EPA430/9-79-009
United States Office of September 1979
Environmental Protection Water Program Operations (WH-547) 430/9-79-009
Aqency Washington DC 20460
An Approach for Comparing
Health Risks of Wastewater
Treatment Alternatives
A Limited Comparison
of Health Risks Between Slow
Rate Land Treatment
and Activited Sludge
Treatment and Discharge
MCD-41
-------
DISCLAIMER STATEMENT
This report has been reviewed by the Environmental Protection Agency and
approved for publication. Approval does not signify that the contents
necessarily reflect the views and policies of the Environmental Protection
Agency, nor does mention of trade names or commercial products constitute
endorsement or recommendation for use. In this report there is no
attempt by EPA to evaluate the practices and methods reported.
NOTES
To order this publication, MCD-41, "An Approach for Comparing Health
Risks of Wastewater Treatment Alternatives," write to:
General Services Administration (8FFS)
Centralized Mailing Lists Services
Building 41, Denver Federal Center
Denver, Colorado 80225
Please indicate the MCD number and title of publication. Multiple copies
may be purchased from:
National Technical Information Sercice
Springfield, Virginia 22151
-------
EPA 430/9-79-009
Technical Report
AN APPROACH FOR COMPARING HEALTH RISKS OF
WASTEWATER TREATMENT ALTERNATIVES
A Limited Comparison of Health Risks
Between Slow Rate Land Treatment
and Activated Sludge
Treatment and Discharge
by
Ronald W. Crites
Ants Uiga
Bel ford L. Seabrook
Lam K. Lim
Project Officers
September 1979
U.S. Environmental Protection Agency
Office of Water Program Operations
Municipal Construction Division
Washington, D.C. 20460
MCD-41
-------
ACKNOWLEDGMENTS
The inspiration of Mr. Belford L. Seabrook has been very
helpful in preparing this report. Mr. Seabrook and Mr. Lam
K. Lim, Environmental Protection Agency Project Officers,
provided assistance. The direction and review by Mr.
Richard E. Thomas, Mr. Sherwood C. Reed, and Mr. Robert K.
Bastian are gratefully acknowledged.
Dr. Robert C. Cooper, University of California, Berkeley,
authored Chapters 3 and 4 and provided valuable assistance
in the preparation of the report. The project was conducted
under the supervision and direction of Mr. Charles E. Pound,
Vice President of Metcalf & Eddy, Inc., Palo Alto,
California. The report was written by Mr. Ronald W. Crites,
Project Manager, and Mr. Ants Uiga, Project Engineer.
11
« E TCALF S, EDO/
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FOREWORD
The objective of this report is to develop an approach for
comparing the health effects of land treatment and
conventional treatment and discharge systems. Because a
great deal of information is available and a large number of
studies are currently underway, this is necessarily a
limited comparison. The methodology is presented, however,
for a more complete and detailed comparison as more data are
generated.
The risk of human exposure to pathogens is as low with land
treatment as it is with conventional treatment and
discharge. There are, however, more concerns voiced about
the health effects of land treatment. It is in the interest
of the public and the engineering profession to know the
relative health risks of each system. When these risks are
understood more clearly, state regulatory authorities and
public health officials should be able to assess the
standards that are needed in their communities.
111
METCALF 4, EDOY
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Chapter
CONTENTS
ACKNOWLEDGMENTS ii
FOREWORD iii
TABLES vi
FIGURES vii
1 INTRODUCTION 1
Public Health 1
Purpose 2
Basis of Comparison 3
Approach 3
2 CONCLUSIONS AND RECOMMENDATIONS 5
Conclusions 5
Recommendations 6
3 WASTEWATER CONSTITUENTS AFFECTING HEALTH 7
Infectious Agents 7
Bacteria 10
Virus 11
Parasites 13
Chemical Constituents 13
Inorganic Chemicals 14
Organic Chemicals 15
4 DOSE RESPONSE AND PROBABLE RISK 17
Indicator Organisms 17
Dose Response - Infectious Agents 17
Dose Response Analysis - Infectious Agents.... 18
Dose Response - Toxic Chemicals 21
Dose Response - Carcinogenic Agents 22
Acceptable Risk 22
5 REMOVAL MECHANISMS 24
Infectious Agents 24
Conventional Treatment 24
Land Treatment 27
Inorganic Constituents 33
Nitrogen 33
Trace Metals 34
IV
-------
CONTENTS (Concluded)
Chapter
6 RISK ASSESSMENT 35
7 EXAMPLE ASSESSMENT 37
Land Treatment System 37
Basis of Comparison 38
Activated Sludge System 40
Assessment 40
Identify Wastewater Constituents 40
Concentrations of Wastewater Constituents 40
Agent-Host Transmission Cycle 41
Contact Intensity 42
Contact Duration 42
Results of Example Assessment 44
Infectious Agents 44
Nitrate Nitrogen 44
Trace Metals 44
Trace Organics 44
Risk Evaluation 47
Site Workers 47
General Public 47
8 DISCUSSION OF THE EXAMPLE 49
Fail-Safe Aspects 49
Food Crops 50
Comparison to Non-United States Conditions 51
Alternative Land Treatment Systems
and Management 52
Rapid Infiltration 52
Overland Flow 53
Site Management and Design Changes 54
9 GLOSSARY 55
10 REFERENCES 61
V
METCALF * EDDV
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TABLES
No. Page
1 Summary Information on Reported
Waterborne Disease in the United States 9
2 Waterborne and Nonwaterborne Morbidity
and Mortality Data for Infectious Agents 10
3 The Amounts and Expected Percent Distribution
of Selected Constituents in the U.S.
Drinking Water Supplies 16
4 Dose Response for Selected Enteric Microorganisms.... 17
5 Enteric Microorganism Reduction by
Conventional Treatment 25
6 Value of Disinfection Constant K for
Various Waterborne Microorganisms 25
7 Survival of Infectious Agents in Surface Waters 27
8 Maximum Removal of Enteric Microorganisms
by Lagoon Systems 28
9 Removal of Enteric Microorganisms by Soil Systems.... 28
10 Reductions of Indicator Organisms
by Overland Flow Treatment 32
11 Survival Times of Enteric Microorganisms
in Well Water 32
12 Survival Times of Enteric Microorganisms
on Soils and Vegetation 33
13 Summary of Trace Metals Information,
Concentrations, and Removals 34
14 Types of Reuse Objectives in California
Systems Using Land Treatment 37
15 Estimated Contact Duration Factors 43
16 Land Treatment - Estimates of Infectious Agent Dose.. 45
17 Activated Sludge and River Discharge
Estimates of Infectious Agent Dose 46
18 Summary Comparison of Health Risk Potentials 48
19 Summary Comparison of Removal Mechanisms 48
VI
METAL* «. EODY
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FIGURES
No. Page
1 Relationship Between Waterborne Disease
Cases and Total Disease Cases 8
2 Probability of Disease, as Related to Exposure
to Salmonella sp, Occurring in Bathers 20
3 First Order Total Coliform Die-Off Coefficient 26
4 Removal of Poliovirus from Wastewater by Soil
Columns with Different Infiltration Rates. Added
Concentration of Virus was 3 to 5 x 104 PFU/mL 30
5 Seeded Virus Survival in Soil 31
6 Treatment Flow Sequence Used in Example Comparison.. 39
VII
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Chapter 1
INTRODUCTION
Land treatment of municipal wastewater has been practiced at
various locations in the United States for over 100 years.
Recently the passage of PL 92-500, with its emphasis on land
treatment and recycling of resources, has renewed interest in
land treatment. In addition, guidelines promulgated by the
Environmental Protection Agency (EPA) require evaluation of
such systems in all facilities plans.
There is, however, a general reluctance to equate land
treatment of municipal wastewater with conventional treatment
systems because of either real or speculative public health
impacts. The impacts most often cited are (1) the
transmission of pathogens, including virus, into the
groundwater with the percolate; (2) the pathogens associated
with livestock feed; (3) the potential passage of certain
organics through the soil column and into potable water
aquifers; (4) the introduction of certain heavy metals
directly into the human food chain via vegetable crops or
indirectly through the animals fed on the crops; and (5) the
aerosol transmission of pathogens.
Most of the research findings to date deal with the impact of
pathogen transmission in groundwater and soils. This report
will concentrate on these findings and the related
transmission of inorganic constituents into groundwater or
surface water. Because the major studies on aerosols have not
been concluded, aerosols will not be assessed in this report.
Several research projects in the United States and other
countries are studying the public health implications of
treatment systems. Most of these research programs are new,
however, and conclusions will not be made for several years.
Nevertheless, there is an increasing amount of information
that, when coupled with engineering and scientific logic,
makes a comparison of the public health implications for land
treatment systems and more conventional treatment systems
possible.
PUBLIC HEALTH
The proper collection, transport, treatment, and disposal of
wastewater before it is discharged into the environment has
been a major factor in the maintenance and upgrading of public
health in the United States. Increasing demands on the use of
available water resources and demands of an enlightened public
have resulted in the need for stringent controls on effluent
MCTCALF & CDDV
-------
discharges into the environment, hence minimizing the
potential for waterborne transmission of constituents adverse
to public health.
Many wastewater constituents, such as infectious agents and
inorganic and organic chemical compounds, can produce adverse
health effects. Health problems arise when a particular
sequence of events takes place (e.g.. allowing a susceptible
host to encounter an infective dose). Many factors influence
this sequence, so a health problem occurs only if all the
necessary conditions are present. Consequently, sanitation
practices and public health engineering have concentrated on
removing the links or interrupting the sequence of events that
will allow a susceptible host to encounter a sufficient dose
of a chemical or infectious agent to result in illness.
The maintenance of public health is predicated on the concepts
of (1) interrupting the agent-host cycle of transmission as
much as possible, (2) reducing the quantity of adverse agents,
and (3) limiting the potential for public contact or
ingestion. Each of these three protective steps is
accomplished to a lesser or greater degree by various
wastewater management systems. For example, modern wastewater
sewer systems maintain a distance between waterborne agents
and the public. Modern wastewater treatment facilities,
including the use of disinfection, reduce the number of
adverse agents. The third step may be accomplished by
limiting water-oriented recreation such as swimming and
boating in an area near a wastewater discharge.
PURPOSE
The purpose of this report is to present an approach to comparing
some of the health factors associated with both land treatment
and conventional treatment systems. The report is intended to
provide an approach or framework so that more objective
comparisons can be made as more data become available.
This approach must consider many factors relevant to the
wastewater management systems. Discussing each of these
factors and comparing them collectively should help both the
design engineer and the regulatory or public health official
to understand the strengths and weaknesses of both land
treatment and conventional treatment systems, thereby helping
to ensure the best possible decisions in future wastewater
management planning.
« ETCALF It C 0 DV
-------
BASIS OF COMPARISON
Modern wastewater treatment technology offers a wide variety
of approaches to the treatment and management of municipal
wastewater. An assessment that considers every wastewater
treatment alternative would be voluminous, and is beyond the
scope of this report. Therefore, for purposes of this report,
conventional treatment will be limited to a standard rate
activated sludge plant with discharge to surface waters. Land
treatment systems usually include one or more of three basic
treatment processes: slow rate, rapid irffiltration, and
overland flow. A slow rate system will be used for the
example assessment, because it is the most common land
treatment option.
Generally, conventional wastewater treatment systems are
designed to discharge effluents into a receiving water. .Land
treatment systems, on the other hand, can be designed to
discharge all or a portion of the percolating effluent into
the underlying groundwater aquifer. To reduce the
dissimilarities between conventional and land treatment
systems, the comparison will be made using a slow rate land
treatment system with effluent recovery and discharge into a
receiving water.
APPROACH
In this report, the approach to health risk assessment has
five major steps:
1. Adequately determine and define the limits within
which the relative assessment would be made and the
assumptions required to simplify the approach to
manageable levels.
2. Find available information useful in evaluating
public health risks.
3. Detail the assessment method to facilitate its
subsequent use.
4. Illustrate the assessment method by use of an
example assessment.
5. Discuss the variations and implications of the
assessment example.
»ETCAI_F * E D DV
-------
The structure of the report follows the steps developed for
the assessment procedure.
