EPA-660/2-73-022
December 1973
Environmental Protection Technology Series
Tertiary Treatment
with a Controlled
Ecological System
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C. 20460
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
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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
U. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
degradation from point and non-point sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards.
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not signify that the contents necessarily reflect the views
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For late by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price 90 cents
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EPA-660/2-73-022
December 1973
TERTIARY TREATMENT
WITH A CONTROLLED ECOLOGICAL SYSTEM
by
Las Vlrgenes Municipal Water District
4232 Las Virgenes Road
Calabasas, California 91302
Project 16080 FBH
Program Element 1BB045
Project Officer
Dr. Kenneth E. Biesinger
National Water Quality Laboratory
Duluth, Minnesota 55804
Prepared for
OFFICE OF RESEARCH AND MONITORING
U. S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D. C. 20460
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ABSTRACT
A two-stage pond system was constructed and operated as a process
for polishing secondary sewage effluent. In the shallow first pond a
luxuriant growth of algae was maintained. In the second stage a popu-
lation of Daphnia pulex_effectively removed the algae. Total volume
of the system was 1, 135 cubic meters. A program of chemical and
biological monitoring was followed over a twelve-month period. Ob-
jectives were to demonstrate feasibility of the process for producing
recreational-grade water, acquire operating data on a completely
biological process, and determine its potential for nutrient removal.
The system was operated with about 10 days' detention in each stage.
The Daphnia remained as the dominant zooplankton species in the sec-
ond stage pond throughout the observation period, and during periods
when their concentration was above 500-organisms/liter, were able to
hold water transparence at Secchi disk readings around 2 meters. At
such times COD reduction was above 40 percent across the system.
Significant removal of nutrients occurred only during the months of
July and August when nitrogen and phosphate reductions were 48 per-
cent and 63 percent, respectively. Nutrient removal performance was
hampered by occasional invasions of Daphnia or rotifers in the first
stage pond, which decimated the algae population; such events were
not successfully controlled and remain the principal obstacle to further
development of the process.
This report was submitted in fulfillment of Project Number 16080 FBH
by the Las Virgenes Municipal Water District under the (partial) spon-
sorship of the Environmental Protection Agency. Work was completed
as of December 1971.
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TABLE OF CONTENTS
Section Page
Abstract ii.
List of Figures iv
List of Tables vi
Acknowledgments vii
I Conclusions 1
EL Recommendations 2
III Introduction 3
IV Plant Description 5
V Procedures
Operation 9
Daphnia Separation 10
Analytical Work 11
VI Results
General Performance 15
Nutrient Removal 17
Biological Conditions 23
VII Design Implications 26
VIII References 28
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FIGURES
Page
1 System Flow Diagram 6
2 Pond Construction Details 8
3 Daphnia Separation Apparatus 12
4 Photograph of Pond 1 14
5 Photograph of Pond 2 14
6 Distribution of Phosphate Tracer 22
7 Average Temperature 29
8 Hydraulic Turn- Over Rate 30
9 Liquid Clarity 31
10 Suspended Solids 32
1 1 Chemical Oxygen Demand, Unfiltered 33
12 Total Kjeldahl Nitrogen 34
13 Ammonia Nitrogen 35
14 Nitrate Nitrogen 36
15 Total Phosphate, Unfiltered 37
16 Total Phosphate, Filtered 38
17 Chlorella 39
18 Daphnia and Color - Pond 2 40
iv
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FIGURES (Continued)
No. PaSe
19 pH 41
20 Total Alkalinity 42
21 Calcium 43
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TABLES
No. Page
1 Process Determinations 13
2 Summary Data 16
3 Total Organic Carbon Determinations 17
4 Monthly Average Nutrient Concentrations 18
5 Nitrogen Balance 20
6 Phosphate Balance 21
VI
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ACKNOWLEDGMENTS
A Board of consultants consisting of Dr. Charles R. Hazel, Dr. John
Klock, Dr. James L. Morgan, and Dr. George O. Schumann met three
times during the project and provided valuable advice and assistance.
Mr. Lloyd D. Hedenland, Sanitation Superintendent of the Las Virgenes
Municipal Water District, acted as project field manager. Dr. Andrew
L. Gram of Gram/Phillips Associates provided general direction, de-
signed the pond system, and compiled the final report.
The organic carbon analyses were performed courtesy of the research
and development laboratory of the Los Angeles County Sanitation Dis-
tricts.
vn
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SECTION I
CONCLUSIONS
A two-stage pond process based on growth of algal cells and their
subsequent ingestion by Daphnia can achieve effluent clarity together
with substantial reductions in organic matter, nitrogen, and phosphate
provided that active populations of both organisms are maintained.
In such a process, phosphate removal occurs mainly by precipita-
tion at the elevated pH of the first-stage pond, while nitrogen is con-
verted to solid organic forms by the algae and Daphnia and removed by
sedimentation in the second-stage pond. Effective removal of both
nitrogen and phosphorus occurs only during the warm-weather months.
Daphnia concentrations on the order of several hundred organisms per
liter are easily capable of filtering virtually all algae from a pond of
several days' detention.
The principal obstacle to reliable nutrient removal performance is the
problem of preventing blooms of algal predators which occur in the
first-stage pond.
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SECTION II
RECOMMENDATIONS
The process studied herein is chiefly applicable to the polishing of
effluent from small secondary treatment plants. Where high nutrient
removal efficiencies are necessary, or where land is costly or un-
available, other methods must be used. In order to put the algae-
Daphnia process into the plant designer's practical repertoire, there
should be further investigation to develop design data. The principal
questions relate to biological criteria; performance is closely asso-
ciated with maximizing algae production and maintaining a vigorous
Daphnia population. Increased reliability can only come through pro-
cess modifications which successfully accommodate the various phy-
siological requirements of these organisms. The next logical step
would be to correlate the growth and feeding behavior of Daphnia with
the composition of the treated waste water in which they are to per-
form.
On the basis of one year's operation of a particular pond configuration,
the following tentative design guidelines are suggested for use in sub-
tropical climates (pond temperature 10°C to 25°C seasonal range):
1. First-stage pond: Depth, 60 to 90 cm
Detention, 6 to 8 days
2. Second-stage pond: Depth, 2. 5 meters minimum
Detention, 5 days
3. Provide overflow connection from first pond to second, and
make horizontal distance between the two stages as great as practical.
4. Provide for dewatering and cleaning of ^second pond on an
annual or more frequent schedule.
5. Divide first-stage pond into several compartments, with
capability of operating either in series or in parallel.
