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38 Compost Science & Utilization Winter 2001
Compost Science & Utilization, (2001), Vol. 9, No. 1, 38-49
The Effectiveness of Vermiculture in Human Pathogen
Reduction for USEPA Biosolids Stabilization
Bruce R. Eastman
1
, Philip N. Kane
2
, Clive A. Edwards
3
, Linda Trytek
4
,
Bintoro Gunadi
3
, Andrea L. Stermer
1
and Jacquelyn R. Mobley
1
1. Orange County Environmental Protection Division, Orlando, Florida
2. Florida Department of Environmental Protection, Orlando, Florida
3. Soil Ecology Laboratory, Ohio State University, Columbus, Ohio
4. Tri-Tech Laboratories, Inc., Orlando, Florida
A field experiment tested the feasibility of vermicomposting as a method for elimi-
nating human pathogens to obtain United States Environmental Protection Agency
(USEPA) Class A stabilization in domestic wastewater residuals (biosolids). The ex-
perimental site was at the City of Ocoee’s Wastewater Treatment Facility in Ocoee,
Florida, and Class B biosolids were used as the earthworm substrate. Two windrows
of biosolids 6 m long were heavily inoculated with four human-pathogen indicators,
fecal coliforms, Salmonella spp., enteric viruses and helminth ova. The test row was
seeded with earthworms, Eisenia fetida. The quantity of E. fetida was calculated at a
1:1.5 wet weight earthworm biomass to biosolids ratio and the earthworms allowed
time to consume the biosolids and stabilize the biosolids. The test indicated that all of
the pathogen indicators in the test row were decreased more than in the control row
within 144 hours. The test row samples showed a 6.4-log reduction in fecal coliforms
compared with the control row, which only had a 1.6-log reduction. The test row sam-
ples showed an 8.6-log reduction in Salmonella spp., while the control row had a 4.9-
log reduction. The test row samples showed a 4.6-log reduction in enteric viruses
while the control only had a 1.8-log reduction. The test row samples had a 1.9-log re-
duction in helminth ova while the control row only had a 0.6-log reduction. Dr. Jim
Smith, Senior Environmental Engineer and Pathogen Equivalency Commission
(PEC) Chair, for the USEPA, indicated by personal communications, that a three- to
four-fold reduction in indicator organisms would be sufficient to warrant serious con-
sideration of vermicomposting as an effective stabilization methodology (Smith
1997). These results in conjunction with pilot project results strongly indicate that ver-
micomposting could be used as an alternative method for Class A biosolids stabi-
lization. This was obtained statistically by vermicomposting.
Introduction
Of the 3500-4000 wastewater treatment facilities in 1997 in the State of Florida there
were only nineteen Class AA Type I (> .5 MGD) and four Class A Type I wastewater
treatment facilities. Therefore, the vast majority of these facilities generated a product
below EPA Class A standards. In Florida, approximately 230,000 metric tons (mton) of
biosolids were generated in 1995. Eight percent were burned or incinerated, 9 percent
were distributed and marketed, 17 percent were landfilled, and 66 percent were land
applied (FDEP 1998).
Within the last decade, implementation of the Florida Department of Health,
Chapter 64-E-6, the subsequent USEPA 40 CFR, Part 503, the Florida Administrative
Code 62-640, and other local codes has revolutionized biosolids processing in Flori-
da (FDOH 1998; FDEP 1998). Previously, biosolids stabilization varied greatly and
requirements for septage biosolids stabilization prior to the publication of the cur-
rent rules and regulations were minimal at best. The only requirement was lime sta-
bilization that could be satisfied by inducing a pH of 12 for a minimum duration of
The Effectiveness of Vermiculture in Human Pathogen Reduction
For USEPA Biosolids Stabilization
Compost Science & Utilization Winter 2001 39
2 hours for septic tank biosolids. This was accomplished by adding lime to a pump
truck before picking up biosolids. Agitation of the biosolids and lime mixture while
the truck traveled from point to point was considered sufficient. Adequate stabi-
lization therefore depended on the integrity of the biosolids hauling company. No
records indicating nitrogen loading rates or metals site life were compiled making it
impossible to determine violations of the existing rule, Florida Administrative Code:
17-7 (FDEP 1984).
