It is likely that the organic nitrogen is undergoing ammonification through a process called hydrolysis. As a result organic nitrogen is converted to NH3. Alternatively, if appreciable amount of NH3 is present in the influent, the ammonia gets oxidized to Nitrate in aeration tank and hence, high concentration of Nitrate in the effluent. It is advisable to also measure Total Kjeldahl Nitrogen (TKN) and NH3 in the inlet.

To remove high concentration of Nitrate, ASP needs to be upgraded to include a denitrification chamber.

Hope it helps.

Thanks Akshay, you mean de nitrification chamber at post aeration?

@Imad Najeeb ...

Yes. It is called as the Anoxic Chamber.

There is already pre anoxic chamber, are you recommended post anoxic chamber before settling tank?

In principle, urea is a stable molecule. What could happen; if the medium is infected with bacteria, urea will decompose producing ammonium which will oxidize to nitrates

Thanks Safia..The ammonia at inlet is 64 ppm and at the outlet 48 ppm, I have checked today waiting for TKN test results.

the TKN in inlet 123 mg/l and outlet 25.2.