Particle fouling in submerged microfiltration membranes: effects of hollow-fiber length and aeration rate

The effects of fiber length and aeration rate on permeate flux decline in tests of a single, submerged, hollow-fiber microfiltration at constant pressure are presented. Without aeration, the initial permeate flux was greater for shorter fiber length (0.3 vs. 0.7 vs. 1 m) at a relatively low feed concentration of bentonite particles (0.1 g/L). However, the same pseudo-steady state in permeate flux was eventually reached for all three fiber lengths as fouling progressed. The fouling rate was greatly reduced by aeration rate for all three fiber lengths. However, the effect was larger as fiber length became shorter. Aeration was not effective for removal of the fouling layer formed near the fiber outlet where the local flux is expected to be highest for the longest fiber length. In the absence of aeration, permeate flux decline was over-predicted slightly in a hollow fiber model by using the specific cake resistance from a small-scale, flat-sheet microfiltration test. The explanation may involve the effect of the axial gradient of pressure drop on local cake resistance for compressible cakes. Aeration changed the structure of the fouling layer such that specific cake resistance was lower than obtained from the flat-sheet test wherein the aeration is not simulated.