8.10 - Waste Reduction Methods

Learning Objectives

I. The 3 R’s: Reduce, Reuse, Recycle

• 1. Reduce (Most Sustainable): Reducing waste means cutting down the energy inputs needed to create, ship, and market new goods. Examples: using a reusable metal water bottle instead of plastic, or riding a bike instead of driving to cut gasoline use.

• 2. Reuse: Reusing a product involves no new energy investment. Examples: washing and reusing plastic takeout containers, or buying secondhand clothing.

• 3. Recycle (Least Sustainable): Recycling means taking old solid waste, processing it, and converting it into raw materials for new products. It’s the least sustainable of the three because it still requires a considerable electricity input.
• Pros: It reduces demand for new materials and conserves landfill space. Recycling metals and wood is especially valuable because it cuts the need to harvest those materials, which prevents the associated habitat destruction and soil erosion.
• Example: Making aluminum cans from recycled aluminum takes more than 90% less energy than making new aluminum from bauxite ore, and less bauxite has to be strip mined.
• Cons: It’s costly and takes significant energy for shipping, sorting, and processing. Cities have to find vendors willing to buy the recycled materials, and sometimes recycling gets produced faster than it can be sold, so it just ends up thrown away anyway. Contamination, like food waste or residue, can ruin an entire batch of recycled goods.

II. Composting (Organic Waste Reduction)

• Process: Composting is decomposition under controlled conditions. The bacteria need oxygen, so the organic waste pile has to be regularly mixed or rotated for aerobic decomposition to happen.

• Benefits: Composting reduces landfill volume and produces a rich material that enriches soil. Because it’s aerobic, it produces carbon dioxide ($\text{CO}_2$) rather than methane ($\text{CH}_4$), so it cuts the release of that potent greenhouse gas that anaerobic decomposition in landfills would otherwise generate.

• Drawbacks: Composting can produce smells and may draw rodents or vermin.

III. E-Waste Management

• Hazard: E-waste, meaning discarded electronics like phones and computers, contains heavy metals like lead, mercury, and cadmium. These are endocrine disruptors and neurotoxicants, and they can contaminate groundwater if they leach through the soil in landfills.

• Ideal Handling: E-waste should be collected in specialized facilities, dismantled, and recycled to recover valuable metals like gold, silver, and platinum.

• By the numbers: The world produced a record 62 million tonnes of e-waste in 2022, and only about 22% of it was documented as properly collected and recycled (Global E-waste Monitor 2024).

• Environmental Injustice: Developed nations often ship e-waste to developing nations that lack strong environmental protection laws and worker safety laws. In those nations, cheap labor gets exploited to extract the metals, or the waste is simply piled up and burned or dumped, which lets toxic metals into the ecosystem.

IV. Waste-to-Energy Systems

• Incineration (Burning Trash): Burning trash reduces waste volume and releases heat, which can generate electricity through the familiar sequence: heat, water, steam, turbine, generator, electricity.

• Methane Harvesting: Methane gas produced by anaerobic decomposition in landfills can be harvested with pipes and piped into a natural gas-fired power plant. This generates electricity and reduces the volume of gas in the landfill, which is good because it also reduces demand for new fracking or fossil fuel mining.

• Restoring landfills as parks: Once a landfill is full and capped, the land on top can be restored as habitat or turned into a park, with the methane and leachate systems still running underneath. New York City’s Fresh Kills Landfill on Staten Island, once one of the largest landfills in the world, closed in 2001 and is being turned into Freshkills Park, about 2,200 acres, almost three times the size of Central Park.

V. Practice Calculation (Dimensional Analysis)

1. Set up the units so everything cancels except tons per year:
$$50{,}000 \text{ people} \times \frac{4.9 \text{ lb}}{\text{person} \cdot \text{day}} \times \frac{365 \text{ days}}{1 \text{ yr}} \times \frac{1 \text{ ton}}{2{,}000 \text{ lb}} = 44{,}712.5 \text{ tons/yr}$$

2. Round: the town produces about 44,700 tons of MSW per year.

3. Composting 30% diverts $44{,}712.5 \times 0.30 \approx 13{,}400$ tons per year from the landfill.

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