Gary Amy

Characterization of DOM as a function of MW by fluorescence EEM and HPLC-SEC using UVA, DOC, and fluorescence detection

To investigate the composition of dissolved organic matter (DOM) as a function of apparent molecular weight (MW) by rapid analytical methods, high performance liquid chromatography (HPLC)-size exclusion chromatography (SEC) was conducted with sequential on-line detectors consisting of UV, fluorescence, and quantitative DOC measurement. Fluorescence excitation-emission matrix (EEM) spectrophotometry was used to select wavelengths for the HPSEC on-line fluorescence system. The chosen peak maxima locations of excitation-emission wavelengths were 278-353 nm for protein-like substances and 337-423 nm for fulvic-like substances based on an analysis of EEM spectra for various samples and reference materials. This system provides quantitative and qualitative information on the specific MW components of DOM, including proportion of DOC (by DOC measurement), aromaticity (by comparison of UV and DOC measurements), and chemical properties (by fluorescence measurement). It further allows determination of organic matter characteristics (e.g., fulvic-like, protein-like, and polysaccharide-like substances) as a function of MW. Three types of samples (Irvine Ranch ground water (IRWD-GW), Barr Lake surface water (BL-SW), and Hawaii wastewater secondary effluent) were analyzed by the HPSEC-UVA-fluorescence-DOC system. These results were compared with fluorescence EEM for samples fractionated by HPLC-SEC. The DOM fraction in the high apparent MW range (over 10,000g/mol) consisted of polysaccharide-like substances for IRWD-GW and a mixture of polysaccharide-like/protein-like substances for BL-SW and wastewater secondary effluent. Minimal amounts of fulvic-like substances were found in the wastewater secondary effluent sample. The DOM fractions in a medium apparent MW range (5000-1000 g/M) showed higher aromaticity (fulvic in character) than any other fractions for all samples. For the DOM fraction in the low apparent MW range (below 680 g/M), additional aliphatic organic matter was found in IRWD-GW, while BL-SW contained protein-like processes. DOM plays an important role in drinking water and wastewater treatment processes. An enhanced HPSEC technique with multiple on-line detectors enables a better understanding of quantitative and qualitative DOM properties and can help to design and optimize water/wastewater treatment facilities.

Relationships between the structure of natural organic matter and its reactivity towards molecular ozone and hydroxyl radicals

Abstract Oxidation reaction rate parameters for molecular ozone (O3) and hydroxyl (HO) radicals with a variety of hydrophobic organic acids (HOAs) isolated from different geographic locations were determined from batch ozonation studies. Rate parameter values, obtained under equivalent dissolved organic carbon concentrations in both the presence and absence of non-NOM HO radical scavengers, varied as a function of NOM structure. First-order rate constants for O3 consumption (kO3) averaged 8.8×10−3xa0s−1, ranging from 3.9×10−3xa0s−1 for a groundwater HOA to >16×10−3xa0s−1 for river HOAs with large terrestrial carbon inputs. The average second-order rate constant (kHO,DOC) between HO radicals and NOM was 3.6×108xa0lxa0(molxa0C)−1xa0s−1; a mass of 12xa0gxa0C per mole C was used in all calculations. Specific ultraviolet absorbance (SUVA) at 254 or 280xa0nm of the HOAs correlated well (r>0.9) with O3 consumption rate parameters, implying that organic π-electrons strongly and selectively influence oxidative reactivity. HO radical reactions with NOM were less selective, although correlation between kHO,DOC and SUVA existed. Other physical–chemical properties of NOM, such as aromatic and aliphatic carbon content from 13C-NMR spectroscopy, proved less sensitive for predicting oxidation reactivity than SUVA. The implication of this study is that the structural nature of NOM varies temporally and spatially in a water source, and both the nature and amount of NOM will influence oxidation rates.

Fouling characteristics of wastewater effluent organic matter (EfOM) isolates on NF and UF membranes

