Inactivation Of Bacteria In Water Research Articles

Enhanced inactivation of Escherichia coli through hydrogen peroxide decomposition assisted by nanoscale cupric oxide-decorated activated carbon

In this study, nanoscale cupric oxide-decorated activated carbon (nCuO@AC) was synthesized by impregnation-calcination and employed to assist the decomposition of H2O2 for effective sterilization with Escherichia coli as target bacteria. Characteristic technologies demonstrated that copper oxide particles of 50–100 nm were uniformly distributed on AC surface. Owing to electron transfer from hydroxyl and aldehyde to CuO on AC, surface-bonded Cu(II) was partially reduced to Cu(I) in the nCuO matrix. The resultant Cu(I) expedited the decomposition of H2O2 and converted it into ·OH radicals which were identified by quenching experiment and electron paramagnetic resonance test. Due to oxidation attack of generated ·OH, the nCuO@AC-H2O2 system achieved a much higher inactivation rate of 6.0 log within 30 min as compared to those of 2.1 and 1.3 log in the nCuO@AC and nCuO-H2O2 systems. It also exhibited excellent pH adaptability and high inactivation efficiency under neutral conditions. After four cycles, the nCuO@AC-H2O2 system could still inactivate 5.5 log bacteria, indicating excellent stability and reusability of nCuO@AC. Spent nCuO@AC could be regenerated by eluting surficial copper oxides with hydrochloric acid, and re-coating nCuO particles through impregnation-calcination with a regeneration rate of 96.6%. Our results demonstrated that nCuO@AC was an efficient and prospective catalyst to assist the decomposition of H2O2 for effective inactivation of bacteria in water.

Inactivation of Bacteria in Water by Ferrate(VI): Efficiency and Mechanisms.

Ferrate (Fe(VI)) is an emerging green disinfectant and has received increasing attention nowadays. This study conducted systematic analyses of Fe(VI) disinfection on six typical bacteria in different water matrices. The results showed that Fe(VI) was more effective in inactivating Gram-negative (G-) bacteria than Gram-positive (G+) bacteria, and the disinfection performance of Fe(VI) was better in a phosphate buffer than that in a borate buffer and secondary effluent. The inactivation rate constants of G- bacteria were significantly higher than those of G+ bacteria. The cell membrane damage of G- bacteria was also more severe than that of G+ bacteria after Fe(VI) treatment. The cell wall structure, especially cell wall thickness, might account for the difference of the inactivation efficiency between G- bacteria and G+ bacteria. Moreover, it is revealed that Fe(VI) primarily reacted with proteins rather than other biological molecules (i.e., phospholipids, peptidoglycan, and lipopolysaccharide). This was further evidenced by the reduction of bacterial autofluorescence due to the destruction of bacterial proteins during Fe(VI) inactivation. Overall, this study advances the understanding of Fe(VI) disinfection mechanisms and provides valuable information for the Fe(VI) application in water disinfection.

Hydrodynamic tearing of bacteria on nanotips for sustainable water disinfection

Water disinfection is conventionally achieved by oxidation or irradiation, which is often associated with a high carbon footprint and the formation of toxic byproducts. Here, we describe a nano-structured material that is highly effective at killing bacteria in water through a hydrodynamic mechanism. The material consists of carbon-coated, sharp Cu(OH)2 nanowires grown on a copper foam substrate. We show that mild water flow (e.g. driven from a storage tank) can efficiently tear up bacteria through a high dispersion force between the nanotip surface and the cell envelope. Bacterial cell rupture is due to tearing of the cell envelope rather than collisions. This mechanism produces rapid inactivation of bacteria in water, and achieved complete disinfection in a 30-day field test. Our approach exploits fluidic energy and does not require additional energy supply, thus offering an efficient and low-cost system that could potentially be incorporated in water treatment processes in wastewater facilities and rural communities.

Efficient treatment of bio-contaminated wastewater using plasma technology for its reuse in sustainable agriculture

Water-related crisis represents one of the significant challenges of the rapidly growing world population. This study demonstrates an example of the novel technology of Non-Thermal Plasma (NTP) wastewater treatment for its sustainable recovery and reuse in agriculture. NTP treatment of wastewater not only causes microbial decontamination but produces Reactive Oxygen and Nitrogen Species (RONS), which can consequently improve seed germination and plant growth. We investigated the effects of the new Fountain Dielectric Barrier Discharge air plasma reactor for the treatment of bulk quantity water contaminated by Staphylococcus epidermidis or Escherichia coli bacteria. Then, employing the treated water for barley seed germination showed >20% enhancement compared to using tap water. The inactivation of bacteria in water was determined in dependence on pH, Oxidation-Reduction Potential, and correlated with chemical RONS produced in the water (hydrogen peroxide, nitrites, and especially nitrates). By utilizing the Responses Surface Methodology, we identified the optimal plasma treatment time per litre required for efficient RONS production and bactericidal effect in the wastewater treatment, which was linearly scalable with water volume. After the optimum plasma treatment time, a sharp drop in pH, and the concentrations of nitrites and hydrogen peroxide were observed, which is related to the peroxynitrite formation leading to the significant bacterial reduction up to 7-log.

