Topic 8.9 Notes – Solid Waste Disposal

What Solid Waste Is

Solid waste is any discarded material that is not a liquid or gas. It comes from domestic, business, industrial, and agricultural sources.

Common examples include:

• Household trash like food scraps and broken items
• Packaging like cardboard, plastic wrap, and containers
• Industrial residues left from manufacturing
• Construction debris like wood, drywall, and concrete
• Agricultural waste such as manure or crop leftovers
• Discarded electronics like old devices

The key idea here is simple. Throwing something away does not make matter disappear. Waste gets moved, buried, burned, or concentrated somewhere else.

The disposal methods you need to know are:

• Sanitary landfilling
• Incineration
• Improper disposal such as illegal dumping and ocean dumping

Sanitary Landfills and How They Work

Landfills are the most common solid waste disposal method. In a sanitary landfill, waste is put in a specific area, compacted, and covered in sections called cells. This is very different from an open dump because it is engineered to limit pollution.

This cross-section highlights the main systems APES expects you to recognize, especially the liner, leachate collection, cap, and methane collection.

Modern sanitary landfill design

Main landfill parts

• Bottom liner
  Made of plastic, clay, or both. It helps separate waste from the soil and groundwater below.

• Leachate collection system
  Leachate is contaminated liquid formed when water moves through trash. Pipes collect it and send it away for treatment.

• Stormwater collection system
  Diverts runoff away from the landfill so less water enters the trash. Less water means less leachate forms.

• Cap
  Seals the landfill after it is full. It reduces water infiltration, erosion, and exposure of the waste.

• Methane collection system
  Captures landfill gas, especially methane from decomposition. This lowers fire, explosion, and greenhouse gas risks.

What can go wrong

Even sanitary landfills only reduce risk. They do not remove it.

• Liners can tear
• Pipes can clog
• Leachate can leak into soil and groundwater
• A groundwater plume can carry contamination to wells or connected surface water
• Methane and other gases can escape
• Closed landfills still need long-term monitoring

Landfill decomposition

Decomposition depends on what the trash is made of and the conditions microbes need.

• Biodegradable
  Food waste, paper, yard waste
• Slow or nondecomposing
  Plastics, glass, metals, many synthetics

Important conditions include:

• Moisture
• Temperature
• Oxygen
• pH
• Decomposers

Because landfill waste is tightly compacted, oxygen becomes scarce. That means anaerobic decomposition dominates, producing methane and carbon dioxide. One common mistake is thinking landfills make trash break down quickly. They often slow decomposition.

Other Disposal Methods and Their Effects

Incineration

Incineration means burning waste at high temperatures.

• Main benefit: greatly reduces waste volume
• Main costs: releases air pollutants and leaves behind ash that still needs disposal

Possible pollutants include:

• Particulate matter
• Carbon monoxide
• Nitrogen oxides
• Acidic gases
• Carbon dioxide
• Mercury
• Toxic compounds

The trade-off is classic APES. Less landfill space needed, but more air pollution risk.

Electronic waste

E-waste means discarded electronic devices.

Examples you need to know:

• Televisions
• Cell phones
• Computers

E-waste may contain hazardous substances such as lead and mercury. In landfills, those toxins can enter leachate. If burned, they can enter the air or ash.

Illegal dumping and rejected materials

Some items are not accepted in ordinary sanitary landfills. When dumped illegally, they bypass liners, gas controls, and leachate systems.

A required example is used rubber tires:

• They collect standing water
• That creates mosquito breeding grounds
• More mosquitoes can increase disease spread

Ocean Dumping and Why Disposal Method Matters

Some waste is dumped directly into the ocean. Marine debris also comes from runoff, rivers, shore litter, shipping, and fishing gear. Plastics are the big problem because they persist and break into smaller pieces very slowly.

Ocean currents and gyres concentrate this debris. The Great Pacific Garbage Patch is a broad region with lots of floating trash, especially plastics. The map below shows that it is spread across a large area between Hawaii and California. It is not a solid island.

Great Pacific Garbage Patch

Major biological effects:

• Entanglement in nets, lines, and debris
• Ingestion by birds, sea turtles, fish, and marine mammals
• Digestive blockage, false fullness, injury, or death

So the comparison is:

• Landfilling contains waste but risks leachate and methane
• Incineration reduces volume but creates emissions and ash
• Illegal dumping and ocean dumping have fewer controls and often cause more direct harm