THE EVALUATION OF THE FEASIBILITY OF UTILIZING

Environmental Informatics Archives, Volume 2 (2004), 1033-1047 EIA04-105 ISEIS Publication #002 © 2004 ISEIS - International Society for Environmental Information Sciences

The Evaluation Of The Feasibility Of Utilizing Incineration Bottom Ash As Subbase Material Hui-Lan Chang (1)∗, Wen-Chen Jau (2), Kung-Cheh Li (3), Cheng-Fang Lin (3), (1)

* Center for Environmental, Safety and Health Technology Development, Industrial Technology Research Institute, 321 Kuang Fu Road, Section 2 Hsin-Chu, Taiwan 300, R.O.C. (2) Department of Civil Engineering, National Chiao-Tung University, P.O.BOX 25-72 Hsin-Chu, Taiwan 300, R.O.C. (3) National Taiwan University, Graduate Institute of Environmental Engineering, 71 Chou-Shan Road, Taipei, Taiwan 106, R.O.C.

Abstract. 1.1 million tons of Municipal Solid Waste Incineration (MSWI) bottom ash was produced by 19 incinerators across the island of Taiwan by 2002. So far the MSWI bottom ash’s major function was to serve as the cover of sanitary landfill. Other ways of handling excessive MSWI bottom ash need to be established. This study investigated the MSWI bottom ash with an aim to assess feasibility of reuse in subbase. The heavy metal contents in the raw MSWI bottom ash was tested according to the Toxicity Characteristic Leaching Procedure (TCLP) technique (Kosson et al., 1996) and the engineering properties were also studied comprehensively. Both the basic characteristics and the engineering test results demonstrate that the MSWI bottom ash, after modification is suitable to be reused as subbase aggregates. During the environmental compatibility process, some gel-like substance was observed. When the substance dries, it tends to crystallize and this may damage the subbase due to the expanding of its volume. Therefore it is suggested that the raw MSWI bottom ash without pre-washing process should not directly expose to the local soil. It must be paved with concrete, asphalts or a waterproof layer, on top of the raw MSWI bottom ash and underneath it, to prevent the rain/acid rain infiltration and possible groundwater contamination due to leaching. Keywords: Utilizing, MSWI bottom ash, Subbase, TCLP, Environmental compatibility

1. Introduction According to the statistic data of EPA of 2003, there were 17 incinerators operated and 77 million tons of bottom ash was produced in Taiwan in 2001. EPA suggested that there would be 32 incinerators and 181 million tons of bottom ash in 2006. The best treatment to the vast amount of municipal solid waste incineration（MSWI）bottom ash is to reutilize it. According to Table 1, it clearly shows the amount of the incineration ash and the reutilization ratio in the eveloped countries. The reutilization ratios of the developed countries such as France, Germany, the Netherlands and Denmark are 45﹪, 60﹪and 90﹪, respectively.

∗

Corresponding author: [email protected]

Environmental Informatics Archives, Volume 2 (2004), 1033-1047

Table 1 The Statistic data of the amount of incinerators and incineration ash in the developed countries (Sakai, 1996) Item The amount of garbage generated (million tons) The amount of *MSW incinerated (million tons) Incineration ratio **MSWI bottom ash generated (million tons) Recycled ratio of **MSWI bottom ash The number of incinerators Note:

American Canada France Germany

The Denmark Sweden Japan Netherlands 12.8 2.6 3.2 50.2 (1993) (1994) (1991) (1992)

207 (1993)

23.2 20.0 (1992) (1996)

43.5 (1993)

32.9 (1993)

1.2 8.0 (1992) (1991)

11.0 (1993)

2.8 (1993)

1.5 (1994)

1.7 (1991)

37.3 (1992)

16% 6.84 (1990)

5% 42% 0.3 2.5 (1993) (1991)

25% 3.0 (1993)

23% 0.65 (1993)

58% 0.5 (1993)

55% 0.43 (1990)

74% 5.0 (1991)

0% (1990) 148

0% 45% (1993) (1991) 17 198

60% (1993) 53

90% (1993) 11

90% (1993) 31

0% (1990) 21

0% (1991) 1841

*MSWI: Municipal Solid Waste

**MSWI: Municipal Solid Waste Incineration

Now the complexity and feasibility of the reutilization technology of MSWI bottom ash are shown in Table 2 Table 2 The complexity and feasibility of the reutilization technology of MSWI bottom ash (NREL, 1996) Complexity The reutilization technology Feasibility Explanation Low Filler, Subbase material, the cover High The least treatment procedure and cost, any of sanitary landfill shape of aggregate can be used. Medium Use as asphalt concrete (hot-mixed Medium Can be used in asphalt concrete but need to meet asphalt concrete, cold-mixed relevant standards. asphalt concrete) High Extract expensive metal, Low Reclaim the expensive metal in bottom ash, or crystallization crystallized bottom ash in high temperature to change the chemical structure of bottom ash in order to detoxify, stabilize, and materialize. For handling excessive MSWI bottom ash further reutilization techniques need to be established. investigated the MSWI bottom ash with an aim to assess the reuse feasibility in subbase.

