Nicholas P. Cheremisinoff. Handbook of Solid Waste Management and Waste Minimization Technologies
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o Prevents erosion and silting on embankments parallel to creeks,
lakes,
and rivers
o Prevents erosion and turf loss on roadsides, hillsides, playing
fields,
and golf courses
• Economic benefits
o Results in significant cost savings by reducing the need for
water, fertilizers, and pesticides
o Produces a marketable commodity and a low-cost alternative to
standard landfill cover and artificial soil amendments
o Extends municipal landfill life by diverting organic materials
from the waste stream
o Provides a less costly alternative to conventional bioremediation
techniques
Within the resource recovery area a range of technologies are available to
complete the recycling loop or add value to reprocessed materials, but a key
factor in every case is that the viability of any process or option should be
determined by deducting recovery and processing costs from the market price. If
this process is subsidized for political purposes to ensure its viability, it is
effectively consuming a greater value of production cost than it is generating.
This is wasteful in economic and environmental terms.
Because of the undercapitalization requirement for major investment in certain
recycling capacity, it is essential that a range of markets be encouraged. Such
markets would have trickle-down values such that lesser grades of material would
go to less sensitive uses. The current position in glass and PET is therefore
unstable as the market for both commodities is far too centralized and the lack of
alternatives could be a major impediment.
Avoided landfill credits may provide additional income; however, resource
recovery is generally constrained less by low landfill gate fees, than by the
resource security requirements of any investor to develop the process,
infrastructure, and markets for the available materials.
With local communities driven by demand for recycling, a predictable (and
perhaps avoidable) imbalance exists between supply and demand for recovered
resources. This inefficiency is manifesting itself as a cost to the community and
industry which is much higher than it need be.
The most powerful motivation for the general public to recycle is considered to
be the ability to make a personal contribution to the quality of the environment.
Social pressure to conform is also a strong influence. Materials are recovered
from the municipal waste streams for recycling more because they are obvious or
easy to isolate than because there is sustained demand for them as essential raw
materials. Most plastics, papers, cardboards, metals or glasses are technically
recyclable, but few qualify on economic grounds because the combined costs of
collection, sorting, transporting, cleaning and reformulating are greater than
those of virgin extraction, especially to achieve a comparable quality and
usefulness.
This highlights one of the major challenges of waste management/resource
recovery: to focus on the development of universal strategies and infrastructure
for the collection, sorting, transport, and beneficiation of materials designed for
reuse/recycling. Then there will be fewer economic constraints on the technical
potential for widespread recycling.
The greatest recycling challenge facing solid waste infrastructure is not in the
process of collecting, separating, and supplying resources recovered from the
waste stream, but in doing so at a competitive cost, and in marketing the
materials at a price, quality, and quantity competitive with virgin materials.
Simply collecting obvious materials and hoping someone will pay enough to
produce a profit is not recycling. Like any other business venture, it must be
carefully planned with the application of life-cycle costing tools.
Several references that provide more in-depth information are provided at the end
of this chapter.
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Chapter 4
LANDFILL OPERATIONS AND
GAS ENERGY RECOVERY
INTRODUCTION
Throughout Europe and the United States, there is a strong reliance on disposing
of waste in landfills. Furthermore, in many developing countries, conditions for
waste disposal are still rudimentary. In 1997, for instance, 99% (around 90,000
tons per day) of Brazil's collected waste was being landfilled or simply dumped.
Each person in the United Staes generates about 4.5 pounds of waste per day,
which is nearly 1 ton per year. Again, most of this waste is deposited in
municipal solid waste (MSW) landfills. As MSW decomposes, it produces a
blend of several gases, including methane (about 50%).
Landfilling is the oldest and most widely practiced waste disposal option. Modern
landfill sites have developed from uncontrolled dumping sites to be an advanced
treatment and disposal option designed and managed as engineering projects. In
addition, modern purpose-built landfill sites normally incorporate a system for
the extraction of landfill gas (arising from the decomposition of bioreactive
wastes), from which energy can be recovered. The types of wastes suitable for
landfilling include biodegradable wastes, aqueous liquids in limited amounts,
inert wastes, and certain special wastes that would not pose toxic threats. Wastes
that are generally considered unsuitable for landfilling include volatile liquids or
solvents, wastes that would introduce unacceptable contamination into the
leachate, and wastes that would interfere with the biological processes in a
landfill site.
