&EPA
United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park NC 27711
October 1988
Air
Sewage Treatment
Plant NSPS:
Responses to
Comments on
April 1986 Proposed
Revisions
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EPA-450/3-84-10b
Sewage Treatment Plant NSPS:
Responses to Comments on April 1986
Proposed Revisions
Emission Standards Division
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, NC 27711
October 1988
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This report has been reviewed by the Emission Standards Division of the Office of Air Quality Planning and Standards,
EPA, and approved for publication. Mention of trade names or commercial products is not intended to constitute
endorsement or recommendation for use. Copies of this report are available through the Library Services Office (MD-35),
U.S. Environmental Protection Agency, Research Triangle Park, N.C. 27711, or from National Technical Information
Services, 5285 Port Royal Road, Springfield, Virginia 22161.
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TABLE OF CONTENTS
Section Page
1.0 Summary 1-1
1.1 Summary of Changes Since Proposal 1-1
1.2 Summary of Impacts of Promulgated Action 1-3
2.0 Summary of Public Comments and Responses 2-1
2.1 Monitoring Requirements 2-1
2.2 Reporting Requirements 2-24
2.3 Performance Test Requirements ... 2-25
2.4 Other Comments 2-29
ill
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LIST OF TABLES
Table Page
2-1 List of Commenters on Proposed Revisions to the
Sewage Treatment Plant NSPS 2-2
2-2 Maximum Annual Cost per Incinerator 2-22
iv
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1.0 SUMMARY
On April 18, 1986, the U. S. Environmental Protection Agency (EPA)
proposed revisions to the monitoring, recordkeeping, reporting and testing
requirements associated with the new source performance standards (NSPS) for
sewage treatment plants (51 FR 13424) under authority of Section 114 of the
Clean Air Act. The standard limits atmospheric emissions of particulate
matter (PM) from new, modified, or reconstructed sewage sludge incinerators.
The April 18, 1986, Federal Register notice proposed additional monitoring,
recordkeeping, and reporting requirements and additional performance test
requirements for owners and operators of existing and future sewage sludge
incinerators subject to the NSPS.
Public comments were requested on the proposal in the Federal Register
notice. The public comment period was extended 1 month to July 17, 1986, to
allow additional commenters to participate. A total of nine comment letters
was received. Commenters included industry representatives, an environmental
group, and a State agency. The public comments are summarized in this
document along with responses to the comments. The comments and responses
serve as the basis for changes and clarifications to the revised standards
made between proposal and promulgation.
1.1 SUMMARY OF CHANGES SINCE PROPOSAL
In response to the public comments, several changes and clarifications
have been made to the proposed monitoring, reporting, and performance test
requirements for sewage sludge incinerators. No comments were received on
the proposed recordkeeping requirements. The comments and the basis for
these changes are included in Section 2.0. These changes are:
The proposed alternative requirement for plants to monitor
incinerator exhaust flow rate in lieu of oxygen content of
incinerator exhaust, temperature profile of incinerator, fuel use,
and sludge moisture and volatiles content has been withdrawn.
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The proposed monitoring, recordkeeping, and reporting requirements
for incinerator temperature, fuel use, and sludge moisture and
volatiles content have been modified to exempt facilities from
which particulate emissions are measured to be less than or equal
to 0.75 Ib/ton of dry sludge input.
A requirement for plants to continuously monitor and record the
sludge feed rate to the incinerator has been added; hourly
averages of sludge feed rate are to be reported for days when a
decrease in scrubber pressure drop or increase in exhaust gas
oxygen content, is reported. This requirement applies only to
facilities from which particulate emissions are measured to be
greater than 0.75 Ib/ton of dry sludge input.
The specific requirements for locating oxygen (O^) monitors has
been replaced with a general requirement that monitors be placed
upstream of sources of dilution air.
The incinerator exhaust oxygen content level triggering reporting
requirements has been made uniform for all facilities: 3 percent
greater than level measured during the most recent performance
test.
The number of thermocouples required in multiple hearth
incinerators to measure the temperature profile of the incinerator
has been reduced from three thermocouples per hearth to one
thermocouple per hearth in the cooling and drying zones and at
least two thermocouples per hearth in the combustion zone.
Similarly, electric incinerators will be required to have one
thermocouple in each of the drying and cooling zones and at least
two thermocouples in the combustion zone and fluidized bed
incinerators will be required to have one thermocouple in the bed
and the outlet of the incinerator.
The performance test requirements for metals analysis have been
modified to allow plants to analyze for arsenic, cadmium,
chromium, copper, nickel, selenium, and zinc either by atomic
absorption or neutron activation.
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1.2 SUMMARY OF IMPACTS OF PROMULGATED ACTION
The environmental, energy, and economic impacts of the proposed
standards are described in the Federal Register proposal notice
(51 FR 13431). The changes in the standard since proposal will have no
effect on the impacts of the proposed standard with one exception. The
added requirement for monitoring and recordkeeping of sludge feed rate may
represent a small cost to some plants. Equipment to monitor sludge feed
rate is expected to be available at most facilities due to the existing
requirements of 40 CFR 60.153(a)(2) for measuring sludge feed rate during
performance tests. However, recording instrumentation may need to be added.
The estimated annual cost of this instrumentation is less than $1,000 per
incinerator.
Similarly, the exemption from monitoring, recordkeeping, and reporting
of incinerator temperature, fuel use, and sludge moisture and volatiles
content for facilities that comply with the particulate emission limit at a
level of 0.75 Ib/ton of dry sludge input or less may reduce compliance cost
for some facilities. The estimated annual cost would be reduced by about
$12,000 per incinerator.
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2.0 SUMMARY OF PUBLIC COMMENTS AND RESPONSES
This section Includes responses to public comments on the proposed
revisions to the monitoring, recordkeeping, reporting and testing
requirements associated with the sewage treatment plant NSPS. A list of the
commenters, their affiliations, and the EPA docket numbers assigned to their
correspondence is given in Table 2-1. The comments are organized according
to topic in the following sections.
2.1 Monitoring Requirements
2.2 Reporting Requirements
2.3 Performance Test Requirements
2.4 Other Comments
2.1 MONITORING REQUIREMENTS
Comment Location of 0- Monitors
Three commenters (IV-D-1, IV-D-4, and IV-D-6) discussed the topic of
the required 0- monitor location.
The first commenter (IV-D-1) cited plugging of suction piping and
"numerous operational and maintenance problems" in his facility's
experiences with 0~ analyzers located upstream of the scrubber. Their
electrochemical Q~ analyzer located downstream of the scrubber, however, has
worked well for four years. The commenter disagrees with EPA's statement
that the injection of center shaft cooling air into the exhaust stack
results in erroneous 02 measurements if the 02 analyzer is located
downstream of the scrubber. According to the commenter, the center shaft
cooling air enters the stack downstream from the 0- analyzers in most
facilities. The commenter further pointed out that erroneous 0-
measurements can result even when the monitor is located on the top hearth
of the incinerator due to influx of air through the sludge inlet.
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TABLE 2-1. LIST OF COMMENTERS ON PROPOSED REVISIONS
TO THE SEWAGE TREATMENT PLANT NSPS
Docket
Item
Number
Date
Commenter and Affiliation
IV-D-1
IV-D-2
IV-D-3
IV-D-4
IV-D-5
IV-D-6
June 12, 1986
June 13, 1986
June 4, 1986
June 12, 1986
June 17, 1986
June 13, 1986
Robert P. Dominak, P.E.
