Evaluation of the effect of chemical disinfection and ultraviolet disinfection on the dimensional stability of polyether impression material: an in-vitro study

BACKGROUND

Various methods, chemical and physical, disinfect dental impressions. Common chemicals include 1% Sodium Hypochlorite and 2% glutaraldehyde, while UV radiation is a prevalent physical method. Few studies compare their effects on dimensional stability in polyether impressions. This study aims to assess such stability using different disinfection methods. Therefore, this study was planned to evaluate the dimensional stability of polyether impression material using different disinfection methods.

METHODS

This in vitro study compared the effects of chemical disinfectants (1% Sodium Hypochlorite and 2% glutaraldehyde) and UV irradiation on the dimensional stability of polyether impression material. Groups A, B, C, and D, each with ten samples (N = 10), were studied. Group A was untreated (control). Group B was treated with 2% glutaraldehyde for 20 min, Group C with 1% Sodium Hypochlorite for 20 min, and Group D with UV rays for 20 min. A pilot milling machine drill was used to make four parallel holes labeled A, B, C, and D in the anterior and premolar regions from right to left. After sequential drilling, four implant analogs were positioned using a surveyor for accuracy. Ten open-tray polyether impressions were made and treated as described in the groups, followed by pouring the corresponding casts. Distortion values for each disinfection method were measured using a coordinate measuring machine capable of recording on the X- and Y-axes.

RESULTS

A comprehensive analysis was conducted using the one-way ANOVA test for distinct groups labeled A, B, C, and D, revealing significant differences in the mean distances for X1, X2, X4, X5, and X6 among the groups, with p-values ranging from 0.001 to 0.000. However, no significant differences were observed in X3. Notably, mean distances for the Y variables exhibited substantial differences among the groups, emphasizing parameter variations, with p-values ranging from 0.000 to 0.033. The results compared the four groups using the one-way ANOVA test, revealing statistically significant distance differences for most X and Y variables, except for X3 and Y4. Similarly, post-hoc Tukey's tests provided specific pairwise comparisons, underlining the distinctions between group C and the others in the mean and deviation distances for various variables on both the X- and Y-axes.

CONCLUSIONS

This study found that disinfection with 1% sodium hypochlorite or UV rays for 20 min maintained dimensional stability in polyether impressions.

Performance evaluation for the inactivation of multidrug-resistant bacteria in wastewater effluent by different disinfection technologies

The escalating presence of antibiotic-resistant bacteria (ARB) in aquatic ecosystems underscores the critical role of wastewater treatment plants (WWTPs) in mitigating antibiotic resistance. Disinfection is the final, pivotal step in WWTPs, and it is essential to control the dissemination of ARB before water discharge. This study utilized both phenotypic analysis and transcriptome (RNA-seq) approach to investigate the efficiency and mechanisms of disinfection using chlorination, ultraviolet (UV), and peracetic acid (PAA) on multidrug-resistant bacteria (MRB). Our results demonstrated that the use of 100 mg min L-1 of chlorine, 8.19 mJ cm-2 of UV irradiation or 50 min mg L-1 of PAA significantly reduced the abundance of MRB. Intriguingly, RNA-seq clarified distinct mechanisms of chlorination and UV disinfection. UV radiation triggered the SOS response to cope with DNA damage, induced the expression of multi-drug resistance genes by increasing the expression of efflux pump transporters. UV radiation also promoted the absorption of iron through chelation and transportation to participate in various cell life processes. Chlorination, on the other hand, significantly up-regulated osmotic response elements, including the synthesis of glycine betaine, iron-sulfur clusters, and related transporters. Both chlorination and UV significantly down-regulated key metabolic pathways (P < 0.05), inhibiting the process of amino acid synthesis and energy metabolism. Imbalance in energy homeostasis was the most important factor leading to cytotoxicity. These results provide useful insights into optimizing the wastewater disinfection process in order to prevent the dissemination of ARB in aquatic environment.

