‘Continuous’ thermal hydrolysis AD plant to be built for UK water utility

Water treatment technology firm Doosan Enpure has secured a competitively tendered ‘Design and Build’ contract, valued in excess of £20 million, with Severn Trent Water for the development of an Advanced Anaerobic Digestion (AAD) Plant at Strongford Sewage Treatment Works (STW), near Stoke-on-Trent.

Strongford STW is a major treatment works serving Newcastle-under-Lyme and Stoke-on-Trent with a population equivalent of c350,000. The scheme is of strategic importance to Severn Trent Water as it demonstrates their commitment to reduce their carbon footprint by 10% through AMP6, and to produce an enhanced product for 25% of all of their biosolids.

Doosan will be working collaboratively with its partners, North Midland Construction (NMC Nomenca), and Dutch technology provider Sustec BV who will be supplying their Continuous Thermal Hydrolysis Plant (cTHP) – Turbotec® – which will be the first of its kind in the United Kingdom.

The key objectives for the project are to maximise biogas production, reduce sludge volumes, produce an Enhanced digestate, whilst achieving the lowest TOTEX cost. Doosan says that during the tender evaluation process it actively demonstrated how it would achieve these objectives, using its extensive knowledge and expertise in Advanced Anaerobic Digestion and utilising the strategic partnerships it has established to help execute this significant scheme, especially in response to OFWAT’s Water 2020 initiative to open up the sludge market.

As a regional Sludge Treatment Centre, the new AAD plant will need to handle indigenous and imported thickened raw sludge (Primary and Secondary), imported raw sludge cake and imported industrial trade effluent. The plant will be capable of processing 80 tonne dry solids per day (tds/d) on average, with a peak of 94 tds/d, and producing a thermally hydrolysed sludge with a target Dry Solids content of 10% w/w. In order to achieve such an output, the scope of works will include imported screened sludge cake reception, indigenous sludge storage, pre-cTHP screening & dewatering, Sustec Turbotec® cTHP, Doosan Puriser® pasteuriation, upgrading of existing mesophilic anaerobic digesters, liquors treatment, steam generation, upgraded biogas storage and a new waste gas flare. The enhanced biogas generated will be utilised by the recently installed Gas-to-Grid plant, the existing CHP installation, and the new steam generation system. The Enhanced digestate will be used by the local land bank as a sustainable Bio-fertiliser.

Avtar Jirh, Chief Executive Officer of Doosan Enpure, said “From the outset of the procurement process, Severn Trent Water indicated that they were willing to consider a range of thermal hydrolysis technologies now available to the marketplace, so I’m very proud that Doosan were able to offer an alternative option, utilising our international Technology Provider relationships along with our in-house Process Engineering and EPC capabilities. We are excited to be working with Sustec BV to deliver the first continuous Thermal Hydrolysis Plant in England and in addition we look forward to further cementing our relationship with North Midland Construction who are already our partner in the DNM Alliance, working together with Severn Trent on the Birmingham Resilience Project”.

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