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Characteristics of air pollution control residues of MSW incineration plant in Shanghai

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Characteristics of air pollution control residues of MSW

incineration plant in Shanghai

Pin-Jing He

a,

, Hua Zhang

a

, Can-Gang Zhang

b

, Duu-Jong Lee

c aState Key Laboratory of Pollution Control and Resources Reuse, Tongji University, Shanghai 200092, China bEnvironment Protection and City Sanitation Management Bureau of Shanghai, Pudong New Area, Shanghai 200135, China

cChemical Engineering Department, National Taiwan University, Taipei 10617, Taiwan

Received 20 December 2003; received in revised form 1 September 2004; accepted 9 September 2004 Available online 22 October 2004

Abstract

A unique type of waste – air pollution control (APC) residues – has received increasing attention in China since the first large-scale incinerator, Shanghai Yuqiao municipal solid waste (MSW) incineration plant, was installed in the country in 2002. The APC residues of this particular plant are similar to other residues that will be produced in other incineration plants under construction in China. This work examines for the first time the benchmark contaminants of APC residues from the Yuqiao Plant, with reference to soluble salts, heavy metals and dioxins. Experimental findings reveal that the residues contained a marked amount of soluble salts, of up to 17.4–21.9% (mostly chlorides), 0.98–1.5 ng TEQ/g ash of dioxins and various heavy metals. Lead is of particular concern, and requires stabilization before disposal. Heavy metal speciation schemes were implemented herein to determine the leaching characteristics. The correlation between the amounts of soluble salts or chemical speciation of the heavy metals and the leaching toxicity of these heavy metals in the residues is considered.

© 2004 Elsevier B.V. All rights reserved.

Keywords: Municipal solid waste incineration; Air pollution control residues; Soluble salts; Heavy metals; Dioxins

1. Introduction

Air pollution control (APC) residues are formed as a by-product from municipal solid waste (MSW) incinera-tion plants. Dioxins, heavy metals and other species are the main contaminants. These residues are often classi-fied as hazardous wastes that require special treatment and disposal [1,2]. Two large-scale modern MSW incinerators were recently installed in Shanghai, each with a capacity of 1000 t/day, together accounting for approximately 12.5% of the 16,040 t/day of MSW generated in the city[3].

MSW in Shanghai has high water content, and therefore a relatively low heat value. The installed incinerators are

de-∗Corresponding author. Tel.: +86 21 6598 1383; fax: +86 21 6598 1383.

E-mail address: xhpjk@mail.tongji.edu.cn (P.-J. He).

signed with waste pits that store the MSW to be drained over 5 days to reduce the water content before combustion. There-fore, 165 t of water were removed per 1000 t of MSW received by the incinerator from October 2002 to September 2003. Accordingly, the Yuqiao MSW incineration plant, installed in the Pudong New Area of Shanghai, was able to incinerate the local MSW effectively, meeting EU emission standards and design specifications.

This study reports the characteristics of the APC residues from the Yuqiao MSW incineration plant. The levels of heavy metals, dioxins and water-soluble salts, and the correlation between these contaminants are considered. The first large-scale incinerator is now being used to treat typical MSW in China, and the APC residues generated by the Yuqiao incin-eration plant can be regarded as representative of APC waste in China.

0304-3894/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2004.09.009

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Fig. 1. The composition of MSW from Shanghai Pudong New Area.

2. Materials and methods

2.1. Samples

Fig. 1depicts the compositions of MSW collected from the Pudong New Area of Shanghai City at a refuse transfer station from June 2002 to April 2003[4]. Most of the solid waste is food waste; the rest of the waste includes a little paper and wood. The water content in the collected MSW reaches 50–70%. The correlation analysis between the water content and the amount of food waste (sample number (S) of 21 andα = 0.01, critical r = 0.549) revealed no correlation (at a correlation coefficient of 0.11) in the received MSW.

The Yuqiao MSW incineration plant removes acid gas from the flue gas using lime slurry (10% (w/w)), heavy metals and dioxins using activated carbon (50 mg/m3); and particu-lates by bag filters (Fig. 2). The APC residues are collected from the semidry reactors and from the fabric filter.