Fluorescence Spectroscopy for the Assessment of Microbial Load in UVC Treated Water

In this article, Fluorescence spectroscopy has been employed for the assessment of microbial load and it has been compared with the gold standard colony forming unit (CFU) and optical density (OD) methods. In order to develop a correlation between three characterization techniques, water samples of different microbial loads have been prepared by UVC disinfection method through an indigenously developed NUVWater sterilizer, which operates in close cycle flow configuration. A UV dose of 58.9 mJ/cm2 has been determined for 99.99% disinfection for a flow rate of 0.8 l/min. The water samples were excited at 270 nm which results in the tryptophan like fluorescence at 360 nm that decreases gradually with increase of UVC dose, indicating the bacterial degradation and it has been confirmed by OD and CFU methods. In addition, it has been proved that a close cycle water flow around UV lamp is imperative so that an appropriate dose must be delivered to microorganisms for an efficient disinfection. It has been found that due to the sensitive nature of Fluorescence spectroscopy, it yields immediate results, whereas, for CFU and OD methods, water samples needs to be inoculated for 24 h. Fluorescence spectroscopy, therefore, provide a fast, online, reliable and sensitive method for the monitoring of pathogenic quantification in drinking water.

Occurrence and removal of conventional pollutants, estrogenicities, and fecal coliform in village sewage treatment plants along the Yangtze River, China

The present study investigated the occurrence and removal efficiency of some conventional pollutants, estrogenic effects, and fecal coliform in influents and/or effluents of village sewage treatment plants (STPs) in the upper, middle, and lower reaches of the Yangtze River Basin. The water quality of sewage from the village STPs showed significant seasonal and spatial variability. The removal rates of conventional pollutants by the village STPs were mostly lower than urban STPs, thereby resulting in that the water quality compliance rate of the effluents was only 33.3%. In addition, the average removal rate of estrogenic compounds was only 22.2%, which caused the estrogenicity of effluent to exceed the safety threshold. And E2 was determined to be the main estrogenic component. Moreover, ultraviolet (UV) disinfection, as the main disinfection treatment process of sewage along the Yangtze River Basin, was unable to meet the discharge standard of fecal coliform. The sequential chlorine (10 mg L^-1)-UV (20 mJ cm^-2) disinfection was found to both achieve up-to-standard discharge of fecal coliform and increase the removal rate of estrogenic effect from 3.78 to 9.86%. Overall, the present study provides valuable information on the conventional pollutants, estrogenic effects, and fecal coliform in sewage from village STPs along the Yangtze River Basin, and practical suggestions for basin-wide pollution control.

Volatile organic compounds generation pathways and mechanisms from microplastics in water: Ultraviolet, chlorine and ultraviolet/chlorine disinfection

Disinfection in water treatments induces microplastics (MPs) to produce various derivative products, among which the volatile organic compounds (VOCs) are still poorly understood. Ultraviolet (UV), chlorine and UV/chlorine disinfections were used to treat polypropylene (PP), polystyrene (PS) and polyvinylchloride (PVC) in this study. Modifications were observed on the MP surfaces, including melting, cracks, folds, and even forming oxygen-containing structures, resulting in the release of a diversity of VOCs. The polymer types of MPs influenced the VOCs characteristics. PP released alkanes, alkenes and aldehydes, while PVC released alkanes, alkenes and halogenated hydrocarbons. VOCs from PS were dominated by unique aromatic alkanes, alkenes and aldehydes. These derived VOCs are generated during different disinfections with distinct mechanisms. UV-C at 254 nm induced direct scission and radical oxidation on MPs. The derived VOCs were mainly bond-breaking fragments. Chlorination relied on HOCl/OCl^- electrophilic reactions, resulting fewer VOCs since C-C skeleton MPs have strong resistance to electrophilic reactions. UV/chlorination promotes the generation of chlorine radicals and hydroxyl radicals, thereby causing oxidative damage. Various oxidized VOCs, such as benzaldehyde and acetophenone, were formed. The disinfection reactions can produce various VOCs from MPs, posing potential risks to the ecological environment and human beings.

