PURIFICATION OF WATERS.
The Rivers Pollution Commission of 1874, says, as regards filtration:
“No process has yet been devised for cleaning surface water once
contaminated with sewage, so as to make it fit for drinking.” Others
say it is not safe to trust to dilution, storage, agitation, or
filtration for periods of time, for the complete removal from water
of disease-producing elements whatever they may be.
Dr. Frankland states:
“I believe the noxious parts in sewage is that which is held in
mechanical suspension, not held in solution. I would not say it is
impossible to remove it, but no system of filtration will secure
its removal. There are only two processes by which it can be
effectually removed--one by boiling for a long time, and the other
by distillation.”
The methods adopted for filtration of water are:
“1. Infiltration--by intercepting underground currents through
natural formations of beds or banks of water-courses.
“2. Filtration--mechanically by artificial beds of sand, gravel,
etc., chemically by charcoal, iron, etc.
“3. Subsidence--clarification by deposition; storage reservoirs.
“4. Aeration--spontaneous purification by oxidation.
“5. Covered reservoirs--to prevent atmospheric influences.
“6. Precipitation of carbonates--Clark’s System.”
The infiltration system is resorted to where natural means for
permeation are found; the galleries for intercepting the water being
constructed in the sand or gravel banks or bed.
The clarification, however, is necessarily restricted, owing to the
general high rate of filtration.
Lowell, Mass., has a gallery in the gravel banks of the Merrimack
River, 1,300 feet in length, 8 feet by 8 feet, the bottom 8 feet
below the river bed. The capacity is six million gallons, and rate of
flow 150 gallons per square foot in twenty-four hours.
Lawrence, Mass., has a similar gallery.
Brookline’s (Mass.) gallery is 762 feet in length; 6 feet below the
river bed. Rate of flow is 490 feet per square foot.
Newark, N. J., tried the experiment of driven wells. They drove
sixty-three-inch tubes 28 feet apart, 40 feet deep, into the bank of
the Passaic, three hundred feet from the shore line. The tubes were
attached to three lines of suction pipes, and the latter united in
one twenty-four-inch main for the supply of their five million pump.
As their expectations as to the quality and quantity of water were
not realized, a well was substituted.
Columbus, O., has a gallery under the Scioto River, 600 feet in
length, with a capacity of eight millions daily.
Toronto, Canada, has a basin excavated in an island of Lake Huron,
opposite the city, 13½ feet below low water, and 3,090 feet in
length; the rate of flow is 52 imperial gallons per square foot for
twenty-four hours.
Lyons, France, has two covered galleries along the banks of the
Rhone; the area of bottoms 17,200 square feet; capacity six millions,
and rate of flow at lowest stage 100 gallons per square foot.
Toulouse, France, has three covered galleries along the banks of
the Garonne River. The last gallery constructed is 1,180 feet long;
capacity, two and a half millions; rate of flow, 228 gallons per
square foot of bottom area.
Perth, Scotland, has a gallery in an island of the River Tay, 300
feet long, 4 feet wide by 8 feet high, 2½ feet below the surface of
the river; rate of flow, 182 gallons per square foot per diem.
Genoa, Italy, has a gallery in the valley of the northern slope
of the Mantine Alps, 1,181 feet above the sea level. It is 1,780
feet long, 5 feet wide and 7 to 8 feet high, and extends, in part,
beneath the bed of the river Scrivia, transversely from side to side,
and in part along the bank. It has a delivery of 6,412 gallons for
twenty-four hours per lineal foot.
The city of Glasgow made two failures in attempting to furnish a
supply by this system. The first experiment was the construction of
a reservoir on the northern bank of the Clyde, below the level of
the river. Beneath the bottom of the reservoir was thirty-two-feet
cylindrical tunnels made of wedged-shape bricks without mortar. The
failure was due to the inability to keep the interstices free from
the deposit of impurities. In the second plan, they excavated shallow
wells, 10 feet in diameter, 6 feet deep, and 20 feet apart, in the
stratum of sand adjacent to the river. The wells were connected by
pipes. The scheme was a worse failure than the first one.
It often happens, as in the case of Waltham, Massachusetts, in
locating these galleries, that spring water is intercepted in place
of the desired water of the flowing stream. The difference in
temperature and increased hardness of the spring water, determine the
class of water.
