Absorption of toluene in silicone oil: effect of the solvent viscosity on hydrodynamics and mass transfer

International audienceThe purpose of this study was to compare toluene absorption performances using two PDMS of different viscosities (η = 5 and 50 mPas respectively) in terms of hydrodynamics and mass transfer. Three types of packing were tested in a counter-current packed gas-liquid contactor, Raschig rings, IMTP®, and Flexipac®. Hydrodynamic results showed that the viscosity of PDMS 50 is not a hurdle to be used with IMTP® or Flexipac®; the pressure drop being around 288 Pa m−1 for Flexipac® at the flooding point (FG = 0.99 Pa1/2; L’ = 4.95 kg m−2 s−1), which corresponds to an acceptable value for an industrial application. The determination of the loading zones showed that Raschig rings were not suitable for solvents having a high viscosity, such as PDMS 50; they resulted in high pressure drops if compared to IMTP® and Flexipac®. The mass transfer study showed that 100% removal efficiency can be reached for both PDMS using Flexipac®. For IMTP®, the removal efficiency is limited to 88% in the presence of PDMS 50. As a result, PDMS 50 should be a relevant absorbing liquid for the removal of toluene in the absorption–biodegradation process, and Flexipac® packing should be preferred to IMTP

Removal of gas-phase ammonia and hydrogen sulfide using photocatalysis, nonthermal plasma, and combined plasma and photocatalysis at pilot scale.

International audienceThis study focuses on the removal of gas-phase ammonia (NH3) and hydrogen sulfide (H2S) in a continuous reactor. Photocatalysis and surface dielectric barrier discharge (SDBD) plasma are studied separately and combined. Though the removal of volatile organic compounds by coupling plasma and photocatalysis has been reported on a number of studies in laboratory scale, this is as far as we know the first time that it is used to remove inorganic malodorous pollutants. While each separate process is able to degrade ammonia and hydrogen sulfide, a synergetic effect appears when they are combined at a pilot scale, leading to removal capacity higher than the sum of each separate process. The removal capacity is higher when the gas circulates at a higher flow rate and when pollutant concentration is higher. The presence of water vapor in the gas is detrimental to the efficiency of the process. Operating conditions also influence the production of nitrogen oxides and ozone

Toluene degradation by a water/silicone oil mixture for the design of two phase partitioning bioreactors

International audienceToluene degradation performances were studied in a 10 L Two-Phase Partitioning Bioreactor (TPPB). The liquid phase consisted of a mixture of water and PDMS 50 (Poly DiMethylSiloxane, i.e. silicone oil, viscosity of 46 mPa.s) in the volume ratio of 75%/25%. Two series of experiments were carried out: in the first, the reactor was sequentially supplied with toluene whereas in the second, toluene was continuously supplied. Activated sludge from the wastewater treatment plant of Beaurade (Rennes, France) was used at an initial concentration of 0.5 dry mass g.(mixture L)(-1). The elimination capacity (EC) was investigated as well as the change in biomass concentration over time. Toluene biodegradation was very efficient (removal efficiency, RE = 100%) for toluene flows ranging from 0.2 to 1.2 ml.h(-1), corresponding to elimination capacities of up to 104 g.m(-3).h(-1). For a toluene flow of 1.2 ml.h(-1), the biomass concentration measured at the end of the experiment was 4.7 dry mass g.(mixture L)(-1). The oxygen concentration in the liquid phase was clearly not a limiting factor in these operating conditions. Based on these results, an extrapolation leading to the design of a large-scale pilot TPPB can now be considered to study toluene degradation performances in industrial conditions

Absorption of toluene in silicone oil: effect of the solvent viscosity on hydrodynamics and mass transfer

International audienc

Determination of the toluene removal capacity of a semi-continuous two-phase partitioning bioreactor

International audienc

Characterization and selection of PDMS solvents for the absorption and biodegradation of hydrophobic VOCs

International audienceBACKGROUND : Four silicone oils (PolyDiMethylSiloxane, PDMS) of different viscosities, namely 5, 20, 50, and 100 mPa s were characterized to select the most suitable polymer for the biol. treatment of toluene. The PDMS volatilities and the partition coeffs. of toluene between air and PDMS were investigated. Toluene biodegrdn. tests were also carried out to assess the absence of toxicity of the considered PDMS vis-a-vis the microorganisms. RESULTS : PDMS 20, 50 and 100 had negligible volatilities at 25 °C and 35 °C, whereas PDMS 5 was volatile even at 25 °C. The results indicate that the amt. of VOCs emitted by PDMS increased with the temp. according to a logarithmic law. The partition coeff. of toluene between air and the four PDMS were similar (H = 2.9 Pa m3 mol-1) indicating that the affinity between toluene and PDMS was identical whatever their viscosity. Moreover, biodegrdn. tests allowed the conclusion that the four PDMS tested are not toxic for microorganisms. CONCLUSION : PDMS 20, 50 and 100 were suitable at 25 °C for the biol. treatment of toluene. Since all these PDMS were satisfactory at 25 °C, it could make sense to select the least viscous oil for use in the process, i.e. PDMS 20. © 2015 Society of Chem. Industry

Role of the Type VI secretion system of Pseudomonas fluorescens Pf29Arp in biofilm process.

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Separation of silicone oil droplets dispersed in activated sludge

International audienceA process in three steps involving a gas-liquid contactor with an organic phase, a TPPB and a liquid/liquid separator to recover the organic phase for its recycling was proposed to treat hydrophobic Volatile Organic Compounds. Among the processes tested for liquid/liquid separation (settling, hydrocyclone and centrifugation), the latter appeared to be the most efficient. The centrifugal acceleration needed for the separation of oil and water was found to be dependent on the viscosity of the oil used and the presence of microorganisms. The force required for phases' separation was found to be reduced in the presence of selected commercial demulsifiers

Influence of Belowground Herbivory on the Dynamics of Root and Rhizosphere Microbial Communities

International audienceRecent studies are unraveling the impact of microorganisms from the roots and rhizosphere on interactions between plants and herbivorous insects and are gradually changing our perception of the microorganisms' capacity to affect plant defenses, but the reverse effect has seldom been investigated. Our study aimed at determining how plant herbivory influences the dynamics of root and rhizosphere microbial community assemblages and whether potential changes in root metabolites and chemical elements produced during herbivory can be related to microbial community diversity. We conducted our study on oilseed rape (Brassica napus) and its major belowground herbivore, the cabbage root fly (Delia radicum). We further assessed the influence of initial soil microbial diversity on these interactions. Different microbial diversities based on a common soil matrix were obtained through a removal-recolonization method. Root and rhizosphere sampling targeted different stages of the herbivore development corresponding to different perturbation intensities. Root bacterial communities were more affected by herbivory than some rhizosphere bacterial phyla and fungal communities, which seemed more resistant to this perturbation. Root herbivory enhanced the phylum of gamma-Proteobacteria in the roots and rhizosphere, as well as the phylum of Firmicutes in the rhizosphere. Herbivory tended to decrease most root amino acids and sugars, and it increased trehalose, indolyl glucosinolates, and sulfur. Higher abundances of four bacterial genera (Bacillus, Paenibacillus, Pseudomonas, and Stenotrophomonas) were associated following herbivory to the increase of trehalose and some sulfur-containing compounds. Further research would help to identify the biological functions of the microbial genera impacted by plant infestation and their potential implications in plant defense