r/EPA
United States
Environmental Protection
Agency
Biosolids Technology Fact Sheet
Use of Incineration for Biosolids Management
DESCRIPTION
Incineration is combustion in the presence of air.
Incineration of wastewater solids takes place in two
steps. The first is drying the solids, so that their
temperature is raised to the point that water in the
solids evaporates. The second step is the actual
combustion of the volatile fraction of the solids.
Combustion can only take place after sufficient
water is removed.
Wastewater solids are dewatered to between 15 to
35 percent solids prior to incineration. The
incineration process then converts biosolids into
inert ash. Sixty-five to 75 percent of the solids are
combustible, and thus the volume of ash is
significantly lower than that of the original
biosolids. This ash can be used or disposed of more
readily due to its low volume and inert nature. If
solids are dewatered to approximately 30 percent
solids and their heat value is sufficient, the process
can be self-sustaining, and supplemental fuel is not
required to sustain combustion. Nonetheless,
supplemental fuel is always needed during initial
start-up operations and periodically throughout
operations to accommodate fluctuation in feed
solids characteristics.
Ash generated by incineration of wastewater solids
is usually landfilled, but some facilities use other
innovative methods to reuse the ash, including:
• Filler in cement and brick manufacturing.
• Subbase material for road construction.
Daily landfill cover (must be pelletized
first).
Ingredient in footing at athletic facilities,
including baseball diamonds, and equestrian
facilities, such as race tracks and arenas.
Two types of incineration systems are commonly
used for wastewater solids combustion - multiple
hearth furnaces (MHFs) and fluidized bed furnaces
(FBFs). Both use high temperatures to thermally
process the solids in the presence of air. Because
FBFs are generally better at meeting federal
emission standards, most new installations use this
technology. Some facilities with MHFs
incorporate FBF technology to comply with more
recent federal regulations. The following
paragraphs describe the two systems in greater
detail.
Multiple Hearth Furnace Technology
The multiple hearth technology has historically
been the most common system used for wastewater
solids incineration. MHF systems may be operated
continuously or intermittently; however, the costs
and energy requirements for start-up and standby
are high, making continuous operation preferable.
The furnace consists of a refractory-lined, circular
steel shell with several shelves (or hearths) and a
central, rotating hollow cast iron shaft from which
arms extend. Solids are fed onto the top hearth and
raked slowly to the center in a spiral path. The
solids burn on the middle hearth, producing
temperatures in excess of 482°C (900°F). Ash is
cooled on the bottom zone prior to discharge.
Solids burning on the hearth release heat and
generate a flow of hot gases that rise
countercurrent to incoming solids. This
countercurrent flow of air and solids is reused to
optimize combustion efficiency - while most of
the exhaust air is discharged through the hollow
central shaft, a portion is piped to the lowest hearth
where it is further heated by the hot ash and used
to dry the incoming solids. Discharged air is sent
through a scrubber to remove fly ash, and is then
processed further to meet air permit requirements.
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Ash removal at MHFs is accomplished by the
rabble arms which push the hot ash on the lowest
hearth through a drop out port. Conveyors or
pneumatic equipment move the ash either into
temporary on-site storage or directly into trucks for
transport off- site.
A typical MHF has 5 to 12 hearths, is 1.8 to 7.6 m
(6 to 25 ft) in diameter, and 3.6 to 19.8 m (12 to 65
ft) in height. Nine hearths are generally required
Cooling Air
Discharge
for complete combustion of wastewater solids that
contain 75 to 80 percent moisture. Figure 1 shows
a cross section of a typical MHF.
Fluidized Bed Furnace Technology
Most wastewater solids incineration installations
over the past 20 years have been FBFs, which are
more efficient, more stable, and easier to operate
than are MHFs. Like MHFs, FBFs are vertically
Sludge Cake,
Screenings,
and Grit
Auxiliary
Air Ports
Rabble Arm
2 or 4 Per
Hearth
Gas Flow
Clinker
Breaker
Burners
Supplemental
Fuel
Combustion Air
Shaft
Cooling Air Return
Solids Flow
** Drop Holes
Ash
Discharge
Shaft Cooling
Air
Source: WEF, 1992a.
