PRODUCTION OF BIOETHANOL FROM OIL PALM TRUNK USING SACCHARIFICATION AND COFERMENTATION METHOD
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Abstract
The increasing global demand for renewable and sustainable energy sources has intensified research into bioethanol production from non-food lignocellulosic biomass. This study investigates the production of bioethanol from oil palm trunk (OPT), an abundant agricultural residue generated during replanting cycles in oil palm plantations in Nigeria, to optimize pretreatment and fermentation conditions to maximize fermentable sugar yield and ethanol production efficiency.
Oil palm trunk samples were collected from Idogbo, Benin City, Nigeria, and processed through size reduction, drying, and sieving to a 500 µm particle size. Chemical composition analysis confirmed that OPT contains 29 to 45% cellulose, 12 to 29% hemicellulose, and 18 to 23% lignin, validating its suitability as a second-generation bioethanol feedstock. Pretreatment was carried out using dilute sodium hydroxide (NaOH) at a concentration of 20% to disrupt the lignocellulosic matrix and enhance cellulose accessibility for enzymatic hydrolysis. Response Surface Methodology (RSM) based on a Box-Behnken design was employed to optimize three key pretreatment variables, namely acid concentration (1 to 6%), reaction time (10 to 120 minutes), and temperature (30 to 120°C), with fermentable sugar yield as the response variable. A total of 17 experimental runs were conducted, and the results were fitted to a quadratic model. Analysis of variance (ANOVA) confirmed the statistical significance of the model, with an F-value
of 115.99 and a p-value of less than 0.0001. The model demonstrated excellent predictive accuracy,
with a coefficient of determination (R²) of 0.9933, an Adjusted R² of 0.9848, and an Adequate Precision ratio of 28.27, confirming a strong signal-to-noise ratio and reliable navigability of the design space. Acid concentration (A), reaction time (B), temperature (C), their interaction terms (AB and BC), and quadratic terms (A², B², and C²) were all identified as statistically significant factors influencing sugar yield (p less than 0.05).
The optimum pretreatment condition was established at an acid concentration of 3.5%, a temperature of 120°C, and a reaction time of 120 minutes, yielding a maximum fermentable sugar concentration of 553.54 mg/g. Three-dimensional response surface plots demonstrated that sugar yield increased progressively with moderate acid concentration and rising temperature, but declined at extreme values due to thermal and acid-induced sugar degradation and the formation of inhibitory compounds, including furfural and hydroxymethylfurfural (HMF). Enzymatic hydrolysis of the pretreated OPT biomass was performed using commercial cellulase enzymes, followed by fermentation with Saccharomyces cerevisiae. Fermentation performance was monitored over four days using the 3,5-dinitrosalicylic acid (DNS) colorimetric method at 610nm. Sugar concentration decreased progressively from 3.8 mg/g on day one to 0.405 mg/g by day four, confirming active microbial metabolism and efficient conversion of released fermentable sugars into ethanol.
The findings of this study demonstrate that oil palm trunk is a technically viable and sustainable lignocellulosic feedstock for second-generation bioethanol production. The optimized pretreatment conditions effectively balanced lignin disruption and cellulose preservation, maximizing sugar recovery while minimizing inhibitor formation. The results support the potential of OPT waste valorization as a pathway toward renewable energy generation, reduced agricultural waste burden, and enhanced energy security in palm oil-producing regions of Nigeria. Future work
should focus on co-culture fermentation systems capable of utilizing both hexose and pentose sugars, detailed techno-economic analysis, and life-cycle assessment to establish the commercial and environmental viability of large-scale OPT-based bioethanol production.
Oil palm trunk samples were collected from Idogbo, Benin City, Nigeria, and processed through size reduction, drying, and sieving to a 500 µm particle size. Chemical composition analysis confirmed that OPT contains 29 to 45% cellulose, 12 to 29% hemicellulose, and 18 to 23% lignin, validating its suitability as a second-generation bioethanol feedstock. Pretreatment was carried out using dilute sodium hydroxide (NaOH) at a concentration of 20% to disrupt the lignocellulosic matrix and enhance cellulose accessibility for enzymatic hydrolysis. Response Surface Methodology (RSM) based on a Box-Behnken design was employed to optimize three key pretreatment variables, namely acid concentration (1 to 6%), reaction time (10 to 120 minutes), and temperature (30 to 120°C), with fermentable sugar yield as the response variable. A total of 17 experimental runs were conducted, and the results were fitted to a quadratic model. Analysis of variance (ANOVA) confirmed the statistical significance of the model, with an F-value
of 115.99 and a p-value of less than 0.0001. The model demonstrated excellent predictive accuracy,
with a coefficient of determination (R²) of 0.9933, an Adjusted R² of 0.9848, and an Adequate Precision ratio of 28.27, confirming a strong signal-to-noise ratio and reliable navigability of the design space. Acid concentration (A), reaction time (B), temperature (C), their interaction terms (AB and BC), and quadratic terms (A², B², and C²) were all identified as statistically significant factors influencing sugar yield (p less than 0.05).
The optimum pretreatment condition was established at an acid concentration of 3.5%, a temperature of 120°C, and a reaction time of 120 minutes, yielding a maximum fermentable sugar concentration of 553.54 mg/g. Three-dimensional response surface plots demonstrated that sugar yield increased progressively with moderate acid concentration and rising temperature, but declined at extreme values due to thermal and acid-induced sugar degradation and the formation of inhibitory compounds, including furfural and hydroxymethylfurfural (HMF). Enzymatic hydrolysis of the pretreated OPT biomass was performed using commercial cellulase enzymes, followed by fermentation with Saccharomyces cerevisiae. Fermentation performance was monitored over four days using the 3,5-dinitrosalicylic acid (DNS) colorimetric method at 610nm. Sugar concentration decreased progressively from 3.8 mg/g on day one to 0.405 mg/g by day four, confirming active microbial metabolism and efficient conversion of released fermentable sugars into ethanol.
The findings of this study demonstrate that oil palm trunk is a technically viable and sustainable lignocellulosic feedstock for second-generation bioethanol production. The optimized pretreatment conditions effectively balanced lignin disruption and cellulose preservation, maximizing sugar recovery while minimizing inhibitor formation. The results support the potential of OPT waste valorization as a pathway toward renewable energy generation, reduced agricultural waste burden, and enhanced energy security in palm oil-producing regions of Nigeria. Future work
should focus on co-culture fermentation systems capable of utilizing both hexose and pentose sugars, detailed techno-economic analysis, and life-cycle assessment to establish the commercial and environmental viability of large-scale OPT-based bioethanol production.
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