Waste management is literally the process of managing waste materials (normally those produced as a result of human activities). It involves the collection, transport, processing and/or disposal of waste materials. Historically, the aim of waste management has been to prevent or reduce the impact of waste materials on human health or local amenity. Over the last thirty years, however, the focus of waste management in developed countries has shifted to reducing the impact of waste on the environment and recovering resources from waste materials.
Waste management can involve solid, liquid and/or gaseous wastes, and the methods involved for each are disparate. Entire fields of expertise exist for the management of each type of waste.
Waste management practices are often very different between urban and rural areas, and residential and industrial/commercial producers, even within the same local region. Waste management for non-hazardous residential and institutional waste streams in metropolitan areas is usually (but not always) the responsibility of local government authorities. Waste Management for non-hazardous commercial and industrial wastes is usally (but not always) the responsibility of the generator. The management (and composition) of waste is usually quite different in developed and developing nations, for a number of reasons.
Waste Management Concepts
The field of waste management has a number of different concepts, which vary in their usage between countries or regions.
The Waste Hierarchy
The waste hierarchy, as a concept, classifies different waste management strategies according to their desirability. The term ‘3 Rs’, or ‘Reduce-Reuse-Recycle’, has also been used for the same purpose. The waste hierarchy has taken many forms over the past decade, but the basic concept has remained the cornerstone of most waste minimisation strategies. The aim of the waste hierarchy is to extract the maximum practical benefits from products and to generate the minimum amount of waste.
Some waste management experts have recently incorporated a 'fourth R': "Re-think", with the implied meaning that the present system may have fundamental flaws, and that a thoroughly effective system of waste management may need an entirely new way of looking at waste. Some "re-think" solutions may be counter-intuitive, such as cutting fabric patterns with slightly more "waste material" left -- the now larger scraps are then used for cutting small parts of the pattern, resulting in a decrease in net waste. This type of solution is by no means limited to the clothing industry.
Extended Producer Responsibility
Extended producer responsibility (EPR) is the practice of holding the producer of a product responsible to some extent for the management of the waste products associated with that product. The producer is responsible to recover products that contain toxic and hazardous constituents which may present a threat to the safety of the community and which may place a burden on the end-of-life management of the product, for example motor vehicles, whitegoods, tyres, electronic equipment and mobile phones.
This concept has arisen in recent years due to the belief that an industry's responsibility for a product should not end with the sale of that product, but should extend to its reuse and/or disposal. EPR is often a voluntary measure within an industry, but in some countries it is a legislated requirement.
Product stewardship is sometimes referred to as a subset of EPR. Product stewardship shares responsibility between all elements of the supply chain including government, consumers, brand owners, producers and recyclers. It is usually employed for more environmentally benign products - products that do not present a major environmental impact – such as beverage containers or packaging materials.
Waste Management Techniques
Managing domestic, industrial and commercial waste has traditionally consisted of collection, followed by disposal. Depending upon the type of waste and the area, a level of processing may follow collection. This processing may be to reduce the hazard of the waste, recover material for recycling, produce energy from the waste, or reduce it in volume for more efficient disposal.
Collection methods vary widely between different countries and regions, and it would be impossible to describe them all. For example, in Australia most urban domestic households have a 240-litre bin that is emptied weekly by the local Council. Many areas, especially those in less developed areas, do not have a formal waste-collection system in place.
Disposal methods also vary widely. In Australia, the most common method of disposal of solid waste is to landfills, because it is a large country with a low-density population. By contrast, in Japan it is more common for waste to be incinerated, because the country is smaller and land is scarce.
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.
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 groundwater. Until recently, safe disposal of incinerator waste was a major problem. In the mid-1990s successful experiments in France and Germany used electric plasma 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 lye, 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 resources (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).
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, recycling, 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.
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.
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.
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.
Human waste management