Inactivation Efficiency Research Articles

Removal of antibiotic resistant bacteria and plasmid-encoded antibiotic resistance genes in water by ozonation and electro-peroxone process

The electro-peroxone (EP) process is an electricity-based oxidation process enabled by electrochemically generating hydrogen peroxide (H2O2) from cathodic oxygen (O2) reduction during ozonation. In this study, the removal of antibiotic resistant bacteria (ARB) and plasmid-encoded antibiotic resistance genes (ARGs) during groundwater treatment by ozonation alone and the EP process was compared. Owing to the H2O2-promoted ozone (O3) conversion to hydroxyl radicals (•OH), higher •OH exposures, but lower O3 exposures were obtained during the EP process than ozonation alone. This opposite change of O3 and •OH exposures decreases the efficiency of ARB inactivation and ARG degradation moderately during the EP process compared with ozonation alone. These results suggest that regarding ARB inactivation and ARG degradation, the reduction of O3 exposures may not be fully counterbalanced by the rise of •OH exposures when changing ozonation to the EP process. However, due to the rise of •OH exposure, plasmid DNA was more effectively cleaved to shorter fragments during the EP process than ozonation alone, which may decrease the risks of natural transformation of ARGs. These findings highlight that the influence of the EP process on ARB and ARG inactivation needs to be considered when implementing this process in water treatment.

Recent Advances in High Pressure Processing of Milk and Milk Products - A review

As the global consumers’ demand towards minimally processed freshlike foods has been continuously increasing, efforts to develop novel food processing technologies have been intensified. Among non-thermal food processing technologies, high pressure processing (HPP) seems to be more advantageous due to its environmentally friendly nature, cost efficiency, suitability for processing foods in any form and its positive impacts on foods’ shelf-life as well as providing efficient microbial safety. Microbiological inactivation efficiency of HPP has been well documented but the role of this technology in digestion efficiency of milk compounds is yet to be elucidated in detail. Also, the potential safety hazards and challenges of HPP in foods require more intense studies. This review deals with the recent developments in HPP treatment to milk and milk products.

Photo-Fenton and TiO2 Photocatalytic Inactivation of Model Microorganisms under UV-A; Comparative Efficacy and Optimization.

Photocatalytic inactivation of pathogens in aqueous waste is gaining increasing attention. Several homogeneous and heterogeneous photocatalytic protocols exist using the Fenton's reagent and TiO2, respectively. A comprehensive study of homogeneous and heterogeneous photocatalysis on a range of microorganisms will significantly establish the most efficient method. Here, we report a comparative study of TiO2- and Fe+3-based photocatalytic inactivation under UV-A of diverse microorganisms, including Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria, bacterial spores (Bacillus stearothermophilus spores) and viruses (MS2). We also present data on the optimization of TiO2 photocatalysis, including optimal catalyst concentration and H2O2 supplementation. Our results indicate that both photo-Fenton and TiO2 could be successfully applied for the management of microbial loads in liquids. Efficient microorganism inactivation is achieved with homogeneous photocatalysis (7 mg/L Fe+3, 100 mg/L H2O2, UV-A) in a shorter processing time compared to heterogeneous photocatalysis (0.5 g/L TiO2, UV-A), whereas similar or shorter processing is required when heterogenous photocatalysis is performed using microorganism-specific optimized TiO2 concentrations and H2O2 supplementation (100 mg/L); higher H2O2 concentrations further enhance the heterogenous photocatalytic inactivation efficiency. Our study provides a template protocol for the design and further application for large-scale photocatalytic approaches to inactivate pathogens in liquid biomedical waste.

Structural and Mechanistic Basis for the Inactivation of Human Ornithine Aminotransferase by (3S,4S)-3-Amino-4-fluorocyclopentenecarboxylic Acid.

