Analysis of CDC Bioreactor Internal Thermal Measurements and Sample Coupon Temperatures

The CDC Biofilm Reactor is an integral laboratory tool for the Environmental Control and Life
Support Systems (ECLSS) biofilm formation and growth research program. Critical to this research is the
need to adjust and maintain various surface temperatures of the coupons housed within the CDC Biofilm
Reactor. The purpose of this study was to provide quantitative temperature gradient information when the
CDC Biofilm Reactor was operating according to several process scenarios. Two primary process parameters
were evaluated. For the first set of test parameters, the liquid level was maintained at 350 mL, with an inlet
flowrate of 0.1 mL/min, 1 mL/min, 10 mL/min. The liquid was allowed to gravity drain out of the outlet
spout. For the second set of test parameters, the liquid level within the reactor was maintained at 550 mL,
with an inlet flow of 0.1 mL/min, 1 mL/min, 10 mL/min and draining intermittently controlled to 0.8 mL/min
to maintain the 550 mL level. Due to the placement of the thermocouple in the reactor, a difference in
temperature occurred between the coupon surfaces and target biofilm reactor temperature when operated
according to the first set of test parameters. When the reactor was operated according to the second set of
parameters, which resulted in the thermocouple being submerged, the temperature gradient was eliminated.
The results demonstrated minimal temperature gradient between the top and bottom coupon surfaces for
coupons placed in a single rod within the CDC Biofilm Reactor for both sets of test parameters evaluated.
The collection of this information helped to explain previous ECLSS biofilm formation test runs, along with
providing guidance on best operating practices for future ECLSS experiments. The placement of the
thermocouple also helps to explain the challenge of achieving and maintaining bulk liquid temperatures when
biofilm is grown according to the standardized test methods.