(176d) Filtration Behaviours of Hollow Fiber Membranes

Hollow fiber membranes play an important role in the water and wastewater treatment. Pressurised and immersed hollow fiber membrane modules are the dominated membrane modules used for the water purification, while for the wastewater treatment, most of the large scale MBR plants use immersed hollow fiber membrane modules in combination with biological wastewater treatment processes. Understanding the filtration behaviour of the hollow fiber membranes is of crucial importance for the membrane module design and the optimisation of the filtration operation condition. This paper presents modeling, experimental, and XMI observation results on the filtration behaviours of the hollow fiber membranes. The modelling results revealed the effect of the fiber dimension, solution and particle properties, and operation conditions on the cake resistance distribution, the non-uniformity of the local flux, and the suction pressure-time profiles. It has been found that the suction pressure time profile, which is usually used as an indication of the membrane fouling under the constant flux condition, could be significantly affected by the fiber diameter, flux level, and size of particles in the solution. The experimental results indicated that under the crossflow or bubbling condition, the small diameter fiber and the axial fiber arrangement could be more beneficial than the larger diameter fiber and the horizontal fiber arrangement, respectively. Through the DOTM observation used in a filtration of a yeast suspension under crossflow and controlled flux conditions, it was observed that some yeast particles randomly deposited and sticked to some specific locations of the surface of a hollow fiber membrane and the attached particles could grow to a large particle conglomeration through constantly attachment of the individual particles from the bulk. The selective deposition to a certain location, instead of forming a cake layer by layer, may imply that the slow irreversible fouling development under the low flux and crossflow conditions could be related to the heterogeneous properties of the membrane and particle surface chemistry. The non-invasive XMI observation revealed the fiber micro-surface properties could have significant effect on the lumen flow of a hollow fiber membrane, resulting in a strong fluctuation in the filtration behaviour of the hollow fibers. Based on the modeling and experimental results, the key factor affecting the filtration performance of the hollow fiber membrane modules will also be discussed.