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

Abstract

Thames Water treats approximately 2800Ml/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 (RGF), standard co-current dissolved air flotation (DAF) and counter-current dissolved air flotation/filtration (COCO-DAFF®) 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.

Effect of Ozone on the Formation and Breakup of Flocs in Raw Waters with High Algae Content

“…The autumn bloom is predominantly composed of filter-blocking algae, such as Melosira sp. [17,18] The basic raw water quality characteristics such as turbidity, pH, temperature, particulate organic carbon (POC) and Melosira sp count are summarized in Table 1.…”

Flotation of blue-green algae using methylated egg ovalbumin

“…Several attempts for removal of blue-green algae have been reported [1][2][3][4]. Among them, dissolved air flotation (DAF) method [5][6][7][8][9] has been a promising technique for more effective treatment of blue-green algae removal.…”

Analysis of the Impacts of Flocculation Modes and Coagulant Dose on Dissolved Air Flotation

“…The theoretical value of floc strength can be calculated by Eq. (2): where, d (1) was the average size of the flocs formed by flocculating reaction, and d (2) was that of the smaller broken flocs generated under shear-induced breakage. The larger SF value is, the greater floc strength is.…”

“…Some traditional technologies such as coagulation/flocculation /sedimentation can not effectively remove algae. Since algae are low-density particles and algal flocs generated by coagulation are very light, dissolved air flotation (DAF) has proved to be more advantageous than sedimentation for treating algal-rich water [1][2][3][4].…”