Lake Mead is the primary drinking water source for the Las Vegas Valley and supplies water to 25 million people in the Lower Colorado River Basin. Historically, Lake Mead per- and polyfluoroalkyl substances (PFAS) concentrations have been low; however, decreasing lake levels from drought may result in increased impact from the Las Vegas Wash (LVW) leading to increased PFAS levels. Thus, there is a need to better map Lake Mead PFAS sources. Herein, samples were collected from (1) Lake Mead, rainwater, and snowmelt; (2) wastewater, groundwater, and stormwater sources to the LVW; and (3) sewershed sampling for two wastewater treatment plants (WWTP) in the Las Vegas Valley. Nineteen PFAS were quantified via liquid chromatography tandem mass spectrometry. Additionally, some samples were either analyzed using non-targeted high resolution mass spectrometry or processed using the total oxidizable precursor (TOP) assay method. Total PFAS in the Boulder Basin area of Lake Mead was 3.84 ng/L and was dominated by short-chain perfluorocarboxylic and perfluorosulfonic acids. The Colorado River was the primary source of PFAS to Lake Mead (65% of total PFAS loading) and the LVW was an important secondary source (27%). Total PFAS in precipitation samples were low (0.329–1.51 ng/L) with rainwater dominated by long-chain perfluoroalkyl acids while only perfluorobutane sulfonic acid (PFBS) was detected in snowmelt. Domestic wastewater was the primary WWTP PFAS source due to high residential and domestic flow contributions (63%–94%) and lack of industry, while laundry and PFAS-containing cosmetics are significant PFAS sources in residential wastewater (i.e., estimated mass flow contributions of 11%, 9.3% and 2.2% for household laundry, shampoo and cosmetic cream, respectively). These results provide a better understanding of the PFAS sources to Lake Mead, and similar systems, and will help inform future efforts to manage PFAS flows to this important drinking water source.

De facto reuse (DFR) refers to the unplanned inclusion of treated wastewater in drinking water supplies due to upstream wastewater treatment plant effluents. Nearly half of drinking water treatment plants (DWTPs) in the USA are impacted to some extent by DFR, with maximum estimated DFR percentage streamflow approaching 90% in some cases. DFR is not unique to the U.S. but been reported globally in Asia, Europe, Africa, and others. Treated wastewater discharged to surface waters can contain significant levels of inorganic (e. g. bromide and iodide) and organic compounds (e. g. micropollutants, extracellular products, and nitrogen-containing organic matter) that serve as precursors to both regulated and unregulated disinfection by-products (DBPs) in downstream DWTPs. Although identified as a national concern over a decade ago, the lack of standardized methodologies for quantifying and reporting DFR hinders comparative assessments and regulatory decision-making. We believe DFR is underappreciated or outright ignored as compared to the water community focus on highly managed and regulated indirect and direct potable reuse - although risks from DFR are just as real and important to address. This review explores how DFR contributes to DBP risks at DWTPs and discusses strategies for monitoring, modeling, and managing these risks considering recent research.

Utility research programs can provide solutions to a wide range of challenges and help utilities prepare for the future. Utilities are uniquely positioned to blend fundamental and applied research. Core research themes pursued by the Southern Nevada Water Authority include regulatory compliance, infrastructure protection, and contaminants of emerging concern.

Industrial discharges are a significant source of chemical contaminants to municipal wastewater, many of which are challenging to remove, highly toxic, or interfere with water treatment processes below health guidelines in median wastewater effluent. Significant research efforts have focused on chemical removal by advanced treatment processes; however, meta-analysis is generally needed to calculate removal through whole reuse treatment trains including wastewater treatment. This review aims to assess numerous industrial chemicals for their potential to pass through or interfere with potable reuse treatment trains in order to (1) prioritize chemicals for monitoring and enhanced source control and (2) identifying knowledge gaps for chemicals with known toxicity but sparse water treatment data. Key chemical barriers in three common reuse treatment trains were evaluated as part of this review, namely: (A) reverse osmosis and UV/H2O2; (B) ozonation, biofiltration, granular activated carbon, and UV disinfection; and (C) ozonation, biofiltration, reverse osmosis, and UV/H2O2. Results indicate monitoring and treatment of per- and polyfluoroalkyl substances (PFAS), 1,4-dioxane, and certain heavy metals (e.g., uranium, thallium, and cobalt) should be prioritized for all treatment trains because of their high toxicity. Additionally, in Train B, certain metals and inorganic compounds, and short-chain PFAS would have <90 % removal. By contrast, 1,4-dioxane, N-nitrosodimethylamine, nitrobenzene, nitrate, iodide, and boron were the only compounds reviewed known to potentially have <90 % removal in Train A. Low molecular weight compounds, such as ethylene thiourea, epichlorohydrin, and 1,4-dithiane, merit further research based on their high toxicity and low removal in evaluated processes. Interference hazards include polyfluoroalkyl substances, bromide, iodide, iodinated contrast media, and methadone. Overall, results from this study will help inform monitoring, treatment train selection, and development of enhanced source control programs for future potable reuse projects.

