Comag

 

Ballasted clarification systems use a dense material to intensify biological or chemical floc formations and dramatically improve the settling of suspended solids in water. Faster, settling leads to smaller clarifies and so smaller footprints. Ballasted clarification technique has been applied where very low phosphorous limits are required. down to 0.04 mg/L.

CoMag P removal refers to the CoMag system, a wastewater treatment technology from Evoqua Water Technologies (now part of Xylem) that uses magnetite (a dense iron ore) to efficiently remove phosphorus (P) and other contaminants, achieving much faster solids settling for smaller, more cost-effective treatment plants, often meeting stringent environmental standards. The process involves adding a coagulant, then magnetite to ballast the floc, and a polymer to bind it, allowing for rapid settling and magnetic recovery of the magnetite for reuse, making it a sustainable solution for tertiary treatment

How it works

• Coagulation: A metal salt coagulant (like iron or aluminum) is added to precipitate soluble phosphorus into solid flocs.
• Ballasting: Magnetite, a heavy, inert iron ore, is mixed in, embedding into the chemical floc and significantly increasing its density.
• Settling: The weighted flocs settle much faster (up to 10-30 times faster than conventional methods) in smaller clarifiers, a process called ballasted flocculation.
• Magnetic Separation: A magnetic drum recovers most of the magnetite from the settled sludge for reuse, improving sustainability.
• Polymer Addition: A polymer coagulant helps bind the floc and ballast together for better performance. 

Key benefits

• High Efficiency: Achieves very low phosphorus levels (down to 0.04 mg/L).
• Compact Footprint: Requires much smaller clarifiers, saving space and cost.
• Sustainable: Recovers and reuses the magnetite, reducing operational costs and resource use.
• Versatile: Can be used for primary or tertiary treatment, removing phosphorus, solids, and heavy metals. 

Ballasted clarification systems use a dense material – in Xylem’s case, magnetite – to intensify biological or chemical floc formations and dramatically improve the settling of suspended solids in water. This technique has been applied where very low phosphorous limits are required.

Xylem offers two ballasted clarification systems:

BioMag™ for biological processes  

BioMag uses magnetite to deliver the world’s leading proven settling clarification technology for biological floc, allowing capacity expansion and performance improvement with minimal plant modifications at the lowest cost possible.

CoMag™ system for chemical processes  

CoMag uses magnetite as a ballasting agent into traditional chemical floc to effectively reduce the total phosphorus levels to the lowest levels that are consented. Settles floc up to 20-30 times faster than conventional settlement treatment.

Technology in action – Yorkshire Water case study

Xylem’s ballasted clarification system is already achieving very low p levels for water companies – in some cases exceeding targets. Recent success include:

Knostrop wastewater treatment works (WwTW) is Yorkshire Water’s largest treatment site, serving a population equivalent of 990,000 in and around the city of Leeds, with a full flow-to-treatment (FFT) of 5,600 l/s.

Discharges from the site were required to undergo advanced biological treatment to reduce levels of phosphorous returned to the River Aire. Knostrop’s new compliance level was set at 0.4mg/l total phosphorus. To achieve this, in 2023 Yorkshire Water began a £60m upgrade of the site, implementing a range of advanced treatment technology from solutions providers including Xylem.

The solution 

A CoMag ballasted clarification system was installed to provide a new tertiary solids removal process, as part of the wider upgrade at Knostrop WwTW. Due to the efficiency of the process, just one 32m high-rate CoMag clarifier was required at Knostrop WwTW.

Results

Following commissioning in September 2024, Knostrop’s CoMag system provides tertiary solids removal to 75% of the site’s full flow-to-treatment, helping achieve average total phosphorous of 0.25mg/l – exceeding the target of 0.4mg/l. The results were immediate and the ultra-low level of 0.1mg/l was recorded during the performance test period.

The technology is processing a significant treatment flow, has increased treatment capacity and improved the quality of tertiary filtration, all with a smaller footprint compared to conventional methods.

The benefits to the River Aire ecosystem would have been felt quickly, due to the efficiency and speed of the CoMag process. Importantly for Yorkshire Water, the innovative technology continuously recovers most of the magnetite, which will support the plant’s sustainability requirements and budget.

Sam Akeroyd, capital delivery programme manager, Yorkshire Water, said: “The CoMag system from Xylem has provided Yorkshire Water with a stand-out solution for reducing phosphorus levels to meet new environmental consents. We can now confidently fulfil and surpass our commitments to reduce phosphorus at our Knostrop STW, while meeting our cost and ongoing operational objectives.”

Following the success at Knostrop, Yorkshire Water has selected CoMag technology for another large site requiring phosphorous removal. The technology is also in use at Severn Trent’s Longbridge and Spernal works, demonstrating its effectiveness in meeting tightened phosphorous consent across the UK.