Exploring the microbiome, antibiotic resistance genes, mobile genetic element, and potential resistant pathogens in municipal wastewater treatment plants in Brazil

Wastewater treatment plants (WWTPs) have been widely investigated in Europe, Asia and North America regarding the occurrence and fate of antibiotic resistance (AR) elements, such as antibiotic resistance genes (ARGs), mobile genetic elements (MGEs) and antibiotic resistant bacteria and pathogens. However, monitoring data about AR elements in municipal WWTPs in Brazil are scarce. This study investigated the abundance of intI1, five ARGs (sul1, tetA, blaTEM, ermB and qnrB) and 16S rRNA in raw and treated wastewater of three WWTPs, using different sewage treatments named CAS (Conventional activated sludge), UASB/BTF (UASB followed by biological trickling filter) and MAS/UV (modified activated sludge with UV disinfection stage). Bacterial diversity and the presence of potentially pathogenic groups were also evaluated, and associations between genetic markers and the bacterial populations were presented. All WWTPs decreased the loads of genetic markers finally discharged to receiving water bodies and showed no evidence of being hotspots for antimicrobial resistance amplification in wastewater, since the abundances of intI1 and ARGs within the bacterial population were not increased in the treated effluents. UASB/BTF showed a similar performance to that of the CAS and MAS/UV, reinforcing the sanitary and environmental advantages of this biological treatment, widely applied for wastewater treatment in warm climate regions. Bacterial diversity and richness increased after treatments, and bacterial communities in wastewater samples differed due to catchment areas and treatment typologies. Potential pathogenic population underwent considerable decrease after the treatments; however, strong significant correlations with intI1 and ARGs revealed potential multidrug-resistant pathogenic bacteria (Aeromonas, Arcobacter, Enterobacter, Escherichia-Shigella, Stenotrophomonas and Streptococcus) in the treated effluents, although in reduced relative abundances. These are contributive results for understanding the fate of ARGs, MGEs and potential pathogenic bacteria after wastewater treatments, which might support actions to mitigate their release into Brazilian aquatic environments in the near future.

Ultraviolet disinfection efficacy test method using bacteria monolayers

Monolayers of bacterial cells of Staphylococcus aureus and Pseudomonas aeruginosa were inoculated on glass slide carriers using an automated inoculum spray deposition system. The use of bacterial monolayers allows for control of critical variables for testing and verification of light-based disinfection technologies. This approach avoids the variability associated with manual inoculation and high inoculum titers, which can engender clustering of cells and the associated photoprotection that clustering incurs. The use of glass slide carriers avoids problems caused by irregular microscopic surface features, which can impact the efficacy evaluation of light-based disinfection technologies. Scanning electron micrographic (SEM) imaging was used to verify the surface topography and the presence of monolayers. The spray deposition method produced a mean density of >10⁶ colony forming units (CFU) per carrier. The inoculated carriers were exposed to ultraviolet light for 120 s from a focused multivector ultraviolet (FMUV) light system. A mean log CFU reduction of 4.8 was achieved for S. aureus (p < 0.0001). A mean log CFU reduction of 5.1 was achieved for P. aeruginosa (p < 0.0001). The test method presented herein will facilitate increased accuracy in the measurement of ultraviolet susceptibility rate constants.

Average and longest expected treatment times for ultraviolet light disinfection of rooms

BACKGROUND

Planning Ultraviolet-C (UV-C) disinfection of operating rooms (ORs) is equivalent to scheduling brief OR cases. The study purpose was evaluation of methods for predicting surgical case duration applied to treatment times for ORs and hospital rooms.

METHODS

Data used were disinfection times with a 3-tower UV-C disinfection system in N=700 rooms each with ≥100 completed treatments.

