Sewage disposal . s, some may be held in reserve forthe storm flows; or, if all of the units are used in tandem duringdry weather, the storm flows could be handled by operating allin parallel. The advantage of dividing tanks into units is particularlyapparent where purification works are planned to allow for afuture increase in population. In such cases the sewage flowwill be very small at first and will increase gradually during thefirst few years that the system is used. Another advantage ofseparate units lies in the facility for cleaning and the avoidanceof large quantities of sludge to be
Sewage disposal . s, some may be held in reserve forthe storm flows; or, if all of the units are used in tandem duringdry weather, the storm flows could be handled by operating allin parallel. The advantage of dividing tanks into units is particularlyapparent where purification works are planned to allow for afuture increase in population. In such cases the sewage flowwill be very small at first and will increase gradually during thefirst few years that the system is used. Another advantage ofseparate units lies in the facility for cleaning and the avoidanceof large quantities of sludge to be handled at one time. All DETAILS OF TANK CONSTRUCTION 105 works, no matter how small, must have at least two units, andplants of considerable size should have many more. Details of Tank Construction. Both experiment and theoryindicate that a tank for plain sedimentation should be deeper atthe inlet end, in order to provide space for the deposited materialwithout unduly decreasing the cross section of the tank. The. Fig. 28. Diagram of Efficient and Faulty Tank Construction (afterSteurnagel, 1904.) $% si A + o a) ! Platform J. /^%m/-. Inlet |p p:35> — Tjf jg%>utleM£ mm Fig. 29. Sedimentation Tank at Cologne (after Steurnagel, 1904). stirring up of the solids deposited in the tank by temporary in-crease in velocity of flow is also avoided by such design (seeFigs. 28 and 29). The floors of sedimentation tanks are almost universally builtof concrete, as this material may be readily adapted to thedesired shape of the floor. The cost of concrete is less than 106 PRELIMINARY TREATMENT BY SEDIMENTATION that of any other satisfactory material. Usually a thickness of6 inches will afford a sufficiently water-tight floor, although insome cases, where the ground is soft, it may be desirable toincrease the thickness or to use steel reinforcement. Thedurability of concrete where exposed to sewage has beenquestioned in certain instances, when there have been re-po
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Keywords: ., bookcentury1900, bookdecade1910, bookpublisherlondo, bookyear1919
