Water companies are investing a record £6 billion in nutrient removal schemes during AMP8 (2025–2030) — around double the spend of PR19. This funding will enable phosphorus reduction at roughly 900 sites, helping utilities meet tightening environmental consents and rising expectations from regulators and customers.
Although phosphorus is an essential nutrient, excess levels in watercourses trigger algal blooms that deplete oxygen and damage ecosystems.
According to the Environment Agency, around 60% of phosphorus is from sewage effluent – In England, excess phosphorous remains the most common reason for waterbodies failing to achieve ‘good’ ecological status. As such, consents of under 0.4 mg/L TP will be typical in AMP8, making phosphorous removal both a regulatory must and an operational challenge.
While new wastewater treatment works are often designed for low phosphorus discharge, existing facilities that predate the current regulatory environment were not. Consequently, water companies are looking for the best ways to upgrade their facilities for the lowest possible lifecycle cost.
The good news is proven technology is already helping companies achieve very low consents at scale at treatment works across the UK. One of the more recent arrivals to the market is ballasted clarification with magnetite – a technique developed in the USA and introduced to the UK on wastewater about five years ago – which is proving to be simpler, more robust and cost effective than many typically used processes.
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.
- To learn more about phosphorus regulations and treatment options, download Xylem’s whitepaper Phosphorous solutions for wastewater treatment
