C.J. Krueger | USGS Science

USGS1998

Biodegradation of the surfactant linear alkylbenzenesulfonate in sewage-contaminated groundwater: A comparison of column experiments and field tracer tests

Transport and biodegradation of linear alkylbenzenesulfonate (LAS) in sewage-contaminated groundwater were investigated for a range of dissolved oxygen concentrations. Both laboratory column and an 80-day continuous injection tracer test field experiments were conducted. The rates of LAS biodegradation increased with increasing dissolved oxygen concentrations and indicated the preferential biodegradation of the longer alkyl chain LAS homologues (i.e., C12 and C13) and external isomers (i.e., 2-and 3- phenyl). However, for similar dissolved oxygen concentrations, mass removal rates for LAS generally were 2-3 times greater in laboratory column experiments than in the field tracer test. Under low oxygen conditions (<1 mg/L) only a fraction of the LAS mixture biodegraded in both laboratory and field experiments. Biodegradation rate constants for the continuous injection field test (0.002-0.08 day-1) were comparable to those estimated for a 3-h injection (pulsed) tracer test conducted under similar biogeochemical conditions, indicating that increasing the exposure time of aquifer sediments to LAS did not increase biodegradation rates.Transport and biodegradation of linear alkylbenzenesulfonate (LAS) in sewage-contaminated groundwater were investigated for a range of dissolved oxygen concentrations. Both laboratory column and an 80-day continuous injection tracer test field experiments were conducted. The rates of LAS biodegradation increased with increasing dissolved oxygen concentrations and indicated the preferential biodegradation of the longer alkyl chain LAS homologues (i.e., C12 and C13) and external isomers (i.e., 2- and 3-phenyl). However, for similar dissolved oxygen concentrations, mass removal rates for LAS generally were 2-3 times greater in laboratory column experiments than in the field tracer test. Under low oxygen conditions (<1 mg/L) only a fraction of the LAS mixture biodegraded in both laboratory and field experiments. Biodegradation rate constants for the continuous injection field test (0.002-0.08 day-1) were comparable to those estimated for a 3-h injection (pulsed) tracer test conducted under similar biogeochemical conditions, indicating that increasing the exposure time of aquifer sediments to LAS did not increase biodegradation rates.

Environmental Science & Technology↗

USGS1998

Fate and transport of linear alkylbenzenesulfonate in a sewage- contaminated aquifer: A comparison of natural-gradient pulsed tracer tests

Two natural-gradient tracer tests were conducted to determine the transport and biodegradation behavior of linear alkylbenzenesulfonate (LAS) surfactant under in situ conditions in a sewage-contaminated aquifer. The tests were conducted in two biogeochemically distinct zones of the aquifer: (1) an aerobic uncontaminated zone (oxic zone) and (2) a moderately aerobic, sewage-contaminated zone (transition zone). Chromatographic separation of the surfactant mixture was observed in both zones and attributed to the retardation of the longer alkyl chain homologues during transport. No significant loss of IAS mass was observed for the oxic zone while 20% of the LAS mass injected into the transition zone was removed due to biodegradation. Biodegradation preferentially removed the longer alkyl chain homologues and the external isomers (i.e., 2- and 3-phenyl). The removal of LAS mass coincided with a decrease in dissolved oxygen concentrations, the appearance of LAS metabolites, and an increase in the number of free-living bacteria with a concomitant change in bacteria morphology. The formation of LAS metabolites accounted for 86% of the LAS mass removed in the transition zone. Over the duration of the test, sorption and biodegradation enriched the LAS mixture in the more water-soluble and biologically resistant components.Two natural-gradient tracer tests were conducted to determine the transport and biodegradation behavior of linear alkylbenzenesulfonate (LAS) surfactant under in situ conditions in a sewage-contaminated aquifer. The tests were conducted in two biogeochemically distinct zones of the aquifer: (1) an aerobic uncontaminated zone (oxic zone) and (2) a moderately aerobic, sewage-contaminated zone (transition zone). Chromatographic separation of the surfactant mixture was observed in both zones and attributed to the retardation of the longer alkyl chain homologues during transport. No significant loss of LAS mass was observed for the oxic zone while 20% of the LAS mass injected into the transition zone was removed due to biodegradation. Biodegradation preferentially removed the longer alkyl chain homologues and the external isomers (i.e., 2- and 3-phenyl). The removal of LAS mass coincided with a decrease in dissolved oxygen concentrations, the appearance of LAS metabolites, and an increase in the number of free-living bacteria with a concomitant change in bacteria morphology. The formation of LAS metabolites accounted for 86% of the LAS mass removed in the transition zone. Over the duration of the test, sorption and biodegradation enriched the LAS mixture in the more water-soluble and biologically resistant components.

Environmental Science & Technology↗