1058RECYCLING WASTE MATERIALS
Reclamation of waste materials for the purpose of reuse
is a commonly accepted definition of recycling. Although
water is the substance reused in greatest volume, it will not
be covered here. (See Biological Treatment of Wastewater;
Municipal Wastewater; Physical and Chemical Treatment of
Wastewater; Water Reuse; Water Treatment). Impurities in
the air are considered only after removal. Baghouses are an
example.
Recycling, or reuse, is based on economics. A used
material will be discarded if reclamation costs exceed the
cost of new (virgin) material. Disposal costs, however, have
increased greatly in the last decade and it is no longer as
easy to “throw away” many things. Acceptable disposal sites
increasingly are in short supply and transportation costs
have become a much more significant part of the expenses
of disposal. A typical municipal solid waste can be expected
to be somewhat close to the following, by weight:Paper 35%
Yard wastes 16%
Food wastes 15%
Metals 10%
Glass 10%
Plastics, rubber and leather 7%
Textiles 2%
Miscellaneous 5%These percentages will vary with the season.
More acute public awareness of environmental pollution
has added to the pressure for recycling. Resources are not
limitless and many non-renewable materials will be seri-
ously depleted in the not-too-distant future. Raw materi-
als for plastics are petroleum based. Oil has not had a very
stable price since the early 1970’s.
Landfills have served as repositories for municipal and
industrial solid wastes since before the turn of the century.
Waste was placed in a dump without regard to separation or
segregation of materials. Odors and rodents were common
problems. Little planning went into site selection of solid
waste disposal areas. As urban areas grew, many dumps at
the edge of town were bypassed and were then within the city
limits. In many cases, these sites were covered and homes
and buildings constructed. These structures all too frequently
settled unevenly on the poorly compacted material. At pres-
ent there is interest in use of decomposition gases from old
landfills. Removal of these gases, primarily methane, givesa saleable product and also aids in compaction. Results have
been mixed, at best.
Kitchen wastes, organic in nature, appear in unsegre-
gated garbage and trash. Some authorities view these kitchen
wastes as suitable for incineration. Older incinerators give
rather poor performance, due to high water content in the
garbage lowering process temperatures. Problems were
common. Improved technology promises higher tempera-
tures and cleaner stack effluents. Ideally, such installations
will burn wastes, produce steam and generate electrical
energy. The stream and electricity can then be sold and gen-
erate sufficient income to pay for the whole operation. It has
been proposed that suitably prepared sewage sludge might
be added to the combustible mixture. However, the NIMBY
(Not in my backyard!) Syndrome complicates the situation.
Every group wants to dispose of waste from an upstream
vantage point. In the 1990’s everyone is downstream from
someone else. It is obvious that properly designed and
implemented recycling programs can aid in alleviating both
technical problems and public perception difficulties.
Ease of separation is fundamental in conversion of waste
to a profitable product. Industrial wastes are more easily
separated than are municipal solid wastes. Industrial wastes
can be collected unmixed and in bulk quantities. Municipal
solid waste requires separation techniques, increasing costs
to a degree depending on the number of steps.
Reducing the volume of the waste stream reduces ultimate
disposal costs by making recyclable materials more readily
available and lessening the volume necessary to contain the
wastes. About 2000 communities in the US are practicing
curbside pick up of recyclables or plan to do so in the near
future. The most important consideration in planning such a
program is selection of the materials to be included. Decisions
must be made as to which materials will be collected, both at
startup and later in the program. If all materials are included
at the planning stage, the equipment will be adequate, even if
lesser numbers are initially processed. Trucks will be of suf-
ficient size and will have enough compartments. Processing
equipment will be in place and able to handle all the mate-
rials. Recyclable materials are usually segregated by the
householder or industrial generator. It is necessary to make
economic projections for the waste. Glass requires separation
as to color.
In the 1960’s plastic (polymeric) containers began to
replace glass containers in many uses. Milk and soft drinks
had been sold in glass bottles and deposits helped ensureC018_003_r03.indd 1058C018_003_r03.indd 1058 11/18/2005 11:05:15 AM11/18/2005 11:05:15 AM