Enhanced Al/Fe electro-flocculation for phosphorus separation from eutrophic lake water by manipulating algal...

Phosphorus (P) crisis poses a threat to global food security, while P eutrophication has caused algal blooms in lakes. Recovering P from eutrophic lake water can help mitigate eutrophication and promote the recycling of valuable P resources. Currently, electro-flocculation has been tested to recover P from eutrophic water, but improving recovery efficiency remains a key technical challenge. Here, we propose a new strategy to enhance P recovery from eutrophic lake water through electro-flocculation by simply manipulating algal decomposition processes. To test it, high-algae water with an initial algal concentration of 300 mg/L at different decomposition stages was subjected to a series of electro-flocculation experiments at the 10 V using Fe and Al electrodes. The results showed that Al electrodes outperformed Fe electrodes, achieving maximum P separation efficiencies of 99.0 % and 75.4 %, respectively. As algae decomposed, Al electro-flocculation can be accelerated twofold due to the shift from particulate to dissolved P, while Fe electro-flocculation can be enhanced by 30 % due to the production of macropolymers. Relative to Al hydroxides, Fe hydroxides typically have a smaller surface area and exhibit weaker flocculation for P separation. Polymer molecular weight distribution analysis indicated that macropolymers (> 100 kDa) serve as bridging agents, facilitating Fe electro-flocculation, but this effect diminishes over time as these macropolymers break down. The proposed strategy has accordingly reduced both time and economic costs. These findings can advance the application of Al/Fe electro-flocculation in recycling P from eutrophic lake water.