Wastewater effluent organic matter (EfOM) was isolated into different fractions including colloids, and hydrophobic (HPO) and transphilic (TPI) fractions. The EfOM isolates were characterized by different techniques, for example, size exclusion chromatography (SEC) with on-line UVA and DOC detectors, Fourier transform infrared (FTIR), specific UVA (SUVA), and total sugars analysis. The colloidal fraction is primarily composed of polysaccharides, proteins, and/or aminosugars, providing a hydrophilic character. The HPO and TPI fractions possessed characteristics of humic substances, i.e. high aromaticity and carboxylic functional groups. A superimposition of the EfOM isolates reflects characteristics of bulk wastewater effluents, consisting of refractory natural organic matter (NOM) conveyed from the drinking water source and soluble microbial products (SMP) derived during biological processes of wastewater treatment. Each EfOM isolate exhibited different characteristics in fouling of NF and UF membranes due to their distinct characters. The colloidal fraction showed high flux decline and fouling on NF and UF membranes primarily due to the effects of pore blockage. The HPO and TPI fractions exhibited less fouling and flux decline than the colloids due to their molecular size as well as electrostatic repulsion between organic acids and the membrane surface. However, hydrophobic interactions play a significant role with hydrophobic membranes, causing a reduction of permeate flux. Membrane autopsies using FTIR identified functional groups of organic foulants, supporting the evidence of flux decline by each EfOM isolate. Polysaccharides and/or aminosugars from the colloids in wastewater effluent were found to play an important role in fouling of NF and UF membranes.

Membrane filtration of natural organic matter: factors and mechanisms affecting rejection and flux decline with charged ultrafiltration (UF) membrane

Abstract We studied natural organic matter (NOM) rejection and the membrane’s flux decline during natural water filtration using a charged ultrafiltration membrane based on thin-film-composite technology. NOM rejection mechanisms such as steric exclusion and aromatic/hydrophobic and charge interactions were considered. Water composition factors affecting NOM rejection and flux decline were investigated, including ionic strength, pH, and calcium ion concentration. The membrane’s effective relative molecular mass cutoff for the NOM in our study was between 1500 and 2300 (significantly lower than the manufacturer’s nominal value of 8000) and depended on the NOM characteristics in the source water. In particular the ratio of UV absorbance at 254xa0nm to dissolved organic carbon (related to the humic content) correlated with the rejection. Comparison of relative molecular mass distributions between fractionated NOM and recovered membrane foulants indicates that the foulants are the larger-sized neutral and/or basic NOM components, and not the humic substances that were efficiently rejected by this membrane.

Membrane filtration of natural organic matter: initial comparison of rejection and flux decline characteristics with ultrafiltration and nanofiltration membranes

Two source waters containing natural organic matter (NOM) with different physical and chemical characteristics were crossflow-filtered using four types of membranes having different material and geometric properties. Transport measurements of NOM rejection and flux decline were made. A resistances-in-series model was used to represent and quantitatively compare membrane flux decline and recovery. As anticipated, the resistance due to specific adsorption depended on the concentration at the membrane interface. For the two membranes showing evidence of NOM adsorption, reducing the initial flux (which we infer to also reduce the interfacial NOM concentration) also lowered the measured resistance assigned to adsorption in our protocol. Relative molecular mass (RMM) distribution measurements (by size exclusion chromatography) were used to calculate the average RMM of the NOM and persuasively illustrated that the nominal relative molecular mass cut-off (MWCO) of a membrane is not the unique predictor of rejection characteristics for NOM compounds. Size exclusion, electrostatic repulsion, and NOM aromaticity all influenced the NOM rejection. For a given water composition (including pH and ionic strength), membrane characteristics (such as the surface charge, hydrophobicity and nominal MWCO) can be combined with the NOM properties (such as total dissolved organic carbon, specific UV absorbance at 254 nm and humic content) to provide a consistent qualitative rationale for the transport results.

Impact of enhanced and optimized coagulation on removal of organic matter and its biodegradable fraction in drinking water

The presence of biodegradable organic matter (BOM) can affect drinking water quality. A variety of treatment processes can be used to control BOM during drinking water production. Studies of enhanced coagulation (coagulation optimized for removal of dissolved organic material as well as particles) showed that removal of DOC could be improved from the current average of 29% (plant conditions termed baseline coagulation) to an average of 43% for optimized coagulation at the 10 sites tested. Similarly, removal of biodegradable dissolved organic carbon (BDOC) could be improved from the current baseline level of 30% to 38% through the application of optimized coagulation. At lower pH, ferric coagulants generally performed better for removal of organic carbon than did alum or polyaluminum chloride. In most of the cases, assimilable organic carbon (AOC) was not affected by coagulation, probably because the AOC fraction was composed of small molecular weight, non-humic compounds that are not amenable to coagulation.

