RO/DI Solution for high TDS tapwater?

[blmeier7]

I am curious to see how everyone with high TDS tapwater readings (above 750 ppm) are setting up their RO/DI units. Has anyone found a good way to get long life (over a year) out of their membrane? Any advice would be appreciated.

FWIW here is my current setup:

10m sediment
5m carbon block
1m carbon block
50pgd Filmtec membrane
2-refillable DI canisters

Tapwater TDS: 1200 ppm

Within a couple of weeks after changing all prefilters and membrane I get a TDS reading of 15-20 ppm (after DI). I go through about two membranes a year and don't replace until my TDS is readings are around 100ppm before DI.

 

[RichConley]

Talk to AzdesertRat. Hes got that nasty rock-water like you have.


I think hes reccomending the spectrapure stuff at this point.

 

[AZDesertRat]

A 0.5 or 0.2 micron prefilter and a 0.5 micron carbon block work for me. This is the configuration Spectrapure recommends and they are located here in the Phoenix area with tap water TDS that is in the 750 to 1000 range. I just replaced a 0.5 prefilter and carbon block after 8 months of usage and only had a 2 psi pressure drop increase over the 8 month period. I replaced it with a 0.2 micron prefilter and had a 4 psi drop right off the bat but I like the 10x surface area increase on the 0.2 so I am going to see how it works over time.

Prefilters and carbons have little to no effect on RO TDS, they are there strictly to protect the membrane. Prefilters and carbons mostly remove TSS or Total Suspended Solids which are much larger particles than the TDS or total Dissolved Solids which the membrane removes. By switching to a finer micron rated prefilter you greatly increase the protection you provide for the membrane and switching to a finer carbon greatly increases the amount of chlorine, chloramines and VOCs or Volatile Organic Chemicals you adsorb. If you have high sediment like sand or particulates you might go with a roughing prefilter like a 10 or 5 micron up front than 0.5 prefilter and 0.5 carbon. The roughing filter can be changed out as needed but the others should go 6 months easily.

My Tap TDS is 850+ right now, RO only TDS is 6.2 to 6.4 and RO/DI is 0 for in excess of 650 gallons per DI cartridge. The membranes ( I now have a dual membrane system) are Spectraselect hand tested membranes from Spectrapure and the DI is the MaxCap system which I highly recommend for waters like yours and mine. You might contact them and see what they would suggest for your area, they have been great to our local club members.

 

[blmeier7]

Thanks DesertRat, thats the info I was looking for.

Based on Spectrapure's website the prices (membranes and DI cartridges) are just about double what most other sites are for the "standard" replacements. Are you experiencing longer life out of your membranes and resulting longer life out of the DI cartridge to make the initial cost worth it?

By the way, which MaxCap DI setup are you using?

Thanks in advance

 

[AZDesertRat]

The first MaxCap DI cartridge went about 630 gallons before I saw a reading of 2 TDS. With my previous Typhoon configuration and brand new fresh DI resin I was getting 150 gallons per DI cartridge before I saw the same 2 TDS. I have not had the system long enough to comment on the life of the RO membrane(s) but based on what I have seen in their test facility and what people like Randy Holmes Farley have experienced (over 9 years from the same membrane) I expect to get much longer membrane life also.
I figure I would have been well into my 5th DI cartridge by now but with the MaxCap I just started my second cartridge so there is a big cost savings in my case. My unit started out as a 90 GPD MaxCap RO/DI system but I have since added a piggyback membrane using one of their 150 GPD SpectraSelect membranes so I now have a 240 GPD system. I understand they are having trouble getting enough of the 150 GPD membranes that meet their criteria and could not keep up with demand so they are not being offered at this time. I was one of the lucky ones to get one of the original batch!
So far I am averaging 99.23% rejection with RO only which is a testament to the quality of their hand tested membranes. Well worth the cost difference if you have nasty water like we do.

 

[blmeier7]

Sounds like its definitely worth trying. I will get an order placed within the next day or two. Thanks for the help.

When you say you have a second membrane piggybacked...is this an additional membrane being used for more water production (split after pre filters) or do you have two membranes running in-line?

 

[AZDesertRat]

The waste from the first goes through the second so I get twice the production. There are diagrams on most websites including Spectrapures.