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Fs and unintentional persistent organic pollutants
Journal Pre-proof Efficacy of the novel continuous sampling system for PCDD/Fs and unintentional persistent organic pollutants Yen-Chen Hsu, Shu-Hao Chang, Moo Been Chang PII:
S0045-6535(19)32683-9
DOI:
https://doi.org/10.1016/j.chemosphere.2019.125443
Reference:
CHEM 125443
To appear in:
ECSN
Received Date: 4 September 2019 Revised Date:
13 November 2019
Accepted Date: 21 November 2019
Please cite this article as: Hsu, Y.-C., Chang, S.-H., Chang, M.B., Efficacy of the novel continuous sampling system for PCDD/Fs and unintentional persistent organic pollutants, Chemosphere (2019), doi: https://doi.org/10.1016/j.chemosphere.2019.125443. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.
1
Efficacy of the novel continuous sampling system for PCDD/Fs and unintentional
2
persistent organic pollutants
3
Yen-Chen Hsu, Shu-Hao Chang, Moo Been Chang
4 5
Graduate Institute of Environmental Engineering, National Central University, Chungli 320, Taiwan
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*Telephone/Fax: +886-3-4226774
7 8
E-mail: [email protected]
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Abstract
10
Long-term sampling is essential for monitoring the air pollutants emitted from stack since it can
11
monitor the pollutants emission continuously including the stages of start-up, shutdown and normal
12
operation. However, commercial continuous sampling equipment such as AMESA faces the
13
challenges of high weight and complicated sampling procedures. This study has developed a
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long-term and automatic sampling system (National Central University continuous stack sampling
15
system, NCU-CS3), and compared the efficiency with manual sampling train (MST). The results
16
indicate that relative standard deviation (RSD) of PCDD/Fs concentrations measured between
17
NCU-CS3 and MST is < 20%, demonstrating that the difference between NCU-CS3 and MST in
18
measuring PCDD/Fs is insignificant. Besides, the effects of adsorbent temperature, adsorbent amount
19
and type of adsorbent on breakthroughs of PAHs and unintentional-persistent organic pollutants
20
(UPOPs) such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated
21
biphenyls (PCBs), chlorinated phenols (CPs), chlorinated benzenes (CBs) and polychlorinated
22
naphthalenes (PCNs) are evaluated. The results indicate that the breakthrough of pollutants increases
23
with increasing temperature of XAD-2 and decreases with increasing XAD-2 amount. Moreover,
24
XAD-4 is used as alternative adsorbent to test the breakthrough and the results indicate that the
25
breakthroughs of UPOPs of XAD-4 as adsorbent are lower than that with XAD-2 due to higher
26
specific surface area of XAD-4. Furthermore, the residual of PCDD/Fs with NCU-CS3 as the
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sampling train is relatively low (1.5-3.8%), which meets the regulation of EN 1948-5 (10%).
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Key words: long-term sampling, PAHs, unintentional persist organic pollutants(UPOPs), flue gas
29
sampling
30 31
1. Introduction
32
During the past a few decades, emissions of polycyclic aromatic hydrocarbons (PAHs) and
33
unintentional-persistent organic pollutants (UPOPs) such as polychlorinated dibenzo-p-dioxins and
34
dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), chlorinated phenols (CPs), chlorinated
35
benzenes (CBs) and polychlorinated naphthalenes (PCNs) have caused much public concern due to
36
their threats to human health (Van Caneghem et al., 2010; Rostami and Juhasz, 2011). Some toxic
37
congeners of PCDD/Fs, dl-PCBs, PCNs, CPs and CBs are listed on the Stockholm Convention to
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protect human health and the environment from persistent organic pollutants (POPs), while PAHs are
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carcinogenic to threaten human health. Among these hazardous pollutants, only PCDD/Fs emitted
40
from municipal wastes incinerators (MWIs) are rigorously regulated by the developed countries
41
worldwide while emissions of PAHs and other UPOPs are not restricted by most countries yet
42
(Cheruiyot et al., 2016; UNEP Chemicals, 1999). In order to further protect the human health from
43
the hazards caused by these pollutants, investigation on the characteristics of PAHs and UPOPs
44
emitted from MWIs is essential.
45
Previous studies indicate that concentrations of PAHs and UPOPs emitted from MWIs vary
46
significantly with waste composition, combustion condition, operating stage and air pollution control
47
devices adopted (Everaert and Baeyens, 2001; Lemieux et al., 2003; Tejima et al., 2007; Chen et al.,
48
2008; Aurell and Marklund, 2009; Liu et al., 2014; Li et al., 2017; Wang et al., 2017). Besides, some
49
studies indicate that the PCDD/Fs formation is closely related to the precursors such as PAHs, CPs
50
and CBs, while PCBs and PCNs have the similar formation pathway as PCDD/Fs (Hajizadeh et al.,
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2011; Li et al., 2016; Cheruiyot et al., 2016). It has been found that PCDD/Fs concentrations
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measured in stack gases during the start-up, shutdowns or operation failures are up to 2 to 3 order
53
higher than those measured during normal operation (Tejima et al., 2007; Chen et al., 2008;
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Reinmann et al., 2010). Lothgren and Bavel (2005) indicate that start-up is the main stage of
55
increased PCDD/Fs emissions, which has been proved by continuous monitoring covering all periods
56
of operation. Besides, it has been found that even with several short-term measurements a year, real
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emission of PCDD/Fs from MWIs still cannot be effectively monitored (Reinmann et al., 2006).
58
Arkenbout and Esbensen (2017) indicate that the short-term sampling scheme is seriously flawed on
59
PCDD/Fs measurement. In fact, significantly elevated dioxins emissions were measured in flue gas
60
during events of unstable combustion conditions by continuous long-term measurements. Besides,
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the dioxin congener patterns from long-term flue gas sampling show similar patterns as the
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congeners found in the samples nearby the MWIs, indicating that elevated dioxins in samples is
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associated with the emissions from the incinerator. Consequently, applying continuous long-term
64
sampling to monitor PAHs and UPOPs emitted from MWIs can provide more reliable data compared
65
with short-term samplings.
66 67
Three commercial systems, (dioxin emission continuous sampling (DECS), dioxin monitoring
68
system (DMS) and adsorption method for sampling of dioxins (AMESA)) have been developed
69
respectively based on three long-term sampling methods for sampling PCDD/Fs in flue gas, i.e. (1)
70
the filter/condenser method, (2) the dilution method, and (3) the cooled probe method in European
71
method (EN1948) (Oleszek-Kudlak et al., 2007). However, the heavyweight of AMESA and DECS
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and memory effect of AMESA have been found in previous studies and may cause danger and
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difficulty during sampling campaign for old stack and overestimating the PCDD/Fs concentration
74
owing to memory effect, respectively (Idczak et al., 2003; Lin et al., 2012). Moreover, Lewandowski
75
and Gemmill (2006) compare the results of two automatic sampling systems (AMESA and DMS)
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and two manual sampling methods and indicate the no significant difference is found between
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AMESA and DMS. On the other hand, notable difference exists between two manual sampling
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methods owing to human error and complex operating procedures of standard sampling methods (EN
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1948) (Vicaretti et al., 2012). Therefore, developing an automatic long-term sampling system based
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on filter/condenser method not only complies with the regulations promulgated in Taiwan but also
81
overcomes the disadvantages of manual sampling”.
82
Breakthrough test of the adsorbent applied is essential to determine the sampling efficiency
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during long-term sampling. Effects of adsorbent temperature, adsorbent amount and type of
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adsorbent on breakthrough have been verified in previous sampling campaigns (Wilbring and
85
Gerchel, 1997; Mayer et al., 2000; Kahr, 2004; Lee et al., 2004; Reinmann et al., 2008a). Relevant
86
studies indicate that the breakthrough of PCDD/Fs would not occur in the AMESA if the adsorbent
87
temperature is maintained <50oC (Wilbring and Gerchel, 1997; Mayer et al., 2000; Reinmann et al.,
88
2008a). Kahr (2004) indicated that breakthrough would not take place for DMS as long as the
89
adsorbent temperature is controlled ≤ 40oC and the breakthrough is < 5% with the adsorbent
90
temperature of 60oC. During the period of testing the AMESA system, no PCDD/Fs breakthrough is
91
observed during four weeks continuous sampling campaign when 70 g XAD-2 is applied as the
92
adsorbent (Wilbring and Gerchel, 1997; Reinmann et al., 2008a, 2008b). On the other hand, the
93
specific surface area and pore size of adsorbents may affect the adsorption amount and efficiency of
94
pollutants during sampling (Lee et al., 2004).
