Field demonstration of UV-LED disinfection at small and decentralized water facilities.

Ultraviolet light-emitting diodes (UV-LED) can be a good option for disinfecting water in small and decentralized facilities. A flow-through UV-LED disinfection module was evaluated at three remote locations in Japan. The disinfection efficiency of the module was monitored for over one year, targeting indigenous Escherichia coli, total coliforms, standard plate count, and heterotrophic plate count (HPC) bacteria. The physicochemical parameters of the source water, including UV transmittance (UVT), were also monitored to understand their natural fluctuation and impacts on UV disinfection. Overall, the UV-LED module showed efficient disinfection at all locations, achieving 2.7 log inactivation of E. coli at 30 L/min in a community-based water supply. HPC inactivation did not significantly differ among the three test sites (p > 0.01). One test site experienced a decrease in HPC inactivation after 10 months, whereas the other two sites did not show performance deterioration after one year. HPC inactivation was not correlated with the UVT of source water at any location, implying the difficulty to use UVT as a single parameter to predict disinfection efficiency in practical applications. This study demonstrates the effectiveness of UV-LED technology for water disinfection in small and decentralized water supply systems.

Mycobacterial contamination in tap and shower waters in Thailand.

Waterborne disease is increasingly becoming associated with opportunistic premise plumbing pathogens (OPPPs), which can resist residual chlorination, regrow throughout drinking water distribution systems, and colonize premise plumbing. Nontuberculous mycobacteria (NTM) include clinically important species and exert a high burden on healthcare systems. We briefly report a qPCR-based survey of Mycobacterium spp. numbers in tap, POU-treated, and shower waters from Bangkok, Thailand. Non-stagnant tap waters and non-stagnant shower waters had mean numbers of 1.3 × 103 and 2.4 × 103 copies/mL, respectively. Water stagnation resulted in mean numbers higher by up to 1.0 log. The lowest number, 25 copies/mL, was obtained from a POU-treated sample, while the highest number, 2.0 × 104 copies/mL, came from a stagnant tap. Comparing with international data, mean numbers in this study were greater than those in nine out of 11 (82%) comparable studies, and the maximum numbers in this study were also high. Our samples of Bangkok waters exhibited relatively high Mycobacterium spp. numbers, suggesting the need for appropriate POU treatment systems where NTM infection is a health concern. This survey data can be used to set inactivation performance targets in POU water disinfection system design and may also lead to quantitative microbial risk assessment (QMRA) studies.

Conformation-dependent UV inactivation efficiency of a conjugative, multi-drug resistant plasmid.

A conjugative, multi-drug-resistant plasmid was irradiated in-vivo and in-vitro with a 265-nm UV-light emitting diode (UV-LED) to investigate the gene inactivation efficiency of a plasmid deoxyribonucleic acid (pDNA) carrying DNA transfer and replication genes. The clinical-isolate 60 kb RP4 plasmid of the IncPα group containing the traG gene, was irradiated intracellularly in E. coli DH5α and extracellularly in a water medium at pH 8.5. Real-time quantitative polymerase chain reaction (RT-qPCR) measurements of the UV-fluence response gene inactivation rate constants revealed a decreasing pattern via a pseudo-1st-order inactivation kinetics in all forms examined. Our findings showed that the intracellular-supercoiled conformation, with k = 6.1 × 10-3 cm2/mJ, has the lowest UV susceptibility (lowest inactivation rate). UV absorbance measurements and a computational approach showed that the host's RNA provides the photo-shielding, demonstrating this high UV resistance. When UV exposure was measured in-vitro, the condensed DNA exhibited a self-shielding effect over supercoiled and denatured DNA due to the hypochromic-hyperchromic effects. This study has shown that large-sized conjugative plasmids with conformation-dependent UV/UV-LED-based gene inactivation play a significant role in preventing the spread of antibiotic resistance.

Inactivation kinetics of 280 nm UV-LEDs against Mycobacterium abscessus in water.

