Use a concentration polarization of $1\mathrm{.}5,$ when calculating the water flux and solute flux through the membrane. A reverse osmosis membrane to be used at $25C$ for a NaCl feed solution containing $)=(999\frac{kg}{m^3}$ has a water permeability constant $Aw=4\mathrm{.}81{10}^{-4}$NaC$\frac{l}{s}.m^2$ atm and a solute $(NaCl)$ permeability constant $As=4\mathrm{.}42{10}^{-7}\frac{m}{s}.$ The membrane $P=27\mathrm{.}20$atm.