THE 
TREATMENT OF SEWAGE 
IN LONDON. 
BY 
SAMUEL G. DIXON, 
Professor of Hygiene, University of Pennsylvania. 
REPRINTED FROM THE THERAPEUTIC GAZETTE, OCTOBER 15, 1889. 
DETROIT, MICH. : 
GEORGE S. DAVIS, PUBLISHER. 
1889. THE TREATMENT OF SEWAGE 
IN 
LONDON. 
Gentlemen :-This morning at io a.m. 
Mr. W. I. Dibdin, chemist to the London 
County Council, met me at the Charing Cross 
Pier with his steam launch. For many miles 
below London Bridge we steamed through a 
much clearer water than that of the Schuyl- 
kill at Philadelphia below Fairmount dam, 
which stream is fast becoming a cesspool. A 
few minutes before we arrived at Crossness 
(fourteen miles below London Bridge), the 
smell of sewage was quite perceptible. At 
this point the intercepting sewer, for all the 
Surrey side of London pours its contents, 
mixed with the rainfall, into the Thames, yet 
it is robbed of its solid matter, which is pre- 
cipitated by the mixing of lime and sulphate 
of iron (four grains of lime, one grain of sul- 
phate of iron to the gallon), and the effluent, 
i 2 
as it pours into the Thames, is treated with per- 
manganate of potassium. This is not added 
in sufficient quantity, owing to the fact that 
two hundred thousand pounds a year-the 
sum allowed for the sewage-works of Lon- 
don-is not sufficient to properly treat one 
hundred and sixty millions of gallons a day. 
I think you will agree with me when I say 
this process is the best chemical one in use. 
One great advantage over the chlorinated 
lime process is that the micro-organisms are 
not destroyed, consequently the endless cycle 
of physical change is not interfered with. 
The sludge is pumped into vessels, from 
which it is distributed on the high seas. 
The process that you will be particularly 
interested in, and for which I paid my visit 
to Crossness, is that accomplished by means 
of electrolysis. It would seem that this 
process was first applied by W. W. Webster, 
F.C.S., who claims for it that it is the most 
effective and the cheapest manner for sepa- 
rating organic matter and at the same time 
of disinfecting. It does appear to be a most 
satisfactory solution of the question of the 
separation of organic matter in sewage and 
the rendering the effluent innocuous. The 
following result is claimed : 
Sewage. 
Effluent. 
Sulphuretted hydrogen 
Present. 
None. 
Nitrogen as (free) ammonia 
1.89 
0.83 
Nitrogen as organic matter 
o-54 
0.24 
Oxygen required to oxidize organic 
matter 
z-57 
1.21 
Total suspended matter 
15-43 
2.28 
Total suspended matter, of which 
mineral 
7-43 
1.99 
Total suspended matter, of which 
organic 
8.00 
0.29 3 
The process of obtaining this result at the 
Crossness Works is about as follows, and is 
so described by Mr. Webster: 
First, starting with the engine-shed. The 
engine is about twenty-five horse-power, nom- 
inal. This pumps the sewage and drives the 
dynamo. The latter is an Edison-Hopkin- 
son, capable of developing an energy of 
forty-three horse-power. From the dynamo 
the loads run through resistance-frames, by 
means of which the amount of current can 
be regulated without varying the speed of 
the engine. These are then connected with 
the iron electrodes in both the precipitating- 
tanks and the shoot. The precipitating-tanks 
are used for taking experimental measure- 
ments, so as to discover the best mode of 
arranging the electrodes or plates made of 
wrought iron ; cast iron would certainly an- 
swer the purpose. The shoots are of wood. 
The sewage is pumped from the sewer into 
the elevated end of the first shoot. While 
flowing through the shoot, it comes in con- 
tact with the electrodes or plates, which are 
arranged parallel to each other, and run 
longitudinally through the shoot, about two 
inches apart. It is then directed to the set- 
tling-tank, when it separates into sludge and 
effluent. It is claimed that the current 
density employed in the shoot is about one 
ampere per eleven square feet of surface, 
the total current being about five hundred 
amperes. The sewage occupies about ten 
minutes in travelling the full length of the 
shoot, which is about four hundred feet in 
length. The total quantity of electricity em- 4 
ployed is at the rate of twenty-five ampere- 
tones per gallon of sewage. 
The chemical treatment of sewage in dif- 
ferent towns would appear to cost from 
thirty shillings to seventy shillings per one 
million gallons, whereas it is calculated that 
by means of electrolysis it will only cost 
about twenty shillings per million. The 
waste of iron at the positive pole is esti- 
mated at about i gramme per gallon of sew- 
age acted upon. The hypochlorite of iron 
formed at the positive pole is acted on by the 
free ammonium, sodium, and potassium, and 
magnesium hydrates, and the ferrous hy- 
drated oxide precipitated. This oxide of 
iron has the property of combining with or- 
ganic matter. It appears to take up more 
organic matter than if precipitated chemi- 
cally. The whole of the suspended matter 
appears to be carried with the iron oxide, to- 
gether with a large proportion of the organic 
matter in solution. At first the oxidized mat- 
ter is carried to the top by the hydrogen gas 
issuing from the negative pole. This floccu- 
lent matter, however, soon subsides. If this 
process proves to be what is claimed for it, 
the next most important question will be how 
to dispose of sludge to the best advantage. 
This from London sewage amounts daily to 
about three thousand tons.