Development of novel immobilizing hydrogels for thermophilic hydrogen production

In the last decades, the production of molecular hydrogen by microbial dark fermentation has been given great attention, employing suspended or immobilized cultures. It has been demonstrated that immobilized cell cultures have advantages over the suspension cultures, in terms of higher biomass concentration, growth rate of cells which can be controlled near to zero and cells separation from the medium. On this basis, in this work several immobilizing hydrogels have been synthesized and investigated to evaluate the interaction with the hydrogen-producing bacterium Thermotoga neapolitana. Acrylic copolymers, with different hydrophilic character and buffering activity, were employed as support matrices for cell cultures. Anaerobic fermentation was carried out at 80°C. It has been observed that all materials allowed hydrogen production. In particular, the supporting materials containing cationic comonomers enhanced the hydrogen production rate, with respect to the neutral hydrogels. A further enhancement was recorded in presence of buffering groups on the polymeric supports. The presence of positively charged groups on the supports allowed the polymeric surface to be colonized by a great number of cells laying in a biofilm-like arrangement. This demonstrated that positive interaction between cells and cationic hydrogels