Thomas Thiebault

Adsorption Mechanisms of Emerging Micro-pollutants with a clay Mineral: Case of Tramadol and Doxepine Pharmaceutical Products

A sodium exchanged smectite clay mineral (Mt) was used as geo-sorbent for the adsorption of tramadol and doxepin: two pharmaceutical products (PPs) defined as emerging pollutants due to their presence at significant concentration in numerous water compartments. The adsorption isotherms for both the temperatures of 20 and 40°C and the derived data determined through the fitting procedure by using Langmuir, Freundlich and Dubinin-Radushkevich equation models explicitly pointed out that the sorption of both tramadol and doxepin is mainly driven by electrostatic interaction. The studied PPs are intercalated in a monolayer arrangement within the interlayer space through a cation exchange in stoichiometric proportion with the Na(+) cations leading to adsorbed PPs amounts that match the cation exchange capacity (CEC) of Mt. Due to their hydrophobic character, additional doxepin molecules could be adsorbed by weak molecular interaction driving to an increase of the adsorbed amount beyond the CEC at low temperature (20°C). The confinement of PPs within the interlayer space of Mt confirms the use of clay minerals as potential material for the wastewater treatment as well as it drives to an amorphous or glassy state, which can find echo in biopharmaceutical applications for a controlled release of PPs.

Adsorption of diclofenac onto organoclays: Effects of surfactant and environmental (pH and temperature) conditions.

Among pharmaceutical products (PPs) recalcitrant to water treatments, diclofenac shows a high toxicity and remains at high concentration in natural aquatic environments. The aim of this study concerns the understanding of the adsorption mechanism of this anionic PP onto two organoclays prepared with two long-alkyl chains cationic surfactants showing different chemical nature for various experimental pH and temperature conditions. The experimental data obtained by a set of complementary techniques (X-ray diffraction, elemental analyses, gas chromatography coupled with mass spectrometry, and Fourier transform infrared spectroscopy) and the use of Langmuir, Freundlich and Dubinin-Radushkevish equation models, reveal that organoclays show a good affinity to diclofenac which is enhanced as the temperature is under 35°C and for pH above 4.5 (i.e. >pKa of diclofenac) while the chemical nature of surfactant appears to play a minor role. The thermodynamic parameters derived from the fitting procedure point out the strong electrostatic interaction with organic cations adsorbed within the interlayer space in the organoclays for the adsorption of diclofenac. This study stress out the application of organoclays for the adsorption of a recalcitrant PPs in numerous aquatic compartments that can be used as a complement with activated carbon for waste water treatment.

Clayey–sand filter for the removal of pharmaceuticals from wastewater effluent: percolation experiments

The objective of the study was to evaluate the sorption of a pool of pharmaceutically active compounds (PhACs) onto a clay–sand filter in a dynamic sorption experiment. The chosen adsorbent should have suitable chemical properties for the removal of the targeted PhACs and also a consistent hydrodynamic behavior regarding field application. In this aim, the impact of interfoliar cations (Ca2+ or Na+) intercalated into natural montmorillonite (Swy2) was tested by using different clay–sand ratios (from 0% to 100% of clay minerals). Only Ca-Swy2 showed a consistent hydraulic conductivity for field application with a value of 4.78 × 10−8 m s−1 for a 5%/95% clay–sand ratio. The sorption of PhACs onto this filter was investigated using œdometer cells by varying two parameters: the solution matrix (ultra-pure water or natural effluent) and the injection pressure (0.1 MPa and 0.2 MPa). The PhACs were effectively adsorbed onto the filter for each experiment at different levels. The drop in injection pressure was a favorable factor for sorption whatever the matrix was, with median global removal of ∼45% at 0.2 MPa and ∼75% at 0.1 MPa. The effect of the matrix exhibited two different trends as a function of the molecular charge of each PhAC. While cationic compounds were more effectively sorbed in the ultra-pure water matrix than in the effluent matrix, the sorption of anionic PhACs was more effective in the effluent matrix than in ultra-pure water. This indicates that the charge of the pollutant is a key parameter in controlling the efficiency of the adsorbent. Despite these removal variations, the filter exhibited a significant sorption capacity especially at 0.1 MPa. It can therefore be an efficient solution for the removal of PhACs by tertiary filtration.

Temporal dynamics of human-excreted pollutants in wastewater treatment plant influents: toward a better knowledge of mass load fluctuations

The occurrence of 25 drug target residues (illicit drugs or pharmaceutically active compounds) was investigated during 85 consecutive days in the influents of a wastewater treatment plant in the Region Centre-Val de Loire, France. This long tracking period allowed a better understanding of the patterns affecting the occurrence of this type of contaminants. Among them, 2 were never detected (i.e. heroin and amphetamine). Concerning illicit drugs two patterns were found. Cocaine and ecstasy median loads varied considerably between weekdays and weekend days (i.e. 18.3 and 35.9% respectively) whereas cannabis and heroin (based on 6-mono-acetylmorphine loads) loads were within the same order of magnitude with a significant statistical correlation with pharmaceuticals such as acetaminophen or ketoprofen. The consumption of selected drugs was back-calculated from the loads. Among illicit drugs the highest consumption was found for cannabis with a median consumption of 51mg·day-1·inhabitant-1 (inh) whereas the median consumption for cocaine (based on benzoylecgonine loads) and ecstasy was 32 and 6mg·day-1·103·inh-1 respectively. The highest consumption values of pharmaceutically active compounds (PACs) were found for acetaminophen and acetylsalicylic acid with 108.8 and 34.1mg·day-1·inh-1 respectively, in good agreement with national sales data. A statistically significant weekly pattern was found for several PACs such as metoprolol and trimethoprim, but with the opposite pattern to that of illicit drugs. The variations in daily PAC loads could provide information about the mobility of people in the catchment, especially on the basis of daily taken PACs (i.e. to treat chronicle diseases).

Competitive adsorption of a pool of pharmaceuticals onto a raw clay mineral

The removal of a Pharmaceutically Active Compound (PhAC) pool using a well referenced clay mineral from Wyoming (SWy-2) as a geosorbent was studied for a better understanding of the environmental fate. As expected, the selected material shows its particular adsorption properties to PhAC under different experimental conditions with two main features depending on the chemical nature of the emerging micro-pollutants. Cationic PhACs, for which the driving force for their adsorption results from electrostatic interaction via the exchange with the inorganic cations of the clay mineral, are almost completely removed for all studied experimental conditions where it appears that the S/L ratio plays a minor role and the only one limitation for their removal is the cation exchange capacity of the adsorbent. In contrast, anionic and neutral PhACs are adsorbed to the clay mineral surface (silanol groups on the sheet edges, inorganic cations…) through other interactional mechanisms involving ion–dipole, van der Waals interaction, leading to a competition of all organic molecules where their chemical nature (electric charge, hydrophobicity) may also play a role in their adsorption. While the adsorption of ketoprofen, naproxen, diclofenac and salicylic acid anionic PhACs slightly increases with the increase of the S/L ratio, the removal of the neutral and the other anionic PhACs (gemfibrozil and ibuprofen) seems to be independent of that ratio and is particularly enhanced. The efficiency of the removal for a global pool of PhACs even in low S/L ratio stresses the control of the selected natural minerals on the dynamics of PhACs in the environment.

Correction: Competitive adsorption of a pool of pharmaceuticals onto a raw clay mineral

Correction for ‘Competitive adsorption of a pool of pharmaceuticals onto a raw clay mineral’ by T. Thiebault et al., RSC Adv., 2016, 6, 65257–65265.