v>EPA
United States
Environmental Protection
Agency
Municipal Environmental
Research Laboratory
Cincinnati OH 45268
Technology Transfer
Handbook
Septage
Treatment and
Disposal
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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 commerical products does not consti-
tute endorsement or recommendation for use.
13.
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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, an'd" radiation. A
vital part of EPA's national pollution control effort is the constant
development and dissemination of new technology.
The proper treatment and disposal of septage is becoming an increasingly
difficult management problem for nonurban communities where the use of on-
site sewage disposal systems is prevalent. Federal and state regulations
regarding the disposal of septage have become significantly more restrictive
in recent years. As a result, traditional methods of disposing of septage
may not be appropriate in many areas. In addition, more and more local
nonurban communities are beginning to recognize the importance of encourag-
ing proper septic system maintenance (routine septic tank pumping), in
order to maximize the life of individual septic systems, and thereby avoid
the expense of centralized sewer systems.
In light of this, the demand for septage disposal facilities is great, and
is expected to be even greater in the near future. Unfortunately, most
local public officials and many design engineers are not fully aware of all
the options for managing the proper treatment and disposal of septage. The
purpose of this handbook is to present a full range of practical alterna-
tives, and provide technical advice to aid in the- evaluation of these
alternatives. This includes general design criteria and cost information,
as well as advice concerning the operation and management of septage facili-
ties.
This handbook is one of several publications available from Technology
Transfer to describe technological advances and present new information.
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ACKNOWLEDGMENTS
Many individuals contributed to the preparation and review of this Handbook.
Contract administration was provided by the Municipal Environmental Research
Laboratory of the Office of Research and Development of the U.S. Environ-
mental Protection Agency (EPA) in Cincinnati, Ohio.
CONTRACTOR-AUTHORS
Major Authors: Kenneth C. Wiswall, Glenn M. Johnson/ Larry Y.H.
Lin, and Arijit Dasgupta, Roy F. Weston Consult-
ing Engineers, Westchester, PA
Arild Schanke Eikum, Norweigian Institute for
Water Research, Oslo, Norway
Steven D. Freedman, Stearns and Wheler, Cazenovia,
NY
Pio Lorabardo, Lombardo and Associates, Boston, MA
CONTRACT SUPERVISION
Project Officer: James F. Kreissl, EPA-MERL, Cincinnati, OH
TECHNICAL PEER REVIEWERS
Burton A. Segall, University of Lowell, Lowell, MA
Arthur J. Condren, James M. Montgomery Consulting Engineers, Pasadena,
CA
James W. Cox, Virginia State Water Control Board, Richmond VA
Denis J. Lussier, EPA-CERI, Cincinnati, OH
Robert K. Bastian, EPA-OWPO, Washington, D.C.
Marie Perez, EPA-OWPO, Washington, D.C.
Robert P.G. Bowker, EPA-MERL, Cincinnati, OH
G. Kenneth Dotson, EPA-MERL, Cincinnati, OH
Steven W. Hathaway, EPA-MERL, Cincinnati, OH
IV
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CONTENTS'
Chapter Page
FOREWORD iii
ACKNOWLEDGMENTS iv
LIST OF FIGURES viii
LIST OF TABLES ' xiii
1 INTRODUCTION
1.1 Purpose 1
1.2 Scope 1
1.3 Use of the Handbook 2
2 TECHNICAL OPTIONS AND STRATEGIES
2.1 Introduction 4
2.2 Septage Management Options 4
2.3 Selecting a Septage Management Option 9
2.4 Legal and Regulatory Considerations 11
2.5 Other Considerations ' 14
2.6 References • ' -15
3 SEPTAGE CHARACTERIZATION
3.1 Introduction 16
3.2 Septage Quantity 18
3.3 Characteristics of Septage 23
3.4 Comparison of Septage and Domestic Wastewater
Characteristics 31
3.5 References ' 34
4 RECEIVING STATION DESIGN
4.1 Introduction 37
4.2 Dumping 'Station 43
4.3 Screening 48
4.4 Grit-Removal 50
4.5 Storage and.Equalization 56
4.6 Odor Control 58
4.7 References 68
v
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CONTENTS (continued)
Chapter Page
5 LAND DISPOSAL
5.1 Introduction 70
5.2 Raw Septage versus Septage Residuals
(Sludge) 70
5.3 Disposal Options 72
5.4 Project Development 79
5.5 Management, Operations, and Monitoring 104
5.6 References 104
6 CO-TREATMENT OF SEPTAGE AND SEWAGE
6.1 Introduction ' 106
6.2 Feasibility of Co-Treatment 106
6.3 Modes of Septage Addition 107
6.4 Co-Treatment of Septage in the Liquid Stream 113
6.5 Co-Treatment of Septage in the Solids Stream 135
6.6 References 140
7 INDEPENDENT TREATMENT OP SEPTAGE
7.1 Introduction ' 143
7.2 Lagoons 146
7.3 Composting of Septage 153
7.4 Biological Secondary Treatment Processes 160
7.5 Aerobic Digestion 161
7.6 Anaerobic Stabilization of Septage 171
7.7 Lime Stabilization of Septage 182
7.8 Chlorine Oxidation 194
7.9 Conditioning 201
7.10 Dewatering 214
7.11 Disinfection 229
7.12 Odor Control 241
7.13 Ultimate Disposal 242
7.14 Mobile Septage Dewatering 247
7.15 References 252
VI
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CONTENTS (continued)
Chapter
8
Page
OPERATION AND MANAGEMENT CONSIDERATIONS
8.1 Overview of Management Concerns
8.2 Onsite Systems Management
8.3 Management of Septage Pumping and Hauling
Activities
8.4 Monitoring the Quantity and Quality of
Incoming Septage
8.5 Facility Operation and Maintenance
8.6 Performance Monitoring
8,7 Financial Arrangements
8.8 References
259
262
265
268
271
273
273
277
FACT SHEETS
9.1 Introduction
9.2 References
279
294
APPENDIX SUMMARY OF STATE REQUIREMENTS REGARDING LAND
DISPOSAL OF SEPTAGE
298
Vll
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FIGURES
Number Page
1-1 Sequence of Chapters 3
2-1 Basic Septage Management Options 5
2-2 Illustration of Decisions In Selecting Most
Appropriate Technical Option 6
2-3 Sequenced Selection of a Septage Disposal Option 10
3-1 Typical Septic System 17
3-2 Septage Loading Pattern at Lebanon, Ohio 20
3-3 Volume of Septage Received at Enga Treatment Plant,
Norway 20
3-4 Variation in Monthly Average Septage Quantities at
Lebanon, Ohio 22
3-5 Variation in Daily Average Septage Quantities
at Enga, Norway 22
3-6 Variations in NH3 and H2S Concentrations
at TAO Treatment Plant When Receiving Septage,
February 24, 1976 30
3-7 Variations in NH3 and H2S Concentrations
at TAU Treatment Plant When Receiving Septage,
May 31, 1976 30
4-1 Receiving Station for Septage at Ekebyhov Treatment
Plant, Sweden 38
4-2 Receiving Station where Septage Is Fed to An
Anaerobic Digester in West Germany 38
4-3 Receiving Station including Screening and Grit Removal
at Lillehammer Treatment Plant, Norway 38
4-4 Receiving Station with Pretreatment Prior To
Equalization (Batch Pretreatment} 39
viii
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FIGURES (continued)
Number Page
4-5 Receiving Station with Equalization Prior To Pretreat-
ment (Controlled Rate Pretreatment) 39
4-6 Interceptor Receiving Station 41
4-7 Receiving Station at STP Where Existing
Pretreatment Facilities Can Be Used to Treat Septage 41
4-8 Computerized interceptor Receiving station 42
4-9 Septage Transfer Station 44
4-10 Basic Layout of Dumping Station 45
4-11 Recommended Dumping Station Inlet Arrangement 47
4-12 Mechanically Cleaned Bar Screen at Dokka Treat-
ment Plant, Norway 49
4-13 Drained Screw Conveyor Used for Dewatering
Material from the Bar Screen 51
4-14 Helical Flow Pattern in Aerated Grit Chamber 53
4-15 Typical Section Through Aerated Grit Chamber 53
4-16 Aerated Grit Dewatering Unit Placed Above the Grit
Chamber at Lillehammer Treatment Plant, Norway 53
4-17 Cyclone Degritter 55
4-18 Chemical Scrubber, Type Steuler 59
4-19 Chemical Scrubber, Type Pepcon 59
4-20 Carbon Filter for Odor Reduction 61
4-21 Full Scale Soil Filter at TAU Treatment Plant,
Tonsberg, Norway 63
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FIGURES (continued)
Number Page
4-22 Soil Filter System - Mercer Island, WA Pump Station
Odor Control 63
4-23 Effect of input Concentration of H2S Removal
Efficiency by Soil Filters 65
4-24 Soil Filter installation at TAU Treatment Facility 66
4-25 Air Collection and Blower Equipment at TAU Treatment
Facility 66
5-1 Technical Options For Land Application of Septage 71
5-2 Liquid Sludge Spreading System in Forest Land
Utilizing Temporary Storage Ponds 76
5-3 Ridge and Furrow irrigation Method for Applying
Septage to Land 76
5-4 Overland Flow Method of Applying Septage to Land 76
5-5 Subsurface Soil Injection 78
5-6 Terreator Apparatus for Subsurface Soil Injection 78
5-7 Technical Evaluations Involved In Implementing A Land
Disposal Project 80
5-8 Typical Septage Disposal Site 87
6-1 Technical Options for Co-Treatment of Septage 108
6-2 Septage Addition in A Typical Sewage Treatment Plant 110
6-3 Allowable Septage Volume to Be Added to Municipal
Treatment Plant per German Guidelines 116
6-4 Estimated Waste Sludge Production in Primary
Clarifier Treating Septage and Sewage 12°
6-5 Allowable Rates of Equalized Septage Addition (8) i23
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FIGURES (continued)
Number . Page
6-6 Additional Oxygen Required for Septage Additions
in Activated Sludge Treatment Plants 123
6-7 Estimated Waste Sludge Production from Biological
Treatment Processes Receiving Septage 126
6-8 Acceptable Septage Flows As A Function of Plant
Capacity (without Equalization Facilities) 131
6-9 Estimated Oxygen Requirements for Biological
Treatment processes Receiving Septage 133
7-1 Technical Options For Independent Treatment of Septage 145
7-2 Septage Lagoon Variations 147
7-3 Alternating Lagoons - Batch Treatment 149
7-4 Parallel Operation of Continuous Discharging Lagoons 149
7-5 The Lebo Aerator . 154
7-6 Forced Aeration Static Pile Composting System 156
7-7 RBC Septage Treatment Facility-Wayland Sudbury
Massachusetts 162
7-8 Fecal Coliform Colonies Remaining After Aerobic
Digestion 164
7-9 Fecal Streptococci Colonies Remaining After Aerobic
Digestion 164
7-10 Reduction of VSS in Batch Aerobic Digestion With Time 167
7-11 Oxygen uptake Rate Versus Detention Time in Aerobic
Digester 172
7-12 Change in pH During Storage of Septage Vs Lime Dosage 184
xi
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FIGURES (continued)
Number
7-13 Change in Odor Intensity Index During Storage of Lime
Stabilizaed Septage 184
7-14 Common Lime Stabilization Process Trains 188
7-15 Lime Dosage Vs Desired pH Endpoint 191
7-16 Chlorine Oxidation System 198
7-17 Typical Sand Drying Bed Construction 217
7-18 Vacuum Filtration Process 221
7-19 Vacuum Assisted Drying Bed System 226
7-20 Sequence of Operations in Vacuum Assisted Drying Bed
System -227
7-21 Electron Beam Scanner and Septage Spreader 241
7-22 Cobalt-60 irradiation Facility at Geiselbullach, West
Germany 242
7-23 Reduced Travel Distance Through On-the-Road Dewatering 248
7-24 Mobile Dewater ing/Hauler Truck 250
7-25 Vacuum Filter for Septage Dewatering 250
8-1 Septage Management System for Acton, Massachusetts 276
xii
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TABLES
Number Page
3-1 Septic Tank Sludge Received at Enga Treatment
Plant, Norway 21
3-2 Monthly Peaking Factors for Selected Localities
in the United States and Norway 24
3-3 Variations of Septage Volume Received at Four Municipal
Treatment Plants in Norway 25
3-4 Physical and chemical Characteristics of Septage,
as Pound in the Literature, with Suggested
Design Values " 2?
3-5 Heavy Metal Concentrations Found in Septage as
Reported in the Literature and as Compared to
Those Values Reported in Typical Domestic Waste-
water Sludges, with Suggested Design Values 29
3-6 Pathogen Concentrations in Domestic Sludges
Based on Niva Research 32
3-7 Indicator Organism and Pathogen Concentrations in
Domestic Septage 32
3-8 Comparison of Septage and Municipal Sewage 33
4-1 Typical Design information for Aerated
Grit Chambers 52
4-2 Screened-Raw-Septage Supernatant Characteristics
Following Aeration and Two Hours Settling 57
4-3 Specifications for Future Soil Filters at Mercer
Island, Washington Pumping Station 62
4-4 Design Parameters for Soil Filters used for Odor
Reduction 67
5-1 Characteristics of Land Disposal Options 73
5-2 Annual Nitrogen, Phosphorus, and Potassium Utilization
by Selected Crops 83
xiii
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TABLES (continued)
Number
5-3 Annual Cadmium Limits
5-4 Suggested Total Amount of Septage Metals To Be
Applied TO Agricultural Land 85
5-5 Recommended Slope Limitations for Land Application
of Sludge 88
5-6 General Guide to Months Available for Septage
Application to Different Crops in North Central
States 90
5-7 Estimated Annual Nitrogen Uptake by Forest
Species 92
5-8 Organic Nitrogen Mineralization Factors 94
6-1 Characteristics of Primary Clarifier affluents
at Marlborough, Massachusetts 118
6-2 Characteristics of Influents and Effluents at
Marlborough, Massachusetts 125
6-3 Characteristics of influents and Effluents at
Medfield, Massachusetts 134
7-1 lagoon Performance Data — Acton, Massachusetts 150
7-2 Septage Lagoon Design Guidelines AS Suggested by the
New England interstate Water Pollution Control
Commission
7-3 Operational Parameters for Septage Composting
7-4 Summary of Research Studies on Aerobic Digestion of
Septage
165
7-5 Aerobic Stabilization of Septage Typical Design
Criteria 17°
7—6 Removal of pathogenic Bacteria During Anaerobic
Digestion of Sewage Sludge
xiv
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TABLES (continued)
Number Page
7-7 Summary of Anaerobic Digestion of Septage Studies 174
7-8 Comparison of Sludge Digestion Design Criteria
with Reported Values for Mesophilic Anaerobic
Digestion of Septage 176
7-9 Typical Design Criteria for Anaerobic Stabilization
of Septage 179
7-10 Substances and Concentrations Causing Toxiclty
in Wastewater Sludge Digestion 181
7-11 Bacteria in Raw and Lime-Stabilized Septage at
Lebanon, Ohio 186
7-12 Chemical Composition of Raw and Lime
Stabilized Septage at Lebanon, Ohio 187
7-13 Reported Values of Lime Requirements for Septage
Stabilization 190
7-14 Typical Design Criteria - Lime Stabilization
of Septage 193
7-15 Bacteriological Data Purifax ™ Treatment of
Septage 196
7-16 Typical Design Criteria for Chlorine Stabilization
of Septage 200
7-17 Summary of the Characteristics of Septage-
Conditioning Chemicals 202
7-18 Summary of Studies on Thickening Raw Septage 203
7-19 Summary of Ferric Chloride and Fettic Chloride/Lime
Conditioning Studies 204
7-20 Summary of Alum Conditioning Studies 205
xv
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TABLES (continued)
Number Page
7-21 Summary of Acid and Acid/Lime Conditioning Studies 206
7-22 , Typical Design Criteria Conditioning with
Metal Salts and Lime 212
7-23 Summary of Septage Dewdlering Studies 215
7-24 Summary of Studies on Sand Bed Dewatering of Septage 219
7-25 Vacuum Filtration of Septage 222
7-26 Septage Dewatering by Solid-Bowl Centrifugation 224
7-27 Summary of Septage Centrate Water Quality 225
7-28 Pathogenic Human Viruses Potentially in Septage 231
7-29 Pathogenic Human Bacteria Potentially in Septage 232
7-30 Pathogenic Human and Animal Parasites Potentially
in Septage 234
7-31 Time and Temperature Tolerance for Pathogens and
Indicators in Septage 237
7-32 Laboratory Study on Days of Storage Required
for 99.9% Reduction of Viruses and Bacteria in
Sludge 240
7-33 Treatment/Disposal of Liquid Fraction — Advantages,
Disadvantages, and Design Criteria 243
7-34 Ultimate Disposal of Raw Septage and Septage Solids —
Advantages, Disadvantages, and Design Criteria 245
8-1 institutional Capability Matrix 263
8-2 Conventional and Alternative Financing Techniques
for Septage 274
xvi
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CHAPTER 1
INTRODUCTION
1.1 Purpose
The principal purpose of this handbook is to present an up-to-date re-
view of available designf performance, operation and maintenance,
cost, and energy information pertaining to the receiving, treatment,
and disposal of septage. Septage is the liquid and solid material
pumped from a septic tank or cesspool when it is cleaned. Recommended
procedures for planning and design, along with state-of-the-art in-
formation on treatment performance, energy considerations, and health
and environmental effects, are presented. Cost information is provided
for selected processes in the form of Fact Sheets contained in Chapter
9.
This document should serve as a practical guide for planners, design
engineers, state and Federal reviewers, and local government officials
involved in planning, evaluating, and designing septage handling fa-
cilities in response to the increasing demands for such facilities.
1.2 Scope
This handbook provides information needed to facilitate the design of
septage receiving stations, pretreatment processes, new sewage treat-
ment plants with provisions for receiving septage, and independent
septage treatment and disposal alternatives. Methods for septage
treatment and disposal discussed in this handbook are:
1. Land treatment and disposal.
2. Co-treatment at existing wastewater treatment facilities.
3. Independent facilities for treatment and disposal.
Individual treatment processes are discussed in detail and specific
design guidance is provided.
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1.3 Use of the Handbook
Figure 1—1 presents the suggested sequence to follow when using this
handbook. Chapter 2 presents the technical options applicable for the
management of septage in sufficient detail to enable a planner/de-
signer to begin the decision process. A detailed discussion of septage
characteristics, including quantities generated, is contained in Chap-
ter 3. Chapter 4 discusses septage receiving station design. Chapters
5 through 7 offer specific technical advice pertaining to the design of
land treatment, co-treatment, and independent septage treatment facil-
ities, respectively. Chapter 8. discusses facility operation and program
management considerations. Fact Sheets are presented in Chapter 9.
These are a series of two-page capsule summaries of selected septage
treatment methods, with generalized capital and operation and mainte-
nance costs.
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FIGURE 1-1
SEQUENCE OF CHAPTERS
Introduction
Chapter 1
Technical Options
and Strategies
Chapter 2
Septage
Characteristics
Chapter 3
Receiving
Station
Design
Chapter 4
(Use Only Appropriate! Chapters As Required)
i !~~1
* i i
Land
Disposal
Co-Treatment
With
Sewage
I
Chapter 5
L_
I
Chapter 6
Independent
Treatment
I
Chapter 7
_J
Management
Flan
Chapter 8
Fact Sheets
Chapter 9
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CHAPTER 2
TECHNICAL OPTIONS AND STRATEGIES
2.1 Introduction
This chapter presents the information needed by a planner or designer
to begin making decisions relevant to the receiving, treatment, and
disposal of septage. Topics covered in this chapter include septage
management options, technical considerations (i.e., selection cri-
teria), applicable Federal and state guidelines, and other considera-
tions, such as potential environmental impacts, public acceptability,
and cost.
2.2 Septage Management Options
The basic methods of treating and disposing, of septage are briefly de-
scribed in the following sections, although each is discussed in
greater detail in the individual design chapters {5 through 7}. Figure
2-1 illustrates the various pathways (i.e., technical options) avail-
able for septage management. Figure 2-2 depicts the various decisions
that must be made in selecting the most appropriate technical option.
2.2.1 Land Disposal
Three basic methods of land application apply for septage disposal.
These include:
1. Land spreading.
2. Subsurface incorporation.
3. Burial.
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FIGURE 2-1
BASIC SEPTAGE MANAGEMENT OPTIONS
Raw
Septage
Independent
Treatment
Land Spreading
Trench/Lagoon/Landfill Burial
Subsurface Incorporation
Addition to Liquid Stream
-Addition to Sludge Stream
• Addition to Both Streams
Stabilization Lagoon
Composting
Conventional Biological Treatment
Aerobic Digestion
Anaerobic Digestion
Lime Stabilization
Chlorine Oxidation
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FIGURE 2-2
ILLUSTRATION OF DECISIONS IN SELECTING MOST
APPROPRIATE TECHNICAL OPTION
Determine the Quantity ol Septage
to be Treated and/or Disposed
(Chapter 3)
lapte
T
Determine Characteristics of Septage:
Physical, Chemical, Biological
(Chapter 3)
Review Applicable Guidelines for
Disposal of Septaga:
Foderal/Stale/Local
(Chapters 2 and 8)
Preliminary Planning Consideration
* Public Acceptance
• Transport Distance (Chapter Z)
* Land Area Requirement
• STP Available Capacity and Potential to Accept Septage
1
Site Evaluation and Selection
* Compatibility with Existing and Future Land Use
Aesthetics
Site Acquisition
SDK Characteristics
(Chapters 2, 5, 6, and ?)
I
Two or More
Proceed to 1
Appropriate w
Design Chapter
Review Some of the
Following Chapters:
* Technical Option Design
(Chapters 4 Through 7)
• Rev ew Fact Sheets (of Design and Costs
(Chapters)
* Rev ew Management Plan
(Chapter 8)
Factors lor Consideration
(Chapters 2 and 8)
• Cost Effectiveness
* Short- and Long-Term Environmental Impacts
* Other Impacts
- Implementability
- Financing
- Reliability
- Public Health
• Flexibility
- Public Acceptability
One Best ^, ^_
Option ^
1
Combination of
Options
f
Adipltd From "Prociti Dttlgn Minuit (or
Land Application ol Munlclpil Sludgo" (1)
Implement the Best Option or Combination
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Land spreading has been the most common septage disposal method in the
United States. Surface spreading of septage is generally accomplished
by the same techniques as municipal liquid wastewater sludge spreading,
which may simply involve the septage pumping truck emptying its con-
tents on the field while slowly driving across the site. This technique
has very low operation and maintenance requirements. A more controlled
and preferred approach is to use a holding tank to receive septage
loads when the soil is not suitable for spreading due to climatic con-
ditions. A special vehicle can then be used to spread the septage when
weather and soil conditions permit. Unfortunately, land spreading is
often done without regard to site suitability. However, state regula-
tory agencies are beginning to exert more stringent control over this
practice.
Subsurface incorporation techniques have gained wide acceptance as an
alternative for disposal of liquid sludge and, to some extent, septage.
Three basic approaches are available:
1. Incorporation using a farm tractor and tank trailer with at-
tached subsurface injection equipment,
2. Incorporation using a special purpose tank truck with subsur-
face injection equipment.
3. Incorporation using tractor-mounted, subsurface injection
equipment in conjunction with a central holding facility and
flexible "umbilical cord." Liquid sludge is continually
pumped from the holding tank to the injection equipment.
Disposal of septage by buria] *n excavated trenches is another common
disposal technique. Since trench dimensions vary with site location,
the space between trenches should be sufficient to allow movement of
heavy equipment. A series of trer ^hes is usually dug by a backhoe to
allow sequential loading and maximum dewatering. Septage is usually
applied in successive layers. When the trenches are full, the solids
can be excavated and placed in a landfill if they have dewatered suf-
ficiently, or the trenches can be covered with soil. A thorough site
evaluation is essential to prevent groundwater contamination with this
disposal technique.
Sanitary landfills in the United States generally accept a multiplic-
ity of materials such as refuse, industrial wastes, and sometimes haz-
ardous or toxic wastes. All of these wastes are compiled on a daily
basis at the landfill and are buried under a soil cover. The accept-
ance of septage at a landfill depends chiefly on the ratio of the mix-
ture of septage to refuse to maintain moisture control. However, a few
states do not allow landfill disposal of septage, and some others do
not recommend it because of potential runoff and leachate problems.
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2.2.2 Co-Treatment
The treatment of septage at municipal sewage treatment plants is prac-
ticed in both the United States and Europe. The constituents of sep-
tage/ although highly concentrated and much stronger than domestic sew-
age/ are generally similar to domestic sewage. Therefore/ the same
processes used to treat domestic sewage can also be used for co-treat-
ment of septage and domestic sewage. This method of treatment for sep-
tage is encouraged by many state, county, and Ic-cal environmental
health agencies (4). Co-treatment is generally considered when homes
served by septic tanks are within an economical hauling distance of
the sewage treatment plant: 16 km (10 miles) is considered to be an
economical distance; a distance greater than 32 km (20 miles) is
usually excessive (3).
The quantity of septage that may be treated at a sewage treatment plant
is normally limited by available aeration and/or solids handling ca-
pacity. At relatively small plants a 4 to 12 m3 (1,000 to 3,000 gal)
truckload of septage, discharged in a period of minutes, can impose a
significant shock load on the plant. Before septage is treated at a
treatment plant, it should be determined if sufficient capacity exists
to handle the increased organic and hydraulic loadings associated with
septage.
Three methods exist for treating septage at wastewater treatment fa-
cilities:
1. Addition to the liquid stream (upstream from the plant or at
various points within the plant).
2. Addition to sludge stream.
3. Addition to both liquid and sludge streams.
The first two each have advantages under certain conditions, while the
third offers optimum flexibility. For example, addition to the liquid
stream is best when the plant employs primary clarification since this
effectively removes most of the septage solids with the primary sludge.
However/ for extended aeration plants, septage addition to the waste-
water flow may have a severe impact on the organic loading, SRT, and
aeration capacity of the system. In this case, introducing the septage
into the sludge stream is desirable. With each method, solids produc-
tion will increase. Septage holding facilities allow addition of the
septage to the treatment plant at appropriate rates and times to avoid
major process upsets.
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2.2.3 Independent Treatment
Facilities have been constructed exclusively for handling septage.
These systems vary from stabilization lagoons to sophisticated treat-
ment plants. Such processes as lime stabilization, chlorine oxidation,
aerobic digestion, composting, anaerobic digestion, and chemical
treatment have been used to treat septage. Mechanical treatment sys-
tems, as opposed to simple lagoon systems, are generally more capital-
intensive and usually cost more to operate. However, such systems have
been found*to be cost-effective in areas of significant septic system
density, such as Long Island, New York (5). In rural areas, simpler,
less expensive alternatives are preferred. Lagoons are the most common
and among the least expensive independent septage handling alterna-
tives.
2.3 Selecting a Septage Management Option
The selection of a suitable septage management option does not depend
strictly on technical considerations. For example, regulatory require-
ments may take precedence over the technical issues (these are further
discussed in Section 2.4). Site availability may prohibit the selec-
tion of a particular land disposal option, or the distance to an ex-
isting municipal treatment plant may obviate co-treatment due to ex-
cessive hauling costs. Figure 2-3 is a useful guide for selecting a
disposal option.
2.3.1 Land Availability and Site Selection
Of the three disposal options presented, the land disposal option is
most dependent on the availability of land. The amount of land required
for land application includes the area required for treatment, buffer
zones, receiving and pretreatment facilities, access roads, and main-
tenance buildings. After the total amount of land required is esti-
mated, additional work is necessary to determine if the site is suit-
able. Factors to be considered include soils, topography, hydrogeology,
current and planned land use, neighboring land use, zoning, and dis-
tance from septage service area. Additional details are contained in
Chapter 5.
2.3.2 Transport Distance
The hauling distance to a suitable disposal site must be considered
when selecting options. It is desirable to locate the disposal site as
close as possible to the area in which the septage is generated. Al-
though, there are little data regarding costs for the transport of
septage over long distances, studies investigating the liquid transport
of wastewater sludge indicate that truck transport may not be economi-
cal for one-way distances of greater than 32 kilometers (20 miles) (3).
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FIGURE 2-3
SEQUENCE SELECTION OF A SEPTAGE DISPOSAL OPTION
Refer
To
Chapter
5
Yes
Yes
Land Disposal Option
Is land disposal of septage
publically and legally acceptable?
I .
Estimate land area and
pretreatment requirements
I
Is there an available site(s)
suitable for land disposal?
No
No
Refer
To
Chapter
6
Yes
Co-Treatment At A
Municipal Treatment Plant
• Will the treatment facility
accept septage?
No
Yes
I
Does the treatment plant have adequate
capacity to accept additional loading?
No
2fer (
Co )
rr I
Refer
To
Chapter
Yes
Independent Treatment
• Have the other disposal options
been considered and judged
inappropriate?
10
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Factors to be considered for hauling septage by truck include:
1. State and local restrictions.
2. Septage volume to be transported.
3. Number of trips per day.
4. Distance to disposal site.
5. Fuel costs.
6. Labor costs.
7. Cost of disposal.
Potential environmental impacts, such as noise and general disruption
due to increased truck traffic, will also have to be addressed.
2.4 Legal and Regulatory Considerations
Regulatory factors play a major role in the planning and design of
septage treatment and disposal facilities. It is the intent of this
section to review those that apply specifically to septage. In many
cases, however, septage is dealt with in conjunction with wastewater
sludge management.
2.4.1 Federal Regulations
The following are Federal laws that deal with septage as part of over-
all sludge management:
1. The Clean Water Acts (CWA) of 1981 (PL 97-117) and 1977 (PL
95-217), and the Federal Water Pollution Control Act Amend-
ments of 1972 (PL 92-500), authorize Federal funding of eli-
gible costs involved in the construction of municipal waste-
water treatment facilities, including septage treatment and
disposal; authorize U.S. EPA to issue comprehensive septage
and wastewater sludge management guidelines and regulations;
authorize the NPDES (National Pollution Discharge Elimination
System) for point source discharges and development of area-
wide waste treatment or water quality management plans for
non-point source pollution; require the implementation of
pretreatment standards for industrial discharges that enter
POTW's; and establish a research and demonstration program to
develop improved wastewater treatment and sludge and septage
management practices.
11
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The U.S. EPA is authorized under the CWA, as amended, to pro-
vide grant assistance to municipalities for the building of
wastewater treatment projects. Grant assistance may be up to
75 percent of the allowable costs of building the project and
include an allowance for facilities planning and design. Af-
ter 1 October 1984, the Federal share will be 55 percent of
these costs. Innovative and alternative (I/A) technology proj-
ects may receive an additional 20 percent Federal share, up
to a maximum of 85 percent (up to 75 percent after 1 October
1984).
Eligible I/A projects include processes and techniques for
the treatment and use of effluents, such as land treatment,
aquifer recharge and aquaculture; total containment ponds and
ponds for treatment and storage of wastewater prior to land
application; individual and other onsite treatment systems
with subsurface or other means of effluent disposal; and fa-
cilities constructed for the specific purpose of septage
treatment. The cost of land used as an integral part of the
treatment process is allowable for grant funding up to 85
percent (up to 75 percent after 1 October 1984) as are pumper
trucks for the transport of septage to a disposal site.
2. The Resource Conservation and Recovery Act of 1976, PL 94-580
(RCRA), authorizes Federal financial assistance to state and
local governments for development of solid waste management
plans that provide for the safe disposal of solid wastes
including septage; provides for technical assistance to help
establish acceptable solid waste management methods; requires
stringent regulations for the disposal of hazardous and non-
hazardous wastes (including septage); and encourages the re-
search and demonstration of more effective solid waste dis-
posal and resource conservation technologies.
3. The Marine Protection Research and Sanctuaries Act of 1977,
PL 92-532 (MPRSA), phased out ocean disposal of sewage sludge
and septage "which may degrade or endanger human health, wel-
fare, amenities, or the marine environment ecological systems,
or economic benefits" as soon as possible or, in any event,
no later than 31 December 1981. MPRSA also gave the U.S. EPA
the authority to determine a reasonable compliance schedule
for the implementation of land-based disposal alternatives.
However, there has been increasing interest in and pressure
exerted to cause the agency to reconsider the potential for
continuing many of the existing ocean disposal projects, as
well as allowing the establishment of new projects.
12
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4. The Clean Air Act Amendments of 1970 and 1977, PL 91-604 and
PL 95-95 (CAA), authorized the development of State Implemen-
tation Plans (SIP's) for the purpose of meeting Federal am-
bient air quality standards. To meet the CAA objectives, the
U.S. EPA has developed an emission offset policy for new or
modified incinerator and heat drying facilities, as well as a
procedure for preventing the significant deterioration of am-
bient air quality. The CAA also authorizes regulations for
the control of hazardous air pollutants and new source per-
formance standards.
5. The Safe Drinking Water Act of 1975, PL 93-523 (SDWA) , re-
quires coordination with the CWA and RCRA to protect drinking
water from contamination.
6. The National Environmental Policy Act of 1969, PL 91-190
(NEPA), authorizes regional administrators, at their discre-
tion, to require Environmental Impact Statements (EIS) (40
CFR, Part 6) if potentially adverse social, economic, or en-
vironmental impact is suspected for a new or modified sludge
or septage disposal facility or practice. An EIS or negative
declaration (40 CFR, Part 35, Section 35.925-8) is also re-
quired when applying for Federal construction grants.
7. The Toxic Substances Control Act of 1976, PL 94-469 (TSCA),
Section 9, requires coordination with the Clean Air Act and
the Clean Water Act to restrict disposal of toxic wastes.
Presently, only PCB (polychlorinated biphenyl) is specifical-
ly addressed by Federal regulations with regard to sludge
disposal under TSCA.
2.4.2 State and Local Regulations
State laws and regulations concerning septage vary widely. In some in-
stances, no overall state regulations apply, and septage practices are
controlled by local governing bodies at the county or municipal level.
Typically, septage regulations deal with licensing requirements,
equipment used, pretreatment requirements, allowable disposal prac-
tices, and regulation enforcement. A matrix describing pertinent sep-
tage regulations regarding land application of septage from various
states based on a telephone survey and review of existing regulations
is presented in Appendix A.
13
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2.5 Other Considerations
Beyond the technical and regulatory considerations, the planner/de-
signer should be aware of other general factors that might influence
the choice of a particular septage management option. In implementing
any septage management program, it is critical that the treatment fa-
cilities be environmentally safe, reasonable in cost, and acceptable
to the public.
Environmental impacts refer to those changes in the environment
brought about by the implementation of a particular septage management
option. Many of the regulations and guidelines that exist have been
developed so that septage hauling and disposal practices will not re-
sult in an adverse impact on the environment or human health.
The cost of a project not only includes the capital for initial imple-
mentation, but also the cost for operating and maintaining the system.
It is important that the entire extent of the cost of the project be
estimated as accurately as possible before any option is implemented.
Often when dealing with wastewater treatment projects, the extent of
this economic impact may not always be realized until the project has
been implemented. This may result in a facility having relatively low
capital cost but unaffordably high operation and maintenance costs.
The effectiveness of a septage treatment facility is directly dependent
on the skill and training of the plant operator. A facility can be de-
signed to provide the highest degree of treatment technology possible,
but it is the individual operator who actually makes a plant perform
at its design capability. The importance of properly trained operators
cannot be over-stressed as a basic design consideration.
The implementation of a particular septage management option depends
highly on securing the acceptance of the public. Gaining public ac-
ceptance is enhanced by working from the beginning with responsible
local officials, landowners, and other affected parties. The public
should be made aware of the various options under consideration, along
with their benefits, risks, and costs. This may be done by holding
public meetings, conducting surveys and workshops, distributing pam-
phlets, and advertising on local radio, television, and in newspapers.
Establishing open discussions with the public will often lead to the
selection of the most cost-effective and environmentally-acceptable
management option.
14
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2.6 References
1. U.S. Environmental Protection Agency. Process Design Manual for
Land Application of Municipal Sludge. U.S EPA Report No. 625/1-83-
016, October 1983.
2. U.S. Environmental Protection Agency. Monitoring Septage Addition
To Wastewater Treatment Plants, Volume I: Addition To the Liquid
Stream. U.S. EPA Report No. 600/2-79-132, NTIS Publication No. PB
80-143613, November 1979.
3. U.S. Environmental Protection Agency. Process Design Manual for
Sludge Treatment and Disposal. U.S. EPA 625/1-79-011, 1979.
4. Florida Department of Environmental Regulation. Resource Recovery
and Management, Part IV FAC, Chapter 17-7, Tallahasee, Florida,1984.
5. Rezek, J.W. and I.A. Cooper. Septage Management. U.S. EPA Report
No. 600/8-80-032, NTIS Publication No. PB 81-142481, August 1980.
15
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CHAPTER 3
SEPTAGE CHARACTERIZATION
3.1 Introduction
Septage is generally defined as the liquid and solid material pumped
from a septic tank or cesspool during cleaning. Septage is normally
characterized by large quantities of grit and grease, a highly offen-
sive odor, great capacity to foam upon agitation, poor settling and
dewatering characteristics, and high solids and organic content. Its
high waste strength is due to the accumulation of sludge and scum in
the septic tank. Typically, a septic tank will retain 60 to 70 percent
of the suspended solids and oil and grease introduced from the dwelling
served. The bulk of the suspended solids settles to the bottom of the
tank, and the oil and grease and other flotable materials are retained
between the inlet and outlet baffles, as shown in Figure 3-1. Over a
period of time, the sludge and scum can build up to a point where it
occupies from 20 to 50 percent of the total septic tank volume.
In addition to being a highly concentrated waste, septage character-
istics vary widely from one location to another. This variation is due
to several factors, including: the number of people utilizing the
septic tank and their cooking and water use habits? tank size and
design? climatic conditionsj pumping frequency; and the use of tribu-
tary appliances such as garbage grinders, water softeners, and washing
machines.
Knowledge of septage characteristics and variability is important in
determining the proper handling and disposal alternatives. Data on
local septage characteristics are extremely valuable for design
purposes? however, they are not always available. In such cases,
engineering judgement must be utilized in applying typical design
values,
16
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FIGURE 3-1
TYPICAL SEPTIC SYSTEM
To
Absorption
Field
Sludge
17
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3.2 Septage Quantity
The 1980 U.S. Department of Commerce, Census Bureau, estimated that
the number of housing units with septic tanks in the United States was
21.9 million (1). This number represented a 31.9 percent increase over
the 16.6-million units noted from the 1970 census (1). Based on an
average septic tank volume of 2.84 m^ (750 gallons), and being pump-
ed out once every three years, approximately 21-nillion cubic meters
(5.5 billion gallons) of septage are generated annually.
3.2.1 Per Capita Septage Generation Rates
Septage generation rates reported in the literature vary widely. Based
on the assumptions presented above and 3.5 persons per housing unit,
an estimate of septage generation rate in the U.S. is approximately
237 liters (55 gallons) per capita per year. A study in Suffolk County,
New York estimated 340 to 380 liters (90 to 100 gallons) per capita
per year, based on frequent pumpouts and larger than average tank
volumes (2). Septage generation in the Poughkeepsie, New York area .was
estimated to be 190 liters (50 gallons) per capita per year (3). The
State of Connecticut recommends using 190 to 265 liters (50 to 70
gallons) per capita per year in its lagoon-design guidelines. Recent
Norwegian guidelines recommend 250 liters (66 gallons) per capita per
year, while Swedish guidelines recommend 225 liters (60 gallons) per
capita per year (4). Results of a survey carried out in Germany reveal
values varying between 110 and 4,380 liters (30 to 1,160 gallons) per
capita per year (4).
In light of the significant variation in septage generation rates from
one locality to another, every effort should be made to obtain actual
records of septage quantities (i.e., from existing treatment plants
receiving septage, or from local haulers) for a particular service
area. When these data cannot be obtained, an average per capita sep-
tage generation rate of 230 liters (60 gallons) per capita per year
can be used for planning and design purposes. An alternate method of
estimating septage quantities is to multiply the number of septic
tanks in the service area by the average annual pumpout volume per
unit (i.e., the total volume of a typical septic tank divided by the
average number of years between pumpouts). This method tends to give
more accurate results than the per capita method, provided the number
of septic tanks is known and the estimate of average pumpout interval
is realistic. Commercial, institutional, and industrial sources should
be accounted for by addition to the results from either method. The
two methods are illustrated as follows:
18
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Method 1; Per Capita Generation Rates
Annual Volume - Service Area Population x 230 liters/Capita/Year
= (Service Area Population x 60 Gal/Capita/Year)
(Note: Per capita generation rate (volume/person served by septic
tanks) can be adjusted up or down based on local knowledge of septic
tank cleaning practice.)
Method 2; Typical Tank Volume/Pumpout Frequency Assumption
Annual Volume =
No. Septic TanksxTypicalVolume (gallons or liters)
Pumpout Interval (years)
(Note: A pumpout interval of 3 to 5 years is realistic in areas where
homeowners are moderately conscientious about septic tank cleaning.)
3.2.2 Seasonal Variations in Septage Quantities
The pumping of septic tanks usually follows a seasonal pattern, with
most of the pumping occurring during times of high groundwater or ex-
tended periods of rainfall or snowmelt (i.e., early spring, fall, and
summer) due to the mistaken belief that tank pumping would relieve
surface failure symptoms. In colder climates, less septage is pumped
during the winter due to the difficulty of uncovering septic tanks in
frozen ground. Some septage pumping does take place year round, such
as for emergency system repair, and for service of institutions and
commercial establishments such as schools, restaurants, and motels.
Thus, septage volumes are not uniformly distributed throughout the
year. While a mandatory pumping schedule would normalize septage
volumes throughout the year, the development of such regulations,
although very practical, have proven to be difficult to implement.
Figure 3-2 shows a typical septage pumping pattern taken from the Leb-
anon, Ohio STP for the year 1972 (5). As can be seen from the figure,
most of the pumping occurs during the months between May and August,
with significantly less pumping in the months between December and
March. On an extended scale, daily peaks must be considered in deter-
mining receiving station component sizing. It is extremely important
to provide adequate capacity for peak loading periods in order to
avoid having to deny discharges, which will undoubtedly result in
illegal dumpings.
19
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FIGURE 3-2
SEPTAGE LOADING PATTERN AT LEBANON, OH 1972
120
100
1 «H
o
£
5 60
•H-
(a
c
JS
To
0 40J
20-
MAMJJ ASOND
Month
FIGURE 3-3
VOLUME OF SEPTAGE RECEIVED AT
ENGA TREATMENT PLANT, NORWAY (4)
J F M AMJJASONDJFM A M J J A S O N D
1978 1979
20
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Additional information on the variations in septage quantities is
available from a Norwegian study that analyzed actual operating data
for several municipal treatment plants with facilities for handling
septage (4). A representative plot of septage quantity variability
characteristics for one of these facilities (Enga, Norway) is given in
Figure 3-3. Maximum days and minimum days for each month are plotted,
as well as monthly averages. Table 3-1 presents the data with which
these plots were made, including coefficients of variation.
TABLE 3-1
SEPTIC TANK SLUDGE RECEIVED AT ENGA TREATMENT PLANT, NORWAY (4)
Year/Month
No. Days
Receiving
Sludge
Monthly
Volume
Daily Volume
Average
Maximum
Minimum
1979
January
February
March
April
May
June
July
August
September
October
November
December
Average
20
19
20
19
21
21
22
22
20
24
22
20
22
15
25
34
44
37
41
36
39
46
31
24
33
64
41
55
62
84
65
81
69
89
90
61
46
6
3
6
5
8
5
16
14
9
22
8
3
The variability data from Lebanon, Ohio, and Enga, Norway have been
used to produce the plots given in Figures 3-4 and 3-5, which show the
variation in septage quantities produced in different months of the
year in terms of the ratio of monthly and daily averages to annual
averages. The pattern shown in Figure 3-2 for Lebanon, Ohio is believed
to be more applicable in the U.S. based on general knowledge of septic
tank cleaning practices in various parts of the country.
21
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FIGURE 3-4
VARIATION IN MONTHLY AVERAGE SEPTAGE
QUANTITIES LEBANON, OH (5)
2.0-h
i—I—I—I—I—I—I—I—I
M
M
J J
Month
FIGURE 3-5
VARIATION IN DAILY AVERAGE SEPTAGE
QUANTITIES ENGA, NORWAY (4)
2.0--
1.8-
o
C 1,6-
Q
01
1.4-
<
°3
3
i
<
«^
1
#H
ns
o
1.2-
1.0-
.8-
1.1
X
Ann.
Avg.
41
Adjusted Average
a
I
c
.4.
.2-
M
M
J J
Month
22
-------
These plots illustrate that the bulk of the septage quantities pro-
duced are generated in the spring, summer, and fall, specifically Ap-
ril through November for Lebanon, and March through December for Enga.
If the data points for these periods aloiie are averaged, an adjusted
average daily or average monthly septage generation rate can be deter-
mined. This adjustment factor can be used to develop a more realistic
estimate of daily or monthly average septage flow during the critical
spring-summer-fall period, based on annual septage quantity estimates.
Based on the Lebanon, Ohio data, an adjustment factor of 1.4 is indi-
cated. For general planning and design purposes, the average design
capacity for septage handling and treatment facilities can be esti-
mated as being approximately 1-1/2 times the annual average daily
generation rate. ,
3.2.3 Peaking Factors
It is of the utmost importance to .estimate the volume of septage to be
treated and the rate at which it will be received as correctly as pos-
sible. The rate at which it is generated {i.e., daily flows) depends
on many factors, including time of year, weather conditions, and local
septic tank cleaning practices. The use of peaking factors allows the
designer to estimate the range of flow conditions to be expected. The
peaking factor may be defined as the ratio of the maximum/average
septage quantity received over a particular period (i.e., week, month,
year) . Table 3-2 lists • the ratio of the" peak monthly to the mean
monthly septage volume received at various treatment facilities in the
U.S. and Norway, corresponding to the month when the maximum septage
volume is received over a period of a year. Table 3-3 is a summary of
peaking factors for the four municipal treatment plants studied in
Norway.
In addition to monthly variations, weekly and daily variations must be
taken into consideration. While little data exist on actual weekly and
daily peaking factors, various planning studies in the U.S. have
recommended weekly peaking factors ranging from 1.8 to 3.6, and daily
peaking factors ranging from 4,0 to 4.8 {6} {7}*
3.3 Characteristics of Septage
The following section presents data that describe the characteristics
of septage. However, the data presented are not intended to replace
site-specific data. Due to the extensive variation in septage char-
acteristics between loads, it is recommended that nearby facilities
with similar service areas be investigated and proper factors of
safety be applied in designing receiving and treatment facilities.
23
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TABLE 3-2
MONTHLY PEAKING FACTORS FOR SELECTED LOCALITIES IN THE
UNITED STATES AND NORWAY
Location
Month
Ratio of Peak Monthly
to Mean Monthly
Year Septage Volume
Reference
Essex, Connecticut
Old Saybrook,
Connecticut
Salem, New Hampshire
Lebanon , Ohio
Winston-Salem, North
Carolina
Enga, Norway
Heisted, Norway
Brumunddal, Norway
June
July
August
June
October
June
May
May
May
October
October
September
November
October
October
1978
1975
1976
1977
1978
1974
1975
1972
1972
1978
1979
1979
1977
1978
1979
2.0
2.5
2.1
1.9
1.5
1.3
1.2
1.8
1.8
1.4
1.6
1.7
1.9
2.1
2.2
(25)
(25)
(6)
(5)
(26)
(4)
(4)
(4)
Iiillehammer, Norway October
1979
1.9
(4)
24
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TABLE 3-3
VARIATIONS OF SEPTAGE VOLUME RECEIVED AT FOUR
MUNICIPAL TREATMENT PLANTS IN NORWAY (4)
Maximum Month
Maximum Day
Treatment Plant Year Annual Monthly Average Annual Daily Average
Enga
Heistad
Brumunddal
Lillehammer
1978
1979
1979
1977
1978
1979
1979
1.42
1.57
1.73
1.93
2.14
2.22
1.88
3.42
2.73
2.94
4.42
3.70
4.52
4.88
Table 3-4 reports septage characteristics from 12 studies conducted in
the U.S. and from 6 studies conducted in Europe and Canada. The data
for a particular parameter were often reported as a range and a mean
value? however, the parameters reported, as well as the number of in-
dividual samples taken varied widely from one study to another. As can
be seen from the table, there is a close correspondence between the
data collected in the U.S. and those collected in Europe and Canada.
The lower values found in Europe/Canada, versus the U.S. for total
solids and total volatile solids, may be related to pumping frequency.
The Norwegian Department of Ecology requires each homeowner to empty
his septic tank at least once a year (once every three years for tanks
at recreational homes). German guidelines do not comment specifically
on how often the septic tanks should be emptied; however, in a study
by Resch, it was found that for those in the study, 25 percent were
cleaned annually and 34 percent were cleaned every two years (8).
It is important to note the range of values reported for many of the
parameters. As mentioned previously, the cause of this variability may
be the result of a number of factors, including user habits, tank size
and design, pumping frequency, climate and seasonal weather condi-
tions-, and tributary appliances such as garbage grinders, water sof-
teners, and washing machines, as well as difficulties in obtaining
representative samples of the entire tank contents*
25
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Due to inconsistencies and discrepancies in the data base, the rela-
tionship between individual parameters may be misleading. For example,
the average TS value is less than the average TSS value for the Euro-
pean data. This is probably caused by TS values not being reported in
some cases where the TSS value was atypically high. Certain valid re-
lationships between variables have been observed and are worth noting.
For example, Eikum (4) presented data indicating that on the average
VSS concentrations are roughly 75 percent of the Total Suspended Solids
concentration. Other data presented by Eikum (4) showed COD values to
be roughly 25 percent higher than VSS concentrations.
Table 3-4 also presents data compiled by the U.S. EPA's Municipal En-
vironmental Research Laboratory in Cincinnati, Ohio. All three sets of
data compare well considering the variable nature of septage. Based on
these data, Table 3-4 presents suggested design values for the various
physical and chemical constituents of septage where no site-specific
data are available.
3.3.1 Nutrients in Septage
Nutrients in septage, specifically nitrogen and phosphorus, are of
concern due to the growing interest in the treatment and removal of
nutrients from domestic wastewaters. Nitrogen and phosphorus is also
of interest with respect to specific loading rates as they apply for
land treatment of septage.
The concentrations of both nitrogen and phosphorus found in septage
are high as compared to typical domestic wastewater. Typical domestic
wastewater may contain from 12 to 50 mg/L of ammonia-nitrogen, and
from 4 to 15 mg/L of phosphorus, with average concentrations of 25 and
8 mg/L, respectively (22). By comparison, septage, as shown in Table
3-4, contains average concentrations of 97 and 210 for ammonia-nitro-
gen and phosphorus, respectively.
3.3.2 Heavy Metals in Septage
Metal contamination may result from one or more of the following
sources (21): , .
1. Household chemicals that contain trace concentrations of
heavy metals.
2. Leaching of metal from household piping and joints.
3. Contamination of septage in hauler trucks from a previous in-
dustrial waste load.
26
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TABLE 3-4
PHYSICAL AND CHEMICAL CHARACTERISTICS OF SEPTAGE, AS
FOUND IN THE LITERATURE, WITH SUGGESTED DESIGN VALUES3'
United' States (5) (9-19)
Parameter
TS
TVS
TSS
VSS
BODfc
COD
TKN
NH3-H
Total t
Alkalinity
Crease
pH
US
Average
34,106
23,100
12,862
9,027
6,480
31,900
588
97
210
970
5,600
~— ~
Miniaun
1,132
353
310
95
440
1,500
66
3
20
522
208
1.5
110
Maximum
130,475
71,402
93,378
51,500
78,600
703,000
1,060
116
760
4,190
23,368
12.6
200
Variance
115
202
301
542
179
469
16
39
38
8
112
8
2
Suggested
Europe/Canada (4) (20) Design
Average
33,800
31,600
45,000
, 29,900
8,343
28,975
1,067
155
»-
Minimum Maximum Variance EPA Mean
200 123,860 619 38,800
160 67,570 422 25,260
5,000 70,920 14 13,000
4,000 52,370 13 8,720
700 25,000 36 5,000
1,300 114,870 88 42,850
150 2,570 17 677
"7
20 636 32 253
9,090
5.2 9.0 6.9
157
Value
40,000
25,000
15,000
10,000
7,000
15,000
700
150
2SO
1,000
8,000
6.0
150
aValues expressed as mg/L, except foe pH.
''The data presented In this table were compiled from many sources. The inconsistency of individual data sets
results in some skewing of the data and discrepancies when individual parameters are compared. This is taken
into account in offering suggested design values.
-------
Table 3-5 lists the heavy metal concentrations found in the previous-
ly-discussed studies, including the mean, minimum, and maximum concen-
trations observed, and the variability. Table 3-5 compares the heavy
metal concentrations cited in U.S. and European research studies to
those compiled by the U.S. EPA MERL (28) and to those typically found
in domestic sewage sludges (22) . Again, the values presented compare
favorably with those observed by EPA. In contrast, the metal concen-
trations observed in septage are considerably less than those typi-
cally observed in domestic sewage sludge. The level of heavy metal
concentration is of particular significance when consideration is
given to septage application to land. Application of septage to land
and the impact of heavy metals is discussed in Chapter 5.
Septage facility designers should be cognizant of the fact that highly
contaminated industrial sludges, sometimes disposed of together with
domestic septage, can severely upset treatment processes. Monitoring
programs aimed at detecting such illegal discharges should be strongly
encouraged. The treatment facility should be designed to minimize the
effects of such upsets.
3.3.3 Pathogens in Septage
Pathogenic organisms found in septage are discharged by humans who are
infected or carriers of a particular disease. The usual bacteriologi-
cal pathogenic organisms that may be excreted by man cause diseases of
the gastrointestinal tract such as typhoid and paratyphoid fever,
dysentery, diarrhea, and cholera.
Table 3-6 summarizes the investigations carried out at the Norwegian
Institute for Water Research (4) . The concentrations of indicator or-
ganisms in raw septage were found to be in the same range as those
found in untreated primary sludges from municipal treatment plants.
The table also indicates that although variations will be found re-
garding concentrations of pathogens in raw septage, the concentrations
are high for all indicator organisms used.
Table 3-7 presents typical concentration ranges for indicator organ-
isms and bacterial and parasitic pathogens in raw septage found in the
U.S. Although not indicated here, there is no doubt that a variety of
viral pathogens will also be present. These include polio virus, hepa-
titis A, echovirus, coxsackie, Norwalk-like agents, rotavirus and
adenovirus (27). It is evident that raw septage may harbor disease-
causing organisms, thus demanding proper management to protect public
health.
28
-------
TABLE 3-5
HEAVY METAL CONCENTRATIONS IN SEPTAGE COMPARED TO TYPICAL DOMESTIC WASTEWATER SLUDGES3
to
Parameter
Al
As
ca
Cr
Cu
Pe
Hg
Hn
Ni
Pb
Se
Zn
united
Average
48
0.16
0.27
0.92
8.27
191
0.23
3.97
0.75
5.2
0.076
27.4
States (5)
Minimum
2
0.03
0.03
0.6
0.3
3
0.0002
0.2
0.2
2
0.02
2.9
{9-19}
Maximum
200
0.5
10. 8
2.2
34
750
4
32
37
8.4
0.3
153
Europe/Canada (4) (20)
Average Minimum Maximum
.
0.05 0.35
0.63 5.0
4.65 1.25 15.0
0.15 0.2
0.58 2.5
3.88 21.25
38.85 1.25 90
Typical
U.S.
Domestic
Sludge
Ranges (28) b
0- 0.7
0.1- 44
0.9- 1,200
3.4- 416
0- 2.2
O.S- 112
3,2- 1,040
79- 655
EPA Mean
(5)
48
0.16
0.71
1.1
6.4
200
0.28
5
0.9
8.4
0.1
49
Suggested
Design
Value
tot
Septage
50
0.2
0.7
1.0
8.0
200
0.25
5
1
10
0.1
40
aValuea expressed as mg/L.
''Values converted froa jig/g assuming TS » 40,000 mg/L.
-------
FIGURE 3-6
VARIATIONS IN NH3 AND H2S CONCENTRATIONS AT THE TAU
TREATMENT PLANT WHEN RECEIVING SEPTAGE, FEB. 24 -1976 (4)
500
400
•3, 300
S 20QJ
"SL
100
Date: 24.2.76
i Indicates Seplage
Received
10.00 11.00 12.00
-120
-110
-100
-90
-80
-70 |
-60 £
(Q
-50 3^
-40
-30
-20
-10
0
13.00 14.00
Time
15.00 16.00
FIGURE 3-7
VARIATIONS IN NH3 AND H2S CONCENTRATIONS AT THE TAU
TREATMENT PLANT WHEN RECEIVING SEPTAGE, MAY 31 - 1976 (4)
300'
1> 200-
3
o
3
"I.
-100
8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00
Time
30
-------
3.3.4 Odors
Traditionally, the collection and handling of wastewater, septage, and
sludge has been associated with odor problems at treatment facilities.
The most characteristic odor of septage is that of hydrogen sulfide,
which is produced by the anaerobic conversion of sulfate to sulfide.
The compounds causing bad odors when handling septage are sulfides,
mercaptans, amines, aldehydes, skatoles, and organic acids.
Practical experience indicates that the odor intensity varies consid-
erably during the day at plants receiving septage. The reason for this
is that each truckload of septage can vary with respect to the amount
of odorous gases it gives off when the septage is emptied or aerated
at the plant. At the TAU Treatment Plant in Norway, investigations
were made regarding l^S and NH3 concentrations during the day (4).
Composite samples were taken each hour from the room containing the
screen and grit chamber. Results from a typical winter and summer day
are shown in Figures 3-6 and 3-7. The hydrogen sulfide concentrations
varied from approximately 0 to 480 ug/m3, and the ammonia concen-
tration varied from approximately 10 to 280 ug/m3.
