EP A/600/A-94/222
ASSESSMENT OF CONTAMINANT RELEASE RATES AND
POTENTIALS FROM SOLIDIFIED/STABILIZED
MUNICIPAL WASTE COMBUSTION RESIDUES
Teresa T. Kosson, David S. Kosson and Ben Stuart
Rutgers, The State University of New Jersey
Department of Chemical and Biochemical Engineering
P.O. Box 909
Piscataway, NJ 08855-0909
Hans van der Sloot
The Netherlands Energy Research Foundation
Wcsterduinwcg 3, P.O. Box 1
Petten NU.
The Netherlands 17 55ZG
ABSTRACT
The U.S. Environmental Protection Agency (USEPA) initiated a number of studies on MWC
residue, residue disposal facilities, and residue management practices to build a scientific data base to
support regulatory choices. The study was conducted to provide a side-by-side comparison and evaluation
of the effectiveness of MWC S/S technologies for treating bottom ash, APC residues and combined ash.
The specific objective of the study relative to leaching was to compare the effects of the S/S processes on
leaching properties of MWC residues through a range of leaching tests. General conclusions are made
based on the results of the leachability property testing.

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INTRODUCTION
The proper management of Municipal Waste Combustion (MWC) residues is necessary to ensure
that the use of combustion as a solid waste management method is protective of human health and the
environment The U.S. Environmental Protection Agency (USEPA) initiated a number of studies on
MWC residue, residue disposal facilities, and residue management practices to build a scientific data base
to support regulatory choices. The objective of this study was to provide credible data on die effectiveness
of die selected solidiftcation/stalrilization (S/S) processes for treatment of MWC bottom ash, APC residue,
and combined ash.
The study was conducted to provide a side-by-side comparison and evaluation erf the effectiveness
of MWC S/S technologies for treating bottom ash, APC residues and combined ash. The number of
different residues included in the study was limited to bottom ash, APC residue, and combined ash from a
single mass bum MWC facility. This paper provides a summary of the project desip and conclusions.
For complete project details see "Evaluation of Solidification/Stabilization Treatment Processes for
Municipal Waste Combustion Residues."
Background
MWC residue used in this study was collected form a modem mass bum facility with a nominal
capacity rating of 2,100 ton/day. The MWC facility has the following process sequence: (i) primary
combustor with movable grates, (ii) boiler and economizer, (iii) wet/diy scrubber (spray drier) with lime,
and (iv) particulate recoveiy baghouses (fabric filters). Residues from all of the boiler surfaces are included
with the bottom ash stream, which is quenched after exiting from the primary combustor. APC residue
generated is the mixed residuals from the acid gas scrubber and the baghouses. APC residue is combined
with bottom ash and passed through a grisly to remove materials larger than ten inches and trammelled to
pass a 1.5 inch screen in conjunction with iron recovery. The three separate ash streams evaluated in this
study were (i) bottom ash, (ii) APC residue, and (iii) combined ash.
The three residue types used in this study were obtained during a single composite sampling event
from a typical state-of-the-art mass bum municipal waste combustor incorporating a lime slurry spray drier
(wet-dry) acid gas scrubber and a fabric filter particulate removal system. Each bulk residue sample was
dried, size reduced, screened and homogenized prior to use in this program. Thus all process
demonstrations, testing and evaluations were carried out on pre-processed residues to facilitate laboratory
scale testing and direct treatment effect comparisons.
Five S/S processes were evaluated. Four of five of the processes were proprietary vendor
applications of four different generic S/S process categories. The generic S/S process categories
represented by the selected vendors were:
•	S/S with Portland cement and polymeric additives or other proprietary additives
(Process 1);
•	S/S with Portland cement and soluble silicates (Process 2);
•	S/S with cement kiln dust and proprietary additives (Process 3),
•	S/S through addition of soluble phosphates (Process 4).
The fifth process used Type 1 Portland cement only (WES Control Process) The Type 1 Portland
cements only (WES Control Process) was selected to provide a baseline comparison of the treatment
effects of Portland cement without vendor additives.
Objectives
The specific objective of the project relative to leaching was to compare the effects of the S/S processes on
leaching properties of MWC residues through a range of leaching tests. These tests evaluate a range of
leaching properties including contaminant release under diverse environmental conditions, contaminant
release potential, and release rate over a prolonged period of time in various environmental scenarios.
