Medium Pressure UV Research Articles

Bacterial inactivation, DNA damage, and faster ATP degradation induced by ultraviolet disinfection

The efficacy of ultraviolet (UV) disinfection has been validated in numerous studies by using culture-based methods. However, the discovery of viable but non-culturable bacteria has necessitated the investigation of UV disinfection based on bacterial viability parameters. We used quantitative polymerase chain reaction (qPCR) to investigate DNA damage and evaluated adenosine triphosphate (ATP) to indicate bacterial viability. The results of qPCR effectively showed the DNA damage induced by UV when using longer gene amplicons, in that sufficiently long amplicons of both 16S and gadA indicated that the UV induced DNA damages. The copy concentrations of the long amplicons of 16S and gadA decreased by 2.38 log/mL and 1.88 log/mL, respectively, after exposure to 40 mJ/cm2 low-pressure UV. After UV exposure, the ATP level in the bacteria did not decrease instantly. Instead it decreased gradually at a rate that was positively related to the UV fluence. For low-pressure UV, this rate of decrease was slow, but for medium pressure UV, this rate of decrease was relatively high when the UV fluence reached 40 mJ/cm2. At the same UV fluence, the ATP level in the bacteria decreased at a faster rate after exposure to medium-pressure UV.

Potential-Driven Electron Transfer Lowers the Dissociation Energy of the C-F Bond and Facilitates Reductive Defluorination of Perfluorooctane Sulfonate (PFOS).

The widespread environmental occurrence of per- and polyfluoroalkyl substances (PFAS) has attracted significant regulatory, research, and media attention because of their toxicity, recalcitrance, and ability to bioaccumulate. Perfluorooctane sulfonate (PFOS) is a particularly troublesome member of the PFAS family due to its immunity to biological remediation and radical-based oxidation. In the present study, we present a heterogeneous reductive degradation process that couples direct electron transfer (ET) from surface-modified carbon nanotube electrodes (under low potential conditions) to sorbed PFOS molecules using UV-generated hydrated electrons without any further chemical addition. We demonstrate that the ET process dramatically increases the PFOS defluorination rate while yielding shorter chain (C3-C7) perfluorinated acids and present both experimental and ab initio evidence of the synergistic relationship between electron addition to sorbed molecules and their ability to react with reductive hydrated electrons. Because of the low energy consumption associated with the ET process, the use of standard medium-pressure UV lamps and no further chemical addition, this reductive degradation process is a promising method for the destruction of persistent organic pollutants, including PFAS and other recalcitrant halogenated organic compounds.

Full-scale comparison of UV/H2O2 and UV/Cl2 advanced oxidation: The degradation of micropollutant surrogates and the formation of disinfection byproducts

The photolysis of chlorine by UV light leads to the formation of the hydroxyl radicals (OH) as well as reactive chlorine species (RCS) that can be effective as advanced oxidation processes (AOPs) for water treatment. Much of the research to date has been done at laboratory- or bench-scale. This study reports results from a model that demonstrates that the relative effectiveness of the UV/Cl2 AOP compared to the more traditional UV/H2O2 AOP is a function of optical path length. As such, the relative effectiveness of the two treatment options evaluated at small scale may not reflect the relative performance at full-scale, making results previously obtained at small-scale potentially less scalable. This study therefore compares the performance of UV/Cl2 to UV/H2O2 at a full-scale water treatment plant, using sucralose and caffeine as spiked surrogates for contaminants that are reactive solely to OH radicals, and to both OH and RCS, respectively. pH was varied between 6.5 and 8.0. The results demonstrated that when using a medium pressure UV lamp, UV/Cl2 might lead to approximately twice the production of OH radicals as UV/H2O2 at pH 6.5 when using the same molar oxidant concentration, but adding chlorine to the UV reactor at pH 8.0 had a negligible impact on OH radical concentration in comparison to UV alone. The study also confirmed previous small-scale results that RCS can be a major contributor to UV/Cl2 treatment for compounds such as caffeine that are susceptible to RCS, with UV/Cl2 effective at both pH 6.5 and 8.0 for such compounds. Disinfection byproducts were monitored, with adsorbable organohalide (AOX) formation increasing by approximately 10 μg-Cl/L due to chlorine photolysis, but only at pH 6.5 and not at pH 8.0. This implies that UV/Cl2 might increase AOX mostly due to reaction between OH and organic precursors to make them more reactive with chlorine, and not due to RCS. The formation of specific DBPs of current or emerging regulatory interest was minimal under all conditions, except for chlorate. Chlorate yields were in the order of 6–18% of the photolysed chlorine.

