stimulate plasmid transfer from ARB. In this study, conjugal transfer of plasmid pKJK5 was investigated between Pseudomonas putida strains under conditions reflecting electrochemical disinfection. Although the abundance of culturable and membrane-intact donor and recipient cells decreased with applied current (0–60 mA), both transconjugant density and transconjugant frequency increased. Both active chlorine and superoxide radicals were generated electrolytically, and ROS generation was induced. In addition, we detected significant over expression of a core oxidative stress defense gene (ahpCF) with current. Expression of selected conjugation related genes (traE, traI, trbJ, and trbL) also significantly correlated with current intensity. ROS accumulation, SOS response and subsequent derepression of conjugation are therefore the plausible consequence of sublethal current exposure. These findings suggest that sublethal intensities of current can enhance conjugal plasmid transfer, and that it is essential that conditions of electrochemical disinfection (applied voltage, current density, time and mixing) are carefully controlled to avoid conjugal ARG transmission.

Fabrication of SnO2-Sb reactive membrane electrodes for high-efficiency electrochemical inactivation of bacteria and viruses in water

Exposure to waterborne pathogens is still a widespread threat to public health, and efficient and reliable disinfection technologies are urgently needed for decentralized applications. Herein, we developed a novel freestanding and flow-through SnO2-Sb reactive membrane electrode (RME) for electrochemical wastewater disinfection. When water was forced to flow through the porous RME, large amounts of reactive ·OH and H+ were generated within the interior pores of the anode, creating a strongly acidic local environment enriched with ·OH for the rapid inactivation of bacteria and viruses. At an applied voltage of 3.5 V, 100% removal of Escherichia coli (>6.3-log inactivation) was achieved by the flow-through RME at a high flux, which was significantly more effective than the system operated in the conventional flow-by mode (2.7-log inactivation). Using the bacteriophage MS2 strain as a model virus, a disinfection efficiency of 100% (>8.3-log inactivation) was achieved by the RME at 3.5 V. The transmission electron microscopy analysis revealed that E. coli and MS2 in the disinfected water suffered from serious destruction and disintegration, reflecting the strong electrocatalytic oxidation capacity of the charged RME. The SnO2-Sb RME-based electrochemical system performed very well in disinfecting complex municipal wastewater, demonstrating its potential for practical applications.

Platinum disc electrode for in-situ electrochemical inactivation of bacterial growth in culture media

We report electrochemical response of non-adherent E. coli cells on a platinum disc electrode and in-situ inactivation through electro-stimulation to reduce their growth. Anodic peak current in cyclic voltammetry (CV) was gradually enhanced with an increased cell density due to increase in redox protein riboflavin secreted by the viable bacterial cells. The presence of the bacterial cells showed capacitive nature of the electric double layer capacitance and reduced interfacial charge transfer resistance in impedance of Nyquist plot. Formation of bacterial layer on the electrode surface was also evident from the rise in both anodic peak current and potential with scan rate at fixed cell concentration. The electrochemical inactivation of bacterial cells showed significant reduction in colony formation and growth. The observed inhibitory response with electro-stimulation was in comparison with the inactivation of bacterial cells treated with UV irradiation and sonication. Negative bias potential as compare to positive or periodic bias potential has been more effective for inactivation of the viable bacterial cells in suspension.

SWNTs-PAN/TPU/PANI composite electrospun nanofiber membrane for point-of-use efficient electrochemical disinfection: New strategy of CNT disinfection

