Environmental Engineering Reference
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Fig. 4. Laying of plastic nets to protect the juvenile clams from predators
after about three years. In particular during a production cycle the areas devoted to
fattening of Manila clams are seeded in an alternate mode; in the second year the growth of
molluscs, sanitary and environmental conditions are tested, during the third year mature
clams are harvested. Before the subsequent cycle of production the culture beds have to
spend a rest period (Zentilin & Orel, 2009).
5.2 Production system
All further steps of the cultivation in the lagoon are conducted with specific equipments and
boats: lagoon bottom treatment, seeding, laying and removing of plastic nets (if necessary),
cleaning of nets, harvesting. In the past all operations were manually conducted and only
after specific experiments, an accurate planning and a lot of experience, peculiar
mechanized systems were employed for each phase of the processing in this intertidal
environment. Many requirements had to be performed to realize the ideal prototype of
operating machine: the choice of resistant materials adapted to operate in the marine
environment, the choice of the dimension and a correct distribution of weights, the
estimation of the pressure applied to the lagoon sediments and the operating security. These
requirements led to perform three models of operating machine: a model of seeder machine
combined to remove oyster shells from lagoon bottom and a system to lay plastic nets (Fig.
5); a model for the cleaning and removing of plastic nets and finally a model of shallow
hydraulic escalator harvester. The impact of these prototypes, in particular on sediment
texture and benthic community, was accurately studied to verify the environmental
sustainability of each operation system.
Since 2004 a new multifunctional vessel (M/S ADA) is employed in areas with depth up to -
40 cm (Fig. 6). ADA has the following characteristics: 19.34 GT, steel hull, total length 21 m,
7 m in wide and 1.25 m in height. ADA is equipped with a diesel engine of 347 HP and is
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