7.3 Solid Waste

In January 2018, China, which had for decades been the world's largest importer of recyclable waste, suddenly banned imports of most scrap plastic and tightened contamination limits on almost everything else. Within a year, its plastic waste imports had collapsed by more than 95%.

Where did all that waste, previously shipped to China from wealthier countries, go instead?

Use of natural resources generates waste, and that waste can be classified in two different ways: by source, meaning where it was generated, or by type, meaning what kind of material or hazard it presents. The two systems cut across each other: a single item of waste has exactly one source but can belong to more than one type category, and knowing both is what actually determines how it should be handled. Sources include domestic waste (from households), industrial waste (from manufacturing and production processes) and agricultural waste (from farming activity, including crop residue and animal manure). Types include e-waste (discarded electronics), food waste, and biohazardous waste (material capable of spreading disease, such as medical waste).

Sort each item below by its source.

Solid domestic waste (SDW) typically contains a wide mix of material types within a single household's bin: paper, cardboard, glass, metal, plastics, organic matter (kitchen or garden waste), packaging, construction debris and clothing. This diversity is exactly why municipal waste management is difficult: a single collection and disposal system has to somehow deal with materials that decompose at wildly different rates, that have wildly different recycling value, and that in some cases (construction debris, certain packaging) do not fit neatly into standard household collection at all.

The volume and composition of waste varies over time and between societies due to socio-economic, political, environmental and technological factors. Socio-economic factors are the strongest driver of the pattern above: as household income rises, consumption of packaged and manufactured goods rises with it, and the proportion of a household's waste that is organic falls as manufactured, packaged material takes up a larger share. Political factors matter through regulation: a government that bans single-use plastic bags or requires manufacturers to take back packaging directly changes what ends up in the waste stream. Environmental factors include climate and geography: a rural, agricultural society generates a different waste profile from a dense coastal city with heavy imported-goods consumption. Technological factors cut both ways, since new packaging materials and single-use products increase waste volume, while better product design, repairability and recycling technology can reduce it.

The production, treatment and management of waste has environmental and social impacts, and those impacts may be experienced in a completely different location from where the waste was actually generated. Waste is routinely transported long distances, usually from high-income to low-income countries, and this pattern raises real questions of environmental injustice: the burden of managing, and being harmed by, someone else's waste falls disproportionately on people who had no say in producing it and often see little of its economic benefit.

Agbogbloshie, a scrapyard in Accra, Ghana, is a documented real example. Ghana imports roughly 215,000 tonnes of used consumer electronics from Western Europe each year and generates a further 129,000 tonnes of its own e-waste annually, much of which historically passed through informal recycling sites like Agbogbloshie, once one of the largest e-waste processing sites in Africa, handling around 15,000 tonnes of e-waste a year at its peak. Roughly 6,000 workers there dismantled electronics by hand, often burning cable insulation over open fires to recover the copper inside, releasing toxic smoke containing lead and other heavy metals with essentially no protective equipment. The site was formally dismantled by Ghanaian authorities in 2021, but e-waste processing activity in the surrounding area has continued. The core injustice is structural, not incidental: the health costs of processing a smartphone or a laptop are borne by workers thousands of kilometers from the country where that device was purchased and used.

Ecosystems can absorb some waste. A forest floor breaks down fallen leaves, a river dilutes and disperses small quantities of organic matter, and soil microorganisms decompose biodegradable material into harmless simpler substances over time. Pollution occurs specifically when harmful substances are added to an environment at a rate faster than the environment can transform them into harmless substances, overwhelming that natural absorptive capacity. Two concepts describe how quickly this transformation happens: biodegradability, whether and how readily a material can be broken down by natural biological processes at all, and half-life, the time it takes for half of a given quantity of a substance to break down or decay, a concept borrowed from chemistry that is useful for comparing how long different pollutants persist in an ecosystem.

Sort each material below by roughly how long it persists in the environment before breaking down. These are commonly cited estimates: actual rates vary enormously with temperature, moisture, sunlight exposure and burial conditions.

Preventative strategies for waste management, which stop waste or its harm from being created in the first place, are more sustainable than restorative strategies, which clean up or restore damage after it has already occurred. Preventative strategies include altering human behavior, such as reducing consumption in the first place, or controlling the release of pollutants, such as proper waste disposal procedures that prevent contamination before it happens. Restorative strategies include the clean-up and restoration of already-damaged systems, such as attempts to remove plastic already accumulated in oceanic garbage patches. Reduction in the consumption of goods, and therefore in the production of waste in the first place, is consistently the most sustainable option of all, because it avoids the resource use, energy cost and residual pollution involved in every later stage of the waste life cycle, including recycling itself.

Sort each strategy below into the correct category.

Different waste disposal options carry different advantages and disadvantages for societies and ecosystems. There is no single "best" option in every context: the right choice depends on local geography, available infrastructure, cost, and what type of waste is involved.

Sustainable options for managing solid domestic waste can be actively promoted in societies through several distinct policy tools: taxes, incentives, social policies, legislation, education, campaigns, and improved access to disposal facilities. These tools are not interchangeable: each targets a different reason people fail to manage waste sustainably, whether that reason is cost, convenience, habit, or simple lack of awareness.

Match each policy below to the strategy type it best represents.

The principles of a circular economy provide a holistic perspective on sustainable waste management. In a traditional linear economy, resources move in one direction only: extract, manufacture, use, dispose. A circular economy instead designs products and systems so that materials are kept in use for as long as possible, through repair, reuse, remanufacturing and, only as a last resort, recycling, minimizing the amount of virgin material extracted and waste ultimately sent to disposal.

Click the six steps below in the correct order to build the resource path of a circularly managed smartphone, from manufacture through end-of-life recovery back into a new product.