Chapter 3
Chapter 4
Chapter 5
Chapter 6
Chapter 7
Chapter 8
Chapter 9
Chapter 10
Identify wastewater constituents affecting
health, both quantity and nature of
organisms and diseases
Describe the dose-response and probable
risks associated with wastewater
constituents
Describe and quantify the removal
mechanisms for wastewater constituents in
conventional treatment and land treatment
systems
Describe the assessment technique and
steps
Illustrate by example
a. Define areas of probable contact
(1) Site workers
(2) Public at large
b. Prepare a table of comparable
effluent qualities
c. Compare qualitative results and
implications
Discuss the variations in health effects
for the different types of land treatment
systems
Provide a glossary of public health terms
Provide a bibliography of cited
references
« ETCALF * E OOY
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Chapter 2
CONCLUSIONS AND RECOMMENDATIONS
CONCLUSIONS
An example assessment between activated sludge and slow rate
land treatment of wastewater was presented based on the
following assumptions:
• Flow of 3 Mgal/d of domestic wastewater.
• Activated sludge flowsheet with (1) disinfection and
(2) surface water discharge.
• Slow rate land treatment flowsheet with (1) aerated
lagoon preapplication treatment, (2) storage, (3) no
disinfection, and (4) percolate water recovery by
underdrains and surface water discharge.
The following conclusions on the relative health risks were
reached.
1. The qualitative results indicate that both conventional
and land treatment systems, which are well-maintained and
have good operating conditions, provide a large measure
of safety for public health. Land treatment systems that
involve slow infiltration offer greater protection
against parasites and viruses, trace metals, nitrate,
trace organics, and halogenated organics.
2. Adequate removals of parasitic eggs and cysts require
positive measures, such as filtration, or long detention
times in ponds or storage lagoons. As such, the land
treatment alternative offers greater protection from
health risks. The levels of parasites are very low in
the United States, so neither discharge practice appears
to be a significant health risk.
3. The land treatment system removes viruses to a higher
degree than conventional treatment and disinfection
systems. Treatment processes with longer detention
times, such as in ponds and storage lagoons, have better
removals than conventional activated sludge treatment.
4. The health hazard to site workers is slightly greater
than to the general public. The contact by site workers
is generally limited to occasional direct contact.
< ETCALF * E DDV
-------
5. The use of wastewater for irrigation of food crops may
provide a greater risk than irrigation of nonfood crops,
since the agent-host transmission cycle will be shorter
and positive removals by soil are not used. Die-away
varies according to type of crop and infectious agent.
However, present application rates of wastewater to
crops, as suggestedgin California regulations, provides a
safety factor of 10 to 1013 over the last reported
incidents of disease transmittal using "night soil" on
food crops.
6. Intake of trace metals by water sources should not pose
problems because the typically low values in municipal
wastewaters are generally reduced to below drinking water
standards by wastewater treatment.
7. No estimation can be made of the health hazards resulting
from low level exposure to trace organics. The dose
response and health effects are unknown at this time.
RECOMMENDATIONS
Conduct research to resolve the questions on health effects
in the following areas. Definitive conclusions from this
research would improve the prospects for a complete risk
assessment.
1. Potential for disease transmission from passage of
bacterial and viral pathogens through a soil profile
to groundwater supplies, from aerosols, or from direct
application of wastewater and sludge to crops consumed
by humans.
2. The health hazard from persistent organic compounds in
wastewater that may resist biodegradation during land
treatment.
3. Health hazards from human consumption of cadmium as a
result of cadmium uptake by crops.
1ETCALF it EDDY
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Chapter 3
WASTEWATER CONSTITUENTS AFFECTING HEALTH
Domestic wastewater is known to contain a number of infectious
agents whose source is primarily the excrement of man. In
addition, toxic inorganic and organic chemicals may be present
from sources in both industrial and household activities, the
former usually being the major contributor. Each of these
categories of constituents is described and discussed in the
following paragraphs.
INFECTIOUS AGENTS
The infectious agents include various bacteria, viruses, and
parasites. The concern about infectious agents present in
wastewater is due to their waterborne transmission and
potential for causing disease. An important source of data on
disease incidents in the United States is the United States
Public Health Service (USPHS) Center for Disease Control,
Atlanta, Georgia. Using data from the USPHS, waterborne
disease cases for selected infectious agents are compared with
total disease cases in Figure 1 using a log scale.
The waterborne disease cases include any incident in which it
was shown that the infectious agent was transferred by water
used for domestic purposes. The overall waterborne
transmission of disease is low, with reported values ranging
from 0 for amoebiasis to 11.5% for salmonella (typhoid).
However, salmonella had the fewest number of total reported
cases of disease. The cases where waterborne transmission had
been identified included (1) deficiencies in water treatment,
(2) deficiencies in distribution systems, (3) use of untreated
surface water, and (4) use of untreated groundwater. No
reported cases resulted directly from inadequate operation of
a municipal wastewater treatment system.
Disease incidents related to (1) raw wastewater contamination
of water supplies; (2) abuse of commonly accepted wastewater
management practices; and (3) contamination of food crops to
be eaten raw by untreated or partially treated wastewater have
occurred historically and have been summarized by Sepp [1] and
Bryan [2]. Because this study is intended to compare health
factors associated with modern treatment practices, these
incidents of contamination are not discussed here.
In the United States, the pathogenic bacteria that have the
greatest health impacts and have been identified in wastewater
include members of the genera Shigella, Salmonella, and
Escherichia. Viruses and parasites have also been recognized
< ETCALF * E DOV
-------
CO
«c
la
a
u.
o
UJ
200,000
100,000
10,000
1,000
1 00
1 0
LEGEND
D
TOTAL CASES
NOTE. NO WATERBORNE CASES OF
AMOEBUSIS WERE RE PORTED.
L :'"] WATERBORNE CASES
FIGURE 1
RELATIONSHIP BETWEEN WATERBORNE DISEASE CASES
AND TOTAL DISEASE CASES (1971-1974)
METCALF * E DDV
-------
as important within the United States. Hepatitis is the virus
of greatest concern because it has the greatest disease
effect, although numerous other viruses have been reported or
are present in untreated wastewater. Parasites of
significance in the United States include Giardia Iambiia and
Entamoeba histolytica. A summary of available information on
the reported diseases is presented in Table 1.
Table 1. SUMMARY INFORMATION ON REPORTED
WATERBORNE DISEASE IN THE UNITED STATES [3-7]
Wastewater constituent
Disease incidents,
1961-1974
Reported no. Reported no.
Resulting disease of outbreaks of cases
Reported
untreated
wastewater
concentration,
No./lOO rtiL
Indicator organisms
Total coliforms
Fecal coliforms
Bacteria
Shigella sp
Salmonella typhi
Salmonella spa
Escherichia coli
Virus
NS
Hepatitis virus A
Parasites
Entamoeba histolytica
Giardia Iambi ia
Miscellaneous
NS
Chemical agents
NA
NA
Shigellosis
Typhoid fever
Salmonellosis
NS
Hepatitis A
Amoebiasis
Giardiasis
Gastroenteritis d
Chemical poisoning
NA
NA
32
18
11
4b
NA
43
3
15C
85
9e
NA
NA
4,413
326
16,743
188
NA
1,254
39
5,303C
34,538
474e
10o
108
ND
106 to
600
ND
700 to
4xl03
1,900
4x10-!
ND
ND
ND
Note: NA = not applicable; ND = no data; NS = not specified.
a. Excludes S. typhi.
b. None reported during 1971-1974.
c. Incomplete reporting for major incidents only.
d. May include other disease previously reported.
e. For the time interval 1971-1974.
Cholera is a disease prevalent in other parts of the world.
In 1959, 33,953 cases were reported in India and East
Pakistan. Fortunately, cholera is not a problem in the United
States; only two indigenous cases have been reported since
1911 [8, 9], Most of the current cholera cases are reported
in Asia and the Middle East [10].
1ETCALF A ED DV
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Bacteria
The three most important classes of bacteria and their related
diseases are discussed in the following paragraphs.
Shigella. There are six species of Shigella of which two,
Shigella sonnei and S^ flexneri are the most common. Sixty
percent of the reported cases of shigellosis in the United
States are caused by S_^ sonnei and 10% are caused by S.
flexneri. Shigellosis, also known as bacillary dysentery, is
an intestinal disease limited to man and higher apes. It
spreads rapidly under improper sanitary conditions and
primarily from person to person. However, contaminated water
has occasionally been reported as the initiating source. The
reported incidence of shigellosis in the United States in 1975
is presented in Table 2 [11]. It is estimated by the Center
for Disease Control that this incidence probably accounts for
only 5% of the infected population. Thus the actual number of
infections may be almost 1,380 per million population. In
1974, 86 deaths out of 22,600 total waterborne and
nonwaterborne cases were reported.
Table 2. WATERBORNE AND NONWATERBORNE MORBIDITY
AND MORTALITY DATA FOR INFECTIOUS AGENTS [11, 12, 13]
MORBIDITY DATA
Disease
Shigellosis
Shigellosis
Typhoid fever
Salmonellosis
Reported
incidence
90/1063
69.2/106
1.8/106
106/106
Year
1973
1975
1975
1975
Remarks
Center for Disease Control estimates that
reported values are only 5% of occurrences.
—
—
Not known
Gastroenteritis
by £._ coli
Infectious hepatitis 168.2/1Q6
Poliomyelitis <8-l/10^
Amoebiasis 13/10^
Giardiasis Not known
1975
1973-1975
1975
Outbreaks have been reported.
3-year period.
Only incomplete reporting available.
MORTALITY DATA
Disease
Reported deaths Total reported cases
Year
Shigellosis
Typhoid fever
Salmonellosis
(nontyphoid)
Infectious hepatitis
86
3
59
36
22,600
437
21,980
168.2/106
1974
1974
1974
1975
a. Cases per 10*> total population.
10
METCALF t EDDY
-------
Salmonella. The genus Salmonella contains a large number of
species that are pathogenic to man. S. typhi, the causative
agent of typhoid fever, is peculiar to man and causes a severe
enteric fever. Fortunately, the incidence of this disease in
the United States is quite low. In 1974, three deaths out of
437 total cases were reported. The incidence of salmonellosis
(nontyphoid), in the United States has been greater than that
for typhoid fever (Table 2). This disease can be caused by a
large variety of species of Salmonella and is characterized by
diarrhea, abdominal pain, and vomiting. Its predominant cause
(29.4% of all cases) is due to S. typhimurium, the typical
species isolated [14]. In 1974, 59 deaths out of 21,980 total
cases were reported.
E. coli. Since the mid-1940s when E.coli was associated with
diarrheal disease in nurseries, it has become increasingly
clear that varieties of this bacteria known as
enteropathogenic E. coli are involved in waterborne enteric
disease [15]. These pathogenic strains produce mild to severe
cholera-like symptoms in the small intestine and produce an
endotoxin, or they may develop in the colon and penetrate the
epithelial cells and produce shigellosis-like symptoms [16].
Enteropathogenic E. coli has been shown to be the cause of
traveler's diarrhea [17] and waterborne epidemics of diarrhea,
such as the occurrence in Crater Lake National Park in 1975
[18]. The morbidity of this disease in the United States is
unknown because of lack of reporting.
Virus
More than 100 strains of viruses may be present in the
intestines of man and animals and thus viruses find their way
into wastewater. The most important of these, from the
standpoint of the severity of disease produced, is the agent
of infectious hepatitis. The morbidity and mortality of
infectious hepatitis are presented in Table 2.
Before the successful vaccination campaign of the 1950s, the
virus poliomyelitis would have been listed as an important
disease. However, less than ten cases of poliomyelitis per
1,000,000 population were reported from 1973 to 1975 (Table 2)
[19].
The other viruses found in wastewater would include members of
the Coxsakie, the Echo, the Adeno, and Reovirus groups. These
produce various diseases including aseptic meningitis,
myocarditis, respiratory involvement, and gastrointestinal
upset. Children of preschool age have the principal incidence
of infection, and transmission is primarily by person-to-
person contact. The role of water in the transmission of
11
1 E TC AL.F it ED OY
-------
these agents is not clear and some authorities believe it is
not important [20].
The water route of transmission has been implicated in several
outbreaks of poliomyelitis. Outbreaks in Edmonton, Alberta
(Canada), and Huskerville, Nebraska, were attributed to
contaminated water but the evidence is not conclusive [21].
Most authorities agree that in developed countries, the
transmission of poliomyelitis by water is, at most, a rare
occurrence. In underdeveloped countries where sanitation is
poor, however, the transmission of poliomyelitis and other
enteric viruses by water may be a common occurrence.
Three outbreaks of pharyngoconjunctivitis caused by Adenovirus
Type 3 and one of Type 7 have been attributed to contaminated
swimming pools. Isolation of the virus from the pool water
was either unsuccessful or not attempted, and the water route
of transmission was implicated only on the basis of
epidemiologic evidence [22].
