Basic RODI question

[HuduVudu]

Thanks all: I ended up just putting a whole new unit online (cheaper just to buy a whole new RO Buddy system).
Im back to 0 ppm in the product water. I kept the fittings from the old unit as spares.
Jay

So your booster pump was causing grief?

 

[Miami Reef]

I noticed when I don’t compact the di resin HARD I get 2 TDS…from a brand new di resin! I assume the water escapes through the sides and makes its way to the TDS meter.

 

[Jay Hemdal]

So your booster pump was causing grief?

No, this unit doesn't have a booster pump, or pressure gauges. I had purchased a replacement, but was trying to get every last gallon our of the old one before putting the new one online. People responding here about the DI resin preferentially letting weakly bound ions through was what I was worried about, so convinced, I just rigged up the new unit.




Thanks,

Jay

 

[Woodyman]

Thanks all: I ended up just putting a whole new unit online (cheaper just to buy a whole new RO Buddy system).
Im back to 0 ppm in the product water. I kept the fittings from the old unit as spares.
Jay

No, this unit doesn't have a booster pump, or pressure gauges. I had purchased a replacement, but was trying to get every last gallon our of the old one before putting the new one online. People responding here about the DI resin preferentially letting weakly bound ions through was what I was worried about, so convinced, I just rigged up the new unit.




Thanks,

Jay

When your ready to source a regular unit let me know!

 

[Randy Holmes-Farley]

I have a rather basic RODI question. I have a RO Buddie 50gpd RODI system for my home aquarium. The membrane and sediment cartridges are working well, production rate hasn't dropped). However, the DI cart has completely changed color and is exhausted. My raw feed runs about 400 ppm dissolved solids (I have a water softener on a well). When the DI was fresh, I was getting 0 to 1 ppm TDS in the product water. Now I'm getting 3.

My question is: how critical is this 2 ppm increase? Is that 2 ppm just a percentage of the total mix of TDS (1/2% increase, mostly softener salt) or is that 2% comprised preferentially of more problematic compounds such as heavy metals or organic toxins?

Thanks,

Jay

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria by Randy Holmes-Farley - Reefkeeping.com

Several issues arise relating to the depletion of the DI resins that aquarists need to be aware of. Primary among these is that when a DI resin becomes depleted, that does not simply mean that the water passes through just as it came from the RO effluent. It may actually be much worse from an aquarist’s perspective. The reason for this is that while the DI resin is functioning properly, all ions will be caught. But when it is depleted, not only the new ions are coming through and might show up in the product water, but so are all the ions that ever got into the DI resin in the first place. The total concentration of ions coming out of the exhausted DI resin will not be raised as compared to the RO's effluent, but which ions are released may be very different.

In the DI descriptions above, I did not address the fact that some ions will show a greater preference for attachment to the resin than will others. When the resins are not depleted, it does not matter what the ions’ affinity is, as all are bound. But in a depleted scenario, when there are more ions than ion binding sites, those with a higher affinity for the resin will be retained, and those with a lower affinity will be released. It turns out that silicate is found at the lower end of affinity for anion resins. Consequently, if the DI resin has been collecting silicate for a long period and is then depleted, a large burst of silicate may be released.

Perhaps even more of a concern is ammonia. In a system with chloramine in the tap water, the DI resin will serve the important function of removing much of the ammonia produced by the chloramine breakdown. Ammonia has a poorer affinity for many cation-binding resins than do many other cations (e.g., calcium or magnesium). Consequently, when the DI resin first becomes depleted, a big release of ammonia from and through the DI resin is likely. I recently had a DI resin become depleted, and the effluent contained so much ammonia that I could easily smell it.

Other complications can also impact resin depletion. One potentially important issue is that the anion and cation-binding sites may not become depleted at the same time. Figure 10 shows this scenario when both types become depleted together, with sodium and chloride in the effluent. But, it is possible for one to become depleted first, and in that case, the pH of the effluent can swing far from neutral. Figures 11 and 12 show what happens when a lot of carbon dioxide is present, as is the case with some well waters. Initially, it is mostly bound as bicarbonate, and the effluent is essentially pure water. Note, however, that as the bicarbonate is removed, the anion binding resin is being taken up with bicarbonate, while the cation-binding resin is unchanged and is therefore not being depleted.

 

[Jay Hemdal]

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria by Randy Holmes-Farley - Reefkeeping.com

Several issues arise relating to the depletion of the DI resins that aquarists need to be aware of. Primary among these is that when a DI resin becomes depleted, that does not simply mean that the water passes through just as it came from the RO effluent. It may actually be much worse from an aquarist’s perspective. The reason for this is that while the DI resin is functioning properly, all ions will be caught. But when it is depleted, not only the new ions are coming through and might show up in the product water, but so are all the ions that ever got into the DI resin in the first place. The total concentration of ions coming out of the exhausted DI resin will not be raised as compared to the RO's effluent, but which ions are released may be very different.

