WET News

8 WET NEWS JUNE 2017 Investing in a new generation of water treatment • Mayflower WTW is South West Water's flagship project for AMP6, and will be kitted with cutting-edge treatment processes. S outh West Water's (SWW) new £60M state-of-the-art water treatment works in Devon is the company's flagship project in its 2015-2020 business plan. Mayflower Water Treatment Works will use cutting-edge treatment processes, designed and developed by leading Dutch water technology company PWN Technologies, and will serve around 250,000 customers in Plymouth and the surrounding area. It is being built at Roborough Down, and will replace Plymouth's outdated Crownhill WTW. The construction phase is scheduled to finish by the end of March 2018, with Mayflower WTW becoming operational in September 2018. Crownhill WTW will retire from service a few months later. The new works will be capable of producing up to 90Ml of drinking water every day, with an average of 55Ml a day. It will serve more than 6,000 businesses, including Her Majesty's Naval Base Devonport and Derriford Hospital. Constrained Crownhill WTW was built in the 1950s, long before automation, modern water quality standards and operational best practice. Since then, Plymouth has grown significantly and what was a rural works has been absorbed into a very busy city. The site is extremely constrained, which makes operation and access difficult as well as posing risks to site security, with limited room to expand or adapt the current treatment processes. Replacing Crownhill WTW has been a long-term part of SWW's strategic plans for developing the water supply network. There were three options: • Refurbish the existing works • Build a new works with traditional treatment. • Build a new works with innovative treatment. A business case was established for a new-build with an innovative water treatment process which will be the first time this technology has been used in the UK. The investment case was submitted in South West Water's Business Plan for the 2014 Price Review as an exceptional item. The regulator, Ofwat, accepted the case without challenge and commended the innovative approach to the project. The project is being undertaken by the South West Water Delivery Alliance H5O, which has worked with SWW since 2009. Global design and consultancy firm Arcadis is the main design contractor, in partnership with consulting engineer Pell Frischmann. Together they are responsible for all the design work outside of the key treatment process. Pilot plant Infrastructure group Balfour Beatty is the main construction contractor, in partnership with Interserve, with responsibility for the construction of all infrastructure, buildings and pipelines for the new water treatment works, and PWN Technologies is responsible for the design, installation and commissioning of the main water treatment process. Between June 2013 and June 2015, a prototype facility using suspended ion exchange (SIX), inline coagulation (ILCA) and ceramic membrane microfiltra- tion (CeraMac) was tested at Crownhill WTW using water from Burrator Reservoir, the River Tavy and River Tamar. The pilot plant confirmed that the new technology can success- fully treat SWW's raw water sources to produce exception- ally high quality drinking water while minimising the impact on the environment. The new process, which will mark a significant step away from chemical and energy intensive traditional technology, is around five times faster and more robust than traditional treatment processes. • A er screening, ion exchange resin is added to the water and mixed with air as the water and resin flows through a number of tanks. SIX can use a variety of resins in suspension to remove natural organic material. During this time (about 15-30 minutes), natural organic matter and nutrients such as nitrates transfer from the water to the resin • A er contacting time the resin is separated, regenerated with a salty solution and recycled back around the process • The water is then coagulated and filtered by CeraMac with around 900 ceramic membranes encased inside ten vessels. These ceramic membranes filter the water through tiny pores that are less than 1/10,000th of a millimetre. Filtering to this level removes almost all particles including bacteria and other harmful organisms including cryptosporidium • Next the water passes through deep beds of activated carbon where any more natural and man-made dissolved organic matter is removed. Each tiny grain of carbon contains a huge surface area on which organic molecules get trapped • The water is given a final disinfection with ultraviolet light. Prior to being stored on site and making the journey to customers the naturally low pH and hardness of the water is adjusted with lime and carbon dioxide, and a small residual dose of chlorine is added. The new process is very efficient and has a smaller footprint than conventional treatment technology. The ion exchange technology only consumes salt and the resin used can be recycled many times for several years. This reduces the amount of waste produced. The coagulation is essentially the same as in conventional treatment but because of the ion exchange and membrane much less coagulant is required and the overall time of these processes reduces from hours to minutes. This means the process is very compact and therefore reduces the amount of construction materials required. The membrane itself is very special and leads to an exceptionally high water quality. Because the pores are fixed within the ceramic material they are absolute, so no matter what the quality of the raw water, the filtered water is always safe. Ceramic membranes have outstanding features compared to polymeric The route that the pipeline will take. [All photos courtesy of South West Water] ONSITE WATEr TrEATMENT projEcT SpEcS • Build a new works with innovative treatment. An overview of the Crownhill site The pilot plant at Crownhill WTW

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