Multi-criteria analysis of detoxification alternatives: Techno-economic and socio-environmental assessment

Tamara Llano,Cristina Rueda,Elena Dosal,Ana Andrés,Alberto Coz

doi:10.1016/j.biombioe.2021.106274

Abstract

The transformation of fermentable sugars provided from lignocellulosic wastes into biofuels or bioproducts is a key point at second-generation biorefineries. Spent sulfite liquor is a xylose-rich hydrolysate constituting the main residue of sulfite mills producing dissolving cellulose. Due to the presence of the inhibitors in the spent liquor, the most promising valorization options require detoxification before sugars bioconversion.In this work, a multi criteria analysis was implemented to select techno-economic and socio-environmental feasible detoxification alternatives that can be adapted to a wide variety of fermenting scenarios. Total inhibitors removal, phenolics removal, acetic acid removal, lignosulfonates removal, total sugar losses, fixed capital invested, manufacturing costs, waste toxicity, social acceptance, and employment were chosen as the most relevant criteria. The maximum allowable concentration of undesirable inhibitors cannot be established with a general character, and thereby decision-making tools result in feasible and efficient solutions. From a technical viewpoint best solution was anionic resins with a score of 0.68; the most economical alternative was the overliming with a score of 0.76; finally, from a socio-environmental perspective, overliming reached the highest score of 0.78. In addition, three spent liquor biorefinery models were proposed. Based on the multi-criteria analysis and based on the inhibitor's concentration affecting fermentation yields and productivity, the best detoxification alternatives were (1) anionic resins for polyhydroxyalkanoate production; (2) activated carbon for ethanol biorefinery; (3) overliming for xylitol biorefinery.

Highlights

During the last years, many manufactures are trying to transform their processes by minimizing and re-using the obtained wastes in a circular economy thinking
This work is focused on the spent liquor obtained after the sulfite cooking process, that is, a chemical engineering process whose objective is the separation of the fibrous constituent of the wood from the binding agent through the action of several chemicals in digesters at high temperatures and pressure
One of the key challenges to overcome in acid sulfite P&P mills for scaling up into second-generation biorefineries relies on detoxification. Considering this step as the bottleneck, this study aims to establish which kind of detoxification is the most suitable for specific yeast and bacterial fermentation by using an Multi-Criteria Analysis (MCA)-based methodology

Summary

Introduction

Many manufactures are trying to transform their processes by minimizing and re-using the obtained wastes in a circular economy thinking. This work is focused on the spent liquor obtained after the sulfite cooking process, that is, a chemical engineering process whose objective is the separation of the fibrous constituent of the wood (the cellulose) from the binding agent (the lignin) through the action of several chemicals (acid) in digesters at high temperatures and pressure Once this process ends, on one hand, the pulp is obtained and must be washed, bleached, and dried; and on the other hand, the spent sulfite liquor, known as SSL is concentrated to produce energy or to be sold for further treatment [3,4,5]. One of the most promising valorization alternatives consists of their bioconversion into xylitol, ethanol, furfural, poly hydroxyalkanoates, succinic acid, hydrogels, or fertilizers among others [9,10]

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