Plant transpiration in constructed treatment wetland: Effects on water budget and management consequences.

Plant transpiration is an important feature of wetlands with biological and hydraulic impacts. The global objective of this study was to question the influence of transpirational water losses on constructed treatment wetland water budget for a variety of wetland design and time of the year. Biomass and transpiration field measurements were carried out in constructed treatment wetlands (CTWs) submitted to oceanic climate and used for waste- or stormwater management. Measurements were carried out during spring, summer and fall. Biomass and transpiration rate were both significantly affected by season and site configuration, although the effect appears more sharply for season than for site. Transpiration can reach 26% of the incoming flow during the warmest part of the year for wastewater management CTW, when the effect on adjacent water courses is likely to be the most significant. The impact on multi-monthly water budget plummets to 2% of the incoming water volume. For stormwater CTW, transpiration can lead to strong water scarcity, virtually emptying all available water in these stochastically fed systems. As transpiration also plays a significant role in biogeochemical processes in wetlands, it seems important to design this type of ecological infrastructure in close relation with the pursued objectives, be it either the quality of outlet water (emphasis on treatment efficiency) or the quantity of outlet water (emphasis on flow regulation).

Xenobiotics metabolization in Salix alba leaves uncovered by mass spectrometry imaging.

INTRODUCTION: Micropollutants are increasingly monitored as their presence in the environment is rising due to human activities, and they are potential threats to living organisms. OBJECTIVES: This study aimed at understanding the role of plants in xenobiotics removal from polluted environments by following xenobiotics metabolism in leaf tissues. METHODS: Different classes of micropollutants were investigated using liquid chromatography (LC) coupled to quadrupole-time of flight (Q-TOF) high resolution mass spectrometry (HRMS). The tissue localization of xenobiotics in the leaves of a spontaneous (not planted by humans) Salix alba growing near the water flux was further investigated using matrix-assisted laser desorption ionization (MALDI) mass spectrometry imaging (MSI). RESULTS: The LC-Q-TOF analysis revealed the distribution of micropollutants in three different compartments of a tertiary treatment wetland. When further investing the metabolic profile of S. alba leaves using MSI, different distribution patterns were observed in specific leaf tissues. Xenobiotic metabolites were predicted and could also be tentatively identified in S. alba leaves, shedding new light on the metabolic processes at play in leaves to manage xenobiotics uptake from a polluted environment. CONCLUSION: Using complementary metabolomics approaches, this study performed a large-scale exploration of micropollutants spreading in the environment at the exit of a tertiary treatment wetland. The use of MSI coupled with the prediction of xenobiotic metabolites yielded novel insights into plant metabolism during chronical exposure to low doses of a mixture of micropollutants.

Mass spectrometry imaging for biosolids characterization to assess ecological or health risks before reuse.

Biosolids are byproducts of wastewater treatment. With the increasing global population, the amounts of wastewater to be treated are expanding, along with the amounts of biosolids generated. The reuse of biosolids is now accepted for diversified applications in fields such as agriculture, engineering, agro-forestry. However, biosolids are known to be potential carriers of compounds that can be toxic to living beings or alter the environment. Therefore, biosolid reuse is subject to regulations, mandatory analyses are performed on heavy metals, persistent organic pollutants or pathogens. Conventional methods for the analysis of heavy metals and persistent organic pollutants are demanding, lengthy, and sometimes unsafe. Here, we propose mass spectrometry imaging as a faster and safer method using small amounts of material to monitor heavy metals and persistent organic pollutants in different types of biosolids, allowing for ecological and health risk assessment before reuse. Our methodology can be extended to other soil-like matrices.

Diagnosing trace metals contamination in ageing stormwater constructed wetlands by portable X-ray Fluorescence Analyzer (pXRF).

In the context of stormwater management in urban areas, more knowledge is needed about sustainable urban drainage systems (SUDS)' long-term performance. This article reports robust calibration of a portable X-ray Fluorescence Analyzer (pXRF) for a purpose of metal accumulation diagnosis in two stormwater constructed wetlands (SCWs). Two 9-year-old SCWs located in Eastern France and composed of a sedimentation pond and a vertical-flow reed-bed filter (RBF#1) respectively a horizontal-flow RBF (RBF#2) are studied. A focus is made on the RBFs where five target metals (Cr, Cu, Ni, Pb, Zn) are monitored to fulfill three objectives: i) develop a robust analyzing method for both field and laboratory scale; ii) compute a distribution mapping of the metals on the substrate; and iii) identify and quantify contamination hotspots. pXRF measurements present an opportunity for a quick field diagnosis of such ageing systems once calibrated. An optimal 63 s beam shooting time was selected for analyses, and optimal particle size distribution was set below 250 µm. As water content is known to be a critical factor influencing measuring quality, correction factors were determined to allow for field campaign up to 30 % of water content. Metals are more accumulated in RBF#1 than in RBF#2 because of the particle size distribution and hydraulic regime of the RBFs. Moreover, RBF#1 displays a higher metal accumulation at the water supply outputs while the distribution pattern in RBF#2 is more diffuse. Only 34 %, resp. 22 % of RBF#1 and RBF#2 surface is contaminated, with corresponding concentrations ranging among the highest 50 % and 25 % concentrations. Eventually, the RBF#1 upper layer (0-5 cm) higher organic matter content generates more metal retention than its deeper layer whereas in RBF#2 metal concentration is homogeneous along depth. These results can be useful to optimize the long-term maintenance and possibly the sizing of such systems.

Distribution and degradation trend of micropollutants in a surface flow treatment wetland revealed by 3D numerical modelling combined with LC-MS/MS.

