A study by Northwestern Engineering unveils the complexities of using zero liquid discharge (ZLD) desalination to combat water scarcity, emphasizing significant trade-offs in energy use, cost and environmental impact.
In the face of accelerating climate change and growing water scarcity, desalination technology continues to offer a promising solution by harnessing seawater. However, recent findings underscore significant environmental, economic and accessibility challenges that accompany this technology.
A research team led by Jennifer Dunn, a professor of chemical and biological engineering at Northwestern University, has developed an optimization model that evaluates the effectiveness and impact of incorporating zero liquid discharge (ZLD) into desalination processes.
This innovative analysis aims to uncover the balance between increased water recovery and the associated trade-offs in energy use, environmental burden and financial cost.
“Desalination is crucial in certain regions, but it can’t be the only answer to water scarcity,” Dunn said in a news release.
In traditional desalination, seawater is filtered through a membrane that removes salt, producing fresh water and a concentrated brine byproduct.
ZLD technology goes a step further by extracting additional water from the brine, thus reducing waste volume and increasing overall water recovery. While this seems beneficial, the process introduces considerable challenges, particularly with energy requirements and potential environmental effects.
Based on findings published in Nature Water, the team’s model, WaterTap, analyzed multiple scenarios to enhance ZLD efficiency. The study considered seven different treatment train options that integrate various technologies to achieve minimal liquid discharge.
“The big challenge is that you need a lot of energy to desalinate water and increase water production using zero liquid discharge,” added Dunn, who is also the director of the Center for Engineering Sustainability and Resilience. “That energy comes at a high environmental cost, especially if fossil fuels are the primary energy source.”
Energy-intensive desalination processes present a dual dilemma: the need for significant energy to generate freshwater and the environmental footprint of current energy sources. Renewable energy options are under investigation as cleaner alternatives, but their deployment varies greatly depending on location and infrastructure.
Moreover, disposal of high-salinity brine poses another critical environmental concern. Many coastal desalination plants discharge the brine back into the ocean, where the long-term ecological impacts remain uncertain and potentially harmful to marine life in certain areas.
“There’s not enough data on the effects of high-salinity brine on marine ecosystems,” added Dunn. “In some areas, the damage may be minimal, but in others, it could be disruptive. We’re working to fill those gaps.”
In addition to environmental challenges, desalination involves substantial costs for construction, operation and maintenance, making it a less viable solution for low-income regions struggling with water access. While some countries offer subsidies, these financial aids often fall short.
“Desalination can’t be the only solution,” Dunn added. “In some areas, it’s essential, but it must be part of a broader water management strategy.”
Several countries are embracing a holistic approach by combining desalination with water recycling, rainwater harvesting and conservation measures, a blend that helps build resilience against fluctuating water resources and rising demands.
“To make real progress, we need to look at it as one piece of a broader, more sustainable water management strategy that’s adapted to the unique needs and constraints of each area,” Dunn concluded.
As the world grapples with water scarcity, this research underscores the importance of a multifaceted strategy that includes, but is not solely reliant on, desalination technology to create a sustainable future.