&EPA
United States
Environmental Protection
Agency
Office of Health and
Environmental Assessment
Washington, DC 20460
EPA/600/6-88/003
November 1985
Research and Development
Pathogen Risk
Assessment Feasibility
Study
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EPA/600/6-88/003
November 1985
PATHOGEN RISK ASSESSMENT
FEASIBILITY STUDY
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Office of Health and Environmental Assessment
Environmental Criteria and Assessment Office
Cincinnati, Ohio 45268
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DISCLAIMER
This report has been reviewed 1n accordance with U.S. Environmental
Protection Agency policy and approved for publication. Mention of trade
names or commercial products does not constitute endorsement or
recommendation for use.
11
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PREFACE
Pathogens 1n sludge, especially pathogenic bacteria, viruses, protozoa,
helminths and fungi have been studied for many years. Studies range from
enumeration of microorganisms before and after various treatments to
ep1dem1olog1cal documentation of the role of aerosolized pathogens 1n human
Infection and disease. Mathematical models also have been developed. In
order to determine whether the Information and models are sufficient to
adequately define a risk assessment, this study has been undertaken. The
study focuses on an analysis and evaluation of existing data on pathogens
from the viewpoint of their usefulness for risk assessment.
111
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FOREWORD
Section 405 of the Clean Hater Act requires the U.S. Environmental
Protection Agency to develop and Issue regulations that: (1) Identify uses
for sludge Including disposal; (2) Identify specific factors to be taken
Into account 1n determining the measures and practices applicable for each
use or disposal (Including costs); and (3) Identify concentrations of
pollutants that Interfere with each use or disposal. In order to comply
with this mandate, EPA has embarked on a major program to develop four major
technical regulations: land application (Including distribution and market-
Ing), landfUUng, Incineration and ocean disposal. The development of
these technical regulations will address pathogens as well as chemical
constituents of sludge. Public concern related to the reuse and disposal of
municipal sludge often focuses around the Issue of pathogenic organisms.
The purpose of this study was to evaluate the feasibility of conducting risk
assessments for pathogenic organisms for four reuse/disposal options. The
study further evaluated the data bases and models on pathogens In sludge.
The first draft was prepared by Battelle Columbus Laboratories under
Contract No. 68-01-6986.
1v
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DOCUMENT DEVELOPMENT
Authors
Contributors and Reviewers (cent.)
L. Fradkln
S. Lutkenhoff
Office of Health and Environmental
Assessment
Environmental Criteria and Assessment
Office, Cincinnati, OH
U.S. Environmental Protection Agency
£. Lomnltz
Office of Water Regulations
and Standards
Criteria and Standards Division
U.S. Environmental Protection Agency
Washington, DC
B. Cornaby
N.G. Relchenbach
Battelle Columbus Laboratories
Columbus, OH
C.A. Sorber
Dean, College of Engineering
University of Pittsburgh
Pittsburgh, PA
Contributors and Reviewers
.Dr. E. Akin, Director
Dr. H. Jakubowskl
Dr. N.E. Kowal
Toxicology and Microbiology
Division
Health Effects Research Laboratory,
Cincinnati, OH
U.S. Environmental Protection Agency
Dr. C. Brunner
Dr. J. Parrel!
Dr. J. Stern
Dr. A. Venosa
Wastewater Research Division
Water Engineering Research Laboratory,
Cincinnati, OH
U.S. Environmental Protection Agency
Dr. C.S. Clark
Institute of Environmental Health
Ketterlng Laboratory
University of Cincinnati
Cincinnati, OH
Dr. C.B. Gerba
Department of Microbiology and
Immunology
University of Arizona
Tucson, AZ
Dr. C.N. Haas
PMtzker Department of Environmental
Engineering
Illinois Institute of Technology
Chicago, IL
Dr. B.P. Saglk
Drexel University
Philadelphia, PA
Dr. R.L. Ward
3.N. Gamble Institute of Medical
Research
Cincinnati, OH
Dr. M. Dourson
Dr. L. Erdrelch
Dr. V. Holak
Dr. 3.F. Stara, Director
Office of Health and Environmental
Assessment
Environmental Criteria and Assessment
Office, Cincinnati, OH
U.S. Environmental Protection Agency
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TABLE OF CONTENTS
Page
1. SUMMARY AND CONCLUSIONS 1-1
2. INTRODUCTION . . . 2-1
3. OCCURRENCE OF PATHOGENS IN UNTREATED AND TREATED SLUDGE
PRODUCTS: INITIAL CONDITIONS 3-1
3.1. INTRODUCTION 3-1
3.2. PATHOGENS IN PRIMARY, SECONDARY AND MIXED SLUDGES 3-2
3.2.1. Bacteria 3-4
3.2.2. Viruses 3-6
3.2.3. Helminths 3-6
3.2.4. Protozoans 3-7
3.2.5. Fungi 3-8
3.3. DISTRIBUTION AND ABUNDANCE OF PATHOGENS 3-8
3.3.1. Bacteria and Viruses 3-8
3.3.2. Parasites 3-9
3.4. EFFECTS OF CONVENTIONAL SLUDGE TREATMENT PROCESSES
ON PATHOGENS 3-14
3.4.1. Anaerobic Digestion 3-14
3.4.2. Aerobic Digestion . 3-19
3.4.3. Composting 3-24
3.4.4. Lime Stabilization 3-30
3.5. SUMMARY 3-35
4. FATE AND TRANSPORT OF PATHOGENS: DATA BASE 4-1
4.1. INTRODUCTION 4-1
4.2. LANDFILLS 4-2
4.2.1. Pathogens and Microorganisms Present In
Landfills ....... 4-4
4.2.2. Survival Characteristics and Factors
Affecting Survival 4-7
4.2.3. Routes of Movement for Pathogens from
Landfills 4-11
4.3. LAND APPLICATION 4-12
4.3.1. Pathogens and Microorganism In Land
Application 4-14
4.3.2. Survival Characteristics 4-14
4.3.3. Movement of Pathogens 4-18
4.3.4. Routes of Movement for Pathogens from
Land Application 4-26
vl
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TABLE OF CONTENTS (cont.)
4.4. DISTRIBUTION AND MARKETING
4.4.1. Pathogens 1n D&M 4-28
4.4.2. Survival Characteristics 4-28
4.4.3. Movement of Pathogens 4-28
4.4.4. Routes of Movements from D&H Sites . 4-28
4.5. OCEAN DISPOSAL 4-29
4.5.1. Pathogens Isolated from Mater, Sediment,
and Biota 4-32
4.5.2. Transport: Settling, Resuspenslon, and
Dispersal of Pathogens 4-34
4.5.3. Survival of Sludge-Associated Pathogens 1n
the Marine Envlroment 4-39
4.6. INCINERATION . 4-40
4.7. TRANSPORT OF PATHOGENS THROUGH GROUNDWATER, SURFACE
WATER AND AEROSOLS . . 4-40
4.7.1. Movement and Survival Rates of Pathogens In
Groundwater ..... 4-41
4.7.2. Movement and Survival Rates of Pathogens 1n
Surface Water 4-45
4.7.3. Movement and Survival Rates of Aerosolized
Pathogens 4-52
4.8. SUMMARY. 4-53
5. REVIEW OF EXISTING MICROBIOLOGICAL RISK ASSESSMENT MODELS . ... 5-1
5.1. INTRODUCTION 5-1
5.2. MODEL SELECTION . 5-1
5.3. MODEL DESCRIPTIONS 5-2
5.3.1. Seattle Model .... 5-3
5.3.2. Sandla Model 5-6
5.3.3. Wastewater Model 5-10
5.4. RISK ASSESSMENT INFORMATION REQUIREMENTS . . 5-12
5.4.1. Characteristics ... 5-12
5.4.2. Attributes. 5-18
5.5. SCORING PROCEDURE AND MODEL COMPARISONS 5-20
5.6. SUMMARY 5-24
V11
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TABLE OF CONTENTS (cont.)
Page
6. EXPOSURE SITE AND EXPOSURE ASSESSMENT 6-1
6.1. INTRODUCTION 6-1
6.2. LIKELIHOOD OF EXPOSURE 6-1
6.3. INFECTIOUS DOSE 6-8
6.4. SUMMARY 6-14
7. DATA UNCERTAINTIES AND GAPS 7-1
7.1. INTRODUCTION 7-1
7.2. UNCERTAINTIES IN METHODOLOGIES 7-1
7.3. DATA GAPS 7-3
7.4. SUMMARY 7-5
8. REFERENCES 8-1
APPENDIX A: Data Tables A-l
APPENDIX B: Model Scoring Sheets B-l
V111
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LIST OF TABLES
No. Title Page
3-1 Pathogens of Primary Concern 1n Sewage Sludges. 3-3
3-2 Reported Incidences of Disease from All Sources per 1000
People, According to Geographic Region of the United
States, for 1977 3-10
3-3 Percentage of Sludge Samples from Four Northern States
and from Five Southern States that Contained Eggs of
Various Parasites and the Mean Number of Total and
Viable Eggs of Each Parasite Recovered. 3-12
3-4 Analysis of the Relationship of Population, Wastes,
State and Season to the Density of Viable Eggs of
Various Parasites 1n Positive Samples of Undigested
Sludge from Four Northern and Southern States 3-13
3-5 Densities of Various Organisms Before and After
High-Rate Anaerobic Digestion at Full-Scale WWTP 3-18
3-6 Densities of Various Organisms Before and After
(Conventional and Auto-Heated) Aerobic Digestion
at Laboratory and Full-Scale WWTP . 3-22
3-7 Reductions of Pathogens 1n Forced A1r Composting Systems. . . 3-26
3-8 Reductions of Pathogens 1n Deep Pile Bin Composting
Systems 3-27
3-9 Reductions of Pathogens 1n Lime-Stabilized Sludge Types ... 3-32
3-10 Summary of the Effects of Treatment on Pathogens. ...... 3-36
4-1 Numbers of Microorganisms 1n Three Different Solid
Wastes Used In Landfill Studies 4-5
4-2 Gram-Negative Bacteria Isolated from Three Different
Solid Waste Sources ( + = present; - = absent) Used In
Landfill Studies 4-6
4-3 Gram Negative Bacteria Identified 1n Sludge Used
to Construct Lyslmeters 4-8
4-4 Survival Characteristics of Bacteria 1n Leachates
from Lyslmeters Containing Sewage Sludge 4-9
4-5 A Summary of Bacterial Die-Off 1n Soil 4-15
4-6 Soil Factors Affecting Infiltration and Movement
(Leaching) of Bacteria 1n Soil 4-19
1x
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LIST OF TABLES (cont.)
No. Title
4-7 A Summary of Studies on Bacterial Transport Through Soils . ,
4-8 Isolation of Viruses In Wastewater Beneath Land
Application Sites 4-23
4-9 Sizes of Haterborne Bacteria, Viruses, and Parasites 4-25
4-10 Survival Times of Bacteria and Viruses on Crops 4-30
4-11 Human Enteric Viruses Isolated from Water, Sediment or
Crab Samples Obtained In and Around the Philadelphia and
New York Bight Dump Sites (PDS and NYB, respectively)
and Between the Two Dump Sites (BDS) 4-33
4-12 Frequency of Isolation (X of Stations Positive Out
of Number Sampled In Each Zone) of Total Conforms
(TC), Fecal Conforms (FC), Fecal Streptoccod (FS),
and Amoebae (Am) from Sediment Samples as a Function
of Distance from the Center of the Dump Site 4-35
4-13 Frequency of Isolation of Human Enteric Viruses 1n
Samples of Water, Sediment and Crabs In and Around the
Philadelphia and New York Bight Dump Sites (PDS and
NYB, respectively) and Between the Two Sites (BDS) 4-38
4-14 Die-off Rate Constants for Viruses and Bacteria 1n
Groundwater 4-42
4-15 Viral and Bacterial Die-Off Rates 1n Water 4-43
4-16 Die-Off Rates of Viruses 1n Groundwater Samples 4-44
4-17 Survival Time (days) of Pathogens 1n Marine and Freshwater
Environments 4-46
4-18 Survival Time (days) of Pathogens 4-48
4-19 In. situ Survival of Enterovlruses In Ocean Water 4-50
4-20 Survival of Enterovlruses 1n Freshwater Environments. .... 4-51
4-21 Summary of Transfer and Fate Information at the
Disposal Site 4-55
4-22 Summary of Transfer and Fate Information from the
Disposal to the Exposure Site 4-57
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LIST OF TABLES (cont.)
No. Title Page
5-1 Ratings for the Three Risk Assessment Models Selected
for Evaluation Against the "Idealized" Criteria for a
Risk Assessment for Pathogens 1n Sludge ...'.• 5-22
6-1 Likelihood of Exposure of Pathogens to Humans as Related
to Sludge Disposal Methods and Associated Pathways 6-3
6-2 Infectious Dose for Pathogens of Primary Concern 6-10
6-3 Likelihood of Exposure from Pathogens to Humans as
Related to the Number of Organisms Potentially Present
1n Each Pathway and the Infectious Dose 6-13
6-4 Capability of the Three Models Evaluated to Perform a
Risk Assessment for the Most Likely Exposure Pathways
for Each Disposal Method. ......... 6-15
7-1 Summary of Data Gaps. 7-4
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LIST OF FIGURES
No. TUIe
3-1 Reduction of Total Conform Bacteria and Salmonella sp.
at Various Temperatures Achieved During Open Windrow
Composting . 3-28
4-1 Universal Pathway Model for Movement of Pathogens 4-3
4-2 Pathogen Transformations and Transport from the Land
Areas Receiving Sludge 4-13
4-3 Total Conforms 1n Bottom Waters at Various Locations
1n the New York Bight Apex, May 1975, 1977, 1978, and
October 1978 4-37
5-1 Pathways of Mlcroblal Transport from Sludge 1n Compost
Application from Seattle Metro Model 5-5
5-2 General Sludge Treatment Pathway from Sandla Model. ..... 5-8
5-3 Sludge Application Pathway — Fertilizer for Pasture
Crops from Sandla Model 5-9
5-4 Model Scoring Sheet 5-13
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LIST OF ABBREVIATIONS
Am Amoebae
CPU Colony-forming units
D&M Distribution and Marketing
FC Fecal col 1 forms
GDkf Grams dry weight
NYB New York Bight
pdf Probability density function
PDS Philadelphia dump site
PFRP Processes to further reduce pathogens
PFU Plaque-forming units
PSRP Processes to significantly reduce pathogens
TC Total conforms
HWTP Hastewater treatment plant
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1. SUMMARY AND CONCLUSIONS
The general Issue Investigated by this study 1s whether a risk assess-
ment 1s feasible for the health effects of exposure to pathogens 1n sludge.
The emphasis Is on environmental situations rather than worker protection.
The purpose of this study was to analyze and evaluate existing data and
models on pathogens 1n sludge 1n order to determine whether the Information
and models are sufficient to adequately define a pathogen risk assessment
for the five major reuse/disposal options: distribution and marketing, land
application. Incineration, landfllUng and ocean dumping.
The study advances the view that sufficient data exist and models are
available to handle the data. The following summarizes the key points and
findings contained within this document:
1. Varying quantities and qualities of data are available for a limited
number of pathogen species 1n order to conduct a microbiological risk
assessment. Sometimes It Is necessary to substitute one species for
another. For example, details about one pathogenic bacterium species
may not be available for movement In soil, and another bacterium species
may be substituted because It 1s assumed that many bacteria behave
similarly. At least two models of the three evaluated can accept and
!
manipulate these data.
2. The kinds and concentrations of pathogenic bacteria, viruses, helminths,
protozoa and fungi have been documented 1n the literature for sewage and
sludges. Concentrations range from 10* to 10s per gram dry weight
for fecal Indicator bacteria to 101 to 10* for other bacteria,
viruses and parasites. It Is possible to Identify pathogens In sludge
Including Salmonella, hepatitis A virus, rotavlrus, Ascarls and 61ard1a.
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3. Studies on the effects of anaerobic digestion, aerobic digestion, com-
posting and Time stabilization treatment processes revealed reductions
In concentrations of pathogens of 0.5-4 orders of magnitude. Composting
has dramatic reductions of 2 to >4 orders of magnitude for bacteria,
viruses and parasites. By contrast, Hme stabilization treatment
reduces bacteria by 0.5-4 orders, by >4 orders of magnitude for viruses
and by <0.5 orders of magnitude for parasites. The other treatment
methods have Intermediate degrees of reduction.
4. Limited data are available on transport and fate of microorganisms from
disposal slte(s) to exposure s1te(s). At all disposal sites, pathogen
concentrations may be reduced by dilution, temperature, moisture, sun-
light, pH and presence of antagonistic organisms. Physical parameters
also can affect the transport and fate of pathogens. For example, the
soil structure may act as a barrier to movement, allowing viruses
(0.02-0.08 vm} and bacteria (1-10 vm) to pass more freely than
helminth eggs (28+ pm) and protozoa (5-20 ym).
5. Five major pathways from disposal site to exposure sites (surface water,
groundwater, soil/sediments, food, and aerosols/partlculates) are
presented 1n a 14-compartment pathway model and are described 1n
considerable detail 1n the text.
6. The Seattle model and the Sandla model can track pathogens through some
of the pathways mentioned 1n conclusion 5 and to some extent describe
the Influence of environmental variables on pathogen concentrations.
7. The Seattle model 1s simple mathematically and 1s designed to utilize
the existing data base. The Sandla model 1s more complex and requires
more data than presently available. These models can be Improved by
adding transport functions to the Seattle model or eliminating parts of
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the Sandla model and thus simplifying H. Modification of these models,
therefore, makes the risk assessment of pathogens 1n sludge conceptually
feasible at this time.
8. Uncertainties and data gaps are numerous. A major uncertainty arises
from the variety of measurement techniques and varying quality control.
Major data gaps Include population dynamic Information about Important
species, Implications of pathogens bound to sludge, and relationships
between Infectious dose and disease (case histories), which If not
filled would require such extrapolation or Interpolation that the
accuracy of model predictions are seriously compromised.
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2. INTRODUCTION
Pathogenic organisms of human origin found 1n sewage sludge Include
certain bacteria, viruses, fungi, protozoa and helminths. Sludge-borne
pathogens are contaminants of concern especially when sludges are disposed
by the landfill, land application, distribution and marketing, or ocean
options; this concern Is due to the potential for contamination of soils,
air, groundwater and surface waters, and subsequent transmission of these
contaminants to animals and man. Once In the soil, groundwater, surface
water or air, there 1s the potential for pathogenic organisms to enter
drinking water supplies and systems, adhere to plants and be Ingested or be
Inhaled by animals or man. For example, pathogens remain viable on plants
for several days. They can be Ingested and, 1f the dose 1s sufficient,
humans may become Infected and may contract a disease. In the ocean, patho-
gens can be concentrated by organisms such as shellfish 1n their tissues.
Once consumed, pathogens 1n these seafoods can pass through the food chain
to ultimately pose a health hazard to man. In addition, ocean disposal of
sludge may pose additional potential hazards by contaminating recreational
waters, which subsequently affect humans. Thus, pathogens can move from the
human and animal populations through treatment, disposal, and exposure
sites, and If conditions permit survival, pathogens may reach humans and
Infect or relnfect them. Conversely, sludge Incineration effectively
destroys pathogenic organisms; therefore, pathogens should not be of concern
when this method 1s used.
This feasibility study was conducted In order to evaluate the potential
for performing a microbiological risk assessment. The goal of this type of
assessment 1s to provide reasonable predictions of the time-dependent
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concentrations and locations of pathogens within the constraints of data
uncertainties. The concentrations of pathogens can then provide a basis to
assess the likelihood and consequences of undesirable events such as Infec-
tion, disease or fatality. The output of the risk assessment 1s the
probability of the occurrence of an event that can subsequently be used to
analyze trade-offs regarding the benefit of the sludge disposal methods and
the acceptability of predicted consequence. Existing Information was
analyzed and evaluated on pathogens 1n sludge and appropriate risk models In
order to determine whether the Information and models are sufficient to
adequately define risk assessment.
Data on representative species are available on only a few species of
pathogens from the large number present In sludge. The criteria used to
select these representative species Include the following:
• Known occurrence In municipal sludge
• Knowledge that the pathogen causes disease In the general
population
• Hore extensive Information base for the species than for other
species of the principle pathogen groups
• Known Infectious doses
• Survival of species outside the human host
• Greater survlvabllHy of pathogen under environmental conditions
Thus, species are selected as examples from each of the principle pathogen
groups: 1) Salmonella as an example of enteric bacteria, 2) pollovlrus for
viruses, 3) Glardla for protozoans, 4) Ascarls for helminths, and 5) Asper-
glllus fumlgatus for fungi.
The Informational constraints related to specific pathogens 1s a major
consideration when modeling because, although a model can be assembled for
pathogens for which there 1s Uttle or no data, the predictions of such a
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model may be misleading. In other words, models require an adequate data
base to establish relationships between variables. These relationships may
be defined 1n tables, graphs, diagrams, verbal statements, or equations.
The usual connotation of "mathematical model" 1s that of one or more
equations that define one or more cause-effect or prediction-predictor
relationships. Models are an approximation of reality, yet they must still
mimic reality and assure the user that complex matters are being simplified
1n a realistic way. Because a model Is an approximation of reality,
decisions have to be made regarding which components of reality can be
relaxed and which cannot. It 1s more practical to model a few species as
opposed to hundreds of species. Representative species are therefore
selected as species to be modeled and substitutes are used only when needed.
Risk assessment takes all the components previously described concerning
pathways, representative species and modeling, and formulates this Informa-
tion Into better focused output. It permits the evaluation of whether
existing treatments and disposal options should be more or less strict or
whether additional options should be used to reduce the flow of pathogens
from sludges to the human population.
In order to evaluate the potential for performing a microbiological risk
assessment, the following questions must be answered:
Is 1t possible to Identify "bad actor" pathogens 1n sludge?
What Is the variability In the numbers and types of organisms
found 1n sludge?
• Can "worst-case" and "average-case" situations be Identified
for performing risk assessments?
What models exist that can be used In the risk assessment?
What are the strengths and weaknesses of these models?
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• What assumptions must be made 1n performing a risk assessment
for human exposure to pathogens 1n sludge?
» What uncertainties need to be addressed 1n order to permit an
accurate (realistic) assessment?
This report addresses the feasibility of conducting a risk assessment.
A review of pathogens 1n raw sewage representing Initial conditions for a
model, particularly 1n the case of treatment failure 1s presented. Informa-
tion 1s obtained for various treatment options. An assessment of the data
on transport and fate of pathogens between the disposal site and the
exposure site are presented and microbiological risk assessment models are
reviewed for their strengths and weaknesses.
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3. OCCURRENCE OF PATHOGENS IN UNTREATED AND TREATED SLUDGE PRODUCTS:
INITIAL CONDITIONS
3.1. INTRODUCTION
Several studies have documented the kinds of pathogens found 1n
untreated sewage and assessed the effects of sewage treatment processes on
pathogens by reviewing the literature (Pedersen, 1980; BDH Corp., 1980; Hard
et a!., 1984). These three documents were used as primary sources of
Information 1n preparing this chapter. A computer search for additional
literature did not provide more relevant Information.
In the following sections, a synthesis and Integration of Information
relative to pathogens 1n untreated sewage and treated sludge products have
been undertaken. First, the occurrence of pathogens 1n primary, secondary
and mixed sludge was reviewed. Primary sludge 1s produced by primary treat-
ment of sewage, I.e., screening and settling. Secondary sludge 1s sludge
produced by secondary treatment processes, I.e., biological waste treatment.
Mixed sludge 1s a combination of primary and secondary sludge. This Infor-
mation 1s the starting point for knowledge about pathogens and concentra-
tions that can be placed on or In the land and 1n the ocean; It represents
Initial conditions 1n a model. Next, the distribution and abundance of
pathogens relative to regions, seasons, and human population sizes are
presented. This Information also provides Initial conditions for a risk
assessment. An evaluation of the effects of various conventional sludge
treatments on the Inactlvatlon of pathogens follows. Sludge treatment
processes examined Include anaerobic digestion, aerobic digestion, compost-
Ing and lime stabilization. Criteria were established to screen the litera-
ture for evaluating the feasibility of pathogen risk assessment modeling.
Finally, a summary presents the major points of this chapter.
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3.2. PATHOGENS IN PRIMARY, SECONDARY AND MIXED SLUDGES
Sewage contains many potentially harmful constituents. Pathogenic
organisms constitute one class of contaminants found 1n sewage and because
of their potentially harmful effect on the health of humans and other
animals, the disposal of wastewaters, sludge, and by-products must be done
In an acceptable manner minimizing the risk of Infection.
In the literature, the types (species) of pathogenic organisms are well
recognized, but concentrations of organisms present at each stage of waste-
water sludge treatment and disposal are disparate and frequently not
comparable, being affected by many variables such as temperature, detention
time, moisture and solids content, as well as basic composition of the raw
wastewater and sludge. With the exception of a few laboratory experiments
and field monitoring studies reported 1n the literature, the primary source
of quantitative data Is found In Pedersen (1980). Descriptions of patho-
genic organisms 1n sludge and characteristics of the diseases they cause are
discussed In Rehm et al. (1983), Booz-Allen and Hamilton (1983a), and Hard
et al. (1984).
Pathogens of primary concern reported In the literature are listed 1n
Table 3-1. The pathogens of primary concern are those that are 1) asso-
ciated with a relatively high Incidence of disease, 2) found In relatively
high concentrations In sewage sludge, 3) exhibit relatively high resistance
to environmental stresses, 4) detectable with available methods, and
5) exhibit low Infectious doses (Booz-Allen and Hamilton, 1983b; Rehm et
al., 1983).
