xvEPA
. United States
Environmental Protection
Agency
.Office of Water
Washington, D.C.
September 1999
Decentralized Systems
Technology Fact Sheet
Septage Treatment/Disposal
DESCRIPTION
In 1990 the U.S. Department of Commerce, Census
Bureau, estimated that the number of housing units
with septic tanks or cesspools in the U.S. was 24.6
million and approximately 5.5 billion gallons of
septage were being generated each year. "Septage"
is the liquid and solid material pumped from a
septic tank, cesspool, or other primary treatment
source. Scum accumulates on the surface while the
sludge settles at the bottom, comprising 20 to 50%
of the total septic tank volume when pumped. A
septic tank will usually retain 60 to 70% of the
solids, oil, and grease that passes through the
system.
Septage is classified according to the environment
in which it is generated. This fact sheet will focus
solely on domestic septage. Treatment and disposal
of domestic septage is governed by the U.S. Code
of Federal Regulations (40 CFR) Part 503.
Municipalities can also establish local regulations
for septage handling, treatment, and disposal in
addition to the federal and state regulations.
There are several approaches to septage treatment
and disposal which include private or public
ownership. Larger municipalities are capable of
managing the whole process from handling and
treatment to disposal, while other municipalities opt
to use privately owned facilities that alleviate some
of the responsibilities of operating a facility. Land
disposal of septage after adequate treatment is also
a popular option.
Septage characteristics
Factors that affect the physical characteristics of
septage are: climate, user habits, septic tank size,
design, and pumping frequency, water supply
characteristics, piping material, and the use of
water-conservation fixtures, garbage disposals,
household chemicals, and water softeners. Table 1
lists the characteristics and limits of domestic
septage.
TABLE 1 CHARACTERISTICS OF
SEPTAGE CONVENTIONAL
PARAMETERS
Concentration
Parameter Minimum
Total solids
Total volatile solids
Total suspended
solids
Volatile suspended
Biochemical oxygen
demand
Chemical oxygen
demand
Total Kjeldahl
nitrogen
Ammonia nitrogen
Total phosphorus
Alkalinity
Grease
PH
Total coliform
Fecal coliform
1,132
353
310
95
440
1,500
66
3
20
522
208
1.5
107/100mL
106/100 ml_
Maximum
130,475
71 ,402
93,378
51,500
78,600
703,000
1,060
116
760
4,190
23,368
12.6
109/100mL
10^/100 ml
Note: i ne measurements above are in mg/L unless otherwise
indicted.
Source: U.S. EPA, 1994.
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TABLE 2 SOURCES OF SEPTAGE
APPLICABILITY
Description
Rate
Removal
Pump-out
Characteristics
Septic tank
Cesspool
Privies/portabJ
e toflets
Aerobic tanks
Holding tanks
(septic tank
with no drain-
field, typically
a local
requirement
Dry pits
(associated
with septic
fields)
Miscellaneous
May Exhibit
Characteristics
ofSeptage
Private
wastewater
treatment
plants
Boat pump-out
station
Grit traps
Grease traps
2-6 years, but
can vary with
location local
ordinances
2-10 years
1 week to
months
Months to 1
year
Days to weeks
2-6 years
Variable
Variable
Variable
Weeks to
months
Concentrated BOD,
solids, nutrients,
variable toxics
(such as metals),
inorganics (sand),
odor, pathogens,
oil, and grease
Concentrated BOD,
solids, nutrients,
variable toxics,
inorganics,
sometimes high
grit, odor,
pathogens, oil, and
grease
Variable BOD,
soilds, inorganics,
odor, pathogens,
and some
chemicals
Variable BOD,
inorganics, odor,
pathogens, and
concentrated solids
Variable BOD,
solids, inorganics,
odor, and
pathogens, similar
to raw wastewater
solids
Variable BOD,
solids, inorganics,
and odor
Septic tank
Portable toilets
Oil, grease, solids,
inorganics, odor,
and variable BOD
Oil, grease, BOD,
viscous solids, and
odor
Source: Septage Handling Task Force (1997), copyright
Water Environment Federation, used with permission.
Septage is highly variable and organic, with
significant levels of grease, grit, hair, and debris.
The liquids and solids pumped from a septic tank or
cesspool have an offensive odor and appearance, a
tendency to foam upon agitation, and a resistance to
settling and dewatering. Septage is also a host for
many disease-causing viruses, bacteria, and
parasites. As a result, septage requires special
handling and treatment. However, the polymers
and chemical conditioners available today have
considerably reduced these requirements.
