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Will Agencies Regulate Air Emissions from Pyrolysis and Gasification Units Like they Regulate Air Emissions from Combustion Units?

Posted: May 9th, 2022

Authors: Michael M. 

Most people are familiar with combustion in some form or another.  Whether it’s a campfire used to roast marshmallows, the oil burner used to heat your house on a cold winter day, or the engine that powers your car, combustion directly affects our lives on a daily basis.  Many people, however, are not familiar with combustion cousins: pyrolysis and gasification.

As we continue to see a push for increased sustainability and a desire to extend the usefulness of materials, we have also seen an increase in the use of pyrolysis and gasification across many industrial sectors.  Pyrolysis and gasification can be used to convert used plastics, biosolids, municipal solid waste, coal, and wood into fuels or feedstock for industrial chemical and consumer products manufacturing.  The term “Advanced Recycling” has been applied to the conversion of waste materials into usable feedstock for industrial manufacturing; however, several states and industry associations oppose the application of the term “recycling” to these processes, instead preferring terms such as “thermomechanical conversion.”  The use of these technologies to produce alternative fuels is also of interest as industry looks to reduce its use of traditional fossil fuels.

Key Terms

Congress did not anticipate the use of these technologies for waste treatment, so they did not define the terms pyrolysis and gasification in the Clean Air Act (CAA).  However, they do appear in some of the regulations promulgated under CAA section 129 pertaining to solid waste combustion.  Therefore, it is important to understand the definitions of the following terms:

Combustion1 – “The production of heat and light energy through a chemical process, usually oxidation.  Products of complete combustion include water and carbon dioxide, while incomplete combustion can yield partially oxidized organic compounds and carbon monoxide.  Factors that promote complete combustion include the proper fuel-air ratio, temperature range, and adequate amount of time for the fuel and its by-products to complete the combustion reactions.”

Pyrolysis2 – “Thermally decomposes or rearranges materials under process conditions where extremely little to no oxygen is present.”

Gasification3– Process that “converts feed materials (primarily carbonaceous) into syngas (carbon monoxide and hydrogen) and carbon dioxide.  The materials are gasified when they react with controlled amounts of oxygen or steam at high temperatures.”

The following table summarizes which CAA section 129 regulations address pyrolysis and gasification:

Advanced Notice of Proposed Rulemaking

Due to the inconsistency in how pyrolysis and gasification are addressed in CAA section 129 regulations and the number of inquiries received on how to regulate air emissions from new pyrolysis and gasification units, on September 8, 2021, the United States Environmental Protection Agency (U.S. EPA) published an Advance Notice of Proposed Rulemaking (ANPR) to solicit information and comments to assist in the development of regulations for pyrolysis and gasification units. The notice received significant attention, resulting in an extension of the comment period from November 8 to December 23, 2021. Over 170 comments were received. It will be interesting to see how the comments are considered and whether a proposed regulatory action results from the review of the comments, given all U.S. EPA’s other competing priorities and goals and the disparate views on whether pyrolysis and gasification units should be regulated as waste incinerators or whether the process should be considered recycling.  Some commenters asserted that regulating pyrolysis and gasification units under existing waste incinerator rules would stifle innovation and development of these technologies.

CAA Section 114 Request

In the ANPR, U.S. EPA indicated they are considering two potential pathways to regulate pyrolysis and gasification units, and published a draft questionnaire intended to collect data to determine the most appropriate way to regulate theses sources4.  The data collected will be used by U.S. EPA in deciding whether to regulate these sources under CAA section 129 or as specific source categories under CAA section 111 and 112.  CAA section 129 directs U.S. EPA to regulate solid waste incinerators.  CAA section 111 is the underlying statute for the Standards of Performance for New Stationary Sources (NSPS) and CAA section 112 is the underlying statute for the 40 CFR Part 63 National Emissions Standards for Hazardous Air Pollutants (NESHAP).  Regulations promulgated under CAA section 129 are generally more stringent than regulations promulgated under CAA sections 111 and 112.

State Level Regulatory Action

In addition to potential regulatory action related to air emissions from pyrolysis and gasification at the federal level, states may regulate these processes differently.  For example, the Kentucky General Assembly recently approved an amendment to Kentucky Revised Statute (KRS) 224.1-010 to define Advanced Recycling as “a manufacturing process for the conversion of post-use polymers and recovered feedstocks into basic hydrocarbon raw materials, feedstocks, chemicals, and other products through processes that include pyrolysis, gasification, depolymerization, catalytic cracking, reforming, hydrogenation, solvolysis, and other similar technologies.”  Under the proposed legislation, advanced recycling activities would be excluded from definitions related to solid waste, including, but not limited to “disposal” and “municipal solid waste disposal facility.”  According to the American Chemistry Council, Kentucky is the 18th state to pass such an advanced recycling law, designating these types of facilities as manufacturers not waste incinerators.


As more units are being constructed, we are starting to see a significantly growing interest in regulating air emissions from pyrolysis and gasification units at both the state and federal level.  If your facility is using pyrolysis or gasification in your process, you should anticipate agency proposals for additional regulations or amendments to existing regulations.   ALL4 can assist you with determining how your state regulates these processes and what federal regulations might apply.

Completing a Section 114 request is outside the routine responsibilities of a facility’s environmental professional.  If you are preparing for and completing a Section 114 Request, it can involve a significant commitment of time and resources.  While the Section 114 Request is not final, it is not too early to begin preparations for developing a response.

ALL4 has extensive experience in assisting regulated entities navigate the complex web of state and federal environmental regulations and is keeping a close eye on developments related to pyrolysis and gasification.  We will continue to monitor new federal and state regulations are they are developed.  ALL4 has also assisted clients with data gathering and compilation and electronic submittals of information to U.S. EPA.  If you have questions or require assistance with your project, please reach out to me at mmchale@all4inc.com.

1U.S. EPA.  Basic Concepts in Environmental Sciences Glossary.  U.S. EPA.  [Online] January 29, 2010.
2 U.S. EPA.  Draft Survey for Pyrolysis and Gasification Units.  Docket Number EPA-HQ-OAR-2021-0382.
4The information U.S. EPA is proposing to request as part of the Section 114 request includes, but is not limited to the following: 

  • Construction and startup dates
  • Description of the configuration
  • Air emissions data from the pyrolysis and gasification chamber and downstream combustion devices.
  • Purpose of the technology


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