EPA-R3-73-026
JANUARY 1973 Ecological Research Series
The Shagawa Lake Project
^ PRO^°
National Environmental Research Center
Office of Research and Monitoring
U.S. Environmental Protection Agency
Corvallis, Oregon 97330
-------
RESEARCH REPORTING SERIES
Research reports of the office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
<*. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ECOLOGICAL
RESEARCH series. This series describes research
on the effects of pollution on humans, plant and
animal species, and materials. Problems are
assessed for their long- and short-term
influences. Investigations include formation,
transport, and pathway studies to determine the
fate of pollutants and their effects. This work
provides the technical basis for setting standards
to minimize undesirable changes in living
organisms in the aquatic, terrestrial and
atmospheric environments.
-------
EPA-R3-73-026
January 1973
THE SHAGAWA LAKE PROJECT
ERRATA SHEET
A printing error has resulted in transposition of pictures
for Illustrations 15 and 16, pages 45 and 46, in the
Appendix.
-------
-------
EPA-R3-73-026
January 1973
THE SHAGAWA LAKE PROJECT
LAKE RESTORATION
BY NUTRIENT REMOVAL
FROM WASTEWATER EFFLUENT
K. W. Malueg, R. M. Brice, D. W. Schults and D. P. Larsen
Pacific Northwest Environmental Research Laboratory
200 S. W. 35th St.
Corvallis, Oregon 97330
January 1973
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
CORVALLIS, OREGON 97330
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402
Price 85 cents domestic postpaid or 60 cents QPO Bookstore
-------
PROTECTION
-------
ABSTRACT
The U.S. Environmental Protection Agency (EPA) has initiated
a research project at Ely, Minnesota, to demonstrate the restoration
of eutrophic Shagawa Lake by nutrient removal (primarily phosphorus)
from municipal wastewater effluent while permitting such treated
effluent to continue to flow into the lake.
Studies utilizing an advanced wastewater treatment pilot plant
showed that phosphorus could readily be removed and the treated
effluent did not promote algal blooms in the receiving waters.
The National Eutrophication Research Program (NERP) of EPA began
operating and evaluating a full-scale advanced wastewater treatment plant
in early 1973. Nutrient removal in the plant is primarily by chemical
precipitation with lime and is designed to give a final effluent
of 0.05 mg/1 total phosphorus or less.
NERP will evaluate the extent and rate of recovery of Shagawa
Lake until at least 1976. Lake data for this period will be compared
to that obtained during the six years prior to advanced wastewater
treatment.
-------
CONTENTS
Page
Introduction 1
History of the Development of Shagawa Lake Restoration
Project 2
General Description of Shagawa Lake 3
Advanced Wastewater Treatment Pilot Phase 5
Algal Growth Potential Studies 5
Limnology of Shagawa Lake 14
Full-scale Lake Restoration Demonstration Project 20
Modeling of Shagawa Lake Data 27
Summary 31
References 33
Appendix 35
-------
FIGURES
1 Shagawa Lake Project Site
2 Large Basin (150,000 gallon) Batch-Type Experiment
with Chlorophyll a_ 8
3 Effect of Addition of Three Concentrations of
Phosphorus and of Secondary Effluent on Chlorophyll
a_ Levels in Burntside River Water 10
4 Effect of Addition of Three Concentrations of
Phosphorus with Nitrogen, and of Secondary
Effluent on Chlorphyll a_ 11
5 Maximum Chlorophyll a^ Levels Attained in Burntside
River Water Following Addition of Indicated Nutrients .... 12
6 Maximum Chlorophyll a^ Levels Attained in Shagawa
Lake Water Following Addition of Indicated Nutrients 13
7 Effect of Phosphorus Additions to Tertiary
Effluent upon the Growth Response of Selenastrum
capricornutum 15
8 Effect of Nutrient Additions to Burntside River
Water on the Growth of Selenastrum capricornutum 16
9 Organizational Structure 22
10 Flow Diagram 24
11 Process Diagram 25
12 Lime Reactions 26
13 Model of Phosphorus Cycle in Shagawa Lake 29
-------
TABLE
Analytical Values of Effluent from Tertiary
Sewage Treatment Pilot Plant
-------
INTRODUCTION
The progressive enrichment of a body of water with aquatic plant
nutrients and the response of this body of water in terms of increased
biological production and its consequences is known as eutrophication.
Lakes typically evolve from a state of low productivity and relative
purity to one of increased productivity and lessened quality, often
culminating in nuisance algal growths, drastically reduced oxygen content,
and noxious tastes and odors. Under natural conditions this is a
lengthy process, requiring perhaps hundreds or thousands of years.
Where a lake is subjected to heavy human population pressure, however,
eutrophication proceeds much more rapidly. Human waste disposal greatly
increases the rate of flow of nutrients into lakes and thereby profoundly
affects the rate and extent of the eutrophication process. This
phenomenon is known as accelerated or cultural eutrophication and
constitutes a major environmental problem.
In recent years scientists and laymen alike have expressed concern
with the deteriorating quality of our aquatic resources. Their demands
for action have prompted investigations of lake restoration techniques
effective in reversing the tendencies of lakes to be overly productive.
