การผลิตเอทานอลจากทางใบต้นจากโดยใช้เซลล์ตรึงรูป Clostridium xylanolyticum

Abstract

Nipa palm (Nypa fruticans) is one of the major tropical coastal palm species which grow well in brackish water environments. It is expansively distributed in Asia. Nipa palm residues especially fronds and leaves are abundant and have superior chemical composition that could be exploited as alternative lignocellulosic materials for bioethanol production. This research aimed to study the possibility to use nipa palm fronds (without leayes) and leaves as substrate for ethanol production by Clostridium xylanolyticum immobilized either in polyvinyl alcohol (PVA) or on mesoporous silica. After diluted sulfuric acid hydrolysis hydrolyzates derived from unpretreated fronds contained the highest sugars of 11.43 g/L and gave the highest ethanol production of 0.07 g/L after 7 days of fermentation which was significantly different from all other hydrolyzates (p ≤ 0.05). Various sugars were found in fronds and leaves hydrolyzates with xylose as dominant sugar, followed by glucose, arabinose, galactose and rhamnose. Besides, the inhibitors generated during acid hydrolysis including acetic acid (1.10-2.87 g/L), furfural (0.13-0.22 g/L.), 5-hydroxymethylfurfural (0.02-0.04 g/L) and phenolics (0.02-0.12 g/L) were detected. The optimum bacterial entrapment process was to use 10% PVA together with 7% boric acid (w/v) followed by soaking PVA beads in Na,SO, buffer for 2 hrs, producing round shaped PVA beads without agglomeration. This method could prevent the swelling of beads and increase their mechanical strength. However, the bacterial viability was found to be reduced during the cell entrapment process. Meanwhile, the cell immobilization on mesoporous silica by attachment process led to a higher number of immobilized bacterial cells than that of the PVA. The silica-immobilized bacteria produced higher ethanol concentration (0.76 g/L) and yield (0.07 g ethanolg sugar) than that of the PVA (0.51 g/L or 0.04 g ethanol/g sugar). These two immobilized bacteria could producemore ethanol than that of the free cells (0.45 g/l or 0.03 g ethanolg sugar). No sugar and inhibitors except for phenolics were detected after fermentation. The loss of inhibitors was suggested to be mainly due to sorption by silica. Moreover, the silica-immobilized bacteria could maintain their ethanol production activity more than 50% of the initial use throughout repeated application over ten cycles.