Democratic Sentinel, Volume 17, Number 6, Rensselaer, Jasper County, 24 February 1893 — Purification of Sewage. [ARTICLE]

Purification of Sewage.

The Engineering Record quotes the reported results of investigations made by officers of the Hygienic Institute of Munich upon the growth of certain plants in the River Isar as indicative of the process of self-puri-fication in that stream in its downward flow after receiving the sewage of Munich. Prof. Von Pettenkofer, the chief of the bureau, believes that in running streams a moderate quantity of human excreta is decomposed and rendered harmless in the course of a few miles of flow. He supposes this does not depend on mere dilution or subsidence, but on the velocity of the stream, and particularly on the presence of free oxygen in the water, this being connected with the action of green algie and other water plants. Observation shows that a peculiar form of vegetable life, sometimes called the sewage fungus, grows luxuriantly about a mile below the point where the sewage enters the Isar, abounds seven miles lower down, and disappears farther off. The inference is that after about twelve miles of flow the turbulent stream is so far purified from nitrogenous organic matter that it no longer contains enough of it to support the growth of the sewage fungus. 'Also it has been found that at the mouth of the sewer the cubic centimeter of fluid contained 198,000 bacteria, while twenty miles lower the number had diminished to 3,602, and a mere trace a few miles farther. But the purification here referred to applies only to residential sewage, that is, to water fouled with bumap excreta, and not tuthat fouled with industrial waste products of various kinds of manufacture, maDyof which are directly poisonous to both animal and vegetable life in water. It is objected by another writer that probably the purification produced by algaj is insignificant compared with that due to aerobic bacteria, entomostracea, and other forms of animal and plant life. He holds that the importance of the presence of oxygen is undoubted, but that its influence on the organic matter is exerted by favoring the growth of those organisms which require its presence as a condition of life, but that it does not act directly. If a mass of typhoid bacilli were discharged into a rapid current they might be carried to a greater distance before succumbing in the struggle for existence with other organisms than would have been the case with a slower current. The editor thinks that though much has been learned in regard to these things within the last ten years we are not yet sufficiently well informed concerning them to be justified in saying that a stream that has been polluted by sewage will be a safe source of water

supply arter it has flowed a stated number of miles, although people all along the Ohio ltiver and the Mississippi use the water for potable purposes—some Altering it to remove the sediment.