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Municipal Solid Waste
Issues Facing Communities
Companion Slide Script
SMarket Research Center
Staff Report 93-1.
MUNICIPAL SOLID WASTE
ISSUES FACING COMMUNITIES
Companion Slide Script
Robert L. Degner, Rebecca D. Dunning, and Thurston L. Brooks1
This script and accompanying 35 mm slide set are to be used as companions to the booklet,
"Municipal Solid Waste Composting: Issues Facing Communities" by R.D. Dunning,
R.L. Degner, and PJ. van Blockland. Preparation of these materials was supported by the
Extension Service, U.S. Department of Agriculture, and the Florida Cooperative Extension
Service, University of Florida under special project number 91-ESNP-1-5168. To obtain
copies of the booklet and to borrow the slide set, contact your local county cooperative
extension service office.
'Dr. Degner is Director of the Florida Agricultural Market Research Center and Professor
and Ms. Dunning and Mr. Brooks are Research Assistants with the Food and Resource
Economics Department, Institute of Food and Agricultural Sciences, University of Florida.
Municipal Solid Waste Composting: Issues Facing Communities
Municipal solid waste composting gives communities
an alternative to landfilling organic wastes. In the
next half-hour, we'll look at the composting process,
and discuss some of the issues that affect
consideration of this waste management option.
Composting is defined as the accelerated biological
decomposition of organic matter. By controlling
temperature, moisture, and oxygen, the decomposition
that occurs naturally can be accelerated.
The composting process results in carbon dioxide and
moisture, which are released to the atmosphere, while
the remaining organic materials are transformed into
a soil-like substance called "compost" or "humus".
Composting has the potential to reduce the volume of
organic materials by 25 to 50 percent.
Municipal solid waste or "MSW" is the commercial
and residential waste that we usually term "garbage".
MATERIALS INMIRATID IN MSW
MANAGEMENT OF MUNICIPAL SOLID WASTE
GROWTH IN LANDFILL
ALTERNATIVES 1988 to 1992
In a typical community, 60 to 70% of MSW is made
up of organic waste -- food, trimmings from the yard,
wood, and paper. As mentioned earlier, composting
can be used to reduce the volume of organic waste by
25 to 50%. Compost that is produced can be used by
farmers or homeowners, but more about that later.
Most MSW is landfilled, but incineration, recycling,
and composting are three alternatives to landfilling.
Recycling and composting programs have increased
dramatically in the last few years, but almost all
composting plants use only yard wastes. Only 19
facilities were composting MSW in 1992.
Landfilling is still the cheapest waste management
alternative in almost all communities, but MSW
composting is receiving greater interest for several
reasons. Since it reduces the volume of MSW that
must be landfilled, it can extend the life of the
landfill. This can delay construction of a costly new
landfill while avoiding unpleasant siting battles with
Composting creates a soil-like product that can be
used by landfills for landfill cover, or by public works
departments, farmers, landscapers, or homeowners.
Composting recycles wastes into a useful product,
while extending the life of the current landfill.
Many states are setting recycling goals or targets for
landfill diversion. Since composting is considered a
form of recycling, it can be used to help fulfill these
While composting of MSW can provide significant
benefits, there may be problems. MSW composting
plants can be expensive to build and operate. It is
difficult to get precise figures on the costs of
composting, but experts agree that landfilling is far
cheaper than composting in almost every community.
I PROBLEMS WITH COMPOSTING
There has not been a big increase in the number of
MSW composting facilities like there had been for
recycling programs. Expense is one reason, and risk
of failure another. The biggest problem with plants
has been odor, and several big facilities have been
closed for this reason. The most recent closure was
that of the New Castle, Delaware facility in 1993.
The capital costs of the facility were $70 million.
Since 60 to 70% of MSW is organic, MSW
composting can greatly reduce the amount of wastes
going to landfills if it produces a compost that can be
used off site by the public. But it is difficult and
costly to produce a material that is completely free of
all non-organic substances. The most frequent
complaint about compost concerns its appearance.
Fragments of plastic and glass are difficult to screen
out and are often easy to spot in finished compost.
The possible presence of unseen materials, like lead
or other trace metals, is also of concern to users.