Public and privately-owned wastewater treatment facilities were required to sta-
bilize their biosolids to a minimum Class C standard for land application, where most
facilities used aerobic or anaerobic digestion. While record keeping was more orga-
nized than for septage stabilization, it was still insufficient. With the implementation
of the new rules, these facilities are now required to stabilize to a Class B standard with
Class C no longer satisfactory for land application. For most of the small facilities this
was impossible to achieve without prohibitive retrofitting and expansion, as they usu-
ally generated Class C biosolids.
The obvious inherent environmental and health hazards of unstabilized human
waste can be seen in the third world nations. Rampant diseases that have debilitating
consequences are common for people living in these countries. Unstabilized or im-
properly stabilized biosolids are a real concern and the regulations regarding stabi-
lization reflect this ongoing concern.
Hence, we investigated into the feasibility of using vermiculture as a pathogen sta-
bilization method. Vermiculture is the practice of cultivating earthworms, such as Eise -
nia fetida, while transforming solid waste and organic biosolids into a beneficial agri-
cultural soil amendment product. Vermiculture’s potential as a beneficial human
pathogen stabilization and management technique for biosolids has been addressed
(Hartenstein et al. 1979; Neuhauser et al. 1988; Bogdanov 1998). Mitchell (1978) demon-
strated that there was a marked reduction in populations of the pathogenic Salmonel -
la enteriditis, Escherichia coli and other enterobacteriaceae during vermicomposting of
aerobic sewage sludge by Eisenia fetida but these were only laboratory culture studies.
It has not been addressed as a clear methodology for obtaining an USEPA Class A
biosolids product in the field.
E. fetida (the red wiggler or manure worm) is commonly used in vermicomposting
(Princine et al. 1980). Since earthworms are able to consume up to twice their weight
of biosolids per day, a high biomass ratio of earthworms to biosolids makes it possible
to quickly and economically convert the biosolids to earthworm casts (Hartenstein et
al. 1979; Loehr et al. 1985; Huhta et al. 1988). The earthworm casts can then be market-
ed with little additional processing.
The Orange County Environmental Protection Division, in partnership with the
American Earthworm Company, Mid Florida Mining and the City of Ocoee, Florida,
initiated this vermiculture field experiment in March 1996 at the City of Ocoee’s Waste-
water Treatment Facility in Ocoee, Florida.
Initially, a preliminary pilot study was conducted to evaluate vermiculture’s ef-
fectiveness with biosolids on a small scale. The pilot study demonstrated a noticeable
reduction in the four human pathogen indicators, fecal coliforms, Salmonella spp., en-
teric viruses and helminth ova in the biosolids. The next step in the implementation of
this project was to begin a full-scale operation to define its operational feasibility. The
USEPA issued a 2-year experimental permit in March 1997 with project oversight for
the USEPA being performed by the Florida Department of Environmental Protection
(FDEP). From the information gathered throughout the full-scale experiment, Stan-
dard Operating Procedures would be developed for the USEPA methodology.
For vermicomposting to be considered by the USEPA as an alternative method-
ology for Class A pathogen stabilization, the project needed to demonstrate a three-
to four-fold reduction (defined as being divided into a specified number of parts)
of pathogen indicators in the biosolids (Fold 1997). This could provide a suitable sta-
bilization of the biosolids to ensure public health concerns with the vermicompost-
ed product.
Materials and Methods
Pilot Project
A shelter was constructed at the City of Ocoee Wastewater Treatment Facility to
house inoculated experimental plots. A chicken wire fence was installed to keep out
animals. Dewatered biosolids (17 percent solids) were land applied into two windrows
approximately 9 m long by 1.5 m wide by 46 cm deep, utilizing approximately 7.3
mtons of biosolids each. One row was designated the test row and the second row was
designated the control row.
To obtain sufficient levels of all the pathogen indicators (fecal coliforms, Salmonel -
la spp., enteric virus and helminth ova) required for the study, biosolids from another
municipal plant were incorporated. In addition, the biosolids had to be inoculated with
enteric virus. The resulting material was applied on a bed of impermeable clay cov-
ered with filter sand for leachate recapture, if needed.
Three representative samples were analyzed from each row to establish a baseline
for determining the initial concentrations of pathogen indicators. After 68 days, final
samples were collected using the same methodology as the baseline sampling.
The test row was then seeded with E. fetida at approximately 1:1 earthworm bio-
mass to biosolids ratio. Earthworm density was determined by amount of food that
past research suggested E. fetida were capable of consuming in one day. Earthworms
were provided approximately 3.6 mtons of biosolids for a 90-day feeding period.