Nontuberculous mycobacteria (NTM) are opportunistic premise plumbing pathogens (OPPPs) that cause a burdensome waterborne respiratory disease. Due to their resistance to chemical disinfectants and regrowth in biofilms in drinking water distribution systems, treatment can be better performed using small ultraviolet disinfection units at the point-of-use (POU), such as at a tap or showerhead. Ultraviolet light-emitting diodes (UV-LEDs) are well suited for such applications, but fluence-response data are not available for one of the most important NTM, Mycobacterium abscessus. In this study, a bench-scale 280 nm UV-LED apparatus was used to irradiate M. abscessus in a water matrix. The fluence-response profile was sigmoidal, exhibiting both shoulder and tailing phenomena. Simple linear regression and the Geeraerd's inactivation kinetics model yielded k values of 0.36 and 0.37 cm2/mJ, respectively, revealing that M. abscessus is more resistant to UV than Pseudomonas aeruginosa and Legionella pneumophila, which suggests that NTM are among the most UV-resistant OPPPs. Results of this study suggest that 280 nm UV-LED irradiation can be an effective and practical option to inactivate M. abscessus at the POU. Disinfection units that can deliver a fluence of 10 mJ/cm2 are expected to achieve nearly 2 log (99%) inactivation of M. abscessus.

A Simple and Practical Method for Fluence Determination in Bench-Scale UV-LED Setups.

In UV disinfection of water, the fluence of UV required to inactivate a target microorganism is determined based on the procedures developed for conventional mercury-based UV lamps with collimation. In this regard, a simple and practical method with a mathematical model and radiometry is proposed for determining the fluence rate with UV light-emitting diodes (UV-LEDs). This method was applied to a bench-scale UV-LED setup and validated by comparing the calculations with the measurements using either a spectroradiometer or a chemical actinometer. The results showed high accordance with spectroradiometer outputs with a linear regression equation y = 0.997x (x: model calculation, y: spectroradiometer output, r2 = 0.999, P < 0.001 for n = 20) in an experiment varying the distance between the measurement points and the UV-LEDs. Meanwhile, the proposed method and chemical actinometry exhibited 98% concordance. Furthermore, this method was applied to determine the fluence-response profiles of Pseudomonas aeruginosa, and the results demonstrated that the proposed method was appropriate at two different distances between the UV-LEDs and the solutions. To conclude, the proposed method can determine the fluence in a UV-LED bench-scale setup in a simple and practical way, which would potentially promote the research and development of water treatment using UV-LEDs.

Comparative effectiveness of membrane technologies and disinfection methods for virus elimination in water: A review.

The pandemic of the 2019 novel coronavirus disease (COVID-19) has brought viruses into the public horizon. Since viruses can pose a threat to human health in a low concentration range, seeking efficient virus removal methods has been the research hotspots in the past few years. Herein, a total of 1060 research papers were collected from the Web of Science database to identify technological trends as well as the research status. Based on the analysis results, this review elaborates on the state-of-the-art of membrane filtration and disinfection technologies for the treatment of virus-containing wastewater and drinking water. The results evince that membrane and disinfection methods achieve a broad range of virus removal efficiency (0.5-7 log reduction values (LRVs) and 0.09-8 LRVs, respectively) that is attributable to the various interactions between membranes or disinfectants and viruses having different susceptibility in viral capsid protein and nucleic acid. Moreover, this review discusses the related challenges and potential of membrane and disinfection technologies for customized virus removal in order to prevent the dissemination of the waterborne diseases.

Groundwater as a potential cause of Chronic Kidney Disease of unknown etiology (CKDu) in Sri Lanka: a review.

