half reaction for pce to ethene present in groundwater assuming complete decompo

Question

half reaction for pce to ethene present in groundwater assuming complete decomposition of the BTEX compounds at the concentration listed in part b. Express your answer in mg Fe^2+/L. An increasingly common method for treating groundwater contaminated with chlorinated ethenes is bioremediation, using organohalide respiration. In this process, anaerobic bacteria use the chlorinated compounds as electron acceptors; hydrogen is the most widely electron donor. Write a balanced electron donor half reaction for H_2. Write a balanced electron acceptor half reaction for reduction of PCE to ethene. Write an overall reaction for reduction of PCE to ethene by combining the half reactions. Hydrogen is difficult to deliver to the subsurface. A more common approach for delivery is to add a fermentable substrate such as sodium lactate. Suppose each mole of lactate ferments to 2 moles of H_2. If the contaminated groundwater at a hazardous waste site contains an average of 1, 400 ppb of PCE, calculate the minimum concentration of sodium lactate that must be added. Express your answer in mg/L Textbook problem 2.4 (molarity calculation). Textbook problem 2.17 (pH calculation).

Explanation / Answer

Ans- a- balanced donor half reaction- 1/2H2= H^+ + e^-

b- PCE to ethane

1/8CCl2=CCl2+1/2 H+ +e^-

(CCl2 is electron acceptor)

Ans- C-

1/8CCl2=CCl2+1/2 H+ +e^- =1/8CH2= CH2+1/2Cl^-

Ans D-Reaction involving sodium lactate and PCE

2(CCl4)+3(C3H5NaO3)+13 OH= 3Na^+ + 8Cl^- +11CO2+28H+

So 3 ppb sodium lactate is required for treating 2 ppb of PCEFor 1400 ppb of PCE the amount of sodium lactate needed is =1400*1.5 ppb

= 2100 ppb

= .0021 gm/lt

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