Independent trials have shown that:
- The rate of head loss development using EGFM is 30% smaller than sand.
- Filter runs with EGFM may be up to 50% longer than sand.
Material and size specification
*Products used for the treatment of water for human consumption – silica sand and silica gravel; where products are specified by size range and maximum oversize and undersize, products for use in multi-media filters shall have maximum oversize or undersize mass fraction of 5%.
EGFM has a greater voidage than 16/30 filter sand due to it’s more angular particle shape. Greater voidage produces a more open bed structure which leads to lower headloss development.
- The minimum fluidisation velocity for grade 1 EGFM in a 80 cm bed is 25m/h
- The velocity for 20% bed expansion is 40 m/h.
- In practice the backwash velocities required for Grade 1 EGFM are the same as sand
- The use of air scour prior to backwash is recommended with an air flow rate of 50 to 80m3/hr/m2