Higher Inactivation Efficiency Research Articles

Synthesis of activated carbon-supported nano copper oxide and its inactivation performance on Escherichia coli in water

Copper oxide (CuO) is limited in inactivating bacteria due to the deficiency of active Cu(I) that can catalyze dissolved oxygen to produce reactive oxygen radicals. A novel sterilization agent was developed to inactivate Escherichia coli (E. coli) by loading nano copper oxide onto activated carbon (nCuO/AC) with a facile impregnation method. Surface techniques proved that CuO with a size of 100–200 nm was evenly loaded on AC surface, which improved its dispersity and reactivity. XPS analysis further revealed a cycle of surface-bonded Cu(II) to Cu(I) in the nCuO matrix that was driven by reducing groups on AC surface such as hydroxyl. The resultant Cu(I) activated dissolved oxygen to produce reactive oxygen species for bacterial inactivation. Superoxide radical (•O2–) was proved to be the primarily oxidative species during the sterilization process by EPR analysis and quenching investigations. Therefore, the nCuO/AC achieved an enhanced inactivation efficiency of 6.0 log CFU/mL as compared to those of 1.1 and 0.4 log CFU/mL by the nCuO and AC, respectively. The above sterilization reaction was pH-dependent and high inactivation efficiency could be achieved under neutral conditions. Additionally, the nCuO/AC exhibited excellent stability with an inactivation efficiency of 5.4 log CFU/mL after 4 cycles. Spent nCuO/AC showed great potential in renewability because it could inactivate 5.5 log CFU/mL of E. coli by peeling off residual nCuO on AC surface with sulfuric acid and reloading new nCuO through impregnation, with a regeneration rate up to 97.2 %. The above results demonstrated that nCuO/AC could be a promising bactericidal material for water treatment.

Efficacy, kinetics, inactivation mechanism and application of cold plasma in inactivating Alicyclobacillus acidoterrestris spores

As spores of Alicyclobacillus acidoterrestris can survive traditional pasteurization, this organism has been suggested as a target bacterium in the fruit juice industry. This study aimed to investigate the inactivation effect of cold plasma on A. acidoterrestris spores and the mechanism behind the inactivation. The inactivation effect was detected by the plate count method and described by kinetic models. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), the detection of dipicolinic acid (DPA) release and heat resistance detection, the detection and scavenging experiment of reactive species, and cryo-scanning electron microscopy were used to explore the mechanism of cold plasma inactivation of A. acidoterrestris. The results showed that cold plasma can effectively inactivate A. acidoterrestris spores in saline with a 3.0 ± 0.3 and 4.4 ± 0.8 log reduction in CFU/mL, for 9 and 18 min, respectively. The higher the voltage and the longer the treatment time, the stronger the overall inactivation effect. However, a lower gas flow rate may increase the probability of spore contact with reactive species, resulting in better inactivation results. The biphasic model fits the survival curves better than the Weibull model. SEM and TEM revealed that cold plasma treatment can cause varying degrees of damage to the morphology and structure of A. acidoterrestris spores, with at least 50 % sustaining severe morphological and structural damage. The DPA release and heat resistance detection showed that A. acidoterrestris spores did not germinate but died directly during the cold plasma treatment. 1O2 plays the most important role in the inactivation, while O3, H2O2 and NO3− may also be responsible for inactivation. Cold plasma treatment for 1 min reduced A. acidoterrestris spores in apple juice by 0.4 ± 0.0 log, comparable to a 12-min heat treatment at 95 °C. However, as the treatment time increased, the survival curve exhibited a significant tailing phenomenon, which was most likely caused by the various compounds in apple juice that can react with reactive species and exert a physical shielding effect on spores. Higher input power and higher gas flow rate resulted in more complete inactivation of A. acidoterrestris spores in apple juice. What's more, the high inactivation efficiency in saline indicates the cold plasma device provides a promising alternative for controlling A. acidoterrestris spores during apple washing. Overall, our study provides adequate data support and a theoretical basis for using cold plasma to inactivate A. acidoterrestris spores in the food industry.

