Author Topic: Waste management  (Read 9779 times)


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Waste management
« on: April 04, 2007, 05:51:54 AM »
Waste management is the collection, transport, processing (waste treatment), recycling 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 or gaseous substances 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
There are a number of concepts about waste management, which vary in their usage between countries or regions.

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 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.

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 upstream use of toxic materials. Toxics use reduction emphasises 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.

Resource recovery
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.

In some developing nations some resource recovery already takes place by way of manual labourers who sift through un-segregated waste to salvage material that can be sold in the recycling market. These unrecognised workers called waste pickers or rag pickers, are part of the informal sector, but play a significant role in reducing the load on the Municipalities' Solid Waste Management departments. There is an increasing trend in recognising their contribution to the environment and there are efforts to try and integrate them into the formal waste management systems, which is proven to be both cost effective and also appears to help in urban poverty alleviation. However, the very high human cost of these activities including disease, injury and reduced life expectancy through contact with toxic or infectious materials would not be tolerated in a developed country.

Recycling means to recover for other use 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 various everyday waste materials. They are collected and sorted into common groups, so that the raw materials from these 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, but more costly due to the separation and extraction problems. Much electronic waste is sent to Asia, where recovery of the gold and copper can cause environmental problems (monitors contain lead and various "heavy metals", such as selenium and cadmium; both are commonly found in electronic items).

Recycled or used materials have to compete in the marketplace with new (virgin) materials. The cost of collecting and sorting the materials often 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).

The economics of recycling junked automobiles also depends on the scrap metal market except where recycling is mandated by legislation (as in Germany).

However, most economic systems do not account for 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 [1]. For example, recycling 1000 kg of aluminum cans saves approximately 5000 kg of bauxite ore being mined (source: ALCOA Australia) and prevents the generation of 15.17 tonnes CO2eq greenhouse gases [2]; recycling steel saves about 95% of the energy used to refine virgin ore (source: U.S. Bureau of Mines).

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.[citation needed]

Waste management techniques
Managing municipal waste, industrial waste 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 waste, and or recyclables, and or organics on a scheduled basis from residential areas. In rural areas people dispose of their waste at transfer stations. Waste 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 in landfill sites, as 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, mining voids or borrow pits. A properly-designed and well-managed landfill can be a hygienic and relatively inexpensive method of disposing of waste materials in a way that minimises their impact on the local environment. Older, poorly-designed or poorly-managed landfills can create a number of adverse environmental impacts such as wind-blown litter, attraction of vermin, and generation of leachate which can pollute groundwater and surface water. Another byproduct of landfills is landfill gas (mostly composed of methane and carbon dioxide), which is produced as organic waste breaks down anaerobically. This gas can create odor problems, kill surface vegetation, and is a greenhouse gas.

Design characteristics of a modern landfill include methods to contain leachate, such as clay or plastic lining material. Disposed waste is normally compacted to increase its density and stablise the new landform, and covered to prevent attracting vermin (such as mice or rats) and reduce the amount of wind-blown litter. Many landfills also have a landfill gas extraction system installed after closure to extract the landfill gas generated by the decomposing waste materials. Gas is pumped out of the landfill using perforated pipes and flared off or burnt in a gas engine to generate electricity. Even flaring the gas 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.

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

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 use less material, and legislation mandating that manufacturers become responsible for disposal costs of products or packaging (see Product Stewardship and Extended Producer Responsibility). 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 a reduced materials waste stream.

Some futurists have speculated that landfills may one day be mined: as some resources become more scarce, they will become valuable enough that it would be economical to 'mine' them from landfills where these materials were previously discarded as valueless. A related idea is the establishment of a 'monofill' landfill containing only one waste type (e.g. waste vehicle tyres), as a method of long-term storage.

Incineration is a waste disposal method that involves the combustion of waste at high temperatures. Incineration and other high temperature waste treatment systems are described as "thermal treatment". In effect, incineration of waste materials converts the waste into heat, gaseous emissions, and residual solid ash. Other types of thermal treatment include pyrolysis and gasification.

A waste-to-energy plant (WtE) is a modern term for an incinerator that burns wastes in high-efficiency furnace/boilers to produce steam and/or electricity and incorporates modern air pollution control systems and continuous emissions monitors. This type of incinerator is sometimes called an energy-from-waste (EfW) facility.

Incineration is popular in countries such as Japan where land is a scarce resource, as they do not consume as much area as a landfill. Sweden has been a leader in using the energy generated from incineration over the past 20 years. Denmark also extensively uses waste-to-energy incineration in localised combined heat and power facilities supporting district heating schemes.

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 certain hazardous waste materials (such as biological medical waste), though it remains a controversial method of waste disposal in many places due to issues such as emission of gaseous pollutants.

Composting and anaerobic digestionWaste 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 windrow 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.

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 city 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 waste to Michigan at a cost of $22 CAN per tonne (metric ton, 1000 kg).

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 centralised composting capacity. The $100 million co-composter and various recycling programs enable Edmonton to recycle 60% 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.

Mechanical biological treatment
Mechanical biological treatment (MBT) is a technology category for combinations of mechanical sorting and biological treatment of the organic fraction of municipal waste. MBT is also sometimes termed BMT- Biological Mechanical Treatment- however this simply refers to the order of processing.

The "mechanical" element is usually a bulk handling mechanical sorting stage. This either removes recyclable elements from a mixed waste stream (such as metals, plastics and glass) or processes it in a given way to produce a high calorific fuel given the term refuse derived fuel (RDF) that can be used in cement kilns or power plants. Systems which are configured to produce RDF include Herhofand Ecodeco. It is a common misconception that all MBT processes produce RDF. This is not the case. Some systems such as ArrowBio simply recover the recyclable elements of the waste in a form that can be sent for recycling.

The "biological" element refers to either anaerobic digestion or composting. Anaerobic digestion breaks down the biodegradable component of the waste to produce biogas and soil conditioner. The biogas can be used to generate renewable energy. More advanced processes such as the ArrowBio Process enable high rates of gas and green energy production without the production of RDF. This is facilitated by processing the waste in water. Biological can also refer to a composting stage. Here the organic component is treated with aerobic microorganisms. They break down the waste into carbon dioxide and compost. There is no green energy produced by systems simply employing composting.

MBT is gaining increased recognition in countries with changing waste management markets such as the UK and Australia where WSN Environmental Solutions has taken a leading role in developing MBT plants.

Pyrolysis & gasification

Pyrolysis and gasification are two related forms of thermal treatment where waste materials are heated to high temperatures with limited oxygen availability. The process typically occurs in a sealed vessel under high pressure. Converting material to energy this way is more efficient than direct incineration, with more energy able to be recovered and used.[citation needed]

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 (syngas) 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.

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Waste management
« on: April 04, 2007, 05:51:54 AM »


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Re: Waste management
« Reply #1 on: December 28, 2007, 02:34:30 AM »

You copied most of this article from the online Wikipedia including text, photos and diagrams.

The very least you could do is to acknowledge the the material is copied from someone else's work.