EPA/600/R-95/047
April 1995
ANALYSIS OF THE POTENTIAL EFFECTS OF TOXICS ON
MUNICIPAL SOLID WASTE MANAGEMENT OPTIONS
by
Science Applications International Corporation
Falls Church, VA 22043
and
SCS Engineers
Reston, VA 22090
EPA Contract No. 68-C2-0148, WA 2-2
SAIC Project No. 01-0824-03-6608-000
Project Officer
Robert E. Landreth
Waste Minimization, Destruction, and Disposal Research Division
Risk Reduction Engineering Laboratory
Cincinnati, Ohio 45268
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
RISK REDUCTION ENGINEERING LABORATORY
CINCINNATI, OH 45268
Printed on Recycled Paper
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DISCLAIMER
The information in this document has been funded wholly (or in part) by the U S
Environmental Protection Agency under Contract No. 68-C2-0148, WA 2-2, to Science
Applications International Corporation. It has been subject to the Agency's'peer and
administrative review, and it has been approved for publication as an EPA document
Mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
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FOREWORD
Today's rapidly developing and changing technologies and industrial products and
practices frequently carry with them the increased generation of materials that, if improperly
dealt with, can threaten both public health and the environment The U.S. Environmental
Protection Agency is charged by Congress with protecting the Nation's land, air, and water
resources. Under a mandate of national environmental laws, the agency strives to formulate
and implement actions leading to a compatible balance between human activities and the
ability of natural systems to support and nurture life. These laws direct the EPA to perform
research to define our environmental problems, measure the impacts, and search for solutions.
The Risk Reduction Engineering Laboratory is responsible for planning, implementing,
and managing research, development, and demonstration programs to provide an authoritative,
defensible engineering basis in support of the policies, programs, and regulations of the EPA
with respect to drinking water, wastewater, pesticides, toxic substances, solid and hazardous
wastes, and Superfund-related activities. This publication is one of the products of that
research and provides a vital communication link between the researcher and the user
community.
This report summarizes current literature pertaining to the presence of metals and
organics in MSW, and assesses the potential impacts that these contaminants may have on
select MSW management strategies.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
111
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ABSTRACT
n^n^ f PU??e °^ rcp0rt 1S (1) M summarize "* <=•««« literature pertaining to the
presence of metak and organics in MSW; and (2) to examine the potential tapacTlaV bo*
towc metal and orgamcs constituents in MSW may have on MSW mm^me^SSSr
e^r«^?handtheenVir0nmtnt ^ ^^ "^ include: reductions^
f ~T^ * mana8«*»t technique; negative characteristics of products and residuals
generated by me management techniques; and negative effects on human health and the
c^Tr? S6 °f fcgWw CmiSSi0nS> rcsk!ual «»"««««* or contact with products
created. The MSW management options examined include: recycling of paper, plastic and
glass; composting; waste-to-fuel processes; and landfilling.
rnnrfJ"**8 process°fude?1°ping ^ document- EPA «>d i«'s contractor also identified a
number of areas in which additional future research would be valuable.
This report was submitted in fulfillment of Contract No. 68-C2-0148 Work
Assignment 2-2, SAIC Project No. 01-0824-03-6608-000, by Science Applications
Colp°ration'™fer ** «P««"MP of ^ U.S. Environmental Protection Agency
PebnUUy 1W3 to SePttmber 1994> ^ W°rk was '
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TABLE OF CONTENTS
DISCLAIMER u
FOREWORD m
ABSTRACT iv
EXECUTIVE SUMMARY xi
1.0 INTRODUCTION l
2.0 CHARACTERIZATION OF METALS AND ORGANICS IN MSW 3
2.1 Studies of the Presence of Metals in MSW 4
2.2 Organic Toxic Studies 5
2.3 Summary 6
3.0 POTENTIAL EFFECTS OF TOXICS ON RECYCLING 7
3.1 Introduction 7
3.2 Recycling of Paper 7
3.2.1 Presence of Toxics in Discarded Paper 7
3.2.2 Paper Recycling Processes H
3.2.3 Potential Effects of Toxics on Paper Recycling 13
3.2.3.1 Wastewater Characteristics 13
3.2.3.2 Air Emissions 17
3.2.3.3 Solid Waste (Sludge or Fibercake) 19
3.3 Plastic Recycling 22
3.3.1 Presence of Toxics in Plastics 22
3.3.2 Plastic Recycling Processes 27
3.3.2.1 Thermoplastics Recycling 27
3.3.2.2 Coirringled (Mixed) Plastics 29
3.3.2.3 Chemical Recycling 30
3.33 Potential Effects of Toxics on Plastics Recycling 32
3.4 Glass Recycling 33
3.4.1 Presence of Toxics in Glass 33
3.4.2 Glass Recycling Process 35
3.4.3 Potential Effects of Toxics on Glass Recycling 37
3.5 Summary 39
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TABLE OF CONTENTS (continued)
4.0 POTENTIAL EFFECTS OF TOXICS ON MUNICIPAL SOLID WASTE
COMPOSTING
4.1 Introduction ............................... ^
4.2 The Composting Process ........................ .......... 41
4.2.1 Preparation of Compostables ............. .............. 42
4.2.2 Composting .............................. ......... 42
4.2.3 Refining ............................. 43
4.3 Uses for Compost ......................... !!.'.'!'. ......... 43
4.4 Environmental Pathways and Exposure Routes for Releases of
Metals and Organics ........................... 43
4.5 Human Health and Environmental Concerns During the Composting
Process .................................... 45
4.5.1 Emissions Associated with Composting Operations .......... ! ' 45
4.5.2 Primary Pathogens Associated with Composting Operations ...... 47
4.5.3 Bioaerosols Associated with Composting Operations ........... 47
4.5.4 Trace Elements Associated with Composting Operations ..... . . . 47
4.5.5 Other Substances Associated with Composting Operations ....... 49
4.5.6 Possible Leachate Generation During Composting Operations . . . . ! 49
4.6 Concentration of Metals and Organic Compounds in Finished MSW
Compost ..... . ..... ........................ ^Q
4.6.1 Metals ........................ .............. ...... 50
4.6.2 Organic Compounds ........................... 54
4.7 Behavior of Metals and Organic Compounds in Finished MSW Compost 58
4.7.1 Metals ...................................... ' 5g
4.7.2 Organic Compounds ....................... .'!!!! ..... 61
4.8 Effects of Metals and Organics Compounds in Finished MSW Compost
on Soil Microbiota and Vegetation .................... 51
4.8.1 Metals and Organic Compounds in MSW Compost-Amended Soils 61
4.8.2 Effects of Metals on Soil Microbiota ...................... 61
4.8.3 Effects of Metals and Organic Compounds on Vegetation 62
4.8.3.1 Metals ................................. "" 62
4.8.3.2 Organic Compounds ......................... 55
4.9 Effects of Ingesting Compost, Compost- Amended Soil, or Products Grown
in Compost- Amended Soil and Associated Risk ................... 57
4.9.1 Ingestion of Compost or Compost-Amended Soil ......... . . . . 67
4.9.2 Ingestion of Products Grown in Compost-Amended Soil ....... . 68
4.9.3 Risks from Ingesting MSW Compost Directly and Indirectly Through
the Food Chain ................................... 69
4.10 Compost Standards ............................ ....... 72
4.11 Best Management Practices ...................... ....... 75
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TABLE OF CONTENTS (continued)
4.12 Future Research Needs ..................................... 77
4.13 Summary .............................................. 81
5.0 POTENTIAL EFFECTS OF TOXICS ON WASTE-TO-FUEL PROCESSES
83
5.1 Introduction ............................................ *°
5.2 Municipal Solid Waste Combustion ............................ 84
5.2.1 Background ....................................... 84
5.2.2 Conventional MSW Combustion and Emissions Characterization . . 84
5.2.3 The Effect of Materials Handling on the Fate of Metals ........ 87
5.2.4 The Effect of Matrix Parameters on MSW Emissions .......... 87
5.2.5 The Effect of Design and Operational Parameters on MSW
Emisions .......... .............................. °°
5.2.6 Effects of MSW Emissions on the Combustion Equipment and APCD&9
5.3 Toxics in MSW Combustor Ash Residue ........................ 90
5.3.1 General Findings ........ .............................. 9*
5.3.2 Inorganic Contaminant Concentration Research .............. 92
5.3.3 Organic Contaminant Concentration Research ................ 95
5.3.3.1 Summary ................................... 96
5.4 Toxics in MSW Combustor Emissions .......................... 96
5.4.1 MWC Air Emissions Data ............................. 96
5.4.1.1 MWC Report to Congress Emissions Data ............ 97
5.4.1.2 BLIS MWC Emissions Data ...................... 99
5.4.1.3 MWC Air Emimssions Factors .................... 99
5.4.2 Summary of Air Emissions Research ...................... 101
5.5 Waste to Ethanol Processes ................................. 103
5.5.1 Cellulosic Waste to Ethanol ............................ 103
5.5.1.1 Fermentation ................................. 104
5.5.1.2 The Effect of the Presence of Metals on the Waste-to-
Energy Process ............................... 105
ins
5.52 Acid Hydrolysis .................................... 1U*
5.5.2.1 Effect of the Presence of Metals in Acid Hydrolysis ..... 110
5.5.3 Enzymatic Hydrolysis ................................ I10
5.5.3.1 Effect of the Presence of Metals on Enzymatic
Hydrolysis .................................. no
5.6 Summary
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TABLE OF CONTENTS (continued)
6.0 POTENTIAL ADVERSE EFFECTS ASSOCIATED WITH METALS AND
ORGANIC COMPOUNDS IN LANDFBLLED MUNICIPAL SOLID WASTE ... 114
6.1 Introduction ........................
6.2 Behavior of Metals and Organic Compounds in Landfilled MSW ........ 114
6'2'1 ** ''""
.. 114
6.2.1.1 Volatilization .......................
6.2.1.2 Fugitive Dust ..........
6.2.1.3 Landfill Gas ....... i ,
6.2.2 Leachate ''''''''''' '' '"
..... ..
6.2.2.1 Transport of Metals in Leachate ............. ..... 1 18
6.2.2.2 Transport of Organic Compounds in Leachate ......... 121
6.2.3 Transport of Decomposed Waste in Landfill Leachate .... . . 121
6.2.3.1 Soil and Surface Water ...... .......... 122
6.2.3.2 Ground Water .............. ............ ...... 122
6.3 The Effect of Metals and Organic Compounds on Landfill Components 123
6.3.1 Liner System ......................... 123
6.3.2 Leachate Collection/Removal System ........... ........ 126
6.3.3 Leachate Management ...................... ....... !26
6.3.3.1 On-Site Treatment ........ ........... 1T7
6.3.3.2 POTW ................. '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.[' 127
6.3.3.3 Leachate Rccirculation . .
6.3.3.4 Sludge .............
6.4 Health Effects ..................... .'!!.'.'.'.'.'!.'.'.'!! 128
6.5 Summary .................
7.0 FUTURE RESEARCH NEEDS ............................ 131
7.1 Introduction
7.2 Research Needs
................. 31
LITERATURE CITED ............................. 133
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LIST OF TABLES
Table 1. Composition of Municipal Solid Waste 1
Table 2. List of Constituents Considered in This Report 3
Table 3. Daily Newspaper Organics Analysis 8
Table 4. Heavy Metal Content in Paper and Cardboard Found in Swedish
Household Refuse (mg/kg of Dry Solids) 8
Table 5. Elemental Composition of the Paper Fraction of MSW From the Waste
Study (in mg/kg) 9
Table 6. Characteristics of Raw Effluent from Direct Repulping and
Deinking Operations 14
Table 7. Chemical Identified in Effluent Guidelines Study 15
Table 8. Results of NCASI Study of Metal in Recycled Fiber Mill Effluents 16
Table 9. Estimates of 1988 and 1989 SARA Section 313 Form R Chemical
Emissions from Direct Repulping/Deinking and Papermaking Operations . . 18
Table 10. Analysis of Deinking Sludges (in ppm) 20
Table 11. Extraction Procedure (EP) Toxicity Result for Deinking Sludges 21
Table 12. Heavy Metal Content in Swedish Household Refuse (mg/kg Dry Solids) . . 22
Table 13. Heavy Metal Content of Selected MSW Components (ppm) 22
Table 14. Distribution of Metal Content of Various Fractions of Household
Refuse (percent) 23
Table 15. Elemental Composition of the Plastic Fraction of MSW from the Waste
Study (in mg/kg) 24
Table 16. Amounts of Lead and Cadmium in Plastics Fraction of MSW Discards,
1986 26
Table 17. Elemental Analysis of Plastics Separated from MSW (ppm) 26
Table 18. Substitute Products that Replace Lead- and Cadmium-based Colorants ... 27
Table 19. Wastes Likely to be in Plastic Recycling Waste Streams 32
Table 20. Elemental Composition of Metals in Glass (in grams/ton) 34
Table 21. Presence of Lead and Cadmium in the Glass and Ceramic Fraction of MSW 35
Table 22. Volatile Organic Compounds in Blower Exhaust from an Aerated
Static Pile 48
Table 23. Literature Data from U.S. Composting Facilities 51
Table 24. Metal Concentrations in MSW Compost, Soil, and Sludge 52
Table 25. Heavy Metal Content in Composts 53
Table 26. Organic Constituents in Wet Bag Compost 55
Table 27. Pesticides, Dioxin, PCB, and Other Organics in Solid Waste and Solid
Waste Compost 56
Table 28. Leachate Potential for Metals from Finished MSW Compost 59
Table 29. Pathways for Risk Assessment for Potential Transfer of Sludge-Applied
Trace Contaminants 70
Table 30. Comparison of PCB Application Limits for Each Pathway 71
Table 31. Comparison of Chronic Exposure Levels to References Doses 72
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LIST OF TABLES (continued)
Table 32. Summary of Contaminant Standards for MSW Composts 74
Table 33. Canada's Environmental Choice Standards for Compost. 75
Table 34. Compost Quality Verification for the Protection of Public Health
Safety, and the Environment ' 78
Table 35. Principal MSW Emissions and Sources 04
Table 36. Fundamental Parameters that Influence Metals Behavior 86
Table 37. Limits for Toxic Constituents for EPA TOJP Extraction Test 91
Table 38. Air Pollution Control Equipment Included in NUS (1990) Study 93
-rau C !n RCSUltS °f ^y™ on Rang65 of Metals Concentrations in ASD 94
Tab c 40. Results of NUS (1990) Ash Extract Metal Analysis (ppm) 94
Tab e 41. MWC Emissions Data Summary from MWC Report to Congress 98
Table 42. BUS Data for Selected Pollutants for MWCs inn
Table 43. Emissions Factors for MSW Incinerators 102
Table 44. Concentrations of Essential Elements Required for Growth 106
Table 45. Estimations of Potential Inhibitory Interactions of Metals 107
Table 46. Typical Composition f Gas from Municipal Solid Waste Landfills 116
Table 47. Typical Organic Constituents in Landfill Gas 117
Table 48. Range of Various Inorganic Constituents in Lcachate from Municipal
Table 49. ftelirninary Data on Concentrations of Organic Constituents in Leachate
from Municipal Solid Waste Landfills 12n
Table 50. Mined Landfill Soil Oiaracteristics (Collier County Landfill) 122
Table 51. General Chemical Resistance Guidelines of Commonly Used
Geomembranes 125
LIST OF FIGURES
Figure 1. Flow Diagram of the Paper Recycling Process 11
Figure 2. PET and HDPE Recycling .'.'.'.'.'.'.* 79
Figure 3. Comingled Plastic Recycling 30
Figure 4. Chemical Recycling of Thermosets 31
Figure 5. Chemical Recycling of PET . |. * 31
Figure 6. Flow Diagram of Glass Recycling Process 35
Figure 7. Potential Environmental Pathways: MSW Compost 44
Figures. Potential Exposure Pathways for Organisms: MSW Compost . 44
Figure 9. General Fermentation of Cellulosic Waste to Ethanol 105
Figure 10. Generic Acid Hydrolysis of Cellulosic Waste IQO
Figure 11. Enzymatic Hydrolysis of Cellulosic Wastes m
Figure 12. Potential Environmental Pathways: Landfills 115
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EXECUTIVE SUMMARY
According to the United States Environmental Protection Agency's (EPA's)
Siaracterization of Municipal Solid Waste in the United States: 1992 Update," approximately
?5 million tons of municipal solid waste (MSW) is generated each year.1 While the
imposition of MSW varies for different times and locations, a summary of "typical" MSW
imposition is presented below.
COMPOSITION OF MUNICIPAL SOLID WASTE1
Material Percent (by weight)
Paper and Paperboard 37'5
Yard Wastes 17'9
Plastics 8'3
Metals 8'3
Wood 6'3
Glass 6J
Food Wastes 6'7
Other Wastes 8t3
Many alternative waste management practices and strategies are available to manage the
arge quantities of MSW generated every year. These management alternatives include recycling,
composting, waste-to-fueVenergy recovery, and landfilling. In choosing the best possible
management strategy or combination of management alternatives, the potential impacts to human
tiealth and the environment associated with each management alternative must be explored The
presence of metal and organic contaminants in MSW contributes significantly to the potential
risks and damages associated with managing MSW. While past studies have characterized metal
and organic contaminants in MSW, there is not a significant amount of studies available to MSW
managers to evaluate these data and draw practical conclusions when deciding between waste
management options.
The purpose of this report is twofold: 1) to summarize the current literature pertaining
to the presence of metals and organics in MSW; and 2) to assess the potential impacts that these
contaminants may have on select MSW management strategies. These impacts may include:
reductions in the effectiveness of the management technique; negative characteristics of products
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to EPA
The studies and reports reviewed for this report indicate that a variety of
orgamcs are present in fractions of MSW. WhileTe metals facto Sly
" "* "'"ber/leaU.er £2
^ C0ntributt chromiun'
°f
The paper fraction contributes lead, manganese, mercury, copper, and zinc; and
The glass fraction (including ceramics) may contain chromium and zinc.
lead,
Organics present in MSW include pesticides, herbicides, PCBs, VOCs, and SVOCs In
general organics data only were available for MSW landfill leachate, which does not todfcaS
6om which fractton the organics originated. However, one study i
S? f Tr fl^"L ^ P**** °f *"» """to*"* ^
jtnnlt of resadual pesucute, inks, and press cleaner associated with
l
The MSW management options examined include: recycling of
: "d
for farther research are summarized generally below.
Recycling
Sed onK!!tentture.«vfcw» ««J conversations with representatives of industry
rto! f880^0118' "vironmenoU, and research group, iixli^
presence of metals and orgamcs in commonly recycled municipal wasteTsuch as paper
and glass generally do not negmively impact recycling processed NeverfS
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these constituents in recycling process feedstocks can affect the characteristics of the wastes,
effluents, and emissions generated during recycling operations. Available data, however, indicate
that the presence of metals and organics generally is associated with feedstock contaminants
(such as carbonless carbon paper which can impart PCBs), as well as labels, glues, and fines,
rather than the commodity being recycled.
Composting
Metals and organic compounds are present in MSW, and therefore become part of MSW
compost The concentration of metals and organic compounds in MSW feedstock can be
reduced, but not entirely eliminated, through pre-processing or collection of source-separated
organics. Examples of pre-processing include removal of undesirable materials (such as
household hazardous wastes, metals, toxic non-biodegradable substances, rubber). In addition,
to some degree, the retention of toxic materials in the compost also can be altered through the
composting method (e.g., low pH and low oxygen content increase metal solubility, facilitating
metal removal from compost).
Human health concerns exist during composting processes. The hazards encountered are
largely a function of the composition of the MSW. Potential hazards for workers include:
emissions of organic compounds, pathogens, bioaerosols, trace elements, and other hazardous
substances (e.g., asbestos, explosive substances, corrosive materials, caustic wastes). Lead is the
primary metal of concern in composting operations and may be present at concentrations above
the No Observed Adverse Effect Level (depending of the nature of the feedstock). Certain
persistent organic compounds (e.g., particular pesticides, PCBs, and PAHs) also may be found
in MSW compost at low levels. There are limited data on the effects of MSW compost on soil,
microbiota, and the food chain (available studies generally are inconclusive and additional
research may be needed).
Waste-To-Fuel Processes
Research indicates that preprocessing to remove metal laden objects prior to combustion
will significantly reduce metal concentrations in combustion process emissions and residue
streams. In addition, removal of aluminum and ferrous metals, batteries, and glass/grit can
improve combustion efficiency, and may reduce ash volumes and emissions of many acid gases.
The fate of metals that enter the combustion process will be determined by: 1) their type,
concentration, particle size, and volatilization temperature; 2) the chlorine concentration in the
feedstock; and 3) a variety of operating and design parameters of the combustion chamber and
associated air pollution control devices. Research indicates that, in general, metals with high
volatility temperatures will leave the combustion chamber in the bottom ash, while those with
low volatility points will wind up in the fly ash after vaporizing, then condensing either
homogeneously or heterogeneously on the surface of entrained ash particles. An examination of
research on the levels of toxic metals and organics in municipal waste combustor ash reveals that
concentrations vary significantly from sample to sample, and from study to study. Lead and
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cadmium appear most frequently in the. literature as the metals likely to cause the ash to fi»i
TCLP teste, alfcough other metals are found in varying concentration/ SSTcottitenK 2
generally found in ash in extremely low concentrations.
Parameters that affect the destruction of organics undergoing combustion are the type of
organic compound and the concentration of the organic constant in the waste stream oSier
parameters, such as exit temperature and residence time, do not appear to impact
efficiency within customary operating ranges. Dioxins and Furans can be formed <
°f increased foulinS of *« boa* tubes k those municipal solid waste
w nCTate Steam< n° research Was found » ^^ *« *• Presence 5
metals m MSW impeded the operation and maintenance of MSW combustion equipment HC1
as well as other acid gases can cause significant corrosion to combustion and APCD equipment.'
m*~M?U'?*! T t°'thiul01 is a developmental stage process that converts lignocellulosic
material to glucose through acid or enzymatic hydrolysis, then converts the glucose to ethanol
^ iT'*?!!?011',. N°rescarch has "^n identified » suggest that the presence of metals in MSW
would impede the effectiveness of either acid or enzymatic hydrolysis. Available evidence
*• MSW ^ proceed through *
Potential impacts of toxics in landfills include impacts on landfill performance and
risks to human health and the environment due to^oncentrations of STX*E
and landfill gases. Toxics m landfilled MSW may remain in the landfill or be releasedtole
^°± T°tadllZatl011' fcgWve dust> ^ ^^ «» «»«^»» « «° 8«)und and surface water
v,a landfiU leachate Tne behavior of toxics in landfilled MSW is inf^ncedTyTv^e^
charactcristics of *e 1«°dfiU«l waste, environmental conditions at the
> t°p0grvhy> "^ ny^geotogic conditions), as well as landfill operating
There is little data on the effect of toxics in MSW on landfill liner materials Some
studies have indicated that organics may react with geomembranes and cause brittleness 'and that
^£^A*XI**£a>>OU*, ?* *bovc normal MSW concentrations) may cause clay liner
shrinkage and cracking and increase landfill permeability. In addition, metal and organic
particulates may cause clogging of leachate collection/removal systems. Corrosion of landfill eas
collection systems by landfill gases (including hydrogen sulfide) also has been reported.
Emissions or releases of potentially harmful organic compounds and metals in landfill gas
and leachate also may pose a potential threat to human health and the environment Human
health risks are greatest for those who live in close proximity to landfills and are dependent on
XIV
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•ound water from shallow aquifers for their water supply. If present in sufficient quantities and
>le to migrate into buildings, LFG can pose an immediate threat of fire or explosion.
iiture Research Needs
As part of a September 21, 1993 workgroup convened to review and provide comment
n the first draft this document, attendees also were asked to identify priority areas for future
•search regarding the effects of toxics on MSW management options. In the process of
eveloping this document, EPA and it's contractor also identified a number of areas in which
Iditional future research would be valuable. These future research needs were related to:
General MSW management issues (e.g., household hazardous waste and source reduction
initiatives);
Recycling issues (e.g., recycling of batteries, metals, and special wastes, materials
handling and workerAndustrial exposure in recycling processes);
Waste-to-fuel issues (e.g., atmospheric emissions from MSW combustors, environmental
half-life, environmental characteristics of MRFs, emissions characterization for various
waste-to-fuel processes, and other new waste-to-fuel technologies);
Composting issues (e.g., biological process controls and monitoring, bio-aerosols,
comparisons of secondary materials and virgin products; and compost risk analyses); and
Landfill Issues (e.g., landfill gas emissions and landfill reclamation projects).
xv
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0 INTRODUCTION
According to the United States Environmental Protection Agency's (EPA's)
Characterization of Municipal Solid Waste in the United States: 1992 Update," approximately
>5 million tons of municipal solid waste (MSW) is generated each year.1 While the
imposition of MSW varies for different times and locations, a summary of "typical" MSW
stribution is presented in Table 1.
TABLE 1. COMPOSITION OF MUNICIPAL SOLID WASTE1
Material Percent (by weight)
Paper and Paperboard 37<*
Yard Wastes 17-9
Plastics 8'3
Metals 8'3
Wood 6'3
Glass 6<7
Food Wastes 6'7
Other Wastes 8-3
=======
iach material category found in the U.S. MSW stream may be further characterized as follows:
Paper and Paperboard: This category of waste consists of: 1) high-grade printing and
writing paper; 2) news print; 3) corrugated cardboard and paperboard; and 4) tissue and
towel products. The largest paper product waste subcategory in high-grade printing and
writing paper waste that contributes roughly 24 million tons, approximately 12 percent
of the total paper and paperboard stream, annually.
Yard Waste: This category is comprised of wastes from landscaping and lawn care
activities, yard waste has been banned from many landfills in the U.S.
Plastics: Plastic in MSW is present in both durable and nondurable goods, and consists
of the following materials: 1) polyethylene terephthalate or PET (e.g., soft drink
beverage bottles); 2) high-density polyethylene or HDPE (e.g., unpigmented beverage
or milk containers); 3) polyvinyl chloride or PVC (e.g., clear "squeeze" bottles and
piping)' 4) low-density polyethylene or LDPE (e.g., plastic film bags); 5) polypropylene
-------
,V nrth * 0r,clTes): 6> Pol^tyrene or PS (e.g., clear tableware o,
cups); and 7) other or specialty plastics.
Metals: Metal waste in MSW is primarily comprised of durable goods such as
refngerators, washers, dryers, metal furniture, and electronic components. While a large
number of steel and aluminum cans are discarded, the individual weight of these
materials minimizes the contribution of the cans to the municipal waste stream The
composition summary provided above does not include the metal waste stream from large
industrial sources, such as construction industries.
Wood: Wood waste primarily results from the disposal of durable goods, such as
building and construction materials.
Glass: Four basic types of glass are found in the U.S. MSW stream: 1) soda-lime glass-
2) lead glass (lead crystal); 3) borosilicate glass; and 4) specialty glass. Glass waste is
a result of nondurable goods (such as containers) and durable goods (furniture
appliances, and electronics). v ""mure,
Food Waste: The food waste stream consists of uneaten food waste as well as food
preparation wastes. Food preparation wastes include both biodegradable (i e nankins
and paper towels) and non-biodegradable materials (i.e., packaging with foils and waxes).
Other Wastes: For the purpose of the waste composition summary provided above
Other Wastes includes materials such as rubber and leather, textiles, and miscellaneous
inorganic materials (fines and debris, such as concrete)
Many alternative waste management practices and strategies are available to manage the
^ge quantities of MSW generated every year. These management alternatives fnclude
recychng, composting, waste-to-fuel/energy recovery, and landfilling. In choosing the best
^hT.ageTi Strate?y °r combination of management alternatives, potential impacts to
human health and the environment must be explored. The presence of metal and Vrganic
contaminants in MSW contributes significantly to the potential damages associated with
paging MSW. While past studies have characterized metal and organic oooiaSn^I
MSW, there is not a significant amount of studies available to MSW managers to evaluate these
data and draw practical conclusions when deciding between waste management options.
The purpose of this report is twofold: 1) to summarize the current literature pertaining
to the presence of metals and organics in MSW; and 2) to assess the potential impactsfoat these
contaminants may have on select MSW management strategies
-------
0 CHARACTERIZATION OF METALS AND ORGANICS IN MSW
The presence of metals and organics in fractions of MSW may affect the way in which
[SW can be effectively managed. Identifying and analyzing the potential impacts that may
•suit from the presence of these contaminants in MSW may provide justification for source
Auction initiatives to remove metals and organics from the MSW stream. Metals and/or
rganics may inhibit the efficacy of a waste management option or may present significant
atential risks to human health and the environment.
A literature review was conducted to identify studies that quantify the presence of metals
id organics in samples of MSW and in specific waste fractions (i.e., paper, plastics). The
-ports studies, and articles identified through this literature review are described below. It
£uld'be noted that some of the studies presented pre-date the Resource Conservation and
ecoverv Act (RCRA) and/or the 1984 Hazardous and Solid Waste Amendments (HSWA),
PA's Agenda for Action, state waste management mandates, and the national surge in source
sduction and recycling programs.
For purposes of this study, the investigation of evidence of the presence of metals and
•rganics in MSW included those constituents presented in Table 2. Many of these constituents
re or may be, potential carcinogens to humans and many are regulated under current
tivironmental statutes. Such regulations include the Resource
RCRA), Comprehensive Environmental Response, Compensation,
he Clean Air Act (CAA), and the Clean Water Act (CWA).
TABLE 2. LIST OF CONSTITUENTS CONSIDERED IN THIS REPORT
Aluminum
Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Chromium
Copper
Lead
Selenium
Thallium
Vanadium
Zinc
Acetone
Benzene
Chloroform
DDT
Dichloromethane
Ethylenes
Formaldehyde
Glycol ethers
Hexachlorohexane
Hydrogen peroxide
Methylene chloride
Naphthalene
Phenols
Phthalates
Polychlorinated biphenyls
Tetrachloroethylene
Toluene
1,1,1-trichloroethylene
Xylenes
-------
2.1 Studies of the Presence of Metals in MSW
As part of the 1992 WASTE Program study conducted at the Mass Burn MSV
incinerator ,n Burnaby, B.C., Canada, incinerator feed materials (i.e., MSW) were characterize,
with particular emphasis on the trace metals distribution in waste stream components
Throughout the last week of June, 1991, field samples were obtained, sorted, screened, £ dri«
m the field sub-sampled, and preserved for laboratory analysis of trace metal content am
leaching potential. The samples were tested for a variety of metals, including aluminum
antimony, arsenic, boron, barium, beryllium, cadmium, chromium, copper, iron mercurv
manganese, nickel, lead, selenium, tin, and zinc. These results indicate at leit a smat
concentration of each of these metals is present in all of the fractions of MSW tested 2 Since
the composition of MSW varies greatly, these data may not accurately reflect the distribution
of metals in any specific domestic MSW stream.
Newspaper - A Mainr Contributor to the MSW Stream riQflQ)
In a 1989 study, daily and Sunday newspapers were analyzed for organics and heavy
metals. Newspapers were purchased at a convenience store each day for one week and sent to
two separate laborator.es for chemical analysis. The daily newspapers were shredde?
composted, and subjected to a series of analyses to determine the organic and inorganic
constitiients. One Sunday paper was analyzed in this method and a Jond was STr
dioxin/furan. The papers also were subjected to an Extraction Procedure (EP) Toxicity test and
a chemical analysis procedure to analyze for heavy metals. Xylenes, phenols, and toluene were
found in prevalent quantities and manganese, iron, and barium were found to be the most
nZ t '" iy """W"' Recem chang<* i" ^ composition of printing inks and the
papermaking process, however, may limit the application of the results of this study to newsprint
Energy from Waste HOTT)
,h, M ,?" "To19.!7- ^nentitled &"& flam Waste, the National Energy Administration and
the National Swedish Environment Board divided Swedish household MSW into eight fractions
and found that the largest sources of metals (in terms of weight) in the MSW stream were:4
cadmium - metals;
chromium - rubber/ leather, glass, and metal fractions;
mercury - metal, and rubber/leather fractions;
lead - metal and rubber/leather fractions; and
zinc - rubber/leather and metal fractions.
-------
_ ir Component of MSW to the Heavy M«*al Content of MSW and
hmicipal Wast* Combiistor Ash (1939)
This Society of the Plastics Industry report was developed through a review of the
terature on the heavy metal content of the various fractions (e.g., paper, plastics, rubber) of
1SW and calculation of the portion of each metal that the plastics component contributed to
1SW Scientific and technical literature was identified by a computer search. The formal
-arch was supplemented by field interviews of representatives from other resources (e.g.,
ladmium Council, Lead Industries Association and various other resources).
Most of the findings provided in the report are based on municipal waste generated in
weden However, claims made by the authors of the report indicate that the Swedish heavy
ictal analyses are relevant to the U.S. General findings support evidence that lead and zinc are
ound in higher concentrations in the metal fraction of MSW and zinc and chromium are found
n higher concentrations in the rubber/leather fraction of MSW.5
1.2 Organic Toxic Studies
Other studies have been conducted on the residuals associated with MSW management.
[Tiese include MSW landfill leachate and MSW combustor ash. While not identifying the
ractions of MSW from which metals and/or organics originate, these studies offer insight into
vhich organic constituents generally are present in MSW.
Summary of Da*a »" Municipql Snlid Waste landfill Leachat?
A 1988 report by U.S. EPA, Office of Solid Waste (OSW) entitled Summary of Data on
Municipal Solid Waste Landfill Leachate Characteristics examined data from six independent
studies of MSW landfill leachate. These studies together represent an analysis of leachate rrom
83 landfills.6
Of the total 275 constituents for which analyses were performed, only 89 organics (32
percent) were detected. Organics which were sampled for included pesticides, herbicides,
polychlorinated biphenyls (PCBs), volatile organic compounds (VOCs), semivolatile organic
compounds (SVOCs), and other organics.6
-------
2.3 Summary
The *tudies *"
-------
.0 POTENTIAL EFFECTS OF TOXICS ON RECYCLING
.1 Introduction
Recycling is defined as the "result of a series of activities by which materials that would
ecome or otherwise remain waste are diverted from the solid waste stream for collection,
eparation, and processing, and are used as raw materials or feedstocks in lieu of, or in addition
o, virgin materials in the manufacture of goods sold or distributed in commerce, or the reuse
>f such materials as substitutes for goods made from virgin materials".
Metals and organics have not routinely been identified as a concern in recycling
)rocesses Metals and organic contaminants are found in only trace amounts in recyclable
,roducts such as paper, plastic, and glass, and generally do not adversely effect recycling
Accesses nor the integrity of the resulting recycled content product. However, the presence of
netals and/or organics in recycled MSW fractions may contribute unwanted or negative
:haracteristics to the wastes and other byproducts associated with the recycling processes.