Appendix Tables A-l, A-2 and A-3 report densities of pathogens and Indi-
cators In a variety of situations In primary, secondary and mixed sludges,
respectively. Representative and Indicator organisms are Included 1n these
3-2
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TABLE 3-1
Pathogens of Primary Concern In Sewage Sludges*
Type
Organism
Disease
Bacteria
Viruses
Helminths
Protozoans
Fungi
Campylobacter lej
Escher1ch1a coll
{pathogenic strains)
Salmonella sp.
Shlgella sp.
Vibrio cholerae
Enterovlruses
Pollovlrus
Coxsacklevlrus
Echovlrus
Hepatitis A virus
Norwalk viruses
Norwalk-I1ke viruses
Reovlrus
Rotavlrus
Necator amerlcanus
Taenla sp,
Toxocara sp.
Tr1chur1s sp.
Ascarls sp.
Hymenolepls nana
Toxoplasma qond11
Balant1d1um col 1
Entamoeba hlstolytlca
Glardla Iambi la
Cryptospor1d1um
Asperglllus fumlqatus
gastroenteritis
gastroenteritis
gastroenteritis, enteric fever
gastroenteritis
cholera
gastroenteritis, meningitis,
cardHls, central nervous system
Involvement, pneumonia.
Infectious hepatitis
gastroenteritis
gastroenteritis
respiratory infections, gastro-
enteritis
gastroenteritis. Infant diarrhea
hookworm
taenlasls
visceral larva mlgrans
whlpworm Infestation
ascarlasls
taenlasls
toxoplasmosls
balantldlasls
ameblc dysentery
g1ard1as1s
gastroenteritis
asperglllosls or respiratory
Infections
*Source: Last, 1980; Ward et al., 1984
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tables because, although rarely pathogenic, their presence 1s Indicative of
contamination by fecal matter. The densities of total conforms, fecal
conforms, and fecal streptococci have generally been reported 1n variously
treated sludges as Indicators of the effectiveness of pathogen control
procedures. These organisms are the classic Indicator organisms for the
presence of fecal material 1n sewage. Regardless, controversy exists on the
efficacy of bacterial representatives to predict the presence and Inactlva-
tlon of other types of pathogens (Pedersen, 1980).
3.2.1. Bacteria. Published lists of pathogens of primary and secondary
concern 1n sludge are 1n general agreement (Rehm et a!., 1983); however,
there 1s some disagreement over the degree of concern about some genera,
I.e., Leptosplra and Yerslnla. Both are pathogenic bacteria transmitted 1n
animal wastes to humans, but Infections are sporadic, owing to the low
resistance of the pathogens to wastewater treatment.
Salmonella has been studied more than any other pathogenic bacterium
found In sewage. Rehm et al. (1983) cite 1700 types of Salmonella, and
their presence In or reduction through treatment and disposal procedures has
been widely studied (Josephson, 1974; Saglk et al., 1979; Ward et al., 1980;
Kothary et al., 1980a; Reddy et al., 1981; Burge et al., 1981; Slkora et al,
1982). Their virulence varies from strain to strain.
Four species of Shlgella are pathogenic and relatively few data are
reported on their presence 1n raw sewage and sludges and on their response
to treatments other than anaerobic digestion (Sacramento Area Consultants,
1979).
Vibrio cholerae Is considered a pathogen of primary concern even though
cholera transmission from sludges Is considered unlikely (Booz-Allen and
3-4
-------
Hamilton, 1983a). Rehm et al. (1983) lists V. cholerae as a pathogen of
secondary concern because of Us low resistance to wastewater treatment.
Densities of V. cholerae 1n sludges, like many other pathogens, are poorly
known.
Escherichla coll and Campylobacter jejunl can cause severe cases of
gastroenteritis and are listed as pathogens of primary concern by Rehm et
al. (1983). Acceptable concentrations of £_._ coll have been established for
bathing waters (MHO, 1982), and a few monitoring studies have reported E_.
coll densities (Oosephson, 1974; Saglk et al., 1979). Although t. 3e3un1
consistently appears on primary pathogen lists, Us densities 1n sludge are
not enumerated. A Center for Disease Control project has estimated that
this bacterium may outrank Salmonella as the leading cause of bacterial
diarrhea, especially 1n Infants (Rehm et al., 1983).
Densities of pathogenic bacteria 1n raw sewage are extremely site-
dependent and a risk assessment model must accommodate this. Representative
organism densities are the most frequently reported and range from 10s to
10s organisms per 100 ml of raw sewage (WHO, 1982). In primary sludge,
for example. Salmonella densities of 102 to TO3 per gram dry weight are
reported, and a density of 9xl02 1n secondary sludge (Ward et al., 1984)
(see also Appendix Tables A-l and A-2). Thus, densities of some micro-
organisms may not change appreciably In primary, secondary and mixed
sludges. Densities of bacterial pathogens of secondary concern In raw
sewage sludge have been estimated by Saglk et al. (1979) to be 6.0x10*
colony-forming units (CPU) per 100 ms. for Klebslella. 4.6xlOs CFU/100
ma, for Leptosplra. and 5.8x10° CFU/100 mi for Yers1n1a» See Appendix
Table A-3 for additional densities of bacteria and other pathogens 1n mixed
sludges.
3-5
-------
3.2.2. Viruses. There 1s general agreement that the viruses most likely
to cause Infections are the enterovlruses (pollovlruses, coxsacklevlruses A
& B, echovlruses) Norwalk and Norwalk-Uke viruses, and hepatitis A virus
(Kowal, 1982), and rotavlrus (Rehm et a!., 1983; Booz-Allen and Hamilton,
1983b). The 1nact1vat1on of pathogens 1n wastewater have been found to
occur at any time during the sewage treatment process. However, all enteric
viruses survive at low temperatures and may be found at the disposal sites.
Eventually they may cause Infection associated with diseases such as gastro-
enteritis, polio and meningitis.
Densities of viruses 1n raw sewage sludge are on the order of several
hundred plaque-forming units (PFU) per liter (Booz-Allen and Hamilton,
1983b). Bertucd et al. (1977) calculated, dally 1nact1vat1on rates ranging
from 74.9-93.2% 1n seeded experiments with various viruses 1n anaeroblcally
digested sludge. There 1s a general consensus that current deficiencies 1n
recovery techniques, culturlng problems, and the lack of suitable Indicator
organisms hamper the study of virus behavior In sludge. This must be
considered when attempting to model viruses.
3.2.3. Helminths. The eggs of parasitic worms are resistant to many
disinfectants (Pahren et al., 1979) and conventional low temperature sludge
stabilization processes. However, high temperatures found In some sludge
stabilization processes Inactivate many parasitic eggs (Relmers et al.,
1980, 1984). Host of the helminths listed as pathogens 1n sludge are only
Incidentally a problem to humans In the United States, mostly Infecting
dogs, cats and other animals.
A reduction of helminth ova occurs In primary sludge. Ward et al.
(1984) reported 101 to 102 ova/gram dry weight In primary sludge (see
also Appendix Table A-l). Hard et al. (1984) report that no organisms were
3-6
-------
detected 1n secondary sludge from the review of several studies. This may
be due to the fact that 1n many Instances, the relatively heavy parasite
eggs settle out 1n the primary clarlfler and never get to the secondary
treatment. Arther et al. (1981) found that viable ova of Ascarls. Toxacara.
Toxascarls and Tr1churls were capable of surviving anaerobic digestion and
lagoonlng for several months.
3.2.4. Protozoans. Of the four protozoan species listed 1n Table 3-1,
three may be considered as potentially harmful to humans: Entamoeba
hlstolytlca. Glardla lamb11a and Balantldlum coll. The three protozoans
that cause acute enteritis symptoms are E. hlstolytlca. causing amoebic
dysentery In humans; G. lamblla. the causal agent of glardlasls; and B.
coll. causing balantldlasls 1n humans. Toxoplasma gondl1 Is actually an
animal parasite; humans become Infected by accidental Ingestlon of eggs or
cysts, which causes toxoplasmosls. Consequently, transmission of Toxoplasma
gondll through sewage sludge 1s not considered significant (Rehm et al.,
1983).
In marine environments, two strains of pathogenic amoebae {Acanthamoeba
culbertsonl and A. hatchettl) have been found 1n association with sludge
disposal sites (Sawyer et al., 1982). Host probable numbers of these
amoebae were not reported.
Densities of protozoans 1n sewage sludge are frequently not reported In
the literature. Relmers et al. (1980) reported "few" nonvlable G1ard1a
cysts In their field studies of southern sludges. Relmers et al. (1980)
also found viable Entamoebae coll cysts 1n primary sludges, but postulated
that the less resistant ova of £. hlstolytlca. the human pathogen, would
probably not survive past primary treatment. The densities presented 1n
Appendix Tables A-l, A-2 and A-3 from Pedersen (1980) for parasite ova/cysts
are primarily Entamoebae coll and helminths.
3-7
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3.2.5. Fungi. Asperglllus fumlqatus 1s the most common fungus found 1n
wood chips used 1n composting sludges. Investigators agree that this fungus
1n sludge 1s of primary Importance although thus far, studies have shown Its
relatively low disease Incidence (Booz-Allen and Hamilton, 1983a,b; Metro,
1983; Rehm et a!., 1983). However, results from other studies Indicate that
health studies on workers engaged 1n composting waste materials should be
continued since sludge composting has been practiced for a relatively short
time (Clark et a!., 1984).
Hlllner et al. (1977) reported densities of A. fumlqatus on composting
sludge to be >10a colony-forming units (CFU) per gram dry weight. They
further report the presence of the fungus In atmospheric samples up to 8 km
from the compost site at Beltsvllle, Maryland. Investigators at the
Beltsvllle plant reported 3590 CFU/m3 60m downwind from the site (Surge
and HUlner, 1980). Kothary et al. (1980b) reported 3720 CFU/m^ 1n air
samples taken downwind (10 m) from a composting facility In Camden, New
Jersey. Mo density figures are reported for A. fumlqatus spores 1n raw
sewage or primary or secondary sludges. Booz-Allen and Hamilton (1983a)
recommended reducing potential risk from this pathogen by 1) Initiating
compost storage requirements that would reduce CFU to relatively Insignifi-
cant levels If retained over 1 month, 2) restricting locations of facili-
ties, and 3) Imposing buffer zones and employee screening programs.
3.3. DISTRIBUTION AND ABUNDANCE OF PATHOGENS
3.3.1. Bacteria and Viruses. Neither bacteria nor viruses are confined
to specific geographic regions but rather both are widespread throughout
roost areas of the United States (see Appendix Tables A-l, A-2 and A-3),
where conducive environments exist for the development and growth of these
pathogens.
3-8
-------
Pathogenic bacteria and viruses appear to be ubiquitous In sewage,
regardless of Us geographical origin. This 1s especially true for the most
common pathogens, such as Shlqella and Salmonella, and enterovlruses com-
pared with foreign organisms such as V1br16 cholerae. Even though bacteria
and viruses appear to be ubiquitous, Infections from pathogens associated
with sewage are somewhat dependent on community and seasonal variations,
reflecting the proportion of carriers or Incidences of disease present at
any given time.
Incidences of reported diseases that have etlologlcal agents found 1n
sewage are shown 1n Table 3-2. Incidences of Infections similarly show
seasonal variations. Craun (1984) compiled the Information on the variation
of outbreaks of diseases In the United States between 1971 and 1979 result-
Ing from the use of untreated groundwater. Warmer months (Hay through
August) show -13% Incidence of outbreaks compared with 0-8% for colder
months (September through April). Incidences of Infections from enteric
viruses also reach their peaks In warmer months {late summer and early fall;
Metro, 1983). although this seems to be strain-dependent. According to the
Metro study, cold weather viruses Include Hepatitis A, rotavlruses, and
adenovlruses. Warm weather viruses Include coxsacklevlruses, echovlruses
and pollovlruses.
3.3.2. Parasites. The studies by Relmers et al. (1980, 1984) Indicate
that densities of total and viable parasite eggs from helminths observed
were generally slightly lower 1n northern waste sludges than 1n southern
sludges. Furthermore, Ascarls eggs (total and viable) were found to be
variable In some of the northern states with the state of Washington being
higher than Ohio, New York and Minnesota.
3-9
-------
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Table 3-3 gives the percentage of sludge samples from both northern and
southern states that contained the four previously mentioned common
helminths. Mean numbers for all parasites with the exception of Toxocara
were higher In southern states than 1n northern states. Mean Toxocara
densities for the four northern states were nearly double those of the five
southern states.
Relmers et al. (1984) assessed the effects of population, wastes,
regions and seasons on the density of total eggs of the four common
parasites 1n both the northern and southern states. Table 3-4 gives the
probabilities of each test parameter and Its association with the density
levels of viable parasites' eggs for northern and southern states, respec-
tively.
3.3.2.1. NORTHERN STATES — The densities of viable eggs of T. vulpls
and Toxocara were significantly related to the size of the population served
with both occurring 1n decreasing densities with Increasing population 1n
the northern regions. Both Ascarls and T. trlchlura were not found to be
related to the size of the population.
The densities of viable eggs of Ascarls,, T. trlchlura and Toxocara were
found to vary from state to state (see Table 3-4). Greater densities of
viable Ascarls and T. trlchlura eggs were found In sludges from New York and
Washington than from Minnesota. No other differences were noted for these
two parasites. T. vulpls viable egg densities did not vary significantly
between states, while Toxocara viable egg densities were found to be
significantly greater 1n Ohio and New York than 1n Minnesota.
In regard to seasonal differences, only T. trlchlura viable egg
densities varied with fewer viable eggs found 1n the summer and winter than
1n the fall.
3-11
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TABLE 3-3
Percentage of Sludge Samples from Four Northern States and from Five
Southern States that Contained Eggs of Various Parasites and the
Mean Number of Total and Viable Eggs of Each Parasite Recovered3
Eggs
Helminths
AscaMs
T. trlchlura
aSource: Relmers et al.f 1984
bNumber of eggs per kilogram of dry weight of sludge sample
Toxocara
Total
% Positive
Mean No.b
Viable
% Positive
Mean No.b
Total
% Positive
Mean No.b
Viable
% Positive
Mean No.b
54%
1900
4854
. 1400
81%
2800
74%
2500
NORTH
36%
380
25%
200
SOUTH
45%
910
25%
880
42%
290
37%
260
71%
470
61%
430
79%
1400
69%
1100
75%
790
63%
680
3-12
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TABLE 3-4
Analysis of the Relationship of Population, Wastes, State and Season to
the Density of Viable Eggs of Various Parasites 1n Positive Samples of
Undigested Sludge from Northern and Southern States3*^
Helminth
Ascarls
T. trlchlura
T. vulpls
Toxocara
Ascarls
T. trlchlura
!• vulPls
Toxocara
No. of
Samples
79
41
48
118
74
30
48
67
--
C«™». nf
bize or
Populations
Served
NORTHERN STATES
p>0.25
p>0.25
0.05>p>0.01
p<0.001
SOUTHERN STATES
p>0.25
0.05>p>0.01
p>0.25 _-
p>0.25
State
0.05>p>0.01
0.05>p>0.01
p>0.25
0.05>p>0.05
0.25>p>0.10
p<0.001
p>0.25
p>0.25
Season
p>0.25
0.05>p>0
0 . 1 0>p>0
p>0.25
0.25>p>0
p>0.25
p>0.25
0.1>p>0.
.01
.05
.10
05
aSource: Relmers et al'., 1984
bTh1s Is the probability that the listed parameter 1s by chance associated
with the density level of parasite eggs. If the parameter was observed to
be significant (p<0.05), 1t was taken Into account 1n the testing of subse-
quent parameters.
3-13
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3.3.2.2. SOUTHERN STATES — The density of viable T. trlchlura eggs
was found to vary Inversely with the size of the population served. The
other three parasites did not demonstrate a relationship to the population
served (see Table 3-4).
Within regions, T. trlchlura viable egg densities were found to vary
significantly with the Louisiana and Texas Gulf having greater viable egg
densities than Inland Texas. No slgnfleant differences were observed for
Ascarls. T. vulpls or Toxocara viable egg densities for regional analysis.
No significant differences were found to exist between seasons for Ascarls.
X- trlchlura. T. vulpls and Toxocara.
The Information presented on geographic or seasonal variation can be
used to guide and focus efforts 1n a risk assessment. For example, 1f a
pathogen species Is most prevalent during the summer, then the environmental
conditions for this season could be modeled as a worst-case situation.
Similarly, smaller population centers, which may have greater densities of
parasites, may be of greater Interest 1n Initial modeling efforts than large
population centers, which appear to have lower densities.
3.4. EFFECTS OF CONVENTIONAL SLUDSE TREATMENT PROCESSES ON PATHOGENS
3.4.1. Anaerobic Digestion.
3.4.1.1. PROCESS DESCRIPTION AND EFFECTS ON PATHOGENS -- Anaerobic
digestion 1s the microbiological degradation of organic substances present
In sludge 1n the absence of oxygen. Primary and secondary sludges are
digested In an air-tight reactor for varying periods of time. EPA has
designated that for anaerobic digestion to qualify as a Process to Signifi-
cantly Reduce Pathogens (PSRP), residence times In the reactor must range
from 60 days at 20°C to 15 days at 35-55°C. and a 38% reduction 1n volatile
solids must be accomplished (40 CFR Part 257).
3-14
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The three basic types of anaerobic digestion are low-rate digestion,
high-rate digestion and two-stage digestion. The low-rate digestion 1s
where the sludge 1s unmixed In the reactor and the processes of sludge
thickening and liquid solid separation are conducted simultaneously. No
data are available on the pathogen km from low-rate digestion. In high-
rate digestion, the continually mixed reactor 1s heated to speed up the
microblal processing of sludge. High-rate reactors are operated at either
mesophlUc (30-38°C) or thermophlUc (50-60°C) temperatures. High-rate
reactors have shorter detention times than low-rate reactors (I.e., 30-60
days for low-rate digesters versus 10-20 days for high-rate digesters). In
the two-stage process, a high-rate digester 1s linked In series to another
digestion reactor operated as a low-rate digester; 1t 1s unheated and
unmixed. The primary reactor 1s used for digestion, while the second
reactor performs liquid solid separation.
Information on the effects of anaerobic digestion on pathogens 1s avail-
able from laboratory studies and from monitoring of full-scale operations.
In laboratory bench-scale studies, pathogens are frequently added or spiked
Into the sludge and their density levels monitored at different times of
digestion or under different operational conditions. Following a review of
the literature, Pedersen (1980) concluded that, because of different operat-
ing parameters, few laboratory-scale studies can be related to results
obtained at full-scale treatment plants. Pedersen (1980) also concluded
that 1t 1s questionable whether seeded pathogen behavior mimics that of
naturally occurring organisms, which are bonded to various degrees to sludge
particles. In Interpreting the effects of full-scale anaerobic digestion on
pathogens, consideration has to be given to the type of digestion (I.e.,
low-rate, high-rate or two-stage), temperature, retention time, and source
3-15
-------
of sludge. Complicating the picture 1s the fact that standard methods for
the determination of pathogens 1n sludge exist for only a few micro-
organisms, e.g., fecal and total conforms and fecal streptococci. The
uncertainty associated with the various pathogen numbers reported In the
literature further complicates comparisons and Interpretations. More about
this methodological situation 1s discussed In Chapter 7 on data uncertain-
ties and gaps. An additional problem noted by Pedersen (1980) was the lack
of consistent data relative to the die-off ra^te of pathogens during sludge
stabilization. Few of the studies reviewed by Pedersen (1980) reported the
experimental or operating conditions under which data were collected. These
problems hampered the thorough evaluation of the ability of anaerobic diges-
tion and other PSRPs to reduce pathogens. For these reasons, the numbers of
pathogens present and reductions reported In the discussions that follow
should be viewed with these reservations In mind.
3.4.1.2. EVALUATION CRITERIA — Upon examining the available litera-
ture on the behavior of pathogens 1n the anaerobic digestion process, 1t
became necessary to establish criteria to screen the voluminous literature
to arrive at Interpretable pathogen numbers applicable to a risk assessment.
Thus, the following criteria were developed to screen the literature:
1. Reported data are for a full-scale wastewater treatment plant
(WWTP).
2. Data on pathogens 1n raw and digested sludge are presented.
3. The type of anaerobic digester 1s reported.
4. Information on detention time, operational temperature and
volatile solids reduction are reported.
The first criterion was established because many If not most of the
laboratory-scale anaerobic digestion studies on pathogen InactWatlon were
conducted under operating conditions divergent from typical full-scale
3-16
-------
operations. Second, the literature has raised questions about how well the
spiked or seeded organisms mimic naturally occurring pathogens. Finally, H
was noted that data from full-scale operating anaerobic digesters provide
the most realistic numbers on pathogen 1nact1vat1ons.
The criterion that "data on pathogens 1n the raw sludge and digested
sludge are reported" was Imposed so that the reduction efficiency (pathogen
reduction) could be assessed associated with a particular type of anaerobic
digestion process. Because several types of anaerobic digestion processes
(low-rate, high-rate and two-stage} are available, 1t 1s Important to know
what type of system was operative In causing a reduction In pathogens. In
turn, the data can be Interpreted more easily for risk assessment purposes.
The efficacy of anaerobic digesters 1n Inactivating pathogens depends
upon operational conditions In the digester. Major factors known to Influ-
ence pathogen 1nact1vat1on Include sludge detention time, reactor tempera-
ture, and reactor efficiency 1n reducing sludge volatile solids. Without
this Information, It Is difficult to assess whether or not the pathogen
1nact1vat1on observed 1s representative of real world conditions. These
factors can therefore be used to evaluate which values for pathogen 1nact1-
vatlon should be used during Initial conditions In risk assessment models.
3.4.1.3. REDUCTION OF PATHOGENS — Table 3-5 (a summary of Appendix
Table A-4) provides examples of the effects of full-scale anaerobic diges-
tion systems on a variety of pathogens found In sludges. Total conforms
1nact1vat1on by high-rate anaerobic digestion had a log reduction ranging
from 1.78-2.30. The log reduction 1s log... of the number obtained by
dividing the Initial concentration by the final concentration. Fecal
collform bacteria showed log reductions ranging from 1.44-2.33. Fecal
streptococci showed a similar log reduction range of 1.10-1.94. The range
of log reductions reported for Salmonella was 0.91-3.97. Pseudomonas
3-17
-------
TABLE 3-5
Densities of Various Organisms Before and After High-Rate
Anaerobic Digestion at Full-Scale WWTP
Organism
Log
Reduction
Reference
Total conform bacteria
Fecal conform bacteria
Streptococcus spp.
Salmonella spp.
Pseudomonas aeruglnosa
Staphylococcus aureus
Enterovlruses
Parasite ova
2.06
1.78
2.30
<5.4
<2.7
1.66
1.79
1.98
1.44
2.33
<3.3
1.66
1.10
1.94
<3.4
1.75
3.32
3.97
1.89
0.91
2.08
0.149
1.0
Increase
1.36
1.05
<2.67
Lue-H1ng et al., 1977
Berg and Berrnan, 1980
Jewell et al., 1980
Berg and Berrnan, 1980
Berg and Berman, 1980
Lue-H1ng et al., 1977
Berg and Berman, 1980
Jewell et al., 1980
Sacramento Area Consultants, 1979
Sacramento Area Consultants, 1979
Berg and Berman, 1980
Lue-H1ng et al., 1977
Berg and Berman, 1980
Jewell et al., 1980
Stern and Parrel!, 1977
Cooke et al., 1978
Cooke et al., 1978
Cooke et al., 1978
Lue-H1ng et al., 1977
Stern and Farrell, 1977
Jewell et al., 1980
Lue-H1ng et al., 1977
Jewell et al., 1980
Lue-Hing et al., 1977
Jewell et al., 1980
Berg and Berman, 1980
Berg and Berman, 1980
Jewell et al., 1980
3-18
-------
aeruqlnosa was more resistant to 1nactlvat1on by high-rate anaerobic diges-
tion, having a log reduction range of 0.15-1.0. Enterovlruses have a log
reduction of 1.05-1.36. Ova or cysts of parasitic tapeworms, flatworms, and
roundworms survive high-rate anaerobic digestion operated at roesophHlc
temperatures based on the data In Table 3-5.
3.4.1.4. CONCLUSIONS REGARDING ANAEROBIC DIGESTION — The following
conclusions can be reached regarding the effects of high-rate anaerobic
digestion operating at 35°C with a detention time of 14-15 days based on
results from full-scale wastewater treatment plant studies:
Approximately 2-log (actually 1.9H0.73) reduction for total
conforms, fecal conforms, fecal streptococci, Salmonella. and
naturally occurring enterovlruses can be expected.
• Ova and cysts of parasitic worms, 1n general, are resistant to
1nact1vat1on except for Trlchlnella splralls. which are reduced
to below detection levels (Relmers et a!., 1980).
Very few data are reported on the effects of low-rate anaerobic
digesters operated at ambient temperatures on pathogen 1nact1-
vatlon (Pedersen, 1980).
3.4.2. Aerobic Digestion.
3.4.2.1. PROCESS DESCRIPTION AND EFFECTS ON PATHOGENS -- In the
aerobic digestion process, wastewater sludge Is stabilized by biochemical
oxidation of organic matter and endogenous oxidation of the cell tissue of
microorganisms. For aerobic digestion to qualify as a PSRP, volatile solids
reduction should be at least 38% and detention times should be at least 60
days at 15°C, or at least 40 days at 20°C {40 CFR 257). Operational param-
eters of some existing treatment plants may not satisfy these conditions
(Farrah and BHton, 1984). Many aerobic digesters are operated 1n the
mesophlllc temperature range but at detention times of 10-20 days. This Is
because reduction of volatile solids Is the primary objective, and Inactlva-
tlon of pathogens 1s not an operational parameter.
