Grantee Research Project Results
2004 Progress Report: Treatment of Perchlorate Contaminated Water Using a Combined Biotic/Abiotic Process
EPA Grant Number: R831276C010Subproject: this is subproject number 010 , established and managed by the Center Director under grant CR831276
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: UT Center for Infrastructure Modeling and Management
Center Director: Hodges, Ben R.
Title: Treatment of Perchlorate Contaminated Water Using a Combined Biotic/Abiotic Process
Investigators: Katz, Lynn , Speitel, Gerald E.
Institution: The University of Texas at Austin
EPA Project Officer: Aja, Hayley
Project Period: December 1, 2003 through November 30, 2004
Project Period Covered by this Report: December 1, 2003 through November 30, 2004
Project Amount: Refer to main center abstract for funding details.
RFA: Gulf Coast Hazardous Substance Research Center (Lamar University) (1996) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Targeted Research
Objective:
Perchlorate, a water contaminant that interferes with the thyroid’s ability to use iodine to produce growth hormones, has been found in groundwater in a number of states, including Texas and Alabama. Although perchlorate is not regulated by the U.S. Environmental Protection Agency (EPA) at this time, it is listed as one of the contaminants on the EPA Contaminant Candidate List 2 because of potential health concerns.
Anaerobic biodegradation is one of the most promising treatment technologies available. Indeed, a number of bacteria that are capable of using nitrate as an electron acceptor also are capable of using perchlorate. In addition, chemical treatment techniques such as chemical reduction appear to be favorable based on equilibrium calculations; however, perchlorate removal using this process has not been effective because of extremely slow rates of reaction.
This research is designed to evaluate one potential treatment/remediation scheme that involves a combined biotic/abiotic process using zero valent iron (iron filings) and anaerobic bacteria. Preliminary research in our laboratory using the combined system for perchlorate remediation supports this hypothesis but also highlights the need for further research. Several research issues must be addressed to develop this technology: (1) microbial kinetics; (2) water and soil chemistry characteristics as they affect both the ability to control pH and minimize passivation of the iron surface; and (3) process design and operating considerations in meeting the desired treatment goals (i.e., usually < 4 µg/L).
The overall research plan that we envision to complete an evaluation of this project is comprised of three phases. Phase I will provide an improved understanding of the biodegradation process by extending our preliminary work to determine the kinetics of biodegradation at lower perchlorate concentrations and in the presence of varying nitrate concentrations. Phase II will focus on the chemistry aspects of the process, studying the impact of water and soil chemistry characteristics on pH stability and iron passivation. Research in Phases I and II utilizes batch reactors. In Phase III, we will demonstrate performance of the combined Fe(0)/biological process in continuous-flow, laboratory-scale column experiments, based on the information developed in Phases I and II. Several columns will be run in parallel to compare the performance under different conditions of water and soil chemistry. The columns will be packed with either Fe(0) or mixtures of Fe(0) and subsurface soil. In all phases, perchlorate and its degradation products, hydrogen, nitrate, pH, and iron will be measured using standard analytical methods. These studies will allow us to evaluate both in situ remediation and ex situ treatment of perchlorate contaminated waters. The effort has focused primarily on Phase I.
Progress Summary:
Biodegradation Experiments
In preliminary work to date, we have isolated consortia of autotrophic organisms capable of reducing perchlorate using hydrogen gas as the energy source and inorganic carbon as the carbon source. The microbial cultures were maintained in either a 2 L bioreactor or in batch reactors consisting of 250 mL amber glass bottles equipped with Mininert valves. The bacteria were incubated in an oxygen-free environment at ambient temperature and supplied periodically with perchlorate, bicarbonate, hydrogen, a phosphate pH buffer, and basic inorganic nutrients.
