Enhancing Algae Biofilm Quantity and Value Through Controlled Light Intensity for Treatment of Municipal Anaerobic Digestor Effluent

Rotating algae biofilm reactors (RABRs) have been shown to remove nutrients from wastewater and to cultivate algae for bioproducts. Another key variable in RABR technology for cultivating microalgae biomass is light intensity. The goal of this study was to address a gap in the design and operation of algae biofilm reactors by analyzing the effects of light intensity on biomass quality and quantity, chemical precipitation of phosphorus, and phosphorus uptake into biomass. This study utilized a triplicate laboratory-scale experiment with PAR intensities from 10 to 2000 µmol m−2·s−1. Municipal wastewater anaerobic digester effluent (ADE) was utilized as nutrient-rich growth media. The greatest intensification of biomass was observed at 2000 µmol m−2·s−1 for a microalgae biomass surface area productivity of 12.8 g·m−2day−1, and 95% phosphorus removal. Increasing light intensity was correlated with an increase in solution pH, due to photosynthesis, that was observed to increase precipitation of phosphorus salts in addition to phosphorus uptake into biofilm biomass. Both mechanisms of phosphorus removal (chemical and biological) are favorable for bioproducts, specifically bioplastic and biofertilizer. This research is useful for improving engineering design and operation of algae biofilm systems treating ADE for optimization of biofilm quality for bioproducts through intensification of microalgae biofilm biomass.