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

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)

Characterization of Food-Grade Titanium Dioxide: The Presence of Nanosized Particles

Titanium dioxide (TiO₂) is widely used in food products, which will eventually enter wastewater treatment plants and terrestrial or aquatic environments, yet little is known about the fraction of this TiO₂ that is nanoscale, or the physical and chemical properties of TiO₂ that influence its human and environmental fate or toxicity. Instead of analyzing TiO₂ properties in complex food or environmental samples, we procured samples of food-grade TiO₂ obtained from global food suppliers and then, using spectroscopic and other analytical techniques, quantified several parameters (elemental composition, crystal structure, size, and surface composition) that are reported to influence environmental fate and toxicity. Another sample of nano-TiO₂ that is generally sold for catalytic applications (P25) and widely used in toxicity studies, was analyzed for comparison. Food-grade and P25 TiO₂ are engineered products, frequently synthesized from purified titanium precursors, and not milled from bulk scale minerals. Nanosized materials were present in all of the food-grade TiO₂ samples, and transmission electron microscopy showed that samples 1–5 contained 35, 23, 21, 17, and 19% of nanosized primary particles (<100 nm in diameter) by number, respectively (all primary P25 particles were <100 nm in diameter). Both types of TiO₂ aggregated in water with an average hydrodynamic diameter of >100 nm. Food-grade samples contained phosphorus (P), with concentrations ranging from 0.5 to 1.8 mg of P/g of TiO₂. The phosphorus content of P25 was below inductively coupled plasma mass spectrometry detection limits. Presumably because of a P-based coating detected by X-ray photoelectron spectroscopy, the ζ potential of the food-grade TiO₂ suspension in deionized water ranged from −10 to −45 mV around pH 7, and the iso-electric point for food-grade TiO₂ (2 (Si content of 0.026–0.062% and Al content of 0.0006–0.810%) was also different from the case for P25 and would influence the environmental fate of TiO₂. X-ray diffraction analysis confirmed the presence of anatase and/or rutile in the food-grade materials, and although the presence of amorphous TiO₂ could not be ruled out, it is unlikely on the basis of Raman analysis. The food-grade TiO₂ was solar photoactive. Cationic dyes adsorbed more readily to food-grade TiO₂ than P25, indicating very different potentials for interaction with organics in the environment. This research shows that food-grade TiO₂ contains engineered nanomaterials with properties quite different from those of P25, which has previously been used in many ecotoxicity studies, and because food-grade TiO₂ is more likely than P25 to enter the environment (i.e., potentially higher exposure levels), there is a need to design environmental (and human) fate and toxicity studies comparing food-grade to catalytic TiO₂

Characterization, Recovery Opportunities, and Valuation of Metals in Municipal Sludges from U.S. Wastewater Treatment Plants Nationwide

U.S. sewage sludges were analyzed for 58 regulated and nonregulated elements by ICP-MS and electron microscopy to explore opportunities for removal and recovery. Sludge/water distribution coefficients (<i>K</i>_D, L/kg dry weight) spanned 5 orders of magnitude, indicating significant metal accumulation in biosolids. Rare-earth elements and minor metals (Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) detected in sludges showed enrichment factors (EFs) near unity, suggesting dust or soils as likely dominant sources. In contrast, most platinum group elements (i.e., Ru, Rh, Pd, Pt) showed high EF and <i>K</i>_D values, indicating anthropogenic sources. Numerous metallic and metal oxide colloids (<100–500 nm diameter) were detected; the morphology of abundant aggregates of primary particles measuring <100 nm provided clues to their origin. For a community of 1 million people, metals in biosolids were valued at up to US$13 million annually. A model incorporating a parameter (<i>K</i>_D × EF ×$Value) to capture the <i>relative potential for economic value from biosolids</i> revealed the identity of the 13 most lucrative elements (Ag, Cu, Au, P, Fe, Pd, Mn, Zn, Ir, Al, Cd, Ti, Ga, and Cr) with a combined value of US $280/ton of sludge