Ornithine aminotransferase (OAT) is overexpressed in hepatocellular carcinoma (HCC), and we previously showed that inactivation of OAT inhibits the growth of HCC. Recently, we found that (3S,4S)-3-amino-4-fluorocyclopentenecarboxylic acid (5) was a potent inactivator of γ-aminobutyric acid aminotransferase (GABA-AT), proceeding by an enamine mechanism. Here we describe our investigations into the activity and mechanism of 5 as an inactivator of human OAT. We have found that 5 exhibits 10-fold less inactivation efficiency (kinact/KI) against hOAT than GABA-AT. A comprehensive mechanistic study was carried out to understand its inactivation mechanism with hOAT. pKa and electrostatic potential calculations were performed to further support the notion that the α,β-unsaturated alkene of 5 is critical for enhancing acidity and nucleophilicity of the corresponding intermediates and ultimately responsible for the improved inactivation efficiency of 5 over the corresponding saturated analogue (4). Intact protein mass spectrometry and the crystal structure complex with hOAT provide evidence to conclude that 5 mainly inactivates hOAT through noncovalent interactions, and that, unlike with GABA-AT, covalent binding with hOAT is a minor component of the total inhibition which is unique relative to other monofluoro-substituted derivatives. Furthermore, based on the results of transient-state measurements and free energy calculations, it is suggested that the α,β-unsaturated carboxylate group of PLP-bound 5 may be directly involved in the inactivation cascade by forming an enolate intermediate. Overall, compound 5 exhibits unusual structural conversions which are catalyzed by specific residues within hOAT, ultimately leading to an enamine mechanism-based inactivation of hOAT through noncovalent interactions and covalent modification.

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.

Photocatalytic activity of P-doped TiO2 photocatalyst

In this study, P-doped TiO2 photocatalysts with different molar percentages (in the range 0.071–1.25 mol %) of the non-metallic element were prepared and their photocatalytic activity under visible light irradiation was tested. All achieved samples were characterized by XRD, Raman, UV–Vis DRS and SEM–EDX techniques. XRD and Raman analysis showed that all doped photocatalysts were in anatase phase and evidenced that P ions were successfully incorporated into the TiO2 crystal lattice, affecting also the crystallinity degree of the P-doped TiO2 photocatalysts. Noticeably, the UV–Vis DRS spectra evidenced that the highest redshift in absorption edge was observed for the photocatalyst with the lowest P content (0.071PT), which showed also the lowest bandgap (2.9 eV). The photocatalytic performances of all P-doped TiO2 samples were compared with that of commercial TiO2 by evaluating the decolorization of methylene blue (MB) dye under visible light irradiation. Results showed that phosphorus doping strongly promoted photocatalytic activity in the presence of visible light. Furthermore, the most active photocatalyst in visible light tests (0.071PT) also showed better photocatalytic activity than commercial TiO2 in the decolorization of MB under simulated sunlight irradiation. Finally, 0.071PT photocatalyst was preliminarily tested against Escherichia coli (E. coli) under simulated solar light, showing an inactivation efficiency of 90% after 2 h of treatment time.Graphical abstract

Plasma-Generated Nitric Oxide Water Mediates Environmentally Transmitted Pathogenic Bacterial Inactivation via Intracellular Nitrosative Stress.

Over time, the proportion of resistant bacteria will increase. This is a major concern. Therefore, effective and biocompatible therapeutic strategies against these bacteria are urgently needed. Non-thermal plasma has been exhaustively characterized for its antibacterial activity. This study aims to investigate the inactivation efficiency and mechanisms of plasma-generated nitric oxide water (PG-NOW) on pathogenic water, air, soil, and foodborne Gram-negative and Gram-positive bacteria. Using a colony-forming unit assay, we found that PG-NOW treatment effectively inhibited the growth of bacteria. Moreover, the intracellular nitric oxide (NO) accumulation was evaluated by 4-amino-5-methylamino-2',7'-dichlorofluorescein diacetate (DAF-FM DA) staining. The reduction of viable cells unambiguously indicates the anti-microbial effect of PG-NOW. The soxR and soxS genes are associated with nitrosative stress, and oxyR regulation corresponds to oxidative stress in bacterial cells. To support the nitrosative effect mediated by PG-NOW, we have further assessed the soxRS and oxyR gene expressions after treatment. Accordingly, soxRS expression was enhanced, whereas the oxyR expression was decreased following PG-NOW treatment. The disruption of cell morphology was observed using scanning electron microscopy (SEM) analysis. In conclusion, our findings furnish evidence of an initiation point for the further progress and development of PG-NOW-based antibacterial treatments.

