(a) Dead-end/conventional filtration fluid flow perpendicular to the filter medium. (b) Crossflow filtration fluid flow parallel to the filter

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1 FILTRATION

2 (a) Dead-end/conventional filtration fluid flow perpendicular to the filter medium. (b) Crossflow filtration fluid flow parallel to the filter medium.

3 Filtration Generally carry out in the early stage of bioproduct purification, inline with the process design heuristic, i.e. REMOVE THE MOST PLENTIFUL IMPURITIES FIRST Conventional filtration Typically used when product has been secreted from cells. Antibiotic and steroids are typical product treated by this filtration method. Use in sterile filtration in biopharmarceutical production. Crossflow filtration Use to separate cells where the product has been secreted. Concentration of cells. Removal of cell debris which has been lysed. Concentration of protein solutions. Removal of salt in protein solution. Removal of viruses from protein solution.

4 A Buchner funnel is a typical laboratory filtration apparatus as shown above. The liquid is flow through the filter cloth by vacuum. Larger particles cannot pass through the small openings of the filter cloth. A porous filter cake will build up as the filtration proceeds. This cake act as a filter for the suspended particles. As the cake builds up, resistance to flow also increase.

5 CONVENTIONAL FILTRATION

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8 Basic Theory of Filtration

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12 Filtration Equation for Constant-Pressure Filtration

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22 Individual Assignment (Due on Tuesday, 25/2/2014) (d) What is the most effective change you can make to decrease the time required to filter a given volume.

23 Plate-and-frame filter presses Disadvantages Batch process Labour intensive Not suitable for highthroughput processess Not suitable for biohazard filter cake. Require large amount of water for cake washing. Consist of plates and frames assembled alternately with a filter cloth over each side of the plates. The filtrate flows through the filter cloth and the solids build up as a cake on the frame side of the cloth. Filtration proceeds until the frame is completely filled with solids. The frame and the plate are separated and the cake removed. The filter is reassembled and the cycle is repeated.

24 Leaf filter Developed to handle large volume of slurry and more efficient washing. Each leaf is a hollow wire framework covered by a sack of filter cloth. Filtrate flows in the hollow framework and out a header. The was liquid follow the same path as the slurry. To remove cake, the shell is opened

25 Continuous Rotary-Drum Filter The filter filters, washes, and discharge the cake in a continuous, repeating sequence. The drum rotates slowly where it is partially submerged in a slurry reservoir. The drum surface is covered by filter media and a vacuum is maintained below the medium on the inside of the drum. The filtrate leaves through the axle of the filter. The automatic valve provides separate outlets for the filtrate and the wash liquid. Not suitable for viscous liquids or for liquid that must be enclosed. Advantages: filters are continuous and automatic and labour costs are relatively low. However the capital cost is relatively high.

26 Scale-up and Design of Filtration System A filter leaf tests are usually performed to develop data for scaling up a Rotary Vacuum Filter. The objective is to simulate the operation of a large scale rotary vacuum filter.

27 Filter Leaf Apparatus The leaf is allowed to submerge in the broth being filtered for the amount of time that the rotating drum will be submerged. For the washing segment of the rotating drum, the leaf is submerged in water or other liquid for the amount of time equivalent. The leaf is remove from the wash liquid, and air is to be pulled to the cake for dewatering. The three steps above (filtration, washing, and dewatering) are repeated for another cycle. The volume of filtrate and the mass of cake are measured and analysed.

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30 Example

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32 Equations for washing of filter cakes and total cycle time After the filtration time has been completed, the washing of a cake is carried out by displacement of the filtrate and by diffusion. The amount of wash liquid should be sufficient to give the desired washing effect. The conditions during washing i.e. cake structure, is assumed to be similar. For filters where the wash liquid follows a flow path similar to that during filtration, the final filtering rate gives the predicted wash rate. For a constant pressure filtration, In the actual operation, the washing rate may be less than predicted because of cake consolidation, channeling and formation of cracks.