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MEMORANDUM 

To: Amy Hambrick, U.S. EPA, Sector Policies and Programs Division/Natural 

Resources and Commerce Group 

From: Eastern Research Group, Inc. 

Date: January 2011 

Subject: Revised Analysis of Beyond the Maximum Achievable Control Technology 

(MACT) Floor Controls for Existing SSI Units 

1.0 INTRODUCTION 

The U.S. Environmental Protection Agency (EPA), under section 129 of the Clean Air 

Act (CAA), is required to regulate emissions of nine pollutants from existing sewage sludge 

incineration (SSI) units. The nine pollutants are: hydrogen chloride (HCl), carbon monoxide 

(CO), lead (Pb), cadmium (Cd), mercury (Hg), particulate matter (PM), total mass basis 

dioxins/furans (TMB PCDD/PCDF) and toxic equivalency basis dioxin/furans (TEQ 

PCDD/PCDF), nitrogen oxides (NOx), and sulfur dioxide (SO2). The CAA requires EPA to 

determine the maximum achievable control technology (MACT) for each subcategory of sources. 

To do so, EPA must first determine the minimum stringency “floor” requirements. A 

previous memorandum documents the MACT floor analysis for SSI units.1 

EPA must also examine more stringent “beyond-the-floor” (BTF) controls to determine 

MACT. Unlike the minimum stringency requirements of the floor, EPA must consider various 

impacts of the more stringent regulatory options such as costs and emissions reductions in 

determining whether MACT standards are to reflect BTF requirements. This memorandum 

describes the cost and emissions reductions for existing SSI units achieved by applying BTF 

controls. 

Tables 1-1A and 1-1B summarize the costs and emissions reduction calculated for the 

MACT floor level of control and each of the analyzed BTF controls. Table 1-1A shows the cost 

and ‘actual’ emission reductions of the MACT floor and the BTF options, and Table 1-1B shows 

the cost and ‘potential’ emission reductions of the MACT floor and the BTF options applied only 

to larger entities. As described in further detail in the baseline emissions memo2, ‘actual’ emissions 

are based on calculations using actual sludge feed rates, whereas ‘potential’ emissions are based 

on calculations using sludge capacities. 
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Table 1-1. Summary of Cost and Emissions Reductions (tpy) for BTF Controls Analyzed 

A. Costs and Emission Reductions Based on ‘Actual’ Sludge Usage 

Controls 

Analyzed TCI ($) TAC ($/yr) 

Baseline Emissions and Incremental Emission Reductions (tons/year) 

Cd CO HCl Pb Hg NOx PM SO2

PCDD/PCDF 

(mass) 

Baseline Emissions - - 0.9096 8501 28.15 2.3717 0.8942 2380 332.85 702.4 0.000006 1 - MACT Floor $55,047,913 $17,766,866 0.50 0 18.52 1.21 0.0022 6.8 58.1 431.5 0 2 - MACT Floor + AB for MH units $155,314,172 $46,097,268 0.499 6865 18.52 1.21 0.002 6.783 58.1 431.5 0 3 - MACT Floor + AB and ACI/FF for MH units $486,470,566 $138,260,525 0.870 6865 18.52 2.28 0.667 6.783 299.9 431.5 0.00000495 

B. Costs and Emission Reductions Based on ‘Potential’ Sludge Capacity 

Controls 

Analyzed TCI ($) TAC ($/yr) 

Baseline Emissions and Incremental Emission Reductions (tons/year) 

Cd CO HCl Pb Hg NOx PM SO2

PCDD/ 

PCDF (mass) 

Baseline Emissions - - 1.15 11576 43.34 3.0744 1.2099 3277 444.79 1077.5 0.000009 1 - MACT Floor 

$55,047,913 $17,766,866 0.60 0 29.94 1.50 0.0025 15.7 70 697.8 0 

2 - MACT Floor + AB for MH units $155,314,172 $46,097,268 0.60 9354 29.94 1.50 0.00 15.72 69.57 698 0 3 - MACT Floor + AB and ACI/FF for MH units $486,470,566 $138,260,525 1.098 9354 29.94 2.94 0.891 15.72 395.7 697.8 0.00000662 
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The tables show three control scenarios analyzed for SSI units: 

• Combination 1 is the MACT floor level of control for the two subcategories developed 

for existing multiple hearth (MH) units and fluidized bed (FB) units. 

• Combination 2 is the MACT Floor level of control, with the addition of afterburner 

retrofits for additional CO emissions reduction from MH units not already having an 

afterburner. 

