Methyl nitrate as a byproduct in advanced water treatment systems: Liquid chromatographic determination method and cause of formation.

Neutral low-molecular-weight organics such as methyl nitrate that can readily pass through reverse osmosis (RO) membranes employed in potable water reuse facilities attract interest owing to public health considerations. In this study, a novel determination method based on high-performance liquid chromatography, online photochemical conversion to peroxynitrite, and luminol chemiluminescence detection was developed for methyl nitrate measurement in treated water. The maximum photochemical conversion efficiency of methyl nitrate to peroxynitrite was found to be 6.5% using a 222-nm excimer lamp. The calibration curve for the developed method was linear between 1.0 × 10-9 and 1.0 × 10-7 M, and the limit of detection was 0.3 nM (0.03 µg/L) given an injection volume of 200 µL. The methyl nitrate concentrations in RO permeate from reclaimed wastewater and product water after subsequent treatment by a UV/H2O2 advanced oxidation process (AOP) were 2.2 and 22.5 nM (0.17 and 1.7 µg/L), respectively. UV irradiation of RO permeate in the laboratory using a low-pressure Hg lamp confirmed the formation of methyl nitrate in the permeate in the absence of H2O2 and residual chloramines. This chemiluminescent detection method for methyl nitrate will promote a greater understanding of the origin and formation of this treatment byproduct in reclaimed wastewater.

Optimizing Potable Water Reuse Systems: Chloramines or Hydrogen Peroxide for UV-Based Advanced Oxidation Process?

The tapping of municipal wastewater for potable reuse significantly enhances drinking water supply in drought-stricken regions worldwide. Membrane-based potable reuse treatment trains commonly employ ultraviolet-based advanced oxidation processes (UV-AOPs) to degrade trace organic contaminants in water to produce high-quality recycled water. Hydrogen peroxide (H2O2) is used as the default photo-oxidant. Meanwhile, chloramines, which are added to prevent biofouling, pass through the membranes and impact the treatment efficiency of UV-AOP. Water reuse facilities therefore face the dilemma of optimizing H2O2 (an added photo-oxidant) and chloramines (a carry-over photo-oxidant) doses. Utilizing a uniquely designed pilot-scale reactor and real-time recycled water, we evaluated treatment efficiencies of UV-AOP on six important indicator contaminants, with monochloramine (NH2Cl) and H2O2 as photo-oxidants. Hydroxyl radical (HO•) and reactive chlorine species, such as the chlorine atom (Cl•) and chlorine dimer (Cl2•-), were the major reactive species. Overall, radicals generated from photolysis of NH2Cl alone achieved removal of indicator compounds, which can be further improved by optimizing UV fluence, i.e., the UV dose. Furthermore, the addition of H2O2 enhanced HO• formation and improved contaminant removal. However, the addition of H2O2, when the background NH2Cl level was above 2 mg L-1 (as Cl2), provided limited improvement in treatment efficiency. These trade-offs between chloramine and H2O2 as oxidants, and the recommended optimization of the associated effective UV fluence, are critical for energy-efficient and cost-effective potable reuse to address the challenges of global water scarcity.

Pilot-scale evaluation of oxidant speciation, 1,4-dioxane degradation and disinfection byproduct formation during UV/hydrogen peroxide, UV/free chlorine and UV/chloramines advanced oxidation process treatment for potable reuse.

Advanced oxidation using UV/free chlorine and UV/chloramines are being considered as alternatives to UV/H2O2 for treatment of reverse osmosis (RO) permeate in treatment trains for the potable reuse of municipal wastewater. This pilot-scale comparison of the three advanced oxidation processes (AOPs) evaluated three factors important for selecting among these alternatives. First, the study characterized the speciation of oxidants serving as the source of radicals within the AOPs to facilitate process modeling. Kinetic modeling that included consideration of the chloramines occurring in RO permeate accurately predicted oxidant speciation. Modeling of the UV/free chlorine AOP indicated that free chlorine is scavenged by reactions with ammonia and monochloramine in RO permeate, such that oxidant speciation can shift in favor of dichloramine over the short (∼30 s) timescale of AOP treatment. Second, the order of efficacy for degrading the target contaminant, 1,4-dioxane, in terms of minimizing UV fluence was UV/free chlorine > UV/H2O2 ≫ UV/chloramines. However, estimates indicated that the UV/chloramines and UV/H2O2 AOPs could be similar on a cost-effectiveness basis due to savings in reagent costs by the UV/chloramines AOP, provided the RO permeate featured >3 mg/L as Cl2 chloramines. Third, the study evaluated whether the use of chlorine-based oxidants within the UV/free chlorine and UV/chloramines AOPs enhanced disinfection byproduct (DBP) formation. Even after AOP treatment and chloramination, total halogenated DBP formation remained low at <15 µg/L for all three AOPs. DBP formation was similar between the AOPs, except that the UV/free chlorine AOP promoted haloacetaldehyde formation, while the UV/H2O2 and UV/chloramines AOPs followed by chloramination increased chloropicrin formation. However, total DBP formation on a toxic potency-weighted basis was similar among the AOPs, since haloacetonitriles and haloacetamides were the dominant contributors and did not differ significantly among the AOPs.

