Effect of Production Factors on the Bioethanol Yield of Tropical Sawdust

Amaefule, Desmond; Nwakaire, Joel; Ogbuagu, Nneka; Anyadike, Chinenye; Ogenyi, Chiamaka; Ohagwu, Chukwuemeka; Egbuhuzor, Onyekachi

doi:https://doi.org/10.1155/2023/9983840

International Journal of Energy Research

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Abstract Introduction Materials and Methods Results and Discussion Data Availability Conflicts of Interest Acknowledgments References Copyright Related Articles

Research Article | Open Access

Volume 2023 | Article ID 9983840 | https://doi.org/10.1155/2023/9983840

Effect of Production Factors on the Bioethanol Yield of Tropical Sawdust

Desmond Amaefule,¹Joel Nwakaire,²Nneka Ogbuagu,¹Chinenye Anyadike,²Chiamaka Ogenyi,²Chukwuemeka Ohagwu,²and Onyekachi Egbuhuzor³

Academic Editor: Keat Teong Lee

Received06 Oct 2022

Revised07 Mar 2023

Accepted18 Mar 2023

Published18 Apr 2023

Abstract

Bioethanol production from cellulosic materials is important in mitigating the concomitant displacement and exploitation of primary food crops for biofuel production and reducing carbon emissions which exacerbate climate change. The problem of reduced yield in the production and availability of yeast locally poses a barrier to market adoption and penetration of bioethanol. The study examined the effect of particle size and different yeast strains on the yield of bioethanol from waste sawdust that was sourced from a local timber processing centre. The samples of yeast were prepared from baker’s yeast (Saccharomyces cerevisiae) and palm wine yeast (Saccharomyces chevalieri). The sawdust was reduced to 212 μm, 300 μm, and 500 μm particle sizes. The samples of each particle size were pretreated and hydrolyzed with H₂SO₄ and fermented with S. cerevisiae or S. chevalieri yeast. The results obtained show that the weight, pH, density, viscosity, flash point, and heating value of the produced bioethanol ranged between 221.67 and 322.64 g, 6.2 and 6.6, 0.821 and 0.878 g/mL, 1.073 and 1.193, 14 and 16°C, and 20.5 and 23.1 MJ/kg, respectively, while the alcohol content of each of the samples was 69%. Furthermore, the bioethanol yield from Saccharomyces cerevisiae yeast was 213.9 mL, 193.2 mL, and 186.3 mL, for the 212 μm, 300 μm, and 500 μm particles, while for Saccharomyces chevalieri yeast, the yield was 289.8 mL, 255.3 mL, and 220.8 mL for the 212 μm, 300 μm, and 500 μm, respectively. An ANOVA on the effect of particle size on ethanol yield shows a significant difference at 5% level of significance. The study demonstrated that the use of locally produced yeast and increasing the surface area of sawdust increase bioethanol yield. Hence, it was concluded that better yeast strain use and biomass particle size reduction to a level that allows the optimal surface area for the reaction improve the yield of bioethanol. The study outcome can help in ameliorating the continued dependence on fossil fuels and the food security problems arising from displacing or utilizing food for fuel and could also encourage commercial-scale cellulosic ethanol production from waste.

1. Introduction

There is a global energy inadequacy problem, more especially in developing countries [1]. Global fossil fuel demand-supply problems, including violence and economic and political crises around the supply regions, make renewable energy solutions more necessary now than before. Utilizing renewable energy reduces global warming and environmental degradation, since about 85% of the annual greenhouse gas emission reported by Huang et al. [2] result from fossil energy use. On the contrary, appropriate biomass use does not result in environmental degradation, making biomass a sustainable energy source with high availability [3]. Biomass also has a global distribution in diverse forms. Sawdust is an urban solid waste from the timber and wood industry that can be obtained from either hardwood or coniferous sources. Due to its burning capacity, it is typically used as a fuel source for thermal processes. It is also used as an insulating and packing material in several other applications. The disposal of 8.6 million metric tons of sawdust produced annually in Nigeria causes environmental pollution as the most surveyed disposal system is through open burning of biomass [4]. If the open disposal system is replaced with bioethanol production, the national goal of reducing greenhouse gases in line with the Paris Agreement of the National Determined Contributions (NDC) may be achieved. Over the years, technology has geared towards developing new ways to transform waste into wealth. Whereas harnessing this biowaste in the production of bioethanol has numerous advantages [5, 6], Hoang and Nghiem [7] reported that there is very little global commercial production of ethanol from cellulose.

