United States
Environmental Protection
Agency
Office of Water
(WH-5S6)
EPA 822/R-93-004
November 1992
Technical Support Document
for Reduction of Pathogens
and Vector Attraction in
Sewage Sludge
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ACKNOWLEDGMENTS
This document was written by Joseph B. Farrell of the U.S. Environmental Protection
Agency's (EPA's) Risk Reduction Engineering Laboratory, in Cincinnati, Ohio, for the EPA's Health
md Ecological Criteria Division of the Office of Water in Washington, D.C. The document was
idited by Jan Connery of Eastern Research Group, Inc., of Lexington, Massachusetts under contract
o the EPA. Robert M. Southworth, P.E., of EPA's Office of Water, served as the principal
•eviewer.
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TECHNICAL SUPPORT DOCUMENT FOR REDUCTION OF PATHOGENS
AND VECTOR ATTRACTION IN SEWAGE SLUDGE
CONTENTS
1. INTRODUCTION , - I'1
1.1 Background 1-1
1.2 Description of a Part 503 Standard 1-3
1.3 Scope of This Document 1-3
2. COMPONENTS OF DISEASE RISK IN SEWAGE SLUDGE 2-1
2.1 Pathogens of Concern 2-1
2.1.1 Bacteria 2-2
2.1.2 Viruses 2-5
2.1.3 Protozoa • 2-8
2.1.4 Helminths 2-10
2.2 Survival of Pathogens in the Environment 2-11
2.2.1 Air 2-11
2.2.2 Vegetation ... 2-13
2.2.3 Soil .' - 2-13
2.3 Transport of Pathogens to Humans 2-15
2.3.1 Air Transport 2-16
2.3.2 Ground-Water Transport 2-17
2.3.3 Surface-Water Transport 2-18
2.3.4 Transport by Fomites 2-19
2.3.5 Transport by Vectors 2-20
2.4 Transport of Pathogens to and Their Impact
on Plants and Animals 2-21
2.4.1 Salmonella sp. Bacteria 2-22
2.4.2 Taenia sp. .... 2-23
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CONTENTS (cont.)
2.5 Infective Dose 2-24
2.5.1 Salmonella sp. Bacteria 2-24
2.5.2 Enteric Viruses 2-25
2.5.3 Helminths 2-25
2.6 Selection of Microorganisms for Part 503 2-25
2.6.1 Bacteria 2-26
2.6.2 Enteric Viruses 2-27
2.63 Helminth Ova 2-27
2.7 Vector Attraction Reduction 2-28
2.7.1 Vector Attraction Reduction vs. Stabilization 2-28
2.7.2 Measures of Vector Attraction 2-29
2.73 Use of Barriers to Reduce Vector Attraction 2-30
?. APPLICABILITY OF PART 503 PATHOGEN AND VECTOR
ATTRACTION REQUIREMENTS 3-1
3.1 Introduction 3-1
3.2 Land Application 3-2
3.2.1 Bulk Sewage Sludge 3-2
3.2.2 Sewage Sludge Sold or Given Away in a Bag or
Other Container 3-3
3.2.3 Domestic Septage Applied to Agricultural Land,
Forests, or a Reclamation Site 3-3
3.3 Surface Disposal 3-4
3.3.1 Sewage Sludge (Other Than Domestic Septage) 3-4
3.3.2 Domestic Septage 3-5
3.4 When Requirements Must Be Met 3-6
3.4.1 Sewage Sludge That Is Used or Disposed 3-6
3.4.2 At the Time of Use or Disposal , 3-7
3.4.3 At the Time Sewage Sludge Is Prepared for Sale or
Give Away in a Bag or Other Container for Application
to the Land 3-7
IV
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CONTENTS (cont)
3.4.4 At the Time the Sewage Sludge or Material Derived
from Sewage Sludge Is Prepared to Meet the
Requirements in 503.10(b), 503.10(c), 503.10(e),
or 503.10(f) ............ .
4. PART 503 CLASS A PATHOGEN REQUIREMENTS .................. - 4-1
4.1 Introduction ............................ ..... ............ 4-1
4.2 Special Definitions [503.31] ..... ....... . ---- ............ ...... 4-2
4.2.1 Density of Microorganisms ... .............. • .......... 4-2
4.2.2 Specific Oxygen Uptake Rate (SOUR) ............ ...... • 4-3
4.23 Percent Volatile Solids Reduction ....................... 4-3
4.3 Vector Attraction Reduction to Occur with or after
Class A Pathogen Reduction [503.32(a)(2)] .............. . ---- ---- 4-4
4.3.1 Need for the Requirement ............................. 4-4
4.3.2 Scientific Basis for the Requirement ..... ................ • 4-5
4.4 Class A, Alternative 1 — For Thermally Treated Sewage Sludges
[503.32(a)(3)j ... ---- . . . ................. v - ---- - - ....... • • 4-8
4.4.1 Microbiological Monitoring to Demonstrate Pathogen
Reduction [503.32(a)(3)(i)] ......... . ................... 4-9
4.4.2 Time-Temperature Alternative 1(A)— For Sewage Sludges with
at Least 7-Percent Solids [503,32(a)(3)(ii)(A)] ............ • . 4-11
4.4.3 Time-Temperature Alternative 1(B)— For Sewage Sludges with
Suspended Small Particles and at Least 7-Percent Solids
[503.32(a)(3)(ii)(B)] ---- . ................. ... ........ 4-14
4.4.4 Time-Temperature Alternative 1(C)— For Sewage Sludges
with Less Than 7-Percent Solids and Less Than 30
Minutes Contact Time [503.32(a)(3)(ii)(C)] .......... ..... 4-15
4.4.5 Time-Temperature Alternative 1(D)— For Sewage Sludges
with Less Than 7-Percent Solids and at Least 30
Minutes Contact Time at 50° C or Higher
[503.32(a)(3)(ii)(D)] ... .............................. 4-17
4.5 Class A, Alternative 2 — For Sewage Sludge from a High pH-
High Temperature Process [503.32(a)(4)] ....................... . • 4-18
4.6 Class A, Alternative 3 — For Sewage Sludge from Other
Processes [503.32(a)(5)] . . . . ....... . ............ ....... ...... 4-19
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CONTENTS (cont.)
4.7 Class A, Alternative 4—For Sewage Sludge from Unknown
Processes [503.32(a)(6)] 4-20
4.8 Class A, Alternative 5—Use of PFRPs [503.32(a)(7)] 4-20
4.9 Class A, Alternative 6—Use of Processes Equivalent to PFRPs
[503.32(a)(8)] 4-22
5. PART 503 CLASS B PATHOGEN REQUIREMENTS 5-1
5.1 Introduction 5-1
5.2 Class B, Alternative 1—Monitoring of Indicator
Organisms [503.32(b)(2)] 5-1
5.2.1 Explanation of Requirement 5-1
5.2.2 Fecal Coliform Density as an Indicator of Pathogen Reduction . 5-2
5.3 Class B, Alternatives 2 and 3—Use of PSRP and Equivalent Processes
[503.32(b)(3) and (4)] 5-5
5.4 Site Restrictions [503.32(b)(5)j 5-6
5.4.1 Food Crops That Touch the Sewage Sludge [503.32(b)(5)(i)J ... 5-6
5.4.2 Food Crops Below the Soil Surface [503.32(b)(5)(ii) and (iii)] . . 5-7
5.4.3 Food Crops, Feed Crops, and Fiber Crops [503.32(b)(5)(iv)] ... 5-8
5.4.4 Grazing of Animals [503.32(b)(5)(v>] 5-8
5.4.5 Growing of Turf [503.32(b)(5)(vi)j 5-8
5.4.6 Public Access to Sites on Which Sewage Sludge Is Applied
[503.32(b)(5)(vii) and (viii)] 5-9
5.5 Domestic Septage [503.32(c)(l) and (2)] 5-9
5.5.1 Site Restrictions 5-10
5.5.2 pH Adjustment with Site Restrictions for Crop Harvesting .... 5-10
'•>. VECTOR ATTRACTION REDUCTION REQUIREMENTS 6-1
6.1 Introduction 6-1
6.2 Reduction in Volatile Solids Content [503.33(b)(l)] 6-1
6.3 Additional Digestion of Anaerobically Digested Sewage Sludge
[503.33(b)(2)j 6-2
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CONTENTS (cont)
6.4 Additional Digestion of Aerobically Digested Sewage Sludge
[503.33(b)(3)] 1 ................ • •
6.5 Specific Oxygen Uptake Rate (SOUR) for Aerobic Sewage Sludges
[503.33(b)(4)j ................ ..... . • ......... ----- ; • ---- •
6.6 Aerobic Processes at Greater Than 40°C [503.33(b)(5)j . . ---- . ....... 6-6
6.7 Addition of Alkali [503.33(b)(6)] ..... . .......... . ..... • • ....... 6-6
6.8 Moisture Reduction of Sewage Sludge Containing No
Unstabilized Solids [503.33(b)(7)] . ....... ---- ........... .. ...... 6-7
6.9 Moisture Reduction of Sewage Sludge Containing Unstabilized Solids
[503.33(b)(8)] ............................. • ............... 6'8
6.10 Sewage Sludge Injection [503.33(9)] ................. • • • ......... 6-9
6.11 Incorporation into the Soil [503.33(b)(10)] ......... ............... 6-9
6.12 Cover of Sewage Sludge on an Active Sewage Sludge Unit
[503.33(b)(ll)]
6.13 Elevation of pH for Domestic Septage [503.33(b)(12)] ............. • 6-10
COMPARISON OF THE TYPE OF PATHOGEN AND VECTOR
ATTRACTION REDUCTION REQUIREMENTS IN PARTS 257 AND 503 . . 7-1
7.1 Introduction ............................................. 7-1
7.2 Part 257 ........... ........................ .......... 7'2
7.2.1 Pathogens— Sewage Sludge .................. . . ......... 7-2
7.2.2 . Pathogens — Septic Tank Pumpings ........... . ........... 7-3
7.2.3 Vector Attraction Reduction — Sewage Sludge and
Septic Tank Pumpings . ......... ...................... 7-4
7.3 Part 503 ....... ---- . .......................... • • ..... 7-4
7.3.1 Pathogens— Sewage Sludge (Land Application) . . . .......... 7-4
7.3.2 Pathogens— Domestic Septage (Land Application) . . ......... 7-6
7.3.3 Pathogens — Sewage Sludge (Surface Disposal) . . . ---- . . ..... 7-6
7.3.4 Pathogens — Domestic Septage (Surface Disposal) ............. 7-7
7.3.5 Vector Attraction Reduction— Sewage Sludge
(Land Application) ................................... 7-7
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CONTENTS (cont.)
7.3.6 Vector Attraction Reduction—Domestic Septage
(Land Application) 7-8
7.3.7 Vector Attraction Reduction—Sewage Sludge
(Surface Disposal) 7-9
7.3.8 Vector Attraction Reduction—Domestic Septage
(Surface Disposal) 7-9
7.4 Summary 7-10
7.4.1 Land Application—Sewage Sludge 7-10
7.4.2 Land Application—Domestic Septage 7-11
7.4.3 Surface Disposal—Sewage Sludge 7-11
7.4.4 Surface Disposal—Domestic Septage 7-12
REFERENCES 8-1
APPENDIX Subpart D of the Part 503 Regulation 1
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SECTION ONE
INTRODUCTION
1.1 BACKGROUND
Sewage sludge, which is generated during the treatment of domestic sewage in a
treatment works, must be used or disposed properly. It can be used or disposed in a number of
ways, including: application to the land, placement on a surface disposal site, incineration in a
sewage sludge incinerator, and codisposal with municipal solid waste. This document discusses
pathogen and vector application reduction requirements for sewage sludge that is either land-
applied or placed on a surface disposal site.
The term land application encompasses all methods of applying sewage sludge or
material derived from sewage sludge to the soil or incorporating it into the soil. The purposes of
applying sewage sludge to the land are to fertilize crops grown in the soil and to condition the
soil using the organic material in the sewage sludge. Two public health concerns about land
application of sewage sludge are the potential risk posed by pathogens (disease-causing
organisms) in sewage sludge and the potential of the sewage sludge to attract vectors (e.g.,
insects or birds) that can transmit pathogens from sewage sludge to humans.
Surface disposal is the placement of the sewage sludge on land for final disposal. The
major purpose of this practice is to dispose of the sewage sludge rather than to fertilize or
xmdition the soil. There also are concerns about the risks from pathogens in sewage sludge
placed on a surface disposal site and about the potential of the sewage sludge to attract vectors.
Concerns about pathogen and vector attraction of sewage sludge applied to the land or
olaced on a surface disposal site were addressed originally in 1979. At that time, EPA adopted
guidelines for sewage sludge applied to land or disposed in landfills. These guidelines were
ncorporated into 40 CFR Part 257, Criteria for Classification of Solid Waste Disposal Facilities
md Practices, which contained specific requirements for managing sewage sludge. Part 257.3-6
ncluded a requirement that sewage sludge be treated before it is applied to land to reduce
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pathogen levels and to reduce vector attraction. Appendix II of Part 257 listed specific processes
that may be used to treat sewage sludge for pathogen and vector attraction reduction. These
processes were divided into two categories based on the level of pathogen control achieved:
"Processes to Significantly Reduce Pathogens" (PSRPs), which reduce pathogens to a level
comparable to that achieved by a well-run anaerobic digester, and "Processes to Further Reduce
Pathogens" (PFRPs), which reduce pathogens to below detectable levels. Part 257 also specifies
management practices designed to minimize the potential for direct and indirect exposure to
PSRP-treated sewage sludge; a PSRP sewage sludge may still contain some pathogens. Similar,
but slightly less stringent requirements were given for septic tank pumpings. (The Part 257
requirements and their relationship to the Part 503 requirements are discussed further in
Section 7.)
In 1982, EPA established an Intra-Agency Sludge Task Force to recommend procedures
for implementing a comprehensive regulatory program for sewage sludge management. The Task
Force recommended that such a regulatory program be developed using the combined authorities
of Section 405 of the CWA and other existing regulations so that comprehensive coverage could
be provided. Accordingly, two additional regulations were recommended: one that would
establish requirements for state sewage sludge management programs, and the other that would
provide technical criteria for the use or disposal of sewage sludge.
Acting on that recommendation, EPA proposed State Sludge Management Program
Regulations (51 Federal Register, February 4, 1986, page 4458). These regulations proposed that
states develop management programs that comply with existing federal criteria for the use or
disposal of sewage sludge. The proposed State Sludge Management Program Regulations
focused on the procedural requirements for submission, review, and approval of state sewage
sludge management programs. On March 9, 1988, these regulations were proposed again at 53
Federal Register 7642 to reflect changes in requirements for sewage sludge management programs
mposed by the 1987 Water Quality Act. After public comment, these regulations were
oromulgated under 40 CFR Part 501 on May 2, 1989 (54 Federal Register 18716, May 2, 1989).
EPA's Office of Solid Waste (OSW) began the task of preparing the technical criteria
i.e., 40 CFR Part 503) for the use or disposal of sewage sludge in 1980. This task was
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transferred to the Office of Water in 1984. After the Office of Water was reorganized, the
Office of Water Regulations and Standards (OWRS) was renamed the Office of Science and
Technology (OST), and the Wastewater Solids Criteria Branch was renamed the Sludge Risk
Assessment Branch (SRAB). The SRAB developed the pathogen and vector attraction reduction
requirements in Subpart D of the Part 503 regulation based on information in this technical
support document.
1.2 DESCRIPTION OF A PART 503 STANDARD
A standard for the use or disposal of sewage sludge consists of general requirements,
Dollutant limits, management practices, and operational standards. For land application and
surface disposal, operational standards are included in the Part 503 regulation for pathogens and
/ector attraction reduction. A Part 503 standard also contains requirements concerning the
:requency of monitoring, recordkeeping, and reporting when sewage sludge is used or disposed
hrough one of the practices addressed by the regulation.
L.3 SCOPE OF THIS DOCUMENT
This document provides technical support for the pathogen and vector attraction
eduction operational standards in 40 CFR Part 503 (Standards for the Use or Disposal of
Sewage Sludge). Section 2 of this document describes the components of disease risk in sewage
ludge, including the types of pathogens found in sewage sludge that pose a potential public
icalth risk, how well pathogens survive after sewage sludge use or disposal, how they are
ransported and come in contact with humans, and what dose of a pathogen is necessary to cause
nfection. Section 2 also discusses the microorganisms addressed in Part 503 and vector
ittraction reduction in sewage sludge. Section 3 describes the applicability of the Part 503
>athogen and vector attraction reduction requirements. Section 4 discusses the requirements
hat have to be met for a sewage sludge to be classified Class A with respect to pathogens.
lection 5 discusses the Class B pathogen requirements, and Section 6 discusses the vector
ttraction reduction requirements in Part 503. Section 7 compares the type of pathogen and
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vector attraction reduction requirements in Part 503 to the type of pathogen and vector
attraction reduction requirements in 40 CFR Part 257. An appendix to this document provides a
copy of Subpart D of the Part 503 regulation.
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SECTION TWO
COMPONENTS OF DISEASE RISK IN SEWAGE SLUDGE
The disease risk from pathogens in sewage sludge this is used or disposed originates from
:he pathogens in the incoming wastewater at a treatment works. The ultimate risk to public
icalth and the environment depends on several factors:
• How well these organisms survive wastewater and sewage sludge treatment.
• How well these organisms survive exposure to sunlight, ambient temperatures, and
other environmental factors.
• The existence of a pathway or route by which organisms can travel from the
sewage sludge to contact with humans and animals.
• The likelihood that disease results if these organisms are ingested.
Fhis section discusses these factors.
1.1 PATHOGENS OF CONCERN
A pathogen is a disease-causing organism. Sewage sludge can contain many different
?athogens. Pathogens that propagate in the enteric or urinary systems of humans and are
discharged in feces or urine pose the greatest risk to public health. Other pathogens in sewage
Judge originate outside the enteric system (e.g., from soil). Clostridium sp. are a good example.
3ecause fecal matter is not the primary source of pathogens that originate outside the enteric
;ystem, these pathogens are of less concern with respect to the use or disposal of sewage sludge.
Fhe following section discusses the enteric pathogens in sewage sludge that represent the most
dgnificant risk to humans.
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2.1.1 Bacteria
Pathogenic enteric bacteria can colonize portions of the enteric system; indeed the
primary reservoir of these organisms is the enteric systems of animals and humans. These
organisms are not, however, normal inhabitants of the healthy human enteric (intestinal) system.
They are present when an individual contracts a bacterial disease or illness. Consequently, they
occur rarely in an individual's fecal waste, but when they do, high levels can be found. Because
.vastewater discharged to a treatment works contains wastes from many people, pathogens are
usually present, but their densities vary depending oh the prevalence of bacterial disease
outbreaks or the presence of asymptomatic carriers in the local community. Frequently, there
ire periods when certain pathogenic bacteria are below detection limits in the wastewater and in
;he sewage sludge generated during the treatment of the wastewater. Farrell et al. (1990) found
hat salmonellae were frequently undetectable in untreated domestic sewage at small treatment
vorks. Bacterial species present in wastewater and their densities are therefore highly
unpredictable.
2.1.1.1 Types
Kowal (1985) lists several pathogenic enteric bacteria and bacterial species of major
:oncem in sewage sludge and a greater number of less concern. The selection was based on the
density of the bacteria in sewage sludge, the extent of the disease, and the seriousness of the
Ilness produced. Among bacterial species singled out are Shigella sp., Salmonella sp., and
/ersinia sp. All cause enteric disease in large numbers of people in the United States.
2.1.1.2 Densities
The density of pathogenic bacteria in the stool of an infected person may be 1 million per
;ram of solids (Kowal, 1985). Typical values in sewage sludge are much lower, because only a
mall percentage of the population is discharging pathogenic bacteria at a given time. For
•xample, densities of Salmonella sp. over 1,000 per gram in sewage sludge are encountered
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infrequently. On the other hand, the normal bacterial inhabitants of the lower intestines are
found at much higher densities. Obligate anaerobic bacteria have average densities approaching
1,000 million per gram in feces. Facultative bacteria, such as the fecal coliform group, have
average densities around 100 million per gram in feces.
2.1.1.3 Survival
Most research on bacterial survival in sewage sludge has focussed on Salmonella sp.,
vhich include over 2^300 serotypes. These organisms may cause salmonellosis, an acute
gastroenteritis. Salmonellae have been emphasized because they are more frequently identified
n sewage sludge than are other bacterial species, they cause severe illness with relative frequency
'substantially more cases of salmonellosis are reported annually in the United States than
/ersiniosis and shigellosis combined), and a reliable quantitation method exists that can detect
:hem.
Typically, densities of pathogenic bacteria are reduced but not eliminated by conventional
;ewage sludge treatment processes like anaerobic digestion (see Section 5.2.2), but special
irocessing such as pasteurization eliminates them (Section 4.4). Bacterial densities in sewage
,ludge applied to plants decline to low values in less than 30 days (Kowal, 1985). Decline in
.urface soil is rapid—slightly slower than for sewage sludge on plants—but the decline is much
;lower in the soil immediately below the surface. The rate of decline is highest under adverse
invironmental conditions such as high temperature, sunshine, and desiccation (Sorber and
vloore, 1987).
2.1.1.4 Monitoring •
Monitoring sewage sludge on a regular basis to determine the types and densities of
rathogenic bacteria present is desirable but impractical. Quantitation methods for some
lacterial species are difficult and unreliable, and require high skill levels. Too many species have
o be measured, even if measurement is restricted to bacteria of major concern. Fortunately, the
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"jjl
sacterial pathogens most frequently present at high densities, the salraonellae, can be quantified
Adth reasonable accuracy, although the method is difficult and time-consuming. Monitoring for
5almonellae has an advantage over monitoring indicator organisms because salmonellae are
Dathogens.
The best indicators of the potential presence of bacterial enteric pathogens in
anprocessed sewage sludge are the facultative enteric organisms that normally inhabit the
ntestines, such as Escherichia coli. the fecal coliforms, and fecal streptococci. Though these
ndicators do not correlate well with any individual enteric bacterial pathogen species, they do
ndicate the presence of human fecal waste, which is the carrier of the pathogens. Thus, they are
;ood long-term indicators of pathogenic bacteria, but will not always correlate well in the short
erm. A substantial body of research (for example, Berg and Berman, 1980; Farrell et al., 1985)
ndicates that, as sewage sludge is processed, densities of salmonellae and fecal indicators fall in
ibout the same proportion, so the fecal indicators remain good indicators at least of salmonellae,
ind probably for other enteric bacterial pathogens.
When sewage sludge is highly processed to reduce pathogens to below detectable levels, a
•ufficient reduction in bacterial indicator densities can be used to indicate absence of bacterial
ind other pathogens. This approach is used in the drinking water industry, where absence of
ecal coliform (detection limit of approximately 1 MPN [most probable number]/100 mL) is used
o indicate adequate disinfection. Indicator densities are seldom reduced to these levels even in
nghly processed sewage sludge—fecal coliform densities of 1,000 MPN per gram of sewage
Judge solids are used in some circumstances to indicate the absence of pathogens in sewage
•ludge. To be more certain that a specific pathogen is absent, one can specifically test for that
rathogen. This is frequently done for salmonellae. When salmonellae are known to be
ibundant in the unprocessed sewage sludge, their absence in the processed material not only
ndicates their own absence, but can also indicate absence of other pathogens.
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2.1.13 Regrowth
The bacteria of concern are not spore formers so they are relatively easy to destroy by
idverse conditions. On the other hand, they are facultative (i.e., able to grow in the presence or
ibsence of oxygen) and grow readily over a broad temperature range, about 10 to 40°C, if
lutrients are available and competitors and predators are few. The ability to regrow is a
^articular disadvantage in instances where processing kills most predators and competitors. If
lutrients are available when the stress (e.g., elevated temperature) is removed, very rapid
egrowth of the bacteria can occur.
Fecal indicators can still be used as conservative indicators of regrowth of bacteria.
Because the initial densities of fecal indicators are much higher than are pathogen densities, the
ecal indicators survive adverse conditions better than the pathogens survive. Processing may
otally eliminate pathogenic bacteria most of the time but nearly always leaves some fecal
ndicators. These can regrow and indicate the presence of pathogenic bacteria when in fact none
ire present. Thus, fecal indicators may be too conservative in some cases. When this situation is
ikely, a relatively hardy pathogenic bacterial species such as Salmonella sp. may be used as an
ndicator of pathogenic bacterial contamination. Yanko (1988) used a combination of these two
ipproaches to assure product quality at a composting site. He set a coliform standard (10
vlPN/g) before a compost batch could be released to a customer. If the compost could not be
>rought down to this level, he tested the pile for salmonellae and released it if results were
legative.
