Grantee Research Project Results
2001 Progress Report: Role of Microbial Metabolism and Cometabolism in Treating Mixtures of Biodegradable and Nonbiodegradable Chemicals in Granular Activated Carbon Columns
EPA Grant Number: R826170Title: Role of Microbial Metabolism and Cometabolism in Treating Mixtures of Biodegradable and Nonbiodegradable Chemicals in Granular Activated Carbon Columns
Investigators: Speitel, Gerald E.
Institution: The University of Texas at Austin
EPA Project Officer: Aja, Hayley
Project Period: December 1, 1997 through November 30, 2000
Project Period Covered by this Report: December 1, 2000 through November 30, 2001
Project Amount: $304,688
RFA: Exploratory Research - Environmental Engineering (1997) RFA Text | Recipients Lists
Research Category: Safer Chemicals , Land and Waste Management
Objective:
Granular activated carbon (GAC) is widely used to treat water contaminated with synthetic organic chemicals (SOCs). Practically no information is available on combining adsorption and biodegradation to treat mixtures of biodegradable and nonbiodegradable SOCs, a very common problem. Furthermore, virtually no work has been completed on simultaneous metabolism and cometabolism of such mixtures. Biodegradation can increase the GAC service life and improve process performance relative to adsorption alone. This research project seeks to: (1) develop a better understanding of the effect of biodegradation on the service life of GAC columns; (2) identify conditions where metabolism of SOCs is advantageous; and (3) identify conditions where cometabolism of SOCs is advantageous.Progress Summary:
The focus of this past year's work was studying the effect of cometabolism on bioregeneration. To this end, several cometabolism-related background experiments were completed in preparation for running column experiments involving metabolism of toluene and cometabolism of trichloroethylene (TCE). Individual adsorption isotherms were performed on powdered activated carbon for both toluene and TCE. Duplicate isotherms were run and the parameters were within 95 percent confidence limits of each other. Two dual component competitive isotherms also were completed, and the results compared very well with Ideal Adsorbed Solution Theory (IAST) predictions. In both dual component isotherms, the experimental data and IAST predictions were within 95 percent confidence limits of each other. To test pore surface diffusion model (PSDM) predictions of the kinetics of toluene and TCE desorption in a continuous-flow column, a toluene and TCE desorption experiment was performed. The PSDM predictions matched the data reasonably well, although they did slightly underpredict the desorption rate.Toluene-degrading bacteria, consisting of a Pseudomonas species and Rhodococcus
rhodochrous have been cultured. Dual component kinetic experiments were run
with toluene and TCE, where toluene oxygenase enzymes produced via the toluene
degradation pathway degraded TCE (i.e., cometabolism). Results showed that very
little competitive inhibition exists between toluene and TCE at the concentrations
used in the experiments, because there was no visible lag in the initiation
of TCE cometabolism. This is an important finding because enzyme competition
can minimize the usefulness of a cometabolism-based biologically active column.
In further experiments, the TCE cometabolism rate was found to increase, without
a lag in initiation, in the presence of increasing initial toluene concentrations
(up to at least 1.2 mg/L toluene). To increase the TCE cometabolism rate, iron
was added to the culture during growth. In the presence of iron, the toluene
degradation rate increases somewhat. The TCE cometabolism rate, however, is
significantly faster in the presence of iron (4.5 times), essentially making
iron an on-off switch for TCE cometabolism. Using the background adsorption and biodegradation data along with the model,
several cometabolism-based biologically active columns will be designed and
run. It will be necessary to distinguish between the relative contributions
of metabolism and cometabolism to bioregeneration to understand the significance
of cometabolism to process performance. This will be performed by using radiolabeled
SOCs to track metabolism and cometabolism through the concentration of radiolabeled
carbon dioxide that is produced as a result of biodegradation. In general, two
GAC columns will be run simultaneously. In one column, the SOC undergoing cometabolism
will be radiolabeled, while in the other column, the SOC undergoing metabolism
will be radiolabeled. Thus, the biodegradation rates for each chemical will
be measured in parallel experiments. Besides GC and radioactive analyses, toluene
dioxygenase production will be measured spectrophotometrically and the SOC loading
at the end of the column runs will be measured using methanol extraction. A
virgin GAC experiment will be run to culminate the cometabolism study. Two columns
will be run simultaneously, one with the culture grown with iron and one with
the culture grown without iron, so that the increase in service life due to
metabolism and cometabolism can be fully appreciated. This research will fill a significant gap in our knowledge about GAC treatment,
a gap that has economic, process performance, and health ramifications. Biodegradation/
adsorption systems are potentially less costly because the GAC service life
can be longer than with adsorption alone. Ignorance of the process fundamentals
has stymied technological advances beyond the current practice of considering
only adsorption. This work will provide the fundamental information needed to
stimulate innovation in treating mixtures of biodegradable and nonbiodegradable
SOCs or cometabolites. This research will develop a comprehensive experimental
database on the performance of biodegradation/adsorption systems in treating
mixtures of biodegradable and nonbiodegradable SOCs or cometabolites, and will
provide guidance on when biodegradation is attractive relative to adsorption
alone and to what extent the GC service life can be increased. The first data
on cometabolism in GAC columns will be developed and verification of the cometabolism
simulation model will be possible. With this research, sufficient data will
be available to assess biodegradation/adsorption systems with confidence and
to indicate under what circumstances they are competitive with other treatment
processes.
Future Activities:
The next series of experiments to be conducted will focus on continuous-flow TCE
cometabolism. Ongoing investigations involve transformation capacity experiments
for both the iron-fed and non iron-fed cultures as well as a Journal Articles:
No journal articles submitted with this report: View all 9 publications for this project
Supplemental Keywords:
water, adsorption, bioregeneration, bioremediation, innovative technology, synthetic organic chemicals, cometabolism., RFA, Scientific Discipline, Water, Ecological Risk Assessment, Environmental Chemistry, Wastewater, Bioremediation, Environmental Engineering, gas chromatography, cometabolism, kinetic studies, water quality, bioregeneration, granular activated carbon, biodegradation, fate and transport, water treatment, mathematical modelingRelevant Websites:
http://www.ce.utexas.edu/prof/speitel/home.html 
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.