SEWAGE AND REFUSE DISPOSAL

Methods of Sewage Disposal

One of the greatest problems the hygienists and sanitary engineers have to solve is the disposal of sewage and refuse without contaminating the water supply and in other ways rendering the environment unhealthful.

The methods used for the immediate removal of sewage may be either the dry method or the water method. By far the more common one in towns and cities is the water carriage system. In small towns, however, the more prevalent way is to provide a house some distance from the dwelling which contains a privy vault.

Where sewage is removed by the water method and carried through sewers to the waterways, such as rivers and lakes, the great problem which the sanitary engineers have to solve is how to dispose of the sewage and not pollute the water supply of the city.

When there is a sufficient amount of water to insure proper dilution sewage may be emptied directly into it without treatment. But where there is a limited amount of water, as in a small stream, and a very large amount of sewage to be disposed of, the water may become overloaded and thus the supply of other towns become polluted. When sewage is disposed of in the ocean, oyster beds may become contaminated as well as the bathing beaches.

Sewage Purification

It is considered cheaper and at the same time satisfactory from a hygienic standpoint to depend more upon proper filtration than upon any other method of purification.

There are many different methods used for sewage purification. Sewage may be screened. This frees it from the larger particles. It is then placed in tanks and by a slow process of sedimentation relieved of a large amount of the suspended matter that passes through the screens. After these processes it may then be carried to fields for subsurface irrigation. It is carried through porous tile pipes ten to eighteen inches below the surface and two feet to three feet apart. In this way the sewage seeps through into a sandy soil. An acre will take care of the sewage from 150 to 250 people a day. This method can not be used at all in clay soil.

The crude sewage may be applied to the surface of the land and carried by means of ditches, but this is not considered satisfactory. Sand filters are also used, but they require frequent cleaning and renewing.

According to Price the most desirable method of sewage disposal is known as the septic method. In this method the sewage is sorted and the action that follows is bacteriological. The bacteria present act in the absence of air or oxygen. The sewage thus undergoes a process of decomposition, fermentation and purification.

The next step is to pass the sewage that has come from the septic tank through open sand filters very slowly. These sand filters must be properly cleaned and renewed at regular intervals and must at no time be overloaded. This makes the effluent from the filter beds entirely free from germs and harmful matter. It is not necessary for us to consider the construction of these septic tanks. There are any number of different types, but the results are supposed to be the same. The construction of such tanks is in the province of sanitary engineering and not in that of practical hygiene.

Price states that the water which comes from the filter beds after the sewage has first been through the septic tank is free from injurious substances, is capable of supporting life and that even the drinking of it has been known not to be followed by injurious results.

Refuse Disposal

Another great problem is the disposal of refuse such as ashes, garbage, and in the larger cities, street sweepings. It is estimated by Whipple that in the larger cities like New York the refuse will be in round numbers a ton per capita per year. This is an enormous amount of material and the disposal of it becomes a great problem. This is not only of hygienic importance, but also one of economical significance.

The collection of waste material is objectionable from the social viewpoint; also an accumulation of ashes and dust will irritate the eyes and respiratory tract, while piles of garbage and other filth are conducive to the breeding of flies and mosquitoes. Such collections result also in the development of ill-smelling odors and unsightly streets and alleys.

There are different methods used to dispose of this waste material. It may be collected and burned. This method is called incineration. Or the refuse may be collected separately and disposed of. When it is to be disposed of separately there are usually city ordinances which require the householder to keep the garbage and ashes separate and they are then collected by the city in separate wagons. In most cities tall garbage cans are required and the garbage is drained and wrapped in paper, the ashes are placed in cans or containers. They are used for filling in low lands while the garbage is taken away and buried or burned.

For the collection of garbage specially constructed wagons or carts are used. The garbage must be collected frequently and at regular intervals before it becomes decomposed and gives off objectionable odors. The wagons must be properly cleaned for the same reason. In the removal of ashes and other refuse, care should be taken not to create a dust and the wagons should not leak so as to litter the streets and alleys.