Dwr Cymru Welsh Water delivers AD plants early, and moves towards power self-sufficiancy in wastewater management

With the escalating cost of energy, one of the key emerging trends is the need for wastewater treatment works (WwTW) to become power self-sufficient. Dŵr Cymru Welsh Water (DCWW) has recognised this, and as part of the company’s move towards greater sustainability, it has invested in a £70 million programme of Advanced Digestion plants. DCWW’s sludge strategy for AMP5 moves away from energy intensive thermal drying and lime stabilization to Advanced Digestion, with a programme to process 75% of its sludge production across four key sludge treatment centres. It has already achieved power self-sufficient service at Eign (Hereford), and is in the final commissioning stages with two schemes in South Wales, at Cardiff and Afan, where continuous renewable generation of 6.5MW is anticipated.


The development and delivery of Advanced Digestion plants at both Cardiff and Afan WwTWs is at the core of this strategy. These sites alone will process 50,000tDS/y using Cambi Thermal Hydrolysis plants and new digesters. This sustainable approach to sludge treatment has been encouraged and supported by Welsh Assembly Government, Regulators, local planning departments and local communities.

Design, construction and delivery
Full construction and delivery of the Cardiff and Afan schemes was required by April 2011 to maximise the Renewables Obligation Certificate (ROC) benefits, and minimise costs to customers. Imtech Process was selected for the delivery of the process and M&E engineering work, working collaboratively with Morgan Sindall, the civil design and construction partner. A full technical and commercial assessment of available technologies was undertaken with DCWW. The most economic solution for these applications was Cambi Thermal Hydrolysis, due to the very high levels of secondary sludges. The Thermal Hydrolysis option was selected for Cardiff and Afan schemes for the following reasons:

• Best overall economic solution relative to DCWW objectives
• Proven technology experience at the required scale
• Proven delivery capacity and capability
• Process flexibility for various sludge types and quantities
• Proven treatment of SAS
• Process proven on sludge trials
• Higher VM destruction
• Reduced volumes of sludge to agriculture
• Good operational integration with the existing plants
An integrated design team worked closely with key suppliers and operations teams on both the Cardiff and Afan projects,standardising design wherever possible. The project team was co-located on-site at the earliest opportunity. Detailed design activity schedules were developed, integrated with procurement activities and programmed to ensure timely delivery.
A challenging design and delivery programme was developed with the stretch target of completing both projects six months early. This was achieved through active management including a proactive approach to risk management developing risk mitigation plans wherever required and fully resourcing the project to allow effective acceleration of key technology packages during off-site manufacture. This included factory construction, pre-assembly and testing of both Cambi plants before disassembly and transport to site, allowing mechanical installation to be completed within one week of delivery. The key technology suppliers were incentivised to achieve the accelerated project programme with a focus on right first time, to meet the continuous challenges of best practice, time, cost and risk management, with the primary focus on safe delivery

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