The influence of products and by-products obtained by drinking water electrolysis on microorganisms

Removal of antibiotic resistance genes and inactivation of antibiotic-resistant bacteria by oxidative treatments

The persistence of antibiotics in the environment because of human activities, such as seafood cultivation, has attracted great attention as they can give rise to antibiotic resistance genes (ARGs) and antibiotic-resistant bacteria (ARB). In this study, we explored the inactivation and removal efficiencies of Escherichia coli SR1 and sul1 (plasmid-encoded ARGs), respectively, in their extracellular and intracellular forms (eARGs and iARGs) by three commonly used fishery oxidants, namely chlorine, bromine, and potassium permanganate (KMnO₄), at the practical effective concentration range (0.5, 5, and 15 mg/L). Kinetics data were obtained using laboratory phosphate-buffered saline (PBS). Following the same fishery oxidation methods, the determined kinetics models were tested by studying the SR1 and sul1 disinfection efficiencies in (sterilized) pond water matrix. At concentrations of 5 and 15 mg/L, all three oxidants achieved sufficient cumulative integrated exposure (CT values) to completely inactivate SR1 and efficiently remove sul1 (up to 4.0-log). The oxidation methods were then applied to an unsterilized pond water matrix in order to study and evaluate the indigenous ARB and ARGs disinfection efficiencies in aquaculture, which reached 1.4-log and 1.0-log during treatment with fishery oxidants used in pond preparation at high concentrations before stocking (5-15 mg/L), respectively. A high chlorine concentration (15 mg/L) could efficiently remove ARGs (or iARGs) from pond water, and the iARG removal efficiency was higher than that of eARGs in pond water. The method and results of this study could aid in guiding future research and practical disinfection to control the spread of ARGs and ARB in aquaculture.

Electrochemical Disinfection in Water and Wastewater Treatment: Identifying Impacts of Water Quality and Operating Conditions on Performance

Electrochemical disinfection-a method in which chemical oxidants are generated in situ via redox reactions on the surface of an electrode-has attracted increased attention in recent years as an alternative to traditional chemical dosing disinfection methods. Because electrochemical disinfection does not entail the transport and storage of hazardous materials and can be scaled across centralized and distributed treatment contexts, it shows promise for use both in resource limited settings and as a supplement for aging centralized systems. In this Critical Review, we explore the significance of treatment context, oxidant selection, and operating practice on electrochemical disinfection system performance. We analyze the impacts of water composition on oxidant demand and required disinfectant dose across drinking water, centralized wastewater, and distributed wastewater treatment contexts for both free chlorine- and hydroxyl-radical-based systems. Drivers of energy consumption during oxidant generation are identified, and the energetic performance of experimentally reported electrochemical disinfection systems are evaluated against optimal modeled performance. We also highlight promising applications and operational strategies for electrochemical disinfection and propose reporting standards for future work.

Testing the use of cells equipped with solid polymer electrolytes for electro-disinfection

This work focuses on disinfection of water using electrolysis with boron doped diamond (BDD) coatings and faces this challenge by comparing the performance of two different cells manufactured by CONDIAS GmbH (Izehoe, Germany): CONDIACELL® ECWP and CabECO cells. They are both equipped with diamond electrodes, but the mechanical design is completely different, varying not only by geometry but also by the flow conditions. ECWP is a flow-through cell with perforated electrodes while the CabECO cell is a zero-gap cell with a proton exchange membrane as a solid polymer electrolyte (SPE) separating the anode and cathode. At 0.02 Ah dm^-3 both cells attain around 3-5 logs pathogen removal, but design and sizing parameters give an advantage to the CabECO: it can minimize the production of chlorates and perchlorates when operating in a single-pass mode, which becomes a really remarkable point. In this paper, we report tests in which we demonstrate this outstanding performance and we also explain the differences observed in the two cells operating with the same water.

