title: Inhibition of the de novo synthesis of PCDD/Fs on model fly ash by sludge drying gases.
abstract: Sludge drying gases (SDG), evolving from drying and mild thermal decomposition (<300°C) of raw sewage sludge contain NH3 and SO2 as well as other N- and S-compounds. All of these are potential PCDD/Fs suppressants. It is indeed observed that these SDG suppress 2,3,7,8-substitued PCDD/Fs formation on Model Fly Ash (MFA) with an efficiency up to 97.6% in wt. units and 96% in I-TEQ, respectively. This suppression is strong for (the bulk of) PCDD/Fs, adsorbed on the model fly ash; conversely, sludge drying gases enhance PCDD/Fs desorption from MFA. Moreover, TCDD/Fs are suppressed least, possibly following stepwise dechlorination of higher chlorinated PCDD/Fs. Characteristics, such as the type, origins and amount of sludge, its moisture-, nitrogen- and sulfur content and the nature of the thermal treatment applied are all expected to influence upon the suppression capabilities. In this study three types of dry sludge are tested and applied as suppressant in four different amounts or modes. The quality of the sludge drying gases is continuously monitored: the Gasmet results reveal that NH3 and SO2 are the most important components of SDG. The MFA reaction residue is scrutinized by Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS) analysis. A large number of particles attaching to the surface of model fly ash are observed by SEM. Moreover, EDS analysis reveals that part of the chlorine in MFA is carried away with the SDG and replaced by sulfur, so that eliminating chlorine may be part of the inhibition mechanism. However, further research is still needed to establish the optimum operating modes and to confirm the role of both inorganic and organic nitrogen and sulfur compounds in the suppression of PCDD/Fs formation on model fly ash.
authors.affiliation: State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, Zhejiang University, China. Electronic address: chentong@zju.edu.cn.
authors.forename: Tong
authors.initials: T
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, Zhejiang University, China.
authors.forename: Ming-Xiu
authors.initials: MX
authors.lastname: Zhan
authors.affiliation: State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, Zhejiang University, China.
authors.forename: Xiao-Qing
authors.initials: XQ
authors.lastname: Lin
authors.affiliation: State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, Zhejiang University, China.
authors.forename: Xiao-Dong
authors.initials: XD
authors.lastname: Li
authors.affiliation: State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, Zhejiang University, China.
authors.forename: Sheng-Yong
authors.initials: SY
authors.lastname: Lu
authors.affiliation: State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, Zhejiang University, China.
authors.forename: Jian-Hua
authors.initials: JH
authors.lastname: Yan
authors.affiliation: State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, Zhejiang University, China.
authors.forename: Alfons
authors.initials: A
authors.lastname: Buekens
authors.affiliation: State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, Zhejiang University, China.
authors.forename: Ke-Fa
authors.initials: KF
authors.lastname: Cen
mesh_terms: D000641:Ammonia / Q000737:chemistry; D001572:Benzofurans / Q000032:analysis*; D060729:Coal Ash / Q000737:chemistry*; D000072338:Dibenzofurans, Polychlorinated; D005740:Gases / Q000737:chemistry*; D017745:Incineration; D000072317:Polychlorinated Dibenzodioxins / Q000031:analogs & derivatives* / Q000032:analysis; D012722:Sewage / Q000737:chemistry*; D013458:Sulfur Dioxide / Q000737:chemistry
chemical_list: D001572:Benzofurans; D060729:Coal Ash; D000072338:Dibenzofurans, Polychlorinated; D005740:Gases; D000072317:Polychlorinated Dibenzodioxins; D012722:Sewage; D013458:Sulfur Dioxide; D000641:Ammonia
keywords: Inhibition; Model fly ash; PCDD/Fs; Sludge drying gases