UPGRADING LAGOONS
£ \
_ V J _ Z
- * • • • f - uj
USZ£*«
N PRO^
ENVIRONMENTAL PROTECTION AGENCY • Technology Transfer
August 1973
-------
ACKNOWLEDGMENTS
This seminar publication contains materials prepared for the
U.S. Environmental Protection Agency Technology Transfer
Program and has been presented at Technology Transfer design
seminars throughout the United States.
The information in this publication was prepared by D. H.
Caldwell, Ph. D., D. S. Parker, Ph. D., and W. R. Uhte, representing
Brown and Caldwell, Consulting Engineers, San Francisco, Calif.
NOTICE
The mention of trade names or commercial products in this publication
is for illustration purposes, and does not constitute endorsement or recom-
mendation Tor use by the U.S. Environmental Protection Agency.
-------
CONTENTS
Page
Chapter I. Lagoons in Waste Treatment 1
Types of Lagoons 1
Operating Problems 2
References 3
Chapter II. Techniques for Upgrading Lagoons 5
Pond Efficiency Versus Pond Loading 5
Pond Recirculation and Configuration 5
Feed and Withdrawal 9
Pond Transfer Inlets and Outlets 10
Pond-Dike Construction 10
Supplemental Aeration and Mixing 11
Algae Removal 15
References 18
Chapter TIT. Examples of Upgrading Ponds 19
Case 1. Sunnyvale Water-Pollution-Control Plant 19
Case 2. Los Banos Sewage-Treatment Plant 28
Case 3. Stockton Main Water-Quality-Control Plant 32
References 43
iii ¦
-------
Chapter I
LAGOONS IN WASTE TREATMENT
Lagoons aie 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.;
TYPES OF LAGOONS
Waste-treatment lagoons can be divided conveniently into five general classes according to the
types of biological transformations taking place in the lagoon.a Two of these classes, high-rate
aerobic ponds and facultative ponds, arc also called oxidation ponds.
High-Rate Aerobic Ponds
In high-rate aerobic ponds, algae production is maximized by allowing maximum light pene-
tration in a shallow pond. These ponds are generally only 12-18 inches in depth and are inter-
mittently mixed. The main biological processes are aerobic bacterial oxidation and algal photo-
synthesis. Organic loadings range from 60 to 200 pounds 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
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 BOD& 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 BOD^ in the effluent.
aFor a complete review of the technology and art of this form of treatment, sec references 2 and 3.
1
-------
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 stabili-
zation. 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 90-95 percent BOD5 removals are obtainable, depending on
detention time and the degree of solids removal.
Aerated lagoon applications are a relatively new innovation in environmental-engineering
technology. The Missouri Basin Health Council reports over 100 aerated-lagoon installations3 in
the United States, compared to over 3,000 stabilization ponds in 1968.1
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. Bacteria degrade
organic matter according to the following simplified transformation:
bacteria
CH20 + 02 >.C02 + H20 (1-1)
(organics)
Algae, in turn, reuse the carbon (as carbon dioxide) to form algal biomass:
algae
C09 + 2H20 + energy ~ CH20 + 02 + H90 (1-2)
(algae)
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.4
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 (biochemical oxygen
demand) load on the receiving waters and decreased the dissolved oxygen (DO) levels.5-6 In these
cases, the algae from the pond effluent were in on unfavorable environment for either their
maintenance or growth, and they decayed (as in equation T-l).
2
-------
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 aeratcd-lagoon application
achieved only 70 percent BODfj removal; the insertion of a final clarifier in the process allowed 90
percent BOD5 removal because of solids removal.'
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
particularly 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 shore-
line 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
temperature. Typically, in the winter algae activity diminishes. Biological activity may also slow;
methane fermentation in facultative ponds may practically cease.4 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 BOD5.8
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, 1970.
2Second International Symposium for Waste Treatment Lagoons, Missouri Basin 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 WOCRS 17090EHX, July 1971.
4W. 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.
3
-------
SR. C. Bain, P. L. MeCarty, 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.
6D. L. King, A. J. Tolmsoff, and M. J, Athcrton, "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.
7 L. A. Esvelt and H. H. Hart, "Treatment of Fruit Processing Waste by Aeration," J. Water Pollut.
Cont. Fed., 42, 7, 1305-1326, 1970.
8Maurice M. Richmond, "Quality Performance of Waste Stabilization Lagoons in Michigan,"
Second International Symposium for Waste Treatment Lagoons, pp. 54-62, Missouri Basin Engineering
Health Council and Federal Water Quality Administration, Kansas City, Mo., June 23-25, 1970.
4
-------
Chapter II
TECHNIQUES FOR UPGRADING LAGOONS
Many of the techniques available for upgrading lagoons treating primary and secondary effluents
have already been incorporated in designs at one or more locations—often in the original construction
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 BOD removal.
Physical design features that should be considered include configuration, recirculation, feed and with-
drawal variations, pond transfer inlets and outlets, dike construction, supplementation of oxidation
capacity, and algae removal. These features 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 areal BOD
loading3 and detention time.-1 >2 Typical data for canning wastes are shown in figure II-l. A similar,
but not necessarily identical, empirical relationship would apply to domestic wastes. Figure 11-1
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 area] 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 (e.g., case 2, ch. III).
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. 31-2).
"Except for aerated lagoons, where areal BOD loading is not an appropriate design criterion.
5
-------
200
n i
33
95
too-- -
ao\-
w S0'-E-0.659{Y
>- 50 —
Q *Oh
- 3oi-
.33
,90
.74
'75
"58
o71
/0
20
40 6C /OC
200
<"00
>000
lOflOO
Y, lB. BOD/ACRE - DAY
Figure 11-1. BOD-removal relationship for ponds treating canne-y wastes."
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 case example (ch. III).
Three common types of interpond-reciruulation 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 = fir-ii
(l+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:
6
-------
Parallel
RECYC
/ PUV1P STAT ION
INTRAPOND RECIRCULATION
RECYC _£
2
Series
Parollel - Series
INTERPOND RECIRCULATION
Figure 11-2. Common pond configurations and recirculation systems.
s» ¦ rr+ (rr)Sa
1 + r \1 + r
(H-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.'0'
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.
7
-------
2"EDUCTOR
4" AIR 6 VACUUM
RELEASE VALVE
LADDER
PUMP DISCHARGE
POND
SUPPLY
CHANNEL
BAR SCREEN
POND
RETURN
CHANNEL
Figure 11-3. Cross soction of a typical recirculation pumping station.
-------
An auxiliary pump with an air cductor maintains the siphon. Siphon breaks are provided to insure
positive backflow protection.
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. IL
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. 11-4). 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 3,
ch. III). 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.
r-m-
A
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.
9
-------
POND TRANSFER INLETS AND OUTLETS
Pond transfer inlets and outlets should he 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 he 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.
10
-------
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.
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, must operate under winter condi-
tions, or when there is no more room for expansion, supplementation of the ponds' photosynlhetk;
oxidation capacity is required. (When no oxygen is supplied by photosynthesis, the system is called
an aerated lagoon.)
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 arc 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. JI-6) and the
more common turbine and vertical-shaft aerators (fig. II-7). Cage aerators are relatively new in
the United States (see ch. Ill, 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.
