FöRFATTARE
Helmerius, Jonas

INSTITUTION
Tillämpad kemi och geovetenskap / Biokemisk och kemisk processteknik

SAMMANFATTNING
If fossil fuels are to be removed as the main raw material for production of fuels and chemicals an economically competitive process based on renewable resources is required. Succinic acid, produced by microbial fermentation of renewable feed stocks, can substitute chemicals based on benzene and other intermediate petrochemicals for production of polyester and solvents. Other chemicals that can be produced from succinic acid are food ingredients, fuel additives and plant growth stimulants. The micro organism used for succinic acid production in this project is the bacterium Escherichia coli strain AFP184. This strain has been metabolically modified to increase the succinic acid production. The process in this project is a dual-phase fermentation which constitute of an aerobic growth phase and an anaerobic succinic acid production phase. After transition to anaerobic conditions the cells starts to produce succinic acid in large quantities using glucose as the main carbon source. Formation of succinic acid requires CO2 input and hence the process does not contribute to any atmospheric CO2 accumulation. The media used for all the fermentations is a low cost media based on corn steep liquor. Corn steep liquor is an industrial by-product from wet milling of maize and it contains nutrients needed for the cells. The use of E. coli strain AFP184 for fermentative succinic acid production can provide a stable process where the productivity of succinic acid is high and the productivity of other mixed acid fermentation products are low or non. The use of a low cost media makes the strain AFP184 a suitable candidate for large scale succinic acid production.

In order to optimize the growth phase of AFP184 and to get knowledge if a fluctuation within certain domains of four controlled variables will affect biomass production and further succinic acid production, a designed experiment was used. Using design of experiment (DOE) data was collected from the growth phase and analyzed with multivariate data analysis. The controlled variables that were varied in chosen domains were stirring (400 rpm to 1200 rpm), airflow (2 vvm to 10 vvm), temperature (32 °C to 42 °C) and pH (5.5 to 7.5). The responses in the designed experiment were eight different organic acids, dry cell weight, specific growth rate, viable cells and glucose consumption. The results from the analysis were validated by additional experiments, where also the effect on the anaerobic succinic acid production phase was evaluated.

From the analysis of the designed experiment it was shown by additional experiments that the growth rate and cell viability could be increased and the acetic acid formation decreased. The controlled variables temperature and pH could be varied in the chosen domain to produce biomass with moderate acetic acid concentration at the chosen time of transition from aerobic to anaerobic conditions. The additional experiments also showed during the anaerobic succinic acid production phase that productivity and yield of succinic acid decreased compared with the three centre point runs from the designed experiment and that could depend on the physiological state of the cells at the time of transition.

ISSN 1402-1617 / ISRN LTU-EX--07/006--SE / NR 2007:006