Production of exocellular pigment by the marine diatom Haslea ostrearia Simonsen in a photobioreactor equipped with immersed ultrafiltration membranes

A new photobioreactor coupled with an ultrafiltration system (immersed membranes) was investigated for the continuous culture of the microalga Haslea ostrearia in order to improve pigment (marennine) production and recovery. The system presents a commercial interest, because energetic costs were minimized, and the cells were not submitted to any shear stress due to pumping or circulation. To obtain this, since the photobioreactor was of cylindrical type, a membrane module was placed at the bottom of the reactor and the hydrostatic pressure (the height of the water column) used as driving force both for the permeation and periodical backflushing steps. The production of biomass and marennine was stable for a three-week period, with marennine specific productivity ≈30–35 mg 10−9 cell day−1, marennine concentration ≈3 times higher than in a conventional batch photobioreactor. The permeation flux obtained was acceptable (3–10 l h−1 m−2, 3 kPa, 15°C), but for such applications, this type of integrated process needs further improvements. Owing to its simple design, the concept “photobioreactor – ultrafiltration with immersed membranes” has good possibilities in biotechnology and aquaculture for continuous extraction of exocellular metabolites.