Lesson: Waste Management
(corresponding to Chapter 15: Waste Management & Geology)
Human society produces waste, and
lots of it. That waste gets disposed
of in the earth. As the human
population (and the waste it
produces) grows, the issue of how
and where to dispose of our waste
becomes more acute.
The photo shows an innovative
way to deal with the millions of
worn out tires produced each year:
some of them can be turned into
children’s playground toys!
© K. Meldahl, MCC 2004
Summary of Important Concepts
There are two main methods for disposing of wastes:
1. Isolation: removing the waste from the environment in some
way, usually by burial or by sealing it off (encapsulation).
2. Attenuation: getting rid of the waste by diluting it,
incinerating it, or spreading it out thinly over a large area.
Three major waste issues will be considered in this lesson:
1. Municipal Waste Disposal - disposing of waste produced by
construction, commercial activities, and residential activities
in cities and towns.
2. Hazardous Waste Disposal - disposing of toxic fluid or solid
substances.
3. Wastewater Treatment - cleaning up dirty water so it can be
used again.
© K. Meldahl, MCC 2004
Summary of Important Concepts, continued
MUNICIPAL WASTE DISPOSAL
The sanitary landfill is the main system of municipal waste disposal
today. In a modern sanitary landfill, each day’s waste is covered
over and sealed off. When the landfill is full it is covered, graded
for drainage, and leachate (polluted water seeping from the
landfill) is prevented from contaminating ground water.
Different classes (I, II, and III) of landfills indicate the kinds of
substances that they can hold safely. Class ratings reflect how
well leachate is prevented from polluting local water supplies.
Incineration is an alternative to landfills, and is sometimes used in
areas of high population density. Ocean dumping was once a
common method of municipal waste disposal but is no longer
due to strict environmental laws.
© K. Meldahl, MCC 2004
Summary of Important Concepts, continued
The main problems associated with landfills:
• settlement: caused by biodegradation of waste and
compaction; may cause cracks and ponds, allowing water to
sink into the landfill, adding to leachate formation
• gas generation: methane gas caused by biodegradation; can
be explosive if not contained; collected by pipes within the
landfill and then burned
• leachate: contained by impermeable barriers of plastic or
clay at the base of the landfill, collected by a system of pipes
and treated
Reduction of waste for landfills can be accomplished by recycling,
composting, and various waste reduction strategies.
Full landfills can be converted into recreational, commercial, or
residential areas.
© K. Meldahl, MCC 2004
Summary of Important Concepts, continued
HAZARDOUS WASTE DISPOSAL
A secure landfill that can handle hazardous waste:
• is lined with plastic and an impermeable clay layer to prevent
leachate (toxic fluids) from seeping into the ground
• contains drains to collect leachate
Deep well injection involves pumping hazardous fluid waste deep
underground into permeable rock formations that are sealed off
by impermeable rock layers.
CERCLA (Superfund) legislation was passed in 1980 to hold
financially responsible those who have created hazardous toxic
waste sites in the past.
© K. Meldahl, MCC 2004
Summary of Important Concepts, continued
WASTEWATER TREATMENT
Wastewater is treated at special plants to clarify and purify it to
various levels.
- primary treatment: removes solids from the water by settling
and aeration
- secondary treatment: microorganisms (bacteria) are used to
remove organic material
- tertiary treatment: inorganic dissolved materials such and
nitrates and phosphates are removed
Biological oxygen demand (BOD) is a measure of the purity of
treated water. The more organic material in the water, the greater
the demand for oxygen by microorganisms. The cleaner the
water, the lower the BOD.
© K. Meldahl, MCC 2004
Society creates a great deal of waste. Disposing of it properly is an
important responsibility. Water purity, air quality, public health,
and the quality of our scenery depend on getting rid of waste in an
effective manner.
Good waste management involves not only waste disposal, but
reduction of the amount of waste we produce.
There are two main methods for disposing of wastes:
1. Isolation: removing the waste from the environment in some
way, usually by burial or by sealing it off (encapsulation).
2. Attenuation: getting rid of the waste by diluting it, incinerating
it, or spreading it out thinly over a large area.
In this lesson we will be primarily concerned with isolation
methods -- the most common way to get rid of waste.
© K. Meldahl, MCC 2004
Municipal Waste Disposal
Municipal waste is the waste produced by construction,
commercial activities, and residential activities in cities and
towns. The figure below shows the components of typical
municipal waste by sector of the economy (on the right) and by
type of material (on the left).
© K. Meldahl, MCC 2004
Sanitary Landfills
Until fairly recently, many cities and towns had open “dumps”
where trash simply piled up. The trash stank, attracted vermin, and
polluted the ground water when rain washed toxic substances out of
the waste. Today such open dumps are being replaced with cleaner
and safer disposal areas called sanitary landfills.
