PATHOGENS ASSOCIATED
WITH SOLID WASTE PROCESSING
A Progress Report
U.S. ENVIRONMENTAL PROTECTION AGENCY
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PATHOGENS ASSOCIATED WITH SOLID WASTE PROCESSING
A Progress Report
This publication (SW-49?) was written by
MIRDZA L. PETERSON
U.S. ENVIRONMENTAL PROTECTION AGENCY
1971
,830 £'L
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PATHOGENS ASSOCIATED WITH SOLID WASTE PROCESSING
A Progress Report*
Abstract
t Studies were made to determine the presence and levels of microbial
, pathogens associated with municipal solid waste processing. The efficacy
'\
'" ' of several incinerator types to destroy bacteria associated with solid
?
waste were evaluated with emphasis on fecal and food wastes. Microbiological
sampling and analytical procedures were developed and perfected. Samples
of solid waste and its residue after incineration, taken from eight
incinerators of different design, were examined for (l) total bacterial
cell number, (2) total coliforms, (3) fecal coliforms, (4) heat-resistant
sporeformers, (5) selected enteric pathogens. Quench water was analyzed
from three incinerators. Survival of coliforms and enteric pathogens in
the residue after incineration was considered an indication of inadequate
incinerator design or operation or both.
Of the eight incinerators tested, only one produced residue devoid of
fecal coliforms; seven others produced residue containing fecal coliform
populations of less than 1.0 x 101 to k.J x 103 per g. Salmonella organisms
"Progress report on Project RS-03-68-16, Pathogens Associated with
Solid Waste Disposal Processes. The first results of this investigation
were published by Applied Microbiology in July 1969 and January 1970.
The results of other investigations will be published in the International
Journal of Environmental Studies, (England).
i i i
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were found in the quench water and in the quenched residue at one of the
eight incinerators tested.
To measure microbial cell concentrations in the incinerator stack
emissions, a sampler was designed. The measurements showed that a few
viable gram-positive bacilli (2 organisms per cu ft air) were passing
through the stack of a conical burner, but that most of the organisms
were scrubbed out.
Quantitative studies were made on the microbial flora of the dust
from six municipal incinerators, with particular emphasis on bacteria
of proved pathogenic!ty for the respiratory and intestinal tracts and
the skin. Three specific waste handling areas such as the dumping floor,
the charging floor, and the residue area were tested. Total microbial
cell counts in the three areas tested ranged from 1 to 197 organisms per
0.25 cu ft air. Incinerator dust was found to carry Staphylocoeous
auveuSy D-iploooaous pneumonias, and Klebs'ielta pnevmoni>ae, although
these represented only a small percentage of the total microbial number.
Esdhevi,ohi,a col-i was isolated from the dust at five of the six incinerators
tested, and the dust from the. dumping and the charging floor areas of
all six incinerators contained a-hemolytic streptococcus.
l v
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PATHOGENS ASSOCIATED WITH SOLID WASTE PROCESSING
A Progress Report
Mirdza L. Peterson"
Inefficient and improper methods of processing and disposal of solid
waste can create serious health hazards.1 Insects and rodents in (or
associated with) waste a/e vectors of human disease; the housefly transmits
at least 30 bacterial, viral, and parasitic diseases, the rat has been
implicated in the spread of plague, murine typhus, leptospirosis, and
rickettsialpox.2-6 Prompt collection and proper disposal of solid wastes
are considered the most important factors in the control of solid waste
related disease vectors.7
The National Research Council indicated that solid wastes are
disposed of primarily by deposit on or below the surface of the ground
and through discharge into natural waters and the atmosphere.8 The currently
accepted methods for the disposal and volume reduction of municipal solid
wastes are: sanitary landfill ing, composting, and incineration followed
by landfill ing of the residue or unwanted material.9 Reports indicate
that (a) an improperly located or unsealed landfill will leach soluble
salts and alkalies from the refuse and transport them to receiving waters,
"Research Microbiologist, U.S. Environmental Protection Agency.
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(b) a wide variety of pathogenic fungi can survive the composting process,
and (c) incineration byproducts have public health associated implications.10-12
The Federal program in solid waste management, formerly in the
U.S. Public Health Service and now in the U.S. Environmental Protection
Agency, sets forth national goals that would assure that man's health and
quality of his environment are not endangered or degraded. Particular
research objectives to meet these goals were selected and carried out by
the research and development division of the Solid Waste Management Office.
