eBooksRead.com books search new books
Smith & Robinson Brown.

Whiffs of tobacco: being gleanings from the field of literature of ... online

. (page 18 of 35)
Online LibrarySmith & Robinson BrownWhiffs of tobacco: being gleanings from the field of literature of ... → online text (page 18 of 35)
Font size
QR-code for this ebook
supply is to be kept above suspicion.



Digitized by



Google



CHAPTER XII

THE SELF-PURIFICATION OF RIVERS

In previous chapters frequent reference has been made to
this subject ; but it is one of such far-reaching importance as
to merit special and separate consideration. For all practical
purposes the materials polluting our streams may be divided
into two groups — the waste products of manufacturing pro-
cesses, and the contents of drains and sewers, the latter
being by far the more dangerous. When the contaminating
matters from factories become so diluted by the water into
which they are discharged, or the water, after receiving it,
undergoes such a process of self-purification that it presents no
evidence of pollution to the senses, and chemical analysis
reveals nothing objectionable, there is no risk incurred in using
it for drinking purposes. Where the material which fouls the
river contains the waste products of human life, of the body
in disease and health, — in other words, when sewage is the
polluting matter, — this condition no longer obtains. Ample
proof has been already adduced of the fact that dilution and
purification may have taken place to such a degree that the
most careful analysis can detect no element of danger, yet
that the water may be practically poisonous and capable of
causing most serious epidemics of disease. The question in
which we are interested therefore is, not whether a fouled
river-water may regain its pristine appearance of purity, but
whether it can ever again become absolutely safe for drinking
purposes. Ordinary observation enables us to answer the



Digitized by



Google



216 WATER SUPPLIES

first question in the affirmative; all the researches of chemists
and bacteriologists since the days when the Rivers Pollution
Commissioners first experimentally studied this subject, have
failed to answer the second. On the one hand, we have
the Commissioners of Metropolitan Water Supply so satisfied
that sewage-polluted river water can be rendered safe for
human consumption that they recommend the metropolis to
draw still further from this source, and on the other we
have the Massachusetts State Board of Health about the
same time reporting that the results of their investigation of
repeated outbreaks of typhoid fever in cities using such
waters served to confirm the truth of the saying that " no
river is long enough to purify itself." It will be remembered
that the Rivers Pollution Commissioners came to the con-
clusion, from the results of their experiments, that " there is
no river in the United Kingdom long enough to effect the
destruction of sewage by oxidation." The experiments and
observations upon which this opinion was based are recorded
in their 6th Report, and have now become historical. Ex-
perimenting first with the Irwell and Mersey, — rivers so
notoriously polluted by sewage and other refuse organic
matters that " ordinary aquatic life is entirely banished from
their waters," — they found, after making all possible correc-
tions for dilution, etc., that in the Irwell a flow of 11 miles
reduced the organic carbon by to 29*6 per cent, and the
organic nitrogen by to 11*8 per cent. In the Mersey, a
flow of 13 miles reduced the former by to 20*8 per cent,
and the latter by 13*2 to 17*9 per cent. Selecting the Thames
as a much less polluted river, samples were taken about a
quarter of a mile below where it is joined by the Kennet, and
again just above the Shiplake Paper Mills. These points
were selected because in the four intervening miles the river
does not receive any other affluent or pollution of im-
portance. The analytical results showed that even under
very favourable circumstances the reduction in the proportion
of organic matter was very small, " so minute indeed that,



Digitized by



Google



THE SELF-PURIFICATION OF RIVERS 217

even assuming it to go on at the same rate by night and
day, in sunshine and gloom, it would require a flow of 70
miles to destroy the organic matter." To exclude certain
elements of uncertainty, diluted London sewage was next
experimented with. Jt was agitated with air and then
allowed to syphon in a slender stream from one vessel
to another, exposed to light, and falling each time
through 3 feet of air. The results indicated approximately
the effect of oxidation which would be produced by the flow
of a stream containing 10 per cent of sewage for 96 and 192
miles respectively, at the rate of 1 mile per hour. By the
flow of 96 miles the organic carbon was reduced by 6*4 per
cent, and the organic nitrogen by 28*4 per cent, whilst the
flow of 192 miles reduced the former 25 # 1 per cent, and the
latter 33*5 per cent. Fresh urine and deep chalk-well water
were next mixed together and submitted to similar treatment.
Still less effect was produced ; the carbon was but slightly
reduced, whilst the nitrogen showed an actual increase.
Finally, the results were checked by the examination of the
gases dissolved in dilute sewage (5 per cent) after standing
for different periods in accurately-stoppered bottles exposed
to diffused daylight at a temperature of about 17° C The
dissolved oxygen gradually disappeared, but so slowly that
" so far from sewage mixed with twenty times its volume being
oxidised during a flow of 10 or 12 miles, scarcely two-thirds
of it would be so destroyed in a flow of 168 miles, at the
rate of 1 mile per hour, or after the lapse of a week."



