11

Water Filtration and

Disinfection

Kabul, Afghanistan February 2011

This watershed rehabilitation and restoration training was prepared by the U.S. Department of Agriculture (USDA) team of Jon Fripp (Civil Engineer – USDA/NRCS), Melvin Westbrook (Director USDA-NRCS/IPD), Otto Gonzalez (International Agricultural Development Specialist - USDA Foreign Agricultural Service), Clark Fleege, (Nursery Manager, USDA Forest

Service, and George Hernandez (Forester - USDA Forest Service), in consultation with Lief Christenson, (USA CJTF101 Water Resources Coordinator, Afghanistan). Contact Jon Fripp at jon.fripp@ftw.usda.gov or Otto Gonzalez at Otto.Gonzalez@fas.usda.gov for more information on this workshop.

Module Topics: • Why filter water • Types of pollutants • Types of filtration and disinfection

– Focus on low tech methods – Fast sand filter and slow sand filter

• Water Testing

Why do we filter water? • For drinking • For hygiene • For irrigation

Types of Pollutants

• Pathogens • Salt • Chemical • Odor/Color/Taste

Water Quality – disease and mortality

• 1.1 billion people (1/6th of the world) lack access to safe water sources • Water-borne diseases (WBD) include: cholera, typhoid fever, amoebic

and bacterial dysentery and other diarrheal diseases • WBD cause at least 2.2 to 5 million deaths annually • This means that 4-5 people die every minute from WBD.

•WBD the leading cause of childhood sickness and death.

Municipal Treatment most includes these steps

Settlement / sedimentation

Filtration

Disinfection (chemical treatment)

Water Supply

Modified from Robert A. Perdue Water Treatment Plant

Water Source

Filtration – takes the dirt out Disinfection – takes the microbes and other contaminants out

•Common in developed countries •Can Provide Large Quantities of Safe Water •Often Big Operations •Expensive •Training Required to Operate

Treatment Plants Can Be Small

Photos from Jerry Bernard

This one treats water from a small pond for a residence

This system treats and packages water from a well for a school

Low Cost Treatments • Boiling • Chemical • UV/Solar • Distillation • Filtration • Biological Filtration

Water treated with any of these may need additional treatment!

Boiling

•Boil water for 10 minutes •Boiling will kill most pathogens •Does not remove salt •Does not remove sediments •Does not remove most chemicals •Does not help with much improvement of taste or smell

Chemical

•Can be added directly to the water •It will kill most pathogens •Leaves a smell •Does not remove salts •Does not remove sediments •Does not remove most chemicals

•Chlorine Bleach •Chlorine Powder •Chlorine Tablets •Chlorine Liquid •Granular Calcium Hypochlorite •Iodine

These chemicals can be dangerous!

Chemical •Can use bleach for 1%: use 10 drops/liter for 2-6%: use 2 drops/liter for 7-10% use 1 drop/liter •Double the dose if the water is cloudy

one cap of Clorox for every 2 gallons (7.5 liter) of water.

•Do not use too much •Use Regular Clorox Bleach •Do not use bleach with fabric softener or other additives

•Mix the treated water. Allow the treated water to settle for 30 minutes.

•Smell the water. The treated water 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 the container of treated water to sit uncovered for another 30 minutes or pour the water back and forth between two clean containers.

Chemical

for 1%: use 10 drops/liter for 2-6%: use 2 drops/liter for 7-10% use 1 drop/liter

Question: Using a 5.8% chlorine How many drops to purify water in a two liter bottle?

Answer: 2 liters x 2 drops per liter = 4 drops Remember to mix it and allow it to settle

Do not use too much

UV/Solar

•Paint ½ bottle black •Leave in sun for 6 hours •Exposes water to ultraviolet rays from sun •Raises temperature •Kills some pathogens •Does not remove salt •Does not remove sediments •Does not remove chemicals •Does not help with much improvement of taste or smell

Distillation

Heat

Boils water

Water into vapor

Cool water turns water vapor into liquid

•Kills most pathogens •Removes salt •Removes sediments •Removes many chemicals •Can help with improvement of taste or smell

•Boiling produces water vapor which leaves behind pollutants •Water vapor is allowed to cool and turn back into water

Distillation Stills •These can be bought •They can be made

Durastill model 4696A

•Takes a lot of energy •Takes skill to operate

These machines can be dangerous!

Can use distill water on a stove

Distillation

Stove Top Distillation 1. Put the dirty water in the pot 2. Place a collection cup in the

pot 3. Clean the lid and turn it

upside down 4. Boil the water 5. The water condenses on the

lid of the pot and falls into the collection cup.

•Food coloring was placed in the water to represent pollutants •Notice the water in the collection cup is clear

Stove Top Distillation

Distillation

Slow and takes energy

Can use the sun to distill water

Distillation

Solar Distillation

SolAqua Model 550 Rainmaker

Photo from Jeff Wheaton

Solar Distillation 1. The sun heats the water 2. The water evaporates 3. The water condenses on the glass 4. The water runs down to the

collection tray

Only pure water rises to the top

Distillation

Must have a sunny day

•Very slow •Can take a few hours to get a small amount

Solar Distillation

Distillation

Solar Distillation •In the summer, about 8 square feet of glass will produce 1 gallon per day •About half in the winter. •May need several units

Distillation

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

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

Filtration

Filtration

Fast Sand Filter 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.

