Single UV-C Research Articles

Evaluation of disinfection efficacy of single UV-C, and UV-A followed by UV-C LED irradiation on Escherichia coli, B. spizizenii and MS2 bacteriophage, in water

Ultraviolet light-emitting diodes (UV LEDs) have shown ability to inactivate microorganisms and viruses in water. The unique characteristic of the UV-LEDs' diversity in wavelengths ranging from UV-C, UV-B, and UV-A, allows for wavelengths to be combined in different manners for polychromatic irradiation. Previous studies reported no synergy from simultaneous or sequential UV-C and UV-B as well as UV-C or UV-B followed by UV-A irradiation. However, synergy was reported for UV-A followed by UV-C or UV-B irradiation on various microorganisms. Nevertheless, no clear ground has been reached on whether to adopt single UV-C wavelengths or UV-A followed by UV-C LED, irradiation on inactivation of microorganisms and viruses in water. Therefore, this work evaluates the disinfection efficacy of single UV-C as well as UV-A followed by UV-C LED irradiation on Escherichia coli, Bacillus spizizenii spores and MS2 bacteriophage in water. The UV-C wavelengths were represented by 267 and 278 nm UV LEDs, and UV-A by 368 nm UV LEDs. In this study, E. coli was highly susceptible to UV radiation followed by B. spizizenii spores, and lastly MS2. Repair following UV inactivation was only observed in E. coli. The synergistic effect found in both E. coli, and B. spizizenii spores was attributed to the different inactivation mechanisms of the UV-C and UV-A wavelengths. In both single UV-C, and UV-A followed by UV-C LED irradiations, single 267 nm UV-C LED showed higher inactivation efficacy. Meanwhile, single 278 nm UV-C LED showed higher efficacy in terms of suppression of repair, and electrical energy consumption. Using single UV-C LEDs in a water disinfection system cuts down on related extra costs by avoiding combined wavelengths while still attaining better levels of microorganism inactivation, repair suppression and electrical energy consumption. These findings are applicable for the design and implementation of UV LED water disinfection systems.

Characterization of a robot-assisted UV-C disinfection for the inactivation of surface-associated microorganisms and viruses

Microorganisms pose a serious threat for us humans, which is exemplified by the recent emergence of pathogens such as SARS-CoV-2 or the increasing number of multi-resistant pathogens such as MRSA. To control surface microorganisms and viruses, we investigated the disinfection properties of an AI-controlled robot, HERO21, equipped with eight 130-W low pressure UV-C mercury vapor discharge lamps emitting at a wavelength of 254 nm, which is strongly absorbed by DNA and RNA, thus inactivating illuminated microorganisms. Emissivity and spatial irradiance distribution of a single UV-C lamp unit was determined using a calibrated spectrometer and numerical simulation, respectively. The disinfection efficiency of single lamps is determined by microbiological tests using B. subtilis spores, which are known to be UV-C resistant. The required time for D99 disinfection and the corresponding UV-C irradiance dose amount to 60 s and 37.3 mJ•cm−2 at a distance of 1 m to the Hg-lamp, respectively. Spatially resolved irradiance produced by a disinfection unit consisting of eight lamps is calculated using results of one UV-C lamp characterization. This calculation shows that the UV-C robot HERO21 equipped with the mentioned UV-C unit causes an irradiance at λ=254 nm of 2.67 mJ•cm−2•s−1 at 1 m and 0.29 mJ•cm−2•s−1 at 3 m distances. These values result in D99 disinfection times of 14 s and 129 s for B. subtilis spores, respectively. Similarly, human coronavirus 229E, structurally very similar to SARS-CoV-2, could be efficiently inactivated by 3–5 orders of magnitude within 10 - 30 s exposure time or doses of 2 - 6 mJ•cm−2, respectively. In conclusion, with the development of the HERO21 disinfection robot, we were able to determine the inactivation efficiency of bacteria and viruses on surfaces under laboratory conditions.

