United States
Environmental Protection
Agency
Water Engineering Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-86/047 June 1986
Project Summary
Inactivation of Enteric
Pathogens During Aerobic
Digestion of Wastewater
Sludge
Samuel R. Farrah, Gabriel Bitton, and Stephen G. Zam
A study was conducted to provide data
on the ability of aerobic digestion to re-
duce pathogens and to determine the ef-
fect of important variables. Laboratory and
field studies investigated the effects of
aerobic and anaerobic digestion on enteric
viruses, enteric bacteria, total aerobic
bacteria, and intestinal parasites. Under
laboratory conditions, the temperature of
the sludge digestion was the major factor
influencing survival of bacteria and vi-
ruses. The survival of both bacteria and
viruses was increased substantially by
decreasing the temperature of sludge di-
gestion from 28° to 7°C. Lowering the
temperature or dissolved oxygen level
reduced the percentage of solids-asso-
ciated organisms for bacteria but not for
viruses.
Bacteria were inactivated at different
rates during aerobic sludge digestion.
Streptococcus faecalis was more stable
than Salmonella typhimurium or Escheri-
chia coll. Varying detention time or source
of sludge did not affect the rate of inacti-
vation of viruses or bacteria.
Aeration of stock Ascaris suum ova in
0.1 N H2SO4 resulted in 91% embryon-
ation. However, aeration in sludge resulted
in only 19% to 50% embryonation after
30 days. Most of the ova embryonated in
0.1 N H2SO4 (79% to 93%) were infec-
tive for rats. In contrast, only 9% to 12%
of the ova embryonated in aerobically
digesting sludge were infective for rats.
Full-scale aerobic digestion of sludge re-
duced densities of bacteria and entero-
viruses. In most cases, the reductions
were close to the maxima predicted for
completely mixed digesters that contin-
ually receive undigested sludge.
The number of parasitic ova varied
greatly with the community served by the
treatment plant. Parasitic ova were re-
covered from most of the samples of di-
gested and undigested sludge from certain
treatment plants but not from others. The
relatively low numbers of ova recovered
from the sludge samples make it difficult
to evaluate the effects of sludge digestion
on these agents. The inactivation rate of
laboratory-grown bacteria in aerobically
digested sludge was higher than that for
indigenous bacteria. The indigenous bac-
teria were probably better protected from
predation by protozoans and other an-
imals. Predation was the major factor in-
fluencing survival of both indigenous and
laboratory-grown bacteria during aerobic
digestion of sludge under laboratory con-
ditions. Predation had little effect on sur-
vival of viruses, however.
This Project Summary was developed
by EPA's Water Engineering Research
Laboratory, Cincinnati, OH, to announce
key findings of the research project that
is fully documented in a separate report
of the same title (see Project Report order-
ing information at back).
Introduction
A large number of enteric bacteria, viral
pathogens, and parasitic ova may be ex-
creted by infected individuals and may
therefore be present in untreated sewage.
Since a large number of these pathogens
become associated with wastewater so-
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lids, many are not completely inactivated
during sewage treatment processes and
are merely transferred to wastewater slud-
ges. These sludges are processed further,
generally by aerobic or anaerobic diges-
tion, to improve their dewaterability,
reduce their unpleasant odor, and reduce
their pathogen content.
The ability of digestion processes to
reduce sludge pathogens has received
considerable investigation, though num-
erous data gaps exist. The information is
particularly sparse for aerobic digestion.
This investigation was undertaken to pro-
vide more definitive information on the
ability of aerobic digestion to reduce
pathogens and to determine the effects of
important variables. The investigation
studied the effects of aerobic digestion on
pathogenic bacteria, bacterial indicator
organisms, parasitic ova, and animal
viruses.
Experimental Procedures
In laboratory experiments (which em-
ployed temperature-controlled, laboratory,
aerobic and anaerobic digesters), cultured
bacteria and viruses were generally used.
In field studies, conducted at existing
plants in the vicinity of Gainesville, Florida,
indigenous microbial species were used.
Laboratory Experiments
Aerobic digestion was conducted in
temperature-controlled vessels holding 15
L of sludge. Sludge was mechanically
agitated, and humidified air was intro-
duced through spargers. Anaerobic diges-
tion was conducted in externally heated
carboys holding 8 L of sludge. Bacteria and
viruses charged to the digesters were
grown from type cultures. Ascaris suum
ova were obtained from the feces of
naturally infected hogs. Detailed proced-
ures for growing organisms and measur-
ing densities are presented in the report.
