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How South African biological 'bugs' transformed how sewage waste is treated

  • How South African biological 'bugs' transformed how sewage waste is treated
    Credit: Severn Trent

About the entity

Severn Trent
We were founded in 1974 as a regional, state-owned water authority based in the Midlands and responsible for water supply management, and waste water treatment and disposal.

As Severn Trent marks its 50th anniversary, the company is taking a look through its archives to uncover some of its greatest engineering and innovative feats over the last half a century.

As the start of a new millennium approached, Ricky Martin’s Livin' La Vida Loca was topping the UK music charts, the beanie baby craze came to an end and the millennium bug had a grip on the world– remember that?

It was at this point that Severn Trent was looking at a different type of ‘bug’ – one that would transform the way it treated wastewater from customers, that kept customer bills low.

The 90’s, saw the water and waste company scour the world for innovative new methods of waste treatment that led them to South Africa, where they had heard of a new, biological way to remove phosphorus from wastewater that would be introduced to the UK in 2000’s.

Biological nutrient removal – known as BNR, essentially uses bugs to ‘eat’ phosphorus, which helps remove as much of it as possible. Too much phosphorus in rivers can lead to algae blooms that suck oxygen out of the water – and removing it allows fish and other wildlife to thrive.

But thanks to this fact-finding mission in the 90’s Severn Trent is now seen as leaders in phosphorous removal and built what would be the very first treatment works fully focussed on BNR and something that’s now used across many of its sites.

Peter Vale, Circular Economy Architect at Severn Trent, said: “Innovation has always been at the centre of what we do, looking for new and better ways to do things, embracing new technology.  As we’re the only solely in-land water and waste company we have tight phosphorus permits, so we’re seen as one of the leading companies when it comes to phosphorus removal.

“You can remove phosphorus in two ways. By using chemicals, or design a treatment process to encourage certain bacteria to remove phosphorus for you.

“There was lots of new innovations coming from South Africa where a lot of new technology was being developed. We thought it would be a much more sustainable way of treating wastewater as it saves chemical use; it would mean a lower cost to build sewage treatment works if we adopted this method of treatment.

“Another huge benefit of this new method was that it would keep operating costs low, which in turn would keep things such as customer bills low.”

Severn Trent saw the potential of this new ‘different’ type of engineering and thought it could be replicated in the UK, so the company took the learnings and ran pilot trials at its Milcote Sewage Treatment Works in Stratford upon Avon, as well as Derby Sewage Treatment Works.

Towards the end of the decade the company took the decision to build its first treatment plant at Derby that would be fully-focused on this method, called ‘biological nutrient removal’ (BNR), which Severn Trent believe was the first ever in the UK. It was then rolled out across many of its treatment works as we rolled into the 2000’s.

Fast forward to the present, nearly half of the wastewater that comes through its works is treated using this method.

Peter, who was in charge of some of the trials when he joined the company in 2002, added: “It shows the importance of learning from others and being open to innovation and new engineering methods -not being constrained by current thinking. We now think of it as a standard process.

“Scouring the world for this new method, has meant using less chemicals today which also results in lower bills, which is good news for everyone.”

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