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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 Secondary Impacts of Controls for the Sewage Sludge Incineration 

Source Category 

1.0 INTRODUCTION 

This memorandum presents the secondary impacts associated with control devices used 

to comply with the proposed standards for existing and new sewage sludge incineration (SSI) 

units. Secondary impacts result from the consumption of fuel, water, and electricity and 

generation of solid wastes by control devices. 

Section 2.0 presents the background for the proposed standards. Section 3.0 presents the 

secondary impact estimates associated with control devices necessary for all SSI units comply 

with proposed standards. This memorandum focuses only on secondary impacts associated with 

control devices. Section 4.0 summarizes the estimated secondary impacts that would result from 

the compliance of new units expected to come online in the next five years. Section 5.0 

summarizes the emissions resulting from increased fuel and electricity requirements for different 

controls. 

2.0 BACKGROUND 

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

Act (CAA), is required to regulate emissions of 9 pollutants from existing sewage sludge 

incineration (SSI) units. The 9 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 category or subcategory of sources. The SSI 

source category comprises two subcategories: multiple hearth incineration units (MH) and 

fluidized bed incineration units (FB). To determine the MACT for each subcategory, EPA must 

first determine the minimum stringency “floor” requirements. Development of the MACT floors 

for SSI units is described in a separate memorandum.1 An analysis of beyond-the-floor controls 

was also conducted, in which three different control combinations were evaluated: 

• 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. 
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• 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. 

3.0 SECONDARY IMPACT ESTIMATES FOR EXISTING UNITS 

For the control combinations listed above, facilities may need to install the following 

types of control devices on SSI units: 

• Venturi scrubbers (VS) or wet electrostatic precipitators (WESP) to reduce Cd, Pb, 

and PM emissions, 

• Packed-bed scrubbers (PBS) to reduce HCl and SO2 emissions, 

• Selective non-catalytic reduction (SNCR) to reduce NOx emissions, 

• ACI systems, in combination with a FF, to reduce PCDD/PCDF and Hg emissions, 

and 

• Afterburners (AB) to reduce CO and organic compound emissions. 

Electricity is required to operate the pumps and fans associated with WESP, VS, PBS, 

FF, and SNCR systems. Also, water and subsequent wastewater disposal are required to operate 

VS, WESP, and PBS systems. Fabric filter and ACI systems require a method to dispose of the 

dust produced from the systems. Additionally, ACI requires the use of activated carbon. 

Supplemental fuel (i.e., natural gas) is required to operate afterburners for MH SSI units. 

Table 3-1 shows, for each of the controls analyzed, the estimated secondary impacts for 

the FB and MH subcategories. 

The algorithms used in the cost analysis provide annual cost estimates for electricity, 

water, carbon requirements, and supplemental fuel as itemized components of the annual costs 

for the control device.2,3 These cost elements for the control devices anticipated to be installed to 

comply with the standards were then summed to provide an estimate of the overall costs of 

electricity, water, activated carbon, and supplemental fuel. To estimate the secondary impact 

components (e.g., electricity, water, dust), the itemized annual cost of each component was 

divided by the unit price of the component used by the algorithm. 
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Table 3-1. Secondary Impacts for Controls Analyzed 

Controls 

Analyzed 

Subcategory Controls Required 

for Compliance 

Electricity 

Required 

(MWhr/yr) 

Water 

Required 

(gal/yr) 

Activated 

Carbon 

Required 

(ton/yr) 

Dust 

Produced 

(ton/yr) 

Supplemental 

Fuel 

(mmcf ft3

natural 

gas/yr) 

1 - 

MACT 

Floor 

FB units PBS, SNCR 505 32,035,300 - - - 

MH units VS, WESP, PBS 4,915 202,325,500 - - - 

Total VS, WESP, PBS, 

SNCR 5,420 234,360,800 - - - 

2 -

MACT 

Floor + 

AB for 

MH units 

FB PBS, SNCR 505 32,035,300 - - - 

MH VS, WESP, PBS, AB 4,915 202,325,500 - - 1,013 

Total VS, WESP, PBS, 

SNCR, AB 5,420 234,360,800 - - 1,013 

3 -

MACT 

Floor + 

AB and 

ACI/FF 

for MH 

units 

FB PBS, SNCR 505 32,035,300 - - - 

MH VS, WESP, PBS, 

AB, ACI/FF 43,185 202,325,500 4,370 4,890 1,013 

Total VS, WESP, PBS, 

SNCR, AB, ACI/FF 43,690 234,360,800 4,370 4,890 1,013 

4.0 SECONDARY IMPACT ESTIMATES FOR NEW UNITS 

As discussed in the new source analysis memorandum, EPA expects that two new FB 

units would come online in the next five years4. Estimations of the secondary impacts resulting 

from the pollution controls implemented for these units were calculated using the same 

methodology described for existing units in Section 3.0. 

Table 4-1 shows the estimated values for secondary impacts for the two new FB units. 

