The term biodegradable is used to describe materials that decompose through the actions of bacteria, fungi, and other living organisms. Temperature and sunlight may also play roles in the decomposition of biodegradable plastics and other substances. If such materials are not biodegradable, they remain in the environment for a long time, and, if these same substances are toxic, they may pollute the soil and water. Some nonbiodegradable pollutants may be capable of causing harm to organisms in the environment.
Common, everyday substances that are biodegradable include food refuse, tree leaves, and grass clippings. Many communities now encourage people to compost these materials and use them as humus (an organic-rich material in soil) for gardening. Because plant materials are biodegradable, composting is one way to reduce amounts of solid waste that towns and cities otherwise have to dispose in landfills.
In many cases, scientists can come up with biodegradable alternatives to nonbiodegradable products. For example, when household detergents were developed and came into wide use, foam began to clog streams and sewage treatment plants. The foam was caused by the presence of a complex phosphate, sodium tripolyphosphate, an ingredient in the detergent that reacted with, and removed dirt from, the surfaces of clothes. These complex phosphates, collectively called surfactants for their actions on material surfaces, were not biodegradable, and appeared to be harming plants and fish in streams. Detergent manufacturers responded to the problem by replacing phosphates with enzymes like protease and amylase, which are biodegradable.
Nonbiodegradable plastics are a particular problem, because they take up so much room in landfills or require special handling at waste incinerators. Most plastics are petroleum-based, meaning they are made from oil and other petroleum products. Until recently, plastics have been nonbiodegradable. Today, however, various techniques for producing biodegradable plastics are being explored, developed, and marketed. In some cases, organic compounds like sugar, corn starch, silk, and bamboo are being incorporated into the plastic production process. This allows large pieces of plastic to break down into smaller units, but on a molecular level, many of these plastics remain nonbiodegradable. Other researchers have come up with non-petroleum based plastics, using bioengineered organisms, such as bacteria, to produce plastic. In some cases, enzymes produced by the same organism can be used to break down the biologically produced plastic. Currently, these plastics are expensive to produce, but as the technology becomes more readily available, they are likely to become much more common.
Governments and industries have taken various measures to replace nonbiodegradable materials with those that will degrade or decompose. For example, the plastic rings that bind six-packs of soda and beer are required by law to be biodegradable in Oregon and Alaska. Italy has banned all nonbiodegradable plastics. The packaging industry continues to experiment with biodegradable packaging for food and fast food. Several coalitions have been formed to address biodegradable products in the oil and plastics industries, and to evaluate the benefits of recycling stable but nonbiodegradable materials versus developing biodegradable substances that may be costly for both industry and the consumer. The Council for Solid Waste Solutions and the Council on Plastics and Packaging in the Environment are action groups led by industry. Environmental groups like Keep America Beautiful also advocate recycling out of concern that biodegradability tells consumers littering is acceptable, but really, toxic chemicals that may leach out of biodegradable substances can poison groundwater. Interestingly, grain growers and processors strongly favor biodegradable plastics because in some cases, corn starch is used to replace some of the plastic resin during manufacture.
Successful moves toward biodegradable substances have been made in some markets. Europeans have used degradable plastic shopping bags as mulch to cover new crops in the spring since 1975. Lawn bags that degrade would benefit the composting business because nonbiodegradable bags have to be removed before yard waste can be composted. In landfills, where bagged yard waste occupies approximately 20% of the space, decomposing waste and degradable bags produce methane gas that can be recovered and sold for power generation. Marine and coastal environments can benefit from the use of biodegradable plastics in the fishing and boating industries; public outrage over the killing of dolphins, game fish, whales, and sea turtles fuels interest in these industries. In fact, the public is ultimately the driving force behind the development of biodegradable substances because litter on beaches, roadsides, and parks is an eyesore with apparent potential to harm the environment.
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 using 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 be decomposed to yield hydrogen sulfide 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 commonly found in municipal solid waste (sometimes called biodegradable municipal waste, or BMW) 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 kerb-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 where composting facilities exist.
Uses of biodegradable waste
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 the nutrients and compost for the soil 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 own lorries has achieved 1,000,000 kilometers driven with biogas from household waste in the last 15 years.
Areas relying on organic waste
Featured in an edition of The Economist that predicted events in 2014, it was revealed that Massachusetts creates roughly 1.4 million tons of organic waste every year. Massachusetts, along with Connecticut and Vermont, are also going to enact laws to divert food waste from landfills.
In small and densely populated states, landfill capacity is limited so disposal costs are higher ($60–90 per ton in MA compared to national average of $45). Decomposing food waste generates methane, a notorious greenhouse gas. However, this biogas can be captured and turned into energy through anaerobic digestion, and then sold into the electricity grid.
Anaerobic digestion grew in Europe, but is starting to develop in America. Massachusetts is increasing its production of anaerobic digesters.
Climate change impacts
The main environmental threat from biodegradable waste is the production of methane and other greenhouse gases.