Filtration performance and bacteria effect of PVDF membrane on draft beer

Pure draft beer, also known as draft beer, is a kind of aseptic filtration and aseptic filling beer without pasteurization or high-temperature instantaneous disinfection. It is rich in amino acids, carbohydrates, inorganic salts, a variety of vitamins and a variety of active enzymes, which can enhance appetite and promote digestion and other functions, and belongs to the high-grade beer varieties.


Filtration and sterilization is the key link in production.  Membrane separation technology can completely retain various nutrients in food by using the principle of screening, and is applied in the production of turbidity and bacteria removal of draft beer. The liquor produced is clearer and transparent, and the foam retention is longer. Sensitive protein and cold turbidity are filtered by more than 30% lower than 1000 diatoms.  However, the inevitable membrane pollution seriously affects the filtration performance, and the stable equilibrium layer is only about 10L/(m²/h), which limits the application of membrane filtration technology in beer production.


The current chemical cleaning will have a certain impact on the quality of draft beer, and the cost of replacing a new filter membrane is too high, resulting in high operating cost of pure draft beer.  To reduce membrane fouling, the key is to improve the properties of membrane materials. Studies show that hydrophilic membranes can effectively reduce membrane fouling and improve membrane balance flux.  On this basis, if the membrane flux can be restored by water backwashing, it is of great significance to the practical application of draft beer production.  Choose hydrophilic PVDF membrane filtration draft beer, studied the PVDF microfiltration membrane filtration filter bacteria of escherichia coli bacteria suspension performance and membrane structure, membrane aperture, the relationship between two structures were examined microfiltration membranes should be used for filtration sterilization effect of draft beer filtration, membrane flux change and different ways of qing wash cleaning effect, and so on, provide a reference for further application.


The experimental method

The pore size distribution of PVDF membrane was measured by a self-made bubble point flow rate method pore size distribution tester.  Cut off the circular diaphragm on the dry film, soak it in thousands of soaking solution until translucent, take it out and blot the liquid attached to the surface with filter paper, then spread it on the detector for detection.  The immersion solution was isopropyl alcohol and the pressure source was nitrogen.

For contact Angle measurement, a 2cmx2cm square diaphragm was cut, fixed on the slide, and placed on the sample table for detection.  The change of contact Angle of water droplets from dropping onto the membrane surface to completely disappearing was recorded.

Representative membrane samples were taken from the dry membrane, and their upper and lower surfaces were glued to the sample platform with conductive adhesive respectively. After the cross-section was quenched by liquid nitrogen, the cross-section was glued to the sample platform with conductive adhesive, and the sample was placed on the electron microscope platform after vacuum locking.4

Microbial count E. coli count: take the sample to be tested, refer to GB4789.3-2010 for detection.  Total colony count of draft beer: sample of draft beer before and after filtration was taken for detection according to GB4789.2-2010.  Yeast count: take draft beer samples before and after filtration, refer to GB4789.15

The hydrophilic PVDF-n or PVDF-f microfiltration membranes were put into the membrane tank and the whole membrane was autoclaved at 121°C for 20min.  A self-made filter device (see Figure 1) was used to measure the variation of draft beer filtration with filtration time under lOOkPa repulsive force. The experimental process is shown in Figure 2.  The first filtration process of the new membrane is denoted as C.  After filtration for a period of time until the membrane flux attenuation reaches a stable value, the filter membrane is cleaned to recover the membrane flux, and the cleaned membrane continues to filter the draft beer.  The first four cycles of membrane cleaning were soaked with water, and the last four cycles were soaked with 0.05Mo1 /L NaOH solution water, 0.05Mo1 /L HCl solution and water alternately.


The relationship between membrane filtration effect and pore size

Two kinds of hydrophilic PVDF-N membrane with mesh structure and PVDF-F membrane with finger pore structure were used to filter the bacterial suspension containing Escherichia coli. The relationship between the effect of hydrophilic microfiltration membrane and the pore size was determined according to the change of the concentration of EScherichia coli in the liquid before and after filtration.  In the experiment, two groups of parallel filtration experiments were conducted for the microfiltration membrane of each pore size, and two samples of each filtration liquid were taken for parallel detection. The concentration of Escherichia coli before and after filtration was shown in Table 1.6

It can be seen from Table 1 that when two membranes (0.179-0.234µm and 0.199-0.252 µm) with membrane pore sizes of 0.22µm were filtered, the concentration of Escherichia coli in the filtrate was in the range of 0-2cfu/mL.  When two membranes with pore sizes of 0.45µm (0.644-0.579 µm, 0.424-0.652 µm) were filtered, the concentration of E. coli in the filtrate was about 14-20 cfu/mL.

Post time: May-31-2022