Waste disposal is the final stage where materials are permanently placed or destroyed after all recovery efforts have been exhausted. The two primary methods employed globally for managing the vast majority of non-recycled waste streams are Landfilling and Thermal Treatment. These distinct processes address the challenge of waste volume and potential environmental impact.
Landfills The Most Common Disposal Method
Modern sanitary landfills are highly engineered facilities designed to contain waste and prevent contamination of the surrounding environment. The foundation is a composite liner system, typically consisting of compacted clay overlaid by a durable synthetic geomembrane. This layered barrier isolates the trash from the underlying soil and groundwater.
The waste is spread in thin layers, compacted by heavy machinery, and then covered with a layer of soil or alternative material daily. This covering helps to control pests, minimize odors, and prevent windblown debris. Within the sealed environment, the waste decomposes anaerobically (without oxygen).
This decomposition process generates landfill gas (LFG), a potent mixture of methane and carbon dioxide. Because methane is a powerful greenhouse gas, modern facilities employ an active collection system of vertical wells and horizontal pipes to draw the gas out. The collected LFG is frequently converted into energy (LFGTE) to generate electricity or heat.
Another byproduct is leachate, a highly contaminated liquid formed as rainwater percolates through the refuse. A separate collection system is built above the liner to capture this liquid before it breaches the barriers.
The collected leachate is then pumped to an on-site or off-site wastewater treatment plant for purification and safe release into the environment.
Thermal Treatment and Energy Recovery
Thermal treatment, used in Waste-to-Energy (WTE) facilities, involves controlled, high-temperature combustion of non-recyclable waste. This method dramatically reduces solid waste volume by up to 90%, significantly conserving landfill space. The process burns waste in a specialized furnace under controlled conditions, liberating heat energy.
The intense heat is directed to boilers containing water, converting it into high-pressure steam. This steam spins turbines connected to electrical generators, converting the trash’s stored energy into usable electricity. This energy recovery contributes to the electrical grid while addressing disposal needs.
Modern thermal facilities require advanced air pollution control systems to meet stringent environmental regulations. These systems use technologies like scrubbers, fabric filters, and activated carbon injection to remove pollutants. They ensure the emissions meet all regulatory limits before release.
The combustion results in ash, a non-combustible residue reduced to about 10% of the original volume. Ash separates into bottom ash (from the furnace) and fly ash (captured by pollution control equipment).
Bottom ash can sometimes be used in construction materials. However, the remaining ash, particularly fly ash, is managed and disposed of separately in a designated landfill.
Diversion and Reduction Strategies
Waste diversion encompasses proactive methods designed to keep materials out of the final disposal stream. These strategies conserve natural resources and reduce the overall burden on disposal infrastructure.
The primary diversion methods are prioritized because they conserve natural resources and decrease the volume of waste requiring final disposal.
Primary Diversion Methods
- Source reduction focuses on using less material, such as choosing products with minimal packaging.
- Reuse extends the life of a product by finding new applications, saving the energy and materials needed for replacement.
- Recycling involves collecting and processing materials like plastic, glass, and paper to manufacture new products.
- Composting is a specific method for organic waste, allowing food scraps and yard waste to decompose into a nutrient-rich soil amendment.
By emphasizing these upstream efforts, communities can significantly decrease the volume of waste. This action extends the operational lifespan of existing landfills.