IMPORTANT READ FOR RO/DI USERS - long but important!
As many of your know I've been working on a salt mixture and had sent results out to be tested to see how they match my meter and testing. They tested for more then typical salt elements and I found something troubling.
After investigating and doing checking I traced the source problem back to my RO/DI unit. I had just replaced sediment, carbon, membrane and DI filters/resins only 300 gallons or so before doing my salt mix test so I assumed everything was good. NOPE
Further investigating and a few phone calls and I find out that my township doesn't add chlorine to the water but instead produces Chloramines. On top of this they add soda lime or sodium hydroxide (to prevent piping corrosion).
I'm going to quote Charles Mitsis, President SpectraPure Inc. on the following:
"In order to understand the mechanism of chloramine removal, a little background information on the chemistry of chloramines is necessary. Chloramines are formed by the reaction of ammonia and chlorine gas. Chloramines can exist as three chemical species: monochloramine (the predominant species found in tap water), dichloramines and trichloramines. The chloramine species depends upon the pH of the water and the ratios of chlorine to ammonia. At tap water pH levels of 7 to 8.5, the formation of monochloramines is favored. Of the three species, monochloramine is the most stable and difficult to remove, as well as the most damaging to aquatic life."
To add further to this if they pH level of your tap water is 8.5 or higher you are almost guaranteed to have monochloramines.
Below you will see mention of Film-Tec. This is the membrane made by Dow under the name of Film-Tec and is the heart and sole of your RO system. It's the expensive piece that usually sits horizontally on the top of the RO/DI unit and not one of the canisters. Film-Tec membranes are almost universally used in our RO/DI systems.
Quote:
"A "ppm-hour" is defined as the exposure of 1 ppm chlorine/chloramine water for 1 hour.
Film-Tec quotes 300,000 ppm-hours (six years at 1 ppm) of chloramine resistance for their TFC polyamide (PA) membrane material, but only 200 to 1000 ppm-hours of free chlorine resistance. This indicates that chloramines will not damage Film-Tec membranes, while free chlorine levels must be held below 0.1 ppm to prevent oxidation damage. The easiest test for chloramine is with a Total Chlorine Test Kit (SpectraPure Part # TK-CL-10). The TK-CL-10 tests for a combination of free chlorine and chloramines. A sample of the wastewater stream from the RO membrane should show no signs of chlorine."
"Trade-offs exist in almost any circumstance and carbon filtration is no exception.
The smaller the micron rating, the better the removal capacity due to greater surface area. Carbon block filters made with bituminous carbon are more effective than coconut shell carbon filters for removal of monochloramine. On the other hand, in water supplies with chlorine only, the coconut shell carbon may have higher capacities for the removal of free chlorine and low molecular weight volatile organic compounds such as trihalomethanes (chloroform)."
My RO/DI unit was a Typhoon III which uses 2 carbon filters. One is 5 micron and the other is 1 micron. Both are coconut shell carbon filters. <-- good for Chlorine, bad for Chloramines!
Quote:
"Generally, reverse osmosis water is slightly acidic, due to the higher ratio of free CO2 to bicarbonate alkalinity. The exception to this rule is the presence of high pH "soda-lime softening" used by some municipalities. Free CO2 dissolved in water forms carbonic acid that lowers the pH to the range of 5 to 6 pH. In low pH RO product water, the ammonia is converted to the ionized ammonium ion NH4+. Downstream de-ionizing resins can then easily remove this charged species. It is cationic and removed by strong acid cation resins (in the hydrogen form) in either mixed bed or separate bed systems. Aquarists can be certain that when salt is properly added to RO or RO/DI water, the expected salinity and pH will be realized."
Wouldn't you know it my tap water pH is 9.45.
Quote:
"Probably the biggest environmental factor in removal of chloramine is the pH of the tap water. At a pH of 8.3, almost all of the chloramine is in the monochloramine form, which is much harder to remove. As the pH level is lowered, the ratio of dichloramines to monochloramines is increased. Dichloramine is very easy to remove by bituminous activated carbon.
The combination of soda lime softening or sodium hydroxide (to prevent piping corrosion) with chloramines is the worst possible condition. The pH is then often in the 9 to 10 range and at that pH, chloramine is totally converted to monochloramine. The reverse osmosis membrane pores will swell by the combination of high pH and free ammonia. This causes very poor rejection of silica and phosphates, and passage of ammonia through the membrane. Hydroxide ions that are present are also very poorly rejected by the membrane so the pH of the RO product water will be high and ammonia laden, creating additional load to the downstream ion exchange resins."