Batch kinetics experiments utilized bacteria from either the bioreactor or the glass bottles. The bacteria were added to serum vials containing growth media with and without the presence of nitrate. During the hydrogen-limiting experiments, perchlorate was provided in excess (50 mg/L). The hydrogen concentration in the headspace was approximately 1, 2, or 3 percent by volume. In the perchlorate- and nitrate/perchlorate-limiting experiments, hydrogen was provided in excess by supplying 60 mL in the headspace initially and adding 10 mL of hydrogen to the headspace every time a 10 mL liquid sample was taken. The initial perchlorate concentrations were 50 µg/L, 100 µg/L, or 500 µg/L. Samples from these were collected over time and analyzed for perchlorate and hydrogen. Kinetic parameters were determined using the Monod equation:
where
S = substrate concentration (mg/L)
X = bacteria concentration (mg/L)
k = maximum specific growth rate (d-1)
Ks = half saturation coefficient (mg/L)
The application of the general form of the Monod equation depends on the fact that negligible growth takes place during the kinetics experiment; the kinetic parameters (k and Ks) can be estimated in this fashion only if no growth is observed during substrate degradation. Bacteria concentrations were estimated at the beginning and end of each kinetics experiment by measuring absorbance. There was assumed to be no growth during the experiment if the final absorbance value was within 10 percent of the initial value.
During the kinetics test, therefore, the biomass concentration was considered to be constant and the substrate concentration was monitored through time. Using the known values for X and S, the Problem Solver function in Microsoft Excel was used to estimate values for k and Ks that best modeled the substrate degradation observed during the experiment. The values of k and Ks, once known and established through many trials, are accepted widely as a description of the kinetics of biodegradation.
Results from the Hydrogen-Limited Kinetic Experiments
Results for several of the hydrogen-limited kinetic experiments presented in Figure 1 show that the bacteria in this experiment consumed hydrogen similar to what is expected from Monod kinetics, which calls for slower degradation rates as the concentration of the substrate (in this case, hydrogen) decreases. Slower degradation rates are defined by a less negative slope, which can be seen as the curve becomes more flat at lower concentrations and at later times. From these data, it appears that the maximum substrate utilization rate, the kinetics parameter k, is achieved in the bottles with 2 percent and 3 percent initial concentration.
Figure 1. Summary of Hydrogen-Limited Kinetics Experimental Data
Once the data were collected, a best-fit analysis was performed using the Microsoft Excel Problem Solver function to approximate values for Ks and k. The parameter values were estimated for each bottle individually such that the error between the data and the model for each bottle was minimized. Table 1 shows the results of parameters analysis for each data set, including measured initial concentrations, normalized residual sum of error (SR) values, and S0/Ks values
Table 1. Summary of Kinetic Parameters for the Hydrogen-Limited Experiments
Data Set Description | Measured Initial Concentration (µmol/L) |
Ks |
k |
SR |
S0/Ks (dimension-less) |
1% Initial (1) |
8.05 |
0.912 |
0.125 |
0.213 |
8.82 |
1% Initial (2) |
7.21 |
1.30 |
0.134 |
0.047 |
5.56 |
2% Initial (1) |
14.28 |
1.87 |
0.176 |
0.304 |
7.65 |
2% Initial (2) |
14.91 |
1.74 |
0.172 |
0.256 |
8.58 |
3% Initial (1) |
20.74 |
2.92 |
0.327 |
0.220 |
7.09 |
3% Initial (2) |
19.70 |
1.48 |
0.200 |
0.293 |
13.28 |
Table 1 shows that the bottle “3 percent Initial (2)” had the greatest S0/Ks value and therefore was considered the best estimate of the hydrogen-limited kinetic parameters. The parameter values from all the experiments are relatively similar, however, so the average values could be considered a valid overall estimate as well and also are shown in Table 2.
Table 2. Best Estimate of Kinetic Parameters for the Hydrogen-Limited Experiments.
|
Ks |
k |
Best Estimate |
1.48 |
0.200 |
Average of All Data Sets |
1.70 |
0.189 |
Standard Deviation |
0.68 |
0.073 |
Results of Perchlorate-Limited Kinetic Experiments
One of the primary goals of this research was to calculate the approximate rate at which perchlorate biodegradation can occur in water, and this was achieved by evaluating the Monod kinetic parameters for perchlorate. The initial perchlorate concentrations used in the batch kinetic experiments were 50 µg/L, 100 µg/L, and 500 µg/L, with two bottles at each concentration, as mentioned previously. From these data, experiments with initial concentrations of 100 µg/L and 500 µg/L were selected for evaluation of the kinetic parameters because the bacteria in those bottles were most successful at degrading perchlorate. A summary of the data and modeling results for these experiments is shown in Figure 2 and Table 3. Because the values for S0/Ks were not greater than five, there was a linear correlation between the parameters k and Ks for both data sets. The very low S0/Ks value in the 500 µg/L data set indicates the parameter values were relatively imprecise, and we currently are in the process of analyzing several additional sets of data that will be included in the final report.