The involvement of superoxide radicals in medium pressure UV derived inactivation

Today, two types of lamp systems dominate the UV disinfection industry: low-pressure (LP) UV lamps and medium-pressure (MP) polychromatic lamps. Both lamp types have their advantages and disadvantages in microorganism inactivation, with LP lamps being cheaper, having longer life, and working at lower temperature, hence reducing fouling, and MP lamps showing better inactivation per germicidal dose for certain microorganisms. Bacterium-based biosensors were used to compare LP and MP irradiation. These biosensors were Escherichia coli bacteria carrying the lux operon genes under the control of different stress-responding promoters, where activation of the specific promoter is manifested as bioluminescence. MP irradiation, considerably more than LP irradiation, resulted in activation of the superoxide dismutase expression, indicating the formation of superoxide radicals inside the cells. Accordingly, pre-exposure (immunization) of the bacteria to an activator that produces superoxide radicals resulted in lower inactivation and increased resistance to MP irradiation, but not to LP irradiation. This study shows that the difference in germicidal efficiency may result from the production of intracellular superoxide radicals by MP irradiation, at wavelengths other than 254 nm, as emitted by LP lamps.

Micropollutant Degradation by the UV/H2O2 Process: Kinetic Comparison among Various Radiation Sources.

Kinetic comparisons of micropollutant degradation by ultraviolet (UV) based advanced oxidation processes among various radiation sources are an important issue, yet this is still a challenge at present. This study investigated comparatively the kinetics of sulfamethazine (SMN) degradation by the UV/H2O2 process among three representative radiation sources, including low-pressure mercury UV (LPUV, monochromatic), medium-pressure mercury UV (MPUV, polychromatic), and vacuum UV(VUV)/UV (dual wavelengths causing different reaction mechanisms) lamps. Experiments were conducted with a newly developed mini-fluidic MPUV photoreaction system and a previously developed mini-fluidic VUV/UV photoreaction system. Measured and modeled results both indicate that the photon fluence-based SMN degradation rate constant ( kp') followed a descending order of VUV/UV/H2O2 > MPUV/H2O2 (200-300 nm) > LPUV/H2O2, and the kp' of the MPUV lamp was dependent on the wavelength range selected for photon fluence calculation. Analysis of potential errors revealed that a shorter effective path-length could have a lower error, and the maximum errors for the MPUV/H2O2 and LPUV/H2O2 processes in this study were 7.7% and 18.2%, respectively. This study has developed a new method for kinetic comparisons of micropollutant degradation by UV-AOPs among various radiation sources at bench-scale, which provides useful reference to practical applications.

Genotoxicity assay and potential byproduct identification during different UV-based water treatment processes

Formation of genotoxic byproducts during different ultraviolet (UV) -related water/wastewater treatment processes (including medium pressure (MP) UV oxidation, LP UV oxidation, chlorination, biological activated carbon (BAC) treatment, H2O2 oxidation, and two or more combined processes) was investigated by Ames fluctuation test using Salmonella strains TA98 and TA100 with and without rat liver enzyme extract S9. Byproducts responsible for genotoxicity were identified. The results showed that MP UV can induce mutagenicity and LP UV treatment does not induce mutagenicity. H2O2 oxidation could degrade part of genotoxic compounds. Compared with chlorination, BAC treatment is more effective in removing genotoxicity. Mutagenicity was found mostly in samples tested with TA100 instead of TA98, especially with TA100 without S9, indicating that guanosine and/or cytosine adducts contribute to mutation or toxicological effects in MP UV treated samples. Potential genotoxic byproducts were selected, most of which were nitrogenous organic compounds with more than 10 carbon atoms. Nitrosamines and histidine were excluded from potential genotoxic candidates. The results could contribute to evaluation of mutagenicity of various UV-based water treatment processes.