2.1.2 Viruses
Kowal's extensive review lists the human enteric viruses likely to be present in wastewater
ind sewage sludge (Kowal, 1985). These enteric viruses are not normal inhabitants of the
gastrointestinal tract and their presence in the gastrointestinal tract indicates an infection that
nay show no symptoms. These enteric viruses are released into the intestines from cells in the
:astrointestinal tract where they replicate. Consequently, they are present in fecal discharges.
[hey are generally adsorbed to solid particles or enmeshed in clumps of solid particles.
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2.12.1 Types
Kowal lists several enteric viruses of concern: five subclasses of the genus enterovirus
(e.g., polio-, Coxsackie-, Echo-) as well as other enteric viruses, including hepatitis A virus and
rotaviruses. These viruses cause a wide variety of illnesses; for example, hepatitis A virus causes
approximately 40,000 to 50,000 cases of infectious hepatitis in the United States. Rotaviruses
cause acute gastroenteritis, primarily in children. Viral diseases caused by enteroviruses include
paralysis, diarrhea, meningitis, heart disease, and respiratory illness. Most infections are
asymptomatic, so many more infected people shed viruses than is indicated by disease incidence
numbers. A particular enteric virus may or may not be present in the wastewater, depending on
the presence or absence of infected people in the community.
2.12.2 Densities
The densities of enteric viruses in sewage sludge range widely. Brashear and Ward
(1982) report 5-145 PFU/mL (plaque-forming units per milliliter) of a raw sewage sludge.
Assuming 2 percent solids in the sewage sludge, this is equivalent to 250-7,000 PFU/g of solids.
Other sewage sludge could show higher or lower densities. Less information is available on
enteric virus densities than on indicator bacteria or Salmonella sp. densities because of the
complexity of the method for determining densities and the special skills and equipment needed.
2.12.3 Monitoring
There are a variety of methods for identifying viruses in sewage sludge. The most
common procedure, the plaque assay method, is described by Bitton (1980). A viral suspension
extracted from sewage sludge is placed on the surface of an animal cell monolayer that has been
grown on the interior wall of a glass bottle. After providing time for adsorption of the viruses to
:he cell layer, an overlay of agar is poured over the monolayer to immobilize the system and
orovide nutrient and moisture for the cells. Time is allowed for the viruses to invade the cells
and replicate. Each virus invasion leads to an infection zone where cells have been destroyed.
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This localized area is called a plaque. Staining or other techniques are used to identify plaques.
Unfortunately, this and other virus identification methods are expensive and require skilled
personnel.
The plaque-forming method currently in use identifies a wide variety of enteroviruses
(Bitton, 1980). The number depends on the types of cells used in the test. Some important
enteric viruses—Hepatitis A and rotaviruses—are not enumerated by this method. Serological
methods can be used to determine the specific viruses that form the plaques, but this adds
another level of complexity to an already complex procedure.
The plaque-forming method could serve as a useful indicator test for all enteric viruses.
Goyal et al. (1984) report on a round robin comparison of the EPA method and the sonication-
sxtraction method for determining viruses in sewage sludge that resulted in the recommendation
[O accept both as tentative American Society of Testing Materials standard methods.
An alternative to using a virus test to indicate viral densities is to use the fecal coliforms
and/or fecal streptococci test for this purpose. As with pathogenic bacteria (see Section 2.1.1.4),
the fecal indicators are not expected to correlate over the short term with virus densities;
lowever, because they indicate the presence of fecal wastes, they will correlate well over the long
:erm.
Another area of interest is whether indicator organism densities can be used to indicate
-.he effect of sewage sludge processing conditions (e.g., time and temperature) on viral densities.
indicator organisms can be used for this purpose if available data indicate a satisfactory
x)rrelation between the effect of the condition on viral densities and indicator organisms. Such
correlations appear adequate for most but not all processing procedures. For example, Berg and
Berman (1980) demonstrated that, in anaerobic digestion, the decline in viruses showed a
reasonable relationship to the decline in fecal coliforms and fecal streptococci. On the other
land, irradiation of sewage sludge by gamma rays or high-energy electrons requires 20-30
dlorads to reduce coliforms by a factor of 10 (Ward, 1981), but 10 times that dose is needed to
ichieve the same reduction in viruses. With irradiation, a relationship exists between the
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declines in the two types of organisms, but it does not allow coliforms to be an indicator for
druses. Coliforms could be reduced to negligible densities while viruses are still present.
2.12.4 Regrowth
Unlike bacteria, viruses cannot regrow outside their hosts. Consequently, viruses are
•educed permanently by treatment.
2.1.3 Protozoa
2.13.1 Types
Numerous protozoa invade the human gastrointestinal system and cause disease. Their
•ysts are found in municipal wastewater and sewage sludge. The three most important noted by
Cowal (1985) are Entamoeba histolytica. Giardia lamblia. and Balantidium coli. These organisms
ire known to transmit human disease through a water route and by direct contact. The
•haracteristic illness is diarrhea.
2.1.3.2 Densities
Protozoan cysts are excreted in great numbers from infected persons. Infection rates in
he population are low except for Giardia lamblia, where the carrier rate may range from 1.5 to
10 percent (Benenson, 1975). Levels in wastewater have been estimated to be 4 cysts/L for
Sntamoeba histolvtica (Foster and Englebrecht, 1973) and 104 to 2 x 10s cysts/L for Giardia
amblia (Jakubowski and Ericksen, 1979). More recently, Sykora et al. (1991) reported similar
lensities for Giardia lamblia in untreated wastewater from 11 treatment works. Madore et al.
1987) reported Cryptosporidium oocyst densities as high as 10,000 in wastewater and 1,000 in
•ffluent from the activated sludge process.
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Little information is available on the densities of protozoa in sewage sludge. If, as
expected, most are trapped in the sewage sludge, their density in unprocessed sewage sludge on a
volume basis would be about 200 times the density in untreated wastewater. Processing of solids
in any wastewater or sewage sludge treatment process reduces these densities.
In the investigation noted above, Sykora et al. (1991) reported densities in sewage sludges
that ranged up to several thousand per gram. Densities were probably higher because recoveries
were on the order of 10 percent. All these sewage sludges had been processed by anaerobic
digestion except one. The ratio between densities in sewage sludge and wastewater ranged from
3.28 to 1.45 for processed sewage sludges and was 2.7 for unprocessed sewage sludge. These
data indicate that digestion reduces protozoan densities substantially. (Because current viability
techniques were not applicable to indigenous protozoan cysts in sewage sludge, the authors made
no conjectures about the public health hazard represented by the cysts.)
2.133 Survival
Quantitative information on survival of protozoan forms in processing of wastewater and
sewage sludge and subsequent survival on the land is scant. Protozoa and protozoan cysts are
reported to be more sensitive to the adverse effects of sewage sludge treatment processes than
other pathogens. Pedersen (1981) suggested they do not survive anaerobic digestion. Studies of
the effect of anaerobic digestion on survival of G. lamblia are being conducted by Sykora (EPA,
1992a) but results are not yet available. Kowal (1985) cited several publications showing survival
less than 2 weeks, even on damp soil.
Despite the shortage of information, the consensus of opinion from the literature is that
survival for protozoan cysts is much shorter than for the other pathogens. Like viruses and
unlike bacteria, the protozoa of concern do not multiply outside their animal hosts.
Consequently, meeting the Part 503 requirements for pathogen reduction (see Sections 4 and 5),
.vhich limit survival of the other pathogens, will eliminate risk from protozoa. For this reason,
10 further consideration is given to protozoan forms in this document.
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2.1.4 Helminths
2.1.4.1 Types
The helminths of concern are the nematodes, or roundworms, and the cestodes, or
tapeworms. The most common helminths pathogenic to man and likely to be found in sewage
sludge are:
Ascan's lumbricoides (human roundworm)
Ascaris suum (pig roundworm)
Trichuris trichiura (human whipworm)
Taenia saginata (beef tapeworm)
Taenia solum (pork tapeworm)
Toxacara canis (dog roundworm)
Details of the intricate life cycles of these helminths and the diseases they cause are
discussed by Kowal (1985) and Faust et al. (1976). Ascaris create pneumonitis when the ingested
arvae migrate through the lungs. The human roundworm develops in the small intestine with
olockage possible if a number of worms are present. Toxacara canis larvae migrate blindly in the
numan body, where they can seriously damage viscera and other organs, including the eyes.
Whipworms develop from eggs to larvae to worms in the intestines, lodging finally in the large
ntestines. Light infestations are asymptomatic, but heavy infestations can be life-threatening.
Tapeworms can cause pain and digestive disturbances. Tapeworm eggs are primarily a hazard to
livestock. When eggs are ingested, the larvae produced eventually form cystercerci that damage
;he animal's organs. Humans ingest the cysts from poorly cooked meat, develop the tapeworm,
md release the eggs in the feces. Animals ingest eggs when they graze, which completes the
rycle.
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2.1.4.2 Survival
Helminth ova are extremely resistant to environmental exposure and the effects of
chemicals such as lime and chlorine, although they are easily inactivated by temperatures above
50°C (Lee et al., 1989). Of the helminths, ova of Ascaris sp. survive the longest in the
environment. Survival of 7 years under favorable conditions has been reported (Little, 1980).
Reimers et al. (1981) report that in the United States, Ascaris sp. have the highest concentration
of any helminth in sewage sludge. Because of their prevalence and their hardiness, Ascaris sp.
are used as a conservative indicator of viable helminth ova.
2.1.4.3 Monitoring
Except for processes using temperatures above 50 °C, the exceptional hardiness of
lelminth eggs prevents use of reduction in indicator organism densities to indicate reduction in
iclminth eggs. At temperatures above 50°C, a reduction in the densities of indicator organisms
;an be used to infer that processing was of sufficient duration to reduce helminth eggs.
1.2 SURVIVAL OF PATHOGENS IN THE ENVIRONMENT
When sewage sludge is applied to land or placed on a surface disposal site, pathogen
densities are reduced by adverse environmental conditions. How rapidly densities decline
depends on the media: in the air, on plants, on the soil surface, or in soil. Each media is
discussed separately.
2.2.1 Air
Sewage sludge may be present in air in several forms:
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• Large droplets, such as might be created when liquid sludge sewage is applied
using a splash plate on the back of a truck.
• Smaller drops formed when a 2- to 4-percent solid sewage sludge is sprayed from
a high-pressure nozzle.
• As particles in dust when a field to which sewage sludge has been applied is
cultivated.
The large sewage sludge droplets formed by low-pressure sprays present no risk outside
the sewage sludge site, because large droplets do not travel far from the application point. Spray
from a high-pressure nozzle needs more consideration. Kowal (1982) reviewed the health risks
of aerosols formed in spray application of wastewater. The substantial research in this area
shows that the infection risk from pathogens in the aerosols is small. Pathogen densities are
reduced by "aerosol shock," by desiccation, and by solar radiation. Pathogens reaching a human
host are reduced by dilution with ambient air. In a later publication, Kowal (1985) cites results
oy Harding et al. (1981) that showed elevated levels of bacteria at sewage sludge spray irrigation
sites but significantly less than at wastewater spray irrigation sites. He cites the conclusion of
Sorber et al. (1984) that spray application of sewage sludge does not represent a serious threat to
lealth of individuals more than 100 m downwind.
No quantitative data are available on the presence of pathogens in dust raised when fields
:o which sewage sludge has been applied are plowed or cultivated, but consideration of the
Droblem shows that risks will be minimal. Before dust can be raised, the soil surface must be
dry. The exposure to sunlight, as well as the desiccation that occurs during drying (Ward and
Ashley, 1977; Yeager and Ward, 1981), will reduce the density of pathogenic bacteria and viruses
:o very low levels. Viable helminth ova would survive better but they are relatively large and
would be expected to settle out close to the point where the dust was raised.
Workers on the site can be adequately protected from both droplets and dust by wearing
u'r filtering masks and by changing clothing after exposure.
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2.2.2 Vegetation
Sewage sludge is sometimes applied to soil where plants are growing (e.g., in a field of
alfalfa or a woodland). It gets on plant surfaces during application and when rain falling on the
field spatters sewage sludge upward. The leaves of some plants, such as the bottom leaves of
tobacco plants, frequently have an ash content as high as 30 percent, mostly from soil splashed
onto the leaves by rainfall.
Kowal (1985) concluded from his literature review that pathogens in sewage sludge on
plant surfaces die off more quickly than those in sewage sludge on the soil surface, because of
more exposure to sunlight and greater desiccation. Bacteria and viruses are quickly destroyed.
Larkin et al. (1976) show that viral densities are reduced by a factor of one hundred 14 days
after spray irrigation with sewage sludge. Rudolfs et al. (1951) found Ascaris eggs to be
completely degenerated after 27-35 days. On the other hand, Mueller (1953) found that Ascaris
eggs remained viable for several years in the shaded surface soil of a strawberry plot.
Nevertheless, Kowal indicated that the risk from pathogens deposited on plant surfaces during
application should be minimal 1 month after application.
2.23 Soil
The survival of pathogens in soil is complicated by many factors: soil moisture,
temperature, pH, sunlight, organic matter, and antagonistic soil microflora (Gerba et al., 1975).
This large number of variables and their nature make experimentation difficult—several of these
factors cannot be controlled by the experimenter in field experiments, and laboratory experiments
do not simulate field conditions well. As a result^ experiments measuring pathogen survival have
produced a wide range of results. Sorber and Moore (1987) reviewed the available literature and
summarized the most representative data, including microbial die-off rates from several studies in
which sewage sludge was introduced in the upper layer of soil. These die-off rates are
summarized as regression equations that relate days required for 90- and 99-percent die-off (T90
and T99) to soil temperature (t). These equations were used to calculate the die-off rates
presented in Table 2-1 below.
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TABLE 2-1
DIE-OFF RATES FOR SALMONELLAE, FECAL COLIFORM, AND VIRUSES IN SOIL1
Microorganism
Salmonella sp.
fecal coliform
viruses
Depth
(cm)
5-15
0-5
0-15
Temperature
(°C)
5
15
5
15
5
15
T902
(days)
15
63
23
10
24
10
T992
(days)
30
12
44
18
47
19
'Calculated from summary equations developed by Sorber and Moore (1987) from die-off data
in the literature (presented in Sorber and Moore's Table 17).
2T90, T99—days required for microorganisms to be reduced to 90 and 99 percent of the original
value.
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The T90 and T99 days in Table 2-1 show that fecal coliforms survive longer than
salmonellae, which makes them a suitable indicator for salmonellae. Their survival is slightly less
than for viruses in the upper layer of the soil. If allowance is made for this minor difference,
fecal coliform can be used as an indicator for the survival of viruses in the soil.
Viruses evidently survive better when they are below the topsoil. For deeper application
(15 cm), Sorber and Moore (1987) cite the work of Damgaard-Larsen et al. (1977) that showed
that 56 and 100 days were required for 1- and 2-log reductions in viruses.
The ova from helminths such as Ascaris and Toxocara are extremely resistant to
environmental stress. Pedersen (1981) observed that conventional treatment processes have very
little effect on these ova, so they arrive in sewage sludge at a land application site or surface
disposal site virtually at their original concentration in the sewage sludge. Sorber and Moore
(1987) cite results that indicate relatively short survival of the ova when sewage sludge is applied
to the land surface, but much longer survival under a few centimeters of soil. Jakubowski (1988)
reported research with Ascaris that indicated long survival if the sewage sludge is tilled into the
soil. His results indicated 50-percent survival of Ascaris ova after 3 years of exposure in fallow
or tilled plots. On the other hand, Ascaris survival in sewage sludge applied to the surface of
grassed plots was much shorter. Within 3 months, densities were reduced by more than 90
oercent at three field locations.
2.3 TRANSPORT OF PATHOGENS TO HUMANS
The pathogens in sewage sludge applied to land or placed on a surface disposal site pose
a disease risk only if there are routes by which the pathogens can contaminate humans. The
principal routes of contamination are ingestion and inhalation. Absorption through the skin is
relieved to be a minor exposure route. Sewage sludge may be transported to humans by many
routes: aerial; ground water or surface water; adherence to objects that come into contact with
lumans; surficial or internal contamination of crops eaten by humans; and vectors. The vectors
nay be flies, mosquitoes, fleas, or rodents, as well as other animals that transport disease
organisms to humans either mechanically or by biological processes.
•* '
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2.3.1 Air Transport
Some sewage sludges and sewage sludge application methods create dust or spray that
may be inhaled by operators or by others if transported from the site. Inhaled dust or aerosol
usually ends up in the gastrointestinal system. Methods that may create dust or spray include:
• Splash Plate. Sewage sludge is frequently applied to land as a liquid using a splash
plate on the back of a truck; sometimes the sewage sludge applicator is a high-
pressure nozzle.
• Heat Drying. Heat-dried sewage sludge is dry enough to create a dust when
handled and applied.
• Incorporation. Incorporation of surface-applied sewage sludge into the soil may
create dust if the soil has dried out after sewage sludge application.
The likelihood that liquid sewage sludge dripped from the back of a truck or sewage sludge cake
thrown on the soil by a manure spreader transports aerially from the site is extremely low.
rherefore, the risk to humans not engaged in work on the site is negligible.
2.3.1.1 High-Pressure Spray Application
Sewage sludge application with a high-pressure spray designed to reach a distance of
100 m is low in risk (see Section 2.2.1) only if a sufficient distance is provided (100 m) from
ndividuals downwind. This is usually the case. Spray application is used only on large sites or
MI remote sites so irregular or full of obstacles (e.g., a forest) that direct application from the
)ack of a truck is impossible. Distances to individuals or residences are generally much greater
han 100 m.
2.3.1.2 Heat-Dried Sewage Sludge
Heat-dried sewage sludge, although dry and potentially dusty, is not a problem, because
he particles are too large and hard to cause generalized dusty conditions when applied from a
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spreader. Limited local dusting may occur, exposing the operator to dust, but this can be
controlled by using dust masks. Also, heat-dried sewage sludge is usually free of pathogens.
2.3.1.3 Incorporation
Incorporation of sewage sludge into the soil creates no hazard if the soil and sewage
sludge are moist. If they are dry, dust can form and travel for several kilometers. Only light fine
particles travel any distance. By the time the sewage sludge has dried sufficiently to create dust,
however, the pathogens have been greatly reduced (Yeager and Ward, 1981). Exposure to
sunlight further lowers any residual pathogen densities. The hazard for incorporation is expected
to be less than the hazard for spray application, which has been demonstrated to be minimal to
humans off site (see Section 2.3.1.1). Workers on site can be protected by using dust masks.
23.2 Ground-Water Transport
When sewage sludge is applied to the land surface or placed on a surface disposal site,
the soil and sewage sludge particles form an effective filter mat. For the most part, only soluble
and colloidal particles enter the soil. The larger organisms, such as helminth eggs, are retained
Dn'the land surface; however, virus particles and, sometimes, bacteria are small enough to pass
through the soil to ground water. The mechanisms that remove these organisms during soil
transport are quite different: bacteria are removed primarily by filtration whereas viruses are
removed by adsorption.
Coarse sand is the soil medium most conducive to pathogen transport (Kowal, 1985); it
does not provide a good filter medium to remove bacteria and is a poor adsorbent for viruses.
Fine-grained soils, on the other hand, are effective at removing both bacteria and viruses. Cracks
in soils caused by desiccation and root, insect, and animal holes can allow substantial transport of
organisms to the subsoil. Fissured rock and limestone beneath the soil also can allow transport.
However, because free liquid is only occasionally present in soil—as a result of sewage sludge
application or rainfall—the risk of transport of sewage sludge or sewage sludge pathogens to
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ground water is minimized. By contrast, a septic tank leach field creates a far greater risk of
ground-water contamination because the leach field contains flowing pathogen-laden water that
directly encounters all the subsurface pathways in the soil. Similarly, a wastewater application
site that receives a wastewater loading equivalent to 200 cm of rainfall per year provides a far
greater driving force for virus movement than does liquid sewage sludge addition, which
ordinarily contributes only about 2 to 4 cm additional water loading to the annual rainfall loading
at a site.
Viruses in particular appear to have a potential to migrate to ground water; however,
their movement to and within ground water is slow because the water itself moves slowly, and
because the viruses adsorb and desorb on the soil, further slowing their progress (Landry et al.,
1980). Gerba et al.'s recent work (1991) at a wastewater infiltration site showed that adsorption
and/or filtration substantially reduces virus density. Taking into consideration the effect of time
on virus density, densities were reduced at least 2 logs by 15 feet of soil when wastewater was
applied at an infiltration rate of 2 feet per day on a sandy soil. Adsorption at a sewage sludge
application site is expected to produce greater virus reductions because bulk flow of water occurs
only occasionally and at rates almost two orders of magnitude lower than at an infiltration site.
Virus densities also would decline with time. A typical maximum survival time for viruses within
the soil at low temperature (3 to 10°C) is 170 days (see Table 12 in Kowal's 1985 review).' If, as
is likely, movement to ground water is slow, and the movement of ground water itself beyond the
site boundary also is slow, the potential for virus contamination of ground water beyond the site
is negligjble.-
2.3.3 Surface-Water Transport
Surface water can be contaminated by runoff (flow over the surface of the land) from a
and application site or a surface disposal site, or by rainwater leaching pathogens downward and
then moving laterally below the ground surface through root holes, animal burrows, and assures
n rock strata until a stream is reached. Movement through fissures is likely only for sewage
Uudge applied to forest soil. Helminth eggs are transported by rainwater but, because of their
ligh density, they tend to drop out of rivulets and concentrate in deposits in a manner roughly
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analogous to deposits of gold in stream beds. On the other hand, bacteria and viruses can be
carried by fine solids wherever the runoff goes. -As noted earlier, bacteria and viruses generally
die off to low densities about 1 month after application to the soil surface, so the potential health
hazard from runoff after a rainfall disappears about 1 month after sewage sludge is applied.
2.3.4 Transport by Fomites
Fomites are inanimate objects that may be contaminated with infectious organisms and
then transmit those organisms. Crops, soil, equipment, and workers' clothing are fomites because
they are easily contaminated with sewage sludge and are transported off the site. Viruses and
bacteria on exposed crop surfaces die off in less than a month; some helminths probably die off
less rapidly. Restricting the movement of crops from the site until at least 1 month following
application reduces the potential for transporting pathogens from either a land application site or
a surface disposal site. Good sanitary standards at the application site minimizes the transport of
organisms from the site on clothing and equipment.
Crops grown below the soil surface present a much more serious problem than crops
grown above the soil surface. Helminths eggs survive below ground for years rather than months.
The cumulative risk of ingesting a viable helminth egg as a result of ingesting 0.1 gram of sewage
sludge-treated soil per year for 10 years was calculated to be 1 in 70 (Farrell, 1991). This
calculation assumed that sewage sludge containing five viable helminth eggs per gram was
applied once in the 10 years at a rate of 10 metric tons per hectare; helminth egg half-life was 3
/ears; and the first crop was harvested 20 months after sewage sludge application. To adequately
protect against this rather large risk, a longer period between sewage sludge application and
harvesting appears appropriate when root crops are grown. This provides protection by allowing
a longer time for the helminth eggs to die off.
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2.3.5 Transport by Vectors
Vectors are agents capable of transmitting a pathogen from one organism to another
either mechanically (by simply transporting the pathogen) or biologically by playing a specific
role in the life cycle of the pathogen (for example, the role of mosquitos in relation to malaria).
Consideration of vector transport is essential to any disease risk containment effort.
2.3 J.I Conventional Vectors
Insects are the conventional vectors of disease. Hies of several varieties are attracted to
fecal matter including sewage sludge. Unconventional vectors include humans working on the
site who can become ill and become a vector to their families. Animals that graze on land to
which sewage sludge has been applied also can serve as vectors.
The hazards from vector transport in sewage sludge utilization are difficult to quantify
and thus tend to be underestimated. A study reported by Gemmell (1986) demonstrated the
ability of vectors to spread disease. The parasite eggs from fecal wastes from a dog pen were
transported by flies, heavily contaminating 30 hectares of grazing land. Eggs were dispersed over
30,000 hectares. Soil contamination was determined by observing infestation in sentinel animals
grazed at various distances from the source of contamination.
Transport of disease by vectors traditionally has been controlled by eliminating either the
vectors or the reservoir of infection. In this case, sewage sludge is the reservoir of infection.
