SEWAGE (from sew-, the apparent base of sewer) DISPOSAL. The question of the best means for removing household wastes from indi vidual premises was only beginning to receive general attention in 1850; but to-day collection and removal may be considered as no longer in question. The sanitary emancipation of hun dreds of small and scores of large towns and cities followed the introduction of the separate system of sewers (see SEWERAGE AND DRAIN AGE), with its relatively small, cheap, and self cleansing pipe conduit system. But sewers, or the. water carriage system of waste removal, sometimes proved to be only a temporary solu tion of the disposal problem, on account of the consequent pollution of public water supplies and the less important, but much more palpable. offense to the nostril and eye caused by the foul ing of streams and other bodies of water. Thus, in many instances, the burden was merely shifted and the problem left unsolved.
It must be understood that in the long run practically all these household wastes must reach either the water or the soil, and that ulti mately the bulk of the liquid portion reaches the water. Disposal of sewage on land is a recognized method of purification, but dis charge into water, provided the volume of water be large enough, and not used for domestic sup plies. may be just as effective and sanitary. Nature has abundant means for transforming all organic wastes into harmless and useful prod ucts. But the capacity for this in a given area of land, or body of water, is limited. Until the adoption of the water carriage system of sew erage, household wastes were deposited on or in the soil. With the concentration of peoples in cities the soil became overburdened and re course was had to the nearest water. As soon as nuisances arose here, and particularly when it began to be seen that public water supplies were thus endangered, there was a return to land, only the disposal now was collective, in stead of individual, and remote from, instead of upon. each man's premises. Through a lack of knowledge of the principles involved, or because of either a scarcity of proper land or of money to buy and prepare it, the sewage farms, or broad irrigation areas, thus established became oversaturated, clogged, and offensive, or 'sewage sick.'
It was then sought to relieve these areas by removing the solids from the sewage, a plan which had been and continued to be carried out in the case of water disposal. A further mo tive, where the sewage was discharged into water, was the desire to save the fertilizing material in the sewage. Sedimentation, or when this process was hastened, chemical precipita• tion, w•as the method employed. Some people went so far as to believe that chemical precipi tation. alone, would effect all the purification necessary, as well as recover fertilizing mate rial of great value. Unfortunately, the process was only a partial one, and left the decanted liquid, or sewage effluent, in a condition which was likely to give rise to great offense. At the same time the precipitate, or sludge, as the solid matter is called, proved to be unavailable for plant food. The next step was to try to coax a given area of land to do more work than before. The means employed. intermittent fil tration, was to apply the sewage at intervals, on specially prepared areas, called filter beds, with periods of rest between. The raising of crops was made quite secondary, or abandoned. In some cases the filter beds were supplementary to sewage farms, designed to receive the sew age when it would flood the crops; in others, effluent from precipitation works was applied to the beds.
Where suitable land is available intermittent filtration is all that could be desired, in degree of purification effected, but in many sections the proper sort of land (sandy and easily drained) cannot be bad. The relatively high rates of application, as compared with sewage farming, clog the beds with the organic matter retained on and in the filtering material. Re course to sedimentation, or to chemical precipi tation, many times tried, revives the old sludge problem.