TREATMENT OF CITY SEWAGE. 8 1 
impractical, or even impossible, to use it in some localities. The 
soil can absorb only a certain amount of water without becoming 
too wet for the raising of crops. In regions where rains are common, 
all the water is furnished by rain that can be handled by the soil, 
unless it is very sandy, so that the addition of much more water 
would spoil the crops. In many localities, especially in the United 
States, the sewage from a city is very dilute. We are very ex- 
travagant in the use of water, and a given quantity of American 
sewage contains much less fertilizing material than the same amount 
of German sewage. American sewage cannot be valued at more 
than one cent a ton, and it is impossible for any but the most sandy 
soils to absorb to advantage such great quantities of water, for the 
minute quantity of nourishing matter it contains. 
These are some of the reasons why sewage farming is not 
generally successful, and there is little to hope for along these lines 
until some new methods can be devised for making the fertilizing 
ingredients of sewage more easily available and more profitable. 
It must be recognized, however, that this end is to be desired, since 
surely there ought to be some method of saving the enormous loss 
that comes from waste sewage. It can at present be profitably 
undertaken only in dry regions, or where a sandy soil can absorb 
large amounts of water. 
Sewage Disposed of as a Waste Product. For the reasons 
just given it will be understood why sewage has come to be regarded 
as a waste product, to be disposed of as inexpensively, but as ef- 
ficiently as possible, the desire being to destroy it and not utilize it. 
Chemical Treatment. The first method used was to treat the 
sewage with chemicals that partly purify it. This is an expensive, 
method, troublesome and unsatisfactory, and although used for a 
few years, it has been replaced quite generally by the bacterial 
method of treatment, which is the one most commonly adopted 
to-day by communities that need to find some method of sewage 
disposal. 
The Bacterial Treatment of Sewage. This method is based 
upon exactly the same bacterial activities that we have been con- 
sidering in recent chapters, the sewage being treated in a manner 
