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2009
21
Water Filtration
andDisinfection
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 AgriculturalService, 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.
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Why do we filter water?
For drinking
For irrigation
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Types ofPollutants
Pathogens
Where do they come from?Why do we care?
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Types of Pollutants
Chemical
Where do they come from?Why do we care?
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Types of Pollutants
Salt
Where does it come from?Why do we care?
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Municipal Treatmentmost includes these steps
Settlement / sedimentation
Filtration
Disinfection
(chemicaltreatment)
Water SupplyModified from Robert A. Perdue Water Treatment Plant
Water Source
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Municipal Treatment
Can Provide Large Quantities of Safe WaterOften Big Operations
ExpensiveTraining Required to Operate
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Treatment Plants Can Be Small
Photos from Jerry Bernard
This one treats waterfrom a small pondfor a residence
This system treats and packages water for a school
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Low Cost Treatments
Boiling
Chemical
UV/Solar
Distillation
Filtration Biological Filtration
Water treated with any of thesemay need additional treatment!
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Boiling
Boil water for 10 minutesBoiling will kill mostpathogens
Does not remove saltDoes not removesedimentsDoes not remove mostchemicalsDoes not help with muchimprovement of taste or
smell
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Chemical
Can be added directly tothe waterIt will kill most pathogensLeaves a smellDoes not remove saltsDoes not removesediments
Does not remove mostchemicals
Chlorine BleachChlorine Powder
Chlorine TabletsChlorine LiquidGranular Calcium HypochloriteIodine
These chemicals canbe dangerous!
Can use bleach
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ChemicalCan use bleach
for 1%: use 10 drops/literfor 2-6%: use 2 drops/liter
for 7-10% use 1 drop/literDouble the dose if the water iscloudy
one cap of Clorox for every 2gallons (7.5 liter) of water.
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Do not use too muchUse Regular Clorox BleachDo not use bleach with fabricsoftener or other additives
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Mix the treated water. Allowthe treated water to settle for
30 minutes.
Smell the water. The treatedwater should have a slight bleach
odor. If it does not have an odor,repeat the treatment.Taste a little of the treated water.If it has a strong taste of chlorine,
spit the water out. Allow thecontainer of treated water to situncovered for another 30 minutesor pour the water back and forthbetween two clean containers.
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Chemical
for 1%: use 10 drops/literfor 2-6%: use 2 drops/literfor 7-10% use 1 drop/liter
Question:
Using a 5.8% chlorineHow many drops to purify water ina two liter bottle?
Answer:2 liters x 2 drops per liter = 4drops
Remember to mix it and allow it tosettle
Do not use too much
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UV/Solar
Paint bottle blackLeave in sun for 6 hoursExposes water toultraviolet rays from sun
Raises temperatureKills some pathogensDoes not remove saltDoes not remove
sedimentsDoes not removechemicalsDoes not help with muchimprovement of taste orsmell
B ili d t hi h l
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Distillation
Heat
Boils water
Water intovapor Cool water turnswater vapor into
liquid
Kills most pathogensRemoves salt
Removes sedimentsRemoves many chemicalsCan help with improvementof taste or smell
Boiling produces water vapor which leavesbehind pollutantsWater vapor is allowed to cool and turn
back into water
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Di till ti
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Can use distillwater on a stove
Distillation
Stove Top Distillation1. Put the dirty water in the pot2. Place a collection cup in the
pot
3. Clean the lid and turn itupside down
4. Boil the water5. The water condenses on the
lid of the pot and falls intothe collection cup.
Di till ti
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Food coloring wasplaced in the water to
represent pollutantsNotice the water in thecollection cup is clear
Stove Top Distillation
Distillation
Slow and takes energy
Distillation
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Can use the sun to distill water
Distillation
Solar Distillation
SolAqua Model 550 Rainmaker
Photo from Jeff Wheaton
Distillation
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Solar Distillation
1. The sun heats the water2. The water evaporates3. The water condenses on the glass4. The water runs down to the
collection tray
Only pure water rises to the top
Distillation
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Must have a sunny day
Very slowCan take a few hours
to get a small amount
Solar Distillation
Solar Distillation Distillation
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In the summer, about8 square feet of glass
will produce 1 gallonper dayAbout half in thewinter.May need severalunits
Filtration
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Filtration
Cloth Filter1. Tie a cloth around
the lid of a jar orbucket
2. Pour the dirty waterthrough the cloth
3. The cloth will catchthe larger dirt pieces
Filtration
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Cloth Filter A good way to removelarge sediments
Does not remove small
sediments May be good enough for
some sprinkler or dripirrigation
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
Filtration
Filtration
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Filtration
Fast Sand Filter1. Clean bucket or barrel2. Fill with 20-40 cm of sand and
gravel in layers
3. The smaller material is on topand the larger material is atthe bottom
4. As water flows through the
sand, the sediments catchbetween the sand particles.
.
.
.
...
.
.
.
... ..
.
.
.
.
..
..
.
. .
.....
.. .
... ... ....