The research of bioethanol production was sparked by the expanding search for alternative energy sources [8, 9]. Both pure bioethanol and bioethanol combined with gasoline can be used as fuel. It is utilized in flexible fuel vehicles in Brazil as well as the United States as a blended fuel (24% ethanol, 76% gasoline) and as a 10% solution in gasoline (E-10) [10]. E-15 (15% ethanol, 85% gasoline) and E-85 (15% gasoline, 85% ethanol) are other blends. Bioethanol can replace other gasoline fuel additives, such as octane boosters, and ethanol-gasoline blends have the strongest stopping power [11]. Additional advantages of using bioethanol as a biofuel include its complete biodegradability, lack of sulfur, and the less hazardous nature of the by-products of its incomplete oxidation (acetic acid and acetaldehyde).

Bioethanol, an additive or substitute to gasoline, is the most utilized biofuel for transportation globally. It is used in domestic cooking, as ethanol gel, in fuel blending, hydrogen production, and as a precursor for other chemical items [12]. The expanding biofuel industry and the concomitant displacement and exploitation of primary food crops compete directly with food consumption and negatively impact agricultural food availability [13]. Attention has been given to the potential of agricultural waste (cellulose) as a feedstock for second-generation biofuels, to save the food chain, manage waste, and reduce the inflation of food prices [12, 14]. The four main sources of cellulosic materials are wood residues from paper mills and lumber industries, agricultural residues, dedicated energy crops, and municipal solid waste (including paper and other cellulosic materials).

Whereas the production of ethanol has undergone considerable refinement that made the process more efficient in recent years, its basic steps have remained unchanged over time. Bioethanol can be produced from any biological feedstock that contains sugar or that can be converted into sugar following the four basic steps: physical and chemical pretreatment, acidic or enzymatic hydrolysis of sugar polymers, fermentation of the derived sugars, and alcohol distillation [15–17].

While a small amount (5-10%) of foreign matter may be also found in sawdust, the main chemical components of sawdust are carbon (60.8%), hydrogen (5.2%), oxygen (33.8%), and nitrogen (0.9%) [18]. On a dry mass basis, lignocelluloses contain 40-60% cellulose, 20-40% hemicellulose, and 10-25% lignin. Lignocelluloses resist degradation and offer hydrolytic stability and structural robustness mainly due to cross-linking between polysaccharides and lignin through ester and ether linkages [19]. The conversion of cellulose to ethanol requires preparatory delignification to liberate cellulose and hemicellulose from their complex form with lignin.

Feedstock pretreatment also averts the degradation of the sugar (pentose) derived from hemicelluloses and reduces the formation of inhibitory products for the subsequent fermentation process. Feedstock milling is a physical pretreatment process and enhances adequate reagent penetration and rapid continuous processing. Chemical pretreatment with alkali or strong acid solubilizes hemicellulose and degrades the lignin structure’s side chains of esters and glycosides. This increases the accessibility of hemicellulose-degrading enzymes and causes the cellulose to swell. Biological pretreatment degrades lignin through the action of microorganisms like white, brown, and soft rot fungi. The slow rate of hydrolysis is the demerit of this method, but combining it with other pretreatment processes can improve it.

Simultaneous saccharification and fermentation (SSF) and separate hydrolysis and fermentation (SHF) are two methods of producing ethanol from cellulose. Acidic cellulolysis utilizes dilute acids at more than 20°C temperatures and above atmospheric pressure, or concentrated acid at a lower temperature (below 10°C) and atmospheric pressure. It has the advantage of being faster and the disadvantage of reduced cellulose conversion to glucose, as it is more equilibrium driven. In enzymatic cellulolysis, cellulase enzymes under relatively mild conditions (50°C and pH 5) break down cellulose and hemicellulose chains into glucose molecules without the formation of fermentation enzymes-inhibiting by-products. Some process conditions of enzymatic hydrolysis that affect the ethanol yield of the products include the type of feedstock, pretreatment process, presence of inhibitors, and thermostability of enzymes. Others are pH, enzyme and substrate concentration, duration of hydrolysis, enzyme absorption on substrate surface, and rate of medium [20]. The glucose released during the process, however, inhibits cellulase action.