Seven APC residues (samples 1–7) were sampled (approx-imately bimonthly) from Yuqiao incineration plant during May 2002–June 2003 to elucidate the seasonal variation of waste composition (Fig. 1). All samples, except for the first sample (with a 20% water content) collected after wetting to avoid fugitive dust, were of fresh ash with water content of less than 1.5%.

2.2. Analytical methods 2.2.1. Soluble salts

Water-soluble salts in the ash were analyzed. The soluble salts of CO32−, Cl−and SO42−were analyzed by extracting

Fig. 2. Flow diagram of the APC system of Yuqiao incineration plant.

50 g of APC residues using decarbonated distilled water at a liquid-to-solid (L/S) ratio of 5:1, and their concentrations in the filtered extract were measured by gravimetric anal-ysis, H+ titration, AgNO3 titration and BaSO4 gravimetric analysis, respectively[5]. The concentrations of Na+, K+and Ca2+were determined by atomic absorption spectrophotome-ter (AAS; PE5100, Perkin Elmer, USA).

2.2.2. Heavy metals

Ten milliliters of hydrochloric acid was added to ash sam-ple (0.3–0.5 g) in a polytetrafluorethylene digestion vessel and heated on an electric heating plate until only 2–3 mL of hydrochloric acid remained. Then, the sample was vig-orously digested with nitric acid (5 mL), perchloric acid (3 mL) and hydrofluoric acid (5 mL) before AAS testing

[6].

2.2.3. Leaching toxicity and chemical speciation of heavy metals

The extraction procedure for the toxicity of solid waste (EPTSW) test and the sequential chemical extraction (SCE) test were performed herein. In the EPTSW test, 100 g (dry weight) of ash sample was extracted using distilled water at a 10:1 L/S ratio in a 2 L PE bottle that was shaken at 110± 10 rpm for 8 h. After settling for 16 h, the eluate was vacuum-filtered using a 0.45␮m membrane film and the heavy metal contents in the filtrate were measured by AAS

[7].

The SCE test was performed on 1 g of dried ash sample us-ing the extraction sequence presented inTable 1, by a method modified from that of Kerby and Rimstidt[8], Abanades et al.[9] and Tessier et al.[10]. In each step, except the last, 10 mL of the specific reagent was used to extract the ash, and the extract was separated from the solid using a high speed freeze centrifuge (GL-20G-II, Anting, China) at 10,000× g for 30 min. The heavy metal contents in the extract were mea-sured by AAS. In steps 1 and 4, solution pH was modified using nitric acid. The water-soluble or acid-soluble fractions were available for leaching under neutral or acidic conditions, respectively. The Ca-exchangeable fraction would probably be leached out if the brine had moved through an APC residue disposal site. The Ag-exchangeable fraction was of tightly bound complexes, and was unlikely to be released by simply flowing fluids. Fractions differentiated in steps 5–8 were very hard to dissolve[2,8,9,11].

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Table 1

Sequential chemical extraction scheme for the APC residues

Step Speciation Reagent Conditions

1 Water-soluble Deionized water 20◦C, pH 7, continuous agitation, 3 h

2 Ca exchangeable 0.5 M Ca(NO3)2 20◦C, continuous agitation, 3 h

3 Ag exchangeable 0.5 M AgNO3 20◦C, continuous agitation, 3 h

4 Acid soluble 0.5 M CH3COOH + 0.1 M Ca(NO3)2 20◦C, pH 5, continuous agitation, 3 h

5 Organically bound 0.1 M Na4P2O7 85◦C, variable agitation, 3 h

6 Amorphous iron oxide occluded 0.175 M (NH4)2C2O4+ 0.1 M H2C2O4 95◦C, variable agitation, 3 h, without light

7 Crystalline iron oxide occluded 0.1 M Na2EDTA + 0.3 M NH2OH·HC1 95◦C, variable agitation, 24 h

8 Residual 10 mL HCl + 5 mL HNO3+ 3 mL HClO4+ 5 mL HF 0.2–0.3 g of dried solid ash from previous step

was digested

2.2.4. Mineralogy

Mineralogical analyses were performed on 20 g of ash using an X-ray diffractometer (XRD; PW1710, Philips, The Netherlands). The working conditions of the XRD were as follows, tube anode: Cu; generator tension: 40 kV; generator current: 20 A; start and end angles (2θ): 3–70◦; step size (2θ): 0.02◦; time per step: 0.4 s.