VIABIUTY OF MSW COMPOSTING
MSW composting may work in your community. It
is important that community leaders define the waste
management goals clearly before they begin to
consider options. Before we look at some of the
issues that community leaders should keep in mind as
they consider MSW composting, let's go over the
THE COMPOSTING PROCESS
PO S, .T-PROCESING ACIVITIE
Composting consists of several steps: (1) collection
and separation of materials to be composted (2) the
actual transformation of waste into compost (3) post-
processing activities to prepare the compost as a
First, waste must be collected from residents and
businesses. Organic material can be separated out by
residents. In some communities, residents have
different trash receptacles for organic waste, for
recyclables, and all other waste. This is called
In some cases, waste handlers collect the organic
waste and store it separately from other non-organic
waste. This collection method is frequently used for
Another method of separating organic materials is to
collect the waste all mixed together, or after some
recyclables have been removed by residents, then
isolate the organic materials at a centralized location
called a materials recovery facility or "MRF".
Here mixed wasted is dumped onto the "tipping"
....and then it is transported by conveyor to another
location within the facility....
....where workers hand remove non-organic materials
such as metal, plastic, glass, and textiles.
Separation can also be made mechanically, for
example, by magnets that take out ferrous materials
such as steel cans. There are many different types of
sorting technologies which vary greatly in their
sophistication, cost and efficiency. Here we also see
bundles of recyclable materials sorted by the facility.
Windrows are elongated piles....
After sorting, the organic are usually mechanically
ground into smaller pieces. This can make it easier to
transport and manipulate the materials. It also speeds
the composting process. However, it requires
After grinding, the organic are ready for composting.
There are three common methods of processing the
waste into compost. They are aerated windows,
aerated static piles, and in-vessel reactors.
....with a width approximately double to their height.
They are usually placed on cement pads and are
turned 1 to 3 times per week to distribute moisture
and air throughout the pile. This speeds
decomposition and lessens odors that result when
there is in sufficient air in the piles. Eight of the
nineteen composting facilities operating today use
Windrows can be turned by a front-end-loader....
....or by machines specially designed for turning
Here is another type of turning mechanism that is
turning windows in an enclosed building. Enclosing
windows can give plant operators better control over
moisture, temperature and odors.
A second method of composting is to place the
material in piles that are not turned to distribute air,
but instead use mechanical aeration to force air
through the compost. Three of the nineteen facilities
in operation in 1992 use this method of composting.
AERATED STATIC PILE
ANormally, tubes or pipes beneath the compost piles
push or pull air through the pile. This system
facilitates filtration of the air flow which can reduce
In-vessel reactors offer the greatest amount of control
over the composting process. Material is placed
inside these large tunnel-like vessels and slowly
turned to mix and pulverize the MSW. In-vessel
reactors can be located indoors....
....or outdoors. Moisture, oxygen and temperature
levels are closely monitored and adjusted as
PHOTO necessary. This method can speed the initial stages of
OUTDOOR composting by as much as ten-fold. While this is the
most technologically advanced composting method, it
REACTOR is also the most expensive.
In-vessel reactors are normally used in conjunction
with aerated static piles or windows. MSW is put
into the reactor or digestor for 3 to 7 days, then
moved to piles or windows for 2 to 6 weeks. Of the
19 plants in operation, 8 use in-vessel reactors in
conjunction with aerated static piles or windows.
During composting, temperatures are monitored as a
guide as to when piles should be turned.
Moisture will often be added to piles to speed
composting. However, too much moisture can
Excess moisture that results from decomposition, run
off from rainfall or addition of water must be
disposed of just like landfill leachate.
Leachate is held in lined ponds for evaporation.
Leachate is aerated to reduce toxicity and odor.
The composting process can take a week or two to
months depending upon the technology used and the
degree of "finishing" or maturity desired.
As composting occurs, the color, texture, and odor of
the MSW material should come to resemble soil or
Finished compost resembles soil. Note the color and
texture of this finished compost. However, it is
difficult to produce a compost which is completely
free of foreign objects. Even though the color of this
compost is good, small particles of plastic and glass
To improve the quality of the final product, compost
is mechanically screened to remove foreign objects
like plastic and metal. Screening also breaks up
clumps in the material so that it will be easier to
QUALITY CHARACTERISTICS OF
VIABILITY OF MSW COMPOSTING
U COO'I ISUE
POIIA0 N SCA LMT
Now that we've had an overview of the composting
process, let's turn back to the issues of MSW
composting as a possible means of managing waste in
a community. The viability of MSW composting in
your community will depend on a number of
community-specific factors. Basic factors include
technological considerations, economic issues, and the
community's political and social climate.
