[LUM#9] Wastewater: A Resource for the Future
To address water shortages and conserve this increasingly scarce resource, researchers atthe European Membrane Institute are proposing an innovative wastewater treatment process. Their goal is to ensure that water leaving treatment plants meets quality standards and can be reused.
Pesticides, insecticides, pharmaceutical residues, and endocrine disruptors—all of these substances produced by human activities end up in the environment, and water bodies are no exception. This is an especially problematic issue because these micropollutants are harmful even in very small doses.
To preserve this precious resource at a time when water scarcity is becoming a growing concern, researchers are developing new processes designed to effectively remove these substances from wastewater as it leaves treatment plants. This is a significant challenge that addresses a dual environmental goal: limiting the impact of micropollutants on the environment and enabling the reuse of the treated wastewater. A path forward for optimizing water resource management.
Hard-to-treat pollution
“Today, about 80% of micropollutants are removed through biological treatment processes at wastewater treatment plants, thanks to activated sludge that naturally breaks them down,” explains Julie Mendret, a researcher atthe European Membrane Institute (IEM). The problem is that some molecules are not biodegradable and persist in the water even after this treatment. “There remains 20% of refractory pollution that is discharged into the natural environment. In France, unlike other countries such as Switzerland, there are no standards for micropollutants at the treatment plant outlet, ” the researcher points out.
Yet the environmental consequences are well known: these micropollutants, which re-enter the water cycle, accumulate in the sediment and affect the entire ecosystem. “Studies show that fish living near treatment plant outfalls are contaminated by these molecules. These toxic compounds have become a major concern, and future wastewater treatment plants will need to modernize to limit their emissions, ” explains Julie Mendret. The researcher has decided to take on this challenge by proposing an innovative and intensive wastewater treatment process.
Innovative and intensive
Today, there are two types of processes used to treat these micropollutants: membrane processes and advanced oxidation processes.
The first relies on the use of membranes that trap very small molecules while allowing water to pass through. This filtration method is effective but has limitations: “While the pollutants are certainly separated from the water, they are not destroyed, and they must then be removed, ” explains Julie Mendret.
Another solution: advanced chemical oxidation processes. “Ozonation is particularly effective against micropollutants,” the researcher notes. “They are oxidized by ozone, which breaks them down into increasingly smaller molecules until, in the case of complete mineralization, only CO₂ and H₂O molecules remain. ” The pollutant is ultimately eliminated, leaving only harmless water and carbon dioxide molecules. 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 byproducts.
A 2-in-1 process
In light of these limitations, researchers at theIEM came up with the idea of combining these water treatment processes to leverage their respective advantages.
An ambitious project named Saware. “It’s a 2-in-1 process: we combine highly 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 hybrid process offers several advantages: ozone acts more effectively on pollutants that have been concentrated by filtration, and any toxic byproducts generated by ozonation are retained by the membrane and are therefore not released into the environment.
To develop this device, Julie Mendret and André Ayral of theIEM chose ceramic nanofiltration membranes, a material resistant to ozone. “This is the first time this type of catalytic membrane has been used to treat municipal wastewater, ” the specialist notes.
An innovation that could ensure high-quality water leaving wastewater treatment plants—water that could be reused (see box). “Unfortunately, we’re held back by very strict French legislation that limits the reuse of wastewater,” laments Julie Mendret. This is a call for regulatory change to help preserve this invaluable resource.
Water reuse: a powerful tool for conserving water resources
In the face of a global water shortage, wastewater reuse is a promising solution for the future. Once treated, this water can indeed be used for various purposes: irrigating green spaces or crops, firefighting, street cleaning, or even replenishing groundwater aquifers. Some countries, such as Singapore, even go so far as to produce drinking water after treating wastewater.
In France, “reuse” remains underdeveloped. The reasons: a lack of public awareness and very strict regulations. Industry professionals are therefore advocating for a relaxation of the law that strictly regulates the reuse of wastewater, primarily for health reasons. The European Commission recently took up this issue and issued a proposal for a regulation in 2018 dedicated to agricultural irrigation, with the aim of facilitating the reuse of treated wastewater.
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