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Julie Ducrot, Process and Water Treatment Engineer at the Toulouse Métropole Cycle de l’Eau Department and Robert Médina, Toulouse Métropole Vice-President for Water and Sanitation, and, tell us about this choice and the many benefits of this innovative technology.

What does the ultrafiltration solution entail and how did you take it on board?

Julie Ducrot: We use membranes produced by Polymem and made of a copolymer within the structure of Kynar® PVDF. This material imparts its chemical resistance to oxidants and its mechanical strength to the microporous membrane. The copolymer ensures its long lasting hydrophilic property and the stability of the porous structure. So, the water to be treated will pass through these microporous fibers, similar to hollow spaghetti under one millimeter in diameter, to be filtered, or rather ultra-filtered since the scale of the pores is 10 to 20 nanometers (millionths of a millimeter). The product of R&D collaboration between Arkema and Polymem, this innovative solution was first tested on the water treated by the Ginestous-Garonne plant, with a view to reusing the wastewater. The tests conducted during this 18-month pilot trial were highly satisfactory, so it was decided to move on to an industrial scale. The plant commissioned in 2020 is designed to filter up to 1,200 m³ of treated wastewater per day.

Why invest in this solution?

J.D: It’s a good investment because it's an extremely safe system. After passing through the membranes, all suspended solids and any elements in the order of 15 nm including bacteria and viruses, are eliminated. The system thus perfectly fulfills its role regarding everything that is pathogenic, offering the best guarantees to prevent issues of quality non-conformity. In addition, the stability of the porous structure maintains performance and therefore a constant filtration efficiency. This constant efficiency of the treatment can be explained by the fact that these membranes, designed to last at least 10 years, do not lose their porous structure over time. All that is needed is to clean the membranes so they can recover their disinfection performance.

Less frequent cleaning and a long-lasting hydrophilic character for consistent efficiency

Precisely, in terms of cleaning the membranes, isn't this too onerous?

J.D: On the contrary, cleanability is one of the other great strengths of Polymem’s Neophil® solution. This is due to the long-lasting hydrophilic nature of Arkema’s PVDF Kynar® DH100 which requires no additive, so the necessary cleaning operations throughout the membrane lifetime do not need to be as frequent as with other materials, in particular sulfonated polymers. Cleaning frequency is between 20 and 30% lower. On top of this, there is no chemical treatment at the water filtration stage, as this filtration takes place in a single step on the membrane surface by a unique physical process involving the separation of the elements. The only products used are for backwashing the membranes. These are reagents that do not go into the treated water and are neutralized in the discharges fed back to the top of the treatment plant. And, depending on the intended uses, should it be necessary to use chlorination post treatment for residual effect, doses are lower after ultrafiltration.

I can also see other benefits. For example, the fact that it is a relatively easy technology to manage, requiring little maintenance and no frequent physico-chemical tests, apart from regular and automatic checks on the condition of the membranes. In fact, only the membrane elements are replaced, not the casings. Another benefit of this technology is its compactness. Filtration requires no extensive system such as pools or lagoons for the finishing treatment. Instead we have a compact skid that takes up barely 60 m². Finally, we may not have the necessary hindsight yet, but there is evidence that the soundness of the solution and the total cost throughout the life cycle will generate savings in the long term.

How do you use this water once treated?

J.D: The treated wastewater we obtain is top quality (index A) that is entirely suitable for its intended use, namely currently just the watering of green spaces (within the facility as well as the nearby golf course). Nevertheless, we intend to make the most of this resource by developing other uses. Industry is one of the areas in which municipal wastewater can be reused. Indeed, in terms of process water, our membrane ultrafiltration system is well placed insofar as we need disinfected clarified water. There is a strong potential for membranes in these applications.

A solution for adapting water management to climate change

Does this system address the challenges of sustainable development?

Robert Médina: The reuse of treated wastewater is strongly encouraged by public policies in France, in that it helps adapt the country to climate change. It is also one of the targets of our Plan Climat Air Énergie Territorial. For a community like Toulouse Métropole, the challenge of developing the use of unconventional water makes it possible to consume less water and to make its use more efficient, especially in times of drought. The aim here is to reduce the pressure on water resources, but also to reduce the products needed for treatment and the energy cost in comparison with other technologies.

This solution therefore clearly fulfils one of the sustainable development goals of the climate plan. Our manufacturing plant is one of the few in France to be truly operational, and in this sense is of great interest to water treatment equipment manufacturers and the main end-users such as municipalities and industries, as well as researchers and universities. Several of them came to visit our plant. The availability of this innovative technology gives momentum to a circular economy and sound water management within our community. As such, we stand among the French authorities at the forefront of this issue of wastewater reuse.

Toulouse Métropole

Toulouse Métropole is a Public Body for Inter-municipal Cooperation (EPCI) consisting of 37 municipalities, which represent over 760,000 inhabitants, including 475,000 living in Toulouse, France’s 4th largest city. Toulouse Métropole oversees the supply of drinking water produced from 3 plants. It also manages 17 wastewater treatment and purification plants, the largest of which, Ginestous Garonne, is capable of treating up to 160,000 m³ of wastewater daily.