WAstewaTEr puRification by solidification: Simulation by phAse Field mEthod – WATERSAFE

Ice layer crystallisation (ILC) on a cooling wall is an innovative purification process of freezing proposed to concentrate wastewater. Many works demonstrated the process feasibility but because of pollutant incorporation in ice and low ice yield, its industrial up-scaling was not done. The deadlock status of ILC process could however possibly be circumvented through: i) performing a process intensification study in order to improve its global efficiency; ii) improving process issue that include batch to continuous approach (process efficiency and management).To fulfil this, the WATERSAFE project intends to: i) carry out a comprehensive analysis of local phenomena of the ice crystallization explaining how, why, where and when impurities incorporation takes place in the ice and the ice growth rate in the relation of process parameters by using an approach combining simulation of solidification process and experimental observations; ii) improve the ILC global efficiency by operating the crystallisation on continuous and recycle modes on the liquid phase and by optimising the process parameters.To carry out the first target, WATERSAFE project proposes to develop an innovative dynamic model based on the Phase Field Method (PFM) to simulate the 2D axisymmetric non-isothermal solidification of ice issue from a synthetic wastewater in the ICL process. The PFM is a strong innovative way in the chemical engineering science to model a dynamic system in transition to represent i) the liquid/solid front complex morphology by taking into account ice microstructure; (ii) the pollutant migration in ice; (iii) the solid layer morphogenesis; (iv) the liquid phase hydrodynamics. In literature, solidification process simulation was also proposed to link the morphologic crystallisation phenomena to the operating parameters in order to improve the overall process efficiency. But, the works partially failed because of the simplification of the morphogenesis of interfaces, which is not the case of the PFM method. Indeed, the PFM takes advantage of continuous fields defined in the global system to represent the interfaces and phases. The interfaces dynamic is controlled by the dissipative law of energy defined according the thermodynamic functional of Ginsburg-Landau. The model easily handles time dependent complex geometries, which are typically met in freezing process.In parallel, the WATERSAFE project proposes to design a new lab-scale ILC unit. The process will be enable to operate on continuous and recycling modes on the liquid phase and batch mode on the solid phase. It will be equipped with a high-resolution camera in order to capture the ice layer and front morphologies to perform the crystallisation analysis and complete data. The developed tools allow us combining experimental observations and solidification process simulation to complete the targets. The ILC process development is a major of interest for several industrials applications (pharmaceutical and chemical industries, food processing, electronics and energy industries, micro plastics particles water depollution).