There are a couple of options.
One way to sanitize your sponge is to nuke it.
Another way (my way) is to use regular household bleach.
Put the sinks stopper in and fill the sink with hot water.
Add one cup of household bleach.
Throw your sponges in and let sit for 1 hour.
Using a long spoon, remove the stopper to drain.
You will have a sparkling sink, and a really fresh sponge!
Viola!! Sparklie sink and super fresh sponge!