r the so-called
"bacterial" sewage treatment, are but modifications of the filtration
and irrigation methods of sewage disposal. Properly speaking the
bacterial purification of sewage is the scientific application of the
knowledge gained by the study of bacterial life and its action upon
sewage.

In intermittent filtration the sewage is passed through filter beds of
sands, etc., upon which filter beds the whole burden of the
purification of the sewage rests. In the bacterial methods the work of
purification is divided between the septic tanks where the sewage is
first let into and where it undergoes the action of the anaerobic
bacteria, and from these septic tanks the sewage is run to the contact
beds of coke and cinders to further undergo the action of the aerobic
bacteria, after the action of which the nitrified sewage is in a
proper form to be utilized for fertilization of land, etc. The septic
tanks are but a modification of the common cesspool, and are
constructed of masonry, brick, and concrete.

There are a number of special applications of the bacterial methods of
sewage treatment, into which we cannot go here.

=Sewage Disposal in the United States.=--According to its location,
position, etc., each city in the United States has its own method of
final disposition of sewage. Either one or the other, or a combination
of two of the above methods, is used.

The following cities discharge their sewage into the sea: Portland,
Salem, Lynn, Gloucester, Boston, Providence, New York, Baltimore,
Charleston, and Savannah.

The following cities discharge their sewage into rivers and lakes:
Philadelphia, Cincinnati, St. Louis, Albany, Minneapolis, St. Paul,
Washington, Buffalo, Detroit, Richmond, Chicago, Milwaukee, and
Cleveland.

"Worcester uses chemical precipitation. In Atlanta a part of the soil
is cremated, but the rest is deposited in pits 8 x 10 feet, and 5 feet
deep. It is then thoroughly mixed with dry ashes from the crematory,
and afterwards covered with either grain or grass. In Salt Lake City
and in Woonsocket it is disposed of in the same way. In Indianapolis
it is composted with marl and sawdust, and after some months used as a
fertilizer. A portion of the sewage is cremated in Atlanta, Camden,
Dayton, Evansville, Findlay, Ohio; Jacksonville, McKeesport, Pa.;
Muncie, and New Brighton. In Atlanta, in 1898, there were cremated
2,362 loads of sewage. In Dayton, during 30 days, there were cremated
1,900 b