Effective biofilm recovery is essential when characterizing microbial communities on granular filter media in water treatment applications. This study evaluated (1) DNA extraction kit modifications to maximize DNA recovery and (2) low frequency sonication (40 kHz) durations to maximize recovery of viable cells for flow cytometry (FCM) considering filter media type (anthracite and granular activated carbon [GAC]), media age, and filter runtime. Both DNA and intact cell concentrations were greater for new GAC (< 12 months of full-scale operation) and anthracite compared to old GAC (> 20 years). Biomass yields for old GAC were improved by using a less aggressive bead-beating protocol (for DNA) and reduced sonication duration (for intact cells). Finally, collecting media at the beginning of a filter run (i.e., post-backwash) improved biomass recovery compared to sampling after long filter runtimes. Further study of carbon attrition during extraction is recommended.

Haloacetonitriles (HANs) are unregulated nitrogenous disinfection byproducts (N-DBPs) widely distributed in drinking water distribution systems. These N-DBPs originate from the reaction of organic precursors and disinfectants including chlorine, chloramine, or chlorine dioxide. This study was aimed at determining HAN yields from model organic compounds under both chlorination and chloramination conditions by laboratory studies. The specific conditions selected (i.e., doses, sequence, pH, reaction times) were intended to create chemical environments that are similar to those that exist in drinking water treatment systems. Precursor compounds selected for study included some key biochemicals known to be present in drinking waters. Results of these laboratory experiments are presented in the form of molar yields for specific precursor compounds, and some were mathematically compensated for excessive HAN degradation during laboratory testing. Model compound data clearly showed aspartic acid to be the most productive dihaloacetonitrile (DHAN) precursor tested. This compound in its free state has the potential to add substantially to a water's DHAN formation under free chlorination. There are other amino acids, such as histidine and asparagine that may contribute, but these are probably secondary to aspartic acid. While proteins or polypeptides are far less reactive with free chlorine as compared to free amino acids, their greater abundance makes them potential important members of the DHAN precursor pool. In contrast, nucleic acids appear to be relatively insignificant as DHAN precursors. There are other potential precursors such as aromatic amines (i.e., 3-aminophenol), and even some hydroxylated aliphatic amines (i.e., 4-amino-2-hydroxybutyric acid), that could be significant contributors under free chlorination conditions. This study showed that DHAN formation in systems using chloramines depends strongly on the pre‑chlorine contact time. Unlike free chlorine systems, lignin and lignin phenols may be significant DHAN precursors when chloramines are used. Organic amines, such as aspartic acid and asparagine may also contribute as important precursors in chloramination systems.

Correction for ‘N-Nitrosodimethylamine (NDMA) formation and mitigation in potable reuse treatment trains employing ozone and biofiltration’ by Fernanda Bacaro et al., Environ. Sci.: Water Res. Technol., 2019, 5, 713–725, https://doi.org/10.1039/C8EW00926K.

Increasing water scarcity and water quality impairment are drivers for broader implementation of potable reuse. To maximize the sustainability of these systems, it is important to address pathogen log reduction value (LRV) ‘gaps’.