The simple sugar produced from the hydrolysis described above is fermented with yeast to produce ethanol and a by-product (carbon dioxide), as shown in the reaction equation below.

However, yeast’s tolerance to high sugar concentration at the start of fermentation and high ethanol concentration at the end of fermentation [21, 22], and varying pH [23], makes it a suitable organism for fermentation. Horváth et al. (2018) opined that high sugar concentration (up to 320 g/L) did not significantly influence sugar consumption during fermentation. Rollero et al. [25] on the other hand reported that high initial sugar concentration could modify fermentation dynamics, ethanol concentration, and metabolite profile. S. cerevisiae is a common yeast of economic importance in food and beverage industries and can be isolated from sugary foods and beverages such as palm wine [26]. The practice of isolating and evaluating local microbial strains for defined or potential commercial attributes is practiced commonly in industrial microbiology and biotechnology [27]. Baker’s yeast has been long in use for producing ethanol via fermentation and is commercially available and easy to culture. The growth rate of the microorganisms is directly affected by the temperature [10]. Cot et al. [28] reported 20°C to 35°C as suitable to free S. cerevisiae cells and 30°C being optimum.

Distillation of the fermented broth is finally done to extract pure ethanol (distillate) based on the boiling point of 78°C. Part of the acid and water from acid hydrolysis is also recoverable during distillation [29]. This work, therefore, studied the effect of feedstock particle size and the fermentation yeast strain on the amount of ethanol produced from sawdust. The fuel properties and characteristics of the produced bioethanol were also determined. The study outcome can help in ameliorating the continued dependence on fossil fuels and the food security problems arising from displacing or utilizing food for fuel and could also encourage commercial-scale cellulosic ethanol production from waste.

2. Materials and Methods

2.1. Source and Collection of Materials

2.1.1. Sawdust

Tropical sawdust (see Figure 1), was collected from a local timber factory in Ovoko, Nsukka L.G.A. Enugu, Nigeria (Latitude 6.88583°N and Longitude 7.45847°E). Unwanted materials, debris, and foreign components were separated from the sample.

The sample was milled (physical pretreatment) and graded with (Haver and Boeker, Germany) digital sieve shaker number 59302 OELDE into 500 μm, 300 μm, and 212 μm particle sizes. Two samples of 250 g were produced from each particle size and labelled accordingly.

Experimental apparatus and reagents available in the Microbiology Laboratory of the University of Nigeria, Nsukka, were used.

The apparatus included the following: conical flasks: 200 mL, 500 mL, and 2 L; refractometer; alcohol meter; and Ostwald viscometer.

Reagents were as follows: distilled water, yeast peptone dextrose agar (YPDA), yeast extract, urea, chloramphenicol, 18 M H₂SO₄, and 20 N NaOH.

2.2. Sawdust Cellulose Hydrolysis and Fermentation

The SHF was adopted for this research work. The sawdust samples (250 g each) were placed individually in 2 L conical flasks, and 200 mL of distilled water was added to each to make it into the slurry. 250 mL of 18 M H₂SO₄ was then added to each flask at atmospheric conditions. The sawdust samples turned black immediately from the treatment. The conical flask containing the mixture was then placed in a water bath and left at 100°C for 30 minutes. The solution was thereafter filtered using a muslin cloth; a black solid residue was realized. The sugar filtrate had a very low pH (less than 1) and was later neutralized using 20 N NaOH to a pH of 4.5-5.0 so that the yeast could survive in it. The sugar produced was measured in degrees Brix (^oBrix) using a refractometer, and the value was recorded.

2.2.1. Fermentation of the Samples

(1) Identification of S. cerevisiae Yeast. For S. cerevisiae preparation, Baker’s yeast (S. cerevisiae) was purchased from the local market as it is available for bread making. 50 g of Baker’s yeast (STK, Royal instant dry yeast) was dissolved in 200 mL of warm distilled water to activate it in readiness for fermentation.

