&EPA
United States
Environmental Protection
Agency
Office of Research and Development
Municipal Environmental Research
Laboratory
Center for Environmental Research
Information
Cincinnati OH 45268
Office of Water
Office of Water Program
Operations
Washington DC 20460
Technology Transfer
Design
Manual
Municipal
Wastewater
Stabilization
Ponds
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EPA-625/1-83-015
DESIGN MANUAL
MUNICIPAL WASTEWATER STABILIZATION PONDS
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Municipal Environmental Research Laboratory
Center for Environmental Research Information
Office of Water
Office of Water Program Operations
October 1983
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NOTICE >
This document has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved for
publication. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
ii
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FOREWORD
The formation of the Environmental Protection. Agency marked a new era of
environmental awareness in America. This Agency's goals are national in scope
and encompass broad responsibility in the areas of air and water pollution,
solid wastes, pesticides, hazardous wastes, and radiation. A vital part of
EPA's national pollution control effort is the constant development and
dissemination of new technology.
It is now clear that only the most effective design and operation of pollution
control facilities using the latest available techniques will be adequate to
ensure continued protection of this Nation's natural resources. It is
essential that this new technology be incorporated into the contemporary
design of pollution control facilities to achieve maximum benefit from our
expenditures.
The purpose of this manual is to provide the engineering community and related
industry a new source of information to be used in the planning, design, and
operation of present and future stabilization ponds treating municipal
wastewaters. It is the intent of the manual to supplement the existing body
of knowledge in this area.
This manual is one of several available from Technology Transfer to describe
technological advances and present new information.
iii
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ACKNOWLEDGMENTS
Many individuals contributed to the preparation and review of this manual.
Contract administration was provided by the U.S. Environmental Protection
Agency, Center for Environmental Research Information, Cincinnati, Ohio.
CONTRACTOR-AUTHORS
Major Author:
Contributing
Autho rs:
Dr. E. Joe Middlebrooks, Newman Chair of Natural
Resources Engineering, Clemson University
James H. Reynolds, James M. Montgomery Consulting
Engineers, Inc.
Charlotte Middlebrooks,, Middlebrooks & Associates,
Inc.
R. Wane Schneiter, Kennedy/Jenks Engineers
Richard J. Stenquist, Brown & Caldwell Consulting
Engineers
Bruce A. Johnson, Ch^M Hill Engineers
CONTRACT SUPERVISORS
Project Officer:
Reviewers:
Denis J. Lussier, EPA-CERI, Cincinnati, OH
Edwin F. Barth, Jr., EPA-MERL, Cincinnati, OH
Ronald F. Lewis, EPA-MERL, Cincinnati, OH
Sherwood c. Reed, COE-CRREL, Hanover, NH
Richard E. Thomas, EPA-OWPO, Washington, DC
TECHNICAL PEER REVIEWERS
Dr. Ernest F. Gloyna - University of Texas-Austin, Austin, TX
George W, Mann - City of Kissimimee, Kissimmee, FL
Dr. Walter J. O'Brien - Black & Veatch Engineers, Dallas, TX
Dr. A. T. Wallace - University of Idaho, Moscow, ID
Review comments were compiled and summarized by Mr. Torsten Rothman, Dynamac
Corp., Rockville, MD.
iv
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CONTENTS
Chapter Page
FOREWORD 111'
ACKNOWLEDGMENTS iv
CONTENTS v
LIST OF FIGURES vll
LIST OF TABLES xi
INTRODUCTION
1.1 Background and History 1
1.2 Manual Objective and Scope 1
1.3 Types of Ponds 2
1.4 Nutrient Removal Aspects 7
1.5 References 7
PROCESS THEORY, PERFORMANCE, AND DESIGN
2.1 Biology 8
2.2 Biochemical Interactions , 11
2.3 Controlling Factors 16
2.4 Performance and Design of Ponds 20
2.5 Disinfection 53
2.6 Odor Control -64
2.7 References 71
DESIGN PROCEDURES
3.1 Preliminary Treatment , 75
3.2 Facultative Ponds 75
3.3 Complete Mix Aerated Ponds • • 98
3.4 Partial Mix Aerated Ponds 114
3.5 Controlled Discharge Ponds 129
3.6 Complete Retention Ponds • 135
3.7 Combined Systems . 143
3.8 References 144
-PHYSICAL DESIGN AND CONSTRUCTION
4.1 Introduction 147
4.2 Dike Construction 147
4.3 Pond Sealing 150
4.4 Pond Hydraulics 182
4.5 Pond Recirculation and Configuration 185
4.6 References 190
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CONTENTS (continued)
Chapter
5 ALGAE, SUSPENDED SOLIDS, AND NUTRIENT REMOVAL
5.1 Introduction
5.2 In-Pond Removal Methods
5.3 Filtration Processes
5.4 Coagulation-Clarification Processes
5.5 Land Application
5.6 References
6 COST AND ENERGY REQUIREMENTS
6.1 Capital Costs
6.2 Cost Updating
6.3 Energy Requirements ,
6.4 References.
APPENDIX EVALUATION OF DESIGN METHODS
A.I Facultative Ponds
A.2 Aerated Ponds
A.3 References
Page
192
192
202
247
259
271
280
285
288
290
292
312
327
vi
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FIGURES
Number. Page
2-1 The Nitrogen Cycle _ 13
2-2 Calculated Relationship Among pH, C02, C03~, HCC^",
and OH~ 15
2-3 Changes Occurring in Forms of Nitrogen Present in
Pond Environment Under Aerobic Conditions 18
2-4 Schematic Flow Diagram and Aerial Photograph of the
Facultative Pond System at Peterborough,
New Hampshire 21
2-5 Schematic Flow Diagram and Aerial Photograph of the
Facultative Pond System at Kilmichael, Mississippi 23
2-6 Schematic Flow Diagram and Aerial Photograph of the
Facultative Pond System at Eudora, Kansas 25
2-7 Schematic Flow Diagram and Aerial Photograph of the
Facultative Pond System at Corinne, Utah 26
2-8 Facultative Pond BODr Effluent Concentrations 37
2-9 Facultative Pond SS Effluent Concentrations 29
2-10 Facultative Pond Fecal Coliform Effluent Concentrations 31
2-11 Schematic Flow Diagram and Aerial Photograph of the
Aerated Pond System at Bixby, Oklahoma 40
2-12 Schematic Flow Diagram and Aerial Photograph of the
Aerated Pond System at Pawnee, Illinois 41
2-13 Schematic Flow Diagram and Aerial Photograph of the
Aerated Pond System at Gulfport, Mississippi 42
2-14 Schematic Flow Diagram and Aerial Photograph of the
Aerated Pond System at Koshkonong, Wisconsin 44
2-15 Schematic Flow Diagram and Aerial Photograph of the
Aerated Pond System at Windber, Pennyslvania 45
2-16 Aerated Pond BODg Effluent Concentrations 46
2-17 Aerated Pond SS Effluent Concentrations 48
2-18 Aerated Pond Fecal Coliform Effluent Concentrations 49
2-19 Chlorine Dose vs. Residual for Initial Sulfide
Concentrations of 1.0-1.8 mg/1 55
2-20 Changes in Soluble COD vs. Free Chlorine Residual —
Unfiltered Pond Effluent 56
2-21 Chlorine Dose vs. Total Residual—Filtered and
Unfiltered Pond Effluent 57
2-22 Total Coliform Removal Efficiencies—Filtered and
Unfiltered Pond Effluent 58
2-23 Combined Chlorine Residual at 5°C for Coliform =
104/100 ml 60
2-24 Conversion of Combined Chlorine Residual at Temp. 1
to Equivalent Residual at 20°C 61
2-25 Conversion of Combined Chlorine Residual at TCOD 1 and
20°C to Equivalent Residual at TCOD = 60 mg/1 and 20°C 62
2-26 Determination of Chlorine Dose Required for Equivalent
Combined Residual at TCOD = 60 mg/1 and 20°C 63
vii
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FIGURES (continued)
Number Page-
2-27 Conversion of Combined Chlorine Residual at TCOD 1 and
5°C to Equivalent Residual at TCOD = 60 mg/1 and 5°C 65
2-28 Determination of Chlorine Dose Required When S = 1.0
mg/1, TCOD = 60 mg/1, and Temp. = 5°C . 66
2-29 Sulfide Reduction as a Function of Chlorine Dose 67
3-1 Wehner and Wilhelm Equation Chart 93
3-2 kct vs. C0/Cn for,Complete Mix Model 102
3-3 Layout of One Cell of Complete Mix Aerated Pond
System 113
3-4 Layout of Surface Aerators in First Cell of Partial
Mix System 127
3-5 Layout of Aeration System for Partial Mix Diffused
Air Aerated Pond Systemn 128
3-6 Portion of Advected Energy (Into a Class A Pan)
Utilized for Evaporation 138
3-7 Shallow Lake Evaporation as a Function of Class A Pan
Evaporation and Heat Transfer Through the Pan 139
4-1 Eroded Dike Slopes on a Raw Wastewater Pond in a
Dry Climate 149
4-2 Top Anchor Detail--Alternative 1, ATI Linings 167
4-3 Top Anchor Detail—Alternative 2, All Linings 168
4-4 Top Anchor Detail—Alternative 3, All Linings 169
4-5 Top Anchor Detail—Alternative 4, All Linings Except
Asphal t Panel s 170
4-6 Top Anchor Detail--Alternative 5, All Linings 171
4-7 Seal at Pipes Through Slope—All Linings 172
4-8 Seal at Floor Columns--Asphalt Panels 173
4-9 Pipe Boot Detail--All Linings Except Asphalt Panels 174
4-10 Seal at Inlet-Outlet Structure--All Linings 175
4-11 Mud Drain Detail—All Linings 176
4-12 Crack Treatment—Alternatives A and B "177
4-13 Wind and Gas Control 178
4-14 Cost Comparison for Linings in the United States 179
4-15 Special Fiberglass Plug ?. 184
4-16 Common Pond Configurations and Recirculation Systems 187
4-17 Cross Section of A Typical Recirculation Pumping
Station • E 189
5-1 Length of Filter Run as a Function of Daily Mass
Loading for 0.17 mm Effective Size Sand .... 206
5-2 Length of Filter Run as a Function of 'Daily Mass '':"
Loading for 0.4 mm Effective Size Sand V 207
5-3 Length of Filter Run as a Function of Daily Mass t
Loading for 0.68 mm Effective Size Sand 208
vi i i
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FIGURES (continued)
Number Page
5-4 Length of Filter Run as a Function of Daily Mass
Loading for Pond Effluents Having Calcium
Carbonate Precipitation Problems 209
5-5 Sand Grain Size vs; Sand Size Distribution 213
5-6 Sand Grain Size vs. Sand Size Distribution for
AASHO M6 Specifications 216
5-7 Cross Section of a Typical Intermittent Sand Filter 217
5-8 Common Arrangements for Underdrain Systems 219
5-9 Typical Upflow Sand Washer and Sand Separator
Utilized in Washing Slow and Intermittent Sand
Filter Sand , 223
5-10 Plan View, Cross-Sectional View, and Hydraulic
Profile for Intermittent Sand Filter 229
5-11 Biochemical Oxygen Demand (BOD5) Performance of
Large Rock Filter at Eudora, Kansas 232
5-12 Suspended Solids Performance of Large Rock Filter
at Eudora, Kansas 232
5-13 Rock Filter Installation at California, Missouri 233
5-14 Schematic Flow Diagram of Veneta, Oregon
Wastewater Treatment System 234
5-15 Performance of California, Missouri Rock Filter
Treating Pond Effluent 236
5-16 Veneta, Oregon Rock Filter 237
5-17 Performance of Veneta, Oregon Rock Filter , , 238
5-18 SS Removal vs. Hydraulic Loading Rate at
Veneta, Oregon 239
5-19 Dual-Media Filter Effluent Turbidity Profile 245
5-20 Dual-Media Filter Headless Profile 245
5-21 Effect of Alum Dose and pH on Flotation
Performance , 254
5-22 Effect of Alum Dose and Influent SS on Flotation
Performance 254
5-23 Conceptual Design of Dissolved Air Flotation
Tank Applied to Algae Removal 256
6-1 Actual Construction Cost vs. Design Flow for
Discharging Stabilization Ponds 281
6-2 Actual Construction Cost vs. Design Flow for
Nondischarging Stabilization Ponds 282
6-3 Actual Construction Cost Vs. Design Flow for
Aerated Ponds 283
A-l McGarry and Pescod Equation for Area! BOD5 Removal
as a Function of BODc Loading 295
A-2 Relationship Between 6005 Loading and Removal
Rates--Facultative Ponds 296
ix
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FIGURES (continued)
Number ! Page
A-3 Relationship Between COD Loading and Removal Rates-
Facultative Ponds ' 297
A-4 Relationship Obtained with Modified Gloyna Equation-
Facultative Ponds 300
A-5 Arrhenius Plot to Determine Activation Energy 302
A-6 Plot of Reaction Rate Constants and Temperature to
Determine the Temperature Factor 304
A-7 Relationship Between Plug Flow Decay Rate and
Temperature--Facultative Ponds 305
A-8 Relationship Between Complete Mix Decay Rate and
Temperature—Facultative Ponds 306
A-9 Plug Flow Model--Facultative Ponds , 307
A-10 Plug Flow Model--Facultative Ponds 308
A-ll Complete Mix Model--Facultative Ponds 309
A-12 Complete Mix Model--Facultative Ponds 310
A-13 Wehner and Wil helm Equation Chart 311
A-14 Relationship Between Wehner and Wilhelm Decay Rate
and Temperature--Facultative Ponds 314
A-15 Relationship Between Plug Flow Decay Rate and
Temperature—Aerated Ponds 317
A-16 Relationship Between Complete Mix Decay Rate and
Temperature—Aerated Ponds 318
A-17 Relationship Between Wehner and Wilhelm Decay Rate
and Temperature—Aerated Ponds 319
A-18 Plug Flow Model--Aerated Ponds 320
A-19 Complete Mix Model--Aerated Ponds 321
A-20 Schematic View of Various Types of Aerators 324
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TABLES
Number Page
1-1 Wastewater Stabilization Ponds 3
2-1 Design and Actual Loading Rates and Detention Times
for Selected Facultative Ponds 22
2-2 Summary of Design and Performance Data—Selected
Facultative Ponds 34
2-3 Influent Wastewater Characteristics at Selected
Facultative Ponds 37
2-4 Annual Average Ammonia-N Removal by Selected
Facultative Ponds 37
2-5 Influent Wastewater Characteristics at Selected
Aerated Ponds 39
2-6 Design and Actual Loading Rates and Detention Times
for Selected Aerated Ponds 39
2-7 Comparison of Various Equations Developed to Predict
Ammonia Nitrogen and TKN Removal in Diffused-Air
Aerated Ponds 52
2-8 Summary of Chlorination Design Criteria 68
3-1 Facultative Pond Design Equations 77
3-2 Assumed Characteristics of Wastewater and
Environmental Conditions for Facultative Pond Design 79
3-3 Variations in Design Produced by Varying the
Dispersion Factor 95
3-4 Summary of Results from Design Methods 96
3-5 Motor PowerN Requirements for Surface and Diffused
Air Aerators 126
3-6 Climatological Data for Calculating Pond Evaporation
! and Precipitation 137
3-7 Calculated Pond Evaporation Data 140
3-8 Volume and Stage of Pond at Monthly Intervals for
Design Conditions and A = 142,300 m2 141
3-9 Volume and Stage of Pond at Monthly Intervals for
Average Conditions and A = 142,300 m2 143
4-1 Reported Seepage Rates from Pond Systems 151
4-2 Seepage Rates for Various Liners 153
4-3 Trade Names of Common Lining Materials 156
4-4 Sources of Common Lining Materials 159
4-5 Summary of Effective Design Practices for Placing
Lining in Cut-and-Fill Reservoirs 161
4-6 Classification of the Principal Failure Mechanisms
for Cut-and-Fill Reservoirs 181
5-1 Labor Requirements for Full-Scale Batch Treatment of
Intermittent Discharge Ponds 195
5-2 Intermittent Sand Filtration Studies 203
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TABLES (continued)
Number Page
5-3 Sieve Analysis of'Filter Sand 211
5-4 Gradation Requirements for Fine Aggregate in the
AASHO M6 Specification - 215
5-5 Summary of Intermittent Sand Filter Design Criteria 226
5-6 Summary of Design Criteria and Costs for Existing and
Planned Intermittent Sand Filters Used To Upgrade
Pond Effluent 231
5-7 Performance of Rock Filter at California,
Missouri 235
5-8 Summary of Performance of 1-micron Microstrainer
Pilot Plant Tests . 241
5-9 Performance Summary of Direct Filtration with Rapid
Sand Filters 243
5-10 Performance of the Napa-American Canyon Wastewater
Management Authority Dual-Media Filters 246
5-11 Summary of Coagulation-Flocculation-Settling
Performance 248
5-12 Performance of the Napa-American Canyon Wastewater
Management Authority Algae Removal Plant 249
5-13 Summary of Typical Coagulation-Fl otettion Performance 251
5-14 Comparison of Site Characteristics for Land
Treatment Processes 260
5-15 Comparison of Typical Design Features for Land
Treatment Processes 261
5-16 Summary of BOD and SS Removals at Overland Flow
Systems Treating Pond Effluents 263
5-17 Summary of Nitrogen and Phosphorus Removals at
Overland Flow Systems Treating Pond Effluents 264
5-18 Removal of Heavy Metals at Different, Hydraulic
Rates at Utica, Mississippi 265
5-19 BOD Removal Data for Selected Slow-Rate Systems
Treating Pond Effluents 266
5-20 Nitrogen Removal Data for Selected Slow-Rate Systems
- Treating Pond Effluents 266
5-21 Phosphorus Removal Data for Selected Slow-Rate
Systems Treating Pond Effluents 267
5-22 Trace Element Behavior During Slow-Rate Treatment of
Pond Effluents 268
5-23 Nitrogen Removal Data for Selected Rapid Infiltration
Systems Treating Pond Effluents 270
5-24 Fecal Coliform. Removals at Selected Rapid Infiltration
Systems Treating Pond Effluents 270
6-1 Average Nonconstruction Cost Ratios for New
Wastewater Treatment Plants 284
6-2 Comparative Costs and Performance of Various Upgrading
Alternatives and Pond Systems 286
xi i.
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TABLES (continued)
Number Page
6-3 Expected Effluent Quality and Total Energy
Requirements for Various Sizes and Types of
Wastewater Treatment Ponds Located in the
Intermountain Area of the United States 289
A-l Mean Monthly Performance Data for Four
Facultative Ponds 293
A-2 Mean Monthly Performance Data for Five
Partial Mix Aerated Ponds 313
A-3 Types of Aeration Equipment for Aerated Ponds 323
A-4 Calculation of Oxygen Demand and Surface Aerator
Size for Aerated Ponds 325
xiii
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CHAPTER 1
INTRODUCTION
1.1 Background and History
Stabilization ponds have been employed for treatment of wastewater for over
3000 years. The first recorded construction of a pond system in the United
States was at San Antonio, TX, in 1901. Today, almost 7000 stabilization
ponds are utilized in the United States for treatment of wastewaters (1).
They are used to treat a variety of wastewaters from domestic wastewater to
complex industrial wastes, and they function under a wide range of weather
conditions, from tropical to arctic. Ponds can be used alone or in
combination with other wastewater treatment processes. As understanding of
pond operating mechanisms has increased, different types of ponds have been
developed for application to specific situations.
1.2 Manual Objective and Scope
This manual provides a concise overview of wastewater stabilization pond
systems through discussion of factors affecting treatment, process design
principles and applications, aspects of physical design and construction,
suspended solids (SS) removal alternatives, and cost and energy requirements.
Chapter 2 provides a review of physical and biological factors associated with
wastewater stabilization ponds. Empirical and rational design equations, and
their ability to predict pond performance, are also discussed.
Actual design examples employing the rational equations presented in Chapter 2
are outlined in Chapter 3. These examples encompass essentially all types of
wastewater ponds currently in use in the United States.
Physical design and construction criteria are discussed in Chapter 4. These
criteria are vital to effective pond performance regardless of the design
equation employed and must be considered in facility design.
High SS concentrations in pond effluents have traditionally represented a
major drawback to their use. Alternatives for SS removal and control are
presented in Chapter 5.
Chapter 6 contains cost and energy requirements information to aid in process
selection and justification.
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An evaluation of various facultative and aerated pond design methods is
presented in an Appendix. This evaluation was; performed using data collected
on the four facultative and five aerated pond systems presented in Chapter 2.
1.3 Types of Ponds
Wastewater pond systems can be classified by dominant type of biological
reaction, duration and frequency of discharge, extent of treatment ahead bf
the pond, or arrangement among cells (if more than one cell is used). The
method used in this manual is based on that provided by Oswald (2) and is
believed to be the most flexible approach to pond classification.
Ponds are classified below on the basis of dominant biological reaction, types
of influent, and outflow conditions. Classification according to flow pattern
(e.g., series, parallel) and the amount and type of recirculation is discussed
in Chapter 4.
Table 1-1 summarizes information on pond application, loading, and size for
each of the pond types discussed in this section.
1.3.1 Biological Reactions
The most basic classification involves description of the dominant biological
reaction or reactions that occur in the pond. Four principal types are:
1. Facultative (aerobic-anaerobic) ponds \
2. Aerated ponds
3. Aerobic ponds :,
4. Anaerobic ponds
1.3.1.1 Facultative Ponds
The most common type of pond is the facultative pond. Other terms which are
commonly applied are oxidation pond, sewage (or wastewater treatment) lagoon*
and photosynthetic pond. Facultative ponds are usually 1.2 to 2.5 m (4 to 8
ft) in depth, with an aerobic layer overlying an anaerobic layer, often
containing sludge deposits. Usual detention time is 5 to 30 days. Anaerobic
fermentation occurs in the lower layer and aerobic stabilization occurs in the
upper layer. The key to facultative operation is oxygen production by
photosynthetic algae and surface reaeration. The oxygen is utilized by the
aerobic bacteria in stabilizing the organic material in the upper layer.
Algae present in pond effluent represent one of the most serious performance
problems associated with facultative ponds.
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TABLE 1-1
WASTEWATER STABILIZATION PONDS
CO
Pond Type Application
Facultative Raw municipal wastewater
Effluent from primary
treatment, trickling
filters, aerated ponds,
or anaerobic ponds
Aerated Industrial wastes
Overloaded facultative
ponds
Situations where limited
land area is available
Aerobic Generally used to treat
effluent from other
processes, produces
effluent low in
soluble BODc and high
in algae solids
Anaerobic Industrial wastes
Typical Loading
Parameters
22-67 kg BOD5/ha/d
8-320 kg BOD5/1000 m3/d
85-170 kg BOD5/ha/d
160-800 kg BOD5/1000 m3/d
Typical
Detention
Times
25-180 d
7-20 d
10-40 d
20-50 d
Typical
Dimensions
1.2-2.5 m deep
4-60 ha
2-6 m deep
30-45 cm
2.5-5 m deep
Comments -
Most commonly used waste
stabilization pond type
May be aerobic through entire
depth if lightly loaded
Use may range from a supplement
of photosynthesis to an
extended aeration activated
sludge process
Requires less land area than
facultative
Application limited because of
effluent quality
Maximizes algae production and
(if algae is harvested)
nutrient removal
High loadings reduce land
requirements
Odor production usually a problem
Subsequent treatment normally
required
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Facultative ponds find the most widespread application. They are used for
treatment of raw municipal wastewater (usually small communities) and for
treatment of primary or secondary effluent (for small or large cities). They
are also used, in industrial applications,, following aerated ponds or
anaerobic ponds to provide additional stabilination prior to discharge. The
facultative pond is the easiest to operate and maintain, but there are
definite limits to its performance. Effluent BODs values range from 20 to
60 mg/1, and SS levels will usually range from 30 to 150 mg/1. It also
requires a very large land area to maintain area! 8005 loadings in a
suitable range. An advantage, where seasonal food processing wastes are
received during summer, is that allowable organic loadings are generally much
higher in summer than in winter.
The total containment pond and the controlled discharge pond are forms of
facultative ponds. The total containment pond is applicable in climates where
the evaporative losses exceed the rainfall. Controlled discharge ponds have
long hydraulic detention times and the effluent is discharged once or twice
per year when the effluent quality is satisfactory.
1.3.1.2 Aerated Ponds
In an aerated pond, oxygen is supplied mainly through mechanical or diffused
air aeration rather than by photosynthesis and surface reaeration. Many
aerated ponds have evolved from overloaded facultative ponds that required
aerator installation to increase oxygenationi capacity. Aerated ponds are
generally 2 to 6 m (6 to 20 ft) in depth with detention times of 3 to 10 days.
The chief advantage of aerated ponds is that they require less land area.
In some cases, both photosynthesis and mechanical aeration can be effective in
providing oxygen. At Sunnyvale, CA, for example, mechanical cage-type
aerators were installed at the effluent points to eliminate local anaerobic
conditions during seasonal increased loads from a canning plant.
Photosynthesis and surface reaeration provide the necessary oxygen in the
remaining areas of the pond (3).
I
Aerated ponds can also be classified by the amount of mixing provided. If
energy input is sufficient to keep all solids in suspension, and if secondary
clarification with sludge return is utilized, the system approaches an
activated 'sludge process with the associated high BOD5 and SS removal.
Power costs for this system become very high, however, and operation and
maintenance complexity increases.
Aerated ponds are used in both municipal and industrial wastewater treatment
applications. For the former situation, they are often resorted to when an
existing facultative system becomes overloaded and there is minimal land
available for expansion. For industrial wastes, they are sometimes used as a
pretreatment step before discharge to a municipal sewerage system. In both
municipal and industrial applications, aerated ponds may be followed by
facultative ponds. I
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1.3.1.3 Aerobic Ponds
Aerobic ponds, also called high rate aerobic ponds, maintain dissolved oxygen
(DO) throughout their entire depth. They are usually 30 to 45 cm (12 to 18
in) deep, allowing light to penetrate the full depth. Mixing is often
provided to expose all algae to sunlight and to prevent deposition and
subsequent anaerobic conditions. Oxygen is provided by photosynthesis and
surface reaeration, and aerobic bacteria stabilize the waste. Detention time
is short, three to five days being usual.
High-rate aerobic ponds are limited to warm, sunny climates. They are used
where a high degree of 6005 removal is desired but land area is limited.
The chief advantage of the high-rate aerobic pond is that it produces a stable
effluent with low land and energy requirements and short detention times.
However, operation is somewhat more complex than for a facultative pond and,
unless an algae removal step is provided, the effluent will contain high SS.
Short detention times also mean that very little coliform die-off will result.
Because of their shallow depths, paving or covering the bottom is required to
prevent weed growth.
1.3.1.4, Anaerobic Ponds
Anaerobic ponds receive such a heavy organic loading that there is no aerobic
zone. They are usually 2.5 to 5 m (8 to 15 ft) in depth and have detention
times of 20 to 50 days. The principal biological reactions occurring are acid
formation and methane fermentation. The smaller of the two Sunnyvale, CA,
cells was originally an anaerobic cell providing treatment of seasonal cannery
wastes. Effluent from the anaerobic cell enters the larger and shallower
facultative cell.
Anaerobic ponds are usually used for treatment of strong industrial and
agricultural wastes, or as a pretreatment step where an industry is a
significant contributor to a municipal system. Because they do not have wide
application to the treatment of municipal wastewaters, they are not discussed
further in this manual.
An important disadvantage to anaerobic ponds is the production of odorous
compounds. Sodium nitrate has been used to combat odors, but it is quite
expensive and in some cases has not proven effective. Another common approach
is to recirculate water from a downstream facultative or aerobic pond to
maintain a thin aerobic layer at the surface of the anaerobic pond, preventing
transfer of odors to the air. Crusts have also proven effective, either
naturally formed as with grease, or formed from styrofoam balls. A further
disadvantage of the anerobic pond is that the effluent must usually be given
further treatment prior to discharge.
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1.3.2 Pretreatment
Ponds can also be characterized by the degree of pretreatment which the
wastewater receives before discharge into a pond system:
1. None. Ponds receiving raw untreated wastewater direct from the
municipal sewer are often used by small communities to avoid the
added expense of pretreatment. Care must be taken to ensure
that odors do not occur from anaerobic conditions, mats of
rising sludge near the pond inlet, or from greasy scum at the
shoreline. |
2. Screening. Screening or comminution may be employed; however,
this is not common practice.
3. Primary sedimentation. Where primary sedimentation is used, the
pond provides a form of secondary treatment, usually at a much
lower cost than other forms of biological treatment. The Davis,
CA, pond system is an example of sedimentation before pond
treatment.
4. Secondary treatment. Ponds receiving secondary effluent are
normally associated with trickling filter and activated sludge
effluents. Effluent 8005 concentrations from high-rate rock
media trickling filters may be 40 to 75 mg/1, making ponds
practical for further removing and stabilizing the organic
material. Ponds can also be considered for use after trickling
filters when loading increases or discharge requirements are
tightened. Activated sludge and trickling filter effluents can
be further treated by ponds for nutrient removal.
1.3.3 Discharge Conditions
Ponds may also be classified on the basis of discharge conditions:
i
1. Complete retention. These systems rely on evaporation and/or
percolation to reduce the liquid volume at a rate equal to or
greater than the influent accumulation. Favorable geologic and/
or climatic conditions are prerequisite.
2. Controlled discharge. These systems have long hydraulic
detention times, and effluent is discharged when receiving water
quality will not be adversely affected by the discharge.
Controlled discharge ponds are designed to hold the wastewater
until the effluent and receiving water quality arecompatible.
3. Continuous discharge. These systems have no provision for ;
regulating effluent flow and the discharge rate essentially
equals the influent rate.
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1.4 Nutrient Removal Aspects
Both nitrogen and phosphorus in wastewater are affected by passage through
waste stabilization ponds. Nitrogen can undergo a number of chemical and
physical processes, including settling (in organic particulate form),
assimilation into algae cells, ammonification (conversion of organic nitrogen
to ammonia), nitrification, and denitrification. Phosphorus is removed by
assimilation into algae cells and by precipitation. When the alkalinity
increases during the daylight hours, phosphate is precipitated and will settle
out of the wastewater. A reduction in alkalinity at night can result in some
of the phosphorus being dissolved from the sediment. In general, the pond
effluent phosphorus concentration is less than half of the influent wastewater
concentration.
Nutrient removal can be accomplished in ponds using water hyacinths, duckweed
and other plants. Details on the use of aquaculture in wastewater treatment
are presented in Chapter 5 and elsewhere (4).
1.5 References
1. The 1980 Needs Survey. EPA-430/9-81-008, NTIS No. PB 82-131533, U.S.
Environmental Protection Agency, Office of Water Program Operations,
Washington, DC, 1981.
2. Oswald, W. 0. Quality Management by Engineered Ponds. In: Engineering
Management of Water Quality, P. H. McGauhey, ed., McGraw-TTTIl, New York,
NY, 1968.
3. Upgrading Lagoons. EPA-625/4-73-001b, NTIS No. PB 259974, U.S.
Environmental Protection Agency, Center for Environmental Research
Information, Cincinnati, OH, 1977.
4. Aquaculture Systems for Wastewater Treatment: An Engineering Assessment.
EPA-430/9-80-007, NTIS No. PB 81-156689, U.S. Environmental Protection
Agency, Office of Water Program Operations, Washington, DC, 1980.
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CHAPTER 2
PROCESS THEORY, PERFORMANCE, AND DESIGN
2.1 Biology
Enumeration of types of organisms occurring in wastewater ponds possesses
some inherent limitations. Species identification reflects the selective
nature of the isolation method, as well as the particular interests of the
researcher. Also, seasonal changes in pond operation and influent wastewater
characteristics produce variations in the naicrobial populations. Despite
these limitations, general observations pertaining to macro- and micro-
organisms in wastewater ponds are valuable in understanding the process
theory.
2.1.1 Bacteria
2.1.1.1 Aerobic Bacteria
I
Bacteria found in an aerobic zone of a wastewater pond are primarily the same
type as those found in an activated sludge process or in the zoogleal mass of
a trickling filter. The most frequently isolated bacteria include Beggiatoa
alba, Sphaerotilus natans, Achromobacter, Alcali genes, Flavqbacterium,
Pseudomohas, and Zoogloea spp. (1) These organisms decompose the organic
materials present in the aerobic zone into oxidized end products.
"2.1.1.2 Acid Forming Bacteria
Acid forming bacteria are heterotrophs that convert complex organic material
into simple alcohols and acids. These acids are primarily acetic, propionic,
and butyric (2). The activity of these bacteria is important since they
provide one of the substrates for the final reduction of the organic material
into methane gas by the methanogenic bacteria. Acid forming bacteria do not
limit the rate of the anaerobic decomposition and do not require thermophilic
temperatures for optimum growth as do the methanogenic bacteria. Addition-
ally, the acid forming bacteria are able to maintain a near-optimum pH range
for their existence through their own acid production.
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2.1.1.3 Cyanobacteria
Cyanobacteria are commonly known as blue-green algae. Like algae, cyano-
bacteria are able to assimilate simple organic compounds while utilizing
carbon dioxide as the major carbon source, or to grow in a completely
inorganic medium. Cyanobacteria produce oxygen as a by-product of photo-
synthesis, thus providing an oxygen source for other organisms in the ponds.
Ability of the Cyanobacteria to utilize atmospheric nitrogen accounts for
very broad distribution in both the terrestrial and aquatic environment.
Cyanobacteria appear in very large numbers as blooms when environmental
conditions are suitable (3).
2.1.1.4 Purple Sulfur Bacteria
Many species of Chromatiaceae, the purple sulfur bacteria, are actually pur-
ple, but others may be dark orange to brown or various shades of pink or
red. Purple sulfur bacteria may grow in any aquatic environment to which
light of the required wavelength penetrates, provided that carbon dioxide,
nitrogen, and a reduced form of sulfur, or hydrogen, are available. Purple
sulfur bacteria occupy the anaerobic layer below the algae, Cyanobacteria,
and other aerobic bacteria in a pond. Wavelengths of light used by the
purple sulfur bacteria are different from those used by the Cyanobacteria or
algae; thus the sulfur bacteria are able to grow using light that has passed
through the surface layer of water or sediment occupied by aerobic photo-
synthetic organisms. Purple sulfur bacteria are commonly found at a specific
depth, in a thin layer where light and nutrition conditions are optimum (3).
Conversion of odorous sulfide compounds to elemental sulfur or sulfate by the
sulfur bacteria is a significant factor for odor control in facultative and
anaerobic ponds.
2.1.1.5 Pathogenic Bacteria
Pathogenic bacteria frequently discussed with reference to wastewater ponds
include SalI monel1 a, Shi gel!a, Escherichia, Leptospi ra, Francisell a, and
Vibrio. (Viruses and certain protozoa are also pathogenic, but scant inf or-
mation exists.) Water is not the natural environment of the pathogenic bac-
teria, but instead a means of transport to a new host. Pathogenic bacteria
are usually unable to multiply or survive for extensive periods in the
aquatic environment. The decline in numbers of microbial pathogens with
time, within the aquatic environment, involves sedimentation, starvation,
sunlight, pH, temperature, competition, and predation (1).
The most probable number (MPN) of coliform organisms present in a given
volume of a waste is the commonly accepted index of the pathogenic quality of
an effluent. Most literature concerning the performance of ponds report very
high reductions in coliform bacteria, often as high as 99.9 percent, in
-------
facultative ponds. Caution should be exercised in interpreting these fig-
ures, however, as large absolute numbers of coliform may still be present.
2.1.2 Algae
Algae constitute a group of aquatic organisms that may be unicellular or
multicellular, motile or immotile, of which practically all have photo-
synthetic pigments. Being autotrophic, algae utilize inorganic nutrients
such as phosphate, carbon dioxide, and nitrogen. Algae do not fix atmos-
pheric nitrogen, but require inorganic nitrogen in the form of nitrate or
ammonia. Also, some algal species are able to use ami no acids and other
organic nitrogen compounds. Inorganic nutrients utilized by algae are photo-
synthetically converted into cellular organic materials, with oxygen produced
as a by-product.
i
Algae are generally divided into three major groups, based on the color
imparted to the cells by the chlorophyll and other pigments involved in
photosynthesis. Green algae include unicellular, filamentous, and colonial
forms. Brown algae are unicellular and flagellated, and include the
diatoms. Certain brown algae are responsible for toxic red blooms. Red
algae include a few unicellular forms, but are primarily filamentous (3).
Green and brown algae are common to wastewater ponds, with the red algae
occurring infrequently. The predominant algal species at any given time is
thought to be primarily a function of temperature, although the effects of
predation, nutrient availability, and toxins are also important.
It has been generally accepted that algae and bacteria together comprise the
essential elements of a successful stabilization pond operation. Bacteria
break down the complex organic waste components aerobically and anaerobically
into simple products which are then available for use by the algae. Algae,
in turn, produce the oxygen necessary for maintaining the aerobic environment
necessary for the bacteria to perform oxidative functions.
Due to the cyclic biochemical reactions of biodegradation and mineralization
of nutrients by bacteria, and synthesis of new organics in the form of algae
cells, it is feasible that a pond effluent could contain a higher total
organic content than the influent. However, this could occur only under the
most optimum algae growth conditions, which would seldom occur in practice.
2.1.3 Animals
Although bacteria and algae are the primary organisms through which waste
stabilization is accomplished, higher, life forms are of importance as well.
Planktonic Cladocera and benthic Chironomidae lhave been suggested as the most
significant faunaTn the pond community, in terms of stabilizing organic
matter. The Cladocera feed on the algae and promote flocculation and set-
tling of particulate matter. This in turn results in better light pene-
10
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tration and algal growth at greater depths. Settled matter Is further broken
down and stabilized by the benthic feeding Chironomidae. Predators, such as
rotifers, often control the population levels of certain of the lower forms
in the pond, thereby influencing the succession of predominating species.
Mosquitoes do present a problem in some ponds. Aside from their nuisance
characteristics, certain mosquitoes are also the vector for such diseases as
encephalitis, malaria, and yellow fever, and constitute a hazard to public
health which must be controlled if ponds are to be utilized. The most effec-
tive means of control is the control of emergent vegetation. Gambusia, or
mosquito fish, have beeen successfully employed to eliminate mosquito
problems in some ponds in warm climates (4) (5).
2.2 Biochemical Interactions
2.2.1 Photosynthesis
Photosynthesis is the process whereby organisms are able to grow utilizing
the sun's radiant energy to power the fixation of atmospheric C02 and
subsequently provide the reducing power to convert the C02 to organic com-
pounds. Photosynthesis is usually associated with the green plants; however,
certain bacteria as well as algae carry out photosynthesis. In wastewater
ponds, the photosynthetic organisms of interest are the algae, cyanobacteria
(blue-green algae), and the purple sulfur bacteria (5).
Photosynthesis may be classified as oxygenic or anoxygenic depending on the
source of reducing power used by a particular organism. In oxygenic photo-
synthesis, water serves as the source of reducing power, with oxygen being
produced as a by-product. The equation representing oxygenic photosynthesis
is:
2H+ + 2e- (2-1
Oxygenic photosynthesis occurs in green plants, algae, and cyanobacteria. In
ponds, the oxygenic photosynthetic algae and cyanobacteria convert carbon
dioxide to organic compounds that serve as a source of chemical energy, in
addition to organic waste matter, for most other living organisms (3). More
importantly, the by-product oxygen produced in oxygenic photosynthesis allows
the aerobic bacteria to function in their role as primary consumers in
degrading complex organic waste material.
Anoxygenic photosynthesis produces no oxygen as a by-product, thus oc-
curring in the complete absence of oxygen. The bacteria involved in
anoxygenic photosynthesis are largely strict anaerobes, with reducing power
supplied by reduced inorganic compounds. Many anoxygenic photosynthetic
11
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bacteria utilize reduced sulfur compounds or elemental sulfur in anoxygenic
photosynthesis according to the fpllowing equation:
H2S -*• SO + 2H+ + 2e- (2-2)
'
2.2.2 Respiration
Respiration is a physiological process in which organic compounds are
oxidized mainly to carbon dioxide and water. However, respiration does not
only lead to the production of carbon dioxide, but to the synthesis of cell
material as well. Respiration is an orderly process, catalyzed by enzymes
such as the cytochromes and consisting of many integrated step reactions
terminating in the reduction of oxygen to water (6). Aerobic respiration,
common to species of bacteria, protozoa, and higher animals, may be
represented by the following simple equation:
C2H12°6 + 602 enzyt"es > 6C02 + 6H20 + new cells (2-3)
The bacteria involved in aerobic respiration are primarily responsible for
wastewater stabilization in ponds.
In the presence of light, respiration and photosynthesis can occur simul-
taneously in algae. However, the respiration rate is low compared with the
photosynthesis rate, resulting in a net consumption of carbon dioxide and
production of oxygen. In the absence of light, algal respiration continues
while photosynthesis stops, resulting in a net consumption of oxygen and
production of carbon dioxide.
2.2.3 Dissolved Oxygen (DO)
Oxygen is a partially soluble gas, and solubility varies in direct propor-
tion to the atmospheric pressure at any given temperature, and in inverse
proportion to temperature for any given atmospheric pressure. DO concen-
trations of approximately 8 mg/1 are usually considered the maximum available
under ambient conditions. In mechanically aerated ponds, the limited
solubility of oxygen is a significant factor, since it determines the oxygen
absorption rate and, therefore, the cost of aeration (7).
The two natural sources of DO in ponds are surface reaeration and photo-
synthetic oxygenation. In areas of low wind activity, surface reaeration may
be relatively unimportant, depending on the water depth. Where surface
turbulence is created from excessive wind activity, surface reaeration is
significant. Observation has shown that DO in wastewater ponds varies almost
directly with the level of photosynthetic activity, being low at night and
12
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early morning and rising during daylight hours to a peak in the early
afternoon. At increased depth, the effects of surface reaeration and
photosynthetic oxygenation decrease, since the distance from the water-
atmosphere interface increases and light penetration decreases. This can
result in a vertical gradient in DO concentration accompanied by a
segregation of microorganisms.
2.2.4 Nitrogen Cycle
A simplified nitrogen cycle is represented by Figure 2-1.
FIGURE 2-1
THE NITROGEN CYCLE
organic-N ammonification ^ammonium §
E E ^ -^ • —
CD O
OVr-
O +•>
S~ (O
I ^ \s
nitrogen gas-*-
denitrification
In a wastewater pond, organic nitrogen and ammonium nitrogen enter with the
influent wastewater. Organic nitrogen in fecal matter and other organic
materials in the wastewater undergo conversion to ammonia and ammonium ion by
microbial activity. The ammonium in turn is nitrified to nitrite by
Nitrosomonas and then to nitrate by Nitrobacter. The overall nitrification
reaction is:
NH4+ + 202 -»• NOg + 2H+ + H20 (2-4)
The nitrate produced in the nitrification process, as well as a portion of
the ammonium produced from ammonification, can be assimilated by organisms as
a nutrient to produce cell protein and other nitrogen-containing compounds.
The nitrate is utilized in denitrification to form nitrite and then nitrogen
gas. Several bacteria may be involved in the denitrification process
13
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including Pseudomonas, Micrococcus, Achromobacter, and Bacillus. The overall
denitrification reaction"??!
6N03" + 5CH3OH -»• 3N2 + 5C02 + 7H20+ 60H" (2-5)
Nitrogen gas is "fixed" to form organic nitrogen by cyanobacteria, thus
making the nitrogen available as a nutrient and completing the cycle (8).
Nitrogen removal in facultative wastewater ponds can occur by any of the fol-
lowing processes: (1) gaseous ammonia stripping to the atmosphere, (2) am-
monium assimilation in algal biomass, (3) nitrate uptake by plants and algae,
and (4) biological nitrification-denitrification. Ammonium assimilation into
algal biomass depends on the biological activity in the system and is affect-
ed by several factors such as temperature, organic load, detention time, and
wastewater characteristics. The rate of gaseous ammonia losses to the
atmosphere is primarily a function of pH, surface to volume ratio, tempera-
ture, and the mixing conditions. An alkaline pH shifts the equilibrium of
ammonia gas and ammonium ion towards gaseous ammonia production, while the
mixing conditions affect the magnitude of the mass transfer coefficient.
2.2.5 pH and Alkalinity
In wastewater ponds, the hydrogen ion concentration, expressed as pH, is
controlled through the carbonate buffering system represented by the
following equations:
C02 + H20 t H2C03 £ HC03" + H+ (2-6)
I
M(HC03)2 ? M++ -i- 2HC03" (2-7)
HC03" £ C03= + H+ ; (2-8)
where: M s metal ion
C03= + H20 t HC03" + OH" (2-9)
OH" + H+ £ H20 (2-10)
14
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The equilibrium of this system is affected by algal photosynthesis. In pho-
tosynthetic metabolism by algae, carbon dioxide is removed from the dissolved
phase, forcing the equilibrium of the first expression to the left. This
tends to decrease the hydrogen ion concentration and also decrease bicar-
bonate alkalinity. The effect of the resultant decrease in bicarbonate
(HC03~) concentration is to force the third equation to the left and the
fourth to the right, both of which decrease total alkalinity. Figure 2-2
shows a typical relationship between pH, C02, HCOs", C0=, and OH~.
The decreased alkalinity associated with photosynthesis will simultaneously
reduce the carbonate hardness present in the waste. Because of the close
relationship between pH and photosynthetic activity, considerable diurnal
fluctuation in pH is observed.
FIGURE 2-2
CALCULATED RELATIONSHIP AMONG pH, C02, C03=, HC03", and OH~ (7)
100 -
80 -
u>
~ 60 -
CO
o
o
CO
O
J2. 40
.9
20 -
7.0
8.0
9.0
pH
10.0
11.0
15
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2.3 Controlling Factors
2.3.1 Light ,
!
The intensity and spectral composition of light penetrating a pond surface
significantly affects all resident microbial activity. The available light
determines, to a large degree, ,the level of photosynthetic activity and,
hence, oxygen production. Oxygen availability to the aerobic bacterial
organisms is vital. In general, photosynthetic activity increases with
increasing light intensity until the photosynthetic system becomes light
saturated. The rate at which photosynthesis increases in proportion to an
increase in light intensity, as well as the level at which an organism's
photosynthetic system becomes light saturated, depends upon the particular
biochemistry of the species (1). . In ponds, photosynthetic oxygen production
has been shown to be relatively constant within the range of 5,380 to
53,800 lumen m2 (500 to 5,000: foot-candles) light intensity with a
reduction occurring at higher and lower intensities (5).
\
The spectral composition of available light is also crucial in determining
photosynthetic activity. The ability of photosynthetic organisms to utilize
available light energy primarily depends upon their ability to absorb the
available wavelengths. This absorption ability is determined by the specific
photosynthetic pigment of the organism. The main photosynthetic pigments are
the chlorophylls and the phycobilins. Bacterial chlorophyll differs from
algal chlorophyll in both chemical structure and absorption capacity. These
differences allow the photosynthetic bacteria to live below dense algal
layers where they can utilize light not absorbed by the algae (1).
The quality and quantity of light penetrating the pond surface to any depth
depends on the presence of dissolved and particulate matter as well, as the
water absorption characteristics. The organisms themselves contribute to
water turbidity, further limiting the depth of light penetration. Because of
these restrictions, photosynthesis is significant only in the upper pond
layers. This region of net photosynthetic activity is called the euphotic
zone (1).
Light intensity from solar radiation varies with the time of day and
difference in latitudes. In cold climates, light penetration can be
drastically reduced by ice and snow cover—thus the prevalence of mechanical
aeration in these regions.
2.3.2 Temperature
Temperature is a very important factor in the aerobic environment of a pond
and will, at or near the surface, determine the succession of predominant
species of algae, bacteria, and other aquatic organisms. Algae can survive
at temperatures of 5°C to 40°C. Green algae show most efficient growth and
16
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activity at temperatures near 30°C to 35°C. Aerobic bacteria are viable
within the temperature range of 10°C to 40°C, with 35°C to 40°C being optimum
for cyanobacteria (10)(11).
Solar radiation is a major source of heat, generally resulting in a
temperature gradient with respect to depth. This can influence the anaerobic
decomposition of solids settled to the bottom of the pond. The bacteria
responsible for anaerobic degradation, ideally requiring temperatures within
the range of 15°C to 65°C, are exposed to the lowest temperatures, thus
greatly reducing their activity. The other major source of heat is the
influent. In sewerage systems having no major inflow or infiltration
problems, the influent temperature is higher than that of the pond contents.
Cooling influences are exerted by evaporation, contact with cooler ground-
water, and wind action.
Overall effects of temperature, combined with light intensity, are reflected
in the fact that nearly all investigators report improved performance during
summer and autumn months when both temperature and light are at their
maximum. The maximum practical temperature of wastewater ponds is likely
less than 30°C, indicating that most ponds operate at less than optimum
temperature for anaerobic activity (12).
Temperature changes in nonaerated ponds result in vertical stratification
during certain seasons of the year. Stratification results because of an
increase in water density with depth caused by a decrease in temperature.
During the summer, the upper waters are warmed and the density decreased, and
stratification results. The temperature of the upper layer of water is
relatively uniform because of mixing by the wind. Temperatures change
rapidly in the thermocline, and the zone is very resistant to mixing. As
temperatures decrease during the fall, stratification is decreased and the
pond is mixed by wind action. This phenomenon is referred to as the fall
overturn.
The density of water decreases as the temperature falls below 4°C, and a
winter stratification can occur. As ice cover breaks up and the water warms,
a spring overturn can also occur.
During both the spring and fall overturns, significant odors caused by
anaerobic material being brought to the surface can stimulate complaints from
neighbors. Overturn phenomena are the reasons for regulatory requirements
that nonaerated ponds be located downwind {based on prevailing winds during
overturn periods) and away from dwellings.
2.3.3 Nutrient Requirements and Removal
Growth and, to some extent, activity of microorganisms is controlled by the
availability of essential nutrients such as carbon, nitrogen, phosphorus, and
sulfur and a variety of other substances required in small quantities. These
nutrients may be classified as inorganic or organic. Nitrogen, phosphorus,
17
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and sulfur represent the inorganic nutrients, while organic carbon compounds
represent the organic nutrients.
2.3.3.1 Nitrogen
Nitrogen can be a limiting nutrient for primary productivity involving
algae. Figure 2-3 represents the various forms that nitrogen typically
assumes over time in wastewater ponds. The conversion of organic nitrogen to
various other nitrogen forms results in a net loss in total nitrogen (13).
This nitrogen loss may be due to either algal uptake for metabolic purposes
or to bacterial action. It is likely that each mechanism contributes to the
overall total nitrogen reduction. As previously discussed, another factor
contributing to the reduction of total nitrogen is gaseous ammonia stripping
under favorable environmental conditions. Regardless of the specific removal
mechanism involved, ammonia removal in facultative wastewater ponds may
approach 99 percent, with the major removal occurring in the primary cell of
a multicell pond system (9).
FIGURE 2-3
CHANGES OCCURRING IN FORMS OF NITROGEN PRESENT IN A POND
ENVIRONMENT UNDER AEROBIC CONDITIONS (7)
Time, days
18
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2.3.3.2 Phosphorus
Phosphorus is most often the growth-limiting nutrient in aquatic
environments. Municipal wastewater, however, is normally quite rich in
phosphorus even though current restrictions on phosphorus compounds in
detergents has resulted in reduced concentrations. Nonetheless, the
concentration is still adequate to stimulate growth in aquatic organisms.
In aquatic environments, phosphorus occurs in three forms: (1) particulate
phosphorus, (2) soluble organic phosphorus, and (3) inorganic phosphorus.
Inorganic phosphorus, primarily in the form of orthophosphate, is readily
utilized by aquatic organisms. Some organisms may store excess phosphorus as
polyphosphates for future use. At the same time, some phosphate is contin-
uously lost to sediments, where it is locked up in insoluble precipitates (1).
Phosphorus removal in ponds may result from physical mechanisms such as
adsorption, coagulation, and precipitation. The uptake of phosphorus by
organisms in metabolic functions as well as for storage can also add to
phosphorus removal. Phosphorus removal in wastewater ponds has been reported
to range from 30 to 95 percent (13).
Like nitrogen, phosphorus held by algae discharged in the final effluent may
be introduced to receiving waters as organic phosphorus. Excessive algal
"afterblooms" observed in waters receiving effluents have, in some cases,
been attributed to nitrogen and phosphorus compounds remaining in the treated
wastewater. Phosphorus removal in aquaculture is discussed in Chapter 5.
2.3.3.3 Sulfur
Sulfur is a vital nutrient for microorganisms, but is usually plentiful in
natural waters. Because sulfur is rarely limiting, its removal from
wastewater is usually not considered necessary, Ecologically, sulfur is
particularly -important since compounds such as hydrogen sulfide and sulfuric
acid are toxic, and since the oxidation of certain sulfur compounds is an
important energy source for some aquatic bacteria (1).
2.3.3.4 Carbon
The decomposable organic carbon content of a waste is traditionally measured
in terms of its biochemical oxygen demand (BOD), or the amount of oxygen
required under standardized conditions for the aerobic biological stabili-
zation of the organic matter in a waste. Since the time required for
complete stabilization by biological oxidation, depending on the organic
material and the organisms present, can be several weeks, the standard
practice is to use the five-day biochemical oxygen demand (BODs) as an
index of the organic carbon content or organic strength of a waste. The
19
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removal of BOD5 is also a primary criterion for evaluating treatment
efficiency.
BODg reductions in wastewater ponds ranging from 50 to 95 percent have been
reported in the literature. Factors affecting the reduction of BOD5 are
numerous. A very rapid reduction in BODs occurs in a wastewater pond
during the first five to seven days. Later reductions take place at a
sharply reduced rate. BOD5 removals are generally much lower during winter
and early spring than in summer and early fall. This is due primarily to
lower temperatures during these periods. Many regulatory agencies recommend
that ponds be so operated as to prevent discharge during cold periods.
2.4 Performance and Design of Ponds
2.4.1 Facultative Ponds
i i
Performance results from existing pond systems located at Peterborough, NH;
Kilmichael, MS; Eudora, KS; and Corinne, UT, are presented in this section
(14-17). These studies encompassed 12 full months of data collection,
including four separate 30-consecutive-dayj, 24-hour composite sampling
periods, once each season.
2.4.1.1 Site Description !
a. Peterborough, New Hampshire
The Peterborough facultative waste stabilization pond system consists of
three cells operated in series during the evaluation of the performance
described in this chapter. The option to operate the cells in parallel or
combination of series and parallel is available. The total surface area is
8.5 ha (21 ac) and the effluent is chlorinated. A schematic drawing of the
facility 'is shown in Figure 2-4. An effluent chlorine residual of 2.0 mg/1
is maintained at all times. The facility was designed in 1968 on an areal
loading basis of 20 kg BOD5/d/ha (18 Ib BOD5/d/ac) with an initial
average hydraulic flow of 1,890 m3/d (0.5 mgd). At the design depth of 1.2
m (4 ft), the theoretical hydraulic detention time for the system would be 57
days. The results of the study conducted during 1974-1975 indicated an
actual mean area loading of 15 kg BODs/d/ha (14 Ib BODs/d/ac) and a mean
hydraulic flow of 1,011 m3/d (0.27 mgd),, The theoretical hydraulic
detention time based upon the flow entering the plant was 107 days. The
loading rates and detention times for the first cell in the series are shown
in Table 2-1.
20
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FIGURE 2-4
SCHEMATIC FLOW DIAGRAM AND AERIAL PHOTOGRAPH OF THE FACULTATIVE
POND SYSTEM AT PETERBOROUGH, NEW HAMPSHIRE
To chlorine contact tank
21
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TABLE 2-1
DESIGN AND ACTUAL LOADING RATES AND DETENTION TIMES
-FOR SELECTED FACULTATIVE! PONDS
Organic Loading Rate Theoretical
Actual Hydraulic Detention
TotalFTrst Time
Location Design System Gel1 DesignActual
Peterborough, NH
Kilmichael, MS
Eudora, KS
Corinne, UT
20
67*
38
36
kg BOD5/ha/d
15
15
17
12
I
1
1
36
23
43
30
57
79
47
180
days
107
214
231
70
apirst cell.
b. Kilmichael, Mississippi
The Kilmichael facultative waste stabilization pond system consists of three
cells operated in series with a total surface area of 3.3 ha (8.1 ac). The
effluent is not chlorinated. A schematic drawing of the facility is shown in
Figure 2-5.
The design load as specified by the State of Mississippi standards for the
first cell in the series was 67 kg BOD5/d/ha (60 Ib BOD5/d/ac). The
second cell was designed with a surface area equivalent to 40 percent of the
surface area of the first cell. The third cell was designed with a surface
area equivalent to 16 percent of the first cell. The system was designed for
a hydraulic flow of 690 nr/d (0.18 mgd). The average depth of the cells is
approximately 2 m (6.6 ft). This provides for a theoretical hydraulic
detention time of 79 days. The result of the study indicated that the actual
average organic load on the first cell averaged 23 kg BOD5/d/ha (21 Tb
BODs/d/ac) and that the average hydraulic inflow to the system was 280
m3/d (0.07 mgd). The theoretical hydraulic detention time based upon the
flow entering the plant was 214 days. Loading rates and detention times are
summarized in Table 2-1. ;
22
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FIGURE 2-5
SCHEMATIC FLOW DIAGRAM AND AERIAL PHOTOGRAPH OF THE FACULTATIVE
POND SYSTEM AT KILMICHAEL, MISSISSIPPI
23
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c. Eudora, Kansas
The Eudora facultative waste stabilization pond system consists of three
cells operated in series with a total surface area of 7.8 ha (19.3 ac). A
schematic diagram of the system is shown in Figure 2-6. The effluent is hot
chlorinated.
The facility was designed on an area! loading basis of 38 kg BODs/d/ha (34
Ib BODs/d/ac) with a hydraulic flow of 1,'510 m3/d (0.4 mgd). At the
design operating depth of 1.5 m (5 ft), the theoretical hydraulic detention
time would be 47 days. The results of the study indicated that the actual
mean organic load on the system was 17 kg BODs/d/ha (15 Ib BOD5/d/ac).
The actual mean hydraulic flow to the system was 500 m3/d (0.13 mgd), and
theoretical hydraulic detention time in the system was 231 days. A summary
of the loading rates and detention times are shown in Table 2-1.
d. Corinne, Utah
j
The Corinne facultative waste stabilization pond system consists of seven
cells operated in series with a total surface area of 3.8 ha (9.5 ac). A
schematic drawing of the system is shown in Figure 2-7. The effluent is not
chlorinated.
The facility was designed on an area! loading, basis of 36 kg BODs/d/ha (32
Ib BOD5/d/ac) with a hydraulic flow of 265 m3/d (0.07 mgd).
With a design depth of 1.2 m (4 ft), the system has a theoretical hydraulic
detention time of 180 days. The results of the study indicated that the
actual mean organic load on the system was 12 kg BODs/d/ha (11 Ib
BODg/d/ac). The actual average hydraulic flow to the system was 690 m3/d
(O.T8 mgd), and the theoretical hydraulic detention time in the system was 70
days. Loading rates and detention times are summarized in Table 2-1.
-2.4.1.2 Performance ;
a. BODs Removal
The monthly average effluent BODs concentrations for the four previously
described facultative pond systems are presented in Figure 2-8. In general,
all of the systems were capable of providing a monthly average effluent
BODs concentration of less than 30 mg/1 during the major portion of the
year. Monthly average effluent BODs concentrations ranged from 1.4 mg/1
during September 1975 at the Corinne, UT, site,, to 57 mg/1 during March 1975
at the Peterborough, NH, site. Monthly average effluent BODs concentra-
tions tended to be higher during January, February, March, and April at all
24
-------
FIGURE 2-6
SCHEMATIC FLOW DIAGRAM AND AERIAL PHOTOGRAPH OF,THE FACULTATIVE
POND SYSTEM AT EUDORA, KANSAS
Effluent
Influent
25
-------
FIGURE 2-7
SCHEMATIC FLOW DIAGRAM AND AERIAL PHOTOGRAPH OF THE FACULTATIVE
POND SYSTEM AT CORINNE, UTAH
Effluent
©
O Sampling station
(TYP.)
-©
Cell No. 7
0.34 ha J
f
©1
Cell No. 6
0.405 ha
f
/"^"™"'\
(e)
Cell No. 5
0.405 ha
_^^^,
•^^^^
Cell No. 2
0.405 ha
®i
\
Cell No. 3
0.405 ha
®J
1
Cell No. 4
0.405 ha
© ;
00
Cell No. 1
1.49 ha
\
\
\
\
[.•M***"* •* ™" " \ Influent
; ©
\
26
-------
FIGURE 2-8
FACULTATIVE POND BOD5 EFFLUENT CONCENTRATIONS
O)
E
in
Q
O
CO
c
0)
01
d>
OJ
CD
c
o
N D J F M A M
1974-1975
Eudora, Kansas (3 cells)
D Kilmichael, Mississippi (3 cell)
A Corinne, Utah (7 cells)
•- Peterborough, New Hampshire (3 cells)
N
D J F
1975'1976
-------
of the sites. This was especially evident at the Peterborough site when the
cells were covered over by ice due to freezing temperatures. The ice cover
caused the cells to become anaerobic. However, even when the ponds at the
Corinne site were covered over with ice the monthly average effluent BODs
concentration did not exceed 30 mg/1.