Reverse osmosis (RO) and nanofiltration (NF) are widely applied membrane treatment technologies due to their ability to effectively remove particulates, dissolved compounds, bacteria, and viruses. However, in potable reuse applications, RO is given minimal log removal value (LRV) credit of 1-2 for pathogens due to the inability to demonstrate higher LRV performance daily. Therefore, systematic single-element membrane pilot tests (3 different RO and 1 NF membranes) were performed to assess the potential LRVs (> 4) for three chemical markers (i.e., sulfate, sucralose, and uranine) that could potentially enable membrane-based potable reuse systems to achieve higher credit. Lead-and tail-element tests, as well as new and chlorine-oxidized membranes, were tested to assess the effect of membrane location and damage on the marker LRVs. Undamaged and damaged membranes demonstrated LRVs of >5 for MS2 bacteriophage with no statistically significant differences observed for any of the 4 membranes tested regardless of membrane placement (i.e., lead vs. tail) or condition (i.e., new vs. oxidized). Statistical analysis by optimal cluster assignments for each membrane indicated there were little differences in effective LRVs between the three chemical markers. Though the LRVs could not achieve >4, likely due to diffusion limitations, they were > 2 for the three chemical markers that ranged from 2.7 to 3.6 across non -damaged lead-and tail-element tests for all three RO membranes. Uranine, while achieving LRVs of 2.9-3.6 for RO and 2.2-2.3 for NF for non-damaged lead-and tail-element tests, was deemed less preferable due to its high dose requirement and difficult chemical handling. Sulfate and sucralose proved to be effective as well but preferable with non-damaged, lead-and tail-element test LRVs of 2.7-3.5 for RO and 1.4-2.3 for NF. Damaged-membrane testing demonstrated the three conservative chemical markers were sensitive to the chlorine-oxidized membrane compromise, more so for RO than NF, before any virus breakthrough occurred.

Per- and polyfluoroalkyl substances (PFAS) enter surface waters from various sources such as wastewater treatment plants, fire-fighting sites, and PFAS-producing and PFAS-using industries. The Las Vegas Wash in Southern Nevada of the United States (U.S.) conveys wastewater effluent from the Las Vegas metropolitan area to Lake Mead, a drinking water source for millions of people in the U.S. Southwest. PFAS have previously been detected in the Las Vegas Wash, but PFAS sources were not identified. In this study, upstream wash tributaries, wastewater treatment effluents, and shallow groundwater wells were sampled in multiple campaigns during dry-weather conditions to investigate possible PFAS sources. Out of 19 PFAS, two short-chain PFAS—perfluoropentanoic acid (48% of the total molar concentration) and perfluorohexanoic acid (32%) —comprised the majority of PFAS loading measured in the Las Vegas Wash, followed by perfluorooctanoic acid (9%). On a mass loading basis, the majority of total measured PFAS (approximately 90%) and at least 48% of each specific PFAS in the Las Vegas Wash likely entered via municipal wastewater effluents, of which the main source was likely residential wastewater. One of the drainage areas with a major civilian airport was identified as a potential source of relatively enriched perfluorosulfonic acids to a small wash tributary and shallow groundwater samples. Nonetheless, that tributary contributed at most 15% of any specific PFAS to the mainstem of the Las Vegas Wash. Total PFAS concentrations were relatively low for the small tributary associated with an urban smaller airport and the lack of flow in the tributary channel immediately downgradient of an Air Force Base indicates the smaller airport and base were unlikely significant PFAS sources to the Las Vegas Wash. Overall, this study demonstrated effective PFAS source investigation methodology and the importance of wastewater effluent as a PFAS environmental pathway.

Harmful algal blooms (HABs) or higher levels of de facto water reuse (DFR) can increase the levels of certain contaminants at drinking water intakes. Therefore, the goal of this study was to use multi-class supervised machine learning (SML) classification with data collected from six online instruments measuring fourteen total water quality parameters to detect cyanobacteria (corresponding to approximately 950 cells/mL, 2900 cells/mL, and 8600 cells/mL) or DFR (0.5, 1 and 2 % of wastewater effluent) events in the raw water entering an intake. Among 56 screened models from the caret package in R, four (mda, LogitBoost, bagFDAGCV, and xgbTree) were selected for optimization. mda had the greatest testing set accuracy, 98.09 %, after optimization with 7 false alerts. Some of the most important water parameters for the different models were phycocyanin-like fluorescence, UVA254, and pH. SML could detect algae blending events (estimated <9000 cells/mL) due in part to the phycocyanin-like fluorescence sensor. UVA254 helped identify higher concentrations of DFR. These results show that multi-class SML classification could be used at drinking water intakes in conjunction with online instrumentation to detect and differentiate HABs and DFR events. This could be used to create alert systems for the water utilities at the intake, rather than the finished water, so any adjustment to the treatment process could be implemented.

