EDR: a fresh approach to water desalination

Despite covering around 70% of the Earth's surface, 97% of water is too salty to drink, thus, desalination technologies are an integral way to provide safe, drinkable water from saline sources.

Here, Electronic Specifier talks to Wei He, Senior Lecturer in the Department of Engineering at King’s College London, about one promising technology: Electrodialysis Reversal (EDR).

Water scarcity and the need for desalination

The concept of water desalination, whereby salts and minerals are removed from brackish or sea water, has been around for a long time. Over the years, technology has advanced and refined to enable safe water to reach those who previously may not have had access to it.

There are numerous factors that contribute to global water scarcity, including climate change, natural disasters, war, limited infrastructure, population growth, and industrial activities.

To address the critical need for safe water, Wei created EDR technology: “The development of the flexible batch EDR technology was inspired by the critical need to address water scarcity using intermittent solar energy. Roughly a quarter of the world’s population face ‘extremely high’ levels of water stress, and a large population within that rely on groundwater, which is often salty and undrinkable. Traditional desalination and water purification technologies, while effective in many contexts, often rely on grid electricity access and infrastructure to make it work technically and economically."

Wei continued: “Using grid electricity has several potential issues: first, the application is limited to places which have reliable and stable access to the grid. In many remote areas in developing countries like India, dependence on an unstable grid infrastructure limits the usage of conventional solutions. Second, in areas like this, the electricity from the grid is primarily from coal power plants, leading to high carbon emissions. Given solar energy is usually abundant in these places, district solar desalination shows great promise as a sustainable and scalable solution to address water scarcity, particularly in remote areas.”

The basics of desalination technology

Fundamentally, desalination is the process of removing salts and minerals from saline water. The most common methods to achieve this include reverse osmosis (RO) and thermal distillation. However, some challenges associated with these methods are negative costs and energy consumption.

Positively, recent technological advancements have enhanced the efficiency and reduced the costs of these processes. EDR, as Wei notes, is particularly advantageous due to its periodic reversal of electrical polarity, which prevents damage to ion-exchange membranes and prolongs system operation.

The crests and troughs in desalination

Recent advances in desalination technology include the development of new materials like graphene-based filters and biomimetic membranes, which increase filtration efficiency and reduce energy consumption. Energy-efficient systems, such as solar-powered desalination and low-energy RO, are also making significant strides. Additionally, the integration of IoT and Cloud technologies has further improved the monitoring and management of desalination plants.

But despite the progress, desalination technology faces several environmental and economic challenges. Brine disposal, high energy consumption, and infrastructure costs remain significant hurdles. However, ongoing research aims to address these issues. For instance, the flexible batch EDR technology reduces the need for batteries by using solar energy more efficiently.

Wei explains: “Flexible EDR transforms desalination technology into an 'energy storage' mechanism, converting solar energy into drinking water when the sun is out and storing it for later use. This approach cuts costs and relies on renewable energy, expanding the reach of desalination technology in remote areas.”

Case studies for EDR technology

In India, Wei’s flexible EDR system has demonstrated a 50% lower power system cost compared to traditional RO methods for brackish water desalination. This has led to significant improvements in access to clean water in rural regions.

“The developed PV-EDR technology underwent field testing in several locations, including in India. A prototype was constructed in 2017 and tested in a village named Chelluru, near Hyderabad. This field test allowed us to verify the developed PV-EDR (photovoltaic-powered electrodialysis reversal) model and the system design theory, as well as to gain insights on the ground about the water system specifications and costs for rural India. With this understanding, we noticed that the PV-EDR technology at the time could not compete on cost with on-grid RO systems despite lower initial costs than solar RO systems. On-grid RO systems have already been successfully commercialised in rural India, indicating an affordable cost point for desalination technology. This stimulated us to develop the flexible EDR.

“With the verified model and insights gained from the field testing, we reinvented EDR by making it flexible—efficiently adjusting water production to the variation of solar energy available. We built a new prototype and tested it at the Brackish Groundwater National Desalination Research Facility in New Mexico, where we could better monitor and test the new technology. Our results are the efficiencies mentioned above.”

Conclusion

The development of flexible EDR technology represents a significant step forward in addressing global water scarcity. By utilising intermittent solar energy, this technology provides a sustainable and scalable solution, particularly for remote areas with limited access to grid electricity. The successful field tests and reduced power system costs demonstrate the potential of flexible EDR to make a substantial impact on providing clean water in rural regions. As ongoing research continues to refine and improve these systems, the future of water desalination looks promising, with flexible EDR paving the way for more accessible and environmentally friendly solutions.