3.2 Recycling of Paper
3.2.1 Presence of T>*ics in Discarded Paper
Discarded paper and paper products may contain metals and organic chemicals, including
dioxins furans, and chloroform. Metals generally are present in very low concentrations (in the
parts-per-billion range) and result from either residual solvents from printing operations or the
pigmenting agent within the ink. Tables 3, 4, and 5 present the results of three studies that
determined the presence of organics and metals in consumer paper products and discarded paper
products found in MSW.
The results of a study conducted by Sussman (1989), in which newspaper was analyzed
for trace organic compounds, found that five of the seven trace compounds found in the paper
were solvents (including methylene chloride, acetone, toluene, ethylenes, and xylenes)^
According to the report, these five compounds were most likely associated with the inks and
press cleaner residuals on the paper. Of the other organics found, hexachlorocyclohexane, a
pesticide, was likely a residual from the papermaking process. The phenol found in the analysis
also was thought to be a residual from the papermaking process. While heavy metals, such as
barium, cadmium, chromium, copper, iron, lead, manganese, mercury silver, and zinc were
detected, EP Toxicity test results indicated that metals did not leach from the newspaper at levels
above the current hazardous waste regulatory threshold.3
Table 4 presents an analysis of the metal content of paper and paperboard from Swedish
household refuse conducted by Constidine. While most of the findings presented in the report
were based on Swedish MSW, the authors claim that comparisons indicate that the Swedisn
heavy metal results are relevant to U.S municipal waste.5
-------
TABLE 3. DAILY NEWSPAPER ORGANICS ANALYSIS3
Parts per Billion
Organics
• _—
Methylene Chloride
Acetone
Toluene
Ethylbenzene
Xylenes
Hexachlorocyclohexane
Phenols
Daily
~~— — — — ^ _ __ __ ___ __
94
230
130
22
130
23
1100
Sunday
— • __
69
630
1800
480
2300
23
1000
TABLE 4 HEAVY METAL CONTENT IN PAPER AND CARDBOARD FOUND
IN SWEDISH HOUSEHOLD REFUSE (MG/KG OF DRY SOLIDS)*
Cadmium Chromium Mercury Lead
Paper and Cardboard 0.23 7.0 o 09
As part of the WASTE Program study described in Chapter 2, the major sources of trace
ndfied' aS Wdl « *e chemical "mSn^
Stfeam COmP™' P^"-t results S? this study
frcw u "** levels Of "" metals tested for i" the Paper
traction of MSW. In summary, the data indicate that:2
Concentrations of cadm.um ranged from 0.001 mg/kg for glued magazine paper to 1 7
mg/kg for residual m,xed paper. For purposes of comparison, the toxicity value for total
cadmium is 40 mg/kg (based on ingestion of contaminated soil by a 16 kg child 5 year
exposure duration and averaging time, 365 day/year exposure frequency, 200 mg/day
ingcsiionj ,
Concentrations of chromium ranged from 1 .3 mg/kg for glued newsprint to 215 mg/kg
for unglued color newsprint. For purposes of comparison, the toxicity value for total
chromium is 400 mg/kg [(based on the health-based number for chromium (VI) which
assumes a 16 kg child, 70 year averaging time, 365 days/year exposure frequency 5
exposure duration, 200 mg/day ingestion rate, and a risk level of 10*)]-
-------
H
U
o
2S
w &
\O '—i •—•
M
fa
J
fa
. O
IT)
fa
H-3
CO
<
H
-------
fc
o
H
U
H H
HH r/3
C«
O W
C/J
10
-------
Concentrations of lead ranged from 0.005 mg/kg for book paper to 229.4 mg/kg for
residual mixed paper. For purposes of comparison, the toxicity value for total lead is
500 mg/kg [based on a U.S. EPA/Office of Solid Waste and Emergency Response
(OSWER) Policy Directive for lead in soils];
Concentrations of mercury ranged from 0.1 mg/kg for laminate paper and corrugated
brown paper to 2.9 mg/kg for not glued black and white newsprint. For purposes of
comparison, the toxicity value for total mercury is 20 mg/kg (based on ingestion of
contaminated soil by a 16 kg child, 5 year exposure duration and averaging time, 365
day/year exposure frequency, 200 mg/day ingestion); and
Concentrations of zinc ranged from 8 mg/kg for glued newsprint to 208 mg/kg for office
and composition paper. For purposes of comparison, the toxicity value for zinc is 500
mg/kg (based on ingestion of contaminated soil by a 16 kg child, 5 year exposure
duration and averaging time, 365 day/year exposure frequency, 200 mg/day ingestion).
3.2.2 Paper Recycling Processes
In 1990, approximately 29 million tons of paper and paperboard were collected for
recycling. This represents an overall recovery rate of 33.4 percent.7 Figure 1 outlines the basic
process involved in turning recovered paper into a new paper product. This process can be
broken down into 5 main steps: collecting and baling, repulping/deinking, screening, bleaching,
papermaking, and drying. However, not all mills practice deinking and bleaching procedures.
Some mills, such as direct repulping mills, generally produce lower quality paper products that
do not require high brightness or whiteness.
Cotecting
and
Balng
»^
Repulping
and
Cleaning
Deinking
Sold Waste,
Wastewater,
Air Emissions
Deinking Sludge,
Wastewater,
Air Emissions
Screening
^^
Paper
Mttktan/
Drying
J \ I
Sludge Wastewater, Wastewater,
Air Emission* Air Emissions
figure 1. Flow Diagram of the Paper Recycling Process.
Paper recycling starts with collecting, sorting, and baling of the collected papers (e.g.,
Id newspapers, recovered office paper, etc.). The baled paper is sent to a deinking facility for
^pulping and cleaning. In the pulper, paper is immersed in water in a deinking vat and torn
11
-------
apart by rotating steel blades. Deinking methods involve various mechanical or chemical
techniques (also known as washing and flotation type deinking). Deinking reduceTcW
' dlSSiPate$ d*°ical addidVeS- ""* repulped fiber solution
' - * repupe er solution g fr<»n the
deukmg process is approximately 1 percent fiber in the form of a slurry. Wastes Lociated
with the deinking process include deinking sludge, wastewater, and emissions."*10
PrOCeSS> ink P***16* *" removed from fibe« "y means of a
PrOCeSS' Mechanical <«»«!«» systems separate adhesive* and
filler, ^ aa^°a d!in^ng PrOCeSS> a °hemical digestion P™0655 is used to remove inks,
fillers, and coatings A flotation deinking system requires surface active substances for
JfSS.JL"1' ™ *"" C0lleciin8- the ink p**0168' M weu M for ****« *» ** «
the air bubbles. This process is physio-chemical, but is influenced by system eneineerine
parameters such as fluid dynamics and air bubble generation (size and amount). Because of the
current growing demand for better grades of recycled paper and the declining accessibility to
SL^r. t Wattrl many "^ recyding mi"S m moving towards u«ng flotation
processes to demk paperstocks. Unlike washing techniques, which remove only those ink
particles larger than 30 micrometers, flotation also removes approximately 85 percent of the
smaller particles present. Flotation also can cut water usage in half, resulting in a Wh smaller
volume of sludge (ink and washed out pulp) requiring disposal. Howevef, this reducton £
on the nature °f "
aom, ^^ Ch,emical/s that may be used in "«> Process include: caustics, as defiberizing
agents; sod.um silicate (as a stabilizer); hydrogen peroxide (HA) (for ink degradation and
SK T 8,); ^^f^e agents- Aroma^ hydrocarbon solvents suclfas petroleum
naphtha, and chemicals such as 1,2,4-trimethylbenzene, also may be added to the pulpVrs to aid
m the ink removid process. Other deinking chemicals that may be added in the flotation or
washuig stages following repulping include collectors (such as fatty acid soaps), dispersan^
-dull °?T? SUrfaCtaUl °r detergents>. ^ combination "dispersant coUectoTs" or
displactors which are usually proprietary formulations of alkoxylated fatty acid derivatives
Another class of chemicals called "defoamers" often is used to counteract ihe effect of S
surfactant during deinkmg. These defoamers or "thinners" can contain aromatic substances such
rivSlS»X^' n?Phthalfne> CUme"eS> P56"^"1"^, and also other naphthenes and
glycol erters. These chemicals, some of which are considered to be toxic, may be present in
Uie deinking sludge, wastewater, and/or air emissions that are generated as a result of the
GcinJong process.
Chelating agents, such as Versene 100 [Ethylenediaminetetraacetic acid (EDTA)l also
may be added dunng the paper recycling process to inactivate and remove metals from deinked
pulp pnor to peroxide bleaching. Research mdicates that the addition of metal-ion chelant will
have only minimal negative influence on pulp color and cleanliness after washing and/or
12
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Repulped fiber slurry then is pumped into a pulper where debris is screened out. Non-
fibrous contaminants such as dirt, glass, sand, and paper clips are removed by selective
screening or centrifugal cleaning. Fine debris is removed by pressure screens with small
perforated openings or fine flots. Low density contaminants (e.g., plastic, styrofoam, and
coating films) are concentrated in stock-flow vortexes, which are generated in special screens
and reverse-flow cleaners.8-9 The screening process generates a waste sludge material.
Bleaching operations, which may be conducted on some recycled fiber to raise pulp
brightness, can range from less intensive (addition of hydrogen peroxide during pulping and
hydrosulfate at the end of deinking) to extensive (use of a chlorination/hypochlorite or
chloiination/extraction/hypochlorite sequence). The choice of bleaching or brightening agents
is dictated, in part, by the characteristics of the fiber and the final product.7 Wastes associated
with bleaching processes include wastewater and air emissions.
Fiber slurry then is formed into paper. It is sprayed between two fabric belts that
remove water. Paper moves in a continuous sheet at 45 mph. The paper then goes to a steel
roller presser that squeezes it. After pressing, the paper is about 42 percent water. The paper
is then dried further, smoothed and rolled onto reels. This drying stage increases the percent
fiber to approximately 92 percent.9-10
In paper and paperboard making operations, paper machine felts and screens are often
cleaned with solvents to remove "stickies" that can accumulate during the papermaking process
when recycled paper furnish is used. Recycled fiber, in particular, contains residues that can
eventually blind the felts and wire on the paper machine and lead to product imperfections. The
extent to which such solvent cleaning operations occur and the mode of application of the solvent
solution vary widely from mill to mill. The severity of the "stickies" problem at each mill is
strongly dependent on that mill's particular furnish. Volatiles also may be present in paper
machine additives such as defoamers, slimicides and biocides, sizing agents, strength agents,
adhesives, dyes and pigments, binders, pigment fillers, and coatings.7 Wastes associated with
the papermaking process include wastewater and emissions.
3.2.3 Potential Effects of Toxics on Paper Recycling
While there is no evidence to indicate that the presence of metals and organics impacts
the actual paper recycling process, the presence of these constituents can affect the
characteristics of the resulting waste products. Metals and organics present in the recycled paper
stock will, in general, be removed from the stock during the recycling process and appear in the
residuals.
3.2.3.1 Wastewater Characteristics
The characteristics of wastewater from mills using recovered paper vary widely
depending on the type of paper being recycled (furnish), the deinking process employed, pulp
13
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bleaching practices, and final product considerations. In general, the overall wastewater load
from direct repulpmg mills, and recycled paperboard mills in particular, tend to be lower, than
those from mills that must provide additional fiber processing. One report noted that wastewater
flows have decreased significantly over the years for both repulping and deinking operations
while levels of BOD5 and TSS (for deinking in particular) have fluctuated7 Table 6 describes
the overall characteristics of raw wastewater effluent from both repulping and deinking mills
TABLE 6. CHARACTERISTICS OF RAW EFFLUENT FROM DIRECT
REPULPING AND DEINKING OPERATIONS7
Operation
gal/T
avg
BODf
Ib/T avg
TSS
Ib/T avg
Current Direct Repulping
Operations (1988-89)
Deinking Raw Effluent
Characteristics
(1988-89)
140-7350
10,000-30,000
2518
17,100
8.8-39.7
50-256
22.7
128
1.7-44.5
60-990
15.7
468
New Source Performance Standard (NSPS) limitations for effluent from recycled fiber
paperboard operations (40 CFR 430, Subpart E) range from 2.8 to 4.2 Ib/ton for biological
oxygen demand (BOD) and 3.6 to 4.6 Ib/ton for total suspended solids (TSS). However State-
issued discharge permits often are more restrictive than technology-based Federal standards
especially when discharges enter low-flow or water-quality limited streams. A number of mills
also are limited in mass loadings for additional parameters such as heavy metals PCPU
pentachlorophenol, and trichlorophenol.7
Aerated stabilization basins (ASBs) and activated sludge treatment (AST) are used to
reduce BOD and potentially toxic chemicals. NCASI examined the biological treatment systems
of six direct repulping and six deinking mills and found that BOD removal efficiencies ranged
from 95 to 98 percent for repulping mill effluents and 89 to 98 percent for deinking mill
effluents.7 6
The NCASI (1991) report noted that when EPA initiated its effluent guideline review
almost fifteen years ago, treated and untreated effluents were collected from 60 facilities and
analyzed for 64 chemicals whose presence was suspected based on an earlier screening stucy
Table 7 presents data for those constituents which were detected by EPA in the effluent guideline
study. EPA promulgated specific effluent limitations for the industry only for tri- and
pentachlorophenol contained in slimicides (plus zinc for facilities using zinc hydrosulfate
bleaching). However, EPA is revisiting the effluent guidelines for the paper industry Tie
NCASI study shows that the differential between the influent and effluent values also indicates
the relative effectiveness of the treatment techniques. Concentrations of contaminants in treated
effluent was found to be significantly lower than those in untreated raw wastewaters 7
14
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TABLE 7. CHEMICAL IDENTIFIED IN EFFLUENT GUIDELINES STUDY7
Mill Type
Deink Fine
Deink Newsprint
Deink Tissue
Tissue from Recycled
Paper
Paperboard from
Recycled Paper
Chemical
Chloroform
Naphthalene
Pentachlorophenol
Tetrachloroethylene
Toluene
Trichlorocthylene
PCB 1242
Lead
Butyl Benzyl Phthalate
Cyanide
Trichlorophenol
Chloroform
Naphthalene
Pentachlorophenol
Phenol
PCB 1254
PCB 1260
Ethylbenzene
Phenol
Diethylphthalate
Tetrachloroethylene
Zinc
Trichlorophenol
Bromoform
Pentachlorophenol
Phenol
Butyl Benzyl Phthalate
Di-n-Butyl Phthalate
Diethyl Phthalate
PCB 1248
Lead
Zinc
# of Samples
3
3
3
3
3
3
3
3
3
3
6
6
6
6
6
6
6
9
9
9
9
9
18
18
18
18
18
18
18
18
18
18
Avg Influent
(Mg/L)
4190
142
15
95
58
493
3
149
5
1560
48
1367
48
38
119
1
1
27
77
26
74
1316
360
40
356
204
61
32
183
9
443
1811
Avg Effluent
0
-------
i «™ , y ^e '"^totion of metals in the effluent from three recycled paper mills in
1979 also was performed. This study indicated that treatment of raw wastewaters has a
significant effect in reducing the concentrations of metals in plant effluent7 These data
presented in Table 8, are somewhat dated and may not accurately represent the current
concentrations of metals in process wastewater.
TABLES. RESULTS OF NCASI STUDY OF METAL IN
RECYCLED FIBER MILL EFFLUENTS7
Mill A
Metal
Chromium
Copper
Nickel
Lead
Zinc
Mercury
=====
n/a = not analyzed
Mill B
Raw Waste
42
34
4
100
1200
0.3
^^SS^^B^S^SS^SS^S
Effluent
G*g/L)
<6
10
4
6
53
0.2
Raw Waste
(*»g/L)
120
44
9
170
910
n/a
— —
Effluent
(Mg/L)
5
7
8
9
29
n/a
J.TUU i
Raw Waste
(Mg/L)
430
330
27
390
580
n/a
ix
Effluent
G*g/L)
— ^— — i^— ^-™_
18
52
11
16
52
n/a
Several acute toxicity bioassays were carried out on ten deinking tissue mill effluents (a
total of 127 bioassays), three deinking fine paper effluents (18 bioassays), and one deinking
newsprint mill effluent (18 bioassays). Acute responses (LC50s) were found in 33, 1, and 6 of
the tests of tissue, fine paper, and newsprint mill effluents, respectively. Seven-day chronic
bioassays with Ceroqaphnia duMi were conducted on ten deinking tissue (38 bioassays) three
deinking fine (8 bioassays), and one deinking news (9 bioassays) mill effluents. The average
chronic values ranged from 6 to 87 percent, 21 to 100 percent, and 15 percent, for the tissue
fine and news mills, respectively. Seven-day chronic bioassays with fathead minnows also were
conducted on ten tissue (38 bioassays), three deinking fine (6 bioassays), and one deinking news
(9 bioassays) mill effluents. The average chronic values ranged from 17 to 100 percent 17 to
55 percent and 19 percent, for the tissue, fine and news nulls, respectively. However NCASI
(1991) noted that the majority of the acute and chronic bioassay responses of potential' concern
to regulatory agencies either were transient in nature or successfully addressed in subsequent
efforts to eliminate the causative agents through improved treatment processes.7
16
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3.2.3.2 A^r Emissions
Limited data on emissions to air from recycled fiber mills is available. Potential air
emissions include: VOCs resulting from the use of paper machine cleaning solvents and deinking
solvents; chloroform from bleaching sequences using sodium hyppchlorite; and emissions from
deinking sludge burning. Estimates of air emissions from direct repulping and deinking
operations were unavailable at the time the NCASI report was completed in 1991.7
Chloroform emissions from deinking pulp mills that use sodium hypochlorite in their
bleaching process may be of concern. Future trends in recycled fiber bleaching, as well as
bleaching practices currently used at several deinking facilities, are more likely to adopt a
sodium hypochlorite-free bleach sequence. Consequently, chloroform emissions from bleach
sequences that may include such reductive or oxidative bleaching reagents, such as sodium
hydrosulfate, formamidine sulfonic acid, hydrogen peroxide, ozone, and oxygen, are expected
to be reduced significantly, if not eliminated altogether.7
The emissions resulting from the use of solvents as felt cleaners and wire washers depend
largely on the type of solvent used. The cleaning solvents may contain volatile components such
as 1,1,1-trichloroethylene, 1,2,4-trimethylbenzene, cumene, or glycol ethers, or a variety of non-
volatile, non-VOC containing proprietary chemicals. Approximately 97 percent of the solvent
applied to the paper machine felts at a deinking facility is discharged with the wastewater, the
remaining 3 percent is exhausted through the paper machine stacks into the atmosphere.7
Quantitative estimates of chemical emissions from paper and paperboard making
operations are not currently available. However, based on the 1988 and 1989 emissions reported
by various deinking and direct repulping mills under EPA's Superfund Amendment
Reauthorization Act (SARA) Section 313, some of the chemicals of potential interest can be
identified. Emissions of some of the chemicals may have resulted from papermaking operations
as well as repulping/deinking operations. Ammonia is the most common SARA 313 chemical
emitted from these mills. Other chemicals found in these emissions, including 1,2,4-
trimethylbenzene, cumene, dichloromethane, formaldehyde, glycol ethers, naphthalene, 1,1,1-
trichloroethylene, and xylene, are most likely associated with defoamers, felt cleaning solvents,
slimicides, and chemicals used for deinking and coating operations.7 These data are summarized
in Table 9.
Chemicals applied during pulping, deinking, bleaching, or papermaking operations that
are not volatilized in the mill and are not destroyed or converted to other chemicals are
discharged to the mill waste treatment system. A NCASI study model indicated that for
recycling mills, chloroform is the only pollutant of current concern that undergoes significant
volatilization in treatment basins.7
17
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TABLE 9. ESTIMATES OF 1988 AND 1989 SARA SECTION 313 TORM R
CHEMICAL EMISSIONS FROM DIRECT REPULPING/DEEVKING
AND PAPERMAKING OPERATIONS7
8
Discharge to air*
Mill Code Pulp TPD Mill Type
~AB
AD
AG
AI
AB
AD
AG
AI
AJ
AP
AQ
AR
AS
AX
AB
AD
AG
AG
AT
AU
AB
AG
AAF
AB
AO
AB
AD
AG
AN
700
800
300
400
700
800
300
400
200
300
400
180
125
180
700
800
300
300
100
80
700
300
730
700
420
700
800
300
275
Deinking
Deinking
Deinking
Deinking
Deinking
Deinking
Deinking
Deinking
Deinking
Deinking
Direct
Repulping
Deinking
Direct
Repulping
Direct
Repulping
Deinking
Deinking
Deinking
Deinking
Deinking
Deinking
Deinking
Deinking
Direct
Repulping
Deinking
Direct
Repulping
Deinking
Deinking
Deinking
Deinking
Chemical
1 ,2,4-trimethylbenzcnc
1 ,2,4-trimcthylbenzcne
1 ,2,4-trimethyibenzene
1 ,2,4-trimethylbenzene
Ammonia
Ammonia
Ammonia
Ammonia
Ammonia
Ammonia
Ammonia
Ammonia
Ammonia
Ammonia
Cumcne
Cumene
Cumene
Dichloromethane
Formaldehyde
Formaldehyde
Glycol Ethers
Glycol Ethers
Glycol Ethers
Naphthalene
1,1,1 -trichloroethy lene
Xylene
Xylene
Xylene
Xylene
Ib/vr
1988 1989
101,243
231,745
-
15,369
2,909
6,139
2,150
2,292
13,450
37,470
36,900
2,050
25,200
500
20,248
21,590
-
42,500
6,000
15,000
2,750
58,250
2,821
28,983
18,000
60,746
59,638
-
-
106,000
61,000
130,250
.
2,200
7,900
1,410
3,800
24,000
47,023
41,355
2,050
29,326
.
20,400
21,200
41,600
_
8,000
16,000
.
124,000
88
30,300
12,000
66,100
9,500
28,100
4,290
Ib/ton
1988 1989
0.41
0.83
.
0.11
0.01
0.02
0.02
0.02
0.19
0.36
0.26
0.03
0.58
0.01
0.08
0.08
.
0.40
0.17
0.54
0.01
0.55
0.01
0.12
0.12
0.25
0.21
.
-
0.44
0.22
1.24
.
0.01
0.03
0.01
0.03
0.34
0.45
0.30
0.03
0.67
0.08
0.08
0.40
0.23
0.57
.
1.18
0.00
0.12
0.08
0.27
0.03
0.27
0.04
includes fugitive and stack emissions
18
-------
3.2.3.3 Solid Waste (Sludpe or Fibercake)
Various chemical aids are used to enhance the disassociation of inks, coatings, and filler
from pulp fibers. These materials, along with the extracted ink, are discharged to the waste
stream in a slurry. Other rejects or contaminants, including plastics, rubber, fiber bundles, glue
balls, sand, dirt, and foil that are removed from the pulp are discharged as a slurry and/or in
thickened form. Paper coating, filler, and added clay removed in the deinking and washing
process typically comprise the largest component of the wastewater treatment sludge.7
Historically, the presence of heavy metals in printing inks was of concern in paper
recycling. However, ink formulations have changed over the past decade to reduce the level of
metals and other toxic constituents that occur in printed paper. Concerns over safety during
manufacturing and printing have led to a decline in the use of lead, chromium, and cadmium in
ink formulations. Copper, barium, and calcium remain common constituents of printing inks.7
Much of the solid waste derived from the processing of recycled paper enters the
wastewater collection system and is removed as sludge from primary classifiers. Biological
treatment of the wastewater produces a waste bacterial sludge as well. The amount of waste
produced is largely dependent on the grade and sorting standards of the paper to be deinked.
Deinked newsprint mills generally produce less sludge than deinked fine paper or tissue mills,
largely because of the differences in the characteristics of the furnish.7
Solids are separated from deinking wastes during wastewater treatment either by gravity
settling or by flotation. The resulting sludge generally is dewatered prior to disposal. Most
mills with secondary treatment combine secondary sludge with primary sludge prior to
dewatering. This is done to relieve problems with dewatering secondary sludge alone.7
Table 10 summarizes analyses of deinking mill sludge data gathered by NCASI from it's
files and publications, EPA documents, and data provided by individual companies. These data
represent chemical concentrations in dry sludges from 8 deink fine mills, 8 deink tissue mills,
and 2 deink newsprint mills. NCASI (1991) concluded that these data illustrated that sludges
from deinking mills generally are comparable or superior in quality to municipal wastewater
treatment sludges.7
Table 11 presents the results of EP Toxicity characterization tests conducted on six
deinking sludges. EP toxicity testing was used between 1980 and 1990 to determine whether
a waste exhibited a hazardous waste characteristic.7
PCBs have been detected in a variety of paper products, largely due to the incorporation
of PCB-containing carbonless copy paper into the recycled fiber stream. The use of PCBs in
carbonless paper was discontinued in June, 1971. Over time, PCB levels in recycled paper
products have decreased. However, concern still remains regarding the potential for gradual
release of PCBs from contaminated sediments in aerated stabilization basins treating effluents
from recycled paper mills. At least five mills still have PCB monitoring requirements in their
19
-------
TABLE 10. ANALYSIS OF DEINKING SLUDGES (IN PPM)7
Parameter
Aluminum
Arsenic
Barium
Boron
Cadmium
Calcium
Chloride
Chromium
Cobalt
Copper
Cyanide
Iron
Lead
Manganese
Magnesium
Mercury
Nickel
Phosphorus
Potassium
Selenium
Silver
Sodium
Sulfate
Sulfur
Total Kjeldahl Nitrogen
Thallium
Zinc
2 ,4 ,6-Trichlorophcnol
2,3,7,8-TCDD (in ppt)
2,3,7,8-TCDF (in ppt)
SSSS^SSS^SSSSS^SE^SSSi^SS^^^SSS
# of sludges I of samples where
samples constituents was
detected
5 5
4/>
2
4-%
3
3f\
3
9 4
6 6
3 3
11 10
21
1
12 12
1 1
4 4
13 11
3 2
3 3
6 6
10 7
5 5
3 3
1 i
J 2
-
•* 1
4 4
4 4
2 2
5 5
1/\
0
13 13
2 1
3 3
3 3
Minimum
concentration
detected
119
nd
nd
11
nd
2700
35
nd
nd
7.5
188
37.3
nd
nd
309
0.02
nd
0.402
202
nd
nd
332
97.2
848
14.2
nd
0.191
nd
7
16
Maximum
concentration
detected
37800
0.03
88
28
7.7
40,600
841
300
21.7
920
188
1,940
880
63
1,890
2.4
85
739
1,085
5.3
3.7
11,828
17,200
8,914
5,918
nd
1,400
140
12
106
nd = not detected
20
-------
TABLE 11. EXTRACTION PROCEDURE (EP) TOXICITY RESULT
FOR DEINKING SLUDGES7
Metals (ppm)
Arsenic
Barium
Cadmium
Chromium
Lead
Mercury
Selenium
Silver
I of sludges
samples
4
4
6
6
6
4
4
4
# of samples where
constituents were
detected
1
3
4
3
3
3
i
3
Minimum
concentration
nd
nd
nd
nd
nd
nd
nd
nd
Maximum concentration
0.001
0.95
0.02
.09
0.248
0.003
0.0032
0.007
nd = not detected
discharge permits, and at least two have specific limits for the discharge of PCBs. However,
reported PCB concentrations for deinking mills generally are below analytical detection limits
of approximately 0.5 ppb.7
Since PCBs have not been used in paper or printing inks for nearly 20 years, a declining
level of PCBs in sludge and effluent was expected. Some recycled paper supplies, particularly
old newsprint, have been largely unaffected by PCB contamination because this type of paper
is unlikely to contain recycled carbonless copy paper. NCASI studied the PCB content of
recycled paper and products manufactured from recycled paper and concluded that the PCB
content of the nation's wastepaper had declined substantially by 1981. Recent data collected
from several deinking mills show levels of PCBs in sludge typically are less than 3 ppm (dry
weight basis) and often are below the level of detectability.7
Recycled paper mill sludge commonly is disposed of in a number of ways, including on-
site landfills, municipal landfills, combustion, land application, and surface impoundments.13
A representative of the American Forest and Paper Association indicated that both EPA Regional
offices and state environmental agencies have been working closely with mills to give sludge (or
fibercake) a Beneficial Use Designation (BUD) based on its utility in landfill capping and
agricultural applications. Several mills already have been permitted to use fibercake in these
applications. For example, the Erving Paper Mill in Erving, Massachusetts has received permits
from both the State and EPA to cap landfills with the fibercake in the clay layer. One landfill
already has been capped using fibercake and another is in process. Land spreading also has been
permitted in Maine and Wisconsin. Specifically, Pope and Talbert in Wisconsin and Scott Paper
in Maine have been permitted to landspread its fibercake. Fort Howard in Green Bay,
Wisconsin has patented a process that pelletizes the fibercake and uses it in fertilizer.12
21
-------
3.3 Plastic Recycling
3-3.1 Presence of Toxics in
Plastics found in the MSW waste stream may contain metals or organics resultine from
toe presence of additives that enhance the perform^ or appearance of ffi^S MeSs
v±7 "f re y SmaliPortion of "* «Mi»ives used today. However, bec^uTof the large
volume of plastics manufactured (almost 60 billion pounds annually) and large volume of
MetT^ ' f, T a£gregate V°1Ume °f metal additives is Prese«' '« discarded Sties
Metals historically have been added to plastics as colorants, heat stabilizers and
srnr rrization r^ ** iubricams- uta* '*****»« *«s£
?T^ °for8amc «" P^« products discarded as MSW. However, organics may
as plastic additives such as tackifiers.13 y
An April 1989 study sponsored by The Society of the Plastics Industry Inc determined
fte, contribution o the plastics component of MSW to the heavy metal contem of MSW S
DlaTticstr^1 ttratUl;e1review- ^ study was Pearly focused on the contributor
plastics to the heavy metal content of the ash from municipal waste combustors Table 12
details typ,cal meul levels in the plastic fraction of MSW. Table 13 presents heavv
content of selected MSW components [polyvinyl chloride (PVC), p^lyethZe (P? and
plastics]. Table 14 shows the fraction (as a percentage) of total heav^ Sfm MS
from p astic. Although the data presented in this table is derived from a study of
prov e " estimate of ^ amount of metals *« may •* found in "
TABLE 12. HEAVY METAL CONTENT IN SWEDISH HOUSEHOLD REFUSE
(MG/KG DRY SOLIDS)5
TABLE 13. HEAVY METAL CONTENT OF SELECTED MSW COMPONENTS (ppm)!
22
-------
TABLE 14. DISTRIBUTION OF METAL CONTENT OF VARIOUS FRACTIONS
OF HOUSEHOLD REFUSE (percent)5
Plastic
Cd
26
Co
1
Cr
5
Cu
2
Hg
10
Mn
1
Ni
1
Pb
5
Zn
1
As part of the WASTE study described in Chapter 2, the major sources of trace metals
in the waste stream were identified, as well as the chemical composition and teachability of the
metals in the various components. The relevant results of this study are presented in Table 15.
The study found that a number of metals were present in the plastic fraction of MSW. In
summary, the data indicate that:2
• Concentrations of cadmium in plastics ranged from 0.09 mg/kg for clear houseware
plastics to 2,195 mg/kg for videotape/film. For purposes of comparison, the toxicity
value for total cadmium is 40 mg/kg (based on ingestion of contaminated soil by a 16 kg
child, 5 year exposure duration and averaging time, 365 day/year exposure frequency,
200 mg/day ingestion);
• Concentrations of chromium ranged from 2.6 mg/kg for household PVC (i.e., food and
beverage containers) to 595.2 mg/kg for white houseware plastics. For purposes of
comparison, the toxicity value for total chromium is 400 mg/kg (based on the health-
based number for chromium (VI) which assumes a 16 kg child, 70 year averaging time,
365 days/year exposure frequency, 5 year exposure duration, 200 mg/day ingestion rate,
and a risk level of 10"6);
• Concentrations of lead ranged from 25 mg/kg for polystyrene food and beverage
containers to 2,479 mg/kg for yellow houseware plastics. For purposes of comparison,
the toxicity value for total lead is 500 mg/kg (based on a U.S. EPA/OSWER Policy
Directive for lead in soils);
• Concentrations of mercury ranged from 0.1 mg/kg for food and beverage containers
made from several types of plastics resins (including PVC, LDPE, PP, and PS) and blue
and yellow houseware plastics to 0.4 mg/kg for non-identified plastic resin food and
beverage containers. For purposes of comparison, the toxicity value for total mercury
is 20 mg/kg (based on ingestion of contaminated soil by a 16 kg child, 5 year exposure
duration and averaging time, 365 day/year exposure frequency, 200 mg/day ingestion);
and
23
-------
g
•- «- 5f 0> O
m CM co ^- o
-------
1
ul
H ~
*
O
H
S
o
W
u
£
0
cocoino^t
p p
d d
p p
d d
OOOpp'-iPpppcSpp
ddddddddddddd
cs
COCN
r-»
0>
CN
01
0) "O
II
^ ^
§1
•*- £
o .=
c o
1
« a
S 1
25
-------
Concentrations of zmc ranged from 3 mg/kg for PVC food and beverage containers to
1 132 mg/kg for color plastic film. For purposes of comparison, the toxicity value for
total zinc is 500 mg/kg (based on ingestion of contaminated soil by a 16 kg child 5 year
exposure duration and averaging time, 365 day/year exposure frequency, 200 ing/day
incsiioii .
and fatet of ££±' T^"* ^ "* ^i"" lnS™te °f Tecnnology- investigated the sources
and fates of lead and cadmium contained m MSW and resource recovery ash (RRA) residuals
The study employed both a materials How method and an empirical method of determining ash
contammant levels. The study used published data of resource recovery p.ant em"8 ah
residues, and leachates. The authors noted that multiple sources were used because of Te'lack
of peer review of much of the published data. Plastics (a.ong with pigments) were identified I as
the major sources of lead and cadmium in the combustible fraction of MSW Table 16 shows
discards''' Wdght Md Percentage' of Iead and cadmium in the Plastics 'fraction of MSW
TABLE 16. AMOUNTS OF LEAD AND CADMIUM IN PLASTICS FRACTION
OF MSW DISCARDS, 198614
,h K K,' V StUdy by the U'S' DePartment °f the Interior, Bureau of Mines evaluated
he combustible fracuon of MSW to characterize the various combustible components and 'o
identify the principle sources of elements that may exhibit corrosive characteristics Pos"ib e
T^t f , 'T Chr°miUm' C°PPer' lead' nicke1' and zinc were ide«ified through an
analysis of large-volume contributors and an estimate of the total annual usage for the products
found m MSW. Table 17 presents the elemental analysis of the plastics fraction oHhe MSW
bearded asaMSWm' "^ '"" "^ ^ aCCUratdy ^ the CUrrent makeuP of Plastics
TABLE 17. ELEMENTAL ANALYSIS OF PLASTICS
SEPARATED FROM MSW (ppm)15
The primary metals found in plastics disposed of as MSW are cadmium and lead
However, recent state-level legislation based on the CONEG packaging model has greatly
26
-------
reduced the use of metals in plastic packaging manufactured today. Many colorant producers
have begun to phase out or have completely eliminated heavy metals in their products. Table
18 presents some substitute products that replace lead- and cadmium-based colorants. However,
because of the advantages associated with the use of metals as additives, including cost and
process-specific advantages, metal additives are not expected to be completely eliminated
throughout the industry.16 No information was available regarding potential impacts of these
substitute additives on human health and the environment.
