. Preventive medicine and hygiene. eptic Tanks.—Septic tanks are settling tanks large enough toretain the flow of sewage from eight to twenty-four hours or longer, thevelocity of flow varying from 0,3 inch or more per sludge is allowed to remain inthe tanks for long periods, givingopportunity for intensified bac-terial action .to take place in theabsence of oxygen; that is, underanaerobic conditions. As a resultsome of the solid organic matter isliquefied or gasified and theamount of sludge reduced. Thisprocess is spoken of as is accompanied by the presenceof a sc
. Preventive medicine and hygiene. eptic Tanks.—Septic tanks are settling tanks large enough toretain the flow of sewage from eight to twenty-four hours or longer, thevelocity of flow varying from 0,3 inch or more per sludge is allowed to remain inthe tanks for long periods, givingopportunity for intensified bac-terial action .to take place in theabsence of oxygen; that is, underanaerobic conditions. As a resultsome of the solid organic matter isliquefied or gasified and theamount of sludge reduced. Thisprocess is spoken of as is accompanied by the presenceof a scum on the surface of thetank and a continual rising andfalling of sludge through theliquid. The amount of solid or-ganic matter thus digested variesfrom 10 per cent, to 40 per cent.,being greatest in strong domesticsewage. Septic action does not materially improve the quality of the effluent. It may, in fact, make itmore objectionable. Septic action cannot be depended upon to rendersewage safe so far as infections are Fig. 122.—Typical Section of an Im-HOFF Tank. a. Compartment for flowing sewage. /. Sludge digestion compartment. g. Baffle to prevent gases and sludgefrom rising into compartment a, butpermitting sediment to fall into thesludge compartment. h-c. Pipe for withdrawing sludge. 966 SE^YAGE DISPOSAL (4) Digestion Tanks.—The best known type of digestion tank isthe Imhoff. or Emseher, tank. This is a deep septic tank divided bysloping partitions into an upper and a lower compartment, so arrangedthat the sewage flows through the upper compartment, while the sludgesettles through openings in the partition walls into the lower compart-ment, where digestion takes place. The advantage of this t}-pe of septictank is that the sludge alone is submitted to septic action without allow-ing the products of decomposition to mix with the flowing sewageabove, while more complete digestion improves the character of thesludge from the standpoint of subsequent disposal.
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Keywords: ., bookauthorwh, bookcentury1900, bookdecade1910, booksubjecthygiene