Northeast Ohio Regional Sewer District
3826 Euclid Avenue
Cleveland, Ohio 44115-2504
(216) 881-6600
Eric R. Jankel
Narragansett Bay Commission
44 Washington Street
Providence, Rhode Island 02903
(401) 277-6680
William E. Brennan
Central Contra Costa Sanitary District
5019 Imhoff Place
Martinez, California 94553-4392
(415) 689-3890
Al Baturay, P.E.
Carlson Associates Technical
Services, Inc.
7594 Oakwood Avenue
Cleveland, Ohio 44131
(216) 642-0199
Frances Dubrowski, Jessica Landman,
Joan Becker
Natural Resources Defense Council
1350 New York Avenue, N.W.
Washington, D.C. 20005
(202) 783-7800
Charlie J. Williams
Detroit Water and Sewerage Department
Water Board Building
Detroit, Michigan 48226
(313) 224-4800
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TABLE 2-1. LIST OF COMMENTERS ON PROPOSED REVISIONS
TO THE SEWAGE TREATMENT PLANT NSPS (Continued)
Docket
Item
Number Date Commenter and Affiliation
IV-D-7 June 27, 1986 Jorge H. Berkowitz, Ph.D.
State of New Jersey Department of
Environmental Protection
John Fitch Plaza, CN 027
Trenton, New Jersey 08625
(609) 292-5383
IV-D-8 July 17, 1986 David D. Doniger and Ellen S. Kern
Natural Resources Defense Council
1350 New York Avenue, N.W.
Washington, D.C. 20005
(202) 783-7800
IV-D-9 August 21, 1986 Helen Boyer
Metropolitan Waste Control Commission:
Twin Cities Area
350 Metro Square Building
Saint Paul, Minnesota 55101
(612) 222-8423
aThe docket number for this project is A-84-03. Dockets are on file at
EPA's Central Docket Section in Washington, D.C.
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A second commenter (IV-D-4) stated that measuring 02 accurately at the
uppermost hearth is difficult because of air leaking from the openings at
the furnace shell and uneven gas flow within the furnace. A representative
sample of gas flow at this location would require a long probe or sampling
tube and would "present mechanical problems." The commenter suggested that
the "gas outlet breaching" would be a more appropriate location for
measuring 02 content of incinerator exhaust gas.
The third commenter (IV-D-6) agreed with Commenter IV-D-4 on this last
point, stating that his facility has located its oxygen analyzers in the
breach of the incinerators, upstream of any source of ambient air entering
the scrubber, rather than in the first hearth, and believes this location
should be acceptable.
Response
The proposed revisions (51 FR 13432) require incinerator owners and
operators of sewage sludge incinerators to monitor incinerator excess air
levels. As with the scrubber pressure drop monitoring requirement, the main
purpose of monitoring excess air is to identify significant deviations from
conditions during compliance tests that may be indicative of increased
particulate emissions. The monitoring of incinerator excess air levels can
be accomplished by measuring the oxygen content, which is directly related
to excess air levels, in the exhaust gases from the incinerator.
The proposed revisions required the following specific locations for
monitoring oxygen levels. In multiple-hearth incinerators, oxygen levels
would be monitored at the uppermost hearth. For fluidized-bed and other
incinerator types, oxygen levels would be measured at any point upstream of
the inlet to the emissions control device. These locations were specified
to avoid erroneous measurements due to in-leakage of air. As pointed out by.
one commenter (IV-D-1), many multiple-hearth incinerators are designed with
the center shaft cooling air by-pass injected downstream of the scrubber
(not in the incinerator exhaust), so that effects of this in-leakage can be
avoided even if the monitor is placed after the scrubber. Another commenter
pointed out that existing CL monitors at other locations besides the top
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hearth of multiple hearth incinerations yield acceptable 02 measurements
since they are upstream of any significant source of air in-leakage. The
commenters' facilities already have oxygen monitors which would have to be
relocated under the proposed revision.
To avoid unnecessary relocation of existing 02 monitors, EPA is
revising the requirement for oxygen monitors by removing the specific
location requirements for multiple-hearth and fluidized bed incinerators. In
its place, a requirement has been added that CL monitors be located upstream
of significant sources of air dilution including center shaft cooling air
bypass inlets, fans, and ambient air recirculation dampers.
Comment Location of Pressure Drop Monitors
Two commenters (IV-D-6 and IV-D-4) questioned the location requirement
for pressure drop monitors. The first commenter (IV-D-6) explained that his
facility uses ambient air recirculation dampers located upstream of the
scrubbers which allows them to reduce the airflow from the incinerator
without reducing the pressure drop across the scrubber. The commenter
questioned whether his current practice of measuring pressure drop across
the scrubber would meet the location requirements for measuring pressure
drop or if additional differential pressure cells would need to be installed
at other locations.
The second commenter (IV-D-4) stated his opinion that for incineration
systems equipped with venturi scrubbers and impingement plate subcoolers,
monitoring the pressure drop at the venturi would be more meaningful since
the scrubber collection efficiency is a direct function of the pressure drop
at the venturi but not necessarily the pressure drop at the subcooler. He
further pointed out that venturi scrubbers on recently installed sludge
incineration systems typically have adjustable throats and are equipped with
pressure drop monitors that are used to control pressure drop at a constant
level.
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Response
The proposed revisions (51 FR 13432) require owners and operators of
sewage sludge incinerators to continuously monitor and record the pressure
drop of the gas flow "through the wet scrubbing device." The primary
purpose of this requirement is to detect significant decreases in scrubber
pressure drop relative to the pressure drop measured during performance
testing that may be indicative of increased particulate emissions.
Secondarily, the requirement will provide data that EPA may use in the next
4-year review of the standard to establish a correlation between scrubber
pressure drop and particulate emissions that would apply to all
incinerators. Both intents will be served by the existing scrubber pressure
drop monitoring schemes described by the commenters. Further, for
incinerators equipped with variable throat Venturis with built-in pressure
monitors, the location of the existing monitor will meet the requirements of
the standard. Some facilities may have to relocate or add new pressure drop
monitoring equipment to comply with the revised standard. However, EPA
believes that the location of existing pressure drop sensors used to monitor
the operation of wet scrubbers is probably adequate in most cases.
Comment Number and Location of Thermocouples
Four commenters (IV-D-6, IV-D-1, IV-D-3, and IV-D-9) addressed the
proposed requirement for monitoring the incinerator operating temperature.
Specifically, the commenters questioned the need for three thermocouples per
hearth in multiple hearth incinerators and requested clarification on the
requirements for locating and recording the thermocouples.
The multiple hearth incinerators operated by Commenter IV-D-6 currently
are installed with one thermocouple per hearth. According to the commenter,
the proposed'requirement of three thermocouples per hearth would be
"excessive and redundant." The commenter further stated that his facility
would have to install an additional 324 thermocouples to comply with this
proposed change to the regulation and that "major modifications" would have
to be made to their burner management system in order to comply with this
requirement.
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The second commenter (IV-D-1) recommended that no more than two
thermocouples be required in the incinerator hearths in the drying and
burning zone and that only one thermocouple be recorded, with the second
being monitored by a remote indicator. The incinerators operated by this
commenter currently are installed with one thermocouple in the drying and
cooling zones and three thermocouples in the burning zone. One thermocouple
in each hearth is recorded and the additional thermocouples are monitored by
auxiliary indicators.
The third commenter (IV-D-3) questioned whether the temperature to be
recorded was to be an average of the three thermocouples' temperatures, or
if each of the three readings was to be recorded separately. The commenter
added that the location of the thermocouple on the hearth affected its
accuracy, and that proposed Section 60.153, paragraph (a)(6) was not clear
about whether the thermocouples were to have a common location or if each
was to be placed at a different spot on the hearth. The commenter also
stated that since the closeness of the operating burner to the thermocouple
will affect the thermocouple's accuracy, adding more thermocouples could
improve accuracy but would not seem to be necessary since one thermocouple
per hearth does an adequate job of showing the trends in hearth temperature.
