You can read this paper:

.C. Anthonisen, R.C. Loher, T.B.S. Prakasam, E.G. Srinath.Inhibition of nitrification by ammonia and nitrous acid. Journal – Water Pollution Control Federation, 48 (5) (1976), p. 835

Here, you can calculate NH3, then taking into account that TAN=NH3 + NH4+, you can obtain it.

C_NH4+ = (TAN*10^-pH)/(10^-pKa+10^-pH)

pKa is 9.25 in pure water and need to be corrected for ionic-strength effects on the activity of ammonium ions. The Davis equation could be used to estimate activity coefficients at ionic strength lower than 0.5M.

Interested.

I think to must to analysis the water quality.

Very simple

N = 14, NH4= 18

TAN = known

NH4+ =x

(18*TAN)/14 = x

Now put TAN value and you will get result as NH4+.

Oded Nir

In a situation where we have the ability to measure NH4+ in mg/L, can we rearrange the equation to arrive TAN?

C_NH4+ = (TAN*10^-pH)/(10^-pKa+10^-pH)

TAN=((10^-pKa+10^-pH)*C_NH4+)/10^-pH

My end goal is to derive NH3 (TAN, pH, Temp)

Thank you.