RESULTS

The coefficient of variation of mean treatment duration among rooms was 19.6% (99% confidence interval [CI] 18.2%-21.0%); pooled mean 18.3 minutes among the 133,927 treatments. The 50^th percentile of coefficients of variation among treatments of the same room was 27.3% (CI 26.3%-28.4%), comparable to variabilities in durations of surgical procedures. The ratios of the 90^th percentile to mean differed among rooms. Log-normal distributions had poor fits for 33% of rooms. Combining results, we calculated 90% upper prediction limits for treatment times by room using a distribution-free method (e.g., third longest of preceding 29 durations). This approach was suitable because, once UV-C disinfection started, the median difference between the duration estimated by the system and actual time was 1 second.

CONCLUSIONS

Times for disinfection should be listed as treatment of a specific room (e.g., "UV-C main OR16"), not generically (e.g., "UV-C"). For estimating disinfection time after single surgical cases, use distribution-free upper prediction limits, because of considerable proportional variabilities in duration.

Integrated metagenomic and metatranscriptomic analyses of ultraviolet disinfection effects on antibiotic resistance genes and bacterial communities during wastewater treatment

Ultraviolet (UV) disinfection is now widely implemented in wastewater treatment plants (WWTPs) worldwide, but its effect on antibiotic resistome of the surviving bacteria remains unclear. In this study, we employed high-throughput sequencing-based metagenomic and metatranscriptomic approaches to comprehensively elucidate the effects of UV disinfection on the shifts of bacterial community and antibiotic resistance genes (ARGs) on both DNA and mRNA levels in one WWTP. Metagenomic analyses revealed an insignificant change in the bacterial community after UV disinfection, while metatranscriptomic analyses showed that UV disinfection significantly changed the abundance of 13.79% of phyla and 10.32% of genera. In total, 38 ARG-like open reading frames (ORFs) and 327 ARG-like transcripts were identified in the DNA and RNA samples, respectively. The relative abundances of the total ARGs, each ARG type, and each ARG subtype also varied after UV disinfection. Additionally, UV disinfection significantly reduced the expression of total ARGs from 49.40 transcripts per kilobase of exon model per million mapped reads (TPM) to 47.62 TPM, and significantly changed the expression of 10.75% of ARG subtypes in wastewater (p < 0.05). Notably, the significant increase in the expression and obvious increase in the relative abundance of macrolide-lincosamide-streptogramin B (MLSB) resistance genes revealed that UV disinfection increases the potential health risk of MLSB resistance genes in wastewater. Moreover, potential host analyses of ARGs revealed the different preferences of antibiotic resistant bacteria (ARB) to ARGs. This study may shed new light on the underlying mechanism of the UV disinfection effect on antibiotic resistance.

Evaluation of three photosynthetic species smaller than ten microns as possible standard test organisms of ultraviolet-based ballast water treatment

The Ballast Water Management Convention (BWMC) establishes limits for viable organisms in discharged ballast water. However, organisms smaller than 10 μm are not considered in this regulation although they represent, in some regions, the majority of the phytoplankton organisms in marine water. The objective in this study is to assess three photosynthetic species smaller than 10 μm as potential standard test organism (STO) in experimentation focused on the inactivating efficacy of ultraviolet treatments (UV). A growth modelling method was employed to determine the reduction of the viable cell concentration under either light or dark post-treatment conditions to evaluate the importance of the photoreactivation. In spite of its moderate growth rate, the high UV resistance in combination with the abundance and worldwide distribution of Synechococcus sp. and the environmental importance of this species constitute important reasons for considering Synechococcus sp. as a valuable STO for ballast water treatment.

Improving the microalgae inactivating efficacy of ultraviolet ballast water treatment in combination with hydrogen peroxide or peroxymonosulfate salt

Due to the increasing number of ecosystem invasions with the introduction of exogenous species via ballast water, the International Maritime Organization adopted the Ballast Water Convention (BWMC). The BWMC establishes standards for the concentration of viable organisms in a ballast water discharge. Ultraviolet (UV) irradiation is commonly used for treating ballast water; however, regrowth after UV irradiation and other drawbacks have been reported. In this study, improvement in UV treatment with the addition of hydrogen peroxide or peroxymonosulfate salt was investigated using the microalgae Tetraselmis suecica as the target organism. Results reported that each of these reagents added in a concentration of 10 ppm reduced the concentration of initial cells by more than 96%, increased the UV inactivation rate, and enabled reaching greater level of inactivation with the treatment. These improvements imply a reduction of the UV doses required for a consistent compliance with the BWMC standards.

