Closing the Carbon Balance on Membrane Bioreactors

The United Nations identified global warming and climate change as the biggest challenge in modern human development. The reduction in the use of petroleum and oil will be a necessary step in the advancement for every industry using petroleum products. The engineered Escherichia coli strain M0158 produces malate, a food additive and cosmetic chemical. The bioreactor in this study uses carbon dioxide (CO2) delivered through hollow-fiber membranes (HFMs) to dissolve the gas efficiently into the growth solution, eliminating the conventional need for direct bicarbonate supplementation. The current mass balance assumes 100% of the CO2 into the solution was being fixed to the product and standing in the growth solution, or there was no CO2 moving out of the system without being utilized. A system of iterative experimentation was set up to measure the CO2 concentration and flow rate in the outlet gas. In the first iteration of the design, an Arduino microcontroller, a SprintIR-6S-5 CO2 sensor, and a flow rate sensor were used to measure these values at the outlet gas stream. Through the experimentation, the design removed the flow rate sensor at the outlet and added an argon sweep gas controlled with a mass flow controller (MFC). The sensor setup was assessed for its reliability and consistency over a 24-hour long experiment to understand if it could function continuously throughout a 6-day fermentation experiment. Then, characterization curves quantify the amount of CO2 that leaves the system without bacterial consumption and these curves were measured for 8, 10, and 12 HFMs in an abiotic system. Lastly, a bioreactor with active cells was fit with the sensor system and measured for 3 days continuously with 10 HFMs. The results of this final experiment begin to show the consumption rates of the bacteria and quantify the CO2 lost from the system. With this data and further experimentation with other HFM setups and bacteria, the loss of CO2 in membrane bioreactor systems can be quantified and the overall sustainability can be measured.