This paper deals with a model linking bubble dynamics under an acoustic pressure field and production of free radicals in the resulting collapses of this bubble. The bubble dynamics model includes interdiffusion of gas and vapour in the bubble as well as evaporation or condensation at the interface, and it assumes uniformity of the internal pressure and perfect gas law for the gas vapour mixture. At the maximum compression of the bubble, all the reactions of dissociation which can occur are assumed at thermodynamic equilibrium. The local composition (especially in free radicals) in the bubble is then calculated by an algorithm based on free energy minimization using the information concerning the maximum compression provided by the bubble dynamics model resolution. Using this model a comparison of free radicals production has been made for two different driving frequencies (20 kHz and 500 kHz), and at given bubble radius and acoustic pressure, an optimum of liquid bulk temperature has been derived for the production of free radicals very similar to the experimental one concerning oxidation reactions in aqueous phase.

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in Wiley Online Library (wileyonlinelibrary.com).Gas-phase adsorption equilibria of diluted mixtures of methyl-ethyl-ketone and isopropylanol on activated carbon were investigated. Experimental isotherms were determined by a constant volume method. Single-component adsorption isotherms were fitted by the frequently used Toth model with good accuracy. Then adsorption isotherms were determined for different binary mixtures (with different initial ratio of the two components). Binary mixtures adsorption isotherms were calculated using the adsorbed solution theory. Ideal adsorbed solution theory (IAST) could not represent experimental data, but it was observed that increasing amount of MEK led to higher nonideality of the mixture. Then UNIversal QUAsi Chemical (UNIQUAC) and nonrandom twoliquids (NRTL) models were considered to describe activity coefficients of the adsorbed phase. The fitted parameters of UNIQUAC model depend on the ratio of the two components, whereas the NRTL model is able to fit all experiments with the same parameters, whatever the initial ratio may be.

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Indoor air pollution (IAP), defined by a lot of pollutants at low concentrations (microg m(-3)), is recognized as a major environmental health issue. In order to remove this pollution, biofiltration was investigated in this study. Two biofilters packed with compost and a mixture of compost and activated carbon (AC) were compared during the treatment of an influent with characteristics close to those of IAP. Very high removal efficiencies (RE) were achieved for the two biofilters (RE more than 90% for butyl acetate, butanol, formaldehyde, limonene, toluene and undecane at mass loading from 6-24mg m(-3) h(-1) and 19s empty bed retention time). The fact that high RE of hydrophobic compounds (undecane and limonene) were achieved, along with the results of an abiotic sorption study, lead us to suggest a mechanism including adsorption followed by biodegradation at the interface of the biofilm where microorganisms tend to concentrate near the available substrate. Both chemical reactions with the packing materials and biological degradation led to average RE greater than 91.4% for nitrogen dioxide. It was observed that adding AC to compost had significant effects. First, its buffering capacity led to shorter acclimation duration and more stable operation efficiencies than for the compost biofilter. Secondly, the only compound which was not removed by the compost biofilter, trichloroethylene, was strongly adsorbed by the compost/AC biofilter. Finally, the concentration profile along the two biofilters demonstrated that adding of AC could lead to a reduction of the retention time required to reach the maximal RE.

Indoor air pollution, characterized by many pollutants at very low concentrations, is nowadays known as a worrying problem for human health. Among physical treatments, adsorption is a widely used process, since porous materials offer high capacity for volatile organic chemicals. However, there are few studies in the literature that deal with adsorption as an indoor air pollution treatment. The aim of this study was to investigate the adsorption of toluene on to activated carbon at characteristic indoor air concentrations. Firstly, global kinetic parameters were determined by fitting Thomas's model to experimental data obtained with batch experiments. Then, these kinetic parameters led to the determination of Henry's coefficient, which was checked with experimental data of the adsorption isotherm. Secondly, we simulated a breakthrough curve made at an inlet concentration 10 times higher than the indoor air level. Even if the kinetic parameters in this experiment are different from those in batch experiments, it can be emphasized that the Henry coefficient stays the same.

The interest in Indoor Air Quality (IAQ) has increased this past decade due to better knowledge of this kind of pollution. Recent studies have pointed out the Indoor Air Pollution (IAP) impact on health and associated costs. IAQ improvement can be achieved by removal of pollutant with adapted process. Numerous processes, as sorption or UV photocatalysis, have been studied for IAP treatment. However, IAP specificities, including high number of compounds with different physico-chemical properties at low concentrations, still limit process efficiencies. Competition between pollutants and process selectivity are also common limitations. Biofiltration is commonly used to treat effluents containing numerous compounds at low concentration in composting units or wastewater treatment plants. Moreover, since it uses waste as a filtration medium and avoids the addition of chemical products, biofiltration is a sustainable technology. In this study, biofilter performances for IAP treatment are evaluated. The biofilter is packed with compost, a natural medium which has a large range of microorganisms, good physical properties (water retention, pH) and contains nutrients. The model effluent contains 8 compounds (aldehyde, aromatic, chlorinated, inorganic...), at low concentration (sub-ppmv), chosen for their ubiquity in indoor air, their heterogeneous physical and chemical properties (solubility, vapor pressure, biodegradability) and their potential health risk due to chronic exposures. Biofilter performances were evaluated during 75 days in steady state. Three compounds, undecane, limonene and butyl acetate, could not be quantified during the study, removal efficiencies are close to 100 %. Butanol, formaldehyde and toluene were removed with efficiencies close to 100 % during the first 40 days. After this time, efficiency variations were observed and the removal efficiencies decreased to 55.5, 77.8 and 13.9 % for butanol, formaldehyde and toluene, respectively. The decrease of bed moisture content seems to be the main explanation for these phenomena. Removal efficiencies of 86.3 – 99.6 % were achieved for nitrogen dioxide. Only trichloroethylene, known as a not easily biodegradable compound, was not removed by the biofilter: only sorption and desorption phenomena were observed during this time for this compound. In these starvation conditions, biomass cannot grow and only a fraction of the biomass can be maintained in the biofilter. However, this non-negligible biomass fraction can have a biological activity and removes the different compounds contained in the model effluent.

International audienceExperimental studies and numerical modeling were conducted to assess the feasibility of a granular activated carbon column to buffer load variations of contaminants before wastewater treatment devices. Studies of cycles of adsorption, and more especially desorption, of methyldiethanolamine (MDEA) and 2,4-dimethylphenol (2,4-DMP) have been carried out on granular activated carbon (GAC). Dynamic variations of contaminants concentrations were run at several conditions of duration (peaks). GAC fixed-bed exhibited a stable adsorption/desorption capacity after undergoing two conditioning cycles. The study of pollution peaks revealed that attenuation is largely dependent on the targeted pollutant: 2.4 ± 0.5 % attenuation/cm of bed for MDEA and 6.0 ± 1.2 % attenuation/cm of bed for 2,4-DMP. Mass balances calculated from both injected and recovered pollutant during peaks were respected. Finally, a coupling of the linear driving force model and isotherms models was used to fit experimental data for both adsorption breakthrough curves and desorption curves. The model was used to predict adsorption and desorption behaviors of following cycles. Good agreement with experimental values was obtained