This study

2. Outline of Experimental Procedure This study will focus on feasibility study of MSWI bottom ash reuse in subbase. Both material properties and environmental compatibility of the raw MSWI bottom ash were tested. An analysis for the comprehensive engineering properties was also conducted. The study procedure scheme is shown in Figure 1.

1034


MSWI bottom ash

Sampling by quartering

Pretreatment

Engineering properties

Environmental compatibility

Material chemical properties

Feasibility study for subbase Figure 1 The study procedure scheme 2.1. Pretreatment 2.1.1. Sampling Sampling by quartering: The research used the method of quartering to decrease the sample size from 200 to 3 tons. The illustration of quartering of the MSWI bottom ash is depicted in Figure 2.

200 tons

100 tons 50 tons Figure 2 Illustration of quartering of the MSWI bottom ash

3 tons

2.1.2. Composition Analysis The MSWI bottom ash contains iron, non-ferrous metals, china, and porcelain. The picture of MSWI bottom ash is shown in Figure 3. Fe2O3 may damage the bed of incinerator and increase the complexity of reutilization; hence the procedure of pretreatment is recommended. The procedure of pretreatment is illustrated in Figure 4.

Figure 3 MSWI bottom ash after dehydration

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Sample size≒200 T

MSWI bottom ash

Sampling by quartering

Separated combustible material =0.32 T

Screening

Sample size =2.1 T

Diameter ＜ 3 inches

Magnetic separation

Eddy current separation

The sample for study

Sample size≒3 T

Diameter > 3 inches

Sample size=0.58 T

Separated ferrous metal=0.12 T

Separated non-ferrous metal=0.021 T

Sample size=1.959

Figure 4 The procedure of pretreatment The result of MSWI bottom ash pretreatment is shown in Table 3. Table 3 MSWI bottom ash pretreatment analysis data Sample Compositions (tons) Percentage (%) 21.64% Diameter of particle of MSWI bottom ash > 3inches：0.58 T 78.36% Diameter of particle of MSWI bottom ash < 3 inches：2.10 T After pretreatment Stainless Steel：0.020 T 0.95% The iron metal from magnetic separation：0.120 T 5.71% (For particle diameter The non-ferrous metals from eddy current separation：0.001 T 0.05% < 3 inches) 93.29% The sample for study：1.959 T After pretreatment, 1.899 tons of MSWI bottom ash was reduced to the sample size approximately 1 ton for further study. 2.2. Sieve Analysis of MSWI Bottom Ash To test and verify the MSWI bottom ash samples and sieve analysis results, four Taiwan’s research organizations, National Chiao-Tung University (NCTU), China Engineering Consultants, Inc. (CECI), Directorate General of Highways (DGH) and Industrial Technology Research Institute (ITRI), participated in the project. Each organization took 30~60kg MSWI bottom ash to sieve. The sieve analysis data are shown in Table 4. The consistency of results of sieve analysis was verified by the organizations. Table 4 The result of MSWI bottom ash sieve analysis data Research Organizations ITRI1 DGH2 CECI3 19.0mm (3/4") 0 0 0

Particle Size of Screening Samples

NCTU4 0

unit：﹪ Gradation A grade B grade ----1036


12.5mm (1/2") 10mm 9.5mm (3/8") 4.75mm(No.4) 4mm (No.5) 2.36mm (No.8) 2mm (No.10) 1.19mm(No.16) 840um (No.20) (No.40) 75um(No.200) -75um Method