Influence of reverse osmosis membrane age on rejection of NDMA precursors and formation of NDMA in finished water after full advanced treatment for potable reuse.

The influence of reverse osmosis (RO) membrane age on rejection of N-nitrosodimethylamine (NDMA) precursors was evaluated for a full-scale potable water reuse facility. The rejection of NDMA precursors decreased slightly with increased membrane age in most RO membrane products evaluated, but remained high overall (91% average). Chloride rejection was well-correlated with rejection of NDMA precursors. Precursor removal varied (75-98%) by membrane product, with certain membrane products maintaining better precursor rejection over time. NDMA rejection, however, did not decline significantly over time, while passage of other low molecular weight organics (LMWOs) increased with membrane age. Thus, rejection of NDMA was not highly correlated with rejection of these LMWOs, suggesting that NDMA is not a good surrogate for these compounds. Incomplete removal of NDMA precursors by RO and a UV/advanced oxidation process (UV/AOP) led to NDMA formation in the finished water and miles downstream in the transmission pipelines. An average NDMA formation rate of 0.7 ng/L/hr in the transmission lines was observed, despite typical removal of NDMA by UV/AOP to non-detect levels. The study indicates that RO membranes throughout their lifetime are not an absolute barrier to NDMA precursors, and that while older membranes continue to sufficiently remove NDMA precursors to a high degree, NDMA precursor rejection may decrease slightly as membranes age. Thus, the potential exists for NDMA to form from these precursors in purified, potable reuse water after treatment despite the effective removal of NDMA by UV/AOP.

Water Recovery from Advanced Water Purification Facility Reverse Osmosis Concentrate by Photobiological Treatment Followed by Secondary Reverse Osmosis.

Reverse osmosis (RO)-based desalination and advanced water purification facilities have inherent challenges associated with concentrate management and disposal. Although enhanced permeate recovery and concentrate minimization are desired, membrane scaling due to inorganic constituents, such as silica, calcium, phosphate, and iron, hinders the process. To solve this problem, a new diatom-based photobiological process has been developed to remove these scaling constituents by biological uptake and precipitation. In this study, RO concentrate samples were collected from a full-scale advanced water reclamation facility in California and were treated in 3.8 and 57 L photobioreactors inoculated with a brackish water diatom  Pseudostaurosira trainorii PEWL001 using light-emitting diode bulbs or natural sunlight as a light source. The photobiological treatment removed 95% of reactive silica and 64% of calcium and enabled additional water recovery using a secondary RO at a recovery rate up to 66%. This represents 95% overall recovery, including 85% recovery in the primary RO unit. In addition to the scaling constituents, the photobiological treatment removed 12 pharmaceuticals and personal care products, as well as N-nitrosodimethylamine, from RO concentrate samples primarily via photolysis. This novel approach has a strong potential for application to brackish water desalination and advanced water purification in arid and semiarid areas.

Photolysis of Mono- and Dichloramines in UV/Hydrogen Peroxide: Effects on 1,4-Dioxane Removal and Relevance in Water Reuse.

Growing demands and increasing scarcity of fresh water resources necessitate potable water reuse, which has been implemented with the aid of UV-based advanced oxidation processes (UV/AOPs) that remove potentially hazardous trace organic contaminants from reclaimed water. During the potable reuse treatment process, chloramines are added to prevent membrane fouling that are carried over to the UV/AOP, where hydrogen peroxide (H2O2) is commonly added. However, the impact of chloramines on the photolysis of H2O2 and the overall performance of the UV/AOP remains unknown. This study investigated the impacts of the photochemistry of monochloramine (NH2Cl) and dichloramine (NHCl2) associated with the photolysis of H2O2 on the degradation of 1,4-dioxane (1,4-D), a trace organic contaminant ubiquitous in recycled water. Results indicated that NH2Cl and NHCl2 alone functioned as oxidants upon UV photolysis, which produced HO• and Cl2•- as the two primary oxidative radicals. The speciation of chloramines did not have a significant impact on the degradation kinetics. The inclusion of monochloramine in UV/H2O2 greatly decreased 1,4-D removal efficiency. HO• was the major radical in the mixed H2O2/chloramine system. Results from this study suggest that recognizing the existence of chloramines in UV/H2O2 systems is important for predicting UV/AOP performance in the treatment train of potable reuse.

