Can an Old Multiple Hearth Incinerator Meet the New USEPA Sewage Sludge Incinerator Regulations?

This paper discusses the improvements made to the multiple hearth incinerator (MHI) at the advanced water reclamation facility (AWRF) located in Brockton, Massachusetts. The MHI is used for thermal reduction of the residual solids generated at the city's AWRF. In the past, the city had encountered operational challenges with the MHI, including high maintenance due to slag and clinker formation, incomplete burning of the solids due to balling of the solids feed, and limited capacity. In addition, stringent U.S. Environmental Protection Agency (USEPA) sewage sludge incinerator (SSIs) regulations had been proposed that put continued use of the MHI in jeopardy.In June 2009, the city authorized CDM Smith to perform a preliminary design and eventually a final design of upgrades to the MHI. Upgrades to the MHI included installation of a flue gas recirculation (FGR) system to improve emissions and to reduce slag and clinker formation, replacement of the existing wet scrubber with a multi-venturi scrubber, and significant other improvements and repairs to the incinerator. Construction was completed in fall 2010 and emissions compliance testing was conducted on January 21 and 22, 2011.This paper will also discuss the air permitting process with the Massachusetts Department of Environmental Protection (MADEP). MADEP required that air dispersion modeling of the incinerator's emission limits be conducted. The air modeling demonstrated that the incinerator meets the MADEP's Allowable Ambient Limits (AALs) and Threshold Effect Exposure Limits (TELs), as well as the National Ambient Air Quality Standards (NAAQS). Final compliance testing of the incinerator emissions demonstrated that the incinerator met the recently finalized USEPA sewage sludge incinerator regulations (40 CFR Part 60, Subpart MMMM).