Lake restoration techniques which have shown promise in pilot or full-scale
demonstrations include diversion of wastewater effluent around a lake,
in situ chemical treatment of a lake to precipitate nutrients, aeration,
and dredging. Another technique thought to hold promise but not yet
scientifically studied is that of advanced wastewater treatment. The
objective of the Shagawa Lake Project is to demonstrate the restoration
-------
of a eutrophic lake by removing a critical algal growth-promoting
nutrient--phosphorus--by advanced treatment of municipal wastewater while
permitting such treated effluent to continue to flow into the lake. If
this project is successful, the technique could be applied worldwide
to many eutrophic lakes.
HISTORY OF THE DEVELOPMENT OF SHAGAWA LAKE RESTORATION PROJECT
Numerous potential lakes were investigated to select an appropriate site
to demonstrate the restoration of a eutrophic lake by the utilization
of advanced wastewater treatment. Shagawa Lake was chosen for the
following reasons: 1) it had a history of algal blooms; 2) there was
no significant agriculture and industry in the area; hence, municipal
wastewater was the major source of nutrients to the lake; 3)the eutrophic
state of the lake was uncommon among the lakes in northeastern Minnesota;
4) the major surface flow of water to Shagawa Lake, Burntside River, came
from oligotrophic (low nutrient) Burntside Lake; and 5) the water quality
of Shagawa Lake is particularly important because its outflow passes
through parts of the Superior National Forest, the Boundary Waters Canoe
Area, and Canada.
The Shagawa Lake restoration project in Ely, Minnesota, was initiated in
1966 by the Federal Water Pollution Control Administration, a predecessor
of the Environmental Protection Agency. Before construction of a full-
scale advanced wastewater treatment system, primarily to remove phosphorus,
it was necessary to show, on a pilot scale, that wastewater so treated
would not promote excessive growths of algae when mixed with lake water.
Therefore, in 1966 a pilot plant to remove phosphorus from a portion
of the municipal wastewater from the City of Ely was constructed and
its effluent tested to demonstrate its low algal growth-promoting capability.
-------
Additionally, a limnological investigation was initiated to document
the trophic state of the lake.
Based upon the results of the pilot phase studies, the Environmental
Protection Agency in 1971 funded a full-scale advanced wastewater treatment
system. The treatment plant began operation in early 1973. The
rate and extent of recovery of the lake will be documented by continuing
studies for several years to obtain limnological data. Background data
describing biological, physical, and chemical characteristics of the
lake will be used in determining the validity of several mathematical
models which will be developed in an attempt to describe the eutrophic
process. Hence, a portion of future activities will be devoted to the
mathematical modeling of Shagawa Lake and to simulating the changes
expected by advanced wastewater treatment.
GENERAL DESCRIPTION OF SHAGAWA LAKE
Shagawa Lake, (Fig. 1), located adjacent to the City of Ely (population
5000) in northeastern Minnesota, about 80 miles north of Duluth, was
formed, along with numerous other lakes in the region, during the retreat
of the Wisconsin Glacier approximately 10,000 years ago. It has a surface
area of about 2400 acres, a maximum depth of 45 ft., and an average depth
of about 20 ft. Its major tributary, Burntside River, enters the lake
from the west, flowing out of nearby oligotrophic Burntside Lake; several
small tributaries drain the adjacent terrain; Shagawa River, the only outlet,
leaves the eastern edge of the lake and enters Fall Lake within a few miles.
In contrast to the many oligotrophic lakes in this area of Minnesota,
Shagawa Lake is eutrophic. Since natural sources of growth-promoting
nutrients are low, the high productivity of Shagawa Lake has been
-------
FIGURE 1 Shagawa Lake Project site. Sampling locations shown as
-------
attributed to the nutrients entering it from the City of Ely municipal
wastewater which has been discharged to the lake since before 1900.
Originally, Shagawa Lake was the source of drinking water for the town's
populace, but as early as 1932, contamination had increased to such a
level that the town was forced to obtain water from Burntside Lake.
Primary wastewater treatment was employed until 1954 when a secondary
treatment system (high-rate trickling filter) was installed. Neither
of these treatment processes removes significant amounts of nutrients.
ADVANCED WASTEWATER TREATMENT PILOT PHASE
In 1966, under supervision of the Pacific Northwest Water Laboratory,
Corvallis, Oregon (Federal Water Pollution Control Administration), the
pilot phase of the lake restoration demonstration study at Shagawa Lake
was initiated. This phase of the project employed a 28,000 gallon-per-
day advanced wastewater treatment plant.
The pilot plant was designed to provide chemical treatment, flocculation,
settling, filtration, ion exchange, and activated carbon adsorption.
Most impurities could thus be removed from the municipal secondary waste-
water entering this pilot plant. It was determined from these studies
that over 99 percent of the phosphorus was removed by the chemical treatment,
flocculation, settling, and filtration processes leaving a residual
phosphorus concentration of 0.05 mg/1 or less (Table 1).
