GB462941A - Improvements relating to the process of sewage sludge digestion and apparatus therefor - Google Patents

Abstract

462,941. Treating sewage. DORR CO., Inc. May 8, 1936, No. 13020. Convention date, June 21, 1935. [Class 111] Sewage sludge is successively subjected to anaerobic thermophilic digestion at a temperature of 120 to 140‹ F. and anaerobic digestion at a lower temperature, preferably from 80 to 90‹ F. With the apparatus shown, sludge is passed intermittently by a pump 8 from a settling tank 2 through a heat-exchanger H and a pipe 7 to a digesting tank 10, an equivalent amount of sludge simultaneously passing from the tank 10 through a pipe 20, the exchanger H and a pipe 23 to a second digester 17. The contents of the digester 10 are heated by a coil 11, which is in circuit with a section 12 heated by means of a burner 14 to which gases given off in the digesters 10, 17 are supplied by pipes 25. The contents of the digester 17 are cooled by means of a coil 27 to which part of the effluent passing through the discharge pipe 5 of the settling tank 2 is delivered by a pump 29 through pipes 28, 30. This liquid is passed from the coil 27 through a pipe 31 into the inlet pipe 1 of the settling tank, the heat thus given to the raw sewage being stated to promote settlement. The digester 17 is of greater capacity than the digester 10 so that the period of retention for secondary digestion is greater than that for digestion at higher temperature in the tank 10. The tank 17 also serves as a settling tank, clear effluent being discharged through an inverted siphon 26 and sludge being discharged through a pipe 37. Some sludge from the digester 10 can be supplied through a pipe 42 to the sludge passing through the pipe 7, and some from the digester 17 can be supplied through a pipe 36. The pipe 36 has a branch 43 by means of which sludge from the digester 17 can be added to the sludge passing through the pipe 23 to the digester 17. Valves in the pipe connections described allow of sludge being passed direct from the settling-tank 2 to the digester 17. Should it be desirable to heat the liquid in the coil 27, it is circulated through a section 52 heated by a burner 55. The contents of both digesters should be alkaline. If those of the digester 10 become acid, alkaline sludge is passed to this digester from the digester 17. Specification 442,510 is referred to.