In a sanitary landfill, every day the waste is:
- spread out in thin layers and compacted
- covered over and buried by a layer of soil
Once a sanitary landfill is full, it is sealed off with a thicker layer of
soil, and the surface is graded to a gentle slope to allow water to
drain off, preventing water seepage into the landfill. Water
infiltration must be prevented in order to stop leachate – polluted
water that leaks out of landfills – from forming. Prevention of
leachate is a major concern in modern waste management methods.
© K. Meldahl, MCC 2004
This figure shows how in a modern sanitary landfill each day’s
accumulated trash is compacted and covered over with a 6 inch soil
layer, sealing it off from the surface.
© K. Meldahl, MCC 2004
As a modern sanitary landfill is filled to capacity, a final thicker soil
layer (shown at left) is applied. The entire area is graded to allow
water to flow off the surface. Any leachate (polluted water) that
does seep from the landfill goes into a leachate collection system to
be disposed of properly.
© K. Meldahl, MCC 2004
This photograph shows a full, graded sanitary landfill similar to
the diagram shown on the last slide. The surfaces will be planted
to reduce erosion and make it visually more attractive.
© K. Meldahl, MCC 2004
Classes of Landfills
Landfill are ranked into three classes (Class III, II, and I) based
on local geology and the potential for leachate to leak into local
ground water or surface water supplies.
CLASS III landfills (illustrated above) have no barriers to leachate
leaking out, and may even intersect the water table. Class III landfills
can therefore hold only non-water-soluble, non-decomposable, inert
material (e.g. concrete, rubber products, slag, glass).
© K. Meldahl, MCC 2004
CLASS II landfills (illustrated above) are isolated somewhat from
groundwater supplies, either by natural barriers (like an
impermeable clay layer), or by artificial barriers that considerably
reduce leachate migration away from the site. Class II landfills can
hold most normal garbage, including cans, paper products, cloth,
wood, yard clippings, and small amounts of dead animal material,
as well as anything that can go in a Class III landfill.
© K. Meldahl, MCC 2004
CLASS I landfills (illustrated above) are the most isolated from
groundwater. Leachate is fully contained by an impermeable liner
(clay or plastic), and the surrounding geology also has low
permeability. The landfill is not near any water sources, and is in no
danger of flood or washout. Class I landfills can hold toxic
substances, such as chemicals, toilet wastes, pesticides, fertilizers,
and other nasty materials. Class I fills can also hold anything that
could go in a Class II or III landfill.
© K. Meldahl, MCC 2004
Problems of Landfills
As waste in a landfill decomposes, the landfill begins to settle (the
surface sinks downward), gas is produced, and water in the landfill
may create and/or pick up toxic substances, forming leachate. The
three main problems of landfills are settlement, gas generation,
and leachate containment.
Settlement
Landfills settle by inches or even a few feet per year as trash
decomposes and compacts under its own weight. This causes
problems in that cracks and sags (low spots) may form on the
surface, which allow water to seep into the landfill rather than run
off the surface. These problems must be fixed regularly so that
water infiltration is prevented.
© K. Meldahl, MCC 2004
In addition to causing problems of water infiltration, settlement
can also damage structures built on the landfill, as shown in this
photo.
Settlement does have one advantage: it makes more room for
trash!
© K. Meldahl, MCC 2004
Gas Generation
As microorganisms break down landfill wastes – a process called
biodegradation – they produce gas. Biodegradation is useful; it
reduces the volume of trash in the landfill, making room for more.
Many landfills use a process called composting – pumping air
down into the landfill to encourage the growth of decomposing
aerobic bacteria.
The main gas produced by biodegradation is methane (CH4),
which is the main component of natural gas. Methane migrates
upward through landfills and seeps out, creating dangerous
situations. (At concentrations of about 5% in air methane can
explode if lighted.)
Methane is extracted by sinking perforated plastic pipes into the
landfill. The gas is piped away and either sold or used on site to
generate electricity. Power from waste!
© K. Meldahl, MCC 2004
The photo shows a
methane extraction
well being installed in
a landfill. The pipe
(perforated at depth)
will collect the gas
and take it to be
burned and generate
electricity.
© K. Meldahl, MCC 2004
Leachate
The figure here illustrates how leachate seeping from a landfill
could contaminate local water supplies. Leachate containment is a
top priority in landfill management today. Recall the information
earlier in the lesson about the different landfill classes (I, II, and
III). The class indicates the degree of leachate containment.
© K. Meldahl, MCC 2004
The main method of leachate containment is to put impermeable
barriers of plastic and/or clay at the base of the landfill. In the stateof-the-art landfill design shown here, there is a double lining of clay
and plastic layers at the base of the landfill, and the leachate that
collects there is siphoned off into pipes and taken to treatment areas.
Since 1996 federal law requires that all landfills be designed with
double liners to protect the environment from leachate.
