Adsorption behavior of tightly bound extracellular polymeric substances on model organic surfaces under different pH...

Tightly bound extracellular polymeric substances (TB-EPS) play a substantial role on microbial aggregates, which can promote microbial cells to aggregate and adhere onto the carrier in bioreactor. However, the attachment and adsorption of TB-EPS on different surfaces were awaited to be elucidated. In this study, four self-assembled monolayers (SAMs) carrying methyl (CH3-SAM), amino (NH2-SAM), hydroxyl (OH-SAM), and carboxyl (COOH-SAM) terminal groups were prepared to model different surfaces. TB-EPS adsorption on these surfaces under different pH conditions and additional cations were investigated using surface plasmon resonance. The adsorption of TB-EPS dramatically decreased with the decreasing pH values. CH3-SAM surface achieved the maximum adsorption at the same condition. Na(+) promoted the TB-EPS adsorbed on COOH-SAM surface. The Ca(2+)-mediated complexes were attracted by COOH-SAM and repelled by NH2-SAM, respectively. The adsorptions of TB-EPS on the four SAM surfaces were significantly increased by adding Fe(3+). These results demonstrated that the TB-EPS adsorption on the organic surfaces were dependent on the pH and cation of solution.