(2) Identification of S. chevalieri Yeast. Unadulterated fresh palm wine samples obtained from oil palm trees (Elaeis guineensis) were purchased from local palm wine tapers in Ovoko, Nsukka, within the early hours of taping and was firmly covered in a sterile container and brought to the Microbiology Laboratory of the University of Nigeria, Nsukka, for analysis. The palm wine sample was shaken, and a loop full was collected under aseptic conditions and inoculated on Petri dishes containing YPDA supplemented with chloramphenicol antibiotic to prevent the growth of bacteria. The inoculated plates were incubated in an airtight container at 28°C for 48 hours. The isolates were collected under aseptic conditions. They were purified and stored on slants of YPDA for further use. The isolates were confirmed in the Microbiology Laboratory to be yeasts by microscopy (see Figure 2), and the pure isolate S. chevalieri, a dominant species of S. cerevisiae yeast usually found in palm wine.

(a)

(b)

(c)

(3) Inoculum Preparation for Fermentation. The pure isolate was then introduced into 500 mL conical flasks containing sterile liquid yeast peptone dextrose (YPD) broth and incubated at 28°C and atmospheric pressure for 24 hours to produce enough quantity for the fermentation. After incubation, the tubes were agitated by transfer into fresh YPD broth, and urea was added in readiness for fermentation. The fermentation had six different treatment samples as shown in Table 1. After hydrolysis, samples 212A, 300A, and 500A were fermented with baker’s yeast, while samples 212B, 300B, and 500B were fermented with yeast isolated from palm wine. All other reagents such as peptone, dextrose, agar, yeast extract, and urea were available in the Microbiology Laboratory at the University of Nigeria, Nsukka.

(4) Fermentation of the Hydrolyzed Substrate. The fermentation apparatus included cylindrical fitting tubes, stoppers, and 2.5 L thick fermentation bottles. 100 mL of the prepared inoculum was added to the neutralized solution for fermentation to begin. Samples 212B, 300B, and 500B were inoculated with pure palm wine yeast isolate, while samples 212A, 300A, and 500A were inoculated with Baker’s yeast. The initial weight of the sample at the beginning of the fermentation process was noted. The sugar content was measured in °Brix using a refractometer. The samples were weighed and tested on a 12-hour basis for sugar content to determine the rate of conversion of sugar to ethanol. The fermentation was allowed to proceed for 84 hours at 28°C without agitation.

(5) Distillation. The fermented broth was dispensed into a round-bottom flask fixed to a distillation column which was enclosed in running tap water. See Figure 3. A heating mantle on the temperature regulator was set to 78°C which is the boiling point of ethanol and is used to heat the round-bottomed flask containing the fermented broth. The resulting distillate that condensed in the distillation column was collected in bottles and measured using a measuring cylinder in milliliters.

2.3. Test of Physical Properties of the Fermented Broth and Produced Ethanol

The sugar content of the fermented broth was measured on a 12-hour basis for sugar content to determine the rate of conversion of sugar to ethanol. The volume and weight of the ethanol produced were measured and recorded. Some other physical properties of the bioethanol fuel were also measured and compared with the American Society for Testing and Materials International (ASTM) standard [30]. Some of these properties are flash point, viscosity, and heating value.

2.3.1. Sugar Content

A refractometer was used for measuring the sugar content of the fermented broth in °Brix. The corresponding mass of sugar in grams was obtained by calculation from the volume of solution (hydrolase and fermenting broth), as in Equation (2). where 1 °Brix represents 1 g of sugar per 100 g of solution.

2.3.2. Alcohol Content

A premium 137150518 glass model alcohol meter was used to measure the alcohol content percentage after the product has been distilled. Also the use of molecular sieves can significantly improve the percentage alcohol content of fermentation broths.

2.3.3. Flash Point

Following the method used by the Renewable Fuels Association [30], the lowest temperature at which the produced bioethanol ignited was determined by the open cup method. A 220-volt electronic heater, a ceramic crucible, a thermometer, and an ignition source were used.

2.3.4. Heating Value

The amount of heat released during the combustion of a specified amount of bioethanol was measured experimentally in a bomb calorimeter at 25°C.