11
-------
TRANSFEP PfPE INVERT
MIjST EXTEND at least
3 " SF YON'D S: CPE .
Plastic plug
SEE Detail
I iC-Q WOE ACCESS ROACWA Y WfTH 6"Th,CK
AGGREGATE BASF COURSE
-TOP OF •" THICK R!PRAP EL IG5.00
/
POND j /
SUPPLY
CHANNEL \ f
BOTTGM OF ; ¦ THICK RtPRAP—.
EL IOC 00 /' ^ A
/OXIDATION
POND
/
J k
, 2'-0 WOE SAND {TYP)
Y
K-
PPOVICE OVERLAP
AT AlL JOINTS
¦WELD SEEPA5E COLLAR
TO BANDS
J
TYP. SEEPAGE COLLAR DETAIL
NO SCALE
clamps and slots, see section i
Vt FIBERGLASS REtVF
PLASTIC PL'JC -
30 CMP
SIDE ELEVATION
END ELEVATION
9"± '/is . 3 '4
'/g " ' F18E ROL ASS
REINF PLASTIC CLAMP
PROVIDE P1/," i SLOTS AT INTAKE
ENDS OF ALL TRANSFER PIPES
SECT ION M)
TYPICAL PLUG DETAIL
NO SCALE
Figure 11-5. Details of dike design.
12
-------
*1
\^,--SYtAj£TfitCAl ABOUT W
I frjiapI rrtitfM vcw'/y)
COKBi. TE AHCHO#
H5T pmpt or rw5 co*T9*CT
adjustable
PIO/D GiJ'DC
sik'i/T-n *
SOPVGfflFD /
IACH END '
Vt It AtCHOff
CXlm'Vilf ANCHOff
fOT fti&T OF mis CONTRACT
I
HOT P*N7 Qf THIS CCHTtfAQT
AHGtl AHCHOP CUP-OFStCtH
R.*' AT lACHMCHT TO FX3
V- A*C**0* BOLTS 'jrplCAl
LACH A^CHOP TIE')
ADJUSTABLE
fume Gtjioe
STKijT-PfN /
svppormo /
EACH tNO
P'OIC CO'CH
AND
HALAW*r-plN
Si/PPOPTfO
EACH f*0
. HAHDWtL THtS jlDt
/ OF rtAi WHAT ONI r
vp/v #PCVG*7 /eon
I i IMC COHOU'r *!Tt1
cplss Afj;} f'i i/cs ar>iH Funs
FLEXIBLE Cm OF CABLE
l txiAi f cu/iOf e.Ai'i f
MACH1NF fl FCTPC.
KW 80*
W6U<*Ar (TYP EACH BLADED UOTUff
a tiff HAtUWAU
COHDL'IT AKD W. Of H9
MACWi iAJTQP AfJO uf'tCt 5 S^l
0111
NJUIJul
S+iAft HtAfi.Hf,{Trh:
4C**W>"A7 If*!
0 fP)
PlLADFn
PLAN - TYPICAL. POND AERATOR
jrfiNiwt/
r
mm LLCCPlCALJI.JtA.IKJN 8C.<
Dffrvf EQUIPMENT CitvEf?
existing slope —
rP2-i'*;o
r r-COHC A'KHOfi >
.V
2 _
- fnrw
¦ ncxa; —, f< \ | I
pPEPfkAOFZt \ ! /{ \ /
SECTION^
''/"N
SECT
1 Pinned C&MECTION
SECT ION!pr-7
Figure 11-6. floating cage aerator.
-------
s f'HAIt , h() HERT.
EXPLOSION PHOOF COA/OJIT BOX
heavy duty motor eeaniNfj
CO**OStON RESISTAftT
PVC !)ht JACKET COPPER 5 T ft AND ELECT. CABLE
JL APPROVED FQB VND£* WATER SERVICE
\
/—DIFFUSION HEAD, 30* STN. STL CASTING
ANTf-Of FL f C TtON iU&EHT
Ft J i D OCF 11CTON
.X"
TOP StCtM, J04 STH STL , >« QA$E
ANCHOR CABLE
Tt , i* UAGE
HQTQR SHAFT
VOIUTt, iO* STN STL
PQLYURETHAHE
FOAM FILLED FLOAT
PROPELLtfi , ,H6 STN. STL
ST ASHLESS STEEL LQCKN-JTS
USfD BELOW WATCR I/V£
50
hTAHE CONE
AM; tHOSiON PLATE A SSE MBl Y
Figure 11-7. Floating propeller aerator.
-------
Floating cage aerators may be mounted either in the pond or directly off the dike slopes (as at
Sunnyvale, case 3, ch. 111). When mounted off the dike slopes, they can be close to the pond transfer
inlets. The entire dike slope in the immediate area is provided with erosion protection. Units
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.5
Pond aeration and mixing systems serve mainly to increase the oxidation capacity of the pond.
They are useful in overloaded ponds that generate odors.
ALGAE REMOVAL
Physical removal of the solids in pond effluents will insure that virtually all of the carbonaceous
BOD and most of the nitrogenous BOD in the pond effluent will be removed.
Figure II-8 shows the 30-day effluent BOD from the Stockton, Calif., ponds during the canning
season in 1970 (ch. Ill, case 3). Physical removal of the algae removed virtually all of the long-term
BOD. Very few plant effluents are regulated on the basis of ultimate oxygen demand. If pond effluents
are subject to such rigorous investigation, why look only at lagoon treatment? Figure II-9 shows the
30-day BOD for the effluent of an activated-sludge plant in California also receiving a heavy canning
load during the summer of 1970. That effluent also has a high 30-day BOD. Much less can be removed
by solids separation, presumably because more of the nitrogenous BOD was in ammonia form and not
removable by physical separation.
With proper design and operation of the pond-treatment system, the insertion of an algae-removal
step can produce an effluent low in both oxygen-demanding materials and nutrients. Table 11-1
shows recent data obtained by the Napa County Sanitation District6 from an algae-removal pilot
plant treating a tertiary-pond effluent.b The treatment system included lime coagulation, sedimenta-
tion, rapid-sand filtration, and carbon adsorption. The data shown are for operation in the summer
of 1972. As algae activity diminishes in the water, ammonia levels may rise. Ammonia discharged
to the receiving waters, however, might not stimulate algae growth in the river for the same reasons
that pond-algae efficiency drops in the winter. Mechanical removal of algae is described further in
case 3, chapter III.
Nitrogen levels in facultative-pond effluents may be quite low for several reasons. Much of
the nitrogen in the pond influent may be incorporated into the algae cell. There also appears to
be another distinct nitrogen-removal mechanism. Nitrification appears to take place in the ponds
followed by denitrification in the anaerobic bottom zone.
Recovery of algae for animal feed has been investigated over the years; principal problems
lie in developing a market for the product and in finding a means of separating algae in a manner
consistent with the purpose of obtaining a feed. The use of coagulants such as alum generally
diminishes the utility of the product. Dodd, an investigator at the University of California at
Davis, has developed a mechanical system in which paper pulp is precoated on a belt filter; algae
are removed on the filter as the belt winds around a microstrainer drum. The paper-pulp product
is vacuum- and heated-air-dried to produce an algae paper that can be shredded to make feed.c
^Preceded by primary sedimentation and tricklinR filtration.