Prevention of nosocomial legionellosis by best water management: comparison of three decontamination methods

BACKGROUND

Since 2000, the National Health System has adopted international guidelines for assessing Legionella spp. in hospital water systems. The control of water contamination by Legionella spp. is still a matter of research concerning the most effective method in preventing nosocomial infections.

AIM

To compare three different decontamination methods by monitoring colony-forming unit count and number of hospital-acquired legionellosis cases. A secondary objective was to evaluate the long-term effects of the preventive measures on the water pipes.

METHODS

A protocol was developed for the selection of high-risk sampling sites and for the testing of three disinfection methods over the course of 19 years: hyperchlorination and thermal shock (period A, 2000-2005); copper-silver ionization (period B, 2006-2010); and integration of pre-filtering, filtering, pipe-protecting products, and remote control with chlorine dioxide (ClO₂) (period C, 2011-2018).

FINDINGS

The use of shock disinfection and hyperchlorination led to a decrease in contamination level immediately after the procedure, but then it rose again to the previous level in two months. Both copper-silver ionization and ClO₂ disinfection showed a stable and durable decrease in contamination level. Throughout these three phases, six cases of Legionella spp. occurred during period A, six cases during period B, and three cases during period C. With regard to the damage of water pipes, effective copper-silver levels caused corrosion and calcification in water pipes.

CONCLUSION

Both copper-silver ionization and ClO₂ properly controlled Legionella spp. contamination. ClO₂ significantly reduced the number of positive sites (P < 0.001) without damaging the pipelines.

Applications of Light-Emitting Diodes (LEDs) in Food Processing and Water Treatment

Light-emitting diode (LED) technology is an emerging nonthermal food processing technique that utilizes light energy with wavelengths ranging from 200 to 780 nm. Inactivation of bacteria, viruses, and fungi in water by LED treatment has been studied extensively. LED technology has also shown antimicrobial efficacy in food systems. This review provides an overview of recent studies of LED decontamination of water and food. LEDs produce an antibacterial effect by photodynamic inactivation due to photosensitization of light absorbing compounds in the presence of oxygen and DNA damage; however, such inactivation is dependent on the wavelength of light energy used. Commercial applications of LED treatment include air ventilation systems in office spaces, curing, medical applications, water treatment, and algaculture. As low penetration depth and high-intensity usage can challenge optimal LED treatment, optimization studies are required to select the right light wavelength for the application and to standardize measurements of light energy dosage.

Anion-exchange resin adsorption followed by electrolysis: A new disinfection approach to control halogenated disinfection byproducts in drinking water

Bromide and natural organic matter (NOM) are both precursors of halogenated disinfection byproducts (DBPs) in drinking water. During drinking water treatment process, chloride-form anion-exchange resin adsorption is expected to be capable of removing these DBP precursors and in the meantime releasing chloride ions. The released chloride as well as the chloride initially present in source water could be oxidized through electrolysis to generate free chlorine for disinfection. Based on the above assumptions, we developed a new disinfection approach using chloride-form anion-exchange resin adsorption followed by electrolysis to control halogenated DBPs. Parameter setup and optimization were performed for resin adsorption and electrolysis processes. Results showed that 93.7% of NOM and 90% of bromide could be removed at a resin dose of 20 mL per 2 L of simulated source water sample with a contact time of 1 h. Meanwhile, 49.5 mg/L of chloride was released from the resin to the water sample via anion-exchange, and the released chloride was further oxidized by electrolysis (Ti/RuO₂-IrO₂ anode and graphite cathode, current intensity of 0.4 A) to generate free chlorine (5 mg/L as Cl₂) within 192 s. With this new approach, formation of total organic halogen, four trihalomethanes, and five haloacetic acids was reduced by 86.4%, 98.5%, and 93.2%, respectively, compared with chemical chlorination alone. Although the new approach might enhance the formation of some phenolic DBPs by decreasing bromide levels in source water, the overall cytotoxicity of the water samples treated with the new approach was significantly decreased by 68.8% according to a human hepatoma cell cytotoxicity assay. Notably, disinfection ability evaluation showed that the new approach achieved 3.36-log₁₀ reductions of three seeded bacteria (Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus) in 19 s, suggesting that it was not only effective to E. coli but also effective to the chlorine-resistant bacteria (P. aeruginosa and S. aureus).

