Waste
Waste disposal and management is a major issue facing society today. The amount of waste generated and disposed of annually continues to increase, with industries generating over 7.6 billion tons of industrial solid waste each year and it is estimated that over 40 million tons of this waste is hazardous. Nuclear and medical wastes are also increasing in quantity every year. Developed nations generate more waste per capita than developing nations, with the United States generating the most waste per capita of any country.
Landfilling has traditionally been the main method of waste disposal, but it is becoming less desirable and feasible due to declining landfill capacity, stricter environmental regulations, and public opposition. As a result, alternative waste management methods such as recycling, composting and incineration are being considered. However, it is important to note that not all waste is the same, and different materials require different methods of disposal.
In natural systems, everything flows in a natural cycle of use and reuse. However, solid waste is a human concept and refers to materials that are deemed useless or worthless. It is important to reduce the amount of waste produced and recycle valuable resources contained in the waste in order to maintain a livable and sustainable environment.
Sources of Solid Waste
There are several sources of solid waste, including:
- Residential: This includes waste generated by households, such as food scraps, paper, plastics, and other household items.
- Commercial: This includes waste generated by businesses, such as packaging materials, office paper, and other business-related items.
- Industrial: This includes waste generated by factories and industrial processes, such as chemicals, machinery parts, and manufacturing by-products.
- Construction and Demolition: This includes waste generated by the construction and demolition of buildings, such as wood, bricks, and other construction materials.
- Agricultural: This includes waste generated by farming operations, such as crop residue, livestock manure, and other agricultural by-products.
- Medical: This includes waste generated by hospitals and other healthcare facilities, such as medical equipment, sharps, and other hazardous materials.
- Municipal: This includes waste generated by municipal services, such as street sweeping, park maintenance, and other public services.
- Electronic: This includes waste generated by electronic devices, such as computers, smartphones, and other electronic equipment. All sources of solid waste have an impact on the environment and human health, and proper management and disposal of waste is crucial to minimize negative impacts.
Types of Solid Waste
Solid waste can be classified into two main categories: non-municipal and municipal solid waste.
Non-municipal solid waste is the discarded solid material from industry, agriculture, mining, and oil and gas production, and it makes up almost 99 percent of all the waste in the United States. Some common examples of non-municipal waste include construction materials, waste-water sludge, ash, scrubber sludge, and pesticide containers.
Municipal solid waste, on the other hand, is made up of discarded solid materials from residences, businesses, and city buildings. It makes up a small percentage of waste in the United States, only a little more than one percent of the total. Municipal solid waste consists of materials from plastics to food scraps, with paper being the most common waste product, accounting for about 40 percent of the total. Other common components include yard waste, plastics, metals, wood, glass, and food waste. The composition of municipal waste can vary depending on the region and the season.
Hazardous waste is a subset of solid waste that can be detrimental to human health and the environment. It is defined as materials that are toxic, carcinogenic, mutagenic, teratogenic, highly flammable, corrosive, or explosive. Hazardous waste is subject to strict regulations in the United States, but there are some materials that are excluded from these regulations such as hazardous household and small business waste, and mining waste.
Waste Disposal
Solid waste can be disposed of in several ways, including landfilling, ocean dumping, and incineration.
Landfilling is the most common method of disposal, where solid waste is either dumped in a hole or canyon area or a giant mound, and then covered with clay or plastic to prevent redistribution by animals or the wind. Sanitary landfills have layers of clay, sand, and plastic to prevent contamination of local aquifers, and a methane collection system to collect the gas produced by the decomposition of the waste. Secure landfills are designed to handle hazardous wastes and have thicker plastic and clay liners to prevent contamination.
Ocean dumping was a popular method of disposal for coastal communities, but it is now banned in the United States due to pollution problems it created.
Incineration is another method of disposal, where waste is burned at high temperatures to reduce its volume. This method significantly reduces the volume of solid waste but can release air pollutants.
In addition, there are other alternative methods such as recycling, composting, and waste-to-energy conversion. However, each method has its own advantages and disadvantages, and the most suitable method depends on the type and composition of the waste and the local regulations and infrastructure.
