Emissions of gaseous pollutants, polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzo-furans from medical waste combustion in a batch fluidized-bed incinerator

Abstract

The quantities of pollutants emitted during the incineration of medical waste using a batch fluidized-bed system have not yet been well characterized. In this study, the CO, NO, and SO2 in the gaseous emissions of a pilot scale vortexing fluidized-bed incinerator (VFBI) and the toxic polychlorinated dibenzo-p-dioxins and polychlorinated dibenzo-furans (PCDD/Fs) in the fly ash collected from the baghouse were examined. Four kinds of simulated medical wastes with different chlorine contents were used. The effects of the feeding interval, chlorine content, and the addition of calcium carbonate were experimentally evaluated. The results showed that increasing the feeding interval decreased the amount of all pollutants due to the decreased bed temperature and prolonged residence time in the incinerator. The addition of calcium carbonate decreased the emissions of the three gaseous pollutants; however, the concentrations of PCDD/Fs of the fly ash increased while calcium carbonate was added. The concentration of NO and SO2 decreased while CO concentration increased with the increasing of chlorine content in the simulated medical waste. The magnitude of the effects of the operating parameters on the PCDD/F congeners formed followed the order: chlorine content > feeding interval > Ca/Cl ratio. Based on the experimental results, we extrapolate that the threshold value of the chlorine content was about 1% for PCDD/Fs generation. At a lower chlorine content, the PCDDs formation rate is higher than that at a higher chlorine content, especially for 1,2,3,4,6,7,8-HpCDD and OCDD. When the chlorine content exceeds the threshold value of 1%, the formation rate of PCDFs exceeds that of PCDDs.