What are the black bumps on my driftwood?

it may be something bad growing on the wood. You can take it out and bake it in your oven at about 200 degrees and that should kill anything bad on it just keep an eye on it so it doesn't catch fire. Or you could put it in a 5 gallon bucket with water and bleach in it and that will kill anything on it but you will have to make sure to completely rinse it off afterwards and then let it soak in fresh water for awhile and dump it out and then soak it again in another fresh bucket of water to make sure you remove all the bleach or the bleach will kill your fish