Dear Ye Zhao,   Eawag, a ...

Dear Ye Zhao,

 

Eawag, a well known research institute in water issues in Switzerland has done and is still doing research on topic.

 

As far as I know, there is no economic feasible solution to extract the ammonium directly of municipal wastewater (yet). Samewise, it is not possible to retrieve the nitrate once the biological process has been done easily (like stated by Sean below).

However, research has been done to extract ammonium/nitrate from source-separated urine at a rather interesting cost. This is due to the fact that around 80% of ammonia in municipal wastewater is due to urine (approx. the same number for phosphate btw). The advantage is that concentration is higher, and therefore water evaporation becomes a viable option. However, urine has to undergo biological treatment, since in source-separated urine you will find ammonia instead of ammonium due to the high pH (which is a consequence of the hydrolisis of urea), and ammonia evaporates quite easily. The biological treatment allows the transformation of ammonia into nitrate and a reduction of pH. After evaporition, you will have a ammonium-nitrate salt, as well as some phosphate salts, which can be used as a fertilizer.

If you are interested in this solution, please look for the project VUNA from EAWAG : http://www.eawag.ch/en/department/eng/project-overview/vuna/