Mecaflu team

Ph. D. offers

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Contribution to the development of a time-resolved optical measurement method for the study of sediment transport


Whether from the European point of view or more recently within the framework of the United Nations, a priority is to ensure the availability and sustainable management of water and sanitation. Optimal surface water management involves evaluating the load of suspended particulate matter (SPM) present in urban and natural flows. A real-time measurement of the SPM concentration, potentially polluting, is obtained through optical turbidity, a measurement technique massively deployed in the field.

Recent publications [Rymszewicz 2017, Voichik 2017] as well as our own work based on joint optical and acoustic measurements [Pallarès 2017] reveal inconsistencies in the optical data. In exceptional situations, such as rainy periods in sanitation or floods in rivers, the optical turbidity data are false and can lead to a massive underestimation of the concentration of suspended matter. This misinterpretation can have serious consequences for water treatment and management. In the context of sanitation, only our work, based on the study of the acoustic signal backscattered by the environment, questions the optical turbidity measurements.

With the support of SATT-Conectus, our team is currently engaged in the maturation of a new technique for real-time measurement of SPM concentrations, reliable even in exceptional and inexpensive situations intended for hydro-system managers. Therefore, the goal of this thesis is the development of a new instrumental approach based on the exploitation of optical signals obtained by an ultrafast measurement method resolved in time in the nanosecond domain. This technology also allows measurement of the velocity of a fluid. The purpose of this work is the delivery of a prototype of innovative instrumentation capable of proposing turbidity and/or concentration estimates in conjunction with velocity measurements. At the present time, there is no such commercial instrument.

In addition to the acquisition of experimental data, this thesis will focus on the analysis of optical data and their inversion in order to propose simple models relating the signal to the concentrations of suspended particles, which, combined with the measurement of the velocity of the carrier fluid will allow to go back to the flow of particles in the flow. This work will be carried out in close collaboration between the MécaFlu and SMH teams of the ICube Laboratory in Strasbourg. The MécaFlu team masters instrumental development and has the expertise in signal processing and interpretation, the SMH team masters the optical approach resolved in ultra-fast time at low cost derived from its research on medical imaging by optical.

Contact : Anne Pallarès

[Rymszewicz 2017] Rymszewicz, A., O'Sullivan, J. J., Bruen, M., Turner, J. N., Lawler, D. M., Conroy, E., & Kelly-Quinn, M. (2017). Measurement differences between turbidity instruments, and their implications for suspended sediment concentration and load calculations: A sensor inter-comparison study. Journal of Environmental Management, 199, 99.

[Pallarès 2017] Pallarès A. Burckbuchler M., Fischer S., Schmitt P. (2017) Suspended Sediment Monitoring: Comparison between Optical and Acoustic Turbidity, Proceedings of the 14th International Conference on Urban Drainage, Prague, 10-15 September 2017.

[Voichick 2017] Voichick N., Topping D.J, GriffithsR.E., (2018) Technical Note: False low turbidity readings during high suspended sediment concentrations, Hydrol. Earth Syst. Sci. Discuss.

Optimization of wastewater resource recovery by high-rate algal pond

This thesis project focuses on wastewater resource recovery technologies using microalgae. A previous PhD conducted in the laboratory demonstrated the treatment performance and developed a numerical model of a high-rate algal pond (raceway pond).

This study is a continuation of this work. A pilot reactor is already present in the laboratory.

The use of processes combining microalgae and bacteria has a very interesting potential. Indeed, via photosynthesis, algae use sunlight to convert mineral carbon (CO2) and nutrients contained in water (nitrogen, phosphorus) into biomass and oxygen (O2). At the same time, bacteria use the oxygen produced by algae for their metabolism leading to the degradation of organic compounds and oxidation of ammoniacal nitrogen, while producing the nitrates and CO2 required by the algae.

This natural process does not require any additional energy input. In addition, the content of the microalgae produced, which is rich in nutrients and organic matter (especially lipids), can be used as biofuel, fertilizer, etc. The High-Rate Algal Pond (HRAP) is a process that uses this consortium of algae and bacteria. It consists of an open oblong channel with a depth of 0.2 to 1 m. The mixing is carried out via a paddle wheel ensuring a horizontal circulation speed of 0.15 to 0.3 m/s. Previous studies have shown that LHRAs can eliminate more than 90% of the Chemical Oxygen Demand (COD), 79% of total nitrogen, more than 90% of ammonia nitrogen and 57% of total phosphorus.

A first objective will be to develop and make the process more reliable in order to cope with variations in operating conditions: hydraulic residence time, light intensity, nutrient loading and the impact of nitrification, biomass recycling, etc. This will involve proposing strategies to maintain biomass stability within the reactor and performance. This requires a detailed understanding of the biological and chemical processes governing the dynamics of microalgae and bacteria present in the system: physico-chemical analyses, respirometric tests, strains identification, scenario analysis using the numerical model.

The second objective will be to study the potential for valorising the biomass produced according to different operating conditions. Various options will be investigated: methanisation, biodiesel production by transesterification, nutrients (N, P), high added-value compounds.

The PhD thesis will be directed by Julien LAURENT, Senior Lecturer at the Ecole Nationale du Génie de l'Eau et de l'Environnement de Strasbourg (ENGEES) and at the ICube laboratory. The doctoral student will be affiliated with the MecaFlu team of the laboratory.

Depending on the evolution of the work and the opportunities, collaborations will be considered with the University of Science and technology of Hanoi (USTH) for the application of the process in real conditions in a developing country as well as with the Institute of Molecular Plant Biology (IBMP) for the identification by mass spectrometry of potentially valuable compounds within the algae produced.

Contact: Julien LAURENT julien.laurent(at)