95 96
In order to comprehensively understand the emission and characteristics of PAHs and UPOPs
97
from MWIs, developing a continuous stack sampling system that meets the sampling protocols in
98
Taiwan is essential. The objective of this study is to develop a continuous automated sampling
99
system which can fulfill the requirements of NIEA A807.75C, EN 1948-1 and EN1948-5 and
100
overcome the disadvantages of commercial sampling systems. Besides, the effects of XAD-2 amount,
101
temperature of XAD-2 and types of adsorbent (XAD-2 and XAD-4) on the collection efficiencies of
102
PAHs and UPOPs emitted from a large-scale MWI located in southern Taiwan are evaluated with the
103
sampling system developed. Furthermore, comparison between the automated continuous sampling
104
system developed and manual sampling method for short-term sampling of PCDD/Fs is carried out.
105 106
2. Materials and method
107
2.1 Basic information of NCU-CS3
108
National Central University continuous stack sampling system (NCU-CS3) (as shown in Fig. 1) is
109
developed in this study for long-term sampling of PAHs and UPOPs emitted from MWIs. It has the
110
advantages of small size (1,240*660*495 mm), high mobility (< 80 kg) and low power consumption
111
(<1,300 W) since the gas composition analysis system of NCU-CS3 can be controlled with one
112
control unit. Specifically, NCU-CS3 consists of a heated glass sampling tube, filter, oven, two
113
adsorbent cartridges and control unit. The temperature of oven and sampling probe is controlled
114
within the range of 115-120oC which is lower than that specified NIEA A807.75C (120-134oC) to
115
avoid the regeneration and degradation of solid-phase PAHs during the long-term sampling. The
116
control unit is comprised of gas composition analysis system, moisture collection system and
117
isokinetic suction system that controls the gas flow rate, pressure and temperature of flue gas
118
sampled. The flue gas composition analysis system can measure the concentrations of O2, CO2 and
119
CO simultaneously. Besides, average percent isokinetic sampling rate is controlled between
120
94%-106% (Fig. S1), which meets the requirement of NIEA A807.75C (90-110%). As shown in Fig.
121
1, the sampling probe is placed in the center of the stack for continuous sampling. The particulate
122
matter (PM) concentration emitted from the MWI investigated is between 3.2-5.7 mg/Nm3 and the
123
pressure of the system still maintain < 400 mmHg in the condition of continuous operation for 450 hr.
124
Moreover, the leak of flue gas during the sampling period with the NCU-CS3 was less than 5%.
125 126
Fig. 1. Schematic of NCU-CS3 developed for continuous sampling of UPOPs
127 128
2.2 Sample collection by NCU-CS3 and MST
129
Overall, 7 samples (No1 to No 7) were collected isokinetically in parallel during the short-term
130
sampling period (6-7.8 hr) using manual stack sampling train (MST) and NCU-CS3, respectively, to
131
evaluate the performance of NCU-CS3 and make comparison with MST. The manual stack sampling
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method follow Taiwan standard sampling method (NIEA A807.75C) which is modified from the
133
USEPA Method 23. In manual stack sampling method, the sampling probe was made from
134
borosilicate glass and connected with a filter holder placed in the filter oven. The sampling probe and
135
filter oven were kept within a temperature range of 120-134oC. The temperatures at the condenser
136
outlet (and inlet to XAD-2 resin) and silica gel trap outlet are maintained at a temperature < 20oC for
137
efficient capture of PCDD/Fs and water vapor. Isokinetic sampling must be applied to sample the
138
particles correctly. According to the EN1948-5, long-term sampling and manual sampling shall be
139
performed in parallel during a specified time period (at least 40 hr). In this study, long-term sampling
140
as well as the manual sampling is performed for 6 hr to 8 hr. Besides, the effects of adsorbent
141
temperature, adsorbent amount and types of adsorbent (XAD-2 and XAD-4) on the breakthrough
142
were carried out for 10 days. For the test of temperature and adsorbent amount, XAD-2 was used as
143
the adsorbent resin. In addition, three parameters were selected as following: amount of the XAD-2
144
in 1st adsorption cartridge is 35, 70 or 100 g (amount of second XAD-2 is fixed as 70 g); XAD-2
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temperature is adjusted between 10-50oC and types of adsorbent applied include XAD-2 and XAD-4.
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Breakthrough tests with NCU-CS3 were conducted by installing two adsorption cartridges in series
147
and the breakthrough is calculated as the ratios of the TEQ and mass concentration of PAHs or
148
UPOPs collected in second adsorbent cartridge to the total TEQ collected by rinse, filter, first and
149
second adsorbent cartridges (Eq 1). Furthermore, the residual of PCDD/Fs is calculated as the ratio
150
of TEQ in rinse to the total TEQ (Eq 2). The loss rate of PCDD/Fs regulated by Taiwan EPA is
151
calculated as the ratio of the TEQ concentration of residual PCDD/Fs to 0.1 ng TEQ/Nm3 (Eq 3)
152
(Mehl et al., 2003). The TEQ is calculated for PCDD/Fs to evaluate the extent of breakthrough and
153
the breakthroughs of other target pollutants are evaluated based on mass concentration.
154
Breakthrough (%) =
155
Residual (%) =
×100%.......................................... (Eq 1)
×100%.................................................................. (Eq 2)
156
Loss rate (%) =
/ ." # /$%&
×100%....................................................................... (Eq 3)
157
Total mass✽ stands for the total mass of PAHs or UPOPs collected by rinse, filter, first and second
158
adsorbent cartridges.
159 160
2.3 Pretreatment and analysis of PAHs and UPOPs
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All standards are bought from Wellington and Cambridge. For PCDD/Fs analysis, the NIEA
162
A807.75C is followed, while WP-CVS standard is used for dl-PCBs analysis. The PCNs standards
163
are ECN 5558, ECN 2622, PCN-MXA, PCN-MXC, ECN5102, ECN5520, ECN5217, ECN5260,
164
WP-ISS. The chlorobenzene standards are CBS, MCBS, MCBZ-1235, and MCBZ-12345, while the
165
chlorophenol standards include CPS, MCP-246, MCP-345, MCP-23456, MPCS. Solid-phase and
166
gas-phase pollutants were collected by filter and XAD-2, respectively, using isokinetic sampling
167
system with both NCU-CS3 and manual sampling methods. Both filter and XAD-2 adsorbent were
168
spiked with isotopically labeled surrogate standards before sampling. The rinse was collected from
169
washing the sampling tube with three kinds of solvents in the order of acetone, dichloromethane
170
(DCM) and toluene. The filter, XAD-2 and the rinse of sampling tube were pretreated and analyzed
171
following Taiwan NIEA A808.75B. The samples were fortified with 13C-labeld of PAHs and UPOPs
172
as internal standard before extraction and then extracted by Soxhlet method which can be divided
173
into two stages, i.e., DCM/hexane (1:1) used as solvent for the first stage followed by toluene as the
174
second stage. The extracts were concentrated individually and then mixed homogenously. After that,
175
the extract was separated into two fractions for cleanup. One fraction in clean-up followed NIEA
176
A808.75B for PCDD/Fs and PCBs analysis, and the other was eluted in sequence with 50 mL of
177
n-hexane (discard) and 50 mL of n-hexane/DCM (5:1, v/v) (collected and concentrated) in the
178
column that containing 10 g silica and 10 g alumina for the analysis of PAHs and other UPOPs.