2.3.5. Viscosity

The viscosity of the produced bioethanol was obtained by measuring the time of flow of ethanol-water through an Ostwald viscometer at room temperature [31]. The viscosity of the ethanol was then computed with the formula below. where is the viscosity of the liquid, is the viscosity of water (0.891 Pascal seconds), is the flow time of liquid, is the flow time of water, is the density of the liquid, and is the density of water (0.997 g/cm³).

The experiment included a test of the sugar concentration on a twelve-hour basis to determine the rate of fermentation by checking the sugar disappearance, thus determining the exact time required for fermentation.

The effect of particle size ethanol yield was statistically investigated with ANOVA.

Appropriate safety precautions were taken during the production and measurement processes.

3. Results and Discussion

3.1. Sugar Consumption and Fermenting Broth Weight Loss Dynamics

The rate of fermentation was shown in terms of sugar consumption in the fermenting broth from the broth’s weight loss.

3.1.1. Sugar Content of the Fermented Broth

The amount of sugar consumed with varying fermentation times is shown on a twelve-hour basis in Figure 4. Higher sawdust particle size correlated well with lower initial and residual sugar concentration all through the fermentation except for the 500A sample that gave a higher content than 300B after 24 hrs. of fermentation. The sugar content of the palm wine yeast strain was lower for most of the fermentation period for nearly all sawdust particle sizes than that of the Baker’s yeast. The highest sugar yield (27.8 g/100 g of the hydrolysate mixture) came from the 212B sample, while the lowest (19.2 g/100 g) came from the 500B sample. The sugar consumption rate was higher at the beginning of the fermentation and slowed down as the fermentation progressed. Raud et al. [32] obtained sugar yield of 24.29 g/100 g from 3 mm particle barley straw with enzymatic hydrolysis, after steam explosion pretreatment at 200°C. Gasmalla et al. [33] obtained a sugar yield of 84 g/100 g from sugarcane molasses. Molasses is a by-product of sugar production from sugarcane and is a popular feedstock for ethanol production.

3.1.2. The Weight Loss of the Fermenting Broth

The weight loss of the fermented broth with varying fermentation times is shown on a twelve-hour basis in Figure 5. All samples started with a 900 g weight of broth, but the weights reduced continuously with the evolution of CO₂ as the sugar fermented. The results showed that the 500A sample had minimal weight loss. Therefore, the least ethanol production was realized with this sample. The 212B sample had the highest weight loss (73.2 g). Higher ethanol production was obtained with smaller sawdust particle size and the palm wine yeast strain. This may be attributed to the greater specific surface area of such particles. Zabed et al. [34] reported higher cellulosic ethanol yield from a smaller particle size of microalga biomass. Fermentation by Baker’s yeast proceeded at a slower rate, and as a result, the sugar content at every given particle size is lower than that of palm wine yeast, meaning that it had lower ethanol yield as discussed in the subsequent section. Even the 500B sample however had higher weight loss (59.2 g) than the 212A and the two 300 μm samples. Carbon dioxide, glycerol, and yeast cell biomass are reported by Gasmalla et al. [33] as the by-products of sugar fermentation.

3.2. Effect of Particle Size on the Fermentation Process

The effect of particle size on the fermentation process is portrayed in the ANOVA table. However, particle size and fermentation time have a very high significant effect () on the fermentation rate (Tables 2 and 3). This is because of the rapid digestion of the substrate by yeast due to easier substrate penetration for the finer particles and the easier availability and accessibility of sugar to the yeasts. Pepin and Marzzacco [35] found out that the rate of fermentation depends on the concentration of yeast but independent of the concentration of sugar, and it is due to the large number of glucose molecules that surround the enzyme molecules in the reaction mixture.

3.3. Physical Properties of the Bioethanol

The alcohol content, flash point, heating value, viscosity, and pH of the produced ethanol samples are recorded in Table 4. These values were compared with the standard of bioethanol as set by the American Society for Testing and Materials (ASTM) also indicated in the table.

3.3.1. Alcohol Content

From Table 4, all production process treatments gave 69% alcohol with no effect of the feedstock particle size nor the fermentation yeast strain. The alcohol content was far lower than the 97% recommended by the ASTM standard. Improved product distillation may improve the alcohol content. Hoang and Nghiem [7] reported low achievable final ethanol concentration as one of the key issues of ethanol production from biomass. Drapcho et al. [37] recommended 50 g/L ethanol concentration as the acceptable minimum for the fermented broth input to the energy-intensive distillation process. The distillation process is majorly responsible for the alcohol content, density, flash point, and heating value.

