7.13 Multicomponent mass transport modeling of water desalination with reverse osmosis
Reverse Osmosis (RO) is the most important water desalination technology worldwide. RO makes use of a pressure difference to push water through an extremely thin membrane (200 nm thick) to produce almost salt-free water. RO can be applied both for seawater and for water sources with lower salinity (ground water, surface water).
To develop optimal RO-processes, essential is the availability of accurate theoretical models to describe energy consumption and the composition of the product water. These models help in understanding the process better, the development of better membranes and module designs, but more likely, help to design a better process layout for a given objective (to design a water treatment plant that must treat x m3 of water per day). Accurate models help to predict the exact retention of key undesired components, such as boron or ammonia.
However, precise models based on a detailed physical and chemical description of the processes that take place in and around the membrane are not yet developed to make design possible. Recently, a start was made to develop such a model for a simplified geometry . Here all transport processes in the membrane are well described, including the mutual interactions between all ions and water and membrane. Essential is that the model includes all ongoing chemical acid-base reactions between all species, e.g., how water splits in hydronium ions and hydroxyl ions, and how these react, for instance with carbonate ions to form carbonic acid/bicarbonate. Other chemical reactions involve ammonium, boron and sulfate. The developed model  gave a very precise description of experimental observations, and this model is the basis of further work in this project.
The challenge is to extend the existing RO model to the level of describing a full module and small RO plant, and implement the model in relevant software platforms such as Python. Using RO equipment available at Wetsus or with one of our partners, precise experiments are done to validate and upgrade the model. Both artificial seawater and various sources of groundwater and surface water are considered in the project. Using the model, optimal RO operational conditions can be determined. The project aims to produce scientific tools and knowledge, resulting in scientific publications. The modeling framework tries to capture as much as possible known physical and chemical information of the membrane, but not always this information is available of commercially available membranes, such as micropore size (distribution) and ion mobilities in the membrane. Therefore, combination of experimental data with model predictions helps to establish “effective” values of membrane parameters that will be used in the final model.
We are looking for a candidate with an MSc degree in the field of physics, chemical or mechanical engineering, or an equivalent degree. A background in environmental science or water technology is not required. The candidate must have an affinity with 1. doing process-related experiments and the analysis of data, and 2. making and evaluating computer models to study the RO process.
We are looking for a candidate, who
· is interested in doing scientific research, with a strong wish to figure out in detail how things work;
· can communicate their results in writing, presentations and discussions;
· has a strong interest in theoretical modeling of the RO process;
· is precise and dedicated to make sure experiments and calculations are as good as needed;
· is inventive in figuring out new ways to study a system by theory or experiments;
· likes to write.
The research project is part of the Wetsus research theme Advanced Water Treatment.
The following companies are part of the theme: Evides (www.evides.nl), Oasen (www.oasen.nl), Paques (en.paques.nl), Water companies North Netherlands, Heineken (www.heineken.com), Unilever (www.unilever.com).
Promotor: Prof.dr.ir. Walter van der Meer (University of Twente, Membrane Science & Technology)
Wetsus supervisor: Dr. Maarten Biesheuvel
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Wetsus, Leeuwarden, The Netherlands