United States 600R043O1
Environmental Protection WWWI%\/T«JV ^
Agency
Monitoring Approaches for
Landfill Bioreactors
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EPA/600/R-04/301
December 2004
Monitoring Approaches for
Landfill Bioreactors
by
Thabet Tolaymat, Ph.D.
Fran Kremer, Ph.D.
David Carson
Wendy Davis-Hoover, Ph.D.
National Risk Management Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
/T~y Recycled/Recyclable
Printed with vegetable-based ink on
paper that contains a minimum of
50% post-consumer fiber content
processed chlorine free.
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Notice
Technical information used in the creation of this document resulted, in part, from a Cooperative
Research and Development Agreement (CRADA) between the U.S. Environmental Protection Agency
through its Office of Research and Development (ORD) and Waste Management, Inc. Biosites
program. Both parties agreed to jointly examine this operational technique for the benefit of the waste
management community to better protect human health and the environment. It has been subject to the
ORD's internal review process and has been approved for publication as an EPA document.
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Foreword
The U.S. Environmental Protection Agency (EPA) is charged by Congress with protecting the
Nation's land, air, and water resources. Under a mandate of national environmental laws, the Agency
strives to formulate and implement actions leading to a compatible balance between human activities
and the ability of natural systems to support and nurture life. To meet this mandate, EPA's research
program is providing data and technical support for solving environmental problems today and
building a science knowledge base necessary to manage our ecological resources wisely, understand
how pollutants affect our health, and prevent or reduce environmental risks in the future.
The National Risk Management Research Laboratory (NRMRL) is the Agency's center for
investigation of technological and management approaches for preventing and reducing risks from
pollution that threaten human health and the environment. The focus of the Laboratory's research
program is on methods and their cost-effectiveness for prevention and control of pollution to air, land,
water, and subsurface resources; protection of water quality in public water systems; remediation of
contaminated sites, sediments and ground water; prevention and control of indoor air pollution; and
restoration of ecosystems. NRMRL collaborates with both public and private sector partners to foster
technologies that reduce the cost of compliance and to anticipate emerging problems. NRMRL's
research provides solutions to environmental problems by: developing and promoting technologies that
protect and improve the environment; advancing scientific and engineering information to support
regulatory and policy decisions; and providing the technical support and information transfer to ensure
implementation of environmental regulations and strategies at the national, state, and community
levels.
This publication has been produced as part of the Laboratory's strategic long-term research plan. It
is published and made available by EPA's Office of Research and Development to assist the user
community and to link researchers with their clients.
Sally Gutierrez, Acting Director
National Risk Management Research Laboratory
ill
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Abstract
Experimental bioreactor landfill operations at operating Municipal Solid Waste (MSW) landfills
can be approved under the research development and demonstration (RD&D) provisions of 40 CFR
258.4. To provide a basis for consistent data collection for future decision-making in support of the
newly promulgated RD&D requirements, this document outlines an approach for bioreactor landfill
monitoring. This document suggests technical guidance only, and is not intended to be used for
regulatory purposes. It should also be noted that this document should not take the place of site-
specific considerations, nor imply that alternative professional determinations on monitoring and
analysis methods are not appropriate. The ongoing research and experience on bioreactor landfill
projects have provided the basis for this document; however, advances in monitoring and analysis
methods may be identified that warrant future updates to this document.
IV
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Table of Content
Notice •_!!
Foreword U1
Abstract iv
List of Tables vj
List of Figures v|j
Acknowledgment vni
1.0 Introduction and Rational 1
2.0 Document Organization 2
3.0 Anaerobic Decomposition Fundamentals 3
3.1 Phase I and II (Initial Adjustment and Transition) 3
3.2 Phase III (Acid Formation) 3
3.3 Phase IV (Methane Fermentation) 3
3.4 Phase V (Final Maturation) 4
4.0 Key Monitoring Parameters for Bioreactor MSW Landfills 5
4.1 Physical Monitoring Parameters 5
4.1.1 Geotechnical Considerations '. 6
4.1.2 Head on Liner and Leachate Management 6
4.1.3 Mass Balance 7
4.1.4 Moisture Balance 7
4.2 Analytical Monitoring Parameters 7
4.2.1 Leachate Monitoring 7
4.2.2 Solids Monitoring Parameters 9
4.2.3 Gas Monitoring Parameters 10
5.0 Interim Industrial Liquids/Sludge Addition Issues 11
S.lpH 11
5.2 Organic Compounds Content 11
5.3 Metals 11
6.0 Suggested Sampling Techniques 12
6.1 Leachate Sampling 12
6.2 Solid Waste Sampling 12
6.2.1 Waste Sampling for New Cells 12
6.2.2 In-place Waste Sampling 12
6.3 Gas Sampling 13
References 22
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List of Tables
Table 1 Mass Loading Calculation Parameters 5
Table 2 Bioreactor Liquid Addition Monitoring Parameters 5
Table 3 Primary Bioreactor Landfill Leachate Monitoring Parameters 5
Table 4 Secondary Bioreactor Landfill Leachate Monitoring Parameters 6
Table 5 Bioreactor Landfill Solids Monitoring Parameters 6
Table 6 Primary Bioreactor Landfill Gas Monitoring Parameters 6
VI
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List of Figures
Figure 1 Phases of Anaerobic Decomposition in MSW Landfills adopted from (Pohland and
Kim 1999)
.3
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Acknowledgment
The authors would like to thank Dr. Timothy Townsend (University of Florida) for his time and
valuable input. The authors would also like to thank the following reviewers: Mr. Gary Hater and
Roger Green (Waste Management Inc.), Mr. Greg Vogt (SCS Engineering), Mr. David Hansen and
other members of the Solid Waste Association of North America (SWANA) bioreactor committee,
Bob Phaneuf and other members of Association of State and Territorial Solid Waste Management
Officials (ASTSWMO), as well as Dr. K.C. Hustvedt, US EPA Office of Air and Radiation (OAR).
