Calibration and deployment of POCIS and Chemcatcher for the monitoring of explosives on lake-bottom sediments

Luiz Felippe De Alencastro, Nicolas Estoppey
2016
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Résumé

Between 1920 and 1967, approximatively 8000 tons of ammunition waste was dumped into some Swiss lakes. Previous studies based on grab sampling revealed small traces of cyclotetramethylenetetranitramine (HMX), cyclotrimethylenetrinitramine (RDX) and pentaerythritoltetranitrate (PETN) in the water column of two studied lakes; however these researches showed that the ammunition waste at the lake bottom was likely not involved in that contamination. On the contrary, external sources (tributaries contaminated by hot spots such as ammunition destruction locations or ammunition factories) might be the main cause. The ultimate goal of this study is to assess whether explosive monitoring by passive sampling is technically feasible in the affected lakes and rivers, and whether integrative sampling confirm former results obtained by grab sampling. As a first step, POCIS (HLB powder sandwiched by two PES membranes) and Chemcatcher (SDB-RPS disk covered by a PES membrane) were calibrated in a channel system supplied with continuously refreshed lake water spiked with two nitramines (HMX, RDX), one nitrate ester (PETN) and seven nitroaromatics (2,4,6-trinitrotoluene (TNT) and three of its degradation products, 1,3-dinitrobenzene, 2,4- and 2,6-dinitrotoluene). Exposure parameters in the system were kept as close as possible to the ones expected in the first meters above sediments of the studied lakes. Sixteen POCIS and Chemcatcher were simultaneously deployed and removed in duplicates at 8 different intervals over 21 days whereas water analysis (SPE extraction) was carried out daily. PES membranes (pore size of 0.1μm) and sorbent phases were separately extracted and analyzed by UPLC-MS/MS. LDPE strips spiked with PRCs were also deployed in the channel system to obtain dissipation data in the calibration conditions. Results of the calibration showed that the accumulation of HMX and RDX (log Kow

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https://infoscience.epfl.ch/record/221327?ln=fr

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Luiz Felippe De Alencastro, Nicolas Estoppey
2016
Discussion par affiche

Résumé

Official source

https://infoscience.epfl.ch/record/221327?ln=fr

À propos de ce résultat

Concepts associés (13)

Concepts associés

Chargement

Publications associées (12)

Publications associées

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Assessment of passive sampling for the monitoring of explosive residues in surface water

Sylvain Coudret, Luiz Felippe De Alencastro, Nicolas Estoppey

Between 1920 and 1967, approximately 8’200 tons of ammunition waste were dumped into several Swiss lakes. Previous studies based on grab sampling revealed traces of HMX, RDX and PETN in the water column of three studied lakes; however, these researches showed that the ammunition waste at the lake bottom was likely not involved in that contamination. On the contrary, external sources (tributaries contaminated by hot spots) might be the main cause. The goal of this study is to assess whether explosive monitoring by passive sampling is feasible in the affected lakes and rivers, and whether integrative sampling confirms results obtained by grab sampling. As a first step, two kinds of passive samplers (adsorbent covered by a diffusion membrane) were calibrated in a channel system supplied with continuously refreshed lake water spiked with HMX, RDX, PETN and six nitroaromatics (including TNT). Exposure parameters in the system were kept as close as possible to the ones expected in the studied lakes. Sampling rate (RS) of HMX, RDX and PETN were in the range of 30 to 130 mL day 1. RS of nitroaromatics were up to 10 times lower because of the high accumulation of these compounds in the diffusion membrane. This latter was thus used as receiving phase for nitroaromatics, leading to Rs higher than 150 mL day 1. As a second step, the samplers were deployed on lake-bottom sediments (200m depth) with the aid of a remotely operated vehicle. Samplers were also deployed in rivers by fixing iron bars in the riverbed. In lakes, HMX, RDX and PETN were found at very low concentrations (

