Testing RO water

Well, I am always open to learning. I am the first to say "I am wrong" when it is proven. Although you gave me no scientific rebuttal, I decided to dig deeper and I called Jim at the "Filter Guys". He did indeed back up what you said but explained why. I was confusing sediment with ions. He explained either the TDS meter is faulty (something I missed) or the DI resin has been saturated with Co2 either through exposure to open air or the source water has a high Co2 saturation. This is important as I and many aquarists buy bulk resin to refill our cartridges and I did not know the unused portion should be stored in a sealed jar or the such.
So.......for my part I say; "I was wrong", however now that Jim has provided a viable and useful answer, I wanted to pass it along so others can learn and get more use from their DI resin.

"A strong debate, equipped with knowledge and ideas, brings clarity to ones' own beliefs, weather correct or incorrect depends solely on the accuracy of the knowledge and ideas."
--Leon Guzdzial

 

Thanks for all the info.. It's been a BIG help..
At least I know what I need to put together now, And where to get the Parts..
K to you both..

Thanks, Larry

 

My apologies to you. I have re-read that post and I can see where it can be taken very badly and that was not the way it was meant and I hope you will accept my apologies.

The best explanation I have heard when trying to explain sediments is that sediments are what will settle out of a fluid if left sitting still. No water movement, sediments will settle out. Dissolved solids won't. If you mix up saltwater to a salinity of 1.026 and let it sit for a week, the salt and other chemicals in the water won't settle out, they are dissolved.

The only way a sediment filter can remove any dissolved particles is if they happen to be larger than the pore size of the membrane. If the dissolved particle is larger than 1 micron, then a 1 micron membrane will remove it. Typically, that isn't going to happen because of the nature of dissolved solids.

The pore size of an RO membrane is, typically, in the range of .0006 microns or so. I think that depends on who you ask though. I was looking for a reference to give that size and this page gives the .0006 microns:
Reverse Osmosis RO Pure Water Systems
I didn't want to just say it was so without giving a reference to it.

One thing I have never understood, and it may take an email or a phone call to find out, is if H2O can make it through the membrane, it means the holes have to be large enough for a molecule of water to get through. If that is true, how does it "trap" or "reject" and element or compound that is smaller (physically) than a molecule of H2O?

The things I think about sometimes make me question my own sanity.

 

I sent the filter guys an email today asking about the H2O and chemicals question. I searched and searched and never could find anything that actually answered me, so I emailed them. I got an answer at 10:30 on a Friday night. How is THAT for customer service? I have never bought anything from them (not yet anyway) but they are the ones that when I have a question, they usually answer me. They didn't specifically answer my question but sent me this link:

Basics of Reverse Osmosis

Still not sure if my answer is in there but its a good resource so I wanted to share it. Hopefully I can get a DI resource like that as well.

 

is if H2O can make it through the membrane, it means the holes have to be large enough for a molecule of water to get through. If that is true, how does it "trap" or "reject" and element or compound that is smaller (physically) than a molecule of H2O

Can a molecule of water be fluid..? Streatch to gothru a smaller space, where as a solid can't..??

Larry

 

I guess it might be possible but I found an answer last night. It was from Spectrapure instead of the filter guys. Basically, it doesn't stop anything smaller than a water molecule and thats why some things get through the RO (ex: silicates) and the DI or other methods have to deal with them.

 

Ohh! Ohh! I know this answer! Remember that the "DI" means "De-ion". The DI filter attracts and holds the ions from disolved salts and silicates. So, sodium chloride, silica tetroxide ions, etc. are trapped by the DI filter.

Thinking out loud, and dredging up chemistry class knowledge from a long time ago ... There aren't very many compounds that would disolve in water that would be smaller than a water molecule. Carbon monoxide, methane, ethane ... can't think of any others. Even isopropyl alcohol and ethyl alcohol are larger than a water molecule.

 

Most of those are volatile organics and will be adsorbed by the carbon block before it gets to the RO membrane.
I would place trust in Spectrapure before any other since the President of the company is an organic chemist and an absolute genius. The amount of research they do is mind boggling.
I own a Spectrapure MaxCap UHE RO/DI systems myself and it is truly state of the art, nothing else like it on the market today.

 

Whats so different about the MaxCap RO/DI System??
What makes the MaxCapâ„¢ RO/DI System so special?

