High UV Doses Research Articles

Unravelling the UV/H2O2 process using bioelectrochemically synthesized H2O2 to reuse waste nutrient solution

In this study, waste nutrient solution (WNS) was used as a catholyte in a bioelectrochemical cell to directly produce hydrogen peroxide (H2O2), after which the H2O2- containing WNS was integrated with the downstream UV oxidation process to meet quality standards for reuse. The generated current in the bioelectrochemical cell was successfully utilized at the cathode to produce H2O2 in WNS using a two-electron oxygen reduction reaction with different reaction times. The cathodic reaction time with the highest H2O2 production (504 ± 5.2 mg l−1) was 48 h, followed by that obtained from 24 h (368 ± 4.1 mg l−1), 12 h (158.8 ± 2.4 mg l−1), and 6 h (121.1 ± 4.1 mg l−1) reaction times. During H2O2 generation, calcium, magnesium, and phosphate in the WNS were recovered in the form of precipitates under alkaline conditions. The H2O2-containing WNS was further treated with different UV doses. After UV/H2O2 treatment, excitation-emission matrix and molecular weight distribution analyses demonstrated that aromatic compounds were reduced. Moreover, the gene expressions of sul1 (up to 95.65%), tetG (up to 93.88%), and aadA (up to 95.32%) were clearly downregulated compared with those of a control sample. Finally, a high disinfection efficiency was achieved with higher UV doses, resulting in successful seed germination. Thus, our results indicate that the developed method can be a promising process for reusing WNS in hydroponic systems.

Investigating the effects of particle size and relative humidity on bioaerosol disinfection in an in-duct ultraviolet germicidal irradiation system

Ultraviolet germicidal irradiation (UVGI) technology has garnered substantial attention in disinfecting airborne microorganisms during and beyond the COVID-19 pandemic. Given that UVGI inactivation performance varies in complex in-duct environments, this study examines the effects of bioaerosol particle size and relative humidity (RH) on the inactivation efficiencies of an in-duct UVGI system. MS2 bioaerosols, with phosphate-buffered saline as suspending media and subjected to a bioaerosol drying process, were used in UVGI tests. At any given RH condition (25 %, 40 %, or 60 % RH), lower UV rate constants were presented for larger bioaerosols (2.1–7 μm) in comparison to smaller ones (0.65–2.1 μm). For humidity, the UV rate constant initially increased and then decreased as RH increased from 25 % to 60 %, peaking at 40 % RH, irrespective of the particle size. Notably, the absence of the bioaerosol dryer altered this trend, where the inactivation efficiency decreased with the increase in RH. In conclusion, our findings suggest that a higher UV dose is required to mitigate hazards from larger bioaerosols in very humid environments. In addition, this work proposes a comprehensive flowchart, a beneficial tool for engineers and designers, which facilitates the effective design and implementation of UVGI technology in controlling bioaerosol hazards.

The effect of enzymatic and viability dye treatment in combination with long-range PCR on assessing Tulane virus infectivity

Human norovirus (HuNoV) is regularly involved in food-borne infections. To detect infectious HuNoV in food, RT-qPCR remains state of the art but also amplifies non-infectious virus. The present study combines pre-treatments, RNase and propidium monoazide, with three molecular analyses, including long-range PCR, to predominantly detect infectious Tulane virus (TuV), a culturable HuNoV surrogate. TuV was exposed to inactivating conditions to assess which molecular method most closely approximates the reduction in infectious virus determined by cell culture (TCID50). After thermal treatments (56 °C/5 min, 70 °C/5 min, 72 °C/20 min), TCID50 reductions of 0.3, 4.4 and 5.9 log10 were observed. UV exposure (40/100/1000 mJ/cm2) resulted in 1.1, 2.5 and 5.9 log10 reductions. Chlorine (45/100 mg/L for 1 h) reduced infectious TuV by 2.0 and 3.0 log10. After thermal inactivation standard RT-qPCR, especially with pre-treatments, showed the smallest deviation from TCID50. On average, RT-qPCR with pre-treatments deviated by 1.1–1.3 log10 from TCID50. For UV light, long-range PCR was closest to TCID50 results. Long-range reductions deviated from TCID50 by ≤0.1 log10 for mild and medium UV-conditions. However, long-range analyses often resulted in qPCR non-detects. At higher UV doses, RT-qPCR with pre-treatments differed by ≤1.0 log10 from TCID50. After chlorination the molecular methods repeatedly deviated from TCID50 by >1.0 log10, Overall, each method needs to be further optimized for the individual types of inactivation treatment.