CJ. Dodd to D. S. Parker, personal communication, Sept. 1972.
15
-------
250
200
» 150
^-4UNC L T E RED
-------
Table 11-1.— Treatment of pond effluent for algae removal
Constituent
Pond
effluent
Sedimentation
tank1
Multimedia
rapid sand
filter
Activated
carbon
i
Milligram!
per liter
PH
9.4
10.8
8.0
8.5
BOD
30
3.6
4.3
.8
COD2
158
55
37
13
ss
102
23
6
5
Turbidity3
42
9
6
3
P
1.7
1")
C)
C)
Chlorophyll A5
437
59
,4)
19
Organic N
8.3
!.7
1.1
0.46
no3
.16
.18
.27
.18
no2
.18
11
.11
.11
nh3
.21
.35
.26
.17
Total N
9
2.2
<">
.7
'Pond tfflueni treated with 200 mg/l lime as.CaO and 50 mgy'l alum as AljISO^I-] • 1BHjO.
^Chemical oxygen demand.
^Jackson turbidity units IJTU).
^No data.
5ms/i.
The algae can provide the protein and the paper can provide roughage for feeding cattle and sheep.
Cost data so far have not been developed.
The pond system itself can provide for algae removal. Series ponds (fig. 11-2) are recommended
by some State regulatory agencies for encouraging algae sedimentation within the pond cells. A
parallel-series arrangement (fig. 11-2) can also encourage such sedimentation. Sedimentation
ponds, however, are limited in efficiency by such factors as wind mixing and species type. Wind
prevents sedimentation by mixing the water. The smaller the pond, the less influence wind has on
mixing. Sedimentation-pond efficiency also depends on species type. Motile algae and crustaceans
are not removed efficiently in such ponds.
McKinney et al.,5 after an extensive review of available data, concluded that for small ponds
(which are used most often) the best method for algae separation was the series arrangement, with
the final pond used for algae sedimentation. Oswald et al.7 report a series application of ponds where
algae sedimentation follows a high-rate aerobic pond;d algae settle out in the sedimentation pond,
which has a detention time of 13 days and a depth of 8 feet. Oswald further reports that, whilp the
sedimentation pond initially yielded high algae removals, there has been some deterioration, as blue-
green algae grew in the summer of 1972 from nutrients released from anaerobic fermentation of the
sludge layer. Oswald recommends removal of the bottom sludges in the sedimentation pond every
2 years to prevent this problem. The Los Banos case example (ch. Ill, case 2) demonstrates a series
arrangement to encourage algae removal.
^The entire series-treatment system consisted of a facultative pond, n hiRh-rnte aerobic pond, an algae-
sedimentation pond, and two maturation ponds in series.
17
-------
An algac-sed indentation pond, unlike a mechanical system, is subject to variable performance
caused by wind mixing, nutrient recycle from the sludge layer, and changes in algae-removal effi-
ciencies resulting from shifts in algae species. An algae-sedimentation pond cannot be expected
to operate as efficiently as a mechanical system; however, such sedimentation ponds do have a
place in upgrading technology since they are far simpler and more economical than mechanical
systems.
REFERENCES
JD. 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
Conference, 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, edited by R, E. McKinney, June 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, June 1970.
4W. J. Oswald, Chapter 17, Water Quality Management, edited by P. H. McGavhey, University
of California, Sanitary Engineering Research Laboratory, Berkeley, Calif., 1966.
5R. E. McKinney, J. N. Dombush, and -J. W. Vennes, "Waste Treatment Lagoons—State of the
Art," Missouri Basin Engineering Health Council, EPA WPCRS, 1709QEHX, July 1971.
6 Brown and Caldwell, "Contract for Pond Aerators," prepared for city of Sunnyvale, Calif.,
Dec. 1969.
• 7W. J. Oswald, A. A. Meron, and M. D. Zabat, "Designing Waste Ponds to Meet Water Quality
Criteria," Second International Symposium for Was/e Treatment Lagoons, pp. 186-194, Missouri
Basin Engineering Health Council and Federal Water Quality Administration, June 19, 1970.
®R. E. McKinney and H. H. Berijes, Jr., "Evaluation of Two Aerated Lagoons," JSED, i4SC£,
91, SA6, 43-55, 1965.
^Personal communication, Earl Goodwin to D. S. Parker, July 1972.
10Personal communication, W. J. Oswald to D. S. Parker, Sept. 1972.
11 Richmond, Maurice M., "Quality Performance of Waste Stabilization Lagoons in Michigan,"
Second International Symposium for H'asfe Treatment Lagoons, pp. 54-62, Missouri Basin
Engineering Health Council and Federal Water Quality Administration, June 1970.
18
-------
Chapter III
EXAMPLES OF UPGRADING PONDS
CASE 1. SUNNYVALE WATER-POLLUTION-CONTROL PLANT
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, Brow7i
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. III-l and III-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 anaerobically, 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, and 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.
19
-------
Figure 111-1. Cage aerator.
Figure III-2. Cage aerator in operation.
20
-------
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
oxygenation capacity is required. Figure TT-6 shows a drawing of the aerator and figure III-3 shows
a diagram of the ponds. (An aerial view of the ponds, 1969 enlargement, is given in fig. III-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 DO at all times and are odor free. Fish have returned to the slough.
Tables III-l and 1II-2 give design data for before and after upgrading (1967 and 1971). Table III-3
shows operating data for 1970 and 1971. Capital costs for pond upgrading is given in table III-4,
Table I1I-5 shows the operating cost changes caused by plant expansion.
~-~PCND j
Circulating
pump STATION
\ /
V^'
CX I DAT!ON
POND 2
effluent
DISCHARGE
TO GJADA.UPE
SLOUGH
chlor;ne
CONTACT
chamber
Figure HI-3. Diagram of Sunnyvale ponds.
21
-------
Figure 111-4. Sunnyvale sewage-treatment works, 1969 enlargement.
22
-------
Table 111-1.— Sunnyvale watcr-pollution-control plant design data, 1967
Component
Quantity
Design loadings:
Domestic:
Daily average flow, mgd
BOD, mg/l
BOD, lb/day
Suspended so'ids, mg/l
Suspended solids, lb/day
Industrial waste (seasonal):
Daily average flow, mgd
BOD, mg/l
BOD, lb/day
Suspended solids, mg/l
Suspended solids, lb/day
Preaeration tanks, domestic sewage only:
Number
Width, feet
Length, feet
Average water depth, feet
Detention time, hours
Air supplied per tank, cfm
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, gpd/ft2 at daily average flow
Maximum hydraulic capacity, mgd
Maximum hydraulic bypass channel, mgd .
23
-------
Table IIS-1Sunnyvale water-pollution-contrcl-plant data, 1967— Concluded
Component
Quantity
Primary treatment, domestic sewage only:
Assumed BOD reduction, percent
BOD reduction, mg/l
BOD reduction, lb/day
Assumed suspended-solids reduction, percent
Suspended-solids reduction mg/l
35
95
11,800
60
180
Suspended-solids reduction, lb/day
22,400
Primary effluent, domestic sewage only:
BOD, mg/l
BOD, lb/day
Suspended solids, mg/l
Susoended solids, lb/day .