In 1974, five children showed symptoms of a disease with
similar clinical characteristics. The disease was positively
diagnosed as caused by Coxsackie virus Type A16. In this
instance, the infections were acquired while swimming in lake
water that had relatively high fecal coliform counts. The
specific virus was successfully isolated from the lake water.
This is one of the first instances in which a Type A Coxsackie
virus has been shown to be transmitted to bathers 123].
No other enteric viruses have been specifically implicated as
causative agents in documented outbreaks of waterborne viral
disease. However, a virus-like particle similar in appearance
to the hepatitis "A" particle has been reported to be
associated with an acute infectious nonbacterial
gastroenteritis that occurred in Norwalk, Ohio [24].
Clemmer et al. [25] have carefully examined the spread of
subclinical (no physical symptoms for diagnosis) Coxsackie
virus B3 infection in 25 Louisiana families. One-half of the
households (51 children) showed virus infection, which
indicated interfamilial (vertical) spread, but horizontal
transmission from family to family was more difficult to show
[25]. No clinical disease was evidenced in any of the group.
Lennette [20] points out that in an epidemic of Echo virus 30
in Seattle, there occurred many thousands of infections, more
than half of which were subclinical, and only a few cases
resulted in apparent disease. Thus, the disease produced by
many of the enteric viruses is frequently subclinical,
generally inapparent, and results from close person-to-person
contact.
12
M ETC ALF * E D OV
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Parasites
There are a myriad of relatively large parasites associated
with the waste discharge from man and animals. In the United
States those commonly associated with waterborne disease are
the amoeba, Entamoeba histolytica (amoebic dysentary), and the
flagellated protozoan, Giardia lamblia (giardiasis) (Table 1).
In amoebiasis, the amoeba infects the human colon causing
erosion of the superficial mucous membranes. It may
eventually invade the tissue with consequent ulceration. In
certain severe cases, the parasite may metastasize to other
body organs. The parasite has the ability to encyst and these
cysts subsequently enter the environment in infected feces.
When the encysted amoeba reenters a susceptible host, usually
in contaminated food or drink, it germinates in the gut and
infects or reinfects. The morbidity of amoebiasis is shown in
Table 2.
Giardiasis is an intestinal disease produced by infection of
the gut by the protozoan G. lamblia. The disease ranges from
subclinical to severe maladsorption. The parasite produces
cysts that are passed with the stool and spread to other hosts
through fecal contamination. This disease has only recently
been recognized in the United States. In a number of
instances it has been associated with drinking water
contamination [12] . The total incidence of this disease in
the United States is unreported.
CHEMICAL CONSTITUENTS
The chemical constituents, both inorganic and organic, form
the second major category of wastewater constituents that may
have an impact on human health. The numbers of different
types of chemicals that may be present in water are unknown
but it is certain that the numbers are very large. Their
sources are both natural and from human activity. Health
implications of their presence in water are known for only a
few.
The inorganic chemicals that have an impact on human health
are the best understood because the analytical technology is
relatively well developed. There is also a longer history of
recognizing the associated health problems. However, there
are still many gaps in our knowledge particularly in
connection with chronic diseases (e.g., the relationship
between water hardness, sodium, cadmium, and lithium, and
cardiovascular disease) [26].
13
METCALF A EDDY
-------
Inorganic Chemicaljs
The inorganic chemicals found in water that appear to affect
health are arsenic, cadmium, cyanide, fluoride, lead, mercury,
nitrate, and selenium.
Arsenic is common in nature and is present in water in
concentrations as high as 336 jug/L. The recommended level in
acceptable drinking water should not exceed 50 ug/L.
Hyperkeratosis and cancer of the skin can be caused by the
injection of arsenic. The symptoms of chronic arsenic
poisoning are fatigue and lack of energy.
Cadmium is normally present at very low levels in surface
water and groundwater. If present, its concentration in water
ranges from 1 to 20 jig/L with most waters containing less than
1 pg/L. The human intake of cadmium has been attributed to
various ailments, including renal dysfunction and hypertension,
Cyanide is used in industrial activities and may enter surface
water and groundwater. Hydrogen cyanide (HCN) is the most
toxic species and is the most common form of cyanide at pH
levels of surface water or groundwater. When ingested,
cyanide interferes with the body's oxygen transport system
causing illness or death.
Fluoride is a naturally occurring mineral in water. Excess
fluoride can cause dental fluorosis (teeth mottling) and, in
increased doses, can cause bone changes including crippling
fluorosis. Fluoride is sometimes added to drinking water to
prevent tooth decay. This practice has led to illnesses,
including 351 reported cases of fluoride poisoning due to
excess fluoride addition [12].
Lead occurs in water primarily from industrial and domestic
activity. When present in U.S. waters it has been found in
concentrations ranging from 2 to 140 jjg/L. Lead poisoning is
a chronic disease that can produce a variety of symptoms
including anorexia, nausea, vomiting, paralysis, mental
confusion, visual problems, and anemia. It has been suggested
that drinking water not exceed a lead content of 50 jug/L [27] .
Mercury levels in surface water rarely exceed 5 ug/L and
usually are less than 1 jug/L. In groundwater, the level is
generally less than 0.1 jug/L. Chronic poisoning with mercury
is normally associated with industrial exposure particularly
to mercury fumes. The organic mercurials, such as
methylmercury, are more toxic in the natural environment.
Mercury can accumulate in the body and chronic exposure can
produce inflammation of the mouth and gums, swelling of
salivary glands, loosening of teeth, kidney damage, and
personality changes.
14
-------
Nitrates may enter water from various sources: natural,
agricultural, industrial, and domestic. Serious, sometimes
fatal poisoning in infants has occurred following ingestion of
water that contains nitrate. The disease in infants is called
methemoglobinemia in which the nitrate is reduced to nitrite
in the infant's stomach, which in turn seriously impairs the
oxygen carrying capacity of the blood. Cases of
methemoglobinemia due to nitrates in drinking water have not
been reported recently> however, since 1945 approximately
2,000 cases of this disease have been reported in North
America and Europe. Many water supplies in the United States
exceed the recommended maximum level of 10 mg/L nitrate-
nitrogen.
Selenium is highly insoluble in the unoxidized state and very
little data concerning concentrations in U.S. waters are
available. The suggested maximum level in drinking water is
10 ug/L. Selenium toxicity is similar to that of arsenic.
A number of other inorganic constitutents found in water may
be associated with human disease, although a cause and effect
relationship has not been demonstrated. These include the
previously mentioned relationships between water hardness and
heart disease, sodium and heart disease, and the suspect
metalocarcinogens beryllium, chromium, nickel, and
selenium. For more information on these and other inorganic
chemicals in water the reader is referred to reference [28].
Organic Chemicals
Our knowledge about the presence of organic chemicals in water
is limited; however, the identification of chemical species is
increasing rapidly. In the early part of 1975, over 160
organic compounds had been identified in water 129]. The
recognition of their presence in water raised questions
concerning their impact on the health of the public,
particularly in reference to cancer. Constituents found in
U.S. water supplies, reported in an EPA study and selected for
their potential hazard, are shown in Table 3. The
concentration ranges of these compounds and the relative
frequency in which they were found are indicated in this
table. Chloroform and other halogenated methanes were found
in all waters and were greater in concentration than the other
selected organics. The chlorination of water has been assumed
responsible for a good proportion of these compounds. For
more information on these compounds, the reader should see
references [26-29].
15
METCALF * EDDY
-------
Table 3. THE AMOUNTS AND EXPECTED PERCENT DISTRIBUTION
OF SELECTED CONSTITUENTS IN THE
U.S. DRINKING WATER SUPPLIES [29].
Constituent (s)
Carbon tetrachloride
Chloroform ,
Other halogenated CT and C2
Bis (2-chloroethyl) ether
B-chloroethylmethylether
Acetylenedichloride
Hexachlorobutadiene
Benzene13
Octadecane
C8 ~ C30 hydrocarbons
Phthalate esters
Phthalic anhydride ,
Polynuclear aromatics
Amounts, Percent
ug/L distribution3
<2 -
<0.3 -
<0.3 -
0.02 -
3
311
229
0.12
Unknown
<1
%0.2
10
%0.1
<1
^1
<0.1
0.001 -
1
10
100
100
Low
Low
Low
Low
High
High
High
50
Low
High
a. 100% distribution means that tests of all drinking
waters (24) showed the presence of the listed
constituent (s). Percent values are rounded to
the nearest 10%. Where insufficient sites have
been sampled, low or high estimates have been made.
b. Includes summation of all Ci and €2 halogenated
hydrocarbons except carbon tetrachloride and
chloroform.
c. Whereas benzene has not been frequently reported,
its distribution is probably widespread. The amount
and distribution columns here refer to benzene
and the alkylated benzenes up to Cg which have
been reported in many drinking waters.
d. The listed amounts are a summation of the concentra-
tions of individual compounds.
16
• ETCALF * E D DV
-------
Chapter 4
DOSE RESPONSE AND PROBABLE RISK
The evaluation of the health risks involved in the management
of water and wastewater requires knowledge concerning:
(1) the presence of agents that cause disease; (2) the dose
response characteristics of the agents involved (i.e., the
concentration of the agent and the concentration required to
produce disease); and (3) how the agent might come into
contact with susceptible individuals. Unfortunately, in many
instances, data on one or more of the three criteria required
for making risk assessments are not available.
INDICATOR ORGANISMS
Historically, the presence of infectious agents in water and
wastewater has been estimated using the coliform test.
Because of the myriad of microorganisms that may be present,
it was practically and in some instances technically
infeasible to determine the dose of each agent. Thus, the
coliform bacteria group was chosen as an indicator of fecal
contamination. If coliform bacteria were present, one could
assume a probability that other pathogenic microorganisms of
fecal origin might also be present.
DOSE RESPONSE - INFECTIOUS AGENTS
Information on human dose response (production of clinically
recognizable disease) is available for typhoid fever, certain
of the other salmonella, and some strains of E. coli and
Giardia lamblia. There is a notable deficiency in dose
response data involving enteric viruses. Bryan [2] has
compiled a dose response listing for a variety of infectious
agents and a summarized version of his data is shown in
Table 4.
Table 4. DOSE RESPONSE FOR SELECTED
ENTERIC MICROORGANISMS [2]
Microorganism No. per dose3
Shigella sp. 102-103
§_._ typhi 104-107
Salmonella sp.(not §_._ typhi) 106-109
E. coli 106-1010
Vibrio cholerae 103-108
G. Lamblia 101-106(infection without illness)
Virus Not known
a. Needed to produce illness in 25 to 75% of persons taking dose.
17
METCALF * EDDY
-------
As shown in this table, the dose response varies from one
organism to another. In the case of the bacterial diseases,
it normally takes a considerable number of organisms to elicit
a significant response in those challenged. In the case of
the parasitical disease giardiasis, no clinical infections
were seen with total doses as high as a million organisms;
however, a dose as low as ten cysts produced infection in 100%
of those challenged.
As stated previously, data for enteric virus dose response are
not well established, although some believe that one enteric
virus particle will be an effective dose. Others state that
an effective dose requires a much greater number of virus. As
Lennette writes [20] ,
The contention that a single viral particle invariably or
even frequently constitutes a minimal infective dose for
man is simplistic and misleading. It fails to take into
account the considerable amount of data from oral polio
vaccine studies which are nonsupportive of this
contention and ignores the manifold factors associated
with the humoral and cellular immune responses of the
animal as well as the chance factors--which under natural
conditions surely must be enormous—that a single viral
particle contained in a volume of food or drink will find
its way through the mechanical barriers of saliva, mucus,
gastric acid, etc.; encounter a susceptible cell; find
the appropriate receptor site on that cell; and enter and
replicate sufficiently to spread to other cells.
DOSE RESPONSE ANALYSIS - INFECTIOUS AGENTS
The relationship between the numbers of coliforms present in
water and the numbers of enteric bacterial pathogens also
present in water is of considerable importance since the
former are used as indicators of the latter. Kehr and
Butterfield [30] indirectly related the number of S^ typhi per
million coliforms to the morbidity of typhoid in the
community. This relationship can be shown by the equation
y = arn
where y = number of S. typhi per million coliforms
a = a constant
r = the morbidity of the disease per 100,000
n = a constant
Since the present morbidity of typhoid fever in the United
States is 0.18 per 100,000 (r = 0.18 from Table 2) and a = 3
and n = 0.46 [30], 1.4 typhoid bacilli per million coliforms
18
HETCALF it EDDY
-------
(y = 1.4) would be estimated from this equation. Assuming the
same relationship applies for salmonella and shigella, one
would estimate 36 salmonella and 29 shigella organisms per
million coliforms.
