Potential Method for Reducing Emissions of Polycyclic Aromatic

Taiwan, Republic of China, Graduate Institute of. Environmental ... Two incinerating conditions were studied, one directly incinerating ..... In addit...
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Environ. Sci. Technol. 2002, 36, 3420-3425

Potential Method for Reducing Emissions of Polycyclic Aromatic Hydrocarbons from the Incineration of Biological Sludge for the Terephthalic Acid Manufacturing Industry LIN-CHI WANG,† WEN-JHY LEE,† P E R N G - J Y T S A I , * ,‡ A N D S H U I - J E N C H E N § Department of Environmental Engineering, National Cheng Kung University, 1 University Road, Tainan 70101, Taiwan, Republic of China, Graduate Institute of Environmental and Occupational Health, Medical College, National Cheng Kung University, 138 Sheng-Li Road, Tainan 70428, Taiwan, Republic of China, and Department of Environmental Engineering Science, National Pingtung University of Science and Technology, Nei Pu 91207, Pingtung, Taiwan, Republic of China

This study illustrates a potential method for reducing PAH emissions from the incineration of biological sludge by adding a suitable and available waste as a co-fuel. The whole study was conducted on a full-scale fluidized-bed incinerator operated by a terephthalic acid (TPA) manufacturing plant for disposing of biological sludge. Two incinerating conditions were studied, one directly incinerating biological sludge (the normal incinerating condition), and the other adding the waste TPA as a cofuel during the biological sludge incineration process (the trial incinerating condition). Both incinerating conditions used heavy oil as auxiliary fuel. Although the former had a higher heavy oil consumption rate than the latter, both had comparable combustion efficiencies. Results show that the total PAH input mass rate for the former was only 2.35 times higher than the latter, but the total PAH emission factor for the former was 6.52 times higher than the latter. Total PAH output/input mass ratios for both incinerating conditions were lower than unity, but the value for the normal incinerating condition was ∼2.91 times higher than the trial condition. In conclusion, the use of waste TPA as a co-fuel not only saved the consumption of heavy oil but also reduced PAH emissions during the combustion process.

tons of waste TPA and ∼9 × 104 tons of biological sludge (wet basis). This waste TPA includes both low-grade TPA generated from the manufacturing process under abnormal operating conditions and TPA accidentally dropped to the ground during packing and transportation processes. The biological sludge was generated by the wastewater treatment plant that deals with wastewater from both TPA manufacturing and purification processes. Currently, waste TPA is recovered (free of charge) by other industries (such as the plastics industry, which uses it as a process additive for manufacturing some special plastics). Biological sludge is disposed of by incineration in order to reduce the volume. Incineration processes are known to be a source of polycyclic aromatic hydrocarbons (PAHs) emission due to incomplete combustion and/or pyrosynthesis of organic matters during the combustion process (1). To date, PAH emissions from the incineration of various types of wastes have been intensively investigated by many researchers (2-9). However, to the best of our knowledge PAH emissions from the incineration of the biological sludge of the TPA manufacturing industry have never been investigated. Table 1 shows the background information for both the biological sludge and waste TPA. The biological sludge contains a higher moisture content (≈84.9%) than that of the waste TPA (≈9.00%), but the heat value of the former (-353 and 3240 kcal/kg on wet and dry bases, respectively) is lower than that of the latter (3240 and 4340 kcal/kg, respectively). Therefore, it is possible that the use of waste TPA as a co-fuel can increase the heat input during the biological sludge incineration process. It should be noted that the emission of PAHs from the incineration process could be affected by the contents of the feedstock (10). The use of co-fuel has been adopted successfully by Li et al. (5) and Aittola and Viinikainen (11). Li and co-workers used polyethylene (PE) plastic as a co-fuel for the incineration of the oily sludge generated from petroleum refinery industries. Aittola and Viinikainen used the municipal waste as a cofuel for the incineration of wood chips and milled peat. Although the co-fuels used in the above two studies were not directly obtained from the same industry, they did demonstrate the benefit of reducing PAH emissions. The present study was conducted on a full-scale fluidizedbed incinerator operated by a TPA manufacturing plant. The objective of this study was to (1) characterize PAH emissions from the incineration of biological sludge and (2) investigate the feasibility of using waste TPA as a co-fuel in order to reduce PAH emissions. Assuming that the above measure was able to reduce PAH emissions, it could be applied to other industries [such as alkylbenzenesulfonate (ABS) resin and polyacrylonitrile (PAN) manufacturing industries] to use their low-grade products for co-incinerating with their biological sludge generated from the wastewater treatment plants.

