Cleaning wastewater

Managing urban wastewater treatment plants

Stereau, the Group’s engineering subsidiary company, has developed many different wastewater treatment processes, including :

  • reducing the volume of residual treatment sludge
  • optimising energy and reagent consumption
  • reducing plant size
  • eliminating micropollutants (pesticides, drug residues, etc.)
  • reusing treated water


Protecting the resource

Working within the regulatory framework of health and technical recommendations on the use of treated water, Saur is involved in an ongoing programme of research conducted in collaboration with the French National Research Agency (ANR). Focusing directly on the elimination of emerging micropollutants, such as drug residues and pesticides, the purpose of this research work is to develop innovative wastewater treatment processes that will improve the quality of large bodies of water, and reduce the pressure on water resources.

The Saur Aqua-RM®, process that combines traditional biological treatment with membrane filtration is already at work in many of the wastewater treatment plants designed by Stereau. Reducing the use of energy and reagents, AquaRM® membrane technology helps to conserve drinking water resources by producing high-quality treated water for use in agriculture and industry.


Our solutions for rural communities

The Saur Group was born out of the need of rural communities to have access to solutions specific to the needs of their locality.   Rhizostep®* is a 100%-biological, effective, robust and economical wastewater treatment solution.


Developed by Saur, this process provides an effective answer to treating the wastewater needs of communities with between 50 and 2,000 population equivalent by using the purifying properties of soil for treating raw effluent. The clumps of specially-planted reeds (Rhizostep® reed beds) used in this system provide natural filtration. In this way, effluents are treated in a gravity system that requires no added chemical reagents. The visible part of the installation – the reeds – integrates perfectly into the landscape. More than 200 Rhizostep® facilities are now providing 100%-biological treatment of wastewater throughout France.

Plus de 200 Rhizostep® sont en service en France pour une épuration 100 % biologique des eaux usées



Inspecting and optimising private sewage systems (ANCs)

With more than 500,000 diagnostic analyses conducted in rural communities, Saur takes expert care of all the regulatory and technical requirements applying to public services for private sewage systems, and supports local authorities in implementing their private sewage system services (SPANC). Saur provides the following services:


  • regular inspection of installations
  • approval of the design and construction of new installations
  • the refurbishment of old installations
  • environmental studies
  • issue of compliance certificates



We offer users a comprehensive service called, SPANC Confort®*, which includes an annual inspection of the installation, technical monitoring of the septic tank and a 24/7 callout service for home owners.



Reusing residual treatment sludge

Consisting mainly of water, mineral salts and organic matter, wastewater treatment plant sludge is the ultimate waste product of the wastewater treatment process. The Saur Group assists local authorities in their choice of treatment process in full compliance with European and national regulations. Saur provides expert control of every stage in the sludge management process :


  • composting
  • re-use for agriculture (spreading as fertiliser)
  • alternative channels, including dewatering, storage, heat drying, solar drying, heat recovery and landfill



On the upstream side, we focus on using techniques that reduce residual treatment sludge volumes, for which our engineering subsidiary company Stereau has developed a series of biological processes,


  • the. MycET® seeding bioreactor :  MycET® uses a cocktail of fungi to reduce sludge volume by between 25% and 30%
  • The Digesthane™, process uses the anaerobic digester principle to recover energy from sludge, at the same time as reducing its volume by between 30% and 50%
  • Sonoflux® boosts biogas production by up to 30%
  • Rhizophyte® is a 100%-biological process distinctive for its high performance and low operating cost. The visible part of the installation – the reed bed – provides a rated storage of sludge. Rhizophyte® is now in use in more than 100 locations