• Combination 3 is the MACT Floor level of control, afterburner retrofits for MH units 

not already having them, and the addition of activated carbon injection (ACI) in 

combination with a fabric filter for MH units for additional Hg and PCDD/PCDF 

emissions reduction. 

Section 2.0 discusses the selection of more stringent controls or emissions levels than the floor 

level reviewed for this analysis. Section 3.0 discusses the methodology used to estimate costs and 

emissions reductions of the more stringent controls and Section 4.0 summarizes the controls 

selected for the BTF analysis. 

2.0 SELECTION OF MORE STRINGENT CONTROLS 

The MACT floor analysis for existing sources results in emissions levels that each existing 

SSI unit is required to meet. The costs and emissions reduction of the MACT floor requirements 

were estimated using the following assumptions: (1) units that needed to meet the MACT floor 

for Cd, Pb, and PM would add a venturi scrubber (if they did not have one at proposal) or wet 

electrostatic precipitator (WESP), (2) units that needed to meet the MACT floor for HCl, and 

SO2 would add a packed bed scrubber (PBS), and (3) units that needed to meet the MACT floor 

for NOx would add selective non-catalytic reduction (SNCR). All FB and MH units were 

determined to meet the floor level of control for Hg, PCDD/PCDF, and CO, and no additional 

control was necessary. 

The control technologies that were costed to achieve the MACT floor levels for PM, Cd, 

Pb, HCl, SO2, and NOx are the most effective controls available for SSIs to reduce these 

pollutants, given the high moisture content of SSI flue gas streams. The control effectiveness of 

the control devices used in the MACT floor analyses are discussed in the MACT floor cost and 

emission reductions memorandum.3 Since not every SSI unit was determined to need WESP, 

PBS, or SNCR to achieve the MACT floor level of control or operated them currently (i.e., the 

baseline level of control), these controls were analyzed for the entire SSI source category, which 

would require all units that did not have these controls at baseline or for meeting the MACT 

floors to add these controls. 

For other combustion sources, carbon injection in combination with a FF has proven to be 

highly effective in removing Hg. However, for high moisture flue gas streams, such as emitted 

from SSI units, the use of FFs is problematic due to plugging/fouling. In order to use carbon 

injection with a FF with high moisture streams, a waste heat boiler, RTO, or afterburner is 
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necessary to maintain a high enough temperature to keep the stream above the dew point prior to 

sending the stream to the FF. This control combination was costed as the beyond-the-floor 

control for Hg. Additional equipment may also be necessary to reduce the temperature of the flue 

gas to prevent damage to the fabric filter bags. Sufficient information was not collected to 

estimate this cost; for this cost scenario, costs will be underestimated. Data gathered by EPA 

indicates that ACI applied to combustion sources with particulate control can achieve 85-95 

percent reduction of Hg, depending on the type of particulate control, with higher reductions 

achieved by units with fabric filters and lower reductions achieved by units with electrostatic 

precipitators. Based on efficiencies demonstrated in other source categories and in EPA studies, a 

beyond-the-floor reduction of 90 percent for Hg was used for carbon injection in combination 

with FF applied to existing MH unit controls. Previous EPA studies also show that PCDD/PCDF 

can be reduced by as much as 98 percent using ACI and FF together. 

For CO, the MACT floor level of control for existing MH units is 3,800 ppmvd, corrected 

to 7 percent oxygen. An add-on combustion device, such as an afterburner or thermal oxidizer 

was analyzed as a more stringent control device that could be applied to SSI units. CO emissions 

data were collected from nine MH SSI units as part of the data collection efforts supporting the 

development of emissions standards for SSI units. Table 2-1 summarizes the average CO 

concentration levels from these units.4 The table is grouped into three classes of SSI’s: (1) units 

that do not use any combustion controls, (2) units that use an on-hearth afterburner, and (3) units 

that use either a detached afterburner or thermal oxidizer, or use FGR in combination with an onhearth afterburner. 

