Severn Trent trials ground breaking technologies to reduce phosphorus

Posted: Wednesday 25th May 2016

To meet the requirements of the Water Framework Directive (WFD) around phosphorus, Severn Trent is evaluating six technologies at one of its sewage treatment works (STW), two of which are world firsts.

As a result of the requirements of the WFD, where STWs will have limits of less than 0.5mg/l, with some as low as 0.2mg/l, Severn Trent will have to upgrade around 100 works, with many being upgraded to reduce phosphorus for the first time. With existing UK technologies unlikely to be capable of meeting the new limits, the company has decided to evaluate a number of different technologies before deciding which systems to invest in.

Working with partners at Packington STW in Leicestershire, Severn Trent is currently evaluating:

� Pile Cloth Media Filtration;

� Membrane Filtration;

� Ballasted Coagulation;

� Nano-particle Embedded Ion Exchange;

� Immobilised Algal Bioreactor; and

� Absorption Media Reed Beds.

Pete Vale, Technical Lead for Innovation at Severn Trent, said: "Two of the technologies - the ion exchange, and the algal bioreactor - have been developed specially by Cranfield University and put into practical application for the first time.

"It's relatively early days but we've seen some encouraging results from all of the technologies which is heartening given that some of them are genuine world first designs."

The Cranfield University researched systems feature some cutting edge technology:

The Immobilised Algal Bioreactor, which featured detailed design by Atkins, uses low energy LEDs to grow algae that are used to not only reduce levels of phosphorus and ammonia but are also used to help generate additional biogas in on-site anaerobic digesters.

Ion Exchange media embedded with iron nanoparticles enable the selective removal of phosphorus in the Nano-particle Embedded Ion Exchange, with a simple pH switch enabling the high purity recovery of phosphorus. Atkins also provided detailed designs for the system.

The Reactive Media Reed Bed using steel slag media is based on a standard Severn Trent horizontal subsurface flow design and is a relatively low cost design.

The other systems are proprietary, with the Membrane Filtration technology provided by Koch Membrane Systems, Evoqua Water Technologies' CoMag ballasted coagulation system and the Pile Cloth Media Filtration by Mecana and Hydrok Water Engineering Solutions.

"Each of the technologies have their advantages, and their disadvantages, which is why we're running the trials," said Pete.

"As phosphorus is both a key pollutant and an increasingly valuable resource we took a strategic decision several years ago to become exemplars in this field, and now we clearly need to make the right decisions

"And the right solution for a large STW might not be the same for a small STW but, by looking at six such innovative solutions, we're not only putting ourselves at the forefront of the phosphorus issue in the UK, we're also making sure we're making the right decision for our customers."




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