August 12, 2025

NSPS and Emission Guidelines Amendments for Other Solid Waste Incinerators

On June 30, 2025, EPA finalized amendments to the new source performance standards and emission guidelines for other solid waste incinerators (OSWI) regulated under Part 60, Subparts EEEE and FFFF. [90 FR 27910] OSWI are typically smaller capacity incinerators operating at commercial or institutional sources that are not otherwise regulated under another incinerator standard, such as the commercial and industrial solid waste incinerator (CISWI) NSPS of Subpart CCCC. The final rule amends applicability and definitions, revises OSWI subcategories, strengthens emission limits, eliminates the startup, shutdown, and malfunction exemption, and expands administrative requirements.

A key change in the rule is the establishment of a new subcategory for very small municipal waste combustors (VSMWCs) and institutional waste incinerators with capacities ≤10 tons per day. This new subcategory, coupled with a change in the definition of “municipal solid waste,” means small incinerators that burn more than 30% municipal solid waste located on commercial or industrial sites would qualify as VSMWC. As such, these units are no longer subject to the CISWI rules. These changes primarily target oil and gas operations.

VSMWCs also face strengthened emission limits for both new and existing sources effective December 29, 2025. The agency did not, however, strengthen the emission limits for units combusting >10 tons per day. Such limits remain unchanged from the original 2005 rule.

Of particular note is EPA’s decision not to address pyrolysis and gasification in this final rule. Sometimes known as “advanced” or “chemical” plastic recycling, it is argued that these processes emit hazardous air pollutants. In 2020, EPA proposed removing pyrolysis/combustion units from the “municipal waste combustion unit” definition in Part 60, Subparts EEEE and FFFF, but on June 5, 2023, the agency withdrew that proposal. [88 FR 36524] Retaining pyrolysis in the definitions for incinerators and waste combustors keeps this method of plastic recycling subject to more-stringent CAA Section 129 solid waste combustion standards rather than less-stringent CAA Section 111 or 112 provisions.

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