Application of palm pressed fiber as a carrier for ethanol production by Candida shehatae TISTR5843

ABSTRACT

Palm pressed fiber (PPF) is a clean and renewable lignocellulosic material. The PPF and delignified PPF (DPPF) were used as a carrier for immobilization of Candida shehatae TISTR5843 in bioethanol production. PPF was pre-treated by milling to obtain small particles, whereas DPPF was the delignification of PPF using NaClO2. C. shehatae TISTR5843 was grown in modified yeast extract- malt (YM) medium at 30 +/- 2ºC on an orbital shaker at 150 rpm for batch and repeated batch fermentation. In the batch system, immobilized cells on a small size, less than 0.5 mm, of DPPF (sDPPF) gave the maximum ethanol production of 11.5 g L-1 at 24 hrs cultivation period. The ethanol concentration and ethanol yield of sDPPF were 6.2 percent and 6.8 percent higher (ethanol production 11.5 g L-1, ethanol yield 0.47 g g-1) than those of free cells (ethanol production 10.8 g L-1, ethanol yield 0.44 g g-1) after 36 hrs of cultivation. In contrast, the small size of PPF (sPPF) was selected as a carrier in repeated batch fermentation for cost effectiveness. The ethanol productivity of immobilized yeast cells in repeated batch fermentations was 45.2-51.6 percent greater than that obtained from batch fermentations. The immobilized cells on sPPF improved the ethanol production and could be reused 4 times with retaining the activity of 93 percent. In conclusion, PPF is a potential carrier in the immobilization system. The pre-treatment of PPF increases the surface area that enhances cell adsorption and ethanol production by C. shehatae TISTR5843.