Regression model and pathways of halonitromethane formation from amino acids in the presence of bromide ion under UV/monochloramine disinfection

Halonitromethanes (HNMs) including chlorinated and brominated HNMs, a category of nitrogenous disinfection by-products with high toxicity, were formed from amino acids (AAs) in the presence of bromide ion (Br-) under UV/monochloramine (UV/NH2Cl) disinfection. This study developed a regression model using water characteristics (pH, HCO3– and Br-) and disinfection conditions (disinfection time and NH2Cl doses) to predict HNM formation from AAs (tyrosine (Tyr), tryptophan (Trp) and aspartic acid (Asp)) in the presence of Br- under UV/NH2Cl disinfection. Main contributors to the abatement of Tyr and Trp were UV (6.1%-18.7%), HO (18.5%-62.3%), Cl2− (0.3%-17.9%), Br (2.4%-41.3%, kBr•,AA=∼109-1010 M−1·s−1), Br2− (1.3%-11.0%, kBr2•-,AA=∼108-109 M−1·s−1), NO (2.6%-43.0%) and CO3− (0%-43.2%) based on the first-principle kinetic model of UV/NH2Cl/Br- process, while the removal ratio of Asp was low. It was responsible for higher HNM concentrations from Tyr and Trp than those from Asp. Due to the decline in HNM concentrations with prolongation of reaction time, HNM concentrations were considered as the quadratic function of disinfection time with coefficients related to water characteristics and NH2Cl doses. The regression model with backward stepwise regression described HNM formation well. After introducing specific UV absorbance at 254 nm (SUVA254) and interaction terms associated with SUVA254, HNM formation from three AAs was successfully predicted by one regression equation (R2 = 0.91, mean absolute error = 0.46, mean relative error = 37%, root-mean-square error = 0.81). Using the optimal regression model, increasing NH2Cl doses was found to advance the peak time for HNM formation. Besides, obtained heatmaps of HNM formation revealed that a high NH2Cl dose with a high UV dose or low NH2Cl dose helped to limit HNM formation. Lastly, the possible formation pathways of HNMs were presented.

Fungi beyond limits: The agricultural promise of extremophiles.

Global climate changes threaten food security, necessitating urgent measures to enhance agricultural productivity and expand it into areas less for agronomy. This challenge is crucial in achieving Sustainable Development Goal 2 (Zero Hunger). Plant growth-promoting microorganisms (PGPM), bacteria and fungi, emerge as a promising solution to mitigate the impact of climate extremes on agriculture. The concept of the plant holobiont, encompassing the plant host and its symbiotic microbiota, underscores the intricate relationships with a diverse microbial community. PGPM, residing in the rhizosphere, phyllosphere, and endosphere, play vital roles in nutrient solubilization, nitrogen fixation, and biocontrol of pathogens. Novel ecological functions, including epigenetic modifications and suppression of virulence genes, extend our understanding of PGPM strategies. The diverse roles of PGPM as biofertilizers, biocontrollers, biomodulators, and more contribute to sustainable agriculture and environmental resilience. Despite fungi's remarkable plant growth-promoting functions, their potential is often overshadowed compared to bacteria. Arbuscular mycorrhizal fungi (AMF) form a mutualistic symbiosis with many terrestrial plants, enhancing plant nutrition, growth, and stress resistance. Other fungi, including filamentous, yeasts, and polymorphic, from endophytic, to saprophytic, offer unique attributes such as ubiquity, morphology, and endurance in harsh environments, positioning them as exceptional plant growth-promoting fungi (PGPF). Crops frequently face abiotic stresses like salinity, drought, high UV doses and extreme temperatures. Some extremotolerant fungi, including strains from genera like Trichoderma, Penicillium, Fusarium, and others, have been studied for their beneficial interactions with plants. Presented examples of their capabilities in alleviating salinity, drought, and other stresses underscore their potential applications in agriculture. In this context, extremotolerant and extremophilic fungi populating extreme natural environments are muchless investigated. They represent both new challenges and opportunities. As the global climate evolves, understanding and harnessing the intricate mechanisms of fungal-plant interactions, especially in extreme environments, is paramount for developing effective and safe plant probiotics and using fungi as biocontrollers against phytopathogens. Thorough assessments, comprehensive methodologies, and a cautious approach are crucial for leveraging the benefits of extremophilic fungi in the changing landscape of global agriculture, ensuring food security in the face of climate challenges.

