EVALUATION OF BIOETHANOL PRODUCTION POTENTIALS OF SELECTED LIGNOCELLULOSIC WASTES

Abstract

In the last three decades most countries, particularly the developing nations, have been experiencing energy deficit because of overdependence on fossil-based fuels. This development has led to the search for alternative energy sources. Nigeria is rich in biomass and waste materials that are suitable precursors for biofuels, yet these have not been fully explored. This study was therefore designed to evaluate the bioethanol production potentials of multi-substrate lignocelluloses-based wastes. Four lignocellulose-based wastes- Cassava Peels (CP), Yam Peels(YP). Plantain Peels (PP) and Sawdust (SD) were purposively selected. They were subjected to pretreatment, chemical hydrolysis, microbial fermentation and confirmatory biochemical tests following the methods described by the Association of Official Analytical Chemists (AOAC). Grab samples of the wastes were air dried and pulverized. Twenty grammes each of the powdery biomass was treated separately with 100ml 5.6M, 9.4M and 13.1M of H₂SO₄ in a two stage hydrolysis. The first hydrolysis was done at 100⁰C for 60mins, after which the residue was hydrolysed n t 100⁰C for 50mins. The mixed hydrolysates were analysed for glucose and Total Reducing Sugars (TRS). The 13.1M H₂SO₄ gave the best yield of glucose and TRS hence was fermented with Saccharomyces cerevisiae at 30°C for 72 hours. Samples were taken from the fermenting broths every 24 hours for ethanol yield determination. Data were analysed using descriptive statistics, t-test, ANOVA and Spearman-rank correlation at p=0.05. Mean glucose yield and TRS obtained from the 5.6M H₂SO₄ hydrolysis were: CP (50.5±5.0mg/kg. 91.8±3.0mg/kg); YP (231.0±3.6mg/kg, 388.8±6.9mg/kg); PP (255.5±5.4mg/kg, 314.7±5.1mg/kg) and SD (285.7±5.0mg/kg, 374.5±7.3mg/kg). At 9.4M H₂SO₄ hydrolysis, the mean glucose yield and TRS were: CP (71.5±3.0mg/kg, 123.2±5.0mg/kg); YP (240.0±5.0mg/kg, 460.2±4.7mg/kg); PP (278.1±6.5mg/kg, 396.4±6.0mg/kg) and SD (300.7±8.6mg/kg, 453.2±6.6mg/kg). The mean glucose yield and TRS obtained from the 13.1M H₂SO₄ Hydrolysis were: CP (85.1±5.7mg/kg, 209.8±3.7mg/kg), YP (269.2±11.2mg/kg, 541.3±7.8mg/kg), PP (304.0±6.1mg/kg, 461.2±3.6mg/kg) and SD (343.2±4.8mg/kg, 535.9±5.0mg/kg). The mean glucose yield and TRS obtained from the 13.1M were significantly higher than those obtained from the 9.4M and 5.6M H₂SO₄ hydrolysis. The I3.1M hydrolysate was used for the ethanol production and the mean ethanol yield at 24 hours of fermentation were; CP (123.3±11.1mL/kg), YP (172.0±17.5mL/kg), PP (217.7±13.5mL/kg) and SD (240.3±14.0mL/kg) respectively. The maximum ethanol production was obtained at 48 hours, the mean ethanol yield being: CP - 160.0±15.1mL/kg, YP - 211.7 ±15.3mL/kg, PP - 265.0±20.5mL/kg and SD - 280.0±11.5mL/kg. Mean ethanol yield obtained at 48 hours of fermentation were significantly different from those obtained at 24 hours. A significant correlation exists between the ethanol yield of the substrates and the time of fermentation (r=0.95). Sawdust produced the highest glucose and ethanol yields among the substrates. Therefore ethanol production from sawdust should be fully optimized.