Our Ideas

Dan Vercruysse Travels to Cambodia: Part 3 of 5

    Previous Next
    • Dan Vercruysse Travels to Cambodia: Part 3 of 5

      Biosand Water Filters

      The Trailblazer Foundation’s (TF) shop in the town of Siem Reap is the home base of their programs. This is where the fabrication and materials preparation for their biosand filters takes place, in addition to test gardens and offices. Most mornings, upon arrival the staff and volunteers begin by taking apart the steel molds used to cast the concrete biosand filter housings. This is achieved by unbolting the two halves of the mold and using a manual crank press to pull the interior part of the mold (which makes the void of the concrete housing) out of the newly cast filter body. Once all of the mold components are removed, the concrete filter housing is moved to an area where they continue to cure before being ready for painting and installation. The steel molds are then cleaned of any residue from the previous cast, oiled, and then reassembled/bolted back together in preparation of a new casting. The TF crew prepares the thin copper tubing that will be cast into the filter housing’s wall, which is the means in which water makes its way from the bottom of the filter to the pour spout on its side. This piece of the process requires detailed experience to ensure once completed the filter will function properly.

      The casting process is kicked off by the loading of their on-site concrete mixer with cement, sand, and gravel. This gets mixed until a good consistency is obtained and ready to pour. The concrete is transferred to the molds manually, bucket by bucket until the mold is full. Then, the mix inside the mold must be rodded to ensure consistency throughout the mold. Once completed, the next step is to take a heavy rubber mallet and beat the sides of the molds starting at the bottom and working towards the top. This process helps to work any air bubbles within the mix to the surface, thereby reducing the potential for any open voids in the final concrete housing and protecting the integrity of the filter walls. All of these steps can be somewhat physical. (If you’re not used to Cambodia’s high temperatures, this is likely where you will want to take a little water break.)

      The other main activity that happens in the shop is the preparation of the filtration materials that go inside the completed water filter. The materials are simple, but do require some effort to ensure they are clean and fit for use in the filter. There are two sizes of gravel used in the filters, each has to be sifted and washed and rinsed a number of times make sure there is no remaining dust or contaminates on them. They each then get pre-packaged into smaller bags, each sized for one filter. Another main component of the filer is sand. Preparing the sand requires multiple steps, starting with two grades of sieves (wire mesh filters). Sand is shoveled onto the large void sieve and manually shaken through to remove any larger debris that exists within the sand pile. Then it is shoveled onto another fine grain sieve and manually shaken through–this takes some patience and muscle and can make for sweaty work! Once completed, the sand is then transferred to a washing area where each five-gallon bucket receives five to seven rinses to both wash away any remaining dust and/or organic materials, such as dead leaves, grass, dirt, as well as let very fine grains float away so any chance of clogging the filter is minimized. Each filter requires six buckets of washed sand (about three full five-gallon buckets). It is also pre-packaged in recycled fish food bags, one for each water filter.

      On delivery day, the crew and volunteers load the delivery truck with the housings and materials to deliver and install seven complete biosand filters to rural villages. The loading/unloading process requires a bit of muscle, with each concrete housing and sand bag requiring at least two people to get them in and out of the truck. Once ready the entire group gets the luxury of experiencing the beautiful Cambodian countryside from the back of a truck–the all-time best way to see Cambodia! When you arrive at the recipient village, the truck and crew goes from location to location and unloads the materials to assemble the filters in-place. The order of operations is:

      1. Locate long-term filter location–they’re heavy (150 kg, or 300 pounds, when filtration media is installed), so this first step matters.
      2. Rinse out the concrete filter housing to remove any dust.
      3. Set and level housing.
      4. Fill the filter half-full of water, so when the larger gravel is placed in the bottom this prevent pockets of air from being trapped in the sand.
      5. Place larger gravel at bottom of housing.
      6. Place smaller gravel layer over larger gravel layer.
      7. Place sand layer over gravel layers.
      8. Fill the filter with water and let it run until the water stops pouring out of the tube, this equalizes the water level.
      9. Set plastic diffuser plate over filter media layers.
      10. Set galvanized lid on top.

      This assembly process is then followed up with instructional directions to the villagers who will be using the filters. This is important, because even though you can run water through the filter immediately, it is still not safe to use for drinking. The sand filter requires a period of conditioning–time to allow the proper biological agents to become established. This includes things like good bacteria that will help to kill bad bacteria, as well as establish an anaerobic layer within the sand that will not support harmful organisms that require oxygen to survive. This process requires that each filter have approximately five buckets (20 gallons) of water run through them each day for two weeks before it can be used for consumption. This process is very location specific. If you were to relocate the filter in the future, you would have to undertake this process again to ensure that the good biology within the filter had been recalibrated to the new collection of harmful organisms.

      This process is repeated house after house until you have an empty truck, a good work out, and great memories. Throughout the entire day while making deliveries, volunteers get a firsthand chance to see Cambodian village life in action and ask questions. This is a truly fulfilling process for everyone.

      Next up, more about life in Cambodia…

    • biosand water filter assembly
    • water line master
    • concrete boss
    • wet mix
    • vibrating the mold
    • filter housings
    • spigot casting
    • filter media prep
    • ready for delivery
    • rural Cambodia from the back of a truck
    • rural Cambodia
    • the chief
    • level housing and add media layers
    • educational instruction
    • rinse and repeat
    • About the Author

      Dan Vercruysse

      • Architect / Senior Associate
      • dan@msrdesign.com
      • 612 359 3225
      • View Bio