The cause of Chronic Kidney Disease of unknown etiology (CKDu) in the rural dry zone of Sri Lanka remains unidentified, despite vast research efforts that brought about an extensive list of potential risk factors. Among these, the long-term exposure to various nephrotoxic elements through drinking groundwater was widely suspected owing to the unique geographical distribution of the disease. This review focuses on such well-known hypotheses suspecting the relations with fluoride, hardness, major ions, heavy metals, metalloids, organic matter, agrochemical residues, pathogens, and bacterial toxins in the groundwaters of the CKDu-endemic region. It was comprehensively discussed why each of these constituents was considered a risk factor of CKDu, how could they possibly trigger the pathogenesis of the disease, what was the evidence that supported or failed each hypothesis, and whether providing safe drinking water had been effective at mitigating the progression of the disease. Although plenty of circumstantial evidence supported an etiology related to groundwater for CKDu, it was impossible to elucidate the cause-effect relationships between drinking impaired groundwater and the occurrence of the disease. Future research should be effectively designed to clarify the role of groundwater in the onset of CKDu by taking into account the gaps in past research.

UV light-emitting diode (UV-LED) at 265 nm as a potential light source for disinfecting human platelet concentrates.

The risk of sepsis through bacterial transmission is one of the most serious problems in platelet transfusion. In processing platelet concentrates (PCs), several methods have been put into practice to minimize the risk of bacterial transmission, such as stringent monitoring by cultivation assays and inactivation treatment by photoirradiation with or without chemical agents. As another potential option, we applied a light-emitting diode (LED) with a peak emission wavelength of 265 nm, which has been shown to be effective for water, to disinfect PCs. In a bench-scale UV-LED exposure setup, a 10-min irradiation, corresponding to an average fluence of 9.2 mJ/cm2, resulted in >2.0 log, 1.0 log, and 0.6 log inactivation (mean, n = 6) of Escherichia coli, Staphylococcus aureus, and Bacillus cereus, respectively, in non-diluted plasma PCs. After a 30-min exposure, platelet counts decreased slightly (18 ± 7%: mean ± SD, n = 7); however, platelet surface expressions of CD42b, CD61, CD62P, and PAC-1 binding did not change significantly (P>0.005), and agonist-induced aggregation and adhesion/aggregation under flow conditions were well maintained. Our findings indicated that the 265 nm UV-LED has high potential as a novel disinfection method to ensure the microbial safety of platelet transfusion.

Evaluation of groundwater quality and reverse osmosis water treatment plants in the endemic areas of Chronic Kidney Disease of Unknown Etiology (CKDu) in Sri Lanka.

Community-based reverse osmosis (RO) water treatment plants are employed as an interim solution for producing safe drinking water for the endemic areas of Chronic Kidney Disease of Unknown Etiology (CKDu) in the rural dry zone of Sri Lanka. It is recognized that RO-treated groundwater diminishes the progression of CKDu; thus, proper maintenance of these RO plants would be indispensable to protect public health. The present study broadly investigated the quality of groundwater in CKDu-endemic areas, and the performance, operations, and maintenance of the RO plants which purified this groundwater. The feedwater (i.e., groundwater) and treated water from 32 RO plants in Anuradhapura District, comprising 27 in the CKDu high-risk (HR) region and 5 in the low-risk (LR) region, were analyzed for major chemical and biological water quality parameters. Alkalinity, hardness, and microbiological parameters in groundwaters exceeded the maximum allowable levels (MALs) for drinking in all study areas. Additionally, TDS and magnesium exceeded the MALs, exclusively in the HR areas. Elevated occurrence of magnesium-predominant hardness and ionicity in groundwater showed significant relations with the incidence of CKDu. All RO plants achieved high removal rates (>95%) for excessive chemical constituents in groundwater, but the recovery rates were fairly low (~46%). The current disinfection practices in RO plants were insufficient to ensure the microbial safety of the product water. Low demand for product water, scarcity of groundwater, lack of technical capacity of the local communities, poor maintenance practices and unplanned brine removal were the key issues related to RO plant O&M. Unless properly handled, the lack of rules and regulations for RO water treatment in the CKDu-endemic region could lead to numerous environmental and public health issues in the future.