A garden hose was used to irrigate the rows as needed, to provide the earthworms
with optimal moisture. A pitchfork was used to turn the biosolids as needed for in-
spection of the earthworms.
Full-Scale Operation
Biosolids (15-20 percent solids) were land applied into two windrows approxi-
mately 6 m long by 1.5 m wide by 20 cm deep, utilizing approximately 1.4 mtons of
biosolids each. One row was designated the test row and the second row was desig-
nated the control row. These two rows were inoculated with three of the four pathogen
indicators, fecal coliforms, Salmonella spp. and enteric viruses.
The inoculation mixture was prepared as follows for the three pathogen portion
of the project. First, 50 g of cake biosolids were mixed with approximately 50 ml of
deionized water for each pathogen and the pathogen controls were blended into indi-
vidual biosolids/water mixtures. Finally, each mixture was then divided into two one-
liter bottles marked “control” and “test”. Both rows were then inoculated with a min-
imum 105 inoculum of the three pathogen indicators (fecal coliforms, Salmonella spp.
and enteric viruses). Three representative samples were analyzed from each row to es-
tablish a baseline for determining the initial concentrations of pathogen indicators. The
biosolids test row was then seeded with E. fetida at a 1:1.5 earthworm biomass to
biosolids ratio. This ratio represented the earthworm’s feeding rate for a 24-hour peri-
Bruce R. Eastman, Philip N. Kane, Clive A. Edwards, Linda Trytek, Bintoro Gunadi,
Andrea L. Stermer and Jacquelyn R. Mobley
40 Compost Science & Utilization Winter 2001
The Effectiveness of Vermiculture in Human Pathogen Reduction
For USEPA Biosolids Stabilization
Compost Science & Utilization Winter 2001 41
od based on the pilot project. Earthworms were provided approximately 1361 kg of
biosolids for a 14-day feeding period.
The helminth ova portion of the experimental project was conducted at a later date
due to difficulty in acquiring the helminth ova eggs. Biosolids (15-20 percent solids)
were land applied into two rows approximately 2.3 m long by 1.5 m wide by 23 cm deep.
One row was designated as the test row and the other the control row. The helminth
ova inoculation mixture was prepared as follows. Two containers were prepared by
mixing 500 g of cake biosolids with approximately 500 ml of deionized water. Each con-
tainer was then inoculated with the helminth ova. The control row container was inoc-
ulated with one million (84.1% viable) helminth ova (Ascaris spp.) eggs. The test row
container was inoculated with one million (82.6% viable) helminth ova (Ascaris spp.)
eggs. Dr. Robert S. Reimers’ research team of Tulane University Medical Center con-
ducted viability tests of the helminth ova to confirm initial concentrations (Little 1998).
The biosolids test row was then seeded with E. fetida in a way similar to the other three
pathogen tests. Florida peat, the substrate in which the earthworms were held, was
spread across the test row, adding approximately 15 cm to the depth. Earthworms were
provided approximately 531 kg of biosolids for feeding for a 7-day period.
Representative auger samples were collected by using a 46 cm PVC pipe with a 2
cm inside diameter. Augers were autoclaved for 30 minutes at 121°C after each sam-
pling event for sterilization. The sampling regimen consisted of collecting composite
samples 72 and 144 hours after inoculation from the test and control rows. These sam-
ples were analyzed for Salmonella spp. and enteric viruses. The helminth ova sampling
was also conducted after 72 and 144 hour intervals. For fecal coliform analysis to com-
ply with USEPA recommended sampling and testing, three series of composite sam-
ples were collected concurrently from the test and control rows. For each set one com-
posite sample was collected for each of seven consecutive days and analyzed to obtain
counts of the most probable number (MPN) of colonies. Samples of the pathogens were
taken at these intervals to determine how quickly the earthworms were reducing the
pathogens. This data would be used in establishing standard operating procedures
(SOPs) in a future project.
Due to the extremely high numbers of pathogen indicators in the spiked project, the
helminth ova analytical method was modified to obtain the most accurate readings.
A Student’s t-test was used to compare the significance of the difference of the hu-
man pathogens and any decrease in the test and control rows.
Nonchlorinated water (less than 0.2 mg/L) was used to water the test and control
rows as needed, to provide the earthworms with optimal moisture.
