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Forum for discussion on ceramic filters, safe water system, sodis, PUR, watermaker, britta filters, nerox filters, lifestraw, ceramic kiln construction, colloidal silver, chuli filters, bone char filters, biosand filters, waterguard, electrolytic chlorine generators, etc.

Porous Concrete Filters

Postby Constantine » 09 Apr 2011 16:55

Recently, I have been developing low-cost water filters using porous concrete
and recycled (PET) plastic bottles. Although still in development, I believe
porous concrete promises to help deliver safe and affordable drinking water
to millions of poor people.

Basically, I see this tool as a pretreatment filter to make turbid water clear
before using solar disinfection or chlorine.

Please visit my webpage at http://www.h2ohow.com/bottle-filters/ to examine
my progress.

You can download my latest draft on 'Making Porous Concrete Bottle Filters' by clicking
HERE: http://h2ohow.com/porous_concrete/Makin ... ilters.pdf

Your comments and suggestions are appreciated.


Peace,
Constantine Orfan :)
H2oHow.com
constantine@h2ohow.com

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09 Apr 2011 16:55

Last edited by Constantine on 26 Apr 2012 16:43, edited 4 times in total.
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Re: Porous Concrete Filters

Postby JKMakowka » 12 Apr 2011 17:01

hmm, I am a bit surprised that you can reach "sub micron" filtration with porous concrete which as far as I understood depends on larger particles being bound together by cement with larger gaps in between.

Have you made any microbiological tests about CFU reduction? Or do you go only by turbidity improvements?

If it really works it is an interesting concept though, as this is for sure much more easily doable than the burned ceramics filters.

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Re: Porous Concrete Filters

Postby Constantine » 12 Apr 2011 20:07

Brother, the short answer to your question is I have not done formal microbiological tests
for CFU reduction. I plan to pay for independent lab testing and certification - if there is
enough community interest. Again, the filters are still being developed and I'm posting
here to seek advise.


You can download my latest draft on 'Making Porous Concrete Bottle Filters' by clicking
HERE: http://h2ohow.com/porous_concrete/Makin ... ilters.pdf
You will then know almost everything I know about my filters.

Here is my (unproven) hypothesize as to how the filter works, below:

The filter removes turbidity and pathogens from contaminated water in a number of ways
including - biologically, mechanically and chemically. First, the filter typically lays 90°inside
a 5-gallon bucket. Larger sediments and particles fall to the bottom of the bucket and do not
enter the filter. Finer suspended particles are trapped and adsorbed by the concrete all along
the filter. Pathogens will first encounter the biofilm layer. Many of the pathogens will be
killed or injured by the biofilm. Remaining pathogens will be mechanically trapped inside
the concrete and starved. Other pathogens will be adsorbed by the concrete; while still
others will be killed or injured by the chemical alkalines in the concrete. When activated
carbon is used, additional metal and chemical impurities are removed that concrete cannot
affect. Finally, I have experimented with adding silver metal to the filter. Silver has
disinfecting properties and may add a final germ killing barrier. One method is to a lay a
dime sized .999% silver coin on the top opening of the bottle just beneath the cap/spigot.
This way, any remaining (weakened) pathogens come in contact with the silver and are
killed or injured to the point where they cannot reproduce. The coin is re-useable and so
the added $4 cost may be justified.

Thank you for your interest and advise.


Constantine
http://www.h2ohow.com
constantine@h2ohow.com

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Last edited by Constantine on 03 May 2011 14:24, edited 6 times in total.
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Re: Porous Concrete Filters

Postby JKMakowka » 13 Apr 2011 05:47

Ahh, this explains it a bit better.

I think the term porous concrete filter is a bit misleading, as both the use of sand and kieselgur is actually not really according to the common concept of porous concrete (in fact all descriptions I found specifically state that you should not use sand), and since what you have created is basically a kiselgur filter in a concrete "frame" it seems.

I am a bit surprised that the concrete doesn't "block" the small holes in the kieselgur, but if it works that is great. Kieselgur in general is a very proven filter material (I have worked quite a lot with mobile treatment plants using this kind of material for filter-cake creation).

However I am a bit unsure about the rest of your design. The plastic bottle is a nice mold, but it does not stick very strongly to the concrete thus water will run unfiltered in the gap between the bottle wall and the filter. I think you should have another look that typical ceramics filter designs and rethink yours. Maybe if you embed some pipe in the middle of your filter and let the water filter from the outside to the inside somehow (making sure the water REALLY has to pass through the concrete)?
What you want to avoid is to have a possibility that water will find a "shortcut" somehow, even after the filter has taken some abuse (from transport for example).

