EPA-625/4-73-001b Revised
This document has not been
submitted to NTIS, therefore it
should be retained.
Upgrading
Lagoons
EPA Technology Transfer Seminar Publication
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EPA-625/4-73-001b
UPGRADING LAGOONS
ENVIRONMENTAL PROTECTION AGENCY • Technology Transfer
August 1973
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ACKNOWLEDGMENTS
This seminar publication contains materials prepared for the U.S.
Environmental Protection Agency Technology Transfer Program and
presented at Technology Transfer design seminars throughout the
United States. It is a revised version of a publication originally prepared
in August 1973.
The information in this publication was prepared by D. H.
Caldwell, D. S. Parker, W. R. Uhte, and R. J. Stenquist, representing
Brown and Caldwell, Consulting Engineers, Walnut Creek, Calif.
NOTICE
The mention of trade names or commercial products in this publication is for
illustration purposes, and does not constitute endorsement or recommendation for
use by the U.S. Environmental Protection Agency.
Revised June 1977
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CONTENTS
Chapter I. Lagoons in Waste Treatment 1
Types of Lagoons 1
Operating Problems 2
References 4
Chapter II. Upgrading Lagoons Through Process Modification 6
Pond Efficiency Versus Pond Loading 6
Pond Recirculation and Configuration 7
Feed and Withdrawal 10
Pond Transfer Inlets and Outlets 11
Pond-Dike Construction 11
Supplemental Aeration and Mixing 13
References 16
Chapter III. Upgrading Lagoons Through Algae Removal 17
Types of Algae in Oxidation Ponds 18
Coagulation-Clarification Processes 19
Filtration 28
Microstraining 31
Centrifugation 32
Land Treatment 32
In-Pond Removal Systems 32
Summary 34
References 35
Chapter IV. Examples of Upgrading Ponds 38
Case 1. Sunnyvale Water-Pollution-Control Plant 38
Case 2. Stockton Regional Waste Water Control Facility 55
Case 3. Antelope Valley Tertiary Treatment Plant—Lancaster 60
Case 4. Richfield Springs Sewage-Treatment Plant 61
References 66
m
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Chapter I
LAGOONS IN WASTE TREATMENT
Lagoons are one of the most commonly employed secondary waste-treatment systems. In
1968, treatment systems in the general category of "stabilization ponds" constituted 34.7 percent
of the 9,951 secondary treatment systems operating in the United States. Stabilization ponds served
7.1 percent of the 85,600,000 people served by secondary treatment plants. These ponds usually
serve small communities; 90 percent were in communities with 10,000 persons or less.1
TYPES OF LAGOONS
Waste-treatment lagoons can be divided conveniently into five general classes (table 1-1) ac-
cording to the types of biological transformations taking place in the lagoon.a Two of these classes,
high-rate aerobic ponds and facultative ponds, are also called oxidation ponds.
High-Rate Aerobic Ponds
In high-rate aerobic ponds, algae production is maximized by allowing maximum light penetra-
tion in a shallow pond. These ponds are generally only 12-18 inches in depth and are intermittently
mixed. The main biological processes are aerobic bacterial oxidation and algal photosynthesis. Or-
ganic loadings range from 60 to 200 pounds 5-day biochemical oxygen demand (BOD5) per acre per
day. Usually 80-95 percent of the waste organic matter is converted to algae.
Facultative Ponds
Facultative ponds are perhaps the most numerous of the pond systems and are deeper than
high-rate aerobic ponds, having depths of 3-8 feet. The greater depth allows two zones to develop:
an aerobic surface zone and an anaerobic bottom layer. Oxygen for aerobic stabilization in the
Table 1-1.-Types of lagoons
Type
High-rate aerobic pond
Facultative pond
Anaerobic pond
Maturation pond ... . . .
Aerated lagoon
Depth,
feet
1 to 1.5
3 to 8
Variable
3 to 8
Variable
Loading,
Ib BOD5 /acre/day
60 to 200
1 5 to 80
200 to 1 000
<15
Up to 400 Ib/acre/day
BOD
removal
or con-
version,
percent
80 to 95
70 to 95
50 to 80
Variable
70 to 95
aFor a complete review of the technology and art of this form of treatment, see references 2 through 4.
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surface layer is provided by photosynthesis and surface reaeration, while sludge in the bottom layer
is anaerobically digested. Loadings generally range from 15 to 80 pounds BOD5 per acre per day,
and BOD5 removal from 70 to 95 percent, depending on the concentration of algae in the effluent.
BOD5 removals as high as 99 percent have been obtained.
Anaerobic Ponds
Organic loads are so high in anaerobic ponds that anaerobic conditions prevail throughout.
BOD5 loadings are generally in the range of 200-1,000 pounds BOD5 per acre per day, and BOD5
removals are limited to about 50-80 percent. Anaerobic ponds are usually followed by aerobic or
facultative ponds to reduce the BOD5 in the effluent.
Maturation or Tertiary Ponds
The maturation, or tertiary, pond generally is used for polishing effluents from conventional
secondary processes, such as trickling filtration or activated sludge. Settleable solids, BOD5, fecal
organisms, and ammonia are reduced. Algae and surface aeration provide the oxygen for stabiliza-
tion. BOD5 loadings are generally less than 15 pounds BOD5 per acre per day, but may be higher.
Aerated Lagoons
Aerated lagoons derive most of their oxygen for aerobic stabilization by mechanical means,
either air diffusion or mechanical aeration. Photosynthetic oxygen generation usually does not play
a large role in the process. Up to 95 percent BOD5 removals are obtainable, depending on detention
time and the degree of solids removal.
OPERATING PROBLEMS
With increasingly stringent effluent requirements, waste-treatment lagoons, like any other
waste-treatment process, may require modification to meet all objectives. The problems that occur
with individual ponds, however, may not be common to all.
Organic Matter in Effluents
An algal-bacteria symbiosis operates in both aerobic and facultative ponds. Under aerobic con-
ditions, bacteria degrade organic matter according to the following simplified transformation:
CH2O + O2 bactena, CQ2 + H2O (1-1)
(organics)
Under anaerobic conditions, the equation is:
2CH2 O bacteria> CH3 COOH bacteria> CO2 + CH4 (1-2)
Algae, in turn, reuse the carbon (as carbon dioxide) to form algal biomass:
l + O2 H
(algae)
CO2 + 2H2O + energy dgae» CH2O + O2 + H2O (1-3)
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While these equations oversimplify the transformations, they show the recycling of carbon in
ponds. Unless the algae are removed, or the carbon is removed through methane fermentation in an
anaerobic sludge layer, little organic reduction may occur.5
The fate of algae discharged to receiving waters has received relatively little attention, possibly
because severe problems have not developed in most instances. Two studies have shown, however,
that for two differing aquatic environments the algae did constitute a BOD load on the receiving
waters and decreased the dissolved oxygen (DO) levels.6'7 In these cases, the algae from the pond
effluent were in an unfavorable environment for either their maintenance or growth, and they
decayed (as in equations 1-1 and 1-2).
Secondary treatment requirements developed by the EPA limit treatment-plant effluent BOD
and suspended solids (SS) concentrations to less than 30 and 45 mg/1 on a monthly and weekly
average, respectively. Figure 1-1 presents average effluent qualities for three types of lagoons.8 None
have BOD or SS concentrations of less than 30 mg/1, and the facultative lagoon, the type most com-
monly used, has an average SS concentration of 70 mg/1. Figure 1-1 clearly indicates that additional
70
60
50
40
30
20
10
LL
U.
BOD
SS
Facultative
lagoon
Aerated
lagoon
Tertiary
lagoon
Figure 1-1. Performance of lagoon systems.8
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treatment will usually be necessary to enable pond systems to meet the secondary treatment re-
quirements.
Aerated-lagoon effluents, while not containing large amounts of algae, may contain biological
solids resulting from the conversion of a portion of the BOD5. One aerated-lagoon application
achieved only 70 percent BOD5 removal; the insertion of a final clarifier in the process allowed 90
percent BOD5 removal because of solids removal.9
Odors
That lagoons may occasionally emit odors is shown by the very common State requirements
concerning lagoon location, i.e., requirements that lagoons should be located as far from existing or
future residential or commercial development as is practical or reasonable. Anaerobic ponds par-
ticularly tend to have odor problems due to hydrogen sulfide formation, although some methods
have been developed for odor control.
Noxious Vegetative Growths
Without maintenance and good design, aquatic growths may develop in ponds. Deeper ponds
(deeper than 3 feet) will discourage rooted growths, and proper levee maintenance can handle
shoreline problems. If not suitably controlled, noxious plants can choke off hydraulic operation and
create large accumulations of floatable debris. The debris usually becomes septic and creates odors
and conditions detrimental to photosynthetic activity.
Seasonal Performance Variations
In most locales of the United States there are seasonal changes in both available light and tem-
perature. Typically, in the winter algae activity diminishes. Biological activity may also slow;
methane fermentation in facultative ponds may practically cease.5 Thus, in winter BOD5 removals
may be low. In Michigan, no discharge is permitted until the spring thaw when increased biological
activity causes a lower effluent BOD5.10
Despite operating problems, which certainly have not occurred with every lagoon application,
lagoons have been providing economical treatment at thousands of locations for decades. Low
capital cost, simplicity of operation, and low operation and maintenance costs have favored lagoon
treatment. Considering both more stringent water-quality criteria and environmental constraints
posed by encroaching suburbanization, however, many lagoons will have to be upgraded in both
treatment efficiency and mode of operation.
REFERENCES
1 Federal Water Quality Administration, "Municipal Waste Facilities in the United States," No.
CWT-6, Washington, D.C., 1970.
^Second International Symposium for Waste Treatment Lagoons, Missouri Basing Engineering
Health Council and Federal Water Quality Administration, Kansas City, Mo., June 23-25,1970.
3Missouri Basin Engineering Health Council, "Waste Treatment Lagoons—State of the Art,"
EPA-WQCRS 17090EHX, Washington, D.C., July 1971.
4U.S. Environmental Protection Agency, Office of Water Programs, "Wastewater Treatment
Ponds," Technical Bulletin, supplement to Federal Guidelines: Design, Operation, and Maintenance
of Wastewater Treatment Facilities, EPA 430/9-74-011, Washington, D.C., Mar. 1974.
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5W. J. Oswald, A. Meron, and M. D. Zabat, "Designing Waste Ponds to Meet Water Quality
Criteria," Second International Symposium for Waste Treatment Lagoons, pp. 186-194, Missouri
Basin Engineering Health Council and Federal Water Quality Administration, Kansas City, Mo.,
June 23-25,1970.
6R. C. Bain, P. L. McCarty, J. A. Robertson, and W. H. Pierce, "Effects of an Oxidation Pond
Effluent on Receiving Water in San Joaquin River Estuary," Second International Symposium for
Waste Treatment Lagoons, pp. 168-180, Missouri Basin Engineering Health Council and Federal
Water Quality Administration, Kansas City, Mo., June 23-25,1970.
7D. L. King, A. J. Tolmsoff, and M. J. Atherton, "Effect of Lagoon Effluent on a Receiving
Stream," Second International Symposium for Waste Treatment Lagoons, pp. 159-167, Missouri
Basin Engineering Health Council and Federal Water Quality Administration, Kansas City, Mo.,
June 23-25, 1970.
8G. Barsom, U.S. Environmental Protection Agency, Office of Research and Development,
Lagoon Performance and the State of Lagoon Technology, EPA-R2-73-144, Washington, D.C., June
1973.
9L. A. Esvelt and H. H. Hart, "Treatment of Fruit Processing Waste by Aeration," J. Water
Pollut. Cont. Fed., 42, 1,1305-1326,1970.
10Maurice M. Richmond, "Quality Performance of Waste Stabilization Lagoons in Michigan,"
Second International Symposium for Waste Treatment Lagoons, pp. 54-62, Missouri Basin Engi-
neering Health Council and Federal Water Quality Administration, Kansas City, Mo., June 23-25,
1970.
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Chapter II
UPGRADING LAGOONS THROUGH PROCESS MODIFICATION
Many of the techniques available for upgrading lagoons treating primary and secondary efflu-
ents have already been incorporated in designs at one or more locations—often in the original con-
struction and not as a modification. A well-designed pond will incorporate physical features that
minimize upsets, maintenance, and nuisances, and maximize operational flexibility, stability, and
biochemical oxygen demand (BOD) removal. Physical design features that should be considered
include configuration, recirculation, feed and withdrawal variations, pond transfer inlets and
outlets, dike construction, supplementation of oxidation capacity, and algae removal. These fea-
tures will be discussed in this chapter.
The discussion that follows will center on lagoons treating primary or secondary effluents. Many
of the waste-treatment lagoons in the United States, particularly in the Midwest, treat raw sewage.
One of the ways to upgrade such lagoons is to add primary or primary-plus-secondary treatment ahead
of the ponds.
POND EFFICIENCY VERSUS POND LOADING
It is fairly well established that pond-process performance is affected by both area! BOD
loading3 and detention time.1-2 Typical data for canning wastes are shown in figure II-l. A similar,
200
IO
20
4O 60 100 2OO 40O 1000 3OOO IO,OOO
Y, LB. BOD/ACRE-DAY
Figure 11-1. BOD-removal relationship for ponds treating cannery wastes.1
aExcept for aerated lagoons, where areal BOD loading is not an appropriate design criterion.
6
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but not necessarily identical, empirical relationship would apply to domestic wastes. Figure II-1
shows that pond performance can be improved by three techniques.
• Increased detention time will increase BOD removal and can be accomplished by deepening
the pond. The most probable cause of improvement would be increased algae sedimentation.
• Decreased areal BOD loading will increase the BOD removal by decreasing the carbon to be
processed (and recycled to algae). This decreased loading can be accomplished by pretreat-
ment; e.g., placing a primary sedimentation unit before the pond in a system formerly using
only raw-sewage ponds.
• Decreased aeral BOD loading and increased detention time can be accomplished by increasing
the number of ponds in the system.
POND RECIRCULATION AND CONFIGURATION
Pond recirculation involves interpond and intrapond recirculation as opposed to mechanical
mixing in the pond cell. The effluents from pond cells are mixed with the influent to the cells.
In intrapond recirculation, effluent from a single cell is returned to the influent to that cell. In
interpond recirculation, effluent from another pond is returned and mixed with influent to the pond
(see fig. II-2).
Recycle
Pump station
(typical)
INTRAPOND RECIRCULATION
Recycle
1
1
ta»
\J*
*—
1
—*
1
-J
SERIES
Parallel Parallel series
INTERPOND RECIRCULATION
Figure 11-2. Common pond configurations and recirculation systems.
7
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Both methods return active algal cells to the feed area to provide photosynthetic oxygen for
satisfaction of the organic load. Intrapond recirculation allows the pond to gain some of the
advantages that a completely mixed environment would provide if it were possible in a pond. It
helps prevent odors and anaerobic conditions in the feed zone of the pond.
Both interpond and intrapond recirculation can affect stratification in ponds, and thus gain
some benefits ascribed to pond mixing, which is discussed later. Pond recirculation is not generally
as efficient as are mechanical systems in mixing facultative ponds. Both pond mixing and pond re-
circulation are incorporated in the Sunnyvale, Calif., example (ch. IV, case 1).
Three common types of interpond-recirculation systems (series, parallel, and parallel series)
are shown in figure II- 2. Others have been suggested but seldom used.
One objective of recirculation in the series arrangement is to decrease the organic loading in
the first cell of the series. While the loading per unit surface is not reduced by this configuration,
the retention time of the liquid is reduced. The method attempts to flush the influent through the
pond faster than it would travel without recirculation. The hydraulic retention time of the influent
and recycled liquid in the first, most heavily loaded pond in the series system is:
V
T = - (II-l)
(1 + r)F
where V is the volume of pond cell, F is the influent flow rate, r, or R/F, is the recycle ratio, and
R is the recycle flow rate.
Another advantage of recirculation in the series configuration is that the BOD in the mixture
entering the pond is reduced, and is given by the expression:
' (U'2)
where Sm is the BOD of the mixture, S3 is the effluent BOD from the third cell, and Sin is the
influent BOD. Thus, Sm would be only 20 percent of Sin with a 4:1 recycle ratio, as S3 would be
negligible in almost all cases. Thus, the application of organic load in the pond is spread more evenly
throughout the ponds, and organic loading and odor generation near the feed points are less. Recir-
culation in the series mode has been used to reduce odors in those cases where the first pond is
anaerobic.3
The parallel configuration more effectively reduces pond loadings than does the series
configuration, because the mixture of influent is spread evenly across all ponds instead of the first
pond in a series. Recirculation has the same benefits in both configurations.
For example, consider three ponds, either in series or parallel. In the parallel configuration,
the surface loading (pounds BOD5 per acre per day) on the three ponds is one-third that of the
first pond in the series configuration. The parallel configuration, therefore, is less likely to produce
odors than the series configuration.
Recirculation usually is accomplished with high-volume, low-head propeller pumps. Figure
II-3 presents a simplified cross section of such an installation. In this design, the cost and mainte-
nance problems associated with large discharge flap gates are eliminated by the siphon discharge.
