Monday, June 3, 2013

Venturi Effect and Bioreactor Contamination

If you're a rock, potential energy is sitting at the top of a hill.  And kinetic energy is you rolling down that hill.

If you're a volume of fluid, potential energy is pressure.  And kinetic energy is flow.

This principle is the reason why planes fly.  Because of the shape of the plane's wing, the fluid that moves over the top of the wing moves faster than the fluid that moves under the wing.  The faster flow over the top of the wing has higher kinetic energy, and therefore lower pressure.

This lower pressure literally sucks the plane higher into the sky.  This phenomena was enunciated by Daniel Bernoulli in 1783 and bears his name as the Bernoulli Principle.

What's this have to do with the Venturi Effect?

Well, the Venturi Effect describes the fluid motion and properties when fluid is moving through a constriction.  As the fluid moves through the constriction, the linear velocity of the flow increases.  This increase in fluid velocity causes a lower pressure at the point of constriction... per the Bernoulli principle.

If this pressure at the point of constriction is lower than atmospheric pressure, you get a vacuum.

What's this have to do with microbial contamination of bioreactors?

Put simply, bioreactor contaminations can happen when microbes get sucked out of drain manifolds and get pushed into the bioreactor.  Failure Mode: Failure to Keep Out.

Classic signs of contaminations with this root cause can be:
  • Easy-to-kill organisms: Gram-negative species
  • Mixed-culture: multiple species identified
  • Contamination time window includes feeds
We discovered this phenomenon at a West Coast biologics manufacturing facility that was less than 5-years old.  This Venturi effect was unwittingly created during fed-batch operations and has been associated with bioreactor contaminations.  It may not be every time that a bioreactor contaminates, but if the Venturi effect is happening, it's a matter of when, not if.

If you suck at reducing cell culture contaminations, you could be looking at your P&ID and not realizing that this is happening.


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