The real concern with odors is not related to their potential physical
harm to humans, but rather to the psychological stress they produce.
Offensive odors can cause poor appetite for food, lowered water con-
sumption, impaired respiration, nausea and vomiting, and mental per-
turbation (24) . Often the problem of odors is not recognized in the
design of a facility and only becomes apparent after the plant becomes
operational. Proper attention to design details in the design phase
and good housekeeping practices in facility operation will keep odors
to a minimum. The various technologies available for odor control are
presented in Chapter 4 as they relate to septage receiving stations,
where the odor potential is generally the greatest.
3.4 Comparison of Septage and Domestic Wastewater Characteristics
Table 3-8 is a comparison of constituents present in septage and mu-
nicipal wastewater. In many respects, septage is a waste similar in
characteristics to domestic sewage, except that the former is more
concentrated. However, there are also dissimilarities. Septage is
anaerobic and odoriferous. It contains plastic material, hair, and
grit that clog and wear pumps and conduits. Personal contact with sep-
tage for maintenance purposes is highly objectionable from aesthetic
and health points of view. These aspects of septage characteristics
must be considered in the design of septage handling and treatment
facilities.
31
-------
TABLE 3-6
PATHOGEN CONCENTRATIONS IN DOMESTIC SLUDGES (4)
BASED ON NIVA RESEARCH
Type of Sludge
Total Fecal Fecal
Coliforms Coliforms Streptococcus
Anaerobic
Sporeformers,
Clostridium
Perfringens
Septage
Raw Primary
3.5 x 107 3.9 x 106 4.7 x 103 3.3 x 105
5.6 x 107 2.0 x 107 1.1 x 106 3.4 x 105
TABLE 3-7
INDICATOR ORGANISM AND PATHOGEN CONCENTRATIONS
IN DOMESTIC SEPTAGE
Parameter
Toxacara, Ascaris
Lumbricoides, Trichuris
Trichiura, Trichuris Vulpis
Typical Range
(counts/100 ml)
Present
Reference
Total Coliform
Fecal Coliform
Fecal Streptococci
Ps. Aeruginosa
Salmonella Sp.
Parasites
107
106
106
101
1
- 10*
- 108
- 10?
- 103
- 102
(10)
(9)
(9)
(9)
(9)
(10)
(10)
(10)
(10)
(23)
(23)
(23)
(10)
32
-------
TABLE 3-8
COMPARISON OF SEPTAGE AND MUNICIPAL SEWAGEa
Ratio of Septage to
Parameter
TS
TVS
TSS
vss
BOD5
COD
TKN
NH3-N
Total P
Alkalinity
Grease
pH
LAS
Septage*3
40,000
25,000
15,000
10,000
7,000
15,000
700
150
250
1,000
8,000
6.0
150
Sewagec
720
365
220
165
220
500
40
25
8
100
100
Sewage
55sl
68 ;1
68:1
61:1
32:1
30sl
17:1
6:1
31:1
10:1
80:1
aValues expressed as mg/L, except for pH.
^Based on suggested design values in Table 3-4.
GFrom Metcalf and Eddy, 2nd Edition, "medium strength sewage" (22).
33
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3.5 References
1. U.S. Bureau of the Census, Housing Division Census of Housing,
1980: V. 1, Characteristics of Housing Units: Ch. A, General
Housing Characteristics: pt. 1, United States Summary, May 1983.
2. Graner, W.P. An Action Plan for Solid Waste Disposal in Suffolk
County, New York, Volume 2 Report. Suffolk County Department of
Health, Water Resources Section, 1977.
3. O'Brien & Gere Engineers. Septage Feasibility Study for City of
Poughkeepsie, New York. Syracuse, New York, 1976.
4. Eikum, A.S. Treatment of Septic Tank Sludge-European Practice
(Draft). Norwegian Institute for Water Research, EPA Contract
Number 68-03-2971, Municipal Environmental Research Laboratory,
1982.
5. Bowker, R.P.G. and S.W. Hathaway. Alternatives for the Treatment
and Disposal of Residuals from On-Site Wastewater Systems. Waste-
water Alternatives for Small Communities. NTIS Publication No. PB
81-131658, November 1980.
6. Edward C. Jordan Company, Inc. Septage Management in the Southern
Rockingham Region. Prepared for the Southern Rockingham Region
Planning District Commission, Salem, New Hampshire, October 1976.
7. Stearns & Wheler. Septage and Septic System Management Plan.
Sussex County, New Jersey, 1981.
8. Resch, H. Schlamme aud Hausklaranlagen. Der Statertag. Heft 10,
618-622.
9. Feige, W.A., E.T. Oppelt, and J.F. Kreissl. An Alternative Septage
Treatment Method: Lime Stabilization/Sand-Bed Dewatering. EPA-
600/2-75-036, NTIS Report No. PB 245816, September 1975.
10. Noland, R.F., J.D. Edwards, and M. Kipp. Full-Scale Demonstration
of Lime Stabalization. EPA Publication No. 600/2-78-171, NTIS
Report No. PB 286937/AS, September 1978.
11. Kolega, J.J. Design Curves for Septage. Water and Sewage Works 118
(5), May 1971.
12. Feng, T.H. and W.K. Shieh. The Stabilization of Septage by High
Doses of Chlorine. Report for the Division of Water Pollution
Control, Massachusetts Water Resources Commission, June 1975.
34
-------
13. Chuang, F.S. A Bench-Scale Study of an Anaerobic-Aerobic Process
for Treatment of Septic Tank Wastes. Presented at the 1975 Annual
Meeting of the New England Water Pollution Control Association,
Newport, Rhode Island, October 1975.
14. Goodenow, R. Study of Processing Septic Tank Pumpings at Brunswick
Treatment Plant. Journal of Maine Wastewater Control Association,
Volume 1, No. 2, September 1972.
15. Tilsworth, T. The Characteristics and Ultimate Disposal of Waste
Septic Tank Sludge. Report No. IWE-56, Institute of Water
Resources, University of Alaska at Fairbanks, November 1974.
16. Segall, B.A., C.R. Ott, and W.B. Moeller. Monitoring Septage
Addition to Wastewater Treatment Plants, Volume I: Addition to the
Liquid Stream. EPA Publication No. 600/2-79-132, NTIS Publication
No. PB 80-143613, November 1979.
17. Tawa, A.J. Chemical Treatment of Septage. MS Thesis, University of
Massachusetts, Amherst, August 1976.
18. Condren, A.J. Pilot-Scale Evaluations of Septage Treatment Alter-
natives. EPA Publication No. 600/2-78-164, NTIS Publication No. PB
288415/AS, September 1978.
19. Bennett, S.M., J.A. Heidman, and J. Kreissl. Feasibility of Treat-
ment of Septic Tank Waste by Activated Sludge. EPA Publication No.
600/2-77-141, NTIS Publication No. PB 272105/AS, August 1977.
20. Brandes, M. Accumulation Rate and Characteristics of Septic Tank
Sludge and Septage. Research Report W-63 - Applied Sciences
Section, Pollution Control Branch, Ministry of the Environment,
Toronto, Ontario, 1977.
21. Rezek, J.W. and I.A. Cooper. Septage Management. EPA-600/8-80-032,
NTIS Publication No. PB 81-142481, August 1980.
22. Metcalf and Eddy, Inc. Wastewater Engineering: Treatment/Disposal/
Reuse. 2nd Edition, McGraw-Hill, New York, New York, 1979.
23. Deninger, J.F. Chemical Disinfection Studies of Septic Tank Sludge
with Emphasis on Formaldehyde and Glutaraldehyde. M.S. Thesis,
University of Wisconsin, Madison, 1977.
24. Sullivan, R.J. Primary Air Pollution Survey on Odorous Compounds,
A Literature Review. NAPCA Pub. APTD 66-24, 1969.
25. Town of Old Saybrook, Connecticut, Old Saybrook Lagoon Summary,
1979.
35
-------
26. Winston-Salem, North Carolina, unpublished data.
27. Kreissl, J.F. Current Practices — Subsurface Disposal. Proceed-
ings — Microbial Health Considerations of Soil Disposal of Do-
mestic Wastewaters. EPA 600/9-83-017, NTIS Publication No. PB 84-
12210Q, September 1983.
28. Page, A.L. Fate and Effects of Trace Elements in Sewage Sludge
When Applied To Agricultural Lands. U.S. EPA Report No. 670/2-74-
005, NTIS No. PB 231171/AS, January 1974.
36
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CHAPTER 4
RECEIVING STATION. DESIGN
4.1 Introduction
The primary functions of a receiving station are: 1) transfer of sep-
tage from hauler trucks, 2) preliminary treatment of septage (i.e.,
screening and grit removal), and 3) storage and equalization of septage
flows. Receiving station design should encourage simple and reliable
operation, and have the flexibility to accommodate varying flow and
loading conditions.
The overall receiving station design varies with the amount of sep-
tage to be received, design of the tank truck, type of preliminary
treatment to be provided, downstream treatment and ultimate disposal,
and odor considerations or requirements. There are, however, certain
design elements that are fundamental in most receiving stations. These
are listed as follows:
1. Dumping station.
2. Screening.
3. Grit removal.
4, Storage/equalization.
5. Odor control.
Several variations in. receiving station design have been reported for
various treatment plants in Europe (1)(2), as shown in Figures 4-1,
4-2, and 4-3. These examples illustrate the application of several of
the basic design elements mentioned above; however, no one example em-
ploys all the elements of a recommended receiving station design. Fig-
ures 4-4 and 4-5 illustrate two variations of the basic recommended
design incorporating screening, grit removal, and equalization. The
specific provisions for septage dumping and odor control should be
noted as these are important elements of a receiving station design.
37
-------
FIGURE 4-1
RECEIVING STATION FOR SEPTAGE AT EKEBYHOV
TREATMENT PLANT, SWEDEN (1)
FIGURE 4-2.
RECEIVING STATION WHERE THE SEPTAGE IS FED TO
AN ANAEROBIC DIGESTER IN WEST GERMANY (2)
Building
Screen
Manhole
I Sprinkler System
| I ff*- Pipe for Flushing
.__» Forced Aeration
Sludge Supernatant to Plant Inlet
FIGURE 4-3
RECEIVING STATION INCLUDING SCREENING AND GRIT REMOVAL
AT LILLHAMMER TREATMENT PLANT, NORWAY (1)
Mechanically
Cleaned
Screen
Sprinkler
Receiving Channel
38
-------
FIGURE 4-4
RECEIVING STATION WITH PRETREATMENT PRIOR
TO EQUALIZATION (BATCH PRETREATMENT)
Odor Control System;
Carbon or Iron Oxide
Filter
Dumping Station
Inc!. Covered Pit with
Coarse Screen and
Hose Connection
Mechanically
Cleaned
Screen
Aerated Grit
Chamber or
Cyclone Degritter
To Treatment
Process
Pump
Station
Mixed
Storage Tank
(May be Combined With Aerated
Grit Chamber Unit)
FIGURE 4-5
RECEIVING STATION WITH EQUALIZATION PRIOR TO
PRETREATMENT (CONTROLLED RATE PRETREATMENT)
Buried Multiple Receiving/
Storage Tanks
\
k
f
1
V
r— n
(_
j
BO
Dumping Station
Incl. Open Pit with
Coarse Screen and
Hose Connection
Odor Control System;
Carbon or Iron Oxide
Filter
To Treatment Process
Mechanically
Cleaned Screen
Solids
Handling
Pumps
(Note: Pumping
Before Grit
Removal Should
be Avoided if Possible)
Aerated Grit
Chamber
39
-------
As shown in Figures 4-4 and 4-5, equalization tanks can be placed be-
fore or after pretreatment. The advantage of providing storage capacity
before pretreatment is that the grit chamber can be sized on the basis
of a controlled flow rate averaged over a specified period of time.
With pretreatment prior to equalization the grit chamber must have
sufficient aeration and flow capacity to handle the -maximum possible
hydraulic load per dumping. Also, aeration intensity may need to be
adjusted as the hydraulic loading rate varies. However, providing
equalization before pretreatment may necessitate pumping before the
septage has been degritted, which is generally not recommended. In
these cases, care should be taken in specifying pumping equipment
capable of handling grit. . . •
Pretreatment is not usually required when discharging to an interceptor
upstream of a plant, or when discharging to the headworks of a large
existing treatment facility with adequate pretreatment processes (see
Figures 4-6 and 4—7). Equalization is necessary when discharging di-
rectly to the head of a treatment plant in order to control the flow of
septage proportionately to sewage flow. Equalization is not generally
necessary when septage is discharged .to an interceptor at a point far
enough upstream of the plant -to permit complete mixing with the waste-
water, provided that the total quantity of septage discharged repre-
sents less than 1 percent of the sewage flow at that time and loca-
tion. This can be achieved by avoiding septage dumpings during daily
low-flow periods.
An example of a highly sophisticated remote receiving station which
provides for the discharge of septage to an interceptor sewer is shown
in Figure 4-8. This system is presently in use in West Germany (1). It
consists of one inlet'box and two manholes. The first manhole contains
a flow meter for measuring the volume of septage discharged to the
sewer. In addition, a test pipe for taking samples is connected to the
discharge pipe. The second,manhole serves as a rough grit chamber where
stones, etc. .will be collected. This material is removed manually as
often as necessary. The discharge system for septage is connected to a
control computer. The computer system is used for checking and record-
ing information on the septage entering the sewer system. Each user of
the system is issued a coded card that activates the equipment, ena-
bling septage to be discharged into the sewer. The equipment, with
printer, emergency power supply, display, keyboard, isolated signal
inputs and outputs, and a cardreader, is capable of determining "who"
may deposit "how much" of "what" into the sewage system. In addition,
it is possible to record the volume of septage deposited per user over
a period of time and to print out a list of all users and the quanti-
ties of septage deposited by each of them.
40
-------
FIGURE 4-6
INTERCEPTOR RECEIVING STATION
Manhole
\
Interceptor Sewer
Dumping Station
Include Pit with
Locking Cover and
Coarse Screen
FIGURE 4-7
RECEIVING STATIONS AT STP'S WHERE EXISTING PRETREATMENT
FACILITIES CAN BE USED TO TREAT SEPTAGE
Dumping
Station
C
I
Buried Receiving/
Storage Tanks
To Headworks
of Existing Treatment
Facility
Pump Station
(Note: Pumping Before Grit Removal
Should be Avoided if Possible)
41
-------
FIGURE 4-8
COMPUTERIZED INTERCEPTOR RECEIVING STATION (1)
Computer
Sampler
42
-------
When setting up user data records, it is possible to specify "check-
marks." This enables extra recording equipment (e.g., sample-takers or
pen-recorders) to be switched on when these particular users access the
system. The ability to define the times of the day or week when depos-
its by particular users are allowed makes this equipment suitable for
a wide range of waste management applications.
Upper and lower limits for each data input may be set so that if a
particular data value goes outside these limits, a message will be
printed and a relay operated to enable external action to be taken
(e.g., sample-taker switched in). The unit has an internal clock and
calendar and headlines all printed messages with the date and time.
The normal printout shows the values of up to a maximum of eight pos-
sible data inputs. This system enables the municipality to control the
septage quantity and quality that enters either the sewer system or
the wastewater treatment plant. Since no other such systems are known
to exist, it must be considered experimental.
Manual monitoring programs are far more common than automated systems
described herein. The most practical approach is to employ a registra-
tion system for each truck, e.g., plastic credit card acceptance device
which unlocks dumping station access, along with manual spot-check grab
samples by operators. Violations by haulers should be accompanied by
severe penalties.
Another variation in receiving station design may be appropriate where
the transfer or temporary storage of relatively small quantities of
septage is required. One example of such an application would be a
transfer station, as depicted in Figure 4-9, where septage from indi-
vidual hauler trucks is transferred to large tank trucks for transport
to a central treatment facility. A transfer/storage station can also be
used in conjunction with a land application operation where septage is
transferred to specialized application equipment. In this application
septage can be stored over short periods when weather conditions do not
allow land application.
Only authorized hauler trucks should utilize the facility, since this
provides for accurate recordkeeping of septage volumes handled at the
station and prevents system overloading. The haulers may discharge
their septage either under pressure (i.e., by pumping) or by gravity
(through a hose or free discharge).
4.2 Dumping Station
The dumping station is the initial point of reception of septage at a
receiving facility. It should have a slightly sloped ramp to tilt the
truck for complete drainage and facilitate hosing down of spillage to
a central drain. The basic layout of a dumping station is shown in
Figure 4-10 (4).
43
-------
FIGURE 4-9
SEPTAGE TRANSFER STATION (3)
y
^
,'rf •','
*~ Discharge
Trough
C
Gravity Transfer Arrangement
O
• Loading Rack With
Discharge Piping
and Hoses
Receiver - Long
Distance Tank
Truck or Land
Application Equipment
Transfer
Pumps
(Grit Tolerant Pumps)
Delivery Truck
Pumped transfer Arrangement
44
-------
FIGURE 4-10
BASIC LAYOUT OF DUMPING STATION (4)
J U L J
\
Out
Septage Transport Vehicle x
J 1 L j
!^B „,,„,, 3':0'
— r-
i
1
1
i
J.
I
Removable
./ Grate or Cover
>^
'*•
Pitch\
1
i
KA
»j. 1 S'-Q" k.
/
11'
(M
Meet Existing
Grade
Water Hydrant
(For Year-Round Use)
Meet Existing
Grade
Dumping Pit
With Coarse Screen
Profile at Cenierline of Pavement
11 "-O
" (Min)
Existing Grade
Dumping Pit
with Coarse Screen
Section A-A
Cone. Curb
-11'Min.-
Paved
Area
Meet Existing Grade El
-H
6" 3'-0"
Min.
Section B-B
45
-------
Hoses and other washdown equipment should be provided and should be
conveniently located at the dumping station to facilitate cleanup by
each individual hauler. Also, in colder climates, hot steam equipment
might be provided for thawing frozen valves, hose lines, etc.
The septage should be discharged through a hose extending from the rear
of the truck to the dumping station. The connection at the tank truck
must be water-tight in order to prevent spillage and odors. The hose
should be connected to a quick-release discharge tube in the dumping
station to minimize spillage. Figure 4-11 illustrates a recommended
dumping station inlet arrangement, based on several designs in Norway
(1). Heater cables are installed in the bottom of the chambers to pre-
vent freezing in the winter. The discharge tube should extend below
the liquid level in the receiving chambers to minimize the release of
odorous gases. The hose connection and discharge tube is generally 10
cm (4 in.) in diameter.
Discharge into a sewer requires dumping facilities similar to those
described previously. However, in many countries, manholes serve as
the receiving facility, often without any controls. An exception is
West Germany, where it is quite common to discharge septage into man-
holes, but only under very strict regulations regarding the receiving
flow and type of treatment plant downstream (1).
A dumping station should not be designed to allow tank trucks to back
up to the discharge point and release septage without any hose connec-
tion. This lends itself to substantial spillage and release of odors.
The amount of septage to be received and handled at a dumping station,
and the rate at which it passes through the pretreatment facility, must
be accurately estimated during the design phase. It is of utmost im-
portance to estimate septage volumes as accurately as possible and to
design the receiving facilities to handle the range of daily septage
flows expected. The limiting factor affecting a dumping station's peak
flow capacity may be the number of discharge points (i.e., unloading
docks and hose connections). Multiple discharge points might be con-
sidered where high traffic is expected during peak hauling periods.
Similarly, the access arrangement should permit efficient queing of
several pumper trucks in the dumping station area.
46
-------
FIGURE 4-11
RECOMMENDED DUMPING STATION INLET ARRANGEMENT (1)
Side Chamber With Full Opening for Trucks
Not Equipped With Proper Hose Fitting
/
Plan
View
Separate — -"
Covers — .
4-
tv
^ H
r\ '
^ i
1 \
™""""J y
/
Quick Disconnect
Fitting
11
Cover with Lock
Profile
Heater Cables
Quick Disconnect
Hose Fitting
Discharge Tube
Drainage for Flushing and
Cleaning of Tank
47
-------
4.3 Screening
Septage will generally contain various forms of untreatable debris such
as rags, plastics, sticks, stones, and cans. Such debris is separated
from the liquid septage by a coarse bar screen. The screen provides the
initial pretreatment of septage in order to protect unit processes
downstream. One receiving facility at Barnstable, Massachusetts in-
cludes a rock sump (or pit) in the receiving chamber, along with a bar
screen to remove a large portion of large debris and gravel present in
raw septage (5).
A mechanically-cleaned bar screen is desirable for all septage handling
facilities. Different types of mechanically-cleaned screens are in use
at plants receiving septage (see Figure 4-12}. It is important that the
bar screen be designed to handle larger quantities of screenings and
heavier material than an ordinary screen designed for sewage. As noted
in Figure 4-12, the mechanically-cleaned bar screen should have no
moving parts, such as chains, wheels, etc., installed below water
level. Experience in Norway shows that such designs cause considerable
operational problems (1). if a manually cleaned bar screen is unavoid-
able, it must be designed with a bypass (i.e., parallel screen cham-
bers) to permit operation during cleaning of a clogged screen. Simi-
larly, mechanically-cleaned screens should have provisions for bypas-
sing during repairs.
All parts coming into contact with septage should be made of stainless
steel. Mechanically-cleaned bar screens can be either front-cleaned or
back-cleaned. Also, models with fully rotating forks are manufactured.
The most common type is the front-cleaned model with an up- and down-
moving fork.
Operational problems due to overloading of a bar screen can be avoided
by designing the receiving chamber with a short channel, 2- to 3-m (6
to 10 ft) long, in front of the bar screen. This provides for more
uniform septage flow and avoids direct discharge of septage onto the
screen {i.e., dumping directly from hauler truck on the screen).
Another important design parameter involves spacing between the bars.
Too narrow spacing causes clogging and increased organic matter in the
screenings, while too wide spacing causes passage of larger objects
that should be removed at this point. The recommended space between
bars is 10 mm (0.4 in.) in Norway, while the openings in U.S. plants
are usually 19 to 38 mm (0.75 to 1.5 in.5. The U.S. opening has been
found to pass rags and other undesirable materials, but it would be
satisfactory if facilities that would remove or macerate the materials
were provided downstream (e.g., a fine screen or grinder pump).
48
-------
FIGURE 4-12
MECHANICALLY CLEANED BAR SCREEN AT DOKKA
TREATMENT PLANT, NORWAY (1)
lkn?\
(Note: The bypass channel on the right, and
the location of moving parts, i.e., chain drive,
above water level.)
49
-------
Pilot studies have been performed on vibrating fine screens (7) . Use
of a 6—mesh screen (3,4-nun opening) led to malfunctioning of the ap-
paratus due to hair becoming interwoven in the screen, resulting in
complete blinding. Better results were obtained using a 40-mesh vi-
brating screen (0.42-mm opening), with septage loading rates of 300 to
350 m-vm^/day (5 to 6 gal/ft^/min) . The screens provided an av-
erage total suspended solids removal greater than 70 percent. The
screenings volume approximated 3 percent of the original volume of
septage, and the resultant screenings had a moisture content of 50 to
75 percent.
The screenings from septage contain water, organic matter, grease, and
grit, in addition to rags, paper, plastic, and other coarse material,
It is recommended that the screenings be dewatered in order to facil-
itate handling prior to disposal. Different types of dewatering units
are manufactured. Smaller treatment plants receiving septage most
often use a drained screw conveyor to, transport screenings from the
bar screen to a container for disposal (see Figure 4-13). Presses
designed for dewatering screenings are also commercially available.
These presses have been used quite successfully on material from
screens handling septage.
4.4 Grit Removal
In septage, grit consists of material such as sand, gravel, cinders,
and food particles that become enmeshed in the lighter-weight organic
matter and grease, making separation of the grit from septage quite
difficult. Grit content of septage may be higher than normal in areas
with sandy soils and cesspools. The experience in Norway shows that
after the septage passes the screen, it should flow by gravity into the
grit chamber (1). A pumping step must be avoided, if possible, upstream
from the grit chamber because grit material will tend to wear the pump
impellers, causing undue operational problems. If this cannot be
avoided, recessed-impeller or other grit-resistant pumps should be em-
ployed. Enclosed screw pumps might also be considered in these situa-
tions .
The two general types of grit chambers are the horizontal flow type and
the aerated type. The horizontal flow type was more common in the past,
but the aerated chambers have been found to be more effective in sep-
tage treatment applications (1), The horizontal flow type grit chamber,
which accomplishes particle settling by controlling flow, is not ef-
fective at removing grit in septage since the grit particles are em-
bedded into and attached to scum and solids that do not settle at the
prescribed velocities.
50
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FIGURE 4-13
DRAINED SCREW CONVEYER USED FOR DEWATERING
MATERIAL FROM THE BAR SCREEN
51
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In the aerated grit chambers, diffused air is pumped into the chamber
to cause a spiral flow motion that enhances the breakup and ultimate
settling of grit. Figure 4-14 shows the theoretical spiral motion
present in aerated grit chambers, and Figure 4-15 presents a typical
cross-sectional view. Basic design data for aerated grit chambers are
given in Table 4-1. For the most part, the same design criteria apply
to septage applications, except that longer detention times appear to
be warranted.
TABLE 4-1
TYPICAL DESIGN INFORMATION FOR AERATED GRIT CHAMBERS (6)
Item
Range
Value
Typical
Dimensions:
Depth, m (ft)
Length, m (ft)
Width, m (ft)
Detention time at peak
flow, min
Air supply,
m^/min • m of length
(ft3/min « ft)
Transverse velocity
m/sec (ft/sec)
2-5 (7-16)
7.5-20 (25-66)
2.5-7.0 (8-23)
2-5
0.3-0.6 (3.6-7.2)
0.4-0.7 (1.5-2.0)
0.5 (6.0)
0.6 (1.8)
In Norway, aerated grit chambers are the generally recommended method
of removing grit from septage. An aerated grit chamber treating sep-
tage at the Lillehammer Treatment Plant, shown earlier in Figure 4-3,
represents a typical design. The grit chamber has a volume of 55 m3
(14,530 gal) and handles a maximum load of approximately 80 nP
(21,130 gal) of septage per day. The detention time is longer than
that ordinarily used, as compared to a normal design detention period
of 3 minutes at the maximum flow rate suggested by standard design
criteria. The maximum load on the grit chamber occurs when the largest
size tanker truck pumps its content of septage through the pretreat-
ment units. Under these conditions, the detention time in the grit
chamber is designed to be not less than 30 minutes (1).
52
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FIGURE 4-14
HELICAL FLOW PATTERN IN AERATED GRIT CHAMBER (6)
Helical Liquid
Flow Pattern
Outlet Weir
Trajectory of
Grit Panicles
FIGURE 4-15
TYPICAL SECTION THROUGH AERATED GRIT CHAMBER (6)
FIGURE 4-16
AERATED <5RIT DEWATERING UNIT PLACED ABOVE THE GRIT
CHAMBER, AT LILLEHAMMER TREATMENT PLANT, NORWAY (1)
Hose Connection
Receiving Channel
Aeration System
Centrifugal Pumps lor Grit Removal
53
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The grit is collected in hoppers at the bottom of the basin. It can be
removed with a centrifugal pump, a screw conveyer, etc. At the Lille-
hammer Treatment Plant, the grit is removed by centrifugal pumps. Gen-
erally, this grit material should be dewatered before ultimate dis-
posal. The dewatering unit (see Figure 4-16) consists of a small aer-
ated tank with a dewatering screw that moves the material up an incline
and drains the water back to the tank. The tank is supplied with an
overflow that drains back to the grit chamber (1). Several commercial
grit washing, dewatering and conveying systems are available.
At several plants in Scandinavia, the grit chamber has been designed
with enough capacity to serve as a combined holding tank and grit
chamber. The water level in the tank will vary, depending on the daily
routine with respect to dewatering, etc. This is not recommended,
since the change in water level will automatically change the aeration
intensity, etc. This change in aeration will alter the spiral flow
pattern and separation/ settling of grit from the liquid septage, and
thus reduce the effectiveness of the grit chamber. Also, additional
attention must be given to operation of the air diffusers to adjust
for changes in water level, which is not a practical situation.
Cyclone degritters (see Figure 4-17) may also be effective in the
pretreatment of septage since the mixing action achieved is similar to
that in an aerated grit chamber. These degritters are designed to op-
erate in a batch operation mode, which is suited to applications where
septage is treated as it is dumped from the hauler trucks. An added
advantage of the cyclone degritter is that it should generate less odor
than an aerated grit chamber since no forced aeration takes place. The
primary design control factor is flow velocity which is governed by the
pumping units feeding the degritter. The solids concentration should be
less than 2 percent for a cyclone degritter to function property (17).
Individual loads of septage may exceed this limit and may require
equalization or dilution. Cyclone degritters may not be appropriate if
average solids concentration is greater than 2 percent.
The grit removed from septage can be handled in a number of ways. Grit
is normally hauled to the dumping areas in trucks for which loading
facilities are required. In larger plants, elevated grit storage
facilities may be provided with bottom gates through which the trucks
are loaded. Difficulties experienced in getting the grit to flow free-
ly from the storage hoppers have been minimized by applying air beneath
he grit and by the use of vibrators. Facilities for collection and dis-
posal of drippings from the bottom gates are desirable. Grab buckets
operating on a monorail system may also be used to load trucks directly
from the grit chambers or from storage bins at grade.
54
-------
FIGURE 4-17
CYCLONE DEGRITTER
Inlet Nozzle
Overflow (To Treatment Process)
Grit (To Grit Washer)
55
-------
In some larger plants, grit is successfully conveyed to grit-disposal
areas by pneumatic conveyers. This system requires no elevated storage
hoppers and eliminates problems in storage and trucking, but the wear
on piping, especially elbows, is considerable (6).
4.5 Storage and Equalization
Septage holding basins can be used to provide for storage, equaliza-
tion, mixing, and/or aeration of the septage prior to further treat-
ment* Such holding facilities allow a controlled outflow of septage to
downstream treatment processes in order to prevent hydraulic and or-
ganic shock loading.
The design of a holding facility depends on the prior and subsequent
treatment of the septage. The most economical design is an open hold-
ing lagoon (sometimes aerated). Lagoons, however, require considerable
land area and may create odor problems. The ultimate disposal of set-
tled solids is also of concern since it is difficult to maintain com-
plete mixing in lagoons. For treatment at an existing treatment fa-
cility or at independent septage treatment facilities, enclosed tanks
with provisions for mixing and aeration are generally recommended to
control spillage and odors. However, in situations where long-term
storage is required (e.g., during the off-season in land application
systems), lagoon storage may be the only feasible means of holding
large volumes of septage. The design volume of the holding lagoon is
dependent on the required holding time. This holding time may range
from several weeks to several months for land application operations.
The role of holding tanks (where septage is handled independently or
at existing wastewater treatment facilities) is mainly to equalize
flow and mitigate variations in septage characteristics from one load
to the next. In co-treatment applications, a holding facility is
necessary to allow proper metering of septage addition as a function
of treatment plant flow. If the septage is to be added directly to a
sewer or to a primary treatment train, mechanical or diffused-air
aeration and mixing are desirable in the holding tank to improve
treatability and prevent settling of organic solids. However, this
tends to aggravate the odor problem (due to the air stipping effect),
and therefore requires the use of enclosed tanks to control odors.
The major design criterion for a holding tank is detention time. As a
rule, capacity of at least one day's maximum expected volume of sep-
tage should be available for storage; however, it may be highly desir-
able to have storage for several days' peak flow, depending on the
56
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sensitivity of downstream treatment processes and the expected varia-
tion in septage volumes received for treatment. The design of the
equalization basin is site-specific and dependent on the type and mag-
nitude of the input flow variations and facility configuration. If
other preliminary treatment functions, such as preaeration, are to be
performed in conjunction with flow equalization, then adequate deten-
tion times for these functions should be taken into consideration. He-
suits of pilot studies, shown in Table 4-2, revealed negligible changes
in the characteristics of finely-screened septage after 24 hours of
aeration (7). After 96 hours of aeration, however, significant changes
occurred, including improvement of settling characteristics and reduc-
tion of 6005. A holding facility, however, is not intended to pro-
vide this level of treatment, therefore detention periods of less than
48 hours are generally recommended.
Additional design criteria for preaeration facilities include the rate
of air addition, or mixing. Mechanical mixing has been recommended at
0.0071 to 0.0142 kW/m3 (20 to 40 hp/Mgal) of storage, and aeration
at 0.15 to 0.24 L/m3 • S (1.2 to 2 cfm/1,000 gal) of storage (9).
Based on pilot-scale studies, Eikum (1) recommends using 1.3 to 1.7
L/s of compressed air per min/1,000 m3 (10.7 to 13.4 cfm/1,000 gal)
of tank volume to ensure mixing of screened septage.
TABLE 4-2
SCREENED-RAW-SEPTAGE SUPERNATANT CHARACTERISTICS
FOLLOWING AERATION AND TWO HOURS SETTLING (7)
Aeration Period
Parameter 0 Hours 24 Hours 96 Hours
TSS , mg/L
BODs, mg/L
NH3-N, mg/L
Organic-N, mg/L
PO4 , mg/L as P
8,680
5,850
64
204
57
9,550
5,210
49
249
45
1,480
295
6
33
4
57
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4.6 Odor Control
Designers of septage receiving facilities must address odor control
during the design process rather than as a retrofit measure in response
to pressure from nearby residents. Odor problems at septage receiving
facilities can be solved by proper siting and existing technologies,
including chemical scrubbers, filters, combustion, biological proc-
esses, etc. It is very important to identify the main sources of odor
at the facility and treat only the odorous gases. A simple approach to
isolating the odorous gases would be to enclose the component of the
facility generating the odors. The gases would be confined in this
housing structure and thereby isolated from non-odorous air. This will
reduce the volume of air to be treated and thus the overall cost. De-
signers must be cognizant of the dangers of closed spaces to operating
personnel. The following sections discuss various methods for odor
control.
4,6,1 Siting
During the site—selection process, consideration should be given to
the impact that offensive odors may have on nearby residents. Zoning
ordinances and land development patterns must be reviewed. An isolated
area, if residentially zoned, may develop in the near future and result
in pressure being applied to retrofit a facility with expensive odor
control devices. In siting a facility without odor control, care should
be taken to locate the facility in a well-ventilated area (e.g., an
open space on a hilltop) and downwind from existing or projected pop-
ulation centers. Provisions for adding odor control systems in the
future should be considered.
4.6.2 Chemical Scrubbers
Chemical scrubbers use sodium hypochlorite as an oxidizing agent and
have been used successfully in controlling odors from sewage treatment
plants receiving septage. Single-stage, two-stage, or three-stage
scrubbers have been used. In Figure 4-18, a two-stage scrubber is
shown. The first stage is alkaline oxidation (NaOH + NaOCl), and the
second stage is an acidic wash using H2SO4. Automatic dosage
systems are a necessity in preventing accidents when using the con-
centrated chemicals required for this system. Another type of chemical
scrubber used at treatment plants that receive septage (shown in Figure
4-19), generates sodium hypochloride by electrolysis of salt (NaCl).
Because this scrubber produces hypochlorite and no acidic step is
involved, there is less need for special care concerning the delivery,
handling, and dosing of dangerous chemicals.
58
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FIGURE 4-18
CHEMICAL SCRUBBER (TYPE STEULER) (1)
I
Wfflfc.
• Cleaned Air
• Mist Eliminator
4
w
^
t • ttttSfi ««»«t«
I
.4«»4.A««#«*i"
1
t
/^
tttl
1
1 1 r
2 Stage -Acid
1 Stac
^ Incoming Air
Liquid Reservoir
FIGURE 4-19
CHEMICAL SCRUBBER (TYPE PEPCON) (1)
Cleaned Air
Solution of Water/Hypochloride
X
Hypochloride Generator
Power Supply
DD DD
DD
Incoming Air
U
Water
59
-------
The results from total odor strength measurements of different chem-
ical scrubbers show odor reduction efficiencies between 95 and 98 per-
cent (1). The air has been characterized as being "free from sewage
odors, but it smells like chemicals." It seems as if a chemical scrub-
ber always gives this "scrubber odor." If the scrubber, however, is
incorrectly operated, this "scrubber odor" changes to a "chlorine
odor." Cost for operating the chemical scrubbers can be divided into
chemical cost and energy cost. Energy will always contribute most to
the total cost of operation. For the two-stage Pepcon scrubber, the
energy cost will be approximately two-thirds of the total operational
cost. Although some simpler types are available, chemical scrubbers
are generally applicable only at larger treatment plants, where bio-
logical methods of control are not feasible.
4.6.3 Activated Carbon Filters
Carbon filters do not destroy the odor compounds, but only retain them
until the carbon becomes saturated. The depth of the carbon bed must be
sufficient to assure complete odor removal and to. provide excess capac-
ity. The Calgon Corporation recommends a depth of 45 to 90 cm (18 to
36 in.) in order to achieve maximum removal efficiency (8). Since most
odors are caused by a mixture of gases, the possibility exists that
odorous compounds not readily adsorbed by the carbon may leave the
filter. Flow rates must be carefully selected to ensure adsorption of
all compounds. The activated carbon has varying capacity to hold a
specific amount of different odorous compounds, and it may be diffi-
cult to predict when the filter will become saturated. Inspections at
different Norwegian plants identified carbon filters that either
should have been changed earlier, or filters that were changed too
frequently, which can become very expensive (1). In Figure 4-20 an
activated carbon filter used for cleaning exhaust air from a dewa-
tering process is shown. Together with the carbon, the equipment in-
cludes a grease filter and a condensation unit.
Odor strength measurements indicated reduction efficiencies of up to
83 percent when a completely new filter was used (1). Alternately, an
old filter being used twice as long as the manufacturer recommended
showed reduction efficiencies of only 72 percent. The cleaned air from
activated carbon units may still have a sewage smell at these effi-
ciencies. When the filter becomes saturated, no reduction of odors
occurs in the activated carbon units. Carbon filters are applicable to
all sizes of septage handling facilities although cost may become a
limiting factor for larger facilities.
60
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FIGURE 4-20
CARBON FILTER FOR ODOR REDUCTION (1)
Cleaned Air
Exhaust Air
Activated Carbon Unit
Grease Filter Condensing Unit
Condensing Water
61
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4.6.4 Other Filter Media
Extensive work has been carried out in the U.S. (9) and Europe
(10)(11)(12) regarding the use of soil filters for odor reduction.
Filter performance depends on filter loading, type of soil, soil
moisture, and temperature and concentration of odorous components. The
odor removal mechanism taking place in the filter is both chemical and
biological. Figure 4-21 illustrates the typical placement of a soil
filter at a septage receiving facility. Another example of a soil
filter system is depicted in Figure 4-22. This soil filter design was
applied to control pump station odors in Mercer Island, Washington
(13). Specifications for the Mercer Island design are given in Table
4-3 as an example of soil filter design criteria.
TABLE 4-3
SPECIFICATIONS FOR FUTURE SOIL FILTERS AT MERCER ISLAND,
WASHINGTON PUMPING STATION (13)
Flow Soil Filter Area Perforated Pipe Length*
(L/s) (gpm) 1m7) :7ft2!(m) (ft)
<50 <800 2.3 25 0.3-3.0 1-10
50- 115 800-1,800 4.6 50 0.6 -3.0 2-10
125- 160 2,000-2,500 9.3 100 1.2 -3.0 4-10
*10 cm (4 in.) pipes, bottom perforated and laid 0.6 m (2 ft) deep on
0.76 m (2.5 ft) centers and in 20 cm (8 in.) of pea gravel.
Laboratory studies have been performed to determine the efficiency of
hydrogen sulfide gas removal by various soil types (13), It was found
that odor reduction is achieved primarily by biological oxidation of
sulfide to sulfate. An increase in conductivity and decrease in pH due
to this process makes buffering a consideration in order to maintain
satisfactory environmental conditions for bacterial activity. The most
effective soils were moist loam soils kept at a temperature of about
25 to 30°C. The moisture is necessary to sustain life in the soil
and to dissolve the sulfide gas to facilitate utilization by the bac-
teria. In West Germany this was done by installing sprinklers that were
62
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FIGURE 4-21
FULL-SCALE SOIL FILTER AT TAU TREATMENT
PLANT, TONSBERG, NORWAY (1)
Chimney
Screen/ Fan Control
t- 0 100 mm Pipe
Storage Tank (Closed)
FIGURE 4-22
SOIL FILTER SYSTEM - MERCER ISLAND, WA
PUMP STATION ODOR CONTROL (13)
Manometer Capacity = 60 in. Water
Galvanized Steel Pipe
x Ground Surface
i 10 ft. Pertoraled i
p Avg. 1 hole/in, (%-in,) *|
'wjjgswa
20-It. Length, 4-in. Wire Reint. Flexible
Plastic Pipe (House-Trailer Sewer Type)"
J
Loamy, Fertile Topsoil
%e *-»- Existing Soil Clay Sand Mixture
I >-
(Appears Impervious)
K-in. minus Pea Gravel
- 4-in. Perforated Plastic Pipe
63
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activated when moisture dropped below a certain level (1) . Sands and
clays were much less effective in the passage of moisture and gas
through the soil column. The tests indicated that a maximum concentra-
tion of 15 mg/L hydrogen sulfide could be input to a filter if H2S
emanating from the soil filter is to be kept below the threshold odor
limit (see Figure 4-23).
A full-scale soil filter was put into operation in the summer of 1981
at Tonsberg, Norway (see Figure 4-21) (1). The filter treats odors from
the receiving facility for septage only. This facility handles 14,000
m^ (3.7 x 10^ gallons) of septic tank pumpings annually. It con-
sists of screening, grit removal, a storage basin, and dewatering
equipment. The fan inlet is located at the end of the storage basin so
that the odorous air is evacuated through the screen and grit removal
room and into the storage basin. The fan blows the air either through
the soil filter (normal operation) or through the chimney (in case
filter media must be changed).
The filter consists of 35 m2 (375 ft2) of filter area, 0.5 m (20
in.) thick. The air is distributed through a diffuser system with a
0.4-ro (16-in.) header pipe with 10-cm (4-in.) diameter laterals. The
pipes are located in the gravel layer. The air flow through the filter
is 565 L/s (1200 cfm) under constant operation. When a tank truck emp-
ties septage at the plant, the screen automatically goes into oper-
ation, and the fan speed increases to a capacity of 850 L/s (1800 cfm).
When the screen stops, the fan capacity is again reduced to 565 L/s.
The filter loading therefore varies between 57 and 86 m3/ni2/h (187
to 282 ft3/ft2/h). Components of the filter are shown in Figures
4-24 and 4-25. Up to September 1983 no odors had been detected out of
the filteri however, any conclusions regarding long-term performance
are premature.
Design parameters for soil filters from various studies are summarized
in Table 4-4. Eikum (1) concluded in his study that a soil filter
treating odors from a wastewater treatment plant with septage handling
should not be designed with a detention time of less than 30 seconds.
As shown, Helmer and Frechen concluded that compost, rather than soil,
can be used as filter media.
Guidelines for the replacement of soil filters are very limited. How-
ever, it has been suggested that the filter actually regenerates itself
during periods when no odorous gases are passing through it (1). Sys-
tems with high H2S mass loadings may require soil liming and water-
ing to maintain pH and moisture content in optimum ranges. Energy re-
quirements are generally low, with effective pressure drops in the
range of 5 cm (2 inches) (water).
64
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FIGURE 4-23
EFFECT OF INPUT CONCENTRATION ON HYDROGEN SULFIDE
REMOVAL EFFICIENCY BY SOIL FILTERS (10)
80
C
.2 60
•5
cc
(/> 40
n
/
A-
/
/
i Thre-
£ J
/
H2S In Soil
Filter Out
i-.hold Odor
put
) 10 102 103 104 105
H2S In Input to Filter - PPM
o.
a.
•>
3 Q.
i*tf
o
0)
2 E
_c
O)
65
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FIGURE 4-24
SOIL FILTER INSTALLATION (LOCATED BEHIND
BUILDING) AT TAU TREATMENT FACILITY (1)
FIGURE 4-25
AIR COLLECTION AND BLOWER EQUIPMENT AT TAU FACILITY (1. GAS INLET,
2. FAN, 3. BYPASS PIPE TO CHIMNEY, 4. PIPE TO SOIL FILTER) (1)
66
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TABLE 4-4
DESIGN PARAMETERS FOR SOIL FILTERS USED FOR ODOR REDUCTION (1)
Reference
Air Loading Rate
3 2
(m /m /h) Detention Time
Facility Soil Compost (sec.)
Carlson, et al. (13) Test 6 500
Helmer (12) Test 1.4 30-100
Eikum (11) Test 18 80
Mayo (14) Full scale 35-90 20- 40
Frechen (15) Full scale 45 75
The use of soil filters is best suited to small installations with gas
flows less than 22 nrVsec (50,000 cfs) . Applications involving larg-
er volumes of odorous gas should be investigated on a case-by—case
basis.
Another type of filter utilizes an iron oxide/woodchip media. The de-
sign and use of iron oxide filters for odor reduction is not well doc-
umented. Eikum (11) studied the use of an iron oxide filter at a re-
ceiving facility for septage in Norway. The filter media included
woodchips mixed with 0.2 kg Fe2C>3 per kg chips. Chemical processes
(ferric sulfide production) are primarily responsible for the odor re-
duction taking place in the iron oxide filter. A filter installed at
the City of Oslo at its Festningen Municipal Treatment Plant recorded
high odor removal rates with loadings up to 250 m3/m2-h (820
ft3/ft2«h).
4.6.5 Combustion
Combustion of odorous gases from a wastewater treatment plant has been
a common practice for a long time. If" temperature and contact time of
the gases in the combustion chamber are sufficient (temperatures of
about 850°C (1562°F) , and contact time of up to 3 seconds) , odor
reductions of up to 98 to 99 percent may be achieved. A special incin-
erator designed solely for odors at a septage receiving facility, or
even at an independent septage treatment facility, would be very expen-
sive compared to the use of chemical scrubbers. If, however, sludge
gas from a digester at a large treatment facility is available, the
fuel costs can be reduced. The addition of catalysts can lower the
temperatures needed to destroy odors and further reduce fuel costs.
67
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4.6.6 Addition of Odorous Gases To Biological Treatment Systems
Limited success has been reported in reducing odors at a Norwegian ac-
tivated sludge wastewater treatment plant receiving septage by bubbling
odorous gases into the aeration basin (1) . In the United States, this
method of odor control has been successfully practiced at Los Angeles
since 1959 (16). The odorous gases are drawn from the septage storage
area and blown into the activated sludge basin. The method is very
inexpensive and has odor reduction efficiencies of about 90 percent.
Acid-resistant air distribution piping is generally required to resist
corrosion.
This approach has also been applied at trickling filter plants with
mixed results. The design requirements for successful odor control in-
clude a media depth of at least 6m, air retention time of at least 10
seconds, and trickling filter operation in the nitrification stage,
along with underdrain construction of corrosion-resistant materials
(16).
4.6.7 Other Odor Reduction Methods
Many other methods to reduce odors have been used successfully at.
wastewater treatment facilities. These include the use of ozone, oxy-
gen, H202' °<3or counteraction, and odor masking. These methods
have not been applied extensively in connection with septage treatment
and will not be discussed further in this handbook. However, these al-
ternatives may be worth further evaluation where existing equipment at
an operating facility can be utilized.
4.7 References
1. Eikum, A.S. Treatment of Septage - European Practice (Draft). Nor-
wegian Institute for Water Research, EPA Contract Number 68-03-
2971/ Municipal Environmental Laboratory, Cincinnati, Ohio, 2 Sep-
tember 1983.
2. Baumgart, P. Sairanlung, Behandung, Beseitigung, und Verwertung von
Schlammen aus Hausklaranlagen. Technische Universitat Munchen (Un-
published) , 1981.
3. Concept Engineering Report - Septage Management Facilities for
Ocean County Utilities Authority. Roy F. Weston, Inc., October
1980.
4. Kolega, J.J., A.W. Dewey, and C.S. Shu. Streamline Septage Re-
ceiving Stations. Water and Wastes Engineering, July 1971.
68
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5. Whitman and Howard, Inc. A Study of Waste Septic Tank Sludge Dis-
posal in Massachusetts. Division of Water Pollution Control, Water
Resources Commission, Boston, Massachusetts, 1976.
6. Metcalf and Eddy, Inc. Wastewater Engineering: Treatment/Dispos-
al/Reuse, 2nd Edition. McGraw-Hill, New York, New York, 1979.
7. Condren, A.J. Pilot-Scale Evaluations of Septage Treatment Alter-
natives. EPA-600/2-78-164, NTIS Publication No. PB -288415
September 1978.
8. The Calgon Corporation. Effective Odor Control with Calgon Granular
Activated Carbon Systems. Pittsburgh, Pennsylvania, 1981.
9. U.S. Environmental Protection Agency. Innovative and Alternative
Technology Assessment Manual. U.S. EPA Report No. 430/9-78-009
(MCD-53), NTIS Publication No. PB 81-103277, February 1980.
10. Pfeffer, H. Minderung von Geruchsstoffemissionen aus Stationaren
Anlagen. Lecture at the Colloquium, Wiesbaden, May 1981.
11. Eikum, A.S. Reduksjon av lukt fra mottakeranlegg for septikslam.
Proceedings NIF-kurs, Fagernes, Norway, 1976.
12. Helmer, R. Desodorisierung von geruchsbeladener Abluft in Boden-
filtern. Gesundheits-Ingenieur, 95, HI, 1974.
13. Carlson, D.A. and C.P. Leiser. Soil Beds for the Control of Sewage
Odors. Journal of Water Pollution Control Federation, 34: 829-
840, 1966,
14. Mayo, R. Mercer Island Sewer District — Odor Control Study.
Unpublished Report, 1962.
15. Frechen, B. Kompostwerk Huckinger der Stadt Duisburg. Stadtrein-
gungsamt Duisburg, 1967.
16. Pomeroy, R.D. Biological Treatment of Odorous Air. Journal of
Water Pollution Control Federation, 54, 1982.
17. U.S. Water Pollution Control Federation, Manual of Practice No. 8,
Wastewater Treatment Plant Design, 1977.
69
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CHAPTER 5
LAND DISPOSAL
5.1 Introduction
Land application of septage is the most frequently used technique for
septage disposal in the United States today. Septage treatment and
disposal techniques include land spreading from septage hauler trucks
or transfer vehicles such as tank wagonsj spray irrigation; ridge and
furrow irrigation practices; and overland flow. Subsurface application
techniques include plow furrow cover and subsurface incorporation al-
ternatives. Placement in trenches, holding lagoons, and sanitary land-
fills are classified as burial practices. Septage applied to the land
can be stabilized, dewatered, or both, or can be applied without any
pretreatment under certain conditions. Figure 5-1 illustrates the var-
ious technical options to be considered in evaluating land application
alternatives. Properly managed land application is relatively simple,
generally the most economical disposal technique, and can make bene-
ficial utilization of the nutrient value of septage. It should continue
to be a very common means of disposal, although Federal and state reg-
ulations are placing additional restrictions on its use, particularly
in regard to pathogen control in agricultural land application. Fed-
eral Criteria (4) define the terms "Processes to Significantly Reduce
Pathogens" (PSBP) and "Processes to Further Reduce Pathogens" (PFRP).
PSEP is defined by the following technologies; aerobic digestion,
anaerobic digestion, air drying, composting, lime stabilization, or
other techniques which yield similar pathogen reductions. PFRP is de-
fined by the following technologies: beta or gamma ray irradiation,
pasteurization, or other equivalents after a PSRP process or high-
temperature composting, heat drying, heat treatment, and thermophilic
aeration digestion.
5.2 Raw Septage versus Septage Residuals (Sludge)
Currently, as much as two-thirds of the septage generated in this
country is disposed of directly on land. Land application of raw
septage has created concern over the transmissibility of various
pathogenic agents that may be found in septage (viruses, bacteria,
70
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FIGURE 5-1
TECHNICAL OPTIONS FOR LAND APPLICATION OF SEPTAGE
PSRP/PFRP
(Independent Septage
Treatment Facilities]
Transfer
Station
Tractor-
Wagon
PSRP/PFRP
(Independent Septage
Treatment Facilities)
Land Spreading
Landfill
Trench/ Lagoon Burial
Subsurface Incorporation
Receiving/
Holding
Facility
Pumping/
System
Spray Irrigation/Overland Flow
-------
cysts of protozoans, and ova of helminths) . In response to this con-
cern, regulations at various governmental levels are being promul-
gated that will require some form of pretreatment. Ultimate disposal
of the resultant solids fraction, liquid fraction, or the combined
mass from pretreatment processes is likely to be in some form of land
application.
Disposal alternatives that are applicable to the solids fraction, li-
quid fraction, or the combined liquid/solid mass are listed in Table
5-1 and are discussed in the following sections. The methodologies for
determining application rates are presented for the combined liquid/
solid mass. The same procedure could be applied to the solids fraction
by using the concentrations of nutrients or metals in mg/kg of sludge
instead of mg/L of raw septage.
5.3 Disposal Options
A number of techniques that are available for applying septage to the
land are briefly discussed as follows.
5.3.1 Surface Application
Land Spreading; The hauler truck that pumps out the septic tank is
frequently the vehicle that applies septage to the land. However, sep-
tage may be applied to the land in the raw liquid form or as septage
solids by a separate designated vehicle. Consideration should be given
to intermediate holding facilities during periods of inclement weather
when application of septage is impossible due to field conditions, or
when it would result in contaminated runoff escaping from the site.
Pathogen die-off during storage is an additional benefit gained from
onsite storage.
With a storage or transfer facility, disposal can be performed either
by the hauler truck or by a tank wagon pulled by a tractor. The choice
between the two is one of economics. A larger septage hauling/disposal
operation may choose to have its hauler trucks on the road, with sep-
tage spreading being performed by a separate spreading crew, thus
freeing the tank truck to perform the septic tank cleanout functions.
A smaller septage hauler may prefer to use one vehicle to perform both
tasks, thus leveling the work load by spreading septage during slack
hauling time periods. In some instances, soil conditions may require
the use of flotation-type tires, which are not suitable for long-dis-
tance highway use. This would dictate the use of separate collection
and spreading vehicles (1) .
72
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TABLE 5-1
CHARACTERISTICS OF LAND DISPOSAL OPTIONS (1)
Characteristics Advantages Disadvantages
Form of
Land Disposal Method Septage
Surface Application
Spray irrigation*
Ridge and furrow
irrigation*
Overland flow*
Large orifices for
nozzles.
L Surface preparation
and leveling
required.
Usa on steep or
rough land.
Lower power
requirements than
spray irrigation.
Large land area.
High power
requirements.
Odor potential.
Possible pathogen
dispersal.
Storage lagoon for
pathogen destruction
and during periods of
wet or frozen ground.
Irrigation lines to be
drained after
irriagation season.
Limited to 0.5 to 1.50
slopes,
Storage lagoon
required.
Some odor potential.
L
Use on sloping
ground with
vegetation.
Can be applied from
ridge roads,
suitable for
emergency operation.
Difficult to get
uniform distribution.
Extensive site
preparation.
Slopes limited to
Hauler truck spreading*
Farm tractor and wagon
spreading*
1,9 to 7.6 m»
(BOO to 2.000 gal)
trucks.
L/S 3.01011.4m1
(300 to 3,000 gal)
capacity.
Subsurface Incorporation
Tank truck with plow
and furrow cover*
Single furrow plow
mounted on truck.
73
Same truck can be
used for transport
and disposal.
Frees hauler truck
during high usage
periods.
Minimal odor.
Some odor immediately
after spreading,
Storage lagoon during
periods of wal or frozen
ground.
Slopes limited to 8%.
Larger volume trucks
require flotation tires.
Land requires rest
between applications.
Some odor immediately
after dispersal.
Storage lagoons.
Slopes limited to 8%..
Requires additional
equipment.
Land requires rest
between applications.
Slopes limited to 8%,
Storage lagoon during
wet or frozen ground.
Longer time needed for
disposal operation.
-------
TABLE 5-1 (Continued)
Land Disposal Method
Farm tractor with plow
and furrow*
Subsurface injection*
Burial
Trench
Disposal lagoon
Sanitary landfill
Form of
Soptage Characteristics
L Saptage discharge
into furrow ahead
of single plow.
Septaba spread in
narrow swath and
immediately covered
with plow.
L Septage placed in
opening created
by tillage tool.
Keep vehicles off
area for 1 to 2 weeks
after injection.
L/S New trenches
opened whan old
one filled and
covered.
L Lagoon is filled and
dried, then covered
with soil; or sludge
bucketed out to
lendfill from bottom
of septage lagoon.
L/S Septege mixed with
solid wastas at
controlled rates.
Advantages
Minimal odor.
Injector can mount
on rear of some
trucks.
Simplest
operation.
No slope limits,
No climatological
limits.
No slope limits.
No climatological
limits.
No topographic
limits.
Simple operation.
Disadvantages
Slopes limited to 8%.
Longer time needed
than surface disposal.
Storage lagoon during
wet or frozen ground.
Slopes limited to 8%.
Longer time needed for
dispersal.
Not usable in wat.
frozen, or hard
ground.
Odor problems.
High groundwater
restriction.
Long-term land
commitment after
termination of
operation.
Odor problems,
High groundwater
restrictions.
Potential vector
problems.
Odor problems.
Rodent and vector
problems.
Leaching lagoons
L Settled water
usually flows to
percolation-
infiltration beds.
Sludge bucketed out
to landfill from
bottom of lagoon.
Multiple lagoons
required.
No slope limits.
No climatological
limits.
Limited to areas with
less than 90 cm/year
(35 inches) of
precipitation.
Rainfall or leachate
collection or isolate
from groundwater.
Odor problems.
High groundwater
and soil permeability
restrictions.
Vector problems.
