Outstanding sewage treatment design at Minworth

Pick Everard has been working with Severn Trent Water on major improvements to one of the UK's biggest sewage treatment works.

Severn Trent Water is spending over GBP110 million on upgrading the Minworth plant to meet the new discharge quality standards set by the Environmental Agency and the European Union.

The plant, north east of Birmingham, is the primary sewage treatment works for the city.

It routinely treats a remarkable 12.6m3 of effluent per second (average of 5.8m per second), and is able to cope with up to 30m3 per second.

For the new works the inlet channel will be 5m wide, with feed pipes to distribute flow 1.6m in diameter, all delivering to processing units that are at the boundary of engineering experience.

"The need for accuracy has been paramount because the hydraulic profile of the existing works is very constrained, and the necessity to pump flows has significant cost implications," said Nick Thomson, partner at Pick Everard.

"The control of the flows has also been challenging, and a radial gate is to be installed on the inlet channel.

We believe that this is the first time that such a device has been used on a sewage works".

The civil engineering and hydraulic designs were particularly complex because of the very large scale of the works which include installation of a new inlet system and preliminary treatment complex, a settlement tank 'island' of 22 primary tanks and new aeration lanes to biodegrade the liquid waste.

"We are converting the old settling tanks into storm tanks," said Nick Thomson.

"After a severe storm the amount of water coming into the plant can increase enormously, and we have to deal with that.

The least environmentally damaging and most efficient solution was to reuse existing tanks".

Pick Everard is providing hydraulic and civil engineering design, working closely with the integrated design team based at the works.

'Front-line' engineers and technicians are supported by the hydraulic, highways and structural specialists at Pick Everard's Leicester and Glasgow offices.

Computer modelling of unusual complexity was used and physical modelling was employed for the most complicated parts of the project.

Pick Everard also carried out the necessary ground investigations and flood risk assessments before work began.

The work will be carried out in two phases.

Phase 1 is the construction of the primary settlement tanks, the building of the inlet works and the storm tank conversions.

Pick Everard's design work is complete on this and construction has just started.

Phase 2, the aeration lanes and the final tanks to augment the biological treatment process, are still at an early design stage.

The works, a part of a larger scheme, are due to be completed by 2010.

"We are dealing with the legacy of some remarkable historic hydraulic engineering, and on such a large scale it's quite a challenge for our designers to integrate it into a modern system," said Nick Thomson.

"The very large scale of the work we have done on the hydraulic and civil engineering for Minworth puts us at the forefront of design of sewage treatment works in the UK.

It also presents us with a unique opportunity to work with other designers and contractors to turn a cutting edge design into a physical reality.

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