TABLE 18. SUBSTITUTE PRODUCTS THAT REPLACE LEAD- AND
CADMIUM-BASED COLORANTS17
Inorganic Organic Dy«
Nickel Titanium Monoazo Pyrazolone Derivative
Iron Oxide Monoazo Naphthol Azo Dye
Quinacridone
Pcrylcne
3.3.2 Plastic Recycling Processes
There are two general groups of plastics: thermoplastics and thermosets. Most plastics
used in durable goods and single-service items are thermoplastics. Thermoset plastics are used
mostly in durable goods, but in much lower quantities than thermoplastics. Commercial plastic
items typically consist of a base resin or polymer mixed with adjuvant ingredients. Molded or
extruded items often also contain chemical additives such as heat stabilizers, plasticizers,
colorants, and fillers. Plastics often are fabricated as part of a composite material or item.
Composite films may consist of mixtures of plastics or combinations of plastics with paper or
metal foil.8
Thermoplastic materials can be reheated and reformed (i.e., recycled) several times,
while thermoset materials cannot. This is because the initial heating and fabrication of
thermosets causes permanent chemical changes and subsequent heating can cause degradation.8
Plastics can be recycled using three general techniques: single resin, commingled
(mixed) plastic, and chemical recycling or monomer recovery. The following subsections will
discuss each of the processes in detail and provide a corresponding process diagram of each
technique.
3.3.2.1 Thermoplastics Recvcttne
In thermoplastics recycling, the first step after collection of the recyclables is sorting the
collected plastics into three material categories: HOPE, PET, and mixed plastics (or tailings).
The sorted plastics are shredded into chips of approximately 3/8-inch mesh size. Shredded PET
27
-------
SrTn r r P WPE£d PP fiDm baSC CUPS "" ^ which « n« ™>°ved until
later m the recycling process. The shredding stage often is accompanied by air classification
ma cyclone, to remove loose dirt, paper shreds, and other fines. These fines are couS fa
a baghouse with the waste stream from the air classification being less than 1 percent by weight
l "^ ^ • Figure 2 displays *" process for ™& ™" PET «
As indicated, portions of the process are applicable to PET recycling only
The second stage involves rinsing the plastic chips with a heated aqueous detergent This
removes «y residue left m the original containers (e.g., labels), and disintegrates anyremainkj
paper The wash water is filtered with the filter cake being 1 to 2 percent by weieht ofZ
initial sorted plastic. The filter cake can be expected to contain paper, %£ fL labeTs glut
" container ^ flltered wash water "
H, ^if11!816 resi" PET is ^y^' the washed PET chjPs (wni<* are commingled with
other shredded plastic resins) are reslurried with rinse water and pumped through a hydrocvctone
toseparate the "Ugh," components from the "heavy" component Tne light SmpSSST
S PET CZ St H f ' ^ and rings) make up about 10 ^ "y ^ht "f ^
The^ET^hin? g ^ ^y,.00"1?0"6"" «« individually dewatered and dried thoroughly.
The PET chips are passed through an electrostatic separator, where any aluminum from caps or
nngs ,s removed. Of the electrostatic separator waste, only one third by weighTi
with the other two thirds being PET flake that was separated from the aluminum
aluminum waste stream is about 3 percent by weight of the initial sorted PCT
economically feasible to recover the PET flake from the electrostatic separator We "
aluminum) of *• hy^^ -*- » -luded
, included in the
mnu. J*16 .^ -(°r HDPE) Chips may ** melted and P°ured directly into a mold in
conventional plastics converting processes or extruded into pellets that more closely resemb e
wgm resin feed-stocks for later use. No wastes are generated during this final recycL^ •'
28
-------
Fines
_L_
Baghouse
1
PET Recycling Only
PET Recyclng Only
Air
Classification
^^
Wash
Piter
-
V
Hydro-Cydona
t 1
/astewater y
HOPE/
PP Flake
Fitercake, '
Wastewater
„ Electrostatic
Separator
t Cr*
*
arnica!
PET/ Recycling
aluminum
*• Malt
t
To
"^
Pelettizer
To
Molds
Figure!. PET and HDPE Recycling.
3.3.2.2 Crnninnled (Mixed} Plastics
There are several types of recycling processes for commingled plastics. The processes
roughly fit into four categories: 1) intrusion process based on Klobbie's design; 2) continuous
extrusion; 3) the "Reverzer" process; and 4) compression molding. The differences in the
processes' are in the methods of molding. Each of these processes soften and blend the
commingled plastic flake and creates a heterogeneous product with some degree of
contamination. Because of the heterogeneity and contamination of the mixture, commingled
processes are limited to producing products of large cross section (i.e., lumber), where small
internal imperfections will not significantly alter the mechanical properties of the product.19
Commingled processes are identical to single resin recycling processes, excluding the
steps specific to PET. The distinguishing feature of the commingled process is the attention
given to blending. Most commingled processes have intricate blending techniques to homogenize
the different types of plastics to the maximum degree possible. Commingled plastic recyclers
generally mold the melted plastics immediately after blending. Figure 3 presents the recycling
process for commingled plastics. There are no wastes generated from the final portion of the
process.19
29
-------
Fines
Msttt
To
Molds
Flttsfcaks,
WisUwitsr
Figure 3. Comingled Plastic Recycling.
3.3.2.3 Chemical
In the chemical recycling or monomer recovery of thermosets, the chemical structure of
the thermoset is broken down by hydrolysis or glycolysis. Figure 4
recycling processes for thermosets. Hydrolysis of polyurethane and
^ ' ** Carb°n di°Xide by ^ action of hi«h Pressu* steam
and extracted from the steam and the reclamed polyols are
can be
t0 ,hydrolysis' which creates a ne«d to separate diamine and polyol elycolvsis
s
k r. hours. After cooling and treatment with oxide the polyol n
is filtered to remove insoluble materials and is ready for use.19 mi
30
-------
Hydrolysis
Reactor
•Water
•Disoeyanate
•Carbon Dioxide
Potyoto A
Virgin Polyoto
To Molds
ThsrrooMt
>•
Qlycotysis
Polyols A
Virgin Potyois
To
Figure 4. Chemical Recycling of Thermosets.
PET also can be reverted back to polymers using a chemical recycling process such as
methanolysis or glycolysis, as diagramed in Figure 5. In methanolysis, the polyester chain is
broken down into individual monomers. To achieve this, methanol is added to the PET flakes
under heat and pressure to break the polymer down to its original components,
dimethylterephthalate (DMT) and ethylene glycol (EG). The DMT and EG are purified, then
mixed with virgin DMT and EG, and repolymerized. The recycled PET is indistinguishable
from the original virgin polyester. Methanolysis can remove all colorants and impurities.20
Methanolysis
PET ^_]
Virgin DMT
DMT T
EG ^^
Reactor
• To Molds
Virgin EG
Ethylan* Glyool
To Molds
Figure 5. Chemical Recycling of PET.
31
-------
The glycolysis process breaks post-consumer PET down to very low-weieht
"8 Wlth y'ene glyC0' UndCr Pressure' ™s is the^mL
om™
«° P^uce PET pellets with 25 percent post-consumer
— -
3-3-3 Potential Effects of Tori™ m. pasties R«-vrijnP
The primary wastes generated during the plastics recycling process are solid wastes that
are screened out during shredding and cleaning, and wastewater generated
Chapter 5 of this report, "Potential Effects of Toxics on Waste-To-Fuel Processes •
presents the constituents that may be found in waste streams generated duSe
plastics. Generally, the waste constituents are indication! and result? of
techniques rather than the plastics themselves.18
19
of
TABLE 19. WASTES LIKELY TO BE IN PLASTIC
RECYCLING WASTE STREAMS
Recycling Activity (waste generated)
Air Classification (baghousc collections)
Chip Washing (filter cake)
Chip Washing (wastewater)
Hydrocyclone (wastewater)
Electrostatic Separator (aluminum waste)
labels (paper and plastic)
dirt/dust/fines
labels (paper and plastic)
glue
residue from containers
dissolved glue
dissolved residue
PET
aluminum
Initially, the presence of additives was thought to preclude plastics recycling processes
*™ ^ "* " man resins on
to .
used to obtain varying properties. However, most commonly used and high
such as anfoxidants, now are formulated for compatibility Jong differen
32
-------
and should not cause problems when different plastics are melted and remixed during the
recycling process.
However, two additives have been identified as posing potential problems in the
recyclability of the plastic resins. These additives are tackifiers and ethylene vinyl alcohol.
Tackifiers are added to LDPE film to give shrink wrap packing film its stickiness. These
tackifiers cannot easily be detected and, as a result, films with and without tackifiers are almost
impossible to separate. This can impede the recycling of plastics as the presence of tackifiers
in recycled plastic resins imparts an undesirable sticky quality.21-22
The addition of ethylene vinyl alcohol (EVOH) to PP containers as an oxygen barrier was
once thought to preclude recycling. Today, research has shown that although PP resin is not
immediately recyclable if the EVOH additive is present, the problem can be solved with a minor
modification in the recycling process. Combining rubber rougheners and compatibilizers with
plastic flake from the EVOH-containing bottle allows the manufacture of a recycled PP material
that can be used in the same manner as 100 percent polypropylene.21-22
3.4 Glass Recycling
3.4.1 Presence of Toxics in Glass
Glass discarded as MSW may contain a variety of metal constituents. In the WASTE
Program study, glass was found to contain a variety of heavy metals, including aluminum,
antimony arsenic, boron, barium, beryllium, cadmium, chromium, copper, iron, mercury,
manganese, nickel, lead, selenium, tin, and zinc. The data from this study are presented in
Table 20. In summary, the data indicate that:2
• Concentrations of cadmium ranged from 0.3 mg/kg for green glass to 5.4 mg/kg for
unidentified glass. For purposes of comparison, the toxicity value for total cadmium is
40 mg/kg (based on ingestion of contaminated soil by a 16 kg child, 5 year exposure
duration and averaging time, 365 day/year exposure frequency, 200 mg/day ingestion);
Concentrations of chromium ranged from 28.0 mg/kg for clear glass to 943.0 mg/kg for
green glass. For purposes of comparison, the toxicity value for total chromium is 400
mg/kg (based on the health-based number for chromium (VI) which assumes a 16 kg
child, 70 year averaging time, 365 days/year exposure frequency, 5 year exposure
duration, 200 mg/day ingestion rate, and a risk level of 10*);
Concentrations of lead ranged from 20 mg/kg for green glass to 109.3 mg/kg for clear
glass. For purposes of comparison, the toxicity value for total lead is 500 mg/kg (based
on an U.S. EPA/OSWER Policy Directive for lead in soils);
33
-------
TABLE 20. ELEMENTAL COMPOSITION OF METALS IN GLASS
(IN GRAMS/TON)2
Glass
Chemical
^™— ••—•—— ««—^«i
Al
As
B
Ba
Be
Cd
Cr
Cu
Fe
Hg
Mn
Ni
Pb
Sb
Se
Sn
Zn
=====
Clear
—— — — — — — __
13,449
1.0
88.8
340.8
1.0
4.8
28.0
22
2,335
0.2
179
10.1
109.3
144.7
0.77
50
60
===
Green
• . . — _ —
10,819
9.8
44.6
486.6
0.4
0.3
943.0
2,620
0.1
250
62.7
20.0
36.5
0.06
166
21
=^^==3======
— — — — ^— — — __ _ ___ _
Brown
^ — —^ «_
9,796
6.9
29.2
190.7
0.2
1.7
46.2
92
7,568
0.6
256
22.8
103.1
25.4
0.48
27
251
—
1
Other
— — — — — — ___
6,036
0.4
21.5
784.7
0.01
5.4
91.5
29
1,921
0.1
76
12.5
90.0
154.3
0.16
74
1,671
to O^m K °I Ia"8? fr0m °' l mg/kg for green *lass ™d unidentified glass
to 0.6 mg/kg for brown glass. For purposes of comparison, the toxicity value for total
mercury ,s 20 mg/kg (based on ingestion of contaminated soil by a 16 kg "child 5
motion); 0" ""' aVeragi"8 tlme' ^ ^^ af°m *W- 2°° '
Concentrations of zinc ranged from 21 mg/kg for green glass to 1 167
rJT'S'l!! • ^ ?UtPOSeS °f ComPariso". ^ toxicity'vaiue for iotal
mg/kg (based on ingestion of contaminated soil by a 16 kg child
durauon and averaging time, 365 day/year exposure frequency' S
for
34
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In Constidine's (1989) literature review of the metals content of the various fraction of
MSW Ae Zs f^t on was found to contain chromium (342 mg/kg dry solids). However,
Sum W 1 e^l, and zinc were not detected. The resuUs presented by Consudme were
based on d^ regarding Swedish MSW, but may provide insights mto the composite of U.S.
discards.5
* «*»"» »'
glass products that are recycled.14
TABLE 21. PRESENCE OF LEAD AND CADMIUM IN THE GLASS AND
1 CERAMICS FRACTION OF MSW'4
3.4.2 Glass Recycling Process
In the glass recycling process, post consumer glass containers are returned to glass
recvclina centers soW to glass recycling plants, and mixed with silica sand, soda ash, and
taes one SftSTtanL. The moUen glass then is transferred into a fanning machme to
SEE or pr^edtato shape. This section describes the glass "^TS'ILS
^^
recycling process.
Cleaning Process
Glass Production - - -;
R»mov»
Ferrous »
Metal with '
Magnet
T
Solid Waste
Crush
_ Gullet to «
* Uniform '
Size
T
Alr
Emlsslons
Vacuum Paper,
... Plastic, and Light -
^ Aluminum Irom
Culet
T
SoUd Waste,
Air Emissions
Remove Aluminum
f with Non-Magnetic
Metal Detector
*
t / 1
Solid Waste / .
Sc
W
Air
Store
in Slos
Mix Culet
•^ with Raw 9
Material*
\
&t,on*, tmiss,on8
^ 1
f
Froth
Flotation
1
Optical
Sorting
t t
lid Waste, Solid
astewater. Waste
Emissions
^ Melt In »
Furnace '
Air
Emissions
Pour Molten
_ Qlass Into
^ Container
Molds
Me
Emissions
Figure 6. Flow Diagram of Glass Recycling Process.
35
-------
Glass recycling involves recovering postconsumer glass from the MSW stream and
reusmg it as a raw material in new glass products. Approximately 10 percem of tSkS
municipal refuse ,s glass in the form of discarded containers. Recycled g£ss that i in butt fonn
and suitable for remeltmg is referred to as cullet Waste glass (i e., oflsr^ificatioVmteS
and scraps from the manufacture of glass products), also may oe caUeT cuto buTh no
considered recycled because it has not been used by the consumer. The color distribution of
gto m post-consumer MSW is approximately 65 percent flint (colorless), 20 rSnt aTber
and 15 percent green A predominant proportion of the glass is soda-lime botTSs^S
W1a
To be suitable for reuse in melted glass containers, glass cullet must meet
fTf In,geneRl1' ^ ^^ ^ mUSt "" 'ess *" 50 mm and °™a
metals, and refractory matenals can be present only in very small amounts. The
orgamc materials in the cullet can result in the formation of bubbles or seeds in
r^ ^ CaU!f a 6reCn °F amber tint in flint «lass- Particles ^ ^tals may ses
m Ae finished products. The presence of aluminum may reduce silica to silicon ™hicT!
refractory and may produce stones in the melted glass.8
Glass is recovered from the MSW stream in two ways: source separation and resource
recovery Source-separated glass typically is separated in the home from I res Tf T
resident*! waste stream and collected from individuals on the curbside or at a regional
Optimally, cullet is sorted by color (e.g. , amber, green, and flint). However cullet
be mixed m some instances. A small percentage of contamination (i.e , other colors
contamination vary, but usually range
After coUection, cullet is prepared for use in the glass-making process through a series
of cleaning steps. The unbroken cullet first is inspected on a convenor. Fe^ouTmet^ls (U
bottle caps) are removed from the cullet using a magnetic separator. The cutetote^S
iieiZrr r, ** ^ through a vacuum s^m ^™™ ^ £*%£%?
labels) and plastic (e.g., polystyrene labels, plastic rings, and caps) that may be mixed wiul me
i^ZSr11 deteCt°r ideiUifieS 3ny remaining ^Uminum f°r -ov^froS Se
. The cullet cleaning process may generate a solid waste and air emissions.23
Th~ f *u n / • r may ^e emPloyed-' froth flotation and optical
The froth flotation process separates residual organics and metals from the cullet
36
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through jigging and grinding. The jig produces a loose vibrating bed of sohds in a liquid
medium and the solids separate into layers of different specific gravities. Orgamcs move to the
top and are skimmed off, metals (e.g., lead, zinc, and copper) form the bottom layer and are
drawn off, and the glass-rich middle layer is removed separately.8 The froth flotation process
generates a wastewater.
In the optical sorting process, cullet passes through optical sorters that scan each particle
of the feedstock removing opaque particles. When a light beam is broken, an air jet knocks
the opaque particle out of the cullet stream. Color sorting is achieved by comparing each
particle to a standard and rejecting off-color material.8 The optical scanning process generates
a solid waste stream of opaque materials removed from the cullet.
The cullet then is conveyed to silos for storage. From the storage silos, the cullet is
mixed directly with the raw materials of glass (silica sand, soda ash, and limestone) and fed into
a furnace Small quantities of selenium also may be added to the cullet as a decolonzer. The
selenium bonds with the molten glass and its pink tint offsets or neutralizes the green coloration
that can be caused by iron impurities in the raw materials. The mix is melted at an average
temperature of 2700°F. The exact temperature depends on the color of the glass being
produced. The mixture ratio of cullet and raw materials can vary greatly, depending on the
supply of cullet and the amount of contamination in the cullet. A per-bottle average of 45 to 48
percent recycled cullet is not unusual.24
3.4.3 Potential Effects of Toxics on Glass Recycling
Research indicates that there is relatively little waste produced by the glass recycling
process However, wastes may be generated during the process that are not associated with the
glass itself, but are impurities in the cullet feed or wastes generated as a result of the recycling
process (i.e., oils and greases from recycling equipment and air emissions from fossil fuels).
In fact, Kirk-Othmer notes that use of cullet in glass containers may reduce paniculate emissions
sufficiently to obviate the use of expensive furnace air-pollution-abatement equipment that are
typically needed to manufacture glass from exclusively raw materials. In addition, because of
its lower melting temperature, less energy is required to melt cullet than raw materials.
Recycling glass from cullet also is associated with cost reduction activities at container
manufacturing plants since recovered cullet is lower in cost than virgin raw materials.
The presence of material contaminants, as opposed to chemical contaminants, in cullet
feed is a major concern for the glass recycling industry. The primary contaminant found in the
glass recycling process is aluminum. If aluminum is not detected and removed during the
cleaning process, it can cause problems in the finished product, such as weak spots and blisters
in the glass. In addition, paper contamination can lead to a carbon build-up when the paper is
burned in the furnace, causing discoloration of the finished glass product. Other contaminants,
such as rocks, bits of concrete, and similar items, cause physical deformities in the glass.
37
-------
The addition of free heavy metals to the cullet mix, which would be a concern is
unlikely to occur. Heavy metals, such as lead, can be found in specialty glass and glassware
but these types of glass typically are not recycled. The major factors that prevent the recycling
of other glass products with container glass are the difference in melting and setting nointe
between container glass and other types of glass. Therefore, removal of the heavy metals would
not lead to increased recycling of the glass products because glass used in products other than
containers cannot be mixed with container glass as cullet in a furnace.
A review of the literature showed that the wastes generated during the glass recycling
process may include air emissions, solid wastes, and wastewater. Air emissions occur during
the material handling phase as cullet is crushed and transferred to storage silos via elevators
conveyors, or by hand. The emissions generated during material handling are limited to solid
particles that become airborne. There are no chemical reactions during this stage so the
chemical compositions of the glass dust remain the same as the raw material.24
Air emissions also may be generated during the melting process. The particulates
associated with this phase can originate from the vaporization from the molten glass and physical
entramment of batch materials being charged to the melting furnace and from the condensation
of compounds, such as sodium sulfate. The formation of particulates during this phase is
affected by the temperatures in the melting furnace, surface area of the molten glass and the
production rate. Testing has shown that sodium sulfate represents the largest percentage of
particulates from soda lime glass. Higher furnace temperatures have been found to reduce
paniculate emissions, but may lead to an increase in the pollutants released from the burning of
additional fossil fuels required to maintain higher temperatures.24
Generally, most of the air emissions generated during the melting process are associated
with the burning of fossil fuels to heat the refractory furnace. Thus, emissions from the glass
melting process may include nitrogen oxides (NOxs), sulfur trioxide (SO3), sulfur dioxide (SO2)
and water vapor. Incomplete combustion of fossil fuels may cause both carbon monoxide (CO)
and hydrocarbon emissions. When a fuel or oil containing significant quantities of sulfur is
used, the emissions increase in direct proportion to the sulfur content of the fuel.24
Air emissions also may be generated during the forming and finishing phase of the
process. Emissions of hydrocarbons, oxides of nitrogen, oxides of sulfur, metal oxides, metal
chlorides, hydrogen fluoride, ammonia and particulates have been associated with these process
stages. Specific data regarding the quantities of the emissions or concentrations of the
constituents in the emissions were not available.
Wastewater is generated in several steps of the glass recycling process. These waste
water-generating processes include flotation, contact and non-contact furnace cooling glass
product forming, cullet quenching, and final product rinsing.24 No information was available
regarding the characteristics of wastewater from glass recycling plants.
38
-------
waste.
3.5 Summary
Research indicates that the presence of metals and organics in commonly recycled
L w^Tabels, glues, and fines, rather than the commcxhty bemg recycled.
Additional research on the potential affects of metals and organics on the recycling of
other po^STy hSus material^ may be present in MSW, such as battenes and specuu
wastes (such as waste oil and antifreeze), is recommended.
39
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4'° SSSG™CTS °F TOXICS °N ^OPAL SOLID WASTE
4.1 Introduction
As landfills in the United States and abroad reach capacity, alternatives to
approaches for municipal solid waste (MSW) management arfbetag sought
MSW management method has gained attention in recent years is MSW
Hwn ! if composting facilities were in operation across the country
An additional 31 facilities are in advance stages of planning and three were under construction^
No instances of significant adverse impacts are known to have resulted from MSW
composting operations. However, MSW composting may pose potential risks
™errTT' T* W°^er *** due t0 *e varied ^ *«*
These potential nsks may be associated with:
Pathogens;
Bioaerosols (e.g., fungus spores);
Volatile and semi-volatile organic compounds;
Persistent lipophilic organic chemicals (e.g., PCBs, DDT);
Metals and other inorganics (e.g., asbestos);
Allergens; and
Corrosive, explosive, and caustic unprocessed wastes in MSW.
«n m ^ T™^ °? MSW """P08^ has f°c«sed on the effect of metals in the compost
on plant growth and food crop contamination. » Limited studies have demon^tra^Ta
KhT ^ eStr0y Path°genS •"" degrade °rganic comP°unds » the
Nevertheless, dunng compost processing, pathogens; bioaerosols; organic c
anc I corrosive, explosive, metals, and caustic unprocessed wastes are a concemw
Generally, inorganic elements and compounds are found in MSW compost product «
levels. However, some research has found that, depending on the nature of the fa
iimits for
This section presents a brief discussion of the composting process followed bv an
analysis of several areas of potential risks posed by the presence of meta^ ^dTrganics "
MSW, mcludmg the affect that these constituents may have on the viability and
-" ^
of
use °f
Concentration of metals and organics in MSW compost;
Behavior of metals and organics in MSW compost;
Effects of MSW compost on vegetation and soil organisms;
40
-------
Effects caused by direct ingestion of MSW compost or compost-amended soil (animals
and humans); and ..
Effects caused by ingesting products grown in MSW compost-amended soils.
In addition, a discussion of the benefits of source separation (and source reduction) of
MSW prior to composting is presented. These benefits include an increase in compos quality
and a decrease in toeconctntration of metals in the compost. A discussion of compost standards
also is provided to illustrate the usefulness of source separation and source reduction m
hnproving compost quality. Finally, a discussion of future research needs related to MSW
3™stog toarwere-identified by participants at a U.S. EPA/Washington State Department of
Ecology focus group meeting is presented.
The technical literature is not replete with studies that have addressed toe presence of
toxics in MSW compost. Most of the recent research was conducted m the last five years.
W^ever possible, data regarding the effects of the presence of toxics m MSW compost are
taken from tidies of MSW compost rather than studies addressing other types of compost (e.g.,
sewage sludge compost).
The general focus of this chapter is a discussion of the potential risks associated with
MSW compost products due to the presence of metals and/or organics in MSW feedstock^
Although toe presence of these contaminants will not inhibit toe compost proces , an
undersLding L evaluation of potential risks associated with the product is essential to toe
evaluation and design of a MSW management strategy that may include composting as a
management alternative.
4.2 The Composting Process
Composting is a biological process in which microorganisms decompose toe carbon-based
constituents implant and other organic materials into a stable organic product. While composting
is a natural process, it can be accelerated by providing and maintaining a proper environment
to support toe growth of microorganisms. The primary environment* parameters toa must be
£nK include moisture content, oxygen, PH, particle size, composition of the feedstock, and
temperature.27
Though composting technologies differ, certain key elements are common:
• Preparation of compostables (i.e., feedstock);
• Composting stages (high-rate decomposition, stabilization, and curing); and
• Refining.
The extent of feedstock preparation and product refining can affect the quality of the compost.
41
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4.2.1 Preparation
Once a waste material is received, it is subject to a series of processes including materials
separation and size reduction to extract recyclable products and non-compostable materials and
to prepare the remaining organic material for composting. Typically, oversized materials such
as car ores and wood pallets are removed first. The incoming waste stream is then screened to
separate the waste into various sizes, and recyclable material may be removed through means
such as manual sorting, overhead magnets, and eddy current devices for recovery of aluminum
Other unwanted materials such as batteries and oil filters are removed by manual sorting The
remaining material is reduced in size by a shredder to increase surface area and enhance
biodegradahon. The compostable material generally is mixed with water, and other optional
material, such as sludge, may be added. y"«"«u
4.2.2 Composting
The mixture then is placed in aerated windrows, aerated static piles, or in vessels such
as drums or tunnels, for composting. Each method varies in the air supply system, temperature
control mixing/turning methods, and process residence time. The actual amount of time
required for composting is dependent on the rate of decomposition, but generally averages four
to eight weeks. Depending on specific market applications, the compost will be allowed to cure
after the composting process is complete. Curing takes an additional 18 to 20 weeks and usually
is conducted outdoors. uauuiiy
The most commonly used composting process, particularly for source-separated yard
trimmings ,s the windrow method. In the windrow method, materials are placed into elongated
rows or piles up to 7 feet high. The piles are typically trapezoid shaped in cross section, 14 to
16 feet wide at the base and narrower at the top. Piles are turned regularly by a windrow turner
0
The process used for aerated static pile composting is similar to the windrow method
except air blown or drawn through the material eliminates the need to turn the pile The piles
are constructed on top of a network of pipes that are connected to a blower system that
r^Sy f^JUf PUeS' SinCC "* C°ntentS °f the Pile m n0t mixed bv means °f """ing,
a blanket of finished compost may be applied to insulate the pile to ensure that the outer
portions of the pile reach temperatures required for pathogen destruction.
MSW composting typically is performed in enclosed or in-vessel systems. Enclosed or
in-vessel systems are used to better control the composting process. Materials to be composted
are placed in a chamber or vessel. These vessels usually are designed to automatically control
temperature, oxygen, and moisture concentration. These systems eliminate surface runoff and
leachate concerns that are associated with outdoor composting operations.
42
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4.2.3 Refining
Once mature, the compost generally is refined for marketing. Screens typically are used
to remove stones, glass, films, metals, hard plastics, and uncomposted material. The compost
may be shredded to a size needed for specific markets.
4.3 Uses for Compost
The composting process generates a product with significant benefits. The major benefit
of applying compost to soil is related to the resulting increase in organic matter content of the
soil The increased organic content of soil generally improves the physical properties (i.e.,
water holding capacity, total pore space, aggregate stability, temperature ™ulationsod density
erosion resistance) and chemical properties (e.g., pH, cation exchange capacity, nutnent content)
of the soil and enhances biological activity.2'
The uses of compost can be broken down into five main categories:27
Horticulture - commercial operations (such as nurseries) and home use;
Agriculture - food crop production;
Silviculture - growing of trees for harvest;
Land reclamation; and
Landfill cover.
In general, consistency and quality are key to successful market development for any
product, including compost. There is no long term market viability for a product that does not
£oduce consistent results for its user. Compost quality, however, is difficult to define because
parameters used to measure quality differ depending on the ultimate use for the compost.
The agriculture industry is the largest potential user of compost products. Potential
annual demand is estimated to be nearly 900 million cubic yards. Annual demand by other
potential users of compost is estimated to be 145 million cubic yards.2* Mos of the research
on MSW compost quality, therefore, focuses on its use for agricultural applications and its
subsequent effect on crops, livestock, and human consumption.
4.4 Environmental Pathways and Exposure Routes for Releases of Metals and Organics
Figures 7 and 8 provide flow charts that depict various environmental pathways as well
as direct and indirect routes of exposure for organisms. General descriptions of the flow charts
are presented below. More detailed discussions are presented in Sections 4.5 through 4.9.
Figure 7 shows that emissions may be released into the air during MSW composting
operations Since most MSW composting operations are conducted indoors, leachate and rwioff
topically are not concerns during composting operations. Another exposure Pathway results
torn the landfilling of non-compostable residues that are screened out of the compost Once ttie
finished compost is applied to the land, other significant environmental pathways include runoff
43
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MUNICIPAL
SOLID
WASTE
LANDFILL U- RESIDUES
COMPOSTING
FACILITY
COMPOST
4 __
SOIL
AIR
BIOMASS
PERCOLATION
GROUND
WATER
RUNOFF/EROSION
SURFACE
WATER
Figure?. Potential Environmental Pathways: MSW Compost.
COMPOSTING
COMPOST
INHALATION
_. —
HUMAN
nuwl™ INHALATION
CULTIVATORS DERMAL CONTACT S
' INCIDENTAL INGESTION
.
HUMAN «- INGESTION — ANIMAL < INGESTION
PERCOLATION TO
GROUND WATER
HUMAN
(WATER SUPPLY WELL)
T SOIL
0|L 1 DIRECT CONTACT [ L°RGANISMS j
INGESTION 1
Lwl BURROWING
[ ANIMALS
r |
UPTAKE— > PLANT — INGESTION
, —
r > HUMAN
—>\ ANIMAL
RUNOFF/EROSION
TO SURFACE WATER INGESTION
f ANIMAL OR 1 HUMAN
|_ HUMAN | 1 1
Figures. Potential Exposure Pathways for Organisms: MSW Compost.
44
-------
and water transport. Percolation of rainfall through the soil may result in leachate that could
impact ground water. Runoff and erosion of compost-amended soils can affect surface water
and sediments.
As shown in Figure 8, during composting operations, facility workers may be exposed
to emissions of organic compounds, as well as a variety of other MSW-related hazards (see
Section 4.5 for more details). With respect to finished compost, soil organisms (e.g.,
earthworms), plants, and burrowing animals are exposed most directly to compost-amended
soils. Direct human exposure to finished compost is most likely to occur during compost
handling or cultivating activities. Plant and/or animal uptake of compost constituents can result
in indirect exposure to organisms at the next trophic level (e.g., plant -* animal -* human or soil
-» animal -* human). Contact with or ingestion of ground water or surface water affected by
compost-generated leachate or runoff also present indirect modes of contact for organisms.
4.5 Human Health and Environmental Concerns During the Composting Process
Depending on whether a composting operation is conducted indoors or outdoors, different
environmental concerns may arise. For indoor MSW composting operations, the primary
pathway of concern is air emissions.
4.5.1 Emissions Associated with Composting Operations
Organic compounds (natural products and xenobiotics) in MSW compost are the result
of natural, industrial, domestic, and agricultural materials discarded into the MSW stream.
According to Kissel et al emissions of volatile and odorous organic compounds are a concern
for composting facilities as follows:30
• Little direct evidence of VOC emissions from MSW composting operations has been
documented to date. Consequently, estimation of potential releases must rely on evidence
of the presence of VOCs in the municipal waste stream and the likely behavior of such
compounds during composting operations based on their physical and chemical
properties. Given that VOCs are likely to be routinely found in MSW, and that
composting operations (including receiving, processing, and active composting) present
many opportunities for the release of such materials, measurable amounts of VOCs might
reasonably be expected to be found in indoor air in waste handling facilities. These VOC
emissions may be of concern if buildings are inadequately ventilated. Off-site VOC
emissions are unlikely to present a health concern.
• Although organic matter decomposition under aerobic conditions generally does not
produce noxious odors, various phases of composting operations may result in the release
of odorous compounds, for example: odors may be present in the solid waste stream;
odors may be produced during collection, transport, or storage of the waste material; or
45
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produced during improper composting conditions such as inadequate or poorly distributed
aeration or excessive moisture content. Odors in biological processing facilities of
various kinds are generally ascribed to inorganic and organic compounds of sulfur and
nitrogen, low molecular weight aliphatic acids, terpenes, carbonyls, and alcohols The
significance of odor releases from composting facilities is primarily associated with
public acceptance rather than health risk. Although not mentioned by the authors some
of these odorous substances, if present in sufficient concentrations, could present a threat
to worker health.
