Household Water Treatment and Safe Storage Factsheet: Source ...
Household Water Treatment and Safe Storage Factsheet: Source ...
Household Water Treatment and Safe Storage Factsheet: Source ...
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<strong>Household</strong> <strong>Water</strong> <strong>Treatment</strong> <strong>and</strong> <strong>Safe</strong> <strong>Storage</strong><br />
<strong>Factsheet</strong>: Chemical Coagulants<br />
The <strong>Treatment</strong> Process<br />
Potential <strong>Treatment</strong> Capacity<br />
Very Effective For: Somewhat Effective For: Not Effective For:<br />
Turbidity<br />
Bacteria<br />
Viruses<br />
Protozoa<br />
Helminths<br />
Hardness<br />
Taste, odour, colour<br />
Dissolved chemicals<br />
What are Chemical Coagulants?<br />
The sedimentation process can be<br />
quickened by adding coagulants to the<br />
water.<br />
Chemical coagulants are commonly used in<br />
community drinking water treatment systems<br />
though some application in household water<br />
treatment occurs.<br />
The main chemicals used for coagulation<br />
are aluminium sulphate (alum),<br />
polyaluminium chloride (also known as PAC<br />
or liquid alum), alum potash, <strong>and</strong> iron salts<br />
(ferric sulphate or ferric chloride).<br />
Lime (Ca(OH 2 )), lime soda ash (Na 2 CO 3 )<br />
<strong>and</strong> caustic soda (NaOH) are sometimes<br />
used to "soften" water, usually ground water,<br />
by precipitating calcium, magnesium, iron,<br />
manganese <strong>and</strong> other minerals that<br />
contribute to hardness.<br />
How Does it Remove Contamination?<br />
Particles that cause turbidity (e.g. silt, clay)<br />
are generally negatively charged, making it<br />
difficult for them to clump together because<br />
of electrostatic repulsion. But coagulant<br />
particles are positively charged, <strong>and</strong> they<br />
chemically attracted to the negative turbidity<br />
particles, neutralizing the latter’s negative<br />
charge. With mixing the neutralized particles<br />
then accumulate (flocculation) to form larger<br />
particles (flocs) which settle faster. The flocs<br />
can then be settled out or removed by<br />
filtration.<br />
Some bacteria <strong>and</strong> viruses can also attach<br />
themselves to the suspended particles in<br />
water that cause turbidity. Therefore,<br />
reducing turbidity levels through coagulation<br />
may also improve the microbiological quality<br />
of water.<br />
Operation<br />
Users follow the manufacturer’s instructions<br />
<strong>and</strong> add the prepared dose of coagulant to<br />
the water. The water is then stirred for a few<br />
minutes to help create flocs. The flocs can<br />
be settled out or removed by filtration.<br />
Alum block (Credit: www.cdc.org)
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