Laurence Le Coq

Application of sludge-based carbonaceous materials in a hybrid water treatment process based on adsorption and catalytic wet air oxidation

This paper describes a preliminary evaluation of the performance of carbonaceous materials prepared from sewage sludges (SBCMs) in a hybrid water treatment process based on adsorption and catalytic wet air oxidation; phenol was used as the model pollutant. Three different sewage sludges were treated by either carbonisation or steam activation, and the physico-chemical properties of the resultant carbonaceous materials (e.g. hardness, BET surface area, ash and elemental content, surface chemistry) were evaluated and compared with a commercial reference activated carbon (PICA F22). The adsorption capacity for phenol of the SBCMs was greater than suggested by their BET surface area, but less than F22; a steam activated, dewatered raw sludge (SA_DRAW) had the greatest adsorption capacity of the SBCMs in the investigated range of concentrations (<0.05 mol L(-1)). In batch oxidation tests, the SBCMs demonstrated catalytic behaviour arising from their substrate adsorptivity and metal content. Recycling of SA_DRAW in successive oxidations led to significant structural attrition and a hardened SA_DRAW was evaluated, but found to be unsatisfactory during the oxidation step. In a combined adsorption-oxidation sequence, both the PICA carbon and a selected SBCM showed deterioration in phenol adsorption after oxidative regeneration, but a steady state performance was reached after 2 or 3 cycles.

Different families of volatile organic compounds pollution control by microporous carbons in temperature swing adsorption processes

In this research work, the three different VOCs such as acetone, dichloromethane and ethyl formate (with corresponding families like ketone, halogenated-organic, ester) are recovered by using temperature swing adsorption (TSA) process. The vapors of these selected VOCs are adsorbed on a microporous activated carbon. After adsorption step, they are regenerated under the same operating conditions by hot nitrogen regeneration. In each case of regeneration, Factorial Experimental Design (FED) tool had been used to optimize the temperature, and the superficial velocity of the nitrogen for achieving maximum regeneration efficiency (R(E)) at an optimized operating cost (OP(€)). All the experimental results of adsorption step and hot nitrogen regeneration step had been validated by the simulation model PROSIM. The average error percentage between the simulation and experiment based on the mass of adsorption of dichloromethane was 3.1%. The average error percentages between the simulations and experiments based on the mass of dichloromethane regenerated by nitrogen regeneration were 4.5%.

Recovery comparisons—Hot nitrogen Vs steam regeneration of toxic dichloromethane from activated carbon beds in oil sands process

The regeneration experiments of dichloromethane from activated carbon bed had been carried out by both hot nitrogen and steam to evaluate the regeneration performance and the operating cost of the regeneration step. Factorial Experimental Design (FED) tool had been implemented to optimize the temperature of nitrogen and the superficial velocity of the nitrogen to achieve maximum regeneration at an optimized operating cost. All the experimental results of adsorption step, hot nitrogen and steam regeneration step had been validated by the simulation model PROSIM. The average error percentage between the simulation and experiment based on the mass of adsorption of dichloromethane was 2.6%. The average error percentages between the simulations and experiments based on the mass of dichloromethane regenerated by nitrogen regeneration and steam regeneration were 3 and 12%, respectively. From the experiments, it had been shown that both the hot nitrogen and steam regeneration had regenerated 84% of dichloromethane. But the choice of hot nitrogen or steam regeneration depends on the regeneration time, operating costs, and purity of dichloromethane regenerated. A thorough investigation had been made about the advantages and limitations of both the hot nitrogen and steam regeneration of dichloromethane.

Influence on permeability of the structural parameters of heterogeneous porous media.

Abstract Predicting the macroscopic properties of porous media used in treatment processes is a complex task regarding 3‐D structures at micro‐, meso‐ and macro‐levels. Currently, information is scarce concerning the influence, at a microscopic level, of the 3‐D structure of fibrous media on the physical laws governing their macroscopic behaviour. Nevertheless, the relationship between macroscopic properties (pressure drop, treatment efficiency) and microstructure can be assessed thanks to suitable structure modelling theories. In this context, the present study proposes and compares different methods (mercury porosimetry and image analysis) for the structure characterization at a microscopic level of filtering fibrous media, such as nonwoven and woven fabrics. The results obtained show a porous structure gradient in the thickness of the nonwoven media studied in terms of porosity, pore size and tortuosity factor. Moreover, the influence on structural parameters of media compression, when submitted to friction forces exerted by flow during filtration tests, is established. A model for the determination of multi‐level pore size distributions from mercury porosimetry data is proposed. The “equivalent pore” model is used to estimate the tortuosity factor. The influence of measured structural parameters on fibrous media permeability is studied in a classical model for flow through fibrous media.Abstract Predicting the macroscopic properties of porous media used in treatment processes is a complex task regarding 3‐D structures at micro‐, meso‐ and macro‐levels. Currently, information is scarce concerning the influence, at a microscopic level, of the 3‐D structure of fibrous media on the physical laws governing their macroscopic behaviour. Nevertheless, the relationship between macroscopic properties (pressure drop, treatment efficiency) and microstructure can be assessed thanks to suitable structure modelling theories. In this context, the present study proposes and compares different methods (mercury porosimetry and image analysis) for the structure characterization at a microscopic level of filtering fibrous media, such as nonwoven and woven fabrics. The results obtained show a porous structure gradient in the thickness of the nonwoven media studied in terms of porosity, pore size and tortuosity factor. Moreover, the influence on structural parameters of media compression, when submitted to fri...