3-19
-------
There are three types of aerobic digestion processes: conventional
semi-batch digestion, conventional (mesophlUc) continuous digestion and
occasionally autoheated (thermophlUc) continuous digestion. In the
serai-batch operation, solids are pumped directly from the clarlfler Into the
continually aerated digester. When the digester 1s full, aeration continues
for 2-3 additional weeks (U.S. EPA, 1979). The conventional continuous
operation, which closely resembles the activated sludge process, consists of
a flowthrough aerobic digester followed by a clar1f1er/th1ckener. Many
conventional aerobic digesters are operated In the ambient temperature
ranges. Because the majority of these digesters are open tanks, the sludge
temperatures are dependent on weather conditions and can fluctuate exten-
sively. In the autoheated mode of operation, sludge from the clarlflers Is
usually thickened to provide a digester feed sol Ids fraction of >4X. In
these digesters, thermophlUc conditions result from the exothermal heat of
substrate oxidation.
When compared with anaerobic digestion, relatively few studies on the
fate of representative and pathogenic organisms during aerobic digestion of
sludge have been reported. It appears that most of these available data are
on the 1nact1vat1on of pathogens 1n thermophlUc aeroblcally digested
sludge. Pedersen (1980) noted that little research had been conducted on
the effect of mesophlUc aerobic digestion on bacterial and viral pathogens.
The limited number of laboratory and full-scale studies Indicate that
conventional digestion reduces the concentration of viable Indicator
organisms, bacterial and viral pathogens (Farrah and BUton, 1983, 1984;
Scheuerman, 1984). The major factor Influencing the survival of these
organisms was the temperature of sludge digestion. The survival of bacteria
1s also reported to be Influenced by total solids, pH, detention time, and
3-20
-------
the type of bacteria. Because of the hydraulic characteristics of continu-
ous process, the digested sludge will likely have reduced levels of patho-
gens but would not be expected to be free of pathogens.
Full-scale studies show that autoheated aerobic sludge digestion
(54-65°C) 1s more effective than the mesophHlc anaerobic process (35°C) In
reducing the survival of Pseudomonas and Salmonella spp., bacterial Indi-
cators, viruses and parasites (Kabrlck et al., 1979). High bacterial
Inactlvatlon levels are reported for aerobic digestion when operated at
45-56°C (Farrah and Bltton, 1983; Smith et al., 1975).
The Information on the 1nact1vat1on of these organisms during aerobic
digestion should be carefully Incorporated In risk assessment because of the
limited data availability and uncertainties associated with the experimental
methods. Most Importantly, the Information provides Initial conditions for
a model.
3.4.2.2. EVALUATION CRITERIA — Because the Information on pathogen
reduction during aerobic sludge treatment 1s limited, available laboratory
and full-scale data were considered. The following criteria were used In
screening the literature on aerobic digestion:
1. Reported data are for laboratory or full-scale operations.
2. Data are provided on pathogens 1n the raw and aeroblcally
digested sludge.
3. The type of aerobic digester 1s reported.
4. The operational conditions of the aerobic digester are reported
(I.e., detention time and temperature).
3.4.2.3. REDUCTION OF PATHOGENS — Table 3-6 provides a summary of
Appendix Table A-5. Both provide reported data on the reduction of several
organisms during conventional and autoheated continuous digestion and batch
digestion of sludge. The reduction of total and fecal conform bacteria,
Streptococcus spp.. Salmonella spp. and Pseudomonas aeruglnosa was high 1n
3-21
-------
TABLE 3-6
Densities of Various Organisms Before and After (Conventional and
Auto-Heated) Aerobic Digestion at Laboratory and Full-Scale HWTP
Organism
Total collform bacteria
Fecal conform bacteria
Streptococcus spp.
Salmonella spp.
Pseudomonas aeruglnosa
Log Reduction
1.53
1.99
1.02
1,92
0.91
4.5
2.6
4.9
4.6
3.9
1.52
1.09
3.3
3.2
2.7
1.03
1.63
0.77
1.71
1.1
3.8
1.6
4.1
4.0
2.3
4.7
>2.1
>0.88
>2.3
>2.9
>1.1
>2.2
0.70
0.67
Author
Farrah and BHton, 1984
Farrah and BHton, 1984
Farrah and BHton, 1984
Farrah and Bltton, 1984
Farrah and BHton, 1984
Kabrlck et al. 1979
Kabrlck et al. 1979
Kabrlck et al. 1979
Kabrlck et al. 1979
Kabrlck et al. 1979
Farrah and BHton, 1984
Farrah and BHton, 1984
Kabrlck et al., 1979
Kabrlck et al., 1979
Kabrlck et al., 1979
Farrah and BHton, 1984
Farrah and BHton, 1984
Farrah and BHton, 1984
Farrah and BHton, 1984
Farrah and BHton, 1984
Kabrlck et al., 1979
Kabrlck et al., 1979
Kabrlck et al., 1979
Kabrlck et al., 1979
Kabrlck et al., 1979
Kabrlck et al., 1979
Kabrlck et al., 1979
Kabrlck et al., 1979
Kabrlck et al., 1979
Kabrlck et al., 1979
Kabrlck et al., 1979
Kabrlck et al., 1979
Kabrlck et al., 1979
Kabrlck et al., 1979
3-22
-------
TABLE 3-6 (cont.)
Organism
Log Reduction
Author
Pollovlrus type 1 (LSC)<
Echovlrus 1*
Rotavlrus SA-11*
Coxsacklevlrus*
0.77
0.21
0.5
0.18
0.43
0.44
0.46
Scheuerman,
Scheuerman,
Scheuerman,
Scheuerman,
Scheuerman,
Scheuerman,
1984
1984
1984
1984
1984
1984
Scheuerman, 1984
*Laboratory bench study
3-23
-------
thermophHlc conditions even at low hydraulic detention times. Autoheated
digesters appear to be more effective than conventional mesophlllc digesters
1n reducing the concentration of total and fecal conform bacteria and
Streptococcus spp. (see Table 3-6). During the batch digestion, a signifi-
cant decrease 1n the removal of £. typhlmuMum. S. faecal Is. E_. coll and £.
aeruglnosa Is observed as digestion temperature ranges from 28.3°C to 6.2°C.
At the temperature range of 25-29°C, the rate of log reduction of viruses
does not appear to vary significantly with virus type.
3.4.2.4. CONCLUSIONS REGARDING AEROBIC DIGESTION — Based on the
limited Information available, the following conclusions can be reached.
During batch digestion, the reduction of S. typhlmuMum. S. faecalls and E_.
coll 1s approximately a log reduction per day at 28°C. At 6°C, log reduc-
tion per day of these organisms ranges from 0.1-0.23. A temperature change
from 6-2B°C does not affect the rate of reduction of P_. aeruglnosa. During
conventional continuous sludge digestion, the log reduction of densities per
grara of sludge of representative bacteria Is 1-2. During autoheated sludge
digestion, log reduction of total conforms, fecal conforms. Streptococcus
spp., Salmonella spp. and P_. aeruglnosa 1s >2.6, 2.7, 1.6, 0.9 and 0.7,
respectively. Concentration of viruses, as measured by total plaque forming
units, 1s below the detection limits when the digestion temperature and pH
are >40°C and pH 1s >7 (Kabrlck et a!., 1979).
3.4.3. Composting.
3.4.3.1. PROCESS DESCRIPTION — Composting 1s an aerobic microbio-
logical process of decomposing organic matter and producing humus. The
composting of sewage sludge frequently Involves combining dewatered primary
and secondary sludges with bulking agents such as shredded municipal refuse,
wood chips or dry compost to produce a composite of 40-70X solids. This
3-24
-------
material 1s then composted by one of several processes: windrow, forced
aeration or deep pile bin. As the material composts, temperature will
Increase, going from mesophlUc to thermophlUc. The compost mass 1s then
broken down after cooling and 1s allowed to mature or cure 1n stockpiles.
For composting to meet EPA's requirements to be a PSRP, 1t must 1) maintain
a minimum temperature of 40°C within the compost mass throughout the
composting period and 2} attain temperatures of >55°C for at least 4 hours
of the composting period.
3.4.3.2. EVALUATION CRITERIA — The following criteria were used to
screen the literature on the effects of composting on Inactlvatlon of
pathogens:
1. Reported data are for a full-scale wastewater treatment plant.
2. Data on pathogens In the raw sludge and composted sludge are
presented.
3. The type of mesophlUc digestion 1s Identified.
4. Information on composting time, operational temperatures and
location of sampling was provided.
3.4.3.3. REDUCTION OF PATHOGENS -- Tables 3-7 and 3-8 {summaries of
Appendix Tables A-6 and A-7) and Figure 3-1 provide examples of the reported
ranges of representative pathogens found 1n composted sludges. Data are
available showing the log reductions found 1n full-scale forced aeration
composting systems for total conforms, fecal conforms and Salmonella (see
Table 3-7). Similar data are also available for deep pile bin composting
(see Table 3-8). Only limited data on total conforms and Salmonella reduc-
tions during windrow composting are reported 1n the literature (Horvath,
1978). No literature reported the effects of closed composting systems on
Inactlvatlon of pathogens. Some data from laboratory and/or spiking experi-
ments on pathogenic bacteria other than Salmonella are discussed In Pedersen
3-25
-------
TABLE 3-7
Reductions of Pathogens 1n Forced A1r Composting Systems3
Organism
Total conforms
Fecal conforms
Salmonella
Sampling
Point
toe
top
middle
bottom
Internal
top 30 cm
toe
40 cm depth
center
40 cm depth
center
toe
toe
toe
middle
bottom
toe
40 cm depth
40 cm depth
toe
toe
toe
middle
bottom
toe
40 cm depth
center
40 cm depth
center
toe
Log
Reduction
5.1
>6.9
4.7
3.1
2.2
7.0
7.9
3.2
5.8
5.7
5.0
6.3
4.2
4.2
<0.08
<3.3
__
<0.7
2.2
1.7
Reference*1
Epstein et al.. 1976
lacobonl and Le Brun,
lacobonl, 1977
lacobonl, 1977
Epstein et al., 1976
Epstein et al., 1976
Epstein et al., 1976
Epstein et al., 1976
Epstein et al., 1976
lacobonl and Le Brun,
Epstein et al., 1976
Epstein et al., 1976
Epstein et al., 1976
Epstein et al., 1976
Epstein et al., 1976
lacobonl and Le Brun,
Epstein et al., 1976
Epstein et al., 1976
Epstein et al., 1976
Epstein et al., 1976
1978
1978
1978
aSource: Pedersen, 1980
^Epstein's study was conducted at Beltsvllle, Maryland.
was conducted at Carson, California.
lacobonl"s study
3-26
-------
TABLE 3-8
Reductions of Pathogens 1n Deep Pile Bin Composting Systems*
Organism
Total conforms
Fecal conforms
Salmonella
Fecal streptococci
Ascarls lumbrlcoldes
Sampling
Point
m
NR
30 cm
150 cm
120 cm
30 cm
150 cm
bottom
NR
30 cm
150 cm
120 cm
30 cm
150 cm
bottom
NR
30 cm
150 cm
NR
NR
NR
30 cm
Log
Reduction
<3.3
2.2-2.8
7.3
4.7
6.1
5.5
5.5
0.5
>4.0
7.6
4.7
5.4
5.2
5.2
0.2
>5.1
5.7
5.7
1.5
3.1-5.1
2.9
—
Reference
lacobonl and Livingston, 1977
lacobonl, 1977
lacobonl and Le Brun, 1978
lacobonl, 1977
lacobonl and Le Brun, 1978
lacobonl and Livingston, 1977
lacobonl and Le Brun, 1978
lacobonl, 1977
lacobonl and Le Brun, 1978
lacobonl and Livingston, 1977
lacobonl and Le Brun, 1978
lacobonl, 1978
lacobonl and Le Brun, 1978
lacobonl, 1977
lacobonl and Le Brun, 1978
*Source: Pedersen, 1980
NR = Not reported
3-27
-------
Q.
s
•h
z
o
h-
<
cc
liJ
O
Z
O
O
CC
LU
CD
o>
o
O Total Coliform
D Salmonella
A Temperature
10
20 30
TIME, days
40
-i 70
60
o
e
uT
50 a:
a:
UJ
40
bJ
I-
30
20
50
FIGURE 3-1
Reduction of total conform bacteria and Salmonella
temperatures achieved during open windrow composting.
Source: Adapted from Horvath, 1978.
sp. at various
3-28
-------
(I960). In most of the studies on virus 1nact1vat1on by composting, viruses
were seeded Into sludge prior to composting. Pedersen (1980) reviews the
results of a number of laboratory and/or viral seeding experiments on
composting effects or 1nact1vat1on. lacobonl and LeBrun (1978) obtained 2.0
viable ova of AscaMs lumbrlcoldes per gram dry weight (6DW) at a depth of
30 cm, and <1.6 ova/GDW at 150 cm In a deep pile bin composter operating for
24 days at an average temperature of 34°C. Horvath (1978) recovered viable
ova after 69 days In 120 cm deep windrows with Internal temperatures of
54-58°C. AsperqUlus fumlqatus grows on hot (50-60°C) working compost piles
and 1s also found 1n natural environments (Pedersen, 1980). Mlllner et al.
(1977) 1n Pederson (1980) studied Asperqlllus fumlqatus associated with a
forced-aeration static pile compost system. Before composting, levels of A.
fumlqatus 1n sludge were 10* to 103 CFU/GDH and 1n recycled wood chips,
2.6x10* to 6.1xl07 CFU/GDW. After composting 21 days, the A. fumlqatus
found In the composted sludge was dependent on the temperature with samples
collected at 40°C having 2.9xl03 to 4.5x10* CFU/GDW, those collected
from 40-60°C ha>lng 10s to S.OxlO5 CFU/GDW and those collected at 60°C
having no A. fumlqatus.
3.4.3.4. CONCLUSIONS REGARDING COMPOSTING — Based on the available
literature, the following general conclusions can be reached on pathogen
1nact1vat1on by composting:
1. Total conforms decline 1n numbers by more than 3 logs In
composting systems meeting requirements for PSRP.
2. Fecal conforms show decreases of 4 logs or more In numbers.
3. Laboratory studies Indicate that fecal streptococci are more
resistant to composting than total and fecal conforms
(Pedersen, 1980).
4- Salmonella are Inactivated by mesophHlc composting to
negligible densities.
3-29
-------
5. Other bacterial pathogens have not been assessed 1n full-scale
composting systems; thus, their 1nactWat1on behavior 1s
unknown. However, Pedersen (1980) made the following conclu-
sions based on laboratory data:
• Hycobacterlum tuberculosis will survive mesophHU com-
posting.
• Serratla marcescens will be quickly Inactivated.
• Shlgella sonnel and Staphyloccus aureus have been reduced 6
and 5 logs, respectively, by temperature/time conditions of
composting.
6. The viruses of concern 1n sludge are vulnerable to temperature
conditions of composting (Pedersen, 1980). However recent
research has shown that Hepatitis A can survive 80°C.
7. Laboratory studies have reported a 3-log reduction 1n ova In 1
hour at 50°C (Pedersen, 1980). Ascarls lumbrlcoldes ova have
been shown by Horvath (1978) to survive composting 1n full-
scale facilities.
8. Composting temperatures are conducive to the growth of Asper-
qlllus fumlgatus when wood chips are used, thus Increasing the
numbers of this potential pathogen.
3.4.4. Lime Stabilization.
3.4.4.1. PROCESS DESCRIPTION — Lime stabilization Involves applying
lime to sludge In quantities sufficient to raise sludge pH to ~12 for a
period of 2 hours. The high pH of this technique kills many microorganisms
but does not appreciably affect food sources or nutrients 1n the sludge.
H1th this process, a substantial Initial decrease 1n mlcroblal numbers has
been observed, but because the pH level of the sludge may drop greatly 1n a
few hours after lime addition, some bacterial populations are able to regrow
to substantial densities.
Varying the detention time and the pH affects the mortality of
organisms. Ideally, pH should be maintained at or above 12 with lengthened
detention times .at this high pH. This provides better overall pathogen
3-30
-------
destruction because of the Increased sludge-solids contact time 1n the high
pH environment. At wastewater treatment facilities, at least three methods
of lime stabilization are employed:
1. Lime Addition Before Dewaterlng. L1me Is added to the liquid
sludge with approximately a 15-mlnute mixing time; the sludge
1s dewatered and the sludge cake retains a pH of 12 for ~2
hours.
2. Batch L1me Addition. Lime 1s added to the mixed-sludge storage
tank. The sludge 1s then land-applied, with no dewaterlng.
3. Sludge Cake L1me Addition. Lime 1s added to the sludge cake
with mixing. No studies on the effectiveness of this procedure
have been found.
3.4.4.2. EVALUATION CRITERIA — Literature on the effects of Hme
stabilization on pathogens was examined with the following criteria In mind:
1. Reported data are for full-scale wastewater treatment plants.
2. Pathogen densities In raw sludge and finished (lime-stabilized)
sludge are presented.
3. The type of sludge evaluated 1s presented.
4. Information on pH, detention time and percent solids 1s given.
No studies of lime-stabilized sludges at full-scale WWTPs could be located;
therefore, bench- and pilot-scale studies were utilized.
3.4.4.3. REDUCTION OF PATHOGENS — Table 3-9 (a summary of Table A-8)
provides examples of densities for bacterial pathogens and representative
organisms 1n various I1me-stab1l1zed sludges. Only bench- and pilot-scale
data were available for total conform bacteria, fecal conform bacteria,
Salmonella spp. and Pseudomonas aeruqVnosa. In the review by Pedersen;
(1980), data on virus (Sattar et al., 1976} and helminth (egg) survival
(Noland et al., 1978; Relmers et al., 1980} In lime-stabilized sludge were
examined only from bench-scale tests using Inoculated raw sludge. These
studies showed that 1nact1vat1on of viruses occurred but lime-stabilization
had little effect upon helminth ova.
3-31
-------
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*
a>
ex
r-
eu
*0
3
r~
CO
Pathogens In L line-Stabilize!
u-
O
in
i
*j
u
3
T3
O)
ex:
o>
o>
u-
o>
1
Type/Soli ds L(
Rediu
O)
Cn
"O
a
r—
co
Organism
CO CO CO CO
O^ 7^ O~* CT^
rorocoro
flU CJ CJ QJ
"0 -0 -0 T»
O O O 0
z z z z
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•O 13
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re 0> ro L.
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S(
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rorocoro
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>» ro O) -Q
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6 H-> *- o>
Fecal conforms pr
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CO CO CO CO
en en en ^^ en
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«-> >•
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Fecal streptococcus pr
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se
sc
ar
O^ O^ O^ O^ O^
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c c c c c
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o o o o o
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en en en en en en en
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ns
O>
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, e^ i
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o o o o o o>> r- r^- r- r-
l_ u t_ t- U r— ffi OH ffi CT<
JM^^^JfeC »— i— i— r—
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33333 • • • • •
.C X: f f £ r— • • • •
COCOCOCOCO HJ i— r- r- r—
fQ CQ ^ fB
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vi in vi vi i—
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For Indicator bacteria, Noland et al. (1978) reported good reductions 1n
density for total and fecal conform bacteria and fecal streptococcus 1n
primary, waste-activated, septage, and anaeroblcally digested sludges (see
Table 3-9). Similar reductions were noted by Counts and Shuckrow (1974) 1n
laboratory-scale tests with either 2 or 4.4X solids In the sludge. Parrel!
et al. (1974) showed better reductions for fecal conform than fecal strep-
tococcus bacteria after 24-hour detentions at pH 11.5. Type of sludge had
little Impact on reductions of Indicator bacteria with lime-stabilization
according to Counts and Shuckrow (1974) and Noland et al. (1978).
For the two pathogenic bacteria, Salmonella spp. and Pseudomonas aeruql-
nosa. sludge type had Uttle or no Impact on survival (virtually complete
die-off) when lime-stabilization was carried out (Counts and Shuckrow, 1974;
Noland et al., 1978). £. aeruqlnosa was somewhat easier to kill or could
not regrow as well as Salmonella In the 1-hour to 1-day retention time study
of Counts and Shuckrow (1974). £. aeruqlnosa had greater survlvablllty than
Salmonella spp. at slightly lower lime-stabilized pH (10.5) according to
Parrel! et al. (1974). Sludge solids (percent) as studied by Counts and
Shuckrow (1974) showed generally higher survival of both pathogens tested In
the lime-stabilized sludge with higher solids.
3.4.4.4. CONCLUSIONS REGARDING LIME STABILIZATION OF SLUDGES — Based
on the available literature, the following general conclusions can be made
regarding 1nact1vat1on of representative pathogenic organisms.
At pH 11.0-12.4, fecal and total conform bacteria are reduced
(2-7 logs) In lime-stabilized sludges regardless of type of
sludge.
• Fecal streptococci are somewhat more resistant than fecal co!1-
forms with reduction of 1-3 logs. However, regrowth can occur;
1t can occur within 24-hours 1f pH decreases below 11.
• Salmonella spp. and Pseudomonas aeruqlnosa appear to be consis-
tently reduced at pHs near 12, but at lower pH (I.e., 10.5), P.
aeruqlnosa showed higher survival than Salmonella spp.
3-34
-------
Regrowth of Salmonella spp. or £. aeruqlnosa within 24 hours of
lime-stabilization to -12 pH was not evident.
Increasing solids concentration appeared to decrease the
attenuation of certain pathogenic bacteria.
3.5. SUMMARY
There are many Indigenous enteric pathogens 1n sewage. These pathogens
Include bacteria, viruses, helminths, protozoans and fungi. Total coll-
forms, fecal conforms, and fecal streptococci (Indicator bacteria) are
usually present 1n concentrations of 10s to 10a per gram dry weight of
sludge. Pathogenic bacteria, viruses, and parasites are present at lower
concentrations of 10* to 10* per gram dry weight of sludge.
Pathogens are found In all areas of the country. In the case of para-
sites, slightly greater numbers are found In the South than the North for
some species. When treatment facilities break down, greater concentrations
of pathogens are released to the disposal sites. Other trends Include
seasonal variation with higher concentrations present 1n the warmer parts of
the year.
Enteric pathogens are Inactivated to some degree by conventional sludge
stabilization processes designed to reduce volatile solids. However, some
processes are more efficient than others. For example, anaerobic digestion,
aerobic digestion, and liming of sludge can cause considerable destruction
of enteric bacteria and viruses but have little effect on certain parasites.
Composting, 1f properly conducted, 1s the best of the conventional processes
for Inactivating sewage sludge pathogens. Ward et al. (1984) summarized the
expected pathogen reductions associated with conventional sludge stabiliza-
tion processes as shown In Table 3-10.
3-35
-------
TABLE 3-10
Summary of the Effects of Treatment on Pathogens*
PSRP Treatment
Log Reductions
Bacteria
Viruses
Parasites
Mesophlllc anaerobic digestion
Aerobic digestion
Composting
A1r drying
Lime stabilization
0.5-4
0.5-4
2-4
0.5-4
0.5-4
0.5-2
0.5-2
2-4
0.5-4
4
0.5
0.5
2-4
0.5-4
0.5
*Source: Ward et al., 1984
3-36
-------
Hesophlllc anaerobic digestion of sludge results 1n good viral and
bacterial reductions but poor nematode and other helminth reductions {see
Table 3-10). By contrast, the literature shows that anaerobic digestion
effectively Inactivates most all pathogen groups. Data on pathogen Inactl-
vatlon during aerobic digestion of sludges are limited. Studies of labora-
tory, bench-scale and full-scale aerobic digesters Indicate pathogen 1nact1-
vatlon levels similar to those obtained In mesophlUc anaerobic digestion
(Hard et a!., 1984). Composting, 1f properly conducted, effectively Inacti-
vates most primary pathogens. The degree of pathogen Inactlvaton attained
In sludges during composting depends mainly on temperature: the higher the
temperature, the greater the pathogen 1nact1vat1on. However, the surfaces
of compost piles foster the growth of Asperqlllus fumlqatus. which can cause
chronic lung diseases 1n susceptible Individuals. Air drying of sludges to
low moisture levels has been reported (Hard et a!., 1984) to cause large
reductions In viable parasites and viruses 1n sludges. A1r drying 1n the
absence of elevated temperatures has a minimal effect on bacterial
pathogens. For lime stabilization to be an effective process for pathogen
inactlvatlon, a pH of 12 must be maintained for at least 2 hours, time
stabilization of sludges Inactivates viral and bacterial pathogens, but has
minimal effects on parasite ova.
In terms of data for risk assessment purposes, 1t 1s noted that the
literature on the occurrence of pathogens 1n sludge products Is diffuse and
disparate, making Integration and comparisons difficult. Lack of standard
methods for analyzing pathogens other than for a few Indicator organisms
contributes to the uncertainty associated with reported densities In
sludges, and this affects the level of technical rigor of a risk assessment.
3-37
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With the exception of bacterial Indicators (total conforms, fecal
conforms, fecal streptococci). Salmonella and Ascarls Iumbr1co1des. few
data are reported on pathogen Inactlvatlon by full-scale conventional sewage
sludge stabilization systems. For example, we must assume that pathogens
Including rotavlruses and hepatltus A behave as the enterovlruses enumerated
1n the reported virus density tests. Thus, a risk assessment has no alter-
native except to focus on these Indicator and representative organisms
particularly when the operational properties of these facilities have been
monitored and reported along with their efficacy In reducing pathogens. In
turn, such Information represents technically sound, Initial conditions for
a risk assessment study.