0.78 5.77 7.26 --37.16 54.87 60.36 68.97 73.43 --91.19 100

1.5 --7.8 30.8 ---

0 --6.3 31.6 --51.6

0.49 --4.97 29.25 --47.61

54.8 ----80.6 91.3 ---

----81.4 94.4 ---

----72.08 83.4 100

Dry screening Analysis

Washed Sieve Analysis



--------35~70 25~60 45~75 40~70 --------60~85 55~80 --------80~92 70~85 92~98 80~95 ----AASHTO T88

Note: 1 . Center for Environmental, Safety and Health Technology Development, Industrial Technology Research Institute (ITRI). 2 . Materials Laboratory, Directorate General of Highways (DGH). 3 . Department of Materials testing, China Engineering Consultants, Inc. (CECI). 4 . Materials Laboratory, Department of Civil Engineering, National Chiao-Tung University (NCTU). 3.Properties of MSWI Bottom Ash 3.1. The Basic Characteristic Analysis of MSWI Bottom Ash It is essential to acquire the basic characteristics of MSWI bottom ash that included the analyses of chemical compounds, total heavy metal contents, loss of ignition (L.O.I.) and the Toxicity Characteristic Leaching Procedure (TCLP) test for reutilization of the MSWI bottom ash. 3.1.1. The Composition of MSWI Bottom Ash The sample of MSWI bottom ash was dried in the electrical oven at 60℃ to simulate the highest temperature (50~60℃) for roads in general weather condition. By doing so, the sample is purposefully maintained to its natural particle size of bottom ash and is ready for later tests. The results are shown in Table 5. The major component parts are SiO2, CaO, Fe2O3, Al2O3 and soluble salts. The L.O.I. (1000℃) is between 6%~11%, it means that the sample contains a certain amount of organic substances. Table 5 The composition of MSWI bottom ash (2002) Major component parts L.O.I.(1000℃) SiO2 Al2O3 Fe2O3 CaO Mg O Na2O P2O5 K2O Minor component parts CuO ZnO MnO2 TiO2 S

Percent (%) 6.39~11.21 37.68~43.30 5.99~6.08 7.92~9.49 13.03~16.72 1.35~1.39 1.04~3.22 1.87~3.01 1.02~1.06 Percent (%) 0.26~0.40 0.38~0.57 0.14~0.19 0.41~0.47 0.48~0.52

Method Weight Test Method Weight Test Method ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES Method ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES 1037


Others BaO Total-Cr SrO Bi2O3 Co3O4 NiO Sb2O3 SnO2 V2O3 PbO CdO SeO3 Hg

Concentration (mg/kg) 687~1090 258~208 264~378 190~334 46~64 246~318 180~247 381~449 59~76 608~2500 ~29 ~ 0.35

Method ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES Hg analyzers

3.1.2. Toxicity Characteristic Leaching Procedure (TCLP) Test According to NIEA R201.11C method, Table 6 shows the results of TCLP analysis of MSWI bottom ash. The result shows that the bottom ash can be treated as non-hazardous waste due to its low heavy metal contents. It is suitable for reutilization. （Unit=mg/L）

Table 6 The MSWI bottom ash TCLP analysis Sample (particle size) Cd Passed through No. 200 screen --Remained on No. 200 screen --Remained on No. 20 screen --Remained on No. 16 screen --Remained on No. 10 screen --Remained on No. 5 screen --Remained on No. 8 screen ----＞4.75mm --＞9.5mm --＞9.5mm --＞10 mm --＞12.5mm Bottom ash sample 1. --Bottom ash sample 2. --Bottom ash sample 3. --EPA regulation limit 1.00 Note: ---: Below ICP detection

Cr 0.11 0.02 0.02 0.03 0.03 0.08 0.10 0.08 0.05 0.06 0.06 0.06 0.04 0.03 0.04 5.00

Pb --------0.63 --3.33 ----------------5.00

Hg ------------------------------0.20

Se ------------------------------1.00

3.2. The Engineering Properties of The MSWI Bottom Ash Major parts of the MSWI bottom ash contain inorganic material like SiO2, CaO, Fe2O3 and Al2O3. Refer to Directorate General of Highways and the highways engineering construction booklet, the major codes of subbase are as following. －The coarse aggregates particle size are 100 to 2.0mm(No.10) screen and the test for resistance to abrasion by use of the Los Angeles Machine are not more than 50%. －The fine aggregates pass 0.425mm(No.40) screen; the Liquid Limit (LL) does not exceed 25; Plasticity Index (PI) does not exceed 6. －The sieve analysis of aggregates used in subbase is specified by Table 7.

1038


Table 7 The sieve analysis for aggregates used in subbase mm

(No. of screen ) 100mm(4 in) 4.75mm (No.4) 0.075mm(No.200)

Passing percentage (%) 100 25～100 0～25

The methods used in MSWI bottom ash physical and engineering characteristics tests are shown in Table 8. Table 8 The methods used in MSWI bottom ash engineering tests Items PH Test. Test for Apparent Specific Gravity. Test for Compressive Strength. Method of Test for Soundness of Aggregate by Use of Sodium Sulfate or Magnesium Sulfate Standard Specification for Sieve Analysis of Fine and Course Aggregate. Standard Specification for Specific Gravity and Absorption of Course Aggregate Moisture / Density Relations of Soils Using 4.54-kg [10-lb] Rammer and 457-mm [18-in.] Drop Test Method for CBR (California Bearing Ratio) of Laboratory-Compacted Soils Color Determination Test Standard Classification of Soils for Engineering Purposes (Unified Soil Classification System) Standard Test Method for Resistance R-Value and Expansion Pressure of Compacted Soils Los Angeles Abrasion Test

Standards NIEA S410.60T ASTM C373-88 CNS 14602 section 6.2 CNS 1167 A3031 AASHTO T27-97 AASHTO T85-91 (1996) AASHTO T180D ASTM D1883-99 CNS 14602 section 6.6 ASTM D2487-00 CNS 12383-88 CNS 3408

