ศักยภาพของวัชพืชน้ำในการเป็นแหล่งวัตถุดิบสำหรับไบโอเอทานอล

Abstract

Bioethanol production from lignocellulosic biomass has been developed and carried out for a long time, not only to reduce the global energy problem but also to reduce the environmental stress caused by the application of fossil fuels. Thailand is a country with much ecosystem diversity, it has a potential in producing bioethanol from biomass such as forestry residues, agricultural wastes, woody and non woody biomass. However, a few research in ethanol production is a limitation for the development of the bioethanol production in Thailand. Therefore, this research was carried out with the aim to develop the bioethanol production and to fill the gap between research and general application, and bioethanol production in particular. The idea arose from the present trend of widely used organic products. A very important problem in rice plantation is the growth of unwanted weeds in the paddy field. In this study, two weeds, namely gooseweed (Sphenoclea zeylanica) and small-flowered nutsedge (Cyperus difformis), were used to produce bioethanol. Lab-scale experiments were first done to find out suitable conditions for ethanol production and were later scaled up. Both biological and chemical pretreatments were applied. A biological method was carried out using micro -termite to digest powdered raw materials at a ratio 2:1 for 3 days. A chemical method was done by alkaline pretreatment with different concentrations of sodium hydroxide and hydrogen peroxide. The ratio of solid to liquid and time were worked out and optimized by using Box-Behnken experimental design and response surface methodology. Enzymatic hydrolysis using commercial cellulase for 72 hours was applied to produce reducing sugar from the two weeds. The released reducing sugars were fermented by Saccharomyces cerevisiae TISTR 5020 at 35ºC for 9 days. It was shown that the sugar yield from biological pretreatment was lower than that from chemical pretreatment. Treatment with both NaOH and H2O2 gave the highest amount of sugar. Enzymatic hydrolysis with cellulase for 24 hours produced more sugar and the highest ethanol concentration was obtained after 3 days of fermentation. The highest ethanol yield from gooseweed fermentation was 11.84 g/L and that from small-flowered nutsedge was 12.36 g/L. In order to understand the mass transfer, mass balance analysis of bioethanol production process was conducted. Scale-up experiments were carried out with an addition of distillation step using a distiller. The obtained ethanol was tested for energy content with bomb calorimeter. The higher heating value of bioethanol produced from gooseweed and small-flowered nutsedge were 12.61 KJ/g and 25.31 KJ/g, respectively. In conclusion, both gooseweed and small-flowered nutsedge can be promising materials for bioethanol production and applied to create income in the rural community.