That pretty much describes my current problem. I'm fouling membranes very quickly and going through full DI cartridges quickly!
In talking/emailing different vendors the best solution I've gotten so far is (quoted from Charles again):
"Our usual solution to this high pH problem with chloramines is to inject hydrochloric acid (HCL) into the feed water to adjust the pH to about 6.0. This accomplishes three things: it neutralizes the hydroxides, converts monochloramines to dichloramines that are readily removed by the carbon prefilters and lastly any free ammonia (NH3+) is converted to the ionized ammonium form. The ammonium ion is well rejected by the RO membrane and in the acid pH range, the swollen membrane pores return to normal with no lasting damage.
But, with a feed water flow of no more than a liter per minute on a small line pressure RO system, an acid injector would cost many times more than the RO system. So what to do?
Nobody likes this solution but when you have water conditions like yours, you have little choice. Fill a 55-100 gallon reservoir with tap water and acidify with HCL to a pH of 6.0. Attached to this reservoir is a high flow booster pump, its inlet flooded, hooked up to your RO system. Operate at 80 psi and all is wonderful. An added benefit to this solution is a decrease in the Langelier Saturation Index (LSI). At this lower pH level, the calcium carbonate will stay in solution and not foul the membrane. The trick is not to concentrate the reject water too greatly so as to precipitate sparingly soluble salts out of solution and onto your membrane. You can also try a concentrate to product water ratio of 3:1 or even 2.5:1 for an improved recovery rate.
If space does not allow you to set up something like this you can add additional stages of DI resins to your system to handle the increased ionic impurities passed on to the DI stages. A two-bed system consisting of a SAC resin in the hydrogen form followed by a SBA resin in the OH form followed by mixed bed(s) would work well but at a greater operating cost."
My advice to ALL of you is to call your local municipality and find out if they use Chlorine or Chloramines and find out if they also use soda lime or sodium hydroxide
Carlo
PS I was directed to the following thread on RC which is where I quoted the info from: http://reefcentral.com/forums/showt...ighlight=sodium+AND+hydroxide+AND+chloramines
As many of your know I've been working on a salt mixture and had sent results out to be tested to see how they match my meter and testing. They tested for more then typical salt elements and I found something troubling.
After investigating and doing checking I traced the source problem back to my RO/DI unit. I had just replaced sediment, carbon, membrane and DI filters/resins only 300 gallons or so before doing my salt mix test so I assumed everything was good. NOPE
Further investigating and a few phone calls and I find out that my township doesn't add chlorine to the water but instead produces Chloramines. On top of this they add soda lime or sodium hydroxide (to prevent piping corrosion).
I'm going to quote Charles Mitsis, President SpectraPure Inc. on the following:
"In order to understand the mechanism of chloramine removal, a little background information on the chemistry of chloramines is necessary. Chloramines are formed by the reaction of ammonia and chlorine gas. Chloramines can exist as three chemical species: monochloramine (the predominant species found in tap water), dichloramines and trichloramines. The chloramine species depends upon the pH of the water and the ratios of chlorine to ammonia. At tap water pH levels of 7 to 8.5, the formation of monochloramines is favored. Of the three species, monochloramine is the most stable and difficult to remove, as well as the most damaging to aquatic life."
To add further to this if they pH level of your tap water is 8.5 or higher you are almost guaranteed to have monochloramines.
Below you will see mention of Film-Tec. This is the membrane made by Dow under the name of Film-Tec and is the heart and sole of your RO system. It's the expensive piece that usually sits horizontally on the top of the RO/DI unit and not one of the canisters. Film-Tec membranes are almost universally used in our RO/DI systems.
Quote:
"A "ppm-hour" is defined as the exposure of 1 ppm chlorine/chloramine water for 1 hour.
Film-Tec quotes 300,000 ppm-hours (six years at 1 ppm) of chloramine resistance for their TFC polyamide (PA) membrane material, but only 200 to 1000 ppm-hours of free chlorine resistance. This indicates that chloramines will not damage Film-Tec membranes, while free chlorine levels must be held below 0.1 ppm to prevent oxidation damage. The easiest test for chloramine is with a Total Chlorine Test Kit (SpectraPure Part # TK-CL-10). The TK-CL-10 tests for a combination of free chlorine and chloramines. A sample of the wastewater stream from the RO membrane should show no signs of chlorine."
