Combustion Portal: Environmental Compliance for Combustion Processes

Air Emissions Regulations

Large MWC

Small MWC

The U.S. Environmental Protection Agency (EPA), under section 129 of the Clean Air Act (CAA), is required to regulate emissions from certain categories non-hazardous solid waste incinerators and combustors. Section 129 requires EPA to set numerical emissions limitations of nine pollutants from Large and Small Municipal Waste Combustion (MWC) units. The nine pollutants are:

All standards established pursuant to CAA Section 129(a)(2) must reflect maximum achievable control technology (MACT). The MACT "floor," or minimum level of stringency set forth differing levels of minimum stringency that EPA’s standards must achieve, depending on whether they regulate new or existing sources.

The CAA allows EPA to subcategorize a source category based on differences in class, type, or size. The MWC regulations are subcategorized by size and class (see rules for class distinctions):

Municipal solid waste combustors burn waste from households (e.g. waste from residential dwellings, hotel/motel, temporary/permanent housing), commercial or retail (e.g. material discarded by stores, offices, restaurants, warehouses, nonmanufacturing activities at industrial facilities), or institutions (e.g. discarded waste by schools, non medical waste from hospitals, nonmanufacturing activities at prisons and governmental facilities, and other similar establishments or facilities). Wastes from households, commercial/retail, and institutional does include yard waste and refuse-derived fuel. In addition to reducing volume, combustors, when properly equipped, can convert water into steam to fuel heating systems or generate electricity. A variety of pollution control technologies significantly reduce the air emissions.

The enforcement authority is different for the NSPS and EG. The NSPS are directly enforceable federal regulations, and under CAA section 129 (f)(1), become effective 6 months after promulgation. The EG are not themselves directly enforceable. Rather, the EG are implemented and enforced through either an EPA-approved state plan or a promulgated federal plan. States are required to submit a plan to implement and enforce the EG to EPA for approval not later than 1 year after EPA promulgates the EG (CAA section 129 (b)(2)). The state plan must be "at least as protective as" the EG and must ensure compliance with all applicable requirements not later than 3 years after the state plan is approved by EPA, but not later than 5 years after the relevant EG are promulgated. If a state does not develop an approvable implementation plan, EPA will promulgate a federal plan that will apply to existing Large and Small MWC units located in that state.

Sulfur Dioxide/Nitrous Oxide Emissions. Title IV of the CAA establishes a sulfur dioxide/nitrous oxide emissions program designed to reduce the formation of acid rain. Sulfur dioxide releases will be reduced by granting to certain sources limited emissions allowances, which are below previous levels of sulfur dioxide releases. Local governments that operate municipal waste combustors, sewage sludge incinerators, or large boilers/generators may be subject to these requirements (see EPA's Acid Rain Program).

New Source Performance Standards (NSPS)

New Source Performance Standards (NSPS) are federal standards adopted by the U.S. Environmental Protection Agency (EPA) to regulate air emissions of criteria pollutants by many types of industrial facilities. The standards are intended to promote use of the best air pollution control technologies.

All industries subject to NSPS must meet certain general requirements, such as monitoring and recordkeeping. In addition, certain specific requirements apply to each type of industry subject to NSPS. Each NSPS defines the facilities subject to it and prescribes emission limits for specified pollutants, compliance requirements, monitoring requirements, and test methods and procedures.

New Source Performance Standards (NSPS) exist for Large Municipal Waste Combustors (> 250 tons/day of MSW combustion capacity) and Small Municipal Waste Combustors (250 tons/day or less of MSW combustion capacity), which includes both waste to energy plants and combustion units. The rules vary depending on when the units were constructed.

Large Municipal Waste Combustors:

Subpart Cb and Eb standards establish requirements for MWC metals (PM, Cd, Pb, Hg, opacity), MWC organics (dioxins/ furans), MWC acid gases (SO2, HCl), MWC operating practices (CO, flue gas temperature, load level), NOx, and MWC facility siting requirements.

Small Waste Combustors:

Sulfur Dioxide/Nitrous Oxide Emissions. Title IV of the CAA establishes a sulfur dioxide/nitrous oxide emissions program designed to reduce the formation of acid rain. Sulfur dioxide releases will be reduced by granting to certain sources limited emissions allowances, which are below previous levels of sulfur dioxide releases. Local governments that operate municipal waste combustors, sewage sludge combustion units, or large boilers/generators may be subject to these requirements (see EPA's Acid Rain Program).

More information on MSW combustion air pollution:

Solid Waste

The burning of MSW in boilers creates residual ash (fly ash and bottom ash), which can contain any of the elements that were originally present in the waste. MSW combustion units reduce the need for landfill capacity because disposal of MSW ash requires less land area than unprocessed MSW. However, because ash and other residues from MSW operations may contain toxic materials, the power plant wastes must be tested regularly to assure that the wastes are safely contained to prevent toxic substances from migrating into groundwater supplies. Under current regulations, MSW ash must be sampled and analyzed regularly to determine whether it is hazardous or not. Hazardous ash must be managed and disposed of as hazardous waste. Non-hazardous ash may be disposed of in a MSW landfill, an ash monofill or recycled.

More resources for solid waste:

Water Resources Protection

Combustion processes generate wastewater associated with processes such as cooling tower blowdown, flue gas treatment, and washdowns. Discharges of wastewater are regulated under the Clean Water Act (CWA). Facilities which discharge indirectly through a Publically Owned Treatment Works (POTW) are regulated under the Pretreatment Program, which insures that facilities pretreat wastewater to remove pollutants which would affect the pollutant removal ability of the POTW. Facilities that discharge process or non-process wastewater directly streams, rivers, etc. are regulated under the National Permit Discharge Elimination System (NPDES) and must obtain coverage under a General Permit or an Individual Permit.

