United States
Environmental Protection
Agency
Water Engineering Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-85/005 Mar. 1985
<>EPA Project Summary
Liquid Waste Composting
James C. Patterson and John R. Short
This research project was conducted
at the Chesapeake and Ohio Canal
National Historical Park to examine the
feasibility of adapting and using the
sludge composting technique to com-
post liquid waste collected in National
Parks. This study evaluated the com-
posting of two problematic liquid raw
wastes—sanitary toilet pumpings and
septic tank pumpings (septage). Effec-
tiveness of the process was character-
ized by measuring indicator organisms
destruction, nutrient transformations,
heavy metal content, and temperature
and oxygen variation. Effective destruc-
tion of pathogenic microorganisms was
achieved by temperatures in excess of
55° obtained within the composting
pile.
The system was costly on a unit
volume basis, but costs were reasonable
when the value of the compost was
considered. The process provided thor-
ough waste treatment without costly
equipment and specialized construction.
This Project Summary was developed
by EPA's Water Engineering Research
Laboratory, Cincinnati, OH, in coopera-
tion with the U.S. Department of
Interior's National Park Service, to
present key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
The National Park Service Chesapeake
and Ohio Canal National Historical Park
(C&O Canal) was faced with a serious
waste disposal problem in 1975. Several
years prior to 1975, pit toilets were
replaced with sanitary tank-type or port-
able toilets from which raw wastes had to
be pumped and disposed of to municipal
treatment facilities. For a period of time.
waste disposal at local municipal plants
was permitted; however, without warn-
ing, the C&O Canat was refused further
disposal privileges. A thorough investiga-
tion of alternatives led to the selection of
the aerated static pile composting system.
A major question to be addressed was
whether a liquid waste material, at that
time estimated to be greater than 95%
liquid, could be successfully composted.
It was decided in 1976 to initiate a pilot
project and evaluate the feasibility of
composting sanitary toilet waste. As
composting efficiency was obtained, the
C&O Canal decided to investigate com-
posting of a blend of septic tank waste
(septage) and sanitary toilet waste. This
also proved successful.
Materials and Methods
Pile construction began with a mixture
of wood chips, sawdust, and previously
composted material. This mixture was
used as a bulking agent to absorb the
large percentage of liquid in the waste
prior to composting. About 18 cu m(24cu
yd) of bulking agent were required per
3780 L (1000 gal) of liquid waste. After
soaking, the bulking material was incor-
porated into a cone shaped compost pile
4.6 m (15 ft) in diameter and 2.7 m (9 ft)
high. Each pile consisted of a bottom
mattress of previously composted mate-
rial, a core of the waste-soaked bulking
material, and an insulating blanket of
compost material. An oval of perforated
pipe protected by wood chips was laid
between the mattress and the bulking
material during construction and was
connected to the intake manifold of a
blower, A damper between the pile and
the blower provided draft control.
Monitoring and quality control at the
site were critical to accomplishing proper
composting. During the composting cycle
temperature and oxygen readings were
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taken daily at 48 locations within each
compost pile. The temperature was moni-
tored to ensure adequate pathogen de-
struction, and oxygen analyses were
made to ensure adequate aeration.
Weekly compost samples were taken
from internal pile locations. To obtain
representative samples without major
disturbance of the composting mixture,
four access pipes were installed during
pile construction. These access pipes
were capped and covered by blanketing
materials to reduce heat loss during the
sampling procedure.
Compost piles were usually maintained
at a minimum of 55°C for 4 weeks to
ensure good breakdown of organic mate-
rials and adequate destruction of patho-
gens. Longer periods could be maintained
if desired, and some remained for up to 7
weeks. Generally, active compost piles
were maintained for a standing period of
4 weeks to ensure a pathogenically safe
end product. Active composting was
followed by a 3- to 6-month storage
(curing) phase before using the product.
Results
The raw waste and final compost
characteristics are presented in Tables 1
and 2, respectively. These data are means
of measurements from three compost
piles for each type of waste. The raw
waste values are for the liquid waste as
applied to the bulking material, and the
final compost values are for the product of
8 weeks of composting.
Both wastes showed a wide range in
the level of measured parameters' vari-
ability of the wastes as generated. The
septage had generally lower levels for
most of the measured parameters. How-
ever, the heavy metal content of the
septage was higher, probably due to the
use of household products containing
heavy metals.
Samples taken from the sanitary toilet
waste composting piles indicated that
total coliform and fecal coliform levels
dropped to less than 3/gram between the
second and third week of composting for
all pile locations. By the third sampling
cycle, and throughout the additional
samplings, organism counts remained at
these low levels.
The first compost pile constructed
(using only septage} did not perform as
anticipated. Temperatures were generally
lower and the oxygen percentages vari-
able. The second and third piles func-
tioned well with thicker insulation and
longer aeration time.
