United Utilities is installing revolutionary wastewater treatment technology from Holland in four of its treatment plants in North West England over the next five years.

The company was the first in the UK to trial the aerobic granular sludge technology, known as Nereda. Early next year it will launch the new treatment process at Kendal wastewater treatment works in Cumbria, which will be the largest operational example of the Nereda technology in the UK. This will be closely followed by Nereda installations at three more treatment plants in Morecambe, Failsworth and Blackburn.

United Utilities is building the Nereda plant at its Blackburn wastewater treatment in conjunction with its construction partner LiMA. When complete, Blackburn will be Europe’s largest purpose-built Nereda process plant.

Kieran Brocklebank, United Utilities’ head of innovation, said: “We were the first in the UK to invest in a pilot plant for Nereda and we’ve been hard at work testing the process in a number of applications since then.

“Moving away from a conventional process over 100 years old is difficult so we took our time to test Nereda across a broad range of criteria. Nereda also fits well with our long term ambitions on Systems Thinking.”

What is Nereda?

The Nereda technology was developed by Delft University in the Netherlands and engineering consultancy Royal HaskoningDHV. It is a development of the conventional activated sludge process which was discovered in 1914 at Davyhulme wastewater treatment works in Manchester by two engineers, Edward Ardern and W.T. Lockett. Nereda offers a number of advantages over conventional activated sludge due to the nature of the granules. In a conventional activated sludge treatment process, flocs of sludge are suspended in water and take time to settle in the treated wastewater so a secondary settling tank is needed. Nereda granules are dense so settle much faster, and can do so in the same tank in which the treatment process takes place, leading to a significant reduction in the size of the plant footprint.

The compact nature of the granules also leads to the formation of different zones, aerobic, anoxic and anaerobic, which allow the simultaneous removal of organic pollutants from the wastewater, including ammonia, as well as biological phosphorus removal. The ability to remove phosphorus biologically, rather than chemically, is appealing to the UK water industry as not only does it reduce reliance on chemicals, it reduces health and safety risks as well as the amount of sludge produced. It also enables the recovery of phosphorus from the sludge to create a product which can have value as a fertiliser.

Research and development

United Utilities began reviewing the benefits of aerobic granular sludge in 2013 before initiating a research and development project. In 2014, members of the company’s engineering team travelled to Holland to carry out due diligence visits to a number of full scale operational plants, a central control room and to have detailed technical discussions at the supplier’s head office.

The company could see that the technology would help it meet a number of new discharge consent limits as well as upgrading some works that were still using old technology such as trickling filters.


The company conducted a structured assessment of the technology to see if it was technically viable, then for each individual project it investigated whether it was financially viable. The trials were also necessary to ensure the new technology could meet more stringent UK permit requirements for treated wastewater as the technology had at that stage only been used in other countries.

The first trials were conducted at Crewe wastewater treatment works and Davyhulme – 100 years on from the discovery there of the original activated sludge process. It allowed United Utilities to test the technology across a wide range of different parameters including the ability to form granules with conventional activated sludge and to test the process performance in challenging conditions. The robust evaluation process led to the company being able to technically approve the solution for use in its current five year investment programme, and award four construction contracts for Kendal, Morecambe, Failsworth and Blackburn wastewater treatment works.

Additionally, at Macclesfield wastewater treatment works, during 2016 and 2017, a trial was carried out under the Chemical Investigations Programme Phase 2 (CIP2) Innovation Fund to evaluate the potential of the technology to achieve low phosphorus permits and the outcome of the testing was shared with all UK water companies.

Putting it into practice

Kendal wastewater treatment works was identified as an ideal first site for Nereda. The Cumbrian works had suffered significant flood damage following the storms in December 2015. To repair the damage and upgrade the site, a programme of works began in March 2017 and will be complete in early 2019.

Alongside this work the Nereda technology is being installed due to a reduction in the ammonia permit at the site from 8mg/l to 5mg/l which could not be delivered using the existing assets. A low footprint solution was also sought due to space restrictions at Kendal. It is estimated that the technology will provide £1m capital expenditure savings compared to conventional solutions and operational efficiencies of £300,000 a year. United Utilities is also keen to see if the development of the process at Kendal may go a significant way towards meeting a tighter phosphorus requirement in the future without the need for further process units or chemical dosing.


At Blackburn wastewater treatment works, the installation of Nereda technology provides the lowest whole life cost solution through efficient energy usage and the biological removal of phosphorus significantly reduces chemical dosing costs. It’s part of a £100m infrastructure upgrade of the site, aimed at improving local watercourses.

Installing this technology is estimated to save around £7m of capital expenditure and provide £1.3m of operational expenditure savings a year, compared to a conventional solution. The plant will be fully operational in 2021.

In addition to Kendal and Blackburn, United Utilities is also currently delivering two upgrade projects at Morecambe and Failsworth wastewater treatment works, which will also use the Nereda technology.

Nereda will be installed at Morecambe as part of a £70m upgrade of the site aimed at improving local bathing waters and will be delivered by United Utilities’ construction partner C2V+. At Failsworth, the Nereda solution, being delivered by LiMA, also provides lowest whole life cost, future operational savings of £240,000 a year and will futureproof the site for phosphorus removal and product recovery.

Royal HaskoningDHV has collaborated with United Utilities’ construction partners, LiMA and C2V+ to ensure consistency across all four installations. The result is that innovation from C2V+ developed at Morecambe was incorporated into the Failsworth plant design by LiMA, and lessons from the LiMA team at Kendal were incorporated into the design for Blackburn.


To date, Nereda has saved United Utilities £15m of capital expenditure and will save £1.9m of operational expenditure a year. The company has long term ambitions on Systems Thinking, exploiting the advantages of more centralised control and automated decision making. The Nereda technology features an intelligent automated control system, the Nereda Controller, which allows United Utilities to accelerate these ambitions by taking full advantage of this novel technology when it completes commissioning at Kendal.

The learnings from Kendal are being applied to the other Nereda sites at Morecambe, Failsworth and Blackburn with a view to seeing how far United Utilities can push the model of greater centralisation. The company will then look beyond the Nereda plants to see how it can introduce the centralised model of monitoring and control to a greater proportion of its asset base.

United Utilities’ wastewater asset manager, Pippa Smith, said: “Using this technology means we can provide the optimum effluent quality with minimal energy/chemical inputs.

 “The new plants also provide a great opportunity for us to accelerate our ambitions for greater centralised monitoring and control.”