RO/DI Video Part 2- Podcast Episode 106

[Rob]

This is part two in the RO / DI series. In this 30 minutes video i take you through a full break down of an RO / DI unit.
We Cover:
- Component identification
- Inline TDS meter
- RO Membrane dissection
- Filter replacement
- Unit assembly and disassembly

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[DreamWeaver]

Very nice job with this video. I thought it was interesting that you route your drinking water through the DI filter. I installed a drinking water tank for my RO/DI unit and the instructions said to put a T after the RO stage and route one line to the storage tank and the other line through the DI filter. So, basically the drinking water is RO and the aquarium water is RO/DI.

[vanmo92]

This series of shows on RO/DI has really posed some of my comments and questions. I have the exact same brand and model of filter that you have (I noticed the tape over the name on the filter so I assume you don't want me to mention the name). I will mention that it is an ebay unit though.

Mine definitely does not work right. We are on a well at out house and our water definitely has some serious issues with the quality.

Our pressure is rather low (45-60 psi) and the water is cold, like 45-55 (live at 9,700 ft in the rocky mountains in Colorado). I assume this is part of the problem.

I can run my unit for a day and not even get a gallon of good water, so I bought a booster pump (from the same guy I bought the unit from). It is not adjustable and when on boosts the pressure to 160 (which might be to high), but when it is on it only takes about 3 hrs to make a gallon of good water. I don't mind the wait but in the proses it makes about 40-50 gallons of waste (for every 1 gallon of good water).

In addition to those problems the membrane (which I have changed 2X in a year) dose not work right in the fact that the water coming out of it has a TDS of about 70. I have the DI hooked up but don't like to because of the TDS of the filtered water is so high I don't want to burn through the beads quickly.

Luckily we are going into winter and I can melt large quantities of snow easily and that water test better that the water I filter with the unit, so I have been using that for about a month.

Also since the pressure is low and it doesn't work right I don't have the storage tank (which by the way is 4.4 gallons) hooked up because then zero water goes in there and it is just a waste.

I talked to the guy at a reputable fish store (which also sells RO filters) and he concluded that since the membranes that I buy (which are the EXACT same as the one rob has) cost about $30 that they probably had a bacteria in them and was causing them to break pre-maturely (hence the high TDS). This made sense but obviously rob is using them successfully.

He also stated that I had to have a valve on the end of the waste water hose so there would be high back pressure on the membrane and then it would make more water. He offered to sell me one but I figured I could do the same with an airline restrictor and some hot glue to make it hold the pressure. So I did that and yes it worked. He was right, it did increase the amount of water produced, as well as the TDS (but not by much).

What are you guys' opinions about all this?

What would you guys recommend that I do?

If any of you know where I can get a higher quality membrane for a relatively low price?

Rob, do you get your on ebay from the same guy that you bought your membrane from? If not where do you get it?

Any other info, comments, recommendations will be highly appreciated.

[CarmieJo]

Hi Evan,

I don't know the answer to the RO questions. I just hadn't seen you around in a while and wanted the say hi.

[thecoralreefer]

It sound's to me like you should have the tank. These units run about 80Lbs by themelves.
Remember the bladder inside the tank?
And your drain should be open not closed. you could save the waist water for the grass too.
Why do you have a valve on it? By doing that you are fighting against it.
Most cities only run 35 to 60 lbs of pressure anyway, so yours should be fine like that.
Being in a well only means you might have to change filters more.
How deep are you pulling from? your water is probably cleaner than most city water supplies.
I would say the problem is how your unit is hooked up.
You should see the water in Florida!!!

[vanmo92]

the well is 300 ft.

[vanmo92]

And I don't think it is cleaner than city water. When I pour it into my freshwater tanks or into a glass to drink it is actually very cloudy (and no its not dissolved gases). It also has a very metallic taste to it and makes you feel sick when you drink it.

[Astrivian]

Hey rob! I like this video. Did you record it in a studio or did you just add the black background in your house somewhere? Either way, very pro!

I had no idea so much junk was filtered out by the unit. I think i will make the switch to RO/DI to drink.

One question though, where did you get the replacement filters?

[janey]

Thank you, Rob

For the info and video...
Very Informative , I learned alot today ..
You are the MAN>>. God Bless...

Keep up the Great work......



Janet

[Rob]

Hey rob! I like this video. Did you record it in a studio or did you just add the black background in your house somewhere? Either way, very pro!