An auxiliary pump with an air eductor maintains the siphon. Siphon breaks are provided to insure
positive backflow protection.
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POND
SUPPLY
CHANNEL
4-inch air and vacuum
release valve
2-inch eductor
Figure 11-3. Cross section of a typical recirculation
Bar screen
POND
RETURN
CHANNEL
pumping station.
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Pumping stations of this type can be designed to maintain full capacity with minimal increase
in horsepower even when the inlet and discharge surface levels fluctuate over a 3-4-foot range.
Multiple- and/or variable-speed pumps are used to adjust the recirculation rate to seasonal load
changes.
Pond configuration should allow full use of the wetted pond area. Transfer inlets and outlets
should be located to eliminate dead spots and short circuiting that may be detrimental to photo-
synthetic processes. Wind directions should be studied, and transfer outlets located to prevent
dead pockets where scum will tend to accumulate. Pond size need not be limited, as long as proper
distribution is maintained.
FEED AND WITHDRAWAL
Opinion in the literature is nearly unanimous that ponds should be fed by a single pipe, usually
toward the center of the pond. Such design should be used for raw-sewage treatment by ponds. It
has been found that with primary or secondary effluent, a single point of entry into a pond tends
to overload the pond in the feed zone, allowing odors to develop. Brown and Caldwell often employs
a multiple-entry and single-exit approach to distribute evenly the organic load throughout the pond
cell (see fig. II-4). One form of multiple inlet, used for ponds as large as 20 acres, uses inlet head
loss to induce internal pond circulation and initial mixing. The inlet pipe, laid on the pond bottom,
has multiple ports or nozzles all pointing in one direction and at a slight angle above the horizontal.
Port head loss is designed for about 1 foot at average flow, resulting in a velocity of 8 feet per
second. This velocity induces sufficient mass pond movement to permit the pond outlet to be located
near the inlet. A second outlet, with low head loss and controlled by an overflow weir, accommodates
peak wet-weather flow.
The multiple-entry, multiple-exit approach has been used in the Stockton, Calif., ponds (case
2, ch. IV). This system was developed to discourage the development of stagnant surface areas
within the pond that can cause development of blue-green algae mats. Such mats can emit odors.
Single entry
and single exit
Multiple entry
and single exit
^-
^
^-
^-
Multiple entry and multiple exit
Figure 11-4. Methods for feed and withdrawal from ponds.
10
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POND TRANSFER INLETS AND OUTLETS
Pond transfer inlets and outlets should be constructed to minimize head loss at peak recircula-
tion rates, assure uniform distribution to all pond areas at all recirculation rates, and maintain water-
surface continuity between the supply channel, the ponds, and the return channel.
Transfer pipes should be numerous and large enough to limit peak head loss to about 3-4 inches
with the pipes flowing about two-thirds to three-quarters full. Supply- and return-channel sizing
should assure that the total channel loss is no more than one-tenth of the transfer-pipe losses. When
such a ratio is maintained, uniform distribution is assured.
By operating with the transfer pipes less than full, unobstructed water surface is maintained
between the channels and ponds, which controls scum buildup in any one area.
Transfer inlets and outlets usually are made of bitumastic-coated, corrugated-metal pipe, with
seepage collars located near the midpoint. This type of pipe is inexpensive, strong enough to with-
stand rough handling and rapid backfilling, and flexible enough to allow for the differential settle-
ment often encountered in pond-dike construction.
Specially made fiber-glass plugs can be provided to close the pipes. The plugs may be installed
from a boat. Pond recirculation must be shut down to remove the plugs. Such plugs permit any
pipe to be closed without expensive construction of sluice gates and access platforms at each transfer
point. Concrete launching ramps into each pond and channel assure easy boat access for sampling,
aquatic plant control, and pond maintenance.
POND-DIKE CONSTRUCTION
Pond and channel dikes usually can be constructed with side slopes between 6 horizontal to 1
vertical and 2 horizontal to 1 vertical. The final slope selected will depend on the dike material
and the water-erosion protection to be provided. All soils, regardless of slope, will require some type
of protection in zones subject to wave action, hydraulic turbulence, or aerator agitation. Examples
of turbulent zones are areas around the discharge areas at the recirculation pumping station and areas
around the influent and effluent connections.
If the wind is always in one direction, wave-action-erosion protection usually can be limited to
those areas that receive the full force of the wind-driven waves. Protection should always extend
from at least 1 foot below the minimum water surface to at least 1 foot above the maximum water
surface.
Protection against hydraulic turbulence should extend several feet beyond the area subject to
such turbulence. Protection material should not impede the control of aquatic plant growth.
Pond and channel dikes must be kept completely free from grass and aquatic plants if the ponds
are to achieve peak efficiency and operate without odor and insect nuisance. Weeds and aquatic
growths usually are controlled by periodic spraying, although cutting and actual physical removal are
sometimes necessary. Ponds with luxuriant shoreline growths of cattails and other aquatic plants may
seem healthy and beautiful. Closer inspection, however, reveals that such growths harbor heavy
accumulation of septic scum, which causes odors and loss of treatment capability.
The tops of the dikes should be at least wide enough for a 10-foot-wide, all-weather gravel
road. Such a road is essential for pond inspection and for the control of insects, erosion, and plant
growth on the dike surfaces.
Figure II-5 shows some details of dike design.
11
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TRANSFER PIPE INVERT
MUST EXTEND AT LEAST
3" BEYOND SLOPE
POND
SUPPLY
t lO'-O WIDE ACCESS ROADWAY WITH 6" THICK
AGGREGATE BASE COURSE
TOP OF I THICK RIPRAP EL IO5.OO
PLASTIC PLUG
SEE DETAIL
BOTTOM OF I THICK RIPRAP
EL IOO OO
OXIDAT ION
POND
3O" CMP TRANSFER PIPE
CORRUGATED METAL SEEPAGE COLLARS
SEE DETAIL
PROVIDE lO'-O WIDE » 12 "THICK LAYER OF
RIPRAP SYMMETRICALLY AROUND EACH END
OF TRANSFER PIPE BETWEEN EL IO5.OO
AND IOO.OO
TYPICAL DIKE CROSS SECTION AT TRANSFER PIPE
NO SCALE
12 GA. CORRUGATED METAL
2'-0 WIDE BAND (TYP)
PROVIDE OVERLAP
AT ALL JOINTS
WELD SEEPAGE COLLAR
TO BANDS
TYP. SEEPAGE COLLAR DETAIL
NO SCALE
CLAMPS AND SLOTS, SEE SECT/ON I
s~^
'/<" FIBERGLASS REINF.
PLASTIC PLUG
-30 CMP
SIDE ELEVATION
END ELEVATION
'/2 " x 2" FIBERGLASS
REINF PLASTIC CLAMP
PROVIDE z'/i" * 3/i" SLOTS AT INTAKE
ENDS OF ALL TRANSFER PIPES
SECTION(T)
TYPICAL PLUG DETAIL
NO SCALE
Figure 11-5. Details of dike design.
12
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SUPPLEMENTAL AERATION AND MIXING
While intermittent mixing has been applied to shallow, high-rate aerobic ponds,4 greater
attention has been given to mechanical mixing and to aeration within the cells of facultative ponds.
Sometimes, when ponds must treat high, seasonal BOD loading or operate under winter conditions,
or when there is no more room for expansion, supplementation of the ponds' photosynthetic oxida-
tion capacity is required. (When no oxygen is supplied by photosynthesis, the system is called an
aerated lagoon.b)
The supplementation usually is achieved by installing compressed air diffusers or mechanical
aerators. When the ponds' extra needs are relatively minor and uniform throughout the year, com-
pressed-air aeration may be best. Indeed, if the ponds are located in a cold climate, year-round
aeration may be necessary to maintain whatever photosynthetic activity is possible during freezing
weather. Preventing surface freezing also allows direct oxygen transfer. When supplemental
oxygen requirements are high or when the requirements are either seasonal or intermittent,
mechanical aerators are used.
In addition to transferring oxygen to the liquid, aeration breaks up the thermal stratification
that normally develops in oxidation ponds. Marais3 reports that the persistent stratification in
ponds diminishes the nonmotile algae population, because the algae settle below the photic zone
and die from lack of light. Mixing tends to increase algae numbers and to maintain aerobic condi-
tions deeper in the pond. By increasing algae numbers, the pond can produce more oxygen, thus
increasing its capacity for organic loading.
Surface agitation also breaks up the thin surface layer of slick or scum that forms on calm
days. If not destroyed, the scum layer can diminish performance both by decreasing the photo-
synthetic rates and by decreasing surface aeration.
Mechanical aerators generally are divided into two types: cage aerators (fig. II-6)9 and the
more common turbine and vertical-shaft aerators (fig. II-7). Cage aerators are relatively new in the
United States (see ch. IV, case 1) and work particularly well in shallow ponds (less than 5 feet
deep). Propeller aerators require a minimum depth depending on the horsepower of the unit. For
shallow ponds a large number of low-horsepower units are required, and the cost per horsepower
rises.
The cage aerator appears to have an area of influence of as much as 1,200 feet (as determined
by photographs). While no precise comparison has been made, this device appears to have a much
greater pumping capacity than the propeller aerator. The latter device tends to recycle much of
the volume pumped, especially in shallow ponds.
Floating propeller aerators are always mounted out in the pond, far enough apart to
minimize interference with one another or with other pond features. When used for shallow ponds,
they require minimum-depth pits lined with erosion-resistant surfaces. These surfaces are usually
some form of paving, often concrete. Power access is usually via underwater cable, while mainte-
nance access is almost always by boat.
Floating cage aerators may be mounted either in the pond or directly off the dike slopes (as at
Sunnyvale, case 1, ch. IV). When mounted off the dike slopes, they can be close to the pond trans-
fer inlets. The entire dike slope in the immediate area is provided with erosion protection. Units
"For information on design of aerated lagoons, see references 5-8.
13
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CONCRETE ANCHOR
NOT purr or THIS cowwxcr
STHUEmCAL ABOUT )
AERATOR POKE UNIT
tffp)
A'/.''PIPE
iANDRAIL
PL AN - TYPICAL. POND AERATOR
3-2x0 Hiu/nwr
: ANCHOR NOT
SECTION
SECTION
SECTIONf
Figure 11-6. Floating cage aerator.
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LABYRINTH SEAL BUARD
FASTENERS, SAFETY WIPED IN PLACE
MOTOR SHAFT
17-4 PH STH. STL
ONE PIECE
BOLT AND NUT
ia-e STN STL
NOTE - STAINLESS STEEL LOCKNUTS
USED BELOW WATER LINE
SO HP TEFC MOTOR
4fO V, 3 PHASE, CO HERTZ
CLASS V INSULATION
US SERVICE FACTOR
NON HYSROSCOPIC WINDIHSi
HEAVY DUTY MOTOR BEARIN
CORROSION RESISTANT
PAINT
EXPLOSION PROOF CONDUIT BOX
COMPRESSION LOCK SEAL
PVC OBL JACKET COPPER STRAND ELECT. CABLE
U.L. APPROVED FOR UNDER WATER SERVICE
DIFFUSION HEAD, 3O4 STN. STL. CASTING
ANTI-DEFLECTION INSERT
FLUID DEFLECTOR
, TOP SKIN, 3O4 Sr« SH. , 14 SAGE
\
VOLUTE, 3O4 STN. STL
PROPELLER, 3ie STN STL
INTAKE CONE
INTAKE CONE CLIP
ANTI-EROSION PLATE ASSEMBLY
ANCHOR CABLE
BRACKET
OUTER SKIN,
3O4 STN. STL., 14 BASE
9'-6
-POLYURETHANE
FOAM FILLED FLOAT
Figure 11-7. Floating propeller aerator.
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mounted on the slope offer easy access for maintenance and repair and the extra reliability of
above-water power supply.
Most previous pond-aeration systems seem to have used diffused aeration. For best efficiency,
these systems require that the ponds be deepened to 10 feet.10
Pond aeration and mixing systems serve mainly to increase the oxidation capacity of the pond.
They are useful in overloaded ponds that generate odors.
REFERENCES
*D. S. Parker, J. R. Monser, and R. G. Spicher, "Unit Process Performance Modeling and
Economics for Cannery Waste Treatment," presented at the 23d Purdue Industrial Waste Confer-
ence, May 7-9,1968.
2M. G. McGarry and M. B. Pescod, "Stabilization Pond Criteria* for Tropical Asia," Second
International Symposium for Waste Treatment Lagoons, pp. 114-132, Missouri Basin Health
Council and Federal Water Quality Administration, Kansas City, Mo., June 23-25,1970.
3G. V. R. Marais, "Dynamic Behavior of Oxidation Ponds," Second International Symposium
for Waste Treatment Lagoons, pp. 15-46, Missouri Basin Health Council and Federal Water Quality
Administration, Kansas City, Mo., June 23-25, 1970.
4W. J. Oswald, ch. 17, Water Quality Management, edited by P. H. McGavhey, University of
California, Sanitary Engineering Research Laboratory, Berkeley, Calif., 1966.
^Second International Symposium for Waste Treatment Lagoons, Missouri Basin Engineering
Council and Federal Water Quality Administration, Kansas City, Mo., June 23-25,1970.
6G. A. Boulier and T. J. Atchison, Practical Design and Application of the Aerated-Facultative
Lagoon Process, 2nd ed., Hinde Engineering Co., Highland Park, 111., 1975.
7 W. W. Eckenfelder, Jr., Industrial Water Pollution Control, McGraw-Hill, New York, 1966,
ch. 15.
8 Biological Waste Treatment, course given at Manhattan College, New York.
9Brown and Caldwell, Contract for pond aerators, prepared for city of Sunnyvale, Calif., Dec.
1969.
10R. E. McKinney, J. N. Dornbush, and J. W. Vennes, "Waste Treatment Lagoons—State of
the Art," Missouri Basin Engineering Health Council, EPA WPCRS, 17090EHX, Washington, D.C.,
July 1971.
16
-------
Chapter Ml
UPGRADING LAGOONS THROUGH ALGAE REMOVAL
The presence of algae in oxidation-pond effluent is undoubtedly the most common problem in
upgrading lagoons to meet discharge permit requirements. Algae are manifested principally by high
suspended solids and long-term biochemical oxygen demand (BOD) measurements. Figure III-l
shows effluent BOD from the Stockton, Calif., ponds during the 1970 summer canning season (ch.
IV, case 2). Physical separation of the algae removed virtually all the long-term BOD. With proper
design and operation of the pond treatment system, insertion of an algae-removal step can produce
an effluent low in both oxygen-demanding substances and nutrients.
In contrast, figure III-2 shows the effluent BOD for an activated sludge plant also receiving a
heavy canning load. That effluent also has a high 30-day BOD, but much less can be removed by
solids separation because more of the long-term BOD was in the ammonia form and thus not re-
movable by physical separation.
Techniques to remove algae from pond effluent have included coagulation-clarification proc-
esses, filtration, centrifugation, microstraining, chlorination, and land application. In-pond removal
systems include aquaculture, series arrangements, intermittent discharge, chlorine addition, or
coagulant addition to promote sedimentation within the ponds. Because past mistakes can teach as
much as past successes, techniques that have not yet produced adequate results are discussed here
with those that have.
250 r
o>
LU
Q
Z
LU
O
X
o
200
150
100
50
Unfiltered
Filtered
0 K-—-°
10
20
DAYS
30
40
Figure 111-1. Oxygen demand found in filtered and unfiltered
samples of oxidation-pond effluent, September 1970.
17
-------
250 r
Figure 111-2. Oxygen demand found in filtered and unfiltered
samples of activated-sludge effluent, September 1970.
TYPES OF ALGAE IN OXIDATION PONDS
Because the types of algae present in an oxidation pond can influence the effectiveness of the
separation techniques applied to them, it is useful to review those that can occur. Briefly, algae are
divided into four classes: green algae, blue-green algae, diatoms, and pigmented flagellates.
The most frequently observed green algae in oxidation ponds are Chlorella and Scendesumus,
which are small (less than 20 /^m) and nonmotile. Because of their small size and low density, they
will remain in suspension with minimal fluid motion. Green algae also have a negative charge (or
zeta potential) that prevents their natural flocculation in a normal oxidation-pond environment.
The negative charge and the small size of these planktonic green algae make sand filtration or micro-
straining ineffective, and their small size and low density make sedimentation ineffective.
Blue-green algae are nuisance organisms in ponds. The most common species is the filamentous
algae, Oscillatoria. These algae frequently form mats that emit foul odors. These mats also block
light penetration and reduce surface aeration and mixing. Oscillatoria cells are typically 200 to 300
/xm in length with a diameter of about 5 jum, and they generally have a slimy coating. Blue-green
algae have a characteristic gliding movement said to result from the propagation of rhythmic con-
traction waves within the cell. This movement may allow Oscillatoria to pass through restrictions.
Blue-green algae tend to clog filters because of their large size, but when aggregated together, they
are removable by microstraining.