None of the systems studied was significantly affected by the fall overturn;
however, the spring overturn did cause significant increases in effluent
BODc concentrations at two of the sites. At the Corinne site two different
spring overturns occurred. The first occurred in March 1975, with a peak
daily BODs concentration of 36 mg/1. The second occurred during
April 1975, with a peak daily effluent BOD5 concentration of 39 mg/1. At
the Eudora site, the peak daily effluent BOD5 concentration of 57 mg/1
occurred during April 1975. The Kilmichael and Peterborough sites were not
severely affected by the spring overturn period.
The monthly average effluent BODs concentration of the Corinne pond system
never exceeded 30 mg/1 throughout the entire study. The Eudora pond system
monthly average effluent BODs concentration exceeded 30 mg/1 on only two
occasions during the study. The Peterborough pond system monthly average
effluent BOD5 concentration exceeded 30 mg/1 in 4 of the 12 months studied.
Although these systems are subject to seasonal upsets, they are capable of
producing an effluent sufficiently low in BODj that discharge to a waterway
is, in many cases, acceptable. It should be noted that three of the four
systems were underloaded based on a comparison of design vs. actual organic
and hydraulic loadings, as shown in Table 2-1. The Corinne system was
grossly underloaded from an organic standpoint and grossly overloaded from a
hydraulic standpoint.
b. Suspended Solids Removal
The monthly average effluent SS concentrations for each system are presented
in Figure 2-9. i
In general, the SS concentration in facultative pond effluents follows a
seasonal pattern. Effluent SS concentration is high during summer months
when algal growth is intensive and also during the spring overturn periods
when settled solids are resuspended from bottom sediments due to mixing. The
monthly average SS concentration ranged from 2.5 mg/1 during September 1975
at Corinne to 179 mg/1 during April 1975, also at Corinne. The high value of
179 mg/1 occurred during the spring overturn period, which caused a
resuspension of settled solids.
Eudora and Kilmichael illustrate the increase in effluent SS concentration
due to algal growth during the warm summer months. However, Peterborough and
Corinne were not significantly affected by algal growth during the summer
months. In general, Corinne and Peterborough produced a monthly average
effluent SS concentration of less than 20 mg/1. During 10 of the 13 months
28
-------
FIGURE 2-9
FACULTATIVE POND SS EFFLUENT CONCENTRATIONS
ro
o>
(0
CO
0>
_3
£
(U
o>
(0
I
o
100
90
80
70
60
50
40
30
20
10
0
4, 179
_L
i
..A
..A-"
"A"'' I I
0
.-n
..A
N D J F
1974-1975
M
M
0 N
Eudora, Kansas (3 cells)
•- Kilmichael, Mississippi (3 cells)
• • Corinne, Utah (7 cells)
-• Peterborough, New Hampshire (3 cells)
D J
1975
-------
studied, the monthly average effluent SS concentration at the Corinne site
never exceeded 20mg/l. However, the monthly average effluent SS
concentration at Eudora was never less than 39 mg/1 throughout the entire
study.
The results of these studies indicate that facultative ponds can produce an
effluent which has a low SS concentration; however, effluent SS concentra-
tions will be high at various times throughout the year. In general, these
SS are composed of algal cells which may not be particularly harmful to
receiving streams. In areas where effluent SS standards are stringent, some
type of polishing device or controlled discharge will be necessary to reduce
SS concentrations to acceptable levels.
c. Fecal Coliform Removal
The monthly geometric mean effluent coliform concentrations for the four
facultative pond systems are compared with a concentration of 200/100 ml in
Figure 2-10.
Only the Peterborough, NH, system provides chlorine disinfection. As
illustrated in Figure 2-10, the chlorinated effluent at Peterborough never
exceeded 20 fecal coliform organisms/100 ml. This clearly indicates that
facultative pond effluent may be satisfactorily disinfected by the
chlorination process.
For the three systems without disinfection processes, the geometric mean
monthly effluent fecal coliform concentration ranged from 0.1
organisms/100 ml in June and September 1975, at the Corinne, UT, lagoon
system to 13,527 organisms/100 ml in January 1975, at the Kilmichael, MS,
lagoon system. In general, geometric mean effluent fecal coliform
concentrations tend to be higher during the colder periods. The fecal
coliform die-off during periods of ice cover can be expected to be
significantly less than normal due to the reduced amount of sunlight reaching
the organisms. The Eudora, KS, and the Kilmichael, MS, geometric mean
monthly effluent fecal coliform concentrations consistently exceeded 200
organisms/100 ml during winter operation.
The fecal coliform concentration in the Corinne effluent never exceeded 10
organisms/100 ml even though this system did not include any form of
disinfection. This system is composed of seven cells in series. Analysis of
the fecal coliform concentrations between the seven cells indicated that
fecal coliforms were essentially absent after the fourth cell in the series
(17). The other two systems without disinfection only utilize three cells in
series; however; fecal co'liform die-off is primarily a function of actual
hydraulic residence time rather than the absolute number of cells in series.
30
-------
FIGURE 2-10
FACULTATIVE POND FECAL COLIFORM EFFLUENT CONCENTRATIONS
IVJ
105
"5
o —
Q> i-
3 \
3= o
^ 103
sj
Monthly Geometric
Coliform Conceni
D § Q 9
\J
v
1 I 1 I 1 I 1 1 1 1 1 I 1 I 1 I t I I
r^^ '^""VA /
/ V-v
: / /\ :
n — c/ \ n
p^ \ / V \ / Ns x
/ • .7 '•. •« A. •' .-A.
A./ ..A. ..\.A- '. v' /•. •'^''
./ \ ; X'"'\ / "'A-.. .•'' *"•« ..-A
i i + * + y i V i i i v i t i i t" i i
1 AS ON DJFMAMJ J AS ONDJFM
1974-1975 1975«1976
O- Eudora, Kansas (3 cells)
D Kilmichael, Mississippi (3 cells)
Peterborough, New Hampshire (3 cells) (unchlorinated)
Peterborough, New Hampshire (chlorinated)
-------
The results of these studies indicate that facultative pond effluent can be
chlorinated to produce fecal coliform concentrations less than 10 organ-
isms/100 ml. Two of the systems studied could not produce an effluent
containing less than 200 fecal coliforms/100 ml. This was probably due to
hydraulic short circuiting; however, the Corinne, UT, system study clearly
indicated that facultative pond systems can significantly reduce fecal
coliform concentrations by natural, processes occurring in the pond.
•2.4.1.3 Design Criteria for Organic Loading and Hydraulic
Detention Time
Canter and Englande (18) reported that most states have design criteria for
organic loading and/or hydraulic detention time for facultative waste
stabilization ponds. These design criteria are established by these states
in an effort to ensure that the quality of pond effluent would meet
applicable state or Federal standards. Effluents from ponds constructed
according to these design criteria repeatedly fail to meet the quality
standards, thus indicating deficiencies in the current design criteria.
Reported organic loading design criteria averaged 29 kg BODs/ha/d (26 Ib
BODs/ac/d) in the north region (above 42° latitude), 49 kg BODs/ha/d (44
Ib BOD5/ac/d) in the southern region (below 37° latitude), and 37 kg
BODs/ha/d (33 Ib BODs/ac/d) in the central region. Reported design
criteria for detention time averaged 117 days in the north, 82 days in the
central, and 31 days in the south region. !
u
Design criteria for organic loading in New Hampshire was 39 kg BODs/ha/d
(35 Ib BODs/ac/d). The Peterborough treatment system was designed for a
loading of 20 kg BOD5/ha/d (18 Ib BOD5/ac/d) in 1968 to be increased as
population increased to 40 kg BODs/ha/d (35 Ib BODs/ac/d) in the year
2000. . Actual loading during 1974-1975 averaged 15 kg BOD5/ha/d (14 Ib
BODs/ac/d) with the highest monthly loading being 21 kg BODs/ha/d (19 Ib
BODc/ac/d). Although the organic loading was substantially below the state
design limit, the effluent BOD5 exceeded 30 mg/1 during the months of
October 1974 and February, March, and April 1975.
Mississippi's design criteria for organic loading. was 67 kg BODs/ha/d
(60 Ib BODs/ac/d) in the first cell. Based on an overall loading rate, the
Kilmichael treatment system was loaded at 43 kg BODs/ha/d (38 Tb
BOD5/ac/d). Actual loading during 1974-1975 averaged 15 kg BOD5/ha/d (13
Ib BODs/ac/d) with a monthly maximum of 25 kg BODs/ha/d (22 Ib
BODs/ac/d), and yet the effluent BODs exceeded 39 mg/1 twice during the
sample year (November and July).
The design load for the Eudora, KS, system was the same as the state design
limit, 38 kg BOD5/ha/d (34 Ib BOD5/ac/d). Actual loading during
1974-1975 averaged only 17 kg BODs/ha/d (15 Ib BODs/ac/d) with a maximum
of 31 kg BOD5/ha/d (28 Ib BOD5/ac/d). The effluent BOD5 exceeded
30 mg/1 three months during the sample year (March, April, and August).
32
-------
Utah has both an organic loading design limit, 45 kg BODs/ha/d (40 Ib
BOD5/ac/d) on the primary cell and a winter detention time design criteria
of 180 days. Design loading for the Corinne system was 36 kg BOD5/ha/d (32
Ib BOD5/ac/d), and design detention time was 180 days. Although the
organic loading averaged 30 kg BODs/ha/d (34 Ib BODs/ac/d) on the primary
cell, during two months of the sample year it exceeded 56 kg BOD5/ha/d (50
BODs/ac/d). Average organic loading on the total system was 12 kg
BODij/ha/d (11 Ib BOD5/ac/d), and the hydraulic detention time was
estimated to be 88 days during the winter. Regardless of the deviations from
the state design criteria, the average monthly 8005 never exceeded 30 mg/1.
A summary of the state design criteria for each location and actual design
values for organic loading and hydraulic detention time are shown in Table
2-2, Also included is a list of the months the Federal effluent standard for
BODs was exceeded. Note that the actual organic loading for all four
systems are nearly equal, yet as the monthly effluent BODs averages shown
in Figure 2-8 indicate, the Corinne system consistently produced a higher
quality effluent. This may be a function of the larger number of cells in
the Corinne system—seven as compared to three for the rest of the systems.
Hydraulic short circuiting may be occurring in the three cell systems,
resulting in a shorter actual detention time than exists in the Corinne
system. Detention time may also be affected by the location of cell inlet
and outlet structures. As shown in Figure 2-7, the outlet is at the furthest
point possible from the inlet in the Corinne, UT, system. At the Eudora, KS,
system shown in Figure 2-6, large "dead zones" undoubtedly occur in each cell
due to the unnecessarily short distance between inlet and outlet. These dead
zones result in decreased hydraulic detention and increased effective organic
loading rate.
2.4.1.4 Nitrogen Removal
a. Theoretical Considerations
Differences between influent and effluent .nitrogen concentration in
facultative stabilization ponds occur principally through the following
processes:
1. Gaseous ammonia stripping to the atmosphere
2. Ammonia assimilation in algal biomass
3. Nitrate assimilation in algal and other plant biomass
4. Biological nitrification-denitrification
33
-------
TABLE 2-2
SUMMARY OF DESIGN AND PERFORMANCE DATA—SELECTED FACULTATIVE PONDS
co
Organic Loading
Theoretical Hydraulic
Detention Time
Locati on
Peterborough, NH
Kilmidael, MS
Eudora, KS
Corinno, UT
Design
Standard
kg
39
56
38
453
Design
BOD5/ha/d
20
67h
43b
38
363
Actual
(1974-1975)
16
27a
I8b
19
34a
15b
Design
Standard
None
None
None
180
Design
days
57
79
47
180
Actual
107
214
231
70
88C
Months Effluent
Exceeded 30 mg/1 BODs
Oct/Feb/Mar/Apr '
Nov/Jul
Mar/Apr/Aug
None
aPrimary cell,
bEntire system.
cEstimated from dye study.
-------
The following design equations are based on equations describing the loss of
gaseous ammonia to the atmosphere; however, the design parameters also reflect
the influence of all processes associated with ammonia nitrogen removal. The
rate of gaseous ammonia losses to the atmosphere depends mainly on the pH
value, surface to volume ratio, temperature, and the mixing conditions in the
pond. Alkaline pH shifts the equilibrium equation NH3° + H20 £ NH4+ + OH~
toward gaseous ammonia production, while the mixing conditions affect the
magnitude of the mass transfer coefficient. Temperature affects both the
equilibrium constant and mass transfer coefficient.
Ammonia removal in ponds can be expressed by assuming a first order reaction
(19)(20). A conceptual development of the mathematical model is presented
elsewhere (21). The final design equations are given below:
For temperatures of 1°C to 20°C;
^e=__ 1 (2-11)
Co T +^ (0.0038 + 0.000134T)e(1-041 + 0-044T)(PH-6.6)
For temperatures of 21°C to 25"C:
^e= 1 (2-12)
co~ 1 ^(B.osBxio-V1-540^-6'6'
C0 = influent concentration of (NH. + NHg ), mg/1 as N
Ce = effluent concentration of (NH4 + NH3°), mg/1 as N
p
A = surface area of the pond, m
Q = flow rate, m /d
T = temperature, °C
35
-------
b. Pond Systems
• V' ?:ANr> •' ' :;. ' '
The stabilization pond systems located in Peterborough, NH; Eudora, KS; and
Corinne, UT, described earlier, are exposed to similar climatic conditions.
During the winter the water temperatures range between 1°C and 5°C (between
34°F and 41°F), and ice cover is experienced during the winter. During the
summertime the water temperature is approximately 20°C (68°F) and isgenerally
less than 25°C (77°F). The fourth' system at Kilmichael, MS, was excluded
from the analysis because of the different aeration systems and much milder
climate.
The characteristics of the wastewater entering these systems were signif-
icantly different, as shown in Table 2-3. The Eudora wastewater is a typical
medium-strength domestic wastewater; the Corinne wastewater is slightly
alkaline; and Peterborough has a neutral unbuffered wastewater. The pH value
in the ponds has a marked effect on ammonia-N removal. In the Corinne ponds
the pH values were above 9, while in the Peterborough system the pH value
during the summer was 6.7 to 7.4, which is low compared with other ponds.
c. Ammonia-N Removal
The annual average percentage nitrogen removals, calculated as ammonium
nitrogen, at the Eudora and Corinne facultative pond systems were about 95
percent, and at the Peterborough ponds it was about 46 percent. The major
removal occurred in the primary cells. Table 2-4 summarizes these results.
During the months of June through September, ammonia-N removal in the
Peterborough system reached 67 percent, while at Eudora ammonia-N removal was
almost 99 percent. In the winter period of December to March in the primary
cell of the Peterborough system, there was no ammonia-N removal, and in the
total system there was approximately 19 percent ammonia-N removal. In the
Eudora and Corinne systems, during this period, there was about 90 percent
ammonia-N removal with 53-62 percent removal occurring in the primary cells.
2.4.2 Aerated Ponds ;
i :
Results of intensive aerated porid performance studies of aerated ponds at
Bixby, OK; Pawnee, IL; North Sulfport, MS; Lake Koshkonong, WI; and Windber,
PA (22-26) are presented in this section. Data collection encompassed 12
months with four separate 30-consecutive-day, 24-hour composite sampling
periods, once each season.
36
-------
TABLE 2-3
INFLUENT WASTEWATER CHARACTERISTICS AT
SELECTED FACULTATIVE PONDS
Parameter
BOD, mg/1
COD, mg/1
NH4, mg/1
pH
Alkalinity, mg/1 as CaC
Peterborouqh
NH
138
271 .
21.5
7.0
03 107
TABLE 2-4
Eudora
KS
270
559
25.5
7.7
428
ANNUAL AVERAGE AMMONIA-NITROGEN REMOVAL
SELECTED FACULTATIVE PONDS
Parameter
NH4-N, mg/1
Influent
Cell #1 Effluent
Final Effluent
NH4-N Removal , percent
Cell #1
Total System
Theor. Detention Time,
Cell #1
Total System
Peterborough
NH
21.5
16.5
11.5
23.3
46.5
days
44
107
Eudora
KS
25.5
9.2
1.1
63.9
95.7
92
231
Corinne
UT
74
128
7.5
8.4
576
BY
Corinne
UT
7.5
1.4
0.2
81.3
97.3
29
70
37
-------
Aerated ponds are medium-depth, manmade basins designed for the biological
treatment of wastewater. A mechanical aeration device is used to supply
supplemental oxygen to the system; - Well-mixed aerated ponds are aerobic
throughout their entire depth. The mechanical aeration device may cause
turbulent mixing (i.e., surface aerator) or may produce laminar flow
conditions (diffused air systems). The five aerated ponds were considered to
be partial mix systems by the investigators, although data describing the
mixing characteristics were not collected.
The North Gulfport system contains surface aerators; the average depth of the
aerated cells is 1.9 m (6.3 ft). Diffused-aiir aeration systems are used in
the other ponds, and the average depth is 3.0 m (10 ft). The Bixby and North
Gulfport systems consist of two aerated cells in series and the others, three
cells in series. The aerated cells of the North Gulfport system are followed
by settling ponds and a chlorine contact pond. The operating conditions for
these systems and the influent wastewater characteristics entering these
systems were significantly different as shown in Tables 2-5 and 2-6.
2.4.2.1 Site Descriptions
i
a. Bixby, Oklahoma
A diagram of the Bixby, OK, system is shown in Figure 2-11 (22). The system
consists of two aerated cells with a total surface area of 2.3 ha (5.8 ac)
designed to treat 335 kg BOD5/d (737 Ib B0[>5/d) with a hydraulic loading
rate of 1,550 m3/d (0.4 mgd). The design organic loading rate on the first
cell is shown in Table 2-6. There is no chlorination facility at the site.
The design hydraulic retention time was 32 days.
b. Pawnee, Illinois
A diagram of the Pawnee, IL, system is shown in Figure 2-12 (23). The system
consists of three aerated cells in series with a total surface area of 4.45
ha (11.0 ac). The design flow rate 1,890 m3/d (0.5 mgd) with a design
organic load of 386 kg BOD5/d (850 Ib BOD5/d) and a design hydraulic
retention time of 60 days. The design organic loading rate on the first cell
is shown in Table 2-6. The facility is equipped with chlorination
disinfection and a slow sand filter for polishing the effluent. The filter
was removed following the study. Data reported below were collected prior to
the filters and represent only pond performance.
c. North Gulfport, Mississippi
i
A diagram of the North Gulfport, MS, system is shown in Figure 2-13 (24).
The system consists of two aerated cells in series with a total surface area
38
-------
TABLE 2-5
INFLUENT WASTEWATER CHARACTERISTICS AT
SELECTED AERATED PONDS
Parameter
BODg, mg/1
COD, mg/1
TKN, mg/1
NH4-N, mg/1
pH
Alkalinity, mg/
Pawnee
IL
473
1,026
51.4
26.32
6.8-7.4
1 242
Bixby
OK
368
653
45.0
29.58
6.1-7.1
154
Lake
Koshkonong
WI
85
196
15.3
10.04
1.2-1 A
397
Windber
PA
173
424
24.3
22.85
5.6-6.9
67
North
Gulf port
MS
178
338
26.5
15.7
6.7-7.5
144
as CaCOa
TABLE 2-6
DESIGN AND ACTUAL LOADING RATES AND DETENTION TIMES
FOR SELECTED AERATED PONDS
Organic Loading Rate on First Cell
Total System
Theor. Hydraulic
Detention Time
Location
Pawnee, 11
Bixby, OK
Lake Koshkonong, WI
Windber, PA
North Gulf port, MS
Design Actual
kg BOD5/ha/d
154a 150
284b 161
509b 87
497b 285
375C 486
Design
kg BOD5/1
5.8
12.0
20.2
18.6
19.3
Actual
,000 m3/d
5.6
6.7
3.6
9.8
25.1
Design Actual
days
60 144
32 108
30 73
30 48
26d 18
aEqualed or exceeded 7 of the 12 months monitored.
"Not exceeded.
cExceeded 11 of the 12 months monitored.
d Aerated cells only.
39
-------
FIGURE 2-11 I
SCHEMATIC FLOW DIAGRAM AND AERIAL PHOTOGRAPH OF THE AERATED
POND SYSTEM AT BIXBY, OKLAHOMA
Pump 1
Screen
Lift
station
Pump 2
Legend
I Influent
E Effluent
R Return Ref.
A Air
D Drain
Ep Plant Eff.
E1 Lagoon 1 Eff.
E2 Lagoon 2 Eff.
E° Overflow and emergency eff.
FM
I
I
I
I
Blower
house
j
i
i
i
E2
Cell No. 1
1.18 ha
A® J> A
I I
A| |A
<
R
Cell No. 2
1.18 ha
® ® D
«-
I
E1
E°
D^^
Ep
To river
40
-------
FIGURE 2-12
SCHEMATIC FLOW DIAGRAM AND AERIAL PHOTOGRAPH OF THE AERATED
POND SYSTEM AT PAWNEE, ILLINOIS
m
Cell No. 1
Baffle
2.5 ha
Cell No. 2
1 .3 ha
^
Cell No. 3
0.73 ha
1 Manhole
2 Wet well
3 Compressor house
4 Chlorine contact tank
A Sampling station (typical)
41
-------
FIGURE 2-13
SCHEMATIC FLOW DIAGRAM AND AERIAL PHOTOGRAPH OF THE AERATED
POND SYSTEM AT GULFPORT, MISSISSIPPI
15"dia.
4^ Flow monitoring station
/lA Sample monitoring station
(i) Aerator (HP)
=1 Weir Box
O Manhole
42
-------
a theoretical detention
it 1,890 nrVd (0.5 mgd)
of 2.5 ha (6.3 ac) followed by settling ponds with
time of five days. The system was designed to treat
with a total theoretical hydraulic retention time of 26 days.
organic loading rate on the first cell in the series is shown in
The system is equipped with a chlorination facility.
The desi<
Table 2-t
d. Lake Koshkonong, Wisconsin
A diagram of the Lake Koshkonong, WI, system is shown
The system consists of three aerated cells with a total
ha (6.9 ac) followed by chlori nation. The
mgd) with a design organic load of 463 kg
design hydraulic detention time of 30 days.
on the first cell is shown in Table 2-6.
in Figure 2-14 (25).
surface area of 2.8
design flow was 2270 m3/d (0.6
BODs/d (1,020 Ib BOD5/d) and a
The design organic loading rate
e. Windber, Pennsylvania
The Windber, PA, system consists of three cells in series with a total
surface area of 8.4 ha (20.7 ac) followed by chlori nation (Figure 2-15)
(26). The design flow rate was 7,576 m3/d (2.0 mgd) with a design organic
load of approximately 1,540 kg BOD5/d (3,400 Ib BOD5/d). The design
organic loading rate on the first cell is shown in Table 2-6. The design
mean hydraulic residence time was 30 days for the three cells operating in
series.
2.4.2.2 Performance
a.
Removal
The monthly average effluent BODs concentrations for the
described aerated pond systems are presented in Figure 2-16.
five previously
In general, all of the systems, except the Bixby, OK, system, were capable of
producing monthly average effluent BODs concentrations of less than
30 mg/1. Monthly average effluent BODs concentrations appear to be inde-
pendent of influent BODs concentration fluctuations and not significantly
affected by seasonal variations in temperature.
Monthly average influent BODs concentrations at Bixby, OK, ranged from
212 mg/1 to 504 mg/1 with a mean of 388 mg/1 during the study period
reported. The design influent BODs concentration was 240 mg/1, or only 62
percent of the actual influent concentration. The mean flow rate during the
period of study was 520 m3/d (0.12 mgd), which is less than one-third of
43
-------
FIGURE 2-14
SCHEMATIC FLOW DIAGRAM AND AERIAL PHOTOGRAPH OF THE AERATED
POND SYSTEM AT LAKE KOSHKONONG, WISCONSIN
»V r^"]
0 l_ — I
Comminutor and
pumping station
By-pass -
Drainage ditch
to Rock River
1370L.F. 12" Outfall
By-pass -
T — r- 3000 L.F. 12" Force main
f——' ;
Chlorinators
Cell No. 1 I
0.91 ha !
• 4
tell No. 2
0.91 ha
Cell No. 3
0.91 ha
44
-------
FIGURE 2-15
SCHEMATIC FLOW DIAGRAM AND AERIAL PHOTOGRAPH OF THE AERATED
POND SYSTEM AT WINDBER, PENNSYLVANIA
Highland
trunk line
Baffle
45 cm Outfall
60cm
Outfall
Recirculation
.line 10% of
flow
30 cm Gravity flow
• i .•
Pump line
Cell No. 1 Drain
Cell No. 2 By Pass
A Sampling Site No. 1 (Plant Influent)
B Sampling Site No. 2 (Cell No. 1 Effluent)
C Cell No. 2 Effluent
D Cell No. 3 Effluent
E Plant Effluent (After Chlorination)
Manhole
Parshall flume
Grinder & Screen
Grit removal unit
45
-------
FIGURE'2-16
AERATED POND BOD5 EFFLUENT CONCENTRATIONS
cr>
100
90
^ 80
o>
£
to
Q
O
m
c
Q)
_3
UJ
O)
(D
<5
70
60
50
40
30
| 20
o
10
0
l
i
1
1
Pawnee, Illinois
Gulfport, Mississippi
Bixby, Oklahoma
— Windber, Pennsylvania
— Lake Koshkonong, Wisconsin
..... A..
' -A
.-DN
ON DJ FMAMJ J
1975 • 1976
A S 0 N D J F
1976-1977
-------
the design flow rate. The Bi'xby system was designed to treat 336 kg BODs/d
(740 Ib BOD5/d), and apparently a load of only 203 kg BOD5/d (446 Ib
BODs/d) was entering the lagoon. The only major difference between the
Bixby and other aerated lagoons is the number "of cells. Bixby has only two
cells in series. Based upon the results of studies with facultative ponds
which show improved performance with an increase in cell number, this
difference in configuration could account for the relatively poor performance
by the Bixby system. However, there are other possible explanations, i.e.,
operating procedures and short circuiting.
The results of these studies indicate that partial mix aerated ponds which
are properly designed, operated, and maintained can consistently produce an
effluent BOD5 concentration of less than 30 mg/1 . In addition, effluent
quality is not seriously affected by seasonal climate variations.
b. Suspended Solids Removal
The monthly average effluent SS concentrations for each system are presented
in Figure 2-17. With the exception of the Bixby system, the ponds produced
relatively constant effluent SS concentrations throughout the entire year.
Mean monthly effluent SS concentrations ranged from 2 mg/1 at Windber, PA, in
November 1975, to 96 mg/1 at Bixby, OK, in June 1976. The mean monthly
effluent SS concentration for the Windber, PA, site never exceeded 30 mg/1
throughout the entire study period and, at Pawnee, IL, and Lake Koshkonong,
WI, only exceeded 30 mg/1 during one of the months reported.
The results of these studies indicate that aerated pond effluent SS
concentrations are variable. However, a well -designed, operated, and
maintained aerated pond can produce final effluents with low SS concentra-
tions.
c. Fecal Col i form Removal
Only two monthly geometric mean fecal col i form values were available for
Bixby, OK. The monthly geometric mean effluent fecal coliform concentrations
compared to a concentration of 200 organisms/100 ml for all five systems are
illustrated in Figure 2-18.
All of the aerated pond systems except Bixby, OK, have chlorine disinfec-
tion. These data show that aerated pond effluent can be disinfected. In
general, the Windber PA, and the Pawnee, IL, systems produced final effluent
monthly geometric mean fecal coliform concentrations of less than 200
organisms/100 ml. The nonchlorinated Bixby, OK, effluent had a high fecal
coliform concentration. The Gulfport, MS, system produced an effluent
containing more than 200 fecal coliforms/100 ml most of the time, but the
fecal col i forms were measured in effluent samples from a holding pond
47
-------
FIGURE 2-17
AERATED POND SS EFFLUENT CONCENTRATIONS
100
00
Pawnee, Illinois
Gulf port, Mississippi
••• Bixby, Oklahpma
— Windber, Pennsylvania
— Lake Koshkonong, Wisconsin
N D J F
1975. 1976
M
M
N D J F M
1976.1977
-------
FIGURE 2-18
AERATED POND FECAL COLIFORM EFFLUENT CONCENTRATIONS
4s.
105
15 104
o
0)
103
C'Z
(0 .
0) C
S-,2-
4~t
U CO
1-5
E o
o c
0) o
c±:
fg
102
101
10°
0
0
Pawnee,.-ll. (No CL2)
Pawnee, Illinois (CLa)
Gulfport, Mississippi
Windber, Pennsylvania (No CL2)
Windber, Pennsylvania (CL2)
i j i i r r i i r^
—,..j? Lake Koshkonong, Wisconsin (No CL2)
• — Lake Koshkorjpng, Wisconsin (CL2)
Bixby, Oklahoma (No CL2)
N D J F
1975. 1976
O
N D J F M
1976 . 1977
-------
with a long detention time following the addition of the chlorine.
Aftergrowth of the fecal col iform probably accounted for the high
concentrations. Aerated pond systems are capable of producing effluents
containing less than 200 fecal col iforms/100 ml without disinfection.
d. Summary
From the performance data currently available, it appears that (1) aerated
ponds can produce an effluent BODs concentration of less than 30 mg/1, (2)
aerated pond SS concentrations are relatively stable throughout the year, and
(3) an aerated pond effluent can be produced containing less than 200 fecal
coliforms/100 ml.
2.4.2.3 Design Criteria
Most partial and complete mix aerated ponds have been designed using a
complete mix hydraulic model and pseudo-first order removal rates. The
Ten-State Standards (27), which is the basis for the majority of the states'
standards, recommend that a complete mix formula be used. The U.S. Army
Corps of Engineers has designed most of its aerated ponds using the complete
mix formula. Results presented in the Appendix indicate that this formula
does not give the best fit of the performance data for the five selected
partial mix aerated pond systems discussed above.
A plug flow-first order kinetic model best described the performance of these
five partial mix aerated ponds. Use of the plug flow model is illustrated in
a design example in Chapter 3.
Performance data were not collected for complete mix aerated ponds, but
experience has shown that when adequate mixing is applied, the complete mix
hydraulic model and pseudo-first order kinetics can be used for design. A
design example based on the complete mix model is presented in Chapter 3 (28).
The development and analyses of the complete mix, plug flow, and other models
used to design aerated ponds are presented in the Appendix. Environmental
conditions have a significant effect on the design of aerated ponds. Some of
the effects of environmental factors were discussed earlier in this chapter,
and others are discussed in Chapter 3 and in the Appendix.
2.4.2.4 Nitrogen Removal
a. Theoretical Considerations
Ammonia nitrogen exists in aqueous solutions as ammonia or ammonium ions. At
a pH value of 8.0, approximately 95 percent of the nitrogen is in the form of
50
-------
ammonium ion. Therefore, in biological systems such as aerated ponds where
the pH values are usually less than 8.0, the majority of the ammonia nitrogen
is in the form of ammonium ion.
Total Kjeldahl nitrogen (TKN) is composed of the ammonia, ammonium, and
organic nitrogen. Organic nitrogen is a potential source of ammonia and
ammonium nitrogen because of the deamination reactions during the metabolism
of organic matter in wastewater.
TKN reduction in aerated ponds can occur through several processes:
1. Gaseous ammonia stripping to the atmosphere
2. Ammonium assimilation in biomass
3. Biological nitrification
4. Biological denitrification
5. Sedimentation of insoluble organic nitrogen
6. Nitrate assimilation
Table 2-7 contains a summary of selected equations developed by Middlebrooks
and Pano (29) to predict ammonia nitrogen and TKN removal in diffused-air
aerated ponds. All of the equations have a common data base; however, the
data were used differently to develop several of the equations. The "System"
column in Table 2-7 describes the cell or series of cells that were used to
develop the equation. The description "Cells 1, 2, and 3" indicates that the
influent concentrations of TKN or ammonia nitrogen were used in conjunction
with the effluents from the first cell, second cell, and third cell in series
to estimate the removal or detention time necessary to achieve the measured
removal. The description "Total System" indicates that only the influent and
final effluent from the system were used to develop the equations. The
description "All Data" indicates that all possible combinations of the system
were used. In this combination, the results developed under "Cells "1, 2,
and 3," as well as the results developed from the intermediate cells, are
incorporated. For example, the ammonia nitrogen concentration in the
effluent from the first cell of the pond system would be considered the
influent to the second cell, and this influent concentration and the effluent
from the second cell would then be used in the formulas to calculate the
detention time or removal rates. These combinations of data were analyzed
statistically, and the equations presented in Table 2-7 were selected based
upon the best statistical fit of these data for the various combinations that
were tried. Therefore, although the combinations of data are not directly
comparable, the comparison presented in Table 2-7 does take into account the
best statistical fit of the data.
All of the relationships for TKN removal are statistically significant at
levels higher than one percent. Because of the small difference in detention
51
-------
en
TABLE 2-7
COMPARISON OF VARIOUS EQUATIONS DEVELOPED TO PREDICT AMMONIA NITROGEN AND TKN REMOVAL IN
DIFFUSED-AIR AERATED PONDS (48)
Hydraulic
Equation Used to Estimate Correlation Detention
Detention Time Coefficient Time
(Days)
TKN Removal
% TKN Removal » 130-2,324 (Hydraulic Loading Rate)
% TKN Removal = 137-6,511 (I/Detention Time)
In Ce/CQ » -0.0129 (Detention Time)
TKN Removal Rate * 0.809 (Loading Rate)
TKN Removal Rate * 0.0946 (BODg Loading Rate)
TKN Fraction Removed = 0.0062 (Detention Time)
Ammonia-N Removal
% NH4-N Removal = 139-2,498 (Hydraulic Loading Rate)
% NH4-N Removal = 147-7,032 (I/Detention Time)
In Ce/C0 = -0.0205 (Detention Time)
NH4-N Removal Rate = 0.869 (Loading Rate)
NH4-N Removal Rate = 0.0606 (BOD5 Loading Rate)
NH4-N Fraction Removed = 0.0066 (Detention Time)
0.998
0.993
0.911
0.983
0.967
0.959
0.996
0.995
0.798
0.968
0.932
0.936
142
114
125
132
113
129
129
105
79
92
132
121
Compari son
with Max
Detention
Time (% Dif
0
19
12
7
20
9
2
20
40
30
0
8
System
Total System--
Mean Annual Data
Total System-
Mean Annual Data
Cell 1, 2, and 3—
Mean Monthly Data
Total System--
Mean Monthly Data
Total System-
Mean Monthly Data
Cells 1, 2, and 3—
Mean Monthly Data
Total System-
Mean Annual Data
Total System--
Mean Annual Data
All Data-
Mean Monthly Data
Total System--
Mean Monthly Data
Total System--
Mean Monthly Data
Cells 1, 2, and 3-
Mean Monthly Data
; Detention Time = days; Loading Rate =-g/m3/d; BODs * g/m3/d; Removal
Rate - g/m3/d; C« = Effluent TKN or Ammonia-N concentration, mg/1 ; C0 = Influent TKN or Ammonia-N
Hydraulic Loading Rate «
; C«
concentration, mg/1.
-------
times calculated using all of the expressions, there is a good basis to apply
any of the relationships in design of ponds to estimate TKN removal. Using
the mean annual data for diffused-air aerated ponds yields a more
conservative design when employing the hydraulic loading rate relationship.
However, the values obtained using the reciprocal of the detention time
relationship yields a value slightly lower than that recommended by the
majority of the other expressions. In view of the error that might be
introduced by taking annual means, the results based upon the mean annual
data are in excellent agreement with the results obtained using the mean
monthly data. Using any of the above expressions will result in a good
estimate of the TKN removal that is likely to occur in diffused-air aerated
ponds.
The relationships developed to predict ammonia nitrogen removal yielded
highly significant (1 percent level) relationships for all of the equations
presented in Table 2-7. However, the agreement between the calculated
detention times for ammonia nitrogen removal differed significantly from that
observed for the TKN data. This variation is not surprising in view of the
many mechanisms involved in ammonia nitrogen production and removal in waste-
water ponds, but this variation in results does complicate the use of the
equations to estimate ammonia nitrogen removal in aerated ponds. Sta-
tistically, a justification exists to use either of the expressions in Table
2-7 to calculate the detention time required to achieve a given percentage
reduction in ammonia nitrogen.
2.5 Disinfection
2.5.1 Introduction
Since chlorine, at present, is less expensive and offers more flexibility
than other means of disinfection, chlorination is the most practical method
of disinfection. Basic principles of chlorination are presented elsewhere
(7M29H39).
2.5.2 Effects of Chlorinating Pond Effluents
White (31) suggested that chlorine demand increases with high concentrations
of algae commonly found in pond effluents. A chlorine dose of 20-30 mg/1 was
required to satisify chlorine demand and to produce enough residual to
effectively disinfect algae-laden wastewater within 30-45 minutes. Kott (32)
reported increases in demand as a result of algae, but found that a chlorine
dose of 8 mg/1 was sufficient to produce adequate disinfection within 30
minutes. If contact times are kept relatively short, no serious chlorine
demand by algae cells is encountered (32). For pond effluents, a chlorine
demand of only 2.6 to 3.0 mg/1 was exerted after 20 minutes of contact (33).
53
-------
At low chlorine doses, very little increase in chlorine demand is attri-
butable to algae, but at higher doses, the destruction of algal cells greatly
increases demand (34). This occurs because dissolved organic compounds
released from destroyed algal cells are oxidized by chlorine and thus
increase chlorine demand (35).
Another concern regarding the chlorination of pond effluents are the effects
on BOD and COD. Conflicting results have been reported (32-37), indicating
that either an increase or decrease in BOD and COD occurred with increased
chlorine concentrations. A conclusion would be that the effect of
chlorination on BOD and COD is a function of wastewater characteristics,
chlorine application methods and contact time, and other undefined parameters.
The formation of toxic chloramines is also of concern in chlorinating pond
effluents. These compounds are found in waters high in ammonium nitrogen
concentration and are extremely toxic to aquatic life found in receiving
water. For example, a chloramine concentration of 0.06 mg/1 is lethal to
trout (38).
Not all of the side effects of chlorination pond effluents are detrimental.
Kott (39) observed reductions of SS as a result of chlorination. Reductions
of volatile suspended solids (VSS) by as much as 52 percent and improved
water clarity (reduced turbidity) by 32 percent were observed following
chlorination (33). Chlorine may enhance the flocculation of algae masses by
causing algal cells to clump together (35).
Four systems of identically designed chlorine mixing and contact tanks, each
capable of treating 190 m3/d (50,000 gpd), were used to study the
chlorination of pond effluents (40). Three of the four chlorination systems
were used for directly treating the pond effluent. The effluent treated in
the fourth system was filtered through an intermittent sand filter to remove
algae prior to chlorination. The filtered effluent was also used as the
solution water for all four chlorination systems.
Following recommendations of others (41-45), the chlorination systems were
constructed to provide rapid initial mixing followed by chlorine contact in
plug flow reactors. A serpentine flow configuration having a length to width
ratio of 25:1, coupled with inlet and outlet baffles, was used to enhance
plug flow hydraulic performance. The maximum theoretical detention time for
each tank was 60 minutes, while the maximum actual detention time averaged
about 50 minutes.
The pond effluent was chlorinated at doses ranging from 0.25 to 30.0 mg/1
under a variety of contact times, temperatures, and seasonal effluent
conditions from August 1975 to August 1976. Some of the major findings of
this study are summarized below.
"- • i
1. Sulfide, produced as a result of anaerobic conditions in the ponds
during winter months when the ponds are frozen over, exerts a significant
54
-------
chlorine demand (Figure 2-19). For sulfide concentrations of 1.0 to
1.8mg/l, a chlorine dose of 6 to 7 mg/1 was required to produce the same
residual as a chlorine dose of about 1 mg/1 for conditions with no sulfide.
FIGURE 2-19
CHLORINE DOSE vs. RESIDUAL FOR INITIAL SULFIDE
CONCENTRATIONS OF 1.0-1.8 mg/1
15
0>
0)
DC
0)
o
. Residual = 1.552 + 0.346 (dose)
r = 0.956
0
10 15
Chlorine Dose, mg/l
2. For all concentrations of ammonia encountered, adequate disinfection
could be obtained with combined chlorine residual in 50 minutes or less of
contact time. Therefore, breakpoint chlorination, and the subsequent
production of free chlorine residual, was rarely, if ever, necessary in
disinfecting pond effluent.
3. Total COD concentration in a pond effluent was virtually unaffected by
chlorination. Soluble COD increased with increasing concentrations of free
chlorine only. This increase was attributed to the oxidation of SS by free
chlorine. Increases in soluble COD vs. free chlorine residual are shown in
Figure 2-20.
55
-------
FIGURE 2-20
CHANGES IN SOLUBLE COD vs. FREE CHLORINE RESIDUAL -
UNFILTERED POND EFFLUENT
30
24
18
12
I 6
8
o
0
-6
-12
-18
-24
-30
• o
r •
I
Y = 4.692 X -2.948
r = 0.547
I
0
234
Free Chlorine Residual, mg/l
4. Some reduction in SS, due to the breakdown and oxidation, of suspended
particulates, and resulting increases in turbidity were attributed to
chlorination. However, this reduction was of limited importance when
compared with reductions of SS resulting from settling. SS were reduced by
10 to 50 percent by settling in the contact tanks.
5. Filtered pond effluent exerted a lower chlorine demand than unfiltered
pond effluent, due to the removal of algae (Figure 2-21). The rate of
exertion of chlorine demand was directly related to chlorine dose and total
chemical oxygen demand.
6. A summary of total coliform removal efficiencies as a function of a
total chlorine residual for filtered and unfiltered effluent is illustrated
in Figure 2-22. The rate of disinfection was a function of the chlorine dose
56
-------
FIGURE 2-21
CHLORINE DOSE vs. TOTAL RESIDUAL - FILTERED AND
UNFILTERED POND EFFLUENT
Tj
'55
0>
OC
0)
I
o
15
10
0
15
3 10
0)
oc
03
•6
I
o
—— 17.3 Min Contact Time, r = 0.933
— —i 35.0 Min Contact Time, r = 0.933
.. — 49.6 Min Contact Time, r = 0.932
Y = 0.534 X + 0.062
Y = 0.505 X + 0.007
Y = 0.479 X+0.010
10
15
20
Applied Chlorine Dose, mg/l
(a) Filtered Effluent
Y = 0.507 X +0.139
Y = 0.481 X + 0.098
Y=^ 0.460 X +0,076
17.3 Min Contact Time, r = 0.847
• — 35.0 Min Contact Time, r = 0.833
— • 49.6 Min Contact Time, r = 0.822
I I I
6
12
18
24
30
Applied Chlorine Dose, mg/l
(b) Unfiltered Effluent
57
-------
FIGURE 2-22
TOTAL COLIFORM REMOVAL EFFICIENCIES - FILTERED AND
UNFILTERED POND EFFLUENT
0.0
-1
-2
a, -3
-4,
-5
o
0,0
-1.0
-2.0
-3.0
-4.0
-5.0
17.5 Min. Contsict Time, r = 0.922
— — 35.0 Min. Contact Time, r = 0.939
49.6 Min. Contsict Time, r = 0.908
Y==-1.139x
Y==-1.807x
Y==-2.161x
1
4
Total Chlorine Residual, mg/l
(a) Filtered Effluent
17.5 Min. Contact time, r = 0.876
35.0 Min. Contact Time, r = 0,843
49.6 Min, Contact Time, r = 0.823 .
Y = -0.726x
Y = -0.992x
Y=,-1.098*
8
10
Total Chlorine ResiduEil, mg/l
(b) Unfiltered Effluent
58
-------
and bacterial concentration. Generally, the chlorine demand was about 50
percent of the applied chlorine dose except during periods of sulfide
production.
7. Disinfection efficiency was temperature dependent. At colder tempera-
tures, the reduction in the rate of disinfection was partially offset by
reductions in the exertion of chlorine demand; however, the net effect was a
reduction in the chlorine residual necessary to achieve adequate disinfection
with increasing temperature for a specific contact period.
8. In almost all cases, adequate disinfection was obtained with combined
chlorine residuals of between 0.5 and l.Omg/1 after a contact period of
approximately 50 minutes. This indicated that disinfection can be achieved
without discharging excessive concentrations of toxic chlorine residuals into
receiving waters.
2.5.3 Predicting Required Residuals
Using the data from the study summarized in section 2.5.2, Johnson et al.
(40) developed a model to predict the chlorine residual required to obtain a
specified bacterial kill. The model was used to construct a series of design
curves for selecting chlorine doses and contact times for achieving desired
levels of disinfection. An example may best illustrate how these design
curves are applied.
Assume that a particular lagoon effluent is characterized as having a fecal
coliform (FC) concentration of 10,000/100 ml, 0 mg/1 sulfide, 20 mg/1 TCOD,
and a temperature of 5°C. If it is necessary to reduce the FC counts to MPN
of 100/100 ml, or a 99 percent bacterial reduction, and an existing chlorine
contact chamber has an average residence time of 30 minutes, the required
chlorine residual is obtained from Figure 2-23. A 99 percent bacterial
reduction corresponds to log (Ng/N) equal to 2.0. For a contact period of
30 minutes, a combined chlorine residual of 1.3 mg/1 is required. This is
indicated by Point 1 in Figure 2-23.
Going to Figure 2-24, it is determined that if a chlorine dose produces a
residual of 1.30 mg/1 at 5°C, the same dose would produce a residual of
0.95 mg/1 at 20°C. This is because of the faster rate of reaction between
TCOD and chlorine at the higher temperature. This is indicated by Point 2 in
Figure 2-24. For an equivalent chlorine residual of 0.95 mg/1 at 20°C and
20 mg/1 TCOD, it is determined from Figure 2-25 that the same chlorine dose
would produce a residual of 0.80 mg/1 if the TCOD were 60 mg/1. This is
because higher concentrations of TCOD increase the rate of chlorine demand.
Points on Figure 2-25 corresponds to this residual. The chlorine dose
required to produce an equivalent residual of 0.80 mg/1 at 20°C and 60 mg/1
TCOD is determined from Figure 2-26. For a chlorine contact period of 30
minutes, a chlorine dose of 2.15 mg/1 is necessary to produce the desired
combined residual as indicated by Point 4 on Figure 2-26. This dose will
produce a reduction in FC from 10,000/100 ml to 100/100 ml within 30 min at
5°C and with 20 mg/1 TCOD.
59
-------
FIGURE 2-23
COMBINED CHLORINE RESIDUAL AT 5°C FOR COLIFORM = 104/100 ml
5.0
4.0
3.0
2.0
1.0
No. Fecal= 10V100 ml
No. Total = 10V100ml
Fecal Coliform
Total Coliform
Combined Chlorine Residual 1.5 mg/l
f
/ 1.5mg/^T
60
60
-------
FIGURE 2-24
CONVERSION OF COMBINED CHLORINE RESIDUAL AT TEMP. 1
TO EQUIVALENT RESIDUAL AT 20°C
3.5 r-
0.5
1.0 1.5 2.0 2.5 3.0
Combined Chlorine Residual at Temp. 1, mg/l
4.0
4.5
61
-------
FIGURE 2-25
CONVERSION OF COMBINED CHLORINE RESIDUAL AT TCOD 1 AND 20°C
TO EQUIVALENT RESIDUAL AT TCOD = 60 mg/1 AND 20°C
3.5 l-
01
ro
0.5
1.0 1.5 2,0 2.5 3.0 3.5
Combined Chlorine Residual at TCOD 1 and 20°C, mg/l
4.0
-------
FIGURE 2-26
DETERMINATION OF CHLORINE DOSE REQUIRED FOR EQUIVALENT
COMBINED RESIDUAL AT TCOD = 60 mg/1 AND 20°C
5.0 i-
4.0 -
O)
"(5
3
T3
°35
0>
tr
<0
_0
o
T3
0>
c
3
o
o
3.0
2.0
1.0
Chlorine Dose = 10.0 mg/l
10
20
Chlorine Dose = 7.0 mg/l
Chlorine Dose = 5.0 mg/l
Chlorine Dose = 3.0 mg/l
I
30 40
Time, min
50
60
63
-------
If, in the previous example, the initial sulfide concentration were 1.0 mg/1
instead of 0 mg/1, it would be necessary to go directly from Figure 2-23 to
Figure 2-27. Here, chlorine residual of 1.30 mg/1 at the TCOD of 20 mg/1 and
a temperature of 5°C is converted to an equivalent chlorine residual of
1.10 mg/1 for a TCOD of 60 mg/1 and 5°C. This is represented by Point 5 on
Figure 2-27. Going to Figure 2-28, which corresponds to an initial sulfide
concentration of 1.0 mg/1, it is determined that a chlorine dose of 6.6 mg/1
is necessary to produce an equivalent chlorine residual of 1.1 mg/1 after a
contact period of 30 min. Point 6 on Figure 2-28 corresponds to this dose.
The sulfide remaining after chlorination is determined to be 0.4 mg/1 from
Figure 2-29 as indicated by Point 7.
2.5.4
The primary objective of good chlorine contact tank design is to design for
hydraulic performance which will allow for a minimum usage of chlorine with a
maximum exposure of microorganisms to the chlorine. An evaluation of a
number of chlorine contact tanks indicates that mixing, detention time, and
chlorine dosage are the critical factors to consider in providing adequate
disinfection. Good design not only optimizes; disinfection efficiency, but
should also minimize the concentration of undesirable compounds being
discharged to the environment and reduce the accumulation of solids in the
tank by keeping the flow-through velocity high enough to prevent solids from
settling (46). A discussion of chlorine contact chamber hydraulic character-
istics is presented elsewhere (9)(30). Table 2-8 presents a summary of
chlorination design criteria.
2.6 Odor Control
2.6.1 Introduction
Odors are. usually created at wastewater ponds because they are overloaded,
excessive surface scum has been allowed to accumulate, or aquatic and pond
slope weeds are completely uncontrolled. All three of these causes can be
eliminated by adequate design, including design features for effective
operation and maintenance.
2.6.2 Overloading
Process design considerations are discussed in Chapter 3. Careful design
which incorporates the requirements set forth in that chapter should
eliminate pond overloading. These requirements include (1) selection of
loading criteria applicable to the influent loads and the operational
limitations created by local land use and climatic conditions, and (2) design
of a layout which assures the effective utilization of all pond volume. Dead
areas which do not maintain adequate circulation or flow must be eliminated.
64 i
-------
FIGURE 2-27
CONVERSION OF COMBINED CHLORINE RESIDUAL AT TCOD 1 AND 5°C
TO EQUIVALENT RESIDUAL AT TCOD = 60 mg/1 AND 5°C
3.5 r-
Ol
01
la
T3
'
-------
FIGURE 2-28
DETERMINATION OF CHLORINE DOSE REQUIRED WHEN S = 1.0 mg/1,
TCOD = 60 mg/1, AND TEMP. = 5°C
4.0 r-
-------
FIGURE 2-29
SULFIDE REDUCTION AS A FUNCTION OF CHLORINE DOSE
0—o.
Limit of detectability
J_
J_
8 10 12
Chlorine Dose, mg/l
14
16
18
20
-------
TABLE 2-8 .
SUMMARY .OF CHLORINATION DESIGN CRITERIA
Mixing
I. Rapid initial mixing should:be accomplished within 5 sec and before
liquid enters contact tank. Design hydraulic residence time >^ 30
sec for tanks using mechanical mixers,; ,
II. Methods available
1. Hydraulic jump in open channels;.
2. Mechanical mixers located immediately below point of chlorine
application.
3. Turbulent flow in a restricted reactor.
4. Pipe flowing full. Least efficient and should not be used in
pipes with diameter > 7.6 cm (> 30 in).
Contact Chamber ;
I. Hydraulic residence time v • •• . .
1. j> 60 minutes at average flow rate.
2. ^ 30 minutes at peak hourly flow rate.
II. Hydraulic performance
1. Model value obtained in dye studies ^0.6, tp/T > 0<6.
2. Efficiency of disinfection increases as tp/T increases.
3. Design for maximum economical tp/T. ;
III. Length to width ratio ;
1. L/W _> 25:1. .
2. Cross-baffles used to eliminate short circuiting caused by
wind. .-•-.-
IV. Solids removal
1. Baffles arranged to remove floating solids. '•
2. Provide drain to remove solids and liquid for maintenance.
3. Provide duplicate contact chambers.
4. Width between channels should be adequate for easy access to
clean and maintain chamber.
V. Storage of chlorine
1. Provide a minimum of one filled chlorine cylinder for each
one in service.
2. Maintain storage area at a temperature > 13°C (>_ 55°F).
3. Never locate cylinders in direct sunTight or apply direct
heat.
tp «= Time for tracer at outlet of contact tank to reach peak concentration.
T * Volume of contact tank/flow rate = theoretical detention time.
L - Length of contact tank.
W s Width of contact tank.
68
-------
TABLE 2-8 (continued)
VIII,
IX.
6.
7.
8.
Limit maximum withdrawal 'rite* from 45-
150-lb) cylinders to 18 kg/d (40 Ib/d).
Limit maximum withdrawal rate from
cylinders to 182 kg/d (400 Ib/d).
Provide scales to weigh cylinders.
Provide cylinder handling equipment.
Install automatic switchover sytem.
and 68-kg (100- and
909-kg (2,000-lb)
VI. Piping and valves
1. Use Chlorine Institute approved piping and valves.
2. Supply piping between cylinder and chlorinator should be Sc.
80 black seamless steel pipe with 2,000-lb forged steel
fitting. Unions should be ammonia type with lead gaskets.
3. Chlorine solution lines should be Sc. 80 PVC, rubbeHined
steel, Saran-lined steel, or fiber cast pipe approved for
moist chlorine use. Valves should be PVC, rubber lined, or
PVC lined. ,
4. Injector line between chlorinator and injector should be Sc.
80 PVC or fiber cast approved for moist chlorine use.
VII. Chlorinators
1.
2.
Should be sized to provide dosage _> 10 mg/1.
Maximum feed rate should be determined from knowledge of
local
should be used only in small
conditions.
Direct feed gas chlorinators
installations. Check state
certain states.
Vacuum feed gas chlorinators
much safer.
Hypochlorite solutions should
where safety is major concern.
used
regulations.
in
Prohibited
are most widely used and are
be considered in installations
Safety equipment and training
1. Install an exhaust fan near floor level with switch actuated
when door is opened.
2. Exhaust fan should be capable of one air exchange per minute.
3. Gas mask located outside chlorination room.
4. Emergency chlorine container repair kits. .
5. Chlorine leak detector.
6. Alarms should be installed to alert operator when
deficiencies or hazardous conditions exist. ;
7. Operator should receive detailed hands-on training with all
emergency equipment.
Diffusers ,.
1. Minimum velocity through diffuser holes > 3-4 m/sec (> 10-12
ft/sec). / L
2. Diffusers should be installed for convenient removal,
cleaning, and replacement.
69
-------
Whenever possible, influent loadings should be shared with other cells by
means of forced recirculation. Mechanical aeration should be used to supple-
ment natural photosynthesis whenever conservative loading rates cannot be
applied. The intermittent operation of an influent cell mechanical aeration
unit can often be adjusted to compensate for conditions which could not be
anticipated during design. Its availability can then be an excellent tool to
eliminate odors. Temporary relief from odors can be obtained by applying
sodium nitrate to the pond influent on spreading over the surface. Details
on the application of sodium nitrate, other chemicals, and other methods of
odor control are presented in Reference (47).
2.6.3 Scum Accumulation
Scum often accumulates on pond surfaces from debris which enters from the
influent sewer, dead or decaying algae which remains buoyant, and debris
which enters from surrounding areas. Such surface scum often decomposes
without sinking if the surface is quiescent or the scum attaches itself to
riprap, floating debris, or aquatic growth. Small clumps of scum, spread
over a fairly large surface, will not usually create sufficient odor levels
to be an offsite nuisance.
One effective way of eliminating stabilization pond scum buildup is by
providing a means of mechanical agitation. Another means of eliminating scum
accumulation is through the use of recirculation. The Sunnyvale, CA,
secondary oxidation ponds have been receiving a major portion of that plant's
stabilized sludge over the past several years (48). The pond recirculating
system is designed to maintain mixing throughout, and the pond has never
experienced any significant scum accumulation in any of its supply and return
channels or cells.
2.6.4 Scum Attachment
One of the most significant effects of aquatic plants is their ability to
support scum accumulations. If a pond were heavily loaded, the resulting
scum would certainly have no chance of dissipating, and odors would result.
Good housekeeping, which means control of aquatic weeds and berm weeds, is
essential to odor control. Raw wastewater poinds where scum accumulation is
expected should not have riprap which allows scum to accumulate in cracks and
crevices. A concrete or asphalt apron can be used to protect the embankment
where scum accumulation is expected.
70
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2.7 References
1. Lynch, J. M., and N. J. Poole. Microbial Ecology, A Conceptual
Approach. John Wiley & Sons, New York, NY, 1979. 266 pp.
2. Brockett, 0. D. Microbial Reactions in Facultative Ponds - I. The
Anaerobic Nature of Oxidation Pond Sediments. Water Research
10(l):45-49, 1976.
3. Gaudy, A. F., Jr., and E. T. Gaudy. Microbiology for Environmental
Scientists and Engineers. McGraw-Hill, New York, NY, 1980, 736 pp.
4. All rich, A. H. Use of Wastewater Stabilization Ponds in Two Different
Systems. JWPCF 39(6):965-977, 1967.
5. Pipes, W. 0., Jr. Basic Biology of Stabilization Ponds. Water and
Sewage Works 108(4):131-136, 1961.
6. Stanier, R. Y., M. Doudoroff, and E. A. Adelberg. The Microbial World.
2nd ed., Prentice-Hall, Englewood Cliffs, NJ, 1963. 753 pp.
7. Sawyer, C. N., and P. L. McCarty. Chemistry for Environmental
Engineering. 3rd ed., McGraw-Hill, New York, NY, 1978. 532 pp.
8. Process Design Manual for Nitrogen Control. EPA-625/1-75-007, U.S.
Environmental Protection Agency, Center for Environmental Research
Information, Cincinnati, OH, 1975.
9. Middlebrooks, E. J., C. H. Middlebrooks, J. H. Reynolds, G. Z. Watters,
S. C. Reed, and D. B. George. Wastewater Stabilization Lagoon Design,
Performance and Upgrading. Macmillan Publishing Co., Inc., New York,
NY, 1982.
10. Anderson, J. B., and H. P. Zweig. Biology of Waste Stabilization
Ponds. Southwest Water Works Journal 44(2):15-18, 1962.
11. Gloyna, E. F., J. F. Malina, Jr., and E. M. Davis. Ponds as a
Wastewater Treatment Alternative. Water Resources Symposium No. 9,
Center for Research in Water Resources, College of Engineering,
University of Texas, Austin, TX, 1976. 447 pp.
12. Oswald, W. J. Quality Management by Engineered Ponds. In: Engineering
Management of Water Quality, P. H. McGauhey. McGraw-HilTT New York, NY,
1968.
13. Assenzo, J. R., and G. W. Reid. Removing Nitrogen and Phosphorus by
Bio-Oxidation Ponds in Central Oklahoma. Water and Sewage Works
13(8):294-299, 1966.
71
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14. Performance Evaluation of Existing Lagoons-Peterborough, New Hampshire.
EPA-600/2-77-085, NTIS No. PB 272390, U.S. Environmental Protection
Agency, Municipal Environmental Research Laboratory, Cincinnati, OH,
1977. ;
15. Performance Evaluation of Kilmichael Lagoon. EPA-600/2-77-109, NTIS No.
PB 272927, U.S. Environmental Protection Agency, Municipal Environmental
Research Laboratory, Cincinnati, OH, 1977.
\
16. Performance Evaluation of an Existing Lagoon System at Eudora, Kansas.
EPA-600/2-77-167, NTIS No. PB 272653, U.S. Environmental Protection
Agency, Municipal Environmental Research Laboratory, Cincinnati, OH,
1977.
17. Performance Evaluation of an Existing Seven Cell Lagoon System.
EPA-600/2-77-086, NTIS No. PB 273533, U.S. Environmental Protection
Agency, Municipal Environmental Research Laboratory, Cincinnati, OH,
1977.
18. Canter, L. W., and A. J. Englande. States' Design Criteria for Waste
Stabilization Ponds. JWPCF 42(10):1840-1847, 1970.