A Novel Technique Using Advanced Oxidation Process (UV-C/H2O2) Combined with Micro-Nano Bubbles on Decontamination, Seed Viability, and Enhancing Phytonutrients of Roselle Microgreens

Microbial contamination commonly occurs in microgreens due to contaminated seeds. This study investigated the decontamination effects of water wash (control), 5% hydrogen peroxide (H2O2), UV-C (36 watts), advanced oxidation process (AOP; H2O2 + UV-C), and improved AOP by combination with microbubbles (MBs; H2O2 + MBs and H2O2 + UV-C + MBs) on microbial loads, seeds’ viability, and physio-biochemical properties of microgreens from corresponding roselle seeds. Results showed that H2O2 and AOP, with and without MBs, significantly reduced total aerobic bacteria, coliforms, Escherichia coli (E. coli), and molds and yeast log count in seeds as compared to the control. Improved AOP treatment of H2O2 + UV-C + MBs significantly augmented antimicrobial activity against total bacteria and E. coli (not detected,) as compared to control and other treatments due to the formation of the highest hydroxy radicals (5.25 × 10−13 M). Additionally, H2O2 and combined treatments promoted seed germination, improved microbiological quality, total phenolic, flavonoids, and 2,2-diphenyl-1-picrylhydrazyl radical (DPPH•) activity of the grown microgreens. Ascorbic acid content was induced only in microgreens developed from H2O2-treated seeds. Single UV-C treatment was ineffective to inactivate the detected microorganism population in seeds. These findings demonstrated that improved AOP treatment (H2O2 + UV-C + MBs) could potentially be used as a new disinfection technology for seed treatment in microgreens production.

Storage life extension of cherry tomato by alginate-based edible coating in combination with UV-C treatment

Purpose: The aim of this work was to determine the effects of UV-C and alginate coating, alone or in combination, on extending the storability and the quality of cherry tomato. Research method: Tomatoes were covered with a 2% alginate coating in combination with UV-C treatment or alone and stored at 10°C with 90-95% relative humidity for 20 days. Tomatoes were evaluated for weight loss, respiration rate, total soluble solids, titratable acidity, ascorbic acid, lycopene content, total phenolic content, antioxidant content and overall appearance every 5 day. Findings: The results indicated that UV-C +Alginate treatment was highly effective in preserving fruit quality and delaying senescence. Alginate coating preserved brightness and visual quality of fruit while preventing decay. Overall, the integration of UV-C irradiation with alginate coating was the best treatment that could strongly inhibit the increase in the weight loss and respiration and achieved the highest ascorbic acid, total phenolic and antioxidant content. Single UV-C treatment had a positive effect on biochemical compounds at the beginning, but could not maintain this effect at the end of storage. Moreover, lycopene concentration increased as the senescence progressed, but observed higher lycopene contents in control samples. Limitations: No limitations to report. Originality/Value: UV-C + alginate treatment may be a promising method of improving quality and extending the postharvest life of cherry tomatoes.

Preharvest UV-C affects lettuce resistance to Xanthomonas campestris pv. vitians and quality

A series of independent trials were conducted to evaluate the use of UV-C radiation for controlling Xanthomonas campestris pv. vitians (Xcv), the causative agent of bacterial leaf spot in lettuce, and to assess the impact of this treatment on lettuce yield. The first trial involved repeated applications of a pre-established hormetic dose of UV-C (0.4 kJ/m2), for a total dose of 1.6 kJ/m2, which represented a single treatment cycle. Lettuce plants were inoculated with a virulent strain of Xcv 48 h after this treatment cycle. The second trial, which took place after Xcv inoculation, involved additional UV-C treatment cycles (0.5, 1.0 and 1.75 cycles), corresponding to total doses of 2.4, 3.2 and 4.4 kJ/m2 respectively. In the third trial, three weekly UV-C treatments were given at 48 h intervals using the standard 0.4 kJ/m2 dose, beginning the third week after seeding and continuing until the lettuce reached the commercial stage and was harvested. By the time the mature lettuce plants were harvested, they had undergone five treatment cycles, representing a total dose of 8 kJ/m2. A single UV-C treatment cycle resulted in a 90 %, 30 % or 10 % reduction in the susceptibility of the growing lettuce plants to Xcv compared with the control group, depending on when symptoms were evaluated. The application of additional treatment cycles (0.5, 1.0 and 1.75 cycles) resulted in a reduction of 30 %, 45 % and 50 % in susceptibility, respectively, in the treated lettuce plants relative to the controls. The fresh yield of lettuce treated with 2.75 cycles of UV-C (4.4 kJ/m2) was similar to that of the control lettuce; this treatment also resulted in a significant decrease (20 %) in core length, an agronomic trait associated with increased yield when lettuce is processed as fresh-cut ready-to-eat product. UV-C-treated lettuce had a significantly greater dry matter content and higher total mineral concentrations than the control lettuce. These results indicate that repeated preharvest UV-C treatments (0.4 kJ/m2) improve the tolerance of lettuce to Xcv without negative effects.

