Experimental and statistical determination of indicator parameters for the evaluation of fly ash and boiler ash PCDD/PCDF concentration from municipal solid waste incinerators

Emission and distribution of PCDD/Fs, chlorobenzenes, chlorophenols, and PAHs from stack gas of a fluidized bed and a stoker waste incinerator in China

The concentrations, homologue, and congener profiles, as well as the gas/particle distribution of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs), chlorobenzenes (CBzs), chlorophenols (CPhs), and polyaromatic hydrocarbons (PAHs) from stack gas of two different municipal solid waste incinerators in China, were characterized. The incinerators were a stoker furnace incinerator equipped with the advanced air pollution control device (APCD) and a common circulating fluidized bed (CFB) furnace. The concentration of PCDD/Fs in the stack gas of the stoker incinerator ranged 0.011-0.109 ng international toxic equivalent factor (I-TEQ)/Nm³ and was below the current limit for PCDD/F emissions from the municipal solid waste incinerators (MSWIs) in China (0.1 ng I-TEQ/Nm³) in most of the cases. Moreover, the concentration of PCDD/Fs in the stack gas of the stoker incinerator was significantly lower than that of the CFB incinerator (0.734 to 24.6 ng I-TEQ/Nm³). In both incinerators, the majority of the total PCDD/F emissions (above 90%) ended up in the gas phase. 2,3,4,7,8-PeCDF, which occupied 24.3-43.6 and 32.5-75.6% of I-TEQ contribution in MSWIs A and B, respectively, was the most abundant congener. However, different types of incinerators and APCDs induced different congener and homologue distributions. The total concentration of CBzs from the stoker incinerator (0.05-3.2 μg/Nm³) was also much lower than that formed from the CFB incinerator (10.9-75.2 μg/Nm³). The phase distribution of CBzs followed the same pattern as with the PCDD/Fs. Moreover, the emission level of CBz was 100-1000 times higher than that of the PCDD/Fs, which determines the applicability of CBzs as indicators of PCDD/F emissions. High correlations between the emission concentrations of PCDD/Fs, TeCBz, and PCBz in specific ranges were revealed. Furthermore, high concentrations of CPhs (0.6-141.0 μg/Nm³) and PAHs (148.6-4986.5 μg/Nm³) were detected in the stack gases of MSWI B. In some cases, the concentrations were as high as the concentrations in the fumes exiting the boiler of one foreign stoker without flue gas purification indicating the abundance of CPh and PAH emissions in the stack gas of waste incinerators.

Emission characteristics and relationships among PCDD/Fs, chlorobenzenes, chlorophenols and PAHs in the stack gas from two municipal solid waste incinerators in China

An investigation was conducted into polychlorinated dibenzo-p-dioxin and furan formation mechanisms and the relationships with chlorobenzenes, chlorophenols and PAHs in the stack gas from two fluidized bed municipal solid waste incinerators.

A review of dioxin-related substances during municipal solid waste incineration

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) are among the most toxic chemicals and the main restriction on municipal solid waste incineration. To exert more effective control over the formation of dioxin homologues during municipal solid waste incineration, it is significant to investigate dioxin-related compounds. Despite the numerous studies about PCDD/Fs, a unified understanding regarding many problems has yet to be reached because the homologues of PCDD/Fs are excessive, the measurement of PCDD/Fs is difficult, and the formation mechanisms of PCDD/Fs are complicated. Firstly, this paper briefly introduces the different formation mechanisms of PCDD/Fs, including high temperature homogeneous reaction PCDD/Fs formation and low temperature heterogeneous reaction PCDD/Fs formation. Then the sources of PCDD/Fs including precursors (chlorophenols and polycyclic aromatic hydrocarbons) and residual carbon are summarized. In particular, this paper analyzes the substances that influence PCDD/Fs formation and their impact mechanisms, including different categories of chlorine (Cl2, HCl and chloride in fly ash), O2, copper, sulfur, water, and nitrogen compounds (ammonia and urea). Due to the high cost and complexity of PCDD/Fs measurement, PCDD/Fs indicators, especially chlorobenzenes and polycyclic aromatic hydrocarbons, are summarized, to find an effective surrogate for quick, convenient and real-time monitoring of PCDD/Fs. Finally, according to the results of the current study, recommendations for further research and industrial applications prospects are proposed.

Preparation of methacrylic acid-modified rice husk improved by an experimental design and application for paraquat adsorption

Methacrylic acid (MAA) grafted rice husk was synthesized using graft copolymerization with Fenton's reagent as the redox initiator and applied to the adsorption of paraquat. The highest grafting percentage of 44.3% was obtained using the traditional kinetic method. However, a maximum grafting percentage of 65.3% was calculated using the central composite design. Experimental results based on the recipes predicted from the statistical analysis are consistent with theoretical calculations. A representative polymethacrylic acid-g-rice husk (PMAA-g-rice husk) copolymer was hydrolyzed to a salt type and applied to the adsorption of paraquat. The adsorption equilibrium data correlate more closely with the Langmuir isotherm than with the Freundlich equation. The maximum adsorption capacity of modified rice husk is 292.5mg/g-adsorbent. This value exceeds those for Fuller's earth and activated carbon, which are the most common binding agents used for paraquat. The samples at various stages were characterized by solid-state (13)C NMR spectroscopy.

Stack gas emissions of PCDD/Fs from hospital waste incinerators in China

Stack gas samples from 14 domestic-made hospital waste incinerators (HWIs) in China were collected and analyzed for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). The waste burning capacities of the investigated HWIs ranged from 5 to 25 ton d(-1). The stack gas emissions of PCDD/Fs from HWIs exhibited a large variation (0.08-31.60 ng I-TEQNm(-3)). Nine incinerators had the emission levels below the current emission standard in China (0.5 ng I-TEQN m(-3)), while only two facilities exhibited emission levels below the European Union directive emission limit (0.1 ng I-TEQN m(-3)). For two plants, concentrations of PCDD/Fs in stack gas were above 10.0 ng I-TEQN m(-3). The emission factors of PCDD/Fs from the investigated HWIs were in the range of 0.78-473.97 microg I-TEQ ton(-1) medical wastes. It was estimated that 4.87 g I-TEQ of PCDD/Fs was annually released from HWIs to the atmosphere in China in 2006. Principal component analysis and hierarchical cluster analysis were applied to analyze the congener profiles of PCDD/Fs from HWIs in China.