Laboratory studies of the adsorption of two pesticides (diuron and tebuconazole) using a batch design and an experimental flume: influence of contact conditions

The adsorption of two commonly used pesticides, diuron and tebuconazole, on an organic substrate (hemp), which was chosen as an analogue for natural substrates often found in agricultural ditches, has been studied using three different contact schemes: 1) contact in a beaker using a modified batch method; 2) contact in an experimental flume, with a dry start substrate; and 3) same as 2) but with the substrate initially saturated with water. Changes in pesticides concentrations as a function of time as well as adsorption after seven hours have been determined for each case. The highest adsorption is observed for the experiments with a flume initially containing dry hemp. In that case, both the initial condition (hemp initially without water) and the contact conditions between the pesticide solution and the substrate appear to favour adsorption. The lowest adsorption is obtained for the flume containing hemp initially saturated with water. In that case, samples that were obtained at different depths inside the hemp using capillary tubes showed that only the superficial part of the hemp was in equilibrium with the surface water. The presence of an initial water table appears to be a limiting factor for pesticides penetration and further adsorption onto hemp. An intermediate adsorption is obtained for the modified batch method. These results highlight the pronounced influence on adsorption of both the initial hemp humidity conditions and the contact conditions between the pesticides solution and the substrate. This influence should be studied further to assess the potential of agricultural ditches to mitigate pesticides contamination in surface water

Effect of the submergence, the bed form geometry, and the speed of the surface water flow on the mitigation of pesticides in agricultural ditches

EAU+OBO:JMCPesticides, which have been extensively used in agriculture, have become a major environmental issue, especially regarding surface and ground water contamination. Of particular importance are vegetated farm drainage ditches, which can play an important role in the mitigation of pesticide contamination by adsorption onto ditch bed substrates. This role is however poorly understood, especially regarding the influence of hydrodynamic parameters, which make it difficult to promote best management practice of these systems. We have assessed the influence of three of these parameters on the transfer and adsorption of selected pesticides (isoproturon, diuron, tebuconazole and azoxystrobin) into the bed substrate by performing experiments with a tilted experimental flume, using hemp fibres as a standard of natural organic substrates that are found at the bottom of agricultural ditches. There were: 1, the speed of the surface water flow; 2, the submergence; and 3, the geometrical characteristics of the bed forms. The results show that the transfer of the pesticides from the surface water flow into the bed substrate is favoured, both regarding the amounts transferred into the bed substrate and the kinetics of the transfer, when the surface water speed and the submergence increase, and when the bed forms are made of rectangular shapes. The extrapolation of the flume data over a distance of several hundred meters, suggests that an interesting possibility for improving the mitigation of pesticides in ditches would be to increase the submergence and to favour bed forms which tend to enhance perturbations and subsequent infiltration of the surface water flow

role of the surface chemistry of activated carbons in the adsorption of siloxanes for biogas purification

SSCI-VIDE+ATARI+VTN:PGE:LFI:CFE:JMC:GPOInternational audienceTaking into account the continuous increase concern over greenhouse gases, such as methane and carbon dioxide, the biogas mixture produced in landfills or waste water treatment plants can be collected and utilized as a fuel for producing energy. However, the use of biogas as an energy source sets various design requirements for gas quality and gas cleaning systems [1].A special issue regarding biogas concerns the presence of traces siloxanes, semi-volatilemethylated organosilicon compounds containing Si–O bonds. Originating from hygiene,health care and industrial products, siloxanes are converted during biogas combustion process into crystalline silica inducing the engine damage [2].This study aims to investigate the adsorption of siloxane compounds over different activatedcarbon (AC) solids. The objectives are to test octamethylcyclotetrasiloxane (D4) adsorptioncapacity of the ACs from different sources under dry/humid atmosphere, deeply characterizethe solids and then search the dependence between the D4 adsorption capacity and the ACsurface chemistry and textural characteristics

Activated carbons for the removal of siloxane from biogas: in-situ FTIR study of regenerability properties

SSCI-VIDE+ATARI+VTN:PGE:GPO:CFE:JMC:LFINational audienceBiogas produced from sludge in waste water treatment plant, as well as from landfills, can be collected and utilized as a clean energy source. However, a special issue regarding biogas concerns the presence of traces siloxanes, semi-volatile methylated organosilicon (VMS) compounds containing Si–O bonds originating from hygiene, health care and industrial products . During the biogas combustion, siloxanes are converted into crystalline silica inducing the engine damage. The present work aims to investigate the adsorption and thermodesorption of decamethyltetrasiloxane (L4) over two commercial activated carbon (AC) samples (STIX and AP4-50 from ChemEnvirocarb) using the Diffuse Reflection Infrared Spectroscopy (DRIFTS). The polymerization of L4 into PolyDimethylSiloxane (PDMS) accompanied by the release of Hexamethyldisiloxane (L2) was observed. The presence of surface groups was supposed to be responsible for this reaction

role of the surface chemistry of activated carbon in the adsorption of siloxanes for biogas purification: an approach using infrared spectroscopy