Mass Burn Incinerators
Mass burn incinerators are facilities that are used to burn municipal solid waste (MSW) at high temperatures. They are designed to reduce the volume of waste by up to 85 percent. This is done by burning the waste at temperatures of over 1000 degrees Celsius. The ash that remains after the burning process is much more compact than unburned solid waste.
Mass burn incinerators are considered to be one of the most efficient ways to reduce the volume of MSW. However, they also have some disadvantages. For example, they produce pollutants, such as particulate matter, dioxins, and heavy metals, which can harm human health and the environment. Additionally, they require a significant amount of energy to operate, and the ash produced must be disposed of in landfills.
In the US, about 15 percent of the municipal solid waste is incinerated, however, this method has been decreasing in popularity, primarily due to the environmental concerns and the associated costs of operating these facilities.
Effects of Improper Waste Disposal
Improper waste disposal and unauthorized releases can have serious negative effects on the environment and human health. When waste is not disposed of properly, it can lead to pollution of air, water, and soil, and can harm wildlife and ecosystems.
For example, used rubber tires can become breeding grounds for mosquitoes that can spread disease when they are not disposed of properly. Similarly, when waste is dumped into the ocean, it can lead to large floating islands of trash that can harm marine life and damage ecosystems. Wildlife can become entangled in the waste or ingest it, which can lead to injury or death.
Past practices of improper waste disposal have led to numerous contaminated sites where soils and groundwater have been contaminated, posing a risk to public safety. The EPA has identified over 1,400 sites that require immediate cleanup under the Superfund program National Priority List (NPL). Additionally, the Department of Defense maintains 19,000 sites, many of which have been extensively contaminated from a variety of uses and disposal practices.
Accidental spills of hazardous wastes and nuclear materials due to human activities or natural disasters can also cause enormous environmental damage. For example, the 1986 Chernobyl disaster in Ukraine and the 2011 Tohoku earthquake and tsunami in Fukushima, Japan, resulted in severe environmental damage and long-term health effects for the local population.
It is important to continue to enforce regulations and develop new strategies to ensure proper waste disposal and minimize negative impacts on the environment and human health.
Examples of Improper Waste Disposal Around the World
Some specific examples of where improper waste disposal has occurred include:
- Love Canal, New York: In the 1950s, a chemical company disposed of hazardous waste in a canal in Niagara Falls, New York. The waste was not properly contained, and eventually leached into the surrounding soil and groundwater. As a result, residents in the area were exposed to a range of toxic chemicals, leading to a variety of health problems.
- Bhopal, India: In 1984, a gas leak at a chemical plant in Bhopal, India, released a toxic cloud of methyl isocyanate gas, killing thousands of people and injuring hundreds of thousands more. The disaster was caused by a lack of safety measures at the plant, as well as poor waste management practices.
- Gulf of Mexico oil spill: In 2010, an oil spill in the Gulf of Mexico resulted from a blowout at an offshore drilling rig. The spill released millions of barrels of oil into the ocean, causing widespread environmental damage to the Gulf's ecosystems and wildlife.
- Hanford Nuclear Reservation, Washington: In the 1940s and 1950s, the US government produced plutonium at the Hanford Nuclear Reservation in Washington state. The nuclear waste was not properly stored and it contaminated the land and water and still poses a risk for the nearby communities and the environment
- Landfills in developing countries: many developing countries lack proper waste management infrastructure, leading to the proliferation of unregulated, overcrowded landfills. These landfills often do not have proper liners or leachate collection systems, leading to contamination of soil and groundwater.
Frequently Asked Questions
What is solid waste and how is it different from liquid or gas waste?
