Experiments

We ran several experiments throughout the development of the complete bioreactor. After the first few times, we realized that the pumps needed individual calibrations due to a slight error seen after a few days of running it. It was also observed that aeration pump was not fast enough and so, the same stepper motor was worked on and made faster, to aerate at 10 mL per minute. Meanwhile the spring structure of the pump was modified time and again to make a sturdy and stable structure.

Preliminery Runs

The first experiment was carried out using only the pumps and the stirrer, with continuous samples being manually taken to observe the OD using the laboratory spectrophotometer and monitor the growth. We used Escherechia Coli DH5alpha strain in LB medium and ran the experiments for 110 hours and obtained the following results:

Plot of Optical Density versus Dilution rate

Final Experiment

The experiment for characterization of the chemostat Bioreactor consisted of a Batch mode followed by the Continuous mode with 3 different dilution rates. The experiment was designed to keep the dilution rates constant for 3 reactor volumes, so as to obtain constant OD within human sampling error, to achieve Proof of Concept.

The Batch mode ran for 5 hours until we observed OD above the threshold of 1.0 in the reactor to start increasing the dilution rate. The continuous mode was started with dilution rate of 0.1 /h at hour 5. Constant OD was obtained for 9 hours but soon it was observed that the feed pump supplies more medium than the harvest removed by the harvest pump. At hour 30, we decided to modify the Master Control Program to change the speed of the harvest pump. Therefore, the harvest pump rate was changed to pump 30% faster than the feed pump. This can be observed in the reduction in the OD from an average of 0.78 to 0.76. At hour 48, the dilution rate was changed for step 2 of the experiment, to 0.3 /h. The OD was observed to be stable with few variations within pipetting error. The step 3 was carried out at hour 63, with dilution rate at 0.4 /h. This resulted in OD values for 3 reactor volumes, which lasted for 7.5 hours.