UV Disinfection Research Articles

Demo-scale up-flow anaerobic sludge blanket reactor coupled with hybrid constructed wetlands for energy-carbon efficient agricultural wastewater reuse in decentralized scenarios

The impact of climate change on water availability and quality has affected agricultural irrigation. The use of treated wastewater can alleviate water in agriculture. Nevertheless, it is imperative to ensure proper treatment of wastewater before reuse, in compliance with current regulations of this practice. In decentralized agricultural scenarios, the lack of adequate treatment facilities poses a challenge in providing treated wastewater for irrigation. Hence, there is a critical need to develop and implement innovative, feasible, and sustainable treatment solutions to secure the use of this alternative water source. This study proposes the integration of intensive treatment solutions and natural treatment systems, specifically, the combination of up-flow anaerobic sludge blanket reactor (UASB), anaerobic membrane bioreactor (AnMBR), constructed wetlands (CWs), and ultraviolet (UV) disinfection. For this purpose, a novel demo-scale plant was designed, constructed and implemented to test wastewater treatment and evaluate the capability of the proposed system to provide an effluent with a quality in compliance with the current European wastewater reuse regulatory framework. In addition, carbon-sequestration and energy analyses were conducted to assess the sustainability of the proposed treatment approach. This research confirmed that UASB rector can be employed for biogas production (2.5 L h−1) and energy recovery from organic matter degradation, but its effluent requires further treatment steps to be reused in agricultural irrigation. The AnMBR effluent complied with class A standards for E. coli, boasting a concentration of 0 CFU 100 mL−1, and nearly negligible TSS levels. However, further reduction of BOD5 (35 mg L−1) is required to reach water quality class A. CWs efficiently produced effluent with BOD5 below 10 mg L−1 and TSS close to 0 mg L−1, making it suitable for water reuse and meeting class A standards. Furthermore, CWs demonstrated significantly higher energy efficiency compared to intensive treatment systems. Nonetheless, the inclusion of a UV disinfection unit after CWs was required to attain water class B standards.

Enhancing Escherichia coli Inactivation: Synergistic Mechanism of Ultraviolet Light and High-Voltage Electric Field.

This study investigated the bactericidal effects of ultraviolet (UV) radiation, a high-voltage electric field (HVEF), and their combination on Escherichia coli. The results indicated that UV and combined disinfection were more effective with longer exposure, leading to significant reductions in microbial activity. Specifically, the single UV disinfection alone reduced activity by 3.3 log after 5 min, while combined disinfection achieved a 4.2 log reduction. In contrast, short-term HVEF treatment did not exhibit significant bactericidal effects, only achieving a reduction of 0.17 log in 5 min. Furthermore, prolonged exposure to both UV disinfection and an HVEF was found to damage cell membranes, ultimately causing cell death, while shorter durations did not. Despite rapid cell count decreases, flow cytometry did not detect apoptotic or necrotic cells, likely due to rapid cell rupture. This study suggests that combining UV radiation and an HVEF could be a promising approach for inhibiting bacterial reproduction, with HVEF enhancing UV effects. These findings provide insights for using combined HVEF and UV disinfection in food safety and preservation.

The Performance Analysis of a Novel Sterilizable Trombe Wall Based on the Combined Effect of Heat and UV Light

A Trombe wall is a widely applied heating system that has a single function. An interesting thing is that both the solar heat and UV light received by a Trombe wall have an air sterilization effect. Here, the air sterilization and thermal performances of a Trombe wall in different cities were investigated based on an established heat and mass transfer model. The main results were as follows: (1) UV dose accumulation and high temperature were the most important factors that affect the UV and thermal sterilization performance, respectively. The Trombe wall had the thermal characteristics of high accumulation of UV doses in the morning and afternoon and a high temperature level at noon, which was a good match with the UV and thermal sterilization process. (2) A typical sterilization process in a Trombe wall was divided into three areas: the UV inactivation area, UV and thermal inactivation area and UV inactivation area. (3) The weather conditions played an important role in the sterilization performance. UV sterilization was dominant in cloudy weather, and thermal sterilization was dominant in sunny weather. (4) In Nanjing, Shanghai, Xining and Guangzhou, the average daily clean air volumes in heating months were 39.4, 33.5, 32.2 and 39.8 m3/m2, respectively. (5) When the wall height increased from 1.5 m to 3.5 m, the average daily clean air volume in heating months increased from 31.7 to 43.6 m3/m2.