Figure 2. Perchlorate-Limited Kinetics Data for Initial Concentrations of (a) 100 µg/L and (b) 500 µg/L
Table 3. Monod Kinetic Parameters for the Perchlorate-Limited Experiments
Data Set Description |
Measured Initial Concentration (µmol/L) |
Ks |
k |
SR |
S0/Ks (dimension-less) |
100 µg/L Initial Concentration |
0.91 |
0.272 |
0.0016 |
0.012 |
3.35 |
500 µg/L Initial Concentration |
4.90 |
3.386 |
0.0130 |
0.293 |
1.45 |
Future Activities:
We currently are in the process of analyzing several new sets of data and preparing the final report from the Phase I studies conducted for this project.
Journal Articles:
No journal articles submitted with this report: View all 1 publications for this subprojectSupplemental Keywords:
waste, ecological risk assessment, environmental engineering, hazardous waste, advanced treatment technologies, bioremediation, contaminated waste sites, groundwater contamination, petroleum contaminants, hydrocarbon,, RFA, Scientific Discipline, Water, Waste, Environmental Chemistry, Remediation, Hazardous Waste, Drinking Water, Hazardous, Environmental Engineering, contaminated sediments, hazardous waste treatment, advanced treatment technologies, hazardous waste storage, perchlorate, contaminated soil, anaerobic biodegradation, zero valent iron, groundwater remediation, contaminated groundwater, hazardous wate, contaminant removal, drinking water contaminants, drinking water treatment, groundwaterRelevant Websites:
http://dept.lamar.edu/gchsrc/ Exit
Progress and Final Reports:
Original AbstractMain Center Abstract and Reports:
CR831276 UT Center for Infrastructure Modeling and Management Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R831276C001 DNAPL Source Control by Reductive Dechlorination with Fe(II)
R831276C002 Arsenic Removal and Stabilization with Synthesized Pyrite
R831276C003 A Large-Scale Experimental Investigation of the Impact of Ethanol on Groundwater Contamination
R831276C004 Visible-Light-Responsive Titania Modified with Aerogel/Ferroelectric Optical Materials for VOC Oxidation
R831276C005 Development of a Microwave-Induced On-Site Regeneration Technology for Advancing the Control of Mercury and VOC Emissions Employing Activated Carbon
R831276C006 Pollution Prevention through Functionality Tracking and Property Integration
R831276C007 Compact Nephelometer System for On-Line Monitoring of Particulate Matter Emissions
R831276C008 Effect of Pitting Corrosion Promoters on the Treatment of Waters Contaminated with a Nitroaromatic Compounds Using Integrated Reductive/Oxidative Processes
R831276C009 Linear Polymer Chain and Bioengineered Chelators for Metals Remediation
R831276C010 Treatment of Perchlorate Contaminated Water Using a Combined Biotic/Abiotic Process
R831276C011 Rapid Determination of Microbial Pathways for Pollutant Degradation
R831276C012 Simulations of the Emission, Transport, Chemistry and Deposition of Atmospheric Mercury in the Upper Gulf Coast Region
R831276C013 Reduction of Environmental Impact and Improvement of Intrinsic Security in Unsteady-state
R831276C014 Integrated Chemical Complex and Cogeneration Analysis System: Greenhouse Gas Management and Pollution Prevention Solutions
R831276C015 Improved Combustion Catalysts for NOx Emission Reduction
R831276C016 A Large-Scale Experimental Investigation of the Impact of Ethanol on Groundwater Contamination
R831276C017 Minimization of Hazardous Ion-Exchange Brine Waste by Biological Treatment of Perchlorate and Nitrate to Allow Brine Recycle
R831276C018 Integrated Chemical Complex and Cogeneration Analysis System: Greenhouse Gas Management and Pollution Prevention Solutions
The 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.
Project Research Results
Main Center: CR831276
64 publications for this center
18 journal articles for this center