The effect of process variables on the recovery of hardness from water by
acation exchanger was studied. At steady state the process could be represented by
second order nonlinear emperical model. Although this model was less accurate than
the dynamic model,the results show agreement when compared with the experimental
data. The steady state optimization model was used to limit the operating conditions of
the system. The static feed forward control could be used with the aid of on – line
digital computer.