Ever since it was opened in 1894 to treat sewage from Manchester’s rapidly growing population, Davyhulme Wastewater Treatment Works has been at the forefront of innovation in the water industry.
In 1914, Edward Ardern and William T Lockett invented the ground-breaking activated sludge process at the facility’s on-site laboratory – a technique that was quickly adopted worldwide.
What started out as “sewage farm in the countryside” is now flanked by roads, houses and shopping centres, and has grown to become one of the biggest wastewater treatment works in the UK, serving 1.3 million people across Greater Manchester.
Anticipating a fresh population boom in the city over the coming decades and faced with tightening restrictions on levels of ammonia in outflows to the nearby Manchester Ship Canal, in 2015 United Utilities began a massive overhaul of the ageing facility.
Working in partnership with Laing O’Rourke, the company designed and built an activated sludge plant (ASP) consisting of six primary settlement tanks, ten aeration lanes and ten final settlement tanks. It also installed inlet works and a sludge thickening plant, as well as refurbishing existing assets to improve their efficiency.
Four-dimensional modelling was used to combine the civil, mechanical, electrical, instrumentation and supplier plans into a single reference point.
Most of the excavations were reused to minimise outside movements. The new entrance was constructed first, to shift traffic away from the existing entrance and an adjacent housing estate, and tower cranes were installed on rails along the aeration lanes to reduce on-site congestion.
To cut costs, speed up progress and enhance safety, the main concrete structures of the activated settlement plant were all precast off-site. Mechanical equipment such as pipework, steelwork, walkways and platforms was similarly prefabricated in modular form. United Utilities says this approach to construction saved 6,800 on-site working days.
The £187 million project was delivered on budget and ahead of schedule by a team of 400 people, with some leftover cash allowing for further investments in landscaping and odour management to improve the views and smells for nearby residents.
The new ASP began accepting flows in September 2017 – four months before the April 2018 deadline – while the sludge thickening plant was completed 12 months early in May 2017.
To ensure the economic benefits of the investment flowed back to the surrounding community, £50 million was spent with local businesses, creating 26 new construction jobs and supporting 35 apprenticeships.
United Utilities says the newly installed assets are now taking 60 per cent of the works’ flow through the facility, bringing about “significant power and chemical consumption savings”.
The new sludge thickening plant has enabled the facility to produce greater volumes of biogas through anaerobic digestion. This gas is either cleaned and injected into the local gas network or used to fuel the facility’s combined heat and power engines.
Health and safety performance
The project set three core principles:
1. “People are the solution, not the problem” – empowering the workforce to make the right decisions rather than just following instructions. Supported by:
• induction changed from a 3-hour presentation to a 30-minute discussion with visual wall aids around the site hazards. The visual aids changed throughout the project to align with current activities;
• occupational health screenings;
• mental health awareness sessions;
• healthy food for free.
2. “Health and safety is the presence of positives, not the absence of negatives” – equal priority to identifying and communicating excellence and lessons learnt. Supported by:
• “collective insight” sessions reviewing successful operations sharing what went well;
• monthly heroes were identified by the workforce.
3. “Health and safety is an ethical responsibility, not a bureaucratic activity” – streamlining processes and procedures. Supported by:
• “fatal and severe risk” reviews, focusing on high consequence risks;
• “visual task sheets” using pictures to communicate complicated tasks;
• “planned vs actual” sessions empowered the workforce to modify methods through engagement and trust.
All the above contributed to a positive health and safety culture, more than 1,500,000 hours without a RIDDOR (Reporting of Injuries, Diseases and Dangerous Occurrences Regulations) incident.
DMP delivered on its promise to provide a robust, innovative treatment process, protecting the environment for years to come. The new processes passed tests and remains fully environmentally compliant. Data shows the new assets are delivering the required benefits along with further operational savings.
Several of the initiatives which contributed to the success of DMP are embedded into both United Utilities and Laing O’Rourke.
• Full BIM (building information modelling) design reviews. This has been developed further with the use of Virtual Reality at Blackburn WwTW.
• Implementing design for manufacture and assembly (DFMA), not just only pre-cast concrete but embedding DFMA principles fully across all civil, mechanical and electrical installations.
• Investing in the community and local businesses and the benefits of understanding local customer concerns are key to the success of future schemes.
What the judges said…
This project impressed the judges with its potential learnings for the rest of the industry.
The judges were a panel independent from the sponsors
Richard Ratcliff, engineering delivery director, United Utilities
“Over the past five years the Davyhulme modernisation project has been our flagship investment scheme at our biggest wastewater site in the UU region, and its delivery has been absolutely world class.
“From the latest information management and visualisation technology to the way we’ve embraced a design for manufacturer and assembly approach and engaged with the local community, every aspect of this project has been a model for getting things right first time.
“The whole project team should be incredibly proud of what we’ve achieved and winning this award is the icing on the cake.”