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.

Restricted Rotational Flexibility of the C5α-Methyl-Substituted Carbapenem NA-1-157 Leads to Potent Inhibition of the GES-5 Carbapenemase.

Carbapenem antibiotics are used as a last-resort treatment for infections caused by multidrug-resistant bacteria. The wide spread of carbapenemases in Gram-negative bacteria has severely compromised the utility of these drugs and represents a serious public health threat. To combat carbapenemase-mediated resistance, new antimicrobials and inhibitors of these enzymes are urgently needed. Here, we describe the interaction of the atypically C5α-methyl-substituted carbapenem, NA-1-157, with the GES-5 carbapenemase. MICs of this compound against Escherichia coli, Klebsiella pneumoniae, and Acinetobacter baumannii producing the enzyme were reduced 4-16-fold when compared to MICs of the commercial carbapenems, reaching clinically sensitive breakpoints. When NA-1-157 was combined with meropenem, a strong synergistic effect was observed. Kinetic and ESI-LC/MS studies demonstrated that NA-1-157 is a potent inhibitor of GES-5, with a high inactivation efficiency of (2.9 ± 0.9) × 105 M-1 s-1. Acylation of GES-5 by NA-1-157 was biphasic, with the fast phase completing within seconds, and the slow phase taking several hours and likely proceeding through a reversible tetrahedral intermediate. Deacylation was extremely slow (k3 = (2.4 ± 0.3) × 10-7 s-1), resulting in a residence time of 48 ± 6 days. MD simulation of the GES-5-meropenem and GES-5-NA-1-157 acyl-enzyme complexes revealed that the C5α-methyl group in NA-1-157 sterically restricts rotation of the 6α-hydroxyethyl group preventing ingress of the deacylating water into the vicinity of the scissile bond of the acyl-enzyme intermediate. These data demonstrate that NA-1-157 is a potent irreversible inhibitor of the GES-5 carbapenemase.

Bacterial decontamination of process liquids and paints in E-coating lines by pulsed electric field treatment

Cultivation-based and DNA-based methods for determining the bacterial load and the composition of the bacterial spectrum have been successfully established for media in electrodip painting, and used for the detailed analysis of the contamination situation in an E-coating system of an automobile plant in Germany. Dominating representatives of the genus Microbacterium spp., the orders Burkholderiales and Pseudomonadales, the family Cytophagaceae and the genera Corynebacterium spp., Sphingomonas spp., and Stenotrophomonas spp. were used for inactivation experiments. Different pulsed electric field (PEF) parameters were studied for an effective and target-directed inactivation of defined bacterial suspensions containing mixtures of Gram-positive as well as Gram-negative bacteria, but also single species suspensions in adequate liquids. PEF treatment with pulse durations longer than 1.0 µs effectively killed bacteria even in low conductivity media, regardless of whether the pulses were unipolar or bipolar, indicating that the choice of pulse shape does not limit the design of the PEF system. Model calculations showed that for efficient treatment in bypass mode, a high treatment flow rate is required rather than a high inactivation efficiency of the PEF treatment. By using specific treatment parameters, such as bipolar pulses of 50 k Vcm−1 and a treatment energy of 40 J mL−1, a significant reduction in both Gram-negative and Gram-positive bacteria (> 2 log10 reduction) can be achieved while minimizing electrode corrosion and coating degradation. PEF treatment proves to be an effective alternative to the use of biocides in an E-coating system and can help maintain a bacteriostatic environment in the system by operating at different points, in transfer flow or bypass mode, ensuring biocide-free operation.