Electrochemical disinfection of bacteria-laden water using antimony-doped tin-tungsten-oxide electrodes

Electrochemical disinfection has been shown to be an efficient method with a shortrequired contact time for treatment of drinking water supplies, industrial raw water supplies, liquid foodstuffs, and wastewater effluents. In the present work, the electrochemical disinfection of saline water contaminated with bacteria was investigated in chloride-containing solutions using Sb-doped Sn_80%-W_20%-oxide anodes. The influence of current density, bacterial load, initial chloride concentration, solution pH, and the type of bacteria (E. coli D21, E. coli O157:H7, and E. faecalis) on disinfection efficacy was systematically examined. The impact of natural organic matter and a radical scavenger on the disinfection process was also examined. The electrochemical system was highly effective in bacterial inactivation for a 0.1 M NaCl solution contaminated with ∼10⁷ CFU/mL bacteria by applying a current density ≥1 mA/cm² through the cell.100% inactivation of E. coli D21 was achieved with a contact time of less than 60 s and power consumption of 48 Wh/m³, by applying a current density of 6 mA/cm² in a 0.1 M NaCl solution contaminated with ∼10⁷ CFU/mL. Reactive chlorine species as well as reactive oxygen species (e.g. hydroxyl radicals) generated in situ during the electrochemical process were determined to be responsible for inactivation of bacteria.

Efficient bacterial inactivation with Z-scheme AgI/Bi2MoO6 under visible light irradiation

A novel Z-scheme AgI/Bi₂MoO₆ hybrid photocatalyst was fabricated via a solvothermal-precipitation approach to disinfect bacteria in water. Powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopic (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX), high resolution transmission electron microscope (HRTEM), UV-vis diffuse reflectance spectra (DRS), as well as photoluminescence spectra (PL) were employed to characterize the fabricated photocatalyst. Due to the stronger redox potential and better separation of charge carriers induced by the Z-scheme structure, the optimal synthesized AgI/Bi₂MoO₆ exhibited excellent disinfection activity towards both Gram-negative strain Escherichia coli (E. coli) and Gram-positive strain Staphylococcus aureus (S. aureus) under visible light irradiation. 5.0 × 10⁷ CFU mL^-1 of E. coli and S. aureus cells were completely disinfected within 30 min and 90 min, respectively. Ag⁺ ions did not contribute to the disinfection activity, while active species including h⁺, O₂^-, e^-, and H₂O₂ contributed to the cell inactivation. By changing the interaction force and being involved in the photocatalytic reactions, the common anions (Cl^-, NO₃^-, SO₄^2-, and H₂PO₄^-) would affect the disinfection activity. Moreover, AgI/Bi₂MoO₆ exhibited effective disinfection activity in four consecutive reused cycles. Thus, AgI/Bi₂MoO₆ could be used as a promising photocatalyst for water disinfection.

Inactivation, lysis and degradation by-products of Saccharomyces cerevisiae by electrooxidation using DSA

