Page:Popular Science Monthly Volume 92.djvu/478

 462

��Popular Science Monthly

��the final disposal system may be made intermittent by means of an automatic siphon placed in the discharge chamber.

��-CI MANHOLE

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���TOP VIEIW

Fig. 2 : A septic tank of larger dimensions suitable for a family of eight persons, and one that can be used where there is plenty of fall to carry away the liquefied matter

Experience has determined that the settling chamber of a small septic tank should have a capacity of from 5 to 15 cu. ft., or from 40 to 80 gal. per person in the family. The best results are obtained when the capacity approaches a larger limit, so that 18 to 36 hours' sewage from the house may be held at one time, to undergo sedimentation and bacterial ac- tion for this length of time. Care should be taken not to make the tank so large that liquefied sewage remains in it more than 36 hours, lest putrefaction set in.

���daily water consumption. Although a depth of 3 ft. may be sufficient for some classes of sewage, it is better to have the depth from 4 to 8 ft., accord- ing to the number of people, in order to give the sludge a good chance to settle and liquefy. The width of the chamber may ordinarily be about one-third or one-half the length, although this may vary for economy and con- venience. The width should not be less than 3 ft., however. The inlet from the house should be provided with an elbow, so that the discharge will be at least a foot below the contained sewage, thus preventing disturbance of the surface scum. The outlet from the settling chamber should be equipped in the same way. Where the en- trance and discharge velocities are very strong, baffle walls of

wood or concrete should be placed before

these openings to break the current. These

precautions are especially beneficial in the

smaller sized

tanks.

The dis- charge cham- ber should be of

such capacity

and depth as to

discharge

about every 10

or 12 hours. It

may be desir-

a b 1 e to d i s-

charge at more

or less frequent

intervals

according to the

nature of the

���Fig. 4: An automatic siphon that may be set to operate at certain intervals

��Fig. 3: A double chamber septic tank for use of six or more persons. It is practical where the outlet fall is difficult to obtain

For this reason one should make an accu- rate estimate of the daily sewage flow, which will be practically equal to the

��soil in the disposal area. This action may be controlled by the arrange- ment of the discharge chamlDer and the siphon. Where little outlet fall is avail- able it is possible so to construct the dis- charge chamber that its floor will be consid- erably above that of the settling chamber.

The capacity and depth of discharge chamber and the size of siphon will de- pend on the number of persons served and the means of disposal. If a sand filter or a distribution system in

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