Efficient production of ethanol by cells immobilized in loofa (Luffa cylindrica) sponge

Both flocculating and non-flocculating cells were immobilized in loofa (Luffa cylindrical sponge and used for continuous ethanol production in column-type bioreactors. Immobilization of non-flocculating cells (Candida Brassicae) was achieved by addition of chitosan to the reactor. However, the amount of immobilized non-flocculating cells per unit sponge was lower, and consequently the volumetric ethanol productivity was about 20% less than that of the flocculating cells. In comparison with a fixed bed made of a single cylindrical loofa sponge, the amount of sponge per unit reactor volume was 2 times higher when sliced loofa sponge was used to construct the fixed bed. Furthermore, the use of sliced loofa sponge resulted in 2- and 4-fold increases in the amount of immobilized flocculating and non-flocculating cells per unit sponge, respectively. Consequently, higher volumetric ethanol productivities were obtained when sliced loofa sponge was used for bed construction. In the case of flocculating (Saccharomyces cerevisiae IR-2) cells, the volumetric ethanol productivity was 66% higher than that obtained with a cylindrical loofa sponge.