Page 353 - Materials Chemistry, Second Edition

CAT3525_C10.qxd 1/31/2005 12:00 PM Page 324
324 Waste Management Practices: Municipal, Hazardous, and Industrial
3
The heat value of unprocessed landfill gas is 18,600 kJ /standard m (500 Btu/standard cubic
foot), about one half of natural gas, mainly because only one half of landfill gas is methane (Table
10.9). At a small landfill, gas with this heat value can be used to run a modified internal combustion
engine or a generator to convert gas into electrical energy. At a larger landfill, moisture and carbon
dioxide removal (through scrubbing and gas polishing with carbon or polymer adsorption) enables
the gas to be used to run boilers and turbine generators for energy recovery. Purification of landfill
gas to pipeline quality involves greater investment in terms of removal of impurities. In a chemical
sense, landfill gas and pipeline-quality natural gas differ substantially in composition and energy
content. Landfill gas has a lower Btu content, combusts at a lower temperature, is more corrosive,
and contains much greater concentrations of undesirable gases (CO ,H S, O , and N ) than pipeline-
2
2
2
2
quality natural gas. Extensive purification is therefore necessary to remove all components from
landfill gas except methane. The required cleanup protocol includes nearly complete CO removal.
2
Processing increases the heat value of the gas to approximately 1000 Btu/scf. Conversion of landfill
gas into natural gas is sufficiently costly such that only large landfills can attain the economies of
sale necessary to support operations. Fewer than ten U.S. landfills convert gas for pipeline use
(Vesilind et al., 2002)
Municipalities are using landfill gas to produce electricity, heat, or steam for industrial use.
Local governments are discovering that use of landfill gas can reduce electrical demand for local
utilities, delaying the need for building new power plants. The Rhode Island Solid Waste
Management Corporation (RISWMC), responsible for managing the 62 ha (154 acres) Central
Landfill, captures the landfill gas to supply as much as 12.3 MW of electrical power, capacity
sufficient to serve roughly 17,000 households. The company sells this electricity to a local sub-
sidiary of New England Power and pays the RISWMC $50,000 per month in royalties for the rights
to the gas.
Lane County, Oregon, which includes the cities of Eugene and Springfield, constructed a land-
fill gas-to-electricity facility at the Short Mountain Landfill in 1992. The facility generates 1.6 MW
of electrical power (sufficient for about 800 homes) and will increase its capacity to 4 MW by 2010.
There is a roughly 1 cent / kWh profit for the local consumer-owned utility on the electricity sold
to the Bonneville Power Administration. The total annual revenues from gas sales were about
$150,000. Lane County receives a minimum royalty of $15,000 per year and avoids having to build
and operate an expensive collection system (U.S. DOE, 1994).

10.4.18 OTHER AIR CRITERIA
Open burning of solid waste, except for the infrequent burning of agricultural wastes, land-clearing
debris, diseased trees, or debris from emergency cleanup operations, is prohibited at all MSWLFs
(40 CFR Part 258.24).

10.4.19 PUBLIC ACCESS
The general public and other unauthorized persons may be unaware of the hazards associated with
landfills. Potential hazards include:

● The inability of equipment operators to see individuals during equipment operation
● Direct exposure to waste materials (e.g., sharp objects, pathogens)
● Falls
● Exposure to fires
● Earth-moving activities

Operators of MSW landfills must control public access and prevent unauthorized traffic and ille-
gal dumping of wastes (40 CFR Part 258.25). This is accomplished by constructing natural or artifi-
cial barriers. Specific measures include installation of gates and fences, trees, hedges, berms, ditches,