179
Finally, recovery standards were individually added into the extracts and analyzed by HRGC/HRMS
180
for 17 PCDD/Fs and 12 PCBs and HRGC/MS/MS for 4-8Cl PCN, 24 PAHs, 3-5Cl CPs, and 3-6Cl
181
CBs. The recovery efficiency of PCDD/Fs suggurate standards is between 90-110% which fulfill the
182
regulation of NIEA A807.75C (70-130%).
183 184
3. Results and discussion
185
3.1 Manual sampling train vs automated NCU-CS3
186
The PCDD/Fs concentration emitted from the MWI investigated are measured by MST and
187
NCU-CS3, respectively, to evaluate the performances of two methods and the results are summarized
188
in Table 1. The PCDD/Fs concentrations of No 1 –No 6 are lower than the PCDD/Fs emission
189
standard of large-scale MWIs in Taiwan (0.1 ng I-TEQ/Nm3). However, the PCDD/Fs concentrations
190
of No 7 measured by MST and NCU-CS3 are 0.264 and 0.225 ng I-TEQ/Nm3, respectively, which are
191
over the emission standard of MWIs regulated by Taiwan EPA. It is attributed to the fact that No 7
192
sampling was carried out during the shutdown period of MWI and previous studies indicate that
193
incomplete combustion would facilitate the formation of PCDD/Fs since the temperature decreases
194
and fluctuates greatly during shutdown period (Šyc et al., 2015; Li et al., 2017). Based on the above
195
results, long-term sampling is necessary for monitoring the emission of MWIs covering the periods
196
of start-up, shutdown and normal operation.
197
In addition, the results of the relative standard deviation (RSD) and relative percent difference
198
(RPD) between NCU-CS3 and MST are shown in Table 1, and it indicates the RSD of all seven
199
samples are below 35%. The EN 1948-5 indicates that the RSD with PCDD/Fs I-TEQ concentration
200
around 0.1 ng I-TEQ/Nm3 determined by the long-term sampling should be within 35 % of the value
201
determined by the MST measurement to validate the long-term sampling system. If the PCDD/Fs
202
concentrations measured by MST are much lower than 0.1 ng I-TEQ/m3, the value of RSD between
203
the MST and the long-term sampling system should follow the regulation proposed by the EN
204
1948-5. Moreover, Table 1 indicates that RPD of PCDD/Fs concentration between MST and
205
NCU-CS3 methods are < 20%, which is lower than the tolerance level of RPD < 30% as set by JIS
206
K0311. Horie at al (2007) used RPD to compare the MST and AMESA methods and the results
207
indicate that the RPDs of two facilities are in the wide range of 9%-82% due to the uncertainty
208
caused by extremely low PCDD/Fs concentrations. Besides, linear regression of the parallel tests
209
data is shown in Fig. 2. The correlation coefficient (R2) between MST and NCU-CS3 is 0.91, which is
210
in good agreement with the earlier published results of several comparison tests (Idczak et al., 2003;
211
Horie et al., 2007). Based on the results of PCDD/Fs concentrations measured, RSD, RPD and
212
correlation coefficient, we conclude that the difference between the MST and NCU-CS3
213
measurement is relatively insignificant. Previous study indicates that notable difference exists
214
between two manual sampling methods owing to human error and complex operating procedure
215
(Vicaretti et al., 2012), for instance, the adjustment procedure of the isokinetic suction rate of MST is
216
more complicated if compared with NCU-CS3, which may cause the variation of particulate-phase
217
PCDD/Fs concentration measured. The suction rate of MST is supposed to be checked per 10-15 min
218
by the operator while the suction rate of NCU-CS3 can be adjusted automatically every 30 second.
219
Some studies use commercial AMESA system to solve the shortcomings of MST, however, previous
220
study indicates that the memory effect exists with AMESA during the unstable operating condition of
221
incinerator due to the deposition residual PCDD/Fs on the cooling sampling probe and the elbow of
222
the sampling tube (Reinmann et al., 2008b; Wang and Lin, 2015). Thus, it is suggested that
223
automated NCU-CS3 developed in this study is capable to overcome the human errors involved with
224
MST and to reduce the time and cost for sampling preparation (Vicaretti et al., 2012). Compared with
225
other commercial continuous sampling systems, NCU-CS3 has the merits of low weight of
226
equipment, low energy consumption and good compatibility with the sampling method promulgated
227
in Taiwan. Hence, NCU-CS3 is proved as a reliable continuous sampling system for PCDD/Fs
228
sampling.
229 230 231
232 233 234
Table 1 PCDD/Fs concentrations (ng I-TEQ/Nm3) and the differences between NCU-CS3 and MST
235 No
Sampling period
NCU-CS3
MST
RSD
(%)
RPD
(%)
(hr) 1
6
0.054
0.050
5
8
2
6.2
0.028
0.023
14
20
3
6.8
0.023
0.028
14
20
4
7
0.053
0.050
4
6
5
6.4
0.028
0.031
7
10
6
7.3
0.015
0.018
13
18
7
7.8
0.225
0.264
11
16
236
RSD : (standard deviation of PCDD/Fs TEQ concentration between NCU-CS3 and MST divided by
237
the mean of PCDD/Fs TEQ concentration between NCU-CS3 and MST)×100%
238
RPD : (difference of PCDD/Fs TEQ concentration between NCU-CS3 and MST divided by half of
239
the mean of PCDD/Fs TEQ concentration between NCU-CS3 and MST) ×100%
240
241 242
Fig. 2. Linear regression of PCDD/Fs I-TEQ concentrations determined with MST and NCU-CS3 in
243
short-term sampling
244 245 246
3.2 Effects of adsorbent temperature, amount of XAD-2 and type of adsorbent on breakthrough test
247
Firstly, XAD-2 is chosen as the adsorption resin for testing the effects of adsorbent temperature
248
and the adsorbent amount on PCDD/Fs breakthrough of the NCU-CS3 for the continuous operation
249
of 10 days and the results are presented in Fig. 3. The results indicate that the breakthrough of
250
PCDD/Fs increases with increasing XAD-2 temperature and decreases with increasing XAD-2
251
amount. Overall, the PCDD/Fs breakthroughs are < 2% as the XAD-2 temperature is controlled <
252
20oC and the XAD-2 amount are set at 35, 70 or 100 g. Except for 35 g of XAD-2 amount, the
253
PCDD/Fs breakthrough is < 1% as the XAD-2 temperature is controlled < 20oC. Therefore, 70 g of
254
XAD-2 and 20oC of XAD-2 temperature are optimal for operating the NCU-CS3 for effective capture
255
of PCDD/Fs. Interestingly, the breakthrough of PCDD/Fs congeners decrease with increasing
256
chlorinated level and it is attributed to the fact that low chlorinated PCDD/Fs with higher vapor
257
pressures have higher tendency to penetrate through the first XAD-2 cartridge and be captured by the
258
second XAD-2 cartridge and the trend is consistent with that reported in previous studies (Wu et al.,
259
2014; Wang and Lin, 2015).
260
Breakthroughs of UPOPs and PAHs with different XAD-2 temperatures are also evaluated and
261
the results are shown in Fig. 4. The results indicate that the breakthroughs of UPOPs and PAHs
262
increase with increasing XAD-2 temperature. It's worth noting that the breakthrough of PAHs
263
increases significantly with increasing XAD-2 temperature. It is attributed to the fact that low-ring
264
PAHs with higher vapor pressures are easier to penetrate, leading to higher breakthrough. As shown
265
in Fig. S1, low-molecular-weight PAHs (2 to 3 ring PAHs) such as naphthalene (8.94% - 24.4%),
266
phenantrene (5.33% - 12.98%) and pyrene (5.12% - 9.5%) are of higher breakthroughs in
267
comparison with high-molecular-weight PAHs (other PAHs < 1%) as the XAD-2 temperatures are
268
controlled at 20oC, 30oC and 50oC, respectively. It also suggests that the XAD-2 temperature has
269
more significant effect on the breakthrough of low-molecular-weight PAHs compared with
270
high-molecular-weight PAHs. Additionally, breakthrough of 12 dioxin-like polychlorinated biphenyls
271
(PCBs) is slightly higher than that of 17 PCDD/Fs due to lower boiling points of PCBs (340-375oC)
272
in comparison with PCDD/Fs (438-537oC) (Reinmann et al., 2008a). In addition, the results shown in
273
Fig. S2 also indicate that co-planar PCBs (TeCB-77, TeCB-81, PeCB-126 and HxCB-169) with
274
higher adsorption potential exhibit lower breakthrough (< 4%) in compared with non-planar PCBs (>
275
4.5%), which suggests that the structures of the PAHs and UPOPs also affect the breakthrough
276
(Cortes et al., 1991). Polychlorinated naphthalenes (PCNs) are of lower boiling points (260-440oC)
277
(UNEP, 2017), resulting in higher breakthrough in comparison with PCDD/Fs. Furthermore,
278
breakthroughs of PAHs, CBs and CPs are significantly higher than that of PCDD/Fs, PCBs and
279
PCNs due to lower boiling points of PAHs (217-495oC), CBs (219-322oC) and CPs (253-310oC)
280
(Reinmann et al., 2008a).