175
21,800
120
15,000
Oxidation pond, domestic sewage only:
Number
Area, acres
Loading, 5-day BOD, Ib/acre/day
Detention, days
1
325
67
36
Circulation pumps:
Number
Capacity each, gal/min
Head, feet
4
44,000
3.5
Engine-generators:
Number
Rated output, kW (hiqh-low)
Speed, rpm (high-low)
Frequency, cps (high-low)
3
223-167
1,000-750
66-50
Industrial wastes holding pond:
Net water area, acres
Maximum water depth, feet
Maximum capacity, millions of gallons
100
6
200
24
-------
Table \\\-2.—Sunnyvale water-pollution-control-plont
design data, 1977
Component
Design loadings:
Domestic:
Average daily flow, mgd
BOD, mg/l
BOD, lb/day
Suspended solids, mg/l
Suspended solids, lb/day
Industrial waste, seasonal:
Average daily flow, mgd
BOD, mg/l
BOD, lb/day
Suspended solids, ng/l
Suspended solids, lb/day
Preaeration tanks:
Number
Width, feet:
Six at
One at
Length, feet:
Six at
One at
Average water depth, feet:
Six at
One at
Average daily flow, mgd:
Six at
One at
Detention time, hours:
Six at
One at
Air supplied per tank, cfm:
Six at
One at
Air supplied per tank, ft3/gal:
Six at
One at
Maximum hydraulic capacity per tank, mgd:
Six at
One at
Maximum hydraulic capacity bypass channel, mgd
-------
Table ) 11-2.—Sunnyvale wster-pollution-conlrol-plant
design data, 1971—Continued
Component
Sedimentation tanks:
Number
Width, feet
Length, feet
Average water depth, feet
Effluent weir per tank, feet
Detention time, hours
Mean velocity, ft/min
Overflow rate, gal/ft2/day
Maximum hydraulic capacity per tank, mgd ....
Maximum hydraulic capacity bypass channel, mgd
Primary treatment efficiency, domestic only:
Assumed BOD reduction, percent
BOD reduction, mg/l
BOD reduction, lb/day
Assumed suspended-solids reduction, percent
Suspended-solids reduction, mg/l
Suspended-solids reduction, lb/day . . .
Primary effluent, domestic only:
BOD, mg/l
BOD, lb/day
Suspended solids, mg/l . . .
Suspended solids, lb/day . .
Oxidation ponds:
Number
Area, acres
Average depth, feet
Mechanical aerators:
Number
Vlaximum power, input to rotors, hp
Efficiency, lbs 02 input per hp-hr . .
Oxygen input, lb/day
Loading, 5-day BOD, total lb/day:
Noncanning season
Canning season
5-BOD reduction capacity:
Noncanning season (winter months), photosynthetic:
Unit, Ib/acre/day
Total, lb/day
26
-------
Table 111-2 .-Sunnyvale water-pollution-control -plan t
design data, 1971—Concluded
Component
Quantity
Oxidation ponds—Continued
Canning season (summer months):
Photosynlhetic:
Unit, lb/acre,'day
175
Total, lb/day ,
Mechanical aeration, lb/day
Photosynthetic plus mechanical aeration, lb/day
77,000
59,000
136,000
Detention, days;
Noncanning season
Canninq season
27
20
Circulation pumps:
Number
Capacity each, mgd .
Head, feet
4
63.5
3.5
Table II1-3.-BOD5 removals during canning season by ponds before and after
ins la! I a dun of aera tors
Season
Pond
influent BOD
Pond effluent 800
Percent
mg'l
1
| 1G3 lb/day
i
mg/1
\
1 103 lb,'day
removal1
July 8-0ct. 1. 1970 (before aerators)
347.2
' z67
64
I 37
(
89
June 30-Oct. 2, 1971 (after aerators)
405.5
! 4 64
29
I
I 4
94
^8,wi»;! on crass emission, lb/day.
^Max'.rnjm value, 102,000 lb/clay; efflt.ert vf'ne s fairly consistent.
"'Does not includa BOD in effluent from mcn.stnal tioiding pond.
^Maximjm value, 121,000 lb/day-
27
-------
Table 111-4.—Summary of capita! 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
Wain switch gear
Unload, position, and hook up aerators
Total
Cost in dollars
587,000
40.000
28,950
32,000
138,710
140,000
24,000
31,900
1,022.510
Table 111-5.—Operating costs associated with pond upgrading
Cost in dollars
Item
1970
1971
(before aerators)
(after aerators)
Gas and electricity1
15,000
58,000
Chemicals^ . . .
54,000
0
Labor3
0
10,000
Totai
69,000
68,000
'includes power for rcmamasr of plait
ivhicf- was also oxpandoa
in 1971
o
Cslciurr and sodium rutrute, phosphoric acid, and anhydrous ammonia.
3(jpn employee added in 1971.
CASE 2. LOS BANOS SEWAGE-TREATMENT PLAMT
The Los Banos Sewage Treatment Plant, Los Banos, Calif., was constructed in 1961 for two
reasons; the treatment system was too small and in disrepair, and the system could not meet recent
discharge requirements set by the California Water Quality Control Board. Treatment then con-
sisted of a two-compartment, 125,000-gallon-capacity septic tank originally designed to serve 700
people. Population at that time was 6,800, and the average daily flow was 2.5 mgd. Hydrogen
sulfide gas had deteriorated the concrete so much that the system was inoperative.
28
-------
In 1960 the Regional Water Quality Control Board established effluent requirements for
discharge to Mud Slough, the receiving water for the plant effluent. The pertinent portions of the
requirements were as follows:
• DO in the receiving waters was not to he reduced to less than 5 mg/1 for 16 hours in a
24-hour day.
• Settleable solids were not to exceed 0.5 ml/l/hr.
The treatment facility was constructed to meet these requirements. A concurrent plan was
effected to reduce storm water infiltration and to divert cooling water from the milk-processing
industry that was tributary to the plant, thus reducing the plant-influent flow to 0.5 mgd (ADWF).
The facility included a pump station, a comminutor, and two 85-acre raw-sewage lagoons (fig.
111-5). BOD^ removal was 85 percent on filtcrcd-effluent samples.
In 1972 the regional board added more constituent requirements:
• Median BODs must be less than 40 nig/1.
• Median settleable solids must be less than 0.2 ml/1.
• Median MPN must be less than 50/100 ml.
• Chlorine residual must be less than 0.5 mg/1.
• pH must be between 6.5 and 8.5.
Since 1969, shock loads of organics periodically had turned the first pond anaerobic, causing
it to give off odors. The regional board required that DO in the ponds must not be less than
1 mg/1. Additionally, the board required that discharges should not lower the DO concentration
in the receiving waters below 5 mg/1 for 16 hours, and never less than 3 mg/1.
The proposed two-stage plan expands and alters the existing facility. Stage T calls for addition
of a third pond of 170 acres, which will double the pond area (see fig. 111-6). Mechanical aerators
will be installed in the first pond cell, and recirculation will be increased to alleviate initial septicity.
The long detention time of 250 days and the good climate should promote crustacean growth.
