Advances in Water Treatment and Enviromental Management

DEVELOPMENT OF AERATED FILTER PACKAGE PLANT 77Table 1Process Volumetric Loading Ratesfor 90% NitrificationNote:1. Volumetric loading rate (VLR) kgBOD 5 /m 3 media.d2. Food to microorganism ratio (F:M) 0.12Mixed liquor solids (MISS) 3500 mg/13. F:M 0.1, MLSS 3500 mg/14. F:M 0.05, MLSS 3500 mg/15. Dependent on total nitrogen VLRInitial work was carried out on a pilot plant at Thames Water’s Ash Valeresearch facility. The objective of the study was to obtain information onthe performance of an aerated flooded filter with separate high rate solidsremoval stage. Using the process information gained from the pilot plant afull scale aerated filter package plant was designed and installed at CheshamSewage Treatment works.2. PLANTA schematic of the aerated filter pilot plant is shown in Fig.1. The plant isbased on a steel container housing 4 lm x lm x 4m high filter cells with anintegral 4m x 1m x 3m high washwater reservoir. Inlet and outlet connectionsare provided to allow each filter to be operated independently, in parallel orseries, as either aerated treatment units or as an upflow or downflow polishingfilter. Process air was supplied from a coarse bubble aeration grid positionedon the false floor above the plenum chamber of each treatment filter.Washwater was supplied through 4 separate submersible pumps mountedin the washwater reservoir and connected directly to the washwater inlet ofeach plenum chamber. The backwash air scour was supplied by a singleblower mounted within the control section of the container. Backwash liquorswere removed from the top of each filter by submersible pumps and returnedto the main works inlet. Valves were electrically actuated by a computerised