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THE NECESSITY OF COMPETENT SUPERVISION AND
CAREFUL LABORATORY CONTROL IN THE OPERATION
OF WATER PURIFICATION PLANTS 1
By Lewis I Bihdsall 2
Eternal vigilance is the price of pure water. Every water puri-
fication plant from the smallest liquid chlorine installation to the
largest and most complete filtration plant should be operated under
competent supervision and careful laboratory control.
The cheapness and demonstrated effectiveness of liquid chlorine
as a sterilizing agent for water supplies have induced many water
works officials in Minnesota, as elsewhere in the United States, to
rely on chlorine as the sole means of water purification. Such an
installation may, however, merely afford a false sense of security.
Failure to keep up the chlorine treatment continuously and in amount
sufficient for sterilization of the water may mean a typhoid fever
epidemic in the community. This danger is greatest among the
smaller water works plants where one man is frequently responsible
for the operation of the pumps and the chlorine machine. The
result is that the pumps get most of his attention and the chlorine
machine is neglected.
There are many water works plants, and among them some that
are not small plants, that rely for chlorine sterilization on one
machine only, so that when it is necessary to change chlorine cylinders
or to make necessary repairs, the chlorine feed has to be discontinued.
Too much stress cannot be placed on the necessity of duplicate
installations of liquid chlorine machines wherever used, so that when
one machine is taken out of service the other may be put in service
immediately and continuous treatment be obtained. There should
also be kept on hand a supply of extra parts for the chlorine machines,
so that ordinary repairs may be quickly made in case of emergency.
1 Read before the Minnesota Section, December 6, 1919. Discussion of this
paper is requested and should be sent to the Editor.
2 Superintendent of Filtration, Water Works Department, Minneapolis,
Minn.
382
SUPERVISION OF WATER PURIFICATION 383
Our state boards of health should require duplicate installations of
liquid chlorine machines and it would also appear that the manu-
facturers of the machines might be led to see the advantage to
themselves as well as to the various communities served, in making
a substantial reduction in the selling price of two machines to the
same purchaser as compared with the price of one machine. The
price of repair parts should also be kept as low as possible and all
users of the machines be urged to keep a supply of extra parts on
hand.
Chlorine cylinders that are in service should be placed on scales
and a record be kept of the weight of the cylinders every hour, not
only as a check on the manometer gauge of the chlorine machine
but also to accustom the operators of the plant to inspect the
machines frequently to see that they are working properly. The
scales prevent chlorine cylinders from going empty unexpectedly
and the recorded weights serve as a check on the faithfulness of the
operator provided that the amount of water treated each hour is
accurately determined.
But how shall we know that we are adding the proper amount
of chlorine to the water in order to obtain sterilization at all times?
There is no general rule for the amount of chlorine to use. The
suspended matter, dissolved organic matter and the bacterial con-
tent of surface waters, especially river waters, are constantly chang-
ing. The amount of chlorine necessary for sterilization of the water
is influenced by all three of these factors. A filtered water or a
fairly clear and pure water requires less chlorine than does a turbid
water or one containing a large amount of dissolved organic matter.
Whereas a treatment of 0.3 part per million (2| pounds of chlorine
per million gallons) may be satisfactory in the first case, a much
larger dose is required in the latter instance. Residual tastes and
odors must be considered in the treatment of some unfiltered waters.
A slight variation in the amount of chlorine added may mean either
under-treatment and lack of sterilization or over-treatment and
complaints from the water consumers. Sterilization takes place less
readily in cold water than it does in warm water, and so it is neces-
sary to allow a longer period for the reaction in winter than in sum-
mer. Experience has shown that free chlorine disappears much
more rapidly from the treated water when the water is passed through
iron pipes than when it goes through a concrete conduit.
384 LEWIS I. BIRDSALL
It is evident that in order to regulate the chlorine treatment
properly there must be laboratory control. The test for free chlorine
in the treated water, and the determinations of the number of
bacteria and the presence or absence of B. coli in the untreated
and treated waters offer such control tests. Because of the lag of
48 hours in the results of the bacteriological tests made necessary
by the incubation of the inoculated media, it is advisable in most
plants to add sufficient chlorine to the water to produce a slight
residual free chlorine content of approximately 0.05 part per million.
Some waters, as stated above, do not permit of over-treatment,
but such waters are comparatively few, and where they occur, the
treatment requires very careful supervision. In the majority of
cases, therefore, the chemical test for free chlorine becomes the one
on which we rely for sudden changes in the chlorine treatment, and
the test should be made several times each day. The bacteriological
tests indicate the results of the treatment and demonstrate the
purity of the treated water. They should be made daily on both
the untreated and treated waters.
Chlorine is comparatively cheap, much cheaper than human
lives, and therefore it is much more desirable to over-treat a water
supply with chlorine than to under-treat it, if reliance for purifica-
tion is placed on chlorine alone. A chlorine taste in the water,
even though it may be unpleasant, is less harmful to the water
consumers than a tasteless water that contains typhoid bacilli.
