Pilot scale fed-batch cultivations
After the optimal F:G ratio that had been determined in the chemostat
experiments had been confirmed in the laboratory scale fed-batch
experiments, the final step of the investigation was to test whether the
obtained positive results of formic acid co-feeding on biomass yield
were robust to scaling up to pilot scale. To this end, two out of the
four variations of the laboratory scale fed-batch protocol were scaled
up to pilot scale, having F:G ratios of 0 (experiment PF1, scale up of
LF1), and 5 (PF2, scale up of LF3). Again, the dynamic fermentation
process model proved valuable in qualitatively predicting the time
profiles of key fermentation parameters during the seed and main
fermentation stage before executing the experiments (see Supplementary
Materials 1).
The 300 l pilot scale fed batch process demonstrated that also at this
scale Y. lipolytica readily consumes the mixed glucose/ formic
acid feed up to a molar ratio of 1:5. Throughout the fermentations,
supernatant samples were taken and analysed for residual formic acid,
and the concentrations were always low (<0.05 g/l) or below
the detection limit. Figure 5 shows the O2 uptake rate
profiles of the 2 pilot scale fermentations with the batch phases ending
between 10-12h, followed by the carbon-limited fed batch phases. The
oscillation of the OUR of PF2 between 12-16h was caused by a technical
deviation when starting up the feed. The actual OUR profiles are in good
agreement with the profiles of Error! Reference source not
found. B that were simulated to design the experiment.