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The Environmental Protection Agency failed to collect sufficient emissions data before proposing a rule that would require sewage sludge incinerators to control emissions of toxic air pollutants, industry groups, state regulators, and environmental advocates said in comments on the proposed rule.

Water utilities also said in their comments that EPA's flawed mercury emissions estimates in its proposed new source performance standards for sewage sludge incinerators result in emissions limits that are too stringent and unobtainable. Additionally, the utilities also argued EPA's proposal was issued under the wrong section of the Clean Air Act, violating the plain language of the statute.

EPA estimates the rule, proposed Oct. 14, would result in a 76 percent drop in emissions of mercury and cut emissions of eight other hazardous air pollutants from sewage sludge incinerators (75 Fed. Reg. 63,260; 190 DEN A-7, 10/4/10).

The proposed rule would amend 40 C.F.R. Part 60 subparts LLLL and MMMM to set new source performance standards that would require the incinerators to control emissions of mercury, lead, cadmium, hydrogen chloride, particulate matter, carbon monoxide, dioxins and furans, nitrogen oxides, and sulfur dioxide.

New source performance standards are technology-based emissions limits for new or modified sources of hazardous air pollutants, also known as air toxics, such as sewage sludge incinerators. The proposed rule also includes less stringent emissions limits for existing sewage sludge incinerators.

The comment period on the proposed rule closed Nov. 29.

Emissions Data Insufficient
Water utilities, environmental groups, and state regulators all criticized EPA's failure to identify which sewage sludge incinerators represent the best performing 12 percent of the industry as required by the Clean Air Act.

Rather than collecting emissions data from all 218 incinerators in operation, EPA said in the proposed rule it surveyed units in nine municipalities and used that data to extrapolate the pollution controls being achieved by the best performing incinerators. EPA used those estimates to propose emissions limits for the pollutants in the performance standards.

“Because of its decision to hand-pick the recipients of the survey, EPA then had to rely on statistical techniques, some of which may be questionable, to make up for the lack of complete data,” the National Association of Clean Air Agencies said in its comments. “Even though EPA then gathered additional data from test information, the data set was incomplete. While EPA may have knowledge about the performance of [sewage sludge incineration] units, the agency's method does not substitute for the more complete information the agency would have received from a more thorough data-collection effort.”

The Coalition for Responsible Waste Incineration, an industry group that includes Dow Chemical and DuPont, argued EPA did not have enough emissions data from sewage sludge incinerators to set the performance standards and cannot be certain the facilities it tested represent the best performing units in the industry.

As a result, none of the sewage sludge incinerators currently in operation will be able to simultaneously meet EPA's performance standards for all of the regulated pollutants, it said.

Mercury Emissions Overestimated
EPA's proposed rule also overestimates mercury emissions from sewage sludge incineration, the National Association of Clean Water Agencies said. The agency estimates the incinerators emit 3.1 tons per year of mercury. That conflicts with a 2009 Water Environment Research Foundation report that found incinerators emit less than 1 ton of mercury annually, which was consistent with a 1997 report to Congress by EPA.

“The amount of mercury in sewage sludge is decreasing as communities implement efforts to control sources discharging mercury into the sewage system,” NACWA said.

Water utilities argued EPA should reconsider the mercury emissions standards for sewage sludge incinerators in light of another pending agency rule that would require dental offices to take steps to prevent mercury from fillings from entering wastewater. The Water Environment Federation said in its comments between 11 percent and 50 percent of mercury entering treatment facilities comes from dental offices.

According to a 2008 EPA study cited by the Water Environment Federation, requiring dentists to use amalgam separators would reduce the amount of mercury entering sewage treatment facilities by 93 percent.

EPA is expected to propose a rule in 2011 that would require dentists to separate mercury from fillings before their disposal (186 DEN A-6, 9/28/10).

Statutory Authority Questioned
Water utilities argued EPA's proposed rule would improperly regulate under Section 129 of the Clean Air Act rather than under the less stringent emissions standards under Section 112.
Section 112(e)(5) requires EPA to set national emissions standards for hazardous air pollutants (NESHAP) for publicly owned water treatment works as defined by the Clean Water Act, which includes the storage, treatment, recycling, and disposal of sewage residues.

The National Association of Clean Water Agencies argued that language “clearly encompasses” the sewage sludge incinerators being used by treatment facilities as well.

Additionally, the group said EPA cannot regulate the incinerators under Section 129 of the Clean Air Act because sewage sludge does not meet the statutory definition of a solid waste under the Resource Conservation and Recovery Act, which explicitly excludes “solid or dissolved material in domestic sewage.”

However, EPA has proposed a rule that would redefine sewage sludge as a solid waste when it is combusted as part of a package of rules regulating emissions from industrial, commercial, and institutional boilers and commercial and industrial solid waste incinerators. The proposed rule would define when materials are solid wastes, which must be combusted by incinerators subject to emissions standards under Section 129 of the Clean Air Act, and materials that are fuels that can be burned in process heaters and boilers, which are subject to emissions limits under Section 112 (75 Fed. Reg. 31,844).

Some water utilities argued EPA should not regulate sewage sludge as a solid waste in comments on that proposed rule (158 DEN A-9, 8/18/10).

The American Chemistry Council said in its comments on the proposed performance standards that units that are permitted under Section 305 of the Solid Waste Disposal Act and Section 112 of the Clean Air Act should be exempted from EPA's proposed performance standards.

Regulating the incinerators under Section 112 of the Clean Air Act would mean the facilities would not be required to obtain Title V operating permits, the Sierra Club and Earthjustice said in comments on the proposed rule.

Exempting incinerators from the need to obtain the operating permits “would leave these polluters operating without meaningful control, monitoring and reporting requirements,” the environmental groups said.

Rule Would Limit Electric Generation From Sludge
Regulating sewage sludge as a waste rather than as a fuel would discourage it from being used to generate electricity, water utilities said.

“Approximately 17 percent of the 7 million dry tons of wastewater solids produced in the United States each year are incinerated, which could generate a net energy of approximately 360 [kilowatt hours] per dry ton of wastewater solids or 2,900 [gigawatt hours],” the Water Environment Federation said. “This represents a significant renewable energy source that the EPA should be encouraging and promoting.”

Many sewage treatment facilities choose to incinerate sewage sludge because landfills are not locally available, making incineration a more economical choice, the National Association of Clean Water Agencies said.

“Although wastewater treatment agencies rely on having multiple options for managing their sludge, the list of available options has slowly shrunk over the years for many communities,” the association said. “EPA's proposed action, if finalized without significant revision, would severely limit the use of incineration—which is currently used to manage approximately a fifth of the sludge generated annually in the U.S.—into the future and eviscerate progress toward a new, viable source of renewable energy for the country.”

By Andrew Childers