Watermaker brine discharge question - SailNet Community
 
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post #1 of 10 Old 02-12-2009 Thread Starter
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Watermaker brine discharge question

I have a HRO watermaker aboard my new boat and it functions without a problem, all of the pressures and flow rates are correct and the water produced tastes "right" (after using a Brita water filter). But when running at anchor I see that there is a black discharge from the system and don't know what is causing it. The discharge is dark black but does not seem to be oil - neither the high-pressure pump oil level is changing nor does the discharge flow to the surface as an oil/water emulsion might.

My only guess is that this could be normal for watermakers so I am throwing this out here to see if anyone might shed some light on this.


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post #2 of 10 Old 02-12-2009
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My guess it's algea. Try followiing the cleaning instructions. You basically put it through a cycle using an alakaline first and then if that doesn't work you run a cycle using an acidic solution. I'm only doing this from memory so read your instruction manual before proceeding. It is not normal to have a black discharge. The discharge should look pretty much like the incoming water just more saline.
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post #3 of 10 Old 02-12-2009
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^^Yup, sounds like it's been stored without pickling the membrane. I'm sure you know that bleach is a no-no around the membrane. The manual will tell you how to pull the membrane (cleaning and changing it is periodic maintenance). It should be obvious then if that's the problem.

If not...
Automatic systems use a charcoal prefilter that dechlorinates the (fresh) back-flushing water (in case you've filled your tanks from a chlorinated water supply and left the WM on 'auto'). If that filter was releasing its charcoal (say...through a hole in the filter's wrap?), it would follow the backflush pathway and come out the discharge, but not for very long.

That one's a stretch, but I can't think of what else it might be that's black and would still have the unit producing potable water.

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post #4 of 10 Old 02-12-2009
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This is not good. Agree with others that you've got something going on with the membrane. It may be shot -- they do wear out, especially if they've been stored for a while. If it's been stored without biocide, it may be junk.

Also, you shouldn't have to run the product water through a Britta filter - it should be good as it comes out of the desal unit -- colorless, odorless, tasteless water. If any of these are missing, something needs fixing. I always taste and test the water directly out of the desal unit before it goes to the tanks. Are you tasteing (without the Britta) the diluted product from the tanks or the water directly out of the unit?

Do you have a meter to test for TDS (total disolved salts)? This is a good way to tell if the system is working well. I think the WHO standard for drinking water is 500 ppm. I routinely get <100 ppm from my system. (Note: you should test the desal product after a couple of minutes of operation and before you direct the output to the water tanks.)

I think it's a good idea to keep a log of desal operations. I log run time, output in gallons, and TDS of the output and water temperature. When the output begins to drop off (assuming constant water temp), then I know the membrane needs maintenance.

Last edited by billyruffn; 02-12-2009 at 07:13 PM.
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post #5 of 10 Old 02-13-2009 Thread Starter
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The unit is only a year old, but was stored for that whole period, and I don't know if they pickled it correctly or not. The water produced is drinkable, just a slight mildewy taste left over from the tank and as I am away from water sources I haven't gone the way of cleaning out the tanks as that would entail emptying them and I don't want to do that yet, thus the Brita. The unit is still ejecting black water and I will try the backflush charcoal filter next to look for leaks, but as the black water is produced during the pressure and not during the cleaning phase I am not sure if that is the source of the problem.

I will check out the membrane itself, but the pressures and product flows that I see are within the tolerances shown in the manual.

Thanks for the link to the manufacturer's forum - I'll post there are as well and report back any findings.


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post #6 of 10 Old 02-13-2009
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Zanshin,

Taste and test the water coming directly from the desal unit. If there's any taste to it after running a few minutes then the membrane is not working well. You might also change the filters upstream of the membrane, but my guess is the problem is with the membrane. There should be no taste to the product water.
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post #7 of 10 Old 02-14-2009 Thread Starter
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Billyruffn - the taste is coming from the tank, not the water; I had the same taste after I filled the forward tanks at the dock so the source isn't the watermaker.
I sent an e-mail to the manufacturer and am awaiting further information from them.
Thanks!


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post #8 of 10 Old 02-14-2009
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Just a thought, but if you meant it literally when you said it was your 'new boat', wouldn't it be a warranty issue with the builder ?

I've always pickled the membrane right after installing it. That way, the customer has to put the unit back into service instead of just turning it on. Besides, I'm usually doing that kind of stuff in the off season, so it's likely to sit for a few months anyway.
It surprises me that the same wasn't done in your case - I would think that's a no-brainer.

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Quote:
Originally Posted by Zanshin View Post
Billyruffn - the taste is coming from the tank, not the water; I had the same taste after I filled the forward tanks at the dock so the source isn't the watermaker.
I sent an e-mail to the manufacturer and am awaiting further information from them.
Thanks!
I'm unsure from the above if you've taste-tested the water coming directly from the unit. If not, you could be putting bad water in the tanks.

There has to be a source of the dark water coming from the brine discharge -- the last thing before the exhaust seacock is the membrane. My guess is it's contamination on the salty side of the membrane, although it could be in the filters before the membrane and pumps. You'll just have to trace the source of the contamination starting at either end of the process. Have you checked the filters? Color of water coming from the filters?
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post #10 of 10 Old 05-12-2009 Thread Starter
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I neglected to post the solution to the black-discharge question. I had traced the lines incorrectly, the black discharge came from the water exhaust on the generator. It would only be black when run at load, which is why I only saw (see) the issue when making water. The unit should produce 17Amps at 230V for continuous duty, but at 11Amps it seems to be overloaded - which is another topic that I'm trying to solve (a new injector might do the trick)


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