•May require PSRP or PFRP. depeding on crop selection and management practices.
U Liquid Raw Septage.
S; Saptaga Sludge.
74
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Spray Irrigation; Spray irrigation of liquid septage necessitates a
storage lagoon prior to disposal. Portable pipes and nozzle guns are
commonly used rather than fixed or solid sets (see Figure 5-2). Since
the septage must be pumped at 80 to 100 psi through 3/4- to 2-inch
nozzle openings, installation of a screening device either at the
transfer station ahead of or on the lagoon pump suction line is man-
datory in order to prevent clogging of the distribution nozzles. Since
spray irrigation also offers the greatest potential for offensive
odors, knowledge of wind patterns and a well-located site are im-
portant.
Ridge and Furrow Irrigation; This method of disposal has been used to
dispose of septage on relatively level land, usually limited to slopes
in the range of 0.5 to 1.5 percent (see Figure 5-3). This method can be
used to distribute septage to row crops during their growth, provided
the crops are not for direct human consumption.
Overland Flow; This method was studied as part of an overall septage-
sewage and septage-sewage-sludge treatment system at the Brookhaven Na-
tional Laboratory in Upton, New York (10). The overland flow field, as
part of a meadow-marsh-pond treatment system, was planted with reed
canary grass and had a slope of 3 percent (see Figure 5-4). Although
experiments at Brookhaven National Laboratories have been discontinued,
the development of the technique, in combination with the marsh-pond
system, has shown promise.
5.3.2 Subsurface Incorporation
Soil incorporation techniques offer better odor and pest control than
surface spreading techniques and reduce the risk of inadvertent expo-
sure of humans to pathogens. One disadvantage is that less nitrogen
removal is achieved since ammonia volatilization is eliminated,
thereby decreasing the application rate compared to surface applica-
tion. Specialized equipment is generally required, depending on the
method of subsurface disposal practiced.
Plow-Furrow-Cover; A typical setup using this method consists of a
moldboard plow with furrow wheels and coulters. The coulter blade is
used to slit the ground ahead of the plow. Septage is applied to the
land in a narrow furrow 15 to 20 cm (6 to 8 in.) deep and is immedi-
ately covered by the following plow.
75
-------
FIGURE 5-2
LIQUID SLUDGE SPREADING SYSTEM IN FOREST LAND
UTILIZING TEMPORARY STORAGE PONDS (2)
Irrigation
Gun and Stand
Booster
Pump
3" Bail Valve
Primary
Pump
Temporary
Holding
Pond
4" Pipeline 3" Lever Action
Valve (2)
5" Pipeline
Mesh
Strainer
Plastic Liner
(As Required By Regulations)
FIGURE 5-3
RIDGE AND FURROW IRRIGATION METHOD
FOR APPLYING SEPTAGE TO LAND (3)
FIGURE 5-4
OVERLAND FLOW METHOD OF APPLYING
SEPTAGE TO LAND (3)
Spray Application
Slope 2-6%
Evaporation
Grass and Vegetative Litter
Runoff
/ Collection
76
-------
Subsurface Injection; This technique employs a device that injects
either a wide band or several narrow bands of septage into a cavity 10
to 15 cm (4 to 6 in.) below the surface (see Figure 5-5). Some
equipment uses a forced closure of the injection swath.
Terreator; This is a patented device (U.S. Patent No. 2,694,354} that
opens a 9.5-cm (3.75 in.) mole-type hole with an oscillating chisel
point (see Figure 5-6). An 11.4-cm (4.5 in.) diameter curved tube then
places septage 50 cm (20 in.) below the surface.
5.3.3 Burial
Broad forms of septage burial include disposal in holding lagoons,
trenches, and sanitary landfills. Foul odors are inherent to all of
these operations until a final cover is placed over the applied sep-
tage. Site selection is particularly important, not only for odor
control, but also to minimize potential groundwater pollution.
Holding Lagoons; These lagoons are usually a maximum of 1.8 m (6 ft)
deep and allow no effluent or soil infiltration. These disposal la-
goons require placement of septage in small incremental lifts (15 to
30 cm, or 6 to 12 in.) and sequential loading of multiple lagoons for
optimum drying. Odor problems may be reduced by placing the lagoon
inlet pipe below liquid level and having water available for haulers
to immediately wash any spills into the lagoon inlet line.
Trenches; Septage is placed sequentially in multiple trenches in small
lifts, 15 to 20 cm (6 to 8 in.), to minimize drying time. When the
trench is filled with septage, 0.6 m (2 ft) of soil should' be placed
as a final covering,, and new trenches opened. An alternate management-
technique allows a filled trench to remain uncovered to permit as many
solids to settle, as well as liquids to evaporate and leach out, as
possible. Then the solids, as well as some bottom and sidewall mate-
rial, are removed and the trench is reused.
Sanitary Landfills; Leachate production and treatment and odor are the
main problems to be addressed when a sanitary landfill accepts sep-
tage. For moisture absorption, New Jersey formerly recommended a
starting ratio of 0.05 m3 of septage to each m3 of solid wastes
(10 gal of septage to each yd3 of solid wastes) . Septage should not
be disposed of in landfills in areas with over 90 cm (35 in.)/yr of
rainfall, landfills without leachate prevention and control facilities,
or those not having isolated hydrogeological underlying rock strata. A
15-cm (6 in.) earth cover should be applied daily to each area that was
77
-------
FIGURE 5-5
SUBSURFACE SOIL INJECTION (1)
Cross-Section/Sub-Surface
Injection Process
Injector Shank
and Hose
Cavity-
Producing
Sweep
Initial Injection
Cavity
Ulitmate Dispersion
Area After Injection
FIGURE 5-6
TERREATOR APPARATUS FOR SUBSURFACE INJECTION (1)
. Spreader Plate
Terreator Frame
Curved
Injection
Tube
78
-------
dosed with septage, and with 0.6 m (2 ft) of final cover within one
week after the placement of the final lift. Generally, this is not an
economical method of disposal and is not normally recommended.
5.4 Project Development
Certain basic planning elements are common to all land disposal proj-
ects, no matter how or where septage is to be applied. These elements
include preliminary planning, site availability analysis, process de-
sign (which includes determination of sludge application rates), and
facility management and operation. Figure 5-7 presents an overview of
this process. The following sections provide a sequential description
of the planning elements that are characteristic of a septage land ap-
plication project.
5.4.1 Preliminary Planning
Once a program of land disposal has been proposed, a project team
should be assembled and should consist of interested individuals and
technical advisors. Soliciting public support for the project should
be a major activity of the project team. The importance of obtaining
public support cannot be overemphasized, since many land disposal
projects experience stiff opposition from concerned and often misin-
formed citizens. A second activity is the collection of basic data
necessary for a thorough examination of the project, including septage
quantities and characteristics, climatic conditions, and local, state,
and Federal regulations.
5.4.2 Site Availability Analysis
A three—phased approach to site selection is proposed as follows:
1. Preliminary Screening - Based on the basic data collected
during the preliminary planning, a rough estimate of the
total acreage required can be determined by dividing the
total septage quantity by an assumed application rate. (Based
on crop N uptake rates, typical annual application rates
range from 280 m3/ha 130,000 gal/acre] to 1,880 m3/ha
[200,000 gal/acre].)
79
-------
FIGURE 5-7
TECHNICAL EVALUATIONS INVOLVED IN IMPLEMENTING
A LAND DISPOSAL PROJECT
Preliminary Planning Phase
Evaluate Public Sentiment and Formulate
A Public Participation Program
I
Determine Septage Characteristics
Data Gathering
Determine Septage Quantities
Determine Regulatory Requirements
Compare Septage Characteristics To
Regulatory Requirements and Evaluate
Suitability of Septage For A Land
Application Option
Site Availability Phase
Estimate Land Area Required
For Septage Application
^iit#r Availability of Land Area Necessary
Assess Septage Transportation Evaluate Site Determine Land Acquisition
Modes and Distance to Site Physical Characteristics Probability and Cost
Select Alternate Sites
For Further Investigation
Process Design Phase
Identify Design Requirements:
Physical and Regulatory
Cover Crop Selection
Agromonic, Forest, and
Reclaimed Land
Detailed Site Investigation:
• Physical Features, Topography,
Depth to Groundwater, and Soil
Conditions
I
Determine Annual Application
Rates and Land Requirements
Operation and Maintenance Phase
Develop a Record Keeping
Program to Keep Track of
Septage Constituents
Applied to the Land
Operation Scheduled to
Satisfy Farming Techniques
and Loading & Monitoring
Requirements
80
-------
2. Preliminary Site Analysis - Sites identified by the prelim-
inary screening process are characterized as to topography,
land use, soil characteristics, geology, and average distance
from the septage district. The initial characterization is
done using published and readily-available information, such
as soil surveys and topographic maps. Sites can be ranked by
this initial characterization, and the top two or three can
be investigated further with site-specific information during
the process design element.
3. Site Acquisition - Sites can be acquired by purchase or by a
contractual agreement for the right to use private land for
septage utilization. The identified sites should be prelim-
inarily evaluated for these criteria.
5.4.3 Process Design
Once it has been determined that a septage land disposal project is
acceptable to the public and technically feasible, a process design
phase can be undertaken. The design requirements and constraints asso-
ciated with land disposal of septage are dependent on the type of crop
grown, soil condition, and the septage characterization, including
pathogens, organics, N, Cd, Pb, Zn, Cu, and Ni. Since state regulations
vary in different regions, the constraints discussed in the following
sections below are based on Federal regulations presented in 40 CPR
257, "Criteria for Classification of Solid Waste Disposal Facilities
and Practices," Federal Register, 13 September 1979 (Criteria) (4). It
should be noted that many state and local requirements are more re-
strictive than the Federal Criteria.
5.4.3.1 Pathogens
Untreated septage contains a variety of potential pathogens, including
bacteria, protozoa, parasites, and viruses. Chapter 3 presented a bac-
teriological characterization of septage. The "Criteria" states that
septage applied to the land or incorporated into the soil must be
treated by a "process to significantly reduce pathogens" (PSRP) prior
to application or incorporation, unless public access to the facility
is restricted for at least 12 months, and unless grazing by animals
whose products are consumed by humans is prevented for at least 1
81
-------
month. PSRP's include aerobic digestion, air drying, anaerobic diges-
tion, composting, lime stabilization, or other techniques that provide
equivalent pathogen reduction. These pretreatiiient processes are dis-
cussed in Chapter 7. The "Criteria" also require septage to be treated
by a "process to further reduce pathogens" (PFRP) prior to application
or incorporation if crops for direct human consumption are grown within
18 months subsequent to septage application or incorporation where
contact between the septage applied and the edible portion of the crop
is possible. PFRP's include composting, heat drying, heat treatment,
thermophilic aerobic digestion, or other techniques that provide
equivalent pathogen reduction.
The potential for groundwater contamination by land treatment disposal
of septage can be minimized by proper design and management techniques.
It is important to demonstrate to the public that every managerial
precaution has been taken, and that the chance of contamination is ex-
tremely remote.
5.4.3.2 Nitrogen
Nitrogen is the nutrient in septage that is required in the largest
amounts by potential crops selected for the disposal site. However, N
application in excess of the amount required for crops results in the
potential for nitrate (N03> contamination of groundwater supplies.
Elevated N03 levels in water supplies could result in health risks
for infants and livestock. Because nitrogen requirements vary signifi-
cantly from crop to crop, and due to the fact that some nitrogen may
carry over from year to year, close monitoring of nitrogen application
is required. Nitrogen requirements for different crops are given in
Table 5-2.
5.4.3.3 Cadmium
An additional constraint that limits the rate at which septage can be
applied to land used for crop production is the health risk associated
with cadmium (Cd). Cadmium contained in the diet accumulates in the
kidneys and may cause a chronic disease called proteinuria (increased
excretions of protein in the urine). It is difficult to predict the
effect of septage application on Cd in the human diet for the follow-
ing reasons:
82
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TABLE 5-2
ANNUAL NITROGEN, PHOSPHORUS, AND POTASSIUM
UTILIZATION BY SELECTED CROPS3 (3>
Crop
Corn
Corn Silage
Soybeans
Grain Sorghum
Wheat
Oats
Barley
Alfalfa
Orchard Grass
Brome Grass
Tall Fescue
Bluegrass
Yield6
per ha
6 m3
7.2 m3
72 mt
1.8 m3
2.1 m3
9 mt
2.1 m3
2.8 m3
3.5 m3
3.5 m3
18 mt
13.5 mt
1 1 .2 mt
7.9 mt
6.8 mt
Nitrogen
kg per ha
207
269
224
288C
376°
280
140
208
168
168
504"
336
186
151
224
Phosphorus
kg per ha
28
49
39
23.5
32.5
45
24.5
27
27
27
39
49
32.5
32.5
27
Potassium
kg per ha
199
223
339
112
134
186
102
150
140
140
446
348
236
172
167
"Values reported above are from reports by the Potash Institute of America and are for the total above-
ground portion of the plants. Where only grain is removed from the field, a significant proportion of the
nutrients is left in the residues. However, since most of these nutrients are temporarily tied up in the
residues, they are not readily available for crop use.
"Yields expressed as either cubic meter (m3) or metric tons (mt). 1 mt = 2,205 Ib.
"Legumes get most of their nitrogen from the air, so additional nitrogen sources are not normally needed.
83
-------
1. Crops vary markedly in Cd uptake (e.g., leafy vegetables are
significantly higher in Cd than cereal crops).
2. Cd uptake by crops is dependent on soil properties and the
amount of Cd applied.
3. The Cd content of the current human diet is not accurately
known and varies with each individual's diet preferences.
4. Projected increases in dietary Cd are influenced by the
amount of cropland affected, the properties of sludge and
septage applied, types of crops grown, and soil properties.
The "Criteria" (4) specify the limits for annual amounts of Cd applied
to different crops, as given in Table 5-3. It is also required that
the septage and soil mixture pH be maintained at 6.5 or above.
5,4.3.4 Heavy Metal Lifetime Loadings
The lifespan of an application system is limited, based on the cumula-
tive amounts of lead (Pb), copper (Cu), nickel (Ni), zinc (Zn), and
cadmium {Cd} applied to the soil. Maximum application loadings sug-
gested by the U.S. EPA are. listed in Table 5-4. It should be noted
that those loadings are cumulative loadings and are a function of the
soil's cation exchange capacity, when one of the trace elements is
loaded to its maximum allowable limit, septage and/or other sludge
disposal at the site should be terminated. For septage with the mean
characteristics presented in Chapter 3, zinc would be the limiting
metal based on these loading factors.
5.4.3.5 Site Selection
During the site-selection phase, prospective sites should have been
identified. Further investigation is required during the process de-
sign phase to determine the suitability of the site. The following
sections identify restrictions and types of investigations required.
84
-------
TABLE 5-3
ANNUAL CADMIUM LIMITS (4}
Type of Crop
Kg/ha/yr (Ib/acre/yr)
Tobacco, Root Crops,
Leafy Vegetables
Other Pood Chain
Crops (e.g., corn, small grains,
forages)
Animal Feed Only
0.5
(0,45)
2.0 (1.78}a
1,25 (l.ll)b
0.5 (0.45)c
Noned
ato 30 June 1984.
bl July 1984 to 31 December 1986.
°After 1 January 1987.
^A facility plan must be prepared showing the distribution of the
animal feed to preclude human consumption.
TABLE 5-4
SUGGESTED TOTAL AMOUNT OF SEPTAGE METALS
TO BE APPLIED TO AGRICULTURAL LAND (3)
•Maximum Amount of Metal in kg/ha/yr (Ib/acre/yr)
Soil Cation Exchange Capacity (meg/100 g)
Trace Element
0 to 5
5 to 15
15
Pb
Zn
Cu
Ni
Cd
560
280
140
140
6
(500)
(250)
(125)
(125)
(5)
1121
560
280
280
11
(1000)
(500)
(250)
(250)
(10)
2242
1121
560
560
22
(2000)
(1000)
(500)
(500)
(20)
Determined by the pH 7 ammonium acetate procedure.
85
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5.4,3.6 Site Location/Land Requirements
Sane states have guidelines or regulations for buffer zones to re-
strict the minimum setback distances between an area receiving septage
and the adjacent site facilities, such as residential developments,
inhabited dwellings, ponds and streams, and wells and public areas
(parks, schools, roads). Figure 5-8 presents typical minimum setback
requirements for a septage disposal site which are adopted from the
State of Maine (5). The potential contaminants being carried from the
site by surface runoff is the primary reason for these guidelines.
Therefore, flat slopes or the application of dewatered septage may
justify reduced setback requirements.
5.4.3.7 Slope Requirements
The slope of the land determines the potential for contaminated runoff
to leave the application site. The method of land application is dic-
tated to some extent by the slope of the site. The volumes of liquid
septage applied are typically less than the natural annual rainfall in
nearly all regions of the United States. Since these volumes are not
excessive, use of appropriate septage application techniques and runoff
control measures for different soil types and slopes will minimize the
potential for contamination of surface waters. General slope criteria
for sludge are presented in Table 5-5. The measures used to control
surface runoff from soils treated with septage are generally the same
as those designed to prevent soil erosion. These practices include
strip cropping, terraces, grassed waterways, and minimum tillage sys-
tems (e.g., chisel plowing, no-till planting).
5.4.3.8 Depth to Groundwater
The primary concern regarding the depth to groundwater is the poten-
tial for contamination due to nitrate/nitrogen leaching through the
soil. Essentially, all of the applied metals, pathogens, phosphorus,
and organics remain in the upper 12 to 25 cm (5 to 10 in.) of soil.
The ideal septage application site would be a previously-worked agri-
cultural field with deep and well-developed soils to protect the in-
tegrity of the groundwater sources. Greater depth of soil above ground-
water usually reduces the potential for contamination. Local or state
guidelines often specify a minimum distance to groundwater of at least
1m (3.3 ft) during those periods when septage is being applied. How-
ever, it is prudent to specify a minimum distance to the seasonal high
groundwater level of 1 m (3.3 ft) or more to assure groundwater pro-
tection.
86
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FIGURE 5-8
TYPICAL SEPTAGE DISPOSAL SITE (5)
Property Line
Swamp
Without
Stream
Outlet
oo
-j
Stone Wall and
Property Line
Fencing or Other
Barrier Erected to
Indicate Limits of
Spreading Area
Where No Natural
Boundary Exists
Field Area
Approved For
Septage
Landspreading
Swamp
With
Stream
Outlet
Buffer Zone Between
Spreading Area and
Property Line
Access Road
Lockable Gate
Main Road
-------
TABLE 5-5
RECOMMENDED SLOPE LIMITATIONS FOR LAND APPLICATION OF
SLUDGE (COMPILED FROM EXISTING STATE REGULATIONS REVIEWED) (6)
Slope Comment
0 to 3% Ideal; no concern for runoff or erosion of
raw septage or dewatered septage.
«
3 to 6% Acceptable; very slight risk of erosion;
surface application of raw septage or
dewatered septage is acceptable.
6 to 12% Injection of raw septage required for
general cases, except in closed drainage
basin and/or extensive runoff control.
Surface application of dewatered septage
is usually acceptable.
12 to 15% No raw septage application without posi-
tive runoff control; surface application
of dewatered septage acceptable, but im-
mediate incorporation recommended.
Over 15% Slopes greater than 15% are only suitable
for sites with good vertical permeability
(deep, well-drained soils) where the slope
is short and is a minor part of the total
application area.
88
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5.4.3.9 Soil Conditions
A detailed soil sampling and analysis program is important to deter-
mine appropriate loading rates for septage. The amount of available
nutrients must be known in order to determine how much additional nu-
trients can be added via septage application. Soil pH and cation ex-
change capacity influence the uptake of metals by crops. Soil sampling
methods should also be established as part of a long-term monitoring
program to determine when the soil has reached the maximum level of a
particular nutrient or trace element.
5.4.3.10 Cover-Crop Selection and Nutrient Requirements
The basic design goals are maximization of crop yield and quality, and
minimization of environmental damage. These remain constant regardless
of projected land use. Nutrient requirements and regulatory constraints
differ, however, for application to agricultural, forested, and re-
claimed land.
5.4.4 Land Disposal Options
5.4.4.1 Application to Agricultural Land
It is advantageous to maintain or utilize the normal cropping patterns
found in the community. The types of crops grown and crop rotation
patterns have developed over the years in response to local soil con-
ditions, climate, and economic conditions. The nutrient value of the
septage should be utilized as a replacement for commercial fert-
ilizers, while altering farming practices as little as possible.
Interest has developed in recent years regarding the timing and meth-
ods used to apply septage to cropland to maximize yield and minimize
potential health risks. However, the crops selected essentially dictate
the scheduling and methods of application (see Table 5-6}. Since sep-
tage application rates are typically controlled by the nitrogen re-
quired by the crop, crops requiring large amounts of nitrogen (e.g.,
corn, forages, sorghum) will minimize the amount of land required and
the operation costs. However, corn and sorghum actively grow from May
to November, thereby limiting the time available for septage applica-
tions to a few months (i.e., the non-growing season). Although forage
crops, legumes, and grasses consume large quantities of nitrogen and
permit access during most of the growing season, surface application
of septage is feasible only after crops have been mown and baled for
animal feed.
89
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TABLE 5-6
GENERAL GUIDE TO MONTHS AVAILABLE FOR SEPTAGE
APPLICATION TO DIFFERENT CROPS IN NORTH CENTRAL STATES (6)
Month
Corn
Soybeans
Small Grains a
Winter Spring Cottonb
Foragesc
January
February
March
April
May
June
July
August
September
October
November
December
N
N
s/i
S/I
P, S/I
c
c
c
c
H, S/I
s/i
N
N
N
S/I
S/I
P, S/I
P, S/I
c
c
H, S/I
S/I
S/I
N
C
C
c
c
c
c
H, S/I
S/I
s/i
P, S/I
C
c
N
N
S/I
P, S/I
C
C
H, S/I
S/I
S/I
S/I
S/I
N
S/I
S/I
S/I
P, S/I
c
c
c
c
c
S/I
s/i
S/I
N
N
S
C
C
H,
H,
H,
S
H,
S
N
S
S
S
S
N = Surface application may not be allowed due to frozen or snow-
covered soils in some states;
S/I = Surface or incorporated application;
S = Surface application;
C = Growing crop present;
P = Crop planted;
H = Crop harvested.
aWheat, barley, oats, or rye.
^Cotton, only grown south of southern Missouri.
Established forages, legumes (alfalfa, clover, trefoil, etc.), grass
(orchard grass, timothy, brome, reed canary grass, etc.), or legume-
grass mixture.
90
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The amount of fertilizer recommended for different crops is determined
by the nutrients required for optimum yield. Septage application rates
are generally determined by using the same technique. The amounts of
nitrogen, phosphorus, and potassium required to obtain a given crop
yield have been determined experimentally for different crops and soil
types in each region of the country. Table 5-2 lists a variety of
crops that might be grown on sites where septage has been applied,
along with their respective nutrient requirements. For all crops,
yield potential and soil fertility are controlled by such factors as
the amount and distribution of rainfall; soil physical properties
(drainage, crusting, water-holding capacity, and compaction); length
of growing season; available heat units; and incidence of weed, in-
sect, and disease problems. These factors are integrated with the
available nutrients to determine the yield level observed for each
crop.
5.4.4.2 Application to Forested Land
As with agronomic crops, the harvesting of a forest stand removes the
nutrients accumulated during growth. However, the amounts removed
annually in forest harvesting are generally lower than in agronomic
crop harvesting (see Table 5-7). Uptake by vegetative cover will.af-
fect the uptake of N; i.e., plush understory vegetation markedly in-
creases N uptake. Forest systems also rely on soil processes (denitri-
fication) to minimize nitrate leaching into groundwater. In general,
nutrient loadings on forested lands should be less than those on agri-
cultural sites. No annual limitations are set for cadmium, since no
food-chain crops are grown. Lifetime metal limits used for agricul-
tural sites are suggested for forested land; this would minimize metal
toxicity to trees and allow growth of other crops if the area were
cleared at a future date.
5.4.4.3 Application on Reclaimed Land
Septage is usually applied to impoverished lands at rates sufficient
to satisfy the nutrient requirements of the cover crop.
91
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TABLE 5-7
ESTIMATED ANNUAL NITROGEN UPTAKE BY FOREST SPECIES3 (7)
Tree Age,
years
Average Annual
Ni trogen uptake
kg/ha
Eastern Forests
Mixed Hardwoods
Red Pine
Old Field with White
Spruce Plantation
Pioneer Succession
Aspen Sprouts
Southern Forests
Mixed Hardwoods
Southern Pine with No
Onderstory
Southern Pine with
Understory
40 to 60
25
15
5 to 15
40 to 60
20
20
200
100
200
200
100
280
200b
260
Lake State Forests
Mixed Hardwoods 50
Hybrid Poplar** 5
Western Forests
Hybrid Poplarc 4 to 5
Douglas Fir Plantation 15 to 25
100
150
300
200
aOptake rates shown are for wastewater-irrigated forest stands.
"Principle southern pine included in these estimates is loblolly pine.
cShort-term rotation with harvesting at 4 to 5 years} represents first
growth cycle from planted seedlings.
92
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5.4.5 Application Rates
Annual application rates are typically controlled by the nutrient re-
quirements of the crop grown and the cadmium limits established by
regulation. One method establishes nutrient requirements of the se-
lected crop; however, a more conservative method is to select an ap-
plication rate based on the phosphorus requirements of the crop. Since
the P requirements of most crops are approximately 25 percent of the N
requirement, the nitrogen and cadmium applied is considerably less
than under the previous approach. Lifetime loading rates are determined
based on regulatory limits established for the cumulative metal addi-
tions. Septage, or any other sludge applications cease when any one of
the metal limits is reached. The following sections present methodolo-
gies for determining the amounts of nutrients and metals applied, along
with a design example of how to apply the methodologies to determine
application rates and land requirements.
5.4.5,1 Calculation of Nitrogen Applied
The application of septage introduces nitrogen in two different forms:
inorganic nitrogen (almost exclusively ammonia) and organic nitrogen.
Inorganic nitrogen is available for plant uptake immediately upon
application. The amount available for use by the plants is affected by
the application method. For surface applications, as much as 50 per-
cent of the ammonia-nitrogen will be volatilized. The amount of vola-
tilization is influenced by many factors, including pH, soil water
content, temperature, surface roughness, land cover and residue, air
movement, and time elapse between application and next rainfall. If
septage is incorporated immediately into the soil, all of the ammon-
ia-nitrogen is available for use by the crops. The organic nitrogen in
septage must first be mineralized; that is, converted to a plant-
available form. The, rate at which this takes place is a function of
septage characteristics, soil characteristics, climatic conditions,
and the time since application. The rate at which nitrogen decays is a
function of the degree of treatment the septage has received, as shown
in Table 5—8, which summarizes reported mineralization factors com-
monly used for wastewater sludge. These mineralization factors should
be applicable to septage with equivalent treatment conditions. That
is, mineralization rates for septage should be approximately the same
as those for primary wastewater sludge, and anaerobically-digested sep-
tage should have the same mineralization characteristics as anaerobi-
cally-digested sludge.
93
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*»
TABLE 5-8
ORGANIC NITROGEN MINERALIZATION FACTORS3
Primary
and
Primary Primary Waste- Aerobically- Anaerobically-
Years After Wastewater Wastewater Activated Digested Digested Composted
Application Sludge (3) Sludge (8) Sludge (6) Sludge (6) Sludge (6) (6)
First Year
Second Year
Third Year
Fourth Year
Fifth Year
Five to Ten
Years
20
3
3
3
3
3
15 to 20
6
4
2
2
2
40
20
10
5
3
3
30
15
8
4
3
3
20
10
5
3
3
3
10
5
3
3
3
3
aFactors represent the percent of remaining organic nitrogen in applied septage
that is available for plant uptake in a given year.
-------
In order to calculate the annual application rate of nitrogen in a
particular year, the following sources must be included:
1. All of the nitrate (NC^-nitrogen) present in the septage.
2. All or a fraction of the ammonia (NH4~nitrogen) present in
the septage, depending on the form applied and the type of
application.
3. A fraction of the organic nitrogen (No) present in the
septage that is mineralized the first.year.
4. A residual fraction of the organic nitrogen (No) (applied
previously either by adding septage, sludges, or commercial
fertilizers) that is mineralized the current year.
Por the first year of application, the amount of nitrogen applied can
be calculated by the following equation:
CN = S [(N03) + KV(NH4) + P(o_l)
-------
For subsequent years, a three-step calculation is recommended to de-
termine the amount of nitrogen applied each year:
Step 1: Determine the amount of organic-N mineralized from previous
applications of septage.
From records of the septage applied, the organic-N applied each year
can be determined. The amount mineralized each year can be determined
using the factors in Table 5-8.
N0 applied in year 0-1
N0 mineralized in year 0-1
NO remaining in year 1-2
N mineralized in year 1-2
. x N x A
= NoAo-i x
N
remaining in year 2-3
N0 mineralized in year 2-3
etc.
= NOAi-2 x Fl-2
- NoAl-2 ~ cNMl-2
= NoA2-3 x F2-3
- NoA1_2
= cNMl-2
= NoA2-3
= cNM2-3
where:
A
S
N
CNMO-1
N
oAl-2
NoA2-3
F2_3
GNM2-3
= 1 x 10~3-si (8.34 x 10-6-English) .
= Raw septage application rate in m^/ha (gal/acre) .
= Organic-N concentration in septage in mg/L.
= Organic nitrogen applied first year kg/ha (Ib/acre) .
= Mineralization factor first year.
= Plant-available mineralized-N first year kg/ha (lb/
acre) .
= Organic-N remaining second year in kg/ha (Ib/acre) .
* Mineralization factor second year.
= Plant-available mineralized-N second year in kg/ha
(Ib/acre) .
* Organic-N remaining third year in kg/ha (Ib/acre) .
» Mineralization factor third year.
= Plant-available mineralized-N third year in kg/ha
(Ib/acre) .
This calculation continues until each year since the time of applica-
tion is considered. The procedure must be repeated for each previous
year when septage was applied to the site. The amount of mineralized
organic-N available for plant uptake in the current year (Cjjjj) is
the sum of the residual amounts of organic-N that will be mineralized
during the year.
96
-------
Step 2: Determine the amount ofnitrogen applied during the current
year's applicatipn of septage. This can be done from the
equation:
CN = S[(N03) + KV(NH4) -f F0_1(N0)]A
Step 3: The total amount of nitrogen available for plant uptake is
the sum of the two sources:
CN Total = CN * CNM
5.4.5,2 Calculation of Phosphorus Applied
In addition to the nitrogen, septage also provides the plant nutrient
phosphorus. It is assumed that 50 percent of the phosphorus contained
in septage is available for plant uptake as the phosphates normally
applied to soils in commercial fertilizers. The amount of plant-avail-
able phosphorus applied to the soil can be calculated by the following
equation:
Cp = (S)(0.5)(P) x A
where:
Cp = Plant-available phosphorus in kg/ha (Ib/acre).
S = Septage application rate in m3/ha (gal/acre).
P = Phosphorus concentration in mg/L.
A = 1 x 10-3 - SI (8.34 x 10~5 - English).
5.7.3 Calculations of Metals Applied
Annual limits have been established for the amount of cadmium that may
be applied to a site, and total cumulative limits have been establish-
ed for Cd, Pb, Zn, Cu, and Mi. The amount of each metal applied to the
site each year, can be determined by using the same approach used for
the nutrients:
M = S x Mf. x A
97
-------
where:
M = Amount of the metal of concern applied in a given year in
kg/ha (Ib/acre) .
S = Amount of septage applied in a given year in m/ha (gal/
acre) .
Mc = Concentration of the metal of concern in the septage ap-
plied in mg/L,
A « 1 x 10~3 - SI (8.43 x 10~6 - English).
The total cumulative amount of metal applied can be determined by sum-
ming the annual amounts calculated using above equation.
5.4.5.3 Calculation of Additional Nutrient Requirements
Table 5-2 presented the relative amounts of N, P, and K required by a
variety of crops for a projected yield. These yields will not result
unless all the essential nutrients are available in the recommended
amounts. Therefore, it may be necessary to add nutrients via commer-
cial fertilizers to supplement the nutrients available in the septage
applied. By subtracting the amount of nutrient applied in the septage
(as calculated in the previous sections) from the amount of nutrient
required for a desired yield, the amount of supplemental fertilizer
required can, be determined.
5.4.5.4 Application Rate Calculation
A community in the midwest with a population of 24,000 persons and an
average household population of 3 persons/household is served by on-
site septic systems. The town has adopted a septage management program
and will pump septic tanks once every three years. An agreement has
been made with a local farmer to apply raw septage to existing fields
used to grow corn silage. During the first year, septage will be ap-
plied based on the crop N requirement, and, during the second year,
the septage will be applied based on the crop P requirement. Determine
the first and second year annual application rates and land require-
ments:
98
-------
Septage Quantity
24,000 persons divided by 3 persons/household = 8,000 households
(tanks)
Assume septic tank volume .- 2.84 m3 (750 gal)
Annual volume of septage = 8,000 x 2.84 m3 divided by 3 (average
pumping interval in years) = 7573,3 m3 (2,0 million gal)
Septage Characteristics (from Tables 3-4 and 3-5)
1. TKN = 650 mg/L
2. NH4-N = 120 mg/L
3. N03-N - 3 mg/L
4. N0-N =527 mg/L
5. Total P = 250 mg/L
6. Total K = 60 mg/L
7. Pb = 10 mg/L
8. Zn = 40 mg/L
9. Cu = 9.1 mg/L
10. Ni = 1.0 mg/L
11, Cd = 0.7 mg/L
Regulations
1, Annual septage applications cannot exceed either the N re-
quired for the crop grown or 2 kg Cd/ha (1.78 Ib Cd/acre) for
the first two years.
2. Soil must be maintained at pH 6.5 or above.
3. Annual monitoring is not needed other than routine soil test-
ing to determine fertilizer and lime requirements.
4. Records are to be maintained on the amount of septage applied
to each area.
99
-------
Site Soil Properties
1. CEC * 10 meq/lOOg
2. Soil pH (in water ) = 6.0
3. Available P = 15 kg/ha (13.1 Ib/acre)
4. Available K = 75 kg/ha (67 Ib/acre)
5. Lime (to pH 6.5} =5.4 mt/ha (2.4 tons/acre)
Crop Nutrient Requirements
Corn silage is currently being grown on the land. Crop fertilizer re-
quirements were obtained from Table 5-2.
Yield = 72 mt/ha (32 tons/acre)
N = 224 kg/ha (200 Ib/acre)
P* « 24.4 kg/ha (21.8 Ib/acre)
K* = 152.4 kg/ha (136 Ib/acre)
*Reeommendations based on soil test data shown above.
The septage will be applied to the soil by subsurface methods for the
corn silage crop, making the Kv volatilization factor equal to 1.
The mineralization factors for the first two years are FQ_I = 0.4
and F_ =0.2.
Method Is Calculation of First Year Septage Application Rate Using
Nitrogen Basis
CN = S [(N033 -f KV(NH4) + PQ-l(No)] x A
Solve for S knowing CN = 224 kg/ha (200 Ib/acre):
224 kg/ha » S m3/ha[(3 mg/L) + 1.0(120 mg/L) + 0.4(527 mg/L)] x
10-3
S = 671 m3/ha (71,840 gal/acre)
100
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Calculation of FirstYear Cadmium Applied Based onNitrogenLoading
= S x Cd x A
= 671 m3/ha x 0.7 mg/L x 10~3 =0.47 kg/ha (0.42 Ib/acre)
Calculation of Other Nutrients Applied Based On Nitrogen Loading
1. Phosphorus; Assume 50 percent of phosphorus in septage is
available as phosphates.
Cp = S[0.5(P)] x A
Cp = 671 mVha x 0.5 (250 mg/L) x 10~3 = 83.9 kg/ha (74.9
Ib/acre)
Phosphorus required = 24.4 kg/ha, therefore more P is available than is
required by the crop;
2. Potassium; Assume 100 percent availability.
CK = S x K x A
CK = 671 m3/ha x 60 mg/L x 10~3 =40.3 kg/ha (36.0 Ib/acre)
Potassium required = 152.4 kg/ha, therefore more K will be needed in a
supplemental form.
(152.4 - 40,3 = 112.1 kg/ha) (100 Ib/acre)
Calculation of Metals Accumulation
The amount of all metals should be determined on an annual basis and
recorded to determine when the lifetime limits are reached. For illus-
tration purposes onlyf Zn (which will be the controlling metal) accum-
ulation will be calculated.
**Zn ~ S x Zn x A
MZn ~ 671 m3/acre x 40 mg/L x.!0~3 = 26.8 kg/acre (24.0 Ib/acre)
101
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Calculation of the Area Required
A = 7,573.3 m3 - 671 m3/ha = 11.29 ha (27.84 acres)
Method 2: Calculation of Second Year Septage Application Rate Using
Phosphor us Bas is
Cp - S [0.5 (P)] x A
24.4 kg/ha = s m3/ha [0.5(250 mg/I») 1 x 10~3 = 195.2 m3/ha
(20,910 gal/acre)
Calculation of Second Year Cadmium Applied
= S x Cd x A
= 195.2 mVacrgj x 0.7 mg/L x 10~3 = 0.137 kg/ha (0.12
Ib/acre)
Calculation of Additional Nutrient Requirements
Nitrogen
a. Calculate the fraction of the organic-N applied in the first
year that will be mineralized in the second year:
% applied in year 0 to 1 (NQQ-I) = 671 m3/ha x 527
mg/L x 1 x 10~3 = 353.6 kg/ha (315.6 Ib/acre)
N0 mineralized in year 0 to 1 (CNMQ_I) = 353.6 kg/ha x
0.4 » 141.4 kg/ha (126.3 Ib/acre)
N0 remaining in year 1 to 2 (Noi_2> = 353.6 kg/ha - 141.4
kg/ha - 212.1 kg/ha (189.3 Ib/acre)
NO mineralized in year 1 to 2 (CNMi_2> = 212.1 kg/ha x
0.2 = 42.2 kg/ha (37.9 Ib/acre)
102
-------
b. Calculate nitrogen applied in second year:
CN = S[NO3) + KV(NH4) + Fo-l(No)] X A
CN = 195.2 m3/ha [(3 mg/L) + 1(120 mg/L) + 0.4 (527 mg/L) ] x 1 x
10~3 =65.2 kg/ha (58,2 Ib/acre)
c. Calculate the total plant-available nitrogen applied in the
second year?
CN Total = CNM + CN - 42.4 kg/ha + 65,2 kg/ha = 107.6 kg/ha
(96.1 Ib/acre)
Total N required for corn silage * 224 kg/ha (200 Ib/acre)
Additional N required = 224 kg/ha - 107.6 kg/ha = 116.4 kg/ha (103.9
Ib/acre)
2. Potassium
CK * S x K x A
CK * 195.1 ra3/ha x 60 mg/L x 1 x 10~3 =11.7 kg/ha
Total K required for corn silage (yield = 72 mt/ha [32 tons/acre]) -
152.4 kg/ha (136 Ib/acre)
Additional K required = 152.4 kg/ha - 11.7 kg/ha = 140.7 kg/ha (125.5
Ib/acre)
Calculation of Metals Accumulation (Zn)
Year 1; MZn = 26.8 kg/ha (24.0 Ib/acre)
Year 2; MZn » 195.2 m3/ha x 40 mg/L x 1 x 10~3 = 7.8 kg/ha
(6.9 Ita/acre)
Cumulative total Zn = 26.8 kg/ha + 7.8 kg/ha = 34,6 kg/ha (30.9
Ib/acre) (which is less than the limit of 560 kg/ha)
Calculation of Area Required to Apply 2.0 Million Gallons per Year
A = 7573.3 m3 4 .195.2 m3/ha » 38.8 ha (95.6 acres)
103
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5.5 Management, Operations, and Monitoring
Once the system has been constructed, it must be made to run smoothly
and efficiently according to the following;
1. Applications of septage must be scheduled to conform to the
farming requirements. If crops are grown on the disposal area,
tilling, planting, cultivating, and harvesting operations
must all be scheduled. Scheduling is discussed in detail in
references (6) and (8).
2. Operations must be monitored to assure that the system is op-
erating as designed. Septage must be periodically analyzed to
ensure its acceptability to the user and provide a record of
nutrient and metal additions to the soil. Soil, crops, ground-
water, and surface water need to be monitored periodically to
determine if septage nutrients are applied at rates exceeding
the uptake capacity of crops or soils, in a manner generally
prescribed by local or state regulations. If the applied N
equals crop N uptake, the potential groundwater contamination
from septage is minimal.
5.6 References
1. Cooper, I.A. and J.w. Rezek. Septage Management. EPA-600/8-80-032,
NTIS NO. PB 81-142481, August 1980.
2. Water Pollution Control Federation. Design of Wastewater and
Stormwater Pumping Stations, Manual of Practice FD-4, Water Pollu-
tion Control Federation, Washington, DC, 1981.
3. U.S. Environmental Protection Agency. Applications of Sludges and
Wastewaters on Agricultural Lands A planning and Educational
Guide. Office of Water Program Operations, U.S. EPA Report No.
MCD-35, Washington, DC, 1978.
4. Criteria for Classification of Solid Waste Disposal Facilities and
Practices. Federal Register (40 CFR 257), 44:53438-53468, September
13, 1979.
5. Department of Environmental Protection, State of Maine. Checklist
for Septage Disposal. October 1980.
6. U.S. Environmental Protection Agency. Process Design Manual — Land
Application of Municipal Sludge. U.S. EPA Report No. 625/1-83-^016,
October 1983.
104
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7. Stone, E.L. Microelement Nutrition of Forest Treess A Review, in:
Forest Fertilization - Theory and Practice. Tennessee Valley Au-
thority, Muscle Shoals, Alabama, 1968.
8. Keeney, D.R., K.W. Lee, and L.M. Walsh. Guidelines for the Appli-
cation of Wastewater Sludge to Agricultural Land in Wisconsin.
Technical Bulletin No. 88, Wisconsin Department of Natural Re-
sources, 1975.
9. Sommers, L.E., C.F. Parker, and G.J. Meyers. Volatilization, Plant
Uptake, and Mineralization of Nitrogen in Soils Treated with Sew-
age Sludge. Technical Report No, 133, Purdue University, Water Re-
sources Research Center, 1981.
10. Small, M. and C. Wurm. Data Report — Meadow/Marsh/Pond System.
Brookhaven National Laboratory Report No. BNL 50675, April 1977.
105
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CHAPTER 6
CO-TREATMENT OF SEPTAGE AND SEWAGE
6.1 Introduction
The similarity in the characteristics of septage and municipal waste-
water makes co-treatment an attractive method of septage treatment and
disposal. However, appropriate facilities are needed at sewage treat-
ment plants to receive, pretreat, and distribute the septage into the
appropriate process units. Septage, which may be considered a high
strength wastewater, can be either dumped into an upstream sewer or
added directly into various unit processes in a sewage treatment plant.
In both cases it is essentially a slug load of concentrated waste re-
sulting from unloading of septage by tank trucks. For example, a 3.8-
m^ (1,000-gal) tank truck emptying its contents in 10 minutes repre-
sents a hydraulic surge of 6.3 L/sec (100 gpm). Such a hydraulic surge,
when coupled with the concentrated suspended solids,. BOO, and other
pollutants contained in septage, could produce a shock load on the
sewage treatment facility and can be overpowering in the case of small
sewage treatment plants.
6.2 Feasibility of Co-Treatment
The ability of a treatment plant to accommodate septage depends on the
following factors:
1. Plant type, layout, and location.
2. Plant design capacity.
3. Current wastewater flow.
4. Plant effluent limitations, including BOD, suspended solids,
nitrogen, and phosphorus.
5. Septage receiving and pretreatment facilities.
6. Sludge handling facilities, including ultimate sludge disposal
practices.
106
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The quantity of septage that a plant can handle is governed by two ma-
jor factors; 1) quantity and nature of flow and 2) aeration capacity
and solids handling capacity of the plant. The volume of septage rela-
tive to sewage is important since it determines the additional organic
solids load on the STP. The loading limits on the unit processes are
significantly influenced by the nature of the flow of septage, which
could be in the form of either slug loads
-------
FIGURE 6-1
TECHNICAL OPTIONS FOR CO-TREATMENT OF SEPTAGE
Modification to
Primary Clar.
Process
Modification To
Secondary
Processes
Addition to
Liquid Stream
H
O
00
Addition to
Sludge Stream
-------
2. Prevent clogging/fouling and excessive wear and tear on plant
equipment.
3. Allow controlled flow of septage from a holding/equalization
tank into the desired process unit, if required.
4. Prevent fouling of biological treatment processes due to
floating inert materials.
Detailed discussion and design recommendations regarding receiving
stations were given in Chapter 4. The following discussions on co-
treatment of septage and sewage in an STP are based oh the considera-
tion that only screened and degritted septage (preliminary treatment)
will be introduced into a primary or secondary treatment process.
6.3.2 Liquid Stream Addition
Screened and degritted septage can be added to the liquid stream of an
STP at several points at the STP, as well as directly to the intercep-
tor, as shown in Figure 6-2. Septage may be discharged directly from
hauler trucks in slug loads, or it can be gradually fed into the system
using some form of equalization. The point of addition chosen must take
into account a variety of factors, not the least of which are the lo-
cations of plant bypass lines, organic and hydraulic loadings (design
and actual), and physical capacity of unit processes directly and in-
directly affected by septage addition.
Adding septage to a sewer can create the following maintenance problems
in the sewer system:
1. Deposits in the sewers.
2. Clogging of pumps at pumping stations.
3. Increased corrosion of sewer pipes.
4. Odor problems at the point of discharge and at downstream
locations.
Germany has developed guidelines for the addition of septage to the
sewer mains (32):
1. The municipal treatment plant must have a biological step
with enough excess capacity to treat the additional load from
the septage.
109
-------
FIGURE 6-2
POINTS OF SEPTAGE ADDITION IN A TYPICAL SEWAGE TREATMENT PLANT
Is'
Sewer
Si * Sal
84 - Se:
Note:
Bar Grit
Screening » Chamber
Septage Addition Options
to Liquid Stream
Septage Addition Options
to Solids Stream
All Septage Additon Options
(Except Si) assume screening
and grit removal at the
septage receiving station
Ss §3
f ^ \ , , Aeration Tank
I Clarifier I Trickling Filter
[ Sludge Recycle
Primary Sludge
I
( Thickener •*
S,._ ».
Sludge
/_:;
^\
/ Sludae \*.. , .'
I Digester )
Filtrate/ Centrate „ , . Solit
I Clarifier J
Secor
Slue
Treat
)5
js Landfill/
Incineration
-------
2. The effluent quality requirement for the treatment plant must
be kept during periods with addition of septage.
3. At the point of discharge the septage must be diluted at
least 10 times with the municipal wastewater. The time of
discharge must be regulated according to this. Generally sep-
tage should not be added at points in the sewer system where
the municipal wastewater flow is less than the average flow
from 30,000 persons.
4. If the sewer system has overflow weirs downstream from the
point of discharge of septage, no septage must be added
during or soon after rainfall periods.
5. Septage must only be added at the point that is especially
set aside for septage addition.
6. Due to odor problems point of discharge must be located at
least 100 meters from the nearest house.
7. Point of discharge of septage requires regular maintenance.
Quantities and time of discharge must be recorded.
Septage addition to a treatment plant without screening, degritting,
and equalization is not recommended since it produces shock loads on
the plant's hydraulic and organic load-carrying capacity. The impact
of slug loads on performance is, to a certain extent, dependent on the
point of addition of the septage. If trucks discharge directly into
the influent stream of primary clarifiers, little or no control can be
exerted over amounts or timings of loads. Density currents caused by
incomplete mixing of septage and sewage interfere with solids separa-
tion in primary clarifiers. Inefficiencies in suspended solids removal
in primary clarifiers can cause serious malfunctioning of secondary
process units. If septage is to be added before primary treatment and
no equalization facilities are available, one method of minimizing
shock loads is to discharge the septage into a "controlled" manhole
upstream of the plant headworks. By this method, septage is diluted in
the sewers. However, some control may be required to avoid septage
loadings during low flow periods. Addition of septage during low flows
can exert shock loading on the process units in smaller plants and may
also result in the settling of grit in the manhole due to low flow ve-
locities.
Ill
-------
Slug loading of raw septage directly into secondary treatment units is
not recommended. Biological treatment units are very sensitive to in-
creased organic and solids loading and are especially sensitive to
slug loads (2). Shock loads from septage can cause upsets in secondary
process units including oxygen depletion, low BOD removals, and poor
settling of sludge in secondary clarifiers.
The preferred method of septage addition to most plants is continuous
feed at a rate proportional to sewage flow. In this way it is possible
to introduce septage into the sewage flow stream at considerably higher
flow rates than that possible with slug loading. In order to ensure
continuous controlled addition of septage, equalization and metering
facilities are required. Such facilities could be part of a septage
receiving station at the headworks of an STP and should include pro-
visions for mixing, odor control, and controlled rate feeding of sep-
tage. Bar screens and grit chambers are also recommended to protect
the primary and/or secondary unit processes.
Continuous feed of septage after receiving station flow equalization
provides better control of hydraulic and organic loading on primary
and secondary process units, which improves overall performance of the
treatment processes and ensures more uniform effluent quality. It is
recommended that continuous feed systems be utilized for treatment of
septage in small- to medium-sized plants whenever possible.
In large STP's the effects of septage loadings are generally expected
to be low, because the ratio of septage to sewage is generally low and
large STP's are capable of handling shock loads better than smaller
plants. In such cases it may be possible to introduce small quantities
of septage without equalization into an interceptor sewer upstream of
the STP.
6.3.3 Solids stream Addition
Based on the concept that septage is essentially a mixture of settled
sludge and raw sewage, with very high solids content, it is logical to
consider the option of treatment with primary and/or secondary sludges.
Septage addition to the solid stream may be made either at the en-
trance to the sludge stabilization system or to the dewatering system,
as shown in Figure 6-2. Addition to the stabilization system (e.g.,
anaerobic/aerobic digestion) has the advantage that septage may be
added after only screening and degritting, and without equalization.
The characteristics of septage do not significantly interfere with the
digestion process. Moreover, septage is biologically stabilized during
digestion and could be disposed of along with the digested sewage
sludge.
112
-------
If septage is added directly to the sludge dewatering process, chemical
conditioning is required, in addition to screening and degritting, in
order to enhance its dewatering characteristics. Since the septage does
not undergo any biological stabilization when added directly to the
dewatering process, the high concentration of organic matter still
present after dewatering could create odor and nuisances in the dis-
posal of residuals. Chemical conditioning with lime prior to dewater-
ing septage reduces odor problems. However, if composting or incinera-
tion are available methods of ultimate disposal, unstabilized, de-
watered septage sludge can be handled with little concern for odor and
nuisance problems.
Based on practical experience from plants mostly located in Norway, the
following guidance is offered by Eikum (31):
1. Septage must undergo separate screening, grit, and sand
removal prior to adding it to the sludge handling facility.
2. The sludge handling facility must have enough capacity to
handle the additional volumetric and solids load (thicken-
ing, stabilization, and dewatering capacity).
3. The sludge return liquor added to the municipal plant must
not reduce the effluent quality of the treatment plant below
the requirements set by authorities.
4. Addition of sludge return liquor from the sludge treatment
facility must enter a basin with 24 hours detention time.
5. The addition of septage must be managed by the treatment
plant operators.
6. Quantities and time of discharge of septage must be recorded.
7. Plants with septage addition must be located at least 100
meters from nearest house unless the discharge takes place
inside a building and odor reduction equipment is installed.
6.4 Co-Treatment of Septage in the Liquid Stream
Septage addition to the liquid stream of a sewage treatment plant is
one of the most common methods of septage treatment and disposal. While
113
-------
the similarity in characteristics of septage and sewage makes joint
treatment a compatible option, the performance of an STP accepting sep-
tage is dependent on many factors. Design considerations for combined
treatment of septage and sewage vary, depending on:
1. Type of process units in the STP.
2. Design capacity of the plant.
3. Location of septage input to the plant.
4. Volume of septage added daily.
5. Mode of septage addition (i.e., slug or continuous loading).
6. Ratio of current loading of plant to its design loading.'
The impact of septage addition to process units in an STP should be
evaluated based on the following considerations:
1. increased hydraulic loading on primary and secondary treat-
ment units.
2. Increased loading on sludge treatment units (thickeners, de-
watering equipment, etc.).
3. increased sludge volume in clarifiers.
4. Increased organic loading to biological process units.
5. Scum buildup in clarifiers and other facilities.
6. Odor and foaming problems in aeration units.
7. Potential toxic or incompatible substances present in septage
causing inhibition to biological processes.
8. Effluent limitations.
Germany has developed specific guidelines (32) that seek to minimize
operational problems associated with the addition of septage to the
liquid stream in an STP. These guidelines contain the following sug-
gestions:
1. The municipal treatment plant must have a biological step
designed for minimum 10,000 persons.
114
-------
2. The biological step must have enough excess capacity to treat
the additional organic load from the septage. During periods
with high hydraulic load on the plant (rainfall/infiltration)
no septage must be added.
3. Effluent quality requirements for the plant must be kept at
all times. During normal operation this can be achieved by
estimating maximum volumes of septage that can be added to
the plant (see Figure 6-3).
4. The septage volume determined from Figure 6-3 must be added
in at least two batches with several hours in between, and
outside the normal peaking periods at the plant.
5. The septage must be diluted at least 20 times with the munic-
ipal wastewater.
6. Detention basins for septage must be used in those cases
where the truck capacity exceeds the allowable volume that
can be added to the plant in one batch. The same is true if
the trucks arrive at the plants too often to allow the neces-
sary time between discharge of each truck load.
7. If the septage can be added from a detention basin during
several hours and outside peaking periods at the plant, the
volumes estimated from Figure 6-3 can be multiplied by a
factor of 4.
8. The septage must be added upstream from the plant screen.
9. The addition of septage must be managed by the treatment
plant operators.
10. Quantities and time of discharge must be recorded.
6.4.1 Septage Addition to Primary Process Units
The first option for introduction of septage to the liquid stream is
at the entrance of the primary clarifier. This impacts both the primary
and secondary treatment processes.
115
-------
FIGURE 6-3
ALLOWABLE SEPTABE VOLUME TO BE ADDED TO MUNICIPAL
TREATMENT PLANT PER GERMAN GUIDELINES (32)
300-
200-
re
•o
100
10,000
50,000 100,000 500,000 1,000,000
A (persons)
S = Allowable septage volume to be added (mVday)
A = Design capacity of municipal treatment plant (persons)
a = Loading factor = No. of equivalent users (edu's) connected to plant
design capacity (edu's)
116
-------
6.4.1.1 Impact on Primary Treatment Process
Screened and degritted septage may be added to the influent of primary
clarifiers to remove suspended solids. Although some plants add raw
septage at this point and degrit the primary sludge from this process,
this approach is not recommended. Septage usually contains very high
concentrations of suspended solids (10,000 to 20,000 mg/L) compared to
sewage (150 to-300 mg/L). Numerous studies have shown that raw septage
has poor settling characteristics (3) (4) (5) . One of these studies has
noted suspended solids removals as low as 10 percent'after 30 minutes
of settling (5). The same study determined the average suspended solids
removal to be 25 percent after 30 minutes. One reason for this poor
performance is that septage contains extremely high concentrations of
grease which has been well mixed with other solids during the pumping,
transport, and discharge steps. The production of gas bubbles under
anaerobic conditions, often found in septage, also tends to resuspend
solids, thereby affecting settling behavior. However, the addition of
septage, in combination with raw sewage, to primary clarifiers has
been found to be successful in achieving acceptable suspended solids
removal. Dilution of the suspended solids concentration in septage by
sewage renders septage more easily settleable; also, the net increase
in suspended solids in the liquid stream tends to improve overall set-
tling efficiency. Studies by Smith and Wilson (6) , Bennett, et al. (7) ,
and Carroll (8) found an average of 55 to 65 percent suspended solids
removal in primary clarifiers treating septage-sewage mixtures.
Segall and Ott (1) compared performance of a primary clarifier in an
STP at Marlborough, Massachusetts with and without addition of sep-
tage. The results are given in Table 6-1. Under constant septage feed
of 1.25 percent by flow volume, 56 percent of suspended solids were
removed, compared to 52 percent removal without septage addition. In-
creasing septage loading to 2.14 percent resulted in a suspended solids
removal of 75 percent. Further increase in septage addition did not
appear to enhance removal efficiency of suspended solids. Based on
limited data available it was assumed that an average of 55 to 60 per-
cent suspended solids removal could be obtained in primary clarifiers
treating septage-sewage mixtures. The increase in BOD removal efficien-
cy was significant, with removals of 53 percent and 67 percent when
septage was added to sewage, compared to 17 percent without septage
addition. However, increased BOD removals were not expected with higher
septage loadings. It would appear from these data that most of the ad-
ditional BOD loading imposed by the septage addition is removed in
primary clarification.
117
-------
TABLE 6-1
CHARACTERISTICS OF PRIMARY CLAJRIFIER EFFLUENTS
AT MARLBOROUGH, MASSACHUSETTS (1)
Phase 1
Phase 2A
Phase 2B
CD
Q Hastewater, m3/3
Q Septage, m^/d.
Septage, % by Volume
*S, mg/L
TVS, mg/L
ISS, mg/L
VSS, mg/L
B005, mg/L
BOOs-N Supressed, mg/L
COO, mg/L
COD-N Supressed, mg/L
TKN, rag/L
NH-N, mg/L
IP, mg/L
Alkalinity, mg/L
Grease, mg/L
Inf.
0.1
0
0
716
468
221
200
120
87
317
90
20
16
5.6
112
129
Eff.
