Water in glass
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)6
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Slow Sand Filter drawing

The drawing below is of filter 5.

slow sand filter

The diagram below is the recirculation system currently in use with filter 5.
We are using the Raindrip timer set for 1 minute running time every hour. With the pump we
are using this amounts to about 30 gallons in a day (24 hour period); using 2.8 amp hours in a day.
A 60 watt 12 volt solar panel running at half-current (2.5 amps)
for 7 hours will supply 17.5 amp-hours in a day This is Way more than enough to power
the motor during the summer months when there is little or no rainfall. A storage battery of the type used in a small backup power supply, is enough storage to run the motor in this situation.
In Washington state and other northern latitudes, there are 12 hours of sunlight in a day during the summer months - and yes, solar panels do work on a cloudy day.
recirculation schematic

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