Sustainable management of rainwater and wastewater, a necessity of our time

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To create the sustainable neighbourhoods of tomorrow, AGORA is developing a new water management strategy, based in particular on innovative solutions for the retention and reuse of rainwater and wastewater. ‘It’s all about protecting and making the best use of our most precious resource,’ explain AGORA colleagues Alexandre Londot, Yves Biwer and Vanessa Villeneuve, accompanied by Philippe Genot of Shroeder et Associés.

Why is sustainable water management an ecological priority in developing new neighbourhoods?

Alexandre Londot, Director of Operations, AGORA: ‘Water is an essential resource for our lives and all our urban activities, and we know today that it’s in danger of becoming increasingly scarce and that it’s important to safeguard it. AGORA’s concern is as much to ensure that there’s enough water for city dwellers to use as it is to guarantee the quality of watercourses and biodiversity – for example, our renaturation planning of the Alzette at Metzeschmelz. We’re thinking as much about water retention and depollution as we are about our responsibility to limit the negative impact of urban developments on water flows. All of this conforms with a very precise regulatory framework in Luxembourg, which aims to protect watercourses, generalise good flood management practices, limit any abusive use of this precious resource and encourage the retention and recovery of rainwater.’

At the heart of AGORA’s current urban projects, why do you consider wastewater and stormwater management strategies in particular to be of the utmost importance?

Yves Biwer, Managing Director of the Metzeschmelz district: ‘Every drop of water wasted unnecessarily has a negative impact on our ecosystems. It seems clear that a solution to water over-consumption and its increasing scarcity is to improve the use cycles of this precious commodity and rethink the infrastructures for intelligent water use. I would say that, in all European municipalities, wastewater and rainwater treatment is perhaps one of the operations that has changed the least over the years. The standardised systems operated by the majority of municipalities are not based on a water circulation approach or any consideration of possible hydrological cycles. It’s time to address this and make some major changes. Citizens must also adapt to the new situation – water scarcity – and change their behaviour. We’re at a turning point.’

AGORA’s concern is as much to ensure enough water for city dwellers’ use as to guarantee the quality of watercourses and biodiversity.

Alexandre Londot, Director of Operations, AGORA

Can you describe the specific approaches developed at Belval and Metzeschmelz?

Alexandre Londot: : ‘We have a global approach that affects the entire chain of water use, and it would take a long time to explain everything that’s planned. So let’s look at a few noteworthy examples. In particular, there are plans to reuse as much rainwater as possible to water plants and flush toilets. This means building retention basins and other structures to recover this water and filter it if necessary. Wastewater, on the other hand, can be used several times in domestic life, for example, shower water can be filtered and redirected to the toilet. Drinking water, on the other hand, would only be used for human consumption in this scenario, and would cease to be used excessively. We’re also looking at recovering the heat from filtering grey water and converting it into a source of energy. This is a revolutionary new way of doing things, but I’d like to point out that Belval already has a history of recovering rainwater. All the rainwater drained from the Belval district passes through the ArcelorMittal ponds located to the north of the site and is used for the plant’s cooling process. We’re building on this history and going further.’

… at Belval, there’s already a history of rainwater recovery. We’re building on that history and taking it a step further.

Alexandre Londot, Director of Operations, AGORA

What are the biggest technical challenges in implementing the stormwater and wastewater management plan?

Vanessa Villeneuve, Project Engineer, AGORA: ‘In the specific case of Metzeschmelz, a district that we are building almost from A to Z, predicting floods and building structures capable of containing them is a challenge in engineering terms. This involves complex retention volume calculations and creating basins of a size that will fit in well with the urban landscape, or determining how existing basins and the natural levelling of the land can be used.
We’re working on the ‘sponge city’ concept, i.e. a city capable of absorbing rainwater through the ground or on green roofs to regulate flooding, and also to reduce vulnerability in times of drought. The idea is also to increase the number of retention areas, to ensure that as much water as possible is recovered and controlled during heavy downpours or storms. As far as the pipes are concerned, the challenge is to plan future site developments and fit them with pipes that allow the use of the same water several times over. That’s the idea and the way forward.’

Philippe Genot, Chief Innovation Officer, Schroeder Associés : ‘We’ll also be using various techniques to control the flow of streams to maintain the ecological balance. And that’s a considerable challenge! We have to guarantee a certain flow, and also carefully control the quantity of wastewater that, at the end of all the cycles of use by our citizens and industries, could be returned to the Alzette. This water must have been analysed and treated to ensure a low level of pollution. All of this involves skilful calculations of course, but also the installation of structural elements on watercourse surfaces, and sometimes underground. It may seem laborious, but it’s also exciting, and above all, it’s essential in the current circumstances!’

Urban gardens, smart cities, eco-neighbourhoods or temporary occupation of urban space, Through the voice of experts, “Tell me more! ” is a series that explores new trends.

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