476
193
106
72
100
73
247
78
27
17
5.5
136
211
%
Heduc-
tion
34
59
52
64
17
16
22
13
-35 '
-6
2
-21
64
Inf.
0.1
110
1.2
907
683
455
363
218
183
602
35
22
11
142
189
Eff.
592
298
199
137
103
69
310
98
33
28
5.4
192
135
t
Reduc-
tion
35
56
56
62
53
62
49
6
-27
51
35
29
Inf.
0.1
216
2.1
937
595
577
486
- 393
289
905
66
15
9.7
115
268
Eff.
477
206
143
101
128
76
255
80
20
6.1
156
914
%
Reduc-
tion
-
49
65
75
79
67
74
72
-33
37
-36
-241
-------
The impact of septage on primary effluent quality is also an important
consideration for septage addition to primary clarifiers. Since high
suspended solids removal can be successfully achieved in primary clar-
ifiers loaded with septage-sewage mixtures, unduly high concentrations
of organic matter would not be expected in primary effluent. The re-
sults of full-scale tests at Marlborough (1) (see Table 6-1) show that
an approximate three-fold increase in organic loading of influent by
septage produced only a 30 percent increase in the BOD of primary ef-
fluent, with almost no change in COD. This behavior also supports the
hypothesis that a large fraction of organic material in septage is as-
sociated with suspended solids that can be readily removed in primary
clarification. However, there is a relationship between primary efflu-
ent quality and the septage/sewage volumetric ratio which must be con-
sidered in design.
The addition of septage ahead of primary clarifiers not only helps to
remove a substantial quantity of suspended solids present in septage,
but also minimizes the additional organic load on secondary treatment
units created by septage addition; however, it will increase the quan-
tity of sludge produced in primary clarifiers. Estimated sludge pro-
duction due to septage addition in primary clarifiers is given in Fig-
ure 6-4 assuming an average of 60 percent suspended solids removal and
typical septage characteristics given in Table 3-4. Since septage
sludges often contain anaerobic solids, its accumulation at the bottom
of primary clarifiers may cause problems including resuspension of
bottom sludge, short circuiting, and impaired settling in primary
clarifiers. Primary sludge containing septage solids should be removed
at a faster rate than with conventional domestic sewage. The excess
sludge generated will create additional loading on sludge handling
facilities.
Skimmers designed to remove grease in primary clarifiers treating
sewage may not be able to handle the additional grease load caused by
septage addition. Increased grease loads may result in spreading of
the grease-scum layer over the entire surface of a clarifier and cause
nuisance (odorous) conditions, clogging of inlet port of the scum tank,
and removal difficulties due to the limited sweeping radius of the
skimmer blade. Manual water hosing may be required to sweep the scum
to an area suitable for removal with the wiper blade of the skimmer.
High grease concentrations in primary effluent will affect the per-
formance of secondary biological process units. Excess grease carried
over to the mixed liquor of activated sludge aeration units decreases
oxygen transfer, inhibits microbiological activity, and could be toxic
to microorganisms. It may also inhibit settling in subsequent clari-
fiers and reduce final effluent quality.
119 .
-------
FIGURE 6-4
ESTIMATED WASTE SLUDGE PRODUCTION IN PRIMARY
CLARIFIER TREATING SEPTAGE AND SEWAGE
5 -
Q
o
£
o
••o
o
0)
o>
•o
55
Percent Septage Added (Flow Basis)
120
-------
The following solutions are recommended to prevent problems arising
from excessive grease:
1. Limit grease content of septage-sewage influent to primary
clarifiers to 300 mg/L by controlling the rate of septage ad-
dition to sewage flow (proportional control). Although this
would still impose higher oil and grease loads than that com-
monly found in sewage (see Table 3-8), it should be possible
to accommodate the additional load by incorporating minor
modifications in the oil and grease removal mechanism of the
clarifier.
2. Modify skimming mechanisms as required to handle extra
grease, and remove grease from scum tanks at shorter inter-
vals. Increased width of scum tank with appropriate extension
of wiper blade could enhance sweeping radius for better re-
moval of grease. Increasing the speed of skimmer arm may also
accomplish this. Although aimed at the primary clarifier,
these improved scum control arrangmenets might be necessary
for the secondary clarifier and chlorine contact units, as
well.
Grease removed from septage pretreatment units or primary clarifiers
can be landfilled or added to certain sludge treatment processes (e.g.,
anaerobic/aerobic digestion).
The following guidelines are to be considered in the design of primary
clarifiers accepting septage:
1. Design primary clarifiers for handling septage on the basis of
detention time or surface loading criteria used for domestic
wastewater. Typical hydraulic loadings for primary settling
range from 32 to 48 m3/m2/d (800 to 1200 gpd/ft2) for average
flows. Detention times of 1.5 to 2.5 hours are normal (29).
2. Screen and degrit raw septage before addition to the primary
clarifier. In STPs where grit removal is accomplished with
primary clarification followed by degritting primary sludge, it
may be feasible to add septage after just screening.
3. Mix septage with sewage prior to primary settling to achieve
achieve satisfactory removals of suspended solids.
121
-------
4. Ensure frequent removal of excess grease and scum due to sep-
tage addition. Modifications of skimmer mechanisms may be
considered. The rate of septage addition should be controlled
with relation of sewage flow to effect a maximum grease con-
tent of the grease in the primary clarifier of 300 mg/L.
5. The grease content of the primary sludge will be increased,
with potential additional mixing problems for anaerobic di-
gesters. Any treatment plant must consider this problem when
contemplating acceptance of septage.
6.4.1.2 Impact on Suspended Growth Secondary Biological
Processes
Although a considerable fraction of the organic matter in septage is
removed with suspended solids in the primary clarifiers, the soluble
BOD and remaining suspended organic matter exert a significant addi-
tional organic load on secondary biological process units.
If the form of secondary treatment is activated sludge, aeration ca-
pacity and mixed-liquor suspended solids are the two critical items to
be considered for evaluating the impact of adding septage to the pri-
mary clarifier. Activated sludge plants require additional oxygen
(i.e., additional aeration capacity) to accept the increased organic
loading due to septage. The rate of septage addition, measured as a
percentage of total sewage flow, will determine the additional organic
load that is exerted on the activated sludge process after accounting
for removals in primary clarification.
Recommended volumetric feed rates of septage on a constant, equalized
loading basis have been developed by Rezek and Cooper (8), based on
field investigations and earlier findings by Caroll (9), and are shown
in Figure 6-5. The loading rates indicated here are higher (roughly by
an order of magnitude) than those suggested by the earlier cited Ger-
man guidelines (see Figure 6-3). This is most likely due to conserva-
tive assumptions on the part of the Germans regarding the degree of
primary treatment and equalization provided in order to account for
the worst case condition.
The amount of septage that can be added to a plant is a function of
plant capacity and the ratio of present flow to design flow. Addi-
tional oxygen requirements as a function of the amount of septage
added (with and without primary clarification) are given in Figure 6-6
(8). For septage added prior to primary clarification, the additional
122
-------
FIGURE 6-5
ALLOWABLE RATES OF EQUALIZED SEPTAGE ADDITION (8)
Activated Sludge Without
/ Primary Treatment
Activated Sludge
With Primary
Treatment
/ Aerated
Lagoon
Package
Plants
0.8 1.2 1.6 2.0 2.4
Septage Added, Percent of Plant Design Capacity
FIGURE 6-6
ADDITIONAL OXYGEN REQUIRED FOR SEPTAGE ADDITIONS
IN ACTIVATED-SLUDGE TREATMENT PLANTS (9)
26
•a
a>
a»
o»
>>
tt
O
"3
o
"£.
"O
"D
'
24
22
20
18
16
14
12
10
8
6
4
2
Without Primary,
Treatment
W th Primary
Treatment
23456789
Septage Added, 1,000 gal/d
11 12 13 14 15
123
-------
oxygen requirement is about 4.8 kg 02/m^ of septage added (40 Ib
O2/1000 gal). Studies on a full-scale STP at Marlborough, Massachu-
setts indicate an average oxygen requirement of 0.7 kg 02/kg of BOD
in septage (1). This value is very close to that determined from Fig-
ure 6-6 for septage with a BOD of 7000 mg/L.
The organic loading rate to an activated sludge unit is also a very
critical design consideration. Conventional activated sludge units
have successfully operated with continuous septage additions (ahead of
primary unit) of less than 5 percent of flow volume at loadings of
0.33 to 1.1 kg BOD5/kg MLVSS/d and COD loadings of up to 3 kg COD/kg
MLVSS/d. The full-scale STP at Marlborough, Massachusetts was operated
at a loading of 0.42 kg BOD5/kg MLVSS/d without septage addition
which increased to 0.45 and 0.54 kg BOD5/kg MLVSS/d for respective
septage addition rates of 1.25 and 2.14 percent of sewage flow (1). In
those studies, no significant deterioration in secondary effluent
quality was found compared to that without septage addition (see Table
6-2) * Secondary effluent suspended solids concentration increased to
18 mg/L with septage addition, but. did not exceed discharge limita-
tions.
& study conducted on a pilot-scale activated sludge unit at septage
loadings of 2 to 13 percent of sewage flow determined that BOD and
suspended solids concentrations of the secondary clarifier effluent
ranged from 20 to 40 mg/L and 11 to 13 mg/L, respectively, and were
not significantly different from that of the control unit receiving no
septage. However, COD concentrations in the effluent increased with
rise in influent COD (7).
Sludge production in secondary clarifiers following the activated
sludge process is increased due to septage addition. The amount of
sludge produced, depending on the percentage of septage added, is
shown in Figure 6-7 (24).
6.4.1.3 Impact on Fixed Film Secondary Process Units
Fixed film or attached growth systems such as trickling filters and
rotating biological contactors are commonly used for sewage treatment,
particularly in small communities, and have been used to a relatively
limited extent for combined septage-sewage treatment. In general, at-
tached growth systems have been found to be more suitable for handling
variations in hydraulic and organic loads than suspended growth sys-
tems. Some of the advantages of attached growth systems include econo-
my in capital and operation costs, ability to recover from shock loads,
and operation with minimal supervision.
124
-------
TABLE 6-2
CHARACTERISTICS OF INFLUENTS AND EFFLUENTS AT MARLBOROUGH, MASSACHUSETTS (1)
Sewage Only
Characteristic
COD - Total, mg/L
COD - Soluble, mg/L
BODg - Total, mg/L
BOD5 - H - Suppressed
mg/L
Total Solids, mg/L
Total Volatile Solids
mg/L
Suspended Solids, mg/L
Vol. Suep. Solids, rag/L
Total Kjeldahl-N, mg/L
Ammonia-N, mg/L
Hitrate-H, og/L
Total Phosphorus, mg/L
Grease, ng/L
Alkalinity, mg/L as
CaC03
pH
Dissolved Oxygen, mg/L
Temperature
Me talc, mg/L
Cadmium
Chromium
Copper
Nickel
Lead
Zinc
Influent
X S
317
90
120
87
716
468
221
200
20
16
1.0
S.6
129
112
6,8
3.3
10
0.02
0.04
0.20
0.04
0.07
0.27
75
24
40
37
506
493
376
366
6.5
2.8
0.3
2.1
11
21
0.3
1.0
1.4
0.02
0.09
0.05
0.03
0.06
0.09
Secondary
Effluent
x S
55
37
11
4.1
358
111
10
7.6
17
13
3.2
1.0
52
89
6.8
4.4
10
0.02
0
0.75
0.05
0.14
0.72
17
12
5.1
3.0
108
68
4.6
3.8
4.1
2.8
1.0
0.5
19
31
0.3
1.6
2.9
0.02
0
1,78
0.04
0.06
1.43
Sewage +
1.25* Septage
Secondary
Influent* Effluent
X x S
602
218
183
907
683
455
363
35
22
—
11
189
142
6.9
0.01
0.02
0.41
0.01
0.08
0.35
62
52
8.7
2.6
395
158
18
9
18
17
4.4
0.8
35.2
106
7.1
2.1
13
0.02
0
0.06
0.05
0.08
0.12
24
18
6.9
0.6
54
23
4.4
6
0.5
2.1
0.5
0.1
30
0.2
1.4
0
0.02
0
0
0.03
0.11
0.11
Sewage +
Influent*
3(
905
393
289
937
595
577
488
66
15
9.7
268
115
6.7
.
— _
0
0.02
0.48
0
0.22
0.59
2.14% Septaqe
Secondary
Effluent
X S
46
33
7.8
1.9
364
82
10
7.3
13
2.7
0.9
51.2
98
6.7
3.0
14
0.
0.
0.
0.
0.
0.
4
.5
15
3.4
0
0
1
0
0
0
1
0
03
50
09
11
07
21
.4
22
57
.6
.2
—
6
.7
.6
8
.2
2
.6
Note:
1 - Mean
S = Standard Deviation
* = Calculated concentration from sewage and septage characteristics.
125
-------
FIGURE 6-7
ESTIMATED WASTE SLUDGE PRODUCTION FROM BIOLOGICAL
TREATMENT PROCESSES RECEIVING SEPTAGE (24)
4 ••
03
I
•N,
XI
o
o
o
1
T3
o
o>
•O
CO
3 ••
2 ••
1 -.
Activated Sludge With
Primary Clarification
High-Rate Trickling Filter
With Primary Clarification
Contact-Stabilication
Without Primary Clarification
Low-Rate Trickling Filter
With Primary Clarification
Extended Aeration
1.0
2.0
3.0
> Septage Added, Flow Basis
126
-------
a. Trickling Filters
Although trickling filters have been used for combined treatment of
septage and sewage in some plants, performance and design data are
limited. A 83.1-L/s (1,9-mgd) trickling filter plant at Huntington,
Long Island (New York) treats 1.3 L/s (30,000 gpd) of septage with BOD
reductions of 85 to 90 percent and suspended solids removals of 85
percent (8).
Treatment of septage-sewage mixtures in trickling filters should only
be considered in plants where the trickling filter is preceded by pri-
mary treatment. This is because high concentrations of suspended solids
(1 to 3 percent) could cause plugging of the filter media if septage
were added directly to the trickling filter. Although a 55 to 75 per-
cent removal of suspended solids can be obtained (1) , the suspended
solids concentration in the primary effluent is a critical factor to
be considered when applying septage-sewage mixtures to a filter
process.
The design of trickling filters is based on hydraulic and organic
loading. Trickling filters can be designed as 1) low-rate systems with
organic loading varying between 0.08 and 0.32 kg BOD/m-^-d {5 to 20
Ib BOD/1000 ft-Vd) or 2) as high-rate systems with organic loadings
ranging from 0.32 to 0.96 kg BOD/m3-d (20 to 60 Ib BOD/1,000
ft^/d). In the case of septage-sewage treatment, organic content of
primary effluent may be too high, even for a high-rate trickling
filter. It may be possible to operate at a lower hydraulic loading in
order to maintain the desired organic load on the trickling filter.
However, this would increase the problem of filter flies associated
with low-rate trickling filters. There are empirical models available
for design of trickling filters on the basis of organic loading and
other parameters (2). These have been designed for sewage treatment
applications, and modifications required for septage-sewage combined
treatment are not available. However, with due consideration to the
increased strength of trickling filter influent, these models can be
used in designing co-treatment systems.
Sludge production will increase in secondary clarification due to sep-
tage addition. The rate of sludge production is a function of septage-
sewage flow characteristics, hydraulic and organic loading, type of
filter media, and temperature. For example, for a septage input of 1
percent of sewage flow, a low-rate trickling filter would produce about
0.24 kg sludge/m3 (2,000 Ib/million gallons) of flow, which would
increase to 0.3 kg sludge/m3 (2,500 Ib/million gallons) for high-
rate trickling filters. Figure 6-6 gives the estimated production of
sludge from treatment of septage-sewage mixtures by trickling filters
(24).
127
-------
b. Rotating Biological Contactors
Rotating biological contactors (RBC's) feature a microbial bioraass
attached to rotating discs that aerobically break down organic matter
in wastewater flowing over the disc surface. Although RBC systems have
been used for sewage treatment, very few examples of combined treat-
ment of septage and sewage have been reported. Combined treatment of
septage and sewage at the Ellsworth, Maine RBC treatment plant was not
very successful (25) . Addition of less than 1 percent septage to a
sewage flow of 2460 nvVd {0,65 mgd) caused several problems. Roto
strainers used for primary treatment were consistently clogged, and
concentrations of BOD and TSS in the final effluent after RBC treat-
ment were high. This, however, could be in part due to the poor per-
formance of the preliminary treatment unit.
RBC plants should be capable of adequately co-treating septage and
sewage provided accepted design guidelines are followed. Organic
loading rate is a particularly important factor. In studies at 24
facilities with mechanical drive units, first stage organic loadings
above 6 Ib total BOD5/d/l,000 ft2 or 2.5 Ib soluble BOD5/d/l,000
ft^ resulted in an increased frequency of process and mechanical
problems (34) . These problems included excessive biofilm thickness,
nuisance organism growths, and deterioration of process removal ef-
ficiency.
Soluble BOD loading is a critical parameter in the design of RBC units
and should be verified by influent sampling whenever possible. Organic
loading considerations during design must include contributions from
in—plant sidestreams, septage dumps, etc.
It is recommended that septage addition to RBC plants be limited to
those incorporating primary clarification, unless the sustained load-
ing of pretreated septage combined with incoming sewage is less than
the loading rates suggested above. Temporary . high organic loadings
during septage loading may be accommodated to some degree with sup-
plemental aeration of the first stage. Flow equalization should be
incorporated if possible to mitigate the highly fluctuating organic
loadings which may result from random septage dumping.
Control of excessive biological growth and nuisance growths may also
require special ' attention when septage is added to RBC plants. High
influent H2S concentrations can impede RBC performance and acceler-
ate nuisance growths (27).
128
-------
Other more specific guidance pertaining to the design of RBC systems
can be found in recent EPA publications (27) (34).
6.4.1.4 Impact on Sludge Handling and Treatment Systems
Addition of septage to primary clarifiers in STP's results in an in-
creased quantity of primary sludge. Typical additional sludge produc-
tion will be approximately 7.8 kg/m^ of septage (60 lb/1000 gal).
Removal of a large proportion of suspended solids in septage in pri-
mary clarifiers substantially reduces solids and organic loading on
secondary treatment units of the liquid stream. However, this form of
septage treatment could create problems in sludge handling and treat-
ment. The concentration of organic matter increases considerably in
primary sludge due to septage addition. This increase would have to be
considered in determining the organic loading to sludge digestion
units. It may be necessary to adjust the flow of sludge to the di-
gesters to,maintain the desired organic loading.
6.4.2 Septage Addition to Suspended Growth Secondary Process
Units
Extended aeration plants do not normally have primary clarification,
so that septage is introduced directly into the aeration basin. In
such cases, septage may be mixed with the sludge recycle stream en-
tering the aeration basin to ensure a well-mixed influent. Septage
pretreatment in the form of screening and degritting is required prior
to septage addition to secondary biological treatment processes.
The following factors are to be considered for septage addition to ac-
tivated sludge units,:
1. Available aeration capacity.
2. Available hydraulic loading capacity.
3. Excess sludge handling capacity available.
4. Method of septage addition.
5. Septage pretreatment facilities.
129
-------
The performance of an activated sludge plant is significantly influ-
enced by the method of septage addition, i.e., slug or continuous.
Slug loading to an activated sludge unit should be limited so as not
to increase the MLSS concentration by more than 10 to 15 percent per
day in order to maintain a stable sludge quality. Studies also indi-
cate that loss of the system's biomass may result if the change in
MLSS exceeds this range (9). Maintaining loadings below this recom-
mended limit did not cause upsets at the Weaverville wastewater treat-
ment plant in Trinity County, California (6) . Loadings for septage
addition to activated sludge plants with no equalization facilities
have been developed and are shown in Figure 6-8 (8) (9).
The loadings given in Figure 6-5 are for a fully-acclimated biomass in
the aeration basin. When initiating septage feed to an unacclimated
biomass, about 10 percent lower loadings should be used. Septage flows
can be increased rather quickly thereafter until the recommended load-
ing is accomplished because of the rapid increase in dissolved oxygen
uptake normally experienced when domestic septage addition is initiated
(22). Dissolved oxygen should be checked frequently, and gradual
changes made in sludge age for optimum performance (8).
Additional oxygen requirements for activated sludge plants are higher
when septage is added directly to aeration basins without primary
clarification. From Figure 6-6, it can be seen that about 9.6 kg
02/m^ (80 Ib O2/l,000 gal) septage are required when septage is
added directly to an activated sludge aeration system, which is ap-
proximately twice that required if septage addition is made to a pri-
mary clarifier. The higher oxygen requirement is for metabolizing the
high concentration of organic matter in the suspended solids. A large
fraction of the suspended solids are removed when septage undergoes
primary clarification; hence the oxygen requirement in the aeration
basin is lower.
Extended aeration systems can also accept septage for co-treatmentj
however, this means adding the septage directly to the aeration basin
without primary clarification. The design of extended aeration systems
is based primarily on a low ratio of BOD to MLSS (F/M) in the aeration
basin. The microorganisms undergo partial auto-oxidation, which re-
sults in lower sludge production than in conventional activated sludge
processes.
In extended aeration systems, oxygen requirements are higher than for
conventional activated sludge processes. This is because nitrification
usually occurs in extended aeration processes, which requires addition-
al oxygen over that required for removal of carbonaceous BOD. Bowker
130
-------
o»
o
o
0)
•o
T»
<
0)
o»
-S
Q.
0)
88
80
72
84
56
48
40
32
24
16
8
0
FIGURE 6-8
ACCEPTABLE SEPTAGE FLOWS AS FUNCTION OF PLANT
CAPACITY (WITHOUT EQUALIZATION FACILITIES) (8) (9)
With Primary
Treatment
Without Primary.
Treatment
A
10 11 12 13 14 15 16
Wastewater Treatment Plant Capacity mgd
131
-------
(11) estimated that septage addition of 3 percent by volume of influ-
ent wastewater increased TKN and NH^-N concentrations by 48 percent
and 2 percent, respectively. Actual NH3-N concentrations are higher
due to both hydrolysis of organic nitrogen and release of NE^-N dur-
ing auto-oxidation of cellular material. At the full-scale extended
aeration plant in Medfield, Massachusetts, treating septage and sew-
age, oxygen utilization was approximately 0.59 to 0.74 kg Q2/kg BOD
(1). Estimated oxygen requirements for extended aeration plants re-
ceiving septage are given in Figure 6-9 for combined treatment of sep-
tage and sewage.
The food-to-microorganism ratio of extended aeration plants is much
lower than for conventional activated sludge plants. Addition of sep-
tage increased F/M ratios in STP's. Studies conducted at Medfield show
that up to 3.6 percent addition of septage was possible without any
deterioration of effluent quality, when the F/M was maintained between
0.033 and 0.055 (1) . The STP was operating at about 20 percent of hy-
draulic design capacity. The results of studies at Medfield are given
in Table 6-3.
Mean cell residence time (ec) for extended aeration plants treating
sewage range between 20 to 30 days (2). The STP at Medfield, treating
septage at rates of 2 and 3.6 percent of sewage flow, was successfully
operated at mean cell resident times of 36 and 59 days, respectively
(1). The recirculation ratio of sludge return was about 1.7.
Volumetric loadings at Medfield STP for septage-sewage treatment were
0.16 to 0.24 kg BOD/ra3-d (10 to 15 Ib BOD/1000 ft3/d), which is
similar to that provided in extended aeration type sewage treatment
plants (0.16 to 0.4 kg BOD/m3-d [10 to 25 Ib BOD/1000 ft3/dj}.
The characteristics of secondary effluent from the extended aeration
plant at Medfield are given in Table 6-3. An analysis of the variance
of secondary effluent quality indicates that total and soluble COD ap-
pear to increase with septage addition. BOD, total solids, suspended
solids, and volatile suspended solids are relatively unaffected.
Based on the various studies reviewed, extended aeration appears to be
a feasible process for combined treatment of septage and sewage. How-
ever, more information based on full-scale plant operation is required
to establish criteria for design of extended aeration co-treatment
systems,
132
-------
FIGURE 6-9
ESTIMATED OXYGEN REQUIREMENTS FOR BIOLOGICAL
TREATMENT PROCESSES RECEIVING SEPTAGE (24)
Extended Aeration,
0 c = 25 Days
(Nitrification)
5-
re
0
_: 4'
M
JO
O
-------
TABLE 6-3
CHARACTERISTICS OF INFLUENTS AND EFFLUENTS AT MEDFIELD, MASSACHUSETTS (1)
Characteristic
COD - Total, mg/L
COD - Soluble, mg/L
BODj — Total, mg/L
BODj - N - Suppressed
ng/L
HOC, ng/t
Total Solids, mg/L
Total Volatile Solids
mg/L
Suspended Solids, mg/L
Vol. Susp. Solids, mg/L
Anoonia-N, rag/L
Nitrate-H, Mg/I,
Total Phosphorus, mg/L
Grease, og/L
pa
Tenperature, °C
Heavy Metals, og/L
Cadmium
Chromium
Copper
Nickel
Lead
Zinc
Sewage
Influent
I S
276
87
141
93
75
446
185
108
85
13
0
10.6
74
7.1
18
0.04
0.20
0.13
0.10
0.59
0.37
78
23
22
24
10
64
43
56
48
1.7
0
3.7
72
0.2
1.0
0.02
0.28
0.03
0.04
0.10
0.28
Only
Sewage +
1.25% Septage
Secondary Secondary
Effluent Influent* Effluent
X x x s
19.5
17
4
1
13
336
78
4
3
0.2
7.2
0.7
4.5
7.3
19
0.03
0.15
0.06
0,10
0.15
0.22
558
150
238
180
558
265
201
150
16
0
13
144
7.0
17
0.02
0.13
0.30
0.18
0.21
1.71
27
20
3.7
1.0
6.3
326
68
3.2
2.0
2.7
4.1
1.4
3.9
7.1
18
0.02
0.13
0.14
0.11
0.03
0.70
11
7.3
2.7
0.9
4.2
45
22
2.7
1.9
2.0
3.5
0.7
0.6
0.3
1.3
0.01
0.04
0.09
0.01
0.05
1.40
Sewage +
2.14% Septage
Secondary
Influent* Effluent
x 5s s
887
142
246
140
855
538
505
388
18
7.3
15
0.05
0.08
0.16
0.05
0.30
0.41
31
26
2.5
1.4
316
115
1.4
2.1
0.4
12.8
_ —
7.4
14.1
0.01
0.05
0.03
0.01
0.08
0.41
5.0
7.4
1.0
0.8
68
42
1,4
1.4
0.2
1.8
__-
___.
0.3
0.9
0.01
0.04
0.01
0.01
0.02
0.46
Hotes
X » Mean
S • Standard Deviation
* • Calculated concentration from sewage and septage characteristics.
134
-------
Aeration basins are an essential part of any suspended growth systems
used for treatment of septage and sewage. Foaming problems commonly
occur in such aeration basins. For control of foaming, several meth-
ods have been explored at various treatment plants, with some degree
of success. The most common are the use of commercial defoamers and
aeration tank spray water systems. Increased aeration tank freeboard
has also been considered as a means of containing the foam within the
aeration basin.
6.5 Co-Treatment of Septage in the Solids Stream
Addition of septage to the sludge stream, as opposed to the liquid
stream, will have less impact on forward flow treatment processes.
This is true since only the return flows, such as digester super-
natants, thickener overflows, and dewatering filtrates, are recircu-
lated through the major liquid treatment processes. In contrast,
during liquid stream addition of septage, both the direct septage
input and return-flow impacts may be significant.
Septage could be added to the sludge stream in an STP at several
points. It is generally recommended that septage be chemically con-
ditioned or biologically stabilized (aerobic or anaerobic digestion)
prior to dewatering and ultimate disposal. However, in cases where
sludge is to be buried or disposed of at a landfill, it may be more
feasible to add septage directly to the thickening or dewatering proc-
esses.
6.5.1 Addition to Stabilization Processes
6.5.1.1 Addition to Anaerobic Digestion
Stabilization of sewage sludge is commonly accomplished in anaerobic
digesters in STP's. Septage added to sewage sludge could also be
treated by anaerobic digestion for stabilization. In addition to sta-
bilization through reduction of volatile solids in sludge, anaerobic
digestion produces methane gas, which is used as a supplemental source
of energy for heating, mixing, and generation of electricity in STP's.
Few studies have been conducted by researchers on the anaerobic diges-
tion of septage and septage-sewage sludge mixtures. The long detention
time (1 to 2 years) in septic tanks before septage is collected for
disposal allows anaerobic decomposition of septage to take place. Since
135
-------
very little control is available in septic tank operation, organic
matter in septage is only partially stabilized by anaerobic decomposi-
tion. The anaerobic characteristic of septage makes it an ideal candi-
date for anaerobic digestion. Section 7.2.2 discusses the separate
treatment of septage by anaerobic digestion.
Small-scale studies on anaerobic digestion of septage-sewage sludge
mixtures have recommended a limit of about 15 percent septage, loadings
of 1.28 kg VSS/m3-d (0,08 Ib VSS/ft3/d), and a detention time of
30 days (15). The design of septage-sewage sludge anaerobic digestion
units can be based on design criteria used for sewage sludge; however,
the quantity of septage to be added should be determined on the basis
of total organic loading of the combined septage-sewage sludge mixture.
Recommended total loading is normally between 0.5 and 1.6 kg VSS/
m3-d (0.03 to 0.1 Ib VSS
The operation of anaerobic digesters should be monitored for pH, vol-
atile solids reduction, volatile acid concentration, alkalinity, and
gas production. Lowering of pH could result due to buildup of volatile
acids, which would severely affect performance of digesters. Overload-
ing of digesters by increased organic loading is one of the reasons
for enhanced volatile acids production and should be avoided, it is
recommended that septage be screened, degritted, and equalized before
it is added to anaerobic digesters. In the case of multiple digesters
operating in parallel, equal distribution of septage among the di-
gesters is recommended. Recycling digested sludge up to 50 percent of
raw feed per day has been found helpful (8) . Mixing of digester con-
tents is important for maintaining homogeneous conditions in the di-
gester and to prevent settling of digester contents. This is especial-
ly important with septage-sewage sludge mixtures.
6.5.1.2 Addition to Aerobic Digestion
Aerobic digestion can also be used to treat septage. Septage can be
introduced to the aerobic digesters along with primary and secondary
sludges. Aerobic digestion of septage and septage-sewage sludge mix-
tures has been found to be feasible based on experiences at pilot- and
full-scale treatment plants (see Chapter 7).
Aerobic digestion of septage-sewage sludge mixtures has been success-
fully applied in several cases. Septage addition to sewage sludge at
rates up to 20 percent has resulted in average BOD removal as high as
98 percent, with 6 days of hydraulic retention time (HRT) (16). In
Orange County, Florida, good BOD and VSS reductions were reported in
aerobic digesters treating septage—sewage mixtures (5 percent septage)
136
-------
at an organic loading of 2.4 kg VSS/m3-d (0.15 Ib VSS/ft3/d) (16).
At Bend, Oregon, 13 percent septage addition to aerobic digesters pro-
vided good reductions at a loading of 0.3 kg VSS/m3-d (0.02 Ib VSS/
ft3/d) at a 15- to 18-day HRT (18). In addition to good BOD and VSS
reductions achieved with aerobic digestion, improved dewatering and
settleability characteristics were reported by Jewell (17).
Foaming and odor problems are common with aerobic digestion of sep-
tage-sewage sludge mixtures (5) (14)(15)(16)(17). Foaming is dependent
on the amount of detergents present in septage,; however, most inves-
tigators report that foaming is usually diminished after about 24
hours (8) . Methods to minimize foaming problems in aerobic digestion
are similar to those applied to activated sludge systems.
Based on studies at pilot- and full-scale facilities, it is clear that
aerobic digestion is feasible for septage treatment in STP's. Screen-
ing, degritting, and equalization of septage is recommended before
addition to aerobic digesters. As a design guideline, organic loading
of 8 to 16 kg VSS/m3-d (0.05 to 0.1 Ib VSS/ft3/d) are recommended.
VSS and BOD removals of 35 to 40 percent and 70 to 80 percent may be
expected.
6.5.2 Addition to Thickening/Dewatering Processes
6.5.2.1 Addition to Thickeners
Thickening is a process often used to reduce the volume of sludge
prior to digestion and/or dewatering operations. Reduction in volume
decreases capital and operating costs of subsequent sludge processing
systems. Field experience has indicated that thickening also improves
the dewatering characteristics of sludge. Common methods of thickening
used for treatment of sewage sludge are gravity thickening and dis-
solved air flotation. In some cases, chemicals are added to condition
the sludge prior to thickening.
The impact of septage addition to thickening units is dependent on the
type of process used for thickening. Due to poor solids-liquid separa-
tion characteristics of septage, addition to gravity thickeners would
not thicken the septage much further and could create severe odor
problems due to septic conditions. It is recommended that septage be
added directly to sludge digestion units in plants that use gravity
thickening. If dissolved air flotation units are used for thickening,
septage could be added to the unit along with plant generated sludges.
Septage could be thickened in this process unit and then the thickened
137
-------
septage-sewage sludge mixtures added to sludge digesters or other
sludge stabilization systems.- Since large quantities of air would be
added in the dissolved air flotation process, severe odor problems are
not expected. Unfortunately, there are no field-scale data on the ad-
dition of septage to thickeners, primarily because septage is gener-
ally thickened separately from the STP sludges.
6.5.2.2 Addition to Oewatering Systems
Dewatering of sewage sludge can be accomplished using several methods,
including sand drying beds, filtration (e.g., belt and vacuum filters),
centrifugation, and presses. Capillary suction time (CST) is a param-
eter commonly used to determine dewatering characteristics of sludge
for process control purposes.
Septage has poor dewatering properties compared to sewage treatment
plant sludges. The CST of raw (~4 percent TS) septage has been shown
to vary from 120 to 825 seconds (19) . Studies conducted on dewatering
characteristics of septage conclude that septage needs to be chemi-
cally and/or biologically conditioned prior to dewatering in order to
achieve satisfactory performance levels. This means that direct addi-
tion of septage to conventionally used dewatering systems is not rec-
ommended.
The recommended method of adding septage to the dewatering facilities
of the receiving STP is to first pretreat the septage to make the en-
tire septage mass or (when solids separation is employed) the septage
solids amenable to dewatering either with the STP sludge or separately
(22). Although most septage dewatering studies have dealt with separate
dewatering (see Subsections 7.9 and 7.10), some work has been carried
out with mixed septage solids and sludges (20) (22) (23) (33) .
Crowe (20) successfully dewatered mixtures of raw septage and digested
sludge (up to 20 percent septage by volume) with a laboratory vacuum
filter apparatus. The dewatering characteristics of these chemically
treated mixtures were similar to those of the chemically treated di-
gested sludge. Pilot vacuum filter studies of 90 percent (aerobically
digested sludge) and 10 percent (acid/lime treated septage solids) by
volume showed that marginal yields and marginal cake release charac-
teristics could not be significantly enhanced by a wide variety of
chemical additions prior to vacuum filtration (23). Similar studies
with the same volumetric ratio using screened raw septage instead of
conditioned septage solids yielded almost identical results. Ott and
Segall found that conditioned septage solids and thickened waste acti-
vated sludge dewatered better by full-scale coil vacuum filtration
than did the latter by itself (22). These mixtures were made up of up
138
-------
to 50 percent by weight of conditioned septage solids. Ott and Segall
also found that chemical usage could be reduced by up to 50 percent by
first conditioning the septage and mixing with the thickened activated
sludge before final chemical dosing prior to the vacuum filter, as op-
posed to conditioning the entire mass without preconditioning the sep-
tage.
Condren (23) also investigated the dewaterability of 90/10 volumetric
mixtures of aerobically digested sludge and acid/lime-conditioned sep-
tage solids by solid bowl centrifugation and filter pressing at pilot
scale. The centrifuge gave poor results with and without polymer addi-
tion ahead of the unit, while the filter press yielded an excellent
cake (46 percent solids), filtrate (6 mg/L SS), and suspended solids
capture (>99.99 percent).
in Norway, full-scale experience has generally been with mixtures of
screened and degritted septage and primary alum sludges (33). Solid-
bowl centrifuge dewatering of these mixtures are reported to yield
cakes of 20 to 25 percent solids and centrate suspended solids of
<2,000 mg/L with 2 to 4 g of polymer per kg of mixture SS. Eikum (33)
indicates that higher septage/sludge ratios increase cake solids con-
tent without increasing centrate SSf but the BOD content of centrate
does increase. He also indicates that belt filters give similar re-
sults to the centrifuges when testing these mixtures.
Based on full-scale as well as laboratory and pilot-plant data, the
following recommendations are given for the design of dewatering sys-
tems receiving septage and treatment plant sludges:
1. Screen and degrit septage prior to its addition to dewatering
systems. Degritting may not be warranted if sand drying beds
are being used for dewatering.
2. for mechanical types of dewatering systems, chemically condi-
tion septage before mixing with digested primary or secondary
sewage sludge.
3. An application rate of about 25 kg/m2-hr (5 Ib/ft2/hr)
should be used for vacuum filtration of chemically condi-
tioned septage-sludge mixtures.
139
-------
6.5.3 Impact on Ultimate Sludge Disposal Practices
The method of ultimate disposal of the treated septage/sludge mixture
is influenced to a certain extent by the method of septage treatment.
If septage is added to the liquid stream, significant impact on the
current ultimate disposal method is not expected since septage under-
goes secondary biological treatment along with sewage, and character-
istics of the wasted sludge should not be greatly affected. However,
additional sludge will be generated.
If septage is added to the solid stream, it is recommended that sep-
tage be added prior to digestion (i.e., stabilization). The septage,
after undergoing biological stabilization, can be disposed of along
with treated sewage sludge. Addition of septage to the dewatering
process would have to be evaluated for its suitability for ultimate
disposal unless lime stabilization is used. If the high organic matter
in septage is not stabilized, ultimate disposal on land might be re-
stricted. However, composting or incineration could be alternative
methods for ultimate disposal of the dewatered septage-sewage sludge
mixture where dewatering without stabilization is provided.
6.6 References
1. Segall, B.A., C.R. Ott, and W.B. Moeller. Monitoring Septage Addi-
tion to Wastewater Treatment Plants — Volume I: Addition to the
Liquid Stream. U.S. EPA Report No. 600/2-79-132, NTIS No. PB 80-
143613, November 1979.
2. Metcalf & Eddy, Inc. Wastewater Engineering — Treatment, Disposal,
and Reuse (2nd Ed.). McGraw-Hill Book Co., New York, 1979.
3. Feige, W.A., E.T. Oppett, and J.F. Kreissl. An Alternative Septage
Treatment Method: Lime Stabilization/Sand Bed Dewatering. U.S. EPA,
Publication No. 600/2-75-036, NTIS No. PB 245816/4BE, September
1975.
4. U.S. EPA Technology Transfer. Alternatives for Small Wastewater
Treatment Systems — Volume I: Onsite Disposal/Septage Treatment
and Disposal. U.S. EPA Report No. 625/4-77-011, NTIS No. PB
2996085ET, October 1977.
5. Tilsworth, T. The Characteristics and Ultimate Disposal of Waste
Septic Tank Sludge. Report No. IWR-56, Inst. of Water Resources,
University of Alaska at Fairbanks, November 1974.
6. Smith, S.A. and J.C. Wilson. Trucked Wastes: More Uniform Approach
Needed. Water and Wastes Engineering, 10 March 1973.
140
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7. Bennett, S.M., J.A. Heidman, and J.F, Kreissl. Feasibility of
Treating Septic Tank Waste by Activated Sludge. U.S. EPA, Report
No. 600/2-77-141, NTIS No. PB 272105/AS, August 1977.
8. Rezek, J.W. and I.A. Cooper. Septage Management. U.S. EPA Report,
No. 600/8-80-032, NTIS No. PB 81-142481, August 1980.
9. Carroll, R.G., CI^M Hill Inc. Planning Guidelines for Sanitary
Wash Facilities. Report to the U.S. Department of Agriculture,
Forest Service, California Region, January 1972.
10. Feng, T.H. and H.L. Li. Combined Treatment of Septage with Munici-
pal Wastewater by Complete Mixing Activated Sludge Process. Report
No. Env. E. 50-75-4 for Division of Water Pollution Control, Mass-
achusetts Water Resources Commission, May 1975.
11. Bowker, R. P.G. Treatment and Disposal of Septic Tank Sludges. A
Status Report in Design Seminar Handout - Small Wastewater Treat-
ment Facilities, January 1978.
12. Goodenow, R. Study of Processing Septic Tank Pumpings at Brunswick
Treatment Plant. Maine Wastewater, Control Association, 1 January
1972.
13. Feng, T.H. and W.K. Shieh, The Stabilization of Septage by High
Doses of Chlorine. Report for Division of Water Pollution Control,
Massachusetts Water Resources Commission, June 1975.
14. Cooper, I.A. and J.W. Rezek. Septage Disposal in Wastewater Treat-
ment Facilities. In Individual Onsite Wastewater Systems. N. Mc-
Clelland, Ed., Ann Arbor Science Pubs., Ann Arbor, Michigan, 1977.
15. Howley, J.B. Biological Treatment of Septic Tank Sludge. M.S.
Thesis, Civil Engineering, University of Vermont, 1973.
16. Cushnie, G.C., Jr. Septic Tank and Chemical Pumpings Evaluation.
M.S. Thesis, Civil Engineering, Florida Tech. University, 1975.
17. Jewell, W.J., J.B. Howley, and D.R. Perrin. Design Guidelines for
Septic Tank Sludge Treatment and Disposal. Progress in Water Tech-
nology, 7 February 1975.
18. C&G Engineers. The Feasibility of Accepting Privy Vault Wastes at
the Bend Waste Treatment Plant. Prepared for the City of Bend,
Oregon, Salem, Oregon, June 1973.
19. Perrin, D.R. Physical and Chemical Treatment of Septic Tank Sludge.
M.S. Thesis, Civil Engineering, University of Vermont, 1974.
141
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20. Crowe, T.L. Dewatering Septage by Vacuum Filtration. M.S. Thesis,
Clarkson College, New York, 1974.
21. Leseman, W. and J. Swanson, Lab Director and Research Chemist, re-
spectively. Water Pollution Control Sept., City of Tallahassee,
Florida. Unpublished test data.
22. Ott, C.R. and B.A. Segall. Monitoring Septage Addition to Wastewa-
ter Treatment Plants — Volume II: Vacuum Filtration of Septage.
U.S. EPA Report No. 600/2-80-112, NTIS No. PB 81-142663, August
1980.
23. Condren, A.J. Pilot-Scale Evaluations of Septage Treatment Alter-
natives. EPA-MERL Report, EPA-600/2-78-164, NTIS No. PB-288415,
September 1978.
24. Cooper, I.A. Hauled Waste Plan Addendum for 201 Facility Plan for
Wastewater Treatment for Durango, Colorado. August 1979.
25. Telephone Conversation with Mr. James Denison at Ellsworth, Maine
RBC Facility.
26. Antonie, R.L. Application of the Bio-Disc Process to Treatment of
Domestic Wastewater. Proceedings, 43rd Annual Conference of Water
Pollution Control Fed., Washington, DC, October 1970.
27. U.S. EPA. Rotating Biological Contactors: A Checklist for a
Trouble-Free Operation, September 1983.
28. Wastewater Treatment Plant Design. WPCF/ASCE Manual of Practice
MOP-8, 1977.
29. U.S. EPA Technology Transfer. Process Design Manual for Suspended
Solids Removal. U.S. EPA Report No. 625/1-75-003A, January 1975.
30. Opatken, E.J. Rotating Biological Contactors - Second-Order Ki-
netics. Proceedings: 1st International Conference on Fixed-Film
Biological Processes, University of Pittsburgh, April 1982.
31. Eikum, A.S. Septage Quantity, Characteristics, and Treatment
Methods. International Conference on New Technology for Wastewater
Treatment and Sewage in Rural and Suburb Areas, October 1983.
32. ATV-Regelwerk. Behandlung und Beseitigug von Schlamm aus Klein-
klaranlagen. Arbeitsblatt Abwasser, 1974.
33. Eikum, A.S. Treatment of Septage — European Practice. Norwegian
Institute for Water Research Report No. 0-80040, February 1983.
34. U.S. EPA. Design Information on Rotating Biological Contactors,
MERL, 1983.
142
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CHAPTER 7
INDEPENDENT TREATMENT OF SEPTAGE
7.1 Introduction
This chapter presents information on the treatment of septage at a
facility dedicated exclusively to that purpose. Many of the independent
septage facilities in the U.S. are lagoons, which are often favored,
particularly in rural areas, due to their low capital and operating
costs. However, there are examples of mechanical septage treatment
facilities that have been applied in more developed areas. In such
areas, the premium on land discourages the use of land-intensive meth-
ods, and the higher density and larger numbers of septic systems create
certain economies of scale that make the more capital-intensive me-
chanical treatment systems cost-effective.
This chapter describes the following processes typically used for sep-
tage treatments
1. Lagoons.
2. Composting.
3. Biological secondary treatment processes.
4. Aerobic digestion.
5. Anaerobic digestion.
6. Lime stabilization.
7. Chlorine oxidation.
Other supplemental treatment processes are also addressed. These in-
cludes
1. Conditioning.
2. Dewatering.
3. Disinfection.
4. Odor control.
5. Ultimate disposal.
Finally, the relatively new concept of mobile dewatering, as currently
practiced in Scandinavia (!) is briefly discussed.
143
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Figure 7-1 depicts the various process, alternatives for independent
septage treatment. Raw septage can be delivered to a receiving/pre-
treatment facility or directly to a lagoon. The pretreatment step can
also include flow equalization and/or thickening. The pretreated sludge
then typically undergoes some form of stabilization - partial or com-
plete - and is then conditioned and dewatered.
Septage is stabilized in order to eliminate odors, reduce pathogens,
and reduce the potential for putrefaction. Stabilization is a relative
term that refers to the degree of decomposition that limits further
biological activity and renders the product satisfactory for further
handling or utilization. In general, there are four ways to stabilize
septage:
1. Biological reduction of volatile content.
2. Chemical oxidation of volatile matter.
3. Sterilization by heat,
'4. Chemical addition to render the septage unsuitable for micro-
organism survival.
The liquid stream can be disposed of by direct discharge after treat-
ment or by discharge to groundwater via percolation, etc. Although an
acceptable land application site and sufficient accessible STP capacity
were previously assumed not to exist, Figure 7-1 shows these options
of disposal. This is to accomplish a complete array of options for
illustrative purposes, recognizing that if these limitations exist
prior to choosing independent treatment, it would be a rare occurrence
that independent septage processing would then allow their use for
liquid fraction processing. Similarly, the solids residuals can be
disposed of with sludge to land, composted, or incinerated.
If composting is chosen as the stabilization method, the septage is
usually dewatered first, although composting of liquid septage has
been successfully practiced. The stabilized compost can be used for
gardening and soil conditioning and, in some cases, sold as a ferti-
lizer product. It is also possible to go directly from pretreatment to
conditioning and dewatering, especially if the solids are to be incin-
erated.
144
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FIGURE 7-1
TECHNICAL OPTIONS FOR INDEPENDENT TREATMENT OF SEPTAGE
U1
Septage ~*t
"ftatton9 Stabilization *
(i.e. Screening) ""9°°"
^Disposal/""!
N/^X "-^-Subsu
Conditioning/ _- Dewatering
| Stabilization if |
1 , , 1 1 1
Station
Primary Biological
Clarification Treatment
_ L/R""V\J
j_j Conditioning ^ ~\OI»po»ay- j"
V" ••
Receiving 1 11 1 1
Station O *•' ' ' U U
Aerobic *
f" Digestion "1
n r
r-j Thickening!-, 1 Anaerobic* J
1 ' ' 1 Diflc-itron
A ii
,,..m- - 1™ qiihlllriHnn T
•PSRP • Processes Which Siqnilicantlv 1 1
Reduc
"PFRP - Processes Which Further 1 Chlorine" J
Reduce Pathogens Oxidation
• » Spray Irrigation
X"~""\ j • Overland Flow
fEtfluent\ J[
V / 1 ». Marsh
1aoe Incorporation
Sell Product
-— ^ " > Spray Irrigation
l\ EffluenA J^
X — X I ^. Marsh . — ^incorporation
/_T . \ Jt— *"Soll Conditioner
-I Thickening I— i I Disposal/ •— -> Landfill
T /"^^N. I ""e'**"sc"ar9*
^"— S L» Subsurface Disposal
X" "X p* Surface Application
X"^/ 1*. Subsurface
^ IntermiHent Sand
^— «v l^ Filter-Discharge
„ .„,__ /F«lrate\ J.
i 1 1 V_"x I
s^**. -~-^- !_„. subsurface Disposal
I Sludge \_T** LandliU
Xf'v^yl^Subsurtae.
^»—X^ Incorporation
-------
7.2 Lagoons
Lagoons are widely used for the treatment and disposal of septage,
most notably in the northeast region of the U.S. (2). Properly designed
and sited lagoons are easy to operate, and they perform consistently.
They can be operated year-round and are relatively easy and inexpensive
to build and operate.
The simplest septage lagoon systems consist of two earthen basins ar-
ranged in series. The first, or primary, lagoon receives raw septage.
It may be lined or unlined, depending on the geological conditions of
the site. The supernatant from the primary lagoon, which has undergone
some clarification and possibly anaerobic digestion, is drawn off into
the second lagoon, or percolating pond, where it is allowed to infil-
trate into the ground (2) . It is also possible to have multi-celled
lagoon systems with either surface discharge or land application of
effluent. One option involves subsurface disposal of limed lagoon
sludge and use of liquid decant as soil top dressing for sod farming
(33).
7.2.1 Process Considerations
Figure 7-2 shows a number of variations of septage lagoon systems. A
septage receiving facility should be employed at the site to help
eliminate the odors associated with septage. typically, this would
consist of a concrete chamber with a tight-fitting hatch or manhole
designed to allow the septage to be discharged below the liquid level
of the primary lagoon. For further design considerations concerning
receiving facilities, refer to Chapter 4.
Where groundwater separation distances or geological conditions are
unfavorable, septage lagoons should be lined to avoid infiltration.
The liner should be impermeable to liquids, durable, and able to with-
stand heavy equipment used for cleaning and removal of accumulated
solids. Concrete, asphalt, or clay liners are recommended over mem-
branous rubber or plastic liners due to the limited ability of the
rubber and plastic to withstand the stresses of heavy equipment and
their susceptibility to laceration, abrasion, or puncture from sharp
objects such as stones, tree branches, or roots. Lagoons are normally
built above grade with earthen embankments to minimize construction
costs.
146
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FIGURE 7-2
SEPT AGE LAGOON VARIATIONS
Septage
\
Primary
Lagoon
Percolation
Pond
One Cell Lagoon With Percolation Pond (Controlled Discharge)
Septage
TTT
Two Cell Lagoon With Percolation Pond (Controlled Discharge)
Septage
• Recirculating Sand
Filter Discharge
* Spray Irrigation
* Overland Flow
Two Cell Lagoon With Surface Discharge or Land Application (Controlled Discharge)
Two Cell Lagoon With Percolation Pond (Continuous Discharge)
Septage
^
* Recirculating Sand
Filter Discharge
* Spray Irrigation
* Overland Flow
Two Cell Lagoon With Surface Discharge or Land Application (Continuous Discharge)
147
-------
Septage lagoons can be operated with a continuous discharge (i.e.,
through an overflow outlet structure) or with a controlled discharge
using a gate or valve to regulate periodic discharges of effluent.
When actual septage flows are less than design flow, controlling dis-
charges (i.e., minimizing number and frequency of discharges) will
increase detention time and should improve treatment efficiency. Con-
tinuous discharging systems, on the other hand, require less manual
adjustment. The appropriateness of controlled discharge versus con-
tinuous discharge may depend on the type of effluent disposal method
used. Spray irrigation and overland flow, for example, would be more
suitable with controlled discharge, whereas discharges to percolation
ponds or sand filters should be continuous in order to minimize the
effective loading rate.
A percolating pond can be used to receive the supernatant from lagoons
which, in turn, is allowed to infiltrate into the ground, undergoing
further treatment before entering the groundwater table. The outlet
from the lagoon should be designed to prevent flotable materials,
grease, and algae from overflowing into the percolating pond. This can
be done by submerging the outlet pipe or by using a baffle structure.
The pH in a septage lagoon must be maintained at 8.0 or greater to
control odors. This is usually accomplished by adding lime to the
septage before it is discharged to the lagoon (i.e., add bag of lime
to septage in hauler truck) or as it is discharged (i.e., add lime to
receiving chamber).
A major operating consideration with this septage disposal method is
the accumulation of suspended solids. Solids will eventually accumu-
late to the point where the lagoon no longer acts as a clarifier. If
solids accumulate in the percolating pond the infiltrative surface may
become clogged and no longer accept effluent. For this reason, it is
recommended that two parallel systems be constructed to allow for
draining, solids drying, solids removal, and resting in alternate la-
goons as illustrated in Figures 7-3 and 7-4.
Performance data for septage lagoons are limited. Average influent and
effluent concentrations for the Acton septage lagoon facility are pre-
sented in Table 7-1(3). Although these data indicate high removal per-
centages for all parameters measured, the effluent concentrations are
comparable to high strength raw domestic sewage. This indicates that
secondary lagoons should be used to polish the effluent before dis-
posal. Certainly, surface water discharge of lagoon effluent should
not be contemplated without sand filtration or overland flow.
148
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FIGURE 7-3
ALTERNATING LAGOONS IN BATCH TREATMENT
(CONTROLLED DISCHARGE) MODE
Percolation
Pond
Resting
Percolation
Pond
FIGURE 7-4
PARALLEL OPERATION OF CONTINUOUS DISCHARGING LAGOONS
Septage
Active
Primary
Cell
Decant/ Dry
Remove Solids
Active
Secondary
Cell
Inactive
Secondary
Cell
Active
Percolating
Pond
Resting
Percolation
Pond
149
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TABLE 7-1
LAGOON PERFORMANCE DATA, ACTON, MASSACHUSETTS (3)
Influent Effluent Percent
(mg/L) (mg/L) Removal
COD 19,500 1,870 90
BOD 5,890 450 92
Total Solids 11,600 1,610 86
Suspended Solids 9,500 610 94
Total Volatile Solids 8,170 910 89
The roost serious environmental consideration with lagoon systems is
the potential for groundwater contamination. Little control is avail-
able concerning the application rates of nitrogen, phosphorus, organ-
ics, pathogenic bacteria and viruses, and potential heavy metals, as
compared to land application methods. The commonwealth of Massachu-
setts recommends the use of percolation beds (not percolation ponds)
preceded by a two-cell lagoon system in order to maximize the renova-
tion of the effluent before it leaches into the soil (2). At a lagoon
site in Acton, Massachusetts (3), percolation beds were constructed
using 15 cm (6 in.) of coarse sand on top, followed by 15 cm (6 in.)
of fine sand, 46 cm (18 in.) of coarse gravel, and 15 cm (6 in.) or
more of medium and coarse gravel.
A study done by the New England interstate Water pollution Control
Commission (NEIWPCC) recommends that percolation beds use a thicker
subsurface (0.6 to 0.9 m, or 2 to 3 ft) layer of fine sand to increase
the removal of bacteria and other pollutants (3).
Where the risk of groundwater contamination justifies the elimination
of the percolation pond or percolation bed option, surface discharge
and land application alternatives should be seriously considered. Sur-
face discharges should be preceded by some form of polishing, such as
intermittent sand filtration, while land application designs should
follow guidelines provided in available documents addressing land
application of wastewater effluent (4)(5)(6).
150
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7.2.2 Design Guidelines
Design guidelines pertaining to the construction, siting, and opera-
tion of septage lagoons vary from state to state. Table 7-2 presents
recommended guidelines from the NEIWPCC. Although these guidelines
suggest a detention time of at least 20 days, considerably longer
detention times may be necessary to achieve more acceptable treatment
efficiencies. Applying an area loading rate for facultative sludge
lagoons of 0.84 kg VS/day/1,000 m2 (20 lb vs/day/l,000 ft2) (34)
results in a detention time requirement of approximately 500 days for.
a 2.5-m (8-ft) deep lagoon. This should provide greater than 95 per-
cent reduction of BOD and volatile solids. Other aspects of facility
siting and operation are discussed in Chapter 8.
TABLE 7-2
SEPTAGE LAGOON DESIGN GUIDELINES AS SUGGESTED
BY THE NEW ENGLAND INTERSTATE
WATER POLLUTION CONTROL COMMISSION (7)
Parameter Guidelines
Configuration A minimum of two lagoons in series, with
control of discharge to the second lagoon
by release during quiescent periods to
minimize the carryover of suspended solids
into the second lagoon. A parallel series
of similar lagoons should also be install-
ed to facilitate proper maintenance of
each series of lagoons.
or
A minimum of two lagoons installed in
parallel, followed by at least six perc-
olation beds with a total effective area
of 23.6 m2/m3/d (i sq ft/gal/d) of
design flow. The soil in the percolation
bed shall provide a percolation rate of
not over 2 minutes per inch. The base of
the percolation facilities shall be at
least 1.8 m (6 ft) above maximum ground-
water .
151
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TABLE 7-2 CONTINUED
Parameter
Guidelines
* Design Siting
- Minimum height above
maximum groundwater
table
- Groundwater
monitoring
- Buffer zone
'- Lining (percolation
bed)
- Access
- Fencing and signs
- Grading
* Receiving Station
• Odor Control
* Sludge Disposal
• Design Sizing
- Volume
- Basis
- Minimum Depth
pH Control
1.2 m (4 ft) .for both primary and second-
ary lagoons.
Monitoring wells recommended as well as
surface water sampling.
90 m (300 ft) .
Minimum 0.3 m (1 ft) of good filterable
sand.
All-weather roads.
