Metal distribution in incineration residues of municipal solid waste (MSW) in Japan

Waste Management 24 (2004) 381–391 www.elsevier.com/locate/wasman

Metal distribution in incineration residues of municipal solid waste (MSW) in Japan C.H. Junga, T. Matsutoa,*, N. Tanakaa, T. Okadaa a

Laboratory of Solid Waste Disposal Engineering, Graduate School of Engineering, Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo 060-8628, Japan Accepted 18 June 2003

Abstract This study aimed to identify distribution of metals and the influential factors on metal concentrations in incineration residues. Bottom ash and fly ash were sampled from 19 stoker and seven fluidized bed incinerators, which were selected to have a variety of furnace capacity, furnace temperature, and input waste. In the results, shredded bulky waste in input waste increased the concentration of some metals, such as Cd and Pb, and the effect was confirmed by analysis of shredded bulky waste. During MSW incineration, lithophilic metals such as Fe, Cu, Cr, and Al remained mainly in the bottom ash while Cd volatilized from the furnace and condensed to the fly ash. About two thirds of Pb and Zn was found in the bottom ash despite their high volatility. Finally, based on the results obtained in this study, the amount of metal in incineration residues of MSW was calculated and the loss of metal was estimated in terms of mass and money. A considerable amount of metal was found to be lost as waste material by landfilling of incineration residues. # 2003 Elsevier Ltd. All rights reserved.

1. Introduction In Japan, ‘‘The Basic Law for Establishing the Recycling-based Society’’ was enacted in May 2000 to change the ‘‘Throw-away Society’’ to a ‘‘Recycling-based Society’’. Following the enactment of the law, comprehensive measures for waste management and recycling have been promoted by the national government. The ultimate goals for these measures are the reduction of natural resource consumption and environmental burden. In this context, metals should be given higher priority since they are valuable resources and some of them have hazardous characteristics. For better management of metals, it is fundamental and essential to identify their flow in society. Statistics are available for production and consumption, but studies on the flow in the solid waste management (SWM) process have been limited so far although SWM is a critical process in determining the fate of metals. This paper focuses on the incinerator process, which treats about 80% of municipal solid waste (MSW) generated in Japan and aims to identify metal distribution in incineration residues. * Corresponding author. Tel./fax: +81-11-706-6827. E-mail address: [email protected] (T. Matsuto). 0956-053X/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0956-053X(03)00137-5

Brunner and Monch (1986) investigated the metal distribution for two MSW incinerators, in which different flue gas cooling methods were used. Belevi and Moench (2000) fed two types of waste—household waste, and mixed waste with commercial waste—to an MSW incinerator and determined the distribution of metals. In Japan, Nakamura et al. (1996) and Watanabe et al. (1999) carried out a similar study for selected metals (Pb, Cd, Sn, As) in an MSW incinerator. In a theoretical approach, Verhulst et al. (1996) studied the behavior of metals based on a thermodynamic analysis approach. Fernandez et al. (1992) and Abanades et al. (2002) performed a simulation analysis and compared the results with experimental data. Although much work has been done to date, only a few studies were found in literature in Japan, where the waste material flow in treatment and disposal processes of MSW was changed after the Electric Household Appliance Recycling (EHAR) Law was enacted in April 2001. Furthermore, most studies in the past were done on one or two incinerators, but the metal distribution may have been affected by the type of incineration furnace, furnace capacity, and input waste. Therefore, in this paper, incineration residues were sampled from 26 incinerators in different conditions, then the

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distribution of metals and influential factors was studied. Prior to experimental work, a literature survey was also conducted for metal concentrations in incineration residues in Japan, and this was then statistically analyzed.

2. Experimental work 2.1. Determination of target metal Target metals in this study were selected based on scarcity and toxicity. Table 1 shows reserves (R), productions (P), and the possible year of use (R/P) of metals in the world (World Resources, 1996–1997; Tateda et al. 1997). The metals of R/P below 100 years were defined as scarce metals. Lead, tin, zinc, cadmium, copper, selenium, and bismuth are included in this group. Special attention should be given to these metals due to their highly strained situations. Arsenic, chromium and antimony are selected as toxic metals, while some scarce metals, such as cadmium, selenium and lead, are also toxic. The widespread metals, such as aluminum and iron, were added to the target metals. Table 2 lists the metals selected for this study. 2.2. Description of incineration facilities In Japan, stoker and fluidized bed types of incinerator are widely used. The stoker burns 85% of MSW treated in the incineration process and the fluidized bed burns 12%, according to waste management statistics. Nineteen stoker and seven fluidized bed incinerators were selected in order to provide a variety of furnace temperatures, furnace capacities, and waste input. Table 3 shows the general description for these incinerators. While Al, D1, D5, E1 and E2 plants receive only combustible waste, the other plants treat shredded bulky Table 1 World reserve and production of metals Element