Weight of dissolved Oxygen in
100,000 parts of Water.




•946
•803


Immediately after Mi
After 24 hours


•616


,, 48 „


•315


« w „


•201


» 120 „


•080


„ 144 „


•036


„ 168 „



The Commissioners believed that it was the clarification



Digitized by



Google



21 8 WATER SUPPLIES

by subsidence which takes place in nearly all rivers, which
had led to the belief, so general, but erroneous, in the rapid,
self-purifying power of running water. Their conclusions,
however, were disputed by the late Dr. Tidy and others ; but
inasmuch as, at this period, the part played by the minute
forms of animal and vegetable life in the process of purifica-
tion was unknown, many of the experiments which they
recorded have now little or no interest. One set of observers
held, with the Commissioners, that purification where it took
place was chiefly due to the deposition of suspended im-
purities, others contended that much of the dissolved organic
matter also disappeared. This latter view was strongly
supported by the report of Drs. Brunner and Emmerick
(1875) on the river Isar as it flows through Munich. They
took every precaution to render the results trustworthy,
estimating the quantity and strength of the sewage and
other refuse matters entering the river from the city sewers,
and making due allowance for the effect of dilution by its
tributaries. The results of analyses, inspection, and calcula-
tion proved that the river water two hours' flow below Munich
was practically as pure as the water above the city, or, in
other words, that all the dissolved and suspended impurities
cast into it at Munich had disappeared. The former view
— viz. that subsidence and dilution are the main factors in
producing the so-called self-purification — is still upheld by,
amongst others, Professor Percy Frankland. He undertook
a series of experiments to test this point in connection with
the Thames, taking samples of the water flowing in the
river from different points on the same day. One day at
Oxford, Reading, Windsor, and Hampton ; on another day at
Chertsey and Hampton, etc. His analyses of these waters
are given in a paper contributed to the International Congress
of Hygiene, entitled " The Present State of our Knowledge
concerning the Self -Purification of Rivers," and he concludes,
" From the analytical table it will be seen that the idea of
any striking destruction of organic matter during the river's



Digitized by



Google



THE SELF-PURIFICATION OF RIVERS 219

flow receives no sort of support from my experiments ; the
evidence is in fact wholly opposed to any such supposition/'
At first sight it appears strange that such skilled observers
should arrive at conclusions so diametrically opposed; but
the investigation is beset with difficulties, some practically
insurmountable. The water at different points is not the
same ; even if time be allowed for the water first sampled to
reach the subsequent sampling stages, it will be more or less
diluted by ground water or by tributary streams, and receive
additional polluting matter along its course. The insoluble
matter in suspension, or on the bed and sides of the river,
may by its decomposition be rendered soluble ; hence, unless
the rate at which the soluble matters are oxidised and
destroyed is greater than that at which the insoluble organic
material is rendered soluble, the analysis of the water will
show no improvement, or in fact may, as in Professor Frank-
land's experiments, show even a deterioration. Such de-
terioration is therefore no proof that a process of oxidation
is not taking place ; its true interpretation is probably the
one just given. This is confirmed by the experiments of
Sir F. Abel, Dr. Odling, Dr. Dupr£, and Mr. Dibdin, on the
oxygenation of the Thames water. They found that each
1000 million gallons of water between Blackwall and Purfleet
lost from 25 to 35 tons of oxygen, and retained oxygen to
the extent of from 5 to 15 tons. The quantity of water
passing Erith upwards in the upward flow of the tide was
estimated by the engineers to be 40,000 million gallons.
This should contain 1600 tons of oxygen ; it was found
to contain only 400 tons ; thus 1 200 tons must have
destroyed thousands of tons of dry organic matter, altogether
disregarding the oxygen the river was absorbing from the
atmosphere during the whole time the oxidation was going
on. The experiments of M. Geradin confirm these observa-
tions; they are published in Le Rapport sur V Alteration la
Corruption et Vassouvissement ties Rivieres, and refer to the
river Seine. This river before it reaches Paris contains its