1.8 m (6 ft) fence with locking gate-warn-
ing signs posted on all sides.
Adequate to prevent surface run-off water
from entering lagoons.
Concrete chamber with provisions to dis-
charge septage beneath the liquid level of
the lagoon.
Lime.
Not specified - refer to individual state
requirements.
Each lagoon system should provide a re-
tention time of no less than 20 days
Total of:
1. Domestic flow 0.19-0.27 m3/cap/d
(50-70 gal/cap/d)
2. Commercial flow
3. Industrial flow
0.9 m (3 ft)
6.8 - 7.2 using lime
152
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7.3 Composting of Septage
Composting is the stabilization of organic material through the proc-
ess of aerobic, thermophilic decomposition. It is an alternate septage
treatment technique that offers the potential for good bactericidal
action while achieving up to 25 percent reduction in organic carbon
(8). Septage is transformed into a humus-like material that can be
used as a soil conditioner. The composting of sludge has been success-
fully demonstrated at Beltsville, Maryland (8); Bangor, Maine (9); Dur-
ham, New Hampshire (10); and Windsor, Ontario (11). Also, a descrip-
tion of U.S. composting facilities has been published (72). Composting
characteristics of septage have been found to be the same as sewage
treatment plant sludge.
The composting of liquid septage is accomplished by adding additional
bulking agents (e.g., woodchips, sawdust, bark chips, etc.), or by
dewatering the septage prior to composting. The purpose of the bulking
agent is to decrease the moisture content of the mixture, increase the
porosity of the septage, and to assure aerobic conditions during com-
posting. Liquid septage composting has been demonstrated in several
instances (18) (34) (73).
Composting is generally classified into three types of operations,
which differ primarily by the aeration mechanism they employ. Each are
described briefly in the following sections.
7.3.1 Windrow Composting
In the windrow process, the septage and bulking agent are stacked in
long parallel rows called "windrows." The cross-section of the wind-
rows is either trapezoidal or triangular, depending on the equipment
used for mixing and turning the compost material.
Convective air movement within the windrows is essential for providing
oxygen for the microorganisms. The heat produced by the aerobic reac-
tions warms the air in the windrow, causing it to rise, producing a
natural chimney effect. In order to expose all the organisms within
the pile to oxygen, it must be turned, varying from once a day to
several times per week. This method is highly equipment- and labor-
intensive.
A variation of the windrow process, the Lebo process, is perhaps the
first composting process designed specifically for the treatment of
septage. The Lebo composting process consists of two steps: aeration
and composting. The aeration deodorizes the liquid waste. Figure 7-5
illustrates the patented Lebo aerator. It is installed mostly under-
ground, with only the top exposed. Septage is held in a storage tank
153
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FIGURE 7-5
THE LEBO AERATOR (15)
t
Vent Line
Vent Valve
Hinged Cover
Pressure Gage
Air Outlet
Discharge
154
-------
prior to being pumped to the aerator. Septage flows by gravity into
the aerator where it is aerated under a pressure of 69 to 103.kPa (10
to 15 psi) for approximately 10 minutes (15). At the end of 10 min-
utes, the vent valve on the aerator is closed and the discharge valve
is opened, forcing the septage through the U-tube and a discharge hose
into a sawdust/sludge mixer. After mixing, a front-end loader is used
to transfer the wet mixture to a compost pile. Alternating layers of
septage-sawdust are used until a pile height of 2.5 to 3.0 m (8 to 10
ft) is attained. Pile configuration is generally square with a flat
top to prevent excess heat loss. Provisions for the collection of
leachate are necessary because the material is relatively wet. The
leachate may be collected and recycled or, if the facility is located
at a treatment plant, the leachate may be with the liquid waste stream.
The material in the compost pile is left for 90 to 180 days during
which time the piles reach sufficient temperature (e.g., 50°C or
120°F) to dry the material (15). Then it is moved to a finished pile
for at least 30 days. The outer layer may then be removed and used as
a bulking agent. Although the process appears to be effective, little
data are available. Since the piles are not mixed, it is questionable
as to whether uniform distribution of adequately high temperatures is
consistently achieved to provide complete pathogen destruction.
7.3.2 Aerated Static Pile Composting
One composting technique that appears to offer potential as a septage
treatment alternative is the Beltsville "static pile method." Septage
composting by this technique has been performed at a small National
Park Service facility, which has also used this approach for compost-
ing liquid wastes pumped from portable toilets and vault privies (18).
Some pilot studies have been reported on the static pile composting of
dewatered septage solids, which would not be expected to differ sig-
nificantly from the many studies of dewatered sludge composting (8)
(9) (10) (11) (73).
The aerated static pile system was developed to eliminate many of the
land requirements and other problems associated with windrow com-
posting, and to allow for the composting of raw sludge. The essen-
tial elements of the static pile method are shown in Figure 7-6. An
aeration header consisting of perforated pipe is placed on the ground
and covered with approximately 30 cm (12 in.) of woodchips or unscreen-
ed, previously-composted material. This base acts as an absorbent for
liquids, prevents clogging of pipe holes, and allows" air circulation
below the raw material mixture. A front-end loader or some mixing de-
vice is used to blend the bulking agent (sawdust, woodchips, or other
material) and raw sludge in the appropriate proportion. The mixture is
then placed on the base in the configuration illustrated in Figure
7-6. The pile is covered with a 30-cm (12 in.) layer of screened com-
post to provide insulation (minimizing loss of generated heat) and to
155
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FIGURE 7-6
FORCED AERATION STATIC PILE COMPOSTING SYSTEM (17) (18)
Compost Pile
Screened
Compost
Deodorizing
Pile
General Layout
Compost Blanket
Waste-Bulking
Materials
Base
Blanket __ Woodchips & Previously
and Base Composted Material
Bulking ___ Woodchips, Sawdust and
Material Previously Composted Material
Septage Pile Dimensions
2.7 m (9 ft.) High
4.6m (15 ft.) Diameter
30 cm (12 in.) Base
50 cm (18 in.) Blanket
Cross Section
156
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prevent odors from escaping, vacuum is applied to the header by the
use of a blower. Between the pile and blower, a moisture trap is gen-
erally installed to collect water that condenses in the piping. The
discharge from the blower is operated on a timer, allowing an operator
to adjust the cycle to maintain oxygen concentrations in the pile of
between 5 and 15 percent. A three-week composting period is usually
provided, during which time temperatures and oxygen levels in the pile
are monitored. The composted material is then moved to a stockpile for
a four-week or more curing period. Screening of the material to recover
the woodchips may be effected before or after curing. The compost is
then ready for distribution. Health risks relating to the fungi A.
fumigatus are not usually a problem in septage compost operations due
to their small size and rural locations.
Results of the NPS study indicated that this process is capable of pro-
ducing a stabilized compost product when appropriate ratios of liquid
waste and organic bulking agents are achieved prior to the initiation
of the composting process. Approximate volumetric requirements for the
total compost pile per 3,790 L (1,000 gal) of waste were: base - 5.4
m3 (7 yd3) woodchips; absorbent organic mixture - 7.4 m3 (9.7
yd3) woodchips, 7.4 m3 (9.7 yd3) sawdust, 3.2 m3 (4.2 yd3)
compostj and insulation blanket - 7.7 to 15.3 m3 (10 to 20 yd3)
compost (18).
7.3.3 Mechanical Composting
The mechanical composting method is substantially different from other
methods, instead of a batch mode of composting, mechanical compost-
ing is a continuous process. Organic material and the bulking agent
are introduced daily into the influent end of the reactor. Mixing to
ensure adequate aeration can be done by tumbling, by movement with an
endless belt that lifts and drops the material, or by movement with an
auger. Additional aeration is provided by externally supplying air to
the reactor. This method is popular in Europe for composting municipal
refuse and wastewater sludge (62). It has not found wide-scale appli-
cation in this country. Application to septage composting is limited
by the size of available equipment, which is generally applicable only
to facilities handling greater than 115 m3 (30,000 gal) of septage
per day.
157
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7.3.4 Process Considerations
Composting represents the combined activity of a succession of mixed
populations of bacteria, actinomyeetes, and other fungi associated
with a diverse succession of environments (12).. The principle factors
that affect the biology of composting are moisture, temperature, pH,
nutrient concentration, and availability and concentration of oxygen
(12). Table 7-3 presents generally recommended operating parameters
for septage composting.
7.3.4.1 Moisture
Organic decomposition is dependent upon moisture. The lowest moisture
content at which bacterial activity takes place is from 12 to 15
percent? however, less than 40 percent may limit decomposition. The
optimum moisture content is in the range of 50 to 60 percent. Beyond
60 percent, the proper structural integrity will not be obtained.
Normally the moisture content of septage is in excess of 90 percent.
In order to optimize the composting process, septage should be de-
watered and/or blended with a bulking agent, whichever is more eco-
nomical .
7.3.4.2 Temperature
For the most efficient operation, composting processes depend on
temperatures of from 55° to 65°C (130° to 150°F) but not above
80°C (176°F) . High temperatures are also required for the inacti-
vation of human pathogens in the sludge. Moisture content, aeration
rates, size and shape of pile, atmospheric conditions, and nutrients
affect the temperature distribution in a compost pile. For example,
temperature elevation will be less for a given quantity of heat re-
leased if excessive moisture is present, as heat will be carried off
by evaporation. On the other hand, low moisture content will decrease
the rate of microbial activity and thus reduce the rate of heat
evolution.
158
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TABLE 7-3
OPERATIONAL PARAMETERS FOR SEPTAGE COMPOSTING
Parameter
Optimum Range
(12) (13) (14)
Control Mechanisms
Moisture Content
of Compost Mixture
40-60%
Oxygen
5-15%
Temperature (must reach) 55-65°C
PH
C/N Ratio
5-8
20sl to 30:1
Pretreatment of septage by
dewatering to 10-20% solids
Addition of bulking mate-
rial (woodchips, sawdust),
3:1 bulking agents dewa-
tered septage (by volume)
Periodic turning/natural
convection (windrow, Lebo
composting)
Forced aeration (static
pile)
Mechanical agitation with
compressed air (mechanical)
Natural result of biolog-
ical activity in piles
Too much aeration can
reduce temperature
Generally occurring in sep-
tage, no adjustment
necessary
Addition of bulking
material
159
-------
7.3.4.3 pH
The optimum pH range for growth of most bacteria is between 6 and 7.5,
and between 5.5 and 8.0 for fungi (13). The pH varies throughout the
pile and throughout the composting operation, but it is essentially
self-regulating. A high initial pH resulting from the use of lime for
dewatering will solubilize nitrogen in the compost and contribute to
the loss of nitrogen by ammonia volatilization. It is difficult to
alter the pH in the pile for optimum biological growth, and this has
not been found to be an effective operation control.
7.3.4.4 Nutrient Concentration
Both carbon and nitrogen are required as energy sources for organism
growth. Thirty parts by weight of carbon (C) are used by microorgan-
isms for each part of nitrogen (N) j a C/N ratio of 30 is, therefore,
most desirable for efficient composting, and C/N ratios between 25 and
35 provide the best conditions. The carbon considered in this ratio is
biodegradable carbon. Lower C/N ratios increase the loss of nitrogen
by volatilization as ammonia, and higher values lead to progressively
longer composting times as nitrogen becomes growth-rate limiting (12).
No other macro-nutrients or trace nutrients have been found to be rate-
limiting in composting municipal wastewater sludge.
7.3.4.5 Oxygen Supply
Optimum oxygen concentrations in a composting mass are between 5 and 15
percent by volume (60). increasing the oxygen concentration beyond 15
percent by air addition will result in a temperature decrease because
of the greater air flow. Although oxygen concentrations as low as 0.5
percent have been observed inside windrows without anaerobic symptoms,
at least 5 percent oxygen is generally required for aerobic conditions
(12).
7.4 Biological Secondary Treatment Processes
Since the basic composition of septage is very similar to domestic
sewage, it, is reasonable to assume that processes used in treating
sewage should be suited to the treatment of septage. Although the great
variability in waste strength and characteristics of septage may pre-
sent operational problems for low-SRT activated sludge processes, ex-
tended aeration processes should be more capable of handling such con-
ditions. Fixed growth biological systems at low loadings may be well
suited to septage treatment due to their relative ease of operation.
160
-------
Unfortunately, there is limited documented experience with full-scale
applications of these processes to septage treatment. However, such
designs may represent a cost-effective method of treating septage when
the generally less costly options of land application, lagoons, and
composting are not applicable. One example where a biological second-
ary septage treatment process was selected was in Wayland and Sudbury,
Massachusetts, where a system employing RBC treatment of septage was
determined to be more cost-effective than two other alternatives in-
corporating anaerobic digestion and chlorine oxidation (addressed
later in this chapter) (19). The Wayland-Sudbury treatment facility
provides screening, grit removal, equalization, chemical conditioning,
primary clarification, and secondary treatment using rotating biolog-
ical contactors, followed by sand filtration. The layout of the plant
is illustrated in Figure 7-7.
Given that septage generation is erratic and in many areas seasonal,
secondary treatment processes which are minimally upset by this varia-
bility are more desirable. Condren (29) applied acid/lime treated su-
pernatant (neutralized) to intermittent sand filters at pilot scale.
Although hydraulic loadings were high (1,400 m^/d/ha (150,000 gal/d/
acre)), BOD was reduced by more than 50 percent and effluent SS aver-
aged 31 mg/L.
The performance of biological septage treatment processes is yet to be
fully demonstrated? however, such systems may offer economic and oper-
ational advantages in many situations. The design of a biological sep-
tage treatment system should follow the same basic principles of de-
sign that apply to sewage treatment, by simply taking into account the
higher organic and solids loadings. Other special design and opera-
tional requirements, such as the need for increased scum removal ca-
pacity, are identified in Chapter 6 in discussing the co-treatment of
septage at sewage treatment plants.
7.5 Aerobic Digestion
Aerobic digestion operates in the endogenous respiration phase. Cell
matter is oxidized to carbon dioxide, water, and other inert materi-
als. Aerobic stabilization of septage-sludge mixtures has been widely
used in Europe at small plants (1), although for digestion of septage
alone, the process has not been adopted at full scale (20). Compared
with anaerobic stabilization processes, aerobic processes are easier
to operate and maintain, have lower capital costs, and produce an
odorless, biologically stable residual that dewaters easily (21).
161
-------
FIGURE 7-7
RBC SEPTAGE TREATMENT FACILITY - WAYLAND - SUDBURY, MASSACHUSETTS
to
Three Cell
Recharge
lagoon
(Buried Discharge Lines)
Legend
• •• i Forward Flow
Sludge
——Recycle
- Chemical Addition
===== VentHalton Piping
O Pumps
I | Laim
«— -O-| Jsepar
H ,_Jr-
Two Bay
Drive-Thru
Dumping Station
-------
Aerobic digestion qualifies as a Process to Significantly Reduce
Pathogens (PSRP) as per 40 CFR 257. Kuchenrither and Benefield (22)
found that fecal coliform and fecal streptococci concentrations de-
creased with time during aerobic digestion, and that the rate of
decrease tended to increase as the temperature increased. Figures 7-8
and 7-9 illustrate these findings.
7.5.1 Research on Aerobic Digestion of Septage
Aerobic digestion of septage has been shown to be reasonably effective
in full-scale operations as well as in laboratory and pilot-scale
studies. A common problem/, however, has been the control of both foam
and odors. Foam problems have been controlled by increased freeboard,
up to 1.2 meters (4 feet) or more (23); laboratory experiments have
used foam-retardant devices or chemicals. Table 7-4 presents a summary
of research involving aerobic digestion of septage.
Bowker (20) has provided a summary of available data on the aerobic di-
gestion of septage. He noted that Jewell, et al. (24) investigated
bench-scale batch and continuous-feed aerobic digestion of septage at
detention periods of 1 to 30 days and noted high removals of soluble
organics, but limited reduction of particulate organic material. Re-
moval efficiencies varied widely. Jewell stated that odor and foaming
were eliminated in the batch units in 5 and 11 days, respectively.
Foaming persisted in the continually-fed reactors, but odors were not
a problem in these units after an acclimation period of 3 to 4 days.
Zone settling velocity and CST (capillary suction time), indicators of
settleability and dewaterability, respectively, were improved consid-
erably after aerobic stabilization at loadings of 0.5 to 21 kg/m2/
day (0.03 to 1.3 Ib VSS/cu ft/day), and a detention time of greater
than 30 days (24).
Aerobic digestion is commonly used in Norway for sludge and septage
stabilization because of the large number of small wastewater treat-
ment plants in that country. Eikum and Paulsrud (25) reported on stud-
ies conducted at the Norwegian Institute for Water Research (NIVA) to
determine the solids retention time necessary to produce a fully-
stabilized sludge. They studied primary sludge and mixed primary/
chemical (alum) sludge, as well as septage. They defined a fully-
stabilized sludge as that in which the Odor Intensity Index (Oil)
(ASTM D 1292) does not exceed 11 at any time during 14 days of storage
(i.e., without aeration) at 20oc (68°F), unless the odor can
clearly be classified as a typical "soil" odor. They found that sep-
tage required a minimum solids retention time (aerated) of 44 days at
18oc (64OF) before it could meet the requirements for full stabil-
ization. Primary sludge and mixed primary-chemical sludge required 37
days and 40 days, respectively, at 18oc (64°F) to be considered
fully stabilized.
163
-------
FIGURE 7-8
FECAL COLIFORM COLONIES REMAINING
FOLLOWING AEROBIC DIGESTION (22)
at
=
I
o
O
*5
o
2500
1500
500
20°C-.-
30°C-*-
40°C
5 10 15 20 25 30 35
Digestion Time (Days)
FIGURE 7-9
FECAL STREPTOCOCCI COLONIES REMAINING
FOLLOWING AEROBIC DIGESTION (22)
S 10 15 20 25 30 35
Digestion Time (Days)
164
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TABLE 7-4
SUMMARY OF RESEARCH OF AEROBIC DIGESTION OF SEPTAGE
tn
Time of
Aeration
days
44
10
Batch -
22 to 40
Lagoon -
1 to 30
1
1
4
Raw Septage
Characteristics
mq/L
TSS
VSS
COD
TSS
VSS
BOD 5
COD
TSS
VSS
COD
TSS
BOD 5
COD
TS
BOD5
COD
TSS
BOD 5
- 33,240
- 26,200
- 33,820
- 21,400
- 14,100
- 8,600
- 24,000
- 39,100
- 30,100
- 3,360
- 7,734
- 4,004
- 14,655
- 19,262*
- 7,990
- 25,880
- 8,680
- 5,850
Supernatant
Characteristics
Remarks Reference
mg/L
TSS -
VSS -
BOD5 -
COD -
TSS -
VSS -
COD8 -
TSS -
VSS -
CODg -
TSS -
BOD -
COD -
TS
BOD -
COD -
TSS -
BOD5 -
9,550
5,800
6,900
13,100
40% Red.
43% Red.
75* Red.
16% Red.
20% Red.
74% Red.
1,063
661
3,361
480
1,030
3,310
1,480
295
(screened)
.Aeration tine required to produce fully
stabilized sludge @ 18°C; max. O2 uptake
rate JEor fully stabilized sludge @ 18°C:
0.7 mg 02/g VSS/hr
Bench scale using 6-liter reactors
Batch size - 3 to 6 liters
D.O. maintained at 1 mg/L
Raw septage CST = 223 sec
Lagoon size - 1.75 to 1 0 liters
semi-continuous feed
Pure oxygen atmosphere in a closed
reactor; supernatant reported
after settling
Pure oxygen atmosphere in a closed
reactor; supernatant reported
after settling
Supernatant reflects 2- hours of settling;
improvement in settling characteristics
noted; 90% NH3^N removal and 93% removal
noted in supernatant also
25
26
24
27
28
29
•Digested Sludge Characteristics: TS-37,500 mg/L; TVS-28,100 mg/L
-------
A pilot study at the U.S. EPA Lebanon pilot plant was hampered by ser-
ious foaming problems during batch aerobic digestion of septage (20).
Odors were eliminated and settleability improved in 7 to 13 days, re-
spectively, at air flow rates of 500 L/min/m3 (0.5 scfm/cu ft). Su-
pernatant quality improved sharply from COD values of 31,200 and
26,830 mg/L on days 1 and 12, respectively, to 2,270 mg/L on day 13.
However, supernatant quality did not improve after a 31-day batch aer-
ation study at 250 L/min/m3 (0,25 scfm/cu ft). At the latter air
flow rate, 55 percent reductions of volatile solids were observed,
while 70 percent reductions were achieved at 500 L/min/m3 (0.5 scfm/
cu ft), over the same 31-day period. Perrin (30), in his bench-scale
study on chemical treatment, concluded that the use of short-deten-
tion aerated lagoons for odor reduction and partial stabilization,
followed by chemical conditioning and sand-bed dewatering, may be a
workable alternative to full stabilization by long-term (approximately
40 days) aerobic digestion of septage. Tilsworth (26) noted 80 percent
BOD5 reductions and 41 percent VSS reductions after 10 days of aera-
tion.
7.5.2 Equipment
Conventional aerobic digesters are open-topped tanks or earthen basins
and are affected by ambient temperatures. TO avoid excess heat losses,
tanks have been covered or placed below grade. The mixing and aeration
requirements can be provided by either mechanical mixers or diffusers.
The equipment (basins, aerators, etc.) used for aerobic digestion of
septage is the same as that used for other sludges (1); Because the
solids retention time is generally longer for septage than for other
sludges, the size of the equipment may differ.
7.5.3 Design Criteria
The design of aerobic digestion systems for septage should be based on
the following criteria: solids retention time, VSS loading, aeration
capacity, minimum dissolved oxygen concentration, and operating tem-
perature.
7.5.3.1 Solids Retention Time (SET)
Figure 7-10 shows the reduction of VSS with time in a batch aerobic
digestion system study by likum (31). The solids retention time (SRT)
required for a particular case depends on the degree of septage stabi-
lization required, the characteristics of the septage, and the oper-
ating temperature. If complete stabilization is required, then the SRT
166
-------
FIGURE 7-10
REDUCTION OF VSS IN BATCH AEROBIC DIGESTION WITH TIME (31)
Primary Sludge
Mixed Primary-Chemical (Alum) Sludge
Septic Tank Sludge
o
I
oc
10 20
30 40 50 60
Detention Time (Days)
70
167
-------
should be 30 to 40 days at a temperature of about 18 to 20°C (64 to
68°F). If complete stabilization by aerobic digestion is not re-
quired (e.g., the partially stabilized septage will be land applied),.
then the SRT can be proportionally lower.
7.5.3.2 Solids Loadings
VSS loadings ranging from 0.5 to 21 kg VSS/m3/d (0.03 to 1.3 Ib
VSS/ft3/d) for batch aerated lagoon studies have been reported (32) .
Researchers have recommended that the organic loading for aerobic
digestion be in the range of 1.6 to 21 kg VSS/m3/d (0.1 to 1.3 Ib
VSS/ft3/d) (25). Although these volatile suspended solids loadings
are somewhat higher than volatile solids loadings typically reported
for aerobic digestion of sewage sludge [1.6 to 3.2 kg VSS/m3/d
(0.1 to 0.2 Ib VS/ft3/d)] (21), it should be kept in mind that the
recommended values for septage are derived from a much smaller data
base. Septage loadings should conform to sludge loading recommenda-
tions until further experience in gained. Therefore, septage loadings
for aerobic digestion should be 3.2 kg VS/m3/d (0.2 Ib VS/ft2/d)
or less for design purposes.
7.5.3.3 Air Requirements
Aeration serves two purposes in aerobic digestion: it maintains a
positive dissolved oxygen (D.O.) level, and it keeps the solids in
suspension. The air requirements should ideally be based on oxygen
uptake rate measurements, but the air requirement based on uptake
alone is not sufficient to keep septage solids in suspension (1). An
air flow rate of 50 m3/min/l,000 m3 has been successful at the
U.S. EPA Lebanon pilot plant, with VSS reductions of greater than 70
percent after 30 days of aeration (39). Eikum (1) recommends 80 to 100
m3/min/l,000 m3 based on Norwegian experience. Since Norwegian
septage is heavily concentrated with sand and other heavier organics,
a lower value of 50 to 80 m3/min /1,000 m3 of digester capacity
is recommended for design.
7.5.3.4 Dissolved Oxygen
The aerators must be able to maintain a minimum D.O. level of 1 mg/L
for efficient operation. Experience with wastewater sludges indicates
that aerobically-digested sludge dewaters most efficiently if the D.O.
during digestion is maintained at a level of at least 1 mg/L (34).
168
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7.5.3.5 Operating Temperature
One of the major variables affecting the rate of aerobic digestion is
the operating temperature of the digester. It has been observed that,
for sewage sludge, aerobic digester operation is temperature-dependent,
especially at temperatures below 20°C (68°F) (21) . At higher tem-
peratures, the biological activity - and therefore the oxygen uptake
rate - would increase (25). It was proposed that the oxygen uptake
rate (OUR) be adjusted for the temperature as follows:
/ OURj-2 = «pTl-T2 (1)
= Oxygen uptake rate at temperature T^
OURj-2 = Oxygen uptake rate at temperature T2
= Streeter-Phelps temperature sensitivity coefficient (Eikum and
Paulsrud (25) assumed a value of 1.10)
Eikum (1) also noted that the SRT's for aerobic stabilization of sep-
tage increased dramatically with decreasing temperatures. Bowker and
Hathaway (20) noted that for average annual temperatures lower than
20°F (68°F) , longer SRT's will be required for good VSS reduction.
In extremely cold climates, consideration should be given to heating
the septage or the air supply, and covering and insulating the tanks.
Table 7-5 contains a summary of the design criteria for aerobic
stabilization of septage.
7.5.4 Limitations
Two major problems associated with aerobic digestion of septage are
odors and foaming. -In batch aerobic digestion pilot tests, it was
found that odors were reduced after approximately 3 to 4 days of aera-
tion, and that foaming would dissipate after about 10 days (32). Foam-
ing was caused by washing machine detergents and could be controlled
in the digester by foam fractionation or use of commercial anti-
foamers. In addition, aerobic digestion requires constant monitoring
and operator attention, can be sensitive to toxic substances in the
septage, and requires further handling (e.g., dewatering, transporta-
tion, etc.) prior to ultimate disposal (20).
Because of these limitations,.long detention times required for stabi-
lization, and high capital and operating costs (compared with land
treatment, lagooning, etc.), it is unlikely that aerobic digestion
would be attractive or justifiable for any but large or land-limited
independent septage treatment facilities.
169
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TABLE 7-5
AEROBIC STABILIZATION OF SEPTAGE
TYPICAL DESIGN CRITERIA
Parameter
Value
Remarks
Solids Retention Time,
Days
20 - 40
VSS Loading, kg/m3/d
Requirements for Mixing
Air mixing,
m3/1000 m3/min
Mechanical Aerators,
kw/1000 m3
Oxygen Requirements
kg O2/kg VSS
D.O. Level in Liquid,
mg/L
Operating Temperature,
°C
Tank Design
1 .6 -21
25 - 50
26 - 33
1 .8
1 -
For septage characteristics similar
to Table 3-4, design for 20 - 30
days SRT; for stronger septage, use
longer SRT. For operating temper-
atures > 20°C (68°F), use 20 - 30
days SRT; for lower temperatures,
use longer SRT.
Loading increases with increasing
SS concentration, decreases with
increasing SRT.
To maintain minimum D.O. of approxi-
mately 1-2 mg/L and to keep solids
in suspension.
Aerobic digestion tanks are open and
generally require no special heat
transfer equipment or insulation in
warmer climates. However, in cold
climates, heating influent septage
or air supply, and/or covering and
insulating tanks should be con-
sidered. For small treatment
systems, the tank design should be
flexible enough so that the digester
tank can also act as a thickening
unit. If thickening is to be
utilized in the aeration tank, sock-
type diffusers or mechanical aerators
should be used to minimize clogging.
170
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7.5.5 Monitoring - Aerobic Digestion of Septage
Temperature, pH, total solids, volatile solids, dissolved oxygen, set-
tleable solids, 8005, and alkalinity must be monitored regularly for
process control of aerobic digestion.
A study was conducted to determine which parameters can be used as a
measure of the degree of stability of aerobically-digested sludges
(25). Of the parameters studied, including ATP (adenosine triphosphate)
levels, pH, TSS and VSS reduction, and oxygen uptake rate (OUR) , it
was concluded that OUR is a reliable indicator of sludge and septage
stability, as defined in Section 7.2.1.1. OUR decreases and levels
off with increased detention time, as shown in Figure 7-11. It was also
concluded that aerobically-digested septage could be considered sta-
bilized as long as the OUR remained less than 0.7 mg O2/g VSS/hr at
18°C (25). Thus, OUR can be corrected for temperature using Equation
1.
7.6 Anaerobic Stabilization of Septage
Anaerobic stabilization or digestion is a biological process in which
organic matter is decomposed in the absence of molecular oxygen. The
primary products of anaerobic digestion are methane and carbon diox-
ide? however, some unusable intermediate organics and a relatively
small amount of cellular protoplasm are also produced. The major ap-
plications of anaerobic digestion have historically been in the sta-
bilization of concentrated sludges produced from the treatment of
wastewater and in the treatment of some industrial wastes (21). Be-
cause septage is such a concentrated waste, it follows that anaerobic
digestion would be an appropriate stabilization technique. Only lim-
ited data exist on anaerobic digestion of septage at independent sep-
tage treatment facilities, although anaerobic digestion of septage at
a treatment plant (co-treatment) has been well documented, as dis-
cussed in Chapter 6.
This section presents available design and operating data for anaero-
bic digestion of septage, A complete discussion of the design of mu-
nicipal sludge digestion facilities is given in Subsection 7.2 of the
EPA Manual for Sludge Treatment (36). The basic design approach pre-
sented in the manual can be applied to the design of independent sep-
tage digestion facilities. Anaerobic digestion is classified by EPA as
a process to significantly reduce pathogens (PSRP). Table 7-6 shows
levels of pathogenic bacteria reduction that can be expected during
anaerobic digestion.
171
-------
FIGURE 7-11.
OXYGEN UPTAKE RATE VERSUS DETENTION TIME
IN AEROBIC DIGESTER. (25)
.-. 3.0*
CO
> 2.5 H
en
•v,
Ctl
O
O) 2.0 *
«* 1 C J
DC 1.5 •
0!
IS
J| 1.0 H
0)
at
>•
x
O
0.5
Septage
Mixed Primary Chemical (Al) Sludge
O-—O Primary Sludge
10 20 30 40 50 60 70
Detention Time (Days)
80
90
172
-------
TABLE 7-6
REMOVAL OF PATHOGENIC BACTERIA
DURING ANAEROBIC DIGESTION OF SEWAGE SLUDGE (34)
Bacteria
Digestion
Per iod
(days)
Removal
Remarks
Endamoeba 12
hystolytica
Salmonella
typhosa 20
Tubercle 35
bacilli
Escherichia 49
coli
<100 Greatly reduced populations at
68°F (20°C)
92 85% reduction in 6 days detention
85 Digestion cannot be relied upon for
complete destruction
<100 Greatly reduced populations at
99°F (37°C)
7.6,1 Research - Anaerobic Digestion of septage
Table 7—7 is a summary of five studies in which septage was stabilized
by anaerobic digestion. All five studies operated in the mesophilic
range, 32 to 35°C (90 to 95°F) . The results and conclusions of the
studies are varied. Two studies had limited success with anaerobic di-
gestion of septage. Kolega, et al. (37) experienced very poor gas pro-
duction; the gas that was produced was of very low quality.
Kolega, et al. (44) sampled for the presence of detergent surfactants
in the form of linear alkyl sulfonate (LAS) because foaming was no-
ticed. LAS concentrations ranged from 3 mg/L to 61 mg/L in 30 samples,
indicating the presence of detergent products. Jewell, et al., (24)
experienced digester failure, but the laboratory test was inadequate
to draw any conclusions.
A U.S. EPA study performed at Lebanon, Ohio (39) attempted to deter-
mine the effectiveness of anaerobic digestion of septage alone, as
well as mixtures of septage and primary wastewater sludge. The con-
clusion of the study was that septage mixed with primary sludge had no
adverse effect on the digestion process. The study also revealed the
effectiveness of anaerobically digesting septage alone. With an SRT of
30 days, the gas production from anaerobic digestion of the septage
averaged 9 percent lower than that for primary sludge. Volatile solids
173
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TABLE 7-7
SUMMARY OF RESEARCH ON ANAEROBIC DIGESTION OF SEPTAGE
Average
Loading Total Solids HRT % Reduction Gas Production
Septage
Septage
Septage
Primary Sludge
Septage
Septage
Primary Sludge
kg V3/m3/d %
0.16 0.23
0.48 2.84
0.48-2.6 2.8
0.71-1.8 3.2
0.77 4.2
1.6
1.9
days VSS TS m3/kg VS References
10 38
15 .37
10-30 40 26 0.46-0.70 39
10-30 56 37 0.52-0.87
48 47 35 0.44 24
30 40
35
-------
destruction of septage was also 25 percent less than that of primary
sludge during the test period. Since septage is partially stabilized
(due to anaerobic processes in the septic tank) and contains more
grease than primary sludge, less gas production and less volatile
solids reduction are expected from septage digestion.
A German study also showed that the volatile solids reduction of di-
gested septage (29.5 percent) was less than that of digested primary
sludge (38.5 percent) (40). In this same study there was a 1005 re-
duction of 53 percent for digested septage, compared to a 72 percent
reduction for primary sludge.
The results from these tests cannot be considered conclusive? however,
the data indicate that septage can be anaerobically digested. In the
U.S. EPA study, batches of septage were stored for long periods. Thus,
the digesters were not subject to daily shock loads but were, instead,
fed the same septage over long time periods. This study also shows
that good results were obtained using standard rate digester loadings
in a high rate (i.e., completely mixed and heated) environment.
7.6.2 Equipment
Anaerobic digestion of septage can proceed either in airtight tanks or
in anaerobic and facultative stabilization ponds. Stabilization ponds
were discussed in Section 7.2, which specifically addresses septage la-
goons. The equipment discussed in this section is limited to that for
anaerobic digestion in tanks. The three most commonly used types of
anaerobic digestion are standard—rate (or conventional), high-rate,
and two-stage. Thorough discussions of equipment for anaerobic diges-
tion are available in standard references (21) (34) (36).
7.6.3 Design Criteria
The design of anaerobic digestion systems for septage should be based
on the following criteria: solids retention times, VSS loading, pH
control, mixing, heating requirements, and operating temperature.
7.6.3.1 Loading
As shown in Table 7-7, the VS loading range that produced a VSS reduc-
tion of 40 percent or more was 0.5 to 2.6 kg VS/m3/day (0.03 to 0.16
Ib VS/ft3/day) . This loading is roughly within the same range as for
standard rate mesophilic (25 to 40°C or 77 to 104°F) anaerobic di-
gestion of wastewater sludge, and is lower than the typical high-rate
loading for sludge, as shown in Table 7-8.
175
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TABLE 7-8
COMPARISON OF SLUDGE DIGESTION DESIGN CRITERIA
WITH REPORTED VALUES FOR
MESOPHILIC ANAEROBIC DIGESTION OF SEPTAGE
Primary and
Waste Activated Sludge a'k Reported Values for
Parameter Standard Rate High-Rate Septage Digestion0
Solids Loading,
kg VS/m3/day 0.5 - 1.6 1.6 - 6.4 0.5 - 2.6
Solids Retention
Time, days 30 - 60 10 - 20 10 - 30
Expected Gas
Production,
m3/kg VS added 0.5 - 0.75 0.5 - 0.75 0.25 - 0.62
aEPA, 1974 (34).
bTchobanoglous, 1979 (21).
°Table 7-6.
7.6.3.2 Solids Retention Time (SRT)
Although the septage SRT values listed in Table 7-7 are within the
range of high-rate digestion of sewage sludges, it should be kept in
mind that the septage values are those reported for laboratory and
pilot-scale studies. The criteria listed for sewage sludge digestion
are based on full-scale operations and have been used successfully in
many facilities.
7.6.3.3 pH Control
Based on sewage sludge experience, it is good practice to provide for
pH control of the anaerobic digestion process. The pH in an anaerobic
digester should be maintained in the range of 6.6 to 7.6 for a proper
growth environment for the methane-forming organisms (21). Therefore,
pH control of the septage feed to the digester should be provided.
With a high pH, the production of ammonium increases and the production
176
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of methane slows down (42). Lime, soda ash, sodium bicarbonate, etc.,
can be used to adjust the pH of the septage as required. Sufficient
alkalinity should be present to ensure that the pH will not drop below
6.2, since the methane bacteria cannot function below that level (21).
The alkalinity of undigested primary sludge ranges from 500 to 1500
mg/L (average 600 mg/L) as CaCOj (21). As discussed in Chapter 3,
septage alkalinity typically ranges from 500 to 4000 mg/L (average
1000 mg/L) as CaCO3? therefore pH depression due to insufficient
alkalinity should not be a common problem during anaerobic digestion
of septage.
7.6.3.4 Mixing
Proper mixing is one of the most important considerations in achieving
optimum process performance (21). Draft tubes, mechanical mixers, and
gas recirculation mixers are most commonly used in anaerobic diges-
ters. Mixer sizing and design criteria depend on the type of digester
tank and on the type of mixing system selected.
The researchers whose work was summarized in Section 7.6.1 report no
difficulties in mixing septage, compared with sewage sludge, during
anaerobic digestion. General design guidelines applying to treatment
of sewage sludge (21)(34)(36) should also apply to the treatment of
septage with the exception of grease interference with mixing'. The
major concern which designers must deal with is the high grease con-
centration of septage, which can interfere with proper digester mixing.
7.6.3.5 Heating Requirements
Digester heating requirements consist of the amount needed to: raise
the incoming septage to digestion-tank temperature; compensate for the
heat losses through digester walls, floor, and roof; and make up for
heat losses in external piping (21). The requirements for heating sep-
tage and for insulating against heat losses have not been reported to
be different from those of sewage sludge. Tchobanoglous (21) presents
an excellent procedure for calculating energy requirements for raising
influent temperature and for computing heat losses through the tank
itself and through external piping. This calculation procedure illus-
trates the benefits of insulating and/or burying tankage and piping to
minimize heat losses.
177
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7.6.3.6 Operating Temperature
Optimum temperature ranges for anaerobic digestion are the mesophilic,
30 to 38°C (85 to 100°F) and the thermophilic, 49 to 57°C (120
to 135°F). These higher temperatures provide more rapid pathogen
destruction (as was shown in Figures 7-8 and 7-9) and require shorter
detention times.
7.6.3.7 Typical Design Criteria
Table 7-9 is a summary of the typical design criteria for anaerobic
stabilization of septage.
7.6.4 Limitations
The limitations of anaerobic digestion include its relatively high
capital cost (compared with aerobic digestion), sensitivity to upset,
monitoring requirements, poor quality supernatant (high oxygen demand
and high concentrations of nitrogen and suspended solids), and rela-
tively long detention time required for stabilization (34).
7.6.5 Monitoring
The following parameters must be monitored for control of anaerobic
digestion: pH, temperature, and presence of toxic materials.
7.6.5.1 pH
Close pH control is necessary because methane-formers are extremely
sensitive to slight changes in pH. The pH should be monitored within
the range of 6.6 to 7.6 (36). Methods for maintaining the pH in this
range are discussed briefly in Section 7.6.3.3, and in more detail
elsewhere (21) (34).
7.6.5.2 Temperature
More important than maintenance within a particular temperature range
is maintenance of the chosen temperature for operation at a constant
value. Based on experience with sewage sludge, a temperature change of
178
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TABLE 7-9
TYPICAL DESIGN CRITERIA FOR
ANAEROBIC STABILIZATION OF SEPTAGE
Parameter
Value
Remarks
Solids Retention Time,
days
VSS Loading, kg/m3/d
pH Control
Operating Temperature
Mesophilic
op
Thermophilic
°C
10 - 30
(heated)
0.5 - 1.6
6.6 - 7.6
30 - 38
49 - 57
High-rate: 10 days minimum
Low-rate: 30 days minimum
Higher temperatures require
shorter SRT
For VSS reduction>40%
Sufficient alkalinity required
to maintain pH>6.2; otherwise,
methane-formers cannot func-
tion.
179
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2 or more degrees can be sufficient to disturb the dynamic balance
between the acid and methane formers. Such a disturbance can lead to
an upset because the acid formers are able to respond more rapidly to
changes in temperature than are the methane bacteria (34).
7.6.5.3 Toxicity
Toxicity can be due to an excessive quantity of any material, even a
substance normally considered a nutrient. The concentration at which a
substance starts to exert a toxic effect is difficult to define be-
cause it can be modified by antagonism, synergism, and acclimation. In
addition, the organic loading and biological solids retention time can
cause a stress on the process, and this stress can affect toxicity.
The substances that can produce toxicity when present in municipal
sludge or septage in an excessive concentration include heavy metals,
sulfides, surface active agents, light metals, and certain organics.
General information on some potentially toxic substances is given in
Table 7-10 (34) (36). Compared with sewage sludge, the septage concen-
trations of heavy metals are generally lower, while sulfide and sur-
factant concentrations are generally higher. It can, therefore, be
assumed that any potential for toxic effects during anaerobic diges-
tion would more likely be associated with sulfides and surfactants
rather than heavy metals if septage is purely domestic. However, the
problem of industrial waste contamination and lack of control at the
receiving station could create a significant risk if anaerobic diges-
tion were chosen as the stabilization method.
7.6.6 Process Modifications
The two most common modifications of the anaerobic digestion process
are thermophilic anaerobic digestion and the anaerobic contact proc-
ess. Thermophilic anaerobic digestion operates in the temperature
range of 49 to 57°C (120 to 135°F) . The advantages of thermophilic
over mesophilic anaerobic digestion include faster reaction rates
(which permit lower detention times), improved dewatering of digested
septage, and increased destruction of pathogens (36) . The last advan-
tage places thermophilic digestion into the PFRP category (Process to
Further Reduce Pathogens). Disadvantages of thermophilic digestion
include higher energy requirements for heating; lower quality super-
natant containing larger quantities of dissolved materials; and poorer
process stability. Thermophilic organisms are particularly sensitive
to temperature fluctuation (36).
180
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TABLE 7-10
SUBSTANCES AND CONCENTRATIONS CAUSING TOXICITY
IN WASTEWATER SLUDGE DIGESTION (34) (36)
Substance
Concentration
(mg/L)
Volatile Acids
Sulfides
.Soluble Heavy Metals
Sodium
Potassium
Calcium
Magnesium
Ammonium
Free Ammonia
6,000 - 8,000
200
5,000
4,000
2,000
1,200
1,700
8,000
10,000
6,000
3,500
4,000
150
181
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The anaerobic contact process is the anaerobic equivalent of the ac-
tivated sludge process. The unique feature of this variation is that a
portion of the active biomass leaving the digester is concentrated and
then mixed with the raw feed. This recycling allows for adequate cell
retention time to meet kinetic requirements while operating at a sig-
nificantly reduced hydraulic retention time. This process modification
has not been widely applied for sewage sludge because of the diffi-
culty in achieving the necessary concentration within the return stream
(36), and its use has not been reported for septage.
7.7 Lime Stabilization of Septage
Lime stabilization is a low capital cost, simple technology. Addition
of lime to septage in sufficient quantities to maintain a high pH (>12)
for 30 minutes creates an environment that is not conducive to micro-
organism survival. This criterion (pH > 12 for 30 minutes) has been
found to correlate well with dewaterability and odor conversion in
U.S. practices. As a result, the septage will not putrefy, cause
odors, or pose a health hazard as long as the pH is maintained at a
high enough level (21) (35). Actual dosage may require adjustment due
to local conditions and the period of stability required.
Lime stabilization may be followed by a dewatering step, or the sta-
bilized liquid septage may be spread on the land directly (20). Since
lime stabilization, unlike aerobic or anaerobic digestion, does not
destroy the organics necessary for bacterial growth, the septage must
be disposed of before the pH drops significantly or it can become re-
infested and putrefy (21). Lime addition to septage may reduce nitro-
gen concentration through volatilization of ammonia if conditions
permit this stripping, often enabling greater quantities of stabilized
septage to be applied per unit of land area, since such applications
are often limited by nitrogen loading (see Chapter 5). Lime stabiliza-
tion is, therefore, only a temporary stabilization which enables fur-
ther handling and disposal to take place prior to the onset of desta-
bilization.
7.7.1 Research - Lime Stabilization of Septage
It has been shown that achieving a high pH is not as important as
maintaining a high pH for a certain period of time (1)(45). Enough
lime must be added to provide a sufficient degree of stabilization to
permit a storage/handling time period of about 14 days so that the sep-
tage can be ultimately disposed of in an environmentally-sound manner.
A 14-day time period has been used by researchers to allow for odor
control during storage (46). Paulsrud and Eikum (46) found that the
lime dosages necessary to reach a high initial pH (10.0, 10.5, 11.5)
182
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were not sufficient to maintain a high pH during storage. They further
found that lime dosages to raise the pH to initial values of 12.5 or
higher produced the most stabilized septage samples. These dosages
were sufficient to prevent pH reduction within four weeks of storage,
as shown in Figure 7-12. They concluded that a lime dosage of 100 to
300g lime/kg SS {200 to 600 Ib lime/ton SS) would be necessary to pre-
vent pH reduction and odor production within 14 days of storage. These
dosages are to maintain pH > 11 at 20°C (68°F) during the 14-day
storage period. These researchers found that thickening does not alter
the lime dosage necessary to prevent pH reduction during storage, that
both microbial activity (measured by ATP) and CO2 uptake from the
air are responsible for the pH reduction during storage, and that
higher storage temperatures result in greater pH reductions.
Some investigators have commente'd on the change in odor intensity dur-
ing lime stabilization. Eikum (1) noted that, during storage of lime
stabilized septage, as soon as the pH fell below 11.0, the odor in-
creased considerably. In addition, an increase in the Odor Intensity
Index (Oil) (ASTM Method D 1292) was normally experienced during stor-
age, regardless of the amount of lime added. This increase took place
during the first eight days of storage, but was slowed by higher lime
levels, as shown in Figure 7-13.
Although the odor intensity generally remains the same, the type of
odor changes as a result of lime addition (1) (45). During full-scale
operations at the Lebanon plant (49) it was noted that odor was in-
tense when raw septage was first pumped to the lime stabilization
mixing tank. Odor intensity increased when diffused air was used for
mixing. When lime was added, the septic odor was masked by the odor of
ammonia, which was stripped from the septage by the air bubbled through
it. As mixing proceeded, the treated septage acquired a musty, humus-
like odor. Lime stabilization studies conducted at the Lebanon plant
for both septage and sewage sludge showed that odor reduction was sig-
nificantly greater for sewage sludge than for septage.
High pH not only reduces odors but also inhibits pathogen growth. Work
by Farrell, et al. (47) and Counts, et al» (48) has shown that lime
stabilization will reduce pathogens in sludges. However, most work has
been based on 24-hour storage after lime addition. Since the stability
concept is based on several days of storage after lime addition, it is
necessary to look at the removal of pathogens with respect to lime
dosage and storage period.
183
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FIGURE 7-12
CHANGE IN pH DURING STORAGE OF SEPTAGE AT 20°C (68°F)
USING DIFFERENT LIME DOSAGES (46)
440g Ca(OH)a/kg SS
SS=5 18%, VSS/SS = 77 9%
8 12 16 20
Days of Storage
24
j i
28
FIGURE 7-13
CHANGE IN ODOR INTENSITY INDEX DURING STORAGE
OF LIME STABILIZED SEPTIC TANK SLUDGE AT 68°F (20°C) (1)
20
I 16
s
I 12
"5
i 8
o
S 4
n D
A A
Lime Dosage
None
SOg (Ca(OH)*/kg TSS)
100g Ca OH:/kg TSS
200g Ca OH, /kg TSS
4 8 12 16 20 24
Days of Storage After Lime Addition
28
184
-------
Work done at the Norwegian Institute for Water Research (1) shows that
a reduction of coliforms and fecal streptococci takes place during
storage of sludges (primary, primary/alum/ biological/alum) even
without lime addition. However, this was not found to be true for sep-
tage. Anaerobic spore formers were not affected by storage period
alone. At a lime dosage of 50g lime/kg SS (100 Ib lime/ton SS), it was
found that the concentrations of the organisms investigated were not
reduced. This was true for all types of sludges. With septage, this
dosage of lime, even indicated an increase in the number of organisms
in some cases. A lime dosage of 200g/kg SS (400 Ib lime/ton SS) used
during the investigation clearly showed that the pathogen concentra-
tion can be reduced below the detectable limit of 200 organisms per
100 ml for septage as well as for sludges. In many cases, it took ap-
proximately 2 hours of contact time to get below the detectable limit.
Noland, et al. (45) added lime to septage to maintain pH 12 for 30
minutes. Pathogens were reduced significantly as shown in Table 7-11.
In addition, total COD, phosphate, TKN, and VSS were reduced by lime
stabilization, while alkalinity, soluble COD, ammonia nitrogen, and
TSS increased, as shown in Table 7-12.
7.7.2 Equipment
Two process trains most applicable to the lime stabilization of sep-
tage are shown in Figure 7-14 (1). Lime stabilization facilities
should consist of at least a method of lime feeding, a mix tank, and
pH monitoring. Mixing can be accomplished by either diffused aerators
or mechanical mixers. Thickening, if desired, can occur in a separate
tank or batchwise in the mix tank after shutting off the mixing device.
7.7.3 Design Criteria
The two most important criteria for design of a septage lime stabili-
zation facility are lime dosage/pH and mixing/contact time. Detailed
discussion of the design procedure for lime-handling facilities can be
found elsewhere (36).
185
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TABLE 7-11
BACTERIA IN RAW AND LIME-STABILIZED SEPTAGE AT LEBANON, OHIO (45)
Bacterial Density, Number/100 ml
Parameter
Total Coliformb
Fecal Coliformb
Fecal Streptococci
Saltnonellac
Ps. Aeruginosac
Raw Septage Lime-Stabilized Septage3
2,9 x 108
1.5 x ID7
6.7 x 105
6
754
2.1 x 103
265
665
<3
<3
aTo pH^12 for at least 30 minutes.
kMillipore filter technique used.
cDetection limit =3.
186
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TABLE 7-12
CHEMICAL COMPOSITION OF RAW AND LIME STABILIZED SEPTAGE
AT LEBANON, OHIO (45)
Concentration, average, mg/L
Parameter
Alkalinity
Total COD
Soluble COD
Total Phosphate
Soluble Phosphate
Total Kjeldahl Nitrogen
Ammonia Nitrogen
TSS
VSS
Raw Septage Lime-Stabilized Septage3
1,897
24,940
1,223
172
25
820
92
21,120
12,600
3,475
17,520
1,537
134
2.4
597
110
23,190
11,390
aTo pH^12 for at least 30 minutes.
187
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FIGURE 7-14
COMMON LIME STABILIZATION PROCESS TRAINS
Alternative 1 - Continuous Feed
Septage
Lime
r
Thickener
Mixing
High pH
Supernatant
-M Dewatering
'o'-oo
Alternative 2 - Batch Treatment
Septage Lime
Sludge Dra
4-
4-
****.
C^
' 1
uvnOH 1
High pH
Supernatant
t
Mixture Settles 1
'o-oo
188
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7.7.3.1 Lime Dosage/pH
The amount of lime required to stabilize septage depends primarily on
its chemical composition and solids concentration. Dosages reported by
various investigators are summarized in Table 7-13. A relationship be-
tween pH and lime dosage at various initial SS concentrations is shown
in Figure 7-15 (45). Noland, et al., (45) examined the effects of ex-
cess lime addition above the levels necessary to reach pH 12. They
found that there was a negligible drop in pH over a 10-day period, and
concluded that significant pH decay should not occur once sufficient
lime has been added to maintain the sludge pH at 12.0 for at least 30
minutes. Their conclusion was based on studies with primary sludge.
EPA considers lime stabilization an accepted PSRP (Process to Signif-
icantly Reduce Pathogens). The definition given in 40 CPR 257 calls
for the addition of "sufficient lime to produce a pH of 12 after 2
hours of contact." Based on the findings of Paulsrud and Eikum (46),
lime addition at a rate sufficient to maintain pH 11.0 for at least 14
days of storage at 20°C also would fulfill the PSRP requirement.
The lime dosages predicted by the "Counts Equation" were compared with
the actual lime dosages required at the Lebanon plant (45), The Counts
Equation (Equation 2) was developed to predict lime dosages for pri-
mary and secondary sludges from the trickling filter plant in Rich-
land, Washington (48).
Lime Dose = 4.2 + 1.6 (TS) (2)
where:
Lime dose = Grams lime/liter of sludge
TS = Total solids fraction in sludge
It was found that -with increasing solids concentrations, the Counts
Equation results in lower than actual required lime dosages (45).
7.7.3.2 Mixing/Contact Time
The design objective is to maintain pH above 12 for about 2 hours and
to provide enough residual alkalinity so that the pH does not drop
below 11 for at least 14 days to ensure pathogen destruction, thereby
allowing sufficient time for disposal or use without the possibility
of renewed putrefaction.
189
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TABLE 7-13
REPORTED VALUES OF LIME REQUIREMENTS FOR SEPTAGE STABILIZATION
Total Solids Lime Dosage,
Concentration kg lime/kg dry solids
Reference
45
46
49
Percent
1 to 4.5
5.1
3.1 to 4.5
Average
0.20
0.125
0.10
Range
0.09 to 0
0.10 to 0
0.053 to
.51a
.30b
0.1*.
aLime required to maintain pH^12.0 for 30 minutes.
^Lime required to maintain pH>ll for 14 days.
GLime required to raise pH to 11.5.
190
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FIGURE 7-15
LIME DOSAGE VERSUS pH (45)
13.0
12.0-
11.0
o 10.0
Q.
•o
UJ
73
0)
9.0
8.0
7.0-
6.0
Initial SS =
II
1.5%—•* /
I*- 4.5% /
'
A 3%
1,000
-f-
2,000 3,000
Dosage Ca (OH)2 mg/L
4,000
5,000
191
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The lime mixing tank should be sized to provide a minimum of 30 min-
utes' contact time at peak flow. In the case of a small treatment
facility, where batch processing is most attractive, the mix tank
should be sufficiently large to treat the maximum-day septage produc-
tion in one batch, particularly if the treatment facility is to be op-
erated only one shift per day. Norwegian guidelines call for a mini-
mum of 15 minutes detention in the mixing tank if followed by thick-
ening or aerated storage, with 30 minutes being otherwise required (1).
Mixing can be provided by either diffused air or mechanical mixers,
but the former is preferred both in the United States (45) and Norway
(1). Air requirements of 150 to 250 m3/min/1000m3 (150-250 cfm/
1000 ft3) of mixing tank volume for coarse bubble diffusers have
been suggested (45). The diff users should be mounted such that a spi-
ral roll is established in the mixing tank "away from the point of lime
slurry application. In addition, the diffusers should be accessible,
and piping should be kept against the tank wall to minimize the col-
lection of rags, etc.
Mechanical mixer sizing should be based on the following two criteria
(36):
- Maintaining the bulk fluid velocity (turbine agitator pumping
capacity - cross sectional area of the mixing vessel) above
7.9 m/min (26 ft/ min).
- Using an impeller Reynolds number greater than 1000.
Noland, et al. (1978) (45) reported that mechanical mixing has been
used by previous researchers for lime stabilization, but only on the
pilot scale. Section 9 of the report by Noland (45) discusses selection
of mixer horsepower.
Although lime may be added in the slurry or dry form, the former is
generally preferred for larger installations. Dry lime addition for
batch processing at smaller facilities is less efficient, but far
easier for operators.
A summary of the design criteria for lime stabilization of septage is
presented in Table 7-14.
192
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TABLE 7-14
TYPICAL DESIGN CRITERIA - LIME STABILIZATION OF SEPTAGE
Parameter
Value
Remarks
Lime Dosage
kg lime/kg dry solids
Contact Time, min
Mixing Requirements
Air, m3/1000
Mechanical
Bulk fluid velocity
^m/min
Impeller Reynolds Number
0.1 - 0.3
30
150 - 250
4.6 - 7.9
>1000
Dosage must be sufficient to
maintain pH of 12,0 for at
least 2 hours or above 11.0
until further processing9
At peak flow
aSpecific dosage must be adjusted to the purpose of lime stabilization
and site conditions.
193
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7.7«4 Limitations
Limitations of lime stabilization of septage are:
1. Lower fertilizer value {soluble phosphate, ammonia nitrogen,
TKN, etc.) than comparable digested sludge (45).
2. O&M problems due to scaling in the lime addition system,
3. No reduction of organics.
4. Potential for fecal streptococci to remain viable, although
regrowth of other bacteria is minimal (45).
5. Lime addition significantly increases the quantity of mate-
rial for disposal.
6. High pH sludge liquor to treat or dispose of, if separation
or dewatering follows this process.
7.7.5 Monitoring
As discussed above, the requirements for lime stabilization include
maintaining the pH at 12.5 or greater for at least 30 minutes. This
can be accomplished in a batch system by monitoring the pH throughout
the lime addition, and for a minimum of 30 minutes thereafter.
In continuous flow systems, automated control of lime feeding may be
required. The pH is normally measured in the exit line from the mix
tank. The pH and volume of septage in the mix tank are held constant.
Entering raw septage displaces an equal volume of treated septage.
Lime is added continuously, in proportion to the flow of incoming raw
septage; therefore, the holding time can vary. If the pH of the limed
septage appears to fall too rapidly upon standing, the pH controller
for the lime feed rate can be adjusted to a higher set point.
7.8 Chlorine Oxidation (Pur if ax
The BIF-PurifaxTM process utilizes chlorine gas in solution to ox-
idize various types of waste sludges, including septage. Chlorine ox-
idation stabilizes sludges and septage both by reducing the number of
organisms present and by making organic substrates less suitable for
bacterial metabolism and growth (36).
