Question

When benzene dissolves in water, it can be degraded by various bacteria species through redox reactions depending on which oxidizing agents

answer the following questions:

a. Draw the analogies between benzene degradation by bacteria and organic matter degradation by bacteria discussed in class. Under what conditions is benzene most effectively degraded by bacteria? It is given that the standard free energy change ΔG0 is related to redox potential E0 by the equation ΔG0=-nFEo, where n is the number of electrons being transferred, and F is a positive constant. Your answer should be qualitative. No calculations required.

b. Assuming that the only available oxidizing agent is NO3-, determine how many mg/L of benzene can be degraded by 1mM of NO3-. Will this reaction alone affect the pH of the solution?

c. Assuming that the only available oxidizing agent is Fe3+, determine the concentration of Fe3+ that will be consumed in mg/L, in order to treat water that is contaminated with a concentration of 3.2 ug/L of benzene.

Answer 1

Degradation of an organic matter by bacteria depends on factors like light, oxygen and temperature. Degradation becomes difficult with increase in the number of multiple bonds and presence of halogen as substituent.

More negative value of ∆G indicates the increase in rate of degradation. Since the n and F are constants therefore the rate of degradation doesn't depend on these two factors but electrode potential increases with increase in temperature. Thus the rate of degradation increases as the temperature increases.