United States
Environmental Protection
Agency
Solid Waste
and Emergency Response
(5306W)
EPA530-R-98-008
April 1998
An Analysis of Composting
As an Environmental
Remediation Technology
;:Cv Printed on paper that contains at least 20 percent postconsumer fiber.
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Chapter 1
Introduction
The composting process is currently viewed primarily as a waste management method to
stabilize organic waste, such as manure, yard trimmings, municipal biosolids, and organic
urban wastes. The stabilized end-product (compost) is widely used as a soil amendment to
improve soil structure, provide plant nutrients, and facilitate the revegetation of disturbed or
eroded soil (Cole, 1994; Cole, 1995; Harmsen, 1994; McNabb, 1994). The information and data
presented in this document were compiled and analyzed by Michael A. Cole, Ph.D.
Within the past few years, laboratory-, greenhouse-, and pilot-scale research has indicated
that the composting process and the use of mature compost also provide an inexpensive and
technologically straightforward solution for managing hazardous industrial waste streams (solid,
air, or liquid) and for remediating soil contaminated with toxic organic compounds (such as
solvents and pesticides) and inorganic compounds (such as toxic metals). For example, a large
number of hydrocarbons, which are common industrial contaminants found in soil and exhaust
gas, degrade rapidly during the composting process or in other compost-based processes.
Furthermore, the addition of mature compost to contaminated soil accelerates plant and
microbial degradation of organic contaminants and improves plant growth and establishment in
toxic soils. When mature compost is added to contaminated soils, remediation costs are quite
modest in comparison to conventionally used methods. Mature compost also controls several
plant diseases without the use of synthetic fungicides or fumigants.
This report summarizes the available information on the use of compost for managing
hazardous waste streams (as well as other applications) and indicates possible areas for future
investigations. Attention to cross-media transfer of contaminants during implementation of
various bioremediation technologies presented in this report is recommended. A recent
publication by the U.S. Environmental Protection Agency (EPA), entitled Best Management
Practices (BMPs) for Soil Treatment Technologies (EPA530-R-97-007, May 1997), could be
consulted to address the cross-media transfer concerns.
An Analysis of Composting as an Environmental Remediation Technology
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The Composting Process
Composting is a managed system that uses microbial activity to degrade raw organic
materials, such as yard trimmings, so that the end-product is relatively stable, reduced in
quantity (when compared to the initial amount of waste), and free from offensive odors.
Composting can be done on a large or small scale, with the management requirements and
intensity increasing dramatically as system size increases. In its simplest form, compostable
material is arranged in long rows (windrows) and turned periodically to ensure good mixing
(Figure 1). This process can handle large quantities of input, such as yard trimmings of up to
100,000 cubic yards per year, on only a few acres of land.
Raw materials that tend to be very odorous during composting, such as municipal waste
sludge (biosolids), can be processed in more elaborate systems and in a confined facility where
odorous air can be treated. These systems use rotating drums, trenches, or enclosed tunnels
for initial processing, followed by a covered curing period (Figures 2, 3, and 4). In addition, the
Beltsville Agricultural Research Center in Beltsville, Maryland, developed a composting system
of intermediate complexity, between open-air windrows and the sophisticated systems shown in
Figures 2 to 4 (Parr, 1978; Willson, 1980; U.S. EPA, 1985). The Beltsville system has several
desirable features, and its generic design is adaptable to suit specific purposes. As shown in
Figure 5, air is drawn through the compostable material and scrubbed of odorous compounds in
a soil filter. Mature compost can be substituted for the soil filter. A compost filter has several
advantages over a soil filter, including a higher adsorptive capacity for volatile organic
compounds (VOCs) and better air permeability properties. Compost filters are currently used in
Europe at composting plants to eliminate nearly all volatile emissions.
All composting methods share similar characteristic features and processes. Initially high
microbial activity and heat production cause temperatures within the compostable material to
rise rapidly into the thermophilic range (50 °C and higher). This temperature range is
maintained by periodic turning or the use of controlled air flow (Viel, 1987). After the rapidly
degradable components are consumed, temperatures gradually fall during the "curing" stage
(Figure 6). At the end of this stage, the material is no longer self-heating, and the finished
compost is ready for use. Substantial changes occur in microbial populations and species
abundance during the various temperature stages (Gupta, 1987). Mesophilic bacteria and fungi
are dominant in the initial warming period, thermophilic bacteria (especially actinomycetes)
during the high temperature phase, and mesophilic bacteria and fungi during the curing phase
2 An Analysis of Composting as an Environmental Remediation Technology
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(Finstein, 1975). The resulting compost has a high microbial diversity (Beffa, 1996 and
Persson, 1995), with microbial populations much higher than fertile, productive soils (Table 1)
and many times higher than in highly disturbed or contaminated soils. Therefore, compost
bioremediation takes far less time than natural attenuation of toxic materials (land farming).
Microbial populations in soil (both fertile and contaminated) substantially vary from season to
season. In most cases, the addition of compost greatly increases microbial populations and
activity (Table 2). Since the microbes are the primary agents for degradation of organic
contaminants in soil (Alexander, 1994), increasing microbial density can accelerate degradation
of the contaminants (Cole, 1994). In soil systems, microbial composition is greatly modified by
organic input composition (Martin, 1992 and Struwe, 1986); the same degree of variation can
be expected in composting systems. The impact of initial feedstock composition on
microorganism development in compost needs to be further studied.
Table 1
Microbial Populations in Soil and Mature Yard Trimmings Compost
Material
Fertile soil3
Recently reclaimed soil
after surface mining"
Pesticide-contaminated
mix of silt and clayc
Mature compostd
Bacteria
(millions per gram dry weight)
6 to 46
19 to 170
19
417
Fungi
(thousands per gram
weight)
dry
9 to 46
8 to 97
6
155
Cole, 1976 (for reclaimed soil)
b Cole, unpublished data
cCole, 1994
dCole, 1994
Dramatic changes in chemical composition occur during the composting process. Most
starting materials for composting are plant-derived residues and contain carbon in the form of
polysaccharides (cellulose and hemicellulose), lignin, and tannin. The end-product has a low
polysaccharide content, most of which is microbial cell wall and extracellular gums (Macauley,
An Analysis of Composting as an Environmental Remediation Technology
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1993), with about 25 percent of the initial carbon content present in the form of highly stabilized
humic substances (Chen, 1993). Organic matter content ranges from 30 to 50 percent of dry
weight, with the remainder being minerals. The combination of high organic content and a
variety of minerals makes compost an excellent adsorbent for both organic and inorganic
chemicals.
The practical aspects of using the composting process or mature compost to manage
hazardous industrial waste streams are described in the sources cited above. Additional
information can be found in the documents cited in the Bibliography on page 105.
Table 2a b
Dehydrogenase Activity in Uncontaminated Soil or Pesticide-Contaminated Soil With or
Without Mature Yard Trimmings Compost
Percentage of
Contaminated Soil
100
50
25
0
50
25
0
Matrix
Contaminated soil
Contaminated soil and
Uncontaminated soil
Uncontaminated soil
Contaminated soil and
Compost
Compost
Not Planted
16C
25
25
40
336
613
1,464
Planted
18C
32
59
68
370
575
1,299
a This table shows the high dehydrogenase enzyme activity as a measure of microbial activity in
contaminated soil.
b After preparing the mixtures and transferring them into flower pots, the pots were incubated in a
greenhouse for 6 weeks. Planted treatments had four corn plants per pot, while unplanted treatments
had no plants.
c Units are umoles product formed per 24 hours per gram of soil, with higher values indicating greater
microbial activity.
An Analysis of Composting as an Environmental Remediation Technology
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Figure 1
Windrows of Leaves at a Community Yard Trimmings Composting Site
- ->.,,:. ,.Lj
Height and width of windrows are determined primarily by the size of the turning equipment.
An Analysis of Composting as an Environmental Remediation Technology
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Figure 2
Aerated Rotating Drum Composting System at Aufschafenburg, Germany
The drum temperature and oxygen content are monitored continuously, and air addition and
mixing are done as needed to maintain conditions within designated ranges.
An Analysis of Composting as an Environmental Remediation Technology
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Figure 3
Trench Composting System at Saint Cloud, Minnesota
Air and temperature control is provided by subfloor vents and large blowers. Material is turned
daily and water is automatically added as necessary.
An Analysis of Composting as an Environmental Remediation Technology
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Figure 4
Tunnel Composting System Used in Europe
Exit air is treated in a compost biofilter, and temperature and oxygen content of the air are
monitored.
8 An Analysis of Composting as an Environmental Remediation Technology
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Figure 5
Design of the Beltsville Aerated Pile Composting System
..... ' ' '*
filler
i T:rip fe:,'
Air is drawn through the composting mass and odorous volatile compounds are removed in a
soil biofilter (Willson, 1980).
An Analysis of Composting as an Environmental Remediation Technology
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Figure 6
Temperature Profile and Loss of Initial Organic Material During Composting
:C
3 -1
Time fwfit?*,£,'!
-15
40
35
30
The time scale for the entire cycle would range from about 8 weeks to 6 months, depending on
the composition of the source material and management intensity. Temperature is measured in
degrees Celsius.
1 0
An Analysis of Composting as an Environmental Remediation Technology
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References
Alexander, M. Biodegradation and Bioremediation. San Diego: Academic Press, 1994.
Beffa, T., M. Blanc, L. Marilley, J.L. Fischer, P.P. Lyon, and M. Aragno. "Taxonomic and
Metabolic Microbial Diversity During Composting." In The Science of Composting, by M. de
Bertoldi, P. Bert, and P. Tiziano, 149-161. London: Blackie Academic and Professional, 1996.
Chen, Y. and Y. Inbar. "Chemical and Spectroscopic Analyses of Organic Matter
Transformations During Composting in Relation to Compost Maturity." In Science and
Engineering of Composting, by H.A.J. Hoitinkand H.M. Keener, 551-600. Worthington, OH:
Renaissance Publications, 1993.
Cole, M.A. "Effect of Long-term Atrazine Application on Soil Microbial Activity." Weed Science
24 (1976): 473-476.
Cole, M.A., X. Liu, and L. Zhang. "Plant and Microbial Establishment in Pesticide-Contaminated
Soils Amended With Compost." In Bioremediation Through Rhizosphere Technology, edited by
T.A. Anderson and J.R. Coats, 210-222. Washington, DC: American Chemical Society, 1994.
Cole, M.A., X. Liu, and L. Zhang. "Effect of Compost Addition on Pesticide Degradation in
Planted Soils. In Bioremediation of Recalcitrant Organics, edited by R.E. Hinchee, D.B.
Anderson, and R.E. Hoeppel, 183-190. Columbus, OH: Battelle Press, 1995.
Finstein, M.S. and M.L. Morris. "Microbiology of Municipal Solid Waste Composting."
A dvances in Applied Microbiology 19 (1975): 113-151.
Gupta, V.K., M.P.S. Bakshi, and P.M. Langar. "Microbiological Changes During Natural
Fermentation of Urea-wheat Straw." Biological Wastes 21 (1987): 291-299.
Harmsen, J., H.J. Velthorst, and I.P.A.M. Bennehey. "Cleaning of Residual Concentrations With
an Extensive Form of Landfarming." In Applied Biotechnology for Site Remediation, edited by
R.E. Hinchee, D.B. Anderson, F.B. Metting, Jr., and G.D. Sayles, 84-91. Boca Raton, FL:
Lewis Publishers, 1994.
Macauley, B.J., B. Stone, K. liyama, E.R. Harper, and F.C. Miller. "Compost Research Runs
"Hot" and "Cold" at La Trobe University." Compost Science and Utilization 1 (1993): 6-12.
Martin, T.L., D.A. Anderson, and R. Goates. "Influence of the Chemical Composition of Organic
Matter on the Development of Mold Flora in Soil. So/7 Science 54 (1992): 297-302.
McNabb, D.H., R.L. Johnson, and I. Quo. "Aggregation of Oil- and Brine-contaminated Soil to
Enhance Bioremediation. In Hydrocarbon Bioremediation, by R.E. Hinchee, B.C. Allenman,
R.E. Hoeppel, and R.N. Miller, 296-302. Boca Raton, FL: Lewis Publishers, 1994.
An Analysis of Composting as an Environmental Remediation Technology 11
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Parr, J.F., E. Epstein, and G.B. Willson. "Composting Sewage Sludge for Land Application."
Agriculture and Environment 4 (1978): 123-137.
Persson, A., M. Quednau, and S. Ahrne. "Composting Oily Sludges: Characterizing Microflora
Using Randomly Amplified Polymorphic DMA." In Monitoring and Verification of Bioremediation,
by R.E. Hinchee, G.S. Douglas, and S.K. Ong, 147-155. Columbus, OH: Battelle Press, 1995.
Struwe, S. and A. Kj0ller. "Changes in Population Structure During Decomposition." In
Microbial Communities in Soil, edited by V. Jensen, A. Kj0ller, and L.H. S0rensen, 149-162.
London: Elsevier Applied Science Publishers, 1986.
U.S. EPA. Composting of Municipal Wastewater Sludges. EPA625-4-85-014. Washington,
DC, 1985.
Viel, M., D. Sayag, A. Peyre, and L. Andre. "Optimization of In-vessel Co-composting Through
Heat Recovery." Biological Wastes 20 (1987): 167-185.
Willson, G.B., J.F. Parr, E. Epstein, P.B. Marsch, R.L. Chaney, D. Colacicco, W.D. Surge, L.J.
Sikora, C.F. Tester, and S. Hornick. Manual for Composting Sewage Sludge by the Beltsville
Aerated-Pile Method. EPA600-8-80-022. Washington, DC, 1980.
12 An Analysis of Composting as an Environmental Remediation Technology
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Chapter 2
Remediation of Soils Contaminated With Toxic Organic Compounds
Introduction
Owners of property contaminated with toxic chemicals are required under federal and state
regulations to decontaminate the site or remove contaminated soil to a safe disposal facility,
such as a hazardous or special waste landfill. Decontamination or removal of soil is costly, as
shown by the values in Figure 7. These high cleanup costs may exceed the value of the
property and dramatically decrease the willingness of the property owner to initiate remediation.
Therefore, inexpensive, effective remedial methods could encourage the cleanup of the nearly
1,300 locations on the National Priorities List (NPL or "Superfund"). Thousands of smaller sites
that might pose a threat to adjacent populations also await cleanup. For example,
approximately 75,000 to 100,000 leaking below-ground petroleum storage tanks exist in this
country (Brown, 1985). In the United States alone, there are about 37,000 candidate sites for
Superfund, 80,000 sites covered under the Resource Conservation and Recovery Act (RCRA),
1.5 million leaking underground tanks storing a wide variety of materials, and 25,000
Department of Defense sites in need of remediation (Glass, 1995).