281
Fig. 4 also indicates that breakthroughs of PAHs, CPs and CBs are relatively high as XAD-2 is
282
applied as the adsorbent. In order to ensure the trap efficiency and understand the accurate
283
concentrations of PAHs and UPOPs emitted from the stack gas, appropriate operating parameters of
284
NCU-CS3 for effective capture of PAHs, CBs and CPs are needed. Therefore, XAD-4 is used as
285
alternative adsorption resin to test the breakthroughs of CBs, CPs and PAHs. Fig. 5 shows the
286
comparsion of XAD-2 and XAD-4 on breakthroughs of UPOPs and PAHs with the adsorbent
287
temperature of 35oC and 70 g adsorbent in the first cartridge. The results indicate that the
288
breakthroughs of PAHs and UPOPs with XAD-4 as adsorbent are significantly lower than that with
289
XAD-2 as adsorbent, which is consistent with the previous study (Wang and Lin, 2015). Lower
290
breakthrough can be ascribed to higher specific surface area (750 m2/g) and higher pore volume
291
(0.98 mL/g) of XAD-4 compared with XAD-2 (specific surface area = 300 m2/g and pore volume =
292
0.65 mL/g). Previous studies indicated that XAD-4 was superior to XAD-2 and XAD-16 for PAHs
293
and PCDD/Fs sampling due to the dominance of microspore adsorption (Lee et al., 2004; Wang and
294
Lin, 2015). Hence, it suggests that PCDD/Fs and PCBs can be effectively captured by XAD-2 as the
295
temperature and amount are controlled at 20oC and 70 g, respectively, while XAD-4 is more
296
appropriate as adsorbent for capturing CBs, CPs and PAHs in stack gas.
297 298
Fig. 3. Effects of XAD-2 temperature and XAD-2 amount on the breakthrough of PCDD/Fs sampled
299
with NCU-CS3
300 301
Fig. 4. Effects of XAD-2 temperature on breakthroughs of UPOPs and PAHs with 70 g of XAD-2 in
302
NCU-CS3.
303 304
Fig. 5. Effects of XAD-2 and XAD-4 on breakthroughs of UPOPs and PAHs in NCU-CS3 with 70 g
305
adsorbent and adsorbent temperature of 35oC
306 307
3.3 Residual PCDD/Fs on NCU-CS3
308
Residual PCDD/Fs is collected from washing the sampling probe of the NCU-CS3 with acetone,
309
DCM and toluene in sequence after continuous sampling for 10 days in the MWI investigated. Fig. 6
310
shows the distributions of PCDD/Fs among residual, particle phase and gas phase with NCU-CS3 as
311
the sampling system. The result indicates that the distribution of PCDD/Fs in gas phase (93.2%) is
312
significantly higher than those in particle phase (6.8%) and residual (2.8%), which suggests that the
313
PCDD/Fs emitted from the MWI investigated mainly exist in gas phase. However, it is found that the
314
residual PCDD/Fs measured during the start-up procedure (6.4%) is significantly higher than that
315
measured during normal operation (3%), which is attributed to the fact that the PM concentration of
316
unstable condition (3.5 mg/Nm3) is higher than that of normal operation (< 1 mg/Nm3). Besides, the
317
residual PCDD/Fs is between 1.5-3.8% (with the average value of 2.8%) and the loss rate of
318
PCDD/Fs is between 1-6.4%, which is significantly lower than that reported in the relevant studies
319
which applied AMESA (17.2-37.0%) as sampling system and meet the regulation of EN 1948-5
320
(10%) (Wang and Lin, 2015; Mehl et al., 2003). Higher residual PCDD/Fs observed in AMESA
321
could be attributed to the memory effect and it suggests that PCDD/Fs deposited on the cooled
322
sampling probe and the sampling elbow cannot be completely cleaned, which causes the bias on the
323
PCDD/Fs measurement (Vicaretti et al., 2012). As for NCU-CS3, the sampling probe equipped is
324
heated to avoid the memory effect and decrease the deposition and condensation of PCDD/Fs on the
325
sampling probe during sampling, which is similar to the commercial long-term sampling system such
326
as DMS and DES. On the other hand, due to smaller diameter of the sampling probe in NCU-CS3,
327
the velocity of flue gas would be higher to avoid the deposition of PCDD/Fs on the sampling tube.
328
Interestingly, the results shown in Fig. S3 indicate that the residual of highly chlorinated PCDD/Fs is
329
higher than that of low chlorinated PCDD/Fs. The main PCDD/Fs congeners in residual are OCDD,
330
1,2,3,4,6,7,8-HpCDD, and OCDF and the percentages of OCDD, 1,2,3,4,6,7,8-HpCDD, and OCDF
331
residual in total PCDD/Fs residual are 15.2%, 11.1% and 8.7%, respectively, since highly chlorinated
332
PCDD/Fs with low vapor pressures are more easily condensed and adsorbed on the sampling probe.
333
334
Fig. 6. The percentages of PCDD/Fs among residual, particle phase and gas phase, respectively, in
335
NCU-CS3 for 10 days’ continuous sampling
336 337 338 339
Conclusions
340
A long-term automatic sampling system (NCU-CS3) is developed for sampling PAHs and
341
UPOPs from MWI based on the filter/condense method which is in compliance with the regulations
342
of Taiwan EPA. Besides, the difference between MST and NCU-CS3 has been evaluated in this study.
343
The results indicate that the RSD and correlation coefficient of PCDD/Fs TEQ concentration
344
between MST and NCU-CS3 are < 35% and 0.9, respectively, which suggests that NCU-CS3 is
345
reliable and can overcome the disadvantages of manual sampling train. Furthermore, the effects of
346
adsorbent temperature, adsorbent amount and types of adsorbent on breakthrough are evaluated for
347
NCU-CS3 and the results indicate that the breakthrough increases with increasing temperature and
348
decreasing adsorbent amount. The XAD-2 temperature and amount should be controlled at 20oC and
349
70 g, respectively, for ensuring effective capture of PCDD/Fs emitted from MWIs. Additionally,
350
NCU-CS3 system with XAD-4 as adsorbent can effectively capture UPOPs and PAHs, especially for
351
the pollutants of low boiling points owing to higher the specific surface area. Moreover, low residual
352
PCDD/Fs with NCU-CS3 has been found in this study and it fulfills the requirement of EN1948-5
353
(10%).
354 355
Acknowledgement
356
This study was financially supported by Taiwan Environmental Protection Administration (EPA) and
357
Ministry of science and technology (MOST) (Project no. MOST-105-2221-E-008-006-MY3).
358 359
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Highlights 1. A long-term and automatic sampling system (NCU-CS3) has been developed. 2. The difference between NCU-CS3 and MST in measuring PCDD/Fs is insignificant. 3. Effects of adsorbent temperature, amount and types on tests have been elucidated. 4. Low residual PCDD/Fs with NCU-CS3 has been found in this study.