Conventional wastewater treatment plants are not designed to treat micropollutants; thus, for 20 years, several complementary treatment systems, such as surface flow wetlands have been used to address this issue. Previous studies demonstrate that higher residence time and low global velocities promote nutrient removal rates or micropollutant photodegradation. Nevertheless, these studies were restricted to the system limits (inlet/outlet). Therefore, detailed knowledge of water flow is crucial for identifying areas that promote degradation and optimise surface flow wetlands. The present study combines 3D water flow numerical modelling and liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS/MS). Using this numerical model, validated by tracer experimental data, several velocity areas were distinguished in the wetland. Four areas were selected to investigate the waterflow influence and led to the following results: on the one hand, the number and concentration of micropollutants are independent of the waterflow, which could be due to several assumptions, such as the chronic exposure associated with a low Reynolds number; on the other hand, the potential degradation products (metabolites) were also assessed in the sludge to investigate the micropollutant biodegradation processes occurring in the wetland; micropollutant metabolites or degradation products were detected in higher proportions (both number and concentration) in lower flow rate areas. The relation to higher levels of plant and microorganism metabolites suggests higher biological activity that promotes degradation.

Large scale micropollutants and lipids screening in the sludge layers and the ecosystem of a vertical flow constructed wetland.

Wastewater is one of the major sources of micropollutant release into the environment. In order to reduce the impact of wastewater, wastewater treatment plants (WWTP) have been set up, in the instance of vertical flow constructed wetlands (VFCWs). Besides, micropollutants could represent a vast diversity of compounds and compound's choice could bias studies focused on their fate. To overcome this bias, non-targeted screening approaches can be performed. Therefore, the diffusion of micropollutants from raw wastewater in the VFCW compartments (wastewater, plants and sludge) as well as their fate have been investigated using this non-target approach with liquid chromatography (LC) coupled to high resolution mass spectrometry (HRMS) and gas chromatography (GC) coupled to mass spectrometry. To help the operators in their sludge management, this study will be focused on the following question: Is there a specific distribution of micropollutants according to sludge layers? To eliminate the background contamination found both inside the CW and in the surrounding environment, a control coring was performed in bank. A specific distribution could be observed in the top (191 compounds) and bottom layers (38 compounds). However, a distribution over the whole depth for xenobiotics was observed. Micropollutants classes and the main microbial productivity were preferably found in the top layer. The micropollutants fate could however not be restricted to the sludge compartment. Therefore, the specific micropollutants distribution was analyzed in the outputs of the system in their interactions with wastewater (effluent, sludge, and reed rhizomes) to understand their fate. In our study, the results highlighted a consistent part of compounds found in at least two or three of these compartments, with a similar trend in each compartment. These results underline the interactions between the compartments and the global issues of micropollutants distribution as well as its wide spreading in the whole CW ecosystem.

Seasonal and ageing effect on the behaviour of 86 drugs in a full-scale surface treatment wetland: Removal efficiencies and distribution in plants and sediments.

The presence of human drugs in the aquatic environment is partly due to an incomplete and insufficient removal process of wastewater treatment plants (WWTPs). Thus, drug traces are observed at different concentrations in water bodies, sediments and aquatic plants all over the world. At the same time, Surface Flow Treatment Wetlands (SFTWs) at the outlet of WWTPs are commonly observed in small municipalities as complementary treatment. However, little is known regarding the role of SFTWs in the complementary mitigation of emerging contaminants, such as drugs, and the interactions between drugs, plants and sediment throughout the seasons. For that reason, we conducted sampling sessions over a period of two years on a full-scale SFTW downstream of a vertical-flow constructed wetland. At each session, the SFTW influent and effluent, as well as five different plant species and one composite sediment sample, were sampled. We detected more than fifty pharmaceutical compounds in the inflow and outflow water. The compounds most frequently detected were bisoprolol and ketoprofen. We emphasized that the SFTW removal ability was better in the summer than in the winter, due to the impact of weather on physicochemical parameters. Large variations of removal efficiencies were also observed when considering all of the detected compounds. Large seasonal variations were also observed for each compound. In addition, the study of the five plants showed their ability to uptake drugs from water and soil to the leaves in a species-specific manner. The pharmaceutical composition of the sediment was also correlated with the season: the maximum occurrence was reached in summer, and the minimum was reached in winter. Finally, the continuous decrease in removal efficiencies highlights the ageing effect on SFTW removal ability.

Assessment of rock wool as support material for on-site sanitation: hydrodynamic and mechanical characterization.

This study proposes mechanical and hydrodynamic characterization of rock wool used as support material in compact filter. A double-pronged approach, based on experimental simulation of various physical states of this material was done. First of all a scanning electron microscopy observation allows to highlight the fibrous network structure, the fibres sizing distribution and the atomic absorption spectrum. The material was essentially lacunar with 97 ± 2% of void space. Static compression tests on variably saturated rock wool samples provide the fact that the strain/stress behaviours depend on both the sample conditioning and the saturation level. Results showed that water exerts plastifying effect on mechanical behaviour of rock wool. The load-displacement curves and drainage evolution under different water saturation levels allowed exhibiting hydraulic retention capacities under stress. Finally, several tracer experiments on rock wool column considering continuous and batch feeding flow regime allowed: (i) to determine the flow model for each test case and the implications for water dynamic in rock wool medium, (ii) to assess the rock wool double porosity and discuss its advantages for wastewater treatment, (iii) to analyse the benefits effect for water treatment when the high level of rock wool hydric retention was associated with the plug-flow effect, and (iv) to discuss the practical contributions for compact filter conception and management.