Survival of bacteria and viruses and the
association of these agents with sludge
floes were studied in 11 individual trials.
During each trial, two to four digesters
were operated under different conditions
of temperature, dissolved oxygen, and de-
tention time. Aerobically digested sludge
was obtained from one of three local treat-
ment plants and aerated for 2 to 4 days at
the desired temperature before the exper-
iments were started, thus stabilizing the
sludge at the desired conditions before an
experimental trial was started. An anaero-
bic sludge digester was started using
anaerobically digested sludge obtained
from Tallahassee. At the beginning of each
trial, bacteria and viruses were added to
each of the digesters to obtain an initial
concentration of approximately 105/mL
On each subsequent day, a portion of
sludge was removed from each digester
for analysis, and a portion of wasted
sludge from the plant that was the source
of the aerobically digested sludge was
seeded with bacteria and viruses and add-
ed to the digesters. The wasted sludge
that was used for the daily additions to the
digesters was obtained at the beginning
of each trial and was kept at 4 °C without
aeration. The volume of digested sludge
removed and replaced with wasted sludge
was determined by the detention time de-
sired: 1/15 to 1/40 the volume for 15- or
40-day detention times, respectively.
Laboratory studies were also conducted
on the survival of seeded Ascaris suum in
aerobically digested sludge. Three aeration
procedures were used that produced dif-
ferent degrees of mechanical abrasion on
the ova. Aeration was provided by shak-
ing 200 ml of sludge in 500-mL flasks on
a reciprocal shaker, by mixing 200 ml of
sludge in 1000-mL beakers using a mag-
netic stirrer, or by aerating 200-mL
samples in 500-mL flasks with air dif-
fusers connected to a small air pump. All
three methods provided approximately 5
mg/L of dissolved oxygen. The aerobic
digestion was run under two conditions:
batch operation and daily feeding to sim-
ulate operation with 40-day residence.
Samples of the sludge were examined for
total recovered ova, ova embryonation,
and ova infectivity in rats.
Field Studies
Sludge samples from nearby waste-
water treatment plants were obtained over
two periods: From January to December
1981, and from August to October 1983.
The sludge samples were examined for the
presence of enteric bacteria, enteric
viruses, and parasitic ova. The dissolved
oxygen, temperature, pH, and total solids
of the sludge samples were also deter-
mined. Unlike the laboratory experiments,
no organisms were seeded into the slud-
ges; only densities of indigenous micro-
organisms were measured.
Results and Discussion
Bacteriological Investigations
Laboratory Studies
The influence of temperature and dis-
solved oxygen level on inactivation of
bacteria during aerobic and anaerobic
sludge digestion was studied in 11 trials,
each lasting approximately 9 days. The re-
sults from one trial appear in Table 1,
which presents the log daily change in
bacterial densities. The log daily change
is the difference between the logs of the
bacterial densities of the sludge in the
digester shortly after introduction of the
feed sludge containing the inoculum and
the sludge withdrawn from the digester 24
hr later (before addition of the next batch
of feed). Table 1 shows the effects of
temperature (28.3° and 6.2°C) and
dissolved oxygen concentration on the
bacteria in one of the trials. These results
are typical of those obtained in other trials.
Wasted, aerobically digested sludge from
a nearby plant was added daily to the
digesters to provide a detention time of 15
days. Results show much greater reduc-
tions for S. typhimurium, S. faecalis, and
E. coli than for P. aeruginosa and total
aerobic bacteria. For all bacterial types, the
log daily change was much lower at 6.2 °C
than at 28.3°C (compare Conditions I and
II in Table 1). The presence or absence of
air (compare Conditions I and III in Table
1) produced a small effect that was usually
not significant.
The bacteria in the digesting sludge
were either in the supernatant or were oc-
cluded to solids. Operation at 28.3°C in
the aerobic state showed a markedly dif-
ferent distribution of bacteria from the
other conditions, averaging about 8% in
the supernatant compared with 36% for
the other conditions. Subsequent experi-
ments confirmed that grazing by protozoa
accounted for the lower proportion of bac-
teria in the supernatant at 28.3°C and
contributed to the greater daily reduction
in bacteria obtained at these conditions.
Subsequent trials with sludges from
three different wastewater treatment
plants sludges showed that the source of
sludge did not significantly affect the
results.
