24
6.
Suspended solids loading capacity
In practical terms the shortest back-wash frequency for grossly polluted waste water, industrial water or for a river in spate
conditions is likely to be in the region of 4 hours. Taking 4 hours as the shortest back-wash frequency the maximum solids
load capacity is given in the following table.
Maximum SSmg/l suspended solids concentration for AFM®
filtration
Water flow velocity
m/hr
5
10
15
20
25
30
grade 1
AFM®
mg/l SS
100
50
33
25
20
16
AFM® +
300mm anthracite
mg/l SS
400
200
120
100
80
60
grade 0
AFM®
mg/l SS
65
32
22
16
13
10
AFM® +
300mm anthracite
mg/l SS
250
120
80
60
50
40
Anthracite depth filtration
Anthracite may be used on top of the filter bed to increase solids load or run phase duration. AFM® is a fine polishing
filter media perfect for the removal of sub 20 micron particles. For heavy loads of solids above 20 microns, then a 100mm
to 300mm layer of anthracite is a good solution.
Grade 1 AFM®
1.18 to 2.5mm anthracite
Grade 0 AFM®
0.6 to 1.18mm anthracite
The anthracite may increase the loading
Turning off and starting up a media bed filter
AFM® media bed filters should be operated continuously; they must never be stopped or allowed to go anaerobic. If the
filters must be turned off for a protracted period, the following procedure should be used prior to start up.
Decommissioning and commissioning a filter
Prior to turning off an AFM® filter it should be given a standard backwash with clean water. After the backwash as much
water should be drained off from the filter as possible.
Prior to going back-online, backwash the filter for a period of 5 minutes at a water flow rate that gives a 20% bed expansion
followed by a rinse phase for 10 minutes. Repeat the backwash and rinse phase for a 2 nd and 3 rd time prior to going back
on-line.