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SECTION in
INTRODUCTION
The Controlled Ecology demonstration project was based on a phenome-
non observed in the system of effluent irrigation ponds at the Tapia
Plant of Las Virgenes Municipal Water District. There, water which
had acquired a heavy growth of-algae during short storage in the initial
pond was clarified in the downstream storage pond through the preda-
tory action of a persistent Daphnia population. Five sets of analyses
made between July and October, 1968, showed considerable reductions
of phosphate and nitrate. In the demonstration project a similar sys-
tem of smaller ponds was constructed and operated independently of
the sewage treatment plant. Objectives were (a) to demonstrate tech-
nical and economic feasibility of producing recreational-grade water
from secondary sewage effluent by means of a two-stage algae-crusta-
cean process; (b) acquire operating data which could be used in formu-
lating design criteria and interpreting water quality phenomena in
artificial lakes; and (c) to determine the process's potential for re-
moving nitrogen and phosphorus.
The basic processes involved consist of (1) the photosynthetic growth
of green algae on inorganic carbon, nitrogen, and phosphorus present
in the sewage effluent, and (Z) the consumption of the algae by Daphnia.
The two processes are carried out consecutively in separate ponds so
that the production of algae can be maximized. There are several im-
portant side effects. Oxygen is produced in the first pond as a by-
product of photosynthesis, and is consumed in the second by respira-
tion of the Daphnia and other organisms. During rapid algae growth,
bicarbonate is depleted, resulting in a rise in pH, which in turn pro-
motes the removal of phosphate by precipitation, presumably as cal-
cium, phosphate. Finally, there is an accumulation of organic sedi-
ments on the bottoms of both ponds, made possible by several days'
detention in each under quiescent conditions.
One promising feature of the system is the extent of clarification
attainable. Removal of the algae by Daphnia is very effective, and
costs are negligible in contrast to any other means of algae separation
which has yet been studied. It is also possible to go one step further
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in the food chain and use fish to remove the Daphnia or regulate
population. However a comparison of food intake versus growth of
both fish and Daphnia shows that the removal of nitrogen and phos-
phorus nutrients from the sewage effluent by incorporation in the body
tissues of these organisms would be negligible. For example, Richman
measured enthalpy conversions in a system of Daphnia pulex feeding on
the green alga Chlamydomonas reinhardi. He found that only 4 to 13
percent of the algal heat content reappears in the cell tissue of young
Daphnia, and with adult organisms the conversion is less than 1. 5 per-
cent. Since algae and Daphnia have similar nitrogen and phosphorus
compositions, as well as roughly the same heat value, the Daphnia
could retain no more than about 10 percent of the N and P content of
their algal diet. The same situation prevails during the transformation
of Daphnia into fish tissue. Bennett^ has summarized food conversion
data for several warm water fish; the weight ratio of food fish produced
to food consumed is generally less than 0.4, even when the fish are
actively growing. Any substantial nutrient removal must therefore be
due to other mechanisms, such as conversion to a solid form capable
of sedimentation.
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SECTION IV
PLANT DESCRIPTION
The project was located on the grounds of the District's Tapia Treat-
ment Plant. The site is in Malibu Canyon about 6 kilometers inland
from the Pacific Ocean. Terrain is rather steep and rugged, and the
project ponds were constructed on small level areas which were fortui-
tously available. The climate is temperate and relatively mild, but
the site is somewhat insulated from the ocean's influence by mountains.
Daily air temperatures range from over 32 °C on hot summer days to
below freezing on winter nights.
Scale of the project units was chosen on the basis of simulating natural
environmental conditions at the lowest possible cost. Initially it was
not known to what extent the success of the Daphnia population might
depend on such things as illumination, available water depth, nature
of pond bottom, etc. A relatively deep earth basin was therefore pro-
vided, with a ratio of surface to volume approximating that of the res-
ervoir in which the Daphnia had been observed to thrive. Similarly,
the algae pond was made large enough that sunlight illumination level
and other growth-determining factors would be comparable to those
prevailing in a full-scale plant.
A schematic diagram of the system is shown in Figure 1. The feed
was activated sludge effluent taken from the Tapia Plant's spray irri-
gation system. Flow rates were adjusted manually and were totalized
on 5-cm water meters at three points in the system. Part of the
algae pond effluent could be diverted around the second pond to permit
independent selection of detention periods.
Both ponds were circular in plan. Pond 1 was designed along the lines
of a conventional oxidation pond. Gunite lining was provided to permit
occasional thorough cleaning and to avoid entrainment of sediment.
Water depth was 1. 4m and its volume about 900 cu m. Pond 2 was
left unlined so that natural vegetation could develop, and its 3-meter
depth provided a range of illumination levels. Two tiers of benches
were left in the side slopes to accommodate sediment sample collectors.
The volume of Pond 2 was 340 cu m.
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FIGURE
SYSTEM FLOW DIAGRAM
TO UPPER
STORAGE RESERVOIR
FROM LOWER
STORAGE RERVOIR
EFFUJENT
RETURN
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Inlets to both ponds consisted of a submerged 5-cm steel pipe dis-
.charging at one point near the periphery. In Pond 1 the inlet was 30
cm from the bottom and pointed in a circumferential direction. In
Pond 2 the inlet pipe was 30 cm below the surface and pointed toward
the center. The outlets of both ponds were concrete weir boxes located
diametrically opposite the inlets. Figure 2 shows the general construc-
tion features.
When Pond 2 was first filled with water the leakage rate was about
1. 3 liters per second. It gradually decreased over a period of several
weeks to about 0.6 I/sec. In order to further reduce the loss rate a
ton of bentonite was slurried into the pond and allowed to settle. Leak-
age thereafter remained at about 0. 3 I/sec.
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POND CONSTRUCTION DETAILS
5cm INLET
00
POND I
5cm INLET
BENCHES
OUTLET
WEIR BOX
Scm.GUNITE LINING
1.5m
OUTLET
WEIR BOX
POND 2
WOOD PLANKS
3.3 m
SECTION B-B
0.3 m
SECTION A-A
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SECTION V
PROCEDURE?
OPERATION
The liquid feed to the pond system consisted of activated sludge effluent
of good quality. The District's sewage is almost entirely domestic and
it arrives at the plant in fairly fresh condition. During the period of
pond operation most of the plant's effluent flow was being disposed of
by hillside spray irrigation. For this purpose the plant effluent was
chlorinated and discharged to a storage pond of about two days' capa-
city. From there it was pumped to the spray system. A lateral con-
nection to the spray system was the source of influent for the experi-
mental ponds. At the upper end of the spray system is a second storage
reservoir, which under normal operating conditions has a detention
time of several days. It was in this upper reservoir that the persistent
clarifying effect of Daphnia was observed to occur naturally.