Vlll
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l.U Introduction and Rational
The U. S. Environmental Protection Agency (US EPA) has conducted field research on the use of landfill bioreactors as a
means for managing the nation's solid wastes. This technology has the potential to enhance the rate of degradation of solid wastes
and landfill gas energy recovery, and to reduce possible long-term liabilities associated with conventional landfills. Based on
research conducted to date, this document identifies key parameters, monitoring frequencies, and testing methods that the Agency
believes will be important in the management of landfill bioreactors. The purpose of this document is to assist those responsible
for regulatory oversight and the site owner/operators in monitoring bioreactor landfills.
Although the routine use of full-scale bioreactor landfill operations may be limited under current Resource Conservation and
Recovery Act (RCRA) Subtitle D regulations, experimental and demonstration bioreactor landfill operations at operating
municipal solid waste (MSW) landfills can be approved under the Research Development and Demonstration (RD&D) provisions
of 40 CFR 258.4. In association with these provisions, the Agency seeks to have such demonstration operations develop
consistent data collection procedures and monitoring so as to support future decision-making under the newly promulgated
RD&D requirements. To this end, this document does not make recommendations regarding specific kinds of bioreactor operation
techniques rather it outlines recommended approaches (that is, with respect to monitoring parameters, sampling frequencies, and
sampling procedures) for bioreactor landfill monitoring. The ongoing research and experience on bioreactor landfill projects have
provided the basis for this document; however, advances in monitoring and analysis methods may be identified that warrant future
updates to this document.
This document suggests technical guidance only, and is not intended to be used for regulatory purposes. It should also be
noted that this document should not take the place of site-specific technical arid regulatory considerations, or alternative
professional determinations on monitoring and analysis methods that may be appropriate. Finally, it is the responsibility of the
owner/operator of a landfill to comply with all existing local, state and federal regulations with regard to controlled operations of
the landfill.
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2.0 Document Organization
This document outlines key parameters for monitoring landfill bioreactors. Approaches are recommended with regard to
sampling parameters to be considered, sampling and analytical frequencies, and appropriate standard test methods. A list of
bioreactor landfill references has been developed for the reader.
Parameter lists are presented in two categories: physical and analytical. The analytical parameters are divided based on the
matrix of interest (liquid, solid, gas). Approaches are provided for those parameters considered vital for understanding bioreactor
landfills, including recommendations for those parameters that are relatively inexpensive and simple to measure while
maintaining operational control.
Due to the heterogeneous nature of municipal solid waste, variability in waste streams, between landfills and differences in
environmental and climate conditions, the use of control cells is encouraged. For research and demonstration purposes the control
cells should be comparable in age, depth, and composition of waste, and should be monitored separately to demonstrate impacts
of bioreactor landfill operations on volumes and quality of leachate and landfill gas generated, changes in the waste mass, and
effects on the leachate collection system. Note that, while it is believed that the use of control cells associated with bioreactor
landfill proposals would be beneficial and improve upon the data base being established, it is understood that the use of control
cells may not be feasible in all cases.
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3.0 Anaerobic Decomposition Fundamentals
A MSW landfill does not have a single waste age, but rather different ages associated with the various cells within the landfill
and their respective stabilization stages (Pohland et al. 1993). As a result, the different landfill stabilization phases often overlap.
These phases are usually viewed collectively which tends to limit understanding of their progression. Operating a MSW landfill
as a bioreactor has an effect only on the rates and not the sequence of the degradation phases (Kim and Pohland 2003; Pohland
and Al-Yousfi 1994; Reinhart and Townsend 1998). It is important for those responsible for landfill management to understand
each of these events. A brief discussion of the stabilization phases (presented graphically in Figure 1) is presented below. A
detailed discussion of landfill stabilization phases has been presented elsewhere (Pohland et al. 1993; Pohland 1975).
3.1 Phase I and II (Initial Adjustment and Transition)
After the initial placement of the waste, a short-lived transition from an oxic to an anoxic microbial stabilization processes,
takes place. During that phase, the primary electron acceptors become nitrates and sulfates, rather than oxygen, with the
displacement of oxygen by carbon dioxide in the effluent gas additionally, intermediates such as volatile organic fatty acids
(VFAs) first appear in the leachate.
3.2 Phase III (Acid Formation)
With the hydrolysis of the biodegradable fraction of the solid waste (and other applied liquids), VFAs concentration in the
leachate increase, which results in a decrease in pH. The drop in pH may cause concomitant mobilization and the possible
complexation of metal species. During this stage, nutrients such as nitrogen and phosphorous are released from the waste.
3.3 Phase IV (Methane Fermentation)
Intermediary products appearing during the acid formation phase (mainly acetic acid) are converted to methane and carbon
dioxide. As a result of VFA consumption by methanogens, the pH drift to neutrality (approximately 7). Oxidation-reduction
potentials remain negative indicating a reduced environment. The leachate organic strength (characterized by low biochemical
oxygen demand) is dramatically decreased in correspondence with an increase in gas production.
pH
1.0
0.0
200 400
Stabilization Time, Days
600
-10
Figure 1: Phases of anaerobic decomposition in MSW landfills (adopted from Pohland and Kim 1999).
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3.4 Phase V (Final Maturation)
The final stage of solid waste decomposition is characterized by a lower rate of biological activity. During this stage landfill
methane production is almost negligible. Oxygen and oxidized species may slowly reappear with a corresponding increase in
oxidation-reduction potential. Residual organic materials may slowly be converted, with the possible production of humic-like
substances.