3-38
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4. FATE AND TRANSPORT OF PATHOGENS: DATA BASE
4.1. INTRODUCTION
After treatment by anaerobic, aerobic, composting, Hme stabilization or
other method, the sludge Is transported to reuse or disposal site. These
sites are usually on or 1n the land, but some are 1n the ocean. At the
site, pathogens undergo additional changes 1n concentrations and viability.
This chapter describes the types of available Information necessary to
Implement the fate and transport component In a risk assessment model.
Treated sludges are disposed 1n five major ways. Options are as follows:
Landfill Disposal of sludge 1n dedicated landfill,
trenching
Land application Direct application of sludge to agricul-
tural, pasture land, silviculture, and
reclamation areas
Distribution & marketing Direct application of sludge to gardens
(D&M) and municipal areas such as roadsides,
cemeteries and golf courses
Ocean Dumping sludge Into the ocean from a
barge or tanker
Incineration Combustion of sludge In a multiple hearth
or fluldlzed bed Incinerator
Part of the chapter addresses each of these and follows the general struc-
ture of 1} microorganisms/pathogens present at the disposal site, 2) their
survival characteristics, 3) their movement routes at and from the site, and
4) the routes of potential exposure. A brief presentation 1s provided on
the possible transport of pathogens from the disposal site to the exposure
site 1n surface water, groundwater and aerosols. A universal pathway model
was also developed to provide perspective to this chapter.
4-1
-------
The possible pathways for movement of pathogens from the disposal site
to the exposure site are shown 1n Figure 4-1. The figure Identifies a
number of pathways by which sludge constituents and pathogens can be trans-
/
ferred through the environment to exert potentially adverse effects on
humans. The pathways begin at the point where sewage enters a municipal
treatment plant. The first three portions of Figure 4-1 represent those
sewage treatment and sludge processing procedures necessary to bring the
sludge to the point where 1t 1s disposed or, In the case of distribution and
marketing (D&H), where a treatment plant, a retailer, or a broker can
distribute and market sludge products.
As Indicated In Figure 4-1, pathogens and sludge constituents can travel
various pathways to expose humans: from participates and aerosols In the
air, by direct contact with pathogens In soil, from surface water and leach-
Ing Into groundwater and eventually Into the drinking water supply, and from
pathogens on or 1n food. The universal pathway model yields additional
resolution. For example, pathogens 1n sludge products applied to land can
travel by two human consumption pathways, Ingestlon of crops and Ingestlon
of animal products contaminated by sludge pathogens.
4.2. LANDFILLS
LandfUled sludges are burled (or covered) beneath the surface of the
land at managed sites. To gain some perspective on the fate of microorgan-
isms from landfllled sludges, the discussion focuses on the microorganisms
present, survival characteristics of microorganisms, factors affecting the
survival of microorganisms, and major exposure routes. As much as possible,
the Information presented Is specific to microorganisms originating from
municipal sludge. However, the discussion 1s not limited to municipal
4-2
-------
L
//////////,
Land-Based /
Disposal Site '
(Landfill, Land '
Spread, Distribution'
and Marketing)
Exposure Pathway
Reexposure Pathway
FIGURE 4-1
Universal Pathway Model for Movement of Pathogens
4-3
-------
sludges, which 1s due to the general lack of specific Information, as well
as the fact that municipal sludges are often mixed with other wastes 1n
landfills.
4.2.1. Pathogens and Microorganisms Present 1n Landfills. The types of
microorganisms present 1n sanitary landfills containing sewage sludge depend
on the source of the waste materials and the type of treatment the waste has
undergone. Typical Initial conditions can be found In Chapter 3. Any class
of microorganism (bacteria, fungi, viruses, protozoa) 1s present.
Landfills containing sewage sludges mixed with municipal solid wastes
contain a more diverse mlcroblal population than landfills that contain only
one type of waste material. For example. In an extensive project dealing
with microorganisms In leachate from landfills, Scarplno et al. (1979)
separately characterized sewage sludge, hospital wastes, and municipal solid
wastes for specific mlcroblal groups (Table 4-1). Sewage sludge contained
more fecal Indicator organisms, especially total conforms, compared with
the hospital or municipal wastes. Municipal waste contained especially high
counts of fungi and streptococci.
Both pathogens and nonpathogens are present 1n wastes added to land-
fills. Donnelly and Scarplno (1984) characterized the gram-negative
bacteria associated with the solid wastes used for preparing lyslmeter
models of landfills (Table 4-2). Although many of the organisms listed are
opportunistic and may cause disease under certain conditions, six organisms
1n Table 4-2, Salmonella. Klebslella. Here!lea. Aclnetobacter. Moraxella and
Pasteurella. are considered pathogens. The sewage sludge contained three of
the pathogens, Klebslella. Aclnetobacter and Pasteurella hemolytlca.
4-4
-------
TABLE 4-1
Numbers of Microorganisms 1n Three Different Solid Wastes
Used In Landfill Studies3
Agar Plate Counts
(Colony-forming un1ts/g)
Plate-count agar
Blood — aerobic
Blood-anaerobic
Eosln methylene blue'3
Inhibitory mold
KF streptococcal
Mycoselc
Sabouraudc
Tellur1ted
Host Probable Number
Tubes (HPN/100 q)
Total conforms
Fecal conforms
Fecal streptococci
Sewage
Sludge
1.7xl08
4.1xl08
2.9xl08
1.5x10"
l.OxlQs
3.6xl05
7.5xl07
3.4x10^
2.6x106
2.8x10"
2.4x101°
3.3x10*
Hospital
Waste
3.8xl08
3.9xl08
2.2xl08
3.1x10°
3.89xlOs
3.0x10'
1.6x10'
2.5x10*
6.0x10'
9.0xl010
9.0x101°
8.6x101°
Municipal
Waste
4.3x10*
3.6xl09
3.5xl09
3.4x10*
6.9xl07
4.2xlOe
1.6x10'
2.5x10*
6.6x10'
7.7xlQi°
4.7xlOio
2.5xlOii
aSource: Scarplno et al.» 1979
^Indicates conforms
cFungal medium
dHed1um for streptococd/enterococcl group
4-5
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TABLE 4-2
Gram-Negative Bacteria Isolated from Three Different Solid Waste
Sources (+ = present; - = absent) Used 1n Landfill Studies*
Organism Sewage Hospital Municipal
Sludge Waste Waste
Escherlchla coll 4- 4- 4-
Salmonella sp. -4-4-
Enterobacter sp. +4- 4-
Klebslella sp. 4- 4- 4-
dtrobacter sp. 4-4- 4-
Serratla sp. t 4- 4-
Proteus sp. 4-4- +
Provldencla sp. 4- 4-
Aeromonas - 4- 4-
Flavobacterlum + * +
Herellea sp. 4- 4-
Aclnetobacter sp. 4- 4- 4-
Horaxella sp. . + +
Pasteurella hemolytlca +
Pseudomonas sp. +• + 4-
*Source: Donnelly and Scarplno, 1984
4-6
-------
The microorganisms associated with landfills depend on the waste
materials added. When Donnelly and Scarplno (1984) sampled leachates from a
large commercial landfill that had been In continuous operation for 30
years, organisms other than those listed 1n Table 4-2 were found. These
Included Asperqlllus nlger. Cephalosporlum. Clostr1d1um perfrlngens. Entero-
bacter aqqlomerans. E_. cloacae. Fusarlum. Hycobacterlum (a pathogen), Neuro-
spora. PenlcnUum. Provldenda alcallfadens. Pseudomonas fluorescens and
Streptococcus faecalls. Obviously, over a 30-year period the variety of
wastes added to the landfill would result In a diverse mlcroblal population.
Data concerning other microorganisms, such as viruses, specifically 1n
landfills, are sparse. However, 1t seems reasonable to conclude from
studies dealing with land application of sludges (BHton et a!., 1984) that
viruses added to landfills In municipal sludges may survive and could be
Isolated from landfill leachate. Studies have documented the presence of
viruses In solid waste landfills (Sobsey, 1978).
4.2.2. Survival Characteristics and Factors Affecting Survival. As
discussed above, few studies have dealt with the surv1vab1!1ty of sludge
microorganisms In landfills. The work reported by Scarplno et al. (1979)
and Donnelly and Scarplno (1984) appears to be the most definitive effort to
date. In general, mlcroblal populations were capable of surviving for
several years under landfill or landfill-simulated conditions. For example,
when laboratory lyslmeters were filled with sludge to mimic landfill condi-
tions and were monitored for microorganisms after 2 years, at least one
pathogenic species of bacteria survived (Table 4-3). Many bacteria that
were added Initially 1n the solid waste could not be recovered. In a more
Intensive effort, the lyslmeters containing sewage sludge were monitored
frequently for specific groups of microorganisms (Table 4-4). While the
4-7
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TABLE 4-3
Gram Negative Bacteria Identified In Sludge
Used to Construct Lyslmeters*
Initially Identified 1n
Identified 1n Sludge Lyslmeter Leachate After 2 Years
Aclnetobacter Aclnetobacter
Pasteurella hemolytlca Pseudomonas sp.
Escherlch.Va coll Alcallgenes faecalls
Enterobacter sp. Corynebacterlum acquatlcum
Klebslella sp. Corynebacterlum sp.
dtrobacter sp.
Serratla sp.
Proteus sp.
Flavobacterlum
Pseudomonas sp.
*Source: Donnelly and Scarplno, 1984
4-8
-------
TABLE 4-4
Survival Characteristics of Bacteria 1n Leachates from
Lyslmeters Containing Sewage Sludge3
Growth Medium
AGAR
Plate-count*1
Blood—aerobic6
Blood-anaerobic6
TellurHe bloodf
HPN TUBES
total conforms
Fecal conforms
Fecal streptococci
. Weeks
(CFU/100 g)
Ob
1.7x101°
4.1xl010
2.9xl010
4.3x10'
Weeks
(CFU/100 g)
0*>
2.8x10"
2.4xl010
3.3xl09
After Lyslmeter Construction
(CFU/100 ml)
4C 13C 114C
2.8x10* 1.4xl08 l.OxlO8
1.6x10* 1.9xl07 1.2xl08
l.OxlO3 6.3xl05 1.2xl08
7.5xl03 1.1x10* 4.0xl06
After Lyslmeter Construction
(MPN/100 ma)
5 20 2
2 20 2
7.9xl02 4.9x10* 2
aSource: Scarplno et a!., 1979
^Analysis of solid waste
cAnalys1s of the leachate from the lyslmeter
^Culturable aerobic heterotrophs In leachate. 35°C Incubation
eCulturable, fastidious heterotrophs 1n leachate, 35°C for 48 hours
^Selects for nonspore-formlng, gram positive bacilli
4-9
-------
total number of organisms remained quite high even after 2 years, the
density of fecal Indicator organisms dropped significantly. Compared with
the density of microorganisms added originally 1n the sewage sludge (see
Table 4-1), which presents results based on grams of material added to
lyslmeter, the density of microorganisms recovered In leachate after 2 years
was generally one or two orders of magnitude lower (except for the fecal
Indicator organisms).
The studies cited above show that bacteria and fungi can survive under
landfill conditions. A similar quantitative study concerning the recovery
of viruses from landfill leachates 1s available (Sobsey, 1978). Moore et
al. (1977) reviewed the Information relative to the survival of viruses from
wastewater applied to soil. They showed that certain enteric viruses were
recovered In aquifers beneath land application sites, but that survival In
the soil 1s greatly dependent on the physical and chemical conditions
present. Bltton et al. (1984) showed that viruses are bound to sludge
solids and may be Immobilized In soil when added with digested sewage
sludge. In this case, recovery of viruses In soil leachate was minimal.
Additional study 1s needed to determine 1) the effects of soil physlocheml-
cal conditions and the method of application on the survival and fate of
viruses from landfUled sludges, and 2) the degree binding affects release
rates.
Hlcroblal survival In the environment 1s governed by physical, chemical,
and biological factors. The biological factors are complex and Include
relationships such as parasitism, predatlon, antagonism and competition.
The functioning relationships In landfills are not clear, although It 1s
expected that Interaction typical to soils (such as competition for limiting
4-10
-------
nutrient and moisture) will occur. Physical and chemical factors Important
to microblal survival Include the following (Brock, 1966):
Physical Chemical
Temperature Water activity and structures
Hydrostatic pressure pH
Osmotic potential Nutrients (quality, quantity.
Surface tension Inorganic, organic, macro-.
Radiation mlcronutMents)
Adsorption Gases (quality and quantity)
Growth factors, regulators
Toxic materials
Oxidation-reduction potential.
Although a systematic study of these conditions specific to landfills
apparently Is not available. It 1s clear that some Influencing factors,
I.e., radiation, are less Important 1n landfills than they would be 1n
surface-applied sludge treatment. Others, such as oxidation-reduction
potential, would assume a greater significance In the subsurface conditions
of the landfill. The fact that landfill and landfill-simulating lyslmeter
leachates contain a variety of microorganisms (anaerobes, aerobes, bacteria,
fungi) (see Table 4-4) suggests that a diverse array of physical-chemical
conditions occurs In landfills. In addition, conditions will change depend-
ing on Inputs to the landfill (dry wastes versus wastewater; toxic versus
nontoxlc wastes). Understanding microblal proliferation (especially patho-
gens) In landfills Is needed to organize a risk assessment model; systematic
characterization of these physical and chemical conditions Is warranted for
modeling.
4.2.3. Routes of Movement for Pathogens from Landfills. The major
transport routes of microorganisms and pathogens from managed landfills are
through drainage waters and leachates. Airborne participates are not
problematic because of the subsurface nature of the wastes 1n a landfill.
4-11
-------
It Is possible that microorganisms could move from landfills 1f the land-
filled material were excavated and transported to another disposal site.
However, this would be an unusual condition. Thus, water movement through
the landfill and possibly Into aquifers beneath the landfill or Into surface
waters 1n the landfill drainage basin constitutes the major route.
4.3. LAND APPLICATION
Land applied sludges can be either surface-applied or Incorporated Into
the soil of croplands, pastures, strip mining sites or forests. The sludges
applied to soils may contain pathogens of various species and concentrations
depending upon the treatment process the sludge has undergone, which may
vary from composting to anaerobic digestion as explained 1n Chapter 3. It
1s the Initial concentration of pathogens In sludge and the Interactions of
the pathogens with the soil-sludge matrix that determines the concentration
of pathogens that may eventually enter the various exposure routes.
The Interactions of the pathogens with the soil-sludge matrix Include
biological processes of die-off and reproduction and physical processes such
as adsorption to soil particles (Figure 4-2). These processes and the
extent to which they affect the pathogen population determine which of the
various exposure routes will be of major Importance In risk assessments.
For example, retention by soil particles may be high for soils with a high
clay content, and movement of the pathogens through the soil profile may be
substantially reduced. Therefore, one may be able to deduce that ground-
water contamination would not be considered a major route of exposure with
clay soil conditions. By contrast, sand and gravel permit greater movement.
The retention of pathogens by soil does not, however, reduce the movement of
the pathogen to the exposure route by surface runoff to a freshwater stream.
4-12
-------
Treated
Sludge
New Cells
Dead Cells
Reproduction
Mortality
Pathogens
Soil Matrix
H^HBRaranjuiiRUBH!
Retention
by Soil
Particles
Water
Extractable
Organisms
FIGURE 4-2
Pathogen Transformations and Transport from the Land Areas Receiving Sludge
Source: Adapted from Reddy et al., 1981
4-13
-------
Retention of the pathogens near the surface may In fact enhance the risk
from this exposure route because they could be available for direct
1ngest1on or surface runoff.
To assess the quantity of pathogens reaching the various exposure
routes, data from land application of both wastewater and solid material
were used. When pathogens are applied 1n wastewater, the estimates for
movement rates through soil are high, because pathogens In wastewater are
believed to be loosely bound to the medium and therefore can directly enter
the soil. In contrast, the majority of the pathogens In sludge tend to be
tightly bound to the sludge and must first be eluted from the sludge before
they can move through the soil.
4.3.1. Pathogens and Microorganism 1n Land Application. Pathogens
present In the sludge after various treatment processes were presented In
Chapter 3. Actual pathogen species and populations Initially present on
land application Is dependent upon the waste per se, and treatment process,
though any class of microorganism may be present (bacteria, protozoa,
helminths, fungi, viruses). For example, large populations of Asperqlllus
ftimlgatus are primarily associated with composted sludge, while the numbers
of other pathogens after composting Is generally low. Given Initial popula-
tion estimates of the different pathogen species present In the treated
sludge applied to the land, their potential to survive and move through the
soil-sludge matrix to the exposure routes can be assessed, as part of the
risk assessment activity.
4.3.2. Survival Characteristics. Species specific Information 1s avail-
able when modeling specific situations (Table 4-5, and Information 1n
Torrey, 1979; Weaver et a!., 1976). The minimum and maximum die-off rate
values often cover a large range because studies are conducted under various
4-14
-------
TABLE 4-5
A Summary of Bacterial Die-Off 1n So1la»b
Organism Type
Brucella abortus
Soil Conditions
manure and soil (26°C)
manure and soil (frozen)
stmror
winter
Die-Off Time
29 days
800 days
30 days
100 days
Escherlchla coll
Leptosplra
Mycobacterlum tuberculosis
Salmonella sp.
Inoculated soil
pH 5,8-7.7
pH 3.8-4.5
clay soil
sandy soil
Inoculated loam soil
summer
winter
Inoculated waste on pasture
clay soil
air dry soil
wet soil
manured garden soil
manured pasture
fall
winter
spring
summer
dry weather
clay soil
sandy soil
sprinkled domestic
sewage soil
Inoculated on pasture
Infected feces
semi-liquid manure
bovine manure
bovine manure
manure slurry
poultry manure
9-12°C
13-20°C
30°C
clay soil
45-50 days
10 days
42 days
4-7 days
3.3 daysc
13.4 days
7-8 days
30 days
30 minutes
5 days
213 days
4 months
5 months
2 months
2 months
42 days
4-7 days
4 days
159-180 days
12 weeks
74 days
27-281 days
24 weeks
6 weeks
76 days
19 days
11 days
3 days
30 days
4-15
-------
TABLE 4-5 (cent.)
Organism Type Soil Conditions Die-Off Time
Streptococcus faecal 1s Inoculated soil
pH 7.7-7.8 45-62 days
pH 2.9-3.3 10 days
loam soil
summer 2.7 days
winter 30.1 days
aSource: Crane and Hoore, 1984
^Adapted from Crane (1978, unpublished thesis; In Crane and Moore, 1984).
Die-off defined as the time period to reach the point of no detection or
else not defined by study.
cT1me for 90/4 reduction In organisms population
0171S 4-16 09/28/87
-------
environmental conditions where temperature, abiotic, blotlc, and experi-
mental procedures differed, all of which affect pathogen survival. For
example, the die-off time for Brucella abortus was only 29 days at 26°C In a
manure-soil matrix; 1n a frozen manure soil matrix, the die-off time was 800
days. Similarly pH extremes Influenced E.. coll die-off time, which was
45-50 days 1n soils with a pH from 5.8-7.7 and 10 days In soils with pH
values from 3.8-4.5.
A temperature rise or a decrease In moisture results In an Increase 1n
microorganism mortality. For some species such as Salmonella and Esche-
rlchla coll. moisture was considered to be the primary factor In the
mortality rates (Young and Greenfield, 1923; Beard, 1940). The relationship
between microorganism die-off and pH Is one of an optimal range for
survival, -6-7; and then at either pH extreme, the die-off rates Increase.
The method of application may also affect die-off rates. The data available
would suggest, at least for conform bacteria, that for surface applied
wastes, fecal conform bacteria had lower die-off rates than did the
bacteria 1n wastes Incorporated Into the soil. The effects of moisture
content on the survival and regrowth of bacteria In raw sewage sludge have
also been Investigated (Yeager and Hard, 1981, Ward et a!., 1981).
Less quantitative Information 1s available for protozoa and helminths.
Protozoa, In general, are very sensitive to drying, and survival rates are
usually short. Entamoeba hlstolytlca cysts survived at least 8 days under
optimal soil conditions {Beaver and Deschamps, 1949). Maximum survival time
for protozoa on soil was stated to be 10 days and a common maximum of 2 days
(Kowal, 1983). Helminths are more resistant, and Ascarls eggs may remain
viable for up to 15 years. Similarly, Tr1churls eggs may remain viable 1n
soil for 6 years (Metro, 1983).
4-17
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A study of viruses related to temperature changes has shown that decay
rates become very small as temperatures approach 0°C. For MS-2 collphage
decay 1n groundwater, a linear regression was developed as follows:
decay rate {log1Q day"1} = -0.18089 = 0.02141 X T(°C)
This would Indicate that as groundwater temperatures approach 9°C, virus
1nact1vat1on becomes almost nil, at least over a 3-month period of observa-
tion (Yates. 1984).
Again, as with bacteria and viruses, protozoa and helminth survival
rates are affected by factors such as temperature, moisture and soil compo-
sition. These are not as well quantified as they are for some species of
bacteria or viruses; however, environmental profiles with these details
could be organized as needed to provide Input to risk assessment models.
4.3.3. Movement of Pathogens. In conjunction with the survival rates,
knowledge of pathogen movement through the sludge-soil matrix Is critical.
This Information will determine how long the survival rates can be applied
In a model to more accurately assess the concentration of pathogens entering
the exposure routes. Factors affecting bacteria movement 1n soil Include
physical characteristics of the soil, such as texture and pore size, as well
as environmental and chemical factors, such as temperature and soil water
flux {Table 4-6).
Hagedorn and McCoy (1979) summarized the data on movement of bacteria
(Table 4-7) and concluded that 1) bacteria generally move <1 m when
unsaturated flow conditions prevail and Increase to 30-60 m under saturated
conditions; 2) retention of bacteria Is Inversely proportional to the
particle size distribution 1n the soil profile and under all soil condi-
tions; and 3) adsorption of bacteria to soil surfaces can become a factor
restricting bacterial movement with effectiveness Increasing as soils become
4-18
-------
TABLE 4-6
Soil Factors Affecting Infiltration and Movement (Leaching)
of Bacteria In Soil*
I. Soil physical characteristics
a. Texture
b. Particle size distribution
c. Clay type and content
d. Organic matter type and content
e. pH
f. Cation exchange capacity (CEC)
g. Pore size distribution
II. Soil environmental and chemical factors
a. Temperature
b. Moisture content
c. Soil water flux {saturated vs. unsaturated flow)
d. Chemical make-up of Ions 1n the soil solution and their concen-
trations
e. Bacterial density and dimensions
f. Nature of organic matter 1n waste effluent solution (concentration
and size)
*Source: Crane and Moore, 1984
4-19
-------
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4-21
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less structured and clay content Increases. The values on bacterial move-
ment through soil 1n Table 4-7 would be Indicative of the bacteria transport
after the bacteria have been eluted from the sludge. Therefore, the rates
of movement for bacterial transport through soil presented 1n Table 4-7
would be liberal estimates for bacteria that are bound to sludge and this
would provide Information for a conservative case In a modeling effort.
Movement of viruses through soil were also shown to be 1n the range of
2.4-67 m (Table 4-8, Keswlck, 1984). The values In Table 4-8 are for
viruses 1n wastewater applied to soil and hence are overestimates for
viruses bound to sludge. A study oriented specifically to viruses 1n muni-
cipal sludge samples showed that when seeded sludge samples were deposited
on the surface of lyslmeters containing different soils, no viruses were
Isolated from the percolate (Damgcard-Larsen et al., 1977). This Indicates
the potential for the virus to be tightly bound to sludge or sludge-soil
matrix. The strength of the bond between viruses and sludge may be even
greater for viruses originating In feces and Incorporated Into the sludge
versus viruses seeded Into sludge (Sanders et al., 1979)
The bond between microorganisms, such as viruses, and sludge 1s, at
least 1n part, due to microorganisms being electrically charged particles.
This Influences their Interactions with the sludge/soil through processes
such as adsorption. Divalent cations would, therefore, enhance micro-
organism adsorption; conversely a heavy rainfall, which had a low 1on1c
concentration, might cause the desorptlon of microorganisms and, therefore,
Increase their movement through the soil. Furthermore, soil adsorption 1s
specially evident for viruses, probably due to the amphoterlc properties of
the viruses protein coat (Metro, 1983).