At commencement of operations with the experimental system in August,
1970, Pond 1 was filled with water pumped from the lower storage re-
servoir in the normal manner. Pond 2 was filled from the upper stor-
age reservoir to assure the presence of some Daphnia as seed. Within
one week a dense bloom of algae, mostly Chlorella, had formed in both
ponds. After one month of operation Daphnia appeared at high concen-
tration, first in Pond 1 and a few days later in Pond 2.
The algae were decimated in both ponds. In Pond 2 the Daphnia were
sustained temporarily by feeding water from the upper storage reser-
voir, which at that time had a fairly high algae count. In Pond 1 the
Daphnia died out in several days; feeding with the normal influent
was resumed, and a relatively stable algae population returned. From
this point on, the system operated generally as intended with algae
growth in Pond 1 and subsequent clarification in Pond 2.
Flow rates were initially set at 1. 9 I/sec through both ponds. Begin-
ning in January, 1971, when analyses were being made on a regular
schedule, the flow through the system was reduced to 1.3 I/sec. De-
tention times were then approximately 8. 3 days and 3. 1 days in Ponds 1
-------
and 2 respectively. In June the flow through Pond 1 was dropped to
0. 9 I/sec to encourage more complete nutrient removals. The Pond 2
flow was also lowered at the same time for a different reason. The
Daphnia population began to falter, and the flow was cut to about 0. 4
I/sec to avoid losing them altogether. In September, 1971, the Pond 1
feed was brought back up to 1.9 I/sec as a measure to control Daphnia
plagues.
A continuous temperature record was obtained of the liquid in both
ponds, and of the air in the vicinity of Pond 1. Wooden shelters at
each site housed spring-wound 7-day recorders. Temperature probes
were suspended at mid-depth.
Collection of samples from Pond 1 for chemical and biological analysis
was carried out by casting a tethered bottle from three points on the
pond periphery and pooling the contents. In Pond 2 the Daphnia popu-
lation tended to concentrate somewhat in different regions, so a series
of five samples was taken along a pond diameter. An aluminum boat
was used as a platform, and it was maneuvered by pulling along a fixed
cable suspended above the pond surface. Vertical "core" samples were
taken by lowering a length of 2-cm PVC pipe through the liquid depth,
stoppering the upper end, and removing carefully.
Sediment samplers were placed on the earth benches which had been
provided for them in Pond 2. These consisted of shallow open-top
wooden boxes, one foot square, partially filled with earth in simula-
tion of the natural bottom. Sets of the samplers were removed at in-
tervals during the study, and portions of the accumulated sediment
were analyzed for organic nitrogen and total phosphate. The earth
bedding tended to interfere with subsequent selection of a representa-
tive aliquot of bottom area, and it was difficult to avoid washing of the
open samplers when hoisting them to the surface. In May, 1971, a
different type of sediment collector was installed and proved to be
more suitable. They were short lengths of 5-cm PVC pipe, capped
at the bottom and attached to a steel stake which would hold them on
the pond bottom in a vertical position.
DAPHNIA SEPARATION
There were periods of operation in which the Daphnia population in
Pond 2 increased to a level much greater than was necessary to
10
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consume all of the algae being delivered. Also, as described subse-
quently, there were several instances of Daphnia becoming established
in Pond 1 where their presence was undesired. In both situations it
would have been of some benefit to have available a means of removing
Daphnia without interfering with the liquid flow. A device to accom-
plish this was designed, constructed, and operated successfully,
although it was never used as a regular process component. Figure 3
shows the general features of the apparatus. Water from Pond 2 was
pumped over a 60° sheet metal cone onto a funnel-shaped nylon screen
having 80 filaments per sq cm. Most of the water passed through the
screen and flowed back into the pond. Daphnia accumulated on the
screen and sloughed gradually with a small flow of water to the center
of the funnel. The central 23 cm of the screen could easily handle
6 I/sec of feed, concentrating an initial Daphnia concentration of sev-
eral hundred per liter 20 fold. Passage through the pump mutilated
most of the organisms. If there should be any reason to preserve them
alive, it would be necessary to use gravity flow or some other rela-
tively non-violent means of transport.
ANALY TICAL WORK
The group of analytical determinations carried out on a regular basis
was selected partly to demonstrate process performance, but also to
provide information on process mechanisms. Table I gives a schedule
of the various measurements. "Daily" analyses were normally per-
formed every day except weekends and holidays. In addition to the
regular determinations", organic carbon in the influent and two ponds
was estimated several times with a Beckman analyzer. Also, Kjeldahl
nitrogen and total phosphate were run on bottom samples taken from
the ponds.
Analytical techniques were in accordance with Standard Methods wher-
ever applicable. Transparence in Pond 2 was measured by lowering
a 20-cm Secchi disk to the depth of disappearance. Turbidity was ex-
pressed as percent transmittance of white light through a one-cm
sample thickness. All colorimetric determinations were read on a
Lumetron colorimeter. Suspended solids were measured by filtering
a 25-ml sample through a tared 0. 45-micron Millipore disk, drying
at 103° C, and weighing. The EDTA tltration method was used for
calcium, brucine method for nitrate, direct nesslerization for ammo-
nia, and Kjeldahl nitrogens were read colorimetrically after distillation.
11
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FIGURE 3
DAPHN1A SEPARATION
APPARATUS
DETAIL 'A1
60 cm
-INFLUENT FROM POND 2
DIAM.
DISTRIBUTION
CONE
,80/sq cm
NYLON SCREEN
28 cm
CLEAR
_». WATER
RETURN
SINK DRAIN
FITTING
CONCENTRATED
DAPHNIA SLURRY
SEWN SEAM
NYLON SCREEN
STEEL RING 0.6cm 0 ROD
DETAIL 'A1
12
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"Filtered" determinations were made on the filtrate generated during
the suspended solids procedure-.
Algae counts and identification were carried out under a microscope
at 400X magnification using a haemacytometer cell. Daphnia concen-
trations were determined by manually removing the specimens found
in a 100-ml aliquot of sample using an eye dropper.