Inactivation of feline calicivirus using ultraviolet light-emitting diodes.

Ultraviolet light-emitting diodes (UV-LEDs) with peak emission wavelengths of 265, 280 and 300 nm were applied for the inactivation of feline calicivirus (FCV) in water, and the results were compared to those derived with a common viral surrogate coliphage MS2. The fluence response profiles indicated that the log10-based inactivation rate constant of FCV was 0.113, 0.101 and 0.007 cm2 mJ-1 for the 265, 280 and 300 nm UV-LEDs, respectively, while that of MS2 was 0.034, 0.033 and 0.003 cm2 mJ-1 for the 265, 280 and 300 nm UV-LEDs, respectively. Namely, FCV was about two to three times more sensitive than MS2 to germicidal UV emissions adopted in this study, and the 265 nm and 280 nm UV-LEDs were particularly effective to inactivate FCV. Results of this study are to be a part of database on fluence response profiles of various microorganisms, which would foster the development of disinfection apparatuses equipped with UV-LEDs.

Effects of UV Irradiation by Light Emitting Diodes on Heterotrophic Bacteria in Tap Water.

Ultraviolet light emitting diodes (UV-LEDs) are small mercury-free devices that can be installed at the point of use (POU) of water for disinfection. Considering that heterotrophic bacteria are of concern in drinking water systems, we applied a flow-through UV-LED apparatus to dechlorinated tap water, and determined the heterotrophic plate count (HPC) in samples after UV-LED exposure (UV+) compared to samples without UV-LED application (UV-). The UV+ and UV- samples were maintained at 20°C to track HPC profiles during storage for 7 days. It was confirmed that UV+ samples showed negative HPC or lower HPC than UV- for 5 days of storage after the flow-through test. HPC bacteria formed colonies with different morphological characteristics, and yellow colonies were closest to Novosphingobium sp., with 99% identity, while white and pale pink colonies were closest to Methylobacterium sp., with 99-100% identity, based on 16S rRNA gene sequences. White colonies became dominant in UV+, indicating that UV-LED exposure can select UV-resistant species such as Methylobacterium. This study shows the effects of UV-LED application on HPC bacteria in tap water and implies that future research is required on the significance and impacts of microbial selection by UV-LED exposure.

Inactivation kinetics and efficiencies of UV-LEDs against Pseudomonas aeruginosa, Legionella pneumophila, and surrogate microorganisms.

To demonstrate the effectiveness of UV light-emitting diodes (UV-LEDs) to disinfect water, UV-LEDs at peak emission wavelengths of 265, 280, and 300 nm were adopted to inactivate pathogenic species, including Pseudomonas aeruginosa and Legionella pneumophila, and surrogate species, including Escherichia coli, Bacillus subtilis spores, and bacteriophage Qß in water, compared to conventional low-pressure UV lamp emitting at 254 nm. The inactivation profiles of each species showed either a linear or sigmoidal survival curve, which both fit well with the Geeraerd's model. Based on the inactivation rate constant, the 265-nm UV-LED showed most effective fluence, except for with E. coli which showed similar inactivation rates at 265 and 254 nm. Electrical energy consumption required for 3-log10 inactivation (EE,3) was lowest for the 280-nm UV-LED for all microbial species tested. Taken together, the findings of this study determined the inactivation profiles and kinetics of both pathogenic bacteria and surrogate species under UV-LED exposure at different wavelengths. We also demonstrated that not only inactivation rate constants, but also energy efficiency should be considered when selecting an emission wavelength for UV-LEDs.

Analysis of Hydroxyl Radicals and Inactivation Mechanisms of Bacteriophage MS2 in Response to a Simultaneous Application of UV and Chlorine.