UV fluences required for compliance with ballast water discharge standards using two approved methods for algal viability assessment

This study investigates the extra UV fluence needed to meet the International Maritime Organisation's ballast water discharge standards for the 10–50 μm size-class using the approved vital stain (VS) method compared to the Most Probable Number (MPN) method for organism viability assessment. Low- and medium pressure UV collimated beam treatments were applied to natural algae collected in temperate and tropical water environments and analysed using both methods. About 10 times higher UV fluence was required to meet discharge standards when using VS compared to MPN. Implementing a dark-hold period after UV treatments decreased algal viability. Length of dark-hold period to meet discharge standards decreased with increasing UV fluence. No significant differences between temperate and tropical samples were observed. The results showed that UV treated algae assessed using the VS method could meet discharge standards by increasing fluence and/or introducing a dark-hold period.

Mechanisms and toxicity evaluation of the degradation of sulfamethoxazole by MPUV/PMS process

In this work, a sulfate radical (SO4-)-based advanced oxidation process was applied to the degradation of sulfamethoxazole (SMX). In these experiments, a medium pressure UV (MPUV) lamp was employed to active peroxymonosulfate (PMS). It was found that 98% of SMX was removed by MPUV/PMS at a UV dose of 200 mJ cm−2 (3.95 μM SMX, 0.2 mM PMS, pH0 = 3.7). Direct MPUV photolysis played a remarkable role in SMX removal by MPUV/PMS process. As for the indirect photolysis, SO4- was the major reactive species under acidic and neutral conditions in MPUV/PMS system, while the hydroxyl radical (OH) became the predominant radical under alkaline conditions. The transformation products (TPs) of SMX that formed in the MPUV-only and MPUV/PMS experiments were identified, and the possible degradation pathways were proposed. Photoisomerization of the isoxazole ring was the major pathway of SMX during MPUV-only process. Hydroxylation/oxidation of the aniline and isoxazole ring was the predominant degradation mechanism of SMX by MPUV/PMS. Toxicity evaluation showed that MPUV/PMS was effective at reducing the antibacterial activity of SMX solutions, while MPUV-only was not. However, some TPs with equivalent or even higher antibacterial activity than SMX were formed during the initial degradation period in MPUV/PMS system. Ecotoxicity of SMX and its TPs was also hypothetically predicted via the ECOSAR program, and the results indicated that some TPs could be more toxic than SMX.

Degradation of naphthenic acid model compounds in aqueous solution by UV activated persulfate: Influencing factors, kinetics and reaction mechanisms

