Chieh Lin

Polychlorinated dibenzo-p-dioxins/dibenzofuran mass distribution in both start-up and normal condition in the whole municipal solid waste incinerator.

Although many researches focused on the polychlorinated dibenzo-p-dioxins/dibenzofuran (PCDD/F) emissions from stack, in the bottom ash and in the surrounding environment, researches focused on PCDD/F mass distributions in the whole incineration plant have seldom been addressed. This study determined PCDD/F emissions in the whole plant. A high-resolution gas chromatograph/high-resolution mass spectrometer was utilized for analyzing 17 PCDD/F species. Experimental results displayed that PCDD/Fs were formed during fly ash from super heater (SH), economizer (EC), semi-dryer absorber (SDA) and fabric filter (FF) was transferred to fly ash pit. Mass distribution ratios of PCDD/Fs in g I-TEQ (Toxicity Equivalency Quantity) per week from stack, SH, EC, SDA, FF, generation and bottom residue (BR) in start-up operations were 14.6%, 0.1%, 8.3%, 1.0%, 41.7%, 33.4% and 0.9%, respectively. Above results indicated that main PCDD/F source in the MSWI was from fly ash. However, the fly ash is easily controlled and PCDD/F emitted from stack flue gases will be difficult to be handled. Therefore, we should pay more attention on PCDD/F emission from flue gases especially from start-up procedure. Besides, fly ash should be controlled by sodium hypophosphite before being landfilled. MSWI did require further detoxification treatments for the solid residues and flue gases.

PCDD/Fs formation catalyzed by the copper chloride in the fly ash

The secondary formation of dibenzo-p-dioxin and dibenzofurans (PCDD/Fs) in the flue gas and ash from the municipal solid waste incinerator (MSWI) systems has attracted considerable public concern. The objective of our research was thus to examine reactions in fly ash from an MSWI operated with different precursors with similar chemical compositions, such as dibenzofurans (DFs), and metal chlorides, such as copper chloride (CuCl2). We observed that the concentrations of PCDD/Fs in CuCl2 and in a mixture of CuCl2 and DFs were 369.5 and 5307.8 ng/g, respectively, and thus significantly higher in the latter. Due to the catalytic effect of copper ions and the similar structure of dibenzofurans for PCDFs, the effect of the additive in forming PCDD/Fs were obvious. The concentrations of PCDD/Fs in CuCl2 and copper oxide (CuO) were 369.5 and 97.05 ng/g, respectively. The results also show that the PCDD/Fs concentration when copper chloride was added was four times higher than when copper oxide was added. In addition, the level of activity of the chlorine atoms is greater than that of the oxygen atoms during the formation of PCDD/Fs. This study suggests that the use of metal-containing substances (such as Cu, Cl, Zn) or chlorination precursors (such as DF, chlorobenzene) should be avoided in the combustion process.

Characterization of PCDD/Fs, PAHs, and heavy metals in a secondary aluminum smelter.

This study characterizes polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs), polycyclic aromatic hydrocarbons (PAHs), and heavy metal concentrations in stack flue gas, workplace air, fly ash, bottom ash, and ambient air of a secondary aluminum smelter. The total PAH concentration in workplace air was dominated by 2- and 3-ring PAHs, accounting for 86.2% of the gas phase in the total PAHs. The PCDD/F concentrations in workplace air are 1–7 fold higher than that in ambient air. The mass distribution ratio for total PCDD/Fs was soil > ash > workplace air > ambient air > flue gas. Aluminum and Zn had the highest concentrations. A positive correlation existed between PCDD/Fs and PAHs concentrations (r2 = 0.920). The operation of secondary aluminum smelter affects the pollutant concentrations and surrounding air quality. Experimental results suggest that besides the terminal control technologies for stack flue gases, engineering control technologies in the workplace need further improvement.