3.3.2. Product Density

From Table 4, the highest Baker’s yeast alcohol density was obtained for the 300A sample and the lowest for the 500A sample. The palm wine yeast samples had their highest bioethanol density from the 300B sample and its lowest from the 500B sample. The effect of the yeast strain on the product density could not be established from the results. The density of the produced samples was higher than the 0.789 mg/mL ASTM standard. Higher alcohol content will give lower product density, while higher moisture content correlates with higher density. Ndukwe et al. [38] produced ethanol from sawdust cellulose of 20 different kinds of wood in Southwest Nigeria with varying alcohol concentrations of 1.86 mg/mL to 3.89 mg/mL. Ethanol density of 0.807 g/mL and 96% purity was produced by Gasmalla et al. [33] from sugarcane molasses.

3.3.3. Flash Point

As seen in the table, the highest flash point was for the palm wine yeast-fermented sample, and the least was obtained in the products fermented by both yeast strains. This lowest flash point and the highest were both obtained in the 300 μm sized feedstock. These values were higher than the ASTM standard of 12°C. The higher alcohol content also correlates with a lower flash point. Just like in the fermentation yeast strain, the particle size of the feedstock seems to have no definite influence on the product’s flash point.

3.3.4. Heating Value

The bioethanol lowest heating value was from the 500A sample, and the highest was for the 212B sample. Generally, the palm wine yeast samples had higher heating values than their Baker’s yeast counterparts for any given sawdust feedstock particle size. The heating values were lower than the ASTM standard of 29.7 MJ/kg. Higher alcohol content translates to a higher heating value. Okoro et al. [39] reported a heating value of 21.6 MJ/kg for ethanol fuel. Particle size has been reported as not capable of influencing the heating value of biochemically processed biomass but has a significant effect on the processing of dry biomass through direct combustion [40, 41].

3.3.5. Product Viscosity

The viscosity of the produced bioethanol was lowest for the 212A sample and highest for the 500A sample. The highest viscosity of the palm wine yeast samples was obtained for the 212 μm particle size feedstock. Increasing particle size of feedstock resulted in decreased viscosity for the palm wine yeast-fermented bioethanol samples but resulted in increasing viscosity for the baker’s yeast-fermented samples. The viscosity for the Baker’s yeast-fermented samples was lower than the palm wine yeast-fermented samples from 212 μm and 300 μm feedstocks but higher for the 500 μm feedstock. These values were less than the 1.525 Pa.sec ASTM standard. Gasmalla et al. [33] obtained ethanol of 96% purity and 0.83 cP viscosity from sugarcane molasses.

3.3.6. Product pH

While the feedstock particle size did not show a clear influence on the product’s pH, the Baker’s yeast strain gave a higher product pH than the palm wine yeast samples. The samples from the palm wine yeast were slightly more acidic (6.2 to 6.4 pH) than the ASTM standard: 6.5 to 6.9. The Baker’s yeast sample from the 212 μm feedstock was also more acidic than the standard, while its 300 μm and 500 μm feedstock samples were within the prescribed standard.

3.4. Effect of Particle Size and Yeast Strain on Product Yield

The amount of sugar produced from the average for each production process condition is shown in Figure 6. From the figure, it can be seen that the 212 μm sample gave the highest sugar output and the 500 μm sample produced the least sugar. The amount of sugar produced from the cellulolysis process generally decreased with increasing particle size. Increased surface reaction area might have accounted for the higher sugar release from the lignocellulose materials.