Due to the infectious nature of the experimental pathogens, intense precautionary
measures were taken addressing safety concerns necessary to protect personnel and
the environment. The City of Ocoee’s Wastewater Treatment Facility is completely
fenced in with restricted public access.
Results and Discussion
Pilot Project
The fecal coliform samples collected showed an initial baseline analysis for the test
row of 0.093, 1.05 and 1.05 log most probable number/gram (log MPN/g) (Table 1).
The initial baseline analysis for the control row was 1.05, 1.05 and 1.06 log MPN/g. The
final test row sample results were -.16, -.00 and -.00 log MPN/g. The control samples
were 0.047, 0.058 and 0.049 log MPN/g.
Bruce R. Eastman, Philip N. Kane, Clive A. Edwards, Linda Trytek, Bintoro Gunadi,
Andrea L. Stermer and Jacquelyn R. Mobley
42 Compost Science & Utilization Winter 2001
The Salmonella spp. s a m p l e s
collected showed an initial
baseline analysis for the test
row of 7, 3, and 4 cells/gram
(cell/g) (Table 1). The initial
baseline analysis for the con-
trol row was 9, 2 and 6 cells/g.
The final test row sample re-
sults were <1, <1 and <1
cells/g. The control sample re-
sults were 1, <1 and <1 cells/g.
The enteric virus samples
collected showed an initial
baseline analysis for the test
row of negative, positive and
positive, indicating the pres-
ence or absence of the cyto-
pathic effects (Table 1). The
initial baseline analysis for the
control row was positive, neg-
ative and positive. The final
test row sample results were
negative, negative and nega-
tive. The control sample re-
sults were negative, negative
and negative.
The helminth ova samples
collected showed an initial
baseline analysis for the test
row of 4, 1 and 4 ova/4 grams (ova/4 g) (Table 1). The initial baseline analysis for the
control row was <1, 2 and 1 ova/4 g. The final test row sample results were <1, <1 and
<1 ova/4 g. The control sample results were <1, <1 and <1 ova/4 g.
The project was scheduled to last for 90 days. However, it was terminated earlier
than expected (68 days) on the advice of the contracted vermiculturist. It was believed
that the earthworms were beginning to fast from lack of food. They did in effect eat
up to 1.5 times their body weight each day.
The installed leachate recapture system proved to be unnecessary since leachate
was not produced during the course of the experiment. In addition, there were no un-
usual occurrences.
Final analysis indicated a significant reduction of fecal coliforms. All samples from
the test row were negative for E. coli, Salmonella spp., enteric virus and helminth ova.
Reductions of pathogens were observed in the control row. This reduction could have
been attributed to the natural die-off of the organisms. However, the reductions in the
test row were greater, which can be attributed to the vermicomposting process.
Full-Scale Operation
The fecal coliform samples collected showed an initial baseline analysis for the test
row of 9 3 1 0
9
, 9 3 1 0
9
and 8 3 1 0
9
most probable number/1 gram (MPN/1 g). The ini-
tial baseline analysis for the control row was 9 3 1 0
9
, 7 3 1 0
9
and 9 3 1 0
9
MPN/1 g. Af-
TABLE 1.
"Baseline and final samples of biosolids tested for four
pathogen indicators from Orange County," Florida trial
on stabilization of biosolids using vermiculture.
Vermiculture Control
Test Row Samples Row Samples
Pathogen indicator NE1 C1 SE1 NE2 C2 SE2
Fecal coliform (CFU/g)
1,2
Baseline 301 314 313 313 326 329
Final 2.8 -0.0 -0.0 70 99 76
Fecal coliform (log MPN/g)
3
Baseline 0.093 1.05 1.05 1.05 1.05 1.06
Final -.16 -.00 -.00 0.047 0.058 0.049
Salmonella sp. (cell/g)
Baseline 7 3 4 9 2 6
Final <1 <1 <1 1 <1 <1
Enteric virus
4
(Cytopathic effects)
Baseline neg pos pos pos neg pos
Final neg neg neg neg neg neg
Helminth Ova (ova/4 g)
Baseline 4 1 4 <1 2 1
Final <1 <1 <1 <1 <1 <1
1
Numbers for fecal coliform are the geometric mean of seven grab
sample all taken on the same day.