Introduction

Materials and Methods

Terephthalic acid (TPA) is an important material for manufacturing polyester fiber, plastic containers, polyester film, and engineering plastics. In 2000, ∼3.0 × 106 tons of TPA was produced in the Taiwan area, accompanied with ∼1.5 × 103

Background Information of Incinerations. In this study, a full-scale fluidized-bed incinerator owned and operated by a TPA manufacturing plant was studied. The incinerator is equipped with a cyclone and a wet scrubber (WSB) (installed in series) as its air pollution control devices (APCDs). Two types of incinerating conditions were investigated, denoted the normal incinerating condition and the trial incinerating condition, respectively (see Table 2). For the normal incinerating condition, the incinerator was used to directly incinerate the biological sludge at a feeding rate of 1040 kg/ h. For the trial incinerating condition, the biological sludge

* Corresponding author telephone: +886-6-2088390; fax: +8866-2088391; e-mail: [email protected]. † Department of Environmental Engineering, National Cheng Kung University. ‡ Graduate Institute of Environmental and Occupational Health, National Cheng Kung University. § National Ping Tung University of Science and Technology. 3420

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10.1021/es011293e CCC: $22.00

 2002 American Chemical Society Published on Web 06/26/2002

TABLE 1. Background Information for the Biological Sludge and Waste TPA Generated from the TPA Manufacturing Industry biological sludge

feeding waste

TABLE 3. PAH Compounds and Their Toxic Equivalent Factors (TEFs) Suggested by Nisbet and LaGoy (1992)

waste TPA

contents (%) moisture (W) 84.9 9.00 ash 9.00 2.30 combustible 6.10 88.7 elemental composition of the combustible fraction (%) nitrogen (N) 8.10 1.32 carbon (C) 38.0 58.9 sulfur (S) 1.19 2.36 hydrogen (H) 5.16 6.92 oxygen (O) 47.5 30.4 heat value (kcal/kg) dry basisa 3240 4340 wet basisb -353 3730 a Measured by calorimeter. + W).

b

) 81C + 342.5(H - O/8) + 22.5S - 6(9H

TABLE 2. Background Information for the Normal and Trial Incinerating Conditions incinerating conditions incinerating material incinerating waste feeding rate (kg/h) auxiliary fuel feeding rate (kg/h) combustion condition heat input (103 kcal/h) combustion temp (°C) combustion efficiency (%) O2 content in stack flue gas (%) emission rate stack flue gas (m3/min) cyclone-separated ash (kg/h) wet scrubber effluent (m3/h)

normal

trial

biological sludge 1040 heavy oil 130

biological sludge + waste TPA 900 + 160 heavy oil 55

1304 800 g98 9.0-9.2

1118 810 g98 9.0-9.2

150 105

144 76

37.5

37.4

was fed at 900 kg/h and was co-combusted with waste TPA at 160 kg/h. Both incinerating conditions used heavy oil as an auxiliary fuel. Because the biological sludge contained a lower heat value than that of the waste TPA (Table 1), the heavy oil feeding rate for the former (130 kg/h) was higher than that for the latter (55 kg/h) (Table 2). Nevertheless, the resulting combustion conditions for the above two incinerating conditions were quite comparable in terms of the combustion temperature (800 and 810 °C, respectively), the heat input (1304 × 103 and 1118 × 103 kcal/h, respectively), the oxygen content in the stack flue gas (9.0-9.2% for both), and the combustion efficiency (g98% for both) (Table 2). To minimize the memory effects of PAH emissions from the stack flue gas, cyclone fly ash, and WSB effluent, the sampling was conducted after the given incinerating condition had been operated for 3 h for both normal and trial incinerating conditions. This measure was used to ensure that the combustion efficiency during each individual sampling period was at a steady state. Sampling Strategy. Prior to incineration, seven 20 g samples were collected from each of the three incinerating materials (including waste TPA, biological sludge, and heavy oil) in order to determine PAH input mass for the two studied incinerating conditions. Glass bottles (pretreated with 10% nitric acid, rinsed with distilled water, and wrapped with aluminum foil in order to eliminate the decay of PAHs) were

a

PAH compound

TEF

naphthalene (Nap) acenaphthalene (AcPy) acenaphthene (Acp) fluorene (Flu) phenanthrene (PA) anthracene (Ant) fluoranthene (FL) pyrene (Pyr) cyclopenta(c,d)pyrene (CYC) benzo[a]anthracene (BaA) chrysene (CHR) benzo[b]fluoranthene (BbF) benzo[k]fluoranthene (BkF) benzo[e]pyrene (BeP) benzo[a]pyrene (BaP) perylene (PER) indeno(1,2,3-cd)pyrene (IND) dibenzo(a,h)anthracene (DBA) benzo[b]chrycene (BbC) benzo(ghi)perylene (BghiP) coronene (COR)

0.001 0.001 0.001 0.001 0.001 0.01 0.001 0.001 -a 0.1 0.01 0.1 0.1 -a 1 -a 0.1 1 -a 0.01 -a

No TEF was suggested by Nisbet and LaGoy (1992).