Characterization of Nanomaterials in Metal Colloid-Containing Dietary Supplement Drinks and Assessment of Their Potential Interactions after Ingestion

Little information is available regarding the suitability of analytical methods to evaluate claims regarding the presence of engineered nanomaterials (NMs) in consumer products, their potential toxic effects to humans, or their life cycle after product use. This study was designed to assess the potential interactions across the life cycle of eight commercially available dietary supplement drinks from a single vendor, all purported to contain metal NMs. Analysis showed that all of the products contained metallic NMs with average diameters below 50 nm as determined by dynamic light scattering and transmission electron microscopy. The products’ intended use is human ingestion; in order to examine potential human health effects after ingestion, we investigated the interaction of NMs in the drinks with an in vitro cell system that faithfully mimics human intestinal cells. After exposure to concentrations of NMs as low as 3.5 μg/mL, we found that the number of microvilli decreased relative to untreated controls for all drinks. From a life cycle perspective, consumption of drinks containing NMs will eventually result in sewer discharge of these NMs in feces. Screening tests for NM removal by biosolids in wastewater treatment plants (WWTPs) conducted using the NMs contained in supplement drinks showed variable removal of NMs, with the fractions removed ranging from (99 ± 27)% to (30 ± 0.05)%. The results showed that metal NM-based supplements may have an effect on the number of viable human intestinal microvilli and will likely enter the environment via either water or solids released from WWTPs

Coupling Light Emitting Diodes with Photocatalyst-Coated Optical Fibers Improves Quantum Yield of Pollutant Oxidation

A photocatalyst-coated optical fiber was coupled with a 318 nm ultraviolet-A light emitting diode, which activated the photocatalysts by interfacial photon-electron excitation while minimizing photonic energy losses due to conventional photocatalytic barriers. The light delivery mechanism was explored via modeling of evanescent wave energy produced upon total internal reflection and photon refraction into the TiO₂ surface coating. This work explores aqueous phase LED-irradiated optical fibers for treating organic pollutants and for the first time proposes a dual-mechanistic approach to light delivery and photocatalytic performance. Degradation of a probe organic pollutant was evaluated as a function of optical fiber coating thickness, fiber length, and photocatalyst attachment method and compared against the performance of an equivalent catalyst mass in a completely mixed slurry reactor. Measured and simulated photon fluence through the optical fibers decreased as a function of fiber length, coating thickness, or TiO₂ mass externally coated on the fiber. Thinner TiO₂ coatings achieved faster pollutant removal rates from solution, and dip coating performed better than sol–gel attachment methods. TiO₂ attached to optical fibers achieved a 5-fold higher quantum yield compared against an equivalent mass of TiO₂ suspended in a slurry solution

Potential Environmental Impacts and Antimicrobial Efficacy of Silver- and Nanosilver-Containing Textiles

For textiles containing nanosilver, we assessed benefit (antimicrobial efficacy) in parallel with potential to release nanosilver (impact) during multiple life cycle stages. The silver loading and method of silver attachment to the textile highly influenced the silver release during washing. Multiple sequential simulated household washing experiments for fabric swatches in deionized water with or without detergent showed a range of silver release. The toxicity of washing experiment supernatants to zebrafish (Danio rerio) embryos was negligible, with the exception of the very highest Ag releases (∼1 mg/L Ag). In fact, toxicity tests indicated that residual detergent exhibited greater adverse response than the released silver. Although washing the fabrics did release silver, it did not affect their antimicrobial efficacy, as demonstrated by >99.9% inhibition of E. coli growth on the textiles, even for textiles that retained as little as 2 μg/g Ag after washing. This suggests that very little nanosilver is required to control bacterial growth in textiles. Visible light irradiation of the fabrics reduced the extent of Ag release for textiles during subsequent washings. End-of-life experiments using simulated landfill conditions showed that silver remaining on the textile is likely to continue leaching from textiles after disposal in a landfill