Bioavailability and biodegradation kinetics protocol for organic pollutant compounds to achieve environmentally acceptable endpoints during bioremediation.

Abstract

This paper is an extension of our previous studies on quantitating biodegradation kinetics in soil slurry and compacted soil systems. Previous studies had mainly used phenol as a test contaminant. Phenol represents hydrophilic compounds which exhibit high water solubility and low soil sorption characteristics. This paper extends the experimental protocol using polycyclic aromatic hydrocarbons (PAHs) as the test contaminants. PAHs are hydrophobic compounds with low water solubility and exhibit significant partitioning in soil organic carbon. Degradation rates of PAHs are much slower, thereby requiring acclimation of indigenous soil microbiota using microcosm reactors. The experimental protocol, elaborated in this paper, results in the measurement of biokinetic parameters which can be used to quantitate both ex situ and in situ bioremediation rates and assess the attainable endpoints. Biodegradation studies were conducted for naphthalene using soil slurry, soil wafer, and soil column reactors. Microcosm reactors were set-up to acclimate soil microbiota, and carbon dioxide evolution was used as a measure of acclimation. It was found that reasonable degree of PAH acclimation was achieved after 250 days of microcosm operation. Abiotic adsorption/desorption studies showed that equilibrium was achieved in about 20 hours and approximately 45% of the initial amount of naphthalene is adsorbed by the time equilibrium is attained. Further, desorption was much slower than adsorption with equilibrium being attained in 40 hours. Biokinetic parameters were derived from the cumulative oxygen uptake data of soil slurry, wafer, and column reactors using detailed mathematical models. The cumulative oxygen uptake in all three reactors were almost the same, since naphthalene primarily degraded in the soil phase and the extent of degradation in the aqueous phase was small.