Team:TU Dresden/Human Practices/Sustainability
Sustainability
Total complete efficiency converting reactant to product is incredibly difficult, and in some cases, waste or side product formation is inevitable. The PACE papers describe a variety of different cultivation conditions that unavoidably result in the consumption of chemicals and generation of waste product [1, 2]. A goal of our iGEM project was to reduce the consumption of these chemicals and waste production by optimizing the cultivation process. The team reached out to the department of bioprocess engineering where they got caught on the idea of the project and two students decided to join the team. The department for bioprocess engineering made it possible to use their laboratories and resources for the cultivation experiment. Furthermore they supported us with their experience in continuous E. coli cultivation.
With the goal of increasing the sustainability the cultivation a balance sheet was drawn up for the process. This increased the survey of the process and helped to identify 3 parts of the process which were giving us the possibility to improve the sustainability.
Minimize waste volume
The previous PACE experiments used a CSR with dilutions between 1 – 2.5 h-1 to console the cell density in the bioreactor. To achieve the desired flow rate in the lagoon, most of the flow from the CSR was forwarded into the waste. This waste had to be minimized in order for efficiency to increase. Therefore the flowrates and the volumes were adapted so that no waste from the chemostate was produced. The cell density is controlled over the supplement concentration in the medium.
The idea was to calculate the CSR setup from the end to the beginning. This means from the phage output to the fresh medium input. With regard to the paper of Dickinson et al. [1] a dilution rate of 1 h-1 was chosen (1 lagoon volume change per hour respectively). In order to avoid medium waste production the phage output flow had to be equal to the fresh medium input. Furthermore a minimal volume of medium was to be used in the stirred tank reactor (250 mL for a 1 L Applikon bioreactor).
CSR Parameter approximation:
The cultivation period was set to 72 hours and maximum medium reservoir volume of 5 L was chosen. With the following equation a maximum flow rate of 69.4 mL h-1 was calculated.
Where FL,0 is the medium flow through the system, VR is the reservoir volume and tc is the total cultivation time. Previous cultivations with E. coli done at the Institute of Bioprocess Engineering had shown a dilution rate above 0.15 h-1 was suitable for cultivation. The following equation was used to approximate the dilution rate in the CSR at a medium flow of 69.4 mL h-1.
Minimize medium volume
Reduce antibiotics
- Dickinson, B. C., Packer, M. S., Badran, A. H., Liu, D. R. (2014). A system for the continuous directed evolution of proteases rapidly reveals drug-resistance mutations. Nature Communications, 5, Article number: 5352.
- Esvelt, K. M., Carlson, J. C., Liu, D.R. (2011). A system for the continuous directed evolution of biomolecules. Nature, 472(7344), 499-503.