Effect of sorption and desorption resistance on aerobic trichloroethylene biodegradation in soils

Abstract

Biodegradation of trichloroethylene (TCE) by toluene-degrading bacteria was measured under aerobic conditions in aqueous and soil-slurry batch microcosms. For soil-phase experiments, a freshly contaminated soil and a soil containing only the desorption-resistant fraction of TCE were tested. In both cases, presence of soil resulted in biodegradation rates substantially lower than those determined in the absence of soil. In aqueous-phase experiments, an appreciable increase in the rate and extent of TCE biodegradation was observed in microcosms when toluene was added multiple times. The TCE degradation rates were clearly correlated with toluene dioxygenase (TOD) enzyme activity over time, thus providing an indication of the cometabolic pathway employed by the microbial population. In soil-slurry experiments containing freshly contaminated soil, a TCE degradation rate of approximately 150 microg TCE/kg/h was observed during the first 39-h period, and then the TCE degradation rate slowed considerably to 0.59 and 0.84 microg TCE/kg/h for microcosms receiving one and two additions of toluene, respectively. The TCE degradation rates in soil-slurry microcosms containing the desorption-resistant fraction of TCE-contaminated soil were approximately 0.27 and 0.32 microg TCE/kg/h in microcosms receiving one and two additions of toluene, respectively. It is clear from these results that mass transfer into the aqueous phase limited bioavailability of TCE in the contaminated soil.

Desorption Kinetics of Benzene in a Sandy Soil in the Presence of Powdered Activated Carbon

“…Each flask was allowed to have fine fractions of PAC settled for two days and then the supernatant was decanted to the extent possible and the residual water determined by weight. The desorption process was initiated by adding fresh deionized water to reflect as much possible as the natural conditions that exist during desorption as reported by Lee et al (2002a) and Lee et al (2002b). Triplicate soil slurries were prepared for each soil using desorption procedure described above.…”

“…Both the intercept and slope of desorption isotherms increase with increasing PAC. According to Lee et al (2002a) and Lee et al (2002b), the linear desorption isotherm consists of: (1) a reversible portion q r obeying the conventional linear isotherm, (2) a desorption resistant component q irr . Thus q tot ¼ q irr þ q r .…”

“…This type of model was used by Lee et al (2002a) and Lee et al (2002b) to study the desorption kinetics of both freshly contaminated soils (three days) and aged contaminated soils (three-and five-month old). They reported that the nonlabile fraction increased with increasing contaminant age.…”

“…As pointed out by Lee et al (2002a) and Lee et al (2002b), this would be impractical for volatile compounds since losses by volatilization and biodegradation are inevitable for such long-term studies. For soils with a significant desorption-resistant fraction and/or slow desorption kinetics, therefore, it would be better to modify the biphasic model [Eq.…”

“…The sorption-desorption characteristics including irreversibility, time-dependency, and degree of sorption and desorption hysteresis are interrelated to some extent and important factors affecting the fate of highly soluble hydrocarbons such as BTEX in the subsurface. The desorption characteristic is the important factor to determine the magnitude of irreversibly adsorbed or desorption-resistant fraction of contaminants and to influence on the sequestration (Abu & Smith, 2005;Alexander, 2000;Carroll et al, 1994;Connaughton et al, 1993;Cornelissen et al, 1997;McGroddy & Farrington, 1995;Northcott & Jones, 2001;Pavslostathis & Mathavan, 1992;ten Hulscher et al, 1999) and biodegradation (Alexander, 1995;Kraaij et al, 2001;Lee et al, 2002a;Lee et al, 2002b;Lueking et al, 2000;Nam et al, 1998;White et al, 1999) of contaminants in soils.…”