The sale of contaminated property is difficult at best. Many owners abandon their
contaminated property rather than try to sell or decontaminate it. These abandoned sites, or
brownfields, represent lost opportunities for productive reuse. Long-term use of property for
military operations also results in contamination (most often with organic solvents, petroleum
hydrocarbons, and explosives). As in the private sector, cost can be a critical barrier to military
site remediation. The remediation costs for NPL and RCRA sites alone may reach $750 billion,
an amount equal to the current U.S. military budget for about 15 years (Wilson, 1994). The
cost estimate for remediation of sites in the European Union is between $300 and $400 billion.
At these costs, it is unlikely that more than a small fraction of the most critical sites will ever be
remediated.
One possible solution to these problems is use of remedial methods that are significantly
less expensive than those commonly used, such as removal of contaminated soil. On average,
bioremediation is among the lowest cost methods for detoxification of soils contaminated with
organic compounds (Figure 7), and composting is intermediate in cost among the
An Analysis of Composting as an Environmental Remediation Technology 13
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bioremediation technologies (Figure 8). When comparing the total budget for cleanup of a
large site, the savings associated with the use of bioremediation vs. chemical- or physical-
based technologies give bioremediation an overwhelming monetary advantage (Table 3).
Table 3
Total Project Costs for Various Remedial Options
Remedial Technoloav
Vacuum extraction
Compost-based
Solidification
Thermal desorption
Offsite landfill
Onsite incineration
Total Project Costs3
$2.5 million
$3.6 million
$7.3 million
$11.4 million
$10.8 million
$18. 9 million
a Costs are based on a 1-acre site, 20 feet deep (about 32,000 cubic yards).
Values are an average for a variety of biodegradable contaminants such as fuels,
lubricants, and polynuclear aromatic hydrocarbons.
Applications of Composting or Compost Addition Methodologies
A wide range of common environmental contaminants degrade rapidly in compost, as
summarized in Table 4 and Figure 9. Of the compounds shown in Figure 9, the explosives
2,4,6 trinitrotoluene (TNT) and Royal Demolition Explosives (RDX) are the most widely studied,
in experiments ranging from bench (laboratory) scale to large pilot studies. Most of the
experiments focused on the composting process, with typical results shown in Figure 10. One
study found that up to 30 percent contaminated soil by volume could be mixed with
compostable materials and still achieve thermophilic conditions (Brinton, 1994). Another study
found that the inclusion of 40 percent contaminated soil in a composting mix resulted in
subthermophilic temperatures and reduced degradation of explosives (Williams, 1991). Both of
these studies indicate that a mixture of 30 percent contaminated soil with 70 percent initial
compost feedstock provides the best results. Volume loss of feedstock is typically about 50
percent of initial, so the final, decontaminated mix has about twice the volume of contaminated
soil.
14
An Analysis of Composting as an Environmental Remediation Technology
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Table 4
Contaminants That Degrade in Compost or During the Composting Process
General Class of Contaminant
Petroleum hydrocarbons (TPH)
Polynuclear aromatic hydrocarbons (PAH)
Pesticides
Explosives
Examples
Gasoline, diesel fuel, jet fuel, oil, and
grease
Wood preservatives, coal gasification
wastes, refinery wastes
Insecticides and herbicides
TNT, RDX, nitrocellulose
If contaminants degrade completely, disposal of the extra volume should not be a problem.
If contaminant degradation is incomplete, however, a substantially larger volume of
contaminated material will need to be further treated or disposed of. This problem can be
avoided by following a gradualistic approach from bench-scale to pilot-scale to full-scale
projects, to ensure that reliable degradation of contaminants can be achieved (Saber, 1995 and
U.S. EPA, 1989). One difficulty with this approach, when using the composting process, is that
laboratory-scale composting units may not provide results similar in either extent or time scale
to results obtained in large-scale composting. For example, one study found relatively poor
degradation of the explosive TNT in laboratory reactors (Kaplan, 1982), whereas other studies
indicate good degradation of TNT in pilot-scale studies. Based on this example, even partial
degradation under laboratory test conditions might be justification for conducting larger scale
pilot studies. Increasing the total volume of material is less of a problem when mature compost
is added to contaminated soil, since a mixture of 40 percent (by weight) compost and 60
percent contaminated soil provided good degradation of several pesticides (Liu, 1996).
A common complaint about solid-phase bioremediation methods is that they are too slow.
For example, commonly used procedures for bioremediation of petroleum-contaminated soils
require several months to a year to achieve cleanup, a time scale that may be in excess of
established deadlines or the owner's patience. A recent study compared the time required to
degrade a mixture of volatile organic solvents, polynuclear aromatic hydrocarbons (PAH), and
phenanthrene in a solid-phase system (biopile) and in a slurry-phase reactor. Biopile treatment
time was 94 days and degraded 99 percent of initial volatiles, 91 percent of PAH, and 87
An Analysis of Composting as an Environmental Remediation Technology
15
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percent of phenanthrene. In contrast, a 10-day treatment in a slurry-phase reactor degraded 99
percent of initial volatiles, 63 percent of PAH, and 58 percent of phenanthrene. In this case, the
biopile took substantially longer but resulted in greater contaminant degradation and was
achieved at a lower cost than the slurry-phase reactor. Extended time periods increase cost,
since the site must be monitored and operated for an extended period. Using the composting
process or adding mature compost to biopile-type operations, however, may dramatically
decrease cleanup time, as shown in the following examples.
One recent study examined the degradation of the herbicide dicamba during the
composting process (Dooley, 1995). Successful remediation was achieved in only 52 days, as
shown in Figure 11. Typical degradation rates for dicamba in soil, without the compost, are 1 to
2 mg/kg/month (Goring, 1975). Hence, treatment time for a high concentration of dicamba,
without using composting, would have been 1 year or more.
In another study, a mixture of soil contaminated with mineral oil and grease (35 percent v/v)
was composted with maple leaves (20 percent v/v), alfalfa (35 percent v/v), and other
ingredients. Highly weathered hydrocarbon mixtures, such as those present in the soil studied,
are often resistant to biodegradation. After an initial period of rapid degradation, degradation of
the residual material ceased (Figure 12). During the landfarming phase of the study, only 30
percent of the contaminants degraded after 180 days. In contrast, a 50 percent degradation
rate was achieved by composting in 105 days (73 percent degradation was reached in 287
days). An 85 percent degradation rate was achieved by composting oily sludges containing
hydrocarbon mixes in the lubricating oil and diesel oil molecular weight range (Persson, 1995).
Decomposed horse manure was used to maintain mesophilic (25 °C to 35 °C) composting conditions.
Two recent studies documented the effects of mature compost on hydrocarbon degradation
in soil-compost mixes in laboratory reactors (Stegmann, 1991 and Hupe, 1996). The best
results were achieved by mixing mature, 6-month-old compost with TPH-contaminated soil.
The studies found degradation rates of about 375 mg TPH/kg/day, values much higher than
those reported for in situ biodegradation—40 mg/kg/day (Atlas, 1991). TPH-contaminated soils
frequently contain 5,000 to 20,000 mg TPH/kg. Based on the rates shown in Figure 13, these
materials could be remediated, using compost, in only 2 weeks to 2 months, in contrast to the 6
months or more required for typical landfarming operations. Mass balance studies (Table 5)
indicated that during a 21-day treatment period, substantial mineralization and bound residue
16 An Analysis of Composting as an Environmental Remediation Technology
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formation occurred. The chemical nature of the bound residue was not determined. This
material could be either strongly sorbed hydrocarbon or partially degraded hydrocarbon that
was coupled to humic materials in the compost. A field-scale study (Bartusiak, 1984) achieved
oil degradation rates of about 110 mg/kg/day with a steel mill sludge containing primarily
relatively high molecular weight—and therefore, relatively slowly degraded—hydrocarbons
(Westlake, 1974).
Table 5
Mass Balance for Carbon From Petroleum Hydrocarbons During Incubation of a
Soil-Compost Mixture
Fraction
Extractable TPH
Volatilized
Converted to CO2
Not accounted for (bound residue)
Microbial biomass
Percentage of Initial-C in Fraction
8
4
59
24
4
Source: Hupe, 1996.
Degradation of various aromatic compounds has been studied in composting systems,
including chlorophenols, pesticides, and PAH. The degradation of 2-chloro- and 2,4-
dichlorophenol during composting results in a rapid loss of parent compounds, as shown in
Figure 14 (Benoit, 1995). Mass balance studies indicate that complete mineralization
(formation of carbon dioxide) was relatively limited, with most of the carbon going into a bound
residue fraction (Figure 15). The bound residues might be the result of oxidative coupling of the
chlorophenols, or their metabolites, to humic materials in the compost. Similar behavior of
chlorophenols has been reported in soil (Stott, 1983). A similar study yielded a 90 percent
degradation rate, in 5 days, for easily degraded naphthalene and 1- and 2-methylnaphthalene
during composting of wood preservative-contaminated soil, as well as 80 percent degradation
for slowly degraded PAHs, such as chrysene and pyrene, in 15 days (Civilini, 1996a).
An Analysis of Composting as an Environmental Remediation Technology
17
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In addition to the direct use of composting or mature compost to accelerate contaminant
degradation, microorganisms also can be isolated from compost for both basic biochemical studies
and as inoculants in remediation projects (Civilini, 1996a; Civilini, 1996b; Castaldi, 1995).
The high temperatures achieved during composting also accelerate the relatively slow
chemical reactions in soil, where temperatures are only 15 °C to 30°C in most temperate
climates. By comparison, typical temperatures during composting are 50 °C or higher. Humic
materials can catalyze degradation of atrazine (Li, 1972) and other compounds (Stevenson,
1994). Since the humic content of mature compost can be as high as 30 percent by weight,
whereas typical soils contain less than 5 percent, compost provides a much higher
concentration of reactive material than is found in soil.
Composting of contaminated materials can be done on a field scale using simple designs,
such as those shown in Figures 16 and 17. The designs are mechanically simple, are
inexpensive, and provide full containment of materials while preventing washing away by rain.
If volatile compounds are being processed, air flow can be set to draw air into the pile and pass
it through a biofilter to remove the volatiles. In this case, the complexity is in the biological
component, not the physical components, and the only moving parts are the microbes and the
ventilation system. The result is likely to be an effective, fast-acting, and inexpensive
remediation system. Guidelines for successful operation of these systems are provided in the
references for Chapter 1.
No remedial technology is appropriate for all contaminants and situations. Guidelines for
the best use of composting or addition of mature compost for remediation include:
• Contaminants less than 20 feet deep
• Contaminants that are biodegradable and/or strongly adsorbed to the compost
• Soil that is toxic to plants and microbes
Use of the composting process or addition of mature compost is not likely to be successful for
polychlorinated biphenyls (PCB) because the biodegradability of the more highly chlorinated
congeners is poor. For example, one study found that only the congeners with two or three
chlorines were degraded during composting (Michel, 1997). Similarly, another study found that
benzo(a)pyrene, a 5-ring polynuclear aromatic compound of poor biodegradability, was not
degraded during bench-scale production of municipal solid waste (MSW) compost (Overcash,
18 An Analysis of Composting as an Environmental Remediation Technology
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1993). These authors also found that the PCB 2,2',4,4'-tetrachlorobiphenyl (added at the beginning
of the composting process) was present in the finished compost (i.e., it was not degraded during the
process).
Before composting can be widely accepted as a remedial technology, several issues need
to be resolved. First, substantial anecdotal evidence indicates that the degradation rate of
specific contaminants is affected by the materials being composted. For example, 16 percent
mineralization was found for 14C-labeled pentachlorophenol during 60 days of incubation with
laboratory-produced compost or spent mushroom substrate (a form of compost created from
the material that remains after commercial production of edible mushrooms, Agaricus bisporus).
Thirty percent mineralization occurred, however, in mushroom medium of a lesser degree of
stabilization (Semple, 1995).
Second, a relatively low extent of mineralization of aromatic compounds occurs in compost,
and, in some cases, water-extractable metabolites form. In some studies, potentially toxic
intermediates formed during laboratory composting of explosives (Kaplan, 1982). One recent
study reported a 98 percent transformation of TNT during composting, but the material retained
about 12 percent of its original mutagenicity, and the aqueous leachate still had about 10
percent of its toxicity to an aquatic invertebrate, as shown in Figure 18 (Griest, 1993). When
properly handled, however, field-level composting of explosives can reduce contaminants to
undetectable levels with an extremely low occurrence of toxic intermediates, as was recently
accomplished at the Umatilla Army Depot (Emery, 1996).
The other critical issue is whether the lack of full degradation and formation of
nonextractable metabolites is a satisfactory endpoint of remediation. The behavior of aromatic
compounds in compost is similar to the behavior of hydroxylated or amino aromatic compounds
in soils, where partial degradation occurs, followed by covalent coupling of the metabolite to
humic substances, as shown in Figure 19 (Bertin, 1991; Calderbank, 1989; Richnow, 1994;
Haider, 1994; Sjoblad, 1981). Hydroxylated metabolites form during the degradation of nearly
all aromatic compounds (Kelley, 1993). In some cases, coupling of chlorinated phenols to
humic materials is accompanied by dehalogenation (Dec, 1994). This process, referred to as
formation of bound residues, results in the long-term immobilization of metabolites but not their
complete destruction. The bound residues typically are very slowly degraded (Wolf, 1976 and
Volkel, 1994). Bound residues are defined by the International Union of Pure and Applied
Chemistry (IUPAC) as "chemical species originating from pesticides, used according to good
An Analysis of Composting as an Environmental Remediation Technology 19
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agricultural practice, that are unextracted by methods which do not significantly change the
chemical nature of these residues" (Volkel, 1994). In practice, loss of extractability by organic
solvents is suggestive of bound residue formation (Haider, 1994). The process is not simply
adsorption (Piccolo, 1994), since sorbed low-molecular weight metabolites often remain
solvent-extractable. Bound residue formation results from the synthesis of relatively labile
bonds, such as ester groups, creating relatively low long-term stability.
On the other hand, formation of ether linkages between humic materials and metabolites
results in relatively long-term stabilization of the metabolite in a form of low bioavailability. If the
metabolite is actually incorporated into the core structure of the humic acid (Stevenson, 1994),
the residence time of the metabolite-derived carbon will be decades to centuries. Substantial
amounts of 14C derived from 14C-labelled 2,4-dichlorophenoxyacetic acid (2,4-D) are
incorporated into humic and fulvic acids during composting of yard trimmings containing 2,4-D
(Michel, 1995).
During a recent bioremediation project, Bioremediation Service, Inc., successfully bioremediated
14,000 tons of TNT, RDX, HMX, and other nitroaromatic compound-contaminated soils at the
Umatilla Army Depot. A specific recipe of organic amendments was selected to balance the C:N
ratio, structure, moisture, and porosity and to optimize explosive degradation. At project end, over
75 percent of all samples indicated that the explosives had been degraded to below detection by
EPA SW-846 Method 8330. What remained was a humus-rich soil, with no toxic intermediates, that
has been shown to be a value-added soil additive (Emery, 1996).