Table 1. PROCESS DETERMINATIONS
Measurement
Physical
Flow
Temperature
Transparence
Suspended Solids
Turbidity
Color
Location
I, 1. 2
Air, 1, 2
2
I, 1, 2
I, 1, 2
2
Frequency
Daily
Continuous
Daily
Daily
Daily
Daily
Chemical
pH
Alkalinity
COD, filtered and unfiltered
Calcium
Kjeldahl nitrogen, filtered
and unfiltered
Ammonia nitrogen
Nitrate nitrogen
Orthophosphate, filtered
and unfiltered
Dissolved oxygen
Biological
Algae count and species
Daphnia count
I, 1, 2
I, 1, 2
I, 1, 2
I. 1, 2
I, 1, 2
I, 1, 2
I, 1, 2
I, 1, 2
1, 2
1
1, 2
2/day
2/day
1 /week
1 /week
1 /week
1 /week
I/week
1 /week
2/day
Daily
Daily
13
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Figure 4. Pond 1
Figure 5. Pond 2
14
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SECTION VI
RESULTS
GENERAL PERFORMANCE
Figures 7 through 21 provide a chronological record of system condi-
tions over a 14-month period. On most of the charts parallel records
are given for influent, Pond 1, and Pond 2. The bar-type plots show
the times and spacing of samples, as well as the pattern of change.
Table 2 contains the average results by months of several performance
parameters.
The seasonal temperature progression in the two ponds is shown on
Figure 7. Values ranged from a low.of about 5 ° C in early January to
28° in early August. Daily fluctuations are not shown on the chart, but
the peak-to-peak span was about 5° in Pond 1 and about 1.5° in Pond 2
(during clear weather). Flow data are represented on Figure 8 in the
form of a smoothed hydraulic throughput rate. Plotted values are the
reciprocal of the mean residence time of the current pond contents.
The computation was made under the assumptions of complete mixing
and of steady delivery of flow between daily readings; the residence
time at the end of a given day is given by the formula Tn = V/Qn +
(Tn_i - V/Qn)exp(-Qn/V) where V is pond volume and Qn the volume
of influent during day "n". The spikes in the Pond 1 graph represent
flushing events which were instituted to suppress incursions of Daphnia
and rotifers, as discussed later.
Transparence and clarity of the Pond 2 effluent are shown on Figure 9.
Secchi disk readings were from 2.0 to 2.5 m all through the spring
months. The decline during the subsequent summer corresponds
exactly to a reduction in the Daphnia population. Comparison of influent
and effluent light transmittance in the spring suggests a reduction in
colloidal matter of about 50 percent (log 0. 93 versus log 0. 86). During
the summer Pond 2 was slightly more turbid than the influent because
of incomplete algae removal. Turbidity in Pond 1 was not measured;
at most times it was far greater than that of the influent because of its
algae content. The suspended solids record, Figure 10, illustrates
the growth of algal cells in Pond 1 and their subsequent removal in
15
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Table 2. SUMMARY DATA
Trans- Susp. Diss.
Temp. mittance Solids COD Oxygen
°C % mg/1 mg/J pH rhg/1
Influent
Feb
Mar
Apr
.May
June
July
Aug
Sept
Oct
Pond 1
Feb 10.4 31 95 7.9 20.0
Mar 10.9 42 100 8.2 19.5
Apr 16.6 48 91 8.2 18.2
May 19.4 21 48 8.0 12.0
June 22.5 31 73 8.4 22.8
July 24.7 66 122 9.2 18.6
Aug 25.0 73 89 9.2 20.0
Sept 22.2 49 111 8.3 13.4
Oct 16. 1 48 88 8.2 21.9
Pond 2
84.5
86. 0
88.7
85.3
87.5
88. 1
86.0
83.7
82.2
23
23
15
17
14
31
18
21
21
76
67
71
43
32
43
43
69
51
7.0
7.0
7.1
7.0
7. 1
7.2
7.2
7. 1
7.2
Feb
Mar
Apr
May
June
July
Aug
Sept
Oct
12.7
14.9
18. 1
20.6
22.2
25.2
25.8
23.6
20.1
93.7
94.1
93.4
90.9
81.5
78.7
74.3
79.6
80.1
8
12
11
16
30
35
42
32
16
69
68
56
34
35
60
58
80
38
7.4
7.4
7.7
7.8
7.9
8.7
9.0
8.2
7.6
1.0
0.8
4.6
2. 5
7.0
5.6
12.4
5. 3
1.8
16
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Pond 2. Algae production during the summer months of July and August
was almost twice as great as it was throughout the spring.
The COD values (Figure 11) alsojreflect the transformation of inorganic
carbon to organic form in Pond 1, and its removal in Pond 2. Overall
COD reductions were substantial during the spring period of high
Daphnia activity, but were small or negative during the summer. Or-
ganic carbon analyses made during the spring are given in Table 3. The
samples were composited from once-daily grabs over the periods indi-
cated. Results are quite parallel to the COD's.
Table 3. TOTAL ORGANIC CARBON DETERMINATIONS
Values in mg/1 C
Period Influent Pond 1 Pond 2
2/24 - 3/12 15.8 25.2 11.6
3/15 - 3/31 17.2 35.6 15.0
4/1 - 4/19 14.2 18.4 12.4
4/20 - 4/30 12.0 19.8 10.2
NUTRIENT REMOVAL
Nutrient Removals achieved by the system are shown in Table 4, which
displays monthly average nitrogen and phosphate concentrations, and
on Figures 12 through 16. The removals given in Table 4 are the dif-
ferences between plant influent and effluent concentrations. Signifi-
cance levels are based on Student's "t" distribution using the statistic
t=(xl - X2>/(s \Tl/ni + l/n2). Here x^ and x~2 are the measured average
concentrations for a given month, nj and n2are the numbers of sam-
pies contributing to the averages, and s = -s/ [(nj - l)sf + (n2 - Us^ /
(nj + n2 - 2), where sj and s2 are the sample standard deviations. The
number of degrees of freedom is nj + n2 - 2. The notation N.S. means
that the removal was not significant at the 10 percent level.
Performance in this respect was mediocre throughout the cold weather
months, but in May there was significant reduction in both nutrients.
Best performance was in July and August, when the overall removals
were 48% for nitrogen and 63% for phosphate. It may be noted that
most of the nitrogen removal occurs in Pond 2. In Pond 1, the nitrogen
17
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is incorporated into the algal cells, and in Pond 2 the algae are inges-
ted by Daphnia and other higher organisms and converted to settleable
solids. On the other hand, the bulk of the phosphate is removed in the
first pond, evidently through precipitation as the result of the high pH
environment generated by the algae.