FIGURE 1 CROSS SECTION OF A TYPICAL MHF
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oriented, refractory-lined, steel shell cylinders. The
bottom layer is an inert granular material (usually
sand) that is kept in fluid condition during operation
by an upflow of air. The sand bed, typically
between 0.8-1.0 m (2.5-3 ft) thick, serves as a heat
reservoir to promote uniform combustion. The bed
is preheated to approximately 649°C (1200°F) using
fuel oil or gas before solids are introduced. Solids
are fed through nozzles into the fluidized sand bed,
where solids and heated sands mix. It is here that
liquid is evaporated from the solids and the volatile
fraction of the solids burns. Temperatures between
760-816°C (1400-1500°F) are maintained in the
combustion zone. The overall combustion process
occurs in the bed and in the freeboard area while the
resulting ash and water vapor are carried out
through the top of the furnace. A cyclonic wet
scrubber is used to remove ash from the exhaust
gases, after which it is separated from the scrubber
water in a cyclone separator. Alternately, some
plants use lagoons for long-term storage of wet ash
and periodically dredge the solids from the lagoon.
Plants with limited space use mechanical
dewatering equipment, such as a multiclone or bag
house, in combination with gas cooling equipment.
Figure 2 shows a cross section of a typical FBF,
which is 2.7 - 7.6 m (9-25 ft) in freeboard
diameter with a 0.8 m (2.5 ft) thick sand bed.
Air Pollution Control Equipment
Air pollution control is an integral part of any
incineration facility. Equipment must be able to
control particulate emissions, gases [such as
nitrogen oxides (NOX), sulfur oxides (SOX) and
carbon monoxide (CO)], and other characteristics
such as opacity.
Particulates
Particulates, including trace metals, can be
controlled through use of mechanical collectors, wet
scrubbers, fabric filters, and electrostatic
precipitators.
Mechanical collectors have a relatively low control
efficiency and usually provide only partial
control in a total particulate emissions control
system. Mechanical collectors include settling
chambers, which use gravity to induce particle
settlement; impingement separators, which cause
particles to lose momentum and drop out of the
gas; and cyclone separators, in which the
incinerator exit gas is forced down a cone of
decreasing diameter. The efficiency of mechanical
collectors ranges from 50-95 percent for particles
larger than 10 • m.
Wet scrubbers are commonly used to remove
particulate matter and water soluble air
contaminants such as hydrogen chloride, sulfur
dioxide, and ammonia. There are several types,
but the Venturi scrubber is the most widely used.
These systems can remove 90-98 percent of
particulate matter as small as 1 • m, depending on
operating conditions.
Fabric filters, or bag houses, pass the incinerator
exhaust gas through a series of fabric filters. These
can achieve removal efficiencies of 99 percent of
particles at submicro sizes. Gas temperatures must
be reduced to less than 149-177°C (300-350°F)
before entry into the fabric filter.
Electrostatic precipitators negatively charge
particles which are then attracted to positively
charged plates. Electrostatic precipitators can be
wet or dry. Wet systems contain a washing
mechanism and generally achieve better removal
efficiencies. Electrostatic precipitators are most
effective when used in combination with
mechanical collectors. Efficiencies of 99 percent
or greater can be achieved (WEF, 1992a).
Gases
The emission of problematic gases can be reduced
by controlling production of these gases. The
formation of NOX can be reduced through process
adjustments such as operating the burners with low
excess air, staging the combustion process,
recirculating flue gas, and using low-NOx burners
which limit the exposure of fuel to oxygen in the
combustion zone. Reducing agents such as
ammonia and urea can also be used to limit NOX
emissions. Reduction of SOX emissions can be
accomplished through use of wet or dry scrubbers.
Results of a survey reported in Design of
Municipal Wastewater Treatment Plants indicate
that miscellaneous wet scrubbers, Venturi systems
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Exhaust and Ash
Pressure Tap
:luidizing
Air Inlet
Burner
Sand
Feed
Thermocouple,-.
Sludge
Inlet
Startup
Preheat
Burner
For Hot
Windbox
Source: WEF, 1992a.
FIGURE 2 CROSS SECTION OF A TYPICAL FBF
and impingement and cyclone separators were the
most common types of air pollution control
equipment employed at MHF. Similar results were
reported at FBF facilities (WEF, 1992).
FBFs generally achieve better removal of
problematic gases due to their higher operating
temperatures (temperatures in excess of 871°C
[1600°F] for FBFs compared to temperatures
between 316-482°C [600- 900°F] for MHFs). The
higher temperatures destroy odorous compounds
and hydrocarbons, which helps to meet emission
standards (WEF, 1992). Afterburners can be used
on MHFs to raise exhaust gases to sufficient
temperatures to destroy these problematic
compounds. Afterburners are secondary burners
that operate in a temperature range of 600-650°C
(1,100-1,200°F) with efficiencies of 99 percent or
greater. The need for afterburners on MHFs to
reduce air emissions often gives FBFs an economic
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advantage in comparing the technologies for
specific applications.
