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The environmental problem

 
 

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The environmental problem addressed in LIFE project "Sludge's Wealth" is the disposal of biologic sludges deriving from the cleaning of water and the current inability to exploit them transforming them efficiently into high energy value clusters fuels, for small town plants.

The sludges (with water content of about 85%) are currently subjected to concentration, stabilizing and drying.
In the first phase, the sludges are concentrated by sedimentation and flotation, in the latter are deprived of pathogens with anaerobic, aerobic or chemical treatment and in the third phase the water is partially removed by natural drying or by means of a filter press or a vacuum drying with centrifugation.
Recently, it has been introduced a drying system assisted by hot air requiring use of a sand blasitng to mix the semi-dried sludges and expose new surface for evaporation.
Depending on the final destination of sludges, drying can reach up to 30% (for burning) or 5-10% (for waste).

The procedure described above has significant environmental problems:

  • low energy efficiency of the system
  • treatment takes a very long time
  • low stabilizing effect
  • high water content in the sludge which affects combustion
  • development of unpleasant odors.

In Europe the problem is huge: it is estimated conservatively that each EU citizen produces a daily 12 to 18 grams of dried sludge from biological waste.
The methods of sludge disposal are also linked to the economic aspect: the most commonly used methods are the least penalizing in terms of costs required to achieve the objectives.

In western european countries a third of the sewage sludges are reused in agriculture, while in eastern european countries this is in excess (about 38% of sewage sludge).
The remaining large part is disposed of in landfills, is prevalent the dumping in ground, with obvious environmental consequences.
Even today, for small treatment plants (located in areas populated by less than 100,000 inhabitants), it is not possible to make the incineration of such waste and the sludges’ transportation to plants capable of performing this action is hindered, because not economically and environmentally feasible due to the involvement of huge volumes of product, with its attendant environmental and safety risks.


 

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