Reserves (R) (1000 t)

Production (P) (1000 t/year)

R/P (years)

Aluminuma Antimony Arsenic Bismuth Cadmiuma Chromium Coppera Irona Leaa Selenium Tin Zinca

28 000 000 4700 11 000 250 970 6 700 000 590 000 230 000 000 130 000 130 10 000 330 000

111 024 36 35 3 18 10 000 9523 988 797 2765 2 206 6895

252 130 314 83 53 670 62 233 47 75 49 48

a

Data from 1994 (World Resources, 1996–1997). Others: Data of 1993 (Tateda et al., 1997).

waste in addition to combustible waste. Ash production was calculated on a dry basis and the chemical agent amount used for ash treatment was subtracted. 2.3. Sampling and sample preparation The work of sampling bottom ash and fly ash was performed during a period of 5 months (August 2001– December 2001). Five kilograms of bottom ash was taken three or four times a day at intervals of 2 h from an ash pit after water quenching. Three kilograms of fly ash was sampled four or five times a day at 2-h intervals before it was treated with a chemical agent. A sample preparation was made as shown in Fig. 1. Bottom ash samples were dried at 105  C for 24 h, ground for 2 h in a ball mill and sieved through a 0.5-mm screen. The materials passing the screen were mixed well to obtain a composite sample. Then, the composite sample was divided into three equal sized samples (sub-samples) for metal element analysis. The same procedure was used for fly ash. Shredded bulky waste was analyzed to investigate the contribution of the waste to metal concentration in incineration residues. Approximately 10 kg of shredded bulky waste, which was composed of sieved overflow fraction fed to incinerators, was taken twice from the E3 plant. Sampled wastes were sorted into 11 groups: plastics (not including film), textiles, plastic film, paper, power cords, sponge, electric circuit boards, cans, rubber, wood, and ferrous metals. Each component was cut and ground to particles smaller than 2 mm with a cutting mill (Mitamura Riken 182900/SM-1). Two sub-samples for each component were prepared for analysis of metal content. 2.4. Analytical technique In Japan, aqua regia (AR, HCl:HNO3=3:1, v/v) digestion is generally used to prepare samples for metal concentration analysis. AR does not provide total dissolution of metals from silicate matrices when incineration residues are digested, so a hydrofluoric acid (HF) digestion step is added. A couple of days are needed for sample dissolution. In this study, a microwave assisted (MW) digestion method was used. This method needs only 1 or 2 h to dissolve samples—a dramatically reduced time—yet produces accurate results (Kingston Table 2 Target metals determined based on the possible year of use (R/P) and toxicity Group 1 Scarce metals Group 2 Hazardous metals Group 3 Widespread metals

Lead, zinc, tin, cadmium, copper, selenium, bismuth Arsenic, chromium, antimony Aluminum, iron

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C.H. Jung et al. / Waste Management 24 (2004) 381–391 Table 3 General information on incinerators used for sampling Furnace type

Stoker

Fluidized bed

Facility

Capacity (t/day)

Operation start year

Operating type

Furnace temp. ( C)

Ash productiona (kg/t-feedstock)

Input waste (%) Cb

SBWc

A1 A2 A3 A4 B1 C1 C2 C3 C4 D1 D2 D3 D4 D5 E1 E2 E3 E4 F1

60*2 60*2 60*2 60*2 120*2 150*2 150*3 150*3 150*3 200*2 200*3 200*3 200*3 200*2 300*2 300*3 300*2 300*2 500*3

1978 1994 1984 1988 1994 1994 1998 1992 1996 1979 1983 1995 1986 1976 1974 2001 1992 1995 1997

SCg SC FCh SC FC FC FC FC FC FC FC FC FC FC FC FC FC FC FC

900 900 850 921 900 865 900 850 850 900 900 900 850 885 901 850 884 950 900

100 76.9 91.5 96.4 91.3 95.4 82.9 95.6 97.9 100 95.8 89.4 98.4 100 100 100 91.3 90.5 80.0

