Linear alkylbenzenesulfonate (LAS) is the most widely used anionic surfactant in
commercial detergent formulations. The environmental fate of LAS is of interest because
of its disposal to wastewater treatment facilities and subsequent occurrence as a
micropollutant in surface waters and groundwater. While LAS fate in wastewater
treatment systems and surface waters is well-documented, few studies describe LAS fate
in groundwater. This work investigates the transport and biodegradation of LAS in
sewage-contaminated groundwater using natural-gradient pulsed and continuous field
tracer tests and laboratory column experiments. An "in-vial" disk elution technique that
couples solid phase extraction disk elution of LAS as tetrabutylammonium ion pairs with
injection-port derivatization was developed for the determination of LAS in groundwater.
Pulsed tracer tests then were conducted in an aerobic (~9 mg/L dissolved oxygen)
uncontaminated zone, and a moderately aerobic (~1 mg/L dissolved oxygen), sewage-contaminated
zone. A continuous injection test also was conducted in the sewage-contaminated
zone. Chromatographic separation of the surfactant mixture was observed
and attributed to the greater retardation of the longer alkyl chain homologs during
transport. In the sewage-contaminated groundwater, biodegradation preferentially
removed the longer alkyl chain homologs and external isomers resulting in LAS mixtures
that were enriched in the more mobile and biologically-resistant components. LAS mass
removal coincided with a decrease in dissolved oxygen concentrations, the appearance of
LAS metabolites, and an increase in the number of free-living bacteria. The composition of
the LAS mixture changed in the continuous field and column experiments and
biodegradation rates increased as dissolved oxygen concentration increased. Mass removal
rates were generally 2-3 times greater in the column experiments than in the field for
similar dissolved oxygen concentrations. Rate constants for the continuous and pulsed
tests conducted in the field were comparable indicating that increased exposure time of the
aquifer sediments to the LAS did not increase biodegradation rates. / Graduation date: 1998
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/34020 |
| Date | 05 December 1997 |
| Creators | Krueger, Carolyn J. |
| Contributors | Field, Jennifer A. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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