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Waste management

2007 Schools Wikipedia Selection. Related subjects: Environment

       Environmental science
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     * Waste management

   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.

History of waste management

Waste management concepts

   The waste hierarchy
   Enlarge
   The waste hierarchy

   There are a number of concepts about waste management, which vary in
   their usage between countries or regions.

   The waste hierarchy:
     * reduce
     * reuse
     * recycle

   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.

Recycling

    A materials recovery facility, where different materials are separated
                                                             for recycling
                                                                   Enlarge
    A materials recovery facility, where different materials are separated
                                                             for recycling

   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 "heavy metals" such as selenium and cadmium 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.
   For example, recycling 1000 kg of aluminium cans saves approximately
   5000 kg of bauxite ore being mined (source: ALCOA Australia) and 97% of
   the energy required to refine it; 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.

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 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

                                A landfill compaction vehicle in operation
                                                                   Enlarge
                                A landfill compaction vehicle in operation

   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 minimises
   environmental problems can be a hygienic and relatively inexpensive
   method of disposing of waste materials; however, a more efficient
   method of disposal will be needed in time as less land becomes
   available for such purposes.

   Older or poorly managed landfills can create a number of adverse
   environmental impacts, including wind-blown litter, attraction of
   vermin and pollutants such as leachate, which can leach into and
   pollute groundwater and rivers. Another product of landfills containing
   harmful wastes is landfill gas, mostly composed of methane and carbon
   dioxide, which is produced as the waste breaks down anaerobically.

   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 attracting mice and rats and
   preventing wind-blown litter. Many landfills also have a landfill gas
   extraction system installed after closure to extract the gas generated
   by the decomposing waste materials. This gas is often burnt in a gas
   engine to generate electricity. 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 stronger 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 owners of
   adjacent land. 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, and
   legislation mandating that manufacturers are responsible for final
   packaging and materials disposal costs (as in the manufacturers setting
   up and funding the "Grüne Punkt" in Germany to achieve that end). 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 materials wastestream.

Incineration

   A waste-to-energy plant in Saugus, Massachusetts, the first plant in
   the United States.
   Enlarge
   A waste-to-energy plant in Saugus, Massachusetts, the first plant in
   the United States.

   Incineration is the process of destroying waste material by burning it.
   Incineration is often alternatively named "Energy-from-waste" (EfW) or
   "waste-to-energy"; this is misleading as there are other ways of
   recovering energy from waste that do not involve directly burning it
   (see anaerobic digestion, pyrolysis & gasification).

   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. Many entities now refer to disposal of wastes by exposure to
   high temperatures as thermal treatment (however this also includes
   gasification and pyrolysis). This concept encompasses recovery of
   metals and energy from municipal solid waste (MSW) as well as safe
   disposal of the remaining ash and reduction of the volume of waste.

   Though classic incineration is 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 of municipal solid wastes does produce significant
   amounts of dioxin and furan emissions to the atmosphere. Dioxins and
   furans are considered by many to be serious health hazards. However,
   advances in emission control designs and very stringent new
   governmental regulations have caused large reductions in the amount of
   dioxins and furans produced by waste-to-energy plants. The U.S.
   Environmental Protection Agency (EPA) and the European Union have taken
   the lead in mandating very strict emission standards for incineration
   of wastes.

   Incineration also produces large amounts of ash requiring safe disposal
   so as not to contaminate underground aquifers. Until recently, safe
   disposal of incinerator ash was a major problem. In the mid-1990s,
   experiments in France and Germany used electric plasma torches to melt
   incinerator ash into inert glassy pebbles, valuable in concrete
   production. Incinerator ash has also been chemically separated into lye
   and other useful chemicals. This process, plasma arc waste disposal, is
   now operated commercially, and is used to convert existing waste and
   landfill into power generating gas and construction rubble.

   An incineration technique that avoids ash disposal problems is the
   incorporation of the ash in portland cement furnaces, saving fuel
   otherwise burned for cement kilns. It is important to note that using
   incinerrator ash in concerete or block work may carry a risk of
   spreading dioxins and furans concentrated in the incinerator ash.

Composting and anaerobic digestion

   An active compost heap
   Enlarge
   An active compost heap

   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 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.

Examples of composting and anaerobic 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 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 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.

Mechanical biological treatment

   ArrowBiowet material recovery facility, Hiriya, Tel Aviv, Israel
   Enlarge
   ArrowBiowet material recovery facility, Hiriya, Tel Aviv, Israel

   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.
   ArrowBio UASB anaerobic digesters, Hiriya, Tel Aviv, Israel
   Enlarge
   ArrowBio UASB anaerobic digesters, Hiriya, Tel Aviv, Israel

   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 materials are heated with high temperatures and limited oxygen.
   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.

   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.

   Plasma gasification is the gasification of matter in an oxygen-starved
   environment to decompose waste material into its basic molecular
   structure. Plasma gasification does not combust waste as incinerators
   do. It converts organic waste into a fuel gas that still contains all
   the chemical and heat energy from the waste. It converts inorganic
   waste into an inert vitrified glass.

   Plasma is considered as a 4th state of matter, the other three being
   gas, liquid, and solid. Electricity is fed to a torch, which has two
   electrodes, creating an arc. Inert gas is passed through the arc,
   heating the process gas to internal temperatures as high as 13,000 °C
   (25,000 °F). The temperature a metre from the torch can be as high as
   ~4000 °C (~8,000 °F). Because of these high temperatures the waste is
   completely destroyed and broken down into its basic elemental
   components. There are no tars or furans. At these high temperatures all
   metals become molten and flow out the bottom of the reactor. Inorganics
   such as silica, soil, concrete, glass, gravel, etc. are vitrified into
   glass and flow out the bottom of the reactor. There is no ash remaining
   to go back to a landfill.

   The plasma reactor does not discriminate between types of waste. It can
   process any type of waste. The only variable is the amount of energy
   that it takes to destroy the waste. Consequently, no sorting of waste
   is necessary and any type of waste, other than nuclear waste, can be
   processed.

   The reactors are large and operate at a slightly negative pressure,
   meaning that the feed system is simplified because the gas does not
   want to escape. The gas has to be pulled from the reactor by the
   suction of the compressor. Each reactor can process 20 tonnes per hour
   (t/h) compared to 3 t/h or typical gasifiers. Because of the size and
   negative pressure, the feed system can handle bundles of material up to
   1 metre in size. This means that whole drums or bags of waste can be
   fed directly into the reactor making the system ideal for large scale
   production.

   The gas coming out of a plasma gasifier is lower in trace contaminants
   than with any kind of incinerator or other gasifier. Because the
   process starts with lower emissions out of the reactor, it is able to
   achieve significantly lower stack emissions. The gasifier doesn't care
   about the amount of moisture in the waste. The moisture consumes energy
   to vaporise and can impact the capacity and economics; however, it will
   not affect the process.

   Gas from the plasma reactor can be burned to produce electricity or can
   be synthesised into ethanol to contribute to automotive fuel.

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