FILTRATION
is the artificial method of clarification by mechanical and chemical
means. By the mechanical system heavier impurities are held in
suspense by percolation of water through carefully prepared beds of
sand, gravel, coke, shells, and like substances.
The total area of the London filter beds in 1874 was 68 acres, and
rate of filtration per hour in inches and depth of water, or head on
beds, were:
RATE. DEPTH.
Lambeth Works 10 inches. 7 feet.
Southwark & Vauxhall 4 “ 4 “
Grand Junction 3 “ 4 “
West Middlesex 4 “ 3 “
Chelsea 6 “ 5 “
New River 4½ “ 5 “
East London 3 “ 5 “
The efficiency of filtration is inversely to rate of flow. Humber
says:
“It is now generally admitted that filtration through sand, to be
effective, should not proceed at a higher rate than 6 inches of
descent per hour; or, in other words, there should be at least 1½
square yards of filtering area for each 1,000 gallons per day. This
is, of course, exclusive of reserve area, which will be necessary
to permit of at least one bed being cleansed while sufficient area
remains in operation in the other beds.”
The maintenance of these beds enhance the cost of supplying water,
because they must be cleansed frequently--in some cases once a week.
The regulation and control of the water consumption is an important
consideration, that the rate of increase will be proportioned to the
growth of the city; and not, as in this country, an unaccountable
rapid increase due to the profligate use of water that makes
filtration impossible. Over eleven-twelfths of the water supplied to
London is filtered with the following efficiency:
=======================+=======================+=======================
| BEFORE FILTRATION. | AFTER FILTRATION.
+-----------+-----------+-----------+-----------
| ORGANIC | ORGANIC | ORGANIC | ORGANIC
| CARBON. | NITROGEN. | CARBON. | NITROGEN.
+-----------+-----------+-----------+-----------
|In parts of|In parts of|In parts of|In parts of
| 100,000. | 100,000. | 100,000. | 100,000.
-----------------------+-----------+-----------+-----------+-----------
West Middlesex Works | .209 | .071 | .198 | .043
Grand Junction Works | .262 | .042 | .231 | .032
Southwark & Vauxhall, | | | |
Hampton Works | .321 | .063 | .273 | .042
Battersea “ | .239 | .047 | .226 | .035
Lambeth Works | .273 | .067 | .258 | .038
Chelsea Works | .325 | .076 | .258 | .032
New River, Lea River | .287 | .067 | -- | --
“ New River | .375 | .059 | .227 | .043
“ “ | .350 | .084 | .246 | .042
East London Co., | | | |
Lea Water | .363 | .082 | -- | --
Waltham St. Res | .481 | .092 | .305 | .041
Thames Water | -- | -- | .159 | .030
-----------------------+-----------+-----------+-----------+-----------
Dimensions of filter beds for given volumes (from Fanning):
For 1 million gallons per diem 3 beds 60 feet × 100 feet.
For 2 “ “ “ 3 “ 80 “ × 150 “
For 3 “ “ “ 3 “ 100 “ × 180 “
For 4½ “ “ “ 4 “ 100 “ × 180 “
For 6 “ “ “ 4 “ 100 “ × 240 “
For 8 “ “ “ 4 “ 120 “ × 270 “
For 10 “ “ “ 5 “ 120 “ × 270 “
Analysis of sand from filter beds (in 100,000 parts)
ORGANIC ORGANIC ORGANIC
MATTER. CARBON. NITROGEN.
As removed from filter bed, unwashed 1523.40 314.160 38.674
After washing 804.41 94.921 16.973
It can not be doubted that a small amount of organic matter undergoes
oxidation and destruction during the passage of the water through the
sand; but, independent of this, it appears, from the above analytical
numbers, that one ton of dry sand, washed after previous use, is
capable of removing from water and retaining 16.1 lbs. of peaty
matter.
_Chemical_ filtration may be arranged under the following heads:
1. By use of alum and borax to reduce turbidity.
2. Dr. Gunning’s experiment of the waters of the River Maas, by
reducing the turbidity with .032 gramme of perchloride of iron into
one litre of water.
3. Dr. Bischoff’s (Jr.) process of removing organic matter by
spongy iron, prepared by heating hydrated oxide of iron with carbon.