The fourth commenter (IV-D-9) remarked that "cooling hearth
temperatures have no useful purpose for process control and should be
omitted from the requirement." He added that a requirement for three
thermocouples was "unsupported," asserting that "one properly located and
maintained thermocouple per hearth is satisfactory for process control
relative to air pollution emissions and slagging control." He further
stated that the possibility of exceeding "critical operating temperature"
increases with more than one controlling thermocouple per hearth, and that
"automatic shutdown of the entire system" would then occur. The commenter
concluded that installation and maintenance costs for his firm, were they
required to install the additional thermocouples, would exceed the cost
estimated in the proposed changes to the rule.
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Response
The proposed revisions (51 FR 13432) require owners and operators of
sewage sludge incinerators to monitor the temperature profile of the
incinerator and report temperature data for any period that the monitored
scrubber pressure drop or incinerator exhaust gas oxygen content deviates by
a specified amount the levels measured during the most recent compliance
test. Information on incinerator operating temperatures will be used to
identify whether temperature control problems may be responsible for
excessive cooling air requirements resulting in potential increases in
particulate matter emissions. EPA agrees with the commenters that only one
operating thermocouple is adequate for providing information on incinerator
temperature trends in the drying and cooling hearths of multiple hearth
incinerators. However, the practice reported by one commenter of operating
redundant thermocouples is considered by EPA to be good operating practice
in the event that one or more thermocouples become inoperable. In the
combustion zone, multiple thermocouples may be necessary to determine
representative hearth temperatures due to the larger fluctuation in hearth
temperatures (i.e., from startups and shutdowns) and due to fluctuations in
temperature within the hearth (i.e., depending on proximity to the
burner(s), access hatches, drop holes, etc.). Further, EPA believes it is
common industry practice to operate several thermocouples for control
purposes in the combustion hearths of multiple-hearth incinerators. For
these reasons, EPA is modifying the requirement for monitoring incinerator
operating temperatures to require one thermocouple per hearth in the drying
and cooling hearths and two or more thermocouples per hearth in the
combustion hearths of multiple hearth incinerators. Similarly, EPA is
modifying the requirements for electric and fluidized bed incinerators to
require one thermocouple in each of the drying and cooling zones and at
least two thermocouples in the combustion zone of electric incinerators and
one thermocouple in the bed and outlet of fluidized bed incinerators.
However, it should be noted that EPA encourages the use of redundant
instrumentation (i.e., two or more thermocouples) in all incineration types.
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The location of the thermocouples within the incinerator is not
specified by EPA. It is intended that facilities utilize currently
installed thermocouples to the extent practicable. It is important that
thermocouples remain in the same location during normal incineration
operation and during the compliance test. This will help ensure against
false readings of incinerator temperature trends from changing the location
where temperatures is monitored compared to changes in actual operation
temperatures. The EPA believes it is good practice to locate the
thermocouples away from incinerator features such as burners, access
hatches, and drop holes to minimize fluctuations in temperature resulting
from these features.
When temperature is monitored by more than one thermocouple in a hearth
(or zone), facilities should report the average hearth temperature as part
of the incinerator temperature profile. It is important that temperatures
be reported on the same basis as they were recorded during the compliance
test.
Finally, as described in response to the following comment, some
incinerators will be exempt from continuous monitoring, recording, and
reporting requirements for incinerator temperature.
Comment Need and Basis for Monitoring Requirements
Four commenters (IV-D-2, IV-D-6, IV-D-8, and IV-D-9) commented on the
need and basis for the proposed monitoring requirements.
One commenter (IV-D-9) stated that because of the hourly and daily
variability in the sludge fuel feed, the operating conditions for a given
sludge incinerator are neither constant nor predictable. Further, the
commenter stated that a direct and predictable correlation between
particulate emissions and incinerator operating conditions has not been
verified by actual incinerator operating experience. Since direct
measurement of particulates cannot be accomplished continuously with
current technology, the commenter suggested that EPA consider requiring more
frequent performance test in lieu of the additional monitoring requirements.
According to the commenter, such an approach would be preferable because it
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would provide information on direct measurement of pollutants instead of
indirect information based on monitoring operating parameters. Further, the
commenter stated that annual or more frequent performance tests are both
feasible and affordable. A second commenter (IV-D-6) made a similar
recommendation, stating that his facility performs annual emission tests
using Methods 1-5 and performs hourly opacity readings during daylight
hours. He recommended that EPA reevaluate the need for increased monitoring
of the incinerator process for facilities such as his.
With regard to scrubber pressure drop, Commenter IV-D-9 questioned the
existence of a "direct linear correlation between scrubber pressure drop and
particulate emissions" and said that performance tests at his own facility
have shown no such correlation. He suggested, as an alternative to the
proposed scrubber pressure drop reporting requirement, requiring facilities
to conduct studies to determine whether there is a correlation between
particulate emissions and scrubber pressure drop. If facilities found such
a correlation, the Agency could then "establish the appropriate minimum
scrubber pressure drop to be included in the air operating permit for the
[particular] facility."
The third commenter (IV-D-2) suggested that if EPA is trying to
collect operating data on sludge incinerators in order to correlate
efficiency of particulate emission control systems versus specific
incinerator operating conditions, then only those facilities that must
conduct performance tests should be required to install the proposed new
equipment and comply with "routine data collection and reporting
requirements."
The final commenter (IV-D-8) disagreed with the previous commenters,
stating that a correlation between specific operating variables (including
pressure drop) and performance levels exists, but that EPA was unable to
quantitatively establish such a correlation due to its inability, given the
available data base, to account for other relevant variables. The commenter
stated that higher pressure drops and specific operating practices reduce
particulate emissions within a particular incinerator. He cited the
ICFAR-type optimization programs which show a very large potential to reduce
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PM and fuel consumption and stated that incinerators that have not undergone
such optimization programs should not be described by EPA as "well
operated."
Response
As discussed in the preamble to the proposed revisions (51 PR 13427),
EPA has been unable to establish a direct quantitative correlation between
particulate emissions and scrubber pressure drop that would apply to all
incinerators. The EPA is familiar with the ICFAR optimization program, the
primary purpose of which was to investigate incinerator operating parameters
to optimize incinerator fuel consumption. At one of the facilities included
in the ICFAR study, particulate emission measurements were taken in
conjunction with the incinerator operating modifications. Based on the
findings at this one plant, it appears that incinerator operating practices
that optimize fuel consumption also reduce particulate emissions.
Accordingly, EPA encourages plants to undergo optimization programs such as
those implemented by ICFAR. However, emissions data from one facility are
an insufficient basis to require all plants to undergo optimization
programs.
EPA disagrees with the commenters' (IV-D-6, IV-D-9) recommendations
that periodic performance tests and/or opacity monitoring be required
instead of incinerator and control device monitoring. Annual emission tests
indicate if a facility is in compliance only 4 to 5 days out of the year.
Such a test may or may not be representative of the variations in
incinerator operating conditions that occur throughout the year. Further,
opacity measurements may not be a direct indicator of particulate emissions.
Water vapor would tend to condense after leaving the wet scrubber and could
be measured by opacity readings as particulate emissions. Opacity
monitoring alone also would not provide information on how the incinerator
has been operated or how well the control equipment functions that would be
useful in evaluating causes of potential high particulate emissions.
