Question

An underground storage tank has sprung a leak, sending 184 kilograms of ethanol into the

subsurface soil. Ethanol can be used as an electron donor under either aerobic (oxygen is the

electron acceptor) or sulfate reducing (sulfate is reduced to H

2

S) conditions. a) How many

electrons are transferred during the oxidation of ethanol (C

2

H

5

OH) to carbon dioxide (CO

2

)?

b) Construct the stoichiometric energy generating reaction from the half reactions associated

with the aerobic oxidation of ethanol to CO

2

. c) Construct the stoichiometric energy generating

reaction from the half reactions associated with oxidation of ethanol to CO

2

under sulfate

reducing conditions. e) Calculate the standard free energy (



G

0

) available from the sulfate

reducing energy generating reaction and compare it to the energy derived from the aerobic

oxidation. Which of the two modes of metabolism of ethanol provides more energy to the

organism and why you think this is the case? f) If you want to pump aerated water (7.0 mg

oxygen per liter) into the subsurface to support the mineralization of the ethanol, how many

gallons of water will you have to pump?

Use the tables in the Energy Calculations Appendix as needed.

Answer 1