Comparative Analysis of Bioethanol Production Capacities from Different Chemically Pretreated Rice Straws
Authors: ERJMDDP Wijesekara , AMPC Amarasinghe , EAK Sudharaka , RS Wickramasinghe 
Published: July 2024

The Energy crisis associated with continuous depletion of fossil fuel is one of the prime concerns in the world. Henceforth, there is an increasing interest for renewable energy sources such as biofuels, as environmentally friendly alternatives for replacing fossil fuel. Among that, bioethanol is one of the most promising alternative energy sources for the limited crude oil which can be produced by biocon version of variety of feedstock. Lignocellulosic feed stock such as rice straw is one of the most abundant sources which can be used for the production of second-generation biofuel without competes with the production of food crops. However, the pretreatment of second-generation biomass is critically important to maintain higher efficient anaerobic fermentation, provides higher bioethanol yield, and also to lower the inhibition conditions for fermentation. Also, the lignin removal is significantly valuable through biomass pretreatment, to create more accessibility for enzymes and microorganisms’ fermentation process. In this study, three different chemical pretreatment methods of base treatment, Acid treatment and NH3 Soaking were investigated to identify the optimal technique for maximizing bioethanol yield. Analytical techniques such as Fourier-transform infrared spectroscopy (FTIR) was employed to characterize the structural changes in the biomass during pretreatment. The analytical technique applied to measure the separated lignin weight. The pretreated samples were centrifuged at 500 rpm for 5 minutes and collected and separated lignin content weight and measured. Then total twelve reactors were designed for the fermentation for all chemical treated samples, by adding 8g of yeast, 125 ml of water, and 0.5 g of urea. The reactors are then sealed well and kept for a five to seven days for fermentation. Finally, a rotary evaporator is used to purify the ethanol after the fermentation process. Then, the percentage of ethanol present in the purified samples is obtained by the hand-held alcohol meter. The maximum lignin precipitate separation was recorded as 12 w/w% from NaOH-treated sample, with 4 g/ml % (w/v) concentration. Furthermore, NaOH-treated sample showed the highest peaks for most of the spectrums in the FTIR analysis and showed the highest cellulose and hemicellulose content availability for bioethanol production. Such as 2910 to 2930 cm-1 region for C-H alkane stretching bonds, the absorption peak at around 1650 shows the C=0 bond related to the hemicellulose, and the 1000 to 1100 cm-1spectrum region with the maximum peak reaching around 1035 cm-1characterizes the C-O stretching in cellulose and hemicellulose structure. Finally, the comparing the ethanol yield of the samples, the highest ethanol yield is found in the NaOH pretreated rice straw sample and its ethanol yield is 8.59%(w/w). The ethanol yield of H2SO4 pretreated straw and NH3 pretreated straw was 6.53%(w/w) and 7.14%(w/w) respectively. Ultimately, the rice straw provides a great sustainable 2nd generation biomass for produce renewable bioethanol to replace the fossil fuel. The NaOH deliver an optimum chemically low concentrated pretreatment condition for bioethanol production from rice straw, with better accessibility for cellulose and hemicellulose structure with higher bioethanol yield.