Emission Characteristics of Polychlorinated Dibenzo-p-dioxins and Furans from a Laboratory Waste Incinerator

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Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are extremely toxic chemicals that can bio-accumulate in the biotic materials, cause endocrines disruption. This study describes PCDD/F behavior during the incineration of laboratory waste, including combustible laboratory solid waste (LSW), laboratory plastic waste (LPW), and organic laboratory liquid waste (LLW). Stack flue gas (SFG), input materials, bottom ash (BTA), first quenching tower ash (FQA), secondary quenching tower ash (SQA), and baghouse ash (BHA) were sampled and analyzed using high-resolution gas chromatography/high-resolution mass spectrometry (HRGC/HRMS) assay and bioassay. The PCDD/F concentration of SFG met the standard in Taiwan. The Cl levels of LPW and LLW were roughly equivalent to that of municipal solid waste (MSW). Therefore, the SFG concentration, content of fly ash, and distribution behavior of PCDD/Fs are reasonably similar to those of MSW incinerators. The LSW had an extremely high Cl level (11.4%). The emission factor of the whole incineration system was 888 μg I-TEQ/ton-waste, which is 10-fold higher than that of MSW. The PCDD/F was mainly in BTA (31.6 wt.%) and fly ash (63.1 wt.%), resulting in higher PCDD/F level of ashes compared with that of MSW ashes. Laboratory wastes are discharged from experimental, testing, or analysis processes, and contain various toxic chemical compounds with a high heating-value and a high chlorine content (〉 9%). Elevated PCDD/F emissions are caused by combustion of waste with high chlorine contents, incomplete combustion, and so called memory effects. Even though the duration of cold start-up is short compared with the hours of continuous steady operation in a waste incinerator, its negative effects with regard to PCDD/F emissions on both human health and the environment cannot be neglected. A full-scale laboratory-waste incinerator which is operated for 10 days in each run and has 15 to 20 runs annually was investigated in this study. Eleven PCDD/F samples of stack flue gas were collected during the cold start-up periods (for 60.5 hrs). The gas temperature of the primary combustion chamber was above 850°C, and was maintained at between 850 and 900°C by injecting diesel fuel without waste feed. For first 1.5–7.5 hours, the PCDD/F concentration in the stack flue gas was as high as 0.656–1.15 ng I-TEQ/Nm3. Afterward, during hours 10.5–35.5 and 54.5–60.5, this reduced to 0.159–0.459 and 0.218–0.254 ng I-TEQ/Nm3, respectively. Based on principal component analysis (PCA) and the H/L ratio, the results revealed a lower H/L ratio (0.81) before hour 32, indicating that less chlorinated PCDD/F homologues (tetra- and penta-) dominated, while after hour 32 more chlorinated PCDD/F homologues (hexa-, hepta- and octa-) had a higher concentration and the H/L ratio rises to 2.38. These results indicate that the PCDD/F emissions during cold start-up were caused by memory effects and thermal desorption. Most literatures focused on comparison of different thermal processes or emission characteristics in the various types of incinerator, but this study conducts some surveys with various types of wastes feeding in the same incinerator. The whole system emission factor including the PCDD/F emission of stack flue gas, bottom ash, fly ash, wastewater of wet scrubber were distinguished. PCDF/PCDD ratio, emission factor, output/input ratios (O/I ratios), H(hexa-, hepta- and octa-)/L(tetra- and penta-) ratio High-Chlorinated congeners/Low-Chlorinated congeners were observed to demonstrate the emission characteristic of PCDD/Fs. The unique patterns of PCDD/F can be used as PCDD/F “fingerprints”, but limited studies have evaluated significant PCDD/F fingerprint predictors. More available emission characteristics are needed from different types of sources, to discriminate the category of emission sources to which the individual belongs to. Both HRGC/HRMS analysis and bioassay results show similar PCDD/F emission characteristics during the incineration of LW. In addition, the linear regression between the values acquired using these two methods show a good relation (R2 〉0.84), indicating that Ad-DR bioassay is a promising fast-screen method for determining PCDD/F levels. Additionally, in order to reduce the PCDD/F emissions from the stack flue gas of waste incinerators, is highly recommended that a higher amount of activated carbon injection is used in front of the bag filters.