Intrinsic and bioaugmented aerobic trichloroethene degradation at seven sites

Abstract

Trichloroethene (TCE) is one of the most prevalent contaminants in groundwater pollution worldwide. Aerobic-metabolic degradation of TCE has only recently been discovered at one field site. It has significant advantages over aerobic co-metabolism because no auxiliary substrates are required, and the oxygen demand is considerably lower. This study investigated the intrinsic degradation potential as well as the stimulation potential by bioaugmentation in microcosm experiments with groundwater from seven different sites contaminated with chloroethenes. An enrichment culture metabolizing TCE aerobically served as inoculum. The groundwater samples were inoculated with liquid culture in mineral salts medium as well as with immobilized culture on silica sand. Additionally, some samples were inoculated with groundwater from the site where the enrichment culture originated. The microcosms without inoculum proved the occurrence of aerobic TCE-metabolizing bacteria stimulated by the supply of oxygen in 54% of the groundwater samples. TCE degradation started in most cases after adaptation times of up to 92 d. The doubling time of 24 d indicated comparatively slow growth of the aerobic TCE degrading microorganisms. Bioaugmentation triggered or accelerated TCE-degradation in all microcosms with chlorothene concentrations below 100 mg L^-1. All inoculation strategies (liquid and immobilized enrichment culture or addition of groundwater from the active field site) were successful. Our study demonstrates that aerobic-metabolic TCE degradation can occur and be stimulated across a broad hydrogeologic spectrum and should be considered as a viable option for groundwater remediation at TCE-contaminated sites.

Keywords: Aerobic biodegradation; Chloroethenes; Doubling time; Groundwater remediation; TCE; TCE, trichlorethene.

Fig. 1

TCE concentrations of a microcosm series from site 5 (well I) showing intrinsic degradation without inoculum (□) and without inoculum with mineral nutrient addition (■), compared to the sterile control (∗). TCE was spiked on day 133 (↓). Error bars represent the standard deviation of duplicate measurements.

Fig. 2

Cumulative chloride formation in a microcosm without inoculation from site 5 (well K) measured (□) and stoichiometrically calculated from TCE decrease (◯) with determination of doubling time in exponential phase (■) during aerobic TCE degradation (♦). Error bars represent the standard deviation of duplicate measurements.

Fig. 3

TCE concentrations of a microcosm series from site 4 (well G) without inoculum showing stimulated TCE degradation (□) compared to the sterile control (∗) after nutrient addition (). Error bars represent the standard deviation of duplicate measurements.

Fig. 4

TCE concentrations of a microcosm series from site 4 (well E) without intrinsic degradation (□) and stimulated degradation with liquid (◯) and immobilized culture on silica sand (△) as well as with SF water (◇) compared to sterile control (∗), nutrients were added () with spiking TCE (↓) on day 210. Error bars represent the standard deviation of duplicate measurements.

Fig. 5

Cumulative Chloride formation (□) of a microcosm with liquid culture and additional nutrients from site 4 (well E) during aerobic TCE degradation (♦) and cumulative chloride formation calculated stoichiometrically from the TCE decrease (◯). Nutrients were added () with spiking TCE (↓) on day 210. Error bars represent the standard deviation of duplicate measurements.