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jimmydasaint
Post  Post subject: Clean Water Using Reverse Osmosis  |  Posted: Thu Aug 09, 2012 2:15 am
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I think the reverse osmotic process justifies posting this in the Chemistry Section. As I look around to a multitude of crises across the less economically developed countries, there is a common problem - a lack of clean water. However, looking at the process of reverse osmosis, where pressure is applied to remove solvent across a partially permeable membrane due to its small size, leaving solutes behind in a separate compartment, I can see this as a hugely important mechanism in saving life The question is: am I missing an important part of the puzzle here? Or is it really that simple to deliver clean water to people under threat of a plethora of water borne diseases?

Despite the monotone delivery, this is quite interesting:

[youtube]http://www.youtube.com/watch?v=5MDPBWKdSag&feature=related[/youtube]

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iNow
Post  Post subject: Re: Clean Water Using Reverse Osmosis  |  Posted: Thu Aug 09, 2012 2:31 am
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My immediate thought is that the size of the particulate matter is relevant here, and that reverse osmosis only further clarifies already relatively clean water. I could be wrong, though. Isn't the bigger issue salination of water and salt extraction?

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marnixR
Post  Post subject: Re: Clean Water Using Reverse Osmosis  |  Posted: Thu Aug 09, 2012 6:05 am
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can't see the video at work, but when i think "dirty water" then it's not so much particulate matter that springs to mind, but water-born diseases - how does reverse osmosis handle them ?

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jimmydasaint
Post  Post subject: Re: Clean Water Using Reverse Osmosis  |  Posted: Thu Aug 09, 2012 9:25 pm
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iNow wrote:
My immediate thought is that the size of the particulate matter is relevant here, and that reverse osmosis only further clarifies already relatively clean water. I could be wrong, though. Isn't the bigger issue salination of water and salt extraction?


You are right. It works best with saltwater that is clear of particulates. I was thinking initially about situations where large populations flee from war and turmoil and then end up in large refugee camps where fresh or clean water is unlikely to be available freely. However, for settled populations next to the sea, reverse osmosis is a good solution. Reverse osmosis may be providing solutions for larger populations than I had expected:

http://www.edwardsaquifer.net/desalination.html

marnixR wrote:
can't see the video at work, but when i think "dirty water" then it's not so much particulate matter that springs to mind, but water-born diseases - how does reverse osmosis handle them ?


tridimity wrote:
I would have thought that the pre-filter, and certainly the membrane itself, would be capable of filtering out water-borne bacteria - and possibly viruses.


Agreed, trimidity, the carbon filter is, I believe, composed of activated charcoal and can also supply a pore size that stops bacteria. For viruses, isn't it possible that the membrane itself is porous only to water and that the flow stops viruses from getting through to the tap water. I could also imagine that a pre-carbon filter could also be employed for larger particulate matter - much like a conventional sieve. All speculation of course....

I read something about the US Army using reverse osmosis to provide water for a battallion of soldiers stationed abroad. Unfortunately I cannot find the article right now.

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iNow
Post  Post subject: Re: Clean Water Using Reverse Osmosis  |  Posted: Sat Aug 11, 2012 3:03 am
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jimmydasaint wrote:
Reverse osmosis may be providing solutions for larger populations than I had expected:

http://www.edwardsaquifer.net/desalination.html

I'm ashamed to admit it, but I had no idea they were doing that, and the Edwards Aquifer is right here in my neck of the woods. Cool! :geek:


I saw this a while back and was pretty impressed. It's a relatively low cost option invented by Dean Kamen, the guy who also invented the segway.

http://www.wired.com/wiredscience/2008/ ... t-and-kam/

Quote:
There has been much buzz about the water-purifying machine that Segway inventor Dean Kamen demonstrated on the Colbert Report last week (even taking on the bag of Spicy Sweet Chili Doritos that Colbert added). Everyone has been trying to find out more about his claim that "you stick a hose into anything that looks wet … and it comes out … as perfect distilled clean water."

So far as I can tell however, it’s true. (Note: I still haven’t worked out if it can handle volatile organics like gasoline and benzene.)

So what follows are the numbers behind the hype.

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bunbury
Post  Post subject: Re: Clean Water Using Reverse Osmosis  |  Posted: Sat Aug 11, 2012 5:53 pm
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I believe one of the issues with RO is that the clean water product (permeate) is only a fraction of the total water fed to the unit. Most of the feed water is retained (retentate) with the concentrated contaminants, meaning that the pumping power needed to raise the pressure to the level needed for the RO to work is quite significant.


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jimmydasaint
Post  Post subject: Re: Clean Water Using Reverse Osmosis  |  Posted: Sat Aug 11, 2012 9:21 pm
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bunbury wrote:
I believe one of the issues with RO is that the clean water product (permeate) is only a fraction of the total water fed to the unit. Most of the feed water is retained (retentate) with the concentrated contaminants, meaning that the pumping power needed to raise the pressure to the level needed for the RO to work is quite significant.


