Abstract:
18 types of grasses, collected from the provinces of Chiang Mai, Lampang, Ratchaburi and Petchaburi, were divided into 2 groups: 8 types of forage grasses (napier leaves, mott dwarf elephant leaves, king leaves, bana leaves, purple guinea, ruzi, pangola and atratum) and 10 ecotypes of vetiver grasses (Khamphaeng Phet 2, Songkhla 3, Surat Thani, Sri Lanka, Roi Et, Loei, Nakhon Sawan, Prachuap Khiri Khan, Ratchaburi and Khamphaeng Phet 1). All of the grasses had 51.31 - 77.81 % moisture content and contained cellulose, hemicellulose and lignin at 31.85 - 38.51, 31.13 - 42.61 and 3.10 - 5.64 % on average, respectively. In the study of enzymatic saccharification of grasses in order to select the suitable grasses for fermentation, the grasses were pretreated with alkaline peroxide and followed by enzymatic hydrolysis using cellulase and xylanase produced from Trichoderma reesei. The results showed that the reducing sugar yields of each grass obtained after hydrolysis were rather similar. Therefore, dry matter yields (kg/rai/year) were also included in the calculation. From this selection, 11 types of grasses (all of the forage grasses and 3 ecotypes of vetiver grasses: Sri Lanka, Prachuap Khiri Khan and Ratchaburi) having the reducing sugar yields over 630 kg/rai/year were used as feedstock for ethanol production by simultaneous saccharification and co-fermentation (SSCF) using cellulase and xylanase for hydrolysis and Saccharomyces cerevisiae and Pichia stipitis after 9 and 10 h of cultivation under co-fermentation at 35 °C for 7 days. The results showed that Sri Lanka ecotype vetiver grass had the highest ethanol yield of 1.14 g/l or 0.14 g/g substrate which was equivalent to 32.72 % of the theoretical ethanol yield. When dry matter yields were included in the calculation, Sri Lanka ecotype vetiver grass had ethanol yield of 184.27 litres/rai/year whereas napier leaves had maximum ethanol yield of 435.29 litres/rai/year (0.98 g/l or 0.12 g/g substrate which was equivalent to 30.60 % of the theoretical ethanol yield).