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. 14C -radiochemical kinetic tests performed with TCE provided pseudo-first-order degradation rate constants for cultures grown with and without iron. This iron-dependent cometabolism finding allows for a control method to determine the contribution of cometabolism compared to that of metabolism in bioregeneration. Furthermore, the faster TCE cometabolism occurs, the faster additional adsorption sites on the GAC will be regenerated. Rapid onset of cometabolism should further increase the GAC column service life.
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 14C C-radiolabeled toluene endogenous decay experiment for the iron-fed culture (one already has been completed for the non iron-fed culture). In addition, this research will work on updating the biodegradation/adsorption kinetic model described in Speitel, et al. (1989), with equations from a current cometabolism model (Anderson and McCarty, 1994) so that the kinetic model can account for competitive inhibition and possibly intermediate toxicity, although toxicity would be a more complicated addition to the model.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.
Journal Articles:
No journal articles submitted with this report: View all 9 publications for this projectSupplemental Keywords:
water, adsorption, bioregeneration, bioremediation, innovative technology, synthetic organic chemicals, cometabolism., RFA, Scientific Discipline, Water, Environmental Chemistry, Wastewater, Bioremediation, Ecological Risk Assessment, Environmental Engineering, fate and transport, biodegradation, cometabolism, gas chromatography, bioregeneration, kinetic studies, granular activated carbon, water quality, mathematical modeling, water treatmentRelevant 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.