UV Dose Research Articles

Characterizing and Tuning the Properties of Polydiacetylene Films for Sensing Applications.

Self-assembled, polymerized diacetylene (DA) nanostructures and two-dimensional films have been studied over the past two decades for sensor applications because of their straightforward visual readout. DA monomers, when exposed to UV light, polymerize to produce a visibly blue polymer. Blue phase polydiacetylenes (PDAs) when exposed to an external stimuli, such as temperature or UV light, undergo a chromatic phase transition to a fluorescent, visibly red phase. The tunability of the monomer to blue to red chromatic phase transitions by choice of diacetylene monomer in the presence of metal cations is systematically and comprehensively investigated to determine their effects on the properties of PDA Langmuir films. The polymerization kinetics and domain morphology of the PDA films were characterized using polarized fluorescent microscopy, UV-vis-fluorescent spectroscopy, and Fourier transform infrared spectroscopy (FTIR). Increasing the monomer alkyl tail length was found to strongly increase the UV dose necessary to produce optimally blue films and fully red films. A decrease in the polymer domain size was also correlated with longer-tailed DA molecules. Metal cations have a diverse effect on the film behavior. Alkaline-earth metals such as Mg, Ca, and Ba have a negligible effect on the phase transition kinetics but can be used to tune PDA polymer domain sizes. The Ni and Fe cations increase the UV dose necessary to produce red phase PDA films and significantly decrease the polymer domain sizes. The Zn, Cd, and Cu ions exhibit strong directed interactions with the PDA carboxylic acid headgroups, resulting in quenched fluorescence and a unique film morphology. FTIR analysis provides insight into the metal-PDA binding mechanisms and demonstrates that the coordination between the PDA film headgroups and the metal cations can be correlated with changes in the film morphology and kinetics. The findings from these studies will have broad utility for tuning PDA-based sensors for different applications and sensitivity ranges.

Ultraviolet light and ozone controls Cryptocaryon irritans infection in factory aquaculture

Cryptocaryon irritans is a pathogenic ectoparasitic ciliate that infects marine teleosts, causing massive mortality and economic losses in aquaculture. Ultraviolet light (UV) and ozone (O3) are commonly used for disinfection in factory aquaculture; however, the efficacy of neither method against C. irritans had been evaluated. This study aimed to evaluate the efficacy of UV and ozone in destroying C. irritans. UV or ozone treatment changed or ruptured the shape of C. irritans theronts, although C. irritans tomonts showed some resistance. The minimum in vitro lethal doses of UV and ozone against theronts were 2.88× 105 μWs/cm2 and 0.15 mg/L, respectively. In vivo, UV and ozone-treated theronts lost their ability to infect pompano (Trachinotus ovatus) when exposed to doses above 1.84 × 105 μWs/cm2 and 0.10 mg/L, respectively. Unexpectedly, exposure to low ozone levels (< 0.04 mg/L) enhanced theronts infecting ability. These results provide a reference for C. irritans theronts disinfection in factory aquaculture and further studies on C. irritans.

Characteristics and Mechanisms of Bacteriophage MS2 Inactivation in Water by UV Activated Sodium Persulfate

Viruses in the aquatic environment have strong resistance to common disinfection techniques. To contribute to the development of efficient virus inactivation technologies, the characteristics and mechanisms of virus inactivation in a UV activated sodium persulfate(UV/PS) system were studied. The inactivation rate and kinetic characteristics of bacteriophage MS2 in water samples by the UV/PS were studied. The effects of PS dosage, pH, and the initial concentration of bacteriophages on the inactivation effect were also investigated. Furthermore, the morphologies of phages before and after UV/PS treatment were observed by transmission scanning electron microscope, and the free radicals in the reaction system were identified by electron paramagnetic resonance spectroscopy. By means of a free radical quenching experiment, the contribution rate of various factors in the UV/PS system to phage inactivation was also analyzed and calculated. The results showed that when the UV irradiation intensity was 160 μW·cm-2, the phage MS2 of 4.39 lg could be removed after UV/PS treatment for 4 min, which was 1.44 lg higher than that of the same UV dose alone. The inactivation of phage MS2 by the UV/PS system was in accordance with the first-order kinetic model. Increasing the initial concentration of PS in the system significantly improved the inactivation rate of phages, while pH and the initial concentration of phages had little effect on the inactivation rate. UV/PS treatment damages the capsid of phages and promotes the aggregation of phage particles. The presence of SO4-· and·OH in the UV/PS system was an important factor for the inactivation of MS2 phages. Finally, ·OH contributed more to MS2 phage inactivation than SO4-·.

