6/20/2011
Water Filtration
and
Disinfection
2009
21
This training was prepared by the U.S. Department of Agriculture (USDA) team of Sylvana Li (Branch Chief, Rural Development and Natural Resources - USDA Foreign Agricultural
Service, email: [email protected]), Matt Murphy, and David Gallagher (both Development Resources Specialists - USDA Foreign Agricultural Service,
emails: [email protected], [email protected]), George Hernandez (Forester - USDA Forest Service, email: [email protected]), and Jon Fripp (Civil
Engineer - USDA Natural Resources Conservation Service, email: [email protected]). The USACE provided funding support for the USDA team.
• Why filter water
• Types of pollutants
• Types of filtration and disinfection
– Focus on low tech methods
– Fast sand filter and slow sand filter
• Test kits
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6/20/2011
Filtration
Cloth Filter
1. Tie a cloth around
the lid of a jar or
bucket
2. Pour the dirty water
through the cloth
3. The cloth will catch
the larger dirt pieces
Filtration
Cloth Filter
• A good way to remove
large sediments
• Does not remove small
sediments
• May be good enough for
some sprinkler or drip
irrigation
• Does not kill pathogens
• Does not remove salt
• Does not remove
chemicals
• Does not help much with
improving taste or smell
It is often a good first step
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6/20/2011
Filtration
Fast Sand Filter
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1. Clean bucket or barrel
2. Fill with 20-40 cm of sand and
gravel in layers
3. The smaller material is on top
and the larger material is at
the bottom
4. As water flows through the
sand, the sediments catch
between the sand particles.
Filtration
Fast Sand Filter
•A good way to remove sediments
•Does not kill pathogens
•Does not remove salt
•Does not remove chemicals
•Does not help much with improving taste or smell
• Simple
• Good for preparing water for
drip or sprinkler irrigation
• Often used as a pretreatment
We will now go through the
steps to build a fast sand filter
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6/20/2011
Filtration
Construction of a
fast sand filter
First – separate sand
and gravel with sieve
Filtration
Construction of a
fast sand filter
Then wash the sand
and gravel in clean
water
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6/20/2011
Filtration
Construction of a
fast sand filter
•Select a clean bucket or barrel
•Drill a hole on the side at the
bottom
•Put a pipe or hose through the
hole – this is the outlet pipe
•This pipe or hose must have
many small holes in it
Filtration
Construction of a
fast sand filter
•Seal the end of the outlet pipe or hose to
force the water through the small holes
•Seal around the hole in the bucket
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6/20/2011
Filtration
Construction of a
fast sand filter
•You can wrap the
outlet pipe or hose
with fabric
Filtration
Construction of a
fast sand filter
•Place a few
centimeters of small
rocks on the bottom,
covering the pipe
•Then place a layer of
small pebbles on the
rocks
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6/20/2011
Filtration
Construction of a
fast sand filter
•Place a few inches of
coarse sand on the
small pebbles
•Then place a 20-30
cm of finer sand on
top of that
Filtration
Construction of a
fast sand filter
•Place a layer of the small rocks on
top
•Install the inlet pipe
•This pipe should also have holes.
•Cap the end of this pipe
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6/20/2011
Filtration
Construction of a
fast sand filter
•Pour the water through
inlet pipe
•It will go through the filter
•And out the outlet pipe
Filtration
Construction of a
fast sand filter
Do not drink it!
•Most of the sediments are collected
in the top layers
•You will need to periodically scrape
away this layer and clean the sand
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6/20/2011
Filtration
Water flows rapidly through the fast
sand filter – 2 to 5 meters per hour
Construction of a
fast sand filter
Question:
If we have a fast sand filter
that has a 30 cm diameter
opening.
How many liters of water can
be filtered in 1 hour?
Answer:
15cm x 15 cm x 3.14 = 729
square cm
729 square cm X 2 m/hr = 145.8
liters in one hour
Filtration
Slow Sand Filter
Also called a biologic sand filter
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1. Clean bucket or barrel
2. Fill with 20-40 cm of sand and gravel
3. A pool of water is maintained in the
bucket over the sand.
4. A biologic layer of good microbes
forms on the top of the sand
5. As water flows through the sand,
the good microbes eat the bad
microbes.
6. Also, sediments catch between the
sand particles and in the layer of
good microbes.
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6/20/2011
Filtration
Slow Sand Filter
•Removes sediments
•Will kill many pathogens
•Does not remove salt
•Will remove some chemicals
•Will help some with improving taste
or smell
• Simple
• Slow – mainly for drinking water
• Some additional treatment may be
necessary
• Used all over the world (Nicaragua,
Honduras, Mozambique. Nepal,
Cambodia, Kenya, Haiti, etc)
Photo from CMS
/Connor
We will now go through the steps to build a slow sand filter
Filtration
Construction of a
slow sand filter
•A slow sand filter is built very
similar to a fast sand filter.
•The big difference is that the
outlet pipe goes out of the top
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6/20/2011
Filtration
Construction of a
slow sand filter
•This keeps the good microbes
wet.
•They must not dry out
•Be sure that the outlet pipe is
5 to 10 cm above the sand
•It is also a good idea to use
finer sand in the upper layers
•Do not use dust – it may clog it
Filtration
Construction of a
slow sand filter
•The dirty water must be gradually
put through the filters so to not
disturb the good microbes.
•In this example, it is done with
many small holes put in the lid.
•A small trickle of water brings air
to the microbes
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6/20/2011
Filtration
Construction of a
slow sand filter
•The good microbes are already
present in dirty water
•In 2 to 3 weeks, they will colonise
the upper few centimetres of the
sand and begin to eat the
pathogens
•New water must be added daily.
•This feeds the good microbes,
brings them air, and makes sure
they do not dry.
Filtration
Construction of a
slow sand filter
•Do not put chlorine in
the water that goes
into the filter – it may
kill the good microbes
•But adding a little
chlorine to the outflow
water may be a good
idea
Dirty water in
Clean water out
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6/20/2011
Filtration
Construction of a
slow sand filter
•Eventually, the water flow will
slow down
•The upper layer of sand will
be clogged with dirt and too
many good microbes
•Scoop out the top layer and
replace the sand
•Run water through the slow
sand filter for 2 to 3 weeks to
reintroduce the good microbes
Filtration
Construction of a
slow sand filter
•Can be combined with a fast sand
filter to make two stage treatment.
•This will extend the life of the good
microbes by removing the larger
pieces of dirt
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6/20/2011
Filtration
Construction of a
slow sand filter
Can use different
materials to make a
slow sand filter
Clay pots
are good
Construction
Steps
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6/20/2011
Filtration
Construction of a
slow sand filter
•It takes some time to filter water.
•Water slowly flows through the slow
sand filter - 10 to 20 cm per hour.
Question:
If we have a slow sand filter
that has a 30 cm diameter
opening.
How many liters of water can
be filtered in 1 hour?
Answer:
15cm x 15 cm x 3.14 = 729
square cm
729 square cm X 10 cm/hr =
7.29 liters in one hour
1 gal = 3.78 liter
Photo from CAWST
1 in = 2.54 cm
Summary
Low Cost Treatments
Pollutant
Method
Pathogens Chemical
Salt
Sediments Odour and
/ dirt
Taste
Boiling
Chlorine
UV/Solar
Distillation / still
Solar Still
Stovetop Distillation
Cloth Filter
Fast Sand Filter
Slow Sand Filter
Method is effective at removing many of these pollutants
Method provides some removal of pollutant
Method is not effective at removing pollutant
Water treated with any of these
may need additional treatment!
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6/20/2011
Clean Water has a lot of good uses
The End
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