Monitoring of water quality and remediation: Innovative multifunctional micro-sensor – AQUAE

The AQUAE project relied on a structured methodological approach to develop sensors for the in situ detection of water contaminants, combining photonic infrared spectroscopy (mid-IR) and electrochemistry. Work focused on the design and development of IR photonic sensors based on chalcogenide glass waveguides, suitable for detecting organic compounds in aqueous environments, as well as the design and fabrication of electrochemical sensors, including the development of specific electrodes for the detection of nitrates and other relevant species. The devices were integrated into microfluidic architectures allowing sample handling and conditioning for reliable and repeatable in situ measurements. In addition, a conceptual control and acquisition system was developed to manage and operate both types of sensors on a single platform while maintaining the functional independence of each technology.

Regarding targeted molecules, the work initially focused on BTEX – Benzene, Toluene, Ethylbenzene, and Xylenes, volatile aromatic hydrocarbons – with extensive testing to assess sensor sensitivity, selectivity, and reliability. Preliminary tests on polycyclic aromatic hydrocarbons (PAHs) presented no significant difficulties, confirming the robustness of the sensors for more complex molecules. We therefore chose to tackle a more challenging task, directly driven by the end-user SCIRPE, focusing on two distinct issues: pesticide detection, a major environmental concern in agricultural settings requiring precise measurements for ecosystem preservation, and ibuprofen detection, a widely used anti-inflammatory that can cause environmental and health issues such as endocrine disruption and effects on aquatic organisms.

The modular strategy, designed to facilitate interfacing and support miniaturization, is based on two distinct sensors optimized according to their respective constraints, a harmonized microfluidic design, and integration as “plug-in” modules within a common control system. This organization maintained overall project coherence while addressing the constraints and priorities of AQUAE’s end-user partners, laying the groundwork for potential future developments.

The AQUAE project produced significant scientific results for the development of water pollutant sensors. On the photonic side, Ge-Sb-Se and Ge-Sb-Se-Te waveguides were synthesized from purified targets, reducing absorption bands linked to impurities and improving optical guiding. Thin films deposited by RF magnetron sputtering were characterized by transmission spectroscopy, AFM, and ellipsometry, showing uniform thickness and roughness below 2 nm RMS. Optimization of optical waveguide fabrication via RIE etching achieved state-of-the-art performance, with propagation losses of 2.6 dB/cm at 1.55 µm and a minimum of 1.45 dB/cm at 4.11 µm. Thanks to these optimizations, light propagation was extended up to 11 µm, demonstrating the feasibility of Mid-IR guiding in these chalcogenide transducers.

Integration with polymer membranes (PIB, bio-based PHA) on chalcogenide prisms enabled the demonstration, via ATR-FTIR spectroscopy, of continuous-flow detection (3 ml/min) of aromatic hydrocarbons, pesticides, and ibuprofen, with detection limits of 50 ppb for xylenes and 100 ppb for BTX, and confirmed regenerability over multiple rinse-and-dry cycles. Validation was performed on UV-treated seawater supplied by CEDRE and filtered wastewater from the SCIRPE site, confirming BTEX detection.

In electrochemistry, optimized modified gold microelectrodes allowed nitrate detection with attractive detection and quantification limits covering the target environmental range. The electrodes showed reproducible regeneration, with variations below ±5 % over ten cycles, ensuring measurement reliability. 3D-printed microfluidic devices were validated for flow rates of 3–6 ml/min without leakage, demonstrating robustness and reproducibility. On-site validation confirmed the robustness and accuracy of electrochemical measurements for real-time nitrate monitoring and rapid fluctuation detection.

These results demonstrate the feasibility of sensitive, regenerable photonic and electrochemical sensors suitable for real-time monitoring of organic and inorganic pollutants. They provide a solid foundation for modular systems combining IR and electrochemical technologies, with quantitative and reproducible performance validated both in the laboratory and on-site, paving the way for operational applications in water monitoring, precise environmental tracking, and rapid detection of pollutant concentration changes.

Environmental water pollution is a growing global problem, leading to stricter regulations and an increased demand for improved water quality monitoring solutions. New in situ sensing devices are needed to enhance monitoring, enable the development of pollution control measures, and facilitate efficient water treatment management, particularly in support of the EU “Zero Pollution for Air, Water, and Soil” Action Plan, a key element of the European Green Deal.

