Flux enhancement by air dispersion in cross-flow microfiltration of a colloidal system through spiral wound module

Enhancement of the permeate flux due to reduction of cake layer resistance by air-liquid twophase
flow in a cross flow spiral wound microfiltration membrane has been investigated.
Experiments were carried out with two different suspension systems, namely baker’s yeast
suspension with a dry mass concentration of 5.4 kg m-3 and the colloidal suspension of starch
and bacteria having a dry mass concentration of 3.41 kg m-3. An air-liquid two-phase flow was
generated by injecting the air at the inlet of the membrane module and was fed into a
horizontally mounted assembly of a spiral wound microfiltration membrane. The effect of air
dispersion was studied on flux enhancement, specific cake layer resistance and loading of
cake mass on the membrane surface. This study shows that by air dispersion, the permeate
flux can be enhanced up to 60 percent for the colloidal suspension of starch and bacteria
while a flux enhancement of 40 percent was achieved for yeast suspension. The specific cake
layer resistance reduced by a factor of 10 for both of the suspensions when air was injected
into the feed stream. The results of this study depict that the technique of air dispersion is
effective in increasing the permeate flux for the suspension systems containing below and
above micron sized particulates.