TABLE 4. Mean PAH Contents and Their Corresponding Standard Deviations (SD) of the Three Incinerated Materials (n ) 7) PAH compound Nap AcPy Acp Flu PA Ant FL Pyr CYC BaA CHR BbF BkF BeP BaP PER IND DBA BbC BghiP COR

biological sludge (µg/kg) mean SD 53.4 2.10 1.71 30.7 7.06 0.757 1.5 1.13 0.225 0.13 34.0 3.9 1.00 2.83 1.3 2.11 0.665 1.08 15.6 0.714 0.098

total PAHs 162 LM-PAHs 95.6 MM-PAHs 36.7 HM-PAHs 29.5 total BaPeq 3.23

6.87 0.495 0.204 3.83 0.597 0.052 0.048 0.116 0.055 0.016 1.48 1.36 0.251 0.674 0.227 0.76 0.263 0.171 3.37 0.193 0.026

waste PTA (µg/kg) mean SD

heavy oil (mg/kg) mean SD

61.9 7.96 4.06 10.7 18.1 1.96 12.0 0.31 7.21 2.48 27.2 10.9 24. 25.1 13.1 10.4 9.0 49. 29 23. 0.64

20.7 57.7 66.0 40.6 10.4 18.8 9.21 26.4 78.4 38.1 8.48 5.55 13.5 45.6 32.9 14.3 6.88 25.9 76.5 2.96 2.56

3.7 617 3.80 105 1.55 42.0 4.97 470 0.713 70.3

19.9 1.48 0.450 3.13 1.40 0.341 1.50 0.106 2.46 0.194 4.4 3.68 7.79 7.44 4.2 3.36 2.76 14.4 85.5 5.59 0.205 95. 15. 4.08 110 10.7

601 214 82.1 305 65.7

4.03 18.6 8.89 12.7 2.75 5.52 1.63 8.07 22.4 8.6 2.19 1.51 2.13 8.71 9.04 2.9 1.56 4.40 18.3 0.825 0.83 69.1 19.5 8.09 47. 14.0

used to collect samples in the field and then were transported to the laboratory for PAH analyses. During incineration, nine samples of stack flue gas were collected from each of the normal and trial incinerating conditions, by using a PAHs Sampling System (PSS; Li-Teh Co., Kaushiung, Taiwan). The PSS is comparable to the equipment that is specified by the U.S. EPA’s sampling method of Modified Method 5 (MM5; Code of Federal Regulations, 1996, Title 40, Part 60, U.S. EPA) for collecting semivolatile organic compounds from stack flue gas. This sampling system has been adopted in many studies for PAH VOL. 36, NO. 15, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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sampling in various industrial stacks (5-9, 12). The PSS was equipped with a sampling probe, a cooling device, a glass cartridge, a pump, a flow meter, and a control computer. During sampling, the stack flue gas was sampled isokinetically with the sampling flow rate at ∼10 L/min. The accurate flow rate was determined by averaging the flow rates measured at the beginning and the end of the sampling period by using a critical orifice flow calibrator (General Metal Work GMW25). The sampling temperature of the stack flue gas was ∼30 °C, and sampling duration was ∼60 min per sample. In the PSS, particle-bound PAHs were collected by a tube-type glass fiber filter (Whatman glass fiber thimble, 25 × 90 mm), and gaseous phase PAHs were collected by a two-stage XAD-16 resin/polyurethane foam (PUF) cartridge. Three breakthrough tests were conducted using a three-stage XAD-16/ PUF cartridge, and no significant PAH mass was found at the third stage of the XAD-16/PUF cartridge. After incineration, nine samples each were collected from the cyclone fly ash (20 g for each sample) and the WSB effluent (200 mL for each sample) for each of the two incinerating conditions by using glass bottles (each bottle pretreated with 10% nitric acid, rinsed with distilled water, and then wrapped with aluminum foil). Sample Analysis. Prior to analysis, each collected sample was placed in a solvent solution (the mixture of n-hexane and dichloromethane, v/v ) 500 mL/500 mL) and extracted in a Soxhlet extractor for 24 h. The extract was then concentrated, cleaned up, and reconcentrated to exactly 1.0 or 0.5 mL. PAH contents were determined by using a gas chromatograph (GC) (Hewlett-Packard 5890A) with a mass selective detector (MSD) (Hewlett-Packard 5972) and a computer workstation. This GC-MS was equipped with a Hewlett-Packard capillary column (HP Ultra 2-50 m × 0.32 mm × 0.17 µm) and an HP-7673A automatic sampler and was operated under the following conditions: injection volume, 1 µL; splitless injection at 310 °C; ion source temperature, 310 °C; oven temperature ramped at 20 °C/ min from 50 to 100 °C, at 3 °C/min from 100 to 290 °C, and held at 290 °C for 40 min. The masses of primary and secondary ions of the PAHs were determined using the scan mode. Qualification of PAHs was performed using the selected ion monitoring (SIM) mode (13). The concentrations of 21 PAH species were determined, including naphthalene (Nap), acenaphthalene (AcPy), acenaphthene (Acp), fluorene (Flu), phenanthrene (PA), anthracene (Ant), fluoranthene (FL), pyrene (Pyr), cyclopenta(c,d)pyrene (CYC), benzo[a]anthracene (BaA), chrysene (CHR), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[e]pyrene (BeP), benzo[a]pyrene (BaP), perylene (PER), indeno(1,2,3-cd)pyrene (IND), dibenzo(a,h)anthracene (DBA), benzo[b]chrycene (BbC), benzo(ghi)perylene (BghiP), and coronene (COR). Recovery efficiencies were determined by processing a solution containing known PAH concentrations following the same experimental procedure as used for the treatment of the samples. The recovery efficiencies for the 21 PAH compounds ranged from 0.759 to 1.070 (average ) 0.853). To control losses during sampling, three internal standards (Nap-d8, PA-d10, and PER-d12) were used as presampling spikes and were used for correction purposes. The blank tests for PAHs were accomplished by using the same procedure as the recovery-efficiency tests without the addition of the known standard solution before extraction. Analyses of field blanks, including the glass bottle, glass fiber filter, and PUF/XAD-16 cartridge, found no significant contamination of PAHs (GC-MS integrated area < detection limit). Data Analysis. In this study, the concentration of total PAHs was defined as the sum of the concentrations of the above 21 PAH compounds. In addition, PAH contents were further classified into three categories according to their 3422

