We give a new proof of the central limit theorem for one dimensional symmetric random walk in random environment. The proof
is quite elementary and natural. We show the convergence of the generators and from this we conclude the convergence of the
process. We also investigate the hydrodynamic limit (HDL) of one dimensional symmetric simple exclusion in random environment
and prove stochastic convergence of the scaled density field. The macroscopic behaviour of this field is given by a linear
heat equation. The diffusion coefficient is the same as that of the corresponding random walk.