Injection of sewage sludge into soil so that it is not available to almost all vectors effectively
eliminates it as a reservoir of infection, but this method is not always practical. Disease vectors
could be eliminated by applying toxic material to the sewage sludge, but adding a toxicant to the
environment is clearly not desirable. Vectors can be discouraged from approaching the sewage
sludge by adding a repellent. Heavy applications of chlorine to sewage sludge evidently act at
least partially by this mechanism. Vectors also can be controlled by eliminating whatever is
attracting them. Chemicals can be added that cause biostasis, thereby preventing further
production of compounds that attract vectors. Application of lime appears to have this effect.
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Another common practice is to biologically treat the sewage sludge by aerobic or anaerobic
processes so thoroughly that vectors no longer have an interest in it.
2.33.2 Unconventional Vectors
These approaches may need to be supplemented to eliminate problems from
unconventional vectors. Some vectors, such as birds, are attracted by the appearance of visible
food wastes. Physical pretreatment such as screening and grinding eliminates most of this
problem and the vector attraction reduction process usually eliminates the remainder. The
potential for grazing animals to become disease vectors can be minimized through management
practices.
Transport by humans working on site can be controlled by management practices such as
deariliness and wearing protective equipment. Tracking medical histories and sickness in the
workers' households is valuable for monitoring this risk.
Risks posed by public use of a site can be controlled by limiting access to the site. The
ength of the period of access control needed depends on all the factors that control the die-off
of microorganisms at the site.
2.4 TRANSPORT OF PATHOGENS TO AND THEIR IMPACT ON PLANTS
AND ANIMALS
Pathogens in sewage sludge enter the environment when sewage sludge is applied to the
.and or placed on a surface disposal site. Typically, these organisms do not harm plant life. The
adverse conditions of the environment cause a steady decline in their densities.
Animal life, particularly warm-blooded animals, can be harmed by sewage sludge applied
.o land or placed on a surface disposal site. Enteric viruses can often cross species lines. This is
iven more likely with pathogenic bacteria. The risk to animals is small when sewage sludge is
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applied to agricultural soil or placed on surface disposal sites. Domestic animals are not grazed
on such sites, and wild animal life on these sites is much lower than in grassland, meadows, and
forests, where soil is typically not disturbed by plowing and cultivating.
There is little reliable information on the effect of pathogens in sewage sludge on wild
animal life. More information is available on its effect on grazing animals. In the United States,
the major impact of sewage sludge pathogens is likely to be to cattle grazing on pasture to which
sewage sludge has been applied. Cattle generally ingest substantial amounts of roots and soil as
well as above-ground plant matter when they graze. They thus ingest sewage sludge solids that
have been more protected from environmental stress than the sewage sludge on the above-
ground parts of the plant. A report of the World Health Organization (1981) focuses on
salmonellosis and infestations ofTaenia saginata (beef tapeworm) as the diseases of greatest risk
to grazing animals.
2.4.1 Salmonella sp. Bacteria
There is considerable controversy about the effect of salmonellae in sewage sludge
applied to pasture. Germany and Switzerland require disinfection of sewage sludge before it is
applied to pasture. Strauch (1980) reviews several convincing studies that indicate that sewage
sludge application to the land has been responsible for an increase in salmonellae carriers in the
:attle population and epidemics of salmonellosis in cattle. On the other hand, Pike and Davis
(1984) review data of investigators from the United Kingdom and the Netherlands that show that
salmonellae densities in sewage sludge applied to land fall in less than 4 weeks to densities far
oelow those required to cause infection in cattle. They conclude that these findings taken
together with epidemiologjcal evidence indicate no substantial risk to cattle if sewage sludge is
stabilized and a no-grazing period of about a month is imposed.
Experience in the United States parallels the experience in the United Kingdom. Dorn et
il. (1985) report several investigations in the United States that show infection of domestic
'razing animals only at extremely high densities of salmonellae. Dorn et al. (1985) carried out a
itudy of the incidence of disease in farm inhabitants and domestic animals on farms where
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sewage sludge was applied to croplands and pastures at agronomic rates following EPA and state
requirements. Their study showed no increase'in incidence of disease on farms where sewage
sludge was used over incidence at control farms that did not use sewage sludge.
The experience of the United States appears to parallel that of the United Kingdom
more than Europe. For these reason, there appears to be little reason to impose a stricter
requirement to protect against salmonellae in sewage sludge applied to grazing lands than exists
in the Part 257 regulation. This is the course of action that has been followed in the Part 503.
Part 503 requires that if sewage sludge is processed to reduce fecal indicator densities to
2,000,000 CPU or MPN per gram and if vector attraction is reduced, animals cannot be grazed
for 1 month after sewage sludge application.
2.4.2 Taenia sp.
There is general acknowledgment of a risk from Taenia to cattle grazed on land to which
sewage sludge has been applied. In the United Kingdom, beef tapeworm is a recognized,
ilthough not major, problem. Pike and Davis (1984) describe guidelines for sewage sludge
xpplication to agricultural land in the United Kingdom, which require a no-grazing period of 3-4
veeks after sewage sludge application if the sewage sludge has been anaerobically digested, and a
5-month no-grazing period if the sewage sludge has been aerobically digested or treated with
ime. Evidently, these latter treatments are not as effective in destroying Taenia eggs as
maerobic digestion.
The United States requirement in the Part 257 regulation and the Part 503 regulation
ncludes a 1-month no-grazing period. This is not as stringent as the United Kingdom
-equirement. A major difference in circumstances, however, is the extremely rare occurrence of
Faenia sagjnata in sewage sludges in the United States. For example, Reimers and coworkers
'1981 and 1986) report finding Taenia (possibly dog or cat tapeworm and not beef tapeworm)
)nly once in sewage sludge from 54 treatment works, whereas Ascaris was found in the sewage
.Judge from nearly all the treatment works. Evidently, the total meat inspection practices in the
Jnited States, which remove contaminated carcasses from the food supply, as well as the
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infrequent consumption of uncooked meat breaks the cycle of infection. Since a Taenia problem
essentially does not exist in the United States, there seems to be little reason to increase the no-
grazing period to more than 1 month for stabilization processes that might not destroy the
infective capabilities of the eggs of this parasite.
2.5 INFECTIVE DOSE
To establish a level of concern about the disease risk posed by a particular sewage sludge
pathogen, the infective dose for that organism must be known. Infective dose is the minimum
dose of a pathogen needed to cause infection.
2.5.1 Salmonella sp. Bacteria
Kowal (1985) critically reviewed the literature on infective dose for all pathogen groups
of concern. For bacteria, he concluded that although infective doses for most species of bacteria
are high (i.e., many thousands of organisms are required to cause infection), they can be. low in
some circumstances. He cited Blaser and Newman (1982), who indicated that the infective dose
for Salmonella sp. may be less than 1,000 organisms) For Shigella, the infective dose is low—10
;o 100 organisms (Keusch, 1970). Ward and Akin (1984) are even more pessimistic, citing work
oy D'Aoust (1985) indicating that Salmonella sp. may be infective at doses below 10 organisms.
Ingestion of only 0.1 grams of sewage sludge containing 100 MPN/gram of salmonellae would
orovide a dose of 10 organisms.
Infective dose for salmonellae or other pathogenic bacteria is less relevant than for
/iruses and helminths because of the capacity of bacteria for regrowth. Bacteria densities in
sewage sludge could be lower than the density needed to cause an infection, but there would still
3e cause for concern because the bacteria could grow to higher densities if conditions favorable
or regrowth are created (for example, a poorly composted sewage sludge, cooled in a storage
•)ile from the thermophilic temperature range to the mesophilic range—the temperature range
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most compatible with enteric pathogens), or if the sewage sludge contacts a source of nutrients
such as a moist foodstuff. :
2.53, Enteric Viruses
Currently, the infective dose for enteric viruses is thought to be low (Kowal, 1985)—on
the order of 10 virus particles or less. Because the infective dose is low, it is prudent to
minimize exposure. If the conditions of land application make sewage sludge ingestion probable
(e.g., sewage sludge is applied to food crops to be harvested shortly after application), the sewage
sludge should be essentially devoid of enteric viruses.
2.5.3 Helminths
For helminths, single eggs are infective, to humans. The magnitude or period of infection
is dose-related because most of the worms produced do not multiply in man. However, an
infection may sensitize individuals so that subsequent light infections cause allergic reactions.
Because the infective dose is low, exposure should be minimized. If risk of ingestion is probable,
the sewage sludge should be devoid of viable helminth ova.
2.6 SELECTION OF MICROORGANISMS FOR PART 503
As noted in Sections 2.1-2.4, numerous pathogenic species present in sewage sludge can
cause human disease. Monitoring all these organisms is both unnecessary and impossible.
Many—including protozoa—are easily destroyed by minimal treatment and are therefore of no
omcern. For this reason, protozoa are not regulated under Part 503. Other pathogens do not
need to be enumerated individually. Usually, there is a surrogate organism that behaves similarly
under adverse conditions to the pathogens of concern and can be enumerated more easily than
:he pathogens. A single test on a surrogate organism generally can eliminate the need for
several tests on individual pathogens.
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Part 503 includes requirements for monitoring of certain bacteria, enteric viruses, and
viable helminth ova. This section explains why those organisms were selected.
2.6.1 Bacteria
Part 503 requires monitoring of fecal coliforms using standard procedures (APHA, 1989).
These organisms have been selected as a surrogate for monitoring individual bacterial pathogens.
Fecal coliforms behave similarly to most of the enteric bacterial pathogens of concern and
respond similarly to adverse conditions. For example, if fecal coliforms are reduced in density by
a factor of 10, enteric bacterial pathogens are expected to be reduced by a similar extent.
Fecal coliform densities can be used to estimate that bacterial pathogens are below
detectable limits. Fecal coliforms occur in untreated sludge at extremely high densities—around
100 million per gram. If these densities are reduced by processing to 1,000 per gram (a factor of
100,000), one would expect bacterial pathogens to be reduced to below detection limits because
their initial densities in unprocessed sewage sludge are rarely above 2,000 per gram.
Part 503 also requires monitoring of Salmonella sp. under certain circumstances.
Salmonellae are the bacterial pathogens of principal concern in sewage sludge. Their relative
reduction can be followed by monitoring for fecal coliforms under the approach described above.
However, some members of the regulated community may prefer to monitor for salmonellae,
rather than for a nonpathogen like fecal coliforms. Obviously, a direct test for Salmonella sp. is
,he best indicator of the absence of salmonellae. Also, salmonellae are good indicators of
-eduction of other bacterial pathogens because they are present in higher densities than other
sacterial pathogens and are at least as hardy. If salmonellae are present in an unprocessed
;ewage sludge and below detection limits in the processed material, this is good evidence that
Dther bacterial pathogens have also been reduced to below detection limits. For all these
•easons, a test for Salmonella sp. can be substituted for fecal coliform monitoring in all the
iltematives included under the Class A pathogen reduction requirements (see Section 4).
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2.62 Enteric Viruses
Some of the Part 503 Class A pathogen requirements include monitoring of enteric
viruses by a method developed specifically for enumeration of enteroviruses (ASTM, 1992),
which is a genus constituting many but not all enteric viruses. This method enumerates many but
not all enteric viruses. Important viruses not enumerated are rotaviruses and hepatitis viruses.
The methods for measuring densities of these latter viruses are still under development and are
not yet practical for field use. A reasonable assumption is that the enteric viruses not detected
by the required method behave similarly to those that are detected.
In some circumstances, enteric viruses can be monitored by bacterial indicators such as
fecal coliforms. For example, viral densities are reduced by high temperatures to approximately
the same degree as fecal indicator organisms. This holds true for modest reductions in densities
as well as reduction to densities below detection limits. As noted above in Section 2.5.1, a fecal
aliform density of 1,000 per gram in processed sewage sludge indicates a reduction intensity of a
factor of 100,000. Maximum enteric virus densities in unprocessed sewage sludge are around
2,000 per gram. Consequently, if fecal coliform densities are reduced to 1,000 per gram, enteric
druses are expected to be below detection limits of 1 plaque-forming unit per 4 grams of sewage
sludge.
There are circumstances where bacterial indicators are not good indicators of virus
destruction. For example, viruses are much more resistant to high-energy irradiation than
oacteria, so absence of bacteria in irradiated sewage sludge would not indicate absence of viruses.
\t temperatures below the mesophilic range, viruses may survive much better than bacteria.
Under such circumstances, only the virus test can be used to monitor virus densities.
2.6.3 Helminth Ova
Some of the Part 503 pathogen requirements include monitoring of helminth ova using a
nethod described by Yanko (1987). Helminth ova are extremely resistant to most adverse
•>rocessing and environmental conditions at temperatures in the mesophilic range and below. In
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these circumstances, viable helminth egg densities can only be enumerated by a specific test for
viable helminth eggs. At temperatures of 50 °C and above, surrogate organisms such as the
bacterial fecal indicator organisms can be used to indicate reduction in helminth densities.
2.7 VECTOR ATTRACTION REDUCTION
As noted in Section 2.3.5, transport of pathogens by vectors can play a major role in
disease transmission. The health risk to humans and animals posed by this transmission route
can be reduced substantially by reducing the attractiveness of sewage sludge to vectors.
2.7.1 Vector Attraction Reduction vs. Stabilization
Vector attraction reduction is a relatively new concept in sewage sludge treatment
technology. It was first introduced with the publication of the Part 257 regulation (EPA, 1979).
Until then, it was common to "stabilize" sewage sludge before use or disposal by processes such
as anaerobic or aerobic digestion. Stabilization was carried out for a variety of reasons, but the
principal reason was to make the sewage sludge aesthetically acceptable (i.e., odor and
appearance were changed so that its origin was less evident). Important side effects of
stabilization were a reduction in pathogen densities and a reduction in the characteristics that
ittract vectors.
The 1979 regulation reversed the priorities of this treatment step. Reduction in pathogen
densities and vector attraction became paramount. Reduction in odor was not specifically a
;oncem of the requirement to reduce vector attraction. Nevertheless, the unpleasant odors that
make untreated sewage sludge aesthetically unacceptable also contain the chemical attractants
:hat draw vectors to the area where the sewage sludge is present.
The chemical nature of these attractants is unknown. It is known that when certain
physical, chemical, or biological processes are carried out on sewage sludge, odors apparent to
lumans and attractiveness to vectors both diminish. Typical processes that achieve these effects
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are aerobic and anaerobic digestion, drying, treatment with chemicals such as ozone or lime, and
composting. It is reasonable to assume a direct correspondence between odor intensity and
degree of vector attraction, although this has not been proven scientifically.
2.7.2 Measures of Vector Attraction
The vector attraction reduction requirements of Part 257 were based on field experience
rather than objective scientific criteria. In this approach, the degree of vector attraction of
sewage sludge with a range of values of a parameter thought to be associated with vector
attraction was observed. This route was followed formally for lime stabilization of sewage
sludges (Farrell et al., 1974; Noland et al., 1978; Counts and Shuckrow, 1975) and informally for
:he other processes. Use or disposal sites were observed, the treated sewage sludge was
examined, the literature was reviewed for comments on problems, and a judgment was made
oased on this information. In all cases, when the pathogen requirement was met, the vector
attraction reduction was, at a minimum, satisfactory.
Obviously, it is desirable to have objective scientific tests to measure the attractiveness of
i sewage sludge to vectors and the degree of reduction produced by treatment, but achieving this
s not simple. Wolf (1955) showed that degree of attraction of house flies to sewage sludge
drying on sand beds is reduced as the degree of digestion of a sewage sludge is increased, but
:hat moisture content could be critical; if sufficiently dry spots are not available, the flies would
iot land on the sewage sludge. Thus, a liquid sewage sludge applied to soil might not attract
.•ectors when first applied, would start attracting vectors when there were enough dry landing
;ites, and probably would stop attracting vectors when the sewage sludge dried out to perhaps 60-
Dercent solids. A thick application of sewage sludge probably would be far more attractive than
i thin application because a lower wet layer would be protected by a dried layer on the surface
hat would provide ideal landing sites.
An objective vector attractant test, although difficult to develop, could be worked out, but
t might almost be irrelevant, because field conditions of sewage sludge application vary widely.
Temperature and humidity are uncontrolled in the field and sewage sludge application rates can
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vary widely. An objective test designed to simulate a worst-case scenario is not a reasonable
approach, because it would impose excessive requirements on many facilities.
The low likelihood that an objective scientific test would yield universally applicable
results encouraged simpler approaches. Field experience has shown that percent reduction of
volatile solids content of a sewage sludge correlates satisfactorily with reduced vector attraction.
Also, if a sewage sludge is dry enough, it will not attract vectors. Adding an alkali to bring
sewage sludge to a high-enough pH deters vectors. Several different process-dependent
standards have been developed for measuring vector attraction reduction or indicating
satisfactory reduction: solids content, percent volatile solids reduction, rate of oxygen uptake,
and pH. Evidence of their effectiveness is based on field observation of reduced vector
attraction or odors.
2.73 Use of Barriers to Reduce Vector Attraction
Just as a screened-in porch protects people from insects, a physical barrier such as a
covering of soil prevents insects from contacting sewage sludge. Burial of sewage sludge in
trenches has been practiced and effectively prevents vector attraction. Similarly, the daily
covering of sewage sludge prevents all but temporary vector attraction. The relatively shallow
injection of sewage sludge practiced at land application sites also prevents vector attraction if
application is done carefully and little sewage sludge is left on the soil surface. Application of
sewage sludge to the land surface followed by the incorporation of sewage sludge in the soil also
is effective provided the application rate is not excessive. The soil mass dilutes the sewage sludge
by a factor of approximately 100, and dehydrates the sewage sludge. The very small amount of
sewage sludge that remains on the land surface is typically about as dry as the soil, which makes
it unattractive to vectors.
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SECTION THREE
APPLICABILITY OF PART 503 PATHOGEN
AND VECTOR ATTRACTION REQUIREMENTS
3.1 INTRODUCTION
As described below, Subpart D (the pathogen and vector attraction reduction
requirements) of the Part 503 regulation applies to sewage sludge (both bulk sewage sludge and
sewage sludge that is sold or given away in a bag or other container) and domestic septage
applied to the land or placed on a surface disposal site. Both sewage sludge and domestic
septage must meet pathogen and/or vector attraction reduction requirements. These two types of
reduction requirements are separated in Part 503 (they were combined in Part 257), which allows
flexibility in how they are achieved.
The pathogen requirements for sewage sludge are separated into Class A and Class B
requirements. The Class A requirements are the more stringent requirements. They are
designed to produce sewage sludges with pathogens reduced to below detectable levels. Sewage
sludges that meet the Class B requirements will likely still contain some pathogens, and therefore
require restrictions on the site where the sewage sludge is applied to ensure protection of public
icalth and the environment.
This section discusses the applicability of the Subpart D requirements. The pathogen and
/ector attraction reduction requirements are described in Sections 4-6,
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3.2 LAND APPLICATION
3.2.1 Bulk Sewage Sludge
3.2.1.1 Pathogen Requirements
The final Part 503 regulation requires that bulk sewage sludge applied to agricultural
land, forest, a public contact site, or a reclamation site meet either Class A or Class B pathogen
requirements. When the sewage sludge is Class B with respect to pathogens, restrictions (e.g.,
harvesting of root crops) are imposed on the site where the sewage sludge is applied. Under this
approach, the sewage sludge can be treated to reduce pathogens (Class A) or a combination of
treatment and environmental attenuation (i.e., Class B with site restrictions) can be used to
reduce pathogens.
Bulk sewage sludge applied to a lawn or a home garden must meet the Class A pathogen
requirements. The reason for this requirement is that it is not feasible to impose site restrictions
Dn a lawn or a home garden on which bulk sewage sludge is applied. To avoid having to impose
ute restrictions, which are required when the bulk sewage sludge meets the Class B pathogen
"equirements, the bulk sewage sludge has to meet the Class A pathogen requirements.
3.2.1.2 Vector Attraction Reduction Requirements
One of 10 vector attraction reduction requirements also must be met when bulk sewage
Uudge is applied to the agricultural land, forest, a public contact site, or a reclamation site.
Fhese requirements are designed to reduce the characteristics of the sewage sludge that attract
/ectors such as mosquitos and flies.
One of eight vector attraction reduction requirements has to be met when bulk sewage
•ludge is applied to a lawn or a home garden. The two vector attraction reduction requirements
hat cannot be used when bulk sewage is applied to a lawn or a home garden are injection of the
)ulk sewage sludge below the land surface and incorporation of sewage sludge into the soil.
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Implementation of these requirements for bulk sewage sludge applied to a lawn or a home
garden is difficult, if not impossible.
3.2.2 Sewage Sludge Sold or Given Away in a Bag or Other Container
3.22.1 Pathogen Requirements
Sewage sludge sold or given away in a bag or other container for application to the land
must meet Class A pathogen requirements. It is impossible to impose the site restrictions
required for a sewage sludge that meets the Class B pathogen requirements in this situation.
3.2.2.2 Vector Attraction Reduction Requirements
One of eight vector attraction reduction requirements also has to be met when sewage
sludge is sold or given away in a bag or other container for application to the land. In this
situation, it is not feasible to inject the sewage sludge below the land surface or to incorporate
the sewage sludge into the soil. For injection and incorporation, control of the application site
must be maintained by the appropriate person. There is no site control when sewage sludge is
sold or given away in a bag or other container for application to the land.
3.23 Domestic Septage Applied to Agricultural Land, Forests, or a Reclamation Site
3.2.3.1 Pathogen Requirements
When domestic septage is applied to agricultural land, forest, or a reclamation site, either
;ite restrictions (i.e., the same site restrictions that have to be met when a Class B sewage sludge
s applied to the land) have to be met or a pH requirement for the domestic septage has
:o be met along with site restrictions concerning the harvesting of crops. The first requirement
•elies on the environment to reduce pathogens by restricting certain activities on the site. These
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restrictions prohibit harvesting of crops, grazing of animals, and public access to the site for a
certain period. The second requirement relies on treatment of the domestic septage (i.e., pH
adjustment) and restrictions on harvesting crops to reduce pathogens. Restrictions on harvesting
of crops are part of the second requirement because the Agency concluded that pH adjustment
alone does not achieve adequate pathogen reduction to allow crops to be harvested immediately
after applying the domestic septage. Domestic septage applied to other types of land must meet
the appropriate pathogen requirement for sewage sludge that is applied to the land.
3.23.2 Vector Attraction Reduction Requirements
Vector attraction reduction is achieved when domestic septage is applied to agricultural
land, forest, or a reclamation site if the domestic septage is injected below the surface of the
land, incorporated into the soil after being applied to the land surface,'or when the pH of the
domestic septage is raised to 12 or higher and remains at 12 or higher for 30 minutes. When
vector attraction reduction is achieved by raising the pH of the domestic septage, each container
of domestic septage that is applied to the land must be monitored to demonstrate compliance
with that requirement.
3.3 SURFACE DISPOSAL
3.3.1 Sewage Sludge (Other Than Domestic Septage)
3.3.1.1 Pathogen Requirements
The pathogen requirements in the final Part 503 regulation for sewage sludge (other than
domestic septage) placed an active sewage sludge unit are similar to the existing requirements for
the disposal of sewage sludge on the land in 40 CFR Part 257. Sewage sludge (other than
domestic septage) placed on a surface disposal site has to meet either Class A or Class B
oathogen requirements, except site restrictions, unless a cover is placed on the active sewage
dudge unit at the end of each operating day. When a daily cover is placed on an active sewage
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sludge unit, the sewage sludge does not have to meet a separate pathogen requirement. The
daily cover isolates the sewage sludge and allows the environment to reduce the pathogens in the
sewage sludge. '
Pathogen-related site restrictions do not have to be met when the sewage sludge meets
the Class B pathogen requirements because similar site restrictions are already imposed on an
active sewage sludge unit for other than pathogen reduction (i.e., to prevent exposure to
pollutants). Management practices that address these site restrictions are included in the surface
disposal subpart of Part 503 because the exposure pathway analysis for the surface disposal
pollutant limits did not address activities such as harvesting of crops, grazing of animals, and
exppsure to the sewage sludge by the public.
3,3,1.2 Vector Attraction Reduction Requirements
The vector attraction reduction requirements in the final Part 503 regulation for sewage
sludge placed on a surface disposal site also are similar to the Part 257 vector attraction
reduction requirements. Part 257 requires that the sewage sludge be covered daily or that other
appropriate techniques be used to reduce vector attraction. The final Part 503 regulation
requires that 1 of 10 vector attraction reduction requirements (i.e., "other techniques") be met
•vhen sewage sludge (other than domestic septage) is placed on an active sewage sludge unit or
:hat daily cover be placed on the active sewage sludge unit. As mentioned above, when daily
xiver is placed on an active sewage sludge unit, the sewage sludge does not have to meet a
separate pathogen requirement. The daily cover prevents access to the sewage sludge by vectors.
