Understanding How Critical Growth Parameters Affect Algal Biofilm Growth and Internal Lipid Concentrations

Due to their relatively fast growth rates and high concentrations of specific biocompounds, algal biofilms have great potential for the production of valuable bioproducts. This thesis investigates the critical factors affecting algal biofilm growth rates and their internal lipid concentrations. Results of this thesis have implications for operation of algal biofilm culturing systems. The main factors investigated in this thesis were how nutrient supplies (carbon dioxide, nitrogen and silicon concentrations), light orientation, and photon flux density affects algal biofilm growth and internal lipid concentrations. This was accomplished by growing algal biofilms on glass and polycarbonate growth coupons in culturing systems that facilitated control over the main factors affecting growth. Two separate biofilm culturing systems were developed and utilized to test distinct research objectives. Biofilms were grown for 14-26 days, harvested from growth coupons several times per week, lyophilized to determine productivities (g/m2/d), and in some cases, exposed to chemical treatments to determine lipid content. Irradiating algal biofilms from either the water side, material side, or both sides, while maintaining a total photon flux density (PFD) of 100 μmol/m2/s, did not affect overall algal biofilm biomass productivities. When well-developed algal biofilms were starved of nitrogen and silicon, there was no accumulation of neutral lipids. Fatty acid methyl ester (FAME) concentrations increased from 5% to 8% (w/w) when PFDs were increased from 50 to 150 μmol/m2/s, however, further FAME accumulations were not observed beyond that PFD range. Algal biofilm starvation did, however, induce biofilm growth cessation and sloughing from the growth substratum. At fixed PFDs of 100 μmol/m2/s, increasing inorganic carbon concentrations from 0.04% to 2% (v/v) resulted in significant biomass productivity increases of 0.5 to 2.0 g/m2/d; however, no biomass productivity increases occurred when CO2 concentrations were incrementally increased from 2% to 12%. When PFDs and CO2 concentrations were simultaneously increased (from 50 to 440 μmol/m2/s and 0.04 to 7% CO2), there were significant increases in algae biofilm biomass productivities (from ~1 g/m2/d to 4.4 g/m2/d) i.e. there was an interaction effect. Maximal algal biofilm total FAME productivities were ~0.3 g/m2/d, comparable to the best terrestrial crops.Ph.D