Southern Nevada Water Authority SNWA

Las Vegas, NV, United States

Southern Nevada Water Authority SNWA

Las Vegas, NV, United States
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PubMed | Southern Nevada Water Authority SNWA and University of Nevada, Las Vegas
Type: | Journal: Journal of hazardous materials | Year: 2016

Spatial and temporal variations of trihalomethanes (THMs) in distribution systems have challenged water treatment facilities to comply with disinfection byproduct rules. In this study, granular activated carbon (GAC) and modified GAC (i.e., Ag-GAC and TiO


Dong M.M.,University of Colorado at Boulder | Trenholm R.,Southern Nevada Water Authority SNWA | Rosario-Ortiz F.L.,University of Colorado at Boulder
Journal of Hazardous Materials | Year: 2015

The photochemical degradation of five pharmaceuticals was examined in two secondary wastewater effluents. The compounds, which included atenolol, carbamazepine, meprobamate, phenytoin and primidone, were evaluated for both direct and sensitized photolysis. In the two wastewaters, direct photolysis did not lead to significant compound degradation; however, sensitized photolysis was an important removal pathway for the five pharmaceuticals. Upon solar irradiation, hydroxyl radical (HO) was quantified using the hydroxylation of benzene and singlet oxygen (1O2) formation was monitored following the degradation of furfuryl alcohol. Degradation via sensitized photolysis was observed following five-day exposures for atenolol (69-91%), carbamazepine (67-98%), meprobamate (16-52%), phenytoin (44-85%), and primidone (34-88%). Varying removal is likely a result of the differences in reactivity with transient oxidants. Averaged steady state HO concentrations ranged from 1.2 to 4.0×10-16M, whereas the concentrations of 1O2 were 6.0-7.6×10-14M. Partial removal due to presence of HO indicates it was not the major sink for most compounds examined. Other transient oxidants, such as 1O2 and triplet state effluent organic matter, are likely to play important roles in fates of these compounds. © 2014 Elsevier B.V.


He X.,Southern Nevada Water Authority SNWA | Wert E.C.,Southern Nevada Water Authority SNWA
Water Research | Year: 2016

Colonial cell disaggregation and release of intracellular microcystin were evaluated following chlorine treatment of naturally occurring Microcystis. Microscopic observations of water samples collected from Lake Mead, Nevada, USA, confirmed the presence of colonial Microcystis with cells protected by an outer sheath up to 30 μm thick. During chlorination, two stages of cell decomposition were observed, stage 1: colonial cell disaggregation, and stage 2: unicellular degradation. Following a [Cl2]0:DOC0 ratio of 0.15 (t = 20 min, pH = 8.2-8.5) in unfiltered Lake Havasu samples, total particle count increased from (1.0 ± 0.11) × 105 to 4.2 × 105 particles/mL and fluorescent particle count increased from (1.2 ± 0.50) × 104 to 1.2 × 105 particles/mL, illustrating colonial cell disaggregation. Although total and fluorescent particles increased, the concentration of chlorophyll-a (Chl-a) decreased from 81 μg/L to 72 μg/L, and continued to decrease at higher [Cl2]0:DOC0 ratios. The preliminary second order rate constant for the reaction between Microcystis and chlorine in natural waters was estimated using either Chl-a (k = 15 M-1 s-1) or fluorescence particle count (k = 38 M-1 s-1) as an indicator of cell damage following colonial disaggregation (i.e., at [Cl2]0:DOC0 ratio ≥0.15). Complete release of intracellular microcystin-LR (MC-LR) was observed in both Lake Havasu and Lake Mead samples when applying a [Cl2]0:DOC0 ratio of 0.30 (t = 20 min), which was equivalent to a chlorine exposure of 8 min-mg/L for Lake Havasu samples. With chlorination, DOC increased by 3-18% indicating release of either colony-bound or cell-bound DOC. The results demonstrated the ability of chlorine to disaggregate/inactivate natural Microcystis colonies, and identified oxidation conditions resulting in complete release of intracellular MC-LR. © 2016 Elsevier Ltd.