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TABLE 5. Mean PAH Input Mass Rates and Their Corresponding Standard Deviations (SD) for the Normal Incinerating Condition PAH compound Nap AcPy Acp Flu PA Ant FL Pyr CYC BaA CHR BbF BkF BeP BaP PER IND DBA BbC BghiP COR total PAHs LM-PAHs MM-PAHs HM-PAHs total BaPeq

biological sludge (mg/h) mean SD 55.6 2.20 1.73 31.9 7.38 0.785 1.57 1.10 0.157 0.157 35.3 4.08 1.10 2.98 1.41 2.20 0.628 1.10 16.2 0.785 0.157 168 99.6 38.2 30.6 3.61

heavy oil (mg/h) mean SD

sum (mg/h) mean SD

7.1 0.517 0.206 3.99 0.627 0.054 0.050 0.112 0.039 0.019 1.52 1.42 0.276 0.709 0.241 0.799 0.248 0.175 3.50 0.212 0.042

2690 7500 8580 5280 1350 2440 1200 3430 10200 4950 1100 722 1760 5930 4280 1860 894 3370 9950 385 333

525 2420 1160 1650 358 717 212 1050 2910 1120 284 196 276 1130 1180 378 202 573 2380 107 108

2750 7500 8580 5310 1360 2450 1200 3430 10200 4950 1140 726 1760 5930 4280 1860 895 3370 9960 386 333

533 242 1160 1650 359 720 212 1050 2910 1120 286 198 276 1130 1180 378 202 573 2380 108 108

3.86 3.98 1.60 5.14 0.798

78100 27800 10700 39700 8540

8982 2530 1059 6114 1819

78300 27900 10700 39700 8550

8990 2530 1060 6110 1820

molecular weights, including low molecular weight (LMPAHs; containing two- to three-ringed PAHs), middle molecular weight (MM-PAHs; containing four-ringed PAHs), and high molecular weight (HM-PAHs; containing five-, six-, and seven-ringed PAHs). In addition, the International Agency for Research on Cancer (IARC) has classified several PAH compounds into probable (2A) or possible (2B) human carcinogens (14). In the present study we also determined the carcinogenic potency of each collected sample. In principle, the carcinogenic potency of a given PAH compound can be expressed in terms of its BaP equivalent concentration (BaPeq). The BaPeq for a given PAH compound was calculated as the product of its toxic equivalent factor (TEF) and its concentration. Currently, several TEF lists have been proposed (15-17). Among them, the list proposed by Nisbet and LaGoy was adopted in this study (Table 3) (17). The list has been demonstrated as a better reflection of the actual state of knowledge on the toxic potency of each individual PAH compound with respect to BaP (18). The carcinogenic potency of the total PAHs (i.e., total BaPeq) was estimated as the sum of individual BaPeq values of the 21 PAH compounds. To examine the statistical significance of the observed differences, both the mean value and standard deviation (SD) were calculated and presented in this study.

