Dominique Wolbert

Revisiting the Determination of Langmuir Parameters—Application to Tetrahydrothiophene Adsorption onto Activated Carbon

The selection of a proper sorbent for a given application is a complex problem. The design and efficiency of adsorption processes require an equilibrium adsorption model. Linear transformation is one of the methods available to estimate the adjustable parameters of isotherm models but possesses limitations compared to nonlinear regressions. A different approach to calculate predicted equilibrium isotherm values leading to an alternative nonlinear regression is presented in this paper and compared with usual regression methods. Adsorption isotherm data of gaseous THT onto three activated carbon materials constitute an experimental basis for the discussion. Assessment of the goodness-of-fit of the Langmuir model is supported by different selected test functions. The new nonlinear approach did not obtain the best results for each test function, but raises questions about the inherent combined error in regression procedures.

Ozonation effect on natural organic matter adsorption and biodegradation--application to a membrane bioreactor containing activated carbon for drinking water production.

More stringent legislation on dissolved organic matter (DOM) urges the drinking water industry to improve in DOM removal, especially when applied to water with high dissolved organic carbon (DOC) contents and low turbidity. To improve conventional processes currently used in drinking water treatment plants (DWTPs), the performances of a hybrid membrane bioreactor containing fluidized activated carbon were investigated at the DWTP of Rennes. Preliminary results showed that the residual DOC was the major part of the non-biodegradable fraction. In order to increase the global efficiency, an upstream oxidation step was added to the process. Ozone was chosen to break large molecules and increase their biodegradability. The first step consisted of carrying out lab-scale experiments in order to optimise the necessary ozone dose by measuring the process yield, in terms of biodegradable dissolved organic carbon (BDOC). Secondly, activated carbon adsorption of the DOC present in ozonated water was quantified. The whole process was tested in a pilot unit under field conditions at the DWTP of Rennes (France). Lab-scale experiments confirmed that ozonation increases the BDOC fraction, reduces the aromaticity of the DOC and produces small size organic compounds. Adsorption tests led to the conclusion that activated carbon unexpectedly removes BDOC first. Finally, the pilot unit results revealed an additional BDOC removal (from 0.10 to 0.15 mg L(-1)) of dissolved organic carbon from the raw water considered.

From algal polysaccharides to cyclodextrins to stabilize a urease inhibitor

N-Butyl-phosphorotriamide (NBPT) is a fertilizer widely used for its urease inhibiting properties. Nevertheless, formulations currently commercialized are complex and do not avoid severe decrease of activity due to the low stability of the bioactive compound under acidic conditions. According to its structure, NPBT was thought to be able to interact with both polar additives, by its phosphoramide function, and hydrophobic ones, through its alkyl chain. In this context, and in order to simplify formulations of this bioactive compound, a panel of natural polysaccharides was studied, including starch, β-(1,3)-glucans, carraghenans and alginates. We also used cyclodextrins, characterized the most stable inclusion complex with α-cyclodextrin and evaluated the stability of NBPT thus protected against hydrolysis under acidic conditions.

How Bromate and Ozone Concentrations Can be Modeled at Full-Scale Based on Lab-Scale Experiments – A Case Study

This article presents a full-scale modeling study of an industrial ozonation unit for practical application. The modeling framework combines an integrated hydraulic model (systematic network) with a quasi-mechanistic chemical model. Dealing with natural water, the chemical model has to be parameterized, and the parameters calibrated. This was done based on lab-scale experiments. The calibration results showed that the chemical model is able to account for changes in contact time with ozone, pH, temperature, ozone dose, NOM concentration, bromide concentration. Comparison of residence time distributions showed that the hydraulic model accurately reproduces flow conditions. Six sampling points were installed along an industrial ozonation unit of 487 m3 consisting of two baffled tanks in series. Bromate and ozone concentrations were monitored under varying operational process conditions. After the selection of a value for the kLa, simulations were run. Using the lab-scale calibrated models, simulated and experimental data were found in close agreement: 84% of the simulated concentrations for ozone matched measurements (±experimental error), 60 % for bromate. A readjustment of the kinetics of a single reaction (out of 65) showed that seasonal changes in NOM activity may easily be taken into account based on regular concentration measurements (90% of the bromate concentrations were then modeled accurately).

Ultratrace-level determination of N-Nitrosodimethylamine, N-Nitrosodiethylamine, and N-Nitrosomorpholine in waters by solid-phase extraction followed by liquid chromatography-tandem mass spectrometry

N-nitrosamines are a new class of emerging nitrogenous drinking water disinfection by-products. These compounds are probably carcinogenic which could seriously affect the safety of drinking water consumers. The aim of this study is to develop a simple, fast, and specific analytical method for the routine determination of low part per trillion levels of N-nitrosamines in waters. An ultra high pressure liquid chromatography coupled with tandem mass spectrometry (UHPLC/MS/MS) method was developed for the qualitative and quantitative analysis of N-nitrosamines in waters. N-nitrosamines were extracted, purified and concentrated from water samples in one step using a solid-phase extraction (SPE). The compounds were detected in multiple reaction monitoring via electrospray ionisation source with positive ionisation mode. To achieve symmetrical peak shapes and a short chromatographic analysis time, the mobile phase consisting of acetonitrile, water and formic acid (60:40:0.1, v/v/v) was used in the experiment. Chromatographic separation of N-nitrosamines was done in less than two minutes. All calibration curves had good linearity (r2≥ 0.9989). The intra- and inter-day precision of the assay ranged from 0.59% to 3.11% and accuracy ranged from 99.66% to 104.1%. The mean recoveries of N-nitrosamines in spiked water were 98%-101%. The reproducability was acceptable with relative standard deviations of less than 3.53%. The proposed method yielded detection limits very low which ranges from 0.04 to 0.16 ng L−1. Finally, the developed analytical method was successfully applied to the analysis of N-nitrosamines in natural water sample

