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Old 05-03-2019, 08:52   #1
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Purifying grey water

I have a question about the benefit of purifying grey water vs. making fresh water from salt water. It all started after installing an automatic washing machine on the boat. It works great but it uses a lot of water, about 15 gallons per wash (1 cu ft), half my tank. It pains me to see this mostly clean water go to the sea. It also stresses out my small watermaker.

So, the question is, if I run the soapy water from the washing machine through the water maker, would I get clean water without damaging the membrane or something? I understand that home RO systems can do that but they operate at lower pressure and use different membranes. I can adjust the pressure but do I need to change the membrane as well? Any different pre-filters or treatment? One thought was to let the washing machine and possibly the shower drain to the bilge (fiberglass, relatively clean) then run this through the watermaker. A few months ago I saw an old village marine watermaker and it had two settings, salt water and grey water and I was curious at the time why would anyone design a boat watermaker with the two options. Now, it is beginning to make sense but I am not clear on the details. How clean can I expect the water to be? I usually drink and cook with bottled water but sometimes use the water from the tank.

It seems to make sense (I expect five times more output from grey water vs salt water) but the solution has to be simple and cheap, otherwise I just get a Spectra and stop worrying about this.

Thank you,
SV Pizzazz
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Old 05-03-2019, 09:37   #2
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Re: Purifying grey water

You fit all this on a 31' hunter?!

Youll be money and hassle ahead to fit a larger capacity watermaker than you will filtering the oil/soap/hair/dirt from gray water to reclaim. On top of that if you run nutrient rich gray water to youre bilge you and your boat will literally stink.
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Old 05-03-2019, 10:44   #3
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Re: Purifying grey water

When my membranes are carrying a load of bio buildup and output is down, I circulate a mixture of lye (soap). So soap alone won't hurt the membrane, but the water can't have any amount of chlorine (bleach) and it would have to be heavily filtered. Some detergents may have chlorine in them. Or maybe other additives that would hurt.

I'd expand my watermaker. Sometimes you can ad a membrane and a bigger pressure pump.
Maybe you could fit in another water tank and carry more water from your starting point.
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Old 05-03-2019, 11:15   #4
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Re: Purifying grey water

I've designed and built large industrial systems to treat gray water; I'm a chemical engineer and do this as consulting work. The short answer is a larger desal system will be cheaper and better.
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Old 05-03-2019, 11:46   #5
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Re: Purifying grey water

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I've designed and built large industrial systems to treat gray water; I'm a chemical engineer and do this as consulting work. The short answer is a larger desal system will be cheaper and better.
Thank you, thinwater, appreciate the short answer. So you mind expanding on it? I understand the issue with organics, so water from the sinks and shower goes overboard. But the washing machine water looks very clean to me. Further, I have some small leaks from the overhead hatch, so rainwater collects in the bilge. I thought I could aid this process and feed water collected from the deck, through some (closeable fittings) directly to the bilge (or grey water tank), which I then run through a home style RO system. If it is only a matter of the carbon filter, I already have that.

1) Are the membranes different or would a SW rated membrane also work at lower pressure?

2) I do not need very high quality water as I use bottled water for drinking and cooking. What would it take to just have clean enough water for showering, washing hands and more laundry?

Thank you.
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Old 06-03-2019, 15:55   #6
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Re: Purifying grey water

The cheapest and probably easiest could be to collect rain water (e.g. from the deck) I know many cruisers who use rain water as fresh water - also for drinking. Usually after running it through a filter.
It's cheap, uses (almost) no energy, doesn't break and is environmentally friendly... downside: not very reliable - depends on where you cruise...
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Old 06-03-2019, 16:26   #7
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Re: Purifying grey water

A combination sand filter for the particulates and fibers and a coalescing plate seperator for low density and insoluble contaminants will work. I certainly wouldn't contaminate my watermaker with crap that exits a wash, rinse cycle.

I've built and used the approach mentioned above in the past and it works well. There is a reasonable maintenance workload to keep the filtering system working especially for a compact system.