Digitized by



Google



220 WATER SUPPLIES

full amount of oxygen ; when it gets to Paris the greater
proportion of the oxygen is at once removed, and this
removal can only take place by its use in the oxidation of
organic matter; a few kilometres farther on the river is
found to again contain its normal quantity of oxygen, which
fact is accounted for by the organic matter being disposed
of. — Professor W. R. Smith, "River Water as a Source of
Domestic Water Supply." Journal of State Medicine, April
1894.

The balance of evidence is decidedly on the side of those
who uphold the theory of self-purification, and the diverse
conclusions arrived at by different observers can be accounted
for by the varied and often imperfect character of the experi-
ments, and by the diverse conditions which obtain in different
streams. That river water, grossly befouled by sewage in its
higher reaches, becomes a few miles lower down so pure, from
a chemical point of view, as to be certified by the most
eminent analysts to be fitted for all domestic purposes, and
is actually so used by millions of our population, is a fact
which cannot be gainsaid. Whether this process of purifica-
tion be merely due to sedimentation and dilution, or to
these factors, assisted by oxidation, is, however, a matter of
trifling importance, since it is now fully recognised that the
disease-producing material is not the dead organic matter in
solution, but the living organisms in suspension. The problem
is not a chemical one, but a biological one. If the specific
disease-producing bacteria can be carried long distances by
streams, it matters very little whether they are accompanied
by an increased or decreased amount of the soluble impurities
which were introduced therewith. Unfortunately, biologists
differ as widely as chemists in their views, some contending
that a biologically impure water may, by a few miles' flow,
supplemented by some process of sand filtration, be rendered
biologically pure, whilst others consider that the water of a
river specifically infected at any point cannot afterwards be
rendered safe for domestic purposes by any such means. The



Digitized by



Google



THE SELF-PURIFICATION OF RIVERS 221

opinion of the biologists who hold the latter view is supported
by a large mass of evidence proving that many epidemics of
typhoid fever and cholera in this country, in the United
States, and elsewhere, were due to the use of river water
which had been polluted many miles above the intake of the
water supplied to the imputations amongst which the outbreaks
occurred (vide Chapter IX.). As an example of the evidence
adduced in support of the former view, may be cited the
Report made by the Imperial Board of Health in Mecklenburg
on the water supply to the town of Rostock. This town
takes its water from the river Warnow, which, 80 kilometres
above, is polluted by the sewage of the city of Gustrow.
According to Herr Kummel, 1 " The Imperial Board of Health
sent a committee to investigate this matter, including an
eminent biologist, and these gentlemen made a trip up the
Nebel and Warnow from Rostock to Gustrow. . . . They
tested the water at various places, from above the town of
Gustrow down to the Rostock Waterworks. They found that,
though the town of Gustrow deteriorated the water very much,
and that the water 2 kilometres below was polluted much
more by a large sugar manufactory, the number of microbes
above the town of Gustrow, and that 25 kilometres below the
town and below the sugar manufactory, was nearly the same ;
that whilst in the interval the number of microbes had in-
creased to 48,000 in a cubic centimetre, the number was
again reduced to about 200 ; and at last, just above Rostock,
where the river was said to have been deteriorated by the
sewage of the town above, the number of microbes was less
than it was above the town of Gustrow, and no town at all
was situated above the point where the first test of the water
was taken. This experiment was made twice — once during the
summer, and the second time in October last (1890). The
result of the inquiry had been that the Imperial Board had
declared the town of Gustrow might send its sewage water
into the river."

