Filtration

Filtration is commonly the mechanical or physical operation which is used for the separation of products like solids from fluids by interposing a medium through which only the fluid can pass.

1. FILTRATION Tapeshwar Yadav (Lecturer) BMLT, DNHE, M.Sc. Medical Biochemistry

2. Introduction Filtration  is commonly the mechanical or physical operation which is used for the separation of products like solids from fluids by interposing a medium through which only the fluid can pass. The fluid that passes through is called a filtrate. Filtration is the best established and most versatile method for removing insoluble from dilute streams like fermentation broths.

3. FILTERATION The separation of solids from a suspension in a liquid by means of a porous medium or screen which retains the solids and allows the liquid to pass is termed filtration .

4. Filtration In the laboratory, the suspension is poured into a conical funnel fitted with a filter paper. In the industrial equivalent, difficulties are encountered in the mechanical handling of much larger quantities of suspension and solids. A thicker layer of solids has to form and, in order to achieve a high rate of passage of liquid through the solids, higher pressures are needed, and a far greater area has to be provided.

5. Steps involved in filtration Draining the liquor Filtration Filling with wash water Washing Draining the wash water Opening, dumping and reassembling Filling with slurry.

6. Principle of filtration

7. Principle of Filtration Since the filter medium is permeable only to the fluid, it retains the solid particles and permits only the fluid to pass through which is collected as the filtrate. The volume of filtrate collected per unit time (dV/dt) is termed as the rate of filtration. As the filtration proceeds, solid particle accumulate on the filter medium forming a packed bed of solids, called filter cake. As the thickness of the cake increases  resistance to flow of filtrate increases  rate of filtration gradually decreases. If rate is maintained to be constant then pressure difference driving force (- P) will increase. Therefore, a batch filter is operated either at constant pressure or at constant rate .

8. Constant rate and Pressure Filtration

9. Darcy's law  is a phenomenological derived constitutive equation that describes the flow of a fluid through a porous medium. Darcy's law is a simple proportional relationship between the instantaneous discharge rate through a porous medium, the viscosity of the fluid and the pressure drop over a given distance. The total discharge,  Q  (units of volume per time, e.g., m 3 /s) is equal to the product of the intrinsic permeability of the medium,  k  (m 2 ), the cross-sectional area to flow,  A  (units of area, e.g., m 2 ), and the pressure drop ( P b  - P a ), ( Pascals ), all divided by the viscosity,  μ  ( Pa·s ) and the length over which the pressure drop is taking place (m). General theory of filtration

10. Types of filtration equipment The industrial filtration equipment differs from laboratory filtration equipment only in the amount of material handled and in the necessity for low-cost operation. Fig. Simple laboratory filtration apparatus

11. Filters can also be classified by operating cycle . Filters can be operated as batch , where the cake is removed after a run, or continuous , where the cake is removed continuously. In another classification, filters can be of the gravity type , where the liquid simply flows by means of a hydrostatic head, or pressure or vacuum can be used to increase the flow rates.

12. Some of the most important types of filters: 1. Bed filter 2. Plate-and-frame-filter 3. Leaf Filters 4. Continuous rotary filters a. Continuous rotary vacuum-drum filter b. Continuous rotary disk filter c. Continuous rotary horizontal filter

13. Such filters are useful mainly in cases where relatively small amounts of solids are to be removed from large amounts of water in clarifying the liquid. Fig. Bed Filter 1. BED FILTER

14. 2. PLATE-AND-FRAME-FILTER The feed slurry is pumped which flows through the duct. The filtrate flows through the filter cloth and the solids build up as a cake on the frame side of the cloth. The filtrate flows between the filter cloth and the face of the plate through the channels to the outlet. Fig. Plate-and-frame-filter press

15. 3. Leaf Filters This filter is useful for many purposes but is not economical for handling large quantities of sludge or for washing with a small amount of fresh water. The wash water often channels in the cake and large volumes of wash water may be needed. Fig. Leaf Filter

16. 4. Continuous rotary filters A number of such filters are as follows: a. Continuous rotary vacuum-drum filter b. Continuous rotary disk filter c. Continuous rotary horizontal filter

