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u/watergatornpr 2d ago
Ours does the exact same thing. We call it the ammonia "ball" We have had to go in the pipe every few months and chisel it out. From our understanding it is the hardness coming out due to the pH change. We switched to ammonium sulfate in hopes to correct this problem.
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u/Haunting-Walrus7199 2d ago
Do you have results of the switch yet? I'm going to guess that your change will do the trick. Ammonium sulfate is acidic so you shouldn't be doing any calcium precipitation.
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u/watergatornpr 1d ago
Not really... we have to shut down treatment and pull a manway cover and pump the pipe out to be able to see the build up.
All the other plants around us that use ammonium sulfate stopped having the precipitation problems after they switched though.
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u/Haunting-Walrus7199 19h ago
I work in the industrial world and have worked in WWT and other parts of our processes. We have many scrubbers that need NaOH added to maintain pH. In our plants with high water calcium we always get gypsum buildup from doing essentially cold lime softening. During maintenance down days in our process we add citric acid to the scrubber water and recirculate that for hours. Organic acids like that are good at removing the calcium buildup. Our scrubbers are high in sulfate based on the process so gypsum (CaSO4) is our problem.
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u/Haunting-Walrus7199 2d ago edited 2d ago
My best guess is it's some combination of struvite, limestone and gypsum. Struvite is magnesium ammonium phosphate in a 1:1:1 molar ratio. It forms under alkaline conditions (that would occur where you added aqua ammonia). It has a very low solubility at alkaline pH so that's why it precipitates out onto surfaces. Some WWT plants intentionally make struvite to reduce total nitrogen and total phosphorous in their effluent.
The limestone CaCO3 and gypsum CaSO4 are formed when the pH is increased and their solubility decreases. This is a similar mechanism as cold lime softening in the water treatment world.
Depending on the capabilities of your lab they may be able to determine its composition. But that may not be very helpful for eliminating it because all three precipitates are hard to stop in the conditions that you have there.
A quick test would be to put HCl on a chunk you break off. If it fizzes greatly there is limestone in there. I would guess you could do an orthophosphate test to see if it's struvite. Maybe if neither of those tests come back positive then it's gypsum. But an atomic absorption spectrophotometer (AAS) could tell you immediately what's in it. Or an inductively coupled plasma mass spectrometer (ICP-MS) would do the trick too. I'm in the industrial world so we have these instruments in our main labs for products so I have access to them. I doubt they are common in the POTW world.
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u/kev873212 2d ago
What is that ?
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u/PoopSuitsCA 2d ago
This deposit (scaling?) is at our 19% ammonium hydroxide injection point in our filter effluent channel. Bleach is injected about 10 feet downstream from this point for chloramine disinfection
I don’t know the chemistry. I’m hoping some some here can explain to me
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u/Tasty_Grand9565 2d ago
So, basically, one oxygen atom and two hydrogen atoms are attracted to each other......
Pushing the upvote. This is fascinating.
WWTPO9565 WA Group II
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2d ago
Maybe you could put some cheap, easy to remove, metal bars near there, in hopes it grows on those instead. Then just remove and replace the easy to remove ones.
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u/Gundam_Greg 2d ago
The last of us storyline starts at your facility.