1 Proceedings of International Congress 0/ Hygiene, vol. vii. p. 183.



Digitized by



Google



222 WATER SUPPLIES

On the opposite side we may adduce the Report of the
Massachusetts State Board of Health on the Outbreaks of
Typhoid Fever at Lawrence, Lowell, and Newburyport,
referred to in Chapter IX. In the Newburyport epidemic the
typhoid bacilli must have travelled from Lawrence, a distance
of over twenty miles. The Royal Commission on Metropolitan
Water Supply, notwithstanding the amount of evidence given
by bacteriological experts, felt bound to fall back upon the
" evidence from experience " in order to enable them to decide
whether the Thames could safely continue to be used as the
source of water supply to the city ; but from their report it is
quite evident that even on theoretical grounds they regarded
the danger of disseminating typhoid fever in London by the
use of water from the Thames and Lea as being exceedingly
remote. Selecting the year of highest mortality from typhoid
fever which has been recorded in recent years, allowing seven
attacks for each fatal case, and assuming that the whole of
the discharges from all the cases in the two valleys passed
directly into the rivers at the period of smallest flow, there
would be one typhoid case in the Thames valley to a mass of
water 5 miles in length, 100 yards in width, and 6 feet
in depth, and in the Lea valley to a similar body of water
3 miles in length. But as only a very small proportion
of such discharges ever reach the rivers, the degree of dilution
must be much more considerable. This is an attempt at a
reductio ad absurdum argument, such as Dr. Edwards applied
to the Merrimac River (p. 141). The danger arising from
the flooding of ditches and pools and the washing down of
the contents by heavy rains, is said to be scarcely appreciable,
since the quantity of typhoid matter which would in this
manner reach the streams must be excessively small, and a
still smaller amount will have retained its power of setting
up disease. Typhoid dejecta lose their virulence after a few
days, fifteen being probably the maximum, and as the typhoid
bacillus does not form spores, it is only from typhoid dejecta
of very recent deposit from which danger is to be apprehended,



Digitized by



Google



THE SELF-PURIFICATION OF RIVERS 223

and this clearly reduces very greatly the supposed risk of
specific pollution of the water in times of floods. At such
times also the volume of river water is vastly augmented,
and floods occur chiefly at a time when the temperature of
the water is too low to favour the development of the bacilli,
and when typhoid fever is least prevalent. The Commissioners
also regard typhoid fever as being an exclusively human
affection, and that consequently the dilution of water by
animal manure, however objectionable it may be on other
grounds, cannot be regarded as a possible source of such
disease. Pathogenic bacteria in water are in an unnatural
medium, and whilst the natural water bacteria increase
rapidly, the former undergo rapid attenuation and loss of
virulence, and, being worsted in the struggle for existence,
they speedily succumb. Direct sunlight also destroys these
bacteria, and even diffused light reduces their vitality.
During the process of sedimentation also a large proportion
of the bacteria are deposited. Dr. P. Frankland has shown
that in the process of softening water by the addition of lime,
98 per cent of these organisms are removed in the precipitate.
In the river water as supplied to London no pathogenic
bacteria have ever been discovered. It is admitted by most
bacteriologists also " that small doses of cholera and typhoid
poison may be swallowed with impunity, and some even
believe that these small doses act as a vaccine and render the
imbiber immune. Theoretically, therefore, the danger of an
epidemic of typhoid fever, or even of cholera, from the use of
Thames and Lea water would seem to be remote, especially
when the additional safeguard of careful sand filtration is
introduced. Bacteriology, however, is in its infancy, and our
views on many of the above points may have to be consider-
ably modified ; and whilst the " evidence of experience " in
London has so far justified the conclusion at which the
.Commissioners have arrived, the same kind of evidence,
according to most trustworthy observers in other towns using
polluted river water, leads to a very different conclusion.



Digitized by



Google



224



WATER SUPPLIES



The general acceptation of the Commissioners' views with
reference to the use of sewage-contaminated streams would
be a great national misfortune, and would, it is to be feared,
impede the action of sanitary authorities in their efforts
to secure the freedom of our rivers from pollution by sewage.
The Commissioners, doubtless, never intended that their con-
clusions should apply to any other rivers than the Thames
and the Lea, and this fact should be carefully borne in mind,
since the acceptance as a general principle of a view which is
applicable only to a particular case is illogical and may bring
about disastrous results.

In connection with this subject the recent experience of
Newark is interesting. In August 1893 this town finally
abandoned the use of the filtered Trent water, and the Table
below, kindly prepared for me by Dr. Wills, the Medical
Officer of Health, shows in a striking manner the beneficial
effect of the new deep-well supply.



Table showing number of Cases of Typhoid Fever notified
in Newark-on-Trent, from 1890 to November 1895.