A number of studies on xenobiotic degradation in compost were conducted by measuring the
loss of only the parent compound, but these studies did not adequately measure volatilization or
adsorption of compounds to vessel components, such as plastics. At thermophilic temperatures,
volatilization losses can be significant. One study found that nearly 50 percent of added chlordane is
volatilized, but only about 5 percent is converted to bound residues; the balance is recovered as
parent compound (Petruska, 1985). Another study reported 17 percent volatilization, 45 percent
adsorption to vessel materials, and 25 percent biodegradation of 14C-naphthalene in laboratory
reactors (Silviera, 1995). If the study detailed only the loss of naphthalene, 87 percent of the
naphthalene would have been apparently degraded.
A third issue that requires resolution is the fact that the outcome of remediation experiments
may vary depending on the scale of the experiment. For example, bench-scale results may not
transfer well in terms of degradation rate to pilot-scale or field-scale experiments. In several
20 An Analysis of Composting as an Environmental Remediation Technology
-------
cases, better results are obtained in larger scale experiments when compared to very small-
scale laboratory experiments. Part of the difficulty in this case is probably the result of the
inability to generate typical and authentic composting conditions in small laboratory containers.
For pilot-scale composting studies, a volume of at least 10 to 20 cubic meters of material is
required to achieve the typical thermal profiles seen in large windrows. Hence, the results from
a pilot study of only a cubic meter may not transfer to a larger system.
An Analysis of Composting as an Environmental Remediation Technology 21
-------
Figure 7
Comparative Costs of Remedial Options for Soils or Hazardous Wastes
vacuumiextractior
biotreajtment
2 30- project average :
Ttie Bionsiriediation rttepol, 0/95
cation
thermal
offsi
onsite ir
desorptic
n
e landfill
cineratio
•
ion
100 200 300 400
$ por ton8
500
600
a Values are an average for a variety of biodegradable contaminants such as fuels, lubricants,
and PAH.
Data obtained from The Bioremediation Report, August 1995.
22
An Analysis of Composting as an Environmental Remediation Technology
-------
Figure 8
Comparative Costs of Bioremediation Options for Soils or Hazardous Wastes
biioventin
'
landfairming
CO
slqrry phasJG biorea
white rot fungi
Tipost technology
i 1 i
100 200
$ per ton treated'
300
a Values are an average for a variety of biodegradable contaminants such as fuels, lubricants,
and PAH.
An Analysis of Composting as an Environmental Remediation Technology 23
-------
Figure 9
Structures of Organic Compounds That Have Been Shown to Degrade During
Composting or in Soil Amended With Mature Compost
CH3
NG2
H2CCH2-, ..CH2CH3
Q2N
.N02
CH3
OCH3
ifctobehor
0
I
CICH2C CHCH20CH3
V
CH3CH2-
CH3
CHS
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH3
24
An Analysis of Composting as an Environmental Remediation Technology
-------
Figure 10
Degradation of the Explosive TNT During Composting
is 0:>': -r
16, OK
u.ooo
~' 6.0CC-
fii';:ais ii'iiityle i.- 1 i-IS'siJaiCl il»?
-------
Figure 11
Degradation of the Herbicide Dicamba During Composting
3000
CM,
7 14 31 £S
tin* (ctays)
a A mixture of 10% compost with a waste containing a low concentration of dicamba.
b A mixture of 10% compost with a waste containing a high concentration of dicamba.
Source: Dooley, 1995
26
An Analysis of Composting as an Environmental Remediation Technology
-------
Figure 12
Degradation of Mineral Oil and Grease During Composting
2QOOQ
*^^»
I
50 100
Time (days)
150
200
Figure A: Degradation of mineral oil and grease (all components).
Figure B: Degradation of specific components.
Circles: Degradation of aliphatic polar components.
Source: Beaudin, 1996
An Analysis of Composting as an Environmental Remediation Technology 27
-------
Figure 13
Degradation of Petroleum Hydrocarbons in Compost-Amended Soil
0.8
0.2
0
before treatment
after 12 day treatment
246
Compost age (months)
Source: Stegmann, 1991
28 An Analysis of Composting as an Environmental Remediation Technology
-------
Figure 14
Degradation of 2-Chlorophenol (2-CP) and 2,4-Dichlorophenol (2,4-DCP)
During Composting
100
O 80
*^?
1 60
-*H-*
s
o 40'
20
0
490
,••""*"
•..'+•"*"" CO,
0 5 10 15 20 25
2,,4-DCP
mg.%g
bound
0 5 10 15 20 25
Time
"Bound residues" are compounds that are unextractable by water and/or methanol.
Source: Benoit, 1995
An Analysis of Composting as an Environmental Remediation Technology
29
-------
Figure 15
Distribution of 14C Derived From 2-CP and 2,4-DCP After Composting
COa
Source: Benoit, 1995
46%
23 /b
32%
t
to
10%
74%
to
30
An Analysis of Composting as an Environmental Remediation Technology
-------
Figure 16
A Simple Contained System for Composting of Hazardous Waste or Treatment of
Mixtures of Compost and Contaminated Soil
Lenplh Vanas
wrth Propel Si/r
Project Size
Source: Cole, unpublished
An Analysis of Composting as an Environmental Remediation Technology
31
-------
Figure 17
Enclosed Biofilter Design for Capture of Volatiles Produced During Composting of
Contaminated Soil
t'al en Waller to Sa.-if*fe
W.m*r: %'»nlf:f I-nn ^ '"
:"fte" ::Tiii"! Syptirr
Source: Carlson, 1996
32 >4n Analysis of Composting as an Environmental Remediation Technology
-------
Figure 18
Reduction in Total TNT Content, Leachable TNT, Toxicity, and Mutagenicity of
Explosives-Contaminated Soil During In-Vessel Composting
-O- f A < 'riWO -. •
-ft
Source: Griest, 1993
An Analysis of Composting as an Environmental Remediation Technology
33
-------
Figure 19
Possible Mechanism for Formation of Bound Residues During Composting of Soil
Containing Aromatic Contaminants
,--"'
Source: Humicacid structures (Stevenson, 1994), reactions (Richnow, 1994)
34 An Analysis of Composting as an Environmental Remediation Technology
-------
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Li, G.C. and G.T. Felbeck, Jr. "Atrazine Hydrolysis as Catalyzed by Humic Acids." So/7 Science
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Piccolo, A. "Interactions Between Organic Pollutants and Humic Substances in the
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Semple, K.T. and T.R. Fermor. "Composting Systems for the Bioremediation of Chlorophenol-
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Anderson, and R.E. Hoeppel, 93-100. Columbus, OH: Battelle Press, 1995.
Silviera, A.E. and R.B. Ganho. "Composting Wastes Contaminated With Naphthalene."
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Sjoblad, R.J. and J.M. Bollag. "Oxidative Coupling of Aromatic Compounds by Enzymes From
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152. New York, NY: Marcel Dekker, Inc., 1981.
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Stegmann, R., S. Letter, and J. Heerenklage. "Biological Treatment of Oil-contaminated Soils
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208. Boston: Butterworth-Heinemann, 1991.
Stevenson, F.J. Humus Chemistry. New York, NY: John Wiley & Sons, 1994.
Stott, D.E., J.P. Martin, D.D. Focht, and K. Haider. "Biodegradation, Stabilization in Humus,
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3,4-dichloroaniline to Catechol Rings: A Model for the Formation of Pesticide Bound Residues
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Final Report. CETHA-TS-CR-91053. Washington, DC: U.S. Army Corps of Engineers, 1991.
Wilson, D.J. and A.N. Clarke. Hazardous Waste Site Soil Remediation, 5. New York, NY:
Marcel Dekker, Inc., 1994.
Wolf, D.C. and J. P. Martin. "Decomposition of Fungal Mycelia and Humic-type Polymers
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Soc. Am. J. 40 (1976): 700-704.
38 An Analysis of Composting as an Environmental Remediation Technology
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Chapter 3
Compost-Based Biofilters for Treatment of Contaminated Air and
Wastewater Streams
Introduction
Federal regulations such as the Clean Air Act and RCRA require the treatment of industrial
(and other) wastewater and air streams to prevent the release of toxic or harmful chemicals into
the environment. Granular activated carbon (GAC) is widely used for this purpose and as a
polishing step in wastewater treatment; however, it is expensive and not very effective under
conditions of high air humidity or with liquid wastestreams. GAC's maintenance costs and time
requirements can be high. In addition, when toxic materials are trapped in GAC, it may require
disposal as a hazardous waste. GAC's high cost and maintenance requirements sparked the
search for low-maintenance, relatively inexpensive substitutes. Cost considerations are
particularly acute for livestock operations, which can be very odorous, making them difficult to
site far enough from towns and expanding suburban populations to avoid odor problems
(Nielsen, 1986 and Nielsen, 1988).
Biofilter technologies are an effective alternative to GAC treatment in several applications.
A biofilter is a porous, solid matrix containing attached microorganisms. When contaminated air
or water passes through the filter, the contaminants are transferred from the air or water into
the aqueous phase of the filter or into biomass or filter materials. The compounds can then be
adsorbed and/or degraded by the microbial biofilm, as shown in Figure 20 (Apel, 1993;
Saberiyan, 1994; Standefer, 1993). Sand and gravel biofilters have been used to treat
wastewater for decades (Andersson, 1994 and Tschui, 1994). These filters can be very
effective, removing up to 99 percent of organic compounds and significantly reducing other
odorous or harmful constituents, such as hydrogen sulfide. Several problems are commonly
encountered with these sand and gravel systems, including a tendency for the bed to pack
down, thereby reducing the flow rate unless pressure is increased. In addition, channelization
of flow can occur, and the biofilm can destabilize. Difficulties such as packing are easily solved
by using a dimensionally stable bed material (sand, gravel, or activated carbon). These
materials are not very satisfactory as biomass supports, however, and sloughing of biomass
with resultant loss of performance is common. Sand and gravel also have low adsorptive
An Analysis of Composting as an Environmental Remediation Technology 39
-------
capacities, so the only absorptive material in these systems is the microbial biomass itself.
Using compost as the filter medium—particularly for air streams—provides high porosity, high
adsorptive capacity for organic and inorganic compounds, good moisture retention, and the
ability to support high degradation rates (Devinny, 1994). Compost biofliters have the further
advantage of relatively long lifespans: 1 to 1.5 years of satisfactory performance before bed
materials need to be changed (Leson, 1991; Conrad, 1995; Ottengraf, 1983). In contrast, GAC
filters might need to be changed more frequently, often daily or monthly, depending on the
pollutant content of the incoming air or water stream.
Commercial-scale compost biofilters have been used in Europe for the past 20 years to
treat exhaust gases from composting plants (Bohn, 1975 and Haug, 1993). The number of
VOCs removed is substantial, and removal efficiencies are generally high, as shown in Table 6
(Williams, 1993). Compost biofilters also can be used to treat odorous air from wastewater
facilities, biosolids composting plants, and industrial facilities (Carlson, 1966; Bohn, 1975; Finn,
1997; Leson, 1991; Segall, 1995). The effluent gases from biosolids and MSW composting
facilities are a complex mixture of terpenes, organic solvents (Eitzer, 1993), and biological
products, such as short chain organic acids, amines, and aldehydes (Wilber, 1990 and Miller,
1993). Volatiles content at these facilities is in the range of 20 to 150 mg VOC/m3 of air (Kissel,
1992), and odor intensity is high (Bidlingmaier, 1996). The ability of compost biofilters to
remove such a wide range of compounds at relatively high concentrations indicates these filters
are likely to be effective in a wide range of situations, from wastewater treatment plants to odor-
generating food processing plants (Leson, 1991). Since the VOC spectrum of manures (Kreis,
1978) is similar to that of composting biosolids or MSW, biofilters are likely to be successful for
removing odorous compounds from air exiting animal confinement facilities.
In contrast to compost-based bioremediation (Chapter 2), where there is substantial
published literature and relatively limited practical demonstration, the published literature on
compost biofilters is very sparse, with most of the available information being anecdotal or not
referenced. Most successful biofilters are developed empirically, rather than on a substantial
base of fundamental research. One inventor, for example, tried 30 different mixes for a
compost matrix before finding one that was satisfactory (Conrad, 1995). Technological
innovations frequently follow the increased availability of basic knowledge; in the case of
compost biofilters, there is ample opportunity for improved designs, enhanced performance,
and improved reliability.
40 An Analysis of Composting as an Environmental Remediation Technology
-------
Table 6
Volatiles Removal Efficiencies of Full-Scale Compost Biofilters
Compost
Source
MSW compost
MSW compost
MSW compost
Biosolids
compost
MSW compost
Volatiles
Removed
Ethanol
Diacetyl
Limonene
Acetoin
Total organic-C
Total C
Odorous
organics3
H2Sb
Total C
Inlet Air
Content
391 mg C/m3
16
16
64
557
230 mg C/m3
2,400 odor units
not given
45 mg C/m3
Exit Air
Content
not detected
not detected
5 mg C/m3
not detected
40
8
70 odor units
not given
4 mg C/m3
Percentage
Removed
>99
>99
69
>99
93
97
97
>99.8
94
Adapted from van der Hoek, 1985.
3 Volatile odorous compounds include a range of short-chain organic acids, aldehydes, dimethylsulfide,
dimethyldisulfide, and dimethyltrisulfide.
b Removal of H2S is probably a combination of chemical precipitation ofsulfide as iron sulfide and
microbial oxidation ofsulfide to odorless and nonvolatile sulfate iron.
Compost biofilters are 83 to 99 percent effective at removing hydrogen sulfide gas and
several simple aromatic compounds, as shown in Table 7 (Ergas, 1995). In a recent study, two
biofilters were run in parallel, with substantial differences in performance between the two
filters. The filters were also relatively effective in removing chlorinated aliphatic solvents and
other volatiles (Figure 21), except for trichloromethane and tetrachloroethylene.
In another study, laboratory-scale compost biofilters were shown to be effective degraders
of trichloroethylene (TCE), but only if the inlet air was supplemented with methane or propane
(Watwood, 1995). Methane or propane addition was necessary because TCE-degrading
organisms do not grow with TCE as the sole carbon and energy source (Lu, 1995). The
requirement for a cosubstrate may also explain the relatively poor performance of the filters
tested in similar studies (Ergas, 1995). The percentage of TCE removed was quite high in most
cases, but there were substantial differences in performance among different compost types.
An Analysis of Composting as an Environmental Remediation Technology
41
-------
The specific cosubstrate (methane or propane) used also had a large effect on performance
(Figure 22). Initial removal of TCE from the air phase appeared to be primarily by adsorption
and/or transfer into micropores within the compost, since actual degradation of a single
application of TCE required 10 to 20 days. Overall removal efficiency was 99.2 percent when
inlet air contained 5,000 ug/L of TCE.