Naphthenic acids (NAs) are one of the constituents of concerns in oil sands process water (OSPW) because of their persistence and recalcitrance. Herein, we investigated the degradation of five model NA compounds by UV-activated persulfate (UV/persulfate) process under medium-pressure UV lamp irradiation at pH 8.0. UV/persulfate process showed higher degradation efficiency towards cyclohexanoic acid (CHA) compared to UV/H2O2 process under the same experimental conditions. CHA (0.39 mM) was completely removed within 30 min when 2 mM persulfate was used as oxidant, while more than 60 min were needed for the UV/H2O2 process. The removal of CHA decreased from 100% to 10% when 300 mM tert-butyl alcohol (TBA) was used as the scavenger, indicating that hydroxyl radical (OH) was responsible for the CHA degradation in the UV/persulfate process. Sulfate (SO4−) radicals reacted slowly with CHA in the UV/persulfate process with a second-order rate constant of k = 5.3 × 107 M−1s−1. Relative kinetics studies using binary mixtures of model NA compounds showed similar structure-reactivity to that under UV/H2O2 process. NAs with long carbon chain, cyclic ring, and aromatic ring were more reactive in the UV/persulfate process. The presence of high concentration of chloride ions dramatically inhibited the reaction. The OH radicals in the UV/persulfate process were generated by capturing OH− in solutions, as evidenced by the decrease of the pH value from 8.0 to 2.8 before and after treatment, respectively, in a pure water matrix. Primary intermediate products (oxy-CHA, hydroxyl-CHA, and dihydroxyl-CHA) of UV/persulfate process were confirmed by UPLC-MS.

Synergy of MS2 disinfection by sequential exposure to tailored UV wavelengths

The advantages of polychromatic ultraviolet (UV) light for viral disinfection can be optimized for disinfection using emerging tailored wavelength sources including KrCl excimer lamps and light emitting diodes (LEDs). Disinfection of the common viral surrogate MS2 bacteriophage was measured after exposure to these emerging sources and conventional low pressure (LP) mercury UV lamps in individual or sequential exposures. The first dose response for any virus (MS2) exposed to a KrCl excimer lamp is reported, showing the high efficiency of fluence-based disinfection because of increased viral susceptibility at the low wavelengths emitted by the excilamp. Sequential exposure dose responses indicated synergy from sequential exposures of LP and excimer lamps, which were competitive on an electrical basis at worst-and best-case scenarios of wall plug efficiency with current medium pressure (MP) disinfection. Best-case scenarios for electrical efficiency also showed all sequential exposures to be competitive with MP UV disinfection. Predictive models for sequential exposure dose responses were assessed to support the current feasibility of incorporating sequential UV exposures to optimize tailored wavelength viral disinfection.

Removal of Emerging Contaminants and Estrogenic Activity from Wastewater Treatment Plant Effluent with UV/Chlorine and UV/H₂O₂ Advanced Oxidation Treatment at Pilot Scale.

Effluent of a municipal wastewater treatment plant (WWTP) was treated on-site with the UV/chlorine (UV/HOCl) advanced oxidation process (AOP) using a pilot plant equipped with a medium pressure UV lamp with an adjustable performance of up to 1 kW. Results obtained from parallel experiments with the same pilot plant, where the state of the art UV/H2O2 AOP was applied, were compared regarding the removal of emerging contaminants (EC) and the formation of adsorbable organohalogens (AOX). Furthermore, the total estrogenic activity was measured in samples treated with the UV/chlorine AOP. At an energy consumption of 0.4 kWh/m3 (0.4 kW, 1 m3/h) and in a range of oxidant concentrations from 1 to 6 mg/L, the UV/chlorine AOP had a significantly higher EC removal yield than the UV/H2O2 AOP. With free available chlorine concentrations (FAC) in the UV chamber influent of at least 5 mg/L (11 mg/L of dosed Cl2), the total estrogenic activity could be reduced by at least 97%. To achieve a certain concentration of FAC in the UV chamber influent, double to triple the amount of dosed Cl2 was needed, resulting in AOX concentrations of up to 520 µg/L.

Meta-analysis of the reduction of antibiotic-sensitive and antibiotic-resistant Escherichia coli as a result of low- and medium-pressure UV lamps.