Kinetics and Monte Carlo simulation of UV disinfection of B. subtilis spores and SARS-CoV-2 in dried saliva droplets.

Surfaces can be contaminated by droplets produced through coughing or sneezing. In this exploratory work, the UV disinfection results of Bacillus subtilis spores in dried saliva droplets were fitted to a three-parameter kinetic model (R2 ≥ 0.97). This model has a disinfection rate constant for single organisms and a smaller one for aggregates found in droplets. The fraction of organisms found in aggregates (β) could account for the effects of different-sized droplets in the experimental work. Since a wide spectrum of droplet sizes can be produced, and some of the rate constants were uncertain, Monte Carlo simulation was used to estimate the UV inactivation performance in dried saliva droplets in a variety of conditions. Using conservative distribution for β, the model was applied to the UV disinfection of SARS-CoV-2 in dried saliva droplets. It was shown that a one-log reduction of SARS-CoV-2 was very likely (p>99.9%) and a two-log reduction was probable (p=75%) at a dose of 60 mJ/cm2. Aggregates tend to be variable and limit the log reductions that can be achieved at high UV doses.

Enhanced biodegradation of non-biodegradable plastics by UV radiation: Part 1

Optimum UV pretreatment of polystyrene (PS), polyethylene (PE) and polyethylene terephthalate (PET) plastics for their efficient biodegradation were evaluated in this study. It was found that a longer incubation time and shorter distance to UV source (t2d2 condition) (UV dose of 7.02 × 1012 μW·cm-2·s) resulted in a higher roughness, hydrophilicity, microbial viability, biofilm formation, surface degradation, and a more significant physical and molecular weight reduction. The highest biodegradation within 45 days happened to PE and PS with respective 7.8 and 5.13% physical weight loss, and 4.71 and 2.1 fold molecular weight reduction compared to the “un-pretreated & strain-free bio-treated” (control-3). The hydrophilicity of PS and PE were increased to the “UV-pretreated & bio-treated” samples with a reduction in water contact angle from 105° to 5° in PS and 102° to 60° in PE. Microscopic analysis indicated significant surface property changes or degradation (cracks and holes) on “UV-pretreated & bio-treated” samples. The thermal gravimetric analysis also showed 73, 25 and 20 °C reductions in degradation temperature of “UV-pretreated & bio-treated” PE, PS and PET, respectively. Chemical transformation revealed new peaks in “UV-pretreated & bio-treated” samples, indicating the positive role of UV in biodegradation efficiency. Statistics analysis showed that 45 days was adequate to obtain optimum biodegradation efficiency (p < 0.05).

Artificial neural network modeling of full-scale UV disinfection for process control aimed at wastewater reuse

Accurate modeling of wastewater ultraviolet disinfection is fundamental as support for process optimization and control. Detailed modeling of hydrodynamics and fluence rate via computational fluid dynamics, coupled to laboratory studies of inactivation kinetics, are usually the preferred approach for UV disinfection modeling. Despite this approach often provides accurate predictive performance, it requires significantly high computational time, making it unfeasible for real-time process control. In this study, to enable an effective process control, black-box regression models were assessed as a modeling alternative for UV disinfection, synthesizing hydrodynamics, fluence rate and inactivation kinetics. UV disinfection of a full-scale wastewater treatment plant in Italy was monitored for 10 months, measuring influent and effluent E. coli concentration, turbidity, absorbance at 254 nm, temperature and flow rate at different UV doses. Considering the usually observed distribution of effluent E. coli concentration and the zero inflation of the collected dataset, Poisson, zero-inflated Poisson and Hurdle generalized linear models were tested, as well as two-part models coupling a classifier describing the E. coli zero-count events and a regressor estimating the magnitude of E. coli concentrations in positive-count events. The two-part artificial neural network model showed the best predictive performance, being able of both describing nonlinearities and handling the high proportion of null values in the dataset. The deployment of this model to control ultraviolet disinfection was simulated, estimating a plausible 63% energy saving.