Effect of an UV-C Light-Based Hurdle Strategy for Carrot-Orange Juice Processing on Candida parapsilosis Inactivation and Physiological State: Impact on Juice Sensory and Physicochemical Quality Parameters

In the past two decades, novel preservation technologies have been investigated to achieve sufficient microbial reduction while improving the quality of food and beverages. The effect of UV-C light (UV-C, 1720 mJ/cm2) assisted by mild heat (H, 50 °C) on the inactivation and the physiological state of Candida parapsilosis ATCC 22019 in a carrot-orange juice was studied by flow cytometry. Additionally, the juice samples processed or not (control) by the single (UV-C; H) and combined (UV-C/H) treatments were analyzed for total polyphenol content (TPC), total antioxidant activity (TAA), color, turbidity, °Brix, pH, and pectin methylesterase units (PME) along 13–24-day storage (4 °C). Consumer-profiling studies were conducted on UV-C/H and a pasteurized juice. UV-C/H was highly effective in reducing C. parapsilosis by 5.5 log cycles, whereas the single UV-C and H treatments induced 2.9 and 3.9 log reductions, respectively. Flow cytometry revealed a shift with time from cells with intact membrane and esterase activity to those with permeabilized membrane and without esterase activity, which was significantly higher for UV-C/H samples (98.0%) compared with the single treatments (12.0–46.2%). UV-C/H preserved juice color, pH, °Brix, and turbidity of the juice, which exhibited equal TAA (0.7 mg/mL) and higher TPC (302.1 μg/mL) than the control (TAA = 0.7 mg/mL/TPC = 205.0 μg/mL), remaining constant throughout storage. PME decreased 42–45% for the H and UV-C/H treatments, respectively. A cluster sensory analysis revealed that one group of consumers showed a remarkable interest in the UV-C/H juice, while the conjoint study showed that it was perceived as very healthy. The CATA question determined that the UV-C/H processing prevented the juice from being perceived too particulate or with cooked or artificial taste, as happened with the pasteurized juice.

Inactivation of Candida auris and Candida albicans by Ultraviolet-C

Background:Candida auris is an emerging fungal pathogen that is often resistant to major classes of antifungal drugs. It is considered a serious global health threat because it has caused severe infections with frequent mortality in over a dozen countries. C. auris can survive on healthcare environmental surfaces for at least 7 days, and it causes outbreaks in healthcare facilities. C. auris has an environmental route of transmission. Thus, infection prevention strategies, such as surface disinfection and room decontamination technologies (eg, ultraviolet [UV-C] light), will be essential to controlling transmission. Unfortunately, data are limited regarding the activity of UV-C to inactivate this pathogen. In this study, a UV-C device was evaluated for its antimicrobial activity against C. auris and C. albicans. Methods: We tested the antifungal activity of a single UV-C device using the vegetative bacteria cycle, which delivers a reflected dose of 12,000 µW/cm2. This testing was performed using Formica sheets (7.6 × 7.6 cm; 3 × 3 inches). The carriers were inoculated with C. auris or C. albicans and placed horizontal on the surface or vertical (ie, perpendicular) to the vertical UV-C lamp and at a distance from 1. 2 m (~4 ft) to 2.4 m (~8 ft). Results: Direct UV-C, with or without FCS (log10 reduction 4.57 and 4.45, respectively), exhibited a higher log10 reduction than indirect UV-C for C. auris (log10 reduction 2.41 and 1.96, respectively), which was statistically significant (Fig. 1 and Table 1). For C. albicans, although direct UV-C had a higher log10 reduction (log10 reduction with and without FCS, 5.26 and 5.07, respectively) compared to indirect exposure (log10 reduction with and without FCS, 3.96 and 3.56, respectively), this difference was not statistically significant. The vertical UV had statistically higher log10 reductions than horizontal UV against C. auris and C. albicans with FCS and without FCS. For example, for C. auris with FCS the log10 reduction for vertical surfaces was 4.92 (95% CI 3.79, 6.04) and for horizontal surfaces the log10 reduction was 2.87 (95% CI, 2.36–3.38). Conclusions:C. auris can be inactivated on environmental surfaces by UV-C as long as factors that affect inactivation are optimized (eg, exposure time). These data and other published UV-C data should be used in developing cycle parameters that prevent contaminated surfaces from being a source of acquisition by staff or patients of this globally emerging pathogen.Funding: NoneDisclosures: None

Effect of pilot-scale UV-C light treatment assisted by mild heat on E. coli, L. plantarum and S. cerevisiae inactivation in clear and turbid fruit juices. Storage study of surviving populations

