Comparisons of the growth of six diatom species between two configurations of photobioreactors

The present study reports on the mass culture of six benthic diatom species in two systems termed “ photobioreactors”. One system called “bristles photobioreactor” (PBB) contained polyvinyl chloride (PVC) bristles which provided attachment surface for adhesive diatoms, and an airlift system to provide constant water movement. Results obtained using this apparatus are compared with parallel results obtained when inoculating the same diatom species into a “bubble column photobioreactor” without support bristles (PBC), and a strong column of air bubbles to provide constant agitation. The results showed high efficiency of the PBB in terms of concentration and biomass of the adhesive diatoms Amphora spp., Amphora spp2, Navicula spp. and Nitzschia ovalis, on the support filaments. The lesser adhesive diatoms Nitzschia sp. and Cylindrotheca closterium grew better in suspension in the PBC system. The relation existing between the growth of the microalgae and their accompanying bacterial flora were strongly correlated, indicating simultaneous growth of the two populations. It was also shown that higher bacterial counts were found in the systems having the highest microalgal populations. The present results suggested positive feasibility of growing benthic diatoms of commercial importance, particularly for aquaculture, based on the high degree of adhesiveness of the diatoms produced in the PBB systems. Greater efficiency was obtained in the PBC systems for producing high concentrations and biomass of the lesser adhesive diatom species. This new technology may permit optimizing yields for the mass production of microalgae of commercial importance. Data in the literature suggest that biofilms of benthic diatoms the same as or similar to those presently cultured can aid the settlement and growth of larvae of certain benthic marine invertebrates, some of which are important species in aquaculture.