shovels, but more efficiently and more exactly, was developed by
George P. Baldwin, M. Am. Soc. C. E., under the general supervision
of the Bureau of Filtration, of which the writer was in charge.
However, on account of the unfortunate and earlier arrangement of
other constructive matters, which the City's Legal Department
advised could not be changed without upsetting the contract, the
entrance doors to the original forty-six filters were not built
large enough to permit the rapid and economical transfer of these
machines, and, as this act takes so large a proportion of the total
time of operation, it has not been found economical to use them. The
additional ten filters, recently constructed, with doors especially
designed and large enough to pass the machines, have not yet been
placed in operation. This is said to be on account of lack of funds
and of employees. Therefore, there has been no opportunity to
demonstrate what the scraping machines can do, under the conditions
for which they were designed to operate. The restoring machine, a
complementary device in mechanical operation, which simply replaces
the sand in the same condition that it would be if wheeled back,
but, with a small percentage of moisture, has accomplished its
purpose well and economically. The sand is placed in the filters so
that there is no further settling; with a smooth surface, needing no
additional adjustment; with absolutely no possibility of sub-surface
clogging; and with the filters starting off exceedingly well in
operative results.
_Washington Methods._--In Washington, it is stated that the filters
are still cleaned by the old-fashioned method of scraping with
shovels, throwing the sand into piles, and afterward removing it
with a movable ejector. Between scrapings there is also an
occasional mid-period action of raking the unwatered sand surface,
for the purpose of stirring up the dirty film. This process does not
remove any of the clogging material from the bed, but it is said
that no injurious effects are produced, and that it is economical.
It is stated that the so-called "Brooklyn method," of stirring the
surface of the sand while the water is on the bed, has been tried at
Washington, but with unsatisfactory results. It seems to have been
advocated with greater fervor in some other places.
The method of dry raking does not remove the dirty material, but
loosens up the pores of the surface, and through this porosity
permits clogging to penetrate deeper into the filter. The method of
raking with water on the bed, although it removes some of the
organic dirt, also permits deeper penetration of the remainder. The
latest devised system of washing the sand in place, by upward
spraying with water, called the "Blaisdell method," thoroughly
destroys the _Schmutzdecke_ above, and, at the same time, must
permit the formation of a subsidiary one below. In the Nichols
method, the material removed by shovel scraping is conveyed by an
ejector to a portable separator, where it receives a single washing;
the dirty water overflows to the sewer, while the washed sand is
discharged through a hose and deposited on the recently scraped
surface. As the latter is partly impregnated with impurities, there
is, by this process, a tendency toward sub-surface clogging.
All these processes are marked and serious departures from the
well-tried method of cleaning slow sand filters, which, it is well
known, will operate successfully to purify polluted river waters and
make them safe to drink. In all there is the danger that they have
not been sufficiently and carefully tried, under scientific
observation, as to results and possible effects on the public
health, to be sure that the bacterial efficiency can long continue
to be satisfactory, with the application of specifically infected
waters. It is dangerous, and may even jeopardize the safety of human
lives, to experiment on water which is furnished for drinking
purposes. There is also the added danger, well known from past
experience, that in a few years (it may be more or less, depending
on the extent and intensity of the new workings) the filters will
need renovation, partly, if not wholly, throughout the entire bed.
Thus, considering the total cost during a long term of years, the
apparently cheaper method may become the most expensive.
There is also an interesting query in regard to the Washington
method of replacing sand in the filters, and it is worthy of most
careful thought and attention. If the process described can be
carried on with success and safety, it will prove to be a long and
progressive step in the methods of operation. The difficulty,
however, is in determining from any short-term runs whether such a
process can be continued permanently without impairing the
efficiency of the sand bed. Apparently good conditions may change,
after a few years' trial, and be followed by unsafe results and
predicaments. This replacing of sand with whatever dirt and detritus
may travel with it in the carrying water is certainly not equivalent
to the care with which it has been understood that sand should be
deposited in filters. It is not comparable with the care with which
it is placed, when wheeled from a washer, where dirty water
overflows the lip, or where it is placed by a machine restorer in
the filter, where the transporting water also overflows the weir and
is carried to the sewer.
These cheap and rapid methods of doing the work, advanced in the
interests of economy, and the idea that sand filters, receiving
polluting waters, can operate at higher rates than those which we
have demonstrated, and, therefore, have been led to believe are
safe, is a speeding up of the whole organization and of operating
conditions. It is like speeding up a machine for the purpose of
getting a greater output, with the usual result that fast running
means quicker wearing out of both man and machine. Quicker
operations generally mean carelessness in doing the work, especially
in municipal service. Carelessness is engendered by the thought that
such work can be handled in a rough and rapid way, and, further, by
the ridicule of all these things, which we have learned to be
careful about, as old-fogyish, out-of-fashion, and archaic.
