Mass transfer coefficients of styrene into water/silicone oil mixtures: New interpretation using the "equivalent absorption capacity" concept.

International audienceThe physical absorption of styrene into water/silicone oil systems at a constant flow rate for mixtures of different compositions (silicone oil volume fraction ϕ = 0%, 1%, 2%, 3%, 4%, 5%, 6%, 8%, and 10%) was investigated in laboratory-scale bubble reactors using a dynamic absorption method. Experimental results previously analyzed assuming no contact between gas and silicone oil [10] were reconsidered by applying the "equivalent absorption capacity" concept characterized by the value of the styrene partition coefficient between air and the mixture (Hmix). The results indicate that silicone oil addition slightly hinders the styrene mass transfer rate compared to the air/water system. Moreover, a dramatic decrease in KLa values due to silicone oil addition is observed. In comparison with similar measurements available in the literature, it is noted that this decrease in KLa value could be related to the change in the partition coefficient ratio mR = Hwater/Hoil. Two explanations concerning the relationship between the change in a hydrodynamic parameter (KLa) and that in a thermodynamic parameter (mR) are proposed. Finally, it appears questionable to study the change in KLa in terms of silicone oil addition

Development of Partial Least Square models for the prediction of the concentration of a gustative stimulus in water from physiological data

International audienceClassical physicochemical or sensory methodologies are often inadequate to describe the perception of water and their correlation is complicated. Indeed, the taste of water is difficult to describe due to low concentrations of sapid molecules. The aim of this work was to combine sensory and physiological measurements in order to correlate data with chemical properties of sapid solutions

Removal of Hydrophobic Volatile Organic Compounds in an Integrated Process Coupling Absorption and Biodegradation -- Selection of an Organic Liquid Phase

International audienceSince usual processes involve water as ab- sorbent, they appear not always really efficient for the treatment of hydrophobic volatile organic compound (VOC). Recently, absorption and biodegradation cou- pling in a two-phase partitioning bioreactor (TPPB) proved to be a promising technology for hydrophobic compound treatment. The choice of the organic phase, the non-aqueous phase liquid (NAPL) is based on various parameters involved in both steps of the pro- cess, hydrophobic VOC absorption in a gas - liquid contactor, and biodegradation in the TPPB. VOC sol- ubility and diffusivity in the selected NAPL, as well as NAPL viscosity, seems to be the main parameters during the absorption step, while biocompatibility, namely the absence of toxic effect of the NAPL to- wards microorganisms, non-biodegradability and VOC partition coefficient between NAPL and water were revealed as the key factors during the biodegra- dation step. The screening of the various NAPL avail- able in the literature highlighted two families of compounds matching the required conditions for the proposed integrated process, silicone oils and ionic liquids

Adsorption of pharmaceuticals onto activated carbon fiber cloths - Modeling and extrapolation of adsorption isotherms at very low concentrations

International audienceActivated carbon fiber cloths (ACFC) have shown promising results when applied to water treatment, especially for removing organic micropollutants such as pharmaceutical compounds. Nevertheless, further investigations are required, especially considering trace concentrations, which are found in current water treatment. Until now, most studies have been carried out at relatively high concentrations (mg L(-1)), since the experimental and analytical methodologies are more difficult and more expensive when dealing with lower concentrations (ng L(-1)). Therefore, the objective of this study was to validate an extrapolation procedure from high to low concentrations, for four compounds (Carbamazepine, Diclofenac, Caffeine and Acetaminophen). For this purpose, the reliability of the usual adsorption isotherm models, when extrapolated from high (mg L(-1)) to low concentrations (ng L(-1)), was assessed as well as the influence of numerous error functions. Some isotherm models (Freundlich, Toth) and error functions (RSS, ARE) show weaknesses to be used as an adsorption isotherms at low concentrations. However, from these results, the pairing of the Langmuir-Freundlich isotherm model with Marquardt's percent standard of deviation was evidenced as the best combination model, enabling the extrapolation of adsorption capacities by orders of magnitude

