Ultrafiltration

Detail about Ultrafiltration, its working, principle, membrane fouling, methods to remove membrane fouling and applications of Ultrafiltration.

1. ULTRAFILTRATION

2. Contents Introduction Working and Principle Membrane Membrane Fouling Methods to remove Membrane Fouling Cleaning Applications

3. INTRODUCTION Ultrafiltration (UF) is a variety of  membrane filtration  in which forces like  pressure  or  concentration gradients  lead to a separation through a  semipermeable membrane .

4. INTRODUCTION (CONTINUE..) Ultrafiltration will remove: High molecular weight substances Colloidal materials Organic polymeric molecules Inorganic polymeric molecules

5. INTRODUCTION (CONTINUE..) This separation process is used in industry and research for purifying and concentrating macromolecular (10 3  - 10 6  Da) solutions, especially protein solutions. Pore diameters in the 10-1000 A range.

6. WORKING  Suspended solids and solutes of high molecular weight are retained in the so-called retentate , while water and low molecular weight solutes pass through the membrane in the  permeate(filtrate).

7. PRINCIPLE The relationship between the applied pressure on the solution to be separated and the flux through the membrane is most commonly described by the Darcy equation: Where J is the flux (flow rate per membrane area) TMP is the transmembrane pressure (pressure difference between feed and permeate stream) μ is solvent viscosity R t  is the total resistance (sum of membrane and fouling resistance).

8. MEMBRANE The membrane used for UF should have : High porosity Narrow pore size distribution

9. POLYMERS USED IN MEMBRANES Cellulose acetate (CA) Cellulose triacetate (TCA) Polyvinyl alcohol (PVA) Polysulfone (PS) Polyamide (PA) Porous carbon of aluminia Polyethersulfone (PES)

10. Factors effecting rentity of membranes Size of molecules Shape of the molecule Membrane material Presence of other solutes Membrane configuration Fouling and absorption effects

11. Pore Size of membranes UF membrane have pore sizes larger than Reverse Osmosis Process. These membranes are mostly used for fractionating processes (to separate high molecular weight solutes from low molecular weight). The pore size of UF membrane ranges from 0.001 micron – 0.02 micron.

12. Membrane Fouling The major challenge faced in UF is membrane fouling. Overtime the filtrate will accumulate on the membrane surface and clog the pores. Greatly reduces membrane effectiveness and efficieny . This reduces the effective TMP of the system, therefore reducing permeation rate. The increase in concentrated layer at the membrane wall decreases the permeate flux, due to increase in resistance which reduces the driving force for solvent to transport through membrane surface.  Methods have been developed to reduce this effect for continuous operation.

13. Membrane Fouling (Continue..)

14. Types of Fouling 1. Particulate deposition Standard blocking: macromolecules are uniformly deposited on pore walls Complete blocking: membrane pore is completely sealed by a macromolecule Cake formation: accumulated particles or macromolecules form a fouling layer on the membrane surface, in UF this is also known as a gel layer Intermediate blocking: when macromolecules deposit into pores or onto already blocked pores, contributing to cake formation

15. Types of Fouling (Continue..) 2. Scaling As a result of concentration polarization at the membrane surface, increased ion concentrations may exceed solubility thresholds and precipitate on the membrane surface. These inorganic salt deposits can block pores causing flux decline, membrane degradation and loss of production. The formation of scale is highly dependent on factors affecting both solubility and concentration polarization including pH, temperature, flow velocity and permeation rate.

16. Types of Fouling (Continue..) 3. Biofouling Microorganisms will adhere to the membrane surface forming a gel layer – known as  biofilm. The film increases the resistance to flow, acting as an additional barrier to permeation.

17. Types of Fouling (Continue..)

18. Methods To Reduce Membrane Fouling Optimize pH and ionic strength of the feed solution to minimize the adsorption or deposition of the feed materials. Select an appropriate pre-filtration procedure or other means to remove large molecules. Select a membrane with an optimum pore size . Optimize the operating conditions . This includes increasing transmembrane pressure to maximize flux.

19. Cleaning Cleaning of the membrane is done regularly to prevent the accumulation of foulants . Regular backwashing is often conducted every 10 min for some processes to remove cake layers formed on the membrane surface. By pressurising the permeate stream and forcing it back through the membrane, accumulated particles can be dislodged, improving the flux of the process. 

20. Cleaning (Continue..) Backwashing is limited in its ability to remove more complex forms of fouling such as biofouling, scaling or adsorption to pore walls. These types of foulants require chemical cleaning to be removed. The common types of chemicals used for cleaning are: Acidic solutions for the control of inorganic scale deposits. Alkali solutions for removal of organic compounds. Biocides or disinfection such as Chlorine or Peroxide when bio-fouling is evident.

21. Applications Water Treatment Process water (Remove oxides, acids, bases, pathogens, inorganic salts etc from raw water) Drinking water (viruses and various microorganisms are removed) Waste water (Remove Pollution and reduction of waste from water)

22. Applications (Continue..) Biotechnological Application Separation of Microbial cells Recovery of enzymes Cell washing Product purification

23. Applications (Continue..) Dairy Industry Cheese manufacturing Cheese whey UF Milk Fermented Products

24. Applications (Continue..) Animal Products Industry Red Meat production Gelatin recovery Egg poultry Fish Industry

25. Applications (Continue..) Other applications include : Filtration of effluent from paper pulp mill Removal of pathogens from milk Fruit juice concentration and clarification Dialysis and other blood treatments Alcoholic beverage industries Vegetable oils Sugar industry

26. THANKS