Fluid dynamical considerations in the design of a microalgae photobioreactor

Large-scale microalgal biomass production has the potential to be a part of future sustainable communities as a source of protein for food and feed, lipids for renewable fuel and other energy or carbon sequestration products. For microalgal biomass to be economically competitive for such purposes, reliable, high performance, large-scale production systems will be needed. Closed culturing systems (photobioreactors) provide intrinsic advantages in terms of process control and productivity, but the challenge is to realize these benefits at low capital costs. The presented study is based on a novel photobioreactor concept for achieving productive, scalable and low cost outcomes. An experimental apparatus has been used to investigate the fluid dynamic environment under different operating conditions with a primary focus on mass transfer coefficients and mixing characteristics. Sufficient mass flux is critical for carbon dioxide supply and oxygen removal to support photosynthesis, and needs to be controlled for optimal growth rates and efficiencies. Mixing conditions not only influence mass transfer, but are also critical for the establishment of a light regime tailored to the specific growth requirements of microalgae. The liquid mass transfer coefficient of oxygen and carbon dioxide were determined over the liquid velocity range. These results will be fed into the photobioreactor process model as part of establishing the operating and design parameters of a commercial demonstration photobioreactor