An excimer lamp to provide far-ultraviolet C irradiation for dining-table disinfection

Dining tables may present a risk to diners by transmitting bacteria and/or viruses. Currently, there is a lack of an environmental-friendly and convenient means to protect diners when they are sitting together. This investigation constructed far-UVC excimer lamps to disinfect dining-table surfaces. The lamps were mounted at different heights and orientations, and the irradiance on table surfaces was measured. The irradiation doses to obtain different inactivation efficiencies for Escherichia coli (E. coli) were provided. In addition, numerical modeling was conducted for irradiance and the resulting inactivation efficiency. The surface-to-surface (S2S) model was validated with the measured irradiance. The germicidal performance of far-UVC irradiation, the far-UVC doses to which diners were exposed, and the risk of exposure to the generated ozone were evaluated. The results revealed that an irradiation dose of 12.8 mJ/cm2 can disinfect 99.9% of E. coli on surfaces. By varying the lamp irradiance output, the number and positions of the lamps, the far-UVC irradiation can achieve a 3-log reduction for a dining duration of 5 min. Besides, the far-UVC lamp has a low damage risk to diners when achieving an effective inactivation rate. Moreover, there is virtually no ozone exposure risk in a mechanically ventilated dining hall.

Inactivation mechanism of E. coli in water by enhanced photocatalysis under visible light irradiation

Developing efficient and economical technologies for drinking water disinfection remains a challenge. We synthesized Ag/AgBr/LDH doped with various silver mass concentrations and explored its ability to inactivate E. coli under visible light irradiation (λ ≥ 400 nm). Our results indicated a total inactivation of E. coli (107 CFU·mL−1) within 80 min using 2 % Ag/AgBr/LDH in a laboratory-scale test. The method was evaluated for disinfecting three effluent samples collected from one drinking water treatment plant, covering representative water treatment processes. After five consecutive runs, the inactivation efficiency decreased slightly to 89 % in CFU·mL−1, indicating that the photocatalysts had excellent stability and reusability. The mechanisms were analyzed by combining chemical and biological methods. It was verified that singlet oxygen (1O2), hydrogen peroxide (H2O2), and photo-generated electrons (e−) were significant contributors to the inactivation process. Scanning electron microscopy images analysis showed the disruption of the membrane integrity of E. coli by photocatalytic oxidation. Internal component leakage and reduced enzyme activity were also observed in terms of K+ leakage, β-galactosidase activity, and antioxidant enzyme activity. The results by the transcriptomic analysis implied that Ag/AgBr/LDH regulating the oxidative stress response and cell membrane damage related genes was the main inactivation mechanism.

Application of NaCl in Cold Atmospheric Plasma Jet and Plasma-Activated Solution to Enhance Virus Inactivation

Viruses are serious pathogenic contaminants that gravely threaten human health. There is an urgent need for environment-friendly and novel disinfection methods to inactivate various viruses. In this study, we applied the technique of cold atmospheric plasma (CAP) for virus disinfection. Particularly, we utilized the cold atmospheric plasma jet (CAPJ) and the plasma-activated solution (PAS) approaches for the treatment of bacteriophage MS2, and we added NaCl in the treatment system to enhance the disinfection efficiency. The inactivation effects under different CAPJ-PAS conditions using various plasma working gases were investigated. Also, the involved inactivation mechanisms due to respective active species were scrutinized. Our results showed that the addition of NaCl could considerably enhance the virus inactivation efficiency in the air/oxygen-CAPJ-PAS treatment, and during the direct CAPJ treatment, the primary inactivation factors were attributed to ·OH, <sup>1</sup>O<sub>2</sub>, ONOOH and ClO<sup>-</sup>, while for the indirect PAS treatment, the major inactivation contributors stemmed from <sup>1</sup>O<sub>2</sub> and ClO<sup>-</sup>. This work therefore demonstrates the usefulness of NaCl in the CAPJ-PAS treatment in the virus inactivation and offers new perspectives on the application of CAP technology in disinfection of viruses.