Single-walled carbon nanotubes (SWNTs) can be used as 1D electrochemical disinfection material for point-of-use water treatment but are limited by their poor durability and possible cytotoxicity. Immobilizing SWNTs in nanofibers with electrospinning served as slow-release technology develop a novel with a lasting antibacterial and (eco-) toxicological alleviation of SWNTs. Hence, the single-walled carbon nanotubes-polyacrylonitrile/polyurethane/polyaniline (SWNTs-PAN/TPU/PANI, SPTP) composite electrospun nanofiber membrane was successfully fabricated by co-electrospinning process and the electrochemical filtration and disinfection system of point-of-use drinking water treatment is constructed. In the absence of electrolysis, the SPTP filter is effective for complete removal of bacteria by sieving mechanism. Concomitant electrolysis in the course of filtration results in significantly increased inactivation of sieved bacteria. Application of 3.0 V leads to complete (5 log) inactivation of bacteria within 20 min. 5-cycle experiments, membrane flux and shake flask tests prove that composite restrict the excessive release of SWNTs retaining the long-lasting antibacterial properties of SPTP membrane. At 1.0 and 2.0 V, electrolyte concentration and composition is irrelevant to electrochemical inactivation consistent with oxidation of SPTP filter. Bacterial reactive oxygen species (ROSs) also support an oxidation mechanism. At 3.0 V, electrochemical disinfection mainly relies on indirect oxidation.

Improvement on electrochemical inactivation of Escherichia coli and Clostridium perfringens by assisted alum nanocrystallites approach: parametric and cost evaluation

Improvement on electrochemical inactivation of Escherichia coli and Clostridium perfringens by assisted alum nanocrystallites approach: parametric and cost evaluation

Electrochemical inactivation of bacteria with a titanium sub-oxide reactive membrane

A reactive electrochemical membrane (REM) system was developed with titanium suboxide microfiltration membrane serving as the filter and the anode, and was examined to inactivate Escherichia coli (E. coli) in water at various current densities. After passing through the membrane filter, the concentration of E. coli decreased from 6.46 log CFU/mL to 0.18 log CFU/mL. The REM operation and effects, including membrane pressure, anode potential, protein leakage, and cell morphology, were characterized under different treatment conditions. It was found that several mechanisms, including membrane filtration, external electrical field influence, and direct oxidation, functioned in concert to lead to bacteria removal and inactivation, and direct oxidation likely played the major role. As revealed by scanning electron microscope and extracellular protein analysis, high current density and voltage caused severe cell damage that resulted in partial or complete cell disintegration. The removal of a model virus, bacteriophage MS2, was also investigated at the current density of 10 mA cm−2 and achieved 6.74 log reduction compared to the original concentration (1011 PFU/mL). In addition to illustration of mechanisms, this study may provide a potentially promising approach that is suitable for decentralized treatment to meet dispersed water disinfection needs.

Effective electrochemical inactivation of Microcystis aeruginosa and degradation of microcystins via a novel solid polymer electrolyte sandwich

The treatment of toxic Microcystis aeruginosa (M. aeruginosa) by electrolysis using a boron-doped diamond (BDD) anode with a solid polymer electrolyte (SPE) was investigated. In order to examine the role of oxidizing agents, the electrolysis of M. aeruginosa was conducted in distilled deionised water (DIW) with and without sodium chloride aqueous electrolyte. Furthermore, to verify the system’s ability for freshwater treatment without the addition of chemicals, we also tested filtered local reservoir water. M. aeruginosa cell inactivation and microcystins degradation occurred in the DIW system without a supporting aqueous electrolyte, but cell inactivation occurred at slightly slower rate compared to when 30 mg/L Cl− was added. Even though these rates were even slower in the pre-filtered reservoir water, around 90% inactivation and toxin degradation was still observed after 30 min, and cells were not able to re-grow when subsequently exposed to optimum growth conditions. These results for the first time demonstrate the ability of the SPE system to efficiently treat contaminated freshwaters, even without the addition of chemicals or adjustment of electrical conductivity. Importantly, significant changes in cell morphology after electrolysis in different water matrices were observed. In the DIW with 30 mg/L Cl− test based on the significant differences in oxidants concentrations in the presence and absence of M. aeruginosa suggest that there was a synergistic effect of in situ electro-generated ozone and chlorine species in cell inactivation, however, hydrogen peroxide did not seem to assist in the treatment performance. This study suggests that the electrochemical treatment of BDD with SPE, with and without supporting electrolyte is an effective method for the removal of both toxic cyanobacteria and cyanotoxins.

