8.9 - Solid Waste Disposal

Learning Objectives

I. Solid Waste (MSW) and E-Waste

• Solid waste: Any discarded material that isn’t a liquid or a gas. It comes from four main sectors: domestic (households), industrial, business (commercial), and agricultural. Household trash is only a small part of the total; mining, industry, and agriculture produce far more by weight.

• Municipal Solid Waste (MSW): This is the APES term for solid waste, garbage, trash, or “refuse,” generated largely by households, businesses, and schools.

• MSW Composition: In 2018 (the EPA’s most recent national numbers), the US generated about 292 million tons of MSW, about 4.9 pounds per person per day. About 23% was paper and cardboard, which is recyclable, and about a third was food waste (22%) and yard trimmings (12%), which are compostable. Plastics made up about 12%. Recycling paper and composting organic matter could significantly cut the MSW volume that ends up in landfills.

• E-Waste (Electronic Waste): Discarded electronics like old TVs, computers, phones, and tablets. Even though it’s less than 1% of US MSW by weight (about 2.7 million tons of consumer electronics in 2018), e-waste contains harmful metals and compounds that act as endocrine disruptors, including lead, cadmium, mercury, and PBDEs. E-waste should go to specialized recycling facilities so these compounds don’t leach out of landfills into groundwater or soil.

II. Sanitary Landfills (Developed Nations)

• Liner: A clay or plastic bottom liner is installed to try to keep pollutants from leaking into nearby groundwater or soil. That said, most landfills eventually experience some residual leakage anyway.

• Leachate Collection System: Pipes pump out leachate, which is water that drains through the garbage and carries pollutants with it. That water gets sent to a treatment system.

• Storm Water Collection System: Ditches and drains around and on top of the landfill catch rainwater and carry it away from the trash. Less water soaking through the garbage means less leachate to collect and treat.

• Methane Recovery System: Pipes harvest methane ($\text{CH}_4$) produced by anaerobic decomposition in the low-oxygen environment of the landfill. Methane is removed to prevent explosions, reduce volume expansion, and potentially get used to heat buildings or generate electricity.

• Clay Cap: Once the landfill is full, a clay cap and soil go over the top so the area can be reclaimed with natural vegetation, which also controls smell and deters animals.

III. Landfill Issues and Consequences

• Low Decomposition Rate: Landfills have really low rates of decomposition because the optimal combination of oxygen, moisture, and organic material is rarely there. That’s why 40-year-old newspapers pulled out of landfills are still legible, and why many manufactured items just aren’t biodegradable on any feasible human timeline.
• Composition matters: Food scraps and yard waste break down fairly fast when they get oxygen and moisture. Paper breaks down slowly, and plastic, glass, and metal barely break down at all. Since landfills are compacted, dry, and low in oxygen, even food can last for decades.

• Groundwater Contamination: Leachate leakage can contaminate groundwater with pollutants like heavy metals (lead, mercury), acids from batteries, medications, and bacteria.

• Greenhouse Gas Release: Aerobic decomposition releases carbon dioxide ($\text{CO}_2$), anaerobic decomposition also releases methane ($\text{CH}_4$), and both contribute to global climate change.

• NIMBY and Social Justice: The NIMBY (Not In My Backyard) phenomenon means no citizen wants a landfill near them, because of the sight, the smell, contamination fears, and the vermin they attract. Landfills are disproportionately sited in predominantly communities of color and low-income communities, which is where environmental and social justice issues intersect.

• Items to Divert: Toxic hazardous wastes like antifreeze and motor oil, plus metals like copper and aluminum, should be diverted from landfills. Old tires shouldn’t be left in piles because they collect water and turn into breeding grounds for mosquitoes.
• Illegal dumping: Since many landfills don’t accept tires, they often get dumped illegally in piles. Water collects inside them, and mosquitoes lay their eggs there. The Asian tiger mosquito, which can spread dengue and Zika, reached the US in 1985 in a shipment of used tires from Asia.

IV. Waste Incineration and Ocean Dumping

• Incineration: Waste can be burned to reduce volume by up to 90%, or to generate electricity. But burning releases air pollutants like $\text{CO}_2$, particulate matter, SOx, and NOx.

• Bottom Ash Risk: The leftover bottom ash is toxic, containing concentrated heavy metals like lead, mercury, and cadmium. This ash gets stored in ponds that risk flooding and releasing toxicants into nearby ecosystems.

• Illegal Ocean Dumping: Happens in countries without strong environmental enforcement. It creates large patches of garbage that can suffocate organisms that get tangled in the waste or swallow it, and it limits light penetration into the water.
• Example (Great Pacific Garbage Patch): Ocean currents called gyres collect floating trash in the middle of the oceans. The largest patch, between Hawaii and California, covered about 1.6 million square kilometers (about three times the size of France) and held an estimated 80,000 tonnes of plastic in a 2018 study. Most of it is scattered pieces, not a solid island, and lost fishing nets make up almost half its mass. Sea turtles, seals, and seabirds get tangled in the nets and swallow the smaller pieces.