3.3.2 Domestic Septage
Domestic septage placed on a surface disposal site does not have to meet a pathogen
-equirement. The existing requirements in Part 257 for septic tank pumpings indicate that septic
ank pumpings applied to the land have to be treated in a Process to Significantly Reduce
3athogens (PSRP) or restrictions concerning grazing of animals and access by the public have to
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be imposed on the site where the domestic septage is disposed. Because site restrictions for
those two activities, as well as a restriction on the harvesting of crops, are imposed on all active
sewage sludge units for other than pathogen reduction (i.e., to prevent exposure to pollutants),
the site restrictions for applying domestic septage to the land are met at every active sewage
sludge unit. For this reason, domestic septage placed on an active sewage sludge unit does not
have to meet an additional pathogen requirement.
Vector attraction reduction is achieved when domestic septage is placed on a surface
disposal site if the domestic septage is injected below the land surface or incorporated into the
soil; if the pH of the domestic septage is raised to a certain level and remains at that level for 30
minutes (i.e., "other techniques"); or if the active sewage sludge unit receives a daily cover. The
"other techniques" for domestic septage are limited to injection, incorporation, and pH
adjustment because the EPA concluded that other techniques available for sewage sludge (e.g.,
volatile solids reduction and percent moisture) are not feasible for each container of domestic
septage placed on an active sewage sludge unit. When daily cover is placed on an active sewage
sludge unit, access to domestic septage placed on the unit by vectors is prevented.
3.4 WHEN REQUIREMENTS MUST BE MET
The Part 503 pathogen and vector attraction reduction requirements have to be met at
various times, as discussed below.
3.4.1 Sewage Sludge That Is Used or Disposed
The phrase "sewage sludge that is used or disposed" is used in the final regulation to
indicate that the appropriate pathogen and vector attraction reduction requirements can be met
any time before the sewage sludge is actually used or disposed. For example, sewage sludge may
-)& stored for a period of time after the time-temperature pathogen requirements are met. In
.his case, the time-temperature requirements do not have to be met again just prior to when the
sewage sludge is used or disposed.
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3.4.2 At the Time of Use or Disposal
The phrase "at the time of use or disposal" is used to indicate that the appropriate
pathogen requirements have to be met just prior to when the sewage sludge is used or disposed.
Enough time must be allowed to test the sewage sludge and obtain the test results before the
sewage sludge is used or disposed. The main reason this phrase is used in the regulation is to
ensure that the pathogen regrowth requirement (i.e., either fecal coliform or Salmonella sp.
bacteria density value must be below the specified value) is met at the time the sewage sludge is
used or disposed.
3.4.3 At the Time Sewage Sludge Is Prepared for Sale or Give Away in a Bag or Other
Container for Application to the Land
The phrase "at the time sewage sludge is prepared for sale or give away in a bag or other
container for application to the land" also is used to indicate when certain pathogen
requirements must be met. When sewage sludge is sold or given away in a bag or other
container, the pathogen regrowth requirements cannot be met just prior to when the sewage
sludge is actually applied to the land (e.g., when applied to a home garden). For this reason,
those requirements have to be met when the sewage sludge is prepared for sale or give away in a
bag or other container.
3.4.4 At the Time the Sewage Sludge or Material Derived from Sewage Sludge Is
Prepared to Meet the Requirements in 503.10(b), 503.10(c), 503.10(e), or
503.10(f)
The phrase "at the time the sewage sludge or material derived from sewage sludge is
orepared to meet the requirements in 503.10(b), 503.10(c), 503.10(e), or 503.10(f)" also is used in
:he final Part 503 regulation to indicate when certain pathogen requirements have to be met. In
ihese cases, sewage sludge that meets three quality requirements is not subject to the land
ipplication general requirements and management practices. Because the sewage sludge is not
mbject to further control under Part 503 after it meets the three quality requirements, it may not
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be known when the sewage sludge is actually applied to the land. In that situation, the pathogen
regrowth requirement cannot be met just prior to when the sewage sludge is used or disposed.
For these reasons, the pathogen regrowth requirements have to be met at the time the sewage
sludge is prepared to meet the quality requirements. In most cases, this is the last point at which
there is control over the sewage sludge with respect to the Part 503 requirements.
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SECTION FOUR
PART 503 CLASS A PATHOGEN REQUIREMENTS
4.1 INTRODUCTION
This section explains and provides justifications for the specific Class A pathogen
requirements of Subpart D of the Part 503 regulation. The Class A requirements include six
alternative requirements for demonstrating Class A pathogen reduction. Sewage sludge can meet
any one of these six alternatives to qualify as a Class A sewage sludge. The objective of all these
requirements is to reduce pathogen densities to below detectable limits which are:
Salmonella sp. less than 3 MPN per 4 grams total solids
enteric viruses less than 1 PFU per 4 grams total solids
viable helminth ova less than 1 PFU per 4 grams total solids
Class A sewage sludges must also meet one of the requirements for vector attraction
reduction (see Section 6). Because Class A sewage sludges are vulnerable to regrowth of
Bacterial populations, reduction of vector attraction generally must occur at the same time as or
ifter pathogen reduction (see Section 4.3).
This section is organized according to the specific paragraphs in Subpart D, and uses the
;ame numbering as the Part 503 paragraphs. Section 4.2 discusses some of the special definitions
n the regulation that pertain to the pathogen and vector attraction requirements. Section 4.3
discusses the requirement for vector attraction reduction to occur with or after pathogen
-eduction. The six alternative requirements for pathogen reduction are presented in Sections 4.4
:o4.9.
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4.2 SPECIAL DEFINITIONS [503.31]
Both the Class A and B and the vector attraction reduction requirements refer to certain
terras and units of measurement. These are defined in Part 503.31 of the regulation. Definitions
where explanations are useful are discussed below.
4.2.1 Density of Microorganisms
Density of microorganisms is defined as number of microorganisms per unit mass of total
solids (dry weight). Ordinarily, microorganism densities are determined as number per 100 mL
of wastewater or sewage sludge. They are reported in this manner for wastewater, but are less
appropriate for sewage sludge. The microorganisms in sewage sludge are associated with the
solid phase. When sewage sludge is diluted, thickened or filtered, the number of microorganisms
per unit volume changes markedly, whereas the number per unit mass of solids remains almost
constant. This argues for reporting densities as number per unit mass of solids. For this reason,
sewage sludge solids content should always be determined when measuring microorganism
densities in sewage sludge. A second reason for reporting densities per unit mass of solids is that
sewage sludge application to the land is typically measured and controlled in units of mass of dry
solids per unit area of land. If pathogen densities are measured as numbers per unit mass of
solids, the rate of pathogen application to the land is thus directly proportional to the mass of
dry sewage sludge solids applied.
Density of microorganisms is expressed in different ways for different organisms.
Helminth ova are observed and counted as individuals under a microscope. Viruses are usually
counted in plaque-forming units (PFUs—see Section 2.1.2 for an explanation of this term). For
bacteria, the count is in colony-forming units (CPU) or most probable number (MPN). CPU is a
count of colonies on an agar plate or filter disk. Because a colony might have originated from a
clump of bacteria instead of an individual, the count is not necessarily a count of separate
ndividuals. MPN is a statistical estimate of numbers in an original sample. The sample is
diluted at least once into tubes containing nutrient medium; there are several duplicates at each
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dilution. The original bacterial density in the sample is estimated based on the number of tubes
that show growth.
The detection limits for the pathogens are expressed as numbers, PFUs, CPUs, or MPNs
per 4 grams. This terminology is used because most of the tests started with 100 mL of sewage
sludge which typically contained 4 grams of sewage sludge solids.
4.22 Specific Oxygen Uptake Rate (SOUR)
SOUR is defined as the mass of oxygen consumed per unit time per unit mass of total
solids (dry weight basis) in the sewage sludge. SOUR is usually based on total suspended
/olatile solids rather than total solids, because it is assumed that it is the volatile matter in the
;ewage sludge that is being oxidized. The SOUR definition in Part 503 is based on total solids
Drimarily to reduce the number of different determinations needed. Generally, the range in the
-atio of volatile solids to total solids in aerobically digested sewage sludges is not large. The
standard required for SOUR based on total solids is slightly lower than if it had been based on
/olatile suspended solids.
4.23 Percent Volatile Solids Reduction
Percent volatile solids reduction is defined for a continuous or semi-continuous steady
;tate process as 100 times the difference between the masses of volatile solids in the influent and
iffluent sewage sludges divided by the mass of volatile solids in the influent sewage sludge. For
i batch process, it is defined as 100 times the difference between the masses of volatile solids in
he influent and effluent sewage sludges divided by the mass of volatile solids in the influent
,ewage sludge. The typical operation of an anaerobic digester is semi-continuous feed—sewage
,ludge is charged to a digester at least once a day and an equal volume is withdrawn at least
mce a day. Provided the amount and composition of sewage sludge in the digester remain
ipproximately constant, the relationship defined above for continuous processing applies. In the
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additional digestion tests described later under vector attraction reduction methods, the digestion
is a batch operation. Volatile solids reduction is determined according to the definition above.
The definitions for continuous, semi-continuous, and batch digestion are appropriate for
simple processing schemes, but they need to be interpreted for more complex situations. For
example, when supernatant is removed from a digester, there are two instead of one exiting
streams that can carry off volatile solids. EPA has provided guidance (EPA, 1992b) on ways to
calculate volatile solids reduction for these complex situations.
4.3 VECTOR ATTRACTION REDUCTION TO OCCUR WITH OR AFTER CLASS A
PATHOGEN REDUCTION [S03J2(a)(2>]
For Class A pathogen reduction, the order of pathogen reduction is important when
certain of the vector attraction reduction requirements are met. Part 503.32(a)(2) requires that
Class A pathogen reduction be accomplished before or at the same time as the vector attraction
reduction except for vector attraction reduction by alkali addition [503.33(b)(6)j or drying
[503.33(b)(7) and (8)].
43.1 Need for the Requirement
The need for specifying the order in which vector attraction and pathogen reduction
occur is based on evidence that regrowth of bacterial pathogens can occur if pathogen reduction
follows the vector attraction reduction step. In the early 1980s, both Germany and Switzerland
had regulations requiring disinfection of digested sewage sludge before it could be used on
pasture in the summer. The method of choice was generally pasteurization—exposure to 70 °C
for 0.5 hour. Clements (1983) describes experience in Switzerland where over 70 treatment
tvorks were using pasteurization after sewage sludge digestion. After receiving reports of the
oresence of salmonellae in these treated sewage sludges, the government conducted an
nvestigation that revealed that most of the pasteurized products were contaminated with
pathogenic bacteria. The presence of the bacteria was attributed to downstream bacterial
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contamination in the absence of competitive bacteria. These bacteria grew rapidly to dangerous
levels, even though the sewage sludges had been well digested. Since that time, post-
pasteurization has been abandoned in Switzerland and Germany. Current practice is to
pasteurise the sewage sludge before digestion, or to use aerobic thermophilic digestion, a process
that simultaneously reduces sewage sludge volatile solids content and pathogen densities.
The discovery that bacteria can grow to high densities when vegetative bacteria are
eliminated, even when a sewage sludge is well digested, demonstrates that it is unwise to have the
oathogen reduction process as the terminal processing step unless there is some kind of a
deterrent to regrowth that remains in the sewage sludge. Examples of such deterrents are
iryness, a chemical residual, or the presence of a competitive but nonpathogenic bacterial
Dopulation. .
A much more limited regrowth of pathogenic bacteria can occur when the vector
ittraction process follows the pathogen reduction process. Burge et al. (1987) established that if
i well-composted sewage sludge product is inoculated with salmonellae, regrowth will occur but
vill diminish to low densities in a few days. If the material is sterilized by radiation, regrowth
vill be explosive and prolonged. On the other hand, Yanko (1988) found high frequent
xxurrence of salmonellae, most likely from regrowth, in many compost samples. Frequency of
detection of salmonellae and density when detected increased in proportion to fecal coliform
density. Presumably, these composts were low in vegetative bacteria that deter regrowth and
xmtained too much residual decomposable matter that provided a food source for
nicroorganism growth. Yanko's finding supports the need for a requirement to check the
nicrobiological character of sewage sludge from processes that reduce bacterial densities to
ixtremely low levels, even when pathogen reduction does not follow vector attraction reduction.
4.3.2 Scientific Basis for the Requirement
The potential for regrowth of pathogenic bacteria in sewage sludges that have been
;reatly reduced in pathogens makes it important to ensure that substantial regrowth has not
>ccurred. The experimental work carried out by Yanko (1988) provides a relatively simple
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monitoring requirement. Yanko's extensive data on microbiological properties of compost and
compost products show that in his weekly samples, salmonellae were detected 165 times in 365
measurements, but no salmonellae were detected in the 86 measurements for which the fecal
coliform densities were less than 1,000 MPN per gram. This indicates that if fecal coliform
densities were below 1,000 MPN per gram, likelihood of salmonellae detection would be rare.
Yanko's data demonstrate a good correlation between fecal coliform densities and
frequency of salmonellae detection. Farrell (1992) re-plotted these data on slightly different
coordinates and obtained the correlation shown in Figure 4-1. This correlation can be used to
give an estimate of the frequency of detection of salmonellae when fecal coliform are below
1,000 MPN per gram. Yanko's data show that when the log fecal coliform density was below 3,
the frequency of detection measurements were uniformly distributed in the range of 0 to 3. It is
reasonable to expect that the same behavior will occur in future measurements. In this case, the
expected frequency of detection can be calculated, using the relationship in Figure 4-1, to be
about 2 in 100.
Both estimates show that if fecal coliform densities are below 1,000 MPN per gram, the
ikelihood of salmonellae detection is low. As noted earlier, when fecal coliform density was low
md salmonellae were detected, the salmonellae densities were low. For these reasons—low
ikelihood of occurrence and low density when detected—a fecal coliform density of 1,000 MPN
oer gram indicates that regrowth has not occurred to a substantial extent and that salmonellae
ire unlikely to be present.
Anecdotal reports suggest that some composted sewage sludges may have difficulty
neeting the requirement of below 1,000 MPN fecal coiiform per gram even when salmonellae
ire never detected. This might be expected under several circumstances. For example, very
severe thermal treatment of sewage sludge during composting can totally eliminate salnjonellae
/et leave residual fecal coliforms. If the sewage sludge has been poorly composted and thus is a
»ood food source, fecal coliforms may have regrown after the compost cooled down from
hermophilic temperatures. Because the salmonellae are absent, they cannot regrow. An even
nore probable circumstance could occur if the sewage sludge had been treated with lime before
•omposting. Lime effectively reduces salmonellae in sewage sludge to below detectable limits
4-6
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LOG FECAL COLIFORM DENSITY
Figure 4-1: Relationship between Log Fecal Coliform
Density and Fraction of Salmoneilae Detections
(based on Yanko [1988] Weekly Data)
4-7
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and leaves surviving fecal coliforms (Farrell et al., 1974). Under conditions favorable for
regrowth, the fecal coliforms can regrow to levels higher than 1,000 MPN per gram, but
salmonellae, once totally eliminated, can never regrow.
For this reason, Part 503 allows use of a test to determine that Salmonella sp. are below
detectable limits as a substitute for meeting the fecal coliform requirement. This approach uses
salmonellae as an indicator of the reduction of bacterial pathogens to below detectable limits
rather than of the presence of bacterial pathogens.
4.4 CLASS A, ALTERNATIVE 1—FOR THERMALLY TREATED SEWAGE SLUDGES
[503.32(a) (3)]
This alternative may be used when the pathogen reduction process uses specified time-
emperature regimes to reduce pathogens. Under these circumstances, tests for the presence of
ipecific pathogens can be avoided. It is only necessary to demonstrate (1) that fecal coliform
densities are below 1,000 MPN per gram of total solids (dry weight basis) or, alternatively, that
Salmonella sp. are below detection limits, and (2) that the required time-temperature regimes are
•net.
Four different time-temperature regimes are given in Alternative 1. These regimes are
>ased on the percent solids of the sewage sludge and on operating parameters of the treatment
process. Experimental evidence (described in Sections 4.4.2-4.4.5) demonstrates that these four
ime-temperature regimes are adequate for reduction of the pathogenic organisms to below
detectable limits.
The time-temperature requirements specified apply to every particle of sewage sludge
processed. Time at the desired temperature is readily determined for batch operations, turbulent
low in pipes, or even laminar flow in pipes (time of contact is one-half the contact time
•alculated from the bulk throughput rate). Time can be calculated for a number of completely
nixed reactors in series, but for the very large reductions required to reduce densities to below
4-8
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detection limits, the required time for this type of processing would require so many reactors in
series as to be totally impractical.
The fecal coliform and Salmonella sp. requirements in this alternative are designed to
ensure that the microbiological reductions expected as a result of the time-temperature regimes
have actually been attained, and to ensure that regrowth of bacterial pathogens has not occurred.
Sections 4.4.1-4.4.5 below discuss the individual microbiological and time-temperature
requirements that comprise Alternative 1.
4.4.1 Microbiological Monitoring to Demonstrate Pathogen Reduction [503.32(a)(3)(i)]
For processes that reduce pathogens through elevated temperature, Part 503 sets a fecal
xiliform density of 1,000 MPN per gram of solids or, alternatively, a reduction of salmonellae to
?elow detection limits of 3 MPN per 4 grams of solids as the means to demonstrate that enteric
.druses, viable helminth eggs, and pathogenic bacteria in the sewage sludge have been reduced to
5elow detectable limits. (As discussed in Section 4.3.2, this monitoring also protects against the
Tossibility of regrowth.)
4.4.1.1 Fecal Coliform as an Indicator
There is ample research information that demonstrates that the pathogens of concern are
•educed to below detection limits before the fecal coliform densities are reduced to 1,000 MPN
?er gram of solids. Results of studies by Lee et al. (1988) and by Yanko (1988) show that
lelminths are easily reduced by temperatures above 50°C under time-temperature conditions
hat leave high density levels of fecal coliforms. Martin et al. (1990) showed that at temperatures
ibove 35°C, virus density decline in log density per unit time is more rapid than the decline in
ndicator organism densities. Fecal coliforms start out with densities of about 100 million per
;ram versus about 1,000 per gram for viruses. When the fecal coliform have been reduced by
ibout a factor of 100,000 by the thermal treatment, it is expected that viruses will have been
4-9
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reduced by a least a factor of 1,000. Yanko (1988) analyzed several hundred samples of sewage
sludge composted at temperatures exceeding 55°C. Viruses and viable helminth ova were not
detected in any of the samples, whereas fecal coliforms were present at levels exceeding 1,000
MPN per gram, even shortly after processing (that is, with no opportunity for regrowth).
4.4.1.2 SalmoneUae as an Indicator
The Alternative 1 microbiological requirement also allows demonstration that salmonellae
are below detection limits to indicate that other bacterial pathogens, enteric viruses, and viable
nelminth ova are below detection limits. Yanko's (1988) results discussed for fecal coliforms in
Compost samples in Section 4.4.1.1 above are strong evidence that salmonellae frequently survive
'or regrow, or are introduced by contamination and then regrow) composting at what nominally
*ere EPA's thermal requirements (see the composting requirement in the technologies listed
under 40 CFR Part 257); whereas viable helminth ova and viruses were never found. Yanko's
iata also indicate that, when fecal coliform are at a density of 1,000 MPN/gram of solids or
ower, salmonellae are generally below detection limits or are occasionally detected (see
discussion of Yanko data in Section 4.3.2).
Absence of salmonellae is not quite as good as indicator of presence of pathogens as are
ecal coliforms at 1,000 MPN/gram, but it has the important advantage that salmonellae are
uobably the pathogen of greatest concern. For the salmonellae requirement to be effective as
in indicator of the absence of pathogens, salmonellae must be present in the incoming
vastewater solids to a treatment works. This is common enough in all treatment works that
•outine monitoring of the sewage sludge for salmonellae will detect failure of the process to
•educe pathogens.
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4.4.2 Time-Temperature Alternative 1(A)—For Sewage Sludges with at Least 7-Percent
Solids [503J2(a)(3)(ii)(A)] ^
The time-temperature requirement for sludges with solids contents of 7 percent or higher
is given in Equation 1:
D = (131,700,000) / (lO*140*) (eq. 1)
where: D = time required in days
t = temperature in °C
rhe temperature must be at least 50 °C and the time at least 20 minutes. This requirement does
lot apply when small particles of sewage sludge are heated by either warmed gases or an
mmiscible liquid [such cases are covered by Alternative 1(B) — see Section 4.4.3, below].
4.4.2,1 Explanation of Time-Temperature Equation
The thermal condition required under Alternative 1(A) is similar to the thermal
•equirements in 40 CFR Part 257. Part 257 contains two time-temperature conditions which, if
net, are expected to reduce pathogens of concern to below detection limits.
• Pasteurization by treatment at 70 °C for 30 minutes.
• Composting at 55°C for 3 days.
The pasteurization condition of 70°C for 30 minutes is based on German
•ecommendations and practice. Recommended values (IRGRD, 1968) were 20-25 minutes at
70°C, but practice settled on 30 minutes at 70°C (Barker, 1970).
The requirement to compost for 3 days at 55°C was based on the recommendation of
Surge et'a'l. (1978). This group developed a predictive equation (Burge et al., 1980) based on
he effect of temperature on reduction in density of bacteriophage f-2, an organism with much
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greater resistance to elevated temperatures than any of the pathogens of concern in sewage
sludge. Die-off data for the bacteriophage were determined in a tryptone yeast extract medium
and not in sewage sludge. The predicted log reduction at 3 days and 55 °C was about 23 logs,
which is extremely conservative. Surge et al. (1978) suggested that, because composting was
done in the field with limited ability to assure that all parts of the composting pile achieved the
desired temperature, this conservatism was necessary. In later research of a field compost
operation, Burge and coworkers (ARS, 1982) showed that, at average temperatures around 55 °C,
the f-2 bacteriophage was easily destroyed. Surprisingly, fecal and total coliform survival was
greater than survival of the bacteriophage, despite their expected poorer thermal resistance. At
least in this instance, the conservatism of the recommended requirement appeared warranted.
Figure 4-2 compares EPA's time-temperature requirements for Class A Alternative 1(A)
to data drawn from the literature by Feachem et al. (1983) for the organisms of concern in
sewage sludge, and to the U.S. Department of Health and Human Services requirements for
eggnog (1989). A third EPA time-temperature requirement—5 days at 53 °C—is shown on
Figure 4-2. Burge et al. (1978) showed that this condition is equivalent to 3 days at 55°C. As
previously mentioned, the EPA curve for sewage sludge requires about a 5°C higher temperature
than suggested by Feachem et al. and is clearly conservative. It is similar to the requirements for
eggnog, a food product with flow characteristics similar to sewage sludge and which, like sewage
sludge, contains ingredients that might protect organisms against heat.
The FDA requirements and the estimates of Feachem et al. indicate a linear relationship
between the temperature in degrees Celsius and the logarithm (base 10) of time of exposure.
Consequently, a straight line was constructed through the points at the extremes of the EPA
curve in Figure 4-2 (70°C, log 1/48 day) and (53°C, log 5 days). The resulting equation was
rearranged, converting from logarithmic to exponential form, and is given in Equation 1.
4.4.2.2 Explanation of Restrictions
The use of Equation 1 is restricted to times greater than or equal to 20 minutes and to
temperatures greater than or equal to 50°C. The reason for the minimum time of 20 minutes is
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that it is difficult to heat a sewage sludge with higher solids than 7 percent uniformly. Sewage
sludge of this consistency forms an internal structure that inhibits the mixing caused by the
thermal and hydraulic gradients that contribute to uniform distribution of temperature.
The restriction to temperatures of at least 50°C is imposed because information on the
temperature-time relationship at lower temperatures is uncertain. For example, Brannen et al.
'1975) report that Ascaris ova are destroyed quickly at temperatures over 51°C but are
unaffected by long exposure at 47°C, indicating that much longer times than expected could be
required to inactivate viable helminth ova at temperatures below 50 °C.
4.4.3 Time Temperature-Alternative 1(B)—For Sewage Sludges with Suspended Small
Particles and at Least 7-Percent Solids [50332(a)(3)(ii)fB)]
This alternative applies to sewage sludges with 7 percent or higher solids content that are
;mall particles heated by contact with either warmed gases or an immiscible liquid. For these
sewage sludges, Equation 1 is applied to times not less than 15 seconds and temperatures not
ess than 50°C. Two examples of sewage sludges to which this requirement applies are:
• Sewage sludge cake that is mixed with previously dried solids to make the entire
mass a mixture of separate particles, and is then dried by contact with a hot gas
stream in a rotary drier.
