Membrane Technology for Ammonia Nitrogen Recovery from Wastewater — Ammonia Nitrogen Separation Membrane

(1). Recovery Technology: Ammonia nitrogen in wastewater exists in an ionization equilibrium. When the pH of the wastewater is increased, the nitrogen nitrogen in the wastewater decomposes into gaseous ammonia until equilibrium is reached. At the same time, the wastewater with increased pH enters the ammonia nitrogen separation membrane. Gaseous ammonia will permeate through the micropores of the hydrophobic hollow fiber membrane and react with the absorbent liquid on the outside of the membrane, thereby decomposing ammonia nitrogen in the wastewater again until gaseous ammonia reaches equilibrium. This is based on the Le Chatelier's Principle: In nature, all equilibriums are relative and temporary. Once one of the conditions of the equilibrium system is changed, the equilibrium will shift to counteract this change.

By using the adsorption method with dilute acid, the ammonia nitrogen removal rate can reach above 98%. To employ this method, it is necessary to raise the pH value of the wastewater as much as possible. (This means that alkali needs to be added during operation, and the amount of alkali added is proportional to the ammonia nitrogen removal rate.)

The dilute acid used with the absorption of dilute acid can be dilute sulfuric acid, with a concentration of approximately 15%. The dilute acid is circulated and recycled until it becomes saturated, after which it is discharged or recycled. Based on experience, wastewater typically contains 8 to 10 g/L of ammonia nitrogen. The treatment ratio of dilute acid to ammonia nitrogen wastewater is approximately 1:15 (i.e., treating 15 tons of wastewater with an ammonia nitrogen concentration of 8 to 9 g/L requires 1 ton of 15% dilute acid).

(II). Ammonium Nitrogen Separation Membrane Design Parameters