In all of the previously described ex-
periments, bacteria were added to the di-
gesters daily along with fresh sludge. The
values for change in total bacteria there-
fore reflect changes that occurred in the
first 24 hr following bacterial addition. To
determine whether the rate of daily change
in bacteria would fall off with time, in-
dicating the presence of a resistant frac-
tion of added bacteria, digesters were
operated under aerobic conditions without
the addition of bacteria or sludge. Two
digesters were operated at 28 °C and one
at 6°C. All digesters were operated with
greater than 4 mg/L dissolved oxygen. Re-
sults with S. typhimurium, S. faecalis, and
total aerobic count showed that curves of
log density versus time were approximate
ly linear (with negative slopes) over the
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Table 1. Bacterial Survival and Association with Sludge Floes During Aerobic and Anaerobic Digestion of Sludge: The Influence of Sludge
Digestion Conditions on Individual Bacteria
Sludge Dissolved Total Daily Change Bacteria in
Digestion Temperature Oxygen Solids in Total Supernatant
Bacteria Condition* (°C) (mg/L) pH (g/L) Log10 (%)
Salmonella typhimurium
Streptococcus faecalis
Escherichia coli
Pseudomonas aeruginosa
Total aerobic bacteria
1
II
III
1
II
III
1
II
III
1
II
III
1
II
III
28.3
6.2
28.0
28.3
6.2
28.0
28.3
6.2
28.0
28.3
6.2
28.0
28.3
6.2
28.0
2.7
3.7
0
2.7
3.7
0
2.7
3.7
0
2.7
3.7
0
2.7
3.7
0
6.0
7.4
6.3
6.0
7.4
6.3
6.0
7.4
6.3
6.0
7.4
6.3
6.0
7.4
6.3
20.6
19.6
18.4
20.6
19.6
18.4
20.6
19.6
18.4
20.6
19.6
18.4
20.6
19.6
18.4
- 1.24Ai
-0.238
-0.90A
-0.92A
-0.108
-0.83A
- 1.13*
-0.23°
-0.618
-0.28*
-0.29*
-0.34A
-u.34A
-0.078
-0.098
8C
23B
51 A
12B
50*
47 A
4B
25*
30*
3s
34*
47*
7B
21*
33**
* Condition I = aerobic; Condition II = aerobic; and Condition III - anaerobic.
^Figures in a single column with identical letter superscripts are not significantly different.
course of several days, indicating no per-
sistent fraction of bacteria. The rate of in-
activation was substantially lower in these
experiments than when inocula were add-
ed daily (compare Tables 1 and 2). The
greater reduction in supernatant bacteria
at the higher temperature (Table 2) is con-
sistent with the inoculum experiments.
Field Studies
Summarized data from field studies are
presented in Table 3. Plants 1 and 2 used
aerobic digesters, and Plant 3 used an an-
aerobic digester. For the aerobic digesters,
greater bacterial reductions were achieved
in Trial 2 than in Trial 1. The probable ex-
planation for this difference was digestion
temperature: Trial 1 was conducted during
colder months. All of the digesters were
completely mixed. With complete mixing,
some sludge inevitably short-circuits to
the exit with relatively short-term treat-
ment. Bacterial reduction was calculated
assuming complete mixing and destruc-
tion of bacteria except for bacteria in that
portion of the feed that leaks through to
the exit. Log reductions calculated on this
basis (labeled "maximum possible") are
presented in Table 3 where they can be
compared with experimentally determined
reductions. For Trial 2, experimental and
calculated values are similar; this result
supports the assumptions of the calcula-
tion and indicates that use of complete
mix reactors may contribute to failure to
achieve high bacteria or virus reductions
in digesters.
Virus Investigations
Laboratory Studies
Laboratory studies determined the influ-
ence of several variables on the survival
of viruses during aerobic and anaerobic
digestion of sludge under laboratory con-
ditions. The variables studied included
temperature, dissolved oxygen level, de-
tention time, virus type, and the source of
the sludge used for digestion studies.
The sludge source did not significantly
affect the rate of inactivation of poliovirus
when sludge was aerobically digested
(15-day detention time). At 28 °C and dis-
solved oxygen levels of 5 mg/L, the mean
daily change (Iog10) in inactivation of
seeded poliovirus (Type I, Lsc) for sludges
from three sources ranged from -0.71 to
-0.97, which was not a significant
difference.
