Spatial and Temporal Variation in De Facto Wastewater Reuse in Drinking Water Systems across the U.S.A.

De facto potable reuse occurs when treated wastewater is discharged into surface waters upstream of potable drinking water treatment plant (DWTP) intakes. Wastewater treatment plant (WWTP) discharges may pose water quality risks at the downstream DWTP, but additional flow aids in providing a reliable water supply source. In this work de facto reuse is analyzed for 2056 surface water intakes serving 1210 DWTPs across the U.S.A. that serve greater than 10 000 people, covering approximately 82% of the nation’s population. An ArcGIS model is developed to assess spatial relationships between DWTPs and WWTPs, with a python script designed to perform a network analysis by hydrologic region. A high frequency of de facto reuse occurrence was observed; 50% of the DWTP intakes are potentially impacted by upstream WWTP discharges. However, the magnitude of de facto reuse was seen to be relatively low, where 50% of the impacted intakes contained less than 1% treated municipal wastewater under average streamflow conditions. De facto reuse increased greatly under low streamflow conditions (modeled by Q95), with 32 of the 80 sites yielding at least 50% treated wastewater, this portion of the analysis is limited to sites where stream gauge data was readily available

Assessment of De Facto Wastewater Reuse across the U.S.: Trends between 1980 and 2008

De facto wastewater reuse is the incidental presence of treated wastewater in a water supply source. In 1980 the EPA identified drinking water treatment plants (DWTPs) impacted by upstream wastewater treatment plant (WWTP) discharges and found the top 25 most impacted DWTPs contained between 2% and 16% wastewater discharges from upstream locations (i.e., de facto reuse) under average streamflow conditions. This study is the first to provide an update to the 1980 EPA analysis. An ArcGIS model of DWTPs and WWTPs across the U.S. was created to quantify de facto reuse for the top 25 cities in the 1980 EPA study. From 1980 to 2008, de facto reuse increased for 17 of the 25 DWTPs, as municipal flows upstream of the sites increased by 68%. Under low streamflow conditions, de facto reuse in DWTP supplies ranged from 7% to 100%, illustrating the importance of wastewater in sustainable water supplies. Case studies were performed on four cities to analyze the reasons for changes in de facto reuse over time. Three of the four sites have greater than 20% treated wastewater effluent within their drinking water source for streamflow less than the 25th percentile historic flow

Membrane Fouling by Vesicles and Prevention through Ozonation

Membrane fouling is a major challenge in water and wastewater treatment. Recent observations that ozone mitigates membrane fouling during filtration of secondary effluent prompted this study into the impact of preozonation on membrane fouling caused by biogenic colloids. The focus of this study was on liposomes, synthetic vesicles composed of (phospho)­lipid bilayers, which are representative of the diverse cellular vesicles present in all biologically impacted waters. The overarching hypothesis was that these biologically produced, nonrigid or “soft” colloids (e.g., vesicles) present in wastewater give rise to unique fouling behavior that can be mitigated by preozonation. Using dead-end ultrafiltration (UF) and batch ozonation tests, the key findings of this study were (1) liposomes fouled UF membranes faster (4–13 times membrane cake resistance (<i>R</i>_C) per mgC filtered) than polysaccharides, fatty acids, and NOM on a DOC-normalized basis; (2) based on the estimated carbon distribution of secondary effluent, liposome-like biogenic nanomaterials could be responsible for 20–60% of fouling during UF; and (3) preozonation reduces liposomal fouling during UF, likely due to the disruption of the liposome structure through cleavage of the fatty acid tails at carbon–carbon double bonds

Role of Chlorine Dioxide in <i>N</i>‑Nitrosodimethylamine Formation from Oxidation of Model Amines