Author Contribution Statement Yen-Chen Hsu：Conceptualization, Methodology, Writing - Original Draft, WritingReviewing and Editing Shu-Hao Chang：Conceptualization, Methodology, Validation Moo Been Chang:：Conceptualization, Supervision, Project administration
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
S0045-6535(19)32683-9
DOI:
https://doi.org/10.1016/j.chemosphere.2019.125443
Reference:
CHEM 125443
To appear in:
ECSN
Received Date: 4 September 2019 Revised Date:
13 November 2019
Accepted Date: 21 November 2019
Please cite this article as: Hsu, Y.-C., Chang, S.-H., Chang, M.B., Efficacy of the novel continuous sampling system for PCDD/Fs and unintentional persistent organic pollutants, Chemosphere (2019), doi: https://doi.org/10.1016/j.chemosphere.2019.125443. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.
1
Efficacy of the novel continuous sampling system for PCDD/Fs and unintentional
2
persistent organic pollutants
3
Yen-Chen Hsu, Shu-Hao Chang, Moo Been Chang
4 5
Graduate Institute of Environmental Engineering, National Central University, Chungli 320, Taiwan
6
*Telephone/Fax: +886-3-4226774
7 8
E-mail: [email protected]
9
Abstract
10
Long-term sampling is essential for monitoring the air pollutants emitted from stack since it can
11
monitor the pollutants emission continuously including the stages of start-up, shutdown and normal
12
operation. However, commercial continuous sampling equipment such as AMESA faces the
13
challenges of high weight and complicated sampling procedures. This study has developed a
14
long-term and automatic sampling system (National Central University continuous stack sampling
15
system, NCU-CS3), and compared the efficiency with manual sampling train (MST). The results
16
indicate that relative standard deviation (RSD) of PCDD/Fs concentrations measured between
17
NCU-CS3 and MST is < 20%, demonstrating that the difference between NCU-CS3 and MST in
18
measuring PCDD/Fs is insignificant. Besides, the effects of adsorbent temperature, adsorbent amount
19
and type of adsorbent on breakthroughs of PAHs and unintentional-persistent organic pollutants
20
(UPOPs) such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated
21
biphenyls (PCBs), chlorinated phenols (CPs), chlorinated benzenes (CBs) and polychlorinated
22
naphthalenes (PCNs) are evaluated. The results indicate that the breakthrough of pollutants increases
23
with increasing temperature of XAD-2 and decreases with increasing XAD-2 amount. Moreover,
24
XAD-4 is used as alternative adsorbent to test the breakthrough and the results indicate that the
25
breakthroughs of UPOPs of XAD-4 as adsorbent are lower than that with XAD-2 due to higher
26
specific surface area of XAD-4. Furthermore, the residual of PCDD/Fs with NCU-CS3 as the
27
sampling train is relatively low (1.5-3.8%), which meets the regulation of EN 1948-5 (10%).
28
Key words: long-term sampling, PAHs, unintentional persist organic pollutants(UPOPs), flue gas
29
sampling
30 31
1. Introduction
32
During the past a few decades, emissions of polycyclic aromatic hydrocarbons (PAHs) and
33
unintentional-persistent organic pollutants (UPOPs) such as polychlorinated dibenzo-p-dioxins and
34
dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), chlorinated phenols (CPs), chlorinated
35
benzenes (CBs) and polychlorinated naphthalenes (PCNs) have caused much public concern due to
36
their threats to human health (Van Caneghem et al., 2010; Rostami and Juhasz, 2011). Some toxic
37
congeners of PCDD/Fs, dl-PCBs, PCNs, CPs and CBs are listed on the Stockholm Convention to
38
protect human health and the environment from persistent organic pollutants (POPs), while PAHs are
39
carcinogenic to threaten human health. Among these hazardous pollutants, only PCDD/Fs emitted
40
from municipal wastes incinerators (MWIs) are rigorously regulated by the developed countries
41
worldwide while emissions of PAHs and other UPOPs are not restricted by most countries yet
42
(Cheruiyot et al., 2016; UNEP Chemicals, 1999). In order to further protect the human health from
43
the hazards caused by these pollutants, investigation on the characteristics of PAHs and UPOPs
44
emitted from MWIs is essential.
45
Previous studies indicate that concentrations of PAHs and UPOPs emitted from MWIs vary
46
significantly with waste composition, combustion condition, operating stage and air pollution control
47
devices adopted (Everaert and Baeyens, 2001; Lemieux et al., 2003; Tejima et al., 2007; Chen et al.,
48
2008; Aurell and Marklund, 2009; Liu et al., 2014; Li et al., 2017; Wang et al., 2017). Besides, some
49
studies indicate that the PCDD/Fs formation is closely related to the precursors such as PAHs, CPs
50
and CBs, while PCBs and PCNs have the similar formation pathway as PCDD/Fs (Hajizadeh et al.,
51
2011; Li et al., 2016; Cheruiyot et al., 2016). It has been found that PCDD/Fs concentrations
52
measured in stack gases during the start-up, shutdowns or operation failures are up to 2 to 3 order
53
higher than those measured during normal operation (Tejima et al., 2007; Chen et al., 2008;
54
Reinmann et al., 2010). Lothgren and Bavel (2005) indicate that start-up is the main stage of
55
increased PCDD/Fs emissions, which has been proved by continuous monitoring covering all periods
56
of operation. Besides, it has been found that even with several short-term measurements a year, real
57
emission of PCDD/Fs from MWIs still cannot be effectively monitored (Reinmann et al., 2006).
58
Arkenbout and Esbensen (2017) indicate that the short-term sampling scheme is seriously flawed on
59
PCDD/Fs measurement. In fact, significantly elevated dioxins emissions were measured in flue gas
60
during events of unstable combustion conditions by continuous long-term measurements. Besides,
61
the dioxin congener patterns from long-term flue gas sampling show similar patterns as the
62
congeners found in the samples nearby the MWIs, indicating that elevated dioxins in samples is
63
associated with the emissions from the incinerator. Consequently, applying continuous long-term
64
sampling to monitor PAHs and UPOPs emitted from MWIs can provide more reliable data compared
65
with short-term samplings.
66 67
Three commercial systems, (dioxin emission continuous sampling (DECS), dioxin monitoring
68
system (DMS) and adsorption method for sampling of dioxins (AMESA)) have been developed
69
respectively based on three long-term sampling methods for sampling PCDD/Fs in flue gas, i.e. (1)
70
the filter/condenser method, (2) the dilution method, and (3) the cooled probe method in European
71
method (EN1948) (Oleszek-Kudlak et al., 2007). However, the heavyweight of AMESA and DECS
72
and memory effect of AMESA have been found in previous studies and may cause danger and
73
difficulty during sampling campaign for old stack and overestimating the PCDD/Fs concentration
74
owing to memory effect, respectively (Idczak et al., 2003; Lin et al., 2012). Moreover, Lewandowski
75
and Gemmill (2006) compare the results of two automatic sampling systems (AMESA and DMS)
76
and two manual sampling methods and indicate the no significant difference is found between
77
AMESA and DMS. On the other hand, notable difference exists between two manual sampling
78
methods owing to human error and complex operating procedures of standard sampling methods (EN
79
1948) (Vicaretti et al., 2012). Therefore, developing an automatic long-term sampling system based
80
on filter/condenser method not only complies with the regulations promulgated in Taiwan but also
81
overcomes the disadvantages of manual sampling”.
82
Breakthrough test of the adsorbent applied is essential to determine the sampling efficiency
83
during long-term sampling. Effects of adsorbent temperature, adsorbent amount and type of
84
adsorbent on breakthrough have been verified in previous sampling campaigns (Wilbring and
85
Gerchel, 1997; Mayer et al., 2000; Kahr, 2004; Lee et al., 2004; Reinmann et al., 2008a). Relevant
86
studies indicate that the breakthrough of PCDD/Fs would not occur in the AMESA if the adsorbent
87
temperature is maintained <50oC (Wilbring and Gerchel, 1997; Mayer et al., 2000; Reinmann et al.,
88
2008a). Kahr (2004) indicated that breakthrough would not take place for DMS as long as the
89
adsorbent temperature is controlled ≤ 40oC and the breakthrough is < 5% with the adsorbent
90
temperature of 60oC. During the period of testing the AMESA system, no PCDD/Fs breakthrough is
91
observed during four weeks continuous sampling campaign when 70 g XAD-2 is applied as the
92
adsorbent (Wilbring and Gerchel, 1997; Reinmann et al., 2008a, 2008b). On the other hand, the
93
specific surface area and pore size of adsorbents may affect the adsorption amount and efficiency of
94
pollutants during sampling (Lee et al., 2004).