– 23.1 8.5 3.2 3.0 4.6 17.2 4.4 2.1 – 2.1 10.6 1.6 – – – 8.8 8.7 20.0

G1 G2 G3 G4 H1 H2 H3

50*2 50*2 50*2 50*2 150*2 150*1 150*2

1992 1996 1989 1992 1986 1984 1994

SC SC SC SC FC FC FC

875 885 850 900 900 875 950

92.8 97.6 97.8 87.6 87.6 98.5 97.7

4.3 2.4 2.2 12.4 12.4 – 2.3

Othersd

BAe

– – –

90.2 64.6 88.4 68.3 68.2 109.3 67.4 127.6 60.3 63.3 71.8 76.5 72.2 66.0 102.6 82.5 120.9 105.0 167.3

12.6 38.3 17.5 18.3 36.1 36.2 45.3 27.7 34.0 11.7 30.2 18.7 21.6 19.9 24.4 18.3 19.9 26.5 34.1

–i – – – – – –

106.3 65.5 86.3 85.1 92.5 109.0 75.1

0.4 5.7 – – – – – 2.1 – – – – – – – – 3.0 – – – – 1.5 –

FAf

a

Combustible waste. Shredded bulky waste. c Sludge, Incombustible waste. d Bottom ash. e Fly ash (ESP or BF ash). f Ash production was calculated on a dry basis and the amount of chemical agent used for ash treatment was subtracted. g Semi-continuous incinerator. h Full-continuous incinerator. i In fluidized bed incinerators, incombustible material (bottom ash) remaining in the bottom of the furnace represents a very small percentage or nil, so it is ignored in this study. b

and Walter 1992). AR and HF digestion are based on the Sewage Test Method and Sediment Test Method of Japan. MW digestion was conducted using microwave techniques (CEM, MDS-2000) similar to the proposed SW-846 Method 3052 (EPA). Figs. 2 and 3 explain the procedure of AR digestion, HF digestion, and MW digestion, respectively. In the last step, boric acid was added to dissolve fluoride precipitates and to eliminate the excess HF in hydrofluoric acid digestion (Abanades et al., 2002; Kirby and Rimstridt, 1993). Concentrations of metal elements were measured by atomic absorption spectrometry (AAS, Hitachi A-2000 and Z-8200). Aluminum, antimony, bismuth, cadmium, chromium, copper, iron, lead, tin, and zinc were analyzed by flame AAS (Al: nitrous oxide/acetylene flame, the others: Air acetylene flame). Arsenic and selenium

were determined by graphite furnace AAS. Palladium matrix modifier was added to improve sensitivity.

3. Results and discussion 3.1. Literature survey on metal concentration in incineration residues Data of fly ash and bottom ash were collected from scientific journals that had been published from 1993 to 2000 in Japan. A summary of the survey is given in Table 4. In fluidized bed incinerators, no bottom ash is produced except discharged incombustibles. Data on bismuth, antimony, and tin were not found in fly ash. Also, the quantity of data for arsenic, selenium, and

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Fig. 1. Procedure for sample preparation for metal concentration analysis. 124 h at 105  C, 22 h in a ball mill, 3sieving through a 0.5 mm screen, 4 smaller than 2mm.

Fig. 2. Procedure for aqua-regia and hydrofluoric acid digestion. Chemicals used were JIS (Japanese Industrial Standards) special grade manufactured by Wako, Japan.

Fig. 3. Procedure for microwave assisted digestion. Chemicals used were JIS (Japanese Industrial Standards) special grade manufactured by Wako, Japan.

antimony is very limited. The concentration varies widely for most metals and the coefficient of variation is very high. A number of factors causing such a high variation were considered, namely, the parameters for incineration (furnace type, capacity, furnace temperature, waste input) and experimental parameters for metal concentrations analysis (sampling method, and sample preparation method, analytical method). But it was impossible to investigate the effect because no information was presented in most literature. Furthermore, the data obtained from literature were expressed as concentration. So, they were useless for calculating metal distribution without ash production amount. Consequently, direct sampling and analytical work was conducted.

