Production of microalgal concentrates by flocculation and their assessment as aquaculture feeds

Type Article
Date 2006-10
Language English
Author(s) Knuckey R1, Brown M2, Robert ReneORCID3, Frampton D2
Affiliation(s) 1 : Northern Fisheries Ctr, Dept Primary Ind & Fisheries, Cairns, Qld 4870, Australia.
2 : CSIRO, Marine Res, Hobart, Tas 7001, Australia.
3 : IFREMER, UMR Physiol & Ecophysiol Mollusques Marins Stn Ex, F-29840 Argenton en Landunvez, France.
Source Aquacultural Engineering (0144-8609) (Elsevier), 2006-10 , Vol. 35 , N. 3 , P. 300-313
DOI 10.1016/j.aquaeng.2006.04.001
WOS© Times Cited 227
Keyword(s) Chaetoceros, Thalassiosira, Flocculation, Concentrate, Bivalve, Algal paste
Abstract A novel technique was developed for the flocculation of marine microalgae commonly used in aquaculture. The process entailed an adjustment of pH of culture to between 10 and 10.6 using NaOH, followed by addition of a non-ionic polymer Magnafloc LT-25 to a final concentration of 0.5 mg L−1. The ensuing flocculate was harvested, and neutralised giving a final concentration factor of between 200- and 800-fold. This process was successfully applied to harvest cells of Chaetoceros calcitrans, C. muelleri, Thalassiosira pseudonana, Attheya septentrionalis, Nitzschia closterium, Skeletonema sp., Tetraselmis suecica and Rhodomonas salina, with efficiencies ≥80%. The process was rapid, simple and inexpensive, and relatively cost neutral with increasing volume (cf. concentration by centrifugation). Harvested material was readily disaggregated to single cell suspensions by dilution in seawater and mild agitation. Microscopic examination of the cells showed them to be indistinguishable from corresponding non-flocculated cells. Chlorophyll analysis of concentrates prepared from cultures of ≤130 L showed minimal degradation after 2 weeks storage.
Concentrates of T. pseudonana prepared using pH-induced flocculation gave better growth of juvenile Pacific oysters (Crassostrea gigas) than concentrates prepared by ferric flocculation, or centrifuged concentrates using a cream separator or laboratory centrifuge. In follow up experiments, concentrates prepared from 1000 L Chaetoceros muelleri cultures were effective as supplementary diets to improve the growth of juvenile C. gigas and the scallop Pecten fumatus reared under commercial conditions, though not as effective as the corresponding live algae. The experiments demonstrated a proof-of-concept for a commercial application of concentrates prepared by flocculation, especially for use at a remote nursery without on-site mass-algal culture facilities.
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