Yeast foulant removal by backpulses in crossflow microfiltration

Direct visual observation (DVO) was used to gain a better understanding of membrane cleaning by individual backpulses. Yeast cells were deposited on cellulose acetate membranes during crossflow microfiltration, after which the membranes were cleaned using individual backpulses at varying backpulse durations, transmembrane pressures, and shear rates. The membrane surface after each single backpulse was observed with microvideophotography and the recovered flux was determined. The recovered flux was observed to increase with increasing shear rate, backpulse pressure and backpulse duration, reaching up to 98% of the clean membrane flux. In some cases, a minimum backpulse duration was required for membrane cleaning, and it increased with decreasing backpulse pressure and shear rate. DVO pictures were used to quantify the fraction of membrane which remain covered in foulant after single or multiple backpulses. The observed. cleaning was used to predict the recovered flux, and these DVO-based predictions are in excellent agreement with the measured recovered fluxes. Finally, multiple short backpulses were found to be more effective in cleaning the membrane surface than fewer, longer backpulses at high shear rate and backpulse pressure; however, the reverse is true at low shear rate or backpulse pressure. Moreover, longer, weaker backpulses led to higher recovered fluxes than did shorter, stronger backpulses. (C) 2002 Elsevier Science B.V. All rights reserved.