The sedimentation process can be quickened by adding special chemicals, also known as coagulants, to the water. Coagulants help the sand, silt, and clay join together and form larger clumps, making it easier for them to settle to the bottom of the container. Common chemicals used are aluminium sulphate (alum), polyaluminium chloride (PAC or liquid alum), and iron salts (ferric sulphate or ferric chloride).

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 are chemically attracted to the negative turbidity particles, neutralizing the latter’s negative charge. With mixing, the neutralized particles then accumulate (a process called flocculation) to form larger particles called flocs, which settle faster. The flocs can then be settled out or removed by filtration. Some bacteria and viruses may 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

The follow the 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.