The simultaneous application of UV and chlorine (expressed as UV/Cl2) as a water treatment method may be a good disinfection option for UV-resistant microorganisms, such as human adenoviruses (HAdVs). In this study, we developed two approaches using UV/Cl2: one to quantitate the OH• radicals based on the degradation of the probe compound para-chlorobenzoic acid (pCBA) and the other to use bacteriophage MS2 to understand the virus inactivation mechanisms in response to UV, chlorine and UV/Cl2 disinfection using reverse-transcription quantitative polymerase chain reaction (RT-qPCR), attachment and genome penetration assays. The results revealed that OH• radicals were produced at a concentration of 2.70 × 10-14 M in the UV/Cl2 treatment with a practical chlorine dose of 1 mg/L and with a minimum UV254 fluence of approximately 10 mJ/cm2, whereas UV or chlorine alone did not produce OH• radicals. In the UV/Cl2 treatment, synergistic effects on viral genome damage were observed, but were not directly due to OH• radicals. The ability of MS2 to penetrate the genome of the host bacteria was impaired, but its ability to attach to the host was not affected by the treatment. We concluded that the major cause of virus inactivation in response to UV/Cl2 was the damage to the viral genome caused by combination actions of chlorine species and OH• radicals.

Effects of Arrangement of UV Light-Emitting Diodes on the Inactivation Efficiency of Microorganisms in Water.

Ultraviolet light-emitting diodes (UV-LEDs) offer high flexibility in the reactor design for water disinfection. To specify the key design factors affecting the performance of a reactor, we examined how the arrangement of UV-LEDs in a cylindrical reactor affects the inactivation efficiency of Escherichia coli and coliphage Qß. A ring-shaped UV-LED apparatus, composed of two units containing ten 285-nm UV-LEDs each, were attached to a quartz cylinder, and microbial suspensions flowed through the cylinder for single pass at altered flow rates. The distance between the two units, L, was altered to examine its effects on inactivation efficiencies. Over 4 log inactivation of E. coli was achieved at 800 mL min-1 regardless of the L values, suggesting that the apparatus has a high potential to disinfect water. The inactivation at L = 20 mm was significantly higher than that at L = 0 in all cases tested (ANOVA, P < 0.05), while this was not true when L was extended to 40 and 60 mm. Therefore, a separate arrangement of UV-LEDs at a certain distance can improve the efficiency, and the distance matters to enhance the performance. This study involves a design concept on how to arrange UV-LEDs in a water disinfection apparatus.

Comparison of chlorination and chloramination in carbonaceous and nitrogenous disinfection byproduct formation potentials with prolonged contact time.

Due to decreasing water demands in Japan, hydraulic retention times of water in piped supply systems has been extended, resulting in a longer contact time with disinfectants. However, the effects of extended contact time on the formation of various disinfection byproducts (DBPs), including carbonaceous DBPs such as trihalomethane (THM) and haloacetic acid (HAA), and nitrogenous DBPs such as nitrosodimethylamine (NDMA) and nitrosomorpholine (NMor), have not yet been investigated in detail. Herein, we compared the formation of these DBPs by chlorination and chloramination for five water samples collected from rivers and a dam in Japan, all of which represent municipal water supply sources. Water samples were treated by either filtration or a combination of coagulation and filtration. Treated samples were subjected to a DBP formation potential test by either chlorine or chloramine for contact times of 1 day or 4 days. Four THM species, nine HAA species, NDMA, and NMor were measured by GC-ECD or UPLC-MS/MS. Lifetime cancer risk was calculated based on the Integrated Risk Information System unit risk information. The experiment and analysis focused on (i) prolonged contact time from 1 day to 4 days, (ii) reduction efficiency by conventional treatment, (iii) correlations between DBP formation potentials and water quality parameters, and (iv) the contribution of each species to total risk. With an increased contact time from 1 day to 4 days, THM formation increased to 420% by chloramination. Coagulation-filtration treatment showed that brominated species in THMs are less likely to be reduced. With the highest unit risk among THM species, dibromochloromethane (DBCM) showed a high correlation with bromine, but not with organic matter parameters. NDMA contributed to lifetime cancer risk. The THM formation pathway should be revisited in terms of chloramination and bromine incorporation. It is also recommended to investigate nitrosamine formation potential by chloramination.