2018

Chargement

The work presented in this thesis was carried out in the framework of two European projects: SOLWATER, and AQUACAT. The global objective of those projects, including the present work, was to set an autonomous system for drinking water production in developing countries using solar energy. More specifically, the technology of drinking water decontamination by photocatalysis using inexpensive TiO2 catalyst and free of charge sun energy was investigated. In details, the research project dealt with the correlation of the TiO2 physicochemical characteristics with its photocatalytic activity on both organic and bacterial removal, the comparison of the photoactivity of suspended and fixed TiO2, and the development of a large scale prototype for fixed catalyst system. Finally, this work also included the creation of a mathematical model to predict the photo and photocatalytic bacterial inactivation. In photocatalytic experiments, phenolic compounds (phenol, 4-nitrophenol, 4-hydroxybenzoic acid and gallic acid) and benzoic acid were used as model organics, and E. coli as model bacterium. The titania physicochemical characteristics, crystalline structure, specific surface area (BET), particle size, aggregate size, and isoelectric point (IEP) of 13 different suspended TiO2 samples were determined and correlated with photocatalytic activity for chemicals and bacteria abatement. Organics degradation kinetics were found to be significantly affected by the TiO2 surface charge, i.e. the IEP. Indeed, the organic compounds degradation was greatly enhanced by negatively charged TiO2 samples. BET affected differently the primary compounds degradation and the total organic carbon mineralization. The primary degradation kinetics of strongly adsorbed pollutants was enhanced by large BET. Whereas, there was an optimum BET value for a total organic carbon removal, for all organic compounds studied. In addition, the mixed crystalline structure anatase-rutile, in the form of the commercially available Degussa P25, was more active for the purpose of organic degradation than pure anatase TiO2. Bacteria abatement was not influenced by BET specific surface area, particle and aggregate size of suspended TiO2. However, surface charge was crucial for the TiO2 and bacteria interaction. Indeed, negatively charged TiO2 were not efficient in inactivating E. coli, probably due to electrostatic repulsions with the negatively charged E. coli outer membrane. Depending on the nature of the contaminants, different catalyst characteristics have to be considered with regards to TiO2 efficiency on water detoxification and disinfection. Thus, it is not possible to draw a general scheme to determine which photocatalyst is the most suitable for the decontamination of particular water. Comparison of suspended and fixed catalyst revealed that the system with suspended TiO2 is more efficient for bacteria inactivation, yet the post-treatment catalyst filtration presents a serious disadvantage compared to fixed TiO2. Large scale experiments in compound parabolic collector (CPC) prototype reactor with fixed TiO2 revealed that a significant photocatalytic effect appeared only at a low bacterial initial concentration (≤ 103 CFU/ml). High organic compounds removal efficiency with fixed TiO2 was observed at laboratory and large scales, with kinetics similar to the ones obtained with suspended TiO2. A mathematical model was developed to predict bacterial photo-inactivation as a function of the light intensity and of the bacteria physiological state. The modelled curves fitted well with the experimental results for both exponential and stationary phases. Moreover, bacteria were more sensitive to light irradiation in the exponential than in the stationary state. Solar photocatalysis with fixed TiO2 was shown to be an efficient technology for organic pollutant removal and could be used as complement to other treatment process. Indeed, due to the slow bacteria inactivation kinetics observed, the technology needs further development to be used as a unique drinking-water treatment.

EPFL2007

Chargement

Typical sand trap flushing systems, such as Büchi and Dufour, require water volumes up to six times the deposited sediment volume for efficient flushing. Furthermore, complete sediment removal particularly in Dufour sand traps can only be realized with drawdown flushing, resulting in operation time and water loss. The objective of the described research project is to improve the flushing system of an existing Dufour sand trap. Numerical simulations, performed with two software packages ANSYS CFX and FLOW-3D, are carried out to investigate the flow dynamics in the flushing system and to investigate the required sediment flushing discharge. The flow in the existing flushing system is first studied to evaluate the actual performance of the system. Numerical simulations of the flow in the new flushing system, using the same sand trap, are performed to assess the induced improvements. A good agreement between the results of the numerical simulations using both software packages is observed. Regarding the velocity field in the flushing channel, the existing system is only efficient on the last third of the channel. In the new system, the velocity magnitude is sufficiently high all along the flushing conduit ensuring a good efficiency of the whole system.

2012

Chargement

EPFL2007