Table 4. MONTHLY AVERAGE NUTRIENT CONCENTRATIONS
February
March
April
May
June
July
August
September
October
Influent
15.2
16.1
13.4
12.0
12.8
15.3
13.6
18.4
18.6
Total Nitrogen, mg/1
Pond 1
15.8
14.3
12.2
11.3
11.1
14.0
14.4
15.6
17.8
Pond 2
13.5
11.6
9.8
8.6
11.4
7.9
6.9
10.3
11.2
Removal
1.7
3.5
3.6
3.4
1.4
7.4
6.7
8.1
7.4
Significance
Level, %
1.5
0.1
1.0
0.2
0.1
0.1
0.1
5.5
February
March
April
May
June
July
August
September
October
Influent
28.4
28.9
27.2
27.7
29.0
29.5
29.3
34. 8
24.4
Total Phosphate, mg/1
Pond 1 Pond 2 Removal
27.0
27.5
25.5
21.4
26.1
13.5
17.7
23.1
23.7
27.3
27.6
24.8
16.6
25.8
10.5
10.9
18.2
23.9
1.4
1.4
1.7
6.3
2.9
17.0
11.6
11.7
0.7
Significance
Level, %
N.S.
9.3
N.S.
0.3
N.S.
0.1
0.1
8.5
N.S.
Balances on the amounts of nutrients passing through Ponds land 2 are
given in Tables 5 and 6. There was very little net change in nitrate
18
-------
nitrogen in either pond, but in Pond 1 part of the ammonia nitrogen was
converted to organic, which was then removed in Pond 2. A similar
conversion of soluble phosphate to insoluble phosphate occurred in
Pond 1, although here it is probable that most of the insoluble phosphate
formed was inorganic. Algal cells contain only about two percent phos-
phate, compared to around nine percent nitrogen. At any rate, during
July and August more than half of the phosphate entering Pond 1 remain-
ed there.
Collection devices had been placed on the bottom of both ponds for the
purpose of acquiring samples of deposited settleable material. Kjeldahl
nitrogen accumulated at the rate of about 4. 5 kg per month in Pond 1,
and at about 5. 5 kg per month in Pond 2, during the summer period
(May through August). These figures agree reasonably well with the
nitrogen removals shown in Table 5. Phosphate accumulated on the
bottom on Pond 2 at about one pound per month, again in agreement with
the liquid measurements. However the Pond 1 bottom samples contain-
ed little or no phosphate above background, suggesting that the removed
phosphate may have been deposited on the concrete pond lining in crysta-
line form.
On September 24, 1971, a phosphate tracer was injected into Pond 1 for
the purpose of observing the distribution process. The tracer was 40
rnillicuries of phosphorus-32 prepared by neutron activation of ammonium
diacid phosphate. Samples of the liquid and bottom sediment in Pond 1
were taken for two weeks, as well as liquid and Daphnia samples from
Pond 2. Filtered and unfiltered portions were later dried on planchets
and counted using a thin-window Geiger system. The results are shown
graphically in Figure 6. There was very rapid initial disappearance of
filtrable phosphate; within two days some 65 percent had been either
precipitated or converted to suspended solids. Tracer removed from
the liquid reached a peak of 45 percent in five days and then slowly be-
gan to reappear, perhaps by exchanging with non-radioactive phosphate.
Samples of bottom sediment showed the same level of radioactivity as
the interior liquid, again suggesting precipitation rathe;; than sedimen-
tation as the dominant mechanism. The peak in the fraction converted
to suspended form may be only apparent since the concentrations were
changing rapidly at that time, and the mass balance calculation hence
subject to inaccuracy. In any case, transformations in the pond were
essentially complete in five days. From then on the only changes which
occurred were the washout of remaining suspended and filtrable tracer,
and the gradual return of tracer previously removed from the liquid.
19
-------
Table 5. NITROGEN BALANCE
(Figures in kg N)
Pond 1
Input
NB^'-N NO3-N
Output
Total Org N NH3-N NO3-N
Total Decrease
Feb
Mar
Apr
May
June
July
Aug
Sept
Oct
10.8
6.2
6.0
2.5
8.9
9.8
3.8
16.0
10.5
50.5
32. 1
42.0
56.2
21.4
44.2
24.1
69.2
45.7
13. 1
16.1
20.5
24.6
12.9
1.7
1.2
1.2
0.7
70.6
54.4
68.6
83.3
43.2
55.6
29.0
86.4
56.9
18.0
12. 7
11.9
12.0
14. 1
22.0
18.0
22.9
16.2
43. 1
18.6
36.1
47.4
10.4
26.9
12.0
47.8
37.0
12.0
17.0
14.2
19.0
12.8
1.8
0.8
1.7
1.2
73. 1
48.3
62.2
78.4
37.3
50.7
30.6
72.4
54.4
-2.5
6.1
6.4
4.9
5.9
4.9
-1.6
14.0
2.5
-3.5
11.3
9.3
5.9
13.6
8.7
-5.6
16.2
4.3
Feb
Mar
Apr
May
June
July
Aug
Sept
Oct
11.7
10.4
8.8
3.9
0.4
11. 1
11.2
6.2
6.0
27.8
19.1
24.8
7.4
8.7
2.7
2.2
10.4
14.2
8.7
15.7
9.4
8.8
5.4
1.0
0.3
0.3
0.5
48.2
45.2
43.0
20. .1
14.5
14.8
13.7
16.9
20.7
2.8
3. 1
3.3
2.0
1.4
3.9
3.5
2.5
4.1
29.6
20.8
21. 1
8.8
7.3
3.4
2.4
7.7
12.1
8.9
13.0
10.0
6.8
4.3
1.0
0.2
0. 1
0.5
41.4
37.0
34.4
17. 7
13.0
8.4
6. 1
10.3
16.6
6.8
8.2
8.6
2.4
1.5
6.4
7.6
6.5
4. 1
14.2
18.2
19. 9
12.2
10.3
43. 3
55.5
38. 7
19. 7
-------
Table 6. PHOSPHATE BALANCE
(Figures in kg PO4)
Pond 1
Feb
Mar
Apr
May-
June
July
Aug
Sept
Oct
Sol
117. 4
91.6
133.7
182. 1
88.5
100.3
60.6
155.6
71.3
Input
Insol
14.2
5.9
5.2
10.2
9.2
6.4
1.8
8.2
3.2
total
131.6
97.5
138.9
192.3
97.7
106.7
62.4
163.8
74.5
Sol
119. 0
86.2
120.0
143.8
77. 5
10.2
25.4
103. 0
70. 3
Output
Insol
6.1
6.6
14.6
5.2
10.2
42. 1
12.5
5.6
4.4
'Total
125. 1
92.8
130.6
149.0
87.7
52.3
37.9
108.6
74.7
Decrease
6.4
4.7
8.3
43.3
10. 0
54.4
24.5
55.2
-0.2
%
4.9
4.8
6. 0
22. 5
10.2
60. 0
39.4
33.7
0.0
Pond 2
Feb
Mar
Apr
May
June
July
Aug
Sept
Oct
77.9
82.0
65.4
16.8
25.8
3.4
7.3
23.8
26.0
5.0
6.2
18.2
8.7
4.6
8.9
5.9
1.3
1.6
82. 9
88.2
83.6
25. 5
30.4
12.3
13.2
25. 1
27.6
80.2
86.7
85.6
28. 1
29.6
9. 5
6.7
19.0
27. 5
3.4
1.5
0.4
1.7
1.0
1.7
2.2
0.4
3.4
83.6
87.6
86.0
29.8
30.6
11.2
8.9
19.4
30. 9
-0.7
0.6
-2.4
-4.3
-0.2
1. 1
4.3
5.7
-3.3
-0. 1
0. 1
-2.9
-17. 1
-0.6
9.2
32.3
22.8
-11.8
-------
DISTRIBUTION OF PHOSPHATE TRACER
tx>
t\3
REMOVED FROM LIQUID
DISPLACED FROM POND
IN FILTRABLE FORM
CONVERTED TO
SUSPENDED FORM
FILTRABLE TRACER
IN POND LIQUID
m
TIME, DAYS
-------
BIOLOGICAL CONDITIONS
Populations of Chlorella and Daphnia throughout the year are shown in
Figures 17 and 18. Small numbers of other algae were occasionally
observed, but Chlorella strongly predominated and cell counts of this
genus were therefore,used as a measure of algal population. Although
the cell concentrations during February and March were similar to
those reached in July, it should be noted that the average cell size was
much smaller in the earlier period, and the biomass concentration was
much greater in summer. The suspended solids determination pro-
vides a more significant measure of algal substance.
