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Household Water Treatment and Safe Storage
Factsheet: Chemical Coagulants
The Treatment Process
Potential Treatment Capacity
Very Effective For:
Somewhat Effective For:
Not Effective For:
 Turbidity






 Dissolved chemicals
Bacteria
Viruses
Protozoa
Helminths
Hardness
Taste, odour, colour
What are Chemical Coagulants?
The sedimentation process can be
quickened by adding coagulants to the
water.
Chemical coagulants are commonly used in
community drinking water treatment systems
though some application in household water
treatment occurs.
The main chemicals used for coagulation
are
aluminium
sulphate
(alum),
polyaluminium chloride (also known as PAC
or liquid alum), alum potash, and iron salts
(ferric sulphate or ferric chloride).
Lime (Ca(OH 2 )), lime soda ash (Na 2 CO 3 )
and caustic soda (NaOH) are sometimes
used to "soften" water, usually ground water,
by precipitating calcium, magnesium, iron,
manganese and other minerals that
contribute to hardness.
then accumulate (flocculation) to form larger
particles (flocs) which settle faster. The flocs
can then be settled out or removed by
filtration.
Some bacteria and viruses can also attach
themselves to the suspended particles in
water that cause turbidity. Therefore,
reducing turbidity levels through coagulation
may also improve the microbiological quality
of water.
Operation
Users follow the manufacturer’s instructions
and add the prepared dose of coagulant to
the water. The water is then stirred for a few
minutes to help create flocs. The flocs can
be settled out or removed by filtration.
How Does it Remove Contamination?
Particles that cause turbidity (e.g. silt, clay)
are generally negatively charged, making it
difficult for them to clump together because
of electrostatic repulsion. But coagulant
particles are positively charged, and they
chemically attracted to the negative turbidity
particles, neutralizing the latter’s negative
charge. With mixing the neutralized particles
Alum block (Credit: www.cdc.org)
Household Water Treatment and Safe Storage
Fact Sheet: Chemical Coagulants
Key Data
Inlet Water Quality
 No specific limits
Treatment Efficiency
Bacteria
Laboratory
1
>90 to >99%
Viruses
Protozoa
Helminths
Turbidity
>90 to >99%1
>90 to >99%1
>90 to >99%1
Not available
Not available
Not available
Not available
Not available
2
< 90%
3
95%
Field
1
Sproul (1974), Leong (1982), Payment and Armon (1989) cited in Sobsey (2002)
Ongerth (1990) cited in Sobsey (2002)
3
Wrigley (2007)
2
 Maximum effectiveness requires careful control of coagulant dose, pH and consideration of the
quality of the water being treated, as well as mixing
 Effectiveness of chemical coagulants varies from one to another
Operating Criteria

Flow Rate
Batch Volume
Daily Water Supply
Not applicable
Unlimited
Unlimited
Need to follow manufacturer’s instructions
Robustness


Difficult to optimize without training and equipment
Requires coagulant supply chain and regular purchase
Estimated Lifespan

6 months in liquid form and 1 year in solid form
Manufacturing Requirements
Worldwide Producers:
 Many producers around the world
Local Production:
 Most chemical products are difficult and complex to manufacture and local production is not
feasible
Maintenance

Chemicals should be stored in a dry location and away from children
Direct Cost
Capital Cost
Operating Cost
US$0
US$9-91/year
1
Replacement Cost
US$0
Note: Program, transportation and education costs are not included. Costs will vary depending on location.
1
Sobsey (2002). Assumed 25 litres/household/day.
Household Water Treatment and Safe Storage
Fact Sheet: Chemical Coagulants
Key Data
Other

Jar testing can be undertaken to optimize effectiveness of particular coagulants with water
sources
References
Sobsey M. (2002). Managing Water in the Home: Accelerated Health Gains From Improved
Water Supply, Water, Sanitation and Health, Department of Protection of the Human
Environment, World Health Organization, Geneva, Switzerland.
Wrigley. T. (2007) Microbial Counts and Pesticide Concentrations in Drinking Water After Alum
Flocculation of Channel Feed Water at the Household Level, in Vinh Long Province, Vietnam,
Journal of Water and Health; 05:1.
CAWST (Centre for Affordable Water and Sanitation Technology)
Wellness through Water.... Empowering People Globally
Calgary, Alberta, Canada
Website: www.cawst.org
Email: [email protected]
Last Update: October 2009