In the DI descriptions above, I did not address the fact that some ions will show a greater preference for attachment to the resin than will others. When the resins are not depleted, it does not matter what the ions’ affinity is, as all are bound. But in a depleted scenario, when there are more ions than ion binding sites, those with a higher affinity for the resin will be retained, and those with a lower affinity will be released. It turns out that silicate is found at the lower end of affinity for anion resins. Consequently, if the DI resin has been collecting silicate for a long period and is then depleted, a large burst of silicate may be released.

Perhaps even more of a concern is ammonia. In a system with chloramine in the tap water, the DI resin will serve the important function of removing much of the ammonia produced by the chloramine breakdown. Ammonia has a poorer affinity for many cation-binding resins than do many other cations (e.g., calcium or magnesium). Consequently, when the DI resin first becomes depleted, a big release of ammonia from and through the DI resin is likely. I recently had a DI resin become depleted, and the effluent contained so much ammonia that I could easily smell it.

Other complications can also impact resin depletion. One potentially important issue is that the anion and cation-binding sites may not become depleted at the same time. Figure 10 shows this scenario when both types become depleted together, with sodium and chloride in the effluent. But, it is possible for one to become depleted first, and in that case, the pH of the effluent can swing far from neutral. Figures 11 and 12 show what happens when a lot of carbon dioxide is present, as is the case with some well waters. Initially, it is mostly bound as bicarbonate, and the effluent is essentially pure water. Note, however, that as the bicarbonate is removed, the anion binding resin is being taken up with bicarbonate, while the cation-binding resin is unchanged and is therefore not being depleted.

Thanks Randy.

On a side note, the City of Toledo uses an alum feed to reduce turbidity in their city water. I'm not sure which alum they use, but above a certain level, it will damage RO membranes. They actually send out an email prior to raising the feed so everyone can shut off their RO production to preserve their membranes. I'm not sure if other cities use this flocculent.....

Jay

 

[threebuoys]

No, this unit doesn't have a booster pump, or pressure gauges. I had purchased a replacement, but was trying to get every last gallon our of the old one before putting the new one online. People responding here about the DI resin preferentially letting weakly bound ions through was what I was worried about, so convinced, I just rigged up the new unit.




Thanks,

Jay

I've assumed that many of the RO/DI systems available on Amazon are simply a series of canisters with different filtration media leading ultimately to the RO and DI membranes before delivering the final product.

So, when you say you replaced your system, is anything other than the canisters different than what you had before?

I've struggled with the best way to determine if canisters need to be replaced. So I bought a bunch of replacements to have on hand when the need arises. I do periodically test the TDS. But I'm not sure that's definitive. Even with new cartridges, I've had readings over 5 from time to time (municipal water supply). A while back I had high phosphates in the DT which I could not explain. At Randy's suggestion, I ran a test on the RO/DI water and determined its phosphate level was much higher than the level in the DT. I replaced the DI canister, but the phosphate levels remained above 0. Also at Randy's suggestion, I added a second in-line DI canister to the system. That effectively removed the remaining phosphate from the RO/DI output.

Recently, I began streaming the RO waste water through a secondary RO/DI stream to reduce the amount of waste water produced.


I still struggle with the question when Ishould replace the various canisters and if I am missing anything in the way I've approached RO/DI. I have done two ATI water analyses over the past 18 months. Neither indicate a problem.

 

[Jay Hemdal]

I've assumed that many of the RO/DI systems available on Amazon are simply a series of canisters with different filtration media leading ultimately to the RO and DI membranes before delivering the final product.

So, when you say you replaced your system, is anything other than the canisters different than what you had before?

I've struggled with the best way to determine if canisters need to be replaced. So I bought a bunch of replacements to have on hand when the need arises. I do periodically test the TDS. But I'm not sure that's definitive. Even with new cartridges, I've had readings over 5 from time to time (municipal water supply). A while back I had high phosphates in the DT which I could not explain. At Randy's suggestion, I ran a test on the RO/DI water and determined its phosphate level was much higher than the level in the DT. I replaced the DI canister, but the phosphate levels remained above 0. Also at Randy's suggestion, I added a second in-line DI canister to the system. That effectively removed the remaining phosphate from the RO/DI output.

Recently, I began streaming the RO waste water through a secondary RO/DI stream to reduce the amount of waste water produced.


I still struggle with the question when Ishould replace the various canisters and if I am missing anything in the way I've approached RO/DI. I have done two ATI water analyses over the past 18 months. Neither indicate a problem.

No, I just bought a completely new unit, same as I had before. I priced out the cost of replacing all of the cartridges and the RO membrane, and it was pretty close to the cost of a whole new system. Then, the threads on the fitting that go into my kitchen faucet had started to cross thread, so it made sense to just buy the new unit.

Jay

 

[HuduVudu]

No, I just bought a completely new unit, same as I had before. I priced out the cost of replacing all of the cartridges and the RO membrane, and it was pretty close to the cost of a whole new system. Then, the threads on the fitting that go into my kitchen faucet had started to cross thread, so it made sense to just buy the new unit.

Jay

Com'on Jay where's the fun in that.

DIY FOREVA!!!!