Efficacy of pulsed-xenon ultraviolet light on reduction of Mycobacterium fortuitum

Objectives

Hospitals and healthcare facilities rely largely on isolation and environmental disinfection to prevent transmission of pathogens. The use of no-touch technology is an accepted practice for environmental decontamination in medical care facilities, but little has been published about the effect of ultraviolet light generated by a portable pulsed-xenon device use on Mycobacteria. We used Mycobacterium fortuitum which is more resistant to ultraviolet radiation and less virulent than Mycobacterium tuberculosis, to determine the effectiveness of portable pulsed-xenon devices on Mycobacterium in a laboratory environment.

Methods

To determine the effectiveness of pulsed-xenon devices, we measured the bactericidal effect of pulsed-xenon devices on Mycobacterium fortuitum.

Results

In five separate experiments irradiating an average of 10⁶ organisms, the mean (standard deviation) log-kill at 5 min was 3.98 (0.60), at 10 min was 4.96 (0.42), and at 15 min was 5.64 (0.52).

Conclusions

Our results demonstrate that using pulsed-xenon devices is a highly effective modality to reduce microbial counts with this relatively ultraviolet germicidal irradiation-resistant mycobacterium in a time-dependent manner.

Chitra Disinfection Gateway for the Management of COVID 19 in Public Entry Places

Chitra Disinfection Gateway is meant for the decontamination of personnel entering a cleaner private space from a public space. This is equipped with an arrangement for generating hydrogen peroxide mist and ultraviolet rays. Hydrogen peroxide mist will decontaminate clothes, hands and the bags a person carries. The ultraviolet system will decontaminate the chamber once the person has moved out. The system is controlled electronically by sensors and actuators. The sensors fixed in the chamber detect the entry of a person and initiates the hydrogen peroxide atomization process. The person is required to walk through the chamber. When the person exits the chamber, the system will put off the hydrogen peroxide atomization system and will turn on the UV lamp inside the chamber to decontaminate it. The ultraviolet system will be ON for a predefined time and after the process, the next person can enter the walkway. The whole process takes a maximum of 40 s. The safety and efficacy of the system have been validated experimentally through both in vivo and in vitro studies.

Effect of the length of dark storage following ultraviolet irradiation of Tetraselmis suecica and its implications for ballast water management

Meeting the recent biological standards established by the Ballast Water Management Convention requires the application of ballast water treatment systems; ultraviolet irradiation is a frequently used option. However, organisms can repair the damage caused by ultraviolet irradiation primarily with photo-repair mechanisms that are dependent on the availability of light. The objective of this study is to quantify the impact of dark storage following ultraviolet irradiation on the viability of the microalgae Tetraselmis suecica. Results showed that one day of dark storage after ultraviolet irradiation enhanced the inactivation rate by 50% with respect to the absence of dark storage and increased up to the 84% with five days of dark storage. These results are consistent with photorepair, mostly in the first two days, prevented in the dark. The dose required to inactivate a determined ratio of organisms was correlated with the length of the dark post-treatment according to an inverse proportional function. This correlation may help to optimize the operation of ultraviolet ballast water treatment systems. Further, the results show that growth assays can detect organisms that are capable of repair after treatment with UV.