It is vital that harmful bacteria are removed from water and wastewater treatment plants to prevent human/environmental exposure. This paper examines the log reduction of antibiotic-sensitive (AS) and antibiotic-resistant (AR) Escherichia coli (E. coli) as a result of low-pressure (LP) and medium-pressure (MP) UV lamps. A meta-analysis was performed and a mixed-effect model was created in which 303 data points on the log reduction of E. coli from UV treatment were collected. The results show that in order to achieve a 6 log reduction using an MP lamp, on average a UV level of 7.3 mJ/cm2 for AS E. coli and 7.5 mJ/cm2 for AR E. coli were required. Using an LP lamp, a UV level of 8.1 mJ/cm2 for AS E. coli and 8.4 mJ/cm2 for AR E. coli were required. The results show there is no significant difference between the inactivation of AR and AS E. coli at different UV levels. The model predicts that AR or AS E. coli will be inactivated at UV levels lower than the recommended UV operation conditions (40 mJ/cm2), but it is important to use this UV level to inactivate other harmful microorganisms.

Medium pressure UV-activated peroxymonosulfate for ciprofloxacin degradation: Kinetics, mechanism, and genotoxicity

Sulfate radical (SO4rad−)-based advanced oxidation processes (SR-AOPs) are promising technologies for organic micropollutant removal. In this study, medium pressure (MP) UV was used to activate peroxymonosulfate (PMS) as an emerging SR-AOP for the degradation of ciprofloxacin (CIP), which is a typical fluoroquinolone. It was found that ∼80% of CIP was removed at a UV dose of 200 mJ/cm2 in the MPUV/PMS system (3.02 μM CIP, 0.2 mM PMS, pH = 3.75). Scavenging experiments indicated that both hydroxyl radical (radOH) and SO4rad− contributed to CIP removal in the MPUV/PMS system. In acidic conditions, the predominant reactive radical was SO4rad−, while the role of radOH in CIP degradation was enhanced under neutral and alkaline conditions. A high PMS dose, high pH, low CIP concentration and the presence of Cl−, CO32− and NO3− promoted CIP removal. Transformation products (TPs) of CIP were detected in the MPUV-only and MPUV/PMS experiments, and the initial transformation pathways were proposed. Defluorination and transformation of the piperazine ring were found to be the main pathways for degrading CIP during MPUV-only and the MPUV/PMS processes, respectively. An umu test indicated that MPUV/PMS was effective at reducing the genotoxicity of CIP solutions, but the MPUV-only was not. However, some TPs formed during the initial oxidation period in the MPUV/PMS system had equivalent and even higher toxicity than CIP. The results of this study contribute to our understanding of CIP degradation by MPUV/PMS and provide some basic information for use in future studies and applications.

The importance of a photon-based approach to quantum yield determinations

It was recently reported that when using polychromatic light sources, a photon-based approach should be used to determine photochemical parameters instead of an energy-based approach, and that failure to do so would lead to errors. To illustrate whether the errors could be significant, the quantum yield of atrazine photolysis was determined by measuring its decomposition rate using a medium pressure UV lamp. The results showed that the use of the previously-reported method to calculate quantum yield introduced a 9% error. Furthermore, simplification of the equation via expanding the fraction of light absorbed as a Taylor series as previously-reported introduced a 3% error. The errors would be more significant when the photolyzed compound has a higher concentration or has a broader absorption spectrum.

Role of ammonia on haloacetonitriles and halonitromethanes formation during Ultraviolet irradiation followed by chlorination/chloramination

