Filtration

After coagulation and flocculation step, flocs are now present in water. To remove these particles from water a filtration through a mass is then required and will be done into the sand filter.

During filtration, the particles present in water will fill up the free interstices in filter. Therefore, free space between sand grains will reduce and sand filtration quality will improve. However, the filter filling-in will cause an increase of the pressure necessary for the water to go through the filter as well as a slow down of the water flow.

When pressure is rising above a certain pre-determined level or when water flow is becoming insufficient a backwash must be proceeded.

Backwash is the action to make water circulated from the bottom to the top of the filter. The particles, captived by the filtration mass, are then carried away by water evacuated to sewer. A visual tester help to indicate the end of backwash.

Then, filtration can start again.

Sand filter is filled with three different layers what ensure a more lasting period of filtration between two backwash.

After sand filter filtration, our units are equipped with an activated carbon filter. Activated carbon used by LMS France has an important adsorption surface of about 900 m²/g divided in micro and mesopore. It is particularly well-adapted for the treatment of pesticides, HAP, smell, colour...