These numbers are based on the disease rate for the entire
country; however, if there is a local epidemic, then the
number of pathogens per million coliforms would be
proportionately higher. When the dose response data for
typhoid fever and for other salmonella are examined (Table 4)
and evaluated using the Kehr and Butterfield relationship of
pathogens to coliforms, the risk of contacting these diseases
from water seems slight.
Dudley et al. [31] performed a sophisticated statistical
analysis to determine indirectly the risk to swimmers of
contracting typhoid or other salmonella from bathing water.
They used the dose response data shown in Table 4 and assumed
a swimmer would imbibe 10 mL of water. Using the equation and
assuming the morbidity rate is 0 18 per 100,000 and that
untreated wastewater contains 109 coliforms per 100 mL, then
1,300 typhoid bacilli should be present in 100 mL of untreated
wastewater (13,000 organisms/L). If this number of typhoid
bacilli were present in untreated wastewater and were imbibed
by a population of swimmers, the rate of disease would be
about 20 cases or less per 100,000 population as shown in
Figure 2. In the case of other salmonella, the same activity
would be estimated to produce only four cases in 100,000
people.
These predictions should be taken with reservation, because
they assume that people will directly consume untreated
wastewater. They also assume that the parameters used to
determine col iform-to-typhoid ratios are realistic and that
the dose response data are an accurate reflection of dose
response in a large population. Kehr and Butterfield
contended that one typhoid bacilli would cause disease in 1 to
1.5% of those exposed. This rate was in agreement with
observations they made of actual epidemics.
The dose response data used (Table 4) in calculating the risk
of illness when exposed to other species of salmonella did not
include S. typhimurium, which is the major cause of waterborne
salmonellosis. Perhaps the dose response to this
microorganism is much more sensitive than for the type of
salmonella used in the dose response studies. This might
explain why S. typhimurium is so common a cause of intestinal
illness.
19
1 ETCALF * E DDV
-------
1 0
to
1 0
I*'3
I 0
-4
. -5
1 0
1 0
S. TYPHI
OTHER SALMONELLA
7 i i i i i i i i i 111 i i i i i i i i i i 11 i i i I 11 i i i ill i i i i 11 i i i i il i i i i 11 i i i
10" 10° 10'
SALMONELLA, ORGANISMS/L
1 0
1 0"
FIGURE 2
PROBABILITY OF DISEASE, AS RELATED TO
EXPOSURE TO SALMONELLA sp, OCCURRING IN BATHERS [31]
20
METCALF * EDDY
-------
To find the probability of swimmers contacting typhoid or
other salmonella, the truth most probably lies in between the
methods used by Kehr and Butterfield and Dudley, et al. From
laboratory data, it is evident that a considerable number of
salmonella are required to cause clinical disease and that
infectivity of S. typhi is greater than the other tested
salmonella. The relationship between the presence of
coliforms and the presence of pathogenic bacteria discussed by
Kehr and Butterfield is based on reasonable parameters,
although the accuracy of the numbers involved may be
questioned. It should be kept in mind that the data are only
for certain salmonella and do not represent all pathogenic
agents that might be present in contaminated water.
It should also be kept in mind that the presence of salmonella
in wastewater will not be as consistent as will the coliforms
that are shed continually by the entire population. The
salmonella present would most probably not be evenly
distributed in the water. Theoretically, if one assumes an
even distribution of pathogens the chances of contacting
salmonella while drinking water of poor bacteriological
quality may be small.
In fact, however, a discontinuous distribution of salmonella
may result in more effective (greater number of organisms)
doses being delivered, by chance, to more individuals than one
would predict. An example is the 1926 case in Detroit,
Michigan, cited by Kehr and Butterfield. There were eight
cases of typhoid fever and 45,000 cases of gastroenteritis
transmitted by water that contained an average of 6.5
coliforms per 100 mL. The morbidity of typhoid in the area
was estimated to be 27 per 100,000. The previously mentioned
indirect methods would have underestimated this value.
DOSE RESPONSE - TOXIC CHEMICALS
Dose response to toxic chemicals is normally evaluated by
using laboratory animals and the results reported as dose per
animal weight or per body surface area. Estimates of human
dose response relationships are made by extrapolating from
data on animals. In many cases, there is a threshold
concentration of a given chemical below which exposure does no
harm and above which frequency of response increases with
dose. Many of the values for the acceptable concentration of
inorganic chemicals in water are based on these kinds of data.
In developing such standards, the total intake from sources
other than water was also estimated so that the water
contribution will normally be insufficient to raise the total
intake over the threshold value.
21
-------
DOSE RESPONSE - CARCINOGENIC AGENTS
When carcinogens or suspected carcinogens are involved, the
usefulness of a threshold level value may be questionable.
The World Health Organization has identified other issues [32]
1. The self replicating nature of the cancer cell.
2. The possibility that the carcinogenic event is
irreversible.
3. Certain evidence that tumor initiation may be caused
by a single tumor initiating event.
4. The fact that cancer can occur in response to
chemicals long after their disappearance from the
body.
To evaluate the risk of developing cancer from exposure to
water and wastewater, the first problem is to determine the
presence of a carcinogenic or mutagenic agent. The second
problem is to determine the risk to the human population from
the presence of such an agent. The first problem is being
vigorously attacked in many laboratories throughout the world
with many promising results. These activities have been
summarized by Drake et al. [33]. The second problem is more
difficult to study because of the four issues listed.
ACCEPTABLE RISK
One approach to assess the health hazard of exposure to low
doses of carcinogens has been suggested by Friedman [34], who
used the method of Mantel and Bryan [35]. Because a no-
response dose of carcinogenic may not exist, it is necessary
to select some acceptable risk of contracting cancer (e.g., 1
in 100 million as suggested by Mantel and Bryan). From dose
response information obtained when using high doses of
material, Mantel and Bryan extrapolated the dose associated
with the selected risk (i.e., 1 in 100 million).
These values are all arbitrary. However, they are
conservative because the calculation method ignores other
probabilities involved, such as (1) the probability that an
individual will have a given exposure; (2) the probability
that the individual involved will be overshadowed by some
other competing risk; and (3) the age of the individual when
the cancer will occur.
A major difficulty is to set the limit of acceptable risk.
Friedman suggests that the risk level should be associated
with everyday risks of cancer, such as eating a commonly
22
METCALF & EDDY
-------
accepted food with a known level of carcinogen (e.g.,
benzpyrene in broiled beef steak). Using an extrapolation,
the risk of cancer from consuming 70 g of charcoal broiled
steak is 8 in 10 million.
It is obvious that there is much to be determined before
satisfactory dose-response-risk data will be available on
disease agents in water and wastewater. It is probably
Utopian to assume that such data will ever be developed for
all factors involved. However, information now available
or presently being developed provides an insight into what
factors are involved in the transmission and cause of
environmentally associated disease. Present knowledge gives
us some information about the magnitude of various problems.
This knowledge coupled with observation (epidemiological
evidence) helps in the assessment of health risks.
23
IETCALF * EDDY
-------
Chapter 5
REMOVAL MECHANISMS
The infectious organic and inorganic agents in wastewater are
affected by numerous mechanisms that are used in wastewater
treatment and disposal and that reduce health risks. Although
the mechanisms lessen the numbers by removal as well as by
dilution, the term removal mechanisms refers to both. In
conventional treatment, mechanisms include disinfection,
sedimentation, retention time in activated sludge treatment,
and retention time in oxidation lagoons. In land treatment,
mechanisms include filtration, desiccation by sunlight, and
microbial antagonism by naturally occurring soil
microorganisms.
INFECTIOUS AGENTS
The infectious agents in wastewater, which were discussed in
Chapter 3, are reduced in numbers by various mechanisms during
collection, treatment, and discharge. At the source/ the
number of pathogenic and indicator organisms is the largest.
The comparison between "night soil," as is used by many lesser
developed countries, and raw municipal sewage shows that
dilution in a collection system may account for a pathogen
reduction factor of 2 x 10^ to 2 x 10^ [36]. This reduction is
important when extrapolating reported disease incidents result-
ing from use of "night soil" to use of treated effluents.
Although the presence of all infectious agents is assumed from
a public health viewpoint, the removal mechanisms discussed in
this report are limited to the most common agents, such as
Shigella, Salmonella, Escherichia coli, infectious hepatitis,
Coxsackie-, Echo- Adeno-, and Reo-viruses, and the parasites
Entamoeba hystolytica and Giardia lamblia. The reductions of
less prevalent agents should be similar to the behavior of
these common agents. The study of indicator organisms has
been greater than that of the infectious agents. In some
instances, the behavior of the fecal and total coliforms may
serve as guidelines, but caution over their use is expressed
since major differences occur.
Conventional 'Treatment
Conventional treatment provides reductions in infectious
agents by primary treatment (sedimentation), secondary
treatment (aeration and sedimentation), chlorine disinfection,
and dilution and die-off during surface water discharge. The
reductions in the number of the infectious agents are
presented in Table 5. Although the overall removals vary from
24
« ETC Ai-F * E O OV
-------
negligible values to greater than 99% removal, highly
effective mechanisms are required to produce the 4 to 8 log
reductions in numbers that are needed to reduce pathogen
counts to low numbers. Conventional wastewater treatment has
relied heavily on chlorine disinfection to accomplish this die-
off of infectious agents.
Table 5. ENTERIC MICROORGANISM REDUCTION
BY CONVENTIONAL TREATMENT [5, 28, 37, 38]
Primary treatment Secondary treatment
Microorganism removal, % removal, %
Total coliforms
Fecal coliforms
Shigella sp.
Salmonella sp.
Escherichia coli
Virus
Entamoeba histolytica
<10
35
15
15
15
<10
10-50
90-99
90-99
91-99
96-99
90-99
76-99
10
Without disenfection.
The effectiveness of chlorination in the destruction of
infectious agents in wastewater effluents varies depending on
the type of infectious agent, the applied chlorine dose and
contact time, and the quantity of interfering material, such
as suspended solids and ammonium nitrogen. The resistance of
various infectious agents to chlorination was described by
Bauman and Ludwig (cited in [37]). They used a die-off
coefficient, a K value, that was equal to the product of
chlorine dose and contact time. K values for various
waterborne microorganisms are presented in Table 6. E^ coli
had the most rapid die-off with a K value of 2 to 4, while E.
histolytica was most resistant with a K value of 50 to 125.
Table 6. VALUE OF DISINFECTION CONSTANT K FOR VARIOUS
WATERBORNE MICROORGANISMS [37]
Microorganism
E. coli
Salmonella sp.
Poliovirus
Coxsackie A
Hepatitis
E. histolytica
pH range
7.0-8.5
7.0
6.8-9.3
7.0-9.0
6.4
7-8
K value
2-4
2-4
6
6
10
50-125,
25
METCALF » E D DY
-------
Conventional wastewater treatment generally precedes discharge
of the treated effluent into a surface water. Since these
waters occasionally serve as recreation areas and as sources
of potable water, the effects of the receiving waters on the
infectious agents are important. The survival of enteric
microorganisms is less favorable in environments other than
the human body. The die-off mechanisms in surface waters
combine with dilution to promote reduction in populations.
Historical research has generally been focused on trying to
define the die-off behavior of the indicator organisms (fecal
and total coliforms). The die-off of microorganisms is
generally accepted to occur as a first order decay
relationship according to Chick's Law:
In C/C
-Kt
where C
Co
K
t
(t)
concentration at time
initial concentration
die-off coefficient,
-------
The die-off under :in situ subartic river conditions was found
to be 0.5 day-1 at a temperature of 32°F (0°C) [40]. A
reportedly high die-off coefficient of 8.72 day"1 was found
for in situ determinations in Lake Michigan at a water
temperature of 63°F (17°C) [41J. It generally appears that in
situ die-off coefficients are considerably higher than those
observed in laboratory experiments. In addition to the
survival of the indicator organisms in surface waters, limited
information is available for the infectious agents themselves
[42] as shown in Table 7.
Table 7. SURVIVAL OF INFECTIOUS AGENTS
IN SURFACE WATERS [42]
Infectious agent
Time for 99.9%
removal, d
Half-life, h
Removal after
2 d, %
E. coli
S. fecalis
Enterobacter aerogenes
Echo 7
Echo 12
Coxsackie A9
Polio I
5-7
8-18
8-18
7-16
5-12
i8
13-20
12-17
19-43
19-43
17-39
12-29
19
31-48
86-94
54-83
54-83
59-86
68-94
>83
50-65
Land Treatment
Land treatment systems substantially reduce the numbers of
indicator organisms and infectious agents. The removals can
be accomplished by various mechanisms within the treatment
sequence. The treatment sequence can include primary
treatment (reported previously in Table 5), aerated lagoon
secondary treatment, storage, and application to the land.