ALGAL GROWTH POTENTIAL STUDIES
During the pilot phase, studies were undertaken to determine the algal
growth potential of Shagawa Lake water. Experiments on the effects of
treated municipal wastewater on natural lake waters were conducted in
-------
CU
CD
03
O)
IO
(O ^^
i- CTl
*-> ^
s- cr>
cu
CU
cu «
Z3 O)
4- S-
CU CO
4- E
O O
* rO
ro i
to Q-
O)
3 +->
r O
fO
O
rO
ro CU
E i-
CQ
.Q
CU
O
S-
0
OO
cu
o.
E
n3
OO
01
>
P 'ro
ro >
r O
=5 E
e cu
3 o;
o &«
I.I
0
[ , J
o
cu
> 1
r- ro
-P >
rO O
r- E
3 CU
£ o:
3
<_3 ^R
U.
i . i
' ' '
OO
I/)
r
t/)
>NJ
^-<
T5
C
^
OO OO t^ CO LO CvJ C31 I E C r P-.
OOOO^a-OOCDOCMOO cj-
C~^ CTI^ V,Q r^ ^^ C2 ^*** CJ r*^ O^ f""
i i OO UD O
CM r
l£>OOOCMOOOOOi LO
LO^-i£>ooi r~-.coocor^^-
i i CM i CT)
CM
£l_ ft
5J- «* 1 CM S-
O O i O rO
0- O- -E -i- IE
03 00
i O T3 ^ ^ i
rO _E i ' II ro
-P+JCUOOOO i CO -P
O ^- "'"7 T~ CZD rO CU ro f ) O
1 o -z.-z.-z. LL.OOI I
o
1
0
o
1
^
OO
CO
UD
to
r^*
.
-o
S-
ro
"T"
ro
O
CD
O
S-
to
E
O
ro
CD
0
O
O
0
O
LO
"cu
rO
X
o
CL
D-
ro
1
E
0
P
1 ^
ro
CU
Q-
O
to
CU
CU
2
E
o
S-
4-
r
r
<*-
0>
r
,
v^
O
^,
+J
E
O
S-
4_>
c~
Ol
3
i|
^
CU
II
UJ
co
0)
3
OJ
Q.
cu
to
E
O
r
ro
1
0
ro
23
CD
ro
0
0
,
n3
u
*,
E
cu
o
E
0
q
-4_}
c~
CU
3
4-
4-
0)
II
U-
C_5
fleunt.
4-
0)
E
E
r
o
o
E
O
-Q
S-
rO
O
E
O
q
4-3
E
CU
3
I]
4-
O)
II
C_3
CJ>
cu
r
4-
4-
*
-------
80-gallon and 150,000-gallon floating basins. The 80-gallon basins were
constructed of 4 mil transluscent plastic, and suspended in Shagawa Lake
from wood-framed polystyrene floats. The 150,000-gallon basins were
constructed of nylon impregnated with neoprene and floated with aluminum
tubular frames. The top was open and had a surface area of 1,600 square
feet. Because only three 150,000-gallon basins were available for use,
most of the experiments were performed in the smaller 80-gallon basins.
Following are examples of typical in situ assay experiments conducted from
1967 to 1969 (Brice et al., 1969 and Powers et al., 1972):
(1) Assays in large basins using various treated effluents.
In situ algal assays were performed, using mixtures of Shagawa
Lake water or Burntside River water with various amounts of
secondary or tertiary (pilot plant) wastewater added. Burntside
River water was studied intensively because it is the major
source of water for the Lake. These studies included the
observation of variations in natural phytoplankton populations
(measured by chlorophyll ^concentrations) as indices of the
effects of wastewaters on the natural lake waters. Secondary
wastewater always stimulated algal growth in Shagawa Lake and
Burntside River water, whereas tertiary wastewater which had a
residual phosphorus concentration of about 0.05 mg/1 did not
appreciably stimulate algal growth. Results of an experiment
on one of the large basins is shown in Fig. 2.
(2) Assays in small basins using secondary treated wastewater or
nutrient additions.
-------
-
t Qj
> *J
OJ
01 O)
CT> c o c
I- OJ U OJ
0) 3 0) 3
H- r t
<<- ««-
a* LU
o
-------
In these experiments, inorganic salts of nitrogen, phosphorus
and carbon were added to smaller basins. In the first
experiment phosphorus (as ICHPO.) was added in concentrations of
0.001, 0.01, and 0.1 mg/1 to Burntside River water in separate
basins; to another basin was added 2.5 percent by volume of
nonfiltered secondary wastewater effluent; and a fifth, control
basin, was unmodified. All five basins received 1 percent by
volume of Shagawa Lake water to insure an adequate phytoplankton
inoculum. A positive algal growth response was obtained only in
the container that received secondary effluent (Fig. 3).
In the second experiment, each basin receiving phosphorus also
received 1.0 mg N/l as KNO.,. The results strongly indicated that
low nitrogen concentrations had been responsible for the lack
of algal growth in the first experiment and that, in the presence
of abundant nitrogen, the amount of algal growth tended to be in
direct proportion to the quantity of phosphorus added (Fig. 4).