17. A. CONTINUOUS ROTARY VACUUM-DRUM FILTER Fig. Continuous rotary Vacuum drum filter

18. B. CONTINUOUS ROTARY DISK FILTER The filter consist of concentric vertical disks mounted on a horizontal rotating shaft. The filter operates on the same principle as the vacuum rotary-drum filter. Each disk in hollow and covered with a filter cloth and is partly submerged in the slurry. C. CONTINUOUS ROTARY HORIZONTAL FILTER This type is a vacuum filter with the rotating annular filtering surface divided into sectors. As the horizontal filter rotates, it successively receives slurry, is washed, is dried, and the cake is scraped off.

19. Removal of Insoluble Products

20. Rotary Vacuum Filtration slurry is pumped into the trough The vacuum draws liquid and air through the filter media and out the shaft hence forming a layer of cake An agitator is used to regulate the slurry if the texture is coarse and it is settling rapidly Solids that are trapped on the surface of the drum washed and dried, removing all the free moisture

21. Microfiltration/ Ultra filtration Microfiltration usually serves as a pre-treatment for other separation processes such as ultrafiltration, and a post-treatment for granular media filtration. The typical particle size used for microfiltration ranges from about 0.1 to 10 µm. In terms of approximate molecular weight these membranes can separate macromolecules generally less than 100,000 g/mol.

22. The filters used in the microfiltration process are specially designed to prevent particles such as, sediment, algae, protozoa or large bacteria from passing through a specially designed filter. More microscopic, atomic or ionic materials such as water (H 2 O),  monovalent  species such as Sodium (Na+) or Chloride ( Cl -) ions, dissolved or natural organic matter, and small colloids and viruses will still be able to pass through the filter.

23. Microfiltration Separates soluble contaminants remaining within the supernatant Supernatant may include: Other proteins Bio-molecules Un-used growth media Microfiltration image from: http://www.aaflow.de/filtertech/index.html

24. How does Microfiltration work? Pressure driven process Separates: Components in a solution or suspension based on molecular size Particles size range: 10 m m (starches) to aprx . 0.04 m m (DNA, Viruses, and globular proteins) Microfiltration image from: http://www.faireymicrofiltrex.com/Vokes%20Microfiltration/media/images/e-fluor.gif

25. Ultrafiltration Usually used to further separate any contaminants able to pass through the microfiltration membrane using a pressure gradient Ultrafiltration image from: http://www.awatec.ch/produkte/ultrafiltration.jpg

26. How does Ultrafiltration work? Separates: Particle size range: 0.1 m m to 0.001 m m Usually based on molecular weight Typical range: 200 to 300,000 g/mole Ultrafiltration image from: http://www.toltecint.com/how_dialysis_works/how_hemodialysis_works.htm

27. Microfiltration vs. Ultrafiltration Microfiltration: Proteins act as the permeate Ultrafiltration Proteins act as the retentate Images from: http://www.geafiltration.com/html/technology/ftechnology.html

28. Microfiltration vs. Ultrafiltration Microfiltration: Separates larger particles For example- Colloids Fat globules Cells Located upstream to reduce load and fouling capacity on ultrafiltration membrane downstream Ultrafiltration Separates smaller particles For example- Macromolecules However, processes are basically identical

29. Applications of Filtration: Filtration methods are used in the home, in research laboratories, in industrial processes, and in controlling environmental pollution . For example , a coffee filter is used to separate brewed coffee from the grounds, and HEPA filters are used in air conditioners and vacuum cleaners. Some filters are used to clean ambient air by removing dust from the atmosphere . In kidneys :The   kidney  works by filtration of  blood  in the glomerulus , followed by selectively reabsorbing many substances essential for the body.

30. Applications of Filtration: Chemists often use filtration to separate materials from mixtures of different chemical compositions . On an industrial scale, filtration is used by the oil, gas, food and beverage, and pharmaceutical industries, among others. Municipalities use filtration techniques when treating sewage and purifying water. Filtration cleans up river streams or other water streams. Furnaces use filtration to prevent the furnace elements from fouling with particulates.

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