I had no idea so much junk was filtered out by the unit. I think i will make the switch to RO/DI to drink.

One question though, where did you get the replacement filters?
yeah, it was actually done in my photography studio, i figured it shoudl work for video too.. :)



Thank you, Rob

For the info and video...
Very Informative , I learned alot today ..
You are the MAN>>. God Bless...

Keep up the Great work......

Janet
thanks janet, im glad you found it helpful

[BuckeyeFieldSupply]

Rob – thanks for your work in presenting podcasts 105 and 106 regarding RODI systems! There are always lots of questions on these systems and you provided a lot of good information. I want to touch on a few of the more important issues that came to mind while I listened and watched the podcasts.

Regarding the amount of water produced by RO membranes
For sake of discussion, let’s talk about a 100 gpd membrane. Under factory specified conditions including water temperature and pressure, the 100 gpd membrane will produce about 100 gallons per day of purified water (a.k.a. “permeate”). About 4 times that amount, or 400 gallons, will be generated as “waste water” (a.k.a. “brine” or “concentrate”). This is the “4 to 1 ratio” you may have heard of. So to use the wording Rob used in the podcast, 100+400=500 gallons of water will be processed per 24 hour period by a 100 gpd membrane.

Regarding rejection rates
The rejection rate is an important criteria you should consider when selecting an RO membrane. The most popular brand of membranes used in this hobby are produced by DOW under the brandname Filmtec. For instance, the 75 gpd Filmtec membrane has a rejection rate of 98%, the 100 gpd Filmtec membrane has a rejection rate of only 90%. This difference will have a significant effect on the useful life span of your DI resin.

Regarding prefilters
Prefilters are the filters that process water before it reaches the RO membrane. On Rob’s system, there were three. Some jargon: Rob’s system appeared to have (in order of water flow) two SEDIMENT FILTERS, and one CARBON BLOCK. Avoid using the terms “sedimentary filter” or “micron filter” – both are misnomers. Sediment filters trap sediment. The size of the “holes” or “pores” in the sediment filter, and therefore the minimum size of the sediment they will trap is measured in microns (one-millionth of a meter). The podcast indicated you should not use a 1 micron sediment filter in the first stage. However, for most municipal water supplies, a 1 micron sediment filter in the first stage is appropriate and recommended. If the feedwater (tap water) has heavy sediment loads, as is the case for Rob, then using a 5 mic sed filter followed by a 1 mic sed filter makes sense. This is often the case will residential well water.

Rob referred to his third stage as a “GAC filter” (granular activated carbon). The filter in his system was actually a carbon block rather than GAC. Standard GAC filters really have no place in the RODI systems used in this hobby. I commonly see them supplied in very low end systems on the popular auction website. GAC prefilters are a holdover from residential RO systems fitted with very low capacity RO membranes (e.g. 12 gpd) that process water very slowly, and process relatively little water over the course of the useful life span of a prefilter. Bottom line – avoid use of standard GAC prefilters. Catalytic GAC is another thing entirely, but I’ll not go into that here. In general, carbon blocks are far superior to GAC, and should be what you look for in a carbon prefilter. Shop for a carbon block by considering price, pore size (in microns), and chlorine capacity (in gallons).

Regarding conductivity
Pure water has a conductivity of nearly zero, and water with higher levels of “contaminants” will have higher conductivity. I think the podcast asserted the opposite.

Regarding TDS meters
Handheld meters don’t in general read higher than in-line meters. There are numerous differences between the two types of meters, with lots of possible or probably sources of errors in the readings they produce. Also – don’t touch the probes on a TDS meter, and be careful the way the probes are aligned on in-line meters.

Regarding frequency of changing filters in an RODI system
A good rule of thumb is to replace your prefilters after six months. A more precise way to maximize the useable life of these filters is to use a pressure gauge to identify when pressure reaching the membrane starts to decline. This is your indication one or more of the filters is clogging. Rob's RODI system doesn't have a pressure gauge - if it did, and based upon the condition of his 5 micron sediment filter, I suspect Rob would have seen a substantial drop in pressure reaching the membrane and he might have changed his prefilters sooner than he did.

