PhD project title: High recovery and chemical-free desalination using advanced electrodialysis... (# of pos: 14)

Background 
Desalination has become a significant alternative water source due to the growing water demand and inadequate conventional water sources in many regions. Desalination removes excess salts and other dissolved solids from water to get clean water for human utilization. Research and development and resulting innovations often aim to lower energy consumption or reduce desalination costs. However, with the available mature membrane and thermal technologies, there seems not to be much room for improvements in both aspects.

Thus, we believe other drivers for innovation can be: (1) decreasing the environmental impact by avoiding chemicals additions and effects of brine discharge, (2) creating valuable water streams or mining of the valuable compounds from brines, while avoiding excess amounts of invaluable compounds, and (3) increasing the added value of already used desalted water for a second use in agriculture or aquifer recharge.

Research challenges
Despite many studies and potential innovations are aiming for the highest possible water recovery, even up to zero liquid discharge (ZLD), real-life applications stay limited. Often these ZLD schemes include recovering solid salts (or organics) from brines, which only occasionally will provide a reasonable business case when the plant owner can reuse these onsite safely and sustainably. Technologies involved use additional chemicals for regeneration, acids and bases for temporary pH adjustments, antiscalants and dispersants, cleaning chemicals. Moreover, high amounts of energy per kilogram of recovered solid and ultimately per water produced are employed. In this project, we aim to create a desalination scheme that splits the saline source water into demineralized product water and multiple concentrated waste streams, with the desired specifications for eventual post-processing and recycling. We aim to achieve these goals without adding (high amounts of) salts or other chemicals, to avoid accumulation of sodium and/or chloride in brines onsite or in the product water for first and second use. Advanced electrodialysis (ED) configurations enable to achieve desalination by manipulating ionic compositions with the feed water and electrical energy as the sole inputs.

Objectives and methodology
In this project, we will advance on chemical-free ED configurations in hybrid desalination schemes. Feed water compositions (overall salinity, monovalent-divalent ionic ratios; eventual valuable elements or organic molecules) will define the possibilities to constitute the best output streams for given use cases from our industrial partners. For selected cases, an ED stack configuration will be designed and tested, based on mass balance and transport rate modelling. The selectivity needed to obtain the multiple concentrate streams will be reached by applying selective membranes (e.g. bi-polar, monovalent/divalent selective membranes) and by controling operational conditions. Input parameters of the model will be based on literature and membrane charachterization experiments. The design will be realized in a laboratory scale ED setup. The setup will be run with both well defined salt water mixtures to validate the model assumptions, and with water from the selected cases as a prelimaniry test for a pilot scale study.