The high sugar concentrations in the HYBRID design resulted in both a reduced fermentation yield at the higher pH as well as a hampered xylose consumption in comparison to the SSCF strategy.
Calculated models proved suitable for the evaluation of extraction processes and the prediction of optimum conditions in terms of high protein yields at the lowest pH possible.
In conclusion this resulted in similar overall ethanol yields at the different pH values for the HYBRID design, despite the improved xylose uptake, whereas a significant increase in overall ethanol yield was found with the SSCF design.
Butyric acid could significantly increase the butanol yield at low pH values if sufficient quantities of primary carbon source (glycerol) were present.
Based on the low yield of HOBB at this pH and compared with the high yield at other pH values (7, 8 and 9) (Fig. 3b), it can be inferred that a neutral or slightly alkaline medium facilitates DBF degradation and HOBB accumulation.
We built this parameter into our simulation, just as we had incorporated pH dependence with a measured pK into the dimer dissociation step and found better correlation between our simulation and the experimental yield at higher pH values (updated Figure 7B).
At pH above 4, mycelial clump formation was observed with a reduced biomass yield at pH 4.5 compared to the control culture (at pH optimum 5.5), which could be attributed to the formation of freely suspended mycelial formation at non-optimum pH conditions (Fig. 1).
Decrease in biosorption yield at higher pH (pH > 7) is not only related to the formation of soluble hydroxylated complexes of the metal ions, but also to the ionized nature of the Sjp of the biosorbent under the studied pH.
The final refolding yield at pH 7.5 was about 69%, similar to 71% at pH 8.0, and only slightly higher than 65% at pH 8.5, indicating that over this limited range pH is not a critical variable.
Cultivation of fungal pellets with the sequential glucose addition resulted in about 96 98 % of theoretical ethanol yield (at acidic pH 3.5 and 3.0) as opposed to 32%% theoretical yield obtained by the mycelial clump culture at the same cultivation conditions.