Consumer growing demands for high-quality and safe food and beverages have stimulated the interest in alternative preservation technologies. Short-wavelength ultraviolet light (UV-C, 254 nm) has proven to be useful for the decontamination of a great variety of clear juices while improving their quality compared to traditional thermal treatments. Suspended solids and coloured compounds in turbid juices, diminish light transmission. The use of UV-C under a hurdle approach, may be a promising strategy for their treatment. The purpose of this study was to analyse Escherichia coli ATCC 25922, Saccharomyces cerevisiae KE 162 and Lactobacillus plantarum ATCC 8014 inactivation in clear pear juice (PJ), turbid orange-tangerine (OT) and orange-banana-mango-kiwi-strawberry (OBMKS) juices processed by single UV-C (390 mJ/cm2, 20 °C) and UV-C assisted by mild heat (UV-C/H, 50 °C) at pilot-scale in a coiled tubing unit and stored under refrigeration (5 °C). Inactivation studies were also conducted in peptone water (PW) and model solution (MS). The adequacy of the Coroller, Weibull and Biphasic Plus Shoulder models was studied. UV-C was highly effective in PW, MS and PJ, achieving up to 5.5-6.3-4.7, 4.8-5.1-4.6 and 4.4-5.5 log reductions for L. plantarum, E. coli,and S. cerevisiae, respectively. Whereas, a moderate inactivation by single UV-C was recorded in the turbid blends, reducing up to 2.4-3.8-1.6 and 3.6-3.7-1.3 log-cycles in OT and OBMKS, respectively. When the UV-C/H treatment was applied, high bacterial inactivation was observed achieving 5.2-5.6, 6.3-6.6 and 5.5-6.7 log reductions in OT, OBMKS and PJ, respectively, while 4.6-4.9 log reductions were determined for the yeast in OBMKS and OT, respectively. Thus, additive inactivation effects between UV-C and H were observed. All the models tested gave useful information regarding the existence of microbial subpopulations with varying resistances. However, the cumulative Weibull distribution function was the most versatile one, fitting inactivation curves with different shapes. Additionally, the frequency distributions of resistances showed that UV-C/H not only increased the UV-C microbicidal effect but changed the distribution of inactivation times. Principal component analysis revealed that UV-C effectiveness was associated to low particle size, a⃰, turbidity and high UV-C transmittance. An increase on the inactivation of treated bacterial populations was recorded along storage, while no yeast recovery was observed, thus emphasizing the contribution of refrigerated storage to microbial inactivation. Microbial inactivation in clear and turbid juices achieved by UV-C (390 mJ/cm2) assisted by mild heat (50 °C) and subsequent refrigerated storage may represent an useful alternative for multiple applications in the juice industry.

A comparison of photolytic, photochemical and photocatalytic processes for disinfection of recirculation aquaculture systems (RAS) streams

The development of technologically advanced recirculation aquaculture systems (RAS) implies the reuse of water in a high recirculation rate (>90%). One of the most important phases for water management in RAS involves water disinfection in order to avoid proliferation of potential pathogens and related fish diseases. Accordingly, different approaches have been assessed in this study by performing a comparison of photolytic (UV-LEDs) at different wavelengths (λ = 262, 268 and 262 + 268 nm), photochemical (UV-LEDs/H2O2, UV-LEDs/HSO5− and UV-LEDs/S2O82−) and photocatalytic (TiO2/SiO2/UV-LEDs and ZnO/SiO2/UV-LEDs) processes for the disinfection of water in RAS streams. Different laboratory tests were performed in batch scale with real RAS stream water and naturally occurring bacteria (Aeromonas hydrophyla and Citrobacter gillenii) as target microorganisms. Regarding photolytic processes, higher inactivation rates were obtained by combining λ262+268 in front of single wavelengths. Photochemical processes showed higher efficiencies by comparison with a single UV-C process, especially at 10 mg L−1 of initial oxidant dose. The inactivation kinetic rate constant was improved in the range of 15–38%, with major efficiency for UV/H2O2 ∼ UV/HSO5− > UV/S2O82−. According to photocatalytic tests, higher efficiencies were obtained by improving the inactivation kinetic rate constant up to 55% in comparison with a single UV-C process. Preliminary cost estimation was conducted for all tested disinfection methods. Those results suggest the potential application of UV-LEDs as promoter of different photochemical and photocatalytic processes, which are able to enhance disinfection in particular cases, such as the aquaculture industry.

