Visualization of the exothermal VOC adsorption in a fixed-bed activated carbon adsorber.

Activated carbon fixed beds are classically used to remove volatile organic compounds (VOCs) present in gaseous emissions. In such use, an increase of local temperature due to exothermal adsorption has been reported; some accidental fires in the carbon bed due to the removal of high concentrations of ketones have been published. In this work, removal of VOCs was performed in a laboratory-scale pilot unit. In order to visualize the increase in local temperature, the adsorption front was tracked with a flame ionization detector and the thermal wave was simultaneously visualized with an infrared camera. In extreme conditions, fire in the adsorber and the combustion of activated carbon was achieved during ketone adsorption. Data have been extracted from these experiments, including local temperature, front velocity and carbon bed combustion conditions.

Estimated costs of implementation of membrane processes for on-site greywater recycling.

Greywater reuse inside buildings is a possible way to preserve water resources and face up to water scarcity. This study is focused on a technical-economic analysis of greywater treatment by a direct nanofiltration (NF) process or by a submerged membrane bioreactor (SMBR) for on-site recycling. The aim of this paper is to analyse the cost of recycled water for two different configurations (50 and 500 inhabitants) in order to demonstrate the relevance of the implementation of membrane processes for greywater recycling, depending on the production capacity of the equipment and the price of drinking water. The first step was to define a method to access the description of the cost of producing recycled water. The direct costs were defined as a sum of fixed costs due to equipment, maintenance and depreciation, and variable costs generated by chemical products and electricity consumptions. They were estimated from an experimental approach and from data found in literature, enabling operating conditions for greywater recycling to be determined. The cost of treated water by a SMBR unit with a processing capacity of 500 persons is close to 4.40 euros m(-3), while the cost is 4.81 euros m(-3) with a NF process running in the same conditions. These costs are similar to the price of drinking water in some European countries.

Absorption and biodegradation of hydrophobic volatile organic compounds: determination of Henry's constants and biodegradation levels.

Biodegradation of three volatile organic compounds (VOCs) was studied. Toluene, dimethylsulphide (DMS), and dimethyldisulphide (DMDS) were introduced into flasks filled with emulsions of Di-2-EthylHexylAdipate (DEHA) in water, containing biomass (activated sludge). The VOC concentrations were analysed in the gas, organic and aqueous phases, and compared to the initial VOC quantities introduced in order to deduce their consumption by biomass. Toluene and DMDS were completely consumed, and then removed from the gas and the organic phases, except when DEHA and water are in the same volume ratio, which appears to be extreme environmental conditions for bacterial growth. The high DMS volatility resulted in an important gas loss, leading to a lower amount of DMS available for activated sludge growth. For all the VOC experiments, some components, characteristics of the DEHA degradation, including 2-ethylhexanal, 2-ethylhexanol, 2-ethylhexanoic acid and adipic acid, were identified.

Biogas pre-upgrading by adsorption of trace compounds onto granular activated carbons and an activated carbon fiber-cloth.

The study assesses the adsorption onto activated carbon materials of selected volatile organic compounds -VOCs- (dichloromethane, 2-propanol, toluene, siloxane D4) in a biogas matrix composed of methane and carbon dioxide (55:45 v/v). Three different adsorbents are tested, two of them are granular activated carbon (GAC), and the last is an activated carbon fiber-cloth (ACFC). The adsorption isotherm data are fitted by different models by nonlinear regression. The Langmuir-Freundlich model appears to be the adequate one to describe the adsorption phenomena independently of the VOC considered or the adsorbent. The adsorbents present attractive adsorption capacity of the undesirable compounds in biogas atmosphere though the maximum adsorption capacities for a VOC are quite different from each other. The adsorption kinetics are characterized through three coefficients: the initial adsorption coefficient, the external film mass transfer coefficient and the internal diffusion coefficient of Weber. The ACFC demonstrates advanced kinetic yields compared to the granular activated carbon materials whatever VOC is considered. Therefore, pre-upgrading of biogas produced from wastewater sludge or co-digestion system by adsorption onto activated carbon appears worth investigating. Especially with ACFC material that presents correct adsorption capacities toward VOCs and concrete regeneration process opportunity to realize such process.

Electrodeposition of copper and iron oxides on to activated carbon fibre cloths: application to H2S and NH3 removal from air.

