STATEMENT ON
PHOSPHATE - THE CRITICAL NUTRIENT
IN THE WATER POLLUTION CONTROL
OF LAKE ERIE AND THE GREAT LAKES
Prepared for the Natural Resources and Power
Subcommittee of the House Committee on
Government Operations.
U.S. DEPARTMENT OF THE INTERIOR
Federal Water Pollution Control Administration
Great Lakes-Illinois River Basins Project
Chicago> Illinois
August 1966
EPA 950-F-66-001
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PHOSPHATE
THE CRITICAL NUTRIENT IN WATER POLLUTION CONTROL
OP LAKE ERIE AND THE GREAT LAKES
Much study has been given in recent years to the problem of
algae and their effect on water quality of rivers and lakes. Water
is the normal environment for algae. Many varieties grow in waters
of all kinds and qualities throughout the world. They are an
important segment of the food chain from bacteria to man. As the
diet of many of the higher aquatic animals, they support the
"vegetarians" of the water world just as our agricultural crops
are the basic foodstuff for man. Algae grow in abundance under the
same general conditions as crops flourish on farmland. Sunlight,
adequate temperature, water, oxygen and carbon dioxide are
required as well as a number of simple and complex chemicals classed
as "nutrients". Any one of these, if absent, or in short supply
will retard growth of a crop. The farmer depends on nature for
adequate sunlight, temperature, water and air. He adds nitrogen,
phosphates, potassium and certain trace minerals to the soil in
order that sufficient nutrients are present to provide the crop
with all it needs for optimum growth. In effect, the farmer is
fertilizing his cropland to counteract the "Law of the Minimum".
This natural law simply states that variation in productivity
is most often determined by limitations imposed by a lack of some
nutritional element. In other words, as the least abundant
nutritional element is used up, productivity decreases. The
farmer thus provides enough nutrients and trace elements in his
fertilizer so that his crop can grow at an optimum rate with only
the factors of sunlight, temperature, water and air controlling
the size of his crop.
The growth of algae in water likewise follows the law of
the minimum. Since algae require the same physical conditions and
nutrients for growth as other plants, the size of any given crop
will depend on the supply of the most critical element necessary
for algal growth. Because the excessive growth of algae in the
lakes and streams is detrimental to our well being, control of
its growth is one of the more important functions of our program
to provide clean waters. The control of algae then becomes a
matter of eliminating or controlling one of the critical nutrients
essential for its propagation and growth. The one nutrient most
susceptible to control is phosphate. Since algae are essential
in the food chain, the problem is not one of eliminating them,
but rather to devise means for limiting the crop to a level which
will foster development of a desirable balanced aquatic biota
with a minimum of interference to important water uses.
The application of heavier nutrient concentrations to the
soil will increase plant growth, but not selectively. For example,
a given field may produce more pounds of plant life, but if the
faster growing weeds dominate the field, production of food plants
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may actually decrease. Similai"ly, increasing nutrients in a lake may
produce more pounds of fish, tut if, in the process of doing so,
conditions develop that make the aquatic environment less suitable
for the desirable commercial and sports fish, the latter will decrease
while trash fish flourish.
Prior to World War II the amount of phosphate in sewage and
municipal wastes was relatively small. Major developments in the
use of phosphorus have resulted in very significant increases in
phosphate in waste discharges. One is the widespread use of household
detergents and the other is the increase in the use of phosphorus
compounds in metal cleaning and rustproofing. Detergents alone will,
in the coming year, consume k billion pounds of phosphate. This
burgeoning use of a key nutrient ultimately becomes a part of our
waste discharges. Not only has the volume of waste water discharges
increased but the concentration of phosphate in the wastes has risen
four to five times above that found before the war. This tremendous
increase, accompanied by the greater frequency and increased extent
of reported nuisance algal blooms clearly points to the necessity of
controlling or removing phosphorus inputs into our waters if we are
to preserve them for many beneficial uses. Unfortunately, present
waste treatment technology removes very little of the phosphate
contained in the incoming waste. For example, primary treatment
removes no soluble phosphate, and removals in conventional secondary
treatment vary from ten percent up to seventy-five percent, depending
on operating and design conditions.
In summary, phosphate is an essential element of biological
life. All plants and animals require phosphate for normal growth and
reproduction. Because of its importance, it can become a controlling
factor in the rate of growth or size of crop where conditions of
limited abundance prevail, or where technical methods are available
for its reduction or removal.