ROS conversion promotes the bactericidal efficiency of Eosin Y based photodynamic therapy.

Photodynamic therapy (PDT) is becoming an efficient antibacterial strategy without drug-resistance. Here, we report a promising reactive oxygen species (ROS) conversion strategy to increase the antibacterial efficiency of an Eosin Y (EOS)-based PDT system. Based on visible-light illumination, EOS generates a high concentration of singlet oxygen (1O2) in the solution. With the introduction of HEPES in the EOS system, it can almost completely convert 1O2 to hydrogen peroxide (H2O2). The orders-of-magnitude increases in the half-lives of the ROS (H2O2vs.1O2) present in the solution can enable more persistent oxidation ability. Thus, it is able to increase the bactericidal efficiency (against S. aureus) from 37.9% to 99.9%, promote the inactivation efficiency of methicillin-resistant S. aureus (MRSA) from 26.9% to 99.4%, and enhance the eradication rate of MRSA biofilm from 69% to 90%. Further in vivo investigation showed that the increased oxidation ability of the EOS/HEPES PDT system can enable quicker healing and maturing (even better than that for vancomycin administration) of MRSA-infected skin wounds on rats. This strategy may find many creative applications for the efficient eradication of bacteria and other pathogenic microorganisms.

Photocatalytic degradation effect and mechanism of Karenia mikimotoi by non-noble metal modified TiO2 loading onto copper metal organic framework (SNP-TiO2@Cu-MOF) under visible light.

In this study, the SNP-TiO2@Cu-MOF composite was prepared successfully by loading non-noble metal modified TiO2 (SNP-TiO2) on the surface of copper metal organic skeleton (Cu-MOF), and compared the inactivation efficiency of different photocatalysts to Karenia mikimotoi (K. mikimotoi) under visible light. The obtained photocatalyst had the characteristic crystal faces of Cu-MOF and SNP- TiO2, and contained functional groups such as Cu-O, -COOH, N-O, P-O, etc., which indicated the structural stability of the photocatalyst. The band gap of SNP-TiO2@Cu-MOF composite was 2.82eV, and it had great light absorption ability in visible light region. It was proved to be a mesoporous adsorption material, which had a huge specific surface area (245m2/g). Compared with other photocatalysts, SNP-TiO2@Cu-MOF composite showed the strongest photocatalytic activity. When the concentration of composite material was set to 100mg/L and the exposure time was 6h, the visible light photocatalytic inactivation efficiency of K. mikimotoi was 93.75 %. By measuring various metabolic indexes of K. mikimotoi under the action of different photocatalysts for 1h, it was confirmed that cell inactivation was due to the increased membrane permeability and degradation of photosynthetic pigments and main life proteins. This research showed that SNP-TiO2@Cu-MOF composite material was full of great potential and application prospect in controlling the outbreak of eutrophication.

Application of Antimicrobial Photodynamic Therapy for Inactivation of Acinetobacter baumannii Biofilms.

Acinetobacter baumannii is a dangerous hospital pathogen primarily due to its ability to form biofilms on different abiotic and biotic surfaces. The present study investigated the effect of riboflavin- and chlorophyllin-based antimicrobial photodynamic therapy, performed with near-ultraviolet or blue light on the viability of bacterial cells in biofilms and their structural stability, also determining the extent of photoinduced generation of intracellular reactive oxygen species as well as the ability of A. baumannii to form biofilms after the treatment. The efficacy of antimicrobial photodynamic therapy was compared with that of light alone and the role of the photosensitizer type on the photosensitization mechanism was demonstrated. We found that the antibacterial effect of riboflavin-based antimicrobial photodynamic therapy depends on the ability of photoactivated riboflavin to generate intracellular reactive oxygen species but does not depend on the concentration of riboflavin and pre-incubation time before irradiation. Moreover, our results suggest a clear interconnection between the inactivation efficiency of chlorophyllin-based antimicrobial photodynamic therapy and the sensitivity of A. baumannii biofilms to used light. In summary, all the analyzed results suggest that riboflavin-based antimicrobial photodynamic therapy and chlorophyllin-based antimicrobial photodynamic therapy have the potential to be applied as an antibacterial treatment against A. baumannii biofilms or as a preventive measure against biofilm formation.

