MICRODYN CAPILLARY MODULES | USER MANUAL
MANN+HUMMEL Water & Fluid Solutions | REVISION DATE: 09/09/2021
13
5.4
PERIODIC BACK PULSE (PBP)
During filtration, some particles will settle down
on the surface of the membrane. This decreases
the performance of the membrane. The purpose
of the periodic back pulse (PBP) system is to
remove these particles from the surface of the
membrane, which helps restore the performance
of the membrane. PBP may also decrease the
system’s overall energy consumption.
During PBP, a small amount of the filtrate is sent
through the backside of the membrane
(reversed flow) and is forced toward the feed
side of the membrane. Figure 10A shows how
the flow direction changes from normal filtration
to back pulsing. In this moment, the filtrate
pressure is higher than the feed pressure (P
F
> P
1
and P
2
), as shown in Figure 10B.
When filtrate is sent through the backside of the
membrane and gets pushed through the feed
side of the membrane, the fouling and scaling
materials are loosened and removed from the
membrane surface. Typically, a back pulse is
done every 5 – 30 minutes, but trials may be
done to determine how frequently a back pulse
should be performed so that the system runs
most efficiently. Figure 10C shows how
important it is to perform regular PBP and
chemical cleanings to help maintain membrane
performance for extended periods of time.
It is recommended to install a PBP overflow for
the concentrate because of the high backflow
volume (nearly 1 L per 1 m
2
of installed
membrane area, or 0.26 gal per 10.8 ft
2
of
membrane area, in a range of 2-5 seconds).
A)
B)
C)
Figure 10.
.
A)
Diagram showing the difference in flow direction
in the capillary membranes during filtration and back pulsing.
B)
During PBP, the filtrate pressure must be higher than the feed
pressure.
C)
A simplified graph showing the decline in membrane
performance without PBP or chemical cleaning. PBP and chemical
cleanings help restore membrane performance by removing
particles from the membrane surface.
