Patent GB-684782-A (GB)
Title: Improvements in or relating to method of and apparatus for treatment of sewage
IPC: C02F3/12
Filed: 1950-04-13
Abstract: 684,782. Treating sewage or waste effluents. RESEARCH CORPORATION. April 13, 1950 [April 23, 1949]. No. 9111/50. Class 111. [Also in Group VI]. Sewage is treated by passage through a biological floc suspended in a tank to which an unbroken stream of liquid having dissolved oxygen is supplied for gradual upward flow in the tank, an oxygenation unit being connected to the upstream end of an influent pipe which opens into the lower end of the tank; the oxygenation unit has a passage with a downwardlyextending run for the flow of an unbroken stream of the liquid towards the influent pipe, an oxygen diffuser located in the lower portion of the downwardly-extending run and apparatus for causing a flow of oxygen through the diffuser into the liquid stream in bubbles most of which are large enough to have a buoyancy that overcomes the downward velocity of the liquid towards the diffuser. Sewage from a pipe-line 10, Fig. 1, is pumped to the top of an oxygenation unit 16 down which it flows in countercurrent to bubbles of oxygen rising from a diffuser 36 supplied by a conduit 37. The oxygen is thus progressively dissolved in the sewage which thereafter flows along a pipe 18 to the base of a tank 20, Fig. 2, in which it is distributed radially by a baffle 48. It rises through biological floc maintained suspended in the tank 20, the top of the floc being located in an upwardly-diverging portion between collectors 28 and 29 and maintained there by adjustment of the rate of introduction of sewage to the tank and of the rate of withdrawal of partiallytreated sewage from collectors 27 and 28. Such sewage together with almost-fullytreated sewage from the collector 29 is withdrawn by a pump 33, Fig. 1, through pipes having valves 35 and fed to the tank 14 where it is used to dilute raw sewage entering by pipe 12, advantageously to such a degree that all the oxygen required for the process can be absorbed in the oxygenation unit. Purified sewage passes from a collector 22 to a drain 25. Additional control of the amount of floc is provided by a valved outlet pipe 43. A collector 40 is provided just beyond the oxygenation unit 16 for the recovery of oxygen formed as bubbles which are too small to overcome the downward velocity of the liquid and hence are carried along with it. Thus no entrained bubbles are permitted to reach the tank 20. The gas supplied to the diffuser 36 is preferably commercially pure oxygen but air may be used. Where oxygen is used the pressure of nitrogen from the atmosphere dissolved in the raw sewage causes some nitrogen to pass into the oxygen bubbles near the top of the unit 16, the proportion of oxygen in the bubbles and of nitrogen in the sewage both being thus reduced; as the sewage passes downward it thus comes into contact with bubbles of progressively higher concentration of oxygen. The distribution of sewage across the full crosssection of the tank 20 may be promoted by a stirrer 54, Fig. 2. The baffle 48 may be replaced by a housing 60, Fig. 5, from which extend pipes 62 having outlets 65 which are preferably directed downwardly but may be disposed so as to give the liquid a spiral flow. In the latter case the pipes. connecting the collectors 27, 28, 29 to the tank 20, Fig. 2, are preferably disposed tangentially.