Combination of ultraviolet (UV) disinfection and chlorination became a common multi-barrier approach taken by water utilities against microbial pathogens in drinking water disinfection. Halogenated disinfection byproducts (DBPs) have been monitored and regulated in drinking water under various jurisdictions around the world for decades. More recently, several nitrogenous DBPs (N-DBPs), like haloacetonitriles (HANs) and halonitromethanes (HNMs), have been identified in chlorinated drinking waters, whose precursors are N-containing organic compounds of various origins and structures. Rising concerns over the N-DBPs formation due to their more potent genotoxic and cytotoxic activity than the regulated carbonaceous-DBPs have prompted extensive research on drinking water disinfection processes. To examine the effect of ammonia nitrogen (NH3-N) on N-DBPs formation during UV disinfection of drinking water followed by chlorination/chloramination, as a first attempt, synthetic waters prepared by humic acid with different NH3-N concentrations were exposed to UV dose up to 300 mJ/cm2 from either low pressure (LP) or medium pressure (MP) lamps, followed by chlorination/chloramination. To investigate trends, the study employed synthetic waters with elevated precursor concentrations and disinfectant exposures to generate significant byproduct formation possible. LP UV treatment had no obvious effect on N-DBP formation, whereas MP UV irradiation produced more dichloroacetonitrile (DCAN). The existence of ammonia (≤1 mg/L-N) increased DCAN concentration in high organics synthetic waters under varying MP UV doses, respectively. In high organics synthetic water samples exposed to a MP UV dose of 300 mJ/cm2 DCAN reached a maximum yield of 13.7 μg/L in the presence of 0.5 mg/L NH3-N, whereas lower yields were observed at NH3-N ≥ 2 mg/L, i.e. 2.9 μg /L and 1.8 μg/L at 2 and 10 mg/L NH3-N, respectively.

Effect of salinity on medium- and low-pressure UV disinfection of Vibrio cholerae.

The problem of biological invasions attributed to ballast water release is an ongoing problem that threatens ecosystems and human health. Ultraviolet (UV) radiation has been increasingly used for ballast water treatment mainly due to the advantages of short contact time and minimized harmful disinfection by products. In this study, the impact of salinity on the inactivation of Vibrio cholerae (NCTC 7253) was examined, and comparison of inactivation level and disinfection kinetics after medium-pressure (MP) (1 kW) and low-pressure (LP) (10 W) UV irradiation was made. MP UV exposure resulted in higher inactivation efficacy against V. cholerae than LP UV exposure especially at lower UV doses (≤3 mJ cm-2) and salinity had a negative impact on both MP and LP UV disinfection, especially at higher UV doses (≥3 mJ cm-2 for MP and ≥4 mJ cm-2 for LP). To understand the mechanisms of salinity effect on V. cholerae, the enzyme-linked immunosorbent assay (ELISA) was employed to determine the number of cyclobutane pyrimidine dimers (CPDs), one major type of DNA damage. No significant effects of salinity were found at the CPDs level except for 3% artificial seawater after LP UV exposure case. It is imperative that site-specific conditions of salinity be taken into account in the design of UV reactors to treat V. cholerae and other species.

A comparison of genotoxicity change in reclaimed wastewater from different disinfection processes

Effluents before disinfection from four wastewater reclamation plants were treated with chlorine (Cl2), ozone (O3), chlorine dioxide (ClO2), medium-pressure ultraviolet (MPUV) and four different combinations of the above, to evaluate the effect of disinfection processes on the genotoxicity removal by the SOS/umu test. Results showed that the genotoxicity increased after MPUV irradiation (10–100 mJ/cm2), but declined when adopting other disinfection processes. The effectiveness of genotoxicity reduction by five chemical disinfectants was identified as: O3 > pre-ozonation with Cl2 ≈ ClO2 > combination of ClO2 and Cl2 > Cl2. The sequential combination of MPUV, Cl2 and O3 reduced the genotoxicity to a level similar to the source water. The influence of differential disinfection process varied on iodinated wastewater, which is closely related to the competitive reactions between disinfectants, iodine and dissolved organic matters. The removal of genotoxic pollutants and the formation of genotoxic disinfection by-products are the two major factors that lead to the change in genotoxicity during disinfection.