APPLICABILITY
Incineration reduces wastewater solids volume by
up to 95 percent. The technology is most applicable
when landfill tipping fees are high, distances to
alternative disposal or beneficial use sites are long,
space at the treatment plant is limited and on-site
treatment of solids is desired, or beneficial use
options are not appropriate.
The composition and characteristics of wastewater
solids are important when considering incineration.
Standards regulate the metals content of incinerated
solids. In addition, moisture content greatly
impacts energy (supplemental fuel) usage.
Incineration is most economical when solids are
dewatered to more than 25 percent solids. In
addition, wastewater treatment plants that find
incineration to be most economical are those that
produce more than 11 Mg dry solids/day (10 dry
tons of solids/day). Usually, the larger the quantity
of solids incinerated, the greater the economies of
scale (i.e., the cost per dry ton goes down as
capacity increases). Many incinerators even receive
wastewater solids from other plants to improve the
economics of the facility. Some wastewater solids
producers generate additional revenues by serving
as regional processing facilities, resulting in cost
savings to both the incinerator operator/owner and
the "customer" solids producers.
Changes in wastewater constituents or solids
processing may impact the potential for energy
recovery. It is generally preferable to burn
raw rather than digested material due to heat
values. The heat of combustion ranges from 18,624-
30,264 kJ/dry kg of solids [8,000 to 13,000
BTU/dry Ib] for primary wastewater solids to
11,640-23,280 kJ/dry kg of solids (5,000 -
10,000 BTU/dry Ib) for combined primary and
waste activated solids. By comparison,
anaerobically digested primary solids have a heating
value of approximately 12,804 kJ/dry kg of solids
(5,500 BTU/dry Ib). Because this incineration is
less efficient, these facilities require more auxiliary
fuel and have additional capital and annual
operation and maintenance costs associated with the
digestion process.
ADVANTAGES AND DISADVANTAGES
Advantages and disadvantages of using
incineration systems for solids disposal, vs.
disposing of solids in a landfill or through
stabilization followed by use as a fertilizer or soil
conditioner, are provided below.
Advantages
Volume reduction.
Generation of stable material. Ash is a
stable, sterile material, effectively
eliminating storage and handling problems.
• Potential energy recovery.
• Minimal land area required.
Disadvantages
• High capital investment.
In most cases, annual operating costs
depend on fuel costs.
• Consumption of non-renewable resources
(oil and/or natural gas).
• Limited feasibility in nonattainment areas.
Potential operating problems. Incinerators
experience significant down time for
routine maintenance and therefore require
redundancy, backup, or storage. High
technology instrumentation is required to
comply with air pollution control permits.
• Potential for public opposition.
Modern incineration facilities generally do not
present a significant health risk to the community
if they are equipped with adequately maintained
process control and air pollution control equipment
and are operated by trained employees. An
important goal of 40 CFRPart503, SubpartEisto
provide assurance that air pollution impacts are
reduced to the maximum extent possible.
Dangtran, et al., 2000, conclude that design
differences between the MFH and FBF
technologies lead to the following advantages for
FBF:
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• Lower NOX, CO, and total hydrocarbon
(THC) formation.
More suitable for intermittent operation.
Allows feed variability and reduces chance
of thermal shock.
• Ease of control and automation.
• Lower auxiliary fuel usage.
Reduced maintenance cost.
• Smaller air pollution control system.
• Lower power requirements.
• Easier ash removal from off gases.
Table 1 presents a comparison of the MHF and FBF
technologies.
DESIGN CRITERIA
The first step in designing an incineration system is
development of a material balance. The total
amount of solids to be processed, including the
average (hourly, daily, monthly) and peak amounts,
must be known. The specific characteristics of the
feed solids, including moisture content, percent
volatile solids, heat value, and concentration of
specific inorganics, must also be known. Based on
this information, a heat balance can be developed
using the proj ected characteristics of the feed solids.
In addition to the furnace, the major physical
components of an incineration system include:
• Conveyance of feed solids to the furnace.
• Ash handling, including removal from the
furnace and final use or disposal.
• Air emission/pollution controls.
• Solids handling during peak production to
equalize feed to the furnace.
Supplemental fuel storage and availability.
Incineration systems are designed to handle a
specific range in solids volume and characteristics
as determined through the mass balance and heat
balance performed in designing a system.
TABLE 1 COMPARISON OF MHF AND FBF
Parameter
Multiple
Hearth
Furnace
Fluidized Bed
Furnace
Flow
Heat Transfer
Solids Detention
Time
Gas Detention
Time at High
Temperature
Combustion
Temperature
Gas Exit
Temperature
Excess Air
Countercurrent
Poor
1/2-3 h
1 to 3 sec
1400 to 1800--F
800 to 1400- -F
75 to 100 percent
Intense back
mixing
High
1 to 5 min
6 to 8 sec
1400to1600"F
1500tol600"F
40 percent
Source: Dangtran, etal, 2000.
