Novel waveguide reactor design for enhancing algal biofilm growth

Abstract

Algal film photobioreactors have the potential to reduce dewatering costs and have a comparable productivity to raceway ponds. Current designs have focused on maximizing productivity and nutrient removal through material selection and design. However, fewer studies have focused on analyzing the effects of illumination and carbon dioxide (CO2) concentration on algal film growth. The transport of light in suspended photobioreactors is considered a serious problem due to cell shading, light scattering and non-uniform optical absorption. To enhance light delivery to algal biofilms, five different waveguide designs were developed Light emitting waveguides are capable of distributing a bright light source over a larger surface area. The light emission from these waveguide designs was characterized and the algal biofilm growth on waveguides was characterized in a parallel plate airlift reactor (17L). The light intensity and CO2 concentration were varied in a 32 factorial design experiment to determine if there were any interaction effects. Light emission from the waveguides could be altered by changing the tapper angle or by notching the surfaces. Algal film growth kinetics on the waveguides were overall non-linear, but had linear regions of growth. The waveguides achieved an algal biofilm surface area productivity of 2.8g/m2day and an aerial productivity of 33.6g/m2day. Algal film productivity displayed saturation kinetics with respect to light intensity and CO2 concentration, but the interaction effect of light and CO2 on productivity is likely non-linear. Algal film biomass per photon consumed decreased with increasing light intensity when the reactor was not CO2 limited. The results indicate the potential for algal biofilms to be grown on light emitting waveguides which opens up the opportunity to explore new algal film photobioreactor configurations.