Originally Posted by Lancerbye
The reject water is the high salt concentrate that has not made it through the membrane and is flushed away by the excess raw water
. The product is the water that has made it through the membrane. Sometimes there is a bit of salt in the line going through the monitor and is dumped as reject. This is usually as a result of the cleaning
or backwashing cycle. With automatic product switching, the monitor watches the part permillion in the test water. This is all dumped in the reject line until the monitor reads 500ppm or less at which point it is sent to the product line.
Automatic switching is the key to all of this, but the way you have stated it can be confusing.
There are 2 outlet streams to RO. RO NEVER BACKWASHES. That's what filters do. Backwashing (reverseing flow for cleaning purposes) would compromise the membrane envelope. That's a whole other discussion-not needed here.
One stream is concentrate/reject/brine/waste. All the same thing.
The other stream is product/permeate-because it has permeated the membrane.
Off spec water can be automaticaly switched to combine with the other stream. When when it reaches quality, it can be automatically diverted back to service
The terminology can be confusing because sometimes (never in a desalination "water maker") the concentrate is what the end user is capturing. For ease of explanation, just think orange juice concentrate,
where permeate water is the reject.