The present study concerns metal electrodeposition onto activated carbon fibre cloths (ACFC) for the treatment of odorous molecules such as hydrogen sulfide and ammonia. Characterizations of virgin, chemical impregnated and electroimpregnated carbon fibre cloths allowed the determination of the physical and chemical properties of such materials. Adsorption kinetics and isotherms in a batch reactor were carried out with non-impregnated and copper- or iron-impregnated ACFC. It was observed that differences in the metal deposit directly influenced the porous structure and elimination kinetics and capacities towards both odorous molecules. Compared to non-impregnated material, the adsorption velocities decrease in the case of chemically impregnated materials whereas they were similar when electrodeposition was used. Moreover, the maximal adsorption capacities were highest when metal was electrochemically deposited.

Biodegradation of endocrine disrupters: case of 17beta-estradiol and bisphenol A.

The biodegradation of 17 beta-estradiol (E2) and bisphenol A (BPA) was compared to that of a reference pollutant, sodium benzoate (SB), known for its high biodegradability. The biodegradation was measured using the Sturm test (ISO 9439 modified Sturm test). The susceptibility of the target pollutants to be degraded by microorganisms of activated sludge from a wastewater treatment plant (WWTP) was evaluated by the production of carbon dioxide (CO2). Sorption experiments onto inactivated sludge were carried out to assess the contribution of sorption in E2 and BPA removal during biological treatment in a WWTP. E2 was more adsorbed than BPA onto inactivated sludge, probably making it less accessible to assimilation by microorganisms. In fact, E2 was less biodegradable than BPA with 66% and 74% of theoretical CO2 formation (Th(co2)) in 28 days, respectively. However, E2 showed faster biodegradation than BPA due to the shorter adaptation time of the microorganisms to start the assimilation. Final concentrations were measured and revealed that, under Sturm test conditions, E2 was totally removed from the aqueous phase while some traces of BPA were detected. This result could be explained by the lower adsorbability of BPA observed in adsorption experiments onto inactivated sludge. To investigate competition in a bi-component solution, Sturm tests were carried out with BPA/SB and E2/SB. Moreover, the biodegradation curves obtained did not indicate a toxicity of the target compounds towards microorganisms, which rapidly degraded SB. In the case of BPA/SB, an inflection in the curve confirmed the adaptation time of 4-5 days for BPA to be degraded.

Analysis of endocrine disrupting compounds in wastewater and drinking water treatment plants at the nanogram per litre level.

The determination of steroid hormones, alkylphenolic compounds and bisphenol A at the ng l(-1) level in environmental water samples (surface water and WasteWater Treatment Plant samples (WWTP)) is performed by a specific analytical procedure. Pre-concentration by solid-phase extraction conditions was optimized using C18 cartridges for steroid hormones and polymeric Oasis HLB cartridges for phenolic compounds. Identification and quantification were performed using a LCMS/MS system with electrospray ionization in the negative mode for both compound families. For steroid hormones, the need to have limits of detection lower than 0.5 ng l(-1) in WWTP samples led to the improvement of a purification step on silica cartridges. In the case of the phenolic compounds, no purification was required because of their lower estrogenicity. The limits of detection in WWTP effluents ranged between 0.02 ng l(-1)and 0.21 ng l(-1) for steroid hormones and 0.4 and 10.2 ng l(-1) for phenolic compounds. The method was then applied to determine concentrations of the target compounds at each step of a WWTP. The process efficiencies were evaluated. Finally, concentrations were measured in influents and effluents of a Drinking Water Treatment Plant showing the complete removal of estrogenicity.

Role of colloids in heavy metal transfer through a retention-infiltration basin.

Runoff waters from a main bridge near Nantes (France), surface waters and pore waters in the infiltration basin collecting runoff were analysed after filtration and ultrafiltration to investigate the role of colloids in the transfer of trace metals (Zn, Cu and Pb) from the road to the groundwater. The role of the basin in mitigation of the variations of physico-chemical parameters and chemical elements concentrations was confirmed. An increase of mobile colloidal phase by comparison with runoff and high concentrations of trace metals were observed in pore waters of the sediment. Up to 100% of Pb and 60% of Cu and Zn may be associated to compounds having a molecular weight above 5 kDaltons. Principal component analysis outlined the variability of the influence of the physico-chemical parameters on trace metals concentrations for the different waters. Speciation calculations pointed out the potential precipitation of Fe and Al oxyhydroxides in all kind of waters.

Influence of complex fibrous media composition on their performances for VOC and particle removal.

