Effects of nitrogen phosphorus ratio and light on phosphorus removal by microalgae in high-phosphorus wastewater

The removal of phosphorus from wastewater has consistently posed a major focus in the field of wastewater treatment. Microalgae-based phosphorus removal is widely acknowledged as an effective biological approach. However, ensuring the microalgae-mediated high phosphorus concentration removal remains a persistent challenge. In this study, a kind of multicellular microalgae, Klebsormidium sp., was used to explore its ability to remove phosphorus in high-phosphorus wastewater. The phosphorus removal rate by Klebsormidium sp. in highly concentrated (>20 mgP/L) wastewater can exceed 90%. To investigate the phosphorus absorption process, various nitrogen and phosphorus concentrations along with light conditions were employed. The results showed that 50% to 80% of the total phosphorus absorbed by microalgae entered the intracellular polymer. The phosphorus concentration and light intensity did not exert any significant effects on the absorption of phosphorus by microalgae. However, the nitrogen concentration and the light-to-dark ratio significantly influenced the storage of phosphorus by microalgae. At a nitrogen concentration over 300 mgN/L, phosphorus absorption by microalgae was inhibited. A higher light-to-dark ratio increased phosphorus transfer by microalgae, while the light duration exceeds 16 h inhibited it. Microalgae have emerged as promising materials for phosphorus removal in high-phosphorus sewage, the study offering potential solutions for a cleaner and more sustainable future.