MM/P PhD defense Diego Pintossi

Salinity gradient energy (SGE) is an energy source derived from the controlled mixing of low and high concentration water streams, e.g., river and seawater. Reverse electrodialysis (RED) is an electro-membrane process to harvest SGE. In RED, cation exchange membranes (CEMs) and anion exchange membranes (AEMs) are stacked alternately to create compartments where the sea and river water flow. The salinity gradient across the ion exchange membranes results in a potential difference over the membranes. When the external circuit is closed, this potential difference is used to drive an ionic current through the stack to power a device. This ionic current is converted into an electronic current by a suitable redox couple recirculated in the electrode compartments. When natural waters (i.e. real river and seawater) are used, colloids, multivalent ions, organic molecules, and microorganisms will induce fouling on the membranes thus decreasing the overall RED stack performance. The aim of this thesis was to investigate the aim and control of fouling in RED, more specifically 1) how to monitor fouling evolution of different foulants in real time, 2) how to prevent it by chemically modifying the membrane surface and 3) how to mathematically model its impact.

Fouling monitoring is a necessity to optimize RED operation and stack cleaning strategies. By applying electrochemical impedance spectroscopy (EIS) on a RED stack, it was possible to follow the evolution of organic fouling on AEMs and CEMs and their recovery during cleaning steps. To mitigate fouling, anti-fouling anion exchange membranes (AEMs) were developed using surface modification of commercial membranes with zwitterionic monomers and brushes. Fouling studies show that these membranes exhibit slower fouling rates and faster recovery rates than unmodified membranes. Finally, the impact of multivalent anions on RED was studied. The results show that the presence of multivalent ions significantly decreases the power output in RED, up to - 25 % at 50 mol. % sulfate in the feedwaters. This is due to uphill ion transport, membrane permselectivity loss, and an increased membrane resistance. These findings were used next to develop a validated RED process model to describe and predict RED fouling taking into account the negative effects of these multivalent ions.

Overall, the results presented in this thesis provide tools and recommendations to mitigate and control fouling in RED bringing it closer to its widespread implementation to harvest SGE.

For more information please contact Prof.dr.ir. Kitty Nijmeijer (d.c.nijmeijer@tue.nl) or Dr. ing. Zandrie Borneman (z.borneman@tue.nl).