Prevention of Polychlorinated Dibenzo-p-dioxins/Dibenzofurans Formation on Municipal Waste Incinerator Fly Ash Using Nitrogen and Sulfur Compounds

Formation of polychlorinated dibenzo- p -dioxins (PCDD) and polychlorinated dibenzofurans on incinerator fly ash can be reduced under laboratory conditions by the addition of ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), or Na 2 S. With these compounds (inhibitors), a reduction in formation of ca. 80−90% is achieved. The inhibitors reduce the ratio of [PCDD]:[PCDF] formed, suggesting that more than one pathway for the formation from carbon exists. EDTA and Na 2 S reduce the degree of chlorination of PCDD; for PCDF, the same effect is seen with Na 2 S. No change was ever seen in the isomer distribution within homologues as a result of the inhibitors added, in accordance with the theory that these isomer distributions are thermodynamically controlled. In additional experiments, NTA gave a good reduction with reaction times of 30−60 min, at temperatures between 300 and 400 °C, and with concentrations in the reaction mixture of 2−10%. With HCl as a chlorinating agent, the inhibition by NTA is >50% for both PCDD and PCDF. These inhibitors show promising results to achieve the reduction of PCDD/F formation. The additional experiments with NTA show that this compound can reduce formation under various conditions, making it suitable for use in the post-combustion zone of an incinerator, where reaction conditions will vary.