Also be cognizant of the chlorine capacity of the carbon block. Some carbon blocks for example will remove 99% of chlorine from 20,000 gallons of tap water presented at 1 gpm. Some original equipment suppliers commonly provide carbon cartridges rated at 2,000 to 6,000 gallons.
<O:p</O:p

Regarding your RO membrane and DI resin, use your TDS meter to measure, record, and track the TDS (expressed in parts per million) in three places:
1. Tap water
2. After the RO but before the DI
3. After the DI.
<O:p</O:p

The TDS in your tap water will likely range from about 50 ppm to upwards of 1000 parts per million (ppm). Common readings are 100 to 400 ppm. So for sake of discussion, let's say your tap water reads 400 ppm. That means that for every million parts of water, you have 400 parts of dissolved solids. How do we go about getting that TDS reading down to somewhere near zero?

If you do some experimenting with your TDS meter, you'll note that your sediment filter and carbon block filter (collectively called “prefilters”) do very little to remove dissolved solids. So with your tap water at 400 ppm, you can measure the water at the “in” port on your RO housing and you'll see it is still approximately 400 ppm.

The RO membrane is really the workhorse of the system. It removes most of the TDS, some membranes to a greater extent than others. For instance, 100 gpd Filmtec membranes have a rejection rate of 90% (i.e., they reject 90% of the dissolved solids in feed water). So the purified water coming from your 100 gpd membrane would be about 40 ppm (a 90% reduction). Filmtec 75 gpd (and below) membranes produce less purified water (aka “permeate”), but have a higher rejection rate (96 to 98%). The life span of a RO membrane is dependent upon how much water you run through it, and how dirty the water is. Membranes can function well for a year, two years, or more. Rob indicaed he changes his membrane yearly - this is much more often than the norm. To test the membrane, measure the total dissolved solids (TDS) in the water coming in to the membrane, and in the purified water (permeate) produced by the membrane. Compare that to the membrane’s advertised rejection rate, and to the same reading you recorded when the membrane was new. Membranes also commonly produce less water as their function declines.

After the RO membrane, water will flow to your DI housing. DI resin in good condition will reduce the 40 ppm water down to 0 or 1 ppm. When the DI output starts creeping up from 0 or 1 ppm, the resin needs to be replaced.

Sometimes people complain their DI resin didn't last very long. Often the culprit is a malfunctioning RO membrane sending the DI resin “dirty” water. This will exhaust the resin quicker than would otherwise be the case. Sometimes the problem is poor quality resin.

Regarding use of pressurized storage tanks in RODI systems
Without special configuration measures, avoid use of pressurized storage containers in RODI systems. If you do want to use one of these tanks, deal with a reputable vendor familiar with water purification for this hobby. The system Rob showed is poorly configured in this regard, and consequently will go through DI resin faster than should be the case. More often than not, I see these poorly configured systems coming from the popular auction website.

Russ @
Buckeye Field Supply

[V]

That...was a kick ass reply, Thanks bud. You can complain about inconsistencies any-day in my book:up:

[CarmieJo]

That was very informative. Thanks!

[Amphibious]

Wow, what a great explanation. Thanks Russ.


Regarding use of pressurized storage tanks in RODI systems
Without special configuration measures, avoid use of pressurized storage containers in RODI systems. If you do want to use one of these tanks, deal with a reputable vendor familiar with water purification for this hobby. The system Rob showed is poorly configured in this regard, and consequently will go through DI resin faster than should be the case.
Would you expand on this a bit? I T’d off right after the RO membrane and run RO water to the pressure tank for drinking water. I don’t see the problem with this configuration. Am I missing something?

Also recently the drinking water (RO water) has been producing a strong unfavorable odor, yet the final product (RO/DI water) does not. All pre filters recently changed. Any suggestions?

Dick

[BuckeyeFieldSupply]

The primary issue involves water pressure. You probably already know that water pressure significantly affects how well an RO membrane works. An empty pressure tank to a lesser extent, and a nearly full pressure tank to a greater extent provides back pressure against the membrane, so whats called the NDP, or Net Driving Pressure is significantly reduced and you'll see slowed production and a substantially reduced rejection rate from the membrane. That all equates to a substantially reduced life span for the DI resin.

With a check valve or two, you can keep that higher tds tank water from flowing back through the DI resin. We can send you the plumbing diagram to our Reef/Residential Series Systems if you'll PM us your email address.

Remember that the water in your tank is not chlorinated, and it is prone to fouling by bacteria. You should be sanitizing the entire system at least once per year. My guess is that you either have a bacterial build up, or the taste and odor cartridge between the tank and your faucet is exhausted and needs to be replaced.



Russ

[V]

rusty, id like a copy of that too please.

veriann@inorbit.com