Enhanced rapid gravity filtration and dissolved air flotation for pre-treatment of river Thames reservoir water

Thames Water treats approximately 2800MI/d of water originating mainly from the lowland rivers Thames and Lee for supply to over 7.3million customers, principally in the cities of London and Oxford. This paper reviews aspects of Thames Water's research, design and operating experiences of treating algal rich reservoir stored lowland water. Areas covered include experiences of optimising reservoir management, uprating and upgrading of rapid gravity filtration (RCF), standard co-current dissolved air flotation (DAF) and countercurrent dissolved air flotation/filtration (COCO-DAFF(R)) to counter operational problems caused by seasonal blooms of filter blocking algae such as Melosira spp., Aphanizomenon spp. and Anabaena spp. A major programme of uprating and modernisation (inclusion of Advanced Water Treatment: GAC and ozone) of the major works is in progress which, together with the Thames Tunnel Ring Main, will meet London's water supply needs into the 21st Century. (C) 1998 IAWQ. Published by Elsevier Science Ltd.