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Old 07-23-14, 09:55 AM   #1
sunspot
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Default sand filter - construction has begun!

I've started building a sand filter for our rain water collection system. It's to be a non-backflushable slow sand filter. The vessel is a 4000 litre (1000 gal) plastic cistern (I made a mistake on the tank size when I first posted - fixed now). I'll be using drain rock, pea gravel, and 20/50 filter sand as media and would like to hear what options I have for a barrier between the pea gravel and filter sand to stop migration of the sand into the gravel. Is landscape cloth food grade? Would a cotton sheet stand the test of time?



Last edited by sunspot; 08-23-14 at 09:21 AM.. Reason: math
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Old 07-27-14, 01:47 PM   #2
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Depending what you're doing with your rainwater, seems like landscape fabric would be ok, its made for gardening after all. I personally wouldn't drink through it. Food grade plastic recycling is number 5, maybe you could find that on the package. I believe its nylon, aka plastic. Asphalt shingles leach carcinogens from the bitament . How will you clean your sand filter when its time? I used a few bio filters for pond pumps, many used a thick nylon filter in them. You can buy a generic cut to size washable a/c filter at the depot. Its blue plastic, 1"x 30x 36 or some thing like that.
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Old 07-27-14, 11:15 PM   #3
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Slow sand filters have been used for centuries. To clean the media when there's not much water flow is to backflush them. As long as the media isn't supersmall from the diameter it was originally and the organizms are still active, they will work for eions. BTW,the media simpky supports the microorganisms.
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Old 08-09-14, 10:44 PM   #4
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I made some progress on the filter today and thought I'd share some thoughts and pictures.

There's lots of information on the web about slow sand filters (bio-sand filters) but much of it concerns very large scale installations. The majority of pictures returned by Google are theoretical schematics. I could find very little nuts and bolts practical information about, or examples of, smaller filters within the realm of DIY.

As mentioned above the tank I'm using is a 1000 gallon cistern that will be just over half buried. The filter will be used for domestic water - yes drinking - filtered from rainwater collected off a steel roof. It's non_backflushable by design. Cleaning when necessary will involve scraping the bioscum off the sand.

I hope it works, it's a major project. The hole in the ground had to be dug by hand. The access lid on the tank is small. I fit through but barely. All the plumbing inside the tank (PVC - 1 1/4" and 6") was taken in in pieces and assembled. The aggregate is poured in a bucket at a time. I still have a ways to go.

Now to the interesting stuff,the pictures!

http://s194.photobucket.com/user/Gre.../sand%20filter

Last edited by sunspot; 08-09-14 at 10:50 PM.. Reason: pictures
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Old 08-22-14, 10:25 PM   #5
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I was wondering what to use to separate the sand from the pea gravel. I ended up using nothing. The pea gravel is 10 mm and the sand I ended up with is 10-20. The photos show good stratification in a test jar- at least initially - even after gentle agitation. I'm encouraged. And happy I don't need some synthetic material in my filter.

sand_in_jar_zps157073c7.jpg Photo by Greg_M_ | Photobucket

sand_in_jar_closeup_zpsfda669e2.jpg Photo by Greg_M_ | Photobucket
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Old 08-23-14, 02:53 AM   #6
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I don't see anything wrong with the sand or the pea gravel. I would suggest getting some sand that's finer to go on top of what you already have.
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Old 08-23-14, 07:31 AM   #7
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400 Liters = how many gallons?

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Old 08-23-14, 09:18 AM   #8
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Quote:
Originally Posted by stevehull View Post
400 Liters = how many gallons?

Steve
Sorry Steve, fat finger typing. That should be 4000 litres, (1000 gallons).
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Old 08-23-14, 08:38 PM   #9
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I was wondering as 400 liters is not a lot of water (but 4000 is!). Include diatomaceous earth as the most fine filter (on top of the sand). Put in about 3-4 inches of thickness.

DE (as it is known) is cheap, very effective and traps bacteria, pollen as well as all algae. You do not need the food grade. Get the kind that goes into swimming pool filters.

After looking at this, you might want to reverse the trapping layers. The last filter element might be the DE, then the sand, then the pea gravel.

Think about it.

Let us know how this works out!


Steve



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Old 08-23-14, 09:07 PM   #10
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[QUOTE=stevehull;40079]After looking at this, you might want to reverse the trapping layers. The last filter element might be the DE, then the sand, then the pea gravel.
/QUOTE]

Too late for that. There's 40 cm (51 bags at 0.44 cu ft ea.) of 10-20 sand in there already. I'm trying to find 40-70 sand for the remaining ~ 3/4 meter.

Cheers, Greg

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