Advanced Digestion in the UK – Technology Developments and Options for Optimisation of Sludge Assets

The potential for improved pathogen reduction; better process stability and increased gas production has led to considerable interest in advanced digestion both within the UK and the US. To date 16 full-scale advanced digestion sites have been commissioned within the UK including pre pasteurisation, thermal hydrolysis, two-stage acid digestion and thermophilic aerobic pre treatment. This paper examines the current state of the art within the UK and discusses why advanced digestion is emerging as the process of choice.Two case studies are presented demonstrating how the two ideal reactor design configurations, completely mixed and plug flow, have been implemented at full scale. The ability of the two processes to convert the complex organic materials in sewage to volatile acids is reported and the potential to produce Class B and Class A biosolids discussed.Finally the potential of advanced digestion to increase current digester loading substantially is discussed along with the potential benefits for increased throughput and energy generation using existing assets.