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Old 05-26-2018, 09:59 AM   #1
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City: Lions Bay, BC
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Vessel Model: Kadey Krogen 42 (1985)
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Chemistry of the head

After spending a fair bit of effort replumbing the forward head due to a significant buildup of Calcium and other mineral deposits, Iím curious about the chemistry that goes on with the reaction of urine and seawater. Muriatic (industrial HCl) reacts with the mineral deposits, producing CO2 as well as H2S gases. Iím not sure if the H2S is entrapped in the mineral deposits or whether it is actually produced as a result of the reaction, but it is definitely released by the reaction with the Muriatic acid.

Iíve found one scientific reference that indicates that Magnesium ammonium phosphate is also one of the precipitates formed in reaction with urine and seawater.

ďThis study concluded that ureolysis extent in a urine-seawater mixture determines the reaction pH that in turn influences the P recovery efficiency significantly; 98% of urine P can precipitate with seawater within 10 min when 40-75% of the urea in urine is ureolysed; the urine to seawater ratio alters the composition of the precipitates. The P content in the precipitates was found to be more than 9% when the urine fraction was 40% or higher. Magnesium ammonium phosphate (MAP) was confirmed to be the predominant component of the precipitates.Ē

Magnesium ammonium phosphate, AKA Struvite, is the mineral in one of the types of kidney stones. Itís formation in scale is also a problem in wastewater treatment:
Struvite is dissolved by acids.

On another forum, I found a comment that suggests ďBacterial action on the nitrogen compounds in urine produces ammonia. The ammonia raises the pH. The raised pH leads to the calcium carbonate being deposited.Ē

This chemical process also makes sense. Has this been verified?

Peggy: your comments on this would be much appreciated. I note that you advocate the weekly use of vinegar to prevent buildup. Can dilute muriatic acid also be used with shorter term exposure?


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Old 05-26-2018, 05:37 PM   #2
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City: Pretty Beach
Country: Australia
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I read a lot about mineral build up in head discharge pipes, yet after thirty years on uncleaned original hoses, our buildup is negligible.
I suspect those with buildup problems don't flush enough clean water through after using the head.
We don't have a holding tank so can flush as much as we wish - may be different if holding tank capacity was a factor.

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