© K. Meldahl, MCC 2004
Other Municipal Waste Disposal Methods
Landfills are the most common way of dealing with municipal
waste. Two other methods are….
• Incineration: Burning waste has the advantage of reducing the
volume of trash produced, and the heat can be used for electrical
generation. However incineration is costly, and the pollutants and
ash produced need to be dealt with. Incineration is most commonly
used in crowded urban regions where there is little room for
landfills.
• Ocean dumping was once a very common method of waste
disposal, particularly of sewage. The adverse effects of sewage
disposal in the oceans lead to the Ocean Dumping Ban of 1988,
which terminated oceanic disposal of raw sewage in the U.S..
Since the ban, coastal communities must process their sewage,
putting only treated sewage water in the ocean, disposing of
remaining sludge in landfills. Ocean dumping of sewage continues
in some countries with less restrictive environmental laws.
© K. Meldahl, MCC 2004
Reducing Municipal Waste by Recycling
Reducing the total amount of waste our society produces can help
immensely with waste disposal problems.
Recycling programs
are growing rapidly
across the U.S..
Recycling of paper
products is especially
helpful, since the
majority of landfill
waste by weight is in
paper (diagram at
left).
© K. Meldahl, MCC 2004
The Concept of Multiple Land Use
Most people might feel that once an area has become a landfill, it is
“off limits” to other human use. Not so. As our population and the
sizes of our urban areas grows, it is important to think creatively
about putting completed landfill areas to other uses. In different
parts of the U.S., landfills have been converted to parkland or even
residential and commercial building areas.
The photograph
shows a landfill
in Santa
Monica, CA,
that has been
converted into a
golf course!
© K. Meldahl, MCC 2004
This photograph shows a commercial development built on a
landfill. To deal with settlement, the buildings are placed on deep
columns that go through the fill to the bedrock beneath. Gas
generation is put to good use – the methane collected from the
landfill is used to fuel the lanterns!
© K. Meldahl, MCC 2004
Hazardous Waste Disposal
Hazardous wastes are toxic substances produced primarily by
industries. These include sludges, solvents, acids, pesticides, and
various corrosive and/or reactive materials. The figure show us the
amounts of various classes of toxic wastes produced in the U.S..
© K. Meldahl, MCC 2004
There are two main methods of disposing of hazardous wastes:
1. Secure landfills. A landfill that can completely isolate the
waste from the environment is considered “secure”. In the
landfill classification described earlier in this lesson, these
would be “Class I” landfills. Such landfills have:
•
linings of plastic and impermeable clay to prevent leachate
contamination of ground water
•
drains to collect leachate
2. Deep well injection. Hazardous fluid waste is pumped deep
underground into permeable rock formations that are sealed
off from groundwater supplies by impermeable rock layers.
Before deep well injection can take place, thorough studies of
underground geology must demonstrate that the waste is
unlikely to leak out and contaminate groundwater supplies.
© K. Meldahl, MCC 2004
The concept of deep
well injection is shown
here. The waste is
pumped below areas
where ground water
exists, into porous rock
layers which are sealed
off from ground water by
impermeable rock layers.
The pipe is lined with
steel to prevent leakage
on the way down.
Problems:
-- the waste may find
ways to leak up to
ground water supplies
-- the waste may leak out
through
the
piping
system on its way down
© K. Meldahl, MCC 2004
Hazardous Waste Legislation
Since 1976, disposal of hazardous waste has been regulated by the
Resource Conservation and Recovery Act (RCRA). Prior to that
there was little regulation, with the result that there are many toxic
waste sites in the U.S. that have caused serious contamination and
human health problems. The community of Love Canal, NY, is one
famous example (see Case Study 15.5 in the book).
In response to the hazards of old, abandoned hazardous waste
disposal sites in the U.S., Congress in 1980 passed the
Comprehensive Environmental Response, Compensation, and
Liability Act (CERCLA), also known as Superfund. The key idea
behind Superfund is that the EPA can clean up polluted sites and
bill the costs of cleanup to those originally responsible. Superfund
has cleaned up many contaminated sites. Unfortunately, about 40%
of Superfund’s money goes not to cleanup costs, but to paying legal
bills involved in convicting the original polluters!
© K. Meldahl, MCC 2004
Wastewater Treatment
Law requires that sewage wastewater be treated at special plants to
clarify and purify it before it can be disposed of or used.
- Primary treatment: removes solids from the water by settling
and aeration.
- Secondary treatment: microorganisms (bacteria) are used to
remove organic material.
- Tertiary treatment: inorganic dissolved materials are
removed, particularly nitrogen and phosphorous. Tertiary
treatment produces water pure enough for human consumption.
Biological oxygen demand (BOD) is a measure of how pure
treated water is. The more organic material in the water, the
greater the demand for oxygen by microorganisms eating the
organic material. The cleaner the water, the lower the BOD. Pure
water has a BOD of zero.
© K. Meldahl, MCC 2004