Solid & Hazardous Waste

You’ll be able to

Describe how municipal solid waste is disposed of in landfills and incinerators
Explain the management of hazardous waste and the role of key U.S. laws
Calculate waste generation and the effect of recycling on landfill volume

Municipal solid waste and landfills

Municipal solid waste (MSW) is everyday trash — paper, food scraps, plastics, yard waste. Most is buried in sanitary landfills, which are engineered with a clay or plastic liner and a leachate collection system to keep contaminated liquid (leachate) from seeping into groundwater, plus systems to vent or capture the methane that forms as buried waste decomposes without oxygen. Landfills take up land, can leak, and generate greenhouse gases, but modern designs are far safer than the open dumps they replaced.

Incineration and reducing waste

The alternative to burial is incineration — burning waste, which reduces its volume by about 80–90% and can generate electricity (waste-to-energy). But incineration releases air pollutants and produces toxic ash that still needs disposal. The best strategies sit higher on the waste hierarchy: reduce, reuse, recycle, and compost. Recycling and composting divert material from landfills, save energy and raw materials, and cut emissions. E-waste (discarded electronics) is a fast-growing stream containing valuable metals but also toxic lead and mercury.

Hazardous waste and the laws

Hazardous waste is toxic, flammable, corrosive, or reactive material that threatens health and the environment. Two U.S. laws govern it. The Resource Conservation and Recovery Act (RCRA, 1976) tracks hazardous waste "cradle to grave," from generation to disposal, and sets standards for landfills. The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA, 1980) — the Superfund — funds the cleanup of abandoned toxic-waste sites and makes polluters liable for the cost. Together they aim to prevent new contamination and clean up old sites.

Waste generation and diversion

total waste = population × per-capita waste rate ; landfilled = total × (1 − recycling rate)

Multiply population by the per-person waste rate for the total, then subtract the recycled fraction to find what still reaches the landfill.

Worked example

A city of 50,000 people generates 2 kg of municipal solid waste per person per day. If the city recycles and composts 30% of its waste, how many metric tons reach the landfill each day? (1 metric ton = 1,000 kg.)

1.Total waste per day = population × per-capita rate = 50,000 × 2 kg = 100,000 kg.
2.Fraction sent to the landfill = 1 − 0.30 = 0.70.
3.Landfilled mass = 100,000 kg × 0.70 = 70,000 kg.
4.Convert to metric tons: 70,000 kg ÷ 1,000 = 70 metric tons per day.

Answer: 70 metric tons per day reach the landfill. Raising the recycling rate to 50% would cut that to 50 metric tons — showing how diversion directly extends a landfill’s lifespan.

Checkpoint

A sanitary landfill includes a bottom liner and a leachate collection system. What is the main purpose of these features?

Tip

Remember the waste hierarchy in order of preference: reduce → reuse → recycle/compost → incinerate (waste-to-energy) → landfill. The most sustainable options prevent waste in the first place; landfilling and incineration are last resorts that manage waste already created.

Checkpoint

Which U.S. law created the "Superfund" to clean up abandoned hazardous-waste sites and hold polluters liable for the cost?

On the exam

For waste calculations, compute the total first (population × per-capita rate), then apply the recycling rate to find what is diverted versus landfilled. Watch unit conversions (kg → metric tons is ÷1,000). Pair RCRA (cradle-to-grave management) with CERCLA/Superfund (cleanup of old sites).

Answer the 2 checkpoints as you read.