The yeast Saccharomyces cerevisiae, a microorganism with cell walls resistant to many types of treatments, was chosen as a model to study electrochemical disinfection process using dimensionally stable anodes (DSA). DSA electrodes with nominal composition of Ti/RuO₂TiO₂ and Ti/RuO₂TiO₂IrO₂ were evaluated in 0.05 mol L^-1 Na₂SO₄ containing yeast. The results showed inactivation about of 100 % of the microorganisms at Ti/RuO₂TiO₂ by applying 20 and 60 mA cm^-2 after 120 min of electrolysis, while a complete inactivation at Ti/RuO₂IrO₂TiO₂ electrode was achieved after 180 min at 60 mA cm^-2. When chloride ions were added in the electrolyte solution, 100 % of the yeast was inactivated at 20 mA cm^-2 after 120 min of electrolysis, independent of the anode used. In the absence of chloride, the energy consumption (EC) was of 34.80 kWh m^-3, at 20 mA cm^-2 by using Ti/RuO₂TiO₂ anode. Meanwhile, in the presence of chloride, EC was reduced, requiring 30.24 and 30.99 kWh m^-3 at 20 mA cm^-2, for Ti/RuO₂TiO₂ and Ti/RuO₂IrO₂TiO₂ electrodes, respectively, The best performance for cell lysis was obtained in the presence of chloride with EC of 88.80 kWh m^-3 (Ti/RuO₂TiO₂) and 91.85 kWh m^-3 (Ti/RuO₂IrO₂TiO₂) to remove, respectively, 92 and 95 % of density yeast. The results clearly showed that yeast, as a model adopted, was efficiently inactivated and lysed by electrolysis disinfection using DSA-type electrodes.

Electrochemical treatment of water containing Microcystis aeruginosa in a fixed bed reactor with three-dimensional conductive diamond anodes

An electrochemical treatment was investigated to remove Microcystis aeruginosa from water. A fixed bed reactor in flow was tested, which was equipped with electrodes constituted by stacks of grids electrically connected in parallel, with the electric field parallel to the fluid flow. Conductive diamond were used as anodes, platinised Ti as cathode. Electrolyses were performed in continuous and in batch recirculated mode with flow rates corresponding to Re from 10 to 160, current densities in the range 10-60Am(-2) and Cl(-) concentrations up to 600gm(-3). The absorbance of chlorophyll-a pigment and the concentration of products and by-products of electrolysis were measured. In continuous experiments without algae in the inlet stream, total oxidants concentrations as equivalent Cl2, of about 0.7gCl2m(-3) were measured; the maximum values were obtained at Re=10 and i=25Am(-2), with values strongly dependent on the concentration of Cl(-). The highest algae inactivation was obtained under the operative conditions of maximum generation of oxidants; in the presence of microalgae the oxidants concentrations were generally below the detection limit. Results indicated that most of the bulk oxidants electrogenerated is constituted by active chlorine. The prevailing mechanism of M. aeruginosa inactivation is the disinfection by bulk oxidants. The experimental data were quantitatively interpreted through a simple plug flow model, in which the axial dispersion accounts for the non-ideal flow behaviour of the system; the model was successfully used to simulate the performances of the reactor in the single-stack configuration used for the experiments and in multi-stack configurations.

Removal of oxyfluorfen from ex-situ soil washing fluids using electrolysis with diamond anodes

In this research, firstly, the treatment of soil spiked with oxyfluorfen was studied using a surfactant-aided soil-washing (SASW) process. After that, the electrochemical treatment of the washing liquid using boron doped diamond (BDD) anodes was performed. Results clearly demonstrate that SASW is a very efficient approach in the treatment of soil, removing the pesticide completely by using dosages below 5 g of sodium dodecyl sulfate (SDS) per Kg of soil. After that, complete mineralization of organic matter (oxyflourfen, SDS and by-products) was attained (100% of total organic carbon and chemical oxygen demand removals) when the washing liquids were electrolyzed using BDD anodes, but the removal rate depends on the size of the particles in solution. Electrolysis of soil washing fluids occurs via the reduction in size of micelles until their complete depletion. Lower concentrations of intermediates are produced (sulfate, chlorine, 4-(trifluoromethyl)-phenol and ortho-nitrophenol) during BDD-electrolyzes. Finally, it is important to indicate that, sulfate (coming from SDS) and chlorine (coming from oxyfluorfen) ions play an important role during the electrochemical organic matter removal.

