Analysis of local fouling in a pilot-scale submerged hollow-fiber membrane system for drinking water treatment by membrane autopsy

An analysis of local fouling in a pilot-scale submerged hollow-fiber membrane water treatment system for drinking water production is described in this paper. Membrane fouling was observed by using microscopic techniques with membrane specimen taken at different longitudinal and horizontal positions of a hollow-fiber membrane module. The resistance-in-series model was used to quantify local fouling resistances of membrane samples. Our results show that the recovery of the permeate flux of the hollow-fiber membrane located near the source of aeration was the highest after performing chemical cleaning. The irreversible fouling resistance was the largest for membrane samples taken near the open ends of the fibers, where the local pressure is expected to be highest. These axial features of irreversible fouling resistance were more pronounced at lower suspended solids concentration or higher set-point flux. However, the local aspect of reversible fouling was relatively less pronounced than the one of irreversible fouling. The results obtained from membrane autopsy were explained well by the local fouling phenomenon driven by the profile of local pressure along the fiber length and transient behavior of this profile during membrane operation. In addition, it was concluded that the individual membrane module experiencing more aeration would have a more localized pattern of membrane fouling, suggesting that the local fouling is more significant under relatively less demanding fouling conditions.