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Tracking Saharan–Sahelian dust across the globe is essential to elucidate its effects on Earth’s climate, radiation budget, hydrologic cycle, nutrient cycling, and also human health when it seasonally enters populated/industrialized regions of Africa, Europe, and North America. However, the elemental composition of mineral dust arising locally from construction activities and aeolian soil resuspension overlaps with African dust. Therefore, we derived a novel “isotope-resolved chemical mass balance” (IRCMB) method by employing radiogenic strontium, neodymium, and hafnium isotopes to accurately differentiate and quantitatively apportion collinear proximal and synoptic-scale crustal and anthropogenic mineral dust sources. IRCMB was applied to two air masses that transported African dust to Barbados and Texas to track particulate matter (PM) spikes at both locations. During Saharan–Sahelian intrusions, the radiogenic content of urban PM(2.5) increased with respect to (87)Sr/(86)Sr and (176)Hf/(177)Hf but decreased in terms of (143)Nd/(144)Nd, demonstrating the ability of these isotopes to sensitively track African dust intrusions even in complex metropolitan atmospheres. The principal aerosol strontium, neodymium, and hafnium end members were concrete dust and soil, soil and motor vehicles, and motor vehicles and North African dust, respectively. IRCMB separated and quantified local soil and distal crustal dust even when PM(2.5) concentrations were low, opening a promising source apportionment avenue for urbanized/industrialized atmospheres.

Virus destabilization and inactivation are critical considerations in providing safe drinking water. We demonstrate that iron electrocoagulation simultaneously removed (via sweep flocculation) and inactivated a non-enveloped virus surrogate (MS2 bacteriophage) under slightly acidic conditions, resulting in highly effective virus control (e.g., 5-logs at 20 mg Fe/L and pH 6.4 in 30 min). Electrocoagulation simultaneously generated H2O2 and Fe(II) that can potentially trigger electro-Fenton reactions to produce reactive oxygen species such as •OH and high valent oxoiron(IV) that are capable of inactivating viruses. To date, viral attenuation during water treatment has been largely probed by evaluating infective virions (as plaque forming units) or genomic damage (via the quantitative polymerase chain reaction). In addition to these existing means of assessing virus attenuation, a novel technique of correlating transmission electron micrographs of electrocoagulated MS2 with their computationally altered three-dimensional electron density maps was developed to provide direct visual evidence of capsid morphological damages during electrocoagulation. The majority of coliphages lost at least 10-60% of the capsid protein missing a minimum of one of the 5-fold and two of 3- and 2-fold regions upon electrocoagulation, revealing substantial localized capsid deformation. Attenuated total reflectance-Fourier transform infrared spectroscopy revealed potential oxidation of viral coat proteins and modification of their secondary structures that were attributed to reactive oxygen species. Iron electrocoagulation simultaneously disinfects and coagulates non-enveloped viruses (unlike conventional coagulation), adding to the robustness of multiple barriers necessary for public health protection and appears to be a promising technology for small-scale distributed water treatment.

Outdoor emissions of primary fine particles and their contributions to indoor air quality deterioration were examined by collecting PM2.5 inside and outside a mechanically ventilated high school in the ultraindustrialized ship channel region of Houston, TX over a 2-month period. By characterizing 47 elements including lanthanoids (rare earth elements), using inductively coupled plasma-mass spectrometry, we captured indoor signatures of outdoor episodic emissions arising from nonroutine operations of petroleum refinery fluidized-bed catalytic cracking units. Average indoor-to-outdoor (I/O) abundance ratios for the majority of elements were close to unity providing evidence that indoor metal-bearing PM2.5 had predominantly outdoor origins. Only Co had an I/O abundance ratio >1 but its indoor sources could not be explicitly identified. La and 17 other elements (Na, K, V, Ni, Co, Cu, Zn, Ga, As, Se, Mo, Cd, Sn, Sb, Ba, W, and Pb), including air toxics were enriched relative to the local soil both in indoor an...