Characterization for the transformation of dissolved organic matters during ultraviolet disinfection by differential absorbance spectroscopy

The transformation of dissolved organic matter (DOM) during various disinfection processes has raised great concerns due to the generation of carcinogenic disinfection by-products (DBPs). Ultraviolet (UV) irradiation is an effective method for drinking water disinfection, during which DOM undergoes changes in functional groups and molecular weight. In this study, the spectrophotometric titration and gel permeation chromatography (GPC) determination were employed to investigate the changes in oxygenated groups and weight-averaged molecular weight (M_w) of two typical DOM during UV irradiation. The differential absorbance spectra (DAS) of DOM could be deconvoluted into six Gaussian bands. The change of relative band intensity was attributed to the change of oxygenated groups (carboxylic and phenolic groups), which was confirmed by combining DAS data and revised Non-Ideal Competitive Adsorption -Donnan model. The GPC result demonstrated that the M_w of DOM decreased after UV disinfection. Moreover, a linear correlation between M_w and the intensity of deconvoluted Gaussian band from DAS was established, which might be served as an alternative approach to estimate M_w and predict the hydrophobicity and DBPs formation potential of DOM in drinking water treatment and monitoring.

Ultraviolet disinfection impacts the microbial community composition and function of treated wastewater effluent and the receiving urban river

Background

In the United States, an estimated 14,748 wastewater treatment plants (WWTPs) provide wastewater collection, treatment, and disposal service to more than 230 million people. The quality of treated wastewater is often assessed by the presence or absence of fecal indicator bacteria. UV disinfection of wastewater is a common final treatment step used by many wastewater treatment plants in order to reduce fecal coliform bacteria and other pathogens; however, its potential impacts on the total effluent bacterial community are seemingly varied. This is especially important given that urban WWTPs typically return treated effluent to coastal and riverine environments and thus are a major source of microorganisms, genes, and chemical compounds to these systems. Following rainfall, stormflow conditions can result in substantial increases to effluent flow into combined systems.

Methods

Here, we conducted a lab-scale UV disinfection on WWTP effluent using UV dosage of 100 mJ/cm² and monitored the active microbiome in UV-treated effluent and untreated effluent over the course of 48 h post-exposure using 16S rRNA sequencing. In addition, we simulated stormflow conditions with effluent UV-treated and untreated effluent additions to river water and compared the microbial communities to those in baseflow river water. We also tracked the functional profiles of genes involved in tetracycline resistance (tetW) and nitrification (amoA) in these microcosms using RT-qPCR.

Results

We showed that while some organisms, such as members of the Bacteroidetes, are inhibited by UV disinfection and overall diversity of the microbial community decreases following treatment, many organisms not only survive, but remain active. These include common WWTP-derived organisms such as Comamonadaceae and Pseudomonas. When combined with river water to mimic stormflow conditions, these organisms can persist in the environment and potentially enhance microbial functions such as nitrification and antibiotic resistance.

Assessing the Feasibility of a Focused Multivector Ultraviolet System Between Surgery Cases with a Parallel Protocol for Enhanced Disinfection Capabilities

A focused multivector ultraviolet (FMUV) light system was used in a parallel process with manual chemical disinfection during operating room (OR) turnovers to assess the impact on cleaning time. The average time to disinfect an OR using only chemical wipes and mops was 19.0 minutes (n = 68); for the FMUV process, the average time was 18.8 minutes (n = 61). The mean cleaning times were equivalent within a 7% margin (P < .17), and total turnover time was not significantly affected.

Evaluation survey of microbial disinfection methods in UV-LED water treatment systems

