Are zeolites capable of
modifying the yield of marine micro-algae cultures? A case study with Emiliania
huxleyi and a product of zeolitic nature
A. Fachini, M.F.C. Leal, M.T.S.D. Vasconcelos-2004
Aquaculture, 237(1-4): 407-419
Abstract:
Growth of the marine alga, Emiliania huxleyi,
and chemical changes in the culture medium were assessed in response to the
addition of differing concentrations of ZESTEC-56, a product of zeolitic
nature (PZN). E. huxleyi was inoculated in natural seawater
containing 0.025, 0.050 and 0.10 g l−1 PZN. In addition,
algae were also inoculated in a PZN elutriate (1.0 g l−1
PZN in seawater stirred for 30 min). Total concentrations of dissolved trace
metals and organic ligands (and respective conditional stability constants)
were determined, in all media including the controls, by anodic and cathodic
striping voltammetry in the initial medium and after 7-day algal growth.
When compared with the control culture, 0.025 and 0.050 g l−1
PZN in situ with E. huxleyi did not significantly change the
micro-algae growth yield. The highest PZN amount (0.10 g l−1)
caused a decrease both in growth rate and yield. In the PZN elutriate
culture cell yield was significantly greater than the controls. The PZN
caused changes in the total concentrations of dissolved metallic
micro-nutrients, adsorbing some (e.g. Zn) and releasing others (e.g. Mn).
The ion-exchange processes seem to be relatively slow, as the extent of
changes in the elutriate culture, where the contact between PZN and medium
was only 30 min, was much lower than that caused by in situ PZN for 7 days.
In addition, the amount of exudates released per cell was also influenced by
the PZN probably due to the changes in the available trace elements. This
work indicated that the changes caused by zeolites in a culture medium, in
terms of micro-nutrient available levels can influence the micro-algae yield
in natural seawater cultures. Hence, it follows that the characteristics and
concentration of the zeolite should be considered when one wishes to use it
in a given aquacultural medium, for instance for stimulation of the
bacterium-mediated decomposition of non-consumed fish feed at reduced levels
of ammonia. Depending on the seawater trace element composition,
characteristics and concentration of the zeolite and algal species, the
presence of a suitable zeolite may improve the yield of the cultures,
reducing the production costs. Otherwise, an inhibition of growth may occur,
which is economically disadvantageous.
(Center of Marine and Environmental Research, CIIMAR,
Rua dos Bragas, 177, 4050-123, Oporto, Portugal, e-mail of Vasconcelos: mtvascon@fc.up.pt)