Pollutants to Products (P2P) Research Initiative, Centre for Research & Innovation, Grande Prairie Regional College, Grande Prairie, Alberta, Canada.
As a promising new biomass source, microalgae provides not only many bio-industrial products for bio-refinery but also help to combat climate change through carbon capture. A key limitation for industrial application is low productivity stemmed directly from microalgae’s low light saturation point at <5-10% of full sunlight, leading to significant midday photo-saturation and photo-inhibition. This report presents a patented breakthrough solution (PCT/CA2014/050450) by spatially diluting sunlight to optimal levels using a unique photo-bioreactor (PBR) system. A 60L PBR test system consists of 48 interconnected round glass tubes placed vertically on the opposite sides of a frame in a staggered arrangement. A computer program actively positions the PBR tubes parallel to the sun’s rays in one degree increments over daylight hours. Chlorella vulgaris was grown auto-tropically for 2 cycles of 3 days under natural sunlight and 3% CO2. Algae density was measured each day. Photo-synthetically active radiation (PAR, µmol/m2/s) was measured continuously on both sides of the frame and in perpendicular to the sun. Over the control period, the PAR on both sides of the PBR frame reached a similar average of 10-20% of the full sunlight with minimum mutual shading. For example, PAR at solar noon was 200-400 µmol/m2/s on both PBR’s surfaces when the full sunlight was 1400-1700. Average Chlorella productivity was equivalent to 106 g/m2/day when calculated on a scaled industrial configuration-more than twice of other reported productivities. With active spatial sunlight dilution, enhanced microalgae areal productivity is achieved by distributing a desirable fraction of sunlight to a more compacted surface area and by diminishing mutual shading, sunlight saturation and photo-inhibition. A pre-commercial 450L system is currently being constructed and tested, and a commercial pilot of 25,000L is planned.