EXPERIMENTAL DESIGN
The experimental design of this program was a full factorial design for the evaluation of five
solidification/stabilization processes for MWC residues. The two experimental factors were the residue
type to be treated and the S/S process. The experimental levels within the residue type factor were (i)
bottom ash, (ii) APC residue, and (iii) combined ash. The six experimental levels within the S/S process
factors were (i) the untreated residue, (ii) the WES Control S/S process, and (iii - vi) the four selected
vendor S/S processes. Thus, two experimental factors at three and six experimental levels respectively,
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resulted in the evaluation of eighteen experimental cases. Each experimental case was evaluated in
triplicate.
Prior to the process demonstration, each vendor developed optimum formulas prior to the process
demonstration using approximately 50 lbs of each residue type. Performance was left to the vendor's
discretion. Each process demonstration replicate consisted of the vendor carrying out the specified
process to produce approximately 100 lb of treated residue. Each experimental case was analyzed for
leaching characteristics using a series of testing procedures including the Toxicity Characteristic Leaching
Procedure (TCLP),Availability Leach Test (ALT), Distilled Water Leach Test (DWLT), Add Neutralization
Capacity (ANC) and the Monolithic Leach Test (MLT). These tests are discussed in the Leaching
Properties Tests section.
Leaching Properties Tests
The TCLP, ALT, DWLT, ANC, MLT were conducted on the treated and untreated residues. Each are
discussed in the following sections.
Toxicity Characteristic Leaching Procedure fTCLP)
The TCLP was selected to be carried out to allow a comparison with a broad database of results
obtained from testing of other materials. The TCLP was carried out in accotdanoe with the method outlined
in the 7 Nov 1986 Federal Register, Volume 40, Part 261 (US EPA, 1986]. This test is carried out on a
sample crushed to less than 9.5 mm. Extraction is carried out at a 20:1 liquid to solid ratio using dilute
acetic acid. The extraction solution is either buffered or unbuffered depending on the alkalinity of the
materia] to be tested. Only a fixed quantity of acid is added for the extraction, and therefore the final pH of
the extract is widely variable. Thus, metals concentrations observed in the extract often reflect the pH
dependent solubility constraints of the specific element. The contaminant concentrations in the test leachate
are compared with a published list of limits.
2.3.2 Availability Leach Test (ALT)
The Availability Leach Test was selected to assess the maximum amount of specific elements or
species which could be released under an assumed "wont case" environmental scenario. This test was
originally developed by the Netherlands Energy Research Center (ECN) (van der Sloot, H.A., et al, 1984],
The test is carried out on a sample crushed and size reduced to less than 300 mm. Two serial extractions
are carried out, each at a 100:1 liquid to solid ratio, using distilled water. The pH is controlled to pH 7
during the first extraction and to pH 4 during the second extraction, using an automatic pH controller which
delivers dilute nitric acid. Thus, the final extraction pH is controlled not the amount of acid used. The first
and second extracts are combined for analysis. The very large liquid to solid ratio insures that the
contaminant release is not constrained by its solubility at the final pH and the amount of contaminant
extracted is the maximum amount which would be available at that pH. This test generally extracts all
species which are not tightly bound in a mineral or glassy matrix. The test does not provide information on
the rate of contaminant release.
2.3.2 Availability Leach Test (ALT)
The Availability Leach Test was selected to assess the maximum amount of specific elements or
species which could be released under an assumed "worst case" environmental scenario. This test was
originally developed by the Netherlands Energy Research Center (ECN) [van der Sloot, HA., et al, 1984],
The test is carried out on a sample crashed and size reduced to less than 300 mm. Two serial extractions
are carried out, each at a 100:1 liquid to solid ratio, using distilled water. The pH is controlled to pH 7
during the first extraction and to pH 4 during the second extraction, using an automatic pH controller which
delivers dilute nitric acid. Thus, the final extraction pH is controlled not the amount of acid used. The first
and second extracts are combined for analysis. The very large liquid to solid ratio insures that the
contaminant release is not constrained by its solubility at the final pH and the amount of contaminant
extracted is the maximum amount which would be available at that pH. This test generally extracts all
species which are not tightly bound in a mineral or glassy matrix. The test does not provide information on
the rate of contaminant release.