Table 1.
Raw Waste Characteristics
Table 2. Final Compost Characteristics
Parameter
BOD
COD
Total Coliforms
(MPN/g)
Fecal Colilforms
(MPN/g)
Salmonella, sp
(neg. or posj
Total Solids <%)
Total Volatile
Solids (% of
Total Solids)
pH
Soluble Salts
Total Kjeldahl
Nitrogen
Total
Phosphorus
Total
Potassium
Cadmium
Copper
Lead
Nickel
Zinc
Sanitary
Toilet Waste
9.700*
33,000
830
810
neg.
2.5
53
7.7-8.2
3,300
160.000
4,500
3,300
1 5
230
31
7.3
41O\
Septage
Waste
2,900
15,000
3,700
1,600
neg.
1 7
59
5.9-6 5
280
13.000
3,000
160
1.8
520
63
12
420
Parameter
Total Coliforms
(MPN/g)
Fecal Colilforms
(MPN/g)
Total Solids (%)
Total Volatile
Solids (% of
Total Solids)
pH
Soluble Salts
Total Kjeldahl
Nitrogen
Ammonium
Total
Phosphorus
Total
Potassium
Cadmium
Copper
Lead
Nickel
Zinc
Sanitary
Toilet Compost
<3*
<3
54
42
58-74
1,600
1 1,000
880
2,900
2,700
3.0
50
73
28
220
Septage
Compost
<3
<3
51
49
63-74
880
6,900
120
2,500
2,100
2.5
91
59
26
190
"All units are ug/l unless otherwise noted.
All values are
piles
means from three compost
*AII units are mg/l unless otherwise noted.
All values are means from three compost
piles.
}A zinc-based disinfectant was used in these
toilets
Analyses of indicator organisms during
septage composting indicated that when
proper compost temperatures were
achieved, the maximum level of total
coliforms dropped to less than 3/gram
between the second and third week of
composting for all sample locations. Fecal
coliform concentrations achieved desired
levels by the second week. As was the
case with sanitary toilet waste compos-
ting, counts for both total coliforms and
fecal coliforms did not increase when the
septage compost piles were taken down
and moved to the storage pit.
Temperature monitoring showed the
lowest temperature readings occurred
within the blanket rather than within the
active composting medium. Low temper-
atures were expected around the lower
sections of the pile because of sloughing
of the blanket materials and concentrated
air movement around the pipe. The
highest temperatures occurred at the top
of the pile and in the central core. The
compost temperature rose above 55°C
within the first 5 days. When compost
activity proceeded normally, temperatures
ranged between 64° and 75°C for a
lengthy period, ensuring a high degree of
pathogen destruction. Temperatures in
excess of 55°C have been maintained at
the C&O Canal for 6 to 7 weeks.
Oxygen data showed composting pro-
ceeded well when the oxygen range was
5% to 15%; however, the preferred range
was 8% to 10%.
Costs
The cost of treating the waste material
generated during the 1 978 project period
was about $0.60/gallon. Thisfigure does
not include land acquisition costs or the
local retail value of the final compost
product. When the value of the compost
material was subtracted from the total
cost, the net cost of treating the wastes
was $0.20/gallon. Labor and equipment
rental made up about two-thirds of the
total costs.
Conclusions
The aerated static pile composting
system provided adequate treatment for
septage and sanitary toilet pumpings.
Within a 3-week period, the waste-
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organic mixture became compost, and
after a short storage (curing) period, the
compost became a valued organic soil
amendment. The system had the follow-
ing features: (1) little capital expenditure
was required when compared with tradi-
tional mechanical systems; (2) no full-
time onsite personnel were required; (3) a
minimum of equipment was needed; (4) a
high degree of waste stabilization was
achieved with little or no release of any
effluent; (5) the user was provided with a
highly flexible and efficient waste recy-
cling alternative that was easily adapted
to remote sites, differing waste loading
needs, and different organic wastes; (6)
wastes could be treated as they accumu-
lated or stored until treatment was
needed; (7) the product contained low
levels of coliform organisms; and (8) the
compost contained low levels of many
micro-nutrients and was an excellent
organic soil amendment, which was used
on disturbed soil areas.
The full report was submitted in fulfill-
ment of Interagency Agreement No. 78-
D-X0298 by the Ecological Services
Laboratory, National Capital Region,
National Park Service, U.S. Department
of the Interior in cooperation with the U.S.
Environmental Protection Agency.
James C. Patterson and John R. Short are with the National Park Service, U.S.
Department of the Interior, Washington, DC 20242.
Robert P. G. Bowker was theEPA Project Officer (see below for present contact).
The complete report, entitled "Liquid Waste Composting," (Order No. PB 85-160
406/AS; Cost: $11.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
For further information Donald S. Brown can be contacted at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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