Electrochemical inactivation of Microcystis aeruginosa using BDD electrodes: Kinetic modeling of microcystins release and degradation

Electrochemical inactivation of cyanobacteria using boron-doped diamond (BDD) electrode were comprehensively investigated in this study. The pulse amplitude modulated (PAM) fluorometry, flow cytometry, and confocal laser scanning microscopy (CLSM) were used to characterize the photosynthetic capacity and cell integrity of Microcystis aeruginosa. Persulfate is in-situ generated and activated during the process and responsible for the inactivation of M. aeruginosa. The inactivation efficiency increases along with the increase of applied currents. Additionally, a kinetic model based on a sequence of two consecutive irreversible first-order processes was developed to simulate the release and degradation of microcystins (MCLR). The model was able to successfully predict the concentration of extracellular, intracellular and total MCLR under different applied currents and extended exposure time.

Sludge disinfection using electrical thermal treatment: The role of ohmic heating

Electrical heating has been proposed as a potential method for pathogen inactivation in human waste sludge, especially in decentralized wastewater treatment systems. In this study, we investigated the heat production and E. coli inactivation in wastewater sludge using electrical thermal treatment. Various concentrations of NaCl and NH4Cl were tested as electrolyte to enhance conductivity in sludge mixtures. At same voltage input (18V), sludge treated with direct current (DC) exhibited slower ascent of temperature and lower energy efficiencies for heat production comparing to that using alternate current (AC). However, DC power showed better performance in E. coli inactivation due to electrochemical inactivation in addition to thermal inactivation. Greater than 6log10 removal of E. coli was demonstrated within 2h using 0.15M of NaCl as electrolyte by AC or DC power. The heat production in sludge was modeled using Maxwell–Eucken and effective medium theory based on the effective electrical conductivity in the two-phase (liquid and solid) sludge mixtures. The results showed that the water and heat loss is a critical consideration in modeling of sludge temperature using ohmic heating. The experimental data also suggested that the models are less applicable to DC power because the electrochemical reactions triggered by DC reduce the concentration of NH4+ and other ions that serve as electrolyte. The results of this study contribute to the development of engineering strategies for human waste sludge management.

Wastewater Disinfection Using Potential Switching Methods on Boron Doped Ultrananocrystalline Diamond Electrodes

Boron-doped diamond (BDD) has attracted considerable attention as an electrode material used for electrochemical disinfection of wastewater, due to its high oxygen evolution over-potential.[1], [2] This property enables the formation of highly reactive oxygen species (ROS) such as hydroxyl radicals, ozone, and hydrogen peroxide.[3]–[6] Despite the promise of BDD as a liquid disinfection electrode, there is little information in literature that details the optimal conditions for ROS generation. Effects of potential switching for inhibiting fouling of the electrode surface, evolving surface chemistry, and resultant energy efficiency in sanitizing wastewater are not widely reported. Knowledge of these conditions and their liquid disinfection properties would allow production of ROS with higher efficiency and therefore lower cost in real-world applications. The present work investigates the generation of ROS and subsequent liquid disinfection of wastewater using as-grown boron-doped ultrananocrystalline diamond (BD-UNCD) electrodes. Static and potential switching methods of generating ROS are compared to determine their effects on liquid disinfection, chlorine generation, energy expenditure, electrode fouling, and electrode surface chemistry. These results build on an evolving understanding of the electrochemical generation of ROS from BDD electrodes. Our results show that liquid disinfection of diluted wastewater can occur with negligible chlorination and efficient energy expenditure using potential switching methods. Comparison of potential switching to static potential methods show differences in energy expenditure, chlorination, and electrode scaling; as well as time needed for disinfection of liquid waste. It is proposed that the electrogeneration of functional groups at oxidative potentials of BD-UNCD allows for an increased current density during the successive electrolysis at reductive potentials, and that this electrogeneration correlates to an enhanced production of H2O2. Through potential switching, these functional groups can be stabilized and used continuously to more efficiently produce H2O2, and potentially other ROS, when compared to static potential methods at these same potentials by optimizing the applied potentials and duty cycle. Moreover, potential switching has been previously used to inhibit electrode fouling,[7]–[10] which is commonplace in liquid waste sanitation, and therefore offers a practical method for electrochemical disinfection of wastewater in large scale applications.