"Trade-offs exist in almost any circumstance and carbon filtration is no exception.
The smaller the micron rating, the better the removal capacity due to greater surface area. Carbon block filters made with bituminous carbon are more effective than coconut shell carbon filters for removal of monochloramine. On the other hand, in water supplies with chlorine only, the coconut shell carbon may have higher capacities for the removal of free chlorine and low molecular weight volatile organic compounds such as trihalomethanes (chloroform)."
My RO/DI unit was a Typhoon III which uses 2 carbon filters. One is 5 micron and the other is 1 micron. Both are coconut shell carbon filters. <-- good for Chlorine, bad for Chloramines!
Quote:
"Generally, reverse osmosis water is slightly acidic, due to the higher ratio of free CO2 to bicarbonate alkalinity. The exception to this rule is the presence of high pH "soda-lime softening" used by some municipalities. Free CO2 dissolved in water forms carbonic acid that lowers the pH to the range of 5 to 6 pH. In low pH RO product water, the ammonia is converted to the ionized ammonium ion NH4+. Downstream de-ionizing resins can then easily remove this charged species. It is cationic and removed by strong acid cation resins (in the hydrogen form) in either mixed bed or separate bed systems. Aquarists can be certain that when salt is properly added to RO or RO/DI water, the expected salinity and pH will be realized."
Wouldn't you know it my tap water pH is 9.45.
Quote:
"Probably the biggest environmental factor in removal of chloramine is the pH of the tap water. At a pH of 8.3, almost all of the chloramine is in the monochloramine form, which is much harder to remove. As the pH level is lowered, the ratio of dichloramines to monochloramines is increased. Dichloramine is very easy to remove by bituminous activated carbon.
The combination of soda lime softening or sodium hydroxide (to prevent piping corrosion) with chloramines is the worst possible condition. The pH is then often in the 9 to 10 range and at that pH, chloramine is totally converted to monochloramine. The reverse osmosis membrane pores will swell by the combination of high pH and free ammonia. This causes very poor rejection of silica and phosphates, and passage of ammonia through the membrane. Hydroxide ions that are present are also very poorly rejected by the membrane so the pH of the RO product water will be high and ammonia laden, creating additional load to the downstream ion exchange resins."
That pretty much describes my current problem. I'm fouling membranes very quickly and going through full DI cartridges quickly!
In talking/emailing different vendors the best solution I've gotten so far is (quoted from Charles again):
"Our usual solution to this high pH problem with chloramines is to inject hydrochloric acid (HCL) into the feed water to adjust the pH to about 6.0. This accomplishes three things: it neutralizes the hydroxides, converts monochloramines to dichloramines that are readily removed by the carbon prefilters and lastly any free ammonia (NH3+) is converted to the ionized ammonium form. The ammonium ion is well rejected by the RO membrane and in the acid pH range, the swollen membrane pores return to normal with no lasting damage.
But, with a feed water flow of no more than a liter per minute on a small line pressure RO system, an acid injector would cost many times more than the RO system. So what to do?
Nobody likes this solution but when you have water conditions like yours, you have little choice. Fill a 55-100 gallon reservoir with tap water and acidify with HCL to a pH of 6.0. Attached to this reservoir is a high flow booster pump, its inlet flooded, hooked up to your RO system. Operate at 80 psi and all is wonderful. An added benefit to this solution is a decrease in the Langelier Saturation Index (LSI). At this lower pH level, the calcium carbonate will stay in solution and not foul the membrane. The trick is not to concentrate the reject water too greatly so as to precipitate sparingly soluble salts out of solution and onto your membrane. You can also try a concentrate to product water ratio of 3:1 or even 2.5:1 for an improved recovery rate.
If space does not allow you to set up something like this you can add additional stages of DI resins to your system to handle the increased ionic impurities passed on to the DI stages. A two-bed system consisting of a SAC resin in the hydrogen form followed by a SBA resin in the OH form followed by mixed bed(s) would work well but at a greater operating cost."
My advice to ALL of you is to call your local municipality and find out if they use Chlorine or Chloramines and find out if they also use soda lime or sodium hydroxide
Carlo
PS I was directed to the following thread on RC which is where I quoted the info from: http://reefcentral.com/forums/showt...ighlight=sodium+AND+hydroxide+AND+chloramines