The handling and disposal of septage are based oh
the characteristics and volume of septic waste.
Knowldege of this information is also useful for
design purposes and determining typical design
values for treatment and disposal. Table 2
summarizes the sources of septage.
ADVANTAGES AND DISADVANTAGES
Advantages
The advantage of using treatment plants is that they
provide regional solutions to septage management.
Disadvantages
May need a holding facility during periods
of frozen or saturated soil.
Need a relatively large, remote land area for
the setup of the septic system.
• Capital and operation and maintenance
costs tend to be high.
• Skilled operators may be required.
• Some limitations to certain management
options of untreated septage include lack of
available sites and potential odor and
pathogen problems. These problems can be
reduced by pretreating and stabilizing the
septage before it is applied to the land.
• Septage treated at a wastewater treatment
facility has the potential to upset processes
if th septage addition is not properly
controlled, and increased requirements for
handling and disposing of residuals.
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DESIGN CRITERIA
Surface application
Septage can be applied to the land as a fertilizer and
soil conditioner. Application rates depend on the
slope, soil type, depth of application, drainage class,
and hydraulic loading. Septage must not be applied
before or during rainfall or on frozen ground. Thus,
an interim storage facility is needed. Some states
require septage to be disinfected before application.
• Spray Irrigation-pretreated (e.g., screened)
septage is pumped at 80 to 100 psi through
nozzles and sprayed directly onto the land.
Spray irrigation can be used on steep or
rough land and minimizes disturbances to
the soil by trucks. It is important to
consider the wind patterns and the site
location when using spray irrigation
because of the offensive odors associated
with septage.
• Ridge and Furrow Irrigation-this is used for
relatively level land, with slopes no greater
than 0.5 to 1.5%. In this disposal method,
pretreated septage is applied directly to
furrows or to row crops that will not be
directly consumed by humans.
Hauler Truck Spreading-septage is applied
to the soil directly from a hauler truck that
uses a splash plate to improve distribution.
The same truck that pumps out the septic
tank can be used for transporting and
disposing the septage.
Farm Tractor and Wagon Spreading-liquid
septage or septage solids are transferred to
farm equipment for spreading. This allows
for application of liquid or solid septage.
However, if the septage was not lime
stabilized, then the septage must be
incorporated into the soil within 6 hours.
Subsurface Incorporation
Subsurface incorporation places untreated septage
, just below the soil surface, reducing odors and
health risks while fertilizing and conditioning the
soil. Septage can only be applied to slopes less than
8%, and the soil depth to seasonal high water table
must be at least 20 inches (or as mandated by local
regulations). A holding facility is required during
periods of wet or frozen ground. To prevent soil
compaction and allow sufficient infiltration,
equipment must not be driven over the site until 1
to 2 weeks after application.
• Plow and Furrow Cover-typically, a
moldboard plow is used with furrow wheels
and coulters. The coulter blade slits the
ground ahead of a plow. Liquid septage is
discharged from a tank into a narrow furrow
about 15 to 20 cm deep and is then covered
by a second plow.
• Subsurface Injection-liquid septage is
injected in a narrow cavity created by a
tillage tool. The opening is about 10 to 15
cm below the surface. Some equipment
uses a forced closure of the injection swath.
Burial
Septage burial includes disposal in holding lagoons,
trenches, and sanitary landfills. There is a high
odor potential during septage application until a
final cover is placed on top. It is essential to select
an appropriate site for disposal not only to control
odors, but to avoid groundwater pollution.
Holding Lagoons- these disposal lagoons
are a maximum of 6 feet deep, with septage
placed in small incremental lifts of 15 to 30
cm and no infiltration. Multiple lagoons are
loaded in sequential order for optimum
drying. To decrease odors, the lagoon inlet
pipe can be placed below liquid level.
Trenches-multiple trenches are filled
sequentially with septage in small lifts of 15
to 20 cm for optimum drying. Each trench
is then covered with soil (2 feet), and new
trenches are opened. Another option is to
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leave a filled trench uncovered to
enable some solids to settle and
liquids to evaporate and leach out.
The solids, along with some bottom
and sidewall material, are removed
and the trench can be reused.
• Sanitary Landfills- the primary problems
that need to be considered when septage is
added to a sanitary landfill are the
production of leachate, treatment, and odor.
Therefore, septage must not be disposed of
in landfills with areas that have over 90 cm
of rainfall, landfills that do not have
leachate prevention and control facilities, or
those not having isolated underlying rock.
