Process and plant for treating sewage

1,008,866. Filters. MEAD CORPORATION. July 20, 1962 [April 10, 1962], No. 28009/62. Heading B1D. A trickling filter treatment plant for sewage and the like, in which the liquid from the trickling filter is discharged into the top portion of a sump disposed directly below the trickling filter and provided with inlet means, and including means for recirculating liquid from the lower portion of the sump to the inlet portion of the trickling filter, is characterized in that the overflow means is connected to a treatment chamber provided with means for selectively recirculating liquids from the lower portion thereof to the trickling filter and the sump. The treatment chamber may be a chlorination chamber provided with means for injecting chlorinating fluid, or it may be a settling chamber provided with overflow means to a chlorination chamber. The trickling filter may be placed directly above the sump, and lint screens, sludge tanks or comminuters may be placed ahead of the sump. In one embodiment, Figs. 1 and 2, sewage or raw waste enters sump tank 27 through feed pipe 29 fitted with jet-forming reducing ell 31 to produce an agitating horizontal peripherally directed discharge stream. Pipe 32 conducts the sewage from the bottom of sump 27 to pump 33 for re-circulation via pipe 16 to filter 11. Partially clarified sewage overflows from sump 27 through pipe 35 into settling chamber 38 from the bottom of which sewage may be recirculated to filter 11 through line 54 and valve 55, and to the sump tank through line 42 and pump 41. Overflow from settling chamber 38 flows through pipe 43 into chlorination chamber 44, chlorinating fluid being injected into pipe 43 by conduit 46. Chlorinated effluent is discharged by pipes 47 and 48, connected to ventilation pipe 50. A recirculation pipe 52, controlled by valve 53, may be used to by-pass the filter, and introduce sewage from the bottom of the sump tank into the top of the sump tank or into the chlorination chamber. In Figs. 1 and 2, the filter 11 comprises a vertically elongated rectangular or cylindrical casing 12 of e.g. metal lined with chemicalresisting material, filled with filter units 13 each formed of horizontally undulated sheets 14 of plastic, metal or impregnated paper separated by flat sheets 15 of similar material. Recirculated liquid enters input chamber 17 of flow box 18, which is divided by baffle 19 defining input chamber 17 and output chamber 20. The latter is connected by discharge tube 21 to distribu