Soiene Guiheneuf, Alfredo Santiago Rodriguez Castillo, Ludovic Paquin, Pierre-Francois Biard, Annabelle Couvert, and Abdeltif Amrane

Abstract The coupling of absorption in a gas-liquid contactor and biodegradation in a two-phase partitioning bioreactor (TPPB) has been shown to be a promising technology for the removal of hydrophobic volatile organic compounds. The choice of the organic phase is crucial, and consequently only two families of compounds comply with the requested criteria, silicone oils and ionic liquids. These latter solvents appear especially promising owing to their absorption capacity towards hydrophobic compounds and their low volatility, as well as the possibility of IL tailoring, allowing a fine-tuning of their physicochemical properties, leading to a wide range of products with various characteristics. Some results on common ionic liquids are highlighted in this chapter: biodegradation rates reported by some authors show that phenol biodegradation in the presence of ILs is up to 40 % higher than those obtained in other multiphase reactors; there is a strong affinity of toluene and DMDS for imidazolium salts, [C4Mim][PF6] or [C4Mim][NTf2]. Performance improvements may be expected from the tailoring of ionic liquid structure, espe­cially towards toxicity reduction. Positive results recorded after cell acclimation to target compounds let expect an important gain from more complex acclimation strategies, including microbial acclimation to both ionic liquids and pollutants.

Keywords Absorption • Activated sludge • Biodegradation • Ionic liquids • Two — phase partitioning bioreactors • Toxicity • Volatile organic compounds • Separation

S. Guiheneuf • L. Paquin

Universite de Rennes 1, Sciences Chimiques de Rennes, UMR CNRS 6226, Groupe Ingenierie Chimique & Molecules pour le Vivant (ICMV), Bat. 10A, Campus de Beaulieu, Avenue du General Leclerc, CS 74205, 35042 Rennes Cedex, France

Universite europeenne de Bretagne, Rennes Cedex, France

A. S.R. Castillo • P.-F. Biard • A. Couvert • A. Amrane (*)

Ecole Nationale Superieure de Chimie de Rennes, CNRS, UMR 6226, Avenue du General Leclerc, CS 50837, 35708 Rennes Cedex 7, France

Universite europeenne de Bretagne, Rennes Cedex, France e-mail: abdeltif. amrane@univ-rennes1.fr

Z. Fang et al. (eds.), Production of Biofuels and Chemicals with Ionic Liquids, Biofuels and Biorefineries 1, DOI 10.1007/978-94-007-7711-8_12,

© Springer Science+Business Media Dordrecht 2014

12.1 Introduction

When absorption is used to remove pollutants present in the atmosphere, an aqueous phase is generally employed, either water or water containing reagents (acid, basis, oxidant, etc.). More rarely, some organic phases (solvents) are implemented, but their cost implicates their recycling, and then, their regener­ation. The use of this type of liquid phase becomes primordial when gaseous pollutants belong to hydrophobic compounds family (i. e. toluene, benzene, xylene, etc.) since their affinity for the liquid phase in which they have to be absorbed must be important. This means that there is an important issue in finding new absorbents, displaying high absorption potentialities facing many volatile organic compounds (VOC), and able to be regenerated. For this purpose, absorbent regeneration could be considered after VOC biodegradation; the latter low cost process appears therefore promising. This implies that the solvent will have to fulfil several conditions, especially the absence of biodegradability.

Among the solvents available on the market, a wide number appears biode­gradable, even if an acclimation time is often needed. Indeed, various com­pounds having very low degradation rates or totally refractory towards microorganisms are described as bio-recalcitrant. However, a total absence of biodegradation, even after an acclimation time is required for the proposed process. Therefore and based on biodegradability and biocompatibility criteria, among the available solvents two classes can be selected: silicone oils and ionic liquids [1]. These latter appear especially promising owing to their solvent capacity and their low volatility (saturated vapour pressure close to zero), as well as the possibility of IL tailoring to fit the characteristics required for specific applications [2]. Only few reports are available dealing with the use of ILs for pollutants removal; phenol biodegradation has been investigated in the presence of an IL [3]; while the previous works of Quijano et al. [4, 5] are the only reports dealing with the affinity of ILs for the absorption of hydropho­bic odorous compounds and their biodegradation in a multiphase bioreactor. These works led to promising results for toluene after cell acclimation to the VOC, while for DMDS more complex strategies, including acclimation to ILs, should be subsequently considered.

The potential of this class of compounds for the absorption of hydrophobic VOCs and the subsequent biodegradation of these compounds in a multiphase bioreactor involving ILs (containing the absorbed VOC) as an organic phase and an aqueous phase containing microorganisms are discussed thereafter. The process considered to implement such solvents in a whole operation is schematically described in Fig. 12.1.