Recycling of nutrient medium to improve productivity in large-scale microalgal culture using a hybrid electrochemical water treatment system

Recycling and reusing of nutrient media in microalgal cultivation are important strategies to reduce water consumption and nutrient costs. However, these approaches have limitations, e.g., a decrease in biomass production, (because as reused media can inhibit biomass growth). To address these limitations, we applied a novel membrane filtration-electrolysis-ultraviolet hybrid water treatment method capable of laboratory-to-largescale operation to increase biomass productivity and enable nutrient medium disinfection and recycling. In laboratory-scale experiments, electrolysis effectively remove the biological contaminants from the spent nutrient medium, resulting in a high on-site removal efficiency of dissolved organic carbon (DOC; 80.3 +/- 5 %) and disinfection (99.5 +/- 0.2 %). Compared to the results for the recycling of nutrient medium without water treatment, electrolysis resulted in a 1.5-fold increase in biomass production, which was attributable to the removal of biological inhibitors from electrochemically produced oxidants (mainly OCl- ). In scaled-up applications, the hybrid system improved the quality of the recycled nutrient medium, with 85 +/- 2 % turbidity removal, 75 +/- 3 % DOC removal, and 99.5 +/- 2 % disinfection efficiency, which was beneficial for biomass growth by removing biological inhibitors. After applying the hybrid water treatment method, we achieved a Spirulina biomass production of 0.47 +/- 0.03 g L-1, similar to that obtained using a fresh medium (0.53 +/- 0.02 g L-1). The on-site disinfection process described herein is practical and offers a cost-saving and environmental friendly alternative for nutrient medium recycling and reusing water in mass and sustainable cultivation of microalgae.

Automated summary

The membrane filtration-electrolysis-ultraviolet hybrid water treatment method improves biomass productivity and enables nutrient medium disinfection and recycling, reducing water consumption and nutrient costs.