2.2.5. Dioxins

The dioxins, including polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and coplanar PCBs (PCBs), in the three ash samples were analyzed by Shimadzu Techno-Research Inc., Japan. The sample was spiked with a mixture of13C12-labeled internal standards and then Soxhlet extracted in 300 mL of benzene for 16 h. The extract was concentrated and spiked with inter-nal standard, before being cleaned up through a multilayer silica gel column and an alumina column. The final elute was micro-concentrated and 13C12 labeled recovery standards were added before the HRGC/HRMS procedure was per-formed using an HP-6890, equipped with a DB-5 MS-fused silica capillary column (60 m× 0.25 mm × 0.25 ␮m, J&W Scientific).Fig. 3 andTable 2 present the flow diagram of the analysis process and the reagents (Cambridge Isotope Laboratory Co. Ltd.) used.

3. Results and discussion

3.1. Water-soluble salts

Fig. 4presents the results of the analysis of soluble salts. The fresh APC residues contained 17.4–21.9% soluble salts, of which Cl− accounted for nearly half, in the form of mainly NaCl and KCl, as indicated by the mineralogical analysis (Fig. 5). It also contained 1.3–1.9% of SO42−and 0.09–0.24% of CO32−(since CaSO4and CaCO3were de-tected by XRD). Na+, K+ and Ca2+ were found to account for 35–40% of all of the soluble matter.

Soluble salts in the residues may pollute groundwater following disposal. Groundwater with more than 2000 mg/L soluble salts is classified as having the worst level of

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Table 2

Chemical reagents used in the dioxins measurement process

Standard solution Internal spiked standard solution Standard solution Internal spiked standard solution

2,3,7,8-TeCDD 13C12-1,3,6,8-TeCDD 2,3,7,8-TeCDF 13C12-1,3,6,8-TeCDF

13C

12-2,3,7,8-TeCDD 13C12-1,2,7,8-TeCDF

13C

12-1,2,3,4-TeCDD 13C12-2,3,7,8-TeCDF

2,3,7,8-PeCDD 13C

12-1,2,3,7,8-PeCDD 1,2,3,7,8-PeCDF 13C12-1,2,3,7,8-PeCDF

1,2,4,7,8-PeCDF 13C 12-1,2,4,7,8-PeCDF 1,2,3,4,7,8-HxCDD 13C 12-1,2,3,4,7,8-HxCDD 1,2,3,4,7,8-HxCDF 13C12-1,2,3,4.7,8-HxCDF 1,2,3,6,7,8-HxCDD 13C 12-1,2,3,6,7,8-HxCDD 1,2,3,6,7,8-HxCDF 13C12-1,2,3,6,7,8-HxCDF 1,2,3,7,8,9-HxCDD 13C 12-1,2,3,7,8,9-HxCDD 1,2,3,7,8,9-HxCDF 13C12-1,2,3,7,8,9-HxCDF 2,3,4,6,7,8-HxCDF 13C 12-2,3.4,6,7,8-HxCDF 1,2,3,4,6,7,8-HpCDD 13C 12-1,2,3,4,6,7,8-HpCDD 1,2,3,4,6,7,8-HpCDF 13C12-1,2,3.4,6,7,8-HpCDF 1,2,3,4,7,8,9-HpCDF 13C 12-1,2,3,4,7,8,9-HpCDF 1,2,3,4,6,7,8,9-OCDD 13C

