Living-Filter: An In-Reservoir Biofiltration System For Phytoplankton Reduction At The Abstraction Point

The Living-Filter (L-F), a hydroponic bed of floating-reeds, was designed by Thames Water and AquaticEngineering and installed in Farmoor II reservoir, Oxfordshire, in July 2012. The structure (1m H x 21m W x 10m L) supports plants of Phragmites australis, Phalaris arundinacea and Carex acutiformis, with a combined system of curtains and baffles. The aim is to reduce phytoplankton loading onto the water treatment works at the abstraction point, consequently reducing chemical dosage and minimizing costs. Weekly surveys were carried out from July - October 2013 to assess the physical, chemical and biological changes likely to be introduced by the L-F. Physicochemical and biological variables were measured at 16 sampling sites. Results show differences between sites in the L-F with a significant accumulation in chlorophyll a (Chla) (as a surrogate of phytoplankton biomass) levels in the L-F platform, although significant Chla reduction has yet to be seen at the abstraction point.