Amongst atmospheric pollutants, two major types can be distinguished: airborne particles such as dust, and gaseous compounds such as Volatile Organic Compounds (VOCs). Fibrous filters are commonly used to remove particles while activated carbon beds trap VOCs. In order to obtain a single-stage device as efficient at collecting particles with a size less than 10 microm (PM10) as removing VOCs, prototype fibrous media containing activated carbon fibers (ACF) associated with cellulose fibers (CF), which are non-adsorptive, have been developed. The influence of ACF ratio and the degree of beating of CF on porous structure, mechanical strength and treatment performances of the medium was studied. Experimental results show that an increase in ACF mass ratio increases the inter-fiber porosity and overall adsorption capacity (the intrinsic adsorption capacity of ACF remains constant whatever the composition), but decreases the mechanical strength and particle collection efficiency of the medium. Moreover, an increase in the beating of CF enhances the mechanical strength of the medium and its particle collection efficiency, but decreases its porosity and has no effect on adsorption capacity. Consequently, a medium containing 50% ACF associated with CF with a low degree of beating (16 degrees SR) presents the best performance for combined filtration.

Antibacterial effects of chitosan powder: mechanisms of action.

Chitosan, the deacetylated derivative of chitin, is a natural D-glucosamine polymer that can be extracted from the shells of seafood such as prawns crabs and lobsters. It can be used as a flocculent, plant disease resistant promoter, anti-cancer agent, wound healing promotion agent and antimicrobial agent. The aim of this paper is the study of the interaction between chitosan powder and various kinds of pathogen microorganisms potentially present in water. First of all, physico-chemical characterisations of chitin and chitosan powder were performed. The deacetylation yields were 35%, 60% and 80 +/- 10%. The experimental studies focused on the measurements of the mortality constant rate for various bacterial strains, Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis and Staphylococcus saprophyticus. An explanation of the antibacterial mechanisms is proposed involving the cell wall disruption due to free amino groups present in chitosan.

Colloidal speciation of heavy metals in runoff and interstitial waters of a retention/infiltration pond.

The thickness of non-saturated zone and physico-chemical conditions are important parameters to assess the impact of infiltration ponds on water resources with respect to heavy metals transfer. As changes in physico-chemical parameters of solutions have a strong impact on the mobility of colloidal phases in sediments and soils, the colloidal facilitated transfer of heavy metals has to be investigated. Therefore, this study focuses on the characterization of runoff, surface and interstitial waters in a retention/infiltration pond collecting runoff waters of a bridge near Nantes. Physico-chemical parameters and chemical analyses were performed on the waters during about one year. The separation of dissolved and colloidal fractions was carried out by filtration and ultrafiltration for one sample of surface and interstitial waters. Until now, the runoff waters were only filtered at 0.45 microm. The comparison of physico-chemical data shows that the minor variations of runoff water parameters are mitigated in basin and in soils but strong variations impact the composition of interstitial waters. High concentrations of zinc, copper and still of lead are measured in runoff. Lead and cadmium seem to be associated to colloidal and particulate fractions while zinc, copper, nickel and chromium are distributed in all fractions.

Photocatalytic oxidation of methyl ethyl ketone over sol-gel and commercial TiO2 for the improvement of indoor air.

This work focuses on the photocatalytic oxidation of gaseous methyl ethyl ketone chosen as a typical indoor air pollutant. Two types of TiO coatings were prepared and deposited on glass plates: one using the commercial Degussa P25 TiO2 and the other one by sol-gel method. The first objective of this study was to compare different ways of preparing thin films of sol-gel TiO2 coated on glass plates, taking into account their general aspect and their photocatalytic efficiency. Several parameters were tested, such as the stabilising agent, the glass type of the support, the number of coatings and the calcination temperature. One of the synthesised materials was then kept to carry out the following study. The study aimed to assess the influence of TiO2 coating types on the effect of water vapour. This was achieved by performing MEK photocatalytic degradation kinetics under two levels of humidity at a fixed temperature. Experimental results were then modelled by the Langmuir-Hinshelwood equation. The obtained parameters gave specific trends in function of the considered catalyst. The second part of this work was to identify MEK degradation byproducts during its photocatalytic oxidation. The main detected intermediate was acetaldehyde, followed by methyl formate. A MEK degradation pathway was then proposed.

Production of porous carbonaceous adsorbent from physical activation of sewage sludge: application to wastewater treatment.