Table 7
Removal Efficiencies of a Compost Biofilter for Hydrogen Sulfide, Benzene, Toluene, and
Xylene Isomers
Analyte
Hydrogen
sulfide
Benzene
Toluene
m- and p-
xylene
o-xylene
Inlet
Concentration
(ug/L)
19,900
900
1,060
260
95
Biofilter 1,
Outlet
Concentration
20
68
75
27
17
Percentage
Removed
99.9
95
97
93
91
Biofilter 2,
Outlet
Concentration
200
210
180
61
25
Percentage
Removed
99.7
83
88
88
88
Adapted from Ergas, 1995.
Field-scale use of compost biofilters to remove odorous compounds and methane from
landfill gas during landfill mining also has been studied (Goschl, 1995). The performance of the
filters was impressive. Shock loads of 3 to 9 percent v/v methane were introduced at irregular
intervals, but the filters effectively removed the methane rapidly, as shown in Figure 23. Most
of the methane removal resulted from very rapid microbial degradation, since methane is
neither very water-soluble nor easily adsorbed to the organic fraction of the filter. The
increased carbon dioxide content and decreased oxygen content of exit air shortly after a pulse
of methane is also consistent with the rapid biodegradation of the gas. This treatment method
provides a simple, effective way to improve air quality, especially because methane is now
regarded as an undesirable atmospheric gas because of its contribution to the greenhouse
effect and smog formation.
42
An Analysis of Composting as an Environmental Remediation Technology
-------
Compost biofilters are also effective at removing the VOCs generated during the recycling
of spray cans (Conrad, 1995). VOCs are released when the cans are punctured. The gas is
passed through a multistage compost biofilter, where 99 percent of the solvents and propellants
are removed. Typical recommendations for maximum VOC concentrations for biofilters are
about 5,000 mg/L of air, above which the solvents can inhibit microbial activity in the compost
(Leson, 1991). With a multistage system, VOC inputs of around 25,000 mg/L can be
processed effectively, a result that demonstrates clearly that substantial improvements can be
made in relation to current biofilter performance.
The majority of compost biofilters are used to treat air streams, but there are indications that
compost is also a suitable material for the treatment of contaminated water. A good example is
a commercial stormwater filter (Conrad, 1995 and Stewart, 1994) that proved effective at
removing oil, grease, and toxic metals found in stormwater runoff.
Regardless of the specific filter material being used, all biofilters have certain operational
requirements that, if neglected, lead to performance losses. A successful compost biofilter has
the following characteristics (Leson, 1991; Ottengraf, 1986; Haug, 1993; Williams, 1993; Ernst,
1987;Toffey, 1997):
• High porosity and water-holding capacity are required. Substantial differences exist among
composts and between compost and peat (Figure 24A). The MSW compost shown in
Figure 24 is not satisfactory as a filter medium because of its low total porosity and rapid
loss of air-filled pore space as moisture content is increased. This material develops a high
back pressure when moist, which greatly increases pump requirements (Figure 24B).
• Performance improves with increased time in service. This benefit results from the selection
of microorganisms tolerant to shock loads and other organisms with a high growth rate
(Figure 25).
• Additional nutrients are required. Although composts typically have 1 to 2 percent w/w
nitrogen, most of that nitrogen is not rapidly bioavailable. As a result, systems handling
high organic loads are likely to be nitrogen-deficient, unless a soluble form such as
ammonium or nitrate is added. A relevant study demonstrated that the performance of a
biofilter treating hexane vapors was improved dramatically by the addition of nitrogen
(Morgenroth, 1996).
An Analysis of Composting as an Environmental Remediation Technology 43
-------
Without a nitrogen supplement, an 80 centimeter column removed only 40 to 70 percent of
the incoming hexane, but a 60 centimeter column, supplied with nitrogen, removed 90 to
100 percent of the incoming hexane.
Moisture content must remain between 50 to 70 percent to ensure high microbial activity.
High moisture content also increases the capture of water-soluble VOCs when compared to
a drier filter. For most applications, humidification of incoming air is required. In some
situations, humidification of air entering the bottom of the filter must be combined with the
addition of liquid water to the top of the filter, in order to maintain proper moisture
conditions.
Operating temperatures must remain between 20 °C and 35 °C. Below 20 °C, microbial
activity is relatively low, and the organisms' ability to degrade contaminants is reduced.
Above 35 °C, many mesophilic organisms display decreased activity. The temperature
requirement imposes a limit on temperature of the incoming air. If air temperature is too
high, filter efficiency will be affected, and the filter will be subject to excess water loss.
Residence time of the gas phase going through the filter should be at least 30 seconds.
With shorter residence times, inadequate capture and degradation of input VOCs are likely.
As a consequence of this requirement, filters are more effective when treating low-velocity
and/or low-volume air streams.
Typical depth of the filter bed should be 1 meter. Shorter depths provide poor performance,
except at very low flow rates. Filter beds greater than 1 meter in depth have a tendency to
compact, thereby increasing air pressure requirements.
The system must be designed to ensure uniform air distribution upon entering the filter, and
the filter medium must be dimensionally stable so that crack formation and channeling of
airflow does not occur. Channeling decreases residence time and the percentage of the
filter that is active, drastically reducing filter performance.
44 An Analysis of Composting as an Environmental Remediation Technology
-------
Figure 20
Mechanisms for Contaminant Removal From Wastestreams
During Passage Through Biofilters
,.,TF;.,T
,/x
1 I
,*-""~l
. A A >
( A '
1-^
•"' ""•'••««"
Analysis of Composting as an Environmental Remediation Technology 45
-------
Figure 21
Removal Efficiency of Compost Biofilters for Synthetic Volatile Organic Compounds
Source: Ergas, 1995 (Figure 5)
46 An Analysis of Composting as an Environmental Remediation Technology
-------
Figure 22
Percentage Degradation of Trichloroethylene During Passage Through Biofilters Made
From Different Kinds of Compost
i- Suiw CcnpssC f
b:i t'i'l
Source: Watwood, 1995 (Figure 4A)
Analysis of Composting as an Environmental Remediation Technology 47
-------
Figure 23
Removal of Methane From Landfill Gas During Mining Operations
100-
Sampling Date
Source: Goschl, 1995 (Figure 2)
48
An Analysis of Composting as an Environmental Remediation Technology
-------
Figure 24
Improved Removal Efficiency of a Compost Biofilter With Increasing
Time in Operation
&'.>
Source: Ergas, 1995 (Table 3)
An Analysis of Composting as an Environmental Remediation Technology 49
-------
Figure 25
Porosity of Several Filter Media as a Function of Water Content and Power Requirements
of Various Materials
Source: Zeisig, 1988 (Figures 1 and 2)
50
An Analysis of Composting as an Environmental Remediation Technology
-------
References
Andersson, B., H. Aspegren, D.S. Parker, and M.P. Lutz. "High Rate Nitrifying Trickling
Filters." Water Science and Technology 29(10-11) (1994): 47-52.
Apel, W.A., P.R. Dugan, M.B. Wiebe, E.G. Johnson, J.M. Wolfram, and R.D. Rogers.
"Bioprocessing of Environmentally Significant Gases and Vapors With Gas-phase Bioreactors:
Methane, Trichloroethylene, and Xylene." In Emerging Technologies in Hazardous Waste
Management III, edited by D.W. Tedder and F.G. Pohland, 411-428. Washington, DC:
American Chemical Society, 1993.
Bidlingmaier, W. "Odour Emissions From Composting Plants." In The Science of Composting,
edited by M. de Bertoldi, P. Bert, and P. Tiziano, 71-79. London: Blackie Academic and
Professional, 1996.
Bohn, H.L. "Soil and Compost Filters of Malodorant Gases." Journal of the Air Pollution
Control Association 25 (1975): 953-955.
Carlson, D.A. and C.P. Leiser. "Soil Beds for the Control of Sewage Odors." Journal of the
Water Pollution Control Association 38 (1966): 829-840.
Conrad, P. "Commercial Applications for Compost Biofilters." BioCycle 36 (October 1995):
57-60.
Devinny, J.S., V.F. Medina, and D.S. Hodge. "Biofiltration for Treatment of Gasoline Vapors."
In Hydrocarbon Bioremediation, by R.E. Hinchee, B.C. Alleman, R.E. Hoeppel, and R.N. Miller,
12-19. Boca Raton, FL: Lewis Publishers, 1994.
Eitzer, B.D. "Survey of Volatile Organic Chemical Emissions From Waste Composting
Facilities." In The Composting Council's Fourth Annual Conference Research Symposium, 9-
11. Arlington, VA: The Composting Council, 1993.
Ergas, S.J., E.D. Schroeder, D.P.Y. Chang, and R.L. Morton. "Control of Volatile Organic
Compound Emissions Using a Compost Biofilter." Water Environment Research 67 (1995):
816-821.
Ernst, A.A. and D. Ritner. "New Ways for Design, Construction, and Operation of Compost
Filters for Special Purposes." In Compost: Production, Quality, and Use, edited by M. de
Bertoldi, 440-452. New York, NY: Elsevier Applied Science, 1987.
Finn, L. and R. Spencer. "Managing Biofilters for Consistent Odor and VOC Treatment."
BioCycle 38 (January 1997): 40-44.
An Analysis of Composting as an Environmental Remediation Technology 51
-------
Goschl, R. "Odor Stabilization in Waste Disposal Sites." In In Situ Aeration: Air Sparging,
Bioventing, and Related Remediation Processes, edited by R.E. Hinchee, R.N. Miller, and P.C.
Johnson, 289-295. Columbus, OH: Battelle Press, 1995.
Haug, R.T. "Biofiltration." In The Practical Handbook of Compost Engineering, 586-600. Boca
Raton, FL: Lewis Publishers, 1993.
Kissel, J.C., C.L Henry, and R.B. Harrison. Biomass and Bioenergy 3(3-4) (1992): 181.
Kreis, R.D. Control of Animal Production Odors: The State-of-the-Art. EPA600-2-78-083.
Washington, DC, 1978.
Leson, G. and A.M. Winer. "Biofiltration: An Innovative Air Pollution Control Technology for
VOC Emissions." Journal of the Air and Waste Management Association 41 (1991): 1045-
1054.
Lu, C.J., C.Y. Chang, and C.M. Lee. "Aerobic Biodegradation of Trichloroethylene by
Microorganisms That Degrade Aromatic Compounds." In Bioremediation of Chlorinated
Solvents, edited by R.E. Hinchee, A. Leeson, and L. Semprini, 1-7. Columbus, OH: Battelle
Press, 1995.
Miller, F.C. "Minimizing Odor Generation." In Science and Engineering of Composting, edited
by H.A. J. Hoitink and H.M. Keener, 219-241. Worthington, OH: Renaissance Publications,
1993.
Morgenroth, E., E.D. Shroeder, D.P.Y. Chang, and K.M. Scow. "Nutrient Limitation in a
Compost Biofilter Degrading Hexane." Journal of the Air and Waste Management Association
46(1996): 300-308.
Nielsen, V.C., J.H. Voorburg, and P. L'Hermite. Odour Prevention and Control of Organic
Sludge and Livestock Farming. London: Elsevier Applied Science Publishers, 1986.
Nielsen, V.C., J.H. Voorburg, and P. L'Hermite. Volatile Emissions from Livestock Farming
and Sewage Operations. London: Elsevier Applied Science Publishers, 1988.
Ottengraf, S.P.P. "Exhaust Gas Purification." Biotechnology, Volume 8, 427-452. Weinheim,
Germany: VCH Verlagsgesellschen, 1986.
Ottengraf, S.P.P. and A.H.C. van den Oever. "Kinetics of Organic Compound Removal From
Waste Gases With a Biological Filter." Biotechnology and Bioengineering 25 (1983): 3089-
3102.
Saberiyan, A.G., M.A. Wilson, E.O. Roe, J.S. Andrilenas, C.T. Esler, G.H. Kise, and P.E. Reith.
"Removal of Gasoline Volatile Organic Compounds via Air Biofiltration: A Technique for
Treating Secondary Air Emissions From Vapor-extract!on and Air-stripping Systems." In
Hydrocarbon Bioremediation, by R.E. Hinchee, B.C. Alleman, R.E. Hoeppel, and R.N. Miller,
1-11. Boca Raton, FL: Lewis Publishers, 1994.
52 An Analysis of Composting as an Environmental Remediation Technology
-------
Segall, L. "Biosolids Composting Facility Opts for In-vessel System." BioCycle 36 (1995):
39-43.
Standefer, S. and C. van Lith. "Biofilters Minimize VOC Emissions." Environmental Protection
(March 1993): 48-58.
Stewart, W. Compost Stormwater Filter Engineering System. Environmental Excellence
Award and Innovator of the Year Award. Association of Washington State Business, 1994.
Toffey, W.E. "Biofiltration—Black Box or Biofilm?" BioCycle 38 (June 1997): 58-63.
Tschui, M., M. Boiler, W. Gujer, J. Eugster, C. Mader, and C. Stengel. Water Science and
Technology 29(10-11) (1994): 53-60.
van der Hoek, K.W. and J. Oosthoek. "Composting: Odour Emission and Odour Control by
Biofiltration." In Composting of Agricultural and Other Wastes, edited by J.K.R. Gasser, 271-
281. London: Elsevier Applied Science Publishers, 1985.
Watwood, M.E. and S. Sukesan. "Biodegradation of Trichloroethylene in Finished Compost
Materials." Compost Science and Utilization 3 (1995): 6-19.
Wilber, C. and C. Murray. "Odor Source Evaluation." BioCycle (March 1990): 68-72.
Williams, T.O. and F.C. Miller. "Composting Facility Odor Control Using Biofilters." In Science
and Engineering of Composting, edited by H.A. Hoitink and H.M. Keener, 262-281.
Worthington, OH: Renaissance Publications, 1993.
Zeisig, H.D. "Experiences With the Use of Biofilters to Remove Odours From Piggeries and
Hen Houses." In Volatile Emissions From Livestock Farming and Sewage Operations, edited
by V.C. Nielsen, J.H. Voorburg, and P. L'Hermite, 209-216. London: Elsevier Applied Science,
1988.
An Analysis of Composting as an Environmental Remediation Technology 53
-------
Chapter 4
Potential for Reclamation of Mine Spoils and Brownfields With Compost
Mineral extraction operations and industrial activities can leave a substantial legacy of
environmental problems in their wake. EPA estimates there are approximately 300,000
abandoned mine sites in the United States. In addition to being unattractive, these sites can
present a significant environmental hazard from the leaching of acid and toxic metals into
groundwater, as well as erosional transport of hazardous constituents and spoil materials into
surface waters. Natural revegetation is often prevented in these areas because of low pH,
phytotoxic concentrations of metals, poor physical structure for plant growth, and slopes too
steep for plant establishment. Even if plants can be established, growth is often so poor that an
economically viable crop, such as hay or pasturage, cannot be generated (Fitzgerald, 1979).
There is no way, therefore, to recover rehabilitation expenses. Depending on the extent of
rehabilitation, costs to reclaim mine spoils can range from $1,000 to $5,000 per acre, values
which fall in the range of valuable farmland.