3.2. Comparison of digestion methods To check the reliability of MW digestion, bottom ash and fly ash from plant E1 and E3 were analyzed. As explained in 2.4, AR+HF digestion is stronger than AR digestion. Therefore, in Fig. 4, MW digestion is compared with AR+HF digestion. For most metals, the ratio of AR+HF digestion to MW digestion is around unity. The lower metal concentration of As and Bi in AR+HF digestion compared to that in MW digestion might be caused by volatilization. Generally, the AR and HF digestion method cause many errors resulting from losses and atmospheric contamination during dissolution (Kingston and Walter, 1992). On the other hand, MW digestion prevents both the volatilization and atmospheric contamination encountered in an

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C.H. Jung et al. / Waste Management 24 (2004) 381–391 Table 4 Metal concentration in fly ash and bottom ash from literature Stoker

Fluidized bed

Fly ash

Bottom ash

n

Min.

Max.

Average

CV

Al As Bi Cd

46 34 – 52

8468 0.5 – 0.3

92 800 37 – 573

47 562 14 – 124

55 81 – 86

79 67 15 77

Cr Cu Fe Hg

37 49 53 34

62 316 3000 0.03

1170 10 600 24 200 41

355 1232 10 794 8

80 150 50 131

74 86 103 63

6.6 77 500 0.001

Pb Sb Se Sn Zn

63 7 8 – 62

223 140 0.4 – 400

79 500 560 100 – 207 000

4460 352 27 – 15 848

226 46 181 – 180

104 18 7 16 103

8 5 0.1 53 500

n

Fly ash

Min.

Max.

Average

CV

n

Min.

10 600 0 1 0.04

147 000 93 23 91

71 377 6 4 15

36 185 135 112

20 5 – 12

24 600 8.3 – 4

2260 13 200 200 000 5.5

375 2818 45 874 0.7

95 107 72 170

11 17 18 5

10 900 306 2.0 1364 33 000

1288 67 0.6 359 4229

102 133 108 107 99

17 – 1 1 21

Max.

Average

CV

93 146 10.0 – 73

58 186 7.4 – 24

29 56 – 83

134 264 12 000 0.3

1020 7700 129 000 1.7

387 3650 37 863 0.9

69 52 76 –

738 – – – 1300

4100 – – – 10 700

1681 – 0.6 240 4719

56 – – – 21

Min, max, average: (mg/kg–ash). CV (coefficient of variation=standard deviation/average): (%).

open system. It is therefore concluded that the MW digestion method is an efficient and speedy sample dissolution method for obtaining metal concentrations from incineration residues. 3.3. Metal concentration in fly ash and bottom ash Table 5 shows the results of experimental work. Lithophilic metals such as iron, copper and aluminum showed high concentrations of bottom ash while volatile metals such as cadmium, lead and zinc were concentrated in fly ash. When compared with the literature survey in Table 4, the concentrations of most metals were lower than those in the literature. The EHAR (Electric Household Appliance Recycling) Law, which was enacted on April 2001, presumably contributed to this decrease by reducing the numbers of refrigerators, TV sets, air conditioners, and washing machines entering the waste stream. Moreover, as can be seen in Table 5, the high coefficients of variation and the broad concentration range for most metals were still found although the same sampling method, sample pretreatment, and analytical method were used. This suggests that experimental factors do not influence the variation of metal concentrations in incineration residues. 3.4. Factors causing variation of metal concentrations in incineration residues To find the influential factor affecting metal concentration in incineration residues, the correlations between metal concentration and incineration parameters such

as furnace type, capacity, temperature, and waste input, were investigated. 3.4.1. Furnace type and capacity Metal concentrations with different furnace types are shown in Table 5. Levels of Al and Cr in fly ash from fluidized bed incinerators were confirmed to be higher than those from stoker incinerators, with a 1% significance level, and Cu and Fe levels were higher with a 5% significance level by t-test. These are all lithophilic metals with low volatility, so higher turbulence and entrainment of solid particles to the fly ash in the fluidized bed might cause the difference. Fig. 5 illustrates the relationship between furnace capacity and metal concentration in fly ash from stoker type incinerators for Pb and Zn. In general, a bigincinerator has an advantage in obtaining stable combustion because of insensitivity to the fluctuation of waste feed. But as shown in Fig. 5, metal concentration varied regardless of capacity of the furnace. The other metals in fly ash and bottom ash also showed a similar result for both types of incinerator. 3.4.2. Furnace temperature In general, volatilization of metals increases with furnace temperature. Therefore, volatile metals such as Cd, Pb, Zn, and As are expected to have higher transfer rates to the fly ash as the furnace temperature increases. Fig. 6 illustrates the correlation between furnace temperature and metal concentration in fly ash from stoker incinerators for Pb and Cd. No correlation was found. This means that the effect of furnace temperature is not significant in the range 850–950  C. The other metal