Wert E.C.,Southern Nevada Water Authority SNWA | Gonzales S.,University of Colorado at Boulder | Dong M.M.,University of Colorado at Boulder | Rosario-Ortiz F.L.,University of Colorado at Boulder
Water Research | Year: 2011

Enhanced coagulation (EC) using ferric chloride was evaluated as a pretreatment process to improve the efficiency of ozone (O 3) for the oxidation of trace organic contaminants in wastewater. At the applied dosages (10-30 mg/L as Fe), EC pretreatment removed between 10 and 47% of the dissolved organic carbon (DOC) from the three wastewaters studied. Size exclusion chromatography (SEC) showed that EC preferentially removed higher apparent molecular weight (AMW) compounds. Subsequent O 3 testing was performed using an O 3:DOC ratio of 1. Results showed that O 3 exposures were similar even though the required doses were reduced by 10-47% by the EC pretreatment process. Hydroxyl radical (HO) exposure, measured by parachlorobenzoic acid (pCBA), showed 10% reduction when using a FeCl 3 dose of 30 mg/L, likely due to the lower O 3 dose and decreased production of HO during the initial phase of O 3 decomposition (t < 30 s). The oxidation of 13 trace organic contaminants (including atenolol, carbamazepine, DEET, diclofenac, dilantin, gemfibrozil, ibuprofen, meprobamate, naproxen, primidone, sulfamethoxazole, triclosan, and trimethoprim) was evaluated after EC and O 3 treatment. EC was ineffective at removing any of the contaminants, while O 3 oxidation reduced the concentration of compounds according to their reaction rate constants with O 3 and HO. © 2011.


Wert E.C.,Southern Nevada Water Authority SNWA | Rosario-Ortiz F.L.,University of Colorado at Boulder
Ozone: Science and Engineering | Year: 2011

Disinfection by-product (DBP) formation was evaluated before and after ozone implementation at two full-scale drinking water facilities in Las Vegas, NV USA. The two treatment plants used preozonation for primary disinfection followed by direct filtration with subsequent chlorination for secondary disinfection. DBP data was evaluated from the finished water of the two treatment plants along with six locations in the distribution system. Results showed that preozonation reduced the formation of total trihalomethanes (TTHM) by up to 10 μg/L and the sum of five haloacetic acids (HAA5) by up to 5 μg/L. These reductions were primarily due to decreases in the diand trichlorinated DBPs such as chloroform, bromodichloromethane, and trichloroacetic acid. Ozonation appeared to shift the speciation of TTHMs and HAA5 to favor increased formation of the di- and tribrominated species such as bromoform, chlorodibromomethane, and dibromoacteic acid. A bromide mass balance showed that <30% of the raw water bromide was accounted for by the formation of TTHMs (8-21%), HAAs (2-3%) and bromate (5%). Reducing the concentration of THMs and HAAs is often not the primary purpose of ozonation, but it can assist utilities in meeting regulatory requirements during drinking water treatment. © 2011 International Ozone Association.


Wert E.C.,Southern Nevada Water Authority SNWA | Wert E.C.,University of Colorado at Boulder | Dong M.M.,Southern Nevada Water Authority SNWA | Rosario-Ortiz F.L.,University of Colorado at Boulder
Water Research | Year: 2013

Depending on drinking water treatment conditions, oxidation processes may result in the degradation of cyanobacteria cells causing the release of toxic metabolites (microcystin), odorous metabolites (MIB, geosmin), or disinfection byproduct precursors. In this study, a digital flow cytometer (FlowCAM®) in combination with chlorophyll-a analysis was used to evaluate the ability of ozone, chlorine, chlorine dioxide, and chloramine to damage or lyse cyanobacteria cells added to Colorado River water. Microcystis aeruginosa (MA), Oscillatoria sp. (OSC) and Lyngbya sp. (LYN) were selected for the study due to their occurrence in surface water supplies, metabolite production, and morphology. Results showed that cell damage was observed without complete lysis or fragmentation of the cell membrane under many of the conditions tested. During ozone and chlorine experiments, the unicellular MA was more susceptible to oxidation than the filamentous OSC and LYN. Rate constants were developed based on the loss of chlorophyll-a and oxidant exposure, which showed the oxidants degraded MA, OSC, and LYN according to the order of ozone>chlorine~chlorine dioxide>chloramine. Digital and binary images taken by the digital flow cytometer provided qualitative insight regarding cell damage. When applying this information, drinking water utilities can better understand the risk of cell damage or lysis during oxidation processes. © 2013 Elsevier Ltd.


