Mercury Reduction at the Largest Municipal Incineration Facility in North America

The Region of Peel (ROP), a regional municipality in the Great Toronto Area, has been using dewatered biosolids incineration since the early 1980's at the G.E. Booth (Lakeview) Wastewater Treatment Plant (GEBWWTP). The incineration facility operates as a regional hub at a rate of approximately 140 dry tonnes per day. Upon expansion of the incineration facility and new regulatory requirements by the Ontario Ministry of Environment (MOE) which limited the mercury emission limit to 70 μg/m3, the ROP decided to proceed with the addition of a mercury reduction process to system. The objective of the investigations undergone by the project team was to recommend an appropriate and reliable air pollution control (APC) system that would comply with the new, more stringent mercury limits. The ROP performed a survey to identify specific sources of mercury into the sewer system, though results were inconclusive. After due analysis, the project team selected a fixed bed granulated activated carbon (GAC) system for this application, to be installed on the flue gas stream of each incinerator. The selection of this technology was driven by the footprint limitation of the site, installation conditions and IDI/Infilco and Black & Veatch experiences. The complete system encompasses a scrubber, demister, radiative recuperator, and a GAC adsorber, which had proven beyond successful in meeting mercury reduction targets in other facilities in North America and Europe. The new APC system at the GEBWWTP was designed to continuously reduce mercury emissions below 50 μg/m3. The basic principle for metallic mercury (Hg) removal is based on a chemsorptive reaction in which the elemental mercury reacts with elemental sulphur forming non volatile mercuric sulphide. Therefore, the carbon media recommended for this application is impregnated with sulphur to improve mercury adsorption. Sulphuric acid is formed from SO2-, water and oxygen content of the gas. The mercury reacts with sulphuric acid, forming mercuric sulphate, a non-volatile compound. Ionic mercury (Hg2+) is removed in the upstream gas scrubbing system to a large extent and the remaining portion is adsorbed by the carbon media. A secondary benefit of the system is the removal of dioxins and furans, as well as residual amounts of sulphur dioxide (SO2) and Corganic. The systems for TOX 3 and 4 were commissioned in October 2010 and the first annual source testing after its implementation was performed in January 2011. Emissions of mercury were recorded at 10.0 and 16.0 μg/dry m3 for TOX 3 and 4, respectively. TOX 1 and 2 were commissioned in August 2010 and the respective annual source test is scheduled to occur in January 2012. With mercury emission limits becoming more stringent and the increase in source generation, the demand for the application of mercury reduction technologies is expanding. This system is the first one of its kind to be installed in Canada.