The crustaceans devour the algae, encouraging clarification and sedimentation. Disinfection will be
accomplished by chlorination. The plant effluent now contains between 20 and 90 mg/1 BOD5,
and little or no settleable solids. If algae removal is effective, the BOD5 of the effluent should be.
quite low. DO levels in the receiving waters are adequate at present and should remain so.
Settleable solids should decrease.
If operating experience indicates inadequate algae removal, the construction of an algal removal
facility is proposed (as stage II). Tables TII-6 and III-7 show design criteria and operating costs,
respectively, for stage I.
29
-------
EFFLJENT TO
VUD SLOUGH
BYPASS
WEIR f N
DIVERSION
MANHOLE
(1.2) *-0
POND 2
:Q5 AC )
(1.2)"*"V
PONO !
(85 AC)
(I.2
•NFL UENr
C».o)
~-CROSSOVER
yfT C H A >N N E L
LEGEND
(J.6) F^OW.mgd (2 NFLUEM PUMPS OPERATING)
~—ARROWS INDICATE NORMAL FLOW DIRECTION
O NORMALLY OPEN GATE
• NCRMALLY CLOSED GATE
1= NORMALLY 03EN CONTROL WEIR
^ NORMALLY CLOSED WEIR
Figure 111-5. Flow diagram for existing conditions at 1 mgd, summer, ADWF.
.EFFLUENT TO
' MUD SLOUGH
(2 O)
Bv PA SS
WEIR iN _
DIVERSION I
MANHOLE 1
(2 0)
30 INCH
¦NTERCEPTQR
POND BYPASS
CONTROL WEIRS
-POND 3 SJPPLY
v C H A N N E L
RETURN PIPEL INS -
RAW SEWAGE
P L MPS -
CONTROL
VAL v£
POND 2
(85 AC )
MECHANICAL
AERATORS
POND I
(85 AC)
PCSID
C IRCULA r ION
PUMPS - -
LEGEND
("7.2) FLOW, t g d (2 I N F L U E N T = UMPS OPERATING)
-* ARROWS INDICATE NORMAL F_OW DIRECTION
O NORMALLY OPEN GATE
• NORMALLY CLOSED GATE
= NORMALLY OPEN CCNT^O^ WEiR
mm NORMALLY CLOSED WEIR
(5>)-»9
CSOSSOVEH
H A N N E
(5.4)-*"Q
!5.4)-*-6
-POND 3 RETURN
CHA NN'E L
Figure 111*6. Flow diagram for staye I design at 2 mgd, ADWF.
30
-------
Table 111-6.—Los Banos design data
Component
1959 ' 1972
Basic loading, flow, average mgd:
Summer season
Winter season
BOD5, 1,000 lb/day
Summer season
Winter season .
Influent pumps:
Number
Capacity, each, mgd
Capacity, one unit out of service, mgd
Oxidation pond system:
Ponds:
Number
Area, net water surface, acres
Volume, millions of gallons .
Allowable loading, summer season:
BOD, lb/surface acre/day . . .
BOD total, 1,000 lb/day . . .
Allowable loading, winter season:
BOD, lb/surface acre/day . .
BOD total, 1,000 lb/day . .
Mechanical aerators:
Number
Total horsepower
Total capacity, 1,000 lb1 BOD per day
Pond circulating pumping units:
Number
Total capacity, mgd
Chlorination:
Chlorination rate, lb/day2 . .
Chlorination capacity, lb/day
2.5
1.0
2.0
1.8
0.7
1.4
4.8
4.0
6.9
6.7
4.6
9.0
4.1
2.8
5.6
2
3
•
3.6
3.6
3.6
7.2
2
3
170
340
*
280
560
40
40
6.8
13.6
20
20
3.4
6.8
3
-
-
60
2.2
-
2
9.0
84
167
400
400
'Based on motor shah horsepower of 0.27 for each pojr-d Qf BOD stabilized per day.
^Based on summer flow and dosaijR of 10 tig/l.
Note.- • indicates "no data."
31
-------
Table 111-7.—Operation and construction costs
Component
Existing J Stage I1
Dollars
Construction cost2
Annual costs:
Operation and maintenance
Capital cost
Total annual cost
885,000 j 490,000
4,000
20,000
16,300
50,400
24,000
66,700
^Estimated.
¦'Includes contingencies, engineering, legal, administrative.
CASE 3. STOCKTON MAIN WATER-QUALITY-CONTROL PLANT
Improving Pond Effluent by Algal Removal
What do you do when you have 630 acres of recently expanded ponds in your treatment
system and a regulatory agency tells you to meet tough new requirements? The answer:
incorporate them into an advanced waste-treatmeni system and accomplish the objective.
The city of Stockton, Calif., is located near the confluence of the San Joaquin and Sacramento
Rivers and has an unusual water-quality problem that requires a unique solution. The cities of the
San Joaquin Valley, and Stockton in particular, have historically been agriculturally oriented. This
orientation has resulted in industries that produce unusually heavy loadings at the city's main
water-quality-control plant during peak canning periods.
Stockton faces the problem of serving six canners and six other major wet industries, including
food processors, in its municipal system. In the summer of 1970, these industries caused a peak
monthly flow to the city's main water-quality-control plant of 35 mgd; BOD loading during that
same time reached a high of 3,200,000 pounds per month. Flows during the remainder of the year
are 15 mgd, with 945,000 pounds per month of BOD. Unfortunately, these peaks occur 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 content of receiving waters to
exceed 3.0 mg/1."
A study of the DO dynamics of the Stockton ship channel, which provides a deep-water link
to San Francisco Bay, established the assimilative capacity of the channel for oxygen-demanding
32
-------
materials discharged from the Stockton main plant.1 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 to the
assimilative capacity of the water indicated that algal removal would permit the DO criterion to be
met. At the same time, algal removal would also accomplish nitrogen removal, since most of the nitro-
gen is in organic form and associated with algae.
To meet the new requirements, Stockton is currently undertaking enlargements and modifica-
tions to its main water-quality-control plant. A phased design-and-construction program has been
prepared that will enable the city to be in compliance with waste-discharge requirements by
February 1974. This program involves improvements to the entire plant including the following
elements:
• Preliminary treatment
• Primary sedimentation
• Secondary treatment (trickling filtration)
• Tertiary treatment (oxidation ponds and algal-removal facilities)
• Disinfection
• Solids treatment
As a part of this program, pilot algal-removal studies were conducted during the summer of
1971 to provide design and operating criteria.
Alternative Means for Removal. Algal removal can be accomplished in two stages, the first
consisting of chemical coagulation and gravity separation and the second of multimedia, rapid-sand
filtration. The first removal stage accomplishes separation of the bulk of the algae (60-90 percent)
and produces an effluent that can be applied to filters without excessive backwashing. This stage
can utilize either flotation (in several modes) or sedimentation. In either case, the well-coagulated
and flocculated solids are removed, leaving only dispersed solids in the first-stage effluent. The
second-stage separation process then removes residual materials, and usually involves the use of a
polymer coagulant aid to enhance removals.
Sedimentation is used widely to clarify many suspensions. When used for the removal of
algae, it is first necessary to coagulate the algae chemically in order to remove the repelling charges
that stabilize the individual particles. The treated particles are then aggregated to form particles
large enough to settle out in the sedimentation tank. Sedimentation thus involves three stages
(shown in fig. I1I-7): chemical coagulation, flocculation, and sedimentation.
