Development of Bioavailability and Biokinetics Determination Methods for Organic Pollutants in Soil to Enhance In-Situ and On-Site Bioremediation

Abstract

Determination of biodegradation rates of organics in soil slurry and compacted soil systems is essential for evaluating the efficacy of bioremediation for treatment of contaminated soils. In this paper, a systematic protocol has been developed for evaluating biokinetic and transport parameters in soil slurry and compacted soil bioreactors. The protocol involves abiotic evaluation of adsorption/desorption rates, and equilibria followed by the use of respirometry to determine biodegradation rates using soil slurry, wafer, and porous tube reactors. In the soil slurry reactor, mimicking ex-situ soil biotreatment, degradation occurs in the aqueous phase by suspended microorganisms and by immobilized microbiota present in the soil phase. In a soil wafer reactor, which consists of a thin layer of soil, biodegradation occurs primarily in the soil phase, as compared to the aqueous phase, which consists of free and bound water in and around the soil particles. The wafer reactor represents biotreatment using bioventing or land farming methods. In the porous tube reactor, rate of oxygen diffusion through the compacted soil affects the overall rate of biodegradation. The porous tube reactor represents in-situ biotreatment. Experiments were conducted to determine the cumulative oxygen uptake using an uncontaminated low organic carbon soil with phenol as the spiked contaminant. Detailed mathematical models were developed for each type of soil reactor (slurry, wafer, and porous tube), and these models were fitted to the cumulative oxygen uptake data to derive the best-fit transport and biokinetic parameters. Application of the transport and biokinetic parameters to determine the attainable treatment end points is discussed in this paper.