Ethanol production from oil palm empty fruit bunch by simultaneous saccharification and fermentation (SSF) with kluyveromyces marxianus and saccharomyces cerevisiae

Abstract

This research purpose is to study the ethanol production from Oil Palm Empty Fruit Bunch (OPEFB) by Simultaneous Saccharification and Fermentation (SSF) with Kluyveromyces marxianus and Saccharomyces cerevisiae. OPEFB is lignocellulosic biomass and their main components are cellulose, hemicellulose and lignin which cross linked into chemically complex. The basic steps for production of ethanol from lignocellulosic biomass is through three major operations; pretreatment for delignification is necessary to liberate cellulose and hemicellulose before hydrolysis of cellulose and hemicellulose to produce fermentable sugars and fermentation of reducing sugars to ethanol. The first section was the study of pretreatment step with sulfuric acid followed by sodium hydroxide and employing Response Surface Methodology (RSM) for designing experiment and optimization. Three factors including, substrate loading (5 – 25 % w/v), reaction time (30 - 90 min) and acid concentration (0.2 - 1 M) were optimized after that pretreated with sodium hydroxide 5 % (w/v) for 20 min. The optimum condition of pretreatment step was substrate loading (15 % w/v), reaction time 53 min and concentration of sulfuric acid 0.2 M gave the highest cellulose yield of 72.10 %wt. and the lowest hemicellulose and lignin yield of 3.24 %wt. and 17.60 %wt. respectively. In addition, the enzyme digestibility of the treated OPEFB 83.5 %. Scanning Electron Microscope (SEM) analysis showed that the acid pretreatment followed by alkali caused great disruptions on the fiber structure by removing the cell wall, hydrolyzing both hemicellulose and lignin. The second section was to study ethanol fermentation with SSF was conducted by using K. marxianus and S. cerevisiae yeasts and employing RSM for designing experiment and optimization. Four factors including, temperature (30 - 45 ºC), substrate loading (5 - 15 % w/v), pH (4 - 6) and yeast concentration (1 – 5 % v/v) were optimized. It was found that the optimum condition of K. marxianus yeast was the fermentation temperature of 36.94 °C, substrate loading (12.24 % w/v), pH 4.5 yeast concentration (2.04 % v/v). The ethanol production was 0.281 g/g biomass at 48 h and the optimal condition of S. cerevisiae was the fermentation temperature is 35.03 °C substrate loading (8.16 % w/v), pH 4.91 and yeast concentration (3.38 % v/v). The ethanol production was 0.320 g/g biomass at 48 h. The final section to study, ethanol fermentation with Separated Hydrolysis and Fermentation (SHF) by select the fermentation conditions from the study in the second section. It found that fermentation by K. marxianus produced ethanol 0.258 g/g biomass and S. cerevisiae produced ethanol 0.302 g/g biomass. Show that production of ethanol by SSF gives ethanol yield more than SHF and decrease fermentation time. Due to Total time in SHF process was used 120 h and SSF process was used 48 h. SSF process used less time 72 h of SHF process.