ABSTRACT
Cassava is considered as a potential source for the commercial production of bioethanol because of its availability and low market price. It can be used as a basic source to support large-scale biological production of bioethanol using microbial amylases. With the progression and advancement in enzymology, starch liquefying and saccharifying enzymes are preferred for the conversion of complex starch polymer into various valuable metabolites. These hydrolytic enzymes can selectively cleave the internal linkages of starch molecule to produce free glucose which can be utilized to produce bioethanol by microbial fermentation. Ethanol is an alcohol with the general formula C2H2n+1OH which can either be produced by manufacture from ethane using steam(the synthetic route), production from biomass waste using bacteria or production from sugars and starches by fermentation using yeast. Principally, this project work investigates the potential for the utilization of cassava as feed stock for the production of bioethanol by hydrolyzing with enzymes malted from sorghum grain. The hydrolysate was then fermented anaerobically using a hybrid of Saccharomyces cerevisiae and Saccharomyces paradoxus followed by distillation of the bioethanol produce to obtain a high graded ethanol. A process involving the use of cassava feedstock as substrate and sorghum malt as enzymes is presented in this report. After a delayed fermentation period of about 30 days, the end product bioethanol was recovered by simple distillation using a oil bath, the fermentation process resulted in the ethanol yield of 0.250L from a totaling starch content of 301 g, leading to a 77% conversion rate of ethanol produced per gramme of starch consumed. The ethanol produced was found to contain about 18 wt% purity using the specific gravity to ethanol chart as shown in the appendix section of this report.
TABLE OF CONTENTS Page Title Page……………………………………………………………………………………i Letter of transmittal…………………………………………………………………………ii Certification…………………………………………………………………………………iii Dedication…………………………………………………………………………………..iv Acknowledgement…………………………………………………………………………..v Table of contents…………………………………………………………………………….vi List of figures………………………………………………………………………………..x List of tables…………………………………………………………………………………xi Abstract……………………………………………………………………………………...xii
CHAPTER ONE: INTRODUCTION…………………………………………………1
1.1 Background of Proposed Study……………………………………………………. 1
1.2 Aim and Objectives…………………………………………………………………3
1.3 Significance of Study ………………………………………………………………4
1.4 Research Scope……………………………………………………………………..4
1.5 Justification of Study……………………………………………………………….4
1.6 Organization of Study………………………………………………………………4
CHAPTER TWO: LITERATURE REVIEW…………………………………………5
2.1 Cassava……………………………………………………………………………..5
2.1.1 History of Cassava…………………………………………………………..5
2.1.2 Cultivation of Cassava………………………………………………………5
2.1.3 Characterization of Cassava…………………………………………………8
2.1.4 Cassava starch content………………………………………………………9
2.1.5 Hydrolysis of Cassava………………………………………………………13
2.1.6 Application of Cassava……………………………...……………………...14
2.2 Yeast…………………………………………………..…………………………...15
2.2.1 Preservation of Yeast Culture…………………..…………………………..15
2.2.2 Saccharomyces cerevisiae……………………..……………………………23
2.2.3 Saccharomyces paradoxus………………………..………………………...24
2.2.4 Mechanism of Yeast Fermentation……………………..…………………..24
2.2.5 Kinetics of Yeast Growth…………………………………..……………….25
2.3 Bioethanol……………………………………………………………..……………27
2.3.1 General Overview…………………………………………..……………….27
2.3.2 Upstream processing in Bioethanol production.............................................28
2.3.3 Feedstock for Bioethanol Production…………………………..……………33.
2.3.4 Advantages and Disadvantages of Bioethanol……………………..……………35
2.3.5 Economic and Environmental Impacts of Bioethanol……………………….37
2.4 Bioethanol from Cassava………………………………….………………………..38
2.4.1 Conventional method of bioethanol production………………………………38
2.4.2 Simultaneous Saccharification and Fermentation (SSF)……………….……..41
2.4.3 Simultaneous Liquefaction Saccharification and Fermentation (SLSF)………41
CHAPTER THREE: METHODOLOGY……………………………….………………….43
3.1 Introduction……………………………………………………………………………43
3.2 Materials and Reagents………………………………………………………………..43
3.3 Apparatus ……………………………………………………………………………..43
3.4 Description of Apparatus……………………………………………………………...44
3.5 Experimental Procedures………………………………………………………………46
3.5.1 Malting of Sorghum Grain…………………………………………………….46
3.5.2 Cassava Feedstock Preparation/Starch Extraction…………………………….48
3.5.3 Starch Hydrolysis with Sorghum Malt………………………………………..50
3.5.4 Preparation of Organism and Inoculums……………………………………...50
3.5.5 Fermentation of the Hydrolysate……………………………………………...51
3.5.6 Distillation……………………………………………………………………..51
3.5.7 Ethanol Concentration…………………………………………………………52
CHAPTER FOUR: RESULTS AND DISCUSSION……………………………………..53
4.1 Results………………………………………………………………………………...53
4.2 Discussion of Results………………………………………………………………….61
CHAPTER FIVE: CONCLUSION AND RECOMMENDATION…………………….63
5.1 Conclusion…………………………………………………………………………….63
5.2 Recommendations……………………………………………………………………..64
REFERENCES……………………………………………………………………………….65
APPENDICES………………………………………………………………………………...72