Nanofiltration

Example of Application in the Dairy Industry: In the dairy industry the nanofiltration process is used to concentrate and partially demineralize liquid whey. Due to the selectivity of the membranes most of the monovalent ions, the NPN, the organic acids, and some of the lactose will pass the membrane.

The typical composition of the different products achieved by nanofiltration of a liquid whey is shown in the table below:

Total Solids Total Protein [%TS] NPN [%TS] Lactose [%TS] Organic Acids [%TS] Ashes [%TS] Fat [%TS]

Raw Whey 6.5% 12.8 0.5 74.4 3.4 7.7 0.7

Concetrated Whey 18.5% 13.5 0.36 77.0 3.37 5.3 0.8

Permeate 0.37% 0 4.32 26.2 4.9 68.8 0

Losses 0% 31% 1.3% 5% 28% 0%

The composition of the ashes of the raw whey and the concentrated whey shows the preferential transport of monovalent ions through the membranes:

Ca [%TS] Mg [%TS] Na [%TS] K [%TS] S [%TS] P [%TS] Cl [%TS]

Raw Whey 0.42 0.12 0.61 2.36 0.16 0.62 1.44

Concetrated Whey 0.41 0.12 0.38 1.48 0.15 0.57 0.68

Permeate 0.7 0.21 6.5 25.2 0.55 2.05 21.1

Losses 6% 6% 40% 40% 12% 12% 54%

For the nanofiltration process, the maximum achievable demineralization rate is about 35 % with a concentration factor of about 3.5 to 4. To reach a higher demineralization rate it is necessary to dilute the partially demineralized whey with demineralized water and run the nanofiltration process again. By applying this so-called diafiltration step, it is possible to achieve a demineralization rate of up to 45 %. On using a special pretreatment of the whey, developed by SAFIR / EURODIA, it is possible to get a demineralization rate of up to 75 % with nanofiltration.

The maximum concentration to be achieved by nanofiltration is between 22 % TS and 24 % TS. Above this concentration, problems can occur due to the precipitation of phosphates; in addition, the viscosity of the concentrated whey is increasing exponentially above 24 % TS.

The concentration that can be most economical achieved with nanofiltration is 18 % TS at a demineralization rate of 28 %. Because of the logarithmic decrease of the permeate flow rate when the concentration increases, further concentrating from 18 % TS up to 24 % TS would require doubling the membrane area.

Applying the nanofiltration process on acidic whey will result in a preconcentrated product that is similar to sweet whey. Running the nanofiltration process on lactic acid whey will give a product that is dramatically decreased in the lactic acid content.

In some specific cases, it is advantageous to use nanofiltration to replace evaporation and partial demineralization. But for most of the dairy applications, a combination of different processes, including nanofiltration, is required to obtain the most valuable products. Please go to the Industries Section/ Dairy of this website for more details.

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