Hazardous dichloromethane recovery in combined temperature and vacuum pressure swing adsorption process.

Organic vapors emitted from solvents used in chemical and pharmaceutical processes, or from hydrocarbon fuel storage stations at oil terminals, can be efficiently captured by adsorption onto activated carbon beds. To recover vapors after the adsorption step, two modes of regeneration were selected and could be possibly combined: thermal desorption by hot nitrogen flow and vacuum depressurization (VTSA). Because of ignition risks, the conditions in which the beds operate during the adsorption and regeneration steps need to be strictly controlled, as well as optimized to maintain good performances. In this work, the optimal conditions to be applied during the desorption step were determined from factorial experimental design (FED), and validated from the process simulation results. The regeneration performances were compared in terms of bed regeneration rate, concentration of recovered volatile organic compounds (VOC) and operating costs. As an example, this methodology was applied in case of dichloromethane. It has been shown that the combination of thermal and vacuum regeneration allows reaching 82% recovery of dichloromethane. Moreover, the vacuum desorption ended up in cooling the activated carbon bed from 93°C to 63°C and so that it significantly reduces the cooling time before starting a new cycle.

SFGP 2007 - Microbial growth onto filter media used in air treatment devices

This work deals with microbial growth onto filter media and focuses on the ability of microbial communities to proliferate onto filter media. Two microorganism types are studied: microorganisms from activated sludge of wastewater treatment plant (SM) and a toluene specific consortium (TSC). The filter media considered for this study contain activated carbon fibres (ACF), combined volatile organic compounds (VOC), particles treatment purposes, activated carbon fibres felt (ACFF) and activated carbon and cellulose fibres felt (AC2F2). Using a static growth procedure during 10 days under 100 % relative humidity, artificially contaminated filters are submitted to microbial colonisation. The final concentration of microorganisms per gram of filter have been assessed using a method developed in the lab, based on filter protein content assay. The average surface charge of inocula and filters fibres are measured to assess the influence of microorganisms adhesion on contamination. The influence of soot particles on TSC proliferation onto AC2F2 filter is then studied. Zeta measures enable the assessment of the implication of soot in microorganisms adhesion onto filter fibres. Consequences of microbial contamination on filter permeability and downstream particles released have then been assessed in a filtration device. Results demonstrate a better resistance of AC2F2 to microbial colonisation. However, SM have more difficulties to proliferate on ACFF than TSC, whereas SM colonise easier AC2F2 than TSC. Charge surface assay has defined an optimal electrostatic compatibility for TSC and AC2F2 and a minimum for SM and ACFF. When soot is added to TSC solution before introduction in AC2F2, high contamination shapes were observed whereas only a slight one occur without soot addition. Zeta potential measures show favourable charge conditions for adhesion of soot on AC2F2 fibres and TSC on soot particles. The soot may thus have played an interface role in microbial adhesion onto media. This means that electrostatic compatibility between particles is a good approach for assessing microbial adhesion onto filters but could not explain the whole mechanism of microbial proliferation. Other parameters like nutrition preferences are certainly involved. The contamination have induced filter characteristics modification. Permeability have decreased until 20 % with microbial concentration. Colonised filters have released up to 450 microbial particles/cm3. Such a release was only observed when AC2F2 was contaminated with fungi using spore as the reproduction vector (inoculum containing TSC and soot).

Use of Experimental Designs to Establish a Kinetic Law for a Gas Phase Photocatalytic Process

Abstract The photocatalytic degradation of three common indoor VOCs – acetone, toluene and heptane – is investigated in a dynamic photocatalytic oxidation loop using Box–Behnken designs of experiments. Thanks to the experimental results and the establishment of a kinetic rate law based on a simplified mechanism, a predictive model for the VOC degradation involving independent factors is developed. The parameters under investigation are initial concentration, light intensity and air velocity through the photocatalytic medium. The obtained model fits properly the experimental curves in the range of concentration, light intensity and air flow studied.