Combination of high-frequency ultrasound with propyl gallate for enhancing inactivation of bacteria in water and apple juice

This study evaluated a combination of high-frequency ultrasound (HFU, 1 MHz, 1.6 W/cm2).and a food-grade antioxidant, propyl gallate (PG, 10 mM), to enhance inactivation rates of Listeria innocua and Escherichia coli O157:H7 in water and clarified apple juice. Treatment times ranged from 5 to 20 min. The study also assessed the potential mechanisms of synergistic interactions based on an evaluation of changes in bacterial permeability, morphology, and intracellular oxidative stress. Within 15 min of treatment time, HFU + PG significantly (reduced by 5.5 log CFU/mL, P < 0.05) decreased the bacterial load of both L. innocua and E. coli O157:H7 from an initial inoculum of 6.5 log CFU/mL in both water and clarified apple juice. Overall, L. innocua demonstrated significantly higher resistance to inactivation than E. coli O157:H7 using a combination of HFU + PG. The synergistic antimicrobial activity of HFU+ PG resulted in enhanced membrane damage and oxidative stress induction in bacteria compared to the individual treatments of HFU or PG alone. Industrial relevanceThis study evaluates the synergistic combination of high frequency ultrasound and the food grade antioxidant propyl gallate for non-thermal processing of liquids. The results illustrate significant (>5 log CFU) and rapid inactivation (∼15 min) of inoculated model Gram positive and Gram negative bacteria in apple juice using a synergistic combination of propyl gallate and high frequency ultrasound. The synergistic interactions result in enhanced membrane damage and oxidative stress induction in bacteria. These results illustrate potential of the synergistic non-thermal thermal processing method for processing liquid beverages. Further studies are required for evaluating the scale up and optimization of the novel processing technology and enhancement in quality attributes of beverages.

Non-thermal plasma-based inactivation of bacteria in water using a microfluidic reactor

Failure of conventional water treatment systems may lead to the contamination of water sources, which can cause outbreaks of waterborne healthcare associated infections. Advanced oxidation processing by non-thermal plasma has the potential to treat water without the addition of chemicals. Antibiotic resistant Pseudomonas aeruginosa and Escherichia coli were chosen to investigate the use of non-thermal plasma generated in a microfluidic reactor to disinfect bacteria contaminated water. The microfluidic reactor used in this study utilized a dielectric barrier discharge, in a gas-liquid phase annular flow regime. Microbiological analysis of water inoculated with P. aeruginosa and E. coli was carried out before and after plasma treatment. Using air as the carrier gas, effective disinfection of water was achieved. At the lowest flow rate (35 µL/min), P. aeruginosa and E. coli viability were drastically reduced, with an approximate 8 log maximum decrease in viability following an estimated residence time of 5 s of plasma treatment. Scanning electron microscopy indicated changes in cell morphology due to the plasma treatment. Live/Dead assays revealed that the membranes of the cells had been damaged after plasma treatment. This work demonstrated that non-thermal plasma has the potential to disinfect against microbial contamination in water.

Self-Assembled PtII8 Metallosupramolecular Tubular Cage as Dual Warhead Antibacterial Agent in Water.

Development of photosensitizer-based self-assembled metallosupramolecular architectures with important applications is an emerging trend in supramolecular chemistry. In this study, we report a new benzothiadiazole-based tetra-pyridyl ligand (L), which upon self-assembly with a cis-block 90° Pt(II) acceptor generated an unprecedented tetrafacial Pt(II)8 photoactive tubular molecular cage (PMB1). This cage could bring an extraordinary photosensitizer, benzothiadiazole, into water which is otherwise insoluble. PMB1 is fluorescent and shows photogeneration of singlet oxygen in an aqueous medium. These features make PMB1 a potent antimicrobial agent in water in both the presence and absence of light. In comparison to its building blocks and water-soluble alkylated charged ligand ([LMe4][4NO3]), the cage shows much enhanced photoinduced antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) as a representative of Gram-positive bacteria and Pseudomonas aeruginosa (PA) as a representative of Gram-negative bacteria. PMB1 is successful at inactivating the bacterial growth via both photoactivation of molecular oxygen and membrane depolarization mechanisms, thus proving to be a dual warhead. Inactivation of bacteria in water using such a supramolecular architecture is noteworthy and can shed light on the generation of new antimicrobial supramolecular systems.

