Elsevier

Biomass and Bioenergy

Volume 34, Issue 8, August 2010, Pages 1189-1194
Biomass and Bioenergy

Fed batch enzymatic saccharification of newspaper cellulosics improves the sugar content in the hydrolysates and eventually the ethanol fermentation by Saccharomyces cerevisiae

https://doi.org/10.1016/j.biombioe.2010.03.009Get rights and content

Abstract

The newspaper is comprised of (w w−1) holocellulose (70.0%) with substantial amount of lignin (16.0%). Bioconversion of the carbohydrate component of newspaper to sugars by enzymatic saccharification, and its fermentation to ethanol was investigated. Of various enzymatic treatments using cellulase, xylanase and laccase, cellulase enzyme system was found to deink the newspaper most efficiently. The saccharification of deinked paper pulp using enzyme cocktail containing exoglucanase (20 U g−1), β-glucosidase (60 U g−1) and xylanase (80 U g−1) resulted in 59.8% saccharification. Among additives, 1% (v v−1) Tween 80 and 10 mol m−3 CoCl2 improved the enzymatic hydrolysis of newspaper maximally, releasing 14.64 g L−1 sugars. The fed batch enzymatic saccharification of the newspaper increased the sugar concentration in hydrolysate from 14.64 g L−1 to 38.21 g L−1. Moreover, the batch and fed batch enzymatic hydrolysates when fermented with Saccharomyces cerevisiae produced 5.64 g L−1 and 14.77 g L−1 ethanol, respectively.

Introduction

Presently most of the bioethanol is produced using corn kernel or sugarcane molasses but lignocellulosics, the second generation biofuel substrate and the least explored renewable resource is yet to be tapped. Lignocellulosics are the most abundant biomass available on earth, comprising mainly of cellulose and hemicellulose [1], [2]. Among various lignocellulosics, the recycled books, magazines and newspaper could have value addition via deinking and reuse of fiber either in manufacturing of new paper or in ethanol production.

An efficient conversion of newspaper to ethanol depends mainly on the extent of carbohydrate saccharification, however, the enzymatic conversion of newspaper is majorly hindered by toner’s ink, which forms a physical barrier, restricting the hydrolysable sites as well as release fermentation inhibitory heavy metal ions [3], [4]. Among various enzymes tested to deink the newspaper pulp [5], only cellulases were found to be the most effective [6]. The deinked paper pulp can be saccharified using either acid [7], [8] or enzymes [9], [10], [11], however, enzymes are preferred over acid because enzymatic hydrolysates are free from any fermentation inhibitory products. The enzymes such as cellulases have been found to be the most effective for this purpose [12]. It is well known that combined action of cellulase and hemicellulase results in a higher sugar production as compared to cellulase alone [13]. Despite the high extent of saccharification efficiency, the lower substrate consistency in the enzymatic suspension resulted into lower sugar concentration during the enzymatic hydrolysis. Raising the substrate concentration in batch hydrolysis helps to obtain higher sugar concentration, but also causes mixing and heat transfer problem due to rheological properties of dense fibrous suspension [14]. While in fed batch hydrolysis, such problem could be avoided by adding the substrate gradually to maintain the low level of viscosity [15]. In the present study, the optimization of enzymatic saccharification using both cellulase and xylanase was carried out to improve the hydrolysis of the newspaper. In order to increase the sugar concentration in enzymatic hydrolysate, the fed batch enzymatic hydrolysis of deinked newspaper was carried out. Thereafter, the enzymatic hydrolysates comprising both the hexose and pentose sugars were fermented to ethanol using Saccharomyces cerevisiae.

Section snippets

Raw material and chemicals

The newspaper procured locally was shredded mechanically into small pieces and the processed substrate was dried in an oven at 80 °C until constant weight was obtained.

Commercial cellulase from Trichoderma reesei (ATCC 26921), β-glucosidase from Aspergillus niger (Novozyme 188), xylanase from Thermomyces languinosus, 1-hydroxylbenzotriazole (HOBT) and 3,5-di nitro salicylic acid (DNS) were purchased from Sigma (St. Louis, Missouri, U.S.A.). Ethanol was purchased from Merck (Darmstadt, Germany).

Compositional analysis of newspaper

Newspaper was found to contain (w w−1), α-cellulose (51.0%), pentosans (19.0%), lignin (16.0%), moisture (8.0%) and ash (2.0%). The high carbohydrate content (holocellulose, 70.0% w w−1) in the newspaper made it a substrate of choice for bioethanol production. The results obtained here were similar to earlier studies, where lignin, holocellulose and moisture content in newspaper were found to be 16–22%, 60–75% and 7–10%, respectively [7], [8].

Deinking of newspaper cellulosics

The dyes fixed on the repeating units of cellulose

Conclusion

The reuse of newspaper for the production of bioethanol seems feasible approach for energy conservation and waste minimization. The fed batch enzymatic hydrolysis of newspaper cellulosics improved the release of sugars (pentose and hexose) and subsequently the ethanol yield. However, the yeast did not utilized pentose sugars from the hydrolysates and non-utilization of pentose sugars limits the economization of ethanol production from cellulosics. Therefore, in order to improve the ethanol

Acknowledgement

The authors are thankful to Dr. Y. P. Khasa for his help during the preparation of this manuscript. The financial support from University of Delhi, Delhi, India is highly acknowledged.

References (39)

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