Microalgae contribute significantly to the global economy, but bottlenecks in culturing and harvesting make large-scale production economically challenging. The isolated cultivation of algal resource utilizing selectivity (ICARUS) process, which integrates a passive membrane photobioreactor configuration with wastewater as a growth medium, is introduced. Eleven membranes of varying porosity and materials were examined in regard to algae productivity. Four ICARUS series (40kDa-PVDF, 0.53 g L-1, 14.1 mg; 0.1µm-PVDF, 0.43 g L-1, 16.6 mg; 12kDa-RC, 0.35 g L-1, 14.5 mg; 0.2 µm-CA, 0.41 g L-1, 14.5 mg) had a final cell density and mass yield that was significantly higher than that of algae suspended directly in wastewater (0.25 g L-1, 9.1 mg). Six series maintained significantly longer exponential growth phases than the suspended cultures. The ICARUS series maintained a significantly lower average pH (9.55) than the suspended culture (10.21). Select membranes from laboratory experiments (12kDa-RC, 40kDa-PVDF, 7µm-NY) were tested in extended field conditions, where the movement of dissolved constituents and biomass productivity were compared to that of closed suspended series. All ICARUS series had higher biomass productivity (RC, 2.87 g L-1; PVDF, 10.6 g L-1; NY, 8.45 g L-1) than the suspended series (0.38 g L-1), which was due to a longer exponential growth phase and passive dewatering in the ICARUS series. Dissolved ions passed readily across each membrane. Gas exchange was slower than expected, which may have been due to attached growth utilizing gases at the membrane surface. Dissolved oxygen concentration did not limit algal growth, and adequate carbon dioxide was available to regulate ICARUS pH (maintaining an average pH of 7.6, compared to 9.8-10.5 in control series). The invasion of endemic wastewater species was dependent on pore size; the RC and PVDF series maintained a monoculture, but the NY series had severe contamination. The resulting research has demonstrated a proof-of-concept of a new microalgal cultivation method which may reduce the cost of large-scale cultivation efforts integrated at wastewater treatment plants or within existing algal production facilities. Investigating various wastewater effluents, membranes, and algal strains has allowed for recommendations for the operation of scaled-up systems. By improving large scale algal cultivation, algal biofuels may become more economically competitive with fossil fuels or other renewables.

Passive membrane photobioreactor for the isolated cultivation of algal resource utilizing selectivity (ICARUS) using wastewater as a feed stock

249th National Meeting (2015)

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