Provisions for temporary holding and storage help
to even out the solids flow to the furnace. Feed
volume should be maintained within the design
range to ensure efficient operations. Incineration
systems can handle routine fluctuations in solids
characteristics, but fluctuations outside the
established acceptable range may necessitate
operational changes, such as increasing the amount
of auxiliary fuel necessary to continue combustion.
Applicability of Windboxes
FBF systems can be designed to use air which is
either preheated or at ambient temperature. With
ambient air (cold windbox technology), no
preprocessing of the air fed to the furnace is
performed. With a hot windbox, combustion air is
preheated to approximately 538'C (1000'F) before
it is introduced to the furnace. This step serves to
increase thermal efficiencies, and reduces fuel
costs by about 60 percent. However, the addition
of preheating equipment may increase system
capital costs by as much as 15 percent (Bruner,
1980). An economic evaluation will determine the
most cost effective option for a particular facility.
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PERFORMANCE
In 1993, EPA estimated that 343 biosolids
incinerators were in operation in the United States.
Of these, approximately 80 percent were MHFs and
20 percent were FBFs. Siting and development of
new incinerators to manage wastewater solids has
been limited in recent years at least partly because
of EPA's beneficial reuse policy for wastewater
solids. Currently, approximately 254 incinerators
for wastewater solids are operating in the United
States. These facilities process an estimated
865,000 Mg (785,000 tons) per year (Dominak,
2001). Dangtran, et al., (2000) indicates that there
have been 43 new incineration systems installed for
managing wastewater solids since 1988, all of
which use the fluid bed technology. Eleven of these
replaced existing multiple hearth facilities.
Wastewater solids incinerators are regulated under
Section 112 of the 1990 Clean Air Act Amendments
(CAAA), which require incinerators classified as a
major source of emissions (those that could emit 9
Mg [10 tons] or more per year of any of 189
identified pollutants or 23 Mg [25 tons] or more per
year of any combination of the 189 pollutants) to
meet technology-based standards. Incinerators that
do not meet the definition as a major emissions
source are still regulated for emission of 30 selected
pollutants, including alkylated lead compounds,
polycyclic organic matter, hexachlorobenzene,
mercury, polychlorinated biphenyls, dioxins, and
furans.
Specific regulatory limits for wastewater solids
incinerators are as follows:
• Particulate emissions may not exceed 0.65
kg/Mg (1.3 Ib/ton) of solids incinerated at 7
percent oxygen (40 CFRPart 60 Subpart O).
Opacity (visible emissions) may not exceed
20 percent for a 6-min average period (40
CFRPart 60 Subpart O).
• Emissions of beryllium and mercury may
not exceed 10 g and 1,200 g, respectively, in
a 24-hour period (40 CFR Part 61 Subparts
C and E).
Average daily concentration of lead fed to
an incinerator may not exceed a
concentration calculated using the
following equation (40 CFR Part 503
Subpart E):
0.1xNAAQSx86,400
DFx(l-CE)xSF
where:
NAAQS = National Ambient Air Quality
Standard for lead (• g/m3).
DF = Dispersion factor as determined in
accordance with 40 CFR Part
503.42(e)('g/m3/g/s).
CE = Incinerator control efficiency for lead
determined through performance
testing in accordance with 40 CFR
Part 503.43(e).
SF = Solids feed rate (Mg/day, dry weight
basis).
Average daily concentrations of arsenic,
cadmium, chromium and nickel fed to an
incinerator may not exceed a concentration
calculated using the following equation (40
CFR Part 503 Subpart E):
RSCx86,400
DFx(l-CE)xSF
where:
RSC = Risk specific concentration (• g/m3)
provided in Tables 1 and 2 of 40
CFR Part 503.43.
DF = Dispersion factor as determined in
accordance with 40 CFR Part
503.42(e)('g/m3/g/s).
CE = Incinerator control efficiency for lead
determined through performance
testing in accordance with 40 CFR
Part 503.43(e).
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SF = Solids feed rate (Mg/day, dry weight
basis).
The monthly average concentration for THC
emissions as propane (corrected for zero percent
moisture and seven percent oxygen) may not exceed
100 ppm on a volumetric basis (40 CFR Part 503
Subpart E).
The National Ambient Air Quality Standards also
apply to wastewater solids incinerators. Any source
emitting more than 92 Mg (100 tons) per year must
obtain a Title V operating permit. Facilities emitting
between 23- 92 Mg (25-100 tons) of NOX per year
may be classified as a major source depending on
area attainment classification.
