Preventing scale in toilet pipes - chemist please?

[Anonymous]

In a recent thread I have been discussing how an inexpensive filter housing with a polyphosphate cartridge (standard item in this part of Spain) can remove the scale problem in kettles and water heaters.

Suppose one places a polyphosphate cartridge in the sea water inlet then the water is conditioned before it enters the bowl.

AFAIK the mechanism for scale in marine toilets is that seawater is very high in carbonates and bicarbonates (hardly surprising since it is in contact with all those chalk cliffs, bones, and sea shells) and when urine decomposes, it forms ammonia which precipitates the carbonates onto the toilet outlet line, building up scale. If you were to flush totally each time there would be no scale buildup but we don't - and I doubt we can ever be relied on to do so.

At the moment I keep mine clear by filling the bowl with fresh water and add a cup of hydrochloric acid (spirits of salts) and pump out leaving the pipes full of dilute acid. I don't turn off the outlet cock when doing this so the seacock area itself is open to the sea, preventing a strong solution from being present for very long. I service my Jabscos every couple of years and there is no apparent deterioration as a result.

However, wouldn't it be lovely if this simple modification would keep the hoses clear? Does anyone with knowledge of chemistry (Vic /forums/images/graemlins/smile.gif) feel able to comment?

 

[VicS]

[ QUOTE ]
(Vic ) feel able to comment

[/ QUOTE ] Absolutely no idea! I suppose it might work. The only difference is that the calcium carbonate is formed by chemical reaction rather than thermal decomposition. I'd feel inclined to try it. There's nothing to loose apart from a few Euros.

 

[cliff]

The % carbonates in sea water is much higher than in "potable" water - your polyphosphate cartridge will be exhausted in no time if you are pumping seawater through it. Better to keep to your established routine and acid flush (white vinegar works as well)
--------------------

"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>

 

[wotayottie]

Carbonates will be converted into soluble chloride salts and carbon dioxide when strong hydrochloric acid is introduced into the loo pipe. What effect the acid will have on the bog, I do not know. And here in the UK you will probably have FOE, RSPB, Greenpeace, the Environment agency, Fisheries protection, Health and Safety, and the Friends of the Lugworm knocking on your hull and making threatening noises.

All the more reason to give it a go - at your own risk of course!

P.S. One thought occurs - hydrochloric will dissolve copper as in sea cock.

 

[Anonymous]

[ QUOTE ]
The % carbonates in sea water is much higher than in "potable" water - your polyphosphate cartridge will be exhausted in no time if you are pumping seawater through it.

[/ QUOTE ] I can't imagine that the solubility of the crystals in sea water will be very different to that in tap water - it isn't as though the polyphosphate 'neutralises' or reacts with the carbonates, it just creates an environment in the solution in which crystals don't form in the way they would have done. I wouldn't think that the cost of the polyphosphate would be more than a couple of euros a year (and about 15 Euros for the bits).

 

[Anonymous]

[ QUOTE ]
I'd feel inclined to try it. There's nothing to loose apart from a few Euros.

[/ QUOTE ]Changing the toilet pipes is a horrible job on my boat (well, it is horrible on most boats come to that but it really is a job for two strong men on mine) so if it fails I am in trouble. I would prefer to test it in a lab first but I don't really have the space or the bits - could be done with a 'toy' chemistry set and child's microscope, if you had one /forums/images/graemlins/smile.gif

It would make a good school project at O level standard (whatever that is in today's currency).

 

[Anonymous]

[ QUOTE ]
... What effect the acid will have on the bog, I do not know. .... One thought occurs - hydrochloric will dissolve copper as in sea cock.

[/ QUOTE ] The HCl does not have any effect on the toilet over three years. The sea cocks, likewise - remember, these are bronze not copper and bronze does not behave like copper in the presence of corrosive liquids (which is why we use 'marine bronze'). Further, the way I do it, the seacock is open so the concentration of HCl is never very high for long.

I had to remove an end by the seacock a few months ago to remove a blockage caused by a visitor and I looked very closely indeed at the metal, scratching the surface with a penknife and looking under a good light. There is no evidence of any change in the alloy, at least not any change that can be detected by colour or form. From first principles we wouldn't expect there to be a problem and when we examine it, there is no evidence of a problem.

 

[Becky]

Simple really. The seawater reacts with the ureac acid in your urine to form the deposits in your loo waste pipes.
SO, either wee over the side, or pump much more than you have in the past. About 5 pumps per meter of waste pipe + a few for safety may solve your problem. If not, speify more pumps per use of your loo.

We always give 20 pumps fpr approx 2 meters of watste pipe, and haven't (as yet) had a problem.

If in doubt, ask the Headmistress, who is sadly partially retired, but who knew EVERYTHING there is to know abouyt marine loos. The 20 pumps was from a thread from her. Look into the archives, its all there, somewhere.