4. Spencer’s process of sand filtration with crushed grains of
a carbide of iron. The carbide, it is claimed, does not require
frequent removal.
5. Sheet-iron strips placed in water decomposes organic matter
rapidly. It is recommended by eminent authority.
6. Charcoal is, possibly, the best substance for removing organisms
chemically; but its efficiency is destroyed by an insoluble
precipitate of either lime or iron. Messrs. Adkins & Co., of
London, have patented a method to overcome this objection, by use
of charcoal plates that may be easily scraped.
_Filtration through spongy iron_ (by Rivers Pollution
Commission--Parts in 100,000 parts):
ORGANIC ORGANIC PREVIOUS
CARBON. NITROGEN. SEWAGE.
Thames water, before .120 .013 1340
Thames water, after .025 .004 10
_Filtration through animal charcoal_:
ORGANIC ORGANIC PREVIOUS
CARBON. NITROGEN. SEWAGE.
Grand Junction Co.’s water, before .164 .030 320
Grand Junction Co.’s water, after .010 .002 950
SUBSIDENCE
is the most popular method of clarification of water by the
deposition of heavy matter, accomplished in large storage reservoirs.
“If the reservoir be very small and shallow, and containing not
more than a day’s supply, for example, it is plain there can be
but little opportunity for subsidence; but even in such cases,
if the reservoir be kept full, or nearly full, the floating
impurities might never enter the circulation. In the case of a
large reservoir, holding many days’ supply, it is quite different.
Time is then afforded for the heavier impurities to settle to
the bottom; and, if the water is admitted at one end and taken
out at the other end of the reservoir, very little, if any, of
the heavier particles can pass into the circulation; and we can
see no reason why any of the superficial impurities, such as
remain on or near the surface, should ever be allowed to enter
the circulation.”--(From Water Supply Commission of Engineers,
Philadelphia, 1875.)
Fanning says:
“Subsidence does not completely clarify the water even in a
fortnight or three weeks’ time.”
London has 262 acres of subsiding reservoirs for removing the
turbidity of the Thames and Lea Rivers, and used as storage at times
of sudden freshets.
Mere exposure to the air, even if accompanied by violent agitation,
is comparatively powerless for the removal of polluting organic
matter from water. Although, however, the flow of a river has thus
but little effect in purifying the water by the oxidation of the
dissolved organic matters, it has a most material influence in
the removal by subsidence of a large proportion of the suspended
impurities both organic and mineral, especially if the flow be
sluggish in places.
In passing through still pools, the turbid streams let fall its
load of grosser mechanically suspended particles, and thus the water
becomes clearer, although the dissolved impurity remains nearly as
great as ever. It is, doubtless, this clarification by subsidence
which has led to the very general but erroneous belief in the rapid
self-purifying power of running water.
RESULTS OF SUBSIDENCE.
===============================+===============================
| SUBSIDENCE FROM 100,000 PARTS.
RIVERS +----------+----------+---------
| MINERAL | ORGANIC | TOTAL
| MATTER. | MATTER. | SOLIDS.
-------------------------------+----------+----------+---------
Irwell, after flow of 11 miles | .88 | .48 | 1.36
Irwell, after flow of 11 miles | .38 | .84 | 1.22
Mersey, after flow of 13 miles | .10 | .04 | .14
Darwin, after flow of 13 miles | .54 | 1.42 | 1.96
-------------------------------+----------+----------+---------
RESULTS OF SUBSIDENCE.
===============================+===============================
| PER CENT OF REDUCTION
| OF MATTER IN SUSPENSION.
RIVERS +----------+----------+---------
| MINERAL | ORGANIC | TOTAL
| MATTER. | MATTER. | SOLIDS.
-------------------------------+----------+----------+---------
Irwell, after flow of 11 miles | 47.8 | 50. | 48.6
Irwell, after flow of 11 miles | 14.3 | 30.9 | 22.7
Mersey, after flow of 13 miles | 10.6 | 13.3 | 11.3
Darwin, after flow of 13 miles | 30.3 | 79.8 | 55.1
-------------------------------+----------+----------+---------
AERATION
is the destruction of animate life by oxidation, and is best
accomplished by placing weirs across streams, sheet flashing, or
spreading of water in thin sheets, or by roughness of beds or banks
of running waters. The benefits may be ascertained, chemically, by
the presence of nitrates and nitrites. The Water Supply Commission of
Engineers, for the investigation of the water system of Philadelphia,
say:
“This is one of nature’s processes for purifying water, not only
of the land, but of the ocean, and bodies of water deprived of it,
other processes are apt to set in. It is, therefore, desirable
that nothing should be done to obstruct this beneficial action.