In older urban industrial areas, substantial land exists where industries failed and the
properties were abandoned. In some cases, these properties, or brownfields, could be
redeveloped or converted to parks if not for their extensive contamination and/or very poor soil
conditions. There are approximately 200,000 to 650,000 brownfields in the United States (Airst,
1996 and Carey, 1996). Using current cleanup technologies, the cost to remediate these sites
would far exceed the value of the properties (Carey, 1996). Since remediation expenses
exceed the value of the property, there is no economically feasible way to recover these costs.
In light of the expenses involved, both mine spoils and brownfields remain unrestored and
relatively worthless, in spite of EPA efforts to accelerate the reuse process (Slutzky, 1995 and
Cichon, 1997). This chapter describes some straightforward and relatively inexpensive
alternative options for remediating these sites using compost to improve soil conditions, reduce
erosion, enhance plant establishment, and immobilize toxic metals.
Mine spoils and brownfields share a number of problems, including:
54 An Analysis of Composting as an Environmental Remediation Technology
-------
• Soil compaction or poor physical structure. This results in poor or no plant development
and contributes to offsite contamination via soil that erodes from the barren site. Eroded
soil transfers contaminated material into surface water and onto adjacent property. The
transfer of pyrite-containing spoil from mine sites results in water acidification. If the
contaminated material is porous, the lack of plant cover results in a transfer of soluble
contaminants into groundwater sources. If plants are present, however, they intercept
some of the contaminants and thereby limit transfer to ground water. Thus, for a variety of
reasons, revegetation of these sites is a significant first step in limiting ongoing
environmental damage.
• The presence of pyrite. Pyrite minerals are very common associates of ore-bearing
minerals. When exposed to air and water, pyrite is converted to soluble iron and sulfuric
acid, resulting in soil acidification and acid drainage. Few, if any, plants will grow in acidified
soil. If plants can be established in this soil, they will compete for water with the
microorganisms that cause acidification and diminish acid formation.
Metals are an important component of industrial activity, but many of these metals are
highly toxic to humans, animals, and plants. The most common metals in this category are
lead, copper, zinc, cadmium, and mercury. Metal contamination of industrial sites and
abandoned mine spoils is common. Transfer of solid toxic metals by wind and water erosion
and by leaching of water-soluble metals is a serious threat to surface and ground waters.
A vast amount of literature exists that strongly indicates that waste organic materials can
alleviate all or many of the problems described above. Part of this literature was used as the
basis for the Clean Water Act Section 503 regulations governing the safe use of biosolids and
biosolids compost (Ryan, 1993). The value of organic materials in improving the structure and
water infiltration of compacted or sandy soils and in enhancing plant establishment is well
known among agriculturalists (Steffen, 1979; Sabrah, 1995; Rodale, 1945).
Biosolids (also known as municipal sewage sludge) were used to enhance plant growth on
mine spoils in the eastern United States (Figure 26) and on spent oil shale in the western
United States (Figure 27). Plants did not absorb the potentially toxic metals in the biosolids, nor
were the metals accumulated by pheasants or swine (Hinesly, 1979) that were fed grain grown
in sludge-amended soils. In addition, the metal content of wild birds who nested in biosolids-
An Analysis of Composting as an Environmental Remediation Technology 55
-------
treated mine spoils was not increased, with a few exceptions (Gaffney, 1979). The toxic metals
remain in a low-bioavailability form for at least 20 years after biosolids application (Chaney,
1994). Taken together, these results indicate that organic-rich materials, such as compost, are
likely to be a useful remediation aid to assist revegetation and to immobilize toxic metals in
mine spoils and brownfields.
When compared to the large amount of information available on the use of compost for
bioremediation of soils contaminated with organic compounds, very little literature is available
on soil reclamation using compost to enhance plant growth and to immobilize toxic metals in
soil. Because of similarities in composition between compost and the products formed by
degradation of waste materials in soil (Almendros, 1991), however, the existing literature
suggests compost may be a useful material for remediation activities. Compost has a number
of advantages over commonly used organic wastes:
• Compost is rich in humic materials, which have residence times in soil of decades to
centuries. Because of this long residence time, improvement in soil structure will be
relatively persistent. In contrast, raw wastes added to soil quickly lose their organic matter
and degrade within a few years. The beneficial effects, encountered soon after applying
raw wastes, quickly decrease. Failure of revegetation efforts is a common problem with raw
wastes, usually occurring 2 or 3 years after planting. Use of persistent organic matter, such
as compost, may be a solution to this problem.
• Improving the structure of compacted soil may require up to 20 percent by weight of organic
materials. If raw wastes are used, this high rate of application may provide excess
nutrients, such as nitrogen, that pose a pollution problem and promote anaerobic soil
conditions under which plants will not thrive. In contrast, nutrient release from composted
materials is quite slow (Tyson, 1993); therefore, high application rates can be used without
producing a nutrient excess. Spent mushroom substrate (a type of compost) has been
used for soil reclamation. An application rate of 175 tons per acre supplied adequate, but
not excessive, nutrient levels. When applied at 175 tons per acre, revegetation was
achieved on slopes averaging 25 percent (Rupert, 1995).
56 An Analysis of Composting as an Environmental Remediation Technology
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• Compost is more effective for revegetation of steep slopes than raw waste materials or
biosolids. Dried biosolids cannot be used to revegetate slopes greater than 12 percent,
because the material washes away (Kerr, 1979). In contrast, spent mushroom substrate
can successfully revegetate slopes up to 25 percent when it is incorporated into soil
(Rupert, 1995). In addition, slopes up to 42 percent have been successfully revegetated
with 3-inch-thick surface applications of yard trimmings compost (Ettlin, 1993). A mature
compost tends to be self-adhesive and forms a flexible, noneroding blanket when applied to
the soil surface. It also provides a good growth medium for plant establishment, because
the organic matter is stabilized and releases nutrients slowly. In contrast, most raw wastes
and uncomposted biosolids have a granular character making them erosion-prone. When
used at high application rates, raw wastes and biosolids can actually prevent, rather than
enhance, plant growth.
• Spent mushroom substrate has been used as a filter medium to treat acid mine drainage
(Stark, 1994). Under relatively low flow conditions, the pH of incoming mine drainage was
increased from 4.0 to 6.5 after passage through the filter. Soluble manganese and iron also
decreased. These results indicate that compost, when added to acidified soils, increases
pH into a range satisfactory for plant growth, reduces the content of water-soluble metal
ions, and maintains these improved conditions over time.
A 25-ton-per-acre application of MSW compost to surface mine spoils resulted in a
decrease in bulk density from 1.74 g/cm3 to 1.49 g/cm3 (Fenton, 1955). Since plant roots have
difficulty penetrating soil with bulk densities over 1.5 g/cm3 (Russell, 1973), the compost
addition brought bulk density into a satisfactory range for plant development. Hydraulic
conductivity was increased 42-fold with compost treatment, resulting in less runoff and more
water penetration into the soil. The combination of plant establishment and increased water
infiltration dramatically reduced soil erosion. Synthetic polymers are frequently used for erosion
suppression, but the benefits on soil properties are small when compared to compost. For
example, application of water-soluble formulations of polyacrylamide are effective at reducing
erosion but increase infiltration only slightly (Trout, 1995). Overall, polymers are less effective
than compost, because they do not improve conditions for plant root growth, even though they
help reduce erosion.
An Analysis of Composting as an Environmental Remediation Technology 57
-------
In one interesting experiment, biosolids and straw compost were applied to colliery spoils;
grass establishment did not occur unless compost was added, as shown in Figure 28 (Atkinson,
1992). In addition, the productivity of the grass was highly correlated with the amount of
compost added (Figure 29). In contrast, compost did not influence the growth of trees planted
in the same material. Composted biosolids were used to successfully revegetate surface-
mined land in the eastern United States (Griebel, 1979). The compost was very effective in
promoting plant growth (Figure 30) and increased soil pH from a pretreatment value of 2.9 to
5.0.
The results in Figure 30 are a striking example of the beneficial effects of compost on initial
plant establishment, but a recent project indicates that using compost for revegetation has
many benefits (Pinamonti, 1996). The results in Figure 31 indicate that compost has three
benefits when used for revegetation projects: (1) early plant establishment is greater when
compost is added, (2) at all time periods, the percentage of plant cover is higher with compost,
and (3) long-term persistence of the initial vegetation is enhanced in comparison to areas
without compost.
Accumulation of sodium in soils near oil wells is a common phenomenon. In order to prime
the wells, brine is often pumped into them and released. The sodium interacts with the soil and
increases bulk density. The high salinity prevents plant growth. If the sodium is not removed,
the soil remains barren. Application of MSW compost and gypsum (calcium sulfate) to saline-
and alkaline-contaminated soil in Israel increased oat yields from 180 kg/ha in untreated plots to
5,560 kg/ha in treated plots. Chloride content decreased from 11,080 kg Cl/ha in untreated
plots to 4,120 kg Cl/ha in treated plots. Depth of root penetration was greater in treated plots
as well (Avnimelech, 1992).
If soils are contaminated with toxic metals, the only available options for remediation are
removal of the soil and burial in a suitable landfill, chemical immobilization, or use of chemical
extractants to remove the metals from soil (Bolton, 1995 and Smith, 1995). All of these options
are expensive and impractical for the large volumes of material present at abandoned mine
sites. Several researchers have suggested investigating alternatives to remediation of large
metal-contaminated sites, such as immobilization—the conversion of the metal to a form of low
bioavailability by combining it with hydroxyapatite (Ma, 1994 and Xu, 1994)—or by reaction with
organic (humic) and inorganic components of compost (Schnitzer, 1977). Modest declines in
water-extractable cadmium, zinc, and nickel, but not copper, occur during the composting of
58 An Analysis of Composting as an Environmental Remediation Technology
-------
sewage sludge (Garcia, 1995). This decline is attributed to adsorption of the metals by the
humic materials in the compost. If compost of low metal contamination is mixed with metal-
contaminated soil, the same reaction is expected to occur, thereby reducing mobility of the
metal. A recent study examined the uptake of toxic metals using soil amended with 25 percent
by weight (equivalent to about 125 tons per acre) of biosolids compost containing 8 mg/kg
cadmium, 323 mg/kg copper, 56 mg/kg nickel, 151 mg/kg lead, 3.6 mg/kg selenium, 219 mg/kg
chromium, and 831 mg/kg zinc (Warman, 1995). Swiss chard, a metal-accumulating plant
species, was used. There were no increases in plant tissue content of zinc, cadmium, copper,
nickel, chromium, or lead when compared to plants grown in soil without compost. Tissue
levels of selenium, however, were elevated. The lack of metal uptake by the plants is a good
indication that compost strongly binds metals and prevents their uptake. The same results can
be expected if compost is added to metal-contaminated soil, thereby preventing transfer of
metals from soil into food chains. Based on the results of this and similar studies, use of
compost to decrease metal availability in contaminated soils might be a viable alternative to soil
removal or chemical extraction. At the present time, however, this treatment is not included at
most composting facilities as an acceptable method for metal remediation (Smith, 1995).
There is a growing interest in the idea that contamination standards should be risk-based,
rather than simply concentration-based (Chaney, 1994; National Research Council, 1994;
Hoddinott, 1992). In a risk-based appraisal, removal of toxic metals from soil may be
unnecessary, if the environmental mobility and bioavailability can be reduced sufficiently.
Application of the risk principle to mine sites and brownfields may be an excellent solution to
two very large-scale contamination problems. Because of the potential financial savings and
social and environmental values of remediating these sites, research to establish feasibility of
this concept should be strongly considered.
An Analysis of Composting as an Environmental Remediation Technology 59
-------
Figure 26
Plant Growth in Mine Spoils With or Without Biosolids Addition
3,000
2,500
2,000
1,500
1,000
500
Seeded grasses and legumes
1974 1975
Year
Biosolids application rate (dry tons/ha)
1976
o H40D75D150
Seeded species
and volunteer growth
1976
Biosolids application rate (dry tons/ha)
0 • 40 D 75 D 150
Source: Kerr, 1979
60 An Analysis of Composting as an Environmental Remediation Technology
-------
Figure 27
Biomass Production by Wheatgrass in Oil Shale With or Without
Organic Amendments
9145
8607
8069
7532
6993
6455
5917
5380
4842
4304
3766
3228
2690
2152
1614
1076
538
| | = no leaching
| | = leaching
NA = no amendments
F = fertilizer
S = sulfur
ST = straw
STS = straw + sulfur
SM = steer manure
SM S = steer manure + sulfur
88 = sewage sludge
SS S = sewage sludge + sulfur
WF = wood fiber
WFS = wood fiber + sulfur
BP = sugar beet pulp
BP S = sugar beet pulp + sulfur
-
•
-
•
-
-
•
-
3=E =d
NA | F S
—
S
—
—
ST
ST
S
SM
—
SMS
SS
SS S
r
__
:Lm_:
WF WF S BP BP S
Fertilizer
Treatments
Note the especially large beneficial effect of sewage sludge (SS treatments).
Source: Williams, 1979
An Analysis of Composting as an Environmental Remediation Technology
61
-------
Figure 28
Biomass Production by Tall Fescue and Birdsfoot Trefoil in Acid Strip Mine Spoil
as Affected by Addition of Biosolids Compost
500
400
1,300
.*
Q
HI
^
200
100
H H vwt/Un
ii i MI/I id
= ±1 s.e. of mean DOLOMITIC
%
X
V
"
V
X
x
N
>
'
S,
s
11 mt/ha LIMESTONE
ROC
>
S
;KPH
V >
V
X
OSPHATE
x
,
S*t
\.
X
x
^
^
X
^
CONTROL 56 112 224 56 112 224 56 112 224
mt/ha mt/ha mt/ha
COMPOST COMPOST COMPOST
kg/ha=kilograms per hectare
mt/ha=metric tons per hectare
Source: Griebel, 1979
62
An Analysis of Composting as an Environmental Remediation Technology
-------
Figure 29
Effect of Compost Addition Rate on Grass Production in Colliery Spoil Material
120
100
I
p
*
-------
Figure 30
Plant Establishment With or Without Compost Addition
_^^
,-,,^-^^f,, - - .7. m:~M^^^^^s *^:fj$^?$fa^Tk ^'^'''-'--•'•'^
- ^V" ""¥;:"^^<----fc^ ."V ": " "- .^s-- •
;
•-•
M. "I.- • • ' ';
". """,." " V-'
. '-',"» I,,, i.,f-'
••• • . •""'
Revegetation occurred only in plots to which compost was added.
Source: Atkinson, 1992
64 An Analysis of Composting as an Environmental Remediation Technology
-------
Figure 31
Enhanced Revegetation of Ski Tracks by Addition of 125 Tons of
Compost Per Hectare
100
k.
> 80
o
1 60
Q.
^ 40
20
+ compost (all plants)
+ compost (grasses)
-*«-«-^ri-Ar-
"""""* —
***"•*» *fc
~~"
1990
Control (all plants)
,(' — ••>••••*•••_• /™\_
- -^-p-»-Ty_j/. . . ..... ^-m^^-^-m-mf^fVjj.™^..^..-..^.~. _.„..