Enhanced activation of peroxymonosulfate by a floating Cu0-MoS2/C3N4 photocatalyst under visible-light assistance for tetracyclines degradation and Escherichia coli inactivation

Transition metal-based photocatalysts have recently attracted much attention in photo-induced Peroxymonosulfate (PMS) activation systems. Herein, a novel floating catalyst Cu0-MoS2/C3N4-expanded graphite (Cu-MSCN-EG) was prepared by a chemical reduction method and applied as a PMS activator to remove tetracyclines (TCs) and inactivate Escherichia coli under visible light irradiation in aqueous solution. Over 99.0 % of TCs and Escherichia coli could be removed and inactivated within 1 h in Vis/PMS/Cu-MSCN-EG system. Compared to the MoS2/C3N4-EG system, the loading of zero-valent copper in the Vis/PMS/Cu-MSCN-EG system increased the reaction rate by 278 %. Raman spectroscopy and density functional theory (DFT) calculations indicated that ·OH and 1O2 were generated via two different adsorption patterns between PMS and copper (≡Cu+-OSO3-–OH and ≡Cu+–OH-OSO3-). With the light assistance, the photo-induced electrons reduced the copper leaching and enhanced the generation of ·SO4- and ·O2–, leading to a high recyclability and mineralization rate. Overall, this study provides a new insight into the fabrication of copper-based PMS activator with high efficiency and durability for contaminants degradation and pathogen inactivation.

Magnetic-field-induced simultaneous charge separation and oxygen transfer in photocatalytic oxygen activation for algae inactivation

Photocatalytic oxygen activation is an excellent strategy for algae control in water. However, the fast recombination of photogenerated charge and slow rate of oxygen transfer limit the reactive oxygen species generation efficiency for algae inactivation. Herein, to solve above issues, magnetic field was introduced to the BiO2−x/Bi3NbO7 system to effectively covert oxygen into reactive radicals. The electrochemical experiment and DFT calculation results indicated the charge separation could be accelerated by the Lorentz force generated by the magnetic field, resulting in increase of electron concentration. Meanwhile, the value of volumetric gas-liquid mass transfer coefficient was increased by 59.79 % with magnetic field, thus more oxygen could be reduced to superoxide radical. Photocatalytic algae inactivation rate by BiO2−x/Bi3NbO7 with magnetic field could be increased by 2.07 times than that without magnet filed. This work further extends the strategy of using magnetic field to simultaneously facilitate the charge separation and oxygen transfer rate.

Biological Impact of Shorter Wavelength Ultraviolet Radiation-C†.

Life on earth has constantly coped with the impact of solar radiation, especially solar ultraviolet radiation (solar UV). Various biological mechanisms protect us from solar UV. New devices emitting shorter wavelengths UV-C, i.e. <254 nm emitted by conventional UV germicidal lamps, have emerged. These shorter wavelength UV-C emitting devices are useful for various purposes, including microorganism inactivation. However, as solar UV-C does not reach the earth surface, biological impacts of UV-C has been studied using 254 nm germicidal lamps, and those using shorter wavelength UV-C is rarely known. To balance the utility and risk of UV-C, the biological effect of these new UV-C emitting devices must be investigated. In addition, our knowledge of biological impacts of the wavelength-dependent entire UV (100-400 nm) must be enhanced. In this review, we briefly summarize the biological impacts of shorter wavelength UV-C. Mechanisms of UV-C-induced cellular damage and factors affecting the microorganism inactivation efficiency of UV-C have been discussed. In addition, we theoretically estimate the probable photocarcinogenic action spectrum of shorter wavelength UV-C. We propose that increasing the knowledge on UV-C will facilitate the adoption of shorter wavelength UV-C emitting new devices in an optimal and appropriate manner.