3.2.1. Comparison of MSWI Bottom Ash properties with CNS14602 Standard TO COMPARE THE MSWI BOTTOM ASH WITH THE CNS14602 CODES, AND THE RESULT IS SHOWN IN TABLE 9. IT INDICATES THE RESULTS OF SIEVE ANALYSIS, ABRASION RATIO （%） AND AMENDMENT CBR （ % ） OF THE MSWI BOTTOM ASH ARE SIMILAR TO SUBBASE MATERIAL NO. CS-20 CATEGORY. THE TESTS OF COLOR DETERMINATION INDICATE POSITIVE REACTION. IT SUGGESTS MSWI BOTTOM ASH STILL CONTAINS A LITTLE COMBUSTIBLE MATERIAL. THE SIEVE ANALYSIS RESULTS ARE NOT CONFORMED TO THE GRADATION DISTRIBUTION OF SUBBASE MATERIAL NO. CS-20. IT MIGHT AFFECT THE ENGINEERING QUALITY SUBBASE WITH BOTTOM ASH. However, the MSWI bottom ash need to be modified to be used in subbase. A. Los Angeles Abrasion Test (CNS 3408) The method of Los Angeles Abrasion Test for MSWI bottom ash is conducted according to the CNS 490. The material of high value in the Los Angeles Abrasion Test cannot produce sufficient strength for road subbase. It is an important test for materials to be used in subbase. The test result is 41.7%, which matches the standards of subbase admixture material requirement (less than 50%). B. Sodium Sulfate Soundness Test (CNS1167) Due to the unique natural environments in Taiwan such as high temperature, and high humidity island-wide, the subbase material should meet strict standards in case of any unpredictable damage of road base. There is no soundness test standard well developed for the road subbase materials yet. In this study, the Sodium Sulfate 1039


Soundness Test (according to CNS1167) was used to test and verify whether the MSWI bottom ash could resist the weathering caused by natural conditions in Taiwan. The test result is 2.304%. It is lower than the subbase aggregate limit of 12%, and it indicates that the MSWI bottom ash could resist the weathering effect of natural conditions.

Table 9 To compare the MSWI bottom ash results with the CNS14602 standard (2002) Item

Result

Color Determination 50mm(2”) S I 37.5mm(1½”) E P 31.5mm(1¼”) V A E 25mm(1”) S 19mm(¾”) S A I 12.5mm(½”) N N A 9.5mm(3/8”) G L 4.75mm(#4) Y 2.36mm(#8) S (%) I 425µm(#40) S 75µm(#200) Bulk density (kg/l) Compressive Strength (kgf /cm2) Loss of Los Angeles Abrasion Test (%) Modified CBR (%)

Positive 100 100 100 100 100 99.51 95.04 70.76 52.40 27.93 16.60 1.111 10.0 41.7 108

C O A R S E A G G R E G A T E S

Bulk Specific Gravity (dry condition)

2.16

Bulk Specific Gravity (surface dry and inside saturated condition)

2.25

Apparent Specific Gravity

2.37

Water Absorption ratio (%)

4.16

The CNS14602 standard CS-40 CS-30 CS-20 Negative 100 --95~100 100 --95~100 ---100 50~80 55~85 95~100 --60~90 ---15~40 15~45 20~50 5~25 5~30 10~35 ------------＜50 ＞30

Note: CNS 14602 A2279 [Steel slag for road construction]

Figure 5 The Los Angeles Abrasion Test C. Resistance R-Value Test (ASTM D2844-94) 1040


The Resistance R-Value of the MSWI bottom ash is determined by Hveem's stabilometer. The thickness of subbase supports the weight of vehicles to prevent the roads from plastic deformation. The Resistance R-value is used to determine the minimal thickness of the pavement layer. The method of Resistance value test is following the ASTM D2844-94. The test result of Resistance R-value was 71~76, which demonstrates the MSWI bottom ash is suitable to be used as gravel substitutes.

Figure 6 The Resistance R-Value test for subbase D. Classification and Identification of Soils (ASTM D2487-00) The Classification and identification of MSWI bottom ash is comparable to cobble, gravel, coarse-grained sand, fine-grained sand and non-plastic or weak soil mixture. E. California Bearing Ratio Test, (ASTM D1883-99) California Bearing Ratio test, (CBR test) determines the bearing capacity of soil. Those data provide a basis of pavement design. It identified the maximum specific value of the bearing capacity of the sample subbase. The results of California Bearing Ratio (CBR) test are as following： According to ASTM D1883-99 method, the Optimum moisture content is 15.0﹪; The maximum dry specific gravity is 1728kg/m3. The CBR value is 108 %. The result of CBR test is offered to design the thickness of road pavement, and at the same time it is the quality control basis of subbase. F. The Color Determination Test According to the test result of CNS 14602 section 6.6, the MSWI bottom ash shows the positive reaction. It means the MSW incineration ash contains a little combustible material. 3.2.2. The Expansion Test During the R-value test, if continuous rinse of the MSWI bottom ash with infiltration water from the R-value test, there was no expansion observed in the MSWI bottom ash sample; if the MSWI bottom ash is left in room temperature to dry, noticeable expansion in volume was observed. For further investigation of properties that influenced the subbase of roads, the following expansion test was conducted. The method of resistance value test was according to CNS 12383-88 (Resistance R-Value And Expansion Pressure of Compacted Soils) to determine the relative moisture content from samples under the exudation pressure of 300psi. The test was performed using the relative moisture content to compact four samples. After measuring the exudation pressure, the sample was put in the steel mold onto the expansion-pressure device. But no water was added to soak the samples. The expansion data shown in Table 10 were observed and recorded after the samples have been left to dry in room temperature.

