Intermediate Thermal Hydrolysis at a large WWTP First Results

Rus, E., Ringoot, D., Kościukiewicz, J.

Joint Conference: Residuals & Biosolids and Innovations in Treatment Technology, 2025

Introduction

Thermal Hydrolysis Process (THP) is a well established technology for efficient pre-treatment of Wastewater Treatment Plant (WWTP) sludges prior to Anaerobic  (AD) (Newman et al., 2011; Williams et al., 2018; and Nicholson et al., 2020). THP carries out hydrolysis, the rate limiting step in AD, prior to the digester (Shana et al., 2013).
In the last decade, several configurations of AD with THP have been trialled (Shana et al., 2012; Shana et al., 2013; and Higgins et al.,2020). The Intermediate Thermal Hydrolysis process (ITHP) is one of those configurations. It consists of a first stage AD followed by THP and a second stage advanced AD. This configuration has proven to be very successful for optimising biogas yields, enhancing Volatile Solids Reduction (VSR), increasing dewaterability and reducing overall carbon emissions (Shana et al., 2013; Mills et al., 2011; and Rus et al., 2017). An ITHP arrangement allows for an initial conventional digestion which reduces the required THP capacity with about one third. Furthermore, the second stage advanced AD can handle a high Organic Loading Rate (OLR), increasing the throughput of the system.
Rus et al., (2017) carried out a one-year ITHP trial at a medium sized pilot plant with a total digester volume of 40m3. Results showed that ITHP increased biogas yield and VSR by up to 15% compared to full THP followed by advanced AD. Furthermore, ITHP helped to further increase the dryness of the final cake with 18%. Both the increase in biogas yield and decreased THP capacity requirement can help to improve the overall energy balance.
The successful lab and pilot tests motivated the full-scale application of the ITHP process at one of the large wastewater treatment plants in Europe.

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