Severn Trent Water, the UK’s second largest water utility and serving over 8 million customers, is facing an increasing need for energy. We need to ensure supply resilience as a consequence of climate change and ever tightening quality standards. Maximizing renewable energy generation from sewage, water and our landholdings is an essential part of our strategy to minimise green house gas (GHG) emissions.
In 2009/10 we generated 183 GWh of renewable energy from sewage gas combined heat and power plants (CHP) and hydro generation which satisfied over 20% of our electricity demand and saved 99,000 tCO2e. We have an ambitious target to generate 30% of our consumption by 2014/15 by investing in other renewable energy technologies.
In order to reach this target Severn Trent began to look at using some of our land to grow crops for crop digestion to generate energy, and last year we completed the construction of UK’s first commercial scale dedicated crop digestion plant which helps to power Nottingham’s main sewage treatment works.
Work on this project started in 2007 when Severn Trent became aware of the development of energy crop anaerobic digestion (AD) plants across mainland Europe. The company commissioned its own feasibility studies to assess the potential of this technology for deployment at its own farms.
In 2008 the outline design of the plant was completed with assistance being provided by German process specialists Schmack Biogas GmbH. Schmack were selected as the preferred process supplier, having already designed and constructed over 230 biogas plants worldwide, and had successfully scaled up this technology in a 10MW gas plant constructed at the company’s headquarters in Schwandorf, Bavaria.
The construction of the 2MWe energy crop AD was completed by May 2010, on programme with the plant ready for the commencement of the commissioning phase. The multiple digestion tanks were filled with around 6000 tonnes of imported farm yard manure and the temperatures within the tanks were gradually raised to the 40 deg C digestion temperature. The biology of the plant was closely monitored during this process to ensure that a healthy biomass was produced.
After three years of planning and construction, the plant achieved its full 2MWe production in October 2010, two months ahead of programme.
The adjacent sewage works which serves the city of Nottingham, previously imported around 1MW of electricity from the national grid, but now that the energy plant is operational, all the sewage works electricity demand is satisfied and a surplus of around 1MW is being exported to the grid. This means that the sewage works has become a net exporter of electricity.
Severn Trent is the largest producer of electricity from sewage gas in the UK which is generated at its 36
New Energy in Severn Trent
Stoke Bardolph Energy Crop Anaerobic Digestion (AD) Plant By Martin Dent, renewable energy development manager |140| ENVIRONMENT INDUSTRY MAGAZINE
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