We’llstudytheFEMforamodelforcompressiblemiscibledisplacementinporousmediawhichincludesmoleculardiffusionandmechanicaldispersioninone-dimensionalspace.Aclassofvertices-edges-elementsinterpolationoperatorinkisintroduced.Withthehelpofink(notellipticprojection),theoptimalerrorestimateinL∞(J;L2(Ω))normofFEMisproved.