A novel strategy for norovirus removal from wastewater based on bacterial-viral interactions

Norovirus is the main pathogen of acute gastroenteritis worldwide. It is highly resistant to the environment. The virus is not effectively inactivated by either UV or chlorine disinfection. Sewage is one of the sources of the spread of norovirus epidemic. This study delved into the capacities and mechanisms employed by Sphingobacterium multivorum in the removal of Norovirus from wastewater. The adsorption process was optimised by response surface method, and adsorption effects were explored by transmission electron microscopy, analysis of monosaccharide, molecular docking. A reduction of 2.42 log units of norovirus in simulated wastewater was facilitated by S S. multivorum. The optimal adsorption performance by S. multivorum was observed under conditions of a pH value of 8.4, a temperature of 25 °C, and a duration of 1.3 h. The effector molecule for norovirus adsorption by S. multivorum was located in the bacterial EPS. The effector molecule is a class of substances with structural similarities to human type A, B and Lewis A histo-blood group antigens, and its monosaccharide component is mainly fucose. The results of molecular interaction docking simulations showed that fucose was able to form hydrogen bonding interactions with amino acids in the norovirus P protein. Norovirus-bacteria interactions provide methods for wastewater norovirus removal and new strategies for other virus removal processes.

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

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

Implementation of Convolutional Neural Network (CNN) Algorithm for Autonomous Robot

In Indonesia, the development of autonomous robots has emerged intensively since the last coronavirus pandemic, especially the autonomous UV disinfection (A-UV) robot. A-UV disinfection robot has the purpose of purifying germs and pathogens in critical areas, such as the hospital. As the minuscule creature can be difficult to control, the anticipation of letting no human have contact with it is one of the other purposes of the A-UV disinfection robot. However, the systematic development of the autonomous robot is the priority, where the robot can offer a collision-free obstacle, and target-lock when arriving at the designated location. In this study, two main contributions are proposed to develop the autonomous robot: 1) Convolutional Neural Network (CNN) algorithm to learn the potential surrounding the lock area from the dataset to ensure collision-free during the operation. 2) Original design to ensure the compactness of the autonomous robot with almost omnidirectional UV light. We design the surrounding area with “BOX” as the obstacle and “SIGN STOP” as the target in our CNN dataset. The performance is validated to have 97% and 99% for training and validation performance and 0.3% for loss. The robot prototype was also developed and tested inside a workspace with a size of 2.1 x 3 m. The robot prototype successfully performed the required tasks.

Evaluating the Performance of UV Disinfection across the 222-365 nm Spectrum against Aerosolized Bacteria and Viruses.

Bioaerosols play a significant role in the transmission of many infectious diseases, especially in enclosed indoor environments. Ultraviolet (UV) disinfection has demonstrated a high efficacy in inactivating microorganisms suspended in the air. To develop more effective and efficient UV disinfection protocols, it is necessary to evaluate and optimize the effectiveness of UV disinfection against aerosolized bacteria and viruses across the entire UV spectrum. In this study, we evaluated the performance of UV disinfection across the UV spectrum, ranging from 222 to 365 nm, against aerosolized bacteria and viruses, including Escherichia coli, Staphylococcus epidermidis, Salmonella enterica, MS2, P22, and Phi6. Six commonly available UV sources, including gas discharge tubes and light-emitting diodes with different emission spectra, were utilized, and their performance in terms of inactivation efficacy, action spectrum, and energy efficiency was determined. Among these UV sources, the krypton chloride excilamp emitting at a peak wavelength of 222 nm was the most efficient in inactivating viral bioaerosols. A low-pressure mercury lamp emitting at 254 nm performed well on both inactivation efficacy and energy efficiency. A UV light-emitting diode emitting at 268 nm demonstrated the highest bacterial inactivation efficacy, but required approximately 10 times more energy to achieve an equivalent inactivation level compared with that of the krypton chloride excilamp and low-pressure mercury lamp. This study provides insights into UV inactivation on bioaerosols, which can guide the development of effective wavelength-targeted UV air disinfection technologies and may significantly help reduce bioaerosol transmission in public areas.

