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Waste not want not

On 1 January, the EU Urban Waste Water Treatment Directive outlawed the dumping of sewage sludge at sea. Damian Arnold reports on how environmental and engineering consultant Entec provided a £200M solution on the Tees which has enabled Northumbrian Water

The Bran Sands wastewater and sludge treatment plants on the south bank of the Tees estuary have provided an immediate and heart warming return on Northumbrian Water's £200M investment. Migratory Salmon reappeared this year in a river that had become a dumping ground for partially treated sewage and industrial effluent.

Phase one of the scheme, designed and project managed by environmental and engineering consultant Entec, was completed by the end of last year in time to meet the requirements of the European Union Urban Waste Water Treatment Directive.

Driven by legislation and the need to clean up one of Britain's most polluted rivers, two major capital investments have come to fruition.

The first is the £140M Tees Estuary Environmental Scheme (TEES) for secondary treatment of municipal sewage and industrial effluent in the Tees conurbation. The second is a sludge strategy including a £70M Regional Sludge Treatment Centre (RSTC), to thermally dry the soon to be doubled amount of sewage sludge arising from the North East.

The TEES scheme includes new pumping facilities at existing sewage treatment plants at Portrack, Cargo Fleet and Eston which will transfer municipal sewage along dedicated pipelines, costing a total of £40M to the Effluent Treatment Works (ETW) at Bran Sands.

The £100M ETW is designed to combine sewage treatment with the treatment of industrial effluents. Waste streams from neighbouring ICI, Du Pont and British Steel plants are already being treated there.

Sewage sludge is piped from the ETW and shipped in from sewage treatment works along the coast to the RSTC which dries the sludge and processes it into usable biopellets.

Entec capitalised on the obvious synergies by integrating what started life as two separate projects into a 52-acre super plant. Project director Ivan Kitchen says: 'Being able to feed the sludge produced on site to the adjoining RSTC, and return the sludge liquor produced from the drying process for further treatment at the ETW is very cost effective.'

He adds: 'Placing them on the same site also brings significant economy of scale. Two major projects went through an integrated planning process and share common infrastructure, access, energy supply and utility supplies.'

Perhaps the most important synergy was the building of a combined heat and power plant - gas turbines that produce electricity and heat - to cater for the different energy needs of the two plants, says Kitchen.

'ETW has a big electricity demand, while the RSTC has a big heat demand. The balance between the two made a combined heat and power plant a very energy-efficient solution.'

The brown field site at Bran Sands located near the mouth of the Tees and leased from ICI, provided a winning application for a centralised plant which could claim to improve the local environment.

'We reached this solution after looking at more than 40 sites,' says Kitchen. 'We drew up a shortlist of sites and used environmental assessment techniques to select the best one and to show the Environment Agency that the local environment would not be adversely affected by our plans.

'Environmental assessments are a statutory requirement in the final stages of a planning application but we went further than this by using the same techniques in our initial assessments.'

The course to the winning planning application was smoothed by investigation and consultation which proved that Bran Sands was environmentally the best option. This avoided the risk of a long-running public inquiry which would have jeopardised the 1998 deadline for phase one.

'When the formal application for Bran Sands went through there were no problems. All parties were very supportive because they believed that the land was being put to good use,' says Kitchen.

The task of building to time and budget a unique plant to combine municipal and industrial effluent treatment along with Europe's biggest sludge drying plant, was facilitated by detailed research and benchmarking.

Looking at the feasibility of treating various different effluents at the ETW started in the laboratories to establish whether each industrial effluent could be biodegraded.

Pilot studies were then undertaken at nearby Billingham to treat combinations of industrial and municipal effluents, to see which combinations of treatment were robust and cost effective. 'We had to be sure we could treat the effluents effectively and economically,' says Kitchen.

Pilot testing has paid dividends, with three industrial streams being successfully treated at Bran Sands and testing of two others on the way.

Establishing the design parameters for the Regional Sludge Treatment Centre involved travelling European highways laden with truck loads of the North East's sludge on their way to be tested at operational plants throughout Europe. 'We needed to see which process suited our sludge best because sludge differs from region to region,' says Kitchen.

Developing a plant to dry raw sludge - still rare in Europe - meant evolving a design solution which Entec was satisfied would get it right first time.

A shortlist of four RSTC process plant suppliers was invited to take part in a design competition, partly funded by contributions from Northumbrian Water for each tenderer. 'It was a very intense four-month exercise, but we needed to be entirely sure that each design was exactly right for us,' says Kitchen.

'Four very well developed and competitively priced tenders were obtained and, in the end, Andritz AG of Austria won the day.'

Early delivery of design information helped Entec to manage the overall project to time and budget. 'We knew exactly what the client wanted and what the contractors were offering. It minimised the risks of changes to scope or costs during the project. Because we built up a lot of knowledge early in the project, the RSTC worked very well from day one and there have been very few problems,' adds Kitchen.

Bran Sands will be fully operational by 2000 but scope remains to develop the site to cater for Northumbrian Water's future strategy needs. Space remains to further develop the effluent treatment works. The first two 'trains' of aeration cells and final settlement tanks are treating effluent, while the third is being designed. The site can be further developed using this 'building block' approach - which has presented a complex project management challenge to Entec in coordinating a step-by -step procurement process.

'Integrating the design and construction process allowed us to be flexible. The ETW started treating effluents while construction was still going on at other parts of the site,' says Kitchen.

It is one of many challenges faced by Entec in delivering a project which is probably unique in terms of the diversity of environmental and engineering issues to be dealt with. 'We have had to integrate a large team, more than 100 strong at peak activity, which has harnessed the skills of virtually every engineering and environmental specialism available within Entec,' says Kitchen.

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