An inline ion-exchange system in a chemiluminescence-based analyzer for direct analysis of N-nitrosamines in treated wastewater.

A newly developed, ion exchange-based inline pretreatment system was used to mitigate the effect of background constituents in natural water and treated wastewater to achieve rapid, reliable, and sensitive analysis of N-nitrosamines. The pretreatment system (anion exchange module, AEM) was incorporated into a high-performance liquid chromatograph (HPLC) coupled with a photochemical reactor (PR) and chemiluminescence (CL) detector (HPLC-PR-CL), which can analyze four hydrophilic N-nitrosamines at ng/L levels. This system requires no pre-concentration of the water sample nor the use of deuterated surrogates, unlike other conventional N-nitrosamine analytical techniques. The AEM converted anions in the eluent to hydroxide ions after HPLC separation and increased eluent pH, allowing for the subsequent photochemical reactions, which are otherwise achieved by pH conditioning with an additional dosing pump of basic chemical. The AEM also removed anionic interfering compounds (e.g. nitrate) from the samples, allowing for improved N-nitrosamine analysis in treated wastewater. The operating conditions of the AEM and PR were optimized to obtain sensitive and stable analytical performance. As a result, the lowest-concentration minimum reporting levels of N-nitrosodimethylamine, N-nitrosomorpholine, N-nitrosomethylethylamine, and N- nitrosopyrrolidine using the optimized system were 0.42, 0.54, 0.58, and 1.4 ng/L, respectively. The improved analytical method was validated by comparing the results with a conventional method based on gas chromatography coupled with a mass spectrometric ion trap detector. These results indicated that HPLC-PR-CL equipped with an inline AEM can be competitively applied as a rapid analytical technique for the determination of N-nitrosamines in various water matrices.

UV Photolysis of Chloramine and Persulfate for 1,4-Dioxane Removal in Reverse-Osmosis Permeate for Potable Water Reuse.

A sequential combination of membrane treatment and UV-based advanced oxidation processes (UV/AOP) has become the industry standard for potable water reuse. Chloramines are used as membrane antifouling agents and therefore carried over into the UV/AOP. In addition, persulfate (S2O82-) is an emerging oxidant that can be added into a UV/AOP, thus creating radicals generated from both chloramines and persulfate for water treatment. This study investigated the simultaneous photolysis of S2O82- and monochloramine (NH2Cl) on the removal of 1,4-dioxane (1,4-D) for potable-water reuse. The dual oxidant effects of NH2Cl and S2O82- on 1,4-D degradation were examined at various levels of oxidant dosage, chloride, and solution pH. Results showed that a NH2Cl-to-S2O82- molar ratio of 0.1 was optimal, beyond which the scavenging by NH2Cl of HO•, SO4•-, and Cl2•- radicals decreased the 1,4-D degradation rate. At the optimal ratio, the degradation rate of 1,4-D increased linearly with the total oxidant dose up to 6 mM. The combined photolysis of NH2Cl and S2O82- was sensitive to the solution pH due to a disproportionation of NH2Cl at pH lower than 6 into less-photoreactive dichloramine (NHCl2) and radical scavenging by NH4+. The presence of chloride transformed HO• and SO4•- to Cl2•- that is less-reactive with 1,4-D, while the presence of dissolved O2 promoted gaseous nitrogen production. Results from this study suggest that the presence of chloramines can be beneficial to persulfate photolysis in the removal of 1,4-D; however, the treatment efficiency depends on a careful control of an optimal NH2Cl dosage and a minimal chloride residue.

High rejection reverse osmosis membrane for removal of N-nitrosamines and their precursors.