A quanta-independent approach for the assessment of strategies to reduce the risk of airborne infection

The Wells-Riley model is extensively used for retrospective and prospective modelling of the risk of airborne transmission of infection in indoor spaces. It is also used when examining the efficacy of various removal and deactivation methods for airborne infectious aerosols in the indoor environment, which is crucial when selecting the most effective infection control technologies. The problem is that the large variation in viral load between individuals makes the Wells-Riley model output very sensitive to the input parameters and may yield a flawed prediction of risk. The absolute infection risk estimated with this model can range from nearly 0 % to 100 % depending on the viral load, even when all other factors, such as removal mechanisms and room geometry, remain unchanged. We therefore propose a novel method that removes this sensitivity to viral load. We define a quanta-independent maximum absolute before-after difference in infection risk that is independent of quanta factors like viral load, physical activity, or the dose-response relationships. The input data needed for a non-steady-state calculation are just the removal rates, room volume, and occupancy duration. Under steady-state conditions the approach provides an elegant solution that is only dependent on removal mechanisms before and after applying infection control measures. We applied this method to compare the impact of relative humidity, ventilation rate and its effectiveness, filtering efficiency, and the use of ultraviolet germicidal irradiation on the infection risk. The results demonstrate that the method provides a comprehensive understanding of the impact of infection control strategies on the risk of airborne infection, enabling rational decisions to be made regarding the most effective strategies in a specific context. The proposed method thus provides a practical tool for mitigation of airborne infection risk.

A data mining-based framework to define optimal operation strategies for in-duct ultraviolet germicidal irradiation systems for different climatic conditions

This paper presents a novel data mining framework for optimizing the operation of in-duct Ultraviolet germicidal irradiation (UVGI) systems employed for air disinfection within air handling units. The performance of the UVGI system is influenced by the operating conditions of air handling units. As a result, under favourable operating conditions, the system produces excessive Ultraviolet C energy beyond the required disinfection levels, causing energy waste and accelerating the degradation of heating, ventilation, and air conditioning (HVAC) components. The framework aims to improve energy efficiency and mitigate material degradation within HVAC components by systematically adjusting UVGI system output based on changing operating conditions of air handling units throughout the year using advanced data mining techniques. The methodology involves several steps: Firstly, data pre-processing is performed to improve data quality. Then, the K-means clustering algorithm is applied to discover patterns in operational data. Subsequently, an effective performance index and baseline are defined to identify energy-saving opportunities within each cluster. Finally, the optimal operation strategy is defined based on the determined baseline. The framework is extended to five distinct climate zones to derive region-specific operation strategies. Results from a case study in a small office building in Montreal and an extension to five distinct climate zones in Canada demonstrate energy savings from 8% to 37%. This study offers a promising approach to optimize UVGI system operation, with potential applications in various energy systems in buildings requiring adaptive operational conditions for optimal performance.

