Thermal Treatment of Wastewater Residuals: Clean Water Act Meets the Clean Air Act

For over thirty years the Clean Water Act has resulted in tremendous improvements in the quality of the wastewater effluent from treatment plants and in the quality of the water in receiving waterways. Similarly, the Clean Air Act has greatly reduced emissions to the atmosphere and improved the air quality in urban areas. For wastewater treatment plant residuals that are thermally treated, the requirements of both the Clean Water and Clean Air Acts must be satisfied.The Clean Water Act Amendments of 1987 required the U.S. Environmental Protection Agency (U.S. EPA) to establish standards for the use or disposal of sewage sludge. These standards defined performance requirements for land application, surface disposal and incineration and were incorporated into Title 40 Part 503 of the Code of Federal Regulations (40 CFR 503). If any of the land application, surface disposal or incineration of biosolids are practiced following the rules defined in the U.S. EPA Part 503 Regulations, and any additional State (or Provincial) regulations, then the risks to the practices are considered safe and the risks to the communities are trivial. In addition, landfilling in a municipal waste landfill, practiced in accordance with applicable EPA rules for solid waste management, is also considered safe.Where thermal treatment is needed to prepare a pelletized soil amendment or combust wastewater residuals, the requirements of the Clean Air Act must also be considered. That the Clean Air Act (CAA) includes requirements for the combustion of wastewater treatment plant residuals is recognized in the Part 503 regulations. However, advancements in thermal treatment technologies and the complexity of the air quality permitting requirements under the CAA makes it timely for these requirements to be reviewed.Before a thermal treatment process for wastewater residuals is constructed or modified it must be reviewed prior to construction of the facility or completion of the planned modifications. The nature of the review depends on the type of facility, the magnitude of the potential emissions and attainment status for the area where the plant is located. If the facility is located in an area that is not in attainment of the National Ambient Air Quality Standards (NAAQS), stringent air pollution control requirements and emissions limits will apply (CAA Part D). A facility located in an area meeting the NAAQS, may still be subject to a comprehensive permit review (CAA Part C), but the resulting emission limits may be less stringent than a facility located in a non-attainment area.Emissions limits are established under the New Source Performance Standards (CAA Sec. 111) and National Emission Standards for Hazardous Air Pollutant regulations (CAA Sec. 112). These limits are minimum requirements. More stringent limits may be established as a result of the Best Available Control Technology or Lowest Achievable Emission Limit review conducted as part of the permitting process. State Air Toxics programs may also establish emission limits of some hazardous air pollutants.Once the facility is constructed, the Operating Permit program assures continued compliance and reporting of actual emissions from the major facilities. The Operating Permit program (Title V of the CAA) consolidates the emission limits established for the entire facility and defines a means to monitor compliance with the limits.The critical issue with respect to permitting thermal treatment units under the Clean Air Act is that approval from the reviewing agency must be received before construction commences. While complying with the requirements of the Clean Air Act can be achieved, the specific emission limits that may apply to a facility may be influence by the attainment status of the facility site, local meteorology or terrain features and the state regulatory requirements. Thus, careful consideration to the air permitting requirements for a thermal treatment system must be made at the early planning and design phases of project.