An Interesting Example of Sewage Disposal 
niter Ded N=' 
As the Essex Fells plant 
now employs each of these 
three stages, it may be of in¬ 
terest to the reader that we 
should describe in some de¬ 
tail the precise operation, as 
well as explain the action by 
which satisfactory results are 
obtained automatically. For 
although different local con¬ 
ditions may vary the partic¬ 
ular manner in which the 
forces of nature should be 
harnessed, the laws govern¬ 
ing these forces are the same 
all the world over. 
Entering the septic tank, 
the sewage is deflected downwards by means 
of a baffle-board. This is because more active 
fermentation by anaerobic bacteria will take place 
if air is excluded as far as possible from mixing 
with the sewage in this tank, and a larger percentage 
of solids will in consequence be liquefied or pass 
off in the form of marsh gas, carbon dioxide, hydro¬ 
gen and nitrogen. The conversion of these solids 
into gases is also of distinct importance in connec¬ 
tion with the liquefaction of other solids. Solids 
unless intermingled with gases are as a rule heavier 
than the sewage water, and naturally therefore grav¬ 
itate to the bottom of the tank. Here they are at¬ 
tacked by bacteria and gases are formed which cause 
the solids in which they are generated to become 
buoyant and to rise and float on the surface until 
these gases have been liberated to atmosphere, when 
they again sink to the bottom, where further gases are 
formed and the process is repeated. In their vertical 
travel they are further subjected to the action of liq¬ 
uefying bacteria, and the result is that not only is a 
large percentage of the suspended solids dissolved, 
but those which are not are nevertheless broken down 
into fine particles so that they are more readily treated 
subsequently in the mineralizing beds. Tbe writer 
IS acquainted with an engineer who counted a large 
mass of solids i8 inches square rise and sink seven¬ 
teen times in two hours, by which time the mass was 
completely broken down and a piece of lemon peel, 
by which it had been identified, sank out of sight. 
The travel of the solids in suspension is therefore 
principally a vertical one, but the weir formation at 
the outlet end of the tank creates a slow even move¬ 
ment of the entire contents of the tank towards the 
outlet, the rate of flow being in accordance with the 
cross sectional measurements of the tank, and the 
varying rates at which the sewage enters. A baffle- 
board at the outlet end reaching above and below the 
water level holds the floating solids from passing 
over the weir, so that the effluent from the tank con¬ 
tains only the finer solids in suspension in addition to 
Section through Filter Bed 
the solids in solution. A ten inch carrier conveys the 
septic sewage to a distributing chamber constructed 
at the entrance to two contact beds. It is here that 
a very ingenious device is employed, which like the 
Field siphon is automatic, and employs no moving 
parts. In other respects, however, it is dissimilar, 
inasmuch as it controls the flow without absorbing 
fall and is operated by the injection of air into spe¬ 
cially shaped passageways in a positive manner, 
by the flow of the sewage. By this device each 
bed is filled to a depth of three feet. Then the inlet 
to one bed closes and that to the other opens. After 
a definite time the outlet from the bed which has 
been filled opens to permit of the drainage of the 
filtrate and remains open until a few moments pre¬ 
vious to the time when the bed again commences to 
refill. This is known as the air-lock method. 
The apparatus is made up of a combination of air 
bells and inverted U-shaped iron passageways, in¬ 
geniously arranged so that the flow of sewage may he 
controlled in a great many different ways according 
to the particular requirements of each sewage plant. 
The action at Essex Fells is as follows: 
Sewage passes through an open inlet into channel 
ways formed of fine cinders placed on the top of the 
broken stone, and through which the sewage per¬ 
colates into the broken stone beneath. This form¬ 
ation of distributing channels is specially useful in 
intercepting particles in suspension which pass 
from the tanks. The outlet to the filter bed has been 
previously closed so that the sewage steadily rises in 
level throughout the filtering material, until it has 
reached a level which permits it to flow into a small 
chamber in which are three air bells. As the liquid 
rises in level these bells become submerged and the 
air contents of the first bell is forced through an air 
pipe into the outlet passageway of the adjoining filter 
bed, which is thus air-locked. The second air bell 
acted upon in a similar manner, forces out water 
from a U-shaped pipe which being connected with 
the inlet of the adjoining bed, allows the confined air, 
8S 
