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 482C (900F). 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 649C (1200F) 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
760-816C (1400-1500F)  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 149-177C  (300-350F)
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 871C
[1600F]  for  FBFs compared to  temperatures
between 316-482C [600- 900F] 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 600-650C
(1,100-1,200F) 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 400F 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 816C and 843C
(1500F-1550F), 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
                                                         MUNICIPAL TECHNOLOGY BRANlfhf

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