Both quantifiable and semi-quantifiable poly-and perfluoroalkyl substances (PFAS) were evaluated in the influent, effluent, and biosolids of 38 wastewater treatment plants. PFAS were detected in all streams at all facilities. For the means of the sums of detected, quantifiable PFAS concentrations were 98 +/- 28 ng/L, 80 +/- 24 ng/L, and 160,000 +/- 46,000 ng/kg (dry weight basis) in the influent, effluent, and biosolids (respectively). In the aqueous influent and effluent streams this quantifiable PFAS mass was typically associated with perfluoroalkyl acids (PFAAs). In contrast, quantifiable PFAS in the biosolids were primarily polyfluoroalkyl substances that potentially serve as precursors to the more recalcitrant PFAAs. Results of the total oxidizable precursor (TOP) assay on select influent and effluent samples showed that semi-quantified (or, unidentified) precursors accounted for a substantial portion (21 to 88%) of the fluorine mass compared to that associated with quantified PFAS, and that this fluorine precursor mass was not appreciably transformed to perfluoroalkyl acids within the WWTPs, as influent and effluent precursor concentrations via the TOP assay were statistically identical. Evaluation of semi-quantified PFAS, consistent with results of the TOP assay, showed the presence of several classes of precursors in the influent, effluent, and biosolids; perfluorophosphonic acids (PFPAs) and fluorotelomer phosphate diesters (di-PAPs) occurred in 100 and 92% of biosolid samples, respectively. Analysis of mass flows showed that, for both quantified (on a fluorine mass basis) and semi-quantified PFAS, the majority of PFAS exited WWTPs through the aqueous effluent compared to the biosolids stream. Overall, these results highlight the importance of semi-quantified PFAS precursors in WWTPs, and the need to further understand the impacts of their ultimate fate in the environment.

Hydraulic performance issues in drinking-water biofilters have sometimes been associated with phosphorus limitation and increased production of extracellular polymeric substances in previous bench-scale studies. However, field studies utilizing phosphorus supplementation to improve biofilter hydraulic performance have produced mixed results. Here, we determined the ratio of activities for phosphatase to glycosidase (PHO:GLY), which are enzymes involved in acquiring orthophosphate and biodegradable organic carbon from complex organic substrates, to assess phosphorus limitation in 21 pilot- and full-scale biofilters. Supplementation of the pilot-scale biofilter influents with 37 mu g/L orthophosphate-P reduced the PHO:GLY from 1.8-40.3 (mean 14.8) to 0.3-15.9 (mean 5.3), demonstrating that increased orthophosphate availability decreases PHO:GLY. In the absence of phosphorus supplementation, the PHO:GLY of the pilot- and full-scale biofilters ranged from 0.3 to 40.3 (mean 10.1), and no hydraulic performance issues were noted. Thus, severe phosphorus limitation appears uncommon in the field, suggesting that phosphorus supplementation is unlikely to improve hydraulic performance in typical drinking water biofilters.

Per-and polyfluoroalkyl substances (PFAS) pose risks to human health and ecosystems and are commonly found in wastewater treatment plant (WWTP) effluents discharged into surface waters. WWTPs continuously discharging PFAS into surface waters are hypothesized to lead to pervasive PFAS for downstream drinking water treatment plant (DWTP) intakes. To investigate the impact of this unplanned (de facto) wastewater reuse, we analyzed river water and WWTP effluent samples for 19 target PFAS and a surrogate chemical (sucralose) in a large watershed, with >165 WWTP discharges and multiple DWTP surface water intakes. The n-ary sumation PFAS concentrations of WWTP effluents (50-200 ng/L) were higher than that of the river water, with the same relative distributions of individual PFAS found in both samples. Surface water samples showed a direct and linear relationship between n-ary sumation PFAS and sucralose concentrations [ n-ary sumation PFAS (ng/L) = 0.0014 x (sucralose (ng/L)) + 19; R2 = 0.92] or predicted de facto reuse levels. Unplanned wastewater reuse could be a widespread source of PFAS for thousands of DWTPs. This study provides valuable guidance for future initiatives aimed at identifying sources of PFAS through de facto reuse modeling and chemical surrogate sampling.