 

[Anonymous]

Are you sure that seawater reacts with the fresh urine itself and not the ammonia from stale urine?

I concur with you about plenty of pumping but is isn't going to happen with any degree of reliability on my boat /forums/images/graemlins/frown.gif 20 pumps for a wee? /forums/images/graemlins/shocked.gif /forums/images/graemlins/wink.gif

 

[Liz_I]

This may be one of those 'stupid' questions. Are men & women different??!! In the uric acid department, that is? 2 heads on our boat. Main, used by male & on suite, used by female. Same lavac system, not much difference in the pipe run, same number of pump/flushes. However, female loo does not calcify up but male loo does. Okay we now need not only a chemist but a specialist on uric acid!

 

[VicS]

Firstly there is no such thing as ureac acid AFAIK.

Secondly urine does not contain uric acid (aka 2,6,8-trihydroxypurine, C5H4N4O3) as far as I am aware. Deposits, however, do cause gout and rheumatism.

Urine contains <u>urea</u> (aka cabamide, H2N-CO-NH2). Bacterial action releases ammonia from urea which increases the pH leading to deposition of calcium carbonate scale from the calcium bicarbonate in seawater.

I believe urine also contains phosphates and that magnesium ammonium phosphate can be precipitated. That may also be the cause of some of the scale formed in toilet pipes.

I belive it is true that there is a difference in male and female urine but what or why I know not (Brendan will know!) but the reason female toilets scale less may just be because the females of the species flush them more thoroughly.

Correction, sorry, small quantities of uric acid are excreted in urine, at least by primates and dalmation dogs!

 

[Anonymous]

Another factor that could affect scaling of toilets in a boat with a couple aboard is if one of them drinks an appreciable amount of C2H5OH. This might possibly reduce fat build up and make scale deposition more likely. We tend to have a 'his' and a 'hers' loo but since they both get a regual HCl treatment I can't draw any conclusions (and in any case, neither of us drinks a significant amount of alcohol).

 

[BrendanS]

My first reply was going to be that there is very little difference between male and female urine in physiological terms, other than trace amounts of hormones etc.

Then I decided to do a bit of research, and came across this. While not a scientific work, it could certainly be expanded on by a research student as a graduate project.

http://biae.clemson.edu/biolab/bubbles.html

 

[Anonymous]

Many beers have chemicals added to improve the head - maybe that gets into the pee, and the fellers drink more beer?

 

[BrendanS]

One of the respondents on that thread suggested something similar! /forums/images/graemlins/smile.gif

Very few chemicals get through the digestive system unaltered though, but would love to know the answer, and if back in the labs would do a somewhat more rigorous analysis, but sadly don't have a lab to play in anymore

 

[Anonymous]

[ QUOTE ]
Very few chemicals get through the digestive system unaltered though, but would love to know the answer, ...

[/ QUOTE ] It seems highly unlikely to be a gender thing and the physical property we are observing is foaming. Whatever is in the male pee has the characteristic of a foaming agent. Aside from detergents, beer is the only thing I can think of that people ingest.

We were in the Mar Menor for a week in May and again at the end of July and I noticed that there was a tendency for the sea water to foam in May, and it was much greater in July. Some chemical is getting into the water - could it be residual in treated sewage, or foam from grey water such as car washes (very popular in Spain)? More interestingly, we make all our water with an RO desalinator and I did not notice a tendency for the water to foam in May but there was a detectable tendency in July - whatever this chemical was could get through our 5 micron pre filter, the RO membrane and our 0.1 micron General Ecology composite drinking water filter. Now we hear that it gets through the liver and kidneys. Persistent stuff, these foaming agents.

 

[BrendanS]

Stranger things have happened, but I doubt that foaming agents are causing the problem.

 

[geoffatstanpit]

I used to have a problem with the females of our species putting bleach down the loo - both at home and on the boat. Kills all known germs so must be good.

I didn't seem able to get it through that bleach is strongly alkaline and will precipitate calcium carbonate (limescale) on the innards when mixed with hard "fresh" water and even more with sea water.

Stick to acid loo cleaners (eg Harpic) and an occasional descale with HCl or proprietary descaler.

 

[Anonymous]

I've never considered the implications of bleach - alkaline - scale but it makes sense. We have never put bleach down the loo.

I have a rule (which is adhered to) that I am consulted before any household chemicals or cleaners are used anywhere on the boat. Not all rules are complied with but thankfully that one is!

 

[wizard]

Some time back I asked Headmistress this very question and the answer was to fill the bowl with fresh water add a cupful of white vinegar and pump a few times to put the solution into the pipe and leave overnight.

We have done this everytime we have left the boat and after three years the outlet pipe is still very flexible ( a sign that the deposits have not built up and made the pipe difficult to bend)

On long trips the scale can be seen to build up in the bowl but with an overnight treatment - its gone !!

/forums/images/graemlins/smile.gif