Compost producers are trying to refine production
processes so that more compost can be used off-site.
While there aren't any federally designated quality
standards for compost, producers and users generally
agree that high quality compost should have the
-Uniform particle size and consistent moisture content
make the material easier for handling and spreading
on land. Lower moisture content can also reduce
-Fewer inerts like pieces of plastic and glass make the
material much more visually appealing for users,
especially homeowners who will have direct contact
with the material.
-Assurance that the levels of trace metals like lead
and cadmium are low can dispel fears about the safety
of having direct contact with the compost or using it
on agricultural land that produces food.
-Greater maturity is required by agriculturalists and
homeowners, because immature compost can harm
plants. By "immature" compost we mean compost
that is decomposing at a high rate. High temperatures
in a compost pile is the most direct indicator that
compost is not mature.
It might not be possible for the community to
compost all residential and commercial waste. It
might be more efficient to target major sources of
organic waste like restaurants. It is important to
know the quantity of the waste to be composted. This
will determine the required size of the facility and
give an indication as to the quality of compost to be
We discussed two basic categories of collection and
separation of the organic in waste--source separation
and separation at a central materials recovery facility.
To decide between the two, decision-makers should
not only compare costs, but also consider whether or
not the public would be willing to separate organic
in the home.
We talked about the basic techniques for processing.
Decision-makers will have to balance the costs and
management expertise required of different
technologies to decide which would be best for their
particular waste management systems.
WHE .S COPSTN IS ADE TO
THE COMMU''NBBITY S WASTEMANAGEMENT
P^^TRt'OGRA 00 TTAL CSiTS T.INCREASE OR^
Economic factors are very important to most
communities. When considering MSW composting as
an option for waste disposal, keep in mind that
composting can only deal with a portion of waste,
therefore, it will be an addition to the existing waste
management system. When looking at costs and
benefits, keep the entire waste disposal system in
mind. Composting can be expensive, and you might
not see a decrease in the costs of disposal when MSW
composting is added. However, "intangible" benefits,
such as prolonged life of the existing landfill or
ability to meet state mandates on recycling should
also be considered.
HO WIL TH OMNIYUEO
The composting facility might have to compete with
other disposal options, such as low cost landfills.
Costs per ton of waste may be even greater if fewer
tons of waste are processed than originally
anticipated. A guaranteed supply of feedstock is
required to keep the composer running as efficiently
as possible. If other disposal options are less costly,
the composer will require a subsidy so that it can
compete, or an assured flow of MSW feedstock must
be mandated by municipal or county governments.
Such control of feedstock is called "flow control."
While it is currently legal for city and county
governments to control the flow of wastes to certain
facilities, the Supreme Court will soon rule on the
legality of flow control. If the Court rules against
flow control, it will have big impacts on the viability
of composters in some areas.
Depending on your states' regulations on compost
quality, it may be difficult to make compost that can
be used away from the landfill. The community must
consider what will be done with finished compost.
Since only 10% of today's compost is actually sold,
a conservative approach would be to assume zero
revenue from compost sales.
fWWv.MM,, There is a growing interest in MSW composting, but
Operational problems have created mixed success for
municipal solid waste composting. The biggest
problem associated with MSW composting is that net
waste disposal costs are likely to be greater than
landfilling. This is particularly true if competition for
feedstock results in less than optimal efficiency for
other waste management programs already in place.
Also, technical problems such as odor control have
plagued many of the composting plants in the U.S.
Further, some plants have experienced limited demand
for finished compost, particularly that of relatively
low quality. In conclusion, socially acceptable waste
management remains a top priority in many
communities across the U.S. If your community is
seeking alternative waste management options, MSW
composting should be examined very carefully to
determine its appropriateness in the community's
overall waste management plan. Also, there are still
technical problems in processing that create odor or
result in a poor quality product that is difficult to get
S *Examine facts carefully before investing in MSW