Control (grasses)
1991
1992
1993
Year
>4n Analysis of Composting as an Environmental Remediation Technology 65
-------
References
Airst, R.L. "Turning Brownfields to Greenbacks." Environmental Protection (November 1996):
28-29, 35.
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An Analysis of Composting as an Environmental Remediation Technology 67
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Sabrah, R.E.A., H.M.A. Magid, S.I. Abdel-Aal, and R.K. Rabie. "Optimizing Physical Properties
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68 An Analysis of Composting as an Environmental Remediation Technology
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Chapter 5
Suppression of Plant Diseases and Pests by Compost
Plants are susceptible to damage or death as a result of attack on their seeds, stems,
leaves, and root systems from a wide range of disease-causing microorganisms, insects, and
nematodes (microscopic worms). Farmers and horticulturists suffer billions of dollars in losses
as a result of this damage. For the past 40 to 50 years, synthetic pesticides have been used to
control these problems. The use of many of these common pesticides—particularly soil
fumigants that are effective controls for fungi and nematodes—has been prohibited or severely
restricted during the past 20 years (Quarles, 1995). Increasingly stringent standards designed
to protect agricultural workers from pesticide exposure also have been developed. These
restrictions on pesticide use have sparked substantial interest in using natural biological
processes to control pests and pathogens.
Biological control is the use of one biological species to reduce populations of a different
species. Successful and commercialized examples include ladybugs to depress aphid
populations, parasitic wasps to reduce moth populations, use of the bacterium Bacillus
thuringenensisto kill mosquito and moth larvae, and introduction of fungi, such as Trichoderma,
to suppress fungal-caused plant diseases. In all of these cases, the idea is not to completely
destroy the pathogen or pest, but rather to reduce the damage below economically significant
values. The development and commercialization of specific biocontrol agents is a lengthy and
expensive process. Many biocontrol products are legally classified as pesticides and are
subject to the same regulatory requirements as synthetic pesticides (Segall, 1995). New
product registration is often costly and time-consuming (Deacon, 1993). There also has been a
fair amount of concern about the unexpected negative impacts of releasing biocontrol agents
outside their natural range (Howarth, 1991; Longworth, 1987; Pimentel, 1980). These issues
have generated interest in finding naturally occurring materials, with pest-controlling properties,
that do not require formal registration. In conjunction with the use of these products, major
changes in overall crop production and soil management systems also might be necessary
(Hoy, 1992).
Among the available candidates for natural products with pest and disease control potential,
the composting process and compost have been relatively widely studied. It is well established
An Analysis of Composting as an Environmental Remediation Technology 69
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that the thermophilic conditions and intense microbial competition during composting kill or
inactivate nearly all the microorganisms that cause plant, animal, or human disease (Farrell,
1993; Bollen, 1996; Avgelis, 1992). One exception to this is the Tobacco Mosaic Virus, which
may survive composting (Hoitink, 1976a). After disease-infested crop residues are composted,
the material is no longer infectious and can be safely applied to farm fields without contributing
to disease problems. In contrast, uncomposted residues can serve as an inoculum for infection
of subsequent crops. The composting process has proven effective at destroying plant
pathogenic nematodes, bacteria, viruses, and fungi (Bollen, 1996; Lopez-Real, 1985; Bollen,
1985).
Mature compost, in many cases, also contains natural organic chemicals and beneficial
microorganisms that kill or suppress disease-causing microorganisms. Several mechanisms of
action for this phenomenon have been proposed (Hoitink, 1986a; Hoitink, 1986b; Hoitink,
1991a; Hoitink, 1993), including interspecific competition for nutrients, production of chemicals
with antimicrobial activity, production of enzymes that destroy the cell walls of pathogens, and
changes in the environmental conditions of the soil, which inhibit pathogen growth.
Among the various compostable materials, wood bark has been the most widely studied as
a growth medium for potted plants and for its disease-suppressive properties. The original
intentions for using wood bark were to find a beneficial use for this abundant and inexpensive
waste material and to reduce the consumption of peat, a relatively expensive and nonrenewable
natural product. Since some barks contain phytotoxic compounds (Self, 1978), composting
became a routine practice for reducing phytotoxicity. Early observations indicated that the
composted bark also reduced disease severity in potted plants (Gerrettson-Cornell, 1976;
Hoitink, 1975; Hoitink, 1976aand 1976b; Hoitink, 1977; Hoitink, 1980; Malek, 1975). Today,
the use of composted bark as a fungicide is widely accepted (Hoitink, 1993). This allows
growers to reduce their reliance on chemical fungicides (Daft, 1979) and to decrease operating
costs and worker hazards associated with chemical fungicide applications.
Figures 32 and 33 show the effectiveness of composted bark potting mixes on decreasing
the severity of root rot in greenhouse-grown poinsettias. Figure 34 illustrates the superior ability
of two composts to suppress plant damage in potting media inoculated with high levels of the
root pathogen Fusarium oxysporum. In both situations, the composted materials provided
much better disease reduction results than did peat.
70 An Analysis of Composting as an Environmental Remediation Technology
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Disease suppression following compost application also has been demonstrated under field
conditions. Compost has been shown to increase the stand density of alfalfa in fields where
yields have been declining, presumably because of increased disease pressure (Logsdon,
1993). Compost also can significantly decrease the severity of gummy stem blight and
damping off diseases in squash, as well as suppress rootknot nematodes and Rhizoctonia root
rot (Logsdon, 1993). Some composts have been found to suppress dollar spot disease in
putting greens as shown in Figure 35 (Nelson, 1991). There are several remarkable features
regarding this discovery, including:
• Large differences in the effectiveness of different composts. One municipal sewage sludge
compost was moderately effective, while another was completely ineffective.
• Large variations in suppressiveness at different sampling times during the same year,
especially when compared to fungicide treatments.
• Very large between-year performance of some composts, but not others. The varied
effectiveness of the composts is similar to behavior of other biocontrol products (Deacon,
1993).
One of the most critical limitations to increased use of biocontrol products, with a few
exceptions, is the inability of these products to control diseases with the same consistency as
synthetic chemicals. The lack of consistent performance is probably the result of complex
interactions between environmental conditions that modify plant susceptibility to a pathogen
and/or change the relative infective potential of the pathogen (Burdon, 1992; Dickman, 1992;
Couch, 1960). The suppressive activity of a biocontrol agent also will vary under different
environmental conditions (Baker, 1982; Mandelbaum, 1990). Plants that are stressed by lack of
moisture and/or elevated temperatures, or whose root systems have been damaged by
nematode or insect attack, are more vulnerable to disease. In general, fungal activity is
regulated by substrate and nutrient availability, water content of the medium, oxygen and
carbon dioxide levels, and the presence of other organisms that compete for materials required
by the fungus. Depending upon which combination of these conditions is present at a given
time, disease incidence can vary greatly, as shown in Figure 35. Conditions were so favorable
An Analysis of Composting as an Environmental Remediation Technology 71
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to pathogen development for the October 18, 1990, sample date, for example, that even
chemical treatment was only partially effective. In such conditions, the ability of a single
biocontrol agent to consistently suppress diseases is limited. A possible solution to this
problem may come from the use of antagonistic fungi and actinomycetes from composted pine
bark and sand mixtures (Hardy, 1995). About 80 percent of these fungi and actinomycetes are
disease-suppressive when inoculated into sterilized compost. Compost containing a mixture of
suppressive organisms also is expected to contain pathogen growth under a wide range of
conditions, as shown in the hypothetical case illustrated in Figure 36. In this case, consistent
suppression of the pathogen by either Trichoderma, Bacillus, or a mixture of the two cannot
occur, because the activity range of the pathogen falls outside the range of either organism or a
combination of them. In contrast, at least one member of the much more diverse group of
antagonists found in compost will be active under any of the conditions where the pathogen is
active. Thus, a likely consequence of increased antagonist diversity is improved biocontrol
under the wide-ranging conditions encountered in the field.
Some composts also can modify bacterial populations in the plant rhizosphere (the root-soil
interface) and increase the abundance of bacteria that are antagonists of various root-
pathogenic fungi, as shown in Figure 37. In laboratory situations, however, fungi isolated from
compost suppressed spore germination in the highly beneficial mycorrhizal fungus Glomus
mosseae (Calvet, 1992). Some composts contain microorganisms that suppress pathogenic
fungi in soil and on the plant root system, whereas other composts may actually have
deleterious effects on root microorganisms.
In addition to controlling fungal pathogens, compost also can modify the severity of
nematode damage (Roy, 1976). One study examined the effects of MSW compost on
populations of rootknot nematode and plant growth in pot and field studies (Marull, 1997). In
pot studies, the addition of 33 percent by weight of compost significantly increased plant growth
and significantly decreased nematode populations in the mixes. Sixty-six percent compost,
however, did not stimulate plant growth or decrease nematode populations any better than the
33 percent treatment. The lack of growth stimulation at 66 percent compost was probably the
result of inhibition of plant growth at high rates of compost addition (see lannotti, 1994, for
example). The effects of municipal waste compost on nematode populations are detailed in
Table 8.
72 An Analysis of Composting as an Environmental Remediation Technology
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Table 8
Effects of MSW Compost on Populations of the Root-Parasitic Nematode Meloidogyne
Javanica and on the Incidence of Root Galls in a Field Study
Treatment
Control
+ compost
Nematode Numbers
per 250 cm3Soil
Non-
fumigated
4380
1410a
Fumigated
7460
1100a
Nematodes per
g Root
Non-
fumigated
17,000
8,010a
Fumigated
13,450
7,760a
Root Gall Severity
Non-
fumigated
90
80
Fumigated
91
73
a Indicates a significant decrease as a result of compost application.
Source: Marull, 1997 (Table 6)
Compost's ability to suppress soil-borne pathogens is well documented; however, a few
reports indicate compost extracts (or "teas") also have disease-reducing properties against
foliar pathogens. Extracts of spent mushroom substrate, cattle manure, and sheep manure
compost proved ineffective at controlling apple scab in orchards (Yohalem, 1994). Results with
control of red pine seedling blight were more encouraging, with extracts of spent mushroom
substrate from three different sources providing significant reductions in disease severity
(Figure 38). There are often substantial differences in the effectiveness of extracts from
different sources (Nelson, 1991). At the present time, producing compost extracts is not a well-
developed technology. Individuals devise various procedures for preparing the extracts, with
substantial differences in the procedures among different workers. Many variables exist in the
production of such materials, including the type and age of compost used and the incubation
and extraction procedures employed. While these extracts may have pathogen-suppressing
activity in some cases, it is not clear if that activity is due to chemicals in the extracts or to the
microorganisms whose growth is favored during extract preparation. This topic is likely to be a
fruitful area for future research.
The specific mechanisms for disease suppression by compost have not been clearly
identified. Understanding of the mechanisms behind compost's suppression of pathogens is
complicated by the fact that raw plant materials, which are composted, might contain organic
compounds with antipathogen properties (Qasem, 1995). In some cases, these organic
An Analysis of Composting as an Environmental Remediation Technology
73
-------
compounds are destroyed by the time compost is mature. It is not always certain, however,
that the composts used for disease suppression studies are mature. A further complication is
the ability of some uncomposted waste materials to affect populations of plant pathogenic fungi
and pests, such as nematodes (Bridge, 1996), and for some composts to have no greater
disease-suppressive properties than the raw materials from which they are made (Figure 39)
(Asirifi, 1994). If an immature compost is used, some of its pathogen-suppressive activity may
be due to the raw input components rather than compost constituents. As a result, the
mechanism of pathogen suppression may vary in compost from lot to lot, in some cases as the
result of chemical control and in other cases of biocontrol. Based on some of the references
cited in Chapter 1, the relative abundance of different microbial species varies with compost
age and composition of input; therefore, biotic composition of different composts is probably
also a variable feature among the work of different researchers. Some composts also contain
VOCs with pathogen-suppressive activity (Tavoularis, 1995).
The use of compost for disease suppression involves a remarkably complicated set of
interactions among various microorganisms, chemical constituents of composted materials, and
plant tissues. It is evident that, in certain situations and with particular specialized growth
media, such as container mixes that include bark, compost is an effective substitute for
synthetic chemicals in the control of pathogens. Since there is a very reduced availability of
synthetic fungicides and a decreased willingness to use them, further research on compost-
based disease control is highly desirable. Several studies indicate that compost is an excellent
source of disease-suppressive bacteria and fungi, and, therefore, it is likely to be a fruitful
source of biological materials for biotechnological applications. Since chemicals in compost
also can affect pathogens, compost may be a useful source of natural products with biocontrol
activity.
74 An Analysis of Composting as an Environmental Remediation Technology
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Figure 32
Root Systems of Poinsettia Plants
Plants were grown in mixes containing peat without disease-suppressive properties (top row),
disease-suppressive peat (middle row), or disease-suppressive composted pine bark (bottom
row). Light-colored roots are healthy, while dark-colored roots are diseased.
Source: Hoitink, 1991a and 1991b
An Analysis of Composting as an Environmental Remediation Technology 75
-------
Figure 33
Severity of Root Rot of Poinsettia Plants
4
O
o
co
o 3
DC
"o
o
DC «
O
A
-• Dark Peat
-O Light
-A
0
10
20 30 40 50 §0
Time (Days) of Plant Growth
70
80
Plants were grown in mixes containing peat without disease-suppressive properties, disease-
suppressive peat, or disease-suppressive composted bark. Root rot severity ranges from *\ to
5, with 5 being the most severe.
Source: Boehm, 1992
76
An Analysis of Composting as an Environmental Remediation Technology
-------
Figure 34
Disease Severity (Percentage of Wilted Carnation Plants) When Grown in Mixes
Containing Peat and Sand (Peat), Composted Bark and Sand (CPB), or Composted Olive
Pumice* and Sand (COP)
103
*-5
13
CP
in
*****
c
CO
Q.
tyu
80
80
40
20
A
oPeat
-
f
/
~^L
100
80
60
40
20
1 3 5
Time
100
so
eo
40
20
*Olive pumice is the waste generated during the processing of olives for oil.
Source: Pera, 1989
An Analysis of Composting as an Environmental Remediation Technology 77
-------
Figure 35
Relative Disease-Suppressing Ability of Composts and Fertilizers Against the Turfgrass
Disease Dollar Spot
120
Compost SourceTLC MMC BC
Date of disease assessment I I 5/25/89
ESC Fungicide OF-CP OF-GR
6/26/89 \~\ 9/4/90 \~\ 10/18/90
Abbreviations: TLC=turkey litter compost, MMC=manure compost, BC=brewery waste compost,
ESC=Endicott sludge compost, fungicide=propiconazole, OF-CP=an organic (not composted)
fertilizer, and OF-GR=another organic (not composted) fertilizer.