The advantages of landfilling as a waste disposal option include:
• It costs less than other disposal options
• A wide variety of wastes are suitable for landfill
• It frequently offers the only final disposal route for residues arising from
end-of-pipe treatment technologies and other waste management options,
such as incineration
• Landfill gas can be collected and utilized for heat and as a low-polluting
fuel for energy generation
• Restored land can provide valuable space for wildlife habitat or leisure
use
The disadvantages of landfilling include:
• Older sites, constructed before the impacts of leachate and landfill gas
were realized, are now sources of pollution with uncontrolled leakages
• There is continued risk of contamination from operational landfill sites
• Some parts of the world are experiencing shortages of suitable landfill
sites close to the source of waste generation
• Landfilling achieves a lower conversion of wastes into energy than other
solid waste management strategies
• The convenience of landfilling tends to discourage the development of
innovative waste management strategies
• Landfilling may produce contaminated land that is unsuitable for some
future uses
• Landfilling causes noise pollution, odors, unsightliness, and often heavy
vehicle movement adding to air pollution problems
Anaerobic decomposition of organic solid waste in the landfill environment
produces landfill gas (LFG). LFG mainly consists of methane and carbon
dioxide, both of which are odorless. Trace constituents of other volatiles, often
malodorous or toxic gases, are also found in LFG. LFG can migrate through soil
into structures located on or near landfills. Since methane presents a fire or
explosive threat, LFG must be controlled to protect property, and public health
and safety. Also, many jurisdictions require landfill owners/operators to reduce
reactive organic gas emissions to improve regional air quality. Thus, engineered
solutions are needed to efficiently and safely monitor, collect, and process
landfill gas. As noted, a positive side to LFG control is energy recovery. Today's
technology allows a landfill owner/operator to recovery the energy in LFG while
reducing gas emissions. Revenue from the sale of LFG or electricity generated
using LFG as a fuel can offset costs for landfill environmental compliance and/or
closure.
This chapter provides an overview of sanitary landfill operations and utilizing
landfill gas as a means of energy. The practice has been successfully applied to
small-scale operations that generate heat and electricity for on-site use, to
relatively large operations that can sell the energy into an off-site grid, thereby
offsetting investment and OM&R costs.
REGULATORY CONSIDERATIONS
The Resource Conservation and Recovery Act (RCRA) establishes landfill design
and performance standards under Subtitle D. Subtitle D requires monitoring of
landfill gas and establishes performance standards for combustible gas migration
control. Landfill owners/operators must:
• Establish LFG monitoring programs. Use of gas monitoring probes is
typical.
• Monitor for subsurface migration of combustible gas on a quarterly
basis.
• Maintain combustible gas concentrations under 5% in soil at the
property line, and under 1.25% in facility structures.
• Mitigate gas hazards if conditions are not in compliance.
The U.S. EPA has proposed control of surface LFG emissions under the Clean
Air Act. The New Source Performance Standards (NSPS) will require LFG
testing and collection system installations at many sites, even those otherwise in
compliance with RCRA Subtitle D. NSPS will require landfill owners/operators
to:
• Estimate total LFG emissions using sophisticated gas models, laboratory
analyses, and gas pump tests.
• Install comprehensive gas collection systems throughout the landfill at
any site shown to have high emissions of non-methane organic
compounds.
• Perform long-term operation and recordkeeping on such landfill gas
systems.
Other federal agencies also have standards that may affect siting, such as Federal
Aviation Administration (FAA) regulations intended to minimize bird hazards to
aircraft.
