Water & Wastewater Treatment Magazine
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www.wwtonline.co.uk | WWT | OCTOBER 2017 | 23 The technology provided a real learning curve Graham murphy DiRECTOR Of EnginEERing, SOuTh WEST WaTER "This technology is a first for the UK, so there's an awful lot of interest from the supply chain and the water industry across the UK. I think it's a site that we will be proud of for many years. Ceramic mem- branes have got an almost infinite asset life – they've been operating in Japan without replacement for in excess of 20 years - which is quite unusual relative to other processes. We are building something here that will be very sustainable and should require minimum maintenance in the future. "We've worked really hard to develop a good collaborative, co-operative relationship between all the project partners. With technology that is new to us, it's been a steep learning curve, and I'm really pleased with the relationship and the effectiveness of the arrangements. Beyond the key partners, there are a number of other smaller suppliers in the region who've all contributed, coming together to make this a success. "We're delivering this project for around 33% less, in terms of capital cost, than the industry norm. To achieve that, it's required the best people with the right design, getting people to work together closely and sticking closely to the programme." • ENGINEER'S VIEW: • TREATMENT PROCESS: 5 STAGES The treatment process being put in at South West Water's new May- flower Treatment works is less chemical and energy intensive than traditional surface water treatment methods, requires a smaller physi- cal footprint, and is also around five times faster. Developed by Dutch company PWN Technologies, it consists of five stages: 1 Suspended Ion Exchange. A•er screening, ion exchange resin is added to the water and mixed with air as the water flows through a number of tanks. Natural organic matter and nutrients like nitrates transfer from the water to the resin. A•er contacting time the resin is removed, regenerated with a salty solution and put back into the process. 2 Inline Coagulation. Coagulant chemicals are injected into the water, in the same way as in conventional treatment; however, because of the ion exchange and membrane stages either side, much less coagulant is required and this stage of the process takes minutes rather than hours. 3 Ceramic Membrane Filtration. The water is filtered by Cera- Mac, a system containing 900 ceramic membranes contained in ten vessels. The membranes have tiny pores that are less than 1/10,000th of a millimetre in diameter, and catch almost all particles including bacteria and harmful organisms such as crypto- sporidium. 4 Granular Activated Carbon (GAC) Filtration. The water then passes through deep beds of granular activated carbon, a more familiar treatment process to most in the UK. The grains of carbon each have a huge surface area which traps any organic molecules le• over from the earlier stages. 5 Ultraviolet (UV) disinfection. The water is subjected to ultra- violet light, a modern form of disinfection. With the powerful early stages of the treatment process, reduced disinfection is required. A small amount of chlorine is then added to protect the water in the pipe network, and lime and CO2 are used to adjust the pH and hardness of the water to make its taste more appealing. One of ten ceramic membrane vessels at the site Visitors hear about the operation of the membranes at the site at Roborough, north of Plymouth