Synthesis and optical characterization of Dy3+ doped barium alumino silicate phosphor

The present article reports the photoluminescence, thermoluminescence and mechanoluminescence behavior of Ba2Al2SiO7: xDy3+ (x = 1–4 mol%) phosphor synthesized via solid-state reaction method. X-Ray powder diffraction technique was used to confirm the phase purity and calculate the average crystallite size. Photoluminescence studies show intense peaks in blue and yellow region, which attributes to 4F9/2→6H15/2 and 6H13/2 transition of Dy3+ respectively and optimum intensity in the photoluminescence emission spectra was found to be at 2 mol% concentration of Dy3+. From the TL glow curve trapping parameter; like activation energy and frequency factor were calculated and it is noticed that TL intensity vary linearly with UV dose up to 15 min of exposure time. Mechanoluminescence studies depicts that, ML intensity increases both with increase in UV dose and height of piston. This suggest that the prepared phosphor may act as a potential candidate for low UV dosimetry and damage sensor.

Mechanisms underlying the effect of chlorination and UV disinfection on VBNC state Escherichia coli isolated from hospital wastewater

The occurrence of viable but non-culturable (VBNC) bacteria in the wastewater system poses a huge threat to environmental and public health, in particular in hospital wastewater treatment system (HWTS). HWTS-oriented studies have been conducted to assess the effectiveness of chlorination and UV disinfection using indigenous bacteria. Results revealed that the VBNC Escherichia coli and ARGs remained persistent even at high chlorination (12 mg/L for 2.5 h) and UV doses (1000 mJ/cm2). The molecular mechanisms underlying chlorination-/UV-induced VBNC state in E. coli were explored through the transcriptomics and results suggested that most energy-dependent physiological activities (e.g., metabolism) have been suppressed in VBNC E. coli, while the pathogenicity-related genes varied insignificantly compared to the culturable cells, indicating that the VBNC E. coli could potentially display pathogenicity. Further Galleria mellonella model experiment has confirmed that although the disinfection-induced VBNC state made cells less infectious, these cells could regain their pathogenicity after resuscitation. This in vitro study can be used as a reference for studies on infections from VBNC bacteria and highlights the health risk due to VBNC pathogens in hospital effluents. There is a need to develop effluent standards specifically for healthcare facilities, and a stricter downstream disinfection strategy should be considered for the removal of VBNC cells and ARGs in the effluent.

The impact of bacterial cell aggregation on UV inactivation kinetics

Reconditioning of food processing water streams for reuse is an increasingly common water management practice in the food industry and UV disinfection is often employed as part of the water treatment. Several factors may impact the effect of UV radiation. Here, we aim to assess the impact of cell aggregation on UV inactivation kinetics and investigate if UV exposure induces aggregation. Three strains, isolated from food processing water reuse lines (Raoultella ornithinolytica, Pseudomonas brenneri, Rothia mucilaginosa) and both an aggregating and a non-aggregating strain of Staphylococcus aureus were exposed to UVC light at 255 nm using UV LED equipment. Total Viable Count and phase-contrast microscopy, coupled with image analysis, were used to compare the UV inactivation kinetics with the average particle size for a range of UV doses. Tailing effect, seen as a strong reduction in inactivation rate, was observed for all strains at higher UV doses (industrial strains ≥ 50 or 120 mJ/cm2, S. aureus strains ≥ 40 or 60 mJ/cm2). The naturally aggregating strains were more UV tolerant, both within and between species. When aggregates of S. aureus were broken, UV tolerance decreased. For the processing water isolates, the lowest applied UV dose (25 mJ/cm2) significantly increased the average particle size. Application of higher UV doses obtained with longer exposure times did not further increase the particle size compared with untreated samples. For the S. aureus strains, however, no consistent change in average particle size was observed due to UV. Our results demonstrate that aggregating strains have a higher degree of protection and that UV radiation induces aggregation in some, but not all bacteria. A better understanding of the mechanisms governing microbial aggregation and survival during UV treatment could help to improve UV applications and predictions of microbial inactivation.

