Teesside's new effluent treatment works at Bran Sands is a flexible multi-effluent plant catering for an increasing number of industrial effluents.
Strategically located in the heart of one of Britain's major petro-chemical and steel centres, the largest combined industrial and municipal effluent plant in the UK has been hailed by the Department of Trade and Industry as a vital piece of infrastructure needed to attract more industry to Teesside.
The £100M activated sludge treatment plant, the first phase of which was completed last year, was preferred to upgrading individual sewage treatment works at nearby Cargo Fleet, Portrack and Eston and building separate effluent treatment works for the industrialists.
Northumbrian Water now has the capacity to treat a combination of municipal sewage and industrial effluents in the new facility. The municipal sewage is transferred to the site via newly laid pipelines up to 1100mm in diameter, with a total length of more than 22km. The industrial effluents are transferred for treatment in dedicated pipelines, mostly of stainless steel construction.
Entec project manager of the ETW, David Harper, says: 'Evaluation of costs for a centralised plant versus upgrading of individual sewage works showed the centralised option to be cost effective. Adding industrial effluent treatment gives the centralised plant a further environmental and financial advantage.'
The activated sludge process on which the new plant is based involves growing a biomass of bacteria and micro organisms in aeration cells which consume the organic matter in the effluent. The 'bugs' thrive in the oxygen- rich environment in the aeration cells, the oxygen in this case being provided via air from a centralised air delivery system using jet aeration technology. The jet aeration system in the plant at Bran Sands is the biggest outside the US.
Bugs are already chomping away on three industrial streams on tap from nearby industrial giants ICI, DuPont and British Steel; sludge liquors from the drying process in the adjoining Regional Sludge Treatment Centre; and sewage from the Portrack flow. From 2000, extra municipal sewage flows from the Teesside conurbation of Middlesbrough and Stockton will be added to the bugs' feast in new aeration cells. Ultimate capacity will be to treat 300,000m3 of effluent a day with a population equivalent of up to 3.5 million.
The activated sludge process is natural and therefore environmentally sustainable for long- term treatment needs. It is also an economic and robust system and the huge plant at Bran Sands can tolerate considerable changes in effluent composition.
Industrial effluents received at Bran Sands are balanced before onward transfer to the biological treatment stage. Any pre-treatment required, such as nutrient addition or pH correction happens at the reception stage. Incoming sewage flows are initially screened and degritted prior to primary treatment before being pumped to the aeration stage.
Each of the current aeration 'trains' consists of 15 aeration cells and four final settlement tanks. These trains are designed to facilitate treatment of industrial effluents and sewage in differing configurations.
Northumbrian Water operates two trains, completed last year as part of the initial phase of the project. Train A treats DuPont UK's pure terephthalic acid effluent and British Steel's coke oven effluent, while Train B treats DuPont's nylon effluent, municipal sewage and sludge liquors from the RSTC.
Train C for treating additional municipal sewage from Portrack, Cargo Fleet and Eston will be ready in December 2000, and a fourth train is on the drawing board to cater for burgeoning industrial clients. Some future industrial effluents may need to be diluted into municipal sewage effluent to reduce the effect of toxic components on the biological process.
The scope of the initial phase of the ETW expanded as each new industrialist 'signed up', attracted by a reliable and economical treatment route for their effluent. The design, therefore, had to be flexible enough to cater for the introduction of each effluent.
It was also essential that the design and construction process ensured the effective treatment of effluents already being received, while other sections were being constructed and commissioned. This was achieved by Entec using state of the art project management and programming techniques.
Industrial effluent deals which demanded delivery on time and the tolling bell of European Urban Waste Water Treatment Directive, created a demanding time scale.
'From turning the first sod of earth we got the ETW up in two and a half years, managing more than 100 contracts from tender to completion on site enabling Northumbrian Water to successfully meet its deadlines,' said Harper.
Sir Robert McAlpine
N G Bailey
Harbour & General