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According to the United Nations, “80% of the world’s wastewater returns to the ecosystem without having been treated or reused,” and this is happening on a global scale. In addition to health risks, this important water resource is not being harnessed in this time of climate change. With the high temperature records reached in recent years, even European countries are suffering from drought and the impacts are massive.
Recycling and reusing wastewater has many economic and environmental benefits, but presents significant challenges in terms of treatment. Indeed, sanitation methods deployed must comply with strict sanitary requirements. This challenge was taken up by Julie Mendret, researcher at the Institut Européen des Membranes (IEM) in Montpellier, France, and lecturer at the University of Montpellier.
At the IEM, as a specialist in the development of membrane processes and materials, Mendret’s project focuses on the sanitation and analysis of water collected in wastewater treatment plants in France. Her research began in March 2017 and led to a proposal for a new advanced wastewater treatment process with no liquid discharge called Saware. The project is part of the wastewater treatment plant modernization effort. Funded by the National Agency of Research, it aims to eliminate organic micro-pollutants like biocides and pharmaceutical substances that contaminate municipal treated water. These are precisely the pollution control processes that take place after the pre-treatment steps that isolate insoluble waste, i.e. solid waste, sand and oils.
A typical sewage treatment plant
Environmental Issues Caused by Micropollutants
Deployed in wastewater treatment plants, biological wastewater treatments consist of using the action of micro-organisms, activated sludge, to absorb and oxidize organic matter present in wastewater. Unfortunately, some harmful molecules are resistant to treatment. The treated water still containing these micro-pollutants is discharged into the receiving watercourse. Mendret explains: “Studies show that fish living close to treatment plant discharges are contaminated by these molecules. These toxic compounds have become a major challenge, and the wastewater treatment plants of the future need to be modernized in order to limit their emissions.”
Saware, a Two-Tiered Depollution Process
Two types of treatments are able to remove this type of molecules from watercourses: membrane processes and ozonation. The first method isolates pollutants by filtering water using a membrane that can be of different types: microfiltration (pore size close to 0.1 μm), ultrafiltration (0.01 μm), nanofiltration (0.001μm) and reverse osmosis (dense membrane) membranes. However, it does not destroy the captured pollutants. The IEM researchers thought of coupling the filtration process to an oxidation process—ozonation—to overcome this limitation. The advantage is twofold. Ozonation is optimized due to a higher concentration of pollutants on the membrane, and toxic by-products that may be formed during ozonation are retained by the membrane.
The nanofiltration and ozonation processes are presented in the following videos:
The system designed by Julie Mendret incorporates ceramic nanofiltration membranes, a material that resists the action of ozone. Thanks to this new depollution process, the water obtained can be used for agricultural land irrigation or firefighting. However, the researcher is disappointed that the Saware project is being blocked “due to very strict French legislation that limits the reuse of wastewater.”