Goethite-activated carbon as a persulfate activator for effective Escherichia coli inactivation

In this work, α-FeOOH modified activated carbon (FeOOH@AC) was prepared through wetness-impregnation and used as a persulfate (S2O82−, PS) activator to inactivate Escherichia coli in water. Surficial analysis displayed that micron-sized (0.5 to 1 μm) goethite was evenly distributed on AC. The structural ferric ions in the FeOOH matrix were partially reduced to ferrous ions by the hydroxyl of AC. The surface-bonded Fe2+ facilitated PS to produce hydroxyl and sulfate radicals (·OH and SO4·−). These radicals effectively inactivated Escherichia coli by destructing bacterial membrane. Therefore, the FeOOH@AC-PS system obtained a higher inactivation rate of 6.0 log as compared to 3.1 log and 0.4 log in the AC-PS and FeOOH-PS systems, respectively. After sterilization, the Escherichia coli did not regrow in the FeOOH@AC-PS system within 48 h, indicating its persistent growth inhibition by radicals. The FeOOH@AC-PS system also showed high inactivation efficiency over a pH range of 3 to 11 and excellent stability in cyclic test. Spent FeOOH@AC was amenable for effective regeneration by eliminating surficial iron oxides with hydrochloric acid and reloading FeOOH through wetness-impregnation with a regeneration rate up to 96.7 %. These results demonstrated that FeOOH@AC can effectively and stably activate PS for inactivating bacteria in water.

Comparative study on the effect of bacteriophage on MDR E.coli from Urinary tract infections

Abstract Introduction/Objective Background: Urinary tract infections (UTIs) associated with urethral catheters are the most common infections during hospitalization. Hospitalization's most common infections are urethral catheter-related UTIs. Bacteriophages infect bacteria exclusively. Phage therapy, especially in Eastern Europe, was widely used before antibiotics. Due to the overuse of antibiotics and the development of resistant bacteria, this therapy approach is regaining popularity. Methods/Case Report Subjects and methods: 2223 UAE-based UTI patients (4–68 years old) were examined. The isolated bacteria were identified biochemically and tested for antimicrobial susceptibility using Mueller-Hinton agar disk diffusion (Kirby Bauer's). TSA (Liofilchem, Italy) kept isolates at 4 °C.for each examination. Tryptic Soy agar (TSA; Liofilchem, Italy) was used to grow one isolated colony overnight at 37 °C. This culture was transferred aseptically to 10 mL of fresh TSB medium and grown overnight at 37 °C to 0.8 optical density. 10 ml CaCl2 in 100 ml LB homogenized EMIRATE sewage water. Overnight homogenates with 9 E. coli isolates—24 hours of 37°C incubation. Samples were centrifuged at 12,000x g for five minutes—a 0.45 mm Millipore (France) filter produced phage lysate. TSA (Liofilchem, Italy) was used as a culture medium, and the centrifuged supernatant as phage suspension for the double-layer method. After 37 °C, plaques were examined. Single-plaque isolations followed. EOP was measured on double-layer agar for bacteria with a clear lysis zone (Adams, 1959). calculated EOP. Phages tested individually. EZ1 and EZ2 were negatively stained with Na-phosphotungstate for morphotype. Results (if a Case Study enter NA) Results: This study found presumptive E. coli colonies in 478 of 2223 (21.5%) samples by plating pre-enriched samples on MacConkey. E. coli B2 and B4 were sensitive to Ciprofloxacin, but most strains were resistant to antibiotics. E. coli B3 was Metronidazole-sensitive. Individual E. coli strains were susceptible to phage infection. Podoviruses were the two phages. 3 log decreased due to E. coli growth. Conclusion This study shows that a single dose of phage can reduce pathogenic MDR E.coli. Phages' high bacterial inactivation efficiency, safety, and prolonged survival, even in urine samples, allow depth studies, especially in vivo studies, to control urinary tract infection and overcome E.coli resistance.

