Content area
Full text
Summary
Fouling of a ceramic membrane with nominal pore size of 0.2 µm was measured under static conditions (adsorption and interaction of milk constituents with membrane surface), and dynamic conditions (concentration polarisation and interaction of milk constituents with membrane interior).
Static fouling (Fs) by milk proteins showed a 0.26 mL/L decline in water flux compared to the initial water flux. Fouling by casein micelles' adsorption was evident by scanning electron microscopy of the membrane surface. Skim milk microfiltration under dynamic conditions during batch circulation decreased subsequent water flux by Fd = 0.74 mL/L, compared to the initial water flux. Active sites of the membrane were silanized using glycidoxypropyltrimethoxysilane or 3-aminopropyltriethoxysilane. Static and dynamic fouling by skim milk after silanization caused similar water flux declines by both silanization treatments, not markedly improving the flux. Soaking the fouled membrane in urea, 6 mol/L (pH 8.5) for 72 h, or in 50 g/L mercaptoethanol in urea, 6 mol/L for 24 h, or in 50 g/L guanidine chloride in urea, 6 mol/L for 24 h, or batch circulation using urea, 6 mol/L did not restore the original water flux completely. The data suggest that proteins are not solely responsible for static and dynamic fouling and/or interaction of milk components with ceramic membrane surfaces.
Introduction
Permeation flux of a solution during membrane processing is usually much lower and decreases with time than permeation flux of water. This decline is rapid during the first several minutes, followed by flux reduction during operation. The main reasons for flux decline include membrane fouling, which is caused by solution particles adsorbing to and interacting with the membrane surface; by concentration polarisation (local increase of solute concentration at the membrane surface); and by penetration of solute particles to and interaction with the membrane interior.
The extent of fouling caused by solute-membrane interactions is strongly influenced by the chemical nature of the membrane.
Other reasons of flux decline include changing the operating conditions, chemical or physical deterioration of the membrane, or changes of food solution properties. The drawbacks of fouling are not only of a technical nature, but also are an economic one. These include lower yield depending on the solute quantity engaged in interaction with the membrane surface, decreased flux requiring increased membrane...