1. Microbial Degradation of Pollutants

Question 1

Describe the Engineer’s View of Microbes

Answer 1

1. Microbes seen as a bag of enzymes
2. Microbes provide the catalyst that transform the harmful wastes into a harmless products
3. New idea: use microbes to convert harmful wastes into a useful product such as energy or medicine

Question 2

Propose a sequence of events that can occur starting with a leaking petroleum hydrocarbon storage tank located subsurface between the ground surface and the ground water.

Answer 2

1. Bulk fluid that leaks out=LNAPL which contains dissolved hydrocarbons
   
   • direction of leaking is down towards the water table
2. Biodegradation converts LNAPL to NAPL
   
   • some residual NAPL gets trapped in pores b/w soil & sediment particles (i.e. where microbes are)
3. As NAPL reaches edge of water table, it forms an oil slick (i.e. smear zone)
4. In the water, it disperses and gets diluted

Question 3

How do microbes avoid being washed into water (where it would die)?

Answer 3

Evolves to have extracellular polysaccharides that help it attach to rocks along river bed

Question 4

Name some treatment options to make waste chemicals less harmful

Answer 4

1. Add microbes directly to the waste chemical source to immediately convert it into a less harmful form
2. Biofilm reactor containing a solid mass of microbes–can be in the form of plastic, rock or activated charcoal–as chems pass through it, microbes convert chems to clean water

Question 5

What is one advantage of using a biofilm reactor to filter out harmful chemicals?

Answer 5

Microbes stay within the biofilm reactor–>output solution doesn’t contain any of the microbes

Question 6

Name 3 hydrocarbons in petroleum that most microbes naturally have enzymes for? Why is it good that maj microbes can break them down?

Answer 6

*note. they are ALL electron donors
1. Octane
2. Benzene
3. Benzo[a]pyrene
Why good: they’re carcinogenic

Question 7

What class do oxygenases fall under and describe their mechanism.

Answer 7

Class: non-specific enzymes
-rxns originally serving a dif function for microbe but will spontaneously react with pollutants
-microbe defense mechanism against other microbes competing for the same food resource
Defense Mechanism: adds O2 to a C-H bond to form a hydroxyl group (C-OH) which can then destroy other microbes

Question 8

What are 5 things that microbial farmers need for their crops?

Answer 8

1. Electron donors and acceptors
2. Nitrogen
3. Phosphorous
4. Micronutrients
5. Water

Question 9

What type of molecule is a good fuel for redox reactions?

Answer 9

Organic electron donor molecules such as CO2
Why: Oxidation of CO2/organic molecules has E’>0 so, when coupled with a reduction rxn, the overall E>0 therefore rxn will be spontaneous

Question 10

Why do we not use hydrogen as a fuel even though it’s a good electron donor?

Answer 10

Because hydrogen is HIGHLY explosive

Question 11

You discover that your oil tank is leaking and that an oil slick has been formed on your land. What are the steps you would take to remedy the situation?

Answer 11

1. Drill wells to take samples of water
2. Try and find oil leak
3. Create an environment that is electron donor rich by adding MgO2 (electron acceptor)
4. MgO2 reacts with H2O to produce O2 gas (which is a good electron donor)

Question 12

What is bioventing?

Answer 12

Method to add oxygen

Question 13

How can Halococcus be used to bioremediate a situation?

Answer 13

Found in the Persian gulf (which is 8x saltier than sea water), it can eat crude oil–>help clean up oil spills

Question 14

Carbon tetrachloride (CT) is used as a degreaser to breakdown oily compounds. However, it is carcinogenic. What molecule can we use to neutralize CT?

Answer 14

Menaquinone-1: Its electron transport chain allows it to catalyze CT to transform into chloroform (but this is an even worse chem)

Question 15

Chlorpyrifos is used as a crop/plant pesticide but it is a neurotoxin. What molecule can we use to neutralize it?

Answer 15

Enterobacter Strain B-14

Question 16

Incomplete degradation: why is it so bad?

Answer 16

Can result in the production of a chemical that is even worse than the original hazardous toxin

Question 17

At the Oak Ridge S3 ponds, it was discovered that it 98% of the soil had depleted uranium and strong acids (5% HNO3). Propose a strategy to clean this up.

Answer 17

1. Remove NO3- by denitrification in fluidized bed reactor w/ ethanol
2. Add additional ethanol to reduce uranium in the ground

We get rid of NO3- first b/c it is a better electron acceptor than uranium