Population 14,500.










i


3


1


§

•-a


►■9


s

3


i

!

p.

a>

00


I

s


2

s


1

1


CO

1


1890


1


4


1


2


3


3


3


1


1


6


20


8


53


1891


25


17


8


5


5




12


7


14


12


15


5


125


1892


1


1


...


5


1


3


5


12


12


7


12


10


69


1893


16


16


4


5


4


5


5


*8


5


4


4


2


78


1894


1




















2


1


2


3


1


10


1895


1














1








1


1


3







* New water supply.



Digitized by



Google



CHAPTER XIII

THE PURIFICATION OF WATEK ON THE LAKCiE SCALE

The water derived from deep wells, springs, and the sub-
soil rarely, if ever, requires filtration or any other form of
purification. Surface water, if collected in sufficiently large
lakes or reservoirs, usually, by sedimentation, becomes so
clarified as to require no further treatment As examples
may be mentioned the water supplies to Glasgow and
Liverpool, derived from Loch Katrine and Vyrnwy Lake
respectively, neither of which are subjected to any form of
filtration, the mere subsidence of the suspended matters
which enter the lakes with the surface drainage effecting all
the purification which is necessary. River water, even if
collected in reservoirs sufficiently large to hold several days'
supply, is rarely sufficiently purified by sedimentation to be
adapted for use without filtration or some other process of
purification. The collection of water in large reservoirs not
only permits the suspended matters, living and dead, to
subside, but the detention of the water in such receptacles
affords time for the pathogenic organisms which may be
present to lose their vitality, by the action of light, or "by
the deleterious action exerted upon them by the harmless
water-bacteria " (P. Frankland). On the other hand, the
storage of water in large open reservoirs has its disadvantages,
as will be pointed out when the storage of water is being
considered. All other processes of purification, such as
boiling, distillation, and precipitation, are only applicable in

Q



Digitized by



Google



226 WATER SUPPLIES

special cases or on the small scale ; and even after the water
has been submitted to these processes, it usually requires
filtering, either to clarify it or render it palatable. Hence
filtration is by far the most important method of purification,
and an accurate appreciation of the factors necessary to
ensure that this is, under all circumstances, as complete as
possible, is absolutely necessary if our polluted rivers are to
continue to furnish the water supplied to our large centres of
population. Until quite recently, the effect of filtration had
been considered exclusively from the chemical point of view,
and that modification which decreased most materially the
proportion of organic carbon or organic nitrogen or albu-
menoid ammonia was regarded as being the most satisfactory.
Inasmuch as this decrease was never very large, the process
was not looked upon with much favour or regarded as of very
great importance, and hence was often performed in a very
careless and haphazard manner. Bacteriological . research,
however, having demonstrated that certain specific diseases
were caused by living organisms, some of which might enter
the system with the drinking water, greater attention was
paid to the subject, and efforts were made to secure greater
clarification and transparency, the results being judged by the
examination of samples of the water in long, glass cylinders.
By this means some of the more important conditions necessary
to ensure the removal of the suspended matters were dis-
covered. Further bacteriological progress, however, succeeded
in demonstrating that water which appeared by such a test to
be perfectly clarified might still contain very large numbers
of those excessively minute organisms, bacteria, certain of
which are capable of causing disease ; and quite recently Mr.
Stodard has proved that a filter which is capable of effecting
almost perfect oxidation of the dead organic matter in a
water, rendering it pure from the chemist's point of view,
may yet permit of cholera bacilli passing through in large
numbers. Evidently, therefore, neither chemistry nor the
physical test of transparency can determine whether any



Digitized by



Google



PURIFICATION OF WATER ON LARGE SCALE 227

process of filtration is efficient We are, therefore, compelled
to resort to the bacteriological test, by which we can obtain
some approximate idea of the quantity and character of the



Online LibrarySmith & Robinson BrownWhiffs of tobacco: being gleanings from the field of literature of ... → online text (page 18 of 35)
Using the text of ebook Whiffs of tobacco: being gleanings from the field of literature of ... by Smith & Robinson Brown active link like:
read the ebook Whiffs of tobacco: being gleanings from the field of literature of ... is obligatory.

Leave us your feedback | Links exchange | RSS feed 

Online library ebooksread.com © 2007-2014