A knowledge of some of the physical properties of lakes of
moderate depth is important to an understanding of the pollution problem
found in Lake Erie. In the Spring and in the Fall such a lake becomes
isothermal, that is, the temperature of the water is the same from top to
bottom. At other seasons the lake water is divided into three zones known
as the epilimnion, the thermocline, and the hypolimnion because of density
differences resulting from different water temperatures in these zones.
The epilimnion comprises the warmer upper waters of the lake, the
thermocline, the zone of rapid temperature change, which separates
the epilimnion and the colder waters of the hypolimnion below the
thermocline. With a well-established thermocline, there is little
interchange between the waters of the hypolimnion and the epilimnion
even during violent storms. The effect of separation of lake waters
by these temperature zones is the virtual isolation of the bottom
waters from the surface of the lake, thereby preventing free exchange
or absorption of oxygen from the atmosphere. In fact, conditions have
been observed under which the epilimnion or surface waters were actually
supersaturated in dissolved oxygen while the hypolimnion had little or
no dissolved oxygen. When such conditions occur, they can lead to the
disappearance of desirable aquatic life dependent upon dissolved oxygen
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which are replaced by an abundance of pollution-tolerant forms.
This changing biological life of a lake affects all forms., restricting
or eliminating fish spawning beds, eliminating the desirable
intermediates in the food chain of the sport fishery, and in many
other ways degrading the water quality of the lake.
The pollution caused by phosphate in Lake Erie is due to the
extensive production of algae which when dead drop to the lake
bottom and decay. During the processes of decay, large quantities
of oxygen are used, producing zones of oxygen depletion below the
thermocline. This has been shown by studies in past years, and
more recently by extensive studies of the Federal Water Pollution
Control Administration Lake Erie Program Office. The results of
these studies are contained in the "Report on Pollution of Lake Erie
and its Tributaries: July, 1965." This report revealed a zone of
oxygen depletion in the hypolimnion of 2600 square miles in the
central basin of the Lake. In the bottom 6 to 10 feet of water
dissolved oxygen seldom exceeded two milligrams per liter, and was
zero in many places. The productivity, and resultant decay that
caused this tremendous oxygen loss was of massive proportions. The
calculated oxygen deficit was over 270,000,000 pounds.
Some have questioned the cause of this deficit and attempt
to explain it by the "oxygen consuming wastes from, cities and indus-
tries discharging into the lake." Some simple calculations,
presented herewith, will show the practical impossibility that this
is the principal cause of the problem and will further show that it
is directly related to the algae produced from the constant daily
inputs of phosphate principally from waste sources.
Referring again to the report on Lake Erie, Table V-l in
Part 1 presents a summary of the municipal waste treatment facilities
in the Lake Erie Basin. Adding up the population equivalents of
municipal waste discharged to the basin, about 5 million PE
(Population Equivalent in terms of oxygen-demanding substances) is
treated by primary plants, another 5 million by secondary plants.
The combined waste discharges of all these plants, should they be
discharged directly to the lake, would produce an oxygen demand on
the waters of the lake of about 1.8 x 10 pounds annually. This
value is arrived at by estimating hO% BOD removal by primary
treatment, 90^ by secondary treatment, one-sixth pound BOD per PE,
and 365 days in a year. This is a sizeable oxygen demand, but not
nearly as great as the oxygen deficit found in the central basin of
Lake Erie in 196*1-. To estimate the size of the deficit found, we
calculate that for each milligram per liter of observed deficit
there are 17^0 pounds of oxygen per square mile per foot of depth
in Lake Erie. Using this factor, an average depth of 10 feet for
the deficit zone, 2600 sq. miles of deficit zone end a measured
deficit of 6 ppm oxygen, our calculation shows (17^0 x 2600 x 10 x 6) =
2.7 x 10& pounds of oxygen to be lost in this central basin.
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This deficit occurred during a period of a few weeks
when the Lake was stratified, closing off the bottom waters to
reaeration from the surface. Since the annual oxygen demanding
waste load to the lake basin is less then the deficit created within
three to four weeks, it is obvious that the oxygen consuming wastes
from the basin are not the direct cause of this problem. Yet this
problem requires an explanation. We find this explanation in the
following fact s:
Table V-8 of the report presents the soluble phosphate
inputs to Lake Erie, with a daily input of about 175., 000 pounds
as determined and estimated from all known sources. The amount
of soluble phosphate leaving Lake Erie via the Niagara River is
about 25.,000 pounds daily, therefore about 150,000 pounds per day
is accumulated in the lake. On an annual basis this is
5«5 x K>f pounds. Three pounds of phosphate can generate 100 pounds
of organic carbon. If all this phosphate were taken up by aquatic
plants and animals it would produce about 1.8 x 109 pounds of carbon.