Source: Nelson, 1991 (Table 3)
78
An Analysis of Composting as an Environmental Remediation Technology
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Figure 36
A Hypothetical Case to Illustrate the Value of a Diverse Disease-Suppressive Population
in Comparison to Single Antagonists or a Mixture of Two Antagonists
Activity range of pathogen
Trichoderma
h
compost isolate 3
i i
compc
1 1 ' 1
S
— I
Bacillus
i
i
cor
i_
r
compost
i
>st isolate 8
i
1 ' 1
MUUVILy Id! lye Ul cU lldyUI llbl
compost isolate 1
i i -—
compost isolate 2
i i
npost isolate 4
i
compost isolate 5
i i
compost isolate 6
1 i
isolate 7
1 1 1
B C D E F
Environmental Conditions
H
An "environmental condition" is a particular combination of moisture content, substrate and
nutrient availability, and oxygen and carbon dioxide content that favors or reduces activity of an
organism.
Source: Cole, unpublished
An Analysis of Composting as an Environmental Remediation Technology
79
-------
Figure 37
Incidence of Bacteria With Suppressive Activity Toward Fungal Pathogens on Plant Root
Systems Growing in Soil or Compost
o
100
80
60
(0
_c
o
1 40
0)
I
o
-52 20
0
Source of
antagonists
4-» 4-» 4-» 4-*
(O W W (0
o o o o
0.0.0.0.
= EEEE
Pathogen Fusarium
Pythium
Verticillium Phytophthora Rhizoctonia
Source: Alvarez, 1995 (Table 4)
80
An Analysis of Composting as an Environmental Remediation Technology
-------
Figure 38
Influence of Extracts of Spent Mushroom Substrate (PMC, HVMF, and GDM) and a
Compost Prepared From Cranberry Waste and Duck Manure on Disease Severity of Red
Pine Blight
CC
CD
if)
CD
CD
CD
C/)
CD
-E 3
Q_
o
CD
c/3
CT3
CD
<*«
?^C
eP*
Source: Yohalem, 1994 (Figure 5)
An Analysis of Composting as an Environmental Remediation Technology
81
-------
Figure 39
Effects of MSW Compost on Green Pepper Growth and Populations of the Root-Parasitic
Nematode Meloidogyne Javanica in a Pot Study
O
o
33% compost
D 6G% compoat
Shoot wt. (g) Root wt. (g) Nematodes/g soil
Source: Marull, 1997 (Table 2)
82
An Analysis of Composting as an Environmental Remediation Technology
-------
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Gerrettson-Cornell, L, F.R. Humphreys, and S.R. Townsend. "Results of a Preliminary
Investigation on the Use of Pinus radiata Bark Against Phytophthora cinnamomi Rands."
Phyton 34(1976): 3-6.
Hardy, G.E. and K. Sivasithamparam. "Antagonism to Fungi and Actinomycetes Isolated From
Composted Eucalyptus Bark to Phytophthora Drechsleri in a Steamed and Non-steamed
Composted Eucalyptus Bark-amended Container Medium." So/7 Biology and Biochemistry
27 (1995): 243-246.
Hoitink, H.A.J. "Composted Bark, A Lightweight Growth Medium With Fungicidal Properties."
Plant Disease 64(1980): 142-147.
Hoitink, H.A.J., M.J. Boehm, and Y. Hadar. "Mechanisms of Suppression of Soilborne Plant
Pathogens in Compost-amended Substrates." In Science and Engineering of Composting,
edited by H.A.J. Hoitink and H.M. Keener, 601-621. Worthington, OH: Renaissance
Publications, 1993.
Hoitink, H.A.J. and P.C. Fahy. "Basis for the Control of Soilborne Plant Pathogens With
Composts." Annual Review of Phytopathology 24 (1986): 93-114.
Hoitink, H.A.J., L.J. Herr, and A.F. Schmitthenner. "Survival of Some Plant Pathogens During
Composting of Hardwood Tree Bark." Phytopathology 66 (1976b): 1369-1372.
Hoitink, H.A.J., Y. Inbar, and M.J. Boehm. "Status of Compost-amended Potting Mixes
Naturally Suppressive to Soilborne Diseases of Floricultural Crops." Plant Disease 75 (1991a):
869-873.
Hoitink, H.A.J., Y. Inbar, and M.J. Boehm. "Compost Can Suppress Soil-borne Diseases in
Container Media." American Nurseryman 178 (September 1991b): 91-94.
Hoitink, H.A.J. and G.A. Kuter. "Effects of Composts in Growth Media on Soilborne Plant
Pathogens." In The Role of Organic Matter in Modern Agriculture, edited by Y. Chen and Y.
Avnimelech, 289-306. Dordrecht, Netherlands: Martinus Nyhoff Publishers, 1986.
Hoitink, H.A.J. and H.A. Poole. "Composted Bark Mediums for Control of Soil-borne Plant
Pathogens." American Nurseryman 144(5) (1976a): 15, 88-89.
Hoitink, H.A.J., A.F. Schmitthenner, and L.J. Herr. "Composted Bark for Control of Root Rot in
Ornamentals." Ohio Reporter 60 (1975): 25-26.
84 An Analysis of Composting as an Environmental Remediation Technology
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Hoitink, H.A.J., D.M. VanDoren, Jr., and A.F. Schmitthenner. "Suppression of Phytophthora
cinnamomi in a Composted Hardwood Bark Potting Medium." Phytopathology 67 (1977):
561-565.
Howarth, F.G. "Environmental Impacts of Classical Biological Control." Annual Review of
Entomology 36 (1991): 485-509.
Hoy, M.A. "Biological Control of Arthropods: Genetic Engineering and Environmental Risks."
Biological Control 2 (1992): 166-170.
lannotti, D.A., M.E. Grebus, B.L. Toth, LV. Madden, and H.A.J. Hoitink. "Oxygen
Respirometry to Assess Stability and Maturity of Composted Municipal Solid Waste." Journal of
Environmental Quality 23(1994): 1177-1183.
Logsdon, G. "Using Compost for Plant Disease Control." BioCycle 34(10) (1993): 33-36.
Longworth, J.F. "Biological Control in New Zealand: Policy and Procedures." New Zealand
Entomologist 10(1987): 1-7.
Lopez-Real, J. and M. Foster. "Plant Pathogen Survival During the Composting of Agricultural
Organic Wastes." In Composting of Agricultural and Other Wastes, by J.K.R. Gasser, 291-300.
London: Elsevier Applied Science Publishers, 1985.
Malek, R.B. and J.B. Gartner. "Hardwood Bark as a Soil Amendment for Suppression of Plant
Parasitic Nematodes on Container Grown Plants." HortScience 10 (1975): 33-35.
Mandelbaum, R. and Y. Hadar. "Effects of Available Carbon Source on Microbial Activity and
Suppression of Pythium aphanidermatum in Compost and Peat Container Media."
Phytopathology 80 (1990): 794-804.
Marull, J., J. Pinochet, and R. Rodriquez-Kabana. "Agricultural and Municipal Composts
Residues for Control of Root-knot Nematodes in Tomato and Pepper." Compost Science and
Utilization 5(1) (1997): 6-15.
Nelson, E.B. and C.M. Craft. "Suppression of Dollar Spot on Creeping Bentgrass and Annual
Bluegrass Turf With Compost-amended Topdressings." Plant Disease 76 (1991): 954-958.
Pimentel, D. "Environmental Risks Associated With Biological Controls." Ecological Bulletin
31 (1980): 11-24.
Qasem, J.R. and H.A. Abu-Blan. "Antifungal Activity of Aqueous Extracts From Some
Common Weed Species." Annals of Applied Biology. 127 (1995): 215-219.
Quarles, W. and J. Grossman. "Alternatives to Methyl Bromide in Nurseries - Disease
Suppressive Media." The IPM Practicioner 17(8) (1995): 1-13.
An Analysis of Composting as an Environmental Remediation Technology 85
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Roy, A.K. "Effect of Decaffeinated Tea Waste and Water Hyacinth Compost on the Control of
Meloidogyne graminicola on Rice." Indian Journal of Nematology 6 (1976): 73-77.
Segall, L. "Marketing Compost as a Pest Control Product." BioCycle 36 (1995): 65-67.
Self, R.L. "Pine Bark in Potting Mixes, Grades and Age, Disease and Fertility Problems."
Proceedings of The International Plant Propogators' Society 28 (1978): 363-368.
Tavoularis, K., A. Papadaki, and V. Manios. "Effect of Volatile Substances Released From
Olive Tree Leave Compost on the Vegetative Growth of Rhizoctonia solani and Fusarium
oxysporum F. sp. lycopersici." Acta Horticulturae 382 (1995): 183-186.
Yohalem, D.S., R.F. Harris, and J.H. Andrews. "Aqueous Extracts of Spent Mushroom
Substrate for Foliar Disease Control." Compost Science and Utilization 2(4) (1994): 67-74.
86 An Analysis of Composting as an Environmental Remediation Technology
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Chapter 6
Compost-Enhanced Phytoremediation of Contaminated Soil
Phytoremediation is a developing technology in which higher plants and microorganisms
associated with plant roots are the active agents for uptake and/or degradation of toxic
inorganic and organic compounds in soil and water. This method successfully intercepts nitrate
and prevents its transfer from groundwater to surface water. It also is used in a number of
applications with organics-contaminated water (Table 9). As indicated in Chapter 4, plants also
reduce the erosional transport of contaminated soil when compared to unvegetated material.
Given this, phytoremediation provides a straightforward approach to both the degradation and
containment of contaminated soil and water, as shown in Figure 40. In this case, contaminated
water is stripped of contaminants as it flows past the plant roots, as a result of waste uptake by
the plants. Depending on the contaminant, degradation might occur in the rhizosphere (the soil
adjacent to plant roots) or within the plant itself. If the compound is not degraded, it will likely
volatilize. Regardless of the ultimate fate of the contaminant, once contact with the plant
occurs, the water is no longer contaminated. This process might be suitable for soil
remediation and/or inexpensive confinement of shallow contaminated water.
Phytoremediation of metal-contaminated soil relies on the ability of plants to accumulate
metals at concentrations substantially above those found in the soil in which they grow (Kelly,
1995; Brown, 1994; Brown, 1995; Cunningham, 1995; Cornish, 1995). Since plant uptake
requires that metals be in an environmentally mobile form (Schnoor, 1995), the use of compost
is likely to be an impediment to successful phytoremediation, as compost immobilizes toxic
metals (see Chapter 4 for examples).
An Analysis of Composting as an Environmental Remediation Technology 87
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Table 9
Phytoremediation of Contaminated Soil or Water3
Contaminated Material
Water (hydroponic system in
laboratory)
Soil
Soil
Contaminated soil
Soil
Contaminants
Nitrobenzene
Trinitrotoluene
Trichloroethylene
Pentachlorophenol and
phenanthrene
Trinitrotoluene
Results
Complete uptake from
solution
Essentially complete
treatment
Enhanced mineralization
Enhanced mineralization
Enhanced degradation
a Adapted from Schnoor, 1995.
Numerous reports indicate that plants can take up and degrade toxic organic compounds in
soil, while other work indicates microorganisms in the rhizosphere are very competent degraders
of soil-borne organics. Rhizosphere microorganisms are able to degrade the herbicide 2,4-
dichlorophenoxyacetic acid (2,4-D) much more rapidly than those in root-free soil and convert a
higher percentage of carbon in 2,4-D to carbon dioxide, as shown in Figure 41 (Shann, 1994). In
contrast, enhanced mineralization of 14C-labeled pyrene was not found in rhizosphere soil
(Schwab, 1994 and Schwab, 1995). These apparently conflicting results are due to the relatively
high mobility of 2,4-D in soil as compared to pyrene. As a result of rapid water uptake by plants,
desorption of contaminants from soil may be the rate-limiting step for degradation (Schnoor,
1995). Based on the examples shown in Table 9, plants might decrease remediation time, as well
as enhance the complete destruction of target compounds. Further work is required to define the
characteristics of plants and soil systems before an understanding of the appropriateness of
phytoremediation for particular situations can be attained.
Phytoremediation has very large economic advantages over mechanically intensive
technologies because plants require little maintenance in comparison to machinery. The
following are the major constraints of the method:
88
An Analysis of Composting as an Environmental Remediation Technology
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• Relatively slow remediation rates. The time until site closure can be years. This constraint
means that phytoremediation cannot be the method of choice when rapid site closure is a
necessity.
• Lack of information about the fate of compounds in planted soil. Losses of volatile 14C from
14C-labeled naphthalene are about 50 percent higher in planted soil than in unplanted soil
(Watkins, 1994). Poor recovery is probably the result of inefficient capture of volatile
organics and/or carbon dioxide and can be solved by the development of better test
systems. Chapter 2 details the issue of whether partial degradation of xenobiotics, followed
by conversion of metabolites into immobile forms, is a sufficient remedy for contamination.
This same issue arises with phytoremediation, because immobilization of carbon from
xenobiotics in conjugated forms is promoted in planted systems. The results, presented in
Figure 42, indicate that studies of the fate of xenobiotic residues when they enter soil would
be appropriate. Because of the complexity of plants, microorganisms, and soil systems and
the uncertainties of chemical behavior in these systems, further research is necessary
before this method can be employed on a large scale.
• Difficulties in establishing plants in toxic, contaminated matrices, and in compacted and
barren materials that are not conducive to plant growth. This constraint can be overcome
by the addition of compost. A small body of research indicates that compost can reduce
toxicity of contaminated soil (probably through the adsorption of the toxic compounds to
organic matter in the compost). Figure 43 compares the growth of herbicide-sensitive weed
species when grown in contaminated material from an agrichemical retail site. In the
absence of compost, little weed growth occurs, but addition of compost detoxifies the soil
and good weed growth occurs. In this case, plant growth also accelerated decontamination
when compared with soil without compost addition, as shown in Table 10.
The amount of compost needed to achieve beneficial effects varies with the project goals. For
example, 20 percent w/w compost is sufficient to maximize plant growth in herbicide-contaminated
soil (Figure 44), but 40 percent compost is needed to accelerate herbicide degradation in the same
soil (Figure 45). The decrease in remediation time for relatively degradable compounds like
metolachlor strongly suggests that phytoremediation—if healthy and vigorous plants can be
An Analysis of Composting as an Environmental Remediation Technology 89
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established—has considerable potential for enhancing bioremediation activities, particularly in
situations such as urban brownfields (Chapter 4), where cost and time are important components in
choosing a remediation method.
