Optimal intensity and biomass density for biofuel production in a thin-light-path photobioreactor.

Production of competitive microalgal biofuels requires development of high volumetric productivity photobioreactors (PBRs) capable of supporting high-density cultures. Maximal biomass density supported by the current PBRs is limited by nonuniform distribution of light as a result of self-shading effects. We recently developed a thin-light-path stacked photobioreactor with integrated slab waveguides that distributed light uniformly across the volume of the PBR. Here, we enhance the performance of the stacked waveguide photobioreactor (SW-PBR) by determining the optimal wavelength and intensity regime of the incident light. This enabled the SW-PBR to support high-density cultures, achieving a carrying capacity of OD730 20. Using a genetically modified algal strain capable of secreting ethylene, we improved ethylene production rates to 937 μg L(-1) h(-1). This represents a 4-fold improvement over a conventional flat-plate PBR. These results demonstrate the advantages of the SW-PBR design and provide the optimal operational parameters to maximize volumetric production.