Submerged hollow fibre membranes in bubbling systems

This study focuses on the optimisation of submerged hollow fibre membrane performance by analysing the role of air sparging on the reduction of membranefouling. In submerged hollow fibre membranes, rising bubbles have been shown to induce shear, liquid movement and fibre displacement. The interactionbetween fibre movement induced by bubbling and the microfiltration performance was assessed for various parameters (fibre tightness, fibre length, fibrediameter, air flowrate, nozzle size, and feed concentration). A model feed of yeast suspension and a series of isolated fibres were used. The fibre movementwas assessed by monitoring the displacement using video recording. Bubble population parameters were also measured. The results suggest that bubbleinducedfibre movement plays an important role in controlling membrane fouling. Investigations of the critical flux at various operating conditions alsosupported these conclusions.Since energy consumption for aeration is a major contributor to the cost in submerged membranes, the potential to minimise the aeration cost has been testedby implementing intermittent aeration and different nozzle sizes. It was found that an optimum condition associated with a low fouling rate could be reachedby combining various aeration intermittencies and nozzle sizes. An attempt to suppress fouling without aeration was made by incorporating vibrations into asubmerged hollow fibre membrane system. The effects of vibration frequency, type of yeast (washed and unwashed) on the filtration performance wereobserved. The impact of coagulant addition on filtration enhancement was also analysed. The performance of microfiltration was evaluated based on itscritical flux value. The findings in this preliminary study indicated potential fouling control by applying vibrations to submerged membranes.A semi-empirical model was developed to predict the filtration behaviour by taking into account the bubble-induced shear and fibre movement. Thepredicted critical flux values suggested that membrane fouling appears to be more prominent at low air flowrate, with tight fibres, and higher feedconcentrations. The model fits the experimental data with discrepancies from approximately 0.3% to 20%. The predicted filtration profiles at differentoperating modes demonstrate the importance of bubble-induced shear and fibre movement in the improvement of filtration performance