Effect of electrogenerated hydroxyl radicals, active chlorine and organic matter on the electrochemical inactivation of Pseudomonas aeruginosa using BDD and dimensionally stable anodes

Abstract In this work, the disinfection of 100 mL of 106 CFU mL−1 Pseudomonas aeruginosa suspensions at pH 5.8 by electrochemical oxidation at 33.3 mA cm−2 is reported. The undivided electrolytic cell was equipped with either a boron-doped diamond (BDD) or an IrO2-based or RuO2-based dimensionally stable anode and a stainless steel cathode. Physisorbed hydroxyl radicals M( OH) formed from anodic water oxidation and active chlorine generated from anodic Cl− oxidation were the main oxidizing species in pure Na2SO4 medium and in the presence of NaCl, respectively. A faster inactivation was always found using the dimensionally stable anodes. In 7 mM Na2SO4, this behavior was associated to the much larger adsorption of the bacteria onto the anode, which accelerated the M( OH)-mediated oxidation and inactivation of the cells. The inactivation rate was strongly enhanced in 7 mM Na2SO4 + 1 mM NaCl due to the larger oxidation power of active chlorine compared to that of M( OH). The effect of NaCl concentration and current density on the disinfection process was examined with BDD and the best performance was obtained in 7 mM Na2SO4 + 7 mM NaCl at 8.3 mA cm−2, with total inactivation in 2 min and energy consumption of 0.059 kW h m−3. The addition of paracetamol in 7 mM Na2SO4 medium inhibited the disinfection at short electrolysis time regardless of the anode, owing to the preferential action of M( OH) on this pollutant. For BDD, the inactivation rate rose over time at higher drug content due to the generation of greater amounts of toxic by-products. For the IrO2-based anode, the progressive formation of toxic and less adsorbable by-products enhanced the process over time, giving rise again to a quicker total disinfection compared to that with BDD.

Electrochemical inactivation of cyanobacteria and microcystin degradation using a boron-doped diamond anode — A potential tool for cyanobacterial bloom control

Cyanobacterial blooms are global phenomena that can occur in calm and nutrient-rich (eutrophic) fresh and marine waters. Human exposure to cyanobacteria and their biologically active products is possible during water sports and various water activities, or by ingestion of contaminated water. Although the vast majority of harmful cyanobacterial products are confined to the interior of the cells, these are eventually released into the surrounding water following natural or artificially induced cell death. Electrochemical oxidation has been used here to damage cyanobacteria to halt their proliferation, and for microcystin degradation under in-vitro conditions. Partially spent Jaworski growth medium with no addition of supporting electrolytes was used. Electrochemical treatment resulted in the cyanobacterial loss of cell-buoyancy regulation, cell proliferation arrest, and eventual cell death. Microcystin degradation was studied separately in two basic modes of treatment: batch-wise flow, and constant flow, for electrolytic-cell exposure. Batch-wise exposure simulates treatment under environmental conditions, while constant flow is more appropriate for the study of boron-doped diamond electrode efficacy under laboratory conditions. The effectiveness of microcystin degradation was established using high-performance liquid chromatography–photodiode array detector analysis, while the biological activities of the products were estimated using a colorimetric protein phosphatase-1 inhibition assay. The results indicate potential for the application of electro-oxidation methods for the control of bloom events by taking advantage of specific intrinsic ecological characteristics of bloom-forming cyanobacteria. The applicability of the use of boron-doped diamond electrodes in remediation of water exposed to cyanobacteria bloom events is discussed.