Inactivation of pathogenic microorganisms under UV/O3 advanced disinfection system in mariculture water

The damage that pathogenic microorganisms cause to mariculture has received a lot of attention lately. Streptococcus agalactiae (S.agalactiae), Escherichia coli (E. coli) and Uronema marinum (U. marinum) are typical harmful microorganisms. This study investigated the inactivation of S.agalactiae, E. coli and U. marinum under UV/O3 system. Results showed that the UV/O3 system could produce hydroxyl radicals (·OH) with strong oxidizing properties, which made the inactivation rate of S.agalactiae reaching 4.31 log in 120 s, the inactivation rate of E. coli reaching 3.1 log in 90 s, significantly more effective than single UV or O3 disinfection system. The efficiency of inactivation will be enhanced by an increase in O3 content and UV intensity. And there was an optimal O3 concentration during the inactivation process. In alkaline and high salinity environment, the inactivation efficiency was greater. Through the detection of chromosomal DNA of S. agalactiae, E. coli and U. marinum before and after inactivation, it demonstrated that the UV/O3 system destroyed the genetic material in the nucleus. The analysis of K+ showed that the system destroyed its physiological function. The non-toxicity of the inactivation approach was demonstrated by the toxicity tests. From the SEM images, it could be seen that the UV/O3 system had an effect on the morphology and structural of bacteria.

Design and optical simulation of heating, ventilation, and air conditioning duct incorporating ultraviolet-C channels based on Bunimovich stadium

A recent breakout of the COVID-19 pandemic inspired researchers to find ideal solutions for removing SARS-CoV-2 from indoor air. In-duct ultraviolet germicidal irradiation was employed in rooms with heating, ventilation, and air conditioning (HVAC) systems to stop the spread of COVID-19. The current investigation introduces Bunimovich stadium-inspired flow channels inside the square-shaped duct. The impact of the Bunimovich channel shape on light distribution is studied and compared with the traditional rectangular-shaped duct. The core of the Bunimovich channel is a square with δ and γ equal to 0.5. A semi-circle surrounds the square's left and right sides. The air velocity in the HVAC system with the Bunimovich channels varies from 10 m/s to 15 m/s, resulting in variation in aerosol particles’ residence period in front of the ultraviolet-C (UVC) source. The Bunimovich channel delivered better UVC irradiance uniformity than a rectangular duct. The uniformity ratio for the Bunimovich channel was 0.788 compared to 0.6949 for the rectangular duct. The UVC dose delivered by the source in the Bunimovich channel varies from 1.48 mJ/cm2 to 3.03 mJ/cm2. The delivered dose is higher than the required 1.2 mJ/cm2 dose for log-4 reduction (i.e. 99.99%).

Identification and Measurement of Biomarkers at Single Microorganism Level for In Situ Monitoring Deep Ultraviolet Disinfection Process.

Since the COVID-19 disease has been further aggravated, the prevention of pathogen transmission becomes a vital issue to restrain casualties. Recent research outcomes have shown the possibilities of the viruses existing on inanimate surfaces up to few days, which carry the risk of touch propagation of the disease. Deep ultraviolet germicide irradiation (UVGI) with the wavelength of 255-280nm has been verified to efficiently disinfect various types of bacteria and virus, which could prevent the aggravation of pandemic spread. Even though considerable experiments and approaches have been applied to evaluate the disinfection effects, there are only few reports about how the individual bio-organism behaves after ultraviolet C (UVC) irradiation, especially in the aspect of mechanical changes. Furthermore, since the standard pathway of virus transmission and reproduction requires the host cell to assemble and transport newly generated virus, the dynamic response of infectious cell is always the vital aspect of virology study. In this work, high power LEDs array has been established with 270nm UVC irradiation to evaluate disinfection capability on various types of bio-organism, and incubator embedded atomic force microscopy (AFM) is used to investigate the single bacterium and virus under UVGI. The real-time tracking of the living Vero cells infected with adenovirus has also been presented in this study. The results show that after sufficient UVGI, the outer shell of bacteria and viruses remain intact in structure, however the bio-organisms lost the capability of reproduction and normal metabolism. The experiment results also indicate that once the host cell is infected with adenovirus, the rapid production of newborn virus capsid will gradually destroy the cellular normal metabolism and lose mechanical integrity.

