Solid waste — core idea

· Guiding question: How can societies sustainably manage waste?
· Solid waste is generated when humans use natural resources; managing it sustainably means reducing waste production and limiting harm to ecosystems and societies.
· Exam answers should link solid waste to resource use, pollution, environmental justice, waste management strategies and the circular economy.

Classifying waste

· Waste can be classified by source: domestic, industrial and agricultural.
· Waste can also be classified by type: e-waste, food waste and biohazardous materials.
· Solid domestic waste (SDW) = waste produced by households and communities.
· Typical SDW includes paper, cardboard, glass, metals, plastics, organic kitchen/garden waste, packaging, construction debris and clothing.

Why waste varies between societies

· Volume and composition of waste vary over time and between societies.
· Socio-economic factors: income, consumption level, urbanization, lifestyle and access to goods affect how much waste is produced.
· Political factors: laws, taxes, recycling targets, waste collection systems and bans affect waste generation and disposal.
· Environmental factors: local climate, land availability and ecosystem sensitivity affect which disposal methods are used.
· Technological factors: product design, packaging materials, e-waste growth, recycling technology and waste-to-energy systems change waste composition.

Environmental and social impacts of waste

· Waste management can cause air pollution, water pollution, soil contamination, habitat degradation, GHG emissions, odour and disease risks.
· Impacts may occur far from where waste was generated because waste is often transported long distances.
· Waste may be exported from high-income countries to low-income countries, creating environmental injustice if receiving communities face pollution, unsafe work or weak regulation.
· Strong exam answers should identify who benefits, who is harmed and where impacts occur.

Pollution, biodegradability and half-life

· Pollution occurs when harmful substances are added to the environment faster than they can be degraded, absorbed or transformed into harmless substances.
· Ecosystems can process some waste, but only within their assimilative capacity.
· Biodegradability = how quickly a material is broken down by biological processes.
· Half-life = time taken for half of a substance to decay or lose activity.
· Persistent pollutants with long half-lives or low biodegradability can accumulate and cause long-term harm.

Waste management hierarchy

· Preventative strategies are generally more sustainable than restorative strategies.
· Prevention/reduction is the best option: reduce consumption so fewer resources are extracted and less waste is produced.
· Reuse/repair extends product life and reduces demand for new raw materials.
· Recycling/composting recovers materials but still requires collection, sorting, energy and infrastructure.
· Recovery/waste-to-energy can reduce landfill volume and produce energy, but may produce emissions and ash.
· Disposal by landfill or unmanaged dumping is usually the least sustainable option.

This diagram shows why IB ESS prioritizes preventing waste before treating or disposing of it. Use it to explain why reducing consumption is more sustainable than cleaning up pollution after it occurs. Source

Preventative vs restorative strategies

· Preventative strategies stop or reduce waste before damage occurs, such as reduced consumption, product redesign, reuse, repair, recycling access and controlled disposal.
· Restorative strategies respond after damage has occurred, such as clean-ups, ecosystem restoration and attempts to remove waste from polluted environments.
· Prevention is more sustainable because it avoids resource extraction, transport, pollution and clean-up costs.
· Example exam phrasing: “Reducing the consumption of goods is the most sustainable option because it prevents waste at source.”

Waste disposal options: merits and demerits

· Landfill: cheap and widely used; disadvantages include leachate, methane, land use, odour, pests and long-term contamination risk.
· Incineration: reduces waste volume quickly; disadvantages include air pollution, toxic ash and high costs.
· Waste-to-energy: produces electricity/heat from waste; disadvantages include emissions, ash disposal and possible reduced incentive to reduce waste.
· Exporting waste: reduces pressure on domestic facilities; disadvantages include transport emissions, weak oversight and environmental injustice.
· Recycling: conserves resources and reduces landfill; disadvantages include contamination, energy use, downcycling and market dependence.
· Composting: treats organic waste and returns nutrients to soil; disadvantages include methane/odour if poorly managed and need for source separation.

This resource supports evaluation of waste-to-energy as both a disposal and energy-recovery strategy. It is useful for discussing trade-offs between reducing landfill use and managing emissions or ash. Source

Composting and organic waste

· Organic waste includes food scraps and garden waste.
· Composting uses biological decomposition to convert organic waste into a soil improver.
· Composting is most effective when organic waste is source-separated from plastics, metals and hazardous materials.
· Benefits: reduces landfill, lowers methane risk from buried organic waste, returns nutrients to soils and supports a more circular nutrient flow.
· Limitations: requires correct moisture, aeration, carbon:nitrogen balance and public participation.

This page supports the idea that food and garden waste can be treated biologically rather than sent to landfill. It is useful for explaining composting as a resource recovery strategy for organic SDW. Source

Promoting sustainable SDW management

· Sustainable SDW management can be promoted through taxes, incentives, social policies, legislation, education, campaigns and improved access to disposal facilities.
· Taxes/charges can discourage landfill or single-use items.
· Incentives can encourage repair, reuse, deposit-return schemes and recycling.
· Legislation can ban certain materials, require producer responsibility or set recycling targets.
· Education and campaigns can change behaviour, reduce contamination and increase participation.
· Access to disposal facilities matters because people are more likely to recycle/compost when systems are convenient, reliable and affordable.

Circular economy and solid waste

· Circular economy = a model that aims to reduce waste by keeping resources in use for as long as possible.
· It contrasts with the linear economy: take → make → use → waste.
· Circular principles include eliminating waste and pollution, circulating products and materials, and regenerating nature.
· Product recovery strategies include maintenance, repair, reuse, refurbishment, remanufacture, recycling and composting.
· Example resource pathway: aluminium can → manufacture → use → collection → sorting → remelting → new can, reducing the need for new bauxite mining.
· Circular economy answers should include a specific resource path from manufacture to recovery.

The butterfly diagram shows how circular economy systems keep materials cycling instead of becoming waste. It is especially useful for explaining product recovery strategies and why inner loops such as repair and reuse usually retain more value than recycling. Source

Exam evaluation points

· Best sustainability option: usually reduce consumption because it prevents waste at source.
· Landfill vs incineration: landfill risks leachate/methane/land use; incineration reduces volume but risks air pollution/ash/high cost.
· Recycling is not perfect: it depends on sorting, uncontaminated waste streams, energy, markets and product design.
· Environmental justice: waste impacts may be displaced onto poorer or less politically powerful communities.
· Systems thinking: waste links resource extraction, production, consumption, transport, disposal, pollution and feedbacks in ecosystems and societies.