Multi-target assessment of advanced oxidation processes-based strategies for indirect potable reuse of tertiary wastewater: Fate of compounds of emerging concerns, microbial and ecotoxicological parameters

Two advanced oxidation processes (AOPs), namely ozone/H2O2 and UV/H2O2, were tested at pilot scale as zero-liquid-discharge alternative treatments for the removal of microbiological (bacteria and viruses), chemical (compounds of emerging concern (CECs)) and genotoxic responses from tertiary municipal wastewater for indirect potable reuse (IPR). The AOP treated effluents were further subjected to granular activated carbon (GAC) adsorption and UV disinfection, following the concept of multiple treatment barriers. As a reference, a consolidated advanced wastewater treatment train consisting of ultrafiltration, UV disinfection, and reverse osmosis (RO) was also employed.The results showed that, for the same electrical energy applied, the ozone/H2O2 treatment was more effective than the UV/H2O2 treatment in removing CECs. Specifically, the ozone/H2O2 treatment, intensified by high pressure and high mixing, achieved an average CECs removal efficiency higher than UV/H2O2 (66.8% with respect to 18.4%). The subsequent GAC adsorption step, applied downstream the AOPs, further improved the removal efficiency of the whole treatment trains, achieving rates of 98.5% and 96.8% for the ozone/H2O2 and UV/H2O2 treatments, respectively. In contrast, the ultrafiltration step of the reference treatment train only achieved a removal percentage of 22.5%, which increased to 99% when reverse osmosis was used as the final step.Microbiological investigations showed that all three wastewater treatment lines displayed good performance in the complete removal of regulated and optional parameters according to both national and the European Directive 2020/2184. Only P. aeruginosa resulted resistant to all treatments with a higher removal by UV/H2O2 when higher UV dose was applied. In addition, E. coli STEC/VTEC and enteric viruses, were found to be completely removed in all tested treatments and no genotoxic activity was detected even after a 1000-fold concentration.The obtained results suggest that the investigated treatments are suitable for groundwater recharge to be used as a potable water source being such a procedure an IPR. The intensified ozone/H2O2 or UV/H2O2 treatments can be conveniently incorporated into a multi-barrier zero-liquid-discharge scheme, thus avoiding the management issues associated with the retentate of the conventional scheme that uses reverse osmosis. By including the chemical cost associated with using 11–12 mg/L of H2O2 in the cost calculations, the overall operational cost (energy plus chemical) required to achieve 50% average CECs removal in tertiary effluent for an hypothetical full-scale plant of 250 m3/h (or 25,000 inhabitants) was 0.183 €/m3 and 0.425 €/m3 for ozone/H2O2 and UV/H2O2 treatment train, respectively.

Pulsed ultraviolet (PUV) disinfection of artificially contaminated seawater seeded with high levels of pathogen disease indicators as an alternative for the shellfish industry depuration systems

The increase in pathogen levels in seawater threatens the safety of entire aquatic ecosystems. Foodborne pathogens can potentially accumulate in shellfish, especially in filter feeders such as bivalves, requiring an efficient depuration process before consumption. Alternative approaches to promote a cost-efficient purge at depuration plants are urgently needed. A small prototype pulsed ultraviolet (PUV) light recirculation system was designed, and its depuration potential was tested in a seawater matrix artificially contaminated with high levels of microbial pathogens Escherichia coli, Staphylococcus aureus, Salmonella typhimurium, Bacillus cereus and Candida albicans. The analysis of treatment parameters including voltage, number of pulses and duration of treatment was performed to ensure the highest reduction in contaminant levels. Optimal PUV disinfection was attained at 60 pulses/min at 1 kV for 10 min (a UV output of 12.9 J/cm2). All reductions were statistically significant, and the greatest was observed for S. aureus (5.63 log10), followed by C. albicans (5.15 log10), S. typhimurium (5 log10), B. cereus (4.59 log10) and E. coli (4.55 log10). PUV treatment disrupted the pathogen DNA with the result that S. aureus, C. albicans and S. typhimurium were not detectable by PCR. Regulations were reviewed to address the applicability of PUV treatment as a promising alternative to assist in the reduction of microbial pathogens at depuration plants due to its high efficiency, short treatment period, high UV dose and recirculation system as currently employed in shellfish depuration plants.