Results and Discussion PAH Input Mass. Table 4 shows the PAH contents of the waste TPA, biological sludge, and heavy oil. Because the heavy oil was directly obtained from the cracking process, it is not surprising to see that it contained the highest mean total PAH content (601 mg/kg) among these three incinerating materials. The lowest mean total PAH content was found in the biological sludge (162 µg/kg) rather than the waste TPA (617 µg/kg), which could have been due to the former containing a much higher moisture content (84.9%) than the latter (9.00%) (Table 1). Table 4 also shows the distributions of PAH homologues contained in the above three

TABLE 6. Mean PAH Input Mass Rates and Their Corresponding Standard Deviations (SD) for the Trial Incinerating Condition waste PTA (mg/h) PAH compound

biological sludge (mg/h)

heavy oil (mg/h)

sum (mg/h)

mean

SD

mean

SD

mean

SD

mean

SD

Nap AcPy Acp Flu PA Ant FL Pyr CYC BaA CHR BbF BkF BeP BaP PER IND DBA BbC BghiP COR

9.90 1.31 0.582 1.75 2.91 0.291 1.89 0.000 1.17 0.437 4.37 1.75 3.93 4.08 2.04 1.60 1.46 8.30 47.5 3.79 0.146

3.19 0.244 0.065 0.509 0.224 0.051 0.236 0.000 0.400 0.034 0.712 0.590 1.25 1.21 0.653 0.515 0.447 2.43 13.7 0.913 0.046

48.1 1.90 1.50 27.6 6.39 0.680 1.36 0.951 0.136 0.136 30.6 3.53 0.951 2.58 1.22 1.90 0.544 0.951 14.0 0.680 0.136

6.20 0.447 0.179 3.45 0.543 0.047 0.044 0.097 0.033 0.016 1.32 1.22 0.239 0.614 0.209 0.690 0.215 0.151 3.02 0.184 0.037

1140 3170 3630 2230 572 1030 507 1450 4310 2100 466 305 743 2510 1810 787 378 1430 4210 163 141

222 1020 490 696 152 303 89. 444 1230 477 120 83.0 117 479 498 160 85.4 243 1010 45.5 45.8

1200 3180 3630 2260 581 1040 510 1450 4310 2100 501 311 747 2520 1810 790 380 1430 4270 167 141

232 1020 490 700 152 30 90.0 444 1230 477 122 85.0 118 482 498 161 86.1 244 1020 46.4 45.8

total PAHs LM-PAHs MM-PAHs HM-PAHs total BaPeq

99.2 16.7 6.70 75. 6 11.2

15.4 2.47 0.650 17.6 1.70

3.34 3.45 1.39 4.45 0.692

33100 11800 4520 16800 3610

145 86.2 33.0 26.5 3.13

incinerated materials. It can be found that the heavy oil and the waste TPA shared the same trend (HM-PAHs > LM-PAHs > MM-PAHs), which was different from that found in the biological sludge (LM-PAHs > MM-PAHs > HM-PAHs). It is known that the carcinogenic potency of a given incinerated material would be affected by its PAH contents. In general, the higher the molecular weight, the higher the carcinogenic potency expected (Table 3). Thus, it is not surprising to find that the highest total BaPeq content was in the heavy oil, followed by the waste TPA and then the biological sludge. Tables 5 and 6 show PAH input mass rates for the two studied incinerating conditions, respectively. For the normal incinerating condition (Table 5), the total PAH input mass rate (78 300 mg/h) was contributed mainly by the heavy oil (78 100 mg/h) rather than by the incinerated waste (i.e., biological sludge) (168 mg/h). A similar trend was found for the trial incinerating condition (Table 6), for which the total PAH input mass rates (33 300 mg/h) contributed by the heavy oil and incinerated waste (including both biological sludge and waste TPA) were 33 100 and 244 mg/h, respectively. Because both incinerating conditions were found to have similar combustion efficiencies, the above results indicated that using waste TPA as a co-fuel not only saved heavy oil consumption (Table 2) but also significantly reduced the total PAH input mass rate. PAH Output Mass. Tables 7 and 8 show output mass rates for the three emission sources (including fly ash from cyclone, effluent from WSB, and stack flue gas) of the two studied incinerating conditions, respectively. For the normal incinerating condition (Table 7), the mean total PAH output mass rates for the cyclone fly ash, WSB effluent, and stack flue gas were 10.6, 562, and 8870 mg/h, respectively (sum ) 9440 mg/h). Obviously, the stack flue gas accounted for the major part (93.9%) of the total PAH output mass rate and was significantly higher than that of WSB effluent (6.0%) and the cyclone fly ash (0.1%). The above results suggest that APCDs had a very low overall removal efficiency for total PAHs (6.1%, by combining both the cyclone and WSB). Among the three investigated PAH homologues, the overall removal