Table 4-1. Secondary Impacts: New Units 

Subcategory Controls Required 

for Compliance 

Electricity 

Required 

(MWhr/yr) 

Water 

Required 

(gal/yr) 

Activated 

Carbon 

Required 

(ton/yr) 

Dust 

Produced 

(ton/yr) 

Supplemental 

Fuel 

(mmcf natural 

gas/yr) 

New Units PBS, ACI/FF, AB 597 17,172,000 67.0 67.9 16.7 

5.0 SECONDARY AIR POLLUTANT IMPACTS 

Emission factors from EPA’s Egrid5 database were used to calculate emissions resulting 

from the electricity required for additional control devices, and emission factors from EPA’s AP42 emission factor document6

 were used to calculate emissions resulting from the combustion of 

additional fuel for afterburners. Increased electrical use from the controls will require additional 
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fuel to be burned in power plants, resulting in emissions of CO2 and criteria pollutants, such as 

SO2, NOx, and CO. Emissions of these pollutants (caused by increase in electricity) were 

estimated using EPA’s Egrid database.5 The Egrid database summarizes emissions of criteria 

pollutants on a per electrical usage basis (lb emitted per MW-hr), on a national average or state 

average basis. For this analysis the national average was used. Afterburners require supplemental 

fuel , such as natural gas, to operate. The afterburner algorithm indicates the amount of fuel 

needed by each unit. To estimate emissions from combustion of natural gas, emission factors 

from EPA’s AP-42 emission factor document were used.6 Tables 5-1 summarizes the resulting 

emissions of CO2, CO, NOx, and SO2 from combustion of natural gas supplemental fuel and 

increase electricity usage for the three control combinations analyzed for existing sources. Table 

5-2 shows the results for new sources, and table 5-3 shows results for combined existing and new 

sources. Table 5-4 shows the Egrid and AP-42 emission factors used for the calculations. 

REFERENCES 

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

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

Protection Agency. January 2011. 

2. Revised Cost and Emission Reduction of the MACT Floor Level of Control. 

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

Protection Agency. January 2011. 

3. Revised Analysis of Beyond the Maximum Achievable Control Technology (MACT) 

Floor Controls for Existing SSI Units. Memorandum from Eastern Research Group, Inc. 

to Amy Hambrick, U.S. Environmental Protection Agency. January 2011. 

4. Revised Estimation of Impacts for New Units Constructed Within Five Years After 

Promulgation of the SSI NSPS. Memorandum from Eastern Research Group, Inc. to Amy 

Hambrick, U.S. Environmental Protection Agency. January 2011.

5. EPA eGRID database eGRID2007 Version 1.1. Year 2005 summary tables located at 

www.epa.gov/cleanenergy/documents/egridzips/eGRID2007V1_1_year05_SummaryTab

les.pdf 

6. U.S. Environmental Protection Agency, 1995. Compilation of Air Pollutant Emission 

Factors (AP-42), Fifth Edition, Volume 1: Stationary and Point Sources, Chapter 1: 

External Combustion Sources. 
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Table 5-1. Secondary Air Pollutant Impacts: Existing Units

All Units Comply

Controls 

Analyzed 

Electricity Requirements and Emissions 

(tons/yr)* 

Supplemental Fuel Requirements and Emissions 

(tons/yr)* 

Total 

MWh per yr 

CO2

Emitted 

NOx

Emitted 

SO2 

Emitted 

ft3 Natural Gas 

per yr 

CO2

Emitted 

CO 

Emitted 

NOx 

Emitted 

CO2

Emitted 

Em

1 - MACT Floor 5420 3602 5.2 14.3 - - - - 3,602 2 - MACT Floor

+ AB for MH 

units 

5420 3602 5.2 14.3 1,013,417,920 60,805 42.6 50.7 64,407 

3 - MACT Floor 

+ AB and ACI/FF 

for MH units 

43689 29039 42.3 114.9 1,013,417,920 60,805 42.6 50.7 89,844 

*Emissions estimated based on emission factors listed in Table 5-4. 

Table 5-2. Secondary Air Pollutant Impacts: New Units after Five Years (2 New Units) 

Electricity Requirements and Emissions 

(tons/yr)* 

Supplemental Fuel Requirements and Emissions 

(tons/yr)* Total Secondary Emi

MWh per yr CO2 Emitted NOx Emitted SO2 Emitted ft3 Natural Gas per yr CO2 Emitted CO Emitted NOx Emitted CO2 Emitted CO Emitted 

Em

597 397 0.58 1.57 16,659,400 1000 0.70 0.83 1,397 0.70 

*Emissions estimated based on emission factors listed in Table 5-4.

Table 5-3. Secondary Air Pollutant Impacts: Combined Existing and New Units after 5 Years 

Controls Analyzed 

Total Secondary Emissions (tons/yr)

CO2

Emitted 

CO 

Emitted 

NOx

Emitted 

SO2 

Emitted 

1 - MACT Floor 1,397 0.7 6.6 15.9 2 - MACT Floor + AB for MH units 65,804 43.3 57.3 15.9 3 - MACT Floor + AB and ACI/FF for MH units 91,241 43.3 94.4 116.5 
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Table 5-4. Emission Factors

Pollutant 

Electricitya Natural Gasb

(lb/MWh) (lb/106 scf) (lb/ft3) (ton/ft3)

CO2 1,329 120,000 0.12 0.00006CO - 84 8E-05 4.2E-08NOX 1.9366 100 0.0001 5E-08SO2 5.2589 - - - a. National emission factors from Egrid5 for EGUs. 

b. Natural gas emission factors from AP-42