Reduction of cake resistance of dead-end membrane filtration by re-aggregation in the pipe

Abstract

The effects of flow conditions and retention time in the pipe placed before and after pump on floc re-aggregation and the effect of floc re-aggregation on cake resistant of membrane were investigated in this study. The $R_f$ value was used to determine flow condition and $R_f$ value was changed from 117 to 1314 $(sec^{ -1})$. The EDSD (Effective Diameter for Shear-Induced Diffusion) was used to determine the polydisperse particle size. For the alumminium-based coagulants and charge neutralization condition it was found that, the broken floc can be re-aggregated in the pipe placed after pump. But only limited re-aggregation occurred in all cases, indicating a significant irreversibility of the floc re-aggregation process. It means that the re-aggregation floc size is smaller than the original floc. The $R_f$ value was important factor on re-aggregation process in the pipe. But, it is difficult to determine the effect of retention time on re-aggregation process in the pipe. The re-aggregation floc size increases when the $R_f$ value decreases under all condition. It was prove that, re-aggregation increased the permeate flux, and also decreased the cake resistance of membrane.