Describe primary secondary and tertiary processes for sewage treatment

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
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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).
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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.

Figure 12-2 Municipal solid waste generation rates, 1960–2008.

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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.

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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
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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.

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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.
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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
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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

Location restrictions

Composite liners requirements

Leachate collection and removal systems

Groundwater monitoring requirements

Closure and postclosure care requirements

Corrective action provisions

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.

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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.”
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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.
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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

Secondary Processing

Aeration

Empty Aeration Tank

Source: Author. Courtesy of the Irvine Ranch Water District, Irvine, California.

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