Fobney Water Treatment Works

Veolia Water Technologies provided the process design, construction, installation, testing and commissioning of 2 Actiflo® High Rate Clarifiers. The project included the sand storage, transfer and recovery system, polymer make up and dosing system, coagulation and pH correction system, MCC and software for the process. The purpose of the project is to increase the treatment capacity of the works while reducing the turbidity loading on the primary filtration stream.

Actiflo® is a very compact process that utilises microsand as a seed for floc formation. The microsand provides surface area that enhances flocculation and also acts as a ballast or weight. The resulting microsand ballasted floc display unique settling characteristics, which allow for clarifier designs with high overflow rates and short retention times. These designs result in system footprints that are between 5 times smaller than classic lamella clarifier or dissolved air flotation and up to 20 times smaller than conventional clarification systems of similar capacity, with an ability to start up from a “standby” mode of operation to a steady state operating mode within minutes.

In order to provide confidence to the potential Client, Veolia Water Technologies installed and operated a total of 16 weeks of pilot plant trials in 2004 and 2005 at the sites of Fobney and Hornsey WTW, treating up to 100 m3/hr.

The pilot plant provided data for Actiflo® performance and subsequent sand filtration. Based on these results Thames Water recognised the ability of Actiflo to cope effectively with the flashy water characteristics of the river Kennet.