Abstract: A large amount of eggshell is produced and discarded in China annually. In order to utilize this waste, Enterococcus mundtii was immobilized on sodium alginate (SA), sodium alginate-polyvinyl alcohol (SA-PVA) or sodium alginate-activated carbon (SA-C) and then used to convert eggshell to calcium lactate. The three immobilized cells were compared in their mechanical strength, mass transfer and calcium lactate production ability and the best one was characterized. The results showed that SA-C was found to be the optimum immobilization carrier that provided the maximum yield of calcium lactate of 101.02 g/L with a conversion rate of 82.43%. The yield of calcium lactate remained high after repeated fermentation for 18 times, and the fermentation cycle tended to be shortened by repeated use. The presence of residual eggshell in the fermentation broth effectively maintained the mechanical stability of the immobilized cells. Compared with the free cells, the operating stability as well as temperature, pH and storage stability of the immobilized cells were significantly improved in a certain range.

Key words: sodium alginate, sodium alginate-polyvinyl alcohol, sodium alginate-activated carbon, eggshell waste, calcium lactate