Table 2
Bacterial Survival and Association with Sludge Floes During Aerobic Digestion of
Sludge without Addition of Fresh Sludge
Daily Change in Total Bacteria in Supernatant
Bacteria Log10 (%)
Bacteria
6°C
28°C
Salmonella typhimurium -0.15
Streptococcus faecalis —0.05
Total aerobic bacteria -0.07
-0.48
-0.23
-0.19
* Figures with the same letter superscript are not significantly different.
6°C
S38*
80A
41C
28°C
3°
2D
3°
The temperature of sludge digestion in-
fluenced the rate of inactivation of po-
liovirus (Table 4), which was highest at
28 °C, intermediate at 17.6°C, and lowest
at 5.5 °C.
Varying the dissolved oxygen between
1 and 6 mg/L at a relatively constant
temperature of 28 °C did not change the
inactivation rate. The mean daily change
(Iog10) ranged from -0.77 to -1.03. Anaer-
obic digestion of the same sludge at 32 °C
produced a mean daily change (Iog10) of
-0.33, significantly lower than for aerobic
digestion.
Varying the detention time of aerobic
digestion between 16 and 40 days did not
change the inactivation rate (log daily
change) of poliovirus.
Poliovirus 1, echovirus 1, coxsackievirus
B3, and the simian rotavirus SA-11 were
all inactivated at similar rates during aero-
bic digestion of sludge at 28 °C. The range
of log daily change was -0.46 to -0.77.
Aerobically digested liquid sludge when
allowed to dry in a centrifuge tube from
about 1 to 50 g/L over 28 days showed
essentially no surviving viruses (polio-
virus), whereas 5% survived in a tightly
capped control.
Field Studies
Viruses were detected in samples of
mixed liquor solids and aerobically di-
gested sludge. The lowest levels were
found in sludge from the second aerobic
digester at the plants studied. However,
the numbers of viruses were so variable
that statistical analyses did not show that
the differences were significant except in
a few cases. Results ranged from 0 to 20
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Table 3.
Treatment
Plant*
Summary of Field Data on Bacterial Reduction During
Aerobic and Anaerobic Digestion of Sludge
Bacteria
Bacterial Reduction^
(Log10)
Trial 1
Trial 2
Plant 1
(aerobic digester)
Plant 2
(aerobic digester)
Plant 3
(anaerobic digester)
Total coliforms
Fecal coliforms
Fecal streptococci
Aerobic bacteria
Maximum possible1
Total coliforms
Fecal coliforms
Fecal streptococci
Aerobic bacteria
Maximum possible'
Total coliforms
Fecal streptococci
Maximum possible'
Plant 1: Influent sludge and second of two 8.5-day residence time aerobic
digesters in series
Plant 2: Sludges in first and second of two aerobic digesters, each with
50 days of residence time
Plant 3: Influent sludge and sludge from an anaerobic digester with 10
days of residence time.
Log bacterial density in digested sludge - log density in undigested sludge.
January through December 1981.
August through October 1983.
- 7.53
- 7.52
- 7.03
-0.35
- 1.86
- 1.02
- 1.09
-0.77
-0.80
- 1.70
—
—
- 1.99
—
- 1.63
—
- 1.86
- 1.92
—
- 7.77
_
- 7.70
-0.91
- 1.10
- 1.00
Calculated assuming total destruction of bacteria except for leakage caused by complete
mixing: 1:72.2 for Plant 1, 1:50 for Plant 2, and 1:10 for Plant 3.
Table 4. Effect of Temperature on Poliovirus (Type 1, Lsc) Survival
in Laboratory-Scale Aerobic Digesters
Temperature
28
17.6
5.5
Dissolved
Oxygen
(mg/L)
5.8
5.2
5.8
Total
Solids
(g/U
10.4
7.9
7.9
Volatile
Solids
(g/U
4.8
5.7
5.2
pH
5.3
6
5.3
Mean Daily
Change in
Virus Survival*
(Log10)
- 0. 77A
-0.5B
-0.21C
Means within the same column with the same letter are not significantly different
at the p = 0.05 level.
plaque-forming units (PFU/g) of sludge
solids.
Poliovirus and coxsackievirus serotypes
were isolated from the different sludge
samples. Compared with wasted sludge
before digestion, the aerobically digested
sludge contained relatively few types of
viruses.
