The issue with ammonia is ...

The issue with ammonia is that it exists primarily as NH4+ until the pH is up to almost 8.0 and it starts to convert NH3. NH3 will air strip, the higher the pH the more ammonia you will remove. To get complete removal with air the pH must be 10.5 . As mentioned in the above posts the potential for sulphate precipitation on the membranes is significant and you you need more analysis. If you raise the pH to get rid of ammonia using air stripping you will greatly increase your potential for fouling.

However if you keep the pH low the RO membrane will give you ok rejection of the NH4+ ionized version of ammonia. So I would avoid air stripping and use the RO for rejection. As mentioned above you need to plug the analytical data into a good RO projection program.