, wr et al (1"2) reP°rted to* little information is available on the actual concentrations
of VOCs produced by composting operations. Limited sampling at a facility in the North-
Central United States in 1991 revealed individual VOC concentrations ranging from below the
detection limit to 1.3 mg/m3 for 2-butanone (for which the corresponding OSHA permissible
exposure limit [PEL] time-weighted average [TWA] is 590 mg/m3).30
Research on VOC emissions from MSW (source separated) composting is being
conducted by the Connecticut Agricultural Experiment Station. In 1992, the following trends
were evident:31 B «««»
Although there are various composting techniques (e.g., in-vessel systems, windrows)
and source management methods (e.g., source separation, on-site separation and co-
composting of MSW with sewage sludge), the VOCs generated remained fairly consistent
across composting methods.
Anthropogenic chemicals (e.g. , toluene, tetrachloroethylene) are rapidly emitted from the
compost as it comes up to the operating temperature for active composting, causing the
highest concentrations of these chemicals to be in the newest active composting region
As the compost matures, the concentrations of these substances rapidly diminishes.
Based on Kissel et al's (1992) review of preliminary data generated by this study VOC
concentrations were found to be at levels well below OSHA and NIOSH standards * In a'report
by the National Audubon Society, Procter & Gamble et al, VOC emissions at the Connecticut
Agricultural Experiment Station composting operations were reported to be similar to those
generated by nine other (MSW or sludge) compost facilities.32
Kissel et al (1992) estimated that the total concentration of volatile organic compounds
m/L™Ch unaccePtable chronic levels in poorly ventilated areas used for acceptance and sorting
of MSW prior to composting. The VOC levels may exceed some recommended exposures for
even non-carcinogenic compound volatiles. The authors noted that the small amounts of
solvents, paints, cleaners, and related materials when combined in MSW can present a
substantial exposure once the MSW is collected and compacted. They recommend pre-sorting
and suggest that waste stream segregation easily could reduce worker exposure M
46
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According to Epstein (1993), data show limited levels of toxic organics in compost from
waste materials. Natural organic compounds such as phenols and terpenes are found in yard and
food wastes; whereas xenobiotics such as PCBs, phthalate, and chlordane are contributed by
industrial MSW components, pesticides, and plastics.33
Emissions data gathered by Van Durme et al were presented by Epstein (Table 22) .M
In all cases, the measured values were several orders of magnitude lower than ACGIH and State
of Virginia allowable limits. Nevertheless, Epstein (1993) recommends that facilities develop
mitigation measures and provide workers with instructions on handling solvents, pesticides, and
other toxic compounds that may be contained in the MSW. In addition, workers should use
good personal hygiene practices to minimize the potential for inadvertent ingestion of chemical
constituents in MSW, feedstock, or finished compost.35
4.5.2 Primary Pathogens Associated with Composting Operations
Primary pathogens consist of bacteria, viruses, parasites, and helminths. According to
Gillett (1992), transmission of pathogens to workers at MSW composting operations has not
been documented.26 Most of the data on pathogens during composting has been derived from
sewage sludge composting operations. Epstein (1993) noted that H.R. Pahren (1987) reported
that total coliform, fecal coliform, and fecal streptococci in municipal wastes are found at the
same levels found in sewage sludge. Although pathogens are destroyed during the composting
process, workers in composting facilities should follow normal practices for good hygiene.33
4.5.3 Bioaerosols Associated with Composting Operations
Bioaerosols, which tend to be released during composting operations, may contain fungal
spores, actinomycetes, microbial products, and other organisms and constituents. According to
Epstein (1993), the bioaerosol of greatest concern is Aspergillusfimigatus. The fungus rarely
invades healthy individuals. Studies at numerous facilities have shown that concentrations of the
fungus approach background levels at approximately 200 to 500 feet from active composting
sites. Thus, residences located greater distances from such areas are not impacted.33
4.5.4 Trace Elements Associated with Composting Operations
Trace elements tend to be concentrated in batteries, other ferrous, and non-ferrous
materials found in MSW, as well as in some combustible components (such as fines and garden
wastes). According to Epstein (1993), workers at MSW composting facilities are exposed to
dust which may contain toxic trace elements. Dust also can be deposited around the composting
site causing potential impacts to the environment. The heavy metals of concern include:
arsenic, cadmium, chromium, copper, mercury, lead, nickel, and zinc. The principle route of
exposure to workers is through incidental ingestion of particles containing toxic trace elements.
47
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TABLE 22. VOLATILE ORGANIC COMPOUNDS IN BLOWER EXHAUST
FROM AN AERATED STATIC PILE34
Restricted Compounds
Acetaldehyde
Acetic Acid
Acetone
Benzene1*
Carbon Disulfidc
Chlorobenzene
Cyclohexane
Cyclohexanone
Cyclopentane
Dichlorobenzene
2-Ethylbenzene
Ethylbenzene
Fluorotrichloromcthanc
Heptane
Heptanone
Methanol
Methylacetate
Methyl Chloridek
Ethyl Ketone
Nonane
Octane
Pentane
Phenol
n-Propanol
Pyridine
Styrene
Toluene
1 , 1 ,2-Trichloroethane
Xylene
GC/MS Results
-------
Other possible exposure routes are through dust inhalation and dermal contact. Environmental
exposure would occur primarily as a result of dust settling on soil or edible plants. This
exposure route should be minimal, especially from facilities that control dust and other emissions
through the use of filters and other practices. No cases of workers being affected by heavy
metal toxicity have been reported.33
4.5.5 Other Substances Associated with Composting Operations
Other substances that may present worker health hazards at composting operations
include but are not limited to, allergens, asbestos, corrosive materials, explosive substances,
and caustic unprocessed wastes. For composting operations that do not involve source separated
MSW additional research on the health effects of these substances and appropriate protective
measures may be required. According to Lisk (1992), when examining compost collected from
26 locations in 13 states, asbestos was found in 46 percent of all composts examined (inclusive
of yard waste, MSW, and sewage sludge compost). Quantities ranging from trace amounts to
1 percent by volume asbestos in ash were detected.36 Note, however, that in demonstration
projects performed at the Connecticut Agricultural Experiment Station involving source separated
MSW, four samples of 10-week-old compost were submitted for asbestos analysis; none showed
the presence of asbestos.32
4.5.6 Ppssible Leachate Generation During Composting Operations
Depending on the nature of the MSW composting operation (e.g., windrows versus in-
vessel), leachate may or may not be generated. As mentioned earlier, most municipalities seem
to be conducting active composting operations either indoors or in a vessel, thus eliminating
leachate concerns. In areas where composting is performed outdoors, the facility should be
designed and managed to minimize leachate generation and run-off from the site (e.g., placing
piles under roofed areas).
In a Minnesota Pollution Control Agency report, a paper by Epstein and Epstein (1989)
was cited that indicated that leachate generation and contamination of surface waters have not
been associated with MSW composting sites since most activities are conducted on sealed, paved
surfaces or under roof. In addition, leachate contamination of ground water, although
theoretically possible, also is unlikely due to the nature of the composting process as well as the
design and engineering controls applied at MSW composting facilities.35 Furthermore, research
conducted by Cole (1993) on yard waste composting operations found that the nitrogen,
phosphorous, and metals are retained in the compost in the solid as opposed to the liquid phase.
Thus the main potential risk posed to surface water is transport of the compost particles.
Furthermore, retention of metals in the solid phase indicates that the nutrients and metals present
low risk to ground water.37
49
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4.6 Concentration of Metals and Organic Compounds in Finished MSW Compost
This section presents available information on the concentration of metals and organic
compounds found in MSW compost.
4.6.1 Metals
Metals are present in finished compost and, depending on their concentrations, oxidation
state, and form, may pose potential impacts on human health and the environment when the
MSW compost is applied to soils used to grow food crops. The primary metals of concern are
cadmium (Cd) chromium (Cr), copper (Cu) lead (Pb), mercury (Hg), nickel (Ni), and zinc (Zn).
Other trace elements in MSW compost that may be of concern to plants and animals in specific
regions of the country are boron (B), molybdenum (Mo), and selenium (Se).38 These elements,
however, also occur naturally in soils (concentration is dependent on the parent material) and
many are essential to plants, animals, and humans. Fertilizers, pesticides, and other materials
added to soils also contain trace amounts of heavy metals.39
Metals are present in compost due to the presence of manufactured materials in compost
feedstock (e.g., pigments, inks, metals, plastics), as well as naturally occurring materials (e.g.,
yard trimmings, food scraps). Metal concentrations in natural vegetation can be compounded
by manmade factors. For example, yard trimmings placed in streets by homeowners and
collected by municipal workers also may contain metals and other elements as a result of a
variety of sources such as traffic exhaust, fallout from industrial emissions, and miscellaneous
discarded debris (although the advent of unleaded gasoline has reduce lead deposited on leaves
and street dirt).39 In general, concentrations of cadmium, copper, lead, mercury, sodium, and
zinc are notably higher in composts made from mixed MSW than in compost made exclusively
from yard trimmings.36
Because there are few operating MSW composting facilities in the United States, there
are limited data on the chemical constituents present in MSW compost products. Available data
for MSW composts produced in the United States are summarized in Table 23. These data
illustrate the variability in metal concentrations in compost produced from different facilities and
even within a single facility.
50
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TABLE 23. LITERATURE DATA FROM U.S. COMPOSTING FACILITIES
Concentration Gig g~l)
Metal
Cd
Cr
Cu
Hg
Ni
Pb
Zn
Average
5.17
90
289
2.70
69
306
886
Standard
Deviation
7.81
116
242
3.77
110
260
894
-^-^— ^— — ^^—
Minimum
0.04
3
22
0.02
1.7
5
74
-— S--9=^=^^^=^^^=^=I
Maximum
40.18
500
1143
20.30
668
1312
6378
Although MSW compost has higher concentrations of metals than background soils, it
typically has lower concentrations of heavy metals than sludge that is considered to be "clean"
(i.e., compost contains levels of heavy metals that, when applied to soil, will not adversely
affect the environment or result in an increase of heavy metals to the food chain). Table 24
shows the level of heavy metals in MSW composts as compared to soil, sludge, and to the EPA
Pollutant Concentrations for sludge (allowable concentrations for land application of sludge)
promulgated by EPA in February of 1993 (58 FR 9248). The data provided in Table 24 indicate
that lead concentrations in MSW compost can be at levels that exceed the EPA standard for
sludge. The lead content varies with the quality of feedstock, and may be reduced through
source separation of waste stream components that appear to be the cause of this problem.
While it is not possible to eliminate metals from MSW compost, removal of many metal-
containing materials from MSW feedstocks can reduce the level of metals in MSW compost.
(Many contaminants are highly diffuse in MSW; others, however, are concentrated in a limited
number of manufactured products and are amenable to separation [See Chapter 2 of this report]).
Compostable materials can either be separated from the waste stream at the point of generation
prior to its transport to the facility (source separated) or non-compostable materials can be
mechanically or manually removed at the composting facility.
Processing conditions also can control metals content in compost. Low oxygen, acidic
conditions increase the solubility of some metals, causing them to leach out; whereas composts
developed under well-aerated conditions with few water-saturated or low pH zones tend to retain
metals.37
51
-------
Metal
Concentration (jig g'1)
SoU
Sludge
Mixed MSW Compost
EPA
Range * Geometric Mean' Medianb Concentration
Standards for
Cd
Cr
Cu
Hg
Ni
Pb
Zn
2.9"
34.8
154
1.27
24.8
215
503
3.5b
43
194
1.5
29
261
563
3.7*
29
349
1.6
31
324
771
0.01-7
23-15,000
1-300
NA
3-300
2.6-25
10-2,000
0.175
NA
18.0
NA
16.5
10.6
42.9
4
409
456
2
18
76
755
39
1,200
1,500
17
420
300
2,800
"Trace Elements in Municipal Solid Waste Compost"
NA Data not available
• E. Epstein, R.L. Chaney, C. Henry, and T.J. Logan (1992).
in Biomass and Bioenergy, Vol. 3, Nos. 3-4 227-238.
Chaney, Rufus L. (1991). "Land Application of Composted Municipal Solid Waste: Public Health, Safety and
Environmental Issues" in Proceedings of the 1991 National Conference, Solid Waste Composting Council, pp. 61-83.
Richard, T.L. and P.B. Woodbury (1992). "The Impact of Separation on Heavy Metal Contaminants iii Municipal
Solid Waste" in Biomass and Bioenergy, Vol. 3, Nos. 3-4: 195-211.
Epstein, Eliot (1991). "Compost Quality A Public Health Perspective" in Proceedings of the 1991 National
Conference, Solid Waste Composting Council, pp. 39-50.
EPA Standards (February 19, 1993) for the Use or Disposal of Sewage Sludge: 40 CFR 503 (§503.13).
There are a limited number of studies addressing compost quality based on the means of
feedstock separation; however, these studies support source separation to reduce the
concentration of metals in finished compost.27 Table 25 presents the results of three studies that
indicate that lesser amounts of heavy metals are found in compost produced from source-
separated organics as compared to compost produced from mixed municipal solid waste.40
However, it is unclear if this is a direct result of the source separation or the composting
methods used. It also should be noted that without examining the raw data used to construct the
results presented in Table 25, this observed difference cannot be assessed for statistical
difference. Further, these data represent only a snapshot of compost metals concentrations and
do not reflect potential changes over time.
52
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TABLE 25. HEAVY METAL CONTENT IN COMPOSTS40
Study 11*
Metal
Cadmium
Chromium
Copper
Lead
Mercury
Nickel
Zinc
ND No data
* Study »\
Compost
from
Central
Separated
MSW
(ppm)
5.5
71
274
513
2.4
45
1,570
compares MSW
Compost
from
Source-
Separated
MSW
(ppm)
1
36
33
133
ND
29
408
that was separat
Study
Compost
from Mixed
MSW
(ppm)
5.5
71.4
274
513
2.4
44.9
1,570
#2
Compost
from Source-
Separated
Organics
(ppm)
0.8
29
43
76
0.2
7
235
cd at the source (waste generator)
Study
Compost
from Mixed
MSW
(ppm)
1.8 - 14
11 -220
80-240
290 - 2,850
1.2-8
20- 73
565-1,255
*3
Compost
from Source-
Separated
Organics
(ppm)
0.5
55
47
62
0.5
14
198
with MSW that is sorted at a central
facility for the purpose of composting.
Composts prepared by separate collection of only the compostable fraction of MSW allow
the production of composts with lower metal residues than can be attained by general pre-
separation, or by central separation of MSW into different fractions. However, Chancy and
Ryan (1993) feel that attainment of lower metals levels is not needed to make MSW compost
utilization on cropland a viable practice in sustainable agriculture. Note, however, that Chancy
and Ryan's data reported a geometric mean for lead of 169 /xg/g for mixed MSW compost,
which is well below the 300 /xg/g NOAEL for lead.41
Many other factors must be considered in assessing viability of MSW composting than
simply the concentration of metals in the compost product. Factors that should be considered
for human risk include:42
• Metal concentration and chemical state;
• Bioavailability (the absorption of a metal from MSW compost compared to absorption
of a soluble salt) of the metal;
• Mode of intake into the body (i.e., respiration or ingestion);
• Interaction between metals; and
• Soil plant barrier (a comparison of the concentration of a metal in a plant that causes
phytotoxicity with the concentration that is toxic to livestock or wildlife).
53
-------
A risk analysis performed by Epstein et al (1992) concluded that mixed MSW compost
does not comprise a significant risk to human health or the environment when compared to
source-separated compost, even though the concentration of metals in the source-separated
compost is lower than mixed MSW compost." Metals and organics in most MSW composts are
far below the NOAEL limits. Because of low limits for lead in the NOAEL to protect children
who ingest compost or compost-amended soil, Chaney (1991) recommends avoidance of lead-
painted wood wastes in MSW source materials. In addition, Chaney recommends separate
collection of household hazardous wastes such as batteries and pesticides in cities where these
substances may be present in compost feedstock at levels of concern.39
4.6.2 Organic Comoounds
Many analyses have been performed on composts to determine the presence of oreanic
chemicals. Studies have tended to focus on pesticides, PCBs, and polycyclic aromatic
compounds (PAHs). Since little information is available on MSW compost, available
information on other types of compost will be included in this section.
Research conducted at the Connecticut Agricultural Experiment Station found no
detectable concentrations of PCBs or pesticides in finished MSW compost produced from source-
separated organic material (Table 26) using an analytical detection limit of 0 002 ppm
However some PAHs were detected. Benzo (a) pyrene was measured at 0.380 ppm and the
sum of the PAH compounds was found to be 3.900 ppm.32
Curtis et al (1991) reported on the results of a laboratory study on an aerated pile of
ffnoT S^L gC (E material ^ ™™*™* is co-composted with MSW) by Racke and Frink
caXyl ™C ^^ eXamined deSradation rates of *"> PAH, phenanthrene, and the pesticide,
The investigators found phenanthrene to be highly persistent (approximately 90 percent
remained unchanged after an 18 to 20 day composting period). Carbaryl, however, degraded
easily with only about two percent remaining unchanged. The difference in degradation was
attributed to the metabolic pathway an organic takes during degradation.43
Kovacic et al (1992) found that yard wastes (a component of mixed MSW compost) may
contain a number of herbicide, insecticide, and fungicide residues. Typical over application or
excessive usage by homeowners was cited as increasing the potential for these substances in yard
wastes. Contrary to the assessments of other researchers, the authors stated that the notion that
all toxicants are readily broken down during the composting process has not undergone thorough
evaluation. They cited the following reasons:44 uuiuugn
After 30 days in a simulated MSW composting environment reported by Snell (1982)
only 28 percent of the initially applied herbicide, 2,4-dichlorophynoxyacetic acid (2 4-D)
was degraded. '
54
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TABLE 26. ORGANIC CONSTITUENTS OF WET BAG COMPOST32
Organk Constituent
PAHs1
Napthalene
Acenaphthalene
Acenaphthene
Fluorcnc
Phenanthrenc
Anthracene
Fluoranthcne
Pyrene
Benzo(a)anthracene
Chrysene
Benzo(b)fluoranthene
Benzo(k)fluoranthene
Benzo(a)pyrene
Indeno(l ,2,3-cd)pyrene
Dibenz(a ,h)anthracene
Benzo(g,h,i)perylcne
PCBs3
Pesticides1
est 0.006
0.024
ND2 (.012)
ND2 (.012)
0.140
0.016
0.510
0.380
0.260
0.480
0.420
0.430
0.380
0.360
0.088
0.340
ND (0.002)
ND (0.002)
ND
i
Non-detected. (Detection limit shown parenthetically.)
All PAH analyses reported by Roy F. Weston, EPA Method 8270, GC/MS (SIM).
PCBs, Pesticides reported by Connecticut Agricultural Experiment Station, CG/ECD, Ref: B. Eitzer, publication in
preparation.
The temperatures attained during composting (about 65°0 C) are inadequate to destroy
pesticides. For example, high concentrations of dicamba and triflurahn require
temperatures in excess of 800° C for complete destruction.
• Chlordane and associated residuals (e.g., cis- and trans-chlordane, chlordane epoxide,
heptachlor, octachlor epoxide, and trans-nonachlor) have been found in composted yard
waste.
According to Epstein (1991), the greatest concern with potentially toxic organic
compounds in MSW is the xenobiotic compounds. Many of these compounds (e.g., DDT
PCBs, dioxins) are very persistent in the environment and degrade slowly. As mentioned
earlier pesticides, household hazardous wastes, industrial wastes, and commercial wastes are
the major sources of these materials. Composting has been shown to degrade many of these
compounds, but data are limited (see Table 27). DDT, methoxychlor, and other chlorinated
hydrocarbons appear to be biodegradable. Epstein reported on results of an evaluation by L.R.
55
-------
Snell (1982) presenting a bar chart on the percent of biodegradation occurring through
composting for selected orgamcs. The chart showed that biodegradation ranged from a low of
nearly 40 percent for dioxins and chlordane to a high of nearly 100 percent for toluene-
70 *™« "'^"n; and PCP and PCBs
Li a later paper, Epstein (1993) described the results of a Cape May, NJ study that
provided a deuiled analysis of phenols, pesticides, PCBs, and total £trolJum hydrSZ
(TPHs). PCBs were not detected and the phenol levels were very low. The data on TPHs were
not considered to be reliable because the study did not differentiate between petroleum products
and animal fats and vegetable oils. Epstein went on to note that sampling and analysis for
organic compounds in MSW is difficult because a single item (e.g., bottle of solvent) c^ skew
^ * AS™
TABLE 27. PESTICIDES, DIOXBV, PCB, AND OTHER ORGANICS
IN SOLID WASTE AND SOLID WASTE COMPOST42
Perimeter
•^^^MHH^H
Aldrin
a-BHC
b-BHC
Lindane
Chlordane
p,p-DDD
p.p-DDE
p.p-DDT
Dicldrin
Endosulfan I
Endosulfan II
Endosulfan sulfate
Endrin
Endrin aldehyde
Heptachlor
Hcptachlor epoxide
Toxaphene
Methoxychlor
Total PCB
bis-(2-Ethylhexyl) phUialate
2,3,7,8-TCDD (Dioxin)
Concentration — pg/1
Solid Waste
<0.80 — 23
7.8-51
<4.8
<6.0
<1500
87 — 130
< 14
<49
57- 110
<9.4-21
34-40
<42
160— 1400
91 — 100
8.4-25
<3.8
<1000
150 - 260
Concentration — pg/g
<1.1
20 — 40
Concentration — pg/g
« (ppb)
MSW Compost
•"—— — — — — — — — — — — — —
<0.13
<0.8
< 1 0
<240
<7.0
4.3
<8.2
<2.7
<2 1
<7.0
<2.2
<5.9
<0.23
<0.63
<170
12.3
(ppm)
<0.33
17
(Ppt)
56
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In 1991 McDonald's commissioned a study of the compostability of its waste.
Analytical testing was performed for VOCs (Method SW 846-8240); SVOCs (Method SW-846-
8270); and organochlorine pesticides and PCBs (SW-846-8080). None of these substances were
detected in the screened McDonald's compost.45
A statewide study conducted in the State of Illinois (1992) examined 1 1 landscape waste
composting facilities. Composts were tested for the presence of organochlorine, carbamate, and
organophosphate pesticides. Although samples also were analyzed for PCBs, none were
detected Average levels of pesticides for raw landscape waste and mature compost were found
to be consistently higher in urban, Chicago-area samples when compared with the rural
"downstate" samples. Pesticide concentrations were compared with maximum allowable
tolerance (MAT) values developed for raw agricultural commodities. For those pesticides that
have a MAT, average levels in mature compost were well below the allowable levels. On a
"worst case" 'basis for an individual sample, only one sample contained a pesticide (Atrazine)
above the MAT level. The Atrazine source was uncertain. Most of the pesticides detected in
the waste material were found to have degraded or leached during the composting process.
However, DDE; methoxychlor; 2,4,5-T; and trifluralin were not completely absent in the
finished compost material.46
An analysis of MSW and sewage sludge co-composted using the Bedminster technology
(a compartmented rotary vessel) was performed by Western Atlas International for:
organochlorine pesticides and PCBs, VOCs, and SVOCc using the same SW-846 methods
referenced in the McDonald's study. Benzoic acid was the only substance detected (at 20
Although it is known that PAHs are biodegradable, the degree to which PAHs biodegrade
during MSW composting is not clear.41 Since many PAHs are carcinogenic, additional research
on the ability of composting operations to degrade PAHs is needed. It should be noted that
Walker and O'Donnel (1991) concluded in their paper that very limited testing of MSW
composts for toxic organic compounds has mostly resulted in the analytes not being detected.
The authors stated that little is known about the suitability of the analytical methods and the
associated limits of detection.48
The introduction of biodegradable plastics into the marketplace presents the question of
how such materials would degrade in a composting process. Research conducted by Ramani
Narayan (1993) at the Michigan Biotechnology Institute and Michigan State University examined
composting of polymeric materials (anthropogenic macromolecules). Studies on polyethylene
(plastic)-coated, uncoated, and biodegradable polymer-coated paperboard showed that
polyethylene was recalcitrant to biodegradation whereas the cellulosic component was completely
biodegraded. Narayan (1993) notes that it is vitally important in the development of
biodegradable plastics that the materials be engineered so as not to break down into toxic,
persistent, or recalcitrant substances, and that the degradation products be completely usable by
soil organisms (e.g., for cellular metabolism with the formation of biomass, new
microorganisms, and generation of Carbon Dioxide (COj) and water).49
57
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4.7 Behavior of Metals and Organic Compounds in Finished MSW Compost
4.7.1 Metals
Metals do not degrade during the composting process, but instead are concentrated as the
organic matter decomposes and reduces in volume.36-50-51 In a study conducted by Leita and De
Nobili (1991), the total concentration of copper, cadmium, lead, and zinc in compost was found
to increase with composting time (stabilization was reached after 40 days). At the end of 160
days, copper increased from approximately 40 to 120 mg/kg; cadmium increased from 3 to 5
mg/kg; lead increased from 80 to 120 mg/kg; and zinc increased from 190 to 210 mg/kg This
trend was related to the concurrent decrease of organic matter content in the compost. The total
soluble carbon decreased the most during the first few days of composting.51
Although the concentration of metals tends to increase during the composting process
in general, the solubility of metals decreases. In several studies, metals were found to be more
difficult to extract as raw compost oxidizes and matures over time.36-50-51 Variations have been
observed in the behavior of different metals due to individual characteristics that affect solubility.
For example, Leita and De Nobili (1991) found:51
• The water-extractable fractions of zinc and lead decreased rapidly during the first days
of composting. This decrease continued at a slower rate of between 10 and 50 days.
After 50 days, the water-extractable fractions of zinc and lead stabilized.
• A completely different behavior pattern for copper and cadmium was noted. Cadmium
exhibited extremely low water-extractable fractions at the beginning of composting and
increased rapidly through the first 20 days of composting. Between days 20 and 72 a
high variability in the extractable fraction was observed. After 72 days, the amount'of
water-extractable cadmium decreased to nearly non-detectable levels.
• For copper, the water-extractable fraction increased slightly at the beginning of
composting and then decreased. Copper did not exhibit the high variability in water-
extractability that cadmium exhibited.
• No relationship between pH and the amounts of water-extractable copper and cadmium
was detected. However, higher amounts of water-extractable lead and zinc were
extracted from samples collected during the first week of composting when pH was still
below neutrality. A ten-fold decrease of the water-extractability fraction of lead and zinc
was observed when pH increased from six to nine.
Henry and Wescott (1992) observed a marked decrease in metal solubility after two
months of composting with the exception of nickel, which retained a fairly high concentration
in the water soluble fraction.52 In contrast, Traina et al (1992) noted a decrease in soluble
metals after 30 days except for lead, which increased.53 Canarutto et al (1991) also observed
58
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decreased water solubility for metals after 60 days of composting, but observed differences in
KNO, and ethylenediaminetetraacetic acid (EDTA) solubility that appeared to be related to the
origin and processing of the compost (anaerobiosis was experienced in one of the composts
tested). They concluded that metals are complexed by humic substances in properly processed
compost.54
In a demonstration project conducted at the Connecticut Agricultural Experiment Station,
the EPA Toxicity Characteristic Leaching Procedure (TCLP) was used to simulate worst-case
conditions. Using this method, metals were extracted from the compost with an acid buffer
Table 28 shows that the resulting leachate metals concentrations were found to be within EPA
hazardous waste regulatory limits.32
TABLE 28. LEACHING POTENTIAL FOR METALS FROM
FINISHED MSW COMPOST32
(Extraction by EPA Method 1311. Analysis by ICP or GFAA)
TCLP Analyte
^^•^•^^MBMH
Arsenic
Barium
Beryllium
Boron
Cadmium
Chromium
Copper
Iron
Lead
Manganese
Mercury
Selenium
Silver
Titanium
Zinc
Sample Concentration
(ppm)
<0.01
0.09
<0.001
<0.5
0.0006
0.02
0.08
0.45
< 0.005
5.1
<0.05
< 0.005
<0.01
0.02
0.98
Standard Deviation
(±ppm)
±0.01
Regulated Lever
(ppm)
±0.01
±0.01
±0.02
±0.04
5
100
100
30
5
0.2
1
5
500
EPA-regulated level is 100 times the drinking water standard.
59
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The fate and transport of trace metals in the environment was studied at the Ohio State
University.53 In the MSW composts used for the study, the trace metal contents were found to
be generally lower than in sewage sludges and lower than EPA's proposed standards for sewage
sludge land application, with the occasional exception of lead (which ranged from 24.1 to 472 8
mg kg-1). Results were as follows:
• The leaching study indicated that application of MSW compost to agricultural lands at
reasonable rates is unlikely to cause any adverse effects on soil properties;
• pH change was found to be minimal;
• Although the salt content of the soil increased after compost application, salt was easily
washed out of the root zone; and
• The amounts of trace metals leached from the compost by water were generally low.
While the lead concentration increased after 30 days incubation, concentrations of the
other metals (e.g., Zn) decreased. Only limited amounts of trace metals were in water
soluble and ion exchangeable forms. Approximately equal amounts of trace metals are
solubilized by Na^Oy (organically bound) and HNO, (mineral precipitate), while NaOH
extracted (recalcitrant organic-bound) significantly less trace metals but much more
boron. Most of the trace metals solubilized by Na4P2O and NaOH were recovered in the
fulvic acid (FA) fraction.
According to Woodbury (1992), when high doses of MSW composts are applied to soils,
the concentrations of many metals in leachate have been shown to exceed drinking water
standards within the first year of compost application, under extreme experimental conditions
(e.g., using higher than normal agricultural, MSW compost, and/or water application rates).
Under field conditions, subsoil will presumably serve as a sink for metals, at least for many
decades.55
A study conducted at the Connecticut Agricultural Experiment Station focused on
determining if composted animal manures could be applied at rates high enough to supply all
nutrients needed by the vegetation in an intensive vegetable production system without
contaminating the ground water with nitrate. The composts included mixtures of horse and
chicken manures mixed with spent mushroom compost, sawdust, cocoa bean shells, cottonseed
meal and/or gypsum. Results showed that compost could be applied for three years to aid in
crop production without producing excessive (greater than 10 ppm) nitrate-nitrogen levels in
ground water. The author concluded that after that period, lower quantities (less than 25
tons/acre) should be applied due to potential cumulative effects.56
Metals in MSW compost may be leached from the soil and enter either ground water or
surface water, particularly at low soil pH. Leaching of metals from MSW compost is most
likely to occur with repeated applications of compost over many years in regions with acidic
sandy soils that are low in organic matter and that receive high rainfall or irrigation. Ground
60
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water is most likely to be affected if it is close to the surface, or if karst formations or other
conditions limit the opportunity for adsorption and complexation of metals by soil components.
The potential for contamination of ground or surface water from application of MSW compost
to soil should be compared to potential contamination by chemical fertilizers.
4.7.2 Organic Compounds
The fate and transport of xenobiotic organic compounds associated with MSW compost
is being studied at the Department of Civil and Environmental Engineering at the University of
Iowa 58 The following compounds were selected as "indicators" of these compounds: bis-
ethylhexyl phthalate (BHEP), benzo [a] pyrene (BaP), chlordane, and pcb (Arochlor 1248). The
fate and transport of these substances is being studied in test plots and then will be compared
against the predictions of the pesticide root zone model (PRZM).
4.8 Effects of Metals and Organic Compounds in Finished MSW Compost on Soil
Microbiota and Vegetation
Available findings on the effects of heavy metals (in general) on soil organisms and
vegetation are summarized below. Data on the effects of organic compounds on soil organisms
were not found during the course of this study.
4.8.1 Metals and Organic Compounds in MSW Compost-Amended Soils
Purves and Mackenzie (1973) noted that in general, the addition of MSW compost to
soils at rates of up to 100 tons per hectare can markedly increase the metals content of the soil.
Application of MSW compost to soils resulted in a significant increase of available levels of
boron, copper, and zinc in soils, elements that plants require in trace quantities. Purves and
Mackenzie (1973) also noted that the concentration of metals remained elevated above natural
soil levels two years after application of the compost. Of the three elements, boron appears to
be taken up most readily by plants. Purves and Mackenzie noted that it seems likely that most
MSW composts that have phytotoxic properties owe these properties to a high content of water-
soluble boron. Copper was found not to be readily taken up by ^plants. Similarly, zinc
concentrations in plant tissues were not found to be abnormally high.59
4.8.2 Effects of Metflk nn Soil Microbiota
At present, no firm conclusions are available about the effects of MSW composts on soil
microbiota Further study may be warranted because soil microbes that alter the chemical form
of important plant nutrients are a crucial link in the biogeochemistry of many elements; some
of these microbes are sensitive to trace metals.55
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ama ?"?"* m £C ^\ *!*** "y McGrath> Br°°kes' Gmer- «* ** ""CHUM identified
apparent adverse effects of sludge-applied heavy metals on the soil microbial biomass and on the
KhKobium strain (a nitrogen-fixing bacteria) which coexists with white clover and other related
species. Experiments showed that the metals caused a decline in the desired Rhizobiwn
population. Long-term experimentation conducted between 1942 and 1961 also indicated an
impact from application of sewage sludge with moderately high metals concentrations (average
r^-Tr /^ 3'°°° ?*. Zn/kg> Il3°° mg Cu' 20° m* Ni' 10° "« Cd, 900 mg »^S
1 000 mg Cr/kg dry weight). The sludge-amended soil favored "selection" (dominance) of a
Nwtoum .strain that formed nodules on the clover which were ineffective in fixing nitrogen
Nitrogen fixation by blue-green algae also was inhibited." However, in a study of soil
contammated with Zn and Cd from a smelting operation, no such effects were observed * The
inconsistent nature of these findings and the tendency for MSW compost to have a lower
concentrations of metals than sewage sludge indicate the need for further research to study the
long-term effects of heavy metals on soil microbes.
4-8-3 Effects of Metals and Organic Compounds on
4.8.3.1 Metals
„ _ Ma"y ,metais « f^gn-zed as essential (in small amounts) for plant growth, including
copper, metal, and zinc. However, high amounts may be phytotoxic (deleterious to plam?
^L?hmTg (e'8-' uCa?miUm> Iead' •"" mercury> « not Considered essential for plani
growth. When compost with high concentrations of metals is applied to soils, the metals may
be ton up by plants and enter the food chain." Metals may be directly available to plants bj
comae through root inception (direct contact). The amount of metals and nutrients that directly
contacts plan roots ,s, however, small; mass flow and diffusion are the most important processes
by which cations are made available to roots.51 p«**sses
on , n,,Hl!.aVf labi'ity,°f *"7 "**** " plimtS' <**" "P"*6' and ** accumulation depend
on a number of soil, plant, and metal characteristics, generalized as follows:42
• Soil pH: Metals are more available to plants when the soil pH is below 6.5.
w tT: f °'ganic1,matter «" chelate and complex heavy metals (i.e. , combine
with a metal to form a chelate nng) so that heavy metals are less available to plants
Since mature composts consist primarily of organic matter, the application of composts
to cropland can actually decrease the uptake of these metals by plants even though the
concentration of metals in the soil may be increased due to the presence of compost."
