Mechanics of the Household / A Course of Study Devoted to Domestic Machinery and Household Mechanical Appliances

by E. S. Keene

Fig. 153.—Sectional view of a two-chamber septic tank with a dosage siphon.

The Septic Tank and Anaerobic Filter.

—In places where the use of the simple septic tank is not possible and where the character of the soil will not permit of a natural sand-bed filter, an anaerobic filter may be constructed through which to pass the effluent from the septic tank.

The anaerobic filter is one in which anaerobic bacterial action is given opportunity to reduce the organic matter in the sewage to its elemental condition. The filter may be constructed in any form that will permit the process of filtration to be carried out in a way that will afford good anaerobic action. The extent to which the purification is to be carried will determine the form and size of the filter.

In Fig. 154 is shown such a plant, where a combined septic tank and anaerobic filter discharges its effluent into a filter ditch in which the purifying process is continued through a bed of gravel of any desired length. The figure illustrates a plant that was designed for a country residence. The septic tank and anaerobic filter are located relatively as shown in the drawing, the filter ditch following the course of a roadway. The water is finally discharged into a little stream, where it mingles with the water from a spring, and flows through a meadow.

Fig. 154.—Sectional view of a septic tank combined with an anærobic filter; together with the details of construction and plan of arrangement.

The septic tank in Fig. 154 is quite similar in construction to the others described except that a section of sewer tile takes the place of the brick wall between the two parts of the tank. The opening O, through which the effluent is discharged, is located a little above the center of the tank.

The anaerobic filter is a tank, rectangular in cross-section, made with brick walls and cemented on the inside. The effluent from the septic tank enters the anaerobic filter in a chamber, that is separated from the main tank by a wooden grating against which rests the filter material. As indicated in the drawing, the bottom is filled with coarse material; stones or broken tiles about 4 inches in diameter. Above this is a layer of material about 2 inches in diameter and above that another layer of 1-inch material; the top is made of gravel. This forms the anaerobic filter, in which takes place the bacterial action away from the presence of air. The interspaces in the filter material allows the effluent from the septic tank to seep through and deposit the particles of matter held in suspension. The arrangement is such as is best suited to the anaerobic action. Here, shut away from the light and air, the organic matter in the effluent undergoes disintegration just as would happen in the earth.