Detoxification of a Lignocellulosic Waste from a Pulp Mill to Enhance Its Fermentation Prospects

Tamara Llano,Alberto Coz,Natalia Quijorna

doi:10.3390/en10030348

Abstract

Detoxification is required for sugar bioconversion and hydrolyzate valorization within the biorefining concept for biofuel or bio-product production. In this work, the spent sulfite liquor, which is the main residue provided from a pulp mill, has been detoxified. Evaporation, overliming, ionic exchange resins, and adsorption with activated carbon or black carbon were considered to separate the sugars from the inhibitors in the lignocellulosic residue. Effectiveness in terms of total and individual inhibitor removals, sugar losses and sugar-to-inhibitor removal ratio was determined. The best results were found using the cation exchange Dowex 50WX2 resin in series with the anion exchange Amberlite IRA-96 resin, which resulted in sugar losses of 24.2% with inhibitor removal of 71.3% of lignosulfonates, 84.8% of phenolics, 82.2% acetic acid, and 100% of furfurals. Apart from exchange resins, the results of evaporation, overliming, adsorption with activated carbon and adsorption with black carbon led to total inhibitor removals of 8.6%, 44.9%, 33.6% and 47.6%, respectively. Finally, some fermentation scenarios were proposed in order to evaluate the most suitable technique or combination of techniques that should be implemented in every case.

Highlights

Pretreatment and delignification followed by hydrolysis and detoxification prior to fermentation is usually required to assure an efficient bioconversion of lignocellulosic biomass into bio-based chemicals, biopolymers, biofuels and energy
The Sulfite Spent Liquor (SSL) used in overliming, adsorption and ionic resins experiments is composed of 422 ± 31.0 g/L of LS and 214 ± 20.1 g/L of sugars which constitute about 82% w/w of dry matter
Evaporation can be considered as a preliminary detoxification stage with total inhibitor removals of removals of last at the lastevaporation effect

Summary

Introduction

Pretreatment and delignification followed by hydrolysis and detoxification (fractionation) prior to fermentation is usually required to assure an efficient bioconversion of lignocellulosic biomass into bio-based chemicals, biopolymers, biofuels and energy. Optimization of these stages permits the integral use of the feedstock, increasing the lignocellulosic biorefinery economic margins and the global demand for the use of biomass renewable resources. The main objectives to be taken into account in detoxification processes are [1]: (i) low cost of chemicals, solvents and other reagents employed; (ii) minimization of waste generation; (iii) preservation of hemicellulose sugars making them more accessible for fermentation;. Some examples found in the literature in Europe [2], Brazil [3], China [4] or Canada [5] for second-generation bioethanol production from non-food raw materials

Objectives

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Conclusion