Like Chlorella among the Pond 1 algae, Daphnia pulex was the sole
dominant invertebrate organism of Pond 2. Various water bugs occur-
red, including some fairly large types, but none in appreciable mass
concentrations compared to the Daphnia. No other cladoceran species
were encountered. The low temperature reached in Pond 2 never
caused complete cessation of asexual reproduction, and they remained
at high concentrations in the face of a hydraulic detention time of five
days (pond volume divided by overflow). The actual wash-out rate of
the organisms could be somewhat less because of rheotaxis; the Daphnia
tended to swim "upstream" in the vicinity of the outlet weir. Through-
out the winter-spring season the Daphnia produced winter eggs (ephip-
pia). These tended to float and frequently collected on the leeward side
of Pond 2 as a granular scum. The period of ephippia production was
approximately November through April.
The potential clarification effect of Daphnia can be estimated from the
filtration rates which have been measured by others. A conservatively
low value is 5 ml/day for an average organism. At this rate 100 or-
ganisms per liter would be sifting their medium once every two days.
Since Pond 2's Daphnia concentrations were frequently above 1000
organisms per liter it is not surprising that they were able virtually to
eliminate the algae at such times.
With the onset of summer the Daphnia population in Pond 2 began to fall
off unaccountably. The cause is not known; possibilities include warm
water temperatures (above 22° C), activity of some unrecognized pre-
O
dator, and some toxic factor. RytherJ has found definite experimental
evidence that senescent Chlorella cells contain a substance which inhi-
bits growth and reproduction of Daphnia magna feeding upon them,
23
-------
while rapidly growing algae exhibit no such antagonistic effect. At any
rate, with the Daphnia concentration less than 100 per liter, as it was
most of the time from June to October, removal of algae was not com-
plete.
Biological upsets of the algae population in Pond 1 occurred in almost
periodic fashion at approximately two-month intervals. The first time,
in September, 1970, Daphnia invaded the pond and slaughtered most of
the algae. After recovery a school of Gambusia was introduced, and
it appeared to be holding the Daphnia under control, since the fish were
observed occasionally in small concentrations for six months. Minor
raids on the algae happened in December and February, but were read-
ily controlled by temporarily increasing the flow. However, a serious
Daphnia pulse came on suddenly about the first of April. The algae
were nearly wiped out, but normal conditions were restored in about
a week by maintaining a high flow rate. Another invasion began about
May 15. This time flushing for several days brought little change,
and the pond was drained. After refilling, the algae population was
quickly reestablished, but it built up rather slowly during June, and
finally reached a peak level around the middle of July. The next upset
was a bloom of rotifers which appeared suddenly at the end of July.
Flushing for two days brought the rotifers under control. Algae recov-
ery was slow; at the end of August their population was about half of
the July peak when a second rotifer bloom again cut them down. The
deterioration in Pond 1 phosphate removal during times of low algae
concentration can be seen in Figure 16.
Intensity of photosynthesis which occurred in Pond 1 is indicated by the
pH and alkalinity data of Figures 19 and 20, and by dissolved oxygen
concentrations given in Table 2. The most sensitive measure is pH.
Influent pH was rather steady throughout the year at about 7.2. In the
pond, however, the removal of carbon dioxide by photosynthesis re-
sulted in higher pH values at nearly all times, with peaks of 10 being
reached under the intense light conditions of summer days. Lapses in
photosynthetic activity caused by loss ,of the algae population are clear-
ly apparent in the pH record. In Pond 2 the pH was normally about 7. 4,
the carbon dioxide having been restored by the respiration of higher
organisms, principally Daphnia. The drop in population of these crea-
tures which occurred with the onset of summer allowed the pH to re-
main elevated during this period. The alkalinity record is also affected
by photosynthesis, though less dramatically. The removal of carbon
dioxide itself does not alter alkalinity, but the incorporation of ammonia
24
-------
nitrogen into algal protein and the precipitation of carbonates and
phosphates at raised pH both consume alkalinity at nearly stoichio-
metric ratios. Alkalinity reductions in Pond 1 coincided with periods
of strong pH rise. In Pond 2 the alkalinity loss persisted although the
pH had been brought back down by new carbon dioxide.
Dissolved oxygen remained high in Pond 1 during the entire period of
operation. Peak daytime values of over 40 mg/1 were experienced
when the algae were actively growing. Influent oxygen demand was
relatively low and as a result the nightly drop in D. O. due to respira-
tion was not pronounced. Typical early morning D. O. readings were
around 5 mg/1 lower than the afternoon highs, meaning that Pond 1
was supersaturated most of the time. In the winter and spring months
the D. O. levels in Pond 2 were quite low, mostly because of Daphnia
respiration. The oxygen consumption rate of Daphnia is on the order
of 0.25 mg/day/mg dry weight . At 1000 organisms per liter and
average organism weight of 0. 02 mg, respiration "would amount to
5 mg/I/day. Exertion of BOD in the pond liquid and bottom sediments
would also reduce dissolved oxygen.
