European WWTP Utilizes Ballasted Clarification for Phosphorus Removal

CoMag system provides cost-effective solution to meet phosphorus discharge limits at wastewater treatment plant


  • Finham will be Europe’s first wastewater treatment plant with a permanent installation of Evoqua’s ballasted settling technology
  • Ballasted settling technology has been proven successful in facilities throughout the United States for more than a decade
  • Evoqua Water Technologies has been selected by Severn Trent Water and its design and construction partner, Costain Ltd., to supply Evoqua’s CoMag® ballasted clarification system
  • Their goal is to reduce phosphorus at the Finham Sewage Treatment Works in Coventry.



For communities that face challenging wastewater characteristics due to industrial discharge or dense populations, the CoMag system is the ideal solution. The tertiary CoMag system will help Severn Trent Water reduce both total suspended solids and phosphorus before the treated water discharges into the River Sowe.

The CoMag system uses magnetite – fully inert, iron ore particles – to enhance the clarification process. The system settles chemical floc up to 30 times faster than conventional clarification.

" After evaluating several technologies, we selected the CoMag system because it allows us to cost effectively meet new phosphorus discharge limits; We are saving a significant amount of money by reusing existing but redundant sand filter infrastructure as the reaction tanks. We are also saving space by using custom-designed clarifiers from Evoqua that can process wastewater ten times faster than a conventional clarifier, thanks to the CoMag system. "

Peter Sugden, programme manager for Severn Trent Water


Algal blooms and poor river ecosystems are triggered by high levels of phosphorus in the river. To combat the blooms and restore water bodies to “good” status, the UK Environment Agency’s National Environment Programme (NEP) is imposing low phosphorus limits on many wastewater treatment plants, including Finham. The CoMag system will significantly decrease the amount of phosphorus that the works discharges and will ensure compliance with the new phosphorus limit of 0.22 mg/l of total phosphorus (T-P).

“For Finham, the CoMag system has been designed to achieve phosphorus limits of less than 0.18 mg/l T-P,” said Simon Radford, UK sales manager of Evoqua’s Municipal Wastewater Treatment business. “This capability gives Severn Trent the confidence that the CoMag system can meet the 0.22 mg/l limit in the future, even if there are increased demands on the facility from population growth or greater amounts of industrial discharge.”

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