Analysis of chlordecone by LC/MS-MS in surface and wastewaters

International audienceChlordecone (also known as Kepone) was used extensively in the French West Indies until 1993. This persistent pollution raises the question of the faith of this pesticide through water treatment plants and its eventual release in the environment. To address this issue, a two-step methodology is herein proposed. First, a complete description of the analysis of \CLD\ is given using liquid chromatography with mass spectrometry (LC/MS-MS). The reliability of this analytical methodology was demonstrated in ultrapure water as well as in the presence of organic and/or inorganic compounds (groundwater, river water and nutritive solutions). The limits of quantification were decreased to 1.5 μg L−1. In a second part, the removal of \CLD\ is considered via the sorption onto activated sludge. Kinetics and isotherms of sorption were determined. Very short times (less than 5 min) were observed to reach the equilibrium. Moreover, a linear relationship was determined for the sorption equilibrium, which led to the conclusion that the solid/liquid partition coefficient was 7600 L kg−1, i.e. log KOC of 3.88, very close to the values encountered for the sorption of \CLD\ in soils

Equivalent Absorption Capacity (EAC) concept applied to the absorption of hydrophobic VOCs in a water/PDMS mixture

International audienceAbsorption of hydrophobic Volatile Organic Compounds (VOCs) in multiphase system gas water PolyDiMethylSiloxane (PDMS, i.e. silicone oils) was considered. Absorption experiments were carried out in a countercurrent gas-liquid absorber filled with Raschig rings as packing. Three absorbing liquids, water, PDMS and a mixture of water/PDMS (90/10 v/v) were used to transfer toluene and dimethyl disulfide (DMDS) selected as VOC targets. Moreover, the Equivalent Absorption Capacity (EAC) concept previously developed to characterize the mixtures of water/PDMS was applied to the experimental data obtained at three different gas flow rates (18, 25 and 32 m3 h-1). Experimental measurements showed that absorption efficiencies (E) were low for water (around 2-8% for toluene and around 12-25% for DMDS) and higher for PDMS (from 88% to 98% according to the operating conditions). For the water/PDMS mixture, it was shown that the PDMS addition increased significantly the absorption of pollutants (E values in the range 25 to 65% according to the operating conditions). Besides, it was emphasized that the EAC concept describes satisfactorily the absorption behavior of the water/PDMS mixture. Finally, results confirmed that pure PDMS has to be used rather than a (90/10 v/v) water/PDMS mixture for hydrophobic VOC absorption. Using pure PDMS as absorbing liquid (dynamic viscosity of 5 mPa s), high absorption efficiencies (up to 98%) were obtained for L’/G’ value around 5 (L’/G’ corresponding to the ratio between the specific flow of the liquid and the specific flow of the gas). Under such conditions, pressure drops (ΔP) in the packed column and overall mass transfer coefficients (KLa) were around 1000 Pa m-1 (G’ = 1.06 kg m-2 h-1) and 5 10-3 s-1, respectively

Biofiltration of high concentration of H2S in waste air under extreme acidic conditions

International audienceRemoval of high concentrations of hydrogen sulfide using a biofilter packed with expanded schist under extreme acidic conditions was performed. The impact of various parameters such as H2S concentration, pH changes and sulfate accumulation on the performances of the process was evaluated. Elimination efficiency decreased when the pH was lower than 1 and the sulfate accumulation was more than 12 mg S-SO42-/g dry media, due to a continuous overloading by high H2S concentrations. The influence of these parameters on the degradation of H2S was clearly underlined, showing the need for their control, performed through an increase of watering flow rate. A maximum elimination capacity (ECmax) of 24.7 g m−3 h−1 was recorded. As a result, expanded schist represents an interesting packing material to remove high H2S concentration up to 360 ppmv with low pressure drops. In addition, experimental data were fitted using both Michaelis–Menten and Haldane models, showing that the Haldane model described more accurately experimental data since the inhibitory effect of H2S was taken into accoun