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4.0 Key Monitoring Parameters for Bioreactor MSW Landfills
The RD&D (FR 2004) rule allows for the controlled introduction of liquids into a MSW landfill to accelerate the
decomposition of biodegradable organics. As briefly discussed earlier, the anaerobic refuse degradation process requires at least
two different groups of microorganisms (acidogenic and methanogenic) (Parkin and Owen 1986; Pohland et al. 1993). These
microorganisms occur naturally in MSW but require different conditions to achieve optimal performance. There are key
parameters, if examined closely, that will collectively ensure the optimal operation of bioreactor landfills and minimize risk to
human health and the environment.
Tables 1 through 6 present suggested monitoring parameters for MSW bioreactor landfills which could enhance operational
control under RCRA subtitle D and the RD&D (FR 2004) rule. It should be noted that the ranges suggested in this document may
not apply to some landfills based on a variety of site-specific factors. It is the responsibility of the owner/operator of a landfill to
comply with all existing local, state and federal regulations with regard to controlled operations of the landfill.
Table 1. Mass Loading Calculation Parameters
Parameter
Visual Landfill Inspection
MassofLandfilledMSW
Mass of Landfilled Construction and Demolition Waste
Mass of Soil (other than daily cover)
Tvpe of Dailv Cover
Mass of Daily Cover
Landfill volume
Settlement
Frequency
Daily
Daily
Daily
Daily
Daily
Daily
Quarterly
Quarterly
Units
MG (tons)
MO (tons)
MG (tons)
MG (tons)
m3 (yd3)
m(ft)
Table 2. Bioreactor Liquid Addition Monitoring Parameters
Parameter
Volume of Leachate Added
Rainfall
Volume Outside Liquid Added (e.g., Groundwater, Industrial
Waste Water
Volume of Leachate Generated
Mass of Sludge Added
Wet Basis Moisture Content of Sludge Added
Frequency
Daily
Daily
Daily
Daily
Daily
Daily
Units
L (gal)
Mm (inch)
L (gal)
L (gal) of leachage generated by the bioreactor cells
onlv
Mass (tons)
Percent (M/M)
Table 3. Primary Bioreactor Landfill Leachate Monitoring Parameters
Parameter
Static head on Liner
Temperature
pH
Conductance (uSm/cm)
Total Dissolved Solids (mg/L)
Alkalinity (mg/L as CaCO3)
Chloride (mg/L)
Bromide (mg/L)
Floride (mg/L)
Sulfate (mg/L)
Chemical Oxygen Demand (mg/L)
Biochemical Oxygen Demand (mg/L)
Total Organic Carbon (mg/L)
Total Phosphorous (mg/L)
Ortho Phosphate (mg/L)
Ammonia (mg/L)
Nitrite (mg/L)
Nitrate (mg/L)
Method
Pressure Transducer. Bubble
Gages. Stand pipes.
Thermometer
EPA* 9045C
Field Electrode
SM* 160. (C)
SM*310.
SM* 300.
SM* 300.
SM* 300.
SM* 300.
SM* 410.4
SM* 405.1
EPA* 9060
SM* 365.2 (C)
SM* 365.2 (C)
SM1' 350.1 (C)
SM* 300.1
SM* 300.1
Frequency
£
Monthly
Monthly
Monthly
Monthly
Monthly
Monthly
Monthly
Monthly
Monthly
Monthly
Monthly
Monthly
Monthly
Monthly
Monthly
Monthly
Monthly
Optimum Range
< 30 cm (1ft)
30 - 38 °C
6.5-8.0
§
§
§
§
§
§
§
§
§
§
§
§
< 5,000 mg/L
§
§
Head on the liner should be monitored continuously, however, it is suggested that a weekly average is reported.
* EPA SW-846 Test Methods for Evaluating Solid Wastes
* EPA Methods for Chemical Analysis of Water and Wastes.
e. Landfill owner operator is responsible for following all existing local, state and federal regulations.
8. Data are currently unavailable. More research is needed.
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Parameter
Volatile Organic Compounds" (VOCs) (ng/L)
Semi-Volatile Organic Compounds (SVOCs)
Volatile Fatty Acids (mg/L)
Arsenic (mg/L)
Barium (mg/L)
Cadmium (mg/L)
Calcium (mg/L)
Copper (mg/L)
Chromium (mg/L)
Iron (mg/L)
Lead (mg/L)
Magnesium (mg/L)
Mercury (ug/L)
Potassium (mg/L)
Sodium
Selenium (mg/L)
Silver (mg/L)
Zinc (mg/L)
Method
SW-846 8260 (B)
SW-846 8270 (B)
GCMS
SW-846 6010(prepared per SW-846 3005)
SW-846 6010 (prepared per SW-846 3005)
SW-846 6010 (prepared per SW-846 3005)
SW-846 6010 (prepared per SW-846 3005)
SW-846 6010 (prepared per SW-846 3005)
SW-846 6010 (prepared per SW-846 3005)
SW-846 6010 (prepared per SW-846 3005)
SW-846 6010 (prepared per SW-846 3005)
SW-846 7470 (prepared per SW-846 3005)
SW-846 7470 (prepared per SW-846 3005)
SW-846 6010 (prepared per SW-846 3005)
SW-846 6010 (prepared per SW-846 3005)
SW-846 6010 (prepared per SW-846 3005)
SW-846 6010 (prepared per SW-846 3005)
SW-846 6010 (prepared per SW-846 3005)
Frequency
Quarterly
Quarterly
Quarterly
Quarterly
Quarterly
Quarterly
Quarterly
Quarterly
Quarterly
Quarterly
Quarterly
Quarterly
Quarterly
Quarterly
Quarterly
Quarterly
Quarterly
Quarterly
Table S. Bioreactor Landfill Solids Monitoring Parameters
Parameter
Average Temperature
Average pH
Average Volatile Solids (% M/M)
Average Wet Based Moisture Content (% M/M)
Method
Thermometer
EPA" 9045C
EPA" 1684
Frequency
Once every 18 months
Once every 18 months
Once every 18 months
Once every 18 months
Optimum Range6
35 - 55 °C
6.5-7.6
Decreasing Trend
< 35 %
*. (EPA, 2003) '
b. (Mehanta et al., 2002)
e. Landfill owner operator is responsible for following all existing local, state and federal regulations.