Adsorption of hydrophobic compounds onto NF/RO membranes: an artifact leading to overestimation of rejection

This study addresses the adsorption of hydrophobic compounds at low concentration (∼100 ppb) onto NF/RO membranes. In this study, three surrogate compounds and three NF/RO membranes were tested under cross-flow conditions. Experimental results showed that the adsorption of hydrophobic compounds was significant for neutral compounds and ionizable compounds when electrostatically neutral. Also, operating conditions such as the permeate flow rate (flux) had a significant effect on the degree of compound adsorption. A comparison of the adsorption observed in dynamic filtration tests with that in static batch adsorption tests suggests that more adsorption sites are accessible for molecules during membrane filtration due to the pressurized advective flow. It was observed that the concentration of the tested compounds changed during filtration tests due to adsorption. Therefore, an accurate evaluation of a given membrane in terms of the rejection of a hydrophobic compound is not possible until saturation of the membrane with the compound of interest is accomplished. The experimental results demonstrated that a relatively large amount of the feed water needed to be filtered to reach saturation conditions.

Ozone enhanced removal of natural organic matter from drinking water sources

Abstract The use of ozone as a pre-oxidant or intermediate oxidant in drinking-water treatment is becoming increasingly common. The ozonation of natural source waters containing natural organic matter produces biodegradable by-products such as organic acids, aldehydes, and ketoacids. These organic by-products serve as carbon source for bacteria, potentially causing regrowth problems in distribution systems. The measurement of biodegradable dissolved organic carbon (BDOC) provides quantitative insight into the amount of BDOC that is present. In drinking-water treatment, removal of BDOC can also reduce the formation potential of chlorination disinfection by-products such as trihalomethanes and haloacetic acids. Removal of BDOC was optimal at an applied ozone:DOC ratio of 2:1 (mg/mg) for source waters containing DOC levels ranging from 3 to 6 mg/liter. The use of biotreatment resulted in a 40–50% decrease in DOC, a 90–100% reduction in aldehydes, and a 40–60% reduction in trihalomethane formation potential. No removal of bromate ion and dibromoacetic acid was observed. A positive correlation was obtained between BDOC and assimilable organic carbon; both parameters indicate a tendency to plateau at an applied ozone/DOC weight ratio of 2:1.

CLEANING STRATEGIES FOR FLUX RECOVERY OF AN ULTRAFILTRATION MEMBRANE FOULED BY NATURAL ORGANIC MATTER

One of the most common problems encountered in water treatment applications of membranes is fouling. Natural organic matter (NOM) represents a particularly problematic foulant. Membranes may be fouled by relatively hydrophilic and/or hydrophobic NOM components, depending on NOM characteristics, membrane properties, and operating conditions. To maximize flux recovery for an NOM-fouled ultrafiltration membrane (NTR 7410), chemical cleaning and hydraulic rinsing with a relatively high cross-flow velocity were investigated as cleaning strategies. The modification of the membrane surface with either an anionic or a cationic surfactant was also evaluated to minimize membrane fouling and to enhance NOM rejection. Foulants from a hydrophobic NOM source (Orange County ground water (OC-GW)) were cleaned more effectively in terms of permeate flux by acid and caustic cleanings than foulants from a relatively hydrophilic NOM source (Horsetooth surface water (HT-SW)). An anionic surfactant (sodium dodecyl sulfate (SDS)) was not effective as a cleaning agent for foulants from either hydrophobic or hydrophilic NOM sources. High ionic strength cleaning with 0.1 M NaCl was comparatively effective in providing flux recovery for NOM-fouled membranes compared to other chemical cleaning agents. Increased cross-flow velocity and longer cleaning time influenced the efficiency of caustic cleaning, but not high ionic strength cleaning. The membrane was successfully modified only with the cationic surfactant; however, enhanced NOM rejection was accompanied by a significant flux reduction.

The reversibility of virus attachment to mineral surfaces

Virus transport through groundwater is limited by attachment to mineral surfaces and inactivation. Current virus transport models do not consider the implications of the reversibility of virus attachment to minerals. To explore the reversibility of virus attachment to mineral surfaces, we attached PRD1, a bacteriophage considered to be a good model of enteric viruses, to quartz and ferric oxyhydroxide-coated quartz surfaces over a range of pH values in equilibrium “static columns.” Following attachment, we detached the viruses by replacing the pore solution with solutions of equal and higher pH. The extent of virus attachment followed an attachment “edge” that occurred at a pH value about 2.5–3.5 pH units above the pHiep of the mineral surfaces. Viruses attached below this edge were irreversibly attached until the pH of the detachment solution exceeded the pH value of the attachment edge. Viruses attached above this edge were reversibly attached. Derjaguin-Landau-Verwey-Overbeek (DLVO) potential energy calculations showed that the attachment edge occurred at the pH at which the potential energy of the primary minimum was near zero, implying that the position of the primary minimum (attractive or repulsive) controlled the equilibrium distribution of the viruses. The results suggest that the reversibility of virus attachment must be considered in virus transport models for accurate predictions of virus travel time.