Typically, MHFs have simple solids feed and ash
handling equipment but produce high CO and NOX
emissions. FBFs have low CO and NOX emissions
but require complex solids feed and ash handling
systems. The main contributor to the formation of
NOX is nitrogen in the wastewater solids, so
operating MHFs at high hearth temperatures causes
NOX emissions to increase by 0.5-1 kg/Mg (1-2
Ib/ton) of solids processed. Conventional external or
top hearth afterburners also produce significantly
higher NOX emissions because they consume large
amounts of fossil fuels.
OPERATION AND MAINTENANCE
The dry solids content in wastewater solids has a
significant effect on the operation of thermal
processes due to the high energy associated with
evaporation. FBFs may be used for intermittent
operation with a minimum amount of start-up time.
FBFs will "warm up" at the beginning of the week
from about 400°F and feed continuously. The week
ends with a gradual cool down and a
discontinuation of feed on Friday afternoon.
Gradual heating and cooling minimizes
maintenance of the refractory lining as well as
downtime. FBFs also require less excess air and
less fuel than MHFs.
• Frequent need for supplementary fuel to
maintain the incineration process.
• Emission of volatile compounds or NOX
from the incinerator.
To overcome the NOX emission problem, oxygen
enrichment can be used to increase the waste
combustion capacity when gas residence time, flue
gas flow rate, or combustion air fan capacity are
the limiting factors. This will provide more oxygen
for combustion for a given amount of flue gas
produced. A second effect of oxygen enrichment
is that it displaces inert nitrogen, which is a heat
sink. Oxygen injection for MHFs has been
demonstrated successfully. The increased
throughput and reduced auxiliary fuel consumption
can be achieved and oxygen injection can be
economically viable. This provides an additional
tool for the furnace operator to respond rapidly to
changes in the feed. A "troubleshooting guide" for
multiple hearth furnaces is provided in Table 2.
Fluidized Bed Furnace
It is important to maintain a steady and consistent
feed rate to a FBF in order to maintain low NOX
emissions. Emissions testing of the FBF confirms
that low average NOX concentrations can be
achieved by maintaining the furnace oxygen
concentration at less than 5.0 percent, keeping
freeboard temperatures between 816°C and 843°C
(1500°F-1550°F), and setting the fluidizing air
blower at a minimum air flow rate (Sapienza et al.,
1998). Table 3 provides a "troubleshooting guide"
for fluidized bed incineration.
Multiple Hearth Furnace
Two main operational problems associated with
MHFs include:
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TABLE 2 TROUBLESHOOTING GUIDE FOR INCINERATION - MULTIPLE HEARTH
INCINERATION
Problem
Probable Cause
Solution
Furnace temperature too high
Furnace temperature too low
Excessive fuel feed rate
Greasy solids
Thermocouple burned out
Moisture content of sludge has
increased
Fuel system malfunction
Excessive air feed rate
Sludge feed rate too low
Air feed rate too high
Air feed excessive above burn zone
Oxygen content of stack gas is too low Volatile or grease content of sludge
has increased
Air feed rate too low
Furnace refractories have deteriorated Furnace has been started up and shut
down too quickly
Unusually high cooling effect from one Air leak
hearth to another
Oxygen content of stack gas is too
high
Short hearth life
Center shaft drive shear pin fails
Uneven firing
Rabble arm is dragging on hearth or
foreign object is caught beneath arm
Furnace scrubber temperature too high Low water flow to scrubber
Stack gas temperatures too low (260
to 320'C [500 to 600T];odors noted
Stack gas temperatures too high (650
to870'C[1,200to1,600'F]
Inadequate fuel feed rate or excessive
sludge feed rate
Excessive heat value in sludge or
excessive sludge feed rate
Decrease fuel feed rate
If fuel is off and temperature is rising,
this may be the cause; raise air feed
rate or reduce sludge feed rate
If temperature indicator is off scale,
this is likely the cause; replace
thermocouple
Increase fuel feed rate until dewatering
system operation is improved
Check fuel system; establish proper
fuel feed rate
If oxygen content of stack gas is
high.this is likely the cause; reduce air
feed rate or increase feed rate
Remove any blockages and establish
proper feed rate
Decrease air feed rate
Check doors and peepholes above
burn zone; close as necessary
Increase air feed rate or decrease
sludge feed rate
Check for malfunction of air supply,
and increase air feed rate, if necessary
Replace refractories and observe
proper heating and cooling procedures
in the future
Check hearth doors, discharge pipe,
center shaft seal, air butterfly valves in
inactive burners, and stop leak
Check all burners in hearth; fire
hearths equally on both sides
Correct cause of problem and replace
shear pin
Establish adequate scrubber water
flow
Increase fuel or decrease sludge feed
rates
Add more excess air or decrease fuel
rate
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TABLE 2 (CONTINUED) TROUBLESHOOTING GUIDE FOR INCINERATION - MULTIPLE
HEARTH INCINERATION
Problem
Probable Cause
Solution
Furnace burners slagging up
Rabble arms are drooping
Burner design
Air-fuel mixture is off
Excessive hearth temperatures or loss
of cooling air
Consult manufacturer and replace
burners with newer designs that
minimize slagging
Consult manufacturer
Maintain temperatures in proper range
and maintain backup systems for
cooling air in working condition;
discontinue scum injection into hearth
Source: Modified from WEF, 1996.