19. Stratton, F. E. Ammonia Nitrogen Losses from Streams. J. Sam't. Eng.
Div., ASCE, SA6, 1968.
21. Pano, A., and E. J. Middlebrooks. Ammonia Nitrogen Removal in
Facultative Wastewater Stabilization Ponds. JWPCF 54(4):344-351, 1982.
22. Performance Evaluation of Existing Aerated Lagoon System at Bixby, OK.
EPA-600/2-79-014, NTIS No. PB 294742, Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, Cincinnati, OH, 1979.
23. Performance Evaluation of the Existing Three-Lagoon Wastewater Treatment
Plant at Pawnee, Illinois. EPA-600/2-79-043, NTIS No. PB 299740,
Municipal Environmental Research Laboratory, U.S. Environmental
Protection Agency, Cincinnati, OH, 1979.
24. Performance Evaluation of the Aerated Lagoon System at North Gulfport,
Mississippi. EPA-600/2-80-006, NTIS No. PB 80-187461, Municipal
Environmental Research Laboratory, U.S. Environmental Protection Agency,
Cincinnati, OH, 1980.
25. Performance Evaluation of Existing Aerated Lagoon System at Consolidated
Koshkonong Sanitary District, Edgerton, Wisconsin. EPA-600/2-79-182,
NTIS No. PB 80-189681, Municipal Environmental Research Laboratory, U.S.
Environmental Protection Agency, Cincinnati, OH, 1979.
26. Performance Evaluation of the Aerated Lagoon System at Windber,
Pennsylvania. EPA-600/2-78-023, NTIS No. PB 281368, Municipal
Environmental Research Laboratory, U.S. Environmental Protection Agency,
Cincinnati, OH, 1978.
72
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27. Recommended Standards for Sewage Works. A Report of the Committee of
Great Lakes-Upper Mississippi River Board of State Sanitary Engineers.
Health Education Services, Inc.,-Albany;- NY, 1978.
28. Metcalf & Eddy, Inc. Wastewater Engineering. McGraw-Hill, New York, NY,
..' 1979. -; .: .,. .*<::/.•< : . . - . . .'
29. Middlebrooks, E. J., and A. Pano. TKN and Ammonia Nitrogen Removal in
Aerated Lagoons. Report submitted to Center for Environmental Research
Information, U.S. Environmental Protection Agency, Cincinnati, OH, 1981.
30. White, G. C. Handbook of Chlorination. Van Nostrand Reinhold Co.,
1972. 744 pp.
31. White, GJ C. Disinfection Practices in the San Francisco Bay Area.
JWPCF 46(1) :89-l 01, 1973.
32. Kott, Y. Chlorination Dynamics in Wastewater Effluents. J. Sanit. Eng.
Div., ASCE 97(SA5):647-659, 1971.
33. Dinges, R. and A. Rust. Experimental Chlorination of Stabilization Pond
- Effluent. Public Works 100(3):98-101, 1969.
34. Brinkhead, C. E. and W. J. O'Brien. Lagoons and Oxidation Ponds. JWPCF
45(10):! 054-1059, 1973.
35. Echelberger, W. F., J. L. Pavom", P. C. Singer, and M. W. Tenney.
Disinfection of Algal Laden Waters. 0. Sanit. Eng. Div., ASCE
97(SA5):721-730, 1971.
36. Horn, L. W. Kinetics of Chlorine Disinfection in an Ecosystem. J. Sanit.
Eng. Div., ASCE 98(SA1):183-194, 1972.
37. Zaloum, R., and K. L. Murphy. Reduction of Oxygen Demand of Treated
Wastewater by Chlorination. JWPCF 46(12);2770-2777, 1974.
38. Zillich, J. A. Toxicity of Combined Chlorine Residuals to Fresh Water
Fish. JWPCF 44(2):212-220, 1972. ,
39. Kott, Y. Hazards Associated with the Use of Chlorinated Oxidation Pond
Effluents for Irrigation. Water Research 7:853-862, 1973.
t
40. Johnson, B. A., J. L. Wight, E. J. Middlebrooks, J. H. Reynolds, and
A.D. Venosa. Mathematical Model for the Disinfection ,of Waste
Stabilization Lagoon Effluent. JWPCF 51(8):2002-2015, 1978.
41. Collins, H. F., R. E. Selleck, and G. C. White. Problems in Obtaining
Adequate Sewage Disinfection* J. Sanit. Eng. Div., ASCE 97(SA5):
549-562, 1971.
42. Kothandaraman, V., and R. L. Evans. Hydraulic Model Studies of Chlorine
Contact Tanks. JWPCF 44(4):626-633, 1972.
73
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43. Kothandaraman, V., and R. L. Evans. Design and Performance of Chlorine
Contact Tanks. Circular 119, Illinois State Water Survey, Urbana, IL,
1974.
44. Kothandaraman, V., and R. L. Evans. A Case Study of Chlorine Contact
Tank Inadequacies. Public Works 105(1):59-62, 1974.
45. Marske, D. M., and J. D. Boyle. Chlorine Contact Chamber Design—A Field
Evaluation. Water and Sewage Works 120(1):70-77, 1973.
46. Hart, F. L., R. Allen, J. DiAlesio, and J. Dzialo. Modifications
Improve Chlorine Contact Chamber Performance, Parts I and II. Water and
Sewage Works 122(9):73-75 and 122(10):88-90, 1975.
47. Zickefoose, C., and R. B. J. Hayes. Operations Manual: Stabilization
Ponds. Contract No. 68-01-3547, U.S. Environmental Protection Agency,
Office of Water Programs Operations, Municipal Operations Branch,
Washington, DC, 1977.
48. Process Design Manual for Sludge Treatment and Disposal. EPA-625/1-
79-011, U.S. Environmental Protection Agency, Center for Environmental
Research Information., Cincinnati, OH, 1979.
74
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CHAPTER 3 •
DESIGN PROCEDURES
3.1 Preliminary Treatment
In general the only mechanical or monitoring and control equipment
required for wastewater pond systems are flow measurement devices,
sampling systems, and pumps. The flow diagrams presented in Chapter 2
illustrate the variety of preliminary treatment options in use. Design
criteria and examples for preliminary treatment components are presented
in several other publications (1-6) as well as in equipment
manufacturer's catalogs. Flow measurement can be accomplished with
relatively simple devices such as Palmer-Bowlus flumes, V-notch weirs,
and Parshall flumes used in conjunction with a recording meter.
Frequently, flow measurements and 24-hour compositing samplers are
combined in a common manhole, pipe, or other housing arrangement. If
pumping facilities are necessary, the wet well is sometimes used as a
point to recycle effluent or to add chemicals for odor control.
Pretreatment facilities should be kept to a minimum at pond systems.
3.2 Facultative Ponds
Facultative pond design is based upon BOD removal; however, the majority
of the suspended solids will be removed in the primary cell of a pond
system. Sludge fermentation feedback of organic compounds to the water
in a pond system is significant and has an effect on the performance.
During the spring and fall, overturn of the pond contents can result in
significant quantities of solids being resuspended. The rate of sludge
accumulation is affected by the liquid temperature, and additional
is added for sludge accumulation in cold climates. Although SS
influence on the performance of pond systems, most
simplify the incorporation of the influence of SS by
reaction rate constant. Effluent SS generally consist
of suspended organism biomass and do not include suspended waste organic
matter.
volume
have a profound
design equations
using an overall
Several empirical and rational models for the design of facultative
wastewater ponds have been proposed. These relationships include the
ideal plug flow and complete mix models, as well as models proposed by
75
-------
Fritz et al., Gloyna, Larson, Marais, McGarry and Pescod, Oswald et al.,
and Thirumurthi (7-14). Of these models, several produce satisfactory
results; however, use may be restricted because of the difficulty in
evaluating specific coefficients or by the model complexity. Equations
from these sources are presented in the Appendix.
Because of the many approaches to the design of facultative ponds, an
attempt will not be made to select the "best" procedure. An evaluation
of several design formulas with the operational data presented in
Chapter 2 failed to show that any of the methods are superior to the
others in terms of predicting the performance of pond systems (see
Appendix). The design methods most : often referenced are summarized in
Table 3-1. Each of these will be used to design a facultative pond for
the domestic wastewater described in Table 3-2. Following the
calculations of the size of the pond system by each method, a summary
and comparison of the results will be presented. i
3.2.1 Areal Loading Rate Procedure ;
I
The BODp. area! loading rate recommended for an average winter air,
temperature of less than 0°C is 11-22 kg/ha/d (10-20 Ib/ac/d) (Table
3-1). The more extreme the environment, the lower the loading rate. In
this hypothetical case, an intermediate BODr loading rate of 17 kg/ha/d
and a minimum hydraulic detention time of 180 days was selected. The
minimum hydraulic detention time of 180 days was selected because of the
severe climatic conditions and long periods of ice cover when effluent
can not be discharged. The detention time must be selected in
consideration of the climatic conditions and values may range from no
minimum value specified up to 180 days as used in this example. The
organic loading rate on the first cell in the system will be limited to
40 kg BODr/ha/d to avoid overloading and anaerobic conditions and odors.
76
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TABLE 3-1
FACULTATIVE POND DESIGN EQUATIONS
AREAL LOADING RATE
(15)
GLOYNA EQUATION
(8)
Design Equation
or
Parameter
Temperature
Adjustment of
Parameters
For Avg. Winter Air Temperature
of above 15°C (60°F)
BOD,- Loading = 45-90 kg/ha/d
D (40-80 Ib/ac/d)
For Avg. Winter Air Temperature
of 0-15°C (32-6p°F)
BOD,- Loading = 22-45 kg/ha/d
3 (20-40 Ib/ac/d)
For Avg. Winter Air Temperature
of below 0°C (32°F)
BOOK Loading = 11-22 kg/ha/d
b (10-20 Ib/ac/d).
BOD,- Loading in first cell is
usually limited to 40 kg/ha/d or
less and the hydraulic detention
time is 120 to 180 days in climates
where the average air temperature
is below 0°C. In mild climates
(air temp. > 15°C) loadings on the
primary cell can be 100 kg/ha/d
Given above
= t = 0.035L. 9
(35-T)
ff
pond volume, m
influent flow rate, 1/d
hydraulic residence time, d
ultimate influent BQO or COO, mg/1
temperature coefficient = 1.085
pond water temperature, °C
algal toxicity factor
sulfide oxygen demand factor
BOD removal efficiency = 80-90%
f = 1.0 for domestic wastes
f = 1.0 for SO. < 500 mg/1
Depth = 1 m for calculation of surface
loading
Depth varies with climate
Depth = 1 m for ideal conditions,
i.e., uniform temp., tropical to
sub-tropical, min. settleable solids.
Depth = 1.25 m for same condition
as above but with modest amounts of
settleable solids.
Depth = 1.5 m for locations with
significant seasonal variation in
temperatures.
Depth = 1.5-2 m for severe climates.
Included in equation
-------
TABLE 3-1
CONTINUED
Design Equation
or
Parameter
Temperature
Adjustment of
Parameters
MARAIS & SHAW EQ.
(COMPLETE MIX MODEL)
(10)
Cn F 1 >
Co [1 + Vn J
C = effluent BODg concentration, mg/1
C = influent BOD,, concentration, mg/1
k = complete mix_Jst order reaction
rate, days"
t = hydraulic residence time in each
pond, days
n = number of ponds in series
rr ) - 70°
lVmax 0.6d + 8
(C ) = maximum pond BODK cone.
e max consistent with aerobic
conditions, mg/1
d = depth of pond, ft
Max. efficiency in a series of ponds is
obtained when t in each pond is equal.
k = k (1.085)T~35
CT C35
k = reaction rate at rain, operating *
T water temperature
k 35= reaction rate at 35°C =1.2 day"
T = minimum operating water
temperature, °C
PLUG FLOW
MODEL
(16) (17)
CG - e-W
^ - e p
C = effluent BOD,- concentration, mg/1
C = influent BODg concentration, mg/1
? = base of natural logarithms, 2.7183
k = plug flow first order reaction
P rate, day"
t = hydraulic residence time, days
k varies with the BODg loading rate
P rate as shown below?
kp
BODg Loading Rate 20_1
kg/ha/d day
22 0.045
45 0.071
67 0.083
90 0.096
112 0.129
kp - kp (1.09)T"ZO
HT K20
kp = reaction rate at min. operating
T water temperature
k = reaction rate at 20°C
V20
T = minimum operating water
temperature, °C
WEHNER-WILHELM EQ. &
THIRUMURTHI APPLICATION
(13) (14) (18)
Ce 4 ae 1/2D
Co (Ha)2 ea/ZD - (l-a)Z e*/W
C = influent BOD- concentration, mg/1
C° = effluent BOD- concentration, mg/1
1 = base of natural logarithms, 2.7183
a = \/l + k t D _1
k = 1st order reaction rate, day
t = hydraulic residence time, d
D = dimensionless dispersion number
D =JL = I!! '":.
VL L2 ^ L
H = axial dispersion :coef., area per
time
v = fluid velocity, length per time
L = length of travel path of a typical
particle, length
kT = k?0 (1.09)1""20
k,. = reaction rate at minimum operating
water temperature i
k2Q= reaction rate at 20°C = 0.15 day"
T = minimum operating water
temperature, °C
00
-------
TABLE 3-2
ASSUMED CHARACTERISTICS OF WASTEWATER AND ENVIRONMENTAL
CONDITIONS FOR FACULTATIVE POND DESIGN
Q = Design flow rate = 1893 m /d (0.5 mgd)
CQ = Influent BOD5 = 200 mg/1
C = Effluent BOD,- = 30 mg/1
€ D
T = Water temperature at critical period of year = 0.5°C
T = Average winter air temperature = <0°C
a
Light Intensity = adequate
Evaporation - rainfall
Suspended Solids = 250 mg/1
SO = <500 mg/1
79
-------
Design Conditions: See Table 3-2.
Requirements: Size a facultative wastewater treatment pond to treat the
wastewater described in Table 3-2, and specify the
following parameters for the system.
1) Detention time in total system and first
cell, t and t,
•*• i
2) Volume in total system and first cell,
V and V1
3) Surface area,in total system and first cell,
A and A^ \.
4) Depth, d !
5) Length, L
6) Width, W
Solution: , .
BOD, Loading = 200 mg/1 (1893 m3/d)(—°° jlters)( ^L )
& • md , 1 x 10°, mg
BODg Loading = 379 kg/d
379 kg/d
40 kg/ha/d
Surface area required in first cell = A, =
AI = 9.5 ha = 95,000 m2 (23.4 ac)
Total surface area required = A = (379 kg/d)/(17kg/ha/d)
.,
A = 22.3 ha = 223,000 m2 ,(55.1 ac)
2
The surface area of 95,000 m (23.4 ac) required in the primary cells is
larger than normally provided in one cell; therefore, the system will be
divided into two parallel systems with a surface area of 47,500 m (11.7
ac) in each primary cell. The remaining surface area requirement will
be divided into two parallel systems with three equal size cells in
series in each parallel system.
Surface area in secondary cell = A2 = (223,000 - 95,000)/
(2 parallel systems)(3 cells in series)
A£ = A3 = A4 = 21,330 m2
Using a length to width ratio of 3:1 and an embankment slope of 4:1, the
dimensions of the cells at the water surface and at maximum depth can be
calculated as follows:
80
-------
AX = Lj x Wx = L(L/3) = L2/3 = 47,500 m2
Lx = 378 m (1240 ft) ' !
Wj = 378/3 = 126 m (413 ft)
A2 = L2/3 = 21,330 m2
L2 = 253 m (830 ft)
W2 = 84 m (277 ft)
Depth selection is usually control Ted by state standards, and
depths specified will range from 1.0 to 2.1 m (3 to 7 ft) in the
primary pond to 2.5 to 3.0 m (8 to 10 ft) in secondary ponds.
Let the depth of primary pond = 2 m (6.6 ft)
Depth includes 0.3 m (1 ft) for ice cover and 0.3 m (1 ft) for
sludge storage.
The "effective" depth in the primary cell = 1.4 m (4.6 ft).
Depth selection in the remaining cells is also controlled by state
standards, and most states will allow greater depths in the
secondary cells.
Let the depth of the other cells = 3, m (10 ft)
Depth includes 0.3 m (1 ft) for ice cover and 0.3 m (1 ft) for
sludge storage.
The "effective" .depth in the secondary cells = 2.4 m (7.9 ft).
The volume of the cells can be calculated using the following formula
for the volume of a rectangular basin with sloped sides and rounded
corners,
V = |(L x W.) + (L-2sd)(W-2sd) + 4 (L-sd)(W-sd)
where,
V = volume, m
L = length of pond at water surface, m
W = width of pond at water surface, m
s = horizontal slope factor, i.e., 3:1 slope, s = 3
d = depth of pond, m
81
-------
The total volume of the primary cells includes the sludge and ice
storage or a total depth of 2 m. The "effective" volume is based on a
depth of 1.4 m and is the vdltifiie used to calculate the theoretical
hydraulic detention time.
Total Volume in One Primary Cell (TVPC) = (378)(126) +
(378-2 x 4 x 2) + (126-2 x 4 x 2) + 4 (378-4 x 2)
(126-4 x 2)
<
TVPC = 87,363 m3 (3.09 x 10^ ft3)
Effective Volume = (378)(l26) * (378-2x4x1.4)(126-2x4x1.4)
+ 4(378-4 x 1.4M126-4 x 1.
••«] ¥
Effective Volume = 62,786 m3 (2.22 x 106 ft3) :
Theoretical hydraulic detention time in primary cell = t,
tj = 62,7867(1893/2) = 66 days
The total volume of the secondary cells includes the ice and sludge
storage for a total depth of 3 m (10 ft). The "effective" volume of the
secondary cells is based on a depth of 2.4 m (7.9 ft), and the
theoretical hydraulic detention time is calculated based on the volume
of the cell at a depth of 2.4 m.
Total Volume in One Secondary Cell (TVSC) =
(253K84)
(253-2 X 4 x 3)(84-2 x 4 x 3) + 4 (253-4 x 3)
(84-4 x 3)If !
TVSC = 52,200 m3 (1.84 x 106 ft3)
Effective Volume in One Secondary Cell =
(253M84) +
(253-2 x 4 x 2.4) (84-2 x 4 X 2.4) + 4 (253-4 x 2.4)
2.4
(84-4 x 2.4)
6
Effective Volume = 43,535 m3 (1.54 X 106 ft3)
j
Theoretical hydraulic detention time i|n secondary cell =
82
-------
t2 = 43,5357(1893/2) = 46 d
t = effective total theoretical hydraulic detention time
t - tj_ + tg + tg + t4
t = 66 + 46 + 46 + 46 = 204 d
The hydraulic residence time calculated for the selected loading rates
exceeds the minimum acceptable residence time of 180 days. The system
can be designed for a hydraulic residence time of 180 days without
discharge during the winter months and discharge during the summer.
Another option is to operate the system as a controlled discharge pond
system. Results such as these will occur frequently when the design is
based on conservative loading rates used in areas with severe climates.
The size of the pond with a 180-day hydraulic detention time is
calculated as follows.
Volume of one primary cell = same as above because of loading limit of
40 kg BOD5/ha/d.
Vj = 62,786 m3 (2.22 x 106 ft3)
tj = 62,786 m3 (1893 m3/d/2) = 66 d
t2 = 180 - 66 = 114 d
Vp = volume in one secondary cell =
114 d (1893 m3/d)/(2)(3) = 35,967 m3 (1.27 x 106 ft3)
There are numerous options as to how the ponds may be arranged besides
the four cells in series selected above. The simplest, but not the best
option, would be a two pond system without baffles. The hydraulic
characteristics of the two pond system could be improved by installing
baffles to direct the flow patterns. In severe climates the use of
baffles must be conducted with care because of the potential for ice
damage. The two parallel systems with each processing one-half of the
flow is an excellent choice because of the flexibility provided by such
a flow configuration. The four ponds in series will provide a hydraulic
residence time that would approach the theoretical value.
Many state standards require that a minimum of 0*6 m (2 ft) of water
depth be maintained in ponds; therefore, the volume required to store
180 days of wastewater flow is based on the volume above the 0.6-m water
depth. The volume allowed for sludge and ice storage in the system will
satisfy this requirement.
The dimensions of the two primary cells will be the same as calculated
above, or 378 m x 126 m at the water surface at maximum depth. The
83
-------
dimensions of the six secondary cells car be calculated using the
formula used above to calculate the volume of a rectangular basin with
sloped sides and rounded corners. Side slopes are 4:1 and the length to
width ratio is 3:1.
V2 = 35,967 =
(L x L/3) + (L - 2 x 4 x 2.4KL/3 - 2 x 4 x 2.4)
+ 4 (L - 4 x 2.4KL/3 - 4 x 2.4) -™
L2/3 + (L - 19.2KL/3 - 19.2) + 4 (L - 9.6)(L/3 - 9.6) = 89,918
L2/3 + L2/3 - 38.4L + 368.64 + 4(L2/3 - 19.2L +.92.16) = 89,918
2 L2 - 115.2L + 737.28 = 89,918 ;
Solve quadratic equation by completing the square.
L2 - 57.6L -f 829.44 = 44,591 + 829.44
(L - 28.8)2 = 45,420
L - 28.8 = 213.1 :
L = 241.9 m, Use 242 m (794 ft)
.
W = 241.9/3 = 80.6 m, Use 81 m (266 ft)
Surface area of water surface in one secondary cell = 242 (81) =
19,602 nT
I ••''•• o
Surface area in all secondary cells = 19,602 (6) = 117,612 m
i
3.2.2 Gloyna Equation
The Gloyna equation and design parameters are summarized in Table 3-1.
Design Conditions: See Table 3-2.
Requirements: Size a facultative wastewater treatment pond to treat the
wastewater described in Table 3-2, and specify the
following parameters for the system. ^: -
1) Detention time in total system and first cell,
t and t,
2) Volume in total system and first cell,
V and V-L
3) Surface area in total system and first cell,
A and Ai
84
-------
4) Depth, d ; ' .. •
: . • •",'".'• . " - '
5) Length, L •
6) Width, W
Solution:
't . ~ ':
Gloyna suggests that the ultimate BOD be used in the equation, and this
is logical because in treatment units using extended detention periods,
the ultimate demand is important. The COD is the logical measure of
oxygen demand if industrial wastes or sulfate on other sulfur compounds
are present. Ultimate BOD values usually are not available, and it is
necessary to use the COD or a multiplier to estimate the ultimate BOD.
A multiplier of 1.2 will be used to estimate the ultimate BOD (8).
= t = 0.035L 9- ff •
x « ;,.....,
L = 1.2 (200 mg/1) = 240 mg/1
a
0 = 1.085
T = 0.5°C
f = 1.0
f ' = 1.0 .
t = 0.035 (240) 1.085(35~°*5)
t = 140 d
V = t (Q) = 140 (1893 m3/d) = 265,000 m3 (9.36 x 1Q6 ft3)
Climate is severe; therefore, the depth should be 2 m (6.6 ft). The
depth of 2 m includes approximately 0.3 m (1 ft) for ice cover and 0.3 m
(1 ft) for sludge storage.
The effective depth of 1 m is to be used in the calculations of surface
loadings and surface areas. " '
Surface area = A = 265,000 m3/! m =26.5 ha (65.5 ac)
Surface area loading rate = 379 kg/d/26.5 ha
Surface area loading rate = 14.3 kg BODc/ha/d
,-!.-.. , t - ' ?, :
The length and width of individual cells can be calculated as shown for
the previous example.
85
-------
More detail on the arrangement of ponds as perceived
available in several publications (8) (19) (20).
by Gloyna is
Gloyna and Tischler (19) have reported that facultative ponds are
effective only in a water temperature range of 5 to 35°C; therefore, it
is unlikely that they would recommend the use of the Gloyna equation at
the design water temperature of 0.5°C used in this example. However,
the results agree well with the areal loading design presented above. A
comparison of these two methods as well as others presented in the
following paragraph is presented at the end of the section on
facultative ponds.
3.2.3 Marais-Shaw Equation
The Marais-Shaw equation is based on a complete mix model and first
order kinetics. The equation and conditions necessary for its
application are shown in Table 3-1.
Design Conditions: See Table 3-2.
Requirements: Size a facultative wastewater treatment pond to treat the
wastewater described in Table 3-2, and specify the
following parameters for the system.
1) Detention time in total system and first cell,
t and ti
2) Volume in total system and first cell,
V and V1
3) Surface area in total system and first cell,
A and Ai "
4) Depth, d
5) Length, L ,
6) Width, W
Solution:
Marais and Shaw (21) proposed that the maximum BOD5 concentration in the
primary cells, (Cjm=v, be 55 mg/1 to avoid anaerobic conditions and
odors. e max
The permissible depth of the pond, d in feet, was found to be related to
(C ) as follows: (Equation must be used with English units because of
the empirical constants that cannot be converted to metric units.)
"Vmax
700
0.6 d + 8
86
-------
55 =
700
0.6 d + 8
d = 7.9 ft (2.4 m)
Use ad = 8 ft (2.4 m)
Detention time in the primary cell is calculated as follows:
n
'n
(c0/cn)
c n
1/n
(1.085)
T-35
-1
=1.2 day
= 1.2 (1.085)0'5"35 = 1.2 (0.0599)
ccT = 0.072 day'1
. = (200/55) - 1
1 0.072
tx = 36.6 d
V1 = 36.6 (1,893 m3/day) = 69,300 m3
Calculate the surface area of the primary cell.
69,300 m3
2.4m
— Aj = 2.9 ha (7.2 ac)
Determine , the number of ponds in series that will be required to produce
an effluent containing 30 mg/1 of BOD,-.
87
-------
30/200 =
n =
1 + 0.072 (36.6)
1.5
n
Two ponds of equal volume in series with a depth of 2.4 m (8 ft) and a
surface area of 2.8 ha (7.0 ac) will be required (Mara (22) has shown
that the most efficient series operation consists of equal volumes).
Calculate the surface loading rate being applied to the primary cell. ,,.
Surface loading rate =
(200 mg/T)(1893 m3/d);
1000 liters
L >3 J
kg
1 x 106 mg
2.8 ha
Surface loading rate = 135 kg of BODg/ha/d
The surface loading rate applied to the primary cell is much higher than
the value of 40 kg BOD5/ha/d normally recommended as the maximum for a
severe climate such as the environmental conditions specified for this
design. Because the method was developed in a warm climate, it is
likely that the method cannot be applied to northern areas. This design
approach does not make any allowance for ice cover and/or sludge storage
to determine an "effective" depth. If t.he 'values used in the previous
examples were applied here, the total depth would approach 3m.
The dimensions of ponds designed by this method are also .calculated as.
shown in the first design example (Section 3.2.1). •
3.2.4 Plug Flow Model
The plug flow equation and design parameters are summarized in Table
3-1. '•"--••
Design Conditions: See Table 3-2.
Requirements: Size a facultative wastewater treatment pond to treat the
wastewater described in Table 3-2, and specify the
following parameters for the system.
1) Detention time in total system and first cell,
t and t.
88
-------
2) Volume in total system and first cell,
• V and Ml
3) Surface area in total system and first cell,
A and A,
1
4) Depth, d
5) Length, L
6) Width, W
Solution:
The difficult part of using any of the design methods is selecting the
reaction rate. The plug flow model is no exception. As shown in Table
3-1, the value of the reaction rate varies with the organic loading
rate. The size of the pond system can be based on an average value for
the tptal system, or the removal in each stage of the system and the
organic loading rate to the succeeding cell can be estimated and the
reaction rate varied for each cell. TheoreticaMy, the latter approach
should be used; however, in most cases an overall k of 0.1 day" is
P20
used to size the system. Both approaches will be illustrated.
Variable kp:
In severe climates the organic loading rate (kg BODc/ha/d) in the
primary cell is limited to 40 kg/ha/d; therefore, a k / value of 0.071
1 29
day" will be used to estimate the removal of BODg in the first cell.
The size of the primary cell will be the same as the value calculated in
the design using organic loading rate criteria.
At = (379 kg/d)/(40 kg/ha/d) = 9.5 ha (23.4 ac)
A total depth of 2 m (6.6 ft) is selected based on the criteria
described earlier. The depth includes 0.3 m (1 ft) for ice cover and
0.3 m (1 ft) for sludge storage. The "effective" depth in the primary
cell is 1.4 m (4.6 ft).
Total Volume in One Primary Cell = 87,363 m3 (3.09 x 106 ft3)
Effective Volume in One Primary Cell = 62,786 m3 (2.22 x 106 ft3)
See Section 3.2.1 for the calculations of the above volumes.
t =62,786 m3/(1,893 m3/d/2) = 66 d ,
89
-------
Calculate the effluent quality of the primary cell.
kp = kp (1.09)1""20 . .
"r P20 i
i'
kD = 0.071 (1.09)0'5"20
T ;•-
kD = 0.013 day"1
C-, -kp t
= e T
Cl -0.013(66)
200 " e
Cj = 200 (0.424) : !
C-L = 85 mg/1
The hydraulic detention time required to remove the remaining BODg is
calculated as follows. The organic loading rate on the cells following
the primary cell is much lower than that applied to the primary., cell .-
It is necessary to select a lower reaction rate of k = 0.045 day .
20
Calculate the t2 necessary to produce an effluent with a BODg
concentration of 30 mg/1 .
kp = 0.045 (1.09)0'5"20
0.0084
30 _ -0.0084 t,
- e 2
- 0.0084 t2 = - 1.041
t2 = 124 d i
V2 = Qt2 = (1,893 m3/d)(124d) !
V2 = 234,700 m3 (8.29 x 106 ft3) .
Most state standards permit the use of a greater depth in cells
following the primary cell. Depths as great as 2.5m (8 ft) are
allowed. A depth of 2.5 m will be used in the secondary cells with an
"effective" depth of 1.9 m.
90
-------
d2 = 1.9 m
A2 = V2/d2 = 234,700 m3/!.9 m
A2 = 123,500 m2 (30.5 ac)
The total detention time in the system is 190 days; therefore, the
minimum acceptable value of 180 days will control,. The size of the pond
system would be calculated the same way as that shown in Section 3.2.1.
Constant k
An average value of kp of 0.1 day" will be used to size the entire
20
system. The size of the primary cell is controlled by the limit of 40
kg of 80Dg/ha/d; therefore, the primary cell will be the same size as
that used in the design using the organic areal loading rate criteria.
Aj = (379 kg/d)/(40 kg/ha/d) = 9.5 ha (23.4 ac)
A depth of 2 m (6.6 ft) is selected based on criteria described earlier.
The depth includes 0.3 m (1 ft) for ice cover and 0.3 m (1 ft) for
sludge storage. The "effective" depth in the primary cell is 1.4 m (4.6
ft).
Effective volume = 125,600 m3
tj_ = 125,600 m3/l,893 m3/d = 66 d
Calculate the effluent quality of the primary cell.
kp = kp (1.09)1""20
*T *20
kp = 0.1 (1.09)0-5"20
k0 = 0.019 day"1
PT
ci _ -
-0.019 (66)
™" 6
Cj = 57 mg/1
To satisfy the effluent standard of 30 mg/1 of BOD,-, a secondary pond
91
-------
will be required. The detention time necessary to produce an effluent
BODg of 30 mg/1 is calculated as follows:
Cx -kp t
• e T
30 _ -0.019t
~ e
t = 34 d
•
The effluent from the secondary pond meets the .standard of 30 mg/1 of
BOD(-; therefore, additional ponds would not be required. Using a
two^pond system is not recommended, but if such a system were selected,
baffling would be necessary to improve the hydraulic characteristics so
that the actual hydraulic residence time approached the theoretical.
3.2.5 Wehner-Wilhelm Equation ; '. •,
The Wehner-Wilhelm (18) equation for arbitrary flow was proposed by
Thirumurthi (14) as a method to design facultative pond systems. The
equation and design parameters are summarized in Table 3-1. Thirumurthi
developed the chart shown in Figure 3-1 to facilitate the use of the
equation. The term kt is plotted versus the percent BOD5 remaining in
the effluent for dispersion factors varying from zero for ideal plug
flow to infinity for a complete mix reactor. Dispersion factors for
ponds range from 0.1 to 2 with most values not exceeding 1.0. Using the
arbitrary flow equation is complicated in that two "constants" must be
selected, the reaction rate (k) and the dispersion factor (D). The
influence of the dispersion factor can be illustrated by using several
values to estimate the detention time required to reduce the BOD5 from
200 mg/1 to 30 mg/1 as specified in the other examples. A value of 0.15
day was recommended for k2Q.
kT = k2Q (1.09)T~20
ky = 0.15 (1.09)0'5"20
k? = 0.028 day"1
C
_§ = Percent BOD,- remaining = (30/200) 100 = 15%
Co 5
Values of kjt, t, V, and A for dispersion factors normally occurring in
pond systems are summarized in Table 3.3. A depth of 2 m (6.6 ft) was
selected based on the criteria outlined in the area! loading method of
design. The "effective" depth is 1.4 m (4.6ft).
92
-------
FIGURE 3-1
WERNER AND WILHELM EQUATION CHART (14)
-------
A typical calculation for a D of 0.1 and a kj of 0.028 day is shown
below. It is necessary to solve the equation by trial and error.
Ce 4ae1/2D
Co " (1+a)2 ea/2D - (1-a)2 e'3/20
a = /1 + 4 kTtD
a = 1/1 + 4 (0.028K0.1) t = /T+ 0.0112 t
First iteration:
Assume t = 50 d
a = 1 + 0.0112(50) = 1.25
4(1.25)
d+1.25)2 e1'25"2"0-" - (1-1.25)2 e-1.25/(2)(0.1)
0.15 ?« - - - =0.283
(5. 06355(518, 01) - (0.0625MO. 00193)
Agreement is not satisfactory; therefore, niust perform iterations until
two sides of equation agree.
nth iteration; ;
Assume t = 80 d
a = Vl + 0.0112(80) = 1.377
4(1.377) ,
(U1.377)2 e1-377/^^0'" - (1-1.377)2 e-1'
0.15 = - 817'46 - - = 0.148
(5.65)(977.50) - (0.142) (0.00102)
Agreement is adequate and the design detention time is 80 days.
94
-------
TABLE 3-3
VARIATIONS IN DESIGN PRODUCED BY VARYING THE DISPERSION FACTOR
D
kTt
t,days
V,m3
A,m2
0.1
2.3
80
151,400
108,200
0.25
2.6
93
176,000
125,700
0.5
3.0
107
202,600
144,700
1.0
3.7
132
249,900
178,500
The selection of a value for D can dramatically affect the detention
time required to produce a given quality effluent. The selection of a
design value for kpn can have an equal effect.
the dimensions of ponds based on this design method are calculated as
previously shown.
3.2.6 Discussion of Design Methods
All of the designs are based on parameters reported in the literature
and no attempt was made to select parameters that would produce
consistent results in all of the methods. Each design was made
independently using the values of constants recommended by the author of
a method.
A summary of the results from the various design methods is shown in
Table 3-4. Numerous and varying requirements are imposed on the designs
by the conditions under which the methods were developed. These
limitations on the design methods make it difficult to make direct
comparisons; however, an examination of the hydraulic detention times
and total volume requirements calculated by all of the methods shows
considerable consistency if the Marais and Shaw method is excluded and a
value of 1.0 is selected for the dispersion factor in the Wehner-Wilhelm
method.
All of the design equations have limitations and several have been
mentioned in the design examples. To determine the limitations of a
particular method, the original reference should be consulted. The
major limitation of all the methods is the selection of a reaction rate
constant or other factors in the equations. Even with this limitation,
if the pond hydraulic system is designed and constructed such that the
theoretical hydraulic detention time is approached, reasonable success
can be assured with all of the design methods. Short circuiting is the
95
-------
TABLE 3-4
SUMMARY OF RESULTS FROM DESIGN METHODS
SURFACE LOADING RATE
10
CTl
DESIGN
METHOD
AREAL
LOADING
RATE
GLOYNA
MARAIS &
SHAW
PLUG FLOW
WERNER &
WILHELM
DETENTION TIME, d
Primary Total
Pond System
66a 180
140
37b 74
66a 180
66a 80-132
VOLUME^ m
Primary
Pond
125,600a
125,600a
69,300b
125,600a
125,600a
Total
System
386,800
265,000
138,600
386,800
151,400 to
249,900
SURFACE
Primary
Pond
9.5
- .
2.8
9.5
9.5
AREA, ha
Total
System
22.3
26.5
5.6
22.3
10.8 to
17.9
Depth
m
2
(1.4)
2
(DC
2.4
2
(1.4)
2
(1.4)
No.
Cells
in
Series
4
c
-
2 -
4
c
c 4
kg BOD5/ha/d
Primary Total
Pond System
40 17
14
135 , 68
40 25
30-48
Controlled by state standards and is equal to value calculated for an areal loading rate of 40 kg/ha/d
and an effective depth of 1.4 m.
Also would be controlled by state standard for areal loading rate; however, the method includes a
provision for calculating a value and this calculated value is shown.
C • " * '
Effective depth.
-------
greatest deterrent to successful pond performance, barring any toxic
effects. The importance of the hydraulic design of a pond system cannot
be overemphasized. ,j • '
The surface loading rate approach to design requires a minimum of input
data, and is based on operational experiences in various geographical
areas of the country. This is probably the most conservative of the
design methods, but attention to the hydraulic design is as important as
the selection of the BODg loading rate.
The Gloyna method is applicable only for 80 to 90 percent BOD removal
efficiency, and it is assumed that solar energy for photosynthesis is
above the saturation level. Provisions for removals outside this range
are not made; however, an adjustment for light can be made by
multiplying the pond volume by the ratio of sunlight in the particular
area to the average found in the Southwest. Mara (23) has discussed the
limitations of the Gloyna equation, and if a detailed critique is
needed, the reference should be consulted.
The Marais and Shaw method of design is based on complete mix hydraulics
and first order reaction kinetics. Complete mix hydraulics are not
approached in facultative ponds, but the greatest weakness in the
approach may lie in the calculation of the volume of a primary cell that
will not turn anaerobic. Mara (22) (23) has also discussed the
limitations of the Marais and Shaw approach and these references should
be consulted.
Plug flow hydraulics and first order reaction kinetics have been found
to describe the performance of many facultative pond systems (14) (16)
(17). As shown in the Appendix, a plug flow model was found to best
describe the performance of the four facultative pond systems summarized
in Chapter 2. Because of the arrangement of most facultative pond
systems into a series of three or more ponds, logically it would be
expected that the hydraulic regime could be approximated by a plug flow
model.
The plug flow design reaction rate used in the above example was based
on values in the literature (14) (16). The 'reaction rate (slope of the
line of best fit) calculated from Figure A-9 in the Appendix, adjusted
.for the temperature using the expression in Table 3-1 for the plug flow
model, yields a hydraulic detention time of over 400 days. This large
difference in detention times (190 versus 400 days) is probably
attributable to the low hydraulic and organic loading rates applied to
the four systems. These low loading rates tend to result in a lower
value for, the reaction rate (16). This discrepancy in reaction rates
further illustrates the difficulty and importance of selecting the
design parameters.
Use of the Wehner-Wilhelm equation requires knowledge of both the
reaction rate and the dispersion factor which further complicates the
design procedure. If knowledge of the hydraulic characteristics of a
proposed pond configuration exists or can be determined, the
97
-------
Wehner-Wilhelm equation will yield satisfactory results. However,
because of the difficulty of selecting both parameters, design with one
of the simpler equations is likely to be as good as one using the
Wehner-Wilhelm equation.
In summary, all of the design methods discussed can provide a valid
design, if the proper design parameters are selected and the hydraulic
characteristics of the system are controlled.
3.3 Complete Mix Aerated Ponds |
Complete mix aerated ponds are designed and operated as flow-through
ponds with or without solids recycle. Most systems are operated without
solids recycle; however, many systems are built with the option to
recycle effluent and solids. Even though the recycle option may not be
exercised, it is desirable to include it in the design to provide
flexibility in the operation of the system. If the solids are returned
to the pond, the process becomes a modified activated sludge process.
Solids in the complete mix aerated pond are kept suspended at all times.
The effluent from the aeration tank will contain from one-third to
one-half the concentration of the influent BOD in the form of solids
(3). These solids must be removed by settling before discharging the
effluent. Settling is an integral part of the aerated pond system.
Either a settling basin or a quiescent portion of one of the cells
separated by baffles may be used for solids removal.
Six factors are considered in the design of an aerated pond: 1) BOD
removal, 2) effluent characteristics, 3) oxygen requirements, 4) mixing
requirements, 5) temperature effects, and 6) solids separation (3). BOD
removal and the effluent characteristics are generally estimated using a
complete mix hydraulic model and first order reaction kinetics. A
combination of Monod-type kinetics, first order kinetics, and a complete
mix model has been proposed, but there is limited experience with the
method (3) (24). The complete mix hydraulic model and first order
reaction kinetics will be used in the following example. Oxygen\
requirements will be estimated using equations based upon mass balances;:
however, in a complete mix system the power input necessary to keep the-
solids suspended is much greater than that required to transfer adequate
oxygen. Temperature effects are incorporated into the BOD removal
equations. Solids removal will be accomplished by installing a settling
pond. If a higher quality effluent is required, the solids removal
devices described in Chapter 5 should be evaluated and one selected to
produce an acceptable effluent quality.
98
-------
3.3.1 Complete Mix Model
The complete mix model using first order kinetics and operating in a
series with n equal volume ponds is shown below.
1 +
k_t
n
where,
C
n
CQ = influent BODg concentration, mg/1
k
= effluent BODr concentration in cell n, mg/1
n o
-i
0
= complete mix first order reaction rate constant, day
(assumed to be constant in all n cells) = 2.5 days" at 20°C
t = total hydraulic residence time in pond system, days
n = number of ponds in series.
If other than a series of equal volume ponds are to be employed, it is
necessary to use the following general equation.
where,
c , k , k = complete mix first order reaction rate
1 2 n constant in each of n ponds. Because of the
lack of better information, all are generally
assumed to be equal.
-i» to» tn ~ hydraulic residence time in each pond, days
3.3.2 Selection of k
The selection of a k value is the critical decision in the design of
any pond system. A Sesign value should be determined for the individual
wastewater in bench or pilot scale tests. If this is impractical, the
experiences of others should be evaluated. As an initial estimate, the
value of 2.5 days" may be used for a complete mix aerated pond system.
99
-------
3.3.3 Influence of Number of Ponds
When using the complete mix model, the number of ponds in series has ta
pronounced effect on the size of the aerated ponds required to achieve a
specific degree of treatment. The decrease in total volume of reactor
required to achieve a given efficiency by increasing the number of ponds
in series can best be illustrated by an example. Rearranging the
complete mix model into the following form makes it more convenient to
calculate the total detention time.
t =
1/n
where,
t
n
k
total hydraulic residence time in pond systems, days
number of ponds in series
complete mix first order reaction rate constant,
2.5 days"1 at 20°C
influent BOD5 concentration, mg/1
effluent BOD,- concentration in cell n, mg/1
When n
4-
L
When -n
4-
L
= 1,
!
2.5
/200V/1
1 30J
- 0
£•»
2
2.5
/200Y/2
. \30/
_i
—j.
1
~j.
, = 2.27 d
= 1.27 d
When n
t
- 3,
= 3
2.5
-1
= 1.06 d
100
-------
When n = 4,
4
t =
2.5
When n = 5,
-1
= 0.97 d
2.5
'2_OoY/5
30/
-1
= 0.92 d
Continuing to increase n will result in the detention
to the detention time in a plug flow reactor
days" .
time being equal
with a k value of 2.5
c
Figure 3-2 is a plot of the complete mix equation for one to four ponds
in series. The figure can be used to estimate the performance or
required detention time when the reaction rate (k ) has been selected.
When the influent (C ) and effluent (C ) BOD,- are known, the value of
C /C is calculated and located on the horizontal axis of the plot. A
vertical line is extended from this point to intersect with the line for
the number of ponds in series. From this point a horizontal line is
drawn to intersect with the k t axis. This value of k t is then divided
by the k value to yield the total detention time required in n ponds in
series. An example is shown on Figure 3-2.
3.3.4 Unequal Volume and k
Mara (22) has shown that a number of equal volume reactors in series is
more efficient than unequal volumes; however, there may be cases where
it is necessary to construct ponds of unequal volume. When this is
necessary, the following example for a three pond series with half the
volume in the first pond and one-fourth in the second and third ponds
will illustrate how to calculate the needed detention time_., or
efficiency. The reaction rate constant is assumed to be 2.5 days~ in
the first pond and 1.5 days" in the second and third ponds to
illustrate the procedure for varying reaction rates in the event they
are available.
where,
C3 = 30 mg/1
k t
1 + k
101
-------
FIGURE 3-2
k t VERSUS C /C FOR COMPLETE MIX MODEL
c on
o
PO
-------
200 mg/1
1/2 t
t3 = 1/4 t
total hydraulic residence time in system, days
30
200
0.15 =
1
1 + 2.5U/2)
1
1 + 1.5(t/4)
1
1 + 1.5(t/4)
(1 + 1.25 t)(l + 0.375 t)(l + 0.375 t)
0.15 =
1 + 2 t + 1.079 t2 + 0.176 t3
0.0264 t3 + 0.162 t2 + 0.3 t - 0.85 = 0
t3 + 6.14 t2 + 11.36 t - 32.2 = 0
The cubic equation can be solved by synthetic substitution as shown
below or solved on a pocket calculator.
2.0
1 + 6.14 + 11.36 - 32.2
+ 2.00 + 16.28 + 55.3
8.14 + 27.64 + 23.1
If the sum of the last two terms are equal to zero, the assumed value
(2.0 in this example) is a root of the equation. In the above iteration
the assumed value is too large; therefore, another value must be
assumed.
1.5
1 + 6.14 + 11.36 - 32.2
+ 1.50 + 11.46 + 34.2
1 + 7.64 + 22.82 + 2.0
The second estimated value is very close to a root and is probably
accurate enough, but to complete the solution another trial will be
completed.
1.45
1 + 6.14 + 11.36 - 32.2
+ 1.45 + 11.00 + 32.4
1 + 7.59 + 22.36 + 0.2
103
-------
For the conditions described above, a total hydraulic detention time of
1.45 days (t)'. would be required. The first pond would have a detention
time of 0.72 days (t/2) and the second and third ponds would have a
detention time of 0.36 days (t/4).
3.3.5 Temperature Effects .
The influence of temperature on the reaction rate is expressed as
follows:
C20
1C"
where,
CT = 0W
T.-20
k_ = reaction rate at design temperature, days"
T • • ' .'."'" •'" • . ':'" '•:''.. . .
kr = reaction rate at 20°C, days"
20
9 = temperature factor;, dimensionless = 1.085
T,, = temperature of pond water, °C
W ' ' - ,
The impact of mixing and the ambient air temperature on the pond water
temperature can be estimated by trial and error using the following
equation developed by Mancini and Barnhart (25) and the complete mix
model presented above. I
AfT. + QT. '•'.'•
Af + Q ;
where, |
T,, = pond water temperature, °C ;
W , ' \- -
T, = ambient air temperature, °C
• i
T^ = influent wastewater temperature, !°C
2 i
A = surface area of pond, m
f = proportionality factor = 0.5
Q = wastewater f 1 ow rate , m /d
104
-------
An estimate of the surface area is made using the complete .mix model
corrected for temperature, and then the water temperature is calculated
using, the Mancini and Barnha'rt equation. 1
After several iterations, when the water temperature used to correct the
reaction rate coefficient agrees with the value calculated with the
Mancini and Barnhart equation, the selection of the detention time in
the aeration ponds is complete.
3.3.6 Mixing and Aeration
Aeration is used to mix the pond contents and to transfer oxygen ,to the
liquid. In complete mix aerated ponds the mixing requirements control
the power input to the system. There is no rational method available to
predict the power input necessary to keep the solids suspended. The
best approach is to consult equipment manufacturers' charts and tables
to determine the power input needed to satisfy mixing requirements.
Malina et al. (26) indicate that a minimum, power level of 5.9 kW/1000 m
(30 hp/Mgal) of aeration tank volume is required to completely mix aa
aerated pond cell. Others indicate that approximately 2.96 kW/1000 m
(15 hp/Mgal) is adequate to maintain solids in suspension (27). These
values can be used as a guide to make preliminary estimates of power
requirements, but the final sizing of aeration equipment should be based
on guaranteed performance by an equipment manufacturer. ...
There are several rational equations available tp estimate the oxygen
requirements for pond systems, and these'equations can be found in many
text books (3.) (4) (20) (24). In most cases, the use of the BODg
entering the pond as a basis to estimate the biological oxygen'
requirements, is as effective as other approaches and has the advantage
of being simple to calculate.
After determining the total horsepower requirement for a pond, the
individual aeration units should be located in the pond so that there is
an overlap of the diameter of influence providing complete mixing.
Several small aerators are better than one or two large units. Large
units create localized mixing; therefore, several small units would
likely be more efficient and economical. Maintenance and repair of
small units would have less of an impact on .performance, and such an
arrangement would provide more operational flexibility.
3.3.7 Design Example
The complete mix model with four equal volume ponds in series will be
used. As discussed above, equal volume ponds in series are more
efficient than unequal volumes, and increases in the number of ponds
beyond four in a series does little to reduce the required hydraulic
detention times. In addition to the benefits of reducing the required
105
-------
detention time, four ponds in series improves the hydraulic
characteristics of the pond system. The following environmental and
wastewater characteristics are given:
Q = 1893 m3/d (0.5 mgd)
CQ = influent BODg = 200 mg/1
C = effluent BOD5 from the nth pond in an n-pond series
lagoon system = 30 mg/1
k = k (1.085)
CT C20 ,
k_ = reaction rate at design temperature, days'
T 1
k ~ reaction rate at 20°C = 2.5 days
C20
T = pond water temperature, °C
W ' :
,
al
= ambient air temperature in winter = 5°C
T_ = ambient air temperature in summer = 30°C
a2
T. = influent wastewater temperature = 15°C
f s proportionality factor = 0.5 i
i • , . . -
Elevation = 100 m
Maintain a minimum dissolved oxygen concentration in ponds -
2.0 mg/1 !,'..,'
i
Requirements: Size a complete mix aerated wastewater pond system to
treat the wastewater and determine the following
parameters for the system.
i • •
1) total detention time, t
2) Volume, total and for each cell , V, V^, etc.
3) Surface area, total and for each cell, A, Ap etc.
4) Depth, d :
5) Length of each cell, L
6) Width of each cell , W
I
7) Aeration requirements
106
-------
Solution:
First iteration
t =
1/n
-1
1/4
Assume that t. = 5°C during the winter.
W
k = 2.5 (1.085)
CT
5-20
kr = 0.74 day
CT
-1
0.74
tr,
= 3.3 d
, & tA = 3.3/4 =.0.825c'd
Vx = 0.825 (1893 m3/day) = 1562 m3 (5.5 x 104 ft3)
The pond depth is limited by the ability of the aeration equipment to
maintain the pond contents at the desired level of mixing. Acceptable
depths for aerated ponds range from 1.5 to 4.5 m (5 to 15 ft). A 3-m
(10-ft) depth is used in this example.
Ax = 1562 m3/3 m = 520 m2 (5597 ft2)
Check the pond water temperature using the surface area of 520 m (5579
ft ) and the other known parameters in the Mancini and Barnhart
equation. /
w
w
w
Af + Q
= 520(0.5H-5) + 1893(15)
520(0.5)+ 1893
= 12.6°C (55°F)
-1300 + 28395
260 + 1893
107
-------
Second iteration "'.',.'.
As the winter pond water temperature increases, the surface area,
detention time, and volume of the pond will decrease; therefore, the
next estimate of T should be approximately equal to the calculated
value of Tw of 12.6°C (55°F). :>r,- ;. '; ' :.. " ••.
Assume T,
w
13°C in the winter.
t =
2.5 (1*085) -•
1.41 day'1
4
1.41
/200\1/4 ,
[W J
- 1.72 d
= 1.72/4 = 0.43 d
= 0.43 (1893) = 814 m3 (2.87 x 104 ft3)
= 814/3 = 271 m2 (2900 ft2)
w
w
271(0.5)(-5) + 1893(15) = -677.5 + 28395
271(0.5) + 1893 2028.5
13.7°C (57°F) i
The assumed value of 13°C is approximately equal to the results of the
second iteration of 13.7°C. The limits of the method do not justify
attempting to balance the temperatures closer than to the nearest
degree. ' ,
The temperature will decrease from pond 1 to pond 2 and from pond 2 to
pond 3, etc., but the decrease is not so great that an average T value
cannot be used.
Final Size of Ponds
t = 1.72 d
tp t2, tg &
= 0.43 d
V = 3256 m3 (11.5 x 104 ft3)
= 814' m3' (2.87 x 104 ft3)
A = 1084 m2 (11.67 x 103 ft2)
108
-------
A2, A3 & A4 = 271 m2 (2.92 x 103 ft2)
Dimensions of Ponds . . \
Using the formula for the volume of a pond with sloped side walls for a
square pond and the required volume in each pond, the dimensions of the
ponds can be calculated. Use a slope of 2:1.
(L x W) + (L-2 sd)(W-2 sd) + 4 (L-sd)(W-sd)
= volume = 814 m3 (2.87 x 104 ft3)
V
where,
V
L = length of pond at water surface, m
W = width of pond at water surface, m
s = horizontal slope factor, i.e., 2:1 slope, s = 2
d = depth of pond = 3 m (10 ft)
d
814 =
(LW) + (L-2x2x3)(W-2x2x3) + 4 (L-2x3)(W-2x3)
In a square pond L = W.
(L-12)a~l2) + 4 (L-6) (L-6)
814 () = L2
6L - 721 + 288 » 1628
L2 - 12L + 48 * 271.3
Solve quadratic equation by completing the square.
L2 - 12L + 36 = 223.3 + 36
(L-6)2 = 259.3
(L-6) = 16.1
L = 22.1 m at the water surface (72.5 ft)
A minimum of 0.6 m (2 ft) of freeboard must be provided; therefore, the
dimensions of a single pond will be 24.5 m x 24.5 m (80.4 ft x 80.4 ft)
at the top of the inside of the dike with a water depth of 3 m (10 ft).
There are no rational design equations to predict the required mixing to
keep the solids suspended in an aerated pond. Using the mass of BODg
entering the system as a basis to estimate the biological oxygeH
requirements is simple and as effective as other approaches.
109
-------
Catalogs from equipment manufacturers must be consulted to ensure that
adequate mixing is provided. Additionally,,, all types of equipment must
be evaluated to ensure that the most economical and efficient system is
selected. A municipal wastewater treatment system designed to provide
complete mixing of the pond contents requires approximately 10 times as
much power as a system designed to meet the oxygen requirements only.
Therefore, an economic analysis along with sound engineering judgment is
required to select the proper aeration equipment.
The following relationship is used to estimate aeration requirements: >
a
- C
L
(1.025)
T. -20
where,
N - equivalent oxygen transfer to tapwater at standard condi-
tions, kg/hr
N, = oxygen required to treat the wastewater, kg/hr
a
a - oxygen transfer in wastewater x n g
oxygen transfer in tapwater ""
C, - minimum DO concentration maintained in the waste, assume
L 2.0 mg/1
C_ ™ oxygen saturation value of tapwater at 20°C and one
atmosphere pressure = 9,17 mg/1
i
T.. = wastewater temperature, °C
W
C = B(C )P = oxygen saturation value of the waste, mg/1
R _ wastewater oxygen saturation value = n 9
1 ~ tapwater oxygen saturation value
C = tapwater oxygen saturation value at temperature, T,
ss w
P = ratio of barometric pressure at plant site to barometric
pressure at sea level, assume 1.0 for the elevation of
100 m
The maximum oxygen transfer will be .required in the summer months. The
Mancini and Barnhart equation can be used to estimate the pond
wastewater temperature during the summer.
110
-------
T - 271(0.5)(30) +1893(15)
w ~ 271(0.5) + 1893
T _ 4065 + 28395 _
'w ~ - - '
C = 9.85 mg/1 at 16°C
o o
BODC in the wastewater = C x Q
o o
= (200 g/m3) (1893 m3/d) (kg/1000 g) (day/24 hr)
= 16 kg/hr
Assume that the oxygen demand of the solids at peak flows will be 1.5
times the mean oxygen demand of 16 kg Op/hr. Therefore,
N = 1.5 x 16 kg QJ\\r = 24 kg 00/hr
a c. c.
ccu, = 0.9(9.85 mg/1) 1.0 = 8.87 mg/1*
oW
24 kg 0?/hr
N = - - - = 39.3 kg 09/hr
0.9
"8.87 - 2.0-1
9.17 J
(1.025)
16-20
Manufacturers' catalogs suggest 1.9 kg 0?/kWh (1.4 kg/hr/hp) for
estimating power requirements. Therefore, the total power required to
satisfy the oxygen demand in the pond system is:
39.3 kg 0,,/hr
= 20.7 kW (27.8 hp)
1.9 kg 02/kWh
The power required to meet requirements for liquid mixing is (27):
minimum power =1.5 kW/1000 m of volume
power required =1.5 kW/1000 m3 (814 m3) = 1.2 kW/cell
power total = (4 cells) (1.2 kW/cetl) = 4.8 kW (6.4 hp)
The power required to meet requirements for solids suspension is (24):
3
minimum power = 15 kW/1000 m of volume
power required = 15 kW/1000 m3 (814 m3/cell) = 12.2 kW/cell
(16.4 hp/cell)
power required = (4 cells)(12.2 kW/cell) = 48.8 kW(65 hp)
111
-------
The power required to maintain solids suspension exceeds the power
required both to meet oxygen demand and for mixing of the pond liquid;
therefore, the power requirement for solids suspension will be used to
select aerators.
i_
Assuming 90 percent efficiency for aerator gearing, the total motor
power for solids suspension is:
48W = 54.2 kW (72.7 hp)
This value represents an approximate power requirement and is used to
select aeration equipment. The power actually applied to the pond
contents may be more or less than this value being determined by the
zone of complete mixing requirements in each cell. Using the data
presented in a catalog by Aqua-Aerobic Systems, Inc. (27), six 2.2-kW
(3-hp) aerators for each cell would provide zones of complete mix having
13-m (42-ft) diameters and would not require a draft tube or
anti-erosion assembly in a pond with a depth of 3 m (10 ft). This
selection in aerators and aerator placement leaves small areas where
solids suspension might occur. However, additional power and, hence,
additional operating cost would not significantly improve efficiency.
Figure 3-3 depicts aerator placement, zones of complete mixing for
solids suspension in one of the four ponds. A settling pond ,with a
hydraulic detention time of two days is provided after the fourth pond.
Summary ' .. '
V = 3256 m3
A = 1084 m3
t = 1.72 d
02 required for treatment = 39.3 kg 02/hr (20.7 kW)
Power required for liquid mixing = 4.8 kW
Power required for solids suspension = 48.8 kW
Power supplied via six aerators per cell = 13.4 kW
112
-------
FIGURE 3-3 ; j
LAYOUT OF ONE CELL OF COMPLETE MIX
AERATED POND SYSTEM
Zone of Complete
Mixing for Solids
Suspension
Influent
Surface Aerators (2.24 kW)
113
-------
3.4 Partial Mix Aerated Ponds
In the partial mix aerated pond system, no attempt is made to keep all of
the solids in the aerated ponds suspended. Aeration serves only to
provide oxygen transfer adeq'uatd iO oxidize the BOD entering the pond.
Some mixing obviously occurs and keeps portions of the solids suspended;
however, in the partial mix aera'ted pond, anaerobic degradation of the
organic matter that settles dofes occur. The system is frequently
referred to as a facultative aerated pond system.
Other than the difference in mixing requirements, the same factors
considered in the complete mix aerated pond system are applicable to the
design of a partial mix system, i.e., BOD removal, effluent
characteristics, oxygen requirements, temperature effects, and solids
separation. BOD removal is normally estimated using the complete mix
hydraulic model and first order reaction kinetics. Recent studies (17)
have shown that the plug flow model and first order kinetics more
closely predict the performance of partial mix ponds using both surface
and diffused air aeration. HoWever, most of the ponds evaluated were
lightly loaded and the reaction rates calculated from the performance
data are very conservative because of the tendency of the reaction rates
to decrease as the organic loading rate (surface loading or volumetric
loading) decreases (16). Because of this lack of better design reaction
rates, it is still necessary to design partial mix aerated ponds using
the complete mix model discussed in detail in Section 3.3. The only
difference in applying this itiddel to partial mix systems is the
selection of a reaction rate coefficient applicable to partial mix
systems. Section 3.3 should be consulted to determine the effect of the
number of ponds in series (3*3.3)* unequal volumes in each pond (3.3.4),
and temperature effects (3.3.5).
3.4.1 Selection of k
I
As mentioned several times, the selection of the reaction rate
coefficient is the most important decision in the design of any pond
system. All other considerations in the design will be influenced by
this selection. If possible, a design k should be determined for the
wastewater in pilot or bench scale tests. Experiences of others with
similar wastewaters and environmental conditions should be evaluated.