• Sewage sludge dried in a multiple-effect evaporator system in which the sewage
sludge particles are suspended in a hot oil that is heated by indirect heat transfer
with condensing steam.
The reason for the restriction of the use of Equation 1 to temperatures not less than
50°C is explained in Section 4.4.2 above. The time at temperature of 15 seconds or more is
illowed because heat transfer between particles and the heating fluid is excellent. Uniformity of
emperature of the sewage sludge particles is expected to be excellent. Note that the
emperature is the temperature achieved by the sewage sludge particles, not the temperature of
he carrier medium.
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The minimum time selected is not unusually short. For example, a minimum time of
contact of 15 seconds is also allowed by FDA for pasteurization of eggnog (U.S. Department of
Health and Human Services, 1989), but much shorter times are allowed for milk (0.01 seconds at
100 °C or greater).
4.4.4 Time-Temperature Alternative 1(C)—For Sewage Sludges with Less Than 7-
Percent Solids and Less Than 30 Minutes Contact Time [503J2(a)(3)(ii)(C)]
If sewage sludge has less than 7-percent solids content, Equation 1 is used for the time-
temperature relationship. The equation applies for times greater than or equal to 15 seconds,
but less than 30 minutes. The maximum time of less than 30 minutes is specified because, as
explained in Section 4.4.5 below, a less stringent condition applies for times above 30 minutes.
Insufficient information is available to apply this less stringent condition to times less than 30
minutes.
The minimum time of 15 seconds is allowed because the sewage sludge with less than 7-
percent solids does not develop the internal structure that inhibits development of a uniform
•.emperature within the sewage sludge when it is heated. As noted in Section 4.4.2 above, the
FDA has applied this same minimum time to eggnog—a material of comparable viscosity to 7-
sercent solids sewage sludge.
Suggested German standards for pre-pasteurization at contact times of 30 minutes or less
are presented in Table 4-1 (see discussion of this table in Section 4.4.5 below). At contact times
,ess than 25 minutes, the German standards are more stringent than those required by Equation
1. They are also more stringent than the standards required by FDA to process eggnog.
Probably the German requirements were made excessively stringent to allow for less- than-
oerfect plug flow in the pre-pasteurizer, or for the presence of large clumps of sewage sludge.
Because each particle of sewage sludge has to achieve the desired time-temperature conditions
ind it is not unusually difficult to meet these conditions for a sewage sludge with less than 7-
jercent solids, the high degree of conservatism in the suggested German standards is not
.varranted for the Part 503 requirements.
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TABLE
GERMAN RECOMMENDED STANDARDS1 FOR PRODUCING
HYGEENICALLY SAFE SEWAGE SLUDGE COMPARED WITH THE TIME-TEMPERATURE
REQUIREMENTS OF EPA'S EQUATIONS 1 AND 2
Process
Pre-pasteurization
Aerobic thermophilic
digestion
Time
30 min.
25 min
20 min.
10 min.
20 hr.
10 hr.
.4hr.
Temperature (°C)
German
Standard
65
70
75
80
50
55
60
Equation 1
70
70.6
71.3
73.4
Equation 2
67
55.1
57.7
60,6
Recommendations of a Joint Working Group of the German Association for Wastewater
Technology (Abwassertechnische Vereinigung) and the Association of Public Cleansing
Enterprises (Verband Kommunaler Stadreiningungsbetriebe). See D. Strauch, 1987.
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4.4.5 Time-Temperature Alternative 1(D)—For Sewage Sludges with Less Than 7-
Percent Solids and at Least 30 Minutes Contact Time at 50°C or Higher
[503.32(a)(3)(n)(D)]
The time-temperature requirement for sewage sludges with less than 7-percent solids and
at least 30 minutes contact time at 50 °C or higher is given by Equation 2:
D = (50,070,000) / (lO9-140*) («!• 2)
where: D = time required in days
t = temperature in °C
Equation 2 is similar to Equation 1 except that, for any given time, the temperature calculated by
Equation 2 is 3°C lower than the temperature calculated by Equation 1. It is the equation of a
straight line through the points (67°C, log 1/48 day) and (50°C, log 5 days), with the resulting
ogarithmic equation converted into exponential form.
As noted in Section 4.4.2.1, the time-temperature relationship given by Equation 1 is
xmservative. Conservatism is required because sewage sludges with 7-percent or higher solids
xintent may be pasty masses or clumps of particles several inches in diameter that are very
difficult to bring to uniform temperatures. For sewage sludges with less than 7-percent solids,
•vhich are easier to bring to uniform temperatures, a less conservative time-temperature
•elationship, such as that given in equation 2, is reasonable.
Some years ago, Swiss and German requirements that sewage sludge be disinfected before
ipplication to pasture land sparked substantial research in the microbiological performance of
ire-pasteurization of sewage sludge before digestion and thermophilic aerobic digestion (TAD)
hat resulted from this research. These conditions have been verified by several studies. For
TAD, Strauch (1988) has shown 100,000-fold reductions in enterobacteriaceae at time-
emperature regimes consistent with the German standard. Fecal coliforms are
mterobacteriaceae and would therefore have similar behavior. Salmonellae would also behave in
his manner. Strauch et al. (1975) observed the complete destruction of salmonellae at a pilot
ilant operated within these time-temperature limits. Albrecht and Strauch (1978) showed that
nteric viruses are destroyed by these conditions. These investigators observed that elevated pH
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level (above 7) and the presence of sewage sludge (as compared to results on enteric viruses in
ampoules protected from the sewage sludge) increased the rate of reduction of enteric virus
densities. Several investigators, including Lee et al. (1989), have shown destruction of Ascaris sp.
ander these conditions.
As Table 4-1 shows, the temperatures at a given time from Equation 2 for sewage sludges
of less than 7-percent solids and 30 minutes treatment or longer exceed the suggested German
standards. The additional safety factor provided by the higher temperatures has been included in
:he U.S. standard because some effects (e.g., the effect of pH on enteric virus reduction) are not
veil understood.
1.5 CLASS A, ALTERNATIVE 2—FOR SEWAGE SLUDGE FROM A HIGH pH-
HIGH TEMPERATURE PROCESS [503.32(a)(4)]
Part 503.32(a)(4) describes the conditions of a process scheme recommended by EPA's
r'athogen Equivalency Committee as equivalent to the Processes to Further Reduce Pathogens
PFRPs) listed in Appendix II of Part 257. This process, described in an EPA guidance
locument (EPA, 1989a), successfully reduces pathogens to below detectable limits. Part
>03.32(a)(4) describes the. process conditions, which include elevating pH to greater than 12 for
72 hours, maintaining the temperature above 52°C for at least 12 hours, and then air drying to
wer 50-percent solids. The hostile conditions of high pH and high temperature allow a variance
o a less severe time-temperature regime than EPA's thermal condition requirements described
ibove. It is only necessary to determine that either fecal coliform densities are reduced to less
han 1,000 MPN/g or that Salmonella sp.,densities are reduced to less than 3 MPN per 4 grams
)f total sewage sludge solids to ensure that pathogens have been reduced to below detectable
evels and regrowth has not occurred (see Section 4.4).
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4.6 CLASS A, ALTERNATIVE 3—FOR SEWAGE SLUDGE FROM OTHER PROCESSES
[503J2(a)(5)]
Part 503.32(a)(5) applies to processes used to treat sewage sludge to meet the Class A
requirements that do not meet EPA's thermal conditions. For a sewage sludge to be Class A,
either the fecal coliform requirement of less than 1,000 MPN/g or salmonellae density
requirement of less than 3 MPN/4 g must be met. The treated sewage sludge must also meet a
requirement of less than 3 PFU/4 g for enteric viruses and less than 1/4 g for viable helminth
ova. Testing for these latter organisms can be complicated by the fact that sometimes they are
not detected in the untreated sewage sludge. When this happens, it is not possible to
demonstrate that the process is able to reduce these organisms to below detection limits. Part
503.32(a)(5) includes an approach devised to overcome this difficulty.
If, for example, enteric viruses are not found in the sewage sludge that enters a
stabilization process (i.e., the feed sewage sludge), the sewage sludge is presumed to be Class A
antil the next time samples of the sewage sludge are tested. No statement is made about the
oathogen-reducing process as yet. Monitoring is continued until enteric viruses are found in the
'eed sewage sludge. At that time, the treated sewage sludge is analyzed to see if enteric viruses
;urvive the treatment. If densities are below detection limits, the process meets Class A
•equirements. Monitoring of this type is continued until the required pathogen reduction is
iemonstrated, unless otherwise specified by a permitting authority. For the sewage sludge to
xmtinue to be Class A, the process must be operated under the same conditions that successfully
•educed densities in the treated sewage sludge to below detection limits. The procedure to be
bllowed when viable helminth ova are not detected in the untreated sewage sludge is the same
is for enteric viruses.
One problem can still cause difficulty. Tests for enteric viruses and viable helminth ova
ake substantial time: 2 weeks to determine whether helminth ova are viable, and 2 weeks or
onger for enteric viruses. The operator does not know whether the feed sewage sludge has
mteric viruses or viable helminth ova until 2 or more weeks after the first samples were taken.
["he solution to this problem is to sample both the feed sewage sludge and the same batch of
ewage sludge after treatment during each monitoring episode and to preserve the samples of
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treated sewage sludge until results of the feed sewage sludge analysis indicate whether analysis of
the treated sewage sludge is necessary. For enteric viruses, the sewage sludge should be stored
frozen. For viable helminth ova, the sewage sludge should be stored at about 4°C.
An advantage of this approach is that it reduces analytical costs. After the pathogen
reduction is demonstrated, only the process parameters have to be monitored.
4.7 CLASS A, ALTERNATIVE 4—FOR SEWAGE SLUDGE FROM UNKNOWN
PROCESSES [503J2(a)(6)]
Part 503.32(a)(6) has been introduced into the Part 503 regulation to handle cases where
either a process in which the sewage sludge is treated is not known, the sewage sludge was
:reated by a process operating at conditions less stringent than the operating conditions at which
:he process qualified as Class A, or the past history of the sewage sludge is not known. This
ilternative requires that the sewage sludge be monitored for (1) fecal coliform or salmonellae,
'2) enteric viruses, and (3) viable helminth eggs. The enteric virus requirement or the viable
iclminth egg requirement may be waived at the discretion of the permitting authority. An
example of a situation where waiving some requirements is appropriate would be a pile of
;ewage sludge that had been stored for many years. If fecal coliform densities are sufficiently
ow, enteric virus survival is unlikely. In such a case, the permitting authority may waive the
•equirement to test for enteric viruses, but would probably insist on measuring viable helminth
igg densities.
t.8 CLASS A, ALTERNATIVE 5—USE OF PFRPs [503 J2(a)(7)]
Under Part 503.32(a)(7), sewage sludge is considered to be Class A if it is treated in one
)f the Processes to Further Reduce Pathogens (PFRPs) listed in Appendix B of the regulation
md if the treated sewage sludge meets the following microbiological requirements: fecal
•oliform density of less than 1,000 MPN per gram,of total solids (dry weight basis) or Salmonella
.p. density of less than 3 MPN per 4 grams of total solids (dry weight basis).
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This requirement is similar to the PFRP requirement in the Part 257 regulation. The
PFRP list in Appendix B of Part 503 differs from the PFRP list in Part 257 in that all
requirements related to vector attraction reduction have been removed (the sewage sludge must
low separately meet the vector attraction reduction requirements of Part 503). The processing
aDnditions required for the processes listed in the Part 257 regulation are expanded in an EPA
oublication (EPA, 1989a). Background for the choice of these conditions is given by Farrell
1980).
The Part 503 requirement also differs from the PFRP requirement in Part 257 in that
nicrobiological monitoring is now required. The implicit microbiological goal a PFRP process is
expected to meet is reduction of pathogenic bacteria, enteric viruses, and viable helminth ova to
Delow detectable levels. Under Part 257, no microbiological monitoring was required and
.herefore very little information has been collected since the publication of Part 257 on whether
sewage sludge of the desired microbiological quality was being produced by the PFRPs. To fill
his information gap, an experimental program that focussed primarily on composted products
vas carried out by Yanko (1988). This investigation showed that pathogenic bacteria
salmonellae) were frequently observed in composted sewage products that presumably had met
he required processing conditions.
Consequently, based on these results and a lack of confidence that a pure technology-
)ased standard was adequate, a microbiological monitoring requirement has been added in the
?art 503 regulation. The monitoring required for the PFRPs is the same as is required for the
)ther Clajs A alternatives—reduce fecal coliform density to below 1,000 MPN/gram or
•almonellae to below 3 MPN/gram (see Section 4.4.1). When either of these requirements is
net, the potential for regrowth of Salmonella sp. bacteria is mitigated.
One of the processes described in Appendix B to Part 503 is aerobic digestion for 10 days
it 55 to 60°C. Appendix B does not specify how to operate this process. Conceivably, it could
ic operated as a well-mixed continuously fed reactor, in which case it would probably not
ichieve the desired pathogen reduction. The original communication (Farrell, 1980) supporting
ise of this process as a PFRP stated that the process should be operated to avoid by-passing,
xjssibly by staging the reactors. It is more effective to avoid by-passing by using draw-and-fill
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feeding, and this procedure should be used with thermophilic aerobic digestion. If operation is
not correct and by-passing does occur, the monitoring requirement will reveal the deficiency.
As has been noted in Section 2.6.2, reductions;in indicator organism densities to low
values are not a good indicator of equivalent reductions in viral densities when the sewage sludge
is treated by high-energy irradiation. Effectiveness of high-energy radiation in deactivating
organisms is inversely related to organism size, so enteric viruses are reduced to a lesser degree
by a given radiation dose than bacteria. Nevertheless, the specified radiation dose of 1 megarad
specified in Appendix B of Part 503 is an extremely conservative dose that was chosen to ensure
:hat no enteric viruses survive. In addition, there is very little uncertainty in the design of an
rradiation process. If the dose is being delivered, the pathogens will be reduced to below
detectable limits.
1.9 CLASS A, ALTERNATIVE 6—USE OF PROCESSES EQUIVALENT TO PFRPs
[S0332(a)(8>]
This alternative is similar to Alternative 5, described above. Under Part 503.32(a)(8),
.ewage sludge is Class A if treated in any process that is equivalent to a Process to Further
Deduce Pathogens and if the treated sewage sludge meets the following microbiological
-equirements: fecal coliform density of less than 1,000 MPN per gram of total solids (dry weight
>asis) or Salmonella sp. density of less than 3 MPN per 4 grams of total solids (dry weight basis).
The Part 257 regulation also allowed use of processes determined to be equivalent to
DFRPs. However, the Part 257 regulation did not require any microbiological monitoring. This
las been added under Part 503 to address regrowth of pathogens.
Under Part 257, recommendations on the equivalency of a process were made by EPA's
3athogen Equivalency Committee (PEC) to the permitting authority. The permitting authority
nade the final determination on equivalency based on the PEC's recommendation. The Part 503
egulation also indicates that equivalency determinations will be made by the permitting
luthority.
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SECTION FIVE
PART 503 CLASS B PATHOGEN REQUIREMENTS
5.1 INTRODUCTION
This section provides explanations and justifications for the Class B pathogen
requirements in subpart D of the Part 503 regulation. These requirements include pathogen
reduction requirements and site restrictions. All Class B sewage sludges also must meet one of
the requirements for vector attraction reduction (see Section 6).
The Class B pathogen requirements for sewage sludge can be met in three different ways.
The implicit objective of all three alternatives is to ensure that pathogenic bacteria and enteric
viruses are adequately reduced in density. Farrell et al. (1985) have shown that, if treated
sewage sludge has a fecal coliform density of 2 million or less MPN or CPU per gram of total
sewage sludge solids, pathogenic bacteria and enteric viruses are reduced. Comparing pathogenic
densities in the influent of a treatment works to pathogenic densities in treated sewage sludge
solids, the 2 million MPN or CPU value represents a reduction of over 2 logs (a factor of 100) in
fecal coliform densities, and is expected to result in a reduction of approximately 1.5 logs in
Salmonella sp. bacteria densities and 1.3 logs in enteric virus densities. The three alternatives for
meeting the Class B pathogen requirements are discussed in Sections 5.2 and 5.3. Site
restrictions are presented in Section 5.4, and pathogen requirements for domestic septage are
discussed in Section 5.5.
5.2 CLASS B, ALTERNATIVE 1—MONITORING OF INDICATOR ORGANISMS
[503.32(b) (2)]
5.2.1 Explanation of Requirement
Class B, Alternative 1 requires that seven samples of sewage sludge that is used or
disposed be collected, and that the geometric mean fecal coliform density of these samples be
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less than 2,000,000 CFU or MPN per gram of sewage sludge solids. As noted in Section 5.2.2
below, the absolute value of the fecal coliform density of a sewage sludge treated in processes
typically used to achieve Class B pathogen reduction is expected to correlate well with average
density of bacterial and viral pathogens in the sewage sludge. Because methods used to
determine fecal coliform density (membrane filter method and the MPN dilution method) have
poor precision and sewage sludge quality varies, at least seven separate samples must be analyzed
;
to reduce the standard error. (
When the Class B fecal coliform value is met (a log mean of 6.3, which is equivalent to a
geometric mean of 2,000,000), the true mean value lies within a confidence interval that depends
on the experimentally determined log standard deviation (i.e., s) of the fecal coliform
determinations. If s = 0.3, which is what would be expected for measurements taken over a 2-
week period using the membrane filter method, the 95-percent confidence interval of the true log
mean is 6.08 (1,200,000 CFU/g) to 6.52 (3,300,000 CFU/g). If s > 0.3, the confidence interval is
larger and there is less assurance that the sewage sludge meets the criterion.
5.2.2 Fecal Coliform Density as an Indicator of Pathogen Reduction
The 503.32(b)(2) requirement assumes that the absolute value of the fecal coliform
density correlates well with the average density of bacterial and viral pathogens. This section
provides the rationale for that assumption. Farrell et al. (1990) showed that the incoming
wastewater solids from several Midwestern treatment works had almost the same indicator
organism densities. This finding was verified by Oliveri et al. (1989) for several treatment works
in the vicinity of Philadelphia. Fecal indicator organisms in raw wastewater are one-to-one
indicators of fecal matter in untreated wastewater. As such, they should be accurate indicators
of pathogen densities over the long term. It turns out that all wastewater solids, rather than all
sewage sludges, are about equal (in the long term) in pathogen content.
Assuming that fecal indicators after sewage sludge is treated are good indicators of
oathogens, their absolute density after treatment should be a good indicator of pathogen density.
Examination of the data (Farrell et al., 1985, 1990) showed that if the treated sewage sludge had
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a fecal coliform density of 2 million MPN or CPU per gram, pathogenic enteric viruses and
bacteria would be reduced. The data also showed that most treatment works practicing
conventional stabilization processes could reach this goal. Comparing densities in suspended
solids in the entering wastewater to densities in solids in treated sewage sludge, there is a fecal
coliform reduction of over a factor of 100, and an expected reduction in salmonellae and enteric
virus densities of about 1.5 logs and 1.3 logs, respectively.
The assumption that fecal coliform densities after processing are good indicators of
oathogen densities needs to be examined. For conventional biological sewage sludge treatment
processes such mesophilic aerobic and anaerobic digestion, information is available that shows
hat pathogenic bacteria and virus densities fall in proportion to the relative reduction in fecal
ndicator organism densities. Martin et al. (1990) obtained data on the relative declines in fecal
ndicators and animal viruses for aerobic digestion at temperatures from 8 to 40 °C. In the
emperature range of 15 to 31 °C, the reductions did not show marked trends with temperature.
Ratios of log reductions for fecal indicators relative to log reductions for viruses were calculated
or seven temperatures in this temperature range. Average ratios and standard error of the
nean are shown in Table 5-1, and are compared with Farrell et al.'s (1985) data for anaerobic
digestion at 35°C. The differences in the effects on virus and indicator organism densities
Between anaerobic and aerobic processes are not great. Fecal coliform densities decline about
1.5 times more rapidly than viral densities. The agreement between declines in fecal
treptococcus and viral densities is very good. These results demonstrate that, for aerobic and
maerobic processes in the commonly used temperature ranges, a decline in fecal indicator
tensities can be used to indicate declines in enteric viruses. Results of investigations by Farrah
•t al. (1986) for aerobic digestion and by Farrell et al. (1985) for anaerobic digestion show
ipproximately a 1.2-log decline for fecal coHform to 1.0-log decline for salmonellae, indicating
hat for this representative bacterial pathogen, a decline in fecal indicator densities can be used
o indicate declines in bacterial pathogen densities.
For treatment processes operated at temperatures higher than 35°C, available
nformation (Martin et al., 1990; Berg and Berman, 1980) indicates that viruses fall faster than
ndicators fall. However, bacterial and viral reductions are much greater than 2 logs at
hermophilic temperatures.
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TABLE 5-1
COMPARISON OF REDUCTIONS IN FECAL INDICATOR DENSITIES TO
REDUCTIONS IN VIRAL DENSITIES DURING AEROBIC DIGESTION AND
MESOPfflLIC ANAEROBIC DIGESTION
Organism
Total coliform
Fecal coliform
Fecal streptococci
Ratio of log density of indicator organism to log density of viruses
Aerobic Digestion
(15-31°C)1
1.31 ± 0.17
1.17 ±0.15
0.96 ±0.12
Anaerobic Digestion
(35°C)2
2.01
1.92
1.07
Calculated from results by Martin et al. (1990).
Calculated from results reported by Farrell et al. (1985).
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Chemicals such as lime, chlorine or ozone are sometimes used to treat sewage sludge,
generally to produce a combined result of pathogen reduction and vector attraction reduction.
The chemical doses required to reduce vector attraction also produce great reductions in
pathogen and indicator densities. For example, for lime treatment, results by Counts and
Shuckrow (1975) and Strauch (1982) show that bacterial and viral densities are greatly reduced
when pH exceeds 12.
53 CLASS B, ALTERNATIVES 2 AND 3—USE OF PSRP AND EQUIVALENT
PROCESSES [503.32(b)(3) and (4)]
Under Alternatives 2 and 3, sewage sludge treated by one of the Processes to
Significantly Reduce Pathogens (PSRPs) listed in Appendix B of Part 503 or an equivalent
process is considered to be Class B. No microbiological monitoring is required. The permitting
authority is responsible for determining PSRP equivalency.
These requirements are similar to the requirements in Part 257 that allowed use of listed
PSRPs or equivalent processes. The PSRPs listed in Appendix B of Part 503 are essentially
identical to those listed in Part 257 except that all requirements that address reduction of vector
attraction have been removed (all Class B sludges must meet separate vector attraction reduction
requirements—see Section 6).
Though not specified in Part 257, the operating conditions of the PSRP processes were
set to reduce the densities of pathogenic bacteria and enteric viruses in the untreated sewage
sludge by approximately 1.0 log. This value was based on work by Berg and Berman (1980) and
Farrell et al. (1985), who showed that conventional anaerobic digestion produced reductions of
:his magnitude. Background information supporting the choice of conditions for the PSRP
orocesses was given by Farrell (1980).
Unlike the comparable Class A requirements (see Sections 4.7 and 4.8), Class B
Alternatives 2 and 3 do not require monitoring for fecal coliform or Salmonella sp. Monitoring
"or those organisms is extremely important for a Class A sewage sludge to demonstrate pathogen
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reduction and to ensure that regrowth has not occurred. Disease risk is not as high for Class B
sewage sludge, because site restrictions prevent the public from coming in direct contact with the
sewage sludge for a certain period of time. The Class B site restrictions, such as restriction of
access and harvesting of crops, provide important barriers separating the public from risk of
disease. Additionally, the presence in sewage sludge treated by PSRPs of competitive organisms
and/or other conditions that inhibit growth prevents the type of regrowth to high densities of
pathogenic bacteria that could occur with Class A sewage sludges.
5.4 SITE RESTRICTIONS [503J2(b)(5)]
Sewage sludge classified as Class B with respect to pathogens may still contain significant
densities of pathogenic bacteria, enteric viruses, and viable helminth eggs. Thus, site restrictions
are needed to reduce exposure to the sewage sludge. Site restrictions are discussed in this
section.
5.4.1 Food Crops That Touch the Sewage Sludge [503J2(b)(5)(i)]
Food crops with harvested parts that are totally above the land surface and likely to touch
:he soil/sewage sludge mixture cannot be harvested for 14 months after application of the sewage
dudge. For clarity, the term "harvested" has replaced the term "grown" used in Part 257.