Carelessness in operation breeds contempt for the art. Some of the
less efficient filter plants, from the standpoint of effect on the
public health, may reflect such ill-considered methods
_Economy with Efficiency in Operation._--It is particularly important to
find out whether one can secure the desired economy, and, at the same
time, the required efficiency. The development of efficiency in every
line of human endeavor is receiving much attention at present, and not
the least cause for this is the growing recognition of the demand for a
high standard of service for the expense caused. One of the first
requirements is to have well-defined ideals and standards. When one
knows how to secure a good and safe result, it is unwise to depart
therefrom for a mere whim, or to secure a supposedly lessened expense,
unless other facts be also determined favorably. The desire for economy
must be tempered by good sense, which means that one should be willing
to change a method only when the wisdom of such has been clearly
demonstrated. Efficient service can only be secured by strict
discipline, accompanied by fair dealing. This means employing no more
men than are actually necessary, paying them on the basis of the
standard of service and output produced, taking an interest in the
working conditions, and providing for their health and welfare.
About twelve years ago, the writer made some investigations of the
efficiency of laboring gangs in scraping and handling sand at filter
beds,[1] and found that ten men was the most economical number to
use in scraping the surface of the Lawrence filter, as then built
and operated. This result was determined by numerous studies of the
output per man per minute, with different numbers of men working
under different conditions. This same sort of study has been carried
further by adepts in the art, in reference to shop and similar
management, but one fails to find corresponding development along
this line in municipal organization except by a few of the scattered
Bureaus of Municipal Research. These results, also, have related to
a few of the more common and general factors, such as determining
the cost per mile, or per square yard, of street cleaned, or per
million gallons of water pumped.
[Footnote 1: _Transactions,_ Am. Soc. C. E., Vol. XLVI, p. 291.]
The cost of the management of water-works, one of the largest
factors of public enterprise, has never been investigated
extensively and thoroughly. There is much possibility in planning
for greater efficiency and in determining what can be accomplished
under economical administration. Every one is aware of the
multiplicity of men in municipal service. Some of these are entirely
incompetent, others partly so; the recent appointees may be more
efficient, but the majority of them gradually deteriorate under the
subtle influence of the prevailing atmosphere, and each new incoming
administration places more and more men on the work, without reason
or necessity. All these tendencies have made the cost and
maintenance of public work greater and greater, and, at the same
time, have resulted in frequently and steadily decreasing the output
and efficiency per employee.
The Washington situation, however, presents an admirable contrast to
this, because of the methods of administration of the public works
of the District of Columbia and their freedom from petty political
influence. The limited number of employees has tended toward
economy, and rendered this plant the envy of all who have desired to
obtain good management. Its cost items have been looked on as a
result long hoped for, but seldom obtained. It is to be regretted,
therefore, that such an abrupt change in methods of removing
clogging material and replacing sand has taken place without years
of experimental trial on filters not furnishing drinking water to
the public, and without an attempt, under such excellent conditions,
to maintain the efficiency by a better labor output and by improved
working and machine methods in the performance of the older and
established order of doing things.
In preparing water for the use of the people, the realms of the
unknown are so much larger than those which have been investigated
and developed that there may be many undiscovered factors affecting
the public health, and many ways in which it is dangerous to depart
from well-known and surely safe methods. Who can say that in some
subtle and, at present, unknown manner, the failure in some places,
where filtration is practiced, to reduce the death rate from typhoid
fever may not be due to the introduction of radical departures from
the older, slower, safer, and more efficient methods which have
produced such excellent results, both in America and in Europe?
Further, in cases where there has been a falling off in the typhoid
death rate, the failure to secure an accompanying improvement in
general health conditions, which follows so closely in communities
supplied by water filtered in accordance with the more conservative
principles, may be due to the introduction of some of these not
thoroughly tried processes. Some day full information may be
available as to the influence of these methods of plant operation on
the health of the community. Until that time, is it not a much
better policy to follow the principles which have been proven by
many years of experience to produce safe results, and to make the
foremost object the improvement of the methods of operation in
accordance with these established truths?