With an objective of production of carbonaceous sorbent for industrial effluent treatment, physical activation by steam of biological sludge collected from the municipal wastewater treatment plant of Nantes (France) was studied and optimised using experimental design. Thus, this activation process consists of a carbonisation under N2 atmosphere at 600 degrees C for 1 h, followed by a thermal oxidation using steam (760 degrees C, 0.5 h, 2.5 L/Umin). The global mass yield of the process is equal to 38%. The thermal treatment allows a specific surface area of up to 225 m2/g to be reached, the porous structure being composed of both micropores and mesopores. The content of acidic surface groups is 0.71 mEq/g whereas that of basic surface groups is 0.55 mEq/g. The adsorption properties of the sorbent made from sludge are estimated with regard to various pollutants representative of industrial pollution of wastewaters and compared with those of commercial activated carbon. Whereas the adsorption capacities of organic micropollutants are quite low because of proportionality to the microporosity, the important mesoporosity of the sorbent leads to interesting properties for macromolecules removal from aqueous solutions, such as dyes (q(m) = 175-200 mg/g). Furthermore, the surface functional groups and Ca2+ ions within the materials allow high copper ion adsorption capacities of 140 mg/g to be obtained. Finally, a techno-economic approach shows that the sludge activation process seems to be economically competitive with regard to incineration.

Numerical-assisted design of a wind tunnel used in the estimation of volatilization from water, waste or soil.

Numerical simulations of the flow inside two wind tunnel geometries used for determining emission volatilization have been conducted. The flow pattern was examined in a plane close to the emitting surface. A reduced surface, characterizing the low velocity zones in this plane, has been defined. The proposed geometry modification, consisting of a convergent/divergent system, decreases the low velocity regions by a factor ranging between 2 and 3.5. Large vortices present in the conventional configuration are almost eliminated. The new velocity distribution, close to the emitting surface, is more uniform and should therefore generate a more efficient mass transfer to the flowing air.

Wood bark as packing material in a biofilter used for air treatment.

Biotechnology has been applied to find green and low cost environmental processes. In the waste gas treatments (odours and volatile organic compounds VOC) one of the main biological systems used is biofilters. This technology works at normal operating conditions of temperature and pressure, and therefore it is relatively cheap with high efficiencies when the waste gas is characterized by high flow and low pollutant concentration. The aim of this work is to use wood barks (Pinus) as packing material in the biofilter. For this purpose, the influence of various parameters such as residence time of the gas and pollutant loads on removal efficiencies was studied for a biofilter pilot unit. Ethanol, methyl ethyl ketone, dichloromethane and toluene were used as pollutant compounds, because they are representative of both volatile organic compounds. Packing material stability and good biodegradation performances were found.

Adsorption of toluene onto activated carbon fibre cloths and felts: application to indoor air treatment.

Due to their bad effects on human health, removing Volatile Organic Compounds from indoor air has become an issue of major interest. In this study, the potential use of six commercial activated carbon felts and cloths for indoor toluene removal was investigated. Both batch and dynamic adsorption studies were performed, at toluene concentrations ranging from 21 to 18160 mg m(-3), for an air velocity representative of indoor air treatment (0.37 m s(-1)). Batch measurements showed that felts exhibited higher adsorption capacities at equilibrium than cloths at high toluene concentrations, whereas this trend may be inverted at low concentrations. Experimental isotherms and kinetics were satisfactorily fitted by the Langmuir-Freundlich model and the Linear Driving Force model respectively. No main differences between the adsorption kinetics of felts and cloths were reported. Dynamic adsorption capacities at saturation appeared to be higher than 120 mg g(-1) for both cloths and felts, irrespective of relative humidity levels and toluene concentrations. The influence of relative humidity on the adsorption capacity of felts was not significant for the higher toluene concentration studied in dynamics (307 mg m(-3)), whereas an increase in relative humidity induced a decrease in adsorption capacity at the lower toluene concentration (38 mg m(-3)). Moreover, experimental curves of breakthrough time versus thickness of medium were satisfactorily fitted by the Adams-Bohart model, and the critical thickness determined by this model appeared to be below 1.3 mm, regardless of the medium or toluene concentration.

Hydrogen sulfide and ammonia removal on activated carbon fiber cloth-supported metal oxides.