Once this carbon becomes a part of the algae, it behaves as
any other organic carbon compound and upon the death or decay of the
algae it becomes an oxygen demanding waste substance. The ultimate
oxygen demand of carbon is 2.68 times its weight, therefore
1.8 x 10° pounds of carbon will produce an oxygen demand of U.9 x 109
pounds per year. This annual demand is at least 27 times as great
as the load produced by all the population discharges into the
lake basin. What is even more important is that this "natural"
load occurs mostly during the warm seasons, and probably in pulses,
which makes its effect on the lake much greater than if it were to
occur continuously throughout the year.
It is thus apparent that a "natural" oxygen demand is
created in Lake Erie from the phosphate inputs to the lake and that
this is the principal cause of the oxygen deficit found there.
This pollution is so large that it affects bathing beaches, fish
and aquatic life, water supply, recreation, and aesthetics.
What can be done to improve this situation? The obvious
solution is a direct reduction of phosphate inputs. In the
Lake Erie report cited earlier it was estimated that of the
175.,000 pounds of daily input, 72,000 pounds could be removed
simply by treating the municipal wastes in the basin by secondary
biological treatment, operated in such a way as to maximize phosphate
removal. This removal alone would account for hQ percent of the
phosphate that is now being metabolized in the lake and should
result in a marked reduction in algae and a corresponding improvement
in the oxygen resources of the central basin. Several weeks ago,
Secretary Udall announced a breakthrough in the problem of phosphate
removal by secondary biological treatment. He said that scientists
of the Federal Water Pollution Control Administration "found that-up
to 90 percent of phosphate in municipal sewage .can be removed by
secondary biological treatment, using modifications in plant operation
practices. This new discovery promises even better control of the
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algal problem, once the treatment plants are built and
operated to maximize phosphate removal in the Lake Erie Basin.
This announcement is attached as an appendix to this report.
The conditions that exist in Lake Erie would also
occur in Lake Ontario were it not for the greater depth of
Lake Ontario. With the phosphate inputs from Lake Erie,
plus those added by Buffalo, Rochester, Toronto and the
streams draining the watershed, Lake Ontario has a sizeable
input which produces large annual crops of algae, especially
cladophora, a type of algae that grows on submerged rocks.
However, Lake Ontario is deeper and has a thicker hypoliranion,
which provides for a larger oxygen reservoir. This does not
mean that in Lake Ontario an oxygen depletion could not
occur. It means only that a longer time will pass before
conditions match those in Lake Erie. Other conditions of
excessive algal growth have been observed including fouling
of beaches by dead cladophora and taste and odor problems in
water supplies. Quantitative data on these factors are being
obtained by the Lake Ontario Program Office of the Federal
Water Pollution Control Administration and will be put to use
in its comprehensive program of water pollution control for
the Lake Ontario basin. Because of the large Canadian population
draining to Lake Ontario, the control of phosphate inputs will
require a joint, coordinated program.
In summary, of the many nutrients subject to control most
scientists agree that the control of phosphate would provide the
best means for the reduction of algae. Their judgment is based
on the following considerations:
1. In most lakes or streams having little or no
algal problems, the phosphate levels are very low.
2. Wherever algal blooms occur, the effect can invariably
be traced to high phosphate and nitrogen levels.
3. Phosphate, when added to waters, will nearly always
result in increased numbers of algae.
h. In many instances, studies have shown that increased
phosphate inputs into lakes has resulted in explosive
increases of algal growth. Examples are Lake Zoar
in Connecticut; Lake Sebasticook in Maine, the
Madison Lakes in Wisconsin; the Detroit Lakes in
Minnesota; Green Lake and Lake Washington in
Washington; Klamath Lake in Oregon, and Lake Erie.
5. The problems of increased algal growths in lakes and
streams closely parallel the increase in use of
phosphate in modern day detergent formulations, metal
cleaning processes and the increased application of
phosphate fertilizer on farmlands.
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Since the bulk of the phosphate reaching streams and lakes
is from waste sources, principally municipal and industrial
wastes, its control can he affected through proper waste treatment.
Conventional secondary waste treatment will remove a large portion
of phosphate present in sewage or industrial waste --as much as
90$ removal has been recorded, and chemical treatment supplementary
to conventional biological treatment can remove the remaining
portion at a nominal cost. Additional controls, through research
on substitution of other chemicals for phosphate in detergents,
could provide further reductions in phosphate inputs.
