Bioethanol Production from Several Tropical Wood Species using Simultaneous Saccharification and Fermentation Processes

Abstract

This study aims to determine the best method to produce bioethanol from several wood species using simultaneous saccharification and fermentation (SSF) processes. Four different tropical wood species namely sengon (Paraserianthes falcataria (L) Nielsen.), gmelina (Gmelina arborea Roxb), pine (Pinus merkusii Jung. et de Vr.) and oil palm (Elaeis guineensis Jacq.) were milled to determine their chemical properties before treatments. The first study was conducted to determine the best pretreatment to produce the highest pulp yield and low kappa number and lignin content. The treatments were conducted under three kinds of alkalinity (active alkali) namely 16, 18and 20% and also two kinds of sulfidity namely 20 and 25% using kraft process. The second study was conducted to determine the best method to hydrolyse (saccharification) and fermentation on SSF processes. SSF runs were performed in 500 mLErlenmeyers using a total slurry 200 mL. The substrate and nutrient media were autoclaved (121 oC and 20 minutes). The samples from the best pretreatment method diluted to 2.5% (w/v) of total slurry was used as substrate. The enzyme preparation used commercial cellulase enzyme. The amount of cellulase added were 4 and 8% (w/w) dry mass of samples. In the other hand, the substrate was added with Aspegillus niger. All SSF processes were inoculated with 10% (v/v) yeast Saccharomyces cereviciae. The SSF experiments were run for 96 hours. The results showed that the species of tropical wood affected the chemical properties of samples significantly. The best pretreatment (alkalinity and sulfidity) for sengon, gmelina, pine and oil palm were 18% and 25%, 20% and 25%, 18% and 25%, as well as 16% and 20%, respectively. Total of sugar and reducing sugar tended to decrease with time of cultivation whereas ethanol concentration increase significantly. The growth of Saccharomyces cereviciaeand Aspergillus nigertended to increase at initial cultivation and decrease by the end of cultivation.The best method to hydrolyse (saccharification) and fermentation on SSF processes for all tropical wood species were using cellulase 8% of dry mass and 10% (v/v) of Saccharomyces cereviciae which produced the highest bioethanol concentration on gmelina,sengon, pine and oil palm were 0.98; 0.79; 0.57 and 0.51%, respectively with the yields of 10.02,5.39, 7.65, and 3.28% and also productivity 3045.08, 1796.67, 1530.88, and 794.04L/ha per year respectively.

Pemanfaatan bahan berlignoselulosa sebagai penghasil bioetanol masih terkendala pada proses pengolahan yang lebih rumit, yaitu memerlukan proses pendahuluan berupa penghilangan ekstraktif, delignifikasi, dan proses hidrolisisnya yang lebih sulit dibandingkan bahan berpati dan gula. Meskipun pada dasarnya harga bahan baku berlignoselulosa pada dasarnya secara ekonomis lebih murah dan lebih mudah diperoleh serta dapat dikembangkan pada lahan yang tidak dapat dikembangkan untuk kepentingan pertanian namun pengembangan bahan berlignoselulosa ini masih menemui kendala seperti rendemen bioetanol yang masih rendah dan memerlukan biaya produksi yang tinggi yang terutama diakibatkan oleh rendahnya kerja enzim pada substrat akibat sifat kristalinitas selulosa dan kehadiran zat penghambat yang dapat mengurangi fermentabilitas selulosa dan hemiselulosa menjadi etanol. Oleh karena itu, untuk memproduksi bioetanol dari kayu maka diperlukan optimalisasi teknologi proses produksi terutama pada proses perlakuan pendahuluan, hidrolisis (sakarifikasi) dan fermentasi. Penelitian ini bertujuan menganalisis sifat kimia bahan baku dari beberapa jenis bahan baku dalam hubungannya dengan produksi bioetanol, menentukan metode perlakuan pendahuluan, hidrolisis dan fermentasi yang tepat dalam meningkatkan rendemen bioetanol dari beberapa jenis kayu tropis yang diperoleh melalui proses sakarifikasi dan fermentasi secara simultan (SSF) dan menganalisis hubungan antara karakteristik bahan baku dan metode dengan pertumbuhan mikroba, gula pereduksi, total gula, kadar dan rendemen etanol selama kultivasi serta menganalisis produktivitas bioetanol beberapa jenis kayu tropis.