Towards Promising Platform by Using Annular Photonic Crystals to Simulate and Design Useful Mask

Human masks are considered the mainstay in air filtration and purification technologies and against the spreading of bacterial and viral infections. This paper introduces a novel design of a human mask to increase the ultraviolet germicidal irradiation effect on pathogens. The proposed design consists of a tube with an annular photonic crystal (APC) attached to the mask’s orifice, and a UV source is located in the tube’s center. The main role of this study is the enhancement of UV doses based on the reflectivity of the proposed APC. Therefore, increasing pathogens’ inactivation level in the incoming air to the mask’s orifice could be investigated. The numerical investigations demonstrated that the proposed APC could provide a complete photonic bandgap with a high reflectivity in the wavelength regime from 207 to 230 nm. In addition, we have considered the roles of the thickness of layers, inner core radius, and the azimuthal number. Meanwhile, the results showed the ability to use a wide range of core radius values without almost any variations in the optical properties of the proposed design. Such results could grant the advantage of using this design by the manufacturing of human masks with different sizes besides the inclusions in other ultraviolet germicidal irradiation applications.

Real-time UV index retrieval in Europe using Earth observation-based techniques: system description and quality assessment

Abstract. This study introduces an Earth observation (EO)-based system which is capable of operationally estimating and continuously monitoring the ultraviolet index (UVI) in Europe. UVIOS (i.e., UV-Index Operating System) exploits a synergy of radiative transfer models with high-performance computing and EO data from satellites (Meteosat Second Generation and Meteorological Operational Satellite-B) and retrieval processes (Tropospheric Emission Monitoring Internet Service, Copernicus Atmosphere Monitoring Service and the Global Land Service). It provides a near-real-time nowcasting and short-term forecasting service for UV radiation over Europe. The main atmospheric inputs for the UVI simulations include ozone, clouds and aerosols, while the impacts of ground elevation and surface albedo are also taken into account. The UVIOS output is the UVI at high spatial and temporal resolution (5 km and 15 min, respectively) for Europe (i.e., 1.5 million pixels) in real time. The UVI is empirically related to biologically important UV dose rates, and the reliability of this EO-based solution was verified against ground-based measurements from 17 stations across Europe. Stations are equipped with spectral, broadband or multi-filter instruments and cover a range of topographic and atmospheric conditions. A period of over 1 year of forecasted 15 min retrievals under all-sky conditions was compared with the ground-based measurements. UVIOS forecasts were within ±0.5 of the measured UVI for at least 70 % of the data compared at all stations. For clear-sky conditions the agreement was better than 0.5 UVI for 80 % of the data. A sensitivity analysis of EO inputs and UVIOS outputs was performed in order to quantify the level of uncertainty in the derived products and to identify the covariance between the accuracy of the output and the spatial and temporal resolution and the quality of the inputs. Overall, UVIOS slightly overestimated the UVI due to observational uncertainties in inputs of cloud and aerosol. This service will hopefully contribute to EO capabilities and will assist the provision of operational early warning systems that will help raise awareness among European Union citizens of the health implications of high UVI doses.

Degradation of 2,6-dichloro-1,4-benzoquinone by advanced oxidation with UV, H2O2, and O3: parameter optimization and model building

Abstract Halobenzoquinones are disinfection by-products with cytotoxicity, carcinogenicity, and genotoxicity. In this study, we investigated the removal of the HBQ 2,6-dichloro-1,4-benzoquinone (DCBQ) from water using advanced oxidation processes. The removal of DCBQ from water using UV, H2O2, and O3 advanced oxidation processes individually was not ideal with removal rates of 36.1% with a UV dose of 180 mJ/cm2, 32.0% with 2 mg/L H2O2, and 57.9% with 2 mg/L O3. Next, we investigated using the combined UV/H2O2/O3 advanced oxidation process to treat water containing DCBQ. A Box–Behnken design was used to optimize the parameters of the UV/H2O2/O3 process, which gave the following optimum DCBQ removal conditions: UV dose of 180 mJ/cm2, O3 concentration of 0.51 mg/L, and H2O2 concentration of 1.76 mg/L. The DCBQ removal rate under the optimum conditions was 94.3%. We also found that lower humic acid concentrations promoted DCBQ degradation, while higher humic acid concentrations inhibited DCBQ degradation.

Simulation Design and Optimization of UV-LED Water Purification System Based on Fluid Dynamics and Radiometry

In this paper, we established the flow field and radiation intensity distribution models of water purification equipment based on computational fluid dynamics (CFD) technology and radiometric principles. From geometric shape to hydraulic state and radiation intensity distribution, we fully simulated the real scene of the Ultraviolet LED (UV-LED) water purification system, and provided the reliable data for the UV-LED in the water purification field. Compared with mercury lamp, UV-LEDs have a more flexible layout to produce a variety of radiation intensity distributions. UV dose (the product of radiation intensity over time) is an important indicator. We used a discrete phase model (DPM) to track the path of microbial particles, and found that the residence time of microorganisms in different parts of the model was different. By optimizing the UV-LED layout, the radiation intensity was increased in the sites where the microbes resided longer. The results show that we can improve the efficiency of the water purification equipment by simply adjusting the UV-LED layout without increasing the power, and make the UV dose achieves the national standard.