We have been informed that the cutting of ice, which was formerly
allowed on the Fairmount pool, has been prohibited or discontinued.
We would especially recommend that the cutting of ice on the pool
be resumed, as an important sanitary measure, on account of the
aeration it will afford. If this were done systematically, it
might remedy, at least to some extent, the disagreeable odor which
we learn is sometimes noticed during the winter.”
The aeration adopted by Mr. Moore, Supt. of Cincinnati Water Works,
at Eden reservoir, improved the purity of the water twenty per cent.,
as shown by the analysis of Prof. Stuntz, who recommends the adoption
of the process on a larger scale.
_Covered Reservoirs_, although used by the ancients, are now being
recommended as highly beneficial to the purity of the water, by
depriving the organic germs of their propagation elements of light
and heat of the sun, preventing freezing of water, and reducing
evaporation to a minimum. Paris has two such structures. Chelsea
(London) Water-Works has one of ten million capacity that cost
$110,000.00.
The temporary hardness of water is produced by absorption of
carbonates, and may be reduced to softness by:
Distillation,
Carbonate of soda,
Boiling,
Caustic lime.
Permanent hardness is produced by sulphates, chlorides and nitrates
of lime, and magnesia, and can not be dissipated by boiling.
An imperial gallon of pure water can take up but about two grains of
carbonate of lime, but the presence of carbonic acid in the water
will enable the same 70,000 grains (an imperial gallon) to take up
twelve, sixteen, twenty, or more grains of the carbonate, and for
each grain so taken up is one degree of hardness by the Clarke scale.
The system patented by Dr. Clarke, of England, in 1856, is the most
practical method for the precipitation of lime, effected by means
of a dilution of water with slaked lime, in the proportion of one
of lime-water to ten of hard water. The system is in use in several
small places in England, notably Canterbury, where 100,000 gallons
are reduced, daily, at a cost of twenty-seven shillings per million
gallons, with the following results:
TOTAL SOLID IMPURITIES. ORGANIC CARBON. ORGANIC NITROGEN. HARDNESS.
Before, 33.60 .012 .012 26.3
After, 11.94 .0 .0 4.9
Plumstead water-works, previous to its purchase by the Kent Water
Company, of London, reduced, daily, 1,000,000 gallons by the Clarke
method. The new owners, however, abandoned it.
From the testimony of a number of reputable physicians, before the
Rivers Pollution Commission, of 1874, hard water, to a limited
extent, ten degrees, was not considered injurious, and, by some,
absolutely beneficial to health, although soft water, for a general
water supply, was preferable.
Mr. Homersham, C. E., the designer of several of these works,
testified, before this commission, that it cost £1, 7s. for
precipitating 1,000,000 gallons. To introduce this system into
London, with a consumption of 100,000,000 daily, the cost, he says,
would be $3,000,000 for plant, and requiring over thirty-three acres
of ground for basins, etc.
The relative sanitary condition of cities, in the United Kingdom,
using hard and soft water, is shown in the following table:
AVERAGE CHARACTER AVERAGE RATE
NO. OF TOWNS. POPULATION. OF WATER. OF MORTALITY
PER 10,000.
26 73,366 Not exceeding 5° 29.1
25 81,655 Above 5°, but not 28.3
exceeding 10°
60 44,797 Above 10° 24.3
London 3,254,260 From 16° to 32° 24.6
The celebrated engineer, Mr. Bateman, of England, estimates the
saving to Glasgow, by soft water, at $180,000 per annum; and if
London used the same character of water, the equivalent would be
$2,000,000 annually.
The use of lime, by private consumers, is recommended by the trustees
of the water department of Columbus, O. They say that one ounce of
lime, when added to thirty-six gallons of water, make it superior,
for washing purposes, to the rain-water usually obtained from the
cistern.