Diatoms often occur in oxidation ponds, at least in small numbers. They have a silica shell, are
nonmotile, and are large enough to clog sand filters.
The most frequently observed pigmented flagellates are Euglena and Chlamydomonas. These
algae are motile and can compensate for variations in lighting conditions by swimming. The flexible
cell wall of Euglena allows it to pass through constrictions. These algae have typical maximum di-
18
-------
mensions of 15 to 30 /xm (excluding flagella). They resist removal by sedimentation and flotation
because they can swim away in the process effluent.
COAGULATION-CLARIFICATION PROCESSES
Algae cells do not naturally flocculate to a high degree because they are mutually repulsed by
negative charges. Consequently, they tend to settle at such a low rate that normal pond turbulence
keeps them in suspension. This effect can be overcome by adding chemicals to modify the algae
surface charge and provide a matrix for bridging across algae cells to allow aggregation into floes,
which can then be removed easily by sedimentation or flotation.
Organic polymers have been studied extensively for coagulation, but the consensus is that good
coagulation cannot be achieved in economic doses.1'8 Most successful applications have involved
the use of inorganic coagulants, occasionally in combination with organic polymers acting as coag-
ulant aids.2-5"7'9"16 Alum has been used most widely, and occasionally lime has been selected.
Ferric or ferrous compounds have seldom been used because of the color they impart to the ef-
fluent. Each of these chemicals, alone or in combination with others, may be the most appropriate
in particular circumstances. The coagulant chosen will depend on pond effluent quality, the type
and concentration of predominant algae, process considerations, and total cost (including sludge
disposal). Procedures leading to coagulant selection include jar tests, pilot tests, and engineering
feasibility studies.
Coagulation-Flocculation-Sedimentation
Although sedimentation has been used to clarify many waste streams, it cannot by itself be
used for algae removal. Chemical coagulants must first be added to destabilize the algae. Then the
algae-coagulant particles must be aggregated to form floes large enough to settle and be removed in
a sedimentation tank. Thus sedimentation involves three stages: chemical coagulation, flocculation,
and sedimentation.
A number of investigators have obtained high algae removal using the coagulation-flocculation-
sedimentation sequence.2'9-17'18 Representative performance data are shown in table III-l. Over-
Table 111-1.—Summary of coagulation-flocculation-sedimentation performance
and
location
van Vuuren et al 9
Windhoek, South Africa
Goleuke et al. 2 .
Richmond, Calif.
Goodwin,' 7 Napa, Calif. . . .
Coagu-
lant
Alum3
Limeb
Alum
(Lime
^Alum
Dose,
mg/l
216-300
300-C400
100
d200
45
Over-
rate,
gal/
min/ft2
0 27
.27
78
(e)
tion
time,
200
200
150
(e)
Influ-
ent,
mg/l
27 3
27.3
23 0
30.0
BOD
Efflu-
ent,
mg/l
9 5
3.5
1 0
3.6
Percent
re-
moved
95
87
96
88
Influ-
ent,
mg/l
85
85
199
102
SS
Efflu-
ent,
mg/l
17
8
1 T
23
Percent
re-
moved
sn
92
QQ
79
aAsAI2 (SO4)3 • 14.3 H2O (molecular weight = 600).
bAs CaO.
cpH 10.7.
dpH 10.8.
e!Mot available.
19
-------
flow rates for conventional sedimentation have been in the range of 0.2 to 0.8 gpm/ft2 with hy-
draulic detention times of 3 to 4 hours. The flocculation-tank-design criteria that were found to be
adequate in one study were detention times of 25 minutes with a G value of 36 to 51 s~1.19 Under-
flow solids have generally been quite thin (in the range of 1 to 1.5 percent) when alum or iron is
used.
Reductions in sedimentation tank size now appear possible because of the recent application
of tube settlers (fig. III-3) to the sedimentation process for algae removal. A pilot study conducted
at Regina, Saskatchewan, Canada, indicated that overflow rates with tube settlers could be as high
as 5.0 gal/min/ft2 without deterioration in effluent quality.20 In other cases, however, the allow-
able solids-loading rate (thickening capacity of the sludge) might limit sedimentation tank rates to
values below 5.0 gal/min/ft2. The full-scale Regina facility features two flocculator-clarifiers of
60-foot diameter, fitted with tube settlers having a total capacity of 24 mgd. Design overflow rate in
the 18-foot-deep upflow portion of the clarifier is 3.7 gal/min/ft2, and calculated detention times in
the flocculator and clarifier are 11 minutes and 36 minutes, respectively. The facility is equipped to
employ either alum or lime.21
Neptune Micro-Floe recommends somewhat lower overflow rates for tube settlers than those
used in the Regina facility. Typically, only two-thirds of the sedimentation tank area is covered
with settling tubes, with this area receiving a loading rate of 3.0 to 3.5 gal/min/ft2, while overall
surface loading would be 2.0 to 2.5 gal/min/ft2. These general recommendations are based on
Neptune's full-scale applications similar to algae removal; individual designs might vary from these
numbers for a variety of reasons.22
The Los Angeles County Sanitation Districts have the longest record of experience with a coag-
ulation-flocculation-sedimentation system, at the Antelope Valley Tertiary Treatment Plant in
Lancaster, Calif., constructed in 1970. The Lancaster facility is discussed as case 3 in chapter IV.
In designing a coagulation-flocculation-sedimentation facility, care should be taken to insure
that conditions promoting autoflotation (described under flotation in the following section) are not
encouraged. Floating sludge in the sedimentation tank defeats the purpose of the process. To
prevent this effect, supersaturation should be relieved by preaeration before sedimentation, and
photosynthesis in the sedimentation tank should be prevented by covering the tank surface.
Coagulation-Flotation
The flotation process involves the formation of fine gas bubbles that are physically attached to
the algae solids, causing the solids to float to the tank surface. Chemical coagulation results in the
Influent
Chemical rate
feed control Flocculator Flocculator Settling
chamber
lines
valve
drive
drive
Surface wash pump
Backwash pump
Secondary .
effluent !
Final
effluent
To i
I collection i
| tank i
F loccu lators pen <=* a
cii^ [Jl
~"l rj To backwash nl
I rj waste storage nl
I n_ _rv
'3CJ\To sludge Mixed
disposal media
filter
Effluent
pump
'I 1
Backwash
storage
chlorine
contact
Collection tank
Waste storage tank
Figure 111-3. Tube settlers in a package tertiary plant (courtesy, Neptune Micro-Floe).
20
-------
formation of a floe-bubble matrix that allows more efficient separation to take place in the aeration
tank.
Two means are available for forming the fine bubbles used in the flotation process: autoflota-
tion and dissolved-air flotation. Autoflotation results from the provision of a region of turbulence
near the inlet of the flotation tank (which causes bubbles to be formed from the dissolved gases)
and from oxygen supersaturation in the ponds. In dissolved-air flotation, a portion of the influent
(or recycled effluent) is pumped to a pressure tank where the liquid is agitated in contact with high-
pressure air to supersaturate the liquid. The pressurized stream is then mixed with influent, the
pressure is released, and fine bubbles are formed. These become attached to the coagulated algae
cells. Table III-2 presents a summary of operating and performance data on coagulation-flotation
studies. Snider's data27 are from a full-scale 0.8-mgd, poultry-processing plant; the other data in-
volve pilot studies.
Autoflotation
Information on autoflotation has been developed at Windhoek, South Africa, and Stockton,
Calif.14'15-24'28 For autoflotation to be effective, the dissolved oxygen (DO) content of the pond
must exceed about 13-15 mg/1. Furthermore, it is advantageous to use carbon dioxide (CO2), rather
than acid, as the pH adjustment chemical with alum. This approach increases the partial pressure of
CO2 and increases the probability of bubble formation, which will improve performance (table
III-2).14'24
Autoflotation can perform well under the proper circumstances. Its major disadvantage is that
it depends on the development of gas supersaturation within the oxidation pond. At Windhoek, the
tertiary ponds could be supersaturated around the clock because of their light organic loading and
the presence of favorable climatic conditions. At Stockton, the required degree of supersaturation
was present only intermittently, and then for less than half the day. The Stockton pond organic
loadings (90 pounds BOD per acre per day during summer) are closer to normal facultative pond
loadings than those at Windhoek.
Generally, autoflotation is usable for only a part of the day. The only way to compensate is to
increase the number of flotation tanks accordingly and use the process whenever it is operable. The
extra cost will favor the selection of dissolved-air flotation in nearly all instances.
Dissolved-Air Flotation
The principal advantage of coagulation/dissolved-air flotation over coagulation-flocculation-
sedimentation is the smaller tanks required. Flotation can be undertaken in shallow tanks with
hydraulic residence times of 7 to 20 minutes, rather than the 3 to 4 hours required for deep sed-
imentation tanks. Overflow rates for flotation are higher, about 2.0 gal/min/ft2 (excluding recycle)
compared to 0.8 gal/min/ft2 or less for conventional sedimentation tanks.
Sedimentation, however, does not require the air-dissolution equipment of flotation, making it
a simpler system to operate and maintain. This factor is especially important for small plants, and it
was crucial in the selection of sedimentation over flotation for the Antelope Valley Tertiary Treat-
ment Plant in Lancaster (ch. IV, case 3).10
Another advantage of flotation over sedimentation is that a separate flocculation step is not
required. In fact, a flocculation step after chemical addition has been found to be detrimental when
placed ahead of the introduction of the pressurized flow into the influent.24-29 The normal pur-
pose of a flocculator is to provide, by gentle agitation, the opportunity for large floes to form. The
downstream introduction of the pressurized stream and the resultant turbulent shearing causes floe
21
-------
Table I\\-2.-Summary of typical coagulation-flotation performance
1 ni/pctinfitor
1 1 IV Co LI yd IUI
and
location
Autoflotation:
van Vuuren et al.; 2 3
Windhoek, South Africa
Parker et al.; ' 4 Stockton, Calif
Dissolved-air flotation:
Parker et al.; M Stockton Calif
Ort; 1 6 Lubbock, Tex
Komline-Sanderson; 24 El Dorado, Ark. .
Bare et al.; 2S Logan, Utah
Stone et al.; 26 Sunnyvale, Calif
Snider27
Coagu-
lant
/Alum
lC02
/Alum
\C02
(Alum
\Acid
/Alum
\Acid
Lime
Alum
Alum
(Alum
\Acid
Alum
Dose
220 mg/l
to pH 6.5
200 mg/l
to pH 6.3
200 mg/l
to pH 6.5
225 mg/l
to pH 6.4
1 50 mg/l
200 mg/l
300 mg/l
175mg/1
to pH 6.0-6.3
125 mg/l
f^u^rf Inwv
\J VCI 1 IUW
rate, gal/
m in/ft2
3.5
1.8
2.0
2.0
b2.7
(a)
C4.0
e 1.3-2.4
f2.0
3.3
Deten-
tion
time,
min
8
8
22
22
b17
d12
C8
(a)
f11
/at
Influ-
ent,
mg/l
12.1
12.1
(a)
(a)
46
280-450
93
(a)
(a)
65
BOD
Efflu-
ent,
mg/l
2.8
4.4
(a)
(a)
5
0.3
<3
(a)
(a)
7.7
Percent
re-
moved
77
64
(a)
(a)
89
>99
>97
(a)
(a)
88
Influ-
ent,
mg/l
(a)
(a)
70
156
104
240-360
450
100
150
90
SS
Efflu-
ent,
mg/l
/a I
(a)
11
75
20
0-50
36
4
30
10
Percent
re-
moved
/at
(B)
85
44
81
>79
92
96
80
89
to
to
aNot available.
blncluding 33-percent pressurized (35-60 psig) recycle.
clncluding 100-percent pressurized recycle.
dIncluding 30-percent pressurized (50 psig) recycle.
elncluding 25-percent pressurized (45 psig) recycle.
f Including 27-percent pressurized (55-70 psig) influent.
-------
breakup to occur, defeating the purpose of the upstream flocculation step. Further, the coagulating
power of the chemicals has been lost by this time, and it becomes necessary to add new coagulants
to form good float.
Optimization of Dissolved-Air-Flotation Operation
Operating parameters used in dissolved-air flotation include surface-loading rates, air/solids
ratio, pressurization level, coagulant dose, and pH adjustment. Physical design parameters for the
flotation tank include the coagulant-addition point, the choice of influent versus recycle pressuriza-
tion, and the design details for the flotation tank. The last item is important because most propri-
etary tank designs were developed for sludge-thickening applications, and some manufacturers have
not reevaluated designs for optimal algae removal.
Surface-Loading Rates. Studies at Stockton and Sunnyvale, Calif.,14-15'26 and at Logan City,
Utah,25 indicate that maximum surface-loading rates generally vary from 2.0 to 2.7 gal/min/ft2
(including effluent recycle, where used), depending on tank design. Stone et al.26 found, in pilot
studies at Sunnyvale, that loadings greater than 2.0 gal/min/ft2 caused deteriorating performance.
The flotation tank used in the study was of poor hydraulic design, however, and it was concluded
that higher loading rates might be used in prototype facilities. Stone et al. also concluded that in-
fluent pressurization produced better results than recycle pressurization and allowed use of smaller
tanks as well. Bare25 found that 2.35 gal/min/ft2 was optimum, and Parker et al.14 used 2.7 gal/
min/ft2 at Stockton. Alum was the coagulant used in all cases.
Pressurization and Air/Solids Ratio. The air-solids ratio is defined as the weight of air bubbles
added to the process divided by the weight of suspended solids (SS) entering the tank. Values used
generally range from 0.05 to 0.10.14-25 The air/solids ratio is determined by influent solids con-
centration, pressure level used, and percentage of influent or recycled effluent pressurized. Pres-
surization levels used in dissolved-air flotation generally range from 25 to 80 psi. Pressure may be
applied to all or a portion of the influent or to a portion of the flotation-tank effluent, which is
then recycled to the tank influent. The latter mode has traditionally been used for sludge-thickening
applications when the influent solids have been flocculated and pressurising the influent might
cause floe breakup.
pH Sensitivity of Metal Ion Flocculation. pH is extremely important in alum and iron coag-
ulation. It is possible to adjust the wastewater pH by adding acid (H2SO4, for example), and thus
take full advantage of the pH sensitivity of the coagulation reactions. The acid dose required to
reach a desired wastewater pH level depends on the coagulant dose and wastewater alkalinity.
Figure III-4 shows the effect of pH suppression on effluent SS levels during pilot studies at
Sunnyvale,26 using alum as the coagulant. It was concluded that not much could be gained by
suppressing pH below 6.0, and that the range of 6.0 to 6.3 could be used for optimum performance.
Subsequent neutralization can be accomplished by adding caustic soda.
Alum Dose. Pilot studies at Stockton14 and Sunnyvale26 (fig. III-5) show the effect of in-
fluent total suspended solids (TSS) and alum dose on effluent TSS concentrations. Figure III-5
shows that influent TSS has a relatively minor effect on effluent quality. The benefit of increasing
alum doses is most pronounced up to 150 to 175 mg/1. Beyond that range, increased alum addition
results in only marginal improvement in effluent TSS.
Physical Design. It was noted above that proprietary flotation-tank designs do not possess
certain features found to be important in pilot and full-scale studies of algae removal. Features in-
corporated in the flotation tank designs for Sunnyvale and Stockton (ch. IV, cases 1 and 2) are
shown in figure III-6 and illustrate important design concepts.
23
-------
co
CO
UL
LU
100
80
60
40
20
1 \ \ \ T
Influent TSS = 150mg/l
100 mg/l alum
G
_L
_L
150 mg/l alum
Typical data _
Sept. 19 and
Sept. 20
_J I
5.6 5.8 6.0 6.2 6.4 6.6 6.8
pH
Figure 111-4. Effect of alum dose and pH on flotation perform-
ance (Sunnyvale Pilot Studies26).
DI
co"
50
40
30
LJJ
D
_l
t 20
LLI
10
0
0
I I I I
00
I
25
I
I
I
I
I
125 mg/l alum
150 mg/l alum
175 mg/l alum
»
200 mg/l alum
I
I
50 75 100 125 150 175 200
INFLUENT TSS, mg/l
Figure III-5. Effect of alum dose on flotation effluent suspended solids.
A portion of the flotation-tank influent rather than recycled effluent is pressurized. Better
results were obtained in the Sunnyvale studies using partial influent pressurization and the
same overall hydraulic loading rate. Thus, smaller tanks can be used. Usually pressurization
of 25 percent of the flow will provide good results.
24
-------
Float scraper arm
Float collection trough
Effluent
Feedwell
Float
Alum feed
orifice ring
Figure 111-6. Conceptual design of dissolved-air flotation tanks.
• The location for alum addition is via orifice rings at the point of pressure release where
intense turbulence is available for excellent initial mixing of chemicals. This also permits the
simultaneous coprecipitation of algae, bubbles, and chemical floe and results in excellent
flotation performance. Altering this order of chemical addition invariably leads to perfor-
mance deterioration.