Combined removal and inactivation of the MS2 bacteriophage from model saline (0-100 mM NaCl) waters by electrochemical treatment using a sacrificial aluminum anode was evaluated. Both chemical and electrodissolution contributed to coagulant dosing since measured aluminum concentrations were statistically higher than purely electrochemical predictions using Faraday's law. Electrocoagulation generated only small amounts of free chlorine in situ but effectively destabilized viruses and incorporated them into Al(OH)3(s) flocs during electrolysis. Low chlorine concentrations combined with virus shielding and aggregation within flocs resulted in very slow disinfection rates necessitating extended flocculation/contact times to achieve significant log-inactivation. Therefore, the dominant virus control mechanism during aluminum electrocoagulation of saline waters is "physical" removal by uptake onto flocs rather than "chemical" inactivation by chlorine. Attenuated total reflectance-Fourier transform infrared spectroscopy provided evidence for oxidative transformations of capsid proteins including formation of oxyacids, aldehydes, and ketones. Electrocoagulation significantly altered protein secondary structures decreasing peak areas associated with turns, bends, α-helices, β-structures, and random coils for inactivated viruses compared with the MS2 stock. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) measurements showed rapid initial RNA damage following a similar trend as plaque assay measurements of infectious viruses. However, ssRNA cleavage measured by qRT-PCR underestimated inactivation over longer durations. Although aluminum electrocoagulation of saline waters disorders virus capsids and damages RNA, inactivation occurs at a sufficiently low rate so as to only play a secondary role to floc-encapsulation during residence times typical of electrochemical treatment.

Bench-scale experiments were performed to evaluate virus control by an integrated electrochemical-microfiltration (MF) process from turbid (15 NTU) surface water containing moderate amounts of dissolved organic carbon (DOC, 5 mg C/L) and calcium hardness (50 mg/L as CaCO3). Higher reductions in MS2 bacteriophage concentrations were obtained by aluminum electrocoagulation and electroflotation compared with conventional aluminum sulfate coagulation. This was attributed to electrophoretic migration of viruses, which increased their concentrations in the microenvironment of the sacrificial anode where coagulant precursors are dissolved leading to better destabilization during electrolysis. In all cases, viruses were not inactivated implying measured reductions were solely due to their removal. Sweep flocculation was the primary virus destabilization mechanism. Direct evidence for virus enmeshment in flocs was provided by two independent methods: quantitative elution using beef extract at elevated pH and quantitating fluorescence from labeled viruses. Atomic force microscopy studies revealed a monotonically increasing adhesion force between viruses immobilized on AFM tips and floc surfaces with electrocoagulant dosage, which suggests secondary contributions to virus uptake on flocs from adsorption. Virus sorption mechanisms include charge neutralization and hydrophobic interactions with natural organic matter removed during coagulation. This also provided the basis for interpreting additional removal of viruses by the thick cake formed on the surface of the microfilter following electrocoagulation. Enhancements in virus removal as progressively more aluminum was electrolyzed therefore embodies contributions from (i) better encapsulation onto greater amounts of fresh Al(OH)3 precipitates, (ii) increased adsorption capacity associated with higher available coagulant surface area, (iii) greater virus-floc binding affinity due to effective charge neutralization and hydrophobic interactions, and/or (iv) additional removal by a dynamic membrane if a thick cake layer of flocs is deposited.

Fine particulate matter levels at four air sampling stations in the Houston, TX area are apportioned to quantify the impact of emissions from a local refinery during a reported emission event. Through quantification of lanthanum and lanthanides using a recently developed analytical technique, the impacts of emissions from fluidized-bed catalytic cracking (FCC) units are quantitatively tracked across the Houston region. The results show a significant (33-106-fold) increase in contributions of FCC emissions to PM2.5 compared with background levels associated with routine operation. This impact from industrial emissions to ambient air quality occurs simultaneously with a larger, regional haze episode that lead to elevated PM2.5 concentrations throughout the entire region. By focusing on detailed chemical analysis of unique maker metals (lanthanum and lanthanides), the impact of emissions from the FCC unit was tracked from the local refinery that reported the emission event to a site approximately 50 km downwind, illustrating the strength of the analytical method to isolate an important source during a regional haze episode not related to the emission event. While this source apportionment technique could separate contributions from FCC emissions, improved time-resolved sampling is proposed to more precisely quantify the impacts of transient emission events on ambient PM2.5.