Evaluation of Continuous UVC Treatments and its Combination with UHPH on Spores of Bacillus subtilis in Whole and Skim Milk.

The aim of this study was to evaluate the effectiveness of different UVC treatments, alone or in combination with ultra-high pressure homogenization (UHPH) on Bacillus subtilis spores in milk. Spores of B. subtilis (CECT4002) were inoculated in whole and skim milk to an initial concentration about 6 log CFU/mL. Milk was subjected to different ultraviolet radiation treatments at 254 nm (UVC) using a concentric tubular reactor in a dose ranging from 10 to 160 J/mL. Different number of passes were used to adjust the final dose received by the matrix. In general, increasing the number of passes (defined as number of entries to the tunnel-NET) increased the inactivation of spores of B. subtilis. The best lethality results (above 4 Log CFU/mL) were obtained by applying doses from 100 J/mL with several NET. When the same doses were achieved with a single pass lethality in most cases did not exceed 1 log CFU/mL. Increasing the NET also increased the likelihood for the spores to remain longer in the effective distance from the UVC source, estimated as 0.02 mm for whole milk and 0.06 mm for skim milk. Combination of UHPH and UVC did not clearly increase the efficiency of a single UVC treatment, and a lower lethality was even observed in some cases. UHPH treatments increased the turbidity and absorption coefficient (254 nm) of both whole and skim milk.

Effectiveness of UV-C light assisted by mild heat on Saccharomyces cerevisiae KE 162 inactivation in carrot-orange juice blend studied by flow cytometry and transmission electron microscopy

The aim of this study was to analyze the effectiveness of UV-C light (0–10.6 kJ/m2) assisted by mild heat treatment (50 °C) on the inactivation of Saccharomyces cerevisiae KE 162 in peptone water and fresh carrot-orange juice blend (pH: 3.8; 9.8°Brix; 707 NTU; absorption coefficient: 0.17 cm−1). Yeast induced damage by single UV-C and mild heat (H) and the combined treatment UV-C/H, was investigated by flow cytometry (FC) and transmission electron microscopy (TEM). When studying induced damage by FC, cells were labeled with fluorescein diacetate (FDA) and propidium iodide (PI) to monitor membrane integrity and esterase activity. UV-C/H provoked up to 4.7 log-reductions of S. cerevisiae; whereas, only 2.6–3.3 log-reductions were achieved by single UV-C and H treatments. FC revealed a shift with treatment time from cells with esterase activity and intact membrane to cells with permeabilized membrane. This shift was more noticeable in peptone water and UV-C/H treated juice. In the UV-C treated juice, double stained cells were detected, suggesting the possibility of being sub-lethally damaged, with compromised membrane but still metabolically active. TEM images of treated cells revealed severe damage, encompassing coagulated inner content, disorganized lumen and cell debris. FC and TEM provided additional information regarding degree and type of damage, complementing information revealed by the traditional plate count technique.

Antioxidant activity of high-pressure processed tangerine juice

The objective of the study was to combine shortwave ultraviolet irradiation (UVC-Light) with ultrasonic atomization (UA) to generate microdroplets by atomizing the juices to enhance contact with UVC-Light and to evaluate its effect on the inactivation of Saccharomyces cerevisiae as well as on selected physicochemical parameters of tangerine and grapefruit juices. UVC lamps and an ultrasonic atomizer were used individually and in combination. The effect of lamps' orientation (horizontal or vertical) and the number of lamps (1 or 2) were assessed. No significant (p > 0.05) changes on pH, °Bx, and color of studied juices were observed, since the contact time of the microdroplets with the UVC-Light was short. After processing 250 mL of juice, microbial population was reduced by 0.84 log cycles when using a single UVC lamp combined with UA while a 2.8 log cycles reduction was observed after three passes. Tested configurations with two lamps did not achieve effective inactivation of S. cerevisiae, possibly because the generated microdroplets were not in close contact with UVC-light as was the case with one lamp.The ultrasonic atomization for the UVC-treatment of juices was assessed for the first time in this work. The ultrasonic atomization of juices may be suitable for the inactivation of yeasts when combined with UVC-Light as long as atomization takes place near the irradiation site. These combined technologies have the potential to generate foods minimally processed.

