Patent GB-500546-A (GB)
Title: Improvements in or relating to the treatment of sewage or/and industrial waste
IPC: C02F1/68
Filed: 1937-07-08
Abstract: 500,546. Fluid-pressure servomotorsystems. BAILEY METER CO. July 8, 1937, No. 19014. Convention date, July 8, 1936. [Class 135] [Also in Group I] Flowing sewage &c. is treated with u chemical fluid the proportion of which is varied continuously according to a predetermined schedule of the expected rate of flow of the sewage over a given time, and according to the departure of the expected rate from the actual rate of flow. The treatment may involve precipitation, coagulation and control of the hydrogen ion concentration, the sewage being first screened, then subjected to a coagulating and aeration treatment-with milk. of lime and then discharged into a thickener. Precipitated matter is removed as sludge which may be treated to recover the iron content such as ferric hydroxide. Fig. 1 shows a plant in which 1 represents a mixing and aeration tank for sewage and chemical solution. Two independent chemical solutions may be supplied through pipes 5, 27 and the tank may be fitted with a cell 24 which in conjunction with a device 25 determines the hydrogen ion concentration of the contents of the tank. Sewage enters the tank through a conduit 3. Conduit 3 and pipe 5 arc provided with Venturi tubes 2, 4 connected to tubes 6, 7, 8, 9 containing floats which operate cams 10, 13 acting on indicator arms 11, 14 moving over scales 12, 15. The rates of flow of sewage in the conduit 3 and of chemical solution in the pipe 5 can thus be read directly on the scales 12, 15. A valve 17 controlling the flow of chemical in tube 5 is actuated by mechanism controlled by both arms 11, 14, by the device 25 and by rotating cams cut in accordance with the expected rate of flow of sewage. This mechanism is shown in Fig. 2 and is represented in Fig. 1 by the line 16. The chemical supplied through the pipe 5 is contained in concentrated form in a tank 18 from which it flows into a tank 20 where it is mixed with water supplied through a pipe 19. The specific gravity of the solution in tank 20 is kept constant by a specific gravity recorder 22 which controls the water cock 23. The supply of a second chemical through pipe 27 is regulated by a valve 26 controlled by the device 25. This chemical may consist of a milk of time suspension delivered from a tank 28 to which lime is fed by a feeder 29 and water through a cock 30 controlled by a specific gravity recorder 31. Fig. 2 shows the mechanism for actuating the valve 17 which is operated by compressed air acting on a diaphragm 46. The air supply is controlled by a valve 45 the stem 44 of which is connected by linkwork to the device 25 and arms 11, 14. One of the links 33 is provided with a manually adjustable fulerum 48 and another link 35 with a fulcrum 50 which moves coutinuously under the influence of a rotating cum 52. The shape uf the cam 52 is determined by experimental data for any particular installation and represents expected variations in the rate of sewage flow over a given time, for example a week. In order to prevent waste of chemical solution in the event of the sewage being diluted with rain water but increased in volume, means are provided for controlling the valve stem 44 according to the departure of the expected rate of sewage flow from the actual flow. A link 38 pivoted to the arm 11 is pivoted to a beam 53 carrying a link 54 attached to an arm 55 which is controlled by a rotating cam 56 similar to the cam 52. Beam 53 carries a link 59 pivoted to a beam 60 which is connected through linkwork to a crank arm 47 the lower ohd of which forms a movable fulerum for the link 40. Beam 60 also controls the position of a contactor 62 which controls the direction of rotation of a motor 63 which through reduction gearing rotates a cam 64 which alters the position of the arm 47. A link 62A has a movable fulcrum controlled by the arm 55. Fig. 3 shows a modification in which sewage flows into the tank 1 through a conduit 3 and chemical solution through a pipe 5. The conduit 3 is connected to a sewage meter 101. The chemical solution is obtained from a vessel 28 to which dry chemical is supplied from a feeder 67 controlled by a specific gravity recorder 22. Water is supplied to the vessel 28 from a pipe 104 through a valve 65 controlled by apparatus 103 similar to that shown in Fig. 2 and connected to a water meter 102 connected to the supply pipe 104. The water meter 102 also controls a valve 107 controlling the flow of chlorine solution from a mixer 105 receiving chlorine from a source 106 and water from the pipe 104. The amount of chlorine solution delivered to the tank 1 may be controlled by a valve under the influence of the chemical meter arm 14 and an arm operated by a meter measuring the flow of chlorine solution. Alternatively the chlorine controlling valve may be controlled directly from the valve 45 shown in Fig. 2. Fig. 6 shows a plant to which the above arrangements may be applied and in which a part of the solid constituents of the treated sewage is returned to a coagulating stage in the tank 1 and a part to a thickening or recovery plant. Sludge is withdrawn from settler 109 by a pump 81, through a valve 82 and Venturi tube 83. A meter 84 controls the valve 82. An adjusting device 85 allows the rate of flow of withdrawn sludge to be varied. The tube 83 is connected to a second Venturi tube 88 through a pipe 86 having a branch 87 leading to the thickeners. A valve 89 controls the return flow to the coagulating stage, the rate of flow of returned sludge being indicated by the arm 91 of a meter 90. The arm 91 is connected by links 93, 94 with the link 39 shown in Fig. which is moved vertically in accordance with the actual rate of flow of raw sewage and with the difference between the actual and expected flow. The link 94 actuates a pilot valve 95 which controls the valve 89. A hand adjustment 96 controls the position of the arm 91 and is used for varying the effect of the rate of flow of returned sludge upon the link 93. A continuously rotating cam 52a which rotates with the arm 52 shown in Fig. 2, acts upon the arm 91 to vary the amount of material returned to the tank 1 to keep the rate at which solids re-enter the tank constant. The cam 52a is cut according to the expected rate of flow of material returned to the tank. The valve 89 may also be controlled by u meter placed in the branch pipe 87 and measuring the rate of flow of sludge going to the recovery plant. Specification 425,507, [Group XII], is referred to.