Ammonia is one of the chemical constituents of industrial waste that must be removed in a treatment plant before the waste can safely be discharged into a river or estuary. Ammonia is normally present in wastewater as aqueous ammonium hydroxide (NH⁺₄ OH^-). A two-part process is frequently carried out to accomplish the removal. Lime (CaO) is first added to the wastewater, leading to the reaction 

The hydroxide ions produced in this reaction drive the following reaction to the right, resulting in the conversion of ammonium ions to dissolved ammonia: 

Air is then contacted with the wastewater, stripping out the ammonia. 

(a) One million gallons per day of alkaline wastewater containing 0.03 mole NH₃/mole ammoniafree H₂O is fed to a stripping tower that operates at 68°F. Air at 68°F and 21.3 psia contacts the wastewater counter currently as it passes through the tower. The feed ratio is 300 ft³ air/gal wastewater, and 93% of the ammonia is stripped from the wastewater. Calculate the volumetric flow rate of the gas leaving the tower and the partial pressure of ammonia in this gas. 

(b) Briefly explain in terms a first-year chemistry student could understand how this process works. Include the equilibrium constant for the second reaction in your explanation. 

Exploratory Exercise—Research and Discover 

(c) This problem is an illustration of challenges associated with addressing undesirable releases into the environment; namely, in developing a process to prevent dumping ammonia into a waterway, the release is instead made to the atmosphere. Suppose you are to write an article for a newspaper on the installation of the process described in the beginning of this problem. Explain why the company is installing the two-part process, and then explain the ultimate fate of the ammonia. Take one of two positions—either that the release is harmless or that it jeopardizes the environment in the vicinity of the plant. Since this is a newspaper article, it cannot be more than 800 words.

Transcribed Image Text:

CaO + H20 Ca2+ + 2(OH)