The third in situ experiment was performed in the summer of
1970 using Shagawa Lake and Burntside River water (Powers
et al., 1972). Nutrient additions included phosphorus,
(K2HP04), nitrogen (KN03) and carbon (KHC03) singly and in
various combinations. Each control basin contained only
lake or river water; however, Burntside River water received
1 percent Shagawa Lake water as an algal inoculum. In Burntside
River water (Fig. 5) a positive growth response was elicited only
by the addition of nitrogen and phosphorus together. When
carbon was included with nitrogen and phosphorus, the response
was not as significant. For Shagawa Lake water (Fig. 6), the
addition of phosphorus and nitrogen singly, as well as in
-------
40 r
30
I
20
si
i
10
0
BURNTSIDE RIVER
n 2.5% Secondary
Effluent
O.I mg/l P
o O.OI P
A 0.001 P
± No Additions
8
10 12 14
SEPTEMBER 1969
16
FIGURE 3 Effect of addition of three concentrations of phosphorus
and of secondary effluent on chlorophyll a_ levels in
Burntside River water. September 9-16, 1969. (From Powers,
et al., 1972,)
10
-------
40
I
a
£
I
30
20
10
BURNTSIDE RIVER
n 2.5% Secondary
Effluent
I.Omg/l N
O.I mg/l P
o I.ON
O.OI P
A l.o N
O.OOI P
A No Additions
18
20 22 24
SEPTEMBER 1969
26
FIGURE 4 Effect of addition of three concentrations of phosphorus
with nitrogen, and of secondary effluent, on chlorophyll a_.
(From Powers, et al., 19720
11
-------
CONTROL BURNTSIDE RIVER
::V^-^"--1 JULY 14-30, 1970
O.O5P
w&m
O.37 N
b 0.37N + O.O5P
O.37N+O.O5P + 6.OC
SECONDARY EFFLUENT
0 10 20 30 40 50
CHLOROPHYLL g_ (mg/m3)
FIGURE 5 Maximum chlorophyll a_ levels attained in Burntside River
water following addition of indicated nutrients. July 14-30,
1970. (From Powers, et al., 1972.)
12
-------
$
^
{2
I
SHAGAWA LAKE
COA/77??$ JULY 14-30, 1970
O.O5P
O.37N
J
O.37N + O.O5P
0.37 N + O.O5P+ 6.O C
SECONDARY EFFLUENT
0 10 20 30 40 50 60 70
CHLOROPHYLL a_ (mg/m3)
FIGURE 6 Maximum chlorophyll a_ levels attained in Shagawa Lake water
following addition of indicated nutrients. July 14-30, 1970.
(From Powers, et al., 1972.)
13
-------
combination, significantly stimulated algal growth. Stimulation
of algal growth by phosphorus alone was greater than by nitrogen
alone; and stimulation by nitrogen plus phosphorus was no greater
than that resulting from the addition of phosphorus only.
Addition of carbon with phosphorus and nitrogen did not stimulate
growth beyond that achieved by phosphorus alone or by phosphorus
plus nitrogen.
(3) Laboratory algal assays.
Laboratory algal assays were also performed on the various
wastewater effluents in combination with the natural waters
involved. The results from these experiments demonstrate that
effluent from the advanced wastewater treatment plant would
not support the growth of the test algae unless phosphorus
was added (Fig. 7). Other assays, likewise, showed that effluent
from the advanced treatment plant would not support algal
growth in Burntside River water whereas, secondary treated
effluent, phosphorus, and phosphorus and nitrogen in combination
stimulated growth (Fig. 8). While nitrogen was not growth
limiting in the natural water, assays showed that it became
limiting after phosphorus was added in excess and abundant
algal growth had occurred. Further details of these tests are
found in Miller and Maloney, 1971.
LIMNOLOGY OF SHAGAWA LAKE
Sampling Program
Chemical, physical and biological parameters of Shagawa Lake have been
and continue to be monitored since the start of the project to characterize
14
-------
10*
P
5 10
,o4
,o3
Tert. Eff.
' Tert. Eff.+ .02 mg/L P
*,*~*w~ Tert. Eff. + .06 mg/L P
23456789
TIME IN DAYS
10 II 12 13 14
FIGURE 7 Effect of phosphorus additions to tertiary effluent upon
the growth response of Selenastrum capricornutum. (From
Miller, et al., 1971.)
15
-------
' oc
UJ
I pg
UJ
§;«
"X. ^*
ee "^
tt -5
.
i
1
I
|
1
1
*:
i
,
.
«. 1
- Si -1 'i P.
z\ « »S
,
B
.
^S
i
B
e
FIGURE
-i 5 "I
? ^ ^
E S ! o
S ~i 1
1
11 : I
I1
.
i ,
i
i
1
i
1 3-
I
»
I
i
1
1
1
8 Effect of nutrient additions to Burntside River water on the
growth of Selenastrum capricornutum. (From Miller,
et al . ,
1971.)
16
-------
the lake and its tributaries. The objectives of the characterization
studies are to: 1) determine the hydro "logic and nutrient budgets
of the lake, 2) establish conditions in the lake prior to nutrient
reduction by advanced wastewater treatment and 3) follow the recovery
of the lake after the plant is operational.
Shagawa Lake is presently sampled at Olson's Bay, Brisson's Point and East
End Deep Hole (sampling locations shown in Fig. 1). Each station is
sampled weekly at the surface and at five-foot intervals to the bottom.