Table 6. Primary Bioreactor Landfill Gas Monitoring Parameters
Parameter
Total Gas
Carbon Dioxide
Oxygen
Methane
Carbon Monoxide
Flow
Orifice plate / Mass flow meter (scfm)
Portable gas analyzer (% V/V)
Portable gas analyzer (% V/V)
Portable gas analyzer (% V/V)
Portable gas analyzer (% V/V)
Frequency
At least once a week
Weekly
Weekly
Weekly
Weekly
Optimum Range*
35-40
<5
45-60
= 0
4.1 Physical Monitoring Parameters
4.1.1 Geotechnical Considerations
Landfill slope stability is an important parameter in MSW landfill design. Often landfill slope stability focuses on the
stability of the final landfill configuration. Operating landfills as bioreactors may add more strain on slope stability, not only of
the final configuration but also on the interim slopes. Pore pressure in bioreactor landfills may potentially increase because of the
addition of liquids and the concurrent increase in landfill gas (LFG) generation. As a result, it is important to conduct a detailed
geotechnical analysis of the slopes stability of each bioreactor landfill.
In conjunction with a slope stability study, operators could follow simple guidelines to promote bioreactor landfill slope
integrity. Operators should avoid toe excavation that, if left unbuttressed, could create high stress and may potentially cause a
slide. Operators should also avoid filling waste in cells at steep grades. On-site roads and cover soil may also lead to instability,
thus requiring care with design.
4.1.2 Head on Liner and Leachate Management
As required under CFR 258, leachate head on a landfill bottom liner is not to exceed 30 cm (1 ft). The addition of moisture
into the landfill will cause excess amounts of leachate to reach the bottom liner. Before the addition of moisture into a bioreactor
landfill, an engineer should ensure that the leachate collection system (LCS) design can handle the increase in leachate flow.
Performance of the LCS and removal systems relative to clogging also should also be examined.
Potential clogging of the LCS may lead to moisture buildup within the landfill causing the head on the liner to exceed 30 cm
and create potential leakage and instability issues. Alkalinity, hardness, iron, manganese compounds, total organic carbon,
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chemical and biological oxygen demand, are all involved in reactions which can result in buildup of clogging material in leachate
collection systems (Cooke et al. 2001; Fleming et al. 1999; Rittmann et al. 2003; Rowe et al. 2000). These parameters can
indicate how closely leachate concentrations are to saturation levels for calcium carbonate and other compounds that contribute to
clogs and poor LCS efficiencies. LCS clogging could be caused by settling out of suspended particles from the leachate,
biological growth, or chemical precipitation (Koerner and Koerner 1995).
4.1.3 Mass Balance
It is important for those responsible for the management of bioreactor landfills to keep records of the mass of the landfilled
solid waste in each bioreactor cell. Conducting surveys for volume on a regular basis can be helpful in estimating the density of
solid waste placed. As the solid waste decomposes the density of the landfill tends to increase. Parameters that may assist with
mass loading calculations are presented in Table 1. Visual inspection is also included in Table 1. Although visual inspection does
not assist with mass loading calculation, physical investigation of landfill surface may identify wet, soft areas that may be
precursors to sideweeps and fugitive gas escape zones. Both conditions may require prompt correction.
To minimize perched leachate zones within the landfill, efforts must be made to remove temporary roadways as well as daily
cover prior to waste placement. Thus, the use of tarps or foams as an alternate cover to soil is encouraged. If soil is used as daily
cover, soil type should also be noted (e.g., clay or sand) and it should be removed prior to the placement of fresh waste.
4.1.4 Moisture Balance
The main premise of operating a landfill as a bioreactor is the introduction of moisture into the landfill. Up to a point, the
decomposition and stabilization rate of biodegradable solid wastes increases with increasing moisture content of that waste.
Although research has shown the optimum moisture content for biological degradation to range between 30 and 70 percent
(Pohland et al. 1993; Reinhart and Townsend 1998), an increase in landfill moisture content tends to decrease the landfill's side
slopes stability (see section 4.1.1). Moisture plays an important role in side slopes stability landfill moisture content needs to be
examined regularly.
Assuming the volume of water consumed during waste hydrolysis and evaporation are negligible; moisture balance can be
calculated as presented in the following equation:
AS = Moisturein - Leachateout ,-^
Where "AS" is the net moisture storage, "Leachateout" is the leachate generated by the landfill and "Moisturein" is all liquids added
into the landfill including precipitation. Moisture addition could occur in many different forms including, but not limited to,
leachate, and municipal and industrial waste water addition. Parameters assisting in maintaining a water balance are presented in
Table 2. It is also important to take into account the moisture content of the incoming waste.
