Short CommunicationBiofilm-based photobioreactor absorbing water and nutrients by capillary action

•A simple biofilm-based culture system of the unicellular green alga Pseudochoricystis ellipsoidea strain Obi was developed.•The footprint biomass productivities achieved with this system were 8-10 g m−2 day−1.•This system requires neither irrigation nor supply of CO2-enriched air.

Cells of the unicellular green alga, “Pseudochoricystis ellipsoidea”, were uniformly spread on a cellulosic sheet or on a polytetrafluoroethylene (PTFE) membrane sheet superimposed on a cellulosic sheet at a density of 3.5-5.0 g dry weight per m2, and the sheet was adhered to an inverted V-shaped acrylic plate of 10 cm in height. Several acrylic plates were placed side by side on a tray containing liquid medium at a depth of 0.6 cm, and illuminated from above with a light intensity of 300-340 μmol m−2 s−1. Water and nutrients were supplied to cells by capillary action through the cellulosic sheet. Footprint biomass productivities of cells grown in atmospheric CO2 on this photobioreactor were 8-10 g m−2 day−1. This cultivation system is strongly energy- and labor-saving as it does not require mixing of culture fluid, irrigation of medium, and delivery of CO2-enriched air.