General
In the environmental reclamations it is of pre-eminent importance to have the possibility of selective dredging of the top layers of contaminated sediments, that very often, have a thickness of only few centimetres,thus to avoid the inconvenience of sending to the treatment plants and/or to special disposal areas also the lower layers of non contaminated sediments.
The
traditional dredging systems ( cutter/auger suction dredges, bucket/grab
dredges, trailing suction hoppers ) do not have the capability of selective
dredging of small thickness of sediments.
Indeed, the suction pipe's head plus the part of the cutter below the
suction pipe must be maintained sunken into the sediment, to avoid pumping
clear water, and it represents the minimum thickness that can be dredged.
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The Pneuma Pump, equipped with purpose at low advancement speed ( 1-5 m./min. ) and suspended by the lifting wire to the scheduled depth, guarantees the selective dredging of the polluted sediments only, with an high concentration of solid in the dredged mixture and without any secondary pollution. Therefore considering that the cost per cubic meter of sediments treatment (incineration, chemical treatment, etc.) and/or the cost of purpose built disposal areas are much higher than the cost of the dredging, the utilisation of a system which allows a selective dredging represents an unquestionable advantage in terms of cost saving (see typical example on next page ).
|
 |
Example
|
Surface to be dredged |
100,000 |
sq.m. |
|
Top contaminated layer thickness |
0.30 |
M. |
|
Total quantity of top contaminated sediments |
30,000 |
cu.m. |
|
Dredging estimated cost |
10.0 |
$/cu.m. |
|
Dredging total cost |
300,000 |
$ |
|
Treatment average cost |
125.0 |
$/cu.m. |
|
Total treatment cost ( for 30,000 cu.m.) |
3,750,000 |
$ |
|
Additional quantity of material to be treated for each cm. ( 0.01 m. ) of dredged material exceeding the required 0.30 m. thick. in the total area |
1,000.0 |
cu.m. |
|
Additional cost for dredging the additional 1,000.0 cu.m. |
10,000.0 |
$ |
|
Additional cost for the treatment of the additional 1,000 cu.m. |
125,000 |
$ |
Considering
that with the standard Cutter Suction Dredges the minimum dredged thickness
is approximately not less than 1.00 m. and with the small new dredges
with horizontal auger the minimum dredged thickness is approximately 0.50
m., the addition cost for the treatment of the exceeding dredged sediment
will be respectively of
$ 8,750,000 and $ 2,500,000.