The link (Authors) below might help you some about Nitrogen.

Edward (Ned) C. Fiss, Jr., PE

Robert M. Stein

Good luck,

For typical municipal domestic wastewater (little or no industrial wastewater), the ammonia-N is typically between 20-40 mg/L depending on the strength of wastewater.Higher values exceeding 50 mg/L is also possible depending upon wastewater strength.

For industrial, it is industry specific and could be very low (few mg/L) to >>1000 mg/L.