In response to the commenter (IV-D-9) who recommended that facilities
be required to conduct "studies" based on performance tests to establish an
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appropriate scrubber pressure drop requirement for each incinerator, EPA
believes such a requirement would be more burdensome than the proposed
monitoring requirements. However, based on the data recorded
by facilities as a result of the monitoring requirements, it may be possible
to adopt the approach recommended by the commenter during the next four-year
review of the standard.
The intent of the monitoring requirements is not, as the third
commenter (IV-D-2) stated, to collect operating data that can be used to
correlate efficiency of particulate emission control systems versus specific
incinerator operating conditions. Although the data recorded by facilities
as a result of these requirements will be useful to EPA when performing
subsequent reviews of the standard, the primary purpose of the requirements
is to provide EPA compliance personnel with information on incinerator and
control device operating practices that might result in increased
particulate emissions from these sources after the initial performance test.
After consideration of these comments, EPA reaffirms its position in the
preamble to the proposed regulation (51 FR 13429) that monitoring of
scrubber pressure drop, incinerator exhaust gas oxygen content, incinerator
temperature, fuel use, and sludge moisture and volatiles content are
reasonable and will be useful in detecting an analyzing periods of potential
excess particulate emissions. However, EPA recognizes that compliance with
some of these monitoring requirements may not be necessary for all
facilities, particularly those which are currently operated in such a way
that particulate emissions are well below the standard of 0.65 g of
particulate per kg of dry sludge input (1.3 Ib/ton). Accordingly, EPA has
decided to exempt those incinerators with particulate emission measurements
of less than or equal to 0.38 g/kg of dry sludge input (0.75 Ib/ton) from
all continuous monitoring recording, and reporting requirements except
scrubber pressure drop and incinerator exhaust gas oxygen content. All
sludge incinerators subject to the NSPS will be required to conduct a
performance test following promulgation of these revisions during which all
control device and incinerator parameters (including incinerator
temperature, fuel use, sludge feed rate, and sludge moisture and volatiles
content) are monitored. Following the performance test, all facilities will
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be required to monitor, record and report scrubber pressure drop and
incinerator exhaust gas oxygen as proposed. However, following the
performance test, only those facilities from which particulate emissions
measurements exceed 0.38 g/kg of dry sludge input (0.75 Ib/ton) will be
required to continuously monitor, record, and report incinerator
temperature, fuel use, and sludge feed rate, and to perform daily sampling
and analysis of sludge moisture and volatiles content. EPA believes this
exemption is reasonable because it will focus information collection on
those facilities for which particul ate emission measurements indicate a
facility is operating close to the standard. Variations in incinerator
operation at these facilities are more likely to result in excess emissions
than at facilities where compliance was demonstrated by a wider margin.
This exemption is also expected to provide incentive to incinerator owners
and operators to evaluate and identify those control device and incinerator
operating conditions which ensure low particulate emissions prior to the
performance test.
Comment Incinerator Exhaust Oxygen Measurement
Three commenters took issue with the proposed monitoring requirements
for oxygen content in the incinerator exhaust.
The first commenter (IV-D-3) disagreed with EPA's contention that
limiting the amount of air in excess of that required for combustion and
temperature control would not impose any unreasonable restrictions on
operating practices. If the incinerator is equipped with afterburners, he
stated, the increased afterburner temperature and air flow will increase the
volume of incinerator exhaust but should at the same decrease particulate
discharge. The commenter contended that limiting the volume of exhaust gas
flow would both limit the afterburner's effectiveness in reducing
particulate emissions, and limit the waste-heat boiler's steam production.
The second commenter (IV-D-4) disagreed with EPA's findings regarding
excess air requirements for multiple-hearth furnaces, stating that some of
these furnaces are designed and operated at higher than 100 percent excess
air rates to control individual hearth temperatures, particularly when high
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solid concentration and high calorific sludges are being incinerated. The
high excess air rates for combustion of these sludges are necessary to
protect equipment from high temperatures and prevent fusion of ash in
furnaces.
Commenter IV-D-9 stated that the proposed changes to the regulation
"fail to consider actual operating experience of new sewage sludge
processing facilities" in requiring continuous monitoring and recording of
the oxygen content of flue gas in the top hearth of each multiple-hearth
sludge incinerator (51 FR 13432). The commenter cited lime addition to
sludge in the dewatering phase ("a process still commonly used by many
communities") as a factor in preventing slagging at 75-100 percent excess
air and 1800°F combustion hearth temperature.. However, the commenter's
facility has abandoned the practice of adding lime. The facility has solved
the slagging problem that results by reducing the combustion hearth
temperature to 1600°F, using more excess air for cooling. He added that
although "the amount of excess air required depends on sludge moisture
content and heat content, ... it typically will be 200 + 50 percent."
Therefore, the commenter reasoned, continuous monitoring and recording of CL
content in flue gas "provides inconsequential data regarding oxygen
requirements for actual combustion," since the amount of excess air
facilities such as his use is much more than required for complete
combustion. The commenter recommended, as an alternative, "discretionary
application" of the Q~ monitoring requirement.
Response
As stated previously, the primary purpose of the requirement for
measuring oxygen content of the incinerator exhaust is to provide
information on incineration excess air levels. Significant increases in
excess air levels over that measured during the performance test may be
indicative of increased particulate emissions. This trend applies to all
sludge incinerators regardless of the typical excess air operating levels.
The preamble to the proposed revisions (51 FR 13429) stated that "limiting
the amount of air in excess of that required for combustion and temperature
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control would not Impose any unreasonable restrictions on operating
practices." Based on the comments received, EPA acknowledges that this
conclusion is not applicable to all incinerators. For example, EPA
recognizes that incinerators equipped with afterburners, that burn high
solids and high calorific sludges, or that operate at reduced temperatures
to prevent slagging, may be operated at characteristically higher excess air
levels than other incinerators. The requirement to measure and report
significant deviations in incinerator exhaust oxygen content does not
restrict these facilities from operating at higher excess air levels.
Because this level will be recorded during the performance test, these
facilities will be required to report only those periods when measured
oxygen content exceeds the performance test level by 3 percent. This
requirement is as valid for these facilities as for facilities with
incinerators operated at lower excess air levels because significant
increases in excess air levels for these incinerators may also be indicative
of increased particulate emissions over that measured during the performance
test.
Comment Exhaust Gas Volume Measurement
Three commenters (IV-D-4, IV-D-1, and IV-D-9) commented on the proposed
provision that owners and operators be allowed to measure exhaust gas
volumetric flowrate as an alternative to monitoring and recording oxygen
content of incinerator exhaust gas (51 FR 13430).
The first commenter (IV-D-4) stated that the measurement of gas flow
from the incinerator does not indicate how the incinerator has been operated
or how well control equipment functions. He gave three examples of
undesirable incineration operating practices which might still yield
acceptable exhaust gas volumetric flowrates. First, the furnace could be
overloaded with a high sludge feed rate which may cause incomplete
combustion and high uncontrolled particulate emissions, yet the exhaust gas
flow might be within the normal range of operation. Second, the furnace
operation may be out of control with higher than normal gas outlet
temperature, while the gas flow may be within the design range. And third,
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incineration with a very high excess air rate and lower sludge feed rate
than normal and lower than acceptable gas outlet temperature may product gas
flow within the design rate.
The second commenter (IV-D-1) stated that he did not know of an
accurate and reliable way to measure and record continuously the exhaust gas
volumetric flowrate. He, therefore, recommended that EPA not enact this
change.
The third commenter (IV-D-9) said that, from his facility's experience,
this requirement "is not supported by any data from air pollutant emissions
control." The commenter included with his statement a graph which showed,
he said, "no correlation between participate emissions and flue gas flow
rate." The reason for that is that flue gas flow rate is a function of
sludge feed and heat content, both of which are "variable" in an
incinerator.