An RO/DI system is a set of discreet technologies that must be properly integrated to optimize pure water production and minimize operation costs. In general, a water system is only as good as its weakest component. We wrote this little guide to highlight the challenge and describe the benefits of integrating the best-of-the-best components into the new MaxCap RODI systems.

Basic System Design Considerations
In a properly designed RO/DI system, the most vulnerable and expensive components are placed nearest the point-of-use and are protected by upstream water treatment components that are less vulnerable and expensive. For example, the DI cartridge is the last component in the chain of purification and is one of the most vulnerable and expensive. It is protected by the preceding reverse osmosis membrane that, in turn is protected by the carbon block filter that is preceded by the sediment filter. If any one of these critical components is not properly selected or is of sub-standard quality, premature failure of downstream components can result. This is expensive and can cause grave consequences to the stable conditions of the reef tank environment.

Water Quality
Water quality is commonly measured in units of total dissolved solids (TDS) and is desired by most to at least be less than 1PPM indicated on a reliable sensitive instrument. Be careful of systems touting “ZERO†TDS. Such systems may have Zero Indicated TDS, which may or may not be ultra pure water depending on the sensitivity of the instrument used to measure the purity of the water. Ultra pure water is about 18.2 Mohms or about 0.05 micro siemens. Thus, if there were such a thing as "ZERO TDS", it might be more appropriately measured around 0.05 micro siemens. Unfortunately, most inexpensive TDS meters can resolve at best about 5 micro siemens. That is several decades lower sensitivity than required to be stating so called "ZERO TDS" or “Ultra pure waterâ€. While 5 micro siemens conductivity is very reasonable for break-through detection to signal cartridge replacement required, it is clearly not sufficient to measure or claim “ZERO TDSâ€. For a better measurement tool, we recommend a COM-100 handheld meter, or other suitable instrument having similar or better sensitivity. All MaxCapâ„¢ systems are designed to reliably produce ultra pure, 17-18 Mohm water.


Sediment Filters
First, let's talk about sediment pre-filters and the difference between absolute and nominal micron ratings. In an absolute rated filter all particles larger than the stated micron rating are removed by the filter. In a nominal rated filter a certain percentage of particles larger than the nominal rating will actually pass through the filter. The % efficiency rating of the nominal rated filter tells you how many of the larger particles will pass through. Most sediment filters are of the nominal rating variety. String wound and spun filters have a low % efficiency rating and offer little protection for downstream components. Resin bonded sediment filters offer a very high nominal % efficiency rating and offer good protection. Some micro-sediment filters are absolute filters and provide superior protection of downstream carbon filters and membranes.
The MaxCapâ„¢ uses our new ZetaZorbâ„¢ sediment filter which has truly amazing filter capacity (about five times that of any other sub-micron sediment filter), resulting in extremely long life in the most challenging sediment conditions. As it is a true 0.2 micron absolute filter, it has the ability to remove bacteria and viruses that can cause biofouling. Another benefit from the 0.2 micron absolute filter is your downstream carbon block filter will last much longer (2x) as it will no longer be acting as a secondary sediment filter. Instead, the carbon block can do its job of removing Chloramines, VOC's, etc. Of course, if your sediment filter protects your carbon filter, it will also be protecting your expensive RO membrane as well. Basically, your sediment filter is the first link in your total system performance, and can greatly affect your long term operational cost to produce good clean water.


Carbon Block Filters
Next in line are carbon block filters. The primary function of these filters is to remove chlorine and secondarily further filter out any remaining sediment. They are typically available in three ratings: 10 micron (removes chlorine for up to 3000 gallons), 5 micron (6000 gallons) and 0.5 micron (20000 gallons) which is also effective in removing organic chemicals such as pesticides, herbicides and trihalomethanes. Since carbon block filters are absolute filters and are prone to plugging with sediment, it is essential that they are preceded by a very high efficiency sediment filter such as the ZetaZorbâ„¢; otherwise sediment will displace available carbon sites that would otherwise be used for various organic removal. The best means of determining when to replace the filter is to test the waste water stream for presence of chlorine. Any chlorine level above 0.1 ppm will cause damage to the RO membrane and indicates that the carbon block filter must be changed. All MaxCapâ„¢ systems only use our best 0.5 micron carbon block filter for the greatest removal capacity. Protected by the ZetaZorbâ„¢, it will last its full lifespan, as it will not be plugged prematurely with sediment fines that would pass through larger pore size filters.

