The effect of vibration and coagulant addition on the filtration performance of submerged hollow fibre membranes

Axial vibration of submerged hollow fibre membranes is found to be an effective means of preventing membrane fouling with critical fluxes of 60-80 L h-1 m-2 found to be achievable at vibrational frequencies as low as 10 Hz. Addition of transverse vibrations to the test unit (by means of addition of horizontal vanes) resulted in an approximate doubling of critical flux (to 130 L h-1 m-2 at 10 Hz). Fibre integrity is maintained at the combined longitudinal and transverse vibrations used (equivalent to a pulsating peak shock acceleration of 8.7g at a vibrational frequency of 10 Hz). Performance of the vibrating unit is highly sensitive to coagulation with coagulant addition markedly enhancing the critical flux, particularly at low vibrational frequencies. At a frequency of only 1.7 Hz (100 oscillations per minute (OPM)), critical flux increased from 17 to 46 L h-1 m-2 on addition of 34 mg/L aluminium chlorhydrate (ACH). In the presence of combined axial and transverse vibrations, a five-fold enhancement in critical flux to 86 L h-1 m-2 was achieved at 1.7 Hz in the presence of 34 mg/L ACH. Lower proportional increases in critical flux on addition of coagulant were obtained at higher frequencies presumably as a result of floc breakup under the increasingly turbulent conditions. The results obtained suggest that industrially relevant critical fluxes in submerged membrane units could be achieved by low frequency vibration of the submerged membranes coupled with addition of a suitable coagulant. © 2006 Elsevier B.V. All rights reserved