James E. Kilduff

Probing reactivity of dissolved organic matter for disinfection by-product formation using XAD-8 resin adsorption and ultrafiltration fractionation.

The disinfection by-product (DBP) reactivity (yield and speciation upon reaction with chlorine) of dissolved organic matter (DOM) isolated from two surface waters was investigated. The source waters, each having significantly different specific ultraviolet absorbance (SUVA254), molecular weight (MW) distribution and polarity, were fractionated using XAD-8 resin adsorption and ultrafiltration (UF), with good DOM mass balance closures (based on dissolved organic carbon). It was found that such fractionation preserved both the SUVA and the reactivity of the source waters, as demonstrated by statistically similar DBP formation and speciation from chlorinated source water and source waters reconstituted from XAD-8 or UF fractions. In addition, there was no evidence of synergistic effects among DOM components when reacting with chlorine. Consistent trends between DBP yields and MW were not found. Hydrophobic fractions of DOM (isolated by XAD-8) were the most reactive DOM components; however, hydrophilic components also showed appreciable DBP yields, contributing up to 50% of total DBP formation. In contrast, strong and unique correlations were observed between the SUVA of individual fractions and their trihalomethane (THM) and haloacetic acid (HAA9) yields, confirming that the aromaticity of DOM components is more directly related to reactivity than other physicochemical properties. The finding of a single correlation independent of the fractionation process employed is notable because XAD-8 adsorption and UF fractionate DOM by significantly different mechanisms. These results confirm that SUVA is a distributed parameter that reflects DOM heterogeneity. Therefore, the SUVA distribution within natural water represents an important property that can be used as a reliable predictor of DBP formation. Finally, bromine appears to be more effectively incorporated into low UV-absorbing (i.e., low SUVA), low MW and hydrophilic DOM fractions.

Site energy distribution analysis of preloaded adsorbents.

A methodology relating changes in the isotherm parameters for sorption of one solute by a heterogeneous sorbent to changes in the site energy distributions of that sorbent caused by prior irreversible sorption (preloading) of other solutes is proposed. Approximate site energy distributions underlying three isotherm models commonly used to describe sorption of organic solutes from aqueous solutions are developed using the theory of heterogeneous surfaces. It is demonstrated that, regardless of the type of initial site energy distribution assumed, preloading by a non-desorbable solute results in a loss of surface heterogeneity. The loss occurs preferentially across sites having the highest energies, with the number of sites in the lowest energy ranges actually increasing in some cases. Activated carbon is used to demonstrate the methodology, but the approach is generally applicable to other heterogeneous adsorbents in both natural and engineered systems.

Low fouling synthetic membranes by UV-assisted graft polymerization: monomer selection to mitigate fouling by natural organic matter

Abstract A UV-assisted photochemical graft polymerization technique was used to produce modified poly(ether sulfone) (PES) ultrafiltration (UF) membranes that exhibit reduced interaction with natural organic matter (NOM), as a route to reduce the fouling caused by NOM. We evaluated six different hydrophilic monomers for their ability to reduce fouling by NOM: two are neutral monomers, N -vinyl-2-pyrrolidinone (NVP) and 2-hydroxyethyl methacrylate (HEMA); two are weakly acidic (carboxylic) monomers, acrylic acid (AA) and 2-acrylamidoglycolic acid (AAG); and two are strongly acidic (sulfonic) monomers, 3-sulfopropyl methacrylate (SPMA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). Grafting increased membrane surface wettability and shifted the membrane pore size distribution to smaller sizes, which increased natural organic matter rejection (except in the case of NVP). Total fouling appeared to depend primarily on solute rejection, and varied in a complex way that could be interpreted in the context of the NOM molecular weight distribution. Reversible fouling resulting from cake formation was only weakly dependent on membrane surface chemistry; in contrast, irreversible fouling exhibited a marked dependence on surface chemistry. Membranes modified with the weak acid AA monomer were able to reduce irreversible fouling to zero, in contrast to other strongly hydrophilic monomers such as HEMA and AAG, which increased irreversible fouling relative to the unmodified membrane. We conclude that wettability (or hydrophilicity) is not an appropriate parameter for estimating reduced fouling potential for NOM feeds, as it is for feeds containing protein. We hypothesize that this is a consequence of the structural and chemical heterogeneity of NOM. The AA-modified membranes exhibited excellent filtration performance over multiple runs, and outperformed a regenerated cellulose (RC) membrane having similar initial NOM rejection.

