Optimization for acid pre-treatment of Sweet Sorghum Bagasse to obtain fermentable sugars using Response Surface Methodology

Author Name: *Lavudi Saida,Harinder Singh Oberoi,Birru Bhaskar,Venkata Sri Krishna Kona,Lalitha Udayagiri
Author Email: lavudisaida@jntuh.ac.in

Abstract

Sweet Sorghum Bagasse (SSB), one of the most abundant lignocellulostic residues represents an attractive renewable resource for bioconversion of energy. The present study was focused on utilization of SSB to obtain higher yield of fermentable sugars so as to take it as a substrate in ethanol production. As lignin is found to hinder the overall availability of fermentable sugars, chemical pre-treatment was carried out using variable acid concentration. Results shown that the maximum fermentable sugar production was observed within the range of 0.5- 2 % of sulphuric acid with the provided autoclave temperature of 125oC for 30 min. Response Surface Methodology (RSM) was used to optimize acid pre-treatment. Central Composite Design (CCD) for three variables at five levels was chosen. RSM predicted response for optimal production of glucose 14.41 mg/ml can be carried out at 0.65% acid concentration for 19.83 min at 128.93oC.Validation Results showed the glucose concentration to be 16.40 mg/ml at predicted response conditions.

Keywords

Sweet Sorghum Bagasse, acid pre-treatment, response surface methodology

Introduction

Sweet Sorghum is a renewable, cheap and widely available resource that can be used for bioethanol production. It contains soluble and insoluble carbohydrates & lignin along with various intermediate and secondary metabolites [1]. Major fraction of carbohydrates can be extracted by juice form, and can be easily fermented to bioethanol. The solid residue (bagasse) remained as by-product during processing represents about 30% of whole plant fresh weight. Lignin is physical seal of hemicelluloses and cellulose, which forms an impenetrable barrier in the plant cell wall [2]. The lignin content, crystallinity and degree of polymerization of cellulose decrease the surface area for the enzymatic attack of cellulose fibers towards the production of fermentable sugars which are the precursors for bioethanol production [3]. Therefore Production of fermentable sugars from lignocellulosic materials demands a pre-treatment, which can be carried out by different techniques i.e. using alkalis, acids, heat pressure, solvents, etc [4]. The chemical pre-treatment with diluted sulphuric acid solutions followed by enzymatic hydrolysis is considered to be promising method for the production of fermentable sugars [5]. RSM is a statistical technique, which is used to optimize the process parameters to get the higher yield. It is applied in the present study to optimize the acid pre-treatment conditions to make more concentrations of cellulose available for conversion to fermentable sugars during hydrolysis.

Conclusion:

The main objective of acid pre-treatment is to remove the lignin and hemicelluloses structures, preserving more cellulose to make accessible to enzymatic hydrolysis for producing reducing sugars. Thus the optimal production of glucose of 16.40 mg/ml was achieved at 0.65% acid concentration for 20 min at 129oC. These results showed that three variables effected on yield of glucose.

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