Sequential and Simultaneous Applications of UV and Chlorine for Adenovirus Inactivation.

Adenoviruses are water-borne human pathogens with high resistance to UV disinfection. Combination of UV treatment and chlorination could be an effective approach to deal with adenoviruses. In this study, human adenovirus 5 (HAdV-5) was challenged in a bench-scale experiment by separate applications of UV or chlorine and by combined applications of UV and chlorine in either a sequential or simultaneous manner. The treated samples were then propagated in human lung carcinoma epithelial cells to quantify the log inactivation of HAdV-5. When the processes were separate, a fluence of 100 mJ/cm(2) and a CT value of 0.02 mg min/L were required to achieve 2 log inactivation of HAdV-5 by UV disinfection and chlorination, respectively. Interestingly, synergistic effects on the HAdV-5 inactivation rates were found in the sequential process of chlorine followed by UV (Cl2-UV) (p < 0.05, ANCOVA) in comparison to the separate processes or the simultaneous application of UV/Cl2. This implies that a pretreatment with chlorine may increase the sensitivity of the virus to the subsequent UV disinfection. In conclusion, this study suggests that the combined application of UV and chlorine could be an effective measure against adenoviruses as a multi-barrier approach in water disinfection.

Pepper mild mottle virus as an indicator and a tracer of fecal pollution in water environments: comparative evaluation with wastewater-tracer pharmaceuticals in Hanoi, Vietnam.

We analyzed pepper mild mottle virus (PMMoV) in 36 samples taken from surface water, wastewater, groundwater, tap water and bottled water in Hanoi, Vietnam. We then compared the occurrence and fates of PMMoV with pharmaceuticals and personal care products (PPCPs), which are known wastewater tracers. PMMoV was detected in 94% of the surface water samples (ponds, water from irrigated farmlands and rivers) and in all the wastewater samples. The PMMoV concentration ranged from 5.5×10(6)-7.2×10(6)copies/L in wastewater treatment plant (WWTP) influents, 6.5×10(5)-8.5×10(5)copies/L in WWTP effluents and 1.0×10(4)-1.8×10(6)copies/L in surface water. Among the sixty PPCPs analyzed, caffeine and carbamazepine had high detection rates in surface water (100% and 88%, respectively). In surface water, the concentration ratio of PMMoV to caffeine remained unchanged than that in WWTP influents, suggesting that the persistence of PMMoV in surface water was comparable to that of caffeine. The persistence and the large concentration ratio of PMMoV in WWTP influents to the method detection limit would account for its ubiquitous detection in surface water. In comparison, human enteric viruses (HEV) were less frequently detected (18-59%) than PMMoV in surface water, probably because of their faster decay. Together with the reported high human feces-specificity, our results suggested that PMMoV is useful as a sensitive fecal indicator for evaluating the potential occurrence of pathogenic viruses in surface water. Moreover, PMMoV can be useful as a moderately conservative fecal tracer for specifically tracking fecal pollution of surface water. PMMoV was detected in 38% of the groundwater samples at low concentrations (up to 19copies/L). PMMoV was not detected in the tap water and bottled water samples. In groundwater, tap water and bottled water samples, the occurrence of PPCPs and HEV disagreed with that of PMMoV, suggesting that PMMoV is not suitable as an indicator or a tracer in those waters.

Simultaneous removal of dissolved organic matter and bromide from drinking water source by anion exchange resins for controlling disinfection by-products.