Photochemical modification of poly(ether sulfone) and sulfonated poly(sulfone) nanofiltration membranes for control of fouling by natural organic matter

Poly(ether sulfone) and sulfonated poly(sulfone) nanofiltration membranes were modified by UV irradiation and UV-assisted graft polymerization of N-vinyl-2-pyrrolidinone (NVP) as a strategy for mitigating fouling by naturally-occurring organic compounds (NOM) found in surface waters. Exposure to UV (254 nm) alone increased membrane hydrophilicity, interpreted in terms of either the contact angle, θ, or surface wettability (cos θ). It was possible to increase cos θ above 0.94. FTIR analysis suggests that this was due, in part, to the formation of surface hydroxyl groups. The membrane structure was opened, as evidenced by increased clean water permeability. Fouling by natural organic matter (isolated from a surface water source using reverse osmosis) was reduced significantly, but conditions that minimized fouling also decreased solute (NOM as organic carbon) rejection. In contrast, it is possible to identify UV-assisted graft polymerization reaction conditions which significantly reduced fouling, with clean water permeability and solute rejection similar to as-received membranes. When short reaction times (10 s) were used, clean water permeability decreased and solute rejection increased, presumably as a result of pore blockage by graft polymer chains. The opposite behavior in each respect was observed for long irradiation time (180 s); however, while fouling tendency was reduced relative to as-received membranes, it was not reduced to the same extent as membranes irradiated for 60 s. This observation could be explained by an increase in pore fouling resulting from increased access to enlarged pores by larger molecular weight natural organic matter components.

Isolation of dissolved organic matter (DOM) from surface waters using reverse osmosis and its impact on the reactivity of DOM to formation and speciation of disinfection by-products.

Dissolved organic matter (DOM) from three low-hardness surface waters was isolated and concentrated using a reverse osmosis (RO) membrane system. The efficacy of the RO isolation method and its impact on the subsequent reactivity between DOM and chlorine were examined. DOM mass balances (quantified as dissolved organic carbon) ranged from 96.1 to 102.1% for the three waters tested, and DOM mass recoveries of 93.9 to 98.2% indicated successful isolation, minimal fractionation. and negligible loss of organic matter. RO isolates were diluted using distilled and deionized water in the laboratory to reconstitute the source waters. Both source water (collected at the time of isolation) and reconstituted source water samples were chlorinated. Formation of several disinfection by-products (DBPs: e.g., THMs, HAA9, HANs, and HKs) were measured. For all waters tested, DBP formation of source and corresponding reconstituted source water agreed within 95% confidence intervals. Therefore, RO isolation had no impact on the DOM reactivity of the three low-hardness surface waters tested in this study. In addition, the degree of bromine substitution, as expressed by the bromine incorporation factor, was calculated. Comparison of bromine incorporation factors for source and reconstituted source waters further indicated that, as with the total DBP formations, bromine speciation and the relative occurrence of individual species in THMs and HAA9 did not change as a result of the isolation. Overall, in terms of DBP formation, RO isolation appears to maintain the integrity and reactivity of DOM.

Adsorption uptake of synthetic organic chemicals by carbon nanotubes and activated carbons

Carbon nanotubes (CNTs) have shown great promise as high performance materials for adsorbing priority pollutants from water and wastewater. This study compared uptake of two contaminants of interest in drinking water treatment (atrazine and trichloroethylene) by nine different types of carbonaceous adsorbents: three different types of single walled carbon nanotubes (SWNTs), three different sized multi-walled nanotubes (MWNTs), two granular activated carbons (GACs) and a powdered activated carbon (PAC). On a mass basis, the activated carbons exhibited the highest uptake, followed by SWNTs and MWNTs. However, metallic impurities in SWNTs and multiple walls in MWNTs contribute to adsorbent mass but do not contribute commensurate adsorption sites. Therefore, when uptake was normalized by purity (carbon content) and surface area (instead of mass), the isotherms collapsed and much of the CNT data was comparable to the activated carbons, indicating that these two characteristics drive much of the observed differences between activated carbons and CNT materials. For the limited data set here, the Raman D:G ratio as a measure of disordered non-nanotube graphitic components was not a good predictor of adsorption from solution. Uptake of atrazine by MWNTs having a range of lengths and diameters was comparable and their Freundlich isotherms were statistically similar, and we found no impact of solution pH on the adsorption of either atrazine or trichloroethylene in the range of naturally occurring surface water (pH = 5.7-8.3). Experiments were performed using a suite of model aromatic compounds having a range of π-electron energy to investigate the role of π-π electron donor-acceptor interactions on organic compound uptake by SWNTs. For the compounds studied, hydrophobic interactions were the dominant mechanism in the uptake by both SWNTs and activated carbon. However, comparing the uptake of naphthalene and phenanthrene by activated carbon and SWNTs, size exclusion effects appear to be more pronounced with activated carbon materials, perhaps due to smaller pore sizes or larger adsorption surface areas in small pores.

