The effect of multiple fouling and cleaning cycles on a tubular ceramic microfiltration membrane fouled with a whey protein concentrate -: Membrane performance and cleaning efficiency

We have investigated experimentally the effect of repeated fouling and cleaning cycles upon the membrane performance (quasi-steady permeate flux, irreversible fouling resistance) and cleaning performance (water flux recovery, kinetics) of a 0.1 mum tubular ceramic microfiltration membrane and examined how they influence each other over a number of operational cycles. Whey protein concentrate was selected as a model food suspension. During microtiltration a constant transmembrane pressure of I bar, crossflow velocity of 4 m s(-1) and temperature of 55degreesC produced a steady state flux within two hours. The two-stage chemical cleaning consisted of the sequential application of solutions of sodium hydroxide and nitric acid. The extent of membrane fouling did not vary substantially with cycles as determined from the calculated fouling parameters. Protein retention increased slightly over the last few cycles indicating a change in membrane selectivity. Cleaning efficiency assessed using the flux recovery did not decrease with cycles. Nevertheless flux recovery was generally lower than 100% and the hydraulic cleanliness criterion (i.e. (R-n-R-m)/R-m < 0.05) was most often not verified: the membrane could be considered as not being clean hydraulically and this resulted in the build-up of irreversible residual fouling. Flux recovery arose from the action of sodium hydroxide (via desorption and solubilization of proteins) whereas nitric acid had a detrimental effect on membrane resistance. Cleaning kinetics was characterized using the variation of the fouling resistance with time during sodium hydroxide cleaning. Cleaning kinetics data over multiple cycles are discussed and a possible alkaline cleaning mechanism for the removal of protein deposits is postulated.