Solute concentration:

The solute concentration within the permeate is determined through the associative flow of solute and water as follows.

C_p        =   J_S /J_w

By combining Eqs. 11.41, 11.40, 11.38 and 11.35, an expression for solute retention R can be obtained as given below:

R = 1 - C_p/C_f             = A (P - Π)/ A (P - Π ) + B

It should be noted that water flux and solute flux are inversely proportional to the

membrane thickness but solute retention R that is provide in terms of the fluxes, is independent of membrane thickness. The solute retention rises with net effectual pressure difference (P-Π) and the ratio A/B.