Table 2-1. Summary of Average CO Emissions Collected From MH Units 

Classes Facility Location Unit ID 

Average CO emission level 

(ppmvd @ 7% O2) 

Uncontrolled Boat Harbor VA 1 3,761 

On-hearth afterburner 

Seneca MN 1 1,323 

2 853 

Central Contra Costa CA 1 905 

2 752 

Detached afterburner, 

thermal oxidizer, or 

on-hearth afterburner 

with flue gas 

recirculation 

Columbia Metro SC 1 63 

Mountainview NJ 2 39 

Upper Blackstone MA 

1 28 

3 59 

On-hearth afterburners are the top hearth of a MH unit that has been re-designed so that 

sludge is rerouted to the second hearth. Retrofitting the MH unit with an on-hearth afterburner 

may require modifications to downstream air pollution control systems due to higher temperatures 

and larger volumes of exhaust gases.5 While there will be reductions in CO and total hydrocarbon 

(THC) emissions, the reductions may be limited due to low temperature and limited residence 

time of the gas in the afterburner stage. The use of FGR in combination with an on-hearth 

afterburner shows significantly lower emissions levels than just using an on-hearth afterburner. 

However, this may be a generalization because only one data point for this control combination 
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was reviewed. Additionally, performance of FGR is often influenced by site specific parameters 

which may not be generalized to the entire subcategory. 

Table 2-1 shows that MH units using an add-on afterburner or thermal oxidizer can 

achieve CO emission levels less than 100 ppmv. The Clean Water Act (CWA) "503 Rule" [40 

CFR Part 503] limits sewage sludge incinerators to 100 ppm THC as propane, dry basis, 

corrected to 7% oxygen, averaged for 30 days. The CWA 503 Rule allows substitution of 

100 ppm CO dry basis, corrected to 7% oxygen for the THC originally required. The 100 ppm 

CO level was selected because this level was determined to be a level that would be indicative of 

the THC concentration below 100 ppm. This allows the use of a lower cost, easier to maintain 

CO monitor in place of the difficult to keep online THC monitor. To be consistent with the CWA 

503 regulations for disposal of sewage sludge for the beyond-the-floor calculation, a value of 

100 ppmv was used as the emission level that a MH unit with an afterburner could achieve. 

Beyond-the-floor controls were also evaluated for existing FB units. The proposed SSI MACT 

floor CO level for existing FB units (56 ppmvd, corrected to 7 percent oxygen) is well below the 

100 ppmvd emission level of the CWA 503 rule. The application of an afterburner was determined 

not to achieve appreciable CO reduction form the proposed limit for the cost incurred. Therefore, 

no beyond-the-floor CO limit was considered for the FB subcategory. 

3.0 METHODOLOGY USED TO ESTIMATE COST AND EMISSIONS 

REDUCTIONS 

The methodology used to calculate costs and emissions reductions from applying the more 

stringent controls followed the procedures discussed in the SSI Cost memorandum.3 As described 

above, if a unit already had an afterburner, ACI, PBS, FF, or WESP, or needed one of these to 

meet the MACT floor limits, no additional costs were calculated for the beyond-the-floor analysis. 

Otherwise, these controls were costed out for the unit as appropriate. The algorithms, inputs for 

algorithms, and testing, monitoring, recordkeeping, and reporting costs calculations are the same 

as conducted for the MACT floor and are discussed in detail in the MACT floor cost and 

emissions reductions memorandum. However, ACI/FF combination was not required for units to 

meet the MACT floor, so the ACI and FF cost algorithms are included with this memo, as 

Attachments A and B. Attachment C presents the inputs used for these algorithms. 

Emissions reductions from application of the beyond-the-floor controls relative to the 

MACT floor limits were calculated using the following procedure. First, the reduction efficiency 

of the beyond-the-floor control for each pollutant was applied to the uncontrolled concentration 

to determine the total reduction the control would achieve. The reduction from uncontrolled 

levels to the MACT floor limits was previously calculated for the MACT floor cost and emissions 

reduction analysis.3 For each pollutant, the incremental reduction between the more stringent 

beyond-the-floor control and the MACT floor was calculated by subtracting the MACT floor 

emissions reductions from the reductions achieved by the more stringent control. 

4.0 SELECTION OF REGULATORY OPTIONS 

Tables 4-1 and 4-2 summarize the costs, emissions reductions, and incremental cost 

effectiveness of the controls analyzed in the BTF analysis, for the case where ‘actual’ emission 
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reductions are considered (Table 4-1) and the case where ‘potential’ emission reductions are 

considered (Table 4-2). Further description of ‘actual’ emissions (based on actual sludge feed 

rates) and ‘potential’ emissions (based on unit sludge capacities) can be found in the baseline 

emissions memo.2 The tables indicate that except for the afterburner, all of the controls applied 

result in a high incremental cost-effectiveness. Consequently, these controls, with the exception of 

activation carbon injection in combination with a FF for Hg control at MH units, were considered 

