In-situ removal of aquaculture waste nutrient using floating permeable nutrient uptake system (FPNUS) under mixotrophic microalgal scheme

The current study investigated the in-situ aquaculture nutrient removal from fish tanks using mixotrophic Scenedesmus in a floating permeable nutrient uptake system (FPNUS) and compared with nutrient concentration in control, autotrophy, and bacterial nitrogen removal (BNR) treatments. In the first run, results were not as expected due to the missing PO₄^--P as the mixotrophic growth in flasks with PO₄^--P was 55.86% more than growth in aquaculture wastewater. With PO₄^--P addition in FPNUS, average and maximum removal rates under mixotrophy reached 2.53 and 10.96 mg/(L·d), respectively. The average mixotrophic removal rate was 40.31 and 81.42% higher than removal rates under autotrophy and BNR. Daily nutrient loading and removal were matched only in mixotrophy after fourth day of culture. These results show the great potential for nutrient removal using mixotrophic microalgae-based FPNUS due to its high efficiency, capability of in-situ treatment and nutrient recycling through biomass utilization.