• The point of pressure release is in the feedwell. An orifice, rather than a valve, can be used
on the pressurized line because the dissolved-air-flotation tanks can operate at constant
flow, using the oxidation ponds for flow equalization. In most proprietary designs, a valve is
provided on the pressurized line at the outside tank wall, and this permits bubbles to co-
alesce in the line leading to the feedwell.
• Care is taken to distribute the wastewater flow evenly into the tank. An inlet weir distrib-
utes the flow around the full circumference of the inlet zone and a double ring of gates is
used to dissipate turbulence. One full-scale circular tank introduced the influent unevenly,
causing nearly all the influent to flow through one-quarter of the tank.
• Influent is introduced at the surface rather than below the surface as in most proprietary
tank designs. The buoyancy of the rising influent introduced below the surface causes
density currents that result in short-circuiting of solids into the effluent.
• Provision of sludge and float scrapers and positive removal of sludge and float will aid
performance.
25
-------
• Effluent baffles extending down into the tank inhibit short-circuiting of solids.
In addition, the tank surface should be protected from wind currents to prevent movement of
the relatively light float across the tank. In rainy climates, the flotation tank should be covered
because the float is susceptible to breakdown by rain. Alternatively, the flotation tank could be
shut down during rainy periods, which would necessitate larger tanks to accommodate higher flow
rates in dry weather.
Float Concentration
It is necessary to remove and dispose of the chemical-algae float that rises to the water surface.
Flotation generally can result in a higher sludge concentration than does sedimentation for two
reasons. First, float removal from the flotation unit takes place on the liquid surface where the
operator has good visual control over the thickening process. Second, the float is thickened by
draining the liquid from the float, a procedure with a greater driving force promoting thickening
than the mechanism in sedimentation, which involves settling and compacting the loose algae-alum
floe.
During experimental work at Stockton,14 it was found that variations in skimmer operation
yielded changes in float concentration. For example, improvement in float concentration from 0.13
percent to 2.45 percent resulted from increasing the period between skimming from 2-3 minutes to
15-30 minutes. A further improvement to 3.6 percent occurred when the skimmer was positioned
slightly above the water surface level to minimize the inclusion of water in the float. This increase
occurred even with a simultaneous decrease in the skimming period to 7-8 minutes.
Bare25 reported float concentrations of 1.0 to 1.3 percent with alum-coagulation/dissolved-air
flotation. Concentrations increased to about 2 percent when a second flotation was allowed to
occur in the skimmings receiving tank. Stone et al.26 reported float concentrations of 1.3 to 2.1
percent in the Sunnyvale studies with specific gravities of 0.45 to 0.55.
Solids Handling and Treatment
Satisfactory disposition must be made of the algae-chemical sludge generated by coagulation-
clarification processes. Application of conventional solids-handling and -treatment processes required
increased capital and operating expenses, and this consideration was among those that led
Middlebrooks et al. to recommend against using coagulation-clarification processes for small
plants.28
Most of the relevant work to date has involved alum-algae sludges, with very little work done
with lime-algae sludge. Disposal and dewatering of alum-algae sludge are notoriously difficult, which
is not surprising since algal sludge and alum sludge are difficult to process individually.
Both centrifugation and vacuum filtration of unconditioned algae-alum sludge have produced
marginal results because of dewatering difficulties and the need for using low-process loading
rates.2-15 Heat treatment using the Porteous process at temperatures ranging from 193° to 213° C
has been shown to improve subsequent vacuum filter yield and cake concentration to a limited
extent. Filter yield was low and ranged from 0.9 to 2.5 Ib/ft2/h. Cake concentrations during the
study ranged from 8.3 to 21.6 percent total solids, using raw sludge with a solids concentration of
about 4 percent. * 5
Use of Zimpro low oxidation, at temperatures ranging from 180° to 220° C, has resulted in
vacuum filter cake concentrations ranging from 15 to 19 percent total solids, at a filter-yield rate
ranging from 0.67 to 3.05 Ib/ft2/h.15
26
-------
Zimpro high oxidation, at temperatures ranging from 220 to 275 C, was also investigated
because it would lead directly to ultimate disposal of the sludge. Evaluation showed that cake con-
centration and filter yield were marginal, indicating that ultimate disposal should incorporate
lagoons. The high-oxidation process removes about 97 percent of the volatile suspended solids
(VSS) from the sludge, which is important in producing a stable end product. Although some of the
volatile solids are made soluble in the liquid, the final solids are stable and suitable for lagoon stor-
age.-^
Only limited investigations have been made into the use of centrifugation for concentrating
algae-chemical sludges. At Firebaugh, Calif., a Bird solid-bowl centrifuge and a DeLaval yeast-type
separator were used to dewater sludge. Both devices were considered failures, although the use of
sludge-conditioning aids, such as organic polymers, might be expected to improve their perform-
ance.7 A DeLaval self-cleaning basket machine, also tested, was able to concentrate a 2-3-percent
feed to 10 percent total solids with a recovery of 98 percent.
Centrifugation has been used for lime (calcium carbonate) classification of raw sewage
sludges,30-31 but the only report on its use for algae-lime sludge did not present specific details.16
Another process that has been investigated is a chemical-oxidation scheme, called Purifax, that
employs chlorine as the oxidant. This process was capable of stabilizing the sludge, and yielded a
product that could be dewatered on sand drying beds or in a lagoon; however, chlorine costs are
relatively high.15
Initial work on anaerobic digestion of algae-alum sludge, at the University of California, in-
dicated that the process held little promise for future use.3 2 Volatile matter reduction was less than
44 percent, and the digested sludge was unstable and slow to dewater. Subsequent work has shown
that algae can be anaerobically degraded successfully if they are killed before their introduction into
the digester.33
While these relatively complex processes have generally proved unsatisfactory, there is a com-
paratively simple, and surprisingly effective, solution to the solids-handling problem—return of the
algae-alum sludge to the oxidation pond. The return of algae-alum sludge to a pond loaded at 50
Ib/acre/day has been studied for a period of 90 days, with a control pond monitored for compar-
ative purposes.19 No significant differences were observed between the control and test pond in
terms of predominant species, or in such effluent characteristics as BOD, alkalinity, dissolved alumi-
num, nitrogen, phosphorus, or DO. Effluent solids averaged 341 mg/1 in the control pond and were
only slightly higher, 379 mg/1, in the test pond. The depth of algal sludge accumulated because of
return of the sludge was estimated to be only 1 or 2 inches per year. It was concluded that this tech-
nique would be a simple solution to the problem of disposing of large volumes of chemically pre-
cipitated sludge.19
When algae-alum sludge is returned to the oxidation pond, it must be distributed in such a way
that sludge does not build up at a single point. Furthermore, when air is contained in the float,
procedures must be found to remove it before introducing the sludge into the pond, or floating-
sludge problems will result. Several methods have been investigated for breaking down collected
float, including the use of high-shear pumps, pumps using a vacuum, high-shear mixers, and water
sprays.
Coagulant Recovery
Because chemicals are used in large quantities for coagulation, their generation and reuse may
be a way to reduce overall operating costs. Use of acid to reduce pH to about 2.5 can result in a 70
percent alum recovery.2-34 Because phosphorus is also released at low pH, acid recovery will be
limited to those situations where phosphorus removal is not required.
27
-------
Algae-lime sludge can be centrifuged, with the calcium carbonate being separated into the cake
and the algae going into the centrate. Other studies30-31 have shown that the classified calcium
carbonate can be reclaimed for lime reuse. It is expected, however, that the centrate will be difficult
to dewater because of its algal content.
Although efforts in coagulant recovery from algae sludges have only been exploratory thus far,
there is evidence that further investigations could yield useful results.
FILTRATION
Many efforts have been made to remove algae from pond effluent through some type of filter.
Conventional rapid sand or multimedia filters have been used both for direct filtration of algal laden
waters and tor polishing filtration, which follows coagulation-clarification. Two other types of
filters, which depend in part on biological action for their effectiveness, are submerged rock filters
and intermittent sand filters.
Direct Filtration
Experiments with direct sand filtration generally have resulted in poor SS removals, as in-
dicated in table III-3. Without coagulation, algae have a low affinity for sand; furthermore, green
algae are too small to be efficiently removed by straining. The larger diatoms can be removed effec-
tively, but special precautions must be taken in media design to insure that the filter does not
become rapidly clogged.
In general, work to date indicates that direct filtration of oxidation pond effluent is imprac-
tical unless algae concentrations are low.
Polishing Filtration
Use of a rapid sand or multimedia filter system to reduce SS concentrations in coagulation-
clarification effluent is very effective, with effluent SS levels less than 10 mg/1 and turbidities less
Table 111-3.—Performance summary, direct filtration with rapid sand filters
Investigator
Borchardt et al 35-a
Davis et al.36'a
Foess et al 37-a
Lynam et al *^°'c . ....
McGhee39>d
Coagu-
lant
aid
and
dose,
mg/l
None
Fe: 7
None
None
None
None
None
None
None
Filter
loading,
gal/
min/ft2
0.2-2.0
2.1
.49
.49
1.9
1.9
2.0
1.1
.5-3.0
Filter
depth,
feet
2.0
2.0
/b\
ib\
(b>
/b\
2.0
0-92
2.0
Sand size, mm
dso =0.32
dso =0.40
dso =0.75
dso =0.29
dso =0.75
dso =0.29
dso =0.71
d,0 =0.55
d,0 =0.22 and 0.5
Finding
Removal declines to 21 to 45 percent
after 15 hours.
50-percent algae removal.
22-percent algae removal.
34-percent algae removal.
10-percent algae removal.
2-percent algae removal.
pH 2.5, 90-percent algae removal.
pH 8.9, 14-percent removal.
62-percent SS removal.
22- to 66-percent SS removal.
al_ab culture of algae.
bNot available.
cOxidation pond effluent.
dUpflow sand filter.
28
.. «*«u,Hi^*i4*sfe<4-
-------
than 4 Jackson turbidity units (Jtu).18-26 Diatomaceous earth filters also work efficiently,10 but
filter cycles may be short because of binding of the filter by algae and other particulate matter,
which will result in excessive diatomaceous earth use and high operating costs.
Baumann and Cleasby4 ° have shown that, while there are many similarities between water fil-
tration (for which the most information is available) and wastewater filtration, there are also dif-
ferences that must be properly accounted for in design. In particular, the quantity of solids in
wastewater streams is generally higher and the characteristics much more variable than for water
treatment. Furthermore, filter effluent turbidities and SS concentrations will generally be much
lower for water-treatment applications. Therefore, direct application of designs developed for water-
treatment plants may result in less than optimum operation and performance.
It is essential for filter runs of reasonable length that the filter remove solids throughout the
entire depth of media (deep-bed filtration) and not mainly at the filter surface. Deep-bed filters can
be designed by using high filtering velocities (up to 6 gal/min/ft2), which permit deeper penetration
of the solids into the filter, and by allowing the water to pass through a coarse-to-fine media grada-
tion. It is advantageous in wastewater filtration to use a greater depth of filter media (60 to 70
inches) than in water filtration (30 to 50 inches), to allow for greater floe storage in the filter.
Backwashing operations for wastewater filtration will also differ from those techniques used in
water filtration. Auxiliary agitation of the media is essential to proper backwashing. Either air scour
should be used or surface (and possibly subsurface) washers should be installed to insure that the
original cleanliness and grain classification will be restored.
Figures III-7 and III-8 and table III-4 summarize the performance of a dual-media filter used
for polishing flotation-tank effluent in the Sunnyvale pilot studies.26 The filter material was 48
inches of anthracite (2.4-4.8-mm particle size), above 18 inches of sand (0.8-1.0 mm). The loading
rate was 5.6 gal/min/ft2. Figure III-7 shows effluent turbidity as a function of filter-run duration.
Solids breakthrough occurred after 10 hours. Figure III-8 shows development of the headless profile
with time. The uniform headloss increase at all depths indicates that the filter has removed solids
uniformly throughout the depth of the filter. This factor is important in optimizing filter runs.
Design procedures for effluent filtration are described further in the EPA Technology Transfer
Seminar publication, Wastewater Filtration, Design Considerations.40
2
—j
00
QC
u.
UJ
DC
UJ
5 0
i—r
n r
_L
_L
_L
_L
_L
46 8 10 12 14 16
FILTER RUN DURATION, hours
18 20
Figure III-7. Dual-Media filter effluent turbidity profile (Sunnyvale Pilot
Studies26)
29
-------
00
CC
LU
I-
o
CQ
g
LU
LU 3
2
1
0
Figure
Duration
of filter
run
I
I
I
I
12345
FILTER HEADLOSS, feet
I-8. Filter headloss profile (Sunnyvale Pilot
Studies26).
Table 11 \-4.-FHter-performance summary, Sunnyvale pilot studies
,26
Run date
JU|y 11
JU|y U
Ju|y 25
Julv 2R
JU|y 31
Aug 30
Sept 4
Sept 7 •
Sept 11
Sept 12
Sept 13
Sept 14
Sept 17
Sept 18
Sept 19
Sept 20
Sept 21
Filter run
duration,
hours
3:15
6:45
4:00
6:15
8:10
4:15
8:00
6:10
7:15
7:15
4:45
3:15
8:30
8:00
7:15
6:15
5:10
8:30
Turbidity, Jtu
Influent
6.9
6.9
6.4
7.0
5.8
5.8
7.0
12.0
7.0
12.0
9.9
7.4
4.2
9.0
8.0
8.0
10.0
Effluent
4.2
4.2
.8
2.0
1.0
1.2
.7
.9
2.1
3.0
3.2
3.8
2.0
3.0
2.5
2.6
3.2
TSS, mg/l
Influent
67
67
19
39
28
28
32
22
46
39
32
42
39
33
41
46
38
62
Effluent
34
32
10
22
6
2
18
10
12
11
a4
6
3
5
3
6
2
6
VSS, mg/l
Influent
42
42
15
22
10
10
18
18
29
21
22
26
24
22
23
22
22
39
Effluent
27
22
9
11
1
1
16
8
6
6
a3
4
1
2
2
3
1
4
aAfter Sept. 11, 1973, the preservative added to filtered samples was changed. Values for TSS and VSS before that date are too
high because of postprecipitation in the sample bottles before laboratory analysis.
Submerged Rock Filters
A relatively new experimental approach to algae removal is the submerged rock filter that has
been studied extensively at the University of Kansas.6-41'45 Basically, the system operates by
allowing pond effluent to travel through a porous rock wall, causing the algae to settle out on the
rock surface. The accumulated algae are then biologically degraded.
30
-------
Available data indicate that the rock filter is relatively inactive biologically at cold temper-
atures (less than 10° C); therefore, larger rock filter volumes must be used in cold climates. The
effect of influent solids on removal efficiency is uncertain. Most experimental work has been done
with influent TSS concentrations below 70 mg/1. Because many facultative lagoons operate with
TSS levels of 75 to 150 mg/1, it is necessary to know the performance for such conditions.
An unresolved design consideration for the rock filter is its useful life. Because of the high
ratio of capital to operating expenses, the total cost of the system is very sensitive to the length of
time it is assumed to operate until plugging failure occurs. A life of 20 to 30 years has been calcu-
lated on the assumption that the filter will fail when the voids are full, but experience with other
filtration systems indicates that failure will occur much sooner because of flow channelization
within the media.
Intermittent Sand Filtration
Investigators at Utah State University have reported on the successful experimental application
of the intermittent sand filter for algae removal.46'48 A drawback, however, is the low influent SS
levels encountered. A maximum influent SS concentration of 72 mg/1 resulted in effluent con-
centrations less than 4.0 mg/1 for loading rates of 4.6 and 9.2 gal/day/ft2. The impact of higher SS
levels (75 to 150 mg/1) has not yet been determined.
Another factor that has not been accurately evaluated is the most significant component of
operating costs—sand cleaning. Observations of similar, slow-sand-filter-cleaning operations in water-
treatment applications show that filter cleaning is labor intensive, and this factor may make the
intermittent sand filter uneconomical in many instances.
MICROSTRAINING
Although microstraining has often been used in attempts to upgrade pond effluent, the results
have been consistently disappointing (table III-5). There are many reports describing successful
Table 111-5.—Summary of microstrainerperformance
Investigator and
location
Finding
Golueke et al.,2. . .
Richmond, Calif.
Drydenetal.,10 . .
Lancaster, Calif.
Lynam et al.,38.
Chicago, III.
California Department .
of Water Resources,7
Firebaugh, Calif.
"At the most, only an extremely small amount of algae was removed by the machine
even with the addition of filter ajd, decrease in flow rate, and the slowing of the
rotational speed of the filter."
A 23-jUm microstrainer was tested. "Removals with the microstrainer were totally
inadequate and blinding by the bodies of crustacea and other foreign material oc-
curred quite rapidly."
56-percent BOD removal. 61-percent SS removal. Less than 43 percent of the algae
were removed.
25- and 35-fim screens were tested. "Operation of the unit soon showed that algae
were passing through the finer screen. Removals up to 30 percent were obtained,
but most of this was due to algae settling in the influent and effluent chambers."
