Integrierte Vermeidung und Verminderung der Umweltverschmutzung

Chapter 2
2.1.3.6.3 Description of techniques, methods and equipment
There are two membrane separation techniques used in the FDM sector, i.e. membrane
separation and electrodialysis.
Membrane separation is a pressure driven filtration technique in which a solution is forced
through a porous membrane. Some of the dissolved solids are held back because their molecular
size is too large to allow them to pass through. The size range depends upon the type of
membranes used. Fractionation of the feed stream occurs, with some molecules being
concentrated on the upstream side of the membrane, which is known as the concentrate or
retentate. The smaller molecules pass through the membrane into the permeate stream.
The various membrane separation techniques can be characterised by their membrane pore size.
Cross-flow microfiltration (CMF), can be used to remove bacteria from skimmed milk, or for
fractionation of the skimmed milk into a casein rich retentate and a milk serum devoid of casein;
the membrane pore size ranges from about 0.1 to 5 μm. Ultrafiltration (UF) is applied to both
skimmed milk and whey, to concentrate the respective protein components; the membrane pore
size ranges from about 10 to 100 nm. Nanofiltration (NF) membranes have selective
permeability for minerals and some small organic and inorganic molecules and NF is used
predominantly for concentration and pre-demineralisation (removal of salt) of whey; the pore
sizes of the NF membrane range from about 1 to 10 nm. Reverse osmosis filtration (RO)
membranes are permeable to water but not minerals and are, therefore, used for dewatering;
concentration of whey or skimmed milk; or for polishing NF permeates or evaporator
condensate and in water treatment, e.g. softening and salt removal; the membrane pore size
ranges from about 0.1 to 1 nm.
Electrodialysis is a membrane separation process undertaken in the presence of an applied
electro potential. Low molecular weight ions migrate to an electrical field across cationic or
anionic membranes. These membranes are alternately arranged between the cathode and anode
within a stack. It is principally applied in the dairy industry for the removal of salt from whey.
2.1.3.7 Crystallisation (C.7)
2.1.3.7.1 Objective
The objective of crystallisation is to separate a solute from a solvent.
2.1.3.7.2 Field of application
Crystallisation is applied in the dairy industry, where lactose is produced from cheese whey or
casein whey, and the sugar industry. It is also used in the edible oil industry to modify the
properties of edible oils and fats; in this case it is also called fractionation.
2.1.3.7.3 Description of the technique, methods and equipment
Crystallisation is the formation of solid crystals from a solution. Crystals solidify in a definite
geometric form. They are usually grown by the introduction of nuclei into a supersaturated
solution. Any impurities in the liquid are usually not incorporated into the lattice structure of the
desired crystal. Accordingly, crystallisation is also a purification process.
2.1.3.8 Removal of free fatty acids (ffa) by neutralisation (C.8)
2.1.3.8.1 Objective
The objective of the chemical neutralisation process is to remove the ffa and the phosphatides
from vegetable oils, using caustic and phosphoric acid or, in some cases, citric acid.
22 January 2006 RHC/EIPPCB/FDM_BREF_FINAL