One specific objective was to establish the microbiological quality of
the total effluent from solid waste incineration and to suggest ways of
improving operations of current and to-be-developed incineration processes.
The division of research and development conducted laboratory and
field studies to evaluate incinerator operations from the microbiological
viewpoint. The purpose was to ascertain whether such operations provide
conditions with the capability of destroying refuse-associated pathogenic
microorganisms. Attention was directed to two groups of organisms: those
proved in the past to be pathogenic to man and those pollution indicators
useful in determining the potential presence of pathogens and their
survival after incineration. Refuse from food sources and fecal wastes
found at the incinerator storage pits and in the quenched residue were
examined in particular.
The objectives of the studies were: (l) to determine the distribution
and survival patterns of pathogenic microorganisms before, during, and
after incineration; (2) to evaluate the efficacy of the various incinerator
operations in destroying pathogens; (3) to aid in the development of design
criteria and operational standards for solid waste incineration.
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This progress report describes the efforts which have been made
toward the attainment of the research objectives.
The development and perfection of sampling and analytical methods
were investigated first. Because of the extreme heterogeneity of ordinary
municipal solid wastes, microbiological sampling and analysis procedures
in present use were thought to be inadequate and inappropriate in most
cases. Another upsetting factor was the large day-to-day variation
observed in overall waste characteristics; for example, that essentially
paper only was observed on one day and mostly packing house wastes on
another. The first sample available was too large (a truckload) to
attempt simple mixing for homogenization. The sampling problem was
overcome by taking random 100- to 200-g samples from throughout the
available refuse, compositing into one sample (2,000 to 4,000 g) and,
after thorough mixing, extracting the final 200-g subsample.
Eight municipal incinerators were studied and two to six composite
samples obtained over individual 8-hr-run periods. Each incinerator residue
and quench water sample was obtained after a minimum 2-hr period of
steady operation. This permitted attainment of standard operating
temperatures within the incinerator. Selected refuse samples before
incineration and residue samples after incineration were collected with
sterile tongs and placed in sterile 200-ml specimen cups. Quench water
was collected in 250-ml capped bottles.
A statistical evaluation was made to determine the size and number
of refuse and residue samples required to isolate an enteric pathogen.
As a result of this investigation three subsamples in duplicate, each
weighing 30 g, were analyzed from each of five incinerators.21
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Quench water (1,000 ml) was collected on each sampling day from each
of three incinerators and analyzed for indicator organisms and for the
presence of enteric pathogenic bacteria by concentration on a diatomaceous-
earth layer.
The presence of microorganisms in the stack effluent of a conical
burner at Memphis, Tennessee, was measured in three locations: the primary
outlet, the electrostatic precipitator outlet, and the scrubber stack. The
samples were taken with an impinger method adopted to this type "of
incinerator.13
A quantitative study was made on the microbial flora of the dust from
six municipal refuse incinerators with particular emphasis on bacteria of
proved pathogen!city for the respiratory and intestinal tracts and the
skin. Sampling procedures were carried out with Andersen Sieve Samplers*14
in specific waste handling areas, such as the dumping floor, the charging
floor, and the residue areas.
Materials and Methods
Sampling Procedures. The eight incinerators examined in this study
were located in Cincinnati, Ohio, Chicago, Illinois, Memphis, Tennessee,
Atlanta, Georgia, and New Orleans, Louisiana. The incinerator designs
ranged from relatively old batch-fed units to more modern continuously
fad rotary kiln units. Each incinerator was operating in a normal manner
at the time the samples were collected. No attempt was made to collect
data describing the operating characteristics of the incinerators during
^Mention of a commercial product does not imply endorsement by the
U.S. Government.
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The air samples were taken at three areas of the incinerators: the
dumping floor area, the charging floor, and the residue areas. The
dumping and the charging floor areas are consistently the dustiest areas
of the incinerator. These are the areas where there is the most open-air
handling of the refuse. The refuse falls from the collection truck into
a pit, is lifted by a crane up to the charging floor, and is dropped into
a chute. The samples were taken at a height of approximately 5 ft in work
areas.
