Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | APRIL 2015 | 7 Comment F or many in the UK, the idea of a severe drought can seem a distant prospect – especially as we enter the month of April which is synonymous with showers. However, anybody who witnessed the UK floods in the winter of 2013/14 can be in no doubt that the ef- fects of climate change are already with us; and as our islands gear up for more extreme weather in the future, a lack of water is just as likely to be our problem as an excess of it. With a growing population and limit- ed storage space available for reservoirs, the south of England is the country's most water-stressed region; and water companies there have been highly aware of the need to meet the supply-demand imbalance in their plans, both in this Preparing for a non-rainy day AMP period and in the longer term. Taking more and more water from the environment is not sustainable, so there are only really two approaches to take: either you need to find clever ways of storing our most precious resource, or induce customers to use less of it. This issue of WWT takes a close look at two very different projects which highlight examples of these approaches in action. Thames Water's operational trial to implement Aquifer Storage and Recovery (ASR) in the Lower Greensand aquifer in Kent is a fascinating way of storing clean water away for a non-rainy day. The Thames team are using a series of boreholes to pump clean water 250m below the surface where it can be stored in a 'bubble' in the porous rock. Not only can this method store a huge amount of H2O to protect us in a drought situation, but the water needs minimal disinfec- tion when it emerges, ensuring the most sustainable use of resources. (read more on p15). On the other side of the coin is de- mand management, and Affinity Water has been leading the way on initiatives to ensure customers use less water. Its 'Zoo in the Loo' project, which saw a 30% reduction in water use at a leisure James brockett eDItor JamesBrockett@fav-house.com Twitter: @wwtmag centre through the use of awareness posters, is remarkable evidence of what can be achieved by relatively simple measures to bring about behavioural change. It's a small example of what Affinity is doing now on a much larger scale through its Water Saving Pro- gramme. Not content with metering hundreds of thousands of properties in 2015-20, the supply company is planning around 100,000 home visits in the same period to give customers hands-on advice and devices to boost their water efficiency. Affinity believes that small, subtle changes implemented on a large scale can make a huge difference and help them fill the supply-demand gap. The two industry-leading projects are very different in character, but they do have one thing in common: they are both shortlisted in the same category (Water Resource Management Initia- tive of the Year) in the Water Industry Achievement Awards, which will be handed out on April 21. It only goes to show the high standard of award entries and the difficult choices the judges need to make. Most important is that both approaches could be laying the ground- work for protecting us from painful water shortages in the future. Industry view sponsored by michael Froom business Development Director Veolia Water technologies Compliance with the Water Framework Directive means that phosphorus levels in catchments are going to have to be reduced. At the recent Aqua Enviro conference Phosphorus Removal from Catchments: Technology or Source Control? in Nottingham, there was a good deal of debate about the relative merits of catchment-based solutions versus end of pipe treatment. Certainly some catchment-based solutions have shown some success, but results are not immediate and may take three years or more before any benefit is realised. Also there is a question mark over whether they will be as effective where they are implemented on a wider scale. Future-proofing P Removal In reality, catchment-based approaches will be part of the overall solution but 'end of pipe' solutions will always be required to guarantee meeting standards, and the expectation is that we will see phosphorus consents tightening in AMP7 – some areas will see standards as low as 0.1mg/l P. This means that several hundred sewage works across the UK including small, unmanned works in remote areas will need to retrofit phosphorus removal, and a lot of larger works will need to improve phosphorus residuals. Biological nutrient removal alone will not hit low enough phosphorus concentrations so, inevitably, they will have to rely on chemical precipitation using Al or Fe based coagulants. Even with chemical precipitation, meeting a 0.1mg/l consent will be a challenge because many of the common solid-liquid separation technologies are just not up to the job. That, of course, is all in the future. Or is it? Water companies are about to implement phosphorus removal technologies for AMP6, but are they just a short term fix or have they really been thought through in the context of TOTEX, which surely requires consideration of longer term future-proofing? Veolia has been running pilot trials on tertiary treatment combining coagulation, polymer enhanced flocculation and filtration at three different municipal wastewater treatment plants with similar secondary effluent water quality. In the tests, alum was dosed at a mol ratio about 5-7 Al3+:P and polyelectrolyte at 0.07-0.1 mg/ mg SS, followed by filtration using Veolia's well proven Hydrotech® Discfilter, which is already used as tertiary filtration by a number of UK water companies. This coagulant dose is in the same range as is used for technologies like deep- bed sand filtration, ultrafiltration or ACTIFLO®. The results showed that the combination of coagulant and polymer consistently achieved phosphorus residuals below 0.1 mg/l – significantly better than current tertiary treatment technologies.

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