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DOWNSTREAM PROCESS UNIT OPERATIONS

Downstream processing filtration

Downstream processing filtration is used at several stages in downstream processing of the bioreactor as well as purification of water and other processing fluids e.g. sanitizing agent. the majority of purification types fall under Capture, intermediate purification and polishing. These are:

  • Microfiltration. Used at the start of downstream process to refine what was left after the upstream process and centrifugation
  • Ultrafiltration. this is used between chromatography steps to aid in concentration of the product and change its buffer conditions.
  • Sterilizing filtration. This involves usage of Nano filtration cartridges to eliminate micro-organisms, insoluble proteins and remove adventitious and endogenous viruses in preparation for the final process.

Devices installed with this membranes, are likely to affect two flow types.

  • Direct Flow downstream processing Filtration. In this flow the devices allow the medium to pass through it in a perpendicular flow preventing particulate clogging and preventing the other elements that do not fit from going through.
  • Tangential Flow Filtration. in this flow the device’s membrane is oriented in a way that the medium sweeps across the filtration surface thus minimizing surface fouling by the concentrated unwanted elements and pore plugging.

DIRECT FLOW FILTRATION: (DFF)

A flat membrane disk is utilized to increase the membrane surface area in the filter.  The membrane is folded in a pleated sheet with or without a supporting layer.  The combined filtration layer is then wrapped around a perforated collection core allowing a greater membrane along each fold.

In the DFF cartridge the downstream processing flow is directed through the inlet perpendicularly to the outer surface of the media then collects at the core and exits the device through the downstream port.

TANGENTIAL FLOW FILTRATION (TFF)

In this filter the feed flows tangentially over the membrane’s surface and a portion flows through the membrane as permeate.

The core operating variables of downstream processing here are:

  • Transmembrane pressure
  • Feed cross flow velocity
  • Increased turbulence to enhance mass transfer
  • Process flux
  • Temperature
  • Volume concentration factor
  • Number of infiltration wash volumes

Here the transmembrane pressure drives fluid through the membrane, taking the permeable molecules with it.

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