Decoupling locally enhanced electric field treatment (LEEFT) intensity and copper release by applying asymmetric electric pulses for water disinfection

Copper has well-known anti-microbial properties but is typically not considered for drinking water disinfection because of its health risk to human at efficient biocidal concentrations. Locally enhanced electric field treatment (LEEFT) is a cutting-edge technique that aims to inactivate bacteria by generating aqueous pores on the cell membrane through the application of a strong electric field. LEEFT can also increase the permeability of the cell membrane, which promotes the uptake of chemical disinfectants to reduce the required biocidal concentrations. Previously, a coaxial-electrode copper ionization cell (CECIC) was developed to combine copper disinfection with LEEFT, demonstrating superior disinfection efficiency with low effluent copper concentrations (<0.5 mg/L). However, using direct-current (DC) voltages results in a dilemma that a higher voltage is necessary for effective LEEFT disinfection, but a lower voltage is required to limit Cu release. Here, asymmetric electric pulses are employed to decouple the LEEFT intensity from copper release in the CECIC. In this case, LEEFT intensity is primarily determined by the pulse amplitude while the copper release is controlled by the pulse offset. We have demonstrated that the use of asymmetric electric pulses achieves significantly higher inactivation efficiency compared to the DC voltages with the similar level of Cu release. For the water with conductivity similar to tap water (∼100 μS/cm), a high inactivation efficiency of 4.7-log is achieved with only 0.49 mg/L copper release. These findings highlight the potential of asymmetric electric pulses as a promising alternative to DC voltages for the practical application of LEEFT-Cu systems in the future.

Spoilage bacteria growth reduction and microbial community variation of chilled chicken packaged in PA/PE treated with pulsed light

Maintaining the freshness and safe quality of chilled chicken is essential due to its high susceptibility to spoilage. To address this concern, pulsed light treatment, a strategy to reduce microbial loading of meat and extend food shelf life during storage, was studied. The results show that polyamide/polyethylene composite film bags (PA/PE) as packaging materials are suitable for pulsed light treatment with 80.67% energy transmission and high inactivation efficiency of microorganisms. Based on the results of total viable counts, pH, and total volatile basic nitrogen (TVB-N), the shelf life of chilled chicken in Group BP (pulsed light irradiation before packaging) and Group AP (pulsed light irradiation after packaging) was extended by 2–3 days compared to Group C (control, without pulsed light treatment). Importantly, the pulsed light treatment had no adverse impact on the odor of chilled chicken, as assessed by volatile organic compounds. The microbial community of chilled chicken was significantly altered by pulsed light treatment. In Group C, the dominant spoilage bacteria were Acinetobacter and Pseudomonas, with a relative abundance of 55.14%. In comparison, the top two relative abundances of Acinetobacter and Myroides in Group BP accounted for 67.93%, while in Group AP, Acinetobacter and Vagococcus were the predominant species, making up 62.80% of the microbial community. The findings suggest that pulsed light treatment is applicable to preserve chilled chicken and extend its shelf life.

Inactivation of chlorine-resistant bacteria (CRB) via various disinfection methods: Resistance mechanism and relation with carbon source metabolism

With the widespread use of chlorine disinfection, chlorine-resistant bacteria (CRB) in water treatment systems have gained public attention. Bacterial chlorine resistance has been found positively correlated with extracellular polymeric substance (EPS) secretion. In this study, we selected the most suitable CRB controlling method against eight bacterial strains with different chlorine resistance among chloramine, ozone, and ultraviolet (UV) disinfection, analyzed the resistance mechanisms, clarified the contribution of EPS to disinfection resistance, and explored the role of carbon source metabolism capacity. Among all the disinfectants, UV disinfection showed the highest disinfection capacity by achieving the highest average and median log inactivation rates for the tested strains. For Bacillus cereus CR19, the strain with the highest chlorine resistance, 40 mJ/cm2 UV showed a 1.90 log inactivation, which was much higher than that of 2 mg-Cl2/L chlorine (0.67 log), 2 mg-Cl2/L chloramine (1.68 log), and 2 mg/L ozone (0.19 log). Meanwhile, the UV resistance of the bacteria did not correlate with EPS secretion. These characteristics render UV irradiation the best CRB controlling disinfection method. Chloramine was found to have a generally high inactivation efficiency for bacteria with high chlorine-resistance, but a low inactivation efficiency for low chlorine-resistant ones. Although EPS consumed up to 56.7% of chloramine which an intact bacterial cell consumed, EPS secretion could not explain chloramine resistance. Thus, chloramine is an acceptable CRB control method. Similar to chlorine, ozone generally selected high EPS-secreting bacteria, with EPS consuming up to 100% ozone. Therefore, ozone is not an appropriate method for controlling CRB with high EPS secretion. EPS played an important role in all types of disinfection resistance, and can be considered the main mechanism for bacterial chlorine and ozone disinfection resistance. However, as EPS was not the main resistance mechanism in UV and chloramine disinfection, CRB with high EPS secretion were inactivated more effectively. Furthermore, carbon source metabolism was found related to the multiple resistance of bacteria. Those with low carbon source metabolism capacity tended to have higher multiple resistance, especially to chlorine, ozone, and UV light. Distinctively, among the tested gram-negative bacteria, in contrast to other disinfectants, chloramine resistance was negatively correlated with EPS secretion and positively correlated with carbon source metabolism capacity, suggesting a special disinfection mechanism.

