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BROADBAND TUNABLE QCL BASED SENSOR FOR ONLINE AND INLINE DETECTION OF CONTAMINANTS IN WATER

Periodic Reporting for period 2 - AQUARIUS (BROADBAND TUNABLE QCL BASED SENSOR FOR ONLINE AND INLINE DETECTION OF CONTAMINANTS IN WATER)

Reporting period: 2018-07-01 to 2020-12-31

The aim of AQUARIUS was to provide an online and inline capable mid-IR sensing solution that meets the legal provisions for industrial waste water and drinking water monitoring. To achieve the required sensitivity, the employed laser source and detector had to be improved and combined with an innovative sample extraction method. In addition, waveguides were functionalized with polymers to further improve the limit of detection. The continuous improvements throughout the project allowed measurement campaigns at industrial productions sites and drinking water treatment plants.
As fresh water is essential for human wellbeing and the world economy, its quality is regulated by national and international legislation. Although it is the most abundant substance on Earth’s and used in almost every industrial process (directly or indirectly), fresh water comprises only a small fraction of the total amount of water. It is essential to ensure a good quality of this resource, even though the composition of fresh water can differ significantly. In particular, both, the concentration and the type of the dissolved substances, can vary and are a challenge to the water sector. Thousands of these compounds are used every day and new ones are continually put on the market. Specialized laboratories employ highly optimized detection techniques to measure their presence at low concentrations. Novel water monitoring technologies are needed for all types of water including process water, waste water, sewage and drinking water. These new technologies shall enable pervasive water monitoring which can replace and complement currently laboratory based offline methods by online or inline monitoring strategies.
The AQUARIUS project addressed the development of a new generation of photonic sensing solution in response to the need for pervasive sensing for a safer environment. In particular, components, modules, sub-systems and systems were developed to enhance the sensitivity and specificity measurements in water monitoring. They should adhere to the requirements of regulatory bodies, as well as the needs of selected end-users such as waterworks and the oil producing industry. The main focus in AQUARIUS was the detection of hydrocarbon contaminations (oil in water). AQUARIUS aimed to provide improved quality and effectiveness of online and inline sensors allowing a reliable and continuous real-time monitoring on site. This was achieved by improving external cavity (EC) quantum cascade lasers (QCL) and optimizing suitable detectors. The following key objectives have been addressed by AQUARIUS:
• O1: Enhancement of broadband tunable quantum cascade lasers in terms of spectral coverage and noise (TRL increase: from 4 to 6)
• O2: Realisation of a fully functional spectrometer sub-system consisting of a μEC-QCL and a fast MCT detector including data acquisition (TRL increase: from 3 to 6)
• O3: Advance Oil-in-Water (OiW) monitoring capabilities from offline (state-of-the-art) to online (TRL increase: from 3 to 6)
• O4: Test of the online OiW system at industrial end users (TRL 7)
• O5: Realisation of integrated optical circuits (IOCs) for waveguide based sensing and inline capable sensing configuration (TRL increase: from 2 to 4)
• O6: Assembly and test of the inline OiW system in a laboratory environment (TRL increase: from 2 to 4)
Priority in AQUARIUS was to set up a requirements analysis for online and inline oil in water (OiW) monitoring. Based on the collected requirements, specifications for online and inline OiW analysis were defined and target properties for the broadband mid-IR laser spectrometer were set. It included the definition of modules and the description of interfaces. A feasibility assessment was also performed and requirements for enhanced water analysis were defined.
The central component of the spectrometer was a quantum cascade laser, in which the spectral range was continuously extended throughout the project. The assembled laser modules were optimized in form factor, stability and driving electronics to integrate well with the spectrometer. In the end, they could be operated in pulsed and continuous wave (cw) mode and a scheme for mode-hop related noise reduction was employed. A concept for an all-MOEMS based EC-QCL, including a translational MOEMS component for high spectral resolution was also developed.
The attenuated total reflection (ATR) sensing unit was improved by depositing a mesoporous silica film on top. They were designed to act as enrichment layers for hydrocarbons and allowed fast diffusion into the layer and fast regeneration. Different pore structures and organic functional groups were tested. Thereby, high enrichment factors of > 1000 for aromatic hydrocarbons and limits of detection < 1 ppm were obtained. In addition to sensing applications, a new method for determining porosity and pore size distribution of the films was developed using ATR spectroscopy.
Designing and fabricating photonic integrated circuits (PIC) were also part of AQUARIUS. The propagation loss of the waveguides was measured to be suitable for the targeted applications. Proof-of-concept chips, having waveguides, in- and out- grating couplers and back side micro lenses, have been realised. These chips were tested in a dedicated setup developed for AQUARIUS and the broadband trough-substrate coupling concept was demonstrated. An interface allowing easy exchange of the IOC chip in the spectrometer was designed, tested and proven as useful tool.
Different methods for the extraction process were investigated and compared. Tests were conducted on-site in real world application scenarios; results were taken into consideration to further optimise the system. A modular housing was designed and fabricated to incorporate the prototypes developed in the individual work packages, and the necessary hardware / software was developed to ensure the seamless interplay between all components. Various workshops and conferences about potential application areas of an online analyser were attended; positive feedback was received concerning a prototype of such a system.
In preparation for the evaluation of the online sensor, a sample conditioning unit was designed. This unit is required to interface the system to sampling points of varying water qualities and to ensure flow conditions in accordance with requirements. The main part is a filter to protect the extraction unit from particles and biological matter. It was assembled and tested simultaneously with the extractor prototype; the analyte recovery was reduced by the filtration if the inlet pressure was insufficient. An additional inlet requirement for the sample conditioning unit was defined.
Field experiments with the online analyser were performed at a drinking water treatment plant and an industrial plant. The sensor delivered valuable information about water quality and made it possible to measure the oil content in the process streams continuously.
Results of the feasibility study and feedback from experts led to promising conclusions regarding the applicability and future scaling of the AQUARIUS system. There is a high interest in the technical solutions developed in this project; not only the online sensor, but also the EC-QCLs, improvements of ATRs and PICs are relevant for science and industry. The gained results are a solid base for further developments and can be improved further in upcoming projects.
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