The present investigation attempts to provide mechanisms for the influence of metal catalysts on carbon supports in odorous gas removal. For this purpose, an activated carbon fiber cloth (ACFC) was subjected to successive metal impregnation to modify its surface properties and so increase its treatment capacity. The carbon fiber cloth adsorbent was prepared by classical incipient wetness impregnation followed by calcination in order to obtain metal oxide phases. Different impregnation parameters (type of metal, level of impregnation, calcination temperature) in the removal of hydrogen sulfide and ammonia were studied. Adsorption kinetics and capacities were carried out in a batch reactor at room temperature. It was found that removal activity depended on metal loading as well as on the order of the metal addition and calcination phase. The capacity of ACFC-supported metal oxides to adsorb both pollutants showed great improvement compared to the virgin adsorbent.

External capillary condensation and adsorption of VOCs onto activated carbon fiber cloth and felt.

Adsorption isotherms of some volatile organic compounds (VOCs), present in air at concentrations ranging from 10 to 2500 mg m(-3), were performed onto activated carbon fiber cloth and felt. The VOCs loading air were isopropanol, toluene, acetone, methyl ethyl ketone, ethyl acetate and dichloromethane. Isotherm adsorption data were generated. These experimental values were modeled by the equation of Dubinin and co-workers and by the Langmuir relation. Model parameters are discussed as a function of adsorbent materials and VOC structure. Adsorption capacity was generally found higher for the cloth than for the felt. An effect of external capillary condensation onto the felt of compounds with high surface tension was demonstrated for VOC concentrations above 1500 mg m(-3).

Removal of pesticides from aqueous solution: Quantitative relationship between activated carbon characteristics and adsorption properties.

The adsorption of pesticides (atrazin, atrazin-desethyl and triflusulfuron-methyl) from aqueous solution is performed by activated carbon fibers (ACF) and granular activated carbons (GAC) in static and dynamic reactors, in order to study the co-influence of adsorbent and adsorbate characteristics on the adsorption mechanisms. First, mono-component adsorption equilibrium is carried out in a batch reactor for a wide range of concentrations (from 5 microg 1(-1) to 21.4 mg 1(-1)). Classic models, like Freundlich and Langmuir equations, are applied: the maximum adsorption capacities are high, ranging between 63 and 509 mg g(-1). The comparison of single-solute isotherms tends to confirm the decisive role of the adsorbent properties in the adsorption capacity of pesticides by the activated carbons: the performance of ACF is significantly higher than that of GAC due to a narrower pore size distribution of fibers in the area of micropores. Furthermore, their small diameter (10 microm compared with 1 mm for grains) enables faster adsorption kinetics because of the larger surface area exposed to the fluid. The influence of adsorbate size is also demonstrated. A multiple linear regression enables the co-influence of adsorbent and adsorbate properties to be quantified, a relationship being assessed between Langmuir maximum adsorption capacity and pesticide molecular weight and adsorbent diameter (R2 = 0.90). Secondly, the adsorption of the three pesticides is studied in a dynamic reactor: in this case, the influence of operating conditions (inlet concentration C0, flow velocity U0) is also taken into account. As the initial concentration or flow velocity decreases, the column performance significantly improves. Both operating factors are included in a multiple linear regression (R2 = 0.91) used to predict saturation adsorption capacity, with molecular weight and particle diameter being again designed as influent explicative variables.

Structure characterization and adsorption properties of pyrolyzed sewage sludge.

Sewage sludges produced from wastewater treatment plants continue to set environmental problems in terms of volume and way of reuse. Thermal treatment of sewage sludge is considered as an attractive method in reducing sludge volume, and at the same time, it produces reusable byproducts. This paper deals with porous carbonaceous materials production from sewage sludge by pyrolysis (or carbonization) process with a goal of different industrial applications. Carbonization experiments were carried out on two kinds of sludge, namely viscous liquid sludge and limed sludge by varying carbonization temperature between 400 degrees C to 1000 degrees C. The porous structure and surface chemistry of the materials obtained were characterized using nitrogen adsorption, scanning electron microscopy, elemental analysis, Boehm titration, and pH of zero point of charge determination. The results show that basic character of the carbonized residues increases with increasing carbonization temperature. Then, carbonization allows specific surface area and pore volumes to be developed. Carbonized viscous liquid sludge and carbonized limed sludge are mainly mesoporous in nature, with specific surface areas reaching about 100 m2 g(-1) and 60 m2 g(-1), respectively. Finally, adsorption experiments, in aqueous solution, were carried out and show that carbonized viscous liquid sludges and limed sludge remove effectively the metallic ion Cu2+, acid and basic dyes, and phenol. Pyrolyzed sludges properties seem to be encouraging for the preparation of activated carbon by physical activation process.