Table 10
Effects of Mix Composition and Planting on Pesticide Degradation,
Following 40 Days of Plant Growth3
Mixture Treatment
Initial
concentration
100%
contamination
100%
contamination
50:50 soil
50:50 soil
50:50 compost
50:50 compost
None
Planted
Not planted
Planted
Not planted
Planted
Not planted
Trifluralin Metolachlor Pendimethalin
mg kg"1 soil
2.2 + 0.9
0.80 + 0.82
(0.27)(b)
0.48 + 0.77
(0.77)
nd(c)
0.52 + 0.53
(0.07)
0.36 + 0.33
(0.02)
0.44 + 0.69
(0.08)
3.0 + 0.2
3.4 + 5.0
(0.25)
0.99+ 1.4
(0.25)
nd
0.18 + 0.16
(<0.001)
nd
2.8 + 3.4
(0.29)
11.8 + 5.1
1.6 + 0.4
(0.02)
1.8 + 0.4
(0.02)
0.5 + 0.6
(0.01)
1.0 + 0.2
(0.02)
1.5 + 0.6
(0.02)
2.6 + 3.4
(0.12)
a Values are means + standard deviations of duplicate extractions
b Values in parentheses indicate the probability that the values are
alone (based on a one-tailed t-test for means of unequal variance).
c nd = not detected.
of four replications per treatment.
less than experiences from dilution
Source: Liu, 1995
90
An Analysis of Composting as an Environmental Remediation Technology
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Figure 40
Potential Fates of Xenobiotics in Planted Soils
Volatilization
00
CO,
U plake by Pla n«s or
Degradation in
Rhizosphene
Subaurlace WalerFlaw
00 00 00
An Analysis of Composting as an Environmental Remediation Technology 91
-------
Figure 41
Enhanced Degradation Rates and Mineralization Percentage in Rhizosphere Versus
Non-rhizosphere Soil
CO
N
CD
C
cv
s_
o
Q
4
CM"
100
75
2,4,5-T 2,4-D
Monocot
Dicot
Non-rhizosphere
40
TIME (days)
60
Source: Shann, 1994
92
An Analysis of Composting as an Environmental Remediation Technology
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Figure 42
Influence of Plants on Immobilization of 14C From Aromatic Compounds in Soil
2 10
Soil
Naphthalene
Not I
Source: Walton, 1994 (Table 1)
An Analysis of Composting as an Environmental Remediation Technology
93
-------
Figure 43
Reduction of Phytotoxicity in Herbicide-Contaminated Soil by Compost
25
20
oi 15
Q.
"CD
10
c 5
| soil mixes
| | compost mixes
1,5 6 12.5 25 50
% contaminated soil
100
Source: Cole, 1994
94 An Analysis of Composting as an Environmental Remediation Technology
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Figure 44
Effect of Amount of Compost Added on Plant Growth in Contaminated Soil
20
40 60
% compost (w/w)
80
100
Source: Liu, 1996
An Analysis of Composting as an Environmental Remediation Technology
95
-------
Figure 45
Effect of Amount of Compost Added on Rates of Pesticide Degradation in
Contaminated Soil
o
C
1
|
-3
A=Degradation of trifluralin
B=Degradation of metolachlor
5 10
% compost (w/w)
5 10
% oomposl (w/w)
20 40
20
40
Source: Liu, 1996
96
An Analysis of Composting as an Environmental Remediation Technology
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References
Brown, S.L., R.L. Chaney, J.S. Angle, and A.J.M. Baker. "Phytoremediation Potential of
Thlaspi caerulescens and Bladder Campion for Zinc- and Cadmium-contaminated Soil."
Journal of Environmental Quality 23(1994): 1151-1157.
Brown, S.L., R.L. Chaney, J.S. Angle, and A.J.M. Baker. "Zinc and Cadmium Uptake by
Hyperaccumulator Thlaspi caerulescens and Metal Tolerant Silene vulgaris Grown on Sludge-
amended Soils." Environmental Science and Technology 29 (1995): 1581-1585.
Cornish, J.E., W.C. Goldberg, R.S. Levine, and J.R. Benemann. "Phytoremediation of Soils
Contaminated With Toxic Elements and Radionuclides." In Bioremediation of Inorganics, edited
by R.E. Hinchee, J.L Means, and D.R. Burris, 55-63. Columbus, OH: Battalle Press, 1995.
Cunningham, S.D., W.R. Berti, and J.W. Haung. "Remediation of Contaminated Soil and
Sludges by Green Plants." In Bioremediation of Inorganics, edited by R.E. Hinchee, J.L.
Means, and D.R. Burris, 33-54. Columbus, OH: Battalle Press, 1995.
Kelly, R.J. and T.F. Guerin. "Feasibility of Using Hyperaccumulating Plants to Bioremediate
Metal-contaminated Soil." In Bioremediation of Inorganics, edited by R.E. Hinchee, J.L.
Means, and D.R. Burris, 25-32. Columbus, OH: Battalle Press, 1995.
Liu, X. and M.A. Cole. "Minimum Effective Compost Addition for Remediation of Pesticide
Contaminated Soil." In The Science of Composting, edited by M. de Bertoldi, P. Sequi, B.
Lemmes, and T. Papi, 903-912. London: Blackie Academic and Professional, 1996.
Schnoor, J.L., LA. Licht, S.C. MiCutcheon, N.L Wolf, and LH. Camera. "Phytoremediation of
Organic and Nutrient Contaminants." Environmental Science and Technology 29 (1995):
318A-323A.
Schwab, A.P. and M.K. Banks. "Biologically Mediated Dissipation of Polyaromatic
Hydrocarbons in the Root Zone." In Bioremediation Through Rhizosphere Technology, edited
by T.A. Anderson and J.R. Coats, 132-141. Washington, DC: American Chemical Society,
1994.
Schwab, A.P., M.K. Banks, and M. Arunachalam. "Biodegradation of Polycyclic Aromatic
Hydrocarbons in Rhizosphere Soil." In Bioremediation of Recalcitrant Organics, edited by R.E.
Hinchee, D.B. Anderson, and R.E. Hoeppel, 23-29. Columbus, OH: Battelle Press, 1995.
Walton, B.T., A.M. Hoylman, M.M. Perez, T.A. Anderson, T.R. Johnson, E.A. Guthrie, and R.F.
Christman. "Rhizosphere Microbial Communities as a Plant Defense Against Toxic
Substances in Soil." In Bioremediation Through Rhizosphere Technology, edited by T.A.
Anderson and J.R. Coats, 82-92. Washington, DC: American Chemical Society, 1994.
An Analysis of Composting as an Environmental Remediation Technology 97
-------
Watkins, J.W., D.L. Sorensen, and R.C. Sims. "Volatilization and Mineralization of
Naphthalene in Soil-grass Microcosms." In Bioremediation Through Rhizosphere Technology,
edited by T.A. Anderson and J.R. Coats, 123-131. Washington, DC: American Chemical
Society, 1994.
98 An Analysis of Composting as an Environmental Remediation Technology
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Chapter 7
Development of Special-Purpose (Customized) Composts
The majority of the research described in this report was conducted with little discrimination
among composts, other than their ready availability. Where different types or ages of compost
were compared, substantial differences were found in the ability of the compost to accelerate
degradation of organic compounds (Chapter 2) and in disease-suppressive ability (Chapter 5).
Compost maturity is certainly a factor in revegetation studies, since numerous researchers have
reported that immature composts are phytotoxic. The relatively high success rate for various
projects, in spite of the apparently random selection of compost, strongly suggests that
particular activities of compost can be enhanced, thereby increasing the effectiveness of the
compost. Composts of this type are referred to as "tailor-made" or "designer" composts. The
term "special-purpose compost" is used in this chapter to describe composts that are specially
treated during production to enhance specific attributes, produced from particular feedstocks to
increase activity, to which specific microorganisms have been added, and to which constituents
other than organic feedstocks have been added.
In addition to relatively random selection of compost for their research, most researchers
conducted their studies with unamended compost. Substantial literature indicates minerals play
a major role in controlling the environmental fate and availability of both organic and inorganic
components (Hassett, 1989; Ziekle, 1989; Scow, 1993; Dixon, 1977). Little of this work,
however, has been applied to improving compost. This chapter describes several cases where
the performance of compost was significantly enhanced by special treatment.
The special treatment of feedstock has the potential to improve compost's metal removal
capabilities (Chang, 1995). A recent study conducted with sewage sludge serves as a
precedent for potential improvement of metal-binding activity of biosolids compost. In the
study, various additions were made to a sewage sludge culture. Copper-binding—but not
cadmium-binding—activity varied substantially among the initial cultures (Figure 46). In
addition, particular treatments significantly increased the absorption capacity of the cultures for
particular metals. It is likely that the same type of process could be used to develop biosolids
compost for the types of applications described in Chapter 4.
An Analysis of Composting as an Environmental Remediation Technology 99
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The metal-binding capacity of composts can be improved by the addition of inorganic
materials. For example, the addition of soluble iron and/or phosphate salts to compost
increases lead immobilization as a result of forming complex lead-iron-phosphate minerals.
Similarly, research by several investigators indicates that some clay minerals interact with lead
to form lead-containing minerals in which the bioavailability of the lead is remarkably low (Ryan,
no date). Addition of such clays may enhance the ability of compost to decrease lead
availability. This suggestion raises the issue of whether immobilization of metals is a sufficient
endpoint for remediation (see Chapter 4). Nevertheless, decreased lead availability provides an
illustration of the potential for improving the desirable characteristics of compost.
One promising technique in bioremediation is the establishment of desirable
microorganisms in soil by adding them as an inoculant (Brown, 1993). This process is referred
to as "bioaugmentation." One of the common problems with bioaugmentation is the difficulty in
establishing exogenous microorganisms in the contaminated soil (Alexander, 1994; Van Veen,
1997). The addition of microorganisms in compost often results in a 2- to 15-fold increase in
bacterial and fungal populations for at least 6 weeks after adding the compost to contaminated
soil (Cole, 1996). It appears from these results that the compost protects organisms from
predation and other problems that ordinarily result in their loss when added to soil. If this
statement is true, then production of composts containing particularly good degraders of
pollutants could be a viable approach to microbial introductions into soil.
Disease-suppressive organisms isolated from compost can be added to compost at high
populations (Hoitink, 1990). The resulting compost has better disease-suppressing activity than
uninoculated compost (Hoitink, 1993). In addition, compost with more consistent disease
suppression can be produced by isolating antagonistic organisms from compost, propagating
them in the laboratory, and adding them back to raw materials prior to composting (Nakasaki,
1996). Both of these examples support the suggestion that compost used for bioremediation
can be improved in the same manner.
Several studies in Chapter 3 demonstrate that compost biofilter performance improves
substantially after an extended exposure time to contaminated air. This behavior is strongly
suggestive of selection for a highly competent population of degrading organisms in the
compost. The poor performance of the filters initially might be attributed to the lack of
appropriate organisms in sufficient numbers in the starting material. If this interpretation is
100 An Analysis of Composting as an Environmental Remediation Technology
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correct, then isolation of appropriate microorganisms from effective biofilters and introduction
into ineffective biofilters may be a rapid method for improving filter performance.
Several references in Chapter 1 demonstrate that microbial populations are large and that
their biodiversity is high during the composting process and in mature compost. Since the
environmental conditions during composting are radically different from those experienced by
organisms in most natural environments, it is possible that compost-derived organisms might
have abilities not found in the microbial populations of soil and water. For this reason, further
studies on microbial ecology of compost are likely to have beneficial effects, not only for the
composting industry but also for uses of compost-based materials.
An Analysis of Composting as an Environmental Remediation Technology 101
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Figure 46
Enhancement of Metal-Binding Capacity of Sewage Sludge Cultures by Nutrient Amendment
and Prior Exposure to Subtoxic Concentrations of Copper and Cadmium
10 20
Time, hours
30
Effect of culture acclimation and stimulation of copper uptake efficiencies.
10 20 30
Time, hours
Effect of culture acclimation and stimulation of cadmium uptake efficiencies.
There is substantial diversity among organisms in terms of their ability to accumulate metals.
Given the diversity of organisms in different composts and the wide range of composition
among composts produced from different raw materials (see Chapter 1), it is likely that
substantial variations in metal-binding ability will be found among different composted materials.
Source: Chang, 1995
102 An Analysis of Composting as an Environmental Remediation Technology
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References
Alexander, M. Biodegradation and Bioremediation, 226-247. San Diego: Academic Press,
1994.
Brown, R.A., W. Mahaffey, and R.D. Morris. "In Situ Bioremediation: The State of the
Practice." In In Situ Bioremediation: When Does It Work?, 121-135. Washington, DC:
National Academy Press, 1993.
Chang, D., K. Fukushi, and S. Ghosh. "Stimulation of Activated Sludge Cultures for Enhanced
Heavy Metal Removal." Water Environment Research 67 (1995): 822-827.
Cole, M.A., X. Liu, and L. Zhang. "Plant and Microbial Establishment in Pesticide-
Contaminated Soils Amended With Compost." In Bioremediation Through Rhizosphere
Technology, edited by T.A. Anderson and J.R. Coats, 210-222. Washington, DC: American
Chemical Society, 1994.
Dixon, J.B. and S.B. Weed. Minerals in Soil Environments. Madison, Wl: Soil Science
Society of America, Inc., 1977.
Hassett, J.J. and W.L. Banwart. "The Sorption of Nonpolar Organics by Soils and Sediments."
In Reactions and Movement of Organic Chemicals in Soils, edited by B.L. Sawhney and K.
Brown, 31-44. Madison, Wl: Soil Science Society of America, Inc., 1989.
Hoitink, H.A.J. "Production of Disease Suppressive Compost and Container Media, and
Microorganism Culture for Use Therein." U.S. Patent 4,960,348. February 13, 1990.
Hoitink, H.A.J., M.J. Boehm, and Y. Hadar. "Mechanisms of Suppression of Soilborne Plant
Pathogens in Compost-amended Substrates." In Science and Engineering of Composting,
edited by H.A.J. Hoitink and H.M. Keener, 601-621. Worthington, OH: Renaissance
Publications, 1993.
Nakasaki, K., M. Kubo, and H. Kubota. "Production of Functional Compost Which Can
Suppress Phytopathogenic Fungi of Lawn Grass by Inoculating Bacillus subtilis Into Grass
Clippings." In The Science of Composting, edited by M. de Bertoldi, P. Bert, and P. Tiziano, 87-
95. London: Blackie Academic and Professional, 1996.
Ryan, J.A. and P. Zhang. "Soil Lead Remediation: Is Removal the Only Option?" Unpublished
manuscript distributed on the Internet. No date.
Scow, K.M. "Effect of Sorption-desorption and Diffusion Processes on the Kinetics of
Biodegradation of Organic Chemicals in Soil." In Sorption and Degradation of Pesticides and
Organic Chemicals in Soil, 73-114. Madison, Wl: Soil Science Society of America, Inc., 1993.
van Veen, J.A., L.S. van Overbeek, and J.D. van Elsas. "Fate and Activity of Microorganisms
Introduced Into Soil." Microbiology and Molecular Biology Reviews 61 (1997): 121-135.
An Analysis of Composting as an Environmental Remediation Technology 103
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Ziekle, R.C., T.J. Pinnavaia, and M.M. Mortland. "Absorption and Reactions of Selected
Organic Molecules on Clay Mineral Surfaces." In Reactions and Movement of Organic
Chemicals in Soils, edited by B.L. Sawhney and K. Brown. Madison, Wl: Soil Science Society
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104 An Analysis of Composting as an Environmental Remediation Technology
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Chapter 8
Bibliography
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