North American Case-Studies of Smaller Scale Thermal Hydrolysis

Barber, W.P.F.

Biosolids Conference, 2023

Introduction

Thermal hydrolysis, a pre-treatment typically installed prior to anaerobic digestion, continues to gain popularity around the world. Of the approximately 130+ facilities world-wide, Cambi, the market leader, has 84. Of these, two are in Australia, Oxley Creek in Queensland commissioned in 2007 and more recently St. Marys in Sydney which is being commissioned. Plant sizes range from approximately 10 to over 400 tonnes dry solids/d processed. Thermal hydrolysis involves the application of heat at approximately 165°C for 20 – 30 minutes. The benefits of the technology have been well documented and include – amongst others – improved performance of digestion and dewatering, reduced carbon footprint and sterilization of biosolids resulting in a high-quality product. However, a variety of challenges exist including: the need for energy; the production of refractory compounds with various influences of liquid processing, and elevated levels of nutrients in the digestate (because of improved digestion performance) which need to be treated at cost. Historically, facilities were typically large and, along with perceived complexity, this has led to the misconception that the technology is only suited to bigger plants. In fact, a closer look at the size of Cambi’s installed plants (Figure 1) reveals that three quarters of them are under 100 tonnes dry solids/d and almost half of all plants are smaller than 50 t DS/d.

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