GB692100A - Treating impure liquids - Google Patents

Abstract

692,100. Treating sewage; gravity-separation apparatus. DORR CO. July 6, 1950 [Aug. 26, 1949], No. 16883/50. Class 111 In a process which comprises maintaining a constantly-changing body of liquid from which sediment deposits and from which clarified effluent at a fixed level is released, maintaining within the body a zone of agitated flocculation shielded sidewise from the surrounding body of liquid and having a restricted bottom outlet to the main body, and collecting settled solids from the bottom of the body to a region aligned with the restricted outlet, all e.g., as in Specification 537,469, a collecting trough is located between the confining wall of the body and the settled solids collecting region and incompletely-flocculated solids are returned from the trough to be mixed with incoming liquid so that they are re-flocculated in the flocculation zone. Combined flocculation and sedimentation apparatus for carrying out the above process comprises a sedimentation tank 10, Fig. 1, having a central sludge sump 19 and discharge 40, an open-bottomed flocculation compartment 20 formed by a partition 21 within the tank 10 and containing flocforming and coagmenting means such as cylindrical aerators 35, arranged along the four sides of a square, an inlet pipe 13, 14 for supplying incoming raw liquid to the flocculation compartment and travelling rake means 47, Fig. 5, its characteristic features being an auxiliary sludge trough 18 for the outer lighter sludge and a pipe 25 and air-tube 29 for reconducting the sludge thus collected into the flocculation compartment for re-flocculation therein. The pipe 25 and air tube 29 together constitute an air lift, the upper end of the pipe 25 being at the level of apertures 15, Fig. 5, through which the raw liquid passes from pipe 14 into the flocculation chamber 20. Thus the solids in the raw liquid are flocculated and the re-conducted solids are re-flocculated together. In the embodiment shown diagrammatically in Fig. 1 the pipe 25 and partition 21 are fixed while the upper part of the pipe 14 rotates with the sludge scraper arms under a fixed cap (not shown). In Fig. 5 the pipe 225, pipe 14 and partition 221 forming the flocculation compartment all rotate with the scraper arms 45. The lower end of the pipe 225 travels along the trough 18. In each case the returned light sludge fraction may be separately aerated for a time before it is returned to the raw sewage. The tank may be rectangular rather than round.