When flotation is used, separation depends on the formation of fine bubbles that are physically
attached to the algae causing them to float to the tank-water surface where they are collected and
removed. Chemical coagulation enhances the effect in the same manner as in sedimentation. It
is the algae-bubble-chemical matrix that is desired for good flotation, rather than large aggregates
of chemically bound algae needed for rapid sedimentation. No separate mechanical flocculation
step is provided in flotation.
Two modes are available for the formation of the fine bubbles: dissolved-air flotation and
autoflotation. In dissolved-air flotation, a portion of the effluent or influent, is pumped to a
pressure tank where the liquid is agitated in contact with high-pressure air to supersaturate the
liquid. When this pressurized stream is released into the influent, fine air bubbles arc formed. These
33
-------
CHEMICALS
FL0CCULAT10N
SEDIMENTATION
EFFLUENT
COAGULATION
NFLJENT
i—i
SLUDGE
SEDIMENTATION
CHEMICALS
EFFLUENT
INFLUENT
COAGUL AT ION
PRESSURE
REGULATING
VALVE
SE-TLEABLE
| RECYCLE ( Dissolved
COMPRESSOR
PRESSURIZ AT iCN
FLOTATION
Figure I ] i-7. Alternatives for first-stage alga! removal.
bubbles are then coagulated with the algal cells by the rapid addition of chemicals. The algae-
chemical-bubblc "float" is then removed at the surface of the tank. Autoflotation differs only
in that no pressurization is required for the formation of the fine bubbles.
Flotation with alum coagulation and rapid-sand filtration has proven successful in
Windhoek. South Africa.2 6 The flotation stage produced a reduction in BOD, from 27.3 to 9.5
milligrams per liter (mg/'l) using an alum dose of 350 mg/1. In another test, the suspended solids
were reduced from 280 mg/1 to 94 mg/1. Float solids ranged from 1.4 to 3.7 percent total solids.
In the Windhoek studies it was found that flotation could be obtained without pressurization,
a process termed "autoflotation." For this process to be effective, the DO content of the
pond effluent must be at a supersaturated level and exceed 14 mg/1. The supersaturation is
released by providing aeration or carbon dioxide addition and turbulence. The presence of the
suspended algae or alum-algae floe catalyzes the formation of small oxygen bubbles; this effect
results from the change in oxygen partial pressure. The bubbles then attach themselves to the floe
and rise to the surface. When insufficient DO was present, it was found that flotation could be
achieved by aeration of the water under pressure followed by pressure release. Carbon dioxide was
34
-------
used in conjunction with alum for two purposes: to promote a change in the partial pressure of
oxygen and encourage gas release and to lower pll to the 7.0-to-6.5 range, which is optimum when
alum is used as a flocculant.
The following advantages of flotation are cited by the Windhoek investigators:
• The separation can be accomplished in shallow flotation tanks with residence times as low
as 6-20 minutes as opposed to 3.5 hours in sedimentation.
• The sludge is more concentrated than from a sedimentation unit, and higher tank-overflow
rates can be used.
The other alternative first-stage separation technique, sedimentation, has been thoroughly
evaluated by Dryden and Stern.In jar tests, alum proved to be a more effective coagulant than
either lime or ferric sulfate. Jar tests showed that a pH of 6.0 and an alum dose of 300 mg/1
was necessary to attain turbidities less than 10 JTU and total phosphate less than 0.1 mg/1. A
pilot plant of sedimentation-rapid-sand filtration produced an effluent equivalent to that of a
parallel pilot facility incorporating a pressurized dissolved-air flotation and filtration sequence.
Autoflotation was not observed. At the Interagency Agricultural Waste Water Treatment Center
at Firebaugh, Calif., laboratory tests have shown that the flocculation-sedimentation process could
remove 90 percent of the algae. Sludge, however, could be concentrated in the sedimentation tanks
to only 1 percent.7
Golueke and Oswald6 found in field-scale studies of algal removal by sedimentation that a pH
of 6.5 and an alum dose of 105-120 mg/1 were required. Algal removals of 94-100 percent were
obtained in a sedimentation tank with 2-3 hours residence time. Underflow solids concentration
averaged 1.5 percent.
Incentive for Pilot Study. Both flotation and se.dime,ntation have been established as workable,
dependable processes for the first-stage removal of algae by both pilot-scale and field-scale tests.
Both processes have been tested successfully over the long term. A review of past work indicates
that flotation may be economically superior to sedimentation because higher overflow rates and
lower residence times can be used, equivalent removals can be obtained for approximately the same
chemical dose, and greater sludge concentration is attained.
Given the projected advantages of flotation in the first stage, it was deemed desirable to
operate a pilot-scale process to determine if flotation was applicable to Stockton's waste, and to
develop design concepts and criteria for a full-scale unit. Of special interest was the comparison
of pressurized dissolved-air flotation to the Windhoek mode of oxygen release under supersaturated
conditions (autoflotation).
Pilot Plant. A circular pilot flotation unit was rented for the study and located next to the
final pond at the main plant. The pilot plant was modified to allow transfer from recycle-stream
pressurization for dissolved-air-flotation operation to autoflotation by simple valve changes.
Normal values for the various operating criteria are indicated in table III-8, which shows that
the pilot unit was operated at fairly high overflow rates (2-2.7 gpm/ft2) and fairly low residence
times (17-22 minutes). These rates can be compared to values for the alternative sedimentation-
tank design of 0.9 gpm/ft2 for overflow rate and a detention time of 165 minutes.
Test Period. Flotation was studied from July 9 through September 24, 1971. Fond condi-
tions during the test period were affected by canning operations and are illustrated in figures
III-8 and III-9. It was observed that suspended solids in the pond effluent increased when wind
stirred up the pond. Alkalinity, after fluctuating in July, rose steadily in August and September.
The pH varied both daily and hourly.
35
-------
Tabic 111-8.— Operating criteria for pilot study
1 ten
Autoflotation
without
pressurized recycle
Dissolved-air
flotation with
pressurized recycle
Influent flow rate, gpm
29
29
Recycle, percent
0
33
Recycle flow rate, gpm
0
10
Area for clarification, square feet
14.5
14.5
Area for thickening, square feet
9.5
9.5
Volume, gallons
650
650
Recycle oressurization, psig
(')
35-60
Air rate, scfm
(1)
0.36
Surface loading rate, gpWft2
2.0
22.7
Hydraulic resistance time, minutes
22
..
217
1 Not applicjbUr
ncluriing recycle
* too
jo
20
>* 20
SEPTEMBER
JUL y
Figure If 1-8. Suspended saNds in pond effluent.
36
-------
400
" I
oce
30C
C3
~ QQ
:00
29
IC
SEPTEMBER
2? i"6 3C
AUGUST
Figure 1119. Pond alkalinity and pH.
Pond solids during initial operations were lower than desired for meaningful test work, so the
first nine runs before July 22 were used for equipment checkout and modification and establish-
ment of procedure. Between July 22 and August 25, the autoflotation mode was evaluated
exclusively; from August 26 to Septemher 25, operation was in the dissolved-air flotation mode.