Determination of the Clean Air Delivery Rate (CADR) of Photocatalytic Oxidation (PCO) Purifiers for Indoor Air Pollutants Using a Closed-Loop Reactor. Part II: Experimental Results

The performances of a laboratory PhotoCatalytic Oxidation (PCO) device were determined using a recirculation closed-loop pilot reactor. The closed-loop system was modeled by associating equations related to two ideal reactors: a perfectly mixed reservoir with a volume of VR = 0.42 m3 and a plug flow system corresponding to the PCO device with a volume of VP = 5.6 × 10−3 m3. The PCO device was composed of a pleated photocatalytic filter (1100 cm2) and two 18-W UVA fluorescent tubes. The Clean Air Delivery Rate (CADR) of the apparatus was measured under different operating conditions. The influence of three operating parameters was investigated: (i) light irradiance I from 0.10 to 2.0 mW·cm−2; (ii) air velocity v from 0.2 to 1.9 m·s−1; and (iii) initial toluene concentration C0 (200, 600, 1000 and 4700 ppbv). The results showed that the conditions needed to apply a first-order decay model to the experimental data (described in Part I) were fulfilled. The CADR values, ranging from 0.35 to 3.95 m3·h−1, were mainly dependent on the light irradiance intensity. A square root influence of the light irradiance was observed. Although the CADR of the PCO device inserted in the closed-loop reactor did not theoretically depend on the flow rate (see Part I), the experimental results did not enable the confirmation of this prediction. The initial concentration was also a parameter influencing the CADR, as well as the toluene degradation rate. The maximum degradation rate rmax ranged from 342 to 4894 ppbv/h. Finally, this study evidenced that a recirculation closed-loop pilot could be used to develop a reliable standard test method to assess the effectiveness of PCO devices.

Filtration performances of HVAC filters for PM10 and microbial aerosols— Influence of management in a lab-scale air handling unit

ABSTRACT Filtration performances of air handling unit (AHU) filters for particles and microbial aerosols were investigated. The influence of the AHU operational conditions on the behavior of microorganisms collected on the filters was also studied. A lab-scale AHU with two filtration stages was developed and validated for the study of downsized filters with industrial geometries. Three types of filters of different efficiency were considered: G4, F7, and F9, according to European standard EN 779. Two configurations of filters were studied: G4 pleated/F7 bag and F7/F9 bag. Filters were sequentially clogged by alumina particles, which provided a mineral fraction in the particulate cake, and then by micronized rice particles, which provided the fungus Penicillium chrysogenum and an organic fraction that acts as a substrate for microorganisms. Finally, a microbial aerosol composed of endospores of Bacillus subtilis and spores of Aspergillus niger was nebulized to contaminate filters. After clogging, periods of 5 days on and 2 day weekend stops with restarts of ventilation were simulated for 6 weeks. The results showed that the filter efficiency for particles was quite comparable to that for microbial aerosols expressed in cultivable concentration. The particulate cake composed of alumina and micronized rice particles enabled the growth of the endogenous species P. chrysogenum and the survival of exogenous species B. subtilis and A. niger on filters. During restarts of ventilation, low particle concentrations were detected downstream of the second filtration stages by release but the microbial concentration from the fraction of air sampled was below the detection limit.

Global statistical predictor model for characteristic adsorption energy of organic vapors–solid interaction: Use in dynamic process simulation

Adsorption of Volatile Organic Compounds (VOCs) is one of the best remediation techniques for controlling industrial air pollution. In this paper, a quantitative predictor model for the characteristic adsorption energy (E) of the Dubinin-Radushkevich (DR) isotherm model has been established with R(2) value of 0.94. A predictor model for characteristic adsorption energy (E) has been established by using Multiple Linear Regression (MLR) analysis in a statistical package MINITAB. The experimental value of characteristic adsorption energy was computed by modeling the isotherm equilibrium data (which contain 120 isotherms involving five VOCs and eight activated carbons at 293, 313, 333, and 353 K) with the Gauss-Newton method in a statistical package R-STAT. The MLR model has been validated with the experimental equilibrium isotherm data points, and it will be implemented in the dynamic adsorption simulation model PROSIM. By implementing this model, it predicts an enormous range of 1200 isotherm equilibrium coefficients of DR model at different temperatures such as 293, 313, 333, and 353K (each isotherm has 10 equilibrium points by changing the concentration) just by a simple MLR characteristic energy model without any experiments.