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Downstream Processing

Downstream Processing. Introduction. Desired products are separated and purified after successful fermentation or enzyme reactions This step is up to 60% of total cost, not including the purchase of raw materials

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Downstream Processing

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  1. Downstream Processing

  2. Introduction Desired products are separated and purified after successful fermentation or enzyme reactions This step is up to 60% of total cost, not including the purchase of raw materials Products may be dilute in aqueous medium, temperature sensitive, have multiple items to separate, and/or have properties similar to contaminants Products may require high purification and homogeneity

  3. Solid-Liquid Separations • Products may be biomass, extracellular, or intracellular • Purpose: to separate insolubles from fermentation broth • Cell sizes vary widely, from 1µm (bacteria)to 40µm (suspension plant cells)

  4. Filtration • The separation of particles by forcing the fluid through a filtering medium • Based on particle size and pressure drop • Filters are either based on pressure principle or vacuum

  5. Rate of Filtration Rate of filtration: (dvf/dt) = ΔP · A/ µ(L/K) A= area of filter K= filter’s permeability L= thickness of the filter cake Filtration time (t)= M∞Pc/2ΔP(Vf/A)2

  6. Centrifugation • 2 types: tubular and disk • Disk used in continuous operations: • Has a short, wide bowl 8-20 inches in diameter which turns on a vertical axis • Cone-shaped disks with uniform spacing are placed inside the bowl to separate suspended solids Terminal velocity= vt = dp2(ρs-ρ)a/18µ

  7. Recovery • Fermentation broth consists of dilute aqueous solution from which products have to be recovered and purified. • Overlaps exist between recovery and purification • Extraction and adsorption are exclusively classified as recovery

  8. Extraction (liquid-liquid separation) • Separation of solutes from the feed by contact with another insoluble liquid (solvent) • The effectiveness of the solvent increased with: • optimum pH • addition of counterions (acetate or butyrate)

  9. Types of Extractions • Single stage extraction- either in batch or continuous mode • Overall material balance for the mixer-settler is F + S = R + E and the material balance for the solute is FxF + Sys = Rx + Ey • Multistage extraction • Crosscurrent extraction- use continuously or in batch • Counter-current extraction- more efficient but cannot be operated in batch mode

  10. Adsorption (physical and chemical) • This is effective from separation of very dilute dissolved substances 1- Conventional adsorption -based on intermolecular forces of attraction (Vander Waals force) between the molecules of solid and substance (activated carbon used to purify water) - process is mixing of fruit pits and calcium chloride

  11. Adsorption (continued) 2- Ion Exchange -components include: polymeric network, ionic functional group attached to network and counter ion 3- Affinity adsorption involves chemical interactions between solute and ligand attached to surface of carrier particle

  12. Purification • Methods include precipitation, chromatography, and electrophoresis, and membrane separation • Precipitation- Used for recovery of proteins and is induced by salt, organic solvent, or heat addition • Chromatography- include a mobile phase with solutes to be separated and a stationary phase which may be adsorbent, ion-exchange resin, gel, or porous solid packed in cylindrical column • Electrophoresis- separation of charged species according to migration rates in electrical field

  13. Purification (continued) • Membrane Separation • Microfiltration- separation of suspended material based on pore size of 0.02 to 10 µm • Ultrafiltration- if separation is achieved at the molecular level, most commonly 100 to 200 Å • Reverse osmosis- to separate suspended and dissolved material using high pressure to reverse flow across semipermeable membrane

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