The Effects of Thermal Hydrolysis, Hydraulic Retention Time and Ammonia Concentration on Digestion Rates and Dewatering Across Digestion Sites in Thames Water UK

Panter, K., Fountain, P.

WEF/IWA Residuals and Biosolids Conference, 2019

Abstract

Thames Water owns and operates 8 thermal hydrolysis sludge centers and is planning more. It has operational and R&D experience of most of the ways of implementing thermal hydrolysis process (THP). This paper focusses on the observed differences in biogas yield (m³/ton dry solids) of digesters that receive THP sludge and particularly the effect of ammonia. It is proposed that biogas yields of over 500m³/tds (equivalent to 70% VSR) are possible in digestion projects where sufficient digester volume exists for lower loaded lower DS% feed. Hydraulic retention time (HRT) is generally not the limiting constraint and counter-intuitively it may be
better to aim for shorter retention time digestion with lower levels if ammonia inhibition. The work is from two full scale projects and further lab work is proposed to back up the findings.
When deciding the sizing and implementation of THP on digesters that are currently conventionally loaded the designer has some flexibility depending on desired DS% of Cake, need for Class A, need for more digestion capacity and biogas yield requirement that can lead to reduced capital and operating costs.

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