12-1,2,3,4,6,7,8,9-OCDD 1,2,3,4,6,7,8,9-OCDF 13C12-1,2,3,4,6,7,8,9-OCDF

Standard solution Internal standard solution #81 3,4,45-TeCBa #8113C 12-3,4,45-TeCBa #77 3,3,4,4-TeCBa #7713C 12-3,3,4,4-TeCBa #105 2,3,3,4,4-PeCBb #10513C 12-2,3,3,4,4-PeCBb #114 2,3,3,4,4,5-PeCBb #11413C 12-2,3,3,4,4,5-PeCBb #118 2,3,4,4,5-PeCBb #11813C 12-2,3,4,4,5-PeCBb #123 2,3,4,4,5-PeCBb #12313C 12-2,3,4,4,5-PeCBb #126 3,3,4,4,5-TeCBa #12613C 12-3,3,4,4,5-TeCBa #156 2,3,3,4,4,5-HxCBb #15613C 12-2,3,3,4,4,5-HxCBb #157 2,3,4,4,5-HxCBb #15713C 12-2,3,3,4,4,5-HxCBb #167 2,3,3,4,4,5,5-HxCBb #16713C 12-2,3,3,4,4,5,5-HxCBb #169 3,3,4,4,5,5-HxCBa #16913C 12-3,3,4,4,5,5-HxCBb #180 2,2,3,4,4,5,5-HpCBc #18013C 12-2,2,3,4,4,5,5-HpCBc #170 2,2,3,3,4,4,5-HpCBc #17013C 12-2,2,3,3,4,4,5-HpCBc #189 2,3,3,4,4,5,5-HpCBb #18913C 12-2,3,3,4,4,5,5-HpCBb #7913C 12-3,3,4,5-TeCBb #11113C 12-2,3,3,5,5-PeCBb a Non-ortho-PCBs. b Mono-ortho-PCBs. c Di-ortho-PCBs.

water” in China[12]. Although the “Standard for pollution control on the security landfill site for hazardous wastes” by SEPA does not state limiting concentrations of soluble salts in hazardous waste [13], France and Germany have legislated that the soluble salt content in waste in a landfill should be kept below 5% and 10%, respectively[14]. These standards require that the present APC residues cannot directly be put in a landfill because of their high soluble salt contents.

Fig. 4. Soluble salts analysis of the APC residues.

3.2. Heavy metals 3.2.1. Total amount

Table 3states the concentration of heavy metals in the APC residues from the Yuqiao incineration plant. The Cd, Pb and Zn contents in the APC residues were much lower than the range of the contents of these metals in the dry/semidry APC residues from 20 foreign Mass Burn incinerators (five in Canada, 1986–1991; four in Denmark, 1989–1992; one in Germany, 1982; one in The Netherlands, 1992; four in Sweden, 1985–1988, and five in the USA, 1988–1989)[2]. The data can be compared because similar APC systems are used in these incinerators at incineration temperatures of up to 850◦C, and the ratio of ash production to MSW by weight (4.1% for Yuqiao incineration plant from October 2002 to 2003 and 3–5% for other incinerators stated above) is similar. 3.2.2. Leaching toxicity of heavy metals

Table 3also presents the leaching characteristics of heavy metals in the APC residues and the limits set by the “Identi-fication standard for hazardous waste” (Std A)[15]and the “Standard for pollution control at security landfill sites for hazardous waste” (Std B)[13]. The concentrations of lead of

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Fig. 5. XRD micrograph of the APC residues from Yuqiao incineration plant. present APC residues greatly exceeded those limits, making

the present residues hazardous waste. Cd and Zn were also heavy metals of concern.

3.2.3. Chemical speciation

Fig. 6andTable 3present the analytical results of SCE. The amounts of Cd, Cr, Cu and Ni leached in step 1 of SCE exceeded those in the EPTSW test, indicating that the water-soluble fractions of Cd, Cr, Cu and Ni contributed to the met-als leached in the latter test. The leached Zn in the EPTSW test, however, exceeded that in step 1 of the SCE test, in-dicating that ion-exchangeable Zn was also released during the EPTSW test. This occurrence is probably attributable to the alkaline environment produced by the reaction between residue and water. All metals leached in the EPTSW tests, except for Pb, contributed only a little to the easily leachable fractions of the total metal content (leached amounts in steps 1, 2 and 4 in the SCE test). The leached Pb in the EPTSW tests sometimes exceeded this so-defined easily leachable fraction, revealing that some Pb in the organically bound or crystalline iron oxide-occluded phase was also be released during the EPTSW tests (by distilled water leaching).

