Hi, can anyone tell me of the ideal waste to pure water ratio for a hf4 4021 reverse osmosis membrane. I have heard that a wrong ratio could foul up the membrane. what kind of ratio of output should I be aiming for?
Many thanks
Lee
Basically you find your own sweet spot.
I have an inline tds meter. One of the sensors is on the pure line between the r/o and the di vessel.
By opening and closing the waste gate slightly I can tweek the ratio so the r/o is performing at its lowest ppm output. Mine is around 50/50. If I mess around and throttle the waste back further to say, 60 pure to 40 waste, then the tds of the pure increases a little as the membrane isn't working as efficiently.
If I open the waste valve to 60 waste/40 pure then the output tds remains the same, but I waste water. If I increase the ratio to 70 waste 30 pure, then my pure tds will increase. So for me my optimum ratio for lowest tds pure output and least water to waste is 50/50.
If your sweet spot is 60/40 and you are on a water meter, then you might decide to restrict the waste to reduce your water bill. This means that you will spend a little more on resin. But you are rewarded by saving money on your water bill. Your membranes will also be hammered a little more so won't last as long. Its called 'economies of scale' in the business world.
https://www.investopedia.com/terms/e/economiesofscale.asp.