If I understand you correctly bunbury, particulates or other contaminants are effectively concentrated into a sort of 'sludge' which then needs a higher pressure to overcome. I found another military manual about delivering clean water potentially to a battallion in the field. You have to admire their attention to detail:

Quote:
The settling tank will reduce the solids loading on the ultrafiltration (UF) membranes thereby increasing the time between cleanings. Clarified water from the settling tank is fed to the UF Module by an electric motor driven pump. The UF module is a welded aluminum pipe frame that houses the three 0.1 micron UF membrane cartridges. The HP module houses a diesel engine driven high-pressure plunger pump that pressurizes the feedwater prior to treatment by reverse osmosis. The RO Module contains seven 2.5” diameter RO membranes in Titanium pressure vessels. The chemical injection/cleaning module houses a 20-gallon tank used for batching, mixing, and heating the cleaning solutions for the UF and RO system and to hold fresh product water. There are three, 2.5-gallon tanks for either sodium bisulfite (dechlorinating agent) or coagulant depending on the source water, antiscalant solution for the RO membranes, and a hypochlorite solution for disinfecting the product water. The NBC filter assembly consists of activated carbon to remove chemical warfare agents and ion exchange resin to remove radioactive contaminants. The system is only employed if the presence of NBC agents is suspected.


ftp://ftp.rta.nato.int/PubFullText/RTO/MP/RTO-MP-HFM-086/MP-HFM-086-11.pdf

I could imagine that a 0.1 micron cartridge would slow down the flow rate considerably, but would clear up a number of bacterial contaminants at least.

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jimmydasaint
Post  Post subject: Re: Clean Water Using Reverse Osmosis  |  Posted: Sat Aug 11, 2012 9:28 pm
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iNow wrote:
jimmydasaint wrote:
Reverse osmosis may be providing solutions for larger populations than I had expected:

http://www.edwardsaquifer.net/desalination.html

I'm ashamed to admit it, but I had no idea they were doing that, and the Edwards Aquifer is right here in my neck of the woods. Cool! :geek:


Hey fella! I had no idea that RO could be used at this scale, and was about to write words to this effect, until I did a quick web search and found a Texan RO system. A pleasant surprise. I thought there would be a low flow rate and it would be too low for domestic use. I was wrong.

iNow wrote:
I saw this a while back and was pretty impressed. It's a relatively low cost option invented by Dean Kamen, the guy who also invented the segway.

http://www.wired.com/wiredscience/2008/ ... t-and-kam/

Quote:
There has been much buzz about the water-purifying machine that Segway inventor Dean Kamen demonstrated on the Colbert Report last week (even taking on the bag of Spicy Sweet Chili Doritos that Colbert added). Everyone has been trying to find out more about his claim that "you stick a hose into anything that looks wet … and it comes out … as perfect distilled clean water."

So far as I can tell however, it’s true. (Note: I still haven’t worked out if it can handle volatile organics like gasoline and benzene.)

So what follows are the numbers behind the hype.


This is absolutely awesome, and out of the box thinking! I have marked it as a favourite and I would expect that aid agencies would take note of these methods.

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bunbury
Post  Post subject: Re: Clean Water Using Reverse Osmosis  |  Posted: Sat Aug 11, 2012 9:55 pm
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jimmydasaint wrote:
If I understand you correctly bunbury, particulates or other contaminants are effectively concentrated into a sort of 'sludge' which then needs a higher pressure to overcome. I found another military manual about delivering clean water potentially to a battallion in the field. You have to admire their attention to detail:

Quote:
The settling tank will reduce the solids loading on the ultrafiltration (UF) membranes thereby increasing the time between cleanings. Clarified water from the settling tank is fed to the UF Module by an electric motor driven pump. The UF module is a welded aluminum pipe frame that houses the three 0.1 micron UF membrane cartridges. The HP module houses a diesel engine driven high-pressure plunger pump that pressurizes the feedwater prior to treatment by reverse osmosis. The RO Module contains seven 2.5” diameter RO membranes in Titanium pressure vessels. The chemical injection/cleaning module houses a 20-gallon tank used for batching, mixing, and heating the cleaning solutions for the UF and RO system and to hold fresh product water. There are three, 2.5-gallon tanks for either sodium bisulfite (dechlorinating agent) or coagulant depending on the source water, antiscalant solution for the RO membranes, and a hypochlorite solution for disinfecting the product water. The NBC filter assembly consists of activated carbon to remove chemical warfare agents and ion exchange resin to remove radioactive contaminants. The system is only employed if the presence of NBC agents is suspected.


Except for capacity, this almost exactly describes the system we are currently implementing to clean up pond water in the Canadian oil sands facilities. The water goes first to a flocculation tank, then to ultrafiltration units to remove solid particulates, then to the RO system to remove dissolved minerals. The final product is used as boiler feedwater or can be dumped back into a river if not needed for that purpose. There are various ancillary systems for cleaning in place, back flushing and so on, and some very large pumps. The RO units would clog very quickly without the prior filtration stages.

