Design of Algal Film Photobioreactors for Algal Biomass Production

Microalgae has been identified as a potential feedstock for both biofuels and biochemicals but dewatering algae limits the economic viability. By growing algae as a biofilm, the cost of dewatering can be reduced. Current design of algal film photobioreactors is limited to algal turf scrubbers and rotating algal biofilm systems. There is opportunity to explore new designs based on growing algal biofilms on a light emitting waveguide. The growth of algal films on transparent surfaces with polar surface energy ranging from 7-11.3 mJ/m2 was tested in a Parallel Plate Airlift Reactor. Overall algal biofilm productivity is correlated to the colonization time of the biofilm, with algal films grown on cellulose acetate having the highest productivity of 2.1 g/m2 day. When colonization time was accounted for, the approximate 2 g/m2 day algal biofilm productivity was independent of material. Colonization time was correlated to the polar surface energy and not the water-material contact angle. Lipid content of algal biofilms ranged from 6-8 w%/w and were independent of the material it was grown on. To demonstrate the feasibility of growing algal biofilms on light emitting waveguides, five different waveguide designs were fabricated and the light emission from all the surfaces was measured. Light intensity distribution on the waveguides could be adjusted by surface modification. Algal biofilms grown on these waveguides had overall non-linear growth kinetics and the highest surface area productivity was 2.9 g/m2 day. The productivity was dependent on the light intensity (incident photon flux from 1600-12600 Îźmol/m2 sec) and CO2 concentration (0.04-3% partial pressure), but saturation effects were observed. The interaction effects between light intensity and CO2 concentration on algal biofilm productivity was non-linear. A fundamental model was developed to describe light and inorganic carbon dependent algal biofilm growth. Incident light direction, intensity, and inorganic carbon concertation was varied. A complimentary model based on a partial differential equation was also developed which describes light limited growth. Predicted growth kinetics were sigmoidal in shape and showed agreement with experimental data. Effects such as light-dark cycles were not fully captured by the model, which suggests there is room for improvement.Ph.D