## 3 Results  
### Composite Membrane Characterisation: Before and after Exposure to ABE-Fermentation Broth  
The morphology of the flat composite membranes was studied using SEM microphotographs. As can be seen from Figure 3, the thickness of the selective layer for the PHeptMS membrane was 10 \(\pm\) 3 \(\upmu\)m, and that for PDecMS was 10 \(\pm\) 3 \(\upmu\)m. The thickness of the commercial MDK-3 membrane was 3.1 \(\pm\) 2 \(\upmu\)m.  
Figure 3: SEM images of cross sections of initial membranes: (**a**) MDK-3; (**b**) PDecMS; (**c**) PHeptMS. SEM images of the membranes before and after contact with the fermentation mixture are shown in Figure 4. Before contact with the fermentation broth, the surfaces of the composite membranes were white. The selective polysiloxane layer was visible as a transparent glossy coating on the fluoroplastic surface (Figure 4a,c,e). After contact of the membranes with ABE-fermentation broth for one month, the formation of deposits was observed on the surface of the selective layer (Figure 4b,d,f). The PDecMS membrane (Figure 4b) was visually characterized by more severe contamination, expressed as a complete change in the color of the surface of the selective layer from white to pale brown with an \"oil\" cast in the light. PHeptMS (Figure 4d) and MDK-3 (Figure 4f) membranes were visually less contaminated after contact with the fermentation broth. Orange-brown stains and yellow patches in places were observed on the surface of the selective layer. SEM images of the deposits on the surface of the membranes are shown in Figure 5.  
Figure 4: Photographs of membranes before: (**a**) PDecMS; (**c**) PHeptMS; (**e**) MDK-3 and after one month of contact with ABE-fermentation broth: (**b**) PDecMS; (**d**) PHeptMS; (**f**) MDK-3. Before contact of the membranes with the ABE-fermentation mixture, the surfaces of the selective layer were smooth and homogeneous (Figure 5a,c,e). After one month of contact with the ABE-fermentation medium, deposits were observed on the surfaces of all the studied membranes (Figure 5b,d,f). To determine the elemental composition of the detected deposit, the surface of the membranes was examined using energy dispersive analysis (Table 1). The initial membranes contained silicon, oxygen, and carbon atoms on the surface, whereas on the surface of the membranes after contact with the broth, the presence of nitrogen, sulfur, and phosphorus atoms, and an increase in carbon and oxygen content compared with the initial membrane, was observed. Thus, for the PHeptMS membrane after contact with the fermentation broth, in addition to atoms of carbon, oxygen, and silicon, the presence of 30% wt. of nitrogen and 0.7% wt. of sulfur on the surface of the selective layer is characteristic. Moreover, for this membrane an increase in oxygen atoms content is observed--from 14% wt. for the initial membrane to 20% wt. for the membrane after fouling. For the PDecMS membrane after contact with the fermentation mixture, we observe an increase in the surface content of 0.7% wt. of phosphorus atoms, as well as an increase in oxygen content from 12.1 to 18.1% wt. and in carbon content from 54.2 to 56.3% wt. In the case of the MDK-3 membrane, the presence of fluorine atoms was observed on the surface of the initial membrane, which corresponds to the material of the MFFK-1 substrate (fluoroplastic). On the surface of MDK-3 membrane after fouling, the oxygen  
Figure 5: SEM images of the surface of the selective membrane layer before: (**a**) PDecMS; (**c**) PHeptMS; (**e**) MDK-3 and after one month of contact with ABE-fermentation broth: (**b**) PDecMS; (**d**) PHeptMS; (**f**) MDK-3. content increased by 2% wt. % and the number of fluorine atoms increased 2.25 times. Sulfur atoms also appeared with a concentration of 0.1% wt. Thus, the change in the elemental composition of the selective layer of membranes after one month of contact with the fermentation broth indicates the deposition of various compounds that are products of the vital activity of microorganisms.