Sample Preparation for Analysis. Preliminary Studies. Lack of
information on recovery of viable bacteria from refuse material
necessitated preliminary studies. The Waring Blendor (Model 1088, Waring
Products, Winsted, Conn.) was used for sample homogenization. Autoclaved
refuse samples, inoculated with I-ml aliquots of log phase Esaheriehia
ooli cultures (7.8 to 8.5 x 108 cells per ml) were suspended in cold 0.067 M
phosphate buffer, pH 1.2, and homogenized for varying periods of time at
free running speeds of 17,000 rpm to determine the optimum for maximal
release of viable cells. The optimum homogenization time was found to
be 15 sec.16
Preparation of Field Samples. All samples of refuse and residue
subjected to quantitative analyses were homogenized as slurries in cold
0.067 M phosphate buffer, pH 7-2, in sterile, stainless-steel, Blendor
vessels. Blending time for field samples was 15 sec. After blending,
each homogenate was overlaid with a sterile cheesecloth pad to clarify
the fluid for pipetting. Ten-fold serial dilutions of the homogenates
were prepared in cold, phosphate-buffered water. Salmonella and other
enteric pathogens in quench water samples were concentrated by filtering
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the sampling periods. Sampling times were selected to allow at least 2 hr
of continuous, normal operation before testing. Random 100- to 200-g
samples of refuse before incineration and samples of the residue after
incineration were collected with sterile tongs and placed in sterile 200-ml
specimen cups. The random samples were composited into 1 sample of 2,000-
to 4,000-g size. After thorough mixing a final 200-g subsample was
assayed. Quench water was collected in sterile 250-ml capped bottles.
Quantitative studies enumerated total viable bacterial cells, total
coliforms, fecal coliforms, and heat-resistant spores. Thirty-gram
subsamples of refuse and residue and 800-ml quench water were assayed
for enteric pathogenic bacteria such as Salmonella and Shigella.
Stack effluent samples were taken with an impingement method adapted
to this type of incinerator. The effluent was drawn through a 1/4 in.
sterile, stainless steel tube by a 1.0-cfm vacuum pump. The tube was
cooled by a water jacket. The effluent passed through the tube and was
impinged into a 300-ml aliquot of sterile 0.067 M, pH 1.2, phosphate buffer
in a 1,000-ml bottle.15 The sample was run for 10 min, yielding a 10
cu ft sample.
Air samples were taken with an Andersen sampler. This is a six-stage
multijet sampler that separates airborne particles into six aerodynamic
sizes covering the range for respiratory tract penetration. Each of the
six stages of the sampler covered a petri dish containing 26 to 28 ml of
solid agar medium. Air was drawn through the sampler at 1.0 cu ft per
min (cfm) with a vacuum of 15 in. of mercury. Because of the larger
number of organisms involved, the sampler was run for 15 sec (0.25 cu
ft air) in order to get well separated colonies in the range of 1 to 30.
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an 800-ml sample through a 1-in. diatomaceous-earth (Johns-Manvi1le,
Celite 505) layer placed on the screen of a stainless-steel membrane
filter holder. After filtration, the diatomaceous-earth layer was
removed from the holder, divided in half, and analyzed. Refuse and
residue samples for enteric pathogens were examined directly without
homogenization.
Quantitative and Qualitative Methods. Routine quantitative methods
were modified to suit solid waste or waste material characteristics for
the determination of: (1) total viable bacterial cell number; (2) total
and fecal coliform organism counts; (3) heat-resistant spore count.
Total viable cell counts were made by spreading 0.1-ml aliquots of
the serially diluted homogenates or liquids on the surfaces of blood agar
plates containing trypticase soy-agar base (BBL) and 7 percent defibrinated
sheep blood, and by the pour plate method as described in Standard Methods
for the Examination of Water and Wastewater.15 Total and fecal coliforms
were estimated by the Most Probable Number (MPN) method.15 Lauryl tryptose
broth (Difco) was used in the presumptive tests at 35 C; brilliant green
bile broth (BBL) at 35 C and EC broth (Difco) at M.5 C were employed in
the confirmed tests. Further confirmation of the presence of coliforms
was achieved by streaking aliquots of positive tubes on eosin methylene
blue agar (BBL). The number of heat-resistant spores in the homogenates
or liquids was determined by heating samples diluted in 0.067 M phosphate
buffer, pH 1.2, at 80 C. Viabiliby at 15 and 30 min was determined by
incorporating 1-ml aliquots of the samples into pour-plates of tryptone
glucose extract agar (Difco). All plates were counted after 2k- and ^8-hr
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incubation at 35 C. All populations were calculated as cell numbers per
g wet-weight raw refuse or quenched residue, per 100-ml quench water, and
per cu ft stack effluent.
