Water company expenditure to reduce nutrients in UK rivers is likely to double in the 2025-2030 investment period, with funding expected for around 900 phosphorous removal projects in England and Wales. Evidence shows there have been large reductions in sewage effluent phosphorus loads over the last 25 years, thanks to investment in wastewater treatment plant upgrades.
By Duncan Wildgoose, business development manager – head of wastewater at Xylem UK
However, with tightening consents, due to legislative drivers including Water Industry National Environment Programme (WINEP), Environment Act 21 and Water Environment Regulations, utilities are now seeking technologies that can remove phosphorous to lower-than-ever levels.
Consents of under 0.4 mgl TP will be typical in the next asset management period – AMP8 – with net zero an added consideration for delivery teams, along with expected financial constraints. 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 – a technique developed in the USA and Canada and introduced to the UK on wastewater about five years ago – which is proving to be more sustainable and cost effective than many typically used processes.
Ballasted clarification systems use a dense material – in Xylem’s case, magnetite – to intensify biological or conventional chemical flocs and improve the settling of suspended solids in water. This technique has proven to process wastewater ten times faster than a conventional clarifier
The process can cope with higher loading rates in a reduced site footprint and components can often be installed within existing assets, without the need to build complete new tanks. Water companies are now increasingly considering it as an effective solution for P-removal in AMP8, particularly on medium to large sites where it is most cost effective.
Through AMP7, Xylem has worked with four UK utilities to install 14 ballasted clarification systems in larger treatment works, one of which – a major facility serving a large city – now contains the biggest application of the technology in the world.
Combined, these sites can treat up to one-and-a-half-billion cubic metres per day and can bring total phosphorous down to as low as 0.15mg per litre, which will result in significantly healthier rivers in their local environments. Many of these projects have reused existing onsite assets, including, in one location, repurposed rapid gravity filters, which had been out of operation for 15 years.
For water company planners looking at phosphorous removal options for AMP8, now is a good time to talk to suppliers about technology availability and to establish capital costs and ongoing operational expenditure. It will also be worthwhile finding out if new systems can be installed within existing assets, to lower cost and footprint.
Reducing the sector’s reliance on ferric and other chemicals for phosphorous removal is also of increasing importance, for reasons of sustainability, resilience, health and safety, and to mitigate the rising cost of chemicals.
Depending on the site specifications, ballasted clarification can potentially use 20-30% less ferric than existing processes and requires minimal operator intervention or any manual cleaning, which would have significant environmental and financial benefits, over a 20-year life span.
Looking beyond AMP8, Xylem hopes to see more investment in technologies that can recover phosphorus and convert it into sustainable fertilisers.
This is happening successfully in many parts of the world, including Dublin, Madrid and the US, where the Metropolitan Water Reclamation District of Greater Chicago partnered with Xylem technology partner Ostara to open the world’s largest nutrient recovery facility in 2016 – an installation that was celebrated in the Netflix movie Brave Blue World.
Back in the UK, the utilisation of phosphorus recovery has so far not been viewed as a viable or cost-effective option, despite the many benefits, and a long-term approach will be needed to deliver a similar system at scale. This presents an extraordinary opportunity for UK water companies wishing to take a lead and be among the first to embrace a truly circular approach to phosphorous removal and reuse.
