Chapter 12
Solid and Liquid Wastes
Learning Objectives
By the end of this chapter the reader will be able to:
• Describe trends in the production of solid waste
• Discuss methods for source reduction of solid waste
• Discuss the role of landfills for disposing of solid
waste
• Describe methods for primary, secondary, and tertiary
sewage treatment
• Discuss hazards of poorly designed solid waste
disposal sites and improperly processed sewage
Problems Caused by Growing
Volume of Waste
• Difficulties in disposal
• Dump sites being filled
• Increases in pollution of aquatic environments,
e.g., waterways and oceans
Municipal Solid Waste (MSW)
• This is trash or garbage.
• In 2008, the United States–residents,
businesses, and institutions–produced
approximately 250 million tons of MSW
(before recycling).
Figure 12-2 Municipal solid waste
generation rates, 1960–2008.
Source: Adapted and reprinted from US Environmental Protection Agency, Solid Waste and Emergency Response (5306P). Municipal Solid Waste Generation,
Recycling, and Disposal in the United States: Facts and Figures for 2008. Washington, DC: US Environmental Protection Agency; 2009, p.1.
Components of the MSW Stream
(Examples)
•
•
•
•
Packaging
Furniture
Clothing
Bottles
•
•
•
•
Food waste
Papers
Batteries
Organic materials
Total MSW Generation (by Material), 2008-250 Million Tons (Before Recycling)
Source: Adapted and reprinted from U.S. Environmental Protection Agency, Solid Waste and Emergency Response (5306P).
Municipal Solid Waste Generation, Recycling, and Disposal in the United States: Facts and Figures for 2008. Washington, DC:
U.S. Environmental Protection Agency; 2009, p. 4.
The Four Dimensions
of MSW Disposal
•
•
•
•
Recycling
Landfilling
Composting
Combustion
Major Components of MSW Management
Source: Reprinted from U.S. Department of Energy, Energy Information Administration, Office of Coal, Nuclear, Electric
and Alternate Fuels. Available at:
http://www.eia.doe.gov/cneaf/solar.renewables/renewable.energy.annual/backgrnd/fig8.htm. Accessed May 2, 2010.
EPA’s Hierarchy for Management
of MSW
• From more favored to less favored
– Source reduction
– Recycling
– Disposal
Source Reduction
• Source reduction refers to “reducing the
amount of waste created, reusing whenever
possible, and then recycling what is left.”
Components of Source Reduction
• Two important components
– Waste reduction aims to reduce the amount of
waste produced at the source.
– Waste recycling refers to reuse of materials in the
waste.
Programs for Recycling Wastes
Source: Adapted and reprinted from U.S. Environmental Protection Agency, Recycle City, Dumptown Game. Available at:
http://www.epa.gov/recyclecity/gameint.htm. Accessed March 25, 2010.
Recycling
• The EPA defines recycling (reuse) as the
process of “Minimizing waste generation by
recovering and reprocessing usable products
that might otherwise become waste (i.e.,
recycling of aluminum cans, paper, and
bottles, etc.).”
Advantages of Recycling
• Reduces emissions of greenhouse gases
• Prevents pollution generated by the use of new
materials
• Decreases the amount of materials shipped to landfills
• Preserves natural resources
• Opens up new manufacturing employment
opportunities
• Saves energy
Recycling Rates
Source: Adapted and reprinted from U.S. Environmental Protection Agency, Solid Waste and Emergency Response (5306P). Municipal Solid Waste
Generation, Recycling, and Disposal in the United States: Facts and Figures for 2008. Washington, DC: U.S. Environmental Protection Agency;
2009, pp. 2, 3.
Composting
• “the aerobic biological decomposition of
organic materials [e.g., leaves, grass, and food
scraps] to produce a stable humus-like
product….Biodegradation is a natural, ongoing
biological process that is a common
occurrence in both human-made and natural
environments.”
• Produces a useful material that resembles soil
and that can be used in gardening.
Composting Success
• The state of Massachusetts has one of the most
successful composting programs in the U.S.
• Yard and food waste are composted,
preventing 37,500 tons of waste from entering
the disposal process and saving approximately
$2 million each year.
Landfill Design
• A landfill is composed of four major parts:
–
–
–
–
a bottom liner
a system for collecting leachates
a cover
an appropriate location that minimizes the
contamination of groundwater by materials
released from the site
Side View of a Landfill
Source: Adapted and reprinted from U.S. Department of Energy, U.S. Energy Information Administration. Energy
explained. Available at: http://tonto.eia.doe.gov/energyexplained/images/landfill.gif. Accessed May 4, 2010.
How a Landfill Works
• The bottom is lined with a dense layer of clay
and sealed with thick plastic sheeting to contain
leaks of hazardous materials.
• A flexible membrane liner holds in toxic
chemicals that might contaminate groundwater.
• A leachate sump collects leachates, which then
can be subjected to further treatment.
How a Landfill Works (continued)
• Garbage is piled up in rows; bulldozers and
rollers compact the garbage; at the end of the
day, the newly added garbage is covered with
soil and other materials.
• After the garbage is covered, anaerobic
bacteria aid in the decomposition of organic
materials and produce methane gas.
Dangers Associated with Landfills
• Air pollution and groundwater contamination
• Leachates, which may include:
– Toxic heavy metals
– Solvents and cleaning agents.
• Gases such as methane
Gaseous Emissions from Landfills
• Methane, volatile organic compounds (VOCs),
and other gases
– Methane vented from landfills poses a fire hazard
and is a greenhouse gas.