There is opportunity for the upbuilding of greater efficiency in the
conduct of employees and in securing the maximum output, by
establishing more comfortable and healthful conditions than usually
exist. The elimination of political influence from municipal service
is also a task which challenges the people of to-day, and the
operating and managing engineer is in a position to perform an
important part in accomplishing this end. The number of employees
can be reduced to those actually needed, and the way opened for the
employment of men who thoroughly understand the necessities of
honesty and efficiency in the conduct of public affairs. It should
be remembered that to design and construct well is only half the
job; to operate economically and efficiently is even more of a
problem than to build, and requires just as good talent, just as
keen appreciation of the various problems, and is even more
essential to public welfare. It seems to the writer that the logical
development of the art of obtaining economy as well as efficiency
should be along these lines, rather than to revolutionize methods,
without having a long-period test of their value, and at the same
time allow political influences to control, to a large extent, the
labor item.
_Preliminary Treatment._--The decision as to the preliminary
treatment of the Potomac River water before filtration is of
interest, particularly because various other conclusions have been
reached in different sections of the country. However, in the main,
these decisions have been due to differences in the character of the
waters, but it must be evident that they have sometimes been the
result of ill-considered action, or the desire to promote some
special interest. The use of preliminary filters, which involves a
large investment, is not always to be commended, particularly
because at times of reasonably good water the removal of some of the
organic matter is really injurious and lessens the effect of the
final filters.
For a long time, the writer has believed that, where other things
are equal, and where there is no important reason for double or
preliminary filtration, long periods of storage, accompanied by the
use of coagulant at times of severe and extreme muddiness, as
planned at Washington, solves the problem in the most practical and
economical way. It is true that the investment for a large storage
basin may equal, or even exceed, that required for preliminary
filters; but the influence of storage on the quality of raw water is
never injurious, and, by ripening the condition of the water, may be
greatly beneficial in the process of filtration.
The storage available in such a basin makes it possible to shut off
the supply from the river during the worst conditions of the water.
The duration of the most troublesome spells ordinarily does not
exceed a few days, and it is usually possible to secure sufficient
capacity in the basin to tide over these periods. Then again, long
periods of storage, in addition to assisting in breaking up organic
matter, permit the dying out of bacteria, particularly many of the
pathogenic kind, and, therefore, the water is rendered much safer
from this standpoint. In other words, there is additional insurance
in long storage against the faulty and careless operation of
incompetent filter employees. The addition of coagulant, especially
the fact that only a very small investment of capital is required
for the necessary apparatus for dosing the water, and that the cost
of the coagulating materials has to be met only when used, seems to
give the process, in a most satisfactory manner, the requirement for
economical management and thoroughness in preparing the water for
final filtration.
_Parking Public Works._--It is disappointing that the author has not
mentioned some of the steps contemplated in reference to the
landscape treatment of the Washington filtration area. Probably
every one has been impressed by the barren aspect of the works as
they are approached, and as one looks over them. Recently, however,
it is stated that some steps have been taken to lay out the grounds,
treat the surface in an attractive manner, and make a park of the
area. The writer has a firm opinion that when an investment is made
for public works, it costs but little in addition to construct
buildings along appropriate architectural lines, to treat the
grounds in a pleasing manner, and to make the entire works a credit
to the municipality from an artistic standpoint. When treated on
broad lines, such areas become public parks, and afford open
breathing places for the residents, and, if near centers of
population, may well be equipped with playground facilities for the
children. When thus developed they should have care, that the
planting and equipment should not deteriorate and the last state
become worse than the first.
The influence which these ever-present examples of attractiveness
have on the community is becoming better recognized by students of
social progress, and there seems to be no doubt that spending money
on such features is not only desirable from the artistic standpoint,
but is justified on practical grounds as well. It is cheaper than to
create parks, when necessity and demand can no longer be resisted,
by buying property and occasionally tearing down buildings and
constructing _de novo._ That this work is now being done in
Washington, even after construction, is certainly a recognition of
the advisability of original efforts in this direction.
~George C. Whipple, M. Am. Soc. C. E.~ (by letter).--Mr. Hardy's
paper is an excellent presentation of the results of the operation
of the Washington water filtration plant from the time of its
construction in 1905 until June, 1910. Papers of this character are
altogether too infrequent, and the actual results from the filters
now in use are not readily accessible in detailed form. Yet it is
only by studying the results obtained by filters in actual use that
improvements can be made and the art advanced.
Among the many important facts brought out by Mr. Hardy, only a few
can be selected for discussion. One of these is the operation of
filters under winter conditions. It is well known that the
efficiency of sedimentation basins and filters is lower during
winter than at other times, yet it is just at this season of the
year that there is the greatest danger of typhoid fever and similar
water-borne diseases being transmitted by water. Most of the great
typhoid epidemics have occurred during cold weather, and the very
use of the term "winter cholera" is of significance. Apparently,
typhoid bacilli and similar bacteria are capable of living and
retaining their vitality longest during that season of the year.