Electrochemical disinfection of simulated ballast water on PbO2/graphite felt electrode

A novel PbO2/graphite felt electrode was constructed by electrochemical deposition of PbO2 on graphite felt and characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) analysis. The prepared electrode is a viable technology for inactivation of Escherichia coli, Enterococcus faecalis, and Artemia salina as indicator organisms in simulated ballast water treatment, which meets the International Maritime Organization (IMO) Regulation D-2. The effects of contact time and current density on inactivation were investigated. An increase in current density generally had a beneficial effect on the inactivation of the three species. E.faecalis and A.salina were more resistant to electrochemical disinfection than E. coli. The complete disinfection of E.coli was achieved in <8min at an applied current density of 253A/m(2). Complete inactivation of E. faecalis and A.salina was achieved at the same current density after 60 and 40min of contact time, respectively. A. salina inactivation follows first-order kinetics.

Electrochemical disinfection of toilet wastewater using wastewater electrolysis cell

The paucity of proper sanitation facilities has contributed to the spread of waterborne diseases in many developing countries. The primary goal of this study was to demonstrate the feasibility of using a wastewater electrolysis cell (WEC) for toilet wastewater disinfection. The treated wastewater was designed to reuse for toilet flushing and agricultural irrigation. Laboratory-scale electrochemical (EC) disinfection experiments were performed to investigate the disinfection efficiency of the WEC with four seeded microorganisms (Escherichia coli, Enterococcus, recombinant adenovirus serotype 5, and bacteriophage MS2). In addition, the formation of organic disinfection byproducts (DBPs) trihalomethanes (THMs) and haloacetic acids (HAA5) at the end of the EC treatment was also investigated. The results showed that at an applied cell voltage of +4 V, the WEC achieved 5-log10 reductions of all four seeded microorganisms in real toilet wastewater within 60 min. In contrast, chemical chlorination (CC) disinfection using hypochlorite [NaClO] was only effective for the inactivation of bacteria. Due to the rapid formation of chloramines, less than 0.5-log10 reduction of MS2 was observed in toilet wastewater even at the highest [NaClO] dosage (36 mg/L, as Cl2) over a 1 h reaction. Experiments using laboratory model waters showed that free reactive chlorine generated in situ during EC disinfection process was the main disinfectant responsible for the inactivation of microorganisms. However, the production of hydroxyl radicals [OH], and other reactive oxygen species by the active bismuth-doped TiO2 anode were negligible under the same electrolytic conditions. The formation of THMs and HAA5 were found to increase with higher applied cell voltage. Based on the energy consumption estimates, the WEC system can be operated using solar energy stored in a DC battery as the sole power source.

Reduction of Salmonella enterica on the surface of eggshells by sequential treatment with aqueous chlorine dioxide and drying

The synergistic effects of sequential treatments with chlorine dioxide (ClO2) and drying in killing Salmonella enterica on the surface of chicken eggshells were investigated. Initial experiments were focused on comparing lethalities of sodium hypochlorite (NaOCl) and ClO2. Eggs surface-inoculated with S. enterica in chicken feces as a carrier were immersed in water, NaOCl (50 or 200 μg/mL), or ClO2 (50 or 200 μg/mL) for 1 or 5 min. For 1-min treatments, lethal activities of sanitizers were not significantly different (P>0.05). However, after treatment with ClO2 for 5 min, reductions of S. enterica were significantly greater (P≤0.05) than reductions after treatment with water or NaOCl. The effect of treatment of eggs with ClO2 or NaOCl, followed by drying at 43% relative humidity and 25 °C for 24 and 48 h, were determined. Populations of S. enterica decreased during drying, regardless of the type of sanitizer treatment. ClO2 treatment, compared to water or NaOCl treatments, resulted in additional reductions of ca. >1.3 log CFU/egg during drying. This indicates that sequential treatments with ClO2 and drying induced synergistic lethal effects against S. enterica on the surface of eggshells. These observations will be useful when selecting a sanitizer to control S. enterica on the surface of eggshells and designing an effective egg sanitization system exploiting the synergistic lethal effects of sanitizer and drying.