COSTS
The cost of incineration is a function of many
factors, including:
Furnace type, size, and manufacturer.
• Solids content of the feed. The effect of
solids content on fuel economics will
vary as a function of the type of furnace
and the temperature oxidation design used
(i.e., temperature raised in the furnace
itself or in an external unit before or after
scrubbing of the gases).
• Volatile solids content and heating value of
the feed.
Various design considerations, such as
energy efficiency of the system.
• Local labor costs.
• Air emission control requirements.
The economics of incineration should be evaluated
as part of an overall system design incorporating
dewatering, combustion, air pollution control, and
ash management. Furthermore, the system should
be analyzed on a sensitivity basis, specifically
evaluating the effects of solids concentration on the
capital and annual operation and maintenance
(O&M) costs for each process train.
Due to additional requirements of Part 503
regulations, continuous monitoring of feed rate,
stack gas oxygen content, and stack gas moisture
content have contributed to the increase of
operational costs. These cost increases result in
greater workload for facility operators. Retrofit
costs associated with Part 503 risk reduction from
metal emissions are based on exposure of the most
exposed individual to the metals of concern, and
the risk can be reduced by improving dispersion
characteristics, reducing emissions, or a
combination of both. These retrofitting
adjustments, such as a THC monitor, have been the
primary reason for operational cost increases. The
cost of installing new stacks or extending the
height of the existing stack is site specific and the
cost of extensions or replacement stacks is
dependent on the choice of material and
configuration. Typical annual O&M costs quoted
in one study range from $83-$269/dry Mg ($76-
$245/dry ton) (adjusted using 2002 ENR values)
(Walsh et al., 1990). The adjusted 2002 O&M
costs for a multiple hearth facility retrofitted with
additional air pollution control equipment to
comply with the Part 503 Regulations are
approximately $270/dry Mg ($244/dry ton) per day
processed.
The results of a recent study of one wastewater
solids facility estimated the annual operating costs
(including amortization of capital costs) to be
$22/wet Mg ($20/wet ton) including a $7.39/wet
Mg ($6.70/wet variable nature of operating costs,
this same report notes that actual O&M costs
increased from $17.26-
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TABLE 3 TROUBLESHOOTING GUIDE FOR INCINERATION - FLUIDIZED BED
INCINERATION
Problem
Probable Cause
Solution
Bed temperature is falling
Low (<4%) oxygen in exhaust gas
Excessive (>6%) oxygen in exhaust
gas
Erratic bed depth readings on control
panel
Inadequate fuel supply
Excessive rate of sludge feed
Excessive sludge moisture
Excessive air flow
Low air flow
Fuel rate too high
Sludge feed rate too low
Bed pressure taps plugged with solids
Preheat burner fails and alarm sounds Pilot flame not receiving fuel
Pilot flame not receiving spark
Pressure regulators defective
Bed temperatures too high
Bed temperature reads off scale
High scrubber temperature
Reactor sludge feed pump fails
Poor bed fluidization
Pilot flame ignites but flame scanner
malfunctions
Fuel feed rate too high through bed
guns
Bed guns have been turned off but
temperature still too high because of
greasy solids or increased heat value
of sludge
Thermocouple burned out or controller
malfunction
No water flowing in scrubber
Spray nozzles plugged
Water not recirculating
Bed temperature interlocks may have
shutdown the pump
Pump is blocked
During shutdowns, sand has leaked
through support plate
Increase fuel feed rate or repair any
fuel system malfunctions
Decrease sludge feed rate
Improve dewatering system operation
Reduce air rate if oxygen content of
exhaust gas exceeds 6%
Increase air blower rate
Decrease fuel rate
Increase sludge feed rate and adjust
fuel rate to maintain steady bed
temperature
Tap a metal rod into the pressure tap
when reactor is not in operation
Apply compressed air to pressure tap
while the reactor is in operation after
reviewing manufacturer's safety
instructions
Open appropriate valves and establish
fuel supply
Remove spark plug and check for
spark; check transformer, replace
defective part
Disassemble and thoroughly clean
regulators
Clean sight glass on scanner, replace
defective scanner
Decrease fuel flow rate through bed
guns
Raise air flow rate or decrease sludge
feed rate
Check the entire control system; repair
as necessary
Open valves
Clean nozzles and strainers
Return pump to service or remove
scrubber blockage
Check bed temperature
Dilute feed sludge with water if sludge
is too concentrated
Once per month, clean windbox
Source: Modified from WEF, 1996.
