Stacked Optical Waveguide Photobioreactor for High Density Algal Cultures

In this work, an ultracompact algal photobioreactor that alleviates the problem of non-optimal light distribution in current algae photobioreactor systems, by incorporating stacked layers of slab waveguides with embedded light scatterers, is presented. Poor light distribution in traditional photobioreactor systems, due to self-shading effects, is responsible for relatively low volumetric productivity. The optimal conditions for operating a 10-layer bioreactor are outlined. The bioreactor exhibits the ability to sustain uniform biomass growth throughout the bioreactor for 3 weeks, and demonstrates an 8-fold increase in biomass productivity. Using a genetically engineered algal strain, constant secreted ethylene production for over 45 days is also demonstrated. Since the stacked architecture leads to improved light distribution throughout the volume of the bioreactor, it reduces the need for culture mixing for optimum light distribution, and thereby potentially reducing operational costs.