Soil phosphorus: Phosphorus interacts with certain metal cations to decrease the
availability of metals to plants.
62
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Cation exchange capacity (CEC): CEC is important to the binding of metal cations to
soil particles and the availability of metals to plants.
Moisture, temperature, and aeration: These factors can affect plant growth and the
ability of plants to uptake metals.
• Plant species and varieties: Plant species differ in ability to accumulate metals.
Vegetable crops tend to be more sensitive than grasses to heavy metals.
• Organs of the plant: Grain and fruit accumulate lower amounts of heavy metals than
leafy tissues.
• Reversion: With time, metals may revert to unavailable forms in soil.
lexicological differences: Zinc, copper, nickel, and other metals differ in relative
toxicities to plants and in reactivity in soils.
Several studies have shown that metal toxicity in crop plants is not always directly
correlated with the total amount of metals in soils.51 The amount of metal absorbed by a plant
depends on several factors, including the form of the metal and the soil conditions, such as
pH 43'50 Chancy and Ryan (1993) noted that although increases in metal concentrations in
sludge-amended soils were identified, demonstrations of potential risk from increases in soil
metals were not reported.41
Studies of the effects of MSW compost application and heavy metals uptake and effects
on plant growth generally suggest that metals do not pose significant problems for plant growth.
This is thought to be due to high soil pH and the related limited bioavailability of metals in the
environment. Other studies have shown that ferrous hydrous oxides, phosphates, and organic
components in sludge composts have the ability to reduce the bioavailability of contaminants.
However, it is not known whether MSW compost reduces the bioavailability of metals.
Studies also have found that when MSW compost is added to naturally low magnesium
acidic soils, the resulting rise in pH causes magnesium deficiency in plants. However, this
phenomenon is dependent on factors such as the initial pH of the soil, the native magnesium
level of the soil, and the susceptibility of the plant species. One practice that may mitigate
magnesium deficiency is to supplement the compost with additional magnesium during the
composting process. However, research has not determined the amount of magnesium needed
to avoid magnesium deficiency in susceptible soils.41
Findings from several crop-specific studies reported by Curtis et al (1991), Guidi et al
(1990), and Purves and Mackenzie (1973) are highlighted below:
Curtis et al (1991) reported on a 1973 study that applied 146 tons/acre of MSW compost
to sorghum plants over two years and analyzed the uptake and effects of copper and zinc.
63
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Soil concentrations of zinc increased from six to 436 ppm over the study period While
such an increase in soil zinc concentrations would normally have the potential to'damage
the crop and reduce yield, this negative impact did not occur. It was noted that the level
of zinc 111 plant tissue increased only slightly (from 32 to 36 ppm) during the study
period. This is thought to be due to an increase in soil pH to above 60 At this oH
copper and zinc are not in a form that plants can easily uptake.43 '
In a 1990 study conducted by Guidi et al two different composts were applied to
sunflower spinach, and rye-grass. One compost was derived from vegetable organic
residues and the other from a mixture of the organic biodegradable fraction of MSW and
urban sewage sludge. The study found that the total content of metals in plants grown
on treated soils did not differ from that of the controls. Slight, but not statistically
significant (p = (^increases were noted at higher application rates. This suggests
that the bioavailable fraction of metals in the soils is not increased by the addition of
composts at the rates used in the study (maximum level allowed under Italian laws) The
authors hypothesized that the rise in PH levels in the soils following the addition of
composts depressed the formation of mobile forms of metals.60
Although the water-soluble fraction is subjected to ion exchange when compost is added
to soil and direct toxicity is therefore limited, the concentration of water-soluble heavv
metals can still cause phytotoxicity if the compost is used in the more confined situation
or a potting medium in a greenhouse. Purves and Mackenzie (1973) found that the
degree of soil contamination resulting from applications of MSW compost can lead to an
increase of trace elements in plant tissue. In the experiments with lettuces and dwarf
beans, the levels of boron, copper, and zinc were increased in the leaves The increase
in metal content in dwarf beans was associated with severe toxicity symptoms, including
marked stunting. In affected plants, boron levels were increased by a factor of four and
likely caused the toxicity symptoms.59
Of the three elements studied by Purves and Mackenzie (1973), boron was most easily
taken up by plants (it was noted that a relatively small increase in water-extractable boron
content in soil could result in a substantial increase in boron content in plant leaves) In
the experiment with dwarf beans, most of the additional boron taken up by the beans
remained in the leaves and stems; concentrations in the pods were not high enough to
constitute a hazard to human health. Purves and Mackenzie (1973) also noted that boron
toxicity symptoms have been reported in radishes grown in pots with high levels of MSW
compost and potatoes grown in field soils containing high levels of MSW compost.59
Purves and Mackenzie (1973) found that additional copper was not readily taken up bv
plants grown in compost-treated soils. An increase in copper content in lettuce leaves
was not found to be a danger to human health and increases in copper in bean plants was
found to be small and confined to the leaves and stems. Zinc enhancement in plant
material was noted; however, the concentrations were not abnormally high 59
64
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• Purves and Mackenzie (1973) concluded that while applications of MSW compost at rates
of 50 to 100 tons per hectare can lead to substantial metals contamination of soil, a
phytotoxic hazard only is likely in relation to boron. It is noted that while a single
application of MSW compost is not likely to cause phytotoxic effects in plants, repeated
heavy applications may lead to a progressive build-up of trace elements in the soil which
could lead to toxicity symptoms and a danger to human health.59
Focusing on the effects of metals with respect to plant physiology, Epstein et al (1992)
reviewed available literature and drew the following conclusions with regard to specific
chemicals:38
Cadmium is phytotoxic to plants when added to acidic soils, but it has not been found
to be toxic to plants under natural conditions. In addition, the low ratio of cadmium to
zinc in MSW composts tends to limit the cadmium risk because zinc causes phytotoxicity
at concentrations before cadmium levels become excessive.
• When sewage sludges and MSW composts with typical copper concentrations were land
applied, even at high cumulative loading rates, no evidence of copper phytotoxicity was
observed Only when sludges with high copper concentrations (>2000 mg/kg) were
applied to strongly acidic soils did copper phytotoxicity occur in sensitive crops.
• Plant tolerance to lead in soils is high because lead is strongly adsorbed by soils.
Mercury uptake by plants is low, especially in the above ground portions of plants.
However, some mushroom species accumulate mercury in their basidiocarps (caps).
• Nickel can be phytotoxic in nickel-rich and strongly acidic soils, and significant yield
reduction occurs in economic plant species when the concentration of nickel in the leaves
exceeds 25-50
Only when sludges with high zinc concentrations were applied to strongly acidic soils did
zinc phytotoxicity occur, even in sensitive crops.
In addition, Woodbury (1992) makes the following conclusions related to MSW compost
and its effects on plants:55
Long-term field studies suggest that little increase in the copper content of crops will
occur even with substantial applications of MSW composts (referring to copper content
of the compost and its repeated application over many years). The organic content of
the composts forms complexes with the copper and reduces its availability to plants.
Field studies do not suggest that nickel is likely to cause phytotoxicity due to the
application of MSW composts, since tissue concentrations in these studies were lower
than those reported to cause phytotoxicity.
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Data suggest that applications of MSW compost may greatly increase the zinc content of
soil widi only slight to moderate increases in the zinc content in foliage. CWy Tnder
unusual conditions w,th sensitive species and at low soil pH, could zinc from MSW
composts potentially injure crops.
Chromium in its reduced (trivalent) form presents a rather low toxicity to plants The
oSoLTh" ( r?1161" form) haS a greater P0*"*31 to ^ "«2£ Se «pSe
of chromium by plants growing in soils treated with MSW composts is low since his
usually present m the reduced state, which is not particularly mobife in soU° TOerefore
chromium is unlikely to cause toxicity to plants. "icreiore,
While the application of MSW composts will increase the lead content of soils there i<
s
Mercury can be taken up by plants, particularly when volatilized. Little research has
been done on how mercury may be taken up by plants. MSW composts containing leveh
than the background
4.8.3.2 Organic Cnmoounds
the ri J^!h " 'S aViUlable °" ** effects of "P*** in Msw compost on plants At
the time of Uus report, one study was underway at North Carolina State University « In this
«±8T r6 experi.ments were conduct«l- ^th studies indicated no im
^ n°T,^ *"**«»»* compounds (2,2,4,4' tetrachlorobiphenyl,
and bis (2 ethyl hexyl) phthalic acid ester) in six plant species (potato, letmc
,, to ** at fie-fod o
compost loading rates. Study of the compost-only loading to soil indicated to at 7^
S°i1' ^ ^ °f P°tential 8rowth re*P°"* -nay bSenf whin
"
Curtise'a/(i"1)discussed «>mpost maturity as it relates to phytotoxicity Substances
T aCldS> amm°nia' •"" Cthylene Oxide « ""^ to ^ produced duSTme
of immature compost and can lead to damage of plant roots anTtahS, of
seedling genrnnation. Curtis reported on a method for determining compost
SSiiSS (1f80)H ^ meth0d ^^ CEC "^ ^ Io
value of 60 meg/100 g of ash free material was sufficiently mature to apply on crops «
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4.9 Effects of Ingesting Compost, Compost-Amended Soil, or Products Grown in
Compost-Amended Soil and Associated Risk
This section discusses existing findings gathered by researchers on the effects of ingesting
compost or compost-amended soil and products grown in compost-amended soil. Following
review of this toxicological information, estimated risks associated with ingesting MSW compost
directly and indirectly through the food chain are presented.
4.9.1 Tngestion of Compost or Compost-Amended Soii
Direct ingestion of MSW compost and MSW compost-amended soil is an important
pathway to investigate in the study of MSW compost because ingestion allows the greatest
potential for transfer for many constituents. However, research on the ingestion of MSW
compost only recently began.
Few data are available on the effect of metals and organic compounds in MSW composts
on soil invertebrates. This topic deserves investigation since soil invertebrates are important for
many soil processes, and serve as a food source for other organisms.55 For example,
earthworms have been found to bioconcentrate cadmium and PCBs from soils. The effect of
compost-amended soils on earthworms has not been investigated; however, Chancy and Ryan
(1993) suggested that animals that ingest earthworms, especially earthworms with a digestive
system full of compost-amended soil, may be exposed to a significant exposure route to metals
and PCBs. Animals at higher risk are those with limited territories (e.g., shrews, moles) as
opposed to birds.41-62 Comparison of other mammal species to shrews or other earthworm-
consuming mammals show that cadmium, lead, or PCB transfer from soil is perhaps 10-fold
higher for the shrew than for mice, voles, and other non-earthworm consumers.41
Many studies conducted on the bioavailability of metals in different sewage sludges
ingested by livestock found no increase in bone lead levels. However, other studies have found
a significant increase in tissue lead level with ingestion of lead-containing sludges. Studies
conducted by Utley et al (1972) and Johnson et al (1975) using material similar to MSW
compost (175 and 140 mg/kg lead levels) found small increases in lead levels in kidney and liver
tissue, and in fat of calves (suggesting that the bioavailability of lead in MSW compost may be
greater than that of sludge). However, bone levels are a better indicator of lead absorption and
thus the reliability of these tissue studies is in question.41-63-64
Chancy and Ryan (1993) suggest that the bioavailability of lead through sewage sludge
compost ingestion is limited by the tendency of lead to adsorb to iron oxides, organic matter,
phosphorous, and calcium that are found in the compost. Increasing iron (and potentially
phosphate) levels in MSW compost may help to further reduce the bioavailability of compost
lead.41
67
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Chaney and Ryan (1993) noted that the amount of MSW compost that may be ingested
i A x ?Z approximately 1.5 percent less than the surface-applied fluid sewage
sludge due to differences caused by fluid and dry-applied organic matter. In addition, feeding
studies on PCBs have indicated that sludge organic matter can adsorb PCBs sufficiently to reduce
absorption to cattle by approximately 50 percent (when compared with pure PCBs in corn oil)/"
°'2 IngCStion of Products Ornwn in Cnmpnst-Aimmdgd Sftj|
Limited information is available on the effects on the food chain from ingesting products
grown in compost-amended soils. In an effort to estimate bioavailability of meals lome
researchers have used the findings obtained from sewage sludge studies. The need for^ditiTa!
study ,s illustrated by the complexity of the biochemical synergism evidenced by investigation
onsewage sludge. For example, in studies of the bioavailability of cadmium in sludge frown
food Chaney et al (1978a; 1978b) fed lettuce and Swiss chard to laboratory animals While Z
chard contained significant levels of cadmium, no increases in the liver or kidney cadmium
concentrations were noted. Lettuce containing significant levels of cadmium resulted in a
decrease in kidney cadmium when compared to controls. Chaney et al (1978a- 1978N
concluded that cadmium concentration in crops is not related to the risk of cadmium from those
SSmln bl0availability of "* cr°P cadmium «" «* affected by other dtawTiiMte
. i aiso nas oeen noted that the presence of zinc in compost provides additional
protection from excessive dietary cadmium because the interactions between zinc and cadmium
reduce plant cadmium bioavailability.4165-66 mumium
Plant uptake of PAHs, many of which are carcinogenic, is significant in the case of
carrots; almost all the PAHs in the carrot roots are concentrated in tne peel. Thut ^
^v™,,™ ,.- ^ ™ Qf MSW coropost m home gardens predominantly depends on
Based on a review of available literature, and an understanding of plant animal and
human toxicology, Epstein et al (1992) offers the following qualitative asses nWatS
ingesting products grown in MSW compost-amended soils:" assessments about
i!]^mbinati0n,0f '°W Cadmium levds ""*">«» w'* the low cadmium/zinc ratio in
MSW comports, low potential for crop uptake of cadmium from MSW compost-amended
soils, and low bioavailability of cadmium in crops essentially renders no risk to humans
even if crops from the garden amended with 1000 metric tons of MSW compost per
hectare were the source of all garden foods for 50 years.
Copper has low bioavailability. Copper toxicity to humans and animals rarely occurs.
1 h°^ rfSkK fr°? *? in MSW C°mpOSt is not throu8h PIant "Pfcte °f Compost
ead, but rather the d.rect mgestion of compost and compost-amended soils .hat
contain lead by children or livestock.
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There is no evidence that mercury in MSW compost could cause excessive mercury in
the livers of livestock grazing on compost-amended pastures.
Nickel toxicity to plants occurs before the levels of nickel in the plants could be toxic to
livestock or humans.
As with nickel, zinc toxicity in plants occurs before reaching concentrations in plant
tissues that could be harmful to humans.
4.9.3 Risks from Ingesting MSW Compost Directly and Indirectly Through fog
Chain
Most existing research on health risks from compost focuses on lead from sewage sludge
and reducing risk to the pica child (one who deliberately ingests soils and similar materials),
considered to be the most vulnerable receptor. To estimate (quantitatively) health risks
associated with consumption of MSW compost-amended soils or products grown in MSW
compost-amended soils, a risk assessment can be performed. In 1989, EPA developed a
pathway approach to risk assessment as a means of estimating worst-case risk to humans,
livestock, soil fertility, and wildlife. An example of this pathway approach is presented in Table
29, which shows potential transfer pathways and the Most Exposed Individual (MEI) for trace
contaminants in sewage sludge.41
Using this approach, Chancy and Ryan (1993) indicate that sludge or composts (i.e.,
MSW compost) containing up to 300 mg of lead per kg of dry weight compost will not pose a
significant risk to children ingesting compost products. However, MSW compost generated
from MSW separated at a central facility often contains 200-500 mg/kg dry weight of lead. The
authors therefore suggested that additional efforts may need to be undertaken to divert lead from
the compost stream (either through improved separation or source reduction).41
To evaluate the risk posed by PCBs and PAHs in MSW compost, Chancy and Ryan
(1993) performed a risk assessment for land-applied sewage sludge. The study found that the
following pathways are most limiting to applying persistent, potentially-toxic organic
compounds:41
• Pathway 2 (ingestion by children [pica]),
• Pathway 4 (surface applied compost ingested by grazing livestock), and
• Pathway 9 (accumulation by earthworms which are ingested by wildlife as one-third of
the dry matter in their diet).
Table 30 presents the application limits required for PCBs to avoid risk under each
pathway. In addition, Chancy and Ryan (1993) found that most exposed humans are children
with pica for soil, who are protected at 9.1 /ig PCB/g dry weight. This means that if a child
met the risk model (consumed 200 mg soil/day for 5 years) with soil containing 9.1 /xg PCBs/g,
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TABLE 29.*
OF SLUDGE-APPLIED TRACE CONTAMINANTS41
Most Exposed Individual (MEI)
Sludge-Soil-»Plant-»Human
General food chain, 2.5 percent of all plant-derived foods for
1-Future
l-D&M
2-Future
2-D&M
3
4-Surface
4-Mixed
5
6-Surfacc
6-Mixed
7
8
9
Sludge-Soil-Plant-Human
Sludge-Soil-Plant-Human
Sludge—Soil—Human child
Sludge—Human child
Sludge—Soil—Plant—Animal—H uman
Sludge—Animal—H uman
Sludge-Soil—Animal—H uman
Sludge—Soil—Plants—Animal
Sludge—Animal
Sludge—Soil—Animal
Sludge—Soil—Plant
Sludge—Soil—Soil biota
Sludge—Soil-Soil biota—Predator
Sludge-Soil (Soil biota}-*Predator
Sludge—Soil—Airborne dust—Human
Sludge—Soil-Surface water-*Human
Sludge-Soil-Air—Human
Sludge—Soil-Ground water—Human
^
Home garden 5 yean after last sludge application; 50 percent
of garden foods for a lifetime.
Home garden with annual sludge application; 50 percent of
garden foods for lifetime.
Residential soil, 5 years after last sludge incorporation; 200 me
soil/d.
Sludge product; 200 mg sludge/d for 5 years or 500 me
sludge/d for 2 years.
Rural farm families; 40 percent of meat produced on sludge
amended soil, for lifetime.
Rural farm families; 40 percent of meat produced on sludge
sprayed pastures, for lifetime.
Rural farm families; 40 percent of meat produced on sludee
amended soils, for lifetime.
Livestock fed feed, forages, and grains, 100 percent of which
are grown on sludge amended land.
Grazing livestock on sludge sprayed pastures; 1.5 percent
sludge in diet.
Grazing livestock; 2.5 percent sludge-soil mixture in diet.
Crops; vegetables in strongly acidic sludge amended soil.
Earthworms, slugs, bacteria, fungi in sludge amended soil.
Shrews or birds; 33 percent of diet is earthworms from sludge
amended soil.
Shrews or birds; habitat is sludge amended soil.
Tractor operator.
Water-quality criteria; fish bioaccumulation, lifetime.
Farm households.
Farm wells supply 1QQ percent of water used for lifetime.
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TABLE 30.* COMPARISON OF PCS APPLICATION LIMITS
FOR EACH PATHWAY41
Proposed 503 Rule
Corrected Approach
Pathway _____
1
IF
2F
2D&M
3
4-Surface Application
4-Mixed with Soil
9
Limit Units
kg/ha*yr
kg/ha»yr
kg/ha»yr
kg/ha»yr
kg/ha*yr
kg/ha»yr
kg/ha«yr
kg/ha»yr
kg/ha*yr
Limit Value
4.14
0.264
2.31
7.26
7.26
0.0056
0.0192
0.0192
•
Limit Units
mg/kg soil max.
mg/kg soil max.
mg/kg sludge DW
mg/kg soil max.
kg/ha»yr
mg/kg sludge DW
mg/kg soil max.
kg/ha soil max.
kg/ha*yr
mg/kg soil max.
kg/ha soil max.
kg/ha*yr
Limit Value
17.2
9.09
9.09
18.3
2.46
2.23
2.23
4.46
0.299
4.06
8.12
0.545
this act would cause an increase in lifetime cancer risk of one in 10,000. For Pathways 3 and
4, farm families who consumed about 40 percent of their lifetime meat and milk products from
"homegrown" livestock (which grazed on pastures with sludge applied to the surface annually)
comprise the Most Exposed Individuals. The analyses indicated that the surface application of
sludge containing 2.23 ^g PCBs/g for 70 years would cause an increase in lifetime cancer risk
of one in 10,000. These risk calculations showed that safe concentrations of PCBs are much
higher than the concentrations typically found in MSW compost, less than 0.15 /zg/g. This
suggests a very high safety factor for the low levels of PCBs in sludges and MSW composts. l
Annual applications are based on a 10-year half-life for PCBs in soil. The study assumed
that the fraction of dietary meat and milk products grown in sludge/compost-amended soil is 45
percent (Chancy, Ryan, and O'Connor, 1991); reassessment of this fraction indicates that only
15 percent of all dietary meats and milk products consumed may now come from "homegrown"
livestock, based on more recent dietary surveys. This would increase the allowed PCBs in
sludge, or kg/ha»yr by about 3-fold for Pathways 3, 4, 5, and 6.41
Epstein et al (1992) performed a risk assessment for land application of MSW compost,
co-composts, and source-separated composts. The analysis focused on potential risks from
cadmium, lead, and mercury, and considered human intake of soils, edible plants, milk and
meat, and animal intake of feed crops and pasture. Table 31 presents the results, showing a
comparison of estimated chronic exposure levels with reference doses, which are established
thresholds below which health risk to the most exposed individual (MEI) is not significant.
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™e31,alsoP'esenutslhe hazard quotient (the ratio of the exposure level to the reference
h* ?* VfC1S-1CSS *" °"e' *« is assumed to te no healftrisk. As illustrated km!
able the hazard quotients for mixed MSW compost and source-separated MSW composts were
considerab y less ftan one. Furthermore, this risk assessment indicated negligible different
between nuxed MSW composts and co-composts (MSW and sludge mixtures thft« conJSS
to^h^,rT7??d ^W """P"5'' **"'* SUggeSting m ^ficant tifltance
m me health nsk potenUal for cadmium, lead, and mercury associated with each type of
4.10 Compost Standards
A r -. "° 1ad0nal C°mpOSt quality standards have been developed in the United States
A limited number of states have developed compost standards in response to the facilities thai
are being cited and built within state borders. The metals most commonly regulated under state
requirements include cadmium, chromium, copper, lead, mercury, nickel and zUic PCB
content also has been regulated by some states. Some states establish several classes of compost
and restrict the use of composts that do not meet the most stringent standards Composts
meeting less stringent criteria may be restricted to less sensitive crops such as those not part of
the human food chain or to uses where direct human contact is minimized.
TABLE 31. COMPARISON OF CHRONIC EXPOSURE LEVELS TO
REFERENCES DOSES* *
moronic exposure Hazard Quotient
<^d) (m*/k*
-------
and sets numerical limits for each contaminant to be low enough to achieve a "no observed
adverse effect level" (NOAEL). Such a risk-based standard setting approach assumes that
sufficient information is available to adequately assess the risks and establish thresholds, below
which risks are considered to be negligible or acceptable.
In contrast, a "no net degradation" approach often is used in Europe. Under this
approach, no contaminants are allowed in excess of those levels found in naturally occurring
soils. These standards are derived from soil standards or guidelines that reflect metals levels
in "clean" soils. The allowable concentrations of contaminants in composts and allowable
application rates that will prevent soils from exceeding these background levels are estimated and
established as regulations or guidelines. Because the allowable levels of certain metals are very
low, only composts made from source-separated organic yard and food wastes can meet the
standards.67
A list of compost standards developed by U.S. states and other countries is presented in
Table 32. In addition to these standards, Environment Canada's Environmental Choice program,
a program that certifies environmentally-friendly products, also set limits for metals in compost.
A study of compost from nine full-scale MSW composting facilities was conducted to determine
if, and under what circumstances, the limits set by the Environmental Choice program would
be achievable. The study concluded that the standards are achievable if source separation is
pursued, and not achievable when mixed MSW is processed. However, lack of data was a
problem for some metals (principally arsenic, cobalt, mercury, molybdenum, and selenium).
The Environmental Choice standards are presented in Table 33.M
Prince (1992) noted that significantly more attention has been paid to compost product
(output) standards than to compost inputs; Prince felt equal or more attention should be paid to
the compost inputs. Although product standards are important to ensure that the final product
does not create health or environmental risks, controlling the inputs is a more efficient approach
to improving quality than addressing quality concerns at the back-end of the process. Focusing
only on product quality standards is also problematic because:40
A compost product may be diluted to meet any standard, by adding sawdust or clean
manure, for example, but the absolute amounts of heavy metals remain, regardless of
dilution.
Heavy metals do not dissipate equally throughout the compost; thus, hot spots may occur
and are not detected by a composite sample of material.
No satisfactory standard testing protocol yet exists for evaluating levels of heavy metals
in a compost product. Testing protocols are needed to provide reliable, reproducible data
in a usable form for comparison against regulatory standards. Without standard
protocols, differing results may be produced by various laboratories using different
analytical methods.
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TABLE 33. CANADA'S ENVIRONMENTAL CHOICE STANDARDS
FOR COMPOST68
Metal
As
Cd
Cr
Co
Cu
Pb
Hg
Mo
Ni
Se
Zn
Concentration (ppm)
13
2.6
210
26
128
83
0.83
7
32
2.6
315
• The effect of contaminants such as heavy metals on human health and the environment
depends on site-specific environmental conditions. Soil acidity, for example, affects
plant uptake of heavy metals because a low pH soil has a lower capacity for converting
soluble metals in the compost to an insoluble form. An increase in the soluble metal
content in soils may lead to higher metal concentrations in plants, and thus into the food
chain. Other soil characteristics such as content of clays, bases and oxides, as well as
organic matter content, can also affect the soil capacity for converting soluble metals into
unavailable, insoluble metals.
While these arguments generally are used to promote separation of materials prior to
composting, the arguments also can be used to support source reduction of metals from the
MSW waste stream. During the February 1993 National Recycling Coalition Symposium, a
focus group requested that the National Bark and Soil Producers' Association (NBSPA) develop
a workable set of standards for the source-separated composting industry. Progress made by the
NBSPA will be reported in BioCycle.
4.11 Best Management Practices
In 1991, the Solid Waste Composting Council (now the Composting Council) developed
the Compost Facility Planning Guide for the purpose of promoting a composting approach that
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provides for protection of public health, safety, and the environment while manufacturing a
consistently-marketable compost product.69 The Guide addresses the following topics:
Pre-processing: Separation and preparation;
Composting/high-rate decomposition;
Fresh compost stabilization/maturing;
Compost curing;
Compost refining, storage, and packaging;
Good neighbor issues (complying with state land-use regulations, local zoning
ordinances,; and being a good corporate citizen); and
Public health, safety, and environmental protection.
The environmental protection criteria are general and address:
Dust and noise control;
Equipment guarding for worker safety;
Stormwater run-on and run-off collection and control or treatment;
Enclosure of inspection and sorting stations for incoming MSW;
Ventilation, and management of process air;
Removal of product contaminants; and
Finished market compost analysis.
If leachate is generated by the facility, the Guide suggests that the leachate be collected
and either recycled into the feedstocks (to raise initial moisture content) or separately treated
Leachate should not be recycled into the compost pile after the pathogen reduction phase (to
avoid re-introduction of pathogens and weed seeds). Potential contaminants to the finished
product that are to be removed include:
Household hazardous wastes (e.g., adhesives, batteries, cleaners, explosives gasoline
motor oil, paints, pesticides, and solvents);
• Toxic non-biodegradable substances;
• Rubber; and
• Certain metals (ferrous and heavy metals).
The Guide suggests that analysis and testing of the finished product be performed in
accordance with U.S. EPA standard methods, state standards, or equivalent. The product should
meet the finished product minimum standards for public health, safety and environmental
protection, and industry guidelines for the various grades of compost. (NOTE- Prescribed
values are not included in the Guide.)70
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A draft Model State Regulation for solid waste composting was developed by the Solid
Waste Composting Council in June 1992. The model regulation addresses:71
• Facility design plans (for those receiving only yard waste as well as those receiving solid
waste);
Permitting;
Recordkeeping and reporting;
Operations (including a manual);
Compost testing;
Compost utilization; and
Facility closure.
Table 34 presents a listing of recommended compost testing methods.
4.12 Future Research Needs
In November 1991, U.S. EPA and the Washington State Department of Ecology
conducted a focus group meeting on compost quality and facility standards. As part of this focus
group meeting, participants were asked to identify additional research needs in the area of MSW
compost quality. In general, many participants expressed that not enough information is
currently available on the effects of metals in MSW compost to assess the risks that the product
may present. Participants identified the following needs:72
• Cost/benefit analyses of "cleaning up" (removing the physical contaminants, plastics,
etc., from the final product) mixed MSW compost versus collecting a clean feedstock.
Compare the quality of the end product of mixed MSW versus source separated
feedstock.
• What are the chemical properties of mixed MSW compost?
• What are the appropriate compost sampling procedures and methods considering that
mixing efficiency varies greatly among different process technologies? What determines
a representative sample?
• How does the risk assessment analysis for sludge apply to MSW composts?
• What is the relationship between compost stability, maturity, and bioavailability? How
does it relate to testing and sampling procedures?
• Is mixed MSW compost suitable for daily cover in sanitary landfills?
• What are the safety risks to which workers at MSW compost facilities are exposed?
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TABLE 34. COMPOST QUALITY VERIFICATION TOR THE PROTECTION
OF PUBLIC HEALTH, SAFETY, AND THE ENVIRONMENT71
Parameter
Unit
Test Method
Stability — respirometry*
Soluble SalU — electrical conductivity1
Pathogens*
PH*
Trace Metali per 'No Observable Ad-
vene Effect Level* (NOAEL)"
Cadmium (Cd)k
Copper (Cu)»
Lead(Pb)«
Nickel (Ni)o-
mgOj/kg/hr
mmhos/cm
PFRP*
To be determined*
NCR Publication 221, Method 14*
EPA, 40 CFR Part 257*
NCR Publication 221, Method 14; OR
EPA Method 9045'
mg/kg dry weight
*
AOAC Method ^-
EPA Method 6010A or 7000A; OR
EPA Method 3050A and EPA Method 6010A or 7000A
Mercury (Hg) 4mmr
Film Plastic > 4mm1
mg/kg dry weight AOAC Method 871.21; OR EPA Method 7471A
visual To be determined*
cnWkg To be determined*
Retpirometry is a measure of biological activity and can indicate potential for self-heating, odor, and phytotoxicity.
Several test methods for respirometry are being evaluated by the Solid Waste Composting Council research team headed by Dr H A
J. Hoitink.
Electrical conductivity is a measure of soluble salts and can indicate potential for phytotoxicity.
NCR (North Central Region) Method 14 is contained in Recommended Test Procedures for Greenhouse Growth Media North Central
Regional Publication Number 221 (Revised) 1988.
Pathogens are limited to those of human and animal fecal origin that can be harmful to humans. While the Process to Further Reduce
Pathogens (PFRP) guidelines were originally developed to reduce the numbers of human and animal pathogens of fecal origin the
persistence and variability of plant pathogens also is probably adversely affected. Pathogen control applies to all composts except
possibly some from Specialty Waste.
PFRP is a process standard rather than a product standard. The US-EPA is considering replacing PFRP with a list of indicator
pathogens and limits. This list will be considered for general application to compost products.
US-EPA regulations specified in the PFRP found at 40 Code of Federal Regulations (CFR), Part 257.
pH can relate to metal and nutrient mobility and availability, apparent compost stability, and phytotoxicity.
US-EPA test methods refer to analytic procedure numbers used in EPA Report SW-846 Test Methods for Evaluating Solid Waste
November 1990, as revised.
No Observable Adverse Effect Limit (NOAEL) was developed by Peer Review to identify quality of land-applied sewage sludge and
sludge compost which does not cause significant risk to humans, livestock, or the environment under very conservative, worst-case
risk assessment scenarios, with unlimited application (> > 1,000 metric tons/hectare).
Cadmium can be a human health concern if ingested as a result of plant uptake.
AOAC (Association of Analytical Chemists) Methods 871.21 and 975.03 are contained in AOAC Official methods of Analysis 1990
15th Edition. '
Copper is potentially phytotoxic and can be an animal health concern through direct ingestion.
Lead can be a human health concern through direct ingestion.
Nickel is potentially phytotoxic.
Zinc is potentially phytotoxic.
Mercury can be a human health concern if ingested as a result of mushroom uptake.
Man-made inert material includes glass shards and metal fragments that pose a human and animal safety hazard with unprotected
exposure or through direct ingestion.
Man-made inert content greater than 4 mm (millimeters) will be determined by passing a dried (according to EPA Method 160.3)
and weighed sample of the compost through a 4 mm screen. Material remaining on the screen will be visually inspected and clearly-
identifiable, man-made inerts, including glass, metal, and film plastic will be separated. Material considered injurious will be
identified.
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• What are the impacts to ground and surface waters of runoff from fields that have had
mixed MSW compost applied at agronomic rates?
• What are the long-term effects of metals on micro-organisms in soils?
• How does the presence of lead and mercury in the air (in urban areas) affect compost?
• What is the best available technology for removing metals from the MSW waste stream?
In its Compost Health Risk Assessment (1991), the Minnesota Pollution Control Agency
felt that use of finished compost as a soil amendment in residential gardens or agricultural
settings presented the greatest potential for human exposure to residual chemical constituents in
the compost. Due to the potential for buildup of metals and persistent organic compounds
(depending on rates and times of application), the Minnesota Pollution Control Agency
recommends that the unrestricted use status be examined more closely as it relates to exposure
of people who consume edible products that are raised in or on MSW compost-amended soil.35
Shiralipour et al (1992) note that relatively few studies have continued to monitor crop
yields or document changes in the physical and chemical properties of soil over an extended
period of time with repeated applications of MSW compost. Past research indicates that
bioavailability and leaching of nutrients are influenced by composted MSW, but exact
relationships have not been documented. Long-term studies are needed (five years or longer)
to determine plant uptake of elements from soils that have been amended with composted MSW
containing known concentrations of heavy metals. Predictions of metal loading rates based on
experience with sewage sludge probably are not appropriate for composted MSW, as research
indicates metals are more tightly complexed in MSW than in sewage sludge and this reduces the
bioavailability of the metals until and unless the organic matrix degrades.73
Chancy and Ryan (1993) and Ryan and Chancy (1993) listed a number of research needs
that are most important to MSW composting and marketing. The following is a partial list:41-74
• Will higher iron concentration in MSW compost persistently increase the specific metal
adsorption capacity of compost and thereby reduce the potential for risk from compost
metals, particularly focusing on:
— Bioavailability of compost lead to monogastric animals which ingest compost;
— Phytoavailability of compost cadmium at pH > 5.5;
— Phytoavailability of sludge-applied zinc, copper, and nickel at pH _>_ 5.5; and
— Effects on white clover Rhizobium.