Reverse Osmosis Membranes
The RO membrane is the workhorse of the water purification system. It uses a thin film membrane technology to reject impurities. RO membranes are especially good at rejecting large atoms and molecules and those species that exhibit relatively strong electron charge. It is less effective in rejecting small atoms and molecules (smaller than water) and those with relatively weak electron charge. RO membranes will allow all dissolved gases (such as ammonia and carbon dioxide) to pass through. The % rejection rating for a membrane is an indication of how much of these impurities will pass through the membrane and on to the DI cartridge. A membrane that has a 98% rejection rating will pass only half as many of these impurities as one with a rating of 96%. The direct result of using a 98% rejection membrane as opposed to a 96% membrane is that you will double your DI cartridge lifetime. It is important to note that all membrane manufacturers adhere to a lower % rejection limit for small membranes (2" x 10") of 96% at 60 psi and that the only way to ensure that you are using a higher % rejection membrane is to purchase it from a source which screens for higher % rejection membranes. We have been testing our RO membranes for over 20 years to the industry standard of 60psi. There is a significant amount of data for us to draw upon
when we share performance characteristics with our customers, help them troubleshoot production problems, or back up our ratings claims, for that matter.

For example, the Filmtec 75 GPD membrane that is so popular is rated 75 GPD at 50psi. When we test it at the industry standard of 60 psi, the rating is at 90 GPD. The production rate of RO membranes is directly proportional to the applied pressure, thus the rating difference; this is why we sell our membranes and systems as 90 GPD (at 60 psi and 77F). Unfortunately, most customers in the USA have less than 60 psi (or even 50 psi) available, let alone the 77F water temp that is used in the rating process (average water temp is more like 50F across most parts of the
country). In these cases a pressure-boosting pump can obtain higher production rates. If you live in Hades (Phoenix in the summer) the 77F is not much of a limiting factor as far as production goes. But for our
customers in upstate New York in January, it is a huge factor. Perhaps to be more realistic we should all rate membranes production on systems at 40 psi and 50F, although I doubt our competitors would drop their rating convention in this highly competitive market seemingly driven by perceived cost per gallon production rate. That said, with the membranes that we hand-select and test to insure rejection greater than 98%, we typically see production rates exceeding 100 GPD at 60 psi (and 77 F)!! If you look back at their literature, Filmtec started the 50 psi rating as a sales gimmick wherein they stated that FILMTEC membranes have the same production at 50 psi as the competitors membranes do at 60psi. Great way to snag customers, but it requires customers to look at the production rate charts and how they are derived to really compare membrane production rates. With our hand-selected and tested Filmtec 75GPD membranes, we can make sure that you are purchasing greater than 98% rejection (look at their spec on the DOW website, 96% is the bottom range of the guarantee. They are not all 98% like many think). FILMTEC TW30-1812-75

The MaxCap™ uses tested membranes to insure that rejection is better than 98%, and that production rates are at least greater than stated. The new MaxCap™ 150 and 300 use new proprietary high efficiency membranes that allow a single membrane system to produce an amazing 150 GPD at 60psi (77F). Dual 150’s produce an even more amazing 300 GPD. Our competitors can only produce 180 GPD with the same footprint (two 90GPD membranes). These exceptionally high production rates allow these systems to produce larger amounts of water than competitor systems at colder temperatures, where lower rated membranes really struggle to produce. For example, a 90 GPD production membrane output will be cut approximately in half, or 45 GPD if the water temperature drops from 77F to 55F.

Why all this worry over Rejection Rates?
Why is 1 or 2% improvement in rejection rate so important?? A 2% increase in rejection from 96% to 98% can double your DI cartridge(s) life. Over the life of the membrane that can save you big $$$ in DI cartridges! That is why our hand selection and proprietary testing (we reject more than half that do not meet our SPEC of >98.0% rejection) is worth the extra cost. Who else labels their membranes with actual percent rejection and production rates on the so called "the same" membrane?