Inactivation of Bacteria in Water by Pulsed Power Injection

Inactivation of bacteria in water is demonstrated by using the pulsed‐power method. A large number of micro bubbles are successfully produced by injecting the pulsed power into the water, and then, shock waves are generated with collapse of the bubbles and the instantaneous heating of the water. The synergistic effect of the shock waves, electric shock, and radicals produced by electrical discharge may enhance the inactivation of bacteria. Bacillus subtilis as bacteria are released into the water in a water vessel. We found that 97% of the bacteria are inactivated by firing 100 shots of the pulsed‐power injection. The gross energy efficiency for inactivation reaches (0.6–8.8) × 1012 CFU/kWh. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Effect of Microwave Radiation on Regeneration of a Granulated Micelle–Clay Complex after Adsorption of Bacteria

Granulated micelle–clay complexes including the organic cation octadecyltrimethylammonium (ODTMA) were shown to be efficient in removal of total bacteria count (TBC) from water. Microwave (MW) heating of granules to restore bacterial removal was investigated. Drying of granules by MW required 20-fold less energy than by conventional heating. When water content of granules approached 10%, or less, their heating period by MW had to be below 1 min, e.g., 30 s, and less, in order to avoid ignition and irreversible structural changes. Structural and thermal properties of MW heated samples were studied by FT-IR spectra and thermo gravimetric analyses (TGA). Inactivation of bacteria in water was more efficient by MW than by conventional oven, or by electric plate. For elimination of bacteria from water, MW heating was at least five-fold more efficient than by conventional heating. The results have established an adequate regeneration procedure by MW heating at durations depending on the remaining percentage of water associated with the granules. Tests of first and second regenerations by MW heating, and HCl washing of columns, were carried out. It was concluded that MW treatment may be chosen for optimal regeneration of the granulated micelle–clay complex as an efficient and low-cost procedure.

Effect of Light-Induced ROS Generation Unit on Inactivation of Foodborne Pathogenic Bacteria in Water

Effect of Light-Induced ROS Generation Unit on Inactivation of Foodborne Pathogenic Bacteria in Water

In-situ synthesis of metal nanoparticles@metal−organic frameworks: Highly effective catalytic performance and synergistic antimicrobial activity

M-NP@Zn-BIF (M-NP = Ag or Cu nanoparticle; Zn-BIF is a zinc-based boron imidazolate framework, Zn2(BH(2-mim)3)2(obb); 2-mim = 2-methylimidazole; obb = 4,4′-oxybis(benzoate)) composites were successfully in-situ synthesized by utilizing the reducing ability of the BH bond contained in the Zn-BIF at room temperature without any additional chemical reduction reagents. These composites (225 μg/mL) exhibited excellent catalytic activity to convert 4-nitrophenol to 4-aminophenol in 2.5 min and 6 min with a conversion rate of 99.9 %, respectively. In addition, Ag@Zn-BIF (50 μg/mL) showed highly synergistic antibacterial activity against both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) with a bactericidal rate of approximately 99.9 %. An antibacterial mechanism was proposed for the generation of intracellular reactive oxygen species (ROS) levels. Superoxide radicals (O2–) and hydroxyl radicals (OH) formed during the antibacterial process were shown to accelerate the death of bacteria. They also exhibited highly photocatalytic activity for Rhodamine B (RhB). When the concentration of the composites is 1000 μg/mL, the photocatalytic efficiency of Ag@Zn-BIF and Cu@Zn-BIF increased by 31.62 and 18.13 times compared with Zn-BIF, respectively. All in all, this study developed a simple and versatile integrated platform for the removal of nitrophenols, organic dyes, and the effective inactivation of bacteria in water.

Few-layer MoS2 nanosheets-deposited on Bi2MoO6 microspheres: A Z-scheme visible-light photocatalyst with enhanced activity

A Z-scheme heterostructure, few-layer MoS2/Bi2MoO6, was synthesized and exhibited excellent photocatalytic activity in oxidation of organics and inactivation of bacteria in water under visible light. Layered MoS2 with a thickness of ∼1 nm were successfully deposited on the surface of Bi2MoO6 hierarchical microspheres. Compared with the MoS2 bulk, the band gap of layered MoS2 is widened, which is in favor of the separation of photogenerated charge carriers. After the introduction of MoS2, the photocurrent density was greatly improved on Bi2MoO6 electrode under visible light. This indicates that the recombination of photogenerated h+/e− was effectively suppressed with the modification of MoS2 nanosheets. Correspondingly, the photocatalytic oxidation activity in both the decomposition of organics in water and the inactivation of bacteria was enhanced. Possible mechanisms were proposed and discussed. This work sheds a light on the importance of applying layered MoS2 to improve the oxidation activity of a photocatalyst under visible light.