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Does the addition of MSW compost to lead-rich urban soils reduce the bioavailability of
soil lead to monogastric animals?
Can homogeneity of MSW compost be improved by planned mixing during processing?
• Can any MSW compost cause metal phytotoxicity at pH 5.5 or above to sensitive
vegetable crops?
How important is the potential for lime-induced magnesium deficiency from land
application of MSW compost compared to lime-treated sludges?
• Do particular sources of compostable organics carry undesirable levels of boron lead
cadmium, or zinc, and what can be done to keep materials rich in potential' toxic
constituents out of the compost stream?
Do present levels of mercury in MSW compost or MSW/sludge compost still prevent
their use in mushroom production?
How are organisms affected by the use of MSW compost as a soil amendment? A true
ecological risk assessment including system level impacts (species diversity and
population impacts) needs to be made and needed species data collected.
Other MSW compost research needs that were identified in the preparation of this report include:
• VOC emissions during composting operations should be further characterized to more
completely determine the hazard, if any, posed to human health and safety.33 Effects of
various types of feedstocks and processing methods could be examined as part of such
an effort.
Chemical analysis of MSW composts for toxic, persistent organic compounds should be
conducted to more completely and systematically characterize MSW composts Resulting
compost quality as related to the character of the MSW waste stream and feedstock
separation should be examined more closely to determine when source separation is most
necessary.
• In the development of biodegradable plastics and composting technologies, additional
research may need to be performed to support engineering of biodegradable plastics that
do not break down into toxic, persistent, or recalcitrant substances, and that the
degradation products are completely usable by soil organisms.
To round out existing research on the effects of MSW constituents on soil organisms
research should be conducted to determine the effects of toxic, persistent organic
compounds that may be present in MSW compost and their effects on soil organisms
(e.g., invertebrates and microbiota) and plants (pending the findings of the North
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Carolina University study). Similarly, additional research is needed on the effects of
metals on soil-dwelling invertebrates.
Pending the results of the University of Iowa research on the fate and transport of
xenobiotic compounds associated with MSW compost, additional studies may be needed.
More work is needed on developing an agreement of what types of analytical tests need
to be performed on MSW compost (e.g., parameters such as boron and specific organic
compounds). In addition, agreement needs to be reached on the most appropriate test
methods to be used on MSW composts.
4.13 Summary
Metals and organic compounds are present in MSW, and therefore become part of MSW
compost. The concentration of metals and organic compounds can be reduced, but not entirely
eliminated, through pre-processing or collection of source-separated organics. Examples of pre-
processing include removal of undesirable materials (such as household hazardous wastes,
metals, toxic non-biodegradable substances, rubber). In addition, to some degree, the retention
of toxic materials in the compost also can be altered through the composting method (e.g., low
pH and low oxygen content increase metal solubility, facilitating metal removal from compost).
MSW composting occurs in essentially three stages: high-rate decomposition,
stabilization, and curing. The decomposition of MSW during composting tends to take place
indoors or in vessels, thereby limiting concerns associated with leachate generation. MSW
compost stabilization and curing are more likely to occur outdoors. Facility designs that
minimize leachate generation, control storm water runoff, and inhibit percolation into the ground
(e.g., paving) help to minimize any possible risks that could be posed by the portions of
composting operations.
Human health concerns exist during composting operations. The hazards encountered
are largely a function of the composition of the MSW. Potential hazards for workers include:
emissions of organic compounds, pathogens, bioaerosols, trace elements, and other hazardous
substances (e.g., asbestos, explosive substances, corrosive materials, caustic wastes).
In terms of the chemical makeup of the compost product, the primary metal of concern
appears to be lead. Depending on the feedstock, lead may be present at concentrations that are
above 300 mg/kg NOAEL. Certain persistent organic compounds (e.g., particular pesticides,
PCBs, and PAHs) also may be found in MSW compost, albeit at low levels.
These findings have generated some concern in the research community over whether
metals and persistent organic compounds will accumulate in soils as a result of successive
compost applications. In fact, Purves and Mackenzie (1973) observed that application of MSW
compost at rates of up to 100 tons per hectare have resulted in a marked increase in boron,
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copper, and zinc (elements that plants require only in trace quantities) in the soils. Of these
substances, boron is most readily taken up by plants and therefore is most likely to cause
phytotoxicity. In terms of organic compounds and phytotoxicity, little information exists. North
Carolina State University is currently engaged in a study that examines the effects of three
specific organics found in compost on the yield response for six plant species.
Little information is available on the effects of MSW compost on microbiota.
Researchers have focused on using data generated from studies of sewage sludge metals and
smelting operations. Results from studies of the Rhizobiwn strain (nitrogen fixing) of bacteria
have been conflicting; one study showed no effects and another indicated a decline in the
Rhizobiwn population. Similarly, few data are available on the effects of metals and organic
compounds from MSW compost on soil dwelling invertebrates. Studies on earthworms have
shown that they tend to bioconcentrate cadmium and PCBs from soils.
Limited information is available on the effects of MSW compost on the food chain.
Burrowing animals with limited territories (e.g., shrews) appear to be the mammals at greatest
risk from metals and PCBs that may be present in MSW compost. It should be noted, however,
that earthworm-consumers (e.g., birds) also may be subject to significant levels of exposure.
Ryan and Chancy (1993) recommended that an ecological risk assessment be performed to more
fully estimate the risk posed to the food chain.
In terms of human exposure, plant uptake of PAHs appears to be significant primarily
in carrots, thus creating a potential foodchain exposure pathway for humans. Human risk
assessments examining the potential risks posed by MSW compost have shown that lead
exposure to the pica child have been the primary concern. Chancy and Ryan (1993)
consequently suggested that efforts to divert lead from the MSW compost feedstock should be
undertaken through source separation or source reduction.
Standard practices for MSW compost management were established by the Composting
Council in 1991. Standard parameters and methods for MSW compost analysis are still
evolving. States are developing methods of categorizing compost products to guide safe,
beneficial uses of MSW compost. Most compost standards are based on the "clean sludge"
concept developed for land applied sewage sludge (the quantity of land applied sewage sludge
that does not cause significant risk to humans, livestock, or the environment under very
conservative worst-case risk assessment scenarios), with unlimited application (> 1,000 metric
tons/hectare). Some believe that these limits can be used for MSW compost; however, more
research is necessary.
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5.0 POTENTIAL EFFECTS OF TOXICS ON WASTE-TO-FUEL PROCESSES
5.1 Introduction
In 1990, 31.9 million tons of municipal solid waste were managed in municipal solid
waste combustors. This represented approximately 16 percent of all MSW generated in the
United States that year.75 Although combustion has become a prevalent MSW management
practice, concerns have been raised regarding the effects of toxics present in the waste stream
during combustion. To aid in the development of an understanding of the potential risks
inherent in the combustion of toxics in MSW, a substantive amount of research has been
conducted on the behavior of toxic metals and organics undergoing combustion, their impacts
upon combustion and air pollution control equipment, their concentration in the residual ash and
air emissions resulting from combustion, and the effect of preprocessing of metal laden wastes
on equipment and combustion products. This chapter summarizes the available research on each
of these areas.
Much less data are available on the fates and effects of toxics on emerging waste-to-fuel
technologies that involve converting cellulosic wastes to ethanol. This chapter will describe
these technologies, then attempt to extrapolate from limited existing data and quantify the range
of metals concentrations that may impede the conversion of glucose to ethanol through
fermentation. Insufficient information was identified on the effects of organic toxics on these
processes to perform a corresponding extrapolation. The chapter concludes with an
acknowledgement that regardless of whether the cellulosic waste is readied for fermentation
through the use of acid hydrolysis or enzymatic hydrolysis, most of the metals present in the
feedstock will enter the fermentation tanks and be included in the ethanol or in the fermentation
waste byproducts. No evidence has been found to indicate that metals will negatively affect the
preprocessing or processing equipment associated with waste-to-ethanol technologies.
Scientists and policy makers are currently discussing a number of issues related to
combustion as an MSW management alternative, including: 1) the appropriate testing
methodologies to measure toxics concentrations in combustion residuals; 2) the appropriate
regulatory status for combustion residuals; and 3) the health effects resulting from the release
of toxics to the environment from combustion emissions and residuals. While the information
in this chapter will not resolve any of these questions, it does provide an understanding of the
behavior of toxics within waste-to-fuel technologies, identifies those products and process
residuals where toxics of concern will be present, and reports upon the concentrations of toxics
that have been found in air emissions and residual ash.
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5.2 Municipal Solid Waste Combustion
5.2.1 Background
According to EPA, approximately 16.3 percent of the municipal solid waste generated
in the United States undergoes combustion.75 The advantages of municipal solid waste
combustion include reducing the volume of MSW so that less landfill capacity is used and
generating energy for use by the facility and the surrounding community.
Evaluating the potential hazards of MSW combustion and developing ways to mitigate
these hazards, where necessary, requires an understanding of the behavior of toxics within the
combustion process and the concentrations of those toxics found in the products of combustion.
The following sections report upon research conducted into the behavior and effects of toxics
upon combustion, and the resulting concentrations of toxics in air emissions and ash residue.
5-2.2 Conventional MSW Combustion and Emissions Characterization
A significant amount of research has been conducted on the incineration of MSW.
Modern MSW combustion systems will destroy almost all organic material and control most
pollutants before the pollutants are released to the air. However, emissions of toxic compounds
(including dioxins and furans) and the fate of metals are still a major concern.
MSW, which can contain varying amounts of organic and inorganic materials, leaves the
combustion system as stack gases, fly ash, or bottom ash. Stack gas emissions are either
undestroyed compounds, products from the normal combustion process, or products of
incomplete combustion (PICs). Table 35 lists the potential emissions from MSW combustion
and the principal source of each. Fly and bottom ash consist mostly of noncombustible,
inorganic materials.
TABLE 35. PRINCIPAL MSW EMISSIONS AND SOURCES
Pollutant Principal Source
Particulate Matter Ash in waste stream
Acid gases HC1 Chlorine in waste stream
SO2 Sulfur compounds in waste stream
SO3 Oxidation of SC>2 in flue gas
Fluorocarbons in waste stream
Air and fuel nitrogen conversion
Equilibrium product of combustion
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Pollutant
Principal Source
Heavy metals (arsenic, cadmium,
lead, mercury)
Organic compounds
Metal compounds in waste stream
Products of incomplete (dioxins, furans) combustion
or contained in waste stream
A sizable portion of the MSW stream has an organic content that can be oxidized by the
combustion process. Organic matter that may contain sulfur, nitrogen, and chlorine is converted
to carbon dioxide, water, acid gases, and trace organics. Although most organic compounds are
destroyed by the combustion process; a small fraction is emitted to the atmosphere. These
emissions either are undestroyed material passing out the stack or PICs. Some of the PICs
formed are from chemical reactions that occur at relatively low temperatures downstream of the
combustion chamber. These low temperature reactions can result in the formation of
polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), which are generally
considered the prime organic compounds of concern. (It should be noted that PCDDs and
PCDFs have been used as surrogates for all MSW organics because of the concern regarding
the potential health effects of these compounds. In addition, more is known about the emissions
and controls associated with PCDDs and PCDFs than other organics).76
Unlike the organic portion of the waste stream, the metal fraction only may change form
during the combustion process and cannot be destroyed. The metals, therefore, become
associated with one of the combustor's effluent streams, or adhere to the inside of the
combustion equipment. Metals emitted from the MSW combustion chamber include arsenic,
cadmium, lead, and mercury compounds. These compounds are formed from the combustion
of batteries, plastics, paper products, and metal alloys that are common components of MSW.
Metals may pass through the combustor unchanged and collect as bottom ash from the
furnace grates (i.e., residual ash).77 Metals also can leave the combustion chamber through
entrainment of ash particles (i.e., fly ash). Metals also can vaporize or react to form fumes or
fine paniculate matter and may pass through the combustion chamber.78 This distribution of
metals is called partitioning. Due to matrix parameters, as well as design and operating
parameters, specific metals will preferentially become associated with one or more of these
effluent streams. Each metal tends to partition differently and is affected by a number of
factors.
Table 36 lists fundamental parameters that influence metals behavior. These include
those factors associated with the specific metal and encompassing matrix to be treated, the
operation of the combustor, the design of the combustion chamber, and the type of air pollution
control device (APCD) used.79
Partitioning is highly dependent on the volatility and species of the metal.80 The
temperature of volatilization of a metal can be predicted using basic laws of physical chemistry
85
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chambers as vapor, fume, or fine ±S ^J%fe^C ^ thr°Ugh ** combustion
TABLE 36. FUNDAMENTAL PARAMETERS THAT
INFLUENCE METALS BEHAVIOR
Matrix Parameters
Type and Concentration of Metals
Particle Size Distribution of Metals
Propensity to Fragment
Presence or Concentration of Organometals
Chlorine Content
Design and Operational Parameters
Combustion Chamber Temperature
Afterburner Temperature
°f °Xyge" '° Contaminant in Combustion Zone
Degree of Mixing
Combustion Zone Velocity
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5.2.3 The Effect of Materials Hapdling on the Fate of Metals
Modern MSW combustion technologies in the United States take two forms: 1) mass
burn; and 2) refuse derived fuel (RDF). The majority of MSW combustors in the U.S. are mass
burn'type incinerators, that require little, if any, presorting or processing of the MSW prior to
combustion. RDF combustion involves presorting and preprocessing of MSW to remove bulky
objects, ferrous metals, and other noncombustibles and reduce the size of the incoming waste
through shredding or grinding. Waste presorting includes the separation of recyclables from the
waste stream prior to combustion.
One of the major benefits of presorting MSW prior to combustion is the subsequent
removal of solid waste items known to contain certain pollutant precursors. These are the
elements or compounds, such as metals, that make up a significant percentage of the pollutants
in emissions and residual ash. Presorting also can remove potentially dangerous items that are
highly flammable or explosive, such as aerosol cans.
A 1984 study by National Recovery Technologies measured the stack emissions and ash
characteristics at three mass burn combustors from both "as received" MSW and MSW
preprocessed to remove aluminum metals, ferrous metals, batteries, and glass/grit.82 The study
found that burning pre-sorted MSW reduced air emissions concentrations of seven metals, Pb,
Cd, Hg, Be, Sn, Zn, and As in excess of 40 percent. With the exception of Cd, significant
reductions in the leaching of these metals from the ash were found, as measured by the EP-
Toxicity test.
The same study measured the impact of presorting on gaseous emissions. An average
of the results at the three combustors showed at least a 40 percent reduction in CO, HC, Hf,
HC1, and NOx emissions. In addition, the study found that presorting reduced ash volume,
improved ash burnout, and increased boiler efficiency.
Research is available concerning the effect of materials handling on the fate of metals and
organic toxics during MSW combustion. However, this research was not reviewed during
preparation of this report.
5.2.4 The Effect of Matrix Parameters on MSW Emissions
Combustion is the most efficient means of destroying the organic components in the
MSW stream and reducing it to a much smaller, inorganic ash residue. In general, matrix
parameters that impact MSW combustion include average physical and chemical characteristics,
special or unique constituents, and variability.
Three parameters have been found to impact organic destruction efficiency: (1) the type
of organic compound; (2) the concentration of the organic constituent in the waste stream; and
(3) oxygen concentrations and mixing within the combustion chamber. Although other factors
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such as exit temperature and residence time are important incineration aspects, these parameters
do not appear to control destruction efficiency of well-operated systems
JWKW °f tOXuC metalS' ** concentration «d species of a particular metal in the
MSW help determine the degree to which the metal will volatilize during combustion
Determination of the "volatility- temperatures of each metal compound within a £ven waste
requires significant analytical costs; therefore, it generally is not done. Chlorinated metal
compounds generally are more volatile than corresponding metal oxides or uncombined metals
greatCr Chl°rine C°nte °f vaP°rization f°r certain
* i T^°r?aniC constituents Present ^so has some impact on the volatilization of certain
metals. Additionally, the particle size distribution and propensity to fragment affect the amount
of metals that can become entrained and carried from the combustion chamber as fly ash.79
5'2'5 The Effect of Design and Qneratinnql Parameters nn MSW Emkdnnc
Certain design and operational parameters or practices can have significant effects on the
level and type of emissions from municipal solid waste combustors. For example the nature
of waste preparation can significantly impact the levels of toxic metals present in ash 'residue and
air emissions. Preparation of MSW material varies with the type of combustion system and the
pre-combustion operation of the facility. Most facilities use unsorted MSW as fuel for the
combustion chamber, while others use RDF. In addition, some facilities use MSW that has been
? ™™/Ve ** noncombustible material- Mixing that may occur at a facility that uses
unsorted MSW occurs poor to the point at which material enters the feed chutes of the
combustion chamber. Mixing the wastes to have a more uniform distribution of the different
types of material present can help reduce surges through the system. Facilities that sort the
noncombustible matenal from the MSW stream may have better mixing of the material as a
result of the sorting process. RDF is a thoroughly mixed and processed material and is probably
more consistent throughout the combustion system than other waste mixing operations.
behavior.
Design and operating conditions of combustors affect PCDD/PCDF formation and metals
ior. This includes maintaining optimum combustion conditions and operating an
effective air pollution control system. Temperature, oxygen, and CO monitors are indicators
of combustion performance. Low temperature reactions that occur downstream of the
combustion chamber can lead to the formation of PCDD/PCDF. However it also has been
shown that PCDD and PCDF emissions have been reduced by acid gas controls.81
Combustion chamber temperature effects the volatilization of metals and therefore effects
metals partitioning. The lower the combustion chamber temperature, the less likely the metal
will volatilize. Other potential impacts on partitioning include afterburner temperature and the
stoichiometnc ratio of air to feed in the combustion chamber. The feed rate and percent excess
oxygen determine the stoichiometry in the combustion chamber. It can be expected that
-------
excessive feed rates will result in higher mass flow rates entering the APCD. However, once
the saturation point is reached for the metal species of interest, a transition occurs in which
entrainment is the driving mechanism rather than volatilization.79
The temperature and percent excess oxygen in the combustion chamber has an effect on
the partitioning of some metals. Generally, as the temperature increases, the amount of metals
that partition to the bottom ash will decrease. As organic matter is combusted, localized
conditions are created in which reduction reactions take place. Metal species with lower
oxidation states typically are more volatile than those with higher oxidation states. Increasing
the percent excess oxygen in the combustion chamber should minimize the vaporization of metals
due to reduction reactions.83
The type of APCD, or APCD train, that is employed for incineration of MSW depends
on the type of combustion system and the characteristics of the MSW feedstock. MSW
combustion facilities generally are equipped with an APCD train consisting of two or more
APCDs.84 Currently, it is believed that MSW combustion systems should be designed to convert
acid gases and vaporized metals and organics to a solid form. These solids then can be collected
by electrostatic precipitators or fabric filters.
Temperature is a major factor in APCD effectiveness. As flue gas temperatures
decrease, control effectiveness can increase drastically.81 At flue gas temperature below 280°F,
remaining heavy metal emissions, primarily mercury, are removed primarily by condensation
on paniculate matter that are then removed by conventional paniculate control devices.
Because most metals, or metal compounds, condense as solids if combustor gases are
cool, a quench chamber may be used to cool incineration flue gas by the evaporation of water
injected into the hot gas stream at the beginning of the APCD train.
APCDs will have different efficiencies depending on the specific metals being treated.
In addition, the amount of chlorine present will effect APCD efficiencies in systems using wet
scrubbers. However, the removal of most metals is directly related to the removal of paniculate
material, with the possible exception of mercury. Mercury removal efficiency has been found
to be substantially increased by the addition of powdered activated carbon in the gas stream prior
to the first stage in the APCD train.85
5.2.6 Effects of MSW Emissions on the Combustion Equipment and APCPs
In general, metals in MSW are distributed between the bottom ash and fly ash, with
relatively small amounts of metals remaining in the combustion chamber as slag. The relative
distribution of metals depends on the design of the combustor and the composition of the feed.
If the combustion system is not used to produce steam, it appears that metals cause little
damage to the combustion chamber and the APCDs. If the combustor is used to produce steam,
89
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however, metals can condense on the boiler tubes as the gases cool. This creates metal-rich
fouling (deposits) on the boiler tubes that can fall in the bottom ash during tube cleaning This
additional metal loading may cause the ash to fail leaching tests (TCLP or EP Tox).
In MSW combustion systems, HC1 is present at concentrations 100 times greater than
coal-fired boilers. HC1, as well as other acid gases, can cause significant corrosion. However
the formation of acid gases is unrelated to the metals in the feed.
5.3 Toxics in MSW Combustor Ash Residue
Incineration of municipal solid waste produces an ash consisting primarily of silicon oxide
(SIO^, or glass. Additional components of the ash matrix include aluminum oxide iron oxide
calcium oxide, magnesium oxide, sodium oxide, potassium oxide, titanium oxide, and sulfate'
chloride and phosphate ions.86 '
Potential exists for ground water degradation and risk to human health if contaminants
found in the ash are transported from the ash matrix to other environmental media The primary
constituents of concern in MWC ash are inorganics, specifically toxic heavy metals such as
cadmium, lead, and chromium,87 and certain organic compounds such as PCDDs/PCDFs
Several tests exist to determine the likelihood that potentially hazardous constituents will leach
from the ash and the levels at which they will leach. EPA has chosen the Toxicity Characteristic
Leaching Procedure (TCLP) as the regulatory approved test. The TCLP which was
promulgated in 1991, replaced the Extraction Procedure Toxicity Test (EP-Tox) for determining
leachabihty of hazardous constituents from solid and semi-solid compounds Both the EP-Tox
and the TCLP test use an acetic acid solution to "force" leaching and maintain a prescribed pH
to rapidly extract the metals from ash extracts while simulating worst case scenarios of ash
disposal. These procedures are designed to provide data artificially in the absence of actual field
leachate data to simulate ash leachate characteristics.
The TCLP procedure consists of single batch, 18 hour agitation at pH=4.93 for material
pH<5 (TCLP Fluid No. 1) or pH=2.88 for material pH>5 (TCLP Fluid No.2). Extractions
are run under conditions of low (acidic) pH to mimic conditions typically found in landfills
containing decomposing organic matter. MWC ash generally has a pH> 10 88 The TCLP
procedure analyzes for metals, four insecticides, two herbicides, and 38 organic compounds.
Data obtained from TCLP tests are used to determine whether a solid waste exhibits the
hazardous waste characteristic of toxicity. Solid wastes that fail the TCLP are considered to be
hazardous wastes under RCRA. Solid wastes subjected to the TCLP are considered to exhibit
the TC if the waste sample leaches a TC constituent at a level equal to or exceeding the
regulatory limit set forth in 40 CFR 261.24. These regulatory limits represent 100 times the
maximum contaminant levels (MCLs) established for these constituents under the Safe Drinking
Water Act (SDWA). Table 37 summarizes available TCLP regulatory concentrations SDWA
regulatory levels are reported only where TCLP levels have not been set.
90
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This section will present data reported in several prominent studies on both the total
concentration of inorganic and organic contaminants in MWC ash and potential teachability of
these components based on the results of TCLP tests run on ash samples. The data summarized
below are not comprehensive of all MWC ash data, but represent some of the more
comprehensive studies to date.
TABLE 37. LIMITS FOR TOXIC CONSTITUENTS FOR
EPA TCLP EXTRACTION TEST
Contaminant
Arsenic
Barium
Cadmium
Chromium
Copper
Lead
Manganese
Mercury
Selenium
Silver
TCLP Regulatory Limit Safe Drinking Water Act
5,000 ug/L
100,000 ug/1
1000 ug/L
5,000 ug/L
100 (SMCL)'
5,000 ug/L
50 (SMCL)
200 ug/L
1,000 ug/L
5,000 ug/L
SMCL=Secondary Drinking Water Maximum Contaminant Level
5.3.1 General Findings
The solid residues from a municipal waste combustor consist of 80 to 90 percent (by
weight) bottom ash and 10 to 20 percent fly ash from the dust collection system (electrostatic
precipitators, fabric filters, cyclones). If the incinerator is equipped with a flue gas cleaning
system, a flue gas cleaning residue also will be produced. This may be a dry powder or a wet
slurry, depending on the system used.89
Relatively volatile metals such as cadmium, lead, and zinc tend to be concentrated in the
air pollution control system ashes, whereas more heat stable metals such as chromium and nickel
tend to remain concentrated in the ash discharged from the combustion chamber. Mercury poses
a special problem because it is very volatile and, as a result, is difficult to remove from the flue
gas stream. These volatile elements tend to condense out as soluble forms in the ash, such as
chlorides and/or hydroxides, which potentially can be leached from the ash under certain
environmental conditions.90
91
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ashes are relatively heterogeneous, due to variability in operating characteristics
facility design, feed material composition, and constituent volatility. Reimann (1989) found that
pollutant fluctuations in ash samples appeared to be influenced less by domestic refuse quality
than by the amount of commercial and bulky refuse in domestic refuse.91 Differences in the
amount of commercial and bulky refuse in combustor feedstock result in significant variability
between samples taken at a single facility, and often a greater variability between facilities
Reimann (1989) found as much as a 179 percent difference in lead concentration between
different facilities and an equal fluctuation between samples from one facility Cadmium
concentrations varied by 400 percent, both within and between facilities. NUS (1987) reported
that the variability of contaminant concentrations in MWC ash may, even with the composting
of analyzed samples, preclude obtaining representative "laboratory size" samples.92
The wide range of toxic metal concentrations in MWC ash also may result from
difference in the pollution control equipment employed at the combustor. Different pollution
control equipment types remove different sizes of particles, and as a result, different levels of
inorganics including metals in the removed ashes. The fabric filter dust collectors (baghouses)
which have a higher efficiency of removing smaller particles, collect higher levels of inorganics'
Similarly, pollution control technologies using additives to remove the respirable (less than 5
microns in size) finer particles also will result in ashes containing higher levels of inorganics.92
Fly ash typically exhibits a lower percentage Relative Standard Deviation (RSD) (i e
less than 30 percent) especially when generated over short time periods [1 to 2 days] while
variability for bottom and combined ash is moderate to high compared to the fly ash When the
composition of fly ash and combined ash are compared, the composition of combined ash
consistently is more variable than that of fly ash. Some constituent RSDs in combined ash were
higher than 100 percent, although these high RSDs were most likely due to single outlier
values.
5-3-2 Inoramic Contaminant Concentration Research
Significant research has been conducted on the concentrations of inorganics in municipal
waste combustor ash and the effect of these concentrations of organics on the ability of ash to
pass EP-Toxicity and TCLP tests.
A literature review conducted in 1989 found that cadmium typically is 10 to 100 times
more concentrated in fly ash than bottom ash and that lead typically is 3 to 12 times more
concentrated in fly ash than bottom ash. The same studies found typical concentrations of
cadmium and lead in fly ash to be 700 (high = 1,900) ppm and 30,000 (high=97,000) ppm,
respectively. Typical levels of cadmium and lead in bottom ash were 30 (high=100) and 2,300
(high=3,800) ppm, respectively. The typical concentrations for lead exceed the TCLP
regulatory limit and the typical concentrations for cadmium fall just below, while the high
concentrations for cadmium also exceed the regulatory limits.93
92
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Iron, zinc, and lead generally are the heavy metals found in the highest concentrations
in MWC ash. Lead and cadmium generally are found in MWC ash in concentrations close to
the regulatory limits.93
Several studies conducted in the 1980s on fly, bottom, and combined ash indicated that
the fly and combined ash will fail the EP-Toxicity test a significant portion of the time [e.g.,
NYSDEC, 1987; Knudson, 1986; and Svanda, 1987].
Since the change from the EP-Tox to the TCLP test in 1991, combustion and air
pollution control technologies have changed substantially. However, an early study employing
the TCLP test, NUS (1987), found that when MWC fly ash and combined ash are subjected to
the TCLP test, the limits for lead and cadmium are exceed by the extracts a significant portion
of the time.94 These findings were substantiated by NYSDEC (1987), Shinn (1987), Donnelly
and Jones (1987), and Drye (1987). Data indicate that the ash will fail the TCLP more often
for the fly ash, less for the combined fly ash and bottom ash, and least often for the bottom ash
alone.95
In 1990, EPA and the Coalition on Resource Recovery and the Environment
commissioned NUS, an environmental consulting firm, to complete the most detailed study to
date on MWC ash (i.e., NUS, 1990). This study collected combined bottom and fly ash samples
from five mass-burn MWC facilities, representing the state-of-the-art in pollution control and
representing different regions of the country. The air pollution control devices for each facility
are shown in Table 3S.96
TABLE 38. AIR POLLUTION CONTROL EQUIPMENT INCLUDED
IN NUS (1990) STUDY96
Facility Air Pollution Control Equipment
ZA Lime slurry is injected into flue gas after economizer, fabric filter
baghouses.
ZB Dry lime is injected into flue gas after economizer, fabric filter
baghouses.
Fly ash has phosphoric acid added to it and is agglomerated before being
mixed with bottom ash.
ZC Electrostatic precipitators
ZD Electrostatic precipitators
ZE Lime slurry is injected into flue gas after economizer electrostatic
precipitators.
Fly ash has water added to it and is agglomerated before being mixed
with bottom ash. _______««___.===„
93
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Five daily composite samples were prepared for each facility sampled. Table 39 provides
the total metal concentration analyses for each of the five facilities. All 25 samples also were
analyzed, usmg both the TCLP-1 and TCLP-2 tests, for the metals on the primary L SriEJ
drinking water standards list. The results of these tests, shown below in Table 40 again
confirm that the combined ashes may exceed the TCLP regulatory limits for cadmium and lead
in some cases.
TABLE 39. RESULTS OF ANALYSES ON RANGES OF
METALS CONCENTRATIONS IN ASD
Metals
Arsenic
Barium
Cadmium
Chromium
Copper
Iron
Lead
Manganese
Mercury
Selenium
Silver
Sodium
Zinc
^^^S^SBBSSHSS
ND Not detected.
a Presented in mg/kg
ZA-AH-001-
ZA-AH-005*
37-51
436-554
32-56
55-93
946-7,360
44,100-63,300
1,180-1,820
587-1,360
10.4-25.1
ND
4.1-8.7
9,350-11,000
4,310-6,900
=====1
ZB-AH-001-
ZB-AH-005*
28-56
260-1,000
52-152
53-118
674-9,330
13,600-22,200
1,070-1,740
508-846
7.7-12
ND-5.7
5.4-10.0
8,200-10,600
4,360-15,800
=====
Sample^
ZC-AH-001-
ZC-AH-005*
28-36
193-331
42-52
45-57
524-4,470
20,000-25,000
1,710-2,630
518-1,200
1.1-3.2
ND
5.6-12
7,370-8,940
4,110-7,170
^ i^—
ZD-AH-001-
ZD-AH-005*
30-54
411-545
39-69
52-199
959-1,800
22,900-37,100
2,860-22,400
574-965
0.55-2.10
ND-3.9
6.3-11.0
5,890-6,500
4,260-8,000
-^— "^MiMB^M^M^
ZE-AH-001-
ZE-AH-005*
15-20
391-792
18-38
67-665
930-1,820
33,900-45,100
1,170-1,600
531-640
3.2-13.0
ND-4.7
4.4-13.0
5,880-7,770
2,120-8,280
TABLE 40. RESULTS OF NUS (1990) ASH EXTRACT METAL ANALYSIS (ppm)
Arsenic
Barium
Cadmium
Chromium
Copper
Iron
Lead
Manganese
Mercury
Selenium
Silver
Zinc
ND
161 - 1,850
ND- 1,150
ND - 8.0
5-858
ND - 7.220
ND - 10,500
ND-5,170
ND - 3.8
ND
ND
9.7 - 79,500
TCLP-2 Extract
ND-60
12-809
ND- 1,560
ND-799
5.4- 1,400
ND - 162,000
ND - 26,400
3.8 - 7,370
ND - 4.6
ND
ND
26 - 164,000
94
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One major study, conducted under the auspices of the EPA Risk Reduction Engineering
Laboratory (RREL) (Wiles, 1991), contradicted the above studies, finding that while significant
concentrations of cadmium and lead may be present in combined ash, the concentrations of these
metals in the ash generally will not exceed the TCLP standards.95
5.3.3 Organic Contaminant Concentrations Research
Municipal waste combustor ash also may contain certain organic constituents of concern,
including volatile organic compounds (VOCs), polychlorinated biphenyls (PCBs), polychlorinated
dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polynuclear aromatic
hydrocarbons. The concentration of organics in MWC ash, however, generally is lower than
that of inorganics because large amounts of organics are oxidized into water and carbon dioxide
or volatilized during the combustion process. The result is that most organics left in the ash are
nonvolatile and thermally resistant compounds such as those noted above.97
Hasselriis (1988) studied the relationship between temperature, oxygen, and the formation
of dioxins and furans. His study found that excess oxygen and temperature are good control
parameters to maintain minimum residue toxicity, and that carbon monoxide is a good surrogate
for effective mixing of fuel and air resulting in destruction of organics.81
Organic constituents, including dioxins and furans, consistently are found in very low
concentrations, in the parts-per-billion range, in MWC ash.93 NUS (1987) reported that fly ash,
contains higher concentrations of PCBs, PCDDs, and PCDFs, than do bottom ash and combined
ash. Semivolatile compounds (e.g., naphthalene, phthalates, phenanthrene), on the other hand,
will concentrate in the bottom ash, according to the study.92 NUS (1990) found in an analysis
of ash from five separate plants, discussed above, that of the five ash samples analyzed for the
Appendix DC semivolatile compounds, four samples contained bis(2-ethylhexil)phthalate, three
contained di-n-butyl phthalate, and one contained di-n-octyl phthalate. Two PAHs,
phenanthrene, and fluoranthene, were detected in only one of the five ash samples. These semi-
volatile compounds were detected in the parts-per-billion (ppb) range.96
The same study found PCDDs/PCDFs at extremely low levels in each ash sample. The
total Toxicity Equivalents (TE) for each homolog was calculated and for each ash sample was
below the Center's for Disease Control recommended 2,3,7,8-TCDD TE limit of 1 part per
billion in residential soil. Maximum concentrations of PCBs were found to be 30 ppb in fly ash
and even lower in bottom ash.
