  We examine the validity of the generalized second law of thermodynamics in a
non-flat universe in the presence of viscous dark energy. At first we assume
that the universe filled only with viscous dark energy. Then, we extend our
study to the case where there is an interaction between viscous dark energy and
pressureless dark matter. We examine the time evolution of the total entropy,
including the entropy associated with the apparent horizon and the entropy of
the viscous dark energy inside the apparent horizon. Our study show that the
generalized second law of thermodynamics is always protected in a universe
filled with interacting viscous dark energy and dark matter in a region
enclosed by the apparent horizon. Finally, we show that the the generalized
second law of thermodynamics is fulfilled for a universe filled with
interacting viscous dark energy and dark matter in the sense that we take into
account the Casimir effect.
