Membrane and Desalination Technologies - TCE Moodle Website

132 L. Song and K.Guan Tay
flux. Under certain conditions (thermodynamic restriction), the average flux remains constant
for an initial period of operation before decline in flux can be observed. The behavior has been
reported in the literature and verified with fouling experiments on a 4-m long membrane
channel in the laboratory. This interesting behavior highlights that the decline in average flux
cannot be used as an effective indicator of membrane fouling in a long membrane channel that
is potentially operated under thermodynamic equilibrium regime.
A more effective fouling characterization method is developed to overcome the inadequacy
of using average flux to track fouling in full-scale RO processes. The central idea of the
new characterization method is based on the intrinsic feature of membrane fouling, which is
the increase in the total membrane resistance. The total resistance of the membrane increases
whenever there is membrane fouling. With new fouling characterization method, fouling
development in a long membrane channel can be accurately accounted for, even when no
obvious flux decline is observed in the process. Furthermore, the new characterization
method can also be used to more accurately assess the effectiveness of membrane cleaning.
7. ACRONYMS
BOD ¼ Biochemical oxygen demand
COD ¼ Chemical oxygen demand
MFI ¼ Modified fouling index
NOM ¼ Natural organic matter
RO ¼ Reverse osmosis
SDI ¼ Silt density index
TOC ¼ Total organic carbon
8. NOMENCLATURE
c ¼ Salt concentration (mg/L or g/m 3 )
c0 ¼ Feed salt concentration (mg/L or g/m 3 )
cf0 ¼ Foulant concentration in the bulk flow (mg/L or g/m 3 )
F ¼ Filtration coefficient (m/Pa s)
fos ¼ Osmotic coefficient (Pa L/mg)
H ¼ Height of the membrane channel (m)
¼ Water viscosity (Pa s)
If ¼ Fouling index
j ¼ Foulant deposition rate onto the membrane surface (g/m 2 s)
kf ¼ Fouling potential of the feed water (Pa s/m 2 )
Ks ¼ Coefficient for spacer configuration ( 1)
M ¼ Foulant amount accumulated over time (g/m 2 )
Dp ¼ Driving pressure (Pa)
Dp ¼ Characteristic pressure (Pa)
Dp0 ¼ Feed driving pressure (Pa)
Dp ¼ Osmotic pressure (Pa)
R0 ¼ Total hydraulic resistances at the beginning of the fouling test (Pa s/m)