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Fig. 4. Comparison of microwave assisted (MW) digestion versus aqua regia and hydrofluoric acid (AR+HF) digestion. Values of 24 samples (2 facilities*4 samples/day*3 days) were used. Table 5 Metal concentration in fly ash and bottom ash from experiments in this study Stoker (n=19)

Fluidized bed (n=7)

Fly ash

Bottom ash

Detection limit (mg/l)

Fly ash

Min.

Max.

Average

CV

Min.

Max.

Average

CV

Min.

Max.

Average

CV

Al As Bi Cd

12 860 1.5 – 26

70 630 20.8 845 380

34 127 4.9 89 98

50 88 225 94

43 420 0.1 – 0.8

68 060 3.5 88 14.0

54 675 1.3 18 5.5

13 65 136 79

70 460 0.3 – 8

129 600 5.5 56 28

97 217 1.8 13 17

28 94 164 44

0.1 0.01 0.06 0.002

Cr Cu Fe Pb

20 210 3180 286

128 930 13 340 4940

61 520 6682 1878

48 42 42 70

60 414 22 000 140

256 3720 86 800 1320

112 2081 44 421 673

36 54 48 57

0.02 0.01 0.02 0.05

Sb Se Sn Zn

98 0.6 – 3400

1350 8.8 714 17 600

435 3.0 202 8347

45 75 95 29

0.07 0.005 0.8 0.005

81 81 106 49

37 0.5 – 1280

192 4.5 876 4800

98 2.0 46 2446

47 47 44 53 44 76 436 41

90 940 14 820 414 80 0.2 – 3000

316 6240 53 000 2640 300 4.7 234 6600

192 3517 30 289 1274 155 2.9 113 5029

Min, max, average: (mg/kg–ash), CV(coefficient of variation=standard deviation/average): (%), ‘–’: not detected.

elements in incineration residues from stoker and fluidized bed incinerators showed a similar result. 3.4.3. Waste input Waste fed into incinerators was divided further into three categories in this study: (1) combustible waste, (2) shredded bulky waste, and (3) other (sludge, plastics, incombustible waste). The ratios of waste input are shown in Table 3. The correlation between waste input and metal concentration was investigated. As a result, Cd, Pb, Sb, Se, and Sn for fly ash and Cu, Sb, and Zn for bottom ash were confirmed to be correlated with the ratio of bulky waste residue (with a significant level of 0.05) as shown in Fig. 7. Therefore, shredded bulky waste was sampled at plant E3, which is a stoker type incinerator treating bulky waste (8.8%) in addition to combustible waste, and the contribution ratio of bulky waste residue to metal contents was estimated. The composition and

metal content of bulky waste were determined as shown in Table 6, and the estimated contribution, which is the ratio of the metal amount in shredded bulky waste to total metal amount in incineration residues, is shown in Fig. 8. The result is consistent with the previous result of statistical tests, i.e. metals (Sn, Cu, Sb, Se, Cd) which have a high correlation coefficient show a high contribution ratio of shredded bulky waste as indicated in Fig. 8. 3.5. Distribution of metals to fly ash and bottom ash It is quite significant to identify the distribution of metals in fly ash and bottom ash for recycling of valuable metals and for environmental control of hazardous metals. The distribution ratio of metal elements in fly ash and bottom ash for stoker incinerators was calculated using the ash amount generated in incineration of MSW, and the metal content in fly ash and bottom ash.

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Fig. 5. Correlation between metal concentration in fly ash and furnace capacity (in stoker).

