Household water treatment systems
Water inlet
Sludge drain
Water inlet
Practical Action
Water outlet
Figure 3: Horizontal-flow settling tank
(Illustration by A. Elias based on Cairncross and
Feachem (1993))
Overflow
channel
Water outlet
Figure 4: Upward-flow clarifier (Illustration
by A. Elias based on Cairncross and Feachem
(1993))
Sludge drain
Roughing filters
Roughing filters include a bed of coarse gravel and crushed stones to treat water with high
turbidity (50 NTU). Water is passed horizontally through a tank of about 10m so it can take
advantage of filtration through the medium and by gravity settling. A typical filtration rate for
roughing filters is 0.3-1.0m/h (metres per hour).
Water treated this way can then be passed through a Slow Sand Filter. See Multi Stage
Filtration.
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