Assuming that crops are harvested about 2 months after they are "grown" (i.e., planted),
:he Part 257 regulation effectively required 20 months before these crops could be harvested.
The Part 503 regulation requires only 14 months. Based on data on the relatively high rate of
die-off of viable helminth ova on the soil surface (Jakubowski, 1988), the Agency concluded that
.he 14-month period is adequate to protect public health and the environment.
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5.4.2 Food Crops Below the Soil Surface [503.32(b)(5)(ii) and (Hi)]
Part 503 requires that food crops with harvested parts below the soil surface not be
harvested for 20 months after sewage sludge application provided that the sewage sludge remains
on the soil surface for 4 months prior to incorporation in the soil. If the sewage sludge does not
remain on the soil surface for 4 months, food crops with harvested parts below the soil surface
:annot be harvested for 38 months after sewage sludge application. These site restrictions are
aased on results reported by Jakubowski (1988) which show that viable helminth eggs on the soil
;urface die off after 4 months' exposure on the soil surface, whereas their viability is prolonged
o several years if they are deeper in the soil.
The requirement of 20 months is 6 months longer for root crops than for crops that grow
ibove the surface. This additional time is required because the conditions of growth are so
•adically different for root crops. The above-ground environment is harsh for all pathogens,
vhereas the below-ground environment is benign by comparison. Additionally, the root crop is
iterally bathed in the soil, which may contain pathogens, whereas the above-ground crops only
>ccasionally contact dust or are splattered by rain-splash containing soil particles. The extra 4
nonths provides additional time to overcome the anticipated slower decline in pathogen densities
>elow ground and the increased exposure created by the intimate contact of the crop with the
.oil.
If 4 months of surface exposure is provided, the period between application and harvest is
!0 months. For a September 1994 harvest, sewage sludge could be applied to the soil surface up
o the end of December 1992, plowed or dished into the soil in the spring of 1993, and the crop
•ould be harvested in September 1994.
If surface exposure is less than 4 months, the period between sewage sludge application
tnd harvest is 38 months. Jakubowski's results indicate that survival of viable helminth eggs
•ould be 50 percent after 4 years in the soil in some cases. Long exposure is needed to reduce
isk. The Agency concluded that the 38-month period allows a long enough exposure to reduce
iable helminth ova to below detectable limits.
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5.43 Food Crops, Feed Crops, and Fiber Crops [503J2(b)(5)(iv)]
'-' r~ ' "S «
Food, feed, and fiber crops cannot be harvested for 30 days after application of sewage
sludge. Crops become contaminated with sewage sludge when it is applied to the land. If these
crops are harvested in less than 30 days, they carry contamination into the outside environment.
As mentioned previously, 30 days is long enough for environmental factors such as sunshine,
rain, and desiccation to reduce the density of pathogens in sewage sludge adhering to the crops
to minimal levels. Hay is an example of a feed crop covered by this restriction.
5.4.4 Grazing of Animals [503 J2(b)(5)(v)]
Animals are not allowed to graze on the land for 30 days after application of sewage
sludge. Sewage sludge can adhere to animals that walk on sewage sludge-amended land shortly
after sewage sludge application and can then be brought to humans who come in contact with
the animals (for example, riding horses allowed to graze on sewage sludge-amended pasture).
The purposes of this requirement are prevention of disease in animals, prevention of
transmission of animals' disease to humans, and prevention of direct transmission of disease
organisms in sewage sludge to humans.
Grazing animals are primarily exposed to sewage sludge that has adhered to vegetation.
They would not be grazed on barren or muddy surfaces. As Kowal and others have noted (see
Section 2.2.2), pathogens adhering to vegetation typically are reduced in densities to low values
within about 30 days of exposure of the surface of the vegetation.
5.4.5 Growing of Turf [503 J2(b)(5)(vi)]
Turf grown on land to which sewage sludge has been applied cannot be harvested for 1
/ear after application if the turf is placed either on a lawn or on land with high potential for
oublic exposure. Such uses involve a high potential for human contact with the turfs soil layer.
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The 1-year period allows the environment to reduce the pathogens in the sewage sludge (see
Section 5.4.6 below).
5.4.6 Public Access to Sites on Which Sewage Sludge Is Applied
[50332(b)(S)(vii) and (viii)]
Access is restricted for 1 year after sewage sludge application to land with a high
xrtential for public exposure. This period of restricted access is the same as in the Part 257
•egulation. It protects against exposure to the hardiest pathogens (i.e., the viable helminth eggs,
vhich might survive for long periods on the land surface). If the land has a low potential for
jublic exposure, the period of restricted access is 30 days.
The difference between high and low potential for public exposure is generally evident.
\ farm field used to grow corn or soybeans is an example of a low potential for public exposure.
2ven the farm family itself walks about very little on such fields. On the other hand, a baseball
liamond or a soccer field gets heavy use, and contact with the soil is substantial (players fall on
t and dust is raised which is inhaled and ingested).
?.S DOMESTIC SEPTAGE [503.32(c)(l) and (2)]
Under Part 503.32(c), the potential public health risk associated with pathogens in
lomestic septage applied to agricultural land, forest, or a reclamation site may be controlled in
me of two ways:
• Either site restrictions under 503.32(b)(5)—see Section 5.4, above—have to be
met,
• Or pH of the domestic septage has to be raised to 12 and maintained at 12 for 30
minutes and the site restrictions discussed above in Sections 5.4.1 to 5.4.3
concerning harvesting of crops have to be met.
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When domestic septage is applied to other types of land, the pathogen requirements for sewage
sludge have to be met.
5.5.1 Site Restrictions
For untreated domestic septage, pathogen control is accomplished through the site
restrictions. Site restrictions prevent exposure to the domestic septage for a certain period of
time so that the environment can reduce the pathogens in sewage sludge. The site restrictions
that have to be met are the same site restrictions that have to be met when a Class B sewage
sludge is applied to the land.
5.5.2 pH Adjustment with Site Restrictions for Crop Harvesting
A pH adjustment reduces pathogenic bacteria and enteric virus densities to low levels.
Although the time required by Part 503 for the pH of domestic septage to remain at 12 is less
» '
:han the 2 hours required for the lime stabilization PSRP, the lower time (i.e., 30 minutes)
oroduces pathogen reduction that exceeds the pathogen reduction requirements for a Class B
sewage sludge. Data obtained by Farrell et al. (1974) and literature cited by them indicate that
3.5-hour contact at pH 12 produces a much greater reduction in bacterial and enteric viral
densities than is achieved by conventional anaerobic digestion, which is a PSRP in Appendix B of
Part 503. Research at the University of Wisconsin (Ronner and Cliver, 1987) on destruction of
/iruses by lime treatment of sewage sludge strongly supports this conclusion.
Restrictions on harvesting of crops are part of this requirement because the Agency
xincluded that pH adjustment alone does not reduce pathogens to the level required under Class
A. that would allow crops to be harvested immediately after applying domestic septage to the
and. Site restrictions are imposed to provide the environment time to reduce the pathogens in
he domestic septage.
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SECTION SIX
VECTOR ATTRACTION REDUCTION REQUIREMENTS
6.1 INTRODUCTION
Part 503.33 contains the requirements for vector attraction reduction in sewage sludge
applied to the land or placed on a surface disposal site. These requirements are designed to
ensure reduction of vector attraction either through some form of treatment [503.33(b)(l-8)J, or
by creating a physical barrier that prevents vectors from coming in contact with the sewage
sludge [503.33(b)(9-ll)].
Which requirements are applicable depends on the nature of the sewage sludge (e.g., bulk
sewage sludge, sewage sludge sold or given away in a bag or other container, or domestic
septage) and the use or disposal practice. In every case, only one of a range of allowable options
for demonstrating vector attraction reduction has to be selected.
This section describes and justifies the various vector attraction reduction requirements in
Part 503.33 of the regulation. The section is organized according to the specific paragraphs in
Subpart D, and uses the same numbering as the Part 503 paragraphs.
5.2 REDUCTION IN VOLATILE SOLIDS CONTENT [50333(b)(l)]
Under 503.33(b)(l), vector attraction reduction is achieved if the mass of the volatile
solids in the sewage sludge is reduced by at least 38 percent. (This requirement is the same as it
.vas in Part 257.) The percent reduction is measured from the stabilization process influent to
he sewage sludge that is used or disposed. This includes any additional volatile solids reduction
.hat occurs before the sewage sludge is used or disposed, such as might occur when the sewage
sludge is processed on drying beds.
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The method of volatile solids reduction is not, specified by Part 503 but is typically
achieved by anaerobic or aerobic digestion. These processes degrade most of the biodegradable
material to lower activity forms. Any biodegradable material that remains characteristically
degrades slowly—so slowly that the vectors that would be attracted to unprocessed sewage sludge
are not drawn to it.
This requirement was drawn from the Water Pollution Control Federation's Manual of
Practice No. 8 (Water Pollution Control Federation, 1967). This amount of volatile solids
reduction could be attained at the "good practice" recommended conditions for anaerobic
digestion of 15 days residence time at 35°C in a completely mixed high-rate digester. Volatile
solids reduction is calculated by a volatile solids balance around the digester or by the Van Kleek
formula (Fisher, 1984). EPA has provided guidance on methods of calculation (1992b).
63 ADDITIONAL DIGESTION OF ANAEROBICALLY DIGESTED SEWAGE SLUDGE
[503.33(b)(2)]
Under Part 503.33(b)(2), an anaerobically digested sewage sludge can be shown to have
achieved satisfactory vector attraction reduction if it loses less than 17 percent volatile solids
»vhen it is batch-digested further at 30 to 37°C for an additional 40 days.
Frequently, sewage sludges are recycled through the biological wastewater processes of a
treatment works or reside for long periods of time in the wastewater collection system. During
this time, they undergo substantial biological degradation. If they are subsequently treated by
anaerobic digestion for an adequate period of time, they achieve vector attraction reduction but.
Decause they entered the digester already partially stabilized, the volatile solids reduction is
frequently less than 38 percent. The additional digestion test is extremely useful in
demonstrating that these sewage sludges are indeed satisfactorily reduced in vector attraction.
This requirement is based on information obtained by Jeris et al. (1985). These
nvestigators demonstrated that most of their anaerobically digested sewage sludges could be
further digested to a modest degree, while a few of the sewage sludges showed much more ability
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to digest further. This "ability to digest further" is used as an index of ability to putrefy further
and attract vectors. Twenty to 40 days are needed to complete the determination. The time
requirement makes the alternative infeasible if a sewage sludge must be immediately used or
disposed, but is no obstacle to evaluating an operating process. The test must simply be started
20-40 days before the result is needed.
Jeris et al.'s data showed the following additional percent volatile solids reduction after
40 days of additional digestion for six digested sewage sludges samples taken from full-scale
treatment works: 9,10,13, 22, 36, and 38 percent. The three sewage sludges with the lowest
volatile solids (VS) reduction showed low volatile acid concentrations before the additional
digestion period commenced; the other three showed higher volatile acids, indicating poorer
digestion. The percent VS versus time curves essentially flattened out at 40 days, indicating the
samples were completely digested by this time. For purposes of the Part 503 regulation, a VS
reduction of 17 percent or less on additional batch 'digestion for 40 days was selected as adequate
evidence of satisfactory vector attraction reduction. The 17-percent value is midway between the
upper limit of well-digested samples and the lower limit of the poorly digested samples. This
•eduction is equivalent to the 38-percent volatile solids reduction, based on volatile solids
entering and leaving the digester. Research in progress by Farrell and Bhide (1992) using
iewage sludges digested for 10, 15, and 20 days nominal residence time supports this selection.
Procedures for the test suggested by Farrell and Bhide are presented in EPA (1992b). The use
jf the additional volatile solids reduction to demonstrate vector attraction reduction is allowable
or sewage sludges from anaerobic digestion that are unable to demonstrate 38-percent volatile
solids reduction.
>.4 ADDITIONAL DIGESTION OF AEROBICALLY DIGESTED SEWAGE SLUDGE
[503.33(b)(3)]
Under 503.33(b)(3), an aerobically digested sewage sludge of 2 percent or less solids
ichieves satisfactory vector attraction reduction if it loses less than 15-percent volatile solids
vhen it is batch-digested at 20°C for an additional 30 days.
• 6-3
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The circumstance in which a sewage sludge has been substantially reduced in biological
degradability before it is aerobically digested is veiy common, because aerobic digestion is the
stabilization process most frequently chosen for sewage sludges from extended aeration plants^
In these treatment works, nominal residence time of sewage sludges leaving the wastewater
treatment process generally exceeds 20 days. Consequently, it is difficult to demonstrate 38-
percent volatile solids reduction after aerobic digestion. The additional digestion test is valuable
in demonstrating adequate vector attraction reduction in these cases. The test can be run on
sewage sludges up to 2-percent solids. It does not require a temperature correction for sewage
sludges not initially digested at 20 °C. Details on the most desirable way to run the test are
provided in EPA (1992b).
This requirement is based on data from batch digestion tests on aerobically digested
sewage sludges (Jeris et al. [1985]). These tests showed that after about 30 additional days of
digestion, there was no longer any appreciable loss in volatile solids content. As with anaerobic
digestion (see Section 6.3 above), the loss in volatile solids content was related to the amount of
initial digestion. Farrell and Bhide (1992) have established that a sewage sludge with an initial
solids content of 2-percent or less, when batch aerobically digested for 15 days at 20°C, typically
>vill show under 15-percent additional volatile solids destruction when batch digested for an
additional 30 days. The use of additional volatile solids reduction to demonstrate vector
ittraction reduction is allowable only for sewage sludges from aerobic digesters that are unable
:o demonstrate the 38-percent volatile solids reduction.
5.5 SPECIFIC OXYGEN UPTAKE RATE (SOUR) FOR AEROBIC SEWAGE SLUDGES
[503.33 (b) (4)]
The vector attraction potential of an aerobically digested sewage sludge also can be
;hown to be reduced if the SOUR determined at 20°C is equal to or less than 1.5 mg of oxygen
Der hour per gram of total sewage sludge solids. (See Section 4.2.2 for a definition of SOUR.)
Frequently, aerobically digested sewage sludges are circulated through the aerobic
nological wastewater treatment stage for as long as 30 days. In these cases, the sewage sludge
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entering the aerobic digester is already partially aerobically digested. It is difficult then to
demonstrate an additional 38-percent volatile solids reduction. The SOUR method for
determining vector attraction reduction in this type of sewage sludge has been developed. This
method depends on the rate of oxygen uptake of the sewage sludge.
If a sewage sludge has been treated aerobically to the point at which the biological
organisms present are consuming very little oxygen, the value of the sewage sludge as a food
source for microorganisms is very low. The likelihood that such a sewage sludge will attract
sectors when applied to the land surface is likewise low. Eikum and Paulsrud (1977) have shown
:hat both the odor index of aerobically digested sewage sludges and the oxygen uptake level
decline at about the same rate with increasing nominal residence time in a continuous flow (fed
Dnce a day) digester. The relationship between odor intensity and oxygen uptake rate is
approximately a direct proportion. Eikum and Paulsrud's results indicate that at 20 °C, an
jxygen uptake rate of 1.5 g/hr/g total volatile suspended solids (VSS) or less indicates a well-
itabilized sewage sludge. The oxygen uptake rate depends on the temperature of digestion (i.e.,
.). Within a range of +. 5°C, the oxygen uptake rate obtained at another temperature can be
inverted to the uptake rate of 20 °C by the following relationship:
SOUR (20°C) = SOUR (t°C) x 1.10p(M)
The oxygen uptake rate depends on the conditions of the test and, to some degree, on
he nature of the original sewage sludge before aerobic treatment. Similarly the temperature
:orrection also depends on the nature of the sewage sludge. Research (Farrell and Bhide, 1992)
las shown that the SOUR method may be unreliable at solids content above 2 percent and
•equires a poorly defined temperature correction at temperatures differing substantially from
10°C. Information on test procedures and sewage sludge-dependent factors are provided in EPA
1992b).
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5.6 AEROBIC PROCESSES AT GREATER THAN 40°C [50333(b)(5)]
Vector attraction is considered to be adequately reduced if sewage sludge is aerobically
.reated for 14 days or longer at a temperature over 40° C and an average temperature higher
.han 45 °C. This vector attraction reduction method relates primarily to composted sewage
iludge. The adequacy of this method to reduce vector attraction is demonstrated by field
observation. These conditions are used at numerous within-vessel facilities (e.g., the plant at
Pairfield, Connecticut), and the final compost produced does not attract vectors. (Aerated static
tile, composting facilities typically compost sewage sludge for longer periods than 14 days. This
s not needed for vector attraction reduction but is used to produce a final product of superior
igricultural utility.)
i.7 ADDITION OF ALKALI [503.33 (b) (6)]
Sewage sludge may be reduced in vector attraction by adding sufficient alkali to: (1) raise
he pH to at least 12; (2) remain at pH of at least 12 without addition of more alkali for 2 hours;
md (3) remain at a pH of at least 11.5 for an additional 22 hours.
The vector attraction reduction achieved by adding alkali to produce a sufficiently high
iH is not permanent. Alkali addition does not significantly change the nature of the substances
n the sewage sludge, but instead causes stasis in biological activity. If the pH should drop, the
urviving bacterial spores would become biologically active, and the sewage sludge would putrefy
md attract vectors. The target conditions provided by the 503.33(b)(6) requirement are designed
o ensure that the sewage sludge can be stored for at least several days at the treatment works,
ransported, and applied to the soil without the pH falling to a point where putrefaction occurs
md vectors are attracted.
Noland et al. (1978) have shown that with addition of quicklime or slaked lime, sewage
ludge pH remains high for extended periods. His Figure 9 shows that for a sewage sludge
aised to pH 12.5, pH did not fall to below 12 for 25 days. One reason the pH stays high for
uch a long period is that a substantial portion of the lime is still not dissolved; this excess lime
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ash, may he
, so
j for
stadge even
if a large proportion of the afcali is soluWe.
„ hydros, ion are added using sodiura hy
for 1 « as iong for *. «-
or
- -
more
soluble alkalies than lime are used.
vec,or attraction region method in «Ms rec,—
lttraction reducUon method hy .ime addHion
22 hours, which «s added „
,
.
:he pH stays above 11.5 for an additional 22 hours.
SOLTOS [503J3(b)(7)]
6-7
No
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formation of CaSO4). Because the objective is to determine available water, the best way to
determine whether the material added is "active" .pr "inert" is to subject the sewage sludge/solid
mixture to a drying determination at mild conditions. Method 2540B in "Standard Methods"
(APHA, 1989) is appropriate. The sewage sludge or mixture is dried at 103-105°C. Drying time
should be more than 1 but less than 2 hours.
Drying sewage sludge to near total dryness causes a stasis ,in biological activity. Yeager
and Ward's (1981) data show that bacterial densities in sterilized raw sewage sludge inoculated
with several bacterial species declined rapidly when, the solids contents were over 75-percent,
indicating diminished bacterial activity. Thus, it can be concluded that significant biological
activity will not occur if sewage sludge is maintained above 75-percent solids.
A solids content of 75 percent indicates little likelihood that a sewage sludge will putrefy,
but whether it can attract vectors depends on the nature of the sewage sludge and the manner in
which it was processed. It is important that the sewage sludge not contain unstabilized sewage
sludge as from a primary clarifier, because raw food scraps likely to be present in such a sewage
sludge would attract birds, some mammals, and possibly insects, even if the solids content of the
sewage sludge exceeded 75 percent. The requirement is therefore restricted to sewage sludges
:hat do not contain unstabilized solids, such as sewage sludges treated by an aerobic or anaerobic
biological process. These processes degrade the more easily decomposed portions of these
particles and, when combined with a reduced moisture content (75-percent solids or greater),
adequately reduce vector attraction.
6.9 MOISTURE REDUCTION OF SEWAGE SLUDGE CONTAINING UNSTABILIZED
SOLIDS [503.33(b)(8)]
Under Part 503.33(b)(8), vector attraction of any sewage sludge is adequately reduced if
>olids content is increased to 90 percent or greater. This extreme desiccation deters vectors in all
out the most unusual situations. As noted in Section 6.8 above, the solids increase is achieved by
removal of water and not by dilution with inert solids.
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For sewage sludges containing unstabilized solids, drying to 90 percent or greater
solids—probably by heat drying—further limits biological activity and strips off or decomposes
volatile compounds that attract vectors. This solids content is typical of heat drying processes,
which reach 90-95-percent solids content and have no reported difficulty with vector attraction to
the dried material.
6.10 SEWAGE SLUDGE INJECTION [503J3(b)(9>]
Vector attraction reduction may be achieved by injecting the sewage sludge below the
land surface. Part 503.33(b)(9) requires that no significant amount of sewage sludge be present
on the land surface within 1 hour after injection. If the sewage sludge is Class A with respect to
pathogens, it must be injected within 8 hours after discharge from the pathogen-reducing process.
Injection of sewage sludge beneath the soil places a barrier of soil between the sewage
iludge and vectors. The soil quickly removes water from the sewage sludge, which reduces its
"nobility and its odor. Odor is usually present at the site during the injection process, but it
quickly dissipates when injection is complete.
The following considerations show that sewage sludge presents a negligible disease risk
rom salmonellae regrowth if injection is complete in 8 hours. Salmonellae doubling time is
istimated from Hussong et al. (1985) to be more than 1 hour. In 8 hours there would be eight
doublings. Density would increase to at most 256 MPN per gram (28 = 256). This density level
s far below the usually mentioned levels for infective dose. Also, the sewage sludge is
mderground, rapidly drying out, and out of contact with vectors and humans. Subsequent
mvironmental stresses also are expected to gradually lower densities to negligible levels.
1.11 INCORPORATION INTO THE SOIL [503.33(b)(10)]
Sewage sludge applied to the land surface or placed on a surface disposal site must be
ncorporated into the soil within 6 hours after application or placement. When land applied at
6-9
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agronomic rates, the loading of sewage sludge solids is about 1/200 of the mass of soil in the
olow layer. If incorporation is reasonably good, the dilution of sewage sludge in the soil surface
;an be as high as is typically achieved with soil injection. Odor will be present and vectors will
)e attracted temporarily. As the soil dewaters on the soil surface, this attraction will diminish
jvhen the sewage sludge is mixed with the soil.
The potential for regrowth in 8 hours is the same as for injection, except that instead of
icing underground the sewage sludge is on the land surface ready to be incorporated in 6 hours.
' rhe likelihood of additional regrowth during the maximum of 6 hours allowed for incorporation
s small so no reduction in the time between processing and application to the soil is necessary.
fhe reasons that risk of regrowth is not increased by this additional time on the soil surface are:
• Regrowth is inhibited by the desiccation that starts as soon as the sewage sludge is
applied to the land surface.
• The soil bacteria that invade the sewage sludge as soon as it is applied are effective
inhibitors to rapid regrowth.
5.12 COVER OF SEWAGE SLUDGE ON AN ACTIVE SEWAGE SLUDGE UNIT
[503.33(b)(ll)]
Sewage sludge placed on an active sewage sludge unit must be covered daily to control
'ector attraction. Daily covering with soil or other suitable material reduces vector attraction by
•.reating a physical barrier between the sewage sludge and vectors.
5.13 ELEVATION OF pH FOR DOMESTIC SEPTAGE [503.33(b)(12)]
For domestic septage, raising the pH to at least 12 and maintaining pH at 12 or higher
or 30 minutes without adding more alkali satisfactorily reduces vector attraction. (These
•onditions also accomplish Class B pathogen reduction.)
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This vector attraction reduction requirement is slightly less stringent than the alkali
iddition method for sewage sludge. Time between treatment and disposal is much shorter than
or sewage sludge, so there is less need to ensure that pH is maintained at a high value for a
ong time.
This vector attraction reduction option reduces pathogens at least as well as anaerobic
Jigestion (see Farrell et al., 1974, and Ronner and Oliver, 1987). Experience indicates that if pH
s above 10.5, vector attraction will not occur. It is expected that, in the short time between
ipplication of alkali and application of the treated domestic septage, pH will not have fallen.
Conner and Oliver indicate that this is practiced in the State of Wisconsin, with no reports of
nadequate vector attraction.
6-11
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SECTION SEVEN
COMPARISON OF THE TYPE OF PATHOGEN AND
VECTOR ATTRACTION REDUCTION REQUIREMENTS
IN PARTS 257 AND 503
7.1 INTRODUCTION
The current pathogen and vector attraction reduction requirements for sewage sludge
disposed on the land are in 40 CFR Part 257 (Criteria For Classification of Solid Waste Disposal
Facilities and Practices). These requirements are being replaced by the pathogen and vector
attraction reduction requirements for land application of sewage sludge and for placement of
sewage sludge on a surface disposal site in 40 CFR Part 503 (Standards for the Use or Disposal
Df Sewage Sludge).