High throughput atmospheric pressure plasma-induced graft polymerization for identifying protein-resistant surfaces

Three critical aspects of searching for and understanding how to find highly resistant surfaces to protein adhesion are addressed here with specific application to synthetic membrane filtration. They include the (i) discovery of a series of previously unreported monomers from a large library of monomers with high protein resistance and subsequent low fouling characteristics for membrane ultrafiltration of protein-containing fluids, (ii) development of a new approach to investigate protein-resistant mechanisms from structure-property relationships, and (iii) adaptation of a new surface modification method, called atmospheric pressure plasma-induced graft polymerization (APP), together with a high throughput platform (HTP), for low cost vacuum-free synthesis of anti-fouling membranes. Several new high-performing chemistries comprising two polyethylene glycol (PEG), two amines and one zwitterionic monomers were identified from a library (44 commercial monomers) of five different classes of monomers as strong protein-resistant monomers. Combining our analysis here, using the Hansen solubility parameters (HSP) approach, and data from the literature, we conclude that strong interactions with water (hydrogen bonding) and surface flexibility are necessary for producing the highest protein resistance. Superior protein-resistant surfaces and subsequent anti-fouling performance was obtained with the HTP-APP as compared with our earlier HTP-photo graft-induced polymerization (PGP).

Modeling Flux Decline during Nanofiltration of NOM with Poly(arylsulfone) Membranes Modified Using UV-Assisted Graft Polymerization

Poly(ether sulfone) and sulfonated poly(sulfone) nanofiltration membranes were modified by UV irradiation and UV-assisted graft polymerization of N-vinyl-2-pyrrolidinone (NVP) as a strategy for increasing the wettability of membrane surfaces and mitigating fouling by naturally occurring organic compounds present in surface waters. The UV-assisted graft polymerization approach with 3% NVP and a reaction time of 60 s increased the wettability (increased cos θ) of membrane surfaces, which exhibited a significantly lower propensity to foul. For these conditions, clean water permeability and solute rejection (as organic carbon) were maintained close to that of the as-received membranes. Graft polymerization was carried out using two different methods. With the dip method, membrane coupons coated with a 3% N-vinyl-2-pyrrolidinone solution were UV irradiated under nitrogen. With the immersion method, membrane coupons were irradiated directly in nitrogen-purged 3% NVP solution. Both techniques increased membrane ...

THE OXYGEN SENSITIVITY OF ORGANIC MACROMOLECULE SORPTION BY ACTIVATED CARBON: EFFECTS OF SOLUTION CHEMISTRY

Abstract The influence of solution chemistry (pH, ionic strength and calcium concentration) on the oxygen sensitivity of natural and synthetic dissolved organic macromolecule sorption by granular activated carbon was investigated. Sorption sensitivity to the presence of oxygen was found to decrease with decreasing pH, with increasing ionic strength and with increasing calcium concentration. The influence of oxygen on the extent of sorption by a basic GAC (pH PZC = 8.5) appears to be enhanced by increasing phenolic acidity and/or decreasing macromolecule size. The results suggest that open, flexible molecular configurations of organic macromolecules and the direct interactions of these substances with carbon surfaces are important factors with respect to the effects of oxygen on their sorption from aqueous phase.

Membrane Fouling, Modelling and Recent Developments for Mitigation

Flux decline caused by accumulation of retained species occurs in all membrane processes and must be well managed to assure that the process performs efficiently and cost-effectively over its design life. Fouling, which can be a significant cause of flux decline, occurs when components of the feed stream interact physically or chemically with the membrane or components of the membrane module such as feed spacers. Such fouling can reduce membrane separation performance, increase process operating costs and shorten membrane life. In this chapter, we review the major causes of fouling in desalination and potable water applications, with an emphasis on fouling by organic matter, colloids and biofouling in pressure driven, polymeric membrane processes. We consider organic matter including humic substances and polysaccharides such as transparent exopolymer particles, which bridge dissolved and colloidal organic matter, and may play a significant role in biofouling. Managing biofouling represents a significant challenge in nearly all membrane systems; here we discuss mechanisms, diagnosis and visualisation. Approaches to mitigate fouling are discussed, with an emphasis on novel membrane materials, including surface chemistries and nanoparticle composite approaches.