Four studies conducted in the late 1970s and early 1980s found that the maximum
concentration of PCDDs detected was 220 ppb, the maximum concentration of the most toxic
PCDD (2,3,7,8-tetrachlorodibenzodioxin) was 68 ppb, and that although some PCDDs were
found in all studies in which the presence of PCDDs was analyzed for, studies that differentiated
between fly and bottom ash found higher concentrations in the fly ash.93
95
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Mriu PAH HT es Trted in SAIC (1989) """y"" flyash for PAHs ^ found that
while PAHs did occur in ash, no specified PAHs occur with regularity and in no case did the
concentrations of a particular PAH exceed 0.5 ppm, nor did total PAHs exceed 2 ppm The
PAIHsJ0und *"„•* include benzo(a)anthracene, benzofluoroantheL', and
Jn ' "I*"0"* benzofe.h.Operylene, biphenyl, fluoroanthene, fluorene,
,3-cd)pyrene, perylene, and pyrene have been identified in MWC ash.93
5.3.3.1 Summary
Municipal waste combustor ash will contain both inorganic and organic constituents of
concern. The primary constituents of concern are the heavy metals cadmium and lead
Cadmium and lead are found in higher concentrations in fly ash than in bottom ash Based on
previous studies it appears that MWC ash will fail the TCLP criteria for lead and cadmium
approximately three-quarters of the time, although given the variability of the ash it is impossible
to make a true prediction as to how often the ash will fail the TCLP test.
Organic constituents generally are found in the MWC ash in extremely low
concentrations, in the parts-per-billion range. Dioxins and furans are the primary organic
constituents targeted by previous studies. These constituents primarily are the result of
incomp ete combustion, improper oxygen, and temperature settings, or formation in the post-
combustion environment. The concentrations of organic constituents in MWC ash will vary
according to these variables. ^
5.4 Toxics in MSW Combustor Emissions
Sin™ J^r characterizes air emissions from municipal waste combustors (MWCs)
SS,^ T^T f SUbjeCt t0 regUlati°" Under the CAA' *" overview °f the regulatory
standards applicable to these units is presented first. This is followed by a discussion of MWC
5.4.1 MWC Air Emissions Data
*?. e™ssio"idata from three sources were reviewed: the 1987 MWC Report to Congress
° m BACT/1 Systtm (BLIS>= *«
? "^ ^ 198? MWC Report to C*"*™* Provides some context
for MWC emission rates pnor to the MWC New Source Performance Standards (NSPS) and
for reasons discussed below, arguably represents worst-case emissions. The BLIS data provides
BACT - Best Available Control Technology. LAER . Lowest Achievable Emissions Rate.
96
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a record of what the best new MWCs are emitting. Data from the literature provides some
additional information about modern MWCs emissions.
5.4.1.2 MWC Reportfn Congress Emissions Data
In 1987, EPA prepared a nine-volume Report to Congress (RTC) that compiled available
information on' municipal waste combustion. This report contained an assessment of MWC
emissions data that may be useful in comparing pre-NSPS MWC emissions levels with current
levels. It also may suggest what the emissions from exempt units (i.e., those below 250 tpd unit
capacity or not yet subject to equivalent state emissions standards) may be composed of, since
such units may use a broad range of combustion technologies and air pollution controls.
Table 41 provides a summary of MWC emissions presented as part of the Report to
Congress. This data, which served as the basis for the NSPS, indicates that MWCs emit a
variety of pollutants at widely varying concentrations. The RTC data was drawn from
approximately 30 full scale facilities that employed various air pollution control devices. The
variety of control devices and combustor designs directly contributed to the wide range of
emissions. At the time the data were collected, most existing MWCs were equipped only with
PM control devices, if the units had any controls. Mass burn units, which tended to be larger,
generally used a PM control device, whereas most (36 of 56) modular facilities had no controls.
Modular facilities were smaller and control equipment often was not required due to the small
size of the units. At the time of the RTC, new MWCs were expected to install PM controls.
However, only two facilities were equipped with both scrubbers and PM controls, an indication
that more comprehensive controls were just beginning to be implemented.98
In the Advanced Notice of Proposed Rulemaking (ANPRM) addressing MWCs (52 FR
25405; 7/7/87), the Agency made several observations about the MWC emissions data collected
for that notice,'including the RTC data. These findings include the following:
• The criteria pollutants (PM, SOx, CO, and NOx) constitute a much larger proportion of
stack emissions than the toxic constituents and potentially represent significant health and
welfare concerns;
• Evaluation of baseline emissions of mercury and lead presented as direct inhalation
exposure did not indicate the NESHAP guideline of 1 ug/m3 for mercury or the NAAQS
of 1.5 ug/m3 for lead would be exceeded for new or existing MWCs (such emissions,
however, may contribute to total exposure);
• Several potentially carcinogenic metals (As, Be, Cd, Cr) are emitted from MWCs in
trace quantities. Individual lifetime cancer risk associated with these emissions ranged
from IxlO4 to IxlO-9 for 111 existing facilities and 1x10* to IxlO"11 for 210 projected
MWCs;
97
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TABLE 41. MWC EMISSIONS DATA SUMMARY
FROM MWC REPORT TO CONGRESS98
Pollutant'
•"^••^•^^
PM
S02
NOx
CO
HC1
HF1
As
Be
Cd
Cr
Pb
Hg
Ni
TCDD
TCDF
PCDD
PCDF
Mass Burn
——^————
5.5 - 1,530 mg/Nm3
0.04 - 401 ppmdv
39 - 380 ppmdv
18.5- 1,350 ppmdv
7.5 - 477 ppmdv
0.61 - 7.2 ppmdv
0.452 - 233 ug/Nm3
0.0005 - 0.33 ug/Nm3
6.2 - 500 ug/Nm3
21 - 1,020 ug/Nm3
25 - 15,000 ug/Nm3
9 - 2,200 ug/Nm3
230 -480 ug/Nm3
0.20- l,200ng/Nm3
0.32 - 4,600 ng/Nm3
1.1 - 11,000 ng/Nm3
0.423 - 15,000
ng/Nm3
Modular
^^^•-••^^•••^m^
23 - 300 mg/Nm3
61 - 124 ppmdv
260-310 ppmdv
3.2-67 ppmdv
160 - 1270 ppmdv
1.1 - 16 ppmdv
6.1 - 119 ug/Nm3
0.096-0.11 ug/Nm3
21 -942 ug/Nm3
3.6-390 ug/Nm3
237 - 15,500 ug/Nm3
130 - 705 ug/Nm3
< 1.92-553 ug/Nm3
1.0-43.7 ng/Nm3
12.2 - 345 ng/Nm3
63- 1,540 ng/Nm3
97- 1,810 ng/Nm3
RDF-Fired
•'
220 - 530 mg/Nm3
55-188 ppmdv
263 ppmdv
217 - 430 ppmdv
96 - 780 ppmdv
2.1 ug/Nm3
19 - 160 ug/Nm3
21 ug/Nm3
34 - 370 ug/Nm3
490 - 6,700 ug/Nm3
970 - 9,600 ug/Nm3
170 - 440 ug/Nm3
130 - 3,600 ug/Nm3
3.5 - 260 ng/Nm3
32 - 680 ng/Nm3
54 - 2,840 ng/Nm3
135-9,100 ng/Nm3
All values corrected to 12 percent CO2.
fiih n^ °rganiC carcino8CM (chlorobenzenes, chlorophenols,
formaldehyde, PAH, PCB) were found to pose cancer risks similar to the trace metals!
and
Chlorinated dioxins and dibenzofurans were estimated to pose the most significant risk
of causing cancer, posing a risk range of Ixlfr3 to 1x10* for existing MWCs and lxlO«
to 1x10* for projected MWCs.
98
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These risk levels were used to support an EPA finding that MWC emissions may
reasonably be anticipated to contribute to the endangerment of public health and welfare, and
prompted EPA to regulate MWC emissions through the NSPSs.
5.4.1.2 BLIS MWC Emissions Data
EPA's BACT/LAER Information System (BLIS) contains the current2 permitted
emissions limits for new or modified MWCs for criteria and non-criteria pollutants.3 These
limits represent the maximum allowable emissions of each respective pollutant. BLIS data
represents emissions that result from the use of the best or nearly best pollution control
technologies. Therefore, this data represents best case emissions (i.e., best technologies used
by new facilities subject to the NSPS). Additional data sources must be examined to identify
the complete range of MWC air emissions.
Selected BLIS data for some pollutants is presented in Table 42. The data indicate the
type of combustion unit, unit capacity, and state pollutant emission limit for various facilities.
To allow for comparison, all emission limits were converted to both pounds per million British
Thermal Units and milligrams per dry standard cubic meter. Due to the lack of comprehensive
data, some values had to be estimated. It is believed that the estimated values are correct to the
first'digit. When examining the data in Table 42, it should be noted that the standards have
become increasingly more stringent, as indicated above. The PM10 emission limits have been
reduced by 33 percent (from 0.015 to 0.010 gr/dscm) and emissions of dioxins have been
lowered to as low as 1 ng/dscm, while the NSPS is 30 ng/dscm.
5.4.1.3 MWC Air Emissions Factors
A third source of current MWC air emissions data is an article published in February
1991 and entitled "Toxic Trace Pollutants From Incineration."99 The authors developed
emissions factors for municipal solid waste, hazardous waste, and medical waste incinerators.
In compiling the data for MWCs, data were collected from over 50 resource recovery facilities
in the U.S., Canada, and Europe covering a wide range of fuel types, combustion systems,
throughputs, and pollution control technologies. This article focuses on modern facilities and
averaged test runs to calculate one value for each pollutant measured at each facility. Statistical
analyses then were used to calculate one emission factor for like facilities. The geometric mean
and upper range of these emission factors for municipal solid waste resource recovery facilities
are presented in Table 43.
2 Data was retrieved from BLIS 8/24/93.
3 Criteria pollutants include PM10, NOx, SO2, CO, Pb, and Ozone (VOC). Non-criteria pollutants include
numerous carcinogenic compounds, including the approximately 189 toxic compounds specified for regulation as
air toxics under the 1990 amendments to the CAA.
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It is difficult to compare these emissions levels with the other data since the units are not
standardized. Nevertheless, some observations can be made. Emissions rates vary by over 5
orders of magnitude for different metallic compounds. This is greater than the variability found
in either the hazardous waste or medical waste incinerator emissions examined in the article,
which varied by 3 and 2 orders of magnitude, respectively. The article does not speculate on
the reasons for this, but it is likely due to the inherent variability of MSW. The article indicates
that the metals emissions from MWCs are much lower than for hazardous waste incinerators
(typically in the 1Q-2 to 1(T* range). The article notes that dioxin emissions are highest for
medical waste incinerators and lowest for hazardous waste incinerators, with MWCs falling in
the middle. Comparing the dioxin emissions with the data from the RTC, these emissions fall
at or below the low of the RTC data.
5.4.2 Summary of Air Emissions Research
Municipal waste combustors recently have become subject to stringent regulation under
the Clean Air Act (CAA). These regulations, which are technology-based (i.e., based on an
evaluation of the best demonstrated control technology and not an assessment of risk), are
forcing new MWCs to install the best available air pollution control technology to control air
emissions. For new units, the result is that air emissions levels must fall between the NSPS
standards and the BACT/LAER standards, with facilities being increasingly forced towards the
BACT/LAER level due to the top-down nature of these requirements (i.e., facilities must justify
why the best controls are not feasible). The BACT/LAER data indicate that new MWCs are
subject to stringent air emission standards, standards that are in some cases significantly below
the regulatory standard, and, perhaps most significantly, standards that in all cases represent a
massive improvement over the emissions rates reported in the 1987 RTC.
To supplement the current MWC NSPS standards, the Agency also is required to
establish MWC emissions standards for mercury, lead, and cadmium. These standards, which
are now imposed (if at all) by the states, are likely to further reduce allowable emission rates
for new MWCs. This focuses the question of air emissions quality on exempt units, those that
were built prior to December 20, 1989 (i.e., existing facilities) and those below the 250 tpd
capacity threshold.
Technically, existing units are subject to the MWC guidelines promulgated by EPA.
However, many existing units may not be required to comply with these provisions. If existing
units are not required to comply with the NSPS, these units may be subject to reduced local
requirements (in non-attainment areas) or no emissions regulations. Potentially, these units may
be emitting significantly more toxic air emissions than new units. While the RTC does not
present data focusing on existing MWCs, it does offer some indication of the potential range of
air emissions from these units. The RTC data does not, however, account for the number of
existing facilities, their size, or throughput capacity. Such data may exist in Federal databases,
literature, or state records.
101
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TABLE 43. EMISSIONS FACTORS FOR MSW INCINERATORS99
Pollutant
Dioxins/Furans (ng/Nm3) [U.S. EPA TEF, 1987]'
Antimony (Ib/ton of waste)
Arsenic
Barium
Beryllium
Cadmium
Chromium
Cobalt
Copper
Lead
Magnesium
Manganese
Mercury
Molybdenum
Nickel
Selenium
Silver
Thallium
Tin
Vanadium
Zinc
PCB (ug/Nm3 @ 12% CO2, dry)
Carcinogenic PAH
Aldehydes
Polychlorobenzenes
Polychlorophenols
Geometric Mean
0.33
1.13E-05
7.22E-06
3.38E-04
2.12E-07
2.65E-05
1.04E-04
1.93E-05
1.77E-04
2.86E-04
2.78E-03
6.59E-05
2.74E-03
7.20E-05
8.62E-05
8.19E-06
2.38E-04
1.26E-08
1.15E-04
1.02E-05
1.14E-03
0.47
0.25
417
1.88
3.59
Upper Range
1.11
3.82E-05
4.14E-05
9.19E-04
1.21E-06
1.23E-04
6.22E-04
1.28E-04
4.43E-04
8.23E-04
3.67E-03
4.90E-04
7.23E-03
1.32E-04
5.59E-04
2.13E-05
NA
NA
2.70E-04
4.07E-05
5.00E-03
1.90
1.42
617
4.74
5.47
12 percent CO2, dry, based on mass burn facilities with high efficiency PM and acid gas controls.
102
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Small units (i.e., below 250 tpd capacity) also may be emitting significantly more toxic
air emissions than new units due to reduced regulation. However, EPA also is required to
promulgate air emissions standards for new or modified MWCs with unit capacities of less than
or equal to 250 Mg/day. Thus, future emissions from this category will decrease and only
existing small units will remain outside of the regulatory requirements discussed in this chapter.
Overall, the data reviewed for this chapter indicate that there has been a dramatic
decrease in toxic air emissions from new MWCs with unit capacities above 250 tpd. Given the
magnitude of these reductions and the risk estimates compiled for the MWC ANPRM, it appears
that the decrease in emissions should correlate with a significant reduction in risk to human
health and the environment for these units. Additionally, emissions standards for three new
toxics and small MWCs are being developed, which should further reduce the risk from air
emissions. One implication of the increased level of emissions control is the generation of
greater amounts of potentially toxic ash. With regard to existing and small MWCs, toxic air
emissions may be a more significant concern. If the ranges presented in the RTC data are
representative, these units may be of concern. However, current emissions data is needed to
assess how risk levels associated with these units may be changing.
5.5 Waste to Ethanol Processes
The following sections describe three processes that may be employed to convert MSW
into ethanol that can be used as a fuel. The three processes described include: conversion of
cellulosic waste to ethanol, acid hydrolysis, and enzymatic hydrolysis. As described below, the
presence of heavy metals in the feedstocks for these processes may disrupt each of these
processes. However, MSW feedstocks may contain additional metals that act as micronutrients
that are essential to the metabolism of microorganisms that in effect carry out these processes.
No research has been identified that documents the effect of organic toxics in these emerging
technologies.
5.5.1 Cellulosic Waste to Ethanol
Increasing MSW generation rates combined with limited disposal capacity has sparked
interest in using municipal solid waste as an alternative feedstock for ethanol production.
Processing of municipal solid waste into fuels such as ethanol may give more flexibility in the
use of this waste stream. Although conversion of cellulosic waste to ethanol is not currently
commercially practiced, much research has been conducted on this process. In the future, this
may be an alternative MSW management option.
A large portion of MSW is a type of lignocellulosic material, a material that has great
promise as a substrate for ethanol production. Lignocellulosic materials are composed of
carbohydrate polymers known as cellulose and hemicellulose plus lignin and smaller amounts
of other materials. More common names for cellulosic waste are paper, cardboard, paperboard,
103
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and sawdust, all of which are made from wood, although wood is not the only source of
cellulose. Other examples of lignocellulosic materials include: 1) agricultural residues; 2)
energy crops such as short-rotation woody and herbaceous crops, and 3) residues from logging
operations (e.g., slag, wood chips, sawdust). Relevant differences between each of these
feedstocks are the ratios of the three basic components in the material, cellulose, hemicellulose,
and lignin. Conversion of cellulosic waste from the MSW stream will transform these wastes
to useful products such as ethanol, animal feed, and fructose. Transformation of cellulosic
wastes begins by their separation from the remaining solid waste such as glass, plastics, and
metals. Separation of cellulosic wastes is an essential step since other materials will contaminate
the end products of the conversion process.
The following section briefly describes the cellulosic waste to ethanol process, which
comprises two preprocessing steps: acid and enzymatic hydrolysis, followed by fermentation
to produce ethanol. Many cellulosic materials contain metals, discussed in previous sections,
that will end up either in process residuals or in the ethanol produced.
5.5.1.1 Fermentation
Fermentation is the conversion of glucose to ethanol or other products using a biological
organism. These organisms consume the glucose and produce ethanol and other products as a
waste. The type of organism used varies according to the desired end product.
Preprocessing of the feedstock varies according to the specific operation but may include
grinding, shredding, and slurry making. These steps reduce the particle size and increases the
surface area of cellulose to increase conversion operation speed. The next step is to convert the
cellulose material into glucose, which can be accomplished with acid or enzymatic hydrolysis,
described in detail below. The basic difference between acid and enzymatic hydrolysis is that
the latter has a higher glucose yield but it is much slower than the first method.
After the material is converted to glucose, fermentation can begin by adding a fungus to
the glucose in a fermentation tank. The conditions inside the tank (temperature, pressure, and
pH) are controlled for optimum product yields and these conditions vary according to the type
of fungus that is used for fermentation. The fungus will consume the glucose and produce
ethanol and other materials, such as acetic acid, as a waste. The ethanol then can be distilled
from the solution. This process is illustrated in Figure 9. Fermentation can be affected by other
bacteria and fungus that may be in the feed material. As a result, some processes will include
a sterilization step before fermentation.
Residual materials, referred to as still bottoms, are generated mainly from the distillation
process. These can be incinerated to produce steam for the distillation process. In addition,
some filtrate materials will be discarded. The remaining materials, such as fungus, water, and
slurry materials, are recycled into the process.
104
-------
CaUoste
Waste
Ethanol
Stll Bottoms
Figure 9. General Fermentation of CeUulosic Waste to Ethanol.
5.5.7.2 The Effect of the Presence of Metals on the. Waste-to-Enerw Process
The ethanol and residual products from the waste to ethanol processes may contain metals
previously contained in the MSW. Although many metals are micronutrients and are essential
to the metabolism of microorganisms, the same metals are often toxic at high concentrations.
Metals, especially those referred to as the heavy metals (such as lead, cadmium, and mercury),
may disturb the metabolism of the microorganisms, and therefore the fermentation process.
Metals can be broken into two groups: nutrients and heavy metals. This grouping only is meant
to establish broad categories to separate those metals that are usually nontoxic at most
concentrations, the nutrients, and those metals that are often toxic at low concentrations, i.e.,
the heavy metals.
Nutrients are those elements deemed to be essential to the development of
microorganisms, in this case the fungi, and have well-documented concentration levels at which
normal growth occurs. Because these metals are nontoxic at fairly high levels, little data exist
describing their toxicity towards the fungi. The information that is available delineates required
concentrations for the nutritional aspects of growth. Because these concentrations are at a fairly
high level, some assumptions can be made to determine the negative effects of these same
elements on the microorganisms. In all cases, the concentrations listed in Table 44 are those
at which growth is enhanced.100-101 The concentrations at which growth is retarded will be at
least an order of magnitude greater than those listed.
Initially, the usefulness of these data seems limited. The concentrations at which growth
is enhanced have been identified but have not been correlated to the potential for inhibitory
interactions.
Since copper is considered both a micronutrient and a heavy metal, depending on the
classification system, a comparison of the data on both aspects of copper can be made, as can
a correlation from this information to the rest of the nutrients. As can be seen from Table 44,
105
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the concentration of copper required as a micronutrient is 0.5 mg/L. Literature suggests that
concentrations of copper at approximately 15 mg/L begin to inhibit the production of ethanol in
a batch reactor.102 At 95 mg Cu/L, inhibition is clearly discernable. At the point of minimal
inhibition, the copper concentration is 30 times that of the nutrient level. At the time of
discernable inhibition, it is approximately 200 times that of the nutrient level.
TABLE 44. CONCENTRATIONS OF ESSENTIAL ELEMENTS
REQUIRED FOR GROWTH102
Element
Iron
Potassium
Chloride
Copper
Zinc
Cobalt
Sulfate
Manganese
Boron
Nickel
Molybdenum
Typical Forms
FeSO4(NH4)2, FeCl3
KC1, KH2PO4
KC1, NaCl, CaCl2, MgCl2
CuSO4
ZnSO4, ZnCl2
CoSO4
CuSO4, ZnSO4, CoSO4
MnSO4, MnCl2
H3BO4
NiSO4
Na2MoO4
Concentration (mg/L)
35
120
60-520
0.5
.0023
.0023
.0023 - 35
5
.0073
.0025
.0033
Data also were reviewed for cobalt. At 56 mg/L there was no discernable inhibition of
ethanol production although literature stated that inhibition should begin to occur at
approximately 15 mg/L.102 The 56 mg Co/L point of minimal inhibition is approximately 25,000
times that of the nutrient level. Both the 25,000 times and the 200 times factors will be used
to provide potential concentrations at which the nutrient elements may begin causing inhibitory
reactions. Because every element has different properties, these estimated concentrations should
be used only as gross estimates of potential interactions in lieu of applicable scientific studies.
Table 45 contains the estimated concentrations.
106
-------
TABLE 45. ESTIMATIONS OF POTENTIAL
INHIBITORY INTERACTIONS OF METALS102
Element Estimated Concentration of Inhibitory Effects (mg/L)'
Iron 7000 - 875,000
Potassium 24,000 - 1,000,000
Chloride 12,000-1,000,000
Copper 100 - 12,500
Zinc 0.46 - 58
Cobalt 0.46 - 58
Sulfate 0.46 - 875,000
Manganese 1000 - 125,000
Boron 1.46-182
Nickel 0.5 - 62
Molybdenum 0.66 - 82
Should only be considered as gross estimates in lieu of scientific validation. A range of
200X and 25,OOOX has been provided.
In one study, lead was not seen to inhibit the production of ethanol at concentrations as
high as 250 mg/L.102 This may be due to the interactions of the Pb2+ species with the grape
juice matrix with which the study was conducted. Interactions with a cellulosic matrix may
differ. Discernable inhibition of ethanol production due to cadmium concentration was evident
at approximately 115 mg Cd/L. Bacterial fermentation was reduced by 50 percent at a
concentration of 175 mg Cd/L.103 This is within the same order of magnitude as the effect on
the fungi. Respiration and fermentation were completely inhibited by concentrations of
approximately 1000 mg Cd/L.104 Respiration and fermentation also were completely inhibited
by concentrations of approximately 200 mg Hg/L. Fermentation in bacteria was inhibited 50
percent by concentrations of 20 mg Hg/L and 21 mg Cu/L. This is an order of magnitude lower
than that reported for mercury in the fungi, but is in the same range as that for copper. Nickel
inhibited fermentation in bacteria by 50 percent at concentrations of 160 mg/L.104 This is within
the same range as the estimated value for nickel. In addition to the decreases in fermentation
for the noted heavy metals, a decrease in fermentation time was also observed.
Because the inhibitory effects of metals on both bacteria and fungi seem to be fairly
similar, data from a bacterial study published in 1978 by C.W. Forsberg will be used exclusively
107
-------
for determining the effects of arsenic, chromium, and selenium. A concentration of 73 mg of
selenium/L inhibited fermentation by 50 percent. Trivalent arsenic inhibited fermentation by 50
percent at 304 mg/L, and pentavalent arsenic inhibited fermentation at 1600 mg/L. Bacterial
fermentation was inhibited by 50 percent at concentrations of 70 mg Cr*6/L. The inhibitory
effects for trivalent chromium and/or total chromium are not noted. Because of the extreme
toxicity of Cr"*"6, the toxicity of total chromium and Cr+3 should be considerably less than that
ofCr+V03
Data were not readily available to determine the toxic effects of Al, Sb, Ba, Be, F, Ag,
Tl, and V on the fermentation process. Out of this group, the four metals of concern should be
Sb, Ba, Ag, and Tl. An estimate of the toxicity of these four metals to the fermentation process
may be approximately < 1000 mg/L. Toxicity levels for the other elements, Al, Be, F, and
V, may be estimated at concentrations > 1000 mg/L.
5.5.2 Acid Hydrolysis
Most of the research on acid hydrolysis to date has used residues from logging operations
as the feedstock rather than municipal solid waste. An article, prepared by Hans Grethlein of
Dartmouth College in 1975, found that a model developed from a bench-scale analysis of the
acid hydrolysis of wood chips could accurately predict the performance characteristics of
MSW.105
In the acid hydrolysis process, the cellulosic material is ground and water is added to
produce a slurry or fed into the processing equipment via screw extruders, which dewater and
compress the material. The purpose of acid hydrolysis is to break down the cellulosic material
to fermentable sugars, a process known as saccharination. The acid catalyzes the hydrolysis
reaction. Operating conditions generally consist of a relatively dilute acid (e.g., 1 percent) in
the presence of high temperature conditions (e.g., 240°C). The product is a concentrated
solution of glucose, which is then converted to ethanol via fermentation during subsequent stages
of the process. Figure 10 depicts a generic model of acid hydrolysis. From the literature, it
appears that sulfuric acid is the most commonly used catalyst; other acids mentioned include
nitric acid, hydrogen chloride, and calcium chloride.
108
-------
Stil Bottoms
1
Cellulosic
Waste
Slurry
Preparation
^^
Hydrolysis
Reactor
Storage
Glucose
Solution to
Fermentation
Figure 10. Generic Acid Hydrolysis of Cellulosic Waste.
Three different kinds of acid hydrolysis processes are described in the literature, single-
stage, percolation, and two-stage. In single-stage hydrolysis, acid is added to the feedstock in
a reactor and the product is removed. In percolation, acid is slowly added to the feedstock to
hydrolyze the cellulose and remove the by-products while the sugar diffuses out. Two-stage
hydrolysis achieves higher product yield because the cellulose is hydrolyzed twice. Research
has shifted away from percolation in favor of two-stage acid hydrolysis because of the higher
concentration of sugar in the product.
Residuals from acid hydrolysis may include volatiles (furfural, acetone, and acetic acid),
degradation products (phenols, formic acid, "humic substances," and levulinic acid), and water.
The volatiles can be captured and condensed for recovery. Dewatered lignin from wood can be
used as fuel. Glucose can be recovered from the acid solution and recycled into the hydrolysis
process.
Factors influencing the efficiency of acid hydrolysis include:
• Nature of the feedstock (e.g., type of feedstock and solid/liquid ratio)
• Time of reaction
• Temperature
• Type of acid; and
• Concentration of the acid.
Improper regulation of temperature and time can result in the degradation of the sugar
and lower product yield. Other by-products also may be formed that may interfere with the
hydrolysis and cause equipment fouling.
109
-------
5.5.2.1 Effect of the Presence of Metals in Acid Hydrolysis
As described above, MSW contains metals that could be processed using acid hydrolysis.
While no data have been identified that address the effect that metals concentrations may have
on the acid hydrolysis process itself, metals may be solubilized by the dilute acid and may
continue into the fermentation process.
5.5.3 Enzvmatic Hvdrolvsis
Enzymatic hydrolysis is the conversion of cellulosic material to glucose through the use
of enzymes produced by a biological organism. Several types of fungus have been used for this
process. An example is the Trichoderma viride QM 6a, which is a hypercellulolytic mutant.
Cellulosic materials such as those from MSW are more suited to enzymatic hydrolysis because
these materials have been processed to manufacture goods. This processing exposes more of the
cellulose, but preprocessing of the feedstock, as described earlier, is necessary to further expose
the cellulose.106
An enzyme solution, cellulase, is produced (see Figure 11) by introducing a fungus into
cellulose containing slurry. The fungus will produce an enzyme to convert the cellulose to
glucose and proceed to consume the glucose. After the fungus has consumed the glucose, the
slurry is filtered to remove the solids. The solution, cellulase, contains the enzyme to reduce
the cellulose to glucose. Cellulase is added to the prepared slurry of processed cellulosic
material and water in the hydrolysis reactor. The reactor operates at atmospheric pressure, a
temperature of 50°C, and a pH of approximately 4,8. The reactor conditions vary according
to the specific fungus/enzyme used and the end products. Finally, the syrup is harvested from
the reactor and transferred to fermentation tanks for further processing. The remaining slurry
is recycled into the process. The enzymatic hydrolysis process is sensitive to by-products from
preprocessing that may be poisonous to the fungus used. The process is also sensitive to other
bacteria that may contaminate equipment or produce by-products that may inhibit the enzymes
used in the process. For this reason, some processes include a sterilization step to destroy
bacteria in the feed material.
Process residuals consist of filtrates and filters. Although much of this material is
recycled into the process, some is probably disposed of occasionally. Residuals will result from
cleanup of equipment such as water and any cleaning chemicals.
5.5.3.1 Effect of the Presence of Metals on Enzymatic Hvdrolvsis
As discussed previously, MSW materials contain various amounts of metals. No data
have been identified that address the effect of metals concentrations on the cellulase enzyme.
If an assumption is made that metals should have no effect, metals subjected to the enzymatic
hydrolysis process may be partitioned between the slurry and syrup with similar concentrations
110
-------
entering each phase. Since the slurry is continually added to the reactor, most metals should
eventually end up in the syrup.
Fungus Water
Celluloslc
Waste
Broth
Production
Filtration
Water
Celulase
CellulosJc ^
Waste ^^
Cellulose
Slurry
Preparation
•»^
Hydrolysis
Reactor
Syrup
Harvesting
— ^- Slurry Recycled
— ^^ Syrup to
Fermentation
Figure 11. Enzymatic Hydrolysis of Cellulosic Wastes.
5.6 Summary
This chapter discussed the fates and effects of toxics on the processing and preprocessing
operations associated with waste-to-fuel technologies. It also reported upon the research
undertaken to measure the concentration of toxics in the air emissions and ash residue resulting
from traditional municipal solid waste combustion.
Preprocessing of MSW prior to combustion involves the separation of certain items from
the waste stream and the shredding or grinding of the remaining material. Research indicates
that the removal of metal laden objects prior to combustion will significantly reduce metal
concentrations in combustion process emissions and residue streams. In addition, removal of
aluminum and ferrous metals, batteries, and glass/grit improves combustion efficiency, reduces
ash volumes and causes a reduction in the emissions of many acid gases.
The fate of metals that enter the combustion process will be determined by: 1) the type
of metal, concentration, particle size, and volatilization temperature; 2) the chlorine
concentration in the feedstock; and 3) a variety of operating and design parameters of the
combustion chamber and associated air pollution control devices. Research indicates that, in
general, metals with high volatility temperatures will leave the combustion chamber in the
bottom ash, while those with low volatility points will wind up in the fly ash after vaporizing,
then condensing either homogeneously or heterogeneously on the surface of entrained ash
particles. The presence of chlorine tends to increase the vaporization of certain metals, and
thereby increase their concentrations in the fly ash. Leaching characteristics of bottom and fly
111
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ash vary significantly. While samples of bottom and combined ash most often pass regulatory
leaching tests, fly ash samples often fail because of lead and cadmium concentrations.
Parameters that effect the destruction of organics undergoing combustion are the type of
organic compound and the concentration of the organic constituent in the waste stream. Other
parameters, such as exit temperature and residence time, do not appear to impact destruction
efficiency within customary operating ranges. Dioxins and Furans can be formed downstream
of the combustion chamber as gases cool. This formation can be limited by minimizing the
formation of fly ash.
With the exception of increased fouling of the boiler tubes in those municipal solid waste
combustion facilities that generate steam, no research was found to indicate that the presence of
metals in MSW impeded the operation and maintenance of MSW combustion equipment. HC1,
as well as other acid gases, can cause significant corrosion to combustion and APCD equipment!
An examination of research on the levels of toxic metals and organics in municipal waste
combustor ash reveals that concentrations vary significantly from sample to sample, and from
study to study. Lead and cadmium appear most frequently in the literature as the metals likely
to cause the ash to fail TCLP tests, although other metals are found in varying concentrations.
Organic constituents generally are found in ash in extremely low concentrations.
The examination of toxic air emissions from MWCs found that new or modified MWCs
are subject to stringent, technology-based air emissions standards (i.e., NSPS) that address PM,
opacity, HC1, SO2, and NOx (as well as operating standards that address CO) and that these
standards have resulted in a dramatic decrease in MWC air emissions from new units compared
to 1987 data. Future standards will add to the NSPS emission limits for mercury, lead, and
cadmium. The NSPS currently exempts new units with a combustion capacity below 250 tpd.
However, the Clean Air Act requires EPA to establish air emission standards for these units as
well. Current data for existing MWCs (those built prior to December 20, 1989) were not
identified, and it is these facilities that pose the greatest potential concern regarding toxic air
emissions. Existing MWCs are subject to emission guidelines that are similar to those in the
MWC NSPS, however, these standards are not always implemented. Thus, existing MWCs may
warrant additional evaluation. Overall, the data presented represent the range of MWCs air
emissions from worst-case to best. The data indicate that the trend towards dramatic reductions
in toxic air emissions from MWCs is likely to continue, but it does not fully account for small
and existing units.
Cellulosic waste to ethanol is a developmental stage process that converts lignocellulosic
material to glucose through acid or enzymatic hydrolysis, then converts the glucose to ethanol
via fermentation. No research has been identified to suggest that the presence of metals in MSW
would impede the effectiveness of either acid or enzymatic hydrolysis. Available evidence
suggests that metals present in the MSW will proceed through the hydrolytic processes and into
the fermentation vessel.
