3 ro membrane
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t5Nitro
Valuable Member
Question for you would it be best to run a dual RO membrane in parallel or should it be run in series so the second membrane catches more? I'm wondering why previous posters say you're going to burn through the third membrane quickly. Theoretically that should be your cleanest water out of all of those membranes? But yeah I see your tds is highest at the second and third. Why does tds rise after membrane 1?
chipmunkofdoom2
Always Making Something
You probably don't. Most people don't. The "waste" produced by a hobby RO system is negligible in all but the most fringe cases. For a 100 gallon tank that needs 1 gallon of top off a day and 40g for water changes a month, an RO filter will probably only use 210 gallons of water (assuming a 2:1 brine to permeate ratio). Tap water in the US costs a penny for 5 gallons, which equates to $0.42/month to run your RO unit. Even if you can cut your brine flow in half, you're only saving about 70 gallons a month, or fourteen cents. Even if your water costs are 10x average, another membrane will likely only save you a dollar a month.
Also, the average family in the US uses 300 gallons per day, or 9,000 gallons a month. Using 210 gallons per month to run your RO filter is a drop in the proverbial bucket.
The RO membranes would be in series. So the waste line from RO1 goes into the tap water inlet of RO2. The clean water from RO1 and RO2 are combined and then go to your resins. The waste line from RO2 goes down the drain or can be used to water plants, etc. if you add the 3rd membrane then the waste from RO2 goes into the tap water inlet of RO3, etc.
The waste line from the RO membrane will have a higher tds vs the tap water. So as you continue to use the waste lines to feed other RO membranes they are getting a higher tds water to process.
Yes kenO is correct they are run in series and yes it might take a toll on the 3rd membrane but I haven't seen it yet and the water output is very fast for only using 75gpd membranes the plan is to switch them to premium 150gpd membranes when the time comes and really make water fast. As what water cost it's all by region. I just don't like wasting so I decided to use the most I can
I live in the desert. We value every gallon of water. I use my waste to water plants outside. I have the housing already for a 3rd membrane. When my dual membranes (75gpd) need replacing I’m going to upgrade to higher gpd membranes and add the 3rd one. Between my 2 setups I have almost 700 gallons of SW. It would be nice to make water faster. Right now I can make a little over 200 gallons/day. My storage tank is 105 gallons.
t5Nitro
Valuable Member
I like the idea to make water this quickly more than anything like you said. So my current rodi is a 75gpd system. All I need to do is change the membranes to 150gpd and then 2 of them in series to really ramp up production (along with a booster pump) like this?
Are you wanting to add another 75gpd membrane or getting 2 - 150gpd membranes? The first option gets you 150gpd the 2nd gets you 300gpd. If you go with option 2 make sure you get the correct size flow restrictor for the 150gpd membrane.
t5Nitro
Valuable Member
I like the idea of 2x150 membranes. I have a single 75gpd membrane now. Appreciate it. I might give this a try just for the efficiency in time. Side effect of less water down the drain also a plus even though cost is minimal. With the difference of 1-2 TDS after subsequent membranes in series the DI resin loss should seem negligible.
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Update. So my ro membranes went bad time to change. So I figured I'll replace with 150gpd well it didn't work well I was getting 20 plus tds into the di resin. I now went a different route I added a 4th membrane but in series now I'm basically getting 600gpd into my di resin and 7tds into it. I do waste more water but whatever
