Chapter 18.1
The Solid-Waste Problem
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municipal solid waste: total of all
materials thrown away from homes and
commercial establishments
different from nonhazardous industrial
waste
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includes wastes from construction and
demolition projects, sewage treatment sludge,
wastes generated from industrial processes
disposal of municipal solid waste
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amount of MSW generated in U.S. has
grown steadily
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growing population
increasing use of disposable materials and
excessive packaging
1960 = 2.7 pounds / person / day
2006 = 4.5 pounds / person / day
MSW composition
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refuse generated by municipalities is a mixture
of materials from households and small
businesses
varies based on
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generator (commercial / residential)
neighborhood (affluent / poor)
time of year (spring / summer / fall)
restrictions and prohibitions are bypassed with
careful packing of trash containers
methods of disposal
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until the 1960s, almost all waste was burned in
open dumps
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burning reduced volume and increased lifespan of
dump
produced clouds of smoke and served as breeding
ground for rats, flies, and other pests
open dumps were replaced in 1960s and 70s
with incinerators
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huge furnaces burned waste more completely at high
temperatures
path of trash
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U.S. in 2003
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55.4% = landfill
30.6% = recycling or composting
14% = combustion
percentage of recycled materials is
increasing in U.S.
countries with greater population densities
(i.e. Japan) burn a much higher percentage
landfills
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landfill: waste is put on or in the ground
and is covered with soil
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each day’s fill is covered with at least 6 inches
of soil
helps control air pollution and pests
first landfills did little to consider ecology,
water cycle, or potential for hazardous
products when waste components react
problems of landfills
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subjected to biological and physical factors in
the environment and undergo change over
time
problems:
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leachate
methane production
incomplete decomposition
settling
leachate
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leachate: as water percolates through the
landfill, various chemicals dissolve and are
carried by the solution
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likely to include residues of decomposing organic
matter with iron, mercury, lead, zinc, and other
metals from rusting cans and batteries, along with
paints, pesticides, cleaning fluids, and other
chemicals
areas like Florida, where the groundwater is
often just below the surface, have
experienced extensive water pollution as a
result of unlined landfills
methane production
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because it is about 2/3 organic material, MSW is
subject to natural decomposition
buried wastes do not have access to oxygen,
meaning decomposition is anaerobic
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produces biogas mixture that is about 2/3 methane,
with some hydrogen and carbon dioxide
mixture is highly flammable
may explode under certain conditions
some cities have installed gas wells to tap the
landfill gas
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methane is purified and used for fuel
incomplete decomposition
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common plastics in MSW resist decomposition
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polymers of petroleum-based compounds that cannot be
broken down by microbes
(biodegradable plastic polymers have now been
developed from cornstarch and soybeans)
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demand for products based on two factors:
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1. price of oil
2. demand for environmentally friendly packages
biodegradable materials such as newspaper and
wood often degrade slowly or not at all in landfills
(mostly due to lack of moisture)
settling
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occurs as waste compacts and decomposes
issue for landfills that have been converted to
playgrounds and golf courses
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creates shallow depressions
Chapter 18.1 (cont.)
Siting New Landfills
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from 1988 to 2002, number of municipal
landfills declined from ~8000 to 1767
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increase in size of landfills combined with
increase in recycling means that landfill
capacity is not a problem in the U.S.
however, “regional dislocations” occur
as old landfills close, it’s increasingly
difficult to to find land for new ones
outsourcing
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problem with finding new sites has some
undesirable consequences
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1. drives up costs of waste disposal
2. leads to inefficient practice of long-distance
transport of trash
trash is often carried across state or national lines,
leading to resentment from citizens of the locations
receiving the waste
 10 states import more than 1 million tons of MSW
per year, while 8 states export more than 1 million
tons per year
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combustion
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because of its high organic content, waste
can be burned
process is really waste reduction, not
waste disposal
after incineration, ash must still be
disposed of
advantages of combustion
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can reduce weight of trash by 70% and volume by
90%
toxic or hazardous substances are concentrated into
two streams of ash
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fly ash
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bottom ash
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captured from the combustion gases by air pollution control
equipment
contains most of the toxic substances; can be safely put in a
landfill
from the bottom of the boiler
can be used as fill in some construction sites
no changes are needed in consumer behavior or
trash collection procedures
advantages of combustion (cont.)
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2/3 of combustion facilities are waste-toenergy (WTE) facilities equipped with modern
emission control technologies
when burned, unsorted MSW releases about
35% as much energy as coal
facilities often do resource recovery, which
separates some materials before (and
sometimes after) combustion
drawbacks of combustion
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air pollution and offensive odors
facilities are expensive to build
combustion ash is often loaded with metals
and other hazardous substances
even if it generates electricity, process
wastes both energy and materials unless
recycling and recovery are part of operation
an operating facility
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plant receives about 3000 tons of MSW per day
PROCESS
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1. incoming waste is inspected, and recyclable and
bulky materials are removed
2. waste is then shredded into pieces with a width of
6 inches or less
3. magnets remove 2/3 of ferrous metals for recycling
4. waste is blown into boilers
an operating facility
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PROCESS (cont.)
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5. water circulated through the walls of the boilers
produces steam, which drives turbines for generating
electricity
6. after waste is burned, bottom ash is conveyed to
processing facility where further sorting of metals
occurs (recovers brass, aluminum, gold, copper, and
iron)
7. combustion gases are neutralized to remove sulfur
dioxide and other gases
8. fly ash and bottom ash residues are put into
landfills