11 Water Purification: Physical Treatment: Improvised MechanicalFilter:
Description
This article is from the Water Treatment FAQ, by Patton Turner with numerous contributions by others.
11 Water Purification: Physical Treatment: Improvised MechanicalFilter:
If the materials aren't available to build a slow sand filter, or some
other means of water treatment is preferred, it may still be
advantageous to mechanically filter the water before treating it with
chemicals or passing through a microfilter. Generally the idea is to
allow the water to flow as slowly as possible through a bed of sand.
In a municipal water treatment plant this is called a rapid sand
filter. The particular design below is included, because the
designer, a research engineer at Oak Ridge National Laboratories,
found it particularly effective at removing fallout from water. The
filter will do little or nothing to remove pathogens, though removing
suspended solids allow others water treatment methods to work more
effectively.
Expedient water filter, from Nuclear War Survival Skills, Cresson
Kearny, ORNL
1) Perforate the bottom of a 5 gallon bucket, or similar container
with a dozed nail holes even spread over a 4" diameter circle in the
center of the container.
2) Place a 1 and 1/2" layer of small stones or pebbles in the bottom
of the can. If pebbles aren't available, marbles, clean bottle caps,
twisted coat hangers or clean twigs can be used.
3) Cover the pebbles with one thickness of terrycloth towel, burlap
sackcloth, or other porous cloth. Cur the cloth in a roughly circular
shape about three inches larger then the diameter of the can.
4) Take soil containing some clay (pure clay isn't porous enough, pure
sand is to porous) from at least 4" below the surface of the ground.
(nearly all fallout particles remain near the surface except after
disposition ion sand or gravel.
5) Pulverize the soil, then gently press it in layers over the cloth
that covers the pebbles, so that the cloth is held snugly against the
walls of the can. The soil should be 6-7" thick.
6) Completely cover the surface of the soil layer with one thickness
of fabric as porous as a bath towel. This is to keep the soil from
being eroded as water is being poured into the filter. A dozen small
stones placed on the cloth near it's edges will secure it adequately.
7) Support the filter on rocks or sticks placed across the top of a
container that is larger then the filter can (such as a dishpan)
The contaminated water should be poured into the filter can,
preferably after allowing it to settle as described below. The
filtered water should be disinfected by some method.
If the 6 or 7 inches of filtering soil is a sandy clay loam, the
filter will initially deliver about 6 quarter/hour. If the filter is
any faster than this then the fabric layer needs to be removed and the
soil compressed more. The filtering rate will drop over time as the
filter begins to clog up. When this happens the top 1/2" of soil can
be removed to increase the filtering rate. After 50 or so quarts, the
filter will need to be rebuild with fresh soil.
As with any filter, optimum performance will be achieved if sediment
in the water will be allowed to settle out before passing the water
through the filter
If the water is contaminated with fallout, clay can be added to help
the fallout particles to settle out. The procedure is as follows:
Fill a bucket or other deep container 3/4 full with contaminated
water. Dig pulverized clay or clayey soil from a depth of four or
more inches below ground surface and stir it into the water. Use
about 1 inch of dry clay or clayey soil for every 4" depth of water.
Stir until practically all of the clay particles are suspended in the
water. Let the clay settle for at least 6 hours. This will carry the
fallout particles to the bottom and cover them. Carefully dip out or
siphon the clear water and disinfect it.
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