A Semi-Continuous Efficient Strategy for Removing Phosphorus and Nitrogen from Eel Aquaculture Wastewater Using the Self-Flocculating Microalga Desmodesmus Sp. Pw1

The phosphorus content in eel aquaculture wastewater exceeds the discharge standard, and the amount of wastewater discharged is substantial. Therefore, there is an urgent need to explore an economical and efficient method to treat aquaculture wastewater. This study explored the use of Desmodesmus sp. PW1, a type of microalgae, to treat eel aquaculture wastewater. The results showed that Desmodesmus sp. PW1 not noly has strong phosphorus and nitrogen removal abilities, but also its self-flocculating ability made it an effective method for treating eel aquaculture wastewater. By optimizing the conditions, Desmodesmus sp. PW1 was able to achieve a total phosphorus (TP) removal efficiency of 92.3%, and a total nitrogen (TN) and ammonia nitrogen (NH4+-N) removal efficiency of 99%, using a photoperiod of 24:0, a temperature of 25 ℃, and a 15% inoculation amount. Subsequently, semi-continuous treatment process mode was established with a sewage renewal rate of 90%. The results showed that after four rounds of sewage renewal operations, the microalgae biomass in the sewage treatment system could be maintained between 160.0-220.0 mg/L, and the average removal rate of TP was 0.13 mg/(L • h). The biological macromolecule content of algae cells collected in the semi-continuous treatment system was determined, and it was found that their lipid content was as high as 36.5%, and the biodiesel properties met the biodiesel standards authorized by Europe and the United States. Overall, this study provides an economical and effective strategy for converting wastewater into high-value microalgae products