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The regulatory status of digester gas generated during the anaerobic digestion of sewage sludge has been called into question by a new U.S. Environmental Protection Agency (EPA or Agency) rule.  The same rule will impact the regulatory status of any biosolids or biosolids-derived products that are burned for energy recovery, regardless of the type of combustion unit.  The final rule , Identification of Non-Hazardous Secondary Materials That Are Solid Waste (76 Fed. Reg. 15456), published March 21, 2011, defines as a solid waste any sewage sludge or biosolids that is combusted (See Advocacy Alert 11-12 for additional details on the final rule).  This definition rule, which was developed to assist EPA in the drafting of a series of Clean Air Act (CAA) rules for incinerators and boilers, became effective on May 20, 2011.

While the most visible impact of the new definition rule for clean water agencies is on the regulatory status of sewage sludge incinerators (SSIs), the definition rule has also created confusion over the regulatory status of gas generated from anaerobic digestion of sewage sludge and biosolids and biosolids-derived products that may be combusted in units other than SSIs.

This Advocacy Alert provides additional details on the impact of the definition rule on the management of sewage sludge.  Contact Chris Hornback, NACWA at 202/833-9106 or This e-mail address is being protected from spambots. You need JavaScript enabled to view it if you have any questions.

EPA Clarifies Regulatory Status of Biogas from Anaerobic Digestion, NACWA to Seek Additional Guidance

Though EPA apparently did not intend to impact the regulatory status of digester gas from anaerobic digestion and similar gases such as landfill gas, the Agency’s final solid waste definition rule and supporting background material suggest that these gaseous fuels derived from what is now considered to be a solid waste (i.e., sewage sludge) by EPA, would themselves be considered solid wastes.  If these gaseous fuels are designated as solid wastes, any combustion of the materials, including burning for energy recovery or flaring, would be subject to the regulations for commercial and industrial solid waste incineration (CISWI) units or similar regulations on solid waste incineration.  Through a May 13, 2011, policy letter discussed further below, EPA has clarified that it did not intend to include these gases under its solid waste rules.  Nevertheless, NACWA will seek more formal clarification of the status of these gaseous fuels.

The definition of solid waste under the federal Resource Conservation and Recovery Act (RCRA), which governs the regulation of solid and hazardous wastes, includes ‘contained gaseous material’ as part of the regulated universe of solid waste.  In the past, gaseous materials such as digester gases that were conveyed via pipeline to a combustion unit were not considered ‘contained’ and therefore would not be considered solid wastes.  In its response to comments document associated with the March 21, 2011 definition rule, EPA made statements suggesting that the Agency no longer considered these piped gases to be ‘uncontained’.  The impact of such a change in interpretation would be substantial and a number of industry groups were successful in obtaining a clarification letter from EPA.  The May 13, 2011, letter to Tim Hunt, American Forest and Paper Association, indicates that the response to comments language “does not change any previous EPA positions.  [EPA clarifies] here that the Agency’s previous statements and interpretations remain effective.”  In other words, digester gas piped to a flare or other combustion unit is not considered a ‘contained gas’ and therefore would not be a solid waste under the federal RCRA rules.

NACWA recommends that members who generate and burn digester gas in any manner obtain a copy of the May 13, 2011, letter from its website and maintain it in their files should the regulatory status of their gas operations be called into question.  NACWA along with a number of industry groups will be requesting that EPA provide more formal clarification via Federal Register notice on the regulatory status of these gaseous fuels and NACWA will seek to address this issue during its forthcoming legal challenge of the final definition rule.

Biosolids Burned in Any Manner Now Considered Solid Waste

Effective May 20, 2011, any sewage sludge/biosolids or biosolids-derived products, including material that meets the Part 503 standards, pellets, and any other processed material from sewage sludge, is considered a solid waste when combusted. SSIs – which EPA has determined are not designed to recover energy – will be required to meet the newly promulgated CAA emission standards (see Advocacy Alert 11-11).  Other combustion units (cement kilns and boilers, for example) burning biosolids in any form will be subject to regulation as a solid waste incineration unit (not the SSI CAA standards).  EPA did not include a de minimis threshold quantity of sludge, so any quantity of sludge will impact the regulatory status of the combustion unit.  Biosolids that can meet all three of EPA’s legitimacy criteria for nonhazardous secondary materials used as fuels laid out in the definition rule may be able to avoid regulation as a solid waste:

1. Managed as a valuable commodity;
2. Has a meaningful heating value and is used in a unit that recovers energy; and
3. Contains contaminants at levels comparable in concentration to or lower than those in traditional fuels.

Despite NACWA objections, EPA in its final definition rule made a blanket determination that biosolids fail to meet the third criterion regarding contaminant levels.  This means that clean water agencies must now demonstrate that their biosolids can meet the criteria to avoid solid waste regulation.  EPA provides a non-waste determination process, through which utilities are able to petition EPA to declare their sludge as a legitimate secondary material.  In addition to the legitimacy criteria, the final rule includes other conditions that must also be met to get such a non-waste determination.

Processing and drying of sludge is not likely to reduce the metals concentrations that EPA says are ‘not comparable’ to traditional fuels (i.e., coal).  It is possible, however, that sludge from a particular facility or facilities may have concentrations that fall significantly below the average contaminant levels EPA outlines in the final rule and therefore could be eligible for a non-waste determination.  In such a case, a petition will need to be filed with EPA to seek a determination from the Regional Administrator.  EPA has so far provided few details on how this petition process will work.

NACWA recommends that any members using or providing biosolids as a fuel substitute review the final rules and evaluate the regulatory implications for their utility.

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Again, NACWA will continue to seek additional clarification on the contained gas issue and the regulatory status of digester gas.  NACWA is planning a legal challenge of EPA’s final definition of nonhazardous solid waste and will be raising these and other concerns on behalf of the clean water community.  NACWA’s initial filing in that case will be made on June 17.