Response
The option for plants to monitor and report periods of excessive
incinerator exhaust gas flowrate was included in the proposed revisions to
the standard to provide plant owners and operators that do not already
monitor and record the oxygen content of incinerator exhaust, temperature
profile of incinerator, fuel usage, and sludge moisture and volatiles
content a less burdensome monitoring and reporting alternative. As noted
above, one commenter (IV-D-9) provided test data from his facility which
showed no correlation between particulate emissions and incinerator exhaust
gas flow rate. Another commenter (IV-D-4) described incinerator operating
conditions which could result in elevated particulate emissions within
normal incinerator exhaust rates. Based on review of these comments, EPA
now believes that measurement of incinerator exhaust gas alone would be
insufficient for detecting all periods of potential increased particulate
emissions. To be effective, other incinerator operating parameters would
have to be measured such as incinerator temperature, sludge feed rate, and
sludge moisture and volatiles content. Requiring these additional
monitoring requirements along with the requirement for monitoring exhaust
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gas flow would negate the Intent of providing plants with a less burdensome
monitoring alternative. Further, EPA believes that information on
incinerator exhaust gas flow alone would provide insufficient data for
correlating emission rates with specific incinerator operating parameters
for those facilities with particulate emissions measurements near the
standard. For these reasons, EPA has decided to drop the alternative of
measuring incinerator exhaust flow and require all plants to monitor oxygen
content of incinerator exhaust, temperature profile, fuel use, sludge feed
rate, and sludge volatiles and moisture content in addition to scrubber
pressure drop. As discussed previously, facilities with particulate
emission measurements less than or equal to 0.38 g/kg of dry sludge input
(0.75 Ib/ton) will be required to continuously monitor, record, and report
only the scrubber pressure drop and incinerator exhaust oxygen content.
Comment Frequency of Pressure Drop Measurements
The commenter (IV-D-6) stated that his facility currently monitors and
records hourly the pressure drop across the scrubber. He pointed out that
strip chart recorders and associated instrumentation would have to be
installed to comply with the proposed continuous monitoring requirement.
Response
Hourly measurements of scrubber pressure drop provide only an
instantaneous indication of scrubber operation and would not provide a
record of the scrubber drop variation over the 60 minute period. This
variation is important in detecting periods when the operation of the
incinerator (and control device) may result in increased emissions. For
this reason, EPA is requiring plants to report hourly averages of continuous
pressure drop measurements when they are less than, by a specified amount,
the average pressure drop measured during the most recent performance test.
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Comment Og Monitor Calibration Requirements
Two commenters (IV-D-6 and IV-D-1) objected to the proposed requirement
that 02 analyzers be calibrated every 24 hours (51 FR 13432). The first
commenter said that "daily calibration would be excessive based on our
considerable experience in keeping this equipment in calibration, adding
that daily calibration would not be "cost effective" and that their own
unspecified practices with respect to calibration should be acceptable. The
second commenter agreed, saying that the proposed requirement to calibrate
the analyzers once every 24 hours would not be practical.
A third commenter (IV-D-3) said that the proposed revision to the
standard did not state clearly how the calibration was to be performed.
Response
The EPA believes that calibrating oxygen analyzers every 24 hours is
necessary to ensure accurate measurements. Properly maintained and
calibrated instruments would help eliminate the possibility of violations
based on false readings by out-of-calibration instruments, thus reducing
unnecessary reporting requirements. The time and expense to daily calibrate
the oxygen analyzer is expected to be less burdensome than preparing a
report for increased oxygen content resulting from an out-bf-calibration
instrument. Due to the wide variety of oxygen analyzers available, EPA
recommends calibration according to methods prescribed by the manufacturer.
Comment Alternative/Additional Monitoring Recommendations: Opacity
One commenter (IV-D-3) disagreed with EPA's finding that opacity
measurements of sewage sludge incineration exhaust gas are infeasible
(51 FR 13428), citing that incinerators at his facility are equipped with
visible emission monitoring systems that have operated reliably for the past
two years.
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Response
EPA has Investigated the feasibility of in-stack opacity monitors for
sludge incinerator exhaust gas and concluded that, for most exhaust streams,
they are not feasible. As explained in the preamble to the proposed
revisions to the standard (51 PR 13428), water vapor would tend to condense
after leaving the wet scrubber and would be measured by opacity monitors
resulting in an inaccurate measure of particulate.
Although exhaust gas conditions at some facilities, such as
Commenter IV-D-3's facility, may be amenable to opacity monitors, opacity
monitoring would not be a substitute for the other proposed monitoring
requirements. In addition, opacity monitoring alone would not provide
information on how the incinerator has been operated or how well the control
equipment functions that would be useful in identifying causes of high
particulate emissions.
Comment Alternative/Additional Monitoring Recommendations: CO
One commenter (IV-D-7) supported EPA's proposed 0« monitoring
requirement (51 FR 13430), suggesting that CO be included in the monitoring
since it is an indicator of combustion efficiency.
Response
Although CO monitoring would provide an indication of combustion
efficiency, it would not necessarily indicate particulate emissions. The
EPA is unaware of any additional benefit of requiring CO monitoring in
addition to Q~ monitoring for detecting potential periods of increased
particulate emissions.
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Comment Alternative/Additional Monitoring Recommendations:
Sludge Feed Rate
In addition to measurement and recording of sludge moisture and
volatile solids content (51 FR 13430), the commenter (IV-D-4) suggested that
the amount of hourly sludge feed rate to the incinerator be added, under
previously amended sections of the regulations, to the measurement
requirement for evaluating incinerator performance.
Response
The current new source performance standard for sewage sludge
incinerators requires owners and operators of sewage sludge incinerators to
install, calibrate, maintain, and operate a flow measuring device which can
be used to determine either the mass or volume of sludge charged to the
incinerator during performance testing.
EPA agrees that information on continuous sludge feed rates would be
beneficial to the Agency in evaluating causes for potential periods of
increased particulate emissions (as indicated by changes in either scrubber
pressure drop or oxygen content). The cost of monitoring and recording
sludge feed rates would be minimal since the measuring devices have already
been installed in compliance with performance testing requirements of the
existing standard. Therefore, EPA is including this requirement in the
promulgated standards. The amount of hourly sludge feed, either by mass or
volume, will be monitored and recorded on a continuous basis. The amount of
hourly sludge feed will be reported for periods that must be reported
because of either variations in scrubber pressure drop or changes in exhaust
gas oxygen content. This requirement will apply to all facilities from
which particulate emission measurement exceed 0.38 g/kg of dry sludge input
(0.75 Ib/ton).
Comment Costs of Monitoring Requirements
Three commenters (IV-D-1, IV-D-2, and IV-D-6) took issue with the
Agency's estimate of cost (51 FR 13431). The first commenter (IV-D-1)
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estimated that the cost to his facility to buy and install the equipment
necessary to comply with the proposed revisions would be $235,000.00.
The second commenter (IV-D-2) stated that EPA has underestimated the
cost of complying with the proposed changes and requested more detailed
information on how these costs were developed.
The third commenter (IV-D-6) quoted an installation price of $330,000
to install the equipment required to comply with the proposed changes in the
regulation and cited a $200,000 annual cost thereafter of operating and
maintaining the new equipment. The commenter gave a ten-point breakdown for
the installation cost, including prices for 3 thermocouples per hearth,
324 thermocouple transmitters plus 20 percent spares, conduit, cable,
differential pressure cells, chart recorders, installation of thermocouples,
installation of "other items," salaries for four instrument technicians to
service equipment, and salary for a waste water technician to monitor
incinerator process and generate deviation reports.