One other point to mention - if considering RO as a means to produce drinking water, you have to replace some minerals that were removed because RO essentially produces demineralized water which is lacking some essential minerals that the body needs. Bottled water produced by RO has added minerals. It does remove bacteria and some viruses, but filtration can do that too. I think RO is best suited to desalination, where the retentate can (presumably) be dumped back into the sea.


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jimmydasaint
Post  Post subject: Re: Clean Water Using Reverse Osmosis  |  Posted: Fri Aug 17, 2012 8:24 pm
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bunbury wrote:
Except for capacity, this almost exactly describes the system we are currently implementing to clean up pond water in the Canadian oil sands facilities. The water goes first to a flocculation tank, then to ultrafiltration units to remove solid particulates, then to the RO system to remove dissolved minerals. The final product is used as boiler feedwater or can be dumped back into a river if not needed for that purpose. There are various ancillary systems for cleaning in place, back flushing and so on, and some very large pumps. The RO units would clog very quickly without the prior filtration stages.


Given that we have an expert on these Boards, would this be a suitable mechanism for delivering clean water to refugees in crowded conditions where sewage and drinking waters have been cross contaminated?

bunbury wrote:
One other point to mention - if considering RO as a means to produce drinking water, you have to replace some minerals that were removed because RO essentially produces demineralized water which is lacking some essential minerals that the body needs. Bottled water produced by RO has added minerals. It does remove bacteria and some viruses, but filtration can do that too. I think RO is best suited to desalination, where the retentate can (presumably) be dumped back into the sea.


Then, that answers my first question to a large extent, and is a shame if it cannnot be applied in a 'field' setting. I think, ultimately, we may have to resort to Kamen's idea as suggested by iNow:

Quote:
Wired Science
There has been much buzz about the water-purifying machine that Segway inventor Dean Kamen demonstrated on the Colbert Report last week (even taking on the bag of Spicy Sweet Chili Doritos that Colbert added). Everyone has been trying to find out more about his claim that "you stick a hose into anything that looks wet … and it comes out … as perfect distilled clean water."

http://www.wired.com/wiredscience/2008/03/colbert-and-kam/

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bunbury
Post  Post subject: Re: Clean Water Using Reverse Osmosis  |  Posted: Sat Aug 18, 2012 6:48 pm
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I am not an expert. It just happened that the firm I work for got this project and, the firm lacking experts, I was assigned. There is a vendor involved that has the expertise.

I don't know a bout Kamen's gadget, but on backpacking trips I use a Sawyer filter. This is an absolute filter that takes out solid matter, bacteria and cysts (the main concern for backpackers being giardia), and works simply and efficiently by gravity - no moving parts. There are other versions that will take out viruses. Versions of this filter are used in developing countries for purifying water from contaminated sources. It's reliability, simplicity and cheapness seem to be pluses.

http://www.sawyer.com/sawyersaves/ethi.html


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iNow
Post  Post subject: Re: Clean Water Using Reverse Osmosis  |  Posted: Sun Aug 19, 2012 3:01 pm
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Those devices are quite useful, but I think a serious limitation is that the water needs to begin fairly clean to begin with. In some of these areas where true filtration of water is needed for survival, the original sources tend to be heavily contaminated and even toxic. In other places, the animals are pooing in the water supply, and others are washing filthy clothes there, etc.

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bunbury
Post  Post subject: Re: Clean Water Using Reverse Osmosis  |  Posted: Sun Aug 19, 2012 3:43 pm
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All true - but also partly true of some backcountry water sources. All streams are pood in by animals, hence the giardia. While we always try to use clear streams, sometimes one is forced to use a muddy and smelly pond. The makers suggest prefiltering through a tee shirt to take out the worst of it. In the areas you are considering, a prefilter would be needed to prevent premature clogging of the microfilter. But the point of an absolute filter is that it is absolute, meaning any particle larger than the nominal pore size will not get through, so you can customize the pore size to take out larger or smaller contaminants. Dissolved contaminants will still get through though, which would be where RO would be beneficial, since it works on a molecular scale.


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imp
Post  Post subject: Re: Clean Water Using Reverse Osmosis  |  Posted: Thu Aug 01, 2013 6:25 am

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R-O looks good, on the surface. Delving into the matter, I found it requires a very high (comparatively) pressure be placed across the membrane(s). Sometimes, 1,000 psi or more. Imagine some frigging pump in your kitchen trying to live up to that requirement?

Further looking showed that lots of water was wasted. Like, 80% of what you get as "clean water", goes down the drain.

Believing water is the new petroleum "jackpot", I am holding off on water conditioning. Meanwhile, my wife & I chew up the water supplied to our house before swallowing it.

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