Direct potable reuse is becoming a feasible option to cope with water shortages. It requires more stringent water quality assurance than indirect potable reuse. Thus, the development of a high-rejection reverse osmosis (RO) membrane for the removal of one of the most challenging chemicals in potable reuse - N-nitrosodimethylamine (NDMA) - ensures further system confidence in reclaimed water quality. This study aimed to achieve over 90% removal of NDMA by modifying three commercial and one prototype RO membrane using heat treatment. Application of heat treatment to a prototype membrane resulted in a record high removal of 92% (1.1-log) of NDMA. Heat treatment reduced conductivity rejection and permeability, while secondary amines, selected as N-nitrosamine precursors, were still well rejected (>98%) regardless of RO membrane type. This study also demonstrated the highly stable separation performance of the heat-treated prototype membrane under conditions of varying feed temperature and permeate flux. Fouling propensity of the prototype membrane was lower than a commercial RO membrane. This study identified a need to develop highly selective RO membranes with high permeability to ensure the feasibility of using these membranes at full scale.

Temperature dependence of hydroxyl radical reactions with chloramine species in aqueous solution.

The absolute temperature-dependent kinetics for the reaction between hydroxyl radicals and the chloramine water disinfectant species monochloramine (NH2Cl), as well as dichloramine (NHCl2) and trichloramine (NCl3), have been determined using electron pulse radiolysis and transient absorption spectroscopy. These radical reaction rate constants were fast, with values of 6.06 × 108, 2.57 × 108, and 1.67 × 108 M-1 s-1 at 25 °C for NH2Cl, NHCl2, and NCl3, respectively. The corresponding temperature dependence of these reaction rate constants, measured over the range 10-40 °C, is well-described by the transformed Arrhenius equations:giving activation energies of 8.57 ± 0.58, 6.11 ± 0.40, and 5.77 ± 0.72 kJ mol-1 for these three chloramines, respectively. These data will aid water utilities in predicting hydroxyl radical partitioning and chemical contaminant removal efficiencies under real-world advanced oxidation process treatment conditions.

Reverse Osmosis Shifts Chloramine Speciation Causing Re-Formation of NDMA during Potable Reuse of Wastewater.

UV-based advanced oxidation processes (AOPs) effectively degrade N-nitrosodimethylamine (NDMA) passing through reverse osmosis (RO) units within advanced treatment trains for the potable reuse of municipal wastewater. However, certain utilities have observed the re-formation of NDMA after the AOP from reactions between residual chloramines and NDMA precursors in the AOP product water. Using kinetic modeling and bench-scale RO experiments, we demonstrate that the low pH in the RO permeate (∼5.5) coupled with the effective rejection of NH4+ promotes conversion of the residual monochloramine (NH2Cl) in the permeate to dichloramine (NHCl2) via the reaction: 2 NH2Cl + H+ ↔ NHCl2 + NH4+. Dichloramine is the chloramine species known to react with NDMA precursors to form NDMA. After UV/AOP, utilities generally use lime or other techniques to increase the pH of the finished water to prevent distribution system corrosion. Modeling indicated that, while the increase in pH halts dichloramine formation, it converts amine-based NDMA precursors to their more reactive, neutral forms. With modeling, and experiments at both bench-scale and field-scale, we demonstrate that reducing the time interval between RO treatment and final pH adjustment can significantly reduce NDMA re-formation by minimizing the amount of dichloramine formed prior to reaching the final target pH.

Role of membrane fouling substances on the rejection of N-nitrosamines by reverse osmosis.

The impact of fouling substances on the rejection of four N-nitrosamines by a reverse osmosis (RO) membrane was evaluated by characterizing individual organic fractions in a secondary wastewater effluent and deploying a novel high-performance liquid chromatography-photochemical reaction-chemiluminescence (HPLC-PR-CL) analytical technique. The HPLC-PR-CL analytical technique allowed for a systematic examination of the correlation between the fouling level and the permeation of N-nitrosamines in the secondary wastewater effluent and synthetic wastewaters through an RO membrane. Membrane fouling caused by the secondary wastewater effluent led to a notable decrease in the permeation of N-nitrosodimethylamine (NDMA) while a smaller but nevertheless discernible decrease in the permeation of N-nitrosomethylethylamine (NMEA), N-nitrosopyrrolidine (NPYR) and N-nitrosomorpholine (NMOR) was also observed. Fluorescence spectrometry analysis revealed that major foulants in the secondary wastewater effluent were humic and fulvic acid-like substances. Analysis using the size exclusion chromatography technique also identified polysaccharides and proteins as additional fouling substances. Thus, further examination was conducted using solutions containing model foulants (i.e., sodium alginate, bovine serum albumin, humic acid and two fulvic acids). Similar to the secondary wastewater effluent, membrane fouling with fulvic acid solutions resulted in a decrease in N-nitrosamine permeation. In contrast, membrane fouling with the other model foulants resulted in a negligible impact on N-nitrosamine permeation. Overall, these results suggest that the impact of fouling on the permeation of N-nitrosamines by RO is governed by specific small organic fractions (e.g. fulvic acid-like organics) in the secondary wastewater effluent.