95 96
In order to comprehensively understand the emission and characteristics of PAHs and UPOPs
97
from MWIs, developing a continuous stack sampling system that meets the sampling protocols in
98
Taiwan is essential. The objective of this study is to develop a continuous automated sampling
99
system which can fulfill the requirements of NIEA A807.75C, EN 1948-1 and EN1948-5 and
100
overcome the disadvantages of commercial sampling systems. Besides, the effects of XAD-2 amount,
101
temperature of XAD-2 and types of adsorbent (XAD-2 and XAD-4) on the collection efficiencies of
102
PAHs and UPOPs emitted from a large-scale MWI located in southern Taiwan are evaluated with the
103
sampling system developed. Furthermore, comparison between the automated continuous sampling
104
system developed and manual sampling method for short-term sampling of PCDD/Fs is carried out.
105 106
2. Materials and method
107
2.1 Basic information of NCU-CS3
108
National Central University continuous stack sampling system (NCU-CS3) (as shown in Fig. 1) is
109
developed in this study for long-term sampling of PAHs and UPOPs emitted from MWIs. It has the
110
advantages of small size (1,240*660*495 mm), high mobility (< 80 kg) and low power consumption
111
(<1,300 W) since the gas composition analysis system of NCU-CS3 can be controlled with one
112
control unit. Specifically, NCU-CS3 consists of a heated glass sampling tube, filter, oven, two
113
adsorbent cartridges and control unit. The temperature of oven and sampling probe is controlled
114
within the range of 115-120oC which is lower than that specified NIEA A807.75C (120-134oC) to
115
avoid the regeneration and degradation of solid-phase PAHs during the long-term sampling. The
116
control unit is comprised of gas composition analysis system, moisture collection system and
117
isokinetic suction system that controls the gas flow rate, pressure and temperature of flue gas
118
sampled. The flue gas composition analysis system can measure the concentrations of O2, CO2 and
119
CO simultaneously. Besides, average percent isokinetic sampling rate is controlled between
120
94%-106% (Fig. S1), which meets the requirement of NIEA A807.75C (90-110%). As shown in Fig.
121
1, the sampling probe is placed in the center of the stack for continuous sampling. The particulate
122
matter (PM) concentration emitted from the MWI investigated is between 3.2-5.7 mg/Nm3 and the
123
pressure of the system still maintain < 400 mmHg in the condition of continuous operation for 450 hr.
124
Moreover, the leak of flue gas during the sampling period with the NCU-CS3 was less than 5%.
125 126
Fig. 1. Schematic of NCU-CS3 developed for continuous sampling of UPOPs
127 128
2.2 Sample collection by NCU-CS3 and MST
129
Overall, 7 samples (No1 to No 7) were collected isokinetically in parallel during the short-term
130
sampling period (6-7.8 hr) using manual stack sampling train (MST) and NCU-CS3, respectively, to
131
evaluate the performance of NCU-CS3 and make comparison with MST. The manual stack sampling
132
method follow Taiwan standard sampling method (NIEA A807.75C) which is modified from the
133
USEPA Method 23. In manual stack sampling method, the sampling probe was made from
134
borosilicate glass and connected with a filter holder placed in the filter oven. The sampling probe and
135
filter oven were kept within a temperature range of 120-134oC. The temperatures at the condenser
136
outlet (and inlet to XAD-2 resin) and silica gel trap outlet are maintained at a temperature < 20oC for
137
efficient capture of PCDD/Fs and water vapor. Isokinetic sampling must be applied to sample the
138
particles correctly. According to the EN1948-5, long-term sampling and manual sampling shall be
139
performed in parallel during a specified time period (at least 40 hr). In this study, long-term sampling
140
as well as the manual sampling is performed for 6 hr to 8 hr. Besides, the effects of adsorbent
141
temperature, adsorbent amount and types of adsorbent (XAD-2 and XAD-4) on the breakthrough
142
were carried out for 10 days. For the test of temperature and adsorbent amount, XAD-2 was used as
143
the adsorbent resin. In addition, three parameters were selected as following: amount of the XAD-2
144
in 1st adsorption cartridge is 35, 70 or 100 g (amount of second XAD-2 is fixed as 70 g); XAD-2
145
temperature is adjusted between 10-50oC and types of adsorbent applied include XAD-2 and XAD-4.
146
Breakthrough tests with NCU-CS3 were conducted by installing two adsorption cartridges in series
147
and the breakthrough is calculated as the ratios of the TEQ and mass concentration of PAHs or
148
UPOPs collected in second adsorbent cartridge to the total TEQ collected by rinse, filter, first and
149
second adsorbent cartridges (Eq 1). Furthermore, the residual of PCDD/Fs is calculated as the ratio
150
of TEQ in rinse to the total TEQ (Eq 2). The loss rate of PCDD/Fs regulated by Taiwan EPA is
151
calculated as the ratio of the TEQ concentration of residual PCDD/Fs to 0.1 ng TEQ/Nm3 (Eq 3)
152
(Mehl et al., 2003). The TEQ is calculated for PCDD/Fs to evaluate the extent of breakthrough and
153
the breakthroughs of other target pollutants are evaluated based on mass concentration.
154
Breakthrough (%) =
155
Residual (%) =
×100%.......................................... (Eq 1)
×100%.................................................................. (Eq 2)
156
Loss rate (%) =
/ ." # /$%&
×100%....................................................................... (Eq 3)
157
Total mass✽ stands for the total mass of PAHs or UPOPs collected by rinse, filter, first and second
158
adsorbent cartridges.
159 160
2.3 Pretreatment and analysis of PAHs and UPOPs
161
All standards are bought from Wellington and Cambridge. For PCDD/Fs analysis, the NIEA
162
A807.75C is followed, while WP-CVS standard is used for dl-PCBs analysis. The PCNs standards
163
are ECN 5558, ECN 2622, PCN-MXA, PCN-MXC, ECN5102, ECN5520, ECN5217, ECN5260,
164
WP-ISS. The chlorobenzene standards are CBS, MCBS, MCBZ-1235, and MCBZ-12345, while the
165
chlorophenol standards include CPS, MCP-246, MCP-345, MCP-23456, MPCS. Solid-phase and
166
gas-phase pollutants were collected by filter and XAD-2, respectively, using isokinetic sampling
167
system with both NCU-CS3 and manual sampling methods. Both filter and XAD-2 adsorbent were
168
spiked with isotopically labeled surrogate standards before sampling. The rinse was collected from
169
washing the sampling tube with three kinds of solvents in the order of acetone, dichloromethane
170
(DCM) and toluene. The filter, XAD-2 and the rinse of sampling tube were pretreated and analyzed
171
following Taiwan NIEA A808.75B. The samples were fortified with 13C-labeld of PAHs and UPOPs
172
as internal standard before extraction and then extracted by Soxhlet method which can be divided
173
into two stages, i.e., DCM/hexane (1:1) used as solvent for the first stage followed by toluene as the
174
second stage. The extracts were concentrated individually and then mixed homogenously. After that,
175
the extract was separated into two fractions for cleanup. One fraction in clean-up followed NIEA
176
A808.75B for PCDD/Fs and PCBs analysis, and the other was eluted in sequence with 50 mL of
177
n-hexane (discard) and 50 mL of n-hexane/DCM (5:1, v/v) (collected and concentrated) in the
178
column that containing 10 g silica and 10 g alumina for the analysis of PAHs and other UPOPs.
179
Finally, recovery standards were individually added into the extracts and analyzed by HRGC/HRMS
180
for 17 PCDD/Fs and 12 PCBs and HRGC/MS/MS for 4-8Cl PCN, 24 PAHs, 3-5Cl CPs, and 3-6Cl
181
CBs. The recovery efficiency of PCDD/Fs suggurate standards is between 90-110% which fulfill the
182
regulation of NIEA A807.75C (70-130%).