Just why this is so, bacteriologists have not satisfactorily
explained. Doubtless many factors are involved. Because of the
increased viscosity of the water, sedimentation takes place less
readily at lower temperatures, and inasmuch as sand filtration is
partly dependent on sedimentation, the efficiency tends to fall off
in cold weather. During winter some of the external destroying
agencies are less potent, such as the sterilizing effect of
sunlight, and the presence and activity of some of the larger forms
of microscopic organisms which prey on the bacteria. Another factor
may be the greater amount of dissolved oxygen normally present in
water during cold weather, as experiments have shown that dissolved
oxygen favors longevity.
Still another reason for the larger numbers of bacteria that pass
through a water filter during cold weather may be the effect that
the low temperature has on the size of the bacteria themselves. A
few experiments made recently by the writer appear to indicate that
at low temperatures the gelatinous membrane which surrounds the
bacterial cells tends to become somewhat contracted, thus decreasing
the apparent size of the bacteria as seen under the microscope.
Either this contraction occurs, or the cells themselves are smaller
when they develop in the cold. It is possible also that low
temperature affects the flagella of the organisms in the same way.
It is not unreasonable to suppose that the effect of low temperature
is to form what may be, in effect, a protective coating around the
cells, which tends to make them smaller, less sticky, and less
subject to outside influences. This would tend to make them pass
through a filter more readily. In line with this idea also is the
well-known fact that disinfection is less efficient in cold water
than in warm water.
Another way of viewing the matter is that cold retards the growth of
bacteria on the filter, thus reducing the effect of the
_Schmutzdecke_. Still another view of the greater danger from
bacterial contamination in winter is the theory that cold prolongs
the life of the bacteria by merely preventing them from living
through their life cycle and reaching natural old age and death as
rapidly as in warm weather.
Another topic in Mr. Hardy's paper which has interested the writer
is that of preliminary filters. The experiments described at length
indicate clearly that such devices would prove of little or no
benefit under the conditions existing in Washington, and that when
the river contains considerable amounts of suspended clay nothing
less than chemical coagulation will suffice to treat the water so
that the effluent will be perfectly clear. Preliminary filters have
been used for a number of years at various places and with varying
success. In few instances have they been operated for a sufficient
length of time or been studied with sufficient care to determine
fully their economy and efficiency as compared with other possible
methods of preliminary treatment.
Among other experiments on this matter are those made at Albany, N. Y.,
and published by Wallace Greenalch, Assoc. M. Am. Soc. C. E., in
the Fifty-ninth Annual Report of the Bureau of Water for the year
ending September 30th, 1909. The Hudson River water used at Albany
is quite different in character from the Potomac River water used at
Washington, as it is less turbid and contains rather more organic
matter. The results obtained in these experiments showed that during
the summer the number of bacteria in the effluent from the
experimental sand filter used in connection with a preliminary
filter did not differ widely from the number found in the effluent
of the city filter where there was no other preliminary treatment
than sedimentation. In the winter, however, the numbers of bacteria
did not increase in the effluent from the experimental filter as
they did in the effluent from the city filter. This is shown by
Table 26, taken from the report mentioned.
Apparently, therefore, at Albany the benefits of the preliminary
filter, as far as bacterial efficiency is concerned, would be
confined to a short period of three or four months in each year.
Under such circumstances it may well be questioned whether the
advantages of preliminary filtration justify its cost.
~Table 26--Results of Experiments with
Preliminary Filter at Albany, N. Y.~
==========+==========+==========+============+=============
Month, | Bacteria | Bacteria | Bacteria in|Bacteria in
1906. | in raw | in pre- | effluent | effluent
| water. | liminary | from | from
| | filter |experimental|city filter.
| | effluent.|sand filter.|
----------+----------+----------+------------+-------------
March | 133,480 | 36,000 | 151 | 706
April | 77,420 | 4,810 | 72 | 155
May | 15,800 | 2,250 | 48 | 37
June | 4,520 | 358 | 38 | 34
July | 2,090 | 163 | 25 | 22
August | 2,740 | 121 | 36 | 22
September | 8,280 | 445 | 20 | 24
October | 38,350 | 4,235 | 67 | 227
November | 67,910 | 15,570 | 337 | 341
December | 645,500 | 25,440 | 144 | 2,783
----------+----------+----------+------------+-------------
1907. | | | |
January | 127,560 | 4,660 | 48 | 443
February | 28,000 | 1,800 | 13 | 116
==========+==========+==========+============+=============