2
CFU/g = Colony Forming Units per gram
3
MPN = Most Probable Number
4
The cytopathic effects of enteric virus were measured as PFU/1 g as an
indicator, rather than as PFU/4 g
The Effectiveness of Vermiculture in Human Pathogen Reduction
For USEPA Biosolids Stabilization
Compost Science & Utilization Winter 2001 43
ter 24 hours, the test row samples averaged a 1.9-log reduction, which equates to a six-
fold reduction or 98.65% (percent is based on actual pathogen counts and not logarith-
mic numbers) (Figures 1 & 2). The control row samples averaged a 0.1-log reduction
(less than one-fold or 20.00%). After 72 hours, the test row samples averaged a 5.3-log
reduction (seventeen-fold or 99.99%). The control row samples averaged a 0.5-log re-
duction (up to one-fold or 71.60%). After 144 hours, the test row samples averaged a
6.4-log reduction (twenty-one-fold or 100.00%). The control row samples averaged a
1.6-log reduction (five-fold or 97.44%). After 336 hours (end of the third set), reductions
continued in both rows until the test row achieved a 6.7-log reduction (twenty-two fold
or 100.00%) and the control row samples showed an averaged 3.2-log reduction (ten-
Figure 1. Fecal coliform average decrease (shown in logarithmic scale) in the control and test during 7 days of vermicom-
posting. Vertical T bars represent standard errors.
Figure 2. Fecal coliform average decrease (shown in linear scale) in the control and test during 7 days of vermicompost-
ing. Vertical T bars represent standard errors.
fold or 99.00%). As shown in
Table 2 the initial number of
fecal coliform was not signifi-
cant between the control and
test. Afterwards in the 1st
through 7th days of vermi-
composting, mean number of
fecal coliform in the test was
significantly lower than that
in the control.
The initial baseline analysis
for Salmonella spp. in the test
row was 4.2 3 10
9
, 5.0 3 10
9
and 4.7 3 10
9
cells/25 ml. The
initial baseline analysis for the
Bruce R. Eastman, Philip N. Kane, Clive A. Edwards, Linda Trytek, Bintoro Gunadi,
Andrea L. Stermer and Jacquelyn R. Mobley
44 Compost Science & Utilization Winter 2001
TABLE 2.
Mean numbers of fecal coliform in the control and test
during 7 days of vermicomposting.
Day
Sample Sample Results (MPN/1 g)
Taken Control Test
Day 0 8.33 10
9
± 6.67 3 10
8
8.67 3 10
8
± 3.33 3 10
8
NS
Day 1 6.67 3 10
9
± 3.33 3 10
8
1.16 3 10
8
± 6.67 3 10
6
***
Day 2 1.46 3 10
9
± 1.20 3 10
8
2.90 3 10
5
± 3.21 3 10
4
***
Day 3 2.37 3 10
9
± 1.20 3 10
8
4.33 3 10
4
± 8.82 3 10
3
***
Day 4 2.47 3 10
8
± 1.86 3 10
7
1.13 3 10
4
± 1.45 3 10
3
***
Day 5 3.23 3 10
8
± 1.20 3 10
7
4.66 3 10
3
± 6.67 3 10
2
***
Day 6 2.13 3 10
8
± 2.60 3 10
7
3.66 3 10
3
± 6.67 3 10
2
***
Day 7 8.33 3 10
7
± 1.45 3 10
7
3.40 3 10
3
± 8.08 3 10
2
**
The results are ± SE (n=3); NS = Not significant, ** = p < 0.01, *** = p < 0.001
Figure 3. Salmonella spp. average decrease (shown in logarithmic scale) in the control and test during 6 days of vermicom-
posting. Vertical T bars represent standard errors.
Figure 4. Salmonella spp. average decrease (shown in linear scale) in the control and test during 6 days of vermicompost-
ing. Vertical T bars represent standard errors.
control row was 5.4 3 10
9
, 4.6 3 10
9
and 5.1 3 10
9
cells/25 ml. After 72 hours, the test
row samples averaged a 4.0-log reduction (thirteen-fold or 99.99%) (Figures 3 & 4). The
control row samples averaged a 1.2-log reduction (three-fold or 93.18%). After 144
hours, the test row samples averaged an 8.6-log reduction (twenty-eight fold or
100.00%). The control samples averaged a 4.9-log reduction (sixteen-fold or 99.99%).
