I hope that gross black sludge doesn't just go where other rain water is drained to. I'm really surprised that in 2019 they couldn't have come up with a more healthy and environmentally friendly way to power their trains.
@DelacoursLangur Partially yes, but there was definitely real coal around used for the trains - their stench and the bad air in the train hangar clearly indicated that.
@DelacoursLangur Definitely not and like most zoos they in fact do claim to be doing things for the environment. For example they do in fact at least partially use draft horses rather than vehicles to collect waste around the park and I believe they also have some electrically powered vehicles (golf cart type) for keepers and other staff to use around the zoo. So they're surely not all bad. But they do use coal, pretty much the worst fuel you can use, for their trains, thus defeating their own statements for a substantial part.
I don't have a problem with the train as such, but the coal usage and the resulting crap belched into the air I really didn't like. I liked Pairi Daiza a lot, but it is not without some major flaws and that was one of my chief complaints there: the train and its loud noise and stinky smoke. I'm sure the technical possibilities exist to power their trains differently and I hope they do ASAP.