Membrane and Desalination Technologies - TCE Moodle Website

116 L. Song and K.Guan Tay
Fouling potential k f (Pa.sm –2 )
1.5×10 10
1.2×10 10
9.0×10 9
6.0×10 9
3.0×10 9
4.0×105 8.0×105 1.2×106 1.6×106 2.0×106 0.0
Pressure (Pa)
Fig. 3.9. Fouling potentials at different driving pressures measured with AG membrane.
the experiments. The rapid flux decline can be attributed to the increase in particle deposition,
which is caused by the increase in permeate flux that carries the colloidal particles onto the
membrane surface when pressure is increased. Fouling potential at different pressures is
calculated and presented in Fig. 3.9.
It is shown in Fig. 3.9 that fouling potential determined with AG membrane is not sensitive
to driving pressure in the pressure range tested. The compaction of fouling layer is not
noticeable in the measured fouling potentials in this case. Increase in the permeate flux at
higher pressures is balanced by the same increase in the resistance of the fouling layer. This
nonchalant response of fouling potential to increasing pressure suggests that the duration of
fouling tests to determine fouling potential can be shortened by increasing the driving pressure,
so that permeate flux can decline sufficiently to give meaningful results. However, the lack of
method to determine the critical pressure that gives rise to compaction of fouling layer means
precaution has to be taken when operating the fouling tests at high pressure. For most accurate
measurement, driving pressure should be identical to that used in the full-scale RO process.
4. PREDICTION OF FOULING IN FULL-SCALE REVERSE OSMOSIS
PROCESSES
Fouling in the full-scale RO processes is commonly indicated by the decline of permeate
flux under constant driving pressure or increase in driving pressure to maintain constant
permeate flux. It has been known for a long time that the flux decline in the full-scale RO
processes is quite different from that observed from the fouling test in the laboratory-scale
RO device. This fact makes it impossible to quantitatively predict flux decline in the full-scale