Figure 7 The expansion test Table 10 The expansion test data of the MSWI bottom ash Sample

1

2

3

4 1041


Moisture content (%) The Exudation pressure (psi) The height of sample m m / ( i n ) 1day 7days 14 days The 30 days cumulative 60 days expansion 90 days ratio(%) 120 days 150 days 180 days 190 days

15.2 300

13.0 300

11.5 300

21.1 300

63.92/(2.52)

65.19/(2.57)

67.73/(2.67)

66.46/(2.62)

0.003 0.023 0.161 1.126 2.472 3.238 3.317 3.489 3.497 3.536

0.002 0.006 0.031 0.236 0.997 1.933 2.040 2.094 2.163 2.178

0.003 0.003 0.004 0.063 0.236 0.273 0.285 0.291 0.292 0.297

0 0.003 0.024 0.322 1.324 2.144 2.212 2.219 2.219 2.219

Note: 1.The cumulative expansion ratio= (The cumulative expansion value / The height of sample)×100% 2.The expansion ratio tested by triplet.

The soluble salts contribute to the observed expansion. The MSWI bottom ash contains soluble salts such as CaCl2, KCl, NaCl, etc. Volumetric expansion was observed in four samples after 190 days of drying-up process of the saturated MSWI bottom ash. The cumulative expansion ratios are from 0.2% to 3%. They are higher than those of the cumulative expansion ratios of natural sand and clay, which are 0.06% and 0.1%. The cumulative expansion ratio and test duration is shown in Figure 8. In the first 60 days, the expansion of MSWI bottom ash follows logarithmic rule. Up to the 90th day, no further expansion was observed. The result implies the MSWI bottom ash may be stocked for 90 days or more to reduce its expansion in volume to avoid the possible damage on subbase.

Cumulative expansion ratio(%)

10

1

◆ ■ ▲ ╳

0.1

Sample 1 Sample 2 Sample 3 Sample 4

0.01

0.001 1

7

14

30

60 90 120 150 180

Days

Figure 8 The figure of the cumulative expansion ratio and test duration 3.3 The Environment Compatibility of The MSWI Bottom Ash 3.3.1. Simulation of The Outdoor Pile The purpose of this experiment is to observe the stability and changes of MSWI bottom ash under natural conditions. After simulating the outdoor pile and observe the changes in the MSWI bottom ash in the natural condition, the factors that stabilize the properties of MSWI bottom ash are investigated. The experimental equipment is shown in Figure 9： a 200-liter tank was set in the open air, and then four holes were punched at the bottom of the tank. A filtering film was placed on the bottom to prevent the fine particles from passing through the holes. 90 Kg of MSWI bottom ash was poured into the tank; a water trough is set under 1042


the tank to collect the infiltration water. By observing and analyzing the constituent of the infiltration water of the MSWI bottom ash, the factors that stabilize the chemical as well as affect the physical properties of the MSWI bottom ash were determined. After the rain drip washing process, the infiltration water was collected and analyzed by ICP and the results are shown in Table 11. Table 12 shows the results of the control groups. The infiltration water of the MSWI bottom ash contains salts such as Ca+2. The experimental equipment is shown in Figure 9： a 200-liter tank was set in the open air, and then four holes were punched at the bottom of the tank. A filtering film was placed on the bottom to prevent the fine particles from passing through the holes. 90 Kg of MSWI bottom ash was poured into the tank;

Figure 9 The outdoor pile tank（200 liters） a water trough is set under the tank to collect the infiltration water. By observing and analyzing the constituent of the infiltration water of the MSWI bottom ash, it is found that CaCl2, NaCl, KCl, KCL are the unstable chemicals in MSWI bottom ash. Its impact to the environment requires a longer period observing. Table 11 The infiltration water analysis

