Analysis of cleaning protocols in ceramic membranes by liquid–liquid displacement porosimetry

Membrane technology has experienced an important development in the last years, being more and more employed as an alternative to conventional separation processes. However, the investment due to purchase and replacement of membranes in industrial plants is still a very significant cost. Therefore, it is necessary to analyze the variables that determine the operating lifetime of the membranes. In this research work, the structural changes that take place in ceramic membranes as a consequence of chemical cleaning were evaluated. As a case study, milk ultrafiltration process was selected since this is a typical and well-established application in the food industry, in particular, in cheese making. Three cleaning protocols with increasing aggressiveness were tested, namely basic, basic plus acid and basic plus acid plus disinfectant. At the end of the operational cycles, the changes in permeability, pore distribution and mean pore radius occurred in the membrane active layer for each protocol were analyzed by liquid–liquid displacement porosimetry (LLDP). The results obtained indicate that the membrane after alkaline + acid + oxidant cleaning presented a total number of pores and porosity values higher than the others, while the cleaning protocol less effective was the alkaline one.

Three different chemical cleaning protocols used in the ultrafiltration process in the dairy industry have been tested. Their effects in the pore size distribution of the fouled membrane have been analyzed by means of liquid–liquid displacement porosimetry. The addition of consecutive cleaning agents resulted in protocols that removed more residual materials from membrane since the porosimetry data after 50 cycles was closer to the virgin membrane ones. However, none of the cleaning protocols was able to recover the initial pore distribution of the membrane, neither its original permeability.