Anion exchange resins (AERs) with different properties were evaluated for their ability to remove dissolved organic matter (DOM) and bromide, and to reduce disinfection by-product (DBP) formation potentials of water collected from a eutrophic surface water source in Japan. DOM and bromide were simultaneously removed by all selected AERs in batch adsorption experiments. A polyacrylic magnetic ion exchange resin (MIEX®) showed faster dissolved organic carbon (DOC) removal than other AERs because it had the smallest resin bead size. Aromatic DOM fractions with molecular weight larger than 1600 Da and fluorescent organic fractions of fulvic acid- and humic acid-like compounds were efficiently removed by all AERs. Polystyrene AERs were more effective in bromide removal than polyacrylic AERs. This result implied that the properties of AERs, i.e. material and resin size, influenced not only DOM removal but also bromide removal efficiency. MIEX® showed significant chlorinated DBP removal because it had the highest DOC removal within 30 min, whereas polystyrene AERs efficiently removed brominated DBPs, especially brominated trihalomethane species. The results suggested that, depending on source water DOM and bromide concentration, selecting a suitable AER is a key factor in effective control of chlorinated and brominated DBPs in drinking water.

Investigating sources and pathways of perfluoroalkyl acids (PFAAs) in aquifers in Tokyo using multiple tracers.

We employed a multi-tracer approach to investigate sources and pathways of perfluoroalkyl acids (PFAAs) in urban groundwater, based on 53 groundwater samples taken from confined aquifers and unconfined aquifers in Tokyo. While the median concentrations of groundwater PFAAs were several ng/L, the maximum concentrations of perfluorooctane sulfonate (PFOS, 990 ng/L), perfluorooctanoate (PFOA, 1800 ng/L) and perfluorononanoate (PFNA, 620 ng/L) in groundwater were several times higher than those of wastewater and street runoff reported in the literature. PFAAs were more frequently detected than sewage tracers (carbamazepine and crotamiton), presumably owing to the higher persistence of PFAAs, the multiple sources of PFAAs beyond sewage (e.g., surface runoff, point sources) and the formation of PFAAs from their precursors. Use of multiple methods of source apportionment including principal component analysis-multiple linear regression (PCA-MLR) and perfluoroalkyl carboxylic acid ratio analysis highlighted sewage and point sources as the primary sources of PFAAs in the most severely polluted groundwater samples, with street runoff being a minor source (44.6% sewage, 45.7% point sources and 9.7% street runoff, by PCA-MLR). Tritium analysis indicated that, while young groundwater (recharged during or after the 1970s, when PFAAs were already in commercial use) in shallow aquifers (<50 m depth) was naturally highly vulnerable to PFAA pollution, PFAAs were also found in old groundwater (recharged before the 1950s, when PFAAs were not in use) in deep aquifers (50-500 m depth). This study demonstrated the utility of multiple uses of tracers (pharmaceuticals and personal care products; PPCPs, tritium) and source apportionment methods in investigating sources and pathways of PFAAs in multiple aquifer systems.

Effects of salinity on photoreactivation of Escherichia coli after UV disinfection.

The effects of sodium chloride on photoreactivation of Escherichia coli were examined, assuming the discharge of ultraviolet (UV)-treated wastewater to water environment at different salinities. Suspensions of E. coli were first exposed to a low-pressure UV lamp in phosphate buffer to achieve 3 log inactivation, followed by an exposure to fluorescent light in NaCl solutions at the concentration of 1.0, 1.4, 1.9, 2.4 and 2.9 weight/volume %. When photoreactivation was completed in 3 h, survival ratio was recovered about 2 log in 1.0, 1.4, and 1.9% NaCl solutions, which was equivalent to the recovery observed in phosphate-buffered solution. Meanwhile, the recovery was suppressed to 0.8 log and -0.2 log in 2.4 and 2.9% NaCl solutions, respectively, which was significantly less than the recovery in phosphate buffer according to the t-test (p < 0.05). An endonuclease sensitive site assay demonstrated that the suppressed photoreactivation in 2.9% NaCl solution was due to the failure at repairing UV-induced pyrimidine dimers in the genome. In conclusion, photoreactivation of E. coli was significantly suppressed in NaCl solution at 2.4% or higher but not affected in NaCl solution at 1.9% or lower. This implies that photoreactivation of E. coli may potentially occur in brackish and coastal areas where salinity is rather low.