Solid Waste Disposal Methods: Landfills, Incineration, and Biogas

Every day, cities around the world generate millions of tonnes of solid waste. While reducing and recycling waste are ideal first steps, a large portion of what we discard still needs to be disposed of safely. That’s where solid waste disposal methods come in. From burying waste in engineered sites to burning it for energy or converting it into biogas, modern disposal techniques aim to handle waste responsibly while minimizing environmental harm. Let’s break down the four key methods: sanitary landfills, incineration, waste compaction, and biogas generation.

Sanitary landfills: controlled disposal on land 🔗

A sanitary landfill is an engineered method of disposing non-reusable, non-recyclable solid waste on land. Unlike open dumps, where garbage is left exposed to the elements, sanitary landfills involve spreading waste in thin layers, compacting it with heavy machinery, and covering it with soil at the end of each day. This controlled process helps prevent odours, deters pests, and limits windblown debris.

How a sanitary landfill is designed 🔗

Modern sanitary landfills are far more than holes in the ground. They are carefully planned and constructed with several protective features. According to the U.S. Environmental Protection Agency (EPA), key components include composite bottom liners (made of clay and synthetic materials) to prevent waste from contaminating groundwater, leachate collection and removal systems that sit on top of the liner, and groundwater monitoring wells to detect any potential leaks.

The process works in stages. Waste is dumped into a designated cell, spread in layers, and compacted by heavy machines. At the end of each working day, the compacted refuse is covered with a layer of soil or alternative daily cover material. Once a cell is completely full, it receives a final cap – similar to the bottom liner – to seal the waste and prevent water from entering.

Dealing with landfill gas and leachate 🔗

As waste decomposes inside a landfill, it produces two significant byproducts: leachate and landfill gas. Leachate forms when rainwater percolates through the waste and picks up dissolved chemicals, heavy metals, and organic pollutants. If the liner system fails, this contaminated liquid can reach groundwater.

Landfill gas is primarily composed of methane and carbon dioxide, generated through anaerobic decomposition. Methane is a potent greenhouse gas, so modern landfills install gas collection systems to capture it. Some facilities flare the gas, while others convert it into usable energy such as electricity or renewable natural gas, displacing fossil fuel consumption in the process.

Limitations of landfilling 🔗

Despite being one of the most commonly used waste disposal methods worldwide, landfilling has clear drawbacks. Suitable land near urban centres is increasingly scarce. Community opposition – often called the NIMBY (Not In My Back Yard) attitude – makes siting new landfills difficult. Additionally, even well-engineered landfills carry a risk of future liner failure, and waste stabilisation can take decades or even centuries.

Incineration: reducing waste through controlled combustion 🔗

Incineration is the process of burning solid waste at high temperatures in a controlled combustion chamber. The primary goal is volume reduction – incineration can reduce the solid mass of waste by 80-85% and its volume by up to 95-96%. What remains is incombustible residue in the form of bottom ash and fly ash, along with flue gases that must be treated before release.

How the incineration process works 🔗

The process typically involves several stages. First, incoming waste is sorted to remove bulky items and recyclables. It may also be shredded for more consistent burning. The prepared waste then enters a combustion chamber operating at temperatures between 850°C and 1,100°C, where organic materials break down into their basic chemical components.

After combustion, the hot flue gases are cooled – often through heat recovery systems that generate steam. This steam can drive turbines to produce electricity or provide district heating, making many modern incinerators function as waste-to-energy (WTE) facilities.

Pollution control in incineration 🔗

The biggest concern with incineration is air pollution. Flue gases from incinerators can contain nitrogen oxides, sulfur dioxide, heavy metals like mercury, particulate matter, and potentially harmful compounds like dioxins and furans. This is why pollution control equipment is essential.

Modern incineration facilities use a combination of technologies to manage emissions. These include scrubbers to neutralise acid gases, fabric filters or electrostatic precipitators to capture fine particles, and specialised systems to remove mercury and dioxins. The National Academies Press notes that modern municipal solid waste incinerators are typically equipped for particulate, acid gas, and dioxin and mercury removal. Regulatory agencies require continuous emission monitoring systems to ensure compliance with environmental standards.

Ash management 🔗

Incineration produces two types of ash. Bottom ash is the heavier residue left at the base of the combustion chamber, consisting of non-combustible materials like glass and ceramics. Fly ash, which is captured from the flue gas, is the more hazardous of the two, often containing concentrated heavy metals. Fly ash typically requires disposal in specially designed hazardous waste landfills, while bottom ash can sometimes be processed and reused in construction materials.

Waste compaction: squeezing more out of less space 🔗

Waste compaction is the process of compressing waste materials to significantly reduce their volume. Materials like aluminium cans, plastic bottles, cardboard, and other recyclables are pressed into dense blocks or bales using specialised machinery. While compaction is not a final disposal method on its own, it plays a critical support role in the waste management chain.

How compaction works 🔗

Compaction equipment ranges from small residential trash compactors to large industrial machines. In landfills, heavy steel-wheeled compactors spread and compress waste in layers. At recycling facilities, vertical or horizontal balers compress recyclable materials into neat, uniform bales. Non-compacted waste can occupy up to 20 times more space than compacted waste, which shows just how significant the volume reduction is.

Shredding often accompanies compaction. By first breaking waste into smaller pieces, the material compacts more tightly, resulting in denser blocks with fewer air gaps.