FANCI functions as a repair/apoptosis switch in response to DNA crosslinks.

Cells counter DNA damage through repair or apoptosis, yet a direct mechanism for this choice has remained elusive. When facing interstrand crosslinks (ICLs), the ICL-repair protein FANCI heterodimerizes with FANCD2 to initiate ICL excision. We found that FANCI alternatively interacts with a pro-apoptotic factor, PIDD1, to enable PIDDosome (PIDD1-RAIDD-caspase-2) formation and apoptotic death. FANCI switches from FANCD2/repair to PIDD1/apoptosis signaling in the event of ICL-repair failure. Specifically, removing key endonucleases downstream of FANCI/FANCD2, increasing ICL levels, or allowing damaged cells into mitosis (when repair is suppressed) all suffice for switching. Reciprocally, apoptosis-committed FANCI reverts from PIDD1 to FANCD2 after a failed attempt to assemble the PIDDosome. Monoubiquitination and deubiquitination at FANCI K523 impact interactor selection. These data unveil a repair-or-apoptosis switch in eukaryotes. Beyond ensuring the removal of unrepaired genomes, the switch's bidirectionality reveals that damaged cells can offset apoptotic defects via de novo attempts at lesion repair.

Dopamine-Initiated Photopolymerization for a Versatile Catechol-Functionalized Hydrogel.

Biomimetic catechol-functionalized hydrogels have attracted substantial attention due to their potential in a variety of biomedical applications, such as tissue repair and regeneration, drug delivery, and antimicrobial and antifouling applications. In this study, a one-pot strategy for fabrication of functional catecholic hydrogels using dopamine as a photoinitiator was developed. Under UV irradiation in an acidic solution, dopamine generates free radicals, likely semiquinone radicals, to trigger the addition polymerization, following pseudo-first-order kinetics. The dopamine-initiated photopolymerization provides a straightforward and facile approach and, in addition, prevents the undesirable oxidation to catecholic groups. Superhydrophilic sulfobetaine methacrylate (SBMA) was applied for developing biocompatible hydrogels. 1H nuclear magnetic resonance, UV-vis spectroscopy, gel permeation chromatography, and rheological studies were conducted to explore the polymerization mechanism and optimal experimental conditions in terms of pH, UV doses, and the concentration of dopamine. The unique properties of the resultant catechol-functionalized pSBMA hydrogels were demonstrated by enhanced mechanical properties through metal-catechol complexation, self-healing and injectable capability, high adhesiveness, and fouling resistance. Consequently, the synthetic strategy to design catecholic hydrogels can leverage the use of dopamine in a variety of applications.

Bacterial cellulose adhesive composites for oral cavity applications

Topical approaches to oral diseases require frequent dosing due to limited retention time. A mucoadhesive drug delivery platform with extended soft tissue adhesion capability of up to 7 days is proposed for on-site management of oral wound. Bacterial cellulose (BC) and photoactivated carbene-based bioadhesives (PDz) are combined to yield flexible film platform for interfacing soft tissues in dynamic, wet environments. Structure-activity relationships evaluate UV dose and hydration state with respect to adhesive strength on soft tissue mimics. The bioadhesive composite has an adhesion strength ranging from 7 to 17 kPa and duration exceeding 48 h in wet conditions under sustained shear forces, while other mucoadhesives based on hydrophilic macromolecules exhibit adhesion strength of 0.5–5 kPa and last only a few hours. The work highlights the first evaluation of BC composites for mucoadhesive treatments in the buccal cavity.

Research and development of ship ballast water treatment system

If the ballast water is discharged without treatment, it will cause serious ecological damage to the local port. This paper takes the ship ballast water treatment system as the research object. The existing ballast water treatment system is investigated. A ship ballast water treatment system with capacity of 150m3 /h, filtration accuracy of 40um and UV dose of 350mJ/cm2 is designed. This paper introduces the working principle of the main unit of ship ballast water treatment system, and designs an automatic monitoring system based on PLC and LabVIEW. The results show that the device has high practicability and feasibility.