Autoflotation. The principal concern in the study of autoflotation was to establish whether
it could accomplish algal removal dependably in the face of fluctuating pond conditions at
Stockton.
Successful autoflotation is related to DO concentrations in excess of DO saturation levels
(the saturation level is approximately 9 mg/1 and depends on liquid temperature). It was found
on two occasions that the autoflotation process would not function at all when the DO concentra-
tion fell below 8 mg/1. Once the DO concentration was above 13-15 mg/1, the autoflotation proc-
ess functioned. Since DO levels drop below saturation levels in the night and early morning, auto-
flotation was inoperative for portions of each day.
The jar test work indicated that pH adjustment is essential for optimum autoflotation
performance, for reasons that are apparently twofold. First, alum flocculation is optimum in the
pH 6-7 range; second, a drop in pTT increases the level of carbon dioxide (C02) in solution. An
increase of the COz level in solution will increase the partial pressure of C02 and, therefore,
increase the probability of bubble formation due to combination of DO and C02 to form a bubble.
Adjusting the pH with C02 in autoflotation proved to be more effective than pH adjustment
with acid. Suspended-solids removals with C02 for pH adjustment averaged 79 percent; with acid,
the suspended-solids removal averaged 44 percent (runs 12-19). Alum dose ranged from 75 to
200 mg/'l; acid, when used, ranged from 1.5 to 2.3 milliequivalents per liter (meq/1).
37
-------
In summary, autoflotation exhibited a potential for algal-solids removal, but performance was
erratic. Autoflotation depends on the algal system to produce sufficient supcrsaturation of DO
to allow the release, under proper conditions, of fine bubbles; however, this process is not continuous
and, therefore, autoflotation could not be relied upon as the only means of algal-solids removal. The
field evaluation of autoflotation will allow the positive aspects of the phenomenon to be utilized in
the plant design and the negative aspects to be avoided. For instance, autoflotation can be used to
assist dissolved-air flotation. If, however, flocculation-sedimentation is chosen to be the first-stage
separation process, special efforts would have to be undertaken to avoid the formation of fine
bubbles before sedimentation, and thus avoid flotation in the sedimentation unit.
Dissolved-Air Flotation. After the period of somewhat erratic algal-separation performance
with autoflotation, attention was turned to the evaluation of dissolved-air flotation. This method
involves the mechanical saturation of dissolved air in a portion of the liquid stream (influent or
effluent recycle). The release of the dissolved gases to form fine bubbles in the influent stream
while adding alum or other coagulants allows the separation of suspended materials to take place
by flotation.
Five runs involved the use of alum alone without pi I control or coagulant aids. The alum doses
ranged from 75 to 225 mg/1 and suspended-solids removal averaged 72 percent. The highest, alum
doses generally were associated with high suspended-solids concentrations in the pond. Solids levels
ranged from 53 to 142 mg/1.
Four runs involved pH control with acid and higher alum doses to demonstrate the ability of
flotation to achieve higher removals than were attained when no pH control was used. Suspended-
solids removal averaged 87 percent for an alum dose of 200 to 250 mg/1 and acid addition of 2 to
2.7 meq/1. The acid level was adjusted to yield the optimum pll of 6.4-6.5. Suspended solids in
the influent during this period ranged from 94 to 152 mg/1.
In summary, once initial operating difficulties were resolved, dissolved-air flotation proved to
be an effective process for the first-stage separation of algae. The separation efficiency is closely
related to chemical doso. Because the purpose of the first-stage separation process is the preparation
of an effluent that is suitable for filtration, the first-stage process must be flexible enough to
respond to changes in influent qualify while maintaining consistent effluent quality. A significant
variation in suspended solids can be expected through the canning season (fig. III-8). When
suspended material in the pond effluent is low, alum alone in a dose range of 75 to 150 mg/1 will
yield sufficient suspended-solids removal (on the order of 60-70 percent) before filtration. In
portions of August and September, when increased canning loads cause an increase in pond-effluent
solids, the alum dose will have to be increased to the 150-250-mg/l range, with acid pi I control in
a dose range of 1.5-2.7 meq/1. Flotation removals will thus be increased to 85-92 percent and an
effluent suitable for filtration will result.
Long-Term BOD-Removal Efficiency, Samples of flotation influent (pond effluent) and
flotation effluent during September were subjected to long-term oxygen-demand analyses. Both
total and soluble BOD were determined for the influent and effluent samples (see fig. 111-10).
During the peak of the canning season, most of the BOD is associated with the suspended matter.
Removal of the suspended material by coagulation and flotation caused the total effluent BOD to
be low and nearly equal to the soluble BOD. The difference between filtered influent and effluent
BOD may have been due to the coagulation of colloidal materials.
Float Recovery. Flotation, in addition to the primary- objective of removing the suspended
algal material from the liquid stream, demonstrated a capability of concentrating the separated
materials as float to a much greater extent than can be done in sludge concentration by the
sedimentation process alone. There are two reasons for this capability.
38
-------
sc
70|-
zo-
'5
20
30
0
5
10
DirS
Figure 111-10. Oxygen demand of flotation-unit influent and eff'uent.
First, float removal from the flotation unit takes place on the liquid surface where the operator
has good \isual control over the thickening process. Thus, the operator can see the immediate
effects of changes in operating variables, such as the speed of the float skimmer, float-skimmer
submergence, and float-blanket depth. Second, thickening of the float takes place by drainage of
the liquid from the float. This mechanism has a greater driving force promoting thickening than
the mechanism of thickening in sedimentation that involves setting and compaction of the loose
algae-alum floe.
During the experimental work, it was found that variation in thickening operation did yield
improvements in float concentration. For instance, initial float concentration was improved from
0.13 percent to values averaging 2.45 percent by decreasing the float skimming frequency from
2-3 minutes to 15-30 minutes. A further improvement in float concentration was attained by
altering the float-skimmer submergence so that the skimmer was positioned slightly above the
water-surface level to minimize inclusion of water in the float. This alteration increased float
concentration to an average concentration of 3.6 percent, despite the fact that skimming frequency
was simultaneously reduced to 7-8 minutes.
It was found that an anionic polymer, Dow A-23, could significantly increase float concentra-
tion even further (runs 27-29). As little as 0.25 mg/1 of A-23, employed as a coagulant aid, increased
float concentration to 5.3 percent. No improvement in effluent clarity was obtained over the use
of alum alone. A cationic polymer, Dow C-31, was also tried, but did not improve either float
concentration or effluent clarity when used in conjunction with alum.
39
-------
In summary, flotation has demonstrated an in-process ability to achieve significant thickening
of the algae-alum sludge produced. Such initial thickening has a beneficial impact on the economics
of further solids processing, since processing will not require an extra initial thickening step.
Solids Processing. Solids samples were collected and subjected to alternative treatment
processing by various processes on a batch scale.
Heat treatment by the Portcous process at temperatures ranging from 380° to 415° F improved
the slurry dewaterability on a vacuum filter, but the process was disappointing in terms of both
filter yield and cake concentration. Filter yield was uniformly low in the range of 0.9-2.5 lb/ft2,/hr.
The highest cake concentration achieved was 21.6 percent total solids with a low value of 8.3
percc-nt, which is not a great improvement over the feed concentration of 4 percent. At these cake
concentrations, incineration of the cake would be expensive in terms of fuel costs.