31
-------
applications of microstraining to algae removal for water supplies. However, they usually deal with
removal of the relatively large filter-clogging algae, such as diatoms and clumped blue-green algae,
which are larger than the effective opening of the microstrainers. The desirable species of pond
algae, such as Chlorella and Scendesumus, tend to be smaller than the smallest size microstrainer
opening available, 23
Preliminary studies with ultrafiltration, using membranes with smaller openings, have yielded
SS removals of 98.8 percent on pond effluent when the predominant algae were Chlorella,
Scendesumus, and Euglena.4^ Work with ultrafiltration has not reached the point, however, where
there is practical field application. Uncertainties remain in the areas of membrane cleaning and
economics.
CENTRIFUGATION
Investigators at the University of California have shown that centrifugation, unaided by coag-
ulants, can successfully remove algae from oxidation pond waters.2'7-29'50 It is usually more
expensive than coagulation-clarification, however. Equipment costs are high and power costs are
excessive. For example, an 80-90-percent removal of 200 mg/1 of pond effluent solids has an energy
requirement of 8,000 kWh per million gallons. At 1.5 cents/kWh, the energy cost alone could be
$120 per million gallons.
LAND TREATMENT
In the past, pond effluent has been applied to land more for disposal than for treatment pur-
poses, but land treatment, particularly overland flow, may become more common in the future for
polishing pond effluents before stream discharge. Plans are being developed for upgrading the
Newman, Calif., treatment facilities through overland flow treatment of pond effluent before dis-
charge to the San Joaquin River.51 Effluent SS concentrations for the existing facilities average
about 80 mg/1. Other improvements to be undertaken at the same time include adding a trickling
filter and a chlorine-disinfection system and upgrading the existing septic tanks and oxidation pond.
The overland flow system will provide algae and nutrient removal and dechlorination for the design
flow of 1.1 mgd.
A pilot study at Davis, Calif., involved the use of overland flow for upgrading oxidation-pond
effluent.52 At a loading rate of 0.68 in/day (two 3-hour applications a day), an influent BOD con-
centration of 73 mg/1 was reduced to 18 mg/1 and an SS concentration of 82 mg/1 was reduced to
19 mg/1. But difficulties caused by high winds during a portion of the tests resulted in an increase of
effluent SS concentrations.
IN-POND REMOVAL SYSTEMS
All the foregoing approaches involve the use of tertiary processes to remove algae from
oxidation-pond effluent. Another approach is to modify oxidation-pond construction or operation
to produce a pond effluent that will meet the SS levels set in the discharge requirements. Four
basic, identifiable methods are aquaculture, series pond operation, intermittent discharge, and
chemical addition, perhaps in combination with modified pond operation.
32
-------
Aquaculture
A relatively new approach to algae removal, aquaculture, involves the use of an ecological food
chain to produce a useful product—fish^in contrast to a product requiring further disposal. The
many uses of fish range from reduction to animal food to sale of live fish for bait.
The Oklahoma State Department of Health has been studying aquaculture as an algae-removal
process since 1970.53 In preliminary studies, seven species of fish in a six-cell, series-operated pond
system were studied to determine the ability of such a system to produce an effluent that meets
secondary treatment requirements. Over a 4-month summertime period, the mean BOD, SS, and
coliform organism concentrations were 6 mg/1,12 mg/1, and 20 MPN per 100 ml, respectively. One
drawback to the studies was that no data were presented giving effluent concentrations before the
fish were put into the ponds. Nevertheless, the encouraging results should stimulate further investi-
gations into this unique algae-removal method.
Series Arrangement of Oxidation Ponds
Series ponds are recommended by some State regulatory agencies for encouraging algae sed-
imentation within the pond cells. A parallel-series arrangement can also encourage sedimentation.
The efficiency of sedimentation in ponds, however, is limited by factors such as wind mixing and
algae species. Smaller ponds usually result in less mixing. Pigmented flagellates and crustaceans are
not removed efficiently in sedimentation ponds.
Favorable reports indicating consistent SS reductions with the series arrangement cannot be
found in the literature,54 nor could an EPA task force find examples of successful application of
series-arranged ponds.55
Series Ponds With Intermediate Chlorination
Normally, chlorination is used to disinfect effluent, but it has been observed that chlorine
added to pond water will also kill algae and cause settling. In 1946, a series of four oxidation ponds
near Dublin, Calif., was followed by a chlorine-contact pond. At a 3.75-mgd flow, the chlorine-
contact pond had a retention time of 13.5 hours. All the algae were reportedly killed with a chlo-
rine dose of 12 mg/1. Between pond inlet and outlet, the BOD was reduced from 45 to 25 mg/1, SS
from 110 to 40 mg/1, and turbidity from 170 to 40 mg/1.56 Similar reductions were reported in a
later study, which found that VSS could be reduced 52 percent and turbidity 32 percent through
chlorination.57 The flocculating effect of chlorine is thought to result from rupture of the algae cell
wall and the release of cellular metabolites that may serve as algal flocculants.58
In 1972, Chem Pure, Inc., announced a proprietary system using the chlorine-kill concept.59
In this system, lagoon effluent is dosed with chlorine, then fed into an underground "algae-
destruction chamber" where algae are killed and settled out. Once a month, "a standard septic tank
truck" pumps the algae and other matter out of the bottom of the destruction chamber. Data sug-
gested a residence time of less than an hour, or about the time normally provided in a conventional
chlorine-contact tank.
An adverse side-effect of chlorine use is that algae death and cell lysis cause release of a sub-
stantial amount of soluble BOD into the effluent. It has been found that the effluent BOD5 from
an oxidation pond at Concord, Calif., will increase from 20 mg/1 to as high as 65 mg/1 when 8 mg/1
of chlorine are applied.60 Similar increases in the soluble organic content of chlorinated pond
waters have been observed elsewhere.58
33
-------
Intermittent Discharge Lagoons
The operations of 49 intermittent discharge lagoons in Michigan have been well doc-
umented.61 The lagoons in Michigan usually have very low applied BOD loadings, about 20 lb/acre/
day. All the systems were designed for discharge twice yearly, with wastewater retention between
late November and April 15 and from about May 15 to October 15. Discharge times coincide with
periods of low algae-solids levels. Mean effluent concentrations were about 15 mg/1 BOD and 30
mg/1 SS, low enough to comply with EPA's definition of secondary treatment. This form of treat-
ment is uncertain for warmer climates because suitable periods must be found for pond discharge in
the absence of the severe climatic cycles that exist in States such as Michigan.
Intermittent Discharge Lagoons with Chemical Addition
Several investigations of in-pond precipitation of suspended matter conducted in the Province
of Ontario, Canada, have proved both the simplicity and effectiveness of the procedure when used
under the proper circumstances.62 Alum was applied from a motor boat to small, seasonal retention
lagoons and resulted in low effluent SS concentrations in the subsequent discharge from the
lagoons. Treated SS values were generally less than 10 mg/1 compared with untreated concentrations
of 65 mg/1 or less. Only 2 to 3 man-hours per acre were required for the treatment with liquid alum,
and sludge buildup was less than 0.1 inch per application (two applications a year). At these sludge-
deposition rates, pond dewatering and sludge removal would only be required after many years of
operation. It has been suggested that chemical application be investigated for oxidation ponds in
southern climates where there are high algae levels year round.63
SUMMARY
To put the foregoing information into perspective, a performance ranking has been developed
and is presented in table III-6. It is based on an assumed pond SS level of 150 mg/1. This level would
Table III -6.—Estimated performance of alternative algae-removal systems
System
Mean
effluent
SS,a mg/1
Microstraining
Direct filtration without coagulants
In-pond removal—series arrangement, continuous discharge .
In-pond removal with chlorinationb
Submerged rock filter0
Centrifuge
Intermittent discharge lagoonsd
Aquaculture
Overland flow
Coagulation-flocculation-sedimentation
Coagulation-flotation
Intermittent sand filtration
In-pond chemical addition to intermittent discharge lagoonsd
Coagulation-clarification followed by filtration
>60
>60
>30
>30
<30
<30
<30
<30
<30
10-30
10-30
20
aAssumes pond effluent suspended solids at 150 mg/l, except as noted.
bAccompanied with the release of BOD.
cTentative ranking—full-scale testing to date is based on pond effluent suspended solids averaging less than 73 mg/l.
dMay be limited to northern U.S. climatic conditions.
34
• •—-*
-------
be typical of the average monthly SS level of a facultative oxidation pond in the summer. Lower SS
levels may prevail at other times of the year, but the summertime level was selected because it rep-
resents the level of highest stress on the algae-removal system.
These performance estimates are rough generalizations of the experience gained to date. This
type of projection is somewhat hazardous because performance data from the various investigations
may not be comparable as a result of differences in test methods, algal properties, concentrations,
coagulant type and dose, and quality. Nonetheless, this kind of ranking must be done by the deci-
sionmaker to narrow his range of alternatives in specific situations.
The cost of the alternative systems is the big gap in knowledge. The best established cost/
performance data base is for coagulation-clarification systems, because full-scale examples of these
processes do exist. Most of the other attractive systems have seen only limited pilot testing, and it is
difficult to project their long-range performance or full-scale costs. Based on experience to date,
conclusions must be mostly intuitive concerning which types of systems are simpler, require less
operation and maintenance, or are more economical.
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3North American Aviation, Inc., A Study of the Use of Biomass Systems in Water Renovation
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5M. G. McGarry, "Algae Flocculation with Aluminum Sulfate and Polyelectrolytes," J. Water
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35
-------
19C. E. Parker, "Algae Sludge Disposal in Wastewater Reclamation," doctoral dissertation,
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21 Personal communication, M. J. Stewart to D. S. Parker, Associated Engineering Services,
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22Personal communication, S. P. Hansen to D. S. Parker, Neptune Micro-Floe, Inc., Dec. 1973.
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25W. F. R. Bare, N. B. Jones, and E. J. Middlebrooks, "Algae Removal Using Dissolved Air
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31D. S. Parker, G. A. Carthew, and G. A. Horstkotte, "Lime Recovery and Reuse in Primary
Treatment,"Proc. Am. Soc. Civ. Eng., J. Environ, Eng. Div., 101, 985, Dec. 1975.
32C. G. Golueke, W. J. Oswald, and H. B. Gotaas, "Anaerobic Digestion of Algae," Appl.
Microbioi, 5, 1, Jan. 1957.
33Personal communication, W. J. Oswald to D. S. Parker, July 1975.
34G. L. Gulp and A. F. Slechta, "Water Reclamation Studies at the South Tahoe Public Utility
District," J. Water Pollut. Cont. Fed., 39, 737, May 1967.
35J. A. Borchardt and C. R. O'Melia, "Sand Filtration of Algae Suspensions," J. Am. Water
Works Assoc., 53, 12, Dec. 1961.
36E. Davis and J. A. Borchardt, "Sand Filtration of Particulate Matter," Proc. Am. Soc. Civ.
Eng., J. Sanit. Eng. Div., 92, SA5, Oct. 1966.
37G. W. Foess and J. A. Borchardt, "Electrokinetic Phenomenon in the Filtration of Algae
Suspensions," J. Am. Water Works Assoc., 61, 7, July 1969.
38G. Lynam, G. Ettelt, and T. McAllon, "Tertiary Treatment of Metro Chicago by Means of
Rapid Sand Filtration and Microstrainers," J. Water Pollut. Cont. Fed., 41, 2, Feb. 1969.
39T. J. McGhee, "Upflow Filtration of Oxidation Pond Effluent," University of Nebraska,
Water Resources Research Institute, Technical Completion Report A-034-NEB, June 1975.
40E. R. Baumann and J. L. Cleasby, Wastewater Filtration, Design Considerations, U.S. Envi-
ronmental Protection Agency, Technology Transfer Seminar Publication, EPA-625/4-74007,
Cincinnati, Ohio, July 1974.
41W. J. O'Brien, "Polishing Lagoon Effluents with Submerged Rock Filter," presented at the
Symposium on Upgrading Stabilization Ponds to Meet New Discharge Standards, Logan, Utah, Nov.
1974.
42W. J. O'Brien, R. E. McKinney, M. D. Turvey, and D. M. Martin, "Two Methods of Algae
Removal from Oxidation Pond Effluents," Water Sewage Works, 120, 66,1973.
43J. L. Martin and R. Weller, "Removal of Algae from Oxidation Pond Effluent," masters
thesis, University of Kansas at Lawrence, 1973.
44R. A. Hirsekorn, "A Field Study of Rock Filtration for Algae Removal," masters thesis,
University of Kansas at Lawrence, 1974.
36
-------
45W. J. O'Brien, "Algae Removal by Rock Filtration," presented at Symposium No. 9, Ponds
as a Wastewater Treatment Alternative, University of Texas at Austin, July 22-24,1975.
46J. H. Reynolds, S. E. Harris, D. S. Filip, and E. J. Middlebrooks, "Intermittent Sand Filtra-
tion to Upgrade Lagoon Effluents, Preliminary Report," presented at the Symposium on Upgrading
Waste Stabilization Ponds to Meet New Discharge Standards, Logan, Utah, Aug. 1974.
47E. J. Middlebrooks and G. R. Marshall, "Stabilization Pond Upgrading with Intermittent
Sand Filters," presented at the Symposium on Upgrading Waste Stabilization Ponds to Meet New
Discharge Standards, Logan, Utah, Aug. 1974.
48J. H. Reynolds, S. E. Harris, D. W. Hill, D. S. Filip, and E. J. Middlebrooks, "Intermittent
Sand Filtration for Upgrading Waste Stabilization Ponds," presented at Symposium No. 9, Ponds as
a Wastewater Treatment Alternative, University of Texas at Austin, July 22-24,1975.
49G. Shelef, R. Matz, and M. Schwartz, "Ultrafiltration and Microfiltration Processes for
Treatment and Reclamation of Pond Effluents in Israel," presented at the IAWPR Specialty Con-
ference, Applications of New Concepts of Physical-Chemical Wastewater Treatment, Nashville,
Tenn., Sept. 1972.
50W. J. Oswald and C. G. Golueke, "Harvesting and Processing of Waste-Grown Microalgae,"
Algae, Man and the Environment, Edited by D. F. Jackson, Syracuse University Press, New York,
1968.
51 Brown and Caldwell, Facilities Plan for Wastewater Treatment, city of Newman, Feb. 1976.
52Personal communication, E. D. Schroeder to D. S. Parker, Dec. 1975.
53M. S. Coleman, J. P. Henderson, H. G. Chichester, and R. L. Carpenter, "Aquaculture as a
Means to Achieve Effluent Standards," Wastewater Use in the Production of Food and Fiber--
Proceedings, proceedings of conference at Oklahoma City, Okla., Mar. 5-7,1974, U.S. EPA, Envi-
ronmental Protection Technology Series, EPA 660/2-74-04-041, Washington, D.C., June 1974.
54S. R. Goswami and W. L. Busch, "3-Stage Ponds Earn Plaudits," Water Wastes Eng., 9, 4,
Apr. 1972.
55Personal communication, D. Ehreth to D. S. Parker, U.S. Environmental Protection Agency,
1974.
56D. H. Caldwell, "Sewage Oxidation Ponds," Sewage Works J., 18, 3, May 1946.
57R. Dingus and A. Rust, "Experimental Chlorination of Stabilization Pond Effluent," Public
Works, 100, 3, Mar. 1969.
58W. F. Echelberger, J. L. Pavoni, and P. C. Singer, "Disinfection of Algal Laden Water," Proc.
Am. Soc. Civ. Eng., J. Sanit. Eng. Div., 97, Oct. 1971.
59"Algae Destruction Chamber Upgrades Sewage Lagoon Effluents," Civ. Eng., 42, 11, Oct.
1972.
60L. W. Horn, "Kinetics of Chlorine Disinfection in an Ecosystem," Proc. Am. Soc. Civ. Eng.,
J. Sanit. Eng. Div., 98, Feb. 1972.
61D. M. Pierce, "Performance of Raw Waste Stabilization Lagoons in Michigan with Long
Period Storage Before Discharge," presented at the Symposium on Upgrading Waste Stabilization
Ponds to Meet New Discharge Standards, Logan, Utah, Aug. 1974.
62H. J. Graham and R. B. Hunsinger, "Phosphorus Removal in Seasonal Retention Lagoons by
Batch Chemical Precipitation," unpublished paper, Ontario Ministry of the Environment, Research
Branch, 135 St. Clair West, Toronto, Ontario, Canada, undated.
63R. F. Lewis and J. M. Smith, Upgrading Existing Lagoons, U.S. Environmental Protection
Agency, OR&D, MERL, Cincinnati, Ohio, Oct. 1973.