183 184
3. Results and discussion
185
3.1 Manual sampling train vs automated NCU-CS3
186
The PCDD/Fs concentration emitted from the MWI investigated are measured by MST and
187
NCU-CS3, respectively, to evaluate the performances of two methods and the results are summarized
188
in Table 1. The PCDD/Fs concentrations of No 1 –No 6 are lower than the PCDD/Fs emission
189
standard of large-scale MWIs in Taiwan (0.1 ng I-TEQ/Nm3). However, the PCDD/Fs concentrations
190
of No 7 measured by MST and NCU-CS3 are 0.264 and 0.225 ng I-TEQ/Nm3, respectively, which are
191
over the emission standard of MWIs regulated by Taiwan EPA. It is attributed to the fact that No 7
192
sampling was carried out during the shutdown period of MWI and previous studies indicate that
193
incomplete combustion would facilitate the formation of PCDD/Fs since the temperature decreases
194
and fluctuates greatly during shutdown period (Šyc et al., 2015; Li et al., 2017). Based on the above
195
results, long-term sampling is necessary for monitoring the emission of MWIs covering the periods
196
of start-up, shutdown and normal operation.
197
In addition, the results of the relative standard deviation (RSD) and relative percent difference
198
(RPD) between NCU-CS3 and MST are shown in Table 1, and it indicates the RSD of all seven
199
samples are below 35%. The EN 1948-5 indicates that the RSD with PCDD/Fs I-TEQ concentration
200
around 0.1 ng I-TEQ/Nm3 determined by the long-term sampling should be within 35 % of the value
201
determined by the MST measurement to validate the long-term sampling system. If the PCDD/Fs
202
concentrations measured by MST are much lower than 0.1 ng I-TEQ/m3, the value of RSD between
203
the MST and the long-term sampling system should follow the regulation proposed by the EN
204
1948-5. Moreover, Table 1 indicates that RPD of PCDD/Fs concentration between MST and
205
NCU-CS3 methods are < 20%, which is lower than the tolerance level of RPD < 30% as set by JIS
206
K0311. Horie at al (2007) used RPD to compare the MST and AMESA methods and the results
207
indicate that the RPDs of two facilities are in the wide range of 9%-82% due to the uncertainty
208
caused by extremely low PCDD/Fs concentrations. Besides, linear regression of the parallel tests
209
data is shown in Fig. 2. The correlation coefficient (R2) between MST and NCU-CS3 is 0.91, which is
210
in good agreement with the earlier published results of several comparison tests (Idczak et al., 2003;
211
Horie et al., 2007). Based on the results of PCDD/Fs concentrations measured, RSD, RPD and
212
correlation coefficient, we conclude that the difference between the MST and NCU-CS3
213
measurement is relatively insignificant. Previous study indicates that notable difference exists
214
between two manual sampling methods owing to human error and complex operating procedure
215
(Vicaretti et al., 2012), for instance, the adjustment procedure of the isokinetic suction rate of MST is
216
more complicated if compared with NCU-CS3, which may cause the variation of particulate-phase
217
PCDD/Fs concentration measured. The suction rate of MST is supposed to be checked per 10-15 min
218
by the operator while the suction rate of NCU-CS3 can be adjusted automatically every 30 second.
219
Some studies use commercial AMESA system to solve the shortcomings of MST, however, previous
220
study indicates that the memory effect exists with AMESA during the unstable operating condition of
221
incinerator due to the deposition residual PCDD/Fs on the cooling sampling probe and the elbow of
222
the sampling tube (Reinmann et al., 2008b; Wang and Lin, 2015). Thus, it is suggested that
223
automated NCU-CS3 developed in this study is capable to overcome the human errors involved with
224
MST and to reduce the time and cost for sampling preparation (Vicaretti et al., 2012). Compared with
225
other commercial continuous sampling systems, NCU-CS3 has the merits of low weight of
226
equipment, low energy consumption and good compatibility with the sampling method promulgated
227
in Taiwan. Hence, NCU-CS3 is proved as a reliable continuous sampling system for PCDD/Fs
228
sampling.
229 230 231
232 233 234
Table 1 PCDD/Fs concentrations (ng I-TEQ/Nm3) and the differences between NCU-CS3 and MST
235 No
Sampling period
NCU-CS3
MST
RSD
(%)
RPD
(%)
(hr) 1
6
0.054
0.050
5
8
2
6.2
0.028
0.023
14
20
3
6.8
0.023
0.028
14
20
4
7
0.053
0.050
4
6
5
6.4
0.028
0.031
7
10
6
7.3
0.015
0.018
13
18
7
7.8
0.225
0.264
11
16
236
RSD : (standard deviation of PCDD/Fs TEQ concentration between NCU-CS3 and MST divided by
237
the mean of PCDD/Fs TEQ concentration between NCU-CS3 and MST)×100%
238
RPD : (difference of PCDD/Fs TEQ concentration between NCU-CS3 and MST divided by half of
239
the mean of PCDD/Fs TEQ concentration between NCU-CS3 and MST) ×100%
240
241 242
Fig. 2. Linear regression of PCDD/Fs I-TEQ concentrations determined with MST and NCU-CS3 in
243
short-term sampling
244 245 246
3.2 Effects of adsorbent temperature, amount of XAD-2 and type of adsorbent on breakthrough test
247
Firstly, XAD-2 is chosen as the adsorption resin for testing the effects of adsorbent temperature
248
and the adsorbent amount on PCDD/Fs breakthrough of the NCU-CS3 for the continuous operation
249
of 10 days and the results are presented in Fig. 3. The results indicate that the breakthrough of
250
PCDD/Fs increases with increasing XAD-2 temperature and decreases with increasing XAD-2
251
amount. Overall, the PCDD/Fs breakthroughs are < 2% as the XAD-2 temperature is controlled <
252
20oC and the XAD-2 amount are set at 35, 70 or 100 g. Except for 35 g of XAD-2 amount, the
253
PCDD/Fs breakthrough is < 1% as the XAD-2 temperature is controlled < 20oC. Therefore, 70 g of
254
XAD-2 and 20oC of XAD-2 temperature are optimal for operating the NCU-CS3 for effective capture
255
of PCDD/Fs. Interestingly, the breakthrough of PCDD/Fs congeners decrease with increasing
256
chlorinated level and it is attributed to the fact that low chlorinated PCDD/Fs with higher vapor
257
pressures have higher tendency to penetrate through the first XAD-2 cartridge and be captured by the
258
second XAD-2 cartridge and the trend is consistent with that reported in previous studies (Wu et al.,
259
2014; Wang and Lin, 2015).
260
Breakthroughs of UPOPs and PAHs with different XAD-2 temperatures are also evaluated and
261
the results are shown in Fig. 4. The results indicate that the breakthroughs of UPOPs and PAHs
262
increase with increasing XAD-2 temperature. It's worth noting that the breakthrough of PAHs
263
increases significantly with increasing XAD-2 temperature. It is attributed to the fact that low-ring
264
PAHs with higher vapor pressures are easier to penetrate, leading to higher breakthrough. As shown
265
in Fig. S1, low-molecular-weight PAHs (2 to 3 ring PAHs) such as naphthalene (8.94% - 24.4%),
266
phenantrene (5.33% - 12.98%) and pyrene (5.12% - 9.5%) are of higher breakthroughs in
267
comparison with high-molecular-weight PAHs (other PAHs < 1%) as the XAD-2 temperatures are
268
controlled at 20oC, 30oC and 50oC, respectively. It also suggests that the XAD-2 temperature has
269
more significant effect on the breakthrough of low-molecular-weight PAHs compared with
270
high-molecular-weight PAHs. Additionally, breakthrough of 12 dioxin-like polychlorinated biphenyls
271
(PCBs) is slightly higher than that of 17 PCDD/Fs due to lower boiling points of PCBs (340-375oC)
272
in comparison with PCDD/Fs (438-537oC) (Reinmann et al., 2008a). In addition, the results shown in
273
Fig. S2 also indicate that co-planar PCBs (TeCB-77, TeCB-81, PeCB-126 and HxCB-169) with
274
higher adsorption potential exhibit lower breakthrough (< 4%) in compared with non-planar PCBs (>
275
4.5%), which suggests that the structures of the PAHs and UPOPs also affect the breakthrough
276
(Cortes et al., 1991). Polychlorinated naphthalenes (PCNs) are of lower boiling points (260-440oC)
277
(UNEP, 2017), resulting in higher breakthrough in comparison with PCDD/Fs. Furthermore,
278
breakthroughs of PAHs, CBs and CPs are significantly higher than that of PCDD/Fs, PCBs and
279
PCNs due to lower boiling points of PAHs (217-495oC), CBs (219-322oC) and CPs (253-310oC)
280
(Reinmann et al., 2008a).
