Design of algal film photobioreactors: Material surface energy effects on algal film productivity, colonization and lipid content

• Designed and built a parallel plate airlift reactor for growing algal biofilms on different materials.
• Algal biofilm growth kinetics are linear.
• Algal biofilm productivity is dependent on material type.
• Colonization time is strongly correlated to polar surface energy.

A parallel plate air lift reactor was used to examine the growth kinetics of mixed culture algal biofilms grown on various materials (acrylic, glass, polycarbonate, polystyrene and cellulose acetate). The growth kinetics of the algal biofilms were non-linear overall and their overall productivities ranged from 1.10–2.08 g/m2 day, with those grown on cellulose acetate having the highest productivity. Overall algal biofilm productivity was largely explained by differences in the colonization time which in turn was strongly correlated to the polar surface energy of the material, but weakly correlated to water-material contact angle. When colonization time was taken into account, the productivity for all materials except acrylic was not significantly different at approximately 2 g/m2/day. Lipid content of the algal biofilms ranged from 6% to 8% (w/w) and was not correlated to water-material contact angle or polar surface energy. The results have potential application for selecting appropriate materials for algal film photobioreactors.