37
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Chapter IV
EXAMPLES OF UPGRADING PONDS
CASE 1. SUNNYVALE WATER-POLLUTION-COIMTROL PLANT
Process Modifications
Sewage-treatment facilities for the city of Sunnyvale, Calif., were first placed in operation in
September 1956. They included a primary treatment plant with an average daily capacity of 7.5
million gallons of domestic sewage and nonseasonal industrial wastes, and a holding pond with a
capacity of 200 million gallons for seasonal wastes from two large canneries that processed fruit
and vegetables. Effluents from the primary plant and the holding pond were discharged directly
to Guadalupe Slough, a tributary to south San Francisco Bay.
By 1960, the domestic sewage flow had reached the capacity of the primary plant, and condi-
tions in Guadalupe Slough, because more effluents were discharged from the treatment facilities,
had deteriorated so much that at times they failed to comply with the minimum requirements
established by the Regional Water Quality Control Board. In a study authorized by the city, Brown
and Caldwell recommended doubling the capacity of the primary plant and adding an oxidation
pond. The facilities were not completed until 1967.
Growth of both domestic and industrial wastes since 1960, and the more stringent require-
ments of the Regional Water Quality Control Board, required further improvement of the plant.
This improvement was completed by the canning season of 1971; three more primary settling
basins were added (for a total of nine) and aerators were added to the two ponds. The addition
of aerators is the primary concern of this discussion. (See figs. IV-1 and IV-2.)
Originally, the large pond (325 acres) had been used as an oxidation pond for secondary
treatment of the domestic wastewaters. The wastewater from the canneries was put directly in
the smaller holding pond (100 acres). This pond was designed to operate anaerobic ally, with
odors controlled by calcium or sodium nitrate additives. A considerable quantity of nitrate was
required, resulting in high operating costs during the food-processing season. Attempted close
control of nitrate addition resulted in insufficient amounts being added at times, so that hydrogen
sulfide odors did occur.
Design provided for the effluent from the holding pond to be discharged to the oxidation
pond at a rate that would maintain aerobic conditions in the oxidation pond. Seasonal wastes
increased in quantity and strength beyond expectations, arid the holding pond did not have
sufficient capacity to contain the waste for the entire canning season. From 1960 on it was
necessary to discharge some of the holding-pond contents to Guadalupe Slough during the canning
season.
During the past few years, attempts were made to improve the situation by putting the cannery
waste through the primary plant and operating the two lagoons in parallel. The small pond received
heavier loadings, however, and continued to produce odors. Also, hydrogen sulfide odors continued
to develop in Guadalupe Slough.
In an upgrading step, floating cage aerators were placed near the inlets to the ponds to increase
their oxidation capacity. The aerators are used only during the canning season, when supplemental
38
-, _ „ ^U«f*«**M^-«t
-------
Figure IV-1. Cage aerator.
Figure IV-2. Cage aerator in o
39
operation.
-------
oxygenation capacity is required. Figure II-6 shows a drawing of the aerator and figure IV-3 shows a
diagram of the ponds. (An aerial view of the ponds, 1969 enlargement, is given in fig. IV-4.) The
influent and the recirculation flows are mixed in the channel. The flow is then discharged to the
ponds through a series of pipes along their edges. The aerators are generally near the transfer pipes;
however, no pipes are located near the last two aerators of the large pond. Near the last two
aerators the discharge line leads from the pond to the chlorine contact chamber, and then to
Guadalupe Slough. These two aerators prevent short circuiting of wastewater.
Operating the ponds in this manner substantially has improved effluent quality. The ponds and
Guadalupe Slough contain dissolved oxygen (DO) at all times and are odor free. Fish have returned
to the slough. Tables IV-1 and IV-2 give design data for before and after upgrading (1967 and
1971). Table IV-3 shows operating data for 1970 and 1971. Capital costs for pond upgrading are
given in table IV-4. Table IV-5 shows the operating cost changes caused by plant expansion.
PRIMARY EFFLUENT
EFFLUENT
D ISCHARGE
TO GUAOALUPE
SLOUGH
CHLORINE
CONTACT
CHAMBER
Figure IV-3. Diagram of Sunnyvale ponds.
40
, , . ,***HlptiKWWlL*-
-------
Figure IV-4. Sunnyvale sewage-treatment works, 1969 enlargement.
41
-------
Table IV'-"\.~Sunnyvale water-pollution-control plant design data, 1967
Component
Quantity
Design loadings:
Domestic:
Daily average flow, mgd
BOD, mg/l
BOD, Ib/day
SS, mg/l
SS,Ib/day
Industrial waste (seasonal):
Daily average flow, mgd
BOD, mg/l
BOD, Ib/day
SS, mg/l
SS, Ib/day
Preaeration tanks, domestic sewage only:
Number
Width, feet
Length, feet
Average water depth, feet
Detention time, hours
Air supplied per tank, ft3/min
Air supplied per tank, ft3/gal/min
Maximum hydraulic capacity per tank, mgd ....
Maximum hydraulic capacity bypass channel, mgd
Sedimentation tanks, domestic sewage only:
Number
Width, feet
Length, feet
Average water depth, feet
Effluent weir per tank, feet
Detention time, hours
Mean velocity, ft/min
Overflow rate, gal/day/ft2 at daily average flow . .
Maximum hydraulic capacity, mgd
Maximum hydraulic bypass channel, mgd
15
270
33,600
300
37,400
8.0
1,800
120,000
500
33,000
6
19
35
10.5
0.5
300
0.17
6.75
50
6
19
110
10
164
1.5
1.2
1,200
6.75
50
42
-------
Table \V-1.-Sunnyvale water-pollution-control plant design data, 1967-Concluded
Component
Quantity
Primary treatment, domestic sewage only:
Assumed BOD reduction, percent 35
BOD reduction, mg/l 95
BOD reduction, Ib/day 11,800
Assumed SS reduction, percent 60
SS reduction, mg/l 180
SS reduction, Ib/day 22,400
Primary effluent, domestic sewage only.
BOD, mg/l 175
BOD, Ib/day 21,800
SS, mg/l 120
SS, Ib/day 15,000
Oxidation pond, domestic sewage only:
Number 1
Area, acres 325
Loading, 5-day BOD, Ib/acre/day 67
Detention, days 36
Circulation pumps:
Number 4
Capacity each, gal/min 44,000
Head, feet 3.5
Engine-generators:
Number 3
Rated output, kW (high-low) 223-167
Speed, r/min (high-low) 1,000-750
Frequency, c/s (high-low) 66-50
Industrial wastes holding pond:
Net water area, acres 100
Maximum water depth, feet • 6
Maximum capacity, millions of gallons 200
43
-------
Table \\l-2.-Sunnyvale water-pollution-control-plant
design data, 1971
Component
Quantity
Design loadings:
Domestic:
Average daily flow, mgd 22.5
BOD, mg/l 270
BOD, Ib/day 50,000
SS, mg/l 300
SS, Ib/day 56,000
Industrial waste, seasonal:
Average daily flow, mgd 8.0
BOD, mg/l 1,800
BOD, Ibyday 120,000
SS, mg/l 500
SS, Ib/day 33,000
Preaeration tanks:
Number 7
Width, feet:
Six at 19.0
One at 20.7
Length, feet:
Six at 20.5
One at 58.7
Average water depth, feet:
Six at 10.5
One at 11.0
Average daily flow, mgd:
Six at 2.7
One at 7.5
Detention time, hours:
Six at 0.29
One at 0.32
Air supplied per tank, ft3/min:
Six at 130
One at 250
Air supplied per tank, ft3/gal:
Six at .074
One at .048
Maximum hydraulic capacity per tank, mgd:
Six at 6.75
One at 20
Maximum hydraulic capacity bypass channel, mgd 50
44
-------
Table IV-2.— Sunnyvale water-pollution-control-plant
design data, 1971—Continued
Component
Quantity
Sedimentation tanks:
Number 9
Width, feet 19
Length, feet 110
Average water depth, feet 10
Effluent weir per tank, feet 164
Detention time, hours 1.5
Mean velocity, ft/min 1.2
Overflow rate, gal/ft2/day 1,200
Maximum hydraulic capacity per tank, mgd 6.75
Maximum hydraulic capacity bypass channel, mgd 50
Primary treatment efficiency, domestic only:
Assumed BOD reduction, percent 35
BOD reduction, mg/l 95
BOD reduction, Ib/day 17,000
Assumed SS reduction, percent 60
SS reduction, mg/l 180
SS reduction, Ib/day 34,000
Primary effluent, domestic only:
BOD, mg/l 175
BOD, Ib/day 33,000
SS, mg/l 120
SS, Ib/day 22,000
Oxidation ponds:
Number 2
Area, acres 425
Average depth, feet 4.25
Mechanical aerators:
Number 24
Maximum power, input to rotors, hp 1,800
Efficiency, Ibs O2 input per hph 1.86
Oxygen input, Ib/day 76,500
Loading, 5-day BOD, total Ib/day:
Noncanning season 33,000
Canning season 141,000
5-BOD reduction capacity:
Noncanning season (winter months), photosynthetic:
Unit, Ib/acre/day 80
Total, Ib/day 35,000
45
-------
Table \V-2.-Sunnyvale water-pollution-control-plant
design data, 1971-Concluded
Component
Oxidation ponds— Continued
Canning season (summer months):
Photosynthetic:
Unit, Ib/acre/day
Total, Ib/day
Mechanical aeration, Ib/day
Photosynthetic plus mechanical aeration, Ib/day ... .
Detention, days:
Noncanning season
Canning season
Circulation pumps:
Number
Capacity each, mgd
Head, feet
Quantity
175
77 000
59 000
136 000
27
20
4
63 5
3 5
Table I V-3.-BOD5 removals during canning season by ponds before and after
installation of aerators
Season
July8-Oct 1 1970 (before aerators) . . . .
June 30-Oct 2 1971 (after aerators)
Pond influent BOD
mg/l
347.2
405.5
103 Ib/day
b67
d64
Pond effluent BOD
mg/l
64
29
103 Ib/day
C7
4
Percent
removal8
89
94
aBased on mass emission, Ib/day.
bMaximum value, 102,000 Ib/day; effluent value is fairly consistent.
cDoes not include BOD in effluent from industrial holding pond.
dMaximum value, 121,000 Ib/day.
46
"TT
-------
Table \\/-4.—Summary of capital costs for Sunnyvale aerators
Item
Aerators (24)
Levee riprap ... - . -
Aerator anchor blocks (4 5 cubic yards per aerator) . .
Pond transfer pipes (6 installed; more may be needed
at other installations) . ...
Pond power-load centers (5) .
Direct burial cable . . . .
Main switch gear . ,
Unload position and hook up aerators
Total .
Cost in dollars
587,000
40000
28 950
32000
138710
140,000
24,000
31 900
1,022,560
Table IV-5.— Operating costs associated with pond upgrading
Item
Gas and electricity3
Chemicals'3
Labor0
Total
Cost in c
1970
(before aerators)
15,000
54,000
0
69,000
ollars
1971
(after aerators)
58,000
0
10,000
68,000
Includes power for remainder of plant, which was also expanded in 1971.
bCalcium and sodium nitrate, phosphoric acid, and anhydrous ammonia.
C0ne employee added in 1971.
Ammonia and Algae Removal
Although the 1971 modifications improved the effluent quality of the Sunnyvale plant, the
Federal secondary treatment requirement of 30 mg/1 biochemical oxygen demand (BOD) and sus-
pended solids (SS) could not be met. Moreover, the California Regional Water Quality Control
Board, San Francisco Bay Region, has determined from studies carried out over the past decade
that, to protect the water quality of south San Francisco Bay, existing facilities must produce an
effluent of a quality higher than that defined as secondary-treatment quality. Effluent-quality re-
quirements for Sunnyvale include those presented in table IV-6. The requirement for nondissociated
ammonia in the receiving water necessitates removal (or conversion to nitrate) of ammonia in the
wastewater because of limited dilution available.
47
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Table IV-6.—Summary of Sunnyvale wastewater discharge requirements
Constituent
Effluent limitations:
BOD:
mg/l
Ib/day
SS:
mg/l
Ib/day
Oil and grease:
mg/l
Ib/day
Chlorine residual (as C^), mg/l
Settleable matter, ml/l/h
Turbidity, Jtu
Receiving water limitations:
Nondissociated ammonium hydroxide (as N), mg/l
DO, mg/l
pH
Criteria
30-day
average
10
3,650
10
3,650
5
1,825
.1
Maxi-
mum
daily
20
7,300
20
7,300
10
3,650
Instanta-
neous
maxi-
mum
0
0.2
10
0.025
5.0 minimum; annual median of 80
percent saturation.
Effluent pH must not vary from
ambient pH by more than 0.2 pH
units.
To select the treatment scheme that most fully satisfies the discharge requirements as well as
engineering and economic constraints, an analysis was made of all potentially feasible alternatives.
Two basic alternatives and five subalternatives were identified.1 The two basic alternatives were:
• To retain and upgrade existing treatment facilities and processes and provide additional
treatment facilities to meet the requirements.
• To retain existing primary facilities, abandon oxidation ponds (use them as holding basins),
provide secondary and tertiary treatment processes, and retain existing sludge-handling and
-disposal facilities.
The five subalternatives and their cost estimates are given in table IV-7. The group 1 alterna-
tives, involving retention of the ponds and use of tertiary facilities, were less expensive than the
group 2 alternatives.
The five feasible plans were evaluated as to their compliance with water-quality goals, flex-
ibility and reliability, cost-effectiveness, reclamation potential, and environmental and social im-
pacts. The apparent best alternative project was subalternative l(c), which consisted of adding to
the existing facilities dissolved-air flotation and filtration for algae removal, a fixed-growth reactor
(trickling filter) for ammonia removal, breakpoint chlorination for supplemental ammonia removal,
and dechlorination for toxicity control.
48
,r- *»•*, i.Xtjm.fo<-a»fej^' -J )
I I
-------
Table IV-7.—Sunnyvale treatment alternatives
[Thousands of dollars]
Item
Capital costs3
Annual operation and maintenance costs:
Existing treatment
New treatment
Total
Annual cost of capital investment
Total annual cost of treatment
Group 1. Existing primary treatment
and oxidation ponds, plus flotation,
filtration, and dechlonnation
Plus
breakpoint
chlorination,
alternative
1(a)
6,078
603
1,158
1,761
573
2,334
Plus
ammonia
adsorption
on
clmoptilolite,
alternative
Kb)
9,662
603
740
1,343
911
2,254
Plus
nitrification
in fixed-
growth
reactor,
alternative
1(c)
9,010
603
497
1,100
850
1,950
Group 2. Existing primary
treatment, plus activated
sludge, filtration, and
dechlonnation
Plus
nitrification
in fixed-
growth
reactor,
alternative
2(a)
17,620
480
473
953
1,662
2,615
Plus
breakpoint
chlorination,
alternative
2(b)
14,685
480
1,130
1,610
1,386
2,996
aEngineering News Record, Construction Cost Index 2800, Jan. 1976.
blnterest at 7 percent over a 20-year planning period.
To optimize the design and operational efficiency of the tertiary treatment unit processes,
extensive pilot-plant studies were carried out in 1973 and 1974.1 The results of these pilot studies,
discussed in chapter III, formed the basis for plant design. Design data for the tertiary facilities are
presented in table IV-8. Design criteria for nitrification in fixed-growth reactors (FOR) are pre-
sented in chapter 4 of the Technology Transfer publication, Process Design Manual for Nitrogen
Control.2
Figure IV-5 shows the flow diagram for the tertiary facilities under two operational modes.
Under mode 1, pond effluent undergoes dissolved-air flotation ahead of nitrification in the FGR.
Mode 2 reverses the order of these two unit processes.
The principal advantage of mode 2 operation is reduced chemical costs, as shown in table
IV-9.3 Nitrification produces acidity, and therefore can be used to offset, or perhaps eliminate, the
required acid addition for pH adjustment to optimize dissolved-air flotation when nitrification is
first in the flow diagram. Furthermore, under mode 2, less caustic would need to be added to raise
the pH before discharge. However, because an FGR of a given size will produce higher effluent
ammonia levels under mode 2 than under mode 1, chlorine costs for supplemental breakpoint chlo-
rination are higher for mode 2 when breakpoint chlorination is required, which partly offsets the
advantage of mode 2. Receiving-water requirements indicate that breakpoint chlorination will be
required for interim shallow-water discharge requirements, which will apply until an outfall into the
bay is constructed. For deepwater discharge through the outfall, an effluent ammonia-nitrogen re-
quirement of 4.0 mg/1 is anticipated; for the interim shallow-water discharge, 0.5 mg/1. The pilot
studies demonstrated that the practical limit for the FGR effluent ammonia-nitrogen concentration
is about 2 to 3 mg/1.
