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Biosand water purification

Discussion in 'Back to Basics' started by Equilibrium, Feb 18, 2011.

  1. Equilibrium

    Equilibrium Monkey++

    These can be quite effective, Slow sand water filter construction and study and harvesting rainwater.
    Rainwater harvesting with Sustainable technology: A look at the design, construction and operation of a small scale slow sand water filter. (Building a small slow sand water filter for individual use)
  2. Falcon15

    Falcon15 Falco Peregrinus

    The biosand methods are effective. In third world countries, they build huge retention ponds that sand filter to drinking reservoirs. It is slow and requires specialized maintenance. However, if you have the time, room, and patience it works and has worked successfully.
  3. Nadja

    Nadja RIP 3-11-2013 Forum Leader

    I am finding this very interesting indeed. Thank-you for the info
  4. BTPost

    BTPost Old Fart Snow Monkey Moderator

    The one thing about Biosand Filtering, to make Potable Water, is that the Sand Filter MUST be Back-Flushed, periodically, to maintain the filtering properties of the sand. In the industrial settings, this is done by having two Sand Filter Tanks, in Parallel, and having one Online, while the other is Back-Flushing. This means that you must have a fairly complicated Valving System, in place, to accomplish the Back-Flush Cycle, while still keeping the system active, for Potable Water to the users. You also use a lot more water, in keeping the system running, and if you have a limited source, this would not be the best type of filtering system, to use.

    I have practical experience with this type system, as this is what we were forced into using by the EPA. We process about 50K USG per day, for a summer community of between 300-500 souls. Our water here in Alaska is pristine, and have NEVER had a Quality ISSUE in over 10 Decades, of testing, but we still had to install this stuff. We have a virtually UNLIMITED Water Supply, so that isn't a significant issue, but running this system is still a Pain in the A@@....
  5. ghrit

    ghrit Ambulatory anachronism Administrator Founding Member

    Overview of sand filters. Usually, these are best applied to large scale water supplies. BTP's comment about backwashing is very true, you can't be on a limited source.
  6. Equilibrium

    Equilibrium Monkey++

    Totally agree…. even if a site lends itself to this type of filtration…. it’s doubtful this will be practical for individual homeowners and it’s definitely not going to be the best with or without an adequate source and with or without a sophisticated valve system but…. I added this because I believe it might be the only option available to some communities that are afforded no choice but to “pool” their limited resources. This form of water purification will have its place in some American communities as we are “transitioned” …. er uh…. reduced to third world status alongside our “global” brethren.
  7. Falcon15

    Falcon15 Falco Peregrinus

    On one of the sand filters from the link EQ provided, it stated, rather implicitly, that back flushing would destroy the filter. IIRC the author posted how to remove the top layers of sand in order to keep it functioning. However, I am not an expert on sand filtration.
  8. Equilibrium

    Equilibrium Monkey++

    Slow and rapid sand filtration designs were available and discussed at that link. It depends on the source, source contaminants, and system is all and I got the impression their comments were based on personal experiences with different designs relying upon different sources that were "regulated". You and me were focused on the slow sand filtration design is all. Slow sand utilizing rainwater as the source.... no back flushing by design... back flushing would compromise the integrity of the system at the link but... I'm no expert either but.... the EPA wasn't calling the shots in favor of their "stakeholders" at that site either.
  9. kvr28

    kvr28 Monkey++

    I always wondered if a pool filter would work, aren't they basically slow sand filters?
  10. Country_boy

    Country_boy Monkey+

    No, not at all. They are a rapid sand filter. A slow sand filter (SSF) provides not just mechanical filteration, but a "bio-active" layer that hopefuly kills off pathogens. A SSF has 2-3 times the sand depth, and 1/10 the pressure.

    I've built two, one worked OK (2 log (99%) inactivation of coliforms), the other failed (1 log (90%) inactivation). Both would do an excellent job as a pre filter prior to adding small amounts of chlorine or iodine.

    I want to re run the filter sometimes, I have been told that I should have been looking specifically for fecal coliforms, and they are easier to kill.

    Testing for coliforms, sodis (solar disinfection) didn't meet it's promise either. One possability is 1-2 log may be considered "good enough" for 3rd world counties. Killing 90 or 99% of pathogens is a whole lot better then nothing.
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