Modern landfills do not intentionally burn trash; their fundamental purpose is to contain and bury solid waste for long-term storage. Modern landfilling is a highly engineered system focused on isolating the waste from the surrounding environment. This method relies on decomposition and containment, which is the direct opposite of using fire.
Landfills Versus Incineration
Landfilling and incineration are distinct approaches to managing municipal solid waste. Landfilling is a disposal technique centered on depositing waste into designated, highly regulated areas of land. The goal is long-term containment and isolation from the ecosystem through engineered barriers.
Incineration is a form of thermal treatment, often referred to as waste-to-energy. This process involves the controlled burning of waste at extremely high temperatures, which significantly reduces the volume and mass of the original material. The heat generated during combustion is captured to produce steam, which powers turbines to generate electricity.
The main difference lies in the use of fire: incineration is designed for controlled combustion to recover energy, while a landfill is engineered to prevent fire. Although incineration reduces the bulk of the waste, the resulting ash still requires final disposal in a landfill.
Operational Mechanics of a Modern Landfill
A modern sanitary landfill is a complex, multi-layered structure designed to safely isolate waste and manage its byproducts. Operation begins with the creation of a “cell” where waste is deposited and compacted using specialized heavy equipment. High compaction rates reduce the volume of the waste mass and exclude oxygen, which slows decomposition and prevents fire.
At the close of each working day, the newly deposited trash is covered with a layer of material known as the daily cover. This cover typically consists of soil, but alternative materials like synthetic fabrics or ash may also be used. The daily cover is applied to control odors, deter pests, and act as a fire break to suppress combustion.
As organic materials decompose anaerobically (without oxygen), they generate landfill gas, composed of roughly 50% methane and 50% carbon dioxide. This potent greenhouse gas is managed through a collection system of perforated pipes installed throughout the waste mass. The collected gas is either flared to convert the methane into less potent carbon dioxide or processed for use as a renewable energy source.
Another byproduct of decomposition is leachate, a liquid that forms as water percolates through the waste mass and collects contaminants. Landfills include an intricate liner system—often a composite of clay and durable synthetic sheets—at the base, along with a drainage layer, to capture this liquid. The collected leachate is then removed and transported to a treatment facility to prevent groundwater contamination.
Accidental Fires and Hazards
While the design of a modern landfill is meant to prevent fire, accidental combustion remains a significant operational hazard. Fires are categorized as surface fires, occurring near the daily cover, or subsurface fires that smolder within the buried waste mass. A common cause of surface fires is the dumping of “hot loads,” which are materials already smoldering upon arrival.
Subsurface fires are particularly dangerous and difficult to extinguish because they occur deep within the compacted waste, often fueled by concentrated methane gas. These fires can be initiated by spontaneous combustion, which happens when heat generated by decomposition builds up without dissipating. The presence of oxygen, often caused by cracks in the soil cover, can increase the internal temperature and lead to ignition.
Safety protocols are implemented to minimize these risks, including the prohibition of hazardous materials and rapid response to incoming hot loads. Extinguishing a subsurface fire is challenging, often requiring heavy equipment to excavate the burning material and use soil to smother the flames by cutting off the oxygen supply. These accidental fires release a complex mix of toxic fumes, including carbon monoxide and volatile organic compounds, posing a considerable environmental and public health threat.