Farida Y. Saleh

Kinetics of chromium transformations in the environment

Kinetics of chromium transformations under typical environmental conditions were systematically investigated using batch, microcosm and column experiments. Oxidation and reduction rates were evaluated in single phase water systems and in two phase water-solid systems. Natural and reference waters, sediments and soils representing a broad range of characteristics were used. Some of the investigated reactions, such as the reduction of Cr(VI) by S2- or Fe2+ ions under anaerobic conditions, were instantaneous and the experimental results exactly followed the stoichiometric and equilibrium calculations. Other reactions, such as the reduction of Cr(VI) by organics in sediments and soils, or the oxidation of Cr(III) by MnO2, were much slower and clearly exhibited kinetic controls. Reduction of Cr(VI) by organics was dependent on both the type and amount of organic material. Dissolved oxygen by itself did not induce measurable oxidation of Cr(III), spiked to the experimental waters, after 128 days. Slow Cr(III) oxidation to Cr(VI) was only noted in one of the natural waters and sediments with half-lives ranging from 2 to 9 years. In all cases the extent of Cr(III) oxidation did not exceed 15% of the initial Cr(III) present. The overall results indicate that the transport and transformation of chromium can be predicted using kinetics data derived from a simplified laboratory experiment, the Eh-pH data and the aquatic system characteristics. Results of the microcosm and laboratory experiments were in good agreement with the predicted concentrations.

Effects of suspended solids on the bioavailability of chlordane toDaphnia magna

Research was conducted to assess the importance of suspended solids (ss) types and levels and associated organic carbon contents on the bioavailability of chlordane toDaphnia magna. The dose response relationship ofD. magna to chlordane was established in the absence of suspended solids. Test waters with suspended solids levels of approximately 0, 100, 500, and 750 mg/L contained a chlordane concentration which caused ∼80% mortality of the test population in 48-hr. The effects of different types and levels of suspended solids onD. magna mortality were observed. Both montmorillonite clay (0 organic carbon) and pond sediments (1.7% organic carbon) reduced bioavailability of chlordane toD. magna. Suspended solids characteristics were not a determining factor In the reduction of the bioavailability of chlordane toD. magna as long as a threshold level (>200 to 300 mg/L) of suspended solids was present.

Analysis of Disinfection By-products in Water and Wastewater

Abstract Several analytical methods have been utilized to study the products from the chlorination of water from a southern U.S.A. reservoir. Low molecular weight fragments have been assayed by GC/MS following resin accumulation under acidic or basic conditions. High molecular weight products before and after chlorination have been investigated using size HPLC with aqueous solvent and passivated controlled porosity silica columns. The results show a slight lowering of average molecular weight after chlorination, but more importantly, a nearly uniform level of organic chlorine through the polymer. Total organic halogen measurements confirm that the ratio of non-volatile halogen to trihalomethane halogen is at least 2:1 in all cases studied. The oronation and photolytic oronation products of 2.4.6,2′,4′.6′-hexachloro-biphenyl have been determined and a reaction scheme proposed.

Aqueous solubilities and transformations of tetrahalogenated benzenes and effects of aquatic fulvic acids

The fate of organic pollutants in the environment is largely dependent on their physical and chemical properties. Many of the previous studies on halogenated benzenes have been focused on their photochemistry in an organic solvent system. Studies of halogenated benzenes in aqueous conditions without photochemical effect are rare. Recently, aqueous solubility enhancement of hydrophobic organic pollutants by humic substances was studied. Aqueous solubility enhancement did not occur with all test compounds. In this paper, the authors investigated the transformation of the three most symmetrical tetrahalogenated (fluoro, chloro, bromo) benzenes in absence of the photo effect. Solute and solvent interactions, and influence of aquatic fulvic acids (FA) on aqueous solubilities and transformation of the three tetrachlorobenzenes and 1,2,4,5-TeBB were studied.

Selected organic pesticides, behavior and removal from domestic wastewater by chemical and physical processes

A study was conducted to evaluate the effectiveness of chemical and physical wastewater treatment processes in removing selected organic pesticides from domestic wastewater. A 3785 m3 day−1 (1 MGD) nominal capacity pilot plant consisting of biological, chemical and physical units was used for the study. Biologically treated domestic wastewater was subjected to chemical coagulation, multimedia filtration, and activated carbon adsorption. Eight sequences of treatment processes were studied. Influent and effluent samples were analyzed for selected chlorinated hydrocarbon pesticides and chlorophenoxy herbicides using EC-GC. Confirmatory tests such as TLC, extraction of p-value and CPU-MS-GC were applied on selected samples. Results of the study provided qualitative and quantitative evaluation of the performance of the treatment processes studied. Qualitatively characteristic profiles consisting of a limited number of refractory organic residues were detected as peaks on EC chromatograms of extracts from each treatment unit. Thirteen compounds were confirmed in the biologically treated wastewater. These included DDT and its metabolites, aldrin, dieldrin, and 2,4-D alkyl esters and salts. Concentration levels of these compounds in wastewaters were at the ng l−1 (part per trillion) level. Chemical coagulation with alum-lime or lime-ferric chloride was found to effect slight reduction of the organic residues detected on EC chromatograms. Quantitatively only DDT compounds were more completely removed by chemical treatment. Multimedia filters had no discernible effect in removing organic residues from biologically and chemically treated wastewater. Activated carbon columns were found to be the most effective means for removing the refractory organic residues detected. However, breakthrough of some organic residues was noted after usage of the carbon for over 1 year. The overall results of the study showed that application of several sequences of treatment processes on domestic wastewater can produce a high quality effluent which is virtually free from EC detectable organic residues.