Ultraviolet (UV) disinfection is an early discovered technology that is currently and widely used for water treatment and food hygiene treatment. A newly emerging technology of UV disinfection, that is, UV light-emitting diodes (UV-LEDs), has aroused considerable research attention. UV-LEDs feature numerous advantages compared with traditional UV mercury vapor lamps and are expected to replace traditional UV lamps. Researchers currently perform studies to obtain data and develop methods for UV-LED water treatment systems. This article analyzes the latest research status and discusses the types of inactivation factors, such as the wavelength selectivity of UV light source, control of UV dose, effect of inactivation rate constant (K) (cm²/mJ), working mode of water sample, external auxiliary system, and UV sensitivity of pathogenic bacteria in water. The wavelengths of approximately 260 and 280 nm normally feature strong inactivation characteristics. When compared with the approximately 260 nm wavelength chip, the around 280 nm wavelength chip proves to be a better choice as its higher wavelength light power can result in faster disinfection capacity of bacteria. UV dose can also be used as the reference value for disinfection of drinking water, whereas the inactivation rate constant (K) (cm²/mJ) varies with different microorganism internal structures. Changing the working mode or adding an auxiliary system can also enhance the inactivation effect in water treatment system settings. In addition, we can compare the inactivation capacities of several pathogens as follows: ΦX174 > Escherichia coli > T type bacteriophage >Bacillus subtilis > MS2 or Qβ > human adenovirus. The in-depth investigation and discussion of inactivation factors and the mechanism of action in UV-LEDs water treatment systems will establish a more efficient UV-LED disinfection method in the future, provide a guiding direction, and promote the standardization and normalization of pathogen inactivation mechanism in UV-LED water treatment systems.

Quantitative and qualitative changes in antibiotic resistance genes after passing through treatment processes in municipal wastewater treatment plants

In this study, quantitative and qualitative changes in antibiotics resistance genes (ARGs) were investigated in two municipal wastewater treatment plants (WWTPs) treating pretreated livestock or industrial wastewater as well as municipal sewage. Total eight ARGs (tetX, tetM, tetA, sul1, sul2, ermB, qnrD, and bla_TEM) were quantified, and their relative abundance was assessed by ARGs copies/16S rRNA gene copies. The fate of ARGs was observed to be different between two WWTPs: sul, qnrD, and bla_TEM were proliferated during the treatment processes only in the WWTP1 which received pretreated livestock wastewater. Furthermore, dynamic shifts in patterns of ARGs occurrence were observed during biological, secondary sedimentation and coagulation processes. During biological treatment in both WWTPs, relative abundance of tet and ermB changed: tet increased significantly by 211.6-357.6%, while ermB decreased by 70.4-92.0%. Little variation was observed in sul, qnrD and bla_TEM. Subsequently, the relative abundance of tet decreased during the secondary sedimentation and coagulation in both WWTPs: tet decreased by 56.0-86.3% during sedimentation and by 48.2-75.7% during coagulation, respectively. During the final treatment, different responses of antibiotic resistance bacteria (ARB) and ARGs to ultraviolet (UV) disinfection were found: removal efficiencies of ARB were observed in the range of 34-75%, while obvious reduction in ARGs was not observed at the UV dose of 27mJ/cm². Although ARGs underwent various treatment processes, considerable levels of ARGs remained at discharge amounting to 4.2×10¹⁸ copies/day from WWTP1 and 5.4×10¹⁶ copies/day from WWTP2, respectively.

Comparison of UV-LED and low pressure UV for water disinfection: Photoreactivation and dark repair of Escherichia coli

Studies on ultraviolet light-emitting diode (UV-LED) water disinfection have shown advantages, such as safety, flexible design, and lower starting voltages. However, information about reactivation after UV-LED disinfection is limited, which is an important issue of UV light-based technology. In this study, the photoreactivation and dark repair of Escherichia coli after UV-LEDs and low pressure (LP) UV disinfection were compared. Four UV-LED units, 265 nm, 280 nm, the combination of 265 + 280 (50%), and 265 + 280 (75%) were tested. 265 nm LEDs was more effective than 280 nm LEDs and LP UV lamps for E. coli inactivation. No synergic effect for disinfection was observed from the combination of 265 and 280 nm LEDs. 265 nm LEDs had no different reactivation performances with that of LP UV, while 280 nm LEDs could significantly repress photoreactivation and dark repair at a low irradiation intensity of 6.9 mJ/cm². Furthermore, the UV-induced damage of 280 nm LEDs was less repaired which was determined by endonuclease sensitive site (ESS) assay. The impaired protein activities by 280 nm LEDs might be one of the reasons that inhibited reactivation. A new reactivation rate constant, K_max, was introduced into the logistic model to simulate the reactivation data, which showed positive relationship with the maximum survival ratio and was more reasonable to interpret the results of photoreactivation and dark repair. This study revealed the distinct roles of different UV lights in disinfection and reactivation, which is helpful for the future design of UV-LED equipment.

