Comparison of two membrane - photobioreactors, with free or immobilized cells, for the production of pigments by a marine diatom

The present study concerns the value enhancement of the microalga Haslea ostrearia. This marine diatom bears the peculiarity of synthesizing and secreting in the culture medium a blue-green pigment named marennine. Anticancer research, cosmetics and aquaculture are the fields concerned with the utilizations of this hydrosoluble pigment. The aim of the study is to compare the pigment productivity obtained with two types of photobioreactors. In the first process, cells are free and recycled in a bioreactor combined with a membrane ultrafiltration equipment (external loop). In the second system, cells are entrapped in a tubular agar gel layer in a photobioreactor of original design. The influence of nitrate concentration and renewal rate is examined. Experiments, conducted on long term periods (up to 40 d) without any external contamination, revealed that marennine productivities of more than 5-7 mg 10(9) cell(-1) d(-1) can be reached with both bioreactors. The advantages and drawbacks of each process design are also discussed.