Reusing reject water from an RO plant

RO plant reject water

Hi. I am a student participating in a science project on the re-treatment of RO reject water. I have a small doubt - can the rejected water obtained from a RO plant be subjected again to reverse osmosis? Is it cost efficient? Or can it be treated by bio- remediation? Please give me a possible way of retreating this water and please don't tell me to use in gardens, in toilets, etc.