4.2 Analytical Monitoring Parameters
4.2.1 Leachate Monitoring
Suggested leachate monitoring parameters for MSW bioreactor landfills to enhance operational control under RCRA and the
RD&D (FR 2004) rule are divided into primary (Table 3) and secondary parameters (Table 4). The primary parameters are
relatively inexpensive and easy to examine. Parameters presented in the secondary list are more research-oriented, and are more
time intensive and as a result are relatively costly. Suggested analysis methods and monitoring frequencies are presented in the
tables. It is the responsibility of the owner/operator of a landfill to comply with all existing local, state and federal regulations
with regard to existing monitoring parameters in addition to parameters agreed upon under an RD&D project. A few monitoring
parameters are evaluated further in the following sections.
Sample duplication is necessary to account for the statistical relevance of monitoring data. Caution must also be taken to
hydraulically isolate bioreactor from adjacent conventional landfill cells. The separation would allow for an accurate evaluation of
conditions only within the bioreactor. Hydraulic separation may be achieved in an as-built cell; however, such a separation is
more difficult in retrofit bioreactor landfill cells. In the case of a retrofit bioreactor landfill, it is suggested that the zone of
influence of the liquid application area be examined (see Reinhart and Townsend, 1998 for more details). Leachate samples
representing the bioreactor section of the landfill should be collected only from areas directly under the zone of influence.
4.2.1.1 Leachate Temperature
Research suggests that anaerobic processes occur best within either mesophilic (30-38°C) or thermophilic (50 to 60°C)
temperature ranges (McCarty 1964; Parkin and Owen 1986). Optimum methane generation from solid wastes, however, occurred
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at 41°C (Harts et al. 1982). Regardless of the operational temperatures, the maintenance of a uniform temperature is considered to
be fundamental to anaerobic stabilization process efficiencies. Historically, conventional landfills leachate temperature ranged
from 7 to 25°C while bioreactor landfills leachate ranged from 6 to 37°C (EPA 2003).
Because landfill temperature is not externally controlled, it reflects a combination of ambient temperature conditions,
microbial activities and the extent and effectiveness of insulation provided by the landfill configuration. In cold climates, for
example, leachate temperatures could initially be as low as 6°C. Soon after recirculation the leachate temperatures should steadily
increase. Leachate temperatures at the Outer Loop landfill in Kentucky were initially around 7°C. The leachate temperatures at
the landfill steadily increased to above 30°C within a few months of the bioreactor operation (EPA 2003). While an increase in
leachate temperature is reflective of waste degradation in a landfill, it is not solely indicative of biological activity.
4.2.1.2 Leachate pH
The optimum pH range for anaerobic systems ranges between 6.5 and 7.6 (Parkin and Owen 1986). Gas generation and
stabilization rates have been reported to be the highest at near neutral pH levels (Pohland et al. 1993). Initially the leachate pH
may be neutral, however after the onset of anaerobic conditions there may be a pH drop especially during the acid forming phase
(see section 3.2). The pH drop is most likely caused by VFAs production and accumulation in the leachate. The pH, however, will
tend to move to neutrality as methanogens consume these acids. Historically there may not be a measured difference between the
leachate pH measured in conventional and in bioreactor landfills. The leachate pH ranged between 4.7-8.8 for conventional
landfills (EPA 2003; Kjeldsen et al. 2002; Chu et al. 1994; Krung and Ham 1991) and from 5.4-8.6 for bioreactor landfills (EPA
2003; Pohland and Harper 1986).
There may be a sudden drop in pH following a single injection event of highly degradable industrial waste water (as observed
at the Outer Loop landfill). The decrease in pH should last for approximately a week depending on the volume of liquid added.
Repetitive injection events can prolong the change in pH. It is important not to allow the pH to be suppressed for long periods of
time since low pH inhibits methanogens, reducing waste degradation (see section 5).
4.2.1.3 Volatile Fatty Acids (VFA)
An uncontrolled bioreactor landfill is characterized by acidic leachate (high volatile fatty acids content) and a low methane
production for a prolonged period. Bioreactor leachate becomes acidic as a result of the accumulation of VFAs (acetic, propionic
butyric hexanoic and valeric acids). For more detailed discussion of VFAs see (Barlaz et al. 1989- Kim and Pohland 2003-
Pohland et al. 1993).
4.2.1.4 Leachate Biochemical (BOD) and Chemical Oxygen Demand (COD)
BOD mainly consists of the biologically degradable dissolved organics in the landfill leachate. The ratio of BOD to COD can
potentially be used to assess the relative biodegradability of the leachate substrate. COD is a measure of chemically oxidizable
organics in leachate. Variations in these two parameters may be closely related to those observed with VFAs production and their
ratio can act as an indicator of the biodegradability of organics present in the MSW. BOD values reported in the literature for
conventional landfills ranged from 20 to 152,000 mg/L (EPA 2003; Pohland and Harper 1986a; Kjeldsen et al. 2002; Chu et al.
1994; Krung and Ham 1991). The reported BOD values for bioreactor landfills ranged from 20 to 28,000 mg/L (EPA 2003;
Reinhart and Townsend 1998; Miller et al. 1994; Pohland et al. 1993). COD values ranged from 500 to 60,000 mg/L for
conventional landfills (EPA 2003, Reinhart and Townsend 1998, Miller et al. 1994, Pohland et al. 1993).
Immediately after waste placement, the BOD and COD concentrations are relatively low. This may be caused by the initial
aerobic stabilization of the MSW or by a delay in the hydrolysis of the waste. During the acid formation phase, the majority of the
oxygen demand (both BOD and COD) is caused by the presence of high concentration of VFAs.
BOD and COD concentrations may decrease after the onset of the methane fermentation phase and the conversion of VFAs.
