Figure 6: the respiratory quotient (RQ) of the two pilot scale fed batch fermentations with glucose only (PF1) and a 1:4.6 molar ratio of glucose: formic acid in the feed (PF2)
The key results of fermentations PF1+2 are summarized in Table 2 and demonstrate that the observations in the chemostat and laboratory scale fed-batch, translate well to 300 l pilot scale fed-batch processes. The absolute biomass yields found on pilot scale are somewhat lower than found on laboratory scale. Still, the relative improvement of the Yxs of PF2 over PF1 corresponds well with the relative improvement of the Yxs of LF3 over LF1, where the formic acid to glucose rations were similar. On both scales the Yxs is increased by 21 ± 1%.
In bioprocess development, it is good practice to check the mass, carbon and nitrogen balances of the process to ascertain that no inflows or outflows were missed and that flow measurements as well as offline analytics had a reasonable accuracy. Supplementary Materials 3 presents the results of this check for the fed-batch experiments performed in this study. For the laboratory scale fermentations the balances closed better (mass <3%, C <2%, N <8%) than for the pilot scale fermentations (mass <8%, C <10%, N<19%).