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• Simple • Good for preparing water for

drip or sprinkler irrigation • Often used as a pretreatment

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

Filtration

We will now go through the steps to build a fast sand filter

Filtration

First – separate sand and gravel with sieve

Construction of a fast sand filter

Then wash the sand and gravel in clean water

Filtration Construction of a fast sand filter

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

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

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

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

•Most of the sediments are collected in the top layers •You will need to periodically scrape away this layer and clean the sand

Do not drink it!

Filtration Construction of a fast sand filter

Water flows rapidly through the fast sand filter – 2 to 5 meters per 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

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?

Filtration

Slow Sand Filter Also called a biologic sand filter 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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• 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)

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

Filtration

We will now go through the steps to build a slow sand filter

Photo from CMS /Connor

•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

Filtration Construction of a slow sand filter

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

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 Dirty water in

Clean water out

•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

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

Filtration Construction of a slow sand filter

Can use different materials to make a slow sand filter

Clay pots are good

Construction Steps

Photo from CAWST

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.

Answer: 15cm x 15 cm x 3.14 = 729 square cm 729 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 diameter opening. How many liters of water can be filtered in 1 hour?

1 gal = 3.78 liter 1 in = 2.54 cm

Summary Low Cost Treatments

Water treated with any of these may need additional treatment!

Pollutant

Method Pathogens Chemical Salt Sediments / dirt

Odour and Taste

BoilingChlorineUV/SolarDistillation / stillSolar StillStovetop DistillationCloth FilterFast Sand FilterSlow Sand Filter

Method is effective at removing many of these pollutantsMethod provides some removal of pollutantMethod is not effective at removing pollutant

Water Testing for Potable Water Bacteria Tests: Bacteria (Pathogen) contamination is a significant public health concern. Variety of tests. Concentrations typically require lab tests. Field tests (Hatch whirl bag, dip strips, etc) can detect presence/absence. pH Tests: Simple Litmus paper or “dip” strips. Quick field test that can impact design and material section. Low pH – suggests use stainless steel & PVC. Turbidity: Most important for surface waters. Meter (battery) or Secchi Disk (Field ~ Fill 2 liter bottle look for plastic molding on bottom thru water). Turbid water provides habitat for bacteria. Total Dissolved Solids (TDS or Conductivity): Small compact, low cost meters, Want <500 mg/L or PPM. Mostly taste issue. Indexes to salts Hardness/Alkalinity: “Dip Strips” and low cost meters can be used. Not health issue, but can cause users to reject source Nitrite/Nitrate/Ammonia: Dual pad “Dip Strips”. Nitrite/nitrate indicative of agricultural or fecal contamination. Can serve as quick bacteria indication. Other Tests Depending on Region and Local Activities: Regional Geology Issues and Human Activity – Agriculture, Mining, Farming Arsenic < 0.01 PPM Fluoride < 4 PPM Lead - Mercury -Phosphates -Sulfates

Water Testing •Indicator tests

•Rapid – quick results •Simple

•Detailed tests •More precise •Requires more expertise and time

Water Testing •Time, location, operator issues

Field testing means: •No true LAB equipment •No Incubator •Possibly no electricity available •No temperature control on supplies •“Good Enough” results

Water Quality Survey / Sanitary Survey •Operator dependent •Visual Inspection •Examination of records •Survey residents

Look for conditions that may cause a problem Assess what has happened

Case Study – Water Quality Site Assessment Infrastructure assessment • Existing Source

– Measure flows – Open excavation

• Existing Storage – Measure volume

• Existing Treatment – Type, maintenance, performance

• Existing Distribution – Pipe size, length and condition

Chemical

Spring Development

• Grab samples • Different contaminants tested

Water Quality- Field Tests

• Ok at source • Ok at main storage • Ok at taps • Problems at household storage

School Records • Large numbers of absentees at beginning of rainy

season • Illness reports in rainy season

Water Quality- Survey

Conclusion: Water Quality Contamination Problem • Existing treatment is not adequate and

not maintained to assure water quality • Source is open • Contamination washes into trench during

rainy season – Cattle – Pit toilets

Solution: Protect Source, Good practice on Spring Development

Test Time •Is this water clean to drink? •Would filtration be needed? •Would disinfection be needed?

Answer: Test water! Disinfection may be necessary.

Test Time •What Pollutants might be here? •If we wanted to use this water for drip irrigation, what filtration would be useful?

Answer: for sediment/ dirty water use a cloth filter or a fast sand filter

Answer: for sediment/ dirty water use a cloth filter or a fast sand filter

Test Time •What Pollutants might be here? •If we wanted to use this water for drip irrigation, what filtration would be useful?

Answer: for sediment/ dirty water and for pathogens, use •A fast sand filter then a slow sand filter •Fast sand then chlorine •Fast sand then boiling. •Fast sand then distillation ….all may need additional treatment

Test Time •What Pollutants might be here? •If we wanted to use this water for drinking, what filtration would be useful?

Test Time •What Pollutants might be here? •Could we use this water for drinking?

Answer: This water is probably contaminated with pathogens, excessive chemical and other pollutants. It can probably not be safely treated with the techniques we discussed.

Do not recontaminate filtered or disinfected water

• Make sure you use clean containers that have not been used to store chemicals

• Store water carefully • Use tops on containers • Monitor distribution

Clean Water has a lot of good uses

The End