Chlorine sterilization is a valuable adjunct to other methods of
water purification, but it should not be depended upon as the only
line of defense between a seriously polluted water supply and the
water consumers, unless it is so used as a temporary expedient and
then only under the most careful supervision.
The laboratory tests necessary for the control of a filter plant
are more comprehensive and elaborate than those described for
a chlorine plant. Turbidity, color, alkalinity and the bacterial
content of the untreated water usually determine the amount of
chemical necessary for proper coagulation of the water before it
goes to the filters. The same tests on samples of the water as it
goes to the filters from the coagulation basins determine the effi-
ciency of the pre-treatment. A properly coagulated and filtered
water should have no turbidity and a color of 10 parts per million
or less. The bacterial content of the filtered and sterilized water
SUPERVISION OP WATER PURIFICATION 385
should be as near zero as possible and B. coli should be absent in
50 cc. amounts of the water.
An odor in the untreated water may be caused by algae and a
microscopical examination of the water will disclose the offending
organism. Odors from manufacturing wastes are sometimes more
difficult to eliminate from the water than are those from micro-
organisms. Tests for odor should be made on both the untreated
and the filtered water.
The alkalinity test demonstrates the presence of carbonates and
bicarbonates in the untreated water, and whether or not they are
sufficient in amount to decompose the coagulant to be added. The
filtered water should at all times have residual alkailinity as a safe-
guard against the presence of undecomposed coagulant.
Free carbonic acid frequently occurs in surface waters. A deter-
mination of the amount present should be made where lime is used
in conjunction with iron sulphate as coagulant. The amount of
free carbonic acid in the filtered water should be determined because
of the part it plays in the corrosion of exposed iron surfaces in dis-
tribution pipes.
The test for residual chlorine is essential, as already described
above.
Total hardness tests are made at intervals for the purpose of
record. Complaints regarding the hardness of the water supply
are more easily answered if data are at hand to show that the filtered
water is no harder than the untreated water and that the hardness
of the water is greater at certain times of the year due to natural
causes.
Complete sanitary chemical and mineral analyses of the untreated
and filtered waters are made each month in the larger filtration
plants for the purpose of record. These data are not necessarily
essential for the proper operation of the plant but they are of value
for reference.
Analyses of the chemicals used for water purification are valuable
and there should be frequent tests of the chemical solutions that
are added to the water.
The most essential laboratory tests for the proper control of a
filtration plant are those for turbitity, color, alkalinity, residual
chlorine, number of bacteria per cubic centimeter and B. coli. The
data obtained from these tests will enable the operator to handle
his plant economically and efficiently. He will at all times have the
386 LEWIS I. BIBDSALL
satisfaction of knowing the quality of the untreated water and the
degree of purification obtained by the plant. The health of a com-
munity is the final test by which the purity of a water supply is
judged, but the operator of a water purification plant who knows
each and every day that the water he is supplying is of the highest
purity has nothing to fear from health statistics.
A water softening plant requires certain special laboratory tests
in addition to total hardness, alkalinity and free carbonic acid
determinations. Only under laboratory control can a softening
plant be properly operated.
It seems almost inconceivable that anyone should attempt to
operate a water purification plant without daily laboratory control
tests, but experience has shown that many plants are so operated.
An occasional bacteriological analysis of a water supply, whether
monthly or weekly, has little significance. It merely shows the
condition of the water at the time the sample was taken. The
splendid work of the Sanitary Division of the Minnesota State
Board of Health is tending to raise the standard of water purifi-
cation plants in Minnesota and to demonstrate that the saving of
human lives rather than dollars is the high ideal we should have
constantly before us.
Texas has set an example to other states by organizing a short
course for water works superintendents and purification plant
operators at the University of Texas. The local sections of the
American Water Works Association can do no greater good for
their communities than by stimulating interest in the organization
of similar courses of instruction in their state universities and then
urging the water works men to attend these courses. The farmers
long ago realized the value of short courses at the State University
and now attend them annually. Why cannot the Universities do
for the water works men what they have done for the farmer? The
possibilities for education in this new field are unlimited.
Many small water purification plants are unable to pay the salary
of a competent analyst. Such plants no doubt have some employee
who could learn to perform some of the more simple routine tests,
such as those for turbidity, color, alkalinity and free chlorine, pro-
vided the necessary chemical solutions are prepared for him. The
bacteriological tests are somewhat more difficult, but even these
can be performed by such an employee if he shows an aptitude for
the work and provided the necessary media can be furnished. A
SUPERVISION OF WATER PURIFICATION 387
competent water purification expert could no doubt be employed
by a number of such plants at a comparatively small expense to
train the operator, interpret the laboratory results thus obtained,
furnish the necessary chemical solutions and bacteriological media,
supervise the general operation of the plant, and visit the plant
periodically. Such an arrangement obtains in some sections of the
United States and has been found to work very satisfactorily.
A water purification plant that is operated without laboratory
control is merely furnishing a false sense of security to the com-
munity. The same plant when operated under laboratory control
and competent supervision can and should yield a safe and pure
water at all times.