The roles of species' relatedness and climate of origin in determining optical leaf traits over a large set of taxa growing at high elevation and high latitude.

Climate change is driving many mountain plant species to higher elevations and northern plant species to higher latitudes. However, various biotic or abiotic constraints may restrict any range shift, and one relevant factor for migration to higher elevations could be species' ability to tolerate high UV-doses. Flavonoids are engaged in photoprotection, but also serve multiple ecological roles. We compared plant optical leaf trait responses of a large set of taxa growing in two botanical gardens (French Alps and southern Finland), considering potential constraints imposed by the relatedness of taxa and the legacy of climatic conditions at plants' original collection sites. The segregation of optically measured leaf traits along the phylogeny was studied using a published mega-tree GBOTB.extended.tre for vascular plants as a backbone. For a subset of taxa, we investigated the relationship between climatic conditions (namely solar radiation, temperature and precipitation at a coarse scale) at the plants' original collection site and current trait values. Upon testing the phylogenetic signal (Pagel's λ), we found a significant difference but intermediate lambda values overall for flavonol or flavone index (Iflav) and anthocyanin index (Iant), indicating that phylogenetic relatedness alone failed to explain the changes in trait values under a Brownian motion model of trait evolution. The local analysis (local indicator of phylogenetic association) indicated mostly positive autocorrelations for Iflav i.e. similarities in optically measured leaf traits, often among species from the same genus. We found significant relationships between climatic variables and leaf chlorophyll index (Ichl), but not Iflav, particularly for annual solar radiation. Changes in plants' Iflav across microhabitats differing in UV irradiance and predominately high F v /F m indicated that most plants studied had sufficient flexibility in photoprotection, conferred by Iflav, to acclimate to contemporary UV irradiances in their environment. While not explaining the mechanisms behind observed trait values, our findings do suggest that some high-elevation taxa display similar leaf flavonoid accumulation responses. These may be phylogenetically constrained and hence moderate plants' capacity to adjust to new combinations of environmental conditions resulting from climate change.

Effects of UV-C Disinfection on N95 and KN95 Filtering Facepiece Respirator Reuse.

ABSTRACTThe objective of this study was to evaluate the effectiveness of UV technology for virus disinfection to allow FFR reuse. UV is a proven decontamination tool for microbial pathogens, including the SARS-CoV-2 virus. Research findings suggest that the impacts of UV-C treatment on FFR material degradation should be confirmed using microbial surrogates in addition to the commonly performed abiotic particle testing. This study used the surrogates, E. coli and MS-2 bacteriophage, as they bracket the UV response of SARS-CoV-2. Lower log inactivation was observed on FFRs than predicted by aqueous-based UV dose-response data for MS-2 bacteriophage and E. coli. In addition, the dose-response curves did not follow the trends commonly observed with aqueous data for E. coli and MS-2. The dose-response curves for the respirators in this study had a semicircle shape, where the inactivation reached a peak and then decreased. This decrease in UV inactivation is thought to be due to the degradation of the fibers of the FFR and allows for more viral and bacterial cells to wash through the layers of the respirator. This degradation phenomenon was observed at UV doses at and above 2,000 mJ/cm2. Results have demonstrated that FFR materials yield various results in terms of effective disinfection in experiments conducted on KN95 and N95 face respirators. The highest inactivation for both surrogates was observed with the KN95 respirator made by Purism, yielding 3 and 2.75 log inactivation for E. coli and MS-2 at UV doses of 1,500 mJ/cm2. The KN95 made by Anboruo yielded the lowest inactivation for MS-2 at 0.75 log when exposed to 1,000 mJ/cm2. To further test the degradation theory, experiments used a collimated beam device to test the hypothesis further that degradation is occurring at and above UV doses of 1,500 mJ/cm2. The experiment aimed to determine the effect of “predosing” a respirator with UV before inoculating the respirator with MS-2. In this test, quantification of the penetrated irradiance value and the ability of each layer to retain MS-2 were quantified. The results of the experiments varied from the intact FFR degradation experiments but displayed some data to support the degradation theory.IMPORTANCE Research suggests degradation of FFR materials at high UV doses is important. There appears to be a peak inactivation dose at approximately 1,500 mJ/cm2. The subsequent dose increases appear to have the reverse effect on inactivation values; these trends have shown true with both the N95 and KN95-Purism respirators.

