End of Life: When the sponge is no useful in cleaning your dishes. Throw the sponge at your best friends head. Long as the sponge lands on a patch of grass, it will biodegrade.If you want to speed up the breaking down of the sponge, simply bury it underground or put it in your home compost.If your council collects food waste for composting, you can also put the sponge in the food waste bin.