Biodegradation of Metal-Ethylenediaminetetraacetic Acid (EDTA) Complexes: Modeling and Experimental StudiesEPA Grant Number: U915188
Title: Biodegradation of Metal-Ethylenediaminetetraacetic Acid (EDTA) Complexes: Modeling and Experimental Studies
Investigators: Willett, Anna I.
Institution: Northwestern University
EPA Project Officer: Carleton, James N
Project Period: January 1, 1997 through January 1, 2000
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1997) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Engineering and Environmental Chemistry , Fellowship - Chemical Engineering
The overall goal of this research project 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 objective 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.
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 also are 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 resuspended 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.