TributariesBurntside and Shagawa rivers and Armstrong, Longstorff,
Burgo, and Bjorkman creeks are also sampled weekly. The secondary
treated wastewater effluent was sampled several times a week until mid-
1971 when an automatic system began collecting hourly samples which are
composited (flow rated) and analyzed daily. Stinky Ditch, located adjacent
to the wastewater treatment plant, receives stormwater runoff and some
septic tank seepage. It is sampled on the same regime as the wastewater
effluent. In addition, Burntside and Fall lakes are sampled monthly.
Chemical parameters being measured include total and orthophosphate
phosphorus; nitrate, nitrite, ammonia and Kjeldahl nitrogen; pH; conductivity;
dissolved oxygen; alkalinity and organic carbon. Several times a year
samples are also analyzed for sodium, potassium, calcium, magnesium, silica,
chloride, sulfate and trace metals (Al, Cu, Pb, Zn, Fe, Mn, Mo, Co, Hg).
Biological measurements include algal and zooplankton counts and
identification, chlorophyll and pheo-pigments, primary productivity (light/
dark bottle oxygen method), dry weight, and periodic counts and
identification of benthos.
Physical measurements include temperature, Secchi disc, light penetration
and solar radiation.
17
-------
Physical Conditions
The annual thermal regime, which has become evident based upon six years
of temperature data, is typical of northern United States lakes. An
ice cover forms toward the end of November when the surface temperature
drops to 0°C; temperatures in the deep holes do not drop much below
4°C, and there is a very gradual increase in temperature with depth
throughout the winter season apparently due to a flux of heat through
the lake floor.
Ice breakup occurs toward the end of April. Winds cause a complete and
rather rigorous turnover and the water temperature subsequently rises.
A hypolimnion develops in Shagawa Lake usually in late July or early
August in the deep holes. Once developed, the hypoliranion, which usually
occurs beneath 30 feet, becomes rapidly anaerobic. Epilimnetic temperatures
typically reach 21°C during the summer months, although as a result of
extended periods of high temperature, they may attain 26-27°C. Cooling
during mid-September causes a second complete turnover of the lake. The
water column then remains well mixed until the generation of ice cover.
Specific conductivity typically falls between 50 to 75 ymhos/cm during
the period of stratification. Wide ranges in conductivity measurements
occur during the iced-over months when surface values are generally
below 40 ymhos/cm and values in deeper areas may reach 100 yrahos/cm.
Dissolved oxygen in surface waters is generally at the saturation
level and supersaturation occurs during periods of intense algal activity.
Secclri disc measurements range from a maximum of eleven feet to a
minimum of 2 feet, the latter being typical of periods of high algal
productivity and standing crops of algae.
18
-------
Nutrient Concentrations and Algal Conditions
Total phosphorus and total nitrogen concentrations are generally high,
typically reaching 0.13 mg/1 and 1.3 mg/1, respectively. Orthophosphate
and inorganic nitrogen concentrations attain levels of 0.06 mg/1 and
0.4-0.5 mg/1, respectively. Chlorophyll ^concentrations reach 60-80
ng/1 during the peak growing season while productivity rates, as
measured by the oxygen production method, typically reach 160 mg
C/m /hr over a four-hour period at the depth of maximum photosynthesis.
2
Areal productivity rates reach about 200-250 mg C/m /hr over the four-
hour period.
During the late summer months predominant algae are the blue-greens,
Aphanizomenon spp. and Anabaena spp.; greens are present in large numbers
throughout the summer months; and diatoms are present in appreciable
numbers only during the early spring and late fall.
Hydrologic and Nutrient Budgets
The hydro!ogic budget of the lake was calculated from tributary flow
measurements (by U. S. Geological Survey contract) and rainfall and
evaporation data (obtained from the U. S. Weather Bureau). The USGS
determined, after drilling numerous test wells, that groundwater was not
a significant factor in the water budget. Rainfall was analyzed for the
various forms of phosphorus and nitrogen for use in establishing the
nutrient budget.
The hydraulic retention time of Shagawa Lake is about 8 months. Burntside
River annually contributes about 65 percent of the surface water to
Shagawa Lake while contributing only about 10 percent of the phosphorus.
19
-------
The secondary wastewater treatment plant annually contributes only
about 1 percent of the water and about 70 percent of the phosphorus
loading to the lake. The average annual input of phosphorus into Shagawa
Lake is approximately 16,000 Ibs. Of this input, approximately 70 percent
is discharged through Shagawa River while 30 percent is lost to the sediments
of the lake.
The average annual measured input of nitrogen into Shagawa Lake is about
155,000 Ibs. Slightly more nitrogen leaves the lake through Shagawa
River, indicating that nitrogen fixation may play a role in the nitrogen
budget.
FULL-SCALE LAKE RESTORATION DEMONSTRATION PROJECT
Based on conclusions from the pilot study and the national need to
demonstrate that a eutrophic lake can be restored, the Environmental
Protection Agency awarded funds to the City of Ely to construct an
advanced wastewater treatment plant and provide supplies and services
for its operation. For a period of three years the EPA will operate
both secondary and tertiary municipal wastewater treatment facilities.