Chlorination for Microcystis aeruginosa in the Late Lag Phase: Higher Inactivation Efficiency and Lower Environmental Risk

Chlorine is often employed to dispose cyanobacteria-laden waters for inactivating cells or improving its removal efficiency. However, previous studies mostly focused on cyanobacterial blooms occurring in the exponential or stationary phase, and thus, cyanobacterial characteristics in the unblooming stage (lag phase) and their influence on chlorination were not well understood. Herein, Microcystis aeruginosa in late lag and exponential phases with the same cell density were selected to simulate unblooming and blooming stages, respectively, and their response to chlorination was investigated. Compared with the exponential phase, results showed that cyanobacteria in the late lag phase consumed lower chlorine but produced higher intracellular reactive oxygen species (ROS). Then, higher rate constants of photosynthetic activity inactivation (kf) and membrane damage (km) were found in the late lag phase. Chlorine of >1.0 mg L–1 could degrade microcystin in this phase, and microcystin could be oxidized to below 1.0 μg L–1 by 2.0 mg L–1 chlorine. Besides, lower extracellular dissolved organic carbon (DOC), UV absorbance at 254 nm (UV254), and their variation range were also observed in the late lag phase. These findings indicated that the chlorination performance in the two phases is different, and thus, it is necessary to reduce the applied dosage of chlorine to treat cyanobacteria-laden source waters in the (late) lag phase.

Assessment of pathogenic microorganisms inactivation by electron beam irradiation and physico-chemical characteristics evaluation in sewage sludge

This study mainly focused on detection and quantification of the Salmonella Enterica (S1), Salmonella Bongori (S2), enterococci, and E. coli in domestic sewage sludge samples (SSS) from two different sampling locations which are denominated as point A and B. The aim of this study was to validate the efficiency of electron beam irradiation (EBI) treatment on the inactivation of S1, S2, enterococci, and E. coli. The inactivation was measured in terms of different dose rates by varying irradiation current. Meantime, the absorbed dose and energy were fixed for each experimental portfolio. The dose rate was determined by correlation with the conveyor speed. Irradiation was performed in batch mode and the irradiated samples were then accessed for the detection of S1, S2 enterococci, and E. coli. Detection of S1, S2, and enterococci was conducted based on APHA 9620 and APHA 9260 standard methods. Meanwhile, E. coli were detected by using APHA 9221 standard method. The results attained clearly indicated that EBI treatment is effective on the inactivation of theS1, S2, enterococci and E. coli. The higher inactivation efficiency was observed at a lower dose rate with higher energy. The higher inactivation kinetics constant, k were attained at higher irradiation energy. Thus, this outcome proofs that irradiation energy effectively plays a crucial role in the inactivation of the targeted microorganisms. The physico-chemical properties of the SSS remain intact with variable dose rates. This outcome suggested that the EBI treatment is able to inactivate the microorganisms present onto the SSS without imparting many changes to the properties of the sludge samples. The bacterial re-growth onto the irradiated samples was monitored over a prolonged storage of 60 days. The survival of bacteria was detected for up to 7 days at a very low level. However, the re-growth of the bacteria was not detected at 60 days of storage.