4-22
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TABLE 4-8
Isolation of Viruses 1n Wastewater Beneath Land Application Sites3
Site Location
St. Petersburg, FL
Gainesville, FL
East Meadow, NY
Holbrook, NY
SayvUle, NY
Twelve Pines, NY
North Masaqequa, NY
Babylon, NY
Ft. Devens, HA
Vlneland, NJ
Lake George, NY
Phoenix, AZ
Lubbock, TX
Kerrvnie, TX
Dan Region, Israel
England
Type of
SHeb
S
S
R
R
R
R
R
R
R
R
R
R
S
S
R
S
Virus Types
Polio 1; coxsackle
B4; echo 7
Coxsackle B4;
Polio 1, 2
Echo 12; Uc
Echo 6, 21, 24, 25; U
U
Polio 2; U
Echo 11, 23;
Coxsackle A16
Coxsackle B3; U
U
Polio; coxsackle B3;
echo
Phage
Coxsackle B3
Coxsackle B3
UC
Polio 1, 2, 3
Polio 2,3; coxsackle
B4, 5
Maximum Distance of
Virus Migration (m)
Depth Horizontal
6
3 7
11.4 3
6.1 45.7
2.4
6.4
9.1
22.8 408
28.9 183
16.8 259
45.7 400
18.3 3
30.5
1.4
31-67 60-270
19.4
Source: Keswlck, 1984
R = Rapid Infiltration; S = slow rate Infiltration
CU = unidentified (Identified as polio 1; coxsacklevlrus 83, 84, B5; echo-
virus 11, 21 1n Hoore et al., 1981)
4-23
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The movement of protozoa and helminths appears to be even more restrict-
ed than that for bacteria and viruses. There was no appreciable downward
movement of AscaMs eggs after 15 days (Metro, 1983). Ascarls eggs,
hookworm eggs, and Entamoeba hlstolytlca cysts were unable to pass through a
24-Inch layer of sand (Metro, 1983). These variable rates of movement may
be associated, at least 1n part, with the sizes of the principal pathogen
groups, helminths being larger than protozoa, followed by bacteria and then
viruses (Table 4-9). This size pattern corresponds to the relative movement
patterns of the smallest pathogens downward 1n a soil profile, viruses,
moving on the average from 2-67 m, while helminths do not move any appre-
ciable distances downward.
Other factors Influencing the rate of movement of pathogens, particu-
larly bacteria and viruses, moving to the exposure routes Includes filtra-
tion and adsorption. Adsorption to soil particles has been shown to remove
up to 98% of the bacteria In a liquid effluent (Crane and Moore, 1984). The
clay content and charge on the bacteria were found to be related to the
degree of adsorption. Filtration Is dependent upon 1) actual filtration by
the solid matrix, 2) sedimentation of bacteria 1n the soil pores, and
3) bridging, whereby previously filtered bacteria acted to reduce effective
pore diameters with a subsequent Increase 1n the filtering action of the
soil (Crane and Moore, 1984).
With regard to filtration, die-off, and adsorption of bacteria, Hagedorn
and McCoy (1979) concluded that 1) filtration of organisms at the soil
surface appears to be the main limitation to bacterial flux In the soil for
surface-applied effluents, while sedimentation of bacterial clusters In the
soil pores occurs during saturated flow conditions; 2) adsorption of
bacteria to soil surfaces can become a factor In restricting bacterial
4-24
-------
TABLE 4-9
Sizes of Waterborne Bacteria, Viruses and Parasites*
Microorganism Size
(m)
Bacteria 1-10
Salmonella typhl
Shlqella dysenterlae
Escherlchla coll
Vibrio cholerae
Viruses 0.02-0.08
Enterovlruses (polio, echo, coxsackle)
Rotavlrus
Norwalk-I1ke virus
Hepatitis A
Adenovlrus
Protozoa 5-20
61ard1a lamblla
Entamoeba hystolytlca
Cryptosopor1d1um
Helminths (eggs) 25-38
Ascarls
Taenla
Fungi 35-40
Asperglllus
*Source: Bltton and Gerba, 1984
4-25
-------
travel with effectiveness Increasing as soils become less structured and
clay content Increases; and 3) m1crob1al die-off only becomes an Important
factor during long soil retention periods, such as those found 1n soils
experiencing alternating periods of saturated and unsaturated flow. Such
qualitative Information helps assure realistic assumption on transport
conditions through a soil profile 1n a risk assessment.
4.3.4. Routes of Hovement for Pathogens from Land Application. The
potential exposure routes for pathogens 1n land applied sludges are
1) Ingestlon of soil (children with pica), 2} aerosols, 3) groundwater,
4) surface runoff, 5) food chain, and 6) Ingestlon of soil/dust by children
without pica through normal hand-to-mouth activity. All of the exposure
routes should be considered relative to "good practice" management tech-
niques, which Include adequate distances to groundwater, proper grade of
land, adequate drying time on land, tilling of sludge Into soils (1f appro-
priate) for agricultural applications and/or the restriction of crops that
have the edible portions In direct contact with the soil-sludge matrix.
Even though Ingestlon of soil could occur on an agricultural site, the
likelihood of this event 1s smaller relative to other exposure routes
because the sludge could have been tilled Into the soil and because the
population at risk (children with pica) 1s not large.
Pathogens In sludge Injected Into the soil are generally unavailable to
the aerosol exposure route. Only when sludges are surface-applied might the
pathogens enter the aerosol exposure route. But because drying of the
surface-applied sludge 1s necessary before the partlculate matter could
become suspended In the air (desiccation would Increase pathogen die-off),
the likelihood of the aerosol exposure route being major 1s also low.
4-26
-------
Workers may be exposed to the aerosolized pathogens 1n cases where a sludge
mixture 1s sprayed on the land or from the resuspenslon of dust/soil
particles by wind.
Similarly, because of physical factors that Influence the downward move-
ment of pathogens 1n the soil-sludge matrix, 1t 1s unlikely that leaching to
groundwater 1s a major exposure route. Only In unusual situations, such as
the presence of holes or fissures extending from the surface to the ground-
water zone, would there be any chance for significant groundwater contamina-
tion. If the pathogens remain near the surface, runoff Into surface waters
1s possible. The data available are primarily negative (MSDGC, 1979), which
may again Indicate that pathogens, especially viruses, are tightly bound to
the sludge. However, recent research results have been reported that
Indicate that H may occur. The results show the Isolation of naturally
occurring enterovlruses 1n groundwater 3 m below the soil surface where
sewage sludges have been applied. The viruses were Isolated 11 weeks after
the last sludge application (Lund, 1984).
The food chain exposure route 1s complex and may Involve both animals
and plants. For example, Salmonella from birds feeding 1n sewage-polluted
areas has been reported (Metro, 1983). Conflicting opinions exist regarding
the transfer of parasites, particularly tapeworms, from sludge to animals.
No Indication of disease occurred In experimental ruminant animals variously
exposed to sludges (Metro, 1983). However, given the limited data base
concerning animals and wildlife, the pathway to these organisms can not be
discounted at this time.
4.4. DISTRIBUTION AND MARKETING
Distribution and marketing (D&M) refers to the disposal of sludge based
fertilizers and soil conditioners for private and public purposes. In con-
trast to land application, whose principal sites of application are largely
4-27
-------
agricultural, silviculture, pasture lands, and reclamation, D&M products are
applied to home gardens, lawns, golf courses, cemeteries, and parks. In the
case of D&M, spreading of sludge can be by hand. Because of the commonality
between land application and D&M, much of the material In the previous
section 1s applicable to D&M and will not be repeated.
4.4.1. Pathogens In D&M. In general, D&M sludge products are treated by
heat drying, composting, or air drying before disposal. Observed levels of
pathogens In composted sludges were discussed 1n Chapter 3 on occurrence of
pathogens. Briefly, composting reduces the number of pathogens 2-4 orders
of magnitude for bacteria, viruses, and parasites. Numbers of pathogens 1n
D&M products Is dependent on Initial conditions.
4.4.2. Survival Characteristics. Survival of pathogens 1n garden soil 1s
expected to be like that discussed for soil In the land application section
(see Section 4.3.2).
4.4.3. Movement of Pathogens. Movement of pathogens associated with D&M
sludge products are expected to be similar to movement for the land applica-
tion situation and therefore will not be reported here. Briefly, bacteria
and viruses move only one or a few meters and up to 50-100+ m depending on
the soil water conditions. Helminth and large pathogens, especially 1n the
egg stage, do not move much vertically to groundwater because the soil
serves as a physical barrier and retards their movement. They move a few
centimeters and greater distances 1f soil cracks or fissures permit easy
passage. In addition, 1f there 1s heavy runoff, helminths will move.
4.4.4. Routes of Movement from O&M Sites. In the D&M disposal option,
pathogens 1n sludge products (fertilizers and soil conditioners) could end
up 1n home gardens, potted plants In the home, and 1n areas to which the
public has access (golf courses, cemeteries, parks). The food pathway and
4-28
-------
direct contact with open cuts, rashes, or sensitive skin may be the most
Important one In the garden situation. Concentrations of pathogens 1n the
soil adjacent to food plants are like those described In the survival
section of land application. If the sludge products and wastewater/patho-
gens were sprayed, or otherwise put onto the surface of food plants, the
survival rates on plant parts becomes Important. Table 4-10 shows that
viabilities vary, but are generally not long {generally <1 month and
commonly <1 week). Factors such as low humidity and sunlight control this
rate. Without proper management, Instructions and labeling of sludge
products there could be exposure through the food pathway from D&H products.
4.5. OCEAN DISPOSAL
Wastewater sludge 1s released Into the ocean by two different practices:
ocean discharge and ocean dumping, collectively termed ocean disposal.
Ocean discharge 1s the release of sludge to the ocean through pipes from a
^treatment plant to an offshore site below the ocean surface. In ocean
dumping, the sludge 1s loaded onto barges, towed, and released at a
relatively far offshore dump site. This section reviews current knowledge
of the transport and fate of wastewater sludge-associated pathogens Intro-
duced to the marine environment by ocean disposal, especially ocean dumping.
Sewage sludge Is rich In organic particles of a density lower than or
equal to the density of seawater {U.S. EPA, 1980; Booz-Allen and Hamilton,
1983a). Because bacteria and viruses tend to sorb to solids, their concen-
tration 1n sewage sludge may be several orders of magnitude higher than 1n
the raw sewage or In wastewater effluent. Therefore, the release of sludge
1n coastal waters Is a potential hazard to human health (Goyal et a"!.,
1984). Several outbreaks of Infectious hepatitis and viral gastroenteritis
have been associated with sewage contamination of recreational waters and
shellfish {Gerba and Goyal, 1978; Baron et a!., 1982; Gunn et a!., 1982).
4-29
-------
TABLE 4-10
Survival Times of Bacteria and Viruses on Crops*
Bacterium or Virus
Crop
Survival
Conforms
Escher1ch1a coll
Hycobacterlum
tomatoes
fodder
leaf vegetables
vegetables
grass
grass
lettuce
radishes
>1 month
6-34 days
35 days
<3 weeks
<8 weeks
10-14 days
>35 days
>13 days
Salmonella typhl
Salmonella spp.
Shlgella spp.
Vibrio cholerae
Enterovlrus
vegetables
(leaves and stems)
radishes
lettuce
leaf vegetables
beet leaves
tomatoes
cabbage
gooseberries
clover
grass
orchard crops
tomatoes
apples
leaf vegetables
fodder
orchard crops
vegetables
dates
tomatoes
10-31 days
24-53 days
18-21 days
7-40 days
3 weeks
3-7 days
5 days
5 days
12 days
>6 weeks
>2 days
2-5 days
8 days
2-7 days
<2 days
6 days
5-7 days
-------
TABLE 4-10 (cont.)
Bacterium or Virus
Crop
Survival
Pol1ov1rus
Pol1ov1rus
Pollovlrus
radishes
tomatoes
parsley
lettuce and radishes
20 days
(99% reduction)
>60 days
<12 days
<5 days
<1 day
<2 days
6 days
(99% reduction)
36 days
(100% reduction)
Pollovlrus
Enterovlrus
lettuce and radishes
cabbage
peppers
tomatoes
23 days
4 days
12 days
18 days
*Source: Kowal, 1983
4-31
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The fate of the sludge-associated pathogens 1n the marine environment
may depend on 1) local characteristics of the water and sediment (tempera-
ture, light, salinity), 2) transformation processes (physical fractlonatlon
of sludge particles, chemical and biochemical changes), and 3) transport
processes (settling, dispersion and resuspenslon).
4.5.1. Pathogens Isolated from Water, Sediment and Biota.
4.5.1.1. BACTERIA — Information on anthropogenic bacteria Isolated
from samples obtained In and around a dump site 1s limited to Indicator
species of sewage contamination, namely, total conforms (TC), fecal
conforms (FC) and fecal streptococci (FS) (O'Malley et a!., 1982; Davis and
Ollvlerl, 1984).
4.5.1.2. VIRUSES — Enterovlruses Isolated from samples of water,
sediment, and crabs from the mid-Atlantic dump sites (New York Bight,
12-mile dump site, and Philadelphia dump site) are listed In Table 4-11
(Goya! et a!., 1984).
4.5.1.3. OTHER PATHOGENS — The distribution and survival of conform
bacteria 1n the marine environment has received considerable attention, but
only recently has the presence of pathogens other than bacteria and viruses
been examined. Pathogenic amoebae (Acanthamoeba spp.) have been Isolated 1n
marine sediments In the vicinity of sludge dump sites, but It 1s not clear
whether the cysts of these amoebae are Introduced to the sea or whether
natural populations of amoebae proliferate subsequent to the Introduction of
large numbers of wastewater bacteria that provide a nutritive substrate for
the amoebae (Sawyer et a!., 1982). Quantitative studies on Acanthamoeba 1n
ocean sediment have not been conducted.
4-32
-------
TABLE 4-11 , ,;>>
Human Enteric Viruses Isolated from Water, Sediment or Crab Samples
Obtained In and Around the Philadelphia and New York Bight Dump Sites
(PDS and NYB, respectively) and Between the; Two Dump Sites {BDS)a
Virus
Sample
Site
PFUb
Coxsacklevlrus B3
Coxsacklevlrus B5
Echovlrus 1
Echovlrus 7
Echovlrus 9
Pollovlrus 2
Unidentified
sediment
sediment
water
sediment
crabs
crabs
sediment
sediment
sediment
sediment
sediment
sediment
sediment
sediment
sediment
sediment
sediment
PDS
NYB
,BDS
BDS
PDS
NYB
NYB
BDS
PDS
NYB
BDS ... .
NYB
PDS
PDS
BDS
PDS
NYB
12, 7
108, 84, 14
2
50
12, 3
CPEC
12
15, 12, 8
20
64, 56, 4, 2
56, 4
182
8
12
30
46
18
aSource: Modified from Goya! et a!., 1984
bPlaque forming units (PFU) represent an enumeration of the number of
discrete Infectious viral particles detected 1n a given sample. PFUs are
per 1000 g of sediment or 100 g of pooled gastrointestinal tracts and
haepatopancreas of Rock crabs (Cancer Irroratus). When more than one value
Is given, 1t Indicates enumeration of PFU recorded 1n different samples.
cV1ruses Isolated only by cytopathology under a liquid medium and not by
plaqulng procedure. There, the CPE designation Indicates that the sample
was positive, but does not yield a numerical estimate of the viral particles
present.
4-33
-------
4.5.2. Transport: Settling, Resuspenslon and Dispersal of Pathogens.
Transport of sludge particles and sludge-associated pathogens 1s Influenced
by site-specific physical and meteorological conditions such as depth, wind-
Induced waves and currents, geostrophlc flow, and density gradients
(temperature and salinity stratifications). Approximately 60-70% of sludge
material settles to the bottom In the dumping site area within 1 hour
(Booz-Allen and Hamilton, 1983aJ. A large portion of the remaining sludge
stays In suspension and 1s dispersed along density gradients. The degree of
sediment accumulation Is a function of Input volume, particle size, and
"flush out" rate of a site by currents and of decomposition of the organic
matter. Research at the New York Bight 12-mile dump site (NYB) has revealed
no significant buildup of sludge on the bottom (Booz-Allen and Hamilton,
1983a). In their study at the Philadelphia dump site (PDS), the same
authors suggested that the sludge may be settling In topographic depressions
of the ocean floor and concluded that a portion of the sludge may accumulate
at the site while the remaining portion disperses away from the site.
Limited Information 1s available on the dilution rate of pathogens as a
function of distance from the center of a dump site. O'Halley et al. (1982)
reported the frequency of Isolation of total conforms, fecal conforms,
fecal streptococci, and amoebae 1n sediment samples as a function of
distance from the PDS (Table 4-12). A decrease In the percentage of
positive stations for total conforms and fecal conforms was observed with
Increasing distance from the center of the dump site. Assuming a linear
rate of disappearance, this decrease 1n conform occurrence may be estimated
to be an average of 354 and 2% per km for total conforms and fecal con-
forms, respectively. Beyond a distance of -19-23 km, a slight Increase In
the percentage of total conforms and fecal conforms positive stations was
4-34
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noted. The range of recovery of Indicator bacteria extended 37 km northeast
and 37 km southwest, between the 40 and 70 m Isobaths. The total area In
which organisms originating from the disposal activities were recovered was
estimated at 1190 km2. Site-specific conditions such as wind-Induced
currents and transport of water masses have been suggested as possible mech-
anisms for the Irregular long-range distribution of the sludge-associated
bacteria. No details were given 1n the cited study of the actual counts of
bacteria In the sediment samples except for a general range of 10-2400
HPN/100 g sediment for both total conform and fecal conforms.
A rapid decrease 1n the percentage of stations yielding samples positive
for total conforms and fecal conforms, above and below a certain concen-
tration, with Increasing distance from the dump site was also reported 1n a
recent study at the NYB (Davis and Ol1v1er1, 1984). An Increase 1n
frequency of positive stations for total conforms and fecal conforms near
the shore apparently resulted from anthropogenic sources other than sludge
from the dump site. In another study cited by Davis and Ollvlerl (1984), an
exponential decrease of two orders of magnitude 1n total conforms counts
was observed along a transect of -20 km from the NYB dump site to the shore
(Figure 4-3). Based on a mathematical model for the ocean dumping of sludge
at the NYB site, a IxlO4 to 5xlO*-fold dilution within 4 hours following
disposal was predicted (NYC-DEP, 1983) and. In fact, was confirmed for total
conforms and fecal conforms at the NYB site (Davis and Ollvlerl, 1984).
The only direct evidence of recovery of sludge-associated pathogens
comes from a study by Goya! et al. (1984), who Isolated enterovlruses from
samples of water, sediment and crabs 1n the vicinity of the Philadelphia and
New York Bight dump sites (Tables 4-11 and 4-13). According to this study,
the highest recovery of enterovlruses was In sediment samples. In water
4-36
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100,000
10,000
g 1,000
o
o
100
10
Undetsetabie
13 II
!2-MiI
Site
10 9 6 7
5 4 3 E I 0
Long S§!@fld
FIGURE 4-3
Total conforms in bottom waters at various locations 1u the New York
Bight Apex, May 1975, 1977, 1978 and October 1978. «PN (nsost probable
number)/100 ms. 1s a statistically-derived estimate of the concentration of
collform bacteria.
Source: Davis and Ollvlerl, 1984
4-37
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samples, enterovlruses were recovered only once (out of 37 samples). This
result suggests that most of the dumped sludge settles quickly to the bottom
of the ocean and forms a part of the sediment (Oenklnson, 1972). The
sediment can then play a major role 1n the transport and distribution of the
sludge-associated pathogens In the marine environment. Other studies have
also shown that the concentration of viruses In the sediments 1s much higher
than 1n the overlying water, and that sediment viruses survive longer than
those free In suspension (Gerba et a!., 1977; LaBelle and Gerba, 1982).
Because the amount of sludge dumped Into the ocean Is small 1n relation to
the volume of the receiving water, the probability of Isolation of a virus
from water Is very low. The concentration of viruses 1n the water Is low
under most conditions; density gradients may be an exception and permit
viruses to be locally concentrated.
As In the cases of bacterial studies mentioned above, most of the
stations positive for viruses were located in and several kilometers around
the dump sites (Goyal et a!., 1984). Enterovlruses were also recovered well
away of the center of the dump sites (actual distance not reported).
4.5.3. Survival of Sludge-Associated Pathogens 1n the Marine Environment,.
4.5.3.1. BACTERIA — Most sludge-borne bacteria have a rapid die-off
rate 1n the marine environment (estimated at 90% reduction In 2 days) as a
result of such factors as temperature, salinity, and predatlon (Booz-AHen
and Hamilton, 1983a). Sediment-associated conforms have been shown to
survive longer than free bacteria 1n the water column (Gerba and McLeod,
1976; Goyal et al;, 1977). Under certain environmental conditions, fecal
streptococci may persist much longer than fecal conforms (Sayler et al.,
1975).
4-39
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The effect of temperature on bacterial viability 1n the marine environ-
ment 1s demonstrated by the lower summer frequency of total conforms and
fecal conforms positive stations along transects from the NYB dump site
when compared with winter transects (Davis and Ol1v1er1, 1984). The possi-
bility of photolnactlvatlon of bacteria from greater light Intensity during
summer may be an Important factor In bacterial 1nact1vat1on (O'Halley et
al.t 1982).
4.5.3.2. VIRUSES — Long-term survival of sludge-associated viruses
under natural conditions has been reported by Goya! et al. (1984). One type
of enterovlrus was Isolated In sediment samples obtained from the Phila-
delphia dump site, 17 months after the cessation of the dumping operation 1n
this site (coxsackle virus B3). In fact, viruses may retain 1nfect1v1ty 1n
the marine environment for even longer periods 1n estuarlne environments
(Akin et al., 1976; Lo et al., 1976). It has also been shown that
sediment-associated viruses survive longer than those free 1n suspension
(Gerba et al., 1977; LaBelle and Gerba, 1982) and that solids-associated
viruses are as Infectious as those that are free In suspension.
4.6. INCINERATION
The fifth type of disposal option Is Incineration. None of the previous
subsections 1s germane. High temperatures destroy living organisms.
Combustion temperatures can be 1n excess of 800°C. Unless there are large
unburned or unheated pieces, 1t Is believed that no pathogen will survive
Incineration. Therefore, no further discussion 1s warranted. However, It
should be noted that positive data are not available.
4.7. TRANSPORT OF PATHOGENS THROUGH GROUNDWATER. SURFACE HATER AND AEROSOLS
This section addresses the movement and survival of pathogens from the
disposal site to the exposure site. Information about three principal
4-40
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routes are presented: groundwater, surface water and aerosols. The
Information could be used to model changes In concentrations of pathogens 1n
the various transport media as they move to the exposure site.
4.7.1. Movement and Survival Rates of Pathogens 1n Groundwater. Patho-
genic bacteria and viruses from sludge disposal can move through soils and
thus potentially Into groundwater. This has been discussed 1n the previous
fate and transport section of this chapter regarding landfllUng, land
application, and D&M. For example, Lance (1984) discusses the disposal of
sewage onto land and the potential for bacteria and viruses to move through
soil. Hagedorn (1984) also discusses bacterial and viral transport through
soil as a result of septic tank effluents. Information 1s limited concern-
Ing actual survival and die-off rates of pathogens In groundwater. This
probably 1s a reflection of the fact that groundwater microbiology 1s a
relatively new area of concern and methods for effective sampling and
analysis are only recently being developed (McNabb and Mallard, 1984).
Recent literature concerning the survival of pathogens 1n groundwater,
as summarized by Gerba and BUton {1984}, 1s shown 1n the Table 4-14. This
Information was compiled from a total of five references. These data
Indicate that viruses survive longer than bacteria In groundwater. £. coll
had the most rapid die-off rate of the organisms tested.
Keswlck et al. (1982) show examples of the survival of bacteria and
viruses 1n groundwater and 1n surface water (Table 4-15). In a recent
extensive survey using groundwater collected from 11 different sites around
the United States, Yates et al. (1985) determined the laboratory decay rates
of three different viruses (Table 4-16)« Their results are 1n general
agreement with results summarized by Gerba and BHton (1984), Indicating
that enteric viruses may survive In the groundwater environment. The
4-41
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TABLE 4-14
Die-Off Rate Constants for Viruses and Bacteria 1n Groundwater3
Microorganism Die-Off Rateb
(day'1)
VIRUSES
Po11ov1rus 1 0.046
0.21
0.77
Coxsacklevlrus 0.19
Rotavlrus SA-11 0.36
CoHphage T7 0.15
Collphage f2 1.42
0.39
BACTERIA
Escherlchla coll 0.32
0.36
0.16
Fecal streptococci 0.23
0.24
0.03
Salmonella typhlmurlum 0.22
aSource: Gerba and Bltton, 1984
DAs logig Nr/N0, where Nr equals concentration of organisms after
24 hours and N0 equals the Initial concentration of organisms.
4-42
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TABLE 4-15
Viral and Bacterial Die-Off Rates In Water3
Microorganism
Pol1ov1rus type 1
Echovlrus type 1
Pollovlrus type 1
Pollovlrus type 3
Coxsack1ev1rus type B3
Fecal conforms
Fecal streptococci
Salmonella typhlmuMum
Water Type Decay Rateb
(day-M
estuarlne 1.0
2.8
river 0.77C
1.0
0.83
groundwater 0.36
0.24
0.22
aSource: Keswlck et a!., 1982
t>As log-jo Nr/N0 where Nr equals concentration of organisms after
24 hours and N0 equals the Initial concentration of organisms.
cAt 12-20°C
4-43
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TABLE 4-16
Die-Off Rates of Viruses In Groundwater Samplesa«b
Sample
Wisconsin
Arizona
North Carolina 1
North Carolina 2
University of
Arizona
New York 1
New York 2
Texas 1
Texas 2
California 1
California 2
Temperature
4
12
23
4
12
23
4
12
23
4
12
23
4
12
23
12
12
13
13
18
17
Bacterlophage
MS -2
0.020
0.093
0.244
0.064
0.162
0.578
0.014
0.030
0.187
0.012
0.095
0.262
0.025
0.040
0.325
0.034
0.037
0.077
0.114
0.082
0.075
Decay Rate
Pol1ov1rus 1
ND
0.060
ND
ND
ND
0.357
ND
0.138
ND
ND
0.114
ND
ND
ND
0.676
0.035
0.051
0.036
0.137
0.185
0.081
Echovlrus 1
ND
0.066
ND
ND
ND
0.188
ND
0.186
ND
ND
0.174
ND
ND
ND
0.628
0.054
0.051
0.138
0.079
0.151
0.091
aSource: Yates et a!., 1985
&D1e-off rate = [(Iog10 PFU) day-*]
ND - Not done
4-44
-------
temperature of Incubation greatly affected the decay rate, Illustrating the
effects of the environment on the potential for groundwater survival of
pathogens.