3810 1080 447 2590 769

33300 11900 4560 16900 3630

3820 1080 450 2610 773

efficiency for HM-PAHs [) (4.26 + 148)/1130 ) 13.2%] was higher than that for LM-PAHs [) (5.93 + 388)/7840 ) 6.0%] and that for MM-PAHs [) (0.418 + 26.5)/424 ) 6.4%]. This is likely because the fraction of the particle phase PAHs contained in HM-PAHs was higher than that contained in LM-PAHs and MM-PAHs, and APCDs are known to have a higher removal efficiency on the particle phase than on the gas phase. In addition, PAH compounds with higher molecular weights are known to have higher TEFs (Table 3). Therefore, the overall removal efficiency of APCDs on total BaPeq [) (0.887 + 98.9)/724 ) 13.6%] was higher than that on total PAHs (6.1%). Nevertheless, the above results indicate that the APCDs with cyclone and WSB installed in series were inadequate in controlling PAH emissions. For the trial incinerating condition (Table 8), the mean total PAH output mass rates for the cyclone fly ash, WSB effluent, and stack flue gas were 2.78, 126, and 1250 mg/h, respectively (sum ) 1380 mg/h). Obviously, the above results shared the same trend as the normal incinerating condition. Again, the stack flue gas accounted for the most important part of the total PAH output mass rate (90.6%) and was significantly higher than that contributed by the cyclone fly ash (0.2%) or WSB effluent (9.1%). The overall removal efficiencies of APCDs on total PAHs, LM-PAHs, MM-PAHs, HM-PAHs, and total BaPeq were 9.4% [) (2.78 + 126)/1380], 9.6% [) (2.25 + 99.9)/1150], 4.2% [) (0.158 + 7.43)/165], 28.5% [) (0.372 + 18.2)/67.3], and 33.5% [) (0.079 + 5.64)/ 17.0], respectively. The higher overall removal efficiencies found for HM-PAHs and total BaPeq were again due to more effective removal by APCDs in PAH compounds with high molecular weights than those with low molecular weights. PAH Output/Input Mass Ratio. Figure 1 shows PAH output/input mass ratios for these two studied incinerating conditions. For the normal incinerating condition, the mean output/input mass ratios for LM-PAHs, MM-PAHs, HMPAHs, total PAHs, and total BaPeq were 28.1, 3.96, 2.86, 12.1, and 8.47%, respectively. For the trial incinerating condition, the corresponding output/input mass ratios were 9.64, 1.62, 0.403, 4.14, and 0.471%, respectively. Because the above VOL. 36, NO. 15, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 7. Mean PAH Output Mass Rates and Their Corresponding Standard Deviations (SD) for the Normal Incinerating Condition (n ) 9) cyclone fly ash (mg/h) PAH compound Nap AcPy Acp Flu PA Ant FL Pyr CYC BaA CHR BbF BkF BeP BaP PER IND DBA BbC BghiP COR total PAHs LM-PAHs MM-PAHs HM-PAHs total BaPeq

wet scrubber effluent (mg/h)

stack flue gas (mg/h)

sum (mg/h)

mean

SD

mean

SD

mean

SD

mean

SD

2.44 0.962 1.33 0.927 0.163 0.106 0.058 0.038 0.030 0.176 0.147 0.211 0.363 0.139 0.452 0.309 1.45 0.203 0.936 0.097 0.069

0.411 0.274 0.257 0.165 0.057 0.028 0.015 0.011 0.011 0.043 0.033 0.082 0.090 0.028 0.157 0.043 0.460 0.058 0.162 0.022 0.025

222 49.9 79.2 26.8 5.86 4.08 1.62 1.78 1.39 3.84 19.3 18.4 11.1 3.97 38.4 2.78 0.479 56.4 6.43 7.80 1.05

32.4 10.5 19.2 4.21 1.54 0.894 0.388 0.330 0.388 0.476 6.16 4.02 3.55 0.710 11.2 0.709 0.118 13.0 1.86 1.84 0.164

6060 160 43.1 42.0 1060 82.3 134 195 11.8 26.8 41.8 12.0 24.0 92.4 216 43.3 136 325 46.0 73.0 1.63

1170 47.6 11.8 12.1 375 19.8 32.2 78.7 3.65 8.59 15.8 3.21 6.45 17.9 45.2 12.7 44.8 107 11.7 24.8 0.529

6290 211 124 69.8 1060 86.5 135 197 13.2 30.9 61.2 30.7 35.4 96.5 255 46.4 138 381 53.3 80.9 2.75