Preparation and antibacterial activity of chitosan-based nanocomposites containing bentonite-supported silver and zinc oxide nanoparticles for water disinfection

This study was conducted to develop novel chitosan nanocomposites and to optimize the minimum amount and contact time required to achieve complete inactivation of bacteria in water. Gram-negative Escherichia coli and Gram-positive Enterococcus faecalis bacteria were used to test the antibacterial activity of chitosan cross-linked with glutaraldehyde and chitosan nanocomposites in water. The silver and zinc oxide nanoparticles supported on bentonite were synthesized using microwave-assisted synthesis method. The resulting bentonite-supported silver and zinc oxide nanoparticles were dispersed in a chitosan biopolymer to prepare bentonite chitosan nanocomposites. The obtained bentonite chitosan nanocomposites were characterized with BET surface area measurements, FTIR, XRD, ICP-AES and SEM. When using cross-linked chitosan, it was demonstrated that factors such as pH, particle size and surface area influenced the inactivation of bacteria. For instance, the antibacterial activity of cross-linked chitosan was illustrated to increase with an increase in contact time. Meanwhile, an improvement in the inactivation activity was indicated with the introduction of silver and zinc oxide nanoparticles containing bentonite into the chitosan matrix. Although both silver and zinc oxide containing bentonite chitosan nanocomposites exhibited good antibacterial activity against bacteria, with removal efficiencies of at least 51%, the best antibacterial activity was demonstrated for silver–zinc oxide bentonite chitosan nanocomposite, with a removal efficiency of at least 78%. Furthermore, the antibacterial activity of bentonite chitosan nanocomposites was identified to be influenced by the amount of material, contact time and bacterial concentration. Finally, leaching tests demonstrated that bentonite chitosan nanocomposites were stable and, consequently, could be effectively used as antibacterial materials for water disinfection.

Fe vs. TiO2 Photo-assisted Processes for Enhancing the Solar Inactivation of Bacteria in Water.

Batch solar water disinfection (SODIS) is a known, simple and low-cost water treatment technology. SODIS is based on the synergistic action of temperature increase and light-assisted generation of Reactive Oxygen Species (ROS) on bacteria. ROS are generated via the action of solar photons on i) Natural Organic Matter (NOM), ii) some mineral components of water (Fe oxides or Fe-organic complexes, nitrogen compounds) and iii) endogenous bacteria photosensitizers (e.g. cytochrome). SODIS has proven its effectiveness for remote settlements or urban slums in regions with high incident solar radiation. All of the internal and external simultaneous processes are often driven by photoactive Fe-species present in the cell, as well as in the natural water sources. In SODIS, a temperature of 50 °C is required and due to this temperature dependence, only 1-2 L can be treated at a time. As required exposure time strongly depends on irradiation intensity and temperature, some SODIS households could be overburdened, leading to inadequate treatment and probable bacterial re-growth. This is why TiO(2) photocatalysis and Fe photo-assisted systems (i.e. photo-Fenton reactants) have been considered to enhance the photo-catalytic processes already present in natural water sources when exposed to solar light. Both TiO(2) and Fe-photoassisted processes, when applied to water disinfection aim to improve the performance of solar bacteria inactivation systems by i) enhancing ROS production, ii) making the process independent from the rise in temperature and as a consequence iii) allowing the treatment of larger volumes than 1-2 L of water and iv) prevent bacterial (re)growth, sometimes observed after sole solar treatment.

Development of electroless, potable water sterilisation device based on nanophase modified concrete pebbles

The present research provides an exciting new strategy for surface modification of concrete pebbles using nanomaterials. Cement nanocomposite modified concrete pebbles were used for the treatment of contaminated water. The cement nanobased composite coated concrete pebbles were prepared step by step, mixing and spinning cement with nanomaterials to make a cement nanocomposite paste, coating the cement nanocomposite paste onto the concrete pebbles and drying the coated pebbles in air for device fabrication. This system provides >99% removal of microbial load with only 4 min total contact time. The composite produces a high surface area system for the active and high throughput inactivation of bacteria in water and can be reusable. This not only decontaminates the biological contaminants, but also provides a rigid cement base, which does not allow the nanomaterials to come out into treated water. Moreover, the device does not require any source of energy/voltage or UV light for its functioning. It is very economical and reusable and allows effective bacterial decontamination along with providing a way out for preventing nanomaterial toxicity.