Volumetric mass transfer coefficients characterising VOC absorption in water/silicone oil mixtures

International audienceThe physical absorption of three Volatile Organic Compounds (dimethyldisulphide (DMDS), dimethylsulphide (DMS) and toluene) in "water/silicone oil" systems at a constant flow rate for mixtures of different compositions (f = 0, 5, 10, 15, 20 and 100%) was investigated using a dynamic absorption method. The results indicate that silicone oil addition leads to a dramatic decrease in KLa which can be related to the change in the partition coefficient (Hmix). They confirm the results obtained for styrene absorption using another measurement technique [15]. The interpretation of the results using dimensionless ratios KLa(f)/KLa(f=0%) and KLa(f)/KLa(f=100%) versus f also confirms the importance of the partition coefficient ratio mR = Hwater/Hoil in the KLa change. Moreover, the results obtained for toluene absorption in "air/water/silicone oil" systems (f = 10, 15 and 20%) suggest that the mass transfer pathway is in the order gas→water→oil for these operating conditions

Hydrophobic VOC absorption in two-phase partitioning bioreactors; influence of silicone oil volume fraction on absorber diameter.

International audienceA methodology to determine the diameter of an absorber contacting a gas phase and two immiscible liquid phases (water/silicone oil mixture) is presented. The methodology is applied to a countercurrent gas/liquid randomly packed column for the absorption of three VOCs (toluene, dimethyl sulfide, or dimethyl disulfide). Whatever the silicone oil volume fraction, Eckert's generalized pressure drop correlation was used. The results present the change in the column diameter through the change in the dimensionless ratio D(ϕ)/D(ϕ=1) versus the silicone oil volume fraction for the same operating conditions. For toluene and dimethyl disulfide, characterized by Hvoc,silicone oil values equal to 2.3 and 3.4 Pa m3 mol−1, respectively, it is highlighted that it is unwise to use water/silicone oil mixtures for mass transfer. In these cases, the contact between the polluted air and pure silicone oil requires roughly the same amount of silicone oil as for a (90/10 v/v) water/silicone oil mixture, but enables a 2-fold decrease in the column diameter. For dimethyl sulfide, which is characterized by a larger partition coefficient value (Hvoc,silicone oil=17.7 Pa m3 mol−1), the mass transfer operation should not be considered because large amounts of silicone oil are required (whatever the silicone oil volume fraction), which is not acceptable from an economic point of view. The feasibility of using a bioscrubber for the treatment of hydrophobic pollutants depends mainly on the partition coefficient Hvoc,silicone oil. VOC absorption in TPPB should therefore be restricted to pollutants characterized by a Hvoc,silicone oil value of around 3 to 4 Pa m3 mol−1 or less. In this case, absorption can be efficiently carried out in a biphasic air/silicone oil system

Characterization of gaseous odorous emissions from a rendering plant by GC/MS and treatment by biofiltration.

International audienceThis research focuses on the identification and quantification of odorous components in rendering plant emissions by GC/MS and other analytical methods, as well as the description of phenomena occurring in biofilter in order to improve the removal efficiency of industrial biofilters. Among the 36 compounds quantified in the process air stream, methanethiol, isopentanal and hydrogen sulfide, presented the major odorous contributions according to their high concentrations, generally higher than 10 mg m(-3), and their low odorous detection thresholds. The elimination of such component mixtures by biofiltration (Peat packing material, EBRT: 113 s) was investigated and revealed that more than 83% of hydrogen sulfide and isopentanal were removed by biofilter. Nevertheless, the incomplete degradation of such easily degradable pollutants suggested inappropriate conditions as lack of nutrients and acidic pH. These inadequate conditions could explain the lack of performance, especially observed on methanethiol (53% of RE) and the production of oxygenated and sulfur by-products by the biofilter itself