Mars, 2020

16mar14 h 00 min16 h 00 minSoutenance de thèse de Yin ZHU

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Détails

«Evaluation de la nanofiltration pour l’extraction d’acides gras volatils produits par fermentation».

Le jury sera composé de :

  • Romain KAPEL (Université de Lorraine), Rapporteur
  • Mme Violaine ATHèS (AgroParisTech, Paris), Rapporteure
  • Mme Claire DUMAS (TBI, Université de Toulouse), Examinatrice
  • Mme Anne-Cécile VALENTIN (Aquasource General Manager, SUEZ), Examinatrice
  • José LUIS CORTINA (Université Polytechnique de Catalogne, Espagne) Examinateur
  • Mme Hélène ROUX-DE BALMANN (LGC, Université de Toulouse), Directrice de thèse
  • Sylvain GALIER (LGC, Université de Toulouse), Co-directeur de thèse

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Evaluation of nanofiltration for the extraction of Volatile Fatty Acids from fermentation broth“.

Résumé/Abstract

Nanofiltration (NF) is a pressure-driven membrane process used for liquid-phase separation, which is promising for biomass separation and purification. In this work, two NF membranes (NF-45 and XLE) are used for the separation and valorization of volatile fatty acids (VFAs), one kind of useful chemical building blocks, from fermentation broth produced using municipal solid waste.

The objective of this work is to investigate NF process for the separation and purification of VFAs from fermentation broth. Experiments are carried out with synthetic solutions with increasing complexities, from single, binary and ternary solutions of VFAs, i.e., acetic (Ac), propionic (Pr), and butyric acid (Bu), to mixed solutions containing VFAs and inorganic salts at different compositions. The influence of ionic composition as well as of the solution pH on the transfer of the solutes are discussed. Then, a real fermentation broth containing three VFAs, inorganic ions and organic matters is also investigated.

For synthetic solutions containing dissociated VFAs (pH 8), it is observed that for a given VFAs proportion in the feed, regardless of the total concentration, the proportion of VFAs in the permeate remains constant when the filtration flux is higher than a specific value. From the perspective of mass transfer, this observation means that in a mixed solution, the individual charged solute transfer is controlled by the total amount of charge transferred through the membrane. Indeed, it is found that the individual VFA flux increases linearly with the total solute flux and does not depend on the total concentration but only on the VFAs proportions in the feed.

More complex solutions containing VFAs with the addition of three inorganic salts (Na2SO4, NaCl, and CaCl2) are further investigated. Again, constant permeate proportions for organic and inorganic solutes (anions as well as cations) are observed for a given feed proportion, when the filtration flux is higher than a certain value. Then, it is concluded that, for any couple of VFAs (Ac/Pr, Pr/Bu, or Ac/Bu), the plateau value of the relative proportion of the individual VFA in the permeate is nearly fixed by its proportion in the feed, for all the conditions investigated. This conclusion can be extended to couples of VFAs/inorganic anions and couples of cations.

Solution pH significantly changes the retention of VFAs and the permeate proportion of VFAs. A model to describe the VFAs retention versus pH is presented. It is shown that the model can describe the retention of VFAs versus solution pH by considering an increase of the VFAs pKa values by about 1.2 units or a membrane effective pKa value of about 5.4 to 5.8.

Finally experiments are carried out with a real fermentation broth. It is observed that whatever charged or uncharged solutes, even for unknown organic matters in the real fermentation broth, a constant proportion in permeate is observed when the filtration flux is higher than a certain value. This observation indicates that the plateau value could be related to the nature of solutes and membranes, and this method could be used to compare the separation performances of different membranes. Separation factor is used to characterize the separation performance of the two membranes on the real fermentation broth. The separation factors between VFAs in the real fermentation broth are higher than those obtained with synthetic solutions, indicate that there are additional parameters that could influence the separation performance of the nanofiltration process. The NF-45 membrane can more efficiently change the VFAs proportion in the permeate, Ac and Pr are greatly enriched in the permeate, while Bu is enriched in the retentate. The XLE membrane has a very high VFAs retention (>95%), it can change the proportion of VFAs and other organic matters (OM) in the permeate, and can be used to concentrate the VFAs fermentation broth and remove the hindering organics such as ethanol.

Date et heure

(Monday) 14 h 00 min - 16 h 00 min

Location

Amphi 2 de la Maison de la Valorisation et de la Recherche (MRV)

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