The ethanol yield from all different sieve sample sizes and yeast types is shown in Figure 7. From the figure, it can be seen that the volume of ethanol produced from the palm wine yeast fermentation was generally considerably higher than the ones from the Baker’s yeast fermentation. This shows that yeast strain has a considerable effect on the yield of ethanol. Adebayo et al. [42] reported higher ethanol yield (20.13%; 201 g/L) from S. cerevisiae ATCC 36858 obtained from the Federal Institute of Industrial Research, Oshodi (FIIRO), Nigeria, than for Baker’s yeast strain (8.53%; 85.3 g/L) in the fermentation of Zea mays cob cellulose-derived sugar. The highest yield from the palm wine yeast samples was observed for the 212 μm particle size sawdust feedstock with a value of 289.8 mL from 250 g of sawdust. There was a continuous decrease in the ethanol yield with increasing particle size of the palm wine yeast samples. Increased surface reaction area might have allowed higher sugar release from the lignocellulose materials as fermentation feedstock which is in line with the theory that increased surface area of reactable material directly affects the rate of reaction and yield of products. However, the ethanol yield of palm wine yeasts ranged between 57.96 and 44.16 mL/100 g of sawdust from the 250 g that was used to start the process of bioethanol production. Also, the ethanol yield of Baker’s yeasts ranged between 42.8and 37.26 mL/100 g of sawdust from the 250 g that was used to start the process of bioethanol production. The ethanol percentage purity was obtained to be 69%. The United States Department of Energy [43] reported that the predicted yield of ethanol from hardwood sawdust was about 40.32 ml/100 g. 20 mL of ethanol per 100 g of molasses was obtained by Gasmalla et al. [33] with a purity of 92%. The ratio of sugar to ethanol produced by palm wine yeast for each particle size is distinctly constant unlike that of Baker’s yeast. Palm wine yeast on average yielded 22% more ethanol when compared to Baker’s yeast. This could be attributed to the high ethanol tolerance of palm wine yeast [44] which results in more fermentation of sugar.

3.5. Economic Implications of Bioethanol Production

A fresh approach to business and the economy is the bioeconomy, also known as the biobased economy. It involves producing food, energy, and industrial goods using regenerative biological resources in a sustainable manner. Additionally, it makes use of the untapped potential that millions of tons of biological waste and leftover materials contain. Bioeconomy is about breaking down plants into their constituent parts as completely as possible and transforming them into valuable materials using biorefineries. Municipal solid biowastes and agrowaste such as sawdust, corn stalk, and rice straw/husk are veritable resources for biofuel refining, pyrolysis for energy generation, and biocompositing. The products such as biochemicals, biofertilizer, bioenergy (bioethanol), and animal feed are enablers of economic growth. Example of countries with increased bioeconomy contribution to gross domestic product (GDP) are Germany and South Africa. In Germany, the total contribution of bioeconomy to the 2021 GDP was 436.6 million Euros, while South Africa had 8.3% of their total 2020 GDP from the bioeconomy sector [45, 46]. Hence, with right policies and programmes, Nigeria will benefit from the huge amount of municipal solid waste and agrowaste that are improperly disposed causing global climate change.

3.6. Conclusion and Recommendations

It has been observed that the particle size of sawdust used in production affected the amount of fermentable sugar produced after acid hydrolysis. The samples with the finest particle size (212 μm) were easier to hydrolyze and produced more sugar than those of 300 μm and 500 μm. This is because the delignification reaction has more contact surface area for the reagent’s attack for the release of cellulose and hemicellulose. It could also be deduced that the type of yeast used for fermentation affects the ethanol yield. The palm wine-derived yeast gave higher sugar fermentation and thus more ethanol production than the Baker’s yeast. While the pH of some of the samples was within the ASTM acceptable, the other ethanol fuel properties like alcohol content, flash point, heating value, and viscosity were not. Improved distillation will help in improving these qualities. Further studies are recommended, including those that may lead to a reduction in the overall cost of production of cellulosic ethanol from waste biomass. Researches in genetic engineered organisms that can directly convert cellulose to bioethanol are desirable. These important developments can help overcome our excessive dependence on fossil liquid fuels and reduce food shortages due to ethanol production from food sources. They will also help in the utilization and management of waste and counter the build-up of greenhouse gases that cause global climate change.

The specific recommendation for the increased production and use of biofuels are that countries need to develop and implement sustainable bioeconomy policies, the countries should have robust STI policy that supports research and innovation, and the share of budgetary allocation to research and innovation should be above United Nation’s recommendation.

Data Availability

The experimental data used to support the findings of this study are included within the article.

Conflicts of Interest

The authors declare no conflict of interest.

Acknowledgments

The University of Nigeria Nsukka, Enugu State, 41000, Nigeria, sponsored this research.

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Copyright © 2023 Desmond Amaefule et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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