281
Fig. 4 also indicates that breakthroughs of PAHs, CPs and CBs are relatively high as XAD-2 is
282
applied as the adsorbent. In order to ensure the trap efficiency and understand the accurate
283
concentrations of PAHs and UPOPs emitted from the stack gas, appropriate operating parameters of
284
NCU-CS3 for effective capture of PAHs, CBs and CPs are needed. Therefore, XAD-4 is used as
285
alternative adsorption resin to test the breakthroughs of CBs, CPs and PAHs. Fig. 5 shows the
286
comparsion of XAD-2 and XAD-4 on breakthroughs of UPOPs and PAHs with the adsorbent
287
temperature of 35oC and 70 g adsorbent in the first cartridge. The results indicate that the
288
breakthroughs of PAHs and UPOPs with XAD-4 as adsorbent are significantly lower than that with
289
XAD-2 as adsorbent, which is consistent with the previous study (Wang and Lin, 2015). Lower
290
breakthrough can be ascribed to higher specific surface area (750 m2/g) and higher pore volume
291
(0.98 mL/g) of XAD-4 compared with XAD-2 (specific surface area = 300 m2/g and pore volume =
292
0.65 mL/g). Previous studies indicated that XAD-4 was superior to XAD-2 and XAD-16 for PAHs
293
and PCDD/Fs sampling due to the dominance of microspore adsorption (Lee et al., 2004; Wang and
294
Lin, 2015). Hence, it suggests that PCDD/Fs and PCBs can be effectively captured by XAD-2 as the
295
temperature and amount are controlled at 20oC and 70 g, respectively, while XAD-4 is more
296
appropriate as adsorbent for capturing CBs, CPs and PAHs in stack gas.
297 298
Fig. 3. Effects of XAD-2 temperature and XAD-2 amount on the breakthrough of PCDD/Fs sampled
299
with NCU-CS3
300 301
Fig. 4. Effects of XAD-2 temperature on breakthroughs of UPOPs and PAHs with 70 g of XAD-2 in
302
NCU-CS3.
303 304
Fig. 5. Effects of XAD-2 and XAD-4 on breakthroughs of UPOPs and PAHs in NCU-CS3 with 70 g
305
adsorbent and adsorbent temperature of 35oC
306 307
3.3 Residual PCDD/Fs on NCU-CS3
308
Residual PCDD/Fs is collected from washing the sampling probe of the NCU-CS3 with acetone,
309
DCM and toluene in sequence after continuous sampling for 10 days in the MWI investigated. Fig. 6
310
shows the distributions of PCDD/Fs among residual, particle phase and gas phase with NCU-CS3 as
311
the sampling system. The result indicates that the distribution of PCDD/Fs in gas phase (93.2%) is
312
significantly higher than those in particle phase (6.8%) and residual (2.8%), which suggests that the
313
PCDD/Fs emitted from the MWI investigated mainly exist in gas phase. However, it is found that the
314
residual PCDD/Fs measured during the start-up procedure (6.4%) is significantly higher than that
315
measured during normal operation (3%), which is attributed to the fact that the PM concentration of
316
unstable condition (3.5 mg/Nm3) is higher than that of normal operation (< 1 mg/Nm3). Besides, the
317
residual PCDD/Fs is between 1.5-3.8% (with the average value of 2.8%) and the loss rate of
318
PCDD/Fs is between 1-6.4%, which is significantly lower than that reported in the relevant studies
319
which applied AMESA (17.2-37.0%) as sampling system and meet the regulation of EN 1948-5
320
(10%) (Wang and Lin, 2015; Mehl et al., 2003). Higher residual PCDD/Fs observed in AMESA
321
could be attributed to the memory effect and it suggests that PCDD/Fs deposited on the cooled
322
sampling probe and the sampling elbow cannot be completely cleaned, which causes the bias on the
323
PCDD/Fs measurement (Vicaretti et al., 2012). As for NCU-CS3, the sampling probe equipped is
324
heated to avoid the memory effect and decrease the deposition and condensation of PCDD/Fs on the
325
sampling probe during sampling, which is similar to the commercial long-term sampling system such
326
as DMS and DES. On the other hand, due to smaller diameter of the sampling probe in NCU-CS3,
327
the velocity of flue gas would be higher to avoid the deposition of PCDD/Fs on the sampling tube.
328
Interestingly, the results shown in Fig. S3 indicate that the residual of highly chlorinated PCDD/Fs is
329
higher than that of low chlorinated PCDD/Fs. The main PCDD/Fs congeners in residual are OCDD,
330
1,2,3,4,6,7,8-HpCDD, and OCDF and the percentages of OCDD, 1,2,3,4,6,7,8-HpCDD, and OCDF
331
residual in total PCDD/Fs residual are 15.2%, 11.1% and 8.7%, respectively, since highly chlorinated
332
PCDD/Fs with low vapor pressures are more easily condensed and adsorbed on the sampling probe.
333
334
Fig. 6. The percentages of PCDD/Fs among residual, particle phase and gas phase, respectively, in
335
NCU-CS3 for 10 days’ continuous sampling
336 337 338 339
Conclusions
340
A long-term automatic sampling system (NCU-CS3) is developed for sampling PAHs and
341
UPOPs from MWI based on the filter/condense method which is in compliance with the regulations
342
of Taiwan EPA. Besides, the difference between MST and NCU-CS3 has been evaluated in this study.
343
The results indicate that the RSD and correlation coefficient of PCDD/Fs TEQ concentration
344
between MST and NCU-CS3 are < 35% and 0.9, respectively, which suggests that NCU-CS3 is
345
reliable and can overcome the disadvantages of manual sampling train. Furthermore, the effects of
346
adsorbent temperature, adsorbent amount and types of adsorbent on breakthrough are evaluated for
347
NCU-CS3 and the results indicate that the breakthrough increases with increasing temperature and
348
decreasing adsorbent amount. The XAD-2 temperature and amount should be controlled at 20oC and
349
70 g, respectively, for ensuring effective capture of PCDD/Fs emitted from MWIs. Additionally,
350
NCU-CS3 system with XAD-4 as adsorbent can effectively capture UPOPs and PAHs, especially for
351
the pollutants of low boiling points owing to higher the specific surface area. Moreover, low residual
352
PCDD/Fs with NCU-CS3 has been found in this study and it fulfills the requirement of EN1948-5
353
(10%).
354 355
Acknowledgement
356
This study was financially supported by Taiwan Environmental Protection Administration (EPA) and
357
Ministry of science and technology (MOST) (Project no. MOST-105-2221-E-008-006-MY3).
358 359
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long-term sampling system (AMESA○R ). Aerosol Air Qual Res. 14, 185-196.
Highlights 1. A long-term and automatic sampling system (NCU-CS3) has been developed. 2. The difference between NCU-CS3 and MST in measuring PCDD/Fs is insignificant. 3. Effects of adsorbent temperature, amount and types on tests have been elucidated. 4. Low residual PCDD/Fs with NCU-CS3 has been found in this study.
Author Contribution Statement Yen-Chen Hsu：Conceptualization, Methodology, Writing - Original Draft, WritingReviewing and Editing Shu-Hao Chang：Conceptualization, Methodology, Validation Moo Been Chang:：Conceptualization, Supervision, Project administration
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: