Project Abstract

In-Situ Bioremediation of Organic Compounds: Coupling of Mass Transfer and Biodegradation

Principal Investigators

Dr. Gordon A. Lewandowski
New Jersey Institute of Technology

Dr. Edward J Bouwer
John Hopkins University
E-mail: bouwer@jhu.edu

Goal

Develop predictive/diagnostic tools that better account for the interaction between mass transfer and biokinetic effects
Conduct bench-scale experiments to calibrate the model
Collect field data to validate the model

Rationale

In-situ bioremediation is an extremely important technology for the cost-effective treatment of contaminated soils. Trial-and-error methods of implementing this complex process at a field scale are very inefficient. It is therefore important to develop reliable engineering models that can analyze in-situ treatment options prior to field testing, and can diagnose problems in the field. At present, a critical deficiency is the ability to assess the relative importance of mass transfer (bioavailability) vs. kinetic (biodegradation) effects.

Approach

Two similar models have been developed. One uses a biofilm approach incorporating three compartments: soil particle, biofilm, and groundwater, with mass transfer between compartments. The other model is a porous biocatalyst approach in which the soil is divided into two compartments: an aggregate phase consisting of agglomerated soil particles with relatively stagnant fluid in the interstices, and a mobile phase consisting of groundwater moving between the soil aggregates. Sorption (linear or non-linear), biodegradation (inhibitory or non-inhibitory), and diffusion occur in the aggregate phase. Convective transport occurs in the mobile phase, with mass transfer between the two compartments. Most of the model parameters (such as kinetic rate constants, and sorption constants) are determined in batch experiments. Soil columns are then used to adjust remaining parameters and measure the axial distribution of contaminant. A site of the Baltimore Gas & Electric Co. is being used to field test the model results, and adjust the model as necessary. This site is primarily contaminated with PAHs. Consequently, naphthalene and phenanthrene are currently being used as model pollutants.

Status

Biokinetic parameters have been obtained for naphthalene degraders, and soil microcosms from the Baltimore Gas & Elecetric site have been examined for their ability to degrade PAHs under both aerobic and nitrate-reducing conditions. Numerical solutions of the mathematical models have been obtained, and parameter sensitivity studies conducted. Soil columns have been prepared, and bench-scale experiments initiated.