Response
The EPA estimates a maximum annual cost of $24,200 per incinerator to
achieve compliance with the monitoring, recordkeeping, and reporting
requirements in the revised standard (Docket Item IV-B-1). Table 2-2
provides a breakdown of the maximum annual cost. Facilities which qualify
for the exemption from requirements to monitor, record, and report
incinerator temperature, fuel use, sludge feed rate, and sludge moisture and
volatiles content would incur a maximum annual cost of about $12,000 per
incinerator. The maximum annual cost includes both annualized capital and
operating costs. Annualized capital costs are based on a 5-year equipment
life and 10 percent interest. Annual compliance costs for new and many
existing sewage sludge incinerators are expected to be about $5,600 per
year, taking into account that new and many existing sewage sludge
incinerators already routinely monitor at least some of the incinerator
operating parameters required by the revised standard.
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TABLE 2-2. MAXIMUM ANNUAL COST PER INCINERATOR
Item
Capital Cost
Annual Cost
Monitoring Instruments
Recording Instruments
Maintenance
Recordkeeping and Reporting
Laboratory Analysis
TOTAL
$15,540
$ 8,515
$ 2,725
$26,800
$ 4,100
$ 2,260
$ 4,600
$ 1,480
$11,785
$24,220
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Commenter IV-D-1 estimated that cost to his facility to buy and install
equipment necessary to comply with the proposed revision would be $235,000.
This facility currently owns and operates six sewage sludge incinerators.
Based on EPA's cost estimates, maximum capital cost for six incinerators
would be $161,000. Commenter IV-D-1 did not provide any information on the
basis of their cost estimate. For a sewage sludge incinerator already
monitoring incinerator and control device operating parameters, the capital
cost estimated by EPA is about $8,700.
Commenter IV-D-6 owns and operates 14 sewage sludge incinerators. This
commenter estimated a total capital cost to comply with the revised standard
of $330,000 compared to EPA's estimate of $375,000 (for 14 incinerators).
Commenter IV-D-6 also estimated $200,000 in annual operating and
maintenance. Based on EPA estimates, the proposed revision would result in
a cost ranging from $78,400 to $339,000 per year in annual operating and
maintenance for 14 incinerators. EPA notes that the commenter's cost
estimates fall well within EPA's.
Comment Miscellaneous: Deadline for Installing Monitoring Equipment
One commenter (IV-D-2) requested clarification of the proposed
measure's applicability to existing incinerators. In particular, he
questioned how much time would be allotted to install control and monitoring
equipment after the final regulations are adopted (51 FR 13433).
Response
Section 60.153(e) of the proposed revisions to the standard requires
owners or operators of sludge incinerators on which the required monitoring
systems were not installed at the time of the most recent performance test
to conduct a performance test within 360 days of the effective date of the
revised regulations (the date of promulgation of the final rule). For all
other facilities, the requirements will apply during the initial performance
test, required under Section 60.8 of the General Provisions of Part 60.
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2.2 REPORTING REQUIREMENTS
Comment Levels Triggering Reporting of 02 Level
Two commenters (IV-D-4 and IV-D-9) discussed the reporting of oxygen
levels. The first commenter (IV-D-4) recommended that periods of low oxygen
content should be included in the report for those multiple hearth
incinerators that have oxygen levels less than 7 percent (50 percent excess
air) and for fluid bed incinerators with oxygen levels under 4 percent
(20 percent excess air). The second commenter (IV-D-9) stated that although
a cut-off level of 10 percent oxygen is valid when auxiliary fuel is used,
the cut-off is "meaningless" under conditions of autogeneous combustion,
when excess air is used for cooling.
Response
Although EPA agrees with the commenter (IV-D-4) that substantial
decreases in oxygen content of the incinerator exhaust may be indicative of
incomplete combustion and elevated particulate emissions, EPA believes that
plant operators will tend to correct these incinerator conditions for safety
reasons in a relatively short time, thus limiting the duration of increased
particulate emissions. For this reason, EPA is not adopting the commenter's
suggestion to require reporting of periods of low oxygen levels in the
incinerator exhaust.
Commenter IV-D-9 indicated that the cut-off level of 10 percent oxygen
1s "meaningless" under conditions of autogeneous combustion and excess air
used for cooling. EPA does not consider the cut-off meaningless. The
percent oxygen cut-off is determined during performance testing and is not
always 10 percent. Periods of autogeneous combustion would be rare and when
reported would be supplemented with fuel rates.
According to the proposed standard, if a facility, during performance
testing, recorded less than 10 percent average oxygen, the facility would be
required to report only periods of oxygen levels in excess of 10 percent.
If a facility, during performance testing, recorded an average oxygen
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content greater than 10 percent, he would be allowed an increase in oxygen
content of 3 percent before being required to report. To reduce the
potentially excessive reporting burden on facilities that record oxygen
levels only slightly under 10 percent during the performance testing, EPA
has decided to make the reporting requirements uniform for all facilities.
Accordingly, all facilities will be required to report only periods of
oxygen levels which exceed by 3 percent or more the level measured during
the most recent performance test.
Comment Requirements for Periods When Incinerator is on Stand-by
One commenter (IV-D-6) was not sure about the periods of time for which
the facility would be "accountable for deviations from these regulations,"
(51 FR 13430) and wondered if deviation reports would have to be prepared if
the incinerator was on stand-by.
Response
EPA recognizes that sewage sludge incinerators experience periodic down
time. During the period that the incinerator is on stand-by (excluding the
start-up and shut-down sequence), no emissions are expected to occur.
Requirements for reporting scrubber pressure drop and oxygen levels in the
incinerator exhaust do not apply to incinerators on stand-by. However, they
apply to all other periods when the incinerator is in operation including
during the start-up and shut-down sequence.
2.3 PERFORMANCE TEST REQUIREMENTS
Comment Metals Emissions Testing
Four commenters (IV-D-1, IV-D-2, IV-D-7, and IV-D-9) addressed the
proposed requirements for measuring metals emissions during the performance
test.
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One commenter (IV-D-2) questioned EPA's proposal to test sludge and
emissions for metals in the absence of standards for metals.
The second commenter (IV-D-1) said that his facility currently analyzes
weekly grab samples of sludge for cadmium, chromium, copper, lead, nickel,
zinc, mercury, and PCB's and could analyze for arsenic, beryllium, and
selenium as well. However, the commenter suggested that EPA's proposed rule
for measuring these metals during emissions testing be dropped "once a
correlation between sludge concentration and particulate emission
concentration for these metals is established, preferably by EPA," since
this testing would be difficult and expensive.
The third commenter (IV-D-7) questioned why more attention was not paid
in the proposed revisions to sludge metal content. He cited the Port
Washington study that showed that "significant amounts of metal vaporized in
the incinerator and were not collected by the scrubber." These metal
concentrations are "enriched" in the incinerator emissions and, in some
cases, may not be detected by the standard test methods.
The fourth commenter (IV-0-9) suggested that EPA consider atomic
absorption as an alternative method to neutron activation analysis because
of "lack of availability" and cost per analysis. He said that his firm had
"routinely" used atomic absorption to analyze particulate samples with "no
problems in quantifying the samples." Finally, he stated that a detection
limit should be specified for the metals assay "regardless of the approved
method(s).n
Response
As stated in the preamble, EPA's intention is to consolidate existing
waste management authorities with the broad authorities provided under
Section 405 of the Clean Water Act. Section 405(d) of the Clean Water Act
requires EPA to develop regulation for the use and disposal of sewage
sludge. The measurement of metals will assist the Agency in establishing
guidelines for State and local sludge management programs. Also, this will
allow the Agency to determine if future regulatory action is warranted.