Filtration
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Simple Good for preparing water for
drip or sprinkler irrigation Often used as a pretreatment
Fast Sand FilterA good way to remove sediments
Does not kill pathogensDoes not remove saltDoes not remove chemicals
Does not help much with improving taste or smell
Filtration
We will now go through thesteps to build a fast sand filter
Filtration
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Filtration
First separate sand
and gravel with sieve
Construction of a
fast sand filter
Filtration
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Then wash the sandand gravel in clean
water
FiltrationConstruction of a
fast sand filter
Filtration
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FiltrationConstruction of a
fast sand filter
Select a clean bucket or barrelDrill a hole on the side at thebottom
Put a pipe or hose through thehole this is the outlet pipeThis pipe or hose must havemany small holes in it
Filtration
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FiltrationConstruction of a
fast sand filter
Seal the end of the outlet pipe or hose toforce the water through the small holesSeal around the hole in the bucket
Filtration
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t at oConstruction of a
fast sand filter
You can wrap the
outlet pipe or hosewith fabric
Filtration
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Construction of a
fast sand filter
Place a fewcentimeters of smallrocks on the bottom,
covering the pipeThen place a layer ofsmall pebbles on therocks
Filtration
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Construction of a
fast sand filter
Place a few inches ofcoarse sand on thesmall pebbles
Then place a 20-30cm of finer sand ontop of that
Filtration
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Construction of a
fast sand filter
Place a layer of the small rocks on
topInstall the inlet pipeThis pipe should also have holes.Cap the end of this pipe
Filtration
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Construction of a
fast sand filter
Pour the water throughinlet pipeIt will go through the filter
And out the outlet pipe
Filtration
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Construction of a
fast sand filter
Most of the sediments are collectedin the top layersYou will need to periodically scrapeaway this layer and clean the sand
Do not drink it!
Filtration Water flows rapidly through the fastd fil 2 5 h
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Construction of a
fast sand filter
sand filter 2 to 5 meters per hour
Answer:15cm x 15 cm x 3.14 = 729
square cm729 square cm X 2 m/hr = 145.8liters in one hour
Question:If we have a fast sand filter
that has a 30 cm diameteropening.How many liters of water canbe filtered in 1 hour?
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Slow Sand Filter
Filtration
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Simple Slow mainly for drinking water
Some additional treatment may benecessary
Used all over the world (Nicaragua,Honduras, Mozambique. Nepal,
Cambodia, Kenya, Haiti, etc)
Slow Sand FilterRemoves sediments
Will kill many pathogensDoes not remove saltWill remove some chemicalsWill help some with improving taste
or smell
We will now go through the steps to build a slow sand filter
Photo from CMS
/Connor
Filtration
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A slow sand filter is built verysimilar to a fast sand filter.The big difference is that theoutlet pipe goes out of the top
Construction of a
slow sand filter
Filtration
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Construction of a
slow sand filter
This keeps the good microbes
wet.They must not dry outBe sure that the outlet pipe is5 to 10 cm above the sand
It is also a good idea to usefiner sand in the upper layersDo not use dust it may clog it
Filtration
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Construction of a
slow sand filter
The dirty water must be graduallyput through the filters so to notdisturb the good microbes.In this example, it is done with
many small holes put in the lid.A small trickle of water brings airto the microbes
Filtration
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Construction of a
slow sand filter
The good microbes are alreadypresent in dirty waterIn 2 to 3 weeks, they will colonise
the upper few centimetres of thesand and begin to eat thepathogensNew water must be added daily.
This feeds the good microbes,brings them air, and makes surethey do not dry.
Filtration
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Construction of a
slow sand filter Dirty water in
Clean water out
Do not put chlorine inthe water that goesinto the filter it may
kill the good microbesBut adding a littlechlorine to the outflowwater may be a good
idea
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FiltrationC t ti f
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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 goodmicrobes by removing the largerpieces of dirt
FiltrationC t ti f
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Construction of a
slow sand filter
Can use differentmaterials to make aslow sand filter
Clay potsare good
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ConstructionSteps
FiltrationConstruction of a
It takes some time to filter water.Water slowly flows through the slow
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Photo from CAWST
Construction of a
slow sand filter
y gsand filter - 10 to 20 cm per hour.
Answer:15cm x 15 cm x 3.14 = 729
square cm729 square cm X 10 cm/hr =7.29 liters in one hour
Question:If we have a slow sand filter
that has a 30 cm diameteropening.How many liters of water canbe filtered in 1 hour?
1 gal = 3.78 liter1 in = 2.54 cm
SummaryLow Cost Treatments
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Low Cost Treatments
Water treated with any of thesemay need additional treatment!
Pollutant
Method Pathogens Chemical SaltSediments
/ dirt
Odour and
Taste
Boiling
Chlorine
UV/Solar
Distillation / still
Solar Still
Stovetop Distillation
Cloth Filter
Fast Sand FilterSlow Sand Filter
Method is effective at removing many of these pollutants
Method provides some removal of pollutant
Method is not effective at removing pollutant
Test TimeWhat Pollutants might be here?If we wanted to use this water for
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If we wanted to use this water fordrip irrigation, what filtrationwould be useful?
Answer: for sediment/ dirtywater use a cloth filter or afast sand filter
Test TimeWhat Pollutants might be here?If we wanted to use this water
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Answer: for sediment/ dirtywater use a cloth filter or afast sand filter
for drip irrigation, what filtrationwould be useful?
Test TimeWhat Pollutants might be here?If we wanted to use this water
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Answer: for sediment/ dirty water and forpathogens, use
A fast sand filter then a slow sand filterFast sand then chlorineFast sand then boiling.Fast sand then distillation.all may need additional treatment
for drinking, what filtration wouldbe useful?
Test TimeWhat Pollutants might be here?Could we use this water for
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drinking?
Answer: This water is probably contaminated
with pathogens, chemical and other pollutants.It can probably not be safely treated with thetechniques we discussed.
Test the water!Indicator tests
Rapid quick results
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p qSimpleDetailed tests
More preciseRequired more expertise and
time
Do not recontaminate filtered ordisinfected water
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disinfected water
Make sure you use clean containers thathave not been used to store chemicals
Store water carefully Use tops on containers
Monitor distribution
Clean Water has a lot of good uses
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The End