Parasite Investigations
Laboratory Studies
Three methods of mixing (magnetic stir-
ring, shaking, and aeration with air pumps)
were used to test the effects of aerobic
sludge digestion on the embryonation of
Ascaris ova. When sludge samples were
mixed mechanically by magnetic stirrers,
85% to 90% of the ova were physically
destroyed. Those ova that were recovered
showed gross abnormalities such as vac-
uolation, cracked egg coats, and
granulation.
Shaking the sludge sample on recipro-
cating shakers during aerobic digestion
resulted in 32% embryonation after 40
days of shaking and 19% embryonation
after 35 days. In only one experiment were
52% of the recovered ova embryonated.
No ova were embryonated in one experi-
ment that shook the sludge sample for 49
days. Most of the nonembryonated ova in
this trial were vacuolated, showed in-
creased granulation, and were physically
distorted. The percentages of unfertilized
ova present in shaken sludge samples de-
creased within 10 to 14 days. After 10
days of shaking in one trial, 40% to 60%
of the initially seeded ova were arrested
in the 2-, 4-, and 8-cell stages. This result
indicated that embryonation had been initi-
ated but stopped early in the cleavage
stage of development.
Aeration of aerobic sludge using an air
pump produced the highest percentages
of ova embryonation. After 30 to 35 days
of aeration, 62% to 68% of the ova were
embryonated in sludges. The percentages
of nonembryonated ova consistently de-
creasesd over a 30- to 42-day period of
aeration. Increasing the detention time of
digestion up to 42 days produced little
change in the percentage of the embry-
onation of the Ascaris ova. Embryonated
ova recovered from aerated sludge di-
gesters showed no distortion, vacuolation,
or granulation.
The infectivity of ova recovered from
sludge aerated either by shaking or with
air pumps was examined in two trials. In
each trial, rats were dosed with ova from
sludge, embryonated ova from hog feces
(positive control), and physiological saline
containing no ova (negative control). In the
first trial, an average of 9% (11% and 8%)
of the ova recovered from shaken sludge
were infective to rats, as demonstrated by
the recovery of third-stage larvae from rat
lungs. An average of 93% (95% and 91%)
of the embryonated positive controls and
no larvae from the negative controls were
recovered. In the second trial, an average
of 12% (10% and 14%) of the ova recover-
ed from sludge aerated by air pumps were
infective. Postivie controls showed an
average infectivity of 79% (83% and
75%), and no larvae were demonstrated
in the lungs of negatively controlled rats.
Recovered larvae in all experiments ap-
peared to be normal and active.
Ascaris ova are highly resistant to var-
ious acids, alkalies, and corrosive chem-
icals. The inner, lipoid, vitelline membrane
is primarily responsible for this effect. Ova
surrounded only by these membranes are
resistant to these chemicals. The primary
lipid component of the vitelline membrane
is a waxy alcohol known as ascaryl alco-
hol. Ascaryl alcohol appears to be a mix-
ture of three closely related compounds —
ascosides A, B, and C. The lipid nature of
this membrane makes it susceptible to
organic solvents, surface active agents,
and noxious gases. Possibly, the nonem-
bryonation and physical deformities of ova
may be caused by various chemicals or
gases that are generated during aerobic
-------
digestion and that destroy or alter the
physiological integrity of this vitelline
membrane. Once the membrane is altered,
the primary protective barrier is breached,
and the developing embryo is unprotected.
Alterations occur at this point.
Field Studies
A number of human parasites were de-
monstrated in locally collected, undigested
sludge and sludge obtained from aerobic
and anaerobic digesters. Four human para-
sites were recovered from sludge: Ascaris
lumbricoides, Trichuris trichiura, Enter-
obius vermicularis, and hookworm. These
are the most common of the intestinal hel-
minth parasites of man. The most com-
mon parasite present in sludges from the
four collection sites was the common pin
worm or seat worm, E. vermicularis. The
second most common parasite was the
large intestinal roundworm, A. lumbri-
coides. Hookworm and the whip worm, T.
trichiura, were also present, but to a small
extent. Sludge samples from treatment
plants in Tallahassee, Florida, showed the
highest incidence of indigenous parasite
ova, followed (in order) by the Main Street,
Kanapagha, and University of Florida treat-
ment plants in Gainesville, Florida. Parasite
ova were recovered from all sludges, re-
gardless of their treatment.