Outbreak of Severe Acute Respiratory Syndrome Coronavirus 2 in a Rural Community Hospital during Omicron Predominance.

Healthcare-associated infections due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has increased since the discovery of the Omicron variant. We describe a SARS-CoV-2 outbreak in the medicine-surgery unit of a rural community hospital at the time of high community transmission of Omicron variant in our county. The outbreak occurred in the medicine-surgery unit of an 89-bed rural community hospital in northern Maine. The characteristics of the patients and healthcare workers (HCWs) affected by the outbreak are described. Patient and HCW data collected as part of the outbreak investigation were used in this report. The outbreak control measures implemented are also described. A total of 24 people tested positive for SARS-CoV-2 including 11 patients and 13 HCWs. A total of 12 of the 24 (50%) persons were symptomatic, and rhinorrhea was the most common symptom noted (8/12, 67%). None of the symptomatic persons had gastrointestinal symptoms or symptoms of a loss of sense of smell or taste. All HCWs were vaccinated and 8 of the 11 patients were vaccinated. Outbreak control measures in the affected unit included implementation of full PPE (N95 respirators, eye protection, gowns and gloves) during all patient care, serial testing of employees and patients in the affected unit, cohorting positive patients, closing visitation and thorough environmental cleaning including use of ultraviolet (UV) light disinfection. This outbreak exemplifies the high transmissibility of the Omicron variant of SARS-CoV-2. The outbreak occurred despite a well-established infection control program. We noted that serial testing, use of N95 respirators during all patient care and UV disinfection were some of the measures that could be successful in outbreak control.

Reinforcing Feedbacks for Sustainable Implementation of Rural Drinking-Water Treatment Technology.

Progress toward universal access to safe drinking water depends on rural water service delivery models that incorporate water safety management. Water supplies of all types have high rates of fecal contamination unless water safety risks are actively managed through water source protection, treatment, distribution, and storage. Recognizing the role of treatment within this broader risk-based framework, this study focuses on the implementation of passive chlorination and ultraviolet (UV) disinfection technologies in rural settings. These technologies can reduce the health risk from microbiological contaminants in drinking water; however, technology-focused treatment interventions have had limited sustainability in rural settings. This study examines the requirements for sustainable implementation of rural water treatment through qualitative content analysis of 26 key informant interviews, representing passive chlorination and UV disinfection projects in rural areas in South America, Africa, and Asia. The analysis is aligned with the RE-AIM framework and delivers insight into 18 principal enablers and barriers to rural water treatment sustainability. Analysis of the interrelationships among these factors identifies leverage points and encourages fit-for-purpose intervention design reinforced by collaboration between facilitating actors through hybrid service delivery models. Further work should prioritize health impact evidence, water quality reporting guidance, and technological capabilities that optimize trade-offs in fit-for-purpose treatment design.

Rapid inactivation of antibiotic resistance genes and virulence genes in the building ventilation duct by UV185+254 irradiation

The energy-efficient inactivation of airborne antibiotic resistance genes (ARGs) and virulence genes was seldom investigated in full-scale ventilation systems. This study examined the potential of UV disinfection to inactivate two types of chromosome- or plasmid-encoded ARGs (mecA and amp) and one chromosomal virulence gene (tst1) within two host bacterial species: Staphylococcus aureus and Escherichia coli. UV185+254 disinfection exhibited dual damages (i.e., physical by 254 nm UV and oxidative by the produced ozone) on those target genes, resulting in relatively strong adaptability to temperature and low electrical energy per order in specific gene removal (down to 1 kJ m−3). It was found that the disinfection efficiency of target genes was up to 2 orders of magnitude lower than that of the host bacteria. The target genes with more bases and higher weighted bipyrimidine content were more susceptible to UV185+254 treatment. Thicker cell walls and plasmid carriers prominently hindered UV185+254 deactivation, requiring larger radiation power to enhance the gene removal efficiency in bioaerosols.

