Engineering and Contracting . gicalactivity and the production of gas through thedecomposition of organic matter. FE.\TURES OF DESIGN OF IMHOKF TANKS. The Subsidence Period. — Fundamentally,the subsidence period provided in Imhoff tankinstallations must be sufficiently prolonged atmost critical times (i. e., times of maximumflow or of the discharge of wastes which aremost difficult to treat), to compel as effectivesubsidence as is reasonably possible. Strangelyenough, the available evidence goes to show-that the weaker sewages require as long, ifnot longer, periods of subsidence than do thestr
Engineering and Contracting . gicalactivity and the production of gas through thedecomposition of organic matter. FE.\TURES OF DESIGN OF IMHOKF TANKS. The Subsidence Period. — Fundamentally,the subsidence period provided in Imhoff tankinstallations must be sufficiently prolonged atmost critical times (i. e., times of maximumflow or of the discharge of wastes which aremost difficult to treat), to compel as effectivesubsidence as is reasonably possible. Strangelyenough, the available evidence goes to show-that the weaker sewages require as long, ifnot longer, periods of subsidence than do thestronger. .Xt any rate, the flowing-throughperiod for domestic sewages should never beless than, say, from 1 to 1% hours. Thismeans that the average period of subsidenceshould be considerably greater than this, andthe ma-ximum period, represented by minimumnight flow-, would be still further unclean sedimentation chambers andwith too prolonged storage, there is evidencethat some septic action may take place. In-. Fig. 4. View of Sprinkling Filter In Operation. ently developed certain s|)ecial problems mthe preparatorv treatment of sewage in Imhofftanks, as wellas in septic tanks of the olderCameron type. Recent experience has dem-onstrated the need of more careful design, aswell as painstaking operation. Unfortunately,careful attendance and wise operation havenot as vet obtained in connection with anvImhoff tank installation in California otwhich the writer is aware. For this reason,it has been deemed important to summarizeat this time the main conclusions with respectto certain features of design and operationwhich appear to be warranted by expcrKiici,both in general and in particular, under Cali-fornia conditions. CALIFORNIA CONDITIONS AS AFFECTING SEWAGETREATMENT. (The following paragraph from the articlepublished in ENGiNKERtNO and ;of Dec. 10, lOi:?, is quoted to co-ordinate thereader with California conditions as affectingsewage disposal.
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