In the residues, Cr exhibited weak mobility because it was trapped primarily in phases that could not be easily leached (Fig. 6). In contrast, Cd, Cu and Zn were far more easily leachable, and were primarily acid soluble. The Pb and Ni exhibited moderate mobility, with the former mainly acid sol-uble and the latter, evenly distributed in the first four leaching steps. The rich acid-soluble phase of heavy metals in the APC

Fig. 6. Results of SCE of the APC residues (sampled on October 2002).

residues thus importantly affected their leaching characteris-tics.

3.2.4. Factors that affect leaching toxicity

The analytical results for heavy metals, presented in

Table 3and those for soluble salts presented inFig. 4, re-veal correlation coefficients (r) between the amounts of heavy metals leached in EPTSW and in every step of the SCE test, which were calculated using the following equation. Corre-lation coefficients between soluble salts and heavy metals leached in EPTSW were also evaluated.Table 4summarizes all results ri(m, n) = S j=1(Hi,jm − ¯Him)(Hi,jn − ¯Hin) [Sj=1(Hi,jm− ¯Him)2Sj=1(Hi,jn − ¯Hin)2]1/2 (1)

where i, j are the ith species of heavy metal and jth species of ash, respectively; S the total number of the samples; S = 5 or 7 herein;Hi,jk the amount of the ith species of heavy metal (or water-soluble salt for soluble salt analysis) in the jth species of ash analyzed in the kth test; ¯Hik= (1/S)Sj=1Hi,jk the average of the amount of the ith species of heavy metal in the kth test; m, n, k the array m, array n and array k, whose elements are data concerning the S samples in the mth, nth and kth test (such as soluble salts analysis) or the step of SCE, array m ={Hi,jm}, n = {Hi,jn}, k = {Hi,jk }, j = 1, 2, . . ., S; ri(m, n) the correlation coefficient between array m and array n.

The amount of heavy metals leached in EPTSW correlated with the amount of water-soluble phase more strongly than

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Table 3

Analytical results of heavy metals

Sample Remark (overseas incinerators)

1 (May) 2 (September) 3 (November) 4 (January) 5 (April) 6 (May) 7 (June) Total content (detected after digestion) (mg/kg)

Cd 49.8 65.8 44.9 52.7 50.9 NA NA 140–300 Cr 350 322 329 335 255 NA NA 73–570 Cu 770 667 561 628 665 NA NA 16–1700 Ni 136 131 88.1 115 134 NA NA 19–710 Pb 2480 1620 972 1230 2130 NA NA 2500–10000 Zn 3610 4860 3650 4160 4940 NA NA 7000–20000

Leaching toxicity (EPTSW) (mg/L)

Cd 0.07 0.17 0.12 0.14 0.13 0.20 0.19 0.3a 0.5b Cr 0.14 0.24 0.60 0.08 0.11 0.15 0.12 10a 12b Cu 0.13 0.19 0.12 0.14 0.11 0.32 0.43 50a 75b Ni 0.28 0.63 0.53 0.49 0.44 0.47 0.46 10a 15b Pb 6.88 88.1 27.6 53.7 92.5 98.8 63.2 3a 5b Zn 0.11 7.11 3.73 0.70 4.57 5.42 5.04 50a 75b

Leached metals in step 1 (water-soluble phase, SCE) (mg/kg)

Cd 6.04 2.78 8.73 1.70 9.43 28.2 55.7 Cr 4.95 3.55 6.20 2.04 2.89 3.84 2.76 Cu 3.51 3.78 1.83 1.69 2.73 5.78 6.72 Ni 8.21 9.24 8.13 6.17 9.31 8.10 10.8 Pb 15.9 27.9 17.6 16.9 26.8 27.4 26.4 Zn 3.40 16.6 5.90 4.24 6.16 132 216