<i>N</i>-Nitrosodimethylamine (NDMA) is an emerging disinfection byproduct, and we show that use of chlorine dioxide (ClO₂) has the potential to increase NDMA formation in waters containing precursors with hydrazine moieties. NDMA formation was measured after oxidation of 13 amines by monochloramine and ClO₂ and pretreatment with ClO₂ followed by postmonochloramination. Daminozide, a plant growth regulator, was found to yield 5.01 ± 0.96% NDMA upon reaction with ClO₂, although no NDMA was recorded during chloramination. The reaction rate was estimated to be ∼0.0085 s^–1, and on the basis of our identification by mass spectrometry of the intermediates, the reaction likely proceeds via the hydrolytic release of unsymmetrical dimethylhydrazine (UDMH), with the hydrazine structure a key intermediate in NDMA formation. The presence of UDMH was confirmed by gas chromatography–mass spectrometry analysis. For 10 of the 13 compounds, ClO₂ preoxidation reduced NDMA yields compared with monochloramination alone, which is explained by our measured release of dimethylamine. This work shows potential preoxidation strategies to control NDMA formation may not impact all organic precursors uniformly, so differences might be source specific depending upon the occurrence of different precursors in source waters. For example, daminozide is a plant regulator, so drinking water that is heavily influenced by upstream agricultural runoff could be at risk

Novel Ion-Exchange Coagulants Remove More Low Molecular Weight Organics than Traditional Coagulants

Low molecular weight (MW) charged organic matter is poorly removed by conventional coagulants but contributes to disinfection byproduct formation during chlorination of drinking waters. We hypothesized that CIEX, a new Al-based hybrid coagulant with ion-exchange functional groups, would be new mechanistic approach to remove low MW organic matter during coagulation and would perform better than polyaluminum chloride (PACl) or metal–salt based coagulants. We measured coagulation performance using dissolved organic carbon (DOC) in a high hardness surface water. CIEX achieved excellent turbidity removal and removed 20% to 46% more DOC than FeCl₃, Al₂(SO₄)₃, or PACl, depending on dose. The improved DOC removal was attributable to better removal of low MW organic matter (<2 kDa). We further studied removal mechanisms in a model water containing a low MW organic acid (salicylic acid (SA)). CIEX achieved high removal of organic acids (>90% of SA) independent of pH, whereas removal by metal salts was lower (<15%) and was strongly pH dependent. CIEX ion-exchange capability is facilitated by its covalently bound quaternary ammonium group, which conventional coagulants lack. Plus, unlike other cationic polymers that react with chloramines to form <i>N</i>-nitrosodimethylamine (NDMA), CIEX has a low molar yield (9.3 × 10^–7 mol NDMA per mol CIEX-N)

Titanium Dioxide Nanoparticles in Food and Personal Care Products

Titanium dioxide is a common additive in many food, personal care, and other consumer products used by people, which after use can enter the sewage system and, subsequently, enter the environment as treated effluent discharged to surface waters or biosolids applied to agricultural land, incinerated wastes, or landfill solids. This study quantifies the amount of titanium in common food products, derives estimates of human exposure to dietary (nano-) TiO₂, and discusses the impact of the nanoscale fraction of TiO₂ entering the environment. The foods with the highest content of TiO₂ included candies, sweets, and chewing gums. Among personal care products, toothpastes and select sunscreens contained 1% to >10% titanium by weight. While some other crèmes contained titanium, despite being colored white, most shampoos, deodorants, and shaving creams contained the lowest levels of titanium (<0.01 μg/mg). For several high-consumption pharmaceuticals, the titanium content ranged from below the instrument detection limit (0.0001 μg Ti/mg) to a high of 0.014 μg Ti/mg. Electron microscopy and stability testing of food-grade TiO₂ (E171) suggests that approximately 36% of the particles are less than 100 nm in at least one dimension and that it readily disperses in water as fairly stable colloids. However, filtration of water solubilized consumer products and personal care products indicated that less than 5% of the titanium was able to pass through 0.45 or 0.7 μm pores. Two white paints contained 110 μg Ti/mg while three sealants (i.e., prime coat paint) contained less titanium (25 to 40 μg Ti/mg). This research showed that, while many white-colored products contained titanium, it was not a prerequisite. Although several of these product classes contained low amounts of titanium, their widespread use and disposal down the drain and eventually to wastewater treatment plants (WWTPs) deserves attention. A Monte Carlo human exposure analysis to TiO₂ through foods identified children as having the highest exposures because TiO₂ content of sweets is higher than other food products and that a typical exposure for a US adult may be on the order of 1 mg Ti per kilogram body weight per day. Thus, because of the millions of tons of titanium-based white pigment used annually, testing should focus on food-grade TiO₂ (E171) rather than that adopted in many environmental health and safety tests (i.e., P25), which is used in much lower amounts in products less likely to enter the environment (e.g., catalyst supports, photocatalytic coatings)

