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7.2.4 Simultaneous Air Scrubbing/Reverse Filtration (AS/BW)
Upon completion of filtration, AS/BW starts. Permeate is used as backwash (BW) water in order
to preclude possible contamination of the system permeate side.
The following outlines equipment operation:
The backwash valve AV-4, AS/BW drain valve AV-5, and air supply valve AV-6 open.
Then the backwash pump P-2 and sodium hypochlorite adding pump start simultaneously.
Figure 10
AS/BW Process Flow Diagram
Figure 11 Concept of AS/BW
Backwash
As the following table shows, backwash flow rates required for modules should be such flow
rates that results in backwash water volumes 0.5 to 1.5 times the volumes of water held by the
modules. If the volume of backwash water is insufficient, sodium hypochlorite added for
backwash does not reach modules, leading to insufficient backwash effect. Ensure that the
backwash water volume is larger than the volume of water held by the modules (holdup volume).
Also ensure that the port to add chemicals to backwash water is as close to a rack as possible
since the position of the port is also a factor to determine backwash efficiency. If raw water
contains a lot of contaminants, the flow rate for backwash may be raised for stable operation.
Item
UNA-600A
UNA-660A
UNA-620A
Holdup volume (L/module)
15
20
30
Minimal
backwash
flow
rate
(duration of 60 sec.)
(m
3
/hr/module)
1.0
1.6
2.0
AS/BW
NaClO
AS/BW
BW
Permeate
AV-2
AV-3
AV5
AV-1
Air
P-2
AV-7
Air Compressor