194
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The Purifax™ process involves oxidation of several septage consti-
tuents with high dosages of chlorine gas, which is applied directly to
the septage in an enclosed reactor for a short time. Because of the
reaction of chlorine gas with the septage, significant quantities of
hydrochloric acid are formed, and the stablilized septage has low pH
(about 2) . The reactor vessel is moderately pressurized (207 to 275
kn/m^ or 30 to 40 psi) to ensure more complete absorption of the
chlorine gas as well as adequate chlorination penetration into the
larger particles in the sludge (51). At these pressures, the gases
formed are supersaturated in the treated septage. When discharged from
the reactor vessel at atmospheric pressure, these gases come out of
solution as fine bubbles that float the septage solids. The process is
followed by dewatering, generally on sand beds.
Chlorine oxidation, like lime stabilization, does not completely de-
stroy organic matter or solids during septage treatment. It can, how-
ever, produce a relatively biologically stable end-product, which is
dewaterable and which does not have an offensive odor. Because chlo-
rine reactions with sludge and septage are very rapid, reactor volumes
are relatively small; therefore, compared with biological digestion
processes, Purifax™ system sizes are generally smaller, and capital
costs may be lower, depending on the site-specific circumstances. In
addition, Purifax™ systems can be run intermittently (unlike bio-
logical processes) so long as sufficient storage volume is available
both upstream and downstream of the reactor. As a result, operating
costs are more directly dependent on septage production rates. Septage
treatment facilities utilizing Purifax™ include Babylon, New York;
Ventura, California; Putnam, Connecticut; and Bridgeport, Connecticut.
7.8.1 Research
Pilot testing of the PurifaxTM process was conducted at the Lebanon,
Ohio treatment plant which addressed chlorine requirements, dewatering
rate, and sand bed underdrainage quality (51) . The study concluded the
following:
1. The chlorine oxidation process, in conjunction with sand bed
dewatering, was an effective septage treatment method.
2. The sand bed underdrainage quality, compared with untreated
septage, indicated the following removals: COD, 98 percent;
BOD, 95 to 97 percent; total phosphorus, 99 percent; ammonia,
55 to 75 percent.
195
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3. Mass balance calculations indicate that the sand dewatering
beds following the Purifax™ process were the site of the
majority of the organic and nutrient removal. It is possible
that after repeated application, the removal capacity of the
sand would be exhausted.
4. Large dosages of chlorine (1000 to 3000 mg/L) were required
for the process to operate satisfactorily.
5. Chlorinated organics formed during processing appeared to be
. tied up in the sludge solids. The ultimate fate of these or-
ganics and their effects on the environment are not well doc-
umented.
The pilot testing also showed that Purifax™ treatment of septage
produced a solids fraction with greatly reduced total and fecal coli-
form concentrations, although coliform concentrations in the sand bed
underdrainage were quite high, as summarized in Table 7-15 (20). Anal-
yses of the dried solids for bacteriological regrowth were not per-
formed. The average chlorine dose used during the pilot testing was
0.0021 kg C12/L septage or 0.115 kg Cl2/kg dry solids.
TABLE 7-15
BACTERIOLOGICAL DATA8
PURIFAX™ TREATMENT OP SEPTAGE (20)
Total Coliform Fecal Coliform
(counts/100 ml) (counts/100 ml)
Raw Septage 4.4 x 10? 5.3 x 106
PurifaxTM Treated Septageb 20° 20°
Sand Bed Underdrainage 6.9 x 106 3.2 x 104
aValues are averages of four runs.
"Dewatered solids.
196
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7.8.2 Equipment
A schematic diagram of a chlorine oxidation system is shown in Figure
7-16 (36) . The heart of the Purifax™ system consists of a disinte-
grator, a recirculation pump, two reaction tanks, a chlorine eductor,
and a pressure control pump. The chlorine can be fed to the system
through a chlorinator and/or evaporator. An influent feed pump and
flow meter should also be provided.
Raw septage is pumped through the disintegrator to reduce particle
size and increase particle surface area for contact with the chlorine.
Chlorinated septage from the first reactor is mixed with raw septage
just prior to reaching the recirculation pump. The combined flow then
passes through the first reaction tank. Chlorine is added to the sys-
tem by means of an eductor in the recirculation loop. Recirculation
aids mixing and efficient chlorine use. The ratio of recirculated re-
acted product to raw septage is normally about 7 to 1, System pressure
(210 to 275 kn/m2 (30 to 40 psi) is maintained by a pressure control
pump located at the discharge of the second reactor tank, which has
been provided to increase system detention time to allow for a more
complete reaction between septage and chlorine.
A holding/equalization tank should be provided upstream of the oxida-
tion system. Mechanical mixing can be used, although air mixing is
preferable because it enhances aerobic conditions and reduces odors
(36) . A particular benefit of Purifax™ treatment of septage is that
odor can be controlled in the holding tank by returning a portion of
the filtrate or supernatant from the dewatering process. Ventilation
of such tanks must be provided.
A downstream holding tank is beneficial in that it ensures optimum
functioning of subsequent processes, and it allows the chlorine resid-
ual to drop from approximately 200 mg/L to about 0, and the pH to rise
to between 4.5 and 6.5 (36). Lombardo (33) has noted that this process
takes approximately 48 hours.
197
-------
FIGURE 7-16
CHLORINE OXIDATION SYSTEM (36)
Recirculation
Pump
Pressure
Control
Pump
Conditioned
Sludge
Chlorine
Supply
Chlorinator Evaporator
Raw
Septage
Supply
Pump
198
-------
7.8.3 Design Criteria
7.8.3.1 Size
The Purifax™ unit is available over a wide range of flow capaci-
ties, from 55 m3/d (10 gpm) to a theoretically unlimited maximum.
Sizing information is available from BIF, the manufacturer of Puri-
fax™ (33) . BIF suggests that the system be dimensioned such that
the daily volume of septage can be treated in 4 to 6 hours (42) . Most
chlorine-oxidation units are of a prefabricated, modular design, com-
pletely self-contained and skid-mounted (21).
7.8.3.2 Chlorine Requirements
Chlorine dosages vary from 700 to 3000 mg/L, depending on the solids
content of the septage and the amount of chlorine-demanding substances
present (20). These substances include ammonia, amino acids, proteins,
carbonaceous material, hydrogen sulfide, etc. The Babylon, New York
septage treatment facility uses about 0.6 kg C12/L influent (5 Ib
/1000 gal) (52).
BIP recommends a chlorine dosage of approximately 0.7 kg C12/L in-
fluent (6 lb/1000 gal) for septage with a suspended solids concentra-
tion of 1.2 percent. The chlorine demand varies in proportion to the
solids concentration. For example, if the solids concentration were to
double, the chlorine concentration would double as well (36).
7.8.3.3 Typical Design Criteria
A summary of the typical design criteria for chlorine stabilization of
septage is presented in Table 7-16.
7.8.4 Limitations
Limitations of the chlorine stabilization process center on chemical,
operational, and environmental factors. From a chemical standpoint, the
low pH of chlorine-stabilized septage may require neutralization prior
to mechanical dewatering or before being applied to acid soils. Costs
of neutralization are in addition to chlorine costs. Chlorine stabili-
zation does not reduce sludge mass nor produce methane gas as a by-
product for energy generation. The process consumes relatively large
amounts of chlorine. Special safety and handling precautions must be
199
-------
used when employing this system. If high alkalinity wastes are proc-
essed, C02 generated during chlorination may promote cavitation in
downstream pumps (36). The potential for production of carcinogenic
compounds by the chlorine-oxidation process has been a major concern,
since these compounds may leach into the ground or contaminate surface
waters as a result of sludge or liquid effluent disposal.
TABLE 7-16
TYPICAL DESIGN CRITERIA FOR CHLORINE STABILIZATION OF SEPTAGE3
Parameter Value Reference
System Size To treat daily septage volume within 42
4 to 6 hours
Chlorine Dosage 0.7 kg/L for 1.2% TS - chlorine 36
demand varies directly with TS
3BIF - purifax Process.
The effluent (filtrate, supernatant) from the dewatering step is not
suitable for direct discharge into surface waters. Infiltration/per-
colation beds have been used for effluent disposal (33). Alternative
disposal methods have included direct recycle to a treatment plant or
direct discharge following activated carbon adsorption (36).
7.8.5 Monitoring
The major parameters used to control the Purifax™ process are
treated septage color, effluent pH, and effluent chlorine residual.
The chlorine dose can be adjusted until the effluent stream is a light
buff color with a pH of 2 to 2.5, and a chlorine residual of 150 to
200 mg/L (51).
200
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7.9 Conditioning
Septage is conditioned primarily to improve its solids separation and/
or dewatering characteristics. The most commonly used method of septage
conditioning is chemical addition. Chemicals are added to coagulate
septage solids and to release bound water. The chemicals most commonly
used for septage conditioning are ferric chloride, lime, alum, organic
polymers, and, less frequently, acids. These chemicals can be used
alone or in combination. Table 7-17 summarizes the advantages and dis-
advantages of each of these septage-conditioning chemicals. Chemical
selection should be based on several factors, including the following:
ultimate disposal method for the dewatered sludge; local chemical costs
and availability; required operator training and experience; specific
site restrictions and requirements; and conditioning efficiency, based
on laboratory studies.
7.9.1 Research
Many studies have shown that untreated septage neither thickens well
(see Table 7-18) nor filters well. Table 7-19 summarizes conditioning
studies with FeCl3 alone and with lime. Tables 7-20 and 7-21 sum-
marize conditioning with alum and with acid/lime, respectively.
Tawa identified three types of septage (53) . Type I septages are wa-
tery, settle well, and have relatively low solids contents. Type III
septages settle very little (if at all) and have high solids levels.
Between these two extremes are Type II septages, which evidence some
settling 'and have characteristics in the median range. Tawa found that
FeCl3 and alum are equally effective in treating septage, and that a
cationic polymer (Calgon ST-266, which is no longer manufactured)
achieved noticeably better solids settling than inorganic salts, while
at the same time removing more solids from the supernatant portion and
enhancing dewatering.
201
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TABLE 7-17
SUMMARY OF THE CHARACTERISTICS OF SEPTAGE-CONDITIONING CHEMICALS
Chemical
Advantages
Disadvantages
Remarks
o
Ferric Chloride (
with or without line
Cost may be less than alum.
Precipitates solids and phosphorus.
Iron compounds are corrosive.
Increases amount ot solids Cor disposal.
Aluminum Sulfate (Alum) Precipitates phosphorus and solids. Somewhat corrosive when exposed to
f^-2(804)3-14 H20 humidity.
Increases amount of solids for disposal.
Sulfuric Acid
with or without lime
Lime (Ga(OH)2)
Some researchers noted improved phase Highly corrosive to equipment.
separation over both FeClj and
alum.
Dosages determined by jar tests.
FeCl3 reduces ainalinity; nay need
ju^plcmtnlal boucct* ot. antalxruty.
Depresses pH; phosphorus, etc., can
resolubilize if pH drops too low
I pH 4) (53).
Dosages determined by jar tests.
Alum reduces alkalinity; may need
supplemental source of alkalinity.
Depresses pH; phosphorus, etc., can
resolubilize if pH drops too low
( PH 5) (53).
Dosages controlled by pH measurements.
Polymer (s)
Simplified dosage control (no jar
tests).
Precipitates phosphorus and solids.
Precipitates some heavy metals.
Provides some pH control, odor
reduction, disinfection, filter aid
effect.
Improves settleability, dewater-
ability.
Preferred conditioning chemical
for dewatering prior to incineration
— does not lower fuel value of
solids.
Must readjust pH to neutral to protect
subsequent processes and equipment.
Greatly increases solids for disposal.
Dosages determined initially by }ar tests,
but pH generally used.
Most polymers are considerably more
expensive than inorganic conditioners.
Does not remove phosphorus.
Dosages determined by jar tests.
Cationic polymers shown to be most
effective with septage.
Dosage of other conditioning chemical (s)
can be lowered when polymer is used.
-------
TABLE 7-18
SUMMARY OP STUDIES ON THICKENING RAW SEPTAGE
Raw Septage
mg/L
TS -
TVS -
TSS -
BOD5 -
COD -
TS -
TVS -
TSS -
BOD5 -
COD -
TS -
TVS -
SS -
COD -
TS -
TVS -
BOD5 -
COD -
TS -
TVS -
COD -
TS -
TVS -
COD -
18,300
11,530
14,000
12,400
62,500
11,800
9,280
8,680
5,850
20,400
41,900
31,800
39,100
3,360
22,400
15,200
4,794
26,162
39,500
27,370
60,582
29,840
19,910
36,770
Supernatant
mg/L Settling Time
Average 30 minutes
Settleable Solids
24.7%
Nine of 21 samples
showed no separation
TS - 9,630 48 hours
TVS - 8,310
TSS - 4,880
BOD5 - 4,900
No settling observed 1 hour
TSS - 2,350 1 hour
VSS - 1,819
BOD5 - 1,948
COD - 6,343
23 of 26 samples 24 hours
showed no separation
TS - 3,800 ' 1 hour
TVS - 2,510
COD - 23,660
Reference
26
29
54
44
49
55
203
-------
TABLE 7-19
to
o
*>.
SUMMARY OF FERRIC CHLORIDE AND FERRIC CHLORIDE/LIME CONDITIONING STUDIES
Study Type
Rat
Lab Study
FeO.3 Only
(29)
Pilot Study
FeCl3 plus Line
(29)
Lab Study
PeO.3 Only
(55)
pilot Study
FeClj plus Lime
and Jtolymer
(56)
Lab Study
FeO-3 only
(30)
Lab Study
PeCl3 Only
(53)
Lab Study
FeCl3 Only
(53)
Lab Study
PeCIa Only
(S3!
Lab Study
PeCl3 plus Lime
(53)
tab Study
PeCl3 plus Lime
(53)
Influent Soptaqg
•9/1.
ISS
vss
BOO
COD
Alk,
TSS
vss
BOD
COD
Alk.
IS
TVS
COD
TS
SS
VSS
coo
TSS
TS
COD
BOD
TS
COD
BOD
TS
-COD
BOD
TS
COD
BOD
TS
COD
- 9,790
- 7,990
- 7,980
- 26,100
293
- 9,220
- 7,960
- 4,290
- 11,300
743
- 29,000
- 20,000
- 36,800
- 2,390
250
- 2,070
- 2,886
- 17,440
- 5,000
- 10,000
- 5,000
- 15,000
- 15,000
- 7,500
- 45,000
- 45,000
- 25,000
- 15,000
- 15,000
- 7,500
- 45,000
- 45,000
as CaC03
as CaCO3
- 52,700
- 35,000
- 30,000
- 15,000
- 45,000
- 45,000
- 25,000
- 75,000
- 75,000
- 50,000
- 45,000
- 45,000
- 25,000
- 75,000
- 75,000
Overflow Quality
eg/I.
TSS -
VSS -
BOD
COD -
Alk. -
TSS -
VSS -
BOD -
COD
Alk. -
TS
TVS
COD -
TS
TSS -
VSS -
COD
Mo data
TS
COD
SOD
TS
COD
BOD
271
240
664
5,480
135
108
7,960
610
5,480
1,780
2,160
1,180
2,500
3,525
23
22
334
500 -
250 -
100 -
500 -
250 -
100 -
as CaCO3
U CaGO3
2,500
2,500
1,500
2,500
2,500
1,500
Ho supernatant
TS
COD -
BOD
500 -
250 -
100 -
2,500
2,500
1,500
No supernatant
Dotage and Mixing
feCl3 - 400-600 mg/L
Rapid Mix - 30 Bin
Slow Mix - 90 Bin
Settling time - 22 he
Ca(OH)z - 4,000 mg/L
FeCl3 - 400 mg/L
Rapid Mix - 30 tnin
Slow Mix - 90 sin
Settling line - 22 he
FeCl3 - 400-1,000 ng/L
Mix and settling times
not given
PeCJ.3 - 409 ag/L
Ca(OH)2 - 9,595 mg/L
Polymer - 10 mg/L
Clariflocculator
FeCl3 - 360-2,140 mg/L
Mix Time - 30 sec
Settling Time - 60 min
Type I.
FeCl3 - 400-800 mg/L
Rapid Mix - 2 (tin
Slow Mix - 30 min
Settling Time - 30 min
Type II.
Fed 3 - 1,000-2,000 ng/L
Sapid Mix - 2 min
Slow Mix - 30 min
Settling Time - 30 nin
Type in.
FeCl3 - 3,000 mg/L
Rapid Mix - 2 min
Slow Mix - 30 Bin
Settling Time - 30 min
Type II.
FeCl3 - 1,250 mg/L
CajOHJj - 2,000 mg/L
Rapid Hix - 2 Bin
Slow Hix - 30 »in
Settling Time - 30 min
type III.
PeCl3 - 2,000 mg/L
Ca(OH)2 - 3,000 og/L
Con*ents
Difficult to define pftaae
separation. Testing per-
forated on finely-screened
septage
Difficult to define phase
separation. Phosphorous
removal 77%. Testing per-
formed on fine-screened
aeptage.
Dosages necessary to reduce
CST to 50 seconds.
Type I septage - easily
treated, good settling char-
acteristics, 35-75% volume
reduction after settling.
Type II septage - fair
settling characteristics.
10-40% volume reduction
after settling, limited
success using chemicals.
Type III septage - very
poor settling characteristics,
fl-15% volume reduction.
Type II septage - as above
Type III septage - as above
-------
TABLE 7-20
SUMMARY OF ALUM CONDITIONING STUDIES
Study Type
Ref
Pilot Study
C29)
Influent Septage^
ng/L
TSS - 13,400
VSS - 10,600
BOD5 -. 5,250
COD - 13,500
Overland Quality
mg/L
TSS - 183
VSS - 139
BOD5 - 293
COD - 407
Dosage and Mixing
(Alum as Al3)
Alum - 355-950 mg/L
Rapid Mix - 30 min
Slow Mix - 90 Bin
Settling Time - 22 hr
Comments
Pilot plant - 4 cubic meter
(1,000 gal) batch process.
Data obtained using finely-
to
o
en
Pilot Study
(55)
Lab Study
(55)
Lab Study
(30)
TSS
TVS
COD
CST
TSS
TVS
COD
TSS
Avg.TSS
- 9,950
- 7,450
- 16,730
169 sec
- 29,000
- 20,000
- 37,000
- 17,400-52,000
- 33,800
TS
TVS
COD
CST
fS
TVS
COD
No
950
490
750
40 sec
-" 2,500
764
- 2,000
data
Lab Study
(53)
Lab Study
(53)
TS
COD
BODg
15,000-45,000
15,000-45,000
7,500-22,500
TS - 45,000-75,000
TS - 500-2,500
COD - 250-2,300
BOD5 - 10-1,500
No separation
observed
Alum - 80 mg/I»
Mix Time - 30 min
Settling Time - 24 hr
Alum - 100-200 ng/L
Mixing/settling
times not given
Alum - 40-210 mg/L
Avg, - 132 mg/L
Mix Time - 30 sec
Settling Time - 60 ain
Alum - 45-90 mg/L
Rapid Mix - 2 nin
Slow Mix - 30 min
Settling Time - 30 min
Alum - >1 35 mg/L
screened raw septage.
Range of alum does given is
the range tested, not an
optimum dose.
Study performed using
12,000 gal(45 cubic meters)
Alum dosage range for
optimizing septage CST.
Dosage ranges are those
required to reduce CST to
50 seconds.
Dewatering characteristics
poorer than FeClj, Ca(OH)2»
or polymer conditioning.
Type II septage, as defined
in Table 7-19.
Type III septage, as defined
in Table 7-19.
-------
TABLE 7-21
SUMMARY OF ACID AND ACID/LIME CONDITIONING STUDIES
Study Type
Ref
Test Parameters
Initial Septage
Characteristics
Results
Pilot Study
»2f°4
Only
(29)
Acidified to pH 2
dose » 3,000 - 4,000 mg/La
Mixing Time = 2 hr
Settling Time - 22 hr
Screened Septage:
TSS = 2,140 - 22,600 mg/L
{Average <*> 8,690 mg/L
Coliform Count: 4-6
million/100 nl
Pilot Study
H2S04
plus Lima
(29)
Lab Study
H2S04 Only
(57)
Overflow from the acid con-
ditioning described above
was used for the feed to
line conditioning step.
TSS - 83 - 1,900 mg/L
(Average * 393 mg/L)-
Overflow adjusted to pH 11
(Ca{OH)2 dose - 3,500 -
4,500 ag/L), Mixing Time =
30 min. Settling Time = 2 hr
To pH 2-3
Same as above
Supernatant! Vol = 59-92% of
initial septage (Average »
78%). TSS = 83 - 190 mg/L
(Average = 393 mg/L)
Sludge: Vol - 8-41% of
initial septage (Average =
22%), TSS = 9,440 - 52,650
mg/L (Average = 37,300 mg/L)
Effective phase separation
requires minimum 6-8 hr
settling time
Coliform count septage
30,000/100 ml after 4 hn
20/100 ml after 16 hr
Lime neutralization of over-
flow to pH 7 resulted in
formation of minor
precipitate
Supernatant: Vol = 74-95%
of acidified supernatant
(Average = 89%). TSS = 0 -
100 mg/L (Average = 69 mg/L)
Sludge: Vol = 5-26% of
acidified overflow
(Average =• 11%)
TSS = 76 - 5,260 mg/L
(Average » 3,020 mg/L)
Very clear phase separation
Acidification released an
oily scum to the surface
of the overflow
Acidified overflows were
more turbid than alum
conditioned overflows
Acidified sludges settled
slower than alum
Less defined Interface
than with alum
"Pilot studies showed that amount of acid necessary to lower septage pH to 2 was significantly
greater than theoretical amount based on initial alkalinity.
206
-------
Tawa also concluded that lime was the most unpredictable of all chem-
icals tested? there seemed to be no characteristics of a particular
septage that would allow one to predict the effectiveness of lime for
clarification, and lime was inferior to alum, ferric chloride, and
polymer in improving supernatant quality. In addition, lime used in
conjunction with ferric chloride, while greatly improving the dewater-
ing characteristics of the settled solids, gave poorer supernatant
quality than ferric chloride used alone. If, however, lime was added
in a two-step process (i.e., lime added to the settled solids of a
FeCl3~treated sample), the dewatering characteristics of those
solids could be conditioned to a level comparable with that achieved
using ST-266.
Perrin studied the effects of conditioning on sand bed dewatering
(30). The conditioning methods studied included freezing, aerobic di-
gestion, and chemical conditioning. The study determined that freezing
aerobically-digested.septage improved the filterability but suggested
that freezing not be used for conditioning, since it does not reduce
the septic odor and since the dewaterability decreases after thawing
as oxygen again enters the septage. Perrin's criterion for good dewa-
terability was a CST (capillary suction time) of 50 seconds or less,
which resulted in total drainage of the septage on sand beds within 48
hours. The CST techniques employed in this study cannot be directly
converted for use by others. Correlations of CST with dewaterability
are functions the CST test procedure employed, mixing time and total
solids content. Conditioning the septage with ferric chloride, alum,
Purifloc C-31, and Purifloc C-41 resulted in a direct linear relation-
ship between initial CST (i.e., CST of unconditioned septage) and the
chemical dosage required to reduce CST to 50 seconds or less. Perrin
recommended that this relationship be used by sand drying bed opera-
tors to determine the amount of chemical conditioner required to pro-
vide maximum drainage within 48 hours. The dosages of synthetic poly-
electrolytes were found to be at least as high as those required for
alum and ferric chloride for equivalent dewaterability.
Laboratory studies have been conducted to optimize the dosages of fer-
ric chloride, ferric chloride/lime, and Calgon WT-2640 (cationic poly-
mer) to dewater septage by vacuum filtration (58). Septage dewatera-
bility was compared to municipal sludge dewaterability and found to be
more rapid than both unconditioned and optimally-conditioned digested
municipal sludge.
Addition of 1,260 to 1,360 mg/L of ferric chloride, alum, or cationic
polymer improved the dewaterability of septage sufficiently to allow
proper dewatering (20). Laboratory studies show similar improvement in
dewaterability of septage by addition of either 10 to 20 g lime/100 g
dry solids, 5 to 26 g ferric chloride/100 g dry solids, or 1 to 2 g
cationic polymer/100 g dry solids (20).
207
-------
Pilot-scale evaluations of septage conditioning using alum, ferric
chloride, ferric chloride-lime, and acid-lime coagulation resulted in
improved dewatering characteristics (23). High doses (480 to 3,600
g/m3 [4 to 30 lb/1,000 gal]) of chemicals were required however.
Sand drying beds have been used to dewater septage. Anaerobically-di-
gested septage required 2 to 3 times the drying period of similarly
digested sewage sludge (21). Studies have showed that addition of
about 82 kg lime/ton (180 Ib lime/ton) dry solids of septage resulted
in 25 percent solids after sand bed drying for 6 days. Solids in-
creased to 38 percent after drying for 19 days. Use of sand drying
beds for dewatering of septage is feasible with chemical conditioning
prior to drying, it is recommended that depth of application of sep-
tage be limited to a maximum of 20 cm (8 in.), since more depth has
been shown to slow the drying process (3).
Experience indicates that chemical conditioning of septage is
necessary before vacuum filtration, in islip, New York, 95 kg lime/ntt
{190 Ib lime/ton) dry solids and 190 liters (50 gal) of standard
concentration ferric chloride/ton dry solids were used at a now
abandoned facility for chemical conditioning of septage. The
conditioned and settled septage solids were added to the vacuum filter
at a rate of 24 kg/m2-hr (5 Ib/ft2/hr), and found to dewater
satisfactorily (14).
7.9.2 Conditioning with Metal Salts and Lime
The inorganic chemicals used in sludge and septage conditioning in-
clude compounds of iron, aluminum, and calcium. Ferric sulfate, fer-
ric chloride, and aluminum sulfate (alum) are the most commonly used
inorganic chemicals, with calcium hydroxide (lime) often serving aux-
iliary functions (53). The trivalent metal species in ferric chloride
and sulfate (Fe+++) and in alum (Al"*"H") form hydroxometal com-
plexes when added in excess of solubility limits to aqueous sys-
tems (59). The hydrolyzed salts possess a significant charge and some
polymeric properties as well. Therefore, they provide charge neutrali-
zation and enmeshing capabilities toward dispersed material. Hydrated
lime is often used in conjunction with metal salts.
Although lime has some slight dehydration effect on colloids, its use
in conditioning is also for pH control, odor reduction, disinfection,
and filter aid effect (34).
208
-------
Colloid destabilization by metal salt addition to septage is achieved
by adsorption of positively-charged hydroxometal polymers to produce
charge neutralization {59}. Because the alkalinity of septage is high
(see Table 3-4), charge neutralization is relatively difficult since
high alkalinity keeps the pH in the neutral region where the hydroxo-
metal polymers are not highly charged. Destabilization, therefore, can
be accomplished either by using a higher coagulant dosage or by elu-
triating the septage first to remove alkalinity and then destabilizing
with a lower coagulant dosage at a lower pH (59). Due to solubility
considerations, however, the pH should not be reduced below 5 for
aluminum salts, or below 4 for ferric salts (53).
7.9.2.1 Design Criteria: Dosage
The required dosage of inorganic coagulants, particularly ferric chlo-
ride, is a function of the "solids demand" and the "liquid demand"
(60). The solids demand is the amount of coagulant required by the
solids fraction in the suspension and is dependent on the organic or
volatile, matter in the sludge. The liquid demand, on the other hand,
is a function of the alkalinity and solids content of the sludge or
septage. For systems free of chemical reducing agents, oil emulsions,
and a large percentage of fines, the FeCl3 dose can be determined
from the following equation:
Total dose (as % FeC^) = Liquid demand + solids demand
where:
Liquid demand = % H2° * Alkalinity (ppm) x .000108
i solids
Solids demand _ % volatile matter in dried sludge
% ash in dried sludge
Crowe reported the following optimum chemical dosages (58)
FeCl3; 6.5% of total septage solids
FeCl3/Limes FeCla: 2% of total septage solids
Lime: 9% of total septage solids
Crowe found that the CST at the FeCl3 dosage was 32 seconds, and the
vacuum filter cake solids content was 16 percent. At the FeCl3/iime
dosage, the CST was 25 seconds, and the cake solids concentration was
over 17 percent. In both cases, the filtrate COD reduction was 98 per-
cent. Again, the CST values are not universally applicable, but pro-
vide a useful correlation for specific, conditions at the study site.
209
-------
Perrin reported that the conditioner dose required to reduce the in-
itial septage CST to 50 seconds ranged from 1.8 to 7.8 percent of TSS
for PeCl3, and from 1.3 to 7.3 percent of TSS for alum (30).
Ott and Segall (1982) (55) found that septage conditioned with an alum
[as &1+++] dosage of 0.8 percent of TSS did not vacuum filter well.
They concluded that vacuum filtration of alum-treated septage without
the addition of thickened waste activated sludge and without polymer
was not feasible at the facilities they studied.
7.9.2.2 Design Criteria: Mixing/Contact Time
Chemical mixing thoroughly disperses coagulants or their hyrolysis
products so the maximum possible portion of influent colloidal and
fine solids are absorbed and destabilized. Flocculation processes in-
crease the natural rate of contacts between particles. This makes it
possiblei within reasonable detention times, for destabilized colloids
and fines to aggregate into particles large enough for effective sepa-
ration by gravity processes or media filtration (61). Controlling pa-
rameters in mixing and flocculation processes are time (seconds) and
velocity gradient (m/sec/m or fps/ft, or simply sec"-'-). Chemical mix-
ing and flocculation differ primarily in intensity (i.e., velocity
gradient) and duration, although flocculation may also be affected by
the total solids concentration.
Chemical mixing facilities should be designed to provide a thorough
dispersal of chemical(s) throughout the septage being treated to en-
sure uniform exposure to pollutants that are to be removed. The in-
tensity and duration of mixing the coagulants with the septage must be
controlled to avoid overmixing or undermixing. Overmixing excessively
disperses newly formed floe and may rupture existing septage solids.
Undermixing, on the other hand, inadequately disperses coagulants, and
uneven dosing results. This may, in turn, reduce solids removal ef-
ficiency while requiring unnecessarily high coagulant dosages (61).
The mixing and flocculation equipment used in wastewater treatment has
been "borrowed" from water treatment practice. The water treatment
units that have been successful for chemical mixing applications in
sludge and septage treatment are high-speed mixers and variable-speed
mixers. Where flows must be pumped just prior to coagulation, chemical
addition at the pumps is an option. However, if velocity gradient
values are too high, organic solids may be sheared (61).
210
-------
The design criteria for high-speed mixers usually include a 10- to 30-
second detention time and a velocity gradient of about 300 m/sec/m
(300 fps/ft). In some plants, variable-speed mixers allow for varying
requirements for optimum mixing (61).
The proper measure of flocculation effectiveness is the performance of
subsequent solids separation units, in terms of both effluent quality
and operating requirements. Design requirements for flocculation in-
clude a maximum detention time of 15 minutes and paddle speeds of 0.15
to 0.30 m/min (0»5 to 1.0 fpm) (61). Flocculation units should have
multiple compartments and should be equipped with adjustable-speed
mixers to permit meeting changed conditions. In spite of simplicity
and low maintenance, non-mechanical baffled basins are undesirable be-
cause of inflexibility (i.e., G cannot be changed to meet require-
ments, but is instead a function of flow rate through the units), high
head losses, and large space requirements (61).
When lime is used, flocculation parameters may be quite different.
Lime precipitates are granular and do not benefit much from prolonged
flocculation times or very low terminal G values. Detention times
should range from a minimum of 5 minutes to a maximum of about 10
minutes. G values of 100 sec"1 or more are desirable (61).
Batch treatment systems can be designed so that chemical addition and
flocculation can take place in the same tank. It is unlikely that both
flash mixing and flocculation could be accomplished by the same mixer.
Therefore, the following mixing systems can be designed to accomplish
both flash mixing and flocculation in the same tank:
1. Chemical addition at pump discharge; flocculation by paddles
or low-speed mixer in tank.
2. Chemical addition upstream of in-line static mixer; floccula-
tion as above.
3. Chemical addition in tank with rapid mixing by recirculation
of tank contents; flocculation as above.
4. Chemical addition in tank with rapid mixing by coarse bubble
diffusers; flocculation as above.
Design criteria (dosage, contact time) for batch systems would be the
same as for continuous systems.
7.9.2.3 Typical Design Criteria
Table 7-22 summarizes the design criteria for conditioning with metal
salts and lime.
211
-------
TABLE 7-22
TYPICAL DESIGN CRITERIA
CONDITIONING WITH METAL SALTS AND LIME
Dosage
Reference
CHEMICAL DOSAGE
Metal Salts
Fecl3
FeCl3/Lime
Equation 3
6.5% of TS
FeCl3s 2% of TS
60
58
58
FeCl3
Alum (as Al)
Iron Salts (as Fe)
Lime (as Ca (OH) 3) .
Lime: 9% of TS
1.8 to 7.8% of TSS
1.3 to 7.3% of TSS
2 to 6.25% of dry solids
10 to 30% of dry solids
MECHANICAL MIXING CRITERIA
Metal Salts
High-Speed Mixing
Flocculation
Detention Time: 10 to 30 sec
Velocity Gradient: 300 sec~l
Detention Time: 15 minutes maximum
Paddle Speed: 0.15 to 0.30 m/min
Lime High-Speed Mixing Detention Time: 5 to 10 min
Velocity Gradient: 100
COARSE-BUBBLE MIXING
CRITERIA
Air Requirements
m3/1000 m
30
30
36
36
61
61
61
150 to 250
45
212
-------
7.9.3 Conditioning with Polyelectrolytes
Some inorganic chemicals used for conditioning septage, such as ferric
chloride, alum, lime, and sulfuric acid, are difficult to handle due
to their corrosive nature. Use of organic polymer coagulants, by con-
trast, has developed partially due to the ease of handling and simple
facility requirements, effectiveness in operation, and the limited re-
sultant increase in sludge mass.
There is such a wide variety of polymers, along with continuing devel-
opment of new ones, that the selection of a polymer requires a design-
er to work with an individual polymer supplier to obtain specific in-
formation on polymers (relative to the dewatering equipment and proc-
esses to be used, as well as to pilot-test available polymers on sev-
eral septage samples).
There are three basic types of polymers: anionic, cationic, and noni-
onic. Anionic polymers carry a negative charge and are often used with
aluminum sulfate and ferric chloride additions to increase rate of
flocculation, size, and toughness of particles when conditioning
sludges. Anionic polymer addition to septage in laboratory experiments
did not improve dewatering in one experiment (53), but, in another
case, dewatering was enhanced (49).
Cationic polymers carry a positive charge and often serve as primary
coagulants alone or in combination with inorganic coagulants such as
aluminum sulfate. Septage conditioned with various cationic polymers
(53) (26) (58) (49) has shown increased dewatering properties when studied
under some laboratory conditions. Results were not always consistent
due to the variability of septage sources. Eikum (1) reported on sep-
tage conditioning with the cationic polymer Praestol 444 K manufactured
by Chemische Fabrik Stockhausen, a West German firm, which is used in
Europe as a standard polymer for measuring the relative conditionabil-
ity of sludges (1). Dosages of about 0.5 percent of TSS were required
for satisfactory conditioning of untreated septage. He also reported
that aerobic stabilization (20 to 25 days) enhanced conditionability
of septage, and that polymer dosages in the range of 0.135 to 0.5 per-
cent of TSS were required. Perrin reported that cationic polymer dos-
ages of 1.1 to 7.2 percent of TSS (Dow Purifloc C-31), and 3.1 to 12.8
percent of TSS (Dow Purifloc C-41) were required to reduce the GST to
50 seconds or less, as discussed previously (30).
213
-------
Nonionic polymers carry no net electrical charge in aqueous solutions,
but, under some conditions and with some solids, the polymer can be
sufficiently surface-active to perform as a flocculant (36). There are
few data on nonionic polymer addition to treat septage independently;
however, there may be facilities that treat septage in the sludge
train with other wastewater sludges using such polymers.
Design dosages for polymer additions to various wastewater sludge com-
binations range from 7.5 to 15 kg/metric ton dry solids (15 to 30 lb/
ton dry solids). Actual dosages for septage sludges may vary from
these figures and should be confirmed by pilot testing. Manufacturer's
recommendations should be sought on the mixing conditions that optimize
their effectiveness, and these must be supplemented by jar tests. When
coagulant aids are employed, provisions for multiple addition points
should be made at the rapid mixing basin and in the flocculator to
optimize the performance of the coagulant (61).
Septage variability is such that it is doubtful that a consistently
effective polymer can be found for any batch treatment operation. Al-
though the use of continuous flow treatment systems may improve chances
for a relatively consistent polymer, data on successful application of
this treatment concept in the United States is scarce. Based on the
presently available U.S. data, conditioning by polymer alone is not a
viable alternative, although polymer alone has been used for centri-
fuges and belt presses in Europe. However, polymer use as an adjunct
to improve the performance of inorganic conditioning chemicals may be
considered quite economically feasible if pilot studies provide con-
sistently positive results.
7.10 Dewatering
Dewatering is generally required for ultimate disposal of treated sep-
tage. There are two options available for dewatering; namely, gravity
dewatering systems and mechanical dewatering systems. Gravity dewater-
ing includes sand drying beds; mechanical dewatering systems include
vacuum filters, filter presses (including belt filters), centrifuga-
tion, and vacuum-assisted drying beds.
Septage has poor dewatering characteristics (26) (49) (53) (57) , which
warrants the need for conditioning prior to dewatering. Biological
conditioning of raw septage by digestion or use of heat conditioning
followed by dewatering may not be economical at an independent septage
treatment facility due to high capital and operating costs. A summary
of several studies on chemical conditioning of septage is given in
Table 7-23. Chemical conditioning followed by dewatering results in
average cake solids content of approximately 20 to 40 percent, which
214
-------
TABLE 7-23
SUMMARY OF SEPTAGE DEWATERING STUDIES
Equipment
Chemical Addition
Remarks
Reference
Vacuum Filtration
(Full-scale Field
Studies)
Vacuum Filtration
(Pilot Studies)
Vacuum Filtration
(Laboratory
Studies)
Solid Bowl
Centrifugation
(Pilot Studies)
Alum, Ferric Chloride,
Acid, Lime, Polymers,
and Combinations
Alum, Ferric Chloride,
Acid, Lime, Polymers,
and Combinations
Ferric Chloride,
Lime and Polymers
Alum, Ferric Chloride,
Lime and Acid
Conditioned septage with thickened 55
waste activated sludge; achieved cake
solids from 10 to 20%.
Conditioned screened septage alone 29
or combinations of screened septage
and aerobically-digested sludges;
cake solids 9 to 35%.
Conditioned septage and combinations 58
of septage and digested sludges; cake
solids 6 to 15%.
Dewatering of conditioned screened 29
septage, and dewatering of septage
and aerobically-digested sludges;
cake solids 17 to 23%.
Solid Bowl
Centrifugation
(Field Studies)
Filter Press
(Pilot Studies)
Sand Beds
Sand Beds
Sand Beds
Sand Beds
Lime
Alum, Ferric
Chloride, Lime and Acid
Alum
Alum, Ferric Chloride,
Lime and Acid
Alum and Aluminum
potassium Sulfate
Lime
Centrifuge optimal performance with 62
equal parts of septage and primary
chemical wastewater sludges; resulting
sludge total solids cake was approxi-
mately 25%.
Cake solids 26 to 46% with acid-con- 29
ditioned screened septage and up to
55% solids with ferric chloride/lime
and alum-conditioned screened septage.
Alum enhanced dewatering on sand beds. 57
Screened raw septage dewatered to 6%; 29
FeCl3/lime dewatered to 11% cake
solids; alum-treated dewatered to 15%;
and acid/lime conditioned septage de-
watered to cake of 24% cake total
solids in two days.
Conditioning septage to a CST of <50 30
seconds enabled dewatering on sand
beds in 48 hours with cake solids of
20%.
Lime added to pii>10; septage then de- 49
watered on sand beds to 25% cake
solids in 6 days.
215
-------
should be suitable for mechanical or manual methods of cake removal
for ultimate disposal. Details on chemicals used and optimum doses
were discussed in Section 7.9. It is recommended that septage be chem-
ically conditioned prior to dewatering. The degree of dewatering ac-
complished is a function of conditioning chemicals, admixtures of
other sludges with septage, and the dewatering process used.
7.10.1 Sand Drying Beds
Dewatering of septage using sand drying beds is a convenient method
for small communities in areas where land availability is not a major
constraint. Septage is placed on drying beds of sand and gravel and
allowed to dry, Dewatering occurs by drainage through the sand bed and
also by evaporation. As the septage dries, cracks develop on the sur-
face allowing further evaporation and drying in the lower layers. The
filtrate draining through the sand is collected in a perforated, open-
jointed piping system below the sand beds and can either be returned
to the head of the septage treatment plant or treated separately as an
effluent before ultimate disposal. The sludge cake is removed from the
sand bed either by front loaders or by hand shoveling, and it is truck-
ed to an ultimate disposal site. A typical sand bed drying system is
shown in Figure 7-17. Considerations for design of sand drying beds
include type of conditioning, depth of application, and drying time.
With regard to the effect of conditioning on sand bed performance,
Feige noted that the addition of approximately 90 kg lime/metric ton
(180 Ib lime/ton) dry solids of septage resulted in 25 percent solid
cake in 6 days and 38 percent in 19 days (49). Condren's studies (29)
showed that alum-conditioned septage dewatered to 15 percent cake sol-
ids after one day, whereas ferric chloride-/lime-conditioned septage
produced 10 to 11 percent cake solids after 2 days. In comparison, acid
lime conditioning of septage resulted in a cake of 24 percent solids
after 2 days. Perrin (30) evaluated dewatering characteristics of sep-
tage in laboratory-scale studies using capillary suction time (GST) as
the parameter for comparison. Perrin found that septage with a CST of
50 seconds would cease free drainage on a sand drying bed within 48
hours or less, resulting in about 20 percent cake solids content.
Studies by Crowe (58) indicated that a CST of 50 seconds can be
achieved by conditioning septage with 0.1 to 0.2 kg lime/kg dry solids.
However, there is no basis to compare these two CST values due to dif-
ferences in total solids and test methods.
Since evaporation is a contributing factor to the performance of sand
bed dewatering, depth of application of septage is an important design/
operation consideration. One study indicated that chemically-condi-
tioned septage dewatered more readily at a 15-cm (6-in.) depth of ap-
plication than at a 30-cm (12-in.) depth (57). Based on this and other
pilot-scale and full-scale dewatering plants, a septage application
depth of 20 cm (8 in.) is recommended.
216
-------
FIGURE 7-17
TYPICAL SAND DRYING BED CONSTRUCTION (21)
P— rf b— r
«j
1
1
.!
•""*
150 mm
Wi
1
1
Splash Box
I
C
I
fcu
f
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T
3
I
(
jjk r'
Vilrlliad Pipe Laid -X
Plastic Joints
1
i
_ 1
Ul i
i
?
C
1
^
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I
1
jr-rJ' li ..
<•
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3
, 043
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?s
i*
s
i
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I
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I
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~a
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i
t
i
k
JIT
I
1
rtt ** Shear Gate "" *sftil
ua II %l
1-13 "^^
f
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1
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*"<
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1
ct
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3
*
t
t
Q
A
t
V SO mm Plank
PLAN Wa!k
150 mm Fine Sand
75 mm Coarse Sand
75 mm Fine Gravel
75 mm Medium Gravel .
75 to 150 mm Coarse Gravel |
Pipe Column For
Glass-Over
75mm
Medium Gravel
SECTION A-A
,150 mm Underdraln Laid
With Open Joints
217
-------
Drying time is a function of drainage and evaporation. The predominant
function of sand bed dewatering is drainage, most of which usually
occurs within about 7 to 10 days. However, depending on weather condi-
tions, evaporation also contributes significantly to dewatering, par-
ticularly in the latter part of the drying period. Average drying time
for sewage sludge is about 2 to 4 weeks. Since conditioning signifi-
cantly improves dewatering characteristics of septage, it is possible
that the average drying time for conditioned septage may be reduced to
approximately 10 to 15 days. Table 7-24 provides a summary of findings
of some studies on sand bed dewatering of septage. Although bench scale
and pilot plant studies indicate drying time for septage between 2 and
6 days, full scale operations are estimated to require longer drying
time.
Sand bed drying is one of the simplest systems that can be used for
dewatering of conditioned septage. The advantages of this system are:
1) its simple construction; 2) the minimal operator training and at-
tention required; and 3) its low capital and operation costs. The dis-
advantages are: 1) large sand area required; and 2) potential problems
with operation during cold and wet weather seasons unless the beds are
covered.
One of the variations in sand drying bed construction relates to the
choice between asphalt and concrete paved drying beds. Use of mechani-
cal equipment for cleaning unpaved sand beds has resulted in damage to
underdrain pipes. Paved drying beds permit the use of mechanical equip-
ment without damaging underdrains and thereby reduces the cost of
labor and sand replacement. Paved drying beds are usually constructed
with a 1.5 to 2 percent slope toward the center. A perforated drainage
pipe is located in the center beneath a sand drainage strip at a level
below the paved bed. Operation of paved drying beds is economical
since use of mechanical equipment allows removal of sludge with a high-
er moisture content in shorter drying time intervals than in the case
of manual cleaning. The main disadvantage of paved beds is higher
capital cost. The feasibility of using paved drying beds for dewatering
digested sewage sludge has been demonstrated elsewhere (63) (64) (65).
7.10.2 Vacuum Filtration
Vacuum filtration is a common method of dewatering wastewater sludges
in the United States. It has also been used to dewater chemically-con-
ditioned septage, as well.as mixtures of septage and wastewater sludge.
218
-------
TABLE 7-24
SUMMARY OF STUDIES ON SAND BED DEWATERING OF SEPTAGE
Type of Study
Re£
Pilot Study
(29)
Feed Septage
mg/L
TSS - 7,700
TSS - 21,000
Conditioning
Chemical Dosage
«g/L
None
Fed 3 400
Ca(OH)2 4,000
Drying
Tine
days
2
2
Cake Solids
rag/I.
TSS - 59,500
TSS - 105,000
Filtrate
mg/L Comments
TSS - 319 0.2 a3 batches were placed on
1 m2 sand beds
TSS - 46 Conditioned septage was
settled for 22 hours
TSS - 30,600 Alum
TSS - 21,100 Acid (H2SO4)
Ca (OH) 2
Pilot Study TS - 37,200 Ca(OH)2
(49) COD - 58,000
Bench Scale
(30)
Bench Scale
(57)
TSS - 32,000 Aerated
FeCl3
Alum
Polymer
TS - 34,500 Alum
VS - 14,300
COD - 17,000
355 -
955
3,000 - 4,000
3,500 - 4,500
83,000
640 - 1,280
70 - 135
640 - 1,280
100
1 TSS - 153,000 TSS - 79 0.2 m3 screened septage
was placed in 20 cm layers
on a 30.5-cra deep bed with-
an area 0.93 ra2
2 TSS - 241,000 TSS - 53
6 TS - 247,500 Ca(OH)2 dosage is that
19 TS - 380,000 COD 186 - required to raise septage
1,660 pH to 11.5, an average of
4 tests
Sand beds of a 6 a^
area are covered with
septage to a depth of
20 cm
3-4 TS - 200,000
3-4 TS - 200,000
3-4 Ts _ 200,000
3-4 TS - 200,000
1.5 TS - 150,000
Added 0.5 L of septage
to sand drying column
-------
Vacuum filtration is generally accomplished on cylindrical vacuum
drums. These drums have a filter medium that may be a cloth of natural
or synthetic fibers, coil springs, or a wire mesh fabric. The drum is
suspended above and rotates through a vat of conditioned septage (Fig-
ure 7-18). As the drum rotates, part of its circumference is subject
to an internal vacuum that draws the septage to the filter medium. In
this section of the circumference, the water is drawn through the.;
porous filter cake. The piping arrangement within the filter permits
the suction to be maintained until the release point, at which time
compressed air may be blown through the medium to release the cake, or
a scraper assembly may be used to aid discharge. The yield of the
filter, usually expressed in kilograms per square meter per hour
(pounds of dry solids per square foot per hour), may be changed by
varying the suction, the speed of rotation, the portion of the cycle
time during which suction takes place, or the conditioning chemicals
that are added to the septage.
The auxiliary equipment for vacuum-filter operations include? sludge
conditioning tank with mixer, sludge cake conveyor, vacuum pump, and
filtrate receiver and pump.
Chemical conditioning of septage is strongly recommended prior to
vacuum filtration in order to achieve satisfactory dewatering oper-
ation (29) (23) (55) (58) .
At an independent facility in islip, New York, septage solids
conditioned by the addition of lime and ferric chloride were fed to a
vacuum filter at a rate of 24 kg/m2-hr (5 Ib/ft2-hr) and were de-
watered satisfactorily (17). Other studies have indicated that vacuum
filtration of septage after chemical conditioning with lime, ferric
chloride, and a polymer yielded 15 to 17 percent cake solids (58).
Another study (29) demonstrated that good solids capture and cake
solids consistencies were achieved with vacuum filtration of septage.
However, it was difficult to obtain consistent release of the cake.
Coil spring vacuum filtration of chemically conditioned septage has
been investigated in laboratory and field studies (55). Chemical con-
ditioning consisted of either alum, ferric chloride, or sulfuric acid.
These studies showed that chemically conditioned septage produced very
low cake yield ranging from 1 to 3 kg/m2/hr (0.2 to 0.6 lb/ft2/
hr). However, significantly higher cake yields of about 20 kg/m2/hr
(4 Ib/ft2/hr) were achieved when conditioned septage was mixed with
thickened waste activated sludge. Although vacuum filtration of sep-
tage may be technically feasible, due consideration would have to be
given to its high cost when evaluating its feasibility in an indepen-
dent septage treatment system. Table 7-25 summarizes the results of
studies conducted on vacuum filtration of septage.
220
-------
FIGURE 7-18
VACUUM FILTRATION PROCESS (S8)
Vacuum Filtration Drum
Conditioning Chemicals
Mixer
Raw
Septage
Conditioned
Septage
Dewatered Septage
(Filter Cake)
Conditioned •
Storage Vat
Filtrate
Chemical Conditioning
Vacuum Filtration
221
-------
TABLE 7-25
VACUUM FILTRATION OF SEPTAGE
Feed Septage
Conditioning
Type of Study characteriB-
Kef
Full-Seal* TS
Study (55) TVS
IS
TVS
pH
TS
TVS
TS
TVS
Pilot Scale TSS
(29)
TSS
TSS
TSS
tics
- 37,
- 27,
- 51,
- 36,
- 2.6
- 52,
- 35,
- 51,
- 35,
- 22,
- 33,
- 33,
- 30,
180
190
160
100
770
135
468
755
200
000
000
700
mgA-
ng/t
ng/L
mg/t
mg/t
mq/L
mg/t
«g/L
**}/!*
ng/t
mg/L
og/t
Chemical
Al2(S04>3
H2S04
A12 (S04) 3
FeCl3
PeCl3 and
Ca(OH>2
al2(S04)3
M.2(S04)3
Anionic Polymer
H2S04
Ca (OB) 2
Dosage
«g/L
80
as Al+«-
...
130
as M+++
220
as ¥*+++
400
4,000
355 - 955
315
25
3,000
4,000
3,500
4,500
Yield
kg/m2/hr
1.0 TS
TVS
3.0 TS
vs
pH
26.5 TS
VS
20.5 TS
VS
2.5 TS
Cake
- 20%
- 76.2%
Of TS
- 16.8%
- 75.6%
of TS
- 4.4
- 12.5%
- 65%
of TS
- 12.2%
- 65*
of VS
- 35%
TS
TVS
TS
TVS
TS
VS
TS
TVS
TSS
Filtrate
rag/t
- 14,234
- 10,230
- 10,430
- 6,957
- 1,910
- 940
- 2,372
- 1,388
117
Remarks
feats performed on 47 »3
batches
of thickened septage.
fests perforned on 19 «3
batches
Filter
septage
Filter
aeptage
of thickened septage.
feed was 55%
, 45% TWAS
feed was 44.8%
, 55.2% WAS
Pilot Vacuum Filter -
Diane ter -0.9m
2.0 TS
7.5 TS
4.0 TS
- 28%
- 27%
- 27»
TSS
TSS
TSS
80
56
44
Length
Vacuum
- 0.5 m
- 406 mm Ug
Drum Speed - 16 min/
rev
TWAS - Thickened waste activated sludge.
-------
7.10.3 Filter Press
The plate and frame filter press is another mechanical dewatering sys-
tem that has been used for sewage sludge applications. Most independent
septage treatment units are expected to be generally small in size,
perhaps located in relatively remote areas, and subjected to wide vari-
ability in flow conditions. Considering the high cost of the equipment,
the use of plate and frame filter presses to dewater septage would be
highly uneconomical unless very large septage treatment systems are
considered.
Characteristics of filter cake and filtrate from belt filter pressing
of septage were evaluated by Condren (29) using different types of
chemical conditioning (29). Chemicals used for conditioning included
1) ferric chloride and lime, 2) alum, and 3) acid and lime. Norwegian
practice always includes polymer with or without these chemicals. In
all cases, filter press dewatering yielded high cake solids (26 to 55
percent) with run times of about 45 minutes. However, the feasibility
of using belt filter presses at an independent septage treatment fa-
cility would be determined by economics.
7.1p.4 Centrifugation
Centrifugation of wastewater/septage sludges is carried out using
either solid bowl centrifuge or basket centrifuge. "Che use of solid
bowl centrifuges to dewater septage, mixtures of septage, and aero-
bically-digested sewage sludge yielded acceptable cake solids in the
range of 16 to 23 percent (29). However, prior chemical conditioning
of septage was necessary to obtain these levels of cake solids. Re-
sults of these studies are given in Table 7-26. The flow rate used for
the study was 4 L/min (1 gpm). Grit removal is essential before cen-
trifugation to prevent severe wear and tear and damage to centrifuges.
Solid bowl type Centrifugation of septage has been investigated in
Europe at laboratory and full-scale plants. A summary of data from
these studies is given in Table 7-27. likum (1) reported that average
cake solids concentration of about 25 percent and solids capture of 90
to 95 percent are possible with Centrifugation of screened and de-
gritted septage. Polymer requirements for conditioning prior to cen-
trifugation are about 2 to 4 g/kg TSS (0.4 to 0.8 Ib/lb).
223
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TABLE 7-26
SEPTAGE DEWATERING BY SOLID-BOWL CENTRE FUGATION (29)
Feed Source
Ferric Chloride/Lime
Septage Sludge
Alum Septage Sludge
Acid/Lime Septage Sludge
90/10 Mixture3
TSS,
Influent
31,000
33,000
30,700
23,400
mg/L
Centrate
3,970
14,000
17,600
18,400
Cake
1 Solids
16.5
20.6
23.0
20.0
Capture
% of TSS
90.5
62.4
45.0
25.7
aVoluraetric ratio of aerobically digested STP sludge to acid/lime con-
ditioned septage.
7.10,5 Vacuum-Assisted Drying Bed
This is a relatively new system for dewatering water/wastewater/chem-
ical sludges. It is comprised of a drying bed of permeable media to
which polymer-treated sludge is applied to depths of about 30 cm (1 ft)
and allowed to drain by gravity. A vacuum is then applied and held
until the sludge surface cracks. It is then ready for removal by front-
end loaders specially equipped with rubber-bottomed buckets. After a
washing step, the process can again be initiated. The process is sche-
matically illustrated in Figure 7-19. Proprietary systems of three
different manufacturers are available. These systems are quite similar
and are designed on the concept that a vacuum applied to a permeable
mat loaded with sludge significantly improves the dewatering effi-
ciency. Figure 7-20 outlines the steps involved in the operation of a
typical vacuum-aided drying bed.
This system of dewatering septage may have several advantages, as fol-
lows:
1. Simplicity in construction.
2. Minimal operator training and attention.
3. Able to produce truckable sludge cake in 24 hours.
224
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TABLE 7-27
SUMMARY OF SEPTAGE CENTRATE tfATER QUALITY (25)(46)(66)(67)
Quality oi Jentrate from
Untreated Septaqe
Parameter
TSS
(rog/L)
vss
(mg/L)
B007
(mg 02/Lj
CODtotal
(mg 02/L)
Total-P
(mg P/L)
J?O4-P
(mg P/L)
Total-N
(mg H/L)
NH4-N
(rag N/L)
pH
Range
Median
Range
Median
Range
Median
Range
Median
Range
Median
Range
Median
Range
Median
Range
Median
Range
Median
Range
Median
Laboratory
Centrifuge
70-2155
645
45-1943
475
206-3195
1120
378-7998
3373
280-5277
2791
11- 107
47
0.4- 83
30
37- 529
199
35- 288
147
5.5- 7.8
6.3
Pull Scale
Centrifuge
723-11,790
1,710
597-10,430
1,270
515- 2,865
886
1,285- 9,480
3,605
563- 1,525
846
15- 56
33
0.2- 49
16
140- 228
180
65- 128
80
Lime Stabilized Septage
Laboratory
Centrifuge
194-1424
380
119- 896
214
3050-8700
4670
2854-5228
4220
3.4- 20
5.7
0.1- 1.9
0.3
221- 368
288
128- 203
150
9.8- 12.5
12.3
Full Scale
Centrifuge
8,150-14,520
11,430
4,920- 9,945
6,870
___
9,776-28,810
19,200
2,117- 4,586
3,411
39.5- 116
54
0.1- 3.1
0.2
323- 770
553
100- 160
120
9.7- 12.4
12.4
Aerobic Stabilized Septage
Laboratory
Centrifuge
41-102
59
19- 54
29
5- 37
10
79-282
202
100-246
183
1.1- 6.0
2.7
0.4- 2.5
1.1
10.8- 42.4
2U
0.3- 8
0.4
7.8- 8.1
7.9
Full scale
Centrifuge
30-434
146
16-231
69
9- 36
. 15
140-632
181
80-212
159
0.9- 4.
