3 Storage and Detoxification of Bivalve Molluscs as a Tool in a Marketing Strategy
27
Toxic and Non-toxic Microalgae
Alexandrium minutum (AM89BM strain isolated from Morlaix Bay, France) was
batch-cultivated (10 L-vessels) in temperature-controlled rooms (16 ˙ 1
ı C), with
a diurnal photon density flux of 50 ˙ 4 E and a 12/12 h photoperiod. This toxic
strain was also grown in continuous culture systems in two 100-L photobioreactors
at 17
ı C, with an 8 L day
1 renewal of filtered natural seawater enriched with L1
medium (Guillard and Hargraves 1993). In both types of culture vessel used the A.
minutum strain was producing GTX2, GTX3, dcGTX2 and dc GTX3, and reached
a mean toxicity of 1 pg eq.STX cell
1 . Prorocentrum lima (strain PL4V from Vigo,
Spain) was also batch-cultivated according to the same culture conditions as for
A.minutum. Both strains were grown with F/2 medium (Guillard 1975). P. lima was
producing AO and DTX1 and reached a mean toxicity of 10 pg eq.AO cell
1 . A nontoxic strain of Skeletonema costatum was cultured in Provasoli ES medium under
the same conditions as the batch cultures.
Seawater Treatments
Seawater was filtered through either a sand filter or membranes. The sand filter was
tested using three classes of sand with different mean grain sizes: 256 (size ranging
from 26 to 496 m), 389 (size ranging from 21 to 1,018 m) and 392 m (size
ranging from 38 to 599 m). H. triquetra suspensions containing 30,000 cells.mL
1
were fed into the sand filter at a flow rate equal to 3.5 m
3 /m
2 /h.
For the membrane test, an immersed membrane was used in dead-end filtration
mode in seawater containing different concentrations (1,000 or 30,000 cells.mL
1 )
of three micro-algae (H. triquetra, A. minutum, and P. lima). The hollow fibre
surface area was equal to 0.37 m
2 and the average pore size equal to 0.2 m. Air
was injected at 676 L h
1
m
2 below the fibre bundle.
During microfiltration or sand filtration of micro-algal suspensions, the mean
filtrate was sampled in order to evaluate the retention rate RR expressed as:
RR D 1 Cp=Cf;
(3.1)
where Cp is the concentration in the filtrate at the end of filtration and Cf is the
concentration in the feed water.
Toxin Stability and Bioavailability Experiments
For experiments on DSP or PSP toxin bioavailability to shellfish, mussels were
placed in 160-L capacity flume tank equipped with an air-lift system. Seawater was
re-circulated continuously in the flume. Every flume tank contained four baskets
27
Toxic and Non-toxic Microalgae
Alexandrium minutum (AM89BM strain isolated from Morlaix Bay, France) was
batch-cultivated (10 L-vessels) in temperature-controlled rooms (16 ˙ 1
ı C), with
a diurnal photon density flux of 50 ˙ 4 E and a 12/12 h photoperiod. This toxic
strain was also grown in continuous culture systems in two 100-L photobioreactors
at 17
ı C, with an 8 L day
1 renewal of filtered natural seawater enriched with L1
medium (Guillard and Hargraves 1993). In both types of culture vessel used the A.
minutum strain was producing GTX2, GTX3, dcGTX2 and dc GTX3, and reached
a mean toxicity of 1 pg eq.STX cell
1 . Prorocentrum lima (strain PL4V from Vigo,
Spain) was also batch-cultivated according to the same culture conditions as for
A.minutum. Both strains were grown with F/2 medium (Guillard 1975). P. lima was
producing AO and DTX1 and reached a mean toxicity of 10 pg eq.AO cell
1 . A nontoxic strain of Skeletonema costatum was cultured in Provasoli ES medium under
the same conditions as the batch cultures.
Seawater Treatments
Seawater was filtered through either a sand filter or membranes. The sand filter was
tested using three classes of sand with different mean grain sizes: 256 (size ranging
from 26 to 496 m), 389 (size ranging from 21 to 1,018 m) and 392 m (size
ranging from 38 to 599 m). H. triquetra suspensions containing 30,000 cells.mL
1
were fed into the sand filter at a flow rate equal to 3.5 m
3 /m
2 /h.
For the membrane test, an immersed membrane was used in dead-end filtration
mode in seawater containing different concentrations (1,000 or 30,000 cells.mL
1 )
of three micro-algae (H. triquetra, A. minutum, and P. lima). The hollow fibre
surface area was equal to 0.37 m
2 and the average pore size equal to 0.2 m. Air
was injected at 676 L h
1
m
2 below the fibre bundle.
During microfiltration or sand filtration of micro-algal suspensions, the mean
filtrate was sampled in order to evaluate the retention rate RR expressed as:
RR D 1 Cp=Cf;
(3.1)
where Cp is the concentration in the filtrate at the end of filtration and Cf is the
concentration in the feed water.
Toxin Stability and Bioavailability Experiments
For experiments on DSP or PSP toxin bioavailability to shellfish, mussels were
placed in 160-L capacity flume tank equipped with an air-lift system. Seawater was
re-circulated continuously in the flume. Every flume tank contained four baskets