Abstract: Since the US Environmental Protection agency (EPA) imposed restrictive limits on mercury emissions from sewage sludge incinerators, control of mercury emissions has become a high priority at wastewater treatment plants (WWTPs). This presentation will review how two municipalities used different technologies to control the mercury emissions from their fluidized bed sludge incineration systems. It will present the advantages and disadvantages of the two technologies.
The Metropolitan Service District (MSD) of Buncombe County in Asheville, NC used substrate polymer composite (SPC), a membrane filtration technology offered by EnviroCare Technologies. The project replaced the existing wet scrubbers with an EnviroCare multi-venturi scrubber and furnished the SPC filters on top of the scrubber. In February 2016, the incinerator passed its performance test and achieved mercury emissions slightly below the EPA mercury emission limit of 0.037 mg/dscm. Subsequent emissions testing revealed that the SPC system was achieving only about 50-70% removal of mercury, less than expected. After realizing another plant achieved greater than 90% control of mercury emissions with the same technology, temperature was determined to be a factor in efficiency. Electric heating coils were installed at MSD prior to the SPC modules to raise the temperature of the flue gas to 120°F -130°F from its original 70°F - 80°F temperature. With the heated flue gas, the SPC modules have achieved greater than 90% control of the mercury emissions in their two years of service.
The Somerset Raritan Valley Service Authority (SRVSA) in Bridgewater, NJ used activated carbon adsorption to control mercury emissions. SRVSA also has a fluidized bed sludge incinerator for solids disposal. The mercury levels in the WWTP sludge were quite high, requiring that the selected mercury control system achieve mercury removal levels of 95% or higher. While carbon adsorption can achieve high levels of mercury removal, it requires considerably more process equipment than the SPC technology. For SRVSA, the equipment included: a UHF filter, a HEPA filter, tertiary heat exchanger, carbon adsorber, a bypass electrical heater skid, and an ID fan. The incinerator and mercury control system were performance tested on 11/28/2018 thru 12/1/2018 for all nine pollutants listed in 40 CFR Part 62, Subpart LLL. All of the pollutant emissions were well below the emission standard.
