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Enzymatic saccharification of solid residue of olive mill in a batch reactor

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Biochemical Engineering Journal 6 (2000) 177–183

Enzymatic saccharification of solid residue of olive mill in a batch reactor

N. Abdi

a

, F. Hamdache

a

, D. Belhocine

a

, H. Grib

a

, H. Lounici

a

, D.L. Piron

b

, N. Mameri

b,∗ a Ecole Nationale Polytechnique d’Alger, 10 avenue Pasteur, B.P. 182, El Harrach, Alger, Algeria

b Ecole Polytechnique de Montréal, Case postale 6079, succ. Centre-ville, Montréal, Que., Canada H3C 3A7 Received 31 January 2000; accepted 11 July 2000

Abstract

This paper describes the enzymatic hydrolysis of solid residue of olive mill (OMRS) in a batch reactor with the Trichoderma reesei enzyme. Before enzymatic saccharification, crude lignocellulosic material is submitted to alkaline pre-treatment with NaOH. Optimum conditions of the pre-treatment (temperature of T 100C and OMRS–NaOH concentration ratio of about R 20) were determined. The optimum enzymatic conditions determined were as follows: pH of about 5, temperature of T 50◦C and enzyme to mass substrate mass ratio E/S 0.1 g enzyme (g OMRS)−1. The maximum saccharification yield obtained at optimum experimental conditions was about 50%. The experimental results agree with Lineweaver Burk’s formula for low substrate concentrations. At substrate concentrations greater than 40 g dm−3, inhibitory effects were encountered. The kinetic constants obtained for the batch reactor were Km = 0.1g dm−3 min−1 and V m = 800 g dm−3. © 2000 Elsevier Science S.A. All rights reserved.

Keywords: Olive mill; Enzyme bioreactors; Saccharification; Batch processing; Optimisation; Product inhibition

1. Introduction

Olive mill wastes are a by-product of olive oil manufacture which cause environmental pollution. Work on the treatment and valorization of these wastes has been conducted over the last decade. Olive mill wastewaters (OMWW), because of their low content in nitrogenous organic components and richness in carbon sources, offer a highly favourable envi- ronment for the growth of dinitrogen-fixing micro-organisms which provide for the biotransformation of OMWW into an agrobiological product [1]. OMWW have been also used as a substrate for high yield production of extracellular polysaccharides [2]. Production of the microalgae Chorella

pyrenoidosa and Scenedesmas obliquas was realized by us-

ing OMWW as a nutrient medium [3].

Considerable research has also been conducted during this past decade on the new possibilities offered by enzymes in lignocellulosic material valorization and or treatment. The literature concerning this research directed towards devel- oping enzymatic systems for solid wastes has been exten- sively reviewed recently [4]. Enzymatic saccharification of

Corresponding author. Present address: Laboratoire TTRL, De´partement Ge´nie Me´canique, Case postale 6079, succ. Centre-ville, Montre´al, Que., Canada H3C 3A7. Tel.: 1-1514-340-4711/ext. 4593; fax: 1-1514-340-4176.

E-mail address: nabil.mameri@courriel.polymtl.ca (N. Mameri).

different lignocellulosic materials has been utilized to prod- uct sugar and other products [5–8]. Before the development of enzymatic saccharification, the various crude lignocellu- losic materials were pre-treated to render them more acces- sible to saccharification, resulting in an increase in sugar production [9–13].

The purpose of this study was to optimize the enzymatic saccharification of olive mill solid residue (OMRS) after pre-treatment with sodium hydroxide and hydrolyzation in the presence of a commercial cellulase: Trichoderma reesei.

2. Materials and methods

2.1. Enzyme and substrate

A commercial enzyme T. Reesei with a fungal origin (Sigma, France) was used. The enzyme has a reported activity of 5.08 units mg−1 (one unit will liberate 1 µmole of glucose from cellulose in 1 h at pH 5 and T 37◦C). Enzyme solutions with concentrations ranging from 0.5–6 g dm−3 were made with an acetic acid/sodium acetate buffer solution (0.05 M and pH 5).

The substrate was olive mill solid residue which had been collected over 3 years (1995–1998) from the Tadmait (Kabylia region) olive oil plant and which was transported to the laboratory at 4◦C. Although the olive mill residue

1369-703X/00/$ – see front matter © 2000 Elsevier Science S.A. All rights reserved. PII: S1369-703X(00)00085-1

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