4.7.2. Movement and Survival Rates of Pathogens 1n Surface Water. Patho-
gens that have moved from a land application or D&M site or even a landfill
can enter surface waters where their movement and survival rates become
controlled by water. Data on survival rates 1n various types of surface
water are key to Implementing a microbiological risk assessment model.
Huch Information has accumulated over the past 25 years on the fate of
enteric bacteria In both fresh and marine water. Enteric bacteria popula-
tions In ocean water are reduced by physical dilution and by die-off mecha-
nisms as Indicated 1n the ocean dumping section. In the upper ocean, solar
radiation 1s a major mechanism by which conforms are reduced. The die-off
time for 90% of the conform bacteria 1n seawater from solar radiation
varied from 40 hours during the night to 2 hours during the daytime
(Bellalr, '1977). The readily available literature does not Indicate that
solar radiation plays a role In reducing conform bacteria In fresh water
systems, but such action Is likely.
Current literature pertaining to survival time of pathogens In both
marine and fresh water environments 1s compiled In Table 4-17 (Mitchell,
1972). The data listed under marine waters Includes Information on both
bacteria and viruses. Freshwater Includes Information on bacteria and
protozoa from wells, lakes, rivers, farm ponds, tap water sources, streams,
distilled water and storm water.
Table 4-18 summarizes Table 4-17 survival tiroes for specific pathogens
In both fresh and marine waters; however 1t should be cautioned that much of
these data have been generated In laboratories. How well these data
represent actual field conditions 1s unknown at this time.
4-45
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TABLE 4-17
Survival Time (days) of Pathogens 1n Marine and Fresh Water Environments3
Pathogen Marine Water Fresh Water
Salmonella 20cc»0>d, 60cc»ee, 10ff, 1499
Shlqella 25fa, 4C, 70d, 15d 41, 47h, 12r, 22Z
Leptosplra <19 5m
Protozoa 153X, 153V
Viruses 40-90hh, 2.5-911
aSource: Hltchel, 1972
Estuarlne water at 13"C
C£stuar1ne waters at 37°C, 95J4 die-off
Estuarlne waters
eEstuar1ne waters 1054 remained viable due to natural self-purification by
better quality water downstream
Estuarlne waters, Tubercle bacilli, 10% survival
gln 13,000-17,000 ppm chloride
Frozen river
1R1ver
days 1n 70-6350 ppm chloride, both river water and lake water
6°(
1
k6°C river water
25-27°C river water
"tubercle bacilli, vlrllent organisms recovered after 5 days 1n river water
"lake water
°Low salinity
PU Icterobae morrhaqlae
4-46
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TABLE 4-17 (cont.)
^Contaminated with airborne bacteria population of over ,1 million organisms/
ma, 25-32°C
rFarm pond, 20°C
5Ster1le tap water, pH = 7.0, 25-27°C
^Survival after Introduction of heterogenous bacterial populations
U7°C, £. tularensls. stream water
vStream water, survival In 1ce
W<1 hour to 13 days V. cholera, surface water
xEntamoeba hlstolytlca. 12-22°C, distilled water
yEntamoeba hlstolytlca. decreased 3054/10°C rise 1n temperature, natural
waters
zDetectable after 22 days 1n well water
aaf_. tularensls. 9°C, unsterlle, Innoculated with 5 million F. tularensls/
ml 1n well water
bbAt room temperature
Cclrr1gat1on water supply from farmyard waste
ddSummer
eeW1nter
ffUrban storm water, S. typhlmurlum. 10°C
99Urban storm water, S. typhlmurlum. 20°C, 95X die-off
hhSeawater, 99.97% at 3-5°C
11Seawater, 99.97X at 22-25°C
^Seawater, <5 days at 37°C
kkS1mulated rain dosage to treated soils
4-47
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TABLE 4-18
Survival Time (days) of Pathogens3
Pathogen
Bacteria
Viruses
Protozoa
Marine Haters
<1-73
2.5-90 (2-130)b
—
Fresh Waters
<1 hour to 60
(2-188)b
153
^Source: HHchel, 1972
bMeln1ck and Gerba, 1980
4-48
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Work on the fate of viruses 1n marine waters and fresh waters Is
limited. Survival of viruses 1n freshwaters (rivers, lake, wells) 1s of
great Importance because of their potential movement to drinking water
supplies for the general population. Over 100 enteric viruses have been
Isolated 1n sewage that have the potential for entering freshwater systems
(Melnlck and Gerba, 1980) and Include the following (number of types shown
1n parentheses): Enterovlruses (13), Including Pol1ov1rus (34), Coxsackle-
vlrus A (24), Coxsack1ev1rus B (6), new enterovlruses (types 68-71) (4), and
Hepatitis type A (1), Gastroenteritis type A (Norwalk agent) (2), Rotavlrus
(Reovlrus family) (2), Reovlrus (3), arid Adenovlrus (>40).
Virus survival In both marine and freshwaters 1s mainly controlled by
temperature; however, other factors affect viral persistence, which Include
other physical factors as well as chemical and biological factors. Tables
4-19 and 4-20 Illustrate the effect of temperature on viral activity In both
marine and freshwaters, respectively. The survival rates of enteric virus
In various environments {Melnlck and Gerba, 1980) can be summarized as being
2-130 days 1n sea or estuary water, 2-188 days for river water and 5-168
days for tap water.
Survival times In each aquatic environment vary by two orders of magni-
tude with the greatest variability 1n river water. The variability 1n
survival times of enteric viruses In aquatic environments can be used In
risk assessment to model worst-case scenarios. The variability also trans-
lates to a broad range of uncertainties 1n risk assessments.
Host of the Information generated has resulted from laboratory studies,
which must be cautiously applied to field conditions. Normally, laboratory
results Indicate higher survival rates than field results. In fact, In
marine and freshwater systems there Is an antiviral activity (virus
4-49
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TABLE 4-19
In situ Survival of Enterovlruses 1n Ocean Water*
Time (days to cause one log reduction 1n virus tlter)
Virus Type
Winter Summer
T = 4-16°C T . 21-26°C
Po11ov1rus 1 40 20
Coxsack1ev1rus B5 >80 35
Echovlrus 6 55 22
*Source: Melnlck and Gerba, 1980
4-50
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TABLE 4-20
Survival of Enterovlruses 1n Freshwater Environments*
Time (days) Necessary for 3-Log Reduction In Virus Survival
Virus Type
3-6°C 18-27°C
Pollovlrus 19-67 4-16
Coxsacklevlrus 7-10 3-6
Echovlrus 15-60 5-16
*Source: Helnlck and Gerba, 1980
4-51
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1nact1vat1on capacity) that 1s caused by a biological action (enzymatic
degradation), which Is not present 1n laboratory studies. In the field, a
quicker 1nact1vat1on period for marine and freshwater enteric viruses would
follow.
As noted earlier many viruses are associated with suspended sol Ids and
sediments 1n the aquatic environment. Solid-associated viruses survive
longer 1n marine and natural water systems than the viruses not associated
with solids. The solid-virus association Increases survival rate by provid-
ing protection from biological actions and physical factors {however, sedi-
mentation velocity may result 1n Increased rates of removal from the water
column). Viruses also survive longer 1n sediments 1n both marine and
freshwater environments; however, this protective effect 1s not clearly
understood.
4.7.3. Movement and Survival Rates of Aerosolized Pathogens. Survival
rates of pathogens 1n aerosols generated from land disposal and possibly
ocean disposal of sludge are short. Information summarized In a modeling
study by Camann (1980) Indicated die-off rates were 0.02/second for coll-
forms and 0.002/second for enterovlruses (die-off rate being an exponential
kt
decay; e where k 1s the die-off rate constant and t 1s time). The time
for a 1 log,Q reduction based exclusively on die-off rates would then be
115 seconds for total conforms and 19 minutes for enterovlruses. Gerba
(1983) concluded that parasites such as protozoan cysts and helminth eggs
are not present 1n aerosols because of their large size relative to bacteria
and viruses (see Table 4-9).
Sorber et al. (1984) examined aerosols generated from liquid sludge and
applied to land. They enumerated bacteria, Including representative fecal
organisms, and enterovlruses from the aerosolized sludge. However, Sorber
4-52
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et al. (1984) considered that no significant health effect would be posed at
distances >100 meters from the application site In aerosols and discussed
the factors affecting pathogen survival. Thus, the survival rates of
pathogens In aerosols appears to be the shortest of any of the potential
exposure routes. It should be noted, however, that certain pathogens
(Hycobacterlum. Leqlonnella) may survive 1n aerosols for longer periods than
enteric bacteria because pathogens have greater resistance to dehydration.
4.8. SUMMARY
The environments through which pathogens are transported during disposal
are more variable and under less control than during treatment. Character-
istics such as retention times and operating conditions during treatment are
not equally well known for disposal site conditions and for transport from
the disposal site to the exposure site.
The disposal environments to which pathogens are subjected range from
land-based disposal options to ocean disposal and Incineration. The land-
based options Include landfill, land -application and D&H. Sludge-borne
pathogens must contend with established soil microorganisms and moisture and
temperature fluctuations. Landfills often contain mixed solid wastes, which
may contain toxic substances detrimental to pathogen survival but may also
contain other organisms not Indigenous to sludge. Land application and D&H
options also present unique environments. Pathogens disposed 1n oceans must
cope with a shift from freshwater to saltwater conditions. Indnera- tlon
creates a high-temperature environment that cannot be tolerated by pathogens.
The pathogens at these disposal sites are reduced 1n concentration by
Immediate factors such as dilution and changes 1n salinity followed by
longer-term factors such as temperature, solsture, pH fluctuations, and
4-53
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other organisms. The Information on effects of type of disposal can be
organized as components of risk assessment. Conditions depend on the
disposal option (Table 4-21); Chapter 3 on occurrence shows expected Initial
conditions 1n detail and Indicates that Initial concentrations of pathogens
vary, which leads to a great potential for uncertainty 1n a risk
assessment. Rapid die-off 1s generally the case as Indicated 1n column
four. In land applied sludges, the half-lives of most pathogens 1s <1 day,
while In oceans, a 90% reduction occurs 1n 2 days. Dilution, especially 1n
ocean disposal, can occur up to 5x10*.
Long-term changes 1n pathogen concentrations Involve the Influence from
environmental variables such as temperature, moisture and pH. Temperature
Increases of 10°C can double pathogen mortality 1n soils, while a decrease
1n moisture through saline conditions or dry soil also Increases mortality.
A significant factor 1n longevity of pathogens 1n ocean-dumped sludge Is the
effect of their attachment to solids. This attachment Increases longevity,
but further work Is needed to characterize this phenomenon.
Exposure of pathogens to humans may occur at the disposal site or at
some distance In time and space. Movement of pathogens at the disposal site
varies 1n land application and D&M disposal options. They largely remain at
the soil surface where humans may be exposed to them through direct
1ngest1on of soil or on crops. Both options can be management controlled by
such practices as the type of crop grown or harvesting time of crops
relative to survival times on crop surfaces (survival times are generally <1
month and commonly <1 week). It should be noted that certain protozoa and
viruses may remain viable over long periods 1n any environment. Thus, the
real risks can be evaluated more accurately when the viability of specific
pathogens 1s known under defined conditions.
4-54
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When the exposure sHe 1s far from the disposal site, pathogens can move
by surface and ground water, aerosols, and the food chain. The Information
can, as was done for the disposal site, be organized as a series of compo-
nents for conducting risk assessment on representative species through
likely exposure pathways (Table 4-22).
Ground and surface waters are likely exposure routes for pathogens In
land disposed sludges. Survival rates vary with the type of pathogen and
water {ground or surface). Generally, survival times are greater 1n ground
than surface waters. Additional elements associated with the transport
routes are dilution factors as related to distance and variables affecting
die-off rates as related to the time the pathogens reach this system. In
ocean systems, the decrease In conform occurrence can be from 3% to 2% per
km for total conforms and fecal conforms, respectively. Survival time
decreases with Increase In temperature as was noted at the disposal site.
Harked reductions can occur with Increase In temperature such as a 3-log
reduction 1n 4-16 days for viruses 1n surface waters.
The adherence of many of the pathogens to solids (sludge, soil, sedi-
ments) reduces their movement 1n soil, aqueous, or aerosol media. Of the
sludge material disposed 1n oceans, 60-70% settles to the bottom within 1
hour and pathogens 1n aerosolized sludge are not considered to pose a risk
at distances >100 m from the application site. Similarly, movements of
pathogens 1n soil are restricted from almost zero for helminths and protozoa
to <1 m for bacteria In unsaturated conditions.
The type of Information presented 1n Table 4-21 and Table 4-22 Is Inter-
dependent. Risk assessments must be based upon the type of available Infor-
mation. At the present time, the data base Is not sufficiently complete or
precise to provide Input to a complex model.
4-56
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S. REVIEW OF EXISTING MICROBIOLOGICAL RISK ASSESSMENT MODELS
5.1. INTRODUCTION
Modeling the risk from pathogens 1n sludge to the human population
Involves the mathematical description and combination of processes such as
pathogen survival, transport and minimum Infectious dose. Modeling requires
that these processes be described In quantitative terms and, therefore,
requires the proper use of laboratory and field studies and monitoring.
Part of this 1ntegrat1ve process has been done In models such as the Seattle
Metro Model (Metro, 1983) and the Sandla model (BDM Corporation, 1980).
These models vary 1n their degree of computerization and complexity. These
models also differ In the way the processes were modeled and the pathways
considered.
State-of-the-art microbiological risk assessment models are reviewed 1n
this chapter. The model selection criteria, the models selected, and the
evaluation process are described; the various attributes of the models as
they relate to risk assessment are discussed.
5.2. MODEL SELECTION
Model selection centered around the processes required to Identify
existing models, which could either directly determine risk or could be
adapted to determine risk to humans from pathogens 1n sludge from various
disposal procedures. In order to Identify candidate models, general model
screening criteria were established.
As a first screening step, the following criteria were established for
models to have potential application for risk assessment for pathogens In
sludge:
1. Quantitative. Models should describe a system 1n terms of
mathematical formulas. Qualitative models, such as verbal
descriptions of Interactions between competing organisms, are
excluded.
5-1
-------
2. Capable of Computer Simulation. Models should use mathematical
formulas In which appropriate constants can be estimated from
empirical data. Highly theoretical models are, consequently,
excluded.
3. Applicable to Coupling of Processes. Essential components
should Include one or both of the following:
• Waste treatment processes
• Transport/movement processes
These criteria help focus the selection of models toward processes required
In evaluating risk from pathogens 1n sewage sludge. They exclude models
concerned with microorganisms In decomposition of forest leaves and litter
or oil recovery processes.
Models selected through this screening process could be either complete
risk assessment models, or they might be capable of modeling one aspect of
risk assessment such as transport of microorganisms. In this latter case,
several models were evaluated with regard to their potential for application
1n a complete risk assessment model.
5.3. MODEL DESCRIPTIONS
Through the use of the general model selection criteria, three models
were Identified:
• Seattle Metro Model — a risk assessment model for pathogens In
sludge (Metro, 1983}
Sandla Model ~ a risk assessment model for pathogens 1n sludge
(BDM Corporation, 1980}
• Wastewater Model — a risk assessment model for pathogens 1n
wastewater (Haas, 1983}
An overview of these three models follows. The overview Includes 1) the
approach to risk assessment considered 1n the model and 2} the types of
situations where the model 1s applicable. The extent of the review varies
with each model described, because the documentation on each model varied
from journal article descriptions to complete model user's guides.
5-2
-------
5.3.1. Seattle Model. The Seattle Model was designed to assess risk to
humans from pathogens 1n sludge, based on constituents 1n the Seattle Metro
sludge. Concern focused on three types of disposal methods that Seattle
Metro was considering for the reuse of wastewater sludge.
Seattle Metro Initially estimated the concentrations of representative
species of pathogens 1n sludge. The estimates were based on empirical data
from either the Intensive monitoring program of Metro sludge or from a
literature review. Pathogen concentrations were estimated for three time
periods: Initial application, 3 months, and 1 year after application; and
for the different pathways through which exposure to humans could occur:
air, surface water and groundwater, and soil/compost.
The pathogen concentrations In the different media and time periods were
then used 1n conjunction with data on minimum Infectious doses to humans to
estimate the amount of the media that must be consumed or Inhaled at a given
time 1n order to be Infected (I.e., more than 8.8 gallons of groundwater
must be consumed at a given time to result 1n Infection from Salmonella).
These estimates formed the basis for evaluating whether there Is a risk to
humans from pathogens In wastewater sludge applied to the land.
The first component of risk assessment Involved the selection of the
pathogen species. Seattle Metro based their selection on three criteria:
1) known quantities 1n Metro sludge, 2) Infectious doses, and 3) available
data on environmental movement and survival of the pathogen. The represen-
tative pathogens considered for land application sites were Salmonella.
enterovlrus, Ascarls and Glardla. and Asperglllus fumlgatus for composting
only.
The species of pathogens considered by Seattle Metro were then assessed
with regard to their concentrations following sludge treatment. Sludge from
wastewater treatment facilities Is anaeroblcally digested. This stabilizes
5-3
-------
the organic matter 1n sludge and reduces the number of pathogenic bacteria
and viruses by ~90%. The digested sludge Is then dewatered before applica-
tion on the land.
The pathogens 1n the treated sludge were traced through several applica-
tion options considered by Seattle Metro to be the preferable sludge reuse
options: silviculture, compost and land reclamation. For the silviculture
application option, assumptions about the site Included 1) a 200-foot buffer
zone between the sludge-applied area and any type of surface water, 2) a
5-foot minimum distance between sludge-applied soil and drinking water
aquifer, 3} controlled site access, and 4} sludge not applied on a slope
>30%. Exposure routes Included aerosols (Inhalation), surface water or
ground water (Ingestlon), and sludge-soll-lltter mixture composed of 50%
sludge (Ingestlon).
The assumptions associated with the compost application option were the
maintenance of a 55°C temperature throughout the windrow for at least 15
days and. If aerated, the 55°C temperature would be maintained for 3 days.
Exposure routes Included aerosols (Inhalation), compost-soil 1n a mixture
ratio of 1:2 (Ingestlon), surface water as leachate from compost (Inges-
tlon), and groundwater (Ingestlon) (Figure 5-1).
Land reclamation assumptions Included 1} sludge Injected or tilled Into
the soil, 2) a 5-foot minimum distance to an aquifer, 3) site access regu-
lation, 4) sludge not applied on a slope >3054, and 5) controlled surface
runoff. Exposure routes for land application Included surface and ground-
water. Other exposure routes were not considered because site access Is
restricted.
The Information on pathogen concentration and exposure routes to humans
was compared with data on minimum Infectious doses for each of the pathogen
species considered. This Integrated Information was then used to calculate
5-4
-------
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5-5
-------
the amount of the particular medium that must be consumed at a given time 1n
order to be Infected (I.e., more than 1000 m3 must be Inhaled to contract
salmonellosls when sludge Is composted).
.The conclusions for land application of sludge to silviculture Indicated
a minimum risk from pathogens to the public. Disposal of sludge through
composting Indicated that the health risk from Infectious agents 1s
extremely low. It was also concluded that persons hypersensitive to
Asperglllus fumlqatus spores should avoid close association with facilities
producing compost. This recommendation applies to all compost operations,
whether sludge Is used or not. And finally, for a well-managed land
reclamation site, no observable risk was projected.
5.3.2. Sand1a Model. The sewage sludge pathogen transport model by the
BDH Corporation (1980), the Sandla model, used computer simulation to assess
risk. The Sand1a model traced pathogen populations through several sludge
treatments and disposal options and exposure routes. The final pathogen
concentrations were then used to assess whether there was a risk to the
public.
The Sandla model traced pathogens through several different sludge
treatment processes, which Included anaerobic digestion (PSRP) and a
ceslum-137 gamma Irradiation system (PFRP) designed specifically to reduce
pathogen concentrations In sludge. These sludge treatments were then
coupled with likely application techniques, such as composting sludge for
use as a soil conditioner. Exposure routes appropriate to the application
technique were then used In conjunction with human-dose-response data to
estimate the amount of the media that must be consumed at one given time to
become Infected. For example, 1f the exposure route 1s through a vegetable
crop, then the number of carrots, for example, would be estimated that could
lead to a human Infection.
5-6
-------
The pathways for which risk was estimated Included the following:
• Dried raw sludge applied to cropland as a fertilizer
Dried anaeroblcally digested sludge applied to cropland as a
fertilizer
Dried raw sludge used as a feed supplement for ruminant animals
• Composted sludge used as a soil conditioner by the general
public
• Liquid raw or anaeroblcally digested sludge applied to cropland
as a fertilizer.
Implementing these five pathways 1n a computer model was accomplished by
dividing the pathways Into four treatment pathways and nine application
pathways. Figures 5-2 and 5-3 show the pathways and potential routes of
exposure from the treatment to land application of the sludge.
These pathways were used to trace the population of three pathogens
considered to be representative of those found In sludge. Salmonella
species to represent the bacteria; AscaMs species to represent parasites;
and pollovlrus to represent enteric viruses.
Growth, Inactlvatlon and movement of each of these three pathogens were
traced through the five major pathways. Each of these pathways was modeled
using a state-vector approach. The state or compartment 1s a discrete point
along the pathways, such as groundwater or soil surface, where the density
of the pathogen population 1s computed using ordinary linear differential
equations. Parameters considered 1n the calculation of population changes
Included variables such as time, temperature, moisture and nutrients. The
transfer of pathogens between compartments 1s described by ordinary, differ-
ential equations. These sets of equations describing population changes
within a compartment and between compartments were then Integrated to
estimate population changes.
5-7
-------
RAW SLUDGE
!.„,
| ANAEROBIC j
I DIGESTION 2
^
r
PARTICULATES U 1 IRRADIATION
^
r
TRANSPORT TO
AGRICULTURAL
SITE
=f
— >
DRAINAGE
RESIDUE ON
SITE AND
EQUIPMENT
RESIDUE ON
EQUIPMENT
RESIDUE
ON EQUIPMENT
T
APPLICATION
FIGURE 5-2
General Sludge Treatment Pathway from Sandla Hodel
5-8
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5-9
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The model parameters could be modified so that the user could make three
types of comparisons of the final pathogen populations: 1} each species
through a particular pathway, 2} one pathogen through different pathways,
and 3) different parameter values within and between pathways. For example,
the effects of temperature on pathogens could be assessed by executing the
model for temperatures of 10, 15, 20, 25 and 30°C. The final pathogen
populations could then be compared to assess the effect of temperature.
Following the calculation for the final pathogen concentration, a risk
calculation can be conducted. Any one of five exposure pathways, appro-
priate to the chosen application pathway, could be selected. These exposure
routes Include airborne partlculates, soil or residue, vegetable crops, meat
and milk.
Formal calculations of the risk through these various exposure routes
Involve two probabilities: 1) the probability that an Individual will be In
the exposure pathway and 2} the probability that an Individual In the
exposure pathway will Ingest enough pathogens to become Infected. The first
probability was assumed to be one; the second probability was estimated from
data 1n the literature concerning human-dose-response Information (for the
average adult male) and the concentrations of pathogens from the selected
compartments 1n the model. For example, 1n a particular exposure-risk
calculation, the model would determine the volume of air that must be
Inhaled to achieve a dose of pathogen sufficient to Infect. The model would
then calculate the time 1t would require to breathe this amount of contami-
nated air. Judgment as to whether this constitutes a risk to the public 1s
left to the model user.
5.3.3. Hastewater Model. This risk assessment model for wastewater was
designed to test the effects of cessation of wastewater disinfection 1n
5-10
-------
Illinois (Haas, 1983). However, many of the equations and approaches are
applicable to sludge disposal, especially after the pathogens are eluted
from the sludge and enter Into the surface water. In modeling the effect of
effluent disinfection on risks of viral disease transmission through recrea-
tional water exposure, a probabilistic setting was used. Specifically, the
probability that a single primary contact recreation exposure to water of a
given quantity will result 1n Infection was given as a product of the prob-
abilities of two sequential events, the first being the probability that a
single exposure will result In the Ingestlon of microorganisms. The second
probability 1s that once Ingested, a microorganism will cause Infection.
To estimate the first probability, that of Ingesting a certain number of
microorganisms, two types of data were used: 1} pathogen density at the
time of exposure and 2) the volume of water Ingested at the exposure site.
To evaluate the density of pathogens at the exposure site, consideration was
given to the density of the pathogens 1n raw wastewater, the removal of
pathogens In wastewater treatment, the removal of pathogens by death or
physical parameters, and dilution between the time of Introduction at the
wastewater outfall and time of encounter by the downstream recreational
user. A series of equations were used to calculate the above parameters.
Including the optional removal of pathogens through disinfection procedures.
After the mlcroblal density at the point of primary contact was calcu-
lated, the probability that a single exposure and Ingestlon of a given
volume results In the Ingestlon of any organisms was calculated. A Polsson
distribution of microorganisms In the water was assumed 1n this calculation.
Parameter values were estimated from the data In order to estimate the
risk of gastroenteritis for both disinfected and nondlslnfected effluents.
5-11
-------
Furthermore, the probability of contracting a disease once a dose of virus
was Ingested was based on an estimate from the literature. The results of
the estimated risk of viral disease cases caused by swimming downstream of
effluents was then extended to the population at risk.