Wert E.C.,Southern Nevada Water Authority SNWA | Wert E.C.,University of Colorado at Boulder | Rosario-Ortiz F.L.,University of Colorado at Boulder
Environmental Science and Technology | Year: 2013

The formation of total organic halogen (TOX), carbonaceous disinfection byproducts (DBPs) (trihalomethanes (THMs) and haloacetic acids (HAAs)), and nitrogenous DBPs (trichloronitromethane (TCNM) or chloropicrin, haloacetonitriles (HANs), and nitrosamines) was examined during the chlorination or chloramination of intracellular organic matter (IOM) extracted from Microcystis aeruginosa, Oscillatoria sp. (OSC), and Lyngbya sp. (LYN). The percentage of unknown TOX (22-38%) during chlorination indicated that the majority of DBPs were identified among THMs, HAAs, TCNM, and HANs. Bromide was readily incorporated into DBPs with speciation shifting slightly from dihalogenated species to trihalogenated species. During formation potential testing with chloramines, nitrosamine yields from IOM were measured for N-nitrosodimethylamine (NDMA, 10-52 ng/mgC), N-nitrosopyrrolidine (NPYR, 14 ng/mgC), N-nitrosopiperidine (NPIP, 3.7-5.5 ng/mg C), and N-nitrosomethylethylamine (NMEA, 2.1-2.6 ng/mgC). When IOM was added to a natural water matrix, the nitrosamine yields were not realized likely due to competition from natural organic matter. Ozonation increased NDMA and NMEA formation and reduced NPYR and NPIP formation during subsequent chloramination. In addition, ozone oxidation of IOM formed detectable concentrations of aldehydes, which may contribute to DBP formation. Finally, bioluminescence-based test results showed that >99% of the IOM extracted from OSC and LYN was biodegradable. Therefore, a biological treatment process could minimize this source of DBP precursor material during drinking water treatment. © 2013 American Chemical Society.


Korak J.A.,University of Colorado at Boulder | Wert E.C.,Southern Nevada Water Authority SNWA | Rosario-Ortiz F.L.,University of Colorado at Boulder
Water Research | Year: 2015

Intracellular organic matter (IOM) from cyanobacteria may be released into natural waters following cell death in aquatic ecosystems and during oxidation processes in drinking water treatment plants. Fluorescence spectroscopy was evaluated to identify the presence of IOM from three cyanobacteria species during simulated release into natural water and following oxidation processes (i.e. ozone, free chlorine, chloramine, chlorine dioxide). Peak picking and the fluorescence index (FI) were explored to determine which IOM components (e.g., pigments) provide unique and persistent fluorescence signatures with minimal interferences from the background dissolved organic matter (DOM) found in Colorado River water (CRW). When IOM was added to ultrapure water, the fluorescence signature of the three cyanobacteria species showed similarities to each other. Each IOM exhibited a strong protein-like fluorescence and fluorescence at Ex 370nm and Em 460nm (FDOM), where commercial fluorescence sensors monitor. All species also had strong phycobiliprotein fluorescence (i.e. phycocyanin or phycoerythrin) in the higher excitation range (500-650nm). All three IOM isolates had FI values greater than 2. When IOM was added to CRW, phycobiliprotein fluorescence was quenched through interactions between IOM and CRW-DOM. Mixing IOM and CRW demonstrated that protein-like and FDOM intensity responses were not a simple superposition of the starting material intensities, indicating that interactions between IOM and CRW-DOM fluorescing moieties were important. Fluorescence intensity in all regions decreased with exposure to ozone, free chlorine, and chlorine dioxide, but the FI still indicated compositional differences compared to CRW-DOM. The phycobiliproteins in IOM are not promising as a surrogate for IOM release, because their fluorescence intensity is quenched by interactions with DOM and decreased during oxidation processes. Increases in both FDOM intensity and FI are viable qualitative indicators of IOM release in natural waters and following oxidation and may provide a more robust real-time indication of the presence of IOM than conventional dissolved organic carbon or UV absorbance measurements. © 2014 Elsevier Ltd.