The "Ten States Standards" (1) recommends k values of 0.276 day" at
20°C and 0.138 day at 1°C. Using the t«<5 values to calculate the
temperature coefficient (9), yields a 9 value of 1.036. Boulier and
Atchison (28) recommend values of k of 0.2 to 0.3 at 20°C and 0.1 to
0.15 at 0.5°C. A temperature coefficient of 1.036 results when the two
lower or higher values of k are used to calculate 9. Reid (293
suggested a k value of 0.18 at 20°C and 0.14 at 0.5°C based oh
research withp partial mix ponds in central Alaska aerated with
perforated tubing. These values are essentially identical to the "Ten
114
-------
States Standards" recommendations. In the example presented later, the
values recommended by the "Ten States Standards" will be used.
3.4.2 Mixing and Aeration
In partial mix aerated ponds, aerators are used to transfer oxygen to
the liquid at the rate necessary to maintain aerobic conditions in the
ponds. In a complete mix system the power input to each pond in the
series must be adequate to keep the solids suspended; whereas, in a
partial mix system the power input is reduced from pond to pond because
of the reduction in organic matter (BOD) to be oxidized as the
wastewater flows through the system.
The oxygen requirements in each pond can be calculated using rational
formulas developed for activated sludge systems (3) (24); however, it is
doubtful that any of the relationships are more accurate than assuming
that all of the influent BOD,- entering the pond is to be oxidized.
After calculating the required rate of oxygen transfer, equipment
manufacturers' catalogs should be consulted to determine the zone of
complete oxygen dispersion by surface, helical, or air gun aerators or
the proper spacing of perforated tubing.
3.4.3 Design Example
The design of a partial mix aerated pond is performed the same as that
shown for the complete mix system with the exceptions of different
reaction rate coefficients and less power input requirements. The power
input is reduced from one pond to the next to account for the reduction
in organic matter (BOD) to be oxidized as the wastewater flows through
the system.
The complete mix model with four equal volume ponds in series will be
used (see Section 3.3.7 for justification). The following environmental
and wastewater characteristics are given:
Q = 1893 m3/d (0.5 mgd)
C = influent BODK = 200 mg/1
o o
C = effluent BOD,- from the nth pond in an n-pond series
pond system = 30 mg/1
T -20
k = reaction rate at design temperature, days"
115
-------
k = reaction rate at 20°C = 0.276 day"
w
= temperature of pond water, °C
= ambient air temperature in winter = -5°C
T = ambient air temperature in summer = 30°C
a2
T. = influent wastewater temperature = 15°C
f = proportionality factor =0.5
Elevation = 100 m
I
Maintain a minimum dissolved oxygen concentration in ponds =
2.0 mg/1
Requirements: Size a partial mix aerated pond system to treat the
wastewater and determine the following parameters for
the system.
1) Total detention time, t
2) Volume, total and for each cell, V,
etc.
3) Surface area, total and for each cell, A, A-, ,
etc. ...
4) Depth, d
5) Length of each cell, L
6) Width of each cell, W
7) Aeration requirements
Solution:
First iteration
t
t
n
k
pm
4
k m
pm
fC\ 1/n
1 ° 1 -1
c -1
Av
/200\1/4 .
1 30 / "-1
V /
Assume that t = 10°C during the winter.
,10-20
k = 0.276 (1.036)
116
-------
k = 0.194 day'
r
t
*2
4
~ O94
/200\ 1/4
N
= t3 = t4 = 12.5/4 = 3.
-1
1 d
= 12.5 d
Vj = 3.1 (1893 m3/d) = 5868 m3 (2.07 x 105 ft3)
Acceptable depths from partial mix aerated ponds ranged from 1.5 to 4.5 m
(5 to 15 ft). A 3-m (10-ft) depth is used in this example.
Calculate the area of the pond.
The ideal configuration of a pond designed on the basis of complete mix
hydraulics is a circular or a square pond; however, even though partial
mix ponds are designed using the complete mix model, it is recommended
that the ponds be configured with a length to width ratio of 3:1 or 4:1.
This is done because it is recognized that the hydraulic flow pattern in
partial mix systems more closely resembles the plug flow model. As more
field data become available, it is likely that reliable plug flow
reaction rates will be developed, and the plug flow model can be used to
size partial mix systems.
Ponds with sloped side walls (3:1) and a length to width ratio of 4:1
will be used. The dimensions of the ponds can be calculated using the
formula for the volume of a rectangular pond with side slopes that was
presented in Sections 3.2.1 and 3.3.7.
V =
where,
(LxW) + (L-2sd)(W-2sd) + 4 (L-sd)CW-sd)
V = volume of pond = 5868 m3 (2.07 x 105 ft3)
L = length of pond at water surface, m
W = width of pond at water surface, m
s = horizontal slope factor, i.e., 3:1 slope, s = 3
d = depth of pond = 3 m (10 ft)
L = 4W
V | = (4WxW)
(4W-2x3x3)(W-2x3x3) + 4 (4W-2x3)(W-2x3)
4W2 + 4W2 . 9QW + 324 + 16W2 - 120W + 144 = 2V
117
-------
241T - 210W = 2V - 468
W2 - 8.75W = 0.08333V - 19.5
Solve the quadratic equation by completing the square.
W2 - 8.75W + 19.14 = 469.5 + 19.14
(W - 4.375)2 = 488.6
W - 4.375 = 22.10
W = 26.5 m (86.9 ft)
L = 26.5 x 4 = 106.0 m (348 ft)
A = 106.0 x 26.5 = 2809 m2 (3.02 x 104 ft2)
Check the 2pond water temperature using the surface area of 2809 m
(30,236 f t ) and the other known characteristics in the Mancini and
Barnhart equation (Section 3.3.5).
QT1
w
Af + Q
T - 2809(0.5)(-5) + 1893(15) !
'w 2809(0.5) + 1893
T,, = 6.5°C (44°F)
W
Second iteration
The temperature of the pond water will be colder than originally
estimated; therefore, the pond area required will increase and more heat
will be lost. The next estimate will be lower than the value resulting
from the first iteration.
Assume T.. = 5°C
W
pm
cpm
= 0.276(1.036)
= 0.162 day"1
5-20
4
0.162
30 /
200
-1
= 15.0 d
= 15/4 = 3.75 d
3.75(1893) = 7099 m3(2.51 x 105 ft3)
118
-------
VT - 8.75W = 0.08333V - 19.5
(W - 4.375)2 = 572.06 + 19.14
W - 4.375 = 591.2 . ,
W = 28.7 m (93 ft)
L = 28.7 x 4 = 114.8 m (371 ft)
A = 28.7 x 114.8 = 3295 m2 (3.55 x 104 ft2)
T = 3295(0. 5)(-5) + 1893(15)
'w 3295(0.5) + 1893
Tw = 5.7°C (42°F)
The second value of T of 5.7°C is in close agreement with the assumed
value of 5.0°C, ana further refinement is not justified. The
temperature will decrease as the wastewater flows from one pond to the
next, but the change is not large enough to significantly affect the
design based on an average temperature.
Final Size of Ponds
t = 15.0 d
= 3.75 d
28,396 m3 (1.00 x 106 ft3)
Vj_ = V2
V3 « V4 = 7,099 m3 (2.51 x 105.ft3)
A = 13,180 m2 (1.42 x 105 ft2)
(3>55 x 1C)4 ft2)
Al = A2 = A3 = A4 = 3295
A freeboard of 0.6 m (2 ft) should be provided. The dimensions of a
single cell at the top of the inside of the dike will be 40.7 m x 126.8
m (131.4 ft x 409.5 ft). .; .
The advantage of a four cell system can be demonstrated by considering
the detention time and area that would be required for a two -cell
system. Using the same assumptions as those used in the previous case,
with n = 2 and TW = 5°C:
First iteration
t
2
0.162
/ \
/ 200 \
L\30/
1/2
= 19.5 d
119
-------
t, =
t2 = 9.75 d
' 9.75 (1893) =18,457 m3. (6.5xl05 ft3)
8.75W = 0.08333V - 19.5
W2 - 8.75W = 1518.5
(W - 4.375)2 = 1518.5 + 19.14
W - 4.375 = 39.2
43.6 m (143 ft)
W
L = 4 x 43.6 = 174.4 m (572 ft)
A-
7604 m2 (81,850 ft2)
Tw =
7604(0.5)(-5) + 1893(15)
7604(0.5) + 1893
= 1.6°C (35°F)
Second iteration
Let Tw = 1°C
k = 0.276 (1.036)
kpm = 0.141 day'1
1-20
t =
2
0.141
30
•Y/2i
'
= 22.4 d
M1 = 11.2 (1893) = 21,202 m3 (7.49xl05 ft3)
W2 - 8.75W = 0.08333(21,202) - 19.5
(W - 4.375)2 = 1747 +19.14
W - 4.375 =42.0
W = 46.4 m (152 ft)
L = 4 x 46.4 = 185.6 m (609 ft)
120
-------
A = 46.4 x 185.6 = 8612 m2 (9.3xl04 ft2)
T = 8612(0.5)(-5) + 1893(15)
'w 8612(0.5) + 1893
T =
W
(34°F)
The assumed value of T of 1.0°C is in excellent agreement with the
calculated value of 1.1°C; therefore, the design is satisfactory. Using
only 2 cells instead of 4 will increase the detention time required by
approximately 50% and will increase the surface area and volume required
by a factor of approximately 3. This would be undesirable for winter
operations in cold climates because of the enhanced potential for ice
formation and the additional cost for construction.
Equations are available to estimate the oxygen requirements in aerated
ponds; however, the use of these equations requires assuming two or more
parameters which have a wide range of values from which to choose.
Experience has shown that basing the biological oxygen requirements on
1.5 times the mass of BOD,- entering each cell is satisfactory in a mild
climate such as the one described in this example. In cold climates
where solids accumulation will be greater, the factor should be
increased to 2.0 kg O^/kg of BOD,- applied to each cell.
Equipment manufacturers' catalogs must be consulted when selecting
aerators. All types of equipment must be evaluated to ensure that the
most economical system is selected. An economic analysis and good
engineering judgment is required to select aeration equipment.
The following relationship is used to estimate aeration requirements:
N =
where,
a
"Csw-CL "
L GS J
T -20
(1.025) W
«
N = equivalent oxygen transfer to tapwater at standard condi-
tions, kg/hr
N = oxygen required to treat the wastewater, kg/hr
oxygen transfer in wastewater = n g
a oxygen transfer in tapwater
C, = minimum DO concentration maintained in the waste, assume
L 2.0 mg/1
C = oxygen saturation value of tapwater at 20°C and one
atmosphere pressure = 9.17 mg/1
121
-------
TW = wastewater temperature, °C
C_, = B (CCC)P = oxygen saturation value of the waste, mg/1
bW oo
a _ wastewater oxygen saturation value _ 0 g
~ tapwater oxygen saturation value ~
C__ = tapwater oxygen saturation value at temperature, T '
SS ' W
P = ratio of barometric pressure at plant site to barometric
pressure at sea level, assume.1.0 for the elevation of
100 m
The maximum oxygen transfer will be.required in the summer months. The
summer water temperature in the ponds can be estimated using the Mancini
and Barnhart equation.
T = 3295(0.5)(30) + 1893(15) !
'w 3295(0.5) + 1893
i ''"'•"
Tw = 21.98 22°C (72°F) :
Css = 8.72 mg/1
BODC in the influent wastewater = C. x Q
o o
= (200 g/m3)(1893 m3/d)(kg/1000 g)(d/24 hr)
= 16 kg/hr -~ j".
•
BOD5 in the effluent from pond number one can be calculated as
follows: ,
Cn 1 I''-''
Co
Cl
200
0.162(3.75) + 1
= 124 mg/1
BODg in the influent to pond number two =
Cx x Q = 124 mg/1 (1893 m3/d)(kg/
BODg in effluent from pond number two:
x Q = 124 mg/1 (1893 m3/d)(kg/1000 g)(d/24 hr) = 10 kg/hr
122
-------
_ .
124 [0.162(3.75) + ll 2
I 2 J
C2 = 73 mg/1
BODg in influent to pond number three =
C2 x Q = 73(1893)(1/1000)(1/24) = 6 kg/hr
BODg in effluent from pond number three:
fa . i
73 [6.162(3.75) + 11 3
[ 3 J
C3 = 42 mLg/l
BODg in influent to pond number four =
C3 x Q = 42(1893)(l/1000)(l/24) = 3 kg/hr
Assume that the oxygen demand of the wastewater and solids at peak flow
will be 1.5 times the mean oxygen demand entering each cell. Therefore,
N3 = 1.5 x 16 kg/hr = 24 kg/hr
«1
Na « 1.5 x 10 kg/hr = 15 kg/hr
2
Na = 1.5 x 6 kg/hr = 9 kg/hr
Na » 1.5 x 3 kg/hr = 4.5 kg/hr
4
where, the subscripts 1 through 4 represent ponds 1 through 4.
Cei, = 0.9 (8.72 mg/1) 1.0 = 7.85 mg/1
5W
Qy Requirements
Pond #1:
24 kg 0,,/hr
ti , ___ . - ', . -' C
= 39.7 kg 02/hr
123
-------
Pond #2:
15 kg 0,,/hr
N
_
2 Q 9|7.85
U'y 9.
L.
7 2'°1(1 025)22-20
I/ U.U^D;
Pond #3:
9 kg 0,,/hr
N
__
3 n Q7.85
U*y 9.
t_
7 2'°~(1 025)22'20
•J y ^ J. .UdO ^
= 24.8 kg 02/hr
= 14.9 kg 02/hr
Pond #4:
4.5 kg 02/hr
0.9
7.85 - 2.Q-
9.17
(1,
2232Q = 7.4 kg 02/hr
The use of both surface and diffused air aerators will be illustrated.
Using surface aerators, a value of 1.9 kg O^/kWh (1.4 kg/hr/hp) is,
recommended to estimate the power requirements. A value of 2.7 kg!
02/kWh (2 kg/hp/hr) is recommended for diffused air aeration systems by;
tne manufacturers. The gas transfer rate must be verified for the
equipment selected. The total power required to satisfy the oxygen
demand in the ponds using surface aerators is:
Pond #1:
39.7 kg 02/hr
1.9 kg 02/kWh
Pond #2:
24.8 kg 02/hr
1.9 kg 02/kWh
Pond #3:
14.9 kg 02/hr
1.9 kg, 02/kWh
Pond #4:
7.4 kg 02/hr
1.9 kg 02/kWh
= 20.9 kW (28.Q hp)
= 13.1 kW (17.5 hp)
= 7.8 kW (10.5 hp)
= 3.9 kW (5.2 hp)
124
-------
If diffused air aerators are to be used, the same procedure is performed
as shown above with the exception being to divide by the value of 2.7 kg
Op/kWh. The power requirements for a diffused air system is calculated
as follows:
Pond #1:
39.7 kg 02/hr
2.7 kg 02/kWh
Pond #2:
= 14.7 kW (19.7 hp)
24.8 kg 09/hr
= 9.2 kW (12.3 hp)
2.7 kg 02/kWh
Pond #3:
14.9 kg CL/hr
= 5.5 kW (7.4 hp)
2.7 kg 02/kWh
Pond #4:
7.4 kg 02/hr
2.7 kg 09/kWh
= 2.7 kW (3.7 hp)
The surface and diffused air aerators power requirements must be
corrected for gearing or blower efficiency. Assuming 90 percent
efficiency for both gearing and blower efficiency; the total motor power
required is calculated as follows:
Pond #1:
20Q^9kW = 23.2 kW (31.1 hp)
The values for the other ponds are calculated as shown above. The motor
power requirements are summarized in Table 3-5.
The values shown in Table 3-5 represent approximate power requirements
and are used to select aeration equipment. The actual power
requirements for the ponds using surface aeration will be determined by
using the zone of complete oxygen dispersion reported by equipment
manufacturers and the above power requirements.
125
-------
TABLE 3-5
MOTOR POWER REQUIREMENTS FOR SURFACE
AND DIFFUSED AIR AERATORS
POWER REQUIREMENTS, kW
Pond Number Surface Aerators Diffused Air Aerators
#1
n
#3
#4
TOTAL
23.2
14.6
8.7
4.3
5078
16.3
10.2
6.1
3.0
35.6
Using data presented in a catalog by Aqua-Aerobic Systems, Inc. (27),
ten 2.2-kW (3-hp) surface aerators in the first pond would provide a
zone of complete oxygen dispersion with a diameter of 41.2 m (135 ft)
and a zone of complete mixing with a diameter of 13 m (42 ft) without
draft tubes or anti-erosion assemblies in a pond with a depth of 3 m (10
ft). The arrangement of the aerators is shown in Figure 3-4. The
aerators provide considerable overlap in the zones of complete oxygen
dispersion as well as providing a zone of complete mixing at even
intervals along the tank to disperse any channeling of the flow that may
develop. Similar selections and arrangements can be developed for the
remaining three cells but with decreasing power requirements as shown in
Table 3-5. The main concern in the selection of aerators is that there1
is considerable overlap of the zones of complete oxygen dispersion.
Diffused air aeration requirements for all four ponds are 35.6 kW (47.7
hp). Manufacturers supply motor-blower combinations in 10, 15, 20, etc.
hp; therefore, to meet the 47.7-hp (35.6-kW) requirement for aeration
and to provide flexibility in maintenance and operation, three 15-hp
(11.2-kW) and two 10-hp (7.5-kW) motor-blowers are specified. The
blowers are to be operated in combinations providing 50 hp (37.3 kW) of
aeration with the remaining blowers in reserve.
When the air is distributed with fine bubble perforated tubing (Hinde
Engineering Company) the quantity of air added to a pond is assumed to
be directly proportional to the length of tubing placed in a pond.
Approximately 50-60 percent of the tubing in the first pond is placed
within the first third of the pond. The tubing in the remaining ponds \
can be spaced at equal intervals along the length of the ponds in
proportion to the power requirements in each cell. The distribution of
the tubing is shown in Figure 3-5.
Use of the fine bubble perforated tubing requires that a diligent
maintenance program be established. Many communities have experienced
clogging of the perforations, particularly in hard water areas. If this
method of aeration is specified, the design engineer must emphasize the
importance of adhering to the maintenance schedule.
126
-------
FIGURE 3-4
LAYOUT OF SURFACE AERATORS IN
FIRST CELL OF PARTIAL MIX SYSTEM
Zones of complete
x oxygen dispersion
^ Zones of complete mixing
where solids suspension
occurs
Loqatjon of aerators
varied to prevent
channel of flow
Influent
127
-------
FIGURE 3-5
LAYOUT OF AERATION SYSTEM FOR PARTIAL MIX
DIFFUSED AIR AERATED POND SYSTEM
ro
oo
INFLUENT LJ
4-
1.5m j-
, i-
3m
t
l
V
Cell 1
F Blower House Air Distribution Manifod ^
> i X.
Cell 2
LJ
-^
-
V.
•$
Cell 3
•^tCPng-
i
J.
Cm
t
t >*
Cell 4
'
•^
; AFFLUENT
12m
-------
A settling pond with a two-day detention time is provided after the final
aerated pond.
Summary
V = 28,396 m3
A = 13,180 m2
t = 15.0 d
OP required for treatment (See Table 3-5)
n = 4
3.5 Controlled Discharge Ponds
No rational or empirical design model exists specifically for the design
of controlled discharge wastewater ponds. However, rational and
empirical design models applied to facultative pond design may also be
applied to the design of controlled discharge ponds provided allowance
is made for the required larger storage volumes.
result from the long storage periods relative
discharge periods. Application of the ideal plug flow model developed
for facultative ponds can be applied to controlled discharge ponds if
hydraulic residence times of less than 120 days are considered. A study
of 49 controlled discharge ponds in Michigan indicated that discharge
periods very from less than five days to more than 31 days, and
residence times were 120 days or greater (30).
These larger volumes
to the very short
The following design and operating information for controlled discharge
ponds were extracted from a report entitled "Wastewater Treatment Ponds"
(15). The unique features of controlled discharge ponds are long-term
retention and periodic, controlled discharge usually once or twice a
year. Ponds of this type have operated "satisfactorily in the north-
central U.S. using the following design criteria:
Overall organic loading: 22-28 kg BOD,-/ha/d (20-25 Ib
BOD5/ac/d). °
Liquid depth: not more than 2 .m (6 ft) for the first cell,
not more than 2.5 m (8 ft) for subsequent cells.
Hydraulic detention: At least 6 months of storage above
the 0.6-m (2-ft) liquid level (including precipitation), but
not less than the period of ice cover.
Number of cells: At least 3 for reliability, with piping
flexibility for parallel or series operation.
129
-------
The design of the controlled discharge pond must include an analysis
showing that receiving stream water quality standards will be maintained
during discharge intervals, and that the receiving watercourses can
accommodate the discharge rate from the pond. The design must also
include a recommended discharge schedule.
Selecting the optimum day and hour for release of the pond contents is
critical to the success of this method. The operation and maintenance
manual must include instructions on how to correlate pond discharge with
effluent and stream quality. The pond contents and stream must be
carefully examined, before and during the release of the pond contents.
In a typical program, discharge of effluents follows a consistent
pattern for all ponds. The following steps are usually taken:
1. Isolate the cell to be discharged, usually the final one in the
series, by valving-off the inlet line from the preceding cell.
2. Arrange to analyze samples for BOD, suspended solids, volatile
suspended solids, pH, and other parameters which may be
required for a particular location.
3. Plan to work so as to spend full
discharge throughout the period.
time on control of the
4. Sample contents of the cell to be discharged for dissolved
oxygen, noting turbidity, color, and any unusual conditions.
5. Note conditions in the stream to receive the effluent.
6. Notify the state regulatory agency of results of these
observations and plans for discharge and obtain approval.
7. If discharge is approved, commence discharge, and continue so
long as weather is favorable, dissolved oxygen is near or above
saturation values and turbidity is not excessive following the
"prearranged discharge flow pattern among the cells. Usually
this consists of drawing down the last two cells in the series
(if there are three or more) to about 46 to 60 cm (18 to 24 in)
after isolation, interrupting the discharge for a week or more
to divert raw waste to a cell which has been drawn down and
resting the initial cell before its discharge. When this first
cell is drawn down to about 60 cm (24 in) depth, the usual
series flow pattern, without discharge, is resumed. During
discharge to the receiving waters, samples are taken at least
three times each day near the discharge pipe for immediate
dissolved oxygen analysis. Additional testing may be required
for suspended solids.
Experience with these ponds is limited to northern states with seasonal
and climatic influences on algae growth. The concept will be quite
effective for BOD removal in any location. The process will also work
130
-------
with a more frequent discharge cycle than semi -annually, depending on
receiving water conditions and requirements. Operating the isolation
cell on a fill-and-draw batch basis is similar to the "phase isolation"
technique discussed in Chapter 5.
3.5.1 Design Example
In areas of high evaporation rates or high rainfall, the volume of the
pond should be adjusted to compensate for the water loss or gain. In
this example, it is assumed that rainfall is equal to evaporation,
producing no net change in volume. This example illustrates the design
of a controlled discharge pond using a minimum discharge period
criterion.
Design Conditions:
Minimum discharge period = 30 d
Q = Design flow rate = 1893 m /d (0.5 mgd)
C. = influent BOD,- = 150 mg/L
0 0
"
Ce = effluent BODg = 30 mg/L
kp = reaction rate for plug flow at 20°C = 0.1 day
^20
T = water temperature critical period of the year = 2°C
Requirements: Size a controlled discharge wastewater pond system to
treat the wastewater and specify the following parameters:
1) Detention time, t
2) Volume, V
3) Surface area, A
4) Depth, d
5) Length, L
6) Width, W
Solution: t = 365 d - minimum discharge period
= 365 d - 30 d = 335 d
Discharge can occur when the effluent quality satisfies standards or the
receiving stream flow rate is adequate to receive the effluent. More
frequent discharge periods than once a year can be employed, but it is
131
-------
necessary to evaluate the performance of the system for shorter
hydraulic residence times. The methods used to design facultative ponds
can be used to estimate the performance of a controlled discharge pond.
Raw wastewater is not added to the pond being emptied. Raw wastewater
inlets and effluent withdrawal ports are provided in each cell of the
system. The cells are connected in series to facilitate operation and
flexibility. Three cells are used in this example.
An effective depth (d1) of 1.5 m (5 ft) and a total depth (d) of 2 m
(6.6 ft) is used. This depth allows for adequate light penetration to
sustain photosynthetic oxygen production, providing an aerobic
environment through much of the pond contents. The aerobic environment
enhances treatment and reduces odor problems. Also, to control odors
during discharge periods, the pond is emptied to a minimum depth of 0.5
m (1.5 ft). Additional volume must be provided to compensate for this
minimum withdrawal depth.
A/cell =
effective volume _ Q x t 1893 m /d x 335 d
n x effective depth 3 x d1 3 x 1;5 m
= 140,900 nT (35 ac) • j .
This area is used to calculate the total volume for the pond total
depth:
d = 1.5 m + 0.5 m = 2 m (6.6 ft)
V/cell = (A/cell)(d) = (140,900 m2)(2 m)
= 281,800 m3 (74.4 x 106 gal)
Significant volumes of wastewater may be lost through seepage if the
pond bottom is not scaled. For this example seepage rates are
considered minimal.
The length to width ratio of the cells in a controlled discharge pond
has less affect on the performance of the system than in flow through
systems. Dimensions for the cells are selected to avoid short
circuiting during discharge or inter-basin transfer. A length to width
ratio of 2:1 was selected for this example.
Dimensions of Ponds
The dimensions of each pond with side slopes of 4:1 and a length to
width ratio of 2:1 can be calculated using the formula first presented
in Section 3.2.
132
-------
V =
where,
(L x W) + (L - 2sd)(W - 2sd) + 4 (L - sd)(W - sd)l|
Vj = volume of pond fl - 281,800 m3
L = length of pond at water surface, m
W = width of pond at water surface, m
s = horizontal slope factor, i.e., 4:1 slope, s = 4
d = depth of pond = 2 m (6.6 ft)
(281,800) | = (L x -£•) + (L - 2x4x2) (jj- - 2x4x2)
+ 4 (L - 4x2)(?r - 4x2)
3L3 - 721 + 512 = 845,400
L2 - 24L = 281,630
Solve the quadratic equation by completing the square.
L2 - 24L + 144 = 281,630 + 144
(L-12)2 » 281,774
'L-12 = 530.8
L = 542.8 m (1780 ft)
W = 542.8/2 = 271.4 m (890 ft)
A freeboard of 0.6 m (2 ft) should be provided. The dimensions of each
pond at the top of the inside of the dike will be 547.6 m x 276.2 m.
The three ponds shall be interconnected by piping for parallel and
series operation.
Effluent Quality Prediction
In a pond with a hydraulic residence time of over 300 days, it is
obvious that an effluent with a BOD,- concentration of less than 30 mg/1
can be achieved. However, if it beBomes necessary to discharge at other
intervals of time, some method of estimating the effluent quality is
needed. Controlled discharge ponds are basically a facultative pond,
and the effluent quality can be predicted using the plug flow model used
to design a facultative pond in Section 3.2.
133
-------
co !
where,
Cg = effluent BODg concentration, mg/1
C = influent BODj- concentration, mg/1
O 0
e = base of natural logarithms, 2.7183
k = plug flow first order reaction rate, day"
t = hydraulic residence time, d
T -20
k = k (1.09) w
Pt P20
k = reaction rate at minimum operating water temperature, day~
pt
kn - reaction rate at 20°C = 0.1 day"
P20 ;
TW = minimum operating water temperature, °C.
Assume that it becomes necessary to discharge from the ponds after a
mean hydraulic residence time of 100 days when the mean water
temperature during the period was 2°C. What would be the concentration
of BODg in the effluent?
k » 0.1 (1.09)2"20
Pt
k = 0.021 day"1
pt
Ce -0.021(100)
e
Ce = 18 mg/1
i
The BODg concentration of 18 mg/1 in the effluent will easily satisfy
the staHdard of 30 mg/1. Suspended solids concentrations will have to
be monitored on site to ensure that the standards for discharge are met.
The guidelines presented at the beginning of this example must be
followed in operating the controlled discharge pond system.
134
-------
Summary
V = 845,400 m3
A = (542.8)(271.4)(3) = 441,950 m2
t = 335 d
3.6 Complete Retention Ponds
In areas of the U.S. where the moisture deficit, evaporation minus
rainfall, exceeds 75 cm (30 in) annually, a complete retention
wastewater pond may prove to be the most economical method of disposal.
Complete retention ponds must be sized to provide the necessary surface
area to evaporate the total annual wastewater volume plus the
precipitation that would fall on the pond. The system should be
designed for the maximum wet year and minimum evaporation year of record
if overflow is not permissible under any circumstances. Less stringent
design standards may be appropriate in situations where occasional
overflow is acceptable or an alternative disposal area is available
under emergency conditions.
Monthly evaporation and precipitation rates must be known to properly
size the system. Complete retention ponds usually require large land
areas, and these areas are not productive once they have been committed
to this type of system. Land for this-system must be naturally flat or
be shaped to provide ponds that are uniform in depth, and have large
surface areas. The design procedure for a complete retention wastewater
pond system is presented in the following example.
Design Conditions:
Table 3-6 presents data from NOAA (31) for estimating evaporation and
precipitation in southern Arizona. The air temperature and wind speed
data represent mean values over a 54- and 61-year period, respectively.
The precipitation data are the mean of the five wettest years over a
60-year period. The pan evaporation data represent the year with the
lowest evaporation for a 10-year period. These values generally
represent the worst case, thus providing for a conservative design.
The difference between the surface water temperature and the air
temperature is assumed to be 1°C. The selection of this value can have
a significant effect on the evaporation losses as shown in Figure 3-7;
therefore, the value must be selected to reflect local conditions.
Surface water temperature = T = air temperature (T ) minus 1°C.
0 cl
135
-------
TQ - Ta = -1°C.
Q = 950 m3/d (0.25 mgd)
Influent BOD& = 150 mg/1
Seepage = 0.80 mm/d (0.2 in/wk) (32). Seepage is prohibited in some
areas. State agency wastewater facility standards may require the pond
bottom be sealed with an impervious liner, reducing seepage to zero.
Elevation = 300 m (980 ft) above MSL.
Requirements: Size a complete retention wastewater pond with no
overflow for the given geographic area. Specify the following: '.
1 Are, A 0 065 d/yr) ;
' d-(Annual Precip.-Annual Evap.-Annual Seepage)
2. Surface area, A
3. Depth, d
4. Length, L
5. Width, W
Solution: The design procedure^consists of the following steps:
1. Using the data in Table 3-6 with Figure 3-6 (Elevation = 305 m).
and Figure 3-7, determine the mean monthly evaporation from the
pond. The calculation of pond evaporation is shown on the
figures by dashed lines. The results are presented in Table
3-7. ;
2. Using the data presented in Tables 3-6 and 3-7, calculate the
area required for an assumed mean depth for .one year of
operation under design conditions. The mean depth (d) may
range from 0.1 to 1.5 m (0.3 to 5.0 ft). The mean depth is
usually near 1 m (3 ft).
3. Use the A value determined in step 2 to calculate the stage of
the pond at the end of each month of operation during the
design year.
4. Calculate the monthly stage of the pond under average
conditions. If the pond is designed to never overflow, the
average yearly evaporation and seepage must exceed the inflow
and precipitation entering the pond.
5. Repeat steps 2 and 3 until a satisfactory pond depth is
obtained.
136
-------
TABLE 3-6
CLIMATOLOGICAL DATA FOR CALCULATING POND EVAPORATION AND PRECIPITATION
CO
Month .
(Days in
Month )
January (31)
February (28)
March (31)
April (30)
May (31)
June (30)
July (31)
August (31)
September (30)
October (31)
November (30)
December (31)
TOTAL
Mean
Precipitation
mm/month
12.3
12.1
10.1
4.2
2.9
• 2.2
6.8
15.9
10.6
7.8
8.3
14.6
107.8
Air Temp.
°C
12.4
14.9
17.7
21.0
24.6
29.3
32.8
32.4
29.1
22.6
16.8
12.9
Wind Speed
kts.,daya
140.4
148.7
154.2
157.0
154.2
134.9
- 140.4
134.9
115.6
110.1
126.6
143.2
Minimum Ten-Year
Pan Evaporation
mm/month mm/ day
87.5 2.82
130.5 4.66
198.2 6.39
238.1 7.94
332.0 10.71
374.4 12.48
416.0 13.42
347.8 11.22
278.5 9.28
210.4 6.82
137.4 4.58
95.2 3.07
2847.0
Mean Ten-Year
Pan Evaporation
mm/month
105.0
177.5
220.0
271.4
.365.2
423.1
449.3
389.5
323.1
219.9
163.5
131.4
3238.9
Kts = knots = total of nautical miles/hr of wind per day.
-------
FIGURE 3-6
PORTION OF ADVECTED ENERGY (INTO A CLASS A PAN) UTILIZED FOR
EVAPORATION IN METRIC UNITS (33)
0,9 -ii
ELEVATION = 3048 M. ABOVE MSL
ELEVATION = 305 M. ABOVE MSL I
0,2
0,1
2O 3O 0 10 20
PAN WATER TEMPERATURE, *C
138
-------
FIGURE 3-7
SHALLOW LAKE EVAPORATION AS A FUNCTION OF CLASS A PAN EVAPORATION
AND HEAT TRANSFER THROUGH THE PAN IN METRIC UNITS PER DAY (33)
139
-------
Table 3-7
CALCULATED POND EVAPORATION DATA
Month
January
February
March
April
May
June
July
August
September
October
November
December
TOTAL
ap (Fig. 3-6)
0.58
0.62
0.64
0.66
0.71
0.74
0.77
0.77
0.73
0.58
0.62
0.58
Pond Evaporation (Fig. 3-7)
mm/daymm/month
1.7
3.0
4.1
5.2
7.2
8.4
9.0
7.4
6.2
4.4
2.9
1.8
As a starting point, select a mean depth of 0.4 m
required surface area to evaporate the wastewater.
53
84
127
156
223
252
279
229
186
136
87
56
1568
to estimate the
A =
(946 nr/d)(365 d/yr)
0.4 - (0.1078 - 1.868 - 0.277)
= 142,259 nr (35 ac)
Use A = 142,300 m (35 ac) to calculate the stage of the pond at the end
of each month of operation. Table 3-8 contains a summary of the results
of this procedure for the design year of operation assuming the pond is
empty at the beginning of the year.
An examination of the pond stage results in Table 3-8 shows that the
maximum depth of water in the pond during the design year (conservative
design data) would be 0.60 m (2 ft) plus the depth at the beginning of
the design year. The pond stage under average conditions is shown in
Table 3-9. Average evaporation and seepage are within 5 percent of
inflow and precipitation. Assuming that several average years would
occur in sequence, there would be a small accumulation of water in the
pond. Because of the imprecise methods available to predict the
sequence of occurrence of the design year,, maximum, and average years,
the pond surface area of 142,300 m is large enough to prevent overflow
of the pond.
The depth of complete retention ponds is limited only by groundwater
conditions, economics, and evaporation rates. Generally maximum depths
range from 1.0 to 3 m (3 to 10 ft) with a freeboard of 0.6 m (2 ft).
140
-------
TABLE 3-8
VOLUME AND STAGE OF POND AT MONTHLY INTERVALS FOR
DESIGN CONDITIONS AND A = 142,300 nT
Month
(No. of Days
in Month)
Starting Date 1
September (30)
October (31)
November (30)
December (31)
January (31)
February (28)
March (31)
April (30)
May (31)
June (30)
July (31)
August (31)
TOTAL
Starting Date 2
January (31)
February (28)
March (31)
April (30)
May (31)
June (30)
July (31)
August (31)
September (30)
October (31)
November (30)
December (31)
Inflow +
Precipitation'
(m3)
29,888
30,436
29,561
31,404
31,076
28,210
30,763
28,978
29,739
28,693
30,294
31,589
360,631
31,076
28,210
30,763
28,978
29,739
28,693
30,294
31,589
29,888
30,436
29,561
31,404
Evaporation
+ Seepage
(m3)
29,712
22,706
15,624
11,322
10,895
14,981
21,425
25,443
35,086
39,104
43,055
35,940
305,293
10,895
14,981
21,425
25,443
35,086
39,104
43,055
35,940
29,712
22,706
15,624
11,322
Storage
Volume
(m3)
176
7,906
21,843
41,925
62,106
75,335
84,673
88,208
82,861
72,450
59,689
55,338
20,181
33,410
42,748
46,283
40,936
30,525
17,764
13,413
13,589
21,319
35,256
55,338
Pond.
0.00
0.06
0.15
0.29
0.44
0.53
0.60
0.62
0.58
0.51
0.42
0.39
0.14
0.23
0.30
0.33
0.29
0.21
0.12
0.09
0.10
0.15
0.25
0.39
alnflow = Q(no. of days/month); precipitation = (monthly precipitation)
b(A).
Seepage = 0.00076 m/d(no. of days/month)(A); evaporation = (monthly
evaporation)(A).
Storage V = cumulative sum of (inflow + precipitation) - (evaporation
.+ seepage).
Pond stage = storage V/A.
141
-------
TABLE 3-8 (continued)
Month •.?>:.
(No. of Days Inflow + Evaporation Storag
in Month) Precipitation + Seepage Volume
Starting Date 3
(m3) (m3) (m3) (m)
December (31) 31,404 11,322 20,082 0.14
January (31) 31,076 10,895 40,263 0.28
February (28) 28,210 14,981 53,492 0.38
March (31) 30,763 21,425 62,830 0.44
April (30) 28,978 25,443 66,365 0.47
May (31) 29,739 35,086 61,018 0.43
June (30) 28,693 39,104 50,607 0.36
July (31) 30,294 43,055 37,846 0.27
August (31) 31,589 35,940 33,495 0.24
September (30) 29,888 29,712 33,671 0.24
October (31) 30,436 22,706 41,401 0.29
November (30) 29,561 15,624 55,338 0.39
alnflow = Q(no. of days/month); precipitation = (monthly precipitation)
b(A).
Seepage = 0.00076 m/d(no. of days/month)(A); evaporation = (monthly
evaporation)(A).
Storage V = cumulative sum of (inflow + precipitation) - (evaporation
j+ seepage).
Pond stage = storage V/A.
The maximum depth required will depend upon the time of year that
filling of the pond begins and the initial depth of water in the pond
when the design year occurs. It is impossible to predict accurately the
water stage in the pond; therefore, it is necessary to exercise goo|d
judgment based upon the constraints at particular locations. Estimates
beyond the average and design year conditions can be made by analyzing
historical data for the site, but this still is no guarantee of
accuracy.
The water depth in the pond after one year of operation under design
conditions will be equal to the mean depth plus the depth of water at
the beginning of the year. During certain months of the year, the depth
may exceed the mean depth when filling of the pond occurs at the
beginning of the wet season (Table 3-8). Three beginning dates are
shown in Table 3-8 to illustrate the effects of startup date. Using the
above procedure, it is possible for the design engineer to estimate the
stage of the pond under as many conditions as considered necessary.
A maximum depth of 1.2 m (4 ft) would be adequate to avoid overflow from
the pond by providing storage for five average years and a design year
142
-------
in sequence. It is unlikely that five average years of evaporation
would precede the design year. The pond L and W values are calculated
from the A. No restrictions are imposed on the length to width ratio.
Also, the need to divide the pond volume to enhance hydraulic
characteristics is eliminated. The most economical design consists of a
single pond provided the system can be isolated enough to avoid
complaints about odors when solids decompose on exposed slopes.
A = L x W
L = W = A1/2 = (142,300 m2)1/2 = 377 m (1,237 ft)
Summary
1 pond A = 142,300 m2 (35 ac);L = W = 377 m (1,237 ft)
V = 170,800 m3 (45 Mgal);d = 1.2 m (3.9 ft)
TABLE 3-9
VOLUME AND STAGE OF POND AT MONTHLY INTERVALS FOR
AVERAGE CONDITIONS AND A = 142,300 nT
Inflow +
Month Precipitation
«_
Average Year
September
October
November
December
January
February
March
April
May
June
July
August
TOTAL
(nr)'
29,888
30,436
29,561
31,404
31,076
28,210
30,763
28,978
29,739
28,693
30,294
31,589
360,631
Evaporation
+ Seepage
(m3)
33,947
23,480
17,976
14,351
12,404
19,284
23,413
28,551
38,259
43,766
46,231
39,851
341,513
Storage
Vpljume
(m3)
-4,059
6,956
18,541
35,594
54,266
63,192
70,542
70,969
62,449
47,376
31,439
23,177
Pond
j>ta£e
(m)
(no accumu-
0.00 lation)
0.05
0.13
0.25
0.-38
0.44
0.48
0.50
0.44
0.33
0.22
0.16
3.7 Combined Systems
In certain situations it is desirable to design pond systems in
combinations, i.e., an aerated pond followed by a facultative or a
tertiary pond. Combinations of this type are designed essentially the
143
-------
same as the individual ponds. For example, the aerated pond would be
designed as illustrated in Sections 3.3 or 3.4, and the predicted
effluent quality from the aerated pond would be the influent quality for
the facultative pond. The facultative pond would be designed as shown
in Section 3.2. For more discussion on combined pond systems see
References 20, 28, and 34. ,
3.8 References
1. Recommended Standards for Sewage Works., A Report of the Committee
of Great Lakes-Upper Mississippi River Board of State Sanitary
Engineers. Health Education Services, Inc., P.O. Box 7126, Albany^
NY, 1978.
2. Design Criteria for Mechanical, Electric and Fluid System and
Component Reliability. EPA 430/99-74-001, NTIS Report No. PB 227
558, U.S. Environmental Protection Agency, Office of Water Program
Operations, Washington, D.C., 1974.
3. Metcalf and Eddy. Wastewater Engineering. McGraw-Hill, New York,
1979.
4. Al-Layla, M. A., S. Ahma'd, and E. 0. Middlebrooks. Handbook of
Wastewater Collection and Treatment: Principles and Practices.
Garland STPM Press, New York, 1980.
5. Water Pollution Control Federation and American Society of Civil
Engineers. Wastewater Treatment Plant; Design. MOP/8, Washington,
D.C., 1977.
6. Water Pollution Control Federation. Preliminary Treatment for
Wastewater Facilities. MOP/OM-2, Washington, D.C., 1980.
7. Fritz, 0. 0., A. C. Middleton, and D. D. Meredith. Dynamic Process
Modeling of Wastewater Stabilization Ponds. JWPCF,
•51 (11): 2724-2743, 1979.
8. Gloyna E. F. Facultative Waste Stabilization Pond Design. In:
Ponds as a Wastewater Treatment Alternative. Water Resources
Symposium No. 9, University of Texas, Austin, 1976. ;
9. Larson, T. B. A Dimensionless Design Equation for Sewage Lagoons.
Dissertation, University of New Mexico, Albuquerque, 1974.
10. Marais, G. V. R. Dynamic Behavior of Oxidation Ponds. In:
Proceedings of Second International Symposium for.Waste Treatment
Lagoons, Kansas City, Missouri, June 23-25, 1970.
11. McGarry, M. C., and M. B. Pescod. Stabilization Pond Design
Criteria for Tropical Asia. In: Proceedings of Second
144
-------
International Symposium for Waste Treatment Lagoons, Kansas City,
Missouri, June 23-25, 1970.
- i
12. Oswald, W. J., A. Meron, and M. D. Zabat. Designing Waste.Ponds to
Meet Water Quality Criteria. In: Proceedings of Second
International Symposium for Waste Treatment Lagoons, Kansas City,
Missouri, June 23-25, 1970.
13. Thirumurthi, D. Design Criteria for Waste Stabilization Ponds.
JWPCF, 46(9)=2094-2106, 1974.
14. Thirumurthi, D. Design Principles of Waste Stabilization Ponds.
Journal Sanitary Engineering Division, ASCE, 95 (SA2:311-330,
1969.
15. Wastewater Treatment Ponds. EPA 430/9-74/001, U.S. Environmental
Protection Agency, Office of Water Program Opertions, Washington,
D.C., 1975.
16. Neel, J. K., J. H. McDermott, and C. A. Monday. Experimental
Lagooning of Raw Sewage. JWPCF, 33(6):603-641, 1961.
17., Middlebrooks, E. J., C. H. Middlebrooks, J. H. Reynolds, 6. Z.
Watters, S. C. Reed, and D. B. George. Wastewater Stabilization
Lagoon Design, Performance, and Upgrading. Macmillan Publishing
Co., Inc., New York, 1982.
18. Wehner, J. F. and R. H. Wilhelm. Boundary Conditions of Flow
Reactor. Chem. Eng. Sc., 6:89-93, 1956.
19. Gloyna, E. F., and L. F. Tischler. Waste Stabilization Pond
Systems. In: Performance and Upgrading of Wastewater
Stabilization Ponds. EPA 600/9-79-011, NTIS Report No. PB 297504,
U.S. Environmental Protection Agency, Municipal Environmental
Research Laboratory, Cincinnati, Ohio, 1979.
20. Gloyna, E. F. Waste Stabilization Ponds. Monograph Series No. 60.
World Health Organization, Geneva, Switzerland, 1971.
21. Marais, C. V. R., and V. A. Shaw. A Rational Theory for the Design
of Sewage Stabilization Ponds in Central and South Africa.
Transactions, South Africa Institute of Civil Engineers, 3:205,
1961.
22. Mara, D. D. Sewage Treatment in Hot Climates. John Wiley &
Sons, Inc., New York, 1976.
23. Mara, D. D. Discussion. Water Research, 9:595, 1975.
24. Benefield, L. D., and C. W. Randall. Biological Process Design for
Wastewater Treatment. Prentice-Hall, Inc., Englewood Cliffs, N.J.,
1980.
145
-------
25. Mancini, 0. L., and E. L. Barnhart. Industrial Waste Treatment in
Aerated Lagoons. In: Ponds as a Wastewater Treatment
Alternative. Water Resources Symposium No. 9, University of Texas,
Austin, 1976.
26. Malina, 0. F., Jr., R. Kayser, W. W. Eckenfelder, Jr., E. F.
Gloyna, and W. R. Drynan. Design Guides for Biological Wastewater
Treatment Processes. Report CRWR-76. Center for Research in Water
Resources, University of Texas, Austin, 1972.
27. Aqua-Aerobic Systems, Inc. Aqua Jet Aerators. Rockford, Illinois,
1981.
28. Boulier, G. A., and T. J. Atchison. Practical Design and
Application of the Aerated-Facultative Lagoon Process. Hinde
Engineering Company, Highland Park, Illinois, 1975.
29. Reid, L. D., Jr. Design and Operation for Aerated Lagoons in thei
Artie and Subartic. Report 120. U.S. Public Health Service, Artie
Health Research Center, College, Alaska, 1970.
30. Pierce, D. M. Performance of Raw Waste Stabilization Lagoons in
Michigan with Long Period Storage Before Discharge. In:
Upgrading Wastewater Stabilization Ponds to Meet New Discharge
Standards, PRWG151, Utah Water Research Laboratory, Utah Statfr
University, Logan, 1974. :
31. NOAA. Climatic Survey of the United States. National Oceanographic
and Atmospheric Administration, U.S. Department of Commerce,
National Climate Center, Federal Building, Asheville, North
Carolina, 1981.
32. Middlebrooks, E. J., C. D. Perman, and I. S. Dunn. Wastewater
Stabilization Pond Linings. Special Report 78-28, Cold Regions
Research and Engineering Laboratory, Army Corps of Engineers,
Hanover, New Hampshire, 1978.
i
33. U.S. National Weather Service. U.S. Department of Commerce,
National Climate Center, Federal Building, Asheville, North
Carolina, 1981.
34. Rich, L. G. Design Approach to Dual-Power Aerated Lagoons. Journal
Environmental Engineering Division, ASCE, 108 (EE3):532, 1982.
146
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CHAPTER 4
PHYSICAL DESIGN AND CONSTRUCTION
4.1 Introduction
Regardless of the care taken to evaluate coefficients and apply biological or
kinetic models, if sufficient consideration is not given to optimization of
the pond layout and construction, the actual efficiency may be far less than
the calculated efficiency. The physical design of a wastewater pond is as
important as the biological and kinetic design. The biological factors
affecting wastewater pond performance are primarily employed to estimate the
required hydraulic residence time to achieve a specified efficiency. Physi-
cal factors, such as length to width ratio, determine the actual treatment
efficiency achieved.
Length to width ratios are determined according to the design model used.
Complete mix ponds should have a length to width ratio near 1:1, whereas plug
flow ponds require length to width ratios of 3:1 or greater. The danger of
groundwater contamination may impose seepage restrictions, necessitating
lining or sealing the pond. Reuse of the pond effluent in dry areas where
all water losses are to be avoided may also dictate the use of linings.
Layout and construction criteria should be established to reduce dike erosion
from wave action, weather7 rodent attack, etc. Transfer structure placement
and size affect flow patterns within the pond and determine operational
capabilities in controlling the water level and discharge rate. These
important physical design considerations are discussed in the sections that
follow.
4.2 Dike Construction
Dike stability is most often affected by erosion caused by wind-driven wave
action or rain and rain-induced weathering. Dikes may also be destroyed by
burrowing rodents. A good design will anticipate these problems and provide
a system which can, through cost-effective operation and maintenance, keep
all three under control.
4.2.1 Wave Protection
Erosion protection should be provided on all slopes; however, if winds are
predominantly from one direction, protection should be emphasized for those
areas that receive the full force of the wind-driven waves. Protection
147
-------
should always extend from at least 0.3 m (II ft) below the minimum water
surface to at least 0.3 m (1 ft) above the maximum water surface (1). Wave
height is a function of wind velocity and fetch (the distance over which the
wind acts on the water). The size of riprap depends on the fetch length
(2). Riprap varies from river run rocks that are 15-20 cm (6-8 in) to quarry
boulders that are 7-14 kg (15-30 Ib). Uniformly graded river run material,
when used for riprap, can be quite unstable. River run rocks, if not
properly mixed with smaller material and carefully placed, can be loosened by
wave action and caused to slip down the steeper sloped dikes. Broken
concrete pavement can often be used for riprap but can make mechanical weed
control very difficult.
Asphalt, concrete, fabric, and low grasses can also be used to provide
protection from wave action. When riprap is used for wave protection, the
designer must take into consideration its effect on weed and rodent control,
and routine dike maintenance.
4.2.2 Weather Protection l
Dike slopes must be protected from weather erosion as much as from wave
erosion in many areas of the country. The most common method of weather
erosion protection when large dike areas are involved uses grass. Because of
large variations in depth encountered in total containment ponds, they often
have large sloped dike areas which cannot be protected in a more cost-
effective way. Ponds which have only minimum freeboard and have constant
water depth are often protected more cost effectively when the riprap is
carried right to the top of the slope and serves for both wave and weather
protection.
In some cases climate and soil conditions are suitable for completely bare
dike slopes without major weather erosion problems. Figure 4-1 shows the
erosion effects on the bare slopes of a stabilization pond.
Weather erosion, unlike wave erosion, can also affect the top and outside
slopes of the pond diking sstem. The designer should make sure that the
all-weather road system for the top of the dike is of sufficient width to
allow traffic to pass over every part of the surface. Too narrow a road will
result in ruts that can create runoff erosion problems in areas of high rain
intensity. Final grading should be specified to minimize rutting and
frequent maintenance and control surface runoff erosion.
It is also necessary to protect the exterior surface of dikes. A thin layer
of gravel may be used; placement of topsoil and seeding with grass may be
less expensive initially but grass requires periodic cutting. In some
locations sheep can be used to keep exterior grass slopes maintained. Other
native groundcover plantings may also be used. Local highway department
experience on erosion control for cut-and-fill slopes can be a guide.
148
-------
FIGURE 4-1
ERODED DIKE SLOPES ON A
RAW WASTEWATER POND IN A DRY CLIMATE
4.2.3 Rodent Protection
If a stabilization pond is located in an area that supports an exceptionally
high population of burrowing animals, such as muskrats and nutria, good
design can control this threat of dike stability. Broken concrete or other
riprap that does not completely cover the dike soil can become a home for
burrowing rodents. Riprap design and placement-should be aimed toward limit-
ing the creation of voids which allow rodents to burrow near the water
surface.
Varying pond water depth can discourage muskrat infestation (3). Muskrats
prefer a partially submerged tunnel, so design provisions to vary the water
level over a several-week period will discourage them from burrowing in the
dike. Such provisions will often add to the expense of riprap placement for
wave protection but can greatly reduce operation and maintenance expenses.
4.2.4 Seepage
Dikes should be designed and constructed to minimize seepage. Vegetation and
porous soils should be removed and the embankment should be well compacted.
149
-------
Use of conventional construction equipment is usually suitable for this
purpose.
Seepage collars should be provided around any pipes penetrating the dike (4)
(5). The seepage collars should extend a minimum of 0.6 m (2 ft) from the
pipe. Proper installation of transfer pipes can be assured by building up
the dike at least 0.6 m (2 ft) above the pipe elevation, digging a trench for
the pipe and seepage collar, backfilling the trench, and compacting the
backfill. ;
In some circumstances it may be necessary to control seepage and ensure bank
stability at the exterior toe. A filter blanket material can be used (6).
Another method of preventing seepage where embankment material cannot be
adequately compacted is placement of an impervious core in the levee with
imported material.
4.3 Pond Sealing
4.3.1 Introduction
The need for a well-sealed stabilization pond has impacted modern pond
design, construction, and maintenance. The primary motive for sealing ponds
is to prevent seepage. Seepage effects treatment capabilities by causing
fluctuation in the water depth and can cause pollution of groundwater.
Although many types of pond sealers exist, they can be classified into one of
three major categories: (1) synthetic and rubber liners, (2) earthen and
cement liners, and (3) natural and chemical treatment sealers. Within each
category also exists a wide variety of application characteristics. Choosing
the appropriate lining for a specific site is a critical issue in pond design
and seepage control. Detailed information is available from manufacturers,
and in other publications (4)(6). ;
4.3.2 Seepage Rates ;
i
Stander et al. (7) presented a summary of information (Table 4-1) on measured
seepage rates in wastewater stabilization ponds. Seepage is a function of so
many variables that it is impossible to anticipate or predict rates even with
extensive soils test. The importance of controlling seepage to protect
groundwater dictates that careful evaluations be conducted before construc-
tion of ponds to determine the need for linings and the acceptable types.
The Minnesota Pollution Control Agency (8) initiated an intensive study to
evaluate the effects of stabilization pond seepage from five municipal
systems.
150
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TABLE 4-1
REPORTED SEEPAGE RATES FROM POND SYSTEMS (7)a
en
Location
Mojave, CA
Kearney, NBD
Filer City, MI
Pretoria, SAC
Windhoek, SWAd
Pond No. 5
Pond No. 6
Pond No. 7
Pond No. 8
Pond No. 9
Geology of
Pond Base
Desert soil
(sandy soil)
Sand and gravel
Sandy soil
Clay loam and
shale
Mica and schist
Mica and schist
Mica
Mica and schist
Mica and schist
with side wall
seepage to
river
Initial
Seepage
Rate
cm/d
22.4
14.0
—
__
0.41
0.43
0.04
0.15
0.58
m3/m2/d
0.19
0.12
—
0.13
0.003
0.003
0.0003
0.0013
0.005
Hydraulic
Load
n,3/m2/d
0.30
0.13
—
0.05
0.73
1.11
0.67
0.67
0.43
Seepage
Rate as % of
Hydraulic
Load
63
90
__
N/A
0.45
0.32
0.04
0.19
0.12
Settling-in Eventual Seepage Hydraulic
Period Rate Load
cm/d m3/m2/d m3/m2/d
9 mo 0.9 0.007 0.36
1 yr 1.5 0.013 0.04
Average over 0.9 0.007 0.009
5 yr
+ 1 yr 0.8 0.006 0.05
A —— — — — —
e
e
e
e
Seepage
Rate as % of
Hydraulic
Load
2
29
84
13
—
—
—
—
—
aCourtesy of Ann Arbor Science Publishers, Inc., Ann Arbor, MI.
Evaporation and rainfall effects apparently not corrected for. Seepage losses also influenced at times by a high water table.
cConstructed in sandy soil for the express purpose of seeping away Paper Mill NSSC liquor.
^Constructed for the express purpose of water reclamation.
eSettling-in period is nine days after all ponds are in full operation.
-------
The five communities were selected for study on the basis of geologic
setting, age of the system, and past operating history of the pond. The
selected ponds were representative of the major geomorphic regions in the
state, and the age of the systems ranged from 3 to 17 years. ;.
Estimates of seepage were calculated by two independent methods for each of
the five pond systems. Water balances were calculated by taking the
difference between the recorded inflows and outflows, and pond seepage Was
determined by conducting in-place field permeability tests of the bottom
soils at each location. Good correlation was obtained with both techniques.
i
Field permeability tests indicated that the additional sealing from the
sludge blanket was insignificant in locations where impermeable soils were
used in the construction process. In the case of more permeable soils, ;it
appeared that the sludge blanket reduced th£ permeability of the bottom soils
from an initial level of 10"^ or 10~5 cm/sec to the order of 10~6
cm/sec. At all five systems evaluated, the stabilization pond was in contact
with the local groundwater table. Local groundwater fluctuations had a sig-
nificant impact on seepage rates. Reduced groundwater gradient resulted in
a reduction of seepage losses at three of the sites. Contact with ground-
water possibly explains the reduction in seepage rates in many ponds; in the
past this reduction in seepage rates has been attributed totally to a sludge
buildup. In an area underlain by permeable material where little groundwater
mounding occurs, there is probably little influence from the water table on
seepage rates. The buildup of sludge on the bottom of a pond appears to
improve the quality of the seepage water leaving the pond. Sludge accumu-
lation apparently increases the cation exchange capacity of the bottom of the
pond.
Groundwater samples obtained from monitoring wells did not show any appre-
ciable increases in nitrogen, phosphorus, or fecal coliform over the
background levels after 17 years of operation. The seepage from the ponds
did show an increase in soluble salts as great as 20 times over background
levels. Concentrations of 25 mg/1 to 527 mg/1 of chloride were.observed.
A comparison of observed seepage rates for various types of liner material is
presented in Table 4-2 (4). If an impermeable liner is required, it appears
that one of the synthetic materials must be used. . . !
4.3.3 Natural and Chemical Treatment Sealing
The most interesting and complex techniques of pond sealing, either sepa-
rately or in combination, are natural pond sealing and chemical treatment
sealing (5)(9).
Natural sealing of ponds has been found to occur from three mechanisms: (1)
physical clogging of soil pores by settled solids, (2) chemical clogging of
soil pores by ionic exchange, and (3) biological and organic clogging caused
152
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TABLE 4-2
SEEPAGE RATES FOR VARIOUS LINERS9 (4)b
Minimum Expected
Seepage Rate at
6 m of Water Depth
Liner Material Thickness After 1 Yr of Service
cm cm/d
Open sand and gravel
Loose earth
Loose earth plus chemical treatment*
Loose earth plus bentonite*
Earth in cut
Soil cement (continuously wetted)
Gunite
Asphalt concrete
Unreinforced concrete
Compacted earth
Exposed prefabricated asphalt panels
Exposed synthetic membranes
10.2
3.8
10.2
10.2
91
1.3
0.11
244
122
30.5
25.4
30.5
10.2
7.6
3.8
3.8
0.76
0.08
0.003
The data are based on actual installation experience. The chemical and
bentonite (*) treatments depend on pretreatment seepage rates, and in the
btable loose earth values are assumed.
Courtesy of John Wiley & Sons, Inc., New York, NY.
by microbial growth at the pond lining. The dominant mechanism of the three
depends on the characteristics of the wastewater being treated. Chemical
treatment changes the nature of the bottom soil to ensure sealing.
Infiltration characteristics of anaerobic ponds were studied in New Zealand
(10). Certain soil additives were employed (bentonite, sodium carbonate,
sodium triphosphate) in 12 pilot ponds with varying water depth, soil type,
and compacted bottom soil thickness. It was found that chemical sealing was
effective for soils with a minimum clay content of 8 percent and a silt
content of 10 percent. Effectiveness increased with clay and silt content.
Four different soil columns were placed at the bottom of an animal wastewater
pond to study physical and chemical properties of soil and sealing of ponds
(11). It was discovered that the initial sealing which occurred at the top 5
cm (2 in) of the soil columns was caused by the trapping of suspended matter
in the soil pores. This was followed by a secondary mechanism of microbial
growth that completely sealed off the soil from water movement.
153
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A similar study performed in Arizona (12) also found this double mechanism of
physical and biological sealing. Physical sealing of the pond was enhanced
by the use of an organic polymer united with bentonite clay. This additive
could have been applied with the pond full or empty, although it was more
effective when the pond was empty.
