Grantee Research Project Results
Final 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 Amount: $304,688
RFA: Exploratory Research - Environmental Engineering (1997) RFA Text | Recipients Lists
Research Category: Safer Chemicals , Land and Waste Management
Objective:
The objectives of this research project were to: (1) develop a better understanding of the effect of biodegradation on the service life of granular activated carbon (GAC) columns; (2) identify conditions where metabolism of synthetic organic chemicals (SOCs) is advantageous; and (3) identify conditions where cometabolism of synthetic organic chemicals (SOCs) is advantageous.
GAC widely is used to treat water contaminated with 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 done on simultaneous metabolism and cometabolism of such mixtures. Biodegradation can increase the GAC service life and improve process performance relative to adsorption alone.
Summary/Accomplishments (Outputs/Outcomes):
This research was split into two phases, the first focused on metabolism and the second focused on cometabolism on bioregeneration. In the first phase, SOCs over a broad range of characteristics were studied and characterized. Toluene-degrading bacteria, consisting of a Pseudomonas species and Rhodococcus rhodochrous, were cultured. Batch adsorption isotherms (single and dual component), batch kinetic assays, and column adsorption experiments were run to determine basic adsorption and biodegradation data needed to predict behavior in biologically activated GAC column experiments. Two pairs of biodegradable and nonbiodegradable SOCs ultimately were chosen to perform further tests (toluene and perchloroethylene; and benzene and carbon tetrachloride). Several exhausted (preequilibrated), metabolism-only biologically activated carbon (BAC) column experiments were run with varying empty bed contact times (EBCTs), SOC concentrations, and GAC adsorbabilities. In addition, plugs of GAC that were preequilibrated with radiolabeled toluene or benzene (the biodegradable SOCs) were placed at the effluent end of some columns to track the end products of biodegradation. Tracking the formation of 14CO2 allowed for the determination of the overall extent of bioregeneration at the effluent end.
Overall, experiments with exhausted GAC columns demonstrated that bioregeneration of the GAC led to increased adsorption capacity for nonbiodegradable SOCs through decreased competition for adsorption sites. The extent of bioregeneration for toluene and benzene ranged from 28.8 to 45.5 percent in 13 to 14.5 days in these experiments, which is larger than was seen in previous experiments with single chemical systems. In addition, biological activity on GAC likely is to yield greater benefits, with respect to nonbiodegradable SOC removal for moderately adsorbable chemicals. These benefits will increase with increasing concentration. Biodegradable chemicals of low adsorbability also yield a large extent of bioregeneration, but biodegradation of such chemicals does not seem to provide a lot of additional adsorption capacity for nonbiodegradable SOCs. Presumably, the improvement is not as great simply because these chemicals do not have as large an affinity for the GAC surface, so their biodegradation does not reopen as many adsorption sites. Bioregeneration, and the increase in adsorption capacity for nonbiodegradable SOCs, also were a function of the empty bed contact time. Both occurred to a lesser extent in the shorter columns because the liquid phase concentration was not as low as in the longer EBCT columns. Therefore, the concentration gradient for desorption of the biodegradable SOC was not as large.
For the second phase of the research, several cometabolism-related background experiments were completed in preparation for running column experiments involving metabolism of toluene and cometabolism of trichloroethylene (TCE). Individual and dual 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. 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 slightly under predicted the desorption rate. 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). Two almost identical BAC columns then were run, one with a radiolabeled toluene element, and the other with a radiolabeled TCE element. This setup allowed for the determination of the extent of both metabolism-based and cometabolism-based bioregeneration at the effluent end of the columns.
Results showed that very little competitive inhibition exists between toluene and TCE at the concentrations used in the experiments. This was an important finding since enzyme competition can minimize the usefulness of a cometabolism-based biologically active GAC 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. To increase the TCE cometabolism rate, iron was added to the culture during growth. In the presence of iron, the TCE cometabolism rate significantly was faster (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 rates for cultures grown with and without iron. Transformation capacity experiments indicated little or no intermediate toxicity from TCE cometabolism, which is beneficial because the greater the toxicity, the more enzymes or cells will be inactivated and the slower the TCE cometabolism rate. Furthermore, keeping a sufficient level of dissolved oxygen in a BAC column was important in maximizing the potential rate of either metabolism or cometabolism-based bioregeneration. Both the metabolism of the toluene, and the cometabolism of the TCE, renewed adsorption sites in the BAC columns. Similar to what occurred in the metabolism-only experiments, there was an increased adsorption capacity for any noncometabolized TCE because of the decreased competition for adsorption sites. The metabolism and cometabolism-based bioregeneration ranged from 37 percent to 39 percent and 3.2 percent to 7.5 percent in 7-28 days, respectively. In addition, the NADH level was fairly consistent across the length of the columns, whereas the biomass-normalized enzyme activity decreased across the column. The greatest amount of TCE cometabolism was expected to be in the location of the greatest enzyme activity. Therefore, the extent of bioregeneration increased as the EBCT decreased, because the radiolabeled element moved closer to the influent, where the enzyme activity was highest.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 9 publications | 1 publications in selected types | All 1 journal articles |
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Putz A, Losh D, Speitel Jr. G. Removal of nonbiodegradable chemicals from mixtures during granular activated carbon bioregeneration. Journal of Environmental Engineering 2005;131(2):196-205. |
R826170 (Final) |
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Supplemental Keywords:
water, adsorption, bioregeneration, bioremediation, innovative technology, synthetic organic chemical, SOC, chlorinated solvent, toluene, trichloroethylene, TCE, granular activated carbon, GAC, biologically activated carbon, BAC, cometabolism., RFA, Scientific Discipline, Water, Wastewater, Environmental Chemistry, 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/ Exit
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.