2. Description of AFM® product use
2.1.
Filter design
AFM® is a filtration media and direct replacement for filter grade sand in all types of filter used for the
treatment of drinking water.
The scope includes:
• Pressure sand filters.
• RGF Rapid Gravity Filters.
Filtration performance varies inversely relative to filtration velocity; the filters should therefore be
operated with the slowest possible hydraulic loading.
2.2.
Type of Water
AFM® is used for the treatment of drinking water this includes water from the following sources;
• Reservoirs.
• Lakes.
• Rivers.
• Springs.
• Boreholes.
• Brackish water and seawater prior to desalination membranes.
• Wastewater to be recycled as potable water.
2.3.
Pre-treatment of water prior to AFM® filtration
AFM® can be used to treat any type of drinking water source, however in the case of ground water or
water with low oxygen content, it is important that the water is strongly aerated for a period of up to 30
minutes prior to filtration.
Aeration blows off the volatile organic compounds (VOC’s), raises the oxidation potential, drops the zeta
potential and oxidises metals such as ferrous to ferric. If the water contains Manganese then longer
aeration or the use of an oxidising agent such as ozone may be required to oxidise the manganese to the
insoluble oxide form prior to filtration.
2.4.
Back-pressure
With respect to pressure sand filters, the filters must be back-washed before the differential bed pressure
exceeds 0.4bar.
2.5.
Back-washing
Dryden Aqua Ltd
Butlerfield-Bonnyrigg,
Edinburgh EH19 3JQ Scotland
Page 8 of 44
The backwash frequency will depend upon the rate of change of back-pressure. However, if the water
has low solids content such as borehole or ground water the pressure may not reach 0.4 bars. With water
temperatures under 28 o C the AFM® bed should be back-washed once a week with water temperatures
over 28 o C the filter should be back-washed twice a week.