After the wastewater has been applied to the land, removal
mechanisms include retention on soil surface, retention within
the soil profile, die-off by predation, and dilution in
groundwater or surface water. The land treatment processes
(slow rate, overland flow, and rapid infiltration) rely on
some or all of these mechanisms.
Aerated lagoons have been used more as preapplication
treatment methods, because their capital and operating costs
are low, and their low maintenance requirements are generally
compatible with land treatment systems. Some reported maximum
removal capabilities for indicator organisms and infectious
27
1ETCALP * EDDY
-------
agents are presented in Table 8. Adequate system operation
and maintenance is required to maintain these removal
capabilities.
Table 8. MAXIMUM REMOVAL OF ENTERIC
MICROORGANISMS BY LAGOON SYSTEMS3 [7, 37,43]
Enteric microorganism Removal, %
Coliforms
Fecal coliforms
Total bacteria
S. typhi
Virus
P. aeruginosa
60-99.99
99.
99.
99.5
99.99b
99.69
a. Without disinfection.
b. Laboratory study.
Slow rate systems generally include storage facilities that
act as treatment ponds. Predation by bacteria and adverse
environmental factors, such as pH changes and ultraviolet
radiation, should provide at least 99% removal during storage
for most infectious agents.
The capabilities of the soil to remove infectious agents from
solution have been investigated under many conditions for
bacterial and viral pathogenic agents (Table 9). The removal
of fecal coliform indicator organisms was reported to be
essentially complete under many conditions.
Table 9. REMOVAL OP ENTERIC MICROORGANISMS
BY SOIL SYSTEMS [44, 45]
Enteric
microorganisms
Fecal coliforms
Coliforms
Coliforms
Fecal streptococci
Fecal streptococci
Location
Hanover,
New Hampshire
Lodi, California
Whittier Narrows,
California
Santee, California
Santee, California
Removal , %
Essentially
complete
Essentially
complete
Complete
99.5
99.8
Observed
concentration
No . /mL
<1/100
1/100
None
20/100
6.8/100
Observation
depth, ft
5
4-7
>4
a
__b
a. 200 ft of lateral flow.
b. 1,500 ft of lateral flow.
28
L F * E D OY
-------
The removal capabilities of full-scale systems were reported
at Lodi, California, where coliform counts in effluent applied
to a sandy loam soil were reduced to 1/100 mL between a 4 and
7 ft (1.2 to 2.1 m) soil depth [45]. At Whittier Narrows,
California, applied coliform concentrations of 110,000/100 mL
were reduced to 40,000/100 mL at a 3 ft (0.9 m) depth. None
of the coliforms was detected at greater depths. Lateral flow
through sand and gravel at Santee, California, removed fecal
streptococci applied at a concentration of 4,500/100 mL to
20/100 mL at a 200 ft (61 m) distance, 48/100 mL at a 400 ft
(122 m) distance, and 6.8/100 mL at an interceptor ditch.
The rapid infiltration system at Flushing Meadows, Arizona,
has been studied to determine removals of bacteria and virus.
The removal effectiveness depends on the rate of application.
The fecal coliform reduction of applied effluent (10 /100 mL)
was reduced to values from 0 to 100/100 mL at a distance of 30
ft (9.2 m). With 2 to 3 days of continuous inundations, the
total coliforms were reported to be 5/100 mL. As the rate of
application increased, the inundations increased to 2 to 3
weeks; the reported total coliform concentrations after 30 ft
(9.2 m) of travel were 200/100 mL.
After application of seeded virus to rapid infiltration soil
columns at hydraulic rates of 22 and 6 in./d (55 and 15 cm/d),
the detection of virus in the soil column was limited to the
soil depths less than 69 in. (175 cm), as shown in Figure 4.
Virus removal in rapid sand filters for (potable) water
treatment was reported to be greater than 99% at application
rates of up to 36 in./d (91 cm/d) using a sand media [46].
Lesser application rates can be expected to produce greater
removals. A summary of observed travel distance through soil
for virus from wastewater effluents ranged from 8 to 46 in.
(20 to 117 cm) [46].
Slow sand filters with application rates of 15.7 to 39 ft/d
(4.8 to 12 m/d) exhibited virus removal from 98.25 to 99.997%
[47]. At a rapid infiltration site at Santee, California, 3.2
gal (12 L) of concentrated polio vaccine virus was applied to
sand and gravel. None was detected by the gauze pad technique
after travel through 200 ft (61 m) of soil [45]. At Whittier
Narrows, California, a massive community inoculation with the
Sabine oral vaccine occurred during the rapid infiltration
studies. No vaccine viruses were detected in the treated
wastewater after passage through a collection system,
treatment plant, and travel through 2 ft (0.6 m) of soil, but
the detection limit of the method used was estimated to be 5
to 10 PFU/100 mL [45], In contrast to these results, a virus
was isolated in sandy soils (with no silt or clay) using
29
1 TC A LF * ED DY
-------
ADDED VIRUS REMAINING IN WASTEWATER, '/•
D 20 40 60 80 100
50
t 00
1 50
200
FIGURE 4
REMOVAL OF POLIOVIRUS FROM WASTEWATER BY SOIL COLUMNS
WITH DIFFERENT INFILTRATION RATES. ADDED CONCENTRATION
OF VIRUS WAS 3 TO 5 x 104 PFU/mL [48]
30
1CTCALF * EDDY
-------
improved techniques, and a concentration method for using as
much as 150 gal (570 L) of sample (cited in [46]). They
surmised that an extremely heavy rainfall caused virus to be
released from the soil by elution during these singular
events.
The observed survival times of the retained virus in a soil
column was reported to be less than 8 days on bare lysimeters
and up to 32 days on the soil surface of a sod covered
lysimeter, as shown in Figure 5 [4].
TINE OF SAMPLING, d
0 < t 121620242132
-t
H 1 1 1 1
©
TIME OF SAMPLING, d
02461
+—-I 1 1
TIME OF SAMPLING, d
BARE LVSIMETER
SOD LYSIKETER
BARE irSIMETER »2
FIGURE 5
SEEDED VIRUS SURVIVAL IN SOIL [4J
The capabilities of overland flow to reduce total and fecal
coliforms were reported [6]. The results show (Table 10) that
before discharge of the treated runoff water, the effluent may
require additional treatment for pathogen removal. Chlorine
disinfection should require lesser doses for an overland flow
effluent than for a conventional secondary treatment process
due to a low total nitrogen (less than 6 mg/L) and low BOD and
SS values.
31
M ETCALF 1 E DOV
-------
Table 10. REDUCTIONS OF INDICATOR ORGANISMS
BY OVERLAND FLOW TREATMENT [6]
Indicator
organisms
Total
Fecal
coliforms
colif orms
Raw wastewater
applied concentration
7
1
.2
.0
X
X
106
106
Added
None
0.3 x
0.09 x
aluminum sulfate3
14 mg/L
106
106
0.2 x
0.03 x
106
106
20 mg/L
0.2 x
0.02 x
106
106
a. Aluminum sulfate added to enhance phosphorus removal.
Although it is expected that very low infectious agent
concentrations will pass into groundwater from a well-designed
land treatment system, additional reductions do occur in
groundwater movement. The survival of infectious agents in
well water was reported and the results are presented in Table
11 [49]. Times for 99.9% removal varied from 2 days for £>_._
bovis to 11 days for Sh. flexneri.
Table 11. SURVIVAL TIMES OF ENTERIC MICROORGANISMS
TN WELL WATER [49]
Enteric
microorganism
Time for 99.9%
removal, d Half-life, h
Removal after
4 d, %
Coliforms
Sh. dysenteriae
Sh. flexneri
Sh. sonnei
S . typhi
S. equinus
S. bovis
Enterococci
V. cholera
7
9
11
10
3
4
2
9
3
17
22
27
25
6
10
4
22
7
98.1
95.2
91.7
93.7
99.99
99.9
99.9999
95.2
99.99
The die-off of wastewater microorganisms when applied to the
soil surface or vegetation is of interest due to potential
vector transport, site worker contact, or survival on
harvested crops used for food. Microorganism die-off occurs
due to sunlight effects of desiccation and ultraviolet
radiation. Some values reported in the literature are
summarized in Table 12.
32
« ETCALF * E D DV
-------
Table 12. SURVIVAL TIMES OF ENTERIC
MICROORGANISMS ON SOILS AND VEGETATION [1, 50]
Enteric
microorganisms
Coliforms
Shigella sp.
Salmonella sp.
Enterovirus
E. histolytica
Environment
Fodder
Vegetables
Soil surface
Fodder
Leaf vegetables
Orchard crops
Fodder
Soil surface
Leaf vegetables
Orchard crops
Leaf vegetables
Leaf vegetables
Survival
time, d
6-34
35
38
<2
2-7
6
12-<42
15-46
1-40
0.75-<2
15-60
2
Estimated die-off
after 7 d, %a
98
90
88
Below detection
Below detection
Below detection
94
93
98
Below detection
89
Below detection
Calculated from median survival time.
INORGANIC CONSTITUENTS
Nitrogen
Nitrogen occurs in wastewater at concentrations ranging from
20 to 80 mg/L as total nitrogen. Discharge of treated
wastewater to potable water sources from which a concentration
greater than 10 mg/L can be withdrawn should be avoided.
Control of nitrogen discharge to groundwater from land
treatment systems can be accomplished by appropriate design
[51].
Nitrogen removal occurs by crop uptake and denitrification in
slow rate and overland flow systems and by denitrification in
rapid infiltration systems. The final effluent discharge for
overland flow systems is generally to surface water bodies.
Other systems may discharge to either groundwater or surface
water bodies.
Conventional activated sludge treatment does not remove
nitrogen, but modifications of the process can result in
nitrification. Nitrate concentrations meeting drinking water
standards are usually achieved by dilution in the receiving
surface water.
33
I ETCALF i. E O DV
-------
Trace Metals
The concentrations of trace metals in municipal wastewater
only are usually low, because industrial inputs are generally
the major source of trace metals. As shown in Table 13, the
concentrations in untreated municipal wastewater are, at
times, less than the EPA drinking water standard. The
removals from solution by primary and secondary conventional
treatment, as well as the removals by the three land treatment
types, are also presented in Table 13. Land treatment reduces
concentrations to low values, and these values are usually
less than drinking water standards [51].
Table 13. SUMMARY OF TRACE METAL INFORMATION,
CONCENTRATIONS, AND REMOVALS [44, 51-53]
Raw municipal
Mass removal by
land treatment, %a
Component
Arsenic
Cadmium
Chromium
Copper
Fluoride
Iron
Lead
Manganese
Mercury
Selenium
Silver
Zinc
c*et\ UJ. -LiiA-iiiy wa&uewai~e.L
water standard, concentration,
mg/L mg/L
0
0
0
1
1.4
0
0
0
0
0
0
5
.05 0.003
.01 0.004-0.14
.05 0.02-0.7
.0 0.02-3.4
-2.4b
.3 0.9-3.5
.05 0.05-1.3
.05 0.11-0.14
.002 0.002-0.05
.01
.05 0.05-0.60
.0 0.03-8.3
CL xtlLdi. y ijcv-uiiuaa- y — —
treatment treatment Rapid
removal, % removal, % Slow rate infiltration
-------
Chapter 6
RISK ASSESSMENT
The task of assessing health risks involves many factors of
which the existing body of scientific knowledge varies from
essentially zero (speculative) to well-established facts.
Municipal wastewater contains constituents for which current
knowledge spans this entire range. For example, known
relationships exist for challenge (direct) doses of Salmonella
sp., although the dose reponse of virus is not defined, and
the health effects of trace organics are speculative at this
point.
In 1973, Benarde reviewed the health effects literature on
land treatment [54]. He concluded that "from a communicable
disease viewpoint, land disposal is far less hazardous than
disposal into rivers and streams" [54].
More recently risk assessment was the subject of a conference
and Earth presented current EPA research on the subject [55].
