It isn't disgusting that gorillas eat their poop. It's a normal thing. It also happens in the wild.
There are several reasons that they do it. Sometimes they had some very tasty food a day earlier and this way they can enjoy it again. But it's also a way of getting vitamins (especially vitamin b12) and minerals. Whenever one of the adult Burgers' gorillas gets up from the ground to sit up on a platform, I know that in about 2 minutes lots of people (both young and old!) will scream "Oohhwww no, he's eating poop. That's disgusting!!!!". Lots of them turn (and walk) away.
Their poop isn't disgusting. Ours is, because we eat meat; isn't that what makes it smell? The gorillas don't eat meat.