The intermediate thermal hydrolysis process: results from pilot testing and techno-economic assessment

Thermal hydrolysis has proven to be an efficient pre-treatment process for sludge before anaerobic digestion (AD), by thermally enhancing organic matter hydrolysis. Recent research has shown that a new configuration with the existing technology can further enhance the efficiency of the system. The intermediate thermal hydrolysis process (ITHP) has been explored and tested in the Sludge and Energy Innovation Centre pilot plant located at Basingstoke sewage treatment works for a period of 15 months. The pilot facility has allowed operational considerations to be explored and understood to inform the design and construction of full scale. ITHP results showed a volatile solids destruction of 64% and an average overall specific gas production of 503 m³/TDS. Furthermore, techno-economic analysis was used to compare conventional thermal hydrolysis process (THP) with surplus activated sludge (SAS) only THP and ITHP. Data captured from operational sites, laboratory scale experiments and the large scale ITHP pilot plant, was used in the model. The results showed that ITHP offers an excellent solution for energy recovery having the best economic return, but overall the largest CapEx. SAS only THP is the cheapest to build but does not perform as well as conventional THP and ITHP. Conventional THP remains an excellent solution when space and AD volume is constrained.