As the pressure on water companies to be environmentally responsible grows, sludge digestion is becoming an ever more attractive option.
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The process kills two birds with one stone, giving a useful purpose to a waste product and generating clean energy that brings myriad benefits with it including increased sustainability, energy efficiency and lower bills.
At Bran Sands on Teesside, Northumbrian Water’s site housing a Regional Sludge Treatment Centre and Effluent Treatment Works was a perfect candidate for an advanced anaerobic digestion installation.
A new £33M facility was commissioned at the end of 2009, the result of years of work that now mean the Bran Sands site can reduce its depdendence on externally generated electricity by up to 50%.
The new plant processes 40,000 dry solids of indigenous and imported sewage sludge per year, and has a generating capacity of up to 4.7MW.
The project has its origins in a 2005 review of the existing sludge strategy. In January 2006 MWH came on board as lead consultant to determine the feasibility of installing a thermal hydrolysis advanced digestion facility at Bran Sands.
MWH concluded in favour of such a project and produced a notional scheme for a maximum throughput of 40,000tds, which was accepted by Northumbrian Water.
A design and construct contract was deemed to be the most s itable procurement strategy, and Stockton based Aker Solutions − already part of a five year capital maintenance framework for the water company − was awarded a £28M contract to design, construct, install and commission the facility in June 2007.
The new plant required extensive integration with the existing assets, and Aker Solutions was also responsible for supplying specialist advanced digestion thermal hydrolysis equipment, and performance testing after commissioning.
The project has been revolutionary in the region, endowing Bran Sands − one of Northumbrian Water’s largest sites, treating the majority of sludge in the North East − with drying and digestion capabilities, and leading to an entirely new sludge management strategy for the Northumbrian Water region.
Further benefits include fewer carbon emissions, huge reductions in consumption of natural gas and imported electricity (90% and 50% respectively), significant savings on operating costs and qualification for Renewable Obligations Certificates due to the treatment centre’s production of sustainable energy.
The sludge cake that remains after the advanced anaerobic digestion process also has a very low odour impact and is suitable for use as an agricultural fertiliser, negating the need for disposal to landfill. Since its establishment in 1995 the Bran Sands facility has won four environmental awards.
Water special case study: The Bran Sands digestion facility