Rigorous kinetic modelling with explicit radiation absorption effects of the photocatalytic inactivation of bacteria in water using suspended titanium dioxide

This study is focused on the kinetic modelling of the photocatalytic inactivation of bacteria with suspended TiO2. A rigorous model based on a proposed reaction mechanism and accounting explicitly for the rate of photon absorption has been developed. The application of the general kinetic expression to limiting cases suggests that the interaction bacteria–catalyst can be considered to be weak. In contrast, a complex dependence on the radiation absorption rate must be taken into account, as very different radiation conditions may coexist inside the photoreactor, with high absorption rates in the region near to the radiation entrance window and much lower values on the opposite side of the photoreactor. The model has been successfully validated by experimental data, being able to reproduce the evolution of the concentration of viable bacteria in a wide range of values of TiO2 concentration, irradiation power and initial concentration of bacteria with a normalized root mean square logarithmic error of 5.3%. The values of the kinetic parameters are independent of the specific reactor setup or the operating conditions and therefore, the model can be used in a predictive way for photoreactor design and scaling-up, as well as for the optimization of other reactor configurations.

Photocatalytic inactivation of bacteria in water using suspended and immobilized silver-TiO2

Incorporation of silver to titanium dioxide is of great interest for photocatalytic disinfection applications since in addition to the enhancement of the electron–hole separation and interfacial charge transfer and the increase in the visible light response, silver compounds present a strong bactericidal effect. Ag/TiO2 materials used in suspension and immobilized in two different configurations (catalytic wall and fixed-bed reactors) have been prepared, characterized and tested using Escherichia coli as model microorganism. Although the incorporation of silver to powdered Degussa P25 TiO2 increases the activity, the thermal treatment required for the stabilization of the supported metal particles reduces the global efficiency. The comparison with experiments of dye photodegradation indicates that the activity of Ag/TiO2 is mainly due to the bactericidal role of silver and not to the enhancement of the photocatalytic mechanism. The best tested system has been proved to be the Ag/TiO2 catalytic wall reactor with a 0.6wt.% of Ag loading, showing a high activity both in relative (per gram of TiO2) and absolute terms, an optimal use of the radiation source, and a good stability of the film with negligible silver lixiviation, allowing the continuous treatment of water.

紫外線 光触媒処理による水中細菌の不活化

Inactivation of bacteria in water by the phtocatalytic oxidation and repression of the photoreactivation were studied. By counting bacteria with Standard Plate Count (SPC) method and heterotrophic bacteria in the river water, the inactivation and photoreactivation effects under the condition of 254nm-ultraviolet irradiation and that of the black light (maximum intensity: 352nm (300nm-440nm) ) irradiation was examined. The inactivation effect by 254nm-ultraviolet irradiation was particularly remarkable than the black light irradiation, while the oxidative degradation potential was almost equivalent. And it was proved that the photoreactivation of bacteria could be suppressed by using the photocatalyst with 254nm-ultraviolet irradiation. Generation of aldehydes was confirmed in the 254nm-ultraviolet irradiation with photocatalyst of tap water, river water, and groundwater, however, their amount were very limited in typical reaction time for inactivation.

Inactivation of indigenous bacteria in water by ozone and chlorine

The aim of this study was to compare the level of removal and inactivation of indigenous bacteria during drinking water production as evaluated by culture techniques and epifluorescent microscopic counts of metabolically active bacteria (in situ respiring bacteria i.e. able to metabolise CTC: cyano 2,3-ditolyl tetrazolium chloride). Two sets of experiments were designed: a) bacterial counts through a full scale drinking water treatment plant (multibarrier treatment including coagulation-flocculation-settling, sand filtration, ozonation, biological GAC filtration, post-chlorination) and distribution system; b) benchscale disinfection studies in order to re-evaluate the C.t values necessary to inactivate laboratory grown E. coli or indigenous bacteria from water by ozone and chlorine. Main conclusions of this study are: a) significant amounts of in situ respiring bacteria (undetected by the classical culture techniques) are detected in finished water; b) the efficiency of ozone and chlorine recorded by microscopic counts of active bacteria is much less than supposed by classical enumerations of culturable bacteria; c) previous results reported in the literature may have largely overestimated the bactericidal efficiency of disinfectants used for producing drinking water.