Waste-to-Energy Combustors: two sets of pollutants; two different stories

摘要

Few new waste-to-energy (WTE) facilities have been constructed in the Unites States in the past two decades, in part because of concerns over environmental impacts and possible health effects. Concerns about WTE facilities have focused on two pollutants emitted from exhaust stacks: polychlorinated dibenzo(p)dioxins and furans (PCDD/PCDFs), and mercury. In the 1980's and '90's, municipal waste combustion was a relatively large anthropogenic source of these pollutants. Since then, at least three factors have resulted in substantially reduced emissions: (1) flue-gas control technologies have been optimized to minimize PCDD/PCDF formation, (2) the mercury content of solid waste has been reduced; and (3) carbon injection has been added as a back-end control measure, further reducing emission rates of both pollutants. Many waste-to-energy plants have operated for twenty or more years now, and test data taken over time reveal important trends. Exposure and health risk assessments using these data suggest risks to health that are quite small, and indistinguishable from zero. This is especially true for the dioxins and furans, which pose no risk at and below threshold doses. The issues surrounding mercury are less straightforward, and are discussed herein.