An experiment was performed in South Dakota (13) in an effort to relate the
sodium adsorption ratio (SAR) of the in situ soil to the sealing mechanism of
stabilization ponds. No definite quantitative conclusions were formed. The
general observation was made that the equilibrium permeability ratio de-
creases by a factor of 10 as SAR varies from 10 to 80. For 7 out of 10 soil
samples, the following were concluded: (1) SAR did affect permeability of
soils studied; (2) as the SAR increased, the probability that the pond would
seal naturally also increased; and (3) soils with higher liquid limits3
would probably be less affected by the SAR. ,
Polymeric sealants have been used to seal both filled and unfilled ponds
(14). Unfilled ponds have been sealed by admixing a blend of bentonite and
the polymer directly into the soil lining. Filled ponds have been sealed by
spraying the fluid surface with alternate slurries of the polymer and
bentonite. It has been recommended that the spraying take place in three
subsequent layers: (1) polymer, (2) bentonite, and (3) polymer. The
efficiency of the sealant has been found to be significantly affected by the
characteristics of the impounded water. Most importantly, calcium ions in
the water exchange with sodium ions in the bentonite and cause failure of the
compacted bentonite linings.
Davis et al. (15) found that for liquid dairy waste the biological clogging
mechanism predominated. In a San Diego County study site located on sandy
loam, the infiltration rate of a virgin pond was measured. A clean water
infiltration rate for the pond was 122 cm/d (48 in/d). After two weeks of
manure water addition, infiltration averaged 5,,8 cm/d (2.3 in/d); after four
months, 0.5 cm/d (0.2 in/d).
A study performed in southern California (Hi) indicated similar results.
After waste material was placed in the unlined pond in an alluvial silty
soil, the seepage rate was reduced. The initial 11.2 cm/d (4.4 in/d) seepage
rate dropped to 0.56 cm/d (0.22 in/d) after three months, and to 0.30 cm/d
(0.12 in/d) after six months.
4.3.4 Design and Construction Practice
4.3.4.1 Lining Materials i
t
Presentation of recommended pond sealing design and construction procedures
is divided into two categories: (1) bentonite, asphalt, and soil cement
The liquid limit is defined as the water content of a soil (expressed in
percent dry weight) having a consistency such that two sections of a soil
cake, placed in a cup and separated by a groove, barely touch but do not
flow together under the impact of several sharp blows.
154
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liners, and (2) thin membrane liners. This division was selected because of
the major differences between the application techniques. There is some
similarity between the application of asphalt panels and the elastomer liners
and of necessity there will be some repetition in these two discussions. A
partial listing of the trade names and sources of common lining materials is
presented in Tables 4-3 and 4-4.
Regardless of the type of material selected as a liner there are many common
design, specification, and construction practices. A summary of the common
effective design practices in cut-and-fill reservoirs is given in Table 4-5.
Most of these practices are commonsense items and would appear to not require
mentioning. Unfortunately, experience has shown these items to be the most
commonly ignored.
a. Bentonite, Asphalt, and Soil Cement
The application of bentonite, asphalt, and soil cement as lining materials
for reservoirs and wastewater ponds has a long history (4). The following
summary includes consideration of the method of using the materials,
resultant costs, evaluations of durability, and effectiveness in limiting
seepage. The cost analysis is somewhat arbitrary, since this cost depends
primarily on the availability of the materials. A summary of state standards
developed or being developed to control the application of these types of
materials is presented elsewhere (6).
Bentonite is a sodium-type montmorillonite clay, and exhibits a high degree
of swelling, imperviousness, and low stability in the presence of water.
Different ways in which bentonite may be used to line ponds are listed below.
1. A suspension of bentonite in water (with a bentonite concentration
approximately 0.5 percent of the water weight) is placed over the
area to be lined, and the bentonite settles to the soil surface
forming a thin blanket.
2. The same procedure as (1), except frequent harrowing of the surface
produces a uniform soil bentonite mixture on the surface of the
soil. The amount of bentonite used in this procedure is
approximately 4.5 kg/mz (1 lb/ft2) of soil.
3. A gravel bed approximately 15 cm (6 in) deep is first prepared and
the bentonite application performed as in (1). The bentonite will
settle through the gravel layer and seal the void spaces.
4. Bentonite is spread as a membrane 2.5 to 5 cm (1 to 2 in) thick and
covered with a 20 to 30 cm (8 to 12 in) blanket of earth and gravel
to protect the membrane. A mixture of earth and gravel is more
satisfactory than soil alone, because of the stability factor and
resistance to erosion.
155
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Trade Name
Aqua Sav
Armor last
Armorshell
Armortlte
Arrowhead
Biestate Liner
Careymat
CPE (resin)
Cover!ight
Driliner
EPDM (resin)
Flexseal
Geon (resin)
Griffolyn 45
Griffolyn E
TABLE 4-3
TRADE NAMES OF COMMON LINING
Product Description
Butyl rubber
Reinforced neoprene
and Hypalon
PVC-nylon laminates
PVC coated fabrics
Bentonite
Biologically stable PVC
Prefabricated asphalt
panels
Chlorinated PE resin
Reinforced butyl and
Hypalon
Butyl rubber
Ethylene propylene
diene monomer resins
Hypalon and reinforced
Hypalon
PVC resin
Reinforced Hypalon
Reinforced PVC
MATERIALS (4)a
Manufacturer
Plymouth Rubber
Canton, MA
Cooley, Inc.
Pawtucket, RI
Cooley, Inc.
Pawtucket, RI
Cooley, Inc.
Pawtucket, RI
Dresser Minerals
Houston, TX
Goodyear Tire & Rubber Co.
Akron, OH
Phillip Carey Co.
Cincinnati, OH
Dow Chemical Co.
Midland,-MI
Reeves Brothers, Inc.
New York, NY
Goodyear Tire & Rubber Co.
Akron, OH
U.S. Rubber Co.
New York, NY
B. F. Goodrich Co.
Akron, OH
B. F. Goodrich Go.
Akron, OH
Griffolyn Co., Inc.
Houston, TX
Griffolyn Co., Inc.
Houston, TX
156
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Trade Name
Grfffolyn V
Gundline
Hydro!i ner
Hydromat
Hypalon (resin)
Ibex
Koroseal
Kreene
Meadowmat
@>
National Baroid
Nordel (resin)
Panel craft
Paraqual
Petromat
Pliobond
Polyliner
Red Top
TABLE 4-3 (continued)
Product Descri pti on Manufacturer
Reinforced PVC, oil
resi stant
Griffolyn Co., Inc.
Houston, TX
High density polyethylene Gundle Lining Systems, Inc.
Houston, TX
(HOPE)
Butyl rubber
Prefabricated asphalt
panels
Chlor9sulfonated PE
resin
Bentonite
PVC films
PVC films
Prefabricated asphalt
panels with PVC core
Bentonite
Ethylene propylene
diene monomer resin
Prefabricated aspahlt
panels
EPDM and butyl
Polypropylene woven
fabric (base
fabric-spray linings)
PVC adhesive
PVC-CPE, alloy film
Bentonite
157
Goodyear Tire & Rubber Co.
Akron, OH
W. R. Meadows, Inc.
Elgin, IL
E. I. Du Pont Co.
Wilmington, DE
Chas. Pfizer & Co.
New York, NY
B. G. Goodrich Co.
Akron, OH
Union Carbide & Chemical Co.
New York, NY
W. R. Meadows, Inc.
Elgin, IL
National Lead Co.
Houston, TX
E. I. Du Pont Co.
Wilmington, DE
Envoy-APOC
Long Beach, CA
Aldan Rubber Co.
Philadelphia, PA
Phillips Petroleum Co.
Bartlesville, OK
Goodyear Tire & Rubber Co.
Akron, OH
Goodyear Tire & Rubber Co.
Akron, OH
Wilbur Ellis Co.
Fresno, CA
-------
Trade Name
TABLE 4-3 (continued)
Product Description Manufacturer
Royal Seal
SS-13
Sure Seal
Vinaliner
Vinyl Clad
Vi squeen
Void ay
Water Seal
EPDM and butyl
Waterborne dispersion
Butyl, EPDM, neoprene,
and Hypalon, plain
and reinforced
PVC
PVC, reinforced
PE resin
i
Bentonite
Bentonite
U.S. Rubber Co.
Mishawaka, IN
Lauratan Corp.
Anaheim, CA
Carlisle Corp.
Carlisle, PA
Goodyear Tire & Rubber Co.
Akron, OH
Sun Chemical Co.
Paterson, NJ
, Ethyl Corp.
Baton Rouge, LA
American Colloid Co.
Skokie, IL !
Wyo-Ben Products
Billings, MT :
aCourtesy of John Wiley & Sons, Inc., New York:, NY.
158
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TABLE 4-4
SOURCES OF COMMON LINING MATERIALS (4)a
Material
Bentonite
Butyl and EPDM
Butyl and EPDM,
reinforced
CPE, reinforced
Hypal on
Hypalon,
reinforced
EPDM
EPDM, reinforced
Neoprene
Neoprene,
reinforced
Manufacturer
American Colloid Co.
Archer-Daniels-Midland
Ashland Chemical Co.
Chas. Pfizer & Co.
Dresser Minerals
National Lead Co.
Wilbur Ellis Co.
Wyo-Ben Products, Inc.
Carlisle Corp.
Goodyear Tire & Rubber Co.
Aldan Rubber Co.
Carlisle Corp.
Plymouth Rubber Co.
Reeves Brothers, Inc.
Location
Skokie, IL
Minneapolis, MN
Cleveland, OH
New York, NY
Houston, TX
Houston, TX
Fresno, CA
Billings, MT
Carlisle, PA
Akron, OH
Philadelphia, PA
Carlisle, PA
Canton, MA
New York, NY
Goodyear Tire & Rubber Co. Akron, OH
San Jose, CA
Akron, OH
San Jose, CA
Carlisle, PA
Akron, OH
Canton, MA
New York, NY
Burke Rubber Co.
B. F. Goodrich Co.
Burke Rubber Co.
Carlisle Corp.
B. F. Goodrich Co.
Plymouth Rubber Co.
J. P. Stevens Co.
See "Butyl and EPDM"
See "Butyl and EPDM,
reinforced"
Carlisle Corp. Carlisle, PA
Firestone Tire & Rubber Co. Akron, OH
B. F. Goodrich Co. Akron, OH
Goodyear Tire & Rubber Co. Akron, OH
Carlisle Corp. Carlisle, PA
B. F. Goodrich Co. Akron, OH
Firestone Tire & Rubber Co. Akron, OH
Plymouth Rubber Co. Canton, MA
Reeves Brothers, Inc. New York, NY
159
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Material
PE
PE, high quality
PE, reinforced
PVC
TABLE 4-4 (continued)
Manufacturer
Location
PVC, reinforced
Prefabricated
asphalt panels
3110
Monsanto Chemical Co.
Union Carbide, Inc.
Ethyl Corp.
Gundle Lining Systems, Inc.
Griffolyn Co., Inc.
Firestone Tire & Rubber Co.
B. F. Goodrich Co.
Goodyear Tire & Rubber Co.
Pantasote Co.
Stauffer Chemical Co.
Union Carbide, Inc.
Firestone Tire & Rubber Co.
B. F. Goodrich Co.
Goodyear Tire & Rubber Co.
Reeves Brothers, Inc.
Cooley, Inc.
Sun Chemical Co.
Envoy-APOC
Gulf Seal, Inc.
W. R. Meadows, Inc.
Phillip Carey Co.
E. I. Du Pont Co.
St. Louis, Mo.
New York, NY
.Baton Rouge, LA
Houston, TX
Houston, TX
Akron, OH
Akron, OH
Akron, OH
New York, NY
New York, NY
New York, NY
Akron, OH
Akron, OH
Akron, OH
New York, NY
Pawtucket, RI
Paterson, NJ
Long Beach, CA
Houston, TX
Elgin, IL
Cincinnati, OH
Louisville, KY
aCourtesy of John Wiley & Sons, Inc., New York, NY.
160
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TABLE 4-5
SUMMARY OF EFFECTIVE DESIGN PRACTICES FOR PLACING LINING
IN CUT-AND-FILL RESERVOIRS
1. Lining must be placed in a stable structure.
2. Facility design and inspection should be the responsibility of
professionals with backgrounds in liner applications and experience in
geotechnical engineering.
3. A continuous underdrain to operate at atmospheric pressure is recommended.
4. A leakage tolerance should be included in the specifications. The East
Bay Water Company of Oakland, CA (East Bay Municipal Utility District)
developed the following formula for leakage tolerance which can be
modified by inserting more stringent factors in the denominator, i.e.,
100, 200, etc. The equation is empirical and its use must be based on
experience.
Q= A_VH
80
where,
Q = maximum permissible leakage tolerance, gallons/minute
A = lining area, 1000 ft2
H = maximum water depth, ft
5. Continuous, thin, impermeable-type linings should be placed on a smooth
surface of concrete, earth, Gunite, or asphalt concrete.
6. Except for asphalt panels all field joints should be made perpendicular
to the toe of the slope. Joints of Hypalon formulations and 3110
materials can run in any direction, but generally joints run
perpendicular to the toe of the slope.
7. Formal or informal anchors may be used at the top of the slope. See
details in Figures 4-2 to 4-6.
8. Inlet and outlet structures must be sealed properly. See details in
Figures 4-7 to 4-11.
9. All lining punctures and cracks in the support structure should be
sealed. See details in Figures 4-12 and 4-13.
10. Emergency discharge quick-release devices should be provided in large
reservoirs [7.6(104) to 1.2(10*'') m3].
11. Wind problems with exposed thin membrane liners can be controlled by
installing vents built into the lining. See details in Figure 4-14.
12. Adequate protective fencing must be installed to control vandalism.
161
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5. Bentonite 1s mixed with sand at aproximately one to eight volume
ratio. The mixture is, placed in a layer approximately 5 to 10 cm
(2 to 4 in) in thickness on the reservoir bottom and covered with a
protective cover of sand or soil. This method takes about 13.5
kg/m2 (3 Ib/ft2) of bentonite ,(17).
In methods (4) and (5) above, certain construction practices are recom-
mended. They are as follows:
1. The section must be overexcavated [30 cm (12 in)] with drag lines
or graders.
2. Side slopes should not be steeper than two horizontal to one
vertical.
3. Subgrade surface should be dragged to remove large rocks and sharp
angles. Normally two passes with adequate equipment are sufficient
to smooth the subgrade.
I :f
4. Subgrade should be rolled with a smooth steel roller. ;
5. The subgrade should be sprinkled to eliminate dust problems.
6. The membrane of bentonite or soil bentonite should then be placed.
7. The protective cover should contain sand and small gravel, in
addition to cohesive, fine grained material so that it will be
erosion resistant and stable.
The performance of bentonite linings is greatly affected by the quality of
the bentonite. Some natural bentonite deposits may contain quantities of
sand, silt, and clay impurities. Wyoming-type bentonite, which is a high
swelling sodium montmorillonite clay, has been found to be very
satisfactory. Fine ground bentonite is generally more suitable for the
lining than pit run bentonite. If the bentonite is finer than a No. 30
sieve, it may be used without specifying size gradation. But if the material
is coarser than the No. 30 sieve, it should be well graded. Bentonite should
usually contain a moisture content of less than 20 percent. This is
especially important for thin membranes. Some disturbance, and possibly
cracking of the membrane, may take place during the first year after
construction due to settlement of. the subgrade upon saturation. A proper
maintenance program, especially at the end of the first year, is necessary
(16).
Bentonite linings may be effective if the sodium bentonite used has an
adequate amount of exchangeable sodium. Deterioration of the linings has
been observed to occur in cases where magnesium or calcium has replaced
sodium as adsorbed ions. A thin layer, less than 15 cm (6 in), of bentonite
on the soil surface tends to crack if allowed to dry. Because of this, a
162
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bentonite soil mixture with a cover of fine grained soil on top, or a thicker
bentonite layer, is usually placed (18). Surface bentonite cannot be
expected to be effective longer than two to four years. A buried bentonite
blanket may last from 8 to 12 years. .
The quality of the bentonite used is a primary consideration in the success
of bentonite membranes. Poor quality bentdnite deteriorates rapidly in the
presence of hard water, and it also tends to erode in the presence of
currents or waves. Bentonite linings must often be placed by hand and this
is a costly procedure in areas of high labor costs.
Seepage losses through buried bentonite blankets are approximately 0.2
to 0.25 m3/m2/d (0.7 to 0.85 ft3/ftz/d). This figure is for thin
blankets and represents about a 60 percent improvement over ponds with no
lining.
Asphalt linings may be buried on the surface and may be composed of asphalt
or a prefabricated asphalt. Some possibilities are as follows:
1. An asphalt membrane is produced by spraying asphalt at high
temperatures. This lining may be either on the surface or buried.
A large amount of special equipment is needed for installation.
Useful lives of 18 years or greater have been observed when these
membranes are carefully applied and covered with an adequate layer
of fine grained soil.
2. Asphaltic Membrane Macadam. This is similar to the asphaltic
membrane, but it is covered with a thin layer of gravel, penetrated
with hot blown asphalt cement.
3. Buried Asphaltic Membrane. This is similar to (1), except a
gravel-sand cover is applied over the asphaltic membrane. This
cover is usually more expensive than cover in (2) and less
effective in discouraging plant growth.
4. Built-up Linings. These include several different types of
materials. One type could be a fiberglass matting, which is
applied over a sprayed asphalt layer and then also sprayed or
broomed with a sealed coat of asphalt or clay. A 280-g (10-oz)
jute burlap has also been used as the interior layer between two
hot sprayed asphalt layers. In this case the total asphalt
application should be about 11.3 liters/m2 (2.5 gal/yd2). The
prefabricated lining may be on the surface or buried. If buried,
it could be covered with a layer of soil or, in some cases, a
coating of All ox, which is a stabilized asphalt (19).
5. Prefabricated Linings. Prefabricated asphalt linings consist of a
fiber or paper material coated with asphalt. This type of liner
has been used as both exposed and covered with soil. Joints
between the material have an asphaltic mastic to seal the joint.
When the asphaltic material is covered, it is more effective and
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durable. When it is exposed it should be coated with aluminized
paint every three to four years to retard degradation. This is
especially necessary above the water line. Joints also have to be
maintained when not covered with fine grained soil. Prefabricated
asphalt membrane lining is approximately 0.32 to 0.64 cm (0.13 to
0.25 in thick. It may be handled in much the same way as rolled
roofing with lapped and cemented joints. Cover for this material
is generally earth and gravel, although shot-crete and macadam have
been utilized.
Installation procedures for prefabricated asphalt membrane linings and for
buried asphalt linings are similar to those stated for buried bentonite
linings. The preparation of the subgrade is important and it should be
stable and adequately smooth for the lining.
Best results are obtained with soil cement when the soil mixed with ;the
cement is sandy and well graded to a maximum size of about 2 cm (0.75 in).
Soil cement should not be placed in cold weather and it should be cured for
about seven days after placing. Some variations of the soil cement lining
are listed below.
1. Standard soil cement is compacted using a water content of the
optimum moisture content9 of the soil. The mixing process is
best accomplished by traveling mixing machines and can be handled
satisfactorily in slopes up to four to one. Standard soil cement
may be on the surface or buried.
2. Plastic soil cement (surface or buried) is a mixture of soil and
cement with a consistency comparable to that of Portland cement
concrete. This is accomplished by adding a considerable amount of
water. Plastic soil cement contains from three to six sacks :of
cement per cubic meter and is approximately 7.5 cm (3 in) thick.
3. Cement modified soil contains two to six percent volume of cement.
This may be used with plastic fine grained soils. The treatment
stabilizes the soil in sections subject to erosion. The lining is
constructed by spreading cement on top of loose soil layers by a
fertilizer-type spreader. The cement is then mixed with loose sqil
by a rotary traveling mixer and compacted with a sheeps foot
roller. A seven-day curing period is necessary for a cement
modified soil.
Soil cement has been used successfully in some cases in mild climates. Where
wetting or drying is a factor, or if freezing-thawing cycles are present, the
lining will deteriorate rapidly (20).
Water content (expressed in percent dry weight) at which a given soil can
be compacted to its maximum density by means of a standard method of
compaction. ;
164
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Linings of bentonite and asphalt are sometimes unsuitable in areas of high
weed growth, since weeds and tree roots puncture the material readily (20).
Many lining failures occur as a result of rodent and crayfish holes in
embankments. Asphalt membrane lining tends to decrease the damage, but, in
some cases, harder surface linings are necessary to prevent water loss from
embankment failures.
Linings of hot applied buried asphalt membrane provide one of the tightest
linings available. These linings deteriorate less than other flexible
membrane linings (20).
Asphalt linings composed of prefabricated buried materials are best for small
jobs, since there is a minimum amount of special equipment and labor
connected with installation. For larger jobs sprayed asphalt is more
economical.
When fibers and filler are used in asphalt membranes, there is greater
tendency to deteriorate when these fillers are composed of organic
materials. Inorganic fibers are, therefore, more useful (20). Typical
seepage volume through one buried asphalt membrane after 10 years of service
was consistently 0.02 m3/m2/d (0.08 ft3/ft2/d) (21).
Asphalt membrane linings can be constructed at any time of the year. It is
usually convenient, because of low water levels in ponds, to use the late
fall and winter seasons for installing linings. Fall and winter installation
may dictate the use of the buried asphalt membrane lining (20).
Buried asphalt membranes usually perform satisfactorily for more than 15
years. When these linings fail, it is generally due to one or more of the
following causes:
1. Placement of lining on unstable side slopes
2. Inadequate protection of the membrane
3. Weed growth
4. Surface runoff
5. Type of subgrade material
6. Cleaning operations
7. Scour of cover material
8. Membrane puncture
b. Thin Membrane Liners
Plastic and elastomeric membranes are popular in applications requiring
essentially zero permeability. These materials are economical, resistant to
most chemicals if selected and installed properly, available in large sheets
simplifying installation, and essentially impermeable. As environmental
.standards continue to become more stringent, the application of plastic and
elastomeric membranes as pond liners will increase because of the need to
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guarantee protection against seepage. This is particularly true for sealing
ponds containing toxic wastewaters or the sealing of landfills containing
toxic solids and sludges.
Typical standards being developed for the application of liners are presented
elsewhere (6). A partial listing of the trade names, product description,
and manufacturer of plastic and elastomer lining materials is presented! in
Tables 4-3 and 4-4.
The most difficult design problem encountered in liner application involves
placing a liner in an existing pond. Effective design practices ;are
essentially the same as those used in new systems, but additional care must
be exercised in the evaluation of the existing structure and the required
results. Lining materials must be selected so that compatibility is
obtained. For example, a badly cracked concrete lining to be covered with a
flexible synthetic material must be properly sealed and the flexible material
placed in such a way that additional movement will not destroy the new
liner. Sealing around existing columns, footings, etc., are other examples
of items to be considered.
The following paragraphs are a condensation of the discussion by Kays (4) of
effective design practices which have been summarized in Table 4-5. Emphasis
is placed on the details describing the installation of plastic or elasito-
meric materials.
Formal and informal anchor systems are used at the top of the slope :or
dikes. Details of three types of formal anchors are presented in Figures 4-2
through 4-4. Recommended informal anchors are shown in Figures 4-5 and 4-6;
When the lining is pierced, seals can be made in two ways. The techniques
illustrated in Figures 4-7 and 4-8 are commonly used, and a second technique
utilizes a pipe boot which is sealed to the liner and clamped to the entering
pipe as shown in Figure 4-9.
It is recommended that inlet-outlet pipes enter a reservoir through a
structure such as that shown in Figure 4-10. A better seal can be produced
when the liner is attached to the top of the structure. However, such |an
arrangement can result in solids accumulation, and direct free entry into: a
wastewater pond is better.
A drain near the outlet can be constructed as shown in Figure 4-11. Large
reservoirs containing 7.5 x 104 to 1.0 x 105 m3 (2.5 to 4.0 mgal)
should be equipped to empty quickly in case of an emergency. . :
The structure supporting the liner must be smooth enough to prevent damage to
the liner. Rocks, sharp protrusions, and other rough surfaces must be
controlled. In areas with particularly rough surfaces, it may be necessary
to add padding to protect the liner. Cracks can be repaired as shown in
Figures 4-12 and 4-13.
Thin membrane liners may have problems with wind on the leeward slopes.
Vents built into the lining control this problem and serve as an outlet for
gases trapped beneath the liner (Figure 4-14).
166
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FIGURE 4-2
TOP ANCHOR DETAIL—ALTERNATIVE 1, ALL LININGS (4)
Courtesy of John Wiley & Sons, Inc., New York, NY
Mastic
Mechanical anchor system
1/4"x2" aluminum or 3/16"x2"
galvanized steel or
stainless steel bars with
stud anchor bolts
12" max O/G. Use driven
studs only for asphalt
panel linings (2" metal
washers req'd.
Cast
concrete
structure
Lining to concrete
Adhesive Systems
8" Min. for asphalt panels
3" Min. for PVC & Hypalon
6" Min. for all other linings
Stable compacted
soil or existing
concrete, gunite or
asphalt concrete
NOTE
1. Top of concrete should be smooth and
free of all curing compounds.
2. Use min. 1/32." * 2" gasket (mat'l
compatible with lining) between bar and
lining, except no gasket required for
asphalt panels or other linings thicker
than .040".
167
-------
FIGURE 4-3
TOP ANCHOR DETAIL—ALTERNATIVE 2, ALL LININGS (4)
Courtesy of John Wiley & Sons, Inc., New York, NY
Min. 8" wide
x 1/32" thick
chamfer
strip
Cast
concrete
structure
Mechanical anchor system
1/4" x 2" aluminum or 3/16" x 2" galv.
or stainless steel bars with bolts
Min. 1" radius on new concrete
deburr old concrete
Wall lining
Anchor system same as
above - bar should be compatible
with liquid contained
Min. 6" wide x 1/32" elastomer
lining boot - half on wall
and half on slope with
compatible concrete adhesive
Note 2
Slope
lining
Stable compacted
soil or existing
concrete, gunite
or asphalt concrete
NOTE
1. All concrete at seals shall be smooth
and free of all curing compounds.
2. Use compatible adhesive between slope
lining and elastomer boot, and 3" min.
width of compatible adhesive between
slope lining and concrete.
168
-------
FIGURE 4-4
TOP ANCHOR DETAIL—ALTERNATIVE 3, ALL LININGS (4)
Courtesy of John Wiley & Sons, Inc., New York, NY
m
Cast concrete
anchor beam
approx 12" deep
depending on
climatic and
soil conditions
Mechanical anchor system -
1/4" x 2" aluminum or 3/16" x 2"
galvanized steel or
stainless steel bars with
bolt anchor
studs 12" max. O/C. Use driven
studs only for asphalt
panel linings (2" 0 metal
washers req'd )
Stable compacted
soil or existing
concrete, gunite
or asphalt concrete
Lining
NOTE
1. Top of concrete should be smooth and
free of all curing compounds.
2. Use min. 1 /32" x 2" gasket (mat'l compatible with
lining) between bar 8 lining except no
gasket required for asphalt panels or other
linings thicker than .040"
169
-------
FIGURE 4-5
TOP ANCHOR DETAIL—ALTERNATIVE 4,, ALL LININGS EXCEPT
ASPHALT PANELS (4)
Courtesy of John Wiley & Sons, Inc., New York, NY
1% slope
Trench cut by trenching
machine - insert lining
backfill and compact
12"
Top of slope
Stable, compacted soil
or existing concrete,
gunite or asphalt
concrete
Lining
w
170
-------
FIGURE 4-6
TOP ANCHOR DETAIL— ALTERNATIVE ,5, ALL LININGS (4)
Courtesy of John Wiley & Sons, Inc., New York, NY
Trench cut by tilted blade
of bulldozer, motor patrol,
etc., insert lining backfill
and compact
1% slope
Top of slope
12" to 16"
Lining
Stable compacted
soil or existing
concrete, gunite or
asphalt concrete
171
-------
FIGURE 4-7
SEAL AT PIPES THROUGH SLOPE, ALL LININGS (4)
Courtesy of John Wiley & Sons, Inc., New York, NY
Lining
1/8" x 1" Short segments
of T/304 stainless
steel butt joined bars
with bolt anchor studs
6" 0/C. (see note)
Mastic
Concrete collar
or structure
Lining to concrete
adhesive system:
8" Min. for asphalt panels
3" Min. for PVC
6" Min. for all other linings
NOTE
For asphalt panel linings, percussion
driven studs thru 2" min. dia. x 1/16" thick
galvanized metal discs at 6" O/C encased
in mastic may be substituted for anchor shown.
172
-------
FIGURE 4-8
SEAL AT FLOOR COLUMNS—ASPHALT PANELS (4)
Courtesy of John Wiley & Sons, Inc., New York, NY
Concrete or
steel column
Asphalt mastic
Asphalt panel
lining
... .
Asphalt
primer and
adhesive
I1BWL
Stable
compacted
subgrade
Concrete footing
NOTE
Mechanical fasteners not required
173
-------
FIGURE 4-9
PIPE BOOT DETAIL—ALL LININGS EXCEPT ASPHALT PANELS (4)
Courtesy of John Wiley & Sons, Inc., New York, NY
Lining
Lining to lining
adhesive
Pipe boot
Stable compacted
substrate concrete,
gunite, asphalt
concrete
1/4" Wide
stainless
steel band
Metal to
lining adhesive
4" wide
(see note)
NOTE
Clean pipe thoroughly at area of
adhesive application.
174
-------
FIGURE 4-10
SEAL AT INLET-OUTLET STRUCTURE—ALL LININGS (4)
Courtesy of John Wiley & Sons, Inc., New York, NY
Lining
1/8" x 1" T/304 stainless
steel bars, with 1" gap
between bars. Anchor
with bolt anchor
studs, 6" O/C. (See note)
Pipe
Concrete
structure
Lining to concrete
adhesive system
8" Min. for asphalt panels
3" Min. for PVC
6" Min. for all other linings
NOTE
With asphalt panel linings, percussion
driven studs thru 1" min. dia. 1 /16" thick
galvanized metal discs at 6" O/C,
encased in mastic may be substituted for
anchor shown.
175
-------
FIGURE 4-11
MUD DRAIN DETAIL—ALL LININGS (4)
Courtesy of John Wiley & Sons, Inc., New York, NY
1/4" x 1 1/2" Aluminum bar,
1/2"* bolts6"0/Cor
bolt anchor studs
w/solid washers
Mastic
*
M
=: I
/
(Hill
I
^ / /
rr
K^-'-vir-*-
o" ••'•.'»••'.. T'.',«
£>'M&
\\
Concrete collar — * \
Concrete primer *
81 adhesive, 4" wide
s
!
!
T
cd»
'-•» f. :«.- -.* •> • ||(^ l|EdUfe=JI[f=:||{ I T
' •• »• ••-. '+ ... !ii5|ii illjii^f'' lilfr.jilLL
•"• •>•'•'•%**•; .' •"»' IJJ =^/ r=r
/ ^tnhlo nnrth
or other
substrate
i
with valve
!
176
-------
FIGURE 4-12
CRACK TREATMENT—ALTERNATIVES A AND B (4)
Courtesy of John Wiley & Sons, Inc., New York, NY
Firm setting
heavy bodied
mastic
Flexible
continuous
lining
• 1 1/2"min.
* •
Exist.
crack
;.-.:A •••>/•».•. »>V. '^
/
"V" cut
crack at
top
Exist, concrete
A.C. or gunite
Heavy duty, high tensile
curing mastic or
cement grout - use
concrete adhesive
Alternative A
r Flexible
continuous
lining
Metal plate
see note)
Percussion driven
studs - 6" O/C - one
— side of crack only
NOTE
Metal plate must be able to span
crack without buckling from weight of
water bridging the crack. Copper 8
stainless steel are most common choices.
Alternative B
177
-------
FIGURE 4-13
WIND AND GAS CONTROL
Courtesy of Burke Rubber Company, Burke Industries, San Jose, CA
12" to 18" 12" to 18"
Anchor trench
&
Air-gas vent
178
-------
4-1 4
COST COMPARISON FOR LININGS IN THE UNITED STATES (1977 U.S. $j
Courtesy of John Wiley & Sons, Inc., New York, NY
to
In-Piace Cost, $/ft2 v
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7
Polyethylene
PVC
3110
Butyl, Epdm, Ept
Reinforced Butyl, Epdm
Hypalon
Neoprene
Concrete
Steel Tanks
Asphalt Panels
Gunite
Asphalt Concrete
CPE
Compacted Clay
Soil Cement
Bentonite
Waterborne Treatment
\ With Bentonite
I I
I l 1 I 1 I I I
I I I I I I I I I
0 1 2 34 56 7 8 9 10 11 12 13 14 15 16 17 18 19
In-Place Cost, $/m2
-------
Protection of a thin membrane lining is essential, and Kays (4) recommends
that a fence at least 2 m (6.6 ft) high be placed on the outside berm slope
with the top of the fence below the top elevation of the dike to keep :the
membrane out of sight of vandals.
In addition to those manufacturers presented in Table 4-4, there are many
firms specializing in the installation of lining materials. Most of the
installation -companies and the manufacturers publish specifications and
installation instructions and design details. Most of the recommendations by
the manufacturers and installers are similar, but there are differences
worthy of consideration when designing a system requiring a liner. Consult
the manufacturers for details.
F
New products continue to be developed, and with each new material the options
available to designers continue to improve. The future should bring even
more versatile and effective liners for seepage control. If care and common-
sense are applied to the application of liners, the control of seepage
pollution should become a minor problem in the future.
4.3.4.2 Failure Mechanisms
Kays (4) presented a classification of the principal failure mechanism
observed in cut-and-fill reservoirs (Table 4-6). The list is extensive and
case histories involving all of the categories are available; however, the
most frequently observed failure mechanisms were the lack of integrity in the
lining suppport structure and abuse of the liner.
4.3.4.3 Cost of Linings
The cost of linings for ponds are approximations and are estimated based on
values at specific jobs (1978 U.S. $).
Bentonite linings cost approximately $1,.10 to $2.20/m2 ($0.10 to
$0.20/ft2) when applied on the surface. The greater cost will occur for
harrowed „ blankets. Buried blankets cost approximately $3.10/m2
($0.30/ft2).
The average cost of buried asphalt membrane linings with adequate cover is
about $4.20/m2 ($0.40/ft2). |
Prefabricated asphalt materials are generally cheaper than buried asphalt
membrane linings if the prefabricated material can be obtained for less than
$1.10/m2 ($0.10/ft2).
Figure 4-14 presents a cost comparison for the various types of liners used
in the United States (4). '
180
-------
TABLE 4-6
CLASSIFICATION OF THE PRINCIPAL FAILURE MECHANISMS
FOR CUT-AND-FILL RESERVOIRS*
Supporting structure problems
Underdrains
Substrate
Compaction
Texture
Voids
Subsidence
Holes and cracks
Groundwater
Expansive clays
Gassing
Sloughing
Slope anchor stability
Mud
Frozen ground and ice
Appurtenances
Operating problems
Cavitation
Impingement
Maintenance cleaning
Reverse hydrostatic uplift
Vandalism
Seismic activity
Lining problems
Mechanical difficulties
Field seams
Fish mouthsb
Structure seals
Bridging
Porosity
Holes
Pinholes
Tear strength
Tensile strength
Extrusion and extension
Rodents, other animals, and birds
Insects
Weed growths
Weather
General weathering
Wind
Wave erosion
Ozone
kCourtesy of John Wiley & Sons, Inc., New York, NY.
Separation of butyl-type cured sheets at the joint because of unequal
tension in the two sheets.
Cover material over buried membranes is the most expensive part of the
placing procedure. The cover material should, therefore, be as thin as
possible and still provide adequate protection for the membrane. If a
significant hydraulic current is present in the pond, the depth of coverage
should be greater than 25 cm (1 ft), and this minimum depth should only be
used when the material is erosion resistant and also cohesive. Such a
material as a clayey gravel is suitable. If the material is not cohesive, or
if it is fine grained, a higher amount of cover is needed (20).
Maintenance costs for different types of linings are difficult to estimate.
Maintenance should include repair of holes, cracks, and deterioration, weed
181
-------
control expenses and animal damages, and damages caused by cleaning the pond,
if that is necessary. Climate, type of operation, type of terrain, and
surface conditions also influence maintenance costs. Plastic soil cement 7.5
cm (3 in) thick costs about $3.50/m2 ($0.33/ft2).
Cost comparisons of various liners indicate that natural and chemical
sealants are the most economical sealers. Unfortunately, natural ;and
chemical sealers are dependent upon local soil conditions for seal efficiency
and never form a complete seal. Asphalt-type and synthetic liners compete
competitively on a cost basis, but have different practical applications.
Synthetic liners are most practical for zero or minimum seepage regulations,
for industrial waste that might degrade concrete or earthen liners, and |for
extremes in climatic conditions.
4.4 Pond Hydraulics
4.4.1 Inlet and Outlet Configuration
In the past, the majority of ponds were designed to receive influent
wastewater through a single pipe, usually located toward the center of the
pond. Hydraulic and performance studies (22-25) have shown that the center
discharge is not the most efficient method of introducing wastewater to a
pond. Multiple inlet arrangements are preferred even in small ponds [<0.5 ha
(1.2 ac)]. Outlets should be located as far as possible and preferably by
means of a long diffuser. The inlets and outlets should be placed so that
flow through the pond has a uniform velocity profile between the next inlet
and outlet.
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 0.3 m (1 ft) at average flow, resulting in a velocity; of
2.4 m/sec (8 ft/sec).
Single inlets can be used successfully if the inlet is located the greatest
distance possible from the outlet structure and baffled or the flow directed
to avoid currents and short circuiting. Outlet structures should be designed
for multiple depth withdrawal, and all withdrawals should be a minimum of
0.3 m (1 ft) below the water surface.
4.4.1.1 Pond Transfer Inlets and Outlets
Pond transfer inlets and outlets should be constructed to minimize head loss
at peak recirculation rates, assure uniform distribution to all pond areas at
182
-------
all recireulati'on 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 7-10 cm (3-4 in) 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. If the first cell is designed to remove scum, then
the transfer pipes must be submerged.
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 allow for the differential settlement
often encountered in pond-dike construction.
Specially made fiberglass plugs can be provided to close the pipes (Figure
4-15). The plugs may be installed from a boat. Such plugs permit any pipe
to be closed without expensive construction of sluice gates and access
platforms at each transfer point. Launching ramps into each pond and channel
are recommended to assure easy boat access for sampling, aquatic plant
control, and pond maintenance.
4.4.2 Baffling
Better treatment is obtained when the flow is guided more carefully through
the pond. In addition to treatment efficiency, economics and esthetics play
an important role in deciding whether or not baffling is desirable.
Because there is little horizontal force on baffling except that caused by
wave action, the baffle structure need not be particularly strong. It may
also be placed below the pond surface to help overcome esthetic objections.
A typical type of baffle to consider might be a submerged fence attached to
posts driven into the pond bottom and covered with a heavy plastic, flexible
membrane. Commercial float-supported plastic baffling for ponds also is
available.
In general, the more baffling that is used, the better the flow guidance and
treatment efficiency. The lateral spacing and length of the baffle should be
specified so that the cross-sectional area of the flow is as close to a
constant as possible.
Baffling has an additional virtue. The spiral flow induced when flow occurs
around the end of the baffles enhances mixing and tends to break up or
prevent any stratification or tendency to stratify.
183
-------
FIGURE 4-15
SPECIAL FIBERGLASS PLUG
'/4n FIBERGLASS RE INF.
PLASTIC PLUG
CLAMPS AND SLOTS, SEE SECTION I
-30 CMP
SIDE ELEVATION
END ELEVATION
'/Z " * 2" FIBERGLASS
REINF. PLASTIC CLAMP-
V*.
, 9"± '/is
li. e'/z"
*,r
J&>\
^
^/^ ,
1
\
k-51.
•>«--»
J*
L
— p
E
'&
, *
ROVIDE Z'/4" * 3/i" SLOTS AT INTAKE
WS OF ALL TRANSFER PIPES
SECTION(7)
TYPICAL PLUG DiETAIL
NO SCALE
184
-------
Winter ice can damage or destroy baffles in cold climates. Care must be
exercised when designing baffles for a cold climate.
4.4.3 Wind Effects
Wind generates a circulatory flow in bodies of water. To minimize short
circuiting due to wind, the pond inlet-outlet axis perpendicular to the
prevailing wind direction should be aligned. If for some reason the
inlet-outlet axis cannot be oriented properly, baffling can be used to
control, to some extent, the wind-induced circulation. It should be kept in
mind that in a constant depth pond, the surface current is in the direction
of the wind and the return flow is in the upwind direction along the bottom.
4.4.4 Stratified Ponds
Ponds that are stratified because of temperature differences between the
inflow and the pond contents tend to behave differently in winter and
summer. In summer, the inflow is generally colder than the pond so it sinks
to the pond bottom and flows toward the outlet. In the winter, the reverse
is generally true and the inflow rises to the surface and flows toward the
outlet.
A likely consequence of this behavior is that the effective volume of the
pond is reduced to that of the stratified inflow layer (density current).
The result can be a drastic decrease in detention time and an unacceptable
level of treatment.
One strategy to employ is to use selective pond outlets positioned vertically
so that outflow is drawn from the layer with density different from that of
the inflow. For example, under summer conditions the inflow will occur along
the pond bottom. Hence, the outlets should draw from water near the pond
surface. This concept has not been tested but seems likely to improve
performance over "full-depth" outlet structures.
Another approach is to premix the inflow with pond water while in the pipe or
diffuser system, thereby decreasing the density difference. This could be
accomplished by regularly constricting the submerged inflow diffuser pipe and
locating openings in the pipe at the constrictions. The low pressure at the
pipe constrictions would draw in pond water and mix it with the inflow to
alter the density. However, clogging of openings with solid material could
be a problem.
4.5 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
185
-------
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 (Figure 4-16).
Both methods return active algal cells to the feed area to provide photo-
synthetic oxygen for satisfaction of the organic load. Intrapond recircu-
lation 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.
Recirculation is used principally in overloaded or improperly sized ponds.
Other than for dilution in the case where pond influents with very high
concentrations of wastes are being treated, in most cases the increased
energy costs associated with recirculation would dictate against its use.
Three common types of interpond-recirculation systems (series, parallel, and
parallel series) are shown in Figure 4-16. 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 fa~s?er than it would travel without recirculation. The first-pass
hydraulic retention time of the influent and recycled liquid in the first,
most heavily loaded, pond in the series system is:
t- V
(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:
186
-------
FIGURE 4-16
COMMON POND CONFIGURATIONS AND RECIRCULATION SYSTEMS
Recycle ^^^ Pump station
[v>*-] (typical)
Intrapond recirculation
Recycle
Lj
SJeries
Parallel Parallel series
Interpond recirculation
187
-------
where % is the BOD of the mixture, $3 is the effluent BOD from the third
cell, and S-jn is the influent BOD. Thus, Sm would be only 20 percent of
Sjn with a 4:1 recyle ratio, as $3 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. Recirculation in the» series mode has been used to
reduce odors in those cases where the first pond is anaerobic. The
recirculation ratio is selected based on the loading rate applied to the cell
that will not cause a nuisance.
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 is 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 (kg BODs/ha/d) 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. However, the hydraulic improvements in design using a
series configuration generally will offset the benefits of reduced loading in
parallel configuration.
Based upon the analyses of performance data from selected aerated and
facultative ponds (see the Appendix and Chapter 2), four ponds in series are
desirable to give the best 8005 and fecal coliform removals for ponds
designed as plug flow systems. Good performance can be obtained in a smaller
number of ponds if baffles or dikes are used to optimize the hydraulic
characteristics of the system.
Recirculation usually is accomplished with high-volume, low-head propeller
pumps. Figure 4-17 presents a simplified cross section of such an
installation. In this design, the cost and maintenance 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 ensure 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 range of 1.0-1.2 m (3-4 ft). 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 photosynthetic 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.
188
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... FIGURE 4-17
CROSS SECTION OF A TYPICAL RECIRCULATION PUMPING STATION
4-inch air and vacuum
release valve
2-inch eductor
00
to
-------
4.6 References
1. Upgrading Lagoons. EPA-625/4-73-001, NTIS No. PB-259974, U.S.
Environmental Protection Agency, Center for Environmental Research
Information, Cincinnati, OH, 1977.
2. Uhte, W. R. Construction Procedures and Review of Plans and Grant
Applications. In: Proceedings of Symposium on Upgrading Wastewater
Stabilization Ponds to Meet New Discharge Standards, Utah State
University, Utah Water Research Laboratory, Logan, UT, 1974.
3. Operations Manual for Stabilization Ponds. EPA-430/9-77-012, NTIS No.
PB-279443, U.S. Environmental Protection Agency, Office of Water Program
Operations, Washington, DC, 1977.
4. Kays, W. B. Construction of Linings for Reservoirs, Tanks, and Pollution
Control Facilities. Wiley-Interscience Publishers, John Wiley & Sons,
Inc., New York, NY, 1977.
5. Thomas, R. E., W. A. Schwartz, and T. M. Bendixen. Soil Changes and
Infiltration Rate Reduction Under Sewage Spreading. Soil Sci. Soc.
American Proc. 30:641-646, 1966. ,
6. Middlebrooks, E. J., C. D. Perman, and I. S. Dunn. Wastewater
Stabilization Pond Linings. Special Report 78-28. U.S. Army Cold
Regions Research and Engineering Laboratory, Hanover, NH, 1978.
7. Stander, 6. J., P. G. J. Meiring, R. J. L. C. Drews, and H. Van Eck. A
Guide to Pond Systems for Wastewater Purification. In: Developments in
Water Quality Research, Ann Arbor Science Publishers, Inc., Ann Arbor,
MI, 1970.
8. Hannaman, M. C., E. J. Johnson, and M. A, Zagar. Effects of Wastewater
Stabilization Pond Seepage on Groundwater Quality. Prepared by Eugene
A. Hickok and Associates, Wayzata, Minnesota, for Minnesota Pollution
Control Agency, Roseville, MN, 1978.
9. Bhagat, S. K., and D. E. Protector. Treatment of Dairy Manure by
Lagooning. JWPCF 41(5):785-795, 1969.
10. Hill, David J. Infiltration Characteristics from Anaerobic Lagoons.
JWPCF 48(4):695, 1976.
11. Chang, A. C., W. R. Olmstead, J. B. Johanson, and G. Yamashita. The
Sealing Mechanism of Wastewater Ponds. JWPCF 46(7):1715-1721, 1974.
12. Wilson, L. G., W. L. Clark, and G. Gi. Small. Subsurface Quality
Transformations During Preinitiation of a New Stabilization Lagoon.
Water Resour. Bull. 9(2):243-257, 1973.
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13. Matthew, F. L., and L. L. Harms. Sodium Adsorption Ratio Influence on
Stabilization Pond Sealing. JWPCF 41(11) Part 2:R383-R391, 1969.
14. Rosene, R. B., and C. F. Parks. Chemical Method of Preventing Loss of
Industrial and Fresh Waters from Ponds, Lakes and Canals. Water Resour.
Bull. 9(4):717-722, 1973.
15. Davis, S., W. Fairbank, and H. Weisbeit. Dairy Waste Ponds Effectively
Self-Sealing. Trans. Am. Soc. Agric. Eng. 16:69-71, 1973.
16. Robinson, F. E. Changes in Seepage Rate from an Unlined Cattle Waste
Digestion Pond. Trans. Am. Soc. Agric. Eng. 16:95, 1973.
17. Rollins, M. B., and A. S. Dylla. Bentonite Sealing Methods Compared in
the Field. J. Irr. & Dr. Div., ASCE proceedings 96(IR2):193, 1970.
/
18. Dedrick, A. R. Storage Systems for Harvested Water. U.S. Department of
Agriculture. ARS W-22, 1975. p. 175.
19. Asphalt Linings for Seepage Control: Evaluation of Effectiveness and
Durability of Three Types of Linings. Tech. Bull. No. 1440, U.S.
Department of Agriculture, 1972.
20. Linings for Irrigation Canals, U.S. Department of the Interior, 1963.
21. Buried Asphalt Membrane Canal Lining. Research Report No. 12, U.S.
Department of the Interior, 1968.
22. Mangel son, K. A. Hydraulics of Waste Stabilization Ponds and Its
Influence on Treatment Efficiency. PhD Dissertation, Utah State
University, Logan, UT, 1971.
23. George, R. L. Two-dimensional Wind-generated Flow Patterns, Diffusion
and Mixing in a Shallow Stratified Pond. PhD Dissertation, Utah State
University, Logan UT, 1973.
24. Mangelson, K. A., and 6. Z. Watters. Treatment Efficiency of Waste
Stabilization Ponds. J. Sanit. Eng. Div., ASCE 98(SA2), 1972.
25. Finney, B. A., and E. J. Middlebrooks. Facultative Waste Stabilization
Pond Design. JWPCF 52(1):134-147, 1980.
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CHAPTER 5
ALGAE, SUSPENDED SOLIDS, AND NUTRIENT REMOVAL
5.1 Introduction
Stabilization ponds are an effective means of treating wastewater, reducing
BOD5 and coliforms, but can have an occasional high concentration of
suspended solids (SS) in the effluent. During some months of the year, the SS
concentration exceeds the secondary effluent standards specified by regulatory
agencies. SS concentrations can exceed 100 mg/1, but such high levels are
usually limited to two to four months during the year. In the standards
established on October 7, 1977, small flow pond systems were excluded from ;the
Federal SS effluent requirements. For discharge to water quality limited
streams, removal may be required.
A discussion taken from many sources is presented of the various alternatives
available for upgrading the effluent quality from existing ponds and designing
original systems to meet water quality standards (1-3). :
I
5.2 In-Pond Removal Methods
There are several factors to be considered for in-pond removal of particulate
matter:
1. Subsequent degradation of settled matter by microorganisms to
produce dissolved 8005, which could then have an effect on the
receiving water.
2." Possibility that settled material will not remain settled.
3. Lack of positive control Of effluent SS.
4. Problem of eventually filling the pond. ;
5. Possibility that anaerobic reactions within the settled material
will produce malodors. ;
At first glance, it seems that some of these problems could be resolved by
rather simple changes in operation. In ponds that have cells in series, the
settled material could be removed from the bottom of the last cell and
transferred to the anaerobic cell or primary cell in which biological
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degradation is encouraged. Positive control could be achieved by adding
coagulants to the final cell to ensure that settling of the SS takes place.
For example, chemicals such as limes ferric chloride, and alum might be used
in this manner. Generally, complete containment ponds have a life expectancy
of about 20 years (4). In areas short of land, filling could be a problem,
but it might be possible to dredge and remove the solid material after 10 to
20 years have elapsed and to restore the pond to its initial state. In areas
where land is available and land cost is not prohibitive, filling would not be
a problem.
5.2.1 Series Ponds
Series ponds are recommended by some state regulatory agencies to provide for
algae sedimentation within cells. The efficiency of sedimentation in cells,
however, is limited by factors such as wind mixing and algae species. Small
cells usually result in less mixing (5).
5.2.2 Series Ponds with Intermediate Chlorination
Chlorination is normally used to disinfect effluent, but it has been observed
that chlorine added to pond effluent will also kill algae and cause settling.
In 1946 a study was conducted of a series of four oxidation ponds followed by
a chlorine-contact pond near Dublin, CA. At a flow of 14,200 m3/d (3.75
mgd) the chlorine-contact pond had a retention time of 13.5 hr. All the algae
were reported killed with a chlorine dose of 12 mg/1. In addition, between
chlorine-contact pond inlet and outlet, the BOD5 was reduced from 45 to 25
mg/1, SS from 110 to 40 mg/1, and turbidity from 170 to 40 JTUs (6). Similar
reductions were reported in a later study, which found that volatile SS could
be reduced 52 percent and turbidity 32 percent through Chlorination (7).
Laboratory tests with varying chlorine doses showed that 18 to 28 mg/1 of
chlorine could be added without producing a chlorine residual above 0.5 mg/1
in the effluent. In these tests, a 67 percent SS removal (24 mg/1 in the
effluent) and 68 percent 8005 removal (5 mg/1 in the effluent) were
reported. The flocculating effect of chlorine is thought to result from
rupture of the algae cell wall and release of cellular metabolites that may
serve as flocculants (8).
Recent studies at Utah State University on the Chlorination of pond effluent
do not confirm the concerns expressed earlier by Echelberger et al. (8) and
Horn (9) that destruction of algae and lysis of cells will occur with high
doses of chlorine. Rather, these were found to occur only when free residual
chlorine is available (10)(11). These studies have shown relatively little
COD released to the effluent by the Chlorination of algae-laden waters with
chlorine dosages adequate for disinfection, and dosages as high as 30 mg/1
with 63 mg/1 of SS have produced very little change in the COD. In general,
COD increased with free available chlorine residual but, at residual
•concentrations less than 2 mg/1, there appeared to be no consistent pattern.
With a reasonable degree of dosage control, disinfection or killing of algae
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should improve settling and reduce effluent 6005 and SS. The use of high
doses of chlorine could result in the production of toxic chlorinated organic
compounds which may cause problems in receiving streams.
5.2.3 Controlled Discharge Ponds
Controlled discharge is defined as limiting the discharge from a pond system
to those periods when the effluent quality will satisfy discharge
requirements. The usual practice is to prevent discharge from the pond during
the winter, and during spring and fall overturn periods.
The operations of 49 controlled discharge ponds in Michigan have been well
documented (12). Ponds at that latitude usually have low BODs loadings,
averaging about 22 kg/ha/d (20 Ib/ac/d). All the systems studied were
designed for discharge twice yearly, with effluent retention between late
November and mid-April and from about mid-May to mid-October. Discharge times
coincided with periods of low al gae-SS levels. Mean effluent concentrations
were about 15 mg/1 BOD and 30 mg/1 SS.
A similar study of controlled discharge pond systems was also conducted in
Minnesota (12). The discharge practices of the 39 installations studied were
similar to those in Michigan. The results of that study from the fall
discharge period indicated that the effluent BODs concentrations for 36 of
the 39 installations sampled were less than 25 mg/1 and the effluent SS
concentrations were less than 30 mg/1. In addition, effluent fecal coliform
concentrations were measured at 17 of the installations studied. All of the
17 installations reported effluent fecal coliform concentrations of less than
200/100 ml. '
The controlled discharge of pond effluent is a simple, economical and
practical method of protecting receiving water quality. Routine monitoring ,of
the pond contents is necessary to determine the proper discharge period.
These discharge periods may extend throughout the major portion of the year.
It may be necessary to increase the storage capacity of continuous-flow pond
systems if conversion to controlled discharge is contemplated. However, many
pond systems already have sufficient freeboard and thus storage capacity which
could be utilized without significant physical modification.
Controlled discharge is an excellent way to control algae concentrations in
pond effluents where the problem is seasonal. Most facultative ponds can be
operated as controlled discharge ponds for certain periods of the year, and in
many cases this is all that would be required to control the effluent SS.
!
5.2.3.1 Chemical Addition !
I
A series of reports distributed by the Canadian government has indicated
success with the treatment of controlled discharge ponds by adding various
coagulants from a motorboat (13-15). Excellent quality effluents are
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produced, and the costs are relatively inexpensive. The cost of in-pond
treatment and the long detention times required must be balanced against the
alternatives available. Man-hour requirements for the full-scale batch
treatment systems employed in Canada are summarized in Table 5-1.
TABLE 5-1
LABOR REQUIREMENTS FOR FULL-SCALE BATCH TREATMENT
OF INTERMITTENT DISCHARGE PONDS (13)
Man-hours per
appli cati on
Alum, liquid 2 1.6 16
Ferric Chloride,
liquid 1.5 1.2 16
powder 13 9.6 16
Lime,
dry chemical method 24 17.7 125
Haliburton method 1.7 1.4 16
In addition to the usual design considerations applied to controlled discharge
ponds, the following physical design requirements were recommended (13):
1. A roadway to the edge of each cell with a turn-about area
sufficient to carry 45 metric tons (50 tons) in early spring and
late fall or a piping system to deliver the chemical to each
eel 1 and a road adequate enough to get the boats to the pond
edge.
2. A boat ramp and a small dock installed in each cell.
3. Separate inlet and outlet facilities to allow diversion of raw
wastewater during treatment and draw-down in multiple-cell
installations for maintaining optimum effluent quality.
4. A low-level outlet pipe in the pond to allow complete drainage
of the cell contents.
5. An outlet pipe from the pond of sufficient size and design to
allow drainage of the treated area over a 5- to 10-day period.
6. In new, large installations, a number of medium-sized cells of
4-6 ha (10-15 ac) would be better suited to this type of
treatment than one or two large cells. These medium-sized cells
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could be treated individually and drawn down over a relatively
short period of time, thus maintaining optimum water quality in
the effluent.
Using the typical wastewater stabilization pond design required in the State
of Utah with 120 days retention time for cold weather storage and the most
severe conditions likely to occur, three chemical treatments per year would be
required. Designing a system for 1,140 nr/d (0.3 mgd) operation would
result in approximately 136,000 m3 (36 x 10& gal) of stored wastewater per
treatment. Applying alum at a rate of 150 mg/1 would result in 20,400 kg
(44,900 Ib) of alum required per treatment assuming that the hydraulic design
would control the sizing of the storage ponds and neglecting evaporation. The
installations would require approximately 8 ha (20 ac) of pond surface with a
depth of 1.8 m (6 ft). Assuming that a relatively small boat and supply
system would be adequate to distribute and mix the chemicals with the pond
water, a capital investment of approximately $33,000 (1978 US $) would ,be
required to obtain the tank trucks, storage facilities, boat and motor to
carry out the operation. Amortizing the equipment for a useful life of [ 10
years and assuming 7 percent interest, it would cost $4,700/yr. Liquid alum
costs approximately $116/metric ton ($105/ton) (equivalent dry) and using 62
metric tons (68 tons) annually would cost $7,, 140. Approximately 136,000 m3
(36 x 10° gal) of wastewater would be treated before each discharge. Using
the requirements shown in Table 5-1 of 1.6 man-hours/10^ gal and 16 man-
hours for setup and cleanup per application results in a total labor
requirement of 221 man-hours/yr. At labor costs of $20/hr, the cost would be
$4,420/yr. Adding all of the above costs, exclusive of the capital cost of
the pond system, results in an annual cost of $16,260 or $0.040/m3
($150/106 gal) of wastewater treated. ;
The above costs do not include storage facilities for the alum and the
additional design requirements to accommodate the alum handling equipment and
the boats. However, even doubling the estimated costs it is apparent that
intermittent discharge with chemical treatment, is a viable alternative where
applicable.
In addition to the cost advantages outlined above, batch chemical treatment of
intermittent discharge ponds can produce an effluent containing less than 1
mg/1 of total phosphorus. SS and B005 concentrations of less than 20 mg/1
can be produced consistently and only occasionally did a bloom occur durilng
draw down of the pond. Rapid draw down would overcome this disadvantage.
Sludge buildup was insignificant and would allow years of operation before
cleaning would be required. •
5.2.4 Continuous Overflow Ponds with Chemical Addition
Studies of in-pond precipitation of phosphorus, BOD5, and SS were conducted
over a two-year period in Ontario, Canada (16), The primary objective of the
chemical dosing process was to test removal of phosphorus with ferric
chloride, alum, and lime. Ferric chloride doses of 20 mg/1 and alum doses of
225 mg/1, when continuously added to the pond influent, effectively maintained
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pond effluent phosphorus levels below 1 mg/1 over a two-year period. Hydrated
lime, at dosages up to 400 mg/1, v/as not effective in reducing phosphorus
below 1 mg/1 (1 to 3 mg/1 was achieved) and produced no 8005 reduction and a
slight increase in SS concentration. Ferric chloride reduced effluent BODs
from 17 to 11 mg/1 and SS from 28 to 21 mg/1; alum produced no B005
reduction and a slight SS reduction (43 to 28-34 mg/1). Consequently, direct
chemical addition appears to be effective only for phosphorus removal.
A six-cell pond system located in Waldorf, MD, was modified to operate as two
three-cell systems in parallel (17). One system was used as a control and
alum was added to the other for phosphorus removal. Each system contained an
aerated first cell. Alum addition to the third cell of the system proved to
be more efficient in removing total phosphorus, BOD, and SS than alum addition
to the first cell. Total phosphorus reduction averaged 81 percent when alum
was added at the inlet to the third cell and 60 percent when alum was added to
the inlet of the first cell. Total phosphorus removal in the control ponds
averaged 37 percent when alum was added to the third cell and 50 percent when
alum was added to the first cell. The effluent total phosphorus concentration
during the period when alum was added to the first cell was 4.1 mg/1 compared
to 4.8 mg/1 total phosphorus concentration in the control system effluent.
When alum was added to the third cell, the effluent total phosphorus
concentration averaged 2.5 mg/1 with the control pond effluent averaging 8.3
mg/1. Improvements in BOD and SS removal by alum addition were more difficult
to detect and, at times, increases in effluent concentrations were observed.