Retention and Spectral Characteristics of Copper-Natural Ligand Complexes in Reversed Phase C18-HPLC with UV-PDA and Fluorescence Detection

Abstract Copper complexes with fulvic (FA), caffeic (CFCA), vanillic (VA) and salicylic (SA) acids were investigated by reversed-phase HPLC with dual uv-vis photodiode array (PDA) and fluorescence (fl) detection using retention enrichment (RE) and direct complex introduction (DCI) methods. In the RE method VA and FA formed a hydrophobic Cu(II)-complex with measurable shift in retention time (tR). Whether or not there was a shift in tR, the uv-vis spectral characteristics of all complexed ligands in the RE method were of reduced absorption intensities but with the same characteristic absorption bands. In the DCI method only CFCA formed a more hydrophobic Cu(II)-complex with a measurable shift in tR and a distinguishable uv-vis spectrum. Free FA was resolved into seven uv-vis absorbing and fluorescing peaks (binding sites). At molar ratio M:L of 1:1 and pH 7, Cu-FA complex was resolved into the same peaks but with less uv and fluorescence intensities. The complexed peaks contained 69% of the added Cu(II) an...

Characterization of refuse-derived fuel by pyrolysis―gas chromatography and gas chromatography/mass spectrometry

Abstract Pyrolysis-capillary gas chromatography combined with flame ionization, electron capture and mass spectrometric detectors was used to characterize refuse-derived fuel. Pyrograms of solid samples were developed at different temperature profiles. Solid-liquid extraction with hexane, methanol, methylene chloride, or water allowed the extraction of organics of different polarities. Methylene chloride showed the highest extraction efficiency. Reproducibilities of the pyrograms in the solid samples and the solvent extracts were evaluated. Relative standard deviations for liquid extracts and solid material were 5.6% and 6.0%, respectively. Preparative fractions collected after pyrolysis were analyzed by gas chromatography/mass spectrometry and by ion chromatography. Eight oxygenated and hydrocarbon compounds were identified. The organic chloride content of refuse-derived fuel pyrolyzed at 800°C was found to be 0.021% of refuse-derived fuel based on dry weight.

Transport Processes of Naphthalene in the Aquatic Environment

Abstract A study was conducted on the environmental transport processes of naphthalene in three surface water-sediment systems and in Milli-Q water-clay system. Solubility, Henrys law constant (H), volatilization rate constant, photolysis rate constant, and sorption-desorption coefficients, were determined. Aqueous solubilities ranged from 28.0 to 29.4 mg/L and did not show a significant difference in the different waters at a – 0.5. Experimentally determined H were lower in the natural waters than in Milli-Q water possibility due to decrease in surface tension. Estimation of volatilization rates by measuring KVC/KVO was subject to photolysis side effects. Photolysis rate followed first order kinetics and was enhanced in natural waters by factors from 2 to 7. Data on naphthalene sorption-desorption coefficients were not conclusive. Translation of the laboratory data to field or microcosm conditions may reflect different situations than the apparent differences noted in individual process determined in the laboratory. Under well characterized microcosm conditions, volatilization is the major transport process of naphthalene. Photolysis and biotransformation, each account for less than 15% of the kinetic process. The natural water matrix retarded volatilization rates and enhanced photolysis rates. The microcosm sediment partition coefficient was lower than values derived from laboratory data.

Step-Wise Fractionation and Recovery of Aquatic Fulvic Acid by Modified Supercritical Fluid CO2- Methanol Extraction at Near Critical Temperature

Abstract Modified supercritical fluid “SF” CO2 -methanol mixture was used, under step-wise gradient conditions at near supercritical temperature, to fractionate Suwannee River reference fulvic acids (FA) into three fractions. The method was developed after a systematic study of the solubility of FA in SF CO2-methanol solvent system. Optimum supercritical fluid extraction (SFE) conditions were established at constant temperature of 70 °C and constant pressure of 2,500 psi; using modified CO2 fluid mixed with methanol at 18, 24 and 100 percent, respectively. The dynamic extraction conditions were designed to achieve marcketable differences in the fluid solvent power. Fractions were characterized by total uv absorption and fluorescence emission. Under optimum conditions, fractions were collected and characterized by uv absorbance ratio at λ 400/λ 254 nm using non-column HPLC with uv PDA detector. The average total mass recovery of all three fractions was 102 % and coefficient of variation of 6.8%. The first ...