2.1 Landfill

Disposing of waste in a landfill is the most traditional method of waste disposal, and it remains a common practice in most countries. Historically, landfills were often established in disused quarries or mining voids. A well-run landfill can be a hygienic and relatively inexpensive method of disposing of waste materials.

Older or poorly managed landfills can create number of adverse environmental impacts, including wind-blown litter, attraction of vermin and soluble contaminants (leachate) leaching into and polluting groundwater. Another product of landfills containing putrescible wastes is landfill gas (mostly composed of methane and carbon dioxide), which is produced as the waste breaks down.

Characteristics of a modern, well-run landfill should include methods to contain leachate, such as clay or plastic liners. Disposed waste should be compacted and covered to prevent vermin and wind-blown litter. Many landfills also have a landfill gas extraction system installed after they are closed to extract the gas generated by the decomposing waste materials. This gas is often burnt to generate power. Generally, even flaring the gas off is a better environmental outcome than allowing it to escape to the atmosphere, as this consumes the methane (a far more potent greenhouse gas than carbon dioxide).

Many local authorities (especially in urban areas) have found it difficult to establish new landfills, due to opposition from adjacent landowners. Few people want a landfill in their local neighbourhood. As a result, solid waste disposal in these areas has become more expensive as material must be transported further away for disposal.

Some oppose the use of landfills in any way, anywhere, arguing that the logical end result of landfill operations is that it will eventually leave a drastically polluted planet with no canyons, and no wild space. Some futurists have stated that landfills will be the " mines of the future": as some resources become more scarce, they will become valuable enough that it would be necessary to 'mine' them from landfills where these materials were previously discarded as valueless.

This fact, as well as growing concern about the impacts of excessive materials consumption, has given rise to efforts to minimise the amount of waste sent to landfill in many areas. These efforts include taxing or levying waste sent to landfill, recycling the materials, converting material to energy, designing products that require less material, etc. A related subject is that of industrial ecology, where the material flows between industries is studied. The by-products of one industry may be a useful commodity to another, leading to reduced waste materials.

2.2 Incineration

Incineration is the process of destroying waste material by burning it. Incineration is carried out both on a small scale by individuals, and on a large scale by industry. Though still widely used in many areas (especially developing countries), incineration as a waste management tool is becoming controversial for several reasons: both the gases and the ash residue produced may be toxic.

Incineration is often used to produce electricity from waste materials by burning it to produce steam to drive an electrical generator. Energy recovery by incineration is inefficient, however, as even the best incinerator can only recover a fraction of the calorific value of fuel materials.

Modern, well-run incinerators employ elaborate pollution control measures on exhaust gases to reduce the amount of toxic products released. Waste gases are of much greater concern in older and/or poorly run incinerators, which can have a significant negative impact on the health of local populations. In recent years, concern has increased about the levels of dioxins that are released when burning mixed waste.

Incinerator ash is toxic, and its leachate can pollute groundwaterGroundwater is any water found below the land surface. It is found in aquifers, in the pore spaces of rocks, in unconsolidated sediments, as permafrost, and as soil moisture. Groundwater flows to the surface naturally at springs and seeps and can form oas. Until recently, safe disposal of incinerator waste was a major problem. In the mid-1990s successful experiments in FranceThe French Republic or France ( French: Republique francaise or France is a country whose metropolitan territory is located in western Europe, and which is further made up of a collection of overseas islands and territories located in other continents. and GermanyThe Federal Republic of Germany ( German: Bundesrepublik Deutschland is one of the world's leading industrialized countries, located in the middle of the European Union. It is bordered to the north by the North Sea, Denmark and the Baltic Sea, to the east used electric plasmaFor the fluid portion of blood, see blood plasma; also, other uses. There is debate as to whether plasma is an individual state of matter or simply a type of gas. In physics and chemistry, plasma (also called an ionised gas is an energetic gas-phase state torches to melt incinerator waste into inert glassy pebbles, valuable in concrete production. An alterative use for incinerator ash has been to chemically separate it into lyeLye is an alternative name for the chemicals sodium hydroxide ( soda lye) or (less commonly) potassium hydroxide ( potash lye). Lye is used to make soap., and other useful chemicals.

It is also recognised that incineration may be a poor use for many waste materials. Not only is the raw material lost, but also all of the energy and natural resourcenatural resources Natural resources are commodities that are considered valuable in their relatively unmodified ( natural) form. A commodity is generally considered a natural resource when the primary activities associated with it are extraction and purifs (such as water) that was used to produce it. Nevertheless, incineration is recognised as a practical method of disposing of hazardous waste materials (such as biological medical waste).

