Incineration: Incineration, also called waste-to-energy, is a process where plastic waste is burned at high temperatures, usually between 800 to 1000 degrees Celsius. Modern incinerators are equipped with pollution control devices to capture pollutants like heavy metals, particulate matter, and gases in the flue gases produced from burning waste. The heat generated from burning can be used to produce electricity. Incineration reduces the volume of waste by about 90% and the weight by about 75%. It does produce air pollutants and produces ash that may contain toxic elements which require proper disposal. The ash may still need to be sent to a landfill.

Pyrolysis: Pyrolysis is a process where plastic waste is thermally decomposed in an oxygen-free environment at temperatures between 300-800°C. It breaks down the plastic into its basic chemical components like gas, liquid and solid residues. The gases produced can be used to generate energy. The liquid component, called bio-oil can be further refined into transportation fuels or chemical feedstocks. The solid residue contains carbon and ash that can be used for construction materials or backfilled at landfills. Pyrolysis allows plastic to be converted into useful byproducts rather than just seen as waste. It is an energy intensive process and the end products require further refining before use.

Gasification: Similar to pyrolysis, gasification involves the thermal decomposition of plastic waste, but at higher temperatures of 800-1000°C with a controlled amount of oxygen, steam or carbon dioxide. This converts the plastic into syngas, a mixture of carbon monoxide, hydrogen and carbon dioxide. The syngas can then be further processed into transportation fuels through Fischer-Tropsch synthesis. The process helps divert plastic waste from landfills and produces a synthetic fuel. Gasification plants require large capital investments and the syngas needs cleaning before fuel production. There are also air pollution issues around particulates and dioxins that need to be addressed.

Plasma Pyrolysis: In this advanced form of pyrolysis, plastic waste is processed in an oxygen-free plasma reactor heated to extreme temperatures of 10,000-15,000°C. At such high temperatures, the molecular and crystal structure of plastics breaks down completely into simpler molecules within a few seconds. The breakdown results in more energy-dense syngas than conventional pyrolysis or gasification. The ultra-high temperatures in the plasma core destroys all environmental pollutants. Complex equipment and high energy costs make plasma pyrolysis currently not commercially viable on a large scale. Research continues to optimize the process.

Landfills: A common plastic disposal method in many countries has been to dump plastic waste in sanitary landfills. Here, plastic will slowly break down over hundreds of years and eventually degrade. They are not truly degradable in landfill conditions and take up a lot of landfill space for a very long time. As plastic degrades, it also releases greenhouse gases like methane which contribute to global warming. Landfilling also does not derive any value from plastic waste and is seen more of a temporary solution than a proper management approach.

Ocean Dumping: Unfortunately some plastic waste eventually ends up in the ocean through illegal dumping, windblown litter or as marine debris from landfill runoff or rivers. In the ocean, smaller plastic pieces break down into microplastics which are eaten by marine life and enter the food chain. Toxic chemicals in plastic also leach into the ocean over time. Ocean dumping of plastic waste needs to be strictly prevented to avoid damaging marine ecosystems.

Deep Well Injection: Some outdated plastic waste disposal methods involved drilling deep disposal wells underground and injecting molten plastic under high pressure. This was found to contaminate groundwater supplies over time. It is now an illegal waste disposal option due to environmental and health risks from subsurface migration of chemicals. Stringent laws exist worldwide against underground plastic dumping near potable water sources.

While recycling and composting should be priorities, emerging disposal methods like advanced pyrolysis, gasification and plasma treatment are showing promise to safely process plastic into useful byproducts and reduce long term dependence on landfills or incineration. Ongoing research aims to optimize these waste-to-energy technologies and make them commercially viable on scale for sustainable plastic management globally.