Optimizing carbon fibre supports for bioreactors by nitric acid oxidation and calcium ion coverage according to extended DLVO theory.

Optimizing supports for microorganisms is required for bioreactors. Carbon fibres (CF) were employed as supports for microorganisms. To optimize CF supports for immobilizing bacterial cells, we used methods of nitric acid oxidation and calcium ion coverage. We evaluated the capacity of these CF supports (untreated CF, nitric acid oxidation CF and Ca2+-covered CF) via bacterial cell adhesion tests, based on extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. The results implied that because of the high hamaker constants, oxidized CF supports had higher capacity in this regard than untreated CF supports. However, the growing oxygen groups increased the negative zeta potential of CF supports, thus likely to reduce their capacity, in accordance with XDLVO theory. Since the Ca2+ coverage could decrease the negative zeta potentials of CF without reducing the hamaker constants, it could enhance the capacity of oxidized CF supports. We concluded that a combination of nitric acid oxidation and Ca2+ coverage could increase the capacity of CF supports to immobilize bacterial cells.