The intermediate thermal hydrolysis process: results from pilot testing and techno-economic assessment E. Rus a, *, N. Mills a , A. Shana b , A. Perrault a , P. Fountain b , R. B. Thorpe c , S. Ouki c and P. J. Nilsen d a Wastewater Innovation Department, Thames Water Utilities Limited, Reading, UK b Optimisation Team, Thames Water Utilities Limited, Reading, UK c Department of Civil and Environmental Engineering, Surrey University, Surrey, UK d Research & Development Department, CAMBI, As, Norway *Corresponding author. E-mail: ester.rusperez@thameswater.co.uk Abstract 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 hydroly- sis 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 con- siderations 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 m 3 /TDS. Fur- thermore, 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 exper- iments 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. Key words: anaerobic digestion, biogas, intermediate THP, optimisation, renewable energy INTRODUCTION Anaerobic digestion (AD) has been around for over 100 years and is currently the most widely used method of sludge treatment (Appels et al. 2008). It achieves the required pathogen kill to allow for sludge to be recycled to land (Mills 2015). Additionally, it has the added benefit of reducing the dry mass of sludge for disposal and producing a methane rich biogas that can be used as fuel in a com- bined heat power (CHP) plant (Gunaseelan 1997). Although AD is widespread and effective sludge treatment technique for the water industry, it has limitations (Mills 2015). For this reason, several pre-treatment technologies have been explored to enhance AD performance. The thermal hydrolysis process (THP) is the most widespread of these pro- cesses. It is a 20 year old technology with CAMBI ® being the first company to successfully market it to the water companies. This technology uses a combination of high pressure, heat and sudden de-press- urisation prior to AD or flash that hydrolyses organic matter, bursting cell walls and solubilising extra polymeric substances. This makes the organic substrate more readily available for bacteria to digest © IWA Publishing 2017 Water Practice & Technology Vol 12 No 2 406 doi: 10.2166/wpt.2017.031 Downloaded from https://iwaponline.com/wpt/article-pdf/12/2/406/380799/wpt0120406.pdf by guest on 07 June 2020