Solid wastes

Kategorie: Biológia (celkem: 966 referátů a seminárek)

Informace o referátu:

  • Přidal/a: anonymous
  • Datum přidání: 01. července 2007
  • Zobrazeno: 1501×

Příbuzná témata



Solid wastes

Municipal solid waste is the end product of many interacting factors: (1) large populations, (2) high per capita consumption, (3) low product durability, (4) a rash of disposable products, (5) low reuse and recycling rates, (6) a lack of personal governmental commitment to reduce waste.
There are three main approaches: (1) input approach - attempts to reduce excessive consumption, to increase product durability (lifespan), to reduce overpackaging, and others, (2) throughput approach - reducing solid waste production by reusing and recycling materials before they enter waste stream, (3) output approach - finding better ways of dealing with trash - most often this means incinerating trash or finding ways to build safer landfills.
Reuse is the return of operable or reparable goods into the market system for someone to use. Packaging materials, such as cardboard boxes, bottles, and grocery bags, can be reused, saving both energy and materials. Reusable beverage containers can be sterilized, refilled and returned to the shelf.
The advantages of reuse are many: (1) it saves energy, (2) it reduces the land area needed for solid waste disposal, (3) it provides jobs, (4) it reduces litter, (5) it decreases the amount of materials consumed by society, and (6) it helps reduce pollution and environmental degradation.
Recycling is the return of materials to manufacturers, where they can be broken down and reincorporated into new products. Recycling alleviates future resource shortages, reduces energy demand, cuts pollution, saves water, and decreases solid waste disposal and incineration.
Paper recycling use one-third to one-half as much energy as the conventional process of making paper from wood pulp. One of the obstacles to recycling is that many products contain a mixture of materials, making them more difficult to recycle.
Plastic pose a special problem for recycling. Most plastic is perfectly recyclable. The problem is that there are more than 45 different types of plastic commonly used for packaging. Making matter worse, many packages contain two or more types of plastic, making it difficult to recycle.
To reduce solid waste production, change in attitude must occur, from the exploitive one so prevalent today to a nurturing one in which we are willing to make small sacrifices for the good of the earth and future generations.
( Plastic soft drink bottles are used - in N. Y. State - to make filler for pillows and jackets.

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The final and often least desirable option is the output approach. It looks on solid waste as something to be discarded as cheaply and as safely as possible.

Dumps and landfills
The open garbage dumps have been recently replaced by the sanitary landfills. A sanitary landfill is a natural or manmade depression into which solid wastes are dumped, compressed, and daily covered with a layer of dirt. Since trash is covered, odors, flies, insects, rodents, and potential health problems are eliminated or sharply reduced.
The most important problem about landfills is that they require land, which is in short supply around many cities. Second, landfills, like dumps, require a lot of energy for excavation, filling, and hauling trash. Third, they can pollute groundwater, as toxic household wastes (paint thinner, pesticides and other pests) and feces are discarded in municipal landfills where they can leak into groundwater. Fourth, they produce methane gas from the decomposition of organic materials. Methane can seep through the ground into buildings built above and around reclaimed sites, and it is explosive at relatively low concentrations. Fifth, they sink or subside as the organic trash decays, requiring additional regrading and filling. Buildings constructed on top of reclaimed landfills may suffer serious structural damage. Sixth, they have low social acceptability - most people don’t want the noise, traffic, and blowing debris.

Composting
Composting is the most useful output strategy devised. Composting is a process in which organic wastes are allowed to undergo aerobic bacterial decay. The resulting product, compost, is used to build soil fertility.
Where there is abundance of organic matter, such as slaughterhouses and vegetable- and fruit- packing plants, composting is a good strategy (also for manure produced by animals in zoo). Large-scale composting has a few drawbacks: (1) it requires large tracts of land and may produce odor and provide breeding sites for pests, (2) sorting out the noncompostable materials such as metals and glass is costly, (3) the demand for the organic compost is often low, and (4) sites are aesthetically unappealing.
Citizens could be required to sort out recyclable metals, plastics, and glass, thus eliminating the cost of separating the wastes later.

Incineration
Incineration reduces waste volume by two-thirds, saving landfill space. It also produces heat and electricity, turning waste into energy.

For that reason, incinerators are often called waste-to-energy (WTE) plants.
But even with the energy gain, WTE plants are often more costly to build and operate than landfills, and are much more expensive than recycling programs. Incinerators also emit toxic pollutants, especially when plastics are burned. The ash produced by incinerator may also be hazardous to human health.

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