GB691985A - Improvements in or relating to an apparatus and method for treating a liquid - Google Patents

Abstract

691,985. Treating sewage and waste effluent. INFILCO, Inc. Nov. 21, 1950 [Dec. 7, 1949], No. 28417/50. Class 111 A sedimentation tank having a clarified liquid overflow and a lower sludge outlet has also a partition structure extending from the bottom to above the overflow elevation and forming a centrally located chamber in the lower portion of which is a rotor, the rotor being dimensioned and positioned to set up rotational agitation confined to the lower portion, of the chamber but sufficient both to maintain its contents in suspension and to disperse entering liquid and gas therethrough; the tank also has means for discharging entering liquid to be treated and gas for the treatment into the suction flow of the rotor, a constantly-open inlet passageway for partially thickened sludge connecting the lower portion of the chamber with an intermediate level of the tank above the thickened sludge therein, and a constantly-open outlet passageway connecting the upper portion of the chamber with the sedimentation tank and discharging at an elevation above the inlet passageway and below the overflow. As shown in Fig. 1 liquid to be treated is introduced at 50, together with a gas, e.g. oxygen or carbon dioxide, at 51, into the suction flow of a rotor 40 and is immediately dispersed throughout the lower portion 75 of a region bounded by a partition 26, skirt 37 and the central part 11a of the floor of a settling tank 10. Undissolved or unreacted gas initiates an air-lift action above the rotor 40, the liquid on reaching the level of adjustable apertures 30 flowing outwards while most of the gas escapes at the surface. The remainder of the gas leaves the liquid in the downflow region 78 between the partion 26. and an outer partition 31. The liquid finally flows radially outwards above a baffle 35 into an annular settling region 21 of the tank 10 whence clarified effluent passes over a weir 14 and sludge settles towards the bottom 11. Some partially-thickened sludge passes inwards through a substantially continuous slot 36, or a series of apertures, provided between the bottom of the partition 26 and a wall 25 and is constrained by the skirt 37 to move downwards into the suction flow of the rotor 40. Such return sludge assists deposition and flocculation of solids introduced by the raw liquid. Settled sludge in the region 21 is moved to a sump 55 by scrapers 56 depending from a ring 63 resting on wheels 64 which ride on a rail 65, the ring being centred by wheels 66. The ring is driven by gears 68 through an endless cable 67 tensioned by a wheel 69 and spring 70. The partition 26 is supported on the wall 25 by 'struts 27 and in turn supports a platform 48 and has attached to it by brackets 32 the outer partition 31 to which is secured the rail 65. .Apertures 80 in the wall 25 normally closed by gates 81 are provided for returning sludge thicker than that returned through apertures 36 at the beginning of the process or when the nature of the liquid being treated requires it. Liquid reagents may be introduced through a pipe 52. The modification of Fig. 2 is intended to be of smaller capacity than that of the apparatus of Fig. 1. The settling reigon 21 of Fig. 1 is replaced by a region 121 of upwardly-increasing cross-section from the sump 155 of which thickened solids are removed through openings 159 in a pipe 157. In the modification of Fig. 3 the mixing and air-lift region 275 and 220 is bounded at the bottom by a plate 211. The sludge inflow slot 236 is formed between a horizontal baffle 235 and the upper edge of a,partition 225 rising from the plate 211. An annular peripheral filling 237 directs sludge entering at 236 into the region 275. Settled sludge is removed from the apparatus at 257. The gas entering at 51, 151 or 251, is preferably oxygen when the liquid to be treated is sewage and carbon dioxide when the liquid, e.g. tannery waste, has a high content of hydrated lime. In such a case calcium carbonate is precipitated which assists in adsorbing and coagulating the other suspended matter in the waste. Carbon dioxide, when used, may be obtained from an underwater burner .placed in the inner chamber and discharging below the rotor instead of from an outside source.