Inactivation and subsequent reactivation of Aspergillus species by the combination of UV and monochloramine: Comparisons with UV/chlorine

Ultraviolet (UV)/monochloramine (NH2Cl) as an advanced oxidation process was firstly applied for Aspergillus spores inactivation. This study aims to: i) clarify the inactivation and photoreactivation characteristics of UV/NH2Cl process, ii) compared with UV/Cl2 in inactivation efficiency, photoreactivation and energy consumption. The results illustrated that UV/NH2Cl showed better inactivation efficiency than that of UV alone and UV/Cl2, and could effectively control the photoreactivation. For instance, the inactivation rates for Aspergillus flavus, Aspergillus niger and Aspergillus fumigatus in the processes of UV/NH2Cl (2.0 mg/L) was 0.034, 0.030 and 0.061 cm2/mJ, respectively, which were higher than that of UV alone (0.027, 0.026 and 0.024 cm2/mJ) and UV/Cl2 (0.023, 0.026 and 0.031 cm2/mJ). However, there was no synergistic effect for Aspergillus flavus and Aspergillus fumigatus. As for Aspergillus niger, the best synergistic effect can reach 1.86-log10. This may be due to their different resistance to disinfectants, which were related to the size, an outer layer of rodlets (hydrophobins) and pigments. After UV/NH2Cl inactivation, the degree of cell membrane damage and intracellular reactive oxygen species were higher than that of UV alone. UV/NH2Cl had the advantages of high inactivation efficiency and inhibition of photoreactivation, which provides a new entry point for the disinfection of waterborne fungi.

A 265-Nanometer High-Power Deep-UV Light-Emitting Diode Rapidly Inactivates SARS-CoV-2 Aerosols.

ABSTRACTSevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection (COVID-19) is an acute respiratory infection transmitted by droplets, aerosols, and contact. Controlling the spread of COVID-19 and developing effective decontamination options are urgent issues for the international community. Here, we report the quantitative inactivation of SARS-CoV-2 in liquid and aerosolized samples by a state-of-the-art, high-power, AlGaN-based, single-chip compact deep-UV (DUV) light-emitting diode (LED) that produces a record continuous-wave output power of 500 mW at its peak emission wavelength of 265 nm. Using this DUV-LED, we observed a greater-than-5-log reduction in infectious SARS-CoV-2 in liquid samples within very short irradiation times (<0.4 s). When we quantified the efficacy of the 265-nm DUV-LED in inactivating SARS-CoV-2, we found that DUV-LED inactivation of aerosolized SARS-CoV-2 was approximately nine times greater than that of SARS-CoV-2 suspension. Our data demonstrate that this newly developed, compact, high-power 265-nm DUV-LED irradiation system with remarkably high inactivation efficiency for aerosolized SARS-CoV-2 could be an effective and practical tool for controlling SARS-CoV-2 spread.IMPORTANCE We developed a 265-nm high-power DUV-LED irradiation system and quantitatively demonstrated that the DUV-LED can inactivate SARS-CoV-2 in suspensions and aerosols within very short irradiation times. We also found that the inactivation effect was about nine times greater against aerosolized SARS-CoV-2 than against SARS-CoV-2 suspensions. The DUV-LED has several advantages over conventional LEDs and mercury lamps, including high power, compactness, and environmental friendliness; its rapid inactivation of aerosolized SARS-CoV-2 opens up new possibilities for the practical application of DUV-LEDs in high-efficiency air purification systems to control airborne transmission of SARS-CoV-2.