Leached metals in step 2 (Ca exchangeable phase, SCE) (mg/kg)

Cd 4.14 3.61 2.63 2.76 3.03 2.74 2.64 Cr 4.35 4.81 5.01 3.38 4.02 5.39 4.85 Cu 3.05 9.31 2.40 4.65 4.06 4.30 4.26 Ni 11.9 10.5 11.7 9.65 9.78 7.78 7.70 Pb 35.0 57.3 23.5 40.4 44.6 36.1 36.0 Zn 4.57 51.2 8.60 14.1 11.5 16.0 16.9

Leached metals in step 3 (Ag exchangeable phase, SCE) (mg/kg)

Cd 19.8 14.4 12.2 20.4 14.7 25.9 21.5 Cr 1.15 1.23 1.33 0.50 0.85 1.19 0.91 Cu 3.27 2.06 1.47 1.62 3.23 3.95 5.30 Ni 6.66 5.15 4.60 3.95 4.74 4.52 6.37 Pb 11.8 15.4 10.7 17.5 24.2 22.1 22.8 Zn 286 101 132 142 307 369 430

Leached metals in step 4 (acid soluble phase, SCE) (mg/kg)

Cd 18.7 26.9 7.57 14.6 8.81 21.3 18.8 Cr 16.3 8.38 3.30 0.56 1.38 1.56 3.85 Cu 339 351 134 82.0 157 177 395 Ni 12.3 12.7 5.74 7.54 7.41 10.0 10.2 Pb 507 482 239 257 511 400 868 Zn 1190 1950 627 541 830 1090 1640

Leached metals in step 5 (Organically bound phase, SCE) (mg/kg)

Cd 2.68 1.90 1.70 2.45 1.64 2.16 1.55 Cr 15.9 25.2 29.1 11.7 10.8 6.06 7.13 Cu 69.9 52.7 105 125 67.8 84.9 68.4 Ni 5.79 6.30 6.33 5.43 5.15 5.86 6.43 Pb 473 356 233 314 367 353 397 Zn 151 190 225 265 139 251 147

Leaehed metals in step 6 (Amorphous iron oxide occluded phase, SCE) (mg/kg)

Cd 0.77 0.58 0.40 0.78 0.54 0.82 0.66 Cr 10.0 10.1 0.00 21.8 18.9 17.5 19.5 Cu 56.9 75.5 97.0 202 173 269 156 Ni 7.57 5.90 5.67 7.17 6.03 8.49 7.43 Pb 69.4 58.8 50.8 48.0 105 126 110 Zn 322 446 416 446 643 756 468

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Table 3 (Continued )

Sample Remark (overseas incinerators)

1 (May) 2 (September) 3 (November) 4 (January) 5 (April) 6 (May) 7 (June) Leached metals in step 7 (Crystalline iron oxide occluded phase, SCE) (mg/kg)

Cd 4.52 2.81 1.13 8.56 8.17 11.6 5.56 Cr 38.5 25.9 0.00 41.9 87.5 68.0 47.3 Cu 132 82.1 201 153 236 336 229 Ni 38.6 37.1 29.4 36.8 60.6 86.2 69.7 Pb 501 416 1230 1650 2350 2180 1330 Zn 990 773 1810 1430 2290 2840 2150

Leached metals in step 8 (Residual phase, SCE) (mg/kg)

Cd 15.9 4.48 6.52 6.02 5.19 5.71 6.56 Cr 469 177 272 216 242 175 188 Cu 156 39.0 74.3 59.2 104 74.2 82.1 Ni 106 34.5 38.8 53.2 71.6 153 211 Pb 1010 357 762 852 1960 839 688 Zn 1690 339 919 825 1360 1130 1060 aStd A. bStd B.

with that of the acid-soluble phase, because the extractant was distilled water. (The pH values of the leachants exceeded 12 at the end of the extraction.) The amounts of Pb and Cu were positively correlated with the amounts of water-soluble salts. However, the contribution of heavy metals in the other seven phases was not clearly correlated with their leaching capacity (Table 4).