SEM micrographs of human intestine <i>in vitro</i> cell models exposed to gum-E171 nano- or submicron-enriched fractions.

<p>(a) Epithelia exposed to 1 μg/mL of submicron-enriched fraction in the upright configuration resulted in a large number of particles (white arrows) decorating the surface of the epithelium after 7 minutes of exposure. (b) However, exposing replicate samples to the nano-enriched fraction with 1 μg/mL for 7 minutes in the upright configuration resulted in few particles adhered to the epithelial surface. (c) Inverting the epithelium and subsequently exposing the cells with 1 μg/mL of the submicron-enriched fraction for 7 minutes resulted in few particles adhered to the epithelial surface. (d) However, exposing replicate samples in the inverted configuration to 1 μg/mL of the nano-enriched fraction for 7 minutes resulted in relatively more particles adhered to the epithelial surface. All images are shown at identical magnification. Scale bar is 5 μm.</p

A Facile Method for Separating and Enriching Nano and Submicron Particles from Titanium Dioxide Found in Food and Pharmaceutical Products

<div><p>Recent studies indicate the presence of nano-scale titanium dioxide (TiO₂) as an additive in human foodstuffs, but a practical protocol to isolate and separate nano-fractions from soluble foodstuffs as a source of material remains elusive. As such, we developed a method for separating the nano and submicron fractions found in commercial-grade TiO₂ (E171) and E171 extracted from soluble foodstuffs and pharmaceutical products (<i>e</i>.<i>g</i>., chewing gum, pain reliever, and allergy medicine). Primary particle analysis of commercial-grade E171 indicated that 54% of particles were nano-sized (<i>i</i>.<i>e</i>., < 100 nm). Isolation and primary particle analysis of five consumer goods intended to be ingested revealed differences in the percent of nano-sized particles from 32%‒58%. Separation and enrichment of nano- and submicron-sized particles from commercial-grade E171 and E171 isolated from foodstuffs and pharmaceuticals was accomplished using rate-zonal centrifugation. Commercial-grade E171 was separated into nano- and submicron-enriched fractions consisting of a nano:submicron fraction of approximately 0.45:1 and 3.2:1, respectively. E171 extracted from gum had nano:submicron fractions of 1.4:1 and 0.19:1 for nano- and submicron-enriched, respectively. We show a difference in particle adhesion to the cell surface, which was found to be dependent on particle size and epithelial orientation. Finally, we provide evidence that E171 particles are not immediately cytotoxic to the Caco-2 human intestinal epithelium model. These data suggest that this separation method is appropriate for studies interested in isolating the nano-sized particle fraction taken directly from consumer products, in order to study separately the effects of nano and submicron particles.</p></div

Primary particle analysis via TEM reveals a difference in size between nano- and submicron-enriched fractions after the sucrose step-gradient centrifugation procedure.

<p>(a) Submicron-enriched commercial-grade E171 appear large compared to (b) the nano-enriched fraction. (c) Utilizing the same procedure on gum-E171 revealed a large, submicron-enriched fraction and (d) a small, nano-enriched fraction. All images are shown at identical magnification. The scale bar in the lower right corner of each micrograph is 100 nm.</p

Primary particle analysis using TEM for commercial-grade E171 and gum-E171 nano- and submicron-enriched fractions.

<p>Primary particle analysis using TEM for commercial-grade E171 and gum-E171 nano- and submicron-enriched fractions.</p