Llewellyn concluded that from an epidemiologist's point of
view "the best that science and public health practice and
engineering techniques presently have to offer cannot provide
the policy maker with the data for a clear decision regarding
risks of wastewater application or of standards for this
application" [56]. Dorcey, on the other hand, found that it
is "reasonable to expect that the increased consideration
being given by municipalities to options for application of
municipal wastewaters and sludges to the land will lead to
improvements in the analysis of alternatives and their
consequences." He also indicated that the "decision maker's
ideal would be to have quantitative information on the cost of
reducing risk and uncertainty as part of a systematic analysis
of the costs and benefits of alternative plans..." [57],
The risk assessment approach presented in this report is semi-
quantitative. It relies on known public health, sanitary
engineering, and scientific information that describes health-
related problems. The public health information generally
describes the health-related constituents, the available
information on minimum infective dose, requirements for
asymptomatic infection, and symptoms from clinical infection.
In addition, the available morbidity (illness) data provide
information on the waterborne occurrences of the disease in
relation to total public incidents.
The sanitary engineering information describes the controls
exercised by wastewater treatment systems and planned
environmental discharges to maintain and upgrade public health
35
MCTCALF * CODY
-------
objectives. Scientific principles provide assessment
methodology and information on physical behavior in cases
where general behavior is known, but specific case study
information is lacking.
A second level of refinement would include weighting of the
relative health effects. For example, a greater loss value
would be assigned for a disease such as hepatitis than for
salmonellosis. Such an assessment would include a comparison
of the severity of potential diseases and of the number of
cases of a single disease. Weighting factors needed for this
level of assessment should be based on arbitrary or combined
expert evaluation.
A relative health risk assessment is based on an evaluation
of the known principles and tabulations of known data.
The proposed steps for making the relative assessment of
health risks are as follows:
1. List wastewater constituents of concern from
known information about nationwide occurrences of
disease, or from local information obtained from
a public health official.
2. List alternative treatment sequences. Identify
points of contact and assign contact intensity
factors. Estimate contact duration factors based
on staffing requirements or potential public
contact.
3. Describe the reduction of health affecting
constituents in the wastewater treatment
sequence. Assign initial concentrations in
wastewater and compute concentrations after
each subsequent step.
4. Prepare a summary tabulation of the three factors
at agent-host contact points:
a. Expected concentration of each constituent
b. Contact duration factor
c. Contact intensity factor
5. Compare expected concentrations, contact
duration, and contact intensity of each
individual constituent within the alternative
treatment sequences. From these comparisons,
draw conclusions on the major differences and
prepare a statement as to relative risks.
36
METCALF & EDDY
-------
Chapter 7
EXAMPLE ASSESSMENT
The purpose of the example assessment is to illustrate the
procedure set forth in Chapter 6 by comparing the relative
health impacts of land treatment and activated sludge
treatment systems. This same procedure can be followed to
make other comparisons. Since a large number of variations
in treatment processes exist, the most commonly used
treatment sequence was used to provide the reference and
basis for comparison.
Although activated sludge and slow rate were considered
equivalent treatment systems in the example assessment, a
slow rate system will produce a higher quality effluent with
lower BOD values and an increased removal of nitrogen and
phosphorus.
In the following paragraphs, assumed characteristics of each
treatment system will be presented followed by a stepwise
description of the assessment process.
LAND TREATMENT SYSTEM
The land treatment system objectives vary considerably
depending on local conditions. The typical systems assumed
for this report were based on a recent study of wastewater
reclamation facilities in California that listed reuse
objectives and the number of systems employing them (Table
14) [58].
Table 14. TYPES OF REUSE OBJECTIVES
IN CALIFORNIA SYSTEMS USING
LAND TREATMENT [58]
Reuse objectives No. of systems
Fodder, fiber, seed >crop irrigation 139
Landscape irrigation 44
Orchard and vineyard irrigation 16
Processed food crop irrigation 14
Groundwater recharge 8
Industrial uses 8
Food crop irrigation (not processed) 6
Others, including nonrestricted and
restricted recreational impoundments,
landscape impoundments, and pasture
for milking animals 12
37
I ETCAUF * C O OV
-------
Additional information on a typical land treatment system
was compiled in a nationwide survey [59]. This information
is summarized below:
1. Secondary preapplication treatment, usually
including lagoons
2. Operation - 7 d/wk
3. Application to sand, loam, or silt
4. Sprinkler application (humid areas)
5. Surface application (arid areas)
6. Farming zone locations
7. 73% of flows less than 5 Mgal/d
8. No collection of treated water
9. 76% of systems do not have disinfection before
application
10. Application less than 2 in./wk (5 cm/wk)
BASIS OF COMPARISON
A schematic flow diagram for the activated sludge and the land
treatment system used is presented in Figure 6. A population
of 30,000 and a wastewater flow of 3 Mgal/d (0.13 mVs) is
assumed. Industrial toxicants are assumed to be largely
removed by pretreatment.
Land treatment is preceded by aerated lagoon treatment with
winter storage. The activated sludge treatment sequence
consists of grit removal, primary sedimentation, aeration,
secondary sedimentation, chlorination, and surface water
discharge (Figure 6) .'
Staffing requirements were estimated for the alternative
systems to determine degree of worker exposure to health
affecting components. According to the methods published by
the EPA [60] and an assumed flow of 3 Mgal/d, both systems
(slow rate and activated sludge) would require staffing of
about 6 men per year (approximately 9,000 man-hours). Sludge
handling and disposal was not included in the activated
sludge alternative, nor was vegetation planting and harvest
included with the land treatment options.
Planting, harvest, and vegetation management would apply to
the slow rate and overland flow systems. A rapid
infiltration system would require the least staffing with
an estimated 3 men (approximately 4,500 man-hours).
Overland flow would require an estimated staff of 6 men
(approximately 9,000 man-hours).
38
M ETC Al-F * C D 0V
-------
LAND TREATMENT
'BEYOND SCOPE
REPOR
\l
HEADWORKS
AERATED LAGOONS
STORAGE
I
IX
DISTRIBUTION
SYSTEM
l\
K
AEROSOLS WITH
SPRINKLER
DISTRIBUTION
I
SOIL SURFACE
&
VEGETATION
SOIL COLUMN
UNSATURATED FLOW
TO GROUNDWATER
SATURATED FLOW
IN GROUNDWATER
UNDERDRAINS
20-60% RECOVERY
GROUNDWATER
SUPPLY
CONVENTIONAL
TREATMENT
HEADWORKS
PRIMARY
SEDIMENTATION
AERATION BASINS
SECONDARY
SEDIMENTATION
CHLORINATION
RIVER DIE-OFF
& DILUTION
SURFACE WATER
RECREATION
*-*•*
SURFACE WATER
SUPPLY
FIGURE 6
TREATMENT FLOW SEQUENCES USED IN EXAMPLE COMPARISON
39
IETCALF It EDOV
-------
ASSESSMENT
Identify Wastewater Constituents
The initial step is to identify the significant wastewater
constituents affecting health. General information for the
United States (Chapter 3) shows that the infectious agents
of concern are Salmonella sp., Shigella sp., parasites,
Escherichia coli, and viruses. Fecal and total coliforms
are included since they are generally accepted for use as
indicator organisms. Principal inorganic chemicals of
concern are nitrates and trace metals. The list of trace
organic chemicals known or suspected to cause adverse
health effects includes hundreds of compounds. Some were
listed in Table 3.
Overall, these components comprise the major health risk
in most areas. However, in cases where additional
infectious agents are endemic, or as additional or higher
concentrations of chemicals occur, the health risk
assessment should be expanded to comply with local
conditions.
Concentrations of Wastewater Constituents
The process steps for each treatment sequence should be
identified as to their potential to remove a wastewater
constituent from solution, concentrate a wastewater
constituent, or provide an opportunity for contact in the
agent-host transmission cycle. Discussions of each of
these process steps are given for removal, concentration,
or host contact.
No removals of health-related constituents are assumed
during wastewater collection. The headworks in both
treatment systems provide removal of large solids and
opportunities for wastewater contact by site workers,
although reduction of wastewater constituents is
negligible. Various removal capabilities occur in aerated
lagoons, storage lagoons, primary and secondary
sedimentation, and aeration basins.
Disinfection can provide high removals of infectious agents.
In addition, discharge of effluents to surface waters provides
reductions by dilution and die-off. Retention on the soil
surface allows infectious agent die-off by environmental
exposure, while travel through the soil column provides
excellent removals of many constituents. Transport with
groundwater also provides dilution and die-off.
40
1 E TC ALF A E D DY
-------
An estimate was made for the percent removal during each
treatment sequence based on available data, which were
summarized in Chapter 5. Data are not always available, so
extrapolation between similar organisms such as Salmonella
sp. and Shigella sp. was used when necessary. Some
treatment systems report a single removal, so this was used
without change. When a range of values were reported, both
were used, with the high removals used consistently to give
one end of expected range and the low removals used to
estimate the other end.
Agent-Host Transmission Cycle
Opportunities for contact with a host exist at many points
within a treatment sequence. The initial wastewater
collection provides the greatest risk of exposure; however,
in this example, the contact is assumed equal for both
treatment systems and is not discussed. Site operation and
maintenance provides worker exposure at levels that can be
estimated based on staffing requirements. The use of
surface aeration in lagoons and aeration basins provides
opportunities for contact with aerosol droplets. The
disinfection process provides little opportunity for
contact, although discharge to surface waters provides
contact from incidental events, recreational use, and, at
times, potable water supply.
Wastewater application to the land provides opportunities
for incidental contact on the soil surface, and, if
sprinkler applied, aerosol contact. Retention of
wastewater constituents provides contact opportunities on
vegetation, but contact is nil for retention within the
soil profile. Passage to groundwater provides an
opportunity for contact through withdrawal from wells and
seeps.
The assessment of health risks requires quantification of
the wastewater constituents and the transmission cycle to a
susceptible host. The wastewater constituents were
described previously, and the relative numbers were
presented. The transmission cycle is not easily quantified,
so the following method is presented" based on contact
intensity factors and contact duration factors. Contact
intensity describes the relative potential of a contact
producing illness. Contact duration estimates the frequency
of these contacts based on annual exposure. The two factors
are chosen to illustrate the difference between low and high
intensity of contact and long and short durations of
contact. At present, no method exists that allows
comparison between a long duration, low-intensity contact
and a short duration, high-intensity contact.
41
1ETCALF t. E 0 OY
-------
Contact Intensity
Contact intensity factors are defined in four categories to
describe the point of transmission between an infectious
agent and a susceptible host.
Incidental physical contact is the potential physical
contact between a host body and an object that has been
contacted by wastewater or the wastewater itself. This
does not assume direct intake into the body, but rather
makes the assumption that it can occur. This contact
is the least likely to cause infection or illness.
Accidental ingestion is the small volume potential
ingestion from being in the water, as typified by
recreational activities, such as swimming, boating, and
water skiing. This category would also include the
incidental occurrence of using surface water for
potable purposes, such as one-time consumption of
waters.
Potable ingestion is the ingestion of domestic water,
which includes the daily ingestion for drinking, as
well as food preparation, bathing, and other uses.
Although not specifically addressed in this report, the
water ingested for potable purposes would undergo
additional treatment by at least chlorine disinfection
in essentially all municipal and many private water
supply systems drawing from surface water or
groundwater sources. This contact has the greatest
potential to produce infection or illness based on
contact factors alone.
Contact Duration
Contact duration factors are used to assess the exposure of
the total population to various contact opportunities with
the health affecting constituents of wastewater. This
method is a compromise between estimating ingested volume of
treated or untreated water, and incidental contact. For
this report, the contact duration is considered to be the
total annual man-hours of exposure. During the treatment
sequence, the man-hours of contact are estimated from
staffing requirements for operation and maintenance (Table
15). For general public contact through recreation,
municipal surface and subsurface water supply, and private
subsurface water supply, the following annual estimates were
made.
Municipal water supply:
lh 365d
persons = 1.1 x 107, say 107 h/yr.
This example assumes that the entire community (30,000
persons) has contact through the municipal supply.
42
-------
Private water supply (adjacent owners to land treatment):
365 d .. .,„ _ ., , x 1Q3^ gay 1Q4 h/yr.
_
pereons =
This example assumes that 5 families (4 persons each)
have contact from private wells.
Table 15. ESTIMATED CONTACT DURATION FACTORS
Annual Man-Hours [60]
Process
step
0
1
2
3
4
5
6
7
8
Activated
Process
Collection
Headworks
Primary
sedimentation
Aeration and
sedimentation
Disinfection
River die-off
River dilution
Recreation
Municipal water
supply
sludge
Contact
duration
Negligible
2 x 102
6 x 102
3 x 103
2 x 102
Negligible3
Negligible9
105
10?