In addition to compliance with rules covering wastewater generated by combustion units, applicable facilities must be concerned with stormwater runoff.

Each of these topics is summarized below with links to related web pages and documents.

Indirect Discharge

Facilities that discharge wastewater into a sewer system that leads to a municipal treatment plant, also known as Publicly Owned Treatment Works (POTW) are indirect dischargers. The POTW typically is owned by the local municipality or a regional board or sewer authority.

In response to potential problems caused by industrial wastewater being discharged into POTW's, federal pretreatment regulations were developed. These regulations apply to all municipal, industrial and commercial facilities. Local POTW's with approved pretreatment programs have responsibility for enforcing pretreatment requirements. Otherwise, the rules are enforced by the state or EPA regional authority.

All indirect dischargers must meet national General Pretreatment Regulations (40 CFR 403). Additionally, certain types of facilities must also meet applicable categorical pretreatment standards. When a pollutant, discharged by an indirect discharging industry is not specifically limited by pretreatment standards, it is up to the state or local regulatory agency to develop local limits or to determine other appropriate means to control its discharge.

More information on indirect discharges to POTW's:

Direct Discharge

Facilities that discharge process wastewater or cooling water to surface waters are direct dischargers. Direct dischargers must obtain a permit under EPA's National Pollutant Discharge Elimination System (NPDES) program. A NPDES permit sets limits on the amount of specific pollutants that can be discharged to surface waters.

Some states offer general permits for non-contact process water (e.g., cooling water). The purpose of the general permit is to provide a streamlined NPDES permitting process for certain classes or categories of industrial point source discharges. Coverage under a NPDES general permit is unique in that a facility operates and discharges under the requirements of the applicable general permit rule rather than the requirements of an individual permit. Check with your state environmental agency to determine if a general permit is applicable to your facility.

More information on direct discharge NPDES permits:


Leachate from waste unloading and storage operations caused by exposure to precipitation and from residual liquids in the waste itself may contain organic matter, nutrients, metals, salts, pathogens, and hazardous chemicals. Stormwater regulations promulgated under the Clean Water Act help prevent these materials from polluting nearby streams and other water courses. Operations such as MSW combustion units must develop a Stormwater Pollution Prevention Plan (SWPPP), obtain coverage under a NPDES stormwater permit, and implement methods of controlling stormwater pollution, including best management practices. For more information about the Stormwater program, visit the Stormwater Basic Information page.

Throughout most of the nation, U.S. EPA has delegated the stormwater program to the states to administer as they see fit, so long as minimum federal requirements are met. For more information on state stormwater rules see the Industrial Stormwater State Resource Locator. The locator will help you find state-specific information on permitting, technical resources and points of contact.

More information on Stormwater:

Spill Prevention, Control and Counter Measures

EPA promulgated the Spill Prevention, Control and Counter Measures (SPCC) rule to reduce the risk of damaging our waterways from oil spills. These rules are applicable to a very wide range of facilities and operations, including fuel oil storage tanks for combustion units. The rule requires specific facilities to prepare, amend, and implement SPCC Plans. The SPCC rule is part of the Oil Pollution Prevention regulation, which also includes the Facility Response Plan (FRP) rule.

An SPCC Plan is required for facilities which due to their location, could reasonably be expected to discharge oil to surface water or adjoining shorelines and have:

The SPCC regulations require the facility owner/operator to prepare and implement an SPCC plan for their facility. This plan must be well thought out and prepared in accordance with good engineering practices. It must document the location of storage vessels, types of containment, dangers associated with a major release of material from the tanks, types of emergency equipment available at each site, and procedures for notifying the appropriate regulatory and emergency agencies.

To assist facility owners and operators with SPCC compliance, EPA has published a useful document: Spill Prevention, Control, and Countermeasure (SPCC) Regulation.

More resources on SPCC:

Applicable rules: 40 CFR 112.

Pollution Prevention

EPA encourages practices that reduce the amount of waste needing to incinerated, such as waste prevention, recycling, and composting.

Currently, in the United States, 33.8 percent is recovered and recycled or composted, 11.9 percent is burned at combustion facilities, and the remaining 54.3 percent is disposed of in landfills.

General Resources for MSW Combustors

Municipal Solid Waste Publications. An extensive collection of publications covering waste characterization, source reduction and many other topics.

National Solid Waste Management Association. NSWMA is a trade association representing for-profit companies in North America that provide solid, hazardous and medical waste collection, recycling and disposal services, and companies that provide professional and consulting services to the waste services industry.

Association of State and Territorial Solid Waste Management Officials (ASTSWMO). An organization supporting the environmental agencies of the States and trust territories. ASTSWMO focuses on the needs of State hazardous waste programs; non-hazardous municipal solid waste and industrial waste programs; sustainability, recycling, waste minimization, and reduction programs; Superfund and State cleanup programs; waste management and cleanup activities at federal facilities; and underground storage tank and leaking underground storage tank programs.

National Overview: Facts and Figures on Materials, Wastes and Recycling. EPA began collecting and reporting data on the generation and disposition of waste in the United States more than 35 years ago. The Agency uses this information to measure the success of materials management programs across the country and to characterize the national waste stream. These Facts and Figures are current through calendar year 2018.

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