MBR and GAC filtration followed by UV disinfection – implications for wastewater reuse at full scale

ABSTRACT Influences of upstream wastewater treatment on the process combination of granular activated carbon (GAC) and ultraviolet (UV) disinfection were studied and the implications of this for wastewater reuse were assessed. GAC is an efficient chemical barrier but contributes little to the removal of indicator bacteria, and generally increases total bacteria concentrations, necessitating disinfection with UV radiation, for example, to ensure the safe reuse of wastewater. The efficiency of UV disinfection is impacted by factors such as particle concentration and UV absorbance of the water and is thus affected by upstream treatment processes. A full-scale wastewater treatment plant with a membrane bioreactor (MBR) followed by GAC filtration was compared to a treatment plant with a conventional activated sludge process and sand filtration, followed by GAC filtration. The removal of indicator bacteria was higher by the GAC filter that was preceded by an MBR. A UV fluence of 400 J/m2 was sufficient to reach irrigation water quality for both process combinations and to meet the criteria for microbial drinking water quality in the MBR + GAC effluent. One sample was selected for chemical analysis, comprising approximately 100 parameters, demonstrating that the MBR + GAC + UV (400 J/m2) effluent met all drinking water criteria except for nitrate levels.

Effect of dissolved organic matter on bacterial regrowth and response after ultraviolet disinfection

The effect of dissolved organic matter (DOM) on bacterial regrowth in water after disinfection using ultraviolet (UV) light emitting diodes (UVLEDs) is still unclear. Herein, the regrowth and responses of Vibrio parahaemolyticus and Bacillus cereus were investigated after being exposed to UVLEDs at combined wavelengths (265 and 280 nm) in a phosphate-buffered saline consisting of Suwannee River natural organic matter (SRNOM) and Suwannee River fulvic acid (SRFA). Low-molecular-weight (MW) organic compounds, which may form into intermediary photoproducts, and indicate bacterial repair metabolism, were characterized through non-target screening using orbitrap mass spectrometry. This study demonstrates the ability of the UVLEDs-inactivated cells to regrow. After UV exposure, a considerable upregulation of RecA was observed in two strains. With increasing the incubation time, the expression levels of RecA in V. parahaemolyticus increased, which may be attributed to the dark repair mechanism. Coexisting anionic DOM affects both the disinfection and bacterial regrowth processes. The time required for bacterial regrowth after UV exposure reflects the time needed for the individual cells to reactivate, and it differs in the presence or absence of DOM. In the presence of DOM, the cells were less damaged and required less time to grow. The UVLEDs exposure results in the occurrence of low-MW organic compounds, including carnitine or acryl-carnitine with N-acetylmuramic acid, which are associated with bacterial repair metabolism. Overall, the results of this study expand the understanding of the effects of water matrices on bacterial health risks. This can aid in the development of more effective strategies for water disinfection.

Hygienic efficiency of ultraviolet disinfection of water in centralized drinking and household water supply systems (systematic review)

Introduction. Drinking water supplied to the population must be safe in epidemic terms. However, some viruses and parasites are resistant to the disinfecting effect of traditionally used agents for water treatment. The use of UV irradiation ensures the microbiological safety of water, but there are factors affecting its effectiveness. 
 The purpose of the review was to systematize scientific data on the effectiveness of the use of UV irradiation in relation to drinking water.
 Materials and methods. The search for scientific publications was carried out using literature databases MedLine/PubMed, Scopus, and Science Direct. The total number of publications was one thousand six hundred forty-six. The criteria for including the report in the systematic review were: publications in Russian or English with an available full-text version; samples for the study are water from centralized water supply systems or specially prepared microorganisms; any type of research evaluating the effectiveness of a wide range of doses of UV irradiation against microorganisms.
 Results of the analysis of publications. A systematic review included 17 reports about the effect of UV irradiation on bacteria and viruses. The subject of several studies was the resistance of protozoan cysts and helminth eggs to different doses of UV irradiation. According to the results presented in the publication, pathogenic viruses and bacteria, giardia cysts possess of the least resistance to UV irradiation (100% inactivation). 4 log-inactivation was established for Mycobacteia. E. coli and coliphages demonstrate a wide range of indicators of the resistance to ultraviolet radiation due to the diversity of the studied strains. 
 Conclusion. UV disinfection should be used as an additional method in combination with traditional reagents methods of water treatment. It is necessary to study the effect of UV irradiation on helminth eggs and protozoan cysts.