The Membrane Filter Technique was used to determine total and fecal
coliform densities present in raw solid waste, quench water, and residue
from three incinerators (two in Atlanta, Georgia, and one in New Orleans,
Louisiana). At the other five incinerators evaluated, MPN methodology
was used.
To isolate salmonellae and other enteric pathogenic bacteria 30-g
of refuse or quenched residue were placed in each of two wide-mouth, 500-ml
flasks. One flask contained 270 ml selenite F enrichment medium (BBL
product) and the other flask contained 270 ml selenite brilliant green
sulfa (SBG) enrichment medium (Difco product). The flasks were well
mixed and incubated at 39-5 C for 16 to 18 hr. On two occasions, 41.5 C
incubation temperature was used.17
After incubation, dried plates of salmonella-shigella (SS) agar
(Difco), bismuth sulfite (BS) agar (Difco), and McConkey's agar (Difco)
were inoculated by streaking one loopful of the selective enrichment
culture. Each enrichment was streaked on four plates of each agar. Thus,
each sample ultimately required a total of 12 plates. All agars were
freshly prepared except for bismuth sulfite agar, which was used after
3-day refrigeration.18 The inoculated plates were incubated at 37 C for
2k to 48 hr, whereupon three to six characteristic colonies from each
plate were picked to slants of triple sugar iron (TSl) agar (Difco). The
slants were incubated overnight at 37 C. Further identification, biochemical
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differentiation and serological grouping of Salmonella, was based on the
procedures developed at the Communicable Disease Center, Atlanta, Georgia.19
Pathogens concentrated on diatomaceous-earth layer from quench water
samples were isolated by the method described above except that each half
of the layer was suspended in 90-tnl amounts of each enrichment medium.
Analysis of Dust. For analyses of dust the Andersen sampler was used
with two types of media, trypticase soy agar (ISA) (BBL), containing 5
percent sheep blood and eosin methylene blue agar (EMB) (Difco). The
TSA/blood agar was used to isolate a wide range of fastidious organisms
such as Diploaooous pneumonias, beta-hemolyt-ie Streptoeooeuss and
Staphyloeooeus aureus. The EMB agar was used to isolate gram-negative
bacilli. The plates were incubated aerobically at 37 C for 2k hr
(preliminary studies showed that very few organisms in the dust would
grow under anaerobic conditions). The enumeration of colonies was made
with a Quebec counter. Each colony was categorized on the basis of its
macroscopic, microscopic, and physiologic characteristics. The organisms
were placed under four general categories: gram-positive cocci, gram-
negative bacilli, gram-positive bacilli, and fungi. Gram-positive cocci
were further classified as staphylococci, streptococci, and pneumococci.
The count of gram-positive bacilli and fast growing fungi was made from
the TSA/blood agar.
Discussion
Field Survey Sampling Techniques. One of the initial problems was
the establishment of the methodology for sampling and analyzing raw solid
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waste, and incinerator solid, liquid, and gaseous effluents. The sampling
problem of solid waste materials was overcome by taking random samples
from throughout the available refuse and incinerated residue and compositing
into one sample (2,000 to ^,000 g) and after thorough mixing a final 200-g
subsample was extracted and analyzed.
A portable sampler was designed to enumerate viable microbial cells
in incinerator stack emissions. This sampler provided a method for
qualitative sampling of gaseous stack effluents.
An Andersen sampler was employed to determine the viable microbial cell
number in incinerator aerosols.
A statistician was consulted who determined the size and the number
of solid waste and residue samples required so that there would be 95
percent chance that at least one sample would be positive for enteric
pathogenic bacteria. It was postulated that the number of enteric
pathogen cells present in a given quantity of solid waste or waste residue
followed a Poisson probability distribution. From a study (recently submitted
for publication) it was determined that three 30-g subsamples (in duplicate)
are required to yield a pathogen-positive sample.21
Raw refuse and residue samples were homogenized as slurries in cold,
0.067 M, phosphate buffer in sterile, stainless-steel, Blendor vessels.
Preliminary studies showed that the optimum homogenization time was 15 sec.
Routine quantitative methods were adapted or modified to suit raw
solid waste or incinerator waste related material characteristics for the
determination of: total viable bacterial cell number, total and fecal
coliform organism counts, and heat-resistant spore count. Methods were
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developed to isolate Salmonella organisms from solid waste, waste residue,
and quench water.
