Well, they're on strike anyway. April 22nd will be a national strike in Belgium. Travel likely to be chaotic and best avoided. In the past, private bus companies like Fibco have run from Charleroi airport to Brussels centrum, and sometimes a little further, albeit it at very reduced capacity and journey times extended. Nothing else likely to be moving. If you are travelling the best bet is to check BlaBla car, or hitch-hike. It's very easy to get a ride during the strikes, and in you are in a bind I can likely recommend a good spot to get a ride in the big cities.