Solid waste is any discarded material that’s not a liquid or a gas—think household trash, industrial scrap, agricultural residue, and e-waste (old phones, TVs, computers). Unlike liquid waste (sewage, industrial effluent) or gas emissions (CO2, methane), solid waste is a physical, often bulky material that’s handled by collection, recycling, composting, incineration, or landfilling. On the AP CED, municipal solid waste is usually put in sanitary landfills that include a bottom liner (plastic or clay), leachate collection, stormwater controls, a cap, and methane collection—because solids can produce leachate that contaminates groundwater and decompose to release methane gas (a potent GHG). Incineration reduces volume but creates air pollutants and ash residue. For AP review, see the Topic 8.9 study guide (https://library.fiveable.me/ap-environmental-science/unit-8/solid-waste-disposal/study-guide/x0oYfNWgX71t8XELmhY2), the unit overview (https://library.fiveable.me/ap-environmental-science/unit-8), and practice questions (https://library.fiveable.me/practice/ap-environmental-science).
Why do landfills contaminate groundwater and what gases do they release?
Landfills contaminate groundwater because rainwater and buried waste produce a toxic liquid called leachate. As water percolates through trash it dissolves chemicals (heavy metals, nutrients, organic pollutants), and if the bottom liner or leachate-collection system fails or is overwhelmed, that contaminated water can reach groundwater (CED: leachate collection system, bottom liner). Decomposition and compaction also create pressure that pushes leachate downward. Landfills release gases from microbial decomposition—especially methane (CH4) from anaerobic breakdown and carbon dioxide from aerobic/anaerobic processes. They can also emit hydrogen sulfide (H2S) and various volatile organic compounds (VOCs) and odors. Modern sanitary landfills include caps and methane-collection systems to reduce these emissions (EK STB-3.K.2 & STB-3.K.4). For more AP-aligned review, see the Topic 8.9 study guide (https://library.fiveable.me/ap-environmental-science/unit-8/solid-waste-disposal/study-guide/x0oYfNWgX71t8XELmhY2) and extra practice (https://library.fiveable.me/practice/ap-environmental-science).
What's the difference between a regular dump and a sanitary municipal landfill?
A regular dump is basically an open pile of trash with little to no engineering control—trash is just dumped, compacted maybe, and left. That lets rainwater percolate through the waste, creating toxic leachate that can contaminate groundwater, and it allows uncontrolled anaerobic decomposition that releases methane and other gases and odors. A sanitary municipal landfill is engineered to prevent those problems: it has a bottom liner (clay or synthetic) to block groundwater contamination, a leachate collection system, stormwater management, a final cap to seal closed cells, and a methane collection system to capture gas for flaring or energy (CED EK STB-3.K.2 and EK STB-3.K.4). For the AP exam, know those components and why they reduce groundwater contamination and emissions (see MCQ that tests liners in the CED). Review the Topic 8.9 study guide for more detail (https://library.fiveable.me/ap-environmental-science/unit-8/solid-waste-disposal/study-guide/x0oYfNWgX71t8XELmhY2) and practice questions (https://library.fiveable.me/practice/ap-environmental-science).
Can someone explain all the parts of a sanitary landfill like the liner and leachate collection system?
A sanitary landfill has several engineered parts you should know for the APES CED (EK STB-3.K.4): - Bottom liner (plastic geomembrane and/or compacted clay): a low-permeability layer that prevents waste liquids from seeping into groundwater. - Leachate collection system: a sloped layer of gravel with perforated pipes above the liner that collects contaminated liquid (leachate). Collected leachate is pumped out and treated to avoid groundwater contamination. - Stormwater management system: channels, berms, and drains that keep surface runoff from flooding the landfill and mixing with wastes (limits leachate production). - Cap (final cover): layered soil and impermeable materials placed over closed cells to minimize water infiltration, stabilize the site, and support vegetation. - Methane collection system: vertical and horizontal gas wells and piping that capture landfill gas (mainly CH4) for flaring or energy use, reducing greenhouse-gas emissions and explosion risk. These are on the AP exam blueprint (Unit 8 Topic 8.9). For a quick review, see the Fiveable topic guide (https://library.fiveable.me/ap-environmental-science/unit-8/solid-waste-disposal/study-guide/x0oYfNWgX71t8XELmhY2). For more practice, check the APES practice problems (https://library.fiveable.me/practice/ap-environmental-science).