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$23.367 wet ton when processing tonnage dropped
from 82,600 wet Mg (91,000 wet tons) to 75,500
wet Mg (68,500 wet tons). No other system
changes were noted during this time. In
comparison, this same report estimates the
comparable cost of landfilling in this geographic
area to be almost $55/wet Mg ($50/wet ton) and the
cost of land application to be between $66-$88 per
wet Mg ($60-$80 per wet ton) (Dominak, 2001).
Since relatively few new incineration facilities are
being constructed, accurate capital cost information
is difficult to locate. Capital costs for a new FBF
facility constructed in North Carolina in 1994 are
quoted at $6 million. This facility serves two plants
with combined capacity of 136,000 m3/day (36
MGD). This figure does not include dewatering but
does include some ancillary modification to existing
plant buildings. The capital investment in terms of
processing capacity is estimated at $66/dry Mg
($60/dry ton). In comparison, landfill disposal for
the same situation was estimated to be $ 127/dry Mg
($115/dry ton). Land application costs are
approximately $15.40/dry Mg ($14/dry ton [see
EPA's fact sheet on Use of Land Application for
Biosolids Management]).
Table 4 presents the capital costs of the various air
pollution control strategies. This information was
generated to address existing facilities that needed
to be updated to address new regulatory
requirements imposed by Part 503 Regulations.
REFERENCES
Other Related Fact Sheets
Other EPA Fact Sheets can be found at the
following web address:
http://www.epa.gov/owm/mtb/mtbfact.htm
1. Baturay, A., 1999. "Incinerator
Emissions." Water Environment &
Technology. Vol. 11, No. 5, pp. 49 - 53.
2. Bauer, T. andR.B. Sieger, 1993. "Sewage
Sludge Incineration Under Part 503B."
Water/Engineer ing & Management. No. 10,
pp 22-23.
TABLE 4 TYPICAL COSTS OF AIR
POLLUTION CONTROL EQUIPMENT
Equipment
Costs ($)
Multiple Venturi Systems
Wet Electrostatic Precipitator
Internal Afterburner Retrofit
Top Hearth Afterburner Retrofit
Conventional External Afterburner
Side-Flue Afterburner Retrofit
Side-Exit Afterburner Retrofit
Post-Scrubber Afterburner
100,000-200,000
150,000-500,000
50,000-75,000
50,000-75,000
400,000-700,000
300,000-400,000
600,000-800,000
400,000-700,000
* Range based on size
Source: Batuary, 1999.
Brown, J.W., M.F. Brown, J.F. Buresh, and
T.B. Taylor, 1996. "Cost of Compliance
with Part 503 Total Hydrocarbon Limits at
a Large Biosolids Incineration Facility." In
Proceedings of the 10th Annual Residuals
and Biosolids Management Conference: 10
Years of Progress and a Look Toward the
Future. Alexandria: Water Environment
Federation.
Bruner, C., 1980. "Design of Sewage
Sludge Incineration Systems." Pollution
Technology Review No. 71. Park Ridge:
Noyes Data Corporation.
Dangtran, K., J.F. Mullen, and D.T.
Mayrose, 2000. "A Comparison of Fluid
Bed and Multiple Hearth Biosolids
Incineration." In Proceedings of the 14th
Annual Residuals and Sludge Management
Conference. Alexandria: Water
Environment Federation.
Dominak, R.P., 2001. "Current Practices
and Future Direction for Biosolids
Incinerators." In Proceedings of the Water
Environment Federation/American Water
Works Joint Residuals and Biosolids
Management Conference, Biosolids 2001:
Building Public Support. Alexandria:
Water Environment Federation.
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7. Kuchenrither, R.D., P.M. Martin, E.W.
Waltz, and B. Dellinger, 1995. "Clearing
the Air About Sludge Incinerator
Emissions." In Proceedings of the Water 15.
Environment Federation 68th Annual
Conference and Exposition. Alexandria:
Water Environment Federation.
8. Leger, C.B., 1998. "Oxygen Injection for 16.
Multiple Hearth Sludge Incinerators." In
Proceedings of The 12th Annual Residuals
and Biosolids Management Conference.