Relative to conventional landfills, bioreactor landfills may have a higher BOD/COD ratio during the acid forming phase (Reinhart
and Al-Yousfi 1996; Reinhart and Townsend 1998). However, research suggests this ratio may decrease during the methane
fermentation phase. After waste stabilization, both BOD and COD may be influenced by high molecular weight organics present
in the leachate (e.g. humic and fulvics) (Pohland et al. 1993). These residuals tend to elevate COD to a higher level than BOD and
possibly reduce the BOD/COD ratio. For instance, leachate BOD/COD ratios are usually higher than 0.5 for acid formation
phases of decomposition but may decline to less than 0.1 for heavily decomposed waste. It is noted that COD is also influenced
by the increase in ammonia concentration.
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4.2.1.5 Leachate Total Organic Carbon (TOC)
In general, like COD and BOD, after the initial placement of the waste TOC begins to appear as a result of microbial
solubilization of the organics. During the acid forming phase, TOC increases rapidly. An increase in TOC may also be observed
soon after the introduction of highly organic liquid waste. Because of the conversion of the VFAs to methane, TOC concentration
tends to decrease during the methane fermentation phase. TOC of conventional landfills ranges between 30 and 30,000 mg/L
(Chu et al. 1994; EPA 2003; Kjeldsen et al. 2002; Krung and Ham 1991; Pohland and Harper 1986).
4.2.1.6 Leachate Nitrogen Content
Nitrogen is present in MSW leachate mainly in the following forms: total Kjeldhal nitrogen (TKN), ammonia nitrogen, and
nitrate nitrogen. Ammonia is most important since at high concentrations (1,500 - 2,500 mg/L) it tends to inhibit methanogens
(Hansen et al. 1998; Hashimoto 1986), reducing waste degradation. Under anaerobic conditions ammonia tends to accumulate in
the leachate, especially with recirculation. Increasingly higher concentrations of ammonia in leachate may indicate potential for
adverse effects on the methanogenenic population, but it is also a sign of advanced stage of waste decomposition. High ammonia
concentrations may be used to decide when to stop recirculating leachate.
While conventional landfill leachate ammonia concentrations range from 2 to 2200 mg/L (EPA 2003; Pohland and Harper
1986a; Krung and Ham 1991), that of bioreactor landfills range from 6 to 20,000 mg/L (EPA 2003; Reinhart and Townsend 1998;
Miller et al. 1994; Pohland et al. 1993). Care must be taken so the accumulation of ammonia in the leachate does not adversely
affect the methanogenic population.
4.2.1.7 Metals
Metal concentration in the leachate is an important parameter to examine and can affect the cost of off-site leachate
treatment. The lower pH and higher organic content of the leachate during the initial landfill stabilization phases may mobilize
some metals during the acid forming phase (Pohland et al. 1993; van der Sloot and Woelders 2000). However, after the onset of
the methane fermentation phase, metal concentrations tend to decrease. The reduction in these concentrations is caused by a
combination of metal reduction, formation of metal sulfides, precipitation, and complexation with the waste matrix. The
introduction of large concentrations of heavy metals, through solid or liquids, may retard or inhibit solid waste degradation
process stabilization (Pohland and Harper 1986).
4.2.1.8 Semi-Volatile and Volatile Organic Compounds (SVOCs, VOCs)
Analysis of SVOCs and VOCs are of particular importance since there is a potential for the introduction of complex organic
constituents into bioreactor landfills with the application of various industrial wastes. Bioreactor landfills' ability for microbial
assimilation and transformation of organic, and potentially toxic, compounds has been documented (Kim and Pohland 2003). In-
situ reductive dehalogenation of organic compounds (e.g., TCE and HCB) has been demonstrated in bench-scale bioreactor
landfill studies (Kim and Pohland 2003). Monitoring of less attenuated organic compounds, as well as daughter products, in the
leachate is an essential part of operating a controlled bioreactor landfill.
Monitoring data are needed to assess which of the VOC and SVOC compounds are most likely to appear in leachate, in what
concentration ranges, over what time periods, and whether their behavior is different from their behavior in conventional landfills.
4.2.1.9 Phosphate
Phosphate may possibly be the rate controlling micronutrient in landfill environments. The addition of phosphates as a
beneficial micronutrient to laboratory-scale bioreactor landfill cells has been documented (Sheridan 2002). This practice,
however, has not been further examined in the field.
4.2.2 Solids Monitoring Parameters
Unlike leachate and gas, it may also be physically difficult and expensive to obtain samples of waste. Due to the difficulty in
sampling and the time it takes for decomposition to affect waste properties, this document recommends a lower sampling
frequency as presented in Table 4. Suggestions for drilling and sampling methods are discussed in a later section.
Temperature monitoring of the waste surface should be conducted much more frequently than temperature of the interior of
the waste mass. Temperature on the waste surface and at shallow depth may be monitored daily, as well as indications of smoke
and heat, carbon monoxide, and other signs of combustion and lack of moisture. Inspections and monitoring of these parameters
are needed to assure safety, prevent damage to the liner and collection system, and determine where additional water is needed to
moderate temperatures and moisture deficiencies.
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Note that, while it is believed that solids monitoring is scientifically beneficial and adds to the data base being established, it
is understood that solid sampling as suggested in this document may not be feasible.
4.2.2.1 Volatile Solids
As stated earlier, moisture addition stimulates biological activity in bioreactor landfills. This increase may directly translate
to an increase in the degradation of cellulose and hemicellulose and an increase in the settlement rate. A three-year study at Yolo
County landfill (California) demonstrated that the cellulose, hemicellulose and lignin content is strongly correlated to the volatile
solids (VS) content of MSW (Mehanta et al. 2002). It is recommended that bioreactor landfill operators/owners examine the
refuse content of cellulose, hemicellulose and lignin on a regular basis (once every 18 months). Such a practice may be cost
prohibitive, thus VS analysis may substitute as a potential degradability indicator. The main disadvantage of using VS is that,
unlike cellulose, hemicellulose and lignin, the analysis offers a lower level of accuracy and is affected by daily cover application!
