NH3 in pure water systems

[watrdude]

My customer, a small municipal water treatment plant laboratory, is detecting ammonia in their BOD test reagent water following a treatment system that includes carbon, RO, DI & UF. We recently switched to calalytic GAC because of different chemistry with monchloramine (the source is right at the plant, 2.5ppm+). My understanding is that reaction with catalytic carbon produces NHCL4 rather than the NH3 and Cl- like normal carbon, and I'm thinking that would be better rejected by the RO. This plant has also been playing with their ammonia and chlorine injection trying to deal with a THM issue so I can't rule out excess free ammonia beyond the monochloramine combination. Water is cold this time of year, don't know if that's a factor. Any ideas on how to beef up this system? I've seen ammonia sorbents, etc. but I already have a ton of equipment on here, hard to believe that carbon,RO,IX combo can't get it.

 

[aspearin1]

I would suggest checking the RO, DI and UF to determine it's not an extractable off the membranes or ion exchange beads. Might as well start simple to rule it out at least.

 

[watrdude]

Thanks for the reply. I have considered amine throw from the anion resin, but we have tried both "seasoned" resin and virgin highly regenerated resin (cartridge type) as a polisher. The final water ranges up to 1.0 mg/l of ammonia. I think I possibly have a more fundamental problem. If I had free ammonia in my source water it would not be adsorbed by carbon (in fact regular GAC would liberate ammonia from monochloramine to create more), pass right through the RO due to low molecular weight, and not be exchanged by DI because it is a weak base (Kb 1.8 x10^-5).

 

[aspearin1]

Zeolites have found a happy home in ammonia reduction in manure. Not sure about water systems. They may do a weak ion exchange or get caught in the pores. You will have to scavenge all the leached metals, though, before it hits the RO(Ca, K, Na, Al, Si, Mg, ...) Sounds complicated. Another option may be to strip out the ammonia with a warm gas sparge.

 

[watrdude]

I did a quick google search yesterday for "ammonia sorbent" and "ammonia filter media" and saw a couple of products, including a natural zeolite. I could see using this ahead of the system to scavenge free ammonia. I assume the leaching would be less of a problem than if I exposed the media to deionized water. That's probably what I will try next unless someone has a better idea. Remember this is a very small high purity water system under a counter in a lab, I can't heat or cool it, vapor extract, biofilter, etc. I would like to hear from anyone who can confirm or refute my reasoning regarding free ammonia's ability to make it through the existing equipment though to make sure I'm not overlooking something.
BTW I understand the standard method for preparing water for BOD testing suggests distilled quality. I believe the NH3 would also make it into the condensate of a still.