Alexandria: Water Environment Federation.
17.
9. Lewis, F.M., D. Graber, and J. Brand, 1997.
"Increasing the Capacity of Existing Fluid
Bed Sludge Incinerators." In Proceedings
of Water Residuals and Biosolids
Management: Approaching the Year 2000.
Alexandria: Water Environment Federation. 18.
10. Lue-Hing, C., D.R. Zenz, and R.
Kuchenrither, 1992. Municipal Sewage
Sludge Management: Processing,
Utilization and Disposal., Volume 4.
Lancaster: Technomic Publishing. 19.
11. Lundberg, L.A., B.D. Meckel, N.J.
Marchese, 1995. "What To Do With An
Existing Multiple Hearth Furnace:
Rehabilitate, Replace or Convert it to a 20.
Fluidized Bed Furnace." In Proceedings of
the Water Environment Federation 68th
Annual Conference and Exposition.
Alexandria: Water Environment Federation.
Management. Silver Springs: Hazardous
Materials Control Research Institute.
Shamat, N., and Hart, 1992. "Dewatering
and Incinerating Wastewater Solids."
Water Environment & Technology. Vol. 4,
No. 10.
U.S. EPA, 1993. Standards for the Use or
Disposal of Sewage Sludge (40 Code of
Federal Regulations Part 503).
Washington D.C.: U.S. EPA.
Vesilind, P.A., and T.B. Ramsey, 1992.
"Effect of Drying Temperature on the Fuel
Value of Wastewater Sludge." Wastewater
Management and Research, Volume 14,
page 189.
Walsh, M.J., A.B. Pincince, and W.R.
Niessen, 1990. "Energy Efficient
Municipal Sludge Incineration." Water
Environment & Technology. Vol. 2, No.
10. pp. 36-43.
Water Environment Federation, 1992.
Sludge Incineration, Manual of Practice
FD-19. Alexandria: Water Environment
Federation.
Water Environment Federation, 1992.
Design of Municipal Wastewater
Treatment Plants, Volume II, WEFManual
of Practice No. 8. Brattleboro: Book Press,
Inc.
12.
13.
14.
RHOX International, Inc., 1989.
Process Technical Bulletin.
RHOX 21.
Sapienza, F.C., R. Canham, and A. Baturay,
1998. "NOX Emissions from the PWCSA's
Fluidized Bed Sludge Incinerator." In
Proceedings of The 12th Annual Residuals 22.
and Biosolids Management Conference.
Alexandria: Water Environment Federation.
Shamat, N., and S.J. Greenwood, 1989.
"Multiple Hearth Incinerators." In
Proceedings of the National Conference on
Municipal Sewage Treatment Plant Sludge 23.
Water Environment Federation, 1996.
Operation of Municipal Wastewater
Treatment Plants, Manual of Practice
Number 11. Alexandria: Water
Environment Federation.
White, A, D. Mayrose, and J.F. Mullen,
1999. "Replacement of a Multiple Hearth
with a Fluidized Bed Incinerator: The
Greensboro Experience." Presented at
International Conference on Incineration
and Thermal Treatment Technologies.
Zaman, R.U., 1996. "Performance of Fluid
Bed Biosolids Incinerator Systems." In
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Proceedings of the 10th Annual Residuals
andBiosolids Management Conference: 10
Years of Progress and a Look Toward the
Future. Alexandria: Water Environment
Federation.
ADDITIONAL INFORMATION
The following facilities incinerate wastewater
solids:
Allegheny County Sanitary Authority
Carole Shanahan
3300 Preble Avenue
Pittsburgh, Pennsylvania 15233
Prince William County Service Authority
Robert Canham
P.O. Box 2266
Woodbridge, Virginia 22195-2266
Central Contra Costa Sanitary District
Doug Craig
5019 Imhoff Place
Martinez, California 94553
Metropolitan Council
Dave Quast
Mears Park Center
230 East 5th Street
St. Paul, Minnesota 55101
Palo Alto Regional Water Quality Control Plant
Daisy Stark
2501 Embarcadero Way
Palo Alto, California 94303
Northeast Ohio Regional Sewer District
Robert Dominak
3 826 Euclid Ave.
Cleveland, Ohio 44115
The mention of trade names or commercial
products does not constitute endorsement or
recommendation for use by the U.S.
Environmental Protection Agency.
Office of Water
EPA 832-F-03-013
June 2003
For more information contact:
Municipal Technology Branch
U.S. EPA
Mail Code 4204M
1200 Pennsylvania Avenue, NW
Washington, D.C. 20460
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Excellence in compliance through optimal technical solutions
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