Treatment of micropollutant-contaminated water using photocatalytic membrane reactors (PMRs) faces certain operational challenges including catalyst agglomeration and loss of reactor efficiency over time. Designing a PMR with a photocatalytic active layer on the membrane surface could be an alternative strategy to improve the reactor efficiency. Therefore, this study determined the optimum PMR design using commercially available membranes with two different catalysts (ZrO2 and TiO2) in the presence or absence of ultraviolet (UV) light at both high and low fluences for efficient photodegradation of para-chlorobenzoic acid (pCBA) and 15 different organic micropollutants. Comparing the UV types, vacuum UV (VUV) showed 24-36% higher micro-pollutant degradation than low-pressure UV (LUV). Micro-pollutant degradation was 20-36% higher in the presence of the membrane than in its absence and similar at both fluences for both UV types. VUV had 28-35 and 14-21% higher pCBA degradation than LUV at high and low fluences, respectively. The high fluence showed 3.6-6.7 and 12.5-24.5% higher pCBA degradation capacity than the low fluence for LUV and VUV, respectively. Comparing the catalyst types, there was a negligible difference in the degradation efficiency between TiO2 and ZrO2. The results indicate a promising pathway for developing a pilot-scale VUV-equipped PMR for treating micropollutant-contaminated water.

Ozone is a commonly applied disinfectant and oxidant in drinking water and has more recently been implemented for enhanced municipal wastewater treatment for potable reuse and ecosystem protection. One drawback is the potential formation of bromate, a possible human carcinogen with a strict drinking water standard of 10 μg/L. The formation of bromate from bromide during ozonation is complex and involves reactions with both ozone and secondary oxidants formed from ozone decomposition, i.e., hydroxyl radical. The underlying mechanism has been elucidated over the past several decades, and the extent of many parallel reactions occurring with either ozone or hydroxyl radicals depends strongly on the concentration, type of dissolved organic matter (DOM), and carbonate. On the basis of mechanistic considerations, several approaches minimizing bromate formation during ozonation can be applied. Removal of bromate after ozonation is less feasible. We recommend that bromate control strategies be prioritized in the following order: (1) control bromide discharge at the source and ensure optimal ozone mass-transfer design to minimize bromate formation, (2) minimize bromate formation during ozonation by chemical control strategies, such as ammonium with or without chlorine addition or hydrogen peroxide addition, which interfere with specific bromate formation steps and/or mask bromide, (3) implement a pretreatment strategy to reduce bromide and/or DOM prior to ozonation, and (4) assess the suitability of ozonation altogether or utilize a downstream treatment process that may already be in place, such as reverse osmosis, for post-ozone bromate abatement. A one-size-fits-all approach to bromate control does not exist, and treatment objectives, such as disinfection and micropollutant abatement, must also be considered.

Per- and polyfluoroalkyl substances (PFAS) are anthropogenic chemicals that occur ubiquitously in the environment and have been linked to numerous adverse health effects in humans and aquatic organisms. Although numerous environmental monitoring studies have been conducted, only one has evaluated PFAS in surface waters of the northwestern Great Basin, which features unique topography that results in dozens of endorheic basins and terminal lakes with no natural outlet, where PFAS may accumulate. To close this knowledge gap, we evaluated the occurrence of PFAS in grab samples from 15 lakes (headwater and terminal lakes) and 10 rivers in the Great Basin located in Nevada and California of the United States. PFAS and organofluorine were quantified by liquid chromatography tandem mass spectroscopy (LC-MS/MS) and combustion ion chromatography, respectively. The highest concentrations of PFAS occurred in samples taken near sites with known or suspected prior aqueous film forming foam (AFFF) application (~20 to 4754 ng/L). Samples near wastewater treatment plants and in urban areas also tended to have PFAS concentrations greater than those measured in remote, less anthropogenically influenced areas (~2 to 15 ng/L, <3 ng/L respectively). In limited snapshot sampling events PFAS appeared to accumulate in terminal lakes to some extent; in-lake concentrations were two to five times greater than those of their inflows. Fluorotelomer sulfonates were present downstream of a known AFFF application area likely to have had fluorotelomer-based foams applied to it, and the concentrations decayed in a predictable manner, suggesting they may be used as an indicator of PFAS transport away from an AFFF source. In all but two samples, organofluorine concentrations were greater than the sum of targeted PFAS (on a F basis) (median of 0.6 % of organofluorine identified via LC-MS/MS), although there was considerable variability in organofluorine measured in replicate samples.

Although nitrifying microorganisms play an important role in TOrC biotransformation, ammonia-rich environments appear to hinder important cometabolic processes, whereas low-dose monochloramine has minimal impact on biofilter performance.