Each area that is filled with septage should
be covered with 15 cm of soil each day and
2 feet of final cover within 1 week after the
placement of the final lift. In general,
sanitary landfills are not cost-effective
disposal options for septage.
Septage is resistant to dewatering and as a result
conditioning chemicals are used. The amount of
chemical used is based on the load and its
characteristics. A combination of lime and ferric
chloride has been successfully used, along with
certain polymers. Septage treatment plants also use
other processes to de water conditioned septage such
as screw presses, plate and frame presses, belt
presses, rotary vacuum filters, gravity and
vacuum-assisted drying beds, and sand drying beds.
Another feasible option for septage treatment
facilities is composting in locations where bulking
agents are available and the humus product is
needed as a soil conditioner. If the necessary
bulking agents are not accessible, this method can
be expensive. For this reason, it is preferable to
dewater septage before composting.
OPERATION AND MAINTENANCE
The three basic alternatives for septage treatment
and disposal are land application, treatment at
wastewater treatment plants, and treatment at
independent septage treatment plants.
Treatment at independent septage treatment
plants
• Stabilization lagoon.
• Chlorine oxidation.
• Aerobic digestion.
• Anaerobic digestion.
Biological and chemical treatment.
• Conditioning and stabilization.
• Composting
Treatment at wastewater treatment plants
• Addition to upstream sewer manhole.
• Addition to plant headworks.
• Addition to sludge handling process.
• Addition to both liquid stream and sludge
handling processes.
Land application
• Surface application.
• Subsurface incorporation.
• Burial.
Selecting the appropriate septage management
option depends on technical issues and regulatory
requirements. Some of the factors that influence
the process of selection include: land availability
and site conditions, buffer zone requirements,
hauling distance, fuel costs, labor costs, costs of
disposal, and other legal and regulatory
requirements.
Treatment at Independent Septage Treatment
Plants
Independent septage treatment plants use such
processes as chlorine oxidation, aerobic digestion,
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anaerobic digestion, and biological and chemical
treatment. Many septage treatment plants also use
lime to provide both conditioning and stabilization
before the septage is dewatered. The liquid residual
can be discharged to a privately owned treatment
facility or undergo further treatment and then be
discharged. Septage solids are then sent to either a
landfill, composted, applied to the land, or
incinerated.
When suitable land is unavailable and wastewater
treatment facilities are too distant or do not have
adequate capacity, independent septage treatment
plants can be of use. Such treatment plants have
been designed exclusively for treating septage and
have many unit processes to handle both the liquid
and solid portions of septage.
Stabilization is a treatment method that decreases
odors, the levels of disease-causing organisms, and
the potential for putrefaction of septage.
Pretreatment/stabilization is achieved by physical,
chemical, or biological processes. Some methods
of stabilizing septage are discussed below.
Alkali (Lime) Stabilization
Lime or other alkaline material is added to liquid
septage to raise the pH to 12.0 for a minimum of 30
minutes. Although there is a lot of variation in
septage characteristics and lime requirements,
mixing is not very difficult, and'approximately 20
to 25 pounds of lime are used for every 1,000
gallons of septage. The three main stabilization
approaches before land application are to add lime
slurry: 1) to the pumper truck before the septage is
pumped, 2) to the pumper truck while the septage is
being pumped, or 3) to a tank that is storing septage
that was discharged from a pumper truck. The
septage and lime may sometimes be mixed by a
coarse bubble diffuser system located in the tank or
truck. In some states, it is prohibited to use hauler
trucks for the stabilization process. A separate
storage tank is necessary for lime and septage
mixing. This is beneficial because a separate
holding tank allows for more uniform mixing and
easier sampling, monitoring, and control.
Aerobic Digestion
Septage is aerated for 15 to 20 days in an open tank
.to achieve biological reduction in organic solids and
odor potential. The time requirements increase
with lower temperatures. Normally, this is not a
cost-effective option.
Anaerobic Digestion
Septage is retained for 15 to 30 days in an enclosed
vessel to achieve biological reduction of organic
solids. Anaerobic digestion is generally not used
except for co-treatment with sewage sludge.
However, one advantage is that anaerobic digestion
generates methane gas, which can be used for
digester heating or other purposes.
Composting
Liquid septage or septage solids are mixed with a
bulking agent (e.g., wood chips, sawdust) and
aerated mechanically or by turning. Biological
activity generates temperatures that are sufficiently
high to destroy pathogens. The composting process
converts septage into a stable, humus material that
can be used as a soil amendment. This process
tends to create odors that can be a problem if not
handled properly.