Benefits of waste compaction 🔗

Compaction offers several practical advantages. It reduces transportation costs since more waste fits into each collection vehicle, meaning fewer trips to landfills or recycling centres. It conserves landfill airspace, extending the operational life of existing disposal sites. For metals, compacting into dense blocks prevents oxidation by reducing the surface area exposed to air and moisture.

Compacted recyclable materials are also more attractive to recycling facilities. Neatly baled cardboard, plastic, or metal is easier to handle, store, and transport, and can even generate revenue for businesses. According to Compact and Bale, compaction allows for more efficient use of landfill space and helps extend the lifespan of existing sites.

Compaction as a pre-recycling step 🔗

In many waste management systems, compaction is not the end point – it is a stepping stone toward recycling. Compacted bales of aluminium, PET plastic, or corrugated cardboard are shipped to recycling plants where the materials are processed and reintroduced into manufacturing. This makes compaction a vital link between waste collection and material recovery.

Biogas generation: turning waste into renewable energy 🔗

Of all the disposal methods discussed here, biogas generation is perhaps the most forward-looking. Instead of simply disposing of waste, this process converts biodegradable organic waste – food scraps, animal manure, agricultural residues, and organic industrial waste – into a usable energy source.

The anaerobic digestion process 🔗

Biogas is produced through anaerobic digestion, a biological process in which microorganisms break down organic matter in the absence of oxygen. According to the Environmental and Energy Study Institute (EESI), this process takes place inside airtight containers called digesters, where bacteria and other microbes metabolise the organic material.

The process unfolds in three main stages. First, complex organic matter is broken down into simpler molecules like sugars through hydrolysis. Next, these molecules are converted into organic acids by acid-forming bacteria (acidogenesis). Finally, methane-producing bacteria called methanogens convert those acids into biogas during the methanogenesis stage.

What biogas contains and how it is used 🔗

Raw biogas typically contains 50-70% methane, 30-40% carbon dioxide, and trace amounts of other gases like hydrogen sulfide and water vapour. According to the U.S. Energy Information Administration (EIA), raw biogas can be burned directly for heating or electricity generation. With further treatment to remove impurities and carbon dioxide, it can be upgraded to renewable natural gas (RNG) with a methane content of 90% or higher, suitable for injection into natural gas pipelines or use as vehicle fuel.

The International Energy Agency (IEA) notes that biogas can be produced through biodigesters, landfill gas recovery systems, and wastewater treatment plants, each representing a different pathway for capturing energy from organic waste.

Environmental and economic benefits 🔗

Biogas generation offers multiple environmental advantages. It diverts organic waste from landfills, where it would otherwise decompose and release uncontrolled methane emissions. When biogas displaces fossil fuels for energy production, it further reduces net greenhouse gas emissions. The EESI estimates that processing just 100 tonnes of food waste per day through anaerobic digestion can generate enough energy to power 800 to 1,400 homes each year.

Beyond the gas itself, the process produces digestate – a nutrient-rich material that can be used as an agricultural fertiliser or soil amendment. This closes the loop on nutrients, returning them to farmland instead of sending them to landfills.

Feedstock matters 🔗

Not all organic waste digests equally well. Food waste, fats, oils, and greases break down more readily and produce higher biogas yields. Livestock manure is harder to digest but still widely used, especially on farms. Mixing multiple waste types in the same digester – a practice called co-digestion – can boost gas production and improve the overall efficiency of the process. Temperature also matters: digesters maintained at warmer temperatures (30-38°C) tend to break down waste more quickly.

Comparing these methods: which one fits where? 🔗

No single disposal method is a universal solution. Each has its strengths and trade-offs, and most waste management systems use a combination of these approaches.

Sanitary landfills remain the most common disposal option, especially in developing countries, because they are relatively affordable and technically straightforward. However, they consume large areas of land and carry long-term environmental risks. Incineration dramatically reduces waste volume and can recover energy, but it requires expensive pollution control systems and still produces ash that needs disposal. Waste compaction is not a standalone disposal method but an essential support tool that improves efficiency across the entire waste chain. Biogas generation is the most sustainable option for organic waste, converting what would otherwise be a pollutant into clean energy and useful byproducts.

The key takeaway is that effective solid waste management isn’t about choosing one method – it is about integrating multiple methods into a system that maximises resource recovery and minimises environmental harm.

What do you think? Given the environmental trade-offs of each disposal method, which approach do you believe should receive more investment in your region – and could a wider adoption of biogas generation meaningfully reduce our dependence on landfills?

References

1. https://www.britannica.com/technology/sanitary-landfill
2. https://www.epa.gov/landfills/municipal-solid-waste-landfills
3. https://earth911.com/business-policy/how-landfills-work/
4. https://en.wikipedia.org/wiki/Incineration
5. https://engsolutionsinternational.com/2025/05/23/what-is-incineration-in-waste-management/
6. https://www.ncbi.nlm.nih.gov/books/NBK233627/
7. https://en.wikipedia.org/wiki/Waste_compaction
8. https://www.compact-and-bale.com/blog/what-are-the-advantages-and-disadvantages-of-waste-compaction
9. https://www.eesi.org/papers/view/fact-sheet-biogasconverting-waste-to-energy
10. https://www.eia.gov/energyexplained/biomass/landfill-gas-and-biogas.php
11. https://www.iea.org/reports/outlook-for-biogas-and-biomethane-prospects-for-organic-growth/an-introduction-to-biogas-and-biomethane