10: Biostimulation

Question 1

Define biostimulation

Answer 1

The addition of chemicals to a polluted environment to encourage biodegradation by native organisms

Question 2

List three different biodegradation mechanisms that can be stimulated.

Answer 2

1) Providing Electron Donors
	§ Changes the redox conditions
	§ Can result in reductive dehalogenation
	§ Halorespiration
	§ Potential Electron Donors 

2) Providing Electron Acceptors
§ Growth related to aerobic oxidation
§ Changes the redox conditions (anaerobic to aerobic environment)
§ Includes air sparging, and injecting oxygenating water, and injecting oxygen releasing compounds

3) Cometabolism

Simultaneous breakdown to two compounds. The secondary compound cannot be broken down unless the primary compound is present.

Question 3

List four different classes of stimulants that can be injected.

Answer 3

1) Electron Donors
2) Electron Acceptors
3) Inducers
4) Nutrients (N, and P)

Question 4

Describe the cometabolic mineralization of TCE. State the intermediate formed and describe how it affects bioremediation.

Answer 4

Cometabolic mineralization of TCE occurs when certain bacteria are promoted to grow in order to concentrate an enzyme that breaks down TCE.

TCE -> Soluable methane monooxygenase (SMMO), tolunene monooxygenases (2-x3-, and 4-TMO), ammonia monooxygenase (AMO), toluene dioxygenase -> chloral hydrate, TCE epoxide, glyoxylate, or formate

The intermediate compounds may be toxic and hinder the bacterial activity needed for bioremediation

Question 5

Explain the two roles that injected electron donors play. State the ultimate electron donor resulting from different injected organics.

Answer 5

Injecting electron donors (mainly H2) makes the pollutant an electron acceptor, can lower redox potential, and can serve as electron donors in reductive reactions.

Hydrogen gas is the ultimate electron donor by fermentation

Question 6

Discuss the advantages and disadvantages of slow-release versus fast-release compounds.List four fast-release and four slow-release compounds.

Answer 6

Slow release compounds remain in a contaminated aquifer longer than fast-release compounds extending slow release effectiveness and driving down treatment costs.

Fast release compounds rapidly change the environment and reduce startup treatment time compared to slow release compounds.

Fast Release Compounds
	§ Lactate
	§ Ethanol
	§ Molasses
	§ Sodium Benzoate

Slow Release Compounds
	§ HRC
	§ Vegetable Oil Emulsion
	§ HRC-X
        § Mulch and Compost

Question 7

Explain the two roles that injected electron acceptors play.List three potential injections for bioremediation and discuss advantages/disadvantages of each.

Answer 7

Injecting electron acceptors into a contaminated aquifer makes the pollutant the electron donor. Therefore, chlorine is removed from the chlorinated hydrocarbon and is replaced with hydrogen. Electron acceptors may also change the redox conditions.

Potential injections:
§ Air: Cheap material, but difficult to effectively inject
§ Dissolved Oxygen: More effective than air, but is more expensive and requires continual injection

    § Oxidant compound (MgO2): Slowly releases oxygen so most effective, reduces the number the injections, but is the most costly upfront

Question 8

Discuss the advantages and disadvantages of strong oxidant addition. List three.

Answer 8

Advantage: Quickly changes environment from anaerobic to aerobic

Advantage: Redox conditions changes rapidly

Disadvantage: Strong oxidants will kill all microorganisms at higher concentration leading to the halt of biodegradation.

Question 9

List three potential cometabolic inducers and explain how they work to degrade TCE.

Answer 9

Methane, xylene, and phenol are potential cometobolic inducers

Cometoblic inducers can promote growth of bacteria that release enzymes that promote the breakdown of TCE

Question 10

Discuss two different approaches for locating injections.

Answer 10

Approach 1: Treat source

Approach 2: Contain contamination