2.3.4 Acid Neutralization Capacity (ANC)
The Acid Neutralization Capacity (ANC) test was selected to assess the solubility of specific metals
over a broad pH range (Test Methods for Solidified Waste Characterization, 1986], The test was carried
out on a sample crashed and size reduced to less than 300 mm. Eleven separate extractions are carried out
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using separate size reduced subsamples at a liquid to solid ratio of 5:1. The low liquid to solid ratio results
in the extraction being solubility constrained for some analytes. Each extraction receives a different amount
of dilute nitric arid, varying from 0 to 12 meq/g dry untreated or treated residue, resulting in a broad range
of final pHs. A titration curve also is obtained for each material tested.
2.3.5. Monolith Leach Test
The Monolith Leach Test was selected to assess the release rate of specific elements and species
from untreated and treated MWC residues under diffusion controlled conditions. This would be the case
under field conditions where the flow of infiltration or contacting water is predominandy around monolithic
structures (e.g., blocks, other forms or low permeability compacted fill). The Monolithic Leach Test was
carried out based on a modification of the American Nuclear Society (ANS) American National Standard
Measurement of die Leachability of Solidified Low-Level Radioactive Wastes by a Short-Term Test
Procedure,(ANSI-16.1-1986). The test was carried out using a 4 cm dia. by 4 cm cylindrical, monolithic
sample instead of die specified sim test specimen. Treated residues were either vibrated or compacted
using modified proctor compactive effort into PVC plastic molds immediately after being treated. Samples
were cured at 98% relative humidity and 20°C for 28 days prior to testing. Monolithic samples were
extracted by contacting with 8.47 liters distilled water for up to 64 days. Contacting water was replaced
with fresh distilled water at 1,2,4,8,16,32 and 64 days and analyzed for metals and other species.
A new test method was developed for evaluation of compacted granular materials. Release rate data
was obtained for untreated bottom ash and combined ash by compacting each ash at optimum moisture
content, using modified proctor compactive effort, in 4 inch diameter by 4 inch cylindrical polyethylene
molds. Specimens then were cured in the mold for 28 days at 24°C and 98 patent relative humidity. The
exposed face of the specimen in each mold then was covered with a 22mm thick layer of 3mm diameter
glass beads and contacted with 8.47 liters distilled water (Figure 2.1). Contacting water was replaced with
fresh distilled water at 6 hours and 1,2,4,8,16 and 32 days.
Modeling of the release data in conjunction with the results of the availability leach test was used to
determine effective diffusion coefficients, tortuosity and chemical retardation factors for estimating long
term species release rates .
CONCLUSIONS
In summary, general conclusions are made based on the results of the leachability property testing.
Key findings of the study are as follows:
• The S/S processes evaluated generally did not decrease the potential for release of target
contaminants based on comparison of untreated residues with treated residues. The phosphate
process, however did reduce the potential for Pb to be released.
•	Whether the MWC residues were treated or not, release potential for metals (lead, cadmium, zinc,
etc.) typically was a small fraction of the total concentration present in both die untreated and treated
residues. Release rates of the elements were very low for compacted granular untreated bottom ash
and combined ash. Release rates also were very low from bottom ash and combined ash treated by
processes that produced physically durable specimens.
•	The S/S processes evaluated did not successfully treat the residues to reduce the potential for
release of TDS and soluble salts. Whether the MWC residues were treated or not, the release
potential and release rates were high for TDS and the salts of calcium, sodium, potassium, chloride,
and sulfate. The total amounts of these constituents released typically approached the total
concentration in the MWC residues. In the case of the APC residues, the treatment processes
increased the release potential of the salts.
•	The high concentration and ultimate fate of soluble salts in MWC residues should be carefully
considered in the design of treatment processes, utilization and disposal of the residues.
•	Evaluation of S/S process design, performance, and treatment efficiency should be based on a
matrix of several testing protocols. No single test, such as TCLP, can provide all the information
required to evaluate contaminant release potential, contaminant release rate, and physical durability.
An appropriate test matrix to evaluate S/S processes should include tests which will address these
factors.
•	Most processes evaluated in this study most likely were developed based on a limited number of
testing procedures. Variations in Portland cement based and other S/S technologies will influence
the degree of durability and chemical leaching potential. Therefore, substantial improvements in
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S/S process optimization may be obtainable by optimizing process design based on results of
multiple test criteria.
•	The release rate of most potentially toxic metals will be very slow to negligible for S/S treated
MWC residues.