Land treatment
Process
Collection
Headworks
Aerated lagoon
Storage lagoon
Field distribution
Soil surface
Soil column
Groundwater flow
Private water
supply
Municipal water
supply
Contact
duration
Negligible
2 x 102
2 x 103
6 x 102
2 x 103
5 x 102
Negligible
Negligible
104
107
a. All river contact assumed to occur during recreation.
The activated sludge treatment generally uses chlorine
disinfection to reduce the number of infectious agents.
Since the susceptibility of various microorganisms varies
according to the relationship given in Table 6, the percent
die-off will vary for a given chlorine dose and contact
time. For the purposes of the example assessment, the
estimated removals of other wastewater microorganisms based
on a 99.99% die-off for £_._ coli and K values (Table 6) are
given below:
Agent
E. coli
Salmonella sp.
Poliovirus
Coxsackie virus
Hepatitis virus
E. histolytica
Percent die-off at fixed
contact time and dose
99.99 (assumed by design)
99.99
99
99
94
20-45
43
METCALF * EDDV
-------
RESULTS OF EXAMPLE ASSESSMENT
Infectious Agents
The results of the example assessment for land treatment and
activated sludge and river discharge are presented for
infectious agents in tabular form in Tables 16 and 17. As
shown in these tables, there is a dramatic decrease in the
number of water borne infectious agents. Thus, the
incidence of disease because of waterborne infectious agents
is almost nonexistent.
Nitrate Nitrogen
For activated sludge and discharge, nitrate reduction will
occur as a result of dilution. For slow rate, removal of
nitrate can be adequately controlled during system design.
Trace Metals
Trace metals should pose no health concerns in the effluent
portions of the wastewater under the assumed conditions.
Since typical values in untreated wastewater are low, the
removals by either treatment method should produce
concentrations less than drinking water standards. The
retention of metals within the soil profile requires
assessment to ensure that the mass accumulation remains
below recommended limits to prevent plant inhibitory
effects.
Trace Organics
Trace organics can only be described in general terms since
quantitative data are mostly absent. The removal of trace
organics in activated sludge treatment is slight. The major
reduction would be due to dilution with the river water
(assumed 20:1 for this example) and adsorption on settleable
particles. Land treatment provides considerable contact
with soil particles and opportunities for adsorption. The
soil microorganisms provide further opportunities for
microbial breakdown.
The use of chlorine disinfection can form halogenated
organic compounds, some of which are thought to be
carcinogenic. The capabilities of land treatment to provide
high levels of removal without a (chlorine) disinfection
step are noteworthy. The elimination of a chlorine
disinfection step with conventional treatment and discharge
would generally not be accomplished without an increase in
health risks.
44
M ETCALF * E DOV
-------
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46
-------
RISK EVALUATION
Site Workers
The health risk to site workers from either a slow rate land
treatment system or an activated sludge system depends on
three factors: (1) the type of contact (contact intensity);
(2) the length of contact (contact duration); and (3) the
concentration of wastewater constituents at the time of
contact. There is no method at present that relates these
factors, so only a qualitative assessment is presented.
The annual man-hours of worker contact are estimated to be
greater for a slow rate system than an activated sludge
system (Table 15). It cannot be said that this is a direct
indication of increased risk, because wastewater
concentrations vary throughout the process steps. In
addition, although both contact intensities are limited to
incidental and aerosol contacts only, the onsite conditions
change within each type, so comparisons are difficult to
make. In general, the health risks are considered to be
equal, with neither producing a notable health risk. This
is substantiated by a lack of any reports indicating
increased health risk from occupational exposure by a
wastewater treatment plant worker within the United States.
General Public
The relative health risk to the general public after the
treated wastewater effluent is discharged to surface water
or groundwater is shown in Table 18. The basis for
comparison is the estimated concentrations for an activated
sludge discharge (with chlorination) to surface water, and
land treatment discharge to groundwater or withdrawal and
discharge to surface water. Based on the estimated
concentrations of infectious agents, the land treatment
system decreased the relative health risk potential by
providing greater removals.
A summary comparison of the removal mechanisms for slow rate
and activated sludge systems is provided in Table 19. The
decreased risk with slow rate land treatment from infectious
agents was shown in comparing estimated concentrations as
discussed previously. The slow rate land treatment removal
mechanisms provide removals of nitrates, trace elements, and
possibly trace organics. An overall decreased relative
health risk occurs under these conditions.
47
M e TC ALF «, EDDY
-------
Table 18. SUMMARY COMPARISON OF HEALTH RISK POTENTIALS
No. Organisms/100 mL
Wastewater
agent
Coliforms
Salmonella sp.
Shigella sp.
Virus
Parasites
Relative
Surface water
Land
treatment
7.5xlO~6
l.SxlO"7
1. 5xlO-7
1.5xlO~8
2xlO~9
concentration
supply3
Activated
sludge
0.1-1.4
0.5-2xlO~4
0.5-4.5xlO~4
1-400x10-3
4-10
at contact points
Groundwater supply
Land Activated
treatment sludge*3
6xlO-4
2xlO-7
(1.0-1.6)xlO~6
1.9xlO~8
3xlO"9
a. Provides water for municipal supply as well as recreation. Health
risk potentials are different due to different contact intensity and
contact duration.
b. An activated sludge system discharging to surface water would impact
groundwater only if streambed outflow were significantly large.
Table 19. SUMMARY COMPARISON OF REMOVAL MECHANISMS
Wastewater Slow rate Activated
constituent land treatment sludge treatment
Bacteria
Salmonella sp. + +
Shigella sp + +
E. coli + +
Virus, in general +
Parasites
E. histolytica +
G. lamblia +
Nitrate +
Trace elements + +
Trace organics 0 to •¥ Q
Note: Comparisons based on the following notations:
+ Positive removals with little
remaining.
- Minor removals.
0 Behavior unknown, but partial removals
have occurred.
48
M ETCAt-F * E D DV
-------
Chapter 8
DISCUSSION OF THE EXAMPLE
The example assessment was developed to illustrate the
suggested approach to qualitative assessment of public health
factors for activated sludge and land treatment systems. The
example, as would any approach to this type of assessment,
includes assumptions to simplify the approach. In the
assessment, some factors were assumed to be constant although
they change and can influence the assessment; these factors
include:
1. Fail-safe aspects
2. Food crops
3. Perspective with non-United States conditions
4. Alternative systems: rapid infiltration and
overland flow
5. Site management and design changes
A discussion of these factors is presented to show the
differences that can occur for the various land treatment
options. The assessment method is presented for the slow rate
example and can be used to assess other land treatment
options.
FAIL-SAFE ASPECTS
The example assessment showed that well-maintained and
operated treatment systems greatly decrease health risks. The
concentration of infectious agents may be reduced as much as
12 orders of magnitude between collection at a plant and
potable reuse. Inclusion of dilution during collection brings
the total reductions to as high as 17 orders of magnitude.
These reductions are optimistic at times, but the reduction of
health risk is presently occurring under much less favorable
conditions.
When consideration is given to existing primary, secondary,
and miscellaneous discharge of erratically operated (at times)
treatment systems without the demonstration of adverse health
aspects, implicitly it must be agreed that some truth lies
within the example. This does not, however, mean that
standards should change radically or different treatment
policies advocated. As populations and water use increase,
the cycle between wastewater treatment and discharge, and
potable reuse, becomes shorter. The maintenance of p.ublic
health requires consideration of this shorter cycle.
49
METCALF * EDDY
-------
The reliability of the unit processes in conventional
treatment gives an indication of the fail-safe aspects.
Mechanical equipment, such as pumps, feeders, and mixers,
provide continuous and adequate performance only if maintained
and operated properly. Smaller systems generally do not
provide continuous staffing. System upsets are more apt to
occur. The resulting inefficiency depends on engineering
design, but may result in minor or major contamination of
receiving water. Disinfection processes are equally subject
to upset, with results ranging from over-chlorination with
potential halogenated organic and chlorine toxicity, to under
chlorination with insufficient pathogen die-off.
Land treatment systems are also subject to short circuiting in
the preapplication treatment such as in the aerated or storage
lagoons. However, the overall treatment process, including
passage through the soil column, is relatively unaffected by
applied wastewater concentrations. In addition, a slow rate
system is fail-safe (i.e., if too much water is applied, the
soil will not take the water).
The water must also pass through the soil to reach to
groundwater or the underdrains (assuming no fractured rock
for direct transmission). A properly designed land
treatment system should provide reliable treatment greater
than that provided by a well-designed activated sludge
plant. Many additional factors should be considered in
overall assessment. Although not included in the
discussion, consideration should be given to:
1. Storm flow bypasses in conventional treatment
2. Rainfall runoff on land treatment sites
3. Daily and weekly flow variations in conventional
treatment
4. Extreme climatic considerations in land treatment
Both land treatment and conventional treatment exhibit a range
of values for process performance under good operating
conditions. Although little data are available, the
variations in performance would be valuable in assessing
overall reliability.
FOOD CROPS
Although the production of food crops for human consumption
without processing is rare for wastewater irrigation, its
consideration raises much concern. Historically, disease
outbreaks have been attributed to the use of "night soil" on
vegetables that were consumed raw. A comparison shows that
50
1 ETCALF t E D OY
-------
the concentration of infectious agents that came into contact
with the food was probably 10 to 10 greater than present in
untreated (collected) wastewater now. For example, California
regulations require that only oxidized, coagulated, filtered,
and disinfected wastewater be allowed for sprinkler irrigation
of human food crops to be eaten raw. The further reduction in
concentration probably varies by a factor of 10^ to 10^. As
such, the combined difference in infectious agent
concentration between the past reported disease outbreaks and
present practices amounts to a factor as much as 10^ to 1Q13.
Although adverse health effects could occur (as with any
wastewater use), the risk is minimal and is probably similar
to the risk of everyday activities.
COMPARISON TO NON-UNITED STATES CONDITIONS
The health risks from wastewater treatment and discharge vary
considerably according to local conditions. In the United
States, the reported morbidity levels are low and
concentrations of infectious agents are also low. The
artificial and natural mitigation mechanisms provide
considerable removals. The agent-host transmission cycle is
quite large, so the combined factors make the documentation of
a wastewater treatment and discharge related disease incident
a rare event.
Conditions outside of the United States are generally worse,
especially in less developed and highly populated countries.
There have been few reports of infectious disease associated
with irrigation systems using wastewater. Recently
Katzenelson, et al. [61] reported the differences in disease
rates between kibbutzim in Israel in which one group (a total
of 77) used wastewater irrigation and the other (130) did not.
The wastewater used was partially treated, nondisinfected
oxidation pond effluent of poor quality. The incidence of
shigellosis, salmonellosis, typhoid fever, and infectious
hepatitis was 2 to 4 times higher in the kibbutzim using
wastewater. The incidence of influenza-like disease was also
twice as high in the groups using wastewater irrigation. The
latter may have been due to enteric viruses such as Echo and
Coxsackie [61].
Several important changes exist in the agent-host transmission
cycle that are typically uncommon in the United States. The
quality of applied wastewater was poor. Although some
treatment was given, the concentrations of constituents in the
wastewater applied to the land were greater than those of raw
wastewater in the United States. The typical United States
removals by aerated and storage lagoons did not occur so
wastewater concentrations during application (sprinkling and
flooding) and on soil and vegetation surfaces should have been
greater by a factor of 10^ to 104.
51
1 E TC A LF * ED DV
-------
The higher concentrations provided an increased risk from
incidental and aerosol contact. The contact duration is much
greater in the kibbutzim than in United States systems. The
Israeli kibbutzim rely to a greater degree on field workers
rather than equipment for field management. Although an
estimate was made for staffing requirements for United States
on site management, a similar estimate would be difficult
without guidance by the kibbutzim.
Onsite observers have stated that onsite hygiene is poor by
United States standards and that mid-day meals are eaten in
communal dining areas by field workers and other kibbutzim
members. The agent-host transmission cycle between wastewater
applied to fields, site workers, and communal dining areas is
very short. The increased incidence of disease in wastewater
irrigation kibbutzim comes as no surprise because of the much
greater number of risk opportunities. The relevance to United
States conditions is closer to "night soil" irrigation at the
turn of the century, than to present United States land
treatment practices.
ALTERNATIVE LAND TREATMENT SYSTEMS AND MANAGEMENT
In the example assessment the slow rate process of wastewater
treatment was used. Rapid infiltration and overland flow are
additional alternatives that require evaluation. Briefly
described, rapid infiltration treats wastewater by percolation
through more permeable soil horizons. Vegetation is not
usually present and the distribution occurs principally by
flooding. Overland flow treats wastewater during surface flow
over graded terraces. Vvater-tolerant vegetation, microbial
activity, and physical processes on the soil surface are the
principal treatment mechanisms before collection and discharge
of the treated wastewater.
