Before processing these other types of waste, it is necessary that exploitable fractions are selected upstream, through appropriate separate collection systems. That’s why we all do differentiated waste collection. The more different fractions of waste are separated, the more we can transform waste into new raw materials and energy.
In Europe, recovering the energy content of waste takes place mainly through direct combustion processes in dedicated plants, equipped with heat and energy recovery units.
Severe, and increasingly stringent, limits on emissions into the atmosphere have led to develop a fume treatment section which, in recently projected systems, is particularly sophisticated. Final waste (ashes, totally not more than 2% by weight of the initial quantity of waste) produced by waste-to-energy plants can be reused in typical civil engineering applications, for example to replace natural aggregates used in road foundations.
What remains, after waste processing, is disposed of in controlled landfills. Modernly designed landfills, in addition to providing for orderly and organized disposal of waste, are equipped with systems for isolating the landfills themselves from the surrounding environment, in particular from subsoil and underground strata.
To this aim, landfills are equipped with systems for containment of two main flows of pollutants they produce: leachate, that is a liquid stream that collects at the bottom of the landfill (and derives mainly from rainwater that infiltrates and migrates through the storage of waste); and biogas which, consisting of methane and carbon dioxide (the same gases we saw before in anaerobic degradation), is generated by biodegradable organic substances.
If implemented with appropriate methods, such containment systems can significantly mitigate the environmental impact of controlled landfills falling even in areas that present some hydrogeological criticalities.
Suppose that in a certain company the following waste is produced in a week: 200 kg of organic fraction, 1,200 kg of paper, 400 kg of plastic, 110 kg of metals, 330 kg of glass, 240 kg of other waste. Determine the commodity composition (percentage by weight) of the waste production per material.
Calculate the percentages following the below example. If total amount of waste is 200 + 1,200 + 400 + 110 + 330 + 240 kg = 2,480 kg, then the percentage by weight for organic waste can be calculated like this: 200/2,480kg*100 = 8% (correct answer is b).
You can check your answers with this list (be careful, the percentages are in wrong order): a) 48,4% b) 8% c) 16% d) 9,6% e) 13,3% f) 4,4%.