infeasible. Mercury is a high priority pollutant of interest, and additional control beyond the floor 

for Hg was analyzed for the proposed rule. Three different control combinations were therefore 

selected for the beyond-the-floor analysis: (1) MACT Floor control only, (2) MACT Floor 

control with the addition of afterburner retrofits for additional CO control for MH units not 

already having afterburners, and (3) MACT Floor control, afterburners for MH units not already 

having them, and ACI and FF for MH units for additional Hg and PCDD/PCDF control. The 

costs, total emissions reductions, and incremental cost effectiveness of the three control 

combinations are summarized in Table 4-3 (with ‘actual’ emissions) and Table 4-4 (with 

‘potential’ emissions). Attachments D1 and D2 present the costs for each control combination and 

subcategory for each SSI unit. Attachments E1 through E7 present the emission reductions based 

on ‘actual’ sludge usage and supporting details for each beyond the floor control considered, and 

attachments F1-F7 present the emission reductions based on ‘potential’ sludge capacity and 

supporting details for each beyond the floor control considered. 

REFERENCES 

1. Revised MACT Floor Analysis for the Sewage Sludge Incinerator Source Category. 

Memorandum from Eastern Research Group to Amy Hambrick, U.S. Environmental 

Protection Agency. January 2011. 

2. “Revised Estimation of Baseline Emissions From Existing Sewage Sludge Incineration 

Units” Memorandum from Eastern Research Group, Inc. to Amy Hambrick, U.S. 

Environmental Protection Agency. January 2011. 

3. Revised Cost and Emissions Reduction of Complying with the MACT Floor for Existing 

SSI Units. Memorandum from Eastern Research Group to Amy Hambrick, U.S. 

Environmental Protection Agency. January 2011. 

4. Facility, Unit, and Emissions Test Database for the Sewage Sludge Incineration Source 

Category. Memorandum from Eastern Research Group to Amy Hambrick, U.S. 

Environmental Protection Agency. June 2010. 

5. A Comparison of Fluid Bed and Multiple Hearth Biosolids Incineration. Ky Dangtran, 

John Mullen, and Dale Mayrose. Paper presented at the 14th Annual Residuals and Sludge 

Management Conference. February 27-March 1, 2000, Boston MA.
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TABLES AND ATTACHMENTS

Table 4: See BeyondTheFloorMemo_Table4.xlsx 

4-1. Emissions Reductions and Costs by Control: ‘Actual’ Emission Reductions 

4-2. Emissions Reductions and Costs by Control: ‘Potential’ Emission Reductions 

4-3. Emissions Reductions and Costs by BTF Control Combination: ‘Actual’ Emission 

Reductions 

4-4. Emissions Reductions and Costs by BTF Control Combination: ‘Potential’ Emission 

Reductions 

Attachment A. Control Costs: Fabric Filter Algorithm for Incinerators 

See BeyondTheFloorMemo_AttachA-D.xlsx 

Attachment B. Control Costs: ACI Cost Algorithm for Incinerators 

See BeyondTheFloorMemo_AttachA-D.xlsx 

Attachment C. Inputs to BTF Analysis 

See BeyondTheFloorMemo_AttachA-D.xlsx 

Attachment D. Cost Details 

See BeyondTheFloorMemo_AttachA-D.xlsx 

 D1. Fluidized Bed Sewage Sludge Incinerators 

 D2. Multiple Hearth Sewage Sludge Incinerators 

Attachment E. Emission Reduction Details (‘Actual’) 

See BeyondTheFloorMemo_AttachE.xlsx 

 E1. Emission Reductions for Each BTF Control Considered 

 E2. BTF Emissions for SNCR 

 E3. BTF Emissions for Afterburner Retrofit 

 E4. BTF Emissions for PBS 

 E5. BTF Emissions for WESP 

 E6. BTF Emissions for FF 

 E7. BTF Emissions for ACI/FF 

Attachment F. Emission Reduction Details (‘Potential’) 
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See BeyondTheFloorMemo_AttachE.xlsx 

 F1. Emission Reductions for Each BTF Control Considered 

 F2. BTF Emissions for SNCR 

 F3. BTF Emissions for Afterburner Retrofit 

 F4. BTF Emissions for PBS 

 F5. BTF Emissions for WESP 

 F6. BTF Emissions for FF 

 F7. BTF Emissions for ACI/FF 

Attachment G. Correspondence between EPA’s testing and monitoring group and ERG 

 regarding Hg control.