Infectiousness model of expelled droplets exposed to ultraviolet germicidal irradiation coupled with evaporation

Respiratory diseases propagated by droplet-based transmission are a serious public health hazard, leading, in extreme cases, to pandemics such as influenza and the recent Coronavirus outbreak. Droplet infectiousness evolves in response to the environment in such a way that it decreases with time and distance from the source. Droplets can also be treated with ultraviolet germicidal irradiation (UVGI) to accelerate the reduction in their survival rate. In addition, airflow management and furnishings in public spaces can be optimized to reduce exposure to expelled droplets. This introduces a role for engineered medical interventions based on precise modelling of the time evolution of droplet infectiousness. However, information is lacking on computational fluid dynamics (CFD) simulations of the time evolution of droplet infectiousness when exposed to both evaporation and UVGI at the same time. Therefore, in this study, we developed and presented algorithms for tracking droplet infectiousness in a CFD simulation. The variations of droplets’ infectiousness were investigated through the combination of parameters describing humidity and temperature, as well as the deployment of UVGI in confined public space environments. We have shown that, for airborne droplets, increased temperature leads to decreased infectiousness in propagation lengths and entrainment time, while increased humidity leads to increased infectiousness propagation lengths and entrainment times. Smaller droplets with diameters ≤ 110 μm remain entrained longer in the air, whereas droplets with a diameter ≥ 140 μm travel in the air stream for a relatively short time before falling to a surface due to gravity, depending on the specific relative humidity (RH) and temperature conditions. Thus, our data suggest that infectiousness of droplets is substantially reduced due to the influence of evaporation, and it is further decreased when exposed to UV irradiance. We also show that, due to the combined influence of UVGI and evaporation conditions, the infectiousness of droplets decreased faster. Our model can track droplet infectiousness, thus helping to understand how the spread of infectious droplets is reduced in a confined environment.

Mechanism and degradation pathways of photo-Fenton system using Fe(III)-EDDS for Microcystis aeruginosa and microcystin-LR removal

Harmful algal blooms is a global problem of water pollution causing great economic losses to countries. Microcystis aeruginosa, as a dominant algal species in cyanobacterial blooms, has attracted extensive attention. However, most of the current studies on the treatment of alga-containing waters focus on the removal of algal cells or microcystins, lacking the exploration of the degradation pathways and analyses of the toxicity of the products. In this paper, we constructed a photo-Fenton system using Fe(III)-EDDS (EDDS: Ethylenediamine-N,N’-disuccinic acid) complex as an iron source for the simultaneous removal of Microcystis aeruginosa as well as microcystin-LR (MC-LR). The results showed that adding 0.1 mM of Fe(III)-EDDS complex and 1.0 mM of H2O2 achieved 83.3% algal cell removal in 240 min under neutral pH conditions and also degraded 72.5% of MC-LR. Moreover, the degradation products of MC-LR and EDDS were analyzed by LC-MS, which showed that the toxicity of the MC-LR molecule was greatly reduced by benzene ring removal and decarboxylation of partial amino acids, while its degradation resulted from the destruction of amino acids in the MC-LR molecule. The toxicity analyses provide a basis for the practical application of the system, hence consideration can be given to combining or improving it with the existing UV disinfection technologies in water supply plants for potential algal bloom outbreaks. This study was the first time to apply the Fe(III)-EDDS system to the field of microalgae removal and MC-LR detoxication, aiming to provide new development ideas for water purification and photochemical algae removal technology.