Looking ahead, the AQUAE consortium has engaged in the Horizon Europe project IBAIA, which addresses the growing need for advanced water quality monitoring solutions in line with the objectives of the European Green Deal. The project aims to develop four innovative and optimized sensor modules capable of detecting different classes of pollutants, including microplastics, organic compounds, nutrient salts, and heavy metals, while also measuring salinity and various physicochemical parameters. These sensors will be designed, tested, and integrated into an advanced modular multi-sensing platform.

This system will provide a versatile “turnkey” solution suitable for a wide range of end users, such as environmental agencies and industrial stakeholders. By combining multiple detection technologies within a single device, IBAIA will enable reliable, real-time, and comprehensive water quality monitoring. The four standalone modules will be integrated into a single multi-sensor device that is portable, cost-effective, robust, and flexible, based on a single-board computer connected to a custom printed circuit board hosting the required connectors, hardware interfaces, and electronic components for communication with the sensor modules.

Through this technological innovation, the project will directly contribute to the implementation of the European Green Deal by improving environmental monitoring, water resource management, and decision-making for their protection.

There is an urgent need to develop reliable and reproducible sensing technologies for in situ and continuous water monitoring for surface water and wastewaters. The AQUAE project will address this need by specifically developing dedicated chemical sensors that are versatile and adaptable enough to monitor priority substances and their degradation in a wide range of aquatic environments.
Real-time monitoring of water quality using these chemical sensors will be performed in the real environment and at the point of discharge, which is necessary to prevent micropollution, define appropriate corrective actions for environmental remediation and decide when they should be undertaken (SCIRPE, BRGM, IFREMER with CEDRE).

The AQUAE project will provide an attractive solution for real-time monitoring of nutrient concentration to control sustainable remediation processes such as phytoremediation (SCIRPE with DEEP INSA) and nutrient recovery treatment (Bioengine Laboratory, U. Laval, Canada). The development of chemical sensors for on-site detection will skillfully combine infrared photonics (IR) and electrochemical (EC) technology, both well mastered by the consortium (ISCR, KLEARIA, I.FOTON, BRGM & IFREMER). These two spectroscopic methods will be coupled in a portable device with a common microfluidic system for a fast, multivariate and in situ monitoring of organic contaminants. This hybrid prototype combining IR and EC sensors is oriented towards water pollution problems and wastewaters treatment by phytoremediation or nutrient recovery treatment.

In addition to its fabrication for on-site use, a major challenge of the project is to overcome a new scientific barrier by designing and fabricating IR & EC sensors on a unique Lab-on-Chip. This AQUAE's LOC multifunctional sensors with an adapted microfluidic system will be designed to detect various priority substances (BTEX, PAH, pesticides, phthalate, drug residues and nitrates). Its efficiency will be tested at the laboratory scale for a first proof of concept.

The detection concentrations in the AQUAE project for considered micropollutants will be at laboratory scale : BTEX and PAHs in case of vicinity of accidental pollution range from 50-150 µg/L, phthalate DEHP often in the range of 1-100 µg/L in wastewater and rain water, pesticides more than 5 µg/L in polluted sites for which the standard at 0.1 µg/L can be largely exceeded like in the north of France (metolachlor), non-steroidal anti-inflammatory drugs (diclofenac and ibuprofene) with tested range µg/L-mg/L.

For nitrates detected by electrochemical sensor, we will consider the Nitrates Directive (91/676/EEC) which requires Member States to respect the quality standard not to be exceeded for the good status of groundwater (50 mg/L). The recommendation for discharges to water are about 15 mg/L of total nitrogen in the case of a treatment plant with a capacity of more than 600 kg/d. At the national level, the nitrate pollutant load of small treatment plants remains marginal. Reduction efforts must be concentrated on agricultural inputs especially in “vulnerable zones" where specific agricultural practices are imposed to limit the risks of pollution. In the AQUAE project, the sensors robustness will be demonstrated in the range 1-100 mg/L, at least with daily measurements to prevent any accidental event and with a t of 30 min to follow the denitrification process, in agreement with surface water analysis and industrial applications. The 0.05-1 mg/L range is a bonus for seawater analyses.