After the septage is stabilized, it is then sent for
former treatment or disposal, which is described in
the sections that follow.
Land application
Land application of septage is currently the most
commonly used disposal method in the U.S. It is
relatively simple and cost-effective, uses low
energy, and recycles organic material and nutrients
to the land.
With proper management, domestic septage is a
resource containing nutrients that can condition the
soil and decrease the reliance on chemical fertilizers
for agriculture. ^ Septage management maximizes
these benefits of septage while protecting public
health and the environment.
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Land application includes spreading septage from
septage hauler trucks, specially designed land
application vehicles, or tank wagons onto sites
using spray irrigation, ridge and furrow irrigation,
and overland flow.
Treatment at Wastewater Treatment Plants
A convenient and attractive option for septage
treatment is performing the treatment at a
wastewater treatment facility. The constituents of
septage are similar to domestic sewage, even
though septage is stronger and more concentrated.
The advantages of treating septage at wastewater
treatment plants are that many plants are capable of
handling some septage and that it centralizes waste
treatment operations. The four main approaches to
treating septage at a wastewater treatment plant are:
To Upstream Sewer Manhole
When septage is added to a sewer upstream of the
wastewater treatment plant, substantial dilution of
septage occurs prior to it reaching the wastewater
treatment plant. This method is only feasible with
large sewers and treatment plants. It is economical
due to the very simple receiving station design.
However, there is the potential for grit and debris to
accumulate hi the sewer and for odor problems near
the manhole.
To Plant Headworks
Septage can be added to sewage immediately
upstream of the screening and grit removal
processes. This method, like the one mentioned
above, is economical because of the very simple
receiving station design. It also allows the
wastewater treatment plant staff to have control of
the septage discharge.
To Sludge Handling Process
Septage can also be handled as sludge and
processed with wastewater treatment plant sludge
after pretreatment in the receiving station. This
method reduces the loading to liquid stream
processes, and it eliminates the potential for
affecting effluent quality. However, there could be
an adverse effect on the sludge treatment processes,
such as dewatering. Adding septage to the sludge
handling process may also cause clogging of the
pipes and increase wear on the pumps if the septage
is not screened and degritted in the receiving
station.
To Both Liquid Stream and Sludge Handling
Processes
Septage can also be pretreated to separate liquid and
solid fractions, which are then processed
accordingly. This provides more concentrated
sludge for processing and.reduces the organic
loading to liquid stream processes and the hydraulic
loading to sludge processes. Increased operations
are required for septage.- pretreatment at the
receiving station.
COST
Cost considerations cannot be generalized because
of the wide range of options available for septage
management. The cost of a septage management
system is dependent on the treatment and disposal
method used and the regulatory requirements of a
particular area.
Administrators of a septage management program
should be aware of disposal options and the cost
involved. The median cost of disposal (or tipping
fee) typically ranges from 3 to 6 cents per gallon.
REFERENCES
1. Brown, D. V. and R. K. White. December
1977. "Septage Disposal Alternatives in
Rural Areas." Ohio Agricultural Research
and Development Center. Research Bulletin
1096. Cooperative Extension Service. The
Ohio State University Extension Bulletin
624.
2. Septage Handling Task Force. 1997.
Septage Handling. Water Environment
Federation (WEF) Manual of Practice No.
24. WEF. Alexandria, Virginia.
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3. Ungvarsky, J. and K. Mancl. 1982. "Septage
Use and Disposal." Special Circular 317.
The Pennsylvania State University. College
of Agriculture, Extension Service.
4. U.S. EPA, 1984. Handbook: Septage
Treatment and Disposal. EPA Municipal
Environmental Research Laboratory.
Cincinnati, Ohio. EPA-625/6-84-009.
5: U.S. EPA, 1994. Guide to Septage
Treatment and Disposal. EPA Office of
Research and Development. Washington,
D.C. EPA/625/R-94/002.
ADDITIONAL INFORMATION
Lisa Dvello
Director at Large
Town of Flower Mound
2121 Cross Timbers Road
Lewisville, TX 75028
Daniel Balboa
Director at Large
Balboa Septic Design
3470 Jack C. Hays Trail
Buda, TX78610
The mention of trade names or commercial
products does not constitute endorsement or
recommendation for use by the U.S. Environmental
Proteqtion Agency.
For more information contact:
Municipal Technology Branch
U.S. EPA
Mail Code 4204
401 M St., S.W.
Washington, D.C., 20460
iMTB
Excellence m compliance through optimal technical
MUNICIPAL TECHNOLOGY BRANCH
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