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Additionally, EPA evaluated the expense and difficulty of performing
the metals emissions analyses. Since no special emissions testing equipment
and procedures would be needed, the added expense is limited to the
analytical laboratory cost. Based on contacts with laboratories that
perform metal analyses, both atomic absorption and neutron activation
methods are comparable in cost. However, very few laboratories are equipped
for neutron activation analysis. For this reason, EPA is modifying the
requirement for using neutron activation analysis. Since there is no
significant difference in the accuracy of the two methods, atomic absorption
may be used in the place of neutron activation for arsenic, cadmium,
chromium, copper, nickel, selenium, and zinc. The estimated cost to
facilities to perform metals analysis on sludge and particulate emission
samples during performance tests is estimated at $1,200 per test. This cost
would only be incurred once per facility.
It is unclear whether the commenter who requested that the requirement
for metals analysis be deleted, once a correlation between sludge metals
concentrations and metals emissions has been established, was referring to
the establishment of a universal correlation that could be applied to all
incinerators or whether the commenter was referring to establishment of
facility or plant-specific correlations. The emissions of metals are
affected by a combination of factors beyond the metals content of the
sludge, including the incinerator design, its operating condition, and the
particular emission control system applied. Consequently, it is doubtful
whether a universal correlation could be established. However, for a
particular system design and method of operation, it would seem reasonable
that a facility or site-specific correlation could be established.
Regardless, it is not EPA's intention to require each source to perform a
metals analysis for every particular performance test that may be conducted.
As stated previously, the proposed regulation has been modified to indicate
more clearly that this is a one-time analysis.
EPA is aware of the study cited by Commenter IV-D-7 that indicates that
some metals may be vaporized and therefore not collected by the scrubber.
Additional data, however, shows a wide variability in the proportion of
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metals In the sludge that are emitted out of the stack. An example of such
data is presented in the draft report "Air Pollution Discharges from Ten
Sewage Sludge Incinerators" (EPA, February 1981).
Test methods for metals measurement are still in the developmental
stages for some metal species, in particular. Until new and improved
methods are available, the existing test methods must be utilized. EPA has
no basis at this time for specifying detection limits other than what are
given in the specified test methods.
Comment Date of Applicability
One commenter (IV-D-2) was not sure how the proposed changes to the
regulation will affect the performance test his facility has scheduled to
take place before June 1987. The commenter wondered if that test would have
to conform to the proposed requirements with respect to both monitoring
equipment and items to be recorded.
Response
Sewage sludge incinerators subject to the new source performance
standard will be required to conduct a performance test within 360 days of .
the effective date of the revisions (i.e., the date of promulgation of the
final rule) with the prescribed monitors in place, unless a previous
performance test has been conducted consistent with the new monitoring
requirements. The commenter's plant may elect to comply with the proposed
monitoring requirements for its June 1987 performance test to avoid having
to repeat the test at a later date. However, the new performance test
requirements would not be required until the final revisions are promulgated
sometime in late 1987.
Comment Maximum Versus Normal Sludge Feed Rates
One commenter (IV-D-1) said that emission tests at his facility are
conducted at maximum sludge feed rates since the maximum certified capacity
of the incinerator is determined also at that time. He indicated that
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"actual pressure drops are usually lower under normal or average sludge feed
rates." The commenter supported his point with figures from his facility's
most recent emission test. He recommended that performance testing be
required at maximum and normal sludge feed rates.
Response
EPA recognizes that facilities often conduct one performance test for
both EPA compliance purposes and for State and local permit requirements.
For State and local permits, tests may be required at maximum conditions to
determine maximum certifiable emissions. For facilities such as the
commenter's facility, scrubber pressure drop may be lower for normal
operation sludge feed rates. To avoid burdensome reporting of scrubber
pressure drop, some plants may wish to conduct a separate performance test
at normal sludge feed conditions. For some plants, this may require two
performance tests. EPA recommends that each plant decide on a case-by-case
basis whether a performance test at normal sludge feed rate is appropriate
to determine compliance at lower pressure drops, in addition to the test at
maximum feed rate.
2.4 OTHER COMMENTS
Comment Level of Standard
Two commenters (IV-D-7 and IV-D-8) discussed the standard's
effectiveness, or stringency. The first commenter (IV-D-7) stated that the
proposed revisions to the standard concentrate on particulate matter
emissions. Some incinerators can comply with the standard by reducing
scrubber power consumption so the current particulate standard is only
"marginally attained," resulting in increased particulate matter emissions
rates.
According to the second commenter (IV-D-8), if EPA were to persist in
specifying the venturi-impingement tray scrubber as the reference
technology, it should make the standard "substantially stricter," since the
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average incinerator performs much better than the existing standard
requires. The commenter suggested two options to use in formulating a more
stringent standard. The first option would base the standard on the average
of the best performers (90th or 75th percent!le performance level) and would
rely on ICFAR-type optimization processes to bring new units into
compliance. The second option would adopt a ceiling at the present level of
the standard with a percentage reduction requirement from inlet
concentrations as the standard's basis. The commenter noted that this
second option had been applied to sulfur emissions from coal-fired power
plants. In sum, the percentage reduction requirement should not be less
than 98 percent or 99 percent.
Response
The second review of the new source performance standard for sewage
treatment plants, completed in 1984, concluded the current level of the
standard is achievable by all the incinerators when correctly operated and
equipped with an appropriate control device. Although many individual
facilities were found to be achieving the standard with emission rates well
under the required level of 1.3 Ib/ton of dry sludge, some incinerators have
achieved emission rates only slightly below the emission limit. No
information was found during the review to indicate that these incinerators
and associated control devices were not well operated and maintained. The
EPA concluded that no change in the level of the standard was justified for
those existing sources subject to this standard.
This does not rule out the potential for a more stringent emissions
limit for new (not yet constructed) sources subject to this standard.
However, as noted elsewhere, this review of the standard did not include any
technologies other than venturi/tray scrubbers. Two incinerators with
fabric filter control devices are reportedly under construction in
California, and several are used in Europe. Under another program, EPA is
currently investigating the applicability and effectiveness of fabric
filters and other types of control devices. This information will be
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considered during the next 4-year review of the standard. At the conclusion
.of that review, the agency will again determine if this standard should be
revised.
EPA disagrees that the effect of not changing the level of the standard
is that plants will reduce their scrubber efficiency so that the standard is
only marginally maintained. The emission rate from sludge incinerators
depends on a variety of factors in addition to scrubber pressure drop
including the characteristics of the sludge being burned and the method of
operating the incinerator, both of which may vary continuously for a given
incinerator. It is unlikely that facilities could effectively predict the
"minimum" scrubber pressure drop that would allow them to marginally achieve
the emission standard for the various sludge and incinerator operation
conditions.
Comment Technology Basis of Standard
Four commenters (IV-D-3, IV-D-7, IV-D-8, and IV-D-9) discussed the
Agency's selection of the control technology basis of the standard.
The first commenter remarked that his facility is able to meet the
particulate emission limit of 1.3 Ib/ton dry sludge input with a pressure
drop of only 10 inches of water instead of 30 inch pressure drop at which
"most incinerators" that are equipped with scrubbers and achieved compliance
with the standard operate (51 FR 13425). The commenter remarked that their
scrubber manufactured by Krebs may be responsible for this performance
difference.
The second commenter questioned EPA's interpretation of Section 111 of
the Clean Air Act with respect to selecting control technology to achieve
the best emissions control achievable. According to the commenter, the Act
"intends that new source performance standards represent a reasoned
prediction of what can be achieved in the future," rather than maintaining
performance levels achieved in the past. Incinerators already in operation,
according to the commenter, have greatly improved control performance
levels, and the NSPS should take those levels into account.
