Microfiltration and ultrafiltration processes are extensively used today in the dairy industry in order to remove bacterial charge of milk, to fractionate milk proteins and in the concentration of milk in cheese-making [1]. Studies on the flux decline during filtration of protein solutions, suggested that the adsorption of proteins onto the membrane surface or in the pore wall of the membranes is the cause of the early stage of flux decay, and affects the behaviour of the permeate flux [2]. Furthermore, the pre-denatured or pre-aggregated proteins exacerbate this phenomenon with a considerable loss in productivity [3, 4]. Adsorption is a phenomenon that occurs in different areas (biology, medicine, food processing) and determines change in the surface energy properties, protein structures and in their biological functions thus affecting the final product value. In the present work, the contribution of native and pre-heated milk proteins to the adsorptive fouling of polyethersulphone (PES) flat-sheet ultrafiltration membrane with cut-off of 50 kDa was investigated. An experimental evaluation of the components of the hydraulic resistance after adsorption of proteins and during ultrafiltration of skimmed milk was also carried out. The conditioning of the membrane with denatured milk proteins caused a loss in membrane permeability of about 26% higher than the membrane conditioned with native proteins. Fouling analysis showed that the irreversible fouling controlled the flux and the resistance due to adsorption observed when conditioning the membrane with pre-heated milk was 5.18x1012, while the one observed when conditioning the membrane with native milk was 1.54x1012 respectively. Contact angle measurements, performed by using the sessile drop method, showed a higher loss in membrane hydrophilicity upon adsorption of denatured proteins. EDX-SEM analyses [5] have been also performed in order to measure the atomic composition (expressed as theirs ratios to sulfur composition, used as an indicator of the membrane matrix) of new and fouled membrane surfaces: results showed an excess of organic compounds of membranes conditioned with pre-heated milk. The limiting value of the transmembrane pressure (TMPlim) of native and pre-heated milk was found to be 0.8 bar and 0.5 bar, respectively. Filtration runs in concentration mode showed that high axial flow rates allowed to achieve higher volume reduction rate. 1. A. Cassano, E. Drioli, F. Garrafa, G. Dinaro, 1st Workshop Italy-Russia, Cetraro (CS), Italy, 2003; September 17-21. 2. G. Belfort, R. H. Davis, A. L. Zydney, J. of Membrane Science, 1994; 96: 1-58. 3. T. Maruyama, S. Katoh, M. Nakajima, Biotechology and Bioengineering, 2001; 75(2): 233-238. 4. S.T. Kelly, W.S. Opong, A.L. Zydney, J. of Membrane Science, 1993; 80: 175-187. 5. M.R. Baudry, M. Le Maux, B. Chaufer, L. Begoin, Desalination, 2002; 146: 123-128.
INFLUENCE OF PRE-HEATING ON THE ADSORPTIVE FOULING AND PERFORMANCE OF POLYETHERSULPHONE ULTRAFILTRATION MEMBRANE IN MILK PROCESSING
L Donato;E Drioli
2004
Abstract
Microfiltration and ultrafiltration processes are extensively used today in the dairy industry in order to remove bacterial charge of milk, to fractionate milk proteins and in the concentration of milk in cheese-making [1]. Studies on the flux decline during filtration of protein solutions, suggested that the adsorption of proteins onto the membrane surface or in the pore wall of the membranes is the cause of the early stage of flux decay, and affects the behaviour of the permeate flux [2]. Furthermore, the pre-denatured or pre-aggregated proteins exacerbate this phenomenon with a considerable loss in productivity [3, 4]. Adsorption is a phenomenon that occurs in different areas (biology, medicine, food processing) and determines change in the surface energy properties, protein structures and in their biological functions thus affecting the final product value. In the present work, the contribution of native and pre-heated milk proteins to the adsorptive fouling of polyethersulphone (PES) flat-sheet ultrafiltration membrane with cut-off of 50 kDa was investigated. An experimental evaluation of the components of the hydraulic resistance after adsorption of proteins and during ultrafiltration of skimmed milk was also carried out. The conditioning of the membrane with denatured milk proteins caused a loss in membrane permeability of about 26% higher than the membrane conditioned with native proteins. Fouling analysis showed that the irreversible fouling controlled the flux and the resistance due to adsorption observed when conditioning the membrane with pre-heated milk was 5.18x1012, while the one observed when conditioning the membrane with native milk was 1.54x1012 respectively. Contact angle measurements, performed by using the sessile drop method, showed a higher loss in membrane hydrophilicity upon adsorption of denatured proteins. EDX-SEM analyses [5] have been also performed in order to measure the atomic composition (expressed as theirs ratios to sulfur composition, used as an indicator of the membrane matrix) of new and fouled membrane surfaces: results showed an excess of organic compounds of membranes conditioned with pre-heated milk. The limiting value of the transmembrane pressure (TMPlim) of native and pre-heated milk was found to be 0.8 bar and 0.5 bar, respectively. Filtration runs in concentration mode showed that high axial flow rates allowed to achieve higher volume reduction rate. 1. A. Cassano, E. Drioli, F. Garrafa, G. Dinaro, 1st Workshop Italy-Russia, Cetraro (CS), Italy, 2003; September 17-21. 2. G. Belfort, R. H. Davis, A. L. Zydney, J. of Membrane Science, 1994; 96: 1-58. 3. T. Maruyama, S. Katoh, M. Nakajima, Biotechology and Bioengineering, 2001; 75(2): 233-238. 4. S.T. Kelly, W.S. Opong, A.L. Zydney, J. of Membrane Science, 1993; 80: 175-187. 5. M.R. Baudry, M. Le Maux, B. Chaufer, L. Begoin, Desalination, 2002; 146: 123-128.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