Study of the inactivation of some microorganisms in turbid carrot-orange juice blend processed by ultraviolet light assisted by mild heat treatment

The aim of this study was to evaluate the effect of short wave ultraviolet light (UV-C, 0–10.6 kJ/m2) assisted by mild heat treatment (UV-C/H; 40, 45 or 50 °C) on the inactivation of Escherichia coli, Saccharomyces cerevisiae and Pseudomonas fluorescens in freshly squeezed carrot-orange juice blend. In addition, the suitability of three conceptually different models was analyzed to characterize the inactivation kinetics. All treatments provoked moderate to high microbial inactivation depending on temperature and microorganism (2.6–6.0 log reductions). The use of UV-C assisted by mild heat treatment notably improved inactivation compared to single UV-C. Synergistic inactivation effects on E. coli and P. fluorescens were observed at combined UV-C/H (45 and 50 °C). Gompertz and Geeraerd models allowed a better fit and more accurate parameter estimation compared to the Weibull model.

Enhancement of UVC-light treatment of tangerine and grapefruit juices through ultrasonic atomization

Abstract The objective of the study was to combine shortwave ultraviolet irradiation (UVC-Light) with ultrasonic atomization (UA) to generate microdroplets by atomizing the juices to enhance contact with UVC-Light and to evaluate its effect on the inactivation of Saccharomyces cerevisiae as well as on selected physicochemical parameters of tangerine and grapefruit juices. UVC lamps and an ultrasonic atomizer were used individually and in combination. The effect of lamps' orientation (horizontal or vertical) and the number of lamps (1 or 2) were assessed. No significant (p > 0.05) changes on pH, °Bx, and color of studied juices were observed, since the contact time of the microdroplets with the UVC-Light was short. After processing 250 mL of juice, microbial population was reduced by 0.84 log cycles when using a single UVC lamp combined with UA while a 2.8 log cycles reduction was observed after three passes. Tested configurations with two lamps did not achieve effective inactivation of S. cerevisiae , possibly because the generated microdroplets were not in close contact with UVC-light as was the case with one lamp. Industrial relevance The ultrasonic atomization for the UVC-treatment of juices was assessed for the first time in this work. The ultrasonic atomization of juices may be suitable for the inactivation of yeasts when combined with UVC-Light as long as atomization takes place near the irradiation site. These combined technologies have the potential to generate foods minimally processed.

Principal component analysis to assess the efficiency and mechanism for ultraviolet-C/polyaluminum chloride enhanced coagulation of algae-laden water

Polyaluminum chloride (PAC) coagulation, short wavelength ultraviolet (UV-C at 254 nm) treatment and UV-C/PAC treatment of algae-laden water from Meiliang Gulf (Lake Taihu) were conducted. The intrinsic characteristics and correlations of chromophoric dissolved organic matter (CDOM), algae biomass and other contaminants were investigated. Parallel factor analysis determined four CDOM components, and principal component analysis (PCA) identified three integrated principal factors. PCA Factor 1 had correlations with dissolved organic carbon (DOC) (r = 0.798), UV254 (0.645), humic-like CDOM component C3 (0.892) and C4 (0.876), and Factor 2 correlated with in vivo chlorophyll-a (0.768), microcystin-LR (0.713), protein-like C1 (0.782) and C2 (0.759). Factor 3 had correlations with NH3-N (0.851) and total phosphorus (T-P) (0.716). The variation in PCA factor scores revealed that single PAC coagulation preferentially removed algal cells (Factor 2) but had little effect on NH3-N and T-P (Factor 3). Single UV-C treatment induced degradation of protein-like CDOM and decrease of algal biomass (Factor 2), followed by humic-like CDOM increase from ruptured cells (Factors 1 and 3). Compared with single PAC coagulation (20 mg L−1), the combined UV-C/PAC treatment (700 mJ cm−2 + 20 mg L−1) enhanced the removal of PCA Factors 1, 2 and 3 (15%, 32% and 10%).

Sequence specificity of cyclobutane pyrimidine dimers in DNA treated with solar (ultraviolet B) radiation.

Cyclobutane pyrimidine dimers were quantified at the sequence level after irradiation with solar ultraviolet (UVB) and nonsolar ultraviolet (UVC) light sources. The yield of photoproducts at specific sites was dependent on the nucleotide composition in and around the potential lesion as well as on the wavelength of ultraviolet light used to induce the damage. Induction was greater in the presence of 5' flanking pyrimidines than purines; 5' guanine inhibited induction more than adenine. UVB irradiation increased the induction of cyclobutane dimers containing cytosine relative to thymine homodimers. At the single UVC and UVB fluences used, the ratio of thymine homodimers (T mean value of T) to dimers containing cytosine (C mean value of T, T mean value of C, C mean value of C) was greater after UVC compared to UVB irradiation.