MODULE II: WRITTEN ASSIGNMENTS
Session II-1 Biotransformation/Biodegradation Overview
Wiedemeyer Chapter 4 Overview of Intrinsic Bioremediation
Instructions: Answer the following questions in the space provided, using additional sheets if necessary. Your answers may be either hand written or typed. Submit all homework problems for Module II in a note book along with the Examination for Module II. This will be done via surface mail.
II-1. Are organic contaminants in the NAPL phase biodegradable? Why? (pg 164).
II-2. Explain the concept of intrinsic bioremediation. What factors must be present in the subsurface for Intrinsic bioremediation to occur? (Pg 164).
II-3. Describe what happens to the indigenous microbial community in an aquifer when a large amount of organic contaminant, say gasoline, is introduced. (165-166).
II-4. Define and explain the following terms:
Halorespiration
Cometabolism
Session II-1 Biotransformation/Biodegradation Overview
II-5. Explain how the concept of Gibbs Free Energy relates to microbial metabolism. (170,176,177)
II-6. Discuss how the oxidation-reduction potential (ORP) measurement can be used to assess the potential for various oxidation-reduction reactions in ground water containing organic compounds.
Session II-3. Microbial Process Kinetics
II-7. Compare and contrast the two models for biodegradation kinetics (i.e. first order decay vs zero order or "instantaneous reaction."), as discussed on pages 178-182 Wiedemeyer.
II-8. Rework example 4.1 pg 181, Wiedemeyer, assuming the initial benzene concentration is 10 mg/l and the first order decay coefficient is 1.5% day-1.
II-9. Draw a conceptual sketch that goes with Example 4.2 pg 183, Wiedemeyer.
II-10. Note! In Example 4.2, pg 183, in Wiedemeyer the problem statement should read "5.0" mg/L instead of "10.0" mg/L. Also on page 185, Example 4.3, the problem statement should read "0.001" mg/L total microbilal concentration to be consistent with the solution. For problem II-10 rework example 4.3 pg 185 Wiedemeyer assuming a benzene source concentration of 15 mg/l and a total microbial population of 0.002 mg/L.
II-11. Program in the following list of observed centerline concentrations into the BIOSCREEN model for Keesler Air Force Base. Vary the first order decay coefficient until best fit (by eye) of the observed data is obtained. What is the value of this decay coefficient?
| Conc. mg/L | 12.0 | 7.0 | 2.0 | 0.5 | 0.01 | |||||
| Distance (ft) | 0 | 32 | 64 | 96 | 128 | 160 | 192 | 224 | 256 | 288 |
Session II-4. Intrinsic Bioremediation of Petroleum Hydrocarbons
Chapter 5 Wiedemeyer Intrinsic Biodegradation of Petroleum Hydrocarbons
II-12. Provide brief answers to the following questions on the material in section 5.1.
What type of petroleum hydrocarbon compounds are we most concerned with in the subsurface?
What is BTEX?
What is MTBE? Why is MTBE such difficult contaminant to remediate in the subsurface?
Describe the role of microorganisms in producing crude oil. Is it any surprise that microorganisms will also degrade refined oil products?
Why might indigenous microorganisms have an advantage over injected microorganisms in terms of their ability to degrade petroleum products?
What are the common electron acceptors in ground water systems?
Which constituent generally will limit the rate of natural biodegradation?
What is Gibbs Free Energy useful for?
II-13. verify the calculation on page 195 that 3.08 grams of oxygen are required to mineralize 1 gr of benzene. What implications does this have in terms of maintaining aerobic conditions in the subsurface as the biodegradation process continues?
II-14. Summarize the important concepts related to aerobic biodegradation of petroleum hydrocarbons.
II-15. Verify the calculation of the ratio of nitrate to benzene as 4.77 to 1. If this same calculation is done for toluene, ethylbenzene, and xylene, and the results averaged, the average will be the BETX utilization Factor for denitrification shown in Table 5.2
II-16. Summarize anaerobic biodegradation of petroleum hydrocarbons by discussing oxidation hydrocarbons via denitrification, dissimilatory (FeIII) reduction, sulfate reduction, and methanogenesis
Session II-5. Intrinsic Bioremediation of Chlorinated Organics
Chapter 6, Wiedemeyer. Intrinsic biodegradation of chlorinated solvents.
II-17. The biodegradation of chlorinated solvent can be grouped into two broad categories 1) use of the solvent as a primary growth substrate, and 2) cometabolism. Describe the key features of category 1 (solvent as primary growth substrate). Include the concepts of electron donor, electron acceptor, halorespiration and solvent oxidation in your discussion. (pg 242).
II-18. Describe the key features of solvent biodegradation via cometabolism under aerobic (oxidative) as well as anaerobic (reductive) conditions. (pg 242).
II-19. Which biodegradation process (primary growth substrate or cometabolism) is most likely to contribute the most to the natural attenuation of a chlorinated solvent plume? (pg 243).
II-20. Define "reductive dechlorination" . How is "halorespiration" related to reductive chlorination? (pg 244).
II-21. Discuss how fermentation of organics (i.e. natural organic carbon as well as petroleum hydrocarbons in the subsurface), hydrogen production, and halorespiration are related.? (pg 244)
II-22. Describe the complete pathway for reductive dechlorination of chlorinated ethenes as shown in Figure 6.1 and 6.2, pg 244-245 Wiedemeyer. Repeat for chlorinated ethanes as shown in Figure 6.3. Then analyze Figure 6.4 and summarize the biotic and abiotic pathways for the chlorinated ethenes, chlorinated ethanes, and methanes (i.e. describe in words the pathways, and their interrelationships, indicated in Figure 6.4).
II-23. Write the general oxidation-reduction reaction for halorespiration and explain each term in the reaction. Summarize the role of hydrogen and other fermentation products in driving this reaction. (pg 247).
II-24. Discuss the key features of the fermentation process. What are some of the familiar fermentations reactions? What is the role of hydrogen in the fermentation process and what is meant by interspecies hydrogen transfer? (pg 249).
II-25. If BTEX is present in proximity with a chlorinated solvent plume, explain the role that fermentation of BTEX might have on creating the potential for halorespiration. What role does the presence (absence) of methane on site play? (pg 250-51)
II-26. Figures 6.9, 6.10, and 6.11 describe the reaction sequence for chlorinated ethenes, ethanes, and carbon tetrachloride (methanes). How to the degradation rates change as halorespiration proceed toward the final end product in each figure? What restrictions on redox conditions occur as halorespiration proceeds toward the end products? How does the potential for degradation via oxidation (aerobic/anaerobic) and/or hydrolysis change as halorespiration proceeds toward the final end products?(265-266).
II-27. What rules of thumb indicate that reductive dechlorination is occurring at a field site? (pg 267).
II-28. BIOCHLOR sensitivity analysis. Run the default example for Cape Canaveral Fire Training area. Study the input screen to determine the nature of the simulation. Hit "run Centerline" to view the simulation results. Look at the concentration-with-distance-profiles fro PCE, TCE,DCE, VC, and ETH (note that you can view results for each compound separately by clicking on the grey boxes on the right-hand side of the screen). After reviewing each concentration-distance profile answer the following question:
Why do the concentration-distance profiles for VC and ETH increase relative to the "no degradation/production" line?