A novel water disinfection method based on dual-wavelength UV radiation of KrCl (222 nm) and XeBr (282 nm) excilamps

Dual-wavelength ultraviolet (DWUV) radiation has emerged as an advanced tool for water disinfection in view of potential synergistic effect. In the present study, E. coli and E. faecalis in synthetic water at pH 6.4–7.0 were inactivated under simultaneous exposure to DWUV radiation of KrCl (222 nm) and XeBr (282 nm) excilamps (UV222/UV282) at different irradiances. A time-based synergistic effect in terms of 5-log (complete) inactivation was found in all dual-wavelength combinations with synergistic coefficients ranging from 1.3 to 3.8. No dose-based synergistic effect was observed due to comparable dose requirements for single-UV and DWUV disinfection. The DWUV doses for 5-log inactivation were low in all cases and varied in the range of 2.3–5.4 mJ/cm2. Inactivation by advanced oxidation process using hydrogen peroxide (UV222/UV282/H2O2) also showed a time-based synergy and required low doses. The synergistic inactivation at 222 and 282 nm was proposed to be caused by simultaneous action of two key mechanisms: 1) the proteins destruction with subsequent DNA photo- and dark-repair suppression, 2) direct and indirect DNA damage. Photo- and dark-repair experiments supported this concept and showed no cell reactivation after DWUV exposure. High inactivation efficiency, low dose requirements, absence of oxidant’s excess and environmental safety make the UV222/UV282 method more advantageous compared to single-UV and H2O2-assisted method, and applicable to fast and energy-efficient disinfection of low turbid waters.

Effective inactivation of Escherichia coli in aqueous solution by activated carbon-supported α-FeOOH as heterogeneous Fenton catalyst with high stability and reusability

Activated carbon-supported goethite (α-FeOOH@AC) was prepared by a simple impregnation method to catalyze hydrogen peroxide (H2O2) for effective inactivation of Escherichia coli (E. coli) with α-FeOOH and AC as controls. As expected, α-FeOOH particles were uniformly distributed on AC surfaces and surface-bound Fe(III) was partially converted to Fe(II) by structural hydroxyl groups of AC. The resultant Fe(II) catalyzed H2O2 to generate hydroxyl radicals (·OH) for effective E. coli inactivation by destroying its membrane and intracellular substances. The α-FeOOH@AC-H2O2 system therefore achieved an effective inactivation efficiency of 4.5 log, which was much higher than 1.6 log of the α-FeOOH-H2O2 system and 1.9 log of the AC-H2O2 system. Besides, due to the cycle of Fe(III)/Fe(II) redox on AC surface during reaction, high inactivation efficiency and low leaching iron concentration of 0.29 mg/L could be achieved at neutral condition. In addition, the α-FeOOH@AC showed excellent stability and reusability, and the used α-FeOOH@AC could be refreshed by eluting surface-bound iron oxides and reloading α-FeOOH particles with the above impregnation method. Our study demonstrated that α-FeOOH@AC is an effective and stable heterogeneous Fenton catalyst for the inactivation of E. coli in surface water treatment.

Three-dimensional, flow-through silver-magnetite nanocomposite–modified reactive electrochemical system with slow silver ions release for efficient bacterial disinfection of sewage

Although water and wastewater have a myriad of contaminants, waterborne pathogens represent the main threat to negatively affect public health, especially in developing countries. Therefore, there is an urgent demand to develop reliable, highly efficient water disinfection technologies. Here, we developed a high-throughput, flow-through silver-magnetite (Ag-Fe3O4)-modified electrochemical system, which allows high bacterial inactivation with a low energy consumption owing to the enhanced convective mass transport. The reactive electrochemical disinfection system equipped with the Ag-Fe3O4-modified anodes exhibited high bacterial inactivation efficiency (up to 5 logs) at a relatively low applied current density (i.e., 2.1–20.8 µA/cm2) with a slow, controllable release of Ag ions at a ppb level and low energy consumption of 0.3–0.9 Wh/m3. Furthermore, the electrochemical system exhibited a reasonably high bacterial inactivation efficiency of E. coli, Salmonella, and Pseudomonas aeruginosa when fed with secondary-treated sewage at a water flow rate of 5 mL/min and an applied current density of 104 µA/cm2, suggesting that the electrochemical devices can potentially use for water and wastewater disinfection.

