Fibre movement induced by bubbling using submerged hollow fibre membranes

Air bubbling is commonly used with submerged hollow fibre membranes to control fouling. In this paper, we report on an experimental study of the interaction between bubbling and fibre movement in submerged hollow fibre membranes. A model feed of yeast suspension and a set of individual fibres has been used. The effects of various parameters were analysed, including the bubbling conditions (air flowrate and nozzle size), fibre properties (fibre looseness, fibre diameter and fibre length) and feed concentration and viscosity. Characterisation of bubble properties and fibre movement involved analysis of photographic and video images. These observations were then linked to the membrane filtration performance, as expressed by transmembrane pressure (TMP) rise. This study shows that more movement can be achieved at higher air flowrates although the useful range of air flowrate may be relatively narrow. Movement is also increased using smaller fibre diameters, looser fibres and longer fibres. Raised viscosity, simulating higher solids concentrations, significantly attenuates fibre movement. Studies of microfiltration performance suggested that (bubble-induced) fibre movement per se plays an important role in reducing the rate of fouling. The effect of fibre movement alone was also examined by mechanically shifting the fibre without bubbling. Results indicate that mechanical fibre movement was able to reduce the fouling rate (expressed as d(TMP)/dt) by about three times that of the fouling rate using stationary fibres in a non-bubbling system. However, bubble-induced shear and fibre movement were able to reduce the fouling rate by up to 10-fold.