The study of this subject dates back to 1844 when the Healths of Towns Commission of London made the report which first showed the real course of the rapid increase in the death rate of the larger cities. In this country practically nothing was done until 1872 when the Massachusetts Legislature instructed the State Board of Health to investigate and report on the subjects of sewerage, sewage disposal, and the pollution of streams, and to-day Massachusetts leads in the investigation of the best methods of sewage disposal.
Six different methods for the treatment of sewage are now in use. These methods are used separately or in combination, the choice depending upon local conditions and the amount of purification required:—
These methods are:
1— Dilution. 2— Irrigation. 3— Intermittent Downward Filtration. 4— Chemical Precipitation. 5— Septic Tank. 6— Contact Bed.
The purpose of this thesis is to investigate each method and make a comparison along the following lines:
1— Purification. 2— Capacity. 3— Applicability. 4— Cost.
Dilution
Disposal of sewage by dilution is the most common method at the present time, and no doubt will continue to be for some time to come where the stream or body of water is not used for domestic purposes. Under certain conditions this affords a satisfactory solution of the problem. However, if the water into which the sewage is discharged is a source of water supply, two very important questions arise. They are: 1—How large must the dilution be? 2—How far must the polluted stream flow before the water way may be used with safety to public health?
In 1867 Dr. Letheby and others in England made the statement that if sewage is diluted at least twenty times its volume, it will not only be made inoffensive but be thoroughly destroyed after flowing a dozen miles or more.
The Rivers Pollution Commission of Great Britain in 1878 maintained that no river in England was long enough to allow of a complete disappearance of sewage matter discharged into it.