Design of Multistory Settling Tanks in Osaka

To utilize wastewater treatment plant sites efficiently, the city of Osaka in Japan uses multi-story settling tanks; in fact, even aeration tanks assembled above final settling tanks are used in some cases. The following settling tank details are also described: inlet and outlet conduits, sludge withdrawing facilities, driving gears of sludge collectors, safety of daily operation, and design of drainage pumps. The research on inflow rate and effluent quality in a final settling tank, with a triangular notch-type weir for an upper tank and a perforated pipe for a lower tank as outlet equipment, revealed that a large imbalance of influent flow between an upper tank and a lower tank does not affect the suspended solids concentration significantly.