Alginate and kappa -carrageenan gels were tested as bead materials for the co-immobilization of anaerobic and aerobic microorganisms for the mineralization of 2,4,6-trichlorophenol under air-limited conditions. Chemical, mechanical and thermal culture constraints were pre-defined and the gel resistances were established. Alginate was quickly eliminated because of its chemical instability in the culture media. In anaerobic conditions, the microorganisms transformed the substrates into CH4 and CO2. The kappa -carrageenan gel did not enable these gases to diffuse. They remained as bubbles in the core of the beads and made the beads float. Gelatin was added to kappa -carrageenan in order to change the carrier properties. No biogas bubbles appeared in the bead core during the cultures in anaerobic conditions and the beads reacted well to the culture conditions in the reactor. The coimmobilization of the anaerobic and aerobic microbial communities was successfully performed with the kappa -carrageenan/gelatin gel (2% (w/w) of each polymer). The biological activities, measured by the impedancemetry technique, were preserved in the beads.