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With respect to selection of a specific control as the reference
technology, the second commenter characterized EPA's proposed choice of
venturi-impingement tray scrubbers as "based entirely on what the bulk of
the industry has unilaterally chosen to use in the past." Instead, he
stated, EPA should consider a standard based on baghouses. Arguing that
baghouse performance has already been demonstrated on "at least one" sewage
sludge facility, and in "similar other industrial processes," the commenter
quoted a 99 percent + particulate removal rate as "typical." Baghouses also
offer "the best control of fine particles and metals," he said.
The commenter stated that the emission control performance rates for
electric incinerators could be improved if they were fitted with controls
"equal to those on the better multiple-hearth units." If that occurred, he
said, electric incinerators would be the cleanest technology available. The
commenter said that EPA should explain both "the failure of electric
incinerators to operate at pressure drops considered BACT" and "why the
newer electric incinerator technology has not become the appropriate basis
for the NSPS."
Response
As discussed in the preamble to the proposed revisions (51 PR 13427),
EPA has been unable to establish a quantitative correlation between
particulate emission rates and scrubber pressure drops. Performance test
data indicate that new incinerators since 1978 achieved compliance with the
emission standard at pressure drops ranging from 10 to 45 in. W.G. New
incinerators tested between 1973 and 1978 achieved compliance at pressure
drops ranging from 7 to 32 in. W.G. Because no industry-wide correlation
between scrubber pressure drop and particulate emission rates has been
found, EPA is unable to specify a pressure drop requirement that would be
applicable to scrubbers on all incinerators subject to the standard.
During the review of the standard, no newly demonstrated technologies
were found that control particulate emissions more efficiently than those
currently in use. Currently, all sewage sludge incinerators subject to the
new source performance standard control emissions with scrubbers. Two
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incinerators with fabric filter control devices are reportedly under
construction in California, and several are in use in Europe. Under another
program, EPA is currently investigating the applicability and effectiveness
of fabric filters and other types of control devices. This information will
be considered during the next 4-year review of the standard. In the
meantime, facilities using fabric filters as control devices will be
required to monitor, record, and report pressure drop across the fabric
filter in the same way as incinerators with wet scrubbers.
The majority of new sewage sludge incinerators installed are
multiple-hearth type followed by fluidized-bed type. Electric incinerators
are the newest technology, but only a small number have been used
commercially thus far. As indicated in the preamble to the proposed
revisions (51 FR 13426), new electric incinerators installed since 1978 have
experienced difficulty in demonstrating compliance with the standard. The
EPA believes that failure of these incinerators to achieve compliance
occurred because low uncontrolled emission rates of electric incinerators
have led design engineers to specify unreasonably low pressure drop
scrubbers for these incinerators. None of the electric incinerators are in
operation at this time.
The sludge feed capacity of comrnercially used electric incinerators
(less than 1.0 ton of wet sludge per hour) is much less than that of new
multiple-hearth and fluidized-bed incinerators (up to 15 to 18 tons of wet
sludge per hour, respectively). Given the current size limitation of
electric incinerators and other factors, EPA believes it would be
inappropriate to restrict the technology for new incinerators to electric
incinerators.
Comment Factors Affecting Emissions of Toxic Organics
The commenter (IV-D-8) pointed out that the proposed revisions to the
NSPS do not mention temperature and residence time requirements for
destruction of dioxin and organics such as difurans and PCBs. He added that
the residence times and operating temperatures that were discussed—in the
context of rabble arm speeds and burner firing rates—were inadequate to
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destroy these emissions. The commenter said that EPA should look into ways
to raise incinerator temperatures sufficiently to prevent formation of
dioxins and PCBs.
Also, the commenter suggested that EPA impose a gas cooling requirement
to enhance metal emission controls. He also suggested specifying a maximum
temperature at the control device inlet.
Response
In regard to the commenter's concern that the standard does not contain
provisions sufficient to ensure metals emission reduction, it should be
pointed out that the new source performance standard for sewage treatment
plants currently applies only to particulate emissions. The EPA is
currently investigating other regulatory actions under Section 405(d) of the
Clean Water Act for sewage treatment plants. These actions will include
regulations specifically aimed at metals emissions and will take into
account the recommendations of the commenter.
Comment Regulatory Action Under Section 405 of the CWA
Two commenters (IV-D-7 and IV-D-5) urged EPA to proceed with further
regulatory action affecting sewage sludge incinerators under Section 405 of
the Clean Water Act.
One commenter (IV-D-7) stated his concern that cancer risk assessment,
dispersion modeling and stack height were not addressed in the proposed
revisions. He added that sludge incinerators "traditionally" have short
stacks which cause plume downwash and speculated that cancer risk in the
range of 1 to 1,000 for a 70 year lifetime may be associated with emissions
from these operations. He recommended that regulatory actions under
Section 405 of the Clean Water Act address health effects from dispersion of
metal emissions.
The second commenter (IV-D-5) stated that EPA's revision of the sewage
treatment plant NSPS under Section 111 of the Clean Air Act, does not
"relieve the agency of its obligation, under Section 405 of the Clean Water
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Act," to Issue comprehensive regulations for the use and disposal of sewage
sludge." The commenter further stated that regulations adopted under
Section 405 affecting sewage sludge Incinerators must be broader In scope
than the proposed NSPS revisions. In particular, he Indicated that
Section 405 regulations should address all sewage sludge Incinerators and
not just those facilities subject to the NSPS. Also, the Section 405
regulations should address all sludge pollutants that may interfere with
incineration as a disposal technique. The list of sludge pollutants that
EPA will measure during performance tests under the added NSPS requirement
is insufficient. Finally, the commenter noted that the Clean Water Act set
1978 as the deadline for EPA's issuance of Section 405 sludge regulations
but that EPA has not acted yet.
Response
As explained in the preamble to the proposed revisions (51 FR 13425),
EPA recognizes the need for an integrated approach for regulating the use
and disposal of municipal sewage sludge. Accordingly, EPA is consolidating,
where practicable, its exiting sludge management authorities with the broad
authorities provided under Section 405 of the Clean Water Act. Under this
authority, EPA has initiated an action to review, revise, or develop
regulations which will establish guidelines for State and local sludge
management programs and technical guidelines for the following disposal and
use methods: distribution and marketing, land application, landfill, ocean
dumping, and incineration. Unlike the proposed revisions to the NSPS under
Section 111 of the Clean Air Act, the review of sewage sludge incineration
under Section 405 of the Clean Water Act will consider all existing
incinerators, and not just incinerators built after the NSPS was in effect.
Further, the review of sewage sludge incineration will consider
concentrations of pollutants which may interfere with incineration as a
disposal technique.
[Note to Office of Water reviewers: Please add a brief discussion of
the status of these review activities and the current schedule.]
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Comment Sewage Sludge Incineration Growth Potential
A single commenter (IV-D-8) disagreed with the EPA's projection of the
rate of construction for new incinerators. According to the commenter,
EPA's projection does not consider increasing demand for sludge incinerators
due to "the phase-out of ocean dumping and the decline of available landfill
sites." The commenter suggested a revised estimate which reflects this
increased demand.
Response
EPA's projection of the rate of construction for new incinerators
presented in the preamble to the proposed revisions (51 FR 13425) is based
on a survey of ongoing and future construction projects at wastewater
treatment plants conducted in 1982. Current investigations by EPA under
Section 405 of the Clean Water Act will update these projections based on
more current information reflecting the phase-out of ocean dumping and the
decline of available landfill sites.
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