An unexpected observation during ex-
amination of the sludge samples was the
high incidence of the intestinal helminth
E. vermicularis in Tallahassee, Florida. This
parasite has a wide geographic range in
the United States. Cheng reported an in-
fection rate of 32.9% in the American
population. Enterobius is the most com-
mon helminth infection in the United
States, sometimes reaching infection rates
of 60% in children and adults in various
institutions in Florida. An infection rate of
26.8% was reported among students of
five elementary schools in and around
Tallahassee, Florida, These various studies
suggest that Tallahassee, Florida, is an
endemic loci of enterobiasis in the state
of Florida.
Ascaris and Trichuris are the most com-
mon and cosmopolitan helminth infections
in the world. The prevalence of these in-
fections in the population of North Amer-
ica has been estimated at 4 million for
Ascaris and 2.2 million for Trichuris. These
two infections are still extremely common
in the rural areas of the southern United
States. With the prevalence of these infec-
tions in the population and with the fecun-
dity of these parasites (Ascaris produces
200,000 ova/day per female, and Trichuris
produces 1,000 to 46,000 ova/day per
female), it is not surprising that these
parasitic ova were found in locally col-
lected sewage sludge.
Conclusions
Indicator and pathogenic bacteria were
inactivated during aerobic digestion of
sludge under laboratory conditions. Proto-
zoans and other predators were the pri-
mary agents responsible for inactivating
bacteria. Bacterial densities in undigested
sludge are reduced during aerobic treat-
ment of sludge under field conditions.
The addition of fresh, undigested sludge
to aerobic digesters results in contamina-
tion of the digested sludge with undi-
gested sludge and thus diminishes the ef-
fectiveness of the process for reducing
bacterial densities.
Enteric viruses are also inactivated dur-
ing the aerobic digestion of sludge under
laboratory conditions. In contrast with
bacteria, the presence or absence of pre-
dators had little influence on the inactiva-
tion of viruses. Aerobic treatment of
sludge under field conditions reduces the
density of enteric viruses. As with bac-
teria, contamination of digested sludge
with fresh, undigested sludge leads to the
presence of viruses in the digested sludge.
Aeration of Ascaris suum ova in the
presence of 0.1 N H2SO4 contamination
with fungi led to embryonation of more
than 90% of the ova. Approximately 80%
of these ova were infective for rats. In con-
trast, aeration in aerobically digested
sludge resulted in embryonation of 50%
or fewer of the ova. Only some 10% of
these ova were infective for rats. Thus
aerobic treatment of sludge reduces the
ability of ova in the sludge to embryonate
and reduces the infectivity of those ova
that are embryonated. The relatively low
numbers of parasitic ova in undigested and
aerobically digested sludge from treatment
plants made it difficult to determine the
effects of aerobic sludge treatment on
these ova under field conditions.
Recommendations
The presence of bacterial pathogens,
enteric viruses, and parasitic ova in aero-
bically digested sludge suggests two ma-
jor areas of future research: (1) the fate of
these microbes during subsequent treat-
ment or after disposal (including during
sludge drying and application to land), and
(2) modif^ition of existing sludge treat-
ment processes to reduce pathogens fur-
ther. One modification of sludge treatment
that should be considered is the aeration
of sludge in batches without addition of
fresh, undigested sludge. All sludge re-
moved from digesters operated in this
manner would be treated for the same
length of time and would not be contam-
inated with the bacterial pathogens, enter-
ic viruses, and parasitic ova that are often
found in undigested sludge. The possibility
of raising the temperature of sludge diges-
tion should also be considered.
Additional studies are needed on the fate
of parasitic ova during aerobic sludge di-
gestion. Additional laboratory studies are
required to confirm our findings on the ef-
fects of aerobic sludge digestion on the
embryonation and infectivity of Ascaris
suum ova. Larger volumes of sludge from
treatment plants should be processed to
provide the large numbers of ova needed
for embryonation and infectivity studies.
The full report was submitted in fulfill-
ment of Grant No. R806290 by the Univer-
sity of Florida under the sponsorship of the
U.S. Environmental Protection Agency.
.S. GOVERNMENT PRINTING OFFICE: 1986/646-116/20852
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-------
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Samuel R. Far rah, Gabriel Bitton, and Stephen G Zam are with the University of
Florida, Gainesville, FL 32611.
B. V. Salotto was the EPA Project Officer (see below for present contact).
The complete report, entitled "Inactivation of Enteric Pathogens During Aerobic
Digestion of Waste water Sludge, "(Order No, PB 86-183 084/A S; Cost: $11.95,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
For further information, contact Joseph B. Farrell at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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Official Business
Penalty for Private Use $300
EPA/600/S2-86/047
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