Ethanol Production from High Solid Loading of Rice Straw by Simultaneous Saccharification and Fermentation in a Non-Conventional Reactor

Inês C Roberto,Rafael C A Castro,João Paulo A Silva,Solange I Mussatto

doi:10.3390/en13082090

Abstract

Simultaneous saccharification and fermentation (SSF) at high solid loading is a potential approach to improve the economic feasibility of cellulosic ethanol. In this study, SSF using high loading of rice straw was assessed using a vertical ball mill reactor. First, the conditions of temperature and number of glass spheres were optimized at 8% (w/v) initial solids (41.5 °C, 18 spheres). Then, assays were carried out at higher solid loadings (16% and 24% w/v). At 8% or 16% solids, the fermentation efficiency was similar (ηF~75%), but the ethanol volumetric productivity (QP) reduced from 1.50 to 1.14 g/L.h. By increasing the solids to 24%, the process was strongly affected (ηF = 40% and QP = 0.7 g/L.h). To overcome this drawback, three different feeding profiles of 24% pre-treated rice straw were investigated. Gradual feeding of the substrate (initial load of 16% with additions of 4% at 10 and 24 h) and an inoculum level of 3 g/L resulted in a high ethanol titer (52.3 g/L) with QP of 1.1 g/L.h and ηF of 67%. These findings demonstrated that using a suitable fed-batch feeding strategy helps to overcome the limitations of SSF in batch mode caused by the use of high solid content.

Highlights

The first-generation ethanol production based on well-established processes from sugarcane and corn as feedstock will not be able to satisfy the world’s growing energy needs
This study demonstrated that the vertical ball mill (VBM) reactor, equipped with an adjustable flat-disk impeller and operated with glass spheres as shear agents, can be effectively used for processing lignocellulosic biomass at high solid loading
Simultaneous saccharification and fermentation (SSF) operation in fed-batch mode was an efficient strategy for ethanol production from pre-treated rice straw at high solid loading (24% w/v)

Summary

Introduction

The first-generation ethanol production based on well-established processes from sugarcane and corn as feedstock will not be able to satisfy the world’s growing energy needs. Lignocellulosic biomass is viewed as a key feedstock to provide enough renewable energy for the future [1]. Among the different types of lignocellulosic biomass, agricultural residues including rice straw, corn stover, wheat straw and sugarcane bagasse have been pointed out as the major feedstock for ethanol production due to their large availability and high content of polysaccharides (cellulose and hemicellulose) that can be hydrolyzed into fermentable sugars [2]. In addition to the large availability and significant content of polysaccharides, non-sugar fractions and wastes generated during the biomass processing could be converted into valuable products, adding value within a biorefinery [4]. Since the technologies required to obtain fermentable sugars from lignocellulosic feedstock are more complex, the costs of the second-generation ethanol production are still higher when compared to the first-generation ethanol production [5]

Objectives

Methods

Results

Conclusion