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 os trearia. This marine diatom bears the peculiarity of synthesizing and secre ting in the culture medium a blue-green pigment named "marennine". Anticanc er research, cosmetics and aquaculture are the fields concerned with the ut ilizations of this hydrosoluble pigment. The aim of the study is to compare the pigment productivity obtained with two types of photobioreactors. In t he 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 o riginal 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.