Rapid Infiltration
Rapid infiltration systems show significant differences from
slow rate systems. Application rates are considerably
greater, so total land requirement is diminished. Daily
operations apply treated wastewater by flooding to diked
basins, so aerosol contact is minimal and surface runoff from
basins is nonexistent. Site maintenance is limited to annual
maintenance of basin surfaces and flow diversions to maintain
applications cycles, so overall contact by site workers is
lessened.
The removals of infectious agents, and inorganic and organic
chemicals are slightly less than for a slow rate system, with
the greatest differences occuring during infiltration through
52
METCALF I> EDDY
-------
coarse sands and gravels. Nitrate removals have been
demonstrated to be a function of application cycle and
infiltration rates, so operation becomes more important for
consistent removal [52]. Percolation of treated wastewater to
a nonpotable aquifer would remove concern over potable
consumption in water supplies, so the overall system would
offer a lesser risk because of (1) limited worker contact,
(2) negligible aerosol contact, and (3) decreased land area
for incidental contact. Percolation to a potable aquifer
would be a greater risk to health. Site specific conditions
would be required to compare the risks of a rapid infiltration
system with a slow rate system.
Overland Flow
Overland flow systems use the soil surface to treat
wastewater; however, the slightly permeable or impermeable
soils needed to prevent percolation require that the collected
effluent be discharged to surface water or by other methods
that do not rely on soil percolation [51]. Overland flow
system is evaluated as a land treatment system from the site
contact considerations, but as a treatment and discharge
system for considerations of health risks from the water
supply.
A comparison of the land application portion with slow rate
systems shows that greater and lesser risks occur. Worker
contact duration is increased because applications occur in
each terrace 5 to 7 d/wk. The smoothly graded, 2 to 8% slopes
require additional maintenance time to prevent erosion and
short circuiting. Aerosol transport would be minimal with
bubbling orifice distribution, although sprinkler distribution
is also employed. Human food crops would not be a concern
since the continuously wetted surface conditions require water
tolerant grasses.
The overland flow discharge to surface waters should be
compared with activated sludge treatment. The removal of
chemical constituents, especially nitrogen, is considerably
higher for overland flow than for activated sludge treatment.
The removal of infectious agents for overland flow is
comparable to activated sludge systems. The chlorine dose to
achieve adequate disinfection can be substantially less
following overland flow due to nitrogen removal, so
disinfection can be improved and the potential formation of
halogenated organic compounds is lessened.
53
-------
Site Management and Design Changes
The design of land treatment systems offers options that may
change the overall public health risks. In many instances,
the changes are minor and may not constitute a major impact on
overall health risk. In high population density areas, public
health concerns may be a major consideration, so design
considerations may be worthy of inclusion.
Site Location. Site location is a major option in planning
and design considerations. Within reasonable distances,
higher and lower population densities are usually available.
Site choice can reflect predominate wind direction or
groundwater flow, so potential for adjacent residential
contact can be lessened.
Distribution System. Distribution systems offer some
flexibility within the range of local topography [51].
Surface distribution systems are favored in many cases because
aerosol contact becomes negligible. When sprinkler systems
are used, options such as downward sprays and low pressure
systems may limit aerosol formation.
Application Rates and Schedules. Application rates and
schedules are design options based on pumping equipment
capacity and staff requirements. Less applications per week
favor less site worker contact, and allow a greater infectious
agent die-off between application cycles.
54
-------
Chapter 9
GLOSSARY
Case—A reported incident of disease involving a single
person.
Clinical—Type of symptoms of disease that can be diagnosed
by apparent effects, such as fever, or other physical
effects.
Communicable disease--An illness due to a specific
infectious agent or its toxic products which arises through
transmission of that agent or its products from a reservoir
to a susceptible host, either directly, as from an infected
person or animal, or indirectly, through an intermediate
plant or animal host, vector, or the inanimate environment.
Contact--A person or animal that has been in such
association with an infected person or animal or a
contaminated environment as to have had opportunity to
acquire the infection.
Contamination--The presence of an infectious agent on a body
surface; also on or in clothes, bedding, toys, surgical
instruments or dressings, or other inanimate articles or
substances including water, milk and food. Pollution is
distinct from contamination and implies the presence of
offensive, but not necessarily infectious matter, in the
environment. Contamination on a body surface does not imply
a carrier state.
Cyst—A sporelike cell with a resistant, protective wall.
Disinfection—Killing of infectious agents outside the body
by chemical or physical means, directly applied. Concurrent
disinfection is the application of disinfective measures as
soon as possible after the discharge of infectious material
from the body of an infected person, or after the soiling of
articles with such infectious discharges, all personal
contact with such discharges or articles being minimized
prior to such disinfection.
Dose response—The number of human hosts exhibiting
clinically recognizable symptoms from an infectious agent
dose of known concentration.
55
METCALF A EDDY
-------
Encyst—To enclose or become enclosed in a cyst.
Endemic—The constant presence of a disease or infectious
agent within a given geographic area; may also refer to the
usual prevalence of a given disease within such area.
Hyperendemic expresses a persistent intense transmission,
e.g., malaria.
Endotoxin—The toxic protoplasm liberated when a
microorganism dies and disintegrates.
Enteric—Of or pertaining to the alimentary canal, extending
from the mouth to the anus.
Epidemic—The occurrence in a community or region of cases
of an illness (or an outbreak) clearly in excess of normal
expectancy and derived from a common or a propagated source.
The number of cases indicating presence of an epidemic will
vary according to the infectious agent, size and type of
population exposed, previous experience or lack of exposure
to the disease, and time and place of occurrence;
epidemicity is thus relative to usual frequency of the
disease in the same area, among the specified population, at
the same season of the year.
Gastrointestinal—Refers to stomach and intestines.
Host.—A man or other living animal, including birds and
arthropods, which affords subsistence or lodgment to an
infectious agent under natural conditions. Some protozoa
and helminths pass successive stages in alternative hosts
of different species. Hosts in which the parasite attains
maturity or passes its sexual stage are primary or
definitive hosts; those in which the parasite is in a
larval or asexual state are secondary or intermediate
hosts. A transport host is a carrier in which the organism
remains alive but does not undergo development.
Hyperkeratosis—A thickening of the horny layer of skin.
Illness—Synonymous with infection with manifest (visible)
symptoms.
Immune person—A person (or animal) that possesses specific
protective antibodies or cellular immunity as a result of
previous infection or immunization, or is so conditioned by
such previous specific experience as to respond adequately
with production of antibodies sufficient to prevent
clinical illness following exposure to the specific
infectious agent of the disease. Immunity is relative; an
ordinarily effective protection may be overwhelmed by an
56
MCTC ALF t. C OOV
-------
excessive dose of the infectious agent or via an unusual
portal of entry; may also be impaired by immuno-suppressive
drug therapy or concurrent disease.
Inapparent infection—The presence of infection in a host
without occurrence of recognizable clinical signs or
symptoms. Inapparent infections are only identifiable by
laboratory means. Synonym: subclinical infection.
Incidence rate—A quotient (rate), with the number of cases
of a specified disease diagnosed or reported during a
defined period of time as the numerator, and the number of
persons in the population in which they occurred as the
denominator. This is usually expressed as cases per 1,000
or 100,000 per annum.
Indigenous (endemic)—Originating in and characterizing a
particular region or country.
Infected person—A person who harbors an infectious agent
and who has either manifest disease or inapparent infection.
An infectious person is one from whom the infectious agent
can be naturally acquired.
Infection—The entry and development or multiplication of an
infectious agent in the body of man or animals. Infection
is not synonymous with infectious disease; the result may be
inapparent or manifest. The presence of living infectious
agents on exterior surfaces of the body, or upon articles of
apparel or soiled articles, is not infection, but
contamination of such surfaces and articles.
Infectious agent—An organism, chiefly a microorganism but
including helminths, that is capable of producing infection
or infectious disease.
Infectious disease--A disease of man or animals resulting
from an infection.
Metastasize--Transmission of disease from an original site
to one or more sites elsewhere in the body, as in
tuberculosis or cancer.
Morbidity rate—An incidence rate used to include all
persons in the population under consideration who become ill
during the period of time stated.
Occurrence—A reporting of the number of disease cases for a
specified area by number of cases as a portion of 100,000
population. See epidemic.
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Outbreak—A number of occurrences resulting from a single
source, see Epidemic.
Pathogenicity—The capability of an infectious agent to
cause disease in a susceptible host.
Report of^ a_ disease—An official report notifying
appropriate authority of the occurrence of a specified
communicable or other disease in man. Diseases in man are
reported to the local health authority. Some few diseases
in animals, also transmissible to man, are reportable. Each
health jurisdiction declares a list of reportable diseases
appropriate to its particular needs. Reports also list
suspect cases of diseases of particular public health
importance, ordinarily those requiring epidemiologic
investigation or initiation of special control measures.
When a person is infected in one health jurisdiction and the
case is reported from another, the authority receiving the
report should notify the other jurisdiction, especially when
the disease requires examination of contacts for infection,
or if food or water or other common vehicles of infection
may be involved. In addition to routine report of cases of
specified diseases, special notification is required of all
epidemics or outbreaks of disease, including diseases not on
the list declared reportable.
Resistance—The sum total of body mechanisms which interpose
barriers to the progress of invasion or multiplication of
infectious agents or to damage by their toxic products.
a. Immunity—That resistance usually associated with
possession of antibodies having a specific action on
the microorganism concerned with a particular
infectious disease or on its toxin.
b. Inherent resistance—An ability to resist disease
independent of antibodies or of specifically developed
tissue response; it commonly resides in anatomic or
physiologic characteristics of the host and may be
genetic or acquired, permanent or temporary. Synonym:
nonspecific immunity.
Subclinical—See inapparent infection.
Susceptible—A person or animal presumably not possessing
sufficient resistance against a particular pathogenic agent
to prevent contracting a disease if or when exposed to the
agent.
58
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Transmission of infectious agents—Any mechanism by which a
susceptible human host is exposed to an infectious agent.
These mechanisms are:
a. Direct transmission—Direct and essentially immediate
transfer of infectious agents (other than from an
arthropod in which the organisms has undergone
essential multiplication or development) to a receptive
portal of entry through which infection of man may take
place.
b. Indirect transmission--
(1) Vehicle-borne. Contaminated materials or objects
such as toys, handkerchiefs, soiled clothes, bedding,
cooking or eating utensils, surgical instruments or
dressings (indirect contact); water, food, milk,
biological products including serum and plasma; or any
substance serving as an intermediate means by which an
infectious agent is transported and introduced into a
susceptible host through a suitable portal of entry.
The agent may or may not have multiplied or developed
in or on the vehicle before being introduced into man.
(2) Vector-borne. (a) Mechanical: includes simple
mechanical carriage by a crawling or flying insect
through soiling of its feet or proboscis, or by passage
of organisms through its gastrointestinal tract.
(b) Biological: propagation (multiplication), cyclic
development, or a combination of these
(cyclopropagation) is required before the arthropod can
transmit the infective form of the agent to man.
(3) Airborne. The dissemination of microbial aerosols
to a suitable portal of entry, usually the respiratory
tract. Microbial aerosols are suspensions in the air
of particles consisting partially or wholly of
microorganisms. Particles in the 1 to 5 micron range
are easily drawn into the alveoli of the lungs and may
be retained there; many are exhaled from the alveoli
without deposition. They may remain suspended in the
air for long periods of time, some retaining and others
losing infectivity or virulence. Not considered as
airborne are droplets and other large particles which
promptly settle out. The following are airborne and
their mode of transmission is direct: (a) Droplet
nuclei: usually the small residues which result from
evaporation of fluid from droplets emitted by an
infected host. Droplet nuclei also may be created
purposely by a variety of atomizing devices, or
59
M ETCALF * CODY
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accidentally as in microbiology laboratories or in
abattoirs, rendering plants or autopsy rooms. They
usually remain suspended in the air for long periods of
time. (b) Dust: the small particles of widely varying
size which may arise from soil (as for example fungus
spores separated from dry soil by wind or mechanical
agitation), clothes, bedding, or contaminated floors.
(4) Waterborne. Communicated by water.
Toxic—Pertaining to, affected with, or caused by a toxin or
poison; or acting as, or having the effect of a poison.
60
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Chapter 10
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