What is e-waste and why is it a bigger problem than regular trash?
E-waste = discarded electronic devices (TVs, cell phones, computers). It’s a bigger problem than regular trash because devices contain toxic metals (lead, mercury, cadmium) and persistent chemicals that can leach into groundwater or release hazardous gases if burned. E-waste also has valuable rare metals that are lost when not properly recycled, increasing pressure on mining. Many municipal sanitary landfills don’t accept certain electronics, so e-waste is often illegally dumped or shipped to countries with informal recycling—where burning and acid baths pollute air, soil, and water. Plus e-waste grows faster than other waste because devices have short lifespans. For the AP exam, link this to EK STB-3.K.3 (definition), landfill contamination (EK STB-3.K.2), and illegal dumping (EK STB-3.L.3). Review Topic 8.9 on Fiveable (study guide: https://library.fiveable.me/ap-environmental-science/unit-8/solid-waste-disposal/study-guide/x0oYfNWgX71t8XELmhY2) and practice questions (https://library.fiveable.me/practice/ap-environmental-science).
I'm confused about how decomposition works in landfills - what factors affect it?
Decomposition in landfills depends mostly on what’s in the trash and the conditions microbes need to break it down (EK STB-3.L.1). Key factors: - Waste composition: food/yard waste and paper decompose fast; plastics, glass, metals hardly decompose. - Oxygen: aerobic breakdown (with O2) is faster and produces CO2; anaerobic (no O2) is common in landfills and produces methane—why landfills have methane collection systems (CED EK STB-3.K.4). - Moisture: microbes need water; too dry = slow decomposition, too wet = leachate problems. - Temperature & pH: warmer, neutral pH speeds microbial activity. - Particle size & compaction: smaller pieces and less compaction increase surface area for microbes; heavy compaction and daily cover slow decomposition. - Time scale: organic matter may take years; synthetic plastics can last centuries. For AP review, this maps to EK STB-3.L.1 and landfill design (EK STB-3.K.1–K.4). For a focused study guide, see Fiveable’s Topic 8.9 page (https://library.fiveable.me/ap-environmental-science/unit-8/solid-waste-disposal/study-guide/x0oYfNWgX71t8XELmhY2). For extra practice, try the Unit 8 practice problems (https://library.fiveable.me/practice/ap-environmental-science).
Why do we incinerate some waste instead of just putting everything in landfills?
You incinerate some waste because it solves problems landfills can’t. Burning (incineration/waste-to-energy) significantly reduces the volume of trash and can generate electricity, so it’s used when landfill space is limited or for wastes that aren’t accepted in sanitary landfills (like some hazardous or infectious wastes). But incineration creates ash residue and releases air pollutants (particulates, dioxins, heavy metals) so emissions control is required—that tradeoff is exactly what EK STB-3.K.2 and EK STB-3.L.2 cover in the CED. Landfills, even sanitary ones (liner, leachate and methane collection, cap), risk groundwater contamination and methane release, so managers choose incineration sometimes to shrink waste and recover energy while accepting stricter air-pollution controls. For more AP-aligned review on disposal methods and effects, see the Topic 8.9 study guide (https://library.fiveable.me/ap-environmental-science/unit-8/solid-waste-disposal/study-guide/x0oYfNWgX71t8XELmhY2) and practice questions (https://library.fiveable.me/practice/ap-environmental-science).
What are the pros and cons of incineration vs landfills for solid waste disposal?
Incineration - Pros: greatly reduces waste volume, can generate energy (waste-to-energy), and lowers the need for landfill space. Good for hazardous or bulky wastes that shouldn’t go to sanitary landfills. - Cons: produces ash residue that still needs disposal, releases air pollutants (dioxins, particulates, heavy metals), and can be costly to run and scrub. AP tip: know that incineration “significantly reduces volume but releases air pollutants” (EK STB-3.L.2). Sanitary landfills - Pros: engineered with a bottom liner (plastic/clay), leachate collection, stormwater management, cap, and methane collection system to limit groundwater contamination and capture methane for energy (EK STB-3.K.4). - Cons: can still contaminate groundwater if systems fail, release landfill gases (methane), and take long to decompose depending on anaerobic/aerobic conditions (EK STB-3.L.1). Some items (e-waste, tires) aren’t accepted and get illegally dumped (EK STB-3.L.3). For AP review, study the sanitary landfill components and trade-offs on the Topic 8.9 study guide (https://library.fiveable.me/ap-environmental-science/unit-8/solid-waste-disposal/study-guide/x0oYfNWgX71t8XELmhY2) and practice questions (https://library.fiveable.me/practice/ap-environmental-science).