Bioreactor operator/owner should expect MSW VS content to decrease as the refuse decomposes because of cellulose and
hemicellulose content loss from the waste.
4.2.2.2 Moisture Content
The moisture content of the decomposing solid waste should be examined to insure equal distribution of the liquids added to
the bioreactor landfill. The moisture content of the "fresh" incoming solid waste needs to be evaluated as well to establish
baseline measurements. Moisture content of the incoming waste plays a major role in the moisture balance calculations which
may be used in slope stability evaluation.
4.2.3 Gas Monitoring Parameters
During the solid waste biodegradation process, landfills generate measurable quantities of methane and carbon dioxide (both
are undesirable greenhouse gases). Controlling and monitoring the emissions of these gases is an essential element of any
controlled landfill operations. The rate of landfill gas production at bioreactor landfills is estimated to be between two (Reinhart
and Townsend 1998) and ten (Mehanta et al. 2002) times higher than that at conventional landfills. With that in mind, bioreactor
landfill gas collection systems need to be designed to handle larger flow rates than conventional landfills. It may also be necessary
to begin gas collection in bioreactor landfills earlier than the 180 days required under the National Emissions Standards for
Hazardous Air Pollutants (NESHAP) regulations (40 CFR part 63, subpart AAAA).
One of the regulatory concerns associated with bioreactor landfills has been concern for the potential for subsurface fires
from spontaneous combustion. Literature suggests that carbon monoxide is a useful indicator of subsurface fires. Monitoring
carbon dioxide is useful both in determining if carbon monoxide concentrations in bioreactor landfill gas are typical of what
would be seen in conventional landfill gas and as an indicator for subsurface fires (Sperling and Hendersons 1996).
As with conventional landfills, methane constitutes between 15 and 60% of bioreactor landfill gas. Carbon dioxide comprises
approximately 35-40 % of the gas while the oxygen content should be lower than 5%. Nitrogen comprises the balance of the
landfill gas.
It may be necessary to measure landfill gas emission at the flare and also fugitive gas emissions using a static flux chamber.
The Flux chamber test may be rather expensive, however, it will give important data regarding the flux (mg/m2/sec) through the
surface of the landfill. Methane, carbon dioxide, and none-methane organic compounds could be measured at the flare and surface
emissions may be measured using a flux chamber on the bioreactor landfill. EPA TO-14A compounds may also be examined. See
applicable NESHAP (40 CFR part 63, subpart AAAA) regulations regarding bioreactor landfills for more details.
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5.0 Interim Industrial Liquids/Sludge Addition Issues
The RD&D (FR 2004) rule gives landfill owners/operators latitude in the types of liquids (including industrial waste
water and sludges) to be introduced into bioreactor landfills. Ultimately, the owner/operator of a landfill has the final
responsibility to insure that the addition of industrial liquids or sludge does not inhibit the degradation process and is
compliant with existing state and federal regulations. Little is known about interactions between industrial waste liquids and
bioreactor landfill operations, so general liquids selection criteria are presented here based on the limited research experience
at the Outer Loop landfill in Kentucky and other sites. The following sections will outline general selection criteria for
industrial liquid/sludge addition to bioreactor landfills. Note, bioreactor landfill operations require the addition of aqueous
liquids, rather than oily or petroleum-based liquids. Liquids containing petroleum-based fuels should not be introduced into a
bioreactor landfill.
5.1 pH
The strength of the acid or base plays a large role in determining the compatibility of the liquid waste with the refuse in
the MSW landfill. Because pH is a sensitive parameter in the anaerobic decomposition process, liquid waste with an acidic
pH (pH <4.0) should not be introduced to a landfill unless the liquid can be neutralized prior to addition. Liquid waste with a
basic pH may be introduced, however, these liquids should be injected over a large area so that they are readily neutralized. It
is assumed that MSW landfills have the buffering capacity to better accommodate basic liquids (pH > 9). Field tests on a
waste specific basis are highly encouraged. Testing may be as simple as adding the liquid waste of interest to a small
controlled area of refuse and performing extractions and pH measurements over time. An example liquid waste stream is
beverage waste (e.g., soft drinks, etc). This particular liquid waste contains high concentrations of organic compounds with a
low pH. Finally, if there are liquid waste streams that may be constant in composition for longer periods of time (weeks or
months), then some laboratory testing could be done to measure the waste alkalinity or acidity to characterize its strength
(EPA 2003).
5.2 Organic Compounds Content
There are two potential issues with the addition of industrial waste containing high levels of organic compounds. The
first is the introduction of rapidly fermentable organic compounds and the second is the potential toxicity of some organic
compounds.
Liquids that contain rapidly fermentable compounds will likely be acidic or will result in a local accumulation of
carboxylic acids when added to refuse. As explained earlier, acidic conditions may have an adverse, in some cases inhibitory,
impact on refuse decomposition. If the application of liquids containing rapidly fermentable organic compounds is still
desired, the liquids should be applied at a low rate and only to refuse that is either in a methane fermentation state or to well
decomposed refuse. A good practice would also involve blending of new waste streams with recirculated leachate.
Although toxicity is chemical specific, the addition of high concentrations of organic pollutants has been shown to retard
refuse decomposition. The long-term effect of organic pollutants on refuse decomposition is still unclear, however. If organic
pollutants present in the waste are known, a simple literature search could determine whether that pollutant is toxic and/or
biodegradable in an anaerobic environment. If there is a liquid stream for which no data are available, laboratory toxicity test
may be required. A lab test on liquid being added to waste mass is advisable to see if methane is inhibited at various liquids
to mass ratios.
