WET News

10 WET NEWS OCTOBER 2014 More than 800 Phragmifiltre systems treating raw sewage from 20 to 5,000 population equiva- lents in France Severn Trent goes natural at Hulland Ward • For the first time in the UK a leading water company has commis- sioned the installation of a constructed wet- land as a full primary treatment system at a sewage works. Dean Stiles reports. TECHKNOW • Phragmifiltre is a vertical flow constructed wetland that has been used as a primary treatment system • Two-stage design with rotating rest periods • The beds are up and running in eight to 12 weeks, depending on the weather NEED TO KNOW 1 Installing reed beds working within an existing operation treatment works 2 Conventional sewage treatment works require weekly operator visits, while Phragmifiltre sites require monthly visits 3 Integrated sludge treatment, therefore no tankering and associated access features required 4 The Phragmifiltre treatment has low to zero energy consumption 5 Integration into the landscape and no nuisance such as odours or noise. H ulland Ward Sewage Treatment Works (STW) in Derbyshire currently treats wastewater from a popu- lation of just under 900. Severn Trent Water has started work at the treatment works to replace a 50-year old conventional, bio- logical filter works with a pri- mary treatment system. Severn Trent Water is work- ing in partnership with reed bed specialist ARM and construction firm MWH Treatment to install Phragmifiltres. Phragmifiltre, brought to the UK by ARM through its French partner EpurNature, is a vertical flow constructed wetland that has been successfully used as a primary treatment system throughout rural communities in France since the 1990s. Reed bed wastewater treat- ment systems are now widely being used worldwide for the full treatment of sewage through the application of the Phragmi- filtre system. Treatment wetlands have tra- ditionally been used as a ter- tiary treatment, 'final polish', solution, secondary treat- ment, and nitrification. Phrag- mifiltre wetlands can provide treatment to raw unsettled sewage. The system comprises verti- cal flow constructed wetlands for the full treatment of sew- age and has been successfully operating in France through Epur Nature and Société d'Ingénierie Nature & Tech- nique. There are more than 800 PROJECT SPECS • Replace a 50-year old conventional, biological filter works with a primary treatment system • Install wetland as the full primary treatment system at the works • Demolish an old primary tank and part of the old inlet to complete the third reed bed THE VERDICT • A major change in thinking towards a natural and sustainable alternative for sewage treatment in the UK. • Cost-effective and sustainable solution ONSITE PRIMARY TREATMENT Phragmifiltre systems treating raw sewage from 20 to 5,000 population equivalents. 'Sticking plaster' The systems are typically designed to have two stages. The first stage filters and dewa- ters the solids in the raw waste- water on the surface of the bed. The filtrate passes down through the reed bed which acts as a typical batch flow vertical flow reed bed, reducing BOD primar- ily but also undertaking nitrifi- cation of ammonia. The second stage vertical flow beds provide additional BOD reduction and complete nitrification of ammonia prior to discharge. Wastewater is fed to each bed in rotation thereby allowing all the beds to have a rest period. The use, where pos- sible, of siphon technology for dosing both stages minimises, or even eliminates, power requirements. In the past, the UK sewage treatment industry has tended to use constructed wetlands at the back-end of the works as a "sticking plaster" solution for upstream process deterioration. The adoption of Phragmifiltre by Severn Trent is a major step- change in thinking and indi- cates recognition of the totex benefits. Conventional sewage treat- ment works generate sludges that have to be taken from small rural works to larger sewage treatment works for treatment. Phragmifiltre stores and

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