House and Garden 
by a natural process (without 
recourse to chemicals) effect 
the mineralization of the or¬ 
ganic impurities in the sewage 
water previous to its passage 
into the sand. It was also de¬ 
termined to reduce the cost of 
maintenance to a minimum as 
well as insure certainty of action 
hy taking advantage of the la¬ 
test developments m automatic 
appliances. The type of oxi¬ 
dizing or mineralizing beds 
selected was that operated un¬ 
der what is generally known as 
the “contact” system. These 
are water tight reservoirs hold¬ 
ing broken stone or other suita¬ 
ble material, ranging in size 
from I inch to i inch in diame¬ 
ter and in which the sewage 
collects and then stands at rest, allowing time 
for each particle of impurity in the sewage 
water to gravitate and adhere to the piece of 
stone nearest to it, just as a chip of wood will gravi¬ 
tate and adhere to the side of a boat at rest in calm 
water. Thus when later the outlet at the bottom of 
this reservoir is opened and the outflow of the liquid 
contents is regulated so that it does not drain away 
too rapidly, the organic matters to be mineralized 
wdl become separated from the water by adherence 
to the pieces of stone, the surfaces of which are in¬ 
habited by millions of health preserving bacteria. 
These micro-organisms in the presence of the air 
which occupies the space vacated by the water, con¬ 
sume and thus change poisonous matters into harm¬ 
less mineral salts. It is important that the organic 
matters entering into the interstices of the broken 
stone shall be many thousands of times smaller than 
the pieces of stone of which the contact bed is com¬ 
posed. 
As much as 25 per cent of polluting matters in sew¬ 
age being solids in suspension, it follows that some 
means must be adopted for dissolving as large a pro¬ 
portion of these as is possible and for breaking down 
into minute particles such as are allowed to pass to 
coarse grain filters. Consequently, the construction 
of two contact beds at Essex Fells, each measuring 
35' X 50' X 3' in depth, was carried out in conjunc¬ 
tion with what was comparatively but a slight change 
in the structure of the dosing tank, but which change 
brought about a very radical difference in the use of 
this tank. A deep baffle-board placed across the in¬ 
let to the grit chamber above described, and another 
across the outlet end of the rectangular tank with a 
weir over which sewage gravitates, instead of being 
withdrawn by the Field siphon, quickly converted a 
dosing tank into what is now known as a “septic” or 
“resolution tank,” that is to say, a liquid holding 
reservoir, in which the whole or a part of one day’s 
flow is held, so that anaerobic bacteria, which liquefy 
and gasify organic solids, may be utilized, and for 
this purpose are supplied with food as the sewage 
slowly passes from inlet to outlet. It is more than 
ten years since Cameron of England, demonstrated 
by means of his famous Exeter tanks, the practical 
usefulness of septic as compared with chemical anti¬ 
septic methods of sewage treatment. Extravagant 
claims were at first made, so that many erro¬ 
neously believed that the use of such tanks meant 
“sewage disposal made easy,” while others disbe¬ 
lieved in their usefulness, and instead held faith in 
the full efficacy of the sand filter. Time has how¬ 
ever shown that while both methods are good they 
are insufficient alone for present day requirements, 
and indeed that as in the particular plant which is 
the subject of this paper, (if constant manual atten¬ 
tion is to be avoided,) coarse grain mineralizing beds 
are relatively of equal, if not of more importance in 
combination with the other two methods, than is the 
third leg of a three-legged stool. In other words, 
there are three stages in sewage treatment: 
1. The preliminary treatment of matters in suspen¬ 
sion. 
2. The intermediary method of oxidizing or miner¬ 
alizing organic matters. 
3. The final process of clarification of the sewage 
water from the mineral “ash,” as well as of further 
bacterial purification. 
The last process, however, may generally be left to 
those who are responsible for seeing that water fil¬ 
tration precedes the delivery to the consumer of any 
drinking water taken from districts which are not 
thoroughly policed and guarded from every sort of 
pollution besides that of sewage. 
84 