•	The unconsolidated, granular nature of the ash material required thai a useful method for estimating
diffusion controlled release from compacted granular materials be developed. Such a method was
developed for this evaluation and the application of a modified monolith leach test to determine
intrinsic leaching properties for granular materials has been proven to be very consistent, and data
are comparable with results from other type of diffusion measurements. The tortuosity data
obtained in the experimental setup are consistent with diffusion measurements, using radiotracers.
•	TCLP was not a good indicator of release from untreated and treated residues for several reasons.
Variable end-point pH for the extraction resulted in wide variation in estimated metals release
because of pH dependent solubility constraints. The low liquid to solid ratio for the TCLP (20:1)
also may have resulted in solubility limitations for many elements of concern. Finally, TCLP (toes
not provide for determination of the total release of soluble salts and anions.
•	The monolithic leach test (MLT) for construction materials and stabilized products provides
intrinsic information on long term leaching effects and usefulness in relation to product quality.
The MLT also provides useful information for product quality improvement By focusing on die
controlling parameter requiring adjustment, initial estimates of release rates and fluxes for varied
application scenarios can be obtained. The distinction between physical retention and chemical
retention and the release mechanisms (dissolution, wash-off and diffusion) can be made. Existing
regulatory tests do not provide such useful information.
ACKNOWLEDGEMENT AND DISCLAIMER
This work was funded by die USEPA, Risk Reduction Engineering Laboratory under cooperative
agreement number CR818178-01-0. Carlton Wiles is the Project Manger. The views expressed in this
paper are those of the authors and do not necessarily express views or policies of the USEPA.
REFRENCES
Kosson, David S„ Teresa Kosson, and Hans van der Sloot "Evaluation of Solidification/Stabilization
Treatment Processes for Municipal Waste Combustion Residues" Cooperative Agreement No. CR
818178 -01-01, USEPA/RREL, 1993.
van der Sloot, H.A., etal, "A Standard Leaching Test for Combusiton Residues", Technical Report Bureau
of Energy Research Projects BEIP-31. The Netherlands. 1984.
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TECHNICAL REPORT DATA
(Fkaae tad Itmrvaiau oo the nwne before oompktia*)
1. REPORT NO.
EPA/600/A-94/222
2,

4. title and subtitle Assessment of Contaminant Release Rates and
Potentials from Solidified/Stabilized Municipal Waste
Combustion Residues
5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7.author® Teresa T, Kosson, David S. Kosson, and Ben Stuart
at Rutgers and Hans van der Sloot at The Netherlands Energy
Research Foundation
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS Rutgers, The State
University of New Jersey, Department of Chemical and
Biochemical Engineering, P.O. Box 909,
Piscataway, NJ 08855-0909
The Netherlands Energy Research Foundation, Westerdiunweg
3, P.O. Box 1, Petten N.H., The Netherlands 17 55 ZG
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
CR818178-01-0
12. SPONSORING AGENCY NAME AND ADDRESS
IB EPA, Risk Reduction Engineering Laboratory
26 W. Martin Luther King Drive
Cincinnati, OH 45268
13. TYPE OF REPORT AND PERIOD COVERED
Proceedings
14. SPONSORING AGENCY CODE
EPA/600/14
is. supplementary notes Project Officer: Carlton C. Wiles, 513-569-7795
1993 International MWC Conference Research Triancrle Park, NC, Mav 1993; Da 1-5
16.abstract The U.S. Enviromental Protection Agency (USEPA) initiated a number of studies on
MWC residue, residue disposal facilities, and residue management practices to build a
scientific data base to support regulartory choices. The study was conducted to provide a
side-by-side comparison and evaluation of the effectiveness of MWC S/S technologies for
tretaing bottom ash, APC residues and combined ash. The specific objective of the study
relative to leaching was to compare the effects of the S/S processes on leaching properties
of MWC residues through a range of leaching tests. General conclusions are made based on
the results of the Teachability property testing.
17, KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
MDENWIERS/OPEN ENDED TERMS
C. COSAT1 FMd/Ql0U|S
Municipal Waste Combustion Residues
Solidified/Stabilized


18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (Tim Rtpat)
Unclassified
2i. NO. OF PAGES
6
20. SECURITY CLASS (to*
Unclassified
22. PRICE
EPA F«m 2220-1 (Rn. 4-77) PREVIOUS EDTTION IS OBSOLETE

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