Granular Activated Carbon
PLACEMENT OF GAC
Fill the vessel with water to about 2/3 the final level of GAC. Gradually add GAC into the water until reaching a level 2% above the desired finish level, ensuring that the water level remains above the level of GAC.
Allow the GAC to soak for a minimum of 24 hours to effectively de-aerate and prevent particles from floating.
WASHING OF GAC
After soaking in water for a minimum of 24 hours, backwash at a low rate for 5 minutes and slowly increase to the maximum design backwash rate for the vessels. Wash at the maximum rate for about 15 minutes. This allows for any air to be removed form the bed. Any very fine material will be removed through the backwash troughs during the low rate wash when the water will look reasonably dirty.
After this initial washing, the filter is drained and a layer of fine material is removed from the surface of the GAC by scraping with flat bladed shovels.
Backwash again at the maximum design rate for 20 minutes then drain and check the surface for any fines. At this stage the fines should be minimal and if no patches of fines are visible, the vessel is ready for service.
If some patches of fines are visible, remove them by scraping and then backwash again at the maximum design rate for 15 minutes. Check again for surface fines. Repeat these steps until inspection shows no more surface fines. Once all fines are removed, the vessel is ready for service.