Unit: mg/L

Date Al Ba Ca Cd Cr Cu Fe K Mg Na P Pb 2002.8.2 0.4 1.5 > 0.0 0.1 16.3 0.1 2791.9 0.2 4023 3.2 0.4 2002.8.2 0.3 1.5 > 0.0 0.1 16.4 0.1 2814.9 0.2 4008 3.2 0.3 2002.8.3 0.3 1.5 > 0.0 0.1 16.3 0.1 2807.1 0.2 3993 3.0 0.3 2002.8.3 0.9 2.1 > 0.0 0.1 29.0 0.0 4106.4 0.6 > 1.3 -2002.8.5 9.2 1.4 > 0.0 0.0 9.7 0.1 1142.4 0.1 1640 1.9 0.6 2002.8.7 0.8 2.7 > 0.0 0.0 17.1 0.0 1773.5 0.2 2539 1.1 0.0 2002.8.8 1.5 5.7 > 0.0 0.1 43.3 0.0 4451.1 1.2 > 0.9 0.0 2002.9.6 0.8 0.8 > 0.0 0.1 8.1 0.0 2511.9 5.9 4016 0.2 0.0 2002.9.6 9.3 1.1 > 0.0 0.1 8.3 0.0 2297.5 0.4 3847 0.7 0.1 2002.9.6 1.8 0.9 > 0.0 0.1 8.6 0.0 2203.0 1.8 3688 0.2 -2002.9.7 3.6 0.5 > 0.0 0.0 5.5 0.0 1297.9 0.8 2165 -- 0.0 2002.9.9 0.6 0.8 > 0.0 0.1 8.3 0.0 1567.4 0.9 2535 0.0 -2002.9.15 1.0 1.2 > 0.0 0.1 13.0 0.0 3529.6 4.9 > 0.5 -Note: >: Higher than detectable limit; the detectable limit, for Ca is 220,000 mg/L --: Lower than detectable limit

Si 2.8 2.8 2.8 1.5 1.6 0.8 3.2 1.2 1.8 1.3 0.7 1.4 2.0

Sr 4.7 4.7 4.7 7.1 2.9 4.4 9.4 3.6 3.6 3.4 2.2 2.8 5.7

Zn Cl 0.1 9226.6 0.1 9362.1 0.1 9293.2 0.1 13168.0 0.1 3649.6 0.1 5667.2 0.2 15215.9 0.1 9044.1 0.0 9228.8 0.1 8580.2 0.0 7469.0 0.1 5677.7 0.1

Table 12 The rain dropping analysis Parameter Al

Ba Ca Cd Cr 2002.8.5 0.08 0.01 2.67 0.00 0.00 2002.8.7 0.12 0.01 3.11 0.01 0.00 2002.8.10 0.09 0.02 9.62 0.01 0.00 2002.9.6 0.11 0.02 2.15 0.00 0.00 2002.9.6 0.09 0.03 8.38 0.00 0.00 2002.9.7 0.10 0.02 2.18 0.00 0.00 Note: -- Lower than detectable limit

Unit: mg/L Cu 0.00 0.01 0.02 0.01 0.03 0.01

Fe 0.01 0.01 0.01 0.01 0.01 0.01

K 1.43 2.64 2.33 4.54 2.33 3.01

Mg 0.19 0.39 0.94 0.56 1.48 0.39

Na 2.06 2.41 5.82 5.29 9.21 3.31

P -------

Pb 0.02 0.03 0.02 0.02 0.02 0.01

Si -0.05 0.53 -0.14 --

Sr 0.01 0.01 0.03 0.01 0.03 0.01

Zn 0.06 0.06 0.16 0.07 0.17 0.08

Cl ------

3.3.2. Unstable materials A. The Crystallized Salts from The MSWI Bottom Ash 1043


The MSWI bottom ash has approximately moisture content of 20%. The white crystallized salts started to form on the surface of bottom ash while the moisture went down to 7% to 8%. As the moisture increased, less white crystallized salts were found. In order to extract the salts in the ash, 2 liters of de-ion water was completely mixed with one kilo and two kilos of MSWI bottom ash, separately. After 24 hours of mixing process, the mixture was filtered. These steps were repeated for 3 times to collect the solution. The moisture in the solution was gradually evaporated at 50℃, and the salts residue was collected.

Figure 10 The crystallized salt from the MSWI bottom ash B. The Qualitative Analyses of The Water-Soluble Salts by X-ray Fluorescence (XRF) By conducting the XRF analysis, the major elements of the water-soluble salts observed are Ca, Cl, Al, K, S, Na, etc. The compositions of salts are shown in Table 13. The salts dissolve in water, and crystallize in the absence of water. Table 13 The qualitative analysis of water-soluble salts by X-ray Fluorescence (XRF) Sample 1 Major Trace 2 Major Trace

Elements Ca、Cl、Al、K、S、Na、Fe、Cu、Br、Si、Sr Mg、Ti、Zn、Ru、Rh、Ag、Sb、Ba、Au Ca、Cl、K、Al、S、Na、Fe、Br、Cu、Si、Zn、Sr Mg、P、Ni、Ru、Rh、Sb、Ba

