Effect of Temperature and CaO Addition on the Removal of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans in Fly Ash from a Medical Waste Incinerator

Ya-Fen Wang,Hsing-Wang Li,Lien-Te Hsieh,Hung-Chi Jiang,Yue-Sheng Lin,Cheng-Hsien Tsai,Lin-Chi Wang

doi:10.4209/aaqr.2011.06.0079

Abstract

The effects of thermal treatment temperature and CaO addition on polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) content in the fly ashes from a medical waste incinerator with high chlorine content (7.5%) were investigated. Two kinds of batch mode were examined: without CaO addition under the temperature range of 50–850°C, and with CaO addition at various Ca/Cl molar ratios (CCR = 0.8–44.3) at 250°C. The results show that the PCDD/F content in raw fly ash was 6.20 ng I-TEQ/g. When elevating the temperature from 50 to 400°Cwithout CaO addition, the PCDD/F content dramatically increased from 5.38 to 575 ng I-TEQ/g. Even at 850°C, the PCDD/Fs were not destructed apparently and were still with a concentration of 401 ng I-TEQ/g. However, with the addition of CaO at CCR = 17.7 at only 250°C, the removal ratio of PCDD/Fs reached to 87.2% and the PCDD/F content was significantly reduced to 0.889 ng I-TEQ/g, which meets the soil pollution standard of Taiwan EPA (1 ng I-TEQ/g) and could be considered as backfill. CaO addition was proven efficiently to enhance the reduction rate of PCDD/Fs in fly ashes during the thermal treatment at a low temperature, as well as inhibit the formation of PCDD/Fs.

Highlights

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) have become a concern due to their adverse health effects (US EPA, 2000)
With the addition of calcium oxide (CaO) at Ca/Cl molar ratio (CCR) = 17.7 at only 250°C, the removal ratio of PCDD/Fs reached to 87.2% and the PCDD/F content was significantly reduced to 0.889 ng I-TEQ/g, which meets the soil pollution standard of Taiwan EPA (1 ng I-TEQ/g) and could be considered as backfill
From the thermal gravimetric analysis (Fig. 1), the patterns indicate the weight loss of fly ashes are apparently found at the intervals of room temperature-100°C, and 400–550°C, indicating the water and volatile matter are the major compositions in the fly ashes

Summary

Introduction

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) have become a concern due to their adverse health effects (US EPA, 2000). The combustion temperature and chlorine content of raw materials plays an important role in PCDD/F formation (Lee et al, 2003; Wang et al, 2003b; Li et al, 2007; Wang et al, 2010). High concentrations of PCDD/Fs were formed, deposited (Wang et al, 2010; Huang et al, 2011) and found in small fly ash particles with large amounts of chlorine (Cobo et al, 2009). Three major mechanisms for PCDD/F emission from incinerators are: (1) high-temperature gas phase formation (300°C–600°C) (Everaert and Baeyens, 2002); (2) precursors transformation: such as chlorophenols, polychlorinated diphenyl ethers and chlorobenzenes (Lustenhouwer et al, 1980; Hutzinger and Blumich, 1985); and, (3) production via de novo synthesis in the low-

Methods

Results

Conclusion