Zimpro low oxidation, at temperatures ranging from 180° to 220" C, yielded vacuum filter
cake concentrations ranging from 15 to 19 percent total solids at filter yield ranging from 0.67
to 3.05 lb/ft2/hr. Incineration of the filter cake under these conditions would still be costly.
Zimpro wet-air oxidation was also investigated as a process which would lead directly to
ultimate disposal of the sludge. In evaluating this process, cake concentration and filter yield were
marginal, indicating that ultimate disposal should incorporate lagoons. In this process, the reduction
of volatile solids is the important step in producing a stable end product. The high-oxidation process
removes about 97 percent of the volatile suspended solids from the sludge. Although some of the
volatiles are solubilized in the liquid, the final solids are stable and would be suitable for lagoon
storage.
Two other processes investigated were chemical oxidation schemes that employ chlorine as the
oxidant. Both processes, Pepcon and Purifax. were capable of achieving stabilization of the sludge
and yielded a product that could be dewatered on sand drying beds or in a lagoon.
Conclusions. Field tests have proved that dissolved-air flotation is a viable alternative to
sedimentation for algal removal at Stockton. Further, capital costs will be less, owing to the much
smaller tanks required for flotation than for sedimentation. If sedimentation facilities were to be
designed for canning-season use, special attention would have to be given to providing facilities to
prevent autoflotation.
The facilities at Stockton will be designed as dual-purpose units so that the tanks can be used
for sedimentation during the low-flow, noncanning period. The system employing flotation and
filtration is currently under design. Four 80-foot-diameter, circular flotation units are planned.
By 1974, Stockton will be operating a 55-mgd algal-removal facility, the largest of its type in the
world.
Design Criteria for Tertiary Facilities at Stockton
The existing Stockton plant consists of the following sequence of processes: preliminary
treatment, primary sedimentation, trickling filters, secondary sedimentation, tertiary ponds, and
effluent chlorination. Solids treatment is by digestion and sludge lagoons.
Improvements will be made to all treatment stages. Data summarized here are concerned
only with upgrading of the tertiary ponds by algae removal.
Design data for the existing ponds, the algal removal facility, and chlorine contact channel
are shown in table III-9, while the process-flow diagram is shown in figure III-ll.
40
-------
Tal)!e 11 \-9.-Design data for Stockton tertiary facilities
Component
Quantity
Tertiary ponds, existing:
Number
Area, net water surface, acres
Volume, mg (million gallons)
Loading during noncanning season:
BOD total, 1,000 lb/day
BOD, pounds per surface acre per day
Loading during canning season:
BOD Total, 1,000 lb/day
BOD pounds per surface acre per day
Detention during noncanning season, days
Detention during canning season, days
Circulation pumping units:
Number
Capacity, each, myd
Circulation ratio, at peak
Flotation tanks, new:
Peak weekly flow rate, mgd
Number
Diameter, feet
Sidewater depth, feet
Surface-loading rate, gal/ft2/day (includes pressurized flow)
Solids loading rate, lb/ft2/day
Pressurized flow, percentage of total
Pressurized, ps!g
Alum dosage, mg/l, peak rate
Polymer dosage, mg/l, peak rate
Acid dosage, peak, ml/I
Assumed float concentration, percent
Assumed float weight, lb/ft3
Float collection arms, number each tank
Float collection troughs, number each tank
Peak float discharge rate, gpm
Filters, new:
Number
Area per filter (bifurcated), square feet
Design-filtration rates, gpm/ft2:
All filters in service
One filter backwashing
Anthracite coal:
Depth, feet
Effective size, mm
4(4)
630
1,320
3.2
5
57
90
57
23
3
65
3.4
55
4
85
7
2.7
6.8
26
40
250
1
3
3
41
4
2
600
4
1,700
5.6
7.4
4
2.4-4.8
41
-------
Table 111-9,—Design data for Stockton tertiary facilities-Concluded
Component
Filters, new—Continued
Sand:
Depth, feet
Effective si7e, mm
Pea gravel depth, feet
Backwash:
Air:
Rate, cfm/ft2
Pressure, psig
Water:
Wash rate, gpm/ft2:
Minimum
Maximum
Chlorine contact canal, new:
Length, feet
Depth, feet
Average width, feet
Residence time, peak flow, minutes ....
Chlorine disinfection dosage rate, mg/l . .
Chlorine for NH- removal, lb C^'lb CMH3)
Sulfur dioxide dosage, peak, rng/l
Reoxygenation, mg/l
i>-
BAPID SAND FILTERS
FLOTATION TANKS
Chlorine
contact
CHANNEL
TO SOLiDS
DISPOSAL
TO PONDS
SYSTEM
TO POND
STSTEM
Figjre 111-11. Tertiary alyal-rerroval facility.
42
-------
The chlorine-contact channel is a multipurpose unit serving for chlorine contact, backwash-
water storage, ammonia removal by superchlorination, dechlorination with sulfur dioxide, and
postaeration.
The original cost estimate for the tertiary facilities (excluding the ponds) was $3,600,000
(December 1972 prices), but was for a facility using sedimentation rather than flotation. The
revised design required smaller tanks: four 85-foot-diameter flotation tanks with 7-foot sidewater
depth instead of four 130-foot-diameter sedimentation tanks with 20-foot sidewater depth. A
revised cost estimate had not been completed as of November 1, 1972.
Annual operating costs of the tertiary facility (excluding ponds) are estimated at $40 to $45
per million gallons, based on year-round operation of the tertiary facilities (1972 costs prorated
to design-year flows).
REFERENCES
1 Brown and Caldwell, "Benefits of Proposed Tertiary Treatment to San Joaquin River Water
Quality," report prepared for the city of Stockton, Nov. 1970.
2L. R. J. Van Vuuren and F. A. Van Duuren, "Removal of Algae from Waste Water Maturation
Pond Effluent," -J. Water Pollut. Cont. Fed., 37, 9, 1256-1262, 1965.
3G. J. Stander and L. R. J. Van Vuuren, "The Reclamation of Potable Water from Wastewater,"
J, Water Pollut. Cont. Fed., 41, 3, 355-367, 1969.
4 G. G. Cillie, L. R. J. Van Vuuren, G. J. Stander, and F. F. Kolbe, "The Reclamation of
Sewage Effluent for Domestic Use," 3d Annual Conference IAWPR, Munich, Germany, 1966.
^L. R. J. Van Vuuren, P. G. J. Meiring, M. R. llenzen, and F. F. Kolbe, "The Flotation of
Algae in Water Reclamation," Int. 3, Air Water Pollution, vol. 9, pp. 823-832, 1965.
6Frank D. Dryden and Gerald Stern, "Renovated Waste Water Creates Recreational Lake,"
Environ. Sci. Technol, 2, 4, 268-278, Apr. 1968.
"Louis A. Beck, "Nitrogen Removal from Agricultural Wastewater," Advanced Waste Treatment
Seminar, San Francisco, Calif., Oct. 1970.
8C. G. Golueke and W. J. Oswald, "Harvesting and Processing Sewage Grown Planktonic Algae,"
J. Water Pollut. Cont. Fed., 37, 4, 471-498, Apr. 1965.
43
------- |