NIR and EIS : towards a whole characterisation of organic complex fluids
During many years, the environmental quality of wastewater treatment plant was only defined on the basis of the water quality which was rejected in the natural ecosystem. Sludge treatment and reuse was totally neglected. However, to protect aquatic resources, approved and perennial channels of sludge evacuation are needed.
Practically, sludge is a complex material of unknown composition. Thus, its rheological properties are highly dependent on the interactions between the different compounds. The interactions between water and solid compounds were especially proved to be closely related to sludge rheological properties (Baudez, 2001; Agoda-Tandjawa et al., 2014). However, to monitor and optimise sludge treatment processes, those rheological properties cannot be ignored. To design plant facilities, it is then of major importance for professionals to a priori defining sludge rheological properties.
In the manufacturing industry, materials composition is usually well known which allows the determination of abacus describing rheological behaviour. On the contrary, each sludge sample is representative of nothing but itself. Thus, determining sludge rheological properties during a process becomes a problem and professionals are waiting for reliable methods, usable online, to instantaneous correlate sludge rheological behaviour with representative indicators. Previous works have shown that near infrared spectroscopy and electrical impedance spectroscopy are powerful techniques either to indicate the evolution of rheological parameters (Dieudé-Fauvel et al., 2009, 2014) or to understand the relationship between water and solid compounds (Mas et al, 2014 to be published).
In that purpose, our works tend toward a multidisciplinary approach, using different physical characterisation techniques. The aim of the Post-Doc consists in defining a bunch of descriptors, easily and rapidly measurable, representative of sludge structure, composition and interactions between the compounds. These descriptors would participate to form kind of “topological ball” defining sludge rheology: two sludge samples in the same ball would show the same rheological behaviour.Specific attention will be paid on the experimental approach.
This Post-Doc is integrated to a binational project, ‘NEXT’. The goal of this project is to investigate the in-line and real-time use of novel holistic sludge descriptors to measure, monitor, model and predict sludge behaviour through sludge treatment processes and use this knowledge for the optimization of design and operation of treatment processes. It will lean on previous works developed by 2 Irstea teams (on the one hand on organic fluids characterisation based on electrical measurements and rheology and on the other hand on near infrared (NIR) spectroscopy on turbid fluids and soils). Its purpose consists in generating a matrix of data, representing sludge characterisation and from which it will be possible to link sludge macroscopic behaviour, microscopic structure and indicators of sludge composition.
In that way, NIR spectroscopy will be related to rheological and electrical analysis to understand how sludge evolves during treatment processes, e.g. anaerobic digestion.
Thus, at the end of this work, we intend to be able to characterise both the dynamic of evolution of the rheological behaviour (based on electrical measurements) and instantaneous pictures (based on NIR spectroscopy). The characterisation method that will be developed will allow us to analyse and optimise treatment processes via in-situ measurements.
On a methodological point of view, this Post-Doc work will be divided into two parts. In a first time, focus will be done on NIR spectroscopy and rheology measurements: specific attention will be paid on optics and mathematical analysis, including experimental development. The second part will be dedicated to rheology and electrical measurements, then simultaneous characterisation using NIR. First part will be realized in Montpellier (South of France) and second in Montoldre (Auvergne, Centre of France). This experimental work will start with the study of the state of the art.
This Post-Doc will happen commonly within two Irstea teams: one located on the Centre of Montpellier, the other on the Centre of Clermont-Ferrand, on the site of Montoldre (Allier). The Post-Doc subject being at the interface of the activities of these two teams, the applicant will be supervised by two researchers, Ryad Bendoula and Emilie Dieudé-Fauvel.
The first team, located in Montpellier is well-known for its research in material characterisation and more precisely in near infra-red spectroscopy. It develops specific sensors and models for characterizing complex media like wastes, soils or turbid liquid (e.g. micro algae). It has developed a knowledge internationally recognised in NIR spectroscopy and chemometrics as shown by the chair of the 16th major international NIR conference in 2013 and of the 11th major international chemometrics conference in 2008. Original optical mountings have been set up for addressing turbid and complex matter and dedicated modelling techniques have been developed for overcoming the calibration robustness problems. These innovations are currently transferred to industrial partners e.g. in the context of waste sorting (TRI+ project).
The second team, based in Auvergne (more precisely in Montoldre) is known for its pioneering work on sludge management and sludge rheology. Its experience in wastewater treatment domain will also allow us to keep in mind the professionals’ concerns. For the last 12 years, specific attention has been paid to biosolids characterisation (mainly talking about sewage sludge), using rheology, texturometry or electrical impedance spectroscopy. All those methods are dedicated to study complex materials behaviour. Such tools allowed us to develop the fields of application and many projects like the study of sewage sludge dewatering or biosolids transformation processes are realized. Many partnerships are developed in France and abroad: with industrials (Faure Equipements, Veolia, etc.), public institutions (ADEME, Water Agencies, Ministry in charge of the Ecology, etc.), and universities (Limoges (France), Liege (Belgium), Delaware (US), Carleton (Canada), Melbourne (Australia)…).
Skills in physics and/or optic and/or material sciences
Interest for environmental issues and process engineering
This Post-Doc is a pluridisciplinary subject and the applicant will be integrated within teams who are used to applied techniques. Skills in all domains are not demanded but very good adaptation ability is needed.
Driving licence will be appreciated