Can Desalination Solve Our Water Crises?

By  //  July 23, 2022

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Desalination converts salt water to fresh water. But there are drawbacks.

Largely because of environmental concerns, California recently rejected Orange County’s large-scale Poseidon desalination project, a project twenty-five years in the making. Despite this defeat, officials took care to state that California remains open to desalination. Governor Newsom has long considered desalination to be an important tool for coping with drought.

In many parts of the world, populations have been facing the limits of their water supplies. In 2018, Cape Town, South Africa narrowly averted a Day Zero crisis, and the news that a major modern city had almost run dry startled the world.

To deal with the crisis, Cape Town developed large-scale desalination. Was this the right solution? “It kind of depends on how bad you need the water,” was the way Amy Childress, USC Director of Environmental Engineering, put it. Cape Town needed the water badly.

Viability of Desalination

The main obstacles to desalination have always been high energy costs and the difficulty of brine disposal.

Israeli advances in reverse osmosis in recent years have done much to reduce the energy costs. Although reverse osmosis costs more than getting fresh water from natural freshwater sources, it is now viable in more scenarios than ever. For example, Spain is making desalination work for agricultural irrigation, an application that until now had been regarded as prohibitively expensive.

The concentrated saline brine that is a byproduct of desalination can harm marine ecosystems. But the effects can be mitigated with the help of thoughtful studies of environmental impact, appropriate location and design of intakes and outfalls, and adequate monitoring. One example is the model desalination plant that ended the water crisis in Trinidad. The plant earned high praise from Harvard University’s Zofnass Program for Sustainable Infrastructure for its eco-friendly design and environmental monitoring program.

The Trinidad plant also exemplifies how newer financing models can render desalination practicable. The project was delivered using a build-own-operate financing arrangement with a private water company. The company’s Water-as-a-Service® model, also followed by other companies, helped overcome the problems of the high initial cost and long-term operation and maintenance. These are problems that many desalination infrastructure projects face.

Decentralized Desalination

A quarter century of studies, negotiations, and resources went down the tubes when Orange County’s Poseidon plant was rejected. What went wrong?

From design to completion, large-scale desalination is a high-stakes undertaking with many moving parts. Even when these kinds of big projects are completed successfully, they are often disparaged as white elephants if projections miss the mark.

Poseidon’s proposed service area was large, containing many voices in a state known for eco-awareness and tight regulation. Mega-plants also generate an enormous amount of brine that it is hard to safely diffuse into the ocean. So the potential environmental impact and actual political difficulties finally defeated the project.

But smaller desalination plants produce less brine, and their smaller capacity is appropriate for smaller service areas. Both the environmental impact and the politics are easier to cope with when desalination is decentralized. Decentralization is the practice of locating relatively small plants right where they are needed. This is often easier to accomplish than trying to unite a much larger region.

Desalination by reverse osmosis of brackish water is also much cheaper than desalination of seawater, and the groundwater in aquifers is much more brackish than fresh water. Florida, for instance, has extensive brackish groundwater resources.

The drawbacks of desalination can be managed, and the process can deliver water where it is badly needed. But as Cape Town learned, the best time to build desalination plants is before the need for water is desperate.