A highly sensitive liquid chromatography-tandem mass spectrometry method for the analysis of a toxic water disinfection by-product, N-nitrosomethylethylamine

Recently, among the emerging contaminants, N-nitrosomethylethylamine has become of special concern because it is a potent human mutagenic and carcinogenic contaminant detected in chlorinated or chloraminated drinking waters and wastewaters. In this work a sensitive and robust method, which was based on solid-phase extraction followed by ultra-high-pressure liquid chromatography coupled with tandem mass spectrometry, was developed for the determination of N-nitrosomethylethylamine in water at ultra-trace levels. Chromatographic separation was performed on a C18 column. Quantification of N-nitrosomethylethylamine was achieved by using a triple quadrupole mass spectrometer that was equipped with an electrospray interface and was operated in positive ionization mode. Under optimized conditions, the calibration curve was linear from 0.1 to 100 μg L−1 (r2 ≥ 0.999). The precision of the intra- and inter-day values was found to be less than 2.5%, and the accuracy of the method was within ±3%. Moreover, an extraction efficiency greater than 86% was obtained at different concentration levels with relative standard deviation, RSD < 4.2%. Therefore, the experimental results showed that the proposed analytical method can be used successfully to determine N-nitrosomethylethylamine at ultra-trace levels (ng L−1) in aqueous samples.

Detoxification And Disinfection By O3/H2O2 For Greenhouse Effluents Reuse Using Static Mixers

Abstract The use of an ozone - hydrogen peroxide advanced oxidation reactor system is discussed for the detoxification as well as for disinfection of greenhouse influents and effluents. Using static mixers as a reactor allows for short contact times and thus results in a very compact setup. The in situ efficiency of the treatment with an ozone dose of 10 g.m−3, a H2O2/O3 mass ratio of 0.15 g.g−1 and a contact time of about 1 s, is presented. Its application allows the use of water resources with poor chemical and microbiological qualities and/or the recycling of the effluent with a satisfactory equilibrium control for a closed loop management of the greenhouse.

Large-Scale Experimental Validation of a Model for the Kinetics of Ozone and Hydroxyl Radicals with Natural Organic Matter

A unified model for the kinetics of O3 and •OH with NOM was proposed, calibrated and validated based on large experimental data sets. Single-phase batch experiments were done on 11 water samples from seven resources. Seasonal variations were studied on three resources. Effects of reaction time with ozone, ozone dose, pH, temperature, radical scavenger adding, and NOM dilution were studied. The experiments represented more than 1200 and 900 concentration measurements, respectively, for ozone and pCBA (•OH tracer). Mechanistic models were used for ozone self-decomposition and carbonate species kinetics. Results showed that the proposed model is robust and can handle different water characteristics and different experimental conditions: 75% of the experiments were modeled satisfactorily (for ozone and pCBA). Next, the domain of validity was determined: 6 ≤ pH ≤ 8; 1 meq.L−1 ≤ alkalinity ≤ 6 meq.L−1; 0–0.5 mgC.L−1 ≤ TOC ≤ 3.1 mgC.L−1. Only water samples with high organic (TOC > 2.4 mg.L−1) and low inorganic contents (alkalinity < 0.3 meq.L−1) could not be modeled adequately. Seasonal comparisons showed that the quality of the predictions decreases only for pCBA when having calibrated the model at another season. The model gave good results when using only 6 single batch experiments for calibration.

Pilot scale degradation of mono and multi volatile organic compounds by surface discharge plasma/TiO 2 reactor: Investigation of competition and synergism

This paper mainly deals with the isovaleraldehyde degradation with the help of a nonthermal plasma surface discharge (NPSD) coupled with photocatalysis. The efficiency of NPSD reactor, for gas treatment, was studied for different binary mixtures: (1) mixture of aldehydes (Isovaleraldehyde and Butyraldehyde) and (2) mixture of aldehyde and amine (Isovaleraldehyde and Trimethylamine). A planar continuous reactor is used to investigate the effect of addition of another pollutant on the performance of oxidation process. A synergetic effect was observed by combining NPSD and photocatalysis for the degradation of mixture of pollutants. In addition, combined NPSD/photocatalysis has significantly enhanced the CO2 selectivity, as compared to NPSD alone. This is attributed to the formation of more reactive species due to the presence of TiO2 in the plasma discharge zone. Moreover, ozone and UV light on TiO2, produced by plasma, have activated the surface leading to enhanced mineralization. In addition, the byproducts of each binary mixture were identified and evaluated.

Improved Determination of Dichloroacetic and Trichloroacetic Acids in Water by Solid Phase Extraction Followed by Ultra-high Performance Liquid Chromatography–Tandem Mass Spectrometry

ABSTRACT A simple, rapid, and sensitive ultra-high performance liquid chromatography–electrospray ionization tandem mass spectrometry method was developed for the determination of dichloroacetic acid and trichloroacetic acid in water. Analytes were extracted and concentrated by solid phase extraction. Under the optimized conditions, the extraction recoveries ranged from 98.13 to 100.57% for both analytes. The separation was performed on a reversed phase C18 column by using gradient elution. Detection was performed in multiple reaction monitoring mode using negative electrospray ionization. The developed method yielded limits of detection from 0.04 to 0.08 ng/mL. The intra-day and inter-day precisions for the analytes were less than 4% and the accuracy was between 99.12 and 102.38%. To the best of our knowledge, this work describes for the first use of solid phase extraction with ultra-high performance liquid chromatography tandem mass spectrometry for dichloroacetic acid and trichloroacetic acid in water.