What can be done with the residue / roughage left after straining the juice?

• You can use the leftover roughage as a scrub for your face, instead of soap
• You can compost it 

We don't advise making satvic chapatis with the leftover juice roughage because all the nutrition of the vegetable has gone into the juice. The leftover residue contains no or very little nutrition. It's much better to use freshly grated vegetables for making satvic chapati.