The EPA National Environmental Research Center, Corvallis, Oregon (National
Eutrophication Research Program) will continue to assess biological, chemical,
and physical properties of the lake. The latter will also relate the
characterization of the lake after initiation of nutrient removal to the
characterization which has been established for the five years prior to
nutrient removal.
Overall project management is the responsibility of the Project Chief
(Supervisory Research Chemical Engineer) who is a member of the Lake
Restoration Section, National Eutrophication Research Program. The
20
-------
Project employs the following six permanent personnel: Project Chief, Physical
Scientist, Sanitary Engineer (plant superintendent), Analytical Chemist,
Biological Laboratory Technician, and Administrative Clerk. Twenty-two
temporary, full-time personnel are employed: one Aquatic Biologist, twelve
Plant Operators and Mechanics, and nine Physical Science or Biological
Laboratory Technicians. Three other Plant Operators have been assigned to
the Project by the City of Ely. In addition, one Mathematician and one
Aquatic Biologist are located in Corvallis for data processing and
mathematical modeling. Fig. 9 shows the organizational structure of the
Shagawa Lake Project.
Design of the advanced wastewater treatment plant was done by Toltz, King,
Duvall, Anderson, and Associates, Inc., Architects and Engineers. The
total cost of the advanced wastewater treatment facility is estimated to
be $2,870,000 which includes the design, construction and operation of the
plant until January 1976. Over 93 percent of the cost was provided by
EPA with the remainder from the City of Ely.
The advanced wastewater plant unit processes consist of two chemical
treatment stages in series followed by dual-itedia filtration. Lime
precipitation, achieved in the first stage, was selected for Ely wastewater
as the most appropriate system to achieve the extremely low phosphorus
levels desired while providing a sludge that could be readily dewatered
for acceptable land disposal.
The second stage will permit the optional use of alum and/or a polymeric
flocculating agent to further reduce the phosphorus to minimal levels.
For the two stage system, both solids-contact clarifier units (Wilcox,
1972} are made highly efficient by recirculation of large volumes
of previously precipitated solids. These solids act as nuclei to
21
-------
§ ^
D- O
0)
rc c -o
000
o: -r- J-
< +j D-
LU o
00 O) C
UJ (/> O
^ O (O
o - s_
1-H +-> O
1 to +J
et S- V)
O O OJ
D- 01
O VI
O) fO
rs ci
«<
+-> "O
IO C
Q IO
1O
O VI
4-> O
i >
<: oo
V)
TD
3
00
TD
o>
u_
£
* M-
t-
<_> OO
Physical
Studies
C
0
C S-
IO Ol
i Q.
D- O
|
plankton
1 I
V
C
Ol
S-
+J
t.
D
O
O
h f
1 1
)
a
a
ra
s:
n
D-
t->
C
Ol
S- V)
4-> 4->
3 01
^ CO
1 ID
t. 3
01 ca
3
Lake
Analyses
1 V)
0
0
O)
-o
C
IO
benthos
1
V)
Ol
c s-
o +J
C 3
C
IO
Ilimnologi
parameter
i
>,
Tributar
Analyses
;enance
C C
<0 T-
r IO
Q- s:
V)
OJ
macrophyt
I
o>
IO
I
-!-> 01
C cn
r- JZ
-a o
01 X
V) Ol
o
c
IO
>
-o
=c
FIGURE 9 Organizational structure of the Shagawa Lake Project.
22
-------
which newly formed precipitates adhere, creating a smaller number
of larger, denser, and more easily settled particles. The clarified
effluent from the second treatment stage will go through dual media
(anthracite and sand) filters to remove any remaining suspended solids.
Underflow sludge from each of two clarifiers will be thickened in
a gravity thickener and then dewatered to about 40 percent solids
in a rotary-belt vacuum filter before disposal to landfill. The
flow diagram for the advanced wastewater treatment plant is shown in
Fig. 10.
It is planned that digester sludge from the secondary plant will also
be added to the gravity thickener with the chemical sludge, thus providing
acceptable disposal form for all sludges generated. The State of Minnesota
Pollution Control Agency has approved disposal of the dewatered sludge
in a sanitary landfill site about 12 miles south of Ely.
Chemical feed capability and points of addition are shown in Fig. 11
which is a process diagram for the main treatment units. The reactions
for the two-stage treatment system are shown in Fig. 12. The main reaction
is that between lime and orthophosphate to form calcium hydroxyapatite.
Lime is added to the first clarifier to raise the pH to about 11.5 where
calcium carbonate, calcium hydroxyapatite and magnesium hydroxide are
formed. At this pH, considerable excess calcium is present in the system.
Both the magnesium hydroxide and calcium carbonate precipitates act as
flocculants and aid in the removal of the gelatinous calcium hydroxyapatite
as well as other solids.
Ely municipal wastewater is quite low in alkalinity and hardness.
Although this means relatively little lime is required to complete the
reactions, it also means that the resultant calcium carbonate and magnesium
23
-------
£
O
z
O
O
UJ
o
o
z
z
UJ
FIGURE 10 Flow diagram.(From Wilcox, 1972.)
24
-------
|lsl
ili«
FIGURE 11 Process diagram. (From Wilcox, 1972.)
25
-------
o
0>
f
IO
o
Q.
IO
o
CM
ro
O
Q.