The control of inputs of other nutrients, although possible,
would be less fruitful for various reasons such as: (a) The
methods of control of nitrogen inputs do not provide complete
removal (b) Nitrogen can be "fixed" by certain algae and bacteria
from the air, thereby partially offsetting its removal (c) Inputs
of potassium and iron are usually a small fraction of that already
available in the stream or lake environment (d) The factors for
control of other nutrients such as "vitamins" and trace metals are
poorly defined.
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For Release July 28, 1966
MAJOR BREAKTHROUGH IN POLLUTION CONTROL
A review of operational data on three sewage treatment plants in San
Antonio, Texas is expected to lead to the major and early breakthrough in
!
water pollution control, Secretary of the Interior Stewart L. Udall announced
i
today.
He said that scientists in the Department of the Interior's Water
Pollution Control Administration have under development a fast and relatively
inexpensive way to deal with one of the most baffling problems in water
pollution control—the explosive, water-choking, fish-killing growth of algae.
Algal blooms, a-s these aquatic malignancies are called, now constitute
a principal pollution problem in the Potomac River below Washington and countless
other water resources. It is these tiny organisms that are slowly killing Lake
Erie, threatening Lake Tahoe, and spoiling other waters all across the country.
Secretary Udall said that the newly-discovered technique for dealing with
the problem was still in the pilot stage but that work would begin immediately
to make it operational at the earliest possible time. Studies are already
under way to apply the new knowledge to the lower Potomac, Secretary Udall
said.
In brief, what the scientists at WPCA are working on is a way to cut off
the food supply on which algae thrive so that they will literally starve to
death and in time disappear. . •
This can be done, moreover, according to WPCA, with relatively simple
modifications of current waste treatment techniques. Normally, the most
complete waste treatment now in use removes most of the impurities from
domestic wastes — except phosphates. And these phosphates provide algae with
a rich food supply.
Water pollution experts have been trying for years to find an economical
way to remove phosphates in large scale waste- treatment operations. As is
often in the case of scientific investigations, the clue the experts were
looking for came about almost by accident.
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Operational data on waste treatment works, around the country are
regularly reviewed for various purposes by scientists and engineers of the
Water Pollution Control Administration in Washington. This is one of the
ways they have of determining how the water pollution control methods are
progressing from month to month.
In the course of these reviews it became evident.'late last year that
either there was something wrong with the data on the three plants in San
Antonio or that there was something going on there that was worth looking
into.
The reports on two of the plants were like the reports on other such
plants anywhere in the country. The plants were performing very effectively,
with typically low phosphate removal. •
But for some reason, virtually no phosphates were getting through the
'other, plant. Yet it is basically the same kind-of plant as the other two
and treats the same kind of wastes.
Dr. Leon Weinberger, Assistant Administrator of WPCA for research and
development, started an investigation.
For four months, scientists and engineers from the WPCA's Robert S. Kerr
Research Center in Ada, Oklahoma, studied the San Antonio plants in every
detail. Now they know the answer.
A secondary waste treatment plant, such as those in San Antonio and
elsewhere, employ an activated sludge process involving two principal stages--
settling and aeration, and the use of bacteria to break down and assimilate
biological impurities that remain after the settling-out stage.
The operation of such plants is effective by their structural and hydraulic
design and by the rate of input of the liquids being treated, the amount of '
aeration, the concentration of bacteria used, and other operational features
which can be modified. The WPCA investigators found that the San Antonio
plant with the high phosphate removal was being operated differently from the
other two in a number of ways, • . .
They then changed five of the operational features of one of the other
plants--one that had been removing no phosphates—and phosphate removal
suddenly shot up to over 90 percent.
The investigators got this result by increasing the aeration, increasing
the concentration of bacteria, reducing the time for settling, decreasing the
time that settled materials remained in the settling tank, and increasing the
ratio of bacteria to organic materials. It is. not yet known what brought
about the increased phosphate removal--whether it was the result of one or
several or all of these changes.
Since then, wastes at several other plants around the country have been
treated experimentally in the same manner and without exception, very high
phosphate removal has been achieved.
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Pollution control, experts at WPCA pointed out that with the mounting algae
problem, interest in phosphate removal has been intensifying in recent years
•and that a considerable amount of research and developmental work by industry
is under way in this area.
Dr.- Weinberger said that WPCA scientists and engineers will begin an
intensive program of coordinated investigations with non-governmental researchers
in an attempt to accelerate the development ^s-f maximum*removal of phosphates as
a regular part of municipal waste treatment. ' -
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