MIT study highlights benefits of smaller, modular desalination plants

Global warming, drought conditions, and population growth in coming decades could usher in an era of uncertain access to water.
Global warming, drought conditions, and population growth in coming decades could usher in an era of uncertain access to water.

Global warming, drought conditions and population growth in coming decades are ushering in an era of uncertain access to water. Now an MIT-based research team has evaluated these potential problems and suggest a new approach.

The study looks at the city of Melbourne, where a 12-year drought from 1997 to 2009 led to construction of the $5 billion Victorian Desalination Plant. The facility was approved in 2007 and opened in 2012, at which time the drought had already passed. As a result, the plant has barely been used.

As an alternative, the study suggests, smaller, modular desalination plants could have met Melbourne’s needs at a lower price.

“If you build too much infrastructure, you’re building hundreds of millions or billions of dollars in assets you might not need,” says Sarah Fletcher, a PhD candidate in MIT’s Institute for Data, Systems and Society (IDSS), lead author of the new paper.

The study does not argue that a single solution applies to all cases, but presents a new method for pinpointing the best plan. It notes that, in many cases, “moderate investment increases, together with flexible infrastructure design, can mitigate water-shortage risk significantly.”

The new paper, Water Supply Infrastructure Planning: Decision-Making Framework to Classify Multiple Uncertainties and Evaluate Flexible Design, was recently published in the Journal of Water Resources Planning and Management.

The MIT team’s new framework for water-supply analysis incorporates several uncertainties that policymakers must confront in these cases, and runs large numbers of simulations of water availability over a 30-year period. It then presents planners with a decision tree about which infrastructure options are best calibrated to their needs.

The significant uncertainties include climate change and its effects on rainfall, as well as the impact of water shortages and population growth.

Melbourne case study

In the Melbourne study, the researchers looked at six infrastructure alternatives, including multiple types of desalination plants and a possible new pipeline to more-distant sources, and combinations of these things.

The results highlight a vexing problem in water-access planning: shortages can be acute, but they may last for relatively short periods of time. The team ran 100,000 simulations of 30-year conditions in Melbourne and found that in 80% of all years, there would be no water shortages at all. For the years where drought conditions did hold, large water shortages were more common than minor water shortages.

As a result, when costs were factored into the analysis, simply building no new infrastructure was the best option around 50% of the time. However, doing nothing was also the “worst-performing alternative” around 30% of the time.

This is why building smaller desalination plants can make sense. The Melboune desalination plant can produce 150 million m3 of water per year. But in MIT’s simulations, building a desalination plant half that size usually works well. It was the best-performing option in 20% of the simulations, and in the top three of 90% of the simulations.  

Building smaller at first also gives planners the ability to bring a new plant online quicker and then scale up if needed.

“You only build a certain number of modules in the beginning, and you can add a certain number later,” Fletcher says. “That’s different than building a small plant and then another small plant. You’re being proactive and planning to adapt in the future.”

The researchers acknowledge that the results of their study would likely vary from region to region, but they think the framework could help planners make the case that building on a smaller scale may position cities and countries best in the long run.

“We’re used to building large-scale desalination plants, and there’s less of history of building more modular plants,” Fletcher says. “It’s challenging because these are large investments with long lifetimes. But if you think of a modular plant as an insurance policy against drought, maybe you want to have it around.”