Quote:
Originally Posted by molotov
From what I've read the less stages you have the less waste? Also the less GPD the less waste.
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Neither of these are true.
The best you can do is about 1:1 waste but you will probably go through RO membranes quicker. The waste water is used to flush the membrane as you're making water. Less flushing means the membrane clogs up with scaly residue quicker.
I am doing an experiment lately. I have a 150 gpd RO membrane that I am using a 75 gpd flow restrictor on it. My tap is about 60-62 psi. I get about 40 gallons in 8 hours (I think...I should measure). I am getting about 1.25:1 (good:waste). I tested the TDS coming out of the RO (before the DI) at 2 ppm before I started my experiment and I have made about 700 gallons of good water since doing this and the RO membrane is still putting out only 2 ppm. However, I am not getting 1.25:1 anymore as the membrane is getting clogged up which forces more water through the waste line. I recently got some citric acid to soak the membrane in to hopefully remove the scaly deposits...I'm still researching the procedure for this.
Get creative using the waste water. I collect the waste water outside (in the summer months) and use a Mag 3 pump on a hose to water the flower gardens by hand or go to the washing machine where I can use the waste water for the wash cycle. I would suggest a bigger pump because this one is a bit slow...it's just what I have on hand. It is surprising how quickly you can use up waste water in the laundry room! We are getting some stackable laundry machines to make room in the laundry room to keep a waste water bin in there over winter. I am going to install a float switch on that bin because it is inside, and because float switches can be unreliable I will not rely on it. I will still maintain vigilance and try to remember to stop the water before it even gets to the float. Some people keep the water turned on all the time, and use the float switch to automatically turn the water back on as soon as some is used. This is when people have troubles with switches failing, and flooding the house.
Normally I like to support local fish stores, but I like to use Bulk Reef Supply for all RO equipment. They have great prices, really good shipping policies, and particularly because they have everything you need in stock! Don't forget to order a TDS meter. I like handheld meters because they are easier to calibrate and are easier to use when you want to test the TDS coming out of the RO before the DI stage. This is important when figuring out if the RO membrane is exhausted or if only DI is exhausted. I usually replace DI 2-3 times before I need to replace the RO membrane.