Among most Advanced oxidation processes (AOPs), cavitation reactors are novel and are the simplest way to design and operate. Cavitation is defined as the formation, growth, and subsequent collapse of the cavities occurring in an extremely small interval of time (milliseconds), releasing large magnitudes of energy. The effects of those cavity collapses are the creation of hot spots, the release of highly reactive free radicals, solid surface cleansing, and enhancement in mass transfer rates. The collapse of bubbles generates localized ‘‘hot spots’’ with transient temperatures of about 5000 to 10000 K and pressures of about 700 to 1000 atm. Under such extreme conditions, water molecules are dissociated into OH and H radicals. These radicals then diffuse into the bulk liquid medium where they react with organic pollutants and oxidize them.
The two main mechanisms for the destruction of organic micropollutants using cavitation are (1) the thermal decomposition/pyrolysis of the volatile pollutant molecule entrapped inside the cavity and (2) the reaction of OH radicals with the pollutants. The hydrodynamic cavitation is produced by pressure variation in a flowing liquid, which is obtained by providing flow constrictions such as orifice and venturi. When the liquid passes through the constriction, the kinetic energy/ velocity increases at the expense of the pressure. When the pressure at the throat or “vena-contracta” falls below the vapor pressure of the liquid, the liquid flashes, generating a number of vaporous cavities. These cavities are then collapsed when they came in downstream of constriction where the pressure recovers. The comparative study of hydrodynamic cavitation and acoustic cavitation suggested that hydrodynamic cavitation is more energy efficient and gives higher degradation as compared to acoustic cavitation for equivalent power/energy dissipation.
Hydrodynamic cavitation (HC) has been successfully applied for industrial wastewater treatment and improving landfill leachate biodegradability. HC may be combined with H2O2, ozone or catalysts to increase free radical formation during HC treatment and increase oxidative capacity. PFOS removal and breakdown products as a function of reaction time have been investigated in a proof-of-concept HC reactor, but the full potential of PFAS removal via HC has not yet been explored.
Many sites in the world are impacted by poly- and perfluoroalkyl substances (PFAS) due to historic use of Aqueous Film-Forming Foam (AFFF). The rate and extent of PFAS transport from source zones is both PFAS- and soil-specific. Brusseau et al. (2020) have reported that PFAS are present in soils across the globe, and indicate that soil is a significant reservoir for PFAS which raise the concern of long-term migration potential to surface water, groundwater, and the atmosphere.
In the frame of this project, it is aimed first to design and test a pilot scale hydrodynamic cavitation in the laboratory for the degradation of model compounds. The data collected from this first project phase will be used to feed a COMSOL model allowing to determine the best HC design and operating conditions. One of the ambitions is to generate data that can be used by AI / Machine Learning powered by in-situ (IoT) sensors, ideally in real time. The developed treatment strategy will be applied on European demonstration cases in collaboration with BRGM (Orléans, France), to test the enhanced HC technology on real groundwater samples contaminated by PFAS compounds. On site treatment will be applied to collected groundwater samples via combined hydrodynamic cavitation (HC) as pre-treatment and biological treatment as post-treatment. The HC operating conditions will be first optimized at lab-scale (capacity of 100 L/h), after which an upscaled version (treatment capacity up to 10 m3/hour) will be built to treat groundwater sample. Effects of operational conditions (e.g. recirculation cycle, flow rate) on treatment performance will be monitored by quantifying residual PFAS concentrations.
This research study is developed in the frame of the PROMISCES European Project funded by European Research Executive Agency (REA) (Green deal Call, H2020 2021-2025). This study will be conducted in close cooperation with ISB WATER (https://optimum-water.com/) and IPGP (Biogeochemistry at the Anthropocene of Elements and Emerging Contaminants Unit) and in collaboration with the other PROMISCES partners.
Appointment period: The PhD position is for three years, located in Paris (France – IPGP – http://www.ipgp.fr/en), with travels in Europe, in the frame of exchanges with the partners of the PROMISCES Green Deal project.
Brusseau, M. L., Anderson, R. H., & Guo, B. (2020). PFAS concentrations in soils: Background levels versus contaminated sites. Science of the Total Environment, 740, 140017. https://doi.org/10.1016/j.scitotenv.2020.14001
Funding category: Contrat doctoral
IPGP – Financement H2020
PHD title: Doctorat Terre et Environnement
PHD Country: France
Desired skills and experience
A person fulfils the general entry requirements if he/she:
- has been awarded a Master of Science degree in chemical engineering
Specific requirements also include
- knowledge in the field of advanced oxidation processes
- knowledge about modelling, as well as R and Python programming languages is required
- experience on process application for the removal of organic micropollutants in complex matrices
- be able to solve problems
- have the ability to work independently (in autonomy) as well as interact well in a research group
- demonstrated ability to work effectively in a multi-disciplinary team
- a high proficiency in written and spoken English.
- experience of working with advanced oxidation processes for organic micropollutants removal and modeling experience would place the candidate at an advantage
- the ability to speak French would also be a merit.