Wednesday, September 12, 2012

Double Block and Bleed - Contamination

When filling up a bioreactor with media (colloquially called, "batching"), the media is delivered through a dedicated pipe.  When the batching is complete, there needs to be a way to contain the bioreactor... which is why there is a "near-to" block valve.

And the excess media (not required per specification) is sent to drain via a bleed valve that is on the non-sterile side of the block valve.

single block and bleed
Figure 1: Single Block and Bleed

This is pretty standard for fermentors and bioreactors... in the 1980's.

After the media line has delivered the media, it is dirty because the nutrient-rich media has coated the pipes and will promote growth unless cleaned.

And if you have single-block-and-bleeds, your cleaning and rinse solutions are going to pound against that block valve.  Should it fail, you're going to have a contaminated bioreactor.

Modern plants... those with the luxury of building from scratch install two blocks and two bleeds, hence
double block and bleed
Figure 2: Double Block and Bleed

In this scenario, when the media is delivered, both block valves shut simultaneously and both bleed valves are opened simultaneously.  The excess media is sent to drain via the valves farther away from the bioreactor.

Subsequent manipulations to that line (e.g. post-use integrity tests, cleaning, sterilization) are isolated from the bioreactor by two block valves... prophylaxis for disturbances to the sterile envelope.

Read About A Successful Contamination Response

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