Anuj K. Chandel, Ellen C. Giese, Felipe A. F. Antunes, Ivy dos Santos Oliveira and Silvio Silverio da Silva

Abstract Sugarcane residues (bagasse and leaves/trash) are the principal feedstock in Asia, South America, Africa, and other parts of the world. The judicious applica­tion of this feedstock into value-added products such as fuel ethanol, xylitol, organic acids, industrial enzymes, etc. may provide a strong economic platform along with clean and safe environment. Pretreatment is an inevitable process to harness the car­bohydrate fraction of sugarcane bagasse and leaves into readily available sugars by cellulase-mediated process for the production of house-hold commodities. Several methods (physical, physico-chemical, chemical, and biological) have been adopted for the pretreatment of sugarcane residues. Pretreatment methods with pros and cons are employed either to depolymerize hemicellulosic fraction or lignin degradation to make cellulose more amenable for improved cellulolytic enzymes action. The choice of pretreatment methods depends upon its precise mechanistic action on lignin or hemicelluloses with fewer inhibitory products, minimal sugar loss by increasing the cellulosic surface area for subsequent enzymatic action to obtain desired sug­ars recovery. Furthermore, economics and environmental impacts are two important considerations for the selection of pretreatment method. This chapter aims to ex­plore a better understanding of multiple pretreatment methodologies applied to the sugarcane residues along with economics and environmental impacts.

Keywords Sugarcane bagasse ■ Sugarcane leaves ■ Pretreatment ■ Enzyme hydrol­ysis ■ Bioethanol ■ Biomass recalcitrance ■ Fermentable sugars

16.1 Introduction

In recent years, numerous efforts have been considered to harness the commercial potential of sugarcane residues (bagasse and leaves) into value-added products of commercial significance such as ethanol, xylitol, organic acids, industrial enzymes,

A. K. Chandel (H) ■ S. S. da Silva (H) ■ E. C. Giese ■

F. A. F. Antunes ■ I. dos S. Oliveira

Department of Biotechnology, School of Engineering of Lorena, University of Sao Paulo (USP), Lorena 12.602.810, Brazil e-mail: anuj. kumar. chandel@gmail. com; silvio@debiq. eel. usp. br

Z. Fang (ed.), Pretreatment Techniques for Biofuels and Biorefineries,

Green Energy and Technology,

DOI 10.1007/978-3-642-32735-3_16, © Springer-Verlag Berlin Heidelberg 2013

and others [1, 2]. The judicious application of sugarcane based feedstock into com­mercial entities is a sustainable process which may influence the economy at the forefront in sugarcane producing countries [3, 4]. Countries in Asia, Asia pacific, SouthAmerica, andAfrica grow a copious amount of sugarcane, which has a key role in their economy [5]. Table 16.1 presents the major sugarcane producing countries in the world.

Production of sugar from cane juice and ethanol from either juice or cane mo­lasses are two major driving forces of agro-economy in these countries. This impact could be wider if the residues of sugarcane (sugarcane bagasse (SB) and sugarcane leaves(SL/ST)) are being used for the production of household commodities em­ploying biotechnological routes [3, 7]. In 2011, the annual worldwide production of sugarcane residues was recorded around 279 million metric tons [2, 5]. From the data of sugarcane production in the world, it can be estimated that a huge amount of sugarcane residue is generated every year which is totally renewable and could be a promising source of bioenergy and other value-added products generation. Each ton of sugarcane yields about 140 kg of humid bagasse, which is a fibrous residue obtained after crushing sugarcane in sugar producing factories, and is currently used for steam generation in boilers [1, 2, 5]. During the harvesting of sugarcane in agri­culture fields, cane leaf residues are removed from the cane stem and left on the fields, causing loss of green energy [2, 8]. SL/ST is generated in huge amount in fields (6-8 tons from one hectare of sugarcane crop) [8]. Sugarcane derived lignocel — lulosic feedstock (SB and SL/ST) are being used in industries now-a-days for steam or electricity generation. Together, both residues constitute a foreseeable amount of biomass, which can be used for bioethanol production and other bio-products of high economic value (Fig. 16.1).

Apart from bioenergy generation from these residues, products of high economic value such as industrial enzymes, organic acids, food/feed products, amino acids, vitamins or cosmetics can also be produced by microbial fermentation. A lot of re­search work is underway in this line. However, a full technological road-map is yet to come for the industrial production of these commodity chemicals from SB/SL. SB and SL contain an appreciable amount of carbohydrates in cell wall along with the lignin. Pretreatment is an inevitable process to break down the carbohydrate fraction into simpler sugars making them readily available for fermenting by microorganisms

[9-11]. The aim of pretreatment of SB/SL is either to remove lignin or hemicellulose for enhancing the amenability of cellulases toward cellulosic fraction of cell wall. Hemicellulose is generally degraded by weak acid catalyzed process removing its heterogeneity by producing monomeric sugars (xylose, arabinose, mannose, galac­tose, and glucose) [12]. Lignin is degraded by alkali based reactions or microbial action by selective lignin degraders and thus leaving cellulose and hemicellulose net­work together, but in less compacted form. The pretreated material is subsequently hydrolyzed by cellulolytic enzymes for sugar recovery toward the fermentation of

other value-added products [1,2, 12, 13]. In past, a number of pretreatment strate­gies (physical, physico-chemical, chemical, and biological) have been developed by researchers considering hemicellulose and/or lignin removal [9-11, 14-17]. An ideal pretreatment method should render lignocellulosics completely susceptible to the action of cellulases, be economic, and pose less environmental pollution load [10, 13, 17]. This chapter describes the various pretreatment strategies applied to the sugarcane residues, process parameters, mechanism of pretreatment methods, economic, and environmental aspects.