Clean Your Water With Dirt by
Ted
Praast
continued from
page two
So, how much water
will one of these process? Well, that all depends upon how large it is.
A small filter (five gallons) will give perhaps less than a gallon an hour
- not much. Smaller systems aren't quite as effective as deeper systems,
but will provide clean water. A larger version, fit for a homestead,
would process about four gallons an hour. Since a part of the slow sand
filter is a storage tank, called a “clear well”, four gallons per hour is
quite reasonable, since the filter runs 24/7. If two barrels are used,
eight gallons per hour is the total, about 192 gallons per day -lots of
water, usable for drinking, showering, or whatever your heart desires.
With a storage cistern, called a “clear well”, of perhaps 250 gallons,
your home is well supplied with good water. Of course, if more water is
needed, just add more sand filters. The general system is shown below.
So What is a Slow Sand
Filter?
In basic form, it
consists of a barrel (50 gallon food quality plastic barrel, for practical
use), a bottom layer of pea gravel four inches thick, a middle layer of
coarse graded sand, and a top layer of finer graded sand, all being washed
before using so there isn't any dust remaining. If the sand and gravel
isn't clean, the output water will be murky for a while, so not very
appealing as drinking water. A collector pipe is installed in the gravel,
and distribution pipes are installed above the top layer. Flow is limited
by having the collector pipe output at the high water level of the input.
The basic filter construction is shown below.
It's important that
the input water doesn't disturb the schmutzdecke, so the water is evenly
distributed by the small holes in the PVC pipe. Collection should also be
through small holes drilled in the PVC pipes installed in the pea gravel
layer at the bottom of the filter barrel. It must be noted that these
barrels will be very heavy, so be certain that the support for each filter
is sufficient to handle the weight.
This filter requires
several days of operation to be effective. To be absolutely certain,
allow a few weeks of operation, and always test the water before use. The
schmutzdecke (or schmutzedecke), is formed in a few days. After this
layer is active, water processed through the filter will have nearly all
organisms removed. Testing shows an average processed purity of 99.98% in
laboratory terms, or no detected harmful biologicals evident in
standardized tests. That's better than your local municipal water supply.
Now, it may not seem to you a good thing to drink water that's been
through a system that looks like pond scum, but the scientific world
assures us that not only is it safe, it's better than downtown. However,
the development time of the schmutzdecke means you need at least two sand
filters so one can be shut down for maintenance. Start the second filter
at least two or three weeks after the first one is started.
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