Open main menu

Page:Popular Science Monthly Volume 18.djvu/827

This page has been validated.
807
THE PURIFICATION OF SEWER-WATERS.

kilogrammes of solid matter, of which one kilogramme and a half is merely in suspension. This stuff, flowing into the Seine, causes an accumulation of 110,000 cubic metres of mud in a year at the mouths of the conduits, and makes necessary for its removal an annual expenditure of nearly 200,000 francs. Even this sum is not adequate for the purpose. Far from securing the removal of the obstruction, it is not even sufficient to prevent a continued accumulation, and the muddy deposits are constantly extending farther down the river, and at the same time becoming thicker. Since 1875 they have become about a yard thick, and occupy nearly a quarter of the bed of the river from Asnières to beyond Chatou. The Seine has, moreover, been made foul, and its waters have become unfit for domestic use, poisonous to fishes, and a source of fetid emanations.

The authorities of Paris have been for many years considering measures to remove these sources of impurity from the river. As they are rich in fertilizing matters, the thought was suggested that they might be turned to good account for purposes of agriculture. It was therefore resolved to apply them to works of irrigation in the peninsula of Gennevilliers, where, passing through the thin soil of red earth underlaid with gravel, they might leave their rich manures on the arid land, and be returned to the Seine purified. Five hectares (twelve and a half acres) of land were chosen to be irrigated by the sewer-water, which was conducted in trenches around garden-beds. These lands in return produced abundant crops of the coarser vegetables. Three years afterward, in 1869, independent gardeners began to take in the sewer-water, and the demand for it increased, so that, in 1876, 115 hectares were irrigated, and in 1880 more than 300 hectares. Had the use of the sewage-water as a fertilizing material been the only condition to be fulfilled, the success might have been pronounced complete. The principal object, however, was the purification of the Seine, and in this only the most insignificant result was obtained; for the gardens were capable of taking only a minute fraction of the sewage that had to be disposed of. Complaints of bad effects upon health were increased rather than diminished, so that, in 1875, the Minister of Public Works appointed a commission to devise some means of remedying the unpleasant situation.

A plan was submitted by eminent engineers, under which it was believed the Seine could be definitely relieved of the noxious substances which were defiling it. This plan contemplated the convection, by means of new machinery and conduits which were to be constructed for the purpose, of the foul waters to the peninsula of St. Germain, where it was thought 6,300 hectares of land might be applied to the reception and disposition of them. Of this tract, 1,500 hectares f denuded and sterile land in the forest of St. Germain might be employed as a place of deposit, where the sewage that was not used in irrigation could be turned on and absorbed into the ground, for it was