A rapid and reliable technique for N-nitrosodimethylamine analysis in reclaimed water by HPLC-photochemical reaction-chemiluminescence.

A fast and reliable analytical technique was evaluated and validated for determination of N-nitrosodimethylamine (NDMA) formation and rejection by reverse osmosis (RO) membranes in potable water reuse applications. The analytical instrument used in this study is high-performance liquid chromatography (HPLC), photochemical reaction (PR) and chemiluminescence (CL) - namely HPLC-PR-CL. Results reported here show that HPLC-PR-CL can be used to measure NDMA with a similar level of accuracy compared to conventional and more time-consuming techniques using gas chromatography and tandem mass spectrometry detection in combination with solid phase extraction. Among key residual chemicals (i.e. monochloramine, hydrogen peroxide and hypochlorite) in reclaimed wastewater, hypochlorite was the only constituent that interfered with the determination of NDMA by HPLC-PR-CL. However, hypochlorite interference was eliminated by adding ascorbic acid as a reducing agent. Direct injection of ultrafiltration (UF)-treated wastewater samples into HPLC-PR-CL also resulted in an underestimation of the NDMA concentration possibly due to interference by organic substances in the UF-treated wastewater. Accurate determination of NDMA concentrations in UF-treated wastewater was achieved by reducing the sample injection volume from 200 to 20 µL, though this increased the method detection limit from 0.2 to 2 ng/L. In contrast, no interference was observed with RO permeate. These results suggest that RO membranes could remove part of substances that interfere with the NDMA analysis by HPLC-PR-CL. In addition, RO treatment experiments demonstrated that HPLC-PR-CL was capable of evaluating near real-time variation in NDMA rejection by RO.

Kinetic study of the reactions between chloramine disinfectants and hydrogen peroxide: temperature dependence and reaction mechanism.

The temperature-dependent kinetics for the reaction between hydrogen peroxide and chloramine water disinfectants (NH2Cl, NHCl2, and NCl3) have been determined using stopped flow-UV/Vis spectrophotometry. Rate constants for the mono- and dichloramine-peroxide reaction were on the order of 10(-2)M(-1)s(-1) and 10(-5)M(-1)s(-1), respectively. The reaction of trichloramine with peroxide was negligibly slow compared to its thermal and photolytically-induced decomposition. Arrhenius expressions of ln(kH2O2-NH2Cl)=(17.3±1.5)-(51500±3700)/RT and ln(kH2O2-NHCl2)=(18.2±1.9)-(75800±5100)/RT were obtained for the mono- and dichloramine peroxide reaction over the temperature ranges 11.4-37.9 and 35.0-55.0°C, respectively. Both monochloramine and hydrogen peroxide were first-order in the rate-limiting kinetic step and concomitant measurements made using a chloride ion selective electrode showed that the chloride was produced quantitatively. These data will aid water utilities in predicting chloramine concentrations (and thus disinfection potential) throughout the water distribution system.

Molecular characterization of effluent organic matter identified by ultrahigh resolution mass spectrometry.

Effluent dissolved organic matter (EfOM) collected from the secondary-treated wastewater of the Orange County Sanitation District (OCSD) located in Fountain Valley, California, USA was compared to natural organic matter collected from the Suwannee River (SRNOM), Florida using ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Furthermore, the two different treatment processes at OCSD, activated sludge and trickling filter, were separately investigated. The blend of these two effluents was further evaluated after it had passed through the microfiltration process of the Advanced Water Purification Facility (AWPF) at Orange County Water District (OCWD). EfOM contained 872 different m/z peaks that were unambiguously assigned to exact molecular formulae containing a single sulfur atom and carbon, hydrogen and oxygen atoms (CHOS formulae). In contrast, the SRNOM sample only contained 152 CHOS formulae. The trend in CHO molecular compositions was opposite with 2500 CHO formulae assigned for SRNOM but only about 1000 for EfOM. The CHOS-derived mass peaks with highest abundances in EfOM could be attributed to surfactants such as linear alkyl benzene sulfonates (LAS), their co-products dialkyl tetralin sulfonates (DATS) and their biodegraded metabolites such as sulfophenyl carboxylic acids (SPC). The differences between the treatments were found minor with greater differences between sampling dates than treatment methods used.

