Delivering a strategy for wastewater sludge
Several factors and trends have resulted in the increase of sludge volumes in Europe and the UK over the past ten years, including implementation of the European Union’s Urban Waste Water Treatment Directive and similar legislation, while the options available for wastewater sludge recycling on land have become more restrictive. Strict rules on nitrogen application rates; concerns over metals; changes to farming practices; and reduction in brownfield reclamation have limited this recycling option.
Consequently, United Utilities formulated a wastewater strategy to reduce its reliance on land application from approximately 80% to 50% by increasing capacity at its existing digested sludge incineration facility (Shell Green) and building a new solution to deal with sludge that is currently treated with lime – predominantly from treatment works in Lancashire.
Expanding and refurbishing Shell Green
The £91 million investment will not only increase capacity but will also improve its efficiency and contribute significantly towards operating flexibility. The project which is expected to be completed by spring 2010 started on site in January 2008 and is being delivered by a joint venture between Veolia Water Solutions and Technologies and Costain Ltd - known as S3JV.
Added to this is a project on the pipeline which runs between Bury and Bolton. This is being replaced and the six sludge pumping stations serving the site are being refurbished. The refurbishment of the pipeline will increase the reliability of the whole system.
Not content with a brand new extension, a project has also been undertaken to refurbish the two existing incineration streams at Shell Green. The incinerators are 10m high, 6.5m in diameter at their widest point, and are fabricated with vertical external steel ribs, in filled with 8mm thick steel plate panels. Detailed examination of the steel panels found that 40% needed replacing. The work was completed on schedule in March 2009 with no accidents, a high standard of work (verified by external specialists) and within budget.
Bridging the gap
There were originally over 30 different options identified on how to deal with the 57,000 tonnes of limed sludge predominantly from Lancashire. Ten of these options were chosen to go forward for examination with three potential solutions receiving further investigation:
- Existing treatment of liming followed by recycling to land;
- Raw incineration; and
- Advanced digestion at Davyhulme
The final decision was made in September 2007 with advanced digestion at Davyhulme – our largest Wastewater Treatment Works – prevailing. The benefits of the solution now entitled Sludge Balanced Asset Programme (SBAP) include:
- Reduced carbon footprint from existing scenario – saving over 32,000 tonnes carbon dioxide equivalent per year
- Maximizes existing asset use
- Significantly increases renewable energy generation
- Improves biosolids quality enabling land recycling to new outlets
- Minimizes incineration requirement
- Enables maximum flexibility
We are currently looking to award the construction contract and the facility should be operating by the end of 2011.
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