Later, when the Daphnia population had fallen off, there were wide
daily fluctuations in the dissolved oxygen on Pond 2. High influent
D. O. and some photo synthetic activity produced supersaturation in
the daytime, while respiration (of bottom sediments and a varied
pelagic population) lowered the oxygen during the night down to a few
milligrams per liter. Lack of oxygen by itself was probably not the
reason for disappearance of the Daphnia, since they thrived at con-
siderably lower D. O. levels earlier in the year.
25
-------
SECTION VII
DESIGN IMPLICATIONS
From a nutrient removal standpoint, optimization of the process con-
sists in achieving both maximum algae growth and complete algae
entrapment. The inorganic carbon in the feed should be photosynthe-
sized to an extent which raises the pH above 10, since only then will
there be extensive precipitation of phosphate. Uptake of nitrogen is
also proportional to algae production. To accomplish relatively com-
plete conversion the hydraulic throughput must be controlled so as to
pace the growth rate. Basically this means giving each volume of
liquid its due quota of solar radiation. During portions of July and
August when the pH of Pond 1 was being driven above 10, the hydraulic
feed rate was about 11 cm/day. It may be inferred that this application
rate represents an approximate upper limit for good carbon conversion
in the summertime. The corresponding algae production was about
11 gm/sq m/day. To obtain equal results in the winter, when tempera-
tures and light intensity are both lower, would require a considerable
reduction in surface loading.
In the algae stage it is desirable to maintain as shallow a depth as
possible, consistent with total absorption of impinging light. For a
given pond surface area, shallower depth is associated with shorter
residence time; short average generation time for the algae is desir-
able for maintaining a vigorous culture and minimizing loss of synthe-
sized tissue by endogenous respiration. Since the phosphate removal
process is substantially complete in a few days, it would seem possible
to reduce the Pond 1 depth from 1.4m used to 1.0m or less with some
advantage.
Under favorable environmental conditions Daphnia begin to produce
broods of young at an age of less than two weeks. Each brood contains
around a dozen new organisms, so that the effective generation time is
only one or two days. As far as maintenance of the Daphnia population
is concerned, the second-stage detention time could be very short, but
it is also necessary to attain complete algae removal. The Daphnia
can easily consume their own weight in algae each day. Using this as
a loading criterion, the detention time should be at least equal to the
26
-------
weight ratio of algae feed concentration to Daphnia pond concentration.
A parallel criterion is that the pond detention time should be several
times the turnover time for Daphnia filtration. Under normal circum-
stances the feed ratio criterion would control. With an algae concen-
tration of 50 mg/1 and a Daphnia population consisting of 500 organisms
per liter with 0. 02 mg average weight, the detention time should be at
least five days.
Depth in the Daphnia stage does not seem to be critical. Economics
of construction and maintenance suggest using a fairly deep pond, on
the order of 5 meters. One feature of probable importance is provision
for seasonal cleaning. When the Daphnia are filtering effectively, most
of the organic nitrogen received by the pond as algae remains as bottom
sediment. Removal once a year, by draining and scraping, for exam-
ple, would prevent the eventual resuspension of the deposited nutrients.
Predator incursions in the algae stage are a major operating problem.
Control of these higher organisms by mechanical screening may be
feasible, but such measures would destroy the system's principal vir-
tue of simplicity and low cost. Another means of coping with predator
plagues would be to divide the algae pond into multiple compartments,
so that not all of the algal biomass would be simultaneously exposed.
Upon the appearance of Daphnia in one compartment, it would be drained
and refilled with culture from an adjacent unit. To reduce opportunity
for seeding of the algae stage with Daphnia, it would be helpful to sepa-
rate the two pond stages physically. A free overflow weir at the outlets
of all algae units will prevent entry of Daphnia which might have worked
their way upstream.
27
-------
SECTION VIII
REFERENCES
1. Richman, S. , The Transformation of Energy by Daphnla
pulex. Ecol. Monographs. 28:273, 1958.
2. Bennett, G. W. , Management of Lakes and Ponds. New York,
Van Nostrand Reinhold, 1971. 365 p.
3. Ryther, J. H. , Inhibitory Effects of Phytoplankton upon the
Feeding of Daphnia magna with Reference to Growth, Reproduc
tion and Survival. Ecology. 35:522, 1954.
28
-------
AVERAGE TEMPERATURE
SEPTEMBEB , OCTOBER NOVEMBER , DECEMBER JANUARY , FEBRUARY , MARCH APRIL MAY , JUNe JULY AUGUST -JJPTEMBLR OCTQBEFt
ro
CTQ
p
-i
n>
SEPTEMBER OCTOBER NOVEMBER
DECEMBER
1970
JANUARY
1971
FEBRUARY MARCH APRIL MAV JUNE
-------
>-
<
a
o
o 0
o.
Ul
a
Ul
to
5
HYDRAULIC TURN-OVER RATE
JANUARY . ftaiBMRt . MARCH . APRIL , MAY '97' JUNE JULY
+
f
_AuaugT . KPTEMBER . OCTOaER
"' ' ""' "I" \ I «5
POND NO. I
POND NO. 2
JANUARY ' FEBRUARY ' MARCH ' APRIL
MAY ^ JUNE ' JULY ' AUGUST ' SEPTEMBER1 OCTOBER
1971
TO
oo
-------
LIQUID CLARITY
SEPTEMBER i OCTOBER I NOVEMBER I DECEMBER JANUARY
FEBRUARY i MARCH
JULY i AUOU5T . SEPTEMBER . OCTOBER
TRANSPARENCE
o
. z
X
SEPTEMBER ' OCTOBER ' NOVEMBER I DECEMBER JANUARY I FEBRUARY ' MARCH
1970 97
-------
SUSPENDED SOLIDS
1970 1971
|20 SEPTEMBER | OCTOBER j NOVEMBER j DECEMBER [ JANUARY | FEBRUARY j MARCH j APRIL
80
40
200
160
KJ
120
BO
4O
0
120
40
0 <-
. JULV i AUGUST . SEPTEMBER . OCTOBER ^n
INFLUENT
POND 1
POND 2
juu
SEPTEMBER ' OCTOBER ' NOVEMBER
DECEMBER
1970
JANUARY
(971
FEBRUARYr MARCH
80
40
200
160
130
8O
40
0
120
80
40
ora
(S
H
O
AUGUST ' SEPTEMBER ' OCTOBER
-------
CHEMICAL OXYGEN DEMAND. UNFILTERED
U70 I»7I '
StfTtMBEB 1 OCiOatR . MOVEMBER | DECEMBER | JANUARY . FEBRUARY i MARCH i APRIL I MM i JUNE i JULY I AUGUST
SEPTEMBER . OCTOBER
120
ioo
ao
60
40
IZO
00
60
60
4O
100
SO
60
40
INFLUENT
100
80
60
40
120
100
80
60
40
100
80
60
O
2
Q
O
u
POND 2.
