20
feed back the filtrate water from the backwashing tank to the membrane
module. During backwash, chemical feed pump can be operated to dose
chemical to the backwash water. The dosing chemical is usually sodium
hypochlorite and the dosing ratio should be up to 50 mg/L as Cl
2
.
The flow rate of backwash water is set up in advance for 1.0 to 1.5 times
filtrate water flow rate (Do not exceed Max. Backwash Flow described in
(4) After backwashing for a fixed time (normally 30 seconds, up to 60 seconds),
close the backwashing valve (V-6) and stop the backwashing pump.
(5) Open the air exhaust valve (V-4) and the air-scrubbing valve (V-2) for
air-scrubbing for a fixed time (normally 30 seconds, up to 60 seconds).
The air flow rate for air-scrubbing should be within
the range below. Excessive air flow rate may
damage the hollow fiber membrane.
HFU-2020HN: 4.8
– 9.0 Nm
3
/h, normally 6.0 Nm
3
/h
(2.8
– 5.3 scfm, normally 3.5 scfm)
The maximum required air pressure during the
air-scrubbing for inside of the module will be 40 kPa
(6 PSI).
(6) Close the air-scrubbing valve (V-2) and open the drainage valve (V-3).
(7) Close the drainage valve (V-3) after the water is all drained out.
(8) Run the feed water pump and open the feed water valve (V-1).
(9) Close the air exhaust valve (V-4) after the air is purged from the module.