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Re: Porous Concrete Filters

Postby Constantine » 13 Apr 2011 15:09

Yes, thank you for your valuable advice. Your cautions are valid and should be addressed.

The kind of concrete you mention is also known as pervious concrete, and consists of aggregates (no sand), cement and water in the right proportions. My recipe is different, so maybe I should call it - hard sand or man-made sandstone. For now, I like porous concrete. I appreciate your advice on water shortcuts and channeling. Water will always follow the path of least resistance. Early on I watched and tested for this problem. I observed this problem with more brittle recipes of concrete and with larger (2-liter) smooth surface bottles. Cured blocks of concrete would slip out of the bottles (a bad sign). To mediate this problem, I adopted the smaller 1-liter handgrip ribbed type of bottle and made my special cement admixture (which I describe in my draft.) The porous concrete I use soaks up water like a sponge. Also, when the filter is submerged under water, the added wall pressure helps keep separation under control. Channels and shortcuts are not (yet) apparent. The path of least resistance – is through the concrete. Although, cracks and shortcuts may develop due to wear and handling (as with all ceramics.) These potential problems will continue to be monitored.

My goal is to develop do-it-yourself (DIY) water purification techniques that poor people can afford and sustain. My draft paper gives details on this DIY project. I challenge others to DIY some filters and get back with some results. I don’t intend to patent or profit from this idea in anyway that I can foresee.
My aim is to publish a final DIY manual and make it available for free.

Again, thank you for your valid cautions and advice.


Constantine
H2oHow.com

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Re: Porous Concrete Filters

Postby JKMakowka » 13 Apr 2011 15:53

Well the problem I see with depending on a special kind of bottle to minimize the channeling along the border, is that these bottles might not be available in many places, and especially if you publish that as a DIY instruction kit then people will use other bottles for it for sure, which might result in a bad filtration. A more fool-proof system would be advisable there.

I also had another look at the recipe of your "man made sand stone"... maybe I was wrong about the kiselguhr filter I talked about previously... the amount of kiselguhr is probably too low to do the mail filtration effect, and the filter is more of a concrete fixed sand bed filter (e.g. sort of like sand-stone as you describe). Is the diatomite/kieselguhr really needed at all? Because I am quite sure this is also not so easily available in many places.

However if it is the sand that does the filtration mainly, then I guess the pathogen reduction rate will be not very satisfying due to the probably low filter-strenght of this relatively short filter.

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Re: Porous Concrete Filters

Postby Constantine » 13 Apr 2011 20:54

Again, thank you for your keen insights and challenges – I hope my reply is adequate.

First, from what I have seen, the kind of bottle I recommend is one of the most common bottle shapes used to distribute bottled drinking water (worldwide). It is also the most common type used in SODIS. I think any 1-liter (PET) bottle with irregular edges for hand griping will suffice. Millions of these bottles are wasted, annually. Maybe we have another use for this waste.

Next, as you know, Portland cement is very caustic. Concrete made from Portland cement has a high ph (~13) and alkalinity due to ingredients like sodium oxide and calcium hydroxide that results from hydration. Pozzolans like volcanic ash, when combined with calcium hydroxide, make concrete with less cement and have been used since Roman times. Nowadays, fly ash from coal burning plants is commonly used. My idea is to use as little caustic cement to achieve the same or better concrete. In my research, I learned to use a natural prozzolan like (food grade) diatomaceous earth (DE). This is the safest way I found to reduce the alkalinity of concrete while keeping strength and porosity. People eat this ingredient as a nutritional supplement and dewormer. Food-grade DE can to purchased online ($16 for 10lbs). A little DE goes a long way. You can omit the DE from the recipe, but you will end up with a concrete filter that's either too soft and crumbly or too hard and brittle, clogs quickly and produces foul alkaline water – nobody wants to drink. I’ve been there, done that.

Finally, I do agree with you that pathogen removal may be limited. Nonetheless, I have found the little bottle filter to be a marvelous turbidity fighter. The US EPA has concluded that where pathogens and turbidity occur in the source water, pathogen removal correlates well with turbidity/particle removal. Hence, there is reason for optimism. However, I still need to do independent lab testing. This is a 30-cent solution to a big nasty problem - in the end, we may only get what we pay for. In conclusion, even as a low-cost turbidity treatment coupled with SODIS or chlorine for disinfecting, I believe the little bottle filter has an important role to play. Low turbidity presupposes SODIS and effective chlorination.



Regards,
Constantine
H2oHow.com

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