Influence of ultraviolet wavelengths on kinetics and selectivity for N-gases during TiO2 photocatalytic reduction of nitrate

For drinking water applications, photocatalytic reduction processes beneficially transform aqueous nitrate to innocuous nitrogen gases (N-gases) but can produce nitrite and ammonia as undesirable aqueous by-products. We hypothesize that by-product selectivity is a function of light source and photon fluence dose, such that discrete wavelengths can increase yield of desirable N-gases. Experiments performed under different wavelength irradiation (ultraviolet- [UV] A, B, C) reduced nitrate in water to differing extents based on pH over the range of 1–8 or the presence of soluble organic electron donors. At an equivalent photon fluence dose, the most rapid nitrate loss in acidic solutions occurred using a combination of three UV-light emitting diodes (285nm, 300nm, 365nm) closely followed by a polychromatic medium pressure UV lamp. A polychromatic xenon light source was least effective in reducing nitrate. Nitrite is an important intermediate during photocatalytic reduction of nitrate. Nitrite absorbs 330–380nm light with high quantum efficiency. Thus, polychromatic or monochromatic light sources with strong UV-A emission more rapidly convert nitrite to by-products than UV-C monochromatic light sources. Nitrous acid (HONO) has a higher molar absorptivity (ε) and quantum efficiency than nitrite ion (pKa=3.39) around 350–370nm. Selectivity towards N-gases is bifurcated at the nitrite intermediate and is strongly influenced by direct photolysis instead of photocatalytic reduction. Thus, the selectivity of by-products can be controlled by delivering light in the 350–370nm wavelength range, where it enables photocatalytic processes to rapidly initiate NO3− reduction and delivers photons for direct photolysis of HONO.

Tetraselmis as a challenge organism for validation of ballast water UV systems

Transport and release of waterborne organisms as a result of ballasting and de-ballasting operations is widely acknowledged to represent an important mechanism for invasions by non-indigenous species. Regulatory requirements have been implemented globally to require treatment of ballast water before its release to the environment as a means of minimizing risks of invasion. UV-based processes represent an option for ballast water treatment; however, their use will require development of appropriate methods for reactor validation. To address this need, Tetraselmis was examined as challenge organism using a most probable number (MPN) assay for quantification of the concentration of viable (reproductively active) cells in suspension. A low pressure collimated-beam reactor was used to investigate UV254 dose-response behavior of Tetraselmis. Based on the experimental conditions applied, Tetraselmis indicated 4.5–5 log10 units of inactivation for UV254 doses of approximately 120 mJ/cm2, with no apparent change of resistance resulting from repeated exposure. A medium pressure UV collimated-beam reactor equipped with a series of narrow bandpass optical filters was used to investigate the action spectrum of Tetraselmis for wavelengths ranging from 228 nm–297 nm. Radiation with wavelengths in the range 254–280 nm was observed to be most efficient for inactivation of Tetraselmis. Additionally, DNA was extracted from Tetraselmis to allow measurement of its absorption spectrum. These results indicated strong absorbance from 254 nm to 280 nm, thereby suggesting that damage to DNA plays an important role in the inactivation of Tetraselmis sp. However, deviations of the action spectrum shape from the shape of the DNA absorption spectrum suggest that UV-induced damage to biomolecules other than DNA may contribute to Tetraselmis inactivation at some wavelengths in the UVC range.

Bromate formation from the oxidation of bromide in the UV/chlorine process with low pressure and medium pressure UV lamps

When a bromide-containing water is treated by the ultraviolet (UV)/chlorine process, hydroxyl radicals (HO) and halogen radicals such as Cl or Br are formed due to the UV photolysis of free halogens. These reactive species may induce the formation of bromate, which is a probable human carcinogen. Bromate formation in the UV/chlorine process using low pressure (LP) and medium pressure (MP) lamps in the presence of bromide was investigated in the present study. The UV/chlorine process significantly enhanced bromate formation as compared to dark chlorination. The bromate formation was elevated with increasing UV fluence, bromide concentration, and pH values under both LP and MP UV irradiations. It was significantly enhanced at pH 9 compared to those at pH 6 and 7 with MP UV irradiation, while it was slightly enhanced at pH 9 with LP UV. The formation by UV/chlorine process started with the formation of free bromine (HOBr/OBr−) through the reaction of chlorine and bromide, followed by a subsequent oxidation of free bromine and formation of BrO and bromate by reacting with radicals.