Département Ressources aquatiques et eau potable

Awareness concerning sustainable groundwater consumption under the context of land use and climate change is gaining traction, raising the bar for adequate understanding of the complexities of natural and anthropogenic processes and how they affect groundwater quality. The heterogeneous characteristics of aquifers have hampered comprehensive source, transport and contaminant identification. As questions remain about the behavior and prediction of well-known groundwater contaminants, new concerns around emerging contaminants are on the increase. This review highlights some of the key contaminants that originate from anthropogenic activities, organized based on land use categories namely agricultural, urban and industrial. It further highlights the extensive overlap, in terms of both provenance as well as contaminant type, between the different land use sectors. A selection of case studies from literature that describe the continued concern of established contaminants, as well as new and emerging compounds, are presented to illustrate the many qualitative threats to global groundwater resources. In some cases, the risk of groundwater contamination lacks adequate gravity, while in others the underlying physical and societal processes are not fully understood and activities may commence without adequately considering potential impacts. In the agricultural context, the historic and current application of fertilizers and plant protectants, use of veterinary pharmaceuticals and hormones, strives to safeguard the growing food demands. In the context of a sprawling urban environment, waste, human pharmaceuticals, and urban pesticide outputs are increasing, with adequate runoff and sanitation infrastructure often lagging. Finally, industrial activities are associated with accidental leaks and spills, while the large-scale storage of industrial byproducts has led to legacy contaminants such as those stemming from raw mineral extraction. With this review paper, we aim to underscore the need for transdisciplinary research, along with transboundary communication, using sound science and adaptive policy and management practice in order to procure sustainable groundwater quality.

Production volumes of cerium dioxide nanoparticles (CeO₂ NP) are predicted to increase in the near future, which will result in increasing amounts of CeO₂ NP discharged into wastewater systems and their accumulation in the sewage sludge. At the same time, thermal treatments of sewage sludge, especially incineration, are gaining in importance. Therefore, knowledge on the physical–chemical transformations of CeO₂ NP during wastewater treatment and sludge incineration is critical for assessing possible (eco-) toxicological effects related to the increased use of CeO₂ NP. We, thus, incinerated unspiked municipal sewage sludge as well as sludge spiked with CeO₂ of different particle sizes (4 nm (CeO₂-s1), 26 nm (CeO₂-s2) and >16 μm (CeO₂-s3)) in a pilot fluidized bed reactor to investigate the (size dependent) transformation of CeO₂ under conditions mimicking full-scale incineration facilities. We used Ce K- and LIII-edge X-ray absorption spectroscopy (XAS) complemented by analytical electron microscopy to assess the changes in Ce speciation and to characterize the morphology of the pristine and the transformed Ce-(nano)particles. After one week of incubation in digested sludge under anaerobic conditions, CeO₂-s1 already showed partial reduction (≈40%) to a Ce(III)-phase. Cerium dioxide of larger particle size (CeO₂-s2 and -s3) was less reactive and did not show any detectable reduction within the same reaction time. Incineration of the sludge in general led to a further reduction of Ce, irrespective of whether the Ce was spiked (CeO₂-s1, CeO₂-s2, CeO₂-s3) or already present in the sludge. Reduction during incineration was nearly complete for CeO₂-s1 but much less pronounced for CeO₂-s2 and -s3. Ce(IV) in larger (primary-) particle sizes thus was more resistant to reduction during anaerobic digestion and incineration. In addition, elemental distribution maps of the CeO₂-s1 fly ash revealed elevated Ce signal intensities evenly distributed over areas of several 100 nm. The complementary results obtained from spectroscopic and microscopic analyses indicate that incineration led to the reductive decomposition of the initial CeO₂-s1 NP and the sequestration of Ce(III) into a mineralogical phase with probably allanite-like local Ce(III) coordination. Our results, thus, highlight the importance of particle size and the surrounding matrix both affecting the transformation of CeO₂ during sewage sludge incineration.

This study focused on the effects of ozonation on the photochemical and photophysical properties of dissolved organic matter (DOM). Upon ozonation, a decrease in DOM absorbance was observed in parallel with an increase in singlet oxygen (¹O₂) and fluorescence quantum yields (Φ_1O2 and Φ_F). The increase in Φ_1O2 was attributed to the formation of quinone-like moieties during ozonation of the phenolic moieties of DOM, while the increase in Φ_F can be explained by a significant decrease in the internal conversion rate of the first excited singlet state of the DOM (¹DOM*). It is a consequence of an increase in the average energy of the first electronic transition (S₁ → S₀) that was assessed using the wavelength of maximum fluorescence emission (λ_F,max). Furthermore, ozonation did not affect the ratio of the apparent steady-state concentrations of excited triplet DOM (³DOM*) and ¹O₂, indicating that ozonation does not affect the efficiency of ¹O₂ production from ³DOM*. The consequences of these changes for the phototransformation rates of micropollutants in surface waters were examined using photochemical model calculations. The decrease in DOM absorbance caused by ozonation leads to an enhancement of direct photolysis rates due to the increased transparency of the water. Rates of indirect photooxidation induced by ¹O₂ and ³DOM* slightly decrease after ozonation.