Sewage, seawater, rain… looking for new sources against drought

Sewage, seawater, rain… looking for new sources against drought

Since the end of July, France has been facing an historic drought that is causing water shortages in a large part of the country. While this scenario is doomed to repeat itself due to climate change, scientists are searching for new resources. Inspired by pioneers abroad, especially in desert lands, they experimented with different techniques.

In a hundred French communes, the pipes are empty and the water no longer flows through the taps. The extraordinary drought that has ravaged the country since late July, the worst since 1959, has drained rivers and groundwater. To cope, the government, municipalities and population are resorting to the D system, between strict restrictions, the transport of water in tankers and the distribution of bottles.

At the same time, many voices are being raised that are looking for new ways of using water. Among the techniques mentioned: reuse of waste water, desalination of seawater or even democratization of the use of rainwater… Measures that are already widespread in some countries, but often difficult to implement in France due to strict regulations and environmental concerns.

reuse waste water

“France and the European Union have to catch up when it comes to recycling wastewater,” says Julie Mendret, a researcher at the University of Montpellier’s Membranes Institute. “Today in France less than 1% of the treated water is reused. In Italy it’s 8% and in Spain 14%,” she explains. “We’re a long way from certain countries where this is fully democratized, particularly in the Gulf countries like the United Arab Emirates, Kuwait and Qatar. In Israel, a pioneer in this field, we reach 80%.”

As a reminder, traditionally, the water that enters our taps is extracted from groundwater and then purified in drinking water treatment plants. After consumption, it is treated in sewage treatment plants before being discharged into the aquatic environment. When it is recycled, it is not discarded but reintroduced into the pipes.

Specifically, France recycles 19,000 m3 of wastewater every day that is used to irrigate agricultural crops and irrigate golf courses. “We could completely expand these uses to clean streets or irrigate green spaces,” says Julie Mendret. “And why not go further and reproduce drinking water from this recycled water?”

In the Vendée, the Jourdain project will soon experiment with this solution. Instead of being discharged into the sea, part of the water from the Sables-d’Olonne treatment plant is recovered and treated before being fed back into the drinking water circuits. “That would be a novelty in Europe, but it already exists in Singapore or Namibia, for example,” says the specialist.

According to her, France is hampered by “overly demanding regulations” and difficulties in getting these projects accepted at local level. However, in March the government expanded the use of recycled water to replenish groundwater or fight fires. At the European level, on August 3, member countries called for “speeding things up”.

“In any case, we will not be able to recycle all the water. Sometimes denying it is imperative to keep nearby rivers flowing and preserve biodiversity. You shouldn’t solve a problem by creating a new one,” she stresses. “But this option remains very interesting, especially for coastal areas where wastewater is often discharged into the sea. Freshwater is lost.”

Democratization of the use of rainwater

For her part, Fabienne Trolard, research director at the National Research Institute for Agriculture and the Environment (Inrae), calls for the general use of rainwater, which is not potable, especially among individuals. “In France, all the water we consume is drinkable. We only have the right to use rainwater to water our plants,” she laments. “Households in Belgium and Germany have been working with two-circuit systems for a long time: drinking water only comes to the taps for drinking and showering. The rest is supplied with rainwater, which is stored in individual tanks,” she explains.

With this system, “we could even reuse this ‘grey water'” [l’eau non potable] multiple times. Some of our neighbors recycle it three or four times. In Israel it’s five or six.”

desalinate seawater

In Haute-Corse and Brittany, in the small towns of Rogliano and on the island of Groix, mayors wanted to experiment with a different solution to the drought: seawater desalination.

This technology, like wastewater recycling, is already widespread abroad. The International Desalination Association, which brings together scientists, industrialists and non-governmental organizations, counts more than 17,000 plants of this type worldwide. In total, more than 300 million people depend on it for their water needs. “The first users are Saudi Arabia and Israel. The Maghreb countries have also made massive investments in recent years,” explains Fabienne Trolard. “The reason is simple: In these dry countries, where fresh water is sorely lacking, it is one of the rare solutions.” cubic meters of drinking water per year, i.e. around 750 million liters of water per day.

But this technique has its share of disadvantages. “These factories are very energy-intensive and therefore not very economical for the municipalities,” notes Fabienne Trolard. “But above all, it produces waste, brines that we don’t know what to do with.” According to a UN report, for every liter of fresh water, an average of 1.5 liters of this salty mud is released, usually into the ocean, disrupting ecosystems.

Capture fog and dew

Elsewhere in the world there are countless small solutions. In Latin America, for example, Chile harvests several liters of water from fog each year. This technique, which has existed since pre-Columbian times, is very simple: very dense nets are installed on foggy days. The droplets stick to it and then run off towards the container. A cheap, ecological, natural process that only works under very specific weather conditions.

In the same way, Laurent Royon, researcher at the Interdisciplinary Laboratory Energy of Tomorrow in Paris, is studying the possibility of recovering dewdrops. “This technique could be used anywhere, even in the deserts where it’s cold at night,” he says, listing ongoing experiments in India, Benin and Morocco. But usage remains limited with just under 0.5 liters per cubic meter harvested approximately per night.

Moving icebergs, dropping rain… controversial “miracles”

If all the measures mentioned are already being used more or less extensively around the world, other scientists want to go even further and try to open up untapped water reservoirs. In a study published in May entitled “Unconventional Water Resources,” researchers at the United Nations University list a dozen of them.

However, some of these tips ultimately prove to be counterproductive. For example cloud seeding which would trigger rain on command. The idea, which has been studied primarily in China since the 1960s, consists of using the water present in the Earth’s atmosphere in the form of vapor in the clouds. In fact, only 10 to 15% of the water contained in these clouds falls as rain. By sending aerosols, for example with small rockets or firecrackers, researchers are trying to increase the amount of precipitation. Problem: Not only is the effectiveness of the technology disputed, but changes in the weather could trigger chain reactions that are difficult to predict elsewhere on earth.

Equally surprising, scientists are studying the possibility of moving icebergs, which are made of fresh water. For nearly forty years, this route occupied French engineer Georges Mougin, who was attempting to transport these huge blocks of ice to drought-prone countries. His experiments led him to conclude in 2010 that it would take five months and 4,000 tons of oil to ship an iceberg from Canada to the Canary Islands. A route that seems to harbor as many technological, environmental and financial problems.