## 3 Results
### Composite Membrane Characterisation: Before and after Exposure to ABE-Fermentation Broth
To determine the functional composition of the observed deposits, IR spectra of the membranes were obtained before and after their contact with the fermentation medium. Figures 6 and 7 show a comparison of the IR spectra of the PDecMS, PHeptMS, and MDK-3 membranes before and after exposure to the fermentation mixture. The spectra of PDecMS and PHeptMS membranes fully correspond to the chemical structure of the polyalkylsiloxane polymer of the membrane selective layer [56]. In Figure 6 it is seen that the most intense split band at 1014 cm\({}^{-1}\) refers to the valent vibrations of the -O-Si-O- bonds of the main chain of the polymer. The intense band at 795 cm\({}^{-1}\) characterizes the valent vibrations of the Si-C bonds. The band at 1258 cm\({}^{-1}\) is associated with deformation vibrations in the methyl group at the silicon atom, and bands at 2850-2960 cm\({}^{-1}\) and 1460 cm\({}^{-1}\) refer respectively to the valent and deformation vibrations in the decyl substituent. In the spectrum of MDK-3 membrane, which differs in chemical structure from PHeptMS and PDecMS, in addition to the siloxane bands described above, the bands of the aromatic ring (1602 and 1506 cm\({}^{-1}\)) and the C=O bond (1772 cm\({}^{-1}\)) are present. In addition, long alkyl chains at the MDK-3 silicon atom are absent; the relative intensity of the bands from the C-H alkyl bonds (2840-2960 cm\({}^{-1}\)) changes. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Membrane** & **Condition** & \multicolumn{6}{c}{**Element Weight Concentration, \%**} \\ \hline  & & **C** & **O** & **Si** & **N** & **S** & **P** & **F** \\ \hline PHeptMS & initial & 50.7 & 14.3 & 35.0 & - & - & - & - \\  & after ABE & 24.6 & 20.0 & 24.7 & 30.0 & 0.7 & - & - \\ \hline PDecMS & initial & 54.2 & 12.1 & 33.7 & - & - & - & - \\  & after ABE & 56.3 & 18.1 & 24.9 & - & - & 0.7 & - \\ \hline MDK-3 & initial & 52.4 & 18.6 & 27.9 & - & - & - & 0.5 \\  & after ABE & 52.3 & 20.6 & 25.5 & - & 0.1 & - & 0.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: EDX analysis data of PHeptMS, PDecMS, and MDK-3 membranes before and after contact with the fermentation broth. Figure 6: IR spectra of the membranes. In the spectrum of PDecMS and PHeptMS, all bands characterizing the structure of polyalkylsiloxane are preserved after exposure in the fermentation broth, and only the intensities of almost all bands drop significantly (Figure 6). It can be assumed that the drop in the intensity of the main polysiloxane bands in the spectra of membranes after ABE is due to the appearance of a new thin layer of polypeptide from microorganisms on the membrane surface. The decrease in intensity of all siloxane bands after contact with the fermentation medium can be related to the deposition of a thin layer of dead microorganisms or their spores on the membrane surface. In addition, new bands appear that are in good agreement with the spectrum of the polypeptide chain of protein molecules contained in the cell membranes of bacteria or their spores. The new bands in the spectra of the membranes after exposure include: (1) A broad mid-intensity band in the 3284 cm\({}^{-1}\) region (Figure 7), which usually characterizes the hydrogen-bonded amino groups in the polypeptide chains of -C(O)-NH-protein molecules. In addition, this region can contain bands of valent vibrations of -NH-bonds in purine and pyrimidine nucleotide bases, as well as bands of valent vibrations of OH-water. (2) A broad split band of medium intensity in the range of 1650 cm\({}^{-1}\) (Figure 7), which well reflects amide I (1653 and 1625 cm\({}^{-1}\)) and amide II (1553 cm\({}^{-1}\)) bands in the spectra of protein molecules. In the same region (1597, 1510 cm\({}^{-1}\)) lies the bands of skeletal vibrations of aromatic nitrogenous nucleotide bases. (3) A weak band in the region of 1408 cm\({}^{-1}\) shifted relative to the 1410 cm\({}^{-1}\) band from the spectrum of the original siloxane membrane also always appears in the IR spectra of polymeric amino acids.