Fig. 6. Correlation between metal concentration in fly ash and furnace temperature (in stoker). Table 6 Metal content in shredded bulky waste

Plastics Textiles Plastic film Paper Power cords Sponge Electric circuit boards Cans Rubber Wood Total

Wt.%

As

Bi

Cd

Cr

Cu

Pb

Sb

Se

Sn

Zn

7.3 2.5 0.3 0.2 1.6 1.7 0.7 0.7 2.5 63.5

0.18 – – – 0.03 0.02 0.06 – 0.14 – 0.4

– – – – – 0.4 – – – – 0.4

3.6 0.02 – – – – 2.5 – 0.3 0.6 7.1

2.3 4.3 0.2 – 1.3 0.7 1.5 0.1 4.7 – 15.1

1 2 3 0.1 9399 22 1193 6 12 11 10 648

7 5 2 0.2 37 12 37 0.1 10 31 141

210 2 3 0.1 13 6 4 0.7 19 39 295

1.4 0.01 0.01 – 0.01 0.02 0.02 – 0.02 0.27 1.7

8 – – – 11 15 51 – – – 85

16 27 1.2 1.0 3.0 21 35 0.5 98 155 358

Unit: (mg/kg-shredded bulky waste), ‘–’: not detected.

Distribution of metal elements to exhaust gas was assumed to be zero in this study. Fig. 9 presents the result, in which the abscissa represents metal content in incineration residues (bottom ash+fly ash) per 1 ton of waste, while the ordinate shows distribution ratio of metal elements to fly ash. Although the production rate of ash is considered to contain some errors, the distribution ratios of metals could be presumed.

3.5.1. Lithophilic metal elements: Fe, Al, Cu, Cr Iron and aluminum are mostly fed to incinerators in metallic form and their oxides are very stable, so no volatilization occurs during incineration of MSW. The small fractions found in fly ash are due to particulate matters carried over from the furnace in the flue gas (Chandler et al., 1997). The behavior of copper in incineration of MSW is similar to that of iron.

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Fig. 7. Metal concentrations in fly ash and bottom ash, with the ratio of shredded bulky waste in waste input.

Chromium compounds are not considered thermally mobile during incineration and therefore should remain mainly in the bottom ash. 3.5.2. Volatile metal elements: Cd, Zn, Pb, As, Sb According to thermodynamic calculation, cadmium and cadmium oxide are preferentially converted into CdCl2 during incineration. Furthermore, not only the metal itself, but cadmium chloride and, to a limited extent, cadmium oxide can be vaporized (Verhulst et al., 1996; Chandler et al., 1997). Consequently, the bulk of the cadmium entering the incinerator will be transferred to fly ash as shown in Fig. 9. Zinc is not as volatile as cadmium, but the ZnCl2 and traces of metallic zinc are volatilized. However, the conversion into ZnCl2 is limited since a substantial amount of the zinc is already present in the waste in oxide form. Eventually, the bulk of the zinc remains in the bottom ash. The metallic form of lead is potentially volatile. The most preferential reaction for lead during the incineration process is to produce PbCl2, then vaporizes (Verhulst et al. 1996; Chandler et al. 1997). The unexpectedly low distribution of lead to fly ash in Fig. 9 is thought to be caused by the fact that the metal melts and drips through the grates before reaching the vaporization temperature (Chandler

Fig. 8. Contribution ratio of shredded bulky waste to metal content in incineration residues at plant E3.

et al., 1997). The distribution of arsenic and antimony in incineration residues was quite different according to incinerator, as shown in Fig. 9. 3.5.3. Others: Bi, Se, Sn The concentration of bismuth and selenium in fly ash and bottom ash is very low or nil. Selenium is slightly enriched in fly ash. The distribution ratio of bismuth and selenium to fly ash varies considerably with incin-

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Fig. 9. Distribution of metal elements to fly ash in stoker incinerators. X: Metal contents in incineration residues (fly ash + bottom ash), per 1 ton of waste; Y: distribution ratio of metal elements to fly ash.

Table 7 Metal amount in incineration residues of MSW in Japan

Al As Bi Cd Cr Cu Fe Pb Sb Se Sn Zn

Metal amount in incineration residues (ton/year) (D)a

Annual consumption of metal (C)b

D/C*100 (%)

International market price of metal ($/kg) (P)c

233 626 9 139 112 468 8118 151 392 4218 748 10 365 16 862

3 852 000 – 452 2512 522 000 1 489 300 128 715 000 270 600 564 177 27 814 622 400

6.1 – 30.8 4.5 0.1 0.5 0.1 1.6 132 5.6 1.3 2.7

1.4 1.1 6.3 1.5 4.0 1.6 0.25 0.5 2.6 8.3 4.4 0.8

Monetary loss (L)d (dollar/year)

