GB411425A - Improvements in and connected with the purification of sewage and other impure liquids - Google Patents

Abstract

411,425. Treating sewage. ACTIVATED SLUDGE, Ltd., and COOMBS, J. A., 100, Victoria Street, London. Sept. 29, 1932, Nos. 27062/32 and 24573/33. [Class 111.] In treating sewage by means of activated sludge the normal flow is treated on the continuous-flow method but during periods of peak flow or " peak strength " the sewage or a part thereof is caused to accumulate in the aerating tanks, where it is subjected to more prolonged aeration, and allowed to pass on to the settling tanks or for further treatment only when the flow has again become normal. Figs. 1 and 2 show a group of parallel tanks 1 .. 8, tanks 1, 2, 3, being reserved for the aeration of mixed sewage and sludge and tanks 7, 8 for the reactivation of sludge, returned from settling-tanks 13, while the tanks 4, 5, 6 can be used for either purpose as required. During normal flow the sewage from sewer 37 passes through a well 38, and pipe 39 to a channel 9 where it is mixed with re-activated sludge overflowing from the tanks 7, 8, and is distributed to the tanks 1, 2, 3. It flows continuously through the tanks to a channel 10 and well 11 and through a float-supported weir or outlet therein to a passage 18 from which it is distributed to settling-tanks 13. The sludge settling in the tanks 13 is discharged through pipes 22 to a well 23 communicating with a pump well 26 from which it is forced by pumps 25 through a pipe 27 to a trough 28, which distributes it to the tanks 7, 8. The weir or outlet 15, Fig. 3 from the well 11 is connected to a telescopic pipe 16, attached to a float 14 which is connected by a weighted chain 34 to a counterweight 35. The arrangement is such that when the supply of sewage to the apparatus increases the float 14 and outlet 15 will rise in a greater degree and flow from the treating tanks be retarded. Step-by-step upward motion of the float 14 may be secured by providing loose weights 44, 44<r>, on the connection between the float 14 and the chain 34. When liquid ceases to flow through the well it is ponded in the tanks 1, 2, 3. If however liquid in the well 11 reaches to the level of a weir 12<xx> it will flow thereover to the settling tanks. The float can be moved manually by worm gear 47 if desired. While flow through the tanks 1, 2, 3 is normally under gravity from the sewer 37, pumps 41 may be provided to force the sewage from the well 38 into the tanks when the level in the tanks rises. Electrical, pneumatic or hydraulic power for actuating the pumps 41 is controlled by floats 42 in the well 38. The floats 42 may also control the outlet 15 and the floats 42 or the float 14 may control the number of the pumps 25 in operation to ensure that the latter return a greater quantity of less concentrated sludge to the reactivating tanks during the period when the sewage is ponded in the tanks 1, 2, 3. The sludge normally passes from the settling-tanks to the well 23 through adjustable outlets 29, Fig. 4, but the floats 42 in rising may cause valves 31 on the pipes 29 to be opened pneumatically. During the period when the sewage is ponded in the treating-tanks it is circulated therein, and sometimes also in the tanks used for re-activation of sludge, by means of an air-lift in the channel 10. Air under pressure is supplied to the tanks 1 .. 8 and channels 9, 10, through diffusers 56. The supply of air from compressors may be regulated in accordance with the difference in liquid level between the tanks 1, 2, 3 and the tanks 7, 8, the liquid level in the latter, from which the liquid overflows, being constant. A valve device for controlling the air supply is shown in Figs. 9 and 10. The air supply pipe 61 communicates with a passage 63 through which a cylindrical valve member 65 with tapered slots 64 slides so as to uncover to the passage 63 wider or narrower portions of the slots and allow a larger or smaller flow of air through the cylinder 65 to the pipe 62 and the air diffusers. The cylinder 65 is attached to a spindle 66 so that it is moved vertically with it by a piston 70, the sides of which are subjected through pipes 71, 72 respectively to air pressures depending on the liquid levels in the tanks 1, 2, 3 and in the tanks 7, 8. A step-by-step movement of the cylinder 65 may be ensured by providing loose weights 74 which are engaged by shoulders 76 on the spindle. A preliminary adjustment of the valve is made by means of a hand wheel 68 and sleeve 67 which turn the spindle 66 and cause the cylinder 65 to move vertically. The various valves &c. may be operated manually or under control of a clock instead of under the automatic control described. In a modified apparatus an air lift device, shown in Fig. 12, may be placed in the channel 10. A baffle 86 situated above the up-cast shaft 84 of the lift is moved from side to side by means of pistons 87, controlled by a float in the inlet channel, so that the liquid is circulated through the tanks towards one side of the device only or through all the tanks 1 to 8.