Photocatalytic ozonation inactivation of bioaerosols by NiFeOOH nanosheets in situ grown on nickel foam

Inactivation of bioaerosols is critical to prevent the spread of microbial pathogens in air. Photocatalytic inactivation processes are environmental friendliness, while time-consuming and insufficient reactive oxygen species (ROSs) generation to irreversibly inactivate bacteria in bioaerosols. In this work, a novel photocatalytic ozonation (PCO) system was constructed, consisting of in situ grown NiFeOOH nanosheets on nickel foam (NiFeOOH NSs/NF) and trace concentration of ozone (O3). Specifically, the PCO system exhibited remarkable photocatalytic inactivation efficiency (99.99%) within an ultrashort retention time of 8.07 s (RH = 90%) while no bacteria survived after 24-h cultivation. The irreversible inactivation of bacteria in this PCO system attributes to the synergistic effect of physical destruction by NiFeOOH NSs/NF and oxidative damage by photogenerated ROSs. This research provides a better alternative for efficient inactivation of bioaerosols and opens the door for the application of PCO system in reducing the exposure risk of bioaerosols.

Synthesis of multi-layered nanoswabs for simultaneous and expeditious removal of antibiotic-resistant bacteria, dyes, and antibiotics from wastewater

Multi-layered glyoxylic-functionalized triptycene nanoswabs (G-TCNS) were synthesized using a novel one-step intercalation cross-linked polymerization process for simultaneous removal of different types of water contaminants. In this study, expeditious adsorption of the dyes methylene blue(MB) and rhodamine B (RhB), the antibiotics gentamicin (GM) and ofloxacin (OFL), and antibiotic-resistant genes (ARGs), and the removal of three types of emerging antibiotic-resistant bacteria (ARB) from water were studied. A contaminant removal efficiency of 99 % was achieved within 7 min using G-TCNS dosage of 20 mg L−1 at pH 8 and 295 K. The adsorption capacities (Qe) of G-TCNS for the different contaminants were in the range 450–556 mg g−1. The G-TCNS exhibited high adsorption capacities as a result of their multi-layered micro-porous structure and high surface area, and improved water purification due to their excellent water selectivity. The NRs also showed high efficiencies of bacteria removal and inactivation against 107 CFU mL−1 of ARB. They were more effective as an antibacterial agent compared to (unfunctionalized) triptycene nanoswabs (TCNS) and other commercially available antibiotics. The results also revealed that G-TCNS is an efficient, highly recyclable, and eco-friendly adsorbent for the simultaneous removal of various contaminants from water.

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.

Effects of Electrical Pulse Width and Output Irradiance on Intense Pulse Light Inactivation.

The effects of electrical pulse width and output irradiance on the inactivation effect of intense pulse light (IPL) are studied in this paper. The measured radiant efficiency of pulsed xenon lamp can be more than 50%, and its irradiance can reach levels 100-times greater than that of a low-pressure mercury lamp. Staphylococcus aureus is used in inactivation experiments. When the irradiance and dose are both constant, there is no significant difference in inactivation efficiency when the pulse width is changed. However, a narrow pulse width corresponding to high irradiance at the same single-pulsed dose displays better inactivation effect. Experimental results are compared between the xenon lamp and low-pressure mercury lamp. The reduction factor (RF) value of the xenon lamp is more than 1.0 higher under the condition of both the same dose and irradiance. In order to achieve the same RF value, the dose of continuous-wave light must be at least three-times greater than that of pulsed light. The spectral action of the pulsed light is also studied. It is confirmed that UVC plays a major role across the whole spectrum. The experimental results show that extreme high-pulsed irradiance presents the main contributing factor behind the excellent bactericidal effect of IPL.