SSCI-VIDE+ATARI+VTN:PGE:LFI:CFE:JMC:GPOInternational audienceTaking into account the continuous increase concern over greenhouse gases, such as methane and carbon dioxide, the biogas mixture produced in landfills or waste water treatment plants can be collected and utilized as a fuel for producing energy. However, the use of biogas as an energy source sets various design requirements for gas quality and gas cleaning systems. A special issue regarding biogas concerns the presence of traces siloxanes, semi-volatile methylated organosilicon compounds containing Si–O bonds. Originating from hygiene, health care and industrial products, siloxanes are converted during biogas combustion process into crystalline silica inducing the engine damage.This study aims to investigate the adsorption of siloxane compounds over different activated carbon (AC) solids. The objectives are to test octamethylcyclotetrasiloxane (D4) adsorption capacity of the ACs from different sources under dry/humid atmosphere, deeply characterize the solids and then search the dependence between the D4 adsorption capacity and the AC surface chemistry and textural characteristics. To reach these goals, the following characterization techniques were used: N2 adsorption–desorption isotherms, chemical analysis, XRD, TG-DTA, SEM, TEM, XPS, Raman and FTIR. The adsorption experiments were performed under dry or humid atmosphere by contacting the powders with siloxane vapors in a DRIFTS cell, connected to a conventional gas manipulation apparatus, which allows in situ preconditioning and adsorption studies at variable temperature

Activated carbons as adsorbents of siloxanes: Adsorption and desorption study by in-situ FTIR.

SSCI-VIDE+ATARI+VTN:PGE:LFI:CFE:JMC:GPOInternational audienceBiogas produced from sludge in waste water treatment plant, as well as from landfills, can be collected and utilized as a clean energy source. However, a special issue regarding biogas concerns the presence of traces siloxanes, semi-volatile methylated organosilicon (VMS) compounds containing Si–O bonds originating from hygiene, health care and industrial products [1]. During the biogas combustion, siloxanes are converted into crystalline silica inducing the engine damage.The present work aims to investigate the adsorption and thermodesorption of decamethyltetrasiloxane (L4) over two commercial activated carbon (AC) samples (STIX and AP4-50 from ChemEnvirocarb) using the Diffuse Reflection Infrared Spectroscopy (DRIFTS). The physicochemical properties of ACs were characterized using various techniques like N2 adsorption at 77K, XRD, SEM and TGA. The adsorption experiments were performed by contacting a stream of L4 (40 ppm) in nitrogen with a mixture of AC/KBr at room temperature. The spectra recorded during this step are dominated by the response of the gas phase. Therefore, the adsorbed phase can be hardly observed. Upon saturation, the cell was purged under N2 flow during 16h to eliminate L4 in the gas phase. The exhausted ACs underwent thermal programmed desorption from 25°C to 300°C (for STIX) or 400°C (for AP4-50). At 25°C, the spectra of ACs exhibit very weak bands of L4 in adsorbed phase. Upon heating, STIX sample shows mainly the decomposition of L4 into L2 between 80 and 200°C accompanied by a small desorption of L4. Further heating leads to the polymerization of L4 into PolyDimethylSiloxane (PDMS) [2]. This compound is weakly volatile and cannot be completely removed at 300°C. For AP4-50, the release of L4 into the gas phase can be observed throughout the heating process (mainly between 175 and 350°C). Small formation of L2 is noticed when heating up to 145°C. No evidence of the polymerization can be found for this sample.The transformation of L4 during the thermodesorption can be related to its reaction with the surface functional groups of ACs. The determination of these groups which are responsible for the formation of PDMS seems to be important for improving the regenerability properties and the reuse of ACs.References[1]. R. Dewil, L. Appels, J. Baeyens, Energy. Convers. Manag. 47 (2006) 1711–1722.[2]. V.T.L. Tran, P. Gélin, C. Ferronato, L. Fine, J.M. Chovelon, G. Postole, Catal. Today. (2017) http://dx.doi.org/10.1016/j.cattod.2017.01.00

Geotextile fibres retention properties to prevent surface water nonpoint contamination by pesticides in agricultural areas

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