Thames Water owns and operates eight 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 520 m3/tds (equivalent to 70% VSR) are possible. 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 of ammonia inhibition. The work is from two full scale projects and further lab work is proposed to back up the findings.
The paper reviews previously published results from Long Reach STW and then focuses on the start up and conversion from conventional digestion to post-THP digestion during start up of THP at Basingstoke STW during the spring of 2018. Biogas rates were measure before and after acclimation to high ammonia digestion. Bacterial populations were also studied.
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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