EPA Grant Number:
Title:
Investigator:
Institution:
EPA Project Officer:
Project Period:
Project Amount:
Research Category:
Objectives/Hypotheses:
The overall objective of this research is to investigate
the aerobic biodegradation of the synthetic chelating
agent ethylenediaminetetraacetic acid (EDTA) in a
controlled environment by using a combination of computer
modeling and laboratory experimentation. The specific
goal is to determine the effect of aqueous speciation on
EDTA biodegradation. We show that, in the absence of
nutritional or other growth limitations, EDTA
biodegradation in a single-phase batch reactor is highly
dependent on its aqueous speciation. Specifically, the
rate and extent of EDTA biodegradation are determined by
the concentration of a single complexed form of EDTA.
Rationale:
Forty years of nuclear reactor and
weapons manufacturing operations in the United States
have resulted in the subsurface co-disposal of
radioactive material and the synthetic chelating agents,
such as EDTA, that were originally used to clean the
equipment. Radioactivity has been detected in sediments
and groundwater away from the disposal sites indicating
that transport through the subsurface is occurring. The
presence of EDTA and its interaction with radioactive and
heavy metal ions are implicated in this transport. EDTA
forms stable, water-soluble complexes with metals
hindering their adsorption to soil particle surfaces.
Biodegradation of EDTA in these environments can lead to
enhanced adsorption and immobilization of the
radionuclides and heavy metals. However, limited research
on the biogeochemistry of such systems has made
specification of procedures for encouraging EDTA
biodegradation and preventing radionuclide migration
difficult.
Approach:
We are conducting a series of computer modeling trials
and laboratory experiments for a system consisting of
EDTA-metal complexes and an EDTA degrading microorganism
(BNC1, DSM 6780). We have modeled EDTA biodegradation in
the presence of metal ions with CCBATCH, a biogeochemical
computer model developed at Northwestern University.
CCBATCH couples equilibrium EDTA speciation reactions
with kinetically-controlled EDTA biodegradation reactions
to predict the concentration profiles of all
biologically-affected species over time. We are also
experimentally determining the rate and extent of EDTA
biodegradation in batch reactors using cultures of BNC1.
Cells are grown at 35 °C in agitated flasks containing a
defined mineral and vitamin medium until exponential
phase growth. The cultures are then washed and
re-suspended in media containing EDTA and metals. Biomass
is measured by correlating optical density measurements
with biomass dry weight. Total EDTA concentration is
measured by high-performance liquid chromatography.
Carbon dioxide produced from EDTA biodegradation is
monitored by acidification of the culture medium and
analysis of the carbon dioxide concentration in the
reactor headspace. In filtered culture media, dissolved
oxygen is measured by an oxygen microelectrode, ammonium
by an ammonium ion-selective electrode, and metals by
spectroscopy. We will compare experimental data with
CCBATCH output to aid in experimental data
interpretation, validate the model, and improve its
predictive capabilities. Once optimized, CCBATCH can be
used to accurately predict the EDTA biodegradation rate
in a wide variety of aqueous environments.
Status:
Pre-experimental modeling has been completed. Laboratory
experiments are in progress. It is expected that the
research will be competed in late 2000.
Expected Results:
Papers and Publications:
Supplemental Keywords:
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