Effect of bipolar electrode material on the reclamation of urban wastewater by an integrated electrodisinfection/electrocoagulation process

This work presents an integrated electrodisinfection/electrocoagulation (ED-EC) process for urban wastewater reuse that employs iron bipolar electrodes. Boron doped diamond (BDD) was used as the anode and stainless steel (SS) as the cathode. A perforated iron plate was introduced between the anode and cathode to function as a bipolar electrode. This ED-EC combined cell makes it possible to conduct the simultaneous removal of microbiological content and elimination of turbidity from urban wastewater. The results show that current densities greater than or equal to 6.70 A m(-2) enable complete disinfection of the effluent and the removal of more than 90% of its initial turbidity. Hypochlorite and chloramines formed during the ED-EC process were found to be the main compounds responsible for the disinfection process. Furthermore, a cell configuration of cathode (inlet)-anode (outlet) improves the process performance by enhancing turbidity removal. Finally, the influence of the bipolar electrode material (iron or aluminium) was assessed. The results indicate that the efficiency of the electrodisinfection process depends mainly on the anodic material and is not influenced by the material of the bipolar electrode. In contrast, the removal of turbidity is more efficient when using iron as a bipolar electrode, especially at low current densities, due to the formation of a passive layer on the aluminium that hinders the dissolution of the bipolar electrode.

Bactericidal mechanisms of Ag₂O/TNBs under both dark and light conditions

Ag(2)O/TNBs were fabricated by depositing Ag(2)O nanoparticles on the surface of TiO(2) nanobelts (TNBs). The disinfection activities of Ag(2)O/TNBs on two representative bacterial types: Gram-negative Escherichia coli ATCC15597 and Gram-positive Bacillus subtilis, were examined under both dark and visible light conditions. Ag(2)O/TNBs exhibited stronger bactericidal activities than Ag(2)O nanoparticles and TNBs under both dark and light conditions. For both cell types, disinfection effects of Ag(2)O/TNBs were greater under light conditions relative to those under dark conditions. The bactericidal mechanisms of Ag(2)O/TNBs under both dark and light conditions were explored. Ag(+) ions released from Ag(2)O/TNBs did not contribute to the bactericidal activity of Ag(2)O/TNBs under dark conditions, whereas the released Ag(+) ions showed bactericidal activity under visible light irradiation conditions. Active species (H(2)O(2), O(2)(-)·, and e(-)) generated by Ag(2)O/TNBs played important roles in the disinfection processes under both dark and visible light irradiation conditions. Without the presence of active species, the direct contact of Ag(2)O/TNBs with bacterial cells had no bactericidal effect.

Formation of hazardous inorganic by-products during electrolysis of seawater as a disinfection process for desalination

From our previous study, an electrochemical process was determined to be a promising tool for disinfection in a seawater desalination system, but an investigation on the production of several hazardous by-products is still required. In this study, a more intensive exploration of the formation patterns of perchlorate and bromate during the electrolysis of seawater was conducted. In addition, the rejection efficiencies of the targeted by-products by membrane processes (microfiltration and seawater reverse osmosis) were investigated to uncover the concentrations remaining in the final product from a membrane-based seawater desalination system for the production of drinking water. On the electrolysis of seawater, perchlorate did not provoke any problem due to the low concentrations formed, but bromate was produced at a much higher level, resulting in critical limitation in the application of the electrochemical process to the desalination of seawater. Even though the formed bromate was rejected via microfiltration and reverse osmosis during the 1st and 2nd passes, the residual concentration was a few orders of magnitude higher than the USEPA regulation. Consequently, it was concluded that the application of the electrochemical process to seawater desalination cannot be recommended without the control of bromate.