Why can't we put tires in regular landfills and what problems do they cause?
You can’t usually put tires in regular sanitary landfills because they cause physical and environmental problems. Tires trap air and don’t compact, creating voids that can collapse or cause “floaters” that punch through liners and caps (risking groundwater contamination). They also collect rainwater and become mosquito-breeding sites, spreading disease (EK STB-3.L.3). Tire piles are a big fire risk—tire fires burn hot, are hard to extinguish, and release toxic gases and particulate air pollution. Tires also slow microbial decomposition (affecting landfill decomposition factors, EK STB-3.L.1) and can interfere with leachate and methane collection systems used in modern landfills (EK STB-3.K.4). For AP prep, remember tires are often banned from sanitary landfills and may require recycling, retreading, or specialized disposal—details in the Topic 8.9 study guide (https://library.fiveable.me/ap-environmental-science/unit-8/solid-waste-disposal/study-guide/x0oYfNWgX71t8XELmhY2). For extra practice, check unit resources (https://library.fiveable.me/ap-environmental-science/unit-8) and practice questions (https://library.fiveable.me/practice/ap-environmental-science).
How does plastic waste end up forming those huge garbage patches in the ocean?
Most plastic reaches the ocean from land—trash dumped illegally, trash that blows out of landfills, and waste carried by rivers from cities and farms. Because plastics are buoyant and resist microbial decomposition, they float at or near the surface for decades to centuries instead of breaking down like food waste (EK STB-3.K.1, EK STB-3.L.1). Surface currents and wind then push floating plastic into large circulating systems called subtropical gyres; these concentrate debris into areas like the Great Pacific Garbage Patch. Sunlight and waves fragment larger pieces into microplastics but don’t fully biodegrade them, so the plastic accumulates and harms wildlife through entanglement and ingestion (EK STB-3.L.4). For AP review, study ocean dumping and the Great Pacific Garbage Patch in the Solid Waste Disposal guide (https://library.fiveable.me/ap-environmental-science/unit-8/solid-waste-disposal/study-guide/x0oYfNWgX71t8XELmhY2) and more unit resources (https://library.fiveable.me/ap-environmental-science/unit-8). Practice applying these ideas with Fiveable practice problems (https://library.fiveable.me/practice/ap-environmental-science).
What happens to animals when they eat or get tangled in ocean waste?
When animals eat or get tangled in ocean waste, the effects can be severe and often fatal. Ingestion: animals (sea turtles, seabirds, fish, marine mammals) can mistake plastics for food; small plastics and microplastics can block digestive tracts, reduce feeding, cause malnutrition, internal injury, and bioaccumulate toxins up the food web. Entanglement: animals can get wrapped in nets, ropes, or six-pack rings, which restrict movement, cause wounds and infections, reduce feeding ability, and lead to drowning or starvation. These outcomes link to Topic 8.9 concepts like ocean dumping and the Great Pacific Garbage Patch and illustrate how illegal or poor disposal creates wildlife harm. For AP exam relevance, you should be able to describe these biological effects and connect them to sources and solutions (sanitary landfills vs. ocean dumping, waste reduction). Review the Topic 8.9 study guide (https://library.fiveable.me/ap-environmental-science/unit-8/solid-waste-disposal/study-guide/x0oYfNWgX71t8XELmhY2) and Unit 8 overview (https://library.fiveable.me/ap-environmental-science/unit-8); practice questions are at (https://library.fiveable.me/practice/ap-environmental-science).