Results of the studies on microflora associated with municipal solid
waste at eight municipal incinerators showed that the average number of
viable bacterial cells in the raw refuse samples before incineration
were relatively constant from one incinerator site to another; total
viable bacterial population in raw refuse ranged from 4.0 x 105 to 6.8 x
108 organisms per g; total coliform densities ranged from 3.4 x 105
to 5.1 x 107 organisms per g (Table 1). The presence of the coliform group
in large numbers indicated sewage pollution; in lesser amounts it could
denote contamination from other sources since coliform subgroups are
known to occur in animal excreta, soils, grains, grasses, and other
vegetation. The estimated total number of coliforms discharged daily
by one man is 13 million organisms per g.20
Fecal coliform population in raw refuse from the eight incinerators
ranged from 1.5 x 104 to 8.1 x 106 organisms per g (Table 1). The
significance of fecal coliform organisms to waste quality is that the
origin of this organism is from the intestinal tract of warm-blooded
animals, including man. Consequently, the presence of fecal coliform
bacteria in the waste can be interpreted as an indicator of contamination
of the waste by fecal matter. The contamination of waste by fecal matter
may be one avenue of transmission of pathogenic microorganisms to the
environment and man.
11
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Total Incinerator Effluent Microblal Quality Showed Large Variation.
Significant differences were found in the microbial quality of residue from
the eight incinerators tested. Incinerator I produced the residue of poorest
quality in terms of total viable cells, heat-resistant spores, total and
fecal coliform organisms (Table 1). Incinerators VI, VII, and VIM produced
residues containing small numbers of total viable cells, spores, and
coliforms (Table l). The best residues in terms of fecal coliform densities
were obtained from Incinerators IV and VIM, fecal coliform densities were
less than 10 organisms per g of residue for both incinerators (Table 1).
Quench water tested from Incinerators VI and VII showed coliform
densities of less than 100 organisms per 100 ml. Total and fecal coliform
counts of 2.9 x 104 and 1.7 x 10^ organisms per 100 ml were found in quench
water from Incinerator VIM (Table 1).
Salmonella derby and Salmonella st. paul were isolated from quench
water and residue obtained from Incinerator I.21 The health significance
of this finding is that if such a rich flora can be found in the burned
residue, pathogens buried with the waste material can survive for an
undetermined time and can be transported out of the fill by way of leaching
water, can reach a waterway, and can become health hazards. Waterborne
outbreaks of typhoid, paratyphoid fevers, and other intestinal disorders
due to Salmonella organisms have been well documented.22
None of the incinerators tested in this study produced a sterile
residue. The recorded incinerator temperatures (1,200 to 2,000 F) would
eliminate all viable microorganisms if the refuse itself approached such
temperatures during the burning process. Unburned material such as
13
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vegetables and even newspapers were seen in the residue at some of the
incinerators tested. Survival of large numbers of microorganisms in the
residue indicated that the temperatures recorded at these municipal
incinerators provided no assurance of a satisfactory operation from the
standpoint of public health.
The presence of microorganisms in the stack effluent was measured
at Incinerator V (conical burner). The stack data from this indicated
that a few gram-positive bacilli (2 organisms/cu ft air) were passing
through the stack, but that most were scrubbed out.23
Results of studies made on dust from the waste dumping areas, the
charging floors, and the residue areas at six municipal incinerators
showed that total viable microbial cell counts ranged from 10 to 197
organisms per 0.25 cu ft air in the waste storage areas; 20 to 160 and 1
to 105 organisms per 0.25 cu ft air in the charging floor and the residue
areas (Figures 1 to 3). The commonest organisms present in the dust were
fungi, gram-positive cocci, and gram-negative bacilli, most of which are
associated with body wastes and the earth material in the refuse. In
Incinerator VI (rotary-kiln type), the level of microbial cells was
considerably lower than in other incinerators. This difference was
presumably because Incinerator VI was newer and kept cleaner than the
other incinerators sampled.
Comparative data for airborne microbial populations in various
environments per 1 cu ft air is shown below211:
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Envi ronment
Total microbial levels
(colonies per cu ft air)
Country ai r
General offices and schools
City streets
Factories
56
95
72
113
The levels of microorganisms in the dumping and the charging floor areas of
the municipal incinerator studied were often 4 to 10 times higher when
compared with the levels in those other environments. By comparison,
city streets contained approximately 18 viable organisms of all these types
for the same volume of air (0.25 cu ft).