Subtitle D regulations also establish national minimum standards for landfills that
receive household waste. These national minimum standards are incorporated
into each state's landfill permitting standards. However, states also may impose
more restrictive criteria. Under RCRA, the U.S. Environmental Protection
Agency (EPA), Washington, D.C, regulates solid waste landfilling with regard
to:
• Groundwater quality protection
• Landfill gas controls
• Air pollution control
• Basic operating procedures
• Safety issues
• Flood plains
• Seismic and slope stability
• Disturbance of endangered species
• Surface water discharges
• Site closure and long-term care
• Closure and long-term care financial assistance
State regulations vary widely. Nevertheless, most states require a regulatory body
to approve landfill engineering plans. State regulations often specifically address
geologic or other factors unique to a region. In addition, state and local
governments also regulate other landfill-related issues. These include conditional
use zoning, highway issues (heavy loads and traffic), water discharge/water
quality control, mining regulations (excavations), building permits, fugitive dust
and emissions controls, and closure permits.
All applicable regulations should be considered when planning a landfill.
Government standards generally can be classified into engineering design
standards and performance standards. Engineering design standards are similar to
building codes, which describe how a facility must be built. For example, a new
landfill may be required to have a 6-foot-high fence surrounding the facility.
Design standards are prescriptive and don't offer much flexibility. In contrast,
performance standards are applicable over a facility's life and require a certain
level of environmental control. For example, the state agency regulating
groundwater quality may specify the maximum allowable contaminant
concentration that may be present in the groundwater below or adjacent to the
site.
Site operators must incorporate the necessary control systems to comply
with the groundwater standard. Performance standards allow for some design
flexibility provided the standard is met.
Despite the pervasiveness of federal, state, and local landfill regulations, these
criteria are legally viewed as minimum performance requirements. Therefore,
even if all the applicable regulations have been followed, if a problem arises, the
landfill developer still may be liable for the legal consequences. Claiming
compliance with regulatory standards has not been an effective defense against
pollution damage claims. To increase public acceptance and reduce long-term
risk, many landfill developers now design facilities that exceed regulatory
requirements in some key aspects.
Since October 1979, federal regulations promulgated under Subtitle D of RCRA,
which regulates the siting, design, construction, operation, monitoring, and
closure of MSW landfills, have required controls on migration of methane in
landfill gas. These regulations do not address other components of landfill gas. In
1991,
EPA issued standards for landfill design and performance that apply to
MSW landfills active on or after October 9, 1993. The standards require methane
monitoring and establish performance standards for methane migration control.
Monitoring requirements must be met at landfills not only during their operation,
but also for a period of 30 years after closure. Landfills affected by RCRA
Subtitle D are required to control gas by establishing a program to periodically
check for methane emissions and prevent off-site migration. Landfill owners and
operators must ensure that the concentration of methane gas does not exceed:
• 25% of the EL (explosion limit) for methane in the facilities' structures
(1.25%
by volume)
• The LEL (lower explosion limit) for methane at the facility boundary
(5%
by volume)
Permitted limits on methane levels reflect the fact that methane is explosive
within the range of 5% to 15% concentration in air. If methane emissions exceed
the permitted limits, corrective action (i.e., installation of a landfill gas collection
system) must be taken. The Subtitle D RCRA regulations for MSW landfills can
be found in 40 CFR Part 258.
Under NSPS/EG of the CAA, EPA requires affected landfills to collect and
control landfill gas. The NSPS/EG target reductions in the emissions of landfill
gas due to odor, possible health effects, and safety concerns. The rules use
NMOCs (which contribute to local smog formation) as a surrogate for total
landfill gas to determine if control is required. Landfills meeting certain design
capacity and emissions criteria are required to collect landfill gas and either flare
it or use it for energy. Landfills that meet both of the following criteria must
collect and control landfill gas emissions.
• Capacity: design capacity greater than or equal to 2.5 Mg and 2.5
million cubic meters.
• Emissions: annual NMOC emission rate greater than or equal to 50 Mg.
The basic requirements are the same for both existing and new landfills. Existing
landfills are defined as landfills that received waste after November 8, 1987, and
began construction before May 30, 1991. These are regulated through the EG.
New landfills are defined as landfills that began construction, reconstruction, or
modification on or after May 30, 1991. These are subject to the NSPS. The CAA
regulations (NSPS/EG) for MSW landfills can be found in 40 CFR Part 60,
Subparts Cc and WWW. State plans and a federal plan to implement the EG for
existing landfills can be found in 40 CFR Part 62.