LuizJ. Visioli, Fabiane M. Stringhini, Paulo R. S. Salbego, Daniel P. Chielle,
Gabrielly V. Ribeiro, Juliana M. Gasparotto, Bruno C. Aita, Rodrigo Klaic,

Jessica M. Moscon, Marcio A. Mazutti*

Department of Chemical Engineering, Federal University of Santa Maria, Santa Maria, Brazil
* Corresponding author email: mazutti@ufsm. br

OUTLINE

INTRODUCTION

The last years have verified a pronounced demand for fossil fuels worldwide due to increase in industriali­zation and motorization (Agrawal et al., 2007). Nowa­days, fossil fuels represent around 80% of all primary energy consumed in the world, where 58% is employed in the transport sector (Escobar et al., 2009). The esti­mates show that the global energy demand is projected to grow by more than 50% by 2025, with much of this in­crease in demand emerging from several rapidly devel­oping nations. Clearly, increasing demand for finite petroleum resources cannot be a satisfactory policy for the long term (Ragauskas et al., 2006).

Biofuels are a renewable energy source produced from natural (plant) materials, which can be used as a substitute for petroleum fuels (Demirbas, 2011). The global demand for liquid biofuels more than tripled in last decade, indisputably showing the increasing trend
toward the use of fuels derived from plant feedstock (Ferreira-Leitao et al., 2010).

Agroindustrial and forestry residues, which are by­products of key industrial and economical activities, stand out as potential raw materials for the production of renewable fuels, chemicals and energy (Ferreira- Leitao et al., 2010). Biofuels can also be derived from fishery products or municipal wastes, also including by-products and wastes originated from agroindustry, food industry and food services (Nigam and Singh,

2011) . The key advantage of the utilization of renewable sources for the production of biofuels is the utilization of natural bioresources (that are geographically more evenly distributed than fossil fuels) and the produced bioenergy provides independence and security of en­ergy supply (Nigam and Singh, 2011). The use of agricul­tural residue and waste substrates as raw materials is advantageous as their availability is not hindered by a requirement for arable land for the production of food

Bioenergy Research: Advances and Applications http://dx. doi. org/10.1016/B978-0-444-59561-4.00003-6

and feed. Reusing agricultural waste products is one goal of environmental sustainability and has become an option to add value to producers (Manique et al.,

2012) . In addition, waste utilization prevents its accumu­lation, which is of great environmental concern due to its potential for contamination of rivers and underground water (Ferreira-Leitao et al., 2010).

The most well-known first-generation biofuel is ethanol (Nigam and Singh, 2011), which is currently be­ing produced from sugarcane or corn and will often be referred to as bioethanol (Demirbas, 2011). Ethanol has long been considered as a suitable alternative to fossil fuels either as a sole fuel in cars with dedicated engines or as an additive in fuel blends with no engine modifica­tion requirement when mixed up to 30%. Today, bio­ethanol is the most dominant biofuel and its global production showed an upward trend over the last 25 years. Worldwide production capacity in 2006 was about 49 x 109 liters per year, and total output in 2015 is forecast to reach over 115 x 109 liters (Talebnia et al., 2010).

Feedstock containing significant amounts of sugar, or materials that can be converted into sugars, such as starch or cellulose, can also be used in the production of ethanol (Nigam and Singh, 2011). The production of ethanol from cellulosic feedstock has a growing interest worldwide. Cellulosic biomass is an abundant renew­able resource on earth and includes various agricultural residues. Some of these agricultural residues such as straw, corn husk, and sugarcane residue represent an abundant, inexpensive, and readily available source of renewable lignocellulosic biomass. At the present time, this readily available biomass is considered as a waste and is disposed of through agricultural burning after harvest (Dawson and Boopathy, 2007).

Agricultural residues are produced in large quantities throughout the world. Approximately, 1 kg of residue is produced for each kilogram of grain harvested. These residues are renewable resources that could be used to produce ethanol and many other value-added products (Dawson and Boopathy, 2007). Among these residues, ethanol can be produced from biomass feedstocks such as sucrose-containing feedstocks (e. g. sugar beet, sweet sorghum, and sugarcane), starchy materials (e. g. wheat, corn, barley, cassava, and rice), and lignocellulosic biomass (e. g. wood, straw, grasses, and various crop res­idues). These biomass feedstocks can reduce about 50% of the price of the ethanol produced, depending on the type of the biomass used (Hong and Yoon, 2011).

Lignocellulosic waste materials obtained from energy crops, wood and agricultural residues represent the most abundant global source of renewable biomass. Among the agricultural residues, wheat straw is the largest biomass feedstock in Europe and the second largest in the world after rice straw. About 21% of the world’s food depends on the wheat crop and its global production needs to be increased to satisfy the growing demand of human consumption; therefore, wheat straw would serve as a great potential feedstock for produc­tion of ethanol in the twenty-first century (Talebnia et al., 2010).

The use of lignocellulosic energy crops, and particularly low-cost biomass residues, offers excellent perspectives for large-scale application of ethanol in transportation fuels. These materials will increase the ethanol production capacity and reduce production cost to a competitive level. Bioethanol from these materials provides a highly cost — effective option for CO2 emission reduction in the trans­portation sector (Patle and Lal, 2007).

The utilization of lignocellulosic biomass has been closely associated with a new technological concept, so-called biorefinery, which emerges as key to the significant expansion of the desired production of ethanol. Fermentative processes stand out, where microbial metabolism is used for the transformation of simple raw materials in products with high aggre­gate value. Experts believe that the biorefineries are likely to be a key industry of the twenty-first century, even responsible for a new industrial revolution, because of the importance of the technologies they employ and their effects on the actual industrial model (Santos et al., 2010).

Regarding crop residues that have proper application in energy supply, the energetic generation cost for useful energy is a matter for consideration. Studies done so far suggest that, when transport distances are similar, the most efficient energetic use of lignocellulosic materials such as agricultural residues is the application for the generation of electricity. Applied in this way, crop resi­dues are most efficient in replacing fossil fuels, much more so than when crop residues are converted to ethanol for use in cars. However, when road transport distances to power-generating plants are very large, it may be that energetic uses that require a much lower input of transport fuel become energetically more attrac­tive (Reijnders, 2008).

Based on these aspects, the main objective of this work is to present an overview about bioethanol production from agroindustrial residues, which were based on low-priced feedstocks such as crop residues, municipal/industrial solid waste, and food residues. For this purpose, papers and overviews since 2006 were reported.