Start-up of a nutrient removal system using Scenedesmus vacuolatus and Chlorella vulgaris biofilms

Microalgal biofilm-based technologies are of strong interest due to their high biomass concentrations and ability to remove nutrients from wastewater, utilize CO2 and produce secondary valuable products. This study investigated the biomass production and nutrient removal efficiency of the microalgae Scenedesmus vacuolatus ACUF_053 and Chlorella vulgaris ACUF_809 from a synthetic wastewater, describing a start-up process in a new biofilm photobioreactor (PBR) configuration. Two sets of experiments were performed. The first one compared the performance of a suspended and attached cell system under batch conditions. The second set of experiments was addressed under semi-batch conditions to study the microalgae biofilm development in the PBR. Five stages in the development of the biofilm were identified for S. vacuolatus: attachment, biofilm formation, maturation I, adaptation and maturation II. The biofilm development phases had a different nutrient removal efficiency. S. vacuolatus biofilm showed a higher phosphate demand during the first attachment and formation phases, while it had a higher nitrate demand during the subsequent phases. C. vulgaris biofilm formation was affected by the pH increase (up to 10.6). The biofilm PBR design using both S. vacuolatus and C. vulgaris showed potential for wastewater treatment due the higher nutrient removal rates.