Waste is something which has lost its apparent value to its owner. It is a misplaced resource.

Waste can exist in any phase of matter (solid, liquid, or gas). When released in the latter two states, gas especially, the wastes are referred to as emissions. It is usually strongly linked with pollution.

Sources of waste

Sources of waste for European Environment Agency countries, 1992-1997.Waste produced in the wild is reintegrated through natural recycling processes, such as dry leaves in a forest decomposing into soil. Outside of the wild these wastes may become problematic, such as dry leaves in an urban environment. The highest volume of waste, outside of nature, comes from human industrial activity: mining, industrial manufacturing, consumer use, and so on1.

Almost all manufactured products are destined to become waste at some point in time, with a volume of waste production roughly similar to the volume of resource consumption. Many manufactured goods are unable to be recycled due to the impracticality of separating the materials of glass, metal and plastic from each other, or the inability to separate a metal alloy back to its base components. This could create a logistical nightmare scenario in terms of how or where the various types of buildings (and the many contents they contain) of present day towns and cities will be disposed of in the distant future.

Post-consumer waste is the waste produced by the end-user (the rubbish one puts outside in the rubbish bin). This is the waste people usually think of. But though the most visible, this is very small compared to the waste created in the process of mining and production.

Waste Management

Waste management is the collection, transport, processing or disposal of waste materials, usually ones produced by human activity, in an effort to reduce their effect on human health or local aesthetics or amenity. A subfocus in recent decades has been to reduce waste materials’ effect on the natural world and the environment and to recover resources from them.

Waste management can involve solid, liquid, gaseous or plasmic, with different methods and fields of expertise for each.

Waste management practices differ for developed and developing nations, for urban and rural areas, and for residential, industrial, and commercial producers. Waste management for non-hazardous residential and institutional waste in metropolitan areas is usually the responsibility of local government authorities, while management for non-hazardous commercial and industrial waste is usually the responsibility of the generator.

Waste management concepts

Waste management has a number of different concepts, which vary in their usage between countries or regions.

The waste hierarchy

The waste hierarchy classifies waste management strategies according to their desirability. The waste hierarchy has taken many forms over the past decade, but the basic concept has remained the cornerstone of most waste minimization 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. Source reduction involves efforts to reduce hazardous waste and other materials by modifying industrial production. Source reduction methods involve changes in manufacturing technology, raw material inputs, and product formulation. At times, the term “pollution prevention” may refer to source reduction.

Another method of source reduction is to increase incentives for recycling. Many communities in the United States are implementing variable rate pricing for waste disposal (also known as Pay As You Throw – PAYT) which has been effective in reducing the size of the municipal waste stream.

Source reduction is typically measured by efficiencies and cutbacks in waste. Toxics use reduction is a more controversial approach to source reduction that targets and measures reductions in the upfront use of toxic materials. Toxics use reduction emphasizes the more preventive aspects of source reduction but, due to its emphasis on toxic chemical inputs, has been opposed more vigorously by chemical manufacturers. Toxics use reduction programs have been set up by legislation in some states, e.g., Massachusetts, New Jersey and Oregon.

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 (63.4 gallon) 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.

In Canadian urban centres curbside collection is the most common method of disposal, whereby the city collects garbage, and or recyclables, and or organics on a scheduled basis from residential areas. In rural areas people dispose of their waste at transfer stations. Garbage collected is then transported to a regional landfill.

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.

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, mining voids or borrow pits. Running a landfill that minimalises environmental problems 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 pollutants such as leachate which can leach into and pollute 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 landfill include methods to contain leachate, such as lining 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, which is a far more potent greenhouse gas than carbon dioxide. Some of it can be tapped for use as a fuel.

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. 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

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. It is recognised as a practical method of disposing of hazardous waste materials, such as biological medical waste.

Though still widely used in many areas, especially developing countries, incineration as a waste management tool is becoming controversial for several reasons.

First, it may be a poor use of many waste materials because it destroys not only the raw material, but also all of the energy, water, and other natural resources used to produce it. Some energy can be reclaimed as electricity by using the combustion to create steam to drive an electrical generator, but even the best incinerator can only recover a fraction of the caloric value of fuel materials.

Second, incineration creates toxic gas and ash, which can harm local populations and pollute groundwater. Modern, well-run incinerators take elaborate measures to reduce the amount of toxic products released in exhaust gas. But concern has increased in recent years about the levels of dioxins that are released when burning mixed waste.

Until recently, safe disposal of incinerator waste was a major problem. In the mid-1990s, experiments in France and Germany used electric plasma torches to melt incinerator waste into inert glassy pebbles, valuable in concrete production. Incinerator ash has also been chemically separated into lye and other useful chemicals.

An incineration technique that avoids ash disposal problems is the incorporation of it at portland cement furnaces, with savings of fuel, a double benefit.

Volume reduction

This means various techniques for making the waste fit into less space and easier to handle in bulk. Usually achieved by compaction or fragmentation.

Compaction

A landfill compaction vehicle in operation

The waste is compacted or compressed. It also breaks up large or fragile items of waste.

This process is conspicuous in the feed at the back end of many garbage collection vehicles.

See car crusher

In landfill sites, the waste is often compacted by driving over it with a heavy excavator-type vehicle with spiked wheels.

Shearing

The waste is sliced with heavy metal shears.

Grinding

The waste is ground up by a hammer mill.

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 acknowledgement 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

A sorting facility, where different materials are separated for 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.

Composting and digestion

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

There are a large variety of composting and digestion methods and technologies, varying in complexity from simple window composting of shredded plant material, to automated enclosed-vessel digestion of mixed domestic waste. These methods of biological decomposition are differentiated as being aerobic in composting methods or anaerobic in digestion methods, although hybrids of the two methods also exist.

Composting and digestion programs

The Green Bin Program, a form of organic recycling used in Toronto, Ontario and surrounding municipalities including Markham, Ontario, Canada, makes use of anaerobic digestion to reduce the amount of garbage shipped to Michigan, in the United States. This is the newest facet of the 3-stream waste management system has been implemented in the town and is another step towards the goal of diverting 70% of current waste away from the landfills. Green Bins allow any organic waste that in the past would have formed landfill waste to be composted and turned into nutrient rich soil. Examples of waste products for the Green Bin are food products and scraps, soiled papers and sanitary napkins. Currently, Markham– like the other municipalities in the Greater Toronto Area– ships all of its garbage to Michigan at a cost of $22 CAN per metric tonne.

The Green Bin Program is currently being studied by other Municipalities in the province of Ontario as a way of diverting waste away from the landfills. Notably, Toronto and Ottawa are in the preliminary stages of adopting a similar program.

The City of Edmonton, Alberta, Canada has adopted large-scale composting to deal with its urban waste. Its composting facility is the largest of its type in the world, representing 35 per cent of Canada’s centralized composting capacity. The $100-million co-composter allows Edmonton to recycle 65 per cent of its residential waste. The co-composter itself is 38,690 square metres in size, equivalent to 8 football fields. It’s designed to process 200,000 tonnes of residential solid waste per year and 22,500 dry tonnes of biosolids, turning them into 80,000 tonnes of compost annually.

Incineration, pyrolysis and gasification

Use of incinerators for waste management is controversial, and most Americans passionately oppose it. This controversy roots from the understandable conflict between short-term concerns and long-term ones, in this case between burning the wastes now, or postponing this problem by passing the waste burden to future generations. Whether any form of incineration or thermal treatment should be defined as “resource recovery” is a matter of dispute in policy-making circles.

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.