Temperature-controlled bacteria biofilm adhesion and formation for CO/CO2 bioconversion to ethanol by grafting N-isopropylacrylamide@SiC

Biofilm with high biomass density and high gas–liquid mass transfer efficiency is one of the most efficient bacterial culture modes for ethanol fermentation using CO/ CO 2 gas. However, it is very difficult and requires a long time for bacteria to form a stable biofilm due to the weak adhesion ability between bacterial cells and the substrate. To synergistically enhance bacterial adhesion during biofilm formation and biofilm detachment after fermentation to reuse the substrate, a substrate surface with controllable properties is expected. Thus, in this study, a temperature responsive substrate was prepared by grafting a thermosensitive hydrogel of N -isopropylacrylamide onto the surface of a silicon carbide (SiC) substrate to accelerate the formation of biofilm. The hydrophobicity of the modified substrate surface changed from 52.6° to 89.4° as the temperature increased from 25 °C to 37 °C (the optimal cell culture temperature). The adhesion free energy between the bacterial biofilm and the substrate changed from −4.11 MJ m −2 to −41.7 MJ m −2 , indicating a stronger adsorption capacity. Moreover, the surface zeta potential increased from −7.7 mV to +7.6 mV, forming an electrostatic attraction between the cell (-27 mV) instead of electrostatic repulsion force. All the above making the bacteria easier adhere and forming biofilm faster. Compared with that on the original SiC substrate, the bacterial biofilm-forming rate was increased by 6.2 times, which shortened the stable biofilm-forming time to 4 days. The mean ethanol productivity was 0.54 g/L d -1 , 116 % higher than that on the original SiC substrate. Therefore, controlling bacterial adhesion on the temperature responsive substrate was an efficient way to enhance ethanol production by CO/CO 2 fermentation.