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Martijn B.J.,PWN Technologies | Kruithof J.C.,Center of Excellence for Sustainable Water Technology | Hughes R.M.,University of New Hampshire | Mastan R.A.,Wageningen University | And 2 more authors.
Journal - American Water Works Association | Year: 2015

Just as with chlorination, medium-pressure (MP) ultraviolet (UV) treatment applied for disinfection purposes has been found to cause formation of genotoxic compounds, measured by the Ames test. By lowering the nitrate and dissolved organic carbon (DOC) content, the Ames test response was reduced substantially. The impact of nitrate photolysis on formation of genotoxic compounds was confirmed. A representative organic micropollutant selection had no significant impact on the Ames test response. Formation of genotoxic compounds was found after MP UV disinfection, photolysis, and advanced oxidation of pretreated groundwater. In addition to nitrate and DOC content, aromaticity of organic matter had a strong impact. Ames test responses were converted into 4-nitroquinoline oxide (4-NQO) equivalent concentrations to enable quantitative comparison and to apply simple risk assessment. Based on the threshold for toxicological concern, already at doses applied for MP UV disinfection, the 4-NQO equivalent concentration of formed genotoxic compounds in nitrate-rich water exceeded the limit of no risk. © 2015 American Water Works Association. Source


Semitsoglou-Tsiapou S.,Imperial College London | Semitsoglou-Tsiapou S.,Center of Excellence for Sustainable Water Technology | Templeton M.R.,Imperial College London | Graham N.J.D.,Imperial College London | And 4 more authors.
Water Research | Year: 2016

The degradation kinetics of three pesticides - metaldehyde, clopyralid and mecoprop - by ultraviolet photolysis and hydroxyl radical oxidation by low pressure ultraviolet hydrogen peroxide (LP-UV/H2O2) advanced oxidation was determined. Mecoprop was susceptible to both LP-UV photolysis and hydroxyl radical oxidation, and exhibited the fastest degradation kinetics, achieving 99.6% (2.4-log) degradation with a UV fluence of 800 mJ/cm2 and 5 mg/L hydrogen peroxide. Metaldehyde was poorly degraded by LP-UV photolysis while 97.7% (1.6-log) degradation was achieved with LP-UV/H2O2 treatment at the maximum tested UV fluence of 1000 mJ/cm2 and 15 mg/L hydrogen peroxide. Clopyralid was hardly susceptible to LP-UV photolysis and exhibited the lowest degradation by LP-UV/H2O2 among the three pesticides. The second-order reaction rate constants for the reactions between the pesticides and OH-radicals were calculated applying a kinetic model for LP-UV/H2O2 treatment to be 3.6 × 108, 2.0 × 108 and 1.1 × 109 M-1 s-1 for metaldehyde, clopyralid and mecoprop, respectively. The main LP-UV photolysis reaction product from mecoprop was 2-(4-hydroxy-2-methylphenoxy) propanoic acid, while photo-oxidation by LP-UV/H2O2 treatment formed several oxidation products. The photo-oxidation of clopyralid involved either hydroxylation or dechlorination of the ring, while metaldehyde underwent hydroxylation and produced acetic acid as a major end product. Based on the findings, degradation pathways for the three pesticides by LP-UV/H2O2 treatment were proposed. © 2016 Elsevier Ltd. Source


van der Kooij D.,KWR Watercycle Research Institute | Martijn B.,PWN Technologies | Schaap P.G.,Water Supply Company Noord Holland PWN | Hoogenboezem W.,Het Waterlaboratorium | And 2 more authors.
Water Research | Year: 2015

Assessment of drinking-water biostability is generally based on measuring bacterial growth in short-term batch tests. However, microbial growth in the distribution system is affected by multiple interactions between water, biofilms and sediments. Therefore a diversity of test methods was applied to characterize the biostability of drinking water distributed without disinfectant residual at a surface-water supply. This drinking water complied with the standards for the heterotrophic plate count and coliforms, but aeromonads periodically exceeded the regulatory limit (1000 CFU 100 mL-1). Compounds promoting growth of the biopolymer-utilizing Flavobacterium johnsoniae strain A3 accounted for c. 21% of the easily assimilable organic carbon (AOC) concentration (17 ± 2 μg C L-1) determined by growth of pure cultures in the water after granular activated-carbon filtration (GACF). Growth of the indigenous bacteria measured as adenosine tri-phosphate in water samples incubated at 25 °C confirmed the low AOC in the GACF but revealed the presence of compounds promoting growth after more than one week of incubation. Furthermore, the concentration of particulate organic carbon in the GACF (83 ± 42 μg C L-1, including 65% carbohydrates) exceeded the AOC concentration. The increased biomass accumulation rate in the continuous biofouling monitor (CBM) at the distribution system reservoir demonstrated the presence of easily biodegradable by-products related to ClO2 dosage to the GACF and in the CBM at 42 km from the treatment plant an iron-associated biomass accumulation was observed. The various methods applied thus distinguished between easily assimilable compounds, biopolymers, slowly biodegradable compounds and biomass-accumulation potential, providing an improved assessment of the biostability of the water. Regrowth of aeromonads may be related to biomass-turnover processes in the distribution system, but establishment of quantitative relationships is needed for confirmation. © 2015 Elsevier Ltd. Source


Dow N.,Victoria University of Melbourne | Roehr J.,Victoria University of Melbourne | Murphy D.,Melbourne Water | Solomon L.,Melbourne Water | And 10 more authors.
Water Practice and Technology | Year: 2015

Combining ceramic membranes with ozonation and allowing ozone residual to contact the membrane surface is well known to control fouling, allowing for higher membrane fluxes. This means that the more robust, longer lasting and higher integrity ceramic material can potentially be used in water recycling in a cost competitive way. This paper presents additional results from a previously reported ozonation/ceramic membrane trial in Melbourne, Australia. The results assisted in understanding the cause of the high fluxes by quenching the residual ozone upstream of the membrane, to isolate its effects on organic species from those on the membrane. Ozone quenching was directly attributed to lost membrane performance which confirmed that ozone has a direct effect on the membrane which contributes to the higher fluxes. Tests to reduce cleaning chemical use (sodium hypochlorite) at high fluxes were also conducted. Sodium hypochlorite consumption generally was not significant, but trading better stability and higher fluxes for reduced chemical use needs to be justified. Ceramic membranes coupled with pre-ozonation exhibit unique properties in water treatment, offering potential advantages such as increased backwash disinfection, as well as higher flux rates or reduced chemical consumption. © IWA Publishing 2015. Source


Shorney-Darby H.L.,PWN Technologies | Galjaard G.,PWN Technologies | Metcalfe D.,South West Water | Rockey C.,South West Water
AWWA/AMTA 2014 Membrane Technology Conference and Exposition | Year: 2014

Pilot-scale trials of four different pre-treatments to ceramic membranes were performed for a surface water in southwest England. A study of the organic character of the feed and treated waters by liquid chromatography-organic carbon detection (LC-OCD) provided an indication of which fraction of organics was contributing to fouling. It appears that the large molecular weight organics, identified as biopolymers by LC-OCD, contributed to fouling when ion exchange was used as pre-treatment, and coagulation is also needed to help control fouling for the source waters of this study. Copyright © 2014 by the American Water Works Association. Source

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