Ammonia indicate – first stage of decomposition of organic matter.
Nitrates Indicate - fully oxidized organic matters
Nitrites indicate – partially oxidized organic matters
Health effects of Nitrates are seen in infants below 6 months , disease is called methaemoglobinemia / blue baby disease.
In Sewage Treatment Plant if Ammonical nitrogen is found it is evident that oxygen is under capacity - increase the oxygen supply and treatment will be 100% positive