3.3.3. Infiltrating Test on Sample Columns A. The Framework of Experiment Based on the research related to environmental compatibility of the MSWI bottom ash to the subbase in other countries, the simulated subbase construction is tested and observed for a period of time in order to verify the environmental compatibility of tested objects (Hjelmar, 1990; Vehlow, 1996; Hjelmar, 1996; Sakai, 1996). This study used the cylindrical container to simulate the real subbase and its compositional profile. The infiltrating test was conducted on the cylindrical structure for its environmental compatibility. B. Preparation of Samples The purpose of the study is to determine the pH and conductivity of the infiltration water which simulated rainwater leaching through the MSWI bottom ash column. (a) The MSWI bottom ash has been pretreated to remove the metal and perishable contents. (b) The acrylic cylindrical column is 18 cm in diameter and 35 cm in height as show in Figure11. The consolidation condition will affect the percolation of water through soil and weathering to the soil. According to AASHTO T180 D, compacting the MSWI bottom ash in the cylinder is general subbase compact method. (c) In order to keep the bottom ash from being washed off, a multi-porous pad was put on at the bottom of the sample column. Also the sample column was put above the water collection funnel and collects the infiltration water under the funnel. (d) In order to simulate the acid rain flows from surface to subbase; an infiltrating test of sample column was conducted. The water poured into test column was 7 times the volume of the cylinder of the sample column. The acid rain was simulated and formulated with HNO3 and H2SO4 to reach the pH value of 5.5. The pH value 1044


and conductivity of infiltration water were determined with the auto-monitoring device SUNTEX, RM230 and the software VISUAL VSCADA, as shown in Figure 12. C. The Experimental Result of Infiltrating Test The infiltrating test of MSWI bottom ash was performed under continuous flow. Using the auto-monitoring device to record the pH change and conductivity of infiltration water. The total volume of the infiltrating water is 14 liters. The result is shown in Figure 13. (a) The higher the concentration of electrolytes in soil, the higher the conductivity of infiltrated water. According to the result of the auto-monitoring recorder, the conductivity of the collected infiltration water was 20mmho/cm at the beginning. After a long period of infiltration, the conductivity decreases to 1.3mmho/cm. The study suggests that the raw bottom ash without pre-washing process should not directly be exposed to the local soil. The conductivity of natural soil less than 4mmho/cm is safe only for certain plants of high salt-durability.

18 cm 35 cm MSWI bottom ash Figure 11 The compacted and finished sample column

Figure 12 The infiltrating test of sample column and auto-monitoring device (b) The initial pH value of leaching test is 7.37. The pH value of the infiltration water gradually increased to 11. This escalation of pH is because of soluble salts dissolved and leached out along with the water. (c) The result of infiltrating test suggests that MSWI bottom ash should be properly treated before the reuse. The test results also reveal that the raw bottom ash before pretreatment should not be put in direct contact with local soil. On the surface of raw MSWI bottom ash layer, a layer of concrete or asphalts should be paved to prevent the rainfall infiltration. Under the raw MSWI bottom ash, a waterproof layer should be used to keep the raw MSWI bottom ash from being leached out by the groundwater and, furthermore, causing serious physical and chemical damage to the environment. 4. Results and Discussion This study on the reutilization of MSWI bottom ash as sub-base material was evaluated at three levels: basic characteristics, engineering material tests and the environmental compatibility. The results are as following: 1. According to engineering material test results, it indicates that the MSWI bottom ash needs to be modified before it is used as subbase substitute. The test results of physical property also support this statement. 2. According to the analysis of basic characteristics, it shows that the MSWI bottom ash can be categorized as 1045


non-hazardous waste. It is safe to be recycled and reused. The basic chemical compositions of the MSWI bottom ash vary from site to site. Therefore, further investigation is suggested and the test results should be taken with more precautions for all the MSWI bottom ash to be used in order to avoid possible damage on the local environment. 3. The volume of the sample expands perceptibly after the saturated water in MSWI bottom ash has dried up. This significant expansion in volume observed was induced by the high concentration of salts in the MSWI bottom ash. Its applicability as subbase of roads and civil engineering substitutes needs further investigation. 4. The evaluation of environmental compatibility demonstrates the physical bonds of MSWI bottom ash have been disintegrated during the drying process due to the volumetric expansion caused by the crystallization of the water-soluble salts such as Ca, Cl, Al, K, S, Na, etc. Using the simulated acid rain to infiltrate through the MSWI bottom ash sample column, the measurements of conductivity of the infiltration water can reach 20mmho/cm and the pH value is up to 11. The high conductivity and pH of infiltration water may limit the growth of plantations, because most plants can only afford a low salt concentration.

Figure 13 The pH change and conductivity of the infiltration water from MSWI bottom ash Table 14 The result of basic characteristics and engineering material tests of the MSWI bottom ash Items L.O.I.