Wert E.C.,Southern Nevada Water Authority SNWA | Wert E.C.,University of Colorado at Boulder | Korak J.A.,University of Colorado at Boulder | Trenholm R.A.,Southern Nevada Water Authority SNWA | Rosario-Ortiz F.L.,University of Colorado at Boulder
Water Research | Year: 2014

The release of intracellular microcystin-LR (MC-LR), 2-methylisoborneol (MIB), and geosmin was investigated after the oxidation of three cyanobacteria (Microcystis aeruginosa (MA), Oscillatoria sp. (OSC), and Lyngbya sp. (LYN)). During the oxidation of 200,000cells/mL of MA, release of intracellular MC-LR exceeded the World Health Organization (WHO) guideline of 1μg/L during the lowest oxidant exposures (CT) tested: ozone (0mg-min/L, below the ozone demand), chlorine (<40mg-min/L), chlorine dioxide (<560mg-min/L), and chloramine (<640mg-min/L). As the CT increased, ozone, chlorine, and chlorine dioxide were able to oxidize the released MC-LR. During the oxidation of OSC (2800 cells/mL) and LYN (1600 cells/mL), release of intracellular MIB and geosmin exceeded reported threshold odor values after exposure to chlorine, chlorine dioxide, and chloramine, which have low reactivity with these taste and odor compounds. Ozone oxidation of OSC yielded an increase in MIB concentration at lower exposures (≤2.9mg-min/L), likely due to insufficient oxidation by hydroxyl radicals. The release of intracellular organic matter (IOM) was also measured to determine the potential of bulk measurements to act as a surrogate for cyanotoxins and metabolite release. In all cases, the dissolved organic carbon (DOC) release was less than 0.25mgC/L, which lacked the sensitivity to indicate the release of MC-LR, MIB, or geosmin. The fluorescence index proved to be a more sensitive indicator of intracellular organic matter release than DOC for MA. These results illustrate that toxic or odorous compounds may be released from cyanobacteria cells during oxidation processes with minimal changes in the DOC concentration. © 2013 Elsevier Ltd.


PubMed | Southern Nevada Water Authority SNWA
Type: | Journal: Water research | Year: 2016

Colonial cell disaggregation and release of intracellular microcystin were evaluated following chlorine treatment of naturally occurring Microcystis. Microscopic observations of water samples collected from Lake Mead, Nevada, USA, confirmed the presence of colonial Microcystis with cells protected by an outer sheath up to 30m thick. During chlorination, two stages of cell decomposition were observed, stage 1: colonial cell disaggregation, and stage 2: unicellular degradation. Following a [Cl2]0:DOC0 ratio of 0.15 (t=20min, pH= 8.2-8.5) in unfiltered Lake Havasu samples, total particle count increased from (1.00.11)10(5) to 4.210(5) particles/mL and fluorescent particle count increased from (1.20.50)10(4) to 1.210(5) particles/mL, illustrating colonial cell disaggregation. Although total and fluorescent particles increased, the concentration of chlorophyll-a (Chl-a) decreased from 81g/L to 72g/L, and continued to decrease at higher [Cl2]0:DOC0 ratios. The preliminary second order rate constant for the reaction between Microcystis and chlorine in natural waters was estimated using either Chl-a (k=15M(-1)s(-1)) or fluorescence particle count (k=38M(-1)s(-1)) as an indicator of cell damage following colonial disaggregation (i.e., at [Cl2]0:DOC0 ratio 0.15). Complete release of intracellular microcystin-LR (MC-LR) was observed in both Lake Havasu and Lake Mead samples when applying a [Cl2]0:DOC0 ratio of 0.30 (t=20min), which was equivalent to a chlorine exposure of 8min-mg/L for Lake Havasu samples. With chlorination, DOC increased by 3-18% indicating release of either colony-bound or cell-bound DOC. The results demonstrated the ability of chlorine to disaggregate/inactivate natural Microcystis colonies, and identified oxidation conditions resulting in complete release of intracellular MC-LR.

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