The low construction bid for the project was $10,460,000 (September 1975), about $2 million
below the engineer's estimate. (It was believed that a lack of available construction projects in the
49
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Table \V-8.—Design data, Sunnyvale tertiary treatment facilities
Parameter
Value
Basic design loadings:
Design population, thousands
Design flow, mgd:a
Canning season
Noncanning season
Maximum TSS, mg/l
Pond effluent pH, maximum
Peak ammonia loading as N, mg/l:
High-temperature operation11
Low-temperature operation13
Plant influent structures:
Pond pumping station:
Number of pumps
Capacity each, mgd
Total dynamic head, feet
Biological nitrification:
FGR pumps:
Number
Capacity each, mgd
Total dynamic head, feet
FGR's:
Number
Diameter, feet
Media depth, feet
Top surface area per unit, ft2
Total media volume, 1,000 ft3
FGR media unit surface area, ft2
Hydraulic loading, gpm/ft2
Recirculation ratio, percent
Surface loading rate, ft2/lb IMH3 oxidized per day
Ammonia conversion as N, mg/l:
Mode 1 :c
High-temperature operation13
Low-temperature operation15
Mode 2:c
High-temperature operation15
Low-temperature operation13
Solids removal:
Dissolved-air flotation system:
Number of units
Diameter, feet
Sidewater depth, feet
Area per unit, ft2
Flow rate per unit, mgd
Surfacing loading rate, gal/min/ft2
124
24
16
175
8
25
22
3
8
20
3
16
36
3
92
19
6,650
379
42
1.7
100
5,000
21
15
16
11
3
60
7
2,820
8
2.0
50
-------
Table \V-8.-Design data, Sunnyvale tertiary treatment facilities—Continued
Parameter
Value
Solids removal— Continued
Dissolved-air flotation system-Continued
Solids loading rate, Ib/ft2/day
Influent pressurization flow, percent of total
Air to solids ratio, Ib air per Ib influent solids
Pressurization level, psig
Influent pH
Assumed TSS removal, percent
Assumed TSS removal per unit, Ib/day
Float-removal system:
Assumed float-production rate, gal/min/unit .
Assumed solids concentration, percent
Assumed float density, Ib/ft3
Float ejectors:
Number
Capacity each, gal/min
Design TDH, feet
Float mixers
Number
Horsepower each
Float pumps:
Number
Capacity each, gal/min
Discharge pressure, psi
Effluent filtration:
Dual-media filters:
Number
Dimensions per half filter:
Length,feet
Width, feet
Area per filter, ft2
Filtration rate, gal/min/ft2
Maximum backwash rate, gal/min/ft2
Air backwash:
Rate, ft3/min/ft2
Pressure, psig
Assumed filter bed expansion, percent
Filter media depth, inches
Anthracite:
Depth, inches
Effective size, mm
Sand:
Depth, inches
Effective size, mm
Pea gravel depth, inches
Filtered-water pumping station:
Number of pumps
Capacity each, mgd
Total dynamic head, feet
4.2
25
0.10
80
6.0-6.3
75
9,000
114
2
31
6
75
8
2
15
3
125
60
32
15
960
5.8
35
4
5
10
66
48
1.18
18
0.94
7.5
4
8
16
51
-------
Table IV-8.— Design data, Sunnyvale tertiary treatment facilities—Concluded
Parameter
Value
Effluent filtration— Continued
Backwash-water-pumping station:
Number of pumps
Capacity each, gal/min
Total dynamic head, feet
Breakpoint chlorination:
Level, NH3-N, mg/l
CI2/NH3 dosage ratio
pH control point
Maximum CI2 dose, mg/l
Disinfection:
Chlorine contact tank:
Maximum CI2 dose, mg/l
CI2 mixer horsepower
Number of cells
Dimensions per cell:
Width, feet
Depth, feet
Length per pass, feet
Total volume, 1,000 ft3 ,
Detention time, minutes
Dechlorination:
Dechlorination mixing basin:
Maximum S02 dose, mg/l
SO2 mixer horsepower
Chemical treatment:
Chlorine feed capacity, 1,000 Ib/day
Sulfer dioxide feed capacity, 1,000 Ib/day .
Sulfuric acid:
Feed capacity, 1,000 Ib/day
Maximum dosage rate, mg/l
Alum, AI2(S04)3 • 14.3 H20:
Feed capacity, Ib/day
Maximum dosage rate, mg/l
Polyelectrolyte:
Feed capacity, Ib/day
Maximum dosage rate, mg/l
Caustic soda:
Feed capacity, 1,000 Ib/day
Maximum dosage rate, mg/l:
With breakpoint chlorination ..
Without breakpoint chlorination
3
8,400
20
8
10:1
7.0
80
15
10
3
10
12
124
134
60
12
10
24
6
20
98
30
150
1,000
5
34
170
80
aIncludes allowance for 6.7 percent backwash recycle flow for dual-media filters.
bHigh-temperature range = 13° C to 19° C. Low-temperature range = 7° C to 11° C.
cMode 1 operation = nitrification of dissolved-air flotation tank effluent. Mode 2 operation
before dissolved-air flotation.
nitrification of pond effluent.
52
-------
Primary
effluent
Float discharge
to oxidation ponds
Nitrification fixed-
growth reactor
(mode 2 operation)
Nitrification fixed-
growth reactor
(mode 1 operation)
Backwash water discharge
to oxidation
Chlorination
(with breakpoint
chlorination
capability)
Dechlorination
Tertiary treatment
plant effluent
Figure IV-5. Sunnyvale tertiary facilities flow diagram.
area at the time resulted in a bid lower than would normally have been expected.) Construction
began in January 1976 and is expected to be completed in November 1977. A breakdown for the
construction cost is shown in table IV-10. Estimated 1978 annual operation and maintenance costs
53
-------
Table IV-9.— Comparative chemical costs, Sunnyvale tertiary facilities
Chemical
Unit cost,
dollars
per ton
Annual costs, thousand dollars
With breakpoint
chlorination
Mode 1
Mode 2
Without breakpoint
chlorination
Mode 1
Mode 2
Chlorine
Acid . . .
Caustic .
200
44
140
170.7
125.2
498.1
231.5
8.4
401.1
Total
794.0
641.0
85.3
125.2
318.7
529.2
85.3
8.4
159.4
253.1
Table IV-10.— Sunnyvale tertiary-treatment facilities construction costs, September J9753
Item
Capital
cost,
dollars
Mobilization 35,000
Site work 220,000
Pond pump station 220,000
Pond access bridge 190,000
Tower pump station 260,000
FGR's 2,400,000
Flotation distribution structure 300,000
Flotation tanks 1,375,000
Control building 775,000
Blower and chemical-feeder building 640,000
Dual-media filters 1,375,000
Filtered-water pump station 300,000
Chlorine mixer and distribution structure 160,000
Chlorine contact tanks 160,000
Dechlorination tank 100,000
Backwash pump station 120,000
Outside piping 675,000
Chemical storage tanks 200,000
Chlorination building 170,000
Dechlorination system 12,000
Temporary outfall facilities 23,000
Primary/secondary plant improvements 750,000
Total construction cost 10,460,000
are $1,500,000 per year with breakpoint chlorination and $900,000 per year without it. This es-
timate corresponds to unit costs of $230 and $140 per million gallons, respectively, for flows of 16
mgd during 8 months of the noncanning season and 22 mgd during 4 months of the canning season.
54
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CASE 2. STOCKTON REGIONAL WASTE WATER CONTROL FACILITY
The city of Stockton, Calif., located near the confluence of the San Joaquin and Sacramento
rivers, has an unusual water-quality problem that requires a unique solution. Historically, the cities
of the San Joaquin Valley, particularly Stockton, have been agriculturally oriented. This orientation
has resulted in industries that produce unusually heavy loading at the city's Regional Waste Water
Control Facility during peak canning periods.
Stockton serves six canners and six other major wet industries, including food processors, in its
municipal system. In the summer of 1975, these industries caused a peak monthly flow of 40 mgd
to the city's treatment plant. BOD loading during that period reached a high of 5,300,000 Ib/mo.
Flows during the remainder of the year are 16 mgd, with 1,300,000 Ib/mo. of BOD. Unfortunately,
the peak occurs at the period of critical water quality and low flow in the San Joaquin River, a tidal
estuary of San Francisco Bay, into which the plant's effluent is discharged.
The Central Valley Regional Water Quality Control Board has established discharge require-
ments that include the following provisions:
• The waste discharge shall "not cause the dissolved oxygen of the receiving waters to fall
below 5.0 mg/1 at any time."
• The waste discharge shall "not cause the total nitrogen control of receiving waters to fall
below 3.0 mg/1 at any time."
A study of the DO dynamics of the Stockton ship channel, which provides a deepwater link to
San Francisco Bay, established the assimilative capacity of the channel for oxygen-demanding ma-
terials discharged from the Stockton Regional Waste Water Control Facility.4 The long-term oxygen
demand was found to be associated principally with algae; therefore, physical removal of the algae
from the pond effluent eliminated most of the long-term BOD. A projection of long-term BOD
loads compared with the assimilative capacity of the river indicated that algal removal would permit
the DO criterion to be met. At the same time, algal removal would also accomplish nitrogen re-
moval, because most of the nitrogen is in organic form and associated with algae.
To meet the new requirements, Stockton is currently enlarging and modifying its treatment
plant. A phased design and construction program has been prepared that will enable the city to be
in compliance with waste-discharge requirements by 1978. This program involves improvements to
the entire plant, including the following elements (fig. IV-6):
• Preliminary treatment
• Primary sedimentation
• Secondary treatment (trickling filtration)
• Tertiary treatment (oxidation ponds and algal-removal facilities)
• Disinfection
• Solids treatment
Pilot Algae-Removal Studies
Pilot studies were conducted at the Stockton plant during the summer of 1971 to develop
design criteria for the tertiary algae-removal facilities. At that time pilot-scale and plant-scale tests
55
-------
Raw
influent
Pond
•i^B^H^
circulation
Figure IV-6. Stockton regional wastewater control facility flow diagram.
had established both coagulation-flocculation-sedimentation and coagulation-flotation as workable,
dependable procedures for removal of algae from pond effluents. An economic analysis indicated
that flotation would be superior to sedimentation because of higher allowable overflow rates and
shorter residence times. It was anticipated that greater sludge concentration could be obtained at
approximately the same chemical dose, and smaller tanks could be used.
Because of these anticipated advantages of flotation over sedimentation, it was decided to
operate a pilot flotation process to determine if flotation was applicable to Stockton's wastes and to
develop design concepts and criteria for a full-scale unit.5 Of particular interest was the comparison
of pressurized dissolved-air flotation with autoflotation. Results of the studies indicated that while
autoflotation exhibited a potential for algae removal, its overall performance was erratic because
there was DO supersaturation in the ponds for only a part of the day. Some of the pilot-study
results are summarized in chapter III.
Full-Scale Tertiary Facilities
Studies of dissolved-air flotation showed the process to be feasible, and it was chosen sub-
sequently for use in the full-scale facility. In addition to dissolved air-flotation, effluent polishing
will be provided by dual-media filtration. Breakpoint chlorination will also be available for ammonia
removal if it is required at those times when the dissolved-air-flotation unit is not being operated.
Effluent disinfection and dechlorination facilities will also be provided. Construction of the tertiary
facilities started in March 1976 and will be completed in September 1978. A flow diagram for the
tertiary-treatment facilities is shown in figure IV-7 and design data are given in table IV-11.
Bids for construction of the tertiary facility were opened on January 27,1976, and ranged
from $16,600,000 to $18,800,000. Annual operation and maintenance costs are estimated at
56
-------
From pond
To ponds
To solids
disposal
system
Chlorine
contact
channel
To pond
system
Figure IV-7. Stockton tertiary facilities flow diagram.
Table IV-1 \.-Design data, Stockton tertiary facilities
Parameter
Value
Tertiary ponds, existing:
Number
Area, net water surface, acres
Volume, million gallons
Loading during noncanning season:
BOD total, 1,000 Ib/day
BOD, pounds per surface acre per day
Loading during canning season:
BOD total, 1,000 Ib/day
BOD, pounds per surface acre per day
Detention, days:
During noncanning season
During canning season
Circulation pumping units:
Number
Capacity each, mgd
Circulation ratio, at peak
Dissolved-air-flotation loadings:
Flow, mgd
SS concentration, mg/l
pH, peak
Ammonia, peak concentration, mg/l
4(4)
630
1,320
3.2
5
57
90
57
23
4
60
4.4
55
170
9.5
6.5
57
-------
Table IV-11.— Design data, Stockton tertiary facilities—Continued
Parameter
Value
Chemical treatment:
Alum, peak rates:
Dry dose, mg/l (17 percent A}^03)
Volume, 1,000 gal/day (8.3 percent AI2O3)
Sulphuric acid, peak rate (93 percent H2S04):
Dose, meq/l
Volume, gal/day
Polyelectrolyte, peak rate (0.5 percent solution):
Dose, mg/l
Volume, gal/min
Chlorine, peak capacities:
Prechlorination:
mg/l
1,000 Ib/day
Filter influent:
mg/l
1,000 Ib/day
Disinfection:
mg/l
1,000 Ib/day
Ammonia removal:
mg/l
1,000 Ib/day
Dechlorination:
Sulphur dioxide, peak rate, mg/l
1,000 Ib/day
Raw-water pumping station:
Traveling water screens:
Number
Capacity each, mgd
Basket width, each, feet
Depth through screen, feet:
Low-pond elevation
High-pond elevation
Velocity through screen, peak, ft/s:
Low-pond elevation
High-pond elevation
Raw water pumps:
Number
Capacity each, mgd
Total head each, feet
Flotation tanks:
Number
Diameter each, feet
Side water depth, feet
Solids loading rate, Ib/ft2/day
250
21.2
3.0
4,700
2.0
15.0
17.5
8
17.5
8
5
2.3
105
48
8.3
3.8
3
43
5
4
7
2.5
1.5
4
13.75
11.0
4
85
7
5.1
58
-------
Table IV-11 .—Design data, Stockton tertiary facilities—Continued
Parameter
Value
Flotation tanks—Continued
Assumed float concentration, percent 3
Assumed float weight, Ib/ft3 41
Peak float-discharge rate, gal/min 600
Surface loading rate, including pressurized flow, gal/min/ft2 2.4
Pressurized flow, gal/min 4,500
Pressure, maximum, psig 80
Air flow, maximum, scfm 80
Air/solids ratio, minimum, Ib air per Ib solids:
Mode 1 0.179
Mode 2 0.179
Dual-media filters:
Number (bifurcated) 4
Width, feet 34
Length, feet 50
Filtration rate, gal/min/ft2:
All filters in service 5.7
One in backwash 7.5
Media:
Anthracite coal:
Depth, feet 4
Effective size, mm 1.0-1.1
Sand:
Depth, feet 1.5
Effective size, mm 0.65-0.75
Gravel depth, feet 0.67
Backwash:
Air:
Rate, ft3/min/ft2 4
Volume, ft3 /min 3,400
Water:
Rate, gal/min/ft2:
Minimum 13
Maximum 26
Volume, mgd:
Minimum 16.0
Maximum 32.0
Filtered-water pumping station:
Number of pumps 3
Capacity each, mgd 21.5
Total head, feet 15.7
Chlorine contact canal:
Length, feet 1 ;030
Average width, feet 1 g.26
59
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Table IV-11.— Design data, Stockton tertiary treatment facilities—Concluded
Parameter
Value
Chlorine contact canal— Continued
Depth, feet
Detention time, minutes . ..
Reaeration blowers:
Number
Capacity each, ft3/min
7.63
30
2
1,500
$1,100,000 per year, based on 3 months of operation. This corresponds to a unit cost of $250 per
million gallons.
CASE 3. ANTELOPE VALLEY TERTIARY TREATMENT PLANT-LANCASTER
The Los Angeles County Sanitation Districts (LACSD), at their Antelope Valley Tertiary
Treatment Plant in Lancaster, Calif., have the longest operating experience record with a coagula-
tion-flocculation-sedimentation algae-removal system. The plant was designed and constructed in
1970 by the LACSD after several years of process research conducted in cooperation with the U.S.
Public Health Service.6 The purpose of the facility is water reclamation. Algae and phosphorus are
removed from the oxidation pond effluent by alum precipitation, settling, and filtration (fig. IV-8).
Sludge is disposed of by pumping it back to the treatment plant's headworks. Treatment ahead of
the tertiary plant consists of primary sedimentation followed by oxidation ponds. Primary sludge is
processed through digestion.
300 mg/l AI2 (SO4)3
+ 4 mg/l Cl,
Filter backwash and
studge returned
to treatment plant
Figure IV-8. Antelope Valley tertiary treatment plant flow diagram.
60
-------
Table IV-12.-Antelope Valley tertiary-treatment-plant operation
Parameter
Influent3 flow-rate rngd
Mean time between filter backwash hours
Influent quality:
SS mg/l
Effluent quality:
Turbidity Jtu
Total phosphate mg/l
February
1973
0.089
16
C243 + d44
6.2 to 6.6
112
156+19
234 + 4
30.2 ± 5.9
9.3 to 9.8
9±2
1.0 + 0.3
0.1 9 ±0.05
September
1973
0.563
17
337 + 31
6.3 to 6.8
14
129 ±10
251 ±3
25.6 + 5.0
9.3 to 9.5
18±2
0.8 ± 0.3
0.1 5 ±0.05
alnfluent to tertiary plant.
^Backwash water and sludge returned to headworks.
cMean value (typical).
dStandard deviation (typical).
