Examining enzymatic digestibility of vegetable stalks (tomato, pepper and eggplant) for bio-ethanol production

Increase in environmental pollution and energy dependency forces researchers to search for alternative energy resources, and bio-ethanol seems to be an effective alternative motor fuel. Compared to the petroleum based materials, bio-ethanol had lower combustion and releases lower rates of CO, CO2, non-combustible hydrocarbons, nitrogen oxides, and volatile organic compounds.The aim of this study is to investigate bio-ethanol production from vegetable stalks (tomato, pepper and eggplant). Vegetable stalks are lignocellulosic materials with no economic value burnt or left in the field after harvests leading to environmental pollution. These materials have high polysaccharide contents (%65-80), and they seem to have potential for bio-ethanol production. For the study, integrated steam explosion/dry-milling and chemical pretreatments were applied before enzymatic hydrolysis. Stalks were steam exploded at 198-200 ºC at 15 psi for 5 minutes and dry milled using mechanical grinder. Subsequently, each sample was pretreated with chemicals at a solid loading of 10% (w/v) of sodium borohydrate (NaBH4), sodium hydroxide (NaOH), and sulfuric acid (H2SO4). The chemical pretreatments were made with 2% (w/v) concentration under the temperature of 121 ºC at 15 psi for residence times of 30 and 90 min.Results showed that after enzymatic hydrolysis of Celluclast 1.5 L (700 U/g) and Novozym 188 (250 U/g) mixture, the highest sugar yields of 30.1% and 27.4% (% out of dry matter) were observed for steam exploded and milled materials respectively after they were both treated with NaOH for 30 min. According to the observed results of this thesis research, vegetable stalks make good alternative raw material for bio-ethanol production.