Abstract:
Agricultural wastes namely; corn cob, bagasse, dried longan and rice straw comprise of 73.99, 81.74, 78.36 and 83.61 %(w/w) cellulose, respectively was employed as starting material through an acid pretreatment for ethanol production. Even though the use of high sulfuric acid concentration (0-1.5 %,w/v), temperature (120, 140 and 160 °C), time (15 and 60 min) and a combination with high pressure gave high yield of reducing sugars, but higher concentration of fermentation inhibitors e.g. furfural, hydroxymethylfurfural, acetic acid were also produced. Pretreatment by using 0.75 %(w/v) sulfuric acid and autoclaved at 121°C, 15 lbs/inc2 for 60 min. gave rise of maximum glucose at 159.38 mg/g when using dried longan as starting material followed by bagasse, corn cob, and rice straw at 133.56, 75.29 and 8.41 mg/g, respectively. In term of xylose, a maximum yield of 184.06 mg/g was obtained from corn cob while those by bagasse, rice straw and dried longan gave yield at 110.46, 77.90, 3.50 mg/g, respectively. Corn cob produced the highest level of furfural at 0.121 g/l followed by bagasse, dried longan and rice straw at 0.107, 0.088 and 0.072 g/l, respectively. Hydroxymethylfurfural was found maximum from bagasse at 1.522 g/l followed by dried longan, corn cob and rice straw at 1.157, 0.812 and 0.107 g/l, respectively. The highest acetic acid concentration at 2.288 g/l was produced from corn cob followed from bagasse, rice straw and dried longan at 1.823, 0.83 and 0.286 g/l, respectively. Enzymatic hydrolysis of acid pretreated agricultural wastes by the cellulase mixture; Cyto (R) CL and GC 220 at 81 (endoglucanase) units, endoglucanase: β-glucosidase activity at 3:1, 50°C, pH 4.5 for 48 hrs. gave maximum glucose yield from corn cob at 13.39 g/l and dried longan 13.36 g/l, followed by bagasse 11.68 g/l and rice straw 10.71 g/l. Fermentation of the reducing sugar from agricultural waste hydrolysate after the addition of 0.4 %(w/v) ammonium sulfate, 10 g/l glucose and pH adjusted to 4.5 by Sacchoromyces cerevisiae TISTR 5596 in static culture, room temperature for 72 hrs. produced maximum amount of ethanol at 24.43 %(w/w) from dried longan followed by corn cob (20.78%,w/w), bagasse (20.76%,w/w) and rice straw (16.58%,w/w), respectively. Based on the above results we proposed that the potential ranking of acid pretreated agricultural wastes tested for using as starting materials for ethanol fermentation by Sacchoromyces cerevisiae was dried longan > corn cob = bagasse > rice straw.