Planning to use reject water of one RO plant as feed stream for another RO plant - What difficulties will we face?

Dear all,

We have two RO plants working in our industry and we are planning to use the reject stream of our existing RO plants as a feed stream of our new RO plant. Reject water has a TDS of 12000, we have designed a plant that could work on 14500 TDS.

What are the difficulties that we will face ? Is it happening any where around the world ?