CO
IO
o
O
1
o
+ CM
IO
o
o
o
o
o
o»
2»
t
t
IO
O
O
Q.
I
O
CM
O
CM
IO
o
o
o
o
t
CM
O
O
O
CM
h-
LU
UJ
(T
O
IO
CM
O
o
CM
I-
0>
CM
+
o
O
UJ
2
_J
FIGURE 12 Lime reactions. (From Wilcox, 1972.)
-------
hydroxide precipitates cannot be expected to completely flocculate the
calcium hydroxyapatite. Therefore, a polymeric flocculating agent is
used as a coagulant aid. Solids are removed from the bottom of the
clarifier unit while the clear water flows by gravity to the second
unit for further phosphorus reduction.
In the second clarifier unit, carbon dioxide is added to remove excess
calcium as indicated by the last equation of Fig. 12. The calcium
carbonate thus formed will provide a second flocculation step. Recarbonation
will also help lower the pH to a desirable range for discharge. Alum
addition can be used to remove any phosphorus that is liberated due to
the pH reduction from addition of carbon dioxide in the second clarifer.
Activated carbon may be added to one or both of the clarifiers to
remove organic compounds.
The wastewater treatment facilities are operated and monitored 24 hours
a day, 7 days a week to achieve the desired project objective. Complete
laboratory capabilities have been established as part of the monitoring
process of the plant's operation.
MODELING OF SHAGAWA LAKE DATA
In an attempt to understand the mechanisms which control the eutrophic
process in Shagawa Lake, a mathematical model will be developed. Test of
the model response against field data collected from the Shagawa Lake
system will provide a mechanism by which judgments can be made concerning
the understanding of the eutrophication process.
The background data obtained from the Shagawa Lake system offers an ideal
opportunity to test presently held concepts of the eutrophication process.
27
-------
In addition, the advanced wastewater treatment plant will reduce the
phosphorus input to the system very appreciably; a manipulation of this
sort offers an excellent chance to test concepts against observed changes
within the system.
One of the major purposes of the modeling is to identify various components
of the phosphorus cycle within the lake system. Various elements
(compartments) within the lake and relationships between these elements
will be defined. For the purposes of this study, the elements are indicated
as boxes (Fig. 13); the arrows indicate predominant direction of flow
of phosphorus. For example, orthophosphate may be consumed by algae
which may in turn, die, be acted upon by decomposers to produce orthophosphate,
or be eaten by herbivores. These elements and processes are internal
to the lake system.
In addition, several factors which are external to the system acting as
sources or-sinks for various elements will be studied. For example, the
amount of orthophosphate which is contributed by tributaries and wastewater
treatment plant effluent can be varied in the model. Similarly, the
sediments and outflow tributary which act as sinks for phosphorus can also
be simulated using the model.
Models of several levels of complexity are envisioned. Initially, an
attempt will be made to account for the observed concentrations of the
various forms of phosphorus (inorganic phosphorus, algal phosphorus, total
phosphorus) within the lake based upon the rates of input and output from
the system without trying to incorporate processes within the system. The
goal of this phase of the project is to establish a phosphorus nutrient
budget and to determine what proportion of the nutrient budget can be
accounted for by the wastewater input. A similar scheme will be prepared
for the nitrogen cycle.
28
-------
CO
I-
Z)
Q_
I-
ID
O
1
D >-
OQ nr
. <
C PHOSPHORU
z
OL
0
2
> J
PHOSPHORUS
0
ORGAN
, t
in
UJ
O
z
tt
in
UJ
rr
0
CO
o:
UJ
i
UJ
X
CO
CO
h-
Z)
Q_
FIGURE 13
Model of phosphorus cycle in Shagawa Lake. Boxes indicate
reservoirs of phosphorus, arrows indicate predominate
direction of flow.
29
-------
The first model will be simple, i. e., in the form of a differential
equation relating time change of concentration of phosphorus within the
lake to inputs and outputs. This model can be used to simulate the
effect of decreasing the phosphorus input upon initiation of phosphorus
removal by advanced wastewater treatment. The measured time varying inputs
and outputs will be incorporated into the differential equation.
A model of greater complexity will be developed to incorporate those
processes within the lake which are considered important. Mathematical
relationships will be developed to describe as well as possible the
relationships identified in Fig. 13. A mechanistic approach will be used
wherever possible. For example, the rate of growth of algae will be
related to light, temperature, and the concentration of growth-limiting
nutrients (inorganic phosphorus and inorganic nitrogen).
After the various mathematical relationships have been identified and
incorporated into a model, a comparison with the lake system will be made
in an attempt to validate the model. The sensitivity of the model output
will be tested against variation in parameters identified for different
relationships to determine which have greatest effect upon the model output.
Manipulations such as the decrease in phosphorus input upon completion of
the treatment plant will be simulated and results compared with data
collected during the next several years.
30
-------
SUMMARY
1. A research project has been initiated by EPA to demonstrate lake
restoration by nutrient removal (primarily phosphorus) from wastewater
effluent while permitting such treated effluent to continue to flow into
the lake.
2. Shagawa Lake, at Ely, Minnesota, was chosen for this demonstration
because of its near ideal study characteristics.