5.2.5 Autoflocculation and Phase Isolation
Autoflocculation of algae, predominantly Chlorella, has been observed (18-21).
Laboratory-scale continuous-flow experiments with mixtures of activated sludge
and algae have produced large bacteria-algae floes with good settling
characteristics (21)(22).
Floating algae blankets in the presence of chemical coagulants have been
reported (23)(24). This phenomenon may be caused by the entrapment of gas
bubbles produced during metabolism or by the fact that in a particular
physiological state the algae have a neutral buoyancy. In a 3.2-liter/sec
(50-gpm) pilot plant (combined flocculation and sedimentation), a floating
algal blanket occurred with alum doses of 125 to 170 mg/1. About 50 percent
of the algae removed were skimmed from the surface (24).
Because of the infrequent occurrence of conditions necessary for
autoflocculation, and poor understanding of the actual mechanism involved, it
is not a viable alternative for removal of algae from ponds at this time.
Phase isolation is an attempt to design a pond system in which the various
processes involved in wastewater ponds are separated, and ponds performing
these special functions are placed in series. Field studies of phase
isolation have yielded inconclusive results (25)(26).
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5.2.6 Aquacul ture
Aquaculture is a centuries-old technique for producing food and fiber products
for direct or indirect human consumption. Application of waste materials, for
their nutritive value, to aquaculture systems has been a common practice for
many years in some parts of the world. The use of designed aquaculture
systems for treatment and management of municipal wastewaters is a relatively
new concept. As recently as 1978, Duffer and Moyer (27) concluded that
additional developmental research was needed to establish reliable design
criteria. They presented a comprehensive literature review and were
optimistic that several types of aquatic organisms could be developed that
would be attractive in terms of treatment effectiveness, cost, and energy
usage. A 1980 engineering assessment of aquaculture systems for wastewater
treatment is available (28). ',
Although aquaculture shows promise as a potential wastewater treatment
process, much remains to be learned at this time regarding removal mechanisms,
design parameters, and overall applicability. The following sections present
results from recent research utilizing various types of organisms (29-33).
5.2.6.1 Invertebrates
Invertebrate organisms which feed on algae include Daphnia and related species
(water fleas), Artemia (brine shrimp), and assorted bivalve mollusks (oysters,
clams, and mussels).
Design considerations for culturing invertebrates must take into account their
environmental requirements. These include pond site selection, construction
of berms and baffles, inlet and outlet structures, mixing and depth,
substrate, and pH regulation. Culture ponds require rigid operational control
and extensive management (34).
Based upon the experiences with invertebrates in wastewater ponds to remove
algae, their use does not appear to be feasible at this time.
5.2.6.2 Water Hyacinth '
Water hyacinth is an aquatic plant native to South America that was introduced
into the United States in 1884. The species currently grows throughout
Florida, Southern Georgia, Alabama, Mississippi, Louisiana, and in parts of
Texas and California. Temperatures below freezing will kill the plant. The
plants form dense mats, interfering with most uses of waterways; the hyacinth
has been designated a noxious weed by the U.S. Government. Under favorable
conditions, the total plant mass can double in periods of a few weeks. In
order to support this rapid plant growth, hyacinths consume large amounts of
nitrogen and phosphorus, making it a potentially useful means for nutrient
removal from pond effluent.
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Dinges (35) experimented with using water hyacinths cultivated in shallow
basins for treating pond effluent from the Williamson Creek Wastewater
Treatment Facility at Austin, TX. Effluent BODs levels through the
experimental system were reduced by 97 percent; SS by 95 percent; and COD by
90 percent. Mean effluent 8005 and SS levels were less than 10 mg/1 and
effluent total nitrogen was less than 5 mg/1.
Wolverton and McDonald (36) diked off a 2.0 ha (5.0 ac) portion of a pond with
an average depth of 1.2 m (4 ft) and stocked it with water hyacinths. Before
the hyacinths were introduced the pond produced no reduction in effluent SS
and a 76 percent reduction in 6005. After the water hyacinths were
introduced, SS were reduced an average of 87 percent and BOD5 an average of
94 percent.
Chambers (37) experimented with water hyacinths at the Exxon Baytown Refinery
over a two-year period. Following introduction of water hyacinths in August,
a 78 percent reduction in effluent SS was obtained in September. The tops of
plants were damaged by coots, a duck-like bird, by early November.
Subfreezing weather killed the tops in the winter and surface coverage by the
hyacinths was reduced from 80 percent of the pond to 50 percent in January.
After mechanical harvesting in late January as planned, surface coverage
dropped to zero in March and effluent quality was the same as in control
ponds. Experience the next year was similar. This study demonstrates the
seasonal nature and some of the potential management problems associated with
water hyacinths.
>
Water hyacinth systems are capable of removing high levels of BOD, SS, metals,
and nitrogen, and significant removal of refractory trace organics (28).
Removal of phosphorus is limited to the plant needs and probably will not
exceed 50 to 75 percent of the phosphorus present in the wastewater.
Phosphorus removal will not even approach that range unless there is a very
careful management program with regular harvests. In addition to plant
uptake, the root system of the water hyacinth supports a very active mass of
organisms that assist in the treatment. The plant leaves also shade the water
surface and limit algae growth by restricting light penetration.
Multiple-cell pond systems where water hyacinths are used on one or more of
the cells are the most common system design (28). Based on current
experience, a pond surface area of approximately 1600 ha/106 m^ ^5 ac/
10" gal) seems reasonable for treating primary effluent to secondary or
better quality. An area of about 500 ha/106 m3 (5 ac/106 gal) should be
suitable for systems designed to polish secondary effluent to achieve higher
levels of BOD and SS removals. For enhanced nutrient removal from secondary
effluent, an area of approximately 1300 ha/106 m3 (12 ac/106 gal) seems
reasonable. Effluent quality from such a system might achieve: <10 mg/1 for
BOD and SS, <5 mg/1 for N, and approximately 60 percent P removal. This level
of nutrient removal can only be obtained with careful management and harvest
to yield 110 dry metric tons/ha (50 tons/ac) per year.
The organic loading rates and detention times used for water hyacinth systems
are similar to those used for conventional stabilization ponds that treat raw
wastewater (28). However, the effluent from the water hyacinth system can be
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much better in quality than from a conventional stabilization pond,
particularly with respect to SS (algae), metals, trace organics^ and
nutrients.
Harvest of the water hyacinth or duckweed plants may be essential to maintain
high levels of system performance (28). It is essential for high levels' of
nutrient removal. Equipment and procedures have been demonstrated for
accomplishing these tasks. Disposal and/or reuse of the harvested materials
is an important consideration. The water hyacinth plants have a moisture
content similar to that of primary sludges. The amount of plant biomass
produce (dry basis) in a water hyacinth pond system is about four times the
quantity of waste sludge produced in conventional activated sludge secondary
wastewater treatment. Composting, anaerobic digestion with methane
production, and processing for animal feed are all technically feasible.
However, the economics of these reuse and recovery operations do not seem
favorable at this time. Therefore only a portion of the solids disposal costs
will be recovered unless the economics can be improved. ;
The major cost and energy factors for water hyacinth systems are construction
of the pond system, water hyacinth harvesting and disposal operations,
aeration (if provided), and greenhouse covers where utilized (28). Evapo-
transpiration in arid climates can be a critical factor. The water loss from
a water hyacinth system will exceed the evaporation from a comparably sized
pond with open water. Greenhouse structures may be necessary where such water
loss and related increase in effluent TDS are a concern.
Mosquito control is essential for water hyacinth systems and can usually be
effectively handled with Gambusia or other mosquito fish. Legal aspects are
also a concern. The transport or sale of water hyacinth plants is prohibited
by Federal and state law in many situations. The inadvertent release of the
plants from a system to local waterways is a potential concern to a number, of
different agencies. A fixed barrier can be used to prevent escape of the
plants to the outside environment. Water hyacinth plants cannot survive or
reproduce in cool waters so the concept is limited to "warm" areas unless
climate control is provided. Other floating plants, such as duckweed,
alligator weed, and water primrose, have a more extensive natural range but
only limited data on their performance in wastewater treatment are available.
5.2.6.3 Fish
In Asia, fish, most commonly members of the carp family, have been cultured; in
highly enriched water for centuries. Schroeder (38) has shown that fish can
be effectively combined with plankton and bottom fauna to produce a system
that is biologically balanced with stable DO and pH levels.
Experiments at the Exxon Baytown Refinery using Golden Shiners, fathead
minnows, Tilapia noloticia, and mullet were unsuccessful; in fact, effluent SS
levels increased.Stomach analysis of the fish revealed that, in addition to
algae, they fed on alga-feeding invertebrates. Reid (39) concluded that there
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was a serious gap between fish culture and constraints of sanitary
engineering, pointing towards the need for further research.
Preliminary experiments at Benton, AR, compared parallel three-cell
stabilization ponds receiving equal volumes of the same wastewater (BOD - 260
mg/1, SS - 140 mg/1) (28). The cells in one set were stocked with silver,
grass, and bighead carp while the other set received no fish and was operated
as a conventional stabilization pond. The comparative study continued for a
full annual cycle. Results indicated generally similar performance of the two
systems but the fish culture units consistently performed somewhat better than
the conventional pond. For example, the effluent BOD from the fish system
ranged from about 7 to 45 mg/1 with values less than 15 mg/1 obtained more
than 50 percent of the time. The conventional pond system had effluent BOD
ranging from 12 to 52 mg/1 with values less than 23 mg/1 about 50 percent of
the time. SS were very similar in the effluents for both systems except in
July when the concentration was about 110 mg/1 for the conventional pond and
60 mg/1 for the fish system.
In the second phase of the study at Benton, the six cells were all connected
in series and a baffle constructed in each to reduce short circuiting. Silver
carp and bighead carp were stocked in the last four cells and additional grass
carp, buffalofish, and channel catfish in the final cell. No supplemental
feed or nutrients were added to the fish culture cells. Estimated fish
production after 8 months was over 3,300 kg/ha (7,200 Ib/ac).
Effluent quality steadily improved during passage through the six-cell system.
BOD removal for the entire system averaged 96 percent for the 12-month study
period. About 89 percent of that removal was achieved in the first two
conventional cells. SS removal averaged 88 percent in the entire system,
with 73 percent occuring in the two conventional cells. It is not clear
whether the fish or the additional detention time or some combination is
responsible for the additional 7 percent BOD removal in the final four fish
culture cells.. The final average effluent BOD concentration of about 9 mg/1
is typical for a six-cell conventional stabilization pond system of comparable
detention time. It seems very likely that the fish contributed significantly
to the low SS in the final effluent (17 mg/1) via algal predation. A value
two or three times that high might be expected for conventional stabilization
ponds.
5.2.6.4 Integrated Systems
Experiments have been conducted on combinations of several types of
algae-reducing organisms. Ryther (40) concluded that highly enriched
environmental systems were relatively unstable and difficult to control, often
failing to develop a diversified biological community.
A prototype integrated aquaculture treatment system was constructed in
Hercules, CA, by Solar AquaSystems, Inc. (41). Startup problems were
encountered because of poor construction practices and efforts were
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unsuccessful to make the system function parallel to the experiences of ;the
pilot facilities. The system has been abandoned.
5.2.7 Baffles
The encouragement of attached microbial growth in ponds is an apparent
practical solution for maintaining biological populations, obtaining the
desired treatment, and reducing the SS level. Although baffles are considered
useful primarily to ensure good mixing and eliminate the problem of
short-circuiting, they may also provide a surface on which bacteria, algae,
and other microorganisms can grow. In a study of anaerobic and facultative
ponds with baffling, the microbiological community consisted of an algae
gradient, from photosynthetic chromogenic bacteria to nonphotosynthetic,
nonchromogenic bacteria (42)(43). In these baffle experiments, the presence
of growth attached to the baffles was the reason attributed for the higher
efficiency of treatment than that found in a nonbaffled system.
5.3 Filtration Processes
5.3.1 Intermittent Sand Filtration
5.3.1.1 Summary of Investigations
Literature reviews are available discussing the history, theory, design,
operation, performance, modeling, and economics of intermittent sand, slow
sand, rapid sand, and other media filtration of potable water and wastewater
(44-58). The following is a condensation of these reviews and contains a
brief history of intermittent sand filtration of wastewater as well as a
summary of studies concerning intermittent siand filtration to upgrade pond
effluents (see Table 5-2).
These studies indicate that, with proper design and operation, intermittent
sand fiftration is an effective and economical process to upgrade wastewater
stabilization pond effluent to meet present and future discharge requirements.
The effective sand size has been found to be the most important variable
relative to quality of effluent and the ability of the process to meet
effluent requirements. Hydraulic loading rate does not have a great effect;on
the effluent quality but does play an important role in the economics of
filter run time. Lengthening the filter run time requires either a decrease
in loading rate, which in turn creates a larger initial construction cost
along with increased maintenance costs, or a sacrifice in the quality of
effluent. Neither variation guarantees any consistent run time because pond
effluent quality can fluctuate greatly during the year and can increase or
decrease the filter run time.
202
-------
TABLE 5-2
INTERMITTENT SAND FILTRATION STUDIES
o
co
Pond Type
Facultative
Facultative
Facultative
Facultative
Aerated
Anaerobic*5
Facultative
Load! ng
u* Rate
.mgad
5.8 0.1
0.2
0.3
9.74 0.2
0.4
0.6
0.8
1.0
1.0
6.2 0.5
1.0
1.5
9.73 0.25
0.5
1.0
9.73 0.5
1.0
HA 0.1
0.35
0.5
9.7 0.2
0.4
Influent
rag/1
13.7
13.7
13.7
30.3
30.1
34.0
23.9
28.5
24.3
32.4
32.4
32.4
70.7
197
108
158
68.7
353
208
194
23.0
20.8
SS
Effluent
rag/I
4.0
4.8
6.0
3.5
2.9
5.9
4.7
5.1
3.7
8.6
7.8
6.4
10.1
15.6
11.8
52.5
32.9
45.5
46.5
45.1
2.7
3.5
Removal
percent
71
65
56
88
90
83
80
82
85
74
76
80
86
92
89
67
52
87
78
77
88
83
influent
ntg/1
9.2
9.2
9.2
23.0
22.5
25.9
15.2
21.5
18.6
21.9
21.9
21.9
38.8
155
83.0
71.1
36.6
264
162
175
17.8
18.5
VSS
Effluent
™9/1
2.0
2.1
2.3
1.3
3.4
3.1
1.2
2.5
1.6
3.3
3.2
3.3
6.5
11.9
8.8
13.2
11.3
28.1
35.3
35.7
1.0
2.3
Removal
percent
78
77 >
75
94
85
88
92
88
91
85
85
85
83
92
89
81
69
89
78
80
95
88
Influent
mg/1
6.3
6.3
6.3
19.5
20.6
25.6
2.8
13.5
6.1
10.7
10.7
10.7
20.2
71.4
34.0
34.4
19.6
123
108
107
10.9
11.5
BOD
Effluent
~~rog7l
1.2
1.3
2.0
1.9
2.5
4.2
1.8
2.6
2.2
1.8
2.0
2.3
6.6
9.4
13.0
5.1
, 11.7
19.5
43.7
67.6
1.1
2.6
Removal
percent
82
80
69
90
88
84
36
81
64
83
82
79
67
87
62
85
40
84
60
37
90
77
Reference
44
47
48
49
49
50
51
aResults for best overall performing 0.17 mm e.s. filters.
''Dairy waste.
*u = uniformity coefficient.
-------
5.3.1.2 General Design Considerations
*> .-.'•.- '
In general, the design and construction of intermittent sand filters ;for
polishing pond effluents is similar to that used for conventional slow sand
filters used in potable water treatment. Because pond systems are designed to
be relatively low-maintenance systems, intermittent sand filters designed to
augment pond systems should also be designed as low-maintenance systems. The
initial capital cost of constructing intermittent sand filters will be reduced
substantially if filter material (i.e., embankment, sand and gravel) are
locally available or can be processed on site. It is obvious that importation
of these materials to the construction site will significantly increase the
cost of construction. In such instances, a complete economic comparison of
various pond effluent polishing techniques should be performed.
Basically, there are two different configurations employed for intermittent
sand filtration of pond effluent, single-stage and series. Single-stage
intermittent sand filtration consists of passing pond effluent through a
single intermittent sand filter employing a reasonably small (0.20 mm to 0.30
mm) effective sand size. Series intermittent sand filtration consists of
passing pond effluent through two or more separate intermittent sand filters
with each filter employing a different effective sand size. The initial
filter sand size in a series operation is relatively large (0.60 mm to 0.70
mm) while the subsequent filters employ smaller sands (0.15 mm to 0.40 mm).
5.3.1.3 Configuration ;
The decision to use a single-stage or a series intermittent sand filtration
system should be based on the effluent quality required, desired length of
filter run, hydraulic head available, and availability of various filter sand
sizes. Each of the above considerations has a direct impact on the economics
of the configuration selected. :
The effluent quality produced by an intermittent sand filter is almost totally
a function of the filter sand size employed. The smaller filter sand sizes
also plug faster and thus reduce the length of filter run. In areas where a
high quality effluent is not required (i.e., 8005 £30 mg/1) and SS <30
mg/1), a single-stage filter with a medium filter sand size will produce a
reasonable filter run length and the required effluent quality. If a high
quality effluent is desired (BOD5- <10 mg/1 and SS <10 mg/1), 'then series
intermittent sand filtration with a small final stage Tilter sand size should
be considered. In addition, series intermittent sand filtration is applicable
in cases where the lower operation and maintenance costs associated with long
filter run lengths are desirable at the expense of initial capital costs. •
Series intermittent sand filtration may also not be economically feasible
where sufficient hydraulic head is not available to allow flow from one filter
to the next. Siphons and pumps may be used to transfer effluent from one
filter to the next in series; however, the operational costs involved should
be closely examined.
204 :
-------
Series intermittent sand filters may not be economically feasible in areas
where different filter sand sizes are not readily available. Again, an
economic comparison should be made.
In general, series intermittent sand filtration is capable of producing an
effluent equal to or better than a single-stage filter and will generally have
longer filter runs. Tjhe costs of series intermittent sand filtration may be
more than those associated with single-stage intermittent sand filtration. To
date, there is more reliable design and operational data for single-stage
intermittent sand filtration than for series filtration. ,
5.3.1.4 Hydraulic Loading Rate •
The removal efficiency by an intermittent sand filter does not appear to be
seriously affected by variations in hydraulic loading rates (44-47)(59)(60).
Effluent quality deteriorated only slightly with significant increases in
hydraulic loading rate (48).
The length of filter run is also not directly affected solely by nydraulic
loading rate. Rather, length of filter run is affected by a combination of
hydraulic loading rate and influent SS concentration. Attempts have been made
to relate the time a filter performs between cleanings to the mass of organic
material removed or applied, i.e., (hydraulic loading rate) x (influent SS
concentration) (45-47). Experience with full-scale units summarized in
Figures 5-1 through 5-4 represent the relationship between mass loading and
the time between cleaning the filters (47)(51)(61). Figures 5-1 through 5-3
represent the performance of filters with sands of various effective size
located in an area with relatively soft water (total hardness <250 mg/1), and
Figure 5-4 applies to areas with hard waters where calcium' carbonate
precipitation is likely to occur during periods of active algal growth (61).
a. Single-Stage
Information available from full-scale operations indicates that hydraulic
loading rates of 0.37 to 0.56 m^/m^/d (0.4 to 0.6 mgad) may be employed
using single-stage intermittent sand filtration. In areas where high influent
SS concentrations are anticipated (above 50 mg/1 average) lower hydraulic
loading rates, 0.19 to 0.37 nr/m2/d (0.2 to 0.4 mgad), are recommended.
These lower hydraulic loading rates are suggested to increase the time of
filter run. If the time a filter will perform is not a significant design
consideration, i.e.> when filters are very small, less than 90 m2 (1000
ft2), the higher loading rates may be employed; however, operation and
maintenance costs will increase.
In areas where land is relatively inexpensive, lower hydraulic loading rates
are suggested so that the time between filter cleanings may be increased. In
this case, the initial capital costs will be higher, but the annual operating
costs will be significantly lower. This is especially true for cold weather
205
-------
FIGURE 5-1
LENGTH OF FILTER RUN AS A FUNCTION OF DAILY MASS LOADING
FOR 0.17 mm EFFECTIVE SIZE SAND (61)
300 r
200
CO
-a
O)
"c
CO
_03
O
c
0)
0)
CO
(
o.
100
days = 2529 (SSL)
r = 0.801
-1.733
0
10
20
30
40
50
SS Loading (SSL), g/mVd
206
-------
FIGURE 5-2
LENGTH OF FILTER RUN AS A FUNCTION OF DAILY MASS LOADING
FOR 0.4 mm EFFECTIVE SIZE SAND (61)
200
ro
o
to
TJ
O)
C
'c
03
jl)
O
c
0)
I
m
T3
O
'C
0)
Q.
100
0
days = 8859 (SSL)-1-625
r = 0.900
0
50
SS Loading (SSL), g/mVd
100
130
-------
FIGURE 5-3
LENGTH OF FILTER RUN AS A FUNCTION OF DAILY MASS LOADING
FOR 0.68 mm EFFECTIVE SIZE SAND (61)
200
ro
o
oo
w
CO
•o
CO
0>
'c
co
JB
o
c
0)
0)
B
d>
m
100
days = 12,350 (SSL)'1-445
r = 0.979
0
0
50 100
SS Loading (SSL), g/mVd
130
-------
FIGURE 5-4
LENGTH OF FILTER RUN AS A FUNCTION OF DAILY MASS LOADING FOR POND EFFLUENTS
HAVING CALCIUM CARBONATE PRECIPITATION PROBLEMS (0.17 mm EFFECTIVE SIZE SAND)
50 r
ro
o
CO
T5
to
O)
co
O
c
CD
0)
•o
o
*l_
CD
CL-
40
30
20
0
days = 319 (SSL)-1-119
r = 0.948
I
I
10
20 30 40
SS Loading (SSL), g/mVd
50
60
70
-------
climates. The optimum design in cold weather climates would allow for Jong
filter run times during the freezing months to eliminate filter scraping
during this period of the year. A single-stage filter at Logan, UT, with a
hydraulic loading rate of 0.19 m3/m2/d (0,2 mgad) operated for 189 days
during the winter season before scraping was necessary (45).
b. Series Operation
Series intermittent sand filters have been used only on a pilot-scale.
Details of this experience can be obtained elsewhere (48).
c. Seasonal Variations
Because length of filter runs are affected by a combination of hydraulic
loading rate and influent SS concentration, seasonal variations in hydraulic
loading rates may be advantageous. Higher hydraulic loading rates may be
employed during periods of low influent SS concentration. However, filter
design must be based on the minimum hydraulic loading rate employed during the
year. ;
5.3.1.5 Filter Size and Shape
The total filter area required for a single-stage intermittent sand filtration
system is obtained by dividing the anticipated influent flowrate by the
hydraulic loading rate selected for the system. For a series intermittent
sand filtration system, the total area thus obtained must be supplied by each
stage of the filtration system. Thus, if the same hydraulic loading rate is
specified for a single-stage system and a three-stage series system treating
the same influent flowrate, the total area required for the three-stage series
system would be three times greater than the total area required for : the
single-stage system. However, in practice, the same hydraulic loading rates
would not be employed to design both filter systems.
Depending upon the work schedule during cleaning operations, a filter may be
totally out of service for several days. Thus, at least one spare filter
should be included in the system to accommodate the cleaning schedule.
Alternately, sufficient holding capacity could be included in the pond systems
to allow storage of filter influent during filter cleaning operations. In any
event, provisions must be made to accommodate down time during the cleaning
operation. No system should have less than two filters, and three filters are
preferred.
The exact size of an intermittent'sand filter will depend on the influent
flowrate and the hydraulic loading rate. However, if it is anticipated that
sand scraping and filter cleaning operations are to be achieved by mechanical
means, the filters should be large enough to allow relatively easy movement of
210 ; ..
-------
machinery on the filter surface. For very small systems, sand scraping may be
accomplished by hand. In such systems the maximum surface area per filter
should not exceed approximately 90 m2 (1,000 ft2). For mechanically
scraped filters, Huisman and Wood (62) recommended that it not exceed
approximately 5,000 m2 (55,000 ft2).
The design of odd or random shaped filters to make the best use of available
land may benefit the initial capital cost of construction; however, if
mechanical cleaning is anticipated, equal size rectangular beds are preferred
(59). Equal sized beds allow the alternation of loading between filters with
a minimum of upset to the total system operation. In addition, cleaning and
operational procedures may be standardized with equal sized filters.
5.3.1.6 Sand
Selected sand is generally used as a filter media; however, other granular
substances, such as crushed coal and burnt rice husks, have been used when
suitable sand was not available (62). The use of materials other than sand
should be carefully evaluated in a pilot-scale filter before being used in a
prototype intermittent sand filtration system.
Filter sands are generally described by their effective size (e.s.) and
uniformity coefficient (u). The e.s. is the 10 percentile size, such that 10
percent of the filter sand by weight is less than that size. The uniformity
coefficient is the ratio of the 60 percentile size to the 10 percentile size.
An example procedure for determining e.s. and u for a specific filter sand
follows:
Problem: For a sand with the characteristics shown in Table 5-3,
determine effective size (e.s.) and uniformity coefficient
(u).
TABLE 5-3
SIEVE ANALYSIS OF FILTER SAND
U.S. Sieve Size of Sieve Percent
Designation Opening Passing
No. mm
3/8 in 9.53 10.0
4 4.76 95
8 2.38 66
16 1.19 41
30 0.59 20
50 0.297 6
100 0.149 1
211
-------
Solution:
1. Construct a plot of sand grain size (size of sieve opening)
versus sand size distribution (percent passing) as shown in
Figure 5-5.
2. Determine the 10 percentile size, PIQ» by reading the 10
percentile line intersection on the curve in Figure 5-5.
PIQ = 0-38 mm
3. By definition, PIQ is equivalent to e.s.
e.s. = PIQ = 0.38 mm
4. Determine the 60 percentile size, Pg0, by reading the 60
percentile line intersection on the curve in Figure 5-5.
= 2.00 mm
5. By definition, u is P5Q divided by
" = P60/Pl0
=2.00 mm/0.38 mm
= 5.22
Filter sand of the required e.s. and u may be produced from stock sands by
removing a given fraction that is either too large or too small. Alternately,
the specified sand may be produced by mixing two sands with different
characteristics. Mixing of the sands must be carried out very thoroughly,
preferably in a concrete mixer. The procedures for mixing and the
calculations for determining the proper portions for producing a given filter
sand are described elsewhere (62) (63). ;
The filter may be clean river, beach, or bank sand with either sharp ; or
rounded grains. It should be free from clay, dust, dirt, and organic
impurities. It is desirable that the filter sand be washed prior to placement
in the filter bed. If the sand has not been washed prior to installation, a
poor quality filter effluent will result during the first few weeks 'of
startup. The deterioration in quality is caused by washing of fine inorganic
and organic material from the sand. However, once this material has been
washed from the sand, a high quality effluent can be expected. The sand
grains should be of a hard material which will not break down with wear and
contact with water. . ....
Experience indicates that, generally, pit run concrete sand is suitable for
use in intermittent sand filters, provided the e.s. and u are suitable. Costs
may be reduced substantially if a sand source can be located which does not
require screening or washing. It is strongly recommended that a natural iOr
pit run sand not requiring specialized grading be employed where possible.
212
-------
FIGURE 5-5
SAND GRAIN SIZE vs SAND SIZE DISTRIBUTION
98
0
_N
"tf)
o>
0>
CD
•D
C
CO
+->
en
o>
c
'(/)
CO
CD
Q.
+->
CD
O
03
•.. Q. '
CO
u
C/5
JD
CD
.Q
O
CD
E
95 h-
90
50
10
0.1
0.01
0.1
I I I | I I I I |
Effective size = e.s. = P10 = 0'.38 mm
Uniformity coefficient = fj=^-= ^-00 mm _ g
"10 O.Jo mm
I r
P60 = 2.00 mm
P10 = 6.38 mm
I
1 il I 1 I 111
I
0.5 1.0
Sand Grain Size (size of sieve opening), mm
213
-------
a. Single-stage ;
Filter sand for a single-stage intermittent <;and filter should have an e.s.
ranging from 0.20 to 0.30 mm, a uniformity coefficient of less than 7.0, and
less than 1 percent of the sand smaller than 0.1 mm. A higher quality
effluent will be produced from filter sand with an e.s. near 0.20 mm while a
slightly poorer quality effluent will result from using a filter sand with an
e.s. near 0.30 mm. Most of the recent research on intermittent sand
filtration has been conducted using a 0.17 mm e.s. sand (44-47)(60).
Previous reports (44)(45)(63) have recommended u values of 1.70 to 3.27, and u
for slow sand filters for potable water treatment of less than 2.0 are
suggested by Huisman and Wood (62). However, the recent work with polishing
pond effluents utilized filter sand with a u of 9.74 (45-47). Hill et al.
(48) employed filter sands with u values ranging from less than 2.0 to 9.74
with little effect on effluent quality.
It appears that the u has little effect on the quality of effluent produced
from an intermittent sand filter. However, u values greater than 7.0 should
be avoided. In general, u values ranging between 1.5 and 7.0 are acceptable.
b. Series Operation
In a series operation, the filter sand e,s. should decrease with each
succeeding stage of the filter. Very little data exist to determine exact
filter sand sizes for series operation. Hill et al. (48) reported using a
0.72 mm e.s. sand in the first-stage filter, a 0.40 mm e.s. sand in the
second-stage filter, and a 0.17 mm e.s. sand in the third-stage filter., Based
on these data for a three-stage series operation, the range of e.s. values for
the first-stage filter should be 0.65 to 0.75 mm, the range for the
intermediate stage 0.35 to 0.45 mm, and the range for the final stage 0.20 to
0.30 mm.
A careful pilot-scale study should be conducted before determining the filter
sand e.s. for a two-stage series filter operation. The u values for sands
used in series filter operations should be similar to those used in
single-stage intermittent sand filtration.
c. Use of Highway Sand
Many highway specifications require that fine aggregate for concrete conform
to the requirements of the American Association of State Highway and
Transportation Officials (AASHO M6) (64). Such sand is applicable ,in
intermittent sand filters used to polish pond effluents. The AASHO M6
gradation requirements are shown in Table 5-4.
214
-------
TABLE 5-4
GRADATION REQUIREMENTS FOR FINE AGGREGATE
IN THE AASHO M6 SPECIFICATION (64)
U.S. Sieve Percent
Designation Passing
3/8 in 100
4 95-100
16 • 45-80
50 10-30
100 2-10
The sand size distribution of this sand at the specific upper and lower limits
of specification are shown in Figure 5-6. Analysis of this figure indicates
that the e.s. of this sand will range from 0.15 to 0.30 mm with u ranging from
4.23 to 5.39.
As can be seen in Figure 5-6, the No. 50 and No. 100 sieve are the critical
points of gradation. The 10 percentile sand size must lie between these two
sieve sizes because the e.s. is determined by the 10 percentile size sand.
Generally, a filter sand with an e.s. of between 0.20 and 0.30 mm should be
used for single stage and the final stage in series intermittent sand filters.-
The restrictions on u for sand employed in intermittent sand filtration are
not severe. Thus, the limit on gradations for the No. 4 and No. 16 sieves are
not exceptionally critical. However, 100 percent of the sand should pass a
3/8-inch sieve.
5.3.1.7 Filter Bed
The filter bed consists of the filter sand and the gravel layer between the
filter sand and the underdrain system. A cross section of a typical
intermittent sand filter is shown in Figure 5-7.
a. Filter Sand Bed
In general, the filter sand should conform to the e.s. and u criteria outlined
above. The sand depth should be sufficient to produce a high quality effluent
and also provide a sufficient reserve to allow for several cleaning cycles.
It has been reported that at least 45 cm (18 in) of filter sand are required
to produce an adequate quality effluent (44). Huisman and Wood (62) recommend
at least 70 cm (28 in) of filter sand be provided for slow sand filters
215
-------
FIGURE 5-6
SAND GRAIN SIZE vs SAND SIZE DISTRIBUTION FOR
AASHO M6 SPECIFICATIONS
99.99
99.9
i r I i
1 r
i r
(0
W
(0
Q.
*-•
CD
(0
O
0)
CO
X)
O
ol
"5
E
Specification
Upper Limit
Lower Limit
Effective SiEe
(mm)
0.15
0.30
Uniformity
Coefficient
4.23
5.39
99
98
95
90
50
£ 10
2
1
Upper Limit
Lower Limit
0.1
0.01
J_
I I I I I I I
I
I I I I I I I
0.1
0.5 1.0
Sand Grain Size (size of sieve opening), mm
10
216
-------
FIGURE 5-7
CROSS SECTION OF A TYPICAL INTERMITTENT SAND FILTER
Liner
1.8 cm Max dia. rock
^3.8 cm Max dia. rock
Section 2-2
Sand and gravel placement
Supply
line —v
N f
1
I
N. '
/
i
j
k. ™ t
i\ !
/ » \
1 1 \
I
_iner and filter bed >
I \ '
O ~*.
V
\
i
i
\!
^ j
'\ '
N
\
/
\
1 \ III N
1\ 1 ' \
\ \\~
t lir
1
33 1 between
er and pipe
— Seal
.Seal between
Section 1-1
Liner section
Liner
Seal between drain pipe X
and liner with suitable
material
Drain
217
-------
treating potable water. Research studies using a minimum of 60 cm (24 in) of
filter sand have produced a high quality effluent (45-48)(60). Based upon the
above data, it appears that an intermittent sand filter should not be operated
with less than 45 cm (18 in) of filter sand.
In addition, sufficient sand for at least one year of cleaning cycles should
be provided. Approximately 2.5 to 5 cm (1 to 2 in) of sand are removed during
each cleaning cycle. If the anticipated length of filter run is 30 days, at
least an additional 30 cm (12 in) of filter sand should be provided. ; In
.general, the total initial depth of filter sand employed on intermittent sand
filters is 90 cm (36 in).
b. Gravel Bed
In general, a graded gravel layer 30 to 45 cm (12 to 18 in) in depth separates
the filter sand from the underdrain system. If the underdrain system consists
of perforated pipe as opposed to a conventional tiled or block underdrain
system, the gravel will completely enclose the drain pipe. The gravel system
is built up of various layers, ranging from fine at the top to coarse at the
bottom. The -layers are designed to prevent filter sand from entering and
plugging the underdrain system. In general, the bottom gravel layer should
consist of particles with an e.s. at least four times greater than the
openings into the underdrain system. Each successive layer should be graded
so that its e.s. is not more than four times smaller than that of the layer
immediately below.
The research on polishing pond effluents at Logan, UT, was conducted with a
gravel bed 30 cm (12 in) deep composed of three 10-cm (4-in) layers (45-47).
The bottom layer consisted of gravel ranging from 1.9 to 3.8 cm (0.75 to 1.5
in) in diameter, the middle layer consisted of 1.3 to 1.9 cm (0.5 to 0.75 in)
diameter gravel, and the top layer consisted of 0.32 to 0.64 cm (0.12 to 0.25
in) diameter gravel. This arrangement has proven to be satisfactory.
c. Underdrain Systems
The underdrain system may consist of porous or perforated unglazed drainage
tiles, glazed pipes laid with open joints, or perforated asbestos or
polyvinyl chloride (PVC) pipe (62). Experience has indicated that a
corrugated, perforated PVC pipe (similar to that used for irrigation drainage)
provides an adequate drain system for minimum cost. If drain pipes are used,
they should be placed within the bottom gravel layer of the filter to collect
the flow as it infiltrates through the sand. Filter bottoms should slope
toward the drainage pipe for efficient collection of effluent.
Typical drain schemes are shown in Figure 5-8. The drain pipes should be laid
with sufficient slope to produce "scour velocity" in the pipes under average
flow conditions. This will allow the drain system to be self-cleaning and
thus reduce maintenance costs.
218
-------
FIGURE 5-8
COMMON ARRANGEMENTS FOR UNDERDRAIN SYSTEMS (62)
1 1 1
t 1 1
1 1 1
i ' 1
1
|i!
! i t
— - *•
i '
i i
> i
! -
!
! !
i i
«l .!.•!•.
III
219
-------
The drains should be designed so that they are fully exposed to the air. It
is imperative that air be able to circulate through the drain system into;the
sand filter bed. Intermittent sand filters are an aerobic system and thus
must have an adequate air circulation if they are to perform properly. Outlet
drains should be exposed to the atmosphere and not submerged.
5.3.1.8 Influent System
The influent system may be gravity flow, or utilize pumps or automatic dosing
siphons depending on the configuration of operation and the topography of jthe
site. When a relatively large amount of slope is not associated with the
filter site, series intermittent sand filtration operations will require a
pump lift station between filters to lift the effluent from one filter to the
influent level of the next filter in the series.
The influent system should be designed with sufficient capacity to enable the
total daily hydraulic load to 'be applied to the filter in less than 6 hr. For
filters less than 90 m2 (1,000 ft2) in area, the daily hydraulic load may
be applied to the filter in less than 1 hr for a relatively small investment.
For larger filter systems, the dosing time should be accomplished in less than
6 hr. This method of operation allows the maximum head buildup on the filter
and also, because the influent will drain through the filter quickly, the
maximum bed aeration time is achieved. Influent velocities should r be
sufficient to prevent settling of solids in the lines.
The influent distribution system need not be complicated or elaborate. Even
distribution of the influent across the filter surface will be accomplished by
the water buildup on the filter caused by the short dosing time (i.e., less
than 6 hr). Water may not be distributed evenly across the entire filter at
first, but within a short time after loading begins the water will be standing
several centimeters deep over the entire filter surface. '< .
Simple channels which overflow at regular intervals across the filter bed will
provide adequate distribution of the influent. Discharge velocities from
these channels onto the fil ter surface shoul d be smal1 enough to prevent
•serious sand erosion. Splash pads may be necessary in some cases to reduce
sand erosion near inlet structures. In addition, inlet channels should be
equipped with drains or "weep holes" so that they may drain completely dry
during periods of freezing temperatures. This should prevent the buildup lof
ice within the influent channels.
The influent system should be fully automated so that pumps, siphons, or
transfer structures may be activated routinely without continual personal
supervision. Provisions should be made so that the system can be operated
either during day or night. Flexibility should be designed into the system so
that each filter may operate independently. Series intermittent filtration
influent systems should be constructed so that operation can be either ;in
series or in parallel as a single-stage filtration system. In addition,
manual overrides should be provided for all systems in case of power failures.
Alternatively, an auxiliary power source should be available. Spare pumps and
220 :
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metering systems should be provided. In general, the same degrees of
flexibility should be provided for a pond system as that found in a
conventional treatment plant.
5.3.1.9 Filter Walls
Filter walls may be constructed as earthen embankments or from conventional
building materials such as concrete, steel, or wood. In general, earthen
embankments are much more economical, especially for larger filters, and are
recommended for most designs. Steel or concrete filter walls may be
applicable for small filters where embankment materials are not readily
available or space is limiting.
When materials other than earthen embankment are employed for filter wall
construction, care must be exercised to prevent "short-circuiting," the
downward percolation of water along the inner wall face without passing
through the filter bed. Short-circuiting may cause deterioration of "effluent
quality and is a particular problem in small sand filters. Structural
precautions should be taken to guard against it. It is no problem with
sloping walls or earthen wall embankments because the sand tends to settle
tightly against these types of walls. However, with smooth vertical walls, it
may be necessary to incorporate devices such as built-in grooves or artificial
roughening of the internal surface. The most effective precaution is to give
the walls a slight outward batter, so as to obtain the advantages of a sloping
wall (62).
Earthen filter embankment construction should be similar to that used in a
normal well-designed pond system. Embankments are usually designed with side
slopes from 6:1 to 2:1 with 3:1 being the most common. Embankment top width
should be at least 3 m (10 ft) and provide a 30-cm (1-ft) thick all-weather
gravel road. Road surfaces should be crowned to assure rainwater runoff and
minimum erosion.
The interior embankment should be impervious to prevent both exfiltration of
filter influent and infiltration of seepage groundwater. Most state
regulatory agencies have a standard for maximum seepage losses. Figure 5-7
illustrates the use of a liner to create an impervious embankment. Such
liners are only economically feasible on relatively small intermittent sand
filtration systems. In general, an impervious clay layer or similar material
used to seal the pond system would be sufficient to seal the filter
embankment.
Interior slopes should also be designed to prevent erosion due to wave action.
Erosion protection can be provided by cobbles, broken or cast-inplace
concrete, wooden bulkheads, or asphalt strips. Emphasis should be placed on
shoreline control and reduction of aquatic weed growths. In addition, each
filter should be provided with a ramp for easy access and routine maintenance
of the system. The ramp can be used for both entry of cleaning equipment and
as a boat ramp.
221
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Embankments should provide at least 30 cm (1 ft) of head on the filter and 0.5
to 1 m (1.6 to 3.3 ft) of freeboard to prevent wave action from washing over
the dike.
5.3.1.10 Sand Cleaning
An intermittent sand filter is considered to be plugged when the amount of
water applied to the filter will not percolate through the sand bed before ;the
next dose is applied. When the filter is plugged, it is taken out of service
and the top 2.5 to 5 cm (1 to 2 in) of sand are removed or scraped from the
filter surface.
Huisman and Wood (62) present a review of the current practice of sand washing
associated with slow sand filters employed in potable water treatment. The
design engineer should become thoroughly familiar with the current practice of
sand reclamation before proceeding with the design of intermittent sand
filters. Sand from an intermittent sand filter may be washed by conventional
means, used as a soil conditioner, or disposed of in a landfill. In most
cases, economic considerations will dictate that the sand be cleaned and
reused rather than discarded. A typical sand washing device is shown in
Figure 5-9. Basically, these sand washing devices consist of an upflow
clarifier with sufficient velocity for removal of organic matter, without
washing away the sand. The organic matter washed from the sand may be
recycled back through the pond system. Once the sand has been cleaned, it can
be stockpiled and eventually recycled to the filter.
Whether to dispose of or reuse the spent filter sand is largely dependent on
the local availability of the filter sand. When sand costs are high, the
removed sand should be stockpiled, washed, and recycled. Storage of the sand,
in layers approximately 30 cm (1 ft) in depth and washing with 20 cm (8 in) or
more of clean water, has successfully refurbished used sand on an experimental
basis (65). Consideration of this approach appears particularly attractive in
wet climates. It is also possible that filter effluent could be used to clean
the sand by this technique.
The sand washing equipment should be sized to accommodate the sand washing
over several days at a time. Thus, the equipment may be smaller than required
for immediate sand washing.
The use of the spent sand as a soil conditioner has been investigated on, a
limited basis (65). The sand is rich in nutrients and organic matter, and
appears to be a good conditioner, especially for clay soils. If the pond
effluent is high in heavy metals concentrations, use of the spent filter sand
as a soil conditioner may be restricted since these metals may precipitate
from the sand particles.
The disposal of the spent filter sand in a land disposal site may be
economically feasible for very small sand filters where replacement filter
sand is readily available. However, a careful economic evaluation should :be
conducted before complete sand disposal is practiced. In addition, there may
222
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FIGURE 5-9
TYPICAL UPFLOW SAND WASHER AND SAND SEPERATOR UTILIZED IN WASHING
SLOW AND INTERMITTENT SAND FILTER SAND (63)
Water carrying
sand to be washed
Water carrying
washed sand
Sand settles
against rising
water.
Pressure water,
to ejector.
r
Water
rises ,,
to 4
overflow
Overflow
carrying
washings
or fine
sand
Overflow
water
Tn
i
\
Water carrying
.iwashed sand
I
Sand
settles
t
Displaced
water rises
.Sand
• Shear gate
Fluid sand
Make-up water
if needed
(A)
Sand washer
(B)
Sand separator
223
-------
be regulatory agency restrictions against placing the spent filter sand in
landfills due to possible leaching of heavy metals and other toxic materials.
The filter media and the filtered matter provide an excellent environment for
weeds and grass to grow. Weed control during the growing season is achieved
by complete weed removal using manual labor or with mechanical raking devices.
The best method of weed control is continuous monitoring and removal of early
growth.
When a filter is observed to be plugged or approaching plugged conditions, it
is necessary to rejuvenate the filter surface. Two approaches are available.
The first method consists of raking the media surface and breaking the surface
mat of filtered matter. Raking makes the cleaning process more economical by
obtaining optimum use of the media surface prior to removal. Raking can be
accompl i shed manual ly wi th a garden rake or wi th a tractor and a 1 andscape
rake. A maximum of two rakings before cleaning is recommended.
When the raking process no longer rejuvenates the filter surface due to the
accumulation of the filtered matter in the top layer of the media, removal of
the solids laden layer is necessary. The removal process can be performed
manually or with mechanical devices. A four-wheel-drive garden size tractor
equipped with a hydraulically operated scraper, bucket loading device, and
either flotation-type tires or dual rear tires works well (59). A small
floating dredge has been proposed as a means of cleaning a large [4-ha (10-
ac)] system in Wyoming (66). Heavy equipment such as road graders or heavy
front loaders should not be used on the filter.
5.3.1.11 Winter Operations ;
Winter operations are basically the same as summer operations except that
cleaning of the filters during the winter is far more difficult. The cold
season should be started with clean filters and in most instances the filters
will operate through the cold weather without a cleaning being required. The
system must be designed to prevent the accumulation of water in the filter
underdrain to a depth near the media surface where freezing can occur.
Operation of experimental intermittent sand filters at Logan, UT, during
freezing and sub-zero temperatures was investigated by Harris et al. (45-47).
Experience with these experimental and full-scale systems indicates that the
systems operated without any preparation of the sand surface. If severe water
conditions are expected, the most economical method for winter operation
appears to be the "ridge and furrow" technique.
The ridge and furrow technique requires that the sand filter surface be plowed
into small ridges and furrows. The ridges are spaced approximately 0.6 to 1.0
m (24 to 40 in) apart with 30 to 45 cm (12 to 18 in) deep furrows in between
each ridge. The basic idea of the ridge and furrow technique is to allow the
formation of a floating ice cover which will settle on the peaks of the ridges
as the water percolates through the sand filter bed. The furrows allow the
influent water to run under the settled ice cover during the filter hydraulic
224
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loading period and thus float the ice cover. Occasionally, the ice cover may
break up due to its own weight as it rests upon the ridges. This also allows
the influent water to infiltrate through the sand surface.
For very small filters it may be economically feasible to construct an
insulated cover over the filter for winter operation. With such a covered
structure, it might also be feasible to provide auxiliary heat to prevent
freezing. In severe climates with long freezing periods, insulated filter
covers may be essential for winter operation.
Covered filters also prevent algal growth on the filter surface during summer
periods. Thus, the length of filter runs may be substantially increased.
5.3.1.12 Operational Modes
Length of filter runs may be increased if the filter influent SS are low. It
may be advantageous, therefore, to hold pond effluents during high algal
periods and discharge during periods of low algal growth (i.e., early spring
and late fall). These periods may not result in a high quality of pond
effluent in terms of 6005, but the filter is capable of significantly
reducing the 6005. Loading the filters at night rather than during the day
has also increased length of filter runs. This is due to the reduction of
algal growth on the filter itself during dark hours.
5.3.1.13 Summary of Design Considerations
A summary of intermittent sand filter criteria is presented in Table 5-5.
5.3.1.14 Typical Design of Intermittent Sand Filter
a. Assumptions
1. Design Flow = 378.5 m3/d (0.1 mgd).
2. Hydraulic Loading Rate (HLR) = 0.29 m3/m2/d (0.3 mgad).
3. Minimum Number of Filters = 2 (Table 5-5).
4. Designed to minimize operation and maintenance.
5. Gravity flow.
6. Topography and location are satisfactory.
225
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TABLE 5-5
SUMMARY OF INTERMITTENT SAND FILTER DESIGN CRITERIA
Design Topic
Hydraulic Loading Rate
Filter Size/Number
Filter Shape
Depth of Filter Media
Size of Filter Media
and Underdrain Media
Filter Containment
Influent Distribution
Underdrain System
Maintenance
Considerations
Maintenance Required
Cleaning Frequency
Method of Cleaning
Typical Description
Equal to or less than 0.47 m3/m2/d using two or more
equal dosings per day.
Minimum of two filter units. Area of individual filters
<0.4 ha.
Dependent upon site plan and topography with rectangular
shape desirable to improve distribution of wastewater.
Large gravel-minimum cover of 10 cm (leveled), medium
gravel - 10 cm, pea gravel - 10 cm , filter sand -
0.6-1.0 m.
Large gravel (avg. dia. = 3.3 cm), medium gravel (avg.
dia. = 1.9 cm), pea gravel (avg. dia. = 0.64 cm), sand
(0.15 mm to 0.30 mm e.s., u <7).
Compacted earthen bank of reinforced concrete; freeboard
X).5 m.
Dosing basin with siphon or electrically actuated valves
with timer control and piping to gravel splash pads.
Splash pad gravel should be 3.8-7.6 cm in diameter and
surface area and depth should be 1.2 m^ and 25 cm.
Network of clay tile or perforated PVC pipe at a slope
of 0.025 percent serve as laterals. Pipes are placed in
sloped ditches and attached to larger drain manifolds.
Minimum lateral size is 15 cm in diameter and manifold
should be adequate to transport design flowrate at a'
velocity of 1.0-1.2 m/s when flowing full. Maximum
spacing of laterals is 1.4 m.
Grass encroachment, rodent activity,
access to filter by cleaning devices.
serviceability,
Removal of vegetation on filter surface. Raking and
cleaning of top 2-5 era of filter sand when plugged.
Dependent on hydraulic loading rate and the SS
concentration in the applied water (1 month to >1 year).
Raking maximizes the efficiency of the cleaning by fully
utilizing the top layer of sand. Manual or mechanical
equipment cleaning can be used.
226
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7. Adequate land is available at reasonable cost.
8. Filter sand is locally available.
9. Filters are considered plugged when, at the time of dosing, the water
from the previous dose has not dropped below the filter surface.
b. Calculate Dimensions of Filters
Area of Each Filter = design flow/HLR
= (378.5 m3/d)/(0.29 m3/m2/d)
= 1,357 m2 (14,800 ft2)
Letting L = 2W, Area = 2W2
W = (Area/2)0-5
= (l,357/2)°-5
= 26 m (86 ft)
L = 2W
= 2(26)
= 52 m (172 ft)
Construct two filters 26 m x 52 m (86 ft x 172 ft) side-by-side as shown in
Figure 5-10.
c. Influent Distribution System
Assumptions:
1. Use of dosing basin with gravity feed to the filters.
2. Loading sequence will deliver one-half the daily flowrate
to each filter unit per day in two equal doses.
3. Loading system will consist of two electrically activated
valves that are operated alternately by a simple electronic
control system triggered by a float switch or two
alternating dosing siphons.
4. Pipe sizes are selected to avoid clogging and to make
cleaning convenient. Hydraulics do not control.
227
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Dosing Basin Size:
Design Flow Rate = 378.5 m3/d/2 filters
= 189.3 m3/d (0.05 mgd) ,
Dosing Basin Volume = 189.3 m3/d/2 doses/d
= 95 m3 (25,000 gal) !
Use a square shape and a water depth of 1.0 m (3.3 ft) to minimize velocity in
distribution system. Use 0.3 m (1 ft) freeboard and install overflow pipe.
Total depth = 1.3 m (4.3 ft).
Dosing Basin Area = volume/depth
= 95 m3/1.0 m
= 95 m2 (1030 ft2) I
Dosing Basin Width = (95 m2)0-5
= 9.75 m (32.2 ft)
Dosing Basin Size = 9.75 m (32.2 ft) square x 1.3 m (4.3 ft) deep
Distribution manifold from the two valves leading to the individual filters
would be 20-cm (8-in) diameter pipe. Each of the outlets from the manifold
will serve 6 m (20 ft) of the long side of the filter unit. The manifold
outlets will discharge onto splash pads constructed of gravel 3.8 to 7.6 cm
(1.5 to 3 in) in diameter placed in a 75-cm (2.5-ft) square configuration at
each outlet opening.
d. Filter Containment and Filter Underdrain System
(See Figure 5-10)
Use a reinforced concrete retaining structure or a 20-mil plastic liner to
prevent infiltration and exfiltration to adjacent groundwater.
Slopes of filter bottom are dependent on drain pipe configuration using 0.025
percent slope with lateral collection lines 4.6 m (15 ft) on center.
Utilization of 15-cm (6-in) diameter perforated PCV pipe as collecting
laterals and 20-cm (8-in) diameter collection manifolds will provide adequate
hydraulic capacity and ease of maintenance.
Minimum Freeboard Required:
Depth = volume/area = 95 m3/!,357 m2 = 7.0 cm (2.8 in)
228
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FIGURE 5-10
PLAN VIEW, CROSS SECTIONAL .VIEW, AND HYDRAULIC
PROFILE FOR INTERMITTENT SAND FILTER
Plan view
Influent
Alternating manifold
dosing
siphons "Y
Influent •
Overflow
pipe
A-*-
15 cm Perforated laterals
@ 0.025 percent slope
spaced 4.6 m
Laterals
Influent
outlet
0.7m x 0.7m Gravel
splash pads
A-*-
r
20 cm Collection
manifold
Effluent
Sectional view A-A
0.3m Freeboard
Influent manifold
/—Splash pad
0.6m Filter sand
Underdrain media
tic liner J
Plastic liner
Drain manifold
Laterals •
•Ground
level
Reinforced concrete wall
Hydraulic profile
Influent
elev 100m
Inve
srph
Bottom
99.1m
y
rted'
ons
Yuverriow pipe
,
*" Top of sand
I Media
'— ._
98.2m
-_
-96.2m
229
-------
Minimum freeboard required to accommodate wastewater when filter is plugged at
time of application of the dose is 7.0 cm (2.8 in). However, with infrequent
inspection by an operator it is recommended that a safety factor be specified
and the value of 30 cm (1 ft) mentioned above be used.
5.3.1.15 Summary of Design Criteria for Existing and Planned
Filters
A summary of the design criteria and costs associated with existing and
proposed intermittent sand filters used to upgrade pond effluent is presented
in Table 5-6.
5.3.2 Rock Filtration
A rock filter operates by allowing pond effluent to travel through a submerged
porous rock bed, causing algae to settle out on the rock surface and into the
void space. The accumulated algae are then biologically degraded. Algae
removal with this system filter has been studied extensively at Eudora, KS,
beginning in 1970 (67)(68). :
Two experimental rock filters at Eudora used a submerged rock depth of 1.5 m
(5 ft) and rock of 1.3 cm (0.5 in) in one and 2.5 cm (1.0 in) in the other
filter (68). Influent to the filter submerges the rock bed, which is
contained in a diked area, and effluent is drawn off at the bottom of the bed.
The period of peak efficiency of the rock filter is in the summer and early
fall and hydraulic loading can be increased in this period. The filters at
rates up to 1.2 m3/m3/d (9 gpd/ft3) I in
decreased to 0.4 m3/m3/d (3 gpd/ft3) in
pond effluent having a BOD5 of 10 to 35
showed that the rock filter reduced 8005
by only a relatively small amount (however, the final concentration was always
below 30 mg/1) and would reduce SS to 20 to 40 mg/1 (Figures 5-11 and 5-12).
It was concluded that the rock filter could be operated to meet effluent
requirements of 30 mg/1 BOD5 and it was doubtful that the filter could
consistently reduce the SS to 30 mg/1. It was postulated that the filter would
not become plugged for more than 20 years. One drawback is the production of
hydrogen sulfide during the summer and early fall when the filter becomes
anaerobic. Aeration of the effluent would be required prior to discharge.
Eudora were operated at loading
the summer and this loading was
the winter and spring. Tests on
mg/1 and SS level of 40 to 70 mg/1
A rock filter was constructed at California, MO, in 1974 to upgrade an
existing pond (67). This was placed along one side of a tertiary pond as
illustrated in Figure 5-13. The rock filter was designed for a hydraulic
loading rate of 0.4 m3/m3/d (3 gpd/ft3). In 1975, a 757 mr/d (0.2
mgd) rock filter was constructed in Veneta, OR. In 1977 and 1978, extensive
monitoring programs were conducted by Oregon State University to determine
removal mechanisms and efficiency of this filter (69)(70). A schematic of the
Veneta system is presented in Figure 5-14.
230
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TABLE 5-6
SUMMARY OF DESIGN CRITERIA AND COSTS FOR EXISTING
AND PLANNED INTERMITTENT SAND FILTERS USED TO
UPGRADE POND EFFLUENT (59)
co
Location
Covello, CA
Mt. Shasta, CA
Tonal es, CA
dmarron, NM
Cuba, NM
Mori arty, NM
Portal les, NM
Roy, NM
Adel, GA
Alley, GA
Cummings, GA
Douglas County, GA
School
Nursing Home
Shellman, GA
Stone Mountain, GA
Huntington, UT
Design
Flow
1/s
3.5
0.7Lb
1.8
6.6
6.1
8.8
87.8
2.5
48.3
3.5
8.8
0.6
1.5
6.6
0.9
13.2
Pond
Type9
F
A
A
F
ASF
ASF
ASF
F
A
F
ASF
F
F
F
F
F
Retention
Time
days
49
20L>>
29
55
20
20
20
60
30
70
36
5
45
55
1
214
Filters
Number
4
3
2
• 2
4
8
3
2
2
2
4
2
2
4
1
3
Size
ha
0.048
0.405
0.012
0.04
0.02
0.028
0.405
0.028
0.405
0.06
0.06
0.008
0.012
0.032
0.081
0.271
Loadl ng
Rate
m3/m2/d
0.48
0.67
0.55
0.76
0.57
0.57
1.91
0.72
0.48
0.38
0.29
0.29
0.48
0.48
0.14
0.19
e.s.
mm
0.6-0.7
0.37
0.15-0.30
NA
NA
0.2
0.4
0.4
.0.25
0.25
0.25-0.80
0.3
0.35-0.75
0.35-0.75
0.45-0.55
0.2-0.25
u
NA
5.1
1.5-2.5
NA
NA
4.1
3.2
3.2
3.4
3.3
<4
3.67
<3.5
<3.5
H.5
<3
Sand
Depth
m
0.6
0.6
0.9
0.6
0.6
0.6
0.8
0.6
1.2
0.8
0.7
0.8
0.8
0.9
0.8
1.2
Filter Costs
capital USM
lotai Year
$/m3 flow
0.11
0.05 0.01
0.07
-
0.04C
0.03 0.01
—
0.01
0.02
0.05 0.01
0.03
0.04
0.01
0.03
0.04
1977
0.06 1976
1978
1975
1976
0.04 1976
1976
1976
1978
0.06 1976
1978
1976
1978
1979
1976
1976
aA = Aerated.
F = Facultative.
I>L = Dry Weather Flow.
cTwenty percent of total capital cost.
-------
FIGURE 5-11
BIOCHEMICAL OXYGEN DEMAND (BOD5) PERFORMANCE OF LARGE
ROCK FILTER At EUDORA, KANSAS (68)
I i i I
POND EFFLUENT
FILTER EFFLUENT
CO
Q
_J
O
CO
O
UJ
Q
z
UJ
a.
CO
:D
CO
AS ON
MONTH
FIGURE 5-12!
SUSPENDED SOLIDS PERFORMANCE OF LARGE ROCK FILTER
AT EUDORA, KANSAS (68)
M AM
POND EFFLUENT
FILTER EFFLUENT
MAMJJ ASONDJ
232
-------
FIGURE 5-13
ROCK FILTER INSTALLATION AT CALIFORNIA, MISSOURI (67)
Effluent
discharge
'condary
— _ —
Tertiary
^?£PS?
\
cell i
i
Q •> J
\ , -^/
_j A
\
i
u 1
cell i
1
:!p'i~*i^|-^'?;^/
1
^
Pri-
mary
Cell
-s
~ ^: \: ~ •
'
Single per-
• A forated pipe
Double per-
forated pipe
9.37 m
5.03 m
1.68 m.
1
MRock Mat
11.89 m
^-Effluent
Structure
Section A-A
233
-------
FIGURE 5-14
SCHEMATIC FLOW DIAGRAM OF VENETA, OREGON WASTEWATER
TREATMENT SYSTEM (69)
Raw_
wastewater"
Cell No. 1
4.51 ha
Cell No. 2
1.47 ha
Pond
effluent
samples
Rock filter
effluent
samples
Pump
stat.
Rock
filter
0.57 ha
I Discharge
1 Tom River
Cl,
234
-------
A performance evaluation of the California, MO, rock filter was conducted
during March and April 1975 (67). The results of that evaluation indicated
that the actual average hydraulic load on the filter was 0.25 m3/m3/d (1.9
gpd/ft3). A summary of the rock filter performance is reported in Table
5-7. During the evaluation period, the rock filter average effluent 8005
concentration was only 21 mg/1. The rock filter average influent SS
concentration was 69 mg/1 while the rock filter average effluent SS
concentration was 22 mg/1.