• VOC emissions
– Potentially carcinogenic
– May cause complaints about odors and symptoms
of respiratory irritation
Megafills
• Megafills take in from 5,000 to 10,000 tons of
trash per day and serve regional needs for
waste disposal.
• Tend to be more cost effective than incinerators
for disposal of solid waste.
Federal Landfill Standards
1. Location restrictions
2. Composite liners
requirements
3. Leachate collection and
removal systems
4. Groundwater
monitoring
requirements
5. Closure and
postclosure care
requirements
6. Corrective action
provisions
7. Financial assurance
Source: Adapted and reprinted from US Environmental Protection Agency. Municipal Solid Waste:
Landfills. Available at: http://www.epa.gov/osw/nonhaz/minicipal/landfill.htm. Accessed March 25. 2010.
Incineration
• Can be used to generate energy while at the
same time reducing the volume and weight of
waste.
• No attempt is made to separate the trash into
components; at the high temperatures of
incinerating plants, glass and aluminum in the
trash melt.
• Metals from the residues of combustion can be
recycled into scrap metal; remaining ash is
deposited in landfills.
Disadvantages of Incineration
• Emissions may be potentially hazardous to
human health and the environment.
• Toxic materials emitted may cause air
pollution or be deposited on the land.
Disposal of Hazardous
Materials and Wastes
• Hazardous wastes are disposed of legally in
the U.S. by:
–
–
–
–
Discarding them on the surface of the land
Storing them in slurry ponds
Dumping them into landfills or into the ocean
Incineration
Sources of Hazardous Wastes
• Hazardous materials used in the home-Pesticides, cleaning products, automotive
products, painting supplies, and other
flammable and nonflammable products
• Medical waste--Chemicals, infectious agents,
and radioactive materials
• Industrial hazardous waste--Heavy metals
from plating operations, toxic chemicals,
solvents, and residues from the manufacture of
pesticides
Sources of Hazardous Wastes
(continued)
• Radioactive waste--Spent nuclear fuel and
tailings from uranium processing
• Mining wastes and extraction wastes--Toxic
chemicals left over from mining operations
include acids and heavy metals.
Scope of the Hazardous
Waste Problem
• More than 400 million tons are generated
worldwide on an annual basis.
• Developed world generates most of the toxic
wastes.
• Some developing nations will take hazardous
wastes for cash payments; this practice may
endanger the health of the local population.
Uncontrolled Hazardous Waste
Sites in the U.S.
• An estimated 40,000 of these sites have been
reported to federal agencies.
• 1,300 sites are on the National Priorities List
(NPL).
• Superfund legislation mandates the cleanup of
hazardous waste sites.
Toxic Waste Dump and Workers in
Protective Clothing
Source: Reprinted from CDC Public Health Image Library, ID #1193 and ID #1530. Available at: http://phil.cdc.gov/Phil/details.asp. Accessed
March 25, 2010.
Impacts of Uncontrolled Sites
•
•
•
•
Potential adverse human health effects
High costs of cleanup
Reductions in property values
Potential ecological damage
Love Canal
• Was the former site for disposal of toxic
wastes
• Later used for residential construction
• Became identified with hazardous chemical
exposures and their possible harmful
influences on human health
• Led to the creation of the Superfund
Medical Waste
• “any solid waste that is generated in the
diagnosis, treatment, or immunization of
human beings or animals, in research
pertaining thereto, or in the production or
testing of biologicals….”
• More than 3.5 million tons are produced
annually in the U.S.
Definition of Sewage
• “The waste and wastewater produced by
residential and commercial sources and
discharged into sewers.”
History of Sewage Disposal
• Romans constructed a sewage system and
aqueducts.
• The Middle Ages were a time of regression for
the sanitary disposal of sewage.
• During the 19th century, methods for the
treatment of sewage began to improve.
Modern Sewage Treatment
and Disposal
• Modern technology involves :
– Removing solids
– Deactivating microbes
– Producing wastewater that can be returned safely
to waterways or in some cases can be reused or
recycled.
Primary Stage of
Sewage Treatment
• The primary stage aims to remove large
materials, which can be composted or shipped
to landfills.
Secondary Stage of
Sewage Treatment
• Secondary processing promotes microbial
digestion of organic material that remains in
the sewage.
• Microorganisms that are present naturally in
sewage or that may be added to enhance
microbial action aid in the digestion of the
liquor during aeration.
Tertiary Stage of
Sewage Treatment
• Tertiary (high-level) processing is directed at
removal of remaining solids and
microorganisms from the liquid portion of
sewage.
• Various methods exist for high-level
processing including filtration through sand
and charcoal filters and deactivation of
microorganisms (disinfection) by using
chlorine or UV radiation.
Sewage Processing System
Primary
Tank
Aeration
Source: Author. Courtesy of the Irvine Ranch Water District, Irvine, California.
Secondary
Processing
Empty
Aeration
Tank
U.S. Sewage Requirements
• Most jurisdictions in the U.S. require that
wastewater receive at least secondary
treatment.
• Water that has received only primary treatment
is not recommended for any use and generally
needs secondary or tertiary treatment for
common purposes such as landscape irrigation.
Other Methods for Sewage
Disposal
• Composting toilets
• Septic systems
Hazards Posed by Animal Wastes
• Contamination from nutrients, organic
materials, microorganisms, residues of
medicines, and potentially toxic gases
• Workers in contact with livestock exposed to
pathogenic microorganisms
• Creation of antibiotic-resistant bacteria that
may endanger human health