3. Advanced wastewater treatment pilot plant studies were conducted
showing that phosphorus can readily be removed.
4. Algal growth potential studies were conducted demonstrating that
the chemical treatment processes of the pilot plant were effective in
controlling algal blooms in the receiving waters.
5. A full-scale, advanced wastewater treatment plant has been designed and
constructed and will be operated under EPA supervision until January 1976.
Nutrient removal in the plant is primarily by chemical precipitation with
lime. The estimated cost of the plant, including operation, and monitoring
for three years is $2,870,000.
6. A three-year program has been developed to evaluate the effectiveness
of the plant and to demonstrate the recovery of the lake.
7. Mathematical modeling studies have also been initiated to help
understand the mechanisms which control the eutrophic process in
Shagawa Lake.
31
-------
REFERENCES
Brice, R. M. and C. F. Powers. 1969. The Shagawa Lake, Minnesota,
eutrophication research project, p. 258-269. Ir± E. J. Middlebrooks,
T. E. Maloney, C. F. Powers, and L. M. Kaack, Proc. Eutrophication-
Biostimulation Assessment Workshop, June 19-21, 1969.
Miller, W. E. and T. E. Maloney. 1971. Effects of secondary and tertiary
wastewater effluents on algal growth in a lake-river system. 0.
Water Pollution Control Federation 43:2361-2365.
Powers, C. F., D. W. Schults, K. W. Malueg, R. M. Brice, and M. D. Schuldt.
1972. Algal responses to nutrient additions in natural waters. II.
Field Experiments, p. 141-154. In G. E. Likens, Nutrients and
eutrophication (Special Symposia, Vol. I), Am. Soc. Limnol. Oceanog.,
Lawrence, Kansas.
Wilcox, R. L. 1972. Removing in excess of 99 percent phosphorus at Ely,
Minnesota. Paper presented at 73rd National Meeting of Am. Inst.
Chem. Eng., Minneapolis. August 29, 1972. Published by Ecodyne
Corp.: Union, New Jersey; Technical Reprint T-219, 9 p.
33
-------
APPENDIX
35
-------
APPENDIX
1. Pilot plant prior to completion.
2. Pilot plant building.
3. Secondary wastewater treatment plant.
4. Beginning construction of the advanced wastewater treatment (AWT)
plant.
5. Construction of the AWT plant.
6. Basic shell of AWT plant showing lime hoppers.
7. Basic shell of AWT plant.
8. Construction of AWT plant near office/laboratory area,
9. Construction of AWT plant nearing completion.
10. AWT plant nearing completion.
11. Aerial view of Shagawa Lake: iron mine in left foreground; wastewater
treatment plant left center; and 150,000 gallon basins in lake near
wastewater treatment plant.
12. Aerial view of Shagawa Lake and City of Ely showing 150,000 gallon
in situ basins.
36
-------
13. 150,000 gallon basin and project weather station.
14. Series of 80 gallon basins.
15. Sampling one of the 80 gallon basins.
16. Instrumentation used in limnology monitoring of Shagawa Lake.
17. Lake monitoring during the winter; equipment sled is pulled by
a snowmobile.
18. Lake sampling through the ice.
19. Southwest section of lake showing Longstorff and Armstrong creeks
in foreground and Burntside River in upper left.
20. Burntside River with Shagawa Lake/Ely in background,
21. Staff gage measurement of Bjorkman Creek.
22. Office/laboratory building.
37
-------
1. Pilot plant prior to completion.
2. Pilot plant building.
38
-------
3. Secondary wastewater treatment plant.
4. Beginning construction of the advanced wastewater treatment (AWT)
plant.
39
-------
J
5. Construction of the AWT plant.
6. Basic shell of AWT plant showing lime hoppers.
40
-------
... I,-: I*»j#i;<.jyc«
IF- 1.
'%!,.,
7. Basic shell of AWT plant.
8. Construction of AWT plant near office/laboratory area.
41
-------
9. Construction of AWT plant nearing completion,
10. AWT plant nearing completion.
42
-------
11. Aerial view of Shagawa Lake: iron mine in left foreground; wastewater
treatment plant left center; and 150,000 gallon basins in lake near
wastewater treatment plant.
12. Aerial view of Shagawa Lake and City of Ely showing 150,000 gallon
in situ basins.
43
-------
13. 150,000 gallon basin and project weather station,
14. Series of 80 gallon basins.
44
-------
15. Sampling one of the 80 gallon basins,
45
-------
Ib. instrumentation used in limnology monitoring of Shagawa Lake.
46
-------
17. Lake monitoring during the winter; equipment sled is pulled by
a snowmobile.
18. Lake sampling through the ice.
47
-------
19. Southwest section of lake showing Longstorff and Armstrong creeks
in foreground and Burntside River in upper left.
20. Burntside River with Shagawa Lake/Ely in background.
48
-------
21. Staff gage measurement of Bjorkman Creek,
22. Office/laboratory building.
49
-------
SELECTED WA TER ' * *" '- '-' ' 4 S P $
-------
U.S. Environmental Protection Agency
Regions, Library (PL-12 J)
77 West Jackson Boulevard, 12UI FlOOf
Chicago, 1L 60604-3590
------- |