ABSTRACT

The yield of bioethanol from cassava peels hydrolysed with Aspergillus niger and crude enzymes (amylase, cellulase and pectinase) was examined in this study. Cassava peels were pretreated by soaking and a combination of soaking and boiling which removes 67% of cyanide. After hydrolysis, Zymomonas mobilis and Saccharomyces cerevisiae were used to ferment the hydrolysates separately at room temperature for five (5) days. The result showed that pretreatment by soaking and boiling for up to 120 minutes removed the highest amount of cyanide and increased carbohydrate but reduced the fibre content (37.04±0.01mg/g, 71.42±0.02%, and 10.38±0.42%). Hydrolysis using Aspergillus niger yielded up to 95.44±0.11mg/g reducing sugar while hydrolysis using enzymes yielded up to 72.38±0.06mg/g reducing sugar.  Highest ethanol yield when the hydrolysates were fermented with Zymomonas mobilis and Sacchromyces cerevisiae were 3% and 2% respectively. Proximate composition of the fermented waste showed 6.37±0.08, 2.71±0.03, 25.49±0.01, 8.97±0.02 and 34.41±0.16% ash, fat, protein, crude fibre and carbohydrate respectively while nitrogen, phosphorus and potassium of the residue was 4.08±0.50, 0.40±0.28 and1.84±0.15% respectively. The work reveals that cassava peels is a suitable agricultural waste for bioethanol production and fermentation with Zymomonas mobilis yielded high ethanol compare to Saccharomyces cerevisiae. The work also proved that the waste product of fermentation may be used as animal feedstock or fertilizer to enrich the soil for plant growth.

CHAPTER ONE

INTRODUCTION

Cassava is one of the important food crops that survive conditions of low nutrient availability and drought (John, 2004). History revealed that cassava originates from Brazil and was introduced into West Africa by Portuguese and today, over 600 million people from Africa, Asia and Latin America depend on cassava for food (Asegbeloyin and Onyimonyi, 2007). Cassava was introduced into Nigeria 300 years ago and became generally accepted and cultivated in late 1990s (Nigeria Cassava Master Plan, 2006). Today, Nigeria is the highest producer of cassava in the world, producing higher than Brazil, Thailand and Indonesia (Asegbeloyin and Onyimonyi, 2007). Cassava has been a raw material globally for industrial production of textiles, papers, adhesives, pharmaceuticals and various food products because it is rich in carbohydrate with high energy density and has generated great impact in world economics (Aigbe and Remison, 2010). Cassava and it is by – products are renewable source of energy that pose no threat to the environment and has been used by several researchers in the production of biofuel (Musatto and Teixira, 2010). Interest in the production of biofuel from agricultural wastes is driven by several reasons such as: global search for alternative source of energy and transportation fuel to replace the depleting fossil fuel. It was also because of several benefits derivable from the use of ethanol. These benefits includes: the use of ethanol as solvents, germicides, antifreeze and intermediates for other organic chemicals (Kingsley, 2012). Bioethanol can be produced by fermenting sugars in plant materials as opposed to synthetic ethanol production from petrochemical sources (Oyeleke a Jibrin, 2009). Ethanol is pollution free, biodegradable, renewable, cause no climate change and the by – product of fermentation can be used as animal feedstock (Adelekan, 2010; Teerapatr, Lerdluk and La-aied, 2010). It has been estimated that 2.96 million metric tons of cassava peels is generated annually in Nigeria from processing cassava to various food products (Nwabueze and Otunwa, 2006). These enormous wastes that constitute 20 – 35% of the weight of cassava tuber are discarded with consequent implication of environmental pollution. In view of this, it has become necessary to convert this waste to useful end products in other not to pose threat to the environment (Nwabueze and Otunwa, 2006).

 

 

• QUEST FOR ALTERNATIVE ENERGY SOURCES

The earth experienced an increase in the mean temperature in the 19^th century due to emission of greenhouse gases. Carbon dioxide has been the largest greenhouse gas emitted through combustion of fossil fuel as coal, oil and natural gases (Sun and Cheng, 2002). United States alone is responsible for 25% of global energy consumption and 25% of the world carbon dioxide emission. Researches have shown that the deposit of crude oil in the earth crust is gradually depleting with time. This reason couple with the continuous hike in the pump price has driven global attention to the search for a renewable energy source to serve as transportation fuel and power industrial machines (Jin, Michel, Wyman and Dale, 2003).  Bioethanol produced from fermentation of sugars in plants has been discovered to be a perfect replacement for gasoline in some advanced countries (Sharma, Kalra, Oberoi and Bansal, 2007).

• STATEMENT OF RESEARCH PROBLEM

 

Large tons of cassava wastes are discarded annually in Nigeria when cassava is processed to various food products. This waste ends up in open dumps or drainage systems, threatening both surface water and ground water quality. It is therefore necessary to convert these wastes to useful end products rather than allowing them to become nuisance to the environment.

 

• JUSTIFICATION

 

The global search for alternative renewable transportation fuel to replace the depleting fossil fuel is on the increase due to hike in petroleum price and global warming. This research work is aimed at investigating the possibility of transforming cassava peels to valuable products like ethanol, animal feedstock or fertilizer, thereby contributing toward alternative energy supply as well as creating employment opportunity.

 

• RESEARCH AIM AND OBJECTIVES

 

AIM

 

The aim of this research work is to produce ethanol from Cassava peels using Zymomonas mobilis and Saccharomyces cerevisiae and compare ethanol yield of the two organisms.

 

 

OBJECTIVES

 

The overall objectives of this work are:

1. To determine the pretreatment method for cyanide removal in cassava peels.
2. To determine the condition for enzyme hydrolysis of pretreated cassava peels.
3. To establish fermentation condition for hydrolyzed cassava peel.
4. To determine the yield of ethanol produced from fermentation by Zymomonas mobilis and Saccharomyces cerevisiae
5. To assess the fermentation residue for possible organic fertilizer or animal feedstock.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CHAPTER TWO

LITERATURE REVIEW

2.1 CASSAVA PRODUCTION IN AFRICA

Nigeria became the highest producer of cassava in the world in 2010, producing 37 million tons of the 230 million tons of world cassava production.