One Solution for a “Water-Stressed” Future?

/ 12 Feb 2017

One Solution for a “Water-Stressed” Future?

RABAT—Nearly 20 years ago, the vice president of the World Bank predicted that the wars of the 21st century would be waged over water.

He was making a point about the increasing scarcity of fresh water supplies across the globe. The UN estimates that nearly half of the world’s population will be living on water-stressed lands by 2030, a large number of them in the Arab world.

One Moroccan engineer wants to help his country survive the coming droughts with a system of small-scale water plants to turn seawater into fresh drinking water. Other experts have expressed doubt that the concept will ever be financially realistic.

Statistics from the World Bank say more than one third of rural communities in Morocco lack modern access to clean water, such as private or communal taps. Many villages still rely on unprotected wells, which may eventually run dry. “Moroccans live in a semi-arid region and it is likely climate change will decrease the country’s water availability,” said Mohamed Tahiri, an engineer at Mohammed V University-Agdal in Rabat.

At the same time, Morocco lacks energy independence. “We are one of the only Arab countries without oil,” said Tahiri. “But we do have a vast shoreline and plenty of sun. For me, that’s why it makes sense to use solar energy for desalination. The idea is to make a solution out of two problems.”

Tahiri is developing a prototype of a small solar-powered desalination plant, about 2 meters in height and 1.5 meters in length and width. His trial plant heats up seawater; dry air is then introduced to the system, which soaks up the moisture from evaporation. The air then moves to another chamber where it’s cooled to release the water as salt-free rain. “We are trying to mimic the natural water cycle on a small scale,” said Tahiri. The main difference from what happens in nature is that in the first chamber he’s left with a highly concentrated saline solution, which is discarded.

Tahiri would not estimate how much one of his units would cost, saying he has more development to do before he can provide an accurate figure. But he said he’d like to see his mini plants peppered along Morocco’s Mediterranean and Atlantic coasts in rural communities. “The capacity of air to soak up moisture isn’t sufficient to do this on a large scale, you’re not going to see a huge one deployed in Casablanca,” he said. Each of the plants would supply sufficient water supply for as many as 3,000 homes, according to his calculations.

“It sounds like a very expensive proposal,” said Yoram Cohen, a chemical engineer at the University of California, Los Angeles. Over the last few years, Cohen has collaborated with delegations from Saudi Arabia’s Ministry of Agriculture and Water regarding desalination issues. “People think of solar energy as a free source,” he says, “but they forget the panels mean a substantial upfront cost.”

Energy source aside, Cohen thinks an alternative desalination method, called reverse osmosis, would be a more sensible and less costly plan. It involves pushing the seawater through an artificial membrane at high pressure. The salt molecules are too big to pass through the membrane and so the result is fresh water on the other side. Such a process just uses energy at the pump, whereas mimicking the water cycle means using energy to heat water and more energy later to cool air.

Before Tahiri is willing to put a price tag on his mini desalination units, he’s working on perfecting the temperature, humidity and pressure levels to extract as much fresh water as possible.

Cohen can’t speak to Tahiri’s model without seeing the specifics. But he did say a desalination plant that provides fresh water to about 50 homes in remote U.S. communities would cost between $150,000 and $200,000. (The average American home consumes 40 percent more water than its Moroccan counterpart.)

While Cohen remains skeptical of the proposal’s financial practicality, Tahiri is hopeful that private investment could help to shoulder some of the cost. “If General Electric or someone wants to help us,” he says, “their money is more than welcome.”




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