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Waste is the material result from a technological process of obtaining material products or services. In other words waste is the useless result from the processing of raw materials.
Firstly appeared as the municipal dump in the city of Athens, around 400 BC, the precursors of future health service become the first community services provided. That time employees were gathering the trash from streets and store it into containers. Later, during Middle Ages in England the Parliament issued a law that made compulsory to leave the garbage in special places.The first law against throwing waste on the streets is dated (1657) in New Amsterdam (nowadays Manhattan).
A brief classification of waste would include municipal waste (household and commercial), which represent about 14% of the entire amount of waste and industrial waste, e.g. these summarized 33 million tones generated in 1998 in EU.
|Type of waste||Equivalent energy – product equivalent through recycling processes||Repeatability|
|1 ton of glass||1.2 tons of raw material||it can be recycled indefinitely without losing quality|
|1 ton plastic||700-800 kg crude oil|
|10 PET||manufacture of a shirt /1 meter carpet|
During the construction processes, either for buildings or for infrastructure targets (road construction and maintenance) may result different types of waste which represent 25% of all the waste generated in the EU. This is stored on special landfills and later on processed by incineration, obtaining an average recycling rate of 80%. A significant source of waste is generated by the disposal of used electronics and electrical equipments, as final processing products of mining, and agriculture.
The selection of waste consists on the storage of it on special containers for collecting and recycling. By recycling we understand the collection, separation and processing of the main components of garbage for endeavor their transformation into useful products. It has been proven that most of the materials from what we consider waste or garbage may be the subject of a recycling process with different energetic efficiencies.
So, some data can become useful information regarding the recycling process (table1, fig. 4).
To print a widely known newspaper takes about 300 m3 of timber, meaning about 1,500 trees of 50 years old. Meanwhile, for the production of 700 paper bags it takes one 15 years old tree meaning that every ton of recycled paper may save 17 trees.
Because related data are giving more weight to words, it is relevant that recycling a single PET we can save enough energy to light a bulb for 6 hours continuously.
One effective method of processing the selected and deposited waste is the incineration, having as outcomes heat delivered as vapors or hot gases and ash. Through this method it can be burned waste on both solid and liquid state. The incineration power-plant is equipped with special ovens having either direct push feeder or overturned ones. These furnaces can burn waste with low caloric value of about 10 MJ/kg.
On figure 5 is the process-map representation of an incineration power-plant with a rotary kiln. Co-incineration – the joint incineration of hazardous waste, in any form becomes widely known. To achieve an effective recycling process the pre-selection of the waste is compulsory. Some spectacular types of recycling refers to the beer cans that allow to recycle aluminum; spray cans that allow the recovery other metals; paper recycling from food packaging, newspapers and magazines. The recycling process begins in warehouses by efficiently sorting the material
(fig. 6). From the selection process of waste can be obtained biodegradable materials (organic, from semi-liquid household waste) through whose fermentation on special reactors biogases can be generated and also a secondary solid product fertilizer type for agriculture.The biogas can be used to generate heat energy having a caloric power of 20-25 MJ/kg.
It can be burnt in thermal power-plants, for house hold applications or as primary energy source for turning on turbines on micro- power-plants. Consequently, manure is far from useless trash and the enormous amounts of waste deposited in the vicinity of large urban agglomerations offer significant potential of energy sources, next to renewable energy, for future integrated energy systems.