TABLE 5-7
PERFORMANCE OF ROCK FILTER AT CALIFORNIA, MISSOURI (67)
BODfi SS DO
Ijif 1 uent EffluenT Influent Effluent' Influent Effluent
mg/1 mg/T mg/T
3/5/75 15 8 35 24 19 6.6
3/13/75 14 6 64 26 16.8 7.9
3/19/75 19 7 80 24 — 12.9
3/26/75 25 13 94 20 12.9 5.2
4/2/75 30 15 74 16 13.3 4.6
Average 21 12 69 22 16 7.4
A routine monitoring program for the California, MO, rock filter was initiated
by the Missouri Department of Natural Resources (71) in March 1975, and the
results of this work are summarized in Figure 5-15. All solids determinations
were made on grab samples. The performance of the rock filter was sporadic
and failed to meet the federal discharge standard of 30 mg/1 of SS in the
effluent on 11 of the 19 sampling dates.
The Veneta rock filter (Figure 5-16) is of a different design (69)(70).
Influent enters the rock filter through a pipe laid on the bottom and running
through the center of the filter. The water rises through 2 m (6.6 ft) of
rock, 7 ...5 to 20 cm (3 to 8 in) in diameter, and is collected in effluent weirs
on the sides of the rock filter. The Veneta rock filter can consistently meet
daily maximum effluent limits of 20 mg/1 BODg and 20 mg/1 SS for hydraulic
loadings of 0.3 m3/m3/d (2.2 gpd/ft3) (Figure 5-17). The relationship
between the SS removal and the hydraulic loading rate of the Veneta facility
is shown in Figure 5-18.
Principal advantages of the rock filter are its relativley low construction
cost and simple operation. Odor problems can occur, and the design life for
the filters and cleaning procedures have not yet been firmly established.
235
-------
FIGURE 5-15
PERFORMANCE OF CALIFORNIA, MISSOURI ROCK FILTER
TREATING POND EFFLUENT (71)
150
(173)
100
A
o Influent (pond effluent)
• Effluent
O>
50
0
\ -
\ -
M
O N
D J F
1975-1976
M
A M
236
-------
FIGURE 5-16
VENETA, OREGON ROCK'FILTER (69)
•^
^
Influent
<
\
/•
X
Effluent ^
^...,, ^
36.9 m
^7.3 m
Influent
pipe
V
r^ ^s
1
36.9 m
«^_
7.3 m ^
^
7.3m -
52.4m
y
7.3 m
_- if
^
7
y
\
I
Effluent
weir ••-
7.3 m
Plan
73.8m
7.3 m
Profile
237
-------
FIGURE 5-17
PERFORMANCE OF VENETA, OREGON ROCK FILTER (69)
_ 50
en
c
_o
2
•*-'
03
u
I
• Influent SS
• Influent BODg
D Effluent SS
o Effluent BOD5
>
•-
'• ••* * t» I
••••
on
1314 15 16 17 18 19
11/77
1334567
1/78
5 6 7 8 9 1011
2/78
I I I I I I I I I I I I I I I I I I I I I I I I
56 7 89 1011
3/78
16 17 18 I92O2I22
4/78
14 B 16 1718 192O 3O3 I 2 3 4 5
5/78 7-8/78
238
-------
FIGURE 5-18
SS REMOVAL vs HYDRAULIC LOADING RATE AT VENETA, OREGON (69)
CO
100
80
c
-------
5.3.3 Micros-trainers
Early experiments with microstrainers to remove algae from pond effluents were
largely unsuccessful (72-75). This was generally attributed to the algae
being smaller than the mesh size of the microstrainers tested.
Envirex, Inc. has tested a one-micron polyester mesh microstrainer for algae
removal from pond effluents. A portable pilot unit was used at 10 locations
in 1977 and 1978 (76). The results of seven of these tests are summarized in
Table 5-8. Algae removal was best for the larger species of algae; smaller
species of algae, such as Chlorella, were removed only when a thin algal mat
was maintained on the screerfl SIime growth on the screen can be controlled by
chlorine without harming the polyester mesh,. SS and BODg levels below 30
mg/1 were consistently achieved during the test periods.
Unsuccessful tests of one-micron and six-micron screens were reported by Union
Carbide (77). Algae samples taken several days before and two weeks after the
tests indicated that predominant algae species removed were Aphanizomenon and
Lyngbya. These algae both have a;width of one to two microns. Heavy rainfall
accompanied by a large amount of colloidal material in the pond occurred
during the tests and there is some question as to how representative the SS
content of the pond was at that time. Addition of polymer in relatively large
doses (23 to 65 mg/1) was necessary to produce an effluent SS <30 mg/1. This
experience emphasizes the need to identify the algae species to be removed and
conduct pilot studies under representative conditions.
The tests represented in Table 5-8 are of relatively short duration.
Microstraining performance and reliability at pond sites over an extended
period of time has yet to be proved.
The first full-scale microstrainer application to pond effluent, a 7,200
nr/d (1.9 mgd) unit, was placed in operation at Camden, SC, in December 1981
(78H79). Typical design criteria include surface loading rates of 90 to 120
m3/m2/d (1.5 to 2.0 gpm/ft2) and head losses up to 60 cm (2 ft) (76).
Other process variables include backwash rate and pressure, and drum speed,
which are normally determined depending upon influent quality and desired
effluent quality. The service life of the screen is reported to be longer
than five years; however, actual field experience on the one-micron screen is
limited. For a 3 m by 3 m (10 ft x 10 ft) unit it would take 12 to 16 man-
hours to replace all the screens (77). The microstrainer portion of the plant
at Camden cost $1.5 million and is estimated to cost $71,000/year to operate
(1979 US $). Limited performance data are available, but the results indicate
that the system can meet an effluent standard of 30 mg/1 BOD5 and SS (78).
5.3.4 High Rate Filtration
Conventional rapid sand or multimedia filters have been used both for direct
filtration of algae-laden waters and for polishing filtration, which follows
coagulation-clarification.
240
-------
ro
TABLE 5-8
SUMMARY OF PERFORMANCE OF 1-micron MICROSTRAINER PILOT PLANT TESTS (76)
Test Site
Adel , Georgia
Owasso, Oklahoma
Greenville, Alabama
Camcien, South Carolina
Gering, Nebraska
Blue Springs, Missouri
Gumming s, Georgia
Length of
Test
hr
60
60
50
22
90
90
100
Lagoon Effluent
SS
mg/1
69
58
44
126
44
64
26
BOD5
mg/1
72
30
45
38
—
32
—
Microscreen Effluent
SS
mg/1
9
15
12
19
13
22
6
BODc
mgTl
9
15
14
23
. —
16
—
-------
5.3.4.1 Direct Filtration
Experiments with direct sand filtration have generally resulted in poor SS
removals, as indicated in Table 5-9. 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 effectively, but
special precautions must be taken in media design to ensure that the filter
does not become rapidly clogged.
At least one investigation with direct filtration has proved successful.
Wilkinson tested two types of mixed media filters for removing algae from
stabilization pond effluent at the Exxon Baytown Refinery (80). A 45-cm (1.5-
ft) diameter downflow deep bed was constructed using 45 cm (1.5 ft) of gravel
support, 60 cm (2 ft) of 0.6 to 0.75 mm sand, and 75 cm (2.5 ft) of 0.7 to 0.9
mm anthracite coal. A downflow 43-cm (17-in) diameter Neptune-Microfloc
shallow bed filter pilot unit was also used. It contained 30 cm (1 ft) of
gravel support, 7.6 cm (3 in) rough garnet, 11 cm (4.5 in) of 0.33 mm garnet,
23 cm (9 in) of 0.4 to 0.6 mm sand, and 57 cm (22.5 in) of 1.0 to 1.1 mm
anthracite c.oal. Side-by-side comparisons indicated no run length advantages
for deep bed filtration. Acceptable filter operation for both filters with
influent SS in the range of 20 to 60 mg/1 was obtained using alum with 0.5 to
1.0 mg/1 anionic or 1.0 to 2.0 mg/1 cationic polyelectrolyte. Alum dosages of
25 mg/1 produced only marginal improvement, while 40 to 50 mg/1 provided good
performance. The hydraulic loading rate was 175 to 300 nrYm2/d (3 to 5
gpm/ft2). At a constant SS feed of 30 mg/1, tests with the Neptune
Microfloc filter indicated that the percent backwash flow increased from 8
percent at 235 m3/m2/d (4 gpm/ft2) to 11.8 percent at 350 m3/m2/d (6
gpm/ft2), and to 17.5 percent at 470 m3/m2/d (8 gpm/ft2). In general,
work to date indicates that direct filtration of oxidation pond effluent is
impractical unless algae concentrations are low.
5.3.4.2 Polishing Filtration
Use of a rapid sand or multimedia filter system to reduce SS concentrations
following coagulation-clarification is very effective, achieving final
effluent SS levels less than 10 mg/1 and turbidities less than 4.0 JTUs (86).
Diatomaceous earth filters also work efficiently, but filter cycles may be
short because of filter binding by algae and other particulate matter. This
results in excessive diatomaceous earth use and high operating costs.
Baumann and Cleasby (87) have shown that, while there are many similarities
between water filtration (for which the most information is available) and
wastewater filtration, there are also differences that must be properly
accounted for in design. In particular, the quantity of solids in wastewater
is generally higher and the characteristics much more variable than for water.
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 in wastewater treatment.
242 :
-------
1HSBUE 5-8
PERFORMANCE SUMMARY OF DIRECT FILTRATION WITH'RAPID SAND FILTERS
CO
Coagulant
and Dose
mg/1
None
Fe: 7
None
None
None
None
None
None
None
None
Filter
Loading
m3/m2/d
11.7-117
123
28.8
28.8
111
111
117
64.5
29.3-58.7
29.3-176
Filter
Depth
cm
61
61
_.b
-_b
__b
— b
61
28
131
61
Sand
Size
Finding
Reference
mn
d50 =
d50 =
d50 =
d50 =
d50 -
d50 =
d50 =
dio =
d50 =
d!0 =
and
0.32
0.40
0.75
0.29
0.75
0.29
0.71
0.55
0.22
0.22
0.5
Removal declines to 21-45 % after 15 hr
50 percent al gae 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
0-76 percent SS removal
20 to 45 percent SS removal
22 to 66 percent SS removal
'
81a
82a
83a
75^
84d
85d
aLab culture of algae.
bNot available.
C0xidation pond effluent.
dUpflow sand filter.
-------
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 350 m3/m2/d (6 gpm/ft2) which permit deeper
penetration of the solids into the filter, and by allowing the water to pass
through a coarse-to-fine media gradation. It is advantageous in wastewater,
filtration to use a greater depth of filter media * 150 to 175 cm (60 to 70
in), than in water filtration, 75 to 130 cm (30 to 50 in), 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 shoul'd be used or surface
(and possibly subsurface) washers should be installed to ensure that the
original cleanliness and grain classification is restored.
The ability of mixed media beds to capture large particles in the top layer of
the bed and small particles in the lower region, allowing for greater
penetration of the suspended matter throughout the filter with subsequent
lower head losses and long filter runs, has; been- demonstrated by several
researchers. :
A dual-media filter consisting of 120 cm (48 in) of anthracite coal (2.4-4.8
mm) and 45 cm (18 in) of sand (0.8-1.0 mm) was used for polishing
flotation-tank type effluent in a pilot study at Sunnyvale, CA (86). The
loading rate was 330 nr/nr/d (5.6 gpm/ft2). Figure 5-19 shows effluent
turbidity as a function of filter-run duration. Solids breakthrough occurred
after 10 hours. Figure 5-20 shows development of the head loss profile with
time. The uniform head loss increase at al 1 depths indicates that the filter
has removed solids uniformly throughout the filter depth. This factor is
important in optimizing filter runs.
The average SS removal performance was 89 percent (3.0 to 6.0 mg/1 effluent)
using influent with concentration of 32 to 62 mg/1/. Generally one-half to
two-thirds of the effluent SS was volatile solids.' '"•
• '*.&'
A similar type of filter was used by the Napa-American Canyon (California)
Wastewater Management Authority to polish effluent, from the coagulation-
sedimentation process (88). Filter media .was 50 cm (20 in) of 1.0-1.2 mm
anthracite coal, 45 cm (18 in) of 0>4-0.5 mm sand, and 15 cm (6 in) of silica
gravel support material. The pla;nt used six filters with a combined capacity
of 58.300 m3/d (15.3 mgdh Filter loading rate was 290 m3/m2/d (5
gpm/ft2). Table 5-10 presents a* summary of the data from the treatment
plant for the first nine months of operation. BOD5 removal data through the
filter were not available, but effluent 8005 values were reported. There is
consistent removal of SS.
244
-------
FIGURE 5-19
DUAL-MEDIA FILTER EFFLUENT TURBIDITY PROFILE (86)
£
I 2
.3
®
SE i
111
<5
i i ii
i i r i
i i i
_L
_L
2 46 8 10 12 14 16 18 20
f:ilter Run, hr
FIGURE 5-20
DUAL-MEDIA FILTER HEADLOSS PROFILE (86)
in
to
ca 5
I <
i *
•i i.
Duration
of filter
run in
hours
I
_l
I
12 3
Filter Headless, ft
245
-------
TABLE 5-10
PERFORMANCE OF THE NAPA-AMERICAN CANYON WASTEWATER
MANAGEMENT AUTHORITY DUAL-MEDIA FILTERS (88)
Month
1978
October
November
December
1979
January
February
March
April
May
June
Average
BOD5a
SS
Effluent InfluentEffluent
mg/l
5.5
4.4
3.8
4.3
5.2
7.3
3.2
5.7
5.2
mg/l
14
22
25
22
23
13
14
19
19
19
mg/l
6.6
9.1
9.2
6.1
4.3
3.3
4.2
8.1
7.4
6.5
Removal
percent
53
59
63
72
81
75
70
57
61
66
aFilter influent 8005 not monitored.
bpirst 11 days of month, plant does not operate in
summer.
The importance of grain size selection in producing long filter runs was
demonstrated by Hutchinson, et a!. (89). It was found that diatoms were
clogging the upper layers of mixed media filters. By increasing the effective
grain size of the upper coal layer from 0.9 to 1.5 mm, while keeping the lower
sand layer at an effective grain size of 0.5 mm, the length of filter run was
increased from 5-12 hr to 12-20 hr. This increase was attributed to the
ability of the new coal layer to capture the diatoms in a more uniform fashion
throughout its depth. The quality of filter effluent was not diminished
because the sand layer retained the ability to capture the smaller suspended
matter.
Design
(87).
procedures for effluent filtration are described in detail elsewhere
246
-------
5.4 Coagulation-Clarification Processes
5.4.1 Introduction
Coagulation followed by sedimentation has been applied extensively for the
removal of suspended and colloidal materials from water. Lime, alum, and
ferric salts are the most commonly used coagulating agents. Each of these
chemicals, alone or in combination with others, may be the most appropriate
under 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.
5.4.2 Coagulation-Sedimentation
Although sedimentation has been used to clarify many types of wastewater, it
cannot by itself be used for algae removal. Chemical coagulants must first be
added to destabilize the algae. The algae-coagulant particles must then be
aggregated to form floes large enough to settle and be removed in a
sedimentation tank. Thus, the sedimentation process involves three stages:
1) chemical coagulation, 2) flocculation, and 3) settling.
A number of investigators have obtained high algae removals using th;e
coagulation-flocculation-settling sequence. Representative performance data
are shown in Table 5-11. Overflow rates for conventional sedimentation
processes have been 12 to 50 nr/m*/d (0.2 to 0.8 gpm/ftO with hydraulic
detention times of three to four hours. Flocculation tank design criteria
that were found to be adequate were detention times of 25 min with a G value
of 36 to 51 sec (81). Underflow total solids have generally been in the range
of 1.0 to 1.5 percent when alum or iron is used.
Table 5-12 presents _month!y averages of daily data collected at the Napa, CA,
algae removal plant during its first nine months of operation. This facility
used lime coagulation-flocculation followed by settling and dual media
filtration. The effluent COD and BODg removal percentages apply to the
entire algae removal plant whereas the SS data .are for only the coagulation-
flocculation-settling process. Influent SS varied throughout the year but a
consistent SS effluent quality from the clarifiers was maintained by adjusting
the chemical dosage.
As shown in Table 5-11, most applications have involved alum or lime. In
.using these coagulants, pH control is important. Golueke and Oswald (72)
found that pH for flocculation with alum was in the range of 6.3 to 6.8. This
pH range applies whether alum dosages are relatively low, as with the Golueke
and Oswald studies (100 mg/1), of relatively high, as with the studies at
Lancaster (240-360 mg/1). When lime is added, the major effect is to raise
the pH to about 11 where a magnesium hydroxide [Mg(OH)2] precipitate forms,
247
-------
TABLE 5-11
SUMMARY OF COAGULATION-FLOCCULATION-SETTLING PERFORMANCE
r\>
-£>
oo
Location
Windhoek, South Africa (24)
Richmond, California (72)
Napa, California
Pilot Plant (88)
Napa, California
Prototype* (88)
Coagulant
Alum8
L1meb
Alum
L1me
Alum
L1me
Dose
mg/1
216-300
300-40QC
100
200
-------
TABLE 5-12
PERFORMANCE OF THE NAPA-AMERICAN CANYON WASTEWATER
MANAGEMENT AUTHORITY ALGAE REMOVAL PLANT (88)
t\3
Ji>
UD
Month
1978
October
November
December
1979
January
February
March
April
May
Junec
Average
Influent
mg/1
39
32
27
27
23
44
36
45
61
37
BODa
Filtered
Effluent
mg/1
5.5
4.4
3.8
4.3
5.2
7.3
3.2
5.7
7.0
5.2
Removal
percent
86
86
86
84
77
83
91
87
89
85
Influent
mg/1
103
82
90
55
42
57
62
183
194
96
ssb
Clarified
Effluent
mg/1
14
22
25
22
23
13
14
19
19
19
Removal
percent
82
73
71
60
52
74
77
89
90
74
following dual-media polishing filtration.
bAhead of dual-media polishing filtration.
cFirst 11 days of month, plant does not operate in summer.
-------
attaches to algae cells, and causes their sedimentation. Required lime dosage
will fluctuate daily, generally from 200 to 400 mg/1. Mean lime dosage at the
Napa, CA, algae removal plant for the first six months of 1979 was 246 mg/1;
monthly mean lime dosages during this period ranged from 200 to 300 mg/1 (88).
Tests conducted by Al-Layla and Middlebrooks (91) found that the most
significant variables, in order of importance, were (1) alum dosage, (2)
temperature, (3) flocculatiori time, (4) paddle speed, and (5) settling time.
They found that large water temperature differences, even during the day,
could be important. ;
The Los Angeles County Sanitation Districts have the longest record of
experience with a coagulation-flocculation-settling system at the Lancaster
Tertiary Treatment Plant, constructed in 1970. The Lancaster plant utilizes
alum coagulation, sedimentation, and dual-media gravity filtration. The
system has consistently produced an effluent with turbidity below 1.7 JTUs,
In designing a coagulation-flocculation-settling facility, care should be
taken to ensure that conditions promoting autoflocculation are not encouraged.
Floating slujdge in the sedimentation tank defeats the purpose of the
sedimentation 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.
5.4.3 Flotation
The flotation process involves the formation of the fine gas bubbles that
become physically attached to the algal solids, causing them to float to the
tank surface. Chemical coagulation results in the formation of a floe-bubble
matrix that allows more efficient separation to take place in the flotation
tank.
Two means are available for forming the fine bubbles used in the flotation
process: autoflotation and dissolved-air flotation (DAF). Autoflotation
results from the provision of a region of turbulence near the inlet of the
flotation tank (which causes bubble formation from dissolved gases) and from
oxygen 'supersaturation of the pond effluent. In DAF, a portion of the
influent (or recycled effluent) is pUmped to a pressure tank where the liquid
is agitated with high pressure air to supersaturate the liquid. The
pressurized stream is then mixed with the influent, the pressure is released,
and fine bubbles are formed. These become cittached to the coagulated algal
cells. Table 5-13 presents a summary of operating and performance data, on
coagulation-flotation studies.
5.4.3.1 Autoflotation
Autoflotation is the natural flotation of algae brought about by gas
supersaturation in stabilization ponds. Information on autoflotation has been
250
-------
5-13
SUMMARY OF TYPICAL COAGULATION-FLOTATION PERFORMANCE
ro
en
Location
Autoflotatlon
Windhoek, South Africa (91)
Stockton, California (92)
Dissolved A1r Flotation
Stockton, California (92)
Lubbock, Texas (93)
El Dorado, Arkansas (94)
Logan, Utah (95)
Sunnyvale, California (86)
Coagulant
Alum
C02
C02
Alum
Acid
Alum
Acid
time
Alum
Alum
Alum
Acid
Dose
mg/1
220 mg/1
to pH 6.5
to pH 6.3
200 mg/1
to pH 6.5
225 mg/1
to pH 6.4
150 mg/1
200 mg/1
300 mg/1
175 wg/1
to pH 6.0-
,.6.3
Overflow
Rate
m3/m2/d
205
106
117
158
__a
235C
76-1416
••::.ii/ -
Detention
Time
m1n
8
8
22
17b
12d
8C
__a-
11'
Influent
mg/1
12.1
12.1
a
46
280-450
93
a
a
BODg
Effluent
mg/1
2.8
4.4
a
5
0.3
<3
a
-.a
Removal
percent
77
64
~a
89
>99
>97
-.a
,.a
Influent
mg/1
— a
—a
156
104
240-360
450
100
150
~
ss
Effluent
mg/1
a
a
75
20
0-50
36
• 4 ;:
30
Removal
percent
—a
-_a
44
81
>79
92
96
80
••
aNot available.
blnclud1ng 33 percent pressurized (35^-60 pslg) recycle.
^•Including 100 percent pressurized recycle.
•"Including 30 percent pressurized (50 pslg)-recycle.
6Includ1ng 25 percent pressurized (45 pslg) recycle.
flncludlng 27 percent pressurized (55-70 pslg) recycle.
9lnclud1ng 50 percent pressurized recycle.
-------
developed at Windhoek, South Africa, and Stockton, CA (58)(92)(93)(95)(97).
For autoflotation to be effective, the DO content of the pond must exceed
about 13 to 15 mg/1 and the pH must be greater than 11.
Autoflotation can perform well under the proper circumstances. The major
disadvantage is dependence on the development of gas supersaturation within
the oxidation pond. At Windhoek, the tertiary pond is 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 BODs loadings of 37 kg/ha/d (33 Ib/ac/d) during the summer are
closer to normal facultative pond loadings than those at Windhoek.
Generally, autofl otation is usable only for a part of the day. The only way
to compensate is to store the effluent and increase the number of flotation
tanks accordingly and use the process whenever it is operable. The extra cost
for more tanks will favor the selection of dissolved air flotation in nearly
all instances.
5.4.3.2 Dissolved Air Flotation (DAF)
The principal advantage of coagulation-DAF 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 sedimentation tanks. Overflow rates for
flotation are higher^ about 120 m3/m2/d (2 gpm/ft2) (excluding recyclej
compared to 50 nr/m2/d (0.8 gpm/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 Lancaster Tertiary Treatment Plant (74).
Another advantage of flotation over sedimentation is that a separate
flocculation step is not required. In fact, a flocculation step after
chemical addition and before introduction of the pressurized flow into the
influent has been found to be detrimental (95)(98).
a. Optimization of DAF Operation
Ramirez et al. (99) used electrocoagulation prior to DAF and achieved good
results. The electrocoagulation cell, a LectroClear system, supplies a
current to the influent of 0.53 ampere-minute/I. The system operates on 24
volts and has a capacity of 3,000 amperes. This helps to destabilize the
algae's negative charge, making chemical coagulation more effective.
252
-------
Operating parameters used in DAF include surface-loading rates, air/solids
ratio, pressurization level, coagulant dose, and the coagulant-addition point,
the choice of influent versus recycle pressurization, and the design details
for the flotation tank. The last item is important because most proprietary
tank designs were developed for sludge-thickening applications, and some
manufacturers have not reevaluated designs for optimal algae removal.
b. Surface Loading Rates
Studies at Stockton and Sunnyvale, CA (86)(93)(97) and at Logan, UT (96)
indicate that maximum surface loading rates generally vary from 120 to 160
nr/nr/d (2 to 2.7 gpm/ft2), including effluent recycle, where used)
depending on tank design. Stone et al. (86) found, in prior studies at
Sunnyvale, that loadings greater than 120 m3/m2/d (2 gpm/ft2) caused
deteriorating performance. However, the flotation tank used in the study was
of poor hydraulic design and it was concluded that higher loading rates might
be used in prototype facilities. It was also concluded that influent
pressurization produced better results than recycle pressurization and allowed
use of smaller tanks as well. Bare et al. (96) found that 140^ m3/m2/d
(2.4 gpm/ft2) was optimum and Parker et al. (93) used 160 m3/
gpm/ft2) at Stockton, CA. Alum was the coagulant used in all cases.
c. Pressurization and Air/Solids Ratio
'"''•,.,-',''•;:' - - ' '
air/solids ratio is defined as the weight of air bubbles added to the
process divided by the weight of SS entering the tank. Values used generally
range from 0.05 to 0.10 (93)(96). The air/solids ratio is dependent on
influent solids concentration, pressure level used, and percentage of influent
or recycled effluent pressurized,. Pressurization levels used in DAF
-generally range from 1.7 to 5.4 atm. Pressure may be applied to all or 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 pressurizing
the influent might cause floe breakup.
d. pH Sensitivity of Metal Ion Flocculation
The pH is extremely important in alum and iron coagulation. It is possible to
lower the wastewater pH by adding acid (^$04), 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 5-21 shows the effect of lowering the pH ,on effluent SS levels during
pilot studies at Sunnyvale (86), using alum as the coagulant. It was
concluded that not much could be gained by lowering the pH below 6.0, and that
253
-------
FIGURE 5-21
EFFECT OF ALUM DOSE AND pH ON FLOTATION PERFORMANCE (86)
100
o>
80
60
§ 40
20
I I I
lnfluentTSS=150mg/l
100 mg/l alum
150 mg/l alum
Typical data
Sept. 19 and
Sept. 20
5.6 5.8 6.0
6.2
PH
6.4 6.6
6.8
FIGURE 5-22
EFFECT OF ALUM DOSE AND INFLUENT SS ON FLOTATION PERFORMANCE (86)
50
o>
E
C/5
40
30
®
= 20
7
LLI
10
T
125 mg/l alum
^S
1150 mg/l alum
^_A H
175 mg/l alum
f '
200 mg/l alum
I
I
I
I
I
25 50 75 100 125 150
Influent TSS, mg/l
175 200
254
-------
the range of 6.0 to 6.3 could be used for optimum performance. Subsequent
neutralization can be accomplished by adding caustic soda.
e. Alum Dose
Pilot studies at Stockton (93) and Sunnyvale (86) (Figure 5-22) show the
effect of influent TSS and alum dose on effluent TSS concentrations. The
results presented in Figure 5-22 show that influent TSS have a relatively
minor effect on effluent quality. The benefit of increasing alum doses is
most pronounced up to about 175 mg/1. Beyond that range, increased alum
addition results in only marginal improvement in effluent TSS levels.
f. Physical Design
It was noted above that proprietary flotation tank designs do not possess
certain features important in pilot- and full-scale studies of algae removal.
Features incorporated in the flotation tank designs for Sunnyvale and Stockton
are shown in Figure 5-23 and illustrate important design concepts.
o 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 position of chemical addition invariably leads to
performance deterioration.
o The point of pressure release is in the feedwell. An orifice,
rather than a valve, can be used on the pressurized line because
the DAF tanks can operate at constant flow, using the 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 coalesce in the line leading to the
feedwel 1.
o Care is taken to distribute the wastewater flow evenly into
the tank. An inlet weir distributes the flow around the full
circumference of the inlet zone and a double ring of weirs are
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.
o 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.
255
-------
FIGURE 5-23
CONCEPTUAL DESIGN OF DISSOLVED AIR FLOTATION TANK
APPLIED TO ALGAE REMOVAL
Effluent
Float scraper arm
Float collection trough
Feedwell
Alum feed
orifice ring
256
-------
o Provision of sludge and float scrapers and positive removal of
sludge and float will aid performance.
o 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.
g. Float Concentration
It is necesary to remove and dispose of the chemical-algal float that-rises to
the water surface. Flotation general ly 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 algal-alum floe.
Bare et al. (96) reported float concentrations of 1>0 to 1.3 percent with alum
coagulation/DAF; Concentrations .increased to about 2.0 percent when a second
flotation was allowed to occur in the skimmings receiving tank. Stone et al.
(86) reported float concentrations of 1.3 to 2.1 percent in the Sunnyvale, CA,
studies with specific gravitiejsL of 0.45 to 0.55.
' h. Solids Handling and Treatment
Satisfactory disposition must be made of the algal-chemical sludge generated
by coagulation-clarification processes. Application of conventional
solids-handling and treatment processes requires increased capital and
operating expenses. This consideration was among those that led Middlebrooks
et al. (58) to recommend against using coagulation-clarification processes for
small plants.
Most of the relevant work to date has involved alum-algal sludges, with very
little work done with lime-algal sludge. Disposal and dewatering of
alum-algal 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 algal-alum sludge
have produced marginal results because of dewatering difficulties and the need
for using low process loading rates (72)(97). Heat treatment using the
Porteous process at temperatures of 193 to 213 °C has been shown to improve
•257
-------
subsequent vacuum filter yield and cake concentration to a limited extent.
Filter yield was low and ranged from 4.4 to 12.2 kg/m2/h (0.9 to 2.5
Ib/ft2/hr). Cake concentrations during the study were 8.3 to 21.6 percerit
total solids, using raw sludge with a solids concentration of about four
percent in the feed algal-alum sludge (97).
Use of Zimpro low-temperature oxidation, at temperatures of 180 to 220 °C, has
resulted in vacuum filter cake concentrations of 15 to 19 percent totaj
solids, at filter-yield rates of 3.3 to 14.9 kg/m2/h (0.7 to 3.0 IB
ft2/hr) (97).
Zimpro high-temperature oxidation, with 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 concentrations and filter yield
improvements were marginal, indicating that ultimate disposal should
incorporate ponds. The high-oxidation process reduces VSS in the sludge by
about 97 percent, 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 pond storage (96).
Only limited- investigations have been made into the use of centrifugation for
concentrating algal-chemical sludges. At Firebaugh, CA, a Bird solid-bowl
centrifuge and a DeLaval yeast-type separator were used to dewater sludge
(100). Both devices were considered failures, although the use of sludge
conditioning aids, .such as organic polymers, might be expected to improve
their performance. A DeLaval self-cleaning basket machine, also tested, was
able to concentrate a two to three percent feed to 10 percent total solids
with a recovery of 98 percent.
Centrifugation has been used for lime classification of raw wastewater sludges
(101M102), but the only report on its use for algal-lime sludge did not
present specific details (94).
Another process that has been investigated is a chemical-oxidation scheme,
called Purifax, that employs chlorine as the oxidant. This process was
capable of stabilzing the sludge, and yielded a product that could be
dewatered on sand drying beds or in a pond; however, chlorine costs are
relatively high (97).
Initial work on anaerobic digestion of algal-alum sludge, at the University of
California, indicated that the process held little promise for future use
(103). 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.
While these relatively complex processes have generally proved unsatisfactory
there is a comparatively simple, and potentiality effective, solution to the
solids-handling problem—return of the algal-alum sludge to the pond (104,).
When algae-alum sludge is returned to a pond, it must be distributed to reduce
accumulation at a single point. Furthermore, when air is contained in the
sludge float, procedures must be found to remove it before introducing the
258
-------
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 (100).
i. Coagulant Recovery
Because chemicals are used in large quantities for coagulation, their
regeneration 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 (100).
Because phosphorus is also released at low pH, acid recovery will be limited
to those situations where phosphorus removal is not required.
Although efforts in coagulant recovery from algae sludges have only been
exploratory thus far, there is evidence that further investigations could
yield useful results.
5.5 Land Application
5.5.1 Introduction
Land application systems can be classified into one of three categories:
overland flow (OF) (involving flow over grassed terraces); irrigation of crops
by conventional methods, or slow-rate treatment (SR); and rapid infiltration
(RI) systems. The following subsections discuss design criteria and
performance of the three system types when used in conjunction with pond
effluent. Comparison of typical characteristics and design criteria for land
treatment processes are presented in Tables 5-14 and 5-15 (105).
5.5.2 Overland Flow
Overland flow is a land treatment process which can be used specifically on
sites containing soils with limited permeability. In an OF process,
wastewater is distributed along the top portion of sloped terraces and allowed
to flow across a vegetated surface to runoff collection ditches. The
wastewater is renovated as it flows in a thin film down over the sloping
ground surface. Since the system does not rely on percolation into the soil,
overland flow can be used on clay and silty type soils with low infiltration
capacity.
The treatment mechanisms of an OF system are similar in some respects to most
land treatment systems. Biological oxidation, sedimentation, and grass
filtration are the primary removal mechanisms for organics and SS. Phosphorus
and heavy metals are removed principally by adsorption, precipitation, and ion
exchange in the soil. Some are also removed by plant uptake. Dissolved
259
-------
TABLE 5-14
COMPARISON OF SITE CHARACTERISTICS FOR
LAND TREATMENT PROCESSES (105)
ro
01
o
Grade
Soil
Permeability
Depth to
Groundwater
Climatic
Restrictions
Slow Rate
Less than 20% on
cultivated land;
less than 40% on
noncultivated land
Moderately slow to
moderately rapid
0.6-1.0 m minimum13
Storage often needed
for cold weather
and precipitation
Rapid Infiltration
Not critical;
excessive grades
require much
earthwork
Rapid (sands, sandy
loams)
0.3 m during flood
cycle; 1.5-3.0 m
during drying
cycle
None (possibly modify
operation in cold
weather)
Overland Flow
Finish slopes 2-
Slow (clays, silts,
soils w/impermeable
barriers)
Not critical0
Storage often needed
for cold weather
treatment
aSteeper grades might be feasible at reduced hydraulic loadings.
bUnderdrains can be used to maintain this level at sites with high groundwater table.
clmpact on groundwater should be considered for more permeable soils.
-------
TABLE 5-15
COMPARISON OF TYPICAL DESIGN FEATURES FOR
LAND TREATMENT PROCESSES (105)
ro
en
Application
Techniques
Application
Rate
Field Area
Requi red"
Typ. Weekly
Application
Rate
Minimum Pre-
appHcation
Treatment
Provided in
U.S.
Disposition
of Applied
Wastewater
Need for
Vegetation
Slow Rate
Sprinkler or
surface9
0.5-6.0 m/yr
23-280 ha
1.3-10 cm
Primary
sedimentation^
Evapotranspi ration
and percolation
Required
Rapid Infiltration
Usually surface
6-125 m/yr
3-23 ha
10-240 cm
Primary
sedimentation
Mainly
percolation
Optional
Overland Flow
Sprinkler or
surface
3-20 m/yr
6.5-44 ha
6-40 cmc
Grit removal and
comminution6
Surface runoff and
evapotranspiration
with some
percolation
Required
alncludes ridge-and-furrow and border strip.
bField area (not including buffer area, road, or ditches) for 3,785 m^/d flow.
cRange includes raw wastewater to secondary effluent, higher rate for higher level
of preapplication treatment.
dWith restricted public access; crops not for direct human consumption.
eWith restricted public access.
-------
solids are removed by plant uptake, ion exchange, and through leaching. Algae
removal by OF systems has been inconsistent and it should be evaluated
carefully before using OF as a means of algae removal.
Nitrogen levels can also be significantly reduced by several soil and plant
processes. An aerobic zone is maintained in the top layer of liquid flow
where ammonia is oxidized into nitrite and then nitrate. Immediately below
the soil surface, in the top few millimeters, an anaerobic zone is established
where denitrifying bacteria convert the nitrates into nitrogen gas, resulting
in high overall reduction in the total applied nitrogen. Plant uptake and
volatilization under proper pH conditions are other important removal
mechanisms, but permanent nitrogen removal by plant uptake is only possible if
the cover crop is harvested and removed from the field.
The basic differences between the OF systems cited in Tables 5-16 through 5-18
are the application methods and rates. Two types of application can be used:
(1) sprinkler, or; (2) gravity surface irrigation by means of grated pipe or
bubbling orifice. The most .common method is sprinkler, which ensures even
distribution and can be automatically controlled.
5.5.3 Slow-Rate or Crop Irrigation
In humid climates, SR systems are generally designed for the maximum possible
hydraulic loading to minimize land requirements. Systems of this type have
been successfully designed for forests, pastures, forage grasses, corn, and
other crop production. In arid climates, where water conservation is more
critical, wastewater is often applied at rates that just equal the irrigation
needs of the crop. Water rights must also be given careful consideration in
arid climates prior to diverting pond effluent to another location for land
treatment.
Design of SR systems for typical municipal effluents is usually based on
either the limiting permeability of the in situ soils or on meeting nitrate
requirements in the groundwater, if the site overlies a potable aquifer. The
wastewater hydraulic loading rate is calculated for both conditions, and the
limiting value then controls design (105).
Performance and design data for selected SR systems treating pond effluent are
summarized in Tables 5-19 through 5-22.
5.5.4 Rapid Infiltration
The principal difference between RI and SR is that hydraulic loading rates are
greater. Highly permeable soils must be available. Nitrogen removal
mechanisms rely less on crop uptake and more on nitrification-denitrification
within the soil. It has been suggested that such systems only be allowed when
groundwater quality is either of no consequence or when the percolate can be
controlled (106).
262
-------
TABLE 5-16
SUMMARY OF BOD AND SS REMOVALS AT OVERLAND FLOW SYSTEMS
TREATING POND EFFLUENTS3 (105)
ro
en
Location
f
Pauls Valley, OK
Utica, MS
Easley, SC
Slope
Length
m
46
46
46
Application
Rate
m^/m/hr
0.06
0.032
0.065
0.049
0.13
0.10
0.23
Hydraulic
Loadi ng
Rate
cm/d
1.66
1.27
2.54
2.54
5.08
1.27
3.58
Application
Period
hr/d
12
18
18
24
18
6
7
Frequency
d/wk
7
5
5
7
5
5
5
BOD
Influent
27.7
22
22
22
22
22
28
Effluent
mg/1
20.5
3.5
4.0
5.5
7.5
8.6
15
SS
influent
114
30
30
30
30
30
60
Effluent
72.8
5.5
8.0
13.0
13.0
6.4
40
Performance during warm season.
-------
TABLE 5-17
SUMMARY OF NITROGEN AND PHOSPHORUS REMOVALS AT OVERLAND
FLOW SYSTEMS TREATING POND EFFLUENTS3 (105)
ro
Locati on
Pauls Valley, OK
Utica, MS
Easley, SC
Hydraulic
Loadi ng
Rate
cm/d
1.66
1.27
2.54
2.54
5.08
1.27
3.58
Total
influent
15.5
20.5
20.5
20.5
20.5
20.5
6.7
N
Effluent
11.4
4.3
7.5
7.3
10.0
7.0
2.1
Ammonia-N
Influent Effluent
1.7
15.6
15.6
15.6
15.6
15.6
1.0
mg/1
0.4
0.1
0.8
0.7
1.1
0.8
0.4
Nitrate-N
Influent Effluent
<0.1 0.2
<1.0 1.0
<1.0 2.6
<1.0 3.1
<1.0 4.8
<1.0 3.2
2.4 1.1
Total
Influent
6.3
10.3
10.3
10.3
10.3
10.3
3.8
P
Effluent
5.1
4.9
6.1
5.9
8.2
7.1
2.2
aPerformance during warm season.
-------
TABLE 5-18
REMOVAL OF HEAVY METALS AT DIFFERENT HYDRAULIC
RATES AT UTICA, MISSISSIPPI (105)
cm/a
1.27
2.54
3.81
5.08
Cadmium
0.0046
0.0036
0.0079
0.0142
Nickel Copper
mg/1
0.0131 0.0129
0.0217 0.0293
0.0302 0.0382
0.0486 0.0524
Zinc
0.0558
0.0525
0.0757
0.0853
Removal Efficiency
Cadmi urn
Nickel
Copper
Zinc
percent
85
91
78
63
92
88
80
66
93
82
74
64
88
87
79
75
en
on
-------
TABLE 5-19
BOD REMOVAL DATA FOR SELECTED SLOW-RATE SYSTEMS
TREATING POND EFFLUENTS (105)
Location
Dickinson, ND
Huskegon, MI
Hydraulic
Loadi ng
Rate
cm/yr
140
130-260
290
Surface
Soil
Sandy loams
and loamy
sands
Sands and
loamy sands
Clay and
clay loam
In Applied
Wastewater
mg/1
42
24
89
BOD
In Treated
Wastewater
mg/1
1.3
0.7
Removal
percent
>98
94
99
Sampl i ng
Depth
m
<5
4
2.1
TABLE 5-20
NITROGEN REMOVAL DATA FOR SELECTED SLOW-RATE
SYSTEMS TREATING POND EFFLUENTS (105)
Location
Dickinson, ND
Helen, GA
San Angel o, TX
Total Nitrogen
1n Applied
Wastewater
mg/1 as N
11.8
18.0
35.4
Total Nitrogen
1n Percolate
or Affected
Groundwater
mg/1 as N
3.9
3.5
6.1
Removal
percent
67
80
83
Sampling
Depth
m
11
1.2
10
Total Nitrogen
in Background
Groundwater
mg/1 as N
1.9
0.17
—
266
-------
TABLE 5-21
PHOSPHORUS REMOVAL DATA FOR SELECTED SLOW-RATE SYSTEMS
TREATING POND EFFLUENTS3 (105)
PO
CTl
Location
Agricultural
Systems
Dickinson, ND
Muskegon, MI
Forest System
Helen, GA
Hydraulic
Loading
Rate
cm/yr
140
130-260
380
Surface
Soil
Sandy loams
and loamy
sands
Sands and
loamy sands
Sandy loam
P04
In Applied
Wastewater
mg/1 as P
6.9
1.0-1.3
13.1
Soluble P04
in Affected
Groundwater
mg/1 as P
0.05
0.03-0.05
0.22
Distance
Samp! 1 ng from
Removal Depth Site
percent m m
99 <5 30-150
95-98 1.5 0
98 1.2 0
Soluble P04
in Background
Groundwater
mg/1 as P
0.04
0.03
0.21
aTotal phosphate concentration.
-------
TABLE 5-22
TRACE ELEMENT BEHAVIOR DURING SLOW-RATE
TREATMENT OF POND EFFLUENTS (105)
ro
Ch
co
El ement
Cadmium
Chromium
Copper
Lead
Manganese
Mercury
Z1nc
EPA Drinking
Water Standard
mg/1
0.01
0.05
1.0
0.05
0.05
0.002
5.0
Raw Municipal
Wastewater
Concentration
mg/1
0.004-0.14
0.02-0.7
0.02-3.4
0.05-1.3
0.11-0.14
0.002-0.05
0.03-83
Muskegon,
Michigan3
Percolate
Concentration Removal
mg/1
<0.002
0.004
0.002
<0.050
0.26
<0.002
0.033
Percent
90
90
90
>40
15
95
San Antonio,
Percolate
Concentration
mg/1
<0.004
<0.005
0.014
<0.050
-- ;
0.102
Texasb
Removal
Percent
-d
>98
85
_.d
~
25
Melbourne,
Australia0
Percolate
Concentration Removal
mg/l
0.002
0.03
0.02
0.01
—
0.0004
0.04
Percent
80
90
95
95
—
85
95
aAverage annual concentrations (1975) found 1n underdralns placed at a depth of 1.5 m below Irrigation site.
bAverage annual concentrations (November 1975 - November 1976) found In two seepage creeks adjacent to the irrigated area.
cAverage annual concentrations (1977) found in underdrains placed at depths of 1.2 to 1.8 m below the irrigation site.
"Percent removal was not calculated since influent and percolate values are below lower detection limit.
-------
There are numerous examples of rapid infiltration of treated effluent.
Hydraulic loading rates for secondary effluent range down from 2.1 m/wk (7 ft/
wk) at Flushing Meadows, AZ, on sandy soil to 20 cm/wk (8 in/wk) at Westby,
WI, on silt loam. For primary effluent, loading rates of 57 cm/wk (22 in/wk)
are used at Hoi lister, CA (105).
The few examples of RI with pond effluent are presented in Tables 5-23 and
5-24. Of particular concern would be whether the algae would clog the soil.
The data accumulated so far at Flushing Meadows seem to indicate that algae
have a greater clogging potential than an equal mass of SS from secondary
treatment (activated sludge) at the higher loading rates employed in that
system. This fact is ordinarily of no consequence for the more common
low-rate systems applying approximately 2.5 to 7.5 cm/wk (1 to 3 in/wk).
However, Hicken et al. (107) observed prolific algal growths on nonvegetated
control plots at application rates of 5 to 15 cm/wk (2 to 6 in/wk) (100).
Contrary to observations, the algal mats did not increase the hydraulic
impedance on these sites. Perhaps the explanation lies in the great
difference in application rate between the two systems.
269
-------
TABLE 5-23
NITROGEN REMOVAL DATA FOR SELECTED RAPID INFILTRATION
SYSTEMS TREATING POND EFFLUENTS (105)
Location
Brookings, SD
1X3
•-4
O
Total N
in Applied Loading
Wastewater Rate
mg/1
10.9
FECAL
m/yr
12.2
BOD:N
2:1
TABLE
Flooding
Time: Dry ing
Time
1:2
5-24
COLIFORM REMOVALS AT SELECTED RAPID
SYSTEMS TREATING POND EFFLUENTS (1
Renovated Water
NOri-N Total N
r- •J. ,. , . . "
mg/1
5.3 6.2
INFILTRATION
L05)
Total N
Removal
percent
43
Location
Hemet, CA
Milton, WI
Santee, CA
Soil Type
Sand
Gravelly
sands
Gravel ly
sands
Fecal Coliforms
Applied Wastewater Renovated Water
MPN/100 ml
60,000
TNTCa
130,000
130,000
11
0
580
<2
Distance of
Travel
m
2
8-17
61
762
aAt least one sample too numerous to count.
-------
5.6 References
1. Process Design Manual for Suspended Solids Removal. EPA-625/l-75-003a,
U.S. Environmental Protection Agency, Center for Environmental Research
Information, Cincinnati, OH, 1975.
2. Upgrading Lagoons. EPA-625/4-73-001b, NTIS No. PB 259974, U.S.
Environmental Protection Agency, Center for Environmental Research
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3. Process Design Manual for Upgrading Existing Wastewater Treatment
Plants. EPA-625/l-71-004a, U.S. Environmental Protection Agency, Center
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4. Oswald, W. J. Advances in Anaerobic Pond Systems Design. In: Advances
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5. Goswami, S. R., and W. L. Busch. 3-Stage Ponds Earn Plaudits. Water
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7. Dinges, R., and A. .Rust. Experimental Chlorination of Stabilization
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14. Polluted! Pollution Advisory Services, Ltd. Nutrient Control in Sewage
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17. Engel, W. T., and T. T. Schwing. Field Study of Nutrient Control in a
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18. Golueke, C. G., and W. J. Oswald. Harvesting and Processing
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• ' - }
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36. Wolverton, B. C., and R. C. McDonald. Upgrading Facultative Wastewater
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37. Chambers, G. V. Performance of Biological Alternatives for Reducing
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38. Schroeder, G. L. Some Effects of Stocking Fish in Waste Treatment
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39. Reid, G. W. Algae Removal by Fish Production. In: Ponds as a
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40. Ryther, J. H. Controlled Eutrophication-Increasing Food Production from
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41. Serfling, S. A., and C. Alsten- An Integrated, Controlled Environment
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42. Reynolds, J. H. The Effects of Selected Baffle Configurations on the
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43. Nielsen, S. B. Loading and Baffle Effects on Performance of Model Waste
Stabilization Ponds. M.S. Thesis, Utah State University, Logan, UT,
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44. Marshall, G. R., and E. J. Middlebrooks. Intermittent Sand Filtration
to Upgrade Existing Wastewater Treatment Facilities. PRJEW 115-2, Utah
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45. Harris, S. E., J. H. Reynolds, D. W., Hill, D. S. Filip, and E. J.
Middlebrooks. Intermittent Sand Filtration for Upgrading Waste
Stabilization Pond Effluents. Presented at 48th Annual Water Pollution
Control Federation Conference., Miami Beach, FL, October 1975.
46. Harris, S. E., J. H. Reynolds, D. W. Hill, D. S. Filip, and E. J.
Middlebrooks. Intermittent Sand Filtration for Upgrading Waste-
Stabilization Pond Effluents. JWPCF 49(1):83-102, 1977.
47. Harris, S. E., D. S. Filip, J. H. Reynolds, and E. J. Middlebrooks.
Separation of Algal Cells from Wastewater Lagoon Effluents, Volume I:
Intermittent Sand Filtration to Upgrade Waste Stabilization Lagoon
Effluent. EPA-600/2-78-033, NTIS No. PB 284925, U.S. Environmental
Protection Agency, Municipal Environmental Research Laboratory,
Cincinnati, OH, 1978.
48. Hill, F. E., J. H. Reynolds, D. S. Filip, and E. J. Middlebropks.
Series Intermittent Sand Filtration to Upgrade Wastewater Lagoon
Effluents. PRWR 153-1, Utah Water Research Laboratory, Utah State
University, Logan, UT, 1977.
49. Bishop, R. P., J. H. Reynolds, D. S. Filip, and E. J. Middlebrooks.
Upgrading Aerated Lagoon Effluent with Intermittent Sand Filtration.
PRWR&T 167-1, Utah Water Research Laboratory, Utah State University,
Logan, UT, 1977.
50. Messinger, S. S. Anaerobic Lagoon-Intermittent Sand Filter System for
Treatment of Dairy Parlor Wastes. M.S. Thesis, Utah State University,
Logan, UT, 1976.
274
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51. Tupyi, B., J. H. Reynolds, D. S. Filip, and E. J. Middlebrooks.
Separation of Algal Cells from Wastewter Lagoon Effluents, Volume II:
Effect of Sand Size on the Performance of Intermittent Sand Filters.
EPA-600/2-79-152, NTIS No. PB 80-120132, U.S. Environmental Protection
Agency, Municipal Environmental Research Laboratory, Cincinnati, OH,
1979.
52. Daniels, F. E. Operation of Intermittent Sand Filters. Sewage Works
Journal .17(5): 1001-1006, 1945.
53. Pincince, A. B., and J. E. McKee. Oxygen Relationships in Intermittent
Sand Filtration. J. Sanit. Eng. Div., ASCE 94(SA6):1093-1119, 1968.
54. Massachusetts Board of Health. The Condition of an Intermittent Sand
Filter for Sewage After Twenty-Three Years of Operation. Engineering
and Contracting 37:271, 1912.
55. Calaway, W. T., W. R. Carroll, and S. K. Long. Heterotrophic Bacteria
Encountered in Intermittent Sand Filtration of Sewage. Sewage and
Industrial Wastes Journal 24(5):642-653, 1952.
56. Furman, R. des., W. T. Calaway, and G. R. Grantham. Intermittent Sand
Filters--Multipie Loadings. Sewage and Industrial Wastes Journal
27(3):261-276, 1955.
57. Grantham, G. R., D. L. Emerson, and E. K. Henry. Intermittent Sand
Filter Studies. Sewage and Industrial Wastes Journal 21(6):1002-1015,
1949.
58. Middlebrooks, E. J., D. B. Porcella, R. A. Gearheart, G. R. Marshall, J.
H. Reynolds, and W. J. Grenney. Techniques for Algae Removal from Waste
Water Stabilization Ponds. JWPCF 46(12):2676-2695, 1974.
59. Russell, J. S., E. J. Middlebrooks, and J. H. Reynolds. Wastewater
Stabilization Lagoon-Intermittent Sand Filter Systems. EPA-600/2-80-032,
NTIS No. PB 80-201890, U.S. Environmental Protection Agency, Municipal
Environmental Research Laboratory, Cincinnati, OH, 1980.
60. Reynolds, J. H., S. E. ' Harris, D. W. Hill, D. S. Filip, and E. J.
Middlebrooks. Intermittent Sand Filtration for Upgrading Waste
Stabilization Ponds. Second Annual National Conference on Environmental
Engineering Research, Development and Design, Environmental Engineering
Division, ASCE, University of Florida, Gainesville, FL, July 1975.
61. Cowan, P. A., and E. J. Middlebrooks. A Model and Design Equations for
the Intermittent Sand Filter. Environment International 4:339-350,
1980.
62. Huisman, L., and W. E. Wood. Slow Sand Filtration. World Health
Organization, Geneva, 1974.
275
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63. Fair, G. M., 0. C. Geyer, and D. A. Okun. Water and Wastewater
Engineering, Vol. II. Water Purification and Wastewater Treatment and
Disposal. John Wiley and Sons, Inc., New York, NY, 1968. ;
64. American Association of State Highway and Transportation Officials, 444
N. Capitol Street, Washington, DC 20001.
65. Elliott, J. T., D. S. Filip, and J. H. Reynolds. Disposal Alternatives
for Intermittent Sand Filter Scrapings Utilization and Sand Recovery.
PRJER 033-1, Utah Water Research Laboratory, Utah State University,
Logan, UT, 1976.
66. Benjes, H. H. Personal communication. Culp/Wesner/Culp, 1777 South
Harrison, Denver, CO 80210, 1981.
67. O'Brien, W. J. Algal Removal by Rock Filtration. In: Transactions 25th
Annual Conference on Sanitary Engineering, University of Kansas,
Lawrence, KS, 1975.
68. O'Brien, W. J., and R. E. McKinney. Removal of Lagoon Effluent
Suspended Solids by a Slow-Rock Filter. EPA-600/2-79-011, NTIS No. PB
297454, U.S. Environmental Protection Agency, Municipal Environmental
Research Laboratory, Cincinnati, OH, 1979.
69. Swanson, G. R., and K. J. Williamson. Upgrading Lagoon Effluents with
Rock Filters. J. Sanit. Eng. Div., ASCE 106(EE6):1111-1119, 1980.
70. Williamson, K. J., and G. R. Swanson. Field Evaluation of Rock Filters
for Removal of Algae from Lagoon Effluents. In: Performance and
Upgrading of Wastewater Stabilization Ponds, EPA-6T5D/9-79-011, NTIS No.
PB 297504, U.S. Environmental Protection Agency, Municipal Environmental
Reserach Laboratory, Cincinnati, OH, 1978.
71. Forester, T. H. Personal communication. Missouri: Department of
Natural Resources, Jefferson City, MO, 1977.
72. Golueke, C. G., and W. J. Oswald. Harvesting and Processing
Sewage-Grown Planktonic Algae. JWPCF 37(4):471-498, 1965.
73. California Department of Water Resources. Removal of Nitrate by an
Algal System. EPA WPCRS, 1303ELY4/71-7, Washington, DC, April 1971. :
74. Dryden, F. D., and G. Sterm. Renovated Wastewater Creates Recreational
Lake. Environmental Science and Technology 2:268-278, 1968.
75. Lynam, G., G. Ettelt, and T. McAloon. Tertiary Treatment at Metro
Chicago by Means of Rapid Sand Filtration and Microstrainers. JWPCF
41(2):247-279, 1969.
76. Kormanik, R. A., and J. B. Cravens. Remove Algae through
Microscreening. Water and Wastewater Engineering 15(11):72-74, 1978.
276
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77. Union Carbide Corporation. Algae Removal from the Seadrift Plant
Wastewater Treatment System. Port Lavaca, TX, January 1979.
78. B. P. Barber & Associates. Recommended Design for the City of Camden,
South Carolina, Wastewater Treatment Facility. Prepared for the City of
Camden, SC, 1977.
79. Harrelson, M. E., and J. B. Cravens. Use of Microscreens to Polish
Lagoon Effluent. JWPCF 54(1):36-42, 1982.
80. Wilkinson, J. B. A Discussion of Algae Removal Techniques and
Associated Problems and Process and Economic Considerations of Ponds for
Treatment of Industrial Wastewater. In: Ponds as a Wastewater
Treatment Alternative, Water Resources Symposium No. 9, University of
Texas, Austin, TX, 1976.
81. Borchardt, J. A., and C. R. O'Melia. Sand Filtration of Algae
Suspensions. JAWWA 53(12), 1961.
82. Davis, E., and J. A. Borchardt. Sand Filtration of Particulate Matter.
J. Sanit. Eng. Div., ASCE 92(SA5):47-60, 1966.
83. Foess, 6. W., and J. A. Borchardt. Electrokinetic Phenomenon in the
Filtration of Algae Suspensions. JAWWA 61(7), 1969.
84. Forbes, J. H. Algae Removal by Upflow Filtration. NTIS No. PB 242369,
University of Nebraska, prepared for the Office of Water Research and
Technology, December 1974.
85. McGhee, T. J. Upflow Filtration of. Oxidation Pond Effluent. University
of Nebraska, Water Resources Research Institute, Technical Completion
Report A-034-NEB, June 1975.
86. Stone, R. W., D. S. Parker, and J. A. Cotteral. Upgrading Lagoon
Effluent to Meet Best Practicable Treatment. JWPCF 47(8):2019-2042,
1975.
87. Wastewater Filtration Design Considerations. EPA-625/4-74-007, NTIS No.
PB 259448, U.S. Environmental Protection Agency, Center for
Environmental Research Information, Cincinnati, OH, 1974.
88. Napa-American Canyon Wastewater Management Authority. Personal
Communication. Napa, CA, 1979.
89. Hutchinson, W., and P. D. Foley. Operational and Experimental Results
of Direct Filtration. JAWWA 66(2):79-87, 1974.
90. Brandt, H. T., and R. E. Kuhn. Apollo County Park Wastewater
Reclamation Project, Antelope Valley, CA. EPA-600/1-76-022, NTIS No.
PB 252997, U.S. Environmental Protection Agency, Cincinnati, OH, 1976.
277
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91. Al-Layla, M. A., and E. J. Middlebrooks. Algae Removal by Chemical
Coagulation. Water and Sewage Works 121(9):76-80, 1974.
92. van Vuuren, L. R. J., P. 6. J., Meiring, M. R. Henzen, and F. F. Kolbe.
The Flotation of Algae in Water Reclamation. International Journal of
Air and Water Pollution 9:823, 1965.
93. Parker, D. S., J. B. Tyler, and T. J. Dosh. Algae Removal Improves Pond
Effluent. Water and Wastes Engineering 10(1):26-29, 1973.
94. Ort, J. E. Lubbock WRAPS It Up. Water and Wastes Engineering,
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95. Komline-Sanderson Engineering Corp. Algae Removal Application of
Dissolved Air Flotation, Peapac, NJ, August, 1972.
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Using Dissolved Air Flotation. JWPCF 47(1):153-169, 1975.
97. Brown and Caldwell. Report on Pilot Flotation Studies at the Main Water
Quality Control Plant. Prepared for the City of Stockton, CA, 1972.
98. Ramani, A. R. Factors Influencing Separation of Algal Cells from Pond
Effluents by Chemical Flocculation and Dissolved Air Flotation.
Doctoral dissertation, University of California at Berkeley, 1974.
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Solids and Algae from Aerobic Lagoon Effluent to Meet Proposed 1983
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106. Wallace, A. T. Land Application of Lagoon Effluents. In: Performance
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279
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CHAPTER 6
COST AND ENERGY REQUIREMENTS
The costs associated with wastewater treatment facilities are usually divided
into capital costs and operations and maintenance (O&M) costs. The 0AM costs
are significantly influenced by energy consumption in most wastewater treat-
ment facilities. Where O&M costs are available, the data are presented;
however, there is a limited amount of data for the operation and maintenance
of wastewater ponds. The costs and energy requirements will be discussed
individually in the following sections.
6.1 Capital Costs
The majority of the cost data presented in this section were extracted from a
technical report distributed by the Environmental Protection Agency (1).
These data reflect the grant-eligible costs associated with the construction
of publicly owned wastewater treatment facilities and were derived from the
actual winning bid documents. These cost data are the most complete data
available and represent all types of wastewater processes. If comparison of
the pond costs are to be made with other.types of treatment facilities, it is
suggested that the design engineer consult the above-referenced report, which
has a detailed explanation of the data base and techniques used to analyze
the data.
These data are useful for preliminary design and planning purposes. Conven-
tional estimating procedures should be used during final design. The costs
shown in Figures 6-1 through 6-3 are national averaged costs indexed to
Kansas City/St. Joseph, MO, during the fourth quarter of 1978. Individual
data points are included on the graphs to illustrate the wide variation that
occurred in construction costs around the country.
