Water & Wastewater Treatment

WWT November 2018

Water & Wastewater Treatment Magazine

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Page 13 of 39

14 | NOVEMBER 2018 | WWT | www.wwtonline.co.uk The Works: Drinking Water Treatment • CHEMICAL-FREE WATER TREATMENT O ne of the key advantages of chlorine is its ability to persist in treated water, protecting against disease as water passes through oen lengthy distribution networks. While alternative disinfection processes such as UV and ozone are well established, the absence of a residual effect means water passing through the distribution network may be prone to microbiological contamination before it reaches the customer's tap, potentially posing serious health risks. Despite this, countries such as the Netherlands, Germany, Denmark, Swit- zerland and Austria have been able to implement systems that operate without chlorine. The approach depends on using the best quality source water possible and maintaining the distribution network to sufficiently high standards; multiple steps are also used to ensure adequate water purification, such as sand filtra- tion, ozone, carbon treatment, membrane filtration and UV treatment. Should there be any issues with the process that lead to contamination, chlorine may need to be introduced as a temporary measure, and boil-water orders are used as a further backstop where necessary. The system appears to work for the Dutch, with better water quality and fewer water quality incidents than most developed countries. But while chlorine-free drinking water is gaining ground globally, the prevailing view has been that UK water companies lack the high-quality distribution network required to adopt the approach. Anglian Water is taking steps to under- Chlorine gas cannisters being used for water treatment stand what would need to change before the use of chemicals, including chlorine, could be reduced. As part of its Innova- tion Shop Window, the company has set itself seven long-term, aspirational goals, which include '100 per cent compliant drinking water and chemical-free water treatment'. Chlorine is one of the three most significant chemicals – in terms of cost and volume – used by Anglian Water, together with orthophosphoric acid for lead control, and the salt used as part of ion exchange processes to remove nitrate from groundwater sources. Anglian's long-term strategy around drinking water quality includes a focus on all three. With regard to chlorine, Anglian has begun work with the University of Sheffield to determine the viability of chemical-free water treatment, with a PhD researcher, Natalie Lamb, carrying out a study using water from the region on test rigs to understand the effect of reducing chemical use. As part of her stud- ies, Lamb has carried out a literature review to understand the specific circumstances that have led to other countries making the deci- sion to stop having a residual level of chlorine in their distribution systems. She has looked at water quality, the age and type of mains materials present in the distribution system, together with regulatory and societal factors in each country. The town of Vsetín in the Czech Republic soon plans to join the list of areas to switch off chlorine supplies, and Lamb paid a visit this summer to learn from the innovative pipe flushing programme taking place there in prepa- ration for the project. The next stage of Lamb's research will be to understand the biostability of mains water in the Shop Window area in Newmarket, and across the Anglian region, looking carefully at the interac- tion between orthophosphoric acid and chlorine. This work will involve experiments at the cutting-edge distribu- tion rig facilities at the University of Sheffield, together with pipe rigs at live water treatment works within the Shop Window. "We're a very long way off considering reducing the amount of chlorine we use within our water treatment works," Robin Price, head of water quality at Anglian Water, says. "But we know that gaining a further understanding of the characteris- tics of a water distribution network with the capability of maintaining safe, clean drinking water right through to every cus- tomer without the addition of chemicals is a worthwhile piece of work, and we know that such a network will bring us and our customers many other benefits in terms of reductions in leakage and interruptions to supply."

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