OCTOBER ' NOVEMBER ' DECEMBER I JANUARY ' PEaRUABy I MARCH I"
(70 | O7I
«*Y ' ' JUNE 1 JULV 'AUOUST ' SEPTEMeER ' OCTOBER
era
-------
TOTAL KJELDAHL NITROGEN
(70 I ItTt
MPTCMMR . OCTOBER . NOVEMBER i DECEMBER
JANUARY PEBRUARY MARCH APRIL MAY , JUNE JULY
INFLUENT
POND 1
.
-
POND 2
EPTtMBER ' OCTOBER ' NOVIMWR ' DECEMBER
ItTO
AUGUST SEPTEMBER OCTOBER
.
-
.
JANUARY ' FEBRUARY ' MARCH APRIL ' MAY ' JUNE JULY ' AUGUST SEPTEMBER OCTOBER
1*71
8
16
4
2
K>
6
4
t
0
14
12
10
6
4
2
0
12
10
8
6
4
Z
0
IS
18
14
12
10
a
8
4
X
o
14
12
to
8
8
4
OQ
-------
OJ
z
I
*1
IS
10
»
0
15
10
5
0
15
10
6
0
l«70
SEPTEMBER OCTOBER i NOVEMBER , DECEMBER
1971
JANUAf
IjjFLUENT
-
POND 1
POND 2
-
-
l«70
AMMONIA NITROGEN
1 I FEBRUARY MARCH *
APRIL
1871
MAY JUNE
MAY JU^fe "
. JULY i AUGUST . SEPTEMB
1
1
till
ER
1
JULY ' AUGUS
OCTOBER
-
-
-
-
T SEPTEMBER OCTOBER
IS
10
5
0
15
10
5
0
IS
10
5
0
-------
w
X
o
2
z*
1
f
6
4
Z
6
4
2
0
e
4
2
0
INFLUENT
-
-
POND 1
POND Z
-
"
. SEPTEMBER ' OCTOBER '
tw iv
NOVEMBER i DECEMBER
l>
,
1 1 , ,
1 1 1
NOVEMBER ' DECEMBER
1*70
JANUARY
.
|
JANUf
|
1RY
,
|
1
|
FEBRUARY MARCH APRIL MAY
FEBRUARY 1 MAR
H ' APRIL ' MAY
| JUNE JULY | AUCUiT ( SEPTEMBER j OCTOBER
-
-
-
ii i i ! , 1 ,.ll . . .1,
;
-
-
H . 1 1 H h i . , i 1 1 1 it
-
-
HI . 1 1 1 1. 1. , , ii i H
1 JUNE ' JULY ' AUGUST ' SEPTEMBER ' OCTOBER
1*71
-------
TOTAL PHOSPHATE. UNFILTERED
SEPTEMBER i OCTOBER i NOVEMBER . DECEMBER JANUARY i FEBRUARY j MARCH i APRIL
JULY i AUGUST , SEPTEMBER . OCTOBER
40
30
20
10
INFLUENT
40
30
20
10
30
0*
Q.
20
10
30
10
POND I
POND 2
30
30
ZO r
10
SEPTEMBER I OCTOBER I NOVEMBER
DECEMBER
1970 I
JANUARY
[971
IFEBRUARY
SEPTEMBER
-------
30
20
10
OD
30
20
10
0
30
20
10
1970 1 1971
SEPTEMBER i OCTOBER i NOVEMBER i DECEMBER 1 JANUAI
INFLUENT
POND 1
POND 2
SEPTEMBER > OCTOBER I NOVEMBER ' CM
IUI AL KMU^KMAI t* NLJ LKtU
*Y FEBRUARY MARCH i APRIL i M
AY JUNE JULY i AUCU ST
III ,
. SCPT
1
1
CEMBCR 1 JANUARY ' FEBRUARY 1 MARCH ' APRIL 1 MAY '. JUNE 1 JULY 1 AUGUST
1970 ' 1471
'SEPT
EM
.MB
Eft OCTOBER
Eft OC
-
T06CR
-
30
20
10
0
30
20
10
0
30
20
10
0
-------
JEPTtMiCR OCTOBER
NOVEMBER
1*70 UTI
DECEMBER , JANUARY
CHLORELLA
FEBRUARY i MARCH
JUNE JULY- AUGUST SEPTEMBER OCTOBER
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-------
SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
ort So.
3. Acc-.-r'oK'ffr
w
4. Title Tertiary Treatment with a Controlled
Ecological System
/. Author($) Gram, Andrew L.
9. Organization Gram/Phillips Associates, Inc. under contract
to Las Virgenes Municipal Water District
5, Re port Da: ^
6.
8. PerfortttmrOrgat-'zatioB
10. Project Mo.
15. Supplementary Motes
11. Contract/Grant I'1 v.
16080 FBH
13. Type ( " Repor and
Period Covered
Environmental Protection Agency report number,
EPA-660/2-73-022, December 1973.
r, 1
16.
Abstract A two-stage pond system was operated as a process for polishing
secondary sewage effluent. The shallow first stage was an oxidation pond
in which a heavy growth of algae was permitted to develop. In the second
stage a population of Daphnia pulex consumed the algae. Detention times
were about 10 days in each stage. Chemical and biological monitoring were
carried out over a year's period to determine feasibilityof using the process
to produce recreational-grade water and reduce algae growth potential.
While the Daphnia remained as the dominant zooplankton species in
the second pond throughout the observation period, their concentration varied
between 100 and 1, 500 organisms/liter. Excellent water clarity was obtained
when the Daphnia were above 500 organisms/liter, and at such times the
over-all COD reduction was greater than 40 percent. Significant removal of
nutrients occurred only during the months of July and August, when N and P
reductions were 48 percent and 63 percent respectively. Performance was
hampered by occasional invasions of Daphnia or rotifers in the first-stage pond,
which decimated the algae. Such events were not successfully controlled and
remain the principal obstacle to further process development.
i7a. Descriptors Waste water treatment, Water reclamation, Aquatic biology
17b. Identifiers
Biological processes, Oxidation ponds, Zooplankton
17c. COWRR Field & Group
18. Availability
IS. S-"urityC'ass.
(Report)
i
; 20. Security Class.
I
21.
K->. of
Pages
22. Price
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON, D. C. 2O24O
Abstractor Andrew L. Gram | Institution Gram/Phillips Associates, Inc
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