This section compares the type of pathogen and vector attraction reduction requirements
n Part 257 to those in Part 503. This comparison does not address the requirements themselves
;e.g., which processes are a Process to Further Reduce Pathogens). Further information on the
ictual requirements is provided in Part 257, Part 503, and (for the Part 503 requirements) in the
other sections of this technical support document.
The Part 257 pathogen and vector attraction reduction requirements found in 40 CFR
257.3-6 apply to a facility or practice. A facility is "any land and appurtenances thereto used for
:he disposal of solid wastes" and a practice is "the act of disposal of solid waste." Neither a
facility nor a practice can exist unless the Part 257 pathogen and vector attraction reduction
requirements are met.
The term "disposed" in Part 257 is equivalent to the terms "applied" and "placed" in Part
503. Thus, the Part 257 requirements applied to both land application of sewage sludge and
surface disposal of sewage sludge. Similarly, Part 257 also applied to land application and
,urface disposal of septic tank pumpings.
7-1
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There was one case when the. Part 257 disease requirements did not apply when sewage
sludge or septic tank pumpings were disposed on the land. This was when sewage sludge or
septic tank pumpings were disposed by a trenching or burial operation. A trenching or burial
operation is "the placement of sewage sludge or septic tank pumpings in a trench or other
natural or man-made depression and the covering with soil or other suitable material at the end
of each operating day such that the wastes do not migrate to the surface." Thus, an additional
Part 257 disease requirement did not have to be met when the sewage sludge or septic tank
pumpings were covered at the end of each operating day. This approach also is reflected in the
Part 503 pathogen requirements.
7.2 PART 257
7.2.1 Pathogens—Sewage Sludge
Part 257 requires that sewage sludge that is applied to the land or incorporated into the
soil be treated in a Process to Significantly Reduce Pathogens (PSRP). Processes designated as
PSRP are listed in Appendix II of Part 257. In addition, public access has to be restricted to the
facility for 12 months and animals whose products are consumed by humans cannot be grazed for
at least 1 month. Note that both requirements (i.e., treatment in a PSRP and site restrictions)
have to be met when sewage sludge is applied to the land surface or incorporated into the soil.
Part 257 also requires that sewage sludge be treated in a Process to Further Reduce
Pathogens (PFRP) when the edible portion of a crop for direct human consumption touches the
soil and is grown within 18 months after the sewage sludge is applied or incorporated. When the
edible portion of a crop for direct human consumption does not touch the sewage sludge (e.g.,
corn), the above requirements (i.e., treat in PSRP and site restrictions) have to be met. When
crops for direct human consumption are not grown on the land, the above treatment and site
restriction requirements also have to be met.
7-2
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As mentioned previously, when the sewage sludge is covered at the end of each operating
day, the Part 257 disease requirements do not apply. In this case, neither the requirement to
treat the sewage sludge nor the site restrictions have to be met.
7.2.2 Pathogens—Septic Tank Pumpings
Part 257 requires that septic tank pumpings applied to the land or incorporated into the
soil be treated in one of the PSRPs listed in Appendix II in Part 257 or that the site restrictions
mentioned above (i.e. restrict public access for 12 months and do not graze animals whose
products are consumed by humans for at least 1 month) be met. The difference between the
Part 257 pathogen requirements for sewage sludge and for septic tank pumpings is that the site
restrictions must be met when sewage sludge is applied or incorporated, but are an alternative to
:he treatment requirement for septic tank pumpings. This is reflected in the Part 503 pathogen
requirements discussed in Section 7.3 below.
The Part 257 pathogen requirements for septic tank pumpings applied to land surface or
ncorporated into the soil when crops whose edible portion touch the soil are grown within 18
•nonths are the same as the pathogen requirements for sewage sludge. In this case, the septic
ank pumpings have to be treated in a PFRP. When the period before crops with edible portions
hat touch the soil are grown is longer than 18 months or when the edible portion of the crop
does not touch the soil, the above pathogen requirements (i.e., treat the septic tank pumpings in
i PSRP or meet the site restrictions) have to be met. When no crops with edible portions are
jrown on the land, either the above treatment requirements or site restrictions have to be met.
The Part 257 pathogen requirements for septic tank pumpings do not apply when the
;eptic tank pumpings are covered at the end of each operation day (i.e., disposed in a burial or
renching operation). Neither the requirement to treat the septic tank pumpings nor the site
•estrictions have to be met in this case.
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1.12 Vector Attraction Reduction—Sewage Sludge and Septic Tank Pumpings
Part 257 requires that "the facility or practice shall not exist or occur unless the on-site
population of disease vectors is minimized through the periodic application of cover material or
other techniques as appropriate so as to protect public health." This requirement applies to the
disposal of both sewage sludge and septic tank pumpings.
Periodic application of cover is the application and compaction of soil or other suitable
material over disposed solid waste (e.g., sewage sludge or septic tank pumpings) at the end of
each operating day or at such frequencies and in such a manner as to reduce the risk of fire and
to impede vector's access to the waste. In this case, the cover material keeps the vectors away
from the sewage sludge or septic tank pumpings.
"Other techniques" for vector attraction reduction are not identified in Part 257.
However, many of the process descriptions for a PSRP and a PFRP in Appendix II contain
"other techniques" for vector attraction reduction. For example, the description of anaerobic
digestion indicates that a minimum of 38 percent volatile solids reduction must be achieved. The
purpose of this requirement is to reduce the attraction of vectors to the sewage sludge treated in
this process. For other processes, such as lime stabilization, the treatment requirements for the
process achieve both pathogen and vector attraction reduction.
7.3 PART 503
73.1 Pathogens—Sewage Sludge (Land Application)
The Part 503 pathogen requirements for sewage sludge applied to the land are similar to
;he Part 257 pathogen requirements. The sewage sludge has to be treated to reduce pathogens
or a combination of treatment and restrictions on the site where the sewage sludge is applied is
used to reduce pathogens. .
7-4
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When the Class A pathogen requirements in Part 503 are met, sewage sludge can be
applied to the land without any restrictions being imposed on the site. In this case, the pathogen
density levels that a Class A sewage sludge has to meet are equivalent those achieved by treating
the sewage sludge in a PFRP (i.e., density levels are below the detection limit). Sewage sludge
generated at each treatment works must meet the appropriate requirements for that sewage
sludge to be considered Class A with respect to pathogens.
For a process to classified a PFRP, the process must reduce pathogens to the levels
required for the sewage sludge to be classified Class A under Part 503. However, the PFRP
demonstration does not have to be made at every treatment works. The demonstration can be
made at one location and the results verified by EPA. After that initial demonstration, the
PFRP process can be used at other locations without a further pathogen reduction demonstration
as long as the process is operated in the same manner it was operated to achieve a PFRP
designation.
In certain cases, only the Class A pathogen requirements can be met when sewage sludge
is applied to the land. These cases are when bulk sewage sludge is applied to a lawn or a home
garden, or when sewage sludge is sold or given away in a bag or other container for application
to the land. In these two cases, it is not feasible to impose site restrictions on the land where the
sewage sludge is applied. Consequently, the Class A pathogen requirements have to be met.
When the combination of treatment and site restrictions are used to reduce pathogens,
:he Class B pathogen requirements must be met for each sewage sludge. In addition, restrictions
xmceming harvesting of crops, grazing of animals, and public access must be met at each land
application site. The site restrictions prohibit certain activities at the site for certain times so
:hat the environment can further reduce the pathogens in the sewage sludge.
7-5
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7.3.2 Pathogens—Domestic Septage (Land Application)
^ ^'
The Part 503 pathogen requirements for domestic septage applied to the agricultural
land, forest, or a reclamation site are similar to the Part 257 pathogen requirements for septic
tank pumpings disposed on the land. Part 503 has two alternative pathogen requirements for
domestic septage applied to those types of land.
The first alternative is to impose restrictions on the site where the domestic septage is
applied. In this case, the restrictions prevent exposure to the domestic septage until the
environment has the opportunity to reduce the pathogens in the domestic septage. The site
restrictions that have to be met are the same as the site restrictions when a Class B sewage
sludge is applied to the land.
The second alternative is that the pH of the domestic septage be adjusted (i.e., raised to
12 or above and remain at 12 or above for 30 minutes) and that site restriction concerning
harvesting of crops be met. The site restrictions are part of this alternative because it is not
feasible for each load (e.g., each tank truck load) of domestic septage to be treated to meet the
Class A pathogen requirements (i.e., raising the pH of the domestic septage to 12 or above and
-------
The exposure assessment used to develop the surface disposal pollutant limits only
addressed certain pathways of exposure. For this reason, site restrictions are imposed on each
surface disposal site to prevent exposure to pollutants in the sewage sludge after placement on an
active sewage sludge unit. These restrictions address growing of crops, grazing of animals, and
restricting public access to the surface disposal site. They are more stringent than the site
restrictions that have to be met when a Class B sewage sludge is applied to the land.
There is one case when neither the Class A nor Class B pathogen requirements have to
be met when sewage sludge is placed on an active sewage sludge unit. In this case, the sewage
sludge has to be covered at the end of each operating day. This is equivalent to a burial or
trenching operation as defined in Part 257. The Part 257 pathogen requirements did not apply
when sewage sludge was disposed in a trenching or burial operation. This also is the case in Part
503.
73.4 Pathogens—Domestic Septage (Surface Disposal)
There are no pathogen requirements in Part 503 for domestic septage placed on an active
sewage sludge unit because of the site restrictions that apply to all surface disposal sites. As
mentioned previously, site restrictions are imposed on all surface disposal sites to prevent
exposure to the pollutants in sewage sludge placed on an active sewage sludge unit.
7.3.5 Vector Attraction Reduction—Sewage Sludge (Land Application)
As mentioned previously, Part 257 requires that sewage sludge applied to the land be
covered at the end of each operating day to reduce the attraction of vectors or that other
-.echniques be used to reduce vector attraction. The Part 503 vector attraction reduction
requirements recognize that daily cover is not a feasible vector attraction reduction alternative
for land application of sewage sludge. Instead, Part 503 has "other techniques" for vector
attraction reduction.
7-7
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There are 10 alternative vector attraction reduction requirements in Part 503 for land
application of sewage sludge (see Section 6). The first eight of these alternatives require
treatment of the sewage sludge (e.g., pH adjustment). The other two alternative address how the
sewage sludge is applied (i.e., injection below the land surface or incorporation into the soil).
When bulk sewage sludge is applied to agricultural land, forest, a public contact site, or a
reclamation site, any 1 of the 10 vector attraction reduction requirements can be met. However,
when bulk sewage sludge is applied to a lawn or a home garden, one of the eight treatment-
related alternatives has to be met. In these cases, injection and incorporation are not considered
feasible alternatives for vector attraction reduction.
When sewage sludge is sold or given away in a bag or other container for application to
the land, one of the eight treatment-related vector attraction reduction requirements has to be
met. Injection and incorporation also are not feasible in this case.
7.3.6 Vector Attraction Reduction—Domestic Septage (Land Application)
Part 503 requires that one of three alternative vector attraction reduction requirements
be met when domestic septage is applied to agricultural land, forest, or a reclamation site.
Vector attraction reduction can be achieved by injecting the domestic septage below the land
surface, by incorporating the domestic septage into the soil, or by treating the domestic septage.
When domestic septage is injected below the land surface or incorporated into the soil,
vectors do not have access to the domestic septage. For this reason, the attraction of vectors to
the domestic septage is reduced.
To achieve vector attraction reduction by treatment, pH adjustment of the domestic
septage is required. In this case, the pH of each container (e.g., each tank truck load) of
domestic septage has to be adjusted prior to applying the domestic septage to agricultural land,
forest, or a reclamation site.
7-8
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The domestic septage pH adjustment requirement only applies to domestic septage
applied to agricultural land, forest, or a reclamation site. If domestic septage is applied to other
types of land, one of the alternative vector attraction reduction requirements for sewage sludge
must be met.
7.3.7 Vector Attraction Reduction—Sewage Sludge (Surface Disposal)
When sewage sludge is placed on an active sewage sludge unit, Part 503 requires that 1 of
11 alternative vector attraction reduction requirements be met. The first 10 of these
requirements are the same as the alternative vector attraction reduction requirements for sewage
sludge applied to the land. These "other techniques" include eight treatment alternatives and two
alternatives concerning how the sewage sludge is placed on the land (i.e., injection or
incorporation).
The last alternative vector attraction reduction requirement is to cover sewage sludge
placed on an active sewage sludge unit at the end of each operating day. When this alternative is
met, no additional requirements are imposed for vector attraction reduction.
7.3.8 Vector Attraction Reduction—Domestic Septage (Surface Disposal)
Part 503 contains four alternative vector attraction reduction requirements for domestic
septage placed on an active sewage sludge unit. These include injection below the land surface,
ncorporation into the soil, daily cover, and pH adjustment.
When domestic septage is injected below the land surface, incorporated into the soil, or
;overed at the end of each operating day, access to the domestic septage by vectors is prevented.
Fhis reduces the attraction of vectors to the domestic septage.
Adjusting the pH of domestic septage also reduces the attraction of vectors. The high
iH affects, the properties of domestic septage that attract vectors.
7-9
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7.4 SUMMARY
The types of Part 257 and Part 503 pathogen and vector attraction reduction
requirements are summarized below by use or disposal practice. Requirements are presented
both for sewage sludge and domestic septage applied to the land or placed on a surface disposal
site.
7.4.1 Land Application—Sewage Sludge
Pathogens:
Type of land
Agricultural land,
forest, public contact
site, or reclamation
site
Lawn or home garden
Part 257
Requirements
PSRP with site
restrictions or
PFRP when crops
that touch soil are
grown with 18 months
Same as above
Part 503
Requirements
Class A or Class
B with site
restrictions
Class A
Vector attraction reduction:
Type of land
Agricultural land,
forest, public contact
site, or reclamation
site
Lawn or home garden
Part 257
Requirements
Cover at the end
of each operating
day or other
techniques
Same as above
Part 503
Requirements
One of 10
alternative
techniques (daily
cover not
included)
One of eight
alternatives
techniques (daily
cover not
included)
7-10
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7.4.2 Land Application—Domestic Septage
Pathogens:
IVpe of land
Agricultural land,
•brest, or
•eclamation site
Dther types
/ector attraction reduction:
[Vpe of land
Agricultural land,
brest, or
eclamation site
Dther types
Part 257
Requirements
PSRP or site
restrictions; or
PFRP when crops that
touch the soil are
grown within 18 months
Same as above
Part 257
Requirements
Cover at the end
of each operating
day or other
techniques
Same as above
7.43 Surface Disposal—Sewage Sludge
'athogens:
tVpe of land
Surface disposal
ite
Part 257
Requirements
PSRP with site
restrictions or
PFRP when crops that
touch the soil are
grown within 18 months
Part 503
Requirements
Site restrictions
pH adjustment
restrictions on
harvesting crops
Meet the
requirements for
sewage sludge
applied to the
land
Part 503
Requirements
Injection,
incorporation, or
pH adjustment
Meet the
requirements for
sewage sludge
applied to the
land
Part 503
Requirements
Class A, Class B,
or cover at the
end of each
operating day
7-11
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Vector attraction reduction:
Type of land
Surface disposal
site
Part 257
Requirements
Cover at the end
of each operating
day or other
techniques
7.4.4 Surface Disposal—Domestic Septage
Pathogens:
Type of land
Surface disposal
site
Vector attraction reduction:
Type of land
Surface disposal
site
Part 257
Requirements
PSRP or site
restrictions; or
PFRP when crops that
touch the soil are
grown within 18 months
Part 257
Requirements
Cover at the end
operating day or
other techniques
Part 503
Requirements
One of 10
alternative
techniques or
cover at the end
of each operating
day
Part 503
Requirements
None. Site
restrictions
imposed for other
than pathogen
reasons
Part 503
Requirements
Injection,
incorporation,
pH adjustment, or
cover at the end
of each operating
day
7-12
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SECTION EIGHT
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risks associated with the agricultural use of sewage sludge: knowledge and needs."
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Gerba, C.P., D.K. Powelson, M.T. Yahya, L. G. Wilson, and G.L. Amy. 1991. Fate of viruses in
treated sewage effluent during soil aquifer treatment designed for wastewater
reclamation and reuse. Wat. Sci. Tech. 24(9):95-102.
Gerba, C.P., C. Wallis and J.L. Melmick. 1975. Fate of wastewater bacteria and viruses in soil.
J. Irrig. Drain Div. Am. Soc. Civ. Engineers 101:157-174.
3oyal, S.M., S.A. Schaub, P.M. Wellings, D. Berman, J.S. Glass, CJ. Hurst, D.A. Brashear,
C.A. Sorber, B.E. Moore, G. Bitton, P.H. Gibbs, and S.R. Farrah. 1984. Round robin
investigation of methods for recovering human enteric viruses from sludge. Applied &
Environ. Microbiology 48:531-538.
larding, H.J., R.E. Thomas, D.E. Johnson and C.A. Sorber. 1981. Aerosols generated by
liquid sludge application to land. Rept. No. EPA-600/1-81-028. Washington, DC:
U.S. EPA, Office of Research and Development.
-Tussong, D., W.D. Burge, and N.K. Enkiri. 1985. Occurrence, growth, and suppression of
salmonella in composted sewage sludge. Appl. & Envir. Microbiology 50(4):887-893.
RGRD (International Research Group on Refuse Disposal). 1968. Pp. 3230-3340 in
Information Bulletin Numbers 21-31, August 1964 to December 1967, reprinted by U.S.
Dept. H.E.W., Bur. of Sol. Waste Manag., Rockville, MD (1969).
akubowski, W. 1988. Ascaris ova survival in land application conditions. EPA Administrator's
Item Deliverable No. 2799 (May, 1988). Unpublished.
akubowski, W. and T.H. Ericksen. 1979, Methods for detection of Giardia cysts in water
supplies. Pp. 193-210 in Jakubowski, W. and J.C. Hoff, eds. Waterborne transmission
of giardiasis. Rept. No. EPA-600/2-85-001. Cincinnati: Health Effects Research
Laboratory.
eris, J.S., D. Ciaricia, E. Chen and M. Mena. 1985. Determining the stability of treated
municipal sludges. Rept,-No. EPA-600/2-85-001. (NTIS PB-85 147189/AS.) Cincinnati:
Risk Reduction Engineering Laboratory;
lenner, B.A. and H.A. Clark. 1974. Determination and enumeration of Salmonella and
Pscudomonas aeruginosa. J. Wat. Poll. Contr. Fed. 46(9):2163-2171.
leusch, G.T. 1970. Shigella infections. Clin. Gastroent. 8:645-662.
8-4
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Kowal, N.E. 1982. Health effects of land treatment: microbiological. Kept. No. EPA-660/
1-85-015. Research Triangle Park, NC: Health Effects Research Laboratory.
Kowal, N.E. 1985. Health effects of land application of municipal sludge. Rept.
No. EPA-600/1-85-015. Research Triangle Park, NC: Health Effects Research Laboratory.
Larkin, E.P., J.T. Tiemey and RJ. Sullivan, 1976. Virus on sewage-irrigated vegetables.
J. Env. Eng. Div. (ASCE) 102 (EEl):29-35.
Lee, K.M., J.B. Farrell, A.E. Eralp, and R.A. Rossi. 1985. Bacterial density reduction in
activated sludge processes. In press.
Lee, K.M., C.A. Brunner, J.B. Farrell, and A.E. Eralp. 1989. Destruction of enteric bacteria and
viruses during two-phase digestion. Jour. WPCF 61 (8): 1422-1429.
Little, M.D. 1980. Agents of health risk: parasites. In "Sludge - Health Risks of Land
Application", ed. Bitton, G., B.L. Damron, G.T. eds. and J.M. Davidson, Ann Arbor
Sci. Pub., Ann Arbor, Mich., pp. 47-58.
Madore, M.S., et al., 1987. Occurrence of Crvptosporidium oocysts in sewage effluents and
selected surface waters. J. Parasitology 73(4);702-705.
Martin, J.H., Jr., H.E. Bostian, and G. Stern. 1990. Reductions of enteric microorganisms
during aerobic sludge digestion. Wat. Res. 24(11):1377-1385.
Mueller, G. 1953. Investigations on the lifespan of Ascaris eggs in garden soil. Zentrabl.
Bakteriol. 159:377-379.
Noland, R.F., J.D. Edwards and M. Kipp. 1978. Full-scale demonstration of lime stabilization.
Rept. No. EPA-600/2-78-171. Cincinnati, OH: Risk Reduction Engineering Laboratory.
Dliveri, V.P., L. Cox, M. Sarai, J.L. Sykora, and P. Gavaghan. 1989. "Selected indicator and
pathogenic microorganisms removal during conventional sludge treatment processes."
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be published.
Pedersen, D.C. 1981. Density levels of pathogenic organisms in municipal wastewater sludge:
a literature review. Rept. No. EPA-600/2-81-170. Cincinnati: Risk Reduction
Engineering Laboratory.
Pike, E.B. and R.D. Davis. 1984. Stabilization and disinfection - their relevance to agricultural
utilisation of sludge. In "Sewage Sludge Stabilization and Disinfection." A.M. Bruce., ed.
Pub. for Water Res. Centre by Ellis Horwood Ltd., Chichester.
3incince, A.E. and CJ. Foumier. 1984. "Chlorinated organic compounds in digested, heat-
conditioned, and Purifax-treated sludges." Rept. No. EPA-600/2-84-117, September.
'osthuma, A.R., J.N. Marcus, and W.H. Millard. 1976. Chemical oxidation of sludge with
8-5
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Posthuma, A.R., J.N. Marcus, and W.H. Millard. 1976. Chemical oxidation of sludge with
chlorine at Alma, MI, presented at the sfst Annual Conference of the Mich.
Wat. Poll. Contr. Assoc., Boyne Falls, MI, June 13-16.
Reimers, R.S., MJD. Little, AJ. Englande, D.B. Leftwich, D.D. Bowman and R.F. Wilkinson.
1981, Investigation of parasites in southern sludges and disinfection by standard
sludge treatment processes. Rept. No. EPA-600/2-81-166. Cincinnati: Health Effects
Research Laboratory.
Reimers, R.S., MD. Little, AJ. Englande, Jr., D.B. McDonnell, D.D. Bowan, and J.M. Hughes.
1986. Investigation of parasites in sludges and disinfection techniques. EPA Rept. No.
600/1-85-022. U.S. EPA.
Ronner, A.B. and D.O. Cliver. 1987. Disinfection of viruses in septic tank and holding tank
waste by calcium hydroxide (lime).. Small-scale Waste Management Project, University of
Wisconsin-Madison, June 1987.
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polluted soil: II. field and laboratory studies on Entamoeba cysts. Sew. Indust.
Wastes 23:478-485.
Sorber, C.A. and B.E. Moore. 1987. Survival and transport of pathogens in sludge-amended
soil: a critical literature review. Rept. No. EPA-600/2-87-028. Cincinnati: Risk
Reduction Engineering Laboratory.
Sorber, C.A., B.E. Moore, D.E. Johnson, HJ. Harding and R.E. Thomas. 1984.
Microbiological aerosols from the application of liquid sludge to land.
J. Wat. Poll Contr. Fed. 56:830-836.
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8-6
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regrowth of bacteria in wastewater sludge. Appl. Environ. Microbiol. 41(5):1117-1122.
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APPENDIX
Subpart D of the Part 503 Regulation
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38 Federal Register / Vol. 5?. He. 32 / Friday, February 19, 1993 / Rules and Regulations
iction requiremants in § S03.33(b)(l)
ugh S 503.33(b){8) when one of those
lirements is met) have been met This
rmlnation has been made under my
ction and supervision in accordance with
system designed to ensure that qualified
onnel properly gather and evaluate the
rmation used to determine the [pathogen
.irements and vector attraction reduction
.irements if appropriate) have been met
aware that there are significant penalties
also certification including the
.ibility of fine and imprisonment"
ii) A description of how the
logen requirements in § 503.32 (a),
Z), (b)(3), or (b){4) are met when one
lose requirements is met.
v) A description of how one of the
or attraction reduction requirements
503.33 (b)(l) through (b)(8) is met
n one of those requirements is met.
) The owner/operator of the surface
>osal site, shall develop the
wing information and shall retain
information for five years. *
i The concentration of each
utant listed in Table 2 of § 503.23 in
sewage sludge when the pollutant
:entrations in Table 2 of § 503.23 are
or when site-specific pollutant
ts in § 503.23(b) are met.