I don't understand the leachate collection system - how does it work and why do we need it?
Leachate collection systems catch and remove the polluted liquid that forms when rainwater percolates through trash and dissolves chemicals. In a sanitary landfill (EK STB-3.K.4) you have a bottom liner (clay or plastic) to block downward flow, then a network of perforated pipes laid on that liner. Leachate drains into those pipes, flows to a sump, and gets pumped out for treatment or safe disposal. We need it because untreated leachate can seep past liners or around faults and contaminate groundwater with heavy metals, toxins, and pathogens (EK STB-3.K.2). On the AP exam, know the components (liner, leachate collection, methane collection, cap) and the pollutant/groundwater risk for questions tied to Topic 8.9. For a quick review, see the Topic 8.9 study guide (https://library.fiveable.me/ap-environmental-science/unit-8/solid-waste-disposal/study-guide/x0oYfNWgX71t8XELmhY2) and practice problems (https://library.fiveable.me/practice/ap-environmental-science).
What kinds of air pollutants are released when we burn trash in incinerators?
Incineration (municipal waste-to-energy) cuts trash volume but emits several air pollutants you should know for the CED: particulate matter (PM), carbon monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO2), and volatile organic compounds (VOCs). It can also produce highly toxic persistent organics—dioxins and furans—and release heavy metals like mercury and lead. Acid gases and ash residue (fly ash and bottom ash) are byproducts too; fly ash can carry concentrated toxins and must be landfilled or treated. EK STB-3.L.2 notes incineration reduces volume but releases these pollutants, so pollution control (filters, scrubbers, and ash management) matters. For a quick topic review, see the Topic 8.9 study guide (https://library.fiveable.me/ap-environmental-science/unit-8/solid-waste-disposal/study-guide/x0oYfNWgX71t8XELmhY2) and check practice problems (https://library.fiveable.me/practice/ap-environmental-science).
Why do some countries still dump waste in the ocean if it's so bad for the environment?
Mostly it’s about money, infrastructure, and enforcement. Proper disposal (sanitary landfills with liners, leachate and methane-collection systems) and incineration cost money, technology, and regulation. Some countries lack the funds or facilities, so ocean dumping—or illegal dumping—becomes the cheapest option. Weak laws, poor enforcement, and corruption make it easier, and international shipping of waste can shift the problem to countries with fewer controls. The result: large floating trash patches (e.g., the Great Pacific Garbage Patch), wildlife entanglement and ingestion, and degraded marine ecosystems (CED: ocean dumping, Great Pacific Garbage Patch, wildlife impacts). For AP prep, know the trade-offs and public-policy drivers (economic vs. environmental) and be ready to link disposal methods to effects in FRQs. For a quick review, see the Topic 8.9 study guide (https://library.fiveable.me/ap-environmental-science/unit-8/solid-waste-disposal/study-guide/x0oYfNWgX71t8XELmhY2) and practice questions (https://library.fiveable.me/practice/ap-environmental-science).
How do methane collection systems in landfills work and why is methane dangerous?
Methane collection systems capture gas produced by anaerobic decomposition in landfills. Pipes (vertical wells and horizontal collectors) are placed through the trash layer and connected to blowers or pumps. A cap (final cover) helps direct gas into the pipes; collected gas is either flared (burned) or used for energy (reduces landfill methane emissions and recovers energy). This system is part of a sanitary landfill’s methane collection system (CED EK STB-3.K.4). Methane is dangerous because it’s a potent greenhouse gas (much stronger than CO2 over 20–100 years), so it drives climate change, and it’s flammable/explosive in confined spaces—posing explosion and safety risks. It can also displace oxygen in enclosed areas, creating asphyxiation hazards. Harvesting landfill methane for energy is an AP-acceptable mitigation strategy (see unit content and solutions in the study guide: https://library.fiveable.me/ap-environmental-science/unit-8/solid-waste-disposal/study-guide/x0oYfNWgX71t8XELmhY2). For extra practice, check AP practice problems (https://library.fiveable.me/practice/ap-environmental-science).