1200 58.4 31.3 16.5 377 20.7 32.6 79.0 4.04 9.10 22.0 7.31 10.1 18.6 56.6 13.5 45.4 120 13.8 26.7 0.719

10.6 5.93 0.418 4.26 0.887

0.981 0.682 0.064 0.554 0.212

562 388 26.5 148 98.9

8870 7450 397 981 625

1200 1290 92.6 177 216

9440 7840 424 1130 724

1320 1340 98.7 220 244

120 51.2 5.99 42.4 27.8

TABLE 8. Mean PAH Output Mass Rates and Their Corresponding Standard Deviations (SD) for the Trial Incinerating Condition (n ) 9) cyclone fly ash (mg/h)

wet scrubber effluent (mg/h)

stack flue gas (mg/h)

sum (mg/h)

PAH compound

mean

SD

mean

SD

mean

SD

mean

SD

Nap AcPy Acp Flu PA Ant FL Pyr CYC BaA CHR BbF BkF BeP BaP PER IND DBA BbC BghiP COR

1.35 0.093 0.250 0.234 0.290 0.034 0.057 0.071 0.003 0.008 0.022 0.110 0.016 0.003 0.034 0.015 0.121 0.014 0.022 0.028 0.005

0.478 0.032 0.033 0.077 0.051 0.008 0.012 0.014 0.001 0.002 0.007 0.035 0.004 0.001 0.008 0.002 0.034 0.005 0.007 0.004 0.002

50.4 2.71 16.6 16.1 12.3 1.78 2.64 2.09 0.424 0.915 1.79 3.75 2.09 0.626 3.27 1.48 1.57 1.28 0.839 2.67 0.230

5.26 0.520 3.23 1.13 1.87 0.181 0.407 0.299 0.113 0.207 0.526 0.634 0.405 0.100 0.709 0.246 0.537 0.314 0.253 0.745 0.063

764 20.3 24.0 30.4 199 7.43 104 45.3 0.60 1.84 6.52 3.30 3.31 1.54 4.45 2.16 4.02 2.45 2.73 7.26 16.9

210 6.00 4.84 4.92 61 1.90 9.45 3.57 0.138 0.715 1.51 1.21 0.648 0.577 1.06 0.750 1.53 0.741 1.11 2.90 5.96

815 23.1 40.9 46.7 211 9.25 107 47.4 1.03 2.76 8.33 7.16 5.42 2.17 7.75 3.66 5.71 3.74 3.59 10.0 17.1

216 6.55 8.10 6.12 62.6 2.09 9.87 3.89 0.252 0.924 2.05 1.88 1.06 0.679 1.78 1.00 2.10 1.06 1.37 3.65 6.03

total PAHs LM-PAHs MM-PAHs HM-PAHs total BaPeq

2.78 2.25 0.158 0.372 0.079

0.471 0.431 0.015 0.038 0.016

126 99.9 7.43 18.2 5.64

output/input mass ratios were less than unity, the two studied incinerating conditions would lead to depletion, rather than generation, of PAHs that were originally contained in the incinerating materials. However, it should be noted that the above inference was not true for Nap at the normal incinerating condition (output/input mass ratio ) 230%). This suggests that part of the high molecular weight PAHs 3424

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24.1 11.7 1.77 4.78 1.37

1250 1040 158 48.7 11.3

227 239 13.0 7.15 1.25

1380 1150 165 67.3 17.0

252 251 14.8 12.0 2.63

might be decomposed and converted into Nap during the combustion process. On the other hand, as we examine the output/input mass ratio of Nap at the trial incinerating condition, although the value () 68.0%) was lower than unity, we do find the value was much higher than those of other PAH compounds () 0.08-36.4%). The above results further confirm the conversion of high molecular weight PAHs into

FIGURE 1. PAH output/input ratios for the two studied incinerating conditions.

tions on total PAHs, LM-PAHs, MM-PAHs, HM-PAHs, and total BaPeq, the normal incinerating conditions were 6.69 () 8670/1240), 5.42 () 6710/1028), 2.45 (362/148), 16.2 () 969/ 60), and 41.3 () 619/15) times higher than the trial incinerating conditions (Figure 2). However, for input mass rates on total PAHs, LM-PAHs, MM-PAHs, HM-PAHs, and total BaPeq, the values for the former were only 2.35 () 78 300/ 33 300), 2.34 () 27 900/11 900), 2.35 () 10 700/4560), 2.35 () 39 700/16 900), and 2.36 () 8550/3630) times higher than the latter (Tables 5 and 6). On this basis, the intrinsic difference in the PAH input mass rates could not fully account for the difference in the PAH emissions for the above two incinerating conditions, which suggested that the waste TPA could act as a catalyst associated with the PAH depletion during the combustion process. In conclusion, the use of waste TPA as a co-fuel not only saved the consumption of heavy oil but also reduced PAH emissions during the combustion process.