Even though polymeric nanofiltration (NF) and reverse osmosis (RO) membranes often operate on surface waters and surficial groundwaters whose temperature varies over time and with season, very little detailed mechanistic information on temperature effects on membrane selectivity is available to date. Hence, a study was undertaken to investigate the effects of operating temperature (5-41 degrees C) on the morphology and structure of two commercially available thin film composite NF membranes. Application of hydrodynamic models to experimental rejection of dilute solutions of hydrophilic neutral alcohols, sugars, and poly(ethylene glycol)s revealed changes in both the sieving coefficient and permeability of solutes below the membrane glass transition temperature. The vast majority of pores were smaller than 2 nm for both membranes (network pores) even though evidence for a small fraction of larger aggregate pores (approximately 30 nm) was also obtained for one membrane. Increasing temperature appears to cause structural changes in network pores by increasing its pore size while simultaneously decreasing pore density. These increases in pore sizes partially explain reported reductions in contaminant (e.g. arsenic, salts, natural organic matter, hardness, etc.) removal by NF and RO membranes with increasing temperature.

Constant pressure experiments were performed using track-etched polycarbonate membranes and rod-shaped bacteria (viz., Brevundimonas diminuta and Serratia marcescens) to study flux decline and backwashing during the early stages of microfiltration. The intermediate blocking law originally derived for spherical particles was modified to account for the approximate cylindrical shape of the selected bacteria. A deposition factor was introduced to empirically account for the morphology of bacterial deposits. The initial stages of flux decline prior to the secretion of new extracellular polymeric substances (EPS) was quantitatively described by the intermediate blocking law before transitioning to cake filtration at later times. Scanning electron microscopy (SEM) provided additional visual evidence that bacteria simultaneously deposited directly on the membrane and on each other during early stages of filtration as assumed bythe intermediate blocking law. Empirical deposition factors decreased with initial permeate flux indicating its effect on bacteria deposition patterns, which was also confirmed by SEM. Bacteria were easily removed following short filtration times before significant secretion of new EPS by simply rinsing with ultrapure water, thereby completely restoring the clean membrane permeability. In contrast, this rinsing procedure did not completely recover the membrane permeability following longer durations when significant amounts of new EPS proteins and polysaccharides were secreted. Consequently, backwashing effectiveness during water and wastewater microfiltration will be high prior to EPS production whereas flux recovery may not be possible solely by hydrodynamic means once EPS are secreted.

The formation and speciation of disinfection byproducts (DBPs) resulting from chlorination of nanofilter permeates obtained from various source water locations and membrane types are examined. Specific ultraviolet absorbance and bromide utilization are shown to decrease following nanofiltration. Both dissolved organic carbon (DOC) concentration and ultraviolet absorbance at 254 nm were found to correlate strongly with trihalomethane (THM), haloacetic acid (HAA), and total organic halide (TOX) concentrations in chlorinated nanofilter permeates, suggesting that they can be employed as surrogates for DBPs in nanofiltered waters. Because smooth curves were obtained for individual THM and HAA species as well as bromine and chlorine incorporation into THMs and HAAs as a function of Br-/DOC molar ratio, it is likely that mole fractions of these DBPs are more strongly influenced by chlorination conditions, Br-, and DOC concentrations than NOM source and membrane type. Mole fractions of mono-, di-, and trihalogenated HAAs were found to be independent of Br-/DOC. Even at a very low Br-/DOC of 2.9microM/mM, the mixed bromochloro- and tribromoacetic acids constituted 20% of total HAAs on a molar basis. This increased to approximately 50% as Br-/DOC increased to approximately 25microM/mM or more, proving that a large fraction of HAAs may not be covered under existing federal regulations. Total THM and HAA9 concentrations decreased in permeate waters with increasing Br-/DOC suggesting that nanofilter permeates are limited with respect to DBP precursors.

