LONGITUDINAL FLOWRATE DISTRIBUTION AND BYPASS FLOW MEASUREMENT OF BROKEN HOLLOW FIBER MEMBRANES

Abstract

 Loss of membrane integrity causes deterioration of treated water quality and poses increased risk of microbial diseases. Although there have been several integrity testing methods applied to the full-scale membrane treatment plants, water flow in broken membrane has not been elucidated based on experimental studies. Therefore, this study aimed to directly measure the bypass flow and filtration flow using a novel particle counting method. Nanoparticles greater than the pore size of hollow fiber membrane, but smaller than the inner diameter was suspended to the feed water and both particles deposited on the membrane as a parameter of flux, and the particle in the permeate were measures by the SEM imaging combined with the computer-aided particle conting method, which was verified to be highly accurate. About 0.98% of nanoparticles filtered through the membrane was attached on the membrane, and there was a log-linear relationship between the numbers of particles filtered and the numbers of particles attached on the membrane. The filtration flow was about 20% of the flow rate from the broken end of the membrane, which was about 35% less than the estimated flow by the conventional method. This result indicated that the actual decreases of the log reduction values of the broken membranes are slightly smaller than the ones estimated from the conventional method. The filtration flux from the intact segments of the broken membrane was the lowest at the broken end, and increased along with the length of the membrane to the middle, but the slightly decreased to the outlet, which was considered to be complex flow within the broken hollow fiber membrane.