Advancements in Desalination Technologies: Applications of Electrodeionization

Hello! My name is Caroline Kaden and I am a rising senior studying chemical engineering. This summer I was able to work in the Advanced Materials Division of Argonne National Laboratory, more specifically within the Water-Energy Nexus with Dr. YuPo Lin. Water plays a crucial role in energy and fuel production, from usage in power plant cooling towers, to fracking, to acting alone as a renewable source by hydroelectric power. Similarly, energy is needed to produce usable water from various sources. Pumping, desalinating and distributing water all require energy. Factors such as climate change, and regional variance including population, geography, weather, and occurrences of natural disasters all contribute to the importance of the Water-Energy Nexus because these factors can shift water and energy demands greatly and unexpectedly over short periods of time.

One of the most consumptive and least efficient processes is thermoelectric cooling. Focusing on the optimization of this could therefore greatly decrease water and energy use. More specifically, minimizing the energy used to desalinate water as well as having more usable water for cooling towers will make a large difference in the Water-Energy-Nexus because cooling towers account for almost 50% of interdependent water withdrawal within the US. The inefficiencies of cooling towers are that high mineral, contaminant, and salt content promote scaling therefore decreasing functionality, the blowdown water can be very difficult to treat or dispose of due to high salinity and contaminant content, and even with heavy monitoring, withdrawal of water for make-up usage is very large and increases the impact within the nexus.

However, Electrodeionization (EDI) technology can help solve these issues. EDI is a far more energy-efficient and economical pretreatment than previous water treatment solutions, which means blowdown frequency can be reduced. Sea water, brackish water, produced water and treated municipal effluents are all possible candidates for makeup water if treated sufficiently and economically, and reduce the amount of freshwater needed for makeup water in the cooling tower. These solutions are largely beneficial as developing and optimizing water reuse technologies can reduce cooling tower water consumption by up to 40%.

This summer I did research specifically working with removing silica from water. Silica is especially difficult to remove because it is almost always present in both the reactive and unreactive forms and it is nearly impossible to control which form is present. Additionally, the solubility is affected by time, pH, and temperature. The experiments I ran involved building an EDI stack, with resin wafers inside to promote ionic transport. I then pumped a silica solution through the system as a batch operation, taking the conductivity and pH of both the feed and concentrate regularly to analyze the concentration. The set up is shown below. The EDI stack is in the back left. 

I found that silica does not move through the tower as easily as salt, as not all of the silica originally put into the system is accounted for in the feed nor the concentrate at the end of the experiment. I hypothesize that the the silica being adsorbed onto the resin beads. Because of this, the next steps to take include: changing components out, such as using different resins and/or different membranes to better promote silica transfer to concentrate stream, changing operating conditions such as flowrate, voltage applied, and running continuous feed of silica solution to test for a steady-state point of separation.

Overall this summer’s work was very rewarding and interesting as it combined my background in chemical engineering with my interest in sustainability and I look forward to seeing where EDI and separation technology lead to!