Acknowledgments We thank the National Science Council in Taiwan for supporting this research work (Grant NSC-86-2113-M-006018).

Literature Cited

FIGURE 2. PAH emission factors for the two studied incinerating conditions. Nap during the combustion process. Similar results have been found by Fa¨ngmark et al., who showed that good combustion conditions on a pilot fluidized-bed incinerator (as mentioned before, the combustion efficiencies for both incinerating conditions of this study were >98%) favored the formation of low molecular weight PAHs (such as Nap) (10). Furthermore, as we examined the mean output/input mass ratios on LM-PAHs, MM-PAHs, HM-PAHs, total PAHs, and total BaPeq for the two studied incinerating conditions, we found that the values for the trial incinerating condition were consistently lower than those for the normal incinerating condition. This indicates that the use of waste TPA as a cofuel enhanced the depletion of PAHs that were originally contained in the feedstock. PAH Emission Factor. As shown in Figure 2, the emission factors of total PAHs, LM-PAHs, MM-PAHs, HM-PAHs, and total BaPeq for the normal incinerating condition (8270, 6700, 362, 969, and 619 µg/kg‚feedstock, respectively) were consistently higher than those for the trial incinerating condition (1237, 1028, 148, 60.4, and 15.2 µg/kg‚feedstock, respectively). Because the combustion conditions and combustion efficiencies between the above two incinerating conditions were quite comparable, it seems that the above results were due to the higher PAH input mass rate for the former than for the latter (Tables 5 and 6). However, with regard to the mean emission factors for both studied incinerating condi-

(1) Flenklach, M.; Clary, D. W.; Yuan, T.; Gardine, C. W.; Stein, S. E. Combust. Sci. Technol. 1988, 74, 283. (2) Colmsjo¨, A. L.; Zebu ¨ hr, Y. U.; O ¨ stman, C. E. Atmos. Environ. 1986, 20, 2279. (3) Kamiya, A.; Ose, Y. Sci. Total Environ. 1987, 61, 37. (4) Yasuda, K.; Kaneko, M. J. Air Pollut. Control Assoc. 1989, 39, 1557. (5) Li, C. T.; Lee, W. J.; Mi, H. H.; Su, C. C. Sci. Total Environ. 1995, 170, 171. (6) Yang, H. H.; Lee, W. J.; Chen, S. J.; Lai, S. O. J. Hazard. Mater. 1998, 60, 159. (7) Lee, W. J.; Lai, S. O.; Chen, S. J.; Hsueh, H. J. Air Pollut. 1999, 45, 357-366. (8) Li, C. T.; Mi, H. H.; Lee, W. J.; You, W. C.; Wang, Y. F. J. Hazard. Mater. 1999, A69, 1. (9) Mi, H. H.; Chiang, C. F.; Lai, C. C.; Wang, L. C.; Yang, H. H. Aerosol Air Qual. Res. 2001, 1, 83. (10) Fa¨ngmark, I.; Bavel, B.; Marklund, S.; Sto¨mberg, B.; Berge, N.; Rappe, C. Environ. Sci. Technol. 1993, 27, 1602. (11) Aittola, J.-P.; Viinikainen, S.; Juha, R. Chemosphere 1989, 19, 353. (12) Tsai, P.-J.; Shieh, H.-Y.; Hsieh, L.-T.; Lee, W.-J. Atmos. Environ. 2001, 35, 3495. (13) Tsai, P.-J.; Shieh, H.-Y.; Lee, W.-J.; Lai, S.-O. Sci. Total Environ. 2001, 278, 137. (14) IARC. In IARC Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans: Polynuclear Aromatic Compounds; World Health Organization: Lyon, France, 1987; Vol. 32, p 123. (15) Chu, M.; Chen, C. Evaluation and estimation of potential carcinogenic risks of polynuclear aromatic hydrocarbons; presented at the Pacific Rim Risk Conference, Honolulu, HI, 1984. (16) Thorslund, T.; Farrer, D. Development of Relative Potency Estimated for PAHs and Hydrocarbon Combustion Product Fractions Compared to Benzo[a]pyrene and Their Use in Carcinogenic Risk Assessments; U.S. Environmental Protection Agency (EPA): Washington, DC, 1991. (17) Nisbet, C.; LaGoy, P. Regul. Toxicol. Pharmacol. 1992, 16, 290. (18) Petry, T.; Schmid, P.; Schlatter, C. Chemosphere 1996, 32, 639.

Received for review September 19, 2001. Revised manuscript received April 30, 2002. Accepted April 30, 2002. ES011293E

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