Reconstruction and variability of high daily erythemal ultraviolet doses and relationship with total ozone, cloud cover, and albedo in Novi Sad (Serbia)

AbstractIn this paper, a method previously developed for reconstructing daily erythemal ultraviolet (UVery) doses in Novi Sad (Serbia) was improved and used for estimating daily UVery over the period 1971–2018. The proposed new method uses reanalysed total ozone column (TOC) data and snow cover as an input and is based on the empirical relationship between relative sunshine duration and relative UVery doses. Introducing reanalysed TOC data and snow cover data significantly improved the quality and accuracy of the reconstructed UVery time series, particularly in the winter season. The reconstructed time series revealed the statistically significant increase in summer and winter UVery in the 1980s and the first half of the 1990s (+8.78% and + 13.14% per decade, respectively), which was linked to the statistically significant decline in TOC (−4.13 and −7.36% per decade, respectively). The study focuses on days with high erythemal UV dose (highUVery), which is defined based on the 90th percentile of the daily UVery for each month. Moreover, the influence of low TOC, low cloud cover conditions, and high surface albedo on highUVery was analysed on a seasonal basis. The results of this study show that highUVery days increased from the 1980s, particularly strongly in the period of TOC depletion. A fraction of highUVery days in the last two decades was large (12.29%), which is higher than in the previous periods (6.97 and 8.68% in the period before and during TOC depletion, respectively). The occurrence of highUVery days was influenced mostly by low cloud cover (89.71% of days), and low TOC (82.23% of days). In the winter season, high surface albedo influenced the appearance of 19.18% of highUVery days. However, overall the interaction of low cloud cover and low TOC in all seasons most often led to the appearance of highUVery days.

The UV Dose Used for Disinfection of Drinking Water in Sweden Inadequately Inactivates Enteric Virus with Double-Stranded Genomes.

Irradiation with ultraviolet light (UV) at 254 nm is effective in inactivating a wide range of human pathogens. In Sweden, a UV dose of 400 J/m2 is often used for the treatment of drinking water. To investigate its effect on virus inactivation, enteric viruses with different genomic organizations were irradiated with three UV doses (400, 600, and 1000 J/m2), after which their viability on cell cultures was examined. Adenovirus type 2 (double-stranded DNA), simian rotavirus 11 (double-stranded RNA), and echovirus 30 (single-stranded RNA) were suspended in tap water and pumped into a laboratory-scale Aquada 1 UV reactor. Echovirus 30 was reduced by 3.6-log10 by a UV dose of 400 J/m2. Simian rotavirus 11 and adenovirus type 2 were more UV resistant with only 1-log10 reduction at 400 J/m2 and needed 600 J/m2 for 2.9-log10 and 3.1-log10 reductions, respectively. There was no significant increase in the reduction of viral viability at higher UV doses, which may indicate the presence of UV-resistant viruses. These results show that higher UV doses than those usually used in Swedish drinking water treatment plants should be considered in combination with other barriers to disinfect the water when there is a risk of fecal contamination of the water.

Identification and characterization of a prokaryotic 6-4 photolyase from Synechococcus elongatus with a deazariboflavin antenna chromophore.

Synechococcus elongatus, formerly known as Anacystis nidulans, is a representative species of cyanobacteria. It is also a model organism for the study of photoreactivation, which can be fully photoreactivated even after receiving high UV doses. However, for a long time, only one photolyase was found in S. elongatus that is only able to photorepair UV induced cyclobutane pyrimidine dimers (CPDs) in DNA. Here, we characterize another photolyase in S. elongatus, which belongs to iron-sulfur bacterial cryptochromes and photolyases (FeS-BCP), a subtype of prokaryotic 6–4 photolyases. This photolyase was named SePhrB that could efficiently photorepair 6–4 photoproducts in DNA. Chemical analyses revealed that SePhrB contains a catalytic FAD cofactor and an iron-sulfur cluster. All of previously reported FeS-BCPs contain 6,7-dimethyl-8-ribityllumazine (DMRL) as their antenna chromophores. Here, we first demonstrated that SePhrB possesses 7,8-didemethyl-8-hydroxy-5-deazariboflavin (8-HDF) as an antenna chromophore. Nevertheless, SePhrB could be photoreduced without external electron donors. After being photoreduced, the reduced FAD cofactor in SePhrB was extremely stable against air oxidation. These results suggest that FeS-BCPs are more diverse than expected which deserve further investigation.

ИССЛЕДОВАНИЕ ЧУВСТВИТЕЛЬНОСТИ «ЗЕМНЫХ» И «КОСМИЧЕСКИХ» ШТАММОВ BACILLUS LICHENIFORMIS К ЭКСТРЕМАЛЬНЫМ ФАКТОРАМ КОСМИЧЕСКОГО ПОЛЕТА

The paper presents the results of studying resistance of spores from «terrestrial» and «space» Bacillus licheniformis strains to antimicrobial agents, ultraviolet and radiation. It was established that the resistance of «space» strains to the influence of these extreme factors was noticeably more than for "terrestrial" strains. The most probable explanation of the stronger resistance of «space» strains can be genetic changes aimed to activate intracellular adaptive mechanisms preserved in succeeding generations. Spores from B. licheniformis 24 strain isolated from the ISS environment and exposed to the outer space as part of the EXPOSE-R2 experiment were found to have weakened resistance to antimicrobial agents in subsequent generations. Some of the «space» strains showed the ability to survive exposure to high doses of pulsed UV (1 kJ/m2) and ionizing radiation (20 kGy).

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.

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.

Effect of hypoxia factors gene silencing on ROS production and metabolic status of A375 malignant melanoma cells

The innate response of melanocytes to exogenous or endogenous stress stimuli like extreme pH and temperature, metabolite and oxygen deficiency or a high UV dose initiates a cellular stress response. This process activates adaptive processes to minimize the negative impact of the stressor on the pigment cell. Under physiological conditions, a non-cancer cell is directed to apoptosis if the stressor persists. However, malignant melanoma cells will survive persistent stress thanks to distinct "cancerous" signaling pathways (e.g. MEK) and transcription factors that regulate the expression of so-called "survival genes" (e.g. HIF, MITF). In this survival response of cancer cells, MEK pathway directs melanoma cells to deregulate mitochondrial metabolism, to accumulate reduced species (NADH), and to centralize metabolism in the cytosol. The aim of this work was to study the effect of gene silencing in malignant melanoma A375 cells on metabolic processes in cytosol and mitochondria. Gene silencing of HIF-1α, and miR-210 in normoxia and pseudohypoxia, and analysis of its effect on MITF-M, and PDHA1 expression. Detection of cytosolic NADH by Peredox-mCherry Assay. Detection of OCR, and ECAR using Seahorse XF96. Measurement of produced O2•− with MitoTracker Red CMXRos. 1H NMR analysis of metabolites present in cell suspension, and medium. By gene silencing of HIF-1α and miR-210 the expression of PDHA1 was upregulated while that of MITF-M was downregulated, yielding acceleration of mitochondrial respiratory activity and thus elimination of ROS. Hence, we detected a significantly reduced A375 cell viability, an increase in alanine, inositol, nucleotides, and other metabolites that together define apoptosis. Based on the results of measurements of mitochondrial resipiratory activity, ROS production, and changes in the metabolites obtained in cells under the observed conditions, we concluded that silencing of HIF-1α and miR-210 yields apoptosis and, ultimately, apoptotic cell death in A375 melanoma cells.

Dose fractionation as a promising strategy to improve UV disinfection

Survival curves for bacteria exposed to germicidal radiation (254 nm) usually exhibit a decreased slope at high doses, because bacterial populations contain a small proportion of cells able to tolerate the effects of the radiation. These cells could survive due to external shielding by aggregation or association with inert particles. However, it has been proposed that transient and reversible phenotypic changes modifying UV susceptibility also occur and lead to a phenomenon of persistence. Using Escherichia coli as a model organism, and comparing the effects of continuous exposures to those of irradiations separated by incubations in the dark, we found that in most of the survivors to high UV doses, the condition conferring tolerance (possibly self-aggregation) is transient and reversible, as would be expected in a persistent sub-population. Splitting the irradiations into two exposures reduced viable counts to the detection limit (6.32 orders of magnitude) under conditions in which continuous irradiations produced a reduction no greater than 4 orders of magnitude. In those processes where it is feasible, UV dose fractionation could improve the effectiveness of disinfection by ultraviolet radiation.