But packaging them on a boat will be a challenge. I've always built custom solutions (portable workshop as the commercial offerings are all industrial scale.

I'm not ready to tackle our washer and drier install, on a Liberty 458, until next year.
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Old 06-03-2019, 16:35   #8
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Re: Purifying grey water

My guess is that your brine discharge overboard will be a visible bubble bath trail in your wake.
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Old 06-03-2019, 16:46   #9
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Re: Purifying grey water

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Originally Posted by Pizzazz View Post
>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>
But the washing machine water looks very clean to me.

>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>

But it's not. Where do you think all the dirt from your clothes goes? Into the water. On the one hand you're complaining that the machine uses a lot of water and then you say it looks clean? You really can't have it both ways. Plus, isn't there a first rinse cycle and then a final rinse?


Nice job, BTW, shoehorning that puppy into your boat.
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Old 06-03-2019, 20:18   #10
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Re: Purifying grey water

Not much dirt and filth on a boat to dirty clothes unless you crawl around in the engine sump and/or a fairly filthy bilge. The most usual reason for washing clothes is that you contaminate them with sweat and the oil on your skin and you need to remove the oil residue and bacteria causing them to smell. Consequently it would appear that the water from the washing machine should be re-usable if you remove any solids and kill any bacteria in it.

It would not be to difficult to filter out the solids and kill the bacteria in order to make the grey water re-usable in a washing machine.

Lye is not soap. However the soap making process uses lye (a metalic hydroxide, usually caustic and consequently harmful to biologic tissue) in the saponification process which creates the soap molecules which are water soluble on one end and oil soluble on the other.
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Old 06-03-2019, 20:24   #11
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Re: Purifying grey water

It seems that the consensus is, use the watermaker as designed, setup the boat for rainwater collection (through a small pump and a filter directly into the tank), if it rains wash more often, if it doesn't keep the water maker running.

My basic calculation is, one wash per week, 80AH, 10 hours of water making on top of the regular use. Doable.

By the way, it rains so much in California these days that I would not even bother with a watermaker. But then again we had three years of a dry spell
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Old 06-03-2019, 21:34   #12
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Re: Purifying grey water

Quote:
Originally Posted by Pizzazz View Post
Thank you, thinwater, appreciate the short answer. So you mind expanding on it? I understand the issue with organics, so water from the sinks and shower goes overboard. But the washing machine water looks very clean to me. Further, I have some small leaks from the overhead hatch, so rainwater collects in the bilge. I thought I could aid this process and feed water collected from the deck, through some (closeable fittings) directly to the bilge (or grey water tank), which I then run through a home style RO system. If it is only a matter of the carbon filter, I already have that.

1) Are the membranes different or would a SW rated membrane also work at lower pressure?

2) I do not need very high quality water as I use bottled water for drinking and cooking. What would it take to just have clean enough water for showering, washing hands and more laundry?

Thank you.

It's not that it can't be done, it's just more complicated than it seems. You have added detergents to body oils. If you don't filter out everything, it will get smelly. Running detergents and oils through a membrane system will chew up prefilters fast.


There have been numerous attempts to recirculate shower water. It seems obvious enough to take a longer shower without using a lot of freshwater. Google it and you will see that they are complicated. The smaller you try to make it, the worse the problem gets and the more operator attention it requires. I'm sure I could build it, but I doubt I'd want to fool with it after the novelty wore off.
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Old 06-03-2019, 21:39   #13
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Re: Purifying grey water

When I was growing up my mother always saved the rinse water for the next wash cycle, machine was designed to do this and saved a lot of water on multiple load wash days. Would be doable.
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Old 06-03-2019, 21:47   #14
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Re: Purifying grey water

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There have been numerous attempts to recirculate shower water. It seems obvious enough to take a longer shower without using a lot of freshwater. Google it and you will see that they are complicated. The smaller you try to make it, the worse the problem gets and the more operator attention it requires. I'm sure I could build it, but I doubt I'd want to fool with it after the novelty wore off.
Normally use a UV filter as a part of the system too. I've been looking at it on and off but haven't tried building anything yet.
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