Indeed, there is some contradiction in your original question. If your task is to get close to TN=N-Kjeld then you need to reduce as much as possible N-NOx. While if your target is to get close to TN=N-NO3 then you should look to reduce N-Kjeld and therefore N-org and N-NH4. From your comment, I assume that your goal is the latest.  My second concern is related to the fact that in the real world, it is usually impossible to get concentrations equal exactly to "0". So you should better set an acceptable threshold (less than ...) rather than try to get to zero. Then, on the technological side you should act on three components: 1) N-org (in suspended solids); 2) N-org dissolved and 3) N-NH4 dissolved.  The first can be reduced by tertiary filtration (sand or active carbon --> microfiltration --> ultrafiltration --> RO depending how much you want to push your system). N-org dissolved can be reduced by improving biology in your system but if it is composed by recalcitrant compounds you could also think about adsorbtion on GAC or advanced oxydation technologies or again RO N-NH4 can be reduced by improving nitrification or again by use of tertiary treatment.

Published March 16, 2018 10:34 by Simone Milanolo, Senior Engineer / Consultant at Hydro-Engineering Institute Sarajevo