Comparative evaluation of 2-isopropyl-3-methoxypyrazine, 2-isobutyl-3-methoxypyrazine, and 2,4,6-trichloroanisole degradation by ultraviolet/chlorine and ultraviolet/hydrogen peroxide processes

2-Isopropyl-3-methoxypyrazine (IPMP), 2-Isobutyl-3-methoxypyrazine (IBMP), and 2,4,6-Trichloroanisole (TCA) are the primary emerging taste and odor (T&O) compounds in water systems with low thresholds (ng L−1). The selected T&O compounds are known to be difficult to remove using conventional water treatment processes. In this study, we compared the removal characteristics of the three T&O compounds using UV/Cl2 and UV/H2O2. The removal rates of the three compounds by direct photolysis at 254 nm were less than 10%, even at a high UV dose (approximately 1000 mJ cm−2). Under conditions of an oxidant injection volume of 5 mg L−1 and UV dose of 1000 mJ cm−2, the degradation rate of the target compounds in the UV/H2O2 process exceeded that of the UV/Cl2 process. Moreover, the results revealed that pH has a significant impact on the removal of the T&O compounds during the UV/Cl2 process. The IPMP, IBMP, and TCA were found to be more reactive with hydroxyl radicals than reactive chlorine species (RCS). A predictive tool was developed to determine the optimal operating condition using the generalized reduced gradient (GRG) nonlinear solver. In the UV/H2O2 process, the EED value for 90% removing rate was 0.156 kWh m−3 for the IPMP, 0.135 kWh m−3 for the IBMP, and 0.154 kWh m−3 for the TCA, respectively. In case of the UV/Cl2, the EED value for 50% removing rate was 0.174 kWh m−3 for the IPMP, 0.138 kWh m−3 for the IBMP, and 0.169 kWh m−3 for the TCA, respectively.

UV/chlorination process of algal-laden water: Algal inactivation and disinfection byproducts attenuation

The disinfection of algal-impacted surface waters results in high concentrations of disinfection byproducts (DBPs). Here, the formation of DBPs when water containing Pseudanabaena limnetica (P. limnetica) was disinfected combining chlorination and ultraviolet irradiation (UV) was investigated. Because of UV/chlorination to inhibit algal growth and reduce DBP formation effectively, the effects of UV doses, free chlorine doses, reaction time and pH on the formation of DBPs during UV/chlorination were studied. The results showed that higher UV dose, longer oxidation time, neutral and acidic pH were beneficial in controlling DBPs. Moreover, UV/chlorination could enhance the formation of brominated DBPs, and reduce the formation of chlorinated DBPs in algal solutions containing bromide. In addition, the DBP formation from intracellular and extracellular organic matter (IOM and EOM, respectively) derived from algae was compared. Finally, the economic efficiency of our system using the electrical energy per order (EE/O) was evaluated, which was calculated to be 18.68 kWh/m3 during the reaction. This information indicated that UV/chlorination was a feasible treatment method for algal-rich water.

Experimental and computational evaluation of a flow-through UV-LED reactor for MS2 and adenovirus inactivation

The design of efficient ultraviolet light emitting diode (UV-LED) reactors is of paramount importance for delivering a high UV dose (fluence). This is particularly critical to the disinfection of UV-resistant organisms, such as adenovirus, in continuous UV systems, given the low wall plug efficiency of UV-LEDs. The UV-LED offers reactor design flexibility, allowing to conform the reactor fluence rate to its hydrodynamics to a high degree, leading to improved design efficiency. In this study, we designed and fabricated a flow-through multi-baffle UV-LED reactor containing 18 UV-LEDs for delivering high UV fluence to a flow of water. Further, we developed a computational model for simulating the reactor performance, to fine-tune the fluence rate and hydrodynamics conformity through exploring several design concepts. The model was evaluated by experimental studies using male-specific-2 (MS2) bacteriophage and adenovirus as the model UV resistance microorganisms. The radiant field was adjusted through the LED arrangement and radiation profile modification. The reactor performance was studied under six different LED arrangements, three irradiation modes, and flow rates of 0.75, 1, and 2 L min−1. Adenovirus inactivation at 1 L min−1 from 1.6 logs increased to 4.1 logs through radiant field modification and enhancing the design efficiency. It was observed that the flexibility offered by UV-LEDs in adjusting the radiation pattern and hydrodynamics could lead to the design of highly-efficient reactors through positively correlating the UV fluence rate profile with the velocity filed. This study presents a detailed discussion concerning irradiation methods and provides insights applicable to UV-LED reactor design.