Question

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

asked Dec 18, 2021 199k views

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 waste water as aqueous ammonium hydroxide (NH4OH-). A two-part process is frequently carried out to accomplish the removal. Lime (CaO) is first added to the wastewater, leading to the reaction

CaO + H2O --> Ca2+ + 2(OH-)
The hydroxide ions produced in this reaction drive the following reaction to the right, resulting in the conversion of ammonium ions to dissolved ammonia:

NH4+ + OH- <--> NH3(g) + H2O(l)
Air is then contacted with the wastewater, stripping out the ammonia.

a. One million gallons per day of alkaline wastewater containing 0.03 mol NH3/mole ammonia-free H2O is fed to a stripping tower that operates at 68oF. Air at 68oF and 21.3 psi contacts the wastewater countercurrently 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.