Removal of pharmaceutical and personal care products from reverse osmosis retentate using advanced oxidation processes.

The application of reverse osmosis (RO) in water intended for reuse is promising for assuring high water quality. However, one significant disadvantage is the need to dispose of the RO retentate (or reject water). Studies focusing on Pharmaceutical and Personal Care Products (PPCPs) have raised questions concerning their concentrations in the RO retentate. Advanced oxidation processes (AOPs) are alternatives for destroying these compounds in retentate that contains high concentration of effluent organic matter (EfOM) and other inorganic constituents. Twenty-seven PPCPs were screened in a RO retentate using solid phase extraction (SPE) and UPLC-MS/MS, and detailed degradation studies for 14 of the compounds were obtained. Based on the absolute hydroxyl radical (HO•) reaction rate constants for individual pharmaceutical compounds, and that of the RO retentate (EfOM and inorganic constituents), it was possible to model their destruction. Using excitation-emission matrix (EEM) fluorescence spectroscopy, the HO• oxidation of the EfOM could be observed through decreases in the retentate fluorescence. The decrease in the peak normally associated with proteins correlated well with the removal of the pharmaceutical compounds. These results suggest that fluorescence may be a suitable parameter for monitoring the degradation of PPCPs by AOPs in RO retentates.

Absolute kinetics and reaction efficiencies of hydroxyl-radical-induced degradation of methyl isothiocyanate (MITC) in different quality waters.

Methyl isothiocyanate (MITC), a toxic and corrosive skin and respiratory irritant, is a common soil fumigant byproduct which has become an atmospheric, aqueous, and soil contaminant. The work described here examines the degradation and potential removal of MITC from contaminated waters via free radical reactions. We have measured the oxidizing hydroxyl radical ((·)OH) reaction rate constant with MITC over a range of temperatures relevant to wastewater treatment conditions, determining a room temperature value of (5.69±0.56) x 10(8)M(-1)s(-1) and a corresponding Arrhenius activation energy of 12.90±0.82 kJ mol(-1). Hydroxyl radical reaction efficiencies with MITC in pure water, an associated matrix of model real-world waters, and a reverse osmosis permeate water have also been determined. While solutions containing these constituents had significantly decreased MITC removal efficiencies (5.5-14.7%) as compared to pure water (54.4±3.4%), relative rate calculation corrections showed that the (·)OH radical efficiencies for solutions containing DOM were the same as in pure water. However, the slightly higher efficiencies for carbonate-containing solutions indicated that some additional MITC degradation occurred from carbonate radical reactions.

N-nitrosodimethylamine (NDMA) removal by reverse osmosis and UV treatment and analysis via LC-MS/MS.

N-nitrosodimethylamine (NDMA) is a probable human carcinogen found in ng/l concentrations in chlorinated and chloraminated water. A method was developed for the determination of ng/l levels of NDMA using liquid chromatography-tandem mass spectrometry (LC-MS/MS) preceded by sample concentration via solid-phase extraction with activated charcoal. Recoveries were greater than 90% and allowed a method reporting limit as low as 2ng/l. Using this method, the removal of NDMA was determined for the Interim Water Purification Facility (IWPF), an advanced wastewater treatment facility operated by the Orange County Water District (OCWD) in Southern California. The facility treats effluent from an activated sludge treatment plant with microfiltration (MF), reverse osmosis (RO), and an ultraviolet-hydrogen peroxide advanced oxidation process (UV-AOP). Six nitrosamines were surveyed: NDMA, N-nitrosomethylethylamine (NMEA), N-nitrosodiethylamine (NDEA), N-nitrosodi-n-propylamine (NDPA), N-nitrosopiperidine (NPip), and N-nitrosopyrrolidine (NPyr). Only NDMA was detected and at all treatment steps in the IWPF, with influent concentrations ranging from 20 to 59 ng/l. Removals for RO and UV ranged from 24% to 56% and 43% to 66%, respectively. Overall, 69+/-7% of the original NDMA concentration was removed from the product water across the advanced treatment process and, in combination with blending, the final concentration did not exceed the California drinking water notification level of 10 ng/l. NDMA removal data are consistent with findings reviewed for other advanced treatment facilities and laboratory studies.