Emission of unintentionally produced persistent organic pollutants (UPOPs) from municipal waste incinerators in China

Highlights

• Level of PCDD/Fs, PCBs, PeCBz, and HxCBz in flue gas from MWI in China was reported.

• Emission factors of PeCBz (144 μg/t) and HxCBz (84.7 μg/t) in flue gas from MWI were given.

• Profiles of PCBs and dl-PCBs in both gaseous and fly ash phase were stated.

• Removal efficiencies of PCDD/Fs, PCBs, PeCBz, and HxCBz by air pollution control device were evaluated.

Abstract

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), pentachlorobenzene (PeCBz) and hexachlorobenzene (HxCBz), which are listed in the Stockholm Convention, are commonly known as unintentionally produced persistent organic pollutants (UPOPs). As municipal waste incinerators (MWIs) have burgeoned in China, the emission of UPOPs is of great concerns. Compared to the extensive studies of PCDD/Fs emission, not much information of non-dioxin UPOPs (i.e., PCBs, HxCBz, and PeCBz) is available. In the present study, samples from raw gas (RG) after boiler, stack gas (SG) after air pollution control devices (APCDs) and fly ash (FA) samples were collected from typical MWIs in China. The analyses of SG samples indicate that PCDD/Fs are the major contributor to TEQ value, but non-dioxin UPOPs are the dominant compounds in terms of mass concentration. The mean emission factors of dl-PCBs, PeCBz, and HxCBz in SG are 0.372, 144, and 84.7 μg/t, respectively. In contrast with gaseous samples, FA contains higher mass concentration of PCDD/Fs and PCBs than that of PeCBz and HxCBz. In terms of homologues distribution of PCBs, di- to tetra-CBs were the predominant species in both SG and FA samples. PCB-126 is the major contributor to the TEQ concentration. The comparison of UPOPs composition in SG and RG samples shows that activated carbon adsorption process is capable of removing most PCDD/Fs, but less efficient for the removal of non-dioxin UPOPs.

Introduction

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), pentachlorobenzene (PeCBz) and hexachlorobenzene (HxCBz) are categorized as unintentionally produced persistent organic pollutants (UPOPs) due to their toxicities, long range transport and bioaccumulation and are therefore listed in the Stockholm Convention. Previous studies have shown that UPOPs could be formed and emitted from thermal processes like municipal waste incinerator (MWI) (Fiedler, 2007, Hung et al., 2016, Liu and Zheng, 2013, Olie et al., 1977, U.S. EPA, 2006, Wallerstein, 1999) and from chemical manufacturing processes (Lysychenko et al., 2015, Weber et al., 2008). According to China Statistical Yearbook 2014 (NBS, 2014), as of 2013, 166 large-scale MWIs were in operation and their disposal capacities reached 4.63 × 10⁷ t/a. More incinerators are currently under construction or in planning stage to combat the increasing amount of municipal waste. As MWIs have burgeoned in China, the emission of UPOPs receives great attention and concerns due to their adverse impact in environment.

In the past decades, the emission level and profile of PCDD/Fs have been extensively studied (Chi et al., 2005, Jansson and Andersson, 2012, Ni et al., 2009, Šyc et al., 2015, Weber and Hagenmaier, 1999, Yan et al., 2006, Zhang et al., 2013). However, not much attention has been paid on the non-dioxin UPOPs (i.e., PCBs, HxCBz, and PeCBz). Studies have shown that their existence are favorable for the formation of PCDD/Fs in flue gas (Liu et al., 2013, Nie et al., 2011) and could be indicator of PCDD/Fs (Hung et al., 2013, Kaune et al., 1996, Lavric et al., 2005, Öberg and Bergström, 1985).

The emissions of PCBs in flue gas from MWIs have been reported in Japan (Kim et al., 2004, Sakai et al., 2001, Sakurai et al., 2003), Korean (Shin et al., 2006), and the EU (Dyke et al., 2003, Šyc et al., 2015). Recently, a few studies have focused on the emissions of PCBs in other sources, including iron ore sintering plant (Tian et al., 2012), metallurgical process (Nie et al., 2011, Nie et al., 2012), and medical waste incineration (Chen et al., 2015) in China. Unfortunately, studies on PCB emissions from MWIs in China are extremely limited (Yan et al., 2010). As for PeCBz and HxCBz, some valuable studies on the basis of full scale (Kaune et al., 1996, Weber and Hagenmaier, 1999) and pilot scale (Fangmark et al., 1993, Fangmark et al., 1994) are available, which calls for more in-depth researches based on full-scale incinerator.

In addition, most of the reported data are mainly based on stack gas samples, which is strongly affected by APCDs. In contrast, information from RG samples collected before APCDs could truly reflect the emission pattern and is also important for the evaluation of APCDs performance. However, such information is rarely provided. Moreover, aside from flue gas, the emission pattern of non-dioxin UPOPs in fly ash has not been fully investigated yet.

In this study, in addition to stack gas samples, also raw gas and fly ash samples were collected from MWIs in China. The emission factors as well as emission pattern of non-dioxin UPOPs in different matrix were reported. The performance of APCDs on removing non-dioxin UPOPs was evaluated. The results are not only important supplements for UPOPs emission inventory, but also provide guidance to the improvement of APCDs.