THE FIRST GERMAN MUNICIPAL EXPOSITION.
(DRESDEN, 1903.)
III.
E. PUBLIC HEALTH AND SAFETY. Continued.
Sewerage. Because technically connected with the same municipal department as streets, the subject "sewerage" was placed under the general head "traffic" in the official catalogue of the exposition. The discussion of this subject, however, belongs logically here.
i . Types of sewers. The ordinary sewers are either circular or egg-shaped with the small end downward. The latter is the more modern form. Having the smaller end downward effects a bringing together of the contents of the sewer when the stream flowing through it is small, and insures a current. The best mod- ern sewers, however, are of the double-conduit type adapted to the modern system of purifying sewage before discharging it into the rivers. When conditions are such that the sewage may be allowed to flow directly into a river, without purification, the former types of sewer suffice ; but when, as is usually the case, further treatment of the sewage is necessary, the double- conduit system commends itself. By this latter system sewage and drainage are separated. The rain-water is led directly to the point of discharge. It may be noted here, however, that in Bielefeld, the central point of the Westphalian linen trade, even the drainage water is cleared before being discharged into the river; for the water of the latter is used by the bleaching estab- lishments. The sewage, on the contrary, kept separate by the construction of the sewers, is led to the purifying plants. There is an extra cost of sewer construction, but a saving in cost and operation of the purifying plants, as there is not so great an amount of sewage to be treated. The two sewer pipes may be laid separately, or may be combined in a double pipe. Kiel is converting her system to the double-conduit system, but will use
812