1.
0.2- 1.
0.
12.4- 34.
24
0.2- 6.
0.
7.6- 7.
7.
7
5
3
2
0
4
5
7
6
number of samples
23
225
-------
FIGURE 7-19
VACUUM ASSISTED DRYING BED SYSTEM (69)
Septage Bed
Access Ramp
Polymer Feed System
Central Filtrate Sump'
Distribution Piping
Vacuum System and Control Panel Skid
226
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FIGURE 7-20
SEQUENCE OF OPERATIONS IN VACUUM ASSISTED
DRYING BED SYSTEMS (69)
..
••&•.'••
Conditioned sludge is distributed on the permeable mat. Immediately large particles
begin to settle onto the mat as free water drains.
A Cohesive layer ol large particles formed on the mat traps finer sludge particles as
free water continues to drain.
-------
4. Porous blocks generally resist clogging and blinding and
require only hosing down for cleaning.
5, High loading rate capability.
Although open air drying beds may require large areas, the provision
of the vacuum significantly reduces the area requirement over that for
conventional sand drying beds. Moreover, the ability to remove sludge
cake in 24—hour or less cycles reduces the total bed area requirements.
As with other dewatering systems for septage, conditioning is required
prior to application on the bed. The level of septage conditioning re-
quired prior to bed application is not yet tested, but experience with
STP sludge would indicate that lime stabilization or aerobic or anaero-
bic digestion would suffice prior to polymer treatment.
Cake solids ranging from 15 to 25 percent are claimed to be achieved
in 24 hours or less for sewage sludge, which is a very high yield com-
pared to gravity sand drying beds (69).
This system of dewatering appears to be well-suited for independent
septage treatment since it combines the simplicity of a gravity dewa-
tering system with the rapid dewatering rates of a mechanical system.
Since, in many cases, independent septage treatment systems may be
small in size and may be located in relatively remote areas, a simple,
efficient system with low maintenance requirements is highly desir-
able. Depending on the pattern of septage generation and climatic con-
ditions, these beds will generally require heated enclosures in north-
ern regions. No performance data on application of this system for
septage treatment are currently available. Conventional sand drying
beds may be loaded from 10 to 270 kg dry solids/m2/yr (2 to 55 lb/
ft2/yr) depending on type of sludge, weather, dryness required, and
whether the bed is covered or uncovered. Loading for operating vacuum-
assisted sludge drying beds has ranged up to 950 kg dry solids/m2/yr
(195 Ib/ft2/yr), with typical polymer additions between 2 and 6 kg/
metric tons of dry solids (4 and 12 Ib/ton) (69) . Manufacturers claim
that significantly higher loadings are possible (68).
228
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7.11 Disinfection
Septage disinfection or the destruction or inactivation of pathogenic
organisms in the septage is carried out principally to minimize public
health risks. Destruction is the physical disruption or disintegration
of a pathogenic organism, while inactivation is the removal of a patho-
gen's ability to infect. This section will identify certain pathogenic
organisms found-in septage, briefly describe their characteristics, and
discuss methods for reducing the number of pathogenic organisms in sep-
tage.
7.11.1 Applicability of Disinfection
Disinfection of septage is most applicable when there is a potential
risk of humans coming into contact with the septage during the disposal
process. The most common disposal process and the one with the largest
potential for human contact is application of raw untreated septage or
pretreated septage to the land. Federal, state, and/or local regula-
tions may require some form of disinfection prior to land application.
At the present time in the United States, the use of a process to sig-
nificantly reduce pathogens (PSRP) is required for land application of
septage unless public access is controlled for 12 months, and grazing
animals whose products are consumed by humans is prohibited for one
month after application. In addition, production of crops for direct
human consumption are prohibited for 18 months after the application
of septage, unless the edible portion in no way touches the wastes or
the septage has been treated by a process to further reduce pathogens
(PPRP) (50) . This section will briefly describe the pathogens of con-
cern, and will present a brief description of many of the accepted
PSRP's and PFRP's that might be applied to reduce the risk of pathogen
contamination.
7.11.2 Characteristics of Pathogenic Organisms
A pathogen or pathogenic agent is any biological species that can
cause disease in the host organism. This section will limit discussion
to pathogens that produce disease in man and complete their life cycles
229
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in climates typical of the United States. There are four broad categor-
ies of pathogenic organisms: viruses, bacteria, parasites, and fungi.
Viruses, bacteria, and parasites enter the septic systems of typical
homes by several sources:
1. Human wastes, including feces, urine, and oral and nasal
discharges.
2. Food wastes.
3. Domestic pet feces and urine.
Fungi are secondary pathogens and are only numerous in septage when
given the opportunity to grow during some treatment or storage process.
7.11,2.1 Viruses
Viruses depend on host cells to perform most of the metobolic functions
necessary for replication. Viruses are small particles whose protein
surface charge changes in magnitude and sign with pH. Most viruses have
a negative surface charge in the pH range typical of most septage. Some
viruses demonstrate considerable resistance to environmental factors
such as heat and moisture.
The major virus subtypes transmitted in human excrement are listed in
Table 7-28, together with the disease they cause. Viruses are excreted
by man in numbers up to IQlO per day. However, little information is
reported on the survival of viruses in septage.
7.11.2.2 Bacteria
Bacteria are able to reproduce outside the host organism. They can
grow and reproduce under a wide range of environmental conditions;
however, low temperatures cause dormancy and high temperatures may
result in inactivation. The major pathogenic bacteria are listed in
Table 7-29. Man excretes up to lO1^ coliforms and 1016 other
bacteria in his feces every day.
230
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TABLE 7-28
PATHOGENIC HUMAN VIRUSES POTENTIALLY IN SEPTAGE (36)
Name
Disease
Adenoviruses
Coxsackie virus, Group A
Coxsackie virus, Group B
ECHO virus PO types)
Poliovirus (3 types)
Reoviruses
Hepatitis virus A
Norwalk agent
Rotavirus
Adenovirus infection
Coxsackie infection? viral meningitis;
AFRIa; hand, foot, and mouth disease
Coxsackie infection, yiral meningitis;
viral carditis, endemic pleurodynia,
AFRIa
ECHO virus infection; aseptic meningitis;
AFRIa
Poliomyelitis
Reovirus infection
Viral hepatitis
Sporadic viral gastroenteritis
Winter vomiting disease
aAFRI is acute febrile respiratory illness.
231
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TABLE 7-29
PATHOGENIC HUMAN BACTERIA POTENTIALLY IN SEPTAGE (36)
Species
Disease
Arizona hinshawii
Bacillus cereus
Vibr io cholerae
Clostridium perfringen's
Clostriclium tetani
Escherichj.a cpli
Leptospira spp
Mycpbacterium tuberculosis
Salmonella spp
(over 1,500 serotypes)
Shigella spp
Yersinia
Arizona infection
Gastroenteritis; food poisoning
Cholera
Gastroenteritis; food poisoning
Tetanus
Enteropathogenic E. coli infection;
acute diarrhea
Leptospirosis (Weils disease)
Tuberculosis
Salmonellosis; acute diarrhea; paratyphoid
fever; typhoid fever
Shigellosis; bacillary dysentery;
acute diarrhea
Gastroenteritis
232
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7.11.2.3 Parasites
Common pathogenic parasites, including protozoa, nematodes, and hel-
minths are listed in Table 7-30. Pathogenic protozoa enter the host
organism as environmentally-insensitive cysts. Once in the host or-
ganism, the cysts transform into active organisms, mature and repro-
duce, releasing cysts in the feces.
Roundworms and hookworms are commonly recognized nematodes that may
reach sizes up to 36 cm (14 in.) in the human intestine. Nematodes may
migrate to other body tissue such as the eye, causing inflammation.
Nematodes cannot be transmitted from one man directly to another, but
must go through an embryonic stage - usually in the soil - for a period
of about two weeks.
Helminths are flatworms, such as tapeworms, that may be more than 30
cm (12 in.) long. Helminths are ingested when man eats raw or inade-
quately cooked meats. Tapeworms usually develop in the intestine,
causing minor diseases, but may locate in the ear, eye, heart, or cen-
tral nervous system, causing a much more serious disorder.
7.11.2.4 Fungi
Fungi are single-celled plants that lack chlorophyll and therefore the
ability to photosynthesize. They reproduce by developing spores,
which, when released, cluster together to form colonies. Pathogenic
spores are roost dangerous when inhaled by someone already suffering
from a disease such as diabetes. Spores are secondary pathogens that
grow in stored or partially treated septage.
7.11.3 Disinfection Methods
The disinfection methods discussed in this section apply to raw septage
or the solids fraction of treated septage. The liquid fraction of
treated septage may be handled in a manner similar to that for effluent
from a municipal wastewater treatment facility. Since the ultimate dis-
posal method for most septage or septage sludge is land application,
regulations have been promulgated to reduce the potential threat to
public health. EPA regulations (40 CFR 257 "criteria") for land ap-
plication of septage require that the septage be treated by a process
to significantly reduce pathogens (PSRP), unless: 1) public access to
the facility is controlled for at least 12 months; and 2) grazing by
animals whose products are consumed by humans is controlled for at
least 1 month after the last septage application. Crops for direct hu-
man consumption are prohibited for 18 months after septage application,
233
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TABLE 7-30
PATHOGENIC HUMAN AND ANIMAL PARASITES POTENTIALLY IN SEPTAGE (36)
Species
Disease
A. Protozoa
Acanthamoeba sp
Balantidium coli
Dientamoeba fragilis
Bntamoeba histolytica
Giardia lamblia
Isopora bella
Naegleria fowleri
Toxoplasma gordii
B. Nematodes
Ancyclostoma dirodenale
Ancyclostoma sp
Ascaris lumbricoides
Enterobius vermicular is
Necator americanus
Strongyloides stercoralis
Toxocara canis
Toxocara cati
Trichusis trichiura
C. Helminths
Diphyllobothr ium laturn
Echinococcus granulosis
Echinococcus multilocularis
Hymenolepis diminuta
Tymenolepis nana
Taenia saginata
Taenia soliurn
Amoebic meningoencephalitis
Balantidiasis, Balantidial dysentery
Dientamoeba infection
Amoebiasis; amoebic dysentery
Giardiasis
Coccidiosis
Amoebic meningoencephalitis
Toxoplasmosis
Ancylostomiasis; hookworm disease
Cutaneous larva migrans
Ascariasis; roundworm disease; Ascaris
pneumonia
Oxyuriasis; pinworm disease
Necatoriasis; hookworm disease
Strongyloidiasis; hookworm disease
Dog roundworm disease, visceral larva
migrans
Cat roundworm disease; visceral larva
migrans
Trichuriasis; whipworm disease
Fish tapeworm disease
Hydated disease
Aleveolar hydatid disease
Rat tapeworm disease
Dwarf tapeworm disease
Taeniasis; beef tapeworm disease
Cysticercosis; pork tapeworm disease
234
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unless the edible portion in no way touches the waste or unless the
septage has been treated by a process to further reduce pathogens
(PFRP) (50).
Some stabilization processes that will significantly reduce pathogens
are: aerobic and anaerobic digestion, composting, lime stabilization,
air drying, and long-term storage. This section will highlight, the
disinfection capabilities of these processes. A more detailed descrip-
tion of these processes has been presented earlier in this chapter.
EPA has identified several processes that achieve a further reduction
in pathogens as: high temperature composting, heat drying, heat treat-
ment, and thermophilic aerobic digestion. Any of the following proc-
esses, provided they follow an acceptable PSRP process, may be consid-
ered as a PFRP: beta ray irradiation, gamma ray irradiation, and
pasteurization. Disinfection methods that qualify as PSRP's and PFRP's
will be discussed further in the following sections.
7.11.3.1 Pathogen Reduction During Digestion
Aerobic or anaerobic digestion are common methods for septage stabili-
zation in the United States. Well-operated digesters can reduce virus
and bacteria levels but are less effective against parasitic cysts.
Sections 7.5 and 7.6 presented detailed discussions of aerobic and an-
aerobic digestion of septage.
7.11.3.2 Chemical Disinfection
A number of chemicals used for septage stabilization, including lime
and chlorine, also reduce the number of pathogenic organisms. However,
the high suspended solids conentrations of some septage may prevent
adequate contact between the chemical and the pathogenic organisms.
a. Lime
Pathogenic bacteria reduction occurs at high pH (11 to 13) and improves
with exposure time (EPA Process Design Manual - Sludge Treatment and
Disposal). Virus studies on limed septages have not been reported, but
a pH in excess of 11.5 should inactivate known viruses (70). Lime sta-
bilization is described in more detail in Section 7.7.
235
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b. Chlorine
Chlorine is a strong oxidizing agent used for disinfecting drinking
water and wastewater effluent. Provided adequate mixing is achieved
and application is in sufficient quantity to develop a free chlorine
residual in the solution being treated, chlorine can be effective for
bacteria and virus inactivation. However, cysts and ova of parasites
are resistant to chlorine. Chlorine oxidation is discussed in Section
7.8.
c. Formaldehyde
Formaldehyde treatment of septage that had been adjusted to pH 10 has
proved to be a successful disinfection procedure during studies con-
ducted on the disinfection of septage (71). Formaldehyde at a concen-
tration of 1000 mg/L was able to reduce bacteria to undetectable limits
after 12 hours of contact time when the sludge was adjusted to pH 10.
d. Glutaraldehyde
Glutaraldehyde has the advantage over formaldehyde of being effective
in the neutral pH range and of producing more rapid bacterial kills
(71) . As with formaldehyde, the recommended dosage concentration is
1000 mg/L.
e. Other Chemicals
Other strong oxidizing chemicals such as ozone have been successfully
used to disinfect drinking water and wastewater effluent. Due to the
high solids concentration, their applicability to septage may be sus-
pect and is as yet untried.
7.11.3.3 Heat Disinfection
Sufficient temperatures and exposure times will inactivate most micro-
organisms as well as the eggs and cysts of parasites. Table 7-31 pre-
sents the exposure times and temperature levels required .to reduce the
population of some pathogenic viruses and bacteria to undetectable
limits. Heat processes applicable to septage include: pasteurization,
heat conditioning, heat drying, high temperature processes, and com-
posting.
236
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TABLE 7-31
TIME AND TEMPERATURE TOLERANCE
FOR PATHOGENS AND INDICATORS IN SEPTAGE (36)
Exposure Time for Organism
Inactivation, min
o
Temperature, C
Species 50
Viruses
Mycobacter ium tuberculosis
Micrococcus pygogenes
Escherichi coli
Salmonella typhi
Fecal streptococci
Fecal coli forms
Corynebacteriunt diptheriae
Brucella abortus
Cysts of Entamoeba histolytica 5
Eggs of Ascaris lumbricoides 60
Aspergillus flavus conidia
55 60 65 70
25
20
20
60 5
30 4
60
60
45 4
60 3
7
60
237
-------
a. pasteurization
Pasteurization qualifies as a PFRP provided it follows an approved
PSRP. The critical requirement for pasteurization is that all of the
septage be held above a predetermined temperature for a minimum time
period. Incomplete mixing of septage due to the non-homogeneous con-
sistency of septage creates heating problems and reduces the efficiency
of the process. The application of the pasteurization process to sep-
tage is not well documented.
b. Heat Conditioning
Heat conditioning includes processes where raw or partially-treated
septage is pressurized with or without oxygen, and the temperature is
raised to 177° to 240°C (350° to 400°P) and maintained for 15
to 40 minutes (36), These processes will destroy or inactivate all
pathogens in septage. Heat conditioning of septage, although techni-
cally feasible, may not be practical on a large scale.
c. Heat Drying
Heat drying of septage could be accomplished in a flash drier or a
rotary kiln. Heat drying would achieve sufficient temperatures and
contact times to significantly reduce the number of pathogens? how-
ever, fuel costs may be prohibitive if applied to a full-scale septage
facility.
d. High Temperature processes
High temperature processes include incineration, pyrolysis, or a com-
bination thereof (starved-air combustion). These processes raise the
septage temperature above 500°C (930°P), thereby destroying the
physical structure of all septage pathogens and effectively steriliz-
ing the septage. The product of a high temperature process would be
sterile unless shortcircuiting occurs within the process. The fuel
cost for this type of system would still be high, but the volume of
solids to be disposed of would be reduced significantly. No septage
studies have been reported with these systems.
238
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e. Composting
Composting, depending on the temperature levels and exposure times,
can be considered as either a PSRP (40°C for 5 days or 55°C for 4
hours, using the within-vessel or windrow methods) or a PFRP (55°C
for 5 days using the within-vessel method and 55°C for 15 days using
the windrow method) (36) . Composting is considered a heat process
because a major aim of septage composting operations is to produce a
pathogen-free compost by achieving and holding a thermophilie temper-
ature. Greater detail on the process of composting is provided in Sec-
tion 7.3.
7.11.3.4 Long-Term Storage
Pathogen reduction has been recognized for years as a side benefit of
septage storage in lagoons. The U.S EPA has listed long-term storage
(air drying) as an acceptable process to significantly reduce patho-
gens. Raw septage is .allowed to drain and/or dry on under drained sand
beds, or on paved or unpaved basins at an average depth of 23 cm (9
in.). A minimum of three months is needed, two months of which the
average daily temperatures must exceed 0°C. Table 7-32 presents the
results of a laboratory study on the number of days required to achieve
a 99.9 percent reduction of pathogens in sludge.
7,11.3.5 Disinfection with High-Level Radiation
High-energy radiation has shown promise for the disinfection of
wastewater sludges. Facilities in the U.S. and Europe are currently
utilizing both beta and gamma rays to destroy or inactivate pathogenic
organisms in municipal wastewater sludge. The same principles applied
to sludge disinfection would also apply to septage. Beta rays are
high-energy electrons, generated with an accelerator for use in
disinfection, while gamma rays are high—energy protons released from
atomic nuclei. Both beta and gamma ray irradiation are considered by
U.S. EPA as PPRP's.
a. Beta Ray Irradiation
Accelerated electrons produce both biological and chemical effects as
they scatter off material in the septage. Direct ionization by the
electrons causes damage to the DNA in bacteria cell nuclei and the DMA
or RNA of viruses. A second way beta irradiation destroys pathogens is
by producing ozone and hydroperoxides. These compounds then attack
organics in the septage, including pathogens, thereby promoting oxida-
tion, reduction, dissociation, and other forms of degradation.
239
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TABLE 7-32
LABORATORY STUDY ON DAYS OF STORAGE REQUIRED FOR 99.9% REDUCTION
OF VIRUSES AND BACTERIA IN SLUDGE (22)
Number of Days
Organism at 4°C at 20°C at 28°C
Poliovirus 1
Echovirus 7
Echovirus 12
Coxsackievirus A9
Aerobacter aerogenes
Escherichlia coli
Streptococcus faecalis
110
130
60
12
56
48
48
23
41
32
—
21
20
26
17
28
20
6
10
12
14
The disinfection power of the electron beam is limited because electron
penetration is only about 0.5 cm (0.2 in.). Septage, which would re-
quire pretreatment, must flow past the electron beam in a thin uniform
film. Figure 7-21 presents a typical configuration for an electron
beam disinfection unit. This unit would require a minimum level of
electron irradiation of 400,000 rads. This energy level would ensure
penetration of 0.5 cm <0.2 in.). No septage studies have been reported
with beta ray irradiation.
b. Gamma Ray Irradiation
Gamma rays' disinfection properties are very similar to beta rays;
however, there are two major differences between the two. First, gamma
rays are much more penetrating? a layer of water 64-cm (25 in.) deep
is required to stop 90 percent of the rays from a cobalt-60 source; in
comparison, a l.MeV electron can only penetrate about 1 cm (0.4 in.)
of water. Second, gamma rays are emitted from decaying radioactive
isotopes. The decay is continuous and uncontrolled; it cannot be
turned on and off as with the electron generator.
240
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FIGURE 7-21
ELECTRON BEAM SCANNER AND SEPTAGE SPREADER (36)
Inclined
Feed Ramp
Electron Beam
Scanner
High Energy
Disinfection
Zone
Septage
Receiving
Tank
Output
.(Disinfected
Septage)
Two isotopes, Cs-137 and Co-60, have been used as fuel sources for
disinfection processes. Cs-137 has a half life of 30 years but
produces only half as much energy as does Co-60, which only has a half
life of 5 years. Two general types of gamma ray irradiation systems
have been proposed for septage disinfection. Figure 7-22 presents a
typical design for a batch-type system for septage, where a volume of
septage would be circulated in a closed vessel surrounding the gamma
ray source. The second system is similar in design to the beta system
illustrated previously. Dried septage would be carried on a conveyor
belt past the gamma ray source. As of this date no such facilities are
in operation.
7.12 Odor Control
Odor control is a critical element in the design of a septage treat-
ment facility. As a general rule, all process units should be self con-
tained, individually covered, or contained within buildings vented
through an odor removal system. This is especially true for preliminary
treatment processes, any process where the wastewater is mixed or aer-
ated. The degree of odor control warranted at a particular facility
will depend on the typical characteristics of the incoming septage, the
location of the plant in relation to residential areas, the existence
of natural buffers (i.e., wooded areas), and local microclimates (i.e.,
typical wind direction, potential for inversions, etc.).
241
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FIGURE 7-22
COBALT-60 IRRADIATION FACILITY
AT GE1SELBULLACH, WEST GERMANY (36)
Septage
Inlet
Vent
Ground
Level
The basic components of an odor control system are the process or build-
ing containment structure, the air collection and ventilation system, and
the odor removal system (scrubber or filter). The design of containment
structures is a function of equipment design, building design, and site
layout. The design of the ventilation system should follow general heat-
ing, ventilation, and air conditioning design practice. Several odor
removal systems are discussed in Chapter 4 under receiving station de-
sign.
7.13 Treatment and Disposal o£ Liquid Fraction
Methods that can be used for treatment/disposal of the liquid fraction
from an independant septage treatment facility are: 1) land treatment; 2)
direct discharge to surface water after further treatment; and 3) dis-
charge to STP. Table iJ-33 summarizes applicable processes for each
method, as well as advantages, disadvantages, and general design criteria
for each process. Land treatment is the most commonly practiced treat-
ment/disposal method for solid and .liquid fractions of septage. Table
7-34 summarizes the advantages, disadvantages, and general design cri-
teria for several land disposal processes for raw septage and septage
solids, as well as for incineration. Many fo the processes listed in
these tables have been described elsewhere in this handbook. Descrip-
tions of those processes not discussed in this handbook are available
elsewhere (21) (35) (36). Tables 7-33 and 7-34 emphasize those processes
that would most likely be considered for an independent septage treatment
facility (because of plant location, operational requirements, funding,
etc.).
242
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TABLE 7-33
TREATMENT/DISPOSAL OF LIQUID FRACTION —
ADVANTAGES, DISADVANTAGES, AND DESIGN CRITERIA {21} (35)
Process
Advantages
Disadvantages
Design Criteria
Land Treataen t
Irrigation
* Effluent quality excellent
* Large land requirement
• Limited &y soil type/ depth
topography, climate, etc.
• Sprinkler clogging, odors
• Storage required for cold weather
Area req'cU 3UO to 3,000 ha/I,UUO m^/d
BOD loading: 0.2 to 5.6 Kg/ha/d
Depth to Groimdwater: 0*9 to 1.2 ra (mm)
Slope: 20% maximum
Soil Permeability: Mod. slow to mod. capid
to
$*
OJ
Rapid infiltration
Overland Plow
Wetland Application
* Simple operation
• Least land-intensive
* Cold weather does not affect
operation
• Nitrate, nitrite removals low
• Limited by soil type, depth,
hydraulic capacity, etc.
* Soil clogging not a problem * Limited by soil type, crop water
* Depth to groundwater not critical tolerances, climate slope
* Vegetation required
* Potential odor, vector problems
• Good for small flows
* Low cost, aiiaple
• In developmental stage - design
information limited
* Climate may be major limitation
* Large area requirement
* K>tential for mosquito breeding
* Area req'd; 20 to 300 ha/1,ODD raVd
* BOD loading: 22.4 to 112 kg/ha/d
» Depth to Groundwater: 3 m (minj
* Slope; Not critical
• Soil Permeability* Rapid (.sands, loamy sands)
* Area req'd: 200 to 5UO ha/l,uOO roVd
o BOD loading: 5.6 to 56 kg/ha/d
* Depth to Groundwater: Not critical
* Slo$>«; Finish slopes 2 to g$
* Soil pernteabiiity: Slow (clays, siits, ana soils with
impermeable barriers)
* Site and project specific
-------
TABLE 7-33
(CONTINUED)
Advantages
Disadvantages
Design Criteria
^ Stir face.
Water
Lagoons
M
Attached Growth
Suspended Growth
(Activated Sludge,
Extended Aeration,
etc.)
Discharge to STP
* Simple operation
* IjOw cost
* High reliability
* Long service life
* Less solid residue generation
than with other secondary
processes
* Process more controllable than
lagooning, land treatment
* J?er£ori$anee well-docusienteei £or
wastewater treatment
* Small land requirement
* Process store controllable than
lagooning, land treatment
* Performance Hell-documented for
wastewater treatment
e Small land requirement
' Construction and maintenance of
liquid stream treatment facility
noc required
* Large land requirement
* Cold weather problems
• Potential for seepage to ground-
water
* Potential odor, vector problems
* Effluent quality marginal
• Higher capital, operating costs
than lagooning, land treatment
* Higher capital, operating costs
than lagooning, land treatment
May have adverse irapact on POTW,
especially if flow equalization
not provided, or if stream is
high-strength
Detention, d
Depth* m
pH
temp., °C
Opt. Temp., °C
Organic loading;
kg/ha/d
3-10
2-6
6.5 to a.O
0-40
20
11-33S
Facultative
20-ltiU
1-2.5
6.5 to 9.0
2-32
11-11Q
* Depends on selected method; available in literature
Depends on selected asethod; available in literature
Depends on PQfW
Implications, design criteria, etc., discussed in
Chapter 6
-------
TABLE 7-34
ULTIMATE DISPOSAL OP RAW SEPTAGE AND SEPTAGE SOLIDS —
ADVANTAGES, DISADVANTAGES, AND DESIGN CRITERIA (21)(35)(36)(7)
Advantages
Disadvantages
Design Criteria
Land Disposal
Spreading (Liquid
Septage)
Trench Fill
{Liquid or Solids
Frafction)
* Soil conditioning, fertilization * Septage should be stabilized
* Dewatering not required to avoid problems from odors,
* Inexpensive liquid transfer vectors? etc.
* Large area required
Suitable for unstabilized
septage
Low Initial costs
* Wet-weather problems
* Daily soil cover required
for vector control
* Large land area
to
•fc
in
Area Pill Mound « Suitable in shaUow-watertable1 » Stabilized septage re-
(Septage Solids)
areas or where excavation not
possible
Verv reliable disposal method
Area Pill Layer • Solids content can be as low as
(Septage Solids) 15%
• Very reliable disposal method
quired
* Large land area required
* Leachate must be controlled
« High manpower and equip-
requiceiaents
• Wet-weather problems
» Large area required
* Requires relatively level
ground
* Stabilized aeptage re-
quired
* Ground slope: 5 to S» maximum
» Soil Permeability: 1.5 to 15 cm/he(O.b to 6 in/hr)
• Soil pH: alkaline or neutral ( pH 6.5)
Narrow Trenches
Widths
Septage
Solids
Contents
Application •
Kate:
Surface Soil
Cover :
Depth to
Groundwater;
<3 m
3 to 28»
2,270 to 10,5dU
1.3 ra
0.6 to 1.5 in
>3 n
>20U
6,050 to 27,400 ra3/ha
1 to 1.5 m
0.6 to 1.5 m
Stptage Solids Content: 20%
Septage Characteristics; Stabilized
Ground Slope: No limitation if suitably prepared
Bulking Satio: 0.5 to 2 soi-1: 1 suptaye solids
Septage Application Hate: 5,670 to 26,450 ntVha
Hound Height: 2 m
Soil Cover Heiynt: 1 to 1.5 m
* Septage solids Content 0
• Septage Characteristics: Stabilized
• Ground slope: Level preferred
* Bulking Ratio: 0.25 to 1 soil: 1 septage solids
* Septage Application Rate; 3.7BU to 17,000 m/^na
* Layer Height: U.15 to 1 in
* Soil Cover Height: Q.15 to 0.3 in
-------
TABLE 7-34
(CONTINUED)
Process
Advantages
Disadvantages
Design Criteria
Diked Containment
{Septage Solids)
Lagooning
(Septage}
Incineration
* Stabilisation not required
* Bulking agent not required
* Efficient land use
« Simple operation
* Economical
* Stabilization, dewatering not
required
* Septage may be stored
indefinitely
* Very siaall quantities of solids
foe disposal
* stabilization not required
* Total or partial conversion*
primarily to C02 and water
• Possibility for co-incineration
with municipal refuse
* Possibility for steam/ electric
generation, heat recovery, etc.
• Small land area required
> Controls for leachate
outbreaks required
• Odor probless
* Large area required
• Treatment of supernatant
say be required
* Ash disposal required
* High costs
* Air pollution control
devices norsally required
* Dewater ing required
• Complex operation
* Septage Solids Content:> 20%
* Septage Characteristics: Stabilized or unstabilized
* Ground Slope: Level ground or steep terrain if suitably prepared
» Bulking Ratio: 6 to O.S soil: 1 septage
* Septage Application Rat«: 9,070 to 2*2,300 ra3/ha
* Interim Cover {Occasional}; 0.3 to 1.0 »
e Final cover (Filling Discontinued): l.u to 1.5 ia
• Typical Dimensions; 15 to 3U m wide, 30 to 60 ID long, 3 to 9 n
deep
• Depth: 1 to 1.5 ra - other dimensions depend on
design life of lagoon
* Dike Slopes; 1:2 exterior, 1:3 interior
* Bottora Separation from Gcoundwater; 1,2 12 minimum
• Cells: Minimum oi two
» Loading Bates; 35 to 38 kg solids/m3/yr
0.8 to 1.5 kg solids/m^ of surface/30 days of use
* Solids Removal; 1-5 to 3 yr intervals
* Depends on method chosen (multiple-hearth, fluidized bed, etc.)
-------
7.14 Mobile Septage Dewataring
A novel approach to septage treatment, which has had limited practice
in Europe, is the use of a mobile septage processing unit where raw
septage is lime-conditioned and dewatered in the same truck used for
the pumpout operation. A proprietary mobile dewatering/hauler truck,
which pumps out septic tanks and then dewaters the septage in transit,
has been tested (1). After dewatering, the reject liquor is emptied
into the next septic tank after it is pumped out. The dewatered sludge
can be discharged to an STP sludge stream or applied directly to the
land. Some of the advantages and disadvantages of this treatment
scheme are as follows (see also Figure 7-23):
Advantages
1. The liquid volume of septage to be disposed of (i.e., after
dewatering) is reduced considerably.
2. The septage sludge to be disposed of has a dry solids content
consistently in the range of 16 to 23 percent. By producing a
stabilized dewatered sludge, direct disposal at nearby land-
fills or directly on farmland is more feasible.
3. Mobile dewatering/hauler trucks could service more septic
tanks before disposal is required since the bulk of the
liquid volume is returned to empty septic tanks in the form
of reject liquor. This minimizes the time and associated cost
in traveling to and from disposal sites.
Disadvantages (for the Absorption Field)
1. The resting period which normally follows pump-out is elimi-
nated and could affect the long-term performance of the ab-
sorption field.
2. High suspended solids effluent and high pH effluent to absorp-
tion field for a period after pumping.
3. Potential public health risk of transferring pathogens be-
tween residences even though- lime use may minimize survival.
247
-------
FIGURE 7-23
REDUCED TRAVEL DISTANCE THROUGH ON-THE-ROAD
DEWATERING OF SEPTAGE (1)
/TT-CW
Final Disposal
Conventional Routes
Route for the Mobil Dewatering Unit
248
-------
7.14.1 Process Description
The proprietary mobile dewatering/hauler truck (see Figure 7-24) con-
sists of the following components:
1. 90 m (295 ft) of hose on a motorized windlass.
2. A lime conditioning unit (storage and injection pump).
3. A 4.5 m^ (1200 gal) holding tank for conditioned septage.
4. A sludge feed system to maintain appropriate levels in the
dewatering unit.
5. Vacuum filter for dewatering.
6. A 3 m-3 (800 gal) sludge cake container.
7. A 4.5 m3 (1200 gal) tank for reject liquor.
8. Reject liquor feedback pipe.
This equipment is mounted on a 22 metric ton (24 ton) truck and can be
remotely operated by one man servicing the septic tank.
The sequential steps in the collection and dewatering of the septage
from the septic tank are listed below:
1. Preparation of tank (includes gaining access to tank and
preparing equipment).
2. Suction of contents from tank. Suction can be facilitated by
periodically blowing air or reject liquor into the septic
tank and scraping the sides of the tank to mix or liquify the
contents.
3. The septage is conditioned with lime and injected in-line
before it enters the storage tank.
4, After all the septage is removed from the septic tank, -the
reject liquor from the previous dewatering operation is
pumped into the septic tank.
249
-------
FIGURE 7-24
MOBILE DEWATERING/HAULER TRUCK (1)
1. Hose
2. Lime Conditioning Unit
3. Holding Tank, Conditioned Septage
4. Sludge Feed . . 1
5. Dewatering Unit
6. Sludge Tank
7. Refect Liquor Collection Tank
8. Reject Liquor Feed Back Tank
FIGURE 7-25
VACCUM FILTER FOR SEPTAGE DEWATERING (1)
1 Attachment Zone
2 Vacuum Zone
3 Drying Zone
4 CakeBlow-Off
5 Roller Pressure Rear Royer Forward Roller
Adjustable 0-30 Bar
Scraper
Filter Cloth
Rubber Coated
Steel Roller
Reject Liquor
to Separate Tank
To Sludge Cake
Conditioned Septage
From Holding Tank
250
-------
5. Dewatering of the conditioned septage from the storage tank
can begin as soon as the reject liquor return operation is
finished. The reject liquor tank is gradually filled as
dewatering progresses, simultaneously emptying the septage
storage tank. This process will continue until the next
septic tank is ready for pumping.
6. Final maintenance check and septic tank closure.
7.14.2 Dewatering Equipment
The dewatering process is performed with a vacuum filter press designed
to handle non-homogeneous septage. Figure 7-25 shows a typical press
which consists of two parallel rollers partially submerged in the con-
ditioned septage reservoir. The only additional time required is for
the refilling of the septic tank (Step 4 above).
7.14.3 Mobile Dewatering Performance
The mobile dewatering/hauler truck has been used in Norway and Sweden
(1) . The time required for the septic tank cleaning operation is very
similar to the time for conventional pumping (generally less than 1
hour).
The septage sludge has a dry solids content of 16 to 23 percent. A
significant reduction in pathogenic microorganisms occurs due to the
high pH levels from lime conditioning. If sufficient lime is added to
produce a pH of 12 after 2 hours, the process could qualify as a
process to significantly reduce pathogens (PSRP). PSRP treatment
eliminates many restrictions placed on land application of septage
sludge (see Chapter 5).
The reject liquor returned to the septic tanks has a suspended solids
content in the range of 600 to 2000 mg/L. After three days the levels
drop to an average of 200 to 500 mg/L, and to less than 200 mg/L with-
in 16 days. The high pH {12 to 13) introduced with the reject liquor
was reduced to approximately pH 8 after 7 days, and back to a normal
value of 6 to 7 within 16 days. It is claimed that the disposal field
should not be subject to any ill effect from the pumping/dewatering
operation, provided reserved capacity is left when the reject liquor
is returned to the septic tank and proper care is demonstrated in the
use of the system immediately after pumping(1). However, the potential
for impact on disposal field performance needs to be further investi-
gated.
251
-------
Eikum (1) did note that poor reject Liquor quality was encountered in
instances when septage quality was poor (i.e., septage age^>3 years)
when conditioning was insufficient, or when septage contained excessive
grease, oil, or substances that interfere with filtration. The conclu-
sions drawn from the NIVA studies (1) were that mobile dewatering witn
this machine is an attractive alternative in rural areas, provided
thats
1. Pumping frequency is kept in the order of I to 3 years.
2. Septic tanks containing excessive grease or oil are avoided.
3. Operation is performed by skilled personnel.
4. Disposal sites for high pH sludge cakes can be found.
5. Transport distances to treatment facilities are unfavorable
for conventional collection.
7.15 References
1. Eikum, A.S. Treatment of Septage - European Practice. Norwegian
Institute of Water Research, Report No. 0-80040, February 1983.
2. Vivona, M.A. and W. Herzig. The use of Septage Lagoons in New
England Sludge. March-April 1980.
3. New England interstate Water Pollution Control Commission.
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4. U.S. Environmental Protection Agency, process Design Manual for
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5 U.S. Environmental Protection Agency. Land Treatment of Municipal
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6. Hinrichs, D.J., J.A. Faisst, and D.A. Pivetti. Assessment of Cur-
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7. New England Interstate Water Pollution Control Commission Guide-
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T6M-1, August 1976.
252 '
-------
8. Epstein, E., G.B. Willson, W.D. Burge, D.C. Mullen, and N.K.
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9. Mosher, D. and R.K. Anderson. Composting Sewage Sludge by High-
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253
-------
20. Bowker, R.R.G., and S.W Hathaway. Alternatives for the Treatment
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254
-------
32. Howley, J.B. Biological Treatment of Septic Tank Sludge, M.S.
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\
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255
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257
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72. Willson, G.B. and D. .Dalmont. Sewage Sludge Composting in the
United States, Biocyele, 2£(5), 1983.
73. Lombardo, P. "Septage Composting," Compost Science, 1£(6), 1977.
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CHAPTER 8
OPERATION AND MANAGEMENT CONSIDERATIONS
8,1 Overview of Management Concerns
Each of the major components of septage disposal, i.e., pumping and
hauling, treatment, and final disposal, have certain operational re-
quirements that require specific management responsibilities. Manage-
ment, by definition, is the process of controlling, directing, and
handling a resource, facility, or group of people. The management of
septage disposal includes any actions taken to ensure the proper plan-
ning, design, and operation of facilities and equipment to handle this
waste. Proper management is just as important to the success of a sep-
tage hauling and disposal program as is the design of the hauling,
treatment, and disposal systems.
This chapter presents a review of the management activities involved
in implementing a successful septage management program. The reader
should recognize that the information presented in this chapter serves
as input to the formulation of a .septage management plan. A septage
management plan is a strategy document that outlines the actions that
are necessary for implementing proper controls on the hauling, treat-
ment, and disposal of septage.
One of the first questions that should be asked by the individual who
is interested in developing a septage management plan is "What are the
management needs?" Management needs can be expressed as the services
or activities that need to be provided to ensure proper design and op-
eration of septage facilities. Once the needs are defined, the ques-
tion then is, "Who is responsible for carrying out the management
services?" Answering these questions requires that the appropriate
management functions and institutional arrangements be specifically
described. Management functions and institutional arrangements, as
used in this context, can be defined as follows:
Management Functions - The range of services and activities to be
provided to ensure the proper design and operation of septage fa-
cilities.
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Institutional arrangements - The assignment of responsibilities to
the principle participants in the management process.
The basic types of management functions and institutional arrangements
that apply to septage management are discussed as follows.
8.1.1 Typical Septage Management Functions
A complete septage management program might include the following bas-
ic management functions:
On-Site System Management - Closely linked to any septage manage-
ment program is the design, installation, and maintenance of on-
site wastewater disposal systems. Onsite system maintenance in-
volves the routine inspection and pumping of septic tanks. Since
septage is generated from the maintenance of onsite systems, the
relationship of onsite system maintenance and septage management
is an important one.
Management of Pumping and Hauling Activities - There are several
techniques that can be used to ensure the proper performance of
the septage hauler; a key factor is a septage management program.
The septage hauler is basically responsible for pumping septage
and transporting the wastes to an acceptable location for treat-
ment and disposal. The control techniques commonly used to regu-
late haulers include licensing, certification, and registration.
Treatment/Disposal Facility Operations - The actual operation of
the treatment/disposal facility will require the provision of a
variety of maintenance and repair services, depending on the type
of technology involved.
Treatment/Disposal Facility Performance Monitoring - The purpose
of performance monitoring is to assure regulatory agencies that a
facility is meeting operating permit conditions and, if not, de-
termine necessary corrective actions. These conditions provide the
regulatory agency with the necessary authority to conduct onsite
inspections and review performance data on a routine basis.
System Financing - Financing a septage facility and transport sys-
tem involves securing grants and loans to cover capital expendi-
tures (e.g., equipment, vehicles, and physical plant), and col-
lecting revenues to support annual debt retirement and operating
costs. The choice of financing methods will depend on the types of
costs to be incurred and the entity that is responsible for the
costs.
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The number of management functions to be provided and the complexity
of the services involved will vary from one program to another. Spe-
cific examples of the types of management functions that may be in-
cluded in a management program are discussed later in this chapter.
8.1.2 Institutional Arrangements
Having defined the range of management functions to be provided, ar-
rangements for implementing the various activities involved need to be
made. This task requires the allocation of responsibilities between
the public and private sectors and the designation of a management
agency (i.e., the lead or principle institutional entity responsible
for program implementation). The various entities that might take on
different management responsibilities include:
State Agencies - Environmental "protection agencies, health depart-
ments, and public utility commissions are involved in a variety of
septage management tasks, particularly in regulating haulers and
disposal facilities, enforcement, and financing. Each state is or-
ganized differently and has different sets of laws and regulations
governing septage disposal.
Municipalities - Cities, towns, villages, etc. can provide a range
of services to its constituents, including septage hauling and
treatment. Municipalities can also adopt and enforce special rules
and regulations concerning septage disposal. Cooperative agree-
ments among municipalities enable several adjoining communities to
participate in a septage management program.
Counties - A county can help coordinate municipal activities in
septage disposal or provide a variety of planning and operational
services on its own.
Special Purpose Entities - Single or multiple purpose entities
such as special districts and public authorities (e.g., sewage au-
thorities) can be established for the purpose of providing septage
management services, either independently or in conjunction with
other public service functions (e.g., sewage treatment of solid
waste management). Special purpose agencies are legal governmental
entities, but they operate outside the regular governmental frame-
work for a specific purpose. State laws define the organizational
characteristics, powers, jurisdiction, and financial authority of
special purpose entities within each state.
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Private Corporations — These include private enterprises such as
small private firms (e.g., septage haulers, septic system contrac-
tors, plumbers, etc.). Private utilities can own and operate fa-
cilities and provide a variety of services in a septage management
program. Such privately owned and operated facilities (which oper-
ate at a profit) are typically regulated by state public utility
commissions.
Nonprofit Corporations - These can be public or private entities.
A public nonprofit corporation can be formed by cooperating munic-
ipalities (e.g., a waste disposal utility). Typical private non-
profit corporations include rural cooperatives and property owners
associations.
The choice of specific type of management agency for septage manage-
ment depends on many factors, including legal authority, financing
capability, service area flexibility, and willingness to provide sep-
tage management functions. Table 8-1 briefly summarizes the capabili-
ties of each of the aforementioned institutional arrangements related
to the provision of septage management functions.
The remainder of this chapter describes the key management considera-
tions in developing a septage management plan, namely:
1. Management of onsite (septic) systems.
2. Management of septage pumping and hauling.
3. Monitoring of the quality and quantity of incoming septage.
4. Facility operation and maintenance,
5. Performance monitoring.
6. System financing.
These management concerns are basically consistent with the major man-
agement functions described previously.
8.2 Onsite Systems Management
A major concern in implementing a septage management program is the
transport of septage from septic systems to the treatment/disposal fa-
cility.
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TABLE 8-1
INSTITUTIONAL CAPABILITY MATRIX
Implementing Entity
Special Private Nonprofit
Coun- Municipal- Purpose Corpora- Corpora-
Management Function States ties ities Agencies tions tions
Onsite Management X X X X x
System Inspections
Septage Pumping
Management of Septage
Pumping and Hauling XXX
Vehicle inspections
Hauler Regulation
Recordkeeping
Treatment/Disposal Facility
Operations X X X X x
Receiving Stations
Periodic Maintenance
Process Control
Recordkeeping
Treatment/Disposal Facility
Performance Monitoring X X X X X X
Facility Inspections
Monitoring
Reporting
System Financing X X X X X X
Capital Financing
Operations Financing
Recordkeeping
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The scheduling of septic tank pumping is a primary means of control-
ling the volume of septage received at treatment and disposal facili-
ties. A number of approaches can be taken to directly or indirectly
control septic tank pumping. Some examples, in increasing order of
public agency involvement are:
1. Leaving septic tank system maintenance solely to the discre-
tion of homeowners, with the need for pumping to be determined
as they deem necessary. This is, in essence, no control, and
is the predominant situation throughout the country.
2. Providing general public education material to septic tank
system owners to acquaint them with their maintenance re-
sponsibilities.
3. Sending scheduled, personal "reminder cards" to homeowners to
have their system inspected and pumped, if necessary. To be
totally effective, such a system must have a response mechan-
ism to determine which people have done so. This would allow
for either a follow-up reminder card or scheduling of the
next reminder for those who have acted on the recommendation.
4. Requiring septic systems to be inspected and pumped, if nec-
essary, when a home is sold (i.e., before the transfer of
title can take place) . Homes are sold every five to seven
years on the average.
5. Scheduling and arranging for septic tank inspection and main-
tenance (e.g., via an onsite wastewater management district).
To effectively implement such a system, the onsite system
management entity must have access to the onsite wastewater
disposal system. This can generally be granted through an on-
site wastewater management district ordinance.
Also involved in the management of septage generation is the concern
for septage characteristics. Public education programs aimed at the
homeowner should address the proper use of a septic system; that is,
elimination of the use of chemicals, degreasers, or other additives to
the septic tank.
It is obvious that the greater the degree of public control of onsite
system maintenance, the greater can be the control of the quantity and
quality of septage that must be "managed." Left totally to homeowner
discretion, septage flow has a tendency to be crisis-generated; that
is, need being determined by occurance of problems. Since problems can
often be seasonal or climate-related (e.g., more problems during wet
264
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periods), the quantity of septage generated can vary greatly from day
to day, and from month to month. Greater public control can minimize
the difference between extremes in septage flow. Otherwise such irreg-
ularities must be compensated for at the treatment and disposal facil-
ities by constructing relatively large equalizing facilities, or by
over-designing all processes to handle peak volumes. Both of these can
add significantly to the cost of the facilities. Unless septage is
treated at a facility with built-in capacity to handle peak volumes,
the scheduling of septic tank maintenance should be considered as an
integral part of the septage management program.
Many communities have instituted programs which attempt to control the
practice of septic tank pumping. In Marin County, California, the
County Health Department requires the renewal of septic tank mainte-
nance permits every two years (1) . Renewal of the permits involved
inspection of the septic tank and pumpings of the tank if deemed nec-
essary by the inspector (i.e., County Sanitarian). Inspections and
tank pumping are scheduled evenly throughout the year. A similar pro-
gram was implemented in Santa Cruz, California, with the exception that
a specially created County Septic Tank Maintenance District actually
peformed the necessary maintenance, including tank pumping, on a
schedule where tanks were generally pumped once every three years on
the average (2).
Two communities in Massachusetts have created a joint on-site systems
management program under which homeowners are required to have their
septic tanks pumped every three years (3). The towns notify homeowners
when the tank pumpings must take place, and the pumpings must be con-
firmed by submission of a receipt to the towns.
8.3 Management of Septage Pumping and Hauling Activities
The pumping of septage from individual septic tanks and hauling to
disposal sites is done primarily by private septage haulers. Since the
pumping and hauling of septage is a key aspect of a septic management
program, some degree of public control of this activity is important.
Such a program should address the regulation of hauler activities, as
well as the regulation of adequate disposal facilities. Specific ac-
tivities involved include:
1. Regulation of individuals involved in the design, installa-
tion, cleaning, or repair of septic systems.
2. Regulation of individuals involved in the transport of sep-
tage for treatment.
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3. Recording of septage pumping events, volume of residuals
transported, and location of disposal.
4. Establishment of hauler vehicle specifications.
5. Mandatory periodic inspection and approval of all vehicles
used to transport residuals.
6. Prohibiting of industrial waste hauling trucks from pumping
out domestic tanks.
7. Restricting the disposal of septage to approved sites.
The regulation of haulers can be accomplished through licensing, cert-
ification, and registration. Licensing is the most restrictive of
these three control techniques. Licensing regulates the haulers by im-
posing certain limitations or conditions on their activities. Licenses
can be an effective regulatory tool, especially if the licenses are
revoked when the performance of the individual (or firm) is not satis-
factory. (Vehicles can also be licensed. In fact, the management agen-
cy should decide who or what to regulate, i.e., the hauler, the firm,
or the vehicle.)
Many states license septage haulers (Delaware, Florida, Illinois, and
Wisconsin) (2). However, state licensing programs generally are not ef-
fective at controlling the practices of individual haulers. Some local
licensing programs, such as the one in Fairfax County, Virginia re-
quire haulers to display color-coded decals, issued by the County, on
their trucks (4). The haulers can not use County-operated septage
treatment facilities without a valid license decal.
Certification and registration, on the other hand, are typically vol-
untary mechanisms. Certification is a confirmation or assurance that
the individual (or firm) is competent and qualified to provide hauling
services (or that the vehicle meets all specifications). A qualifica-
tion exam (or vehicle inspection) may be a prerequisite to certifica-
tion. Registration is the least restrictive technique, merely requir-
ing the individual (or firm) to register (i.e., "sign up") for a par-
ticular activity.
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Certification or registration allows the operator of a septage treat-
ment facility to limit use of the facility to recognized and approved
haulers. In Acton, Massachusetts, for example, haulers must be regis-
tered with the town, and must purchase coupons from the town in order
to discharge septage at the Acton septage lagoon facility (1)(4).
Coded registration numbers or decals such as used in Fairfax County,
Virginia (4) can also serve to identify currently registered or
certified haulers.
Whichever techniques are chosen to control hauler activities, periodic
inspections of hauler vehicles and equipment, as well as a manifest
(i.e., recordkeeping) system, should be instituted for quality assur-
ance. These conditions can, in fact, be linked to a mandatory licensing
requirement.
Maintaining accurate files of septage pumping events and disposal lo-
cations can be ensured by the implementation of a trip ticket or mani-
fest system. An additional benefit of such a system can be its built-
in monitoring or recordkeeping mechanism. This system can take on many
forms, but it basically requires the written documentation of the ori-
gin of each load of septage brought to the treatment and disposal fa-
cilities. All manifest systems use some type of onsite system mainte-
nance form (also called manifest, trip tickets, and septic tank pump-
ing permit) on which pertinent information (i.e., pumping and hauling
firm, date, property location and owner, volume, etc.) relative to a
particular load of septage is recorded. Verification of the report is
by means of a signature of the representative of the firm and the own-
er or resident of the property from which the septage was pumped. The
form is provided in multiple copies, which can be left with or sent to
the owner, the operator of the treatment and disposal facilities, the
management entity, and the pumping and hauling firm.
In Marin County, California (1) the hauler provides a receipt to the
homeowner who in turn must submit the receipt to the County Health
Department as proof that the septic tank was pumped. A record of septic
tank pumpings is kept with the individual permit file. In Acton, Massa-
chusetts (1) the hauler must purchase coupons from the town in order
to use the town septage facility. Upon discharging septage at the fa-
cility, the hauler must submit a filled out coupon indicating name of
hauler, quantity of septage, and origin of septage. The Town of Somers-
worth. New Hampshire issues coupons to individual homeowners. The
coupons are given to the hauler when a tank is pumped, and the hauler
turns in the coupon at the treatment plant as payment for treatment.
The coupon, which indicates the origin of the load (i.e., homeowner's
name or address) is maintained on file.
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An innovative approach to hauler regulation is the requirement for the
submission of hauler plans as a condition to the issuance of hauler
licenses or permits to operate within a jurisdiction or service area,
The hauler plans would essentially:
1. Identify the disposal sites permitted to be used.
2. Show proof of use of these sites.
3. Set forth the operational provisions for septage, nondomestic
septage.
4. State provisions for disposal during cold and wet weather.
5. Identify reporting and recordkeeping procedures.
6. Show general service areas of operation.
7. Identify standard service contract-type agreements made with
homeowners and industries for septage hauling services.
The maintenance of a septage hauler plan with a manifest system (to
record each pumping event) is a beneficial management tool in that it
not only identifies septage pumping events, but also assists in sched-
uling septage disposal facility operations.
8.4 Monitoring the Quantity and Quality of Incoming Septage
The next phase of septage management programs is the delivery of sep-
tage to a facility for final treatment and disposal. As discussed in
previous chapters, some type of receiving station will need to be pro-
vided at a treatment/disposal facility tq hold or store the waste un-
til it can be treated. Regardless of the type of receiving station
that is chosen, a system for checking the quantity and quality of in-
coming septage is necessary to ensure the smooth, efficient operation
of the septage treatment and disposal facility.
The following is a suggested sequence of activities to be accomplished
in monitoring the volume and characteristics of incoming septage flows
to its treatment/disposal destination:
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1« Record the name of the hauler, the origin of the septage, and
the time of arrival. This can be done at the facility en-
trance or at the receiving station by a plant operator or
clerk. The coupon systems mentioned earlier can serve this
purpose, or more sophisticated credit card type systems can
be used.
One system administered by the Seattle METRO Public Authority
involves the use of magnetically coded credit cards (5). The
credit cards, which are issued to haulers, provide access to
approved disposal sites and automatically record a hauler
identification code and time of arrival. A computerized in-
terceptor receiving station in Germany (see Figure 4-8} uses
a credit card to provide access, and record hauler identifi-
cation (6). The computerized receiving station also records
septage volume, and takes a representative sample which is
held for future testing if an inappropriate discharge is
suspected.
2. Record theseptage volume of the incoming vehicle. Septage
quantity can be monitored by requiring site glasses on the
trucks or by directly measuring the volume of septage deliv-
ered.
This can be done roughly by estimating capacity of truck, or
can be directly determined by flow measurement or by weighing
the truck.
The computerized receiving station discussed earlier (6) in-
corporates an in-line flow meter. Such equipment will be ex-
pensive and will require routine calibration and maintenance.
The use of truck scales also involves considerable capital
investment, but should require considerably less routine main-
tenance and calibration. The Wayland-Sudbury septage. facility
utilizes a pair of truck scales which provide digital read-
outs and print-outs of truck weight and corresponding septage
amount (7). The Tryon Creek Plant in Portland, Oregon uses a
system where the operator manually records the time, load
volume, pH, source of load, and hauled identification uu Lu«=
payment receipt, a copy of which is maintained on file (0). '
3. Sample septage quality prior to discharge or during dis-
charge . This can be done for individual truck loads where
there is a concern for the identification and elimination of
harmful industrial and hazardous waste discharges to the
treatment facility that may cause an upset to the treatment
processes and/or cause a violation of permit requirements, A
grab sample could be taken of the incoming waste for each and
every incoming truck load, for truck loads where odors or
other suspicious indicators identify a potential problem, or
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on a simple random basis. As a routine maintenance activity,
random samples should be performed from time to time to es-
tablish a trend analysis of septage quality characteristics
or to adjust for pH. Samples could then be analyzed immedi-
ately (delaying septage discharge) or stored for a length of
time equal to the flow-through time of the incoming septage
through the treatment facility. If a problem arises with the
facility operations (per this latter option), individual sam-
ples could be analyzed accordingly and traced back to the in-
dividual hauler.
This procedure is practiced at the computerized German inter-
ceptor receiving stations discussed earlier (6) . The same
procedure is carried out manually at the Ocean County, New
Jersey sewage treatment plant (9) where samples are taken
from each truckload and stored in a refrigerator for at least
24 hours. The septage is held in storage tanks where oxygen
uptake rate (OUR) is constantly monitored. (A significant de-
crease in OUR indicates toxic effects or non-biodegradabil-
ity). If plant upset results from introducing septage from a
given storage tank, all samples representing loads dumped to
that tank are tested to determine which load contributed the
incompatible waste.
4. Supervise hauleractivities during discharge. Visual inspec-
tions during the unloading process are all that is necessary
to make sure that the wastes are properly discharged to the
facility.
5. Keep the unloading area clear of debris and residue. This
will help control odors and improve the access of hauler ve-
hicles to the tipping area. Haulers who disregard this re-
quirement might be fined, or their disposal privileges may be
revoked for repeated violations.
6. Maintain a manifest ("trip-ticket")system. This involves the
maintenance of a hauler billing schedule and origin-destina-
tion report on the volume, source, and quality of incoming
septage. Coordination with another agency, such as a local
municipality, a septic tank management district, or a health
department, may be necessary to support septic system main-
tenance program activities.
Manpower requirements for this phase of septage management can be min-
imal. The sampling and laboratory analysis activities, however, could
significantly add to the manpower requirements in conducting these
tasks.
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8.5 Facility Operation and Maintenance
The operation and maintenance activities of a septage treatment and
disposal facility are similar in many ways to those typically perform-
ed at conventional wastewater treatment plants or. land application
sites for wastewater and sludges. This section outlines the general
requirements for proper operation and maintenance of a septage treat-
ment and disposal facility.
Many of the operational concerns of a septage treatment and disposal
facility are related to the fact that septage is a highly concentrated
waste as compared to sewage. Septage characteristics dictate greater
attention to the operation of screening and grit and grease removal
facilities at the receiving station and primary treatment systems. For
example, bar screens at a septage receiving station are designed to
handle larger quantities of screenings and heavier material than for a
sewage treatment facility. This will result in more material to be
disposed of, in addition to increased cleaning of the equipment to
maintain proper working order.
