Environmental Chemistry

Homework Assignment 9 (20 points)

1. What are the two processes by which the activated sludge process removes soluble carbonaceous material from sewage?
2. How many liters of methanol would be required daily to remove the nitrogen from a 200,000-L/day sewage treatment plant producing a effluent containing 50 mg/L of nitrogen? Assume that the nitrogen has been converted to NO₃^- in the plant. The denitrifying reaction is:

   6 NO₃^- + 5 CH₃OH + 6 H⁺ (Denitrifying bacteria) → 3 N_2(g) + 5 CO₂ + 13 H₂O
   

3. Assume that a waste contains 300 mg/L of biodegradable {CH₂O} and is processed through a 200,000 L/day sewage-treatment plant which converts 40% of the waste to CO₂ and H₂O. Calculate the volume of air (at 25 °C, 1 atm) required for this conversion. Assume that the O₂ is transferred to the water with 20% efficiency.
4. If all of the {CH₂O} in the plant described in question 3 could be converted to methane by anaerobic digestion, how many liters of methane, at STP, could be produced daily?
5. Consider municipal drinking water from two different kinds of sources, one a flowing, well-aerated stream with a heavy load of particulate matter, and the other an anaerobic ground water. Describe possible differences in the water treatment strategies for these two sources.

   The equations for aerobic and anaerobic digestion of biomass are:

   {CH₂O} + O₂ → CO₂ + H₂O

   {CH₂O} → ½ CH₄ + ½ CO₂
   

   

   ENV 440 Homework

Environmental Chemistry -- ENV 440
Last Updated:  03/23/04