Emission, distribution and formation characteristics of polybrominated dibenzo-p-dioxins and dibenzofurans during co-disposal of hexabromocyclododecane-containing waste in cement kiln

Abstract

Hexabromocyclododecane (HBCD)-containing waste was co-disposed in a cement kiln to evaluate its destruction removal efficiency (DRE) and its impact on polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) formation. The DRE of HBCD exceeded 99.9999 %. The residual HBCD after disposal was mainly found in kiln head ash and clinker. Stack gas at kiln head and tail exhibited average PBDD/Fs emission levels (sum of 13 2,3,7,8-PBDD/Fs congeners) of 0.36 and 0.42 ng m−3, respectively, with octa-BDD predominating. However, in the kiln tail ash, hexaBDF and hepta-BDF were secondarily generated, leading to an increase in PBDFs concentration. Notably, most HBCD underwent debromination and ring-opening in the calciner, with released bromine absorbed and removed by CaO. Its decomposition products such as polycyclic aromatic hydrocarbons, biphenyls and their derivatives served as carbon sources for PBDD/Fs synthesis. However, co-disposal of HBCD did not significantly raise PBDD/Fs emissions but altered their homolog distribution from PBDDs to PBDFs. Emission factors of HBCD and PBDD/Fs were the highest in the clinker at 6.55 × 102 and 0.55 × 102 μg t−1, respectively. Therefore, attention was needed for the potential secondary release of pollutants during the transportation and utilization of clinker. These findings enhanced understanding of the distribution and formation pathways of PBDD/Fs during cement kiln co-processing, providing insights for their source control.