Biodegradable waste includes any organic matter in waste which can be broken down into carbon dioxide, water, methane or simple organic molecules by micro-organisms and other living things by composting, aerobic digestion, anaerobic digestion or similar processes. In waste management, it also includes some inorganic materials which can be decomposed by bacteria. Such materials include gypsum and its products such as plasterboard and other simple organic sulfates which can decompose to yield hydrogen sulphide in anaerobic land-fill conditions.
In domestic waste collection, the scope of biodegradable waste may be narrowed to include only those degradable wastes capable of being handled in the local waste handling facilities.
Biodegradable waste can be found in municipal solid waste (sometimes called biodegradable municipal waste, or as green waste, food waste, paper waste and biodegradable plastics). Other biodegradable wastes include human waste, manure, sewage, sewage sludge and slaughterhouse waste. In the absence of oxygen, much of this waste will decay to methane by anaerobic digestion.
In many parts of the developed world, biodegradable waste is separated from the rest of the waste stream, either by separate curb-side collection or by waste sorting after collection. At the point of collection such waste is often referred to as green waste. Removing such waste from the rest of the waste stream substantially reduces waste volumes for disposal and also allows biodegradable waste to be composted.
Biodegradable waste can be used for composting or a resource for heat, electricity and fuel by means of incineration or anaerobic digestion. Swiss Kompogas and the Danish AIKAN process are examples of anaerobic digestion of biodegradable waste. While incineration can recover the most energy, anaerobic digestion plants retain nutrients and make compost for soil amendment and still recover some of the contained energy in the form of biogas. Kompogas produced 27 million Kwh of electricity and biogas in 2009. The oldest of the company's lorries has achieved 1,000,000 kilometers driven with biogas from household waste in the last 15 years.
The main environmental threat from biodegradable waste is the production of landfill gases. Landfill gas (LFG) is generated by degradation of the biodegradable waste fraction, and is influenced by waste physicochemical composition and environmental variables. Studies have shown that the actual rate of gas production in a landfill is a function of waste composition (organic content), age (or time since placement), climate variables, moisture content, particle size, compaction and buffering capacity. LFG mainly consists of carbon dioxide (CO2), methane (CH4) and numerous trace components. Methane is the second most important anthropogenic greenhouse gas after CO2 and is responsible for approximately 40% of global warming over the past 150 years.  Further, for the past 25 years, global anthropogenic methane emissions have exceeded those from natural sources. Emissions from landfill sites account for 30% of the total anthropogenic methane emissions in Europe, 34% of those in the US, and 10% of anthropogenic methane emissions worldwide. Landfill gas emissions are one of the largest anthropogenic sources of methane especially because of food waste.  Globally, if food waste could be represented as its own country, it would be the third largest greenhouse gas emitter, behind China and the U.S.  It has become important to reduce food waste related emissions by distinguishing between waste arising at two different stages in the food system: pre-consumer waste (from the manufacturing, processing, distribution and retailing of food) and consumer waste (arising in households, after purchase). A distinction is also made between two different types of emission; embedded emissions (generated during the production of food that is wasted) and waste disposal (from the processes of disposing waste food).