The results presented represent only construction costs and do not show other
costs. These other costs include eligible Step 1 and Step 2 planning costs
as well as those associated with Step 3 construction effort: administration,
architect/engineer fees, contingency allowances, etc. Table 6-1 contains the
average ratios of all these Step 3 cost categories to the total construction
costs for new projects. There are 15 categories of costs identified in Table
6-1. Only five of these cost categories were found in the majority of the
projects: administrative/legal costs, architect/engineer basic fees, other
architect/engineer fees, project inspection costs, and contingencies. These
five categories equal approximately 20 percent of the construction costs as a
national average. However, including all of the 15 categories, the national
average costs were approximately 50 percent of the construction costs. In
280
-------
FIGURE 6-1
ACTUAL CONSTRUCTION COST vs DESIGN FLOW FOR
DISCHARGING STABILIZATION PONDS
(COST BASE 1978)
o
o
I I I I I I I M
I I I I I I I I
o
1 1 1 1 1 ll
C=(1.31 X 106)Q°-77
r = 0.78
Note: Nonconstruction costs not included
1 1 I 1 I I I I I I I L 11111
0.05
0.1 0.5 1.0
Design Flow, Q (mgd)
5.0 10.0
281
-------
FIGURE 6-2
ACTUAL CONSTRUCTION COST vs DESIGN FLOW FOR
NONDISCHARGING STABILIZATION PONDS
(COST BASE 1978)
1.0
0.8
0.6
_ 0.4
c
E
2t 0.2
o
I I I I I I I |
O
o
O
O
O
I i 0 I I I I I
o
00
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c 0.1
I 0.08
t5 0.06
c
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CD
3
+-i
O
0.04
0.02
0.01 L
0.01
o
8
C = (1.18X 106)Q°-75
r = 0.74
Note: Nonconstruction costs not included
I I I I I I I I I I i I I 1 I
0.05 0.1
Design Flow, Q (mgd)
0.5
1.0
282
-------
FIGURE 6-3
ro
oo
to
10.0
8.0
6.0
' 4.0
o
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(A
O
o
c
o
2.0
1.0
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? 0.6
o
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ro 0.4
1
0.2
0.1
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ACTUAL CONSTRUCTION COST vs DESIGN FLOW FOR
AERATED PONDS
(COST BASE 1978)
I I I I I I I I]
O
I I I I I I I I 1
I
o o
I II llll|
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I I I I 11
I
o
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C = (2.47X 106)Q°-73
r = 0.87
Note: Nonconstruction costs not included
I I I I I I I I I I I I I I I
0.05 0.1 0.5
Design Flow, Q (mgd)
1.0
5.0
10.0
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en
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CS
s
o
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o
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s?
s
o
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1
» 2 § S
till
in ^ 0 c
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1 1=1
I *•! E
m • ^ .c
i | | «
o » ». ^
» *j O 0)
«2 c
§ £ i o
- 8, U =
V 5 = ^ >-
^ ^*5 ^ °
s Jl 1 I
** J2 C OJ
in w> ;2 o c
g. *- * « g
i" -ts-o _ S
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s Ifl^-fS
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o •<-> o> c o Q
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i jijiji
tn -5 ,Q in 4J "O S
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284
-------
addition to the Step 3 nonconstruction costs, the Steps 1 and 2 costs
(preliminary and detailed design) must also be included. These two costs
were calculated as a fraction of the total construction cost and are
presented at the bottom of Table 6-1. The costs were 2.33 and 5.55 percent
for Steps 1 and 2, respectively. The information presented in Table 6-1 can
be used to estimate the nonconstruction costs for a wastewater treatment
facility by adding the total construction costs, total Step 3 nonconstruction
costs, as well as the Step 1 and Step 2 costs.
6.2 Cost Updating
The costs may be updated to other geographical areas by using the following
formul a:
Latest LCAT or SCCT Index
Total Project Cost for Desired Area = Updated Cost (6-1)
from Figures 6-1 x 4th Quarter 19/8 LCAT or
through 6-3 SCCT Index for Desired Area
where
LCAT = EPA large city advanced treatment index
SCCT = EPA small city conventional treatment index
The LCAT and SCCT indexes are published quarterly by the Environmental
Protection Agency.
The cost data presented in Figures 6-1 through 6-3 do not cover the options
available to upgrade pond effluents to meet secondary or advanced secondary
levels. Additional data have been collected from selected projects around
the country to provide individual cost data for comparative purposes.
Cost and performance values shown in Table 6-2 represent the best available
information for all of the processes listed. In several cases the costs are
based on estimates derived from pilot plant studies or engineering esti-
mates. Where actual bid prices are available, the location of the facility
is given. All costs are site specific and can be expected to vary widely.
Costs are reported as shown in the literature, and changes in value of the
dollar are not corrected for. This was done to allow the reader to use the
system appropriate for his/her area to adjust the costs to a current base.
Corrections were made to all capital costs to reflect a 7 percent interest
rate and a 20-year life except for systems known to have shorter operating
periods. The exceptions are identified in Table 6-2.
The selection of the cost-effective alternative must be made based upon good
engineering judgment and local economic conditions. Cost variations in one
285
-------
TABLE 6-2
COMPARATIVE COSTS AND PERFORMANCE OF VARIOUS UPGRADING
ALTERNATIVES AND POND SYSTEMS
Process or System
and Location
Overland Flow0
EPA Estimate
EPA Estimate
Davis, CA
Surface Irrigation15
EPA Estimate
EPA Estimate
Spray Irrigation-Center Pivot1*
EPA Estimate
EPA Estimate
Spray Irrigation-Solid Set0
EPA Estimate
EPA Estimate
Rapid Infiltration
EPA Estimate
EPA Estimate
Intermittent Sand Filtration
Me tea If & Eddy Capital Cost
Est. and European OSM=
Huntlngton, UT
Kennedy, AL
Alley, GA
Mortarty, KM
White Bird, ID
Ht. Shasta, CA
Hlcroscreens
cMVIREX
Caroden, SC
Dissolved Air Flotation
Snider
Coaoulatlon-notatlon-
Sedlmentatlon-Fl itratlon
Los Angeles Co., CA
Rock Filters
Warden, HO
Delta. HO
California, MO
Luxemburg, MI
Veneta, OR
Design
Flow
Rate
m3/d
1,140
1,140
18,900
1,140
1,140
1,140
1,140
1,140
1.140
1,140
1,140
1,140
1,140 2,
318
303 5,
760 2,
114 3,
2,650 6,
6 440—8 520
' 7,200
3,030
1,890
303
303
1,360
1,510 0
830 0
Design
Loading
5 cm/wk
20 cm/wk
20 cm/wk
5 cm/wk
10 cm/wk
5 cm/wk
10 cm/wk
5 cm/wk
10 cm/wk
20 cm/wk
60 cm/wk
_
800 m3/ha/d
935 m3/ha/d
610 m3/ha/d
810 m3/ha/d
740 m3/ha/d
550 m3/ha/d
0 (
—
—
0.76 fl|3/
pop. eg.'
0.76 m3/
pop. eq.
.40 n3/m3/d
.27 m3/m3/d
Annual Costs'*
Capital
0.071
0.050
0.026
0.053
0.045
0.050
0.042
0.069
0.050
0.045
0.034
0.042
0.095
0.053
0.032
0.048
0.050
1?Q_n (T376
i£y— U.U-3/ w
0.038
0.037
0.034
0.011
0.013
0.011
O.OOSe
0.013
O&M
S/nr>
0.037
0.026
0.013
0.050
0.040
0.048
0.034
0.040
0.032
0.026
0.021
0.042
0.005
0.010
0.010
o!o27
0.016
0.079
Total
0.108
0.076
0.039
0.103
0.085
0.098
0.076
0.109
0.082
0.071
0.055
0.084
0.058
0.042
0.060
' 0.065
0.053d
0.113
Cost
Base
1973
1973
1976
1973
1973
1973
1973
1973
1973
1973
1973
1975
1975
1975
1975
1975
1978
1976
1 1 Q7O
J AJ/O
1979
1975
Cap
1970
O&M
1973
1974
1974
1974
1974
1975
1975
Referer
(2)
2)
(3)
(2)
(2)
(2)
(2)
(2)
(2)
(2)
(2)
(4)(5)
8$
(9)(1S
(10)
(18)
(24)
(12)
(13)
(14)
(14)
(15)
(16)
(17)
Effluent
Concentration
BOOc SS
as
<30 <20
<30 <30
286
-------
TABLE 6-2
CONTINUED
Process or System
and Location
Intermittent Discharge-
Chemical Addition
Canadian Experience
Total Containment Ponds
Huntington, UT
Weilsville, UT
Tabiona, UT
Smithfield, UT
Southshore, UT
Facultative Ponds
Huntington, UT
Wardell, MO
Delta, MO
Unknown, ID
Long Valley, UT
Smithfield, UT
Challis, ID
Colfax, WA
Hampton-Princeton, ID
Tensed, 10
Aerated Ponds
Luxemburg, MI
Sugarbush, VA
Paw Paw, HI
Luxemburg-, Ml
White Bird, ID
Design
Flo*
Rate
m3/d
1,140
1,140
1,080
114
3,260
3
1,140
303
303
6,440
541
3,250
780
2,270
60
114
1,510
620
1,510
1,510
114
Design Annual Costs1
Loading Capital 04M Total
S/ra3
Alum: 0.011f 0.021 0.032
150 mg/1
Det. Time!:
120 days
0.0959
0.098
45 kg BOD5/0.372e
ha/d
45 kg BOD5/0.148e
ha/d
o.o?g
0.087
Primary Cell 0.077
38 leg 800s /
ha/d
2nd Cell
0.3 (Pri. cell
surface area)
3rd Cell
0.1 (Pri. cell
surface area)
Same as 0.108
Wardell
22/kg/ha/d 0.082
45 kg/ha/d 0.135e
45 kg/ha/d 0.1826
45 kg/ha/d 0.103e
in primary cell
0.0556
45 kg/ha/d 0.201e
67 kg/ha/d 0.122^
Det. time - 0.082s
35 days
1.127
0.069
36 kg BOOs/d 0.119 0.085 0.203
23 kg 80D5/d 0.370
Cost
Base
1976
1975
1974
1980
1979
1978
1975
1974
1974
1978
1979
1979
1978
1979
1978
1977
1974
1974
1978
1978
Effluent
Concentration
Reference 80Dr SS
(18)
(6)
(6)
(6)
(6)
" (19)
(6)
(14)
(W)
(19)
(6)
(6)
(10)
1977
(10)
(10)
(16)
(20)
(Anon.
(21)
(10)
<30 <10
No No
dis- dis-
charge charge
No No
dis- dis-
charge charge
No No
dis- dis-
charge charge
Varies Varies
with with
design design
& time & time
of yr of yr
(10)
Varies Varies
with with
design design
& time & time
of yr of yr
)
aCosts amortized at 7 percent and a 20-year life.
^Values can vary by 50 percent and prices do not include land costs.
clncludes land costs with no credit for salvage value.
dExcludes sludge disposal costs.
eEngineer's estimate.
fAmortized at 7 percent and a 10-year life.
9Bid but not constructed.
287
-------
item, such as filter sand or land, can change the relative position of a
process dramatically. In brief, Figures 6-1 through 6-3 and Table 6-2 cannot
6e substituted for good engineering.
All of the processes listed in Table 6-2 are capable of meeting secondary
standards, and several are capable of producing a much higher quality
effluent. Variations in design and operation also alter the quality of the
effluent dramatically in most of the processes. A careful study of all
alternatives must be made before selecting a system. The literature
referenced herein will provide all details needed, but engineers should
remain aware of current developments and use other alternatives as more
information becomes available.
6.3 Energy Requirements
Energy consumption is a major factor in the operation of wastewater treatment
facilities. Many of the plans for water pollution management in the United
States were developed before the cost of energy and the limitations of energy
resources became serious concerns for the Nation. As wastewater treatment
facilities are built or updated to incorporate current treatment technology
and to meet regulatory performance standards, energy must be a major
consideration in designing and planning the facilities. Information on
energy requirements for various systems must be made available to planners
and designers in order that a treatment system may be developed which
incorporates the most efficient use of energy for each particular wastewater
problem.
6.3.1 Energy Equations
Equations of the lines of best fit for the energy requirements of pond
systems based on the data reported by Wesner et al. (22) (25) were used to
develop Table 6-3. Details about the conditions imposed upon the equations
can be obtained from this reference.
6.3.2 Effluent Quality and Energy Requirements
Table 6-3 shows the expected effluent quality and the energy requirements for
various pond systems. Energy, requirements and effluent quality are not
directly related. Utilizing facultative ponds and land application
techniques, it is possible to obtain an excellent quality effluent and expend
small quantities of energy.
288
-------
IN3
00
TABLE 6-3
EXPECTED EFFLUENT QUALITY AND TOTAL ENERGY REQUIREMENTS FOR VARIOUS SIZES AND TYPES OF
WASTEWATER TREATMENT PONDS LOCATED IN THE INTERMOUNTAIN AREA OF THE UNITED STATES (23)
Total Energy Requirements at Various Flow Rates
Treatment Systems
Facultative Pond
+ Hicroscreens 23u
Facultative Pond
+ Intermittent
Sand Filter
Aerated Pond +
Intermittent
Sand Filter
Overland Flow-Facul-
tative Pond
Flooding
Rapid Infiltration-
Facultative Pond
Flooding
Slow Rate (Irri-
gation )-Fac.
Pond-Ridge and
Furrow Flooding
Effluent
BOD5
30
15
15
5
5
1
SS
30
15
15
5
1
1
Quality, mg/1
Total Total
Phos. Nttro-
as P gen as N
15
10
20
5 3
2 10
0.1 3
0.05 mgd
Elec-
tricity,
kHh/yr
11,300
5,840
20,800
5,700
1,540
2,800
Fuel,
Million
Btu/yr
148
150
151
148
148
149
0.1
Elec-
tricity,
kWh/yr
Z0.300
10,920
39,500
10,700
2,810
5,300
mgd
Fuel,
Million
Btu/yr
181
186
186
181
181
183
0.5
Elec-
tricity,
kHh/yr
83,100
50,540
184,800
50,070
12,140
24,700
mgd
Fuel,
Million
Btu/yr
320
345
345
320
320
330
1.
Elec-
tricity,
kHh/yr
154,600
99,270
364,500
98,810
23,050
48,050
0 mgd
Fuel,
Million
Btu/yr
433
483
483 1
433
433
• 453
3.0 mqd
Elec- Fuel,
tricity, Million
kWh/yr Btu/yr
419,800 745
291,800
,079,100
392,600
64,300
139,100
896
896 1
745
745
805
5.0
Elec-
tricity,
kWh/yr
670,900
482,200
,790,900
485,080
103,900
228,400
mgd
Fuel,
Million
Btu/yr
988
1,240
1,240
988
988
1,090
-------
6.4 References
1. Construction Costs for Municipal Wastewater Treatment Plants: 1973-1978,
EPA-430/9-80-003, NTIS No. PB 118697, U.S. Environmental Protection
Agency, Facility Requirements Division, Washington, DC, 1980.
2. Environmental Protection Agency. Cost of Wastewater Treatment by Land
Application, EPA-430/9-75-003, NTIS No. PB 257439, U.S. Environmental
Protection Agency, Office of Water Program Operations, Washington, DC,
1975.
3. Brown and Caldwell. Draft Project Report, City of Davis - Algae Removal
Facilities. Walnut Creek, CA, November 1976.
4. Metcalf & Eddy, Inc. Draft Report to National Commission on Water
Quality on Assessment of Technologies and Costs for Publicly Owned
Treatment Works Under Public Law 92-500. April 1975.
5. Huisman, L., and W. E. Wood. Slow Sand Filtration. World Health
Organization, Geneva, Switzerland, 1974.
6. Valley Engineering. Personal communication. Logan, UT, December 1976
and 1980.
7. Gilbreath, Foster & Brooks, Inc. Personal communication.
Tuscaloosa, AL, November 29, 1976.
8. McCrary Engineering Corporation. Personal communication. Atlanta, GA,
November 29, 1976.
9. Molzen-Corbin & Associates. Personal communication. Albuquerque, NM,
1976.
10. Hamilton and Voeller, Inc. Personal communication. Moscow, ID,
December 1978.
11. Kormanik, R. A., and J. B. Cravens. Microscreening and Other Physical -
Chemical Techniques for Algae Removal. In: Performance and Upgrading
of Wastewater Stabilization Ponds, EPA-"STTO/9-79-011, NTIS PB 297504,
U.S. Environmental Protection Agency, Municipal Environmental Research
Laboratory, Cincinnati, OH, 1979.
12. Snider, E. F., Jr. Algae Removal by Air Flotation. In: Ponds as a
Wastewater Treatment Alternative. Water Resources Symposium No. 9,
University of Texas, Austin, TX, 1976.
13. Parker, D. S. Performance of Alternative Algae Removal Systems. In;
Ponds as a Wastewater Treatment Alternative. Water Resources Symposium
No. 9, University of Texas, Austin, TX, 1976.
290
-------
14. Gaines, 6. F. Personal communication. C. R. Troter and Associates,
Dexter, MO, 1977.
15. Kays, F. Personal communication. Lane-Riddle Associates, Kansas City,
MO, 1977. '
16. Miller, D. L. Personal communication. Robert E. Lee and Associates,
Inc., Green Bay, WI, 1977.
17. Williamson, K. J., and G. R. Swanson. Field Evaluation of Rock Filters
for Removal of Algae from Lagoon Effluent. In; Performance and
Upgrading of Wastewater Stabilization Ponds, EPA-600/9-79-011, NTIS No.
PB 297504, U.S. Environmental Protection Agency, Municipal Environmental
Research Laboratory, Cincinnati, OH, 1979.
18. Middlebrooks, E. J., C. H. Middlebrooks, J. H. Reynolds, G. Z. Watters,
S. C. Reed, and D. B. George. Wastewater Stabilization Lagoon Design,
Performance, and Upgrading. Macmillan Publishing Co., Inc., New York,
NY, 1982.
19. Nielson, Maxwell & Wangsgard. Personal communication. Salt Lake City,
UT, February 1981.
20. Jupka, J. Personal communication. Lane-Riddle Associates, Kansas
City, MO, 1977. •
21. Robert E. Lee & Associates. Personal communication. Green Bay, WI,
November 1980.
22. Wesner, G. M., L. J. Ewing, Jr., T. S. Lineck, and D. J. Hinricks.
Energy Conservation in Municipal Wastewater Treatment. MCD-32.
EPA-430/9-77-011, NTIS PB 276989, U.S. Environmental Protection Agency,
Office of Water Program Operations, Washington, DC, 1978.
23. Middlebrooks, E. J., and C. H,, Middlebrooks. Energy Requirements for
Small Flow Wastewater Treatment Systems, Special Report 79-7. Corps of
Engineers, Cold Regions Research and Engineering Laboratory, Hanover,
NH/1979.
24. Harrelson, M. E., and J. B. Cravens. Use of Microscreens to Polish
Lagoon Effluent. JWPCF 54(1):36, 1982.
25. Middlebrooks, E. J., C. H. Middlebrooks, and S. C. Reed. Energy
Requirements for Small Wastewater Treatment Systems. JWPCF
53(7):1172-1197, 1981.
291
-------
APPENDIX
EVALUATION OF DESIGN METHODS
A.I Facultative Ponds
A.1.1 Introduction
A summary of the facultative pond performance data used to evaluate the
various design methods is presented in Table A-l. These data were collected
for the four facultative pond systems described in Chapter 2. "Only the
characteristics of the influent wastewater and the effluent from the primary
(first) cell of the systems are presented in Table A-l for the four systems.
Most of the kinetic analyses of the systems are limited to the performance
obtained in the primary cell because BODs and COD of the primary cell
effluent appear to represent performance of the systems far more than the
following cells. Algae succession, changes in nutrient concentration, and
the buffering capacity of the total system appear to exert more influence on
the cells following the primary cell. The commonly used design methods are
discussed individually in the following sections.
Theoretically, most of the models evaluated should have a line of best fit
that has an intercept of zero or unity, but an analysis of the data infre-
quently yields such an ideal relationship. Therefore, all of the attempts to
fit the data to a model were evaluated with the least squares technique with
an intercept and with the line of best fit forced through an intercept of
zero. The equations describing the lines of best fit for both cases are pre-
sented on each figure along with the corresponding correlation coefficients.
In general, if both correlation coefficients are significant (5 percent
level) and approximately equal, it can be assumed that the intercept is
approximately zero, and the data describe the model to an acceptable degree.
A.1.2 Empirical Design Equations
In a survey of the first cell of facultative ponds in tropical and temperate
zones, McGarry and Pescod (1) found that area! BODs removal (Lr, Ib/ac/d)
may be estimated through knowledge of area! BODs loading (L0, Ib/ac/d)
using
Lr = 9.23 + 0.725 LQ (A-l)
292
-------
TABLE A-l
MEAN MONTHLY PERFORMANCE DATA FOR FOUR FACULTATIVE PONDS
MONTH
Jan
Feb
Mar
Apr
Hay
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Oan
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
INF
BOD
rag/1
122
107
58
49
62
52
40
40
92
87
85
99
140
332
258
303
400
326
303
373
284
209
179
270
298 ,
197
170
144
123
131
128
101
157
133
113
123
137
200
172
106
135
107
187
140
278
278
321
301
247
200
CELL
#1
BOD
31
38
57
33
33
30
29
36
35
34
30
21
21
41
49
41
53
56
35
49
44
57
42
55
69
43
46
48
65
70
68
50
36
38
37
30
25
23
24
21
20
27
16
17
26
25
31
15
17
14
INF
SOL
BOD
40
28
19
16
15
17
9
11
25
22
24
32
50
125
116
184
182
169
123
181
129
95
78
140
178
70
49
49
40
37
43
33
73
56
49
56
50
57
52
36
50
39
55
37
80
96
96
74
75
79
CELL
#1
SBOD
5
5
10
6
5
6
5
5
5
4
5
6
9
11
13
11
22
18
10
14
15
13
11
19
15
n
10
22
51
53
46
36
31
21
22
12
9
. 5
4
3
3
3
3
5
5
6
7
3
4
3
INF
COD
mg/1
173
140
135
114
105
78
75
81
141
178
132
189
192
633
552
576
614
573
631
635
580
375
458
533
544
334
303
245
204
201
263
181
425
249
223
315
313
254
333
204
232
225
470
312
628
626
746
572
535
458
CELL
#1
COD
118
125
126
113
117
95
131
162
168
146
114-
89
68
183
226
156
,163
174
180
186
172
284
204
265
246
203
207
155
158
154
151
128
110
174
213
230
161
138
123
120
128
164
103
90
89
121
140
52
108
102
INF
SOL
COD
81
64
47
46
40
37
35
38
54
SO
58
64
88
277
225
265
260
224
234
236
173
117
128
201
224
136
102
101
94
73
94
78
250
116
114
142
125
114
101
81
81
• 78
108
81
154
192
235
168
164
191
CELL
#1
SCOD
47
48
39
37
38
45
45
44
38
39
42
46
54
83
107
63
71
74
76
60
71
76
52
83
91
128
82
84
106
100
93
79
77
101
126
98
88
68
52
42
35
30
38
49
50
71
94
60
73
67
DET
TIME
DAYS
44.43
22.72
19.56
23.23
28.47
27.29
20.73
18.97
21.07
17.64
37.14
63.66
55.76
83.82
87.86
89.00
101.34
102.99
66.08
70.36
80.47
95.46
101.12
116.83
109.41
48.61
50.89
50.78
48.29
45.74
37.90
35.87
42.09
44.61
43.06
43.21
41.30
189.80
189.80
189.80
182.50
54.31
115.98
82.38
185.37
191.48
456.34
171.11
111.93
165.37
TEMP
°C
2
1
5
9
12
18
22
19
16
9
4
2
2
22
17
10
4
4
3
7
14
21
24
26
25
9
6
4
5
3
4
7
17
21
24
22
17
14
9
10
11
12
18
23
27
29
29
20
20
18
LIGHT
LAN
190
265
385
495
590
630
640
550
430
335
210
145
190
430
285
230
180
190
280
345
440
530
560
580
435
240
165
115
130
230
280
400
450
525
500
450
340
260
200
205
270
340
450
550
530
450
470
370
340
250
TSS
mg/1
52
61
55
69
74
56
65
87
95
85
66
27
18
89
124
79
71
84
74
112
85
130
121
172
137
70
74
44
27
26
21
23
37
47
63
76
49
57
82
86
74
107
65
47
52
43
55
46
33
28
VSS
mg/1
45
54
52
59
61
43
53
76
81
71
57
25
15
76
95
68
65
78
70
97
72
102
109
151
120
...
--
--
--
--
_-
_ —
—
..
—
--
— •
~
—
—
—
..
-•-
—
--
..
—
..
—
LOCATION
Corinne, UT
n
n
n
n
n
n
n
Eudora, KS
n
n
n
n
11
n
n
n
n
n
n
n
: n
n
n
"
Peterborough, NH
it
n
"
it
n
11
n
n
n
n
n
Kllmichael, MS
II
11
II
11
11 -
II
II
II
II
II
II
II
293
-------
The regression equation had a correlation coefficient of 0.995 and a 95 per-
cent confidence interval of + 33 kg/ha/d (29 Ib BODs/ac/d) removal (Figure
A-l). The equation was reported to be valid for any loading between 34 and
560 kg BOD5/ha/d (30 and 500 Ib BOD5/ac/d). McGarry and Pescod (1) also
found that, under normal operating ranges, hydraulic detention time and pond
depth have little influence on percentage or area! 6005 removal. With such
a large 95 percent confidence interval, it is impractical to apply the equa-
tion to pond systems loaded at rates of 34 kg/ha/d (30 Ib BODs/ac/d) or
less as was the situation with the majority of the months of operation for
the four facultative pond systems described previously.
Relationships between organic removal and organic loading for the lower rates
observed at the four facultative pond systems were developed using BOD5,
soluble biochemical oxygen demand ($6005), chemical oxygen demand (COD),
and soluble chemical oxygen demand (SCOD). Statistically significant rela-
tionships were observed for all four organic carbon estimating analyses, but
the best relationships were observed when the organic removals were calcula-
ted using the influent 6005 and the effluent SBOD5 (ITBODs and
ESBODs) and the influent COD and the effluent SCOD (ITCOD and ESCOD). The
BODs and SBODs relationship is shown in Figure A-2, and the COD and SCOD
relationship is shown in Figure A-3. The 95 percent confidence intervals for
the BOD5-SBOD5 and the COD-SCOD relationships are much smaller than the
value reported by McGarry and Pescod (1) and are shown in Figures A-2 and Ai-3.
Larsen (2) proposed an empirical design equation, developed by using data
from a one-year study at the Inhalation Toxicology Research Institute,
Kirtland Air Force Base, NM. The Institute's facultative pond system con-
sists of one 0.66 ha (1.62 ac) cell receiving waste from 151 staff members,
1,300 beagle dogs, and several thousand small animals. Larsen found that the
required pond surface area could be estimated by use of the following
equation.
MOT « (2.468RED + 2.468TTC + 23.9/TEMPR + 150.0/DRY)*106 (A-2)
where the dimensionless products are:
2 2 1/3
MOT = (surface area, ft ) (solar radiation, Btu/ft /d) x n 0783 x 107)
(influent flow rate, gal/d) (influent BODg, mg/l)1/3
(influent BODC, mg/1) - (effluent BOD,-, mg/1)
npn 0 O
(influent BOD, mg/1)
(windspeed, miles/hr) (influent BODC, mg/1)
TTC = 5 * x 0.0879
(solar radiation, Btu/ft^/d)1'1*
294
-------
FIGURE A-l
ICGARRY AND PESCOD EQUATION FOR AREAL BOD5 REMOVAL AS A FUNCTION
OF BOD5 LOADING
100
0}
DC
Q
O
30 40 50 60 70 80 90 100
First Cell Areal BOD Loading (L0), Ib/ac/d
295
-------
FIGURE A-2
ro
to
en
70
60
50
10
Q
O
40
ui
Q
O
CO
t 30
•O
0
§
0)
Q
O
CO
20
10
0
0
RELATIONSHIP BETWEEN BOD5 LOADING AND
REMOVAL RATES - FACULTATIVE PONDS
Y = 0.940 X-1.04
r = 0.965
10
20 30 40
BOD Applied (ITBOD5), Ib/ac/d
50
60
70
-------
.FIGURE A-3
RELATIONSHIP BETWEEN COD LOADING AND
REMOVAL RATES - FACULTATIVE PONDS
110 r-
10
90
1
CO
Q
O 70
CO
LU
O
O
O
I 50-
o
E
-------
TEMPR = (Pond liquid temperature, °F)
(air temperature, °F)
DRY = relative humidity, percent
To determine the effect of using the Larsen equation on multicell facultative
ponds, it was applied to both the entire system and the primary cell for each
of the four locations. In each case the Larsen equation underestimated the
pond surface area required for a particular BODs removal. Prediction
errors for multiple cell ponds ranged from 190 to 248 percent. Prediction
errors for the primary cell surface areas ranged from 18 to 98 percent. Use
of the Larsen equation is not recommended.
Gloyna (3) proposed the following empirical equation for the design of facul-
tative wastewater stabilization ponds:
V = 3.5 x 10~J QLa ev°J~" ff (A-3)
>—• —/
where
V = pond volume (m^)
Q = influent flow rate (liters/day)
La = ultimate influent BODU or COD (mg/1)
e = temperature coefficient
T = pond temperature (°C)
f = algal toxicity factor
f' = sulfide oxygen demand factor
The 6005 removal efficiency can be expected to be 80 to 90 percent based on
unfiltered influent samples and filtered effluent samples. A pond depth of
1.5 m is suggested for systems with significant seasonal variations in tem-
perature and major fluctuations in daily flow. Surface area design using the
Gloyna equation should always be based on a 1-m depth. The additional 0.5 m
of depth is provided to store sludge. According to Gloyna (3), the algal
toxicity factor (f) can be assumed to be equal to 1.0 for domestic wastes and
many industrial wastes. The sulfide oxygen demand (f) is also equal to 1.0
for S04= ion concentration of less than 500 mg/1. Gloyna (3) also suggests
using the average temperature of the pond in the critical or coldest month.
In this equation, sunlight is not considered to be critical in pond design
but may be incorporated into the Gloyna equation by multiplying the pond
volume by the ratio of sunlight in the particular area to the average found
in the Southwest.
298
-------
The data used to evaluate the Gloyna equation are shown in Table A-l.
Although ultimate BOD data were not available, COD, SCOD, BODs, and SBODs
data were used. Use of the Gloyna equation with the data in Table A-l failed
to produce any good relationships. The relationships obtained with the COD,
SCOD, BODs, and SBODs data were statistically significant, but the data
points were scattered. The relationship shown in Figure A-4 was the best fit
bbtained for the data, and the resulting design equation follows:
LIGHT (35-T)
V/Q = 0.035 (BOD5, mg/1) (1.099) 25° (A-4)
t = detention time, days
V/Q = t
where
T = temperature, °C
LIGHT = solar radiation, langleys/day
V = volume of primary pond, m
Q = flow rate, m /d *
The validity of the above expression is questionable because of the scattered
data, but the relationship is statistically significant. The use of this
Relationship will be left to the discretion of the design engineer.
Although not directly comparable, the results obtained with this equation and
fesults obtained with the relationship shown in Figure A-2 are presented
feelow to show the variation between the two approaches.
Assuming a design flow rate of 3,785 m^/d (1 mgd), a solar radiation
ihtensity of 250 langleys, an influent BODs concentration of 300 mg/1, and
4 temperature of 10 C, Equation A-4 yields a surface area of 420,918 m2
(assuming a water depth of 1m), and the organic loading rate relationship
(Figure A-2) yields a loading rate of 27 kg/ha/d (24 Ib/ac/d). At this rate,
Organic removal will be 24.1 kg/ha/d (21.5 lb/ac/d) (Figure A-2) or an 89.7
percent reduction in BODs. The percent reduction is within the range of 80
to 90 percent expected with a design using the Gloyna equation. The results
cfbtained with Equation A-4 appear to be conservative when compared with the
6rganic loading-removal relationship (Figure A-2) principally because of the
temperature correction factor in Equation A-4. Although it is logical to
expect temperature to exert an influence on BODs removal, the plot shown in
Figure A-2 was unaffected when temperature relationships were incorporated
into the relationship. The most logical explanation for this phenomenon is
that the systems are so large that the temperature influence is masked in the
process. This observation is also pursued in the following section.
299
-------
FIGURE A-4
RELATIONSHIP OBTAINED WITH MODIFIED 6LOYNA EQUATION
FACULTATIVE PONDS (EQUATION A-4)
o
o
I 4
"
in
cs
Q
O
m
in
CO
0)
I 2
c
o
•4-*
§
•!-•
ID
O
n
Y = 0.0947 X (zero forced fit)
r = 0.913
D
a
D
a
a
a
a
a
a
0
I
10
15
20
35-T
25
30 ..
35
-------
A.1.3 Rational Design Equations
Kinetic models based on plug flow and complete mix hydraulics and first order
reaction rates have been proposed by many authors to describe the performance
of wastewater stabilization ponds. The basic models are modified to reflect
the influence of temperature. The basic models are:
Plug Flow;
^ = e p (A-5)
or: In Ce/CQ = -kpt (A-6)
Complete Mix;
(A-7)
or: f ~ - 1 ) = krt (A-a)
'e
where
C0 = influent BQDs concentration, mg/1
Ce = effluent BQDs concentration, mg/1
k« B plug flow first order reaction rate constant, time"!
t = hydraulic Residence time, days
e = base of natural logarithms, 2.7183
kc = complete mix first order reaction rate constant, time"-'-
The influence of temperature on the reaction rate constants is most frequent-
ly expressed by using the Arrhenius (4) relationship:
RT
301
-------
where
k s reaction rate constant
Ea = activation energy, calories/mole
R = ideal gas constant, 1.98 calories/mole-degree
T « reaction temperature, -Kelvin
Integrating Equation A-9 yields the following expression:
In k = - ^ + In B
where B is a constant.
(A-10)
Experimental data can be plotted as shown in Figure A-5 to determine the
value of Ea. Equation A-9 can be integrated between the limits of TI and
1*2 to obtain Equation A-ll.
FIGURE A-5
ARRHENIUS PLOT TO DETERMINE ACTIVATION ENERGY
Slope = -E,/R
1/T
302
-------
(A-ll)
In most biological wastewater treatment processes, it is assumed that
is a constant, C, and Equation A-ll reduces to
, (A-14)
where e = temperature factor. Plotting experimental values of the natural
logarithms of l<2/ki versus (T2~T]J as shown in Figure A-6, the value
of e can be determined.
The plug flow and complete mix models, along with modifications suggested by
various investigators, were evaluated using the data shown in Table A-l.
The influence of temperature on the calculated reaction rates was evaluated.
As shown in Figures A-7 and A-8, the reaction rates calculated with the plug
flow and complete mix equations were essentially independent of the tempera-
ture. This lack of influence by the liquid temperature was also observed in
the section on empirical design equations (Figures A-2 and A-3). The logical
explanation for the lack of influence by temperature is that the pond systems
are so large that the temperature effect is masked by other factors. There
is no doubt that temperature influences biological activity, but for the
systems listed in Table A-l, the influence was overshadowed by other
parameters that may include dispersion, detention time, light, species of
organisms, etc.
After observing the lack of influence by the water temperature, the data in
Table A-l were fitted to the plug flow (Equation A-5) and the complete mix
(Equation A-7) models to determine if the systems could be defined by these
simple relationships. As shown in Figures A-9 through A-12, the fit of the
data is less than ideal but is statistically highly significant (1 percent
level). Further attempts to incorporate various types of temperature and
light intensity relationships into the plug flow and complete mix models were
not successful. The best statistical relationships obtained with the data
are shown in Figures A-9 thorugh A-12.
Thirumurthi (5) stated that a kinetic model based on plug flow or complete
mix hydraulics should not be used for the rational design of stabilization
3d3
-------
ponds. Thirumurthi found that facultative ponds exhibit nonideal flow pat-
terns and recommended the use of the following chemical reactor equation
developed by Wehner and Wilhelm (6) for pond design:
(A-15)
Co " (1+a)2 ea'2D - (1-a)
2
where
Ce s effluent BODs, mg/1
C0 = influent BODs, mg/1
a =\/l + 4ktD
k = first order BODs removal coefficient, day1
FIGURE A-6
PLOT OF REACTION RATE CONSTANTS AND TEMPERATURE TO
DETERMINE THE TEMPERATURE FACTOR
c
—I
Slope = l_n 6
T2-T,
304
-------
FIGURE A-7
RELATIONSHIP BETWEEN PLUG FLOW DECAY RATE
AND TEMPERATURE - FACULTATIVE PONDS
CO
o
en
-T3
C
OC
2.0
1.5
1.0
0.5
0.0
Q~ -0.5
J> Q
Q
IT'S
|t -1-0
-1.5
-2.0
-2.5
Y = -0.0388 X (zero forced fit)
r = 0.659
Y =-0.0197 X-0.335
r = 0.263
D
D
I
-5.0
0.0
5.0
10.0 15.0
T2-T,
20.0
25.0
30.0
-------
FIGURE A-8
RELATIONSHIP BETWEEN COMPLETE MIX DECAY RATE
AND TEMPERATURE - FACULTATIVE PONDS
CO
o
CTi
2.0 i-
1.5 -
1.0
-------
yFIGURE A-9
PLUG FLOW MODEL - FACULTATIVE PONDS
CO
o
Y = -0.0158 X (zero forced fit)
r = 0.926
Y = -0.0096 X - .0.722
r = 0.746
-3.0
0
n
20
60
80 100 120
Detention Time, days
140
160
180
200
-------
FIGURE A-10
PLUG FLOW MODEL - FACULTATIVE PONDS
CO
o
00
0.0 K
-0.5 -
Y = -0.0279 X (zero forced fit)
r = 0.904
Y = -0.0113 X- 1.92
r = 0.689
-5.0
0 20 40 60 80 100 120
Detention Time, days
140 160
180 200
-------
FIGURE A-ll
COMPLETE MIX MODEL - FACULTATIVE'PONDS
co
o
100
90
80
70
1 60
in
Q
O
CO
tu 50
in
Q
O
EB 40
30
20
10
0
Y = 0.281 X (zero forced fit)
r = 0.896
Y = 0.269 X+ 1.35
r = 0.738
I
0 20 40 60 80 100 120
Detention Time, days
140
160
I
I
180 200
-------
CO
I—»
o
20
18
16
14
JL 12
in
o
o
CD
ID 10
tn
Q
O
£ 8
o
FIGURE A-12
COMPLETE MIX MODEL - FACULTATIVE PONDS
Y = 0.0554 X (zero forced fit)
r = 0.889
Y = 0.0514 X + 0.462
r = 0.714
D
Q
n.
n a
I
I
0 20 40 60 80 100 120
Detention Time, days
140
160 180
200
-------
t = mean detention time, days
D = dimensionless dispersion number
D-!L
vL
Ht
7
where
H * axial dispersion coefficient, area/time
v « fluid velocity, length/time
L = length of travel path of typical particle, length
Thirumurthi (5) prepared the chart shown in Figure A-13 to facilitate the use
of Equation A-15. The dimensionless term "kt" is plotted versus the percent
BOD-5 remaining for dispersion numbers varying from zero for an ideal plug
flow unit to infinity for a complete mix unit. Dispersion numbers measured
in stabilization ponds range from 0.1 to 2.0 with most values less than 1.0.
FIGURE A-13
WEHNER AND WILHELM EQUATION CHART
4 6 8 10 20
BOD Remaining, percent
50
311
-------
The data in Table A-l were used to calculate values of k for three different
dispersion numbers (0.1, 0.25, and 1.0) by an iterative process. The values
of k were normalized and plotted versus temperature as illustrated in Figure
A-14. Less than 12 percent of the regression was explained by a linear rela-
tionship indicating that temperature exerts little influence on the perfor-
mance of the ponds.
Values of k calculated using the influent total BODs and the effluent solu-
ble BODc concentrations with a dispersion number of 0.25 ranged from 0.011
to 0.282/d with a mean vajue of 0.073/d and a median value ofo0.055/d. The
mean temperature was 13.5°C and the median temperature was 12°C. Using the
design data presented with the Gloyna equation (Q = 3.785 nr/d, BODs =
300 mg/1, and T = 10°C), a k of 0.055/d adjusted linearly for temperature to
yield a value of 0.046/d (10°C/12°C x 0.055 = 0.046), a dispersion number of
0.25, and, assuming 90 percent removal of the BOD5 (TBOD5-SBOD5), a
detention time of 74 days is obtained. This detention time is less than the
value of 100 days obtained with the Gloyna equation (Equation A-4), but con-
sidering the differences in approach, agreement is reasonable.
A. 2 Aerated Ponds
A. 2.1 Introduction
A summary of the partial mix aerated pond performance data used to evaluate
the various design methods is presented in Table A-2. These data were col-
lected at the five aerated pond systems described in Chapter 2. Only the
characteristics of the influent wastewater and the effluent from the primary
(first) cell of the systems are presented in Table A-2.
Most of the kinetic analyses of the systems are limited to the performance
obtained in the primary cells because BODs and COD of the primary cell
effluent appear to represent performance of the systems far more than the
following cells. Species succession, nutrient concentrations, and the
buffering capacity of the systems appear to have more of an effect on the
cells following the primary cell. The more commonly used design methods for
aerating ponds are discussed individually in the following paragraphs.
A. 2. 2 Design Equations
The most commonly used aerated pond design equation is presented in the Ten
State Standards (7).
2.3 k (100-E)
312
-------
TABLE A-2
MEAN MONTHLY PERFORMANCE DATA FOR FIVE PARTIAL MIX AERATED PONDS
MONTH
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Pec
Jan
Feb
Mar
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Dec
Jan
Feb
Mar
Apr
May
Jin
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
INF
BOD
mg/1
368
422
414
392
379
413
355
313
330
388
364
283
277
468
470
452
602
578
799
548
554
395
296
233
177
203
152
220
185
155
202
182
145
172
173
106
89
96
75
37
55
71
86
93
118
113
102
87
178
214
199,
192
178
175
171
134
151
170
171
206
CELL
#1
BOD
68
150
60
98
81
87
58
64
87
106
117
61
13
33
20
16
20
28
9
9
9
10
18
14
19
43
30
68
38
46
66
69
64
48
39
45
11
12
10
14
12
18
14
23
25
34
' 25
17
49
63
68
76
67
58
66
53
56
62
82
73
INF
SOL
BOD
222
244
227
127
136
122
140
105
142
136
147
119
58
75
89
'130
136
143
127
129
126
97
83
39
74
76
61
110
81
58
108
103
91
82
69
66
34
46
41
29
. 31
26
37
34
18
21
18
38
94
88
86
117
79
76
71
55
68
74
74
119
CELL
. #1
SBOD
55
87
40
23
9
13
14
9
5
8
7
9
7
17
10
10
11
10
5
5
4
5
- 1)
' 7
15
42
25
65
34
21
58
46
44
37
14
34
— •
'
—
—
—
—
—
—
—
—
—
—
32
41
46
35
36
31
37
30
36
38
41
42
INF
COD
mg/1
664
524
671
610
552
606
594
589
646
773
774
619
440
753
1147
1208
1921
1208
1572
1156
1115
779
649
367
267
376
211
192
206
270
435
431
356
749
1062
537
209
229
244
116
127
160
186
229
299
194
200
168
510
457
454
369
431
291
359
203
201
230
221
324
CELL
#1
COD
152
186
192
212
202
175
138
180
285
268
254
178
86
131
113
82
143
132
74
77
78
68
75
89
37
48
57
52
56
95
207
190
137
109
131
146
34
52
45
52
48
54
56
74
44
48
36
32
105
96
105
98
105
120
101
80
86
82
101
108
INF
SOL
COD
321
368
319
215
240
267
254
223
259
278
249
224
83
146
231
252
361
298
290
294
246
213
170
53
58
97
74
64
75
135
211
190
210
199
242
191
'34
46
41
29
31
26
37
34
18
21
18
38
144
120
115
138
112
102
92
69
86
89
86
151
CELL
#1
SCOD
68
133
101
79
61
104
54
62
68
57
71 ,
67
61
89
63
60
99
68
62
58
70
60
•59
61
33
36
47
35
38
16
97
101
77
65
52
52
22
44
37
30
28
24
29
36
25
26
21
27
60
56
55
52
55
56
46
46
51
49
57
69
DET
TIME
DAYS
66.59
68.26
60.26
45.87
52.49
66.94
59.92
33.32
52.89
59.58
55.28
49.85
85.15
77.53
82.36
86.40
83.69
88.44
86.61
96.76
87.09
115.11
76.36
66.57
29.73
29.53
14.81
14.47
15.71
14.'52
20.00
22.92
16.24
15.71
16.48
15.94
26.15
28.91
25.74
18.82
20.30
22.41
22.65
22.86
22.77
23.40
24.23
48.95
7.06
6.04
8.22
8.21
7.64
7.03
6.73
5.75
5.84
7.19
9.30
7.84
TEMP
°C
5
10
16
19
20
26
29
28
24
13
9
7
5
12
19
23
26
19
11
5
3
3
8
6
19
14
12
12
13
14
20
26
25
24
22
17
' 4
-1
1
4
11
12
21
23
22
16
12
7
12
14
19
16
22
23
28
29
29
27
24
18
LIGHT
LAN
190
250
350
435
590
600
560
550
470
350
265
200
520
485
415
555
510
395
255
220
165
245
320
345
140
110
135
225
275
470
460
500
510
470
345
225
85
150
225
290
415
510
590
575
530
400
255
180
240
250
365
280
505
490
550
480
475
400
345
255
TSS
rag/1
93
63
101
74
74
61
67
89
109
166
127
59
56
51
41
33
43
58
31
53
23
17
37
51
19
21
38
32
25
52
104
123
51
60
88
26
7
5
' 7
22
16
19
20
30
12
20
6
6
38
37
50
53
52
51
98
56
61
42
75
40
VSS
mg/1 LOCATION
64 Bixby, OK
40
63
59
74
53
50
76 ' "
78
140
103 ' "
44
20 Pawnee, IL
33
29
24
30
41 "
17
27
16
8
21
18
12 Windber, PA
13
28
22 "
18
37
72
81
31
41 "
73
21
6 Lake Koshkonong, WI
4 "
6 "
20
15
18 "
19 "
27
10
13
5
5 "
33 North Gulf port, MS
33
44 "
41
43
35
63 "
33 "
42
30
55
27
313
-------
FIGURE A-14
RELATIONSHIP BETWEEN WEHNER AND WILHELM DECAY
RATE AND TEMPERATURE - FACULTATIVE PONDS
co
2.5
2.0
£ 1-0
go,
I -1.0
-1.5
-2.0
-5.0
Y = -0.0242 X (zero forced fit)
r = 0.554
Y =-0.0227 X - 0.0263
r = 0.342
D
0.0
5.0
10.0
15.0
20.0
25.0
30.0
-------
where
t = detention time, days
E = percent BODs to be removed in an aerated pond
fcl = reaction coefficient, aerated pond, base 10. [For normal
domestic wastewater, the KI value may be assumed to be 0.12/d
at 20°C and 0.06/d at 1°C according to the standards (7).]
Equation A-16 is equivalent to Equation A-8 presented in the section on
Rational Design Equations for facultative wastewater stabilization pond
design. By manipulating Equation A-16 as shown below, it can be shown that
the two equations are equal.
2.3 kxt = T/ (A-17)
100
2.3 kxt = x ^."/r r ^ — (A-19)
100 -
100 - 100 C 1C
t -
l ~ 100 - 100 t 100 C/C
2.3 k,t = p _ i (A_2l)
1 e
The only difference between Equation A-16 and Equation A-8 is that the con-
stant in Equation A-8 is expressed in terms of base e and the other is
expressed in terms of base 10.
Equation A-8 is the most commonly used equation to design aerated ponds.
Practically every aerated pond in the United States has been designed with
this simple complete mix model. In the design process, the reaction rate
coefficient is adjusted to reflect the influence of temperature on the
biological reactions in the aerated ponds by using Equation A-14.
The plug flow (Equation A-5), complete mix (Ten State Equation and Equation
A-8), and Wehner-Wilhelm (Equation A-15) models were evaluated using the BOD
and COD data shown in Table A-2. The effect of water temperature on the
reaction rates calculated with each of the models using the influent total
315
-------
and the effluent SBOD5 are shown in Figures A-15 through A-17. The
Wehner-Wilhelm equation was solved using a dispersion number of 0.25.
Although the relationships between decay rates and temperature differences
are statistically significant at the 1 or 5 percent level, the data points
are scattered and less than 30 percent of the variation is explained by the
regression analyses. Using the analyses for the regression of data through
the origin, temperature factors (&) of 1.07, 1.09, and 1.07 were obtained for
the plug flow, complete mix, and Wehner-Wilhelm models, respectively, using
the influent total BODs and effluent soluble BOD5 to estimate the sub-
strate strength, respectively. The temperature factors are in agreement with
values reported in the literature (3)(8)(9). The above values are recom-
mended for use when adjusting the reaction rates to compensate for tempera-
ture effects in aerated ponds.
The relationships shown in Figures A-15 through A-17 were the best obtained
for all combinations of the BOD and COD data. Better relationships were
observed between the reaction rates and temperature for the aerated ponds
than for the facultative ponds. This was probably attributable to the mixing
in the aerated ponds. The relationships between the plug flow and
Wehner-Wilhelm models' reaction rates and temperature provided a better fit
of the data than the relationship observed for the complete mix model. These
results indicate that the plug flow and Wehner-Wilhelm models provide a
better approximation of the performance of the aerated ponds than the com-
plete mix model. All of the aerated ponds were designed using the complete
mix model (Equation A-8).
Because of the relatively poor relationship between the reaction rates and
temperature, the data in Table A-2 were used to determine if the plug flow
and complete mix models could be used, to estimate the performance of the
aerated ponds. As shown in Figures A-18 and A-19, the fit of the data to
both the plug flow and complete mix models yields statistically significant
(1 percent level) relationships. The data fit the plug flow model better
than the complete mix model even though the complete mix model was used to
design the systems. This is not surprising if the flow patterns in the
diffused air aeration systems is considered. Ponds using the Hinde Engi-
neering Company aeration system (diffused air) are operated essentially as a
plug flow, tapered aeration, activated sludge system without cellular
recycle. Therefore, the plug flow model would be expected to more closely
describe the performance of these systems. Surface aeration systems could be
designed so that either flow model would describe the performance of a pond.
For example, an aeration basin with a high length to width ratio with surface
aerators would approximate a plug flow pattern, but a circular or square
basin with surface aerators would be expected to approach complete mix
conditions. In practice the flow patterns in ponds are imperfect and vary
with each system. Logically, a model such as the Wehner-Wilhelm equation
(Equation A-15) would be expected to provide the best estimate of the
performance of pond systems. Unfortunately, none of the simple models is
obviously superior to the others.
316
-------
FIGURE A-15
RELATIONSHIP BETWEEN PLUG FLOW DECAY RATE
AND TEMPERATURE - AERATED PONDS
oo
3.0 r
2.5
2.0
So
0) 03
a ~
._
O)
1.0
0.5
0.0
-0.5
-1.0
Y = 0.0707 X (zero forced fit)
r = 0.829
- : n
Y = 0.0416 X + 0.415
r = 0.524
-5.0
0.0
5.0
10.0
15.0
20.0
25.0
30.0
-------
FIGURE A-16
CO
t-»
00
RELATIONSHIP BETWEEN COMPLETE MIX DECAY RATE
AND TEMPERATURE - AERATED PONDS
4.0
3.5
3.0
~ 2.5
x —
CM It)
~§ 2.0
0)111
S-a 1.5
cc c
(0 ">
oo i n
OJQ i.u
_x —
ii 0.5
QJ t3
+^ 0}
Is o.o
o
o
-0.5
-1.0
-1.5
-2.0
Y = 0.0858 X (zero forced fit)
r = 0.724
Y = 0.0362 X + 0.836
r = 0.274
a
I
l_
-5.0
0.0
5.0
10.0 15.0
T2-ti
20.0
25.0
30.0
-------
FIGURE A-17
RELATIONSHIP BETWEEN WEHNER AND WILHELM DECAY
RATE AND TEMPERATURE - AERATED PONDS
CO
c
_l _^
. In
TOO
CC CD
3.0
2.5
2.0
1.5
CD LU
lo
^S
E- 0.5
o.o
c
-0.5
-1.0
-1.5
Y = 0.0638 X (zero forced fit)
r = 0.821
Y = 0.0498 X +0.312
r = 0.542
-5.0
0.0
5.0
10.0
15.0
20.0
25.0
30.0
T2-Ti
-------
co
ro
o
FIGURE A-18
PLUG FLOW MODEL - AERATED PONDS
D
D
Y = -0.0501 X (zero forced fit)
r = 0.936
Y = -0.0344 X - 0.968
r = 0.822
Q
O
CO
H
in
Q
O
CQ
(/>
UJ
D
-5
60
Detention Time, days
80
100
120
-------
160r-
140
120
FIGURE A-19
COMPLETE MIX MODEL - AERATED PONDS
Y = 0.654 X (zero forced fit)
r = 0.816
Y = 0.818 X- 10.1
r = 0.745
"- 100
oo
ro
Q
O
CD
Q
O
00
80
60
40
20
I Dl I "I
0 10 20 30 40
50 60 70 80
Detention Time, days
90 100 110 120
-------
A.2.3 Oxygen Requirements
There is no rational design equations to predict the mass rate of transfer of
DO and the required mixing to keep the solids suspended in an aerated pond.
Using the mass of 8005 entering the system as a basis to calculate the
oxygen requirements is simple and as effective as other approaches. To
predict the aeration needed for mixing, it is necessary to rely on empirical
methods developed by equipment manufacturers. Oxygen requirements do not
control the design of aeration equipment in aerated ponds unless the
detention time in the aeration tank is approximately one day. Such a short
detention time is- not recommended for aerated ponds; therefore, mixing is the
major concern in the design.
Catalogs from equipment manufacturers must be consulted to ensure that
adequate pumping, or mixing, is provided. The types of aeration equipment
available are listed in Table A-3 and shown schematically in Figure A-20.
Graphs or tables are available from all aeration equipment manufacturers, and
all types of equipment must be evaluated to ensure that the most economical
and efficientssystem is selected. The oxygen demand can be estimated using
the procedure outlined in Table A-4. Suspension of solids (complete mix
system) will require approximately 10 times as much power for mixing than for
oxygen supply. Therefore, an economic analysis along with engineering
judgment must be used to select the proper aeration equipment.
The system should be divided into a minimum of three basins and preferably
four basins to improve the hydraulic characteristics and improve mixing
conditions. The division of the basins can be accomplished by using separate
basins or baffles. There are simple plastic baffles commercially available.
Aerators should be selected and spaced through the basins to provide
overlapping zones of mixing, and spaced in proportion to the expected oxygen
demand (see Chapter 3). The oxygen demand will decrease in each succeeding
cell.
322
-------
TABLE A-3
TYPES OF AERATION EQUIPMENT FOR AERATED PONDS (10)
lb
(Standard Condition)
Oxygen
Production
lb 02/hp
Power
Requirements
hp/106 gal
Common
Depth
ft
Advantages
Disadvantages
co
ro
co
Floating Mechanical Aerator
High Speed
Low Speed
Rotor Aeration Unit
(brush type)
Plastic Tubing Diffuser
Diffused Aeration
Air-Gun
Helical Oiffuser
1.8-4.5/hp
3.5/hp
0.2-0.7/100 ft
0.8-1.6/unit
1.2-4.2/unit
1;5 35
2.5 to 3.5 25
0.5 to 1.2 100
12-20
10-15 Good mixing and aeration
capabilities; easily
removed for maintenance
3-10 Probably unaffected by
freezing; not affected by
sludge .deposits; good for
oxidation ditches
3-10 Not affected by floating
debris or ice; no ragging
problem; uniform mixing
& oxygen distribution
12-20 Not affected by ice; good
mixing
8-15 Not affected by ice;
relatively good mixing
Ice problems during
freezing weather;
ragging problems with-
out clogless impeller
Requires regular clean-
ing of air diffusion
holes; energy conversion
efficiency is lower
Requires regular clean-
ing of air diffusion
holes; energy conversion
efficiency is lower
Calcium carbonate build-
up blocks air holes;
potential ragging prob-
lem affected by sludge
deposits ;'
Potential ragging prob-
lem; affected by sludge
deposits'
-------
FIGURE A-20
SCHEMATIC VIEW OF VARIOUS TYPES OF AERATORS (10)
Diffuser head
Motor
Float
Propeller--' L T— Intake volute
Floating surface aerator
Rotor
Motor
Motor mount
I_
Water surface
/-Rotor blades
Air supply
tubing
^ Float
Floating rotor aerator
Water.
flow
Air
supply.
Concrete
base
Helical aerator
Air gun aerator
Air hole
Pond bottom
Plastic tube aerator
324
-------
TABLE A-4
CALCULATION OF OXYGEN DEMAND AND SURFACE AERATOR SIZE FOR AERATED PONDS
Design Conditions
Design flow = 3,785 m^/d
Influent BOD5 = 300 mg/1
Pond temperature = 15°C
Barometric pressure = 760 mm of mercury
Oxygen Requirements
BOD5 in wastewater = (300 mg/1) (3,785 m3/d)(l,000 Iiters/m3)/l06
= 1,136 kg/d
Assume that 02 demand of the solids and at peak flows will be 1.5
times the mean value of 1,136 kg/d
Oxygen requirements (Na) = 1,136 x 1.5 = 1,703 kg/d
= 71 kg/hr
Aerator Sizing
After determining Na, the equivalent oxygen transfer to tapwater (N) at
standard conditions in kg/hr can be calculated using the following equation:
n noc-
a - * - (1.025)
I - s J
Wh re oxygen transfer to waste
oxygen transfer to tapwater
C-w = oxygen saturation value of the waste in mg/1 calculated
from the expression:
Where e = oxy9en saturation value of the waste
oxygen saturation value of tapwater
325
-------
GSS ~ oxygen saturation value of tapwater at the specified
waste temperature
p _ barometric pressure at the plant site
barometric pressure at »sea level
\ "* "*' . ' '
CL = DO concentration to be maintained in the waste (mg/1)
C- = oxygen saturation value of tapwater at 20°C and 1
atmosphere pressure = 9.17 mg/1
T « pond water temperature (°C)
The design conditions are:
N - 71 kg (Uhr ,
a 6. • •..,..
a « 0.9 ,
3 - 0.9
P » 1.0 atmosphere
CL = 2.0 mg/1
T = 15°C' . ' • '"'.r: : \ '
Csw = 0.9 (10.15) 1.0 = 9.14 mg/1
71 71
ha P9.14 - 2.01 h n«A ~ °-9 x 0.78 x 0.884
°'9 [_ 9.U J °'884
= 114 kg 02/hr
Assume 1.4 kg 02/hp-hr for the aerator for estimating purposes (taker) from
catalogs)
Total hp required is 114/1.4 = 81 brake horsepower (bhp) (60 kW)
Aerator drive units should produce at least 81 bhp (60 kW) at the shaft
Assume 90 percent efficiency for gear reducer
Therefore, total motor horsepower = 90 hp (67 (kW)
326
-------
A.3 References
1. McGarry, M. 6., and M. B. Pescod. Stabilization Pond Design Criteria
for Tropical Asia. 2nd International Symposium for Waste Treatment
Lagoons, Missouri Basin Eng. Health Council, Kansas City, MO, 1970, pp.
114-132.
2. Larsen, T. B. A Dimensionless Design Equation for Sewage Lagoons.
Dissertation, University of New Mexico, Albuquerque, NM, 1974.
3. Gloyna, E. F. Facultative Waste Stabilization Pond Design. In: Ponds
as a Wastewater Treatment Alternative. Water Resources Symposium No. 9,
Center for Research in Water Resources, University of Texas, Austin, TX,
1976.
4. Arrhenius, S. Z. Physik. Chem. 1, 631, 1887.
5. Thirumurthi, D. Design Criteria for Waste Stabilization Ponds. JWPCF
46(9):2094-2106, 1974.
6. Wehner, J. F., and R. H* Wilhelm. Boundary Conditions of Flow Reactor.
Chemical Engineering Science 6:89-93, 1956.
7. Recommended Standards for Sewage Works. A Report of the Committee of
Great Lakes-Upper Mississippi River Board of State Sanitary Engineers.
Health Education Services, Inc., Albany, NY, 1978.
8. Metcalf Eddy, Inc. Wastewater Engineering. McGraw-Hill, New York,
NY, 1979. ,
9. Oswald, W. J. Syllabus on Waste Pond Design Algae Project Report.
Sanitary Engineering Research Laboratory, University of California,
Berkeley, CA, 1976.
10. Process Design Manual: Wastewater Treatment Facilities for Sewered
Small Communities. EPA-625/1-77-009, U.S. Environmental Protection
Agency, Center for Environmental Research Information, Cincinnati, OH,
1977.
327
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