To: AQUA-L@LISTSERV.ifmt.nf.ca
From: Joao Navalho <necton@mail.telepac.pt>
GREEN WATER/ALGAE CONCENTRATION
QUESTION:
We are beginning to expand our production of algae (nannochloropsis) for use in rotifer production and for green water for larvae. We have been concentrating the algae using a centrifuge with 6 250 ml plastic bottles. A laborious task but doable with low production of algae. Now that we are ramping up to 100 L/day, we will be using for green water, use of this centrifuge is not feasible. We are looking at continuous
feed rotors for a centrifuge, but they are rather expensive. Does anybody out there have any particular techniques for concentrating algae without having to buy a $15,000 centrifuge & rotor? Or does anybody have an old centrifuge or rotor for sale that they used for
continuous feed of water/algae that is not being used? In terms of green water.... We found that delta smelt (Hypomesus transpacificus) larvae survived and grew much better when rearing water was kept green. The question I was wondering is if other people using green water bother to concentrate the algae or just dump in the algae and water and fertilizer salts. Has it been detrimental to other larval species?
COMMENTS 1:
The ways normally used to concentrate microalgae are, flocculation and centrifugation. The first you can use when you want one product from the algae rather than the algae itself e.g. "Beta Carotene" from Dunaliella. To use the algae for green water or to feed molluscs/zooplanktons, not talking about the inert live food replacements, you need the algae "free" and not in floccules. For that you can use centrifugation techniques; there are also some ultrafiltration systems too, as expensive as centrifuges but more running costs effective.
Of course we can talk too in production systems for microalgae. In fact it is another way of concentrating the biomass, you can get a system that optimizes the culture conditions to your algae and in that way you can get cultures with more algae per volume unit, that is another interesting discussion issue.
I don't think there are so many people using continuous feed centrifuges
rotor to concentrate such quantities, 100 L/day is still a laboratory scale and the price of those centrifuges is very high as you notice. Even for the majority of the commercial hatcheries, buying a centrifuge or build/buy a sophisticated microalgae production system is still too expensive.
What people normally do in hatcheries facilities is simply to add the algae cultures to the larvae pond. If you take care on your microalgae cultures I'm sure that you will not have problems with that.
Joao Navalho - necton@mail.telepac.pt
Necton - Companhia Portuguesa de Culturas Marinhas
Unidade Piloto de Belamandil
8700 OLHAO - PORTUGAL
Tel/FAX: +351 89 703961
COMMENTS 2:
Algae can be concentrated by flocculation, using either alum or chitosan. Alum is readily available, but chitosan is more efficient. The flocculated algae can be frozen and will remain viable for several months. You can also sun-dry the paste you collect, but should store the powder like dried paste. Before feeding the flocculant, you should stir with a magnetic stirrer or blender to break up clumps.
See Morales, J.; J de la Noue; G. Picard. 1985. Harvesting marine
microalgae species by chitosan flocculation. Aquaculture Engineering 4
: 257-270.
While old cream separators work well, they are increasingly difficult
to find.
C. Angell
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