AWWA ACE59833

The effects of fiber length and aeration rate on permeate flux decline in tests of a single, submerged hollow fiber at constant pressure are presented. Without aeration, the initial rate of flux decline was greater for a longer fiber length (1 vs. 0.7 vs. 0.3 m) at a relatively low feed concentration of bentonite particles (100 mg/L). However, the same pseudo-steady state in permeate flux was observed for all three fiber lengths as fouling progressed. The fouling rate was greatly reduced by aeration for all three fiber lengths. However, the effect was larger as fiber length became shorter. It was concluded that aeration was not as effective for removal of the fouling layer formed near the fiber outlet where the local flux is highest for the longest fiber length. Permeate flux decline (without aeration) was over predicted by using the specific cake resistance from a small-scale, flat sheet test in a hollow-fiber model. The explanation may involve the effect of axial gradient of pressure drop on local specific cake resistance for compressible cakes. Small-scale tests cannot account for this axial dependency. Includes 8 references, figures.