Table 3 shows that initial mean number of Salmonella spp. was not significant between
the control and test. Afterwards in the 3rd and 6th days of vermicomposting, mean
number of Salmonella spp. i n
the test was significantly low-
er than that in the control.
The initial baseline analy-
sis for enteric viruses in the
test row was 2.3 3 1 0
5
, 1.5 3
1 0
5
and 2.1 3 1 0
5
plaque form-
ing units/4 grams (PFU/4 g).
The initial baseline analysis in
the control row was 1.3 3 1 0
5
,
2.2 3 1 0
5
and 1.7 3 1 0
5
P F U / 4
g. After 72 hours, the test row
samples averaged a 2.0-log re-
duction (six-fold or 98.92%)
(Figures 5 & 6). The control
row samples averaged a 0.3-
log reduction (one-fold or
53.85%). After 144 hours, the
test row samples averaged a
4.6-log reduction (fifteen-fold
or 99.99%). The control row
samples averaged a 1.8-log re-
duction (six-fold or 98.46%).
Table 4 shows that initial
mean number of the enteric
virus was not significant be-
tween the control and test. Af-
terwards in the 3rd and 6th
days of vermicomposting,
mean number of enteric virus
in the test was significantly
lower than that in the control.
After 72 hours, the test
row samples showed a 0.3-log
reduction (less than one-fold
or 47.54%) from an original inoculum of 8.26 3 1 0
5
helminth ova (Ascaris spp.) (Figures
7 & 8). The control row samples had a 0.0-log reduction (less than one-fold or 0.00%)
from an original inoculum of 8.41 3 1 0
5
helminth ova. After 144 hours, the test row sam-
ples had a 1.9-log reduction (six-fold or 98.87%). The control row samples had a 0.6-log
reduction (one-fold or 74.24%). As shown in Table 5 the initial number of helminth ova
was not significant between the control and test. Afterwards in the 3rd till 6th days of
vermicomposting, mean number of helminth ova in the test was significantly lower
than that in the control.
The Effectiveness of Vermiculture in Human Pathogen Reduction
For USEPA Biosolids Stabilization
Compost Science & Utilization Winter 2001 45
TABLE 3.
Mean numbers of Salmonella spp. in the control and test
during 6 days of vermicomposting
Day
Sample Sample Results (cells/25 ml)
Taken Control Test
Day 0 5.03 3 10
9
± 2.33 3 10
8
4.63 3 10
9
± 2.33 3 10
8
NS
Day 3 3.43 3 10
8
± 4.37 3 10
7
4.73 3 10
5
± 4.91 3 10
4
***
Day 6 5.66 3 10
4
± 1.76 3 10
4
12.66 ± 2.19 **
The results are +SE (n=3); NS = Not significant, ** = p < 0.01, *** = p < 0.001
TABLE 4.
Mean numbers of enteric virus in the control and test
during 6 days of vermicomposting
Day
Sample Sample Results (PFU/4 g)
Taken Control Test
Day 0 1.73 3 10
5
± 2.60 3 10
4
1.96 3 10
5
± 2.40 3 10
4
NS
Day 3 8.00 3 10
4
± 2.08 3 10
4
2.13 3 10
3
± 1.45 3 10
2
**
Day 6 2.66 3 10
3
± 6.67 3 10
2
5.00 ± 2.88 **
The results are ± SE (n=3); NS = Not significant, ** = p < 0.01
TABLE 5.
Mean numbers of helminth ova in the control and test
during 6 days of vermicomposting
Day Sample Results (oval/4 grams dry wt.)
Sample
Taken Control Test
Day 0 8.41 3 10
5
± 0 8.26 3 10
5
± 0 NS
Day 3 9.33 3 10
5
± 8.82 3 10
4
4.33 3 10
5
± 1.45 3 10
5
**
Day 6 2.16 3 10
5
± 1.76 3 10
4
9.33 3 10
3
± 1.45 3 10
3
***
The results are ± SE (n=3); NS = Not significant, ** = p < 0.01, *** = p < 0.001
The experiment demonstrates that the earthworms can reduce the USEPA
pathogen indicators in as short a time as 144 hours. Since vermicomposting
demonstrates such a great reduction in pathogen indicators in the spiked test, it
shows that Class A stabilization equivalency is obtainable, as indicated in the pi-
lot project. The reductions occurred greatly exceeded the required USEPA three-
to four-fold reduction necessary for consideration of vermicomposting as a
Class A stabilization method. The vermicomposting method is an inexpensive
low-technological procedure for achieving results comparable to other more in-
Bruce R. Eastman, Philip N. Kane, Clive A. Edwards, Linda Trytek, Bintoro Gunadi,
Andrea L. Stermer and Jacquelyn R. Mobley
46 Compost Science & Utilization Winter 2001
Figure 5. Enteric virus average decrease (shown in logarithmic scale) in the control and test during 6 days of vermicom-
posting. Vertical T bars represent standard errors.