The overall effectiveness of a septage treatment and disposal facility
is dependent upon the skill of the operator. No matter how well a fa-
cility is designed, it may not live up to its capability if the oper-
ator is not thoroughly familiar with the function of each process in
the plant, how each process accomplishes its function, how to evaluate
the operation of each process, and how each process fits in the over-
all treatment scheme. This includes being familiar with the character-
istics of the septage received for treatment (as discussed in Section
8.4) and monitoring the treatment processes to make the necessary ad-
justments to plant operations. Of particular concern to operators at
sewage treatment plants which accept septage is maintaining a proper
blending rate of incoming septage with sewage to avoid both hydraulic
and organic overloads of treatment processes.
In addition to the proper operation of a septage facility, it is im-
portant to provide proper maintenance. A proper maintenance program
will help reduce breakdowns, extend equipment life, and provide more
efficient manpower utilization and performance. Any maintenance pro-
gram should follow these few simple rules:
1. Start with good housekeeping, and keep a clean, neat, and or-
derly facility.
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2. Make sure that personnel are familiar with each piece of
equipment (how it works, and what function it is to perform).
They will then be able to spot possible failures or, if and
when failures do occur, they can pinpoint the trouble and act
to correct the failure in the shortest possible time.
3. Establish a routine service and maintenance schedule for each
piece of equipment.
4. Keep manufacturers' catalogs, manuals, blueprints, etc.
available and stored in an indexed file for ready reference.
Care must be taken in handling this information because it
may have to last throughout the life of the equipment.
5. Maintain operating and maintenance records on each piece of
equipment, with emphasis on lubrication frequencies and un-
usual incidents or faulty operating conditions.
6. Procure and maintain an adequate stock of the tools required
to perform maintenance, with due consideration of accessibil-
ity and security.
7. Maintain a spare parts inventory for each piece of equipment.
Consult manufacturers' recommendations for a listing of spare
parts required,
8. Observe good safety procedures.
These rules may be applied to any of the methods previously discussed
for the treatment and disposal of septage. Establishing effective op-
eration and maintenance procedures at the onset will ensure effective
treatment over the expected lifetime of the project.
Although the basic operation and maintenance requirements of a septage
facility are similar to those of a typical sewage treatment plant,
special attention should be given to certain aspects of septage han-
dling and treatment. Increased labor will be necessary to operate and
maintain the receiving station and preliminary treatment processes
(i.e., supervision of dumping operations, cleaning of dump area, dis-
posal of screenings and grit, sampling and testing of septage, etc.).
Increased sludge and scum production in the primary treatment process
will also require greater operator attention (i.e., process control,
maintenance of clarifier equipment, pumps, and transport equipment,
etc.). Fluctuating aeration requirements as a function of septage
loading will necessitate greater process control flexibility and
operator attention. Finally, additional administrative and clerical
labor may be required to administer hauler billings and maintain
manifest system records.
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These special management requirements should be considered when esti-
mating the cost of operating independent treatment facilities or when
determining the incremental additional cost of handling septage at a
sewage treatment facility.
8.6 Performance Monitoring
Monitoring the performance of septage treatment and disposal facili-
ties is an important aspect of overall septage management. As discuss-
ed in the previous section, performance monitoring aids the facility
operator in evaluating the overall effectiveness of the septage treat-
ment and disposal facility. This information will indicate to the op-
erator whether any adjustments or changes to the treatment and dis-
posal processes have to be made in order to ensure that the minimum
requirements are met.
Where treatment processes result in a liquid effluent discharge to
surface waters, conventional water quality monitoring is used to check
conformance with applicable effluent discharge requirements. Facil-
ities employing land application, either surface or subsurface, must
also include groundwater monitoring. Individual states have specific
requirements for performance monitoring that should be consulted be-
fore establishing a monitoring protocol.
8.7 Financial Arrangements
The final consideration with regard to septage management is the fi-
nancing of the septage transport and treatment process. Financing
basically involves the raising of revenue to cover debt service (from
capital investments), and operation and maintenance expenses. There are
many conventional and alternative financing techniques that can be
used by the public and private sectors to provide funding for capital
projects and to fund their subsequent operations, maintenance, and re-
placement. These techniques will generally fall into the categories
shown in Table 8-2.
In the financing of septage management facilities, the appropriate fi-
nancing mechanism will depend upon:
1* who owns and operates the transport vehicles.
2. Who owns and operates the treatment and disposal facility.
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TABLE 8-2
CONVENTIONAL AND ALTERNATIVE FINANCING TECHNIQUES FOR SEPTAGE (10)
Conventional Financing
Private Financing
Privatization
Risk Reduction and
Cost Reduction of Debt
Revenue Sources
Property taxation (i.e., Sale and leasebacks
general funds) as the
primary source of
revenue
General obligation
bonds
Revenue bonds
Short-term notes used
as interim financing
before bonds are
issued
Conventional leasing
Limited partnership
financing
Contracting for
operations and
naintenance
Bond pooling, State infra-
structure banks, and loan
Bond banks, bond insurance,
and letters of credit
Treatment fees
Handling fees
Private (tax-exempt Zero-coupon bonds, floating User charges
financing interest rate bonds, etc.
Alternative taxes
(luxury foods, local
income tax, etc.)
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3. Whether septage pumping is mandatory (i.e., part of a formal-
ized onsite management program) or voluntary (i.e., at the
homeowner's discretion).
As discussed in the overview of management concerns (Section 8.1), and
as was shown in Table 8-1, both public and private entities can become
involved in the transport, treatment, and disposal of septage. The
precise financing arrangement to be applied, therefore, will depend on
the ownership-operational status of the facility (i.e., whether it is
publicly or privately owned) and the type of facility (i.e., transport
vehicle, receiving station, treatment plants, etc.).
Regardless of the financing methods chosen and the ownership-operation-
al status of the facilities, there are several different financing op-
tions by which revenues could be collected to finance capital and op-
erating costs. These options are described below, as they apply to the
financing of septage pumping and hauling, and septage treatment and
disposal. Some of the alternatives include the provision for a "trip
ticket" system, which is part of a manifest program to identify the
source of the .septage. The manifest program can also be part of a
formal onsite management program (as described in Section 8.2), Figure
8-1 illustrates how a trip ticket operation works in the financing of
septage disposal costs for a municipally-owned septage treatment fa-
cility in Acton, Massachusetts.
The following options could serve as possible methods for funding sep-
tage pumping and hauling, and treatment and disposal:
Septage Pumping and Hauling
1. The hauler would simply bill the homeowner for the costs of
septage pumping and hauling.
2. Costs for pumping and hauling would be raised through an
annual user charge levied by an onsite management district.
Included in the user charge would be one tank pumping every
five years. (The precise interval between pumpings can be de-
termined by each management agency.)
3. The homeowner could enter into a septic system service con-
tract with a hauler. One of the provisions of the contract
would be to have the system pumped periodically (e.g., once
every five years) or when necessary (as determined by the
hauler and homeowner).
275
-------
FIGURE 8-1
SEPTAGE MANAGEMENT SYSTEM FOR ACTION, MASSACHUSETTS (2)
Disposal
Site
Attendant
Town Offices
.(Health Dept.)
NOTES:
1. Haulers purchase coupons (usually coupon booklets) from town of-
fices (one coupon for each 500 gallons pumped). This entitles the
hauler to dispose of septage at the town-owned disposal site at no
extra cost.
2. Haulers pump septage from property owner on request, (The town's
biennial pumping requirement is not actively enforced.) Property
owner pays the hauler for pumping.
3. A trip ticket is filled out by the hauler in triplicate. Hauler
gives one copy of the ticket to the disposal facility operator.
fhe ticket shows the name of the pumper, the location of the sep-
tic tank pumped, the quantity pumped, and the date of pumping. One
copy remains with the hauler, and the third with the property own-
er.
4. The disposal facility attendant submits daily receipts to the town
offices, where daily and monthly log summaries are tabulated.
5. A copy of the trip ticket is placed in a file kept for each sys-
tem installed or repaired in the town. This file contains: a copy
of the original percolation tests results, the installation per-
mit, copies of the system design drawings, an as-built drawing,
any repair permits, correspondence concerning the system, and any
septage pumping trip tickets. Files that collect a large number of
trip tickets within a short period of time are noted as potential
problems and visited by a Town Health Department Officer.
276
-------
Septage Treatment and Disposal
1. The hauler would be charged for septage treatment services by
the plant operator on a per-event basis.
2. The hauler would purchase a coupon from the plant operator
(or representative). The cost of the coupon would reflect the
treatment charge per septic tank. The hauler would present
this prepaid ticket to the plant operator prior to the un-
loading of the truck contents.
3. The coupon could be sold directly to the homeowner by the
plant operator (or representative). The homeowner would give
the coupon to the hauler, who would then present it to the
plant operator as proof of purchase for septage treatment
services.
4. The cost of septage treatment would be included as part of an
annual user fee paid by the homeowner (e.g., from an onsite
management program or from a private service contract ar-
rangement) .
5. The plant operator could assess each hauler (based on the
number of vehicles he operates) a flat fee for vehicle regis-
tration and septage treatment. The flat fee would entitle the
hauler to an unlimited use of the facility for septage treat-
ment. (Or a ceiling could be established with a surcharge
payment for truck loads delivered to the site beyond the
ceiling limit.)
The choice of the actual financial arrangement will depend on whether
a manifest system is to be used (i.e., incorporated as part of the
trip ticket concept), and the degree of control desired by the plant
operator over the origin of wastes and the haulers utilizing the fa-
cility. These are important considerations to be made in designing a
septage management program.
8.8 References
1. Ciotoli, P.A. and K.C. Wiswall. Interim Report - Management of
On-Site and Small Community Wastewater Systems - Case Studies. Roy
F. Weston, Inc., November 1979.
2. Small Scale Waste Management Project, Management of Small Waste
Flows, Appendix D. University of Wisconsin, U.S. EPA Report No.
600/2-78-173, NTIS No. PB 286560/AS, September 1978.
277
-------
3. New England interstate Water Pollution Control Commission, Guide-
lines for Septage Handling and Disposal. NEIWPCC Report No. TGM-1,
August 1976.
4. Ciotoli, P.A. and K.C. Wiswall. Management of On-Site and Small
Community Wastewater Systems. U.S. EPA Report No. 600/8-82-009,
OTIS No. PB 82-260829, July 1982.
5. Rezek, J.W. and I.A. Cooper. Septage Management. U.S. EPA Report
No. 600/8-80-032, NTIS No. PB 81-142481, August 1980.
6. Eikum, A.S. Treatment of Septage - European Practice. Norwegian
Institute of Water Research, Report No. 0-80040, February 1983.
7. Roy P. Weston, Inc. Preliminary Draft Operation and Maintenance
Manual for Wayland Sudbury Septage Treatment Facility, 1982.
8. Bowner W.C. An Engineering Study of Septic Tank Content Disposal
in Douglas County, Oregon. County Engineer's Office, Roseburg,
March 1972.
9. loy F. Weston, Inc. Concept Engineering Report - Septage Management
Facilities for Ocean County Utilities Authority. October 1980.
10. Peterson, J.E. and W.C. Hough. Creative Capital Financing for
State and Local Governments. Government Finance Research Center,
Municipal Finance Officers Association, March 1983.
278
-------
Chapter 9
Fact Sheets
9.1 Introduction
In order to provide a summary of technical guidelines pertaining to the design of septage treatment facilities,
brief fact sheets addressing selected processes are presented. The fact sheets presented represent
technologies which are considered to be most applicable to septage treatment, and are intended to provide
specific guidance relevant to septage treatment applications which is generally lacking in currently available
guidance documents. The cost information provided is somewhat limited due to the lack of cost data for full-
scale operating facilities. In some cases, rough estirpates of capital and operating costs are provided in the
form of unit costs or cost curves. These estimates should be used only for general planning purposes to
determine brder-of-magnitude costs.
The fact sheets presented include:
• Receiving Stations (Dumping Station/Storage Facilities)
* Receiving Stations (Dumping Station/Pretreatment/Equalization Facilities)
» Land Disposal
« Lagoons
• Composting
« Lime Stabilization
• Odor Control (Soil Filters)
A more detailed discussion of technical considerations for each of these processes is presented in the
respective design chapters:
• Chapter 4 Receiving Station Design
• Chapter 5 Land Application
• Chapter 6 Independent Septage Treatment
The co-treatment of septage at sewage treatment facilities is not addressed in fact sheet form because design
criteria and most information cannot be generalized considering the wide range of facility designs and
operational conditions that are possible. The reader is referred to Chapter 6 for specific technical guidance
pertaining to the impact of septage co-treatment on individual unit processes.
The following common assumptions apply unless otherwise noted on individual fact sheets:
• Labor (including fringe benefits, etc.) $12.10/hr
• Electrical Energy - $.05/kwh
• Construction and O & M costs based on average design flow.
» Construction costs do not include external piping, electrical, instrumentation, land and site work cost,
contingencies, or engineering, legal, and administrative fees.
279
-------
Receiving Station (Dumping Station/Storage Facility) Fact Sheet 1
Description
A septage receiving station with dumping station and storage facilities provides for the transfer of septage from
hauler trucks to a temporary holding tank from which it can be drawn at a controlled rate. With such a facility,
septage can be discharged to an interceptor sewer or directly to the headworks of a treatment plant. The
dumping station should provide for both direct hose connections (preferred) and open pit discharges. The
dumping pit should be equipped with a coarse bar screen, and should be covered and preferably locked when
not in use. A manual-controlled or timer-controlled pump discharge facilities feeding septage at a
predetermined rate over specific periods of time in order to maximize the dilution of septage by sewage.
Common Modifications
Where septage is to be transferred from haulers' trucks to other vehicles (e.g., large tanker trucks for transport
to centralized treatment facilities, or specialized land application equipment), the same basic facilities as
described above could be used, with the exception that tanker trucks or trailers would replace the permanent
storage tanks. Where land application is involved longer term storage may be required during adverse weather
conditions, lagoon storage facilities should be considered in such cases. If septage is to be discharged to an
Interceptor sewer where flows are high, storage facilities might not be required. Odor control may be required
depending on station location.
Pretreatment and Post-Treatment Requirements
No pretreatment of the septage is required before discharge to a receiving station. Post-treatment requirements
will be determined based on the location of the station and the specific treatment method to be applied.
Technology Status
Widespread use of septage receiving stations is documented in Europe, specifically Germany, Sweden, and
Norway; relatively fewer operating examples exist in the United States.
Typical Equipment
Dumping pit with cover; coarse bar screen; holding tank(s); solids handling pump(s); piping, valves, and hose
connections.
Residuals Generated
Grit and solids which may accumulate in holding tank must be cleaned out periodically. This can be
accomplished by removing the solids using vacuum truck equipment, or by flushing the solids out of the tank
using high pressure water. Periodic removal of screenings will also be required.
Design Criteria
Bar Screen - 1/2 in. x 11/z in. bar stock, % in. - 3A in. spacing
Hauler Truck Hose Connection - 4 in. diameter
Piping and Valves - 8 in. diameter
Holding Tank Capacity -1 day peak flow (not including supplemental storage requirements associated with
land application systems etc.)
Unit Process Reliability
Extremely reliable with properly designed connections and tank sizes.
Environmental Impact
Land requirements are generally minimal; small energy requirement; odor problems with spillage.
References
1,2,3,4,5.
280
-------
Flow Diagram
Fact Sheet 1 (Cont.)
Raw
Septage
Dumping
Station
and
Bar Screen
Receiving/
Storage
Tank(s)
Solids
Handling
Pump(s)
To
Headworks
of Treatment
Plant or
Interceptor
Sewer
Energy Notes - only energy requirements is for electrical power to operate pumps. Power consumption would be a function
of motor horsepower and run time which will be determined by design flow and operational period (i.e. 8-hour
shift vs. 24 hour operation.)
Costs - Assumptions: ENR Index = 3875
Construction cost includes equipment, materials, and installation.
Operating labor costs based on a minimum manpower requirement of 1 hour/day plus 1 hour/day every 10,000 gpd
of septage received.
Electrical power costs based on pumping intermittently to meet design flow over 24 hour period on a 5-day week.
Does not include cost of accessory buildings, access roads, or grit and screenings disposal.
Construction Cost
Operation & Maintenance Cost
£
I
a
e
to
u.uuu
1,000
100
10
1,0
. ••
.."*
9
•«•
*
s
.
/
00 10.000 100,000 1,000,000
3
a
1,000
100
10
1
Septage Flow, gal/d
1,000 10,000 100,000
Septage Flow, gal/d
100
L
10,000 100,000 1,000,000
Population Equivalent
10,000 100,000 1,000,000
Population Equivalent
281
-------
Receiving Station (Dumping Station, Pretreatment, Equalization) Fact Sheet 2
Description
When septage is to be ultimately treated at a wastewater treatment plant or independent septage treatment
facility, a receiving station is required in order to provide preliminary treatment and equalization. This normally
consists of a dumping pit with screening, grit removal, and flow equalization. Features which should be
provided include: sloped ramp and hose-down facilities at unloading location; channel in front of bar screen for
more uniform flow and to avoid direct discharge of septage onto screen; manually or mechanically cleaned bar
screens; solids handling pumps; sampling/monitoring capability; ventilation system and odor control.
Pretreatment and Post-Treatment Requirements
No pretreatment of the septage is required prior to discharge to a receiving station. Post-treatment
requirements will be determined based on the specific treatment method to be applied.
Technology Status
The pretreatment processes involved have been widely used since the origins of municipal wastewater treat-
ment. Application to septage is widespread in Europe and more recently is being employed in the United
States.
Typical Equipment
Bar screens or racks (mechanically cleaned screens are preferable, but may be impractical due to cost);
receiving tank/pit; aerated grit chamber; flow equalization tanks; pump(s); odor control equipment (ventilation
systems, blowers, filters, etc.).
Residuals Generated
Screenings and grit, plus accumulated solids which settle out in flow equalization tanks. Provisions must be
made for removal and disposal of these residuals. Landfilling is the most common method of disposal
Design Criteria
Bar Screen - Vz in. x 1 Vz in. bar stock, Vz in. - % in. spacing
Hauler Truck Hose Connection - 4 in. diameter
Piping and Valves - 8 in. diameter
Degritting Equipment - per manufacturer's specifications for design flow
Equalization Tanks - multiple tanks, total capacity twice peak daily flow
Pumps - sized according to average design flow and operational schedule
Environmental Impact
Requires land; energy use for pumping, mechanically cleaned bar screens and aerated grit chambers. Solids
will be generated, requiring disposal; odors may be associated with dumping, pretreatment, and residuals
disposal operations.
Reference
1.2,3,4.5.6.7.
Common Modifications
Grit removal can either precede storge and equalization or follow it. If a grit chamber precedes equalization, it
must be designed to handle the discharge of individual or multiple truckloads of septage as they come. If
storage and equalization precede grit removal the grit removal process can be designed to handle the average
flow, and can be operated according to a set schedule coinciding with subsequent treatment operations.
Cyclone degritters may be substituted for aerated grit chambers if average septage solids concentration is less
than 2 percent
282
-------
Flow Diagram
Fact Sheet 2 (Cont.)
Raw
Septage
Exhaust Air
Odor Control
System
Dumping
Station
and-
Bar Screen
Receiving
Storge
Tank(s)
Solids
Handling
Pump(s)
TO
Treatment
Processes
Aerated
Grit
Chamber
or
Cyclone
Degritter
Energy Notes - Electrical power required for pumps, as well as operation of mechanical screening and degritting equipment.
Power requirements for specific equipment to be specified by manufacturer.
Costs - Assumptions: ENR Index 3875
• Facility includes dumping pit, manually cleaned bar screen, equalization storage tanks, pumping station, and aerated
grit chamber.
Construction cost includes equipment, materials, and installation.
Operating labor costs based on a minimum manpower requirement of 1 hour/day plus 1 hour/day for every 10,000
gpd of septage received.
Electrical power costs based on pumping as required to meet design (low over 24 hour period (5-day week.
Does not include cost of accessory buildings, access roads, or grit and screenings disposal.
Construction Cost
Operation & Maintenance Cost
o
O
10,000
1,000
100
10
1,0
ll*^
0
*
4
V*
'
l'—
00 10,000 100,000 1,000,000
2
S
o
o
,uuv
100
10
1
1,0
.''
«'
^
.1*
re
^
*
P^
tal
>
P^
via
S
?
te
PC
:;
' i <
*•- -
ial i.
wer
-ii —
ibor-
,i'
ind
00 10,000 100,000 100
Septage Flow, gal/d
Septage Flow, gal/d
ii i i I 11
10,000 100,000 1,000,000
Population Equivalent
I
10,000 100,000 1,000,000
Population Equivalent
283
-------
Land Application of Septage Fact Sheet 3
Description
Raw septage and septage solids may be spread on the surface of the land or incorporated into the subsurface
topsoil layers. Surface spreading includes spreading from septage hauler trucks or transfer vehicles such as
tank wagons, spray irrigation, ridge and furrow practices, and overland flow. Application by the hauler trucks is
the most common method practiced. Spray irrigation of septage requires the use of high-pressure large nozzle
systems to prevent clogging. Ridge and furrow methods involve spreading septage in the furrows and planting
crops on the ridges. Overland flow methods are best suited to lands with a slope of 2 to 6 percent.
Subsurface application techniques include plow furrow cover (PFC), subsurface injection (SSI), and injection
using a device such as a Terreator (a patented device). The PFC method of application applies septage in a
narrow furrow created by the plow shear and is immediately covered by the plow moldboard. The SSI method of
application applies septage in a narrow band behind a sweep which opens a cavity 10 to 15 cm (6 to 8 in.)
deep. A Terreator or similar device opens a mole-type hole with an oscillating chisel point and injects the
septage into the hold.
Common Modification
The most common modifications to a septage land application site are related to variations in the method of
application and the type of crop grown.
Pretreatment and Post-Treatment Requirements
Federal "criteria" (40 CFR 257) specify that septage applied to .the land or incorporated into the soil must be
treated by a "process to significantly reduce pathogens" (PSRP) prior to application or incorporation, unless
public access to the facility is restricted for at least 12 months after application has ceased, and unless grazing
by animals whose products are consumed by humans is prevented for at least 1 month after application.
PSRP's include aerobic digestion, air drying, anaerobic digestion, composting, lime stabilization, or other
techniques which provide equivalent pathogen reduction.
The criteria also require septage to be treated by a "process to further reduce pathogens" (PFRP prior to
application or incorporation, if crops for direct human consumption are grown within 18 months subsequent to
application or incorporation, and if contact between the septage applied and edible portion of the crop is
possible. PFRP's include composting, heat drying, heat treatment, thermophilic aerobic digestion, or other
techniques that provide equivalent pathogen reduction
Technology Status
Successfully implemented on a full-scale basis in the United States and Europe.
Typical Equipment
See Description section above.
Limitations
Constituents of the septage may limit the acceptable rate of application, the crop that can be grown, or the
management or location of the site. Nitrogen requirements of the crop normally dictates the annual septage
application rates. It is also required that soil pH be maintained at 6.5 or above to minimize the uptake of the
trace elements.
The potential for contaminated runoff, soil compaction, crop damage, or trucks getting stuck preclude the
application of septage during periods when soil moisture is too high. Therefore, septage application is limited
only a portion of the year. For the period of the year when septage can not be applied, storage facilities must be
provided. Many states regulate the total volume of septage that can be applied as a function of soil drainage
characteristics. *
Performance
Septage contains all of the essential plant nutrients. It can be applied at rates which will supply all the nitrogen
and phosphorus needed by most crops.
Design Criteria
Application rates depend on septage composition, soil characteristics, and cropping practices. Annual
application rates have varied from 282 m3/ha (30,000 gal/acre) to 1,880 m3/ha (200,000 gal/acre). Applying
septage at a rate to support the nitrogen needs of a crop avoids problems with overloading the soil.
Unit Process Reliability
As a disposal process, very reliable/ as a utilization process, careful monitoring and control should be
exercised to maximize the efficiency and minimize health risks
Environmental Impact
Potential for heavy metals and pathogens to contaminate soil, water, air, vegetation, and animal life, and
ultimately to be hazardous to humans. Accumulations of metals in the soil may cause phytoxic effects, the
degree of which varies with the tolerance level of the particular crop. Toxic substances such as cadmium that
accumulate in plant tissues can subsequently enter the food chain, reaching human beings directly by
ingestion or indirectly through animals, if available nitrogen exceeds plant requirements, it can be expected to
reach groundwater in the nitrate form. Toxic materials can contaminate groundwater supplies or can be trans-
ported by runoff or erosion to surface waters if improper load.ng occurs. Aerosols which contain pathogenic
organisms may be present in the air over a landspreadin<~ site, especially where spray irrigation is the means of
septage aplication. Other potential impacts include public acceptance and odor.
References
8.9.10,11.12.13.
284
-------
Flow Diagram
Fact Sheet 3 (Cont.)
Storage
Lagoon
Land
Application
Site
•See Receiving Station Fact Sheets
Energy Notes - Energy required to apply septage to the land will range from approximately (20,000 Btu/wet ton) for hauler truck
spreading to (80,000 Btu/wet ton) for subsurface injection.
Costs - Assumptions:
ENR Index = 3875
Construction cost includes equipment, materials, installation, and land.
Land $5,000/A includes 200' buffer strip around disposal area
Fuel costs $l.25/gal
10
Si 8
o
_L
5 10 15 20 25
Septage (Thousand Gallons/Day)
§
<=>.
s
i
I
c
1
0 5 10 15 20 25
Septage (Thousand Gallons/Day)
Construction cost includes land (assuming surface application on fescue field), storage lagoon (6 week capacity), spreading
equipment land preparation, equipment storage buitding, site protection and improvement
Reference 14
285
-------
Lagoon Disposal Fact Sheet 4
Description
The use of lagoons for the disposal of septage is a common alternative in rural areas. The design and
operation of lagoons vary from simple septage pits to sealed basins with separate percolation beds. Most
lagoons are operated in the unheated anaerobic of faculative phase.
A typical lagoon system consists of two earthen basins arranged in series. The first or primary lagoon receives
the raw septage via a vertical discharge chamber entering under the surface of the liquid near the lagoon
bottom to minimize odors. It may be lined or unlined, depending on the geological conditions of the site. The
supernatant from the primary lagoon, which has undergone some clarification and possibly anaerobic
digestion is drawn off into the second lagoon or percolation bed where it is allowed to percolate into the
ground. Once the solids have accumulated in the primary lagoon until the point where no further clarification
occurs, the lagoon is drained and the solids are allowed to dry. The dried solids are then removed, sometimes
further dewatered, and disposed of at a landfill or buried.
Common Modifications
Aeration may be applied to supplement the supply of oxygen to the system and for mixing. Lagoons may be
lined with various impervious materials such as rubber, plastic, or clay as required by geological conditions.
Where groundwater quality is of concern, the effluent from septage lagoons can be applied to the land or
treated and discharged to a surface water, rather than use percolation beds.
Pretreatment and Post-Treatment Requirements
The pH of the lagoon must be maintained at 8.0 or greater to control odors. This may be accomplished with the
use of hydrated lime added each time a truckload is discharged to the receiving chamber. Lagoon effluent can
be disposed of by applying spray irrigation or overland flow. If the effluent is to be discharged to a surface
water it should be further treated using either polishing ponds of sand filters, and disinfected as required.
Technology Status
Fully demonstrated and in use throughout the United States for the treatment of municipal wastewaters in areas
where real estate costs are not a restricting factor; limited experience with septage lagoons, mostly in the
northeastern United States.
Typical Equipment
Lining systems and hydraulic control structures (i.e., inlest and outlets); a simple receiving station (i.e.,
providing coarse screening) is recommended.
Limitations
In very cold climated, reduced biological activity occurs and ice may form on the surface. Overloading may
create potential odor problems. Potential exists for groundwater contamination with percolation beds and
seepage pits or lagoons. Extensive site evaluation recommended inn all cases.
Performance
Limited data available.
Residuals Generated
Settled solids from primary lagoon have to be removed and properly disposed of periodically (every few months
to once every 5 or 10 years depending on size of lagoon).
Design Criteria
Detention Time - 20 to 30 days for settling alone; 1 to 2 years for stabilization (i.e., 80-90% removal of BOD
and volatile solids)
Area Loading Rate - 20 Ibs. vs./day/1,000 square feet (facultative sludge lagoon (38))
pH - 8.0 using lime
Minimum Depth - 0.9 m (3 ft) (Plus additional depth for sludge storage and anaerobic zone.)
Minimum Separation Distance from High Groundwater Level -1.3 m (4 ft)
Land Application of Effluent - see References 15,16
Unit Process Reliability
Estimated service life of 20 to 30 years with periodic cleaning (see above); little operator expertise required
overall; the system is highly reliable.
Environmental Impacts
Potential for groundwater contamination. Groundwater should be monitored near the lagoon site. Odor and
vector problems possible in immediate vicinity of lagoons.
References
17,18.19,20.
286
-------
Flow Diagram
Fact Sheet 4 (Cont.)
Septage
Receiving
Structure/
Lime Addition
Multi-Cell
Lagoon
•
Percolating
Lagoon or
Other
Disposal
Method
Energy Notes - Faculative lagoons generally have no energy requirements, although surface aerators are optional; sludge
removal operation will involve fuel costs.
Costs - Assumptions: ENR Index = 3875
Facility includes multi-cell lagoon, receiving structure, lime storage building, and fencing.
Construction cost includes equipment, materials, and installation.
Operating labor costs based on minimum manpower requirement of .5 hour/day plus .5 hour/day for every 10,000
gpd ol septage treated.
Lime Dosage - 8.4 Ibs. Ca(OH)z/1,000 gallons septage
Does not include cost of accessory buildings (other than lime storage), access roads, sludge removal.
Construction Cost
Operation a Maintenance Cost
1-000
100
1,000 10.000 100,000 1,000,000 1,000 10,000 100,000 TOO
Septage Flow, gal/d Septage Flow, gal/d
li=) J;T; ,i .t i i ml | i j i i i mil ..J.,,L,,J..J Ull J.I
10,000 100,000 1,000,000 10,000 100,000 1,000,000
Population Equivalent Population Equivalent
Land Requirement*
2 1,000
Nousands of Dol
o
o
10
-
t
Inclu
utfsr,
|
1
t
ling -
!one) "
•*
J
"
•n
A
01
r
-
f<
"I —
I1
: Net
Area
1,000 10,000 100,000 1,000,000
Septage Flow, gal/d
i 1 i 1 LjiiHi I I i I 1.1 I 111
10,000 100,000 1,000,000
Population Equivalent
287
-------
Composting (Aerated Static Pile) Fact Sheet 5
Description
Composting Is the stabilization of organic material through the process of aerobic, thermophilic decomposition.
It is a disposal technique that offers good bactericidal action and up to 25 percent reduction in organic carbon.
Septage is transformed into a humus-like material that can be used as a soil conditioner.
Composting is classified into three types of operations, which differ principally by the aeration mechanism they
employ. They are windrow, aerated static pile, and mechanical composting. Although all three methods may be
applied for composting septage, the method that appears to offer the greatest potential as a septage treatment
alternative is the aerated static pile method because it permits more uniform composting and minimizes land
requirements,
Septage is usually first dewatered and then mixed with bulking agents (e.g., woodchips, sawdust, bark chips,
leaves, etc.) prior to composting to decrease the moisture content of the mixture, increase the porosity of the
septage, and assure aerobic conditions during composting. The mixture is then constructed into a pile as
shown in the illustration presented under "Flow Diagram." A blanket of finished compost completely surrounds
the composting mixture in order to reduce heat loss and minimize odors.
The aerated pile undergoes decomposition by thermophilic organisms, whose activity generates a concomitant
elevation in temperature to 60°C (140°F) or more. Aerated conditions in the pile are maintained by drawing air
through the pile at a predetermined rate. Exhaust air is forced through a small pile of screened finished
compost for odor control. The composting period normally lasts 3 weeks.
Following the composting period, the aerated piles are taken down, moved and stored in piles for 4 or more
weeks to assure no offensive odors remain, and to complete stabilization. The composted material can be
separated from the bulking agent which is generally recycled for further usage. The finished compost material
is then ready for utilization as a low-grade organic fertilizer, soil conditioner, or for land reclamation.
Common Modifications
Windrow and mechanical composting are commonly used to stabilize wastewater sludges, and can be adapted
to treat septage. The Lebo process which is a variation of windrow composting treats raw septage without
dewaterlng, by first aerating the septage in a reactor and then mixing it with sawdust before composting, which
takes up to 6 months. The aerated static pile method can also be used to compost raw septage, however,
excessive quantities of bulking agent are required to maintain the desired moisture content.
Prelreatrnent and Post-Treatment Requirements
Dewatering of septage is recommended prior to composting to minimize the amount of bulking agent required.
However, if large quantities of bulking agent are available at reasonable cost, raw septage can be treated.
Technology Status
Well developed technology in use, or in the design stage at over fifty locations in the United States for
wastewater sludge and septage treatment.
Typical Equipment
Commonly available equipment can be used including front-end loader, 4-in. perforated plastic pipe, blower,
rotary screen, etc.
Limitations
In areas of significant rainfall it may be necessary to provide a cover for the pile. A drainage and collection
system is generally required to control storm water runoff and leachate from the pile.
Performance
Septage is generally stabilized after 21 days, during which time septage odors and pathogens are destroyed..
Residuals Generated
Final product is compost; leachate from piles may be generated in some cases.
Design Criteria
Composting represents the combined activity of succession of mixed populations of bacteria, actinomycetes,
and other fungi. The principle factors that affect the biology of composting are moisture, temperature, pH,
nutrient concentration, and availability and concentration of oxygen. A summary of pertinent design parameters
follows:
Moisture Content - 40-60% Septage Pile Dimensions
Oxygen - 5-15% 2.7 m (9 ft) High
Temperature Peak - 55-65°C (130°-150°F) 4.6 m (1 5 ft> Diameter
PH - 5-8 0,3 m (12 in.) Base
C/N Ratio - 20:1 - 30:1 0.5 m (18 in.) Blanket
Land Requirement - 0.2-0.3 acre/dry ton septage solids/day Q 75 m3 (1 cu yd) Filter Pile
(0.09-0.13 ha/dry metric ton/day)
Blower Size 1/«KW{1/3HP)
Unit Process Reliability
High degree of process reliability through simplicity of operation.
Environmental Impact
Potential odor problems can occur for a brief period between the time the septage arrives at the site and is
mixed and covered by the insulation layer.
References
21, 22, 23, 24, 25,26,27,28,29, 37.
288
-------
Flow Diagram
Fact Sheet 5 (Cont.)
Screened or
Unscreened Compost
Filter Pile
Screened
Compost
Sludge and
Bulding Agent
Perforated
Pipe
Drain For
Condensates
. Exhaust Fan
Energy Requirements - Electrical power to operate blowers (7.5-17.5 KW hr/dry ton/day); fuel to drive front end loaders (1,1
gal. gasoline/dry ton/day), (2.7-3.5 gal. diesel fuel/dry ton/day), (ref. 37).
Costs - Assumptions: ENR Index = 3875
Capital cost not including purchase of front end loader, estimated at $85/dry ton septage solids treated annually (ref.
31).
Operating cost estimated at $66/dry ton septage solids (ref. 31).
Assuming septage isdewatered ( 20% solids prior to composting.
Costs of dewatering not included.
Construction Cost
Operation & Maintenance Cost
10,000
5 1,000
"3
a
•o
c
100
10
0.1 1 10
Septage Solids (dry ton/day)
100
£
re
o
o
•a
c
8
1,000
100
10
0
>
r
/
?
F-
,i
/
y
r
...:.
1 1 10 1C
Septage Solids (dry ton/day)
289
-------
Ume Stabilization Fact Sheet 6
Description
Addition of lime to septage in sufficient quantities to maintain a high pH (>pH 12 for 30 min) creates an
environment that will effectively destroy most pasthogenic and odor producing microorganisms. Lime-
stabilized septage is typically disposed of on land. Lime stabilization improves septage dewaterability; the
stabilization may be followed by a dewatering step, or the stabilized liquid septage may be spread on the land
directly.
Common Modifications
Dry lime can be added directly to the hauler truck prior to discharging to a holding facility, treatment facility, or
land application site. In smaller facilities, lime is often added manually in the form of bagged lime.
Pretreatment and Post-Treatment Requirements
Septage must be screened prior to lime stabilization to remove rags and other debris. Grit removal is optional
and depends on the equipment in the process train. Grit removal should be provided to protect downstream
pumps and/or dewatering equipment
Lime-stabilized septage may be dewatered prior to disposal, although the stabilized liquid may be applied
directly on a land disposal site. Stabilized septge may be stored prior to land disposal. Because pH drops
during storage, it is desirable to dispose of the stabilized septage as soon as possible to avoid regrowth of
organisms and resulting noxious odors.
Technology Status
Lime has been in widespread use for over 100 years, both for sludge and septage treatment. Shipping,
handling, and feeling techniques for lime are well proven.
Typical Equipment
Chemical feed equipment; pH instrumentation; lime storage bins; sludge handing and control equipment.
Limitations
Lime treatment provides essentially no reduction or organics, O&M problems due to scaling in the lime addition
system; lime addition increased the quantity of material for disposal.
Performance {4}
A full-scale study indicated the following effects of lime treatment on pathogenic bacteria (initial pH = 12.5,
maintained at pH>-12 for at least 30 min). Units: orgamisms/100 ml of sample.
Parameter Raw Septage Lime-Stabilized Septage
Total Coliform8 2.9 x108 2.1 x103
Fecal Coliform3 1.5 x107 265
Fecal Streptococci 6.7 x105 665
Salmonella" . • 6 <3
Ps. Aeruginosa® 754 <3
aMillIpore filter technique used.
^Detection limit = 3,
Residuals Generated
Lime addition increases the quantity of material for disposal. Lime-stabilized septage can be disposed of
directly on land or can be dewatered first
Design Criteria
Lime dosage to maintain>-pH 12.5 for at least 30 min: 0.1 - 0.3 kg lime/kg dry solids (0.1 - 0.3 Ib lime/lb dry
solids)
Mixing Requirements:
Air: 150 - 250 m»/1,000 mVmin (150 - 250 cfm/1,000 ft3)
Mechanical: iulk fluid velocity = 7.9 m/min (26 ft/min)
Unit Process Reliability
Highly reliable from a process standpoint Operator must clean and maintain frequently in order to avoid
corrosion and scaling, and to ensure the mechanical reliability of the lime feed.
Environmental Impact
The quantity of solids for disposal is increased, compared With other methods of stabilization. However, lime
stabilization can significantly reduce the number of pathogenic bacteria, and attentuate the odor normally
associated with septage, making it more acceptable for land disposal in most cases.
References
6.30.31,32.
290
-------
Flow Diagram
Fact Sheet 6 (Cont.)
From Septage
Receiving Facility
ID
Hydrated Lime
(50 Ib bags)
, Mixing Tank
To Dewatering
or
Land Disposal
Energy Notes - Energy costs are relatively minor compared to labor and chemical costs.
Costs - Assumptions: ENR Index = 3875
Facility includes mixing tanks, mechanical mixers, sludge pumps, portable pH meters, and lime storage building.
Construction costs includes equipment, materials, and installation,
Operating labor cost based on minimum manpower requirement of 2 hours/day plus 2 hours/day for every 10,000
gpd of septage treated.
Lime dosage - 26-60 Kg lime/m3 (15-35 Ib lime/1,000 gal) septge $70 ton
Construction Cost
Operation & Maintenance Cost
o
Q
TS
i
10,000
1,000
100
10
1,000 10,000 100,000
Septage Flow, gal/d
o
a
3
O
ti
tl
'3
1,000
100
1,000,000
1
1,000
10,000 100,000
Septage Flow, gal/d
100
10,000 100,000 1,000,000
Population Equivalent
10,000 100,000 1,000,000
Population Equivalent
291
-------
Odor Control (Soil and Iron Oxide Filters) Fact Sheet 7
Description
Soil filters provide breakdown of malodorous compounds by both chemical and biological means. This is
accomplished by collection and forcing air from contained process units through networks of perforated pipe
buried in the soil, or through a mixture of iron oxide and woodchips.
Common Modifications
Use of compost rather than soil as filter media; above ground, enclosed filters for smaller volumes of gas; use
of rooted vegetation to maintain loose soil and enhanced biological activity. Alternative odor control methods
include exhaust gas scrubbing in aeration basins, and incineration in sludge combustion units. Chemical
scrubbers and activated carbon filters have also been used with mixed success.
Pretrealment and Post-Treatment Requirements
None.
Technology Status
Extensive use in Europe; more recent adoption in United States at smaller facilities.
Typical Equipment
Ventilation systems, fans, piping, etc.
Limitations
Cessation of biological activity due to inhibiting or toxic substances may render filter ineffective. Design life for
soil filter is not well documented.
Performance
Odorous gases are contained and vented to the soil filter area via a piping network. Given sustained biological
activity, filters may regenerate during periods when no gases are passing through. Pilot-scale sutdies have
demonstrated complete elimination of odors by use of soil filters (i.e., no detectable odors in vicinity of soil
filter). Gases with H*S concentrations greater than 100 mg/l have been deodorized (HzS<1 mg/I) by this
method.
Residuals Generated
None.
Design Criteria
Minimum Soil Depth - 0.5 m (20 in.)
Air Loading Rate - 60 m3/m2/hr (200 ft3/ft2hr) for soil filters at full scale
Detention Time - not lett than 30 sec at peak air flow
Soil Type - moist loam, sandy ioam, compost
Soil Temperature - above 3°C (38°F)
Soil Moisture - sprinkling may be required in dry summer periods; proper drainage must be provided to
prevent saturation of the soil.
Unit Process Reliability
Excellent under normal conditions of use.
Environmental Impact
Potential release of odorous gases if filter malfunctions; land requirements are relatively small.
References
1,8,9,10,11,12,13,14,15,16, 39, 40, 41, 42, 43, 44.
292
-------
Flow Diagram
Fact Sheet 7 (Cont.)
Bypass
i
Soil Filter
Fan/Ventmq ^WWW-^ ~ " "..\\\\\
Controls System ^^T°AS°'L^^X
U 1 A ' " Gravel' "
Raw
Septage Pretreatment To
*• Facilities ^ Treatment >
Process Air e
From J 1
Facility
^ Perforated
-TTT< Piping
Manhole
Ej''w^
< '; FezOs/Wood Chip,
•S Mixture S
Iron Oxide
Filter
A
Vent
FT1
U
Energy Notes - Electrical power to operate fan. Power consumption will depend on operating schedule.
Costs - Assumptions: ENR Index = 3875 ..,., . .,
Facility includes exhaust fans, piping, electrical controls, and filter unit (either soil filter or iron oxide
filter
Maximum Air Flow -1800 cfm per 10,000 gpd septage treated
Operating labor costs assume 0.5 hour/day for 10,000 gpd facility, and 1 hour/day for 50,000 gpd
facility.
Soil filter life - at least 5 years
Iron oxide media life - 2 years
Construction Cost
Operation & Maintenance Cost
lousands of Dollars
S 8 |
0 0 c
K
10
:|
re
in
P
- Filter -^
• i
,•
/'
'V
• '
X
-4
^
s
F
-i
^ _
oil
Iter
! =
Q
•5
f 100
3
O
::: §
c
c
1
Iro
A i
i'
n Oxi
Filter
IrrN
r
g
=i
de
N
oil
te
S
N
.«'
S'1
k(l
(I1
1,000 10,000 100,000
Septage Flow, gal/d
1,000,000 1,000 10,000 100,000
Septage Flow, gal/d
100
J
10,000 100,000 1,000,000
Population Equivalent
.I i I
10,000 100,000 1,000,000
Population Equivalent
293
-------
9.2 References
1. Eikum, A.S. Treatment of Septage - European Practice. Norwegian
Institute for Water Research, Report No. 0-80040, February 1983.
f
2. Baumgart, P. Sammlung, Behandung, Beseitigung, und Verwertung von
Schlanunen aus Hausklaranlagen. Technische Universitat Munchen,
draft report, 1984.
3. Roy F. Weston, Inc. Concept Engineering Report - Septage Manage-
ment Facilities for Ocean County utilities Authority. October
1980.
4. Kolega, J.J., A.W. Dewey, and C.S. Shu. Streamline Septage Re-
ceiving Stations. Water and Wastes Engineering, JJ, July 1971.
5. Whitman and Howard, inc. A Study of Waste Septic Tank Sludge Dis-
posal in Massachusetts. Division of Water Pollution Control, Water
Resources Commission, Boston, Massachusetts, 1976.
6. Metcalf and Eddy, Inc. Wastewater Engineering: Treatment/Dispos-
al/Reuse, 2nd Edition. McGraw-Hill, New York, New York, 1979.
7. Condren, A.J. Pilot-Scale Evaluations of Septage Treatment Alter-
natives. U.S. EPA Report No. 600/2-78-164, NTIS No. PB -288415/AS,
September 1978.
8. Rezek, J.W. and I.A. Cooper. Septage Management. U.S. EPA Report
No. 600/8-80-032, NTIS No. PB-81-142481, August 1980.
9. U.S. Environmental Protection Agency. Applications of Sludges and
Wastewaters on Agricultural Land: A Planning and Educational
Guide. U.S. EPA Report No. MCD-35, March 1978.
10. Criteria for Classification of Solid Waste Disposal Facilities and
Practices. Federal Register, 44:53438-53468, 13 September 1979.
11. U.S. Environmental Protection Agency. Process Design Manual for
Land Application of Municipal Sludge, U.S. EPA Report No. 625/1-83
-016, October 1983.
12. Stone, E.L. Microelement Nutrition of Forest Trees: A Review. In:
Forest Fertilization - Theory and Practice. Tennessee Valley Au-
thority, Muscle Shoals, Alabama, 1968.
294
-------
13. Keeney, D.R., K.W. Lee, and L.M. Walsh, Guidelines for the Appli-
cation of Wastewater Sludge to Agricultural Land in Wisconsin.
Technical Bulletin No. 88, Wisconsin Department of Natural Re-
sources, 1975.
14. U.S. Environmental Protection Agency. Preliminary Draft Handbook
for the Design and implementation of Septage Disposal Alternatives
{unpublished}. Municipal Environmental Research Laboratory, EPA
Contract No. 68-03-2971, 1982.
15. U.S. Environmental Protection Agency. Process Design Manual for
Land Treatment of Municipal Wastewater. U.S. EPA Report NO. 625/
1-77-008, October 1977.
16. Hinrichs, D.J., J.A. Faisst, and D.A. Pivetti. Assessment of Cur-
rent information on Overland Flow Treatment of Municipal Waste-
water. U.S. EPA Report No. 430/9-80-002, NTIS No. PB81-168403, May
1980.
17, Vivona, M.A. and W. Herzig. The Use of Septage Lagoons in New
England. Sludge. March-April 1980.
18. New England interstate Water Pollution Control Commission.
Evaluation of Acton's Septage Disposal Facility. 1980.
19. The Connecticut Department of Environmental Protection Water Com-
pliance Uirit. Guidelines for the Design of Septage Lagoons.
20. New England Interstate Water Pollution Control Commission. Guide-
lines for Septage Handling and Disposal. NEIWPCC Report No. TGM-1,
August 1976.
21. Epstein, E., G.B. Willson, W.D. Gurge, R. Mullen, and L.D. Enkiri.
A Forced Aeration System for Composting Wastewater Sludge. Journal
Water Pollution Control Federation. 48 (4), April 1976.
22. Mosher, D. and R. K. Anderson. Composting Sewage Sludge by High-
Rate Suction Aeration Techniques. U.S. EPA Interim Report No.
SW-614d, 1977.
23. Wolf, R. Mechanized Sludge Composting at Durham, New Hampshire.
Compost Science Journal of Waste Recycling, November-December 1977.
24. Heaman, J. Windrow Composting - A Commercial Possibility for Sewage
Sludge Disposal. Water Pollution Control, January 1975.
25, Poincelot, R.P, The Biochemistry of Composting Process. National
Conference on Composting Municipal Residues and Sludges, Infor-
mation Transfer, inc., Rockville, Maryland, August 1977.
295
-------
26. Golueke, C.G. Composting - A Study of the Process and Its Princi-
ples. Rodale Press, Emmaus, Pennsylvania, 1972.
27. Wesner, G.M. Sewage Sludge Composting. U.S. EPA Technology Seminar
Publication on Sludge Treatment and Disposal, Cincinnati, Ohio,
September 1978.
28. Rennie, B.B. The tebo and Groco Methods of Composting. Proceedings
of National Conference on Municipal and Industrial Sludge Compost-
ing - Materials Handling, information Transfer, Inc., Washington,
DC, November 1980.
29. Stearns and Wheeler, inc. Draft interim Septage Management Plan,
Sussex County, New Jersey. Municipal Utilities Authority, April
1980.
30. Bowker, R.P.G. and S.W. Hathaway. Alternatives for the Treatment
and Disposal of Residuals from Onsite Wastewater Systems. U.S. EPA
Training Seminar on Wastewater Alternatives for Small Communities,
OTIS NO. PBS1-131658, August 1978.
31. U.S. Environmental Protection Agency, innovative and Alternative
Technology Assessment Manual. U.S. EPA Report No. 430/9-78-009,
NTIS No. PB81-103277, February 1980.
32. Noland, R.F., J.D. Edwards, and M. Kipp. Full-Scale Demonstration
of Lime Stabilization. U.S. EPA Report No. 600/2-78-171, NTIS No.
PB-286937/AS, September 1978.
33. Weber, W.J. Physiochemical Processes for Water Quality Control.
Wiley-Interscience, New York, New York, 1972.
34. Condren, A.J. Pilot-Scale .Evaluations of Septage Treatment Alter-
natives. U.S. EPA Report No. 600/2-78-164, NTIS No. PB-288415/AS,
September 1978.
35. Perrin, D.R. Physical and Chemical Treatment of Septic Tank Sludge.
M.S. Thesis, University of Vermont, Burlington, Vermont, February
1974.
36. Crowe, T.L. Dewatering of Septage by Vacuum Filtration, M.S.
Thesis, Clarkson College of Technology, Potsdam, New York, 1975.
37. U.S. Environmental Protection Agency. Process Design Manual for
Sludge Treatment and Disposal. U.S. EPA Report NO. 625/1-79-011,
September 1979.
296
-------
38. U.S. Environmental Protection Agency. Process Design Manual for
Suspended Solids Removal. U.S. EPA Report No. 625/l-75-003a,
• January l'975.
;
39. The Calgon Corporation. Effective Odor Control with Calgqn Granular
Activated Carbon Systems. Pittsburgh, Pennsylvania, 1981.
40. Pfeffer, H. .Minderung von Geruchsstoffemissionen aus Stationaren
Anlagen. Lecture at the Colloquium, Wiesbaden, May 1981.
41. Eikum, A.S. Reduksjon av lukt fra mottakeranlegg for septikslam.
Proceedings NIF-kurs, Pagernes, Norway, 1976.
42. Helmer, R. Desodorisierung von geruchsbeladener Abluft in Boden-
filtern. Gesundheits-ingenieur, 95, HI, 1974.
43. Carlson, D.A. and C.P. Leiser. Soil Beds for the Control of Sewage
Odors. Journal of Water Pollution Control Federation, 34; 1966.
44. Frechen, B. Kompostwerk Huckinger der Stadt Duisburg. Stadtrein-
gungsamt Duisburg, 1967.
297
-------
APPENDIX A
SUMMARY OF STATE REQUIREMENTS REGARDING LAND DISPOSAL OP SEPTAGB
State
Land Disposal
Allowed
Land Application
Permit Required
Comments
Alabama
Masks
Arkansas
Arizona
California
Colorado
Connecticut
Delaware
Florida
Georgia
Idaho
Illinois
Indiana
information
unavailable
Yes
Yes
Yes
Yes
Yes
Information
unavailable
Yea
Yes
Yes
Information
unavailable
Information
unavailable
Information
unavailable
Information
unavailable
Yes
Yes } lagoon
design in-
cluded
Information
unavailable
Yes
Information
unavailable
Information
unavailable
Yea
Disposal approval by local DPH. Method of disposal
reviewed by county health officer. Sanitary sewers
and waste treatment plants used for disposal. Per-
mits required since 1982.
DEC requires review. Reluctant to allow septage to
treatment plants because of upsets. DEC may require
pretreatment before STP.
STP also used for disposal.
County Health Department nay approve disposal at
STP or burial.
RHQCB may approve disposal at STP or Class II sani-
tary landfill. Landfills must have surface drainage
and leachate controls, and are limited to accepting
25 to 40 gallons of septage per cubic yard of ref-
use in bay area.
Municipalities have ordinances on disposal. STP
also used. Land disposal regulated by counties.
DEP requires permits for STO, lagoons, occasional
landfill.
Two of three counties go to STP. Other county
"plows in," with road setback of 300 feet.
Sites inspected by state. State prefers use of STP,
Land application allowed but septage must be
treated first.
Counties regulate disposal. STP most common method.
STP also used.
State code regulates disposal. It:PA and State
Health Department require permits for 1) applica-
tion to farm land, 2} landfill, 3) STP, and 4)
sludge drying beds.
state prefers use of STP, subject to municipal ap-
proval, written approval for landfill as contin-
gency only. Burial on private property with owner's
approval.
298
-------
State
Land Disposal Land Application
Allowed Permit Required
Comments
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
Montana
Nebraska
Nevada
New Hampshire
New Jersey
New Mexico
New York
Yes
Yea
Yea
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Information
unavailable
Yes
Ho
Information
unavailable
Information
unavailable
Yes
Yes
Yes
Yes
NO
Yes
MO
Information
unavailable
NO
information
unavailable
No
Yes
Yes
Yes
Sixteen out of 105.counties have regulations, other
approved methods of disposal include l) STP, 2)
plow under in cropland, 3) sanitary landfill, and
4} dewatering by vacuum filtration.
Burial 200 yds from residences and roads. STP also
used.
Land disposal options include soil absorption
trenches, sand filter beds, and small oxidation
ponds. Discharges greater than 3,000 gal oust go to
STP.
Disposal is municipal responsibility subject to DEP
approval, except STP. Recommended practices include
1) STP, 2) land spreading, 3) spray irrigation, and
4) lagooning.
V
DHMH must approve all sites in writing. Set back
200 feet from highway.
State prefers STP, but needs local approval. Land
spreading and/or burial permitted. It must be 1,000
feet from property, and with written approval of
owner and local Health Department.
Land spreading with written approval of owner and
Health Department. STP also used.
No state regulations governing disposal. Little en-
forcement of few laws that apply to disposal. STP
also used.
Ho statewide rules; responsibility of municipali-
ties.
No statewide regulations; responsibility of coun-
ties.
Local Health Department regulates disposal in some
areas. Options include 1) shallow trench disposal,
2) soil injection, 3) lagoons, 4) STP, and 5) bur-
ial (under certain conditions).
STP also used for disposal.
Disposal site reviewed by DEHS. Options include 1}
seepage pits, 2) trench dewatering, and 3) land
spreading.
1982 statewide septage disposal law set up regional
disposal sites (STP). Commercial haulers utilize
some land application.
Rural areas (and the need to conserve water) pro-
mote individual systems under state guidelines.
Such systems include 1) land application, 2) sand
filters, 3) split flow systems, and 4) evapotrans-
piration. SfP used in urban areas,
Different levels of government have different regu-
lations Cor disposal. Disposal sites (STP, lagoons,
etc.) must be permitted with owner's approval.
299
-------
State
Land Disposal
Allowed
Land Application
Permit Required
Comments
North Carolina Yes
North Dakota Yes
Ohio
Oregon
Yes
Yes
Pennsylvania Yea
Rhode island Yea
South Carolina Yea
'South Dakota Yes
Yes
Ho
Information
unavailable
No
Yes
Tennessee
Texas
Yes
Yes
Yes
No
Information
County responsible for less than 3,000 gal. Biv.
Environmental Management responsible for greater
than 3,000 gal.
STP with permission. Land spreading or burial 1,000
feet from residences or roads.
Land spreading on farmland most common. STP also
used for disposal.
Disposal site approved by DEQ. DEQ recommends 1)
STP, 2} lagoons, 3) land disposal on fields without
crops, and 4) plowing under if near habitations.
State recommends use of SIP, but land disposal most
frequent. 90-95% septage to land; 5-10% to STP.
Landfills, lagoons, and trenches also allowed. Five
out of 62 counties have regulations (state issues
guidelines).
Disposal site approved by Department of Health. STP
disposal most common.
Trench absorption and STP most common methods of
disposal.
Burial or other jwith written approval of DWNK).
STP also used for disposal.
Local Health Department has regulations for dis-
posal, land spreading or burial 200 feet from roads
or residences.
Disposal site set back 300 feet from highway unless
buried or treated. Department of public Health en-
courages STP.
Vermont
Yes
Yes
Disposal is broken up as follows: 60% land, 25%
trench dewatering, and 15% STP. At present time all
regulations are proposed; hopefully will become law
soon.
Virginia
Washington
Yes
Yes
Information
unavailable
Yes
He«t Virginia Yes
Wisconsin Yes
Hyoaing
Yes
Yes
Yes
Yes
In unsewered metropolitan areas, disposal via dis-
charge to a municipal wastewater treatment plant.
In rural areas, disposal to designated pit or
trench for septage disposal, sometimes at a solid
waste landfill site which may be publicly or pri-
vately operated.
Disposal in sewer or STP with local approval. La-
goons, sludge beds, and incineration are accept-
able. Burial requires approval of State Department
of Health.
STP and sanitary landfill most common. Burial, land
integration, and spreading-are allowable 200 feet
from well or reservoir and 500 feet from place of
habitation (1,000 feet of land spreading is used).
STP most common. Landfill used if STP unavailable.
>O.S. GOVEKMSNI PRINT1KG OFFICE: 1 994-5 15-003/01 04 3
300
------- |