5.4. RISK ASSESSMENT INFORMATION REQUIREMENTS
As part of the review of existing models on risk assessment of pathogens
In sludge, general Information requirements were developed (Figure 5-4) for
Implementing a model. This 11st of requirements represents an "Idealized"
11st of Information necessary to perform a risk assessment model for
pathogens.
The two major topics considered were Information requirements and model
attributes. The former Included characteristics of the components Involved
In risk assessment (e.g., pathogens, disposal site, exposure site, humans).
while the latter considered how the components were mathematically coupled
and treated 1n the actual modeling effort. Figure 4-1 Indicates the major
sites a pathogen follows from the raw sewage stage through treatment and
disposal to contact humans after disposal. Each Important part of the
unidirectional pathway on this figure will be referred to under the appro-
priate categories discussed below.
5.4.1. Characteristics. The Information required (see Figure 5-4) for a
risk assessment model was segregated Into five major categories to conform
to the actual situation of a pathogen moving from disposal to exposure to
humans:
• Pathogen population characteristics
• Disposal site characteristics
• Transport to exposure site
• Exposure site characteristics
• Human population characteristics.
5-12
-------
INFORMATION REQUIREMENTS
A. Pathogen Population Characteristics
1. Population structure
fixed
variable
2. Reproductive rates
fixed
variable
3. Death rates (Includes processes such as predatlon, competition}
fixed
variable
4. Virulence
fixed
variable
B. Disposal Site Characteristics
1. Media
single
multiple
2. B1ot1c components
fixed
variable
3. Physical components
fixed
variable
4. Chemical components
fixed
variable
C. Transport to Exposure Site
1. Media or vector or food chain
single
multiple
2. Rates
fixed
variable
FIGURE 5-4
Model Scoring Sheet
5-13
-------
3. B1ot1c components
1 species
greater than 1 species
4. Physical components
. fixed
variable
5. Chemical components
fixed
variable
D. Exposure Site Characteristics
1. Media
single
multiple
2. Blotlc components
fixed
variable
3. Physical components
fixed
variable
4. Chemical components
mixed
variable
E. Human Population Characteristics
1. Size of population
fixed
variable
2. Structure
fixed
variable
3. Susceptibility
fixed (= uniform)
variable
4. Measure and route of exposure (1nhalat1on/1ngest1on rates, surface
area exposure).
fixed
variable
FIGURE 5-4 (cont.)
5-14
-------
MODEL ATTRIBUTES
A. Method of Simulation
1. Hand calculation
2. Computer program
B. Process Modeling
1. Macroprocesses
2. Mlcroprocesses
C. Component coupling
1. Static
2. Dynamic
D. Risk Assessment
1. Deterministic
2. Stochastic
E. Documentation
1. Described 1n Article
2. User's Guide Available
FIGURE 5-4 (cont.)
5-15
-------
5.4.1.1. PATHOGEN POPULATION CHARACTERISTICS — Pathogen population
characteristics are composed of species-specific Information such as the
structure of the population, reproductive rates, and death rates. The
structure of the population could Include, where applicable, differences In
the life stages, sexes and ages. If population structure 1s considered 1n
the model, then the parameters may be fixed during a particular execution of
the program or variable. In the latter case, 1f during an execution of the
program, the age structure 1s allowed to vary because of differential
mortality to the ages, then the population structure would be considered
variable. Similarly, for reproductive rates, death rates and virulence,
these may be either fixed or allowed to vary during a particular execution
of the risk assessment.
Reproductive and death rates, though being single-word descriptors of
biological attributes of a species, embody a large number of variables such
as competition between species or for substrates, predatlon and other
1nter/1ntra-spec1f1c Interactions and responses to abiotic parameters such
as temperature, moisture and pH.
The final characteristic of the pathogen 1s virulence. This may change
with the age of the pathogen or the particular genetic strain.
All of these pathogen population characteristics such as structure,
virulence, reproductive rates and death rates allow the calculation of
population changes over time.
5.4.1.2. DISPOSAL SITE CHARACTERISTICS — The disposal site 1s the
medium and site where the treated sludge 1s disposed. The disposal site may
be removed from the exposure site or the two may be the same site. An
example of the former 1s when sludge Is deposited on agricultural land and
5-16
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the nearby exposure site 1s a home with contaminated and untreated drinking
water. An example of the latter 1s sludge use on forest lands directly
accessible to the public for recreational purposes.
5.4.1.3. TRANSPORT TO EXPOSURE SITE — When the exposure site 1s
removed from the disposal site, the focus becomes the transport of the
pathogens. The mechanism of transport may be through air or water and
through the food chain by a vector such as an Insect. One or more of the
transport media may be Involved In movement of the pathogen to the exposure
site; hence the medium of transport may be single or multimedia.
Other characteristics, which again provide Input to the pathogen popula-
tion characteristics 1n order to calculate population changes, are blotlc,
physical, chemical and rate. This last characteristic refers to the rate at
which the pathogens move through the system. This may be either fixed or
variable, and provides Input data of time In transit to calculate changes In
the pathogen populations.
5.4.1.4. EXPOSURE SITE CHARACTERISTICS — Exposure site characteris-
tics are essentially the same as those described under the disposal site.
As noted above. In some situations, the disposal site 1s the same as the
exposure site, hence the similarity In the characteristics considered under
the two sites.
5.4.1.5. HUMAN POPULATION CHARACTERISTICS — Human population charac-
teristics consider the population that will be exposed to the pathogen. As
with the pathogen population characteristics, the one-word descriptors used,
such as size of population, structure, measure and route of exposure (Inha-
Iat1on/1ngest1on rates, surface area exposure), and especially susceptibil-
ity, encompass many complex and poorly understood processes. For example,
the population structure encompasses different age classes of Individuals,
5-17
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sexes, races, or other factors that represent segments of the population
with different levels of susceptibility to pathogens, while the measure and
route of exposure defines the volume of air, water or soil taken In by the
Individual or surface area exposed. The latter allows for the calculation
of the number of pathogens to which the Individual 1s exposed. As 1n
previous descriptions on site characteristics, human population characteris-
tics may be either fixed or variable. For Instance, the Inhalation rates
may be fixed as an average rate an Individual might breathe per day, or the
model may Incorporate rates that can be adjusted to the dally activities of
an Individual (I.e., variable rates).
5.4.2. Attributes. The criteria used to summarize the modeling process
and the state of development of the model Include the following attributes:
• Method of simulation
• Process modeling
Component coupling
• Risk statement
* Documentation.
5.4.2.1. METHOD OF SIMULATION — The method to simulate risk assess-
ment could either be done by hand calculation or by a computer where asso-
ciated software was sufficiently well developed.
5.4.2.2. PROCESS MODELING — The actual processes modeled, such as
the 1nact1vat1on rate for specific pathogens during sludge treatment, could
be modeled by not knowing many Interrelations and using a "black box"
approach or by knowing how specific environmental parameters affect pathogen
survival rates. When Information only on Initial and final concentrations
of pathogens after treatment are known, the black box or static approach
must be used (macroprocesses). On the other hand, 1f H 1s known how
5-18
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temperature, moisture and pH Interact to affect pathogen survival rates,
then dynamic or mlcroprocess modeling Is possible. That 1s, given unit
process, the temperature, pH, and moisture levels during treatment, and the
Initial concentration of pathogens, the final concentration of pathogens can
be predicted. The latter approach allows for greater flexibility 1n
addressing "what 1f-type questions such as what will the pathogen concen-
tration be If. the temperature during treatment 1s raised or lowered by 5°C.
5.4.2.3. COMPONENT COUPLING — Component coupling Is closely related
to process modeling. Static coupling Implies that the model can only be
executed using certain discrete Input levels of a particular parameter. All
macroprocess models fall Into this category. By contrast, mlcroprocess
models may be either static or dynamic. For example, If In the modeling of
temperature effects, the model equations relate an Independent variable such
as continuous temperature function with a dependent variable such as Inactl-
vatlon rates, the two are dynamically related. Likewise, temperature can be
varied and Its effects seen on the responding pathogen concentrations. If
static coupling 1s used, then the user would have to Insert different
survival rates 1n the model simulating different temperature regimes. The
two variables, temperature and 1nact1vat1on rates, are not dynamically
related 1n this case.
5.4.2.4. RISK ASSESSMENT — The statement generated by the model may
be either 1) a probability statement {stochastic} or 2) a deterministic
statement, such as "an Individual must consume 5 carrots at one time 1n
order to become Infected." The former considers the likelihood (chance) that
a particular event will occur such as a 1014 chance of being Infected given
the Individual Ingested 20 viral units. The deterministic statements do not
consider chance, but rather define a situation where an Infection will
result.
5-19
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5.4.2.5. DOCUMENTATION — Computer models that are In an advanced
state of development and Implementation usually have a user's guide asso-
ciated with them. These models are generally available on magnetic tape and
can be used by other organizations. On the other hand, models that
presently have only been described In a scientific article may be available
but would likely be difficult to use. Generally, the Input of Information
and output options are not as well developed so as to be accessible to the
general user. If there are severe constraints, one should go with the
available model and adapt It as needed.
5.5. SCORING PROCEDURE AND MODEL COMPARISONS
The Information requirements and model attributes described above were
listed on a scoring sheet. In turn, the 11st (see Figure 5-4) was used to
evaluate the three risk assessment models Identified 1n this study.
The scoring procedures consisted of the following steps. If a charac-
teristic was present In the model, a plus (+) was recorded; If the charac-
teristic was absent, a negative sign (-) was recorded. The major categories
(I.e., pathogen population characteristics) were given alphabetic designa-
tions under model Information requirements. Components of each major
characteristic were given numeric designation, each of which had two levels:
fixed (single) or variable (multl). For example, a model might have
pathogen population characteristics that Included fixed death rates. In
this case, the model would receive a plus In three locations on the scoring
sheet: one for the pathogen population characteristic, another for death
rates, and the last plus under fixed (the one of the two levels under death
rates). This scoring procedure would allow for models to be compared
characteristic by characteristic not only against one another, but relative
to the Ideal criteria (see Figure 5-4) necessary for a biological exposure
assessment model. •
5-20
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Model attribute Information was scored at the numeric level only and was
primarily used as a means to summarize Information about the modeling
processes used and the level of development of the model.
The scores recorded for each model with respect to the "Ideal" model
revealed the relationship of Information requirements and model attributes
to an Ideal situation. Thus, one could better assess 1f enough Information
and the correct model Is available to organise such Information for deter-
mining risk to the public from pathogens In wastewater sludge under several
disposal options.
The scoring procedure facilitated the comparison of the three risk
assessment models to the Ideal risk assessment model criteria and against
each another. Table 5-1 shows the ratings for the three risk assessment
models that were evaluated. They all were able or could be able to trace a
pathogen from Us Initial condition (I.e., the treatment site) through
disposal and to the exposure site and then some assessment of risk. As can
be seen the Seattle Metro model scored low 1n all categories except
transport. The Sandla model had average scores across all categories except
the human population where a low score was recorded.
The wastewater model by Haas (1983) received average scores for only
transport and human population categories. The other category scores were
low. However, this model was the only one that translated the risk assess-
ment to number of cases of diseases for a given population density (see
Table 5-1).
In general, biological risk assessment by the three models addressed the
major categories of risk assessment: pathogen and human population charac-
teristics, treatment, storage disposal, exposure site characteristics, and
5-21
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transportation/movement characteristics. Though being comprehensive, all of
the models were lacking 1n their level of detail for each of the major
categories 1n a risk assessment model.
The models varied 1n their state of development as well as how processes
were coupled. The Sandla model was the most highly developed model; It
Included some mlcroprocess modeling and contained a user's guide. The
wastewater model Is well described In the article by Haas {1983} and could
be Implemented on a computer or could be calculated by hand. Finally, the
Seattle model could also be calculated by hand and the data base 1s well
documented by Metro (1983).
Regarding the applicability of these various models to risk assessment
situations the Sandla model could be utilized for land application of either
composted or anaeroblcally digested sludge. This model might also be
adapted to describe treated sludge 1n landfills. The exposure routes
considered are the food chain, aerosols and water.
The designers of the Sandla model cautioned that the exact pathogen
concentrations predicted by the model nay not be accurate. This lack of
accuracy was due primarily to the lack of data necessary to quantitatively
describe the processes required for modeling. They considered their model
to be best used for relative assessments of risk, that 1s, to determine
whether one disposal treatment or disposal technique relative to another
results In a lower or higher risk.
The Seattle model risk estimates have applicability to the Seattle Metro
area. The geographical restriction 1s due to parts of the data base used In
the model, which was specific to sludges In the Seattle area. However, the
methodology used In the Seattle Metro model could be applied to other areas.
5-23
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As with the Sandla Model, the Seattle Hetro model 1s oriented toward land
application of composted or anaeroblcally digested sewage sludge. The
exposure routes are also similar to the Sandla model In considering air and
water contamination.
The models evaluated were primarily concerned with land application
methods of sewage sludge. The best approach for modeling efforts would be
to utilize the modified (computerized) version of the Seattle Hetro model
with added components on transport both In fresh water and marine situa-
tions. This would Ideally be Implemented on a personal computer. Another
approach 1s to use the Sandla Model with emphasis on relative evaluation.
5.6. SUMMARY
Three existing models were evaluated:
• Seattle Metro model - a risk assessment model for pathogens In
sludge with emphasis on land application
• Sandla model - a risk assessment model for pathogens Hn sludge
with emphasis on various disposal techniques on land
• Wastewater model - a risk assessment model for pathogens 1n
wastewater
The models were Identified using criteria as follows:
Quantitative models as opposed to qualitative models
• Computer simulation capabilities
• Applicability to microorganism populations
Components Included all or one of the following:
- wastewater/sludge treatment processes
- transport/movement processes
- epldemlologlcal processes and endpolnts
The Seattle Metro model uses Input Information based on an extensive
monitoring program. The model considers various representative species:
Salmonella for bacteria, Enterovlrus for viruses, Ascarls for helminths,
5-24
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Glardla for protozoan, and Asperglllus fumlqatus for fungi. The model
handles the pathogens as simple Input/output (macroprocesses) to each
component and does not have predictive capacity. Risk estimates were based
on amount of food, water or air necessary to Ingest or Inhale a minimum
Infectious dose. Although the model was designed for the Seattle area, 1t
could be transferred to other geographical locations. It can be performed
on a hand calculator and 1t Is possible to computerize the whole process.
The Sandla model Is a complex computer model. Information to run the
model 1s based on an extensive literature base. Three species were consid-
ered: Salmonella. Ascarls and pollovlrus. The model can handle variables,
particularly temperature (mlcroprocesses), that affect population levels of
pathogens. However, most functions are Input/output type, such as the
Seattle Metro model. Risk estimates are as 1n the Seattle Metro model. The
Sandla model Is not specific to a geographical area, but H 1s relatively
difficult to Implement because It 1s Information-voracious and the operation
of the model requires a mainframe computer.
The wastewater model developed by Haas (1983) can be operated on a hand
calculator. Information Is derived from the literature. Only one pathogen,
enterovlrus, 1s considered. Macroprocesses are handled In a probabilistic
setting. Risk estimates are based on probability. The study was done for
an Illinois situation. The model was designed to handle wastewater, but the
functions 1n the model are similar to those needed for the sludge applica-
tion, and some of these functions could be adopted.
Each model was compared with an Idealized set of Information require-
ments for performing risk assessment for pathogens 1n sludge. Information
requirements were organized Into five characteristics: pathogen population.
5-25
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disposal site, transport to exposure site, exposure site and human popula-
tion. Within each of the five characteristics, four more specific consider-
ations were used to evaluate the type of Information utilized by the model.
For example, under pathogen population, the four Hems were 1} population
structure, 2) reproductive rates, 3} death rates and 4) virulence. In
addition, each model was evaluated for five modeling related Hems: method
of simulation, processing modeling, component coupling, form and unit of
risk statement, and documentation. The evaluation of the models showed that
the level of detail In each category was low; the models were primarily
concerned with macroprocesses and were static models. Also, land disposal
methods were emphasized. The quantity and quality of available Information
may not be adequate to operate complex models such as the Sandla model.
There 1s a need for a model (more sophisticated than the Seattle Metro but
less sophisticated than the Sandla model) that can be Implemented on a
personal computer. The upgrading (computerization and addition of functions
such as transport) to the Seattle Model Is a reasonable approach. This
conclusion Is based on the quantity and quality of available Information and
the assumption that risk modeling 1s needed now. A second option 1s to
simplify or eliminate portions of the Sandla Model and add transport compo-
nents. Simplifications would begin where data gaps are small (see Chapter 7
of this report) with the goal of Implementing on a personal computer.
5-26
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6. EXPOSURE SITE AND EXPOSURE ASSESSMENT
6.1. INTRODUCTION
The purpose of this chapter 1s to Integrate the data and Interpretations
from the previous chapters. More Importantly, the chapter 1s to provide an
overall appraisal as to the feasibility of performing a microbiological risk
assessment.
First, the likelihood of exposure of humans to pathogens relative to
4
treatments and four different disposal methods and associated environmental
pathways 1s presented. For example, the likelihood of a helminth moving
from a landfill through groundwater to the public 1s considered relative to
a virus moving along the same pathway. A matrix 1s used to summarize these
Interpretations. Infectious doses are then presented. This Information Is
Integrated to evaluate which pathogens can survive that the public 1s Hkely
to be exposed to by various pathways. Finally, the disposal options/expo-
sure pathway/pathogen combinations considered to be the most Important are
related to the different capabilities of the four models reviewed.
6.2. LIKELIHOOD OF EXPOSURE
The possibility of contact between pathogens 1n sludge and humans 1s
always present. Likelihoods of exposure can be estimated for pathogens as
they move from the various sludge treatment and disposal options through the
exposure pathways. As demonstrated In previous chapters, treatment, manage-
ment practices of sludge at the treatment site, sludge disposal methods, and
pathogen survival and mobility In soil, water and air greatly affect patho-
gens and limit exposure to humans. For example, helminth eggs are large,
relative to viruses, and move downward very Uttle 1n a soil profile. Thus,
helminth egg movement Into groundwater Is unlikely unless the water table Is
near the surface, the soil 1s very porous, or a fissure exists that connects
the land surface with the saturated zone. Aerosols provide another example.
6-1
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Exposure to pathogens 1n aerosols 1s unlikely for properly managed landfills
because a layer of soil covers the sludge. Further, half-lives of viruses
1n aerosols are short {1n the order of seconds). Thus, certain Judgments
based on the Information previously presented can be applied with some
confidence.
Table 6-1 1s a qualitative scoring of the likelihood of contact between
some .types of pathogens and humans. The Information considers the various
exposure routes as related to the sludge disposal options. Designations In
the table for likely contact range from a single + (assuming contact can
never be defined as zero) to four +-H-K
Exposure from landfill 1s most likely to be through contaminated ground-
waters. The smaller viruses and bacteria are the most likely pathogens for
this pathway compared with the larger-sized and less mobile protozoans and
helminths. Further, landfills that use polyethylene liners and clay may
even have greater reductions 1n the probabilities of pathogen movement from
the landfill through groundwater. Nonetheless, pathogens, especially
viruses and bacteria, could move Into the groundwater and eventually be
carried by water to contaminate a source for drinking water. If the
drinking water undergoes treatment before consumption by people, treatment
further reduces the number of pathogens. Thus, the likelihood and signifi-
cance of contact with humans 1s reduced. Untreated water drawn from wells
does not have this additional barrier and given the low number of viral
units required for Infection, this exposure route cannot be discounted.
Movement of pathogens 1n surface waters 1s a possible exposure route
especially In flooding of the landfill and surface water contamination from
contaminated groundwaters. In the case of flooding and "ponding," pathogens
might be washed Into the surface waters. Consumption, both Intentionally
and accidentally, 1s the primary way of contact with surface waters.
6-2
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Accidental 1ngest1on 1s associated with recreational activities such as
swimming. The population at risk has Infrequent contact with the contami-
nated medium and consumes only small quantities of water relative to the
volumes of drinking water normally consumed by people.
An additional way of contact between pathogens and humans, which could
happen with contaminated surface waters and groundwater, 1s dermal contact.
The actual exposure potential by this route Is unknown because of the many
variables, which Include the probability of a pathogen entering through the
skin and the minimal Infectious dose associated with contact versus 1nges-
tlon routes of exposure. Nevertheless, the probability of Infection through
this pathway Is considered to be minimal. However, skin contamination and
self-Inoculation by placement of fingers 1n the nose and mouth may be of
concern.
Soil and food are unlikely routes of exposure for pathogens 1n landfills
because of their restricted use, and the nonagrlcultural use, respectively.
Water contamination by pathogens 1n sludges applied to land 1s the most
likely route of exposure. Because pathogens have to move vertically to
contact the saturated zone, only those small pathogens, such as bacteria and
viruses, are likely to move sufficient distances to enter the saturated
zone. Proper site selection with attention to the depth of the unsaturated
zone would further reduce the probability of viral or bacterial contamina-
tion of groundwater. In unusual cases of a high water table or highly
porous soil, other pathogens such as helminths or protozoa might enter
groundwater systems. Future uses of landfills and land application sites
may be affected by the persistent viability of some parasites. The actual
6-4
-------
contact between pathogens and humans for the groundwater exposure pathway
from landspread as described above, 1s by treated and untreated drinking
water.
Surface waters may also be a route of exposure. This scenario 1s
similar to the discharge of treated wastewater Into a receiving stream.
Pathogen contamination of surface waters might arise from storm events or
poor site selection (a steep gradient). Any or all of the pathogen groups
might be Involved, especially pathogens that move little and are retained
near the surface where they would be available for transport to surface
waters through surface run-off. Pathogens 1n contaminated surface waters
could contact humans through the routes previously described under landfill.
The food chain Is a possible route of exposure for land application of
sludges. Contact can occur through consumption of crops with 1) pathogens
on the crop surface or 2) pathogens Infecting animals that are, In turn,
consumed by humans. Mashing and cooking of food provides substantial
protection to pathogen contact with humans. Delayed harvesting times or
selection of crops where edible parts are removed from the ground are
additional ways to minimize exposure.
Direct Ingestlon of pathogens 1n soil and soil-sludge Is also a possible
exposure route, especially 1f children are represented In a community near
the land application site. The risk of Ingestlon 1s Increased for children
with pica. However, exposure can be controlled 1f restrictions on site
access are enforced. Any of the principal pathogen groups could be Involved-
1n this exposure pathway. Dermal contact with pathogens 1n soil Is also:
possible, but as previously described for dermal contact with pathogens 1n
water, the data base Is Insufficient to describe the likelihood of Infection
through this route of contact. This pathway 1s unlikely to be a major one.
6-5
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Finally, aerosols are a likely route of exposure for workers during
spray application of the sludge. Because of the smaller size of viruses and
bacteria relative to helminths and protozoa, these former groups are more
likely to be Involved In the aerosol exposure pathway. Inhalation of
contaminated air by workers near the spraying operations Is possible, but
the potentially-exposed population 1s small. In one recent study, 1254 of
wastewater Irrigation workers had antibodies to Leglonella as opposed to
1.2% and 1.4X 1n persons using clean water and control groups (Shuval,
1984). Further, proper safety precautions for the workers should keep the
potential for exposure through this pathway minimal.
The food chain Is a possible route of exposure for land application of
sludges. Contact can occur through consumption of crops with 1} pathogens
on the crop surface or 2) pathogens Infecting animals that are 1n turn
consumed by humans. Washing and cooking of food provides substantial
protection to pathogen contact with humans.
The third disposal method 1s distribution and marketing of treated
sludges. This disposal method Is concerned primarily with a home gardener
situation. In contrast to the land application of sludges where ground-
waters were the primary exposure pathways, the food exposure pathway 1s
Judged to be the primary exposure pathway. The home garden Is readily
available to many persons. The produce can locally be consumed often
without processing. Enforcement of the management practices Indicated 1n
land application Is more difficult 1n the home garden situation than Is
agricultural or pastureland situations and, thus, exposure may be greater.
As with land application, the exposure pathways of soil (Ingestlon/
contact), ground and surface water (Ingestlon/contact) are possible and are
6-6
-------
scored. The aerosol route Is considered possible because although sludges
applied to gardens are not usually sprayed, pathogens are likely to be
aerosolized during tilling of soil.
Finally, ocean disposal of sludges may result 1n contamination of filter
feeders such as shellfish and thus, that pathway has been scored most likely
from contaminated food. If seafood were cooked, some protection would be
provided.
Additional exposure pathways Include accidental 1ngest1on by people
swimming in contaminated surface marine waters. Proper selection of the
disposal site would reduce the probability of exposure. Both dilution
processes as well as Increased transport time from the disposal to the
exposure site would be controlling factors.
For ocean disposal, aerosollzatlon 1s also possible because of the wave
and surf action. But again, the likelihood of sufficient quantities of
pathogens being aerosolized (considering dilution factors) and the potential
distance between a properly located disposal site and a likely exposure
site, deem this route unlikely.
Other exposure routes through marine water and sediments are considered
to be unlikely because of the unlikely nature of contact.
The overall assessment of potential exposure routes, when considered 1n
light of the various sludge disposal options. Indicates that groundwater for
landfills, food In D&M, groundwater and aerosols for land application, and
food for ocean disposal are the primary potential exposure routes. This
scoring of the various exposure routes 1s meant to guide and focus modeling
and data collection efforts for assessing risks from pathogens In sludge
disposed 1n various ways on land or 1n the ocean.
