Solid and Hazardous Waste Study Guide
Solid Waste Overview and Global Trends
Waste generation is directly correlated with economic prosperity and development levels.
Highly developed countries produce significantly more waste compared to less prosperous nations.
Materials that are typically thrown away in affluent societies would be repaired, reused, or recycled in less affluent nations due to resource scarcity and economic necessity.
Types and Composition of Solid Waste
Municipal Solid Waste (MSW):
Defined as the combined residential and commercial waste produced within a municipal area.
It constitutes less than of the total waste generated.
Sources include homes, offices, stores, restaurants, schools, hospitals, prisons, libraries, and other commercial/institutional facilities.
Typical contents: Paper and paperboard, yard waste, plastics, food waste, metals, rubber, leather, textiles, wood, and glass.
Nonmunicipal Solid Waste:
This category identifies waste generated by large-scale industry, agriculture, and mining operations.
U.S. MSW Production Trends (–):
Total production increased steadily every five years until the late .
Individual per-capita waste production also rose, reaching a plateau around the year .
Between the years and , there was a noted decrease in both total and per-capita production, which is likely attributable to the global economic downturn.
Disposal of Solid Waste: Traditional Methods and Landfills
Waste is generally regarded as material that is no longer useful and requires disposal via four primary methods: dumping, burying, burning, or recovery.
Open Dumps:
An older method that is now illegal in most jurisdictions.
These sites were unsanitary, malodorous, and attracted pests like rats and flies.
Environmental hazards included the release of methane gas and the leaching of hazardous materials into soil and groundwater.
Frequent fires occurred, releasing acrid and toxic smoke.
Sanitary Landfills:
These have replaced open dumps and currently receive approximately of municipal waste.
Design and Construction:
Modern landfills use a double-liner system at the bottom consisting of repeating layers: Plastic, clay, plastic, clay.
Unlike open dumps, they are designed not to pollute local surface or groundwater.
Waste is spread in thin layers, compacted into small sections called cells, and covered daily with a shallow layer of soil.
They include sophisticated leachate collection systems and leak detection systems between clay liners.
Management and Challenges:
Leachate: Liquid that seeps through solid waste; it must be collected and treated.
Methane: Produced during decomposition; it can be collected and used to generate energy.
Siting: Landfills eventually fill up, and "NIMBY" (Not In My Backyard) attitudes make finding new locations difficult.
Seepage from older, unlined landfills remains a threat to water supplies.
Special Problems: Plastics and Incineration
The Problem of Plastic:
The volume of plastic in solid waste is increasing, with packaging accounting for more than half of it.
Plastics are chemically stable and do not decompose naturally.
Some regions have banned specific types, such as PVC.
Alternatives:
Photodegradable: Breaks down when exposed to light, but ineffective if buried in a landfill.
Biodegradable: Decomposed by microorganisms; however, preliminary studies indicate these do not actually break down effectively in the anaerobic conditions of a landfill.
Incineration:
This process reduces the volume of solid waste by .
Benefits: Generates heat for buildings or electricity (waste-to-energy); paper, plastic, and rubber are the best fuels.
Drawbacks: Air pollution (CO, particulates, heavy metals); produces toxic ash that requires hazardous waste disposal; high operational costs for pollution control.
Items that must be removed before burning include glass, food waste, and mercury-containing items like batteries and fluorescent lights.
Types of Incinerators:
Mass Burn: Large furnaces that burn all waste except very large unburnables like refrigerators.
Modular: Smaller, pre-fabricated, and less expensive.
Refuse-derived Fuel: Burns only the combustible portion after removing glass and metals.
Recovery: Composting and Recycling
Composting:
Best method for recovering yard waste (a substantial portion of MSW), food scraps, sewage sludge, and manure.
Converts waste into soil conditioners (compost or mulch) that provide nutrients to soil.
Widely used for landscaping in public parks and sold to home gardeners.
Recycling Materials:
Conserves natural resources; for example, recycling one ton of paper saves: trees, of water, of energy, and of landfill space.
Paper: The U.S. recycles of paper/paperboard; Denmark recycles .
Glass: The U.S. recycles . Glass is crushed into cullet, which is cheaper than virgin materials. Colors must be separated to maintain value.
Metals: Aluminum is the greatest success in the U.S., with of beverage cans recycled. Recycling aluminum uses far less energy than raw production. Other metals include lead, gold, silver, iron, steel, and zinc. New steel contains an average of recycled scrap.
Plastic: Only of plastic packaging is recycled in the U.S. Economics depend on petroleum prices. There are common types of plastic that must be separated before processing.
Tires: Used for retreading, playground equipment, trash cans, garden hoses, and rubberized asphalt. Can also be burned for electricity.
Waste Prevention and Source Reduction
Waste Prevention Goals:
Reduce total waste: Purchase products with less packaging or those that are repairable/durable.
Decrease consumption: Questioning the necessity of new purchases.
Source Reduction:
Designing and manufacturing products to decrease waste.
Aluminum Cans: Now lighter than in the .
Dematerialization: Making smaller, more durable products to replace larger, wasteful ones.
Reuse: Example includes refillable glass bottles returned to bottlers.
Integrated Waste Management:
A consolidated program combining various techniques: waste minimization, source reduction, recycling, incineration, and landfilling.
Hazardous Waste
Also known as toxic waste; accounts for approximately of the U.S. solid waste stream.
Includes discarded chemicals that are reactive, corrosive, ignitable, or toxic in solid, liquid, or gas form.
There are different chemicals in existence, many with unknown toxicity levels.
Polychlorinated Biphenyls (PCBs):
A group of industrial chemicals produced in the U.S. between and .
Banned by the EPA in the , but they do not degrade rapidly and persist in landfills and sewers.
Health risks: Liver/kidney damage, skin and eye issues, reproductive harm, and endocrine disruption (thyroid). They may be carcinogenic.
Management and Regulation of Toxic Waste
Management Strategies:
Source Reduction (Best): Using "Green Chemistry" to redesign processes and use nonhazardous materials.
Toxicity Reduction (Second Best): Chemical, biological, or physical treatment (e.g., incineration, though ash remains hazardous).
Long-term Storage (Third Option): Toxic waste landfills or deep-well injection.
Disposal Technologies:
Toxic Waste Landfills: Feature double clay and plastic liners with leak detection and leachate detoxification.
Deep-well Injection: For liquid waste like explosives/pesticides, injected between impermeable layers deep underground.
Chemical Accidents:
The National Response Center (NRC) must be notified of incidents.
Principle of Inherent Safety: Redesigning industrial processes to make accidents less likely; a form of source reduction.
Federal Laws:
Resource Conservation and Recovery Act (RCRA): Passed in (amended ). EPA identifies hazardous waste and sets standards for treatment and recycling (reformed ).
Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA/Superfund): Established in . Deals with past/abandoned waste sites. Provides for cleanup of sites where waste has polluted soil or groundwater. The most dangerous sites are put on the National Priorities List.