De-ionization Cartridges
The DI cartridge serves as a final polish of the water before it sees the actual application. The cartridge contains a mixed bed of anion and cation resins that uses an ion exchange mechanism to remove the small amount of impurities that pass through the RO membrane such as silica, phosphates, nitrates, ammonium and other trace impurities. Like a filter, the DI cartridge must be monitored for performance and replaced when it becomes exhausted. The best way to accomplish this is through use of a resistivity monitor. Another way is through the use of color change resins that give a visual indication of when the resins are exhausted. It is difficult to determine the exact replacement point of color change cartridges. Failure to do so often results in dumping of silica and other contaminants back into the water. Each MaxCapâ„¢ RO/DI System uses the revolutionary MaxCapâ„¢ DI cartridge as a first super high capacity roughing cartridge. The MaxCap DIâ„¢ cartridge has 3.5 times more capacity than any other Mixed-Bed or Hi-Silica-removal deionizing cartridge. When installed upstream of a Silica Buster or other DI cartridge, the life of your downstream DI cartridge will increase significantly. This incredible breakthrough in DI cartridge technology reduces your costs to produce DI water by over 50%, often paying for the system in less than two years on savings alone in replacement DI cartridges. In most applications, the MaxCap DIâ„¢ is installed up-stream of a Mixed-Bed or Hi-Silica removal cartridge. For example, if the RO water entering the MaxCap DIâ„¢ has 20 ppm TDS (Total Dissolved Solids), the original DI cartridge may process about 400 gallons of pure DI water. By placing a MaxCap DIâ„¢ cartridge in front of the original cartridge, 1200 gallons of water will pass through both cartridges before the MaxCap DIâ„¢ is exhausted. The original DI cartridge will be only one-third exhausted. A second MaxCap DIâ„¢ will process another 1200 gallons and the original cartridge will now be two-thirds exhausted. Only after a third MaxCap DIâ„¢ cartridge processes another 1200 gallons will the original cartridge finally become fully exhausted. That's 3600 gallons purified with only 4 (3 MaxCap DIâ„¢ + 1 Mixed-Bed) cartridges, not 9 (9 x 400 = 3600). The MaxCapâ„¢ systems use the Silica Busterâ„¢ as the second stage of DI polish to insure that silica removal is at its highest, and to make sure the product water is ultra pure.

Cost of Ownership
There are at least two costs when purchasing a RO/DI system, the first everyone is aware of is the initial purchase price, and the second is rarely given much thought; the cost to operate and maintain the system to produce water. This second cost is often overlooked during the excitement of the initial purchase, which is unfortunate as often the cost to maintain and operate the system chosen exceeds the system purchase price within the first year or so. For example, poor sediment filtration will result in premature carbon block filter life, which in turn prematurely consumes the RO membrane by increasing its load factor. As the deteriorating membrane rejection rate allows a larger downstream load of impurities to pass to the DI stages, their lifespan is correspondingly decreased. Each system is only as good as the weakest link. Each must be carefully selected to optimize performance. Under Phoenix Metro water test conditions, the MaxCapâ„¢ RO/DI 90, 150 or 300 will typically pay for itself in less than one year over any competitor system in savings due to its total system integrated performance, top notch components, and proprietary membrane, sediment filtration and DI cartridge technology.


Charles Mitsis
Bruce Huling
SpectraPure

 

What is ZERO TDS? Is it real??
I thought I would comment on the common misnomer "ZERO TDS". Persons stating ZERO TDS I assume are referring to Zero Indicated TDS. What's the difference you ask? Well, quite a bit when you are really talking about ultrapure water. Ultrapure water is about 18.2 mohms or about 0.05 microseimens. Most Reefers are after such ultrapure water in our experience. Thus, if there were such a thing as "ZERO TDS", it might be more appropriately measured around 0.05 micro siemens. Unfortunately, most (not all) inexpensive TDS meters can resolve at best about 5 micro seimens. That is several decades less sensitivity than required to be stating so called "ZERO TDS".

While 5 micro siemens conductivity (at an affordable price and rugged instrument easily operated and maintained) is very reasonable for for break-through detection to signal cartridge replacement required, it is clearly not sufficient to measure or crow about having “ZERO TDS†. Thus, postings where one has "measured" a system or component performance and state they have "ZERO TDS" should be careful to quantify the accuracy of the instrument they are using to make such a claim. Hopefully this will shed some light on... zero is not always zero.
bruce
spectrapure