Abstract
The UK water industry has huge, but as yet under-developed, potential to generate sustainable energy from the main by-product created in the treatment of wastewater. Sewage sludge is an energy rich sustainable biomass resource with a similar calorific value to woodchip. Until recently, technologies and processes for further energy recovery have not been efficient or viable for large-scale use, but this research has shown that developments and innovations are now available and can realistically be brought into use. Using a combination of detailed techno-economic analysis and data from several large scale demonstration plants this research has shown that the renewable energy produced from sewage sludge in the UK could be significantly increased. A typical conventional AD site will achieve 15% electrical conversion efficiency; this can be improved to 20% with the Thermal Hydrolysis Process (THP). Second generation THP developed during the project could boost recovery to 23% with other benefits such as reduced support fuel requirements and sludge transport volumes. By combining THP, sustainable thermal drying and pyrolysis, gross conversion efficiencies of 34% to electricity are achievable. All of the scenarios developed by the project have been proven to environmentally & economically sustainable and have been demonstrated at a large scale as part of this project. A UK wide study in conjunction the Department of Energy & Climate Change showed that an economic deployment across the UK of second generation THP, followed by drying and pyrolysis, could generate to 2,216GWh or an additional 1,310GWh pa of renewable electricity from sewage sludge.