6AsCaC03.
fAsP04.
Effluent from the Lancaster plant is delivered to the county of Los Angeles for use in recre-
ational lakes. The 0.5-mgd facility was completed at a construction cost of $243,000. Cost of
operation and maintenance for fiscal year 1973-74 was $304 per million gallons, exclusive of
amortization. Seasonal flows vary. During summer months at design capacity, operation and main-
tenance costs are $200 to $240 per million gallons; in winter months at low flows, unit operation
and maintenance costs are in the range of $600 to $800 per million gallons.7 Operating costs are
borne by the County Parks and Recreation Department.
Operating data for 2 representative months of operation are shown in table IV-12.7 Summer-
time flows are at design capacity, while wintertime flows decline because of seasonal evaporation-
precipitation patterns and because no releases are made from the lakes in the winter. Operating data
confirm that the plant removes algae as well as phosphates very efficiently and consistently. Alum
doses are higher than would normally be required for algae removal alone. The preliminary pilot
work demonstrated that effluent phosphate levels on the order of 0.05 mg/l would aid in preventing
algae regrowth in the lakes.6 It was projected that aluminum sulfate doses of about 300 mg/l (525
mg/l as alum [A12 (SO4)3 • 14.3 H2O]) would be required for obtaining low phosphate residuals,
whereas only about 70 to 120 mg/l of aluminum sulfate (120 to 210 mg/l as alum) is normally re-
quired for removing algae when phosphorus is not a critical problem. For those facilities operated
exclusively for algae removal, therefore, operation and maintenance costs should be lower than at
Lancaster.
CASE 4. RICHFIELD SPRINGS SEWAGE-TREATMENT PLANT
Richfield Springs is a town of approximately 1,600 persons, located in central New York State
about 60 miles west of Albany. One of the first communities of its size to install sanitary sewers,
61
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Richfield Springs installed the initial lines in 1895 and added sewers and a primary plant in 1927.
As a result of increasingly stringent discharge requirements developed to protect nearby Lake
Canadarago from eutrophication, a new treatment facility was designed and constructed in 1972.
Upgraded Plant
The flow diagram for the upgraded facility that provides phosphorus removal is shown in
figure IV-9, and design data are given in table IV-13. Treatment consists of two series-operated
aerated lagoons followed by a package tertiary-treatment unit (two Neptune Micro-Floe SWB 150's)
providing flocculation, tube settling clarification, and mixed media filtration. Chlorine disinfection
precedes discharge to Ocquionis Creek.
Measured daily flows have ranged from less than 0.05 mgd to 2.5 mgd under drought and
storm conditions, respectively. The aerated lagoons can treat a peak wet-weather flow of 2.5 mgd,
caused by the combination of very old sewers and a periodically high ground water table. The ter-
tiary units have a design capacity of 0.3 mgd. When the flow into the lagoon exceeds the tertiary-
treatment capacity, the lagoons act as an equalizing reservoir. Lagoon effluent bypasses the tertiary
units to the chlorine contact tank when the lagoon's storage capacity is reached.
After pretreatment, wastewater is pumped to lagoon 1. From there it flows by gravity to
lagoon 2 and is pumped to the tertiary unit. After tertiary treatment, the wastewater flows by
gravity to the chlorine contact tanks before entering Ocquionis Creek. Flows bypassing the tertiary
Bypass
J— *•
Aerated
No. 1
j
1
k
Aerated
lagoon
No. 2
l
Flows in
excess of
tertiary
treatment
capacity
Figure IV-9. Richfield Springs sewage treatment plant flow diagram.1
62
-------
Table IV-13.— Design data, Richfield Springs Sewage Treatment Plant
Parameter
Value
Flow, mgd:
Average dry weather
Peak wet weather
Aerated lagoons:
Number
Surface area, acres
Depth, feet
Detention time at average dry weather flow, days
Lagoon air supply:
Number of compressors
Capacity each, ft3/min
Aeration-tubing length, feet
Tertiary treatment units:
Number
Design flow each, mgd
Alum dose, mg/l
Flocculator detention time, minutes
Tube settler overflow rate, gal/min/ft2
Multimedia filter:
Depth, total, inches
Garnet
Sand
Anthracite
Specific gravity:
Garnet
Sand
Anthracite
Effective size, mm:
Garnet
Sand
Anthracite
Loading rate, gal/min/ft2
Backwash rate, gal/min/ft2
Backwash flow each, mgd
0.30
2.5
2
2.25
6-12
18
2
210
12,000
2
0.15
70-120
20
2.6
30.0
4.5
9.0
16.5
4.2
0.6
1.5
0.30
0.45
1.00
4.0
16
0.03
unit flow by gravity to the chlorine contact tank. The tertiary unit backwash water and solids enter
a large holding tank where solids settling takes place. The supernatant is pumped back to the plant
headworks, and the sludge is put on drying beds or spread on land.
The lagoons use 12,000 feet of Air-Aqua aeration tubing with the closest tube spacing near the
inlet of the first lagoon. The design aeration air supply, using one of two blowers, is 210 ft3/min.
The lagoon surface area is about 2.25 acres with a volume of 26 acre-ft at a depth of 11.5 feet.
Normal operating depths range from 6 to 12 feet.
63
-------
Each Neptune Micro-Floe SWB 150 unit is designed for a flow of 150,000 gal/day. The tube
settlers (see fig. III-3) contain 39-inch-long tubes with a cross-sectional area of 2.0 in2 each, placed
on a slope of 7.5 degrees from the horizontal. The 30-inch-deep filter bed is composed of garnet,
sand, and anthracite. The filter-loading rate is 4.0 gal/min/ft2. The filters are backwashed for 8-10
minutes every 4 to 5 hours.
Plant Performance
In 1973 and 1974, the New York State Department of Environmental Conservation, Environ-
mental Quality Research Unit, conducted an extensive monitoring program at the Richfield Springs
plant8 as a part of a larger study on eutrophication of Canadarago Lake. Raw sewage, lagoon ef-
fluent, and final effluent were sampled and analyzed for BOD, chemical oxygen demand (COD), SS,
nitrogen compounds, phosphorus, sulfate, turbidity, coliform organisms, and DO.
Tables IV-14 and IV-15 show plant performance for a full 2-year period and a low-flow,
summertime period, respectively. The data in table IV-15 represent a period when algal activity in
the lagoons would be greatest and the raw wastewater strongest. For the long-term period (table
IV-14), BOD and SS removals each averaged 94 percent. Total phosphorus removal averaged 87
percent. Final effluent concentrations for BOD, SS, and total phosphorus averaged 4.0, 7.0, and
0.34 mg/1, respectively.
Table IV-14.-Richfield Springs plant performance, February 1973 through February 1975s
Constituent3
Flow mgd
COD b mg/l
BOD, mg/l
TSS mg/l
TKN, mg/l
NH3 as N mg/l
Total N mg/l
NO3 as N mg/l
Total P mg/l
Alk,d mg/l
864 b mg/l
Turbidity, Jtu
pH
Coliforms MPNI\ 00 ml
DO, mg/l
Raw
influent
058
145
642
103
13.6
49
152
0.60
2 63
212
127
7.47
Lagoon
effluent
51 3
169
307
C6.4
2 7
8.2
1 8
1 18
191
115
34.2
7.84
e29 081
11.0
Removal,
percent
64 6
738
700
52.9
46 1
55 1
Final
effluent
0 37
23 2
4 0
7 0
5.3
29
69
1 6
0 340
134
167
0.97
7.39
e302
10.9
Lagoon-
final
removal,
percent
54 6
723
77 2
17.0
158
71 2
97.2
99.0
Raw-
final
removal,
percent
840
938
932
61.0
54 7
87 1
aBased on a 2-week sampling frequency.
bFrozen sample data.
cMay be low because of inclusion of some soluble organic N values in average.
dField data; as CaCO3.
eLogarithmic mean.
64
T
-------
Table \V-"\5.-Richfield Springs plant performance-September 25 through November 7, 1973 (low-flow period)*
Constituent3
Flow mgd
COD b mg/l
BOD mg/l
TSS mg/l
TKN mg/l
NH3 as N mg/l
N03 as N mg/l
Total N mg/l
Total P mg/l
Alk d mg/l
S04 b mg/l
Turbidity, Jtu
Coliforms /W/V/100 ml
DO mg/l
Raw
influent
0.36
294
98.5
131.2
15.0
5.3
0.25
15.3
6.2
78.3
170
Lagoon
effluent
93.6
28.5
46
C7.0
5.4
2.47
9.5
2.34
166.7
199
61
e33,884
10.1
Removal,
percent
68.3
71.0
64.9
53.3
_
_
37.9
62.3
_
_
_
Final
effluent
0.36
34.1
4.55
14
5.4
3.2
1.90
7.3
0.543
126
206
3.5
e 1,053
8.4
Lagoon-
final
removal,
percent
63.5
84.0
69.6
23.0
,
_
76.8
76.8
_
..
94.3
96.9
Raw-
final
removal,
percent
_
88.5
95.4
89.3
64.0
52.3
91.2
__
aBased on a two-week sampling frequency.
bFrozen sample data.
cMay be low because of inclusion of some soluble organic N values in average.
dField data; as CaCO3.
el_ogarithmic mean.
Cost
The Richfield Springs plant was placed in operation in January 1973, at a total construction
cost of $577,000. The cost attributable to the tertiary portion of the plant was about $170,000. A
construction cost breakdown is given in table IV-16.
Table \\l-\Q.-Construction cost, Richfield Springs Sewage Treatment Plant, 79T28
Item
Fencing
Total plant construction cost
Cost,
dollars
60,000
52,000
185,000
38,000
7,000
110,000
15,000
28,000
10,000
47,000
25,000
a577,000
aCost for tertiary system estimated at $170,000.
65
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Table IV-17 gives operating costs for the Richfield Springs plant and estimated operating costs
for the tertiary-treatment units. Table IV-18 presents treatment costs in dollars per year and dollars
per million gallons.
Table IV-17.-Operating costs, Richfield Springs Sewage Treatment Plant*
[Dollars]
Item
Labor
Power
Chemicals
Miscellaneous
Total
Estimate
for tertiary
plant
1 500
500
3500
500
6000
Total
8000
4000
4500
2500
19000
Table IV-18.—Total treatment costs, Richfield Springs Sewage Treatment Plant8
[Dollars]
Amortized capital cost:3
Per year
Per million gallons at 0.58
Per million gallons at 0.37
Operating cost:
Per year
Per million gallons at 0 58
Per million gallons at 0.37
Total cost:
Per year
Per million gallons at 0.58
Per million gallons at 0.37
mgd
mgd
mgd
mgd
mgd
mgd
Plan
Secondary
38500
180
13 000
61
51 500
241
t
Tertiary
16000
120
6000
44
22000
164
T--*_|
54 500
19000
73500
aAmortized at 7 percent over 20 years.
REFERENCES
!R. W. Stone, D. S. Parker, and J. A. Cotteral, "Upgrading Lagoon Effluent for Best Practi-
cable Treatment," J. Water Pollut. Cont. Fed., 47, 2019, 1975.
2U.S. Environmental Protection Agency, Office of Technology Transfer, Process Design
Manual for Nitrogen Control, EPA-625/1-75-007, Cincinnati, Ohio, Oct. 1975.
66
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3Brown and Caldwell, "Report on Design Criteria, Tertiary Facilities," prepared for the city of
Sunnyvale, Feb. 1975.
4 Brown and Caldwell, "Benefits of Proposed Tertiary Treatment to San Joaquin River Water
Quality," prepared for the city of Stockton, Nov. 1970.
5D. S. Parker, J. B. Tyler, and T. J. Dosh, "Algae Removal Improves Pond Effluent," Water
Wastes Eng., 10, 1, Jan. 1973.
6F. D. Dryden and G. Stern, "Renovated Wastewater Creates Recreational Lake," Environ.
Sci. Technol, 2, 4, Apr. 1968.
7 Personal communication, F. D. Dryden to D. S. Parker, County Sanitation Districts of Los
Angeles County, May 1975.
8T. J. Tofflemire, I. G. Carcich, F. T. Martin, and R. Bloomfield, "Tertiary Treatment for
Phosphorus Removal by Alum Addition," New York State Department of Environmental Conser-
vation, Environmental Quality Research Unit, Technical Paper No. 59, Apr. 1975.
U.S. GOVERNMENT PRINTING OFFICE. 1977-757-056/56H( Region No. 5-11 67
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METRIC CONVERSION TABLES
Recommended Units
Description
Length
Area
Volume
Mass
Force
Moment or
torque
Flow (volumetric)
Unit
meter
kilometer
millimeter
micrometer or
micron
square meter
square kilometer
•quare millimeter
hectare
cubic meter
litre
kilogram
gram
milligram
tonne
newton
newton meter
cubic meter
per second
liter per second
Symbol
m
km
mm
mn or /J
m2
km*
mm2
ha
m3
1
kg
g
mg
t
N
N-m
m3/s
l/s
Comments
Basic SI unit
The hectare (10,000
m2) is a recognized
multiple urttt and will
remain m interna-
tional use
Basic S/ unit
1 tonne = 1,000 kg
The newton is that
force that produces
an acceleration of
1 m/s2 in a mass
of 1 kg
The meter is mea-
sured perpendicular
to the line of action
of the force N.
Not a joule
Customary
Equivalents*
3937 m = 3281 ft =
1.094 yd
0 6214 mi
0 03937 in
3.937 X 105m=lX JO4 A
1Q76sqft = \ 196sqyd
0 3861 sq mi = 247.1 acres
0.001550 sq in
2 471 acres
3531cuft= 1.308 cu yd
1.057 qt = 0.2642 gal *
0.81 07 X 1 Quaere ft
2.205 Ib
0 03527 01= 1543gr
0 01543 gr
09842 ton (long) -
1.102 ton (short)
0.2248 Ib
= 7 233 poundals
0.7375 Ib ft
23.73 poundal ft
15860gpm =
2,119cfm
15 SSgpm
Description
Velocity
linear
angular
Viscosity
Pressure or
stress
Temperature
Work, energy.
quantity of heat
Power
Application of Units
Description
Precipitation,
run-off,
evaporation
Flow
Discharges or
abstractions.
yields
Usage of water
Unit
millimeter
cubic meter
per second
liter per second
cubic meter
per day
cubic meter
per year
Itter per person
per day
Symbol
mm
m3/s
l/s
m3/d
m3/year
I/person/
day
Comments
For meteorological
purposes, it may be
convenient to meas-
sure precipitation in
terms of mass/unit
area (kg/m2)
1 mm of ram =
1 kg/m2
1 l/s * 86 4 m3/d
Customary
Equivalents*
35.31 cfs
15.85gpm
0 1835 gpm
264 2 gal/year
0 2642 gcpd
Description
Density
Concentration
BOD loading
Hydraulic load
per unit area.
e g., filtration
rates
Air supply
Optical units
Recommended Units
Unit
meter per
second
millimeter
per second
kilometers
per second
radians per
second
pascal second
centi poise
newton per
square meter
or pascal
kilo new ton per
square meter
or kilopascal
bar
Celsius (centigrade)
Kelvin (abs.)
joule
kilo|oule
watt
kilowatt
loule per second
Symbol
m/s
mm/s
km/s
rad/s
Pa-s
Z
N/m2
or
Pa
kN/m2
or
kPa
bar
°C
°K
J
kj
W
kW
J/s
Comments
1 /oule = 1 N m
where meters are
measured along
the line of action
of force N.
1 watt = 1 J/s
Customary
Equivalents'
3.281 fps
0003281 fps
2,237 mph
9.549 rpm
0.6722 poundal(s)/sq ft
1 450 X 10 ' Reyn (p)
00001450 Ib/sq in
0.14507 Ib/sq in
14 50 Ib/sq in
f F-321/1 8
°C » 273 2
2 778 X 10 7
kw-hr •
3 725 X 10 7
hp hi = 0 7376
ft Ib = 9.478 X
10"4 Btu
2778X1u"4kwhr
44 25 ft-lbs/mm
1.341 hp
3.4l2Btu/hr
Application of Units
Unit
kilogram per
cubic meter
milligram per
liter (water)
kilogram per
cubic meter
per day
cubic meter
per square meter
per day
cubic meter or
liter of free air
per second
lumen per
square meter
Symbol
kg/m3
mg/l
k9/m3/d
m3/m2/d
m3/s
l/l
lumen/m2
Comments
The density of water
under standard
conditions u 1,000
kg/m3 or 1,000 g/l
or 1 g/ml
If this is converted
to a velocity, it
should be expressed
in mm/s llmm/s =
86.4 m3/m2/dayl
Customary
Equivalents'
0.06242 Ib/cu It
1 ppm
0 06242 Ib/cu ft/day
3281 cu ft/sq ft/day
0.09294 ft candle/sq It
'Miles are U.S statute, qt and gal are U S liquid, and oz and Ib are avoirdupois
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U.S. ENVIRONMENTAL PROTECTION AGENCY • TECHNOLOGY TRANSFER
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