Flux indicates the productivity of membrane and defined as equation (1). Table 1 summarizes the three different units commonly used.


1  ————————– (1)


Symbol Three different units commonly used
 J Flux LMH gfd m/d
VP Permeate volume L gal m3
A Membrane area m2 ft2 m2
Δt  Time duration hr day day

The above units can be inter-converted using the following conversion factors.

1.00 gfd  = 1.70 LMH
1.00 gfd  = 0.041 m/d
1.00 m/d = 41.7 LMH
1.00 m/d = 24.5 gfd
1.00 LMH = 0.59 gfd
1.00 LMH = 0.024 m/d

Concentration factor (CF)

Concentration factor of membrane process is defined as the ratio of feed water volume over concentrate volume and calculated as equation (2). This is an important operating parameter in crossflow tubular membrane and reverse osmosis (RO). But this concept is not used in MBR with immersed membranes.
2————————– (2)


VF =feed water volume (m3)
VP= permeate volume (m3)
QF = feed flow rate (m3/hr)
QP= permeate flow rate (m3/hr)


Recovery is a derivative variable from CF and indicates the efficiency of fresh water use in RO. It is calculated as equation (3).


3————————– (3)


where VP is permeate volume (m3). All the volumetric parameters can be substituted with corresponding flow rate parameters.


© Seong Hoon Yoon