Although all liquid waste streams should be characterized before landfill application, the following waste streams are
particularly problematic and should not be allowed into bioreactor landfills: surfactant based waste streams, waste streams
containing oily or petroleum fuels, pickling wastes streams, streams related to aluminum dross, and waste streams with high
sulfate concentrations.
5.3 Metals
Under the RD&D (FR 2004) rule the addition of non-hazardous heavy metals bearing liquids is permitted but
discouraged. High metal content has been observed to retard the onset of the methane fermentation phase and even inhibit
methane production altogether (Pohland and Harper 1986). Care must be taken to insure residence time, within the landfills,
to allow metal attenuation.
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6.0 Suggested Sampling Techniques
The following sections outline suggested sampling techniques. Comparable sampling techniques may be employed if
necessary.
6.1 Leachate Sampling
Landfills receive a wide variety of wastes from municipal, agricultural and industrial sources. As a result leachate
composition varies significantly not only among different geographical regions but also within different cells at the same
landfill. Sample duplication is necessary to account for the statistical relevance of monitoring data. Caution must also be
taken to hydraulically separate bioreactor cells from adjacent conventional landfill cells. The separation would allow for an
accurate evaluation of conditions only within the bioreactor. Hydraulic separation may be achieved in an as-built cell;
however, such a separation is more difficult in retrofit bioreactor landfill cells. In the case of retrofit bioreactor landfill, it is
suggested that the zone of influence of the liquid application area be examined (see Reinhart and Townsend, 1998 for more
details). Leachate samples representing the bioreactor section of the landfill should be collected only from areas directly
under the zone of influence.
A common practice at most landfills is to pool the leachate generated at the facility at one sump prior to pumping for
treatment or recirculation. As a result leachate from various areas of the landfill (bioreactor areas and conventional) is mixed.
Leachate sampling should not occur at central sumps, but rather at a point before bioreactor leachate is mixed with that of
conventional landfill cells. Operating a particular landfill as a bioreactor is highly discouraged unless leachate generated by
the bioreactor cells is sampled separately. The inability to do so would prohibit accurate assessment of biological activity and
moisture loading calculation in the landfill bioreactor, which may result in operational problems.
Atmospheric interactions may cause a change in leachate temperature, pH and total solids after sampling. To minimize
these effects temperature and pH measurement should be taken immediately at the point of leachate sampling.
6.2 Solid Waste Sampling
6.2.1 Waste Sampling for New Cells
This particular sampling process is mainly used at newer bioreactor landfills. This procedure is also used with newly
placed (within two weeks of initial placement) waste (EPA 2003). A transect line is created along the length and in the center
of the area of the landfill to be sampled. The transect line is further divided into five equally spaced sections and these
sections are surveyed. Samples are collected using a backhoe at a depth of three feet and six feet at each location for a total of
ten samples.
MSW temperature may be measured using a long-stemmed thermometer (e.g., meat thermometer) as the waste is
brought to the surface and recorded. The pH of the MSW may also be measured using, for example, a "pocket pen" pH meter
(available from a number of scientific supply houses). A one-liter plastic container is filled halfway with MSW. Distilled
water is added to the MSW until it just covers the refuse. The mixture is shaken for approximately two minutes and the pH of
the mixture is then measured and recorded.
After measuring the temperature and pH, each sample is placed a in plastic bag. Each bag is then sealed and placed in a
five gallon pail with a scalable lid. Care must be taken to expel excess air from the bags after placement of the waste. A tag
attached to the bag should contain important information such as the landfill name, address, date, and sample coordinates
from the survey. Similarly, a label should be placed on the outside of the pail to ensure no confusion arises in the laboratory.
Samples collected could be analyzed for moisture content, volatile solids, cellulose, hemicellulose, and lignin content (EPA
2003).
6.2.2 In-place Waste Sampling
This procedure is used for as-built (except for the baseline sampling outlined in section 6.2.1) and retrofit bioreactor
landfills (EPA 2003). MSW samples are collected using a bucket auger. Boring locations should be surveyed, labeled with
coordinates and safe drilling depth. Drilling should be avoided within 3 m (10 ft) from the bottom liner.
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One shovel of MSW is sampled from each auger brought to the surface of the landfill. These "shovel" samples are mixed
to make a composite MSW that represents 1.5 m (5ft) intervals. For example, a composite sample would represent MSW
augured between 3 and 5 m (10 and 15 ft). Sample handling as well as temperature and pH measurements follows the same
methodology outlined in section 6.2.1.
6.3 Gas Sampling
Gas sampling should follow National Emissions Standards for Hazardous Air Pollutants (NESHAP) requirements (40
CFR part 63, subpart AAAA). The requirements include extensive monitoring of the well head gas to ensure proper
collection and periodic surface monitoring for leaks, cracks and fissures or under-designed collection systems.
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References
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Development, Cincinnati, OH.
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stabilization in simulated landfills." 234.
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Pohland, F., and Kim, J. (1999). "Insitue Anaerobic Treatment of Landfills for Optimum Stabilization and Biogas Production."
Water Science and Technology, 40(8), 203-210.
Pohland, F. G. (1975). "Sanitary landfill stabilization with leachate recycle and residual treatment." EPA-600/2-75-043, U.S.
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Reinhart, D., and Al-Yousfi, B. (1996). "The Impact of Leachate Recirculation on Municipal Solid Waste Landfill Operating
Characteristics." Waste Management and Research, 14, 337-346.
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Rittmann, B., Banaszak, J., Cooke, A., and Rowe, R. (2003). "Biogeochemical Evaluation of Mechanisms Controlling CaCO3(s)
Precipitation in Landfill Leachate Collection Systems." Journal of Environmental Engineering, 129(8), 723-730.
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