112
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While research demonstrates the levels at which certain metals serve as nutrients to the
fungi central to the fermentation process, very little research can be found that identifies the
levels of these or other metals that impedes fermentation. Limited information concerning the
inhibitory levels of copper and cobalt result in estimates of inhibitory concentration ranging from
200 to 2500 times the documented nutrient level. Inhibitory levels were observed for lead at 250
mg/L, cadmium at 115 mg/L, mercury at 200 mg/L, and nickel at 160 mg/L. Using data from
a bacteriological study, 73 mg of selenium/L inhibited fermentation by 50 percent, pentavalent
arsenic inhibited fermentation at 1600 mg/L, and chromium at 70 mg/L. Data were not
available to determine the toxic effects of Al, Sb, Ba, Be, F, Ag, Tl, and V.
113
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6.0 POTENTIAL ADVERSE EFFECTS ASSOCIATED WITH METALS AND
ORGANIC COMPOUNDS IN LANDFILLED MUNICIPAL SOLID WASTE
6.1 Introduction
Landfills represent the most commonly used waste management method in the United
States. In 1990, almost 196 million tons of MSW were generated in the United States.75 Of this
amount, approximately 130 million tons (67 percent) was landfilled. When evaluating the use
of landfills as a MSW management option, one area of concern is the potential effect that metals
and organic compounds present in the waste may have on landfill performance, as well as the
potential risks to human health and the environment.
The purpose of this section is to assess the potential effects of the presence of metals and
organic toxics on landfill components (e.g., leachate collection/removal systems) and residuals
(e.g., leachate). This section presents a brief discussion of potential transport pathways (e.g.,
surface water, fugitive dust, leachate, and decomposed waste) for metals and organic compounds
and how landfill performance may be affected by metals and organic compounds, including: 1)
clogging of leachate collection/removal systems; 2) ferruginous bacterial growth; 3) corrosion
of system piping; and 4) leachate management.
6.2 Behavior of Metals and Organic Compounds in Landfilled MSW
Once landfilled, metals and organic compounds in MSW may migrate from decomposing
waste to leachate, and potentially the environment (e.g., air, surface water, and ground water),
as shown in Figure 12. This section presents an overview of metals and organic compounds
migration.
6.2.1 Air
The three primary mechanisms by which metals and organic compounds enter the
atmosphere include volatilization, fugitive dust, and landfill gas emissions. Each of these are
discussed in the following subsections
6.2.1.1 Volatilization
There is a potential for metals and organic compounds in landfilled MSW to volatilize.
However, the total amount of metal that is volatilized generally is small relative to the total
amount of metal concentrated in leachate; the converse relationship holds for organic
compounds.
114
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MUNICIPAL
SOUD
WASTE
DUST/
LANDFILL GAS
GROUND
WATER
BIOMASS :
SURFACE
WATER
Figure 12. Potential Environmental Pathways: Landfills.
The principal source for metal and organic compound volatilization is at the initial point
of disposal, especially where trash compactors or loaders are employed and exposure to the air
is greatest. Once the MSW is overlain by daily cover, the potential for metal and organic
volatilization diminishes. Volatilization is determined by:
• The extent of contact between the free product and the unsaturated zone;
• The vapor pressure of the spilled or exposed compounds; and
• The diffusion rate of the compounds in the different mediums (e.g., air).107
VOC emissions to the atmosphere can lead to the formation of ozone, which is identified
as a priority air pollutant under the CAA. The amount of VOC (nonmethane organics)
emissions from active MSW landfills nationwide was reported in one study to be in the range
of 200,000 to 300,000 megagrams per year.108
6.2.1.2 Fugitive Dust
Another major migration path for metals and organic compounds into the air is from
fugitive dust created during landfilling activities. Before daily cover is placed, MSW exposed
to the wind may disperse VOCs or yield small particles of metal-containing dust. For example,
dust from waste paint often contains high concentrations of lead and other heavy metals. These
materials can be transported from the landfill as fugitive dust emissions and deposited around
the landfill site.
115
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6.2.1.3 Landfill Gas
In addition to volatilization, decomposition of organic waste materials (e.g., paper, lawn
clippings, food waste, and agriculture residues) in landfills produces landfill gas (LFG). LFG
is composed of approximately 50 percent methane, 40 to 50 percent carbon dioxide, and 0.5 to
1 percent of hydrogen, oxygen, nitrogen, VOCs, and other trace gases (e.g., hydrogen sulfide)
as shown in Table 46.108 Decomposition begins shortly after initial placement of MSW when
moisture is present and oxygen is limited. Depending on the organics distribution present and
the packing density of the landfill, LFG is generated at a rate of approximately 210 cubic feet
per year per cubic yard of waste.109
TABLE 46. TYPICAL COMPOSITION OF GAS FROM
MUNICIPAL SOLID WASTE LANDFILLS108
Component Percentage (dry-volume basis)
Component Study 1 Study 2 Study 3 Study 4
Methane
Carbon dioxide
Nitrogen
Oxygen
Paraffin hydrocarbons
Aromatic and cyclic hydrocarbons
Hydrogen
Hydrogen sulfide
Carbon monoxide
Trace Compounds
44.0
34.2
20.8
1.0
—
~
~
0.4-0.9
—
—
47.5
47.0
3.7
0.8
0.1
0.2
0.1
0.01
0.1
0.5
50.0
35.0
13.0
1.7
~
—
0.3
—
~
—
53.4
34.3
6.2
0.05
0.17
—
0.005
0.005
0.005
—
The resulting LFG consists of a mixture of gases that migrates as a plume. Production
of LFG creates a positive pressure in the landfill; this pressure acts as a driving force
(convection), causing LFG to migrate into surrounding soils and through surface soils. In
addition, a concentration gradient causes diffusive flow of LFG (i.e., LFG flows from areas of
high concentration into areas of low concentration). Normally, most of the LFG will vent
through the fill surface into the atmosphere before landfill closure or migrate laterally once the
final cover system is installed. Depending on site conditions, LFG can migrate an average of
1000 feet and may cause problems (e.g., flammable conditions) in nearby structures (e.g.,
basements). As a result, measures must be taken to reduce LFG concentrations to acceptable
levels and contain LFG migration upon landfill closure, especially in an unlined landfill.
116
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LFG collection and control are accomplished through passive and active control systems.
Passive migration control systems create a path of least resistance and provide venting of LFG.
Such systems include vent trenches, vertical well vents, open ditches, slurry walls, and subslab
ventings. Active control systems create negative or positive pressure gradients to control
subsurface LFG movement. Some of the more common active migration control systems include
collection trenches, extraction well systems, subslab extraction, and air injection or air curtains.
When feasible, LFG is recovered to produce energy. There are more than 150 LFG recovery
projects in the country, either in operation or in the planning stage. Constituents of LFG also
may have deleterious effects on LFG systems. For example, acid gases, such as hydrogen
sulfide, can accelerate corrosion of metallic system components.
Table 47 presents a list of typical organic compounds found in landfill gas generated from
MSW landfills.108 This study found concentrations of benzene, tetrachloroethylene, toluene,
vinyl chloride, and xylene above NIOSH/OSHA permissible exposure levels (as indicated by
underlined values).
TABLE 47. TYPICAL ORGANIC CONSTITUENTS IN LANDFILL GAS
108
Compound
Benzene
Ethylbenzene
Heptane
Hexane
Isopentane
Methylcyclohexane
Methylcyclopentane
Methylene Chloride
Nonane
Tetrachloroethylene
Toluene
1,1,1 -Trichloroethane
Trichlorethylene
Vinyl Chloride
Xylene
m-Xylene
0-Xylene
Concentration
Range
(Vppm)
0 -
0 -
0 -
0 -
0.05
0.017
0 -
0 -
0 -
0 -
0 -
0 -
0 -
0 -
0 -
1.7
0 -
12
91
11
31
- 4.5
- 19
12
118
24
186
357
2.4
44
10
111
- 76
19
Median
Concentration
(Vppm)
0.3
1.5
0.45
0.8
2.0
3.6
2.8
0.83
0.54
0.03
6.8
0.03
0.12
12
0.1
4.1
1.8
Exposure Limit
(TWA Unless Noted) ppm
N1OSH"
0.1
100.ST125
85,C440
50
NA
400
NA
b
NA
2mg/m3
100.ST 150
ST150
25
c
100.ST 150
100.ST150
100.ST150
OSHA
1,ST5
100.ST125
400.ST500
50
NA
400
NA
500.C1000
NA
2mg/mJ
100.ST150
ST150
50.ST200
1.C5
100.ST150
100.ST150
100.ST150
ST
C
TWA
NIOSH Pocket Guide to Chemical Hazard , U.S. Dcpt. of Health & Human Services, June 90.
Reduce exposure to lowest feasible concentration
Lowest reliability detectable concentration
Value is measured over a 15-minutc period unless noted otherwise.
OSHA ceiling concentrations must not be exceeded during any part of the workday.
Time weighted average
117
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6.2.2 Leachate
Liquid leachate formation results from precipitation, refuse moisture, and as a by-product
of waste decomposition that percolates through the waste material and extracts water-soluble
compounds and paniculate matter. Metals and organic compounds may occur in leachate in
many forms, including: free ions; insoluble species; metal/ligand complexes; adsorbed species;
species held on a surface by ion exchange; or species differing by oxidation state (e.g.,
chromium (HI) and (VI).110 Organic compounds in leachate may be present as dissolved organic
liquids, dissolved organic solids, and/or suspended organic liquids. The 1984 EPA Report to
Congress on solid waste disposal noted that leachate escaping from MSW landfills was the most
commonly reported MSW mismanagement event.108
Tables 48 and 49 illustrate the typical chemical concentration ranges of municipal landfill
leachate.108
6.2.2.1 Transport of Metals in Leachate
The movement of metals in leachate is dependent on a number of complex interactions.
These interactions can be grouped into three basic types of processes:
• Advection: Liberation of metals from their source and transportation by the motion of
landfill contents and gravity;
• Colloidal suspension: Adsorption of metals to the surface of small particles of organic
material and transportation with the particles; and
• Solute transport: Metals may become soluble and move with the liquids (i.e., leachate)
in the landfill. Solubility is the ability of a substance to form a solution with another
substance. For some metal compounds, water is an excellent solvent.111 The solubility
of metals is dependent upon pH (metals become more mobile at low pH and high pH)
and oxidation-reduction potential (Eh).112
118
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TABLE 48. RANGE OF VARIOUS INORGANIC CONSTITUENTS IN LEACHATE
FROM MUNICIPAL SOLID WASTE LANDFILLS' 1(*
Compound
Aluminum
Antimony
Arsenic
Barium
Berylium
Boron
Cadmium
Chloride
Chromium (Total)
Copper*
Cyanide
Fluoride'1
Lead'
Nitrate
Nitrite
Selenium
Sulfate
Thallium
Vanadium
Zinc
Concentration
Range
(ppm)
0.01-5.8
0.0015-47
0.0002-0.982
0.11-5
0.001-0.01
0.63-12
0.007-0.15
31-5.475
0.0005-1.9
0.003-2.8
0.004-0.02
0-. 11-302
0.005-1.6
0.01-51
0.005-0.2
0.0008-0.05
8-1,400
0.004-0.86
0.009-0.029
0.03-350
Median
Concentration
(ppm)
2.4
0.066
0.0135
0.58
0.005
4
0.0135
594
0.06
0.054
0.03
0.39
0.063
0.22
0.03
0.02
111
0.08
0.08
0.68
Status
Reg.
L
F
4
F
F
L
F
T
F
F
P
F
F
F
F
F
P
F
L
L
Standard
MCLGb
(mg/e)
-
0.006
2
0.004
-
0.005
4
0.1
1.3
0.2
4
0
10
1
0.05
f
0.005
-
-
MCLC
(mg/e)
-
0.006
0.05
2
0.004
-
0.005
-
0.1
IT*
0.2
4
TT
10
1
0.05
f
0.002
-
-
EPA's Drinking Water Regulations and Health advisories, May 1993
A non-enforceable concentration of a drinking water contaminant that is protective of adverse human health effects and allows an
adequate margin of safety.
Maximum permissible level of a contaminant in water which is delivered to any user of a public water system.
Under Review
Copper - Action Level 1.3 mg/e
No more than 5 percent of the samples per month may be positive. For systems collecting fewer than 40 samples/month, no more
than 1 sample per month may be positive.
Lead - Action Level 0.0IS mg/e
Final
Listed for regulation
Proposed
Tentative
Not available
Treatment technique
Maximum Contaminant Level Goal
Maximum Contaminant Level
119
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TABLE 49. PRELIMINARY DATA ON CONCENTRATIONS OF ORGANIC
CONSTITUENTS IN LEACHATE FROM MUNICIPAL SOLID WASTE
LANDFILLS108
Compound
Benzene
Bromomethane
Carbon tetnchloride
Chloroethane
Chloroform
Chloromethane
2,4-D
Dibromomethane
Dichlorodifluoromethane
1 , 1 -Dicholroethane
1 ,2-Dichloroethane
Cii-1 ,2-Dichloroethylene
Trans- 1 ,2-Dichloroethylene
1 ,2-Dichloropropane
1 ,3-Dichloropropene
Endrin
Ethylbenzene
Isophorone
Lindane
Pentachlorophenol
1 , 1 ,2,2-Tetrachloroethane
Tetrachloroethylene
Toluene
Toxaphene
1 , 1 ,2-Trichloroethane
Trichloroethylene
1 ,2,3-Trichloropropane
Vinyl Chloride
Xylenes
Concentratioa
Range
(ppb)
4-1,080
170-170
6-398
11-860
27-31
170-400
7-220
5-5
10-450
4-44,000
1-11,000
190-470
2-4,800
0.03-500
18-30
004-50
6-4,900
4-16,000
0.017-0.023
3-470
210-210
2-620
6-18,000
1-1
30-630
1-1,300
230-230
8-61
32-310
Median
Concentration
(ppb)
37
170
202
28
29
175
130
5
274
165
10
330
92
9
124
0.25
58.5
76
0.020
45
210
55
413
1
426
43
230
40
71
Status
Reg.
F
T
F
L
T
L
F
L
L
L
F
F
F
F
L
F
F
L
F
F
L
F
F
F
F
F
L
F
F
Standard
MCLG
(mg/e)
Zero
-
Zero
-
Zero
-
0.07
-
-
-
Zero
0.07
0.1
Zero
-
0.002
0.7
-
0.0002
Zero
-
Zero
1
Zero
0.003
Zero
-
Zero
10
MCL
(mg/e)
0.005
-
0.005
-
0.1
-
0.07
-
-
-
0.005
0.07
0.1
0.005
-
0.002
0.7
-
0.0002
0.001
-
0.005
1
0.003
0.005
0.005
-
0.002
90
Definitions
MCLG Maximum Contaminant Level Goal. A non-enforceable concentration of a drinking water contaminant that is protective of advene
human health effects and allows an adequate margin of safety.
MCL Maximum Contaminant Level. Maximum permissible level of a contaminant in water which is delivered to any user of a public water
system.
F Final
L Listed for regulation
T Tentative
NA Not available
TT Treatment technique
120
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EPA (1986) examined metal leaching in landfills where MSW and sludge are codisppsed,
and found that metal concentrations in MSW appear to diminish consistently through the life of
the landfill cell, either due to rapid leaching following initial disposal or adsorption of metal
cations onto soil and organic particles within the landfill unit. Also, these findings point to a
significant relationship between pH and metal teachability: cells with a lower pH in this study
effectively released the metals at a higher rate.113
The study also evaluated the formation of sulfides, which form insoluble metal-sulfide
precipitates. Organic sulfur, present in sludge, is converted to various sulfur forms which shift
in predominance as anaerobic decomposition progresses. Under anaerobic conditions found in
landfills and pH levels below 8, sulfates are reduced to hydrogen sulfide, which is evolved with
methane and carbon'dioxide. Reservoirs of sulfides could precipitate the more toxic and less
soluble heavy metals such as copper, zinc, and nickel. Because of its reactivity with metals, the
strength of sulfides to stand alone in this study as an analytical parameter was weak and testing
was discontinued.
Finally, the composition of waste put into a landfill has an impact on metal leaching.
MSW is less uniform in nature than sludge, which tends to be more homogenous. This physical
difference influences the hydraulic characteristics of a landfill cell. MSW lends itself to
development of water pockets and is more permeable than sludge; fluid flow will increase the
mass transport of soluble metal compounds downward in a given MSW landfill cell, as compared
to a cell containing only sludge.114
6.2.2.2 Transport of Organic Compounds in Leachate
The movement of organic compounds in leachate is controlled by a number of complex
organic reactions which are subject to different physical, chemical, and biological processes.
Organic reactions may transform one compound into another, change the state of a compound,
or cause a compound to combine with other organic or inorganic chemicals. Five basic organic
reactions (hydrolysis, sorption, cosolvation and ionization, biodegradation, and volatilization and
dissolution) affect the states of organic compounds.107 Molecular diffusion and advective
transport are the two potential processes that govern the complex movement of organic
compounds in landfills.
6.2.3 Transport of Decomposed Waste in Landfill Leachate
Metals and organics that are not released from the landfill via the air or the leachate
collection system may remain within the decomposed waste in the landfill. The persistence of
metals in a landfill are illustrated by the results of a study conducted at the Collier County
Landfill in Florida. The metal contents of mined landfill materials from this landfill are
presented in Table 50.
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TABLE 50. MINED LANDFILL SOIL CHARACTERISTICS
(COLLIER COUNTY LANDFILL)115
Concentration (ppm)
Metal
Cadmium
Copper
Nickel
Lead
Zinc
< 1/2 inch material
0.3
43.10
8.00
56.00
150.00
3 inch material
0.6
49.00
8.00
57.00
150.00
6.2.3.1 Soil and Surface Water
The most common path for metals and organic compounds to enter surface waters is
through side slope "seeps," run-off control deficiencies, or proximity to a wetland or floodplain
(recently promulgated landfill siting requirements will help eliminate these problems). Leachate
seeps occur when leachate is allowed to "back up" or otherwise is released to the surface of the
ground. Leachate seeps flow along the topographic surface of the ground and may reach nearby
surface water bodies. Along the way, metals or organic compounds may adsorb or precipitate
from the solution, thus contaminating surface soils.
According to EPA case studies, discharges from MSW landfills to surface water bodies
are more likely to cause subtle changes to the aquatic environment than acute catastrophic
impacts. For example, a five-year study was conducted to determine the impacts a MSW landfill
had on benthic (bottom) organisms in a nearby stream. The study concluded that the diversity
of benthic organisms downstream was much less than that found upstream, and the few species
that survived downstream were more tolerant of the higher metal concentrations that were
present as a result of the landfill.108
6.2.3.2 Ground Water
Aside from metal and organic compound migration via landfill leachate, metals and
organic compounds have been documented and measured in ground water beneath older landfill
units. Once in the ground water, some of the metals may dissolve, while others may adsorb
onto the aquifer medium. VOCs may dissolve into the ground water, volatilize into the
unsaturated zone, or penetrate deep (VOCs that are denser than water) into aquifers and remain
in an immiscible phase for a prolonged period of time. In areas where potable water supplies
exist, the presence of metals and organic compounds at or above federal MCLs can pose a
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potential health risk. The 1984 Report to Congress on solid waste disposal stated that drinking
water or ground water was the most frequently affected receptor in the event of a landfill
release.108
New landfill designs have addressed this concern with the use of composite liners,
integrated leachate detection, and collection/removal systems. In addition, some states require
a minimum vertical separation (e.g., 3 feet) between the bottom liner and the highest ground
water level. For these newer systems, metal-and organic compound-laden leachate moves
toward the engineered leachate collection/removal network. However, there is some evidence
that solvents discarded in MSW landfills can degrade otherwise highly impermeable clay liners
and penetrate through the subsurface soil.
In the event that mechanical failures or other imperfections occur in a liner system,
leachate can penetrate through the subsurface soil or into the ground water aquifer. Heavy
metals and some organic compounds (e.g., 1,1,1-trichloroethene) will sink and spread to a
deeper or larger area faster than other substances, causing the worst-case physical extent of
contamination. On the other hand, some metals may go through chemical reactions and become
less toxic and immobile.
Aquifer characteristics also can affect the fate and transport of metals and organic
compounds.108 Aquifers with low flow rates (1 m/year or 3 x 1O6 cm/sec) will have relatively
slow plume migration rates, but high contaminant concentrations. In aquifers with high flow
rates (1,000 to 10,000 m/year or 3 x 10'3 to 3 x 10'2 cm/sec), plumes grow and dissipate rapidly.
In moderate flow rate (10 to 100 m/year or 3 x 10'5 to 3 x 10"4 cm/sec) aquifers, plumes grow
rapidly and contaminant concentrations remain above threshold values for a long period of time.
As a result, moderate flow rate aquifers that are contaminated with undesirable amounts of
metals and organic compounds typically cause the most resource damage to the environment.
6.3 The Effect of Metals and Organic Compounds on Landfill Components
The purpose of this section is to review the potential effects of metals and organic
compounds on the performance of landfill components. A typical landfill system consists of a
liner system and a leachate collection/removal system. Both of these landfill components can
be impacted by the presence of metals and organic compounds in landfilled MSW.
6.3.1 Liner System
A composite liner generally provides protection from the migration of metals or organic
compounds into the ground water or subsurface soil. A composite liner consists of several
different layers, each of which contributes to the ability of the liner system to contain landfill
leachate. The top component of the composite liner consists of a geomembrane (such as PVC
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or HDPE) that will not be affected by metals and organics concentrations typical of MSW
leachate. The higher density of a geomembrane, the better it's chemical resistant properties.
However, in some instances, organic compounds may react with the plastizers in some
geomembranes causing them to become brittle. A general chemical resistance guideline for
commonly used geomembranes is presented in Table 51.116
In geosynthetic liners, one factor that can greatly influences liner performance is
penetration. Sharp metal objects, such as rebar, have the potential to cause damage to a
geomembrane liner through puncturing. Some landfill designers have included an additional
layer of stone to the liner system (above the leachate collection layer) to act as a protection layer
to prevent such damage.
The bottom component of a composite liner typically is compacted clay. Clay has a
natural negative charge that will attract positively charged metal ions and prevent the transport
of the metal ions. Studies regarding the attenuation of pollutants from municipal landfill leachate
suggest that lead, zinc, cadmium, and mercury are readily removed from leachate by clay liners.
One such study concluded that the removal of the heavy metals could be attributed to cation
exchange mechanisms, but acknowledged that precipitation and filtration likely play a major role
in metals removal.117 Another study reported that organic compound movement through clay
liners was retarded due to sorption of organic compounds onto the clay. For non-sorbed organic
compounds, breakthrough of a one-meter clay liner may occur in less than 10 years. Metals
typically do not degrade the clay structure and thus do not compromise the integrity of the clay
liner. Metal salts, such as sodium chloride, actually may decrease the hydraulic conductivity
of the clay liner. Studies show that soils containing monovalent cations, such as sodium, have
low hydraulic conductivity.118
However, organic compounds present in high concentrations can cause clay liners to
shrink and crack. Experiments indicate that if pure solvents penetrate into the clay, the solvents
may displace water within the clay structure, leading to shrinkage, cracking, and an increase in
permeability of the clay structure. Fortunately, the solubilities of solvents are thousands of
milligrams per liter (mg/e) or less. As a result, the impact of the solvents on the clay can be
expected to be minimal.107 Nevertheless, the effect of thousands of milligrams per liter of
chemical concentrations could have a major impact on ground-water quality. The leachate
conductivity test (using SW-846 method 9100) can be used to determine the compatibility of a
clay liner with the expected leachate.
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6.3.2 Leachate Collection/Removal System
Leachate is generated throughout the active life of a landfill and continues to be generated
long after landfill closure. The rate at which leachate generation continues depends on the
effectiveness of the cover system, as well as the waste constituents. Leachate collection/removal
systems are installed to control leachate generation and migration. These systems typically
consist of a system of perforated pipes surrounded by sand or geonet filter and are situated in
a gravel trench. The pipes are sloped to drain to a central collection/removal point where
leachate is removed. Leachate collection/removal systems must operate continuously over the
entire designed life span of the landfill and during its post-closure care period.
Clogging is the primary cause of concern for the long-term performance of leachate
collection/removal systems. Paniculate clogging by metals and organic compounds in leachate
can occur through:
• Chemical precipitation of metals: Metals and organic compounds (i.e., iron ocher,
sulfides, and carbonates) may precipitate from high pH leachate prior to leachate
removal. These precipitated metals may collect on the surface of collection/removal
systems (e.g., clogging the drainage gravel, sand and geotextile filters, and geonet) and
inhibit leachate flow.
• Increased bacterial growth: Bacteria that use metals as an energy source can grow on
surfaces such as the sand filter found in many leachate collection/removal systems and
cause clogging of the leachate collection system.119 For example, ferruginous bacteria
(bacteria that use iron as an energy source) pose a substantial threat for leachate
collection systems because the bacteria tend to proliferate in anaerobic environments such
as those found in landfills. The orange coloring that characterizes many leachate seeps
can be attributed to activity of such bacteria.
6.3.3 Leachate Management
Once leachate is collected from the base of the landfill unit, there are several options for
leachate treatment. Treatment issues that must be considered before these options can be
employed include:
• The types and concentrations of chemical constituents present in the initial leachate;
• Particle size and physical properties of suspended solids; and
• Target treatment limits (e.g., pretreatment standards).
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Options for leachate treatment include:
• On-site leachate treatment for either direct discharge or indirect discharge to a Publicly-
Owned Treatment Works (POTW);
• Discharge to a POTW without pretreatment; and
• Leachate recirculation or spray irrigation (with or without pretreatment).
6.3.3.1 On-Site Treatment
On-site treatment may be used to discharge leachate directly to surface waters under a
National Pollutant Discharge Elimination System (NPDES) permit, to spray irrigate, or to
comply with the pre-treatment discharge limitations for a POTW. If on-site treatment is
selected, possible processes for treatment include:
• Biological treatment (i.e., activated sludge). This type of treatment generally is used to
reduce or remove organic constituents; and
• Physical treatment using gravity (i.e., sedimentation) or air stripping/aeration.
Sedimentation is a physical process that takes advantage of gravity to remove suspended
solids and associated metals from an aqueous waste stream. Some metals will become
insoluble, precipitate, and settle by gravity if the pH is raised (the pH level depends on
the metal to be removed) or if chemicals are added to react with the metals species
present. Air stripping or aeration is another type of physical treatment process, which
typically is used to strip solvents and remove VOCs.
Further treatment will be required where metals or organic compounds are present in
significant concentrations. Ion exchange, microporous membrane filtration, adsorption, and
chemical oxidation can be used to decrease the dissolved solids content in leachate. Carbon
adsorption can be used to remove organic compounds.
6.3.3.2 POTW
Discharging directly to a POTW often offers the easiest solution for leachate management
if the leachate complies with the pretreatment requirements. The feasibility of this option
depends on the distance the leachate will have to be hauled to the POTW or discharge manhole.
POTWs generally use biological treatment combined with solids removal to reduce pollutant
loads.
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6.3.3.3 Leachate Recirculation
One of the renewed approaches to MSW leachate management is recirculation In this
process, the withdrawn leachate either is sprayed over newly disposed MSW or sludge in a
landfill or pumped into a network of drain pipes above or in the MSW or sludge. According
to an EPA survey conducted six years ago, approximately three percent of MSW landfills
employed recirculation techniques.
Most research on recirculation to date has focused on the decrease of the leachate
strength (usually measured as COD and BOD), rather than on the effect on metals or organic
compound concentration. A three year research project in Sonoma County, California showed
gradual increases in some metals concentrations in the leachate (e.g., lead and mercury) but
gradual declines in the concentrations of other metals (e.g., calcium and magnesium).120 '
Another full-scale leachate recirculation study was performed at the MSW landfill located
in Lycommg County, Pennsylvania. The research concluded that leachate recirculation
facilitated organic waste decomposition, increased methane production, and increased the waste
stabilization rate. However, leachate recirculation also has some disadvantages related to an
increased leachate production rate. The increased volume of leachate may clog the leachate
collection/removal system and create increased threat of releases to ground water As a result
the accumulation of leachate over time may require the disposal of leachate using one of the
other processes discussed above.
6.3.3.4 Sludge
Biological and physical treatment processes generate a residue sludge. The sludge from
physical or biological processes tends to be laden with the metals and organics that were
removed from the treated waste. The principal potential contaminants of concern are excess
nitrogen, heavy metals, persistent organics, and pathogens. The more traditional practice for
municipalities has been to dewater and stabilize sludge and then dispose of the material in MSW
landfills. Therefore, metals and organics removed via the leachate collection system likely will
be placed back in the landfill.
6.4 Health Effects
VOCs in MSW generally present the most risk to human health and animals due to their
nigh mobility as compared to other organic compounds. As a result, VOCs are being closely
monitored in air and ground water monitoring programs. However, the long-term effects of
semi-volatile and non-volatile organic compounds in the MSW stream on human health and the
environment are starting to attract attention from the general public and regulators Concerns
about VOCs in landfills has lead the State of California to enact a law that requires monitoring
for 26 VOCs. VOCs that are predominantly detected at landfills include: benzene
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dichloromethane, 1,2-dichloroethylene, ethylenebenzene, tetrachloroethylene, trichloroethylene,
toluene, and vinyl chloride.
Exposure to harmful substances or releases from landfills only can occur when an
individual inhales or ingests a contaminated substance. The level of harmful health effects
caused by exposure depends on the dose; the duration; the route or pathway; and characteristics
and genetic make-up of the individual (e.g., age, gender, and state of health). According to the
1988 EPA RTC, the following human health risk were reported:108
• Across all 6,034 MSW landfills in the baseline, EPA estimated that the average
maximum exposed individual (MEI) over a 300-year modeling period would be exposed
to a cancer risk ranging between zero to lxl(T*. A risk of IxlO4 indicates that exposed
individuals would bear a 1 in 10,000 chance of contracting cancer in their life time as
a result of the exposure.
• Approximately 12 percent of all MSW landfills pose cancer risks in the IxlO"5 to 1X1O6
range.
• Approximately 6 percent of all MSW landfills pose cancer risks in the Ixia5 to IxKT1
range.
The results also indicated that vinyl chloride, 1,1,2,2-tetrachloroethane, and
dichloromethane are the principal constituents contributing to the estimated risk.
6.5 Summary
The metals and organic compounds that are present in MSW create concerns for human
health and the environment. The need for careful management of MSW is addressed through
EPA's recently revised criteria for MSW landfills (40 CFR Part 258). Potential impacts of
toxics in landfills include impacts on landfill performance and potential risks to human health
and the environment due to concentrations of toxics in leachate and landfill gases. Toxics in
landfilled MSW may remain in the landfill or be released to the air through volatilization,
fugitive dust, and landfill gas emissions or released to ground and surface water via landfill
leachate. The behavior of toxics in landfilled MSW is influenced by a variety of factors,
including the characteristics of the landfilled waste, environmental conditions at the landfill (e.g.,
climate, topography, and hydrogeologic conditions), as well as landfill operating procedures.
There is little data on the effect of toxics in MSW on landfill liner materials. Some
studies have indicated that organics may react with geomembranes and cause brittleness and that
high organic concentrations (far above normal MSW concentrations) may cause clay liner
shrinkage and cracking and increase landfill permeability. In addition, metal and organic
particulates may cause clogging of leachate collection/removal systems. Corrosion of landfill
gas collection systems by landfill gases (including hydrogen sulfide) also has been reported.
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Emissions or releases of potentially harmful organic compounds and metals in landfill gas
and leachate also may pose a potential threat to human health and the environment. Human
health risks are greatest for those who live in close proximity to landfills and are dependent on
ground water from shallow aquifers for their water supply. If present in sufficient quantities and
able to migrate into buildings, LFG can pose an immediate threat of fire or explosion.
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7.0 FUTURE RESEARCH NEEDS
7.1 Introduction
On September 21,1993, U.S. EPA Office of Research and Development, Risk Reduction
Engineering Laboratory convened a workshop to review and provide comment on the Interim
Final Draft of the document "Analysis of the Potential Effects of Toxics on Municipal Solid
Waste Management Options." As part of the review process, workshop attendees were asked
to identify priority areas for future research in the area of how toxics in MSW effect MSW
management options. In the process of developing this document, EPA and the workshop
participants also identified a number of areas in which additional future research would be
valuable.
7.2 Research Needs
EPA and workshop participants identified a number of research areas that may need to
be addressed in the future. These research areas are listed below:
General MSW Management Issues
• Household hazardous waste (HHW) - The presence of HHW may impact MSW
management techniques. These potential impacts should be investigated.
• Source reduction initiatives - Current and future source reduction projects (e.g.,
reductions of mercury in household batteries and reductions in the use of metals in
printing inks) may impact MSW management techniques. These impacts should be
considered.
Recycling Issues
• Recycling of batteries, metals, and special wastes - The potential environmental impacts
of recycling particular potentially hazardous components of the MSW waste stream
(including waste oil, antifreeze, refrigerants) should be researched and evaluated.
• Materials handling - The potential environmental effects associated with recyclables
handling should be investigated.
• Worker/industrial exposure in recycling processes - Recycling facility workers may be
exposed to a variety of toxic materials. The potential health effects of this exposure
should be evaluated.
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Waste-To-Fuel Issues
• Atmospheric emissions from MSW combustors - The issue of emissions from MSW
combustors remains significant and would benefit from additional research.
• Environmental half-life issues (e.g., dioxins) - The generation and fate of dioxins and
furans in the environment is a controversial issue that warrants additional study.
• Environmental characteristics of MRFs - The potential environmental impacts of the
operation of MRFs should be considered.
• Emissions characterization for various waste-to-fuel processes (e.g., ethanol, pyrolysis,
gasification, and biogasification) - New waste-to-fuel technologies may have
environmental effects that should be researched and evaluated.
• Other new waste-to-fuel technologies - Additional, innovative waste-to-fuel technologies
should be researched.
Composting Issues
• Biological process controls and monitoring - Compost controls and monitoring should be
evaluated to determine the contribution these controls and monitoring techniques make
to the environmental impacts associated with the production and use of MSW compost.
• Bio-aerosols - The environmental impacts of the presence of bioaerosols should be
researched and evaluated.
• Comparisons of secondary materials and virgin products (e.g., compost vs lime) - The
manufacture and use of secondary materials may have associated environmental impacts.
These impacts should be compared to those impacts associated with virgin products.
• Compost risk analyses - Risk analyses for compost derived from MSW, similar to those
performed for sludge biosolids, should be conducted.
Landfill Issues
• Landfill gas emissions - Toxics in MSW may contribute to environmental impacts via
landfill gas emissions. These potential effects should be researched and evaluated.
• Landfill reclamation projects - The impacts of the presence of toxics on landfill
reclamation projects should be researched.
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*U.S. GOVERNMENT PRINTING OFFICE: 1995-650-006/22004
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