How to separately collect Ammonia from wastewater?

We are trying to separate the ammonium from wastewater (Chinese municipal  wastewater plant located in Beijing.), so that it can be utilized for other purpose. 

Is there any way to selectively separate and collect ammonium nitrogen from wastewater? 

Recovery could be above 90%, and the outlet concentration of ammonia nitrogen in this wastewater is below 1 ppm. Your suggestions would be appreciated. Cheers.