6-7
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6.3. INFECTIOUS DOSE
A part of exposure estimation 1s the dose of pathogens required to cause
Infection. Host Infections from pathogens follow a dose-response relation-
ship and, therefore, as the concentration of pathogens consumed Increases,
there Is a greater likelihood of Individuals In a population becoming
Infected, which Is expressed as an Increase 1n Incidence rate.
The dose 1s typically the number of organisms to which the hosts are
exposed. The response that 1s measured, that Is, the endpolnt, varies from
one Investigation to another and also for the type of Infectious agent under
study. The measured response to an organism challenge could be lack of
Infection, Infection without Illness, or Infection with Illness In an
Increasing proportion of test subjects (Kowal, 1982). Whether or not a
response 1s noted Is dependent not only on the dose of the pathogens
received but also the susceptibility of the Individuals and the virulence of
the pathogenic organisms. Detection of Infection 1s accomplished by Identi-
fying progeny bacteria .In body products such as nasal secretion, blood and
feces, or by host response such as antibody formation that results from
Infection.
Host response to challenge with an Infectious agent has also been
measured 1n terms of disease production, that 1s, visible signs of Illness.
However, this Is a much less objective measure of response and does not
Include Inapparent Infections In which no clinical disease Is produced, but
the agent 1s still shed 1n body products In a viable, communicable form.
Viral 1nfect1v1ty can be measured by similar responses to those
described for bacteria. Viruses are also measured 1n cell cultures (Ward
and Akin, 1984). Cell culture methods require that the viruses replicate
and kill the Infected cell and that progeny viruses. In turn, replicate and
6-8
-------
km other cells 1n the culture. The presence of the Infectious virus Is
detected by Us ability to cause destruction throughout the cell monolayer
(cytopathlc effect) or to cause cell destruction 1n restricted regions of
the monolayer (plaque formation) {Ward and Akin, 1984).
Infectlvlty of protozoans 1s measured by the detection of cysts In feces
of the host. Generally, 1-10 cysts can produce an Infection depending on
the strain; many of these Infections are asymptomatic (Kowal, 1982).
Likewise, a single egg of helminths can produce human Infections as measured
by Identification of eggs 1n the host feces.
The terms "Infective dose" and "minimal Infectious dose" are actually a
discrete part of the dose-response relationship mentioned previously.
Generally, the minimal Infectious dose 1s considered to be the dose required
to Infect 50% of the population {ID5Q). Variations of this measure of the
Infectious doses could be used, such as ID»5 or ID,, for worst-case
scenarios.
Minimum Infectious doses for bacteria are generally high, being In the
order of 102 to 10B (Table 6-2). Even though these doses are high, such
concentrations can be found 1n some sludges. In contrast to the bacteria
are the viruses, where as few as one viral unit may Initiate an Infection
(see Table 6-2). In this particular case It was considered that -1% of the
human population would become Infected from exposure to one viral unit
(Davis and Ol1v1er1, 1984). High doses (5-30 viral units) would be expected
to be the minimum Infectious doses for certain viruses If 50% of the popula-
tion were expected to respond (Ward and Akin, 1984). However, this study
was for one virus type. The minimal Infectious doses for helminths and
protozoa are lower than for bacteria (see Table 6-2). Most of the helminths
listed as pathogens In .sludge are only Incidentally a problem to humans 1n
6-9
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TABLE 6-2
Infectious Dose for Pathogens of Primary Concern
Pathogen
Infectious Dose
Reference
BACTERIA
Salmonella
Campylobacter jejunl
Shlge.na dysenterlae
Escherlchla coll
Vibrio cholerae
VIRUSES
Hepatitis A virus
Enterovlruses
Coxsacklevlrus A
Coxsacklevlrus B
•Echovlrus 12
Rotavlrus
Norwalk-I1ke agents
Pollovlrus
102 to TO5
to 102
10« to 10"
10* to 10"
1-10 viral units
4-72 TCID50
1-10 viral units
1-10 viral units
1-10 viral units
10 PFU young,
100 PFU adults
1-10 viral units
72 TCID50
Metro, 1983
Keswlck, 1984
Keswlck, 1984
Keswlck. 1984
Keswlck. 1984
Metro, 1983
Keswlck, 1984
Keswlck, 1984
Keswlck, 1984
Kowal, 1982
Keswlck. 1984
Ward and Akin. 1984
6-10
-------
TABLE 6-2 (cont.)
Pathogen
Infectious Dose
Reference
HELMINTHS
Ascarls spp.
Toxocara
Taenla
Trlchurls trlchlura
Necator amerlcanus
Hymenolepls nana
PROTOZOANS
Entamoeba hlstolytlca
G1ard1a lamblla
BHantldlum coll
Toxoplasma gondll
FUNGI
Asperqlllus fumlgatus
1 egg
1 egg
1 egg
1 egg
1 egg
1 egg
10 cysts
10-25 cysts
10 cysts
10 cysts
10 cysts
Implied from Kowal, 1982
Implied from Kowal, 1982
Implied from Kowal, 1982
Implied from Kowal, 1982
Implied from Kowal, 1982
Implied from Kowal, 1982
Booz-Allen and Hamilton, 1983a
Keswlck, 1984
Booz-Allen and Hamilton, 1983a
Burge and H1liner, 1980
6-11
-------
the United States, Infecting dogs, cats and other animals as a rule. A
single egg 1s Infectious to man {Metro, 1983), although some researchers
assume 10 cells or cysts to be an Infective dose (Shlmlzu, 1948; Rendtorff,
1954a,b).
Much less 1s known about Infectious doses for fungi. As Indicated 1n
the chapter on occurrence of pathogens, Burge and Mlllner (1980), Olver
(1979) and Clark et al. (1984) point out that Individuals predisposed to
lung problems may be at high risk from Inhalation of Asperglllus spores from
composting sludge. However, the actual Infective dose for Asperqlllus 1s
not known, but as Booz-Allen and Hamilton (1983a) state, "Exposure to the
fungus seems to be much less Important than levels of abnormal susceptibil-
ity to the disease."
The Information on minimal Infectious dose can be systematically
Integrated with Information on the number of pathogens that are likely to be
present 1n the various exposure pathways (Table 6-3). Consideration was
given to .the survival and transport capabilities of each of the principal
pathogen groups as they related to the various exposure pathways; for
example, helminths move very little In soil and their contamination of
groundwater 1s unlikely. In contrast, viruses can move through a soil
profile and contaminate groundwater. Coupled with this Information 1s the
very low Infectious dose for viruses. This Integration leads to a high
likelihood of occurrence of viral Infection relative to the previously
described example with a helminth.
Relative to helminths and protozoa, bacteria and viruses have a greater
likelihood of penetrating and being transported 1n exposure pathways and
coming 1n contact with humans. This Information, when coupled with Infec-
tious doses for viruses and bacteria would direct risk assessment efforts
6-12
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toward viruses because of the presence of large numbers of viruses 1n
sludge, their relative mobility and their low Infectious dose.
These "most Hkely" pathways were then examined relative to the current
capabilities of the three mathematical models reviewed. Capabilities of the
three models In relation to likely disposal options/exposure pathways are
limited. The models can simulate some of the conditions or scenarios.
However, none of the models could simulate a Iandf1ll/groundwater/v1rus or
ocean dlsposal/food/vlrus scenario (Table 6-4). Most of the models are
oriented toward land-based disposal options and could simulate scenarios
such as distribution and marketlng/son/vlrus and helminth, or land appH-
catlon/groundwater/vlrus and helminth. At best, the models currently
available, can handle three out of the five scenarios.
6.4. SUMMARY
Data from throughout the report are Integrated 1n this chapter. The
focus of this Integration 1s a series of Interrelated matrices:
• Likelihood of exposure of pathogens to humans based on four
disposal methods and five pathways
• Likelihood of exposure from four specific taxa of pathogens In
five pathways
• Capability of the three models to model the five most likely
pathogens 1n the most likely exposure pathways.
The results of the first matrices Indicate that most likely exposure
situations are as follows:
Drinking contaminated groundwater from landfill
Drinking contaminated groundwater from land application sites
• Eating food from distribution and marketing and disposal sites
Next, Infectious doses are presented. For bacteria an Infectious dose
ranges from 101 to 10«. For viruses 1t ranges from 1-10> viral units.
6-14
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TABLE 6-4
Capability of the Three Models Evaluated to Perform a Risk Assessment
for the Host Likely Exposure Pathways for Each Disposal Method
Disposal Option/
Pathway
Most Likely
Pathogen3
Model
Seattle
Metro
Sandla
Wastewater
LandfUl/groundwater
"-b
Land application/
groundwater {+•++)
Distribution and
marketing/soil (++•*•)
Distribution and
marketing/food {<•<•++)
Ocean disposal/food
••
Ocean disposal/surface
water {•»•*}
virus
virus
virus/
helminths
virus/
helminths
virus
virus
Xc
X
X
X
X
aMost Hkely pathogen (+•+++•) as described In Table 6-3
bL1ke!1hood designation as described 1n Table 6-1;
= likely, -n- = possible
most Hkely,
CX = Model Is capable of simulating
6-15
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Infectious doses for helminths and protozoa are 1-10 eggs and 10-25 cysts,
respectively. The likelihoods of exposure could be combined with Infectious
doses to calculate the likelihood of Infection. The following pathogens
have the highest likelihoods of occurring:
• Viruses 1n surface water, groundwater, soil/sediments and food
• Helminths 1n soil/sediments and food
Some of these major potential exposure situations can be modeled by the
three models reviewed 1n Chapter 5. Briefly, the Seattle Metro Model can
handle land appllcatlon/groundwater and D&M/soU, the Sandla can handle the
above two as well as the D&M/food situation. The wastewater model would
have to be adapted to handle sludge application.
6-16
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7. DATA UNCERTAINTIES AND GAPS
7.1. INTRODUCTION
Information for performing a risk assessment must be adequate for the
key variables. Adequacy refers to the degree of completeness and the
quality of that Information both 1n terms of accuracy and precision. Data
must be available to quantitatively describe the major components such that
the Inputs and output reflect "real life" situations.
Uncertainties 1n the data (precision and accuracy) refer to the
certainty or confidence associated with existing numbers recorded over the
years during various research or monitoring efforts. In other cases, the
absence of data 1s the Issue (completeness of the data base). Data
uncertainties associated with methodologies used to enumerate pathogens will
first be considered. Then, data gaps, both major and those of secondary
concern, will be presented.
7.2. UNCERTAINTIES IN METHODOLOGIES
Some uncertainties exist 1n the methodologies used to enumerate patho-
gens 1n sludges, soils, groundwater, and surface water* and the quantitative
assumptions used 1n modeling risk exposure must take this Into account.
Many uncertainties are the results of procedural differences among labora-
tories, even while Implementing the same so-called "standard procedure." For
example, Gerba (1983), 1n reviewing the literature on the efficiency of
pathogen removal from sewage during treatment processes, emphasized that
quantitative Information should be compared within orders of magnitude.
This may be true of detection of pathogens In general because of the
laboratory-to-laboratory variability 1n methods, and the differences In
pathogen recovery within a single laboratory depending on what methods are
chosen (Dudley et al., 1980). Also, as new methods are developed and older
7-1
-------
methods Improved, the number of organisms typically Isolated from sewage and
sludge will probably Increase. Subsequent attempts to compare the new
results with older results could be problematic.
Campylobacter spp., for example, can cause enteritis as a result of
contaminated drinking water supplies. With the Increased attention being
given to Campy!obacter enteritis, new methods are being evaluated that are
resulting 1n greater recovery of the organism. Recently, Rubin and Woodward
(1983}, Martin et al. (1983), Chou et al. (1983) and Wang et al. (1983)
evaluated various methods for recovery of Campylobacter from various speci-
mens. Pretreatment, medium type. Incubation time and temperature, and pre-
enrlchment techniques all affected the quantitative results. In summary,
results of standard tests (APHA, 1981} even for representative species are
subject to variability among different laboratories.
One way to evaluate the suitability of quantitative data among different
laboratories 1s round-robin testing. This Involves simultaneous analyses of
the same sample of material by several different laboratories. Goyal et al.
(1984) evaluated two methods for recovery of enterovlruses from sludge using
a round-robin study among eight laboratories. Both methods received
favorable evaluations, but there was significant laboratory-to-laboratory
variability In the quantitative results. The authors concluded that the
round-robin variability 1n results would have been even greater had fewer
experienced personnel conducted the tests.
These various citations serve to support the conclusion by Gerba (1983)
that quantitative detection of pathogens, especially viruses (which 1s due
to the Inherent difficulties 1n their quantitative recoveries), 1s not
highly precise. For purposes of modeling, the variabilities need to be
7-2
-------
accounted for. An order of magnitude of variation may be the only reason-
able starting point, In lieu of rigorous Interlaboratory development of
standard methods for detecting pathogens from sludge.
7.3. DATA SAPS
Hany data gaps have been Identified during the assessments (Table 7-1).
They are not of equal Importance to organizing a risk assessment method and
may be classified as 1) Important data gaps essential to accurate pathogen
risk prediction that should be filled and 2) other data gaps less critical
to the assessment.
Important gaps Include those specific pieces of Information that If not
filled would require such extrapolation or Interpolation that the accuracy
of model predictions would be seriously compromised. The amount of
predictive reliability gained 1s commensurate with the cost. It should be
emphasized that these Important data gaps are those dealing with Information
directly applicable to the specifics of a pathogen risk assessment. Those
gaps deemed Important for the work are shown with an asterisk (see
Table 7-1).
Other data gaps Include those for which Information would be useful to
the understanding of pathogen/human Interactions but not critical to the
risk assessment. Data would provide valuable knowledge about the pathogen
environment and have basic research significance, but they would not be
critical to the development of the model. These gaps may be filled If time
and money permit. Indeed, the lesser data gaps may be filled Initially
through expert Judgment of what Is and 1s not likely to occur.
Major data gaps (see Table 7-1) Include the following for various
components of a risk assessment:
• pathogens - population dynamics of Important pathogen species
7-3
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TABLE 7-1
Summary of Data Gaps
Component of Model
Data Gaps
Pathogens
Treatment/Sludge
Species of pathogens 1n sludges
Population dynamics of Important species*
Degree of virulence In population
Survival rates outside host
Inability to quantify Important bacterial
and viral pathogens known to be 1n sludge*
Effects of aerobic digestion
Key variables
Relationship of key variables (tempera-
ture, moisture) to pathogen survival
Implications of pathogens bound to sludge
particles*
Disposal/Treatment/Exposure
Relationship of key environmental vari-
ables to pathogens, particularly Implica-
tions of pathogens being bound to sludge*
Movement rates In soil, water, air and
food chains
Municipal
fills
sewage sludges alone 1n land-
Bloaccumulatlon 1n filter feeders
Humans/Effects
Infectious dose
Relationship of Infection to disease
(case histories)*
Technical basis for extrapolation
Defined endpolnts for Infection/disease
Effects of pathogen species, pathogen and
chemicals (antagonisms, potentlatlon)
*Major data gaps
7-4
-------
treatment/storage - Implications on survival rates of pathogens
bound to sludge particles
disposal/transport/fate - relationship of key environmental
variables to pathogen survival and movement, especially as
related to pathogens bound to sludge particles
humans/exposure - relationship of Infection to,, disease (case
histories)
Information 1s lacking on several key species of pathogens such as hepa-
titis. Extrapolations from data on pollovlrus to hepatitis 1s unlikely to
provide a sound data base for modeling effects of hepatitis, especially
through exposure routes like the food chain (shellfish). The dynamic nature
of some pathogens bound to sludge particles may cause reduced die-off rates
during treatment and at the disposal/exposure site. On the other hand,
there may be a decrease 1n the rates of pathogen movement, allowing for
greater retention times at a given site. To date, these processes are not
quantified and there Is a lack of conclusive evidence (case histories) of
diseases resulting from pathogens In treated sludge.
Additional data gaps of secondary concern are listed also In Table 7-1.
7.4. SUMMARY
Uncertain and missing data limit the completeness and level of detail of
data needed to develop risk assessment models. Worst-case scenarios and
sensitivity analysis can partially compensate for these Inconsistencies and
major data gaps. Thus, data uncertainties and gaps do not mean that model-
1ng 1s Impossible, but rather that modeling, at this time, must be oriented
toward a relatively simple effort.
7-5
-------
-------
8. REFERENCES
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pollovlrus 1 1nfect1v1ty 1n marine waters. Water Res. 10: 59-63.
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Arther, R.G., P.R. Fitzgerald and 3.C. Fox. 1981. Parasite ova In anaero-
blcally digested sludge. 3. Water Pollut. Control Fed. 53(8): 1334-1338.
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Bellalr, J.T. 1977. Effect of solar radiation on conform bacteria 1n
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Berg, G. and D. Berman. 1980. Destruction by anaerobic mesophlUc and
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Bertucd, J.J., C. Lue-H1ng, D. Zenz and S.J. Sedlta. 1977. InactWatlon
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Bond, 3.0. 1958. The risk of Ascarls Infestation from the use of human
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organisms commonly found In municipal sludge. Prepared for U.S. EPA, Office
of Mater Regulations and Standards, Washington, DC. Contract No. 68-01-4930.
Bovay Engineering, Inc. 1975. Feasibility of land application for Spokane,
Washington wastewater solids. Spokane, WA. (Cited In Pedersen, 1980}
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Burge, W.O. and P.O. Mlllner. 1980. Health aspects of composting: Primary
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BHton et al., Ed. Ann Arbor Science Publishers, Inc., Ann Arbor, MI.
p. 245-264.
Burge, W.D., D. Colaclcco and W.N. Cramer. 1981. Criteria for achieving
pathogen destruction during composting. 0. Water Pollut. Control Fed.
53(12): 1683-1690.
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Camann, D. 1980. A model for predicting dispersion of microorganisms 1n
wastewater aerosols. In: Wastewater Aerosols and Disease, H. Pahren and W.
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8-19
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-------
APPENDIX A
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APPENDIX 8
MODEL SCORING SHEETS
-------
-------
LIST OF INFORMATION REQUIREMENTS
FOR SEATTLE MODEL
A. Pathogen Population Characteristics
1. Population Structure
a. Fixed
b. Variable
2. Reproductive rates
a. Fixed
b. Variable
3. Death rates (includes processes such as predation, competition)
a. Fixed
b. Variable
4. Virulence
a. Fixed
b. Variable
B. Treatment Site Characteristics +
1. Biotic components (other species)
a. 1
b. >1
2. Physical components (aeration, UV, ph, moisture, temperature) +
a. Fixed +
b. Variable
3. Chemical components (nutrients, toxic compounds)
a. Fixed
b. Variable
4. Temporal components (duration)
a. Fixed
b. Variable
B-l
-------
C. Storage Site Characteristics (optional)
1. 61ot1c components (other species)
a. 1
b. >1 -
2. Physical components (aeration, UV, ph, moisture, temperature)
a. Fixed
b. Variable
3. Chemical components (nutrients, toxic compounds)
a. Fixed
b. Variable
4. Temporal components (duration)
a. Fixed
b. Variable
D. Disposal Site Characteristics +
1. Media +
a. Single +
b. Multi -
2. Biotic component
a. Fixed
b. Variable
3. Physical
a. Fixed
b. Variable
4. Chemical
a. Fixed
b. Variable
B-2
-------
E. Transport to Exposure Site : v : +
1. Media or vector of food chain ? ; +
a. Single +
b. Multl -
2. Rates .., - • .:•«<.;•;-..-: -, - ••>•, ••-.- +
a. Fixed +
b. Variable
3. Biotlc component
a. 1 -
b. >1
4. Physical
a. Fixed
b. Variable
5. Chemical
a. Fixed
b. Variable
F. Exposure Site Characteristics +
1. Media +
a. Single +
b. Multi
2. Biotic component •?
a. Fixed
b. Variable
3. Physical -
a. Fixed
b. Variable
4. Chemical
a. Fixed
b. Variable
B-3
-------
6. Human.Population Characteristics +
1. Size of Population
a. Fixed
b. Variable
2. Structure _
a. Fixed
b. Variable
3. Susceptibility
a. Fixed (= uniform)
b. Variable
4. Measure and Route of Exposure +
a. Fixed +
b. Variable
H. Model Attributes
1. Method of Simulation +
a. Hand calculation . +
b. Computer program
2. Process Modeling +
a. Macroprocesses +
b. Microprocesses
3. Component coupling +
a. Static +
b. Dynamic
4. Risk Assessment +
a. Deterministic +
b. Stochastic
5. Documentation +
a. Described in article +
b. User's guide available
B-4
-------
LIST OF INFORMATION REQUIREMENTS
FOR SANDIA MODEL
A. Pathogen Population Characteristics +
1. Population Structure
a. Fixed
b. Variable
2. Reproductive rates +
a. Fixed ' +
b. Variable
3. Death rates (includes processes such as predation, competition) +
a. Fixed +
b. Variable
4. Virulence
a. Fixed
b. Variable
B. Treatment Site Characteristics +
1. Biotic components (other species)
a. 1
b. >1 -
2. Physical components (aeration, UV, phs moisture, temperature) +
a. Fixed +
b. Variable
3. Chemical components (nutrients, toxic compounds)
a. Fixed
b. Variable
4. Temporal components (duration) +
a. Fixed +
b. Variable
B-5
-------
C. Storage Site Characteristics (optional) +
1. Biotic components (other species)
a. 1
b. >1
2. Physical components (aeration, UV, ph, moisture, temperature) +
a. Fixed +
b. Variable
3. Chemical components (nutrients, toxic compounds)
a. Fixed
b. Variable
4. Temporal components (duration) +
a. Fixed +
b. Variable
D. Disposal Site Characteristics +
1. Media +
a. Single ..+
b. Multi
2. Biotic component
a. Fixed
b. Variable
3. Physical +
a. Fixed +
b. Variable
4. Chemical
a. Fixed
b. Variable
B-6
-------
E. Transport to Exposure Site +
1. Media or vector of food chain +
a. Single +
b. Multi +
2. Rates +
a. Fixed +
b. Variable
3. Biotic component
a. 1
b. >1
4. Physical +
a. Fixed +
b. Variable
5. Chemical
a. Fixed
b. Variable
F. Exposure Site Characteristics +
1. Media +
a. Single +
b. Multi -f
2. Biotic component
a. Fixed
b. Variable
3. Physical +
a. Fixed •+•
b. Variable
4. Chemical
a. Fixed
b. Variable
B-7
-------
G. Human Population Characteristics +
1. Size of Population
a. Fixed
b. Variable
2. Structure
a. Fixed
b. Variable
3. Susceptibility
a. Fixed (= uniform)
b. Variable
4. Measure and Route of Exposure +
a. Fixed +
b. Variable
H. Model Attributes
1. Method of Simulation +
a. Hand calculation
b. Computer program +
2. Process Modeling +
a. Macroprocesses +
b. Microprocesses +
3. Component coupling +
a. Static +
b. Dynamic +
4. Risk Assessment +
a. Deterministic +
b. Stochastic
5. Documentation +
a. Described in article
b. User's guide available +
B-8
-------
LIST OF INFORMATION REQUIREMENTS
FOR WASTEMATER MODEL , :
A. Pathogen Population Character!sties +
1. Population Structure
a. Fixed
b. Variable
2. Reproductive rates V
a. Fixed
b. Variable
3. Death rates (includes processes such as predation, competition) +
a. Fixed +
b. Variable
4. Virulence >
a. Fixed
b. Variable
B. Treatment Site Characteristics *
1. Biotic components (other species)
a. 1 ..."..'
b. >1 -
2. Physical components (aeration, UV, ph, moisture, temperature)
a. Fixed
b. Variable
3. Chemical components (nutrients, toxic compounds) +
a. Fixed +
b. Variable
4. Temporal components (duration)
a. Fixed
b. Variable
B-9
-------
C. Storage Site Characteristics (optional)
1. Biotic components (other species)
a. 1
b. >1
2. Physical components (aeration, UV, ph, moisture, temperature)
a. Fixed
b. Variable
3. Chemical components (nutrients, toxic compounds)
a. Fixed
b. Variable
4. Temporal components (duration)
a. Fixed
b. Variable
0. Disposal Site Characteristics
+
1. Media +
a. Single +
b. Hulti
2. Biotlc component
a. Fixed
b. Variable
3. Physical
a. Fixed
b. Variable
4. Cheaical
a. Fixed
b. Variable
B-10
-------
E. Transport to Exposure Site •
1. Media or vector of food chain
a. Single
b. Multi
2. Rates • .
a. Fixed
b. Variable
3. Biotic component
a. 1
b. >1
4. Physical ' ; - ^-x* : - +
a. Fixed . , +
b. Variable
5. Chemical . -
a. Fixed
b. Variable
F. Exposure Site Characteristics
1. Media
a. Single
b. Multi
2. Biotic component
a. Fixed
b. Variable
3. Physical
a. Fixed
b. Variable
4. Chemical
a. Fixed
b. Variable
B-n
-------
6. Human Population Characteristics +
1. Size of Population +
a. Fixed +
b. Variable
2. Structure
a. Fixed
b. Variable
3. Susceptibility
a. Fixed (= uniform)
b. Variable
4. Measure and Route of Exposure +
a. Fixed +
b. Variable
H. Model Attributes
1. Method of Simulation +
a. Hand calculation +
b. Computer program +
2. Process Modeling +
a. Macroprocesses +
b. Microprocesses
3. Component coupling +
a. Static +
b. Dynamic +
4. Risk Assessment +
a. Deterministic
b. Stochastic +
5. Documentation +
a. Described in article +
b. User's guide available
OU.S. GOVERNMENT PRINTING OFFICE: 1 9 8 8.5 it 8-1 5 eft 7 0 1 0
B-12
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