Guy W. Sewell

Water quality at five marinas in Lake Texoma as related to methyl tert-butyl ether (MTBE).

Water quality in five marinas on Lake Texoma, located on the Oklahoma and Texas border, was monitored between June 1999 and November 2000. Focus was to evaluate lake water associated with marinas for methyl tert-butyl ether (MTBE). Lake water was collected at locations identified as marina entrance, gasoline filling station, and boat dock. Occurrence of MTBE showed a direct seasonal trend with recreational boating activity at marina areas. There was a positive correlation with powerboat usage ratio, which was directly related to the gallons of gasoline sold. Sampling before and after the high boat use holiday weekends determined the apparent influence of powerboat activity on MTBE contamination. Boat dock locations were the most sensitive sites to MTBE contamination, possibly due to gasoline spillage during engine startup. The most common compound of the BTEX series found with MTBE was toluene and co-occurrence was most frequent at gasoline filling stations.

Kinetics of chromate reduction during naphthalene degradation in a mixed culture

A mixed culture of Bacillus sp. K1 and Sphingomonas paucimobilis EPA 505 was exposed to chromate and naphthalene. Batch experiments showed that chromate was reduced and naphthalene was degraded by the mixed culture. Chromate reduction occurred initially at a high rate followed by a decrease in rate until chromate reduction ceased. Chromate reduction decreased in the mixed culture when a lower ratio of S. paucimobilis EPA 505 to Bacillus sp. K1 was utilized. A kinetic model incoporating a term for the cell density ratio is proposed to describe chromate reduction in the mixed culture under both chromate limited and electron donor limited conditions. The validity of the model, and its parameter values, was verified by experimental data generated under a variety of initial population compositions and a broad range of chromate concentrations. The consistent result of experimental data with model predictions implies that the model is useful for evaluating the interactions and the use of mixed culture for chromate removal.

Determination of chloroethenes in environmental biological samples using gas chromatography coupled with solid phase micro extraction

SummaryAn analytical method has been developed to determine the chloroethene series, tetrachloroethene (PCE), trichloroethene (TCE),cisdichloroethene (cis-DCE) andtransdichloroethene (trans-DCE) in environmental biotreatment studies using gas chromatography coupled with a solid phase micro extraction (SPME) technique. The volatile chlorinated compounds in aqueous solution can be analyzed directly without solvent extraction, purge and trap, or thermal heating. The calibration curves have demonstrated good linear relationships within 50.0 to 3000.0 μg L−1 concentration range. Detection limits are 18.0, 5.0, 25.0, and 42.0 μg L−1, for PCE, TCE,cis-DCE andtrans-DCE, respectively. Factors which affect the SPME process, such as sample adsorption time, thermal desorption time, and concentration of salt in the matrix, have also been evaluated.

AN IMPROVED METHOD OF HYDROGEN PRODUCTION AS ELECTRON DONOR FOR ANAEROBIC BIOREMEDIATION

This paper investigated an improved electrochemical approach that is able to provide hydrogen for anaerobic bioremediation of chloroethenes in subsurface. Hydrogen is the ultimate electron donor of biodechlorination processes. In experiments, iron wire was used as electrodes, an anaerobic bacteria enrichment collected from a site contaminated with chloroethenes as test microbes, perchloroethylene (PCE) as model chloroethene. Experiments were conducted by switching the polarities of electrodes periodically and supplying electrical power in an intermittent way. The results showed that an electrochemical bioreactor that was switched 1 time/10 min and operated only 8 h a day was able to produce more hydrogen than that operated 24 h a day at 0.4 V without polarity switching, stimulating microbial growth more effectively. The intermittent operation also resulted in periodical release of overpotentials that built up on electrode surfaces, thus prevented charged ions and particles from attaching on electrodes. The hydrogen produced was available for microbial growth and PCE dechlorination. It is suggested that the improved electrochemical process developed in this study has significant implications to anaerobic bioremediation.

Simultaneous Determination of Chromate and Aromatic Hydrocarbons in Environmental Samples by Capillary Electrophoresis

Abstract An analytical method was developed to determine simultaneously, the inorganic anion CrO2− 4, and organic aromatic compounds including benzoate, 2-Cl-benzoate, phenol, m-cresol and o-/p-cresol by capillary electrophoresis (CE). Chromate and the aromatics were separated in a relatively short time with the use of a tetradecyltrimethylammonium bromide (TTAB) modified buffer solution. The detection limits of all the analytes were in the sub mg/L level with the consumption of a very small volume of sample (< 0.06 μL). Calibration curves with high regression coefficient (r2) values (0.999–1.000) were obtained within two orders of magnitude of concentrations. Factors affecting the separation and the determination of chromate and the organic aromatics, such as the buffer electrolyte concentration, the voltage applied and the TTAB concentration, were investigated. The effect of TTAB on the direction and the magnitude of the electroosmotic flow (EOF) was also discussed. A study of the microbial catalyzed ch...

Microbial utilization of vadose zone organic carbon for reductive dechlorination of tetrachloroethene

Abstract Aqueous extracts from a calcareous spodosol were used as the primary substrate to study the reductive dechlorination of tetrachloroethene (PCE). A comparison was made between extracts obtained using pure water and water saturated with trichloroethene (TCE). The latter solutions were intended to simulate solutions formed by rainwater percolating through TCE‐contaminated soils. The results indicated that TCE‐saturated water apparently mobilized more organic materials than did pure water. The extracts obtained from TCE‐saturated water were noticeably more turbid than those obtained using pure water, suggesting greater mobilization of colloids. After centrifugation, the extracts contained similar amounts of dissolved organic carbon (DOC), 16 and 20 mg/L, respectively. Microcosm studies indicated that both centrifuged extracts were capable of sustaining reductive dechlorination of PCE as evidenced by the production of TCE, dichloroethene (DCE), and methane. These results indicate that the inclusion of...