## 3 Results
### Composite Membrane Characterisation: Before and after Exposure to ABE-Fermentation Broth
It was shown in [60,61] that the presence of such components in the fermentation broth contributes to an increase in the activity of the ABE-fermentation broth. A comparison of the partial fluxes of the components and separation factors at 30 \({}^{\circ}\)C for the initial and contaminated membranes in the separation of the real ABE-fermentation broth is shown in Figure 8.  
The total permeate flux for the PHeptMS, PDecMS, and MDK-3 composite membranes at separation of the model mixture was 0.32, 0.44, and 0.77 kg/m\({}^{2}\cdot\)h, respectively. The flux for MDK-3 was almost twice as high, which correlates well with the difference in the thicknesses of the selective layers of the membranes studied. It is worth noting that the greatest contribution to the total flux for all membranes was made by water. This fact is related to the low concentration of organic components in the model fermentation mixture. The partial flux of water for the MDK-3 membrane was 2-4 times higher than that for the PHeptMS and PDecMS membranes. In addition, the partial fluxes of acetone, ethanol, and n-butanol were comparable. The butanol flux showed the maximum values among the extracted organic components for all the membranes studied. This experimental picture is well reflected in the data of Figure 9b. Thus, acetone/water and n-butanol/waterseparation factors are 1.5-2 times higher for the initial PHeptMS and PDecMS membranes than for MDK-3. The ethanol/water partition factors are small and comparable for all membranes studied. The data obtained are in agreement with the values of contact wetting angles and distance interaction parameters. When passing to contaminated membranes, the picture changes. Total (up to 0.12, 0.06, and 0.39 kg/m\({}^{2}\).h for PHeptMS, PDecMS, and MDK-3, respectively) and partial fluxes for all membranes decrease (Figure 8a). This confirms the EDX and IR data indicating the formation of a film of proteins and peptides on the surface of the selective layer. Thus, microbial cells remaining in the fermentation broth were previously adsorbed on the surface of the selective membrane layer and prevented the transport of permeate through it. Moreover, some compounds from the yeast extract contained in the ABE-fermutation broth can be adsorbed on the surface of the composite membrane, which leads to a decrease in its hydrophobicity [62, 63]. A similar assumption was made in the present article in the analysis of contact wetting angle data. Moreover, all the membranes were characterized by a decrease in water flow after their contamination (Figure 8a). The negative effect of membrane contamination on its separation properties is mainly observed for the PDecMS membrane. It is characterized by the highest surface contamination (Figure 4b), a decrease in flux, and a decrease in the separation factor. Apparently, on this membrane due to its increased affinity for organic substances, the adsorbed protein layer was the largest, which significantly increased the hydrophilicity of the selective layer  
Figure 8: Comparison of partial fluxes (**a**) and separation factors (**b**) at 30 \({}^{\circ}\)C of PHeptMS, PDecMS, and MDK-3 membranes before and after membrane contact with ABE-fermutation broth. Figure 9: Comparison of PSI at 30 \({}^{\circ}\)C of PHeptMS, PDecMS, and MDK-3 membranes before and after membrane contact with ABE-fermutation broth. and hindered the diffusion transfer through the membrane as a whole. For the PHeptMS and MDK-3 membranes, the picture is significantly different. For the PHeptMS membrane, a decrease in total and partial fluxes was observed. However, the ABE/water partition factors, on the contrary, increased. Thus, the n-butanol/water separation factor increased from 33 for the initial membrane to 41 for the membrane after clogging. By comparison, for PDecMS and MDK-3 membranes, a slight decrease in the butanol/water separation factor was observed: from 27 to 21 for PDecMS and from 14 to 13 for MDK-3.