The incinerator dust was found to carry pathogenic microorganisms,
such as Stophylooocous aureus, Diplooooous pneumonias, and Ktebsielta
pneimoniae, although these represented a small percentage of the total
number (Table 2). These organisms are associated with skin and upper
respiratory tract ailments. Esaheriohia ool-i was found in the dust at
five incinerators tested, indicating the presence of fecal wastes.
There was a great deal of variability in microbial types found in
dust between one incinerator and others, and even between the dumping and
the charging floor area of one incinerator. This was expected because of
the fact that the dust is undergoing constant movement and change of
composition. Although the kinds of specific organisms varied widely from
one incinerator to another there was a pattern which was common to all
incinerator sites sampled. The dust from the dumping and charging floor
areas of all the incinerators investigated contained a-hemolytic
18
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streptococcus, which is usually considered to be human-borne, present in
the upper respiratory tract of all normal individuals. This organism has
been shown to be a good index for the presence of respiratory tract
pathogens.25 It is an easily recognized organism and survives well In
air. It seems from the data that respiratory tract pathogens should get
the major consideration in view of the small number of fecal col I forms
observed. Experimental studies have shown that the number of small
particles necessary to infect through the alveoli of the lung is very
small, often 10 organisms or less, whereas the doses necessary to infect
with larger particles through the upper respiratory tract are uniformly
great, often 1,000 to 10,000 organisms or more.26 Thus, any incinerator
air rating method should probably include a consideration of the total
number of viable organisms and a consideration of the a-hemolytic
streptococcus as an indicator organism.
It should be noted that this discussion pertains to the threat of
upper respiratory tract conditions and disregards the other threats to
the health of incinerator workers such as dermatitis.
The data obtained from this study reinforces the already obvious
fact that adequate dust removal equipment is needed to prevent the creation
of infective aerosols. If, in the future, epidemiologlc justification
for microbial control measures in air during waste processing becomes
evident, this report might serve as a guideline to feasibility. The
techniques employed in this study and parameters used might be considered
effective in a monitoring program.
20
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This report has been compiled to disseminate as widely as possible
the latest information and findings of a research project on microbiological
quality of municipal waste and incinerator residue.
It is hoped that this report will provide useful information to those
working in the solid waste management field and assist in developing
approaches to the solutions of their solid waste disposal problems associated
with microbiological hazards.
Project Summary
Objectives. There were three primary objectives of this study: (1)
to determine the distribution and survival patterns of pathogenic microorganisms
before, during, and after incineration; (2) to evaluate the efficacy of
various functional incineration operations employed in destroying pathogens;
(3) to aid in the development of design criteria and operational standards
for solid waste incineration.
Approach. Microbiological methods were developed to measure the
levels of microbial pathogens associated with municipal waste. The
efficacy of several incinerator types to destroy bacteria associated with
solid waste was evaluated, with emphasis on fecal and food sources. Solid
waste samples and incinerator residue taken from eight municipal
incinerators of different design were examined for total bacterial cell
number, total coliforms, fecal conforms, heat-resistant spores, and
selected enteric pathogens.
Results. Of the eight incinerators tested, only one produced residue
devoid of fecal coliforms; the seven others produced residue containing
21
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fecal coliform population of less than 1.0 x 101 to 4.7 x 103 per g.
Salmonella organisms were found in quench water and residue from one of
the eight incinerators tested.
Stack analysis showed that a few viable bacterial cells (2 gram-
positive bacilli) were passing through the stack of a conical burner.
Dust samples taken from six municipal incinerators at three specific
waste handling areas showed total microbial cell counts of 1 to 197
organisms per 0.25 cu ft air. Organisms associated with upper respiratory
and intestinal tracts were found.
Ack now1edgmen t s
This investigation was initiated and completed by the former Public
Health Effects Projects Branch under the Division of Research and
Development, Solid Waste Management Office.
We are appreciative of the encouragement, guidance, and assistance
given by personnel from the Division of Research and Development and
Technical Operations during this study. Appreciation and thanks are
especially extended to Dr. Fred J. Stutzenberger, Messrs. David Armstrong,
Donald F. Spino, and Henry Johnson, and Mrs. Janet C. Blannon for their
technical assistance and consultation. We gratefully acknowledge the
valuable criticism and assistance of Mr. Louis W. Lefke In the
preparation of this report.
22
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