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A complete system for reusing treated wastewater tested on a real-life scale

© SAUR

11/23/2015

A research project led by a consortium of 5 companies and 3 research laboratories including Irstea has enabled testing a complete system for reusing treated wastewater, from treatment processes at the treatment plant to water distribution to the place of usage: an absolute first!

 

Although reusing treated wastewater is a solution for the increasing demand for water, especially for irrigation and water stored in case of drought, very little wastewater is recycled in France: just under 20,000 cubic meters per day, which represents only 2% of the amount of water recycled in other European countries. This solution faces various regulatory, sanitary, environmental, economic, sociological and technological challenges.
 
A project to test and develop a complete system for reusing treated wastewater in France was started in 2011 on a pilot site in Mauguio (Hérault). Two years were spent exploring technical solutions, followed by two years of experiments and analysis.

PROJECT PROFILE

  • NOWMMA - New Process for Optimizing Wastewater Reuse from Mauguio to the Mediterranean Area in support of the French Reuse Directive
  • Eco-Industries call for projects by the Ministry of Industry – 2011-2015
  • Consortium of 9 partners: 5 companies and 3 research laboratories, including Irstea. Project led by SAUR with the support of the EAU Competitive Cluster (France Water Team Network).
  • Aim: develop complete system for reusing treated wastewater in France.
  • Irstea researchers involved in the project: Bruno Molle, Séverine Tomas and Souha Gamri.
  • Find out more about Cemib

An R&D platform

A complete R&D platform was set up, combining a processing unit, a development unit and a control plot. “We don’t often have the opportunity to work this way!” highlighted Bruno Molle, researcher at Irstea’s Montpellier center.

All stages, from treatment procedures for wastewater treatment plant output to point of use distribution of water, could be analyzed on-site. The entire process was automated and remote-controlled to ensure water quality was monitored as precisely as possible. This was a modular project that can be transferred across the whole Mediterranean basin.

The package includes:

  • a processing unit: filtration, buffer storage, ultraviolet disinfection reactor, used to test a variety of innovations (microfiltration, ultrasound, ultraviolet light to destroy pathogens).
  • and a development unit: a control plot, sown with grass and divided into 3 irrigated sections (sprinkler, surface or subsurface drip irrigation). Two of the sections used water at two different quality levels output from the processing unit while the third, control, section used water typically used in the region for agricultural applications.

View of the processing unit © SAUR

Irstea’s expertise: clogging, drifting and transfers

Irstea’s expertise was particularly relevant in this second part of the project, specifically, evaluating and improving the performance of irrigation systems on the control plot, “while remaining aware of the distribution process to avoid any risk of contamination, specifies Molle.

To start, scientists look inside the device. What was happening there? “Where the water is full of nutrients as it is here, bacteria tend to multiply and form biofilms as a way of protecting themselves against external predators. This creates a significant risk of blockages or clogging within the device.”

Scientists also focused on drifting phenomena in spraying devices. In windy conditions, there is a risk that microdroplets could escape from the spray zone. This leads to a risk of contamination. “In order to reassure the public, it must be possible to explain how much water is involved. Our work therefore involved defining how wind affects aerosol drifts around the spray zone,” explains Molle. This data was subsequently used to change regulations (Decree of June 25, 2014 modifying Decree of August 2, 2010), specifying maximum wind limits (depending on device pressure) for the safe spraying of wastewater.

“This initial approach allowed us to look to the future, towards the application of phytosanitary treatments sing irrigation systems. Since we can control devices for wastewater, we can also do it for phytosanitary products. Obviously, experiments were carried out using products currently used in organic farming, in line with current regulations.”

The issue of managing contamination was expanded to include the use of high pressure cleaners using wastewater, to clean streets for example. Nearby bystanders may be exposed during these operations. Scientists have therefore attempted to define transfer distances for these aerosols. How? By using water mixed with dyes with very low detection limits. These initial results are promising: to be confirmed and continued.

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