GB684607A - Improvements in or relating to a sewage treating process - Google Patents

Abstract

684,607. Treating sewage. INFILCO, Inc. Aug. 18, 1949 [June 11, 1949]. No. 21508/49. Class 111. [Also in Group II]. A process for treating polluted liquid comprising introducing polluted liquid to be treated, an oxygen-containing gas and calcium .carbonate into, and mixing them in, an aeration zone and separating clarified liquid from the solid portions of the mixture, is characterized by maintaining in the aeration zone a suspension of calcium carbonate in polluted liquid undergoing treatment, continuously introducing liquid to be treated, fresh calcium carbonate and oxygen-containing gas into the suspension and agitating the suspension to hold it against sedimentation and to disperse the newly-entering liquid and. oxygen-containing gas through the suspension, withdrawing a portion of the suspension from the aeration zone, separating clarified liquid from the withdrawn suspension, returning a portion of the solids of the withdrawn suspension to the aeration zone and withdrawing the balance of the solids to waste. The apparatus of Fig. 1 of Specification 679,635 may be used, modified by the addition of a pipe for introducing calcium carbonate with solid state or as a slurry into the raw sewage pipe just before it enters the tank, together with or instead of a pipe leading from the top of the tank to just inside one of the baffles in the aeration chamber. In the apparatus of Fig 1 of this Specification return sludge and calcium carbonate slurry are introduced into a pipe leading from the right to the centre of the base of the tank and air or oxygen is introduced at the left, the mixture being fed into the suction zone of a rotor and there dispersed. Calcium carbonate may also be added by a pipe shown on the right of the rotor. Mixed liquid is withdrawn from an upper launder and passed to a clarifier. The proportion of calcium carbonate to sludge may be varied over a wide range depending on the source of liquid being treated and the degree of purification required; for example it may be from 30 to 50 per cent of the suspended solids present. In the apparatus first referred to above the oxygen-containing gas may be introduced in an amount only just sufficient to establish air-lift action when the proportion of calcium carbonate is high. The calcium carbonate may be water-softener sludge or derived from reaction of lime with carbon dioxide, or it may be finely-ground limestone, e.g. dolomitic limestone. It may contain a considerable quantity of magnesium carbonate. The calcium carbonate may alternatively be added at spaced points if a longitudinal aerating basin is used. Specification 654,917 also is referred to.