327 076 000 9900 875 700 138 000 1 872 000 12 988 800 37 848 000 2 109 000 1 944 800 83 000 1 606 000 13 489 600 Total 400 040 800

a D: Metal amount in incineration residues, D=Mj  Aj (j=type of ash) where, Mj: Metal content (see average in Table 5), Aj: annual ash generation=MSW incinerated (a)  ash generation rate (b), A1: stoker fly ash=35 million tons/year  25.8 kg/ton=0.9 million tons/year, A2: stoker bottom ash=35 million tons/year  88.0 kg/ton=3.0 million tons/year, A3: fluidized bed fly ash=5 million tons/year  88.5 kg/ton=0.4 million tons/year, (a) MSW incinerated was based on national statistics on MSW management, ash generation rate: average value calculated from Table 3 was used. b C was obtained from Mineral Handbook (2001) . c P was from Metalbulletin.com and Metalprice.com. d L=D*P.

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Fig. 10. Comparison of this study versus literature for distribution ratio of metals in output products of MSW incineration. Waste input; (2)-1: household waste, (2)-2: mixed waste of commercial and residential origin, (6): regular MSW from residential as well as trade and commerce sources, (7)-1: household waste, (7)-2: household waste + shredded bulky waste, (8): mainly household waste.

erator. Tin can volatilize in reducing circumstances, thermodynamically (Verhulst et al., 1996). Tin was found only in fly ash for most plants except the A2 plant. The distributions of metal elements in incineration residues of MSW in this study were compared with those in literature from Switzerland, Germany, Austria, and Japan. As can be seen in Fig. 10, the ratio of most metals among incineration residues is very similar between studies. In thermodynamic equilibrium calculations, Zn and Pb are easily volatilized due to their high volatility and As is also completely volatilized above 650  C (Verhulst et al., 1996). However, in real plants, about two thirds of Pb, Zn, and As are distributed to bottom ash and one third in fly ash. The fact that that distribution ratio of metals to exhaust gas is almost zero justifies our decision to neglect metals in the gas phase.

Japan were calculated. The assumption used and the procedure of calculation are shown in Table 7. Moreover, the loss of valuable metals was estimated in terms of mass and money by using annual consumption of metals and the international market price. The result reveals that considerable amounts of metals are lost as waste material because incineration residues are landfilled directly without any recycling process.

4. Conclusion To study the influential factors on metal concentrations and the distribution of metals in incineration residues of MSW, 19 stoker and seven fluidized bed full-scale incinerators were investigated. The results obtained are as follows:

3.6. Metal amount in incineration residues of MSW Based on the result obtained in this study, the amounts of metal in incineration residues of MSW in

 A literature survey showed a high variation in data regarding metal concentrations in fly ash and bottom ash.

C.H. Jung et al. / Waste Management 24 (2004) 381–391

 Factors causing variation of metal concentration in incineration residues were studied. Correlations with furnace type, capacity, furnace temperature, and waste input were investigated. Of these parameters, shredded bulky waste in waste input was the most influential factor affecting the variation of metal concentrations in fly ash and bottom ash. The concentrations of Cd, Pb, Sb, Se, and Sn in fly ash, and Cu, Sb, and Zn in bottom ash increased with the ratio of shredded bulky waste in feed waste.  During incineration, lithophilic metals such as Fe, Cu, Cr, and Al remained mainly in bottom ash while volatile Cd transferred to fly ash. Two thirds of Pb and Zn remained in bottom ash despite their high volatility.  Finally, based on the results obtained from this study, the loss of metal was calculated in terms of mass and money. A considerable quantity of metal elements was found to be lost through landfilling of incineration residues. References Abanades, S., Flamant, G., Gagnepain, B., Gauthier, D., 2002. Fate of heavy metals during municipal solid waste incineration. Waste Management and Research 20, 55–68. Anon., 1997. World Resources 1996–1997 (A Guide to the Global Environment). World Resources Institute, United Nations Environment Program, United Nations Development Program, The World Bank. Belevi, H., Moench, H., 2000. Factors determining the element behavior in municipal solid waste incinerator. 1. Field studies. Environmental Science and Technology 34, 2501–2506. Brunner, P.H., Monch, H., 1986. The flux of metals through municipal solid waste incinerators. Waste Management and Research 4, 105–119.

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