The characteristic of N-nitrosodimethylamine precursor release from algal organic matter and degradation performance of UV/H2O2/O3 technology

Seasonal cyanobacterial blooms in eutrophic water releases algal organic matter (AOM), which contains large amount of dissolved organic nitrogen (DON) and is difficult to be removed effectively by conventional treatment processes (e.g., coagulation and sand filtration) because of its high hydrophilicity. Moreover, N-nitrosodimethylamine (NDMA) can be generated by the reaction of AOM with disinfectants in the subsequent disinfection process. In this study, the formation of NDMA from different AOM components was explored and the control of algal-derived NDMA precursors by UV/H2O2/O3 was evaluated. The results showed that the hydrophilic and polar components of AOM with the low molecular weight had higher NDMA yields. UV-based advanced oxidation process (AOPs) is effective in degrading NDMA precursors, while the removal rate can be affected greatly by UV doses. The removal rate of NDMA precursors by UV/H2O2/O3 is higher than by UV/H2O2 or UV/O3 which can reach 95% at the UV dose of 400 mJ/cm2. An alkaline environment reduces the oxidation efficiency of UV/H2O2/O3 technology, while an acidic environment is conducive to its function. Inorganic anions such as HCO3−, SO42−, Cl− and NO3− are potential to compete with target algal-derived NDMA precursors for the oxidants reaction and inhibit the degradation/removal of these precursors. The degradation of algal-derived NDMA precursors by UV/H2O2/O3 is mainly accomplished by the oxidation of DON with secondary amide groups, and the main degradation mechanism by UV/H2O2/O3 was through the initial decomposition of macromolecular organic compounds such as biopolymers and humic substances and the further degradation of resulting small molecular components.

Micropollutant abatement and byproduct formation during the co-exposure of chlorine dioxide (ClO2) and UVC radiation

Photolysis of ClO2 by UVC radiation occurs in several drinking water treatment scenarios (e.g., pre-oxidation by ClO2 with post-UVC disinfection or a multi-barrier disinfection system comprising ClO2 and UVC disinfection in sequence). However, whether micropollutants are degraded and undesired byproducts are formed during the co-exposure of ClO2 and UVC radiation remain unclear. This study demonstrated that four micropollutants (trimethoprim, iopromide, caffeine, and ciprofloxacin) were degraded by 14.4–100.0% during the co-exposure of ClO2 and UVC radiation in the synthetic drinking water under the environmentally relevant conditions (UV dose of 207 mJ cm−2, ClO2 dose of 1.35 mg L−1, and pH of 7.0). Trimethoprim and iopromide were predominantly degraded by ClO2 oxidation and direct UVC photolysis, respectively. Caffeine and ciprofloxacin were predominantly degraded by the radicals (HO• and Cl•) and the in-situ formed free chlorine from ClO2 photolysis, respectively. The yields of total organic chlorine (12.5 µg L−1 from 1.0 mg C L−1 of NOM) and chlorate (0.14 mg L−1 From 1.35 mg L−1 of ClO2) during the co-exposure were low. However, the yield of chlorite was high (0.76 mg L−1 from 1.35 mg L−1 of ClO2), which requires attention and control.

Removing Plant Pathogenic Bacteria by Solar Ultraviolet Radiation in Hydroponic Systems

Removing plant pathogens with the sun as a free, available, clean, and sustainable source of energy is interesting. However, there is no data for disinfecting major plant pathogenic bacteria such as Pseudomonas syringae and Clavibacter michiganensis subsp. michiganensis by solar ultraviolet radiation. To obtain the required time for killing these bacteria at different temperatures, a bacterial suspension of active growing cells (approximately 107 CFU mL-1) was prepared and subjected to heat inside a water bath. The minimum required time for killing both of the bacteria was achieved 420, 45, and 15 min at 50, 55, and 60 °C, respectively. To examine the effect of solar ultraviolet radiation, the bacteria suspensions inside a quartz tube were exposed to the sun on a horizontal surface at the constant temperature of 50 °C within the water bath (water depth: 0.1 m). Both of the bacteria were killed after one hour by receiving 95.481 kJ m-2 ultraviolet and 2.79315 MJ m-2 solar radiation doses. The synergy of heat and solar UV could considerably reduce the killing time of the bacteria (7 to 1 hours) at 50 °C. The recommended solar UV dose is 95.481 kJ m-2 for this condition.