[LUM#9] Wastewater, a resource for the future
To tackle water shortages and preserve this increasingly scarce resource, researchers atthe European Membrane Institute are proposing an innovative wastewater treatment process. The goal is to produce high-quality water at the outlet of treatment plants that can be reused.
Pesticides, insecticides, pharmaceutical residues, endocrine disruptors—all these substances produced by human activities end up in the environment, and water is no exception. This phenomenon is all the more problematic because these micropollutants are harmful even in very small doses.
To preserve our precious water resources at a time when water scarcity is becoming a growing concern, researchers are developing new processes designed to effectively remove these substances from wastewater treatment plants. This is a real challenge that meets a dual ecological objective: limiting the impact of micropollutants on the environment and enabling the reuse of treated wastewater. This is a promising avenue for optimizing the management of water resources.
Refractory pollution
"Today, around 80% of micropollutants are eliminated by biological treatments implemented in wastewater treatment plants, thanks to activated sludge that breaks them down naturally," explains Julie Mendret, a researcher atthe European Institute of Membranes (IEM). The problem is that some molecules are not biodegradable and remain in the water even after this treatment. "Twenty percent of refractory pollution remains and is released into the natural environment. In France, unlike other countries such as Switzerland, there are no standards for micropollutants at the outlet of treatment plants, " the researcher points out.
However, the consequences for the environment are well known: these micropollutants, which return to the water cycle, are deposited in silt and affect the entire ecosystem. "Studies show that fish living near wastewater treatment plant discharges are contaminated by these molecules. These toxic compounds have become a major issue, and future wastewater treatment plants will need to be modernized in order to limit their emissions, " explains Julie Mendret. The researcher has decided to take up this challenge by proposing an innovative and intensive wastewater treatment process.
Innovative and intensive
Today, there are two types of processes that can be used to treat these micropollutants: membrane processes and advanced oxidation processes.
The first relies on the use of membranes that retain very small molecules and allow water to pass through. This filtration method is effective but has its limitations: "The pollutants are isolated from the water, but they are not destroyed, and must then be eliminated, " explains Julie Mendret.
Another solution: advanced oxidation chemical processes. "Ozonation is particularly effective on micropollutants," the researcher points out. They are oxidized by ozone, which breaks them down into smaller and smaller molecules until, in the case of complete mineralization, they become CO2 and H2O molecules. " The pollutant is ultimately eliminated, leaving only harmless water and carbon dioxide molecules. It is an effective but imperfect method: on the one hand, ozonation is not very cost-effective for pollutants that are highly diluted in water, and on the other hand, it can lead to the formation of toxic by-products.
A 2-in-1 process
Faced with these limitations, researchers at theIEM came up with the idea of combining these water treatment processes to combine their respective advantages.
An ambitious project called Saware. "It's a 2-in-1 process: we combine very advanced filtration, nanofiltration, with an advanced ozone-based oxidation process. The molecules are retained by the membrane and simultaneously oxidized through ozonation, " explains Julie Mendret.
This hybridization offers several advantages: ozone acts more effectively on pollutants that have been concentrated by filtration, and toxic byproducts that may be generated by ozonation are retained by the membrane and are therefore not released into the natural environment.
To develop this device, Julie Mendret and André Ayral from theIEM opted for ceramic nanofiltration membranes, a material resistant to the action of ozone. "This is the first time this type of catalytic membrane has been used to treat urban wastewater, " the specialist points out.
This innovation could guarantee high-quality water at the outlet of wastewater treatment plants, which could then be reused (see box). "Unfortunately, we are hampered by very strict French legislation that limits the reuse of wastewater," laments Julie Mendret. This is a call for change in regulations to help preserve this invaluable resource.
Reuse, a powerful lever for conserving water resources
Faced with a global water shortage, wastewater reuse, also known as "reuse," is the way forward. Once treated, this water can be used for a variety of purposes, including irrigating green spaces and crops, fighting fires, washing roads, and replenishing groundwater reserves. Some countries, such as Singapore, even go so far as to produce drinking water from treated wastewater.
In France, reuse remains underdeveloped. The reasons for this are a lack of public awareness and very strict regulations. Professionals in the sector are therefore campaigning for a relaxation of the law, which strictly regulates the reuse of wastewater, primarily for health reasons. The European Commission recently took up this issue and in 2018 issued a proposal for a regulation dedicated to agricultural irrigation with the aim of facilitating the reuse of treated wastewater.
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