Investigation of the chemical characteristics and anticancer effect of plasma‐activated water: The effect of liquid temperature

AbstractThe liquid temperature during the preparation of plasma‐activated water (PAW) seriously affects the PAW chemical characteristics and its biological effect. In this study, four different temperatures (4°C, 25°C, 40°C, and 70°C) of deionized water are selected as variable parameters to investigate the effect on PAW. The results show that the physicochemical properties and the concentration of reactive oxygen and nitrogen species of PAW are significantly reduced when the temperatures are higher than 25°C; moreover, the above indexes are slightly decreased when the temperature is down to 4°C. Furthermore, by comparing the results of cell viability and apoptosis, it is found that the PAW of 25°C has a higher inactivation efficiency than other temperatures. Research on the temperature effect during PAW production is beneficial for tailoring the plasma–liquid system to enhance production efficiency.

Smartphone-powered efficient water disinfection at the point of use

Clean water free of bacteria is a precious resource in areas where no centralized water facilities are available. Conventional chlorine disinfection is limited by chemical transportation, storage, and the production of carcinogenic by-products. Here, a smartphone-powered disinfection system is developed for point-of-use (POU) bacterial inactivation. The integrated system uses the smartphone battery as a power source, and a customized on-the-go (OTG) hardware connected to the phone to realize the desired electrical output. Through a downloadable mobile application, the electrical output, either constant current (20–1000 µA) or voltage (0.7–2.1 V), can be configured easily through a user-friendly graphical interface on the screen. The disinfection device, a coaxial-electrode copper ionization cell (CECIC), inactivates bacteria by low levels of electrochemically generated copper with low energy consumption. The strategy of constant current control is applied in this study to solve the problem of uncontrollable copper release by previous constant voltage control. With the current control, a high inactivation efficiency of E. coli (~6 logs) is achieved with a low level of effluent Cu (~200 µg L−1) in the water samples within a range of salt concentration (0.2–1 mmol L−1). The smartphone-based power workstation provides a versatile and accurate electrical output with a simple graphical user interface. The disinfection device is robust, highly efficient, and does not require complex equipment. As smartphones are pervasive in modern life, the smartphone-powered CECIC system could provide an alternative decentralized water disinfection approach like rural areas and outdoor activities.

Response of high-, mid- and low-abundant taxa and potential pathogens to eight disinfection methods and their interactions in domestic hot water system

Eight disinfection methods were applied to control biofilm contamination in domestic hot water system. The inactivation efficiency, responses of high- (≥1%), mid- (0.1% ~ 1%) and low-abundant taxa (≤0.1%) to disinfection, and interactions within and across three sub-communities were investigated. Ultraviolet was the most effective disinfection method for total bacteria and Escherichia coli, and chlorine dioxide had the highest inactivation efficiency on heterotrophic bacteria, while silver ions exhibited poor performance on all of them. At the phylum level, the responses of microorganisms to eight disinfection methods were different, but Proteobacteria and Firmicutes dominated in most samples. Eight disinfection methods had a greater impact on the proportion of high- and mid-abundant taxa than that of low-abundant taxa, and led to dissimilar transformations of genera among high-, mid- and low-abundant taxa in each sample. High-, mid- and low-abundant taxa of different samples showed similar structures and were roughly clustered into three Groups. Moreover, high-abundant taxa had more complex internal interactions than mid- and low-abundant taxa, and mainly presented co-occurrence patterns. The associations between high- and low-abundant taxa were close, and some low-abundant genera were identified as hub bacteria, such as Paracoccus, Thioalkalispira and Flavitalea. Furthermore, a total of 23 potential pathogens were detected in this study, and they mainly showed positive interactions, with Mycobacteria and Streptococcus as keystone genera. These results highlight the dissimilar responses of high-, mid- and low-abundant taxa to disinfection, and the critical role of some low-abundant genera in the microbial network, as well as the co-occurrence patterns among potential pathogens.