Practical preventive medicine . Fig. 16.—Twin Imhoff settling tanks at Chambersburg Sewage-TreatmentPlant. (Mebus, Engineering Record, 1914.) run into large open tanks for sedimentation to take is accomplished by the employment of lime, fer-rous sulphate or alum. The principles are similar to the em- 112 PRACTICAL PREVENTIVE MEDICINE ployment of coagulants in water purification which will bespoken of later in more detail. 6. Activation.—In the sedimentation chambers previouslydescribed, the decomposition of the sludge is anaerobic incharacter, offensive gases are produced a
Practical preventive medicine . Fig. 16.—Twin Imhoff settling tanks at Chambersburg Sewage-TreatmentPlant. (Mebus, Engineering Record, 1914.) run into large open tanks for sedimentation to take is accomplished by the employment of lime, fer-rous sulphate or alum. The principles are similar to the em- 112 PRACTICAL PREVENTIVE MEDICINE ployment of coagulants in water purification which will bespoken of later in more detail. 6. Activation.—In the sedimentation chambers previouslydescribed, the decomposition of the sludge is anaerobic incharacter, offensive gases are produced and the stable sludgefinally produced has little value. In the activation process,compressed air is admitted to the tanks through porous platesin the bottom, and as a consequence aerobic processes of decom-position are facilitated. The sludge is rapidly oxidized, is non-offensive and has considerable value as a fertilizer (Fig. 17).. Fig. 17.—Air-diffusers in sloping bottom of activated sludge tank.{Engineering Record, 1915.) 7. Roughing Filters.—These are large vats or tanks filled withcoke, crushed stone, or similar material, and filled with a consequence of the rock or other inert material present,sedimentation is facilitated, since the vertical distance a sus-pended particle has to pass to reach a firm support is verymuch reduced. 7. Sludge Disposal.—The amount of suspended mattercollected in the tanks is considerable and since (except in thatcollected in the activation process), its value is slight or nothing,the disposal of sludge is usually considerable of a task and aproblem. Digestion measures considerably reduce the volumeto be disposed of, but do not altogether dispose of the following additional measures are employed: (a) Pressing the sludge in filter presses to remove the surplus EXCRETA DISPOSAL 113 moisture. This is necessary to permit its ready handling. After a drier slu
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectprevent, bookyear1920