Results 6.0 % ～ 11.2 %

TCLP Lower than the EPA regulations. Leaching Test The sieve analysis results are not consistent Sieve Analysis with the gradation of subbase. Test for Los Resistance ratio=42.7 % Angeles (1) Loss of the soundness ＝2.3 % Soundness (2) It shows that the MSWI bottom ash has high Tests anti-weathering potential. CBR Test

Basic Characteristics and Engineering Material Tests (1) It contains combustible materials. (2) The instability caused by organic material should be taken into account. Cd＜1.00mg/L; T-Cr＜5.00 mg/L Pb＜5.00 mg/L; Hg＜0.20 mg/L Se＜1.00 mg/L CNS 14602 The average standard of the subbase mixtures material should be lower than 50%. (1) The fine aggregate, the soundness test ＜10%. (2) The sub-base aggregate ＜12%

(1) (1) CBR＝108% (2) The California bearing ratio of the MSWI bottom ash is better than the stone base. (2)

The regulation of steel slag for road construction MS-25 > 80%; subbase material CS-20＞30% CNS 14602 1046


5. Conclusion Both the basic characteristics and the engineering test results demonstrate that the MSWI bottom ash, after modification is suitable to be reused as subbase aggregates. However, the sieve analysis results are not consistent with the gradation of subbase, it might affect the engineering quality of bottom ash as subbase. The organic materials and the water-soluble salts may influence the stability of MSWI bottom ash. It needs to be mixed with nature gravel to adjust the grain-size distribution. The pretreatment of lowering the amount of organic contents and the water-soluble salts is strongly recommended and considered to be a necessity process for road construction. The study suggests that the raw bottom ash without pre-washing process should not directly expose to the local soil. It must be paved with concrete, asphalts or a waterproof layer on top of the raw MSWI bottom ash and underneath it, to prevent the rain /acid rain infiltration and the groundwater leaching action. Acknowledgement I would like to thank several individuals for their help and contribution in making this project a success. First I would like to acknowledge the contribution from my supervisor Dr. Wen-Chen Jau Ph.D., and advisor Kung-Cheh Li Ph.D., who were the calm in the storm. Furthermore, this project could not have been completed in the time frame established without the dedication of Mr. Jia-Rong Wu, ITRI, Chemical Analysis Department Lab Specialist, Engineer Mr. An-Bang Lin, and Director Shyh-Yih Chen, Materials Laboratory of DGH, whose instrumentation experience and attention to detail proved invaluable. Finally I would like to thank Mr. Jia-Yuh Huang, Lab Head of Material Lab of Department of Civil Engineering of NCTU, who donated all the knowledge about aggregate materials for the experiments and provided unlimited access to their lab, which proved extremely beneficially. References Kosson, D. S.; van der Sloot, H. A. and Eighmy, T. T. (1996). An Approach for Estimation of Contaminant Release During Utilization and Disposal of Municipal Waste Combustion Residues. Journal of Hazardous Materials. 47, 43-75. Hjelmar, O. (1990) Regulatory and Environmental aspects of MSWI ash utilization in Demark, Proceedings of the Third international conference on ash utilization and stabilization (ash III), Arlington, Virginia, 59-70. Sakai, S; Sawell, S. E.; Chandler, A. J.; Eighmy, T. T.; Kosson, D. S.; Vehlow, J.; van der Sloot, H. A.; Hartlen, J. and Hjelmar, O. (1996). World Trends in Municipal Solid Waste Management. Waste Management, 16, 341-350. Van der Sloot, H.A. (1996). Present Status of Waste Management in the Netherlands. Waste Management. 16, 375-383. Vehlow, J. (1996). Municipal Solid Waste Management in Germany. Waste Management. 16, 367-374. Chandler et al., (1994 Sakai. Sakai.). An International Perspective on Characterization and Management of Residues from Municipal Solid Waste Incineration. Summary Report, International Energy Agency. Chandler,A,J.,T.T.Eighmy,J.Hartlen, O. Hjelmar,D.S.Kosson,S.E. Sawell,H.A. van der Sloot, and, and J. Vehlow. (1997). Municipal Solid Waste Incinerator Residues. Studies in Environmental Science 67, The International Ash Working Group, Elsevier, Science B.V., New York. Chester, W. H., R. J. Collins, and T. Fung. (1986). The Characterization of Incinerator Residue in the City of New York. Proceedings of the 1986 National Waste Processing Conference. ASME Solid Waste Processing Division. National Renewable Energy Laboratory (NREL). (1996). Beneficial use and recycling of municipal waste combustion residues-a comprehensive resource document. Hjelmar, O. (1996). Waste Management in Denmark. Waste Management, Vol.16, Nos5/6, 389-394. Sakai, S. I. (1996). Municipal Solid Waste Management in Japan. Waste Management, Vol.16, Nos5/6, 395-405. The Turner-Fairbank Highway Research Center (TFHRC). Federal Highway Administration. User Guidelines for Waste and By-Product Materials in Pavement Construction, U.S. http://www.tfhrc.gov/ 10-1~10-26, (1997).

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