GB285944A - Improvements in or connected with the activated sludge process of purifying sewage and other impure liquid - Google Patents

Abstract

285,944. Activated Sludge, Ltd., and Coombs, J. A. Oct. 27, 1926. Aerating; gravity-separation apparatus; plant. -The activated-sludge process of treatment is carried out in two stages, each stage comprising the addition of sludge and aeration. The sludge used for the different stages is separately revivified. The first stage of treatment leads to the separation of carbonaceous material and the second to the conversion of the ammonia compounds present into nitrites and nitrates, the conversion being effected by bacteria cutivated in sludge which has not been in contact with sewage containing large quantities of carbonaceous material. Preliminary treatment may include the removal of detritus, aeration and settling. Surplus sludge obtained in the main treatment may be mixed with the sewage during the preliminary treatment. Grease may be separated from the sewage either during the preliminary treatment or at a subsequent stage. Fig. 1 shows a suitable arrangement of tanks. Sewage is mixed in a main 4 with sludge from revivifying tanks 2 and delivered to the firststage treatment tanks 1, whence it passes through pipes 23 to settling tanks 3. The effluent from the tanks 3 passes to the main 6, is mixed with sludge from revivifying tanks 2<1> and delivered to treatment tanks 1<1>. The mixed liquid from the tanks 1<1> passes to settling-tanks 3<1>. Effluent from the settling-tanks 3<1> enters the discharge main 9. Sludge from the settling- tanks 3 is raised by air lifts 11 in wells 12 to the tanks 2, and sludge from the tanks 3<1> is transferred similarly to tanks 2<1>. The tanks 1 may be provided with transverse walls 74 with valves 75, so that the ends of the tanks may be shut off and used for impounding liquid. Surplus sludge from the second stage of the treatment may be passed back through pipes 76, 77 to the tanks 1. Fig. 3 shows a settling-tank with a central inlet 32, sludge discharge passage 35 with adjustable outlet 37 in a chamber 36, and effluent outlets 33 on a pipe 34 leading to a trough 41 separated by a valve 42 from a discharge conduit 43. When the valve 42 is partially or wholly closed the liquid level is raised and grease overflows into a trough 45. The raising of the level will cause the passage 35 to be flushed. Fig. 4 shows plant including a preliminary aerating tank 60 and settling-tank 61. The sludge from the tank 2 can be passed into the conduit 4 or direct through valves 52 into the tank 1. Surplus sludge is conveyed from the well 12 through a chamber 55 either to an entrance chamber 59 or through valves 66 into the tanks 1. In another form of apparatus a tank is provided in which sludge from the tank 2 undergoes more prolonged aeration in an additional tank and is then returned to the tank 2 or passed direct to the tank 1. In the apparatus shown in Fig. 6, sludge from the tank 2 is passed in part to an inlet chamber 59 of the tank 1 and in part to a chamber 72 where it is mixed with a highly oxidized sludge from a tank 2<x> and afterwards delivered to the tank 1. Specifications 21976/14, 104,187, 161,164, 170,263, and 270,012 are referred to.