Biodegradation of Desorption -Resistant Organic Contaminants in Wetland Soils.

Abstract

Contaminant bioavailability depends on physicochemical processes such as adsorption/desorption, diffusion, and dissolution. The rates of sorption and desorption of trichloroethylene (TCE) and 1,3-Dichlororbenzene (1,3-DCB) were studied. Desorption kinetics of 3-month and 5-month old contaminated soils showed that progressively less amount of contaminant was available for facile desorption compared to freshly contaminated soil in an empirical non-linear model. Microcosm batch studies were conducted to study the biodegradation of 1,3-DCB in the aqueous and soil phase containing a freshly contaminated soil and a soil containing only the desorption resistant fraction. The presence of the soil reduced the rates of biodegradation. It is clear that from the freshly contaminated soil, 1,3-DCB readily desorbed into the aqueous phase and was bioavailable from microbial consumption whereas for the soils containing the desorption-resistant 1,3-DCB, mass transfer into the aqueous phase limited the contaminant availability. Biodegradation of TCE by toluene-degrading bacteria was measured under aerobic conditions in aqueous and soil-slurry batch microcosms containing a freshly contaminated soil and a soil containing only the desorption resistant fraction of TCE. Presence of soil resulted in biodegradation rates substantially lower than those determined in the absence of soil. An appreciable increase in the rate and extent of determined in the absence of soil. An appreciable increase in the rate and extent of TCE biodegradation was observed in microcosms when toluene was added multiple times. The availability of CB-sorbed soils to CB degrading bacteria was assessed using a kinetic mineralization assay. It was demonstrated that soil-sorbed CB was available to CB-degrading bacteria, and that the extents of bioavailability of soil-sorbed CB decreased with prolonged aging. The rates of sorption and desorption of 1,4-DCB depend on aging, and soil types, and were investigated with the aid of Freundlich isotherm. According to a hysteresis index, hysteresis was not necessarily correlated with aging. Desorption isotherms demonstrated that desorption patterns in marsh soil were linear than in PPI soil even when the contaminant was aged. Bioavailability of 1,4-DCB was occurred both in freshly bounded into soil as well as in desorption resistant fraction in soils without a distinctive difference in two fractions. No significant differences in biodegradation were monitored in different wetland soil types containing various organic fractions.