3 Resource Recovery Techniques

A relatively recent idea in waste management has been to treat the waste material as a resource to be exploited, instead of simply a challenge to be managed and disposed of. There are a number of different methods by which resources may be extracted from waste: the materials may be extracted and recycled, or the calorific content of the waste may be converted to electricity.

The process of extracting resources or value from waste is variously referred to as secondary resource recovery, recyclingRecycling is the reuse of materials that would otherwise be considered waste, usually in some other form (as compared to reuse which is reuse of the material in the same form). Those materials can be sources from pre-consumer waste (materials used in manu, and other terms. The practice of treating waste materials as a resource is becoming more common, especially in metropolitan areas where space for new landfills is becoming scarcer. There is also a growing acknowledgment that simply disposing of waste materials is unsustainable in the long term, as there is a finite supply of most raw materials.

There are a number of methods of recovering resources from waste materials, with new technologies and methods being developed continuously.

3.1 Recycling

Recycling means to reuse a material that would otherwise be considered waste. The popular meaning of ‘recycling’ in most developed countries has come to refer to the widespread collection and reuse of single-use beverage containers. These containers are collected and sorted into common groups, so that the raw materials of the items can be used again (recycled).

In developed countries, the most common consumer items recycled include aluminium beverage cans, steel food and aerosol cans, HDPE and PET plastic bottles, glass bottles and jars, paperboard cartons, newspapers, magazines, and cardboard. Other types of plastic ( PVC, LDPE, PP, and PS: see resin identification code) are also recyclable, although not as commonly collected. These items are usually composed of a single type of material, making them relatively easy to recycle into new products. The recycling of obsolete computers and electronic equipment is important although more costly due to the separation and extraction problems. The recycling of junked automobiles also depends on the scrap metal market.

Recycled or used materials have to compete in the marketplace with new (virgin) materials. The cost of collecting and sorting the materials usually means that they are equally or more expensive than virgin materials. This is most often the case in developed countries where industries producing the raw materials are well-established. Practices such as trash picking can reduce this value further, as choice items are removed (such as aluminium cans). In some countries, recycling programs are subsidised by deposits paid on beverage containers (see container deposit legislation ).

Not accounted for by most economic systems are the benefits to the environment of recycling these materials, compared with extracting virgin materials. It usually requires significantly less energy, water and other resources to recycle materials than to produce new materials. For example, recycling 1000 kg of aluminium cans saves approximately 5000 kg of bauxite ore being mined and 95% of the energy required to refine it (source: ALCOA Australia).

In many areas, material for recycling is collected separately from general waste, with dedicated bins and collection vehicles. Other waste management processes recover these materials from general waste streams. This usually results in greater levels of recovery than separate collections of consumer-separated beverage containers, but are more complex and expensive.

3.2 Composting and Digestion

Waste materials that are organic in nature, such as food scraps and paper products, are increasingly being recycled. These materials are put through a composting or artificial digestion process to decompose the organic matter and kill pathogens. The organic material is then recycled as mulch or compost for agricultural or landscaping purposes.

There are a large variety of composting methods and technologies, varying in complexity from simple window composting of shredded plant material, to automated enclosed-vessel digestion of mixed domestic waste. Composting methods can be broadly categorised into aerobic or anaerobic methods, although hybrids of the two methods also exist.

Aerobic (meaning ‘requiring air’) methods of composting seek to aerate the organic material continuously or frequently, in order to promote rapid and odourless decomposition. Anaerobic (‘not requiring air’) methods of composting seek to maximise the generation of gases such as methane during the process, in order to produce power from the waste materials.

3.3 Pyrolysis and Gasification

Pyrolysis and Gasification are two related forms of thermal treatment where materials are incinerated with limited oxygen. The process typically occurs in a sealed vessel, under high temperature and pressure. Converting material to energy this way is more efficient than direct incineration, with more energy able to be recovered and used.

Pyrolysis of solid waste converts the material into solid, liquid and gas products. The liquid oil and gas can be burnt to produce energy or refined into other products. The solid residue (char) can be further refined into products such as activated carbon. Gasification is used to convert organic materials directly into a synthetic gas composed of carbon monoxide and hydrogen. The gas is then burnt to produce electricity and steam. Gasification is used in biomass power stations to produce renewable energy and heat.

4 See also

• Litter
• Remediation
• Life cycle assessment
• Industrial Ecology
• Post-consumer waste
• Product lifecycle
• By-product
• Renewable resource

4.1 Human waste management

• Outhouse
• Pit toilet
• Septic tank
• Sewer
• Waste disposal

Topics related to waste

Compost | E-waste | Garbage truck | Greywater | Incineration | Landfill | Pollution | Radioactive waste | Recycling | Sewage | Scrap | Sewage treatment | Toxic waste | Waste management

Waste

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