Figure 6. Enteric virus average decrease (shown in linear scale) in the control and test during 6 days of vermicomposting.
Vertical T bars represent standard errors.
tensive and expensive USEPA biosolids stabilization methods. Also, a difference
from other low-technology vermicomposting projects is the elimination of pre-
composting. Until recently, this step was thought to be necessary to eliminate
pathogens before adding earthworms. However, this project confirms that the
earthworms greatly reduce the pathogens from the biosolids during vermicom-
posting making the pre-composting unnecessary. The use of earthworms to ver-
micompost biosolids exceeded even the initial experimental expectations for
pathogen reductions.
The Effectiveness of Vermiculture in Human Pathogen Reduction
For USEPA Biosolids Stabilization
Compost Science & Utilization Winter 2001 47
Figure 7. Helminth ova average decrease (shown in logarithmic scale) in the control and test during 6 days of vermicom-
posting. Vertical T bars represent standard errors.
Figure 8. Helminth ova average decrease (shown in linear scale) in the control and test during 6 days of vermicompost-
ing. Vertical T bars represent standard errors.
This project also showed that there were reductions of pathogens in the control
row. This was attributed to the natural die-off of the organisms after inoculation. One
of the requirements of an indicator organism is that it does not live long in the envi-
ronment so that its presence is indicative of human contamination. However, the re-
ductions in the test row were greater and quicker than in the control row due to the
vermicomposting stabilization.
Observations were made which potentially affected the results. The introduc-
tion of earthworms to the helminth ova test row may have been more appropriate
without the inclusion of Florida peat (substrate in which the earthworms were
held). Due to the addition of the peat, the pathogen reduction times were probably
slightly elevated compared to the previous test with the other three-pathogen indi-
cators without peat. Slower reductions may have occurred because the earthworms
already had a food source in the peat. Observations indicated the earthworms re-
mained in the peat and did not migrate immediately to the biosolids thereby po-
tentially increasing the stabilization time.
The helminth ova graph appears to indicate an increase in concentrations in the
control row from the initial time to Day 3 (Figure 8). But, this may be an anomaly. The
original helminth ova were counted and adjusted for viability. Representative sam-
ples, extrapolated for the amount of biosolids used in the control row, can indicate
greater numbers of organisms. There was not an actual increase in the overall number
of helminth ova (Ascaris spp.) eggs.
Conclusions
Based on experimental analyses from both the pilot and the full-scale opera-
tion, vermiculture can be used effectively as an USEPA process to treat pathogens
and potentially produce Class A biosolids. Biosolids can be seeded with E. fetida
by calculating a consumption rate of 1.5 times their biomass every 24 hours pro-
portionally with the percentage of earthworm biomass to biosolids at a 1:7 ratio
weekly. Additional biosolids should not be incorporated for a minimum of 144
hours to maximize pathogen reduction. Earthworms should not be harvested be-
fore this time.
Kg biosolids 4 7 = Biosolids per day 4 1.5 (consumptive rate of earthworms) =
Kg of earthworms required for stabilization
This ratio is a baseline guide for quantity of earthworms and amount of biosolids
to be stabilized as described. These population levels may not be practically sustain-
able. Therefore, due to earthworm population sustainability and fluctuation, the sta-
bilization time will need to be proportionally adjusted until a stabilization equilibrium
is obtained and maintained as confirmed by sampling analysis.
Acknowledgements
We would like to acknowledge Dr. Robert S. Reimers, School of Public Health and
Tropical Medicine, Tulane University Medical Center, New Orleans, Louisiana, for his
assistance in the viability reports of the helminth ova.
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The Effectiveness of Vermiculture in Human Pathogen Reduction
For USEPA Biosolids Stabilization
Compost Science & Utilization Winter 2001 49