) The following certification
iment:
certify, under penalty of law, that the
igement practices in $ 503.24 and the
>r attraction reduction requirement in
rt one of the requirements in § 503.33
) through (b)(ll) if one of those
Bremen ts is met] have been met. This
•mination has been made under my
tion and supervision in accordance with
ystem designed to ensure that qualified
jnnel properly gather and evaluate the
mation used to determine that the
igement practices [and the vector
rtion reduction requirements if
apriate) have been met. I am aware that
are significant penalties for false
Ication including the possibility of fine
mprisonment"
i) A description of how the
agement practices in § 503.24 are
•) A description of how the vector
ction reduction requirements in
3.33 (b){9) through (b)(ll) are met if
of those requirements is met.
• When domestic septage is placed
surface disposal site:
If the vector attraction reduction
irements in § 503.33(b)(12) are met,
>erson who places the domestic
ige on the surface disposal site shall
lop the following information and
retain the information for five
The following certification
ment: •
Certify, under penalty of law, that the
r attraction reduction requirements in
S 503.33(b)(12) have been mat This
determination has been made under my
direction and supervision in accordance with
the system designed to ensure that qualified
personnel properly gather and evaluate the
information used to determine that the vector
attraction requirements have been met I am
aware that there are significant penalties for
false certification including the possibility of
fine and imprisonment"
(ii) A description of how the vector
attraction reduction requirements in
§ 503.33(b)(12) are met
(2) The owner/operator of the surface
disposal site shall develop the following
information and shall retain that
information for five years:
(i) The following certification
statement:
"I certify, under penalty of law, that the
management practices in § 503.24 and the
vector attraction reduction requirements in
[insert § 503.33(b)(9) through §5O3.33(b)(ll)
when one of those requirements is met) have
been met This determination has been made
under my direction and supervision in
accordance with the system designed to
ensure that qualified personnel properly
gather and evaluate the information used to
determine that the management practices
[and the vector attraction reduction
requirements if appropriate) have been met.
I am aware that there are significant penalties
for false certification including the
possibility of fine or imprisonment."
(ii) A description of how the
management practices-in § 503.24 are
met.
(iii) A description how the vector
attraction reduction requirements in
§ 503.33(b)(9) through § 503.33(b)(ll)
are met if one of those requirements is
met.
(Approved by the Office of Management and
Budget under control number 2040-0157)
150X28 Reporting-
Class I sludge management facilities,
POTWs (as defined in 40 CFR 501.2)
with a design flow rate equal to or
greater than one million gallons per day,
and POTWs that serve 10,000 people or
more shall submit the information in
§ 503.27(a) to the permitting authority
on February 19 of each year.
(Approved by the Office of Management and
Budget under control number 2040-0157)
Subpart D—Pathogens and Vector
Attraction Reduction
§503 .30 Scop*.
(a) This subpart contains the
requirements for a sewage sludge to be
classified either Class A or Class B with
respect to pathogens.
(b) This subpart contains the site
restrictions for land on which a Class B
sewage sludge is applied.
(c) This subpart contains the pathogen
requirements for domestic septage
applied to agricultural land, forest, orfe
reclamation site.
(d) This subpart contains altematr
vector attraction reduction requiremi
for sewage sludge that is applied to the
land or placed on a surface disposal site.
f 503.31 Special definition*.
(a) Aerobic digestion is the
biochemical decomposition of organic
matter in sewage sludge into carbon
dioxide and water by microorganisms in
the presence of air.
(b) Anaerobic digestion is the
biochemical decomposition of organic
matter in sewage sludge into methane
gas and carbon dioxide by
microorganisms in the absence of air.
(c) Density of microorganisms is the
number of microorganisms per unit
mass of total solids (dry weight) in the
sewage sludge.
(d) Land with a high potential for
public exposure is land that the public
uses frequently. This includes, but is
not limited to, a public contact site and
a reclamation site located in a populated
area (e.g, a construction site located in
a city).
(e) Land with a low potential for
public exposure is land that the public
uses infrequently. This includes, but is
not limited to, agricultural land, forest,
and a reclamation site located in an
unpopulated area (e.g., a strip mine
located in a rural area).
(f) Pathogenic organisms are disease-
causing organisms. These include, but
are not limited to, certain bacteria,
protozoa, viruses, and viable helminth
ova.
(g) pH means the logarithm of the
reciprocal of the hydrogen ion
concentration.
(h) Specific oxygen uptake rate
(SOIJH) is the mass of oxygen consumed
per unit time per unit mass of total
solids (dry weight basis) in the sewage
sludge.
(i) Total solids are the materials in
sewage sludge that remain as residue
when the sewage sludge is dried at 103
to 105 degrees Celsius.
(j) Unstabilized solids are organic
materials in sewage sludge that have not
been treated in either an aerobic or
anaerobic treatment process.
(k) Vector attraction is the
characteristic of sewage sludge that
attracts rodents, flies, mosquitos, or
other organisms capable of transporting
infectious agents.
(1) Volatile solids is the amount of the
total solids in sewage sludge lost when
the sewage sludge is combusted at 55C
degrees Celsius in the presence of
excess air.
A-l
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Federal Register / Vol. 58. No. 32 / Friday. February 19, 1993 / Rules and Regulations
9399
a.32 P
a) Sewage sludge—Class A. (I) The
uirement in § 503.32(a)(2) and the
uirements in either § 503.32(a)(3),
4). (a)(S). (a)(6). (a)(7). or (a)(8) shall
net for a sewage sludge to be
>siiied Class A with respect to
hogens.
1) The Class A pathogen
uirements in S 503.32 (a)(3) through
3) shall be met either prior to
ating or at the same time the vector
action reduction requirements in
)3.33, except the vector attraction
action requirements in § 503.33
5) through (b)(8), are met.
i) Class A—Alternative 1. (i) Either
density of fecal coliform in the
age sludge shall be less than 1000
;t Probable Number per gram of total
ds (dry weight basis), or the density
almonella sp. bacteria in the sewage
ige shall be less than three Most
aable Number per four grams of total
ds (dry weight basis) at the time the
age sludge is used or disposed; at
time the sewage sludge is prepared
sale or give away in a bag or other
tainer for application to the land: or
IB time the sewage sludge or
erial derived from sewage sludge is
jared to meet the requirements in
3.10 (b), (c). (e). or (f).
i) The temperature of the sewage
Ige that is used or disposed shall be
ntained at a specific value for a
od of time.
i) When the percent solids of the
age sludge is seven percent or
ler, the temperature of the sewage
ige shall be 50 degrees Celsius or
ler; the time period shall be 20
utes or longer; and the temperature
time period shall be determined
g equation (2), except when small
icles of sewage sludge are heated by
ar warmed gases or an immiscible
• id.
131,700,000
10O.I«Ol
Eq. (2)
re,
me in days.
nperature in degrees Celsius.
) When the percent solids of the
age sludge is seven percent or higher
small particles of sewage sludge are
ed by either warmed gases or an
iiscible liquid, the temperature of
;ewage sludge shall be 50 degrees
ius or higher; the time period shall
5 seconds or longer; and the
Derature and time period shall be
rmined using equation (2).
) When the percent solids of the
ige sludge is less than seven percent
the time period is at least 15
seconds, but less than 30 minutes, the
temperature and time period shall be
determined using equation (2).
(D) When the percent solids of the
sewage sludge is less than seven ,
percent; the temperature of the sewage
sludge is 50 degrees Celsius or higher;
and the time period is 30 minutes or
longer, the temperature and time period
shall be determined using equation (3).
50,070,000
D= Eq. (3)
10oi«a •
Where.
D=time in days.
t=temperature in degree* Celsius.
(4) CJass A—Alternative 2. (i) Either
the density of fecal coliform in the
sewage sludge shall be less than 1000
Most Probable Number per gram of total
solids (dry weight bqsis), or the density
of Salmonella sp. bacteria in the sewage
sludge shall be less than three Most
Probable Number per four grams of total
solids (dry weight basis) at the time the
sewage sludge is used or disposed; at
the time the sewage sludge is prepared
for sale or give away in a bag or other
container for application to the land; or
at the time the sewage sludge or ,
material derived from sewage sludge is
prepared to meet the requirements in
§ 503.10 (b),(c).(e). or (0.
(ii) (A) The pH of the sewage sludge
that is used or disposed shall be raised
to above 12 and shall remain above 12
for 72 hours.
(B) The temperature of the sewage
sludge shall be above 52 degrees Celsius
for 12 hours or longer during the period
that the pH of the sewage sludge is
above 12.
(C) At the end of the 72 hour period
during which the pH of the sewage
sludge is above 12, the sewage sludge
shall be air dried to achieve a percent
solids in the sewage sludge greater than
50 percent.
(5) Class A—Alternative 3. (i) Either
the density of fecal coliform in the
sewage sludge shall be less than 1000
Most Probable Number per gram of total
solids (dry weight basis), or the density
of Salmonella sp. bacteria in sewage
sludge shall be less than three Most
Probable Number per four grams of total
-solids (dry weight basis) at the time the
sewage sludge is used or disposed; at
the time the sewage sludge is prepared
for sale or give away in a bag or other
container for application to the land; or
at the time the sewage sludge or
material derived from sewage sludge is
prepared to meet the requirements in
§503.10(b),(c),(e),or(f).
(ii) (A) The sewage sludge shall be
analyzed prior to pathogen treatment to
determine whether the sewage sludge
contains enteric viruses.
(B) When the density of enteric
viruses in the sewage sludge prior to
pathogen treatment is less than one
Plaque-forming Unit per four grams of
total solids (dry weight basis), the
sewage sludge is Class A with respect to
enteric viruses until the next monitoring
episode for the sewage sludge.
(C) When the density of enteric
viruses in the sewage sludge prior to
pathogen treatment is equal to or greater
than one Plaque-forming Unit per four
grams of total solids (dry weight basis).
the sewage sludge is Class A with
respect to enteric viruses when the
density of enteric viruses in the sewage
sludge after pathogen treatment is less
than one Plaque-forming Unit per four
grams of total solids (dry weight basis)
and when the values or ranges of values
for the operating parameters for the
pathogen treatment process that
produces the sewage sludge that meets
the enteric virus density requirement
are documented.
(D) After the enteric virus reduction
in paragraph (a)(5)(ii)(C) of this section
is demonstrated for the pathogen
treatment process, the sewage sludge
continues to be Class A with respect to
enteric viruses when the values for the
pathogen treatment process operating
parameters are consistent with the
values or ranges of values documented
in paragraph (a)(5)(ii)(C) of this section.
(iii)(A) The sewage sludge shall be
analyzed prior to pathogen treatment to
determine whether the sewage sludge
contains viable helminth ova.
(B) When the density of viable
helminth ova in the sewage sludge prior
to pathogen treatment is less than one
per four grams of total solids (dry
weight basis), the sewage sludge is Class
A with respect to viable helminth ova
until the next monitoring episode for
the sewage sludge.
(C) When the density of viable
helminth ova in the sewage sludge prior
to pathogen treatment is equal to or
greater than one per four grams of total
solids (dry weight basis), the sewage
sludge is Class A with respect to viable
helminth ova when the density of viable
helminth ova in the sewage sludge after
pathogen treatment is less than one per
four grams of total solids (dry weight
basis) and when the values or ranges of
values for the operating parameters for
the pathogen treatment process that
produces the sewage sludge that meets
the viable helminth ova density
requirement are documented.
(D) After the viable helminth ova
reduction in paragraph (a)(5)(iii)(C) of
this section is demonstrated for the
pathogen treatment procuss, the sewage
A-2
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•O Federal Register / Vol. 58, No. 32 / Friday. February 19, 1993 / Rules and Regulations
ga continues to be Class A with
ect to viable helminth ova when the
es for the pathogen treatment
ess operating parameters are
•istent with the values or ranges of
es documented in paragraph
)(iii)(C) of this section.
] Class A—Alternative 4. (i) Either
iensity of fecal coliform in the
ige sludge shall be less than 1000
t Probable Number per gram of total
is (dry weight basis), or the density
Tlmonella sp. bacteria in the sewage
ge shall be less than three Most
able Number per four grams of total
Is (dry weight basis) at the time the
ige sludge is used or disposed; at
irae the sewage sludge is prepared
ale or give away in a bag or other
ainer for application to the land; or
e time the sewage sludge or
•rial derived from sewage sludge is
ared to meet the requirements in
3.10 (b). (c), (e), or (f).
) The density of enteric viruses in
.ewage sludge shall be less than one
ue-forming Unit per four grams of
solids (dry weight basis) at the time
.ewage sludge is used or disposed;
e time the sewage sludge is
ared for sale or give away in a bag
her container for application to the
; or at the time the sewage sludge
aterial derived from sewage sludge
spared to meet the requirements in
3.10 (b). (c). (e). or (f). unless
rwiae specified by the permitting
ority.
i) The density of viable helminth
,n the sewage sludge shall be less
one per four grams of total solids
weight basis) at the time the sewage
ge is used or disposed; at the time
ewage sludge is prepared for sale or
away in a bag or other container for
i cation to the land; or at the time
.ewage sludge or material derived
. sewage sludge is prepared to meet
equirements in §503.10 (b). (c), (e).
), unless otherwise specified by the
lilting authority.
) Class A—Alternative 5. (i) Either
iensity of fecal coliform in the
igo sludge shall be less than 1000
t Probable Number per gram of total
Is (dry weight basis), or the density
ibnonclla, sp. bacteria in the sewage
ge shall be less than three Most
>able Number per four grams of total
is (dry weight basis) at the time the
ige sludge is used or disposed; at
ime the sewage sludge is prepared
alo or given away in a bag or other
ainer for application to the land; or
e time the sewage sludge or
irial derived from sewage sludge is
ared to meet the requirements in
3.10(b), (c). (e). or (f).
(ii) Sewage sludge that is used or
disposed shall be treated in one of the
Processes to Further Reduce Pathogens
described in appendix B of this part.
(8) Class A—Alternative 6. (i) Either
the density of fiscal coliform in the
sewage sludge shall be less than 1000
Most Probable Number per gram of total
solids (dry weight basis), or the density
of Salmonella, sp. bacteria hi the sewage
sludge shall be less than three Most
Probable Number per four grams of total
solids (dry weight basis) at the time the
sewage sludge is used or disposed; at
the time the sewage sludge is prepared
for sale or given away in a bag or other
container for application to* the land; or
at the time the sewage sludge or
material derived from sewage sludge is
prepared to meet the requirements in
§503.10(0). (c). (e). or(f).
(ii) Sewage sludge that is used or
disposed shall be treated in a process
that is equivalent to a Process to Further
Reduce Pathogens, as determined by the
permitting authority.
(b) Sewage sludge—Class B. (l)(i) The
requirements in either § 503.32(b)(2),
(b)(3), or (b)(4) shall be met for a sewage
sludge to be classified Class B with
respect to pathogens.
(ii) The site restrictions in
§ 503.32(b)(5) shall be met when sewage
sludge that meets the Class B pathogen
requirements in § 503.32(b)(2). (b)(3). or
(b)(4) is applied to the land.
(2) Class B—Alternative 1.
(i) Seven samples of the sewage
sludge shall be collected at the time the
sewage sludge is used or disposed.
(ii) The geometric mean orthe density
of fecal coliform in the samples
collected in paragraph (b)(2)(i) of this
section shall be less than either
2,000,000 Most Probable Number per
gram of total solids (dry weight basis) or
2,000,000 Colony Forming Units per
gram of total solids (dry weight basis).
(3) Class B—Alternative 2. Sewage
sludge that is used or disposed shall be
treated in one of the Processes to
Significantly Reduce Pathogens
described in appendix B of this part.
(4) Class B—Alternative 3. Sewage
sludge that is used or disposed shall be
treated in a process that is equivalent to
a Process to Significantly Reduce
Pathogens, as determined by the
permitting authority.
(5) Site Restrictions, (i) Food crops
with harvested parts that touch the
sewage sludge/soil mixture and are
totally above the land surface shall not
be harvested for 14 months after
application of sewage sludge.
(ii) Food crops with harvested parts
below the surface of the land shall not
be harvested for 20 months after
application of sewage sludge when the
sewage sludge remains on the land '
surface for four months or longer prior
to incorporation into the soil.
(iii) Food crops with harvested part
below the surface of the land shall not
be harvested for 38 months after
application of sewage sludge when the
sewage sludge remains on the land
surface for less than four months prior
to incorporation into the soil.
(iv) Food crops, feed crops, and fiber
crops shall not be harvested for 30 days
after application of sewage sludge.'
(v) Animals shall not be allowed to
graze on the land for 30 days after
application of sewage sludge.
(vi) Turf grown on land where sewage
sludge is applied shall not be harvested
for one year after application of the
sewage sludge when the harvested turf
is placed on either land with a high
potential for public exposure or a lawn,
unless otherwise specified by the
permitting authority.
(vii) Public access to land with a high
potential for public exposure shall be
restricted for one year after application
of sewage sludge.
(viii) Public access to land with a low
potential for public exposure shall be
restricted for 30 days after application of
sewage sludge.
(c) Domestic septage. (1) The site
restrictions in § 503.32(b)(5) shall.be
met when domestic septage is appliec
agricultural land, forest, or a
reclamation site; or
(2) The pH of domestic septage
applied to agricultural land, forest, or a
reclamation site shall be raised to 12 or
higher by alkali addition and. without
the addition of more alkali, shall remain
at 12 or higher for 30 minutes and the
site restrictions in § 503.32 (b)(5)(i)
through (b){5)(iv) shall be met.
§ 503.33 Vector Bttraction reduction.
(a)(l) One of the vector attraction
reduction requirements in § 503.33
(bKl) through (b)(10) shall be mat when
bulk sewage sludge is applied to
agricultural land, forest, a public contact
site, or a reclamation site.
(2) One of the vector attraction
reduction requirements in § 503.33
(b)(l) through (b)(8) shall be met when
bulk sewage sludge is applied to a lawn
or a home garden.
(3) One of the vector attraction
reduction requirements in § 503.33
(b)(l) through (b)(8) shall be met when
sewage sludge is sold or given away in
a bag or other container for application
to the land.
(4) One of the vector attraction
reduction requirements in § 503.33
(b)(l) through (b)(ll) shall be met wht
sewage sludge (other than domestic
A-3
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Federal Register / Vol. 58. No. 32 / Friday, February 19. 1993 / Rules and Regulations J4M
ptage) is placed on an active sewage
udgeunit.
(5) One of the vector attraction
duction requirements in § 503.33
)(9), (b)(10). or (b)(12) shall be met
hen domestic septage is applied to
ricultural land, forest, or a
damation site and one of the vector
traction reduction requirements in
503.33 (b)(9) through (b)(12) shall be
at when domestic septage is placed on
active sewage sludge unit
(b)(l) The mass of volatile solids in
e sewage sludge shall be reduced by
ninimum of 38 percent (see
Iculation procedures in
invironmental Regulations and
chnology—Control of Pathogens and
'Ctor Attraction in Sewage Sludge",
A-625/R-92/013,1992. U.S.
vironmental Protection Agency,
icinnati, Ohio 45268).
;2) When the 38 percent volatile
lids reduction requirement in
03.33(b)(l) cannot be met for an
aerobically digested sewage sludge,
-tor attraction reduction can be
monstrated by digesting a portion of
! previously digested sewage sludge
aerobically in the laboratory in a
ich-scale unit for 40 additional days
a temperature between 30 and 37
grees Celsius. When at the end of the
days, the volatile solids in the
vage sludge at the beginning of that
-iod is reduced by less than 17
•cent, vector attraction reduction is
lieved.
3) When the 38 percent volatile "
ids reduction requirement in
03.33(bHD cannot be met for an
obically digested sewage sludge,
;tor attraction reduction can be
nonstrated by digesting a portion of
previously digested sewage sludge
t has a percent solids of two percent
ess aerobically in the laboratory in
ench-scale unit for 30 additional days
:0 degrees Celsius. When at the end
he 30 days, the volatile solids in the
/age sludge at the beginning of that
iod is reduced by less than 15
cent, vector attraction reduction is
ieved.
0 The specific oxygen uptake rate
>UR) for sewage sludge treated in an
obic process shall be equal to or less
n 1.5 milligrams of oxygen per hour
gram of total solids (dry weight
is) at a temperature of 20 degrees
sius.
;) Sewage sludge shall be treated in
lerobic process for 14 days or longer.
ing that time, the temperature of the
age sludge shall be higher than 40
rees Celsius and the average
perature of the sewage sludge shall
liglier than 45 degrees Celsius.
(6) The pH of sewage sludge shall be
raised to 12 or higher by alkali addition
and. without the addition of more alkali,
shall 'remain at 12 or higher for two
hours and then at 11.5 or higher for an
additional 22 hours.
(7) The percent solids of sewage
sludge that does not contain
unstabilized solids generated in a
primary wastewater treatment process
shall be equal to or greater than 75
percent based on the moisture content
and total solids prior to mixrnc with
other materials. •
(8) The percent solids of sewage
sludge that contains unstabilized solids
generated in a primary wastewater
treatment process shall be equal to or
greater than 90 percent based on the
moisture content and total solids prior
'to mixing with other materials.
(9)(i) Sewage sludge shall be injected
below the surface of the land.
(ii) No significant amount of the
sewage sludge shall be present on the
land surface within one hour after the
sewage sludge is injected.
(Hi) When the sewage sludge that is
injected below the surface of the land is
Class A with respect to pathogens, the
sewage sludge shall be injected below
the land surface within eight hours after
being discharged from the pathogen
treatment process.
(10)(i) Sewage sludge applied to the
land surface or placed on a surface
disposal site shall be incorporated into
the soil within six hours after
application to or placement on the land.
(ii) When sewage sludge that is
incorporated into the soil is Class A
with respect to pathogens, the sewage
sludge shall be applied to or placed on
the land within eight hours after being .
discharged from the pathogen treatment
process.
(11) Sewage sludge placed on an
active sewage sludge unit shall be
covered with soil or other material at
the end of each operating day.
(12) The pH of domestic septage shall
be raised to 12 or higher by alkali
addition and, without the addition of
more alkali, shall remain at 12 or higher
for 30 minutes.
Subpart E—Incineration
f 503.40 Applicability.
(a) This subpart applies to a person
who fires sewage sludge in a sewage
sludge incinerator, to a sewage sludge
incinerator, and to sewage sludge fired
in a sewage sludge incinerator.
(b) This subpart applies to the exit gas
from a sewage sludge incinerator stack.
i 503.41 Special definition*. '
(a) Air pollution control device is one
or more processes used to treat the exit
gas. from a sewage Kludge incinerator
stack.
(b) Auxiliary fuel is fuel used to
augment the fuel value of sewage
sludge. This includes, but is not limited
to, natural gas, fuel oil, coal, gas
generated during anaerobic digestion of
sewage sludge, and municipal solid
waste (not to exceed 30 percent of the
dry weight of sewage sludge and
• auxiliary fuel together). Hazardous
wastes are not auxiliary fuel.
(c) Control efficiency is the mass of a
pollutant in the sewage sludge fed to an
incinerator minus the mass of that
pollutant in the exit gas from the
incinerator stack divided by the mass of
the pollutant in the sewage sludge Gad
to the incinerator.
(d) Dispersion factor is the ratio of the
increase in the ground level ambient air
concentration for a pollutant at or
beyond the property line of the site
where the sewage sludge incinerator is
located to the mass emission rate for the
pollutant from the incinerator stack.
(e) Fluidized bed incinerator is an
enclosed device in which organic matter
and inorganic matter in sewage sludge
are combusted in a bed of particles
suspended in the combustion chamber
gas.
(f) Hourly average is the arithmetic
mean of all measurements, taken during
an hour. At least two measurements
must be taken during the hour.
(g) Incineration is the combustion of
organic matter and inorganic matter in
sewage sludge by high temperatures in
an enclosed device.
(h) Monthly average is the arithmetic
mean of the hourly averages for the
hours a sewage sludge incinerator
operates during the month.
(i) Risk specific concentration is the
allowable increase in the average daily
ground level ambient air concentration
for a pollutant from the incineration of
sewage sludge at or beyond the property
line of the site where the sewage sludge
incinerator is located.
(j) Sewage sludge feed rate is either
the average daily amount of sewage
sludge fired in all sewage sludge
incinerators within the property line of
the site where the sewage sludge
incinerators are located for the number
of days in a 365 day period that each
sewage sludge incinerator operates, or
the average daily design capacity for all
sewage sludge incinerators within the
property line of the site where the
sewage sludge incinerators are located.
(k) Sewage sludge incinerator is an
enclosed device in which only sewage
sludge and auxiliary fuel are fired.
(1) Stack height is the difference
between the elevation of the top of a
sewage sludge incinerator stack and the
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