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Sugar, as the final product of the technology of sugar production, has to satisfy rigorous quality demands. Among others, it means low content of non-sucrose compounds, as well as the smallest possible share of coloured matters. Ultrafiltration and nanofiltration can be one of the solutions for a more effective separation of non-sucrose compounds from the intermediate products from which sucrose can directly be crystallized. Applying this procedure energy can be saved and the environment protected. Syrup solution from sugar-beet processing which contains 39.2% d.m. is being ultra- and nanofiltered.Polymer membranes with different MWCO (15–20 kDa, 6–8 kDa and 0.5 kDa) are used. Effects of UF are carried at 30°C and 60ºC, with flow rates at 200 and 400 L/h and in the range of transmembrane pressure between 1–4 bar. NF is carried at 30°C and 50ºC, with flow rates at 300 and 400 L/h and in the range of pressure between 1–30 bar. The separation of non-sucrose compounds is the most effective on a membrane with MWCO of 0.5 kDa, if the transmembrane pressure is kept at 30 bar and at a flow rate range between 300–400 L/h. Under these conditions colour and turbidity became lower for 76% and 80% respectively, if related to feed.

On the basis of the experiments done on the syrup UF at 30°C and 60°C, on transmembrane pressure in the range of 1–4 bar, and NF at 30°C and 50°C, on pressure from 5–30 bar, it could be concluded, that: • The permeate flux in UF at 200 L/h above pressure of 2 bar, and on 400 L/h above pressure 3 bar does not depend on transmembrane pressure. The same phenomenon is registered • • • in the case of NF on flow rate of 400 L/h, but then the transmembrane pressure was over 20 bar. The permeate flux got on membrane I and II reaches its own greatest value aat transmembrane pressure around 4 bar, flow rate around 400 L/h and at temperature around 60°C. The separation of coloured matters on the membrane I and II is the best on transmembrane pressure around 4 bar, flow rate around 400 L/h and at temperature around 30ºC. Under these conditions on membrane I the permeate has 55% and on membrane II 58% less coloured matters than in syrup solution. Permeate turbidity is less for 82% and 85% according to the syrup solution turbidity, by using membrane I and membrane II, respectively. The maximal permeate flux on membrane III is reached of transmembrane pressure with the value of about 30 bar, flow rate of 400 L/h and temperature at 60ºC. The effect of decolourization on membrane III is the best when transmembrane pressure is held on the level of about 30 bar within the flow rate range of 300–400 L/h and at temperature of 30°C. Under the mentioned conditions the permeate colour is for 78% less than the colour of the syrup solution. In this case turbidity is for 80% less in relation to feed. Information about the molecule sizes of syrup coloured matters could be obtained by comparing the colour of permeate and feed: 55% molecules of coloured matters are larger than 15 kDa, 3% has molecules between 6 and 15 kDa, 20% of coloured matters has molecules between 0.5 and 6 kDa and 22% molecules are smaller than 0.5 kDa.