Effect of turbulence on fouling control of submerged hollow fibre membrane filtration

In this study, we investigated the effect of turbulence on hollow fibre membrane filtration in terms of membrane fouling performance experimentally. In particular, a special setup with a turbulence generator using a vibrating perforated plate was constructed in the laboratory. The setup enabled the hollow fibre membrane filtration to be carried out within a design ambient with targeted levels of turbulence without mean shears. The non-intrusive laser imaging approach of Particle Image Velocimetry (PIV) was used to quantify the characteristics of the turbulence ambient. Subsequently, by monitoring the rate of trans-membrane pressure (TMP) rise with constant permeate flux experiments using 4 g/L yeast feed suspensions, we obtained unique data sets that revealed the quantitative effects of turbulence on membrane fibre filtration, which are not available in the literature so far. Overall, the results indicated that the presence of turbulence moderated the membrane fouling and reduced the corresponding rate of TMP rise (dTMP/dt). Two key turbulence parameters, namely, turbulence kinetic energy (TKE) and eddy length scale, were found to relate to the membrane fouling reduction, with the rate of TMP rise generally decreasing when TKE or eddy length scale increases. In addition, there exists an optimum eddy length scale beyond which the eddy size (comparable to approximately ten times of the hollow fibre diameter in the present study) has no more influence on the fouling behaviour. A direct comparison between turbulence and membrane vibration for fouling control was also performed. The implications of the present results on the design of membrane bioreactors (MBRs) are discussed.