A study was undertaken to determine trihalomethane (THM) and haloacetic acid (HAA) precursor removal by nanofiltration (NF). Cross-flow experiments were conducted with three NF membranes and six natural waters spanning total organic carbon (TOC) concentrations in the range 3.3−13.1 mg/L and bromide ion concentrations in the range 0.5−2.3 μM. Permeate and feedwaters were analyzed for all nine HAA species containing bromine and chlorine. The rejection of THM and HAA precursors decreased with increasing feedwater recovery suggesting that the transport of these materials is controlled by molecular diffusion across the polymeric membranes rather than by physical sieving at membrane surfaces. Therefore, the maximum feedwater recovery in NF systems designed for disinfection byproduct control may be limited by deteriorations in permeate water quality in addition to fouling caused by precipitation of sparingly soluble salts. High rejections of TOC coupled to low removals of bromide ion by some NF membranes resulte...

An expanded understanding of membrane technology is fostering new environmental applications.

A mechanistic model was derived for direct flow microfiltration (MF), one which lends more insight into the factors that control MF performance compared to a statistical curve-fitting procedure that is often used to estimate chemical cleaning intervals at pilot-scale. This theoretical approach to MF fouling was based on fundamental feed water, membrane, and cake characteristics and was shown to predict well pilot-scale experimental specific flux profiles when backwash effectiveness is used as a fitting parameter. Long-term experimental specific flux profiles obtained during the constant flux filtration of natural colloidal materials are reported under conditions typical of water treatment applications. Cakes formed during the filtration of untreated surface waters were found to be highly resistant and compressible. Longer chemical cleaning intervals (and higher values of the backwash effectiveness parameter)were obtained during the constant flux filtration of natural colloidal materials by a decrease in flux, feed water turbidity, and/or backwash interval.

Particle residence time distributions in a membrane channel are interpreted to elucidate mechanisms of particle transport and colloidal fouling in membrane filtration. A comparison of particle size distributions in the membrane feed suspensions and deposited cakes provides evidence for selective particle transport and accumulation on membranes. These data support a previously hypothesized minimum in particle back-transport from the membrane as a function of particle size. The back-transport of smaller particles is apparently due to Brownian diffusion, while larger macrocolloids are controlled by an orthokinetic mechanism such as shear-induced diffusion. In all cases, cake specific resistances measured in the dead-end mode were higher than those of the corresponding feed suspensions. Also, cake specific resistances measured under a crossflow were higher than those in the dead-end mode. Further, the specific resistance of particle deposits on membranes increased with shear rate and decreased as the initial ...

Particle transport and deposition studies in laminar cross-flow membrane filtration are reported. Particle residence time distributions (RTDs) in experimental conditions typical of ultra- and microfiltration are compared with theoretical predictions incorporating the effects of hydrodynamic, Coulombic, electrodynamic, and external gravity forces. Numerical simulations show that, for a given flow field, mechanisms controlling lateral migration in the far-field region in membrane afters depend primarily on inertial, gravity, and permeation drag forces. The theory accurately predicts first passage times and multimodal RTDs under conditions of high membrane permeability and fast axial flows.

The trans-Atlantic transport of North African dust by summertime trade winds occasionally increases ambient particulate matter (PM) concentrations in Texas above air quality standards. Exemptions from such exceedences can be sought for episodic events that are beyond regulatory control by providing qualitative supportive information such as satellite images and back-trajectories. Herein we demonstrate that chemical mass balancing can successfully isolate, differentiate, and quantify the relative contributions from local and global mineral dust sources through detailed measurements of a wide suite of elements in ambient PM. We identified a major dust storm originating in Northwest Africa in mid-July 2008 which eventually impacted air quality in Houston during July 25, 26, and 27, 2008. Daily PM2.5 and PM10 samples were collected at two sites in Houston over a 2-week period encompassing the Saharan dust episode to quantify the transported mineral dust concentrations during this peak event. Average PM concentrations more than doubled during the Saharan intrusion compared with non-Saharan. Relative concentrations of several elements often associated with anthropogenic sources were significantly diluted by crustal minerals coincident with the large-scale Saharan dust intrusion. During non-Saharan days, local mineral dust sources including cement manufacturing and soil and road dust contributed in total 26% to PM2.5 mass and 50% to PM10 mass; during the three-day Saharan episode the total dust contribution increased to 64% for PM2.5 and 85% for PM10. Importantly, this approach was also able to determine that local emissions of crustal minerals dominated the period immediately following the Saharan dust episode: simple quantification of bulk crustal materials may have misappropriated this elevated PM to trans-Atlantic transport of Saharan dust.