The teachability of Cd, Ni and Pb was found to be affected by the soluble salts in the residues, especially Cl−, perhaps because the HC1 generated during incineration was released into the flue gas and finally intercepted in the APC residues, hence affecting the speciation of heavy metals.

3.3. Dioxins

Samples of the APC residues for dioxin analysis were collected in January, May and June 2003. The corresponding MSW compositions and water contents varied noticeably. For example, the leachate pumped from the waste pit was 0.07 t/t of MSW in January but as high as 0.22 t/t of MSW in the

sum-Table 4

Correlation coefficients r between heavy metals leached in EPTSW (array m) and array n

Array n Cd Cr Cu Ni Pb Zn

Water-soluble (SCE) 0.591 0.811 0.902 0.072 0.881 0.337

Ca exchangeable (SCE) −0.586 0.418 0.126 −0.165 0.688 0.724

Ag exchangeable (SCE) 0.366 0.636 0.802 −0.546 0.754 0.031

Acid soluble (SCE) 0.412 0.000 0.566 −0.146 0.231 0.641

Organically bound (SCE) −0.515 0.826 −0.291 0.376 −0.107 −0.222

Amorphous iron oxide occluded (SCE) 0.098 −0.904 0.291 −0.498 0.456 0.365

Crystalline iron oxide occluded (SCE) 0.371 −0.764 0.362 −0.126 0.462 0.163

Residual (SCE) −0.770 0.077 −0.204 −0.378 0.175 −0.577

Total (detected after digestion) 0.663 0.195 0.091 0.359 0.040 0.702

Total soluble salts 0.970 0.227 0.537 0.948 0.815 0.855

Cl− 0.986 0.043 0.618 0.912 0.887 0.837

SO42− 0.596 0.783 0.114 0.787 0.196 0.490

When S = 7 andα = 0.01, rc(critical r) = 0.874, and if r > rc, the two arrays are the so-called obviously correlated.

mer. For the first time, the dioxin level in the APC residues from China was measured (Table 5). The concentrations of dioxins ranged from 0.98 ng TEQ/g ash in the January sample to 1.5 ng TEQ/g ash in the May sample. The concentration of dioxins apparently increased with the amounts of plastic and water in the collected MSW.

The dioxin contents were in a similar range to those of the APC residues from some overseas incinerators (Table 6)

[16–25]. Although the composition of MSW in Shanghai dif-fers from that of refuse in other parts of the world, the dioxin level in the APC residues was only slightly different.

Current regulations in China, such as the “Environmen-tal quality standard for soils”[26]or the “Standard for pol-lution control at secure landfill sites for hazardous wastes”

[13], do not control dioxin concentrations. The APC residues examined herein do not comply with the environmental qual-ity standards for soil applications (<1 ng TEQ/g ash) that are specified by the “Law concerning special measures against dioxin” in Japan[27]. However, the levels are acceptable for landfill (<3 ng TEQ/g ash[27]).

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Table 5

Dioxin contents of the APC residues from Shanghai Yuqiao incineration plant

Time Sample 4 (January) Sample 6 (end of May) Sample 7 (start of June)

Measured content PCDDs (ng/g) 11 28 16 PCDFs (ng/g) 30 45 40 PCDDs/Fs (ng/g) 41 73 56 PCDDs/Fs (ng TEQ/g) 0.97 1.5 1.2 TEQ PCBs (ng TEQ/g) 0.013 0.023 0.016 Total (ng TEQ/g) 0.98 1.5 1.2 Discharged leachate/MSW (wt.%) 6.60 21.8 22.0 Table 6

Dioxin contents of APC residues from overseas MSW incinerators

Denmark UK Spain Korea EU

Incinerators (number) 19 11 8 11 Newly installed

References [16] [17] [18] [19] [20]