Metagenomic insights into ultraviolet disinfection effects on antibiotic resistome in biologically treated wastewater

High-throughput sequencing-based metagenomic approaches were used to comprehensively investigate ultraviolet effects on the microbial community structure, and diversity and abundance of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in biologically treated wastewater. After ultraviolet radiation, some dominant genera, like Aeromonas and Halomonas, in the wastewater almost disappeared, while the relative abundance of some minor genera including Pseudomonas and Bacillus increased dozens of times. Metagenomic analysis showed that 159 ARGs within 14 types were detectable in the samples, and the radiation at 500 mJ/cm(2) obviously increased their total relative abundance from 31.68 ppm to 190.78 ppm, which was supported by quantitative real time PCR. As the dominant persistent ARGs, multidrug resistance genes carried by Pseudomonas and bacitracin resistance gene bacA carried by Bacillus mainly contributed to the ARGs abundance increase. Bacterial community shift and MGEs replication induced by the radiation might drive the resistome alteration. The findings may shed new light on the mechanism behind the ultraviolet radiation effects on antibiotic resistance in wastewater.

Influence of a total joint infection control bundle on surgical site infection rates

Quality improvement initiatives combined with pulsed xenon ultraviolet room disinfection were implemented to reduce surgical site infections (SSIs) in patients undergoing total joint procedures. After 12 months, knee SSIs were reduced from 4 to 0 (P = .03) and hip SSIs were reduced from 3 to 0 (P = .15) for a combined prevention of 7 SSIs (P = .01) and a savings of $290,990.

Clostridium difficile infections before and during use of ultraviolet disinfection

BACKGROUND

We previously reported a significant decrease in hospital-acquired (HA) Clostridium difficile infection (CDI) coincident with the introduction of pulsed xenon ultraviolet light for room disinfection (UVD). The purpose of this study was to evaluate CDI cases in greater detail to understand the effect of UVD.

METHODS

CDI rates (HA and community acquired [CA]), CDI patient length of stay, room occupancy, and number of days between a CDI case in a room and an HA CDI case in the same room were studied for the first year of UVD compared with the 1-year period pre-UVD.

RESULTS

Compared with pre-UVD, during UVD, HA CDI was 22% less (P = .06). There was a 70% decrease for the adult intensive care units (ICUs) (P < .001), where the percentage of room discharges with UVD was greater (P < .001). During UVD, CA CDI increased by 18%, and length of stay of all CDI cases was lower because of the greater proportion of CA CDI. No significant difference was found in days to HA CDI in rooms with a prior CDI occupant.

CONCLUSION

These data suggest that UVD contributed to a reduction in ICU-acquired CDI where UVD was used for a larger proportion of discharges. Evaluation of UVD should include data for hospitalized CA CDI cases because these cases may impact the HA CDI rate.

Enhancing disinfection by advanced oxidation under UV irradiation in polyphosphate-containing wastewater flocs

In this paper, the role of naturally occurring polyphosphate in enhancing the ultraviolet disinfection of wastewater flocs is examined. It was found that polyphosphate, which accumulates naturally within the wastewater flocs in the enhanced biological phosphorus removal process, is capable of producing hydroxyl radicals under UV irradiation and hence causing the photoreactive disinfection of microorganisms embedded within flocs. This phenomenon is likely responsible for the improved UV disinfection of the biological nutrient removal (BNR) effluent compared to that of conventional activated sludge effluent by as much as 1 log. A mathematical model is developed that combines the chemical disinfection by hydroxyl radical formation within flocs, together with the direct inactivation of microorganisms by UV irradiation. The proposed model is able to quantitatively explain the observed improvement in the UV disinfection of the BNR effluents. This study shows that the chemical composition of wastewater flocs could have a significant positive impact on their UV disinfection by inducing the production of oxidative species.