Electrochemical Inactivation of Proteolytic and Lipolytic Hide Bacteria

Electrochemical Inactivation of Proteolytic and Lipolytic Hide Bacteria

Electrochemical inactivation of Bacillus spores in drinking water using a quaternary oxide electrode

Bacillus spores are resistant to disinfection methods and they represent a potential threat that requires improved methods to ensure water safety. Bacillus thuringiensis (BT) and B. anthracis Sterne (BA) spores were used to investigate the effectiveness of the electrochemical (EC) disinfection process. We tested the quaternary metal oxide (TiO2–Sb2O5–SnO2–RuO2) as the anode material in an EC cell for the inactivation of the spores. The presence of chloride ions at low concentrations was found to be critical for the effective inactivation of BT spores. Active chlorine was produced in-situ by anodic oxidation of chloride in the solutions. Local tap water used as a realistic test solution was found to contain average chloride concentrations of 1.2 mM. High concentrations of active chlorine were generated in the range of 0.35 to 0.5 mM (25 to 35 mg/L) to ensure that the high concentrations of spores were inactivated. We showed that the amount of active chlorine produced in the EC cell can be readily controlled by the operating conditions, including potential, flow rate and chloride content. Scanning electron images of the EC treated spores indicate damage to the outer membranes resulting in disruption and leakage of the spore contents. EC water disinfection processes using inexpensive electrode materials are a promising alternative as shown by inactivation of challenging biological threats such as Bacillus spores.

Drinking water disinfection by hemin-modified graphite felt and electrogenerated reactive oxygen species

The electrochemical inactivation of microorganisms by a hemin/graphite felt (GF) composite electrode was investigated, and Escherichia coli was treated as the testing species. The composite electrode was constructed by chemically bonding hemin molecules onto an amino-mineralized GF (AGF) surface. Then, the electrode was characterized systematically by electrochemical methods, and the kinetic parameters of the modified electrode were investigated. The hemin molecules on the surface of the composite electrode have high activity for the reduction of O 2. When the composite electrode was applied with negative potentials, the dissolved oxygen was electrochemically reduced to reactive oxygen species (ROS, such as H 2O 2 and OH) at the cathode surface. The ROS can cause biological damage and can eventually result in the death of bacteria. A sterilizing rate up to 99.9% could be obtained after 60 min of inactivation. Thus, this composite electrode could be applied to disinfect drinking water efficiently at a low potential (−0.6 V vs. SCE) without any addition of chloride.

Electrochemical inactivation kinetics of boron-doped diamond electrode on waterborne pathogens

A boron-doped diamond (BDD) electrode was constructed as a water disinfector for the inactivation of water borne pathogens. The bactericidal effect of the disinfector was evaluated on artificially contaminated waters containing, respectively, Escherichia coli, Pseudomonas aeruginosa and Legionella pneumophila at high density. By treating the bacterial suspensions with 4 V of constant voltage between the BDD and the counter-electrode for 50 min, the population of E. coli and P. aeruginosa decreased from (10E + 7-8 colony-forming unit mL(-1)) to below the detection limits of the colony-formation method. Meanwhile, L. pneumophila were reduced to virtually zero when analyzed by fluorescence-based staining. The influences of production parameters (voltage, NaCl concentration and flow rate) on the disinfection kinetics of the BDD disinfector were examined with respect to operational conditions. Voltage was the most significant factor for adjusting the extent of electrolysis, followed by NaCl concentration and flow rate, to influence the disinfection efficiency. The disinfection of natural river water samples containing numerous microbes was performed for a practicability investigation of the BDD electrode. Approximately 99.99% bactericidal efficiency was confirmed by viability detection for E. coli and common germs in treated water. The results showed that the BDD electrode is a promising tool for various wastewater disinfections to combat waterborne diseases.