Dioxins (ng TEQ/g) 0.1–3.8 0.033–5.80 0.07–3.5 0.13–21 0.81–1.8

Japan Taiwan

Incinerators (number) 1 3 4 1 4 (>900 t/day) 2 (<150 t/day)

References [21] [22] [23] [24] [25] [25]

Dioxins (ng TEQ/g) 2.63 7.3–641 0.5–6.7 0.65 0.26–6.95 23.8, 28.9

3.4. Managing APC residues in Pudong New Area

The amounts of contaminants in APC residues depend on the characteristics of MSW, the incineration temperature and the removal efficiency of the APC system. Further works on the effect of characteristics of MSW (including some minor constituents such as used batteries) on those of APC residues were undertaken in the authors’ laboratory. In Shanghai, used batteries have been recovered for 5 years, and efforts in this area continue to be made. A policy will soon be implemented in Shanghai to charge for plastic bags in supermarkets to con-trol their use. The effect of these management measures on the polluting characteristics of APC residues will gradually become evident.

As stated above, Pb, Cd and Zn are the heavy metals of concern in APC residues. In particular, the level of Pb sub-stantially exceeded the permitted level of leaching toxicity for landfill. The residues also contained considerable amounts of soluble salts, with a strong potential to pollute groundwa-ter afgroundwa-ter landfill. Accordingly, heavy metals in APC residues should be stabilized and soluble salts should be flushed out before final disposal. The state-of-the-art MSW management practice in the Pudong New Area of Shanghai comprises an incineration plant, a recycling facility and a sanitary landfill site. The City Government plans to construct a second land-fill site. Available heavy metals may be released when water flows through APC residues, so the use of a mono-landfill unit for APC residues, with a cover, is more suitable than the use of co-landfill with MSW, because the food waste in the latter generates a very large amount of leachate to promote metal leaching.

4. Conclusions

The contaminant characteristics of air pollution control (APC) residues of the first large-scale municipal solid waste (MSW) incinerator in China, located in the Pudong New Area of Shanghai, were investigated in this work. The distributions of heavy metals in the APC residues examined herein dif-fered notably from those from other overseas incinerators: lead (Pb) was the heavy metal that made the residues haz-ardous waste. The leaching toxicity of heavy metals (except Pb) extracted by the extraction procedure for toxicity of solid waste (EPTSW) test depended primarily on the content in the water-soluble and acid-soluble phase, as determined in sequential chemical extraction (SCE) tests. However, the Pb leached in the EPTSW tests was in a more tightly bound form.

The APC residues contained substantial amounts of solu-ble salts, primarily Cl−, whose concentrations were related to the leaching toxicity of the heavy metals. The total amount of soluble salts also exceeded the amounts in the regulations set in various countries for landfill.

The content of dioxins in the APC residues herein was related to the data collected at similar incinerators world-wide, ranging from 0.98 to 1.5 ng TEQ/g ash. These values were not consistent with the environmental quality standard for soils (<1 ng TEQ/g ash) but were acceptable for a land-fill site (<3 ng TEQ/g ash), according to Japanese regulations. Accordingly, the residues were proposed to be disposed of in a dedicated mono-landfill unit, with a pollution control sys-tem, following stabilization of the heavy metals and flushing out of the soluble salts.

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Acknowledgments

We thank Shanghai Council of Science and Technology, China Ministry of Construction, and Shanghai Municipal Government for their financial support through the project “Research on beneficial use of MSW incineration residues and its demonstration project” (032312043), “Characteri-zation and beneficial use of MSW incineration residues” (03-2-051), and the Key Subject Project, respectively. We appreciate Shimadzu Techno-research Co. for their measurement of